@phdthesis{Zona2024,
  author    = {Zona, Carlotta Isabella},
  title     = {Visuo-linguistic integration for thematic-role assignment across speakers},
  doi       = {10.25932/publishup-63185},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-631857},
  school      = {Universit{\"a}t Potsdam},
  pages     = {147},
  year      = {2024},
  abstract  = {This dissertation examines the integration of incongruent visual-scene and morphological-case information ("cues") in building thematic-role representations of spoken relative clauses in German. Addressing the mutual influence of visual and linguistic processing, the Coordinated Interplay Account (CIA) describes a mechanism in two steps supporting visuo-linguistic integration (Knoeferle \& Crocker, 2006, Cog Sci). However, the outcomes and dynamics of integrating incongruent thematic-role representations from distinct sources have been investigated scarcely. Further, there is evidence that both second-language (L2) and older speakers may rely on non-syntactic cues relatively more than first-language (L1)/young speakers. Yet, the role of visual information for thematic-role comprehension has not been measured in L2 speakers, and only limitedly across the adult lifespan. Thematically unambiguous canonically ordered (subject-extracted) and noncanonically ordered (object-extracted) spoken relative clauses in German (see 1a-b) were presented in isolation and alongside visual scenes conveying either the same (congruent) or the opposite (incongruent) thematic relations as the sentence did. 1 a Das ist der Koch, der die Braut verfolgt. This is the.NOM cook who.NOM the.ACC bride follows This is the cook who is following the bride. b Das ist der Koch, den die Braut verfolgt. This is the.NOM cook whom.ACC the.NOM bride follows This is the cook whom the bride is following. The relative contribution of each cue to thematic-role representations was assessed with agent identification. Accuracy and latency data were collected post-sentence from a sample of L1 and L2 speakers (Zona \& Felser, 2023), and from a sample of L1 speakers from across the adult lifespan (Zona \& Reifegerste, under review). In addition, the moment-by-moment dynamics of thematic-role assignment were investigated with mouse tracking in a young L1 sample (Zona, under review). The following questions were addressed: (1) How do visual scenes influence thematic-role representations of canonical and noncanonical sentences? (2) How does reliance on visual-scene, case, and word-order cues vary in L1 and L2 speakers? (3) How does reliance on visual-scene, case, and word-order cues change across the lifespan? The results showed reliable effects of incongruence of visually and linguistically conveyed thematic relations on thematic-role representations. Incongruent (vs. congruent) scenes yielded slower and less accurate responses to agent-identification probes presented post-sentence. The recently inspected agent was considered as the most likely agent ~300ms after trial onset, and the convergence of visual scenes and word order enabled comprehenders to assign thematic roles predictively. L2 (vs. L1) participants relied more on word order overall. In response to noncanonical clauses presented with incongruent visual scenes, sensitivity to case predicted the size of incongruence effects better than L1-L2 grouping. These results suggest that the individual's ability to exploit specific cues might predict their weighting. Sensitivity to case was stable throughout the lifespan, while visual effects increased with increasing age and were modulated by individual interference-inhibition levels. Thus, age-related changes in comprehension may stem from stronger reliance on visually (vs. linguistically) conveyed meaning. These patterns represent evidence for a recent-role preference - i.e., a tendency to re-assign visually conveyed thematic roles to the same referents in temporally coordinated utterances. The findings (i) extend the generalizability of CIA predictions across stimuli, tasks, populations, and measures of interest, (ii) contribute to specifying the outcomes and mechanisms of detecting and indexing incongruent representations within the CIA, and (iii) speak to current efforts to understand the sources of variability in sentence comprehension.},
  language  = {en}
}
@phdthesis{Zimmermann2018,
  author    = {Zimmermann, Marc},
  title     = {Multifunctional patchy silica particles via microcontact printing},
  doi       = {10.25932/publishup-42773},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427731},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IX, 121, xiii},
  year      = {2018},
  abstract  = {This research addressed the question, if it is possible to simplify current microcontact printing systems for the production of anisotropic building blocks or patchy particles, by using common chemicals while still maintaining reproducibility, high precision and tunability of the Janus-balance Chapter 2 introduced the microcontact printing materials as well as their defined electrostatic interactions. In particular polydimethylsiloxane stamps, silica particles and high molecular weight polyethylenimine ink were mainly used in this research. All of these components are commercially available in large quantities and affordable, which gives this approach a huge potential for further up-scaling developments. The benefits of polymeric over molecular inks was described including its flexible influence on the printing pressure. With this alteration of the µCP concept, a new method of solvent assisted particle release mechanism enabled the switch from two-dimensional surface modification to three-dimensional structure printing on colloidal silica particles, without changing printing parameters or starting materials. This effect opened the way to use the internal volume of the achieved patches for incorporation of nano additives, introducing additional physical properties into the patches without alteration of the surface chemistry. The success of this system and its achievable range was further investigated in chapter 3 by giving detailed information about patch geometry parameters including diameter, thickness and yield. For this purpose, silica particles in a size range between 1µm and 5µm were printed with different ink concentrations to change the Janus-balance of these single patched particles. A necessary intermediate step, consisting of air-plasma treatment, for the production of trivalent particles using "sandwich" printing was discovered and comparative studies concerning the patch geometry of single and double patched particles were conducted. Additionally, the usage of structured PDMS stamps during printing was described. These results demonstrate the excellent precision of this approach and opens the pathway for even greater accuracy as further parameters can be finely tuned and investigated, e.g. humidity and temperature during stamp loading. The performance of these synthesized anisotropic colloids was further investigated in chapter 4, starting with behaviour studies in alcoholic and aqueous dispersions. Here, the stability of the applied patches was studied in a broad pH range, discovering a release mechanism by disabling the electrostatic bonding between particle surface and polyelectrolyte ink. Furthermore, the absence of strong attractive forces between divalent particles in water was investigated using XPS measurements. These results lead to the conclusion that the transfer of small PDMS oligomers onto the patch surface is shielding charges, preventing colloidal agglomeration. However, based on this knowledge, further patch modifications for particle self-assembly were introduced including physical approaches using magnetic nano additives, chemical patch functionalization with avidin-biotin or the light responsive cyclodextrin-arylazopyrazoles coupling as well as particle surface modification for the synthesis of highly amphiphilic colloids. The successful coupling, its efficiency, stability and behaviour in different solvents were evaluated to find a suitable coupling system for future assembly experiments. Based on these results the possibility of more sophisticated structures by colloidal self-assembly is given. Certain findings needed further analysis to understand their underlying mechanics, including the relatively broad patch diameter distribution and the decreasing patch thickness for smaller silica particles. Mathematical assumptions for both effects are introduced in chapter 5. First, they demonstrate the connection between the naturally occurring particle size distribution and the broadening of the patch diameter, indicating an even higher precision for this µCP approach. Second, explaining the increase of contact area between particle and ink surface due to higher particle packaging, leading to a decrease in printing pressure for smaller particles. These calculations ultimately lead to the development of a new mechanical microcontact printing approach, using centrifugal forces for high pressure control and excellent parallel alignment of printing substrates. First results with this device and the comparison with previously conducted by-hand experiments conclude this research. It furthermore displays the advantages of such a device for future applications using a mechanical printing approach, especially for accessing even smaller nano particles with great precision and excellent yield. In conclusion, this work demonstrates the successful adjustment of the µCP approach using commercially available and affordable silica particles and polyelectrolytes for high flexibility, reduced costs and higher scale-up value. Furthermore, its was possible to increase the modification potential by introducing three-dimensional patches for additional functionalization volume. While keeping a high colloidal stability, different coupling systems showed the self-assembly capabilities of this toolbox for anisotropic particles.},
  language  = {en}
}
@phdthesis{Zimmermann2007,
  author    = {Zimmermann, Beate},
  title     = {Spatial and temporal variability of the soil saturated hydraulic conductivity in gradients of disturbance},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-16402},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {As land-cover conversion continues to expand into ever more remote areas in the humid tropics, montane rainforests are increasingly threatened. In the south Ecuadorian Andes, they are not only subject to man-made disturbances but also to naturally occurring landslides. I was interested in the impact of this ecosystem dynamics on a key parameter of the hydrologic cycle, the soil saturated hydraulic conductivity (synonym: permeability; Ks from here on), because it is a sensitive indicator for soil disturbances. My general objective was to quantify the effects of the regional natural and human disturbances on the saturated hydraulic conductivity and to describe the resulting spatial-temporal patterns. The main hypotheses were: 1) disturbances cause an apparent displacement of the less permeable soil layer towards the surface, either due to a loss of the permeable surface soil after land-sliding, or as a consequence of the surface soil compaction under cattle pastures; 2) 'recovery' from disturbance, either because of landslide re-vegetation or because of secondary succession after pasture abandonment, involves an apparent displacement of the less permeable layer back towards the original depth an 3) disturbances cause a simplification of the Ks spatial structure, i.e. the spatially dependent random variation diminishes; the subsequent recovery entails the re-establishment of the original structure. In my first study, I developed a synthesis of recent geostatistical research regarding its applicability to soil hydraulic data, including exploratory data analysis and variogram estimation techniques; I subsequently evaluated the results in terms of spatial prediction uncertainty. Concerning the exploratory data analysis, my main results were: 1) Gaussian uni- and bivariate distributions of the log-transformed data; 2) the existence of significant local trends; 3) no need for robust estimation; 4) no anisotropic variation. I found partly considerable differences in covariance parameters resulting from different variogram estimation techniques, which, in the framework of spatial prediction, were mainly reflected in the spatial connectivity of the Ks-field. Ignoring the trend component and an arbitrary use of robust estimators, however, would have the most severe consequences in this respect. Regarding variogram modeling, I encouraged restricted maximum likelihood estimation because of its accuracy and independence on the selected lags needed for experimental variograms. The second study dealt with the Ks spatial-temporal pattern in the sequences of natural and man-made disturbances characteristic for the montane rainforest study area. To investigate the disturbance effects both on global means and the spatial structure of Ks, a combined design-and model-based sampling approach was used for field-measurements at soil depths of 12.5, 20, and 50 cm (n=30-150/depth) under landslides of different ages (2 and 8 years), under actively grazed pasture, fallows following pasture abandonment (2 to 25 years of age), and under natural forest. Concerning global means, our main findings were 1) global means of the soil permeability generally decrease with increasing soil depth; 2) no significant Ks differences can be observed among landslides and compared to the natural forest; 3) a distinct permeability decrease of two orders of magnitude occurs after forest conversion to pasture at shallow soil depths, and 4) the slow regeneration process after pasture abandonment requires at least one decade. Regarding the Ks spatial structure, we found that 1) disturbances affect the Ks spatial structure in the topsoil, and 2) the largest differences in spatial patterns are associated with the subsoil permeability. In summary, the regional landslide activity seems to affect soil hydrology to a marginal extend only, which is in contrast to the pronounced drop of Ks after forest conversion. We used this spatial-temporal information combined with local rain intensities to assess the partitioning of rainfall into vertical and lateral flowpaths under undisturbed, disturbed, and regenerating land-cover types in the third study. It turned out that 1) the montane rainforest is characterized by prevailing vertical flowpaths in the topsoil, which can switch to lateral directions below 20 cm depth for a small number of rain events, which may, however, transport a high portion of the annual runoff; 2) similar hydrological flowpaths occur under the landslides except for a somewhat higher probability of impermeable layer formation in the topsoil of a young landslide, and 3) pronounced differences in runoff components can be observed for the human disturbance sequence involving the development of near-surface impeding layers for 24, 44, and 8 \% of rain events for pasture, a two-year-old fallow, and a ten-year-old fallow, respectively.},
  language  = {en}
}
@phdthesis{Zimmermann2009,
  author    = {Zimmermann, Alexander},
  title     = {Rainfall redistribution and change of water quality in tropical forest canopies : patterns and persistence},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-32556},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {Motivations and research objectives: During the passage of rain water through a forest canopy two main processes take place. First, water is redistributed; and second, its chemical properties change substantially. The rain water redistribution and the brief contact with plant surfaces results in a large variability of both throughfall and its chemical composition. Since throughfall and its chemistry influence a range of physical, chemical and biological processes at or below the forest floor the understanding of throughfall variability and the prediction of throughfall patterns potentially improves the understanding of near-surface processes in forest ecosystems. This thesis comprises three main research objectives. The first objective is to determine the variability of throughfall and its chemistry, and to investigate some of the controlling factors. Second, I explored throughfall spatial patterns. Finally, I attempted to assess the temporal persistence of throughfall and its chemical composition. Research sites and methods: The thesis is based on investigations in a tropical montane rain forest in Ecuador, and lowland rain forest ecosystems in Brazil and Panama. The first two studies investigate both throughfall and throughfall chemistry following a deterministic approach. The third study investigates throughfall patterns with geostatistical methods, and hence, relies on a stochastic approach. Results and Conclusions: Throughfall is highly variable. The variability of throughfall in tropical forests seems to exceed that of many temperate forests. These differences, however, do not solely reflect ecosystem-inherent characteristics, more likely they also mirror management practices. Apart from biotic factors that influence throughfall variability, rainfall magnitude is an important control. Throughfall solute concentrations and solute deposition are even more variable than throughfall. In contrast to throughfall volumes, the variability of solute deposition shows no clear differences between tropical and temperate forests, hence, biodiversity is not a strong predictor of solute deposition heterogeneity. Many other factors control solute deposition patterns, for instance, solute concentration in rainfall and antecedent dry period. The temporal variability of the latter factors partly accounts for the low temporal persistence of solute deposition. In contrast, measurements of throughfall volume are quite stable over time. Results from the Panamanian research site indicate that wet and dry areas outlast consecutive wet seasons. At this research site, throughfall exhibited only weak or pure nugget autocorrelation structures over the studies lag distances. A close look at the geostatistical tools at hand provided evidence that throughfall datasets, in particular those of large events, require robust variogram estimation if one wants to avoid outlier removal. This finding is important because all geostatistical throughfall studies that have been published so far analyzed their data using the classical, non-robust variogram estimator.},
  language  = {en}
}
@phdthesis{Zillmer2003,
  author    = {Zillmer, R{\"u}diger},
  title     = {Statistical properties and scaling of the Lyapunov exponents in stochastic systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001147},
  school      = {Universit{\"a}t Potsdam},
  year      = {2003},
  abstract  = {Die vorliegende Arbeit umfaßt drei Abhandlungen, welche allgemein mit einer stochastischen Theorie f{\"u}r die Lyapunov-Exponenten befaßt sind. Mit Hilfe dieser Theorie werden universelle Skalengesetze untersucht, die in gekoppelten chaotischen und ungeordneten Systemen auftreten. Zun{\"a}chst werden zwei zeitkontinuierliche stochastische Modelle f{\"u}r schwach gekoppelte chaotische Systeme eingef{\"u}hrt, um die Skalierung der Lyapunov-Exponenten mit der Kopplungsst{\"a}rke ('coupling sensitivity of chaos') zu untersuchen. Mit Hilfe des Fokker-Planck-Formalismus werden Skalengesetze hergeleitet, die von Ergebnissen numerischer Simulationen best{\"a}tigt werden. Anschließend wird gezeigt, daß 'coupling sensitivity' im Fall gekoppelter ungeordneter Ketten auftritt, wobei der Effekt sich durch ein singul{\"a}res Anwachsen der Lokalisierungsl{\"a}nge {\"a}ußert. Numerische Ergebnisse f{\"u}r gekoppelte Anderson-Modelle werden bekr{\"a}ftigt durch analytische Resultate f{\"u}r gekoppelte raumkontinuierliche Schr{\"o}dinger-Gleichungen. Das resultierende Skalengesetz f{\"u}r die Lokalisierungsl{\"a}nge {\"a}hnelt der Skalierung der Lyapunov-Exponenten gekoppelter chaotischer Systeme. Schließlich wird die Statistik der exponentiellen Wachstumsrate des linearen Oszillators mit parametrischem Rauschen studiert. Es wird gezeigt, daß die Verteilung des zeitabh{\"a}ngigen Lyapunov-Exponenten von der Normalverteilung abweicht. Mittels der verallgemeinerten Lyapunov-Exponenten wird der Parameterbereich bestimmt, in welchem die Abweichungen von der Normalverteilung signifikant sind und Multiskalierung wesentlich wird.},
  language  = {en}
}
@phdthesis{Ziese2014,
  author    = {Ziese, Ramona},
  title     = {Geometric electroelasticity},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-72504},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 113},
  year      = {2014},
  abstract  = {In this work a diffential geometric formulation of the theory of electroelasticity is developed which also includes thermal and magnetic influences. We study the motion of bodies consisting of an elastic material that are deformed by the influence of mechanical forces, heat and an external electromagnetic field. To this end physical balance laws (conservation of mass, balance of momentum, angular momentum and energy) are established. These provide an equation that describes the motion of the body during the deformation. Here the body and the surrounding space are modeled as Riemannian manifolds, and we allow that the body has a lower dimension than the surrounding space. In this way one is not (as usual) restricted to the description of the deformation of three-dimensional bodies in a three-dimensional space, but one can also describe the deformation of membranes and the deformation in a curved space. Moreover, we formulate so-called constitutive relations that encode the properties of the used material. Balance of energy as a scalar law can easily be formulated on a Riemannian manifold. The remaining balance laws are then obtained by demanding that balance of energy is invariant under the action of arbitrary diffeomorphisms on the surrounding space. This generalizes a result by Marsden and Hughes that pertains to bodies that have the same dimension as the surrounding space and does not allow the presence of electromagnetic fields. Usually, in works on electroelasticity the entropy inequality is used to decide which otherwise allowed deformations are physically admissible and which are not. It is alsoemployed to derive restrictions to the possible forms of constitutive relations describing the material. Unfortunately, the opinions on the physically correct statement of the entropy inequality diverge when electromagnetic fields are present. Moreover, it is unclear how to formulate the entropy inequality in the case of a membrane that is subjected to an electromagnetic field. Thus, we show that one can replace the use of the entropy inequality by the demand that for a given process balance of energy is invariant under the action of arbitrary diffeomorphisms on the surrounding space and under linear rescalings of the temperature. On the one hand, this demand also yields the desired restrictions to the form of the constitutive relations. On the other hand, it needs much weaker assumptions than the arguments in physics literature that are employing the entropy inequality. Again, our result generalizes a theorem of Marsden and Hughes. This time, our result is, like theirs, only valid for bodies that have the same dimension as the surrounding space.},
  language  = {en}
}
@phdthesis{Ziemann2022,
  author    = {Ziemann, Niklas},
  title     = {Four essays on the role of distance for economic decision-making},
  doi       = {10.25932/publishup-59107},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-591073},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 128},
  year      = {2022},
  abstract  = {Distances affect economic decision-making in numerous situations. The time at which we make a decision about future consumption has an impact on our consumption behavior. The spatial distance to employer, school or university impacts the place where we live and vice versa. The emotional closeness to other individuals influences our willingness to give money to them. This cumulative thesis aims to enrich the literature on the role of distance for economic decision-making. Thereby, each of my research projects sheds light on the impact of one kind of distance for efficient decision-making.},
  language  = {en}
}
@phdthesis{Ziehe2005,
  author    = {Ziehe, Andreas},
  title     = {Blind source separation based on joint diagonalization of matrices with applications in biomedical signal processing},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5694},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {This thesis is concerned with the solution of the blind source separation problem (BSS). The BSS problem occurs frequently in various scientific and technical applications. In essence, it consists in separating meaningful underlying components out of a mixture of a multitude of superimposed signals. In the recent research literature there are two related approaches to the BSS problem: The first is known as Independent Component Analysis (ICA), where the goal is to transform the data such that the components become as independent as possible. The second is based on the notion of diagonality of certain characteristic matrices derived from the data. Here the goal is to transform the matrices such that they become as diagonal as possible. In this thesis we study the latter method of approximate joint diagonalization (AJD) to achieve a solution of the BSS problem. After an introduction to the general setting, the thesis provides an overview on particular choices for the set of target matrices that can be used for BSS by joint diagonalization. As the main contribution of the thesis, new algorithms for approximate joint diagonalization of several matrices with non-orthogonal transformations are developed. These newly developed algorithms will be tested on synthetic benchmark datasets and compared to other previous diagonalization algorithms. Applications of the BSS methods to biomedical signal processing are discussed and exemplified with real-life data sets of multi-channel biomagnetic recordings.},
  subject      = {Signaltrennung},
  language  = {en}
}
@phdthesis{Ziegler2017,
  author    = {Ziegler, Moritz O.},
  title     = {The 3D in-situ stress field and its changes in geothermal reservoirs},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403838},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 110, XV},
  year      = {2017},
  abstract  = {Information on the contemporary in-situ stress state of the earth's crust is essential for geotechnical applications and physics-based seismic hazard assessment. Yet, stress data records for a data point are incomplete and their availability is usually not dense enough to allow conclusive statements. This demands a thorough examination of the in-situ stress field which is achieved by 3D geomechanicalnumerical models. However, the models spatial resolution is limited and the resulting local stress state is subject to large uncertainties that confine the significance of the findings. In addition, temporal variations of the in-situ stress field are naturally or anthropogenically induced. In my thesis I address these challenges in three manuscripts that investigate (1) the current crustal stress field orientation, (2) the 3D geomechanical-numerical modelling of the in-situ stress state, and (3) the phenomenon of injection induced temporal stress tensor rotations. In the first manuscript I present the first comprehensive stress data compilation of Iceland with 495 data records. Therefore, I analysed image logs from 57 boreholes in Iceland for indicators of the orientation of the maximum horizontal stress component. The study is the first stress survey from different kinds of stress indicators in a geologically very young and tectonically active area of an onshore spreading ridge. It reveals a distinct stress field with a depth independent stress orientation even very close to the spreading centre. In the second manuscript I present a calibrated 3D geomechanical-numerical modelling approach of the in-situ stress state of the Bavarian Molasse Basin that investigates the regional (70x70x10km³) and local (10x10x10km³) stress state. To link these two models I develop a multi-stage modelling approach that provides a reliable and efficient method to derive from the larger scale model initial and boundary conditions for the smaller scale model. Furthermore, I quantify the uncertainties in the models results which are inherent to geomechanical-numerical modelling in general and the multi-stage approach in particular. I show that the significance of the models results is mainly reduced due to the uncertainties in the material properties and the low number of available stress magnitude data records for calibration. In the third manuscript I investigate the phenomenon of injection induced temporal stress tensor rotation and its controlling factors. I conduct a sensitivity study with a 3D generic thermo-hydro-mechanical model. I show that the key control factors for the stress tensor rotation are the permeability as the decisive factor, the injection rate, and the initial differential stress. In particular for enhanced geothermal systems with a low permeability large rotations of the stress tensor are indicated. According to these findings the estimation of the initial differential stress in a reservoir is possible provided the permeability is known and the angle of stress rotation is observed. I propose that the stress tensor rotations can be a key factor in terms of the potential for induced seismicity on pre-existing faults due to the reorientation of the stress field that changes the optimal orientation of faults.},
  language  = {en}
}
@phdthesis{Zieger2017,
  author    = {Zieger, Tobias},
  title     = {Self-adaptive data quality},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410573},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 125},
  year      = {2017},
  abstract  = {Carrying out business processes successfully is closely linked to the quality of the data inventory in an organization. Lacks in data quality lead to problems: Incorrect address data prevents (timely) shipments to customers. Erroneous orders lead to returns and thus to unnecessary effort. Wrong pricing forces companies to miss out on revenues or to impair customer satisfaction. If orders or customer records cannot be retrieved, complaint management takes longer. Due to erroneous inventories, too few or too much supplies might be reordered. A special problem with data quality and the reason for many of the issues mentioned above are duplicates in databases. Duplicates are different representations of same real-world objects in a dataset. However, these representations differ from each other and are for that reason hard to match by a computer. Moreover, the number of required comparisons to find those duplicates grows with the square of the dataset size. To cleanse the data, these duplicates must be detected and removed. Duplicate detection is a very laborious process. To achieve satisfactory results, appropriate software must be created and configured (similarity measures, partitioning keys, thresholds, etc.). Both requires much manual effort and experience. This thesis addresses automation of parameter selection for duplicate detection and presents several novel approaches that eliminate the need for human experience in parts of the duplicate detection process. A pre-processing step is introduced that analyzes the datasets in question and classifies their attributes semantically. Not only do these annotations help understanding the respective datasets, but they also facilitate subsequent steps, for example, by selecting appropriate similarity measures or normalizing the data upfront. This approach works without schema information. Following that, we show a partitioning technique that strongly reduces the number of pair comparisons for the duplicate detection process. The approach automatically finds particularly suitable partitioning keys that simultaneously allow for effective and efficient duplicate retrieval. By means of a user study, we demonstrate that this technique finds partitioning keys that outperform expert suggestions and additionally does not need manual configuration. Furthermore, this approach can be applied independently of the attribute types. To measure the success of a duplicate detection process and to execute the described partitioning approach, a gold standard is required that provides information about the actual duplicates in a training dataset. This thesis presents a technique that uses existing duplicate detection results and crowdsourcing to create a near gold standard that can be used for the purposes above. Another part of the thesis describes and evaluates strategies how to reduce these crowdsourcing costs and to achieve a consensus with less effort.},
  language  = {en}
}
@phdthesis{Ziege2022,
  author    = {Ziege, Ricardo},
  title     = {Growth dynamics and mechanical properties of E. coli biofilms},
  doi       = {10.25932/publishup-55986},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-559869},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 123},
  year      = {2022},
  abstract  = {Biofilms are complex living materials that form as bacteria get embedded in a matrix of self-produced protein and polysaccharide fibres. The formation of a network of extracellular biopolymer fibres contributes to the cohesion of the biofilm by promoting cell-cell attachment and by mediating biofilm-substrate interactions. This sessile mode of bacteria growth has been well studied by microbiologists to prevent the detrimental effects of biofilms in medical and industrial settings. Indeed, biofilms are associated with increased antibiotic resistance in bacterial infections, and they can also cause clogging of pipelines or promote bio-corrosion. However, biofilms also gained interest from biophysics due to their ability to form complex morphological patterns during growth. Recently, the emerging field of engineered living materials investigates biofilm mechanical properties at multiple length scales and leverages the tools of synthetic biology to tune the functions of their constitutive biopolymers. This doctoral thesis aims at clarifying how the morphogenesis of Escherichia coli (E. coli) biofilms is influenced by their growth dynamics and mechanical properties. To address this question, I used methods from cell mechanics and materials science. I first studied how biological activity in biofilms gives rise to non-uniform growth patterns. In a second study, I investigated how E. coli biofilm morphogenesis and its mechanical properties adapt to an environmental stimulus, namely the water content of their substrate. Finally, I estimated how the mechanical properties of E. coli biofilms are altered when the bacteria express different extracellular biopolymers. On nutritive hydrogels, micron-sized E. coli cells can build centimetre-large biofilms. During this process, bacterial proliferation and matrix production introduce mechanical stresses in the biofilm, which release through the formation of macroscopic wrinkles and delaminated buckles. To relate these biological and mechanical phenomena, I used time-lapse fluorescence imaging to track cell and matrix surface densities through the early and late stages of E. coli biofilm growth. Colocalization of high cell and matrix densities at the periphery precede the onset of mechanical instabilities at this annular region. Early growth is detected at this outer annulus, which was analysed by adding fluorescent microspheres to the bacterial inoculum. But only when high rates of matrix production are present in the biofilm centre, does overall biofilm spreading initiate along the solid-air interface. By tracking larger fluorescent particles for a long time, I could distinguish several kinematic stages of E. coli biofilm expansion and observed a transition from non-linear to linear velocity profiles, which precedes the emergence of wrinkles at the biofilm periphery. Decomposing particle velocities to their radial and circumferential components revealed a last kinematic stage, where biofilm movement is mostly directed towards the radial delaminated buckles, which verticalize. The resulting compressive strains computed in these regions were observed to substantially deform the underlying agar substrates. The co-localization of higher cell and matrix densities towards an annular region and the succession of several kinematic stages are thus expected to promote the emergence of mechanical instabilities at the biofilm periphery. These experimental findings are predicted to advance future modelling approaches of biofilm morphogenesis. E. coli biofilm morphogenesis is further anticipated to depend on external stimuli from the environment. To clarify how the water could be used to tune biofilm material properties, we quantified E. coli biofilm growth, wrinkling dynamics and rigidity as a function of the water content of the nutritive substrates. Time-lapse microscopy and computational image analysis revealed that substrates with high water content promote biofilm spreading kinetics, while substrates with low water content promote biofilm wrinkling. The wrinkles observed on biofilm cross-sections appeared more bent on substrates with high water content, while they tended to be more vertical on substrates with low water content. Both wet and dry biomass, accumulated over 4 days of culture, were larger in biofilms cultured on substrates with high water content, despite extra porosity within the matrix layer. Finally, the micro-indentation analysis revealed that substrates with low water content supported the formation of stiffer biofilms. This study shows that E. coli biofilms respond to the water content of their substrate, which might be used for tuning their material properties in view of further applications. Biofilm material properties further depend on the composition and structure of the matrix of extracellular proteins and polysaccharides. In particular, E. coli biofilms were suggested to present tissue-like elasticity due to a dense fibre network consisting of amyloid curli and phosphoethanolamine-modified cellulose. To understand the contribution of these components to the emergent mechanical properties of E. coli biofilms, we performed micro-indentation on biofilms grown from bacteria of several strains. Besides showing higher dry masses, larger spreading diameters and slightly reduced water contents, biofilms expressing both main matrix components also presented high rigidities in the range of several hundred kPa, similar to biofilms containing only curli fibres. In contrast, a lack of amyloid curli fibres provides much higher adhesive energies and more viscoelastic fluid-like material behaviour. Therefore, the combination of amyloid curli and phosphoethanolamine-modified cellulose fibres implies the formation of a composite material whereby the amyloid curli fibres provide rigidity to E. coli biofilms, whereas the phosphoethanolamine-modified cellulose rather acts as a glue. These findings motivate further studies involving purified versions of these protein and polysaccharide components to better understand how their interactions benefit biofilm functions. All three studies depict different aspects of biofilm morphogenesis, which are interrelated. The first work reveals the correlation between non-uniform biological activities and the emergence of mechanical instabilities in the biofilm. The second work acknowledges the adaptive nature of E. coli biofilm morphogenesis and its mechanical properties to an environmental stimulus, namely water. Finally, the last study reveals the complementary role of the individual matrix components in the formation of a stable biofilm material, which not only forms complex morphologies but also functions as a protective shield for the bacteria it contains. Our experimental findings on E. coli biofilm morphogenesis and their mechanical properties can have further implications for fundamental and applied biofilm research fields.},
  language  = {en}
}
@phdthesis{Zickfeld2003,
  author    = {Zickfeld, Kirsten},
  title     = {Modeling large-scale singular climate events for integrated assessment},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001176},
  school      = {Universit{\"a}t Potsdam},
  year      = {2003},
  abstract  = {Erkenntnisse aus pal{\"a}oklimatologischen Studien, theoretischen Betrachtungen und Modellsimulationen deuten darauf hin, dass anthropogene Emissionen von Treibhausgasen und Aerosolen zu großskaligen, singul{\"a}ren Klimaereignissen f{\"u}hren k{\"o}nnten. Diese bezeichnen stark nichtlineare, abrupte Klima{\"a}nderungen, mit regionalen bis hin zu globalen Auswirkungen. Ziel dieser Arbeit ist die Entwicklung von Modellen zweier maßgeblicher Komponenten des Klimasystems, die singul{\"a}res Verhalten aufweisen k{\"o}nnten: die atlantische thermohaline Zirkulation (THC) und der indische Monsun. Diese Modelle sind so konzipiert, dass sie den Anforderungen der "Integrated Assessment"-Modellierung gen{\"u}gen, d.h., sie sind realistisch, recheneffizient, transparent und flexibel. Das THC-Modell ist ein einfaches, interhemisph{\"a}risches Boxmodell, das anhand von Daten kalibriert wird, die mit einem gekoppelten Klimamodell mittlerer Komplexit{\"a}t erzeugt wurden. Das Modell wird durch die globale Mitteltemperatur angetrieben, die mit Hilfe eines linearen Downscaling-Verfahrens in regionale W{\"a}rme- und S{\"u}ßwasserfl{\"u}sse {\"u}bersetzt wird. Die Ergebnisse einer Vielzahl von zeitabh{\"a}ngigen Simulationen zeigen, dass das Modell in der Lage ist, maßgebliche Eigenschaften des Verhaltens komplexer Klimamodelle wiederzugeben, wie die Sensitivit{\"a}t bez{\"u}glich des Ausmaßes, der regionalen Verteilung und der Rate der Klima{\"a}nderung. Der indische Monsun wird anhand eines neuartigen eindimensionalen Boxmodells der tropischen Atmosph{\"a}re beschrieben. Dieses enth{\"a}lt Parmetrisierungen der Oberfl{\"a}chen- und Strahlungsfl{\"u}sse, des hydrologischen Kreislaufs und derHydrologie der Landoberfl{\"a}che. Trotz des hohen Idealisierungsgrades ist das Modell in der Lage, relevante Aspekte der beobachteten Monsundynamik, wie z.B. den Jahresgang des Niederschlags und das Eintritts- sowie R{\"u}ckzugsdatum des Sommermonsuns, zufrieden stellend zu simulieren. Außerdem erfasst das Modell die Sensitivit{\"a}tdes Monsuns bez{\"u}glich {\"A}nderungen der Treibhausgas- und Aerosolkonzentrationen, die aus komplexeren Modellen bekannt sind. Eine vereinfachte Version des Monsunmodells wird f{\"u}r die Untersuchung des qualitativen Systemverhaltens in Abh{\"a}ngigkeit von {\"A}nderungen der Randbedingungen eingesetzt. Das bemerkenswerteste Ergebnis ist das Auftreten einer Sattelknotenbifurkation des Sommermonsuns f{\"u}r kritische Werte der Albedo oder der Sonneneinstrahlung. Dar{\"u}ber hinaus weist das Modell zwei stabile Zust{\"a}nde auf: neben dem niederschlagsreichen Sommermonsun besteht ein Zustand, der sich durch einen schwachen hydrologischen Kreislauf auszeichnet. Das Beachtliche an diesen Ergebnissen ist, dass anthropogene St{\"o}rungen der plantetaren Albedo, wie Schwefelemissionen und/oder Landnutzungs{\"a}nderungen, zu einer Destabilisierung des indischen Monsuns f{\"u}hren k{\"o}nnten. Das THC-Boxmodell findet exemplarische Anwendung in einem "Integrated Assessment" von Klimaschutzstrategien. Basierend auf dem konzeptionellen und methodischen Ger{\"u}st des Leitplankenansatzes werden Emissionskorridore (d.h. zul{\"a}ssige Spannen an CO2-Emissionen) berechnet, die das Risiko eines THC-Zusammenbruchs begrenzen sowie sozio{\"o}konomische Randbedingungen ber{\"u}cksichtigen. Die Ergebnisse zeigen u.a. eine starke Abh{\"a}ngigkeit der Breite der Emissionskorridore von der Klima- und hydrologischen Sensitivit{\"a}t. F{\"u}r kleine Werte einer oder beider Sensitivit{\"a}ten liegt der obere Korridorrand bei weit h{\"o}heren Emissionswerten als jene, die von plausiblen Emissionsszenarien f{\"u}r das 21. Jahrhundert erreicht werden. F{\"u}r große Werte der Sensitivit{\"a}ten hingegen, verlassen schon niedrige Emissionsszenarien den Korridor in den fr{\"u}hen Jahrzehnten des 21. Jahrhunderts. Dies impliziert eine Abkehr von den gegenw{\"a}rtigen Emissionstrends innherhalb der kommenden Jahrzehnte, wenn das Risko eines THC Zusammenbruchs gering gehalten werden soll. Anhand einer Vielzahl von Anwendungen - von Sensitivit{\"a}ts- {\"u}ber Bifurkationsanalysen hin zu integrierter Modellierung - zeigt diese Arbeit den Wert reduzierter Modelle auf. Die Ergebnisse und die daraus zu ziehenden Schlussfolgerungen liefern einen wertvollen Beitrag zu der wissenschaftlichen und politischen Diskussion bez{\"u}glich der Folgen des anthropogenen Klimawandels und der langfristigen Klimaschutzziele.},
  language  = {en}
}
@phdthesis{Zhou2024,
  author    = {Zhou, Xiangqian},
  title     = {Modeling of spatially distributed nitrate transport to investigate the effects of drought and river restoration in the Bode catchment, Central Germany},
  doi       = {10.25932/publishup-62105},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-621059},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 168},
  year      = {2024},
  abstract  = {The European Water Framework Directive (WFD) has identified river morphological alteration and diffuse pollution as the two main pressures affecting water bodies in Europe at the catchment scale. Consequently, river restoration has become a priority to achieve the WFD's objective of good ecological status. However, little is known about the effects of stream morphological changes, such as re-meandering, on in-stream nitrate retention at the river network scale. Therefore, catchment nitrate modeling is necessary to guide the implementation of spatially targeted and cost-effective mitigation measures. Meanwhile, Germany, like many other regions in central Europe, has experienced consecutive summer droughts from 2015-2018, resulting in significant changes in river nitrate concentrations in various catchments. However, the mechanistic exploration of catchment nitrate responses to changing weather conditions is still lacking. Firstly, a fully distributed, process-based catchment Nitrate model (mHM-Nitrate) was used, which was properly calibrated and comprehensively evaluated at numerous spatially distributed nitrate sampling locations. Three calibration schemes were designed, taking into account land use, stream order, and mean nitrate concentrations, and they varied in spatial coverage but used data from the same period (2011-2019). The model performance for discharge was similar among the three schemes, with Nash-Sutcliffe Efficiency (NSE) scores ranging from 0.88 to 0.92. However, for nitrate concentrations, scheme 2 outperformed schemes 1 and 3 when compared to observed data from eight gauging stations. This was likely because scheme 2 incorporated a diverse range of data, including low discharge values and nitrate concentrations, and thus provided a better representation of within-catchment heterogenous. Therefore, the study suggests that strategically selecting gauging stations that reflect the full range of within-catchment heterogeneity is more important for calibration than simply increasing the number of stations. Secondly, the mHM-Nitrate model was used to reveal the causal relations between sequential droughts and nitrate concentration in the Bode catchment (3200 km2) in central Germany, where stream nitrate concentrations exhibited contrasting trends from upstream to downstream reaches. The model was evaluated using data from six gauging stations, reflecting different levels of runoff components and their associated nitrate-mixing from upstream to downstream. Results indicated that the mHM-Nitrate model reproduced dynamics of daily discharge and nitrate concentration well, with Nash-Sutcliffe Efficiency ≥ 0.73 for discharge and Kling-Gupta Efficiency ≥ 0.50 for nitrate concentration at most stations. Particularly, the spatially contrasting trends of nitrate concentration were successfully captured by the model. The decrease of nitrate concentration in the lowland area in drought years (2015-2018) was presumably due to (1) limited terrestrial export loading (ca. 40\% lower than that of normal years 2004-2014), and (2) increased in-stream retention efficiency (20\% higher in summer within the whole river network). From a mechanistic modelling perspective, this study provided insights into spatially heterogeneous flow and nitrate dynamics and effects of sequential droughts, which shed light on water-quality responses to future climate change, as droughts are projected to be more frequent. Thirdly, this study investigated the effects of stream restoration via re-meandering on in-stream nitrate retention at network-scale in the well-monitored Bode catchment. The mHM-Nitrate model showed good performance in reproducing daily discharge and nitrate concentrations, with median Kling-Gupta values of 0.78 and 0.74, respectively. The mean and standard deviation of gross nitrate retention efficiency, which accounted for both denitrification and assimilatory uptake, were 5.1 ± 0.61\% and 74.7 ± 23.2\% in winter and summer, respectively, within the stream network. The study found that in the summer, denitrification rates were about two times higher in lowland sub-catchments dominated by agricultural lands than in mountainous sub-catchments dominated by forested areas, with median ± SD of 204 ± 22.6 and 102 ± 22.1 mg N m-2 d-1, respectively. Similarly, assimilatory uptake rates were approximately five times higher in streams surrounded by lowland agricultural areas than in those in higher-elevation, forested areas, with median ± SD of 200 ± 27.1 and 39.1 ± 8.7 mg N m-2 d-1, respectively. Therefore, restoration strategies targeting lowland agricultural areas may have greater potential for increasing nitrate retention. The study also found that restoring stream sinuosity could increase net nitrate retention efficiency by up to 25.4 ± 5.3\%, with greater effects seen in small streams. These results suggest that restoration efforts should consider augmenting stream sinuosity to increase nitrate retention and decrease nitrate concentrations at the catchment scale.},
