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Although the search for promising business models (BMs) is crucial for every profit-oriented venture, searching for those challenges in particular entrepreneurs. Limited resources, missing expertise and absolute uncertainty call entrepreneurs to strongly rely on their cognition in searching for a promising BM. However, as prior studies have examined cognitive search activities in isolation and neglected cognitive differences, explanations of how cognitive factors affect the BM process and outcomes are thus far insufficient.
Addressing the overall question of how BMs emerge, the dissertation contributes to the cognitive perspective in entrepreneurship and BM research. Building on the dual-process theory from cognitive psychology, the micro-foundations of managerial decision-making and insights from framing literature, this dissertation explicitly investigates the impacts of different cognitive dispositions, search activities and visual framing effects. The core assumption is that cognitive dispositions and entrepreneurs’ searches for information determine their BM decision-making. Furthermore, BM visualisations have become popular instruments with which to explain and manage today’s complex business interactions. As they abstract from reality, they can also unfold impacts on the cognitive processes.
This dissertation offers new explanations to these aspects and consists of three studies and one reflective article. The first study explores the impacts of differences in search activities and cognitive dispositions in a qualitative study with 70 entrepreneurship students. The second qualitative study explores the cognitive impacts of 103 BM visualisations. Third, a quantitative PLS-SEM experiment with 197 entrepreneurs illuminates the link between BM visualisations and cognition. The reflective article expresses the results’ meaning for the teaching of BMs.
In sum, the studies have resulted in a new theory of stabilising factors explaining how cognitive dispositions, search activities and visual framing determine entrepreneurs’ decisions to imitate or deviate from existing BMs. It indicates that the decision depends on the context-dependent strategic orientation and cognitive disposition-dependent cognitive safety, that is the correspondence between characteristics of cognitive dispositions and search activities. Moreover, the studies identified five visual framing effects that are independent of cognitive dispositions and prior experiences. This provides fertile contributions to the literature on BM methods and how BM visualisations affect decisions. Most importantly, BM visualisations provide an emotionally stabilising function to rational entrepreneurs, a cognitively stabilising function to experiential participants and do not affect indifferent participants in general.
Deutschland und Frankreich benötigen stetige Metallimporte, um ihr Wirtschaftsmodell aufrechtzuerhalten. Internationale Kooperation ist unerlässlich, damit diese Importe zuverlässig und nachhaltig verlaufen. Doch welche Potenziale bieten sich in diesem Bereich, welche Grenzen sind dabei zu erkennen? Dieser Frage geht Yann Wernert durch einen Fallstudienvergleich mit prozessanalytischen Methoden und auf der theoretischen Grundlage des neoliberalen Institutionalismus nach. Er zeigt, dass beide Länder ihre Bemühungen als reaktive Mittelmächte gestalten. Sie wollen durch staatliche Rohstoffstrategien wirtschaftliche, strategische und Nachhaltigkeitsziele erreichen. Während die Analyse durchaus Kooperationspotenziale ausmacht, fallen diese je nach Ländergruppe und Politikbereich sehr unterschiedlich aus.
This thesis covers the synthesis of conjugates of 2-Deoxy-D-ribose-5-phosphate aldolase (DERA) with suitable polymers and the subsequent immobilization of these conjugates in thin films via two different approaches.
2-Deoxy-D-ribose-5-phosphate aldolase (DERA) is a biocatalyst that is capable of converting acetaldehyde and a second aldehyde as acceptor into enantiomerically pure mono- and diyhydroxyaldehydes, which are important structural motifs in a number of pharmaceutically active compounds. Conjugation and immobilization renders the enzyme applicable for utilization in a continuously run biocatalytic process which avoids the common problem of product inhibition. Within this thesis, conjugates of DERA and poly(N-isopropylacrylamide) (PNIPAm) for immobilization via a self-assembly approach were synthesized and isolated, as well as conjugates with poly(N,N-dimethylacrylamide) (PDMAA) for a simplified and scalable spray-coating approach. For the DERA/PNIPAm-conjugates different synthesis routes were tested, including grafting-from and grafting-to, both being common methods for the conjugation. Furthermore, both lysines and cysteines were addressed for the conjugation in order to find optimum conjugation conditions. It turned out that conjugation via lysine causes severe activity loss as one lysine plays a key role in the catalyzing mechanism. The conjugation via the cysteines by a grafting-to approach using pyridyl disulfide (PDS) end-group functionalized polymers led to high conjugation efficiencies in the presence of polymer solubilizing NaSCN. The resulting conjugates maintained enzymatic activity and also gained high acetaldehyde tolerance which is necessary for their use later on in an industrial relevant process after their immobilization.
The resulting DERA/PNIPAm conjugates exhibited enhanced interfacial activity at the air/water interface compared to the single components, which is an important pre-requisite for the immobilization via the self-assembly approach. Conjugates with longer polymer chains formed homogeneous films on silicon wafers and glass slides while the ones with short chains could only form isolated aggregates. On top of that, long chain conjugates showed better activity maintenance upon the immobilization.
