@phdthesis{Niedermayer2012,
  author    = {Niedermayer, Thomas},
  title     = {On the depolymerization of actin filaments},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-63605},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {Actin is one of the most abundant and highly conserved proteins in eukaryotic cells. The globular protein assembles into long filaments, which form a variety of different networks within the cytoskeleton. The dynamic reorganization of these networks - which is pivotal for cell motility, cell adhesion, and cell division - is based on cycles of polymerization (assembly) and depolymerization (disassembly) of actin filaments. Actin binds ATP and within the filament, actin-bound ATP is hydrolyzed into ADP on a time scale of a few minutes. As ADP-actin dissociates faster from the filament ends than ATP-actin, the filament becomes less stable as it grows older. Recent single filament experiments, where abrupt dynamical changes during filament depolymerization have been observed, suggest the opposite behavior, however, namely that the actin filaments become increasingly stable with time. Several mechanisms for this stabilization have been proposed, ranging from structural transitions of the whole filament to surface attachment of the filament ends. The key issue of this thesis is to elucidate the unexpected interruptions of depolymerization by a combination of experimental and theoretical studies. In new depolymerization experiments on single filaments, we confirm that filaments cease to shrink in an abrupt manner and determine the time from the initiation of depolymerization until the occurrence of the first interruption. This duration differs from filament to filament and represents a stochastic variable. We consider various hypothetical mechanisms that may cause the observed interruptions. These mechanisms cannot be distinguished directly, but they give rise to distinct distributions of the time until the first interruption, which we compute by modeling the underlying stochastic processes. A comparison with the measured distribution reveals that the sudden truncation of the shrinkage process neither arises from blocking of the ends nor from a collective transition of the whole filament. Instead, we predict a local transition process occurring at random sites within the filament. The combination of additional experimental findings and our theoretical approach confirms the notion of a local transition mechanism and identifies the transition as the photo-induced formation of an actin dimer within the filaments. Unlabeled actin filaments do not exhibit pauses, which implies that, in vivo, older filaments become destabilized by ATP hydrolysis. This destabilization can be identified with an acceleration of the depolymerization prior to the interruption. In the final part of this thesis, we theoretically analyze this acceleration to infer the mechanism of ATP hydrolysis. We show that the rate of ATP hydrolysis is constant within the filament, corresponding to a random as opposed to a vectorial hydrolysis mechanism.},
  language  = {en}
}
@phdthesis{PerdigonToro2022,
  author    = {Perdig{\´o}n-Toro, Lorena},
  title     = {On the Generation and Fate of Free Carriers in Non-Fullerene Acceptor Organic Solar Cells},
  doi       = {10.25932/publishup-55807},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-558072},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 191},
  year      = {2022},
  abstract  = {Organic solar cells offer an efficient and cost-effective alternative for solar energy harvesting. This type of photovoltaic cell typically consists of a blend of two organic semiconductors, an electron donating polymer and a low molecular weight electron acceptor to create what is known as a bulk heterojunction (BHJ) morphology. Traditionally, fullerene-based acceptors have been used for this purpose. In recent years, the development of new acceptor molecules, so-called non-fullerene acceptors (NFA), has breathed new life into organic solar cell research, enabling record efficiencies close to 19\%. Today, NFA-based solar cells are approaching their inorganic competitors in terms of photocurrent generation, but lag in terms of open circuit voltage (V_OC). Interestingly, the V_OC of these cells benefits from small offsets of orbital energies at the donor-NFA interface, although previous knowledge considered large energy offsets to be critical for efficient charge carrier generation. In addition, there are several other electronic and structural features that distinguish NFAs from fullerenes. My thesis focuses on understanding the interplay between the unique attributes of NFAs and the physical processes occurring in solar cells. By combining various experimental techniques with drift-diffusion simulations, the generation of free charge carriers as well as their recombination in state-of-the-art NFA-based solar cells is characterized. For this purpose, solar cells based on the donor polymer PM6 and the NFA Y6 have been investigated. The generation of free charge carriers in PM6:Y6 is efficient and independent of electric field and excitation energy. Temperature-dependent measurements show a very low activation energy for photocurrent generation (about 6 meV), indicating barrierless charge carrier separation. Theoretical modeling suggests that Y6 molecules have large quadrupole moments, leading to band bending at the donor-acceptor interface and thereby reducing the electrostatic Coulomb dissociation barrier. In this regard, this work identifies poor extraction of free charges in competition with nongeminate recombination as a dominant loss process in PM6:Y6 devices. Subsequently, the spectral characteristics of PM6:Y6 solar cells were investigated with respect to the dominant process of charge carrier recombination. It was found that the photon emission under open-circuit conditions can be almost entirely attributed to the occupation and recombination of Y6 singlet excitons. Nevertheless, the recombination pathway via the singlet state contributes only 1\% to the total recombination, which is dominated by the charge transfer state (CT-state) at the donor-acceptor interface. Further V_OC gains can therefore only be expected if the density and/or recombination rate of these CT-states can be significantly reduced. Finally, the role of energetic disorder in NFA solar cells is investigated by comparing Y6 with a structurally related derivative, named N4. Layer morphology studies combined with temperature-dependent charge transport experiments show significantly lower structural and energetic disorder in the case of the PM6:Y6 blend. For both PM6:Y6 and PM6:N4, disorder determines the maximum achievable V_OC, with PM6:Y6 benefiting from improved morphological order. Overall, the obtained findings point to avenues for the realization of NFA-based solar cells with even smaller V_OC losses. Further reduction of nongeminate recombination and energetic disorder should result in organic solar cells with efficiencies above 20\% in the future.},
  language  = {en}
}
@phdthesis{Albers2006,
  author    = {Albers, Nicole},
  title     = {On the relevance of adhesion : applications to Saturn's rings},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10848},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Since their discovery in 1610 by Galileo Galilei, Saturn's rings continue to fascinate both experts and amateurs. Countless numbers of icy grains in almost Keplerian orbits reveal a wealth of structures such as ringlets, voids and gaps, wakes and waves, and many more. Grains are found to increase in size with increasing radial distance to Saturn. Recently discovered "propeller" structures in the Cassini spacecraft data, provide evidence for the existence of embedded moonlets. In the wake of these findings, the discussion resumes about origin and evolution of planetary rings, and growth processes in tidal environments. In this thesis, a contact model for binary adhesive, viscoelastic collisions is developed that accounts for agglomeration as well as restitution. Collisional outcomes are crucially determined by the impact speed and masses of the collision partners and yield a maximal impact velocity at which agglomeration still occurs. Based on the latter, a self-consistent kinetic concept is proposed. The model considers all possible collisional outcomes as there are coagulation, restitution, and fragmentation. Emphasizing the evolution of the mass spectrum and furthermore concentrating on coagulation alone, a coagulation equation, including a restricted sticking probability is derived. The otherwise phenomenological Smoluchowski equation is reproduced from basic principles and denotes a limit case to the derived coagulation equation. Qualitative and quantitative analysis of the relevance of adhesion to force-free granular gases and to those under the influence of Keplerian shear is investigated. Capture probability, agglomerate stability, and the mass spectrum evolution are investigated in the context of adhesive interactions. A size dependent radial limit distance from the central planet is obtained refining the Roche criterion. Furthermore, capture probability in the presence of adhesion is generally different compared to the case of pure gravitational capture. In contrast to a Smoluchowski-type evolution of the mass spectrum, numerical simulations of the obtained coagulation equation revealed, that a transition from smaller grains to larger bodies cannot occur via a collisional cascade alone. For parameters used in this study, effective growth ceases at an average size of centimeters.},
  subject      = {Saturn<Planet>},
  language  = {en}
}
@phdthesis{Arora2018,
  author    = {Arora, Ashima},
  title     = {Optical and electric field control of magnetism},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-421479},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ii, 126},
  year      = {2018},
  abstract  = {Future magnetic recording industry needs a high-density data storage technology. However, switching the magnetization of small bits requires high magnetic fields that cause excessive heat dissipation. Therefore, controlling magnetism without applying external magnetic field is an important research topic for potential applications in data storage devices with low power consumption. Among the different approaches being investigated, two of them stand out, namely i) all-optical helicity dependent switching (AO-HDS) and ii) ferroelectric control of magnetism. This thesis aims to contribute towards a better understanding of the physical processes behinds these effects as well as reporting new and exciting possibility for the optical and/or electric control of magnetic properties. Hence, the thesis contains two differentiated chapters of results; the first devoted to AO-HDS on TbFe alloys and the second to the electric field control of magnetism in an archetypal Fe/BaTiO3 system. In the first part, the scalability of the AO-HDS to small laser spot-sizes of few microns in the ferrimagnetic TbFe alloy is investigated by spatially resolving the magnetic contrast with photo-emission electron microscopy (PEEM) and X-ray magnetic circular dichroism (XMCD). The results show that the AO-HDS is a local effect within the laser spot size that occurs in the ring-shaped region in the vicinity of thermal demagnetization. Within the ring region, the helicity dependent switching occurs via thermally activated domain wall motion. Further, the thesis reports on a novel effect of thickness dependent inversion of the switching orientation. It addresses some of the important questions like the role of laser heating and the microscopic mechanism driving AO-HDS. The second part of the thesis focuses on the electric field control of magnetism in an artificial multiferroic heterostructure. The sample consists of an Fe wedge with thickness varying between 0:5 nm and 3 nm, deposited on top of a ferroelectric and ferroelastic BaTiO3 [001]-oriented single crystal substrate. Here, the magnetic contrast is imaged via PEEM and XMCD as a function of out-of-plane voltage. The results show the evidence of the electric field control of superparamagnetism mediated by a ferroelastic modification of the magnetic anisotropy. The changes in the magnetoelastic anisotropy drive the transition from the superparamagnetic to superferromagnetic state at localized sample positions.},
  language  = {en}
}
@phdthesis{Sharma2023,
  author    = {Sharma, Anjali},
  title     = {Optical manipulation of multi-responsive microgels},
  school      = {Universit{\"a}t Potsdam},
  pages     = {207},
  year      = {2023},
  abstract  = {This dissertation focuses on the understanding of the optical manipulation of microgels dispersed in aqueous solution of azobenzene containing surfactant. The work consists of three parts where each part is a systematic investigation of the (1) photo-isomerization kinetics of the surfactant in complex with the microgel polymer matrix, (2) light driven diffusiosmosis (LDDO) in microgels and (3) photo-responsivity of microgel on complexation with spiropyran. The first part comprises three publications where the first one [P1] investigates the photo-isomerization kinetics and corresponding isomer composition at a photo-stationary state of the photo-sensitive surfactant conjugated with charged polymers or micro sized polymer networks to understand the structural response of such photo-sensitive complexes. We report that the photo-isomerization of the azobenzene-containing cationic surfactant is slower in a polymer complex compared to being purely dissolved in an aqueous solution. The surfactant aggregates near the polyelectrolyte chains at concentrations much lower than the bulk critical micelle concentration. This, along with the inhibition of the photo-isomerization kinetics due to steric hindrance within the densely packed aggregates, pushes the isomer-ratio to a higher trans-isomer concentration for all irradiation wavelengths. The second publication [P2] combines experimental results and non-adiabatic dynamic simulations for the same surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the slowdown in photo induced trans → cis azobenzene isomerization at concentrations higher than the critical micelle concentration (CMC). The simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles and observes a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans → cis switching in micelles of the azobenzene-containing surfactants. Finally, the third publication [P3] focusses on the kinetics of adsorption and desorption of the same surfactant within anionic microgels in the dark and under continuous irradiation. Experimental data demonstrate, that microgels can serve as a selective absorber of the trans isomers. The interaction of the isomers with the gel matrix induces a remotely controllable collapse or swelling on appropriate irradiation wavelengths. Measuring the kinetics of the microgel size response and knowing the exact isomer composition under light exposure, we calculate the adsorption rate of the trans-isomers. The second part comprises two publications. The first publication [P4] reports on the phenomenon of light-driven diffusioosmotic (DO) long-range attractive and repulsive interactions between micro-sized objects, whose range extends several times the size of microparticles and can be adjusted to point towards or away from the particle by varying irradiation parameters such as intensity or wavelength of light. The phenomenon is fueled by the aforementioned photosensitive surfactant. The complex interaction of dynamic exchange of isomers and photo-isomerization rate yields to relative concentrations gradients of the isomers in the vicinity of micro-sized object inducing a local diffusioosmotic (DO) flow thereby making a surface act as a micropump. The second publication [P5] exclusively aims the visualization and investigation of the DO flows generated from microgels by using small tracer particles. Similar to micro sized objects, the flow is able to push adjacent tracers over distances several times larger than microgel size. Here we report that the direction and the strength of the l-LDDO depends on the intensity, irradiation wavelength and the amount of surfactant adsorbed by the microgel. For example, the flow pattern around a microgel is directed radially outward and can be maintained quasi-indefinitely under exposure at 455 nm when the trans:cis ratio is 2:1, whereas irradiation at 365 nm, generates a radially transient flow pattern, which inverts at lower intensities. Lastly, the third part consists of one publication [P6] which, unlike the previous works, reports on the study of the kinetics of photo- and thermo-switching of a new surfactant namely, spiropyran, upon exposure with light of different wavelengths and its interaction with p(NIPAM-AA) microgels. The surfactant being an amphiphile, switches between its ring closed spiropyran (SP) form and ring open merocyanine (MC) form which results in a change in the hydrophilic-hydrophobic balance of the surfactant as MC being a zwitterionic form along with the charged head group, generates three charges on the molecule. Therefore, the MC form of the surfactant is more hydrophilic than in the case of the neutral SP state. Here, we investigate the initial shrinkage of the gel particles via charge compensation on first exposure to SP molecules which results from the complex formation of the molecules with the gel matrix, triggering them to become photo responsive. The size and VPTT of the microgels during irradiation is shown to be a combination of heating up of the solution during light absorption by the surfactant (more pronounced in the case of UV irradiation) and the change in the hydrophobicity of the surfactant.},
  language  = {en}
}
@phdthesis{ThielemannKuehn2017,
  author    = {Thielemann-K{\"u}hn, Nele},
  title     = {Optically induced ferro- and antiferromagnetic dynamics in the rare-earth metal dysprosium},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402994},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iv, 121},
  year      = {2017},
  abstract  = {Approaching physical limits in speed and size of today's magnetic storage and processing technologies demands new concepts for controlling magnetization and moves researches on optically induced magnetic dynamics. Studies on photoinduced magnetization dynamics and their underlying mechanisms have been primarily performed on ferromagnetic metals. Ferromagnetic dynamics bases on transfer of the conserved angular momentum connected with atomic magnetic moments out of the parallel aligned magnetic system into other degrees of freedom. In this thesis the so far rarely studied response of antiferromagnetic order to ultra-short optical laser pulses in a metal is investigated. The experiments were performed at the FemtoSpex slicing facility at the storage ring BESSY II, an unique source for ultra-short elliptically polarized x-ray pulses. Laser-induced changes of the 4f-magnetic order parameter in ferro- and antiferromagnetic dysprosium (Dy), were studied by x-ray methods, which yield directly comparable quantities. The discovered fundamental differences in the temporal and spatial behavior of ferro- and antiferrmagnetic dynamics are assinged to an additional channel for angular momentum transfer, which reduces the antiferromagnetic order by redistributing angular momentum within the non-parallel aligned magnetic system, and hence conserves the zero net magnetization. It is shown that antiferromagnetic dynamics proceeds considerably faster and more energy-efficient than demagnetization in ferromagnets. By probing antiferromagnetic order in time and space, it is found to be affected along the whole sample depth of an in situ grown 73 nm tick Dy film. Interatomic transfer of angular momentum via fast diffusion of laser-excited 5d electrons is held responsible for the out-most long-ranging effect. Ultrafast ferromagnetic dynamics can be expected to base on the same origin, which however leads to demagnetization only in regions close to interfaces caused by super-diffusive spin transport. Dynamics due to local scattering processes of excited but less mobile electrons, occur in both magnetic alignments only in directly excited regions of the sample and on slower pisosecond timescales. The thesis provides fundamental insights into photoinduced magnetic dynamics by directly comparing ferro- and antiferromagnetic dynamics in the same material and by consideration of the laser-induced magnetic depth profile.},
  language  = {en}
}
@phdthesis{GostkowskaLekner2024,
  author    = {Gostkowska-Lekner, Natalia Katarzyna},
  title     = {Organic-inorganic hybrids based on P3HT and mesoporous silicon for thermoelectric applications},
  doi       = {10.25932/publishup-62047},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-620475},
  school      = {Universit{\"a}t Potsdam},
  pages     = {121},
  year      = {2024},
  abstract  = {This thesis presents a comprehensive study on synthesis, structure and thermoelectric transport properties of organic-inorganic hybrids based on P3HT and porous silicon. The effect of embedding polymer in silicon pores on the electrical and thermal transport is studied. Morphological studies confirm successful polymer infiltration and diffusion doping with roughly 50\% of the pore space occupied by conjugated polymer. Synchrotron diffraction experiments reveal no specific ordering of the polymer inside the pores. P3HT-pSi hybrids show improved electrical transport by five orders of magnitude compared to porous silicon and power factor values comparable or exceeding other P3HT-inorganic hybrids. The analysis suggests different transport mechanisms in both materials. In pSi, the transport mechanism relates to a Meyer-Neldel compansation rule. The analysis of hybrids' data using the power law in Kang-Snyder model suggests that a doped polymer mainly provides charge carriers to the pSi matrix, similar to the behavior of a doped semiconductor. Heavily suppressed thermal transport in porous silicon is treated with a modified Landauer/Lundstrom model and effective medium theories, which reveal that pSi agrees well with the Kirkpatrick model with a 68\% percolation threshold. Thermal conductivities of hybrids show an increase compared to the empty pSi but the overall thermoelectric figure of merit ZT of P3HT-pSi hybrid exceeds both pSi and P3HT as well as bulk Si.},
  language  = {en}
}
@phdthesis{KranjcHorvat2022,
  author    = {Kranjc Horvat, Anja},
  title     = {Particle physics in high-school education},
  doi       = {10.25932/publishup-56026},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-560260},
  school      = {Universit{\"a}t Potsdam},
  pages     = {137},
  year      = {2022},
  abstract  = {Elementary particle physics is a contemporary topic in science that is slowly being integrated into high-school education. These new implementations are challenging teachers' professional knowledge worldwide. Therefore, physics education research is faced with two important questions, namely, how can particle physics be integrated in high-school physics curricula and how best to support teachers in enhancing their professional knowledge on particle physics. This doctoral research project set up to provide better guidelines for answering these two questions by conducting three studies on high-school particle physics education. First, an expert concept mapping study was conducted to elicit experts' expectations on what high-school students should learn about particle physics. Overall, 13 experts in particle physics, computing, and physics education participated in 9 concept mapping rounds. The broad knowledge base of the experts ensured that the final expert concept map covers all major particle physics aspects. Specifically, the final expert concept map includes 180 concepts and examples, connected with 266 links and crosslinks. Among them are also several links to students' prior knowledge in topics such as mechanics and thermodynamics. The high interconnectedness of the concepts shows possible opportunities for including particle physics as a context for other curricular topics. As such, the resulting expert concept map is showcased as a well-suited tool for teachers to scaffold their instructional practice. Second, a review of 27 high-school physics curricula was conducted. The review uncovered which concepts related to particle physics can be identified in most curricula. Each curriculum was reviewed by two reviewers that followed a codebook with 60 concepts related to particle physics. The analysis showed that most curricula mention cosmology, elementary particles, and charges, all of which are considered theoretical particle physics concepts. None of the experimental particle physics concepts appeared in more than half of the reviewed curricula. Additional analysis was done on two curricular subsets, namely curricula with and curricula without an explicit particle physics chapter. Curricula with an explicit particle physics chapter mention several additional explicit particle physics concepts, namely the Standard Model of particle physics, fundamental interactions, antimatter research, and particle accelerators. The latter is an example of experimental particle physics concepts. Additionally, the analysis revealed that, overall, most curricula include Nature of Science and history of physics, albeit both are typically used as context or as a tool for teaching, respectively. Third, a Delphi study was conducted to investigate stakeholders' expectations regarding what teachers should learn in particle physics professional development programmes. Over 100 stakeholders from 41 countries represented four stakeholder groups, namely physics education researchers, research scientists, government representatives, and high-school teachers. The study resulted in a ranked list of the 13 most important topics to be included in particle physics professional development programmes. The highest-ranked topics are cosmology, the Standard Model, and real-life applications of particle physics. All stakeholder groups agreed on the overall ranking of the topics. While the highest-ranked topics are again more theoretical, stakeholders also expect teachers to learn about experimental particle physics topics, which are ranked as medium importance topics. The three studies addressed two research aims of this doctoral project. The first research aim was to explore to what extent particle physics is featured in high-school physics curricula. The comparison of the outcomes of the curricular review and the expert concept map showed that curricula cover significantly less than what experts expect high-school students to learn about particle physics. For example, most curricula do not include concepts that could be classified as experimental particle physics. However, the strong connections between the different concept show that experimental particle physics can be used as context for theoretical particle physics concepts, Nature of Science, and other curricular topics. In doing so, particle physics can be introduced in classrooms even though it is not (yet) explicitly mentioned in the respective curriculum. The second research aim was to identify which aspects of content knowledge teachers are expected to learn about particle physics. The comparison of the Delphi study results to the outcomes of the curricular review and the expert concept map showed that stakeholders generally expect teachers to enhance their school knowledge as defined by the curricula. Furthermore, teachers are also expected to enhance their deeper school knowledge by learning how to connect concepts from their school knowledge to other concepts in particle physics and beyond. As such, professional development programmes that focus on enhancing teachers' school knowledge and deeper school knowledge best support teachers in building relevant context in their instruction. Overall, this doctoral research project reviewed the current state of high-school particle physics education and provided guidelines for future enhancements of the particle physics content in high-school student and teacher education. The outcomes of the project support further implementations of particle physics in high-school education both as explicit content and as context for other curricular topics. Furthermore, the mixed-methods approach and the outcomes of this research project lead to several implications for professional development programmes and science education research, that are discussed in the final chapters of this dissertation.},
  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{Toenjes2007,
  author    = {T{\"o}njes, Ralf},
  title     = {Pattern formation through synchronization in systems of nonidentical autonomous oscillators},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-15973},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {This work is concerned with the spatio-temporal structures that emerge when non-identical, diffusively coupled oscillators synchronize. It contains analytical results and their confirmation through extensive computer simulations. We use the Kuramoto model which reduces general oscillatory systems to phase dynamics. The symmetry of the coupling plays an important role for the formation of patterns. We have studied the ordering influence of an asymmetry (non-isochronicity) in the phase coupling function on the phase profile in synchronization and the intricate interplay between this asymmetry and the frequency heterogeneity in the system. The thesis is divided into three main parts. Chapter 2 and 3 introduce the basic model of Kuramoto and conditions for stable synchronization. In Chapter 4 we characterize the phase profiles in synchronization for various special cases and in an exponential approximation of the phase coupling function, which allows for an analytical treatment. Finally, in the third part (Chapter 5) we study the influence of non-isochronicity on the synchronization frequency in continuous, reaction diffusion systems and discrete networks of oscillators.},
  language  = {en}
}
@phdthesis{Li2008,
  author    = {Li, Yanhong},
  title     = {Phase separation in giant vesicles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-29138},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Giant vesicles may contain several spatial compartments formed by phase separation within their enclosed aqueous solution. This phenomenon might be related to molecular crowding, fractionation and protein sorting in cells. To elucidate this process we used two chemically dissimilar polymers, polyethylene glycol (PEG) and dextran, encapsulated in giant vesicles. The dynamics of the phase separation of this polymer solution enclosed in vesicles is studied by concentration quench, i.e. exposing the vesicles to hypertonic solutions. The excess membrane area, produced by dehydration, can either form tubular structures (also known as tethers) or be utilized to perform morphological changes of the vesicle, depending on the interfacial tension between the coexisting phases and those between the membrane and the two phases. Membrane tube formation is coupled to the phase separation process. Apparently, the energy released from the phase separation is utilized to overcome the energy barrier for tube formation. The tubes may be absorbed at the interface to form a 2-demensional structure. The membrane stored in the form of tubes can be retracted under small tension perturbation. Furthermore, a wetting transition, which has been reported only in a few experimental systems, was discovered in this system. By increasing the polymer concentration, the PEG-rich phase changed from complete wetting to partial wetting of the membrane. If sufficient excess membrane area is available in the vesicle where both phases wet the membrane, one of the phases will bud off from the vesicle body, which leads to the separation of the two phases. This wetting-induced budding is governed by the surface energy and modulated by the membrane tension. This was demonstrated by micropipette aspiration experiments on vesicles encapsulating two phases. The budding of one phase can significantly decrease the surface energy by decreasing the contact area between the coexisting phases. The elasticity of the membrane allows it to adjust its tension automatically to balance the pulling force exerted by the interfacial tension of the two liquid phases at the three-phase contact line. The budding of the phase enriched with one polymer may be relevant to the selective protein transportation among lumens by means of vesicle in cells.},
  language  = {en}
}
@phdthesis{Allefeld2004,
  author    = {Allefeld, Carsten},