  language  = {en}
}
@phdthesis{Zhou2017,
  author    = {Zhou, Bin},
  title     = {On the assessment of surface urban heat island},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404383},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 119},
  year      = {2017},
  abstract  = {Inwiefern St{\"a}dte unter den Megatrends der Urbanisierung und des Klimawandels nachhaltig gestaltet werden k{\"o}nnen, bleibt umstritten. Dies ist zum Teil auf unzureichende Kenntnisse der Mensch-Umwelt-Interaktionen zur{\"u}ckzuf{\"u}hren. Als die am vollst{\"a}ndigsten dokumentierte anthropogene Klimamodifikation ruft der Urbane Hitzeinsel (UHI) Effekt weltweit Sorgen hinsichtlich der Gesundheit der Bev{\"o}lkerung hervor. Dazu kommt noch ein immer h{\"a}ufigeres und intensiveres Auftreten von Hitzewellen, wodurch das Wohlbefinden der Stadtbewohner weiter beeintr{\"a}chtigt wird. Trotz eines deutlichen Anstiegs der Zahl der UHI-bezogenen Ver{\"o}ffentlichungen in den letzten Jahrzehnten haben die unterschiedlichen Definitionen von st{\"a}dtischen und l{\"a}ndlichen Gebieten in bisherigen Studien die allgemeine Vergleichbarkeit der Resultate stark erschwert. Dar{\"u}ber hinaus haben nur wenige Studien den UHI-Effekt und seine Einflussfaktoren anhand einer Kombination der Landnutzungsdaten und der thermischen Fernerkundung systematisch untersucht. Diese Arbeit stellt einen allgemeinen Rahmen zur Quantifizierung von UHI-Intensit{\"a}ten mittels eines automatisierten Algorithmus vor, wobei St{\"a}dte als Agglomerationen maximal r{\"a}umlicher Kontinuit{\"a}t basierend auf Landnutzungsdaten identifiziert, sowie deren l{\"a}ndliche Umfelder analog definiert werden. Durch Verkn{\"u}pfung der Landnutzungsdaten mit Landoberfl{\"a}chentemperaturen von Satelliten kann die UHI-Intensit{\"a}t robust und konsistent berechnet werden. Anhand dieser Innovation wurde nicht nur der Zusammenhang zwischen Stadtgr{\"o}ße und UHI-Intensit{\"a}t erneut untersucht, sondern auch die Auswirkungen der Stadtform auf die UHI-Intensit{\"a}t quantifiziert. Diese Arbeit leistet vielf{\"a}ltige Beitr{\"a}ge zum tieferen Verst{\"a}ndnis des UHI-Ph{\"a}nomens. Erstens wurde eine log-lineare Beziehung zwischen UHI-Intensit{\"a}t und Stadtgr{\"o}ße unter Ber{\"u}cksichtigung der 5,000 europ{\"a}ischen St{\"a}dte best{\"a}tigt. Werden kleinere St{\"a}dte auch ber{\"u}cksichtigt, ergibt sich eine log-logistische Beziehung. Zweitens besteht ein komplexes Zusammenspiel zwischen der Stadtform und der UHI-Intensit{\"a}t: die Stadtgr{\"o}ße stellt den st{\"a}rksten Einfluss auf die UHI-Intensit{\"a}t dar, gefolgt von der fraktalen Dimension und der Anisometrie. Allerdings zeigen ihre relativen Beitr{\"a}ge zur UHI-Intensit{\"a}t eine regionale Heterogenit{\"a}t, welche die Bedeutung r{\"a}umlicher Muster w{\"a}hrend der Umsetzung von UHI-Anpassungsmaßnahmen hervorhebt. Des Weiteren ergibt sich eine neue Saisonalit{\"a}t der UHI-Intensit{\"a}t f{\"u}r individuelle St{\"a}dte in Form von Hysteresekurven, die eine Phasenverschiebung zwischen den Zeitreihen der UHI-Intensit{\"a}t und der Hintergrundtemperatur andeutet. Diese Saisonalit{\"a}t wurde anhand von Luft- und Landoberfl{\"a}chentemperaturen untersucht, indem die Satellitenbeobachtung und die Modellierung der urbanen Grenzschicht mittels des UrbClim-Modells kombiniert wurden. Am Beispiel von London ist die Diskrepanz der Saisonalit{\"a}ten zwischen den beiden Temperaturen vor allem auf die mit der einfallenden Sonnenstrahlung verbundene Besonderheit der Landoberfl{\"a}chentemperatur zur{\"u}ckzuf{\"u}hren. Dar{\"u}ber hinaus spielt das regionale Klima eine wichtige Rolle bei der Entwicklung der UHI. Diese Arbeit ist eine der ersten Studien dieser Art, die eine systematische und statistische Untersuchung des UHI-Effektes erm{\"o}glicht. Die Ergebnisse sind von besonderer Bedeutung f{\"u}r die allgemeine r{\"a}umliche Planung und Regulierung auf Meso- und Makroebenen, damit sich Vorteile der rapiden Urbanisierung nutzbar machen und zeitgleich die folgende Hitzebelastung proaktiv vermindern lassen.},
  language  = {en}
}
@phdthesis{Zheng2021,
  author    = {Zheng, Chunming},
  title     = {Bursting and synchronization in noisy oscillatory systems},
  doi       = {10.25932/publishup-50019},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-500199},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 87},
  year      = {2021},
  abstract  = {Noise is ubiquitous in nature and usually results in rich dynamics in stochastic systems such as oscillatory systems, which exist in such various fields as physics, biology and complex networks. The correlation and synchronization of two or many oscillators are widely studied topics in recent years. In this thesis, we mainly investigate two problems, i.e., the stochastic bursting phenomenon in noisy excitable systems and synchronization in a three-dimensional Kuramoto model with noise. Stochastic bursting here refers to a sequence of coherent spike train, where each spike has random number of followers due to the combined effects of both time delay and noise. Synchronization, as a universal phenomenon in nonlinear dynamical systems, is well illustrated in the Kuramoto model, a prominent model in the description of collective motion. In the first part of this thesis, an idealized point process, valid if the characteristic timescales in the problem are well separated, is used to describe statistical properties such as the power spectral density and the interspike interval distribution. We show how the main parameters of the point process, the spontaneous excitation rate, and the probability to induce a spike during the delay action can be calculated from the solutions of a stationary and a forced Fokker-Planck equation. We extend it to the delay-coupled case and derive analytically the statistics of the spikes in each neuron, the pairwise correlations between any two neurons, and the spectrum of the total output from the network. In the second part, we investigate the three-dimensional noisy Kuramoto model, which can be used to describe the synchronization in a swarming model with helical trajectory. In the case without natural frequency, the Kuramoto model can be connected with the Vicsek model, which is widely studied in collective motion and swarming of active matter. We analyze the linear stability of the incoherent state and derive the critical coupling strength above which the incoherent state loses stability. In the limit of no natural frequency, an exact self-consistent equation of the mean field is derived and extended straightforward to any high-dimensional case.},
  language  = {en}
}
@phdthesis{Zhelavskaya2020,
  author    = {Zhelavskaya, Irina},
  title     = {Modeling of the Plasmasphere Dynamics},
  doi       = {10.25932/publishup-48243},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-482433},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xlii, 256},
  year      = {2020},
  abstract  = {The plasmasphere is a dynamic region of cold, dense plasma surrounding the Earth. Its shape and size are highly susceptible to variations in solar and geomagnetic conditions. Having an accurate model of plasma density in the plasmasphere is important for GNSS navigation and for predicting hazardous effects of radiation in space on spacecraft. The distribution of cold plasma and its dynamic dependence on solar wind and geomagnetic conditions remain, however, poorly quantified. Existing empirical models of plasma density tend to be oversimplified as they are based on statistical averages over static parameters. Understanding the global dynamics of the plasmasphere using observations from space remains a challenge, as existing density measurements are sparse and limited to locations where satellites can provide in-situ observations. In this dissertation, we demonstrate how such sparse electron density measurements can be used to reconstruct the global electron density distribution in the plasmasphere and capture its dynamic dependence on solar wind and geomagnetic conditions. First, we develop an automated algorithm to determine the electron density from in-situ measurements of the electric field on the Van Allen Probes spacecraft. In particular, we design a neural network to infer the upper hybrid resonance frequency from the dynamic spectrograms obtained with the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrumentation suite, which is then used to calculate the electron number density. The developed Neural-network-based Upper hybrid Resonance Determination (NURD) algorithm is applied to more than four years of EMFISIS measurements to produce the publicly available electron density data set. We utilize the obtained electron density data set to develop a new global model of plasma density by employing a neural network-based modeling approach. In addition to the location, the model takes the time history of geomagnetic indices and location as inputs, and produces electron density in the equatorial plane as an output. It is extensively validated using in-situ density measurements from the Van Allen Probes mission, and also by comparing the predicted global evolution of the plasmasphere with the global IMAGE EUV images of He+ distribution. The model successfully reproduces erosion of the plasmasphere on the night side as well as plume formation and evolution, and agrees well with data. The performance of neural networks strongly depends on the availability of training data, which is limited during intervals of high geomagnetic activity. In order to provide reliable density predictions during such intervals, we can employ physics-based modeling. We develop a new approach for optimally combining the neural network- and physics-based models of the plasmasphere by means of data assimilation. The developed approach utilizes advantages of both neural network- and physics-based modeling and produces reliable global plasma density reconstructions for quiet, disturbed, and extreme geomagnetic conditions. Finally, we extend the developed machine learning-based tools and apply them to another important problem in the field of space weather, the prediction of the geomagnetic index Kp. The Kp index is one of the most widely used indicators for space weather alerts and serves as input to various models, such as for the thermosphere, the radiation belts and the plasmasphere. It is therefore crucial to predict the Kp index accurately. Previous work in this area has mostly employed artificial neural networks to nowcast and make short-term predictions of Kp, basing their inferences on the recent history of Kp and solar wind measurements at L1. We analyze how the performance of neural networks compares to other machine learning algorithms for nowcasting and forecasting Kp for up to 12 hours ahead. Additionally, we investigate several machine learning and information theory methods for selecting the optimal inputs to a predictive model of Kp. The developed tools for feature selection can also be applied to other problems in space physics in order to reduce the input dimensionality and identify the most important drivers. Research outlined in this dissertation clearly demonstrates that machine learning tools can be used to develop empirical models from sparse data and also can be used to understand the underlying physical processes. Combining machine learning, physics-based modeling and data assimilation allows us to develop novel methods benefiting from these different approaches.},
  language  = {en}
}
@phdthesis{Zhang2023,
  author    = {Zhang, Xiaolin},
  title     = {Evaluation of nitrogen dynamics in high-order streams and rivers based on high-frequency monitoring},
  doi       = {10.25932/publishup-60764},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-607642},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 113},
  year      = {2023},
  abstract  = {Nutrient storage, transform and transport are important processes for achieving environmental and ecological health, as well as conducting water management plans. Nitrogen is one of the most noticeable elements due to its impacts on tremendous consequences of eutrophication in aquatic systems. Among all nitrogen components, researches on nitrate are blooming because of widespread deployments of in-situ high-frequency sensors. Monitoring and studying nitrate can become a paradigm for any other reactive substances that may damage environmental conditions and cause economic losses. Identifying nitrate storage and its transport within a catchment are inspiring to the management of agricultural activities and municipal planning. Storm events are periods when hydrological dynamics activate the exchange between nitrate storage and flow pathways. In this dissertation, long-term high-frequency monitoring data at three gauging stations in the Selke river were used to quantify event-scale nitrate concentration-discharge (C-Q) hysteretic relationships. The Selke catchment is characterized into three nested subcatchments by heterogeneous physiographic conditions and land use. With quantified hysteresis indices, impacts of seasonality and landscape gradients on C-Q relationships are explored. For example, arable area has deep nitrate legacy and can be activated with high intensity precipitation during wetting/wet periods (i.e., the strong hydrological connectivity). Hence, specific shapes of C-Q relationships in river networks can identify targeted locations and periods for agricultural management actions within the catchment to decrease nitrate output into downstream aquatic systems like the ocean. The capacity of streams for removing nitrate is of both scientific and social interest, which makes the quantification motivated. Although measurements of nitrate dynamics are advanced compared to other substances, the methodology to directly quantify nitrate uptake pathways is still limited spatiotemporally. The major problem is the complex convolution of hydrological and biogeochemical processes, which limits in-situ measurements (e.g., isotope addition) usually to small streams with steady flow conditions. This makes the extrapolation of nitrate dynamics to large streams highly uncertain. Hence, understanding of in-stream nitrate dynamic in large rivers is still necessary. High-frequency monitoring of nitrate mass balance between upstream and downstream measurement sites can quantitatively disentangle multi-path nitrate uptake dynamics at the reach scale (3-8 km). In this dissertation, we conducted this approach in large stream reaches with varying hydro-morphological and environmental conditions for several periods, confirming its success in disentangling nitrate uptake pathways and their temporal dynamics. Net nitrate uptake, autotrophic assimilation and heterotrophic uptake were disentangled, as well as their various diel and seasonal patterns. Natural streams generally can remove more nitrate under similar environmental conditions and heterotrophic uptake becomes dominant during post-wet seasons. Such two-station monitoring provided novel insights into reach-scale nitrate uptake processes in large streams. Long-term in-stream nitrate dynamics can also be evaluated with the application of water quality model. This is among the first time to use a data-model fusion approach to upscale the two-station methodology in large-streams with complex flow dynamics under long-term high-frequency monitoring, assessing the in-stream nitrate retention and its responses to drought disturbances from seasonal to sub-daily scale. Nitrate retention (both net uptake and net release) exhibited substantial seasonality, which also differed in the investigated normal and drought years. In the normal years, winter and early spring seasons exhibited extensive net releases, then general net uptake occurred after the annual high-flow season at later spring and early summer with autotrophic processes dominating and during later summer-autumn low-flow periods with heterotrophy-characteristics predominating. Net nitrate release occurred since late autumn until the next early spring. In the drought years, the late-autumn net releases were not so consistently persisted as in the normal years and the predominance of autotrophic processes occurred across seasons. Aforementioned comprehensive results of nitrate dynamics on stream scale facilitate the understanding of instream processes, as well as raise the importance of scientific monitoring schemes for hydrology and water quality parameters.},
  language  = {en}
}
@phdthesis{Zhang2020,
  author    = {Zhang, Jianrui},
  title     = {Completely water-based emulsions as compartmentalized systems via pickering stabilization},
  doi       = {10.25932/publishup-47654},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476542},
  school      = {Universit{\"a}t Potsdam},
  pages     = {II, 119},
  year      = {2020},
  abstract  = {Completely water-based systems are of interest for the development of novel material for various reasons: On one hand, they provide benign environment for biological systems and on the other hand they facilitate effective molecular transport in a membrane-free environment. In order to investigate the general potential of aqueous two-phase systems (ATPSs) for biomaterials and compartmentalized systems, various solid particles were applied to stabilize all-aqueous emulsion droplets. The target ATPS to be investigated should be prepared via mixing of two aqueous solutions of water-soluble polymers, which turn biphasic when exceeding a critical polymer concentration. Hydrophilic polymers with a wide range of molar mass such as dextran/poly(ethylene glycol) (PEG) can therefore be applied. Solid particles adsorbed at the interfaces can be exceptionally efficient stabilizers forming so-called Pickering emulsions, and nanoparticles can bridge the correlation length of polymer solutions and are thereby the best option for water-in-water emulsions. The first approach towards the investigation of ATPS was conducted with all aqueous dextran-PEG emulsions in the presence of poly(dopamine) particles (PDP) in Chapter 4. The water-in-water emulsions were formed with a PEG/dextran system via utilizing PDP as stabilizers. Studies of the formed emulsions were performed via laser scanning confocal microscope (CLSM), optical microscope (OM), cryo-scanning electron microscope (SEM) and tensiometry. The stable emulsions (at least 16 weeks) were demulsified easily via dilution or surfactant addition. Furthermore, the solid PDP at the water-water interface were crosslinked in order to inhibit demulsification of the Pickering emulsion. Transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to visualize the morphology of PDP before and after crosslinking. PDP stabilized water-in-water emulsions were utilized in the following Chapter 5 to form supramolecular compartmentalized hydrogels. Here, hydrogels were prepared in pre-formed water-in-water emulsions and gelled via α-cyclodextrin-PEG (α-CD-PEG) inclusion complex formation. Studies of the formed complexes were performed via X-ray powder diffraction (XRD) and the mechanical properties of the hydrogels were measured with oscillatory shear rheology. In order to verify the compartmentalized state and its triggered decomposition, hydrogels and emulsions were assessed via OM, SEM and CLSM. The last chapter broadens the investigations from the previous two systems by utilizing various carbon nitrides (CN) as different stabilizers in ATPS. CN introduces another way to trigger demulsification, namely irradiation with visible light. Therefore, emulsification and demulsification with various triggers were probed. The investigated all aqueous multi-phase systems will act as model for future fabrication of biocompatible materials, cell micropatterning as well as separation of compartmentalized systems.},
  language  = {en}
}
@phdthesis{Zhang2008,
  author    = {Zhang, Bo},
  title     = {Magnetic fields near microstructured surfaces : application to atom chips},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-28984},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Microfabricated solid-state surfaces, also called atom chip', have become a well-established technique to trap and manipulate atoms. This has simplified applications in atom interferometry, quantum information processing, and studies of many-body systems. Magnetic trapping potentials with arbitrary geommetries are generated with atom chip by miniaturized current-carrying conductors integrated on a solid substrate. Atoms can be trapped and cooled to microKelvin and even nanoKelvin temperatures in such microchip trap. However, cold atoms can be significantly perturbed by the chip surface, typically held at room temperature. The magnetic field fluctuations generated by thermal currents in the chip elements may induce spin flips of atoms and result in loss, heating and decoherence. In this thesis, we extend previous work on spin flip rates induced by magnetic noise and consider the more complex geometries that are typically encountered in atom chips: layered structures and metallic wires of finite cross-section. We also discuss a few aspects of atom chips traps built with superconducting structures that have been suggested as a means to suppress magnetic field fluctuations. The thesis describes calculations of spin flip rates based on magnetic Green functions that are computed analytically and numerically. For a chip with a top metallic layer, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a much smaller conductivity. Based on this result, scaling laws for loss rates above a thin metallic layer are derived. A good agreement with experiments is obtained in the regime where the atom-surface distance is comparable to the skin depth of metal. Since in the experiments, metallic layers are always etched to separate wires carrying different currents, the impact of the finite lateral wire size on the magnetic noise has been taken into account. The local spectrum of the magnetic field near a metallic microstructure has been investigated numerically with the help of boundary integral equations. The magnetic noise significantly depends on polarizations above flat wires with finite lateral width, in stark contrast to an infinitely wide wire. Correlations between multiple wires are also taken into account. In the last part, superconducting atom chips are considered. Magnetic traps generated by superconducting wires in the Meissner state and the mixed state are studied analytically by a conformal mapping method and also numerically. The properties of the traps created by superconducting wires are investigated and compared to normal conducting wires: they behave qualitatively quite similar and open a route to further trap miniaturization, due to the advantage of low magnetic noise. We discuss critical currents and fields for several geometries.},
  language  = {en}
}
@phdthesis{Zhang2005,
  author    = {Zhang, Baichen},
  title     = {Dissection of phloem transport in cucurbitaceae by metabolomic analysis},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6644},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {This thesis aimed to investigate several fundamental and perplexing questions relating to the phloem loading and transport mechanisms of Cucurbita maxima, by combining metabolomic analysis with cell biological techniques. This putative symplastic loading species has long been used for experiments on phloem anatomy, phloem biochemistry, phloem transport physiology and phloem signalling. Symplastic loading species have been proposed to use a polymer trapping mechanism to accumulate RFO (raffinose family oligosaccharides) sugars to build up high osmotic pressure in minor veins which sustains a concentration gradient that drives mass flow. However, extensive evidence indicating a low sugar concentration in their phloem exudates is a long-known problem that conflicts with this hypothesis. Previous metabolomic analysis shows the concentration of many small molecules in phloem exudates is higher than that of leaf tissues, which indicates an active apoplastic loading step. Therefore, in the view of the phloem metabolome, a symplastic loading mechanism cannot explain how small molecules other than RFO sugars are loaded into phloem. Most studies of phloem physiology using cucurbits have neglected the possible functions of vascular architecture in phloem transport. It is well known that there are two phloem systems in cucurbits with distinctly different anatomical features: central phloem and extrafascicular phloem. However, mistaken conclusions on sources of cucurbit phloem exudation from previous reports have hindered consideration of the idea that there may be important differences between these two phloem systems. The major results are summarized as below: 1) O-linked glycans in C.maxima were structurally identified as beta-1,3 linked glucose polymers, and the composition of glycans in cucurbits was found to be species-specific. Inter-species grafting experiments proved that these glycans are phloem mobile and transported uni-directionally from scion to stock. 2) As indicated by stable isotopic labelling experiments, a considerable amount of carbon is incorporated into small metabolites in phloem exudates. However, the incorporation of carbon into RFO sugars is much faster than for other metabolites. 3) Both CO2 labelling experiments and comparative metabolomic analysis of phloem exudates and leaf tissues indicated that metabolic processes other than RFO sugar metabolism play an important role in cucurbit phloem physiology. 4) The underlying assumption that the central phloem of cucurbits continuously releases exudates after physical incision was proved wrong by rigorous experiments including direct observation by normal microscopy and combined multiple-microscopic methods. Errors in previous experimental confirmation of phloem exudation in cucurbits are critically discussed. 5) Extrafascicular phloem was proved to be functional, as indicated by phloem-mobile carboxyfluorescein tracer studies. Commissural sieve tubes interconnect phloem bundles into a complete super-symplastic network. 6) Extrafascicular phloem represents the main source of exudates following physical incision. The major transported metabolites by these extrafacicular phloem are non-sugar compounds including amino acids, O-glycans, amines. 7) Central phloem contains almost exclusively RFO sugars, the estimated amount of which is up to 1 to 2 molar. The major RFO sugar present in central phloem is stachyose. 8) Cucurbits utilize two structurally different phloem systems for transporting different group of metabolites (RFO sugars and non-RFO sugar compounds). This implies that cucurbits may use spatially separated loading mechanisms (apoplastic loading for extrafascicular phloem and symplastic loading for central phloem) for supply of nutrients to sinks. 9) Along the transport systems, RFO sugars were mainly distributed within central phloem tissues. There were only small amounts of RFO sugars present in xylem tissues (millimolar range) and trace amounts of RFO sugars in cortex and pith. The composition of small molecules in external central phloem is very different from that in internal central phloem. 10) Aggregated P-proteins were manually dissected from central phloem and analysed by both SDS-PAGE and mass spectrometry. Partial sequences of peptides were obtained by QTOF de novo sequencing from trypsin digests of three SDS-PAGE bands. None of these partial sequences shows significant homology to known cucurbit phloem proteins or other plant proteins. This proves that these central phloem proteins are a completely new group of proteins different from those in extrafascicular phloem. The extensively analysed P-proteins reported in literature to date are therefore now shown to arise from extrafascicular phloem and not central phloem, and therefore do not appear to be involved in the occlusion processes in central phloem.},
  subject      = {phloem},
  language  = {en}
}
@phdthesis{Zeuschner2022,
  author    = {Zeuschner, Steffen Peer},
  title     = {Magnetoacoustics observed with ultrafast x-ray diffraction},
  doi       = {10.25932/publishup-56109},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-561098},
  school      = {Universit{\"a}t Potsdam},
  pages     = {V, 128, IX},
  year      = {2022},
  abstract  = {In the present thesis I investigate the lattice dynamics of thin film hetero structures of magnetically ordered materials upon femtosecond laser excitation as a probing and manipulation scheme for the spin system. The quantitative assessment of laser induced thermal dynamics as well as generated picosecond acoustic pulses and their respective impact on the magnetization dynamics of thin films is a challenging endeavor. All the more, the development and implementation of effective experimental tools and comprehensive models are paramount to propel future academic and technological progress. In all experiments in the scope of this cumulative dissertation, I examine the crystal lattice of nanoscale thin films upon the excitation with femtosecond laser pulses. The relative change of the lattice constant due to thermal expansion or picosecond strain pulses is directly monitored by an ultrafast X-ray diffraction (UXRD) setup with a femtosecond laser-driven plasma X-ray source (PXS). Phonons and spins alike exert stress on the lattice, which responds according to the elastic properties of the material, rendering the lattice a versatile sensor for all sorts of ultrafast interactions. On the one hand, I investigate materials with strong magneto-elastic properties; The highly magnetostrictive rare-earth compound TbFe2, elemental Dysprosium or the technological relevant Invar material FePt. On the other hand I conduct a comprehensive study on the lattice dynamics of Bi1Y2Fe5O12 (Bi:YIG), which exhibits high-frequency coherent spin dynamics upon femtosecond laser excitation according to the literature. Higher order standing spinwaves (SSWs) are triggered by coherent and incoherent motion of atoms, in other words phonons, which I quantified with UXRD. We are able to unite the experimental observations of the lattice and magnetization dynamics qualitatively and quantitatively. This is done with a combination of multi-temperature, elastic, magneto-elastic, anisotropy and micro-magnetic modeling. The collective data from UXRD, to probe the lattice, and time-resolved magneto-optical Kerr effect (tr-MOKE) measurements, to monitor the magnetization, were previously collected at different experimental setups. To improve the precision of the quantitative assessment of lattice and magnetization dynamics alike, our group implemented a combination of UXRD and tr-MOKE in a singular experimental setup, which is to my knowledge, the first of its kind. I helped with the conception and commissioning of this novel experimental station, which allows the simultaneous observation of lattice and magnetization dynamics on an ultrafast timescale under identical excitation conditions. Furthermore, I developed a new X-ray diffraction measurement routine which significantly reduces the measurement time of UXRD experiments by up to an order of magnitude. It is called reciprocal space slicing (RSS) and utilizes an area detector to monitor the angular motion of X-ray diffraction peaks, which is associated with lattice constant changes, without a time-consuming scan of the diffraction angles with the goniometer. RSS is particularly useful for ultrafast diffraction experiments, since measurement time at large scale facilities like synchrotrons and free electron lasers is a scarce and expensive resource. However, RSS is not limited to ultrafast experiments and can even be extended to other diffraction techniques with neutrons or electrons.},
  language  = {en}
}
@phdthesis{Zenichowski2012,
  author    = {Zenichowski, Karl},
  title     = {Quantum dynamical study of Si(100) surface-mounted, STM-driven switches at the atomic and molecular scale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62156},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {The aim of this thesis is the quantum dynamical study of two examples of scanning tunneling microscope (STM)-controllable, Si(100)(2x1) surface-mounted switches of atomic and molecular scale. The first example considers the switching of single H-atoms between two dangling-bond chemisorption sites on a Si-dimer of the Si(100) surface (Grey et al., 1996). The second system examines the conformational switching of single 1,5-cyclooctadiene molecules chemisorbed on the Si(100) surface (Nacci et al., 2008). The temporal dynamics are provided by the propagation of the density matrix in time via an according set of equations of motion (EQM). The latter are based on the open-system density matrix theory in Lindblad form. First order perturbation theory is used to evaluate those transition rates between vibrational levels of the system part. In order to account for interactions with the surface phonons, two different dissipative models are used, namely the bilinear, harmonic and the Ohmic bath model. IET-induced vibrational transitions in the system are due to the dipole- and the resonance-mechanism. A single surface approach is used to study the influence of dipole scattering and resonance scattering in the below-threshold regime. Further, a second electronic surface was included to study the resonance-induced switching in the above-threshold regime. Static properties of the adsorbate, e.g., potentials and dipole function and potentials, are obtained from quantum chemistry and used within the established quantum dynamical models.},
  language  = {en}
}
@phdthesis{Zemanova2007,
  author    = {Zemanov{\´a}, Lucia},
  title     = {Structure-function relationship in hierarchical model of brain networks},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18400},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {The mammalian brain is, with its numerous neural elements and structured complex connectivity, one of the most complex systems in nature. Recently, large-scale corticocortical connectivities, both structural and functional, have received a great deal of research attention, especially using the approach of complex networks. Here, we try to shed some light on the relationship between structural and functional connectivities by studying synchronization dynamics in a realistic anatomical network of cat cortical connectivity. We model the cortical areas by a subnetwork of interacting excitable neurons (multilevel model) and by a neural mass model (population model). With weak couplings, the multilevel model displays biologically plausible dynamics and the synchronization patterns reveal a hierarchical cluster organization in the network structure. We can identify a group of brain areas involved in multifunctional tasks by comparing the dynamical clusters to the topological communities of the network. With strong couplings of multilevel model and by using neural mass model, the dynamics are characterized by well-defined oscillations. The synchronization patterns are mainly determined by the node intensity (total input strengths of a node); the detailed network topology is of secondary importance. The biologically improved multilevel model exhibits similar dynamical patterns in the two regimes. Thus, the study of synchronization in a multilevel complex network model of cortex can provide insights into the relationship between network topology and functional organization of complex brain networks.},
  language  = {en}
}
@phdthesis{Zeitz2022,
  author    = {Zeitz, Maria},
  title     = {Modeling the future resilience of the Greenland Ice Sheet},
  doi       = {10.25932/publishup-56883},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-568839},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 189},
  year      = {2022},
  abstract  = {The Greenland Ice Sheet is the second-largest mass of ice on Earth. Being almost 2000 km long, more than 700 km wide, and more than 3 km thick at the summit, it holds enough ice to raise global sea levels by 7m if melted completely. Despite its massive size, it is particularly vulnerable to anthropogenic climate change: temperatures over the Greenland Ice Sheet have increased by more than 2.7◦C in the past 30 years, twice as much as the global mean temperature. Consequently, the ice sheet has been significantly losing mass since the 1980s and the rate of loss has increased sixfold since then. Moreover, it is one of the potential tipping elements of the Earth System, which might undergo irreversible change once a warming threshold is exceeded. This thesis aims at extending the understanding of the resilience of the Greenland Ice Sheet against global warming by analyzing processes and feedbacks relevant to its centennial to multi-millennial stability using ice sheet modeling. One of these feedbacks, the melt-elevation-feedback is driven by the temperature rise with decreasing altitudes: As the ice sheet melts, its thickness and surface elevation decrease, exposing the ice surface to warmer air and thus increasing the melt rates even further. The glacial isostatic adjustment (GIA) can partly mitigate this melt-elevation feedback as the bedrock lifts in response to an ice load decrease, forming the negative GIA feedback. In my thesis, I show that the interaction between these two competing feedbacks can lead to qualitatively different dynamical responses of the Greenland Ice Sheet to warming - from permanent loss to incomplete recovery, depending on the feedback parameters. My research shows that the interaction of those feedbacks can initiate self-sustained oscillations of the ice volume while the climate forcing remains constant. Furthermore, the increased surface melt changes the optical properties of the snow or ice surface, e.g. by lowering their albedo, which in turn enhances melt rates - a process known as the melt-albedo feedback. Process-based ice sheet models often neglect this melt-albedo feedback. To close this gap, I implemented a simplified version of the diurnal Energy Balance Model, a computationally efficient approach that can capture the first-order effects of the melt-albedo feedback, into the Parallel Ice Sheet Model (PISM). Using the coupled model, I show in warming experiments that the melt-albedo feedback almost doubles the ice loss until the year 2300 under the low greenhouse gas emission scenario RCP2.6, compared to simulations where the melt-albedo feedback is neglected, and adds up to 58\% additional ice loss under the high emission scenario RCP8.5. Moreover, I find that the melt-albedo feedback dominates the ice loss until 2300, compared to the melt-elevation feedback. Another process that could influence the resilience of the Greenland Ice Sheet is the warming induced softening of the ice and the resulting increase in flow. In my thesis, I show with PISM how the uncertainty in Glen's flow law impacts the simulated response to warming. In a flow line setup at fixed climatic mass balance, the uncertainty in flow parameters leads to a range of ice loss comparable to the range caused by different warming levels. While I focus on fundamental processes, feedbacks, and their interactions in the first three projects of my thesis, I also explore the impact of specific climate scenarios on the sea level rise contribution of the Greenland Ice Sheet. To increase the carbon budget flexibility, some warming scenarios - while still staying within the limits of the Paris Agreement - include a temporal overshoot of global warming. I show that an overshoot by 0.4◦C increases the short-term and long-term ice loss from Greenland by several centimeters. The long-term increase is driven by the warming at high latitudes, which persists even when global warming is reversed. This leads to a substantial long-term commitment of the sea level rise contribution from the Greenland Ice Sheet. Overall, in my thesis I show that the melt-albedo feedback is most relevant for the ice loss of the Greenland Ice Sheet on centennial timescales. In contrast, the melt-elevation feedback and its interplay with the GIA feedback become increasingly relevant on millennial timescales. All of these influence the resilience of the Greenland Ice Sheet against global warming, in the near future and on the long term.},
  language  = {en}
}
@phdthesis{Zeckra2020,
  author    = {Zeckra, Martin},
  title     = {Seismological and seismotectonic analysis of the northwestern Argentine Central Andean foreland},
  doi       = {10.25932/publishup-47324},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473240},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 120},
  year      = {2020},
  abstract  = {After a severe M W 5.7 earthquake on October 17, 2015 in El Galp{\´o}n in the province of Salta NW Argentina, I installed a local seismological network around the estimated epicenter. The network covered an area characterized by inherited Cretaceous normal faults and neotectonic faults with unknown recurrence intervals, some of which may have been reactivated normal faults. The 13 three-component seismic stations recorded data continuously for 15 months. The 2015 earthquake took place in the Santa B{\´a}rbara System of the Andean foreland, at about 17km depth. This region is the easternmost morphostructural region of the central Andes. As a part of the broken foreland, it is bounded to the north by the Subandes fold-and-thrust belt and the Sierras Pampeanas to the south; to the east lies the Chaco-Paran{\´a} basin. A multi-stage morphotectonic evolution with thick-skinned basement uplift and coeval thin-skinned deformation in the intermontane basins is suggested for the study area. The release of stresses associated with the foreland deformation can result in strong earthquakes, as the study area is known for recurrent and historical, destructive earthquakes. The available continuous record reaches back in time, when the strongest event in 1692 (magnitude 7 or intensity IX) destroyed the city of Esteco. Destructive earthquakes and surface deformation are thus a hallmark of this part of the Andean foreland. With state-of-the-art Python packages (e.g. pyrocko, ObsPy), a semi-automatic approach is followed to analyze the collected continuous data of the seismological network. The resulting 1435 hypocenter locations consist of three different groups: 1.) local crustal earthquakes (nearly half of the events belong to this group), 2.) interplate activity, of regional distance in the slab of the Nazca-plate, and 3.) very deep earthquakes at about 600km depth. My major interest focused on the first event class. Those crustal events are partly aftershock events of the El Galp{\´o}n earthquake and a second earthquake, in the south of the same fault. Further events can be considered as background seismicity of other faults within the study area. Strikingly, the seismogenic zone encompass the whole crust and propagates brittle deformation down, close to the Moho. From the collected seismological data, a local seismic velocity model is estimated, using VELEST. After the execution of various stability tests, the robust minimum 1D-velocity model implies guiding values for the composition of the local, subsurface structure of the crust. Afterwards, performing a hypocenter relocation enables the assignment of individual earthquakes to aftershock clusters or extended seismotectonic structures. This allows the mapping of previously unknown seismogenic faults. Finally, focal mechanisms are modeled for events with acurately located hypocenters, using the newly derived local velocity model. A compressive regime is attested by the majority of focal mechanisms, while the strike direction of the individual seismogenic structures is in agreement with the overall north - south orientation of the Central Andes, its mountain front, and individual mountain ranges in the southern Santa-B{\´a}rbara-System.},
  language  = {en}
}
@phdthesis{Zaupa2010,
  author    = {Zaupa, Alessandro},
