TY - JOUR A1 - Klose, Ann Kristin A1 - Wunderling, Nico A1 - Winkelmann, Ricarda A1 - Donges, Jonathan T1 - What do we mean, 'tipping cascade'? JF - Environmental research letters : ERL N2 - Based on suggested interactions of potential tipping elements in the Earth's climate and in ecological systems, tipping cascades as possible dynamics are increasingly discussed and studied. The activation of such tipping cascades would impose a considerable risk for human societies and biosphere integrity. However, there are ambiguities in the description of tipping cascades within the literature so far. Here we illustrate how different patterns of multiple tipping dynamics emerge from a very simple coupling of two previously studied idealized tipping elements. In particular, we distinguish between a two phase cascade, a domino cascade and a joint cascade. A mitigation of an unfolding two phase cascade may be possible and common early warning indicators are sensitive to upcoming critical transitions to a certain degree. In contrast, a domino cascade may hardly be stopped once initiated and critical slowing down-based indicators fail to indicate tipping of the following element. These different potentials for intervention and anticipation across the distinct patterns of multiple tipping dynamics should be seen as a call to be more precise in future analyses of cascading dynamics arising from tipping element interactions in the Earth system. KW - tipping cascade KW - domino effect KW - tipping interactions KW - cascading regime KW - shifts KW - early warning indicators Y1 - 2021 U6 - https://doi.org/10.1088/1748-9326/ac3955 SN - 1748-9326 VL - 16 IS - 12 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Rosenau, Philip A1 - Pikovskij, Arkadij T1 - Waves in strongly nonlinear Gardner-like equations on a lattice JF - Nonlinearity / the Institute of Physics and the London Mathematical Society N2 - We introduce and study a family of lattice equations which may be viewed either as a strongly nonlinear discrete extension of the Gardner equation, or a non-convex variant of the Lotka-Volterra chain. Their deceptively simple form supports a very rich family of complex solitary patterns. Some of these patterns are also found in the quasi-continuum rendition, but the more intriguing ones, like interlaced pairs of solitary waves, or waves which may reverse their direction either spontaneously or due a collision, are an intrinsic feature of the discrete realm. KW - nonlinear lattice KW - solitary wave KW - Gardner equation KW - compacton Y1 - 2021 U6 - https://doi.org/10.1088/1361-6544/ac0f51 SN - 0951-7715 SN - 1361-6544 VL - 34 IS - 8 SP - 5872 EP - 5896 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Teichmann, Erik T1 - Using phase dynamics to study partial synchrony BT - three examples JF - European physical journal special topics N2 - Partial synchronous states appear between full synchrony and asynchrony and exhibit many interesting properties. Most frequently, these states are studied within the framework of phase approximation. The latter is used ubiquitously to analyze coupled oscillatory systems. Typically, the phase dynamics description is obtained in the weak coupling limit, i.e., in the first-order in the coupling strength. The extension beyond the first-order represents an unsolved problem and is an active area of research. In this paper, three partially synchronous states are investigated and presented in order of increasing complexity. First, the usage of the phase response curve for the description of macroscopic oscillators is analyzed. To achieve this, the response of the mean-field oscillations in a model of all-to-all coupled limit-cycle oscillators to pulse stimulation is measured. The next part treats a two-group Kuramoto model, where the interaction of one attractive and one repulsive group results in an interesting solitary state, situated between full synchrony and self-consistent partial synchrony. In the last part, the phase dynamics of a relatively simple system of three Stuart-Landau oscillators are extended beyond the weak coupling limit. The resulting model contains triplet terms in the high-order phase approximation, though the structural connections are only pairwise. Finally, the scaling of the new terms with the coupling is analyzed. Y1 - 2021 U6 - https://doi.org/10.1140/epjs/s11734-021-00156-3 SN - 1951-6355 SN - 1951-6401 VL - 230 IS - 14-15 SP - 2833 EP - 2842 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Ritschel, Stefan A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Universality of delay-time averages for financial time series BT - analytical results, computer simulations, and analysis of historical stock-market prices JF - Journal of physics. Complexity N2 - We analyze historical data of stock-market prices for multiple financial indices using the concept of delay-time averaging for the financial time series (FTS). The region of validity of our recent theoretical predictions [Cherstvy A G et al 2017 New J. Phys. 19 063045] for the standard and delayed time-averaged mean-squared 'displacements' (TAMSDs) of the historical FTS is extended to all lag times. As the first novel element, we perform extensive computer simulations of the stochastic differential equation describing geometric Brownian motion (GBM) which demonstrate a quantitative agreement with the analytical long-term price-evolution predictions in terms of the delayed TAMSD (for all stock-market indices in crisis-free times). Secondly, we present a robust procedure of determination of the model parameters of GBM via fitting the features of the price-evolution dynamics in the FTS for stocks and cryptocurrencies. The employed concept of single-trajectory-based time averaging can serve as a predictive tool (proxy) for a mathematically based assessment and rationalization of probabilistic trends in the evolution of stock-market prices. KW - econophysics KW - geometric Brownian motion KW - time-series analysis Y1 - 2021 U6 - https://doi.org/10.1088/2632-072X/ac2220 SN - 2632-072X VL - 2 IS - 4 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kumar, Mohit A1 - Rosenblum, Michael T1 - Two mechanisms of remote synchronization in a chain of Stuart-Landau oscillators JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Remote synchronization implies that oscillators interacting not directly but via an additional unit (hub) adjust their frequencies and exhibit frequency locking while the hub remains asynchronous. In this paper, we analyze the mechanisms of remote synchrony in a small network of three coupled Stuart-Landau oscillators using recent results on higher-order phase reduction. We analytically demonstrate the role of two factors promoting remote synchrony. These factors are the nonisochronicity of oscillators and the coupling terms appearing in the secondorder phase approximation. We show a good correspondence between our theory and numerical results for small and moderate coupling strengths. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.054202 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 5 PB - American Physical Society CY - College Park ER - TY - THES A1 - Canil, Laura T1 - Tuning Interfacial Properties in Perovskite Solar Cells through Defined Molecular Assemblies T1 - Anpassung von Grenzflächeneigenschaften von Perowskit-Solarzellen durch den Einsatz von molekularen Schichten N2 - In the frame of a world fighting a dramatic global warming caused by human-related activities, research towards the development of renewable energies plays a crucial role. Solar energy is one of the most important clean energy sources and its role in the satisfaction of the global energy demand is set to increase. In this context, a particular class of materials captured the attention of the scientific community for its attractive properties: halide perovskites. Devices with perovskite as light-absorber saw an impressive development within the last decade, reaching nowadays efficiencies comparable to mature photovoltaic technologies like silicon solar cells. Yet, there are still several roadblocks to overcome before a wide-spread commercialization of this kind of devices is enabled. One of the critical points lies at the interfaces: perovskite solar cells (PSCs) are made of several layers with different chemical and physical features. In order for the device to function properly, these properties have to be well-matched. This dissertation deals with some of the challenges related to interfaces in PSCs, with a focus on the interface between the perovskite material itself and the subsequent charge transport layer. In particular, molecular assemblies with specific properties are deposited on the perovskite surface to functionalize it. The functionalization results in energy level alignment adjustment, interfacial losses reduction, and stability improvement. First, a strategy to tune the perovskite’s energy levels is introduced: self-assembled monolayers of dipolar molecules are used to functionalize the surface, obtaining simultaneously a shift in the vacuum level position and a saturation of the dangling bonds at the surface. A shift in the vacuum level corresponds to an equal change in work function, ionization energy, and electron affinity. The direction of the shift depends on the direction of the collective interfacial dipole. The magnitude of the shift can be tailored by controlling the deposition parameters, such as the concentration of the solution used for the deposition. The shift for different molecules is characterized by several non-invasive techniques, including in particular Kelvin probe. Overall, it is shown that it is possible to shift the perovskite energy levels in both directions by several hundreds of meV. Moreover, interesting insights on the molecules deposition dynamics are revealed. Secondly, the application of this strategy in perovskite solar cells is explored. Devices with different perovskite compositions (“triple cation perovskite” and MAPbBr3) are prepared. The two resulting model systems present different energetic offsets at the perovskite/hole-transport layer interface. Upon tailored perovskite surface functionalization, the devices show a stabilized open circuit voltage (Voc) enhancement of approximately 60 meV on average for devices with MAPbBr3, while the impact is limited on triple-cation solar cells. This suggests that the proposed energy level tuning method is valid, but its effectiveness depends on factors such as the significance of the energetic offset compared to the other losses in the devices. Finally, the above presented method is further developed by incorporating the ability to interact with the perovskite surface directly into a novel hole-transport material (HTM), named PFI. The HTM can anchor to the perovskite halide ions via halogen bonding (XB). Its behaviour is compared to that of another HTM (PF) with same chemical structure and properties, except for the ability of forming XB. The interaction of perovskite with PFI and PF is characterized through UV-Vis, atomic force microscopy and Kelvin probe measurements combined with simulations. Compared to PF, PFI exhibits enhanced resilience against solvent exposure and improved energy level alignment with the perovskite layer. As a consequence, devices comprising PFI show enhanced Voc and operational stability during maximum-power-point tracking, in addition to hysteresis reduction. XB promotes the formation of a high-quality interface by anchoring to the halide ions and forming a stable and ordered interfacial layer, showing to be a particularly interesting candidate for the development of tailored charge transport materials in PSCs. Overall, the results exposed in this dissertation introduce and discuss a versatile tool to functionalize the perovskite surface and tune its energy levels. The application of this method in devices is explored and insights on its challenges and advantages are given. Within this frame, the results shed light on XB as ideal interaction for enhancing stability and efficiency in perovskite-based devices. N2 - Im Kampf gegen den menschengemachten Klimawandel spielt die Forschung und Entwicklung von erneuerbaren Energien eine tragende Rolle. Solarenergie ist eine der wichtigsten grünen Energiequellen und von steigender Bedeutung für die Deckung des globalen Energiebedarfs. In diesem Kontext hat eine bestimme Materialklasse aufgrund ihrer attraktiven Eigenschaften die Aufmerksamkeit der Wissenschaft erregt: Halogenid-Perowskit. Perowskit-Solarzellen haben im letzten Jahrzehnt eine beeindruckende Entwicklung durchgemacht und erreichen heutzutage Effizienzen, die mit weit entwickelten Photovoltaik-Technologien wie Silizium-Solarzellen vergleichbar sind. Jedoch existieren immer noch mehrere Hürden, die einer marktweiten Kommerzialisierung dieser jungen Technologie im Wege stehen. Eines der kritischen Probleme befindet sich an den Grenzflächen. Perowskit-Solarzellen bestehen aus mehreren Schichten mit unterschiedlichen chemischen und physikalischen Eigenschaften. Damit die Solarzelle bestmöglich funktioniert, müssen diese Eigenschaften aufeinander abgestimmt sein. Diese Dissertation beschäftigt sich mit einigen Herausforderungen im Zusammenhang mit Grenzflächen in Perowskit-Solarzellen, dabei liegt der Fokus auf der Grenzfläche zwischen Perowskit-Absorber und der angrenzenden Ladungstransportschicht. Insbesondere werden organische Moleküle mit spezifischen Eigenschaften verwendet um die Oberfläche des Perowskiten zu funktionalisieren. Dadurch wird eine Bandanpassung erreicht, Grenzflächenverluste reduziert und die Stabilität der Solarzellen erhöht. Zunächst wird eine Strategie zum Anpassen der Bandenergien vorgestellt: Selbst-organisierende Monoschichten dipolarer Moleküle werden auf die Perowskit-Oberfläche abgeschieden, um diese zu funktionalisieren. Dadurch wird eine Anpassung des Energie-Levels im Perowskiten und die Sättigung von ungebundenen Elektronenbindungen (engl. dangling bonds) an der Oberfläche erreicht. Die Richtung der Energielevel-Verschiebung hängt von der Richtung des kollektiven Grenzflächen-Dipols ab. Der Betrag der Energielevel-Verschiebung kann über die Depositionsparameter während der Schichtherstellung eingestellt werden. Die Energielevel-Verschiebung bei der Verwendung verschiedener Moleküle wird mit Hilfe verschiedener non-invasiver Charakterisierungsmethoden untersucht, insbesondere mit der Hilfe von Kelvin-Sonde Messungen. Diese Messungen ermöglichen interessante Erkenntnisse über die Dynamik der Deposition der Moleküle. Es ist möglich die Energielevel in beide Richtungen um mehrere hundert meV zu verschieben. Als Zweites wird die Anwendung dieser Stategie in Perowskit-Solarzellen erforscht. Solarzellen mit Perowskit-Absorbern unterschiedlicher Zusammensetzung (“Dreifach-Kationen-Perowskit” und MAPbBr3) werden präpariert; die beiden Modellsysteme besitzen dann unterschiedliche energetische Offsets an der Perowskit-Lochleiter Grenzfläche. Mit einer maßgeschneiderter Funktionalisierung der Perowskit-Oberfläche zeigen die MAPbBr3 Solarzellen eine permanente Verbesserung der offene-Klemmen-Spannung (engl. open circuit voltage, Voc) um durchschnittlich 60 meV, während der Einfluss auf die Solarzellen mit Dreifach-Kationen-Perowskit gering ist. Dies zeigt, dass die vorgestellte Methode zur Bandanpassung funktioniert, aber ihre Effektivität zudem von weiteren Faktoren abhängt: Die Relevanz des energetischen Offsets im Vergleich zu anderen Verlustmechanismen beeinflusst unter anderem die Effektivität der Funktionalisierung. Abschließend wird beschrieben, wie die präsentierte Methode zur Bandanpassung weiterentwickelt wird, indem das Vermögen, mit der Perowskit-Oberfläche zu interagieren, direkt in einen neuartigen Lochleiter („PFI“) integriert wird. Der Lochleiter kann sich über Halogenbindungen an den Perowskiten anlagern. Das Verhalten von PFI wird verglichen mit dem eines anderen Lochleiters („PF“), welcher die fast gleiche chemische Struktur und sehr ähnliche Eigenschaften aufweist, ausgenommen der Fähigkeit eine Halogenbindung zu formen. Die PFI-Perowskit und PF-Perowskit Interaktion wird durch UV-Vis Spektroskopie, Rasterkraftmikroskopie und Kelvin-Sonde Messungen, kombiniert mit Simulationen, charakterisiert. Beim direkten Vergleich von PFI und PF zeigt sich die Bildung der Halogenbindung in einer bei PFI verbesserten Widerstandskraft gegen Lösungsmittel und Bandanpassung zum Perowskiten. Beim Folgerichtig zeigen Solarzellen mit PFI zusätzlich zu einer verringerten Hysterese einen höheren Voc und eine erhöhte Stabilität während des Betriebs unter Maximum-Power-Point Tracking Zusammenfassend stellt diese Dissertation somit ein vielseitiges Werkzeug zur Funktionalisierung von Perowskit-Oberflächen und der dadurch erreichten Bandanpassung vor. Die Anwendung dieses Werkzeugs an Solarzellen wird erprobt und Einsichten in seine Vorteile und Nachteile erlangt. Die Halogenbindung wird als spezifische Interaktion identifiziert, die sich ideal zur Steigerung von Effizienz und Stabilität von Perowskit-basierten optoelektronischen Bauteilen erweisen könnte. KW - photovoltaic KW - perovskite solar cells KW - interfaces KW - energy levels KW - halogen bonding KW - Grenzflächen KW - Perowskit Solarzellen KW - Photovoltaik KW - Bandenenergien KW - Halogenbindung Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-546333 ER - TY - JOUR A1 - Deb, Marwan A1 - Molho, Pierre A1 - Barbara, Bernard T1 - Tunable exchange-bias-like effect in bi-substituted Gadolinium iron garnet film JF - Physical review applied N2 - Using magneto-optical Faraday and Kerr measurements, we investigate the magnetic and magnetooptical properties of a thick Bi-substituted gadolinium iron garnet film over a broad range of wavelengths (250-850 nm) and temperatures (150-300 K), including the magnetization compensation point, TM. We observe an exchange-bias-like effect in the vicinity of TM. By slightly changing the sample temperature, we can precisely tune the bias field, which reaches a magnitude 6 times higher than the coercive field. We explain this phenomenon by considering the short-range superexchange interaction and a change in the magnetic behavior when moving from the surface to the bulk of the film. This finding may lead to the development of single-film magneto-optical devices based on the exchange-bias effect. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevApplied.15.054064 SN - 2331-7019 VL - 15 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pikovskij, Arkadij T1 - Transition to synchrony in chiral active particles JF - Journal of physics. Complexity N2 - I study deterministic dynamics of chiral active particles in two dimensions. Particles are considered as discs interacting with elastic repulsive forces. An ensemble of particles, started from random initial conditions, demonstrates chaotic collisions resulting in their normal diffusion. This chaos is transient, as rather abruptly a synchronous collisionless state establishes. The life time of chaos grows exponentially with the number of particles. External forcing (periodic or chaotic) is shown to facilitate the synchronization transition. KW - active particles KW - chirality KW - synchronization KW - chaos KW - transient chaos Y1 - 2021 U6 - https://doi.org/10.1088/2632-072X/abdadb SN - 2632-072X VL - 2 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Zheng, Chunming A1 - Tönjes, Ralf A1 - Pikovskij, Arkadij T1 - Transition to synchrony in a three-dimensional swarming model with helical trajectories JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We investigate the transition from incoherence to global collective motion in a three-dimensional swarming model of agents with helical trajectories, subject to noise and global coupling. Without noise this model was recently proposed as a generalization of the Kuramoto model and it was found that alignment of the velocities occurs discontinuously for arbitrarily small attractive coupling. Adding noise to the system resolves this singular limit and leads to a continuous transition, either to a directed collective motion or to center-of-mass rotations. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.014216 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 1 PB - American Physical Society CY - College Park ER - TY - THES A1 - Krämer, Kai Hauke T1 - Towards a robust framework for recurrence analysis BT - automated state space reconstruction, optimal parameter selection and correction schemes N2 - In our daily life, recurrence plays an important role on many spatial and temporal scales and in different contexts. It is the foundation of learning, be it in an evolutionary or in a neural context. It therefore seems natural that recurrence is also a fundamental concept in theoretical dynamical systems science. The way in which states of a system recur or develop in a similar way from similar initial states makes it possible to infer information about the underlying dynamics of the system. The mathematical space in which we define the state of a system (state space) is often high dimensional, especially in complex systems that can also exhibit chaotic dynamics. The recurrence plot (RP) enables us to visualize the recurrences of any high-dimensional systems in a two-dimensional, binary representation. Certain patterns in RPs can be related to physical properties of the underlying system, making the qualitative and quantitative analysis of RPs an integral part of nonlinear systems science. The presented work has a methodological focus and further develops recurrence analysis (RA) by addressing current research questions related to an increasing amount of available data and advances in machine learning techniques. By automatizing a central step in RA, namely the reconstruction of the state space from measured experimental time series, and by investigating the impact of important free parameters this thesis aims to make RA more accessible to researchers outside of physics. The first part of this dissertation is concerned with the reconstruction of the state space from time series. To this end, a novel idea is proposed which automates the reconstruction problem in the sense that there is no need to preprocesse the data or estimate parameters a priori. The key idea is that the goodness of a reconstruction can be evaluated by a suitable objective function and that this function is minimized in the embedding process. In addition, the new method can process multivariate time series input data. This is particularly important because multi-channel sensor-based observations are ubiquitous in many research areas and continue to increase. Building on this, the described minimization problem of the objective function is then processed using a machine learning approach. In the second part technical and methodological aspects of RA are discussed. First, we mathematically justify the idea of setting the most influential free parameter in RA, the recurrence threshold ε, in relation to the distribution of all pairwise distances in the data. This is especially important when comparing different RPs and their quantification statistics and is fundamental to any comparative study. Second, some aspects of recurrence quantification analysis (RQA) are examined. As correction schemes for biased RQA statistics, which are based on diagonal lines, we propose a simple method for dealing with border effects of an RP in RQA and a skeletonization algorithm for RPs. This results in less biased (diagonal line based) RQA statistics for flow-like data. Third, a novel type of RQA characteristic is developed, which can be viewed as a generalized non-linear powerspectrum of high dimensional systems. The spike powerspectrum transforms a spike-train like signal into its frequency domain. When transforming the diagonal line-dependent recurrence rate (τ-RR) of a RP in this way, characteristic periods, which can be seen in the state space representation of the system can be unraveled. This is not the case, when Fourier transforming τ-RR. Finally, RA and RQA are applied to climate science in the third part and neuroscience in the fourth part. To the best of our knowledge, this is the first time RPs and RQA have been used to analyze lake sediment data in a paleoclimate context. Therefore, we first elaborate on the basic formalism and the interpretation of visually visible patterns in RPs in relation to the underlying proxy data. We show that these patterns can be used to classify certain types of variability and transitions in the Potassium record from six short (< 17m) sediment cores collected during the Chew Bahir Drilling Project. Building on this, the long core (∼ m composite) from the same site is analyzed and two types of variability and transitions are identified and compared with ODP Site  wetness index from the eastern Mediterranean. Type  variability likely reflects the influence of precessional forcing in the lower latitudes at times of maximum values of the long eccentricity cycle ( kyr) of the earth’s orbit around the sun, with a tendency towards extreme events. Type  variability appears to be related to the minimum values of this cycle and corresponds to fairly rapid transitions between relatively dry and relatively wet conditions. In contrast, RQA has been applied in the neuroscientific context for almost two decades. In the final part, RQA statistics are used to quantify the complexity in a specific frequency band of multivariate EEG (electroencephalography) data. By analyzing experimental data, it can be shown that the complexity of the signal measured in this way across the sensorimotor cortex decreases as motor tasks are performed. The results are consistent with and comple- ment the well known concepts of motor-related brain processes. We assume that the thus discovered features of neuronal dynamics in the sensorimotor cortex together with the robust RQA methods for identifying and classifying these contribute to the non-invasive EEG-based development of brain-computer interfaces (BCI) for motor control and rehabilitation. The present work is an important step towards a robust analysis of complex systems based on recurrence. N2 - In unserem täglichen Leben spielt die Rekurrenz auf vielen räumlichen und zeitlichen Skalen und in verschiedenen Kontexten eine bedeutende Rolle. Es ist die Grundlage des Lernens, sei