  title     = {Phase synchronization analysis of event-related brain potentials in language processing},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001873},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Das Forschungsthema Synchronisation bildet einen Schnittpunkt von Nichtlinearer Dynamik und Neurowissenschaft. So hat zum einen neurobiologische Forschung gezeigt, daß die Synchronisation neuronaler Aktivit{\"a}t einen wesentlichen Aspekt der Funktionsweise des Gehirns darstellt. Zum anderen haben Fortschritte in der physikalischen Theorie zur Entdeckung des Ph{\"a}nomens der Phasensynchronisation gef{\"u}hrt. Eine dadurch motivierte Datenanalysemethode, die Phasensynchronisations-Analyse, ist bereits mit Erfolg auf empirische Daten angewandt worden. Die vorliegende Dissertation kn{\"u}pft an diese konvergierenden Forschungslinien an. Ihren Gegenstand bilden methodische Beitr{\"a}ge zur Fortentwicklung der Phasensynchronisations-Analyse, sowie deren Anwendung auf ereigniskorrelierte Potentiale, eine besonders in den Kognitionswissenschaften wichtige Form von EEG-Daten. Die methodischen Beitr{\"a}ge dieser Arbeit bestehen zum ersten in einer Reihe spezialisierter statistischer Tests auf einen Unterschied der Synchronisationsst{\"a}rke in zwei verschiedenen Zust{\"a}nden eines Systems zweier Oszillatoren. Zweitens wird im Hinblick auf den viel-kanaligen Charakter von EEG-Daten ein Ansatz zur multivariaten Phasensynchronisations-Analyse vorgestellt. Zur empirischen Untersuchung neuronaler Synchronisation wurde ein klassisches Experiment zur Sprachverarbeitung repliziert, in dem der Effekt einer semantischen Verletzung im Satzkontext mit demjenigen der Manipulation physischer Reizeigenschaften (Schriftfarbe) verglichen wird. Hier zeigt die Phasensynchronisations-Analyse eine Verringerung der globalen Synchronisationsst{\"a}rke f{\"u}r die semantische Verletzung sowie eine Verst{\"a}rkung f{\"u}r die physische Manipulation. Im zweiten Fall l{\"a}ßt sich der global beobachtete Synchronisationseffekt mittels der multivariaten Analyse auf die Interaktion zweier symmetrisch gelegener Gehirnareale zur{\"u}ckf{\"u}hren. Die vorgelegten Befunde zeigen, daß die physikalisch motivierte Methode der Phasensynchronisations-Analyse einen wesentlichen Beitrag zur Untersuchung ereigniskorrelierter Potentiale in den Kognitionswissenschaften zu leisten vermag.},
  language  = {en}
}
@phdthesis{Ata2016,
  author    = {Ata, Metin},
  title     = {Phase-space reconstructions of cosmic velocities and the cosmic web},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403565},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 155},
  year      = {2016},
  abstract  = {In the current paradigm of cosmology, the formation of large-scale structures is mainly driven by non-radiating dark matter, making up the dominant part of the matter budget of the Universe. Cosmological observations however, rely on the detection of luminous galaxies, which are biased tracers of the underlying dark matter. In this thesis I present cosmological reconstructions of both, the dark matter density field that forms the cosmic web, and cosmic velocities, for which both aspects of my work are delved into, the theoretical formalism and the results of its applications to cosmological simulations and also to a galaxy redshift survey.The foundation of our method is relying on a statistical approach, in which a given galaxy catalogue is interpreted as a biased realization of the underlying dark matter density field. The inference is computationally performed on a mesh grid by sampling from a probability density function, which describes the joint posterior distribution of matter density and the three dimensional velocity field. The statistical background of our method is described in Chapter "Implementation of argo", where the introduction in sampling methods is given, paying special attention to Markov Chain Monte-Carlo techniques. In Chapter "Phase-Space Reconstructions with N-body Simulations", I introduce and implement a novel biasing scheme to relate the galaxy number density to the underlying dark matter, which I decompose into a deterministic part, described by a non-linear and scale-dependent analytic expression, and a stochastic part, by presenting a negative binomial (NB) likelihood function that models deviations from Poissonity. Both bias components had already been studied theoretically, but were so far never tested in a reconstruction algorithm. I test these new contributions againstN-body simulations to quantify improvements and show that, compared to state-of-the-art methods, the stochastic bias is inevitable at wave numbers of k≥0.15h Mpc^-1 in the power spectrum in order to obtain unbiased results from the reconstructions. In the second part of Chapter "Phase-Space Reconstructions with N-body Simulations" I describe and validate our approach to infer the three dimensional cosmic velocity field jointly with the dark matter density. I use linear perturbation theory for the large-scale bulk flows and a dispersion term to model virialized galaxy motions, showing that our method is accurately recovering the real-space positions of the redshift-space distorted galaxies. I analyze the results with the isotropic and also the two-dimensional power spectrum.Finally, in Chapter "Phase-space Reconstructions with Galaxy Redshift Surveys", I show how I combine all findings and results and apply the method to the CMASS (for Constant (stellar) Mass) galaxy catalogue of the Baryon Oscillation Spectroscopic Survey (BOSS). I describe how our method is accounting for the observational selection effects inside our reconstruction algorithm. Also, I demonstrate that the renormalization of the prior distribution function is mandatory to account for higher order contributions in the structure formation model, and finally a redshift-dependent bias factor is theoretically motivated and implemented into our method. The various refinements yield unbiased results of the dark matter until scales of k≤0.2 h Mpc^-1in the power spectrum and isotropize the galaxy catalogue down to distances of r∼20h^-1 Mpc in the correlation function. We further test the results of our cosmic velocity field reconstruction by comparing them to a synthetic mock galaxy catalogue, finding a strong correlation between the mock and the reconstructed velocities. The applications of both, the density field without redshift-space distortions, and the velocity reconstructions, are very broad and can be used for improved analyses of the baryonic acoustic oscillations, environmental studies of the cosmic web, the kinematic Sunyaev-Zel'dovic or integrated Sachs-Wolfe effect.},
  language  = {en}
}
@phdthesis{Holler2014,
  author    = {Holler, Markus},
  title     = {Photon reconstruction for the H.E.S.S. 28 m telescope and analysis of Crab Nebula and galactic centre observations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-72099},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {In the presented thesis, the most advanced photon reconstruction technique of ground-based γ-ray astronomy is adapted to the H.E.S.S. 28 m telescope. The method is based on a semi-analytical model of electromagnetic particle showers in the atmosphere. The properties of cosmic γ-rays are reconstructed by comparing the camera image of the telescope with the Cherenkov emission that is expected from the shower model. To suppress the dominant background from charged cosmic rays, events are selected based on several criteria. The performance of the analysis is evaluated with simulated events. The method is then applied to two sources that are known to emit γ-rays. The first of these is the Crab Nebula, the standard candle of ground-based γ-ray astronomy. The results of this source confirm the expected performance of the reconstruction method, where the much lower energy threshold compared to H.E.S.S. I is of particular importance. A second analysis is performed on the region around the Galactic Centre. The analysis results emphasise the capabilities of the new telescope to measure γ-rays in an energy range that is interesting for both theoretical and experimental astrophysics. The presented analysis features the lowest energy threshold that has ever been reached in ground-based γ-ray astronomy, opening a new window to the precise measurement of the physical properties of time-variable sources at energies of several tens of GeV.},
  language  = {en}
}
@phdthesis{Diercke2021,
  author    = {Diercke, Andrea},
  title     = {Physical environment of large-scale high-latitude and polar crown filaments},
  doi       = {10.25932/publishup-51130},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-511301},
  school      = {Universit{\"a}t Potsdam},
  pages     = {133},
  year      = {2021},
  abstract  = {Filaments are omnipresent features in the solar chromosphere, one of the atmospheric layers of the Sun, which is located above the photosphere, the visible surface of the Sun. They are clouds of plasma reaching from the photosphere to the chromosphere, and even to the outer-most atmospheric layer, the corona. They are stabalized by the magnetic field. If the magnetic field is disturbed, filaments can erupt as coronal mass ejections (CME), releasing plasma into space, which can also hit the Earth. A special type of filaments are polar crown filaments, which form at the interface of the unipolar field of the poles and flux of opposite magnetic polarity, which was transported towards the poles. This flux transport is related to the global dynamo of the Sun and can therefore be analyzed indirectly with polar crown filaments. The main objective of this thesis is to better understand the physical properties and environment of high-latitude and polar crown filaments, which can be approached from two perspectives: (1) analyzing the large-scale properties of high-latitude and polar crown filaments with full-disk Hα observations from the Chromospheric Telescope (ChroTel) and (2) determining the relation of polar crown and high-latitude filaments from the chromosphere to the lower-lying photosphere with high-spatial resolution observations of the Vacuum Tower Telescope (VTT), which reveal the smallest details. The Chromospheric Telescope (ChroTel) is a small 10-cm robotic telescope at Observatorio del Teide on Tenerife (Spain), which observes the entire Sun in Hα, Ca IIK, and He I 10830 {\AA}. We present a new calibration method that includes limb-darkening correction, removal of non-uniform filter transmission, and determination of He I Doppler velocities. Chromospheric full-disk filtergrams are often obtained with Lyot filters, which may display non-uniform transmission causing large-scale intensity variations across the solar disk. Removal of a 2D symmetric limb-darkening function from full-disk images results in a flat background. However, transmission artifacts remain and are even more distinct in these contrast-enhanced images. Zernike polynomials are uniquely appropriate to fit these large-scale intensity variations of the background. The Zernike coefficients show a distinct temporal evolution for ChroTel data, which is likely related to the telescope's alt-azimuth mount that introduces image rotation. In addition, applying this calibration to sets of seven filtergrams that cover the He I triplet facilitates determining chromospheric Doppler velocities. To validate the method, we use three datasets with varying levels of solar activity. The Doppler velocities are benchmarked with respect to co-temporal high-resolution spectroscopic data of the GREGOR Infrared Spectrograph (GRIS). Furthermore, this technique can be applied to ChroTel Hα and Ca IIK data. The calibration method for ChroTel filtergrams can be easily adapted to other full-disk data exhibiting unwanted large-scale variations. The spectral region of the He I triplet is a primary choice for high-resolution near-infrared spectropolarimetry. Here, the improved calibration of ChroTel data will provide valuable context data. Polar crown filaments form above the polarity inversion line between the old magnetic flux of the previous cycle and the new magnetic flux of the current cycle. Studying their appearance and their properties can lead to a better understanding of the solar cycle. We use full-disk data of the ChroTel at Observatorio del Teide, Tenerife, Spain, which were taken in three different chromospheric absorption lines (Hα 6563 {\AA}, Ca IIK 3933 {\AA}, and He I 10830 {\AA}), and we create synoptic maps. In addition, the spectroscopic He I data allow us to compute Doppler velocities and to create synoptic Doppler maps. ChroTel data cover the rising and decaying phase of Solar Cycle 24 on about 1000 days between 2012 and 2018. Based on these data, we automatically extract polar crown filaments with image-processing tools and study their properties. We compare contrast maps of polar crown filaments with those of quiet-Sun filaments. Furthermore, we present a super-synoptic map summarizing the entire ChroTel database. In summary, we provide statistical properties, i.e. number and location of filaments, area, and tilt angle for both the maximum and declining phase of Solar Cycle 24. This demonstrates that ChroTel provides a promising dataset to study the solar cycle. The cyclic behavior of polar crown filaments can be monitored by regular full-disk Hα observations. ChroTel provides such regular observations of the Sun in three chromospheric wavelengths. To analyze the cyclic behavior and the statistical properties of polar crown filaments, we have to extract the filaments from the images. Manual extraction is tedious, and extraction with morphological image processing tools produces a large number of false positive detections and the manual extraction of these takes too much time. Automatic object detection and extraction in a reliable manner allows us to process more data in a shorter time. We will present an overview of the ChroTel database and a proof of concept of a machine learning application, which allows us a unified extraction of, for example, filaments from ChroTel data. The chromospheric Hα spectral line dominates the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of magnetic activity. For the Sun, other tracers are typically used to monitor solar activity. Nonetheless, the Sun is observed constantly in Hα with globally distributed ground-based full-disk imagers. The aim of this study is to introduce Hα as a tracer of solar activity and compare it to other established indicators. We discuss the newly created imaging Hα excess in the perspective of possible application for modelling of stellar atmospheres. In particular, we try to determine how constant is the mean intensity of the Hα excess and number density of low-activity regions between solar maximum and minimum. Furthermore, we investigate whether the active region coverage fraction or the changing emission strength in the active regions dominates time variability in solar Hα observations. We use ChroTel observations of full-disk Hα filtergrams and morphological image processing techniques to extract the positive and negative imaging Hα excess, for bright features (plage regions) and dark absorption features (filaments and sunspots), respectively. We describe the evolution of the Hα excess during Solar Cycle 24 and compare it to other well established tracers: the relative sunspot number, the F10.7 cm radio flux, and the Mg II index. Moreover, we discuss possible applications of the Hα excess for stellar activity diagnostics and the contamination of exoplanet transmission spectra. The positive and negative Hα excess follow the behavior of the solar activity over the course of the cycle. Thereby, positive Hα excess is closely correlated to the chromospheric Mg II index. On the other hand, the negative Hα excess, created from dark features like filaments and sunspots, is introduced as a tracer of solar activity for the first time. We investigated the mean intensity distribution for active regions for solar minimum and maximum and found that the shape of both distributions is very similar but with different amplitudes. This might be related with the relatively stable coronal temperature component during the solar cycle. Furthermore, we found that the coverage fraction of Hα excess and the Hα excess of bright features are strongly correlated, which will influence modelling of stellar and exoplanet atmospheres. High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution Hα narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the VTT. ChroTel provided full-disk context observations in Hα, Ca IIK, and He I 10830 {\AA}. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 {\AA} filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments.},
  language  = {en}
}
@phdthesis{Mitzscherling2015,
  author    = {Mitzscherling, Steffen},
  title     = {Polyelectrolyte multilayers for plasmonics and picosecond ultrasonics},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-80833},
  school      = {Universit{\"a}t Potsdam},
  pages     = {93},
  year      = {2015},
  abstract  = {This thesis investigates the application of polyelectrolyte multilayers in plasmonics and picosecond acoustics. The observed samples were fabricated by the spin-assisted layer-by-layer deposition technique that allowed a precise tuning of layer thickness in the range of few nanometers. The first field of interest deals with the interaction of light-induced localized surface plasmons (LSP) of rod-shaped gold nanoparticles with the particles' environment. The environment consists of an air phase and a phase of polyelectrolytes, whose ratio affects the spectral position of the LSP resonance. Measured UV-VIS spectra showed the shift of the LSP absorption peak as a function of the cover layer thickness of the particles. The data are modeled using an average dielectric function instead of the dielectric functions of air and polyelectrolytes. In addition using a measured dielectric function of the gold nanoparticles, the position of the LSP absorption peak could be simulated with good agreement to the data. The analytic model helps to understand the optical properties of metal nanoparticles in an inhomogeneous environment. The second part of this work discusses the applicability of PAzo/PAH and dye-doped PSS/PAH polyelectrolyte multilayers as transducers to generate hypersound pulses. The generated strain pulses were detected by time-domain Brillouin scattering (TDBS) using a pump-probe laser setup. Transducer layers made of polyelectrolytes were compared qualitatively to common aluminum transducers in terms of measured TDBS signal amplitude, degradation due to laser excitation, and sample preparation. The measurements proved that fast and easy prepared polyelectrolyte transducers provided stronger TDBS signals than the aluminum transducer. AFM topography measurements showed a degradation of the polyelectrolyte structures, especially for the PAzo/PAH sample. To quantify the induced strain, optical barriers were introduced to separate the transducer material from the medium of the hypersound propagation. Difficulties in the sample preparation prohibited a reliable quantification. But the experiments showed that a coating with transparent polyelectrolytes increases the efficiency of aluminum transducers and modifies the excited phonon distribution. The adoption of polyelectrolytes to the scientific field of picosecond acoustics enables a cheap and fast fabrication of transducer layers on most surfaces. In contrast to aluminum layers the polyelectrolytes are transparent over a wide spectral range. Thus, the strain modulation can be probed from surface and back.},
  language  = {en}
}
@phdthesis{Breidenich2000,
  author    = {Breidenich, Markus},
  title     = {Polymers at membranes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000284},
  school      = {Universit{\"a}t Potsdam},
  year      = {2000},
  abstract  = {Die Oberfl{\"a}che biologischer Zellen besteht aus einer Lipidmembran und einer Vielzahl von Proteinen und Polymeren, die in die Membran eingebaut sind. Die Beeinflussung der Membran durch Polymere, die mit einem Ende an der Membran verankert sind, wird im Rahmen dieser Arbeit anhand eines vereinfachten biomimetischen Systems studiert. Der entropische Druck, den das Polymer durch St{\"o}ße auf die Membran aus{\"u}bt, f{\"u}hrt dazu, dass sich die Membran vom Polymer weg kr{\"u}mmt. Die resultierende Membranform ist ein Kegel in der N{\"a}he des Ankers und ein Katenoid in grossem Abstand vom Ankerpunkt. Monte Carlo-Simulationen best{\"a}tigen die perturbativ berechneten Resultate. Bei Hinzunahme eines attraktiven Potentials zwischen Polymer und Membran verringert sich die urspr{\"u}nglich vom Polymer induzierte Kr{\"u}mmung. Im Limes starker Adsorption, in welchem das Polymer ganz auf der Membranoberfl{\"a}che lokalisiert ist, verschwindet der Polymerdruck und die durch diesen induzierte Kr{\"u}mmung der Membran. Falls das Polymer nicht direkt auf der Membranoberfl{\"a}che verankert ist, sondern in endlichem Ankerabstand, biegt sich die Membran im adsorbierten Fall zum Polymer hin. Im letzten Teil der Arbeit werden nicht verankerte Polymere in L{\"o}sung betrachtet. Untersucht wird der Einfluss einer solchen Polymerl{\"o}sung auf die Kr{\"u}mmung der Membran. Im Grenzfall einer rein sterischen, repulsiven Wechselwirkung zwischen Polymeren und Membran biegt sich diese, im Gegensatz zur verankerten Situation, zur L{\"o}sung hin. Bei zunehmender Attraktion biegt sich die Membran im Limes starker Adsorption der Polymere von der L{\"o}sung weg.},
  language  = {en}
}
@phdthesis{Patra2013,
  author    = {Patra, Pintu},
  title     = {Population dynamics of bacterial persistence},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69253},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {The life of microorganisms is characterized by two main tasks, rapid growth under conditions permitting growth and survival under stressful conditions. The environments, in which microorganisms dwell, vary in space and time. The microorganisms innovate diverse strategies to readily adapt to the regularly fluctuating environments. Phenotypic heterogeneity is one such strategy, where an isogenic population splits into subpopulations that respond differently under identical environments. Bacterial persistence is a prime example of such phenotypic heterogeneity, whereby a population survives under an antibiotic attack, by keeping a fraction of population in a drug tolerant state, the persister state. Specifically, persister cells grow more slowly than normal cells under growth conditions, but survive longer under stress conditions such as the antibiotic administrations. Bacterial persistence is identified experimentally by examining the population survival upon an antibiotic treatment and the population resuscitation in a growth medium. The underlying population dynamics is explained with a two state model for reversible phenotype switching in a cell within the population. We study this existing model with a new theoretical approach and present analytical expressions for the time scale observed in population growth and resuscitation, that can be easily used to extract underlying model parameters of bacterial persistence. In addition, we recapitulate previously known results on the evolution of such structured population under periodically fluctuating environment using our simple approximation method. Using our analysis, we determine model parameters for Staphylococcus aureus population under several antibiotics and interpret the outcome of cross-drug treatment. Next, we consider the expansion of a population exhibiting phenotype switching in a spatially structured environment consisting of two growth permitting patches separated by an antibiotic patch. The dynamic interplay of growth, death and migration of cells in different patches leads to distinct regimes in population propagation speed as a function of migration rate. We map out the region in parameter space of phenotype switching and migration rate to observe the condition under which persistence is beneficial. Furthermore, we present an extended model that allows mutation from the two phenotypic states to a resistant state. We find that the presence of persister cells may enhance the probability of resistant mutation in a population. Using this model, we explain the experimental results showing the emergence of antibiotic resistance in a Staphylococcus aureus population upon tobramycin treatment. In summary, we identify several roles of bacterial persistence, such as help in spatial expansion, development of multidrug tolerance and emergence of antibiotic resistance. Our study provides a theoretical perspective on the dynamics of bacterial persistence in different environmental conditions. These results can be utilized to design further experiments, and to develop novel strategies to eradicate persistent infections.},
  language  = {en}
}
@phdthesis{Schreck2014,
  author    = {Schreck, Simon Frederik},
  title     = {Potential energy surfaces, femtosecond dynamics and nonlinear X-Ray-Matter interactions from resonant inelastic soft x-Ray scattering},
  pages     = {164},
  year      = {2014},
  language  = {en}
}
@phdthesis{Sborikas2015,
  author    = {Sborikas, Martynas},
  title     = {Preparation and characterization of acoustic electret and electromechanical properties of polypropylene ferroelectrets},
  pages     = {129},
  year      = {2015},
  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{Fang2010,
  author    = {Fang, Peng},
  title     = {Preparation and investigation of polymer-foam films and polymer-layer systems for ferroelectrets},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-48412},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {Piezoelectric materials are very useful for applications in sensors and actuators. In addition to traditional ferroelectric ceramics and ferroelectric polymers, ferroelectrets have recently become a new group of piezoelectrics. Ferroelectrets are functional polymer systems for electromechanical transduction, with elastically heterogeneous cellular structures and internal quasi-permanent dipole moments. The piezoelectricity of ferroelectrets stems from linear changes of the dipole moments in response to external mechanical or electrical stress. Over the past two decades, polypropylene (PP) foams have been investigated with the aim of ferroelectret applications, and some products are already on the market. PP-foam ferroelectrets may exhibit piezoelectric d33 coefficients of 600 pC/N and more. Their operating temperature can, however, not be much higher than 60 °C. Recently developed polyethylene-terephthalate (PET) and cyclo-olefin copolymer (COC) foam ferroelectrets show slightly better d33 thermal stabilities, but usually at the price of smaller d33 values. Therefore, the main aim of this work is the development of new thermally stable ferroelectrets with appreciable piezoelectricity. Physical foaming is a promising technique for generating polymer foams from solid films without any pollution or impurity. Supercritical carbon dioxide (CO2) or nitrogen (N2) are usually employed as foaming agents due to their good solubility in several polymers. Polyethylene propylene (PEN) is a polyester with slightly better properties than PET. A "voiding + inflation + stretching" process has been specifically developed to prepare PEN foams. Solid PEN films are saturated with supercritical CO2 at high pressure and then thermally voided at high temperatures. Controlled inflation (Gas-Diffusion Expansion or GDE) is applied in order to adjust the void dimensions. Additional biaxial stretching decreases the void heights, since it is known lens-shaped voids lead to lower elastic moduli and therefore also to stronger piezoelectricity. Both, contact and corona charging are suitable for the electric charging of PEN foams. The light emission from the dielectric-barrier discharges (DBDs) can be clearly observed. Corona charging in a gas of high dielectric strength such as sulfur hexafluoride (SF6) results in higher gas-breakdown strength in the voids and therefore increases the piezoelectricity. PEN foams can exhibit piezoelectric d33 coefficients as high as 500 pC/N. Dielectric-resonance spectra show elastic moduli c33 of 1 - 12 MPa, anti-resonance frequencies of 0.2 - 0.8 MHz, and electromechanical coupling factors of 0.016 - 0.069. As expected, it is found that PEN foams show better thermal stability than PP and PET. Samples charged at room temperature can be utilized up to 80 - 100 °C. Annealing after charging or charging at elevated temperatures may improve thermal stabilities. Samples charged at suitable elevated temperatures show working temperatures as high as 110 - 120 °C. Acoustic measurements at frequencies of 2 Hz - 20 kHz show that PEN foams can be well applied in this frequency range. Fluorinated ethylene-propylene (FEP) copolymers are fluoropolymers with very good physical, chemical and electrical properties. The charge-storage ability of solid FEP films can be significantly improved by adding boron nitride (BN) filler particles. FEP foams are prepared by means of a one-step procedure consisting of CO2 saturation and subsequent in-situ high-temperature voiding. Piezoelectric d33 coefficients up to 40 pC/N are measured on such FEP foams. Mechanical fatigue tests show that the as-prepared PEN and FEP foams are mechanically stable for long periods of time. Although polymer-foam ferroelectrets have a high application potential, their piezoelectric properties strongly depend on the cellular morphology, i.e. on size, shape, and distribution of the voids. On the other hand, controlled preparation of optimized cellular structures is still a technical challenge. Consequently, new ferroelectrets based on polymer-layer system (sandwiches) have been prepared from FEP. By sandwiching an FEP mesh between two solid FEP films and fusing the polymer system with a laser beam, a well-designed uniform macroscopic cellular structure can be formed. Dielectric resonance spectroscopy reveals piezoelectric d33 coefficients as high as 350 pC/N, elastic moduli of about 0.3 MPa, anti-resonance frequencies of about 30 kHz, and electromechanical coupling factors of about 0.05. Samples charged at elevated temperatures show better thermal stabilities than those charged at room temperature, and the higher the charging temperature, the better is the stability. After proper charging at 140 °C, the working temperatures can be as high as 110 - 120 °C. Acoustic measurements at frequencies of 200 Hz - 20 kHz indicate that the FEP layer systems are suitable for applications at least in this range.},
  language  = {en}
}
@phdthesis{Jappsen2005,
  author    = {Jappsen, Anne-Katharina},
  title     = {Present and early star formation : a study on rotational and thermal properties},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7591},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {We investigate the rotational and thermal properties of star-forming molecular clouds using hydrodynamic simulations. Stars form from molecular cloud cores by gravoturbulent fragmentation. Understanding the angular momentum and the thermal evolution of cloud cores thus plays a fundamental role in completing the theoretical picture of star formation. This is true not only for current star formation as observed in regions like the Orion nebula or the ρ-Ophiuchi molecular cloud but also for the formation of stars of the first or second generation in the universe. In this thesis we show how the angular momentum of prestellar and protostellar cores evolves and compare our results with observed quantities. The specific angular momentum of prestellar cores in our models agree remarkably well with observations of cloud cores. Some prestellar cores go into collapse to build up stars and stellar systems. The resulting protostellar objects have specific angular momenta that fall into the range of observed binaries. We find that collapse induced by gravoturbulent fragmentation is accompanied by a substantial loss of specific angular momentum. This eases the "angular momentum problem" in star formation even in the absence of magnetic fields. The distribution of stellar masses at birth (the initial mass function, IMF) is another aspect that any theory of star formation must explain. We focus on the influence of the thermodynamic properties of star-forming gas and address this issue by studying the effects of a piecewise polytropic equation of state on the formation of stellar clusters. We increase the polytropic exponent γ from a value below unity to a value above unity at a certain critical density. The change of the thermodynamic state at the critical density selects a characteristic mass scale for fragmentation, which we relate to the peak of the IMF observed in the solar neighborhood. Our investigation generally supports the idea that the distribution of stellar masses depends mainly on the thermodynamic state of the gas. A common assumption is that the chemical evolution of the star-forming gas can be decoupled from its dynamical evolution, with the former never affecting the latter. Although justified in some circumstances, this assumption is not true in every case. In particular, in low-metallicity gas the timescales for reaching the chemical equilibrium are comparable or larger than the dynamical timescales. In this thesis we take a first approach to combine a chemical network with a hydrodynamical code in order to study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos. Our initial conditions represent protogalaxies forming within a fossil HII region -- a previously ionized HII region which has not yet had time to cool and recombine. We show that in these regions, H2 is the dominant and most effective coolant, and that it is the amount of H2 formed that controls whether or not the gas can collapse and form stars. For metallicities Z <= 10<sup>-3 Zsun, metal line cooling alters the density and temperature evolution of the gas by less than 1\% compared to the metal-free case at densities below 1 cm<sup>-3 and temperatures above 2000 K. We also find that an external ultraviolet background delays or suppresses the cooling and collapse of the gas regardless of whether it is metal-enriched or not. Finally, we study the dependence of this process on redshift and mass of the dark matter halo.},
  subject      = {Sternentstehung},
  language  = {en}
}
@phdthesis{Jay2020,
  author    = {Jay, Raphael Martin},
  title     = {Principles of charge distribution and separation},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 162},
  year      = {2020},