  title     = {Physical crosslinking of gelatin : a supramolecular approach to biomaterials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52888},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {This work describes the realization of physically crosslinked networks based on gelatin by the introduction of functional groups enabling specific supramolecular interactions. Molecular models were developed in order to predict the material properties and permit to establish a knowledge-based approach to material design. The effect of additional supramolecular interactions with hydroxyapaptite was then studied in composite materials. The calculated properties are compared to experimental results to validate the models. The models are then further used for the study of physically crosslinked networks. Gelatin was functionalized with desaminotyrosine (DAT) and desaminotyrosyl-tyrosine (DATT) side groups, derived from the natural amino acid tyrosine. These group can potentially undergo to π-π and hydrogen bonding interactions also under physiological conditions. Molecular dynamics (MD) simulations were performed on models with 0.8 wt.-\% or 25 wt.-\% water content, using the second generation forcefield CFF91. The validation of the models was obtained by the comparison with specific experimental data such as, density, peptide conformational angles and X-ray scattering spectra. The models were then used to predict the supramolecular organization of the polymer chain, analyze the formation of physical netpoints and calculate the mechanical properties. An important finding of simulation was that with the increase of aromatic groups also the number of observed physical netpoints increased. The number of relatively stable physical netpoints, on average zero 0 for natural gelatin, increased to 1 and 6 for DAT and DATT functionalized gelatins respectively. A comparison with the Flory-Rehner model suggested reduced equilibrium swelling by factor 6 of the DATT-functionalized materials in water. The functionalized gelatins could be synthesized by chemoselective coupling of the free carboxylic acid groups of DAT and DATT to the free amino groups of gelatin. At 25 wt.-\% water content, the simulated and experimentally determined elastic mechanical properties (e.g. Young Modulus) were both in the order of GPa and were not influenced by the degree of aromatic modification. The experimental equilibrium degree of swelling in water decreased with increasing the number of inserted aromatic functions (from 2800 vol.-\% for pure gelatin to 300 vol.-\% for the DATT modified gelatin), at the same time, Young's modulus, elongation at break, and maximum tensile strength increased. It could be show that the functionalization with DAT and DATT influences the chain organization of gelatin based materials together with a controlled drying condition. Functionalization with DAT and DATT lead to a drastic reduction of helical renaturation, that could be more finely controlled by the applied drying conditions. The properties of the materials could then be influenced by application of two independent methods. Composite materials of DAT and DATT functionalized gelatins with hydroxyapatite (HAp) show a drastic reduction of swelling degree. In tensile tests and rheological measurements, the composites equilibrated in water had increased Young's moduli (from 200 kPa up to 2 MPa) and tensile strength (from 57 kPa up to 1.1 MPa) compared to the natural polymer matrix without affecting the elongation at break. Furthermore, an increased thermal stability from 40 °C to 85 °C of the networks could be demonstrated. The differences of the behaviour of the functionalized gelatins to pure gelatin as matrix suggested an additional stabilizing bond between the incorporated aromatic groups to the hydroxyapatite.},
  language  = {en}
}
@phdthesis{Zass2021,
  author    = {Zass, Alexander},
  title     = {A multifaceted study of marked Gibbs point processes},
  doi       = {10.25932/publishup-51277},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512775},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 104},
  year      = {2021},
  abstract  = {This thesis focuses on the study of marked Gibbs point processes, in particular presenting some results on their existence and uniqueness, with ideas and techniques drawn from different areas of statistical mechanics: the entropy method from large deviations theory, cluster expansion and the Kirkwood--Salsburg equations, the Dobrushin contraction principle and disagreement percolation. We first present an existence result for infinite-volume marked Gibbs point processes. More precisely, we use the so-called entropy method (and large-deviation tools) to construct marked Gibbs point processes in R^d under quite general assumptions. In particular, the random marks belong to a general normed space S and are not bounded. Moreover, we allow for interaction functionals that may be unbounded and whose range is finite but random. The entropy method relies on showing that a family of finite-volume Gibbs point processes belongs to sequentially compact entropy level sets, and is therefore tight. We then present infinite-dimensional Langevin diffusions, that we put in interaction via a Gibbsian description. In this setting, we are able to adapt the general result above to show the existence of the associated infinite-volume measure. We also study its correlation functions via cluster expansion techniques, and obtain the uniqueness of the Gibbs process for all inverse temperatures β and activities z below a certain threshold. This method relies in first showing that the correlation functions of the process satisfy a so-called Ruelle bound, and then using it to solve a fixed point problem in an appropriate Banach space. The uniqueness domain we obtain consists then of the model parameters z and β for which such a problem has exactly one solution. Finally, we explore further the question of uniqueness of infinite-volume Gibbs point processes on R^d, in the unmarked setting. We present, in the context of repulsive interactions with a hard-core component, a novel approach to uniqueness by applying the discrete Dobrushin criterion to the continuum framework. We first fix a discretisation parameter a>0 and then study the behaviour of the uniqueness domain as a goes to 0. With this technique we are able to obtain explicit thresholds for the parameters z and β, which we then compare to existing results coming from the different methods of cluster expansion and disagreement percolation. Throughout this thesis, we illustrate our theoretical results with various examples both from classical statistical mechanics and stochastic geometry.},
  language  = {en}
}
@phdthesis{Zarafshani2012,
  author    = {Zarafshani, Zoya},
  title     = {Chain-end functionalization and modification of polymers using modular chemical reactions},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59723},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {Taking advantage of ATRP and using functionalized initiators, different functionalities were introduced in both α and ω chain-ends of synthetic polymers. These functionalized polymers could then go through modular synthetic pathways such as click cycloaddition (copper-catalyzed or copper-free) or amidation to couple synthetic polymers to other synthetic polymers, biomolecules or silica monoliths. Using this general strategy and designing these co/polymers so that they are thermoresponsive, yet bioinert and biocompatible with adjustable cloud point values (as it is the case in the present thesis), the whole generated system becomes "smart" and potentially applicable in different branches. The applications which were considered in the present thesis were in polymer post-functionalization (in situ functionalization of micellar aggregates with low and high molecular weight molecules), hydrophilic/hydrophobic tuning, chromatography and bioconjugation (enzyme thermoprecipitation and recovery, improvement of enzyme activity). Different α-functionalized co/polymers containing cholesterol moiety, aldehyde, t-Boc protected amine, TMS-protected alkyne and NHS-activated ester were designed and synthesized in this work.},
  language  = {en}
}
@phdthesis{Zapata2019,
  author    = {Zapata, Sebastian Henao},
  title     = {Paleozoic to Pliocene evolution of the Andean retroarc between 26 and 28°S: interactions between tectonics, climate, and upper plate architecture},
  doi       = {10.25932/publishup-43903},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439036},
  school      = {Universit{\"a}t Potsdam},
  pages     = {139},
  year      = {2019},
  abstract  = {Interactions and feedbacks between tectonics, climate, and upper plate architecture control basin geometry, relief, and depositional systems. The Andes is part of a longlived continental margin characterized by multiple tectonic cycles which have strongly modified the Andean upper plate architecture. In the Andean retroarc, spatiotemporal variations in the structure of the upper plate and tectonic regimes have resulted in marked along-strike variations in basin geometry, stratigraphy, deformational style, and mountain belt morphology. These along-strike variations include high-elevation plateaus (Altiplano and Puna) associated with a thin-skin fold-and-thrust-belt and thick-skin deformation in broken foreland basins such as the Santa Barbara system and the Sierras Pampeanas. At the confluence of the Puna Plateau, the Santa Barbara system and the Sierras Pampeanas, major along-strike changes in upper plate architecture, mountain belt morphology, basement exhumation, and deformation style can be recognized. I have used a source to sink approach to unravel the spatiotemporal tectonic evolution of the Andean retroarc between 26 and 28°S. I obtained a large low-temperature thermochronology data set from basement units which includes apatite fission track, apatite U-Th-Sm/He, and zircon U-Th/He (ZHe) cooling ages. Stratigraphic descriptions of Miocene units were temporally constrained by U-Pb LA-ICP-MS zircon ages from interbedded pyroclastic material. Modeled ZHe ages suggest that the basement of the study area was exhumed during the Famatinian orogeny (550-450 Ma), followed by a period of relative tectonic quiescence during the Paleozoic and the Triassic. The basement experienced horst exhumation during the Cretaceous development of the Salta rift. After initial exhumation, deposition of thick Cretaceous syn-rift strata caused reheating of several basement blocks within the Santa Barbara system. During the Eocene-Oligocene, the Andean compressional setting was responsible for the exhumation of several disconnected basement blocks. These exhumed blocks were separated by areas of low relief, in which humid climate and low erosion rates facilitated the development of etchplains on the crystalline basement. The exhumed basement blocks formed an Eocene to Oligocene broken foreland basin in the back-bulge depozone of the Andean foreland. During the Early Miocene, foreland basin strata filled up the preexisting Paleogene topography. The basement blocks in lower relief positions were reheated; associated geothermal gradients were higher than 25°C/km. Miocene volcanism was responsible for lateral variations on the amount of reheating along the Campo-Arenal basin. Around 12 Ma, a new deformational phase modified the drainage network and fragmented the lacustrine system. As deformation and rock uplift continued, the easily eroded sedimentary cover was efficiently removed and reworked by an ephemeral fluvial system, preventing the development of significant relief. After ~6 Ma, the low erodibility of the basement blocks which began to be exposed caused relief increase, leading to the development of stable fluvial systems. Progressive relief development modified atmospheric circulation, creating a rainfall gradient. After 3 Ma, orographic rainfall and high relief lead to the development of proximal fluvial-gravitational depositional systems in the surrounding basins.},
  language  = {en}
}
@phdthesis{ZamoraLopez2009,
  author    = {Zamora-L{\´o}pez, Gorka},
  title     = {Linking structure and function of complex cortical networks},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52257},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {The recent discovery of an intricate and nontrivial interaction topology among the elements of a wide range of natural systems has altered the manner we understand complexity. For example, the axonal fibres transmitting electrical information between cortical regions form a network which is neither regular nor completely random. Their structure seems to follow functional principles to balance between segregation (functional specialisation) and integration. Cortical regions are clustered into modules specialised in processing different kinds of information, e.g. visual or auditory. However, in order to generate a global perception of the real world, the brain needs to integrate the distinct types of information. Where this integration happens, nobody knows. We have performed an extensive and detailed graph theoretical analysis of the cortico-cortical organisation in the brain of cats, trying to relate the individual and collective topological properties of the cortical areas to their function. We conclude that the cortex possesses a very rich communication structure, composed of a mixture of parallel and serial processing paths capable of accommodating dynamical processes with a wide variety of time scales. The communication paths between the sensory systems are not random, but largely mediated by a small set of areas. Far from acting as mere transmitters of information, these central areas are densely connected to each other, strongly indicating their functional role as integrators of the multisensory information. In the quest of uncovering the structure-function relationship of cortical networks, the peculiarities of this network have led us to continuously reconsider the stablished graph measures. For example, a normalised formalism to identify the "functional roles" of vertices in networks with community structure is proposed. The tools developed for this purpose open the door to novel community detection techniques which may also characterise the overlap between modules. The concept of integration has been revisited and adapted to the necessities of the network under study. Additionally, analytical and numerical methods have been introduced to facilitate understanding of the complicated statistical interrelations between the distinct network measures. These methods are helpful to construct new significance tests which may help to discriminate the relevant properties of real networks from side-effects of the evolutionary-growth processes.},
  language  = {en}
}
@phdthesis{Zamagni2009,
  author    = {Zamagni, Jessica},
  title     = {Responses of a shallow-water ecosystem to the early Paleogene greenhouse environmental conditions : evolution of Larger Foraminifera and coral communities from the Northern Tethys},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-31853},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {Modern anthropogenic forcing of atmospheric chemistry poses the question of how the Earth System will respond as thousands of gigatons of greenhouse gas are rapidly added to the atmosphere. A similar, albeit nonanthropogenic, situation occurred during the early Paleogene, when catastrophic release of carbon to the atmosphere triggered abrupt increase in global temperatures. The best documented of these events is the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) when the magnitude of carbon addition to the oceans and atmosphere was similar to those expected for the future. This event initiated global warming, changes in hydrological cycles, biotic extinction and migrations. A recently proposed hypothesis concerning changes in marine ecosystems suggests that this global warming strongly influenced the shallow-water biosphere, triggering extinctions and turnover in the Larger Foraminifera (LF) community and the demise of corals. The successions from the Adriatic Carbonate Platform (SW Slovenia) represent an ideal location to test the hypothesis of a possible causal link between the PETM and evolution of shallow-water organisms because they record continuous sedimentation from the Late Paleocene to the Early Eocene and are characterized by a rich biota, especially LF, fundamental for detailed biostratigraphic studies. In order to reconstruct paleoenvironmental conditions during deposition, I focused on sedimentological analysis and paleoecological study of benthic assemblages. During the Late Paleocene-earliest Eocene, sedimentation occurred on a shallow-water carbonate ramp system characterized by enhanced nutrient levels. LF represent the common constituent of the benthic assemblages that thrived in this setting throughout the Late Paleocene to the Early Eocene. With detailed biostratigraphic and chemostratigraphic analyses documenting the most complete record to date available for the PETM event in a shallow-water marine environment, I correlated chemostratigraphically for the first time the evolution of LF with the δ¹³C curves. This correlation demonstrated that no major turnover in the LF communities occurred synchronous with the PETM; thus the evolution of LF was mainly controlled by endogenous biotic forces. The study of Late Thanetian metric-sized microbialite-coral mounds which developed in the middle part of the ramp, documented the first Cenozoic occurrence of microbially-cemented mounds. The development of these mounds, with temporary dominance of microbial communities over corals, suggest environmentally-triggered "phase shifts" related to frequent fluctuations of nutrient/turbidity levels during recurrent wet phases which preceding the extreme greenhouse conditions of the PETM. The paleoecological study of the coral community in the microbialites-coral mounds, the study of corals from Early Eocene platform from SW France, and a critical, extensive literature research of Late Paleocene - Early Eocene coral occurrences from the Tethys, the Atlantic, the Caribbean realms suggested that these corals types, even if not forming extensive reefs, are common in the biofacies as small isolated colonies, piles of rubble or small patch-reefs. These corals might have developed 'alternative' life strategies to cope with harsh conditions (high/fluctuating nutrients/turbidity, extreme temperatures, perturbation of aragonite saturation state) during the greenhouse times of the early Paleogene, representing a good fossil analogue to modern corals thriving close to their thresholds for survival. These results demonstrate the complexity of the biological responses to extreme conditions, not only in terms of temperature but also nutrient supply, physical disturbance and their temporal variability and oscillating character.},
  language  = {en}
}
@phdthesis{Zali2023,
  author    = {Zali, Zahra},
  title     = {Volcanic tremor analysis based on advanced signal processing concepts including music information retrieval (MIR) strategies},
  doi       = {10.25932/publishup-61086},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-610866},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 95},
  year      = {2023},
  abstract  = {Volcanoes are one of the Earth's most dynamic zones and responsible for many changes in our planet. Volcano seismology aims to provide an understanding of the physical processes in volcanic systems and anticipate the style and timing of eruptions by analyzing the seismic records. Volcanic tremor signals are usually observed in the seismic records before or during volcanic eruptions. Their analysis contributes to evaluate the evolving volcanic activity and potentially predict eruptions. Years of continuous seismic monitoring now provide useful information for operational eruption forecasting. The continuously growing amount of seismic recordings, however, poses a challenge for analysis, information extraction, and interpretation, to support timely decision making during volcanic crises. Furthermore, the complexity of eruption processes and precursory activities makes the analysis challenging. A challenge in studying seismic signals of volcanic origin is the coexistence of transient signal swarms and long-lasting volcanic tremor signals. Separating transient events from volcanic tremors can, therefore, contribute to improving our understanding of the underlying physical processes. Some similar issues (data reduction, source separation, extraction, and classification) are addressed in the context of music information retrieval (MIR). The signal characteristics of acoustic and seismic recordings comprise a number of similarities. This thesis is going beyond classical signal analysis techniques usually employed in seismology by exploiting similarities of seismic and acoustic signals and building the information retrieval strategy on the expertise developed in the field of MIR. First, inspired by the idea of harmonic-percussive separation (HPS) in musical signal processing, I have developed a method to extract harmonic volcanic tremor signals and to detect transient events from seismic recordings. This provides a clean tremor signal suitable for tremor investigation along with a characteristic function suitable for earthquake detection. Second, using HPS algorithms, I have developed a noise reduction technique for seismic signals. This method is especially useful for denoising ocean bottom seismometers, which are highly contaminated by noise. The advantage of this method compared to other denoising techniques is that it doesn't introduce distortion to the broadband earthquake waveforms, which makes it reliable for different applications in passive seismological analysis. Third, to address the challenge of extracting information from high-dimensional data and investigating the complex eruptive phases, I have developed an advanced machine learning model that results in a comprehensive signal processing scheme for volcanic tremors. Using this method seismic signatures of major eruptive phases can be automatically detected. This helps to provide a chronology of the volcanic system. Also, this model is capable to detect weak precursory volcanic tremors prior to the eruption, which could be used as an indicator of imminent eruptive activity. The extracted patterns of seismicity and their temporal variations finally provide an explanation for the transition mechanism between eruptive phases.},
  language  = {en}
}
@phdthesis{Zakrevskyy2006,
  author    = {Zakrevskyy, Yuriy},
  title     = {Liquid crystallinity and alignment of ionic self-assembly complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10048},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {In this work the first observation of new type of liquid crystals is presented. This is ionic self-assembly (ISA) liquid crystals formed by introduction of oppositely charged ions between different low molecular tectonic units. As practically all conventional liquid crystals consist of rigid core and alkyl chains the attention is focused to the simplest case where oppositely charged ions are placed between a rigid core and alkyl tails. The aim of this work is to investigate and understand liquid crystalline and alignment properties of these materials. It was found that ionic interactions within complexes play the main role. Presence of these interactions restricts transition to isotropic phase. In addition, these interactions hold the system (like network) allowing crystallization into a single domain from aligned LC state. Alignment of these simple ISA complexes was spontaneous on a glass substrate. In order to show potentials for application perylenediimide and azobenzene containing ISA complexes have been investigated for correlations between phase behavior and their alignment properties. The best results of macroscopic alignment of perylenediimide-based ISA complexes have been obtained by zone-casting method. In the aligned films the columns of the complex align perpendicular to the phase-transition front. The obtained anisotropy (DR = 18) is thermally stable. The investigated photosensitive (azobenzene-based) ISA complexes show formation of columnar LC phases. It was demonstrated that photo alignment of such complexes was very effective (DR = 50 has been obtained). It was shown that photo-reorientation in the photosensitive ISA complexes is cooperative process. The size of domains has direct influence on efficiency of the photo-reorientation process. In the case of small domains the photo-alignment is the most effective. Under irradiation with linearly polarized light domains reorient in the plane of the film leading to macroscopic alignment of columns parallel to the light polarization and joining of small domains into big ones. Finally, the additional distinguishable properties of the ISA liquid crystalline complexes should be noted: (I) the complexes do not solve in water but readily solve in organic solvents; (II) the complexes have good film-forming properties when cast or spin-coated from organic solvent; (III) alignment of the complexes depends on their structure and secondary interactions between tectonic units.},
  subject      = {Fl{\"u}ssigkristall},
  language  = {en}
}
@phdthesis{Zakharova2015,
  author    = {Zakharova, Olga},
  title     = {Analysis and modeling of transient earthquake patterns and their dependence on local stress regimes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-86455},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 94},
  year      = {2015},
  abstract  = {Investigations in the field of earthquake triggering and associated interactions, which includes aftershock triggering as well as induced seismicity, is important for seismic hazard assessment due to earthquakes destructive power. One of the approaches to study earthquake triggering and their interactions is the use of statistical earthquake models, which are based on knowledge of the basic seismicity properties, in particular, the magnitude distribution and spatiotemporal properties of the triggered events. In my PhD thesis I focus on some specific aspects of aftershock properties, namely, the relative seismic moment release of the aftershocks with respect to the mainshocks; the spatial correlation between aftershock occurrence and fault deformation; and on the influence of aseismic transients on the aftershock parameter estimation. For the analysis of aftershock sequences I choose a statistical approach, in particular, the well known Epidemic Type Aftershock Sequence (ETAS) model, which accounts for the input of background and triggered seismicity. For my specific purposes, I develop two ETAS model modifications in collaboration with Sebastian Hainzl. By means of this approach, I estimate the statistical aftershock parameters and performed simulations of aftershock sequences as well. In the case of seismic moment release of aftershocks, I focus on the ratio of cumulative seismic moment release with respect to the mainshocks. Specifically, I investigate the ratio with respect to the focal mechanism of the mainshock and estimate an effective magnitude, which represents the cumulative aftershock energy (similar to Bath's law, which defines the average difference between mainshock and the largest aftershock magnitudes). Furthermore, I compare the observed seismic moment ratios with the results of the ETAS simulations. In particular, I test a restricted ETAS (RETAS) model which is based on results of a clock advanced model and static stress triggering. To analyze spatial variations of triggering parameters I focus in my second approach on the aftershock occurrence triggered by large mainshocks and the study of the aftershock parameter distribution and their spatial correlation with the coseismic/postseismic slip and interseismic locking. To invert the aftershock parameters I improve the modified ETAS (m-ETAS) model, which is able to take the extension of the mainshock rupture into account. I compare the results obtained by the classical approach with the output of the m-ETAS model. My third approach is concerned with the temporal clustering of seismicity, which might not only be related to earthquake-earthquake interactions, but also to a time-dependent background rate, potentially biasing the parameter estimations. Thus, my coauthors and I also applied a modification of the ETAS model, which is able to take into account time-dependent background activity. It can be applicable for two different cases: when an aftershock catalog has a temporal incompleteness or when the background seismicity rate changes with time, due to presence of aseismic forces. An essential part of any research is the testing of the developed models using observational data sets, which are appropriate for the particular study case. Therefore, in the case of seismic moment release I use the global seismicity catalog. For the spatial distribution of triggering parameters I exploit two aftershock sequences of the Mw8.8 2010 Maule (Chile) and Mw 9.0 2011 Tohoku (Japan) mainshocks. In addition, I use published geodetic slip models of different authors. To test our ability to detect aseismic transients my coauthors and I use the data sets from Western Bohemia (Central Europe) and California. Our results indicate that: (1) the seismic moment of aftershocks with respect to mainshocks depends on the static stress changes and is maximal for the normal, intermediate for thrust and minimal for strike-slip stress regimes, where the RETAS model shows a good correspondence with the results; (2) The spatial distribution of aftershock parameters, obtained by the m-ETAS model, shows anomalous values in areas of reactivated crustal fault systems. In addition, the aftershock density is found to be correlated with coseismic slip gradient, afterslip, interseismic coupling and b-values. Aftershock seismic moment is positively correlated with the areas of maximum coseismic slip and interseismically locked areas. These correlations might be related to the stress level or to material properties variations in space; (3) Ignoring aseismic transient forcing or temporal catalog incompleteness can lead to the significant under- or overestimation of the underlying trigger parameters. In the case when a catalog is complete, this method helps to identify aseismic sources.},
  language  = {en}
}
@phdthesis{Zakarias2018,
  author    = {Zakari{\´a}s, Lilla},
  title     = {Transfer effects after working memory training in post-stroke aphasia},
  doi       = {10.25932/publishup-42360},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423600},
  school      = {Universit{\"a}t Potsdam},
  pages     = {178},
  year      = {2018},
  abstract  = {Background: Individuals with aphasia after stroke (IWA) often present with working memory (WM) deficits. Research investigating the relationship between WM and language abilities has led to the promising hypothesis that treatments of WM could lead to improvements in language, a phenomenon known as transfer. Although recent treatment protocols have been successful in improving WM, the evidence to date is scarce and the extent to which improvements in trained tasks of WM transfer to untrained memory tasks, spoken sentence comprehension, and functional communication is yet poorly understood. Aims: We aimed at (a) investigating whether WM can be improved through an adaptive n-back training in IWA (Study 1-3); (b) testing whether WM training leads to near transfer to unpracticed WM tasks (Study 1-3), and far transfer to spoken sentence comprehension (Study 1-3), functional communication (Study 2-3), and memory in daily life in IWA (Study 2-3); and (c) evaluating the methodological quality of existing WM treatments in IWA (Study 3). To address these goals, we conducted two empirical studies - a case-controls study with Hungarian speaking IWA (Study 1) and a multiple baseline study with German speaking IWA (Study 2) - and a systematic review (Study 3). Methods: In Study 1 and 2 participants with chronic, post-stroke aphasia performed an adaptive, computerized n-back training. 'Adaptivity' was implemented by adjusting the tasks' difficulty level according to the participants' performance, ensuring that they always practiced at an optimal level of difficulty. To assess the specificity of transfer effects and to better understand the underlying mechanisms of transfer on spoken sentence comprehension, we included an outcome measure testing specific syntactic structures that have been proposed to involve WM processes (e.g., non-canonical structures with varying complexity). Results: We detected a mixed pattern of training and transfer effects across individuals: five participants out of six significantly improved in the n-back training. Our most important finding is that all six participants improved significantly in spoken sentence comprehension (i.e., far transfer effects). In addition, we also found far transfer to functional communication (in two participants out of three in Study 2) and everyday memory functioning (in all three participants in Study 2), and near transfer to unpracticed n-back tasks (in four participants out of six). Pooled data analysis of Study 1 and 2 showed a significant negative relationship between initial spoken sentence comprehension and the amount of improvement in this ability, suggesting that the more severe the participants' spoken sentence comprehension deficit was at the beginning of training, the more they improved after training. Taken together, we detected both near far and transfer effects in our studies, but the effects varied across participants. The systematic review evaluating the methodological quality of existing WM treatments in stroke IWA (Study 3) showed poor internal and external validity across the included 17 studies. Poor internal validity was mainly due to use of inappropriate design, lack of randomization of study phases, lack of blinding of participants and/or assessors, and insufficient sampling. Low external validity was mainly related to incomplete information on the setting, lack of use of appropriate analysis or justification for the suitability of the analysis procedure used, and lack of replication across participants and/or behaviors. Results in terms of WM, spoken sentence comprehension, and reading are promising, but further studies with more rigorous methodology and stronger experimental control are needed to determine the beneficial effects of WM intervention. Conclusions: Results of the empirical studies suggest that WM can be improved with a computerized and adaptive WM training, and improvements can lead to transfer effects to spoken sentence comprehension and functional communication in some individuals with chronic post-stroke aphasia. The fact that improvements were not specific to certain syntactic structures (i.e., non-canonical complex sentences) in spoken sentence comprehension suggest that WM is not involved in the online, automatic processing of syntactic information (i.e., parsing and interpretation), but plays a more general role in the later stage of spoken sentence comprehension (i.e., post-interpretive comprehension). The individual differences in treatment outcomes call for future research to clarify how far these results are generalizable to the population level of IWA. Future studies are needed to identify a few mechanisms that may generalize to at least a subpopulation of IWA as well as to investigate baseline non-linguistic cognitive and language abilities that may play a role in transfer effects and the maintenance of such effects. These may require larger yet homogenous samples.},
  language  = {en}
}
@phdthesis{Zajnulina2015,
  author    = {Zajnulina, Marina},
  title     = {Optical frequency comb generation in optical fibres},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-88776},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 103},
  year      = {2015},
  abstract  = {Optical frequency combs (OFC) constitute an array of phase-correlated equidistant spectral lines with nearly equal intensities over a broad spectral range. The adaptations of combs generated in mode-locked lasers proved to be highly efficient for the calibration of high-resolution (resolving power > 50000) astronomical spectrographs. The observation of different galaxy structures or the studies of the Milky Way are done using instruments in the low- and medium resolution range. To such instruments belong, for instance, the Multi Unit Spectroscopic Explorer (MUSE) being developed for the Very Large Telescope (VLT) of the European Southern Observatory (ESO) and the 4-metre Multi-Object Spectroscopic Telescope (4MOST) being in development for the ESO VISTA 4.1 m Telescope. The existing adaptations of OFC from mode-locked lasers are not resolvable by these instruments. Within this work, a fibre-based approach for generation of OFC specifically in the low- and medium resolution range is studied numerically. This approach consists of three optical fibres that are fed by two equally intense continuous-wave (CW) lasers. The first fibre is a conventional single-mode fibre, the second one is a suitably pumped amplifying Erbium-doped fibre with anomalous dispersion, and the third one is a low-dispersion highly nonlinear optical fibre. The evolution of a frequency comb in this system is governed by the following processes: as the two initial CW-laser waves with different frequencies propagate through the first fibre, they generate an initial comb via a cascade of four-wave mixing processes. The frequency components of the comb are phase-correlated with the original laser lines and have a frequency spacing that is equal to the initial laser frequency separation (LFS), i.e. the difference in the laser frequencies. In the time domain, a train of pre-compressed pulses with widths of a few pico-seconds arises out of the initial bichromatic deeply-modulated cosine-wave. These pulses undergo strong compression in the subsequent amplifying Erbium-doped fibre: sub-100 fs pulses with broad OFC spectra are formed. In the following low-dispersion highly nonlinear fibre, the OFC experience a further broadening and the intensity of the comb lines are fairly equalised. This approach was mathematically modelled by means of a Generalised Nonlinear Schr{\"o}dinger Equation (GNLS) that contains terms describing the nonlinear optical Kerr effect, the delayed Raman response, the pulse self-steepening, and the linear optical losses as well as the wavelength-dependent Erbium gain profile for the second fibre. The initial condition equation being a deeply-modulated cosine-wave mimics the radiation of the two initial CW lasers. The numerical studies are performed with the help of Matlab scripts that were specifically developed for the integration of the GNLS and the initial condition according to the proposed approach for the OFC generation. The scripts are based on the Fourth-Order Runge-Kutta in the Interaction Picture Method (RK4IP) in combination with the local error method. This work includes the studies and results on the length optimisation of the first and the second fibre depending on different values of the group-velocity dispersion of the first fibre. Such length optimisation studies are necessary because the OFC have the biggest possible broadband and exhibit a low level of noise exactly at the optimum lengths. Further, the optical pulse build-up in the first and the second fibre was studied by means of the numerical technique called Soliton Radiation Beat Analysis (SRBA). It was shown that a common soliton crystal state is formed in the first fibre for low laser input powers. The soliton crystal continuously dissolves into separated optical solitons as the input power increases. The pulse formation in the second fibre is critically dependent on the features of the pulses formed in the first fibre. I showed that, for low input powers, an adiabatic soliton compression delivering low-noise OFC occurs in the second fibre. At high input powers, the pulses in the first fibre have more complicated structures which leads to the pulse break-up in the second fibre with a subsequent degradation of the OFC noise performance. The pulse intensity noise studies that were performed within the framework of this thesis allow making statements about the noise performance of an OFC. They showed that the intensity noise of the whole system decreases with the increasing value of LFS.},
  language  = {en}
}
@phdthesis{Zaehle2005,
  author    = {Zaehle, S{\"o}nke},
  title     = {Process-based simulation of the terrestrial biosphere : an evaluation of present-day and future terrestrial carbon balance estimates and their uncertainty},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5263},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {At present, carbon sequestration in terrestrial ecosystems slows the growth rate of atmospheric CO2 concentrations, and thereby reduces the impact of anthropogenic fossil fuel emissions on the climate system. Changes in climate and land use affect terrestrial biosphere structure and functioning at present, and will likely impact on the terrestrial carbon balance during the coming decades - potentially providing a positive feedback to the climate system due to soil carbon releases under a warmer climate. Quantifying changes, and the associated uncertainties, in regional terrestrial carbon budgets resulting from these effects is relevant for the scientific understanding of the Earth system and for long-term climate mitigation strategies. A model describing the relevant processes that govern the terrestrial carbon cycle is a necessary tool to project regional carbon budgets into the future. This study (1) provides an extensive evaluation of the parameter-based uncertainty in model results of a leading terrestrial biosphere model, the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM), against a range of observations and under climate change, thereby complementing existing studies on other aspects of model uncertainty; (2) evaluates different hypotheses to explain the age-related decline in forest growth, both from theoretical and experimental evidence, and introduces the most promising hypothesis into the model; (3) demonstrates how forest statistics can be successfully integrated with process-based modelling to provide long-term constraints on regional-scale forest carbon budget estimates for a European forest case-study; and (4) elucidates the combined effects of land-use and climate changes on the present-day and future terrestrial carbon balance over Europe for four illustrative scenarios - implemented by four general circulation models - using a comprehensive description of different land-use types within the framework of LPJ-DGVM. This study presents a way to assess and reduce uncertainty in process-based terrestrial carbon estimates on a regional scale. The results of this study demonstrate that simulated present-day land-atmosphere carbon fluxes are relatively well constrained, despite considerable uncertainty in modelled net primary production. Process-based terrestrial modelling and forest statistics are successfully combined to improve model-based estimates of vegetation carbon stocks and their change over time. Application of the advanced model for 77 European provinces shows that model-based estimates of biomass development with stand age compare favourably with forest inventory-based estimates for different tree species. Driven by historic changes in climate, atmospheric CO2 concentration, forest area and wood demand between 1948 and 2000, the model predicts European-scale, present-day age structure of forests, ratio of biomass removals to increment, and vegetation carbon sequestration rates that are consistent with inventory-based estimates. Alternative scenarios of climate and land-use change in the 21<sup>st century suggest carbon sequestration in the European terrestrial biosphere during the coming decades will likely be on magnitudes relevant to climate mitigation strategies. However, the uptake rates are small in comparison to the European emissions from fossil fuel combustion, and will likely decline towards the end of the century. Uncertainty in climate change projections is a key driver for uncertainty in simulated land-atmosphere carbon fluxes and needs to be accounted for in mitigation studies of the terrestrial biosphere.},
  subject      = {Terrestrische {\"O}kologie},
  language  = {en}
}
@phdthesis{Youk2022,
  author    = {Youk, Sol},
  title     = {Molecular design of heteroatom-doped nanoporous carbons with controlled porosity and surface polarity for gas physisorption and energy storage},
  doi       = {10.25932/publishup-53909},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-539098},
  school      = {Universit{\"a}t Potsdam},
  pages     = {145},
  year      = {2022},
  abstract  = {The world energy consumption has constantly increased every year due to economic development and population growth. This inevitably caused vast amount of CO2 emission, and the CO2 concentration in the atmosphere keeps increasing with economic growth. To reduce CO2 emission, various methods have been developed but there are still many bottlenecks to be solved. Solvents easily absorbing CO2 such as monoethanol-amine (MEA) and diethanolamine, for example, have limitations of solvent loss, amine degradation, vulnerability to heat and toxicity, and the high cost of regeneration which is especially caused due to chemisorption process. Though some of these drawbacks can be compensated through physisorption with zeolites and metal-organic frameworks (MOFs) by displaying significant adsorption selectivity and capacity even in ambient conditions, limitations for these materials still exist. Zeolites demand relatively high regeneration energy and have limited adsorption kinetics due to the exceptionally narrow pore structure. MOFs have low stability against heat and moisture and high manufacturing cost. Nanoporous carbons have recently received attention as an attractive functional porous material due to their unique properties. These materials are crucial in many applications of modern science and industry such as water and air purification, catalysis, gas separation, and energy storage/conversion due to their high chemical and thermal stability, and in particular electronic conductivity in combination with high specific surface areas. Nanoporous carbons can be used to adsorb environmental pollutants or small gas molecules such as CO2 and to power electrochemical energy storage devices such as batteries and fuel cells. In all fields, their pore structure or electrical properties can be modified depending on their purposes. This thesis provides an in-depth look at novel nanoporous carbons from the synthetic and the application point of view. The interplay between pore structure, atomic construction, and the adsorption properties of nanoporous carbon materials are investigated. Novel nanoporous carbon materials are synthesized by using simple precursor molecules containing heteroatoms through a facile templating method. The affinity, and in turn the adsorption capacity, of carbon materials toward polar gas molecules (CO2 and H2O) is enhanced by the modification of their chemical construction. It is also shown that these properties are important in electrochemical energy storage, here especially for supercapacitors with aqueous electrolytes which are basically based on the physisorption of ions on carbon surfaces. This shows that nanoporous carbons can be a "functional" material with specific physical or chemical interactions with guest species just like zeolites and MOFs. The synthesis of sp2-conjugated materials with high heteroatom content from a mixture of citrazinic acid and melamine in which heteroatoms are already bonded in specific motives is illustrated. By controlling the removal procedure of the salt-template and the condensation temperature, the role of salts in the formation of porosity and as coordination sites for the stabilization of heteroatoms is proven. A high amount of nitrogen of up to 20 wt. \%, oxygen contents of up to 19 wt.\%, and a high CO2/N2 selectivity with maximum CO2 uptake at 273 K of 5.31 mmol g-1 are achieved. Besides, the further controlled thermal condensation of precursor molecules and advanced functional properties on applications of the synthesized porous carbons are described. The materials have different porosity and atomic construction exhibiting a high nitrogen content up to 25 wt. \% as well as a high porosity with a specific surface area of more than 1800 m2 g-1, and a high performance in selective CO2 gas adsorption of 62.7. These pore structure as well as properties of surface affect to water adsorption with a remarkably high Qst of over 100 kJ mol-1 even higher than that of zeolites or CaCl2 well known as adsorbents. In addition to that, the pore structure of HAT-CN-derived carbon materials during condensation in vacuum is fundamentally understood which is essential to maximize the utilization of porous system in materials showing significant difference in their pore volume of 0.5 cm3 g-1 and 0.25 cm3 g-1 without and with vacuum, respectively. The molecular designs of heteroatom containing porous carbon derived from abundant and simple molecules are introduced in the presented thesis. Abundant precursors that already containing high amount of nitrogen or oxygen are beneficial to achieve enhanced interaction with adsorptives. The physical and chemical properties of these heteroatom-doped porous carbons are affected by mainly two parameters, that is, the porosity from the pore structure and the polarity from the atomic composition on the surface. In other words, controlling the porosity as well as the polarity of the carbon materials is studied to understand interactions with different guest species which is a fundamental knowledge for the utilization on various applications.},