The crosslinking of conjugates, as well as their fixation on the support materials, are important for the mechanical stability of the films obtained from the self-assembly process. Therefore, in a second step, we introduced the UV-crosslinkable monomer DMMIBA to the PNIPAm polymers to be used for conjugation. The introduction of DMMIBA reduced the lower critical solution temperature (LCST) of the polymer and thus the water solubility at ambient conditions, resulting in lower conjugation efficiencies and in turn slightly poorer acetaldehyde tolerance of the resulting conjugates. Unlike the DERA/PNIPAm, the conjugates from the copolymer P(NIPAM-co-DMMIBA) formed continuous, homogenous films only after the crosslinking step via UV-treatment. For a firm binding of the crosslinked films, a functionalization protocol for the model support material cyclic olefin copolymer (COC) and the final target support, PAN based membranes, was developed that introduces analogue UV-reactive groups to the support surface. The conjugates immobilized on the modified COC films maintained enzymatic activity and showed good mechanical stability after several cycles of activity assessment. Conjugates with longer polymer chains, however, showed a higher degree of crosslinking after the UV-treatment leading to a pronounced loss of activity. A porous PAN membrane onto which the conjugates were immobilized as well, was finally transferred to a dead end filtration membrane module to catalyze the aldol reaction of the industrially relevant mixture of acetaldehyde and hexanal in a continuous mode. Mono aldol product was detectable, but yields were comparably low and the operational stability needs to be further improved
Another approach towards immobilization of DERA conjugates that was followed, was to generate the conjugates in situ by simply mixing enzyme and polymer and spray coat the mixture onto the membrane support. Compared to the previous approach, the focus was more put on simplicity and a possible scalability of the immobilization. Conjugates were thus only generated in-situ and not further isolated and characterized. For the conjugation, PDMAA equipped with N-2-thiolactone acrylamide (TlaAm) side chains was used, an amine-reactive comonomer that can react with the lysine residues of DERA, as well as with amino groups introduced to a desired support surface. Furthermore disulfide formation after hydrolysis of the Tla groups causes a crosslinking effect. The synthesized copolymer poly(N,N-Dimethylacrylamide-co-N-2-thiolactone acrylamide) (P(DMAA-co-TlaAm)) thus serves a multiple purpose including protein binding, crosslinking and binding to support materials. The mixture of DERA and polymer could be immobilized on the PAN support by spray-coating under partial maintenance of enzymatic activity. To improve the acetaldehyde tolerance, the polymer in used was further equipped with cysteine reactive PDS end-groups that had been used for the conjugation as described in the first part of the thesis. The generated conjugates indeed showed good acetaldehyde tolerance and were thus used to be coated onto PAN membrane supports. Post treatment with a basic aqueous solution of H2O2 was supposed to further crosslink the spray-coated film hydrolysis and oxidation of the thiolactone groups. However, a washing off of the material was observed. Optimization is thus still necessary.
This dissertation investigates the impact of the economic and fiscal crisis starting in 2008 on EU climate policy-making. While the overall number of adopted greenhouse gas emission reduction policies declined in the crisis aftermath, EU lawmakers decided to introduce new or tighten existing regulations in some important policy domains. Existing knowledge about the crisis impact on EU legislative decision-making cannot explain these inconsistencies. In response, this study develops an actor-centred conceptual framework based on rational choice institutionalism that provides a micro-level link to explain how economic crises translate into altered policy-making patterns. The core theoretical argument draws on redistributive conflicts, arguing that tensions between ‘beneficiaries’ and ‘losers’ of a regulatory initiative intensify during economic crises and spill over to the policy domain. To test this hypothesis and using social network analysis, this study analyses policy processes in three case studies: The introduction of carbon dioxide emission limits for passenger cars, the expansion of the EU Emissions Trading System to aviation, and the introduction of a regulatory framework for biofuels. The key finding is that an economic shock causes EU policy domains to polarise politically, resulting in intensified conflict and more difficult decision-making. The results also show that this process of political polarisation roots in the industry that is the subject of the regulation, and that intergovernmental bargaining among member states becomes more important, but also more difficult in times of crisis.
Fold and thrust belts are characteristic features of collisional orogen that grow laterally through time by deforming the upper crust in response to stresses caused by convergence. The deformation propagation in the upper crust is accommodated by shortening along major folds and thrusts. The formation of these structures is influenced by the mechanical strength of décollements, basement architecture, presence of preexisting structures and taper of the wedge. These factors control not only the sequence of deformation but also cause differences in the structural style.
The Himalayan fold and thrust belt exhibits significant differences in the structural style from east to west. The external zone of the Himalayan fold and thrust belt, also called the Subhimalaya, has been extensively studied to understand the temporal development and differences in the structural style in Bhutan, Nepal and India; however, the Subhimalaya in Pakistan remains poorly studied. The Kohat and Potwar fold and thrust belts (herein called Kohat and Potwar) represent the Subhimalaya in Pakistan. The Main Boundary Thrust (MBT) marks the northern boundary of both Kohat and Potwar, showing that these belts are genetically linked to foreland-vergent deformation within the Himalayan orogen, despite the pronounced contrast in structural style. This contrast becomes more pronounced toward south, where the active strike-slip Kalabagh Fault Zone links with the Kohat and Potwar range fronts, known as the Surghar Range and the Salt Range, respectively. The Surghar and Salt Ranges developed above the Surghar Thrust (SGT) and Main Frontal Thrust (MFT). In order to understand the structural style and spatiotemporal development of the major structures in Kohat and Potwar, I have used structural modeling and low temperature thermochronolgy methods in this study. The structural modeling is based on construction of balanced cross-sections by integrating surface geology, seismic reflection profiles and well data. In order to constrain the timing and magnitude of exhumation, I used apatite (U-Th-Sm)/He (AHe) and apatite fission track (AFT) dating. The results obtained from both methods are combined to document the Paleozoic to Recent history of Kohat and Potwar.