es in einem evolutionären oder in einem neuronalen Kontext. Es erscheint daher selbstverständ- lich, dass Rekurrenz auch ein grundlegendes Konzept in der dynamischen Systemwissenschaft ist. In diesem Zusammenhang ermöglicht die Art und Weise, wie sich Zustände eines Systems wiederholen oder sich auf ähnliche Weise aus ähnlichen Anfangszuständen entwickeln, Infor- mationen über die zugrunde liegende Dynamik des Systems abzuleiten. Der mathematische Raum, in dem wir den Zustand eines Systems definieren (Zustandsraum), ist häufig hoch- dimensional, insbesondere in komplexen Systemen, die darüberhinaus auch eine chaotische Dynamik aufweisen können. Der Rekurrenzplot (RP) ermöglicht es uns, die Rekurrenzen beliebiger hochdimensionaler Systeme in einer zweidimensionalen, binären Darstellung zu visualisieren. Bestimmte Muster in RPs können mit physikalischen Eigenschaften des zugrunde liegenden Systems in Beziehung gesetzt werden, wodurch die qualitative und quantitative Analyse von RPs ein integraler Bestandteil der nichtlinearen Systemwissenschaft wird. Die vorgestellte Arbeit hat einen methodischen Schwerpunkt und entwickelt die Rekurrenzsana- lyse (RA) weiter, indem sie sich mit aktuellen Forschungsfragen befasst, die sich auf eine zunehmende Menge verfügbarer Daten und Fortschritte beim maschinellen Lernen beziehen. Durch die Automatisierung eines zentralen Schritts in der RA, nämlich der Rekonstruktion des Zustandsraums aus gemessenen experimentellen Zeitreihen, und durch die Untersuchung der Auswirkungen wichtiger freier Parameter soll die RA für Forscher außerhalb der Physik zugänglicher gemacht werden. Der erste Teil dieser Dissertation befasst sich mit der Rekonstruktion des Zustandsraums aus Zeitreihen. Hierzu wird eine neue Idee vorgeschlagen, die das Rekonstruktionsproblem so automatisiert, dass weder die Daten vorverarbeitet noch a priori Parameter geschätzt werden müssen. Die Schlüsselidee ist, dass die Güte einer Rekonstruktion durch eine geeignete Kostenfunktion evaluiert werden kann und diese Funktion im Einbettungsprozess minimiert wird. Darüber hinaus kann die neue Methode multivariate Zeitreihen-Eingabedaten verarbei- ten. Das ist insbesondere deshalb von großer Bedeutung, da mehrkanalige sensorgestützte Beobachtungen in vielen Forschungsbereichen allgegenwärtig sind und weiterhin zunehmen. Darauf aufbauend wird dann das beschriebene Minimierungsproblem der Kostenfunktion mit einem Ansatz des maschinellen Lernens bearbeitet. Im zweiten Teil werden einige technische und methodische Aspekte der RA erörtert. Zu- nächst begründen wir mathematisch die Idee, den einflussreichsten freien Parameter in der RA, den Rekurrenzgrenzwert ε, in Bezug auf die Verteilung aller paarweisen Abstände in den Daten festzulegen. Dies ist insbesondere dann wichtig, wenn verschiedene RPs und ihre Quantifizierungsstatistiken verglichen werden, und ist für jede vergleichende Studie von grundlegender Bedeutung. Zweitens werden einige Aspekte der Rekurrenzquantifizierungs- analyse (RQA) untersucht. Als Korrekturschemata für verzerrte RQA-Statistiken, welche auf diagonalen Linien basierenden, schlagen wir eine einfache Methode zum Umgang mit Randeffekten von RPs in der RQA und einen Skeletonisierungsalgorithmus für RPs vor. Dies sorgt in der Folge zu weniger verzerrten (auf diagonalen Linien basierenden) RQA-Statistiken für hoch abgetastete Daten. Drittens wird eine neuartige RQA-Charakteristik entwickelt, die als verallgemeinertes, nichtlineares Leistungsspektrum hochdimensionaler Systeme angesehen werden kann. Das Spike-Powerspectrum transformiert ein Spike-train-ähnliches Signal in seinen Frequenzbereich. Wenn die diagonallinienabhängige Rekurrenzsrate (τ-RR) eines RP auf diese Weise transformiert wird, können charakteristische Perioden, die in der Zustands- raumdarstellung des Systems erkennbar sind, entschlüsselt werden. Dies ist nicht der Fall, wenn die τ-RR Fourier-transformiert wird. ix x Schließlich werden RA und RQA im dritten Teil auf Paläoklima-Seesedimentdaten und im vierten Teil auf EEG-Daten (Elektroenzephalographie) angewendet. Nach unserem besten Wissen ist dies das erste Mal, dass RPs und RQA für die Analyse von Seesedimentdaten in einem Paläoklima-Kontext verwendet wurden. Daher wird zunächst an dem grundlegenden Formalismus und der Interpretation visuell sichtbarer Muster in RPs in Bezug auf die zugrunde liegenden Proxy-Daten gearbeitet. Wir zeigen, dass diese Muster verwendet werden können, um bestimmte Arten von Variabilität und Übergängen im Kaliumdatensatz von sechs kurzen (< 17m) Sedimentkernen zu klassifizieren, die während des Chew Bahir-Bohrprojekts gesammelt wurden. Darauf aufbauend wird der lange Kern (∼ m composite) desselben Standorts analysiert und zwei Arten von Variabilität und Übergängen werden identifiziert und mit dem Feuchtigkeitsindex des ODP-Standorts  aus dem östlichen Mittelmeerraum verglichen. Die Variabilität vom Typ  spiegelt wahrscheinlich den Einfluss des Präzessionsantriebs in den unteren Breiten zu Zeiten mit Maximalwerten des langen Exzentrizitätszyklus ( kyr) der Erdumlaufbahn um die Sonne wider, wobei die Tendenz zu extremen Ereignissen besteht. Die Variabilität vom Typ  scheint mit den lokalen Minima dieses Zyklus verbunden zu sein und entspricht ziemlich schnellen Übergängen zwischen relativ trockenen und relativ nassen Bedingungen. Im Gegensatz dazu wird RQA seit fast zwei Jahrzehnten im neurowissenschaftlichen Kontext angewendet. Im letzten Teil werden RQA-Statistiken zur Quantifizierung der Komplexität in einem bestimmten Frequenzband multivariater EEG-Daten verwendet. Durch die Analyse experimenteller Daten kann gezeigt werden, dass die Komplexität des auf diese Weise über den sensomotorischen Kortex gemessenen Signals abnimmt, wenn motorische Aufgaben ausgeführt werden. Die Ergebnisse stimmen mit den bekannten Konzepten motorischer Gehirnprozesse überein und ergänzen diese. Wir nehmen an, dass die so entdeckten Merkmale der neuronalen Dynamik im sensomotorischen Kortex zusammen mit den robusten RQA-Methoden zur Identifizierung und Klassifizierung dieser zu der nicht-invasiven EEG-basierten Entwicklung von Gehirn-Computer-Schnittstellen (BCI) und zur motorischen Steuerung und Rehabilitation beitragen werden. Die vorliegende Arbeit ist ein wichtiger Schritt zu einer robusten Analyse komplexer Systeme basierend auf Rekurrenz. KW - recurrence KW - state space reconstruction KW - embedding KW - recurrence analysis KW - recurrence quantification analysis KW - Einbettung KW - Rekurrenz KW - Rekurrenzanalyse KW - quantifizierende Rekurrenzanalyse KW - Zustandsraumrekonstruktion/Phasenraumrekonstruktion Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-538743 ER - TY - JOUR A1 - Wang, Wei A1 - Cherstvy, Andrey G. A1 - Kantz, Holger A1 - Metzler, Ralf A1 - Sokolov, Igor M. T1 - Time averaging and emerging nonergodicity upon resetting of fractional Brownian motion and heterogeneous diffusion processes JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - How different are the results of constant-rate resetting of anomalous-diffusion processes in terms of their ensemble-averaged versus time-averaged mean-squared displacements (MSDs versus TAMSDs) and how does stochastic resetting impact nonergodicity? We examine, both analytically and by simulations, the implications of resetting on the MSD- and TAMSD-based spreading dynamics of particles executing fractional Brownian motion (FBM) with a long-time memory, heterogeneous diffusion processes (HDPs) with a power-law space-dependent diffusivity D(x) = D0|x|gamma and their "combined" process of HDP-FBM. We find, inter alia, that the resetting dynamics of originally ergodic FBM for superdiffusive Hurst exponents develops disparities in scaling and magnitudes of the MSDs and mean TAMSDs indicating weak ergodicity breaking. For subdiffusive HDPs we also quantify the nonequivalence of the MSD and TAMSD and observe a new trimodal form of the probability density function. For reset FBM, HDPs and HDP-FBM we compute analytically and verify by simulations the short-time MSD and TAMSD asymptotes and long-time plateaus reminiscent of those for processes under confinement. We show that certain characteristics of these reset processes are functionally similar despite a different stochastic nature of their nonreset variants. Importantly, we discover nonmonotonicity of the ergodicitybreaking parameter EB as a function of the resetting rate r. For all reset processes studied we unveil a pronounced resetting-induced nonergodicity with a maximum of EB at intermediate r and EB similar to(1/r )-decay at large r. Alongside the emerging MSD-versus-TAMSD disparity, this r-dependence of EB can be an experimentally testable prediction. We conclude by discussing some implications to experimental systems featuring resetting dynamics. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.024105 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 2 PB - American Institute of Physics CY - Woodbury, NY ER - TY - JOUR A1 - Born, Artur A1 - Decker, Regis A1 - Haverkamp, Robert A1 - Ruotsalainen, Kari A1 - Bauer, Karl A1 - Pietzsch, Annette A1 - Föhlisch, Alexander A1 - Büchner, Robby T1 - Thresholding of the Elliott-Yafet spin-flip scattering in multi-sublattice magnets by the respective exchange energies JF - Scientific reports N2 - How different microscopic mechanisms of ultrafast spin dynamics coexist and interplay is not only relevant for the development of spintronics but also for the thorough description of physical systems out-of-equilibrium. In pure crystalline ferromagnets, one of the main microscopic mechanism of spin relaxation is the electron-phonon (el-ph) driven spin-flip, or Elliott-Yafet, scattering. Unexpectedly, recent experiments with ferro- and ferrimagnetic alloys have shown different dynamics for the different sublattices. These distinct sublattice dynamics are contradictory to the Elliott-Yafet scenario. In order to rationalize this discrepancy, it has been proposed that the intra- and intersublattice exchange interaction energies must be considered in the microscopic demagnetization mechanism, too. Here, using a temperature-dependent x-ray emission spectroscopy (XES) method, we address experimentally the element specific el-ph angular momentum transfer rates, responsible for the spin-flips in the respective (sub)lattices of Fe20Ni80, Fe50Ni50 and pure nickel single crystals. We establish how the deduced rate evolution with the temperature is linked to the exchange coupling constants reported for different alloy stoichiometries and how sublattice exchange energies threshold the related el-ph spin-flip channels. Thus, these results evidence that the Elliott-Yafet spin-flip scattering, thresholded by sublattice exchange energies, is the relevant microscopic process to describe sublattice dynamics in alloys and elemental magnetic systems. Y1 - 2021 U6 - https://doi.org/10.1038/s41598-021-81177-9 SN - 2045-2322 VL - 11 IS - 1 PB - Springer Nature CY - Berlin ER - TY - JOUR A1 - Keles, Engin A1 - Mallom, Matthias A1 - von Essen, Carolina A1 - Caroll, Thorsten A. A1 - Alexoudi, Xanthippi A1 - Pino, Lorenzo A1 - Ilyin, Ilya A1 - Poppenhäger, Katja A1 - Kitzmann, Daniel A1 - Nascimbeni, Valerino A1 - Turner, Jake D. A1 - Strassmeier, Klaus G. T1 - The potassium absorption on HD189733b and HD209458b JF - Monthly Notices of the Royal Astronomical Society: Letters N2 - In this work, we investigate the potassium excess absorption around 7699 Å of the exoplanets HD189733b and HD209458b. For this purpose, we used high-spectral resolution transit observations acquired with the 2 × 8.4 m Large Binocular Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). For a bandwidth of 0.8 Å, we present a detection >7σ with an absorption level of 0.18 per cent for HD189733b. Applying the same analysis to HD209458b, we can set 3σ upper limit of 0.09 per cent, even though we do not detect a K-excess absorption. The investigation suggests that the K feature is less present in the atmosphere of HD209458b than in the one of HD189733b. This comparison confirms previous claims that the atmospheres of these two planets must have fundamentally different properties. Y1 - 2021 U6 - https://doi.org/10.1093/mnrasl/slz123 VL - 489 IS - 1 SP - L37 EP - L41 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Pikovskij, Arkadij T1 - Synchronization of oscillators with hyperbolic chaotic phases JF - Izvestija vysšich učebnych zavedenij : naučno-techničeskij žurnal = Izvestiya VUZ. Prikladnaja nelinejnaja dinamika = Applied nonlinear dynamics N2 - Topic and aim. Synchronization in populations of coupled oscillators can be characterized with order parameters that describe collective order in ensembles. A dependence of the order parameter on the coupling constants is well-known for coupled periodic oscillators. The goal of the study is to extend this analysis to ensembles of oscillators with chaotic phases, moreover with phases possessing hyperbolic chaos. Models and methods. Two models are studied in the paper. One is an abstract discrete-time map, composed with a hyperbolic Bernoulli transformation and with Kuramoto dynamics. Another model is a system of coupled continuous-time chaotic oscillators, where each individual oscillator has a hyperbolic attractor of Smale-Williams type. Results. The discrete-time model is studied with the Ott-Antonsen ansatz, which is shown to be invariant under the application of the Bernoulli map. The analysis of the resulting map for the order parameter shows, that the asynchronouis state is always stable, but the synchronous one becomes stable above a certain coupling strength. Numerical analysis of the continuous-time model reveals a complex sequence of transitions from an asynchronous state to a completely synchronous hyperbolic chaos, with intermediate stages that include regimes with periodic in time mean field, as well as with weakly and strongly irregular mean field variations. Discussion. Results demonstrate that synchronization of systems with hyperbolic chaos of phases is possible, although a rather strong coupling is required. The approach can be applied to other systems of interacting units with hyperbolic chaotic dynamics. N2 - Тема и цель. Синхронизация в популяциях связанных осцилляторов может быть охарактеризована параметрами порядка, описывающими коллективный порядок в ансамблях. Зависимость параметра порядка от коэффициентов связи хорошо известна для связанных периодических осцилляторов. Целью данного исследования является обобщение этого анализа на ансамбли осцилляторов с хаотическими фазами, а именно, с фазами, распределёнными на гиперболическом аттракторе. Модели и методы. В работе исследуются две модели. Первая – абстрактное отображение в дискретном времени, составленное из гиперболического преобразования Бернулли и динамики Курамото. Вторая – это система связанных хаотических осцилляторов в непрерывном времени, где каждый отдельный осциллятор имеет гиперболический аттрактор типа Смейла–Вильямса. Результаты. Модель в дискретном времени изучается с помощью подхода Отта–Антонсена, который, как показано, инвариантен при применении отображения Бернулли. Анализ полученного отображения по параметрам порядка показывает, что асинхронное состояние всегда устойчиво, а синхронное состояние становится устойчивым выше определенной силы связи. Численный анализ модели в непрерывном времени показывает сложную последовательность переходов из асинхронного состояния в полностью синхронный гиперболический хаос с промежуточными стадиями, которые включают режимы с периодическим во времени средним полем, а также со слабо и сильно нерегулярными вариациями среднего поля. Обсуждение. Результаты показывают, что синхронизация систем с гиперболическим фазовым хаосом возможна, хотя требуется довольно сильная связь. Данный подход может быть применен и к другим системам взаимодействующих звеньев с гиперболической хаотической динамикой. T2 - Синхронизация осцилляторов с гиперболическими хаотическими фазами KW - hyperbolic attractor KW - synchronization KW - collective dynamics KW - иперболический аттрактор KW - синхронизация KW - оллективная динамика Y1 - 2021 U6 - https://doi.org/10.18500/0869-6632-2021-29-1-78-87 SN - 0869-6632 SN - 2542-1905 VL - 29 IS - 1 SP - 78 EP - 87 PB - Saratov State University CY - Saratov ER - TY - GEN A1 - Regenstein, Wolfgang T1 - Strahlenschutzphysik in Stichpunkten N2 - Das Manuskript dient der Vorbereitung der Prüfung der Fachkunde zum Strahlenschutz für Lehrer. Es enthält wichtige Grundlagen der Kernphysik, insbesondere die Eigenschaften der Alpha-, Beta-, Gamma-, Neutronen- und Röntgenstrahlen. Es folgt eine kurze Beschreibung des Einflusses der Strahlung auf belebte Materie. Wichtige Paragrafen der Strahlenschutzverordnung werden beschrieben. Eine Aufgabensammlung dient zur Illustration und Übung. N2 - The paper serves for preparation to the examination to the „Fachkunde zum Stahlenschutz für Lehrer“. It contains important basics of the nuclear physics, especially the quantities of alpha-, beta-, gamma- und neutron radiation. It follows a description of the influence the radiation on lively matter. Important articles oft the „Strahlenschutzverordnung“ are described. A collection of exercises serves to illustration and practice. KW - Strahlenschutz KW - Strahlenarten KW - Dosimetrie KW - Strahlenbiologie KW - Strahlenbelastung KW - Radiation protection KW - kind of radiation KW - dosis measurement KW - radiobiology KW - radiation load Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-513405 ER - TY - JOUR A1 - Dahlenburg, Marcus A1 - Chechkin, Aleksei A1 - Schumer, Rina A1 - Metzler, Ralf T1 - Stochastic resetting by a random amplitude JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Stochastic resetting, a diffusive process whose amplitude is reset to the origin at random times, is a vividly studied strategy to optimize encounter dynamics, e.g., in chemical reactions. Here we generalize the resetting step by introducing a random resetting amplitude such that the diffusing particle may be only partially reset towards the trajectory origin or even overshoot the origin in a resetting step. We introduce different scenarios for the random-amplitude stochastic resetting process and discuss the resulting dynamics. Direct applications are geophysical layering (stratigraphy) and population dynamics or financial markets, as well as generic search processes. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.103.052123 SN - 2470-0045 SN - 2470-0053 VL - 103 IS - 5 PB - American Physical Society CY - Woodbury, NY ER - TY - JOUR A1 - Decker, Regis A1 - Born, Artur A1 - Ruotsalainen, Kari A1 - Bauer, Karl A1 - Haverkamp, Robert A1 - Büchner, Robby A1 - Pietzsch, Annette A1 - Föhlisch, Alexander T1 - Spin-lattice angular momentum transfer of localized and valence electrons in the demagnetization transient state of gadolinium JF - Applied physics letters N2 - The electron-phonon scattering is one of the main microscopic mechanisms responsible for the spin-flip in the transient state of ultrafast demagnetization. Here, we present an experimental determination of the temperature-dependent electron-phonon scattering rate in Gd. Using a static x-ray emission spectroscopy method, where the reduction of the decay peak intensities when increasing the temperature is quantified, we measure independently the electron-phonon scattering rate for the 5d and the 4f electrons. We deduce the temperature dependence of scattering for the 5d electrons, while no effect on the phonon population is observed for the 4f electrons. Our results suggest that the ultrafast magnetization dynamics in Gd is triggered by the spin-flip in the 5d electrons. We also evidence the existence of a temperature threshold, above which spin-flip scattering of the 5d electrons takes place. We deduce that during the transient state of ultrafast demagnetization, the exchange energy between 5d electrons has to be overcome before the microscopic electron-phonon scattering process can occur. Y1 - 2021 U6 - https://doi.org/10.1063/5.0063404 SN - 0003-6951 SN - 1077-3118 VL - 119 IS - 15 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Horovitz, Baruch A1 - Henkel, Carsten T1 - Spin entanglement via scanning tunneling microscope current JF - Physical review : B, Condensed matter and materials physics N2 - We consider a system of two spins under a scanning tunneling microscope bias and derive its master equation. We find that the tunneling elements to the electronic contacts (tip and substrate) generate an exchange interaction between the spins as well as a Dzyaloshinskii-Moriya interaction in the presence of spin-orbit coupling. The tunnel current spectrum then shows additional lines compared to conventional spin-resonance experiments. When the spins have degenerate Larmor frequencies and equal tunneling amplitudes (without spin orbit), there is a dark state with a vanishing decay rate. The coupling to the electronic environment generates significant spin-spin entanglement via the dark state, even if the initial state is nonentangled. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevB.104.L081405 SN - 2469-9950 SN - 2469-9969 VL - 104 IS - 8 PB - American Physical Society CY - Ridge, NY ER - TY - JOUR A1 - Keles, Engin T1 - Spectral signature of atmospheric winds in high-resolution transit observations JF - Monthly Notices of the Royal Astronomical Society N2 - The study of exoplanet atmospheres showed large diversity compared to the planets in our Solar system. Especially Jupiter-type exoplanets orbiting their host star in close orbits, the so-called hot and ultra-hot Jupiters, have been studied in detail due to their enhanced atmospheric signature. Due to their tidally locked status, the temperature difference between the day- and nightside triggers atmospheric winds that can lead to various fingerprints in the observations. Spatially resolved absorption lines during transit such as sodium (Na) could be a good tracer for such winds. Different works resolved the Na absorption lines on different exoplanets which show different line widths. Assuming that this could be attributed to such zonal jet streams, this work models the effect of such winds on synthetic absorption lines. For this, transiting Jupiter-type planets with rotational velocities similar to hot and ultra-hot Jupiter are considered. The investigation shows that high wind velocities could reproduce the broadening of Na-line profiles inferred in different high-resolution transit observations. There is a tendency that the broadening values decrease for planets with lower equilibrium temperature. This could be explained by atmospheric drag induced by the ionization of alkali lines that slow down the zonal jet streams, favouring their existence on hot Jupiter rather than ultra-hot Jupiter. Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab099 VL - 502 IS - 1 SP - 1456 EP - 1468 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Bolotov, Maxim I. A1 - Smirnov, Lev A. A1 - Bubnova, E. S. A1 - Osipov, Grigory V. A1 - Pikovskij, Arkadij T1 - Spatiotemporal regimes in the Kuramoto-Battogtokh system of nonidentical oscillators JF - Journal of experimental and theoretical physics N2 - We consider the spatiotemporal states of an ensemble of nonlocally coupled nonidentical phase oscillators, which correspond to different regimes of the long-term evolution of such a system. We have obtained homogeneous, twisted, and nonhomogeneous stationary solutions to the Ott-Antonsen equations corresponding to key variants of the realized collective rotational motion of elements of the medium in question with nonzero mesoscopic characteristics determining the degree of coherence of the dynamics of neighboring particles. We have described the procedures of the search for the class of nonhomogeneous solutions as stationary points of the auxiliary point map and of determining the stability based on analysis of the eigenvalue spectrum of the composite operator. Static and breather cluster regimes have been demonstrated and described, as well as the regimes with an irregular behavior of averaged complex fields including, in particular, the local order parameter. Y1 - 2021 U6 - https://doi.org/10.1134/S1063776121010106 SN - 1063-7761 SN - 1090-6509 VL - 132 IS - 1 SP - 127 EP - 147 PB - Springer CY - Heidelberg [u.a.] ER - TY - JOUR A1 - Wang, Jingwen A1 - Rychkov, Dmitry A1 - Gerhard, Reimund T1 - Space-charge electret properties of polypropylene films with transcrystalline or spherulitic structures BT - a comparison of functionalities at interfaces JF - Journal of applied physics : AIP's archival journal for significant new results in applied physics / publ. by the American Institute of Physics N2 - Spherulite-related space-charge electret properties of polypropylene (PP) have been widely discussed in the past decades. In the present paper, a less-common crystalline structure in PP-transcrystalline PP-is studied regarding its electret behavior in comparison with the typical spherulitic morphology. Polarized light microscopy and differential scanning calorimetry were employed to characterize the crystallite types and crystallinities of transcrystalline and spherulitic PP. Their electret functionality is investigated by means of thermally stimulated discharge experiments, where the cross-over phenomenon is observed on transcrystalline PP films, whereas surface-potential saturation and undercharging on the surface occur on the spherulitic samples. Besides, an asymmetrical behavior of positive and negative surface-charge stabilities is found on PP with spherulites, the negatively charged spherulitic surfaces show a better charge stability. It is shown that PP electrets are very sensitive to changes in the microscopic crystalline structures and their interfaces as well as in the molecular conformations controlled through adjustments of the respective processing steps. In addition, surface and bulk nanocomposites of PP or low-density polyethylene with inorganic particles are included in the comparison. In view of recent developments in the areas of PP-based electret-fiber filters and cellular-foam ferroelectrets, the observed changes in the charge-storage properties may have particular relevance, as the required film, fiber, or foam processing might significantly modify crystalline morphologies and nano-scale interfaces in PP electrets. Limitations in the charge-storage capabilities of interface structures may also be of interest in the context of high-voltage electrical-insulation materials where reduced space-charge accumulation and slightly increased charge transport can be advantageous. Y1 - 2021 U6 - https://doi.org/10.1063/5.0039867 SN - 0021-8979 SN - 1089-7550 VL - 129 IS - 6 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Letellier, Christophe A1 - Abraham, Ralph A1 - Shepelyansky, Dima L. A1 - Rossler, Otto E. A1 - Holmes, Philip A1 - Lozi, Rene A1 - Glass, Leon A1 - Pikovsky, Arkady A1 - Olsen, Lars F. A1 - Tsuda, Ichiro A1 - Grebogi, Celso A1 - Parlitz, Ulrich A1 - Gilmore, Robert A1 - Pecora, Louis M. A1 - Carroll, Thomas L. T1 - Some elements for a history of the dynamical systems theory JF - Chaos : an interdisciplinary journal of nonlinear science N2 - Writing a history of a scientific theory is always difficult because it requires to focus on some key contributors and to "reconstruct" some supposed influences. In the 1970s, a new way of performing science under the name "chaos" emerged, combining the mathematics from the nonlinear dynamical systems theory and numerical simulations. To provide a direct testimony of how contributors can be influenced by other scientists or works, we here collected some writings about the early times of a few contributors to chaos theory. The purpose is to exhibit the diversity in the paths and to bring some elements-which were never published-illustrating the atmosphere of this period. Some peculiarities of chaos theory are also discussed. Y1 - 2021 U6 - https://doi.org/10.1063/5.0047851 SN - 1054-1500 SN - 1089-7682 VL - 31 IS - 5 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Cherstvy, Andrey G. A1 - Vinod, Deepak A1 - Aghion, Erez A1 - Sokolov, Igor M. A1 - Metzler, Ralf T1 - Scaled geometric Brownian motion features sub- or superexponential ensemble-averaged, but linear time-averaged mean-squared displacements JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Various mathematical Black-Scholes-Merton-like models of option pricing employ the paradigmatic stochastic process of geometric Brownian motion (GBM). The innate property of such models and of real stock-market prices is the roughly exponential growth of prices with time [on average, in crisis-free times]. We here explore the ensemble- and time averages of a multiplicative-noise stochastic process with power-law-like time-dependent volatility, sigma(t) similar to t(alpha), named scaled GBM (SGBM). For SGBM, the mean-squared displacement (MSD) computed for an ensemble of statistically equivalent trajectories can grow faster than exponentially in time, while the time-averaged MSD (TAMSD)-based on a sliding-window averaging along a single trajectory-is always linear at short lag times Delta. The proportionality factor between these the two averages of the time series is Delta/T at short lag times, where T is the trajectory length, similarly to GBM. This discrepancy of the scaling relations and pronounced nonequivalence of the MSD and TAMSD at Delta/T << 1 is a manifestation of weak ergodicity breaking for standard GBM and for SGBM with s (t)-modulation, the main focus of our analysis. The analytical predictions for the MSD and mean TAMSD for SGBM are in quantitative agreement with the results of stochastic computer simulations. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.103.062127 SN - 2470-0045 SN - 2470-0053 VL - 103 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Bernardi, Rafael L. A1 - Berdja, Amokrane A1 - Dani Guzman, Christian A1 - Torres-Torriti, Miguel A1 - Roth, Martin M. T1 - Restoration of images with a spatially varying PSF of the T80-S telescope optical model using neural networks JF - Monthly notices of the Royal Astronomical Society N2 - Most image restoration methods in astronomy rely upon probabilistic tools that infer the best solution for a deconvolution problem. They achieve good performances when the point spread function (PSF) is spatially invariant in the image plane. However, this condition is not always satisfied in real optical systems. We propose a new method for the restoration of images affected by static and anisotropic aberrations using Deep Neural Networks that can be directly applied to sky images. The network is trained using simulated sky images corresponding to the T80-S Telescope optical model, a 80-cm survey imager at Cerro Tololo (Chile), which are synthesized using a Zernike polynomial representation of the optical system. Once trained, the network can be used directly on sky images, outputting a corrected version of the image that has a constant and known PSF across its field of view. The method is to be tested on the T80-S Telescope. We present the method and results on synthetic data. KW - methods: statistical KW - techniques: image processing Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab3400 SN - 0035-8711 SN - 1365-2966 VL - 510 IS - 3 SP - 4284 EP - 4294 PB - Oxford Univ. Press CY - Oxford ER - TY - GEN A1 - Caesar, Levke A1 - Rahmstorf, Stefan A1 - Feulner, Georg T1 - Reply to comment on 'On the relationship between Atlantic meridional overturning circulation slowdown and global surface warming' T2 - Environmental research letters N2 - In their comment on our paper (Caesar et al 2020 Environ. Res. Lett. 15 024003), Chen and Tung (hereafter C&T) argue that our analysis, showing that over the last decades Atlantic meridional overturning circulation (AMOC) strength and global mean surface temperature (GMST) were positively correlated, is incorrect. Their claim is mainly based on two arguments, neither of which is justified: first, C&T claim that our analysis is based on 'established evidence' that was only true for preindustrial conditions-this is not the case. Using data from the modern period (1947-2012), we show that the established understanding (i.e. deep-water formation in the North Atlantic cools the deep ocean and warms the surface) is correct, but our analysis is not based on this fact. Secondly, C&T claim that our results are based on a statistical analysis of only one cycle of data which was furthermore incorrectly detrended. This, too, is not true. Our conclusion that a weaker AMOC delays the current surface warming rather than enhances it, is based on several independent lines of evidence. The data we show to support this covers more than one cycle and the detrending (which was performed to avoid spurious correlations due to a common trend) does not affect our conclusion: the correlation between AMOC strength and GMST is positive. We do not claim that this is strong evidence that the two time series are in phase, but rather that this means that the two time series are not anti-correlated. KW - Atlantic meridional overturning circulation KW - global surface warming KW - ocean heat uptake Y1 - 2021 U6 - https://doi.org/10.1088/1748-9326/abc776 SN - 1748-9326 VL - 16 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Chechkin, Aleksei V. A1 - Sokolov, Igor M. T1 - Relation between generalized diffusion equations and subordination schemes JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Generalized (non-Markovian) diffusion equations with different memory kernels and subordination schemes based on random time change in the Brownian diffusion process are popular mathematical tools for description of a variety of non-Fickian diffusion processes in physics, biology, and earth sciences. Some of such processes (notably, the fluid limits of continuous time random walks) allow for either kind of description, but other ones do not. In the present work we discuss the conditions under which a generalized diffusion equation does correspond to a subordination scheme, and the conditions under which a subordination scheme does possess the corresponding generalized diffusion equation. Moreover, we discuss examples of random processes for which only one, or both kinds of description are applicable. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.103.032133 SN - 2470-0045 SN - 2470-0053 VL - 103 IS - 3 PB - American Physical Society CY - College Park ER - TY - GEN A1 - Zeuschner, Steffen Peer A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Reppert, Alexander von A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Schwarzkopf, Jutta A1 - Boschker, Jos A1 - Herzog, Marc A1 - Bargheer, Matias T1 - Reciprocal space slicing BT - a time-efficient approach to femtosecond x-ray diffraction T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1137 Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-499761 SN - 1866-8372 IS - 1137 ER - TY - JOUR A1 - Zeuschner, Steffen Peer A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Reppert, Alexander von A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Schwarzkopf, Jutta A1 - Boschker, Jos A1 - Herzog, Marc A1 - Bargheer, Matias T1 - Reciprocal space slicing BT - a time-efficient approach to femtosecond x-ray diffraction JF - Structural dynamics N2 - An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2. Y1 - 2020 U6 - https://doi.org/10.1063/4.0000040 SN - 2329-7778 VL - 8 IS - 1 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Kluge, Lucas A1 - Socolar, Joshua E. S. A1 - Schöll, Eckehard T1 - Random logic networks BT - from classical Boolean to quantum dynamics JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We investigate dynamical properties of a quantum generalization of classical reversible Boolean networks. The state of each node is encoded as a single qubit, and classical Boolean logic operations are supplemented by controlled bit-flip and Hadamard operations. We consider synchronous updating schemes in which each qubit is updated at each step based on stored values of the qubits from the previous step. We investigate the periodic or quasiperiodic behavior of quantum networks, and we analyze the propagation of single site perturbations through the quantum networks with input degree one. A nonclassical mechanism for perturbation propagation leads to substantially different evolution of the Hamming distance between the original and perturbed states. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.064308 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 6 PB - American Physical Society CY - Woodbury, NY ER - TY - THES A1 - Diercke, Andrea T1 - Physical environment of large-scale high-latitude and polar crown filaments T1 - Die Physik von polaren Filamenten N2 - 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 Å. 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 Å, Ca IIK 3933 Å, and He I 10830 Å), 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 Å. 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 Å 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. N2 - Filamente sind omnipräsente Strukturen in der Chromosphäre der Sonne. Diese Schicht befindet sich über der Photosphäre, welche die sichtbare Oberfläche der Sonne darstellt. Filamente sind Plasmagebilde, welche in der Photosphäre verankert sind und von der Chromosphäre in die Korona reichen, der äußersten Atmosphärenschicht der Sonne. Diese Strukturen werden durch das Magnetfeld der Sonne stabilisiert. Durch Störungen des Magnetfelds, destabilisiert sich das Filament und das dort enthaltene Plasma kann als Sonneneruption, ein sogenannter koronaler Massenauswurf, ins Weltall geschleudert werden, welcher auch die Erde treffen könnte. Das Verständnis von Filamenten, deren Stabilität und Verbindung zum Magnetfeld sind ungemein wichtig, um Sonneneruptionen besser verstehen und vorhersagen zu können. Ein spezieller Typ von Filamenten, sind polare Filamente, (engl. polar crown filaments). Diese bilden sich an der Grenzfläche des unipolaren Magnetfelds an den Polen und dem Magnetfeld von gemischten Polaritäten in den Aktivitätsgürteln der Sonne. In letzteren werden Reste von bipolaren und zerfallenen Sonnenfleckengruppen zum Pol transportiert. Dieser Transport wird durch den Sonnendynamo initialisiert, so dass die Untersuchung polarer Filamente indirekt Rückschlüsse auf den Sonnendynamo zulässt. Die vorliegende Arbeit untersucht die polaren Filamente aus zwei Perspektiven. Zum einen aus der globalen Perspektive, bei der wir synoptische Beobachtungen der gesamten Sonnenscheibe nutzen, um das zyklische Verhalten der Filamente zu untersuchen. Zum anderen aus einer detailorientierten Perspektive, wobei wir hochaufgelöste Beobachtungen der Filamente auswerten, um mehr über die Verbindung von kühlem chromosphärischem Plasma zum Magnetfeld zu erfahren. Für die Untersuchung des zyklischen Verhaltens von polaren Filamenten nutzen wir Daten des Chromospheric Telescope (ChroTel), welches alle drei Minuten Aufnahmen der Chromosphäre in drei verschiedenen Wellenlängen macht. Die Wasserstofflinie der Balmerserie Hα ist dabei die beste Möglichkeit Filamente in der Chromosphäre abzubilden. Eine während dieser Arbeit entwickelte Methode, zum Korrigieren von Intensitätsungleichmäßigkeiten in Sonnenbildern, legt den Grundstein für alle weiteren Studien mit diesen Daten. Die Filamente können somit aus den Bildern heraus extrahiert werden und damit kann der aktuelle Sonnenzyklus zwischen Maximum und Minimum untersucht werden. Wir konnten die Wanderung der polaren Filamente für den Sonnenzyklus 24 in den Daten lokalisieren und die polwärtsgerichtete Geschwindigkeit bestimmen, welche wir mit vorherigen Ergebnissen verglichen haben. Da die morphologischen Bildbearbeitungsmethode, welche wir zur Extraktion der Filamente benutzt haben, auch andere Strukturen, wie Sonnenflecken nicht ausschließen konnte, haben wir neue Methoden entwickelt, die auf Maschinellem Lernen mit tiefen neuronalen Netzwerken beruhen. Die vorläufigen Ergebnisse sind sehr vielversprechend und auch auf Hα Bildern von anderen Teleskopen leicht übertragbar. Für die Untersuchung der polaren Filamente mit hochaufgelösten Bildern verwenden wir Beobachtungen vom Vakuumturmteleskop (VTT) auf Teneriffa, Spanien. Die Bilder wurden mit Hα Schmal- und Breitbandfiltern aufgenommen und zeigen sowohl die Chromosphäre als auch die Photosphäre. Wir untersuchen dabei die kleinsten auflösbaren Aufhellungen, (engl. bright points), welche in Verbindung mit dem Magnetfeld stehen. Diese kleinskaligen Aufhellungen finden wir vor allem an den Fußpunktregionen der Filamente, die mit starken Konzentrationen vom Magnetfeld korrelieren. Solche hellen Punkte in der Nähe von polaren Filamenten wurden bisher nie mit hochaufgelösten Beobachtungen untersucht. Die statistische Auswertung dieser Strukturen zeigt, dass sie sich kaum von ihren äquatornahen Gegenstücken unterscheiden, mit Ausnahme einer tendenziell größeren Fläche. KW - Solar Physics KW - Sonnenphysik KW - Filaments KW - Filamente KW - Chromosphere KW - Chromosphäre Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-511301 ER - TY - JOUR A1 - Zu, Fengshuo A1 - Warby, Jonathan A1 - Stolterfoht, Martin A1 - Li, Jinzhao A1 - Shin, Dongguen A1 - Unger, Eva A1 - Koch, Norbert T1 - Photoinduced energy-level realignment at interfaces between organic semiconductors and metal-halide perovskites JF - Physical review letters N2 - In contrast to the common conception that the interfacial energy-level alignment is affixed once the interface is formed, we demonstrate that heterojunctions between organic semiconductors and metal-halide perovskites exhibit huge energy-level realignment during photoexcitation. Importantly, the photoinduced level shifts occur in the organic component, including the first molecular layer in direct contact with the perovskite. This is caused by charge-carrier accumulation within the organic semiconductor under illumination and the weak electronic coupling between the junction components. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevLett.127.246401 SN - 0031-9007 SN - 1079-7114 VL - 127 IS - 24 PB - American Physical Society CY - College Park ER - TY - THES A1 - Omelchenko, Oleh T1 - Synchronität-und-Unordnung-Muster in Netzwerken gekoppelter Oszillatoren T1 - Patterns of synchrony and disorder in networks of coupled oscillators N2 - Synchronization of coupled oscillators manifests itself in many natural and man-made systems, including cyrcadian clocks, central pattern generators, laser arrays, power grids, chemical and electrochemical oscillators, only to name a few. The mathematical description of this phenomenon is often based on the paradigmatic Kuramoto model, which represents each oscillator by one scalar variable, its phase. When coupled, phase oscillators constitute a high-dimensional dynamical system, which exhibits complex behaviour, ranging from synchronized uniform oscillation to quasiperiodicity and chaos. The corresponding collective rhythms can be useful or harmful to the normal operation of various systems, therefore they have been the subject of much research. Initially, synchronization phenomena have been studied in systems with all-to-all (global) and nearest-neighbour (local) coupling, or on random networks. However, in recent decades there has been a lot of interest in more complicated coupling structures, which take into account the spatially distributed nature of real-world oscillator systems and the distance-dependent nature of the interaction between their components. Examples of such systems are abound in biology and neuroscience. They include spatially distributed cell populations, cilia carpets and neural networks relevant to working memory. In many cases, these systems support a rich variety of patterns of synchrony and disorder with remarkable properties that have not been observed in other continuous media. Such patterns are usually referred to as the coherence-incoherence patterns, but in symmetrically coupled oscillator systems they are also known by the name chimera states. The main goal of this work is to give an overview of different types of collective behaviour in large networks of spatially distributed phase oscillators and to develop mathematical methods for their analysis. We focus on the Kuramoto models for one-, two- and three-dimensional oscillator arrays with nonlocal coupling, where the coupling extends over a range wider than nearest neighbour coupling and depends on separation. We use the fact that, for a special (but still quite general) phase interaction function, the long-term coarse-grained dynamics of the above systems can be described by a certain integro-differential equation that follows from the mathematical approach called the Ott-Antonsen theory. We show that this equation adequately represents all relevant patterns of synchrony and disorder, including stationary, periodically breathing and moving coherence-incoherence patterns. Moreover, we show that this equation can be used to completely solve the existence and stability problem for each of these patterns and to reliably predict their main properties in many application relevant situations. N2 - Die Synchronisation von gekoppelten Oszillatoren tritt in vielen natürlichen und künstlichen Systemen auf, beispielsweise bei zirkadianen Uhren, zentralen Mustergeneratoren, Laserarrays, Stromnetzen oder chemischen und elektrochemischen Oszillatoren, um nur einige zu nennen. Die mathematische Beschreibung dieses Phänomens basiert häufig auf dem paradigmatischen Kuramoto-Modell, das jeden Oszillator durch eine skalare Variable, seine Phase, darstellt. Wenn Phasenoszillatoren gekoppelt sind, bilden sie ein hochdimensionales dynamisches System, das ein komplexes Verhalten aufweist, welches von synchronisierter kollektiver Oszillation bis zu Quasiperiodizität und Chaos reicht. Die entsprechenden kollektiven Rhythmen können für den normalen Betrieb verschiedener Systeme nützlich oder schädlich sein, weshalb sie Gegenstand zahlreicher Untersuchungen waren. Anfänglich wurden Synchronisationsphänomene in Systemen mit globaler Mittelfeldkopplung und lokaler Nächster-Nachbar Kopplung oder in komplexen Netzwerken untersucht. In den letzten Jahrzehnten gab es jedoch großes Interesse an anderen Kopplungsstrukturen, die die räumlich verteilte Natur realer Oszillatorsysteme und die entfernungsabhängige Natur der Wechselwirkung zwischen ihren Komponenten berücksichtigen. Sowohl in Bereichen der Biologie als auch der Neurowissenschaften gibt es eine Vielzahl von Beipsieln für solche Systeme. Dazu gehören räumlich verteilte Zellpopulationen, Zilien-Teppiche und neuronale Netze, die für das Arbeitsgedächtnis relevant sind. In vielen Fällen unterstützen diese Systeme eine Vielzahl von Synchronität-und-Unordnung-Mustern mit bemerkenswerten Eigenschaften, die in anderen kontinuierlichen Medien nicht beobachtet wurden. Solche Muster werden üblicherweise als Kohärenz-Inkohärenz-Muster bezeichnet, aber in symmetrisch gekoppelten Oszillatorsystemen sind diese auch unter dem Namen Chimära-Zustände bekannt. Das Hauptziel dieser Arbeit ist es, einen Überblick über verschiedene Arten von kollektivem Verhalten in großen Netzwerken räumlich verteilter Phasenoszillatoren zu geben und mathematische Methoden für deren Analyse zu entwickeln. Wir konzentrieren uns dabei auf die Kuramoto-Modelle für ein-, zwei- und dreidimensionale Oszillator-Arrays mit nichtlokaler Kopplung, wobei sich die Kopplung über einen Bereich erstreckt, welcher breiter ist als die Kopplung zum nächsten Nachbarn und von der Trennung abhängt. Wir verwenden die Tatsache, dass für eine spezielle (aber immer noch recht allgemeine) Phasenwechselwirkungsfunktion die langfristige grobkörnige Dynamik der obigen Systeme durch eine bestimmte Integro-Differentialgleichung beschrieben werden kann. Diese ergibt sich aus dem mathematischen Ansatz namens Ott-Antonsen-Theorie. Wir zeigen, dass diese Gleichung alle relevanten Synchronität-und-Unordnung-Muster angemessen darstellt, einschließlich stationärer, periodisch oszillierender und sich bewegender Kohärenz-Inkohärenz-Muster. Darüber hinaus zeigen wir, dass diese Gleichung verwendet werden kann, um das Existenz- und Stabilitätsproblem für jedes dieser Muster vollständig zu lösen und ihre Haupteigenschaften in vielen anwendungsrelevanten Situationen zuverlässig vorherzusagen. KW - phase oscillators KW - networks KW - synchronization KW - dynamical patterns KW - chimera states KW - Phasenoszillatoren KW - Netzwerke KW - Synchronisation KW - dynamische Muster KW - Chimäre-Zustände Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-535961 ER - TY - JOUR A1 - Milde, Peter A1 - Langenhorst, Malte A1 - Hölscher, Hendrik A1 - Rottmann-Matthes, Jens A1 - Hundertmark, Dirk A1 - Eng, Lukas A1 - Hoffmann-Vogel, Regina T1 - Out-of-equilibrium optomechanical resonance self-excitation JF - Journal of applied physics N2 - The fundamental sensitivity limit of atomic force microscopy is strongly correlated to the thermal noise of cantilever oscillation. A method to suppress this unwanted noise is to reduce the bandwidth of the measurement, but this approach is limited by the speed of the measurement and the width of the cantilever resonance, commonly defined through the quality factor Q. However, it has been shown that optomechanical resonances in interferometers might affect cantilever oscillations resulting in an effective quality factor Q(eff). When the laser power is sufficiently increased cantilever oscillations might even reach the regime of self-oscillation. In this self-oscillation state, the noise of the system is partially determined by the interaction with laser light far from equilibrium. Here, we show and discuss how tuning of laser power leads to nonlinear optomechanical effects that can dramatically increase the effective quality factor of the cantilever leading to out-of-equilibrium noise. We model the effects using a fourth order nonlinearity of the damping coefficient. Published under an exclusive license by AIP Publishing. KW - Electrical properties and parameters KW - Ultra-high vacuum KW - Electronic noise KW - Signal processing KW - Noise floor KW - Atomic force microscopy KW - Hooke's law KW - Interferometry KW - Optical resonators KW - Thermo optic effects Y1 - 2021 U6 - https://doi.org/10.1063/5.0054509 SN - 0021-8979 SN - 1089-7550 VL - 130 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Krivenkov, Maxim A1 - Marchenko, Dimitry A1 - Sánchez-Barriga, Jaime A1 - Golias, Evangelos A1 - Rader, Oliver A1 - Varykhalov, Andrei T1 - Origin of the band gap in Bi-intercalated graphene on Ir(111) JF - 2D Materials N2 - Proximity to heavy sp-elements is considered promising for reaching a band gap in graphene that could host quantum spin Hall states. The recent report of an induced spin-orbit gap of 0.2 eV in Pb-intercalated graphene detectable by spin-resolved photoemission has spurred renewed interest in such systems (Klimovskikh et al 2017 ACS Nano 11, 368). In the case of Bi intercalation an even larger band gap of 0.4 eV has been observed but was assigned to the influence of a dislocation network (Warmuth et al 2016 Phys. Rev. B 93, 165 437). Here, we study Bi intercalation under graphene on Ir(111) and report a nearly ideal graphene dispersion without band replicas and no indication of hybridization with the substrate. The band gap is small (0.19 eV) and can be tuned by +/- 25 meV through the Bi coverage. The Bi atomic density is higher than in the recent report. By spin-resolved photoemission we exclude induced spin-orbit interaction as origin of the gap. Quantitative agreement of a photoemission intensity analysis with the measured band gap suggests sublattice symmetry breaking as one of the possible band gap opening mechanisms. We test several Bi structures by density functional theory. Our results indicate the possibility that Bi intercalates in the phase of bismuthene forming a graphene-bismuthene van der Waals heterostructure. KW - graphene KW - bismuth KW - Ir(111) KW - spin-orbit interaction KW - ARPES KW - STM KW - bismuthene Y1 - 2021 U6 - https://doi.org/10.1088/2053-1583/abd1e4 SN - 2053-1583 VL - 8 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Ocampo-Espindola, Jorge Luis A1 - Omel'chenko, Oleh A1 - Kiss, Istvan Z. T1 - Non-monotonic transients to synchrony in Kuramoto networks and electrochemical oscillators JF - Journal of physics. Complexity N2 - We performed numerical simulations with the Kuramoto model and experiments with oscillatory nickel electrodissolution to explore the dynamical features of the transients from random initial conditions to a fully synchronized (one-cluster) state. The numerical simulations revealed that certain networks (e.g., globally coupled or dense Erdos-Renyi random networks) showed relatively simple behavior with monotonic increase of the Kuramoto order parameter from the random initial condition to the fully synchronized state and that the transient times exhibited a unimodal distribution. However, some modular networks with bridge elements were identified which exhibited non-monotonic variation of the order parameter with local maximum and/or minimum. In these networks, the histogram of the transients times became bimodal and the mean transient time scaled well with inverse of the magnitude of the second largest eigenvalue of the network Laplacian matrix. The non-monotonic transients increase the relative standard deviations from about 0.3 to 0.5, i.e., the transient times became more diverse. The non-monotonic transients are related to generation of phase patterns where the modules are synchronized but approximately anti-phase to each other. The predictions of the numerical simulations were demonstrated in a population of coupled oscillatory electrochemical reactions in global, modular, and irregular tree networks. The findings clarify the role of network structure in generation of complex transients that can, for example, play a role in intermittent desynchronization of the circadian clock due to external cues or in deep brain stimulations where long transients are required after a desynchronization stimulus. KW - synchronization KW - networks KW - Kuramoto model KW - electrochemistry KW - chemical KW - oscillations Y1 - 2021 U6 - https://doi.org/10.1088/2632-072X/abe109 SN - 2632-072X VL - 2 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Raman Venkatesan, Thulasinath A1 - Smykalla, David A1 - Ploss, Bernd A1 - Wübbenhorst, Michael A1 - Gerhard, Reimund T1 - Non-linear dielectric spectroscopy for detecting and evaluating structure-property relations in a P(VDF-TrFE-CFE) relaxor-ferroelectric terpolymer JF - Applied physics : A, Materials science & processing N2 - Non-linear dielectric spectroscopy (NLDS) is employed as an effective tool to study relaxation processes and phase transitions of a poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) relaxor-ferroelectric (R-F) terpolymer in detail. Measurements of the non-linear dielectric permittivity epsilon 2 ' reveal peaks at 30 and 80 degrees C that cannot be identified in conventional dielectric spectroscopy. By combining the results from NLDS experiments with those from other techniques such as thermally stimulated depolarization and dielectric-hysteresis studies, it is possible to explain the processes behind the additional peaks. The former peak, which is associated with the mid-temperature transition, is found in all other vinylidene fluoride-based polymers and may help to understand the non-zero epsilon 2 ' values that are detected on the paraelectric phase of the terpolymer. The latter peak can also be observed during cooling of P(VDF-TrFE) copolymer samples at 100 degrees C and is due to conduction and space-charge polarization as a result of the accumulation of real charges at the electrode-sample interface. KW - Non-linear dielectric spectroscopy KW - P(VDF-TrFE-CFE) KW - Relaxor-ferroelectric polymer KW - Dielectric hysteresis KW - Curie-transition KW - Mid-temperature transition Y1 - 2021 U6 - https://doi.org/10.1007/s00339-021-04876-0 SN - 0947-8396 SN - 1432-0630 VL - 127 IS - 10 PB - Springer CY - Berlin ; Heidelberg ; New York ER - TY - JOUR A1 - Klett, Kolja A1 - Cherstvy, Andrey G. A1 - Shin, Jaeoh A1 - Sokolov, Igor M. A1 - Metzler, Ralf T1 - Non-Gaussian, transiently anomalous, and ergodic self-diffusion of flexible dumbbells in crowded two-dimensional environments BT - coupled translational and rotational motions JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We employ Langevin-dynamics simulations to unveil non-Brownian and non-Gaussian center-of-mass self-diffusion of massive flexible dumbbell-shaped particles in crowded two-dimensional solutions. We study the intradumbbell dynamics of the relative motion of the two constituent elastically coupled disks. Our main focus is on effects of the crowding fraction phi and of the particle structure on the diffusion characteristics. We evaluate the time-averaged mean-squared displacement (TAMSD), the displacement probability-density function (PDF), and the displacement autocorrelation function (ACF) of the dimers. For the TAMSD at highly crowded conditions of dumbbells, e.g., we observe a transition from the short-time ballistic behavior, via an intermediate subdiffusive regime, to long-time Brownian-like spreading dynamics. The crowded system of dimers exhibits two distinct diffusion regimes distinguished by the scaling exponent of the TAMSD, the dependence of the diffusivity on phi, and the features of the displacement-ACF. We attribute these regimes to a crowding-induced transition from viscous to viscoelastic diffusion upon growing phi. We also analyze the relative motion in the dimers, finding that larger phi suppress their vibrations and yield strongly non-Gaussian PDFs of rotational displacements. For the diffusion coefficients D(phi) of translational and rotational motion of the dumbbells an exponential decay with phi for weak and a power-law variation D(phi) proportional to (phi - phi(star))(2.4) for strong crowding is found. A comparison of simulation results with theoretical predictions for D(phi) is discussed and some relevant experimental systems are overviewed. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.064603 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Hannemann, Mandy A1 - Wegner, Gino A1 - Henkel, Carsten T1 - No-slip boundary conditions for electron hydrodynamics and the thermal Casimir pressure JF - Universe : open access journal N2 - We derive modified reflection coefficients for electromagnetic waves in the THz and far infrared range. The idea is based on hydrodynamic boundary conditions for metallic conduction electrons. The temperature-dependent part of the Casimir pressure between metal plates is evaluated. The results should shed light on the "thermal anomaly," where measurements deviate from the standard fluctuation electrodynamics for conducting metals. KW - dispersion force KW - metal optics KW - Drude model KW - hydrodynamic model KW - spatial KW - dispersion KW - viscosity KW - non-contact heat transfer Y1 - 2021 U6 - https://doi.org/10.3390/universe7040108 SN - 2218-1997 VL - 7 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Chigarev, Vladimir A1 - Kazakov, Alexey A1 - Pikovskij, Arkadij T1 - Mutual singularities of overlapping attractor and repeller JF - Chaos : an interdisciplinary journal of nonlinear science N2 - We apply the concepts of relative dimensions and mutual singularities to characterize the fractal properties of overlapping attractor and repeller in chaotic dynamical systems. We consider one analytically solvable example (a generalized baker's map); two other examples, the Anosov-Mobius and the Chirikov-Mobius maps, which possess fractal attractor and repeller on a two-dimensional torus, are explored numerically. We demonstrate that although for these maps the stable and unstable directions are not orthogonal to each other, the relative Renyi and Kullback-Leibler dimensions as well as the mutual singularity spectra for the attractor and repeller can be well approximated under orthogonality assumption of two fractals. Y1 - 2021 U6 - https://doi.org/10.1063/5.0056891 SN - 1054-1500 SN - 1089-7682 VL - 31 IS - 8 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Wendt, Martin A1 - Bouche, Nicolas F. A1 - Zabl, Johannes A1 - Schroetter, Ilane A1 - Muzahid, Sowgat T1 - MusE GAs FLOw and Wind V. The dust/metallicity-anisotropy of the circum-galactic medium JF - Monthly notices of the Royal Astronomical Society N2 - We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-Mg II absorber pairs (9-81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from [Zn/Fe] using ultraviolet and visual echelle spectrograph data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method that consists in solving for the depletion from multiple singly ionized ions (e.g. Mn II, Cr II, and Zn II) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and [Zn/Fe] with a Pearson's gamma = 0.70 +/- 0.14. The sightlines along the major axis show [Zn/Fe] < 0.5, whereas the [Zn/Fe] is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by approximate to 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations. KW - galaxies: evolution KW - galaxies: formation KW - intergalactic medium KW - quasars: KW - absorption lines Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab049 SN - 0035-8711 SN - 1365-2966 VL - 502 IS - 3 SP - 3733 EP - 3745 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Bataille-Gonzalez, Martin A1 - Clerc, Marcel G. A1 - Omel'chenko, Oleh T1 - Moving spiral wave chimeras JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We consider a two-dimensional array of heterogeneous nonlocally coupled phase oscillators on a flat torus and study the bound states of two counter-rotating spiral chimeras, shortly two-core spiral chimeras, observed in this system. In contrast to other known spiral chimeras with motionless incoherent cores, the two-core spiral chimeras typically show a drift motion. Due to this drift, their incoherent cores become spatially modulated and develop specific fingerprint patterns of varying synchrony levels. In the continuum limit of infinitely many oscillators, the two-core spiral chimeras can be studied using the Ott-Antonsen equation. Numerical analysis of this equation allows us to reveal the stability region of different spiral chimeras, which we group into three main classes-symmetric, asymmetric, and meandering spiral chimeras. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.L022203 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 2 PB - American Physical Society CY - College Park ER - TY - THES A1 - Brugger, Julia T1 - Modeling changes in climate during past mass extinctions T1 - Modellierung von Klimaveränderungen während vergangener Massenaussterben N2 - The evolution of life on Earth has been driven by disturbances of different types and magnitudes over the 4.6 million years of Earth’s history (Raup, 1994, Alroy, 2008). One example for such disturbances are mass extinctions which are characterized by an exceptional increase in the extinction rate affecting a great number of taxa in a short interval of geologic time (Sepkoski, 1986). During the 541 million years of the Phanerozoic, life on Earth suffered five exceptionally severe mass extinctions named the “Big Five Extinctions”. Many mass extinctions are linked to changes in climate (Feulner, 2009). Hence, the study of past mass extinctions is not only intriguing, but can also provide insights into the complex nature of the Earth system. This thesis aims at deepening our understanding of the triggers of mass extinctions and how they affected life. To accomplish this, I investigate changes in climate during two of the Big Five extinctions using a coupled climate model. During the Devonian (419.2–358.9 million years ago) the first vascular plants and vertebrates evolved on land while extinction events occurred in the ocean (Algeo et al., 1995). The causes of these formative changes, their interactions and their links to changes in climate are still poorly understood. Therefore, we explore the sensitivity of the Devonian climate to various boundary conditions using an intermediate-complexity climate model (Brugger et al., 2019). In contrast to Le Hir et al. (2011), we find only a minor biogeophysical effect of changes in vegetation cover due to unrealistically high soil albedo values used in the earlier study. In addition, our results cannot support the strong influence of orbital parameters on the Devonian climate, as simulated with a climate model with a strongly simplified ocean model (De Vleeschouwer et al., 2013, 2014, 2017). We can only reproduce the changes in Devonian climate suggested by proxy data by decreasing atmospheric CO2. Still, finding agreement between the evolution of sea surface temperatures reconstructed from proxy data (Joachimski et al., 2009) and our simulations remains challenging and suggests a lower δ18O ratio of Devonian seawater. Furthermore, our study of the sensitivity of the Devonian climate reveals a prevailing mode of climate variability on a timescale of decades to centuries. The quasi-periodic ocean temperature fluctuations are linked to a physical mechanism of changing sea-ice cover, ocean convection and overturning in high northern latitudes. In the second study of this thesis (Dahl et al., under review) a new reconstruction of atmospheric CO2 for the Devonian, which is based on CO2-sensitive carbon isotope fractionation in the earliest vascular plant fossils, suggests a much earlier drop of atmo- spheric CO2 concentration than previously reconstructed, followed by nearly constant CO2 concentrations during the Middle and Late Devonian. Our simulations for the Early Devonian with identical boundary conditions as in our Devonian sensitivity study (Brugger et al., 2019), but with a low atmospheric CO2 concentration of 500 ppm, show no direct conflict with available proxy and paleobotanical data and confirm that under the simulated climatic conditions carbon isotope fractionation represents a robust proxy for atmospheric CO2. To explain the earlier CO2 drop we suggest that early forms of vascular land plants have already strongly influenced weathering. This new perspective on the Devonian questions previous ideas about the climatic conditions and earlier explanations for the Devonian mass extinctions. The second mass extinction investigated in this thesis is the end-Cretaceous mass extinction (66 million years ago) which differs from the Devonian mass extinctions in terms of the processes involved and the timescale on which the extinctions occurred. In the two studies presented here (Brugger et al., 2017, 2021), we model the climatic effects of the Chicxulub impact, one of the proposed causes of the end-Cretaceous extinction, for the first millennium after the impact. The light-dimming effect of stratospheric sulfate aerosols causes severe cooling, with a decrease of global annual mean surface air temperature of at least 26◦C and a recovery to pre-impact temperatures after more than 30 years. The sudden surface cooling of the ocean induces deep convection which brings nutrients from the deep ocean via upwelling to the surface ocean. Using an ocean biogeochemistry model we explore the combined effect of ocean mixing and iron-rich dust originating from the impactor on the marine biosphere. As soon as light levels have recovered, we find a short, but prominent peak in marine net primary productivity. This newly discovered mechanism could result in toxic effects for marine near-surface ecosystems. Comparison of our model results to proxy data (Vellekoop et al., 2014, 2016, Hull et al., 2020) suggests that carbon release from the terrestrial biosphere is required in addition to the carbon dioxide which can be attributed to the target material. Surface ocean acidification caused by the addition of carbon dioxide and sulfur is only moderate. Taken together, the results indicate a significant contribution of the Chicxulub impact to the end-Cretaceous mass extinction by triggering multiple stressors for the Earth system. Although the sixth extinction we face today is characterized by human intervention in nature, this thesis shows that we can gain many insights into future extinctions from studying past mass extinctions, such as the importance of the rate of change (Rothman, 2017), the interplay of multiple stressors (Gunderson et al., 2016), and changes in the carbon cycle (Rothman, 2017, Tierney et al., 2020). N2 - In den 4,6 Milliarden Jahren Erdgeschichte wurde die Entwicklung des Lebens durch Störungen unterschiedlichster Art geprägt (Raup, 1994, Alroy, 2008). Ein Beispiel für solche Störungen sind Massenaussterben. Diese sind durch einen außergewöhnlichen Anstieg der Aussterberate einer großen Anzahl von Taxa in einem kurzen geologischen Zeitintervall gekennzeichnet (Sepkoski, 1986). Während der 541 Millionen Jahre des Phanerozoikums traten fünf außergewöhnlich schwere Massenaussterben auf. Viele Massenaussterben stehen mit Klimaveränderungen im Zusammenhang (Feulner, 2009). Die Untersuchung vergangener Massenaussterben ist daher nicht nur faszinierend, sondern gibt auch Einblicke in die komplexen Prozesse des Erdsystems. Diese Dissertation möchte unser Verständnis für die Auslöser von Massenaussterben sowie deren Auswirkungen auf das Leben erweitern. Dazu untersuche ich die Klimaveränderungen während zwei der fünf großen Aussterbeereignisse mit Hilfe eines gekoppelten Klimamodells. Während des Devons (vor 419,2-358,9 Millionen Jahren) entwickelten sich die ersten Gefäßpflanzen und Wirbeltiere an Land, während im Ozean Massenaussterben statt- fanden (Algeo et al., 1995). Die Ursachen dieser tiefgreifenden Veränderungen, ihre Wechselwirkungen und ihre Zusammenhänge mit Klimaveränderungen sind noch wenig verstanden. Daher untersuchen wir die Sensitivität des Klimas des Devons bezüglich verschiedener Randbedingungen mit einem Klimamodell mittlerer Komplexität (Brugger et al., 2019). Im Gegensatz zu Le Hir et al. (2011), die unrealistisch hohe Albedo Werte für den Boden verwenden, finden wir nur einen geringen biogeophysikalischen Einfluss von Änderungen der Vegetationsbedeckung. Außerdem können unsere Simulationen den starken Einfluss von Orbitalparametern, der mit einem Klimamodell mit stark vereinfachtem Ozeanmodell (De Vleeschouwer et al., 2013, 2014, 2017) simuliert wurde, nicht reproduzieren. Die in Proxydaten gefundenen klimatischen Veränderungen im Devon können wir nur durch eine Verringerung des atmosphärischen CO2 simulieren. Dennoch bleibt es eine Herausforderung, eine Übereinstimmung zwischen der aus Proxydaten (Joachimski et al., 2009) rekonstruierten Entwicklung der Meeresoberflächentemperatu- ren und unseren Simulationen zu finden. Dies deutet auf ein niedrigeres δ18O-Verhältnis des Meerwassers im Devon hin. Außerdem finden wir im Rahmen unserer Sensitivitäts- studien eine Klimavariabilität auf einer Zeitskala von Jahrzehnten bis Jahrhunderten. Die quasi-periodischen Schwankungen der Ozeantemperatur werden durch einen physikalischen Mechanismus aus sich verändernder Meereisbedeckung, Konvektion und Umwälzbewegung in den hohen nördlichen Breiten des Ozeans angetrieben. In der zweiten Studie dieser Dissertation (Dahl et al., under review) präsentieren wir eine neue Rekonstruktion des atmosphärischen CO2 für das Devon, die auf CO2-sensitiver Kohlenstoffisotopenfraktionierung in den frühesten Gefäßpflanzenfossilien basiert. Diese zeigt einen viel früheren Abfall der atmosphärischen CO2-Konzentration als bisherige Rekonstruktionen, gefolgt von nahezu konstanten CO2-Konzentrationen während des Mittel- und Spätdevon. Unsere Simulationen für das frühe Devon mit identischen Rand- bedingungen wie in unserer Sensitivitätsstudie (Brugger et al., 2019), jedoch mit einer niedrigen atmosphärischen CO2-Konzentration von 500ppm, zeigen keinen direkten Konflikt mit verfügbaren Proxy- und paläobotanischen Daten. Zusätzlich bestätigen die Simulationen, dass unter den simulierten klimatischen Bedingungen die Kohlenstoff- Isotopenfraktionierung einen robusten Proxy für atmosphärisches CO2 darstellt. Um den früheren CO2-Abfall zu erklären, schlagen wir vor, dass frühe Formen von vaskulären Landpflanzen die Verwitterung bereits stark beeinflusst haben. Diese neue Sichtweise auf das Devon stellt bisherige Vorstellungen über die klimatischen Bedingungen und frühere Erklärungen für die devonischen Massenaussterben in Frage. Das zweite in dieser Arbeit untersuchte Massenaussterben ist das Massenaussterben der späten Kreidezeit (vor 66 Millionen Jahren), das sich von denen im Devon in Bezug auf die beteiligten Prozesse und die Zeitskala der Aussterben unterscheidet. Eine der diskutierten Ursachen dieses Massenaussterbens ist der Chicxulub-Meteoriten-Einschlag. In den beiden hier vorgestellten Studien (Brugger et al., 2017, 2021) modellieren wir die klimatischen Auswirkungen des Chicxulub Einschlags für das erste Jahrtausend nach dem Einschlag. Die durch die stratosphärischen Sulfataerosole verringerte Son- neneinstrahlung verursacht eine starke Abkühlung: die global und jährlich gemittelte Oberflächenlufttemperatur nimmt um mindestens 26◦C ab und erholt sich erst nach mehr als 30 Jahren. Die plötzliche Abkühlung der Ozeanoberfläche löst bis in große Tiefen reichende Konvektion aus, die zum Nährstofftransport aus dem tiefen Ozean an die Ozea- noberfläche führt. Mit Hilfe eines biogeochemischen Modells des Ozeans untersuchen wir die kombinierte Wirkung dieser Durchmischung des Ozeans und eisenreichen Staubs aus dem Meteoriten auf die marine Biosphäre. Sobald wieder genügend Sonneneinstrahlung auf die Erdoberfläche trifft, erreicht die marine Nettoprimärproduktion ein kurzes, aber markantes Maximum. Dieser neu entdeckte Mechanismus könnte toxische Folgen für oberflächennahe Ökosysteme des Ozeans haben. Der Vergleich unserer Modellergebnisse mit Proxydaten (Vellekoop et al., 2014, 2016, Hull et al., 2020) deutet darauf hin, dass zusätzlich zum CO2 aus dem Gestein des Einschlagortes Kohlenstoff aus der terrest- rischen Biosphäre freigesetzt wird. Die Versauerung des Oberflächenozeans durch die Zugabe von CO2 und Schwefel ist nur moderat. Insgesamt deuten die Ergebnisse darauf hin, dass der Chicxulub Einschlag einen wesentlichen Beitrag zum Massenaussterben der späten Kreidezeit leistete, indem er das Erdsystem multiplen Stressoren aussetzte. Auch wenn das heutige sechste Aussterben durch menschliche Eingriffe in die Natur geprägt ist, zeigt diese Dissertation, dass wir aus dem Studium vergangener Massenaussterben viele Erkenntnisse über zukünftige Massenaussterben gewinnen können, wie z. B. die Bedeutung der Änderungsrate (Rothman, 2017), ein besseres Verständnis des Zusammenspiels multipler Stressoren (Gunderson et al., 2016) und die Rolle von Veränderungen im Kohlenstoffkreislauf (Rothman, 2017, Tierney et al., 2020). KW - earth system modeling KW - mass extinctions KW - paleoclimatology KW - climate change KW - Erdsystem Modellierung KW - Klimawandel KW - Massenaussterben KW - Paleoklimatologie Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-532468 ER - TY - THES A1 - Reppert, Alexander von T1 - Magnetic strain contributions in laser-excited metals studied by time-resolved X-ray diffraction T1 - Untersuchung magnetischer Beiträge zur Ausdehnung laserangeregter Metalle mittels zeitaufgelöster Röntgenbeugungsexperimente N2 - In this work I explore the impact of magnetic order on the laser-induced ultrafast strain response of metals. Few experiments with femto- or picosecond time-resolution have so far investigated magnetic stresses. This is contrasted by the industrial usage of magnetic invar materials or magnetostrictive transducers for ultrasound generation, which already utilize magnetostrictive stresses in the low frequency regime. In the reported experiments I investigate how the energy deposition by the absorption of femtosecond laser pulses in thin metal films leads to an ultrafast stress generation. I utilize that this stress drives an expansion that emits nanoscopic strain pulses, so called hypersound, into adjacent layers. Both the expansion and the strain pulses change the average inter-atomic distance in the sample, which can be tracked with sub-picosecond time resolution using an X-ray diffraction setup at a laser-driven Plasma X-ray source. Ultrafast X-ray diffraction can also be applied to buried layers within heterostructures that cannot be accessed by optical methods, which exhibit a limited penetration into metals. The reconstruction of the initial energy transfer processes from the shape of the strain pulse in buried detection layers represents a contribution of this work to the field of picosecond ultrasonics. A central point for the analysis of the experiments is the direct link between the deposited energy density in the nano-structures and the resulting stress on the crystal lattice. The underlying thermodynamical concept of a Grüneisen parameter provides the theoretical framework for my work. I demonstrate how the Grüneisen principle can be used for the interpretation of the strain response on ultrafast timescales in various materials and that it can be extended to describe magnetic stresses. The class of heavy rare-earth elements exhibits especially large magnetostriction effects, which can even lead to an unconventional contraction of the laser-excited transducer material. Such a dominant contribution of the magnetic stress to the motion of atoms has not been demonstrated previously. The observed rise time of the magnetic stress contribution in Dysprosium is identical to the decrease in the helical spin-order, that has been found previously using time-resolved resonant X-ray diffraction. This indicates that the strength of the magnetic stress can be used as a proxy of the underlying magnetic order. Such magnetostriction measurements are applicable even in case of antiparallel or non-collinear alignment of the magnetic moments and a vanishing magnetization. The strain response of metal films is usually determined by the pressure of electrons and lattice vibrations. I have developed a versatile two-pulse excitation routine that can be used to extract the magnetic contribution to the strain response even if systematic measurements above and below the magnetic ordering temperature are not feasible. A first laser pulse leads to a partial ultrafast demagnetization so that the amplitude and shape of the strain response triggered by the second pulse depends on the remaining magnetic order. With this method I could identify a strongly anisotropic magnetic stress contribution in the magnetic data storage material iron-platinum and identify the recovery of the magnetic order by the variation of the pulse-to-pulse delay. The stark contrast of the expansion of iron-platinum nanograins and thin films shows that the different constraints for the in-plane expansion have a strong influence on the out-of-plane expansion, due to the