  language  = {en}
}
@phdthesis{Youakim2020,
  author    = {Youakim, Kris},
  title     = {Galactic archaeology with metal-poor stars from the Pristine survey},
  doi       = {10.25932/publishup-47431},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-474314},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 151},
  year      = {2020},
  abstract  = {The Milky Way is a spiral galaxy consisting of a disc of gas, dust and stars embedded in a halo of dark matter. Within this dark matter halo there is also a diffuse population of stars called the stellar halo, that has been accreting stars for billions of years from smaller galaxies that get pulled in and disrupted by the large gravitational potential of the Milky Way. As they are disrupted, these galaxies leave behind long streams of stars that can take billions of years to mix with the rest of the stars in the halo. Furthermore, the amount of heavy elements (metallicity) of the stars in these galaxies reflects the rate of chemical enrichment that occurred in them, since the Universe has been slowly enriched in heavy elements (e.g. iron) through successive generations of stars which produce them in their cores and supernovae explosions. Therefore, stars that contain small amounts of heavy elements (metal-poor stars) either formed at early times before the Universe was significantly enriched, or in isolated environments. The aim of this thesis is to develop a better understanding of the substructure content and chemistry of the Galactic stellar halo, in order to gain further insight into the formation and evolution of the Milky Way. The Pristine survey uses a narrow-band filter which specifically targets the Ca II H \& K spectral absorption lines to provide photometric metallicities for a large number of stars down to the extremely metal-poor (EMP) regime, making it a very powerful data set for Galactic archaeology studies. In Chapter 2, we quantify the efficiency of the survey using a preliminary spectroscopic follow-up sample of ~ 200 stars. We also use this sample to establish a set of selection criteria to improve the success rate of selecting EMP candidates for follow-up spectroscopy. In Chapter 3, we extend this work and present the full catalogue of ~ 1000 stars from a three year long medium resolution spectroscopic follow-up effort conducted as part of the Pristine survey. From this sample, we compute success rates of 56\% and 23\% for recovering stars with [Fe/H] < -2.5 and [Fe/H] < -3.0, respectively. This demonstrates a high efficiency for finding EMP stars as compared to previous searches with success rates of 3-4\%. In Chapter 4, we select a sample of ~ 80000 halo stars using colour and magnitude cuts to select a main sequence turnoff population in the distance range 6 < dʘ < 20 kpc. We then use the spectroscopic follow-up sample presented in Chapter 3 to statistically rescale the Pristine photometric metallicities of this sample, and present the resulting corrected metallicity distribution function (MDF) of the halo. The slope at the metal-poor end is significantly shallower than previous spectroscopic efforts have shown, suggesting that there may be more metal-poor stars with [Fe/H] < -2.5 in the halo than previously thought. This sample also shows evidence that the MDF of the halo may not be bimodal as was proposed by previous works, and that the lack of globular clusters in the Milky Way may be the result of a physical truncation of the MDF rather than just statistical under-sampling. Chapter 5 showcases the unexpected capability of the Pristine filter for separating blue horizontal branch (BHB) stars from Blue Straggler (BS) stars. We demonstrate a purity of 93\% and completeness of 91\% for identifying BHB stars, a substantial improvement over previous works. We then use this highly pure and complete sample of BHB stars to trace the halo density profile out to d > 100 kpc, and the Sagittarius stream substructure out to ~ 130 kpc. In Chapter 6 we use the photometric metallicities from the Pristine survey to perform a clustering analysis of the halo as a function of metallicity. Separating the Pristine sample into four metallicity bins of [Fe/H] < -2, -2 < [Fe/H] < -1.5, -1.5 < [Fe/H] < -1 and -0.9 < [Fe/H] < -0.8, we compute the two-point correlation function to measure the amount of clustering on scales of < 5 deg. For a smooth comparison sample we make a mock Pristine data set generated using the Galaxia code based on the Besan{\c{c}}on model of the Galaxy. We find enhanced clustering on small scales (< 0.5 deg) for some regions of the Galaxy for the most metal-poor bin ([Fe/H] < -2), while in others we see large scale signals that correspond to known substructures in those directions. This confirms that the substructure content of the halo is highly anisotropic and diverse in different Galactic environments. We discuss the difficulties of removing systematic clustering signals from the data and the limitations of disentangling weak clustering signals from real substructures and residual systematic structure in the data. Taken together, the work presented in this thesis approaches the problem of better understanding the halo of our Galaxy from multiple angles. Firstly, presenting a sizeable sample of EMP stars and improving the selection efficiency of EMP stars for the Pristine survey, paving the way for the further discovery of metal-poor stars to be used as probes to early chemical evolution. Secondly, improving the selection of BHB distance tracers to map out the halo to large distances, and finally, using the large samples of metal-poor stars to derive the MDF of the inner halo and analyse the substructure content at different metallicities. The results of this thesis therefore expand our understanding of the physical and chemical properties of the Milky Way stellar halo, and provide insight into the processes involved in its formation and evolution.},
  language  = {en}
}
@phdthesis{Yin2010,
  author    = {Yin, Fan},
  title     = {Mathematic approaches for the calibration of the CHAMP satellite magnetic field measurements},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41201},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {CHAMP (CHAllenging Minisatellite Payload) is a German small satellite mission to study the earth's gravity field, magnetic field and upper atmosphere. Thanks to the good condition of the satellite so far, the planned 5 years mission is extended to year 2009. The satellite provides continuously a large quantity of measurement data for the purpose of Earth study. The measurements of the magnetic field are undertaken by two Fluxgate Magnetometers (vector magnetometer) and one Overhauser Magnetometer (scalar magnetometer) flown on CHAMP. In order to ensure the quality of the data during the whole mission, the calibration of the magnetometers has to be performed routinely in orbit. The scalar magnetometer serves as the magnetic reference and its readings are compared with the readings of the vector magnetometer. The readings of the vector magnetometer are corrected by the parameters that are derived from this comparison, which is called the scalar calibration. In the routine processing, these calibration parameters are updated every 15 days by means of scalar calibration. There are also magnetic effects coming from the satellite which disturb the measurements. Most of them have been characterized during tests before launch. Among them are the remanent magnetization of the spacecraft and fields generated by currents. They are all considered to be constant over the mission life. The 8 years of operation experience allow us to investigate the long-term behaviors of the magnetometers and the satellite systems. According to the investigation, it was found that for example the scale factors of the FGM show obvious long-term changes which can be described by logarithmic functions. The other parameters (offsets and angles between the three components) can be considered constant. If these continuous parameters are applied for the FGM data processing, the disagreement between the OVM and the FGM readings is limited to \pm1nT over the whole mission. This demonstrates, the magnetometers on CHAMP exhibit a very good stability. However, the daily correction of the parameter Z component offset of the FGM improves the agreement between the magnetometers markedly. The Z component offset plays a very important role for the data quality. It exhibits a linear relationship with the standard deviation of the disagreement between the OVM and the FGM readings. After Z offset correction, the errors are limited to \pm0.5nT (equivalent to a standard deviation of 0.2nT). We improved the corrections of the spacecraft field which are not taken into account in the routine processing. Such disturbance field, e.g. from the power supply system of the satellite, show some systematic errors in the FGM data and are misinterpreted in 9-parameter calibration, which brings false local time related variation of the calibration parameters. These corrections are made by applying a mathematical model to the measured currents. This non-linear model is derived from an inversion technique. If the disturbance field of the satellite body are fully corrected, the standard deviation of scalar error \triangle B remains about 0.1nT. Additionally, in order to keep the OVM readings a reliable standard, the imperfect coefficients of the torquer current correction for the OVM are redetermined by solving a minimization problem. The temporal variation of the spacecraft remanent field is investigated. It was found that the average magnetic moment of the magneto-torquers reflects well the moment of the satellite. This allows for a continuous correction of the spacecraft field. The reasons for the possible unknown systemic error are discussed in this thesis. Particularly, both temperature uncertainties and time errors have influence on the FGM data. Based on the results of this thesis the data processing of future magnetic missions can be designed in an improved way. In particular, the upcoming ESA mission Swarm can take advantage of our findings and provide all the auxiliary measurements needed for a proper recovery of the ambient magnetic field.},
  language  = {en}
}
@phdthesis{Yin2009,
  author    = {Yin, Chunhong},
  title     = {The interplay of nanostructure and efficiency of polymer solar cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-29054},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {The aim of this thesis is to achieve a deep understanding of the working mechanism of polymer based solar cells and to improve the device performance. Two types of the polymer based solar cells are studied here: all-polymer solar cells comprising macromolecular donors and acceptors based on poly(p-phenylene vinylene) and hybrid cells comprising a PPV copolymer in combination with a novel small molecule electron acceptor. To understand the interplay between morphology and photovoltaic properties in all-polymer devices, I compared the photocurrent characteristics and excited state properties of bilayer and blend devices with different nano-morphology, which was fine tuned by using solvents with different boiling points. The main conclusion from these complementary measurements was that the performance-limiting step is the field-dependent generation of free charge carriers, while bimolecular recombination and charge extraction do not compromise device performance. These findings imply that the proper design of the donor-acceptor heterojunction is of major importance towards the goal of high photovoltaic efficiencies. Regarding polymer-small molecular hybrid solar cells I combined the hole-transporting polymer M3EH-PPV with a novel Vinazene-based electron acceptor. This molecule can be either deposited from solution or by thermal evaporation, allowing for a large variety of layer architectures to be realized. I then demonstrated that the layer architecture has a large influence on the photovoltaic properties. Solar cells with very high fill factors of up to 57 \% and an open circuit voltage of 1V could be achieved by realizing a sharp and well-defined donor-acceptor heterojunction. In the past, fill factors exceeding 50 \% have only been observed for polymers in combination with soluble fullerene-derivatives or nanocrystalline inorganic semiconductors as the electron-accepting component. The finding that proper processing of polymer-vinazene devices leads to similar high values is a major step towards the design of efficient polymer-based solar cells.},
  language  = {en}
}
@phdthesis{Yildiz2023,
  author    = {Yildiz, Tugba},
  title     = {Dissecting the role of the TusA protein for cell functionality and FtsZ ring assembly in Escherichia coli},
  doi       = {10.25932/publishup-61713},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-617135},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XI, 171},
  year      = {2023},
  abstract  = {In this work, the role of the TusA protein was investigated for the cell functionality and FtsZ ring assembly in Escherichia coli. TusA is the tRNA-2-thiouridine synthase that acts as a sulfur transferase in tRNA thiolation for the formation of 2-thiouridine at the position 34 (wobble base) of tRNALys, tRNAGlu and tRNAGln. It binds the persulfide form of sulfur and transfers it to further proteins during mnm5s2U tRNA modification at wobble position and for Moco biosynthesis. With this thiomodification of tRNA, the ribosome binding is more efficient and frameshifting is averted during the protein translation. Previous studies have revealed an essential role of TusA in bacterial cell physiology since deletion of the tusA gene resulted in retarded growth and filamentous cells during the exponential growth phase in a rich medium which suddenly disappeared during the stationary phase. This indicates a problem in the cell division process. Therefore the focus of this work was to investigate the role of TusA for cell functionality and FtsZ ring formation and thus the cell separation. The reason behind the filamentous growth of the tusA mutant strain was investigated by growth and morphological analyses. ΔtusA cells showed a retarded growth during the exponential phase compared to the WT strain. Also, morphological analysis of ΔtusA cells confirmed the filamentous cell shape. The growth and cell division defects in ΔtusA indicated a defect in FtsZ protein as a key player of cell division. The microscopic investigation revealed that filamentous ΔtusA cells possessed multiple DNA parts arranged next to each other. This suggested that although the DNA replication occurred correctly, there was a defect in the step where FtsZ should act; probably FtsZ is unable to assemble to the ring structure or the assembled ring is not able to constrict. All tested mutant strains (ΔtusD, ΔtusE and ΔmnmA) involved in the mnm5s2U34 tRNA modification pathway shared the similar retarded growth and filamentous cell shape like ΔtusA strain. Thus, the cell division defect arises from a defect in mnm5s2U34 tRNA thiolation. Since the FtsZ ring formation was supposed to be defective in filaments, a possible intracellular interaction of TusA and FtsZ was examined by fluorescent (EGFP and mCherry) fusion proteins expression and FRET. FtsZ expressing tusA mutant (DE3) cells showed a red mCherry signal at the cell poles, indicating that FtsZ is still in the assembling phase. Interestingly, the cellular region of EGFP-TusA fusion protein expressed in ΔtusA (DE3) was conspicuous; the EGFP signal was spread throughout the whole cell and, in addition, a slight accumulation of the EGFP-TusA fluorescence was detectable at the cell poles, the same part of the cell as for mCherry-FtsZ. Thus, this strongly suggested an interaction of TusA and FtsZ. Furthermore, the cellular FtsZ and Fis concentrations, and their change during different growth phases were determined via immunoblotting. All tested deletion strains of mnm5s2U34 tRNA modification show high cellular FtsZ and Fis levels in the exponential phase, shifting to the later growth phases. This shift reflects the retarded growth, whereby the deletion strains reach later the exponential phase. Conclusively, the growth and cell division defect, and thus the formation of filaments, is most likely caused by changes in the cellular FtsZ and Fis concentrations. Finally, the translation efficiencies of certain proteins (RpoS, Fur, Fis and mFis) in tusA mutant and in additional gene deletion strains were studied whether they were affected by using unmodified U34 tRNAs of Lys, Glu and Gln. The translation efficiency is decreased in mnm5s2U34 tRNA modification-impaired strains in addition to their existing growth and cell division defect due to the elimination of these three amino acids. Finally, these results confirm and reinforce the importance of Lys, Glu and Gln and the mnm5s2U34 tRNA thiolation for efficient protein translation. Thus, these findings verify that the translation of fur, fis and rpoS is regulated by mnm5s2U34 tRNA modifications, which is growth phase-dependent. In total, this work showed the importance of the role of TusA for bacterial cell functionality and physiology. The deletion of the tusA gene disrupted a complex regulatory network within the cell, that most influenced by the decreased translation of Fis and RpoS, caused by the absence of mnm5s2U34 tRNA modifications. The disruption of RpoS and Fis cellular network influences in turn the cellular FtsZ level in the early exponential phase. Finally, the reduced FtsZ concentration leads to elongated, filamentous E. coli cells, which are unable to divide.},
  language  = {en}
}
@phdthesis{Yeldesbay2014,
  author    = {Yeldesbay, Azamat},
  title     = {Complex regimes of synchronization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-73348},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ii, 60},
  year      = {2014},
  abstract  = {Synchronization is a fundamental phenomenon in nature. It can be considered as a general property of self-sustained oscillators to adjust their rhythm in the presence of an interaction. In this work we investigate complex regimes of synchronization phenomena by means of theoretical analysis, numerical modeling, as well as practical analysis of experimental data. As a subject of our investigation we consider chimera state, where due to spontaneous symmetry-breaking of an initially homogeneous oscillators lattice split the system into two parts with different dynamics. Chimera state as a new synchronization phenomenon was first found in non-locally coupled oscillators system, and has attracted a lot of attention in the last decade. However, the recent studies indicate that this state is also possible in globally coupled systems. In the first part of this work, we show under which conditions the chimera-like state appears in a system of globally coupled identical oscillators with intrinsic delayed feedback. The results of the research explain how initially monostable oscillators became effectivly bistable in the presence of the coupling and create a mean field that sustain the coexistence of synchronized and desynchronized states. Also we discuss other examples, where chimera-like state appears due to frequency dependence of the phase shift in the bistable system. In the second part, we make further investigation of this topic by modeling influence of an external periodic force to an oscillator with intrinsic delayed feedback. We made stability analysis of the synchronized state and constructed Arnold tongues. The results explain formation of the chimera-like state and hysteric behavior of the synchronization area. Also, we consider two sets of parameters of the oscillator with symmetric and asymmetric Arnold tongues, that correspond to mono- and bi-stable regimes of the oscillator. In the third part, we demonstrate the results of the work, which was done in collaboration with our colleagues from Psychology Department of University of Potsdam. The project aimed to study the effect of the cardiac rhythm on human perception of time using synchronization analysis. From our part, we made a statistical analysis of the data obtained from the conducted experiment on free time interval reproduction task. We examined how ones heartbeat influences the time perception and searched for possible phase synchronization between heartbeat cycles and time reproduction responses. The findings support the prediction that cardiac cycles can serve as input signals, and is used for reproduction of time intervals in the range of several seconds.},
  language  = {en}
}
@phdthesis{Yang2020,
  author    = {Yang, Xiaoqiang},
  title     = {Spatial and temporal analyses of catchment and in-stream nitrate dynamics},
  doi       = {10.25932/publishup-47702},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-477029},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 146},
  year      = {2020},
  abstract  = {Water quality in river systems is of growing concern due to rising anthropogenic pressures and climate change. Mitigation efforts have been placed under the guidelines of different governance conventions during last decades (e.g., the Water Framework Directive in Europe). Despite significant improvement through relatively straightforward measures, the environmental status has likely reached a plateau. A higher spatiotemporal accuracy of catchment nitrate modeling is, therefore, needed to identify critical source areas of diffuse nutrient pollution (especially for nitrate) and to further guide implementation of spatially differentiated, cost-effective mitigation measures. On the other hand, the emerging high-frequency sensor monitoring upgrades the monitoring resolution to the time scales of biogeochemical processes and enables more flexible monitoring deployments under varying conditions. The newly available information offers new prospects in understanding nitrate spatiotemporal dynamics. Formulating such advanced process understanding into catchment models is critical for model further development and environmental status evaluation. This dissertation is targeting on a comprehensive analysis of catchment and in-stream nitrate dynamics and is aiming to derive new insights into their spatial and temporal variabilities through the new fully distributed model development and the new high-frequency data. Firstly, a new fully distributed, process-based catchment nitrate model (the mHM-Nitrate model) is developed based on the mesoscale Hydrological Model (mHM) platform. Nitrate process descriptions are adopted from the Hydrological Predictions for the Environment (HYPE), with considerable improved implementations. With the multiscale grid-based discretization, mHM-Nitrate balances the spatial representation and the modeling complexity. The model has been thoughtfully evaluated in the Selke catchment (456 km2), central Germany, which is characterized by heterogeneous physiographic conditions. Results show that the model captures well the long-term discharge and nitrate dynamics at three nested gauging stations. Using daily nitrate-N observations, the model is also validated in capturing short-term fluctuations due to changes in runoff partitioning and spatial contribution during flooding events. By comparing the model simulations with the values reported in the literature, the model is capable of providing detailed and reliable spatial information of nitrate concentrations and fluxes. Therefore, the model can be taken as a promising tool for environmental scientists in advancing environmental modeling research, as well as for stakeholders in supporting their decision-making, especially for spatially differentiated mitigation measures. Secondly, a parsimonious approach of regionalizing the in-stream autotrophic nitrate uptake is proposed using high-frequency data and further integrated into the new mHM-Nitrate model. The new regionalization approach considers the potential uptake rate (as a general parameter) and effects of above-canopy light and riparian shading (represented by global radiation and leaf area index data, respectively). Multi-parameter sensors have been continuously deployed in a forest upstream reach and an agricultural downstream reach of the Selke River. Using the continuous high-frequency data in both streams, daily autotrophic uptake rates (2011-2015) are calculated and used to validate the regionalization approach. The performance and spatial transferability of the approach is validated in terms of well-capturing the distinct seasonal patterns and value ranges in both forest and agricultural streams. Integrating the approach into the mHM-Nitrate model allows spatiotemporal variability of in-stream nitrate transport and uptake to be investigated throughout the river network. Thirdly, to further assess the spatial variability of catchment nitrate dynamics, for the first time the fully distributed parameterization is investigated through sensitivity analysis. Sensitivity results show that parameters of soil denitrification, in-stream denitrification and in-stream uptake processes are the most sensitive parameters throughout the Selke catchment, while they all show high spatial variability, where hot-spots of parameter sensitivity can be explicitly identified. The Spearman rank correlation is further analyzed between sensitivity indices and multiple catchment factors. The correlation identifies that the controlling factors vary spatially, reflecting heterogeneous catchment responses in the Selke catchment. These insights are, therefore, informative in informing future parameter regionalization schemes for catchment water quality models. In addition, the spatial distributions of parameter sensitivity are also influenced by the gauging information that is being used for sensitivity evaluation. Therefore, an appropriate monitoring scheme is highly recommended to truly reflect the catchment responses.},
  language  = {en}
}
@phdthesis{Yan2019,
  author    = {Yan, Runyu},
  title     = {Nitrogen-doped and porous carbons towards new energy storage mechanisms for supercapacitors with high energy density},
  doi       = {10.25932/publishup-43141},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-431413},
  school      = {Universit{\"a}t Potsdam},
  pages     = {152},
  year      = {2019},
  abstract  = {Supercapacitors are electrochemical energy storage devices with rapid charge/discharge rate and long cycle life. Their biggest challenge is the inferior energy density compared to other electrochemical energy storage devices such as batteries. Being the most widely spread type of supercapacitors, electrochemical double-layer capacitors (EDLCs) store energy by electrosorption of electrolyte ions on the surface of charged electrodes. As a more recent development, Na-ion capacitors (NICs) are expected to be a more promising tactic to tackle the inferior energy density due to their higher-capacity electrodes and larger operating voltage. The charges are simultaneously stored by ion adsorption on the capacitive-type cathode surface and via faradic process in the battery-type anode, respectively. Porous carbon electrodes are of great importance in these devices, but the paramount problems are the facile synthetic routes for high-performance carbons and the lack of fundamental understanding of the energy storage mechanisms. Therefore, the aim of the present dissertation is to develop novel synthetic methods for (nitrogen-doped) porous carbon materials with superior performance, and to reveal a deeper understanding energy storage mechanisms of EDLCs and NICs. The first part introduces a novel synthetic method towards hierarchical ordered meso-microporous carbon electrode materials for EDLCs. The large amount of micropores and highly ordered mesopores endow abundant sites for charge storage and efficient electrolyte transport, respectively, giving rise to superior EDLC performance in different electrolytes. More importantly, the controversial energy storage mechanism of EDLCs employing ionic liquid (IL) electrolytes is investigated by employing a series of porous model carbons as electrodes. The results not only allow to conclude on the relations between the porosity and ion transport dynamics, but also deliver deeper insights into the energy storage mechanism of IL-based EDLCs which is different from the one usually dominating in solvent-based electrolytes leading to compression double-layers. The other part focuses on anodes of NICs, where novel synthesis of nitrogen-rich porous carbon electrodes and their sodium storage mechanism are investigated. Free-standing fibrous nitrogen-doped carbon materials are synthesized by electrospinning using the nitrogen-rich monomer (hexaazatriphenylene-hexacarbonitrile, C18N12) as the precursor followed by condensation at high temperature. These fibers provide superior capacity and desirable charge/discharge rate for sodium storage. This work also allows insights into the sodium storage mechanism in nitrogen-doped carbons. Based on this mechanism, further optimization is done by designing a composite material composed of nitrogen-rich carbon nanoparticles embedded in conductive carbon matrix for a better charge/discharge rate. The energy density of the assembled NICs significantly prevails that of common EDLCs while maintaining the high power density and long cycle life.},
  language  = {en}
}
@phdthesis{Yadavalli2014,
  author    = {Yadavalli, Nataraja Sekhar},
  title     = {Advances in experimental methods to probe surface relief grating formation mechanism in photosensitive materials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71213},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {When azobenzene-modified photosensitive polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the electric field vector distribution resulting in the formation of surface relief grating (SRG). The exact correspondence of the electric field vector orientation in interference pattern in relation to the presence of local topographic minima or maxima of SRG is in general difficult to determine. In my thesis, we have established a systematic procedure to accomplish the correlation between different interference patterns and the topography of SRG. For this, we devise a new setup combining an atomic force microscope and a two-beam interferometer (IIAFM). With this set-up, it is possible to track the topography change in-situ, while at the same time changing polarization and phase of the impinging interference pattern. To validate our results, we have compared two photosensitive materials named in short as PAZO and trimer. This is the first time that an absolute correspondence between the local distribution of electric field vectors of interference pattern and the local topography of the relief grating could be established exhaustively. In addition, using our IIAFM we found that for a certain polarization combination of two orthogonally polarized interfering beams namely SP (↕, ↔) interference pattern, the topography forms SRG with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures below diffraction limit with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We have also probed for the stresses induced during the polymer mass transport by placing an ultra-thin gold film on top (5-30 nm). During irradiation, the metal film not only deforms along with the SRG formation, but ruptures in regular and complex manner. The morphology of the cracks differs strongly depending on the electric field distribution in the interference pattern even when the magnitude and the kinetic of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. The neutron reflectivity measurements of the metal/polymer interface indicate the penetration of metal layer within the polymer resulting in the formation of bonding layer that confirms the transduction of light induced stresses in the polymer layer to a metal film.},
  language  = {en}
}
@phdthesis{Yadav2023,
  author    = {Yadav, Himanshu},
  title     = {A computational evaluation of feature distortion and cue weighting in sentence comprehension},
  doi       = {10.25932/publishup-58505},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-585055},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 115},
  year      = {2023},
  abstract  = {Successful sentence comprehension requires the comprehender to correctly figure out who did what to whom. For example, in the sentence John kicked the ball, the comprehender has to figure out who did the action of kicking and what was being kicked. This process of identifying and connecting the syntactically-related words in a sentence is called dependency completion. What are the cognitive constraints that determine dependency completion? A widely-accepted theory is cue-based retrieval. The theory maintains that dependency completion is driven by a content-addressable search for the co-dependents in memory. The cue-based retrieval explains a wide range of empirical data from several constructions including subject-verb agreement, subject-verb non-agreement, plausibility mismatch configurations, and negative polarity items. However, there are two major empirical challenges to the theory: (i) Grammatical sentences' data from subject-verb number agreement dependencies, where the theory predicts a slowdown at the verb in sentences like the key to the cabinet was rusty compared to the key to the cabinets was rusty, but the data are inconsistent with this prediction; and, (ii) Data from antecedent-reflexive dependencies, where a facilitation in reading times is predicted at the reflexive in the bodybuilder who worked with the trainers injured themselves vs. the bodybuilder who worked with the trainer injured themselves, but the data do not show a facilitatory effect. The work presented in this dissertation is dedicated to building a more general theory of dependency completion that can account for the above two datasets without losing the original empirical coverage of the cue-based retrieval assumption. In two journal articles, I present computational modeling work that addresses the above two empirical challenges. To explain the grammatical sentences' data from subject-verb number agreement dependencies, I propose a new model that assumes that the cue-based retrieval operates on a probabilistically distorted representation of nouns in memory (Article I). This hybrid distortion-plus-retrieval model was compared against the existing candidate models using data from 17 studies on subject-verb number agreement in 4 languages. I find that the hybrid model outperforms the existing models of number agreement processing suggesting that the cue-based retrieval theory must incorporate a feature distortion assumption. To account for the absence of facilitatory effect in antecedent-reflexive dependen� cies, I propose an individual difference model, which was built within the cue-based retrieval framework (Article II). The model assumes that individuals may differ in how strongly they weigh a syntactic cue over a number cue. The model was fitted to data from two studies on antecedent-reflexive dependencies, and the participant-level cue-weighting was estimated. We find that one-fourth of the participants, in both studies, weigh the syntactic cue higher than the number cue in processing reflexive dependencies and the remaining participants weigh the two cues equally. The result indicates that the absence of predicted facilitatory effect at the level of grouped data is driven by some, not all, participants who weigh syntactic cues higher than the number cue. More generally, the result demonstrates that the assumption of differential cue weighting is important for a theory of dependency completion processes. This differential cue weighting idea was independently supported by a modeling study on subject-verb non-agreement dependencies (Article III). Overall, the cue-based retrieval, which is a general theory of dependency completion, needs to incorporate two new assumptions: (i) the nouns stored in memory can undergo probabilistic feature distortion, and (ii) the linguistic cues used for retrieval can be weighted differentially. This is the cumulative result of the modeling work presented in this dissertation. The dissertation makes an important theoretical contribution: Sentence comprehension in humans is driven by a mechanism that assumes cue-based retrieval, probabilistic feature distortion, and differential cue weighting. This insight is theoretically important because there is some independent support for these three assumptions in sentence processing and the broader memory literature. The modeling work presented here is also methodologically important because for the first time, it demonstrates (i) how the complex models of sentence processing can be evaluated using data from multiple studies simultaneously, without oversimplifying the models, and (ii) how the inferences drawn from the individual-level behavior can be used in theory development.},
  language  = {en}
}
@phdthesis{Xue2004,
  author    = {X{\"u}, Chenggang},
  title     = {Preparation and characterization of vapour deposited films based on substituted 2,5-diphenyl-1,3,4-oxadiazole derivatives},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001358},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Diese Arbeit befasst sich mit dem Einfluss der molekularen Struktur von 2,5-Diphenyl-1,3,4-Oxadiazol-Derivaten auf die Pr{\"a}parierung d{\"u}nner Schichten mittels Vakuumdeposition. D{\"u}nne Schichten von diesen Substanzen wurden auf Si/SiO2 aufgedampft und ihre Struktur systematisch mittels XSR, AFM und IR untersucht. Das Ergebnis zeigt, dass die Schichtstrukturen offenbar von Substratetemperatur (Ts) abh{\"a}ngig sind. Im untersuchten Ts-Bereich bilden etherverbr{\"u}ckte Oxadiazole immer geordnete Schichten und die Schichtperiodicit{\"a}t h{\"a}ngt linear von der L{\"a}ngen der aliphatischen Ketten, w{\"a}hrend sich bei den amidverbr{\"u}ckten Oxadiazolen nur bei hohen Ts geordnete Schichten bilden k{\"o}nnen. Diese Unterschiede sind auf die intermolekularen Wasserstoffbr{\"u}cken zur{\"u}ckzuf{\"u}hren. Der Tilt-Winkel der Molek{\"u}le ist durch die Wechselwirkung zwischen dem aromatischen Teil bestimmt. Die Wechselwirkungen zwischen den Kopfgruppen k{\"o}nnen durch Tempern abgeschw{\"a}cht werden und f{\"u}hren zur Strukturumwandlung von Schichten, die auf etherverbr{\"u}ckten Oxadiazolen basieren. Alle Schichten von etherverbr{\"u}ckten Oxadiazolen haben Doppelschicht-Struktur, aber amidverbr{\"u}ckte Oxadiazole bilden nur Doppelschicht-Strukturen, wenn die Molek{\"u}le eine Kopfgruppe besitzen.},
  language  = {en}
}
@phdthesis{Xiong2018,
  author    = {Xiong, Tao},
  title     = {Vibrationally resolved absorption, emission, resonance Raman and photoelectron spectra of selected organic molecules, associated radicals and cations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418105},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 100},
  year      = {2018},
  abstract  = {Time-dependent correlation function based methods to study optical spectroscopy involving electronic transitions can be traced back to the work of Heller and coworkers. This intuitive methodology can be expected to be computationally efficient and is applied in the current work to study the vibronic absorption, emission, and resonance Raman spectra of selected organic molecules. Besides, the "non-standard" application of this approach to photoionization processes is also explored. The application section consists of four chapters as described below. In Chapter 4, the molar absorptivities and vibronic absorption/emission spectra of perylene and several of its N-substituted derivatives are investigated. By systematically varying the number and position of N atoms, it is shown that the presence of nitrogen heteroatoms has a negligible effect on the molecular structure and geometric distortions upon electronic transitions, while spectral properties are more sensitive: In particular the number of N atoms is important while their position is less decisive. Thus, N-substitution can be used to fine-tune the optical properties of perylene-based molecules. In Chapter 5, the same methods are applied to study the vibronic absorption/emission and resonance Raman spectra of a newly synthesized donor-acceptor type molecule. The simulated absorption/emission spectra agree fairly well with experimental data, with discrepancies being attributed to solvent effects. Possible modes which may dominate the fine-structure in the vibronic spectra are proposed by analyzing the correlation function with the aid of Raman and resonance Raman spectra. In the next two chapters, besides the above types of spectra, the methods are extended to study photoelectron spectra of several small diamondoid-related systems (molecules, radicals, and cations). Comparison of the photoelectron spectra with available experimental data suggests that the correlation function based approach can describe ionization processes reasonably well. Some of these systems, cationic species in particular, exhibit somewhat peculiar optical behavior, which presents them as possible candidates for functional devices. Correlation function based methods in a more general sense can be very versatile. In fact, besides the above radiative processes, formulas for non-radiative processes such as internal conversion have been derived in literature. Further implementation of the available methods is among our next goals.},
  language  = {en}
}
@phdthesis{Xie2023,
  author    = {Xie, Dongjiu},
  title     = {Nanostructured Iron-based compounds as sulfur host material for lithium-sulfur batteries},
  doi       = {10.25932/publishup-61036},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-610369},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 142},
  year      = {2023},
  abstract  = {The present thesis focuses on the synthesis of nanostructured iron-based compounds by using β-FeOOH nanospindles and poly(ionic liquid)s (PILs) vesicles as hard and soft templates, respectively, to suppress the shuttle effect of lithium polysulfides (LiPSs) in Li-S batteries. Three types of composites with different nanostructures (mesoporous nanospindle, yolk-shell nanospindle, and nanocapsule) have been synthesized and applied as sulfur host material for Li-S batteries. Their interactions with LiPSs and effects on the electrochemical performance of Li-S batteries have been systematically studied. In the first part of the thesis, carbon-coated mesoporous Fe3O4 (C@M-Fe3O4) nanospindles have been synthesized to suppress the shuttle effect of LiPSs. First, β-FeOOH nanospindles have been synthesized via the hydrolysis of iron (III) chloride in aqueous solution and after silica coating and subsequent calcination, mesoporous Fe2O3 (M-Fe2O3) have been obtained inside the confined silica layer through pyrolysis of β-FeOOH. After the removal of the silica layer, electron tomography (ET) has been applied to rebuild the 3D structure of the M-Fe2O3 nanospindles. After coating a thin layer of polydopamine (PDA) as carbon source, the PDA-coated M-Fe2O3 particles have been calcinated to synthesize C@M-Fe3O4 nanospindles. With the chemisorption of Fe3O4 and confinement of mesoporous structure to anchor LiPSs, the composite C@M-Fe3O4/S electrode delivers a remaining capacity of 507.7 mAh g-1 at 1 C after 600 cycles. In the second part of the thesis, a series of iron-based compounds (Fe3O4, FeS2, and FeS) with the same yolk-shell nanospindle morphology have been synthesized, which allows for the direct comparison of the effects of compositions on the electrochemical performance of Li-S batteries. The Fe3O4-carbon yolk-shell nanospindles have been synthesized by using the β-FeOOH nanospindles as hard template. Afterwards, Fe3O4-carbon yolk-shell nanospindles have been used as precursors to obtain iron sulfides (FeS and FeS2)-carbon yolk-shell nanospindles through sulfidation at different temperatures. Using the three types of yolk-shell nanospindles as sulfur host, the effects of compositions on interactions with LiPSs and electrochemical performance in Li-S batteries have been systematically investigated and compared. Benefiting from the chemisorption and catalytic effect of FeS2 particles and the physical confinement of the carbon shell, the FeS2-C/S electrode exhibits the best electrochemical performance with an initial specific discharge capacity of 877.6 mAh g-1 at 0.5 C and a retention ratio of 86.7\% after 350 cycles. In the third part, PILs vesicles have been used as soft template to synthesize carbon nanocapsules embedded with iron nitride particles to immobilize and catalyze LiPSs in Li-S batteries. First, 3-n-decyl-1-vinylimidazolium bromide has been used as monomer to synthesize PILs nanovesicles by free radical polymerization. Assisted by PDA coating route and ion exchange, PIL nanovesicles have been successfully applied as soft template in morphology-maintaining carbonization to prepare carbon nanocapsules embedded with iron nitride nanoparticles (FexN@C). The well-dispersed iron nitride nanoparticles effectively catalyze the conversion of LiPSs to Li2S, owing to their high electrical conductivity and strong chemical binding to LiPSs. The constructed FexN@C/S cathode demonstrates a high initial discharge capacity of 1085.0 mAh g-1 at 0.5 C with a remaining value of 930.0 mAh g-1 after 200 cycles. The results in the present thesis demonstrate the facile synthetic routes of nanostructured iron-based compounds with controllable morphologies and compositions using soft and hard colloidal templates, which can be applied as sulfur host to suppress the shuttle behavior of LiPSs. The synthesis approaches developed in this thesis are also applicable to fabricating other transition metal-based compounds with porous nanostructures for other applications.},
  language  = {en}
}
@phdthesis{Waetzoldt2016,
  author    = {W{\"a}tzoldt, Sebastian},
  title     = {Modeling collaborations in adaptive systems of systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97494},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XII, 380},
  year      = {2016},
  abstract  = {Recently, due to an increasing demand on functionality and flexibility, beforehand isolated systems have become interconnected to gain powerful adaptive Systems of Systems (SoS) solutions with an overall robust, flexible and emergent behavior. The adaptive SoS comprises a variety of different system types ranging from small embedded to adaptive cyber-physical systems. On the one hand, each system is independent, follows a local strategy and optimizes its behavior to reach its goals. On the other hand, systems must cooperate with each other to enrich the overall functionality to jointly perform on the SoS level reaching global goals, which cannot be satisfied by one system alone. Due to difficulties of local and global behavior optimizations conflicts may arise between systems that have to be solved by the adaptive SoS. This thesis proposes a modeling language that facilitates the description of an adaptive SoS by considering the adaptation capabilities in form of feedback loops as first class entities. Moreover, this thesis adopts the Models@runtime approach to integrate the available knowledge in the systems as runtime models into the modeled adaptation logic. Furthermore, the modeling language focuses on the description of system interactions within the adaptive SoS to reason about individual system functionality and how it emerges via collaborations to an overall joint SoS behavior. Therefore, the modeling language approach enables the specification of local adaptive system behavior, the integration of knowledge in form of runtime models and the joint interactions via collaboration to place the available adaptive behavior in an overall layered, adaptive SoS architecture. Beside the modeling language, this thesis proposes analysis rules to investigate the modeled adaptive SoS, which enables the detection of architectural patterns as well as design flaws and pinpoints to possible system threats. Moreover, a simulation framework is presented, which allows the direct execution of the modeled SoS architecture. Therefore, the analysis rules and the simulation framework can be used to verify the interplay between systems as well as the modeled adaptation effects within the SoS. This thesis realizes the proposed concepts of the modeling language by mapping them to a state of the art standard from the automotive domain and thus, showing their applicability to actual systems. Finally, the modeling language approach is evaluated by remodeling up to date research scenarios from different domains, which demonstrates that the modeling language concepts are powerful enough to cope with a broad range of existing research problems.},