The results of this research suggest two major events in the deformation history. The first major deformation event is related to Late Paleozoic rifting associated with the development of the Neo-Tethys Ocean. The second major deformation event is related to the Late Miocene to Pliocene development of the Himalayan fold and thrust belt in the Kohat and Potwar. The Late Paleozoic rifting is deciphered by inverse thermal modelling of detrital AFT and AHe ages from the Salt Range. The process of rifting in this area created normal faulting that resulted in the exhumation/erosion of Early to Middle Paleozoic strata, forming a major unconformity between Cambrian and Permian strata that is exposed today in the Salt Range. The normal faults formed in Late Paleozoic time played an important role in localizing the Miocene-Pliocene deformation in this area. The combination of structural reconstructions and thermochronologic data suggest that deformation initiated at 15±2 Ma on the SGT ramp in the southern part of Kohat. The early movement on the SGT accreted the foreland into the Kohat deforming wedge, forming the range front. The development of the MBT at 12±2 Ma formed the northern boundary of Kohat and Potwar. Deformation propagated south of the MBT in the Kohat on double décollements and in the Potwar on a single basal décollement. The double décollement in the Kohat adopted an active roof-thrust deformation style that resulted in the disharmonic structural style in the upper and lower parts of the stratigraphic section. Incremental shortening resulted in the development of duplexes in the subsurface between two décollements and imbrication above the roof thrust. Tectonic thickening caused by duplexes resulted in cooling and exhumation above the roof thrust by removal of a thick sequence of molasse strata. The structural modelling shows that the ramps on which duplexes formed in Kohat continue as tip lines of fault propagation folds in the Potwar. The absence of a double décollement in the Potwar resulted in the preservation of a thick sequence of molasse strata there. The temporal data suggest that deformation propagated in-sequence from ~ 8 to 3 Ma in the northern part of Kohat and Potwar; however, internal deformation in the Kohat was more intense, probably required for maintaining a critical taper after a significant load was removed above the upper décollement. In the southern part of Potwar, a steeper basement slope (β≥3°) and the presence of salt at the base of the stratigraphic section allowed for the complete preservation of the stratigraphic wedge, showcased by very little internal deformation. Activation of the MFT at ~4 Ma allowed the Salt Range to become the range front of the Potwar. The removal of a large amount of molasse strata above the MFT ramp enhanced the role of salt in shaping the structural style of the Salt Range and Kalabagh Fault Zone. Salt accumulation and migration resulted in the formation of normal faults in both areas. Salt migration in the Kalabagh fault zone has triggered out-of-sequence movement on ramps in the Kohat.
The amount of shortening calculated between the MBT and the SGT in Kohat is 75±5 km and between the MBT and the MFT in Potwar is 65±5 km. A comparable amount of shortening is accommodated in the Kohat and Potwar despite their different widths: 70 km Kohat and 150 km Potwar. In summary, this research suggests that deformation switched between different structures during the last ~15 Ma through different modes of fault propagation, resulting in different structural styles and the out-of-sequence development of Kohat and Potwar.
The foreland of the Andes in South America is characterised by distinct along strike changes in surface deformational styles. These styles are classified into two end-members, the thin-skinned and the thick-skinned style. The superficial expression of thin-skinned deformation is a succession of narrowly spaced hills and valleys, that form laterally continuous ranges on the foreland facing side of the orogen. Each of the hills is defined by a reverse fault that roots in a basal décollement surface within the sedimentary cover, and acted as thrusting ramp to stack the sedimentary pile. Thick-skinned deformation is morphologically characterised by spatially disparate, basement-cored mountain ranges. These mountain ranges are uplifted along reactivated high-angle crustal-scale discontinuities, such as suture zones between different tectonic terranes.
Amongst proposed causes for the observed variation are variations in the dip angle of the Nazca plate, variation in sediment thickness, lithospheric thickening, volcanism or compositional differences. The proposed mechanisms are predominantly based on geological observations or numerical thermomechanical modelling, but there has been no attempt to understand the mechanisms from a point of data-integrative 3D modelling. The aim of this dissertation is therefore to understand how lithospheric structure controls the deformational behaviour. The integration of independent data into a consistent model of the lithosphere allows to obtain additional evidence that helps to understand the causes for the different deformational styles. Northern Argentina encompasses the transition from the thin-skinned fold-and-thrust belt in Bolivia, to the thick-skinned Sierras Pampeanas province, which makes this area a well suited location for such a study. The general workflow followed in this study first involves data-constrained structural- and density-modelling in order to obtain a model of the study area. This model was then used to predict the steady-state thermal field, which was then used to assess the present-day rheological state in northern Argentina.
The structural configuration of the lithosphere in northern Argentina was determined by means of data-integrative, 3D density modelling verified by Bouguer gravity. The model delineates the first-order density contrasts in the lithosphere in the uppermost 200 km, and discriminates bodies for the sediments, the crystalline crust, the lithospheric mantle and the subducting Nazca plate. To obtain the intra-crustal density structure, an automated inversion approach was developed and applied to a starting structural model that assumed a homogeneously dense crust. The resulting final structural model indicates that the crustal structure can be represented by an upper crust with a density of 2800 kg/m³, and a lower crust of 3100 kg/m³. The Transbrazilian Lineament, which separates the Pampia terrane from the Río de la Plata craton, is expressed as a zone of low average crustal densities.
In an excursion, we demonstrate in another study, that the gravity inversion method developed to obtain intra-crustal density structures, is also applicable to obtain density variations in the uppermost lithospheric mantle. Densities in such sub-crustal depths are difficult to constrain from seismic tomographic models due to smearing of crustal velocities. With the application to the uppermost lithospheric mantle in the north Atlantic, we demonstrate in Tan et al. (2018) that lateral density trends of at least 125\,km width are robustly recovered by the inversion method, thereby providing an important tool for the delineation of subcrustal density trends.
Due to the genetic link between subduction, orogenesis and retroarc foreland basins the question rises whether the steady-state assumption is valid in such a dynamic setting. To answer this question, I analysed (i) the impact of subduction on the conductive thermal field of the overlying continental plate, (ii) the differences between the transient and steady-state thermal fields of a geodynamic coupled model. Both studies indicate that the assumption of a thermal steady-state is applicable in most parts of the study area. Within the orogenic wedge, where the assumption cannot be applied, I estimated the transient thermal field based on the results of the conducted analyses.