Poisson effect. I show how such transverse strain contributions need to be accounted for when interpreting the ultrafast out-of-plane strain response using thermal expansion coefficients obtained in near equilibrium conditions. This work contributes an investigation of magnetostriction on ultrafast timescales to the literature of magnetic effects in materials. It develops a method to extract spatial and temporal varying stress contributions based on a model for the amplitude and shape of the emitted strain pulses. Energy transfer processes result in a change of the stress profile with respect to the initial absorption of the laser pulses. One interesting example occurs in nanoscopic gold-nickel heterostructures, where excited electrons rapidly transport energy into a distant nickel layer, that takes up much more energy and expands faster and stronger than the laser-excited gold capping layer. Magnetic excitations in rare earth materials represent a large energy reservoir that delays the energy transfer into adjacent layers. Such magneto-caloric effects are known in thermodynamics but not extensively covered on ultrafast timescales. The combination of ultrafast X-ray diffraction and time-resolved techniques with direct access to the magnetization has a large potential to uncover and quantify such energy transfer processes. N2 - In dieser Arbeit untersuche ich den Einfluss magnetischer Ordnung auf die laser-induzierte, ultraschnelle Ausdehnung von Metallen. In Experimenten mit Femto- oder Pikosekunden Zeitauflösung sind magnetische Drücke bisher kaum erforscht. Dies steht im Kontrast zur industriellen Verwendung von magnetischen Invar Materialien oder magnetostriktiven Ultraschallgebern, in denen magnetische Drücke bereits in niedrigeren Frequenzbereichen Anwendung finden. In meinen Experimenten untersuche ich, wie der Energieeintrag durch die Absorption von Femtosekunden-Laserpulsen in dünnen Metallschichten zu einem ultraschnellen Druckanstieg führt. Dabei nutze ich, dass der Druckanstieg zu einer Ausdehnung führt, welche Deformationswellen auf der Nanometerskala, sogenannte Hyperschallpulse, in angrenzende Schichten aussendet. Sowohl die Ausdehnung als auch die Deformationspulse ändern den mittleren Abstand zwischen den Atomen in der Probe, welcher mittels Röntgenbeugung an einer Laser-getriebenen Plasma-Röntgenquelle mit einer Subpikosekunden-Zeitauflösung detektiert wird. Das Verfahren der ultraschnellen Röntgenbeugung gelingt auch in Heterostrukturen mit vergrabenen Detektionsschichten, zu denen optische Methoden aufgrund ihrer limitierter Eindringtiefe in Metallen keinen Zugang haben. Ein Beitrag dieser Arbeit zum Feld der Pikosekunden-Akustik ist es, aus der Ausdehnung einer solchen Detektionsschicht Rückschlüsse auf die initialen Energietransferprozesse zu ziehen. Der direkte Zusammenhang zwischen der eingebrachten Energiedichte in die Nanostrukturen und dem resultierenden Druck auf das Atomgitter ist ein zentraler Punkt in meiner Analyse der Experimente. Das zu Grunde liegende thermodynamische Konzept des Grüneisen-Parameters bildet den theoretischen Kontext meiner Publikationen. Anhand verschiedener Materialien demonstriere ich, wie dieses Prinzip auch zur Analyse der Ausdehnung auf ultraschnellen Zeitskalen verwendet werden kann und sich auch auf magnetische Drücke übertragen lässt. Insbesondere in der Materialklasse der schweren, seltenen Erdelemente sind Magnetostriktionseffekte sehr groß und führen dort sogar zu einem ungewöhnlichen Zusammenziehen des Materials nach der Laseranregung. Solch ein bestimmender Einfluss des magnetischen Drucks auf die Atombewegung ist bisher nicht gezeigt worden. Die Zeitskala des magnetischen Druckanstiegs entspricht dabei der beobachteten Abnahme der helikalen Spin-Ordnung, welche zuvor mittels zeitaufgelöster, resonanter Röntgenbeugung ermittelt wurde. Dies zeigt, dass die Stärke des magnetischen Drucks als Maß für magnetische Ordnung dienen kann, insbesondere auch im Fall von antiparalleler oder nicht-kollinearer Ordnung der magnetischen Momente in Proben mit verschwindender Magnetisierung. In Metallfilmen ist die Dehnung des Atomgitters in der Regel durch Druck von Elektronen und Gitterschwingungen geprägt. Um den magnetischen Druckbeitrag auch in solchen Fällen zu extrahieren, in denen systematische Experimente oberhalb und unterhalb der magnetischen Ordnungstemperatur nicht praktikabel sind, habe ich ein neuartiges Doppelpuls-Anregungsverfahren entwickelt, welches allgemein für die Untersuchung von Phasenübergängen nützlich ist. Der Energieeintrag durch den ersten Laserpuls führt dabei zu einer partiellen, ultraschnellen Demagnetisierung, sodass die Amplitude und Form der Gitterausdehnung nach dem zweiten Puls von der Stärke des verbliebenen magnetischen Drucks und somit von der verbliebenen magnetischen Ordnung abhängt. Mit dieser Methode ist es möglich geworden, einen stark richtungsabhängigen, magnetischen Druckbeitrag im Speichermedium Eisen-Platin zu identifizieren und mittels Variation des Puls-zu-Puls Abstands auch die Rückkehr der magnetischen Ordnung zu zeigen. Die unterschiedliche Ausdehnung von Eisen-Platin Nanopartikeln und dünnen Filmen zeigt dabei, dass die verschiedenen Zwangsbedingungen für die Ausdehnung entlang der Probenoberfläche aufgrund des Poisson-Effekts einen entscheidenden Einfluss auf die ultraschnelle Ausdehnung senkrecht zur Probenoberfläche hat. Ich analysiere, wie die zugrunde liegende Querkontraktion bei der Interpretation der ultraschnellen Ausdehnung auf der Basis von thermischen Ausdehnungskoeffizienten im Quasi-Gleichgewicht berücksichtigt werden kann. Meine Arbeit erweitert die Literatur um einen Beitrag zur ultraschnellen Magnetostriktion und entwickelt eine Methodik mittels derer räumlich und zeitlich variierende Druckbeiträge anhand einer Modellierung der Form der Deformationswellen extrahiert werden können. Energietransferprozesse spiegeln sich dabei durch eine Änderung des Druckprofils gegenüber dem Absorptionsprofil der Laserpulse wider. KW - lattice dynamics KW - magnetism KW - ultrafast KW - X-ray diffraction KW - Gitterdynamik KW - Magnetismus KW - ultraschnell KW - Röntgenbeugung Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-535582 ER - TY - JOUR A1 - Scali, Stefano A1 - Anders, Janet A1 - Correa, Luis A. T1 - Local master equations bypass the secular approximation JF - Quantum : the open journal for quantum science N2 - Master equations are a vital tool to model heat flow through nanoscale thermodynamic systems. Most practical devices are made up of interacting subsystems and are often modelled using either local master equations (LMEs) or global master equations (GMEs). While the limiting cases in which either the LME or the GME breaks down are well understood, there exists a 'grey area' in which both equations capture steady-state heat currents reliably but predict very different transient heat flows. In such cases, which one should we trust? Here we show that, when it comes to dynamics, the local approach can be more reliable than the global one for weakly interacting open quantum systems. This is due to the fact that the secular approximation, which underpins the GME, can destroy key dynamical features. To illustrate this, we consider a minimal transport setup and show that its LME displays exceptional points (EPs). These singularities have been observed in a superconducting-circuit realisation of the model [1]. However, in stark contrast to experimental evidence, no EPs appear within the global approach. We then show that the EPs are a feature built into the Redfield equation, which is more accurate than the LME and the GME. Finally, we show that the local approach emerges as the weak-interaction limit of the Redfield equation, and that it entirely avoids the secular approximation. Y1 - 2021 U6 - https://doi.org/10.22331/q-2021-05-01-451 SN - 2521-327X VL - 5 PB - Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften CY - Wien ER - TY - JOUR A1 - Thapa, Samudrajit A1 - Wyłomańska, Agnieszka A1 - Sikora, Grzegorz A1 - Wagner, Caroline E. A1 - Krapf, Diego A1 - Kantz, Holger A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Leveraging large-deviation statistics to decipher the stochastic properties of measured trajectories JF - New Journal of Physics N2 - Extensive time-series encoding the position of particles such as viruses, vesicles, or individualproteins are routinely garnered insingle-particle tracking experiments or supercomputing studies.They contain vital clues on how viruses spread or drugs may be delivered in biological cells.Similar time-series are being recorded of stock values in financial markets and of climate data.Such time-series are most typically evaluated in terms of time-averaged mean-squareddisplacements (TAMSDs), which remain random variables for finite measurement times. Theirstatistical properties are different for differentphysical stochastic processes, thus allowing us toextract valuable information on the stochastic process itself. To exploit the full potential of thestatistical information encoded in measured time-series we here propose an easy-to-implementand computationally inexpensive new methodology, based on deviations of the TAMSD from itsensemble average counterpart. Specifically, we use the upper bound of these deviations forBrownian motion (BM) to check the applicability of this approach to simulated and real data sets.By comparing the probability of deviations fordifferent data sets, we demonstrate how thetheoretical bound for BM reveals additional information about observed stochastic processes. Weapply the large-deviation method to data sets of tracer beads tracked in aqueous solution, tracerbeads measured in mucin hydrogels, and of geographic surface temperature anomalies. Ouranalysis shows how the large-deviation properties can be efficiently used as a simple yet effectiveroutine test to reject the BM hypothesis and unveil relevant information on statistical propertiessuch as ergodicity breaking and short-time correlations. KW - diffusion KW - anomalous diffusion KW - large-deviation statistic KW - time-averaged mean squared displacement KW - Chebyshev inequality Y1 - 2020 U6 - https://doi.org/10.1088/1367-2630/abd50e SN - 1367-2630 VL - 23 PB - Dt. Physikalische Ges. ; IOP CY - Bad Honnef ; London ER - TY - GEN A1 - Thapa, Samudrajit A1 - Wyłomańska, Agnieszka A1 - Sikora, Grzegorz A1 - Wagner, Caroline E. A1 - Krapf, Diego A1 - Kantz, Holger A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Leveraging large-deviation statistics to decipher the stochastic properties of measured trajectories T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Extensive time-series encoding the position of particles such as viruses, vesicles, or individualproteins are routinely garnered insingle-particle tracking experiments or supercomputing studies.They contain vital clues on how viruses spread or drugs may be delivered in biological cells.Similar time-series are being recorded of stock values in financial markets and of climate data.Such time-series are most typically evaluated in terms of time-averaged mean-squareddisplacements (TAMSDs), which remain random variables for finite measurement times. Theirstatistical properties are different for differentphysical stochastic processes, thus allowing us toextract valuable information on the stochastic process itself. To exploit the full potential of thestatistical information encoded in measured time-series we here propose an easy-to-implementand computationally inexpensive new methodology, based on deviations of the TAMSD from itsensemble average counterpart. Specifically, we use the upper bound of these deviations forBrownian motion (BM) to check the applicability of this approach to simulated and real data sets.By comparing the probability of deviations fordifferent data sets, we demonstrate how thetheoretical bound for BM reveals additional information about observed stochastic processes. Weapply the large-deviation method to data sets of tracer beads tracked in aqueous solution, tracerbeads measured in mucin hydrogels, and of geographic surface temperature anomalies. Ouranalysis shows how the large-deviation properties can be efficiently used as a simple yet effectiveroutine test to reject the BM hypothesis and unveil relevant information on statistical propertiessuch as ergodicity breaking and short-time correlations. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1118 KW - diffusion KW - anomalous diffusion KW - large-deviation statistic KW - time-averaged mean squared displacement KW - Chebyshev inequality Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-493494 SN - 1866-8372 IS - 1118 ER - TY - THES A1 - Petsiuk, Andrei T1 - Investigation of charge carrier transport in metal halide perovskites by THz Spectroscopy T1 - Untersuchung des Ladungstransportes in den Metal Halogenid Perowskiten durch THz Spektroskopie N2 - Halide perovskites are a class of novel photovoltaic materials that have recently attracted much attention in the photovoltaics research community due to their highly promising optoelectronic properties, including large absorption coefficients and long carrier lifetimes. The charge carrier mobility of halide perovskites is investigated in this thesis by THz spectroscopy, which is a contact-free technique that yields the intra-grain sum mobility of electrons and holes in a thin film. The polycrystalline halide perovskite thin films, provided from Potsdam University, show moderate mobilities in the range from 21.5 to 33.5 cm2V-1s-1. It is shown in this work that the room temperature mobility is limited by charge carrier scattering at polar optical phonons. The mobility at low temperature is likely to be limited by scattering at charged and neutral impurities at impurity concentration N=1017-1018 cm-3. Furthermore, it is shown that exciton formation may decrease the mobility at low temperatures. Scattering at acoustic phonons can be neglected at both low and room temperatures. The analysis of mobility spectra over a broad range of temperatures for perovskites with various cation compounds shows that cations have a minor impact on charge carrier mobility. The low-dimensional thin films of quasi-2D perovskite with different numbers of [PbI6]4−sheets (n=2-4) alternating with long organic spacer molecules were provided by S. Zhang from Potsdam University. They exhibit mobilities in the range from 3.7 to 8 cm2V-1s-1. A clear decrease of mobility is observed with decrease in number of metal-halide sheets n, which likely arises from charge carrier confinement within metal-halide layers. Modelling the measured THz mobility with the modified Drude-Smith model yields localization length from 0.9 to 3.7 nm, which agrees well on the thicknesses of the metal-halide layers. Additionally, the mobilities are found to be dependent on the orientation of the layers. The charge carrier dynamics is also dependent on the number of metal-halide sheets n. For the thin films with n =3-4 the dynamics is similar to the 3D MHPs. However, the thin film with n = 2 shows clearly different dynamics, where the signs of exciton formation are observed within 390 fs timeframe after photoexcitation. Also, the charge carrier dynamics of CsPbI3 perovskite nanocrystals was investigated, in particular the effect of post treatments on the charge carrier transport. N2 - Metall-Halogenid Perowskite sind eine Klasse von photovoltaischen Materialien, welche in letzter Zeit sehr viel Aufmerksamkeit von Forschern bekommen haben. Der Grund dafür liegt in ihren vielversprechenden optoelektronischen Eigenschaften, wie beispielsweise hohe Absorptionskoeffizienten, lange Lebenszeiten der Ladungsträger und moderate Beweglichkeiten. Die Beweglichkeit der Ladungsträger und deren Kinetik wurde in dieser Dissertation mit Hilfe von Teraherzspektroskopie in verschiedenen Metall-Halogenide Perowskiten untersucht. Die polykristallinen Halogenide Perowskit-Dünnschichten, bereitgestellt von Dr. M. Stolterfoht von der Universität Potsdam, haben bei Raumtemperatur moderate Ladungsträgerbeweglichkeiten in einem Bereich von 21.5 bis 33.5 cm²V-1s-1. Die Analyse dieser Beweglichkeiten in Abhängigkeit der Temperatur zeigt, dass die Beweglichkeit bei Raumtemperatur durch die Interaktion mit polaren optischen Phononen limitiert wird. Bei niedrigeren Temperaturen sind die Beweglichkeiten durch Streuung an geladenen und neutralen Störstellen limitiert, wobei die Störstellenkonzentration bei ca. N =1017-1018 cm-3 liegt. Weiterhin wird es gezeigt, dass die Reduktion der Anzahl beweglicher Ladungsträger durch Exzitonenbildung ebenfalls bei niedrigen Temperaturen berücksichtigt werden muss. Streuung an akustischen Phononen kann sowohl bei Raum- als auch bei niedrigen Temperaturen vernachlässigt werden. Die Analyse der Beweglichkeitsspektren von Perowskiten mit unterschiedlichen Kationen und bei verschiedenen Temperaturspannen zeigt, dass diese Kationen einen sehr geringen Einfluss auf die Ladungsträgerbeweglichkeit haben. Niederdimensionale Perowskit-Dünnschichten aus alternierenden quasi-2D [PbI6]4− Schichten n (n=3-4) und organischen Trennschichten wurde von S. Zhang von der Universität Potsdam bereitgestellt. Diese zeigen Beweglichkeiten zwischen 3.7 und 8 cm²V-1s-1. Der signifikante Rückgang der beobachteten Beweglichkeit lässt sich auf die Anzahl der Metall-Halogeniden Schichten n zurückführen, in welcher die Ladungsträger räumlich eingeschränkt sind. Die Lokalisationslänge reicht von 0.9 bis 3.7 nm und ist vergleichbar mit der Dicke der einzelnen quasi-2D-Schichten. Ebenfalls ist die Beweglichkeit abhängig von der Schichtenorientierung. Zusätzlich ist die Ladungsträgerdynamik abhängig von der Anzahl der Metall-Halogeniden [PbI6]4−Schichten n. Dicke quasi-2D-Schichten (n = 3-4) zeigen ähnliche Dynamik wie drei dimensionale Perowskite, wogegen die dünnen quasi-2D-Schichten (n = 2) schnelle Exzitonbildung innerhalb 390 fs nach der Ladungsträgeranregung zeigen. Des weiteren wurde die Ladungsträgerdynamik von CsPbI3 Perovskite-Nanokristallen untersucht, insbesondere die Auswirkung von Ligandenaustausch und Temperierung auf die Ladungsträgerbeweglichkeit. KW - Photovoltaics KW - THz Spectroscopy KW - Metal Halide Perovskites KW - Metal Halogenid Perowskiten KW - Photovoltaik KW - THz Spektroskopie Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-515441 ER - TY - JOUR A1 - Cherstvy, Andrey G. A1 - Wang, Wei A1 - Metzler, Ralf A1 - Sokolov, Igor M. T1 - Inertia triggers nonergodicity of fractional Brownian motion JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - How related are the ergodic properties of the over- and underdamped Langevin equations driven by fractional Gaussian noise? We here find that for massive particles performing fractional Brownian motion (FBM) inertial effects not only destroy the stylized fact of the equivalence of the ensemble-averaged mean-squared displacement (MSD) to the time-averaged MSD (TAMSD) of overdamped or massless FBM, but also dramatically alter the values of the ergodicity-breaking parameter (EB). Our theoretical results for the behavior of EB for underdamped or massive FBM for varying particle mass m, Hurst exponent H, and trace length T are in excellent agreement with the findings of stochastic computer simulations. The current results can be of interest for the experimental community employing various single-particle-tracking techniques and aiming at assessing the degree of nonergodicity for the recorded time series (studying, e.g., the behavior of EB versus lag time). To infer FBM as a realizable model of anomalous diffusion for a set single-particle-tracking data when massive particles are being tracked, the EBs from the data should be compared to EBs of massive (rather than massless) FBM. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.024115 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Köhler, Raphael H. A1 - Handorf, Dörthe A1 - Jaiser, Ralf A1 - Dethloff, Klaus A1 - Zängl, Günther A1 - Majewski, Detlev A1 - Rex, Markus T1 - Improved circulation in the Northern hemisphere by adjusting gravity wave drag parameterizations in seasonal experiments with ICON-NWP JF - Earth and Space Science : ESS N2 - The stratosphere is one of the main potential sources for subseasonal to seasonal predictability in midlatitudes in winter. The ability of an atmospheric model to realistically simulate the stratospheric dynamics is essential in order to move forward in the field of seasonal predictions in midlatitudes. Earlier studies with the ICOsahedral Nonhydrostatic atmospheric model (ICON) point out that stratospheric westerlies in ICON are underestimated. This is the first extensive study on the evaluation of Northern Hemisphere stratospheric winter circulation with ICON in numerical weather prediction (NWP) mode. Seasonal experiments with the default setup are able to reproduce the basic climatology of the stratospheric polar vortex. However, westerlies are too weak and major stratospheric warmings too frequent in ICON. Both a reduction of the nonorographic, and a reduction of the orographic gravity wave and wake drag lead to a strengthening of the stratospheric vortex and a bias reduction, in particular in January. However, the effect of the nonorographic gravity wave drag scheme on the stratosphere is stronger. Stratosphere-troposphere coupling is intensified and more realistic due to a reduced gravity wave drag. Furthermore, an adjustment of the subgrid-scale orographic drag parameterization leads to a significant error reduction in the mean sea level pressure. As a result of these findings, we present our current suggested improved setup for seasonal experiments with ICON-NWP.
Plain Language Summary Although seasonal forecasts for midlatitudes have the potential to be highly beneficial to the public sector, they are still characterized by a large amount of uncertainty. Exact simulations of the circulation in the stratosphere can help to improve tropospheric predictability on seasonal time scales. For this reason, we investigate how well the new German atmospheric model is able to simulate the stratospheric circulation. The model reproduces the basic behavior of the Northern Hemisphere stratospheric polar vortex, but the westerly circulation in winter is underestimated. The stratospheric circulation is influenced by gravity waves that exert drag on the flow. These processes are only partly physically represented in the model, but are very important and are hence parameterized. By adjusting the parameterizations for the gravity wave drag, the stratospheric polar vortex is strengthened, thereby yielding a more realistic stratospheric circulation. In addition, the altered parameterizations improve the simulated surface pressure pattern. Based upon this, we present our current suggested improved model setup for seasonal experiments. Y1 - 2021 U6 - https://doi.org/10.1029/2021EA001676 SN - 2333-5084 VL - 8 IS - 3 PB - American Geophysical Union CY - Malden, Mass. ER - TY - JOUR A1 - Büchner, Robby A1 - Fondell, Mattis A1 - Mascarenhas, Eric Johnn A1 - Pietzsch, Annette A1 - Vaz da Cruz, Vinícius A1 - Föhlisch, Alexander T1 - How hydrogen bonding amplifies isomeric differences in pyridones toward strong changes in acidity and tautomerism JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - Steric hindrance of hydration and hydrogen bond enhancement by localized charges have been identified as key factors for the massive chemical differences between the hydroxypyridine/pyridone isomers in aqueous solution. While all isomers occur mainly in the hydroxypyridine form in the gas phase, they differ by more than 3 orders of magnitude both in their acidity and tautomeric equilibrium constants upon hydration. By monitoring the electronic and solvation structures as a function of the protonation state and the O- substitution position on the pyridine ring, the amplification of the isomeric differences in aqueous solution has been investigated. Near-edge X-ray absorption fine structure (NEXAFS) measurements at the N K-edge served as the probe of the chemical state. The combination of molecular dynamics simulations, complete active space self-consistent field (CASSCF), and time-dependent density functional theory (TD-DFT) spectral calculations contributes to unraveling the principles of tautomerism and acidity in multiple biochemical systems based on tautomerism. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpcb.0c10873 SN - 1520-6106 SN - 1520-5207 VL - 125 IS - 9 SP - 2372 EP - 2379 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Henkel, Carsten T1 - Heat transfer and entanglement BT - non-equilibrium correlation spectra of two quantum oscillators JF - Annalen der Physik N2 - The non-equilibrium state of two oscillators with a mutual interaction and coupled to separate heat baths is discussed. Bosonic baths are considered, and an exact spectral representation for the elements of the covariance matrix is provided analytically. A wide class of spectral densities for the relevant bath modes is allowed for. The validity of the fluctuation-dissipation relation is established for global equilibrium (both baths at the same temperature) in the stationary state. Spectral measures of entanglement are suggested by comparing to the equilibrium spectrum of zero-point fluctuations. No rotating-wave approximation is applied, and anomalous heat transport from cold to hot bath, as reported in earlier work, is demonstrated not to occur. KW - entanglement KW - heat transfer KW - non-equilibrium steady state KW - master KW - equation KW - quantum thermodynamics Y1 - 2021 U6 - https://doi.org/10.1002/andp.202100089 SN - 0003-3804 SN - 1521-3889 VL - 533 IS - 10 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Rubio, Jesús A1 - Anders, Janet A1 - Correa, Luis A. T1 - Global quantum thermometry JF - Physical review letters / publ. by the American Physical Society N2 - A paradigm shift in quantum thermometry is proposed. To date, thermometry has relied on local estimation, which is useful to reduce statistical fluctuations once the temperature is very well known. In order to estimate temperatures in cases where few measurement data or no substantial prior knowledge are available, we build instead a method for global quantum thermometry. Based on scaling arguments, a mean logarithmic error is shown here to be the correct figure of merit for thermometry. Its full minimization provides an operational and optimal rule to postprocess measurements into a temperature reading, and it establishes a global precision limit. We apply these results to the simulated outcomes of measurements on a spin gas, finding that the local approach can lead to biased temperature estimates in cases where the global estimator converges to the true temperature. The global framework thus enables a reliable approach to data analysis in thermometry experiments. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevLett.127.190402 SN - 0031-9007 SN - 1079-7114 VL - 127 IS - 19 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Zuo, Guangzheng A1 - Shoaee, Safa A1 - Kemerink, Martijn A1 - Neher, Dieter T1 - General rules for the impact of energetic disorder and mobility on nongeminate recombination in phase-separated organic solar cells JF - Physical review applied N2 - State-of-the-art organic solar cells exhibit power conversion efficiencies of 18% and above. These devices benefit from the suppression of free charge recombination with regard to the Langevin limit of charge encounter in a homogeneous medium. It is recognized that the main cause of suppressed free charge recombination is the reformation and resplitting of charge-transfer (CT) states at the interface between donor and acceptor domains. Here, we use kinetic Monte Carlo simulations to understand the interplay between free charge motion and recombination in an energetically disordered phase-separated donor-acceptor blend. We identify conditions for encounter-dominated and resplitting-dominated recombination. In the former regime, recombination is proportional to mobility for all parameters tested and only slightly reduced with respect to the Langevin limit. In contrast, mobility is not the decisive parameter that determines the nongeminate recombination coefficient, k(2), in the latter case, where k2 is a sole function of the morphology, CT and charge-separated (CS) energetics, and CT-state decay properties. Our simulations also show that free charge encounter in the phase-separated disordered blend is determined by the average mobility of all carriers, while CT reformation and resplitting involves mostly states near the transport energy. Therefore, charge encounter is more affected by increased disorder than the resplitting of the CT state. As a consequence, for a given mobility, larger energetic disorder, in combination with a higher hopping rate, is preferred. These findings have implications for the understanding of suppressed recombination in solar cells with nonfullerene acceptors, which are known to exhibit lower energetic disorder than that of fullerenes. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevApplied.16.034027 SN - 2331-7019 VL - 16 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Guggenberger, Tobias A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Fractional Brownian motion in superharmonic potentials and non-Boltzmann stationary distributions JF - Journal of physics : A, Mathematical and theoretical N2 - We study the stochastic motion of particles driven by long-range correlated fractional Gaussian noise (FGN) in a superharmonic external potential of the form U(x) proportional to x(2n) (n is an element of N). When the noise is considered to be external, the resulting overdamped motion is described by the non-Markovian Langevin equation for fractional Brownian motion. For this case we show the existence of long time, stationary probability density functions (PDFs) the shape of which strongly deviates from the naively expected Boltzmann PDF in the confining potential U(x). We analyse in detail the temporal approach to stationarity as well as the shape of the non-Boltzmann stationary PDF. A typical characteristic is that subdiffusive, antipersistent (with negative autocorrelation) motion tends to effect an accumulation of probability close to the origin as compared to the corresponding Boltzmann distribution while the opposite trend occurs for superdiffusive (persistent) motion. For this latter case this leads to distinct bimodal shapes of the PDF. This property is compared to a similar phenomenon observed for Markovian Levy flights in superharmonic potentials. We also demonstrate that the motion encoded in the fractional Langevin equation driven by FGN always relaxes to the Boltzmann distribution, as in this case the fluctuation-dissipation theorem is fulfilled. KW - anomalous diffusion KW - Boltzmann distribution KW - non-Gaussian distribution Y1 - 2021 U6 - https://doi.org/10.1088/1751-8121/ac019b SN - 1751-8113 SN - 1751-8121 VL - 54 IS - 29 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Mutothya, Nicholas Mwilu A1 - Xu, Yong A1 - Li, Yongge A1 - Metzler, Ralf A1 - Mutua, Nicholas Muthama T1 - First passage dynamics of stochastic motion in heterogeneous media driven by correlated white Gaussian and coloured non-Gaussian noises JF - Journal of physics. Complexity N2 - We study the first passage dynamics for a diffusing particle experiencing a spatially varying diffusion coefficient while driven by correlated additive Gaussian white noise and multiplicative coloured non-Gaussian noise. We consider three functional forms for position dependence of the diffusion coefficient: power-law, exponential, and logarithmic. The coloured non-Gaussian noise is distributed according to Tsallis' q-distribution. Tracks of the non-Markovian systems are numerically simulated by using the fourth-order Runge-Kutta algorithm and the first passage times (FPTs) are recorded. The FPT density is determined along with the mean FPT (MFPT). Effects of the noise intensity and self-correlation of the multiplicative noise, the intensity of the additive noise, the cross-correlation strength, and the non-extensivity parameter on the MFPT are discussed. KW - first passage KW - diffusion KW - non-Gaussian KW - correlated noise Y1 - 2021 U6 - https://doi.org/10.1088/2632-072X/ac35b5 SN - 2632-072X VL - 2 PB - IOP Publishing CY - Bristol ER - TY - JOUR A1 - Diercke, Andrea A1 - Kuckein, Christoph A1 - Verma, Meetu A1 - Denker, Carsten T1 - Filigree in the surroundings of polar crown and high-latitude filaments JF - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics N2 - High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H alpha narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel) provided full-disk context observations in H alpha, CaiiK, and Hei 10830 angstrom. 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 angstrom 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. KW - Chromosphere KW - Quiet KW - Granulation KW - Magnetic fields KW - Photosphere KW - Prominences KW - Quiescent Y1 - 2021 U6 - https://doi.org/10.1007/s11207-021-01776-7 SN - 0038-0938 SN - 1573-093X VL - 296 IS - 2 PB - Springer CY - Dordrecht ER - TY - THES A1 - Lepro, Valentino T1 - Experimental and theoretical study on amoeboid cell-cargo active motion BT - a physical analysis of cell-mediated particle transport N2 - As society paves its way towards device miniaturization and precision medicine, micro-scale actuation and guided transport become increasingly prominent research fields, with high potential impact in both technological and clinical contexts. In order to accomplish directed motion of micron-sized objects, as biosensors and drug-releasing microparticles, towards specific target sites, a promising strategy is the use of living cells as smart biochemically-powered carriers, building the so-called bio-hybrid systems. Inspired by leukocytes, native cells of living organisms efficiently migrating to critical targets as tumor tissue, an emerging concept is to exploit the amoeboid crawling motility of such cells as mean of transport for drug delivery applications. In the research work described in this thesis, I synergistically applied experimental, computational and theoretical modeling approaches to investigate the behaviour and transport mechanism of a novel kind of bio-hybrid system for active transport at the micro-scale, referred to as cellular truck. This system consists of an amoeboid crawling cell, the carrier, attached to a microparticle, the cargo, which may ideally be drug-loaded for specific therapeutic treatments. For the purposes of experimental investigation, I employed the amoeba Dictyostelium discoideum as crawling cellular carrier, being a renowned model organism for leukocyte migration and, in general, for eukaryotic cell motility. The performed experiments revealed a complex recurrent cell-cargo relative motion, together with an intermittent motility of the cellular truck as a whole. The evidence suggests the presence of cargoes on amoeboid cells to act as mechanical stimulus leading cell polarization, thus promoting cell motility and giving rise to the observed intermittent dynamics of the truck. Particularly, bursts in cytoskeletal polarity along the cell-cargo axis have been found to occur in time with a rate dependent on cargo geometrical features, as particle diameter. Overall, the collected experimental evidence pointed out a pivotal role of cell-cargo interactions in the emergent cellular truck motion dynamics. Especially, they can determine the transport capabilities of amoeboid cells, as the cargo size significantly impacts the cytoskeletal activity and repolarization dynamics along the cell-cargo axis, the latter responsible for truck displacement and reorientation. Furthermore, I developed a modeling framework, built upon the experimental evidence on cellular truck behaviour, that connects the relative dynamics and interactions arising at the truck scale with the actual particle transport dynamics. In fact, numerical simulations of the proposed model successfully reproduced the phenomenology of the cell-cargo system, while enabling the prediction of the transport properties of cellular trucks over larger spatial and temporal scales. The theoretical analysis provided a deeper understanding of the role of cell-cargo interaction on mass transport, unveiling in particular how the long-time transport efficiency is governed by the interplay between the persistence time of cell polarity and time scales of the relative dynamics stemming from cell-cargo interaction. Interestingly, the model predicts the existence of an optimal cargo size, enhancing the diffusivity of cellular trucks; this is in line with previous independent experimental data, which appeared rather counterintuitive and had no explanation prior to this study. In conclusion, my research work shed light on the importance of cargo-carrier interactions in the context of crawling cell-mediated particle transport, and provides a prototypical, multifaceted framework for the analysis and modelling of such complex bio-hybrid systems and their perspective optimization. N2 - Im Zuge der fortschreitenden gesellschaftlichen Entwicklung hin zur Miniaturisierung und Präzisionsmedizin, gewinnen Fragen zu Antrieb und zielgerichtetem Transport auf der Mikrometerskala zunehmend an Bedeutung, nicht zuletzt wegen ihres kaum zu unterschätzendem Potentials für Medizin und Technik. Eine vielversprechende Strategie, um den zielgerichteten Transport von Objekten auf der Mikrometerskala, wie zum Beispiel Biosensoren oder mit Medikamenten beladene Mikropartikel, zu bewerkstelligen, ist die Verwendung von lebenden Zellen als intelligenten, biochemisch angetriebenen Transportern. Zellen und Mikroobjekte bilden dabei gemeinsam sogenannte Bio-Hybridsysteme. Inspiriert von Leukozyten - nativen Zellen lebender Organismen, welche sich effizient zu kritischen Zielen, wie Tumorgewebe, bewegen - besteht ein neues Konzept darin, die amöboide Fortbewegung solcher Zellen für den Medikamententransport zu nutzen. Im Rahmen dieser Doktorarbeit kamen experimentelle, numerische und theoretische Modellierungsansätze zum Einsatz, um die Eigenschaften und Transportmechanismen eines neuen Bio-Hybridsystems für den aktiven Transport von Objekten auf der Mikrometerskala zu untersuchen. Dieses Bio-Hybridsystem wird im Folgenden als Zelltransporter bezeichnet. Ein Zelltransporter besteht aus einer sich amöboid fortbewegenden Zelle, dem Transporter, und einem Mikropartikel, der Fracht, welche idealerweise mit Medikamenten für therapeutische Zwecke beladen sein kann. Für die experimentellen Untersuchungen wurde die Amöbe Dictyostelium discoideum als Transporter verwendet. Sie ist ein bekannter Modellorganismus für die Leukozytenmigration und für die Motilität eukaryotischer Zellen im Allgemeinem. Die durchgeführten Experimente zeigten eine komplexe, periodische Zell-Fracht-Relativbewegung, zusammen mit einer intermittierenden Motilität des gesamten Zelltransporters. Die experimentellen Beobachtungen weisen darauf hin, dass die Anwesenheit der Fracht als mechanischer Stimulus auf die amöboide Zelle wirkt und zur Zellpolarisation führt, was wiederum die Zellmotilität fördert und die intermittierende Dynamik des Zelltransportes begründet. So wurde festgestellt, dass das Auftreten der Polarisation des Zytoskeletts entlang der Zell-Fracht-Achse von den geometrischen Merkmalen der Fracht, wie zum Beispiel des Partikeldurchmessers, abhängt. Insgesamt wiesen die gesammelten experimentellen Daten auf eine zentrale Rolle der Zell-Fracht-Wechselwirkungen in der Bewegungsdynamik von Zelltransportern hin. Insbesondere kann die Zell-Fracht-Wechselwirkung die Transportfähigkeiten von amöboiden Zellen erheblich beeinflussen, da die Größe der Fracht die Aktivität des Zytoskeletts und die Repolarisationsdynamik entlang der Zell-Fracht-Achse modelliert, wobei letzteres für die Verlagerung und Neuorientierung des Zelltransportes verantwortlich ist. Darüber hinaus wurde eine Modellierung entwickelt, welche auf den experimentellen Erkenntnissen zum Verhalten der Zelltransporter aufbaut und die relative Dynamik auf Zelltranporterebene, mit der tatsächlichen Partikeltransportdynamik verbindet. Tatsächlich reproduzierten numerische Simulationen des vorgeschlagenen Modells erfolgreich die Phänomenologie des Zell-Fracht-Systems und ermöglichten gleichzeitig die Vorhersage der Transporteigenschaften von Zelltransportern über größere räumliche und zeitliche Skalen. Des Weiteren liefert die theoretische Analyse ein tieferes Verständnis der Rolle der Zell-Fracht-Wechselwirkung beim Massentransport und zeigte insbesondere, wie die Langzeittransporteffizienz durch das Zusammenspiel von Persistenzzeit der Zellpolarität und den Zeitskalen der relativen Dynamik, welche sich aus der Zell-Fracht-Interaktion ergeben, bestimmt wird. Interessanterweise sagt das Modell die Existenz einer optimalen Frachtgröße voraus, wodurch die Diffusivität von Zelltransportern maximiert wird. Dies steht im Einklang mit früheren, unabhängigen experimentellen Daten, für die es vor dieser Studie keine Erklärung gab. Zusammenfassend lässt sich sagen, dass die vorliegende Forschungsarbeit Licht auf die Bedeutung von Transporter-Fracht-Wechselwirkungen, beim Partikeltransports mittels amöboider Zellen, wirft und eine breite Grundlage für die Analyse und Modellierung komplexer Bio-Hybridsysteme und deren perspektivische Optimierung schafft. KW - biophysics KW - bio-hybrid system KW - particle transport KW - active transport KW - amoeboid motion KW - Biophysik KW - Bio-Hybridsystem KW - Partikeltransport KW - aktiven Transport KW - amöboide Bewegung Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-490890 ER - TY - JOUR A1 - Kluge, Lucas A1 - Schewe, Jacob T1 - Evaluation and extension of the radiation model for internal migration JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Human migration is often studied using gravity models. These models, however, have known limitations, including analytic inconsistencies and a dependence on empirical data to calibrate multiple parameters for the region of interest. Overcoming these limitations, the radiation model has been proposed as an alternative, universal approach to predicting different forms of human mobility, but has not been adopted for studying migration. Here we show, using data on within-country migration from the USA and Mexico, that the radiation model systematically underpredicts long-range moves, while the traditional gravity model performs well for large distances. The universal opportunity model, an extension of the radiation model, shows an improved fit of long-range moves compared to the original radiation model, but at the cost of introducing two additional parameters. We propose a more parsimonious extension of the radiation model that introduces a single parameter. We demonstrate that it fits the data over the full distance spectrum and also-unlike the universal opportunity model-preserves the analytical property of the original radiation model of being equivalent to a gravity model in the limit of a uniform population distribution. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.054311 SN - 2470-0045 SN - 2470-0053 SN - 2470-0061 VL - 104 IS - 5 PB - American Physical Society CY - College Park ER - TY - THES A1 - Feigel, Immanuel T1 - Entwicklung und Validierung eines Instruments zur Erfassung von experimentierbezogenen Erfahrungen angehender Physiklehrkräfte N2 - Aufgrund der Bedeutung von Experimenten im physikalischen Erkenntnisprozess, sind diese ein wesentlicher Bestandteil des Physikunterrichts. Um den Einsatz von Experimenten im Physikunterricht zu fördern, sind kompetenzorientiertes Experimentieren und die Reflexion des Einsatzes von Experimenten wichtige Ziele in Lehrkräftebildungsprogrammen. Ablaufmodelle für kompetenzorientiertes Experimentieren unterscheiden typischerweise Phasen der Fragen- und Hypothesenentwicklung, der Planung, der Erforschung und der Schlussfolgerungen. Es ist allerdings unklar, auf welche Weise angehende Physiklehrkräfte Aspekte des kompetenzorientierten Experimentierens in ihrem Unterricht in schulpraktischen Ausbildungsphasen einsetzen, auf welche Weise sie solche Unterrichtsversuche mit Experimentierbezug reflektieren und wie strukturiert (im Sinne der Ablaufmodelle) sie dabei vorgehen. In der vorliegenden Studie wurde deshalb untersucht, auf welche Weise Praxissemesterstudierende Experimentierprozesse in ihren Unterrichtsversuchen reflektieren. Hierfür wurde betrachtet, zu welchen Anteilen die Experimentierphasen in den Reflexionen adressiert werden. Um weiterhin herauszufinden, mit welcher Qualität die Experimentplanung reflektiert wird und inwiefern sich Vorstrukturierung für die Planungsphase zeigt, wurde diese differenzierter betrachtet. Auf Basis empirischer Vorarbeiten wurde vermutet, dass Fragenentwicklung, Hypothesenbildung und Experimentplanung seltener thematisiert werden als die anderen Teilkompetenzen und dass die Planungsphase hauptsächlich stark vorstrukturierte Elemente enthält, statt den Lernenden Freiräume für selbstständige Planungen zu lassen. Zur Untersuchung der Fragestellung wurden Kodiermanuale zur Erfassung experimentierbezogener Kompetenzen in schriftlichen Reflexionen entwickelt und validiert. Analysiert wurden 40 Reflexionstexte von 14 Studierenden des Physik-Lehramts im Praxissemester an der Universität Potsdam. Als Untersuchungsmethode wurde die qualitative Inhaltsanalyse genutzt. Die Texte wurden bezüglich der Umsetzung eines Reflexionsmodells und auf das Vorkommen der Teilkompetenzen des Experimentierzyklus untersucht. Die Ergebnisse bestätigten das geringe Vorkommen der Fragenentwicklung und Hypothesenbildung sowie die tendenziell geschlossenen Planungsinhalte. Zudem konnte festgestellt werden, dass die Planungsphase eher oberflächlich reflektiert und vor allem Arbeitsaufträge wiedergegeben wurden. Allgemein zeigten sich hauptsächlich beschreibende Tendenzen in den Reflexionen und eher wenige Alternativen und Konsequenzen. Aus den Ergebnissen werden Implikationen für die Lehrkräftebildung im Fach Physik abgeleitet. Um die Reflexionskompetenz der angehenden Lehrkräfte zu fördern, sind Hilfestellungen während des Reflexionsprozesses und eine inhaltliche Rückmeldung notwendig. Des Weiteren sollten die angehenden Lehrkräfte für eine ausgewogenere Förderung der Teilkompetenzen in ihrem Unterricht sensibilisiert werden. N2 - Due to the importance of experiments in the physics-based inquiry process, they are an essential part of physics teaching. In order to promote the use of experiments in physics lessons, competence-oriented experimentation and reflection on the use of experiments are important goals in teacher training programs. Process models for competence-oriented experimentation typically distinguish between phases of question and hypothesis development, planning, exploration and conclusions. However, it is unclear in what way prospective physics teachers use aspects of competence-oriented experimentation in their lessons in school-based training phases and in what way they reflect teaching experiments with reference to experimentation and how structured (in terms of reflection models) they proceed in doing so. The present study therefore investigated the ways in which students in their final teaching internship reflect on experimentation processes in their teaching. For this purpose, we looked at the proportions in which the experimentation phases are addressed in the reflections. In order to find out the quality with which the planning of the experiment is reflected and to what extent the planning phase is pre-structured, this was considered in a more differentiated way. On the basis of empirical preliminary work, it was assumed that question development, hypothesis formation and experiment planning are addressed less frequently than the other sub-competencies and that the planning phase mainly contains pre-structured tasks instead of leaving the learners space for exploration and planning. To investigate the question, coding manuals for recording experiment-related competencies in written reflections were developed and validated. 40 reflection texts from 14 physics students in their practical semester at the University of Potsdam were analysed. Qualitative content analysis was used to identify categories in which the teachers reflected. The texts were examined with regard to the implementation of a reflection model and the occurrence of the competencies as defined in the experimentation cycle. The results confirmed the low occurrence of question development and hypothesis formation as well as the tendency towards pre-structed tasks. In addition, it was found that the planning phase was reflected rather superficially and that work assignments were mainly reproductive. More generally, descriptive tendencies were found in the reflections and rather few alternatives and consequences. Implications for teacher training in physics are derived from the results. In order to promote the reflection competence of the prospective teachers, assistance during the reflection process and feedback on the contents are necessary. Furthermore, the prospective teachers should be sensitised to include all competencies as outlined in the experimentation cycle. KW - Experimentierkompetenz KW - Reflexion KW - Physik KW - Lehrkräftebildung KW - quantitative Inhaltsanalyse KW - Experimentierzyklus KW - experimental competencies KW - experimental model KW - reflection KW - physics KW - teacher education KW - content analysis Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-537720 ER - TY - THES A1 - Born, Artur T1 - Electronic structure, quasi-particle interaction and relaxation in 3d-elements from X-ray spectroscopy N2 - Any physical system can be described on the level of interacting particles, thus it is of fundamental importance to improve the scientific understanding of interacting many-body systems. This thesis experimentally addresses specific quasi-particle interactions, namely interactions be- tween electrons and between electrons and phonons. It describes the consequential effects of those processes on the electronic structure and the core-hole relaxation pathways in 3d metals. Despite the great amount of experimental and theoretical studies of these interactions and their impact on the behavior of solid-state matter, there are still open questions concerning the cor- responding physical, chemical and mechanical properties of solid-state matter. Especially, the study of 3d metals and their compounds is a great experimental challenge, since those exhibit a variety of spectral features originating from many-body effects such as multiplet splitting, shake up/off satellites, vibrationally excited states or more complex effects like superconductivity and ultrafast demagnetization. In X-ray spectroscopy, these effects often produce overlapping fea- tures, complicating the analysis and limiting the understanding. In this thesis, to overcome the limitations set by conventional X-ray spectroscopy, two different experimental approaches were successfully refined, namely Auger electron photoelectron coincidence spectroscopy (APECS) and temperature-dependent X-ray emission spectroscopy (tXES), which enabled the separation of different core-hole relaxation pathways and the isolation of the impact of specific many-body interactions in the experimental spectra. APECS was utilized at the new Coincidence electron spectroscopy for chemical analysis (Co- ESCA) station at BESSY II to study the core-hole decay and electron-correlation effects in single- crystal Ni, Cu and Co. The observation of photoelectrons in coincidence with Auger electrons allows for the separation of the initial and final state effects in the Auger electron spectra. The results show that a Cu LV V Auger spectrum can be represented by broadened atomic multiplets confirming the localized nature of the intermediate core-hole states. In contrast, the Co LV V Auger spectrum is band-like and can be represented by the self-convolution of the valence band. Ni behaves mixed, localized and itinerant. Thus, the Ni Auger spectrum can only be represented by a mixture of atomic multiplet peaks and the self-convoluted valence band. In the case of Ni, the LV V Auger electrons in coincidence with the 6 eV satellite photoelectrons were also stud- ied. Utilizing the core-hole clock method, the lifetime of the localized double-hole intermediate 2 p53d9 states of 1.8 fs could be determined. However, a fraction of these states delocalizes before the Auger decay contributing to the main peak. A similar delocalization was observed for the