  abstract  = {The electronic charge distributions of transition metal complexes fundamentally determine their chemical reactivity. Experimental access to the local valence electronic structure is therefore crucial in order to determine how frontier orbitals are delocalized between different atomic sites and electronic charge is spread throughout the transition metal complex. To that end, X-ray spectroscopies are employed in this thesis to study a series of solution-phase iron complexes with respect to the response of their local electronic charge distributions to different external influences. Using resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) at the iron L-edge, changes in local charge densities are investigated at the iron center depending on different ligand cages as well as solvent environments. A varying degree of charge delocalization from the metal center onto the ligands is observed, which is governed by the capabilities of the ligands to accept charge density into their unoccupied orbitals. Specific solvents are furthermore shown to amplify this process. Solvent molecules of strong Lewis-acids withdraw charge from the ligand allowing in turn for more metal charge to be delocalized onto the ligand. The resulting local charge deficiencies at the metal center are, however, counteracted by competing electron-donation channels from the ligand towards the iron, which are additionally revealed. This is interpreted as a compensating effect which strives to maintain local charge densities at the iron center. This mechanism of charge density preservation is found to be of general nature. Using time-resolved RIXS and XAS at the iron L-edge, an analogous interplay of electron donation and back-donation channels is also revealed for the case of charge-transfer excited states. In such transient configurations, the electronic occupation of iron-centered frontier orbitals has been altered by an optical excitation. Changes in local charge densities that are expected to follow an increased or decreased population of iron-centered orbitals are, however, again counteracted. By scaling the degree of electron donation from the ligand onto the metal, local charge densities at the iron center can be efficiently maintained. Since charge-transfer excitations, however, often constitute the initial step in many electron transfer processes, these findings challenge common notions of charge-separation in transition metal dyes.},
  language  = {en}
}
@phdthesis{Kurpiers2019,
  author    = {Kurpiers, Jona},
  title     = {Probing the pathways of free charge generation and recombination in organic solar cells},
  doi       = {10.25932/publishup-42909},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-429099},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 128, xxi},
  year      = {2019},
  abstract  = {Organic semiconductors are a promising class of materials. Their special properties are the particularly good absorption, low weight and easy processing into thin films. Therefore, intense research has been devoted to the realization of thin film organic solar cells (OPVs). Because of the low dielectric constant of organic semiconductors, primary excitations (excitons) are strongly bound and a type II heterojunction needs to be introduced to split these excitations into free charges. Therefore, most organic solar cells consist of at least an electron donor and electron acceptor material. For such donor acceptor systems mainly three states are relevant; the photoexcited exciton on the donor or acceptor material, the charge transfer state at the donor-acceptor interface and the charge separated state of a free electron and hole. The interplay between these states significantly determines the efficiency of organic solar cells. Due to the high absorption and the low charge carrier mobilities, the active layers are usually thin but also, exciton dissociation and free charge formation proceeds rapidely, which makes the study of carrier dynamics highly challenging. Therefore, the focus of this work was first to install new experimental setups for the investigation of the charge carrier dynamics in complete devices with superior sensitivity and time resolution and, second, to apply these methods to prototypical photovoltaic materials to address specific questions in the field of organic and hybrid photovoltaics. Regarding the first goal, a new setup combining transient absorption spectroscopy (TAS) and time delayed collection field (TDCF) was designed and installed in Potsdam. An important part of this work concerned the improvement of the electronic components with respect to time resolution and sensitivity. To this end, a highly sensitive amplifier for driving and detecting the device response in TDCF was developed. This system was then applied to selected organic and hybrid model systems with a particular focus on the understanding of the loss mechanisms that limit the fill factor and short circuit current of organic solar cells. The first model system was a hybrid photovoltaic material comprising inorganic quantum dots decorated with organic ligands. Measurements with TDCF revealed fast free carrier recombination, in part assisted by traps, while bias-assisted charge extraction measurements showed high mobility. The measured parameters then served as input for a successful description of the device performance with an analytical model. With a further improvement of the instrumentation, a second topic was the detailed analysis of non-geminate recombination in a disordered polymer:fullerene blend where an important question was the effect of disorder on the carrier dynamics. The measurements revealed that early time highly mobile charges undergo fast non-geminate recombination at the contacts, causing an apparent field dependence of free charge generation in TDCF experiments if not conducted properly. On the other hand, recombination the later time scale was determined by dispersive recombination in the bulk of the active layer, showing the characteristics of carrier dynamics in an exponential density of state distribution. Importantly, the comparison with steady state recombination data suggested a very weak impact of non-thermalized carriers on the recombination properties of the solar cells under application relevant illumination conditions. Finally, temperature and field dependent studies of free charge generation were performed on three donor-acceptor combinations, with two donor polymers of the same material family blended with two different fullerene acceptor molecules. These particular material combinations were chosen to analyze the influence of the energetic and morphology of the blend on the efficiency of charge generation. To this end, activation energies for photocurrent generation were accurately determined for a wide range of excitation energies. The results prove that the formation of free charge is via thermalized charge transfer states and does not involve hot exciton splitting. Surprisingly, activation energies were of the order of thermal energy at room temperature. This led to the important conclusion that organic solar cells perform well not because of predominate high energy pathways but because the thermalized CT states are weakly bound. In addition, a model is introduced to interconnect the dissociation efficiency of the charge transfer state with its recombination observable with photoluminescence, which rules out a previously proposed two-pool model for free charge formation and recombination. Finally, based on the results, proposals for the further development of organic solar cells are formulated.},
  language  = {en}
}
@phdthesis{Lever2022,
  author    = {Lever, Fabiano},
  title     = {Probing the ultrafast dynamics of 2-Thiouracil with soft x-rays},
  doi       = {10.25932/publishup-55523},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-555230},
  school      = {Universit{\"a}t Potsdam},
  pages     = {129},
  year      = {2022},
  abstract  = {Understanding the changes that follow UV-excitation in thionucleobases is of great importance for the study of light-induced DNA lesions and, in a broader context, for their applications in medicine and biochemistry. Their ultrafast photophysical reactions can alter the chemical structure of DNA - leading to damages to the genetic code - as proven by the increased skin cancer risk observed for patients treated with thiouracil for its immunosuppressant properties. In this thesis, I present four research papers that result from an investigation of the ultrafast dynamics of 2-thiouracil by means of ultrafast x-ray probing combined with electron spectroscopy. A molecular jet in the gas phase is excited with a uv pulse and then ionized with x-ray radiation from a Free Electron Laser. The kinetic energy of the emitted electrons is measured in a magnetic bottle spectrometer. The spectra of the measured photo and Auger electrons are used to derive a picture of the changes in the geometrical and electronic configurations. The results allow us to look at the dynamical processes from a new perspective, thanks to the element- and site- sensitivity of x-rays. The custom-built URSA-PQ apparatus used in the experiment is described. It has been commissioned and used at the FL24 beamline of the FLASH2 FEL, showing an electron kinetic energy resolution of ∆E/E ~ 40 and a pump-probe timing resolution of 190 f s. X-ray only photoelectron and Auger spectra of 2-thiouracil are extracted from the data and used as reference. Photoelectrons following the formation a 2p core hole are identified, as well as resonant and non-resonant Auger electrons. At the L 1 edge, Coster-Kronig decay is observed from the 2s core hole. The UV-induced changes in the 2p photoline allow the study the electronic-state dynamics. With the use of an Excited-State Chemical Shift (ESCS) model, we observe a ultrafast ground-state relaxation within 250 f s. Furthermore, an oscillation with a 250 f s period is observed in the 2p binding energy, showing a coherent population exchange between electronic states. Auger electrons from the 2p core hole are analyzed and used to deduce a ultrafast C -S bond expansion on a sub 100 f s scale. A simple Coulomb-model, coupled to quantum chemical calculations, can be used to infer the geometrical changes in the molecular structure.},
  language  = {en}
}
@phdthesis{HerreroAlonso2023,
  author    = {Herrero Alonso, Yohana},
  title     = {Properties of high-redshift galaxies in different environments},
  doi       = {10.25932/publishup-61328},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-613288},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 114},
  year      = {2023},
  abstract  = {The Lyman-𝛼 (Ly𝛼) line commonly assists in the detection of high-redshift galaxies, the so-called Lyman-alpha emitters (LAEs). LAEs are useful tools to study the baryonic matter distribution of the high-redshift universe. Exploring their spatial distribution not only reveals the large-scale structure of the universe at early epochs, but it also provides an insight into the early formation and evolution of the galaxies we observe today. Because dark matter halos (DMHs) serve as sites of galaxy formation, the LAE distribution also traces that of the underlying dark matter. However, the details of this relation and their co-evolution over time remain unclear. Moreover, theoretical studies predict that the spatial distribution of LAEs also impacts their own circumgalactic medium (CGM) by influencing their extended Ly𝛼 gaseous halos (LAHs), whose origin is still under investigation. In this thesis, I make several contributions to improve the knowledge on these fields using samples of LAEs observed with the Multi Unit Spectroscopic Explorer (MUSE) at redshifts of 3 < 𝑧 < 6.},
  language  = {en}
}
@phdthesis{Schmeja2006,
  author    = {Schmeja, Stefan},
  title     = {Properties of turbulent star-forming clusters : models versus observations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7364},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Stars are born in turbulent molecular clouds that fragment and collapse under the influence of their own gravity, forming a cluster of hundred or more stars. The star formation process is controlled by the interplay between supersonic turbulence and gravity. In this work, the properties of stellar clusters created by numerical simulations of gravoturbulent fragmentation are compared to those from observations. This includes the analysis of properties of individual protostars as well as statistical properties of the entire cluster. It is demonstrated that protostellar mass accretion is a highly dynamical and time-variant process. The peak accretion rate is reached shortly after the formation of the protostellar core. It is about one order of magnitude higher than the constant accretion rate predicted by the collapse of a classical singular isothermal sphere, in agreement with the observations. For a more reasonable comparison, the model accretion rates are converted to the observables bolometric temperature, bolometric luminosity, and envelope mass. The accretion rates from the simulations are used as input for an evolutionary scheme. The resulting distribution in the Tbol-Lbol-Menv parameter space is then compared to observational data by means of a 3D Kolmogorov-Smirnov test. The highest probability found that the distributions of model tracks and observational data points are drawn from the same population is 70\%. The ratios of objects belonging to different evolutionary classes in observed star-forming clusters are compared to the temporal evolution of the gravoturbulent models in order to estimate the evolutionary stage of a cluster. While it is difficult to estimate absolute ages, the realtive numbers of young stars reveal the evolutionary status of a cluster with respect to other clusters. The sequence shows Serpens as the youngest and IC 348 as the most evolved of the investigated clusters. Finally the structures of young star clusters are investigated by applying different statistical methods like the normalised mean correlation length and the minimum spanning tree technique and by a newly defined measure for the cluster elongation. The clustering parameters of the model clusters correspond in many cases well to those from observed ones. The temporal evolution of the clustering parameters shows that the star cluster builds up from several subclusters and evolves to a more centrally concentrated cluster, while the cluster expands slower than new stars are formed.},
  subject      = {Sternentstehung},
  language  = {en}
}
@phdthesis{Rudorf2014,
  author    = {Rudorf, Sophia},
  title     = {Protein Synthesis by Ribosomes},
  pages     = {xii, 145},
  year      = {2014},
  language  = {en}
}
@phdthesis{Sommerfeld2015,
  author    = {Sommerfeld, Anja},
  title     = {Quantification of internal variability of the arctic summer atmosphere based on HIRHAM5 ensemble simulations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85347},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VII, 110, vi},
  year      = {2015},
  abstract  = {The non-linear behaviour of the atmospheric dynamics is not well understood and makes the evaluation and usage of regional climate models (RCMs) difficult. Due to these non-linearities, chaos and internal variability (IV) within the RCMs are induced, leading to a sensitivity of RCMs to their initial conditions (IC). The IV is the ability of RCMs to realise different solutions of simulations that differ in their IC, but have the same lower and lateral boundary conditions (LBC), hence can be defined as the across-member spread between the ensemble members. For the investigation of the IV and the dynamical and diabatic contributions generating the IV four ensembles of RCM simulations are performed with the atmospheric regional model HIRHAM5. The integration area is the Arctic and each ensemble consists of 20 members. The ensembles cover the time period from July to September for the years 2006, 2007, 2009 and 2012. The ensemble members have the same LBC and differ in their IC only. The different IC are arranged by an initialisation time that shifts successively by six hours. Within each ensemble the first simulation starts on 1st July at 00 UTC and the last simulation starts on 5th July at 18 UTC and each simulation runs until 30th September. The analysed time period ranges from 6th July to 30th September, the time period that is covered by all ensemble members. The model runs without any nudging to allow a free development of each simulation to get the full internal variability within the HIRHAM5. As a measure of the model generated IV, the across-member standard deviation and the across-member variance is used and the dynamical and diabatic processes influencing the IV are estimated by applying a diagnostic budget study for the IV tendency of the potential temperature developed by Nikiema and Laprise [2010] and Nikiema and Laprise [2011]. The diagnostic budget study is based on the first law of thermodynamics for potential temperature and the mass-continuity equation. The resulting budget equation reveals seven contributions to the potential temperature IV tendency. As a first study, this work analyses the IV within the HIRHAM5. Therefore, atmospheric circulation parameters and the potential temperature for all four ensemble years are investigated. Similar to previous studies, the IV fluctuates strongly in time. Further, due to the fact that all ensemble members are forced with the same LBC, the IV depends on the vertical level within the troposphere, with high values in the lower troposphere and at 500 hPa and low values in the upper troposphere and at the surface. By the same reason, the spatial distribution shows low values of IV at the boundaries of the model domain. The diagnostic budget study for the IV tendency of potential temperature reveals that the seven contributions fluctuate in time like the IV. However, the individual terms reach different absolute magnitudes. The budget study identifies the horizontal and vertical 'baroclinic' terms as the main contributors to the IV tendency, with the horizontal 'baroclinic' term producing and the vertical 'baroclinic' term reducing the IV. The other terms fluctuate around zero, because they are small in general or are balanced due to the domain average. The comparison of the results obtained for the four different ensembles (summers 2006, 2007, 2009 and 2012) reveals that on average the findings for each ensemble are quite similar concerning the magnitude and the general pattern of IV and its contributions. However, near the surface a weaker IV is produced with decreasing sea ice extent. This is caused by a smaller impact of the horizontal 'baroclinic' term over some regions and by the changing diabatic processes, particularly a more intense reducing tendency of the IV due to condensative heating. However, it has to be emphasised that the behaviour of the IV and its dynamical and diabatic contributions are influenced mainly by complex atmospheric feedbacks and large-scale processes and not by the sea ice distribution. Additionally, a comparison with a second RCM covering the Arctic and using the same LBCs and IC is performed. For both models very similar results concerning the IV and its dynamical and diabatic contributions are found. Hence, this investigation leads to the conclusion that the IV is a natural phenomenon and is independent from the applied RCM.},
  language  = {en}
}
@phdthesis{Kotha2018,
  author    = {Kotha, Sreeram Reddy},
  title     = {Quantification of uncertainties in seismic ground-motion prediction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-415743},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 101},
  year      = {2018},
  abstract  = {The purpose of Probabilistic Seismic Hazard Assessment (PSHA) at a construction site is to provide the engineers with a probabilistic estimate of ground-motion level that could be equaled or exceeded at least once in the structure's design lifetime. A certainty on the predicted ground-motion allows the engineers to confidently optimize structural design and mitigate the risk of extensive damage, or in worst case, a collapse. It is therefore in interest of engineering, insurance, disaster mitigation, and security of society at large, to reduce uncertainties in prediction of design ground-motion levels. In this study, I am concerned with quantifying and reducing the prediction uncertainty of regression-based Ground-Motion Prediction Equations (GMPEs). Essentially, GMPEs are regressed best-fit formulae relating event, path, and site parameters (predictor variables) to observed ground-motion values at the site (prediction variable). GMPEs are characterized by a parametric median (μ) and a non-parametric variance (σ) of prediction. μ captures the known ground-motion physics i.e., scaling with earthquake rupture properties (event), attenuation with distance from source (region/path), and amplification due to local soil conditions (site); while σ quantifies the natural variability of data that eludes μ. In a broad sense, the GMPE prediction uncertainty is cumulative of 1) uncertainty on estimated regression coefficients (uncertainty on μ,σ_μ), and 2) the inherent natural randomness of data (σ). The extent of μ parametrization, the quantity, and quality of ground-motion data used in a regression, govern the size of its prediction uncertainty: σ_μ and σ. In the first step, I present the impact of μ parametrization on the size of σ_μ and σ. Over-parametrization appears to increase the σ_μ, because of the large number of regression coefficients (in μ) to be estimated with insufficient data. Under-parametrization mitigates σ_μ, but the reduced explanatory strength of μ is reflected in inflated σ. For an optimally parametrized GMPE, a ~10\% reduction in σ is attained by discarding the low-quality data from pan-European events with incorrect parametric values (of predictor variables). In case of regions with scarce ground-motion recordings, without under-parametrization, the only way to mitigate σ_μ is to substitute long-term earthquake data at a location with short-term samples of data across several locations - the Ergodic Assumption. However, the price of ergodic assumption is an increased σ, due to the region-to-region and site-to-site differences in ground-motion physics. σ of an ergodic GMPE developed from generic ergodic dataset is much larger than that of non-ergodic GMPEs developed from region- and site-specific non-ergodic subsets - which were too sparse to produce their specific GMPEs. Fortunately, with the dramatic increase in recorded ground-motion data at several sites across Europe and Middle-East, I could quantify the region- and site-specific differences in ground-motion scaling and upgrade the GMPEs with 1) substantially more accurate region- and site-specific μ for sites in Italy and Turkey, and 2) significantly smaller prediction variance σ. The benefit of such enhancements to GMPEs is quite evident in my comparison of PSHA estimates from ergodic versus region- and site-specific GMPEs; where the differences in predicted design ground-motion levels, at several sites in Europe and Middle-Eastern regions, are as large as ~50\%. Resolving the ergodic assumption with mixed-effects regressions is feasible when the quantified region- and site-specific effects are physically meaningful, and the non-ergodic subsets (regions and sites) are defined a priori through expert knowledge. In absence of expert definitions, I demonstrate the potential of machine learning techniques in identifying efficient clusters of site-specific non-ergodic subsets, based on latent similarities in their ground-motion data. Clustered site-specific GMPEs bridge the gap between site-specific and fully ergodic GMPEs, with their partially non-ergodic μ and, σ ~15\% smaller than the ergodic variance. The methodological refinements to GMPE development produced in this study are applicable to new ground-motion datasets, to further enhance certainty of ground-motion prediction and thereby, seismic hazard assessment. Advanced statistical tools show great potential in improving the predictive capabilities of GMPEs, but the fundamental requirement remains: large quantity of high-quality ground-motion data from several sites for an extended time-period.},
  language  = {en}
}
@phdthesis{Varykhalov2005,
  author    = {Varykhalov, Andrei},
  title     = {Quantum-size effects in the electronic structure of novel self-organized systems with reduced dimensionality},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5784},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {The Thesis is focused on the properties of self-organized nanostructures. Atomic and electronic properties of different systems have been investigated using methods of electron diffraction, scanning tunneling microscopy and photoelectron spectroscopy. Implementation of the STM technique (including design, construction, and tuning of the UHV experimental set-up) has been done in the framework of present work. This time-consuming work is reported to greater detail in the experimental part of this Thesis. The scientific part starts from the study of quantum-size effects in the electronic structure of a two-dimensional Ag film on the supporting substrate Ni(111). Distinct quantum well states in the sp-band of Ag were observed in photoelectron spectra. Analysis of thickness- and angle-dependent photoemission supplies novel information on the properties of the interface. For the first time the Ni(111) relative band gap was indirectly probed in the ground-state through the electronic structure of quantum well states in the adlayer. This is particularly important for Ni where valence electrons are strongly correlated. Comparison of the experiment with calculations performed in the formalism of the extended phase accumulation model gives the substrate gap which is fully consistent with the one obtained by ab-initio LDA calculations. It is, however, in controversy to the band structure of Ni measured directly by photoemission. These results lend credit to the simplest view of photoemission from Ni, assigning early observed contradictions between theory and experiments to electron correlation effects in the final state of photoemission. Further, nanosystems of lower dimensionality have been studied. Stepped surfaces W(331) and W(551) were used as one-dimensional model systems and as templates for self-organization of Au nanoclusters. Photon energy dependent photoemission revealed a surface resonance which was never observed before on W(110) which is the base plane of the terrace microsurfaces. The dispersion E(k) of this state measured on stepped W(331) and W(551) with angle-resolved photoelectron spectroscopy is modified by a strong umklapp effect. It appears as two parabolas shifted symmetrically relative to the microsurface normal by half of the Brillouin zone of the step superlattice. The reported results are very important for understanding of the electronic properties of low-dimensional nanostructures. It was also established that W(331) and W(551) can serve as templates for self-organization of metallic nanostructures. A combined study of electronic and atomic properties of sub-monolayer amounts of gold deposited on these templates have shown that if the substrate is slightly pre-oxidized and the temperature is elevated, then Au can alloy with the first monolayer of W. As a result, a nanostructure of uniform clusters of a surface alloy is produced all over the steps. Such clusters feature a novel sp-band in the vicinity of the Fermi level, which appears split into constant energy levels due to effects of lateral quantization. The last and main part of this work is devoted to large-scale reconstructions on surfaces and nanostructures self-assembled on top. The two-dimensional surface carbide W(110)/C-R(15x3) has been extensively investigated. Photoemission studies of quantum size effects in the electronic structure of this reconstruction, combined with an investigation of its surface geometry, lead to an advanced structural model of the carbide overlayer. It was discovered that W(110)/C-R(15x3) can control self-organization of adlayers into nanostructures with extremely different electronic and structural properties. Thus, it was established that at elevated temperature the R(15x3) superstructure controls the self-assembly of sub-monolayer amounts of Au into nm-wide nanostripes. Based on the results of core level photoemission, the R(15x3)-induced surface alloying which takes place between Au and W can be claimed as driving force of self-organization. The observed stripes exhibit a characteristic one-dimensional electronic structure with laterally quantized d-bands. Obviously, these are very important for applications, since dimensions of electronic devices have already stepped into the nm-range, where quantum-size phenomena must undoubtedly be considered. Moreover, formation of perfectly uniform molecular clusters of C60 was demonstrated and described in terms of the van der Waals formalism. It is the first experimental observation of two-dimensional fullerene nanoclusters with "magic numbers". Calculations of the cluster potentials using the static approach have revealed characteristic minima in the interaction energy. They are achieved for 4 and 7 molecules per cluster. The obtained "magic numbers" and the corresponding cluster structures are fully consistent with the results of the STM measurements.},
  subject      = {Nanostruktur},
  language  = {en}
}
@phdthesis{Sander2015,
  author    = {Sander, Andreas Alexander Christoph},
  title     = {Radiatively driven winds of hot stars},
  school      = {Universit{\"a}t Potsdam},
  pages     = {153},
  year      = {2015},
  language  = {en}
}
@phdthesis{Mardoukhi2020,
  author    = {Mardoukhi, Yousof},
  title     = {Random environments and the percolation model},
  doi       = {10.25932/publishup-47276},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-472762},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxii, 103},
  year      = {2020},
  abstract  = {Percolation process, which is intrinsically a phase transition process near the critical point, is ubiquitous in nature. Many of its applications embrace a wide spectrum of natural phenomena ranging from the forest fires, spread of contagious diseases, social behaviour dynamics to mathematical finance, formation of bedrocks and biological systems. The topology generated by the percolation process near the critical point is a random (stochastic) fractal. It is fundamental to the percolation theory that near the critical point, a unique infinite fractal structure, namely the infinite cluster, would emerge. As de Gennes suggested, the properties of the infinite cluster could be deduced by studying the dynamical behaviour of the random walk process taking place on it. He coined the term the ant in the labyrinth. The random walk process on such an infinite fractal cluster exhibits a subdiffusive dynamics in the sense that the mean squared displacement grows as ~t2/dw, where dw, called the fractal dimension of the random walk path, is greater than 2. Thus, the random walk process on the infinite cluster is classified as a process exhibiting the properties of anomalous diffusions. Yet near the critical point, the infinite cluster is not the sole emergent topology, but it coexists with other clusters whose size is finite. Though finite, on specific length scales these finite clusters exhibit fractal properties as well. In this work, it is assumed that the random walk process could take place on these finite size objects as well. Bearing this assumption in mind requires one address the non-equilibrium initial condition. Due to the lack of knowledge on the propagator of the random walk process in stochastic random environments, a phenomenological correspondence between the renowned Ornstein-Uhlenbeck process and the random walk process on finite size clusters is established. It is elucidated that when an ensemble of these finite size clusters and the infinite cluster is considered, the anisotropy and size of these finite clusters effects the mean squared displacement and its time averaged counterpart to grow in time as ~t(d+df (t-2))/dw, where d is the embedding Euclidean dimension, df is the fractal dimension of the infinite cluster, and , called the Fisher exponent, is a critical exponent governing the power-law distribution of the finite size clusters. Moreover, it is demonstrated that, even though the random walk process on a specific finite size cluster is ergodic, it exhibits a persistent non-ergodic behaviour when an ensemble of finite size and the infinite clusters is considered.},
  language  = {en}
}
@phdthesis{Dahlke2020,
  author    = {Dahlke, Sandro},
  title     = {Rapid climate changes in the arctic region of Svalbard},
  doi       = {10.25932/publishup-44554},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445542},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xv, 123},
  year      = {2020},