Accordingly, the structural model that had been obtained in the first step, could be used to obtain a 3D conductive steady-state thermal field. The rheological assessment based on this thermal field indicates that the lithosphere of the thin-skinned Subandean ranges is characterised by a relatively strong crust and a weak mantle. Contrarily, the adjacent foreland basin consists of a fully coupled, very strong lithosphere. Thus, shortening in northern Argentina can only be accommodated within the weak lithosphere of the orogen and the Subandean ranges. The analysis suggests that the décollements of the fold-and-thrust belt are the shallow continuation of shear zones that reside in the ductile sections of the orogenic crust. Furthermore, the localisation of the faults that provide strain transfer between the deeper ductile crust and the shallower décollement is strongly influenced by crustal weak zones such as foliation. In contrast to the northern foreland, the lithosphere of the thick-skinned Sierras Pampeanas is fully coupled and characterised by a strong crust and mantle. The high overall strength prevents the generation of crustal-scale faults by tectonic stresses. Even inherited crustal-scale discontinuities, such as sutures, cannot sufficiently reduce the strength of the lithosphere in order to be reactivated. Therefore, magmatism that had been identified to be a precursor of basement uplift in the Sierras Pampeanas, is the key factor that leads to the broken foreland of this province. Due to thermal weakening, and potentially lubrication of the inherited discontinuities, the lithosphere is locally weakened such that tectonic stresses can uplift the basement blocks. This hypothesis explains both the spatially disparate character of the broken foreland, as well as the observed temporal delay between volcanism and basement block uplift.
This dissertation provides for the first time a data-driven 3D model that is consistent with geophysical data and geological observations, and that is able to causally link the thermo-rheological structure of the lithosphere to the observed variation of surface deformation styles in the retroarc foreland of northern Argentina.
The fabrication of 1D nanostrands composed of stimuli responsive microgels has been shown in this work. Microgels are well known materials able to respond to various stimuli from outer environment. Since these microgels respond via a volume change to an external stimulus, a targeted mechanical response can be achieved. Through carefully choosing the right composition of the polymer matrix, microgels can be designed to react precisely to the targeted stimuli (e.g. drug delivery via pH and temperature changes, or selective contractions through changes in electrical current125).
In this work, it was aimed to create flexible nano-filaments which are capable of fast anisotropic contractions similar to muscle filaments. For the fabrication of such filaments or strands, nanostructured templates (PDMS wrinkles) were chosen due to a facile and low-cost fabrication and versatile tunability of their dimensions. Additionally, wrinkling is a well-known lithography-free method which enables the fabrication of nanostructures in a reproducible manner and with a high long-range periodicity.
In Chapter 2.1, it was shown for the first time that microgels as soft matter particles can be aligned to densely packed microgel arrays of various lateral dimensions. The alignment of microgels with different compositions (e.g. VCL/AAEM, NIPAAm, NIPAAm/VCL and charged microgels) was shown by using different assembly techniques (e.g. spin-coating, template confined molding). It was chosen to set one experimental parameter constant which was the SiOx surface composition of the templates and substrates (e.g. oxidized PDMS wrinkles, Si-wafers and glass slides). It was shown that the fabrication of nanoarrays was feasible with all tested microgel types. Although the microgels exhibited different deformability when aligned on a flat surface, they retained their thermo-responsivity and swelling behavior.
Towards the fabrication of 1D microgel strands interparticle connectivity was aspired. This was achieved via different cross-linking methods (i.e. cross-linking via UV-irradiation and host-guest complexation) discussed in Chapter 2.2. The microgel arrays created by different assembly methods and microgel types were tested for their cross-linking suitability. It was observed that NIPAAm based microgels cannot be cross-linked with UV light. Furthermore, it was found that these microgels exhibit a strong surface-particle-interaction and therefore could not be detached from the given substrates. In contrast to the latter, with VCL/AAEM based microgels it was possible to both UV cross-link them based on the keto-enol tautomerism of the AAEM copolymer, and to detach them from the substrate due to the lower adhesion energy towards SiOx surfaces. With VCL/AAEM microgels long, one-dimensional microgel strands could be re-dispersed in water for further analysis. It has also been shown that at least one lateral dimension of the free dispersed 1D microgel strands is easily controllable by adjusting the wavelength of the wrinkled template. For further work, only VCL/AAEM based microgels were used to focus on the main aim of this work, i.e. the fabrication of 1D microgel nanostrands.
As an alternative to the unspecific and harsh UV cross-linking, the host-guest complexation via diazobenzene cross-linkers and cyclodextrin hosts was explored. The idea behind this approach was to give means to a future construction kit-like approach by incorporation of cyclodextrin comonomers in a broad variety of particle systems (e.g. microgels, nanoparticles). For this purpose, VCL/AAEM microgels were copolymerized with different amounts of mono-acrylate functionalized β-cyclodextrin (CD). After successfully testing the cross-linking capability in solution, the cross-linking of aligned VCL/AAEM/CD microgels was tried. Although the cross-linking worked well, once the single arrays came into contact to each other, they agglomerated. As a reason for this behavior residual amounts of mono-complexed diazobenzene linkers were suspected. Thus, end-capping strategies were tried out (e.g. excess amounts of β-cyclodextrin and coverage with azobenzene functionalized AuNPs) but were unsuccessful. With deeper thought, entropy effects were taken into consideration which favor the release of complexed diazobenzene linker leading to agglomerations. To circumvent this entropy driven effect, a multifunctional polymer with 50% azobenzene groups (Harada polymer) was used. First experiments with this polymer showed promising results regarding a less pronounced agglomeration (Figure 77). Thus, this approach could be pursued in the future. In this chapter it was found out that in contrast to pearl necklace and ribbon like formations, particle alignment in zigzag formation provided the best compromise in terms of stability in dispersion (see Figure 44a and Figure 51) while maintaining sufficient flexibility.