  language  = {en}
}
@phdthesis{Wunderling2021,
  author    = {Wunderling, Nico},
  title     = {Nichtlineare Dynamiken und Interaktionen von Kippelementen im Erdsystem},
  doi       = {10.25932/publishup-52514},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-525140},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 303},
  year      = {2021},
  abstract  = {With ongoing anthropogenic global warming, some of the most vulnerable components of the Earth system might become unstable and undergo a critical transition. These subsystems are the so-called tipping elements. They are believed to exhibit threshold behaviour and would, if triggered, result in severe consequences for the biosphere and human societies. Furthermore, it has been shown that climate tipping elements are not isolated entities, but interact across the entire Earth system. Therefore, this thesis aims at mapping out the potential for tipping events and feedbacks in the Earth system mainly by the use of complex dynamical systems and network science approaches, but partially also by more detailed process-based models of the Earth system. In the first part of this thesis, the theoretical foundations are laid by the investigation of networks of interacting tipping elements. For this purpose, the conditions for the emergence of global cascades are analysed against the structure of paradigmatic network types such as Erd{\"o}s-R{\´e}nyi, Barab{\´a}si-Albert, Watts-Strogatz and explicitly spatially embedded networks. Furthermore, micro-scale structures are detected that are decisive for the transition of local to global cascades. These so-called motifs link the micro- to the macro-scale in the network of tipping elements. Alongside a model description paper, all these results are entered into the Python software package PyCascades, which is publicly available on github. In the second part of this dissertation, the tipping element framework is first applied to components of the Earth system such as the cryosphere and to parts of the biosphere. Afterwards it is applied to a set of interacting climate tipping elements on a global scale. Using the Earth system Model of Intermediate Complexity (EMIC) CLIMBER-2, the temperature feedbacks are quantified, which would arise if some of the large cryosphere elements disintegrate over a long span of time. The cryosphere components that are investigated are the Arctic summer sea ice, the mountain glaciers, the Greenland and the West Antarctic Ice Sheets. The committed temperature increase, in case the ice masses disintegrate, is on the order of an additional half a degree on a global average (0.39-0.46 °C), while local to regional additional temperature increases can exceed 5 °C. This means that, once tipping has begun, additional reinforcing feedbacks are able to increase global warming and with that the risk of further tipping events. This is also the case in the Amazon rainforest, whose parts are dependent on each other via the so-called moisture-recycling feedback. In this thesis, the importance of drought-induced tipping events in the Amazon rainforest is investigated in detail. Despite the Amazon rainforest is assumed to be adapted to past environmental conditions, it is found that tipping events sharply increase if the drought conditions become too intense in a too short amount of time, outpacing the adaptive capacity of the Amazon rainforest. In these cases, the frequency of tipping cascades also increases to 50\% (or above) of all tipping events. In the model that was developed in this study, the southeastern region of the Amazon basin is hit hardest by the simulated drought patterns. This is also the region that already nowadays suffers a lot from extensive human-induced changes due to large-scale deforestation, cattle ranching or infrastructure projects. Moreover, on the larger Earth system wide scale, a network of conceptualised climate tipping elements is constructed in this dissertation making use of a large literature review, expert knowledge and topological properties of the tipping elements. In global warming scenarios, tipping cascades are detected even under modest scenarios of climate change, limiting global warming to 2 °C above pre-industrial levels. In addition, the structural roles of the climate tipping elements in the network are revealed. While the large ice sheets on Greenland and Antarctica are the initiators of tipping cascades, the Atlantic Meridional Overturning Circulation (AMOC) acts as the transmitter of cascades. Furthermore, in our conceptual climate tipping element model, it is found that the ice sheets are of particular importance for the stability of the entire system of investigated climate tipping elements. In the last part of this thesis, the results from the temperature feedback study with the EMIC CLIMBER-2 are combined with the conceptual model of climate tipping elements. There, it is observed that the likelihood of further tipping events slightly increases due to the temperature feedbacks even if no further CO\$_2\$ would be added to the atmosphere. Although the developed network model is of conceptual nature, it is possible with this work for the first time to quantify the risk of tipping events between interacting components of the Earth system under global warming scenarios, by allowing for dynamic temperature feedbacks at the same time.},
  language  = {en}
}
@phdthesis{Wulff2018,
  author    = {Wulff, Alexander},
  title     = {Essays in macroeconomics and financial market imperfections},
  doi       = {10.25932/publishup-42995},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-429956},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 142},
  year      = {2018},
  abstract  = {This dissertation consists of four self-contained papers that deal with the implications of financial market imperfections and heterogeneity. The analysis mainly relates to the class of incomplete-markets models but covers different research topics. The first paper deals with the distributional effects of financial integration for developing countries. Based on a simple heterogeneous-agent approach, it is shown that capital owners experience large welfare losses while only workers moderately gain due to higher wages. The large welfare losses for capital owners contrast with the small average welfare gains from representative-agent economies and indicate that a strong opposition against capital market opening has to be expected. The second paper considers the puzzling observation of capital flows from poor to rich countries and the accompanying changes in domestic economic development. Motivated by the mixed results from the literature, we employ an incomplete-markets model with different types of idiosyncratic risk and borrowing constraints. Based on different scenarios, we analyze under what conditions the presence of financial market imperfections contributes to explain the empirical findings and how the conditions may change with different model assumptions. The third paper deals with the interplay of incomplete information and financial market imperfections in an incomplete-markets economy. In particular, it analyzes the impact of incomplete information about idiosyncratic income shocks on aggregate saving. The results show that the effect of incomplete information is not only quantitatively substantial but also qualitatively ambiguous and varies with the influence of the income risk and the borrowing constraint. Finally, the fourth paper analyzes the influence of different types of fiscal rules on the response of key macroeconomic variables to a government spending shock. We find that a strong temporary increase in public debt contributes to stabilizing consumption and leisure in the first periods following the change in government spending, whereas a non-debt-intensive fiscal rule leads to a faster recovery of consumption, leisure, capital and output in later periods. Regarding optimal debt policy, we find that a debt-intensive fiscal rule leads to the largest aggregate welfare benefit and that the individual welfare gain is particularly high for wealth-poor agents.},
  language  = {en}
}
@phdthesis{Wulf2011,
  author    = {Wulf, Hendrik},
  title     = {Seasonal precipitation, river discharge, and sediment flux in the western Himalaya},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57905},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Rainfall, snow-, and glacial melt throughout the Himalaya control river discharge, which is vital for maintaining agriculture, drinking water and hydropower generation. However, the spatiotemporal contribution of these discharge components to Himalayan rivers is not well understood, mainly because of the scarcity of ground-based observations. Consequently, there is also little known about the triggers and sources of peak sediment flux events, which account for extensive hydropower reservoir filling and turbine abrasion. We therefore lack basic information on the distribution of water resources and controls of erosion processes. In this thesis, I employ various methods to assess and quantify general characteristics of and links between precipitation, river discharge, and sediment flux in the Sutlej Valley. First, I analyze daily precipitation data (1998-2007) from 80 weather stations in the western Himalaya, to decipher the distribution of rain- and snowfall. Rainfall magnitude frequency analyses indicate that 40\% of the summer rainfall budget is attributed to monsoonal rainstorms, which show higher variability in the orogenic interior than in frontal regions. Combined analysis of rainstorms and sediment flux data of a major Sutlej River tributary indicate that monsoonal rainfall has a first order control on erosion processes in the orogenic interior, despite the dominance of snowfall in this region. Second, I examine the contribution of rainfall, snow and glacial melt to river discharge in the Sutlej Valley (s55,000 km2), based on a distributed hydrological model, which covers the period 2000-2008. To achieve high spatial and daily resolution despite limited ground-based observations the hydrological model is forced by daily remote sensing data, which I adjusted and calibrated with ground station data. The calibration shows that the Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall product systematically overestimates rainfall in semi-arid and arid regions, increasing with aridity. The model results indicate that snowmelt-derived discharge (74\%) is most important during the pre-monsoon season (April to June) whereas rainfall (56\%) and glacial melt (17\%) dominate the monsoon season (July-September). Therefore, climate change most likely causes a reduction in river discharge during the pre-monsoon season, which especially affects the orogenic interior. Third, I investigate the controls on suspended sediment flux in different parts of the Sutlej catchments, based on daily gauging data from the past decade. In conjunction with meteorological data, earthquake records, and rock strength measurements I find that rainstorms are the most frequent trigger of high-discharge events with peaks in suspended sediment concentrations (SSC) that account for the bulk of the suspended sediment flux. The suspended sediment flux increases downstream, mainly due to increases in runoff. Pronounced erosion along the Himalayan Front occurs throughout the monsoon season, whereas efficient erosion of the orogenic interior is confined to single extreme events. The results of this thesis highlight the importance of snow and glacially derived melt waters in the western Himalaya, where extensive regions receive only limited amounts of monsoonal rainfall. These regions are therefore particularly susceptible to global warming with major implications on the hydrological cycle. However, the sediment discharge data show that infrequent monsoonal rainstorms that pass the orographic barrier of the Higher Himalaya are still the primary trigger of the highest-impact erosion events, despite being subordinate to snow and glacially-derived discharge. These findings may help to predict peak sediment flux events and could underpin the strategic development of preventative measures for hydropower infrastructures.},
  language  = {en}
}
@phdthesis{Wu2010,
  author    = {Wu, Ye},
  title     = {Nonlinear dynamics in complex networks and modeling human dynamics},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-47358},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {Durch große Datenmengen k{\"o}nnen die Forscher die Eigenschaften komplexer Systeme untersuchen, z.B. komplexe Netzwerk und die Dynamik des menschlichen Verhaltens. Eine große Anzahl an Systemen werden als große und komplexe Netzwerke dargestellt, z.B. das Internet, Stromnetze, Wirtschaftssysteme. Immer mehr Forscher haben großes Interesse an der Dynamik des komplexen Netzwerks. Diese Arbeit besteht aus den folgenden drei Teilen. Der erste Teil ist ein einfacher dynamischer Optimierungs-Kopplungs-Mechanismus, aber sehr wirksam. Durch den Mechanismus kann synchronisation in komplexen Netzwerken mit und ohne Zeitverz{\"o}gerung realisiert, und die F{\"a}higkeit der Synchronisation von small-world und scale-free Netze verbessert werden. Im zweiten Teil geht um die Verst{\"a}rkung der Robustheit der scale-free Netze im Zusammenhang mit der Gemeinden-Struktur. Einige Reaktionsmuster und topologische Gemeinden sind einheitlich. Die Ergebnisse zeigen einen neuen Aspekt der Beziehung zwischen den Funktionen und der Netzwerk-Topologie von komplexen Netzwerken. Im dritten Teil welche eine wichtige Rolle in komplexen Netzwerken spielt, wird die Verhaltens-Dynamik der menschliche Mitteilung durch Daten- und Modellanalysierung erforscht, dann entsteht ein neues Mitteilungsmodell. Mit Hilfe von einem Interaktion priority-Queue Model kann das neue Modell erkl{\"a}rt werden. Mit Hilfe des Models k{\"o}nnen viele praktische Interaktions-Systeme erkl{\"a}rt werden, z.B. E-Mail und Briefe (oder Post). Mit Hilfe meiner Untersuchung kann man menschliches Verhalten auf der Individuums- und Netzwerkebene neu kennenlernen. Im vierter Teil kann ich nachweisen, dass menschliches Kommentar-Verhalten in on-line Sozialsystemen, eine andere Art der Interaktionsdynamik von Mensch non-Poisson ist und dieses am Modell erkl{\"a}ren. Mit Hilfe der non-Poisson Prozesse kann man das pers{\"o}nliche Anziehungskraft-Modell besser verstehen. Die Ergebnisse sind hilfreich zum Kennenlernen des Musters des menschlichen Verhaltens in on-line Gesellschaften und der Entwicklung von {\"o}ffentlicher Meinung nicht nur in der virtuellen Gesellschaftn sondern auch in der Realgesellschaft. Am Ende geht es um eine Prognose von menschlicher Dynamik und komplexen Netzwerken.},
  language  = {en}
}
@phdthesis{Wrzus2008,
  author    = {Wrzus, Cornelia},
  title     = {Similarity in personal relationships : associations with relationship regulation between and within individuals},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-20158},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {People engage in a multitude of different relationships. Relatives, spouses, and friends are modestly to moderately similar in various characteristics, e.g., personality characteristics, interests, appearance. The role of psychological (e.g., skills, global appraisal) and social (e.g., gender, familial status) similarities in personal relationships and the association with relationship quality (emotional closeness and reciprocity of support) were examined in four independent studies. Young adults (N = 456; M = 27 years) and middle-aged couples from four different family types (N = 171 couples, M = 38 years) gave answer to a computer-aided questionnaire regarding their ego-centered networks. A subsample of 175 middle-aged adults (77 couples and 21 individuals) participated in a one-year follow-up questioning. Two experimental studies (N = 470; N = 802), both including two assessments with an interval of five weeks, were conducted to examine causal relationships among similarity, closeness, and reciprocity expectations. Results underline the role of psychological and social similarities as covariates of emotional closeness and reciprocity of support on the between-relationship level, but indicate a relatively weak effect within established relationships. In specific relationships, such as parent-child relationships and friendships, psychological similarity partly alleviates the effects of missing genetic relatedness. Individual differences moderate these between-relationship effects. In all, results combine evolutionary and social psychological perspectives on similarity in personal relationships and extend previous findings by means of a network approach and an experimental manipulation of existing relationships. The findings further show that psychological and social similarity have different implications for the study of personal relationships depending on the phase in the developmental process of relationships.},
  language  = {en}
}
@phdthesis{Wriedt2004,
  author    = {Wriedt, Gunter},
  title     = {Modelling of nitrogen transport and turnover during soil and groundwater passage in a small lowland catchment of Northern Germany},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001307},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Stoffumsatzreaktionen und hydraulische Prozesse im Boden und Grundwasser k{\"o}nnen in Tieflandeinzugsgebieten zu einer Nitratretention f{\"u}hren. Die Untersuchung dieser Prozesse in Raum und Zeit kann mit Hilfe geeigneter Modelle erfolgen. Ziele dieser Arbeit sind: i) die Entwicklung eines geeigneten Modellansatzes durch Kombination von Teilmodellen zur Simulation des N-Transportes im Boden und Grundwasser von Tieflandeinzugsgebieten und ii) die Untersuchung von Wechselwirkungen zwischen Gebietseigenschaften und N-Transport unter besonderer Ber{\"u}cksichtigung der potentiellen N-Zufuhr in die Oberfl{\"a}chengew{\"a}sser. Der Modellansatz basiert auf der Kombination verschiedener Teilmodelle: das Bodenwasser- und -stickstoffmodell mRISK-N, das Grundwassermodell MODFLOW und das Stofftransportmodell RT3D. Zur Untersuchung der Wechselwirkungen mit den Gebietseigenschaften muss die Verteilung und Verf{\"u}gbarkeit von Reaktionspartnern ber{\"u}cksichtigt werden. Dazu wurde ein Reaktionsmodul entwickelt, welches chemische Prozesse im Grundwasser simuliert. Hierzu geh{\"o}ren die Mineralisation organischer Substanz durch Sauerstoff, Nitrat und Sulfat sowie die Pyritoxidation durch Sauerstoff und Nitrat. Der Modellansatz wurde in verschiedenen Einzelstudien angewandt, wobei jeweils bestimmte Teilmodelle im Vordergrund stehen. Alle Modellstudien basieren auf Daten aus dem Schaugrabeneinzugsgebiet (ca. 25 km\&\#178;), in der N{\"a}he von Osterburg(Altmark) im Norden Sachsen-Anhalts. Die folgenden Einzelstudien wurden durchgef{\"u}hrt: i) Evaluation des Bodenmodells anhand von Lysimeterdaten, ii) Modellierung eines Tracerexperimentes im Feldmaßstab als eine erste Anwendung des Reaktionsmoduls, iii) Untersuchung hydraulisch-chemischer Wechselwirkungen an einem 2D-Grundwassertransekt, iv) Fl{\"a}chenverteilte Modellierung von Grundwasserneubildung und Bodenstickstoffaustrag im Untersuchungsgebiet als Eingangsdaten f{\"u}r nachfolgende Grundwassersimulationen, und v) Untersuchung der Ausbreitung von Nitrat im Grundwasser und des Durchbruchs in die Oberfl{\"a}chengew{\"a}sser im Untersuchungsgebiet auf Basis einer 3D-Modellierung von Grundwasserstr{\"o}mung und reaktivem Stofftransport. Die Modellstudien zeigen, dass der Modellansatz geeignet ist, die Wechselwirkungen zwischen Stofftransport und \&ndash;umsatz und den hydraulisch-chemischen Gebietseigenschaften zu modellieren. Die Ausbreitung von Nitrat im Sediment wird wesentlich von der Verf{\"u}gbarkeit reaktiver Substanzen sowie der Verweilzeit im Grundwasserleiter bestimmt. Bei der Simulation des Untersuchungsgebietes wurde erst nach 70 Jahren eine der gegebenen Eintragssitutation entsprechende Nitratkonzentration im Grundwasserzustrom zum Grabensystem erreicht (konservativer Transport). Die Ber{\"u}cksichtigung von reaktivem Stofftransport f{\"u}hrt zu einer deutlichen Reduktion der Nitratkonzentrationen. Die Modellergebnisse zeigen, dass der Grundwasserzustrom die beobachtete Nitratbelastung im Grabensystem nicht erkl{\"a}ren kann, da der Großteil des Nitrates durch Denitrifikation verloren geht. Andere Quellen, wie direkte Eintr{\"a}ge oder Dr{\"a}nagenzufl{\"u}sse m{\"u}ssen ebenfalls in Betracht gezogen werden. Die Prognosef{\"a}higkeit des Modells f{\"u}r das Untersuchungsgebiet wird durch die Datenunsicherheiten und die Sch{\"a}tzung der Modellparameter eingeschr{\"a}nkt. Dennoch ist der Modellansatz eine wertvolle Hilfe bei der Identifizierung von belastungsrelevanten Teilfl{\"a}chen (Stoffquellen und -senken) sowie bei der Modellierung der Auswirkungen von Managementmaßnahmen oder Landnutzungsver{\"a}nderungen auf Grundlage von Szenario-Simulationen. Der Modellansatz unterst{\"u}tzt auch die Interpretation von Beobachtungsdaten, da so die lokalen Informationen in einen r{\"a}umlichen und zeitlichen Zusammenhang gestellt werden k{\"o}nnen.},
  language  = {en}
}
@phdthesis{Wozny2019,
  author    = {Wozny, Florian},
  title     = {Three empirical essays in health economics},
  doi       = {10.25932/publishup-46991},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469910},
  school      = {Universit{\"a}t Potsdam},
  pages     = {200},
  year      = {2019},
  abstract  = {Modern health care systems are characterized by pronounced prevention and cost-optimized treatments. This dissertation offers novel empirical evidence on how useful such measures can be. The first chapter analyzes how radiation, a main pollutant in health care, can negatively affect cognitive health. The second chapter focuses on the effect of Low Emission Zones on public heath, as air quality is the major external source of health problems. Both chapters point out potentials for preventive measures. Finally, chapter three studies how changes in treatment prices affect the reallocation of hospital resources. In the following, I briefly summarize each chapter and discuss implications for health care systems as well as other policy areas. Based on the National Educational Panel Study that is linked to data on radiation, chapter one shows that radiation can have negative long-term effects on cognitive skills, even at subclinical doses. Exploiting arguably exogenous variation in soil contamination in Germany due to the Chernobyl disaster in 1986, the findings show that people exposed to higher radiation perform significantly worse in cognitive tests 25 years later. Identification is ensured by abnormal rainfall within a critical period of ten days. The results show that the effect is stronger among older cohorts than younger cohorts, which is consistent with radiation accelerating cognitive decline as people get older. On average, a one-standarddeviation increase in the initial level of CS137 (around 30 chest x-rays) is associated with a decrease in the cognitive skills by 4.1 percent of a standard deviation (around 0.05 school years). Chapter one shows that sub-clinical levels of radiation can have negative consequences even after early childhood. This is of particular importance because most of the literature focuses on exposure very early in life, often during pregnancy. However, population exposed after birth is over 100 times larger. These results point to substantial external human capital costs of radiation which can be reduced by choices of medical procedures. There is a large potential for reductions because about one-third of all CT scans are assumed to be not medically justified (Brenner and Hall, 2007). If people receive unnecessary CT scans because of economic incentives, this chapter points to additional external costs of health care policies. Furthermore, the results can inform the cost-benefit trade-off for medically indicated procedures. Chapter two provides evidence about the effectiveness of Low Emission Zones. Low Emission Zones are typically justified by improvements in population health. However, there is little evidence about the potential health benefits from policy interventions aiming at improving air quality in inner-cities. The chapter ask how the coverage of Low Emission Zones air pollution and hospitalization, by exploiting variation in the roll out of Low Emission Zones in Germany. It combines information on the geographic coverage of Low Emission Zones with rich panel data on the universe of German hospitals over the period from 2006 to 2016 with precise information on hospital locations and the annual frequency of detailed diagnoses. In order to establish that our estimates of Low Emission Zones' health impacts can indeed be attributed to improvements in local air quality, we use data from Germany's official air pollution monitoring system and assign monitor locations to Low Emission Zones and test whether measures of air pollution are affected by the coverage of a Low Emission Zone. Results in chapter two confirm former results showing that the introduction of Low Emission Zones improved air quality significantly by reducing NO2 and PM10 concentrations. Furthermore, the chapter shows that hospitals which catchment areas are covered by a Low Emission Zone, diagnose significantly less air pollution related diseases, in particular by reducing the incidents of chronic diseases of the circulatory and the respiratory system. The effect is stronger before 2012, which is consistent with a general improvement in the vehicle fleet's emission standards. Depending on the disease, a one-standard-deviation increase in the coverage of a hospitals catchment area covered by a Low Emission Zone reduces the yearly number of diagnoses up to 5 percent. These findings have strong implications for policy makers. In 2015, overall costs for health care in Germany were around 340 billion euros, of which 46 billion euros for diseases of the circulatory system, making it the most expensive type of disease caused by 2.9 million cases (Statistisches Bundesamt, 2017b). Hence, reductions in the incidence of diseases of the circulatory system may directly reduce society's health care costs. Whereas chapter one and two study the demand-side in health care markets and thus preventive potential, chapter three analyzes the supply-side. By exploiting the same hospital panel data set as in chapter two, chapter three studies the effect of treatment price shocks on the reallocation of hospital resources in Germany. Starting in 2005, the implementation of the German-DRG-System led to general idiosyncratic treatment price shocks for individual hospitals. Thus far there is little evidence of the impact of general price shocks on the reallocation of hospital resources. Additionally, I add to the exiting literature by showing that price shocks can have persistent effects on hospital resources even when these shocks vanish. However, simple OLS regressions would underestimate the true effect, due to endogenous treatment price shocks. I implement a novel instrument variable strategy that exploits the exogenous variation in the number of days of snow in hospital catchment areas. A peculiarity of the reform allowed variation in days of snow to have a persistent impact on treatment prices. I find that treatment price increases lead to increases in input factors such as nursing staff, physicians and the range of treatments offered but to decreases in the treatment volume. This indicates supplier-induced demand. Furthermore, the probability of hospital mergers and privatization decreases. Structural differences in pre-treatment characteristics between hospitals enhance these effects. For instance, private and larger hospitals are more affected. IV estimates reveal that OLS results are biased towards zero in almost all dimensions because structural hospital differences are correlated with the reallocation of hospital resources. These results are important for several reasons. The G-DRG-Reform led to a persistent polarization of hospital resources, as some hospitals were exposed to treatment price increases, while others experienced reductions. If hospitals increase the treatment volume as a response to price reductions by offering unnecessary therapies, it has a negative impact on population wellbeing and public spending. However, results show a decrease in the range of treatments if prices decrease. Hospitals might specialize more, thus attracting more patients. From a policy perspective it is important to evaluate if such changes in the range of treatments jeopardize an adequate nationwide provision of treatments. Furthermore, the results show a decrease in the number of nurses and physicians if prices decrease. This could partly explain the nursing crisis in German hospitals. However, since hospitals specialize more they might be able to realize efficiency gains which justify reductions in input factors without loses in quality. Further research is necessary to provide evidence for the impact of the G-DRG-Reform on health care quality. Another important aspect are changes in the organizational structure. Many public hospitals have been privatized or merged. The findings show that this is at least partly driven by the G-DRG-Reform. This can again lead to a lack in services offered in some regions if merged hospitals specialize more or if hospitals are taken over by ecclesiastical organizations which do not provide all treatments due to moral conviction. Overall, this dissertation reveals large potential for preventive health care measures and helps to explain reallocation processes in the hospital sector if treatment prices change. Furthermore, its findings have potentially relevant implications for other areas of public policy. Chapter one identifies an effect of low dose radiation on cognitive health. As mankind is searching for new energy sources, nuclear power is becoming popular again. However, results of chapter one point to substantial costs of nuclear energy which have not been accounted yet. Chapter two finds strong evidence that air quality improvements by Low Emission Zones translate into health improvements, even at relatively low levels of air pollution. These findings may, for instance, be of relevance to design further policies targeted at air pollution such as diesel bans. As pointed out in chapter three, the implementation of DRG-Systems may have unintended side-effects on the reallocation of hospital resources. This may also apply to other providers in the health care sector such as resident doctors.},
  language  = {en}
}
@phdthesis{Wotschack2009,
  author    = {Wotschack, Christiane},
  title     = {Eye movements in reading strategies : how reading strategies modulate effects of distributed processing and oculomotor control},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  isbn      = {978-3-86956-021-2},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-36846},
  school      = {Universit{\"a}t Potsdam},
  pages     = {213},
  year      = {2009},
  abstract  = {Throughout its empirical research history eye movement research has always been aware of the differences in reading behavior induced by individual differences and task demands. This work introduces a novel comprehensive concept of reading strategy, comprising individual differences in reading style and reading skill as well as reader goals. In a series of sentence reading experiments recording eye movements, the influence of reading strategies on reader- and word-level effects assuming distributed processing has been investigated. Results provide evidence for strategic, top-down influences on eye movement control that extend our understanding of eye guidance in reading.},
  language  = {en}
}
@phdthesis{Worseck2007,
  author    = {Worseck, G{\´a}bor},
  title     = {The transverse proximity effect in quasar spectra},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18738},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {The intergalactic medium is kept highly photoionised by the intergalactic UV background radiation field generated by the overall population of quasars and galaxies. In the vicinity of sources of UV photons, such as luminous high-redshift quasars, the UV radiation field is enhanced due to the local source contribution. The higher degree of ionisation is visible as a reduced line density or generally as a decreased level of absorption in the Lyman alpha forest of neutral hydrogen. This so-called proximity effect has been detected with high statistical significance towards luminous quasars. If quasars radiate rather isotropically, background quasar sightlines located near foreground quasars should show a region of decreased Lyman alpha absorption close to the foreground quasar. Despite considerable effort, such a transverse proximity effect has only been detected in a few cases. So far, studies of the transverse proximity effect were mostly limited by the small number of suitable projected pairs or groups of high-redshift quasars. With the aim to substantially increase the number of quasar groups in the vicinity of bright quasars we conduct a targeted survey for faint quasars around 18 well-studied quasars at employing slitless spectroscopy. Among the reduced and calibrated slitless spectra of 29000 objects on a total area of 4.39 square degrees we discover in total 169 previously unknown quasar candidates based on their prominent emission lines. 81 potential z>1.7 quasars are selected for confirmation by slit spectroscopy at the Very Large Telescope (VLT). We are able to confirm 80 of these. 64 of the newly discovered quasars reside at z>1.7. The high success rate of the follow-up observations implies that the majority of the remaining candidates are quasars as well. In 16 of these groups we search for a transverse proximity effect as a systematic underdensity in the HI Lyman alpha absorption. We employ a novel technique to characterise the random absorption fluctuations in the forest in order to estimate the significance of the transverse proximity effect. Neither low-resolution spectra nor high-resolution spectra of background quasars of our groups present evidence for a transverse proximity effect. However, via Monte Carlo simulations the effect should be detectable only at the 1-2sigma level near three of the foreground quasars. Thus, we cannot distinguish between the presence or absence of a weak signature of the transverse proximity effect. The systematic effects of quasar variability, quasar anisotopy and intrinsic overdensities near quasars likely explain the apparent lack of the transverse proximity effect. Even in absence of the systematic effects, we show that a statistically significant detection of the transverse proximity effect requires at least 5 medium-resolution quasar spectra of background quasars near foreground quasars whose UV flux exceeds the UV background by a factor 3. Therefore, statistical studies of the transverse proximity effect require large numbers of suitable pairs. Two sightlines towards the central quasars of our survey fields show intergalactic HeII Lyman alpha absorption. A comparison of the HeII absorption to the corresponding HI absorption yields an estimate of the spectral shape of the intergalactic UV radiation field, typically parameterised by the HeII/HI column density ratio eta. We analyse the fluctuating UV spectral shape on both lines of sight and correlate it with seven foreground quasars. On the line of sight towards Q0302-003 we find a harder radiation field near 4 foreground quasars. In the direct vicinity of the quasars eta is consistent with values of 25-100, whereas at large distances from the quasars eta>200 is required. The second line of sight towards HE2347-4342 probes lower redshifts where eta is directly measurable in the resolved HeII forest. Again we find that the radiation field near the 3 foreground quasars is significantly harder than in general. While eta still shows large fluctuations near the quasars, probably due to radiative transfer, the radiation field is on average harder near the quasars than far away from them. We interpret these discoveries as the first detections of the transverse proximity effect as a local hardness fluctuation in the UV spectral shape. No significant HI proximity effect is predicted for the 7 foreground quasars. In fact, the HI absorption near the quasars is close to or slightly above the average, suggesting that the weak signature of the transverse proximity effect is masked by intrinsic overdensities. However, we show that the UV spectral shape traces the transverse proximity effect even in overdense regions or at large distances. Therefore, the spectral hardness is a sensitive physical measure of the transverse proximity effect that is able to break the density degeneracy affecting the traditional searches.},
  language  = {en}
}
@phdthesis{Won2016,
  author    = {Won, Jooyoung},
  title     = {Dynamic and equilibrium adsorption behaviour of ß-lactoglobulin at the solution/tetradecane interface: Effect of solution concentration, pH and ionic strength},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-99167},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 106},
  year      = {2016},
  abstract  = {Proteins are amphiphilic and adsorb at liquid interfaces. Therefore, they can be efficient stabilizers of foams and emulsions. β-lactoglobulin (BLG) is one of the most widely studied proteins due to its major industrial applications, in particular in food technology. In the present work, the influence of different bulk concentration, solution pH and ionic strength on the dynamic and equilibrium pressures of BLG adsorbed layers at the solution/tetradecane (W/TD) interface has been investigated. Dynamic interfacial pressure (Π) and interfacial dilational elastic modulus (E') of BLG solutions for various concentrations at three different pH values of 3, 5 and 7 at a fixed ionic strength of 10 mM and for a selected fixed concentration at three different ionic strengths of 1 mM, 10 mM and 100 mM are measured by Profile Analysis Tensiometer PAT-1 (SINTERFACE Technologies, Germany). A quantitative data analysis requires additional consideration of depletion due to BLG adsorption at the interface at low protein bulk concentrations. This fact makes experiments more efficient when oil drops are studied in the aqueous protein solutions rather than solution drops formed in oil. On the basis of obtained experimental data, concentration dependencies and the effect of solution pH on the protein surface activity was qualitatively analysed. In the presence of 10 mM buffer, we observed that generally the adsorbed amount is increasing with increasing BLG bulk concentration for all three pH values. The adsorption kinetics at pH 5 result in the highest Π values at any time of adsorption while it exhibits a less active behaviour at pH 3. Since the experimental data have not been in a good agreement with the classical diffusion controlled model due to the conformational changes which occur when the protein molecules get in contact with the hydrophobic oil phase in order to adapt to the interfacial environment, a new theoretical model is proposed here. The adsorption kinetics data were analysed with the newly proposed model, which is the classical diffusion model but modified by assuming an additional change in the surface activity of BLG molecules when adsorbing at the interface. This effect can be expressed through the adsorption activity constant in the corresponding equation of state. The dilational visco-elasticity of the BLG adsorbed interfacial layers is determined from measured dynamic interfacial tensions during sinusoidal drop area variations. The interfacial tension responses to these harmonic drop oscillations are interpreted with the same thermodynamic model which is used for the corresponding adsorption isotherm. At a selected BLG concentration of 2×10-6 mol/l, the influence of the ionic strength using different buffer concentration of 1, 10 and 100 mM on the interfacial pressure was studied. It is affected weakly at pH 5, whereas it has a strong impact by increasing buffer concentration at pH 3 and 7. In conclusion, the structure formation of BLG adsorbed layer in the early stage of adsorption at the W/TD interface is similar to those of the solution/air (W/A) surface. However, the equation of state at the W/TD interface provides an adsorption activity constant which is almost two orders of magnitude higher than that for the solution/air surface. At the end of this work, a new experimental tool called Drop and Bubble Micro Manipulator DBMM (SINTERFACE Technologies, Germany) has been introduced to study the stability of protein covered bubbles against coalescence. Among the available protocols the lifetime between the moment of contact and coalescence of two contacting bubble is determined for different BLG concentrations. The adsorbed amount of BLG is determined as a function of time and concentration and correlates with the observed coalescence behaviour of the contacting bubbles.},
  language  = {en}
}
@phdthesis{Wolff2010,
  author    = {Wolff, Markus},
  title     = {Geovisual methods and techniques for the development of three-dimensional tactical intelligence assessments},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-50446},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {This thesis presents methods, techniques and tools for developing three-dimensional representations of tactical intelligence assessments. Techniques from GIScience are combined with crime mapping methods. The range of methods applied in this study provides spatio-temporal GIS analysis as well as 3D geovisualisation and GIS programming. The work presents methods to enhance digital three-dimensional city models with application specific thematic information. This information facilitates further geovisual analysis, for instance, estimations of urban risks exposure. Specific methods and workflows are developed to facilitate the integration of spatio-temporal crime scene analysis results into 3D tactical intelligence assessments. Analysis comprises hotspot identification with kernel-density-estimation techniques (KDE), LISA-based verification of KDE hotspots as well as geospatial hotspot area characterisation and repeat victimisation analysis. To visualise the findings of such extensive geospatial analysis, three-dimensional geovirtual environments are created. Workflows are developed to integrate analysis results into these environments and to combine them with additional geospatial data. The resulting 3D visualisations allow for an efficient communication of complex findings of geospatial crime scene analysis.},
  language  = {en}
}
@phdthesis{Wolff2011,
  author    = {Wolff, Christian Michael},
  title     = {East African monsoon variability since the last glacial},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-58079},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The impact of global warming on human water resources is attracting increasing attention. No other region in this world is so strongly affected by changes in water supply than the tropics. Especially in Africa, the availability and access to water is more crucial to existence (basic livelihoods and economic growth) than anywhere else on Earth. In East Africa, rainfall is mainly influenced by the migration of the Inter-Tropical Convergence Zone (ITCZ) and by the El Ni{\~n}o Southern Oscillation (ENSO) with more rain and floods during El Ni{\~n}o and severe droughts during La Ni{\~n}a. The forecasting of East African rainfall in a warming world requires a better understanding of the response of ENSO-driven variability to mean climate. Unfortunately, existing meteorological data sets are too short or incomplete to establish a precise evaluation of future climate. From Lake Challa near Mount Kilimanjaro, we report records from a laminated lake sediment core spanning the last 25,000 years. Analyzing a monthly cleared sediment trap confirms the annual origin of the laminations and demonstrates that the varve-thicknesses are strongly linked to the duration and strength of the windy season. Given the modern control of seasonal ITCZ location on wind and rain in this region and the inverse relation between the two, thicker varves represent windier and thus drier years. El Ni{\~n}o (La Ni{\~n}a) events are associated with wetter (drier) conditions in east Africa and decreased (increased) surface wind speeds. Based on this fact, the thickness of the varves can be used as a tool to reconstruct a) annual rainfall b) wind season strength, and c) ENSO variability. Within this thesis, I found evidence for centennialscale changes in ENSO-related rainfall variability during the last three millennia, abrupt changes in variability during the Medieval Climate Anomaly and the Little Ice Age, and an overall reduction in East African rainfall and its variability during the Last Glacial period. Climate model simulations support forward extrapolation from these lake-sediment data, indicating that a future Indian Ocean warming will enhance East Africa's hydrological cycle and its interannual variability in rainfall. Furthermore, I compared geochemical analyses from the sediment trap samples with a broad range of limnological, meteorological, and geological parameters to characterize the impact of sedimentation processes from the in-situ rocks to the deposited sediments. As a result an excellent calibration for existing μXRF data from Lake Challa over the entire 25,000 year long profile was provided. The climate development during the last 25,000 years as reconstructed from the Lake Challa sediments is in good agreement with other studies and highlights the complex interactions between long-term orbital forcing, atmosphere, ocean and land surface conditions. My findings help to understand how abrupt climate changes occur and how these changes correlate with climate changes elsewhere on Earth.},
  language  = {en}
}
@phdthesis{Wolff2020,
  author    = {Wolff, Christian Michael},
  title     = {Identification and reduction of losses in perovskite solar cells},
  doi       = {10.25932/publishup-47930},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-479301},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 158},
  year      = {2020},