  abstract  = {Over the last decades, the Arctic regions of the earth have warmed at a rate 2-3 times faster than the global average- a phenomenon called Arctic Amplification. A complex, non-linear interplay of physical processes and unique pecularities in the Arctic climate system is responsible for this, but the relative role of individual processes remains to be debated. This thesis focuses on the climate change and related processes on Svalbard, an archipelago in the North Atlantic sector of the Arctic, which is shown to be a "hotspot" for the amplified recent warming during winter. In this highly dynamical region, both oceanic and atmospheric large-scale transports of heat and moisture interfere with spatially inhomogenous surface conditions, and the corresponding energy exchange strongly shapes the atmospheric boundary layer. In the first part, Pan-Svalbard gradients in the surface air temperature (SAT) and sea ice extent (SIE) in the fjords are quantified and characterized. This analysis is based on observational data from meteorological stations, operational sea ice charts, and hydrographic observations from the adjacent ocean, which cover the 1980-2016 period. It is revealed that typical estimates of SIE during late winter range from 40-50\% (80-90\%) in the western (eastern) parts of Svalbard. However, strong SAT warming during winter of the order of 2-3K per decade dictates excessive ice loss, leaving fjords in the western parts essentially ice-free in recent winters. It is further demostrated that warm water currents on the west coast of Svalbard, as well as meridional winds contribute to regional differences in the SIE evolution. In particular, the proximity to warm water masses of the West Spitsbergen Current can explain 20-37\% of SIE variability in fjords on west Svalbard, while meridional winds and associated ice drift may regionally explain 20-50\% of SIE variability in the north and northeast. Strong SAT warming has overruled these impacts in recent years, though. In the next part of the analysis, the contribution of large-scale atmospheric circulation changes to the Svalbard temperature development over the last 20 years is investigated. A study employing kinematic air-back trajectories for Ny-{\AA}lesund reveals a shift in the source regions of lower-troposheric air over time for both the winter and the summer season. In winter, air in the recent decade is more often of lower-latitude Atlantic origin, and less frequent of Arctic origin. This affects heat- and moisture advection towards Svalbard, potentially manipulating clouds and longwave downward radiation in that region. A closer investigation indicates that this shift during winter is associated with a strengthened Ural blocking high and Icelandic low, and contributes about 25\% to the observed winter warming on Svalbard over the last 20 years. Conversely, circulation changes during summer include a strengthened Greenland blocking high which leads to more frequent cold air advection from the central Arctic towards Svalbard, and less frequent air mass origins in the lower latitudes of the North Atlantic. Hence, circulation changes during winter are shown to have an amplifying effect on the recent warming on Svalbard, while summer circulation changes tend to mask warming. An observational case study using upper air soundings from the AWIPEV research station in Ny-{\AA}lesund during May-June 2017 underlines that such circulation changes during summer are associated with tropospheric anomalies in temperature, humidity and boundary layer height. In the last part of the analysis, the regional representativeness of the above described changes around Svalbard for the broader Arctic is investigated. Therefore, the terms in the diagnostic temperature equation in the Arctic-wide lower troposphere are examined for the Era-Interim atmospheric reanalysis product. Significant positive trends in diabatic heating rates, consistent with latent heat transfer to the atmosphere over regions of increasing ice melt, are found for all seasons over the Barents/Kara Seas, and in individual months in the vicinity of Svalbard. The above introduced warm (cold) advection trends during winter (summer) on Svalbard are successfully reproduced. Regarding winter, they are regionally confined to the Barents Sea and Fram Strait, between 70°-80°N, resembling a unique feature in the whole Arctic. Summer cold advection trends are confined to the area between eastern Greenland and Franz Josef Land, enclosing Svalbard.},
  language  = {en}
}
@phdthesis{Jaster2003,
  author    = {Jaster, Nicole},
  title     = {Ratchet models of molecular motors},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000867},
  school      = {Universit{\"a}t Potsdam},
  year      = {2003},
  abstract  = {Transportvorg{\"a}nge in und von Zellen sind von herausragender Bedeutung f{\"u}r das {\"U}berleben des Organismus. Muskeln m{\"u}ssen sich kontrahieren k{\"o}nnen, Chromosomen w{\"a}hrend der Mitose an entgegengesetzte Enden der Zelle bewegt und Organellen, das sind von Membranen umschlossene Kompartimente, entlang molekularer Schienen transportiert werden. Molekulare Motoren sind Proteine, deren Hauptaufgabe es ist, andere Molek{\"u}le zu bewegen. Dazu wandeln sie die bei der ATP-Hydrolyse freiwerdende chemische Energie in mechanische Arbeit um. Die Motoren des Zellskeletts geh{\"o}ren zu den drei Superfamilien Myosin, Kinesin und Dynein. Ihre Schienen sind Filamente des Zellskeletts, Actin und die Microtubuli. In dieser Arbeit werden stochastische Modelle untersucht, welche dazu dienen, die Fortbewegung dieser linearen molekularen Motoren zu beschreiben. Die Skala, auf der wir die Bewegung betrachten, reicht von einzelnen Schritten eines Motorproteins bis in den Bereich der gerichteten Bewegung entlang eines Filaments. Ein Einzelschritt {\"u}berbr{\"u}ckt je nach Protein etwa 10 nm und wird in ungef{\"a}hr 10 ms zur{\"u}ckgelegt. Unsere Modelle umfassen M Zust{\"a}nde oder Konformationen, die der Motor annehmen kann, w{\"a}hrend er sich entlang einer eindimensionalen Schiene bewegt. An K Orten dieser Schiene sind {\"U}berg{\"a}nge zwischen den Zust{\"a}nden m{\"o}glich. Die Geschwindigkeit des Proteins l{\"a}sst sich in Abh{\"a}ngigkeit von den vertikalen {\"U}bergangsraten zwischen den einzelnen Zust{\"a}nden analytisch bestimmen. Wir berechnen diese Geschwindigkeit f{\"u}r Systeme mit bis zu vier Zust{\"a}nden und Orten und k{\"o}nnen weiterhin eine Reihe von Regeln ableiten, die uns einsch{\"a}tzen helfen, wie sich ein beliebiges vorgegebenes System verhalten wird. Dar{\"u}ber hinaus betrachten wir entkoppelte Subsysteme, also einen oder mehrere Zust{\"a}nde, die keine Verbindung zum {\"u}brigen System haben. Mit einer bestimmten Wahrscheinlichkeit kann ein Motor einen Zyklus von Konformationen durchlaufen, mit einer anderen Wahrscheinlichkeit einen davon unabh{\"a}ngigen anderen. Aktive Elemente werden in realen Transportvorg{\"a}ngen durch Motorproteine nicht auf die {\"U}berg{\"a}nge zwischen den Zust{\"a}nden beschr{\"a}nkt sein. In verzerrten Netzwerken oder ausgehend von der diskreten Mastergleichung des Systems k{\"o}nnen auch horizontale Raten spezifiziert werden und m{\"u}ssen weiterhin nicht mehr die Bedingungen der detaillierten Balance erf{\"u}llen. Damit ergeben sich eindeutige, komplette Pfade durch das jeweilige Netzwerk und Regeln f{\"u}r die Abh{\"a}ngigkeit des Gesamtstroms von allen Raten des Systems. Außerdem betrachten wir die zeitliche Entwicklung f{\"u}r vorgegebene Anfangsverteilungen. Bei Enzymreaktionen gibt es die Idee des Hauptpfades, dem diese bevorzugt folgen. Wir bestimmen optimale Pfade und den maximalen Fluss durch vorgegebene Netzwerke. Um dar{\"u}ber hinaus die Geschwindigkeit des Motors in Abh{\"a}ngigkeit von seinem Treibstoff ATP angeben zu k{\"o}nnen, betrachten wir m{\"o}gliche Reaktionskinetiken, die den Zusammenhang zwischen den unbalancierten {\"U}bergangsraten und der ATP-Konzentration bestimmen. Je nach Typ der Reaktionskinetik und Anzahl unbalancierter Raten ergeben sich qualitativ unterschiedliche Verl{\"a}ufe der Geschwindigkeitskurven in Abh{\"a}ngigkeit von der ATP-Konzentration. Die molekularen Wechselwirkungspotentiale, die der Motor entlang seiner Schiene erf{\"a}hrt, sind unbekannt.Wir vergleichen unterschiedliche einfache Potentiale und die Auswirkungen auf die Transportkoeffizienten, die sich durch die Lokalisation der vertikalen {\"U}berg{\"a}nge im Netzwerkmodell im Vergleich zu anderen Ans{\"a}tzen ergeben.},
  language  = {en}
}
@phdthesis{Thiel2004,
  author    = {Thiel, Marco},
  title     = {Recurrences : exploiting naturally occurring analogues},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001633},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {In der vorliegenden Arbeit wird die Wiederkehr im Phasenraum ausgenutzt. Dabei werden drei Hauptresultate besprochen. 1. Die Wiederkehr erlaubt die Vorhersagbarkeit des Systems zu quantifizieren. 2. Die Wiederkehr enthaelt (unter bestimmten Voraussetzungen) s{\"a}mtliche relevante Information {\"u}ber die Dynamik im Phasenraum 3. Die Wiederkehr erlaubt die Erzeugung dynamischer Ersatzdaten.},
  language  = {en}
}
@phdthesis{Braun2023,
  author    = {Braun, Tobias},
  title     = {Recurrences in past climates},
  doi       = {10.25932/publishup-58690},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-586900},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxviii, 251},
  year      = {2023},
  abstract  = {Our ability to predict the state of a system relies on its tendency to recur to states it has visited before. Recurrence also pervades common intuitions about the systems we are most familiar with: daily routines, social rituals and the return of the seasons are just a few relatable examples. To this end, recurrence plots (RP) provide a systematic framework to quantify the recurrence of states. Despite their conceptual simplicity, they are a versatile tool in the study of observational data. The global climate is a complex system for which an understanding based on observational data is not only of academical relevance, but vital for the predurance of human societies within the planetary boundaries. Contextualizing current global climate change, however, requires observational data far beyond the instrumental period. The palaeoclimate record offers a valuable archive of proxy data but demands methodological approaches that adequately address its complexities. In this regard, the following dissertation aims at devising novel and further developing existing methods in the framework of recurrence analysis (RA). The proposed research questions focus on using RA to capture scale-dependent properties in nonlinear time series and tailoring recurrence quantification analysis (RQA) to characterize seasonal variability in palaeoclimate records ('Palaeoseasonality'). In the first part of this thesis, we focus on the methodological development of novel approaches in RA. The predictability of nonlinear (palaeo)climate time series is limited by abrupt transitions between regimes that exhibit entirely different dynamical complexity (e.g. crossing of 'tipping points'). These possibly depend on characteristic time scales. RPs are well-established for detecting transitions and capture scale-dependencies, yet few approaches have combined both aspects. We apply existing concepts from the study of self-similar textures to RPs to detect abrupt transitions, considering the most relevant time scales. This combination of methods further results in the definition of a novel recurrence based nonlinear dependence measure. Quantifying lagged interactions between multiple variables is a common problem, especially in the characterization of high-dimensional complex systems. The proposed 'recurrence flow' measure of nonlinear dependence offers an elegant way to characterize such couplings. For spatially extended complex systems, the coupled dynamics of local variables result in the emergence of spatial patterns. These patterns tend to recur in time. Based on this observation, we propose a novel method that entails dynamically distinct regimes of atmospheric circulation based on their recurrent spatial patterns. Bridging the two parts of this dissertation, we next turn to methodological advances of RA for the study of Palaeoseasonality. Observational series of palaeoclimate 'proxy' records involve inherent limitations, such as irregular temporal sampling. We reveal biases in the RQA of time series with a non-stationary sampling rate and propose a correction scheme. In the second part of this thesis, we proceed with applications in Palaeoseasonality. A review of common and promising time series analysis methods shows that numerous valuable tools exist, but their sound application requires adaptions to archive-specific limitations and consolidating transdisciplinary knowledge. Next, we study stalagmite proxy records from the Central Pacific as sensitive recorders of mid-Holocene El Ni{\~n}o-Southern Oscillation (ENSO) dynamics. The records' remarkably high temporal resolution allows to draw links between ENSO and seasonal dynamics, quantified by RA. The final study presented here examines how seasonal predictability could play a role for the stability of agricultural societies. The Classic Maya underwent a period of sociopolitical disintegration that has been linked to drought events. Based on seasonally resolved stable isotope records from Yok Balum cave in Belize, we propose a measure of seasonal predictability. It unveils the potential role declining seasonal predictability could have played in destabilizing agricultural and sociopolitical systems of Classic Maya populations. The methodological approaches and applications presented in this work reveal multiple exciting future research avenues, both for RA and the study of Palaeoseasonality.},
  language  = {en}
}
@phdthesis{Clodong2004,
  author    = {Clodong, S{\´e}bastien},
  title     = {Recurrent outbreaks in ecology : chaotic dynamics in complex networks},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001626},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Gegenstand der Dissertation ist die Untersuchung von wiederkehrenden Ausbr{\"u}chen (wie z.B. Epidemien) in der Natur. Dies gelang anhand von Modellen, die die Dynamik von Phytoplankton und die Ausbreitung von Krankheiten zwischen St{\"a}dten beschreiben. Diese beide Systeme bilden hervorragende Beispiele f{\"u}r solche Ph{\"a}nomene. Die Frage, ob die in der Zeit wiederkehrenden Ausbr{\"u}che ein Ausdruck chaotischer Dynamik sein k{\"o}nnen, ist aktuell in der {\"O}kologie und fasziniert Wissenschaftler dieser Disziplin. Wir konnten zeigen, dass sich das Plankton-Modell im Falle von periodischem Antreiben {\"u}ber die N{\"a}hrstoffe in einem chaotischen Regime befindet. Diese Dynamik wurde als die komplexe Wechselwirkung zweier Oszillatoren verstanden. Ebenfalls wurde die Ausbreitung von Epidemien in Netzwerken wechselwirkender St{\"a}dte mit unterschiedlichen Gr{\"o}ssen untersucht. Daf{\"u}r wurde zun{\"a}chst die Kopplung zwischen zwei St{\"a}dten als Verh{\"a}ltnis der Stadtgr{\"o}ssen eingef{\"u}hrt. Es konnte gezeigt werden, dass das System sich in einem globalen zweij{\"a}hrigen Zyklus, der auch in den realen Daten beobachtet wird, befinden kann. Der Effekt von Heterogenit{\"a}t in der Gr{\"o}sseverteilung ist durch gewichtete Kopplung von generischen Modellen (Zelt- und Logistische Abbildung) in Netzwerken im Detail untersucht worden. Eine neue Art von Kopplungsfunktion mit nichtlinearer S{\"a}ttigung wurde eingef{\"u}hrt, um die Stabilit{\"a}t des Systems zu gew{\"a}hrleisten. Diese Kopplung beinhaltet einen Parameter, der es erlaubt, die Netzwerktopologie von globaler Kopplung in gerichtete Netzwerke gleichm{\"a}ssig umzuwandeln. Die Dynamik des Systems wurde anhand von Bifurkationsdiagrammen untersucht. Zum Verst{\"a}ndnis dieser Dynamik wurde eine effektive Theorie, die die beobachteten Bifurkationen sehr gut nachahmt, entwickelt.},
  language  = {en}
}
@phdthesis{Cemeljic2005,
  author    = {Cemeljic, Miljenko},
  title     = {Resistive magnetohydrodynamic jets from protostellar accretion disks},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001845},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Astrophysikalische Jets sind ausgedehnte, kollimierte Massenausfl{\"u}sse von verschiedenen astronomischen Objekten. Zeitabh{\"a}ngige magnetohydrodynamische (MHD) Simulationen der Jet-Entwicklung m{\"u}ssen den Akrretionsprozess in der Scheibe ber{\"u}cksichtigen, da der Jet aus der Scheibenmaterie gespeist wird. Allerdings ist die simultane Berechnung der Entwicklung von Scheibe und Jet schwierig, da die charakteristischen Zeitskalen unterschiedlich sind. Selbst{\"a}hnliche Modelle zeigten, daß eine Beschreibung der Jetentstehung aus einer Akkretionsscheibe durch rein magnetische Prozesse m{\"o}glich ist.},
  language  = {en}
}
@phdthesis{Boedecker2013,
  author    = {Boedecker, Geesche},
  title     = {Resonance Fluorescence in a Photonic Crystal},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69591},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {The problem under consideration in the thesis is a two level atom in a photonic crystal and a pumping laser. The photonic crystal provides an environment for the atom, that modifies the decay of the exited state, especially if the atom frequency is close to the band gap. The population inversion is investigated als well as the emission spectrum. The dynamics is analysed in the context of open quantum systems. Due to the multiple reflections in the photonic crystal, the system has a finite memory that inhibits the Markovian approximation. In the Heisenberg picture the equations of motion for the system variables form a infinite hierarchy of integro-differential equations. To get a closed system, approximations like a weak coupling approximation are needed. The thesis starts with a simple photonic crystal that is amenable to analytic calculations: a one-dimensional photonic crystal, that consists of alternating layers. The Bloch modes inside and the vacuum modes outside a finite crystal are linked with a transformation matrix that is interpreted as a transfer matrix. Formulas for the band structure, the reflection from a semi-infinite crystal, and the local density of states in absorbing crystals are found; defect modes and negative refraction are discussed. The quantum optics section of the work starts with the discussion of three problems, that are related to the full resonance fluorescence problem: a pure dephasing model, the driven atom and resonance fluorescence in free space. In the lowest order of the system-environment coupling, the one-time expectation values for the full problem are calculated analytically and the stationary states are discussed for certain cases. For the calculation of the two time correlation functions and spectra, the additional problem of correlations between the two times appears. In the Markovian case, the quantum regression theorem is valid. In the general case, the fluctuation dissipation theorem can be used instead. The two-time correlation functions are calculated by the two different methods. Within the chosen approximations, both methods deliver the same result. Several plots show the dependence of the spectrum on the parameters. Some examples for squeezing spectra are shown with different approximations. A projection operator method is used to establish two kinds of Markovian expansion with and without time convolution. The lowest order is identical with the lowest order of system environment coupling, but higher orders give different results.},
  language  = {en}
}
@phdthesis{Inal2013,
  author    = {Inal, Sahika},
  title     = {Responsive polymers for optical sensing applications},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70806},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {LCST-type synthetic thermoresponsive polymers can reversibly respond to certain stimuli in aqueous media with a massive change of their physical state. When fluorophores, that are sensitive to such changes, are incorporated into the polymeric structure, the response can be translated into a fluorescence signal. Based on this idea, this thesis presents sensing schemes which transduce the stimuli-induced variations in the solubility of polymer chains with covalently-bound fluorophores into a well-detectable fluorescence output. Benefiting from the principles of different photophysical phenomena, i.e. of fluorescence resonance energy transfer and solvatochromism, such fluorescent copolymers enabled monitoring of stimuli such as the solution temperature and ionic strength, but also of association/disassociation mechanisms with other macromolecules or of biochemical binding events through remarkable changes in their fluorescence properties. For instance, an aqueous ratiometric dual sensor for temperature and salts was developed, relying on the delicate supramolecular assembly of a thermoresponsive copolymer with a thiophene-based conjugated polyelectrolyte. Alternatively, by taking advantage of the sensitivity of solvatochromic fluorophores, an increase in solution temperature or the presence of analytes was signaled as an enhancement of the fluorescence intensity. A simultaneous use of the sensitivity of chains towards the temperature and a specific antibody allowed monitoring of more complex phenomena such as competitive binding of analytes. The use of different thermoresponsive polymers, namely poly(N-isopropylacrylamide) and poly(meth)acrylates bearing oligo(ethylene glycol) side chains, revealed that the responsive polymers differed widely in their ability to perform a particular sensing function. In order to address questions regarding the impact of the chemical structure of the host polymer on the sensing performance, the macromolecular assembly behavior below and above the phase transition temperature was evaluated by a combination of fluorescence and light scattering methods. It was found that although the temperature-triggered changes in the macroscopic absorption characteristics were similar for these polymers, properties such as the degree of hydration or the extent of interchain aggregations differed substantially. Therefore, in addition to the demonstration of strategies for fluorescence-based sensing with thermoresponsive polymers, this work highlights the role of the chemical structure of the two popular thermoresponsive polymers on the fluorescence response. The results are fundamentally important for the rational choice of polymeric materials for a specific sensing strategy.},
  language  = {en}
}
@phdthesis{Weber2004,
  author    = {Weber, Michael H.},
  title     = {Robotic telescopes \& Doppler imaging : measuring differential rotation on long-period active stars},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001834},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Auf der Sonne sind viele Ph{\"a}nomene zu sehen die mit der solaren magnetischen Aktivit{\"a}t zusammenh{\"a}ngen. Das daf{\"u}r zust{\"a}ndige Magnetfeld wird durch einen Dynamo erzeugt, der sich vermutlich am Boden der Konvektionszone in der sogenannten Tachocline befindet. Angetrieben wird der Dynamo teils von der differenziellen Rotation, teils von den magnetischen Turbulenzen in der Konvektionszone. Die differentielle Rotation kann an der Sonnenoberfl{\"a}che durch beobachten der Sonnenfleckbewegungen gemessen werden.Um einen gr{\"o}ßeren Parameterraum zum Testen von Dynamotheorien zu erhalten, kann man diese Messungen auch auf andere Sterne ausdehnen. Das prim{\"a}re Problem dabei ist, dass die Oberfl{\"a}chen von Sternen nicht direkt beobachtet werden k{\"o}nnen. Indirekt kann man dies jedoch mit Hilfe der Doppler-imaging Methode erreichen, die die Doppler-Verbreitung der Spektrallinien von schnell rotierenden Sternen ben{\"u}tzt. Um jedoch ein Bild der Sternoberfl{\"a}che zu erhalten, bedarf es vieler hochaufgel{\"o}ster spektroskopischer Beobachtungen, die gleichm{\"a}ßig {\"u}ber eine Sternrotation verteilt sein m{\"u}ssen. F{\"u}r Sterne mit langen Rotationsperioden sind diese Beobachtungen nur schwierig durchzuf{\"u}hren. Das neue robotische Observatorium STELLA adressiert dieses Problem und bietet eine auf Dopplerimaging abgestimmte Ablaufplanung der Beobachtungen an. Dies wird solche Beobachtungen nicht nur leichter durchf{\"u}hrbar machen, sondern auch effektiver gestalten.Als Vorschau welche Ergebnisse mit STELLA erwartet werden k{\"o}nnen dient eine Studie an sieben Sternen die allesamt eine lange (zwischen sieben und 25 Tagen) Rotationsperiode haben. Alle Sterne zeigen differentielle Rotation, allerdings sind die Messfehler aufgrund der nicht zufriedenstellenden Datenqualit{\"a}t von gleicher Gr{\"o}ßenordnung wie die Ergebnisse, ein Problem das bei STELLA nicht auftreten wird. Um die Konsistenz der Ergebnisse zu pr{\"u}fen wurde wenn m{\"o}glich sowohl eine Kreuzkorrelationsanalyse als auch die sheared-image Methode angewandt. Vier von diesen sieben Sternen weisen eine differentielle Rotation in umgekehrter Richtung auf als auf der Sonne zu sehen ist. Die restlichen drei Sterne weisen schwache, aber in der Richtung sonnen{\"a}hnliche differentielle Rotation auf.Abschließend werden diese neuen Messungen mit bereits publizierten Werten kombiniert, und die so erhaltenen Daten auf Korrelationen zwischen differentieller Rotation, Rotationsperiode, Evolutionsstaus, Spektraltyp und Vorhandensein eines Doppelsterns {\"u}berpr{\"u}ft. Alle Sterne zusammen zeigen eine signifikante Korrelation zwischen dem Betrag der differenziellen Rotation und der Rotationsperiode. Unterscheidet man zwischen den Richtungen der differentiellen Rotation, so bleibt nur eine Korrelation der Sterne mit antisolarem Verhalten. Dar{\"u}berhinaus zeigt sich auch, dass Doppelsterne schw{\"a}cher differentiell rotieren.},
  language  = {en}
}
@phdthesis{Kornhuber2017,
  author    = {Kornhuber, Kai},
  title     = {Rossby wave dynamics and changes in summertime weather extremes},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 222},
  year      = {2017},
  abstract  = {Extreme weather events like heatwaves and floods severely affect societies with impacts ranging from economic damages to losses in human lifes. Global warming caused by anthropogenic greenhouse gas emissions is expected to increase their frequency and intensity, particularly in the warm season. Next to these thermodynamic changes, climate change might also impact the large scale atmospheric circulation.Such dynamic changes might additionally act on the occurence of extreme weather events, but involved mechanisms are often highly non-linear. Therefore, large uncertainty exists on the exact nature of these changes and the related risks to society. Particularly in the densely populated mid-latitudes weather patterns are governed by the large scale circulation like the jet-streams and storm tracks. Extreme weather in this region is often related to persistent weather systems associated with a strongly meandering jet-stream. Such meanders are called Rossby waves. Under specific conditions they can become slow moving, stretched around the entire hemisphere and generate simultaneaous heat- and rainfall extremes in far-away regions. This thesis aims at enhancing the understanding of synoptic-scale, circumglobal Rossby waves and the associated risks of dynamical changes to society. More specific, the analyses investigate their relation to extreme weather, regions at risk, under which conditions they are generated, and the influence of anthropogenic climate change on those conditions now, in the past and in the future. I find that circumglobal Rossby waves promoted simultaneous occuring weather extremes across the northern hemisphere in several recent summers. Further, I present evidence that they are often linked to quasiresonant-amplification of planetary waves. These events include the 2003 European heatwave and the Moscow heatwave of 2010. This non-linear mechanism acts on the upper level flow through trapping and amplification of stationary synoptic scale waves. I show that this resonance mechanism acts in both hemispheres and is related to extreme weather. A main finding is that circumglobal Rossby waves primarily occur as two specific teleconnection patterns associated with a wave 5 and wave 7 pattern in the northern hemisphere, likely due to the favourable longitudinal distance of prominent mountain ridges here. Furthermore, I identify those regions which are particularly at risk: The central United States, western Europe and the Ukraine/Russian region. Moreover, I present evidence that the wave 7 pattern has and extreme weather in these regions. My results suggest that the increase in frequency can be linked to favourable changes in large scale temperature gradients, which I show to be largely underestimated by model simulations. Using surface temperature fingerprint as proxy for investigating historic and future model ensembles, evidence is presented that anthropogenic warming has likely increased the probability for the occurence of circumglobal Rossby waves. Further it is shown that this might lead to a doubling of such events until the end of the century under a high-emission scenario. Overall, this thesis establishes several atmosphere-dynamical pathways by which changes in large scale temperature gradients might link to persistent boreal summer weather. It highlights the societal risks associated with the increasing occurence of a newly discovered Rossby wave teleconnection pattern, which has the potential to cause simultaneaous heat-extremes in the mid-latitudinal bread-basket regions. In addition, it provides further evidence that the traditional picture by which quasi-stationary Rossby waves occur only in the low wavenumber regime, should be reconsidered.},
  language  = {en}
}
@phdthesis{Hlawenka2018,
  author    = {Hlawenka, Peter},
  title     = {Samarium hexaboride},
  school      = {Universit{\"a}t Potsdam},
  pages     = {116, XXI},
  year      = {2018},
  language  = {en}
}
@phdthesis{Ahlers2001,
  author    = {Ahlers, Volker},
  title     = {Scaling and synchronization in deterministic and stochastic nonlinear dynamical systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000320},
  school      = {Universit{\"a}t Potsdam},
  year      = {2001},
  abstract  = {Gegenstand dieser Arbeit ist die Untersuchung universeller Skalengesetze, die in gekoppelten chaotischen Systemen beobachtet werden. Ergebnisse werden erzielt durch das Ersetzen der chaotischen Fluktuationen in der St{\"o}rungsdynamik durch stochastische Prozesse. Zun{\"a}chst wird ein zeitkontinuierliches stochastisches Modell f{\"u}rschwach 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 der Fokker-Planck-Gleichung werden Skalengesetze hergeleitet, die von Ergebnissen numerischer Simulationen best{\"a}tigt werden. Anschließend wird der neuartige Effekt der vermiedenen Kreuzung von Lyapunov-Exponenten schwach gekoppelter ungeordneter chaotischer Systeme beschrieben, der qualitativ der Abstoßung zwischen Energieniveaus in Quantensystemen {\"a}hnelt. Unter Benutzung der f{\"u}r die coupling sensitivity of chaos gewonnenen Skalengesetze wird ein asymptotischer Ausdruck f{\"u}r die Verteilungsfunktion kleiner Abst{\"a}nde zwischen Lyapunov-Exponenten hergeleitet und mit Ergebnissen numerischer Simulationen verglichen. Schließlich wird gezeigt, dass der Synchronisations{\"u}bergang in starkgekoppelten r{\"a}umlich ausgedehnten chaotischen Systemen einem kontinuierlichen Phasen{\"u}bergang entspricht, mit der Kopplungsst{\"a}rke und dem Synchronisationsfehler als Kontroll- beziehungsweise Ordnungsparameter. Unter Benutzung von Ergebnissen numerischer Simulationen sowie theoretischen {\"U}berlegungen anhand einer partiellen Differentialgleichung mit multiplikativem Rauschen werden die Universalit{\"a}tsklassen der zwei beobachteten {\"U}bergangsarten bestimmt (Kardar-Parisi-Zhang-Gleichung mit S{\"a}ttigungsterm, gerichtete Perkolation).},
  language  = {en}
}
@phdthesis{Kappel2012,
  author    = {Kappel, Marcel},
  title     = {Scattering effects in the sound wave propagation of instrument soundboards},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62676},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {In the western hemisphere, the piano is one of the most important instruments. While its evolution lasted for more than three centuries, and the most important physical aspects have already been investigated, some parts in the characterization of the piano remain not well understood. Considering the pivotal piano soundboard, the effect of ribs mounted on the board exerted on the sound radiation and propagation in particular, is mostly neglected in the literature. The present investigation deals exactly with the sound wave propagation effects that emerge in the presence of an array of equally-distant mounted ribs at a soundboard. Solid-state theory proposes particular eigenmodes and -frequencies for such arrangements, which are comparable to single units in a crystal. Following this 'linear chain model' (LCM), differences in the frequency spectrum are observable as a distinct band structure. Also, the amplitudes of the modes are changed, due to differences of the damping factor. These scattering effects were not only investigated for a well-understood conceptional rectangular soundboard (multichord), but also for a genuine piano resonance board manufactured by the piano maker company 'C. Bechstein Pianofortefabrik'. To obtain the possibility to distinguish between the characterizing spectra both with and without mounted ribs, the typical assembly plan for the Bechstein instrument was specially customized. Spectral similarities and differences between both boards are found in terms of damping and tone. Furthermore, specially prepared minimal-invasive piezoelectric polymer sensors made from polyvinylidene fluoride (PVDF) were used to record solid-state vibrations of the investigated system. The essential calibration and characterization of these polymer sensors was performed by determining the electromechanical conversion, which is represented by the piezoelectric coefficient. Therefore, the robust 'sinusoidally varying external force' method was applied, where a dynamic force perpendicular to the sensor's surface, generates movable charge carriers. Crucial parameters were monitored, with the frequency response function as the most important one for acousticians. Along with conventional condenser microphones, the sound was measured as solid-state vibration as well as airborne wave. On this basis, statements can be made about emergence, propagation, and also the overall radiation of the generated modes of the vibrating system. Ultimately, these results acoustically characterize the entire system.},