For this reason, microgel strands in zigzag formation were used for the motion analysis described in Chapter 2.3. The aim was to observe the properties of unrestrained microgel strands in solution (e.g. diffusion behavior, rotational properties and ideally, anisotropic contraction after temperature increase). Initially, 1D microgel strands were manipulated via AFM in a liquid cell setup. It could be observed that the strands required a higher load force compared to single microgels to be detached from the surface. However, with the AFM it was not possible to detach the strands in a controllable manner but resulted in a complete removal of single microgel particles and a tearing off the strands from the surface, respectively. For this reason, to observe the motion behavior of unrestrained microgel strands in solution, confocal microscopy was used. Furthermore, to hinder an adsorption of the strands, it was found out that coating the surface of the substrates with a repulsive polymer film was beneficial. Confocal and wide-field microscopy videos showed that the microgel strands exhibit translational and rotational diffusive motion in solution without perceptible bending. Unfortunately, with these methods the detection of the anisotropic stimuli responsive contraction of the free moving microgel strands was not possible. To summarize, the flexibility of microgel strands is more comparable to the mechanical behavior of a semi flexible cable than to a yarn. The strands studied here consist of dozens or even hundreds of discrete submicron units strung together by cross-linking, having few parallels in nanotechnology.
With the insights gained in this work on microgel-surface interactions, in the future, a targeted functionalization of the template and substrate surfaces can be conducted to actively prevent unwanted microgel adsorption for a given microgel system (e.g. PVCL and polystyrene coating235). This measure would make the discussed alignment methods more diverse. As shown herein, the assembly methods enable a versatile microgel alignment (e.g. microgel meshes, double and triple strands). To go further, one could use more complex templates (e.g. ceramic rhombs and star shaped wrinkles (Figure 14) to expand the possibilities of microgel alignment and to precisely control their aspect ratios (e.g. microgel rods with homogeneous size distributions).
Over the last years there is an increasing awareness that historical land cover changes and associated land use legacies may be important drivers for present-day species richness and biodiversity due to time-delayed extinctions or colonizations in response to historical environmental changes. Historically altered habitat patches may therefore exhibit an extinction debt or colonization credit and can be expected to lose or gain species in the future. However, extinction debts and colonization credits are difficult to detect and their actual magnitudes or payments have rarely been quantified because species richness patterns and dynamics are also shaped by recent environmental conditions and recent environmental changes.
In this thesis we aimed to determine patterns of herb-layer species richness and recent species richness dynamics of forest herb layer plants and link those patterns and dynamics to historical land cover changes and associated land use legacies. The study was conducted in the Prignitz, NE-Germany, where the forest distribution remained stable for the last ca. 100 years but where a) the deciduous forest area had declined by more than 90 per cent (leaving only remnants of "ancient forests"), b) small new forests had been established on former agricultural land ("post-agricultural forests"). Here, we analyzed the relative importance of land use history and associated historical land cover changes for herb layer species richness compared to recent environmental factors and determined magnitudes of extinction debt and colonization credit and their payment in ancient and post-agricultural forests, respectively.
We showed that present-day species richness patterns were still shaped by historical land cover changes that ranged back to more than a century. Although recent environmental conditions were largely comparable we found significantly more forest specialists, species with short-distance dispersal capabilities and clonals in ancient forests than in post-agricultural forests. Those species richness differences were largely contingent to a colonization credit in post-agricultural forests that ranged up to 9 species (average 4.7), while the extinction debt in ancient forests had almost completely been paid. Environmental legacies from historical agricultural land use played a minor role for species richness differences. Instead, patch connectivity was most important. Species richness in ancient forests was still dependent on historical connectivity, indicating a last glimpse of an extinction debt, and the colonization credit was highest in isolated post-agricultural forests. In post-agricultural forests that were better connected or directly adjacent to ancient forest patches the colonization credit was way smaller and we were able to verify a gradual payment of the colonization credit from 2.7 species to 1.5 species over the last six decades.
With the growth of information technology, patient attitudes are shifting – away from passively receiving care towards actively taking responsibility for their well- being. Handling doctor-patient relationships collaboratively and providing patients access to their health information are crucial steps in empowering patients. In mental healthcare, the implicit consensus amongst practitioners has been that sharing medical records with patients may have an unpredictable, harmful impact on clinical practice. In order to involve patients more actively in mental healthcare processes, Tele-Board MED (TBM) allows for digital collaborative documentation in therapist-patient sessions. The TBM software system offers a whiteboard-inspired graphical user interface that allows therapist and patient to jointly take notes during the treatment session. Furthermore, it provides features to automatically reuse the digital treatment session notes for the creation of treatment session summaries and clinical case reports. This thesis presents the development of the TBM system and evaluates its effects on 1) the fulfillment of the therapist’s duties of clinical case documentation, 2) patient engagement in care processes, and 3) the therapist-patient relationship. Following the design research methodology, TBM was developed and tested in multiple evaluation studies in the domains of cognitive behavioral psychotherapy and addiction care. The results show that therapists are likely to use TBM with patients if they have a technology-friendly attitude and when its use suits the treatment context. Support in carrying out documentation duties as well as fulfilling legal requirements contributes to therapist acceptance. Furthermore, therapists value TBM as a tool to provide a discussion framework and quick access to worksheets during treatment sessions. Therapists express skepticism, however, regarding technology use in patient sessions and towards complete record transparency in general. Patients expect TBM to improve the communication with their therapist and to offer a better recall of discussed topics when taking a copy of their notes home after the session. Patients are doubtful regarding a possible distraction of the therapist and usage in situations when relationship-building is crucial. When applied in a clinical environment, collaborative note-taking with TBM encourages patient engagement and a team feeling between therapist and patient. Furthermore, it increases the patient’s acceptance of their diagnosis, which in turn is an important predictor for therapy success. In summary, TBM has a high potential to deliver more than documentation support and record transparency for patients, but also to contribute to a collaborative doctor-patient relationship. This thesis provides design implications for the development of digital collaborative documentation systems in (mental) healthcare as well as recommendations for a successful implementation in clinical practice.