  abstract  = {Perovskite solar cells have become one of the most studied systems in the quest for new, cheap and efficient solar cell materials. Within a decade device efficiencies have risen to >25\% in single-junction and >29\% in tandem devices on top of silicon. This rapid improvement was in many ways fortunate, as e. g. the energy levels of commonly used halide perovskites are compatible with already existing materials from other photovoltaic technologies such as dye-sensitized or organic solar cells. Despite this rapid success, fundamental working principles must be understood to allow concerted further improvements. This thesis focuses on a comprehensive understanding of recombination processes in functioning devices. First the impact the energy level alignment between the perovskite and the electron transport layer based on fullerenes is investigated. This controversial topic is comprehensively addressed and recombination is mitigated through reducing the energy difference between the perovskite conduction band minimum and the LUMO of the fullerene. Additionally, an insulating blocking layer is introduced, which is even more effective in reducing this recombination, without compromising carrier collection and thus efficiency. With the rapid efficiency development (certified efficiencies have broken through the 20\% ceiling) and thousands of researchers working on perovskite-based optoelectronic devices, reliable protocols on how to reach these efficiencies are lacking. Having established robust methods for >20\% devices, while keeping track of possible pitfalls, a detailed description of the fabrication of perovskite solar cells at the highest efficiency level (>20\%) is provided. The fabrication of low-temperature p-i-n structured devices is described, commenting on important factors such as practical experience, processing atmosphere \& temperature, material purity and solution age. Analogous to reliable fabrication methods, a method to identify recombination losses is needed to further improve efficiencies. Thus, absolute photoluminescence is identified as a direct way to quantify the Quasi-Fermi level splitting of the perovskite absorber (1.21eV) and interfacial recombination losses the transport layers impose, reducing the latter to ~1.1eV. Implementing very thin interlayers at both the p- and n-interface (PFN-P2 and LiF, respectively), these losses are suppressed, enabling a VOC of up to 1.17eV. Optimizing the device dimensions and the bandgap, 20\% devices with 1cm2 active area are demonstrated. Another important consideration is the solar cells' stability if subjected to field-relevant stressors during operation. In particular these are heat, light, bias or a combination thereof. Perovskite layers - especially those incorporating organic cations - have been shown to degrade if subjected to these stressors. Keeping in mind that several interlayers have been successfully used to mitigate recombination losses, a family of perfluorinated self-assembled monolayers (X-PFCn, where X denotes I/Br and n = 7-12) are introduced as interlayers at the n-interface. Indeed, they reduce interfacial recombination losses enabling device efficiencies up to 21.3\%. Even more importantly they improve the stability of the devices. The solar cells with IPFC10 are stable over 3000h stored in the ambient and withstand a harsh 250h of MPP at 85◦C without appreciable efficiency losses. To advance further and improve device efficiencies, a sound understanding of the photophysics of a device is imperative. Many experimental observations in recent years have however drawn an inconclusive picture, often suffering from technical of physical impediments, disguising e. g. capacitive discharge as recombination dynamics. To circumvent these obstacles, fully operational, highly efficient perovskites solar cells are investigated by a combination of multiple optical and optoelectronic probes, allowing to draw a conclusive picture of the recombination dynamics in operation. Supported by drift-diffusion simulations, the device recombination dynamics can be fully described by a combination of first-, second- and third-order recombination and JV curves as well as luminescence efficiencies over multiple illumination intensities are well described within the model. On this basis steady state carrier densities, effective recombination constants, densities-of-states and effective masses are calculated, putting the devices at the brink of the radiative regime. Moreover, a comprehensive review of recombination in state-of-the-art devices is given, highlighting the importance of interfaces in nonradiative recombination. Different strategies to assess these are discussed, before emphasizing successful strategies to reduce interfacial recombination and pointing towards the necessary steps to further improve device efficiency and stability. Overall, the main findings represent an advancement in understanding loss mechanisms in highly efficient solar cells. Different reliable optoelectronic techniques are used and interfacial losses are found to be of grave importance for both efficiency and stability. Addressing the interfaces, several interlayers are introduced, which mitigate recombination losses and degradation.},
  language  = {en}
}
@phdthesis{Wolf2019,
  author    = {Wolf, Mathias Johannes},
  title     = {The role of partial melting on trace element and isotope systematics of granitic melts},
  doi       = {10.25932/publishup-42370},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423702},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 129},
  year      = {2019},
  abstract  = {Partial melting is a first order process for the chemical differentiation of the crust (Vielzeuf et al., 1990). Redistribution of chemical elements during melt generation crucially influences the composition of the lower and upper crust and provides a mechanism to concentrate and transport chemical elements that may also be of economic interest. Understanding of the diverse processes and their controlling factors is therefore not only of scientific interest but also of high economic importance to cover the demand for rare metals. The redistribution of major and trace elements during partial melting represents a central step for the understanding how granite-bound mineralization develops (Hedenquist and Lowenstern, 1994). The partial melt generation and mobilization of ore elements (e.g. Sn, W, Nb, Ta) into the melt depends on the composition of the sedimentary source and melting conditions. Distinct source rocks have different compositions reflecting their deposition and alteration histories. This specific chemical "memory" results in different mineral assemblages and melting reactions for different protolith compositions during prograde metamorphism (Brown and Fyfe, 1970; Thompson, 1982; Vielzeuf and Holloway, 1988). These factors do not only exert an important influence on the distribution of chemical elements during melt generation, they also influence the volume of melt that is produced, extraction of the melt from its source, and its ascent through the crust (Le Breton and Thompson, 1988). On a larger scale, protolith distribution and chemical alteration (weathering), prograde metamorphism with partial melting, melt extraction, and granite emplacement are ultimately depending on a (plate-)tectonic control (Romer and Kroner, 2016). Comprehension of the individual stages and their interaction is crucial in understanding how granite-related mineralization forms, thereby allowing estimation of the mineralization potential of certain areas. Partial melting also influences the isotope systematics of melt and restite. Radiogenic and stable isotopes of magmatic rocks are commonly used to trace back the source of intrusions or to quantify mixing of magmas from different sources with distinct isotopic signatures (DePaolo and Wasserburg, 1979; Lesher, 1990; Chappell, 1996). These applications are based on the fundamental requirement that the isotopic signature in the melt reflects that of the bulk source from which it is derived. Different minerals in a protolith may have isotopic compositions of radiogenic isotopes that deviate from their whole rock signature (Ayres and Harris, 1997; Knesel and Davidson, 2002). In particular, old minerals with a distinct parent-to-daughter (P/D) ratio are expected to have a specific radiogenic isotope signature. As the partial melting reaction only involves selective phases in a protolith, the isotopic signature of the melt reflects that of the minerals involved in the melting reaction and, therefore, should be different from the bulk source signature. Similar considerations hold true for stable isotopes.},
  language  = {en}
}
@phdthesis{Wolf2021,
  author    = {Wolf, Johannes},
  title     = {Analysis and visualization of transport infrastructure based on large-scale geospatial mobile mapping data},
  doi       = {10.25932/publishup-53612},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-536129},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 121},
  year      = {2021},
  abstract  = {3D point clouds are a universal and discrete digital representation of three-dimensional objects and environments. For geospatial applications, 3D point clouds have become a fundamental type of raw data acquired and generated using various methods and techniques. In particular, 3D point clouds serve as raw data for creating digital twins of the built environment. This thesis concentrates on the research and development of concepts, methods, and techniques for preprocessing, semantically enriching, analyzing, and visualizing 3D point clouds for applications around transport infrastructure. It introduces a collection of preprocessing techniques that aim to harmonize raw 3D point cloud data, such as point density reduction and scan profile detection. Metrics such as, e.g., local density, verticality, and planarity are calculated for later use. One of the key contributions tackles the problem of analyzing and deriving semantic information in 3D point clouds. Three different approaches are investigated: a geometric analysis, a machine learning approach operating on synthetically generated 2D images, and a machine learning approach operating on 3D point clouds without intermediate representation. In the first application case, 2D image classification is applied and evaluated for mobile mapping data focusing on road networks to derive road marking vector data. The second application case investigates how 3D point clouds can be merged with ground-penetrating radar data for a combined visualization and to automatically identify atypical areas in the data. For example, the approach detects pavement regions with developing potholes. The third application case explores the combination of a 3D environment based on 3D point clouds with panoramic imagery to improve visual representation and the detection of 3D objects such as traffic signs. The presented methods were implemented and tested based on software frameworks for 3D point clouds and 3D visualization. In particular, modules for metric computation, classification procedures, and visualization techniques were integrated into a modular pipeline-based C++ research framework for geospatial data processing, extended by Python machine learning scripts. All visualization and analysis techniques scale to large real-world datasets such as road networks of entire cities or railroad networks. The thesis shows that some use cases allow taking advantage of established image vision methods to analyze images rendered from mobile mapping data efficiently. The two presented semantic classification methods working directly on 3D point clouds are use case independent and show similar overall accuracy when compared to each other. While the geometry-based method requires less computation time, the machine learning-based method supports arbitrary semantic classes but requires training the network with ground truth data. Both methods can be used in combination to gradually build this ground truth with manual corrections via a respective annotation tool. This thesis contributes results for IT system engineering of applications, systems, and services that require spatial digital twins of transport infrastructure such as road networks and railroad networks based on 3D point clouds as raw data. It demonstrates the feasibility of fully automated data flows that map captured 3D point clouds to semantically classified models. This provides a key component for seamlessly integrated spatial digital twins in IT solutions that require up-to-date, object-based, and semantically enriched information about the built environment.},
  language  = {en}
}
@phdthesis{Wojcik2024,
  author    = {Wojcik, Laurie Anne Myriam},
  title     = {Beyond a single diversity facet: implications for the links between biodiversity, environmental changes and ecosystem functioning},
  doi       = {10.25932/publishup-64692},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-646925},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 189},
  year      = {2024},
  abstract  = {Human activities modify nature worldwide via changes in the environment, biodiversity and the functioning of ecosystems, which in turn disrupt ecosystem services and feed back negatively on humans. A pressing challenge is thus to limit our impact on nature, and this requires detailed understanding of the interconnections between the environment, biodiversity and ecosystem functioning. These three components of ecosystems each include multiple dimensions, which interact with each other in different ways, but we lack a comprehensive picture of their interconnections and underlying mechanisms. Notably, diversity is often viewed as a single facet, namely species diversity, while many more facets exist at different levels of biological organisation (e.g. genetic, phenotypic, functional, multitrophic diversity), and multiple diversity facets together constitute the raw material for adaptation to environmental changes and shape ecosystem functioning. Consequently, investigating the multidimensionality of ecosystems, and in particular the links between multifaceted diversity, environmental changes and ecosystem functions, is crucial for ecological research, management and conservation. This thesis aims to explore several aspects of this question theoretically. I investigate three broad topics in this thesis. First, I focus on how food webs with varying levels of functional diversity across three trophic levels buffer environmental changes, such as a sudden addition of nutrients or long-term changes (e.g. warming or eutrophication). I observed that functional diversity generally enhanced ecological stability (i.e. the buffering capacity of the food web) by increasing trophic coupling. More precisely, two aspects of ecological stability (resistance and resilience) increased even though a third aspect (the inverse of the time required for the system to reach its post-perturbation state) decreased with increasing functional diversity. Second, I explore how several diversity facets served as a raw material for different sources of adaptation and how these sources affected multiple ecosystem functions across two trophic levels. Considering several sources of adaptation enabled the interplay between ecological and evolutionary processes, which affected trophic coupling and thereby ecosystem functioning. Third, I reflect further on the multifaceted nature of diversity by developing an index K able to quantify the facet of functional diversity, which is itself multifaceted. K can provide a comprehensive picture of functional diversity and is a rather good predictor of ecosystem functioning. Finally I synthesise the interdependent mechanisms (complementarity and selection effects, trophic coupling and adaptation) underlying the relationships between multifaceted diversity, ecosystem functioning and the environment, and discuss the generalisation of my findings across ecosystems and further perspectives towards elaborating an operational biodiversity-ecosystem functioning framework for research and conservation.},
  language  = {en}
}
@phdthesis{Wohlgemuth2012,
  author    = {Wohlgemuth, Stephanie-Angelika},
  title     = {Functional nanostructured hydrothermal carbons for sustainable technologies : heteroatom doping and superheated vapor},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-60120},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {The underlying motivation for the work carried out for this thesis was the growing need for more sustainable technologies. The aim was to synthesize a "palette" of functional nanomaterials using the established technique of hydrothermal carbonization (HTC). The incredible diversity of HTC was demonstrated together with small but steady advances in how HTC can be manipulated to tailor material properties for specific applications. Two main strategies were used to modify the materials obtained by HTC of glucose, a model precursor representing biomass. The first approach was the introduction of heteroatoms, or "doping" of the carbon framework. Sulfur was for the first time introduced as a dopant in hydrothermal carbon. The synthesis of sulfur and sulfur/nitrogen doped microspheres was presented whereby it was shown that the binding state of sulfur could be influenced by varying the type of sulfur source. Pyrolysis may additionally be used to tune the heteroatom binding states which move to more stable motifs with increasing pyrolysis temperature. Importantly, the presence of aromatic binding states in the as synthesized hydrothermal carbon allows for higher heteroatom retention levels after pyrolysis and hence more efficient use of dopant sources. In this regard, HTC may be considered as an "intermediate" step in the formation of conductive heteroatom doped carbon. To assess the novel hydrothermal carbons in terms of their potential for electrochemical applications, materials with defined nano-architectures and high surface areas were synthesized via templated, as well as template-free routes. Sulfur and/or nitrogen doped carbon hollow spheres (CHS) were synthesized using a polystyrene hard templating approach and doped carbon aerogels (CA) were synthesized using either the albumin directed or borax-mediated hydrothermal carbonization of glucose. Electrochemical testing showed that S/N dual doped CHS and aerogels derived via the albumin approach exhibited superior catalytic performance compared to solely nitrogen or sulfur doped counterparts in the oxygen reduction reaction (ORR) relevant to fuel cells. Using the borax mediated aerogel formation, nitrogen content and surface area could be tuned and a carbon aerogel was engineered to maximize electrochemical performance. The obtained sample exhibited drastically improved current densities compared to a platinum catalyst (but lower onset potential), as well as excellent long term stability. In the second approach HTC was carried out at elevated temperatures (550 °C) and pressure (50 bar), corresponding to the superheated vapor regime (htHTC). It was demonstrated that the carbon materials obtained via htHTC are distinct from those obtained via ltHTC and subsequent pyrolysis at 550 °C. No difference in htHTC-derived material properties could be observed between pentoses and hexoses. The material obtained from a polysaccharide exhibited a slightly lower degree of carbonization but was otherwise similar to the monosaccharide derived samples. It was shown that in addition to thermally induced carbonization at 550 °C, the SHV environment exhibits a catalytic effect on the carbonization process. The resulting materials are chemically inert (i.e. they contain a negligible amount of reactive functional groups) and possess low surface area and electronic conductivity which distinguishes them from carbon obtained from pyrolysis. Compared to the materials presented in the previous chapters on chemical modifications of hydrothermal carbon, this makes them ill-suited candidates for electronic applications like lithium ion batteries or electrocatalysts. However, htHTC derived materials could be interesting for applications that require chemical inertness but do not require specific electronic properties. The final section of this thesis therefore revisited the latex hard templating approach to synthesize carbon hollow spheres using htHTC. However, by using htHTC it was possible to carry out template removal in situ because the second heating step at 550 °C was above the polystyrene latex decomposition temperature. Preliminary tests showed that the CHS could be dispersed in an aqueous polystyrene latex without monomer penetrating into the hollow sphere voids. This leaves the stagnant air inside the CHS intact which in turn is promising for their application in heat and sound insulating coatings. Overall the work carried out in this thesis represents a noteworthy development in demonstrating the great potential of sustainable carbon materials.},
  language  = {en}
}
@phdthesis{Wittenberg2016,
  author    = {Wittenberg, Eva},
  title     = {With Light Verb Constructions from Syntax to Concepts},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  isbn      = {978-3-86956-329-9},
  issn      = {2190-4545},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-82361},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ii, 139},
  year      = {2016},
  abstract  = {This dissertation uses a common grammatical phenomenon, light verb constructions (LVCs) in English and German, to investigate how syntax-semantics mapping defaults influence the relationships between language processing, representation and conceptualization. LVCs are analyzed as a phenomenon of mismatch in the argument structure. The processing implication of this mismatch are experimentally investigated, using ERPs and a dual task. Data from these experiments point to an increase in working memory. Representational questions are investigated using structural priming. Data from this study suggest that while the syntax of LVCs is not different from other structures', the semantics and mapping are represented differently. This hypothesis is tested with a new categorization paradigm, which reveals that the conceptual structure that LVC evoke differ in interesting, and predictable, ways from non-mismatching structures'.},
  language  = {en}
}
@phdthesis{Wittenbecher2017,
  author    = {Wittenbecher, Clemens},
  title     = {Linking whole-grain bread, coffee, and red meat to the risk of type 2 diabetes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404592},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XII, 194, ii},
  year      = {2017},
  abstract  = {Background: Consumption of whole-grain, coffee, and red meat were consistently related to the risk of developing type 2 diabetes in prospective cohort studies, but potentially underlying biological mechanisms are not well understood. Metabolomics profiles were shown to be sensitive to these dietary exposures, and at the same time to be informative with respect to the risk of type 2 diabetes. Moreover, graphical network-models were demonstrated to reflect the biological processes underlying high-dimensional metabolomics profiles. Aim: The aim of this study was to infer hypotheses on the biological mechanisms that link consumption of whole-grain bread, coffee, and red meat, respectively, to the risk of developing type 2 diabetes. More specifically, it was aimed to consider network models of amino acid and lipid profiles as potential mediators of these risk-relations. Study population: Analyses were conducted in the prospective EPIC-Potsdam cohort (n = 27,548), applying a nested case-cohort design (n = 2731, including 692 incident diabetes cases). Habitual diet was assessed with validated semiquantitative food-frequency questionnaires. Concentrations of 126 metabolites (acylcarnitines, phosphatidylcholines, sphingomyelins, amino acids) were determined in baseline-serum samples. Incident type 2 diabetes cases were assed and validated in an active follow-up procedure. The median follow-up time was 6.6 years. Analytical design: The methodological approach was conceptually based on counterfactual causal inference theory. Observations on the network-encoded conditional independence structure restricted the space of possible causal explanations of observed metabolomics-data patterns. Given basic directionality assumptions (diet affects metabolism; metabolism affects future diabetes incidence), adjustment for a subset of direct neighbours was sufficient to consistently estimate network-independent direct effects. Further model-specification, however, was limited due to missing directionality information on the links between metabolites. Therefore, a multi-model approach was applied to infer the bounds of possible direct effects. All metabolite-exposure links and metabolite-outcome links, respectively, were classified into one of three categories: direct effect, ambiguous (some models indicated an effect others not), and no-effect. Cross-sectional and longitudinal relations were evaluated in multivariable-adjusted linear regression and Cox proportional hazard regression models, respectively. Models were comprehensively adjusted for age, sex, body mass index, prevalence of hypertension, dietary and lifestyle factors, and medication. Results: Consumption of whole-grain bread was related to lower levels of several lipid metabolites with saturated and monounsaturated fatty acids. Coffee was related to lower aromatic and branched-chain amino acids, and had potential effects on the fatty acid profile within lipid classes. Red meat was linked to lower glycine levels and was related to higher circulating concentrations of branched-chain amino acids. In addition, potential marked effects of red meat consumption on the fatty acid composition within the investigated lipid classes were identified. Moreover, potential beneficial and adverse direct effects of metabolites on type 2 diabetes risk were detected. Aromatic amino acids and lipid metabolites with even-chain saturated (C14-C18) and with specific polyunsaturated fatty acids had adverse effects on type 2 diabetes risk. Glycine, glutamine, and lipid metabolites with monounsaturated fatty acids and with other species of polyunsaturated fatty acids were classified as having direct beneficial effects on type 2 diabetes risk. Potential mediators of the diet-diabetes links were identified by graphically overlaying this information in network models. Mediation analyses revealed that effects on lipid metabolites could potentially explain about one fourth of the whole-grain bread effect on type 2 diabetes risk; and that effects of coffee and red meat consumption on amino acid and lipid profiles could potentially explain about two thirds of the altered type 2 diabetes risk linked to these dietary exposures. Conclusion: An algorithm was developed that is capable to integrate single external variables (continuous exposures, survival time) and high-dimensional metabolomics-data in a joint graphical model. Application to the EPIC-Potsdam cohort study revealed that the observed conditional independence patterns were consistent with the a priori mediation hypothesis: Early effects on lipid and amino acid metabolism had the potential to explain large parts of the link between three of the most widely discussed diabetes-related dietary exposures and the risk of developing type 2 diabetes.},
  language  = {en}
}
@phdthesis{Wittek2023,
  author    = {Wittek, Laura},
  title     = {Comparison of metabolic cages - analysis of refinement measures on the welfare and metabolic parameters of laboratory mice},
  doi       = {10.25932/publishup-61120},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-611208},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IV, 160},
  year      = {2023},
  abstract  = {Housing in metabolic cages can induce a pronounced stress response. Metabolic cage systems imply housing mice on metal wire mesh for the collection of urine and feces in addition to monitoring food and water intake. Moreover, mice are single-housed, and no nesting, bedding, or enrichment material is provided, which is often argued to have a not negligible impact on animal welfare due to cold stress. We therefore attempted to reduce stress during metabolic cage housing for mice by comparing an innovative metabolic cage (IMC) with a commercially available metabolic cage from Tecniplast GmbH (TMC) and a control cage. Substantial refinement measures were incorporated into the IMC cage design. In the frame of a multifactorial approach for severity assessment, parameters such as body weight, body composition, food intake, cage and body surface temperature (thermal imaging), mRNA expression of uncoupling protein 1 (Ucp1) in brown adipose tissue (BAT), fur score, and fecal corticosterone metabolites (CMs) were included. Female and male C57BL/6J mice were single-housed for 24 h in either conventional Macrolon cages (control), IMC, or TMC for two sessions. Body weight decreased less in the IMC (females—1st restraint: 6.94\%; 2nd restraint: 6.89\%; males—1st restraint: 8.08\%; 2nd restraint: 5.82\%) compared to the TMC (females—1st restraint: 13.2\%; 2nd restraint: 15.0\%; males—1st restraint: 13.1\%; 2nd restraint: 14.9\%) and the IMC possessed a higher cage temperature (females—1st restraint: 23.7°C; 2nd restraint: 23.5 °C; males—1st restraint: 23.3 °C; 2nd restraint: 23.5 °C) compared with the TMC (females—1st restraint: 22.4 °C; 2nd restraint: 22.5 °C; males—1st restraint: 22.6 °C; 2nd restraint: 22.4 °C). The concentration of fecal corticosterone metabolites in the TMC (females—1st restraint: 1376 ng/g dry weight (DW); 2nd restraint: 2098 ng/g DW; males—1st restraint: 1030 ng/g DW; 2nd restraint: 1163 ng/g DW) was higher compared to control cage housing (females—1st restraint: 640 ng/g DW; 2nd restraint: 941 ng/g DW; males—1st restraint: 504 ng/g DW; 2nd restraint: 537 ng/g DW). Our results show the stress potential induced by metabolic cage restraint that is markedly influenced by the lower housing temperature. The IMC represents a first attempt to target cold stress reduction during metabolic cage application thereby producing more animal welfare friendly data.},
  language  = {en}
}
@phdthesis{Wittbrodt2022,
  author    = {Wittbrodt, Linda},
  title     = {Minimum wage effects in Germany and Europe - four essays},
  doi       = {10.25932/publishup-55697},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-556977},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 184},
  year      = {2022},
  abstract  = {Am 1. Januar 2015 wurde in Deutschland ein allgemeiner gesetzlicher Mindestlohn in H{\"o}he von 8,50 € brutto pro Stunde eingef{\"u}hrt. Diese Dissertation widmet sich den Auswirkungen der Mindestlohneinf{\"u}hrung in Deutschland sowie Lohnuntergrenzen im Europ{\"a}ischen Kontext und tr{\"a}gt damit zur nationalen und internationalen Forschung bei. Das zweite Kapitel dieser Arbeit fasst die in bisherigen Studien herausgearbeiteten kurzfristigen Effekte der Mindestlohnreform in einem {\"U}berblick zusammen. Es zeigt sich, dass die Mindestlohneinf{\"u}hrung einen deutlich positiven Effekt auf die L{\"o}hne am unteren Ende der Verteilung hatte. Allerdings wies kurz nach der Reform noch ein nicht unerheblicher Anteil der Besch{\"a}ftigungsverh{\"a}ltnisse L{\"o}hne unter 8,50 € auf. Weiterhin deutet die Evidenz auf geringe negative Besch{\"a}ftigungseffekte hin, welche durch eine Reduktion von Minijobs getrieben ist. Entgegen der Erwartungen konnten jedoch in der kurzen Frist keine Effekte auf Armut und allgemeine Ungleichheit gefunden werden. Dies h{\"a}ngt insbesondere mit der Tatsache zusammen, dass Arbeitsstunden reduziert wurden und sich die Stundenlohnerh{\"o}hung daher nicht auf die Monatsl{\"o}hne niederschlug. Das dritte Kapitel geht der Frage nach, ob die im Vorfeld prognostizierten Arbeitsplatzverluste im Zuge der Reform kurzfristig eingetreten sind und welche Art der Besch{\"a}ftigung davon gegebenenfalls st{\"a}rker betroffen war. Zur empirischen Identifikation der Effekte wird in diesem (sowie im vierten Kapitel) ein regionaler Differenzen-von-Differenzen-Ansatz verwendet, mit dem die Auswirkungen auf regul{\"a}re Besch{\"a}ftigung (Teil- und Vollzeit) sowie Minijobs gesch{\"a}tzt werden. Unsere Ergebnisse deuten darauf hin, dass der Mindestlohn die Gesamtbesch{\"a}ftigung leicht reduziert hat, was im Wesentlichen auf einen R{\"u}ckgang von Minijobs zur{\"u}ckzuf{\"u}hren ist. Das vierte Kapitel schließt methodisch an das vorige an. Seine Motivation ergibt sich aus der Beobachtung, dass Frauen unter den Niedriglohnempf{\"a}nger:innen h{\"a}ufig {\"u}berrepr{\"a}sentiert sind. Die prim{\"a}re Forschungsfrage in diesem Kapitel ist daher, ob der Mindestlohn zu einer Verringerung der geschlechterspezifischen Lohnl{\"u}cke gef{\"u}hrt hat. Dazu identifizieren wir die Effekte auf die Lohnl{\"u}cke am 10. und 25. Perzentil sowie beim Mittelwert der zugrundeliegenden geschlechtsspezifischen Lohnverteilungen. Unsere Ergebnisse zeigen, dass - verglichen mit Regionen mit niedriger Eingriffstiefe - die geschlechtsspezifische Lohnl{\"u}cke am 10. Perzentil f{\"u}r mindestlohnberechtigte Besch{\"a}ftigte in Regionen mit hoher Eingriffstiefe um 4,6 Prozentpunkte gesunken ist. Wir sch{\"a}tzen, dass dies eine Reduktion um 32\\% im Vergleich zu 2014 bedeutet. Am 25. Perzentil und am Mittelwert sind die Auswirkungen geringer und nicht gleichermaßen robust. Das f{\"u}nfte Kapitel beh{\"a}lt den geschlechterspezifischen Fokus auf die Mindestlohneffekte bei. Im Vergleich zum Rest der Dissertation weitet es jedoch den Blick auf andere L{\"a}nder der Europ{\"a}ischen Union. Gem{\"a}ß der f{\"u}r das vorangegangene Kapitel dargelegten {\"U}berlegungen, k{\"o}nnten Frauen potenziell besonders von einem Mindestlohn profitieren. Dies k{\"o}nnte jedoch auch bedeuten, dass sie dadurch auch {\"o}fter von Arbeitsplatzverlusten oder Arbeitszeitverk{\"u}rzungen betroffen sind. Dieses Kapitel res{\"u}miert daher einerseits vorhandene Evidenz aus EU-Staaten, die sich auf den Zusammenhang zwischen Lohnuntergrenzen und der geschlechtsspezifischen Lohnl{\"u}cke bezieht. Dar{\"u}ber hinaus enth{\"a}lt es eine systematische Zusammenfassung von Studien, die den Einfluss von Mindestl{\"o}hnen auf Besch{\"a}ftigungsverluste oder Arbeitszeitver{\"a}nderungen untersuchen, von denen insbesondere Frauen betroffen sind. Es zeigen sich Hinweise, dass h{\"o}here Lohnuntergrenzen mit einer geringeren geschlechtsspezifischen Lohnl{\"u}cke verbunden sind. Hinsichtlich der Besch{\"a}ftigung scheinen Frauen nicht per se gr{\"o}ßere Besch{\"a}ftigungsverluste zu erleiden als M{\"a}nner. Allerdings zeigen Studien, dass sich der Mindestlohn hier besonders auf Teilzeitbesch{\"a}ftigte auswirkt. Es ist daher nicht auszuschließen, dass der negative Zusammenhang zwischen dem Mindestlohn und dem geschlechtsspezifischen Lohngef{\"a}lle mit den Arbeitsplatzverlusten dieser schlechter bezahlten, oft weiblichen Teilzeitbesch{\"a}ftigten zusammenh{\"a}ngt. Diese spezifische Form der Arbeit sollte daher im Zusammenhang mit dem Mindestlohn besondere Beachtung finden.},
  language  = {en}
}
@phdthesis{Witt2018,
  author    = {Witt, Tanja Ivonne},
  title     = {Camera Monitoring at volcanoes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-421073},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 140},
  year      = {2018},
  abstract  = {Basaltic fissure eruptions, such as on Hawai'i or on Iceland, are thought to be driven by the lateral propagation of feeder dikes and graben subsidence. Associated solid earth processes, such as deformation and structural development, are well studied by means of geophysical and geodetic technologies. The eruptions themselves, lava fountaining and venting dynamics, in turn, have been much less investigated due to hazardous access, local dimension, fast processes, and resulting poor data availability. This thesis provides a detailed quantitative understanding of the shape and dynamics of lava fountains and the morphological changes at their respective eruption sites. For this purpose, I apply image processing techniques, including drones and fixed installed cameras, to the sequence of frames of video records from two well-known fissure eruptions in Hawai'i and Iceland. This way I extract the dimensions of multiple lava fountains, visible in all frames. By putting these results together and considering the acquisition times of the frames I quantify the variations in height, width and eruption velocity of the lava fountains. Then I analyse these time-series in both time and frequency domains and investigate the similarities and correlations between adjacent lava fountains. Following this procedure, I am able to link the dynamics of the individual lava fountains to physical parameters of the magma transport in the feeder dyke of the fountains. The first case study in this thesis focuses on the March 2011 Pu'u'O'o eruption, Hawai'i, where a continuous pulsating behaviour at all eight lava fountains has been observed. The lava fountains, even those from different parts of the fissure that are closely connected, show a similar frequency content and eruption behaviour. The regular pattern in the heights of lava fountain suggests a controlling process within the magma feeder system like a hydraulic connection in the underlying dyke, affecting or even controlling the pulsating behaviour. The second case study addresses the 2014-2015 Holuhraun fissure eruption, Iceland. In this case, the feeder dyke is highlighted by the surface expressions of graben-like structures and fault systems. At the eruption site, the activity decreases from a continuous line of fire of ~60 vents to a limited number of lava fountains. This can be explained by preferred upwards magma movements through vertical structures of the pre-eruptive morphology. Seismic tremors during the eruption reveal vent opening at the surface and/or pressure changes in the feeder dyke. The evolving topography of the cinder cones during the eruption interacts with the lava fountain behaviour. Local variations in the lava fountain height and width are controlled by the conduit diameter, the depth of the lava pond and the shape of the crater. Modelling of the fountain heights shows that long-term eruption behaviour is controlled mainly by pressure changes in the feeder dyke. This research consists of six chapters with four papers, including two first author and two co-author papers. It establishes a new method to analyse lava fountain dynamics by video monitoring. The comparison with the seismicity, geomorphologic and structural expressions of fissure eruptions shows a complex relationship between focussed flow through dykes, the morphology of the cinder cones, and the lava fountain dynamics at the vents of a fissure eruption.},
  language  = {en}
}
@phdthesis{Wist2011,
  author    = {Wist, Dominic},
  title     = {Attacking complexity in logic synthesis of asynchronous circuits},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59706},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Most of the microelectronic circuits fabricated today are synchronous, i.e. they are driven by one or several clock signals. Synchronous circuit design faces several fundamental challenges such as high-speed clock distribution, integration of multiple cores operating at different clock rates, reduction of power consumption and dealing with voltage, temperature, manufacturing and runtime variations. Asynchronous or clockless design plays a key role in alleviating these challenges, however the design and test of asynchronous circuits is much more difficult in comparison to their synchronous counterparts. A driving force for a widespread use of asynchronous technology is the availability of mature EDA (Electronic Design Automation) tools which provide an entire automated design flow starting from an HDL (Hardware Description Language) specification yielding the final circuit layout. Even though there was much progress in developing such EDA tools for asynchronous circuit design during the last two decades, the maturity level as well as the acceptance of them is still not comparable with tools for synchronous circuit design. In particular, logic synthesis (which implies the application of Boolean minimisation techniques) for the entire system's control path can significantly improve the efficiency of the resulting asynchronous implementation, e.g. in terms of chip area and performance. However, logic synthesis, in particular for asynchronous circuits, suffers from complexity problems. Signal Transitions Graphs (STGs) are labelled Petri nets which are a widely used to specify the interface behaviour of speed independent (SI) circuits - a robust subclass of asynchronous circuits. STG decomposition is a promising approach to tackle complexity problems like state space explosion in logic synthesis of SI circuits. The (structural) decomposition of STGs is guided by a partition of the output signals and generates a usually much smaller component STG for each partition member, i.e. a component STG with a much smaller state space than the initial specification. However, decomposition can result in component STGs that in isolation have so-called irreducible CSC conflicts (i.e. these components are not SI synthesisable anymore) even if the specification has none of them. A new approach is presented to avoid such conflicts by introducing internal communication between the components. So far, STG decompositions are guided by the finest output partitions, i.e. one output per component. However, this might not yield optimal circuit implementations. Efficient heuristics are presented to determine coarser partitions leading to improved circuits in terms of chip area. For the new algorithms correctness proofs are given and their implementations are incorporated into the decomposition tool DESIJ. The presented techniques are successfully applied to some benchmarks - including 'real-life' specifications arising in the context of control resynthesis - which delivered promising results.},
  language  = {en}
}
@phdthesis{Wischnewski2011,
  author    = {Wischnewski, Juliane},
  title     = {Reconstructing climate variability on the Tibetan Plateau : comparing aquatic and terrestrial signals},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52453},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Spatial and temporal temperature and moisture patterns across the Tibetan Plateau are very complex. The onset and magnitude of the Holocene climate optimum in the Asian monsoon realm, in particular, is a subject of considerable debate as this time period is often used as an analogue for recent global warming. In the light of contradictory inferences regarding past climate and environmental change on the Tibetan Plateau, I have attempted to explain mismatches in the timing and magnitude of change. Therefore, I analysed the temporal variation of fossil pollen and diatom spectra and the geochemical record from palaeo-ecological records covering different time scales (late Quaternary and the last 200 years) from two core regions in the NE and SE Tibetan Plateau. For interpretation purposes I combined my data with other available palaeo-ecological data to set up corresponding aquatic and terrestrial proxy data sets of two lake pairs and two sets of sites. I focused on the direct comparison of proxies representing lacustrine response to climate signals (e.g., diatoms, ostracods, geochemical record) and proxies representing changes in the terrestrial environment (i.e., terrestrial pollen), in order to asses whether the lake and its catchments respond at similar times and magnitudes to environmental changes. Therefore, I introduced the established numerical technique procrustes rotation as a new approach in palaeoecology to quantitatively compare raw data of any two sedimentary records of interest in order to assess their degree of concordance. Focusing on the late Quaternary, sediment cores from two lakes (Kuhai Lake 35.3°N; 99.2°E; 4150 m asl; and Koucha Lake 34.0°N; 97.2°E; 4540 m asl) on the semi-arid northeastern Tibetan Plateau were analysed to identify post-glacial vegetation and environmental changes, and to investigate the responses of lake ecosystems to such changes. Based on the pollen record, five major vegetation and climate changes could be identified: (1) A shift from alpine desert to alpine steppe indicates a change from cold, dry conditions to warmer and more moist conditions at 14.8 cal. ka BP, (2) alpine steppe with tundra elements points to conditions of higher effective moisture and a stepwise warming climate at 13.6 cal. ka BP, (3) the appearance of high-alpine meadow vegetation indicates a further change towards increased moisture, but with colder temperatures, at 7.0 cal. ka BP, (4) the reoccurrence of alpine steppe with desert elements suggests a return to a significantly colder and drier phase at 6.3 cal. ka BP, and (5) the establishment of alpine steppe-meadow vegetation indicates a change back to relatively moist conditions at 2.2 cal. ka BP. To place the reconstructed climate inferences from the NE Tibetan Plateau into the context of Holocene moisture evolution across the Tibetan Plateau, I applied a five-scale moisture index and average link clustering to all available continuous pollen and non-pollen palaeoclimate records from the Tibetan Plateau, in an attempt to detect coherent regional and temporal patterns of moisture evolution on the Plateau. However, no common temporal or spatial pattern of moisture evolution during the Holocene could be detected, which can be assigned to the complex responses of different proxies to environmental changes in an already very heterogeneous mountain landscape, where minor differences in elevation can result in marked variations in microenvironments. Focusing on the past 200 years, I analysed the sedimentary records (LC6 Lake 29.5°N, 94.3°E, 4132 m asl; and Wuxu Lake 29.9°N, 101.1°E, 3705 m asl) from the southeastern Tibetan Plateau. I found that despite presumed significant temperature increases over that period, pollen and diatom records from the SE Tibetan Plateau reveal only very subtle changes throughout their profiles. The compositional species turnover investigated over the last 200 years appears relatively low in comparison to the species reorganisations during the Holocene. The results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem. Forest clearances and reforestation have not caused forest decline in our study area, but a conversion of natural forests to semi-natural secondary forests. The results from the numerical proxy comparison of the two sets of two pairs of Tibetan lakes indicate that the use of different proxies and the work with palaeo-ecological records from different lake types can cause deviant stories of inferred change. Irrespective of the timescale (Holocene or last 200 years) or region (SE or NE Tibetan Plateau) analysed, the agreement in terms of the direction, timing, and magnitude of change between the corresponding terrestrial data sets is generally better than the match between the corresponding lacustrine data sets, suggesting that lacustrine proxies may partly be influenced by in-lake or local catchment processes whereas the terrestrial proxy reflects a more regional climatic signal. The current disaccord on coherent temporal and spatial climate patterns on the Tibetan Plateau can partly be ascribed to the complexity of proxy response and lake systems on the Tibetan Plateau. Therefore, a multi-proxy, multi-site approach is important in order to gain a reliable climate interpretation for the complex mountain landscape of the Tibetan Plateau.},
  language  = {en}
}
@phdthesis{WindirschWoiwode2024,
  author    = {Windirsch-Woiwode, Torben},
  title     = {Permafrost carbon stabilisation by recreating a herbivore-driven ecosystem},
  doi       = {10.25932/publishup-62424},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-624240},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 104, A-57},
  year      = {2024},