  language  = {en}
}
@phdthesis{Pfrang2023,
  author    = {Pfrang, Konstantin Johannes},
  title     = {Search for light primordial black holes with VERITAS using gamma γ-ray and optical observations},
  doi       = {10.25932/publishup-58726},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-587266},
  school      = {Universit{\"a}t Potsdam},
  pages     = {139},
  year      = {2023},
  abstract  = {The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is an array of four imaging atmospheric Cherenkov telescopes (IACTs). VERITAS is sensitive to very-high-energy gamma-rays in the range of 100 GeV to >30 TeV. Hypothesized primordial black holes (PBHs) are attractive targets for IACTs. If they exist, their potential cosmological impact reaches beyond the candidacy for constituents of dark matter. The sublunar mass window is the largest unconstrained range of PBH masses. This thesis aims to develop novel concepts searching for light PBHs with VERITAS. PBHs below the sublunar window lose mass due to Hawking radiation. They would evaporate at the end of their lifetime, leading to a short burst of gamma-rays. If PBHs formed at about 10^15 g, the evaporation would occur nowadays. Detecting these signals might not only confirm the existence of PBHs but also prove the theory of Hawking radiation. This thesis probes archival VERITAS data recorded between 2012 and 2021 for possible PBH signals. This work presents a new automatic approach to assess the quality of the VERITAS data. The array-trigger rate and far infrared temperature are well suited to identify periods with poor data quality. These are masked by time cuts to obtain a consistent and clean dataset which contains about 4222 hours. The PBH evaporations could occur at any location in the field of view or time within this data. Only a blind search can be performed to identify these short signals. This thesis implements a data-driven deep learning based method to search for short transient signals with VERITAS. It does not depend on the modelling of the effective area and radial acceptance. This work presents the first application of this method to actual observational IACT data. This thesis develops new concepts dealing with the specifics of the data and the transient detection method. These are reflected in the developed data preparation pipeline and search strategies. After correction for trial factors, no candidate PBH evaporation is found in the data. Thus, new constraints of the local rate of PBH evaporations are derived. At the 99\% confidence limit it is below <1.07 * 10^5 pc^-3 yr^-1. This constraint with the new, independent analysis approach is in the range of existing limits for the evaporation rate. This thesis also investigates an alternative novel approach to searching for PBHs with IACTs. Above the sublunar window, the PBH abundance is constrained by optical microlensing studies. The sampling speed, which is of order of minutes to hours for traditional optical telescopes, is a limiting factor in expanding the limits to lower masses. IACTs are also powerful instruments for fast transient optical astronomy with up to O(ns) sampling. This thesis investigates whether IACTs might constrain the sublunar window with optical microlensing observations. This study confirms that, in principle, the fast sampling speed might allow extending microlensing searches into the sublunar mass window. However, the limiting factor for IACTs is the modest sensitivity to detect changes in optical fluxes. This thesis presents the expected rate of detectable events for VERITAS as well as prospects of possible future next-generation IACTs. For VERITAS, the rate of detectable microlensing events in the sublunar range is ~10^-6 per year of observation time. The future prospects for a 100 times more sensitive instrument are at ~0.05 events per year.},
  language  = {en}
}
@phdthesis{Ksianzou2010,
  author    = {Ksianzou, Viachaslau},
  title     = {Second-order nonlinear optical interactions and cascading effects in thinorganic films},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-49186},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {The presented work describes new concepts of fast switching elements based on principles of photonics. The waveguides working in visible and infra-red ranges are put in a basis of these elements. And as materials for manufacturing of waveguides the transparent polymers, dopped by molecules of the dyes possessing second order nonlinear-optical properties are proposed. The work shows how nonlinear-optical processes in such structures can be implemented by electro-optical and opto-optical control circuit signals. In this paper we consider the complete cycle of fabrication of several types of integral photonic elements. The theoretical analysis of high-intensity beam propagation in media with second-order optical nonlinearity is performed. Quantitative estimations of necessary conditions of occurrence of the nonlinear-optical phenomena of the second order taking into account properties of used materials are made. The paper describes the various stages of manufacture of the basic structure of the integrated photonics: a planar waveguide. Using the finite element method the structure of the electromagnetic field inside the waveguide in different modes was analysed. A separate part of the work deals with the creation of composite organic materials with high optical nonlinearity. Using the methods of quantum chemistry, the dependence of nonlinear properties of dye molecules from its structure were investigated in details. In addition, the paper discusses various methods of inducing of an optical nonlinearity in dye-doping of polymer films. In the work, for the first time is proposed the use of spatial modulation of nonlinear properties of waveguide according Fibonacci law. This allows involving several different nonlinear optical processes simultaneously. The final part of the work describes various designs of integrated optical modulators and switches constructed of organic nonlinear optical waveguides. A practical design of the optical modulator based on Mach-Zehnder interferometer made by a photolithography on polymer film is presented.},
  language  = {en}
}
@phdthesis{Bittermann2015,
  author    = {Bittermann, Klaus},
  title     = {Semi-empirical sea-level modelling},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-93881},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 88},
  year      = {2015},
  abstract  = {Semi-empirical sea-level models (SEMs) exploit physically motivated empirical relationships between global sea level and certain drivers, in the following global mean temperature. This model class evolved as a supplement to process-based models (Rahmstorf (2007)) which were unable to fully represent all relevant processes. They thus failed to capture past sea-level change (Rahmstorf et al. (2012)) and were thought likely to underestimate future sea-level rise. Semi-empirical models were found to be a fast and useful tool for exploring the uncertainties in future sea-level rise, consistently giving significantly higher projections than process-based models. In the following different aspects of semi-empirical sea-level modelling have been studied. Models were first validated using various data sets of global sea level and temperature. SEMs were then used on the glacier contribution to sea level, and to infer past global temperature from sea-level data via inverse modelling. Periods studied encompass the instrumental period, covered by tide gauges (starting 1700 CE (Common Era) in Amsterdam) and satellites (first launched in 1992 CE), the era from 1000 BCE (before CE) to present, and the full length of the Holocene (using proxy data). Accordingly different data, model formulations and implementations have been used. It could be shown in Bittermann et al. (2013) that SEMs correctly predict 20th century sea-level when calibrated with data until 1900 CE. SEMs also turned out to give better predictions than the Intergovernmental Panel on Climate Change (IPCC) 4th assessment report (AR4, IPCC (2007)) models, for the period from 1961-2003 CE. With the first multi-proxy reconstruction of global sea-level as input, estimate of the human-induced component of modern sea-level change and projections of future sea-level rise were calculated (Kopp et al. (2016)). It turned out with 90\% confidence that more than 40 \% of the observed 20th century sea-level rise is indeed anthropogenic. With the new semi-empirical and IPCC (2013) 5th assessment report (AR5) projections the gap between SEM and process-based model projections closes, giving higher credibility to both. Combining all scenarios, from strong mitigation to business as usual, a global sea-level rise of 28-131 cm relative to 2000 CE, is projected with 90\% confidence. The decision for a low carbon pathway could halve the expected global sea-level rise by 2100 CE. Present day temperature and thus sea level are driven by the globally acting greenhouse-gas forcing. Unlike that, the Milankovich forcing, acting on Holocene timescales, results mainly in a northern-hemisphere temperature change. Therefore a semi-empirical model can be driven with northernhemisphere temperatures, which makes it possible to model the main subcomponent of sea-level change over this period. It showed that an additional positive constant rate of the order of the estimated Antarctic sea-level contribution is then required to explain the sea-level evolution over the Holocene. Thus the global sea level, following the climatic optimum, can be interpreted as the sum of a temperature induced sea-level drop and a positive long-term contribution, likely an ongoing response to deglaciation coming from Antarctica.},
  language  = {en}
}
@phdthesis{Soriano2016,
  author    = {Soriano, Manuel Flores},
  title     = {Short-term evolution and coexistence of photospheric and chromospheric activity on LQ Hydrae},
  school      = {Universit{\"a}t Potsdam},
  pages     = {90},
  year      = {2016},
  language  = {en}
}
@phdthesis{Mari2012,
  author    = {Mari, Andrea},
  title     = {Signatures of non-classicality in optomechanical systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59814},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {This thesis contains several theoretical studies on optomechanical systems, i.e. physical devices where mechanical degrees of freedom are coupled with optical cavity modes. This optomechanical interaction, mediated by radiation pressure, can be exploited for cooling and controlling mechanical resonators in a quantum regime. The goal of this thesis is to propose several new ideas for preparing meso- scopic mechanical systems (of the order of 10^15 atoms) into highly non-classical states. In particular we have shown new methods for preparing optomechani-cal pure states, squeezed states and entangled states. At the same time, proce-dures for experimentally detecting these quantum effects have been proposed. In particular, a quantitative measure of non classicality has been defined in terms of the negativity of phase space quasi-distributions. An operational al- gorithm for experimentally estimating the non-classicality of quantum states has been proposed and successfully applied in a quantum optics experiment. The research has been performed with relatively advanced mathematical tools related to differential equations with periodic coefficients, classical and quantum Bochner's theorems and semidefinite programming. Nevertheless the physics of the problems and the experimental feasibility of the results have been the main priorities.},
  language  = {en}
}
@phdthesis{Uyaver2004,
  author    = {Uyaver, Sahin},
  title     = {Simulation of annealed polyelectrolytes in poor solvents},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001488},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Polymere sind lange kettenartige Molek{\"u}le. Sie bestehen aus vielen elementaren chemischen Einheiten, den Monomeren, die durch kovalente Bindungen aneinander gekettet sind. Polyelektrolyte sind Polymere, die ionisierbare Monomeren enthalten. Aufgrund ihrer speziellen Eigenschaften sind Polyelektrolyte sowohl in der Molekular- und Zellbiologie von großen Bedeutung als auch in der Chemie großtechnisch relevant. Verglichen mit ungeladenen Polymeren sind Polyelektrolyte theoretisch noch wenig verstanden. Insbesondere gilt dies f{\"u}r Polyelektrolyte in sogenanntem schlechten L{\"o}sungsmittel. Ein schlechtes L{\"o}sungsmittel bewirkt eine effektive Anziehung zwischen den Monomeren. F{\"u}r Polyelektrolyte in schlechtem L{\"o}sungsmittel kommt es daher zu einer Konkurrenz zwischen dieser Anziehung und der elektrostatischen Abstoßung. Geladene Polymere werden im Rahmen der chemischen Klassifikation in starke und schwache Polyelektrolyte unterschieden. Erstere zeigen vollst{\"a}ndige Dissoziation unabh{\"a}ngig vom pH-Wert der L{\"o}sung. Die Position der Ladungen auf der Kette wird ausschließlich w{\"a}hrend der Polymersynthese festgelegt. In der Physik spricht man deshalb von Polyelektrolyten mit eingefrorener Ladungsverteilung (quenched polyelectrolytes). Im Falle von schwachen Polyelektrolyten ist die Ladungsdichte auf der Kette nicht konstant, sondern wird durch der pH-Wert der L{\"o}sung kontrolliert. Durch Rekombinations- und Dissoziationsprozesse sind die Ladungen auf der Kette beweglich. Im allgemeinen stellt sich eine inhomogene Gleichgewichtsverteilung ein, die mit der Struktur der Kette gekoppelt ist. Diese Polymere werden deshalb auch Polyelektrolyte mit Gleichgewichtsladungsverteilung (annealed polyelectrolytes) genannt. Wegen des zus{\"a}tzlichen Freiheitsgrades in der Ladungsverteilung werden eine Reihe ungew{\"o}hnlicher Eigenschaften theoretisch vorhergesagt. Mit Hilfe von Simulationen ist es zum ersten Mal gelungen, zu zeigen daß 'annealed' Polyelektrolyte in relativ schlechtem L{\"o}sungsmittel einen diskontinuierlichen Phasen{\"u}bergang durchlaufen, wenn ein kritischer pH-Werts der L{\"o}sung {\"u}berschritten wird. Bei diesem Phasen{\"u}bergang, gehen die Polyelektolyte von einer schwach geladenen kompakten globul{\"a}ren Struktur zu einer stark geladenen gestreckten Konfiguration {\"u}ber. Aufgrund theoretischer Vorhersagen wird erwartet, daß die globul{\"a}re Struktur in weniger schlechtem L{\"o}sungsmittel instabil wird und sich eine Perlenkettenkonfiguration ausbildet. Diese Vorhersage konnte f{\"u}r 'annealed' Polyelektrolyte mit den durchgef{\"u}hrten Simulationen zum ersten Mal best{\"a}tigt werden - inzwischen auch durch erste experimentelle Ergebnisse. Schließlich zeigen die Simulationen auch, daß annealed Polyelektrolyte bei einer kritischen Salzkonzentration in der L{\"o}sung einen scharfen {\"U}bergang zwischen einem stark geladenen gestreckten Zustand und einem schwach geladenen globul{\"a}ren Zustand aufweisen, wiederum in {\"U}bereinstimmung mit theoretischen Erwartungen.},
  language  = {en}
}
@phdthesis{Stoyanov2011,
  author    = {Stoyanov, Hristiyan},
  title     = {Soft nanocomposites with enhanced electromechanical response for dielectric elastomer actuators},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51194},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 \% reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 \% over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 \% reduction of the driving electric field) as well as in the maximum actuation strain (250 \%). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation.},
  language  = {en}
}
@phdthesis{Maerten2015,
  author    = {Maerten, Lena},
  title     = {Spectroscopic perspectives on ultrafast coupling phenomena in perovskite oxides},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-77623},
  school      = {Universit{\"a}t Potsdam},
  year      = {2015},
  abstract  = {In this thesis, I study ultrafast dynamics in perovskite oxides using time resolved broadband spectroscopy. I focus on the observation of coherent phonon propagation by time resolved Brillouin scattering: following the excition of metal transducer films with a femtosecond infrared pump pulse, coherent phonon dynamics in the GHz frequency range are triggered. Their propagation is monitored using a delayed white light probe pulse. The technique is illustrated on various thin films and multilayered samples. I apply the technique to investigate the linear and nonlinear acoustic response in bulk SrTiO_3, which displays a ferroelastic phase transition from a cubic to a tetragonal structural phase at T_a=105 K. In the linear regime, I observe a coupling of the observed acoustic phonon mode to the softening optic modes describing the phase transition. In the nonlinear regime, I find a giant slowing down of the sound velocity in the low temperature phase that is only observable for a strain amplitude exceeding the tetragonality of the material. It is attributed to a coupling of the high frequency phonons to ferroelastic domain walls in the material. I propose a new mechanism for the coupling of strain waves to the domain walls that is only effective for high amplitude strain. A detailed study of the phonon attenuation across a wide temperature range shows that the phonon attenuation at low temperatures is influenced by the domain configuration, which is determined by interface strain. Preliminary measurements on magnetic-ferroelectric multilayers reveal that the excitation fluence needs to be carefully controlled when dynamics at phase transitions are studied.},
  language  = {en}
}
@phdthesis{Scholz2012,
  author    = {Scholz, Markus Reiner},
  title     = {Spin polarization, circular dichroism, and robustness of topological surface states},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-96686},
  school      = {Universit{\"a}t Potsdam},
  pages     = {153},
  year      = {2012},
  abstract  = {Dreidimensionale topologische Isolatoren sind ein neues Materialsystem, welches dadurch charakterisiert ist, dass es in seinem Inneren isolierend an der Ober {\"a}che jedoch leitend ist. Urs{\"a}chlich f{\"u}r die Leitf{\"a}higkeit an der Ober {\"a}che sind sogenannte topologische Ober- {\"a}chenzust{\"a}nde, welche das Valenzband des Inneren mit dem Leitungsband des Inneren verbinden. An der Ober {\"a}che ist also die Bandl{\"u}cke, welche die isolierende Eigenschaft verursacht, geschlossen. Die vorliegende Arbeit untersucht diese Ober {\"a}chenzust{\"a}nde mittels spin- und winkelauf- gel{\"o}ster Photoemissionsspektroskopie. Es wird gezeigt, dass in den Materialien Bi2Se3 und Bi2Te3, in {\"u}bereinstimmung mit der Literatur, die entscheidenden Charakteristika eines topologischen Ober {\"a}chenzustands vorzu nden sind: Die Ober {\"a}chenzust{\"a}nde dieser Sys- teme durchqueren die Bandl{\"u}cke in ungerader Anzahl, sie sind nicht entartet und weisen folgerichtig eine hohe Spinpolarisation auf. Weiterhin wird durch Aufdampfen diverser Adsorbate gezeigt, dass der Ober {\"a}chenzust{\"a}n- de von Bi2Se3 und Bi2Te3, wie erwartet, extrem robust ist. Ober {\"a}chenzust{\"a}nde topologisch trivialer Systeme erf{\"u}llen diese Eigenschaft nicht; bereits kleine Verunreinigungen k{\"o}n- nen diese Zust{\"a}nde zerst{\"o}ren, bzw. die Ober {\"a}che isolierend machen. Die topologischen Ober {\"a}chenzust{\"a}nde k{\"o}nnen in der vorliegenden Arbeit noch bis zur Detektionsgrenze der experimentellen Messmethode nachgewiesen werden und die Ober {\"a}che bleibt Leitf{\"a}hig. Unter den Adsorbaten be ndet sich auch Eisen, ein bekanntermaßen magnetisches Materi- al. Eine der Grundvoraussetzungen f{\"u}r topologische Isolatoren ist die Zeitumkehrsymme- trie, die Elektronen, welche den topologischen Ober {\"a}chenzustand besetzen, vorschreibt, dass sie eine bestimmte Spinrichtung haben m{\"u}ssen, wenn sie sich beispielsweise nach links bewegen und den entgegengesetzten Spin wenn sie sich nach rechts bewegen. In magnetischen Materialien ist die Zeitumkehrsymmetrie jedoch explizit gebrochen und die gezeigte Robustheit des Ober {\"a}chenzustands gegen magnetische Materialien daher uner- wartet. Die Zeitumkehrsymmetrie sorgt auch daf{\"u}r, dass eine Streuung der Elektronen um 180°, beispielsweise an einem Gitterdefekt oder an einem Phonon strikt verboten ist. Bei einem solchen Streuprozess bleibt die Spinrichtung erhalten, da aber in der Gegenrichtung nur Zust{\"a}nde mit entgegengesetztem Spin vorhanden sind kann das Elektron nicht in diese Richtung gestreut werden. Dieses Prinzip wird anhand der Lebensdauer der durch Pho- toemission angeregten Zust{\"a}nde untersucht. Hierbei wird gezeigt, dass die Kopplung der Elektronen des Ober {\"a}chenzustands von Bi2Te3 an Phononen unerwartet hoch ist und dass sich eine Anisotropie in der Bandstruktur des Selbigen auch in den Lebensdauern der ange- regten Zust{\"a}nde widerspiegelt. Weiterhin wird gezeigt, dass sich die Ein {\"u}sse von magne- tischen und nicht-magnetischen Verunreinigungen auf die Lebensdauern stark voneinander unterscheiden. Im letzten Teil der vorliegenden Arbeit wird untersucht, ob eine Asymmetrie in der Inten- sit{\"a}tsverteilung der winkelaufgel{\"o}sten Photoemissionsspektren, bei Anregung mit zirku- lar polarisiertem Licht, in Bi2Te3 R{\"u}ckschl{\"u}sse auf die Spinpolarisation der Elektronen erlaubt. Bei Variation der Energie des eingestrahlten Lichts wird ein Vorzeichenwechsel der Asymmetrie beobachtet. Daraus l{\"a}sst sich schlussfolgern, dass die Asymmetrie keine R{\"u}ckschl{\"u}sse auf die Spinpolarisation erlaubt.},
  language  = {en}
}
@phdthesis{Krivenkov2020,
  author    = {Krivenkov, Maxim},
  title     = {Spin textures and electron scattering in nanopatterned monolayer graphene},
  doi       = {10.25932/publishup-48701},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-487017},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 176},
  year      = {2020},
  abstract  = {The current thesis is focused on the properties of graphene supported by metallic substrates and specifically on the behaviour of electrons in such systems. Methods of scanning tunneling microscopy, electron diffraction and photoemission spectroscopy were applied to study the structural and electronic properties of graphene. The purpose of the first part of this work is to introduce the most relevant aspects of graphene physics and the methodical background of experimental techniques used in the current thesis. The scientific part of this work starts with the extensive study by means of scanning tunneling microscopy of the nanostructures that appear in Au intercalated graphene on Ni(111). This study was aimed to explore the possible structural explanations of the Rashba-type spin splitting of ~100 meV experimentally observed in this system — much larger than predicted by theory. It was demonstrated that gold can be intercalated under graphene not only as a dense monolayer, but also in the form of well-periodic arrays of nanoclusters, a structure previously not reported. Such nanocluster arrays are able to decouple graphene from the strongly interacting Ni substrate and render it quasi-free-standing, as demonstrated by our DFT study. At the same time calculations confirm strong enhancement of the proximity-induced SOI in graphene supported by such nanoclusters in comparison to monolayer gold. This effect, attributed to the reduced graphene-Au distance in the case of clusters, provides a large Rashba-type spin splitting of ~60 meV. The obtained results not only provide a possible mechanism of SOI enhancement in this particular system, but they can be also generalized for graphene on other strongly interacting substrates intercalated by nanostructures of heavy noble d metals. Even more intriguing is the proximity of graphene to heavy sp-metals that were predicted to induce an intrinsic SOI and realize a spin Hall effect in graphene. Bismuth is the heaviest stable sp-metal and its compounds demonstrate a plethora of exciting physical phenomena. This was the motivation behind the next part of the current thesis, where structural and electronic properties of a previously unreported phase of Bi-intercalated graphene on Ir(111) were studied by means of scanning tunneling microscopy, spin- and angle-resolved photoemission spectroscopy and electron diffraction. Photoemission experiments revealed a remarkable, nearly ideal graphene band structure with strongly suppressed signatures of interaction between graphene and the Ir(111) substrate, moreover, the characteristic moir{\´e} pattern observed in graphene on Ir(111) by electron diffraction and scanning tunneling microscopy was strongly suppressed after intercalation. The whole set of experimental data evidences that Bi forms a dense intercalated layer that efficiently decouples graphene from the substrate. The interaction manifests itself only in the n-type charge doping (~0.4 eV) and a relatively small band gap at the Dirac point (~190 meV). The origin of this minor band gap is quite intriguing and in this work it was possible to exclude a wide range of mechanisms that could be responsible for it, such as induced intrinsic spin-orbit interaction, hybridization with the substrate states and corrugation of the graphene lattice. The main origin of the band gap was attributed to the A-B symmetry breaking and this conclusion found support in the careful analysis of the interference effects in photoemission that provided the band gap estimate of ~140 meV. While the previous chapters were focused on adjusting the properties of graphene by proximity to heavy metals, graphene on its own is a great object to study various physical effects at crystal surfaces. The final part of this work is devoted to a study of surface scattering resonances by means of photoemission spectroscopy, where this effect manifests itself as a distinct modulation of photoemission intensity. Though scattering resonances were widely studied in the past by means of electron diffraction, studies about their observation in photoemission experiments started to appear only recently and they are very scarce. For a comprehensive study of scattering resonances graphene was selected as a versatile model system with adjustable properties. After the theoretical and historical introduction to the topic of scattering resonances follows a detailed description of the unusual features observed in the photoemission spectra obtained in this work and finally the equivalence between these features and scattering resonances is proven. The obtained photoemission results are in a good qualitative agreement with the existing theory, as verified by our calculations in the framework of the interference model. This simple model gives a suitable explanation for the general experimental observations. The possibilities of engineering the scattering resonances were also explored. A systematic study of graphene on a wide range of substrates revealed that the energy position of the resonances is in a direct relation to the magnitude of charge transfer between graphene and the substrate. Moreover, it was demonstrated that the scattering resonances in graphene on Ir(111) can be suppressed by nanopatterning either by a superlattice of Ir nanoclusters or by atomic hydrogen. These effects were attributed to strong local variations of tork function and/or destruction of long-range order of thephene lattice. The tunability of scattering resonances can be applied for optoelectronic devices based on graphene. Moreover, the results of this study expand the general understanding of the phenomenon of scattering resonances and are applicable to many other materials besides graphene.},
  language  = {en}
}
@phdthesis{Kuhlbrodt2002,
  author    = {Kuhlbrodt, Till},
  title     = {Stability and variability of open-ocean deep convection in deterministic and stochastic simple models},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000622},
  school      = {Universit{\"a}t Potsdam},
  year      = {2002},
  abstract  = {Die Tiefenkonvektion ist ein wesentlicher Bestandteil der Zirkulation im Nordatlantik. Sie beeinflusst den nordw{\"a}rtigen W{\"a}rmetransport der thermohalinen Zirkulation. Ein Verst{\"a}ndnis ihrer Stabilit{\"a}t und Variabilit{\"a}t ist daher n{\"o}tig, um Klimaver{\"a}nderungen im Bereich des Nordatlantiks einsch{\"a}tzen zu k{\"o}nnen. Diese Arbeit hat zum Ziel, das konzeptionelle Verst{\"a}ndnis der Stabilit{\"a}t und der Variabilit{\"a}t der Tiefenkonvektion zu verbessern. Beobachtungsdaten aus der Labradorsee zeigen Phasen mit und ohne Tiefenkonvektion. Ein einfaches Modell mit zwei Boxen wird an diese Daten angepasst. Das Ergebnis legt nahe, dass die Labradorsee zwei koexistierende stabile Zust{\"a}nde hat, einen mit regelm{\"a}ßiger Tiefenkonvektion und einen ohne Tiefenkonvektion. Diese Bistabilit{\"a}t ergibt sich aus einer positiven Salzgehalts-R{\"u}ckkopplung, deren Ursache ein Netto-S{\"u}ßwassereintrag in die Deckschicht ist. Der konvektive Zustand kann schnell instabil werden, wenn der mittlere Antrieb sich hin zu w{\"a}rmeren oder weniger salzhaltigen Bedingungen {\"a}ndert. Die wetterbedingte Variabilit{\"a}t des externen Antriebs wird durch die Addition eines stochastischen Antriebsterms in das Modell eingebaut. Es zeigt sich, dass dann die Tiefenkonvektion h{\"a}ufig an- und wieder ausgeschaltet wird. Die mittlere Aufenthaltszeit in beiden Zust{\"a}nden ist ein Maß ihrer stochastischen Stabilit{\"a}t. Die stochastische Stabilit{\"a}t h{\"a}ngt in glatter Weise von den Parametern des Antriebs ab, im Gegensatz zu der deterministischen (nichtstochastischen) Stabilit{\"a}t, die sich abrupt {\"a}ndern kann. Sowohl das Mittel als auch die Varianz des stochastischen Antriebs beeinflussen die H{\"a}ufigkeit von Tiefenkonvektion. Eine Abnahme der Konvektionsh{\"a}ufigkeit, als Reaktion auf eine Abnahme des Salzgehalts an der Oberfl{\"a}che, kann zum Beispiel durch eine Zunahme der Variabilit{\"a}t in den W{\"a}rmefl{\"u}ssen kompensiert werden. Mit einem weiter vereinfachten Box-Modell werden einige Eigenschaften der stochastischen Stabilit{\"a}t analytisch untersucht. Es wird ein neuer Effekt beschrieben, die wandernde Monostabilit{\"a}t: Auch wenn die Tiefenkonvektion aufgrund ge{\"a}nderter Parameter des Antriebs kein stabiler Zustand mehr ist, kann der stochastische Antrieb immer noch h{\"a}ufig Konvektionsereignisse ausl{\"o}sen. Die analytischen Gleichungen zeigen explizit, wie die wandernde Monostabilit{\"a}t sowie andere Effekte von den Modellparametern abh{\"a}ngen. Diese Abh{\"a}ngigkeit ist f{\"u}r die mittleren Aufenthaltszeiten immer exponentiell, f{\"u}r die Wahrscheinlichkeit langer nichtkonvektiver Phasen dagegen nur dann, wenn diese Wahrscheinlichkeit gering ist. Es ist zu erwarten, dass wandernde Monostabilit{\"a}t auch in anderen Teilen des Klimasystems eine Rolle spielt. Insgesamt zeigen die Ergebnisse, dass die Stabilit{\"a}t der Tiefenkonvektion in der Labradorsee sehr empfindlich auf den Antrieb reagiert. Die Rolle der Variabilit{\"a}t ist entscheidend f{\"u}r ein Verst{\"a}ndnis dieser Empfindlichkeit. Kleine {\"A}nderungen im Antrieb k{\"o}nnen bereits die H{\"a}ufigkeit von Tiefenkonvektionsereignissen deutlich mindern, was sich vermutlich stark auf das regionale Klima auswirkt.},
  subject      = {Labradorsee ; Thermohaline Konvektion ; Stochastisches Modell},
  language  = {en}
}
@phdthesis{Kalbitz2011,
  author    = {Kalbitz, Ren{\´e}},
  title     = {Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57276},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Organic thin film transistors (TFT) are an attractive option for low cost electronic applications and may be used for active matrix displays and for RFID applications. To extend the range of applications there is a need to develop and optimise the performance of non-volatile memory devices that are compatible with the solution-processing fabrication procedures used in plastic electronics. A possible candidate is an organic TFT incorporating the ferroelectric co-polymer poly(vinylidenefluoride-trifluoroethylene)(P(VDF-TrFE)) as the gate insulator. Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) as the gate insu-lator. The capacitance spectra of MIS devices, were measured under different biases, showing the effect of charge accumulation and depletion on the Maxwell-Wagner peak. The position and height of this peak clearly indicates the lack of stable depletion behavior and the decrease of mobility when increasing the depletion zone width, i.e. upon moving into the P3HT bulk. The lack of stable depletion was further investigated with capacitance-voltage (C-V) measurements. When the structure was driven into depletion, C-V plots showed a positive flat-band voltage shift, arising from the change in polarization state of the ferroelectric insulator. When biased into accumulation, the polarization was reversed. It is shown that the two polarization states are stable i.e. no depolarization occurs below the coercive field. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flat-band voltage expected during the sweep to accumulation voltages. The measured output characteristics of the studied ferroelectric-field-effect transistors confirmed the results of the C-V plots. Furthermore, the results indicated a trapping of electrons at the positively charged surfaces of the ferroelectrically polarized P(VDF-TrFE) crystallites near the insulator/semiconductor in-terface during the first poling cycles. The study of the MIS structure by means of thermally stimulated current (TSC) revealed further evidence for the stability of the polarization under depletion voltages. It was shown, that the lack of stable depletion behavior is caused by the compensation of the orientational polarization by fixed electrons at the interface and not by the depolarization of the insulator, as proposed in several publications. The above results suggest a performance improvement of non-volatile memory devices by the optimization of the interface.},