Restful choreographies
(2019)
Business process management has become a key instrument to organize work as many companies represent their operations in business process models. Recently, business process choreography diagrams have been introduced as part of the Business Process Model and Notation standard to represent interactions between business processes, run by different partners. When it comes to the interactions between services on the Web, Representational State Transfer (REST) is one of the primary architectural styles employed by web services today. Ideally, the RESTful interactions between participants should implement the interactions defined at the business choreography level.
The problem, however, is the conceptual gap between the business process choreography diagrams and RESTful interactions. Choreography diagrams, on the one hand, are modeled from business domain experts with the purpose of capturing, communicating and, ideally, driving the business interactions. RESTful interactions, on the other hand, depend on RESTful interfaces that are designed by web engineers with the purpose of facilitating the interaction between participants on the internet. In most cases however, business domain experts are unaware of the technology behind web service interfaces and web engineers tend to overlook the overall business goals of web services. While there is considerable work on using process models during process implementation, there is little work on using choreography models to implement interactions between business processes. This thesis addresses this research gap by raising the following research question: How to close the conceptual gap between business process choreographies and RESTful interactions? This thesis offers several research contributions that jointly answer the research question.
The main research contribution is the design of a language that captures RESTful interactions between participants---RESTful choreography modeling language. Formal completeness properties (with respect to REST) are introduced to validate its instances, called RESTful choreographies. A systematic semi-automatic method for deriving RESTful choreographies from business process choreographies is proposed. The method employs natural language processing techniques to translate business interactions into RESTful interactions. The effectiveness of the approach is shown by developing a prototypical tool that evaluates the derivation method over a large number of choreography models.
In addition, the thesis proposes solutions towards implementing RESTful choreographies. In particular, two RESTful service specifications are introduced for aiding, respectively, the execution of choreographies' exclusive gateways and the guidance of RESTful interactions.
During lower sea levels in glacial periods, deep permafrost formed on large continental shelf areas of the Arctic Ocean. Subsequent sea level rise and coastal erosion created subsea permafrost, which generally degrades after inundation under the influence of a complex suite of marine, near-shore processes. Global warming is especially pronounced in the Arctic, and will increase the transition to and the degradation of subsea permafrost, with implications for atmospheric climate forcing, offshore infrastructure, and aquatic ecosystems.
This thesis combines new geophysical, borehole observational and modelling approaches to enhance our understanding of subsea permafrost dynamics. Three specific areas for advancement were identified: (I) sparsity of observational data, (II) lacking implementation of salt infiltration mechanisms in models, and (III) poor understanding of the regional differences in key driving parameters. This study tested the combination of spectral ratios of the ambient vibration seismic wavefield, together with estimated shear wave velocity from seismic interferometry analysis, for estimating the thickness of the unfrozen sediment overlying the ice-bonded permafrost offshore. Mesoscale numerical calculations (10^1 to 10^2 m, thousands of years) were employed to develop and solve the coupled heat diffusion and salt transport equations including phase change effects. Model soil parameters were constrained by borehole data, and the impact of a variety of influences during the transgression was tested in modelling studies. In addition, two inversion schemes (particle swarm optimization and a least-square method) were used to reconstruct temperature histories for the past 200-300 years in the Laptev Sea region in Siberia from two permafrost borehole temperature records. These data were evaluated against larger scale reconstructions from the region.
It was found (I) that peaks in spectral ratios modelled for three-layer, one-dimensional systems corresponded with thaw depths. Around Muostakh Island in the central Laptev Sea seismic receivers were deployed on the seabed. Derived depths of the ice-bonded permafrost table were between 3.7-20.7 m ± 15 %, increasing with distance from the coast. (II) Temperatures modelled during the transition to subsea permafrost resembled isothermal conditions after about 2000 years of inundation at Cape Mamontov Klyk, consistent with observations from offshore boreholes. Stratigraphic scenarios showed that salt distribution and infiltration had a large impact on the ice saturation in the sediments. Three key factors were identified that, when changed, shifted the modelled permafrost thaw depth most strongly: bottom water temperatures, shoreline retreat rate and initial temperature before inundation. Salt transport based on diffusion and contribution from arbitrary density-driven mechanisms only accounted for about 50 % of observed thaw depths at offshore sites hundreds to thousands of years after inundation. This bias was found consistently at all three sites in the Laptev Sea region. (III) In the temperature reconstructions, distinct differences in the local temperature histories between the western Laptev Sea and the Lena Delta sites were recognized, such as a transition to warmer temperatures a century later in the western Laptev Sea as well as a peak in warming three decades later. The local permafrost surface temperature history at Sardakh Island in the Lena Delta was reminiscent of the circum-Arctic regional average trends. However, Mamontov Klyk in the western Laptev Sea was consistent to Arctic trends only in the most recent decade and was more similar to northern hemispheric mean trends. Both sites were consistent with a rapid synoptic recent warming.
In conclusion, the consistency between modelled response, expected permafrost distribution, and observational data suggests that the passive seismic method is promising for the determination of the thickness of unfrozen sediment on the continental Arctic shelf. The quantified gap between currently modelled and observed thaw depths means that the impact of degradation on climate forcing, ecosystems, and infrastructure is larger than current models predict. This discrepancy suggests the importance of further mechanisms of salt penetration and thaw that have not been considered – either pre-inundation or post-inundation, or both. In addition, any meaningful modelling of subsea permafrost would have to constrain the identified key factors and their regional differences well. The shallow permafrost boreholes provide missing well-resolved short-scale temperature information in the coastal permafrost tundra of the Arctic. As local differences from circum-Arctic reconstructions, such as later warming and higher warming magnitude, were shown to exist in this region, these results provide a basis for local surface temperature record parameterization of climate and, in particular, permafrost models. The results of this work bring us one step further to understanding the full picture of the transition from terrestrial to subsea permafrost.