  abstract  = {With Arctic ground as a huge and temperature-sensitive carbon reservoir, maintaining low ground temperatures and frozen conditions to prevent further carbon emissions that contrib-ute to global climate warming is a key element in humankind's fight to maintain habitable con-ditions on earth. Former studies showed that during the late Pleistocene, Arctic ground condi-tions were generally colder and more stable as the result of an ecosystem dominated by large herbivorous mammals and vast extents of graminoid vegetation - the mammoth steppe. Characterised by high plant productivity (grassland) and low ground insulation due to animal-caused compression and removal of snow, this ecosystem enabled deep permafrost aggrad-ation. Now, with tundra and shrub vegetation common in the terrestrial Arctic, these effects are not in place anymore. However, it appears to be possible to recreate this ecosystem local-ly by artificially increasing animal numbers, and hence keep Arctic ground cold to reduce or-ganic matter decomposition and carbon release into the atmosphere. By measuring thaw depth, total organic carbon and total nitrogen content, stable carbon iso-tope ratio, radiocarbon age, n-alkane and alcohol characteristics and assessing dominant vegetation types along grazing intensity transects in two contrasting Arctic areas, it was found that recreating conditions locally, similar to the mammoth steppe, seems to be possible. For permafrost-affected soil, it was shown that intensive grazing in direct comparison to non-grazed areas reduces active layer depth and leads to higher TOC contents in the active layer soil. For soil only frozen on top in winter, an increase of TOC with grazing intensity could not be found, most likely because of confounding factors such as vertical water and carbon movement, which is not possible with an impermeable layer in permafrost. In both areas, high animal activity led to a vegetation transformation towards species-poor graminoid-dominated landscapes with less shrubs. Lipid biomarker analysis revealed that, even though the available organic material is different between the study areas, in both permafrost-affected and sea-sonally frozen soils the organic material in sites affected by high animal activity was less de-composed than under less intensive grazing pressure. In conclusion, high animal activity af-fects decomposition processes in Arctic soils and the ground thermal regime, visible from reduced active layer depth in permafrost areas. Therefore, grazing management might be utilised to locally stabilise permafrost and reduce Arctic carbon emissions in the future, but is likely not scalable to the entire permafrost region.},
  language  = {en}
}
@phdthesis{Winck2011,
  author    = {Winck, Flavia Vischi},
  title     = {Nuclear proteomics and transcription factor profiling in Chlamydomonas reinhardtii},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-53909},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The transcriptional regulation of the cellular mechanisms involves many different components and different levels of control which together contribute to fine tune the response of cells to different environmental stimuli. In some responses, diverse signaling pathways can be controlled simultaneously. One of the most important cellular processes that seem to possess multiple levels of regulation is photosynthesis. A model organism for studying photosynthesis-related processes is the unicellular green algae Chlamydomonas reinhardtii, due to advantages related to culturing, genetic manipulation and availability of genome sequence. In the present study, we were interested in understanding the regulatory mechanisms underlying photosynthesis-related processes. To achieve this goal different molecular approaches were followed. In order to indentify protein transcriptional regulators we optimized a method for isolation of nuclei and performed nuclear proteome analysis using shotgun proteomics. This analysis permitted us to improve the genome annotation previously published and to discover conserved and enriched protein motifs among the nuclear proteins. In another approach, a quantitative RT-PCR platform was established for the analysis of gene expression of predicted transcription factor (TF) and other transcriptional regulator (TR) coding genes by transcript profiling. The gene expression profiles for more than one hundred genes were monitored in time series experiments under conditions of changes in light intensity (200 µE m-2 s-1 to 700 µE m-2 s-1), and changes in concentration of carbon dioxide (5\% CO2 to 0.04\% CO2). The results indicate that many TF and TR genes are regulated in both environmental conditions and groups of co-regulated genes were found. Our findings also suggest that some genes can be common intermediates of light and carbon responsive regulatory pathways. These approaches together gave us new insights about the regulation of photosynthesis and revealed new candidate regulatory genes, helping to decipher the gene regulatory networks in Chlamydomonas. Further experimental studies are necessary to clarify the function of the candidate regulatory genes and to elucidate how cells coordinately regulate the assimilation of carbon and light responses.},
  language  = {en}
}
@phdthesis{Willig2019,
  author    = {Willig, Lisa},
  title     = {Ultrafast magneto-optical studies of remagnetisation dynamics in transition metals},
  doi       = {10.25932/publishup-44194},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441942},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIV, 113, XVII},
  year      = {2019},
  abstract  = {Ultrafast magnetisation dynamics have been investigated intensely for two decades. The recovery process after demagnetisation, however, was rarely studied experimentally and discussed in detail. The focus of this work lies on the investigation of the magnetisation on long timescales after laser excitation. It combines two ultrafast time resolved methods to study the relaxation of the magnetic and lattice system after excitation with a high fluence ultrashort laser pulse. The magnetic system is investigated by time resolved measurements of the magneto-optical Kerr effect. The experimental setup has been implemented in the scope of this work. The lattice dynamics were obtained with ultrafast X-ray diffraction. The combination of both techniques leads to a better understanding of the mechanisms involved in magnetisation recovery from a non-equilibrium condition. Three different groups of samples are investigated in this work: Thin Nickel layers capped with nonmagnetic materials, a continuous sample of the ordered L10 phase of Iron Platinum and a sample consisting of Iron Platinum nanoparticles embedded in a carbon matrix. The study of the remagnetisation reveals a general trend for all of the samples: The remagnetisation process can be described by two time dependences. A first exponential recovery that slows down with an increasing amount of energy absorbed in the system until an approximately linear time dependence is observed. This is followed by a second exponential recovery. In case of low fluence excitation, the first recovery is faster than the second. With increasing fluence the first recovery is slowed down and can be described as a linear function. If the pump-induced temperature increase in the sample is sufficiently high, a phase transition to a paramagnetic state is observed. In the remagnetisation process, the transition into the ferromagnetic state is characterised by a distinct transition between the linear and exponential recovery. From the combination of the transient lattice temperature Tp(t) obtained from ultrafast X-ray measurements and magnetisation M(t) gained from magneto-optical measurements we construct the transient magnetisation versus temperature relations M(Tp). If the lattice temperature remains below the Curie temperature the remagnetisation curve M(Tp) is linear and stays below the M(T) curve in equilibrium in the continuous transition metal layers. When the sample is heated above phase transition, the remagnetisation converges towards the static temperature dependence. For the granular Iron Platinum sample the M(Tp) curves for different fluences coincide, i.e. the remagnetisation follows a similar path irrespective of the initial laser-induced temperature jump.},
  language  = {en}
}
@phdthesis{Willersinn2017,
  author    = {Willersinn, Jochen},
  title     = {Self-Assembly of double hydrophilic block copolymers},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-408578},
  school      = {Universit{\"a}t Potsdam},
  pages     = {119, clxxiv},
  year      = {2017},
  abstract  = {The motivation of this work was to investigate the self-assembly of a block copolymer species that attended little attraction before, double hydrophilic block copolymers (DHBCs). DHBCs consist of two linear hydrophilic polymer blocks. The self-assembly of DHBCs towards suprastructures such as particles and vesicles is determined via a strong difference in hydrophilicity between the corresponding blocks leading to a microphase separation due to immiscibility. The benefits of DHBCs and the corresponding particles and vesicles, such as biocompatibility, high permeability towards water and hydrophilic compounds as well as the large amount of possible functionalizations that can be addressed to the block copolymers make the application of DHBC based structures a viable choice in biomedicine. In order to assess a route towards self-assembled structures from DHBCs that display the potential to act as cargos for future applications, several block copolymers containing two hydrophilic polymer blocks were synthesized. Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone) (PEO-b-PVP) and Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone-co-N-vinylimidazole) (PEO-b-P(VP-co-VIm) block copolymers were synthesized via reversible deactivation radical polymerization (RDRP) techniques starting from a PEO-macro chain transfer agent. The block copolymers displayed a concentration dependent self-assembly behavior in water which was determined via dynamic light scattering (DLS). It was possible to observe spherical particles via laser scanning confocal microscopy (LSCM) and cryogenic scanning electron microscopy (cryo SEM) at highly concentrated solutions of PEO-b-PVP. Furthermore, a crosslinking strategy with (PEO-b-P(VP-co-VIm) was developed applying a diiodo derived crosslinker diethylene glycol bis(2-iodoethyl) ether to form quaternary amines at the VIm units. The formed crosslinked structures proved stability upon dilution and transfer into organic solvents. Moreover, self-assembly and crosslinking in DMF proved to be more advantageous and the crosslinked structures could be successfully transferred to aqueous solution. The afforded spherical submicron particles could be visualized via LSCM, cryo SEM and Cryo TEM. Double hydrophilic pullulan-b-poly(acrylamide) block copolymers were synthesized via copper catalyzed alkyne azide cycloaddition (CuAAC) starting from suitable pullulan alkyne and azide functionalized poly(N,N-dimethylacrylamide) (PDMA) and poly(N-ethylacrylamide) (PEA) homopolymers. The conjugation reaction was confirmed via SEC and 1H-NMR measurements. The self-assembly of the block copolymers was monitored with DLS and static light scattering (SLS) measurements indicating the presence of hollow spherical structures. Cryo SEM measurements could confirm the presence of vesicular structures for Pull-b-PEA block copolymers. Solutions of Pull-b-PDMA displayed particles in cryo SEM. Moreover, an end group functionalization of Pull-b-PDMA with Rhodamine B allowed assessing the structure via LSCM and hollow spherical structures were observed indicating the presence of vesicles, too. An exemplified pathway towards a DHBC based drug delivery vehicle was demonstrated with the block copolymer Pull-b-PVP. The block copolymer was synthesized via RAFT/MADIX techniques starting from a pullulan chain transfer agent. Pull-b-PVP displayed a concentration dependent self-assembly in water with an efficiency superior to the PEO-b-PVP system, which could be observed via DLS. Cryo SEM and LSCM microscopy displayed the presence of spherical structures. In order to apply a reversible crosslinking strategy on the synthesized block copolymer, the pullulan block was selectively oxidized to dialdehydes with NaIO4. The oxidation of the block copolymer was confirmed via SEC and 1H-NMR measurements. The self-assembled and oxidized structures were subsequently crosslinked with cystamine dihiydrochloride, a pH and redox responsive crosslinker resulting in crosslinked vesicles which were observed via cryo SEM. The vesicular structures of crosslinked Pull-b-PVP could be disassembled by acid treatment or the application of the redox agent tris(2-carboxyethyl)-phosphin-hydrochloride. The successful disassembly was monitored with DLS measurements. To conclude, self-assembled structures from DHBCs such as particles and vesicles display a strong potential to generate an impact on biomedicine and nanotechnologies. The variety of DHBC compositions and functionalities are very promising features for future applications.},
  language  = {en}
}
@phdthesis{Wilke2010,
  author    = {Wilke, Franziska Daniela Helena},
  title     = {Quantifying crystalline exhumation in the Himalaya},
  doi       = {10.25932/publishup-4119},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-43138},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IV, 99},
  year      = {2010},
  abstract  = {In 1915, Alfred Wegener published his hypotheses of plate tectonics that revolutionised the world for geologists. Since then, many scientists have studied the evolution of continents and especially the geologic structure of orogens: the most visible consequence of tectonic processes. Although the morphology and landscape evolution of mountain belts can be observed due to surface processes, the driving force and dynamics at lithosphere scale are less well understood despite the fact that rocks from deeper levels of orogenic belts are in places exposed at the surface. In this thesis, such formerly deeply-buried (ultra-) high-pressure rocks, in particular eclogite facies series, have been studied in order to reveal details about the formation and exhumation conditions and rates and thus provide insights into the geodynamics of the most spectacular orogenic belt in the world: the Himalaya. The specific area investigated was the Kaghan Valley in Pakistan (NW Himalaya). Following closure of the Tethyan Ocean by ca. 55-50 Ma, the northward subduction of the leading edge of India beneath the Eurasian Plate and subsequent collision initiated a long-lived process of intracrustal thrusting that continues today. The continental crust of India - granitic basement, Paleozoic and Mesozoic cover series and Permo-Triassic dykes, sills and lavas - has been buried partly to mantle depths. Today, these rocks crop out as eclogites, amphibolites and gneisses within the Higher Himalayan Crystalline between low-grade metamorphosed rocks (600-640°C/ ca. 5 kbar) of the Lesser Himalaya and Tethyan sediments. Beside tectonically driven exhumation mechanisms the channel flow model, that describes a denudation focused ductile extrusion of low viscosity material developed in the middle to lower crust beneath the Tibetan Plateau, has been postulated. To get insights into the lithospheric and crustal processes that have initiated and driven the exhumation of this (ultra-) high-pressure rocks, mineralogical, petrological and isotope-geochemical investigations have been performed. They provide insights into 1) the depths and temperatures to which these rocks were buried, 2) the pressures and temperatures the rocks have experienced during their exhumation, 3) the timing of these processes 4) and the velocity with which these rocks have been brought back to the surface. In detail, through microscopical studies, the identification of key minerals, microprobe analyses, standard geothermobarometry and modelling using an effective bulk rock composition it has been shown that published exhumation paths are incomplete. In particular, the eclogites of the northern Kaghan Valley were buried to depths of 140-100 km (36-30 kbar) at 790-640°C. Subsequently, cooling during decompression (exhumation) towards 40-35 km (17-10 kbar) and 630-580°C has been superseded by a phase of reheating to about 720-650°C at roughly the same depth before final exhumation has taken place. In the southern-most part of the study area, amphibolite facies assemblages with formation conditions similar to the deduced reheating phase indicate a juxtaposition of both areas after the eclogite facies stage and thus a stacking of Indian Plate units. Radiometric dating of zircon, titanite and rutile by U-Pb and amphibole and micas by Ar-Ar reveal peak pressure conditions at 47-48 Ma. With a maximum exhumation rate of 14 cm/a these rocks reached the crust-mantle boundary at 40-35 km within 1 Ma. Subsequent exhumation (46-41 Ma, 40-35 km) decelerated to ca. 1 mm/a at the base of the continental crust but rose again to about 2 mm/a in the period of 41-31 Ma, equivalent to 35-20 km. Apatite fission track (AFT) and (U-Th)/He ages from eclogites, amphibolites, micaschists and gneisses yielded moderate Oligocene to Miocene cooling rates of about 10°C/Ma in the high altitude northern parts of the Kaghan Valley using the mineral-pair method. AFT ages are of 24.5±3.8 to 15.6±2.1 Ma whereas apatite (U-Th)/He analyses yielded ages between 21.0±0.6 and 5.3±0.2 Ma. The southern-most part of the Valley is dominated by younger late Miocene to Pliocene apatite fission track ages of 7.6±2.1 and 4.0±0.5 Ma that support earlier tectonically and petrologically findings of a juxtaposition and stack of Indian Plate units. As this nappe is tectonically lowermost, a later distinct exhumation and uplift driven by thrusting along the Main Boundary Thrust is inferred. A multi-stage exhumation path is evident from petrological, isotope-geochemical and low temperature thermochronology investigations. Buoyancy driven exhumation caused an initial rapid exhumation: exhumation as fast as recent normal plate movements (ca. 10 cm/a). As the exhuming units reached the crust-mantle boundary the process slowed down due to changes in buoyancy. Most likely, this exhumation pause has initiated the reheating event that is petrologically evident (e.g. glaucophane rimmed by hornblende, ilmenite overgrowth of rutile). Late stage processes involved widespread thrusting and folding with accompanied regional greenschist facies metamorphism, whereby contemporaneous thrusting on the Batal Thrust (seen by some authors equivalent to the MCT) and back sliding of the Kohistan Arc along the inverse reactivated Main Mantle Thrust caused final exposure of these rocks. Similar circumstances have been seen at Tso Morari, Ladakh, India, 200 km further east where comparable rock assemblages occur. In conclusion, as exhumation was already done well before the initiation of the monsoonal system, climate dependent effects (erosion) appear negligible in comparison to far-field tectonic effects.},
  language  = {en}
}
@phdthesis{Wilhelm2007,
  author    = {Wilhelm, Susann},
  title     = {Climate induced impacts on lake functioning in summer},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-14599},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {Es gibt bereits viele Hinweise daf{\"u}r, dass Seen sehr sensibel auf die anthropogen verursachte Klimaerw{\"a}rmung reagiert haben. Bis jetzt haben sich die Studien der Klimafolgenforschung haupts{\"a}chlichst auf die Auswirkungen der Erw{\"a}rmung im Winter und Fr{\"u}hling konzentriert. {\"U}ber den Einfluss der Klimaerw{\"a}rmung auf Seen in den gem{\"a}ßigten Breiten im Sommer ist weniger bekannt. In der vorliegenden Doktorarbeit habe ich einige Faktoren, welche die Reaktion von Seen auf die Erw{\"a}rmung im Sommer vermutlich stark mitbestimmt haben, untersucht. Der Schwerpunkt lag dabei auf klimatisch induzierten Auswirkungen auf die thermische Charakteristik und die Ph{\"a}nologie und Abundanz des Planktons eines flachen und polymiktischen Sees (M{\"u}ggelsee, Berlin). Zuerst wurde der Einfluss der Klimaerw{\"a}rmung auf die Ph{\"a}nologie und Abundanz des Planktons in verschiedenen Jahreszeiten untersucht. Das schnellwachsende Phyto- und Zooplankton (Daphnia) im Fr{\"u}hjahr hat sich vorwiegend synchron vorverschoben, wohingegen Ver{\"a}nderungen des Sommerzooplanktons deutlich artspezifisch und nicht synchron waren. Die Ph{\"a}nologie oder Abundanz einiger Sommercopepoden hat sich entsprechend der individuellen thermischen Anforderungen innerhalb bestimmter Entwicklungsstufen, wie zum Beispiel der Emergenz von der Diapause im Fr{\"u}hling, ver{\"a}ndert. Die Studie unterstreicht, dass nicht nur der Grad der Erw{\"a}rmung, sondern auch dessen Zeitpunkt innerhalb des Jahres von großer {\"o}kologischer Bedeutung ist. Um die Auswirkungen des Klimawandels auf die thermischen Eigenschaften des Sees zu erforschen, habe ich die Langzeitentwicklung der t{\"a}glichen epilimnischen Temperaturextrema w{\"a}hrend des Sommers untersucht. Durch diese Studie wurde zum ersten Mal f{\"u}r Seen gezeigt, dass die t{\"a}glichen epilimnischen Minima (Nacht) st{\"a}rker angestiegen sind als die Maxima (Tag), wodurch sich der t{\"a}gliche epilimnische Temperaturbereich deutlich verringert hat. Diese Tag-Nacht-Asymmetrie in der epilimnischen Temperatur wurde durch eine erh{\"o}hte Emission von Langwellenstrahlung aus der Atmosph{\"a}re w{\"a}hrend der Nacht verursacht. Dies unterstreicht, dass nicht nur Erh{\"o}hungen der Lufttemperatur, sondern auch {\"A}nderungen anderer meteorologischer Variablen wie der Windgeschwindigkeit, der Luftfeuchte und der Bew{\"o}lkung eine wichtige Rolle bei der Bestimmung der Seetemperatur im Hinblick auf weitere Klimaver{\"a}nderungen spielen werden. Zudem wurde eine Kurzzeitanalyse zum Schichtungsverhalten des polymiktischen Sees durchgef{\"u}hrt, um die H{\"a}ufigkeit und Dauer von Schichtungsereignissen und deren Einfluss auf den gel{\"o}sten Sauerstoff, die gel{\"o}sten N{\"a}hrstoffe und das Phytoplankton zu untersuchen. Selbst w{\"a}hrend der l{\"a}ngsten Schichtungsereignisse (Hitzewellen 2003 und 2006) unterschieden sich die Auswirkungen auf den See von denen, welche in flachen dimiktischen Seen w{\"a}hrend der kontinuierlichen Sommerschichtung auftreten. Die hypolimnische Temperatur war h{\"o}her, was die Sauerstoffzehrung und die Akkumulation von gel{\"o}sten N{\"a}hrstoffen beg{\"u}nstigt hat. Die thermische Schichtung wird in Zukunft sehr wahrscheinlich zunehmen. Dies l{\"a}sst darauf schließen, dass polymiktische Seen sehr anf{\"a}llig gegen{\"u}ber {\"A}nderungen im Hinblick auf projizierte Klimaver{\"a}nderungen sein werden. Abschließend wurde eine Studie {\"u}ber Lang- und Kurzzeitver{\"a}nderungen in der Entwicklung der planktischen Larven der Muschel Dreissena polymorpha durchgef{\"u}hrt, um den Einfluss der Ver{\"a}nderungen im thermischen und trophischen Regime des Sees zu analysieren. Die Klimaerw{\"a}rmung und die Verringerung in der externen N{\"a}hrstofffracht haben die Abundanz der Larven stark beeinflusst indem sie jeweils auf bestimmte Entwicklungsphasen dieser Art w{\"a}hrend der warmen Jahreszeiten gewirkt haben. Der Anstieg in der Abundanz und der L{\"a}nge der Larven stand im Zusammenhang mit dem R{\"u}ckgang der N{\"a}hrstofffracht und der Ver{\"a}nderung der Phytoplanktonzusammensetzung. Die Hitzewellen in den Jahren 2003 und 2006 haben diesen positiven Effekt auf die Larvenabundanz jedoch durch ung{\"u}nstige Sauerstoffkonzentrationen w{\"a}hrend der sehr langen Schichtung aufgehoben. Die Klimaerw{\"a}rmung kann demzufolge entgegenwirkende Effekte in produktiven flachen Seen, in welchen die externe N{\"a}hrstofffracht reduziert wurde, ausl{\"o}sen. Aus diesen Ergebnissen schließe ich, dass nicht nur die Art des Klimawandels und damit der Zeitpunkt der Erw{\"a}rmung und das Auftreten von Extremen wie Hitzewellen, sondern auch standortspezifische Bedingungen wie Schichtungsverhalten und Trophiegrad entscheidende Faktoren sind, welche die Auswirkungen der Klimaerw{\"a}rmung auf interne Seeprozesse im Sommer bestimmen. Somit sollte sich die weiterf{\"u}hrende Klimafolgenforschung f{\"u}r Seen darauf konzentrieren, wie verschiedene Seetypen auf die komplexen Umweltver{\"a}nderungen im Sommer reagieren, damit ein umfassenderes Verst{\"a}ndnis {\"u}ber den Einfluss von anthropogen verursachten Ver{\"a}nderungen auf Seen der gem{\"a}ßigten Breiten erreicht wird.},
  language  = {en}
}
@phdthesis{Wilhelm2021,
  author    = {Wilhelm, Alina},
  title     = {Stochastic re-acceleration of particles in supernova remnants},
  doi       = {10.25932/publishup-51291},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512915},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IV, 124},
  year      = {2021},
  abstract  = {Supernova remnants (SNRs) are discussed as the most promising sources of galactic cosmic rays (CR). The diffusive shock acceleration (DSA) theory predicts particle spectra in a rough agreement with observations. Upon closer inspection, however, the photon spectra of observed SNRs indicate that the particle spectra produced at SNRs shocks deviate from the standard expectation. This work suggests a viable explanation for a softening of the particle spectra in SNRs. The basic idea is the re-acceleration of particles in the turbulent region immediately downstream of the shock. This thesis shows that at the re-acceleration of particles by the fast-mode waves in the downstream region can be efficient enough to impact particle spectra over several decades in energy. To demonstrate this, a generic SNR model is presented, where the evolution of particles is described by the reduced transport equation for CR. It is shown that the resulting particle and the corresponding synchrotron spectra are significantly softer compared to the standard case. Next, this work outlines RATPaC, a code developed to model particle acceleration and corresponding photon emissions in SNRs. RATPaC solves the particle transport equation in test-particle mode using hydrodynamic simulations of the SNR plasma flow. The background magnetic field can be either computed from the induction equation or follows analytic profiles. This work presents an extended version of RATPaC that accounts for stochastic re-acceleration by fast-mode waves that provide diffusion of particles in momentum space. This version is then applied to model the young historical SNR Tycho. According to radio observations, Tycho's SNR features the radio spectral index of approximately -0.65. In previous modeling approaches, this fact has been attributed to the strongly distinctive Alfv{\´e}nic drift, which is assumed to operate in the shock vicinity. In this work, the problems and inconsistencies of this scenario are discussed. Instead, stochastic re-acceleration of electrons in the immediate downstream region of Tycho's SNR is suggested as a cause for the soft radio spectrum. Furthermore, this work investigates two different scenarios for magnetic-field distributions inside Tycho's SNR. It is concluded that magnetic-field damping is needed to account for the observed filaments in the radio range. Two models are presented for Tycho's SNR, both of them feature strong hadronic contribution. Thus, a purely leptonic model is considered as very unlikely. Additionally, to the detailed modeling of Tycho's SNR, this dissertation presents a relatively simple one-zone model for the young SNR Cassiopeia A and an interpretation for the recently analyzed VERITAS and Fermi-LAT data. It shows that the γ-ray emission of Cassiopeia A cannot be explained without a hadronic contribution and that the remnant accelerates protons up to TeV energies. Thus, Cassiopeia A is found to be unlikely a PeVatron.},
  language  = {en}
}
@phdthesis{WijesinghaAhchige2022,
  author    = {Wijesingha Ahchige, Micha},
  title     = {Canalization of plant metabolism and yield},
  doi       = {10.25932/publishup-54884},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-548844},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 160},
  year      = {2022},
  abstract  = {Plant metabolism is the main process of converting assimilated carbon to different crucial compounds for plant growth and therefore crop yield, which makes it an important research topic. Although major advances in understanding genetic principles contributing to metabolism and yield have been made, little is known about the genetics responsible for trait variation or canalization although the concepts have been known for a long time. In light of a growing global population and progressing climate change, understanding canalization of metabolism and yield seems ever-more important to ensure food security. Our group has recently found canalization metabolite quantitative trait loci (cmQTL) for tomato fruit metabolism, showing that the concept of canalization applies on metabolism. In this work two approaches to investigate plant metabolic canalization and one approach to investigate yield canalization are presented. In the first project, primary and secondary metabolic data from Arabidopsis thaliana and Phaseolus vulgaris leaf material, obtained from plants grown under different conditions was used to calculate cross-environment coefficient of variations or fold-changes of metabolite levels per genotype and used as input for genome wide association studies. While primary metabolites have lower CV across conditions and show few and mostly weak associations to genomic regions, secondary metabolites have higher CV and show more, strong metabolite to genome associations. As candidate genes, both potential regulatory genes as well as metabolic genes, can be found, albeit most metabolic genes are rarely directly related to the target metabolites, suggesting a role for both potential regulatory mechanisms as well as metabolic network structure for canalization of metabolism. In the second project, candidate genes of the Solanum lycopersicum cmQTL mapping are selected and CRISPR/Cas9-mediated gene-edited tomato lines are created, to validate the genes role in canalization of metabolism. Obtained mutants appeared to either have strong aberrant developmental phenotypes or appear wild type-like. One phenotypically inconspicuous mutant of a pantothenate kinase, selected as candidate for malic acid canalization shows a significant increase of CV across different watering conditions. Another such mutant of a protein putatively involved in amino acid transport, selected as candidate for phenylalanine canalization shows a similar tendency to increased CV without statistical significance. This potential role of two genes involved in metabolism supports the hypothesis of structural relevance of metabolism for its own stability. In the third project, a mutant for a putative disulfide isomerase, important for thylakoid biogenesis, is characterized by a multi-omics approach. The mutant was characterized previously in a yield stability screening and showed a variegated leaf phenotype, ranging from green leaves with wild type levels of chlorophyll over differently patterned variegated to completely white leaves almost completely devoid of photosynthetic pigments. White mutant leaves show wild type transcript levels of photosystem assembly factors, with the exception of ELIP and DEG orthologs indicating a stagnation at an etioplast to chloroplast transition state. Green mutant leaves show an upregulation of these assembly factors, possibly acting as overcompensation for partially defective disulfide isomerase, which seems sufficient for proper chloroplast development as confirmed by a wild type-like proteome. Likely as a result of this phenotype, a general stress response, a shift to a sink-like tissue and abnormal thylakoid membranes, strongly alter the metabolic profile of white mutant leaves. As the severity and pattern of variegation varies from plant to plant and may be effected by external factors, the effect on yield instability, may be a cause of a decanalized ability to fully exploit the whole leaf surface area for photosynthetic activity.},
  language  = {en}
}
@phdthesis{Wierzba2017,
  author    = {Wierzba, Marta},
  title     = {Revisiting prosodic reconstruction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403152},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 224},
  year      = {2017},
  abstract  = {In this thesis, I develop a theoretical implementation of prosodic reconstruction and apply it to the empirical domain of German sentences in which part of a focus or contrastive topic is fronted. Prosodic reconstruction refers to the idea that sentences involving syntactic movement show prosodic parallels with corresponding simpler structures without movement. I propose to model this recurrent observation by ordering syntax-prosody mapping before copy deletion. In order to account for the partial fronting data, the idea is extended to the mapping between prosody and information structure. This assumption helps to explain why object-initial sentences containing a broad focus or broad contrastive topic show similar prosodic and interpretative restrictions as sentences with canonical word order. The empirical adequacy of the model is tested against a set of gradient acceptability judgments.},
  language  = {en}
}
@phdthesis{Wieland2015,
  author    = {Wieland, Volkmar},
  title     = {Particle-in-cell simulations of perpendicular supernova shock fronts},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74532},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 89},
  year      = {2015},
  abstract  = {The origin of cosmic rays was the subject of several studies for over a century. The investigations done within this dissertation are one small step to shed some more light on this mystery. Locating the sources of cosmic rays is not trivial due to the interstellar magnetic field. However, the Hillas criterion allows us to arrive at the conclusion that supernova remnants are our main suspect for the origin of galactic cosmic rays. The mechanism by which they are accelerating particles is found within the field of shock physics as diffusive shock acceleration. To allow particles to enter this process also known as Fermi acceleration pre-acceleration processes like shock surfing acceleration and shock drift acceleration are necessary. Investigating the processes happening in the plasma shocks of supernova remnants is possible by utilising a simplified model which can be simulated on a computer using Particle-in-Cell simulations. We developed a new and clean setup to simulate the formation of a double shock, i.e., consisting of a forward and a reverse shock and a contact discontinuity, by the collision of two counter-streaming plasmas, in which a magnetic field can be woven into. In a previous work, we investigated the processes at unmagnetised and at magnetised parallel shocks, whereas in the current work, we move our investigation on to magnetised perpendicular shocks. Due to a much stronger confinement of the particles to the collision region the perpendicular shock develops much faster than the parallel shock. On the other hand, this leads to much weaker turbulence. We are able to find indications for shock surfing acceleration and shock drift acceleration happening at the two shocks leading to populations of pre-accelerated particles that are suitable as a seed population to be injected into further diffusive shock acceleration to be accelerated to even higher energies. We observe the development of filamentary structures in the shock ramp of the forward shock, but not at the reverse shock. This leads to the conclusion that the development of such structures in the shock ramp of quasi-perpendicular collisionless shocks might not necessarily be determined by the existence of a critical sonic Mach number but by a critical shock speed. The results of the investigations done within this dissertation might be useful for further studies of oblique shocks and for studies using hybrid or magnetohydrodynamic simulations. Together with more sophisticated observational methods, these studies will help to bring us closer to an answer as to how particles can be accelerated in supernova remnants and eventually become cosmic rays that can be detected on Earth.},
  language  = {en}
}
@phdthesis{Widdrat2014,
  author    = {Widdrat, Marc},
  title     = {Formation and alteration of magnetite nanoparticles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-72239},
  school      = {Universit{\"a}t Potsdam},
  pages     = {113},
  year      = {2014},
  abstract  = {Magnetite is an iron oxide, which is ubiquitous in rocks and is usually deposited as small nanoparticulate matter among other rock material. It differs from most other iron oxides because it contains divalent and trivalent iron. Consequently, it has a special crystal structure and unique magnetic properties. These properties are used for paleoclimatic reconstructions where naturally occurring magnetite helps understanding former geological ages. Further on, magnetic properties are used in bio- and nanotechnological applications -synthetic magnetite serves as a contrast agent in MRI, is exploited in biosensing, hyperthermia or is used in storage media. Magnetic properties are strongly size-dependent and achieving size control under preferably mild synthesis conditions is of interest in order to obtain particles with required properties. By using a custom-made setup, it was possible to synthesize stable single domain magnetite nanoparticles with the co-precipitation method. Furthermore, it was shown that magnetite formation is temperature-dependent, resulting in larger particles at higher temperatures. However, mechanistic approaches about the details are incomplete. Formation of magnetite from solution was shown to occur from nanoparticulate matter rather than solvated ions. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Synthesis of magnetite nanoparticles at different temperatures was performed and the Arrhenius plot was used determine an activation energy for crystal growth of 28.4 kJ mol-1, which led to the conclusion that nanoparticle diffusion is the rate-determining step. Furthermore, a study of the alteration of magnetite particles of different sizes as a function of their storage conditions is presented. The magnetic properties depend not only on particle size but also depend on the structure of the oxide, because magnetite oxidizes to maghemite under environmental conditions. The dynamics of this process have not been well described. Smaller nanoparticles are shown to oxidize more rapidly than larger ones and the lower the storage temperature, the lower the measured oxidation. In addition, the magnetic properties of the altered particles are not decreased dramatically, thus suggesting that this alteration will not impact the use of such nanoparticles as medical carriers. Finally, the effect of biological additives on magnetite formation was investigated. Magnetotactic bacteria¬¬ are able to synthesize and align magnetite nanoparticles of well-defined size and morphology due to the involvement of special proteins with specific binding properties. Based on this model of morphology control, phage display experiments were performed to determine peptide sequences that preferably bind to (111)-magnetite faces. The aim was to control the shape of magnetite nanoparticles during the formation. Magnetotactic bacteria are also able to control the intracellular redox potential with proteins called magnetochromes. MamP is such a protein and its oxidizing nature was studied in vitro via biomimetic magnetite formation experiments based on ferrous ions. Magnetite and further trivalent oxides were found. This work helps understanding basic mechanisms of magnetite formation and gives insight into non-classical crystal growth. In addition, it is shown that alteration of magnetite nanoparticles is mainly based on oxidation to maghemite and does not significantly influence the magnetic properties. Finally, biomimetic experiments help understanding the role of MamP within the bacteria and furthermore, a first step was performed to achieve morphology control in magnetite formation via co-precipitation.},
  language  = {en}
}
@phdthesis{Wick2023,
  author    = {Wick, Kristin},
  title     = {Motor and cognitive performance in kindergarten children},
  doi       = {10.25932/publishup-59253},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-592532},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 128},
  year      = {2023},
  abstract  = {Childhood compared to adolescence and adulthood is characterized by high neuroplasticity represented by accelerated cognitive maturation and rapid cognitive developmental trajectories. Natural growth, biological maturation and permanent interaction with the physical and social environment fosters motor and cognitive development in children. Of note, the promotion of physical activity, physical fitness, and motor skill learning at an early age is mandatory first, as these aspects are essential for a healthy development and an efficient functioning in everyday life across the life span and second, physical activity behaviors and lifestyle habits tend to track from childhood into adulthood. The main objective of the present thesis was to optimize and deepen the knowledge of motor and cognitive performance in young children and to develop an effective and age-appropriate exercise program feasible for the implementation in kindergarten and preschool settings. A systematic review with meta-analysis was conducted to examine the effectiveness of fundamental movement skill and exercise interventions in healthy preschool-aged children. Further, the relation between measures of physical fitness (i.e., static balance, muscle strength, power, and coordination) and attention as one domain of cognitive performance in preschool-aged children was analyzed. Subsequently, effects of a strength-dominated kindergarten-based exercise program on physical fitness components (i.e., static balance, muscle strength, power, and coordination) and cognitive performance (i.e., attention) compared to a usual kindergarten curriculum was examined. The systematic review included trials focusing on healthy young children in kindergarten or preschool settings that applied fundamental movement skill-enhancing intervention programs of at least 4 weeks and further reported standardized motor skill outcome measures for the intervention and the control group. Children aged 4-6 years from three kindergartens participated in the cross-sectional and the longitudinal study. Product-orientated measures were conducted for the assessment of muscle strength (i.e., handgrip strength), muscle power (i.e., standing long jump), balance (i.e., timed single-leg stand), coordination (hopping on right/left leg), and attentional span (i.e., "Konzentrations-Handlungsverfahren f{\"u}r Vorschulkinder" [concentration-action procedure for preschoolers]). With regards to the scientific literature, exercise and fundamental movement skill interventions are an effective method to promote overall proficiency in motor skills (i.e., object control and locomotor skills) in preschool children particularly when conducted by external experts with a duration of 4 weeks to 5 months. Moreover, significant medium associations were found between the composite score of physical fitness and attention as well as between coordination separately and attention in children aged 4-6 years. A 10-weeks strength-dominated exercise program implemented in kindergarten and preschool settings by educated and trained kindergarten teachers revealed significant improvements for the standing long jump test and the Konzentrations-Handlungsverfahren of intervention children compared to children of the control group. The findings of the present thesis imply that fundamental movement skill and exercise interventions improve motor skills (i.e., locomotor and object control skills). Nonetheless, more high-quality research is needed. Additionally, physical fitness, particularly high performance in complex fitness components (i.e., coordination measured with the hopping on one leg test), tend to predict attention in preschool age. Furthermore, an exercise program including strength-dominated exercises, fundamental movement skills and elements of gymnastics has a beneficial effect on jumping performance with a concomitant trend toward improvements in attentional capacity in healthy preschool children. Finally, it is recommended to start early with the integration of muscular fitness (i.e., muscle strength, muscle power, muscular endurance) next to coordination, agility, balance, and fundamental movement skill exercises into regular physical activity curriculums in kindergarten settings.},
  language  = {en}
}
@phdthesis{Wichura2011,
  author    = {Wichura, Henry},
  title     = {Topographic evolution of the East African Plateau : a combined study on lava-flow modeling and paleo-topography},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52363},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The East African Plateau provides a spectacular example of geodynamic plateau uplift, active continental rifting, and associated climatic forcing. It is an integral part of the East African Rift System and has an average elevation of approximately 1,000 m. Its location coincides with a negative Bouguer gravity anomaly with a semi-circular shape, closely related to a mantle plume, which influences the Cenozoic crustal development since its impingement in Eocene-Oligocene time. The uplift of the East African Plateau, preceding volcanism, and rifting formed an important orographic barrier and tectonically controlled environment, which is profoundly influenced by climate driven processes. Its location within the equatorial realm supports recently proposed hypotheses, that topographic changes in this region must be considered as the dominant forcing factor influencing atmospheric circulation patterns and rainfall distribution. The uplift of this region has therefore often been associated with fundamental climatic and environmental changes in East Africa and adjacent regions. While the far-reaching influence of the plateau uplift is widely accepted, the timing and the magnitude of the uplift are ambiguous and are still subject to ongoing discussion. This dilemma stems from the lack of datable, geomorphically meaningful reference horizons that could record surface uplift. In order to quantify the amount of plateau uplift and to find evidence for the existence of significant relief along the East African Plateau prior to rifting, I analyzed and modeled one of the longest terrestrial lava flows; the 300-km-long Yatta phonolite flow in Kenya. This lava flow is 13.5 Ma old and originated in the region that now corresponds to the eastern rift shoulders. The phonolitic flow utilized an old riverbed that once drained the eastern flank of the plateau. Due to differential erosion this lava flow now forms a positive relief above the parallel-flowing Athi River, which is mimicking the course of the paleo-river. My approach is a lava-flow modeling, based on an improved composition and temperature dependent method to parameterize the flow of an arbitrary lava in a rectangular-shaped channel. The essential growth pattern is described by a one-dimensional model, in which Newtonian rheological flow advance is governed by the development of viscosity and/or velocity in the internal parts of the lava-flow front. Comparing assessments of different magma compositions reveal that length-dominated, channelized lava flows are characterized by high effusion rates, rapid emplacement under approximately isothermal conditions, and laminar flow. By integrating the Yatta lava flow dimensions and the covered paleo-topography (slope angle) into the model, I was able to determine the pre-rift topography of the East African Plateau. The modeling results yield a pre-rift slope of at least 0.2°, suggesting that the lava flow must have originated at a minimum elevation of 1,400 m. Hence, high topography in the region of the present-day Kenya Rift must have existed by at least 13.5 Ma. This inferred mid-Miocene uplift coincides with the two-step expansion of grasslands, as well as important radiation and speciation events in tropical Africa. Accordingly, the combination of my results regarding the Yatta lava flow emplacement history, its location, and its morphologic character, validates it as a suitable "paleo-tiltmeter" and has thus to be considered as an important topographic and volcanic feature for the topographic evolution in East Africa.},