  language  = {en}
}
@phdthesis{Koelsch2005,
  author    = {K{\"o}lsch, Patrick},
  title     = {Static and dynamic properties of soluble surfactants at the air/water interface},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5716},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Amphiphilic molecules contain a hydrophilic headgroup and a hydrophobic tail. The headgroup is polar or ionic and likes water, the tail is typically an aliphatic chain that cannot be accommodated in a polar environment. The prevailing molecular asymmetry leads to a spontaneous adsorption of amphiphiles at the air/water or oil/water interfaces. As a result, the surface tension and the surface rheology is changed. Amphiphiles are important tools to deliberately modify the interfacial properties of liquid interfaces and enable new phenomena such as foams which cannot be formed in a pure liquid. In this thesis we investigate the static and dynamic properties of adsorption layers of soluble amphiphiles at the air/water interface, the so called Gibbs monolayers. The classical way for an investigation of these systems is based on a thermodynamic analysis of the equilibrium surface tension as a function of the bulk composition in the framework of Gibbs theory. However, thermodynamics does not provide any structural information and several recent publications challenge even fundamental text book concepts. The experimental investigation faces difficulties imposed by the low surface coverage and the presence of dissolved amphiphiles in the adjacent bulk phase. In this thesis we used a suite of techniques with the sensitivity to detect less than a monolayer of molecules at the air-water interface. Some of these techniques are extremely complex such as infrared visible sum frequency generation (IR-VIS SFG) spectroscopy or second harmonic generation (SHG). Others are traditional techniques, such as ellipsometry employed in new ways and pushed to new limits. Each technique probes selectively different parts of the interface and the combination provides a profound picture of the interfacial architecture. The first part of the thesis is dedicated to the distribution of ions at interfaces. Adsorption layers of ionic amphiphiles serve as model systems allowing to produce a defined surface charge. The charge of the monolayer is compensated by the counterions. As a result of a complex zoo of interactions there will be a defined distribution of ions at the interface, however, its experimental determination is a big scientific challenge. We could demonstrate that a combination of linear and nonlinear techniques gives direct insights in the prevailing ion distribution. Our investigations reveal specific ion effects which cannot be described by classical Poisson-Boltzmann mean field type theories. Adsorption layer and bulk phase are in thermodynamic equilibrium, however, it is important to stress that there is a constant molecular exchange between adsorbed and dissolved species. This exchange process is a key element for the understanding of some of the thermodynamic properties. An excellent way to study Gibbs monolayers is to follow the relaxation from a non-equilibrium to an equilibrium state. Upon compression amphiphiles must leave the adsorption layer and dissolve in the adjacent bulk phase. Upon expansion amphiphiles must adsorb at the interface to restore the equilibrium coverage. Obviously the frequency of the expansion and compression cycles must match the molecular exchange processes. At too low frequencies the equilibrium is maintained at all times. If the frequency is too fast the system behaves as a monolayer of insoluble surfactants. In this thesis we describe an unique variant of an oscillating bubble technique that measures precisely the real and imaginary part of the complex dilational modulus E in a frequency range up to 500 Hz. The extension of about two decades in the time domain in comparison to the conventional method of an oscillating drop is a tremendous achievement. The imaginary part of the complex dilational modulus E is a consequence of a dissipative process which is interpreted as an intrinsic surface dilational viscosity. The IR-VIS SFG spectra of the interfacial water provide a molecular interpretation of the underlying dissipative process.},
  subject      = {Nichtlineare Optik},
  language  = {en}
}
@phdthesis{Kiel2012,
  author    = {Kiel, Mareike},
  title     = {Static and ultrafast optical properties of nanolayered composites : gold nanoparticles embedded in polyelectrolytes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61823},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {In the course of this thesis gold nanoparticle/polyelectrolyte multilayer structures were prepared, characterized, and investigated according to their static and ultrafast optical properties. Using the dip-coating or spin-coating layer-by-layer deposition method, gold-nanoparticle layers were embedded in a polyelectrolyte environment with high structural perfection. Typical structures exhibit four repetition units, each consisting of one gold-particle layer and ten double layers of polyelectrolyte (cationic+anionic polyelectrolyte). The structures were characterized by X-ray reflectivity measurements, which reveal Bragg peaks up to the seventh order, evidencing the high stratication of the particle layers. In the same measurements pronounced Kiessig fringes were observed, which indicate a low global roughness of the samples. Atomic force microscopy (AFM) images veried this low roughness, which results from the high smoothing capabilities of polyelectrolyte layers. This smoothing effect facilitates the fabrication of stratified nanoparticle/polyelectrolyte multilayer structures, which were nicely illustrated in a transmission electron microscopy image. The samples' optical properties were investigated by static spectroscopic measurements in the visible and UV range. The measurements revealed a frequency shift of the reflectance and of the plasmon absorption band, depending on the thickness of the polyelectrolyte layers that cover a nanoparticle layer. When the covering layer becomes thicker than the particle interaction range, the absorption spectrum becomes independent of the polymer thickness. However, the reflectance spectrum continues shifting to lower frequencies (even for large thicknesses). The range of plasmon interaction was determined to be in the order of the particle diameter for 10 nm, 20 nm, and 150 nm particles. The transient broadband complex dielectric function of a multilayer structure was determined experimentally by ultrafast pump-probe spectroscopy. This was achieved by simultaneous measurements of the changes in the reflectance and transmittance of the excited sample over a broad spectral range. The changes in the real and imaginary parts of the dielectric function were directly deduced from the measured data by using a recursive formalism based on the Fresnel equations. This method can be applied to a broad range of nanoparticle systems where experimental data on the transient dielectric response are rare. This complete experimental approach serves as a test ground for modeling the dielectric function of a nanoparticle compound structure upon laser excitation.},
  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{Hantschmann2023,
  author    = {Hantschmann, Markus},
  title     = {Stimulated resonant inelastic X-ray scattering in transition metal systems},
  doi       = {10.25932/publishup-58476},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-584761},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xv, 160},
  year      = {2023},
  abstract  = {With the implementation of intense, short pulsed light sources throughout the last years, the powerful technique of resonant inelastic X-ray scattering (RIXS) became feasible for a wide range of experiments within femtosecond dynamics in correlated materials and molecules. In this thesis I investigate the potential to bring RIXS into the fluence regime of nonlinear X-ray-matter interactions, especially focusing on the impact of stimulated scattering on RIXS in transition metal systems in a transmission spectroscopy geometry around transition metal L-edges. After presenting the RIXS toolbox and the capabilities of free electron laser light sources for ultrafast intense X-ray experiments, the thesis explores an experiment designed to understand the impact of stimulated scattering on diffraction and direct beam transmission spectroscopy on a CoPd multilayer system. The experiments require short X-ray pulses that can only be generated at free electron lasers (FEL). Here the pulses are not only short, but also very intense, which opens the door to nonlinear X-ray-matter interactions. In the second part of this thesis, we investigate observations in the nonlinear interaction regime, look at potential difficulties for classic spectroscopy and investigate possibilities to enhance the RIXS through stimulated scattering. Here, a study on stimulated RIXS is presented, where we investigate the light field intensity dependent CoPd demagnetization in transmission as well as scattering geometry. Thereby we show the first direct observation of stimulated RIXS as well as light field induced nonlinear effects, namely the breakdown of scattering intensity and the increase in sample transmittance. The topic is of ongoing interest and will just increase in relevance as more free electron lasers are planned and the number of experiments at such light sources will continue to increase in the near future. Finally we present a discussion on the accessibility of small DOS shifts in the absorption-band of transition metal complexes through stimulated resonant X-ray scattering. As these shifts occur for example in surface states this finding could expand the experimental selectivity of NEXAFS and RIXS to the detectability of surface states. We show how stimulation can indeed enhance the visibility of DOS shifts through the detection of stimulated spectral shifts and enhancements in this theoretical study. We also forecast the observation of stimulated enhancements in resonant excitation experiments at FEL sources in systems with a high density of states just below the Fermi edge and in systems with an occupied to unoccupied DOS ratio in the valence band above 1.},
  language  = {en}
}
@phdthesis{Erdmann2005,
  author    = {Erdmann, Thorsten},
  title     = {Stochastic dynamics of adhesion clusters under force},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5564},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Adhesion of biological cells to their environment is mediated by two-dimensional clusters of specific adhesion molecules which are assembled in the plasma membrane of the cells. Due to the activity of the cells or external influences, these adhesion sites are usually subject to physical forces. In recent years, the influence of such forces on the stability of cellular adhesion clusters was increasingly investigated. In particular, experimental methods that were originally designed for the investigation of single bond rupture under force have been applied to investigate the rupture of adhesion clusters. The transition from single to multiple bonds, however, is not trivial and requires theoretical modelling. Rupture of biological adhesion molecules is a thermally activated, stochastic process. In this work, a stochastic model for the rupture and rebinding dynamics of clusters of parallel adhesion molecules under force is presented. In particular, the influence of (i) a constant force as it may be assumed for cellular adhesion clusters is investigated and (ii) the influence of a linearly increasing force as commonly used in experiments is considered. Special attention is paid to the force-mediated cooperativity of parallel adhesion bonds. Finally, the influence of a finite distance between receptors and ligands on the binding dynamics is investigated. Thereby, the distance can be bridged by polymeric linker molecules which tether the ligands to a substrate.},
  subject      = {Biophysik},
  language  = {en}
}
@phdthesis{Korn2007,
  author    = {Korn, Christian},
  title     = {Stochastic dynamics of cell adhesion in hydrodynamic flow},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12997},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {In this thesis the interplay between hydrodynamic transport and specific adhesion is theoretically investigated. An important biological motivation for this work is the rolling adhesion of white blood cells experimentally investigated in flow chambers. There, specific adhesion is mediated by weak bonds between complementary molecular building blocks which are either located on the cell surface (receptors) or attached to the bottom plate of the flow chamber (ligands). The model system under consideration is a hard sphere covered with receptors moving above a planar ligand-bearing wall. The motion of the sphere is influenced by a simple shear flow, deterministic forces, and Brownian motion. An algorithm is given that allows to numerically simulate this motion as well as the formation and rupture of bonds between receptors and ligands. The presented algorithm spatially resolves receptors and ligands. This opens up the perspective to apply the results also to flow chamber experiments done with patterned substrates based on modern nanotechnological developments. In the first part the influence of flow rate, as well as of the number and geometry of receptors and ligands, on the probability for initial binding is studied. This is done by determining the mean time that elapses until the first encounter between a receptor and a ligand occurs. It turns out that besides the number of receptors, especially the height by which the receptors are elevated above the surface of the sphere plays an important role. These findings are in good agreement with observations of actual biological systems like white blood cells or malaria-infected red blood cells. Then, the influence of bonds which have formed between receptors and ligands, but easily rupture in response to force, on the motion of the sphere is studied. It is demonstrated that different states of motion-for example rolling-can be distinguished. The appearance of these states depending on important model parameters is then systematically investigated. Furthermore, it is shown by which bond property the ability of cells to stably roll in a large range of applied flow rates is increased. Finally, the model is applied to another biological process, the transport of spherical cargo particles by molecular motors. In analogy to the so far described systems molecular motors can be considered as bonds that are able to actively move. In this part of the thesis the mean distance the cargo particles are transported is determined.},
  language  = {en}
}
@phdthesis{Kleinen2005,
  author    = {Kleinen, Thomas Christopher},
  title     = {Stochastic information in the assessment of climate change},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5382},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Stochastic information, to be understood as \&quot;information gained by the application of stochastic methods\&quot;, is proposed as a tool in the assessment of changes in climate. This thesis aims at demonstrating that stochastic information can improve the consideration and reduction of uncertainty in the assessment of changes in climate. The thesis consists of three parts. In part one, an indicator is developed that allows the determination of the proximity to a critical threshold. In part two, the tolerable windows approach (TWA) is extended to a probabilistic TWA. In part three, an integrated assessment of changes in flooding probability due to climate change is conducted within the TWA. The thermohaline circulation (THC) is a circulation system in the North Atlantic, where the circulation may break down in a saddle-node bifurcation under the influence of climate change. Due to uncertainty in ocean models, it is currently very difficult to determine the distance of the THC to the bifurcation point. We propose a new indicator to determine the system's proximity to the bifurcation point by considering the THC as a stochastic system and using the information contained in the fluctuations of the circulation around the mean state. As the system is moved closer to the bifurcation point, the power spectrum of the overturning becomes \&quot;redder\&quot;, i.e. more energy is contained in the low frequencies. Since the spectral changes are a generic property of the saddle-node bifurcation, the method is not limited to the THC, but it could also be applicable to other systems, e.g. transitions in ecosystems. In part two, a probabilistic extension to the tolerable windows approach (TWA) is developed. In the TWA, the aim is to determine the complete set of emission strategies that are compatible with so-called guardrails. Guardrails are limits to impacts of climate change or to climate change itself. Therefore, the TWA determines the \&quot;maneuvering space\&quot; humanity has, if certain impacts of climate change are to be avoided. Due to uncertainty it is not possible to definitely exclude the impacts of climate change considered, but there will always be a certain probability of violating a guardrail. Therefore the TWA is extended to a probabilistic TWA that is able to consider \&quot;probabilistic uncertainty\&quot;, i.e. uncertainty that can be expressed as a probability distribution or uncertainty that arises through natural variability. As a first application, temperature guardrails are imposed, and the dependence of emission reduction strategies on probability distributions for climate sensitivities is investigated. The analysis suggests that it will be difficult to observe a temperature guardrail of 2\&deg;C with high probabilities of actually meeting the target. In part three, an integrated assessment of changes in flooding probability due to climate change is conducted. A simple hydrological model is presented, as well as a downscaling scheme that allows the reconstruction of the spatio-temporal natural variability of temperature and precipitation. These are used to determine a probabilistic climate impact response function (CIRF), a function that allows the assessment of changes in probability of certain flood events under conditions of a changed climate. The assessment of changes in flooding probability is conducted in 83 major river basins. Not all floods can be considered: Events that either happen very fast, or affect only a very small area can not be considered, but large-scale flooding due to strong longer-lasting precipitation events can be considered. Finally, the probabilistic CIRFs obtained are used to determine emission corridors, where the guardrail is a limit to the fraction of world population that is affected by a predefined shift in probability of the 50-year flood event. This latter analysis has two main results. The uncertainty about regional changes in climate is still very high, and even small amounts of further climate change may lead to large changes in flooding probability in some river systems.},
  subject      = {Anthropogene Klima{\"a}nderung},
  language  = {en}
}
@phdthesis{FrancoGonzalez2002,
  author    = {Franco Gonz{\´a}lez, Olga},
  title     = {Structural and spectroscopical study of crystals of 1,3,4-oxadiazole derivatives at high pressure},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000572},
  school      = {Universit{\"a}t Potsdam},
  year      = {2002},
  abstract  = {Die Suche nach neuen Materialien von technischem Interesse hat in den letzten Jahren neue Antriebe zu der Untersuchung organischer Verbindungen gegeben. Organische Substanzen haben viele Vorteile wie z.B. die M{\"o}glichkeit, ihre Eigenschaften durch verschiedene chemische und physikalische Techniken im Herstellung-Prozess f{\"u}r ein bestimmtes Ziel zu modifizieren. Oxadiazolverbindungen sind interessant aufgrund ihrer Nutzung als Material f{\"u}r Licht emittierende Dioden und Scintillatoren. Die physikalischen Eigenschaften eines Festk{\"o}rpers h{\"a}ngen von seiner Struktur ab. Unterschiedliche Strukturen entwickeln unterschiedliche intra- und intermolek{\"u}lare Wechselwirkungen. Eine ausgezeichnete Weise, um sowohl die intra- als auch die intermolekularen Wechselwirkungen eines bestimmtes Stoffes zu beeinflussen, ohne seine chemischen Charakteristiken zu {\"a}ndern, ist die Verwendung von hohem Druck. Wir haben den Einfluss von hohem Druck und hoher Temperatur auf die super-molekulare Struktur einiger Oxadiazolverbindungen im kristallinem Zustand untersucht. Aus diesen Untersuchungsergebnissen wurde eine Zustandsgleichung f{\"u}r diese Kristalle bestimmt. {\"U}berdies wurden die spektroskopischen Eigenschaften dieser Materialien unter hohem Druck charakterisiert.},
  subject      = {Oxadiazolderivate ; Kristallstruktur ; Hochdruck ; UV-VIS-Spektroskopie ; Raman-Spektroskopie},
  language  = {en}
}
@phdthesis{RodriguezLoureiro2018,
  author    = {Rodriguez Loureiro, Ignacio},
  title     = {Structural characterization of single and interacting soft interfaces displaying brushes of synthetic or biomolecular polymers},
  doi       = {10.25932/publishup-42367},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423675},
  school      = {Universit{\"a}t Potsdam},
  pages     = {132},
  year      = {2018},
  abstract  = {The interaction between surfaces displaying end-grafted hydrophilic polymer brushes plays important roles in biology and in many wet-technological applications. The outer surfaces of Gram-negative bacteria, for example, are composed of lipopolysaccharide (LPS) molecules exposing oligo- and polysaccharides to the aqueous environment. This unique, structurally complex biological interface is of great scientific interest as it mediates the interaction of bacteria with neighboring bacteria in colonies and biofilms. The interaction between polymer-decorated surfaces is generally coupled to the distance-dependent conformation of the polymer chains. Therefore, structural insight into the interacting surfaces is a prerequisite to understand the interaction characteristics as well as the underlying physical mechanisms. This problem has been addressed by theory, but accurate experimental data on polymer conformations under confinement are rare, because obtaining perturbation-free structural insight into buried soft interfaces is inherently difficult. In this thesis, lipid membrane surfaces decorated with hydrophilic polymers of technological and biological relevance are investigated under controlled interaction conditions, i.e., at defined surface separations. For this purpose, dedicated sample architectures and experimental tools are developed. Via ellipsometry and neutron reflectometry pressure-distance curves and distance-dependent polymer conformations in terms of brush compression and reciprocative interpenetration are determined. Additional element-specific structural insight into the end-point distribution of interacting brushes is obtained by standing-wave x-ray fluorescence (SWXF). The methodology is first established for poly[ethylene glycol] (PEG) brushes of defined length and grafting density. For this system, neutron reflectometry revealed pronounced brush interpenetration, which is not captured in common brush theories and therefore motivates rigorous simulation-based treatments. In the second step the same approach is applied to realistic mimics of the outer surfaces of Gram-negative bacteria: monolayers of wild type LPSs extracted from E. Coli O55:B5 displaying strain-specific O-side chains. The neutron reflectometry experiments yield unprecedented structural insight into bacterial interactions, which are of great relevance for the properties of biofilms.},
  language  = {en}
}
@phdthesis{Herzog2012,
  author    = {Herzog, Marc},
  title     = {Structural dynamics of photoexcited nanolayered perovskites studied by ultrafast x-ray diffraction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62632},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {This publication-based thesis represents a contribution to the active research field of ultrafast structural dynamics in laser-excited nanostructures. The investigation of such dynamics is mandatory for the understanding of the various physical processes on microscopic scales in complex materials which have great potentials for advances in many technological applications. I theoretically and experimentally examine the coherent, incoherent and anharmonic lattice dynamics of epitaxial metal-insulator heterostructures on timescales ranging from femtoseconds up to nanoseconds. To infer information on the transient dynamics in the photoexcited crystal lattices experimental techniques using ultrashort optical and x-ray pulses are employed. The experimental setups include table-top sources as well as large-scale facilities such as synchrotron sources. At the core of my work lies the development of a linear-chain model to simulate and analyze the photoexcited atomic-scale dynamics. The calculated strain fields are then used to simulate the optical and x-ray response of the considered thin films and multilayers in order to relate the experimental signatures to particular structural processes. This way one obtains insight into the rich lattice dynamics exhibiting coherent transport of vibrational energy from local excitations via delocalized phonon modes of the samples. The complex deformations in tailored multilayers are identified to give rise to highly nonlinear x-ray diffraction responses due to transient interference effects. The understanding of such effects and the ability to precisely calculate those are exploited for the design of novel ultrafast x-ray optics. In particular, I present several Phonon Bragg Switch concepts to efficiently generate ultrashort x-ray pulses for time-resolved structural investigations. By extension of the numerical models to include incoherent phonon propagation and anharmonic lattice potentials I present a new view on the fundamental research topics of nanoscale thermal transport and anharmonic phonon-phonon interactions such as nonlinear sound propagation and phonon damping. The former issue is exemplified by the time-resolved heat conduction from thin SrRuO3 films into a SrTiO3 substrate which exhibits an unexpectedly slow heat conductivity. Furthermore, I discuss various experiments which can be well reproduced by the versatile numerical models and thus evidence strong lattice anharmonicities in the perovskite oxide SrTiO3. The thesis also presents several advances of experimental techniques such as time-resolved phonon spectroscopy with optical and x-ray photons as well as concepts for the implementation of x-ray diffraction setups at standard synchrotron beamlines with largely improved time-resolution for investigations of ultrafast structural processes. This work forms the basis for ongoing research topics in complex oxide materials including electronic correlations and phase transitions related to the elastic, magnetic and polarization degrees of freedom.},
  language  = {en}
}
@phdthesis{Richter2007,
  author    = {Richter, Andreas},
  title     = {Structure formation and fractionation in systems of colloidal rods},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-13090},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {Nowadays, colloidal rods can be synthesized in large amounts. The rods are typically cylindrically and their length ranges from several nanometers to a few micrometers. In solution, systems of colloidal rodlike molecules or aggregates can form liquid-crystalline phases with long-range orientational and spatial order. In the present work, we investigate structure formation and fractionation in systems of rodlike colloids with the help of Monte Carlo simulations in the NPT ensemble. Repulsive interactions can successfully be mimicked by the hard rod model, which has been studied extensively in the past. In many cases, attractive interactions like van der Waals or depletion forces cannot be neglected, however. In the first part of this work, the phase behavior of monodisperse attractive rods is characterized for different interaction strengths. Phase diagrams as a function of rod length and pressure are presented. Most systems of synthesized mesoscopic rods have a polydisperse length distribution as a consequence of the longitudinal growth process of the rods. For many technical and research applications, a rather small polydispersity is desired in order to have well defined material properties. The polydispersity can be reduced by a spatial demixing (fractionation) of long and short rods. Fractionation and structure formation is studied in a tridisperse and a polydisperse bulk suspension of rods. We observe that the resulting structures depend distinctly on the interaction strength. The fractionation in the system is strongly enhanced with increasing interaction strength. Suspensions are typically confined in a container. We also examine the influence of adjacent substrates in systems of tridisperse and polydisperse rod suspensions. Three different substrate types are studied in detail: a planar wall, a corrugated substrate, and a substrate with rectangular cavities. We analyze the fluid structure close to the substrate and substrate controlled fractionation. The spatial arrangement of long and short rods in front of the substrate depends sensitively on the substrate structure and the pressure. Rods with a predefined length are segregated at substrates with rectangular cavities.},
  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{Kairaliyeva2023,
  author    = {Kairaliyeva, Talmira},
  title     = {Surfactant adorption at liquid interfaces measured by drop and bubble experiments},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VII, 117},
  year      = {2023},
  language  = {en}
}
@phdthesis{Quade2018,
  author    = {Quade, Markus},
  title     = {Symbolic regression for identification, prediction, and control of dynamical systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-419790},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 134},
  year      = {2018},
  abstract  = {In the present work, we use symbolic regression for automated modeling of dynamical systems. Symbolic regression is a powerful and general method suitable for data-driven identification of mathematical expressions. In particular, the structure and parameters of those expressions are identified simultaneously. We consider two main variants of symbolic regression: sparse regression-based and genetic programming-based symbolic regression. Both are applied to identification, prediction and control of dynamical systems. We introduce a new methodology for the data-driven identification of nonlinear dynamics for systems undergoing abrupt changes. Building on a sparse regression algorithm derived earlier, the model after the change is defined as a minimum update with respect to a reference model of the system identified prior to the change. The technique is successfully exemplified on the chaotic Lorenz system and the van der Pol oscillator. Issues such as computational complexity, robustness against noise and requirements with respect to data volume are investigated. We show how symbolic regression can be used for time series prediction. Again, issues such as robustness against noise and convergence rate are investigated us- ing the harmonic oscillator as a toy problem. In combination with embedding, we demonstrate the prediction of a propagating front in coupled FitzHugh-Nagumo oscillators. Additionally, we show how we can enhance numerical weather predictions to commercially forecast power production of green energy power plants. We employ symbolic regression for synchronization control in coupled van der Pol oscillators. Different coupling topologies are investigated. We address issues such as plausibility and stability of the control laws found. The toolkit has been made open source and is used in turbulence control applications. Genetic programming based symbolic regression is very versatile and can be adapted to many optimization problems. The heuristic-based algorithm allows for cost efficient optimization of complex tasks. We emphasize the ability of symbolic regression to yield white-box models. In contrast to black-box models, such models are accessible and interpretable which allows the usage of established tool chains.},
  language  = {en}
}
@phdthesis{RomanoBlasco2004,
  author    = {Romano Blasco, M. Carmen},