Pillars of Salt
(2019)
Quantum field theory on curved spacetimes is understood as a semiclassical approximation of some quantum theory of gravitation, which models a quantum field under the influence of a classical gravitational field, that is, a curved spacetime. The most remarkable effect predicted by this approach is the creation of particles by the spacetime itself, represented, for instance, by Hawking's evaporation of black holes or the Unruh effect. On the other hand, these aspects already suggest that certain cornerstones of Minkowski quantum field theory, more precisely a preferred vacuum state and, consequently, the concept of particles, do not have sensible counterparts within a theory on general curved spacetimes. Likewise, the implementation of covariance in the model has to be reconsidered, as curved spacetimes usually lack any non-trivial global symmetry. Whereas this latter issue has been resolved by introducing the paradigm of locally covariant quantum field theory (LCQFT), the absence of a reasonable concept for distinct vacuum and particle states on general curved spacetimes has become manifest even in the form of no-go-theorems.
Within the framework of algebraic quantum field theory, one first introduces observables, while states enter the game only afterwards by assigning expectation values to them. Even though the construction of observables is based on physically motivated concepts, there is still a vast number of possible states, and many of them are not reasonable from a physical point of view. We infer that this notion is still too general, that is, further physical constraints are required. For instance, when dealing with a free quantum field theory driven by a linear field equation, it is natural to focus on so-called quasifree states. Furthermore, a suitable renormalization procedure for products of field operators is vitally important. This particularly concerns the expectation values of the energy momentum tensor, which correspond to distributional bisolutions of the field equation on the curved spacetime. J. Hadamard's theory of hyperbolic equations provides a certain class of bisolutions with fixed singular part, which therefore allow for an appropriate renormalization scheme.
By now, this specification of the singularity structure is known as the Hadamard condition and widely accepted as the natural generalization of the spectral condition of flat quantum field theory. Moreover, due to Radzikowski's celebrated results, it is equivalent to a local condition, namely on the wave front set of the bisolution. This formulation made the powerful tools of microlocal analysis, developed by Duistermaat and Hörmander, available for the verification of the Hadamard property as well as the construction of corresponding Hadamard states, which initiated much progress in this field. However, although indispensable for the investigation in the characteristics of operators and their parametrices, microlocal analyis is not practicable for the study of their non-singular features and central results are typically stated only up to smooth objects. Consequently, Radzikowski's work almost directly led to existence results and, moreover, a concrete pattern for the construction of Hadamard bidistributions via a Hadamard series. Nevertheless, the remaining properties (bisolution, causality, positivity) are ensured only modulo smooth functions.
It is the subject of this thesis to complete this construction for linear and formally self-adjoint wave operators acting on sections in a vector bundle over a globally hyperbolic Lorentzian manifold. Based on Wightman's solution of d'Alembert's equation on Minkowski space and the construction for the advanced and retarded fundamental solution, we set up a Hadamard series for local parametrices and derive global bisolutions from them. These are of Hadamard form and we show existence of smooth bisections such that the sum also satisfies the remaining properties exactly.
This is a publication-based dissertation comprising three original research stud-ies (one published, one submitted and one ready for submission; status March 2019). The dissertation introduces a generic computer model as a tool to investigate the behaviour and population dynamics of animals in cyclic environments. The model is further employed for analysing how migratory birds respond to various scenarios of altered food supply under global change. Here, ecological and evolutionary time-scales are considered, as well as the biological constraints and trade-offs the individual faces, which ultimately shape response dynamics at the population level. Further, the effect of fine-scale temporal patterns in re-source supply are studied, which is challenging to achieve experimentally. My findings predict population declines, altered behavioural timing and negative carry-over effects arising in migratory birds under global change. They thus stress the need for intensified research on how ecological mechanisms are affected by global change and for effective conservation measures for migratory birds. The open-source modelling software created for this dissertation can now be used for other taxa and related research questions. Overall, this thesis improves our mechanistic understanding of the impacts of global change on migratory birds as one prerequisite to comprehend ongoing global biodiversity loss. The research results are discussed in a broader ecological and scientific context in a concluding synthesis chapter.
With the emergence of the Internet of things (IoT), plenty of battery-powered and energy-harvesting devices are being deployed to fulfill sensing and actuation tasks in a variety of application areas, such as smart homes, precision agriculture, smart cities, and industrial automation. In this context, a critical issue is that of denial-of-sleep attacks. Such attacks temporarily or permanently deprive battery-powered, energy-harvesting, or otherwise energy-constrained devices of entering energy-saving sleep modes, thereby draining their charge. At the very least, a successful denial-of-sleep attack causes a long outage of the victim device. Moreover, to put battery-powered devices back into operation, their batteries have to be replaced. This is tedious and may even be infeasible, e.g., if a battery-powered device is deployed at an inaccessible location. While the research community came up with numerous defenses against denial-of-sleep attacks, most present-day IoT protocols include no denial-of-sleep defenses at all, presumably due to a lack of awareness and unsolved integration problems. After all, despite there are many denial-of-sleep defenses, effective defenses against certain kinds of denial-of-sleep attacks are yet to be found.
The overall contribution of this dissertation is to propose a denial-of-sleep-resilient medium access control (MAC) layer for IoT devices that communicate over IEEE 802.15.4 links. Internally, our MAC layer comprises two main components. The first main component is a denial-of-sleep-resilient protocol for establishing session keys among neighboring IEEE 802.15.4 nodes. The established session keys serve the dual purpose of implementing (i) basic wireless security and (ii) complementary denial-of-sleep defenses that belong to the second main component. The second main component is a denial-of-sleep-resilient MAC protocol. Notably, this MAC protocol not only incorporates novel denial-of-sleep defenses, but also state-of-the-art mechanisms for achieving low energy consumption, high throughput, and high delivery ratios. Altogether, our MAC layer resists, or at least greatly mitigates, all denial-of-sleep attacks against it we are aware of. Furthermore, our MAC layer is self-contained and thus can act as a drop-in replacement for IEEE 802.15.4-compliant MAC layers. In fact, we implemented our MAC layer in the Contiki-NG operating system, where it seamlessly integrates into an existing protocol stack.