double-hole states produced by the L2L3M4,5 Coster-Kronig process. Additionally, the influence of surface oxidation on the Ni(111) 3p levels was studied with APECS. The Ni 3p PES spectrum is broad and featureless, due to overlapping many-body effects and gives little chance for exact analysis using conventional photoelectron spectroscopy. Utilizing APECS or precisely the final state selectivity of the method, the spectral width of the 3p levels could be narrowed and their positions and the spin-orbit splitting were determined. Moreover, due to the surface sensitivity of the method, the chemically shifted 3p photoelectron peaks originating from the oxidized surface and the bulk Ni were disentangled. For the study of the atomic electron-phonon spin-flip scattering in 3d metals as a spin-relaxation channel, the tXES method at the SolidFlexRIXS station was developed. The atomic spin-flip scat- tering was studied in single-crystal Ni, Cu, Co and in FeNi alloys, which show considerable dif- ferences in their behavior. The scattering rate in Ni increases with temperature, whereas the rate in Cu and Co remains constant within the measured temperature range up to 1000 K. In FeNi alloys, our results reveal that the spin-flip scattering is restricted by sublattice exchange energies J. The electron-phonon scattering driven spin-flips only appear in the case where the thermal energy ex- ceeds the exchange energy kT > J. This thresholding is an important microscopic process for the description of the sublattice dynamics in alloys, but as shown also relevant for elemental magnetic systems. Overall, the results strongly indicate that the spin-flip probability is correlated with the exchange energy, which might become an important parameter in the ultrafast demagnetization debate. Taken together, the applied experimental approaches allowed to study complex many-body effects in 3d metals. The results show that utilizing APECS enabled the distinction and clear assignment of otherwise overlapping features in AES or PES spectra of Ni, Cu, Co and NiO. This is of fundamental importance for the basic understanding of photoionization and core-hole decay processes but also for the chemical analysis in applied science. The measurement of the atomic electron-phonon spin-flip scattering rate utilizing tXES shows that the electron-phonon spin-flip scattering is a relevant atomic process for the macroscopic demagnetization process. Additionally, a temperature-dependent thresholding mechanism was discovered, which introduces an important dynamic factor into the electron-phonon spin-flip model. KW - X-ray spectroscopy KW - photoelectron spectroscopy KW - Auger electron spectroscop KW - X-ray absorption spectroscopy KW - X-ray emission spectroscopy KW - 3d metals KW - electronic structure KW - quasi-particle interaction Y1 - 2021 ER - TY - JOUR A1 - Andersson, Edvin K. W. A1 - Sångeland, Christofer A1 - Berggren, Elin A1 - Johansson, Fredrik O. L. A1 - Kühn, Danilo A1 - Lindblad, Andreas A1 - Mindemark, Jonas A1 - Hahlin, Maria T1 - Early-stage decomposition of solid polymer electrolytes in Li-metal batteries JF - Journal of materials chemistry : A, Materials for energy and sustainability N2 - Development of functional and stable solid polymer electrolytes (SPEs) for battery applications is an important step towards both safer batteries and for the realization of lithium-based or anode-less batteries. The interface between the lithium and the solid polymer electrolyte is one of the bottlenecks, where severe degradation is expected. Here, the stability of three different SPEs - poly(ethylene oxide) (PEO), poly(epsilon-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) - together with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, is investigated after they have been exposed to lithium metal under UHV conditions. Degradation compounds, e.g. Li-O-R, LiF and LixSyOz, are identified for all SPEs using soft X-ray photoelectron spectroscopy. A competing degradation between polymer and salt is identified in the outermost surface region (<7 nm), and is dependent on the polymer host. PTMC:LiTFSI shows the most severe decomposition of both polymer and salt followed by PCL:LiTFSI and PEO:LiTFSI. In addition, the movement of lithium species through the decomposed interface shows large variation depending on the polymer electrolyte system. Y1 - 2021 U6 - https://doi.org/10.1039/d1ta05015j SN - 2050-7488 SN - 2050-7496 VL - 9 IS - 39 SP - 22462 EP - 22471 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Bekir, Marek A1 - Jelken, Joachim A1 - Jung, Se-Hyeong A1 - Pich, Andrij A1 - Pacholski, Claudia A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Dual responsiveness of microgels induced by single light stimulus JF - Applied physics letters N2 - We report on the multiple response of microgels triggered by a single optical stimulus. Under irradiation, the volume of the microgels is reversibly switched by more than 20 times. The irradiation initiates two different processes: photo-isomerization of the photo-sensitive surfactant, which forms a complex with the anionic microgel, rendering it photo-responsive; and local heating due to a thermo-plasmonic effect within the structured gold layer on which the microgel is deposited. The photo-responsivity is related to the reversible accommodation/release of the photo-sensitive surfactant depending on its photo-isomerization state, while the thermo-sensitivity is intrinsically built in. We show that under exposure to green light, the thermo-plasmonic effect generates a local hot spot in the gold layer, resulting in the shrinkage of the microgel. This process competes with the simultaneous photo-induced swelling. Depending on the position of the laser spot, the spatiotemporal control of reversible particle shrinking/swelling with a predefined extent on a per-second base can be implemented. Y1 - 2021 U6 - https://doi.org/10.1063/5.0036376 SN - 0003-6951 SN - 1077-3118 VL - 118 IS - 9 PB - American Institute of Physics CY - Melville ER - TY - GEN A1 - Grebenkov, Denis S. A1 - Metzler, Ralf A1 - Oshanin, Gleb T1 - Distribution of first-reaction times with target regions on boundaries of shell-like domains T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We study the probability density function (PDF) of the first-reaction times between a diffusive ligand and a membrane-bound, immobile imperfect target region in a restricted 'onion-shell' geometry bounded by two nested membranes of arbitrary shapes. For such a setting, encountered in diverse molecular signal transduction pathways or in the narrow escape problem with additional steric constraints, we derive an exact spectral form of the PDF, as well as present its approximate form calculated by help of the so-called self-consistent approximation. For a particular case when the nested domains are concentric spheres, we get a fully explicit form of the approximated PDF, assess the accuracy of this approximation, and discuss various facets of the obtained distributions. Our results can be straightforwardly applied to describe the PDF of the terminal reaction event in multi-stage signal transduction processes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1255 KW - diffusion KW - first-passage time KW - first-reaction time KW - shell-like geometries KW - approximate methods Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-557542 SN - 1866-8372 SP - 1 EP - 23 PB - Universitätsverlag Potsdam CY - Potsdam ER - TY - JOUR A1 - Grebenkov, Denis S. A1 - Metzler, Ralf A1 - Oshanin, Gleb T1 - Distribution of first-reaction times with target regions on boundaries of shell-like domains JF - New Journal of Physics (NJP) N2 - We study the probability density function (PDF) of the first-reaction times between a diffusive ligand and a membrane-bound, immobile imperfect target region in a restricted 'onion-shell' geometry bounded by two nested membranes of arbitrary shapes. For such a setting, encountered in diverse molecular signal transduction pathways or in the narrow escape problem with additional steric constraints, we derive an exact spectral form of the PDF, as well as present its approximate form calculated by help of the so-called self-consistent approximation. For a particular case when the nested domains are concentric spheres, we get a fully explicit form of the approximated PDF, assess the accuracy of this approximation, and discuss various facets of the obtained distributions. Our results can be straightforwardly applied to describe the PDF of the terminal reaction event in multi-stage signal transduction processes. KW - diffusion KW - first-passage time KW - first-reaction time KW - shell-like geometries KW - approximate methods Y1 - 2021 U6 - https://doi.org/10.1088/1367-2630/ac4282 SN - 1367-2630 VL - 2021 SP - 1 EP - 23 PB - IOP Publishing CY - London ET - 23 ER - TY - JOUR A1 - Smirnov, Lev A. A1 - Bolotov, Maxim I. A1 - Osipov, Grigorij V. A1 - Pikovskij, Arkadij T1 - Disorder fosters chimera in an array of motile particles JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We consider an array of nonlocally coupled oscillators on a ring, which for equally spaced units possesses a Kuramoto-Battogtokh chimera regime and a synchronous state. We demonstrate that disorder in oscillators positions leads to a transition from the synchronous to the chimera state. For a static (quenched) disorder we find that the probability of synchrony survival depends on the number of particles, from nearly zero at small populations to one in the thermodynamic limit. Furthermore, we demonstrate how the synchrony gets destroyed for randomly (ballistically or diffusively) moving oscillators. We show that, depending on the number of oscillators, there are different scalings of the transition time with this number and the velocity of the units. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.034205 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 3 PB - American Physical Society CY - Melville, NY ER - TY - THES A1 - Gengel, Erik T1 - Direct and inverse problems of network analysis T1 - Direkte und Inverse Probleme der Netzwerk-Analyse N2 - Selfsustained oscillations are some of the most commonly observed phenomena in biological systems. They emanate from non-linear systems in a heterogeneous environment and can be described by the theory of dynamical systems. Part of this theory considers reduced models of the oscillator dynamics by means of amplitudes and a phase variable. Such variables are highly attractive for theoretical and experimental studies. Theoretically these variables correspond to an integrable linearization of the generally non-linear system. Experimentally, there exist well established approaches to extract phases from oscillator signals. Notably, one can define phase models also for networks of oscillators. One highly active field examines effects of non-local coupling among oscillators, which is thought to play a key role in networks with strong coupling. The dissertation introduces and expands the knowledge about high-order phase coupling in networks of oscillators. Mathematical calculations consider the Stuart-Landau oscillator. A novel phase estimation scheme for direct observations of an oscillator dynamics is introduced based on numerics. A numerical study of high-order phase coupling applies a Fourier fit for the Stuart-Landau and for the van-der-Pol oscillator. The numerical approach is finally tested on observation-based phase estimates of the Morris-Lecar neuron. A popular approach for the construction of phases from signals is based on phase demodulation by means of the Hilbert transform. Generally, observations of oscillations contain a small and generic variation of their amplitude. The work presents a way to quantify how much the variations of signal amplitude spoil a phase demodulation procedure. For the ideal case of phase modulated signals, amplitude modulations vanish. However, the Hilbert transform produces artificial variations of the reconstructed amplitude even in this case. The work proposes a novel procedure called Iterative Hilbert Transform Embedding to obtain an optimal demodulation of signals. The text presents numerous examples and tests of application for the method, covering multicomponent signals, observables of highly stable limit cycle oscillations and noisy phase dynamics. The numerical results are supported by a spectral theory of convergence for weak phase modulations. N2 - Selbsterhaltende Ozillationen finden sich häufig in biologischen Systemen. Sie emergieren aus nichtlinearen Prozessen in einem heterogenen Umfeld und können durch die Theorie dynamischer Systeme beschrieben werden. Ein Teil dieser Theorie befasst ich mit reduzierten Beschreibungen von Oszillationen anhand von Amplituden-, und Phasenvariablen. Selbige sind für theoretische und experimentelle Anwendungen von großer Bedeutung. Im theoretischen Bereich korrespondieren Phasen und Amplituden zur integrablen Linearisierung eines nichtlinearen Systems. Im experimentellen Bereich existieren weit verbreitete Ansätze, Phasenvariablen aus oszillierenden Signalen zu gewinnen. Phasenmodelle können auch für Netzwerke von Oszillatoren definiert werden. Ein aktives Forschungsgebiet befasst sich in diesem Zusammenhang mit nicht-lokalen Kopplungen zwischen den Oszillatoren. Die Fachwelt geht davon aus, dass solche nicht-lokalen Kopplungen eine entscheidende Rolle spielen, wenn die Kopplungen zwischen den einzelnen Einheiten nicht schwach ist. Die Dissertation gibt eine Einführung in dieses Themengebiet und liefert einen Beitrag zum weiteren Verständnis derartiger Probleme. Mathematische Berechnungen gehen vom Stuart-Landau-Oszillator aus. Eine neue numerische Berechnungsmethode für die Phasendynamik von Oszillatoren wird vorgestellt; sie basiert auf vollständiger Kenntnis des dynamischen Systems. Eine numerische Studie der Phasenkopplungen höherer Ordnung verwendet einen Fourier-Fit. Als Beispiele dienen hier das Stuart-Landau-Modell und der van-der-Pol Oszillator. Die vollständige numerische Prozedur wird final getestet für die datengetriebene Bestimmung der Phasenkopplung dreier Morris-Lecar Neuronen. Eine der beliebtesten Methoden zur Phasenextraktion aus Messdaten basiert auf dem Prinzip der Phasendemodulation. Hierfür verwendet man die Hilbert-Transformation. Im Allgemeinen beinhalten Observablen nichtlinearer Oszillatoren kleine - als generisch anzusehende - Variationen ihrer Amplitude. Die dargelegte Arbeit präsentiert eine Möglichkeit, wie der Einfluss derartiger Variationen die Phasendemodulation behindert. Für den idealen Fall reiner Phasenmodulation in Signalen, gehen Amplitudenvariationen gegen null. Dennnoch reproduziert die Hilbert-Transformation auch in derartigen Fällen nicht die tatsächliche Phase des Signals. Die Dissertation stellt eine neue Methode vor, die dieses spezielle Problem behebt. Diese Methode trägt den Namen Iterative Hilbert-Transformations-Einbettung und erlaubt die optimale Demodulation zu finden. Im Text werden zahlreiche Beispiele vorgestellt, insbesondere Multikomponentensignale, Observablen starrer Grenzzyklen und verrauschte Phasendynamiken. Die numerischen Resultate werden unterstützt durch eine spektrale Theorie der Konvergenz für schwache Phasenmodulationen. KW - non-linear oscillators KW - Hilbert transform KW - networks KW - phase demodulation KW - phase-amplitude mixing KW - high-order phase coupling KW - Hilbert-Transformation KW - Phasenkopplungen höherer Ordnung KW - Netzwerke KW - nichtlineare Oszillationen KW - Phasendemodulation KW - Phasen-Amplituden Trennung Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-512367 ER - TY - JOUR A1 - Pasemann, Gregor A1 - Flemming, Sven A1 - Alonso, Sergio A1 - Beta, Carsten A1 - Stannat, Wilhelm T1 - Diffusivity estimation for activator-inhibitor models BT - theory and application to intracellular dynamics of the actin cytoskeleton JF - Journal of nonlinear science N2 - A theory for diffusivity estimation for spatially extended activator-inhibitor dynamics modeling the evolution of intracellular signaling networks is developed in the mathematical framework of stochastic reaction-diffusion systems. In order to account for model uncertainties, we extend the results for parameter estimation for semilinear stochastic partial differential equations, as developed in Pasemann and Stannat (Electron J Stat 14(1):547-579, 2020), to the problem of joint estimation of diffusivity and parametrized reaction terms. Our theoretical findings are applied to the estimation of effective diffusivity of signaling components contributing to intracellular dynamics of the actin cytoskeleton in the model organism Dictyostelium discoideum. KW - Parametric drift estimation KW - Stochastic reaction– diffusion KW - systems KW - Maximum likelihood estimation KW - Actin cytoskeleton dynamics Y1 - 2021 U6 - https://doi.org/10.1007/s00332-021-09714-4 SN - 0938-8974 SN - 1432-1467 VL - 31 IS - 3 PB - Springer CY - New York ER - TY - JOUR A1 - Schröder, Jakob A1 - Evans, Alexander A1 - Mishurova, Tatiana A1 - Ulbricht, Alexander A1 - Sprengel, Maximilian A1 - Serrano-Munoz, Itziar A1 - Fritsch, Tobias A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Bruno, Giovanni T1 - Diffraction-based residual stress characterization in laser additive manufacturing of metals JF - Metals : open access journal N2 - Laser-based additive manufacturing methods allow the production of complex metal structures within a single manufacturing step. However, the localized heat input and the layer-wise manufacturing manner give rise to large thermal gradients. Therefore, large internal stress (IS) during the process (and consequently residual stress (RS) at the end of production) is generated within the parts. This IS or RS can either lead to distortion or cracking during fabrication or in-service part failure, respectively. With this in view, the knowledge on the magnitude and spatial distribution of RS is important to develop strategies for its mitigation. Specifically, diffraction-based methods allow the spatial resolved determination of RS in a non-destructive fashion. In this review, common diffraction-based methods to determine RS in laser-based additive manufactured parts are presented. In fact, the unique microstructures and textures associated to laser-based additive manufacturing processes pose metrological challenges. Based on the literature review, it is recommended to (a) use mechanically relaxed samples measured in several orientations as appropriate strain-free lattice spacing, instead of powder, (b) consider that an appropriate grain-interaction model to calculate diffraction-elastic constants is both material- and texture-dependent and may differ from the conventionally manufactured variant. Further metrological challenges are critically reviewed and future demands in this research field are discussed. KW - laser-based additive manufacturing KW - residual stress analysis KW - X-ray and KW - neutron diffraction KW - diffraction-elastic constants KW - strain-free lattice KW - spacing Y1 - 2021 U6 - https://doi.org/10.3390/met11111830 SN - 2075-4701 VL - 11 IS - 11 PB - MDPI CY - Basel ER - TY - JOUR A1 - Rüdiger, Günther A1 - Schultz, Manfred A1 - Hollerbach, Rainer T1 - Destabilization of super-rotating Taylor-Couette flows by current-free helical magnetic fields JF - Journal of plasma physics N2 - In an earlier paper we showed that the combination of azimuthal magnetic fields and super-rotation in Taylor-Couette flows of conducting fluids can be unstable against non-axisymmetric perturbations if the magnetic Prandtl number of the fluid is Pm not equal 1. Here we demonstrate that the addition of a weak axial field component allows axisymmetric perturbation patterns for Pm of order unity depending on the boundary conditions. The axisymmetric modes only occur for magnetic Mach numbers (of the azimuthal field) of order unity, while higher values are necessary for the non-axisymmetric modes. The typical growth time of the instability and the characteristic time scale of the axial migration of the axisymmetric mode are long compared with the rotation period, but short compared with the magnetic diffusion time. The modes travel in the positive or negative z direction along the rotation axis depending on the sign of B phi Bz. We also demonstrate that the azimuthal components of flow and field perturbations travel in phase if vertical bar B phi vertical bar >> vertical bar B-z vertical bar, independent of the form of the rotation law. Within a short-wave approximation for thin gaps it is also shown (in an appendix) that for ideal fluids the considered helical magnetorotational instability only exists for rotation laws with negative shear. KW - plasma instabilities KW - astrophysical plasmas Y1 - 2021 U6 - https://doi.org/10.1017/S0022377821000295 SN - 1469-7807 VL - 87 IS - 2 PB - Cambridge University Press CY - London ER - TY - JOUR A1 - Nadammal, Naresh A1 - Mishurova, Tatiana A1 - Fritsch, Tobias A1 - Serrano-Munoz, Itziar A1 - Kromm, Arne A1 - Haberland, Christoph A1 - Portella, Pedro Dolabella A1 - Bruno, Giovanni T1 - Critical role of scan strategies on the development of microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing JF - Additive manufacturing N2 - Laser based powder bed fusion additive manufacturing offers the flexibility to incorporate standard and user-defined scan strategies in a layer or in between the layers for the customized fabrication of metallic components. In the present study, four different scan strategies and their impact on the development of microstructure, texture, and residual stresses in laser powder bed fusion additive manufacturing of a nickel-based superalloy Inconel 718 was investigated. Light microscopy, scanning electron microscopy combined with electron back-scatter diffraction, and neutron diffraction were used as the characterization tools. Strong textures with epitaxially grown columnar grains were observed along the build direction for the two individual scan strategies. Patterns depicting the respective scan strategies were visible in the build plane, which dictated the microstructure development in the other planes. An alternating strategy combining the individual strategies in the successive layers and a 67 degrees rotational strategy weakened the texture by forming finer micro-structural features. Von Mises equivalent stress plots revealed lower stress values and gradients, which translates as lower distortions for the alternating and rotational strategies. Overall results confirmed the scope for manipulating the microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing by effectively controlling the scan strategies. KW - Additive manufacturing KW - Laser powder bed fusion KW - Nickel-based KW - superalloys KW - Scan strategies KW - Residual stresses KW - Microstructure and KW - texture Y1 - 2021 U6 - https://doi.org/10.1016/j.addma.2020.101792 SN - 2214-8604 VL - 38 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Dörries, Timo A1 - Loos, Sarah Anna Marie A1 - Klapp, Sabine H. L. T1 - Correlation functions of non-Markovian systems out of equilibrium BT - analytical expressions beyond single-exponential memory JF - Journal of statistical mechanics: theory and experiment : JSTAT N2 - This paper is concerned with correlation functions of stochastic systems with memory, a prominent example being a molecule or colloid moving through a complex (e.g. viscoelastic) fluid environment. Analytical investigations of such systems based on non-Markovian stochastic equations are notoriously difficult. A common approximation is that of a single-exponential memory, corresponding to the introduction of one auxiliary variable coupled to the Markovian dynamics of the main variable. As a generalization, we here investigate a class of 'toy' models with altogether three degrees of freedom, giving rise to more complex forms of memory. Specifically, we consider, mainly on an analytical basis, the under- and overdamped motion of a colloidal particle coupled linearly to two auxiliary variables, where the coupling between variables can be either reciprocal or non-reciprocal. Projecting out the auxiliary variables, we obtain non-Markovian Langevin equations with friction kernels and colored noise, whose structure is similar to that of a generalized Langevin equation. For the present systems, however, the non-Markovian equations may violate the fluctuation-dissipation relation as well as detailed balance, indicating that the systems are out of equilibrium. We then study systematically the connection between the coupling topology of the underlying Markovian system and various autocorrelation functions. We demonstrate that already two auxiliary variables can generate surprisingly complex (e.g. non-monotonic or oscillatory) memory and correlation functions. Finally, we show that a minimal overdamped model with two auxiliary variables and suitable non-reciprocal coupling yields correlation functions resembling those describing hydrodynamic backflow in an optical trap. KW - correlation functions KW - memory effects KW - friction Y1 - 2021 U6 - https://doi.org/10.1088/1742-5468/abdead SN - 1742-5468 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Lever, Fabiano A1 - Mayer, Dennis A1 - Metje, Jan A1 - Alisauskas, Skirmantas A1 - Calegari, Francesca A1 - Düsterer, Stefan A1 - Feifel, Raimund A1 - Niebuhr, Mario A1 - Manschwetus, Bastian A1 - Kuhlmann, Marion A1 - Mazza, Tommaso A1 - Robinson, Matthew Scott A1 - Squibb, Richard J. A1 - Trabattoni, Andrea A1 - Wallner, Måns A1 - Wolf, Thomas J. A. A1 - Gühr, Markus T1 - Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger–Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1180 KW - X-ray KW - photoelectron KW - sulfur KW - thiouracil KW - nucleobases KW - Coster–Kronig KW - Auger–Meitner KW - NEXAFS KW - FLASH Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-524091 SN - 1866-8372 IS - 21 ER - TY - JOUR A1 - Lever, Fabiano A1 - Mayer, Dennis A1 - Metje, Jan A1 - Alisauskas, Skirmantas A1 - Calegari, Francesca A1 - Düsterer, Stefan A1 - Feifel, Raimund A1 - Niebuhr, Mario A1 - Manschwetus, Bastian A1 - Kuhlmann, Marion A1 - Mazza, Tommaso A1 - Robinson, Matthew Scott A1 - Squibb, Richard J. A1 - Trabattoni, Andrea A1 - Wallner, Måns A1 - Wolf, Thomas J. A. A1 - Gühr, Markus T1 - Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser JF - Molecules N2 - In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger–Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy. KW - X-ray KW - photoelectron KW - sulfur KW - thiouracil KW - nucleobases KW - Coster–Kronig KW - Auger–Meitner KW - NEXAFS KW - FLASH Y1 - 2021 U6 - https://doi.org/10.3390/molecules26216469 SN - 1420-3049 VL - 26 IS - 21 PB - MDPI CY - Basel ER - TY - JOUR A1 - Mendez, Vicenc A1 - Maso-Puigdellosas, Axel A1 - Sandev, Trifce A1 - Campos, Daniel T1 - Continuous time random walks under Markovian resetting JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We investigate the effects of Markovian resetting events on continuous time random walks where the waiting times and the jump lengths are random variables distributed according to power-law probability density functions. We prove the existence of a nonequilibrium stationary state and finite mean first arrival time. However, the existence of an optimum reset rate is conditioned to a specific relationship between the exponents of both power-law tails. We also investigate the search efficiency by finding the optimal random walk which minimizes the mean first arrival time in terms of the reset rate, the distance of the initial position to the target, and the characteristic transport exponents. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.103.022103 SN - 2470-0045 SN - 2470-0053 VL - 103 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Wiesner, Karoline A1 - Ladyman, James T1 - Complex systems are always correlated but rarely information processing JF - Journal of physics. Complexity N2 - 'Complex systems are information processors' is a statement that is frequently made. Here we argue for the distinction between information processing-in the sense of encoding and transmitting a symbolic representation-and the formation of correlations (pattern formation/self-organisation). The study of both uses tools from information theory, but the purpose is very different in each case: explaining the mechanisms and understanding the purpose or function in the first case, versus data analysis and correlation extraction in the latter. We give examples of both and discuss some open questions. The distinction helps focus research efforts on the relevant questions in each case. KW - correlations KW - information theory KW - complex systems KW - information KW - processing KW - self-organisation Y1 - 2021 U6 - https://doi.org/10.1088/2632-072X/ac371c SN - 2632-072X VL - 2 IS - 4 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Eerqing, Narima A1 - Subramanian, Sivaraman A1 - Rubio Jimenez, Jesus A1 - Lutz, Tobias A1 - Wu, Hsin-Yu A1 - Anders, Janet A1 - Soeller, Christian A1 - Vollmer, Frank T1 - Comparing transient oligonucleotide hybridization kinetics using DNA-PAINT and optoplasmonic single-molecule sensing on gold nanorods JF - ACS photonics / American Chemical Society N2 - We report a comparison of two photonic techniques for single-molecule sensing: fluorescence nanoscopy and optoplasmonic sensing. As the test system, oligonucleotides with and without fluorescent labels are transiently hybridized to complementary "docking" strands attached to gold nanorods. Comparing the measured single-molecule kinetics helps to examine the influence of the fluorescent labels as well as factors arising from different sensing geometries. Our results demonstrate that DNA dissociation is not significantly altered by the fluorescent labels and that DNA association is affected by geometric factors in the two techniques. These findings open the door to exploiting plasmonic sensing and fluorescence nanoscopy in a complementary fashion, which will aid in building more powerful sensors and uncovering the intricate effects that influence the behavior of single molecules. KW - single-molecule KW - plasmonics KW - whispering gallery modes KW - optoplasmonic KW - DNA-PAINT KW - fluorescence KW - localization microscopy Y1 - 2021 U6 - https://doi.org/10.1021/acsphotonics.1c01179 SN - 2330-4022 VL - 8 IS - 10 SP - 2882 EP - 2888 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Petreska, Irina A1 - Sandev, Trifce A1 - Lenzi, Ervin Kaminski T1 - Comb-like geometric constraints leading to emergence of the time-fractional Schrödinger equation JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - This paper presents an overview over several examples, where the comb-like geometric constraints lead to emergence of the time-fractional Schrodinger equation. Motion of a quantum object on a comb structure is modeled by a suitable modification of the kinetic energy operator, obtained by insertion of the Dirac delta function in the Laplacian. First, we consider motion of a free particle on two- and three-dimensional comb structures, and then we extend the study to the interacting cases. A general form of a nonlocal term, which describes the interactions of the particle with the medium, is included in the Hamiltonian, and later on, the cases of constant and Dirac delta potentials are analyzed. At the end, we discuss the case of non-integer dimensions, considering separately the case of fractal dimension between one and two, and the case of fractal dimension between two and three. All these examples show that even though we are starting with the standard time-dependent Schrodinger equation on a comb, the time-fractional equation for the Green's functions appears, due to these specific geometric constraints. KW - Comb model KW - time-fractional Schrödinger equation KW - Green’ s functions Y1 - 2021 U6 - https://doi.org/10.1142/S0217732321300056 SN - 0217-7323 SN - 1793-6632 VL - 36 IS - 14 PB - World Scientific CY - Singapore ER - TY - JOUR A1 - Silanteva, Irina A. A1 - Komolkin, Andrei A1 - Mamontova, Veronika V. A1 - Gabrusenok, Pavel A1 - Vorontsov-Velyaminov, Pavel N. A1 - Santer, Svetlana A1 - Kasyanenko, Nina A. T1 - Cis-isomers of photosensitive cationic azobenzene surfactants in DNA solutions at different NaCl concentrations BT - Experiment and modeling JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - The DNA interaction with cis-isomers of photosensitive azobenzene-containing surfactants was studied by both experimental methods and computer simulation. It was shown that before the organization of micelles, such surfactants in the cis-conformation form associates of only a single type with a disordered orientation of molecules. In contrast, for trans-isomers, there exist two types of associates with head-to-head or head-to-tail orientations of molecules in dependence on salt concentration in a solution. The comparison of cis- and trans-isomer binding to DNA and the influence of salt concentration on the formation of their complexes with DNA were studied. It was shown that cis-isomers interact with phosphate groups of DNA and that their molecules were also located along the minor groove of DNA. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpcb.1c07864 SN - 1520-6106 SN - 1520-5207 VL - 125 IS - 40 SP - 11197 EP - 11207 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Mutothya, Nicholas Mwilu A1 - Xu, Yong A1 - Li, Yongge A1 - Metzler, Ralf T1 - Characterising stochastic motion in heterogeneous media driven by coloured non-Gaussian noise JF - Journal of physics : A, Mathematical and theoretical N2 - We study the stochastic motion of a test particle in a heterogeneous medium in terms of a position dependent diffusion coefficient mimicking measured deterministic diffusivity gradients in biological cells or the inherent heterogeneity of geophysical systems. Compared to previous studies we here investigate the effect of the interplay of anomalous diffusion effected by position dependent diffusion coefficients and coloured non-Gaussian noise. The latter is chosen to be distributed according to Tsallis' q-distribution, representing a popular example for a non-extensive statistic. We obtain the ensemble and time averaged mean squared displacements for this generalised process and establish its non-ergodic properties as well as analyse the non-Gaussian nature of the associated displacement distribution. We consider both non-stratified and stratified environments. KW - diffusion KW - anomalous diffusion KW - non-extensive statistics KW - coloured KW - noise KW - heterogeneous diffusion process Y1 - 2021 U6 - https://doi.org/10.1088/1751-8121/abfba6 SN - 1751-8113 SN - 1751-8121 VL - 54 IS - 29 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Varghese, Alan J. A1 - Chechkin, Aleksei A1 - Metzler, Ralf A1 - Sujith, Raman I. T1 - Capturing multifractality of pressure fluctuations in thermoacoustic systems using fractional-order derivatives JF - Chaos : an interdisciplinary journal of nonlinear science N2 - The stable operation of a turbulent combustor is not completely silent; instead, there is a background of small amplitude aperiodic acoustic fluctuations known as combustion noise. Pressure fluctuations during this state of combustion noise are multifractal due to the presence of multiple temporal scales that contribute to its dynamics. However, existing models are unable to capture the multifractality in the pressure fluctuations. We conjecture an underlying fractional dynamics for the thermoacoustic system and obtain a fractional-order model for pressure fluctuations. The data from this model has remarkable visual similarity to the experimental data and also has a wide multifractal spectrum during the state of combustion noise. Quantitative similarity with the experimental data in terms of the Hurst exponent and the multifractal spectrum is observed during the state of combustion noise. This model is also able to produce pressure fluctuations that are qualitatively similar to the experimental data acquired during intermittency and thermoacoustic instability. Furthermore, we argue that the fractional dynamics vanish as we approach the state of thermoacoustic instability. Y1 - 2021 U6 - https://doi.org/10.1063/5.0032585 SN - 1054-1500 SN - 1089-7682 VL - 31 IS - 3 PB - American Institute of Physics, AIP CY - Melville ER - TY - JOUR A1 - Ulbricht, Alexander A1 - Mohr, Gunther A1 - Altenburg, Simon J. A1 - Oster, Simon A1 - Maierhofer, Christiane A1 - Bruno, Giovanni T1 - Can potential defects in LPBF be healed from the laser exposure of subsequent layers? BT - A quantitative study JF - Metals : open access journal N2 - Additive manufacturing (AM) of metals and in particular laser powder bed fusion (LPBF) enables a degree of freedom in design unparalleled by conventional subtractive methods. To ensure that the designed precision is matched by the produced LPBF parts, a full understanding of the interaction between the laser and the feedstock powder is needed. It has been shown that the laser also melts subjacent layers of material underneath. This effect plays a key role when designing small cavities or overhanging structures, because, in these cases, the material underneath is feed-stock powder. In this study, we quantify the extension of the melt pool during laser illumination of powder layers and the defect spatial distribution in a cylindrical specimen. During the LPBF process, several layers were intentionally not exposed to the laser beam at various locations, while the build process was monitored by thermography and optical tomography. The cylinder was finally scanned by X-ray computed tomography (XCT). To correlate the positions of the unmolten layers in the part, a staircase was manufactured around the cylinder for easier registration. The results show that healing among layers occurs if a scan strategy is applied, where the orientation of the hatches is changed for each subsequent layer. They also show that small pores and surface roughness of solidified material below a thick layer of unmolten material (>200 mu m) serve as seeding points for larger voids. The orientation of the first two layers fully exposed after a thick layer of unmolten powder shapes the orientation of these voids, created by a lack of fusion. KW - selective laser melting (SLM) KW - additive manufacturing (AM) KW - process KW - monitoring KW - infrared thermography KW - optical tomography KW - X-ray computed KW - tomography (XCT) KW - healing KW - in situ monitoring Y1 - 2021 U6 - https://doi.org/10.3390/met11071012 SN - 2075-4701 VL - 11 IS - 7 PB - MDPI CY - Basel ER - TY - THES A1 - Zheng, Chunming T1 - Bursting and synchronization in noisy oscillatory systems T1 - Bursting und Synchronisation in verrauschten, oszillierenden Systemen N2 - Noise is ubiquitous in nature and usually results in rich dynamics in stochastic systems such as oscillatory systems, which exist in such various fields as physics, biology and complex networks. The correlation and synchronization of two or many oscillators are widely studied topics in recent years. In this thesis, we mainly investigate two problems, i.e., the stochastic bursting phenomenon in noisy excitable systems and synchronization in a three-dimensional Kuramoto model with noise. Stochastic bursting here refers to a sequence of coherent spike train, where each spike has random number of followers due to the combined effects of both time delay and noise. Synchronization, as a universal phenomenon in nonlinear dynamical systems, is well illustrated in the Kuramoto model, a prominent model in the description of collective motion. In the first part of this thesis, an idealized point process, valid if the characteristic timescales in the problem are well separated, is used to describe statistical properties such as the power spectral density and the interspike interval distribution. We show how the main parameters of the point process, the spontaneous excitation rate, and the probability to induce a spike during the delay action can be calculated from the solutions of a stationary and a forced Fokker-Planck equation. We extend it to the delay-coupled case and derive analytically the statistics of the spikes in each neuron, the pairwise correlations between any two neurons, and the spectrum of the total output from the network. In the second part, we investigate the three-dimensional noisy Kuramoto model, which can be used to describe the synchronization in a swarming model with helical trajectory. In the case without natural frequency, the Kuramoto model can be connected with the Vicsek model, which is widely studied in collective motion and swarming of active matter. We analyze the linear stability of the incoherent state and derive the critical coupling strength above which the incoherent state loses stability. In the limit of no natural frequency, an exact self-consistent equation of the mean field is derived and extended straightforward to any high-dimensional case. N2 - Rauschen ist in der Natur allgegenwärtig und führt zu einer reichen Dynamik in stochastischen Systemen von gekoppelten Oszillatoren, die in so unterschiedlichen Bereichen wie Physik, Biologie und in komplexen Netzwerken existieren. Korrelation und Synchronisation von zwei oder vielen Oszillatoren ist in den letzten Jahren ein aktives Forschungsfeld. In dieser Arbeit untersuchen wir hauptsächlich zwei Probleme, d.h. das stochastische Burst-Phänomen in verrauschten anregbaren Systemen und die Synchronisation in einem dreidimensionalen Kuramoto-Modell mit Rauschen. Stochastisches Bursting bezieht sich hier auf eine Folge von kohärenten Spike-Zügen, bei denen jeder Spike aufgrund der kombinierten Effekte von Zeitverzögerung und Rauschen eine zufällige Anzahl von Folge Spikes aufweist. Die Synchronisation als universelles Phänomen in nichtlinearen dynamischen Systemen kann anhand des Kuramoto-Modells, einem grundlegenden Modell bei der gekoppelter Oszillatoren und kollektiver Bewegung, gut demonstriert und analysiert werden. Im ersten Teil dieser Arbeit wird ein idealisierter Punktprozess betrachtet, der gültig ist, wenn die charakteristischen Zeitskalen im Problem gut voneinander getrennt sind,um statistische Eigenschaften wie die spektrale Leistungsdichte und die Intervallverteilung zwischen Neuronen Impulsen zu beschreiben. Wir zeigen, wie die Hauptparameter des Punktprozesses, die spontane Anregungsrate und die Wahrscheinlichkeit, während der Verzögerungsaktion einen Impuls zu induzieren, aus den Lösungen einer stationären und einer getriebenen Fokker-Planck-Gleichung berechnet werden können. Wir erweitern dieses Ergebnis auf den verzögerungsgekoppelten Fall und leiten analytisch die Statistiken der Impulse in jedem Neuron, die paarweisen Korrelationen zwischen zwei beliebigen Neuronen und das Spektrum der Zeitreihe alle Impulse aus dem Netzwerk ab. Im zweiten Teil untersuchen wir das dreidimensionale verrauschte Kuramoto-Modell, mit dem die Synchronisation eines Schwarmmodells mit schraubenförmigen Flugbahnen beschrieben werden kann. Im Fall ohne Eigenfrequenz jedes Teilchensist das System äquivalent zum Vicsek Modell, welches in der Beschreibung der kollektiven Bewegung von Schwärmen und aktiver Materie eine breite Anwendung findet. Wir analysieren die lineare Stabilität des inkohärenten Zustands und leiten die kritische Kopplungsstärke ab, oberhalb derer der inkohärente Zustand an Stabilität verliert. Im Fall ohne Eigenfrequenz wird eine exakte selbstkonsistente Gleichung für das mittlere Feld abgeleitet und direkt für höherdimensionale Bewegungen verallgemeinert. KW - Synchronization KW - Kuramoto model KW - Oscillation KW - stochastic bursting KW - Synchronisation KW - Kuramoto-Modell KW - Oszillatoren KW - Stochastisches Bursting Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-500199 ER - TY - JOUR A1 - Franović, Igor A1 - Omel'chenko, Oleh A1 - Wolfrum, Matthias T1 - Bumps, chimera states, and Turing patterns in systems of coupled active rotators JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Self-organized coherence-incoherence patterns, called chimera states, have first been reported in systems of Kuramoto oscillators. For coupled excitable units, similar patterns where coherent units are at rest are called bump states. Here, we study bumps in an array of active rotators coupled by nonlocal attraction and global repulsion. We demonstrate how they can emerge in a supercritical scenario from completely coherent Turing patterns: a single incoherent unit appears in a homoclinic bifurcation, undergoing subsequent transitions to quasiperiodic and chaotic behavior, which eventually transforms into extensive chaos with many incoherent units. We present different types of transitions and explain the formation of coherence-incoherence patterns according to the classical paradigm of short-range activation and long-range inhibition. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.L052201 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Eckert, Sebastian A1 - Vaz da Cruz, Vinícius A1 - Ochmann, Miguel A1 - Ahnen, Inga von A1 - Föhlisch, Alexander A1 - Huse, Nils T1 - Breaking the symmetry of pyrimidine BT - solvent effects and core-excited state dynamics JF - The journal of physical chemistry letters N2 - Symmetry and its breaking crucially define the chemical properties of molecules and their functionality. Resonant inelastic X-ray scattering is a local electronic structure probe reporting on molecular symmetry and its dynamical breaking within the femtosecond scattering duration. Here, we study pyrimidine, a system from the C-2v point group, in an aqueous solution environment, using scattering though its 2a(2) resonance. Despite the absence of clean parity selection rules for decay transitions from in-plane orbitals, scattering channels including decay from the 7b(2) and 11a(1) orbitals with nitrogen lone pair character are a direct probe for molecular symmetry. Computed spectra of explicitly solvated molecules sampled from a molecular dynamics simulation are combined with the results of a quantum dynamical description of the X-ray scattering process. We observe dominant signatures of core-excited Jahn-Teller induced symmetry breaking for resonant excitation. Solvent contributions are separable by shortening of the effective scattering duration through excitation energy detuning. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpclett.1c01865 SN - 1948-7185 VL - 12 IS - 35 SP - 8637 EP - 8643 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Chaurasia, Swami Vivekanandji A1 - Dietrich, Tim A1 - Rosswog, Stephan T1 - Black hole-neutron star simulations with the BAM code BT - first tests and simulations JF - Physical review : D, Particles, fields, gravitation, and cosmology N2 - The first detections of black hole-neutron star mergers (GW200105 and GW200115) by the LIGO-Virgo-Kagra Collaboration mark a significant scientific breakthrough. The physical interpretation of pre- and postmerger signals requires careful cross-examination between observational and theoretical modelling results. Here we present the first set of black hole-neutron star simulations that were obtained with the numerical-relativity code BAM. Our initial data are constructed using the public LORENE spectral library, which employs an excision of the black hole interior. BAM, in contrast, uses the moving-puncture gauge for the evolution. Therefore, we need to "stuff" the black hole interior with smooth initial data to evolve the binary system in time. This procedure introduces constraint violations such that the constraint damping properties of the evolution system are essential to increase the accuracy of the simulation and in particular to reduce spurious center-of-mass drifts. Within BAM we evolve the Z4c equations and we compare our gravitational-wave results with those of the SXS collaboration and results obtained with the SACRA code. While we find generally good agreement with the reference solutions and phase differences less than or similar to 0.5 rad at the moment of merger, the absence of a clean convergence order in our simulations does not allow for a proper error quantification. We finally present a set of different initial conditions to explore how the merger of black hole neutron star systems depends on the involved masses, spins, and equations of state. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevD.104.084010 SN - 2470-0010 SN - 2470-0029 VL - 104 IS - 8 PB - American Physical Society CY - Ridge, NY ER - TY - JOUR A1 - Feudel, Fred A1 - Feudel, Ulrike T1 - Bifurcations in rotating spherical shell convection under the influence of differential rotation JF - Chaos : an interdisciplinary journal of nonlinear science N2 - The bifurcations of thermal convection in a rotating spherical shell heated from the inner sphere and driven by the buoyancy of a central gravity field are studied numerically. This model of spherical Rayleigh-Benard convection describes large-scale convection in planets and in the outer zones of celestial bodies. In this work, the influence of an additionally imposed differential rotation of the inner sphere with respect to the outer one on the heat transfer and, more generally, on the whole bifurcation structure is investigated. In addition to numerical simulations, path-following techniques are applied in order to compute both stable and unstable solution branches. The dynamics and the heat transfer are essentially determined by a global bifurcation, which we have identified as a homoclinic bifurcation that consists of a collision of a stable modulated rotating with an unstable rotating wave. Y1 - 2021 U6 - https://doi.org/10.1063/5.0063113 SN - 1054-1500 SN - 1089-7682 VL - 31 IS - 11 PB - AIP CY - Melville ER - TY - THES A1 - Keles, Engin T1 - Atmospheric properties and dynamics of gaseous exoplanets inferred from high-resolution alkali line transmission spectroscopy N2 - The characterization of exoplanets applying high-resolution transmission spectroscopy ini- tiated a new era making it possible to trace atmospheric signature at high altitudes in exoplanet atmospheres and to determine atmospheric properties which enrich our under- standing of the formation and evolution of the solar system. In contrast to what is observed in our solar system, where gaseous planets orbit at wide orbits, Jupiter type exoplanets were detected in foreign stellar systems surrounding their host stars within few days, in close orbits, the so called hot- and ultra-hot Jupiters. The most well studied ones are HD209458b and HD189733b, which are the first exoplanets where absorption is detected in their atmospheres, namely from the alkali line sodium. For hot Jupiters, the resonant alkali lines are the atmospheric species with one of the strongest absorption signatures, due to their large absorption cross-section. However, al- though the alkali lines sodium and potassium were detected in low-resolution observations for various giant exoplanets, potassium was absent in different high-resolution investiga- tions in contrast to sodium. The reason for this is quite puzzling, since both alkalis have very similar physical and chemical properties (e.g. condensation and ionization proper- ties). Obtaining high-resolution transit observations of HD189733b and HD209458b, we were able to detect potassium on HD189733b (Manuscript 1), which was the first high-resolution detection of potassium on an exoplanet. The absence of potassium on HD209458b could be reasoned by depletion processes, such as condensation or photo-ionization or high-altitude clouds. In a further study (Manuscript II), we resolved the potassium line and compared this to a previously detected sodium absorption on this planet. The comparison showed, that the potassium lines are either tracing different altitudes and temperatures compared to the sodium lines, or are depleted so that the planetary Na/K- ratio is way larger than the stellar one. A comparison of the alkali lines with synthetic line profiles showed that the sodium lines were much broader than the potassium lines, probably being induced by winds. To investigate this, the effect of zonal streaming winds on the sodium lines on Jupiter-type planets is investigated in a further study (Manuscript III), showing that such winds can significantly broaden the Na- lines and that high-resolution observations can trace such winds with different properties. Furthermore, investigating the Na-line observations for different exoplanets, I showed that the Na-line broadening follows a trend with cooler planets showing stronger line broadening and so hinting on stronger winds, matching well into theoretical predictions