  title     = {Synchronization analysis by means of recurrences in phase space},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001756},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Die t{\"a}gliche Erfahrung zeigt uns, daß bei vielen physikalischen Systemen kleine {\"A}nderungen in den Anfangsbedingungen auch zu kleinen {\"A}nderungen im Verhalten des Systems f{\"u}hren. Wenn man z.B. das Steuerrad beim Auto fahren nur ein wenig zur Seite dreht, unterscheidet sich die Richtung des Wagens auch nur wenig von der urspr{\"u}nglichen Richtung. Aber es gibt auch Situationen, f{\"u}r die das Gegenteil dieser Regel zutrifft. Die Folge von Kopf und Zahl, die wir erhalten, wenn wir eine M{\"u}nze werfen, zeigt ein irregul{\"a}res oder chaotisches Zeitverhalten, da winzig kleine {\"A}nderungen in den Anfangsbedingungen, die z.B. durch leichte Drehung der Hand hervorgebracht werden, zu vollkommen verschiedenen Resultaten f{\"u}hren. In den letzten Jahren hat man sehr viele nichtlineare Systeme mit schnellen Rechnern untersucht und festgestellt, daß eine sensitive Abh{\"a}ngigkeit von den Anfangsbedingungen, die zu einem chaotischen Verhalten f{\"u}hrt, keinesfalls die Ausnahme darstellt, sondern eine typische Eigenschaft vieler Systeme ist. Obwohl chaotische Systeme kleinen {\"A}nderungen in den Anfangsbedingungen gegen{\"u}ber sehr empfindlich reagieren, k{\"o}nnen sie synchronisieren wenn sie durch eine gemeinsame {\"a}ußere Kraft getrieben werden, oder wenn sie miteinander gekoppelt sind. Das heißt, sie vergessen ihre Anfangsbedingungen und passen ihre Rhythmen aneinander. Diese Eigenschaft chaotischer Systeme hat viele Anwendungen, wie z.B. das Design von Kommunikationsger{\"a}te und die verschl{\"u}sselte {\"U}bertragung von Mitteilungen. Abgesehen davon, findet man Synchronisation in nat{\"u}rlichen Systemen, wie z.B. das Herz-Atmungssystem, raumverteilte {\"o}kologische Systeme, die Magnetoenzephalographische Aktivit{\"a}t von Parkinson Patienten, etc. In solchen komplexen Systemen ist es nicht trivial Synchronisation zu detektieren und zu quantifizieren. Daher ist es notwendig, besondere mathematische Methoden zu entwickeln, die diese Aufgabe erledigen. Das ist das Ziel dieser Arbeit. Basierend auf dergrundlegenden Idee von Rekurrenzen (Wiederkehr) von Trajektorien dynamischer Systeme, sind verschiedene Maße entwickelt worden, die Synchronisation in chaotischen und komplexen Systemen detektieren. Das Wiederkehr von Trajektorien erlaubt uns Vorhersagen {\"u}ber den zuk{\"u}nftigen Zustand eines Systems zu treffen. Wenn man diese Eigenschaft der Wiederkehr von zwei interagierenden Systemen vergleicht, kann man Schl{\"u}sse {\"u}ber ihre dynamische Anpassung oder Synchronisation ziehen. Ein wichtiger Vorteil der Rekurrenzmaße f{\"u}r Synchronisation ist die Robustheit gegen Rauschen und Instationari{\"a}t. Das erlaubt eine Synchronisationsanalyse in Systemen durchzuf{\"u}hren, die bisher nicht darauf untersucht werden konnten.},
  language  = {en}
}
@phdthesis{Bergner2011,
  author    = {Bergner, Andr{\´e}},
  title     = {Synchronization in complex systems with multiple time scales},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-53407},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {In the present work synchronization phenomena in complex dynamical systems exhibiting multiple time scales have been analyzed. Multiple time scales can be active in different manners. Three different systems have been analyzed with different methods from data analysis. The first system studied is a large heterogenous network of bursting neurons, that is a system with two predominant time scales, the fast firing of action potentials (spikes) and the burst of repetitive spikes followed by a quiescent phase. This system has been integrated numerically and analyzed with methods based on recurrence in phase space. An interesting result are the different transitions to synchrony found in the two distinct time scales. Moreover, an anomalous synchronization effect can be observed in the fast time scale, i.e. there is range of the coupling strength where desynchronization occurs. The second system analyzed, numerically as well as experimentally, is a pair of coupled CO₂ lasers in a chaotic bursting regime. This system is interesting due to its similarity with epidemic models. We explain the bursts by different time scales generated from unstable periodic orbits embedded in the chaotic attractor and perform a synchronization analysis of these different orbits utilizing the continuous wavelet transform. We find a diverse route to synchrony of these different observed time scales. The last system studied is a small network motif of limit cycle oscillators. Precisely, we have studied a hub motif, which serves as elementary building block for scale-free networks, a type of network found in many real world applications. These hubs are of special importance for communication and information transfer in complex networks. Here, a detailed study on the mechanism of synchronization in oscillatory networks with a broad frequency distribution has been carried out. In particular, we find a remote synchronization of nodes in the network which are not directly coupled. We also explain the responsible mechanism and its limitations and constraints. Further we derive an analytic expression for it and show that information transmission in pure phase oscillators, such as the Kuramoto type, is limited. In addition to the numerical and analytic analysis an experiment consisting of electrical circuits has been designed. The obtained results confirm the former findings.},
  language  = {en}
}
@phdthesis{MontbrioiFairen2004,
  author    = {Montbri{\´o} i Fairen, Ernest},
  title     = {Synchronization in ensembles of nonisochronous oscillators},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001492},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Diese Arbeit analysiert Synchronisationsphaenomene, die in grossen Ensembles von interagierenden Oszillatoren auftauchen. Im speziellen werden die Effekte von Nicht-Isochronizitaet (die Abhaengigkeit der Frequenz von der Amplitude des Oszillators) auf den makroskopischen Uebergang zur Synchronisation im Detail studiert. Die neu gefundenen Phaenomene (Anomale Synchronisation) werden sowohl in Populationen von Oszillatoren als auch zwischen Oszillator-Ensembles untersucht.},
  language  = {en}
}
@phdthesis{Vlasov2015,
  author    = {Vlasov, Vladimir},
  title     = {Synchronization of oscillatory networks in terms of global variables},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-78182},
  school      = {Universit{\"a}t Potsdam},
  pages     = {82},
  year      = {2015},
  abstract  = {Synchronization of large ensembles of oscillators is an omnipresent phenomenon observed in different fields of science like physics, engineering, life sciences, etc. The most simple setup is that of globally coupled phase oscillators, where all the oscillators contribute to a global field which acts on all oscillators. This formulation of the problem was pioneered by Winfree and Kuramoto. Such a setup gives a possibility for the analysis of these systems in terms of global variables. In this work we describe nontrivial collective dynamics in oscillator populations coupled via mean fields in terms of global variables. We consider problems which cannot be directly reduced to standard Kuramoto and Winfree models. In the first part of the thesis we adopt a method introduced by Watanabe and Strogatz. The main idea is that the system of identical oscillators of particular type can be described by a low-dimensional system of global equations. This approach enables us to perform a complete analytical analysis for a special but vast set of initial conditions. Furthermore, we show how the approach can be expanded for some nonidentical systems. We apply the Watanabe-Strogatz approach to arrays of Josephson junctions and systems of identical phase oscillators with leader-type coupling. In the next parts of the thesis we consider the self-consistent mean-field theory method that can be applied to general nonidentical globally coupled systems of oscillators both with or without noise. For considered systems a regime, where the global field rotates uniformly, is the most important one. With the help of this approach such solutions of the self-consistency equation for an arbitrary distribution of frequencies and coupling parameters can be found analytically in the parametric form, both for noise-free and noisy cases. We apply this method to deterministic Kuramoto-type model with generic coupling and an ensemble of spatially distributed oscillators with leader-type coupling. Furthermore, with the proposed self-consistent approach we fully characterize rotating wave solutions of noisy Kuramoto-type model with generic coupling and an ensemble of noisy oscillators with bi-harmonic coupling. Whenever possible, a complete analysis of global dynamics is performed and compared with direct numerical simulations of large populations.},
  language  = {en}
}
@phdthesis{Topaj2001,
  author    = {Topaj, Dmitri},
  title     = {Synchronization transitions in complex systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000367},
  school      = {Universit{\"a}t Potsdam},
  year      = {2001},
  abstract  = {Gegenstand dieser Arbeit ist die Untersuchung generischer Synchronisierungsph{\"a}nomene in interagierenden komplexen Systemen. Diese Ph{\"a}nomene werden u.a. in gekoppelten deterministischen chaotischen Systemen beobachtet. Bei sehr schwachen Interaktionen zwischen individuellen Systemen kann ein {\"U}bergang zum schwach koh{\"a}renten Verhalten der Systeme stattfinden. In gekoppelten zeitkontinuierlichen chaotischen Systemen manifestiert sich dieser {\"U}bergang durch den Effekt der Phasensynchronisierung, in gekoppelten chaotischen zeitdiskreten Systemen durch den Effekt eines nichtverschwindenden makroskopischen Feldes. Der {\"U}bergang zur Koh{\"a}renz in einer Kette lokal gekoppelter Oszillatoren, beschrieben durch Phasengleichungen, wird im Bezug auf die Symmetrien des Systems untersucht. Es wird gezeigt, daß die durch die Symmetrien verursachte Reversibilit{\"a}t des Systems nichttriviale topologische Eigenschaften der Trajektorien bedingt, so daß das als dissipativ konstruierte System in einem ganzen Parameterbereich quasi-Hamiltonische Z{\"u}ge aufweist, d.h. das Phasenvolumen ist im Schnitt erhalten, und die Lyapunov-Exponenten sind paarweise symmetrisch. Der {\"U}bergang zur Koh{\"a}renz in einem Ensemble global gekoppelter chaotischer Abbildungen wird durch den Verlust der Stabilit{\"a}t des entkoppelten Zustandes beschrieben. Die entwickelte Methode besteht darin, die Selbstkonsistenz des makroskopischen Feldes aufzuheben, und das Ensemble in Analogie mit einem Verst{\"a}rkerschaltkreis mit R{\"u}ckkopplung durch eine komplexe lineare {\"U}bertragungssfunktion zu charakterisieren. Diese Theorie wird anschließend f{\"u}r einige theoretisch interessanten F{\"a}lle verallgemeinert.},
  language  = {en}
}
@phdthesis{Kucklaender2006,
  author    = {Kuckl{\"a}nder, Nina},
  title     = {Synchronization via correlated noise and automatic control in ecological systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10826},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {<img src="http://vg00.met.vgwort.de/na/806c85cec18906a64e06" width="1" height="1" alt=""> Subject of this work is the possibility to synchronize nonlinear systems via correlated noise and automatic control. The thesis is divided into two parts. The first part is motivated by field studies on feral sheep populations on two islands of the St. Kilda archipelago, which revealed strong correlations due to environmental noise. For a linear system the population correlation equals the noise correlation (Moran effect). But there exists no systematic examination of the properties of nonlinear maps under the influence of correlated noise. Therefore, in the first part of this thesis the noise-induced correlation of logistic maps is systematically examined. For small noise intensities it can be shown analytically that the correlation of quadratic maps in the fixed-point regime is always smaller than or equal to the noise correlation. In the period-2 regime a Markov model explains qualitatively the main dynamical characteristics. Furthermore, two different mechanisms are introduced which lead to a higher correlation of the systems than the environmental correlation. The new effect of "correlation resonance" is described, i. e. the correlation yields a maximum depending on the noise intensity. In the second part of the thesis an automatic control method is presented which synchronizes different systems in a robust way. This method is inspired by phase-locked loops and is based on a feedback loop with a differential control scheme, which allows to change the phases of the controlled systems. The effectiveness of the approach is demonstrated for controlled phase synchronization of regular oscillators and foodweb models.},
  subject      = {Markov-Prozess},
  language  = {en}
}
@phdthesis{Kuehn2018,
  author    = {K{\"u}hn, Danilo},
  title     = {Synchrotron-based angle-resolved time-of-flight electron spectroscopy for dynamics in dichalogenides},
  school      = {Universit{\"a}t Potsdam},
  pages     = {147},
  year      = {2018},
  language  = {en}
}
@phdthesis{RamanVenkatesan2022,
  author    = {Raman Venkatesan, Thulasinath},
  title     = {Tailoring applications-relevant properties in poly(vinylidene fluoride)-based homo-, co- and ter-polymers through modification of their three-phase structure},
  doi       = {10.25932/publishup-54966},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549667},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 218},
  year      = {2022},
  abstract  = {Poly(vinylidene fluoride) (PVDF)-based homo-, co- and ter-polymers are well-known for their ferroelectric and relaxor-ferroelectric properties. Their semi-crystalline morphology consists of crystalline and amorphous phases, plus interface regions in between, and governs the relevant electro-active properties. In this work, the influence of chemical, thermal and mechanical treatments on the structure and morphology of PVDF-based polymers and on the related ferroelectric/relaxor-ferroelectric properties is investigated. Polymer films were prepared in different ways and subjected to various treatments such as annealing, quenching and stretching. The resulting changes in the transitions and relaxations of the polymer samples were studied by means of dielectric, thermal, mechanical and optical techniques. In particular, the origin(s) behind the mysterious mid-temperature transition (T_{mid}) that is observed in all PVDF-based polymers was assessed. A new hypothesis is proposed to describe the T_{mid} transition as a result of multiple processes taking place within the temperature range of the transition. The contribution of the individual processes to the observed overall transition depends on both the chemical structure of the monomer units and the processing conditions which also affect the melting transition. Quenching results in a decrease of the overall crystallinity and in smaller crystallites. On samples quenched after annealing, notable differences in the fractions of different crystalline phases have been observed when compared to samples that had been slowly cooled. Stretching of poly(vinylidene fluoride-tetrafluoroethylene) (P(VDF-TFE)) films causes an increase in the fraction of the ferroelectric β-phase with simultaneous increments in the melting point (T_m) and the crystallinity (\chi_c) of the copolymer. While an increase in the stretching temperature does not have a profound effect on the amount of the ferroelectric phase, its stability appears to improve. Measurements of the non-linear dielectric permittivity \varepsilon_2^\prime in a poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE- CFE)) relaxor-ferroelectric (R-F) terpolymer reveal peaks at 30 and 80 °C that cannot be identified in conventional dielectric spectroscopy. The former peak is associated with T_{mid}\ and may help to understand the non-zero \varepsilon_2^\prime values that are found for the paraelectric terpolymer phase. The latter peak can also be observed during cooling of P(VDF-TrFE) copolymer samples at 100 °C and is due to conduction processes and space-charge polarization as a result of the accumulation of real charges at the electrode-sample interface. Annealing lowers the Curie-transition temperature of the terpolymer as a consequence of its smaller ferroelectric-phase fraction, which by default exists even in terpolymers with relatively high CFE content. Changes in the transition temperatures are in turn related to the behavior of the hysteresis curves observed on differently heat-treated samples. Upon heating, the hysteresis curves evolve from those known for a ferroelectric to those of a typical relaxor-ferroelectric material. Comparing dielectric-hysteresis loops obtained at various temperatures, we find that annealed terpolymer films show higher electric-displacement values and lower coercive fields than the non-annealed samples - irrespective of the measurement temperature - and also exhibit ideal relaxor-ferroelectric behavior at ambient temperatures, which makes them excellent candidates for related applications at or near room temperature. However, non-annealed films - by virtue of their higher ferroelectric activity - show a larger and more stable remanent polarization at room temperature, while annealed samples need to be poled below 0 °C to induce a well-defined polarization. Overall, by modifying the three phases in PVDF-based polymers, it has been demonstrated how the preparation steps and processing conditions can be tailored to achieve the desired properties that are optimal for specific applications.},
  language  = {en}
}
@phdthesis{Jechow2009,
  author    = {Jechow, Andreas},
  title     = {Tailoring the emission of stripe-array diode lasers with external cavities to enable nonlinear frequency conversion},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  isbn      = {978-3-86956-031-1},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-39653},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ii, 139},
  year      = {2009},
  abstract  = {A huge number of applications require coherent radiation in the visible spectral range. Since diode lasers are very compact and efficient light sources, there exists a great interest to cover these applications with diode laser emission. Despite modern band gap engineering not all wavelengths can be accessed with diode laser radiation. Especially in the visible spectral range between 480 nm and 630 nm no emission from diode lasers is available, yet. Nonlinear frequency conversion of near-infrared radiation is a common way to generate coherent emission in the visible spectral range. However, radiation with extraordinary spatial temporal and spectral quality is required to pump frequency conversion. Broad area (BA) diode lasers are reliable high power light sources in the near-infrared spectral range. They belong to the most efficient coherent light sources with electro-optical efficiencies of more than 70\%. Standard BA lasers are not suitable as pump lasers for frequency conversion because of their poor beam quality and spectral properties. For this purpose, tapered lasers and diode lasers with Bragg gratings are utilized. However, these new diode laser structures demand for additional manufacturing and assembling steps that makes their processing challenging and expensive. An alternative to BA diode lasers is the stripe-array architecture. The emitting area of a stripe-array diode laser is comparable to a BA device and the manufacturing of these arrays requires only one additional process step. Such a stripe-array consists of several narrow striped emitters realized with close proximity. Due to the overlap of the fields of neighboring emitters or the presence of leaky waves, a strong coupling between the emitters exists. As a consequence, the emission of such an array is characterized by a so called supermode. However, for the free running stripe-array mode competition between several supermodes occurs because of the lack of wavelength stabilization. This leads to power fluctuations, spectral instabilities and poor beam quality. Thus, it was necessary to study the emission properties of those stripe-arrays to find new concepts to realize an external synchronization of the emitters. The aim was to achieve stable longitudinal and transversal single mode operation with high output powers giving a brightness sufficient for efficient nonlinear frequency conversion. For this purpose a comprehensive analysis of the stripe-array devices was done here. The physical effects that are the origin of the emission characteristics were investigated theoretically and experimentally. In this context numerical models could be verified and extended. A good agreement between simulation and experiment was observed. One way to stabilize a specific supermode of an array is to operate it in an external cavity. Based on mathematical simulations and experimental work, it was possible to design novel external cavities to select a specific supermode and stabilize all emitters of the array at the same wavelength. This resulted in stable emission with 1 W output power, a narrow bandwidth in the range of 2 MHz and a very good beam quality with M²<1.5. This is a new level of brightness and brilliance compared to other BA and stripe-array diode laser systems. The emission from this external cavity diode laser (ECDL) satisfied the requirements for nonlinear frequency conversion. Furthermore, a huge improvement to existing concepts was made. In the next step newly available periodically poled crystals were used for second harmonic generation (SHG) in single pass setups. With the stripe-array ECDL as pump source, more than 140 mW of coherent radiation at 488 nm could be generated with a very high opto-optical conversion efficiency. The generated blue light had very good transversal and longitudinal properties and could be used to generate biphotons by parametric down-conversion. This was feasible because of the improvement made with the infrared stripe-array diode lasers due to the development of new physical concepts.},
  language  = {en}
}
@phdthesis{Dixit2023,
  author    = {Dixit, Sneha},
  title     = {Tension-induced conformational changes of the Piezo protein-membrane nano-dome},
  school      = {Universit{\"a}t Potsdam},
  pages     = {94},
  year      = {2023},
  abstract  = {Mechanosensation is a fundamental biological process that provides the basis for sensing touch and pain as well as for hearing and proprioception. A special class of ion-channel proteins known as mechanosensitive proteins convert the mechanical stimuli into electrochemical signals to mediate this process. Mechanosensitive proteins undergo conformational changes in response to mechanical force, which eventually leads to the opening of the proteins' ion channel. Mammalian mechanosensitive proteins remained a long sought-after mystery until 2010 when a family of two proteins - Piezo1 and Piezo2 - was identifed as mechanosensors [1]. The cryo-EM structures of Piezo1 and Piezo2 protein were resolved in the last years and reveal a propeller-shaped homotrimer with 114 transmembrane helices [2, 3, 4, 5]. The protein structures are curved and have been suggested to deform the surrounding membrane into a nano-dome, which mechanically responds to membrane tension resulting from external forces [2]. In this thesis, the conformations of membrane-embedded Piezo1 and Piezo2 proteins and their tension-induced conformational changes are investigated using molecular dynamics simulations. Our coarse-grained molecular dynamics simulations show that the Piezo proteins induce curvature in the surrounding membrane and form a stable protein-membrane nano-dome in the tensionless membrane. These membrane-embedded Piezo proteins, however, adopt substantially less curved conformations in our simulations compared to the cryo-EM structures solved in detergent micelles, which agrees with recent experimental investigations of the overall Piezo nano-dome shape in membrane vesicles [6, 7, 8]. At high membrane tension, the Piezo proteins attain nearly planar conformations in our simulations. Our systematic investigation of Piezo proteins under different membrane tensions indicates a half-maximal conformational response at membrane tension values rather close to the experimentally suggested values of Piezo activation [9, 10]. In addition, our simulations indicate a widening of the Piezo1 ion channel at high membrane tension, which agrees with the channel widening observed in recent nearly flattened cryo-EM structures of Piezo1 in small membrane vesicles [11]. In contrast, the Piezo2 ion channel does not respond to membrane tension in our simulations. These different responses of the Piezo1 and Piezo2 ion channels in our simulations are in line with patch-clamp experiments, in which Piezo1, but not Piezo2, was shown to be activated by membrane tension alone [12].},
  language  = {en}
}
@phdthesis{Raetzel2013,
  author    = {R{\"a}tzel, Dennis},
  title     = {Tensorial spacetime geometries and background-independent quantum field theory},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-65731},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Famously, Einstein read off the geometry of spacetime from Maxwell's equations. Today, we take this geometry that serious that our fundamental theory of matter, the standard model of particle physics, is based on it. However, it seems that there is a gap in our understanding if it comes to the physics outside of the solar system. Independent surveys show that we need concepts like dark matter and dark energy to make our models fit with the observations. But these concepts do not fit in the standard model of particle physics. To overcome this problem, at least, we have to be open to matter fields with kinematics and dynamics beyond the standard model. But these matter fields might then very well correspond to different spacetime geometries. This is the basis of this thesis: it studies the underlying spacetime geometries and ventures into the quantization of those matter fields independently of any background geometry. In the first part of this thesis, conditions are identified that a general tensorial geometry must fulfill to serve as a viable spacetime structure. Kinematics of massless and massive point particles on such geometries are introduced and the physical implications are investigated. Additionally, field equations for massive matter fields are constructed like for example a modified Dirac equation. In the second part, a background independent formulation of quantum field theory, the general boundary formulation, is reviewed. The general boundary formulation is then applied to the Unruh effect as a testing ground and first attempts are made to quantize massive matter fields on tensorial spacetimes.},
  language  = {en}
}
@phdthesis{RiveraHernandez2012,
  author    = {Rivera Hern{\´a}ndez, Sergio},
  title     = {Tensorial spacetime geometries carrying predictive, interpretable and quantizable matter dynamics},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61869},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {Which tensor fields G on a smooth manifold M can serve as a spacetime structure? In the first part of this thesis, it is found that only a severely restricted class of tensor fields can provide classical spacetime geometries, namely those that can carry predictive, interpretable and quantizable matter dynamics. The obvious dependence of this characterization of admissible tensorial spacetime geometries on specific matter is not a weakness, but rather presents an insight: it was Maxwell theory that justified Einstein to promote Lorentzian manifolds to the status of a spacetime geometry. Any matter that does not mimick the structure of Maxwell theory, will force us to choose another geometry on which the matter dynamics of interest are predictive, interpretable and quantizable. These three physical conditions on matter impose three corresponding algebraic conditions on the totally symmetric contravariant coefficient tensor field P that determines the principal symbol of the matter field equations in terms of the geometric tensor G: the tensor field P must be hyperbolic, time-orientable and energy-distinguishing. Remarkably, these physically necessary conditions on the geometry are mathematically already sufficient to realize all kinematical constructions familiar from Lorentzian geometry, for precisely the same structural reasons. This we were able to show employing a subtle interplay of convex analysis, the theory of partial differential equations and real algebraic geometry. In the second part of this thesis, we then explore general properties of any hyperbolic, time-orientable and energy-distinguishing tensorial geometry. Physically most important are the construction of freely falling non-rotating laboratories, the appearance of admissible modified dispersion relations to particular observers, and the identification of a mechanism that explains why massive particles that are faster than some massless particles can radiate off energy until they are slower than all massless particles in any hyperbolic, time-orientable and energy-distinguishing geometry. In the third part of the thesis, we explore how tensorial spacetime geometries fare when one wants to quantize particles and fields on them. This study is motivated, in part, in order to provide the tools to calculate the rate at which superluminal particles radiate off energy to become infraluminal, as explained above. Remarkably, it is again the three geometric conditions of hyperbolicity, time-orientability and energy-distinguishability that allow the quantization of general linear electrodynamics on an area metric spacetime and the quantization of massive point particles obeying any admissible dispersion relation. We explore the issue of field equations of all possible derivative order in rather systematic fashion, and prove a practically most useful theorem that determines Dirac algebras allowing the reduction of derivative orders. The final part of the thesis presents the sketch of a truly remarkable result that was obtained building on the work of the present thesis. Particularly based on the subtle duality maps between momenta and velocities in general tensorial spacetimes, it could be shown that gravitational dynamics for hyperbolic, time-orientable and energy distinguishable geometries need not be postulated, but the formidable physical problem of their construction can be reduced to a mere mathematical task: the solution of a system of homogeneous linear partial differential equations. This far-reaching physical result on modified gravity theories is a direct, but difficult to derive, outcome of the findings in the present thesis. Throughout the thesis, the abstract theory is illustrated through instructive examples.},
  language  = {en}
}
@phdthesis{Pick2020,
  author    = {Pick, Leonie Johanna Lisa},
  title     = {The centennial evolution of geomagnetic activity and its driving mechanisms},
  doi       = {10.25932/publishup-47275},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-472754},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 135},
  year      = {2020},
  abstract  = {This cumulative thesis is concerned with the evolution of geomagnetic activity since the beginning of the 20th century, that is, the time-dependent response of the geomagnetic field to solar forcing. The focus lies on the description of the magnetospheric response field at ground level, which is particularly sensitive to the ring current system, and an interpretation of its variability in terms of the solar wind driving. Thereby, this work contributes to a comprehensive understanding of long-term solar-terrestrial interactions. The common basis of the presented publications is formed by a reanalysis of vector magnetic field measurements from geomagnetic observatories located at low and middle geomagnetic latitudes. In the first two studies, new ring current targeting geomagnetic activity indices are derived, the Annual and Hourly Magnetospheric Currents indices (A/HMC). Compared to existing indices (e.g., the Dst index), they do not only extend the covered period by at least three solar cycles but also constitute a qualitative improvement concerning the absolute index level and the ~11-year solar cycle variability. The analysis of A/HMC shows that (a) the annual geomagnetic activity experiences an interval-dependent trend with an overall linear decline during 1900-2010 of ~5 \% (b) the average trend-free activity level amounts to ~28 nT (c) the solar cycle related variability shows amplitudes of ~15-45 nT (d) the activity level for geomagnetically quiet conditions (Kp<2) lies slightly below 20 nT. The plausibility of the last three points is ensured by comparison to independent estimations either based on magnetic field measurements from LEO satellite missions (since the 1990s) or the modeling of geomagnetic activity from solar wind input (since the 1960s). An independent validation of the longterm trend is problematic mainly because the sensitivity of the locally measured geomagnetic activity depends on geomagnetic latitude. Consequently, A/HMC is neither directly comparable to global geomagnetic activity indices (e.g., the aa index) nor to the partly reconstructed open solar magnetic flux, which requires a homogeneous response of the ground-based measurements to the interplanetary magnetic field and the solar wind speed. The last study combines a consistent, HMC-based identification of geomagnetic storms from 1930-2015 with an analysis of the corresponding spatial (magnetic local time-dependent) disturbance patterns. Amongst others, the disturbances at dawn and dusk, particularly their evolution during the storm recovery phases, are shown to be indicative of the solar wind driving structure (Interplanetary Coronal Mass Ejections vs. Stream or Co-rotating Interaction Regions), which enables a backward-prediction of the storm driver classes. The results indicate that ICME-driven geomagnetic storms have decreased since 1930 which is consistent with the concurrent decrease of HMC. Out of the collection of compiled follow-up studies the inclusion of measurements from high-latitude geomagnetic observatories into the third study's framework seems most promising at this point.},