Parlamentarier als Beruf
(2019)
Die politische Professionalisierung hat innerhalb der institutionellen Rahmenbedingungen zur Sozialfigur des Berufspolitikers geführt. Diese Entwicklung wird im theoretischen Teil der Arbeit hergeleitet und im empirischen Teil mit umfangreichen Daten belegt. Bemerkenswert ist, dass es dabei nicht zu erheblichen Veränderungen in den Rekrutierungsmustern und Karriereverläufen der Abgeordneten gekommen ist. Vielmehr erweisen sich die von Dietrich Herzog herausgearbeiteten Karrieretypen auch heute noch als gültig und mussten nur moderat angepasst werden. Es zeigt sich damit eine erstaunliche Kontinuität in der politischen Elitenbildung. Die in Deutschland sehr gefestigten institutionellen Rahmenbedingungen, die den Zugang und die Attraktivität politischer Karrieren determinieren, haben offensichtlich auch zu einer Stabilisierung der Karrieretypen geführt.
Im Mittelpunkt dieser Arbeit standen Analysen zur Charakterisierung der periplasmatischen Aldehyd Oxidoreduktase aus E. coli. Kinetische Untersuchungen mit Ferricyanid als Elektronenakzeptor unter anaeroben Bedingungen zeigten für dieses Enzym eine höhere Aktivität als unter aeroben Bedingungen. Die getroffene Hypothese, dass PaoABC fähig ist Elektronen an molekularen Sauerstoff weiter zu geben, konnte bestätigt werden. Für den Umsatz aromatischer Aldehyde mit molekularem Sauerstoff wurde ein Optimum von pH 6,0 ermittelt. Dies steht im Gegensatz zur Reaktion mit Ferricyanid, mit welchem ein pH-Optimum von 4,0 gezeigt wurde. Die Reaktion von PaoABC mit molekularem Sauerstoff generiert zwar Wasserstoffperoxid, die Produktion von Superoxid konnte dagegen nicht beobachtet werden. Dass aerobe Bedingungen einen Einfluss auf das Auslösen der Expression von PaoABC haben, wurde in dieser Arbeit ebenfalls ermittelt.
Im Zusammenhang mit der Produktion von ROS durch PaoABC wurde die Funktion eines kürzlich in Elektronentransfer-Distanz zum FAD identifizierten [4Fe4S]-Clusters untersucht. Ein Austausch der für die Bindung des Clusters zuständigen Cysteine führte zur Instabilität der Proteinvarianten, weswegen für diese keine weiteren Untersuchungen erfolgten. Daher wird zumindest ein struktur-stabilisierender Einfluss des [4Fe4S]-Clusters angenommen. Zur weiteren Untersuchung der Funktion dieses Clusters, wurde ein zwischen FAD und [4Fe4S]-Cluster lokalisiertes Arginin gegen ein Alanin ausgetauscht. Diese Proteinvariante zeigte eine reduzierte Geschwindigkeit der Reaktion gegenüber dem Wildtyp. Die Bildung von Superoxid konnte auch hier nicht beobachtet werden. Die Vermutung, dass dieser Cluster einen elektronen-sammelnden Mechanismus unterstützt, welcher die Radikalbildung verhindert, kann trotz allem nicht ausgeschlossen werden. Da im Umkreis des Arginins weitere geladene und aromatische Aminosäuren lokalisiert sind, können diese den notwendigen Elektronentransfer übernehmen.
Neben der Ermittlung eines physiologischen Elektronenakzeptors und dessen Einfluss auf die Expression von PaoABC zeigt diese Arbeit auch, dass die Chaperone PaoD und MocA während der Reifung des MCD-Kofaktor eine gemeinsame Bindung an PaoABC realisieren. Es konnte im aktiven Zentrum von PaoABC ein Arginin beschrieben werden, welches auf Grund der engen Nachbarschaft zum MCD-Kofaktor und zum Glutamat (PaoABC-EC692) am Prozess der Substratbindung beteiligt ist. Im Zusammenhang mit dem Austausch dieses Arginins gegen ein Histidin oder ein Lysin wurden die Enzymspezifität und der Einfluss physiologischer Bedingungen, wie pH und Ionenstärke, auf die Reaktion des Enzyms untersucht. Gegenüber dem Wildtyp zeigten die Varianten mit molekularem Sauerstoff eine geringere Affinität zum Substrat aber auch eine höhere Geschwindigkeit der Reaktion. Vor allem für die Histidin-Variante konnte im gesamten pH-Bereich ein instabiles Verhalten bestimmt werden. Der Grund dafür wurde durch das Lösen der Struktur der Histidin-Variante beschreiben. Durch den Austausch der Aminosäuren entfällt die stabilisierende Wirkung der delokalisierten Elektronen des Arginins und es kommt zu einer Konformationsänderung im aktiven Zentrum.
Neben der Reaktion von PaoABC mit einer Vielzahl aromatischer Aldehyde konnte auch der Umsatz von Salicylaldehyd zu Salicylsäure durch PaoABC in einer Farbreaktion bestimmt werden. Durch Ausschluss von molekularem Sauerstoff als terminaler Elektronenakzeptor, in einer enzym-gekoppelten Reaktion, erfolgte ein Elektronentransport auf Ferrocencarboxylsäure. Die Kombination aus beiden Methoden ermöglichte eine Verwendung von Ferrocen-Derivaten zur Generierung einer enzym-gekoppelten Reaktion mit PaoABC.
Die Untersuchungen zu PaoABC zeigen, dass die Vielfalt der durch das Enzym katalysierten Rektionen weitere Möglichkeiten der enzymatischen Bestimmung biokatalytischer Prozesse bietet.