  language  = {en}
}
@phdthesis{Wichitsanguan2016,
  author    = {Wichitsa-nguan, Korakot},
  title     = {Modifications and extensions of the logistic regression and Cox model},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-90033},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 131},
  year      = {2016},
  abstract  = {In many statistical applications, the aim is to model the relationship between covariates and some outcomes. A choice of the appropriate model depends on the outcome and the research objectives, such as linear models for continuous outcomes, logistic models for binary outcomes and the Cox model for time-to-event data. In epidemiological, medical, biological, societal and economic studies, the logistic regression is widely used to describe the relationship between a response variable as binary outcome and explanatory variables as a set of covariates. However, epidemiologic cohort studies are quite expensive regarding data management since following up a large number of individuals takes long time. Therefore, the case-cohort design is applied to reduce cost and time for data collection. The case-cohort sampling collects a small random sample from the entire cohort, which is called subcohort. The advantage of this design is that the covariate and follow-up data are recorded only on the subcohort and all cases (all members of the cohort who develop the event of interest during the follow-up process). In this thesis, we investigate the estimation in the logistic model for case-cohort design. First, a model with a binary response and a binary covariate is considered. The maximum likelihood estimator (MLE) is described and its asymptotic properties are established. An estimator for the asymptotic variance of the estimator based on the maximum likelihood approach is proposed; this estimator differs slightly from the estimator introduced by Prentice (1986). Simulation results for several proportions of the subcohort show that the proposed estimator gives lower empirical bias and empirical variance than Prentice's estimator. Then the MLE in the logistic regression with discrete covariate under case-cohort design is studied. Here the approach of the binary covariate model is extended. Proving asymptotic normality of estimators, standard errors for the estimators can be derived. The simulation study demonstrates the estimation procedure of the logistic regression model with a one-dimensional discrete covariate. Simulation results for several proportions of the subcohort and different choices of the underlying parameters indicate that the estimator developed here performs reasonably well. Moreover, the comparison between theoretical values and simulation results of the asymptotic variance of estimator is presented. Clearly, the logistic regression is sufficient for the binary outcome refers to be available for all subjects and for a fixed time interval. Nevertheless, in practice, the observations in clinical trials are frequently collected for different time periods and subjects may drop out or relapse from other causes during follow-up. Hence, the logistic regression is not appropriate for incomplete follow-up data; for example, an individual drops out of the study before the end of data collection or an individual has not occurred the event of interest for the duration of the study. These observations are called censored observations. The survival analysis is necessary to solve these problems. Moreover, the time to the occurence of the event of interest is taken into account. The Cox model has been widely used in survival analysis, which can effectively handle the censored data. Cox (1972) proposed the model which is focused on the hazard function. The Cox model is assumed to be λ(t|x) = λ0(t) exp(β^Tx) where λ0(t) is an unspecified baseline hazard at time t and X is the vector of covariates, β is a p-dimensional vector of coefficient. In this thesis, the Cox model is considered under the view point of experimental design. The estimability of the parameter β0 in the Cox model, where β0 denotes the true value of β, and the choice of optimal covariates are investigated. We give new representations of the observed information matrix In(β) and extend results for the Cox model of Andersen and Gill (1982). In this way conditions for the estimability of β0 are formulated. Under some regularity conditions, ∑ is the inverse of the asymptotic variance matrix of the MPLE of β0 in the Cox model and then some properties of the asymptotic variance matrix of the MPLE are highlighted. Based on the results of asymptotic estimability, the calculation of local optimal covariates is considered and shown in examples. In a sensitivity analysis, the efficiency of given covariates is calculated. For neighborhoods of the exponential models, the efficiencies have then been found. It is appeared that for fixed parameters β0, the efficiencies do not change very much for different baseline hazard functions. Some proposals for applicable optimal covariates and a calculation procedure for finding optimal covariates are discussed. Furthermore, the extension of the Cox model where time-dependent coefficient are allowed, is investigated. In this situation, the maximum local partial likelihood estimator for estimating the coefficient function β(·) is described. Based on this estimator, we formulate a new test procedure for testing, whether a one-dimensional coefficient function β(·) has a prespecified parametric form, say β(·; ϑ). The score function derived from the local constant partial likelihood function at d distinct grid points is considered. It is shown that the distribution of the properly standardized quadratic form of this d-dimensional vector under the null hypothesis tends to a Chi-squared distribution. Moreover, the limit statement remains true when replacing the unknown ϑ0 by the MPLE in the hypothetical model and an asymptotic α-test is given by the quantiles or p-values of the limiting Chi-squared distribution. Finally, we propose a bootstrap version of this test. The bootstrap test is only defined for the special case of testing whether the coefficient function is constant. A simulation study illustrates the behavior of the bootstrap test under the null hypothesis and a special alternative. It gives quite good results for the chosen underlying model. References P. K. Andersen and R. D. Gill. Cox's regression model for counting processes: a large samplestudy. Ann. Statist., 10(4):1100{1120, 1982. D. R. Cox. Regression models and life-tables. J. Roy. Statist. Soc. Ser. B, 34:187{220, 1972. R. L. Prentice. A case-cohort design for epidemiologic cohort studies and disease prevention trials. Biometrika, 73(1):1{11, 1986.},
  language  = {en}
}
@phdthesis{Wetzel2021,
  author    = {Wetzel, Maria},
  title     = {Pore space alterations and their impact on hydraulic and mechanical rock properties quantified by numerical simulations},
  doi       = {10.25932/publishup-51206},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512064},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XI, 107},
  year      = {2021},
  abstract  = {Geochemical processes such as mineral dissolution and precipitation alter the microstructure of rocks, and thereby affect their hydraulic and mechanical behaviour. Quantifying these property changes and considering them in reservoir simulations is essential for a sustainable utilisation of the geological subsurface. Due to the lack of alternatives, analytical methods and empirical relations are currently applied to estimate evolving hydraulic and mechanical rock properties associated with chemical reactions. However, the predictive capabilities of analytical approaches remain limited, since they assume idealised microstructures, and thus are not able to reflect property evolution for dynamic processes. Hence, aim of the present thesis is to improve the prediction of permeability and stiffness changes resulting from pore space alterations of reservoir sandstones. A detailed representation of rock microstructure, including the morphology and connectivity of pores, is essential to accurately determine physical rock properties. For that purpose, three-dimensional pore-scale models of typical reservoir sandstones, obtained from highly resolved micro-computed tomography (micro-CT), are used to numerically calculate permeability and stiffness. In order to adequately depict characteristic distributions of secondary minerals, the virtual samples are systematically altered and resulting trends among the geometric, hydraulic, and mechanical rock properties are quantified. It is demonstrated that the geochemical reaction regime controls the location of mineral precipitation within the pore space, and thereby crucially affects the permeability evolution. This emphasises the requirement of determining distinctive porosity-permeability relationships by means of digital pore-scale models. By contrast, a substantial impact of spatial alterations patterns on the stiffness evolution of reservoir sandstones are only observed in case of certain microstructures, such as highly porous granular rocks or sandstones comprising framework-supporting cementations. In order to construct synthetic granular samples a process-based approach is proposed including grain deposition and diagenetic cementation. It is demonstrated that the generated samples reliably represent the microstructural complexity of natural sandstones. Thereby, general limitations of imaging techniques can be overcome and various realisations of granular rocks can be flexibly produced. These can be further altered by virtual experiments, offering a fast and cost-effective way to examine the impact of precipitation, dissolution or fracturing on various petrophysical correlations. The presented research work provides methodological principles to quantify trends in permeability and stiffness resulting from geochemical processes. The calculated physical property relations are directly linked to pore-scale alterations, and thus have a higher accuracy than commonly applied analytical approaches. This will considerably improve the predictive capabilities of reservoir models, and is further relevant to assess and reduce potential risks, such as productivity or injectivity losses as well as reservoir compaction or fault reactivation. Hence, the proposed method is of paramount importance for a wide range of natural and engineered subsurface applications, including geothermal energy systems, hydrocarbon reservoirs, CO2 and energy storage as well as hydrothermal deposit exploration.},
  language  = {en}
}
@phdthesis{Wettstein2015,
  author    = {Wettstein, Christoph},
  title     = {Cytochrome c-DNA and cytochrome c-enzyme interactions for the construction of analytical signal chains},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-78367},
  school      = {Universit{\"a}t Potsdam},
  pages     = {120},
  year      = {2015},
  abstract  = {Electron transfer (ET) reactions play a crucial role in the metabolic pathways of all organisms. In biotechnological approaches, the redox properties of the protein cytochrome c (cyt c), which acts as an electron shuttle in the respiratory chain, was utilized to engineer ET chains on electrode surfaces. With the help of the biopolymer DNA, the redox protein assembles into electro active multilayer (ML) systems, providing a biocompatible matrix for the entrapment of proteins. In this study the characteristics of the cyt c and DNA interaction were defined on the molecular level for the first time and the binding sites of DNA on cyt c were identified. Persistent cyt c/DNA complexes were formed in solution under the assembly conditions of ML architectures, i.e. pH 5.0 and low ionic strength. At pH 7.0, no agglomerates were formed, permitting the characterization of the NMR spectroscopy. Using transverse relaxation-optimized spectroscopy (TROSY)-heteronuclear single quantum coherence (HSQC) experiments, DNAs' binding sites on the protein were identified. In particular, negatively charged AA residues, which are known interaction sites in cyt c/protein binding were identified as the main contact points of cyt c and DNA. Moreover, the sophisticated task of arranging proteins on electrode surfaces to create functional ET chains was addressed. Therefore, two different enzyme types, the flavin dependent fructose dehydrogenase (FDH) and the pyrroloquinoline quinone dependent glucose dehydrogenase (PQQ-GDH), were tested as reaction partners of freely diffusing cyt c and cyt c immobilized on electrodes in mono- and MLs. The characterisation of the ET processes was performed by means of electrochemistry and the protein deposition was monitored by microgravimetric measurements. FDH and PQQ-GDH were found to be generally suitable for combination with the cyt c/DNA ML system, since both enzymes interact with cyt c in solution and in the immobilized state. The immobilization of FDH and cyt c was achieved with the enzyme on top of a cyt c monolayer electrode without the help of a polyelectrolyte. Combining FDH with the cyt c/DNA ML system did not succeed, yet. However, the basic conditions for this protein-protein interaction were defined. PQQ-GDH was successfully coupled with the ML system, demonstrating that that the cyt c/DNA ML system provides a suitable interface for enzymes and that the creation of signal chains, based on the idea of co-immobilized proteins is feasible. Future work may be directed to the investigation of cyt c/DNA interaction under the precise conditions of ML assembly. Therefore, solid state NMR or X-ray crystallography may be required. Based on the results of this study, the combination of FDH with the ML system should be addressed. Moreover, alternative types of enzymes may be tested as catalytic component of the ML assembly, aiming on the development of innovative biosensor applications.},
  language  = {en}
}
@phdthesis{Westbury2018,
  author    = {Westbury, Michael V.},
  title     = {Unraveling evolution through Next Generation Sequencing},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-409981},
  school      = {Universit{\"a}t Potsdam},
  pages     = {129},
  year      = {2018},
  abstract  = {The sequencing of the human genome in the early 2000s led to an increased interest in cheap and fast sequencing technologies. This interest culminated in the advent of next generation sequencing (NGS). A number of different NGS platforms have arisen since then all promising to do the same thing, i.e. produce large amounts of genetic information for relatively low costs compared to more traditional methods such as Sanger sequencing. The capabilities of NGS meant that researchers were no longer bound to species for which a lot of previous work had already been done (e.g. model organisms and humans) enabling a shift in research towards more novel and diverse species of interest. This capability has greatly benefitted many fields within the biological sciences, one of which being the field of evolutionary biology. Researchers have begun to move away from the study of laboratory model organisms to wild, natural populations and species which has greatly expanded our knowledge of evolution. NGS boasts a number of benefits over more traditional sequencing approaches. The main benefit comes from the capability to generate information for drastically more loci for a fraction of the cost. This is hugely beneficial to the study of wild animals as, even when large numbers of individuals are unobtainable, the amount of data produced still allows for accurate, reliable population and species level results from a small selection of individuals. The use of NGS to study species for which little to no previous research has been carried out on and the production of novel evolutionary information and reference datasets for the greater scientific community were the focuses of this thesis. Two studies in this thesis focused on producing novel mitochondrial genomes from shotgun sequencing data through iterative mapping, bypassing the need for a close relative to serve as a reference sequence. These mitochondrial genomes were then used to infer species level relationships through phylogenetic analyses. The first of these studies involved reconstructing a complete mitochondrial genome of the bat eared fox (Otocyon megalotis). Phylogenetic analyses of the mitochondrial genome confidently placed the bat eared fox as sister to the clade consisting of the raccoon dog and true foxes within the canidae family. The next study also involved reconstructing a mitochondrial genome but in this case from the extinct Macrauchenia of South America. As this study utilised ancient DNA, it involved a lot of parameter testing, quality controls and strict thresholds to obtain a near complete mitochondrial genome devoid of contamination known to plague ancient DNA studies. Phylogenetic analyses confidently placed Macrauchenia as sister to all living representatives of Perissodactyla with a divergence time of ~66 million years ago. The third and final study of this thesis involved de novo assemblies of both nuclear and mitochondrial genomes from brown and striped hyena and focussed on demographic, genetic diversity and population genomic analyses within the brown hyena. Previous studies of the brown hyena hinted at very low levels of genomic diversity and, perhaps due to this, were unable to find any notable population structure across its range. By incorporating a large number of genetic loci, in the form of complete nuclear genomes, population structure within the brown hyena was uncovered. On top of this, genomic diversity levels were compared to a number of other species. Results showed the brown hyena to have the lowest genomic diversity out of all species included in the study which was perhaps caused by a continuous and ongoing decline in effective population size that started about one million years ago and dramatically accelerated towards the end of the Pleistocene. The studies within this thesis show the power NGS sequencing has and its utility within evolutionary biology. The most notable capabilities outlined in this thesis involve the study of species for which no reference data is available and in the production of large amounts of data, providing evolutionary answers at the species and population level that data produced using more traditional techniques simply could not.},
  language  = {en}
}
@phdthesis{Werth2010,
  author    = {Werth, Susanna},
  title     = {Calibration of the global hydrological model WGHM with water mass variations from GRACE gravity data},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41738},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {Since the start-up of the GRACE (Gravity Recovery And Climate Experiment) mission in 2002 time dependent global maps of the Earth's gravity field are available to study geophysical and climatologically-driven mass redistributions on the Earth's surface. In particular, GRACE observations of total water storage changes (TWSV) provide a comprehensive data set for analysing the water cycle on large scales. Therefore they are invaluable for validation and calibration of large-scale hydrological models as the WaterGAP Global Hydrology Model (WGHM) which simulates the continental water cycle including its most important components, such as soil, snow, canopy, surface- and groundwater. Hitherto, WGHM exhibits significant differences to GRACE, especially for the seasonal amplitude of TWSV. The need for a validation of hydrological models is further highlighted by large differences between several global models, e.g. WGHM, the Global Land Data Assimilation System (GLDAS) and the Land Dynamics model (LaD). For this purpose, GRACE links geodetic and hydrological research aspects. This link demands the development of adequate data integration methods on both sides, forming the main objectives of this work. They include the derivation of accurate GRACE-based water storage changes, the development of strategies to integrate GRACE data into a global hydrological model as well as a calibration method, followed by the re-calibration of WGHM in order to analyse process and model responses. To achieve these aims, GRACE filter tools for the derivation of regionally averaged TWSV were evaluated for specific river basins. Here, a decorrelation filter using GRACE orbits for its design is most efficient among the tested methods. Consistency in data and equal spatial resolution between observed and simulated TWSV were realised by the inclusion of all most important hydrological processes and an equal filtering of both data sets. Appropriate calibration parameters were derived by a WGHM sensitivity analysis against TWSV. Finally, a multi-objective calibration framework was developed to constrain model predictions by both river discharge and GRACE TWSV, realised with a respective evolutionary method, the ε-Non-dominated-Sorting-Genetic-Algorithm-II (ε-NSGAII). Model calibration was done for the 28 largest river basins worldwide and for most of them improved simulation results were achieved with regard to both objectives. From the multi-objective approach more reliable and consistent simulations of TWSV within the continental water cycle were gained and possible model structure errors or mis-modelled processes for specific river basins detected. For tropical regions as such, the seasonal amplitude of water mass variations has increased. The findings lead to an improved understanding of hydrological processes and their representation in the global model. Finally, the robustness of the results is analysed with respect to GRACE and runoff measurement errors. As a main conclusion obtained from the results, not only soil water and snow storage but also groundwater and surface water storage have to be included in the comparison of the modelled and GRACE-derived total water budged data. Regarding model calibration, the regional varying distribution of parameter sensitivity suggests to tune only parameter of important processes within each region. Furthermore, observations of single storage components beside runoff are necessary to improve signal amplitudes and timing of simulated TWSV as well as to evaluate them with higher accuracy. The results of this work highlight the valuable nature of GRACE data when merged into large-scale hydrological modelling and depict methods to improve large-scale hydrological models.},
  language  = {en}
}
@phdthesis{Werhahn2023,
  author    = {Werhahn, Maria},
  title     = {Simulating galaxy evolution with cosmic rays: the multi-frequency view},
  doi       = {10.25932/publishup-57285},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-572851},
  school      = {Universit{\"a}t Potsdam},
  pages     = {5, 220},
  year      = {2023},
  abstract  = {Cosmic rays (CRs) constitute an important component of the interstellar medium (ISM) of galaxies and are thought to play an essential role in governing their evolution. In particular, they are able to impact the dynamics of a galaxy by driving galactic outflows or heating the ISM and thereby affecting the efficiency of star-formation. Hence, in order to understand galaxy formation and evolution, we need to accurately model this non-thermal constituent of the ISM. But except in our local environment within the Milky Way, we do not have the ability to measure CRs directly in other galaxies. However, there are many ways to indirectly observe CRs via the radiation they emit due to their interaction with magnetic and interstellar radiation fields as well as with the ISM. In this work, I develop a numerical framework to calculate the spectral distribution of CRs in simulations of isolated galaxies where a steady-state between injection and cooling is assumed. Furthermore, I calculate the non-thermal emission processes arising from the modelled CR proton and electron spectra ranging from radio wavelengths up to the very high-energy gamma-ray regime. I apply this code to a number of high-resolution magneto-hydrodynamical (MHD) simulations of isolated galaxies, where CRs are included. This allows me to study their CR spectra and compare them to observations of the CR proton and electron spectra by the Voyager-1 satellite and the AMS-02 instrument in order to reveal the origin of the measured spectral features. Furthermore, I provide detailed emission maps, luminosities and spectra of the non-thermal emission from our simulated galaxies that range from dwarfs to Milk-Way analogues to starburst galaxies at different evolutionary stages. I successfully reproduce the observed relations between the radio and gamma-ray luminosities with the far-infrared (FIR) emission of star-forming (SF) galaxies, respectively, where the latter is a good tracer of the star-formation rate. I find that highly SF galaxies are close to the limit where their CR population would lose all of their energy due to the emission of radiation, whereas CRs tend to escape low SF galaxies more quickly. On top of that, I investigate the properties of CR transport that are needed in order to match the observed gamma-ray spectra. Furthermore, I uncover the underlying processes that enable the FIR-radio correlation (FRC) to be maintained even in starburst galaxies and find that thermal free-free-emission naturally explains the observed radio spectra in SF galaxies like M82 and NGC 253 thus solving the riddle of flat radio spectra that have been proposed to contradict the observed tight FRC. Lastly, I scrutinise the steady-state modelling of the CR proton component by investigating for the first time the influence of spectrally resolved CR transport in MHD simulations on the hadronic gamma-ray emission of SF galaxies revealing new insights into the observational signatures of CR transport both spectrally and spatially.},
  language  = {en}
}
@phdthesis{Wendi2018,
  author    = {Wendi, Dadiyorto},
  title     = {Recurrence Plots and Quantification Analysis of Flood Runoff Dynamics},
  doi       = {10.25932/publishup-43191},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-431915},
  school      = {Universit{\"a}t Potsdam},
  pages     = {114},
  year      = {2018},
  abstract  = {This paper introduces a novel measure to assess similarity between event hydrographs. It is based on Cross Recurrence Plots and Recurrence Quantification Analysis which have recently gained attention in a range of disciplines when dealing with complex systems. The method attempts to quantify the event runoff dynamics and is based on the time delay embedded phase space representation of discharge hydrographs. A phase space trajectory is reconstructed from the event hydrograph, and pairs of hydrographs are compared to each other based on the distance of their phase space trajectories. Time delay embedding allows considering the multi-dimensional relationships between different points in time within the event. Hence, the temporal succession of discharge values is taken into account, such as the impact of the initial conditions on the runoff event. We provide an introduction to Cross Recurrence Plots and discuss their parameterization. An application example based on flood time series demonstrates how the method can be used to measure the similarity or dissimilarity of events, and how it can be used to detect events with rare runoff dynamics. It is argued that this methods provides a more comprehensive approach to quantify hydrograph similarity compared to conventional hydrological signatures.},
  language  = {en}
}
@phdthesis{Wen2020,
  author    = {Wen, Xi},
  title     = {Distribution patterns and environmental drivers of methane-cycling microorganisms in natural environments and restored wetlands},
  doi       = {10.25932/publishup-47177},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-471770},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, iii, 152},
  year      = {2020},
  abstract  = {Methane is an important greenhouse gas contributing to global climate change. Natural environments and restored wetlands contribute a large proportion to the global methane budget. Methanogenic archaea (methanogens) and methane oxidizing bacteria (methanotrophs), the biogenic producers and consumers of methane, play key roles in the methane cycle in those environments. A large number of studies revealed the distribution, diversity and composition of these microorganisms in individual habitats. However, uncertainties exist in predicting the response and feedback of methane-cycling microorganisms to future climate changes and related environmental changes due to the limited spatial scales considered so far, and due to a poor recognition of the biogeography of these important microorganisms combining global and local scales. With the aim of improving our understanding about whether and how methane-cycling microbial communities will be affected by a series of dynamic environmental factors in response to climate change, this PhD thesis investigates the biogeographic patterns of methane-cycling communities, and the driving factors which define these patterns at different spatial scales. At the global scale, a meta-analysis was performed by implementing 94 globally distributed public datasets together with environmental data from various natural environments including soils, lake sediments, estuaries, marine sediments, hydrothermal sediments and mud volcanos. In combination with a global biogeographic map of methanogenic archaea from multiple natural environments, this thesis revealed that biogeographic patterns of methanogens exist. The terrestrial habitats showed higher alpha diversities than marine environments. Methanoculleus and Methanosaeta (Methanothrix) are the most frequently detected taxa in marine habitats, while Methanoregula prevails in terrestrial habitats. Estuary ecosystems, the transition zones between marine and terrestrial/limnic ecosystems, have the highest methanogenic richness but comparably low methane emission rates. At the local scale, this study compared two rewetted fens with known high methane emissions in northeastern Germany, a coastal brackish fen (H{\"u}telmoor) and a freshwater riparian fen (Polder Zarnekow). Consistent with different geochemical conditions and land-use history, the two rewetted fens exhibit dissimilar methanogenic and, especially, methanotrophic community compositions. The methanotrophic community was generally under-represented among the prokaryotic communities and both fens show similarly low ratios of methanotrophic to methanogenic abundances. Since few studies have characterized methane-cycling microorganisms in rewetted fens, this study provides first evidence that the rapid and well re-established methanogenic community in combination with the low and incomplete re-establishment of the methanotrophic community after rewetting contributes to elevated sustained methane fluxes following rewetting. Finally, this thesis demonstrates that dispersal limitation only slightly regulates the biogeographic distribution patterns of methanogenic microorganisms in natural environments and restored wetlands. Instead, their existence, adaption and establishment are more associated with the selective pressures under different environmental conditions. Salinity, pH and temperature are identified as the most important factors in shaping microbial community structure at different spatial scales (global versus terrestrial environments). Predicted changes in climate, such as increasing temperature, changes in precipitation patterns and increasing frequency of flooding events, are likely to induce a series of environmental alterations, which will either directly or indirectly affect the driving environmental forces of methanogenic communities, leading to changes in their community composition and thus potentially also in methane emission patterns in the future.},
  language  = {en}
}
@phdthesis{Welsch2022,
  author    = {Welsch, Maryna},
  title     = {Investigation of the stress tolerance regulatory network integration of the NAC transcription factor JUNGBRUNNEN1 (JUB1)},
  doi       = {10.25932/publishup-54731},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-547310},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIII, 116},
  year      = {2022},
  abstract  = {The NAC transcription factor (TF) JUNGBRUNNEN1 (JUB1) is an important negative regulator of plant senescence, as well as of gibberellic acid (GA) and brassinosteroid (BR) biosynthesis in Arabidopsis thaliana. Overexpression of JUB1 promotes longevity and enhances tolerance to drought and other abiotic stresses. A similar role of JUB1 has been observed in other plant species, including tomato and banana. Our data show that JUB1 overexpressors (JUB1-OXs) accumulate higher levels of proline than WT plants under control conditions, during the onset of drought stress, and thereafter. We identified that overexpression of JUB1 induces key proline biosynthesis and suppresses key proline degradation genes. Furthermore, bZIP63, the transcription factor involved in proline metabolism, was identified as a novel downstream target of JUB1 by Yeast One-Hybrid (Y1H) analysis and Chromatin immunoprecipitation (ChIP). However, based on Electrophoretic Mobility Shift Assay (EMSA), direct binding of JUB1 to bZIP63 could not be confirmed. Our data indicate that JUB1-OX plants exhibit reduced stomatal conductance under control conditions. However, selective overexpression of JUB1 in guard cells did not improve drought stress tolerance in Arabidopsis. Moreover, the drought-tolerant phenotype of JUB1 overexpressors does not solely depend on the transcriptional control of the DREB2A gene. Thus, our data suggest that JUB1 confers tolerance to drought stress by regulating multiple components. Until today, none of the previous studies on JUB1´s regulatory network focused on identifying protein-protein interactions. We, therefore, performed a yeast two-hybrid screen (Y2H) which identified several protein interactors of JUB1, two of which are the calcium-binding proteins CaM1 and CaM4. Both proteins interact with JUB1 in the nucleus of Arabidopsis protoplasts. Moreover, JUB1 is expressed with CaM1 and CaM4 under the same conditions. Since CaM1.1 and CaM4.1 encode proteins with identical amino acid sequences, all further experiments were performed with constructs involving the CaM4 coding sequence. Our data show that JUB1 harbors multiple CaM-binding sites, which are localized in both the N-terminal and C-terminal regions of the protein. One of the CaM-binding sites, localized in the DNA-binding domain of JUB1, was identified as a functional CaM-binding site since its mutation strongly reduced the binding of CaM4 to JUB1. Furthermore, JUB1 transactivates expression of the stress-related gene DREB2A in mesophyll cells; this effect is significantly reduced when the calcium-binding protein CaM4 is expressed as well. Overexpression of both genes in Arabidopsis results in early senescence observed through lower chlorophyll content and an enhanced expression of senescence-associated genes (SAGs) when compared with single JUB1 overexpressors. Our data also show that JUB1 and CaM4 proteins interact in senescent leaves, which have increased Ca2+ levels when compared to young leaves. Collectively, our data indicate that JUB1 activity towards its downstream targets is fine-tuned by calcium-binding proteins during leaf senescence.},
  language  = {en}
}
@phdthesis{Wellmann2023,
  author    = {Wellmann, Caroline},
  title     = {Early sensitivity to prosodic phrase boundary cues: Behavioral evidence from German-learning infants},
  doi       = {10.25932/publishup-57393},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-573937},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 136},
  year      = {2023},
  abstract  = {This dissertation seeks to shed light on the relation of phrasal prosody and developmental speech perception in German-learning infants. Three independent empirical studies explore the role of acoustic correlates of major prosodic boundaries, specifically pitch change, final lengthening, and pause, in infant boundary perception. Moreover, it was examined whether the sensitivity to prosodic phrase boundary markings changes during the first year of life as a result of perceptual attunement to the ambient language (Aslin \& Pisoni, 1980). Using the headturn preference procedure six- and eight-month-old monolingual German-learning infants were tested on their discrimination of two different prosodic groupings of the same list of coordinated names either with or without an internal IPB after the second name, that is, [Moni und Lilli] [und Manu] or [Moni und Lilli und Manu]. The boundary marking was systematically varied with respect to single prosodic cues or specific cue combinations. Results revealed that six- and eight-month-old German-learning infants successfully detect the internal prosodic boundary when it is signaled by all the three main boundary cues pitch change, final lengthening, and pause. For eight-, but not for six-month-olds, the combination of pitch change and final lengthening, without the occurrence of a pause, is sufficient. This mirrors an adult-like perception by eight-months (Holzgrefe-Lang et al., 2016). Six-month-olds detect a prosodic phrase boundary signaled by final lengthening and pause. The findings suggest a developmental change in German prosodic boundary cue perception from a strong reliance on the pause cue at six months to a differentiated sensitivity to the more subtle cues pitch change and final lengthening at eight months. Neither for six- nor for eight-month-olds the occurrence of pitch change or final lengthening as single cues is sufficient, similar to what has been observed for adult speakers of German (Holzgrefe-Lang et al., 2016). The present dissertation provides new scientific knowledge on infants' sensitivity to individual prosodic phrase boundary cues in the first year of life. Methodologically, the studies are pathbreaking since they used exactly the same stimulus materials - phonologically thoroughly controlled lists of names - that have also been used with adults (Holzgrefe-Lang et al., 2016) and with infants in a neurophysiological paradigm (Holzgrefe-Lang, Wellmann, H{\"o}hle, \& Wartenburger, 2018), allowing for comparisons across age (six/ eight months and adults) and method (behavioral vs. neurophysiological methods). Moreover, materials are suited to be transferred to other languages allowing for a crosslinguistic comparison. Taken together with a study with similar French materials (van Ommen et al., 2020) the observed change in sensitivity in German-learning infants can be interpreted as a language-specific one, from an initial language-general processing mechanism that primarily focuses on the presence of pauses to a language-specific processing that takes into account prosodic properties available in the ambient language. The developmental pattern is discussed as an interplay of acoustic salience, prosodic typology (prosodic regularity) and cue reliability.},
  language  = {en}
}
@phdthesis{Weisshuhn2020,
  author    = {Weißhuhn, Peter},
  title     = {Assessing biotope vulnerability to landscape changes},
  doi       = {10.25932/publishup-44277},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442777},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 134},
  year      = {2020},
  abstract  = {Largescale patterns of global land use change are very frequently accompanied by natural habitat loss. To assess the consequences of habitat loss for the remaining natural and semi-natural biotopes, inclusion of cumulative effects at the landscape level is required. The interdisciplinary concept of vulnerability constitutes an appropriate assessment framework at the landscape level, though with few examples of its application for ecological assessments. A comprehensive biotope vulnerability analysis allows identification of areas most affected by landscape change and at the same time with the lowest chances of regeneration. To this end, a series of ecological indicators were reviewed and developed. They measured spatial attributes of individual biotopes as well as some ecological and conservation characteristics of the respective resident species community. The final vulnerability index combined seven largely independent indicators, which covered exposure, sensitivity and adaptive capacity of biotopes to landscape changes. Results for biotope vulnerability were provided at the regional level. This seems to be an appropriate extent with relevance for spatial planning and designing the distribution of nature reserves. Using the vulnerability scores calculated for the German federal state of Brandenburg, hot spots and clusters within and across the distinguished types of biotopes were analysed. Biotope types with high dependence on water availability, as well as biotopes of the open landscape containing woody plants (e.g., orchard meadows) are particularly vulnerable to landscape changes. In contrast, the majority of forest biotopes appear to be less vulnerable. Despite the appeal of such generalised statements for some biotope types, the distribution of values suggests that conservation measures for the majority of biotopes should be designed specifically for individual sites. Taken together, size, shape and spatial context of individual biotopes often had a dominant influence on the vulnerability score. The implementation of biotope vulnerability analysis at the regional level indicated that large biotope datasets can be evaluated with high level of detail using geoinformatics. Drawing on previous work in landscape spatial analysis, the reproducible approach relies on transparent calculations of quantitative and qualitative indicators. At the same time, it provides a synoptic overview and information on the individual biotopes. It is expected to be most useful for nature conservation in combination with an understanding of population, species, and community attributes known for specific sites. The biotope vulnerability analysis facilitates a foresighted assessment of different land uses, aiding in identifying options to slow habitat loss to sustainable levels. It can also be incorporated into planning of restoration measures, guiding efforts to remedy ecological damage. Restoration of any specific site could yield synergies with the conservation objectives of other sites, through enhancing the habitat network or buffering against future landscape change. Biotope vulnerability analysis could be developed in line with other important ecological concepts, such as resilience and adaptability, further extending the broad thematic scope of the vulnerability concept. Vulnerability can increasingly serve as a common framework for the interdisciplinary research necessary to solve major societal challenges.},
  language  = {en}
}
@phdthesis{Weissenberger2017,
  author    = {Weißenberger, Martin},
  title     = {Start-up subsidies for the unemployed - New evaluation approaches and insights},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406362},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 239},
  year      = {2017},
  abstract  = {Start-up incentives targeted at unemployed individuals have become an important tool of the Active Labor Market Policy (ALMP) to fight unemployment in many countries in recent years. In contrast to traditional ALMP instruments like training measures, wage subsidies, or job creation schemes, which are aimed at reintegrating unemployed individuals into dependent employment, start-up incentives are a fundamentally different approach to ALMP, in that they intend to encourage and help unemployed individuals to exit unemployment by entering self-employment and, thus, by creating their own jobs. In this sense, start-up incentives for unemployed individuals serve not only as employment and social policy to activate job seekers and combat unemployment but also as business policy to promote entrepreneurship. The corresponding empirical literature on this topic so far has been mainly focused on the individual labor market perspective, however. The main part of the thesis at hand examines the new start-up subsidy ("Gr{\"u}ndungszuschuss") in Germany and consists of four empirical analyses that extend the existing evidence on start-up incentives for unemployed individuals from multiple perspectives and in the following directions: First, it provides the first impact evaluation of the new start-up subsidy in Germany. The results indicate that participation in the new start-up subsidy has significant positive and persistent effects on both reintegration into the labor market as well as the income profiles of participants, in line with previous evidence on comparable German and international programs, which emphasizes the general potential of start-up incentives as part of the broader ALMP toolset. Furthermore, a new innovative sensitivity analysis of the applied propensity score matching approach integrates findings from entrepreneurship and labor market research about the key role of an individual's personality on start-up decision, business performance, as well as general labor market outcomes, into the impact evaluation of start-up incentives. The sensitivity analysis with regard to the inclusion and exclusion of usually unobserved personality variables reveals that differences in the estimated treatment effects are small in magnitude and mostly insignificant. Consequently, concerns about potential overestimation of treatment effects in previous evaluation studies of similar start-up incentives due to usually unobservable personality variables are less justified, as long as the set of observed control variables is sufficiently informative (Chapter 2). Second, the thesis expands our knowledge about the longer-term business performance and potential of subsidized businesses arising from the start-up subsidy program. In absolute terms, the analysis shows that a relatively high share of subsidized founders successfully survives in the market with their original businesses in the medium to long run. The subsidy also yields a "double dividend" to a certain extent in terms of additional job creation. Compared to "regular", i.e., non-subsidized new businesses founded by non-unemployed individuals in the same quarter, however, the economic and growth-related impulses set by participants of the subsidy program are only limited with regard to employment growth, innovation activity, or investment. Further investigations of possible reasons for these differences show that differential business growth paths of subsidized founders in the longer run seem to be mainly limited by higher restrictions to access capital and by unobserved factors, such as less growth-oriented business strategies and intentions, as well as lower (subjective) entrepreneurial persistence. Taken together, the program has only limited potential as a business and entrepreneurship policy intended to induce innovation and economic growth (Chapters 3 and 4). And third, an empirical analysis on the level of German regional labor markets yields that there is a high regional variation in subsidized start-up activity relative to overall new business formation. The positive correlation between regular start-up intensity and the share among all unemployed individuals who participate in the start-up subsidy program suggests that (nascent) unemployed founders also profit from the beneficial effects of regional entrepreneurship capital. Moreover, the analysis of potential deadweight and displacement effects from an aggregated regional perspective emphasizes that the start-up subsidy for unemployed individuals represents a market intervention into existing markets, which affects incumbents and potentially produces inefficiencies and market distortions. This macro perspective deserves more attention and research in the future (Chapter 5).},
  language  = {en}
}