  language  = {en}
}
@phdthesis{Mergenthaler2009,
  author    = {Mergenthaler, Konstantin K.},
  title     = {The control of fixational eye movements},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-29397},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {In normal everyday viewing, we perform large eye movements (saccades) and miniature or fixational eye movements. Most of our visual perception occurs while we are fixating. However, our eyes are perpetually in motion. Properties of these fixational eye movements, which are partly controlled by the brainstem, change depending on the task and the visual conditions. Currently, fixational eye movements are poorly understood because they serve the two contradictory functions of gaze stabilization and counteraction of retinal fatigue. In this dissertation, we investigate the spatial and temporal properties of time series of eye position acquired from participants staring at a tiny fixation dot or at a completely dark screen (with the instruction to fixate a remembered stimulus); these time series were acquired with high spatial and temporal resolution. First, we suggest an advanced algorithm to separate the slow phases (named drift) and fast phases (named microsaccades) of these movements, which are considered to play different roles in perception. On the basis of this identification, we investigate and compare the temporal scaling properties of the complete time series and those time series where the microsaccades are removed. For the time series obtained during fixations on a stimulus, we were able to show that they deviate from Brownian motion. On short time scales, eye movements are governed by persistent behavior and on a longer time scales, by anti-persistent behavior. The crossover point between these two regimes remains unchanged by the removal of microsaccades but is different in the horizontal and the vertical components of the eyes. Other analyses target the properties of the microsaccades, e.g., the rate and amplitude distributions, and we investigate, whether microsaccades are triggered dynamically, as a result of earlier events in the drift, or completely randomly. The results obtained from using a simple box-count measure contradict the hypothesis of a purely random generation of microsaccades (Poisson process). Second, we set up a model for the slow part of the fixational eye movements. The model is based on a delayed random walk approach within the velocity related equation, which allows us to use the data to determine control loop durations; these durations appear to be different for the vertical and horizontal components of the eye movements. The model is also motivated by the known physiological representation of saccade generation; the difference between horizontal and vertical components concurs with the spatially separated representation of saccade generating regions. Furthermore, the control loop durations in the model suggest an external feedback loop for the horizontal but not for the vertical component, which is consistent with the fact that an internal feedback loop in the neurophysiology has only been identified for the vertical component. Finally, we confirmed the scaling properties of the model by semi-analytical calculations. In conclusion, we were able to identify several properties of the different parts of fixational eye movements and propose a model approach that is in accordance with the described neurophysiology and described limitations of fixational eye movement control.},
  language  = {en}
}
@phdthesis{Khosravi2023,
  author    = {Khosravi, Sara},
  title     = {The effect of new turbulence parameterizations for the stable surface layer on simulations of the Arctic climate},
  doi       = {10.25932/publishup-64352},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-643520},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIV, 119},
  year      = {2023},
  abstract  = {Arctic climate change is marked by intensified warming compared to global trends and a significant reduction in Arctic sea ice which can intricately influence mid-latitude atmospheric circulation through tropo- and stratospheric pathways. Achieving accurate simulations of current and future climate demands a realistic representation of Arctic climate processes in numerical climate models, which remains challenging. Model deficiencies in replicating observed Arctic climate processes often arise due to inadequacies in representing turbulent boundary layer interactions that determine the interactions between the atmosphere, sea ice, and ocean. Many current climate models rely on parameterizations developed for mid-latitude conditions to handle Arctic turbulent boundary layer processes. This thesis focuses on modified representation of the Arctic atmospheric processes and understanding their resulting impact on large-scale mid-latitude atmospheric circulation within climate models. The improved turbulence parameterizations, recently developed based on Arctic measurements, were implemented in the global atmospheric circulation model ECHAM6. This involved modifying the stability functions over sea ice and ocean for stable stratification and changing the roughness length over sea ice for all stratification conditions. Comprehensive analyses are conducted to assess the impacts of these modifications on ECHAM6's simulations of the Arctic boundary layer, overall atmospheric circulation, and the dynamical pathways between the Arctic and mid-latitudes. Through a step-wise implementation of the mentioned parameterizations into ECHAM6, a series of sensitivity experiments revealed that the combined impacts of the reduced roughness length and the modified stability functions are non-linear. Nevertheless, it is evident that both modifications consistently lead to a general decrease in the heat transfer coefficient, being in close agreement with the observations. Additionally, compared to the reference observations, the ECHAM6 model falls short in accurately representing unstable and strongly stable conditions. The less frequent occurrence of strong stability restricts the influence of the modified stability functions by reducing the affected sample size. However, when focusing solely on the specific instances of a strongly stable atmosphere, the sensible heat flux approaches near-zero values, which is in line with the observations. Models employing commonly used surface turbulence parameterizations were shown to have difficulties replicating the near-zero sensible heat flux in strongly stable stratification. I also found that these limited changes in surface layer turbulence parameterizations have a statistically significant impact on the temperature and wind patterns across multiple pressure levels, including the stratosphere, in both the Arctic and mid-latitudes. These significant signals vary in strength, extent, and direction depending on the specific month or year, indicating a strong reliance on the background state. Furthermore, this research investigates how the modified surface turbulence parameterizations may influence the response of both stratospheric and tropospheric circulation to Arctic sea ice loss. The most suitable parameterizations for accurately representing Arctic boundary layer turbulence were identified from the sensitivity experiments. Subsequently, the model's response to sea ice loss is evaluated through extended ECHAM6 simulations with different prescribed sea ice conditions. The simulation with adjusted surface turbulence parameterizations better reproduced the observed Arctic tropospheric warming in vertical extent, demonstrating improved alignment with the reanalysis data. Additionally, unlike the control experiments, this simulation successfully reproduced specific circulation patterns linked to the stratospheric pathway for Arctic-mid-latitude linkages. Specifically, an increased occurrence of the Scandinavian-Ural blocking regime (negative phase of the North Atlantic Oscillation) in early (late) winter is observed. Overall, it can be inferred that improving turbulence parameterizations at the surface layer can improve the ECHAM6's response to sea ice loss.},
  language  = {en}
}
@phdthesis{Heinig2003,
  author    = {Heinig, Peter},
  title     = {The geometry of interacting liquid domains in Langmuir monolayers},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000814},
  school      = {Universit{\"a}t Potsdam},
  year      = {2003},
  abstract  = {Es werden die Strukturbildung und Benetzung zweidimensionaler (2D) Phasen von Langmuir-Monolagen im lokalen thermodynamischen Gleichgewicht untersucht. Eine Langmuir-Monolage ist ein isoliertes 2D System von Surfaktanten an der Wasser/Luft-Grenzfl{\"a}che, in dem kristalline, fl{\"u}ssigkristalline, fl{\"u}ssige oder gasf{\"o}rmige Phasen auftreten, die sich in Positionsordnung und/oder Orientierungsordnung unterscheiden. Permanente elektrische Dipolmomente der Surfaktanten f{\"u}hren zu einer langreichweitigen repulsiven Selbstwechselwirkung der Monolage und zur Bildung mesoskopischer Strukturen. Es wird ein Wechselwirkungsmodell verwendet, das die Strukturbildung als Wechselspiel kurzreichweitiger Anziehung (nackte Linienspannung) und langreichweitiger Abstoßung (Oberfl{\"a}chenpotential) auf einer Skala Delta beschreibt. Physikalisch trennt Delta die beiden L{\"a}ngenskalen der lang- und kurzreichweitigen Wechselwirkung. In dieser Arbeit werden die thermodynamischen Stabilit{\"a}tsbedingungen f{\"u}r die Form einer Phasengrenzlinie (Young-Laplace-Gleichung) und Dreiphasenkontaktpunkt (Young-Bedingung) hergeleitet und zur Beschreibung experimenteller Daten genutzt: Die Linienspannung benetzender 2D Tropfen wird mit Hilfe h{\"a}ngender-Tropfen-Tensiometrie gemessen. Die Blasenform und -gr{\"o}ße von 2D Sch{\"a}umen wird theoretisch modelliert und mit experimentellen 2D Sch{\"a}umen verglichen. Kontaktwinkel werden durch die Anpassung von experimentellen Tropfen mit numerischen L{\"o}sungen der Young-Laplace-Gleichung auf Mikrometerskalen gemessen. Das Skalenverhalten des Kontaktwinkels erm{\"o}glicht die Bestimmung einer unteren Schranke von Delta. Weiterhin wird diskutiert, inwieweit das Schalten von 2D Benetzungsmodi in biologischen Membranen zur Steuerung der Reaktionskinetik ein Rolle spielen k{\"o}nnte. Hierzu werden Experimente aus unserer Gruppe, die in einer Langmuir-Monolage durchgef{\"u}hrt wurden, herangezogen. Abschließend wird die scheinbare Verletzung der Gibbs\&prime;schen Phasenregel in Langmuir-Monolagen (nicht-horizontales Plateau der Oberfl{\"a}chendruck-Fl{\"a}che Isotherme, ausgedehntes Dreiphasengebiet in Einkomponentensystemen) quantitativ untersucht. Eine Verschmutzung der verwendeten Substanzen ist demnach die wahscheinlichste Erkl{\"a}rung, w{\"a}hrend Finite-Size-Effekte oder der Einfluss der langreichweitigen Elektrostatik die Gr{\"o}ßenordnung des Effektes nicht beschreiben k{\"o}nnen.},
  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{Ruppert2016,
  author    = {Ruppert, Jan},
  title     = {The Low-Mass Young Stellar Content in the Extended Environment of the Galactic Starburst Region NGC3603},
  school      = {Universit{\"a}t Potsdam},
  pages     = {148},
  year      = {2016},
  language  = {en}
}
@phdthesis{Schlemm2022,
  author    = {Schlemm, Tanja},
  title     = {The marine ice cliff instability of the Antarctic ice sheet},
  doi       = {10.25932/publishup-58633},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-586333},
  school      = {Universit{\"a}t Potsdam},
  pages     = {107},
  year      = {2022},
  abstract  = {The Antarctic ice sheet is the largest freshwater reservoir worldwide. If it were to melt completely, global sea levels would rise by about 58 m. Calculation of projections of the Antarctic contribution to sea level rise under global warming conditions is an ongoing effort which yields large ranges in predictions. Among the reasons for this are uncertainties related to the physics of ice sheet modeling. These uncertainties include two processes that could lead to runaway ice retreat: the Marine Ice Sheet Instability (MISI), which causes rapid grounding line retreat on retrograde bedrock, and the Marine Ice Cliff Instability (MICI), in which tall ice cliffs become unstable and calve off, exposing even taller ice cliffs. In my thesis, I investigated both marine instabilities (MISI and MICI) using the Parallel Ice Sheet Model (PISM), with a focus on MICI.},
  language  = {en}
}
@phdthesis{DeAndradeQueiroz2023,
  author    = {De Andrade Queiroz, Anna Barbara},
  title     = {The Milky Way disks, bulge, and bar sub-populations},
  doi       = {10.25932/publishup-59061},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-590615},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 187},
  year      = {2023},
  abstract  = {In recent decades, astronomy has seen a boom in large-scale stellar surveys of the Galaxy. The detailed information obtained about millions of individual stars in the Milky Way is bringing us a step closer to answering one of the most outstanding questions in astrophysics: how do galaxies form and evolve? The Milky Way is the only galaxy where we can dissect many stars into their high-dimensional chemical composition and complete phase space, which analogously as fossil records can unveil the past history of the genesis of the Galaxy. The processes that lead to large structure formation, such as the Milky Way, are critical for constraining cosmological models; we call this line of study Galactic archaeology or near-field cosmology. At the core of this work, we present a collection of efforts to chemically and dynamically characterise the disks and bulge of our Galaxy. The results we present in this thesis have only been possible thanks to the advent of the Gaia astrometric satellite, which has revolutionised the field of Galactic archaeology by precisely measuring the positions, parallax distances and motions of more than a billion stars. Another, though not less important, breakthrough is the APOGEE survey, which has observed spectra in the near-infrared peering into the dusty regions of the Galaxy, allowing us to determine detailed chemical abundance patterns in hundreds of thousands of stars. To accurately depict the Milky Way structure, we use and develop the Bayesian isochrone fitting tool/code called StarHorse; this software can predict stellar distances, extinctions and ages by combining astrometry, photometry and spectroscopy based on stellar evolutionary models. The StarHorse code is pivotal to calculating distances where Gaia parallaxes alone cannot allow accurate estimates. We show that by combining Gaia, APOGEE, photometric surveys and using StarHorse, we can produce a chemical cartography of the Milky way disks from their outermost to innermost parts. Such a map is unprecedented in the inner Galaxy. It reveals a continuity of the bimodal chemical pattern previously detected in the solar neighbourhood, indicating two populations with distinct formation histories. Furthermore, the data reveals a chemical gradient within the thin disk where the content of 𝛼-process elements and metals is higher towards the centre. Focusing on a sample in the inner MW we confirm the extension of the chemical duality to the innermost regions of the Galaxy. We find stars with bar shape orbits to show both high- and low-𝛼 abundances, suggesting the bar formed by secular evolution trapping stars that already existed. By analysing the chemical orbital space of the inner Galactic regions, we disentangle the multiple populations that inhabit this complex region. We reveal the presence of the thin disk, thick disk, bar, and a counter-rotating population, which resembles the outcome of a perturbed proto-Galactic disk. Our study also finds that the inner Galaxy holds a high quantity of super metal-rich stars up to three times solar suggesting it is a possible repository of old super-metal-rich stars found in the solar neighbourhood. We also enter into the complicated task of deriving individual stellar ages. With StarHorse, we calculate the ages of main-sequence turn-off and sub-giant stars for several public spectroscopic surveys. We validate our results by investigating linear relations between chemical abundances and time since the 𝛼 and neutron capture elements are sensitive to age as a reflection of the different enrichment timescales of these elements. For further study of the disks in the solar neighbourhood, we use an unsupervised machine learning algorithm to delineate a multidimensional separation of chrono-chemical stellar groups revealing the chemical thick disk, the thin disk, and young 𝛼-rich stars. The thick disk is shown to have a small age dispersion indicating its fast formation contrary to the thin disk that spans a wide range of ages. With groundbreaking data, this thesis encloses a detailed chemo-dynamical view of the disk and bulge of our Galaxy. Our findings on the Milky Way can be linked to the evolution of high redshift disk galaxies, helping to solve the conundrum of galaxy formation.},
  language  = {en}
}
@phdthesis{Sauter2016,
  author    = {Sauter, J{\"o}rg},
  title     = {The molecular origin of plant cell wall swelling},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iii, 127 S.},
  year      = {2016},
  abstract  = {In dieser Arbeit werden die Eigenschaften von hydratisierten Hemicellulose Polysacchariden mittels Computersimulation untersucht. Die hohe Quellfähigkeit von Materialien die aus diesen Molek{\"u}len bestehen, erlaubt die Erzeugung von zielgerichteter Bewegung in Planzenmaterialien, ausschließlich gesteuert durch Wasseraufnahme. Um den molekularen Ursprung dieses Quellvermögens zu untersuchen wird, im Vergleich mit Experimenten, ein atomistisches Modell f{\"u}r Hemicellulose Polysaccharide entwickelt und getestet. Unter Verwendung dieses Modells werden Simulationen von kleinen Polysacchariden benutzt um die Wechselwirkungen mit Wasser, den Einfluss von Wasser auf die Konformationsfreiheit der Molek{\"u}le, und die Quellfähigkeit, quantifiziert durch den osmotischen Druck, zu verstehen. Es wird gezeigt, dass verzweigte und lineare Polysaccharide unterschiedliche Hydratisierungseingenschaften im Vergleich zu lineare Polysacchariden aufweisen. Um das Quellverhalten auf Längen- und Zeitskalen untersuchen zu können die {\"u}ber die Begrenzungen atomistischer Simulationen hinausgehen, wurde eine Prozedur entwickelt um {\"u}bertragbare vergröberte Modelle herzuleiten. Die Übertragbarkeit der vegröberten Modelle wird gezeigt, sowohl {\"u}ber unterschiedliche Polysaccharidkonzentrationen als auch {\"u}ber unterschiedliche Polymerlängen. Daher erlaubt die Prozedur die Konstruktion von großen vergröberter Systemen ausgehend von kleinen atomistischen Referenzsystemen. Abschließend wird das vergröberte Modell verwendet um zu zeigen, dass lineare und verzweigte Polysaccharide ein unterschiedliches Quellverhalten aufweisen, wenn sie mit einem Wasserbad gekoppelt werden.},
  language  = {en}
}
@phdthesis{Haase2019,
  author    = {Haase, Nadin},
  title     = {The nascent peptide chain in the ribosomal exit tunnel},
  school      = {Universit{\"a}t Potsdam},
  pages     = {105},
  year      = {2019},
  language  = {en}
}
@phdthesis{Breuer2016,
  author    = {Breuer, David},
  title     = {The plant cytoskeleton as a transportation network},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-93583},
  school      = {Universit{\"a}t Potsdam},
  pages     = {164},
  year      = {2016},
  abstract  = {The cytoskeleton is an essential component of living cells. It is composed of different types of protein filaments that form complex, dynamically rearranging, and interconnected networks. The cytoskeleton serves a multitude of cellular functions which further depend on the cell context. In animal cells, the cytoskeleton prominently shapes the cell's mechanical properties and movement. In plant cells, in contrast, the presence of a rigid cell wall as well as their larger sizes highlight the role of the cytoskeleton in long-distance intracellular transport. As it provides the basis for cell growth and biomass production, cytoskeletal transport in plant cells is of direct environmental and economical relevance. However, while knowledge about the molecular details of the cytoskeletal transport is growing rapidly, the organizational principles that shape these processes on a whole-cell level remain elusive. This thesis is devoted to the following question: How does the complex architecture of the plant cytoskeleton relate to its transport functionality? The answer requires a systems level perspective of plant cytoskeletal structure and transport. To this end, I combined state-of-the-art confocal microscopy, quantitative digital image analysis, and mathematically powerful, intuitively accessible graph-theoretical approaches. This thesis summarizes five of my publications that shed light on the plant cytoskeleton as a transportation network: (1) I developed network-based frameworks for accurate, automated quantification of cytoskeletal structures, applicable in, e.g., genetic or chemical screens; (2) I showed that the actin cytoskeleton displays properties of efficient transport networks, hinting at its biological design principles; (3) Using multi-objective optimization, I demonstrated that different plant cell types sustain cytoskeletal networks with cell-type specific and near-optimal organization; (4) By investigating actual transport of organelles through the cell, I showed that properties of the actin cytoskeleton are predictive of organelle flow and provided quantitative evidence for a coordination of transport at a cellular level; (5) I devised a robust, optimization-based method to identify individual cytoskeletal filaments from a given network representation, allowing the investigation of single filament properties in the network context. The developed methods were made publicly available as open-source software tools. Altogether, my findings and proposed frameworks provide quantitative, system-level insights into intracellular transport in living cells. Despite my focus on the plant cytoskeleton, the established combination of experimental and theoretical approaches is readily applicable to different organisms. Despite the necessity of detailed molecular studies, only a complementary, systemic perspective, as presented here, enables both understanding of cytoskeletal function in its evolutionary context as well as its future technological control and utilization.},
  language  = {en}
}
@phdthesis{Sposini2020,
  author    = {Sposini, Vittoria},
  title     = {The random diffusivity approach for diffusion in heterogeneous systems},
  doi       = {10.25932/publishup-48780},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-487808},
  school      = {Universit{\"a}t Potsdam},
  year      = {2020},
  abstract  = {The two hallmark features of Brownian motion are the linear growth < x2(t)> = 2Ddt of the mean squared displacement (MSD) with diffusion coefficient D in d spatial dimensions, and the Gaussian distribution of displacements. With the increasing complexity of the studied systems deviations from these two central properties have been unveiled over the years. Recently, a large variety of systems have been reported in which the MSD exhibits the linear growth in time of Brownian (Fickian) transport, however, the distribution of displacements is pronouncedly non-Gaussian (Brownian yet non-Gaussian, BNG). A similar behaviour is also observed for viscoelastic-type motion where an anomalous trend of the MSD, i.e., <x2(t)> ~ ta, is combined with a priori unexpected non-Gaussian distributions (anomalous yet non-Gaussian, ANG). This kind of behaviour observed in BNG and ANG diffusions has been related to the presence of heterogeneities in the systems and a common approach has been established to address it, that is, the random diffusivity approach. This dissertation explores extensively the field of random diffusivity models. Starting from a chronological description of all the main approaches used as an attempt of describing BNG and ANG diffusion, different mathematical methodologies are defined for the resolution and study of these models. The processes that are reported in this work can be classified in three subcategories, i) randomly-scaled Gaussian processes, ii) superstatistical models and iii) diffusing diffusivity models, all belonging to the more general class of random diffusivity models. Eventually, the study focuses more on BNG diffusion, which is by now well-established and relatively well-understood. Nevertheless, many examples are discussed for the description of ANG diffusion, in order to highlight the possible scenarios which are known so far for the study of this class of processes. The second part of the dissertation deals with the statistical analysis of random diffusivity processes. A general description based on the concept of moment-generating function is initially provided to obtain standard statistical properties of the models. Then, the discussion moves to the study of the power spectral analysis and the first passage statistics for some particular random diffusivity models. A comparison between the results coming from the random diffusivity approach and the ones for standard Brownian motion is discussed. In this way, a deeper physical understanding of the systems described by random diffusivity models is also outlined. To conclude, a discussion based on the possible origins of the heterogeneity is sketched, with the main goal of inferring which kind of systems can actually be described by the random diffusivity approach.},
  language  = {en}
}
@phdthesis{Dominis2006,
  author    = {Dominis, Dijana},
  title     = {The role of binary stars in searches for extrasolar planets by microlensing and astrometry},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10814},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {When Galactic microlensing events of stars are observed, one usually measures a symmetric light curve corresponding to a single lens, or an asymmetric light curve, often with caustic crossings, in the case of a binary lens system. In principle, the fraction of binary stars at a certain separation range can be estimated based on the number of measured microlensing events. However, a binary system may produce a light curve which can be fitted well as a single lens light curve, in particullary if the data sampling is poor and the errorbars are large. We investigate what fraction of microlensing events produced by binary stars for different separations may be well fitted by and hence misinterpreted as single lens events for various observational conditions. We find that this fraction strongly depends on the separation of the binary components, reaching its minimum at between 0.6 and 1.0 Einstein radius, where it is still of the order of 5\% The Einstein radius is corresponding to few A.U. for typical Galactic microlensing scenarios. The rate for misinterpretation is higher for short microlensing events lasting up to few months and events with smaller maximum amplification. For fixed separation it increases for binaries with more extreme mass ratios. Problem of degeneracy in photometric light curve solution between binary lens and binary source microlensing events was studied on simulated data, and data observed by the PLANET collaboration. The fitting code BISCO using the PIKAIA genetic algorithm optimizing routine was written for optimizing binary-source microlensing light curves observed at different sites, in I, R and V photometric bands. Tests on simulated microlensing light curves show that BISCO is successful in finding the solution to a binary-source event in a very wide parameter space. Flux ratio method is suggested in this work for breaking degeneracy between binary-lens and binary-source photometric light curves. Models show that only a few additional data points in photometric V band, together with a full light curve in I band, will enable breaking the degeneracy. Very good data quality and dense data sampling, combined with accurate binary lens and binary source modeling, yielded the discovery of the lowest-mass planet discovered outside of the Solar System so far, OGLE-2005-BLG-390Lb, having only 5.5 Earth masses. This was the first observed microlensing event in which the degeneracy between a planetary binary-lens and an extreme flux ratio binary-source model has been successfully broken. For events OGLE-2003-BLG-222 and OGLE-2004-BLG-347, the degeneracy was encountered despite of very dense data sampling. From light curve modeling and stellar evolution theory, there was a slight preference to explain OGLE-2003-BLG-222 as a binary source event, and OGLE-2004-BLG-347 as a binary lens event. However, without spectra, this degeneracy cannot be fully broken. No planet was found so far around a white dwarf, though it is believed that Jovian planets should survive the late stages of stellar evolution, and that white dwarfs will retain planetary systems in wide orbits. We want to perform high precision astrometric observations of nearby white dwarfs in wide binary systems with red dwarfs in order to find planets around white dwarfs. We selected a sample of observing targets (WD-RD binary systems, not published yet), which can possibly have planets around the WD component, and modeled synthetic astrometric orbits which can be observed for these targets using existing and future astrometric facilities. Modeling was performed for the astrometric accuracy of 0.01, 0.1, and 1.0 mas, separation between WD and planet of 3 and 5 A.U., binary system separation of 30 A.U., planet masses of 10 Earth masses, 1 and 10 Jupiter masses, WD mass of 0.5M and 1.0 Solar masses, and distances to the system of 10, 20 and 30 pc. It was found that the PRIMA facility at the VLTI will be able to detect planets around white dwarfs once it is operating, by measuring the astrometric wobble of the WD due to a planet companion, down to 1 Jupiter mass. We show for the simulated observations that it is possible to model the orbits and find the parameters describing the potential planetary systems.},
  subject      = {Mikrogravitationslinseneffekt},
  language  = {en}
}
@phdthesis{Hainich2015,
  author    = {Hainich, Rainer},
  title     = {The Wolf-Rayet stars of the nitrogen sequence in environments of different metallicities},
  school      = {Universit{\"a}t Potsdam},
  pages     = {161},
  year      = {2015},
  language  = {en}
}
@phdthesis{Deneke2012,
  author    = {Deneke, Carlus},
  title     = {Theory of mRNA degradation},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61998},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {One of the central themes of biology is to understand how individual cells achieve a high fidelity in gene expression. Each cell needs to ensure accurate protein levels for its proper functioning and its capability to proliferate. Therefore, complex regulatory mechanisms have evolved in order to render the expression of each gene dependent on the expression level of (all) other genes. Regulation can occur at different stages within the framework of the central dogma of molecular biology. One very effective and relatively direct mechanism concerns the regulation of the stability of mRNAs. All organisms have evolved diverse and powerful mechanisms to achieve this. In order to better comprehend the regulation in living cells, biochemists have studied specific degradation mechanisms in detail. In addition to that, modern high-throughput techniques allow to obtain quantitative data on a global scale by parallel analysis of the decay patterns of many different mRNAs from different genes. In previous studies, the interpretation of these mRNA decay experiments relied on a simple theoretical description based on an exponential decay. However, this does not account for the complexity of the responsible mechanisms and, as a consequence, the exponential decay is often not in agreement with the experimental decay patterns. We have developed an improved and more general theory of mRNA degradation which provides a general framework of mRNA expression and allows describing specific degradation mechanisms. We have made an attempt to provide detailed models for the regulation in different organisms. In the yeast S. cerevisiae, different degradation pathways are known to compete and furthermore most of them rely on the biochemical modification of mRNA molecules. In bacteria such as E. coli, degradation proceeds primarily endonucleolytically, i.e. it is governed by the initial cleavage within the coding region. In addition, it is often coupled to the level of maturity and the size of the polysome of an mRNA. Both for S. cerevisiae and E. coli, our descriptions lead to a considerable improvement of the interpretation of experimental data. The general outcome is that the degradation of mRNA must be described by an age-dependent degradation rate, which can be interpreted as a consequence of molecular aging of mRNAs. Within our theory, we find adequate ways to address this much debated topic from a theoretical perspective. The improvements of the understanding of mRNA degradation can be readily applied to further comprehend the mRNA expression under different internal or environmental conditions such as after the induction of transcription or stress application. Also, the role of mRNA decay can be assessed in the context of translation and protein synthesis. The ultimate goal in understanding gene regulation mediated by mRNA stability will be to identify the relevance and biological function of different mechanisms. Once more quantitative data will become available, our description allows to elaborate the role of each mechanism by devising a suitable model.},
  language  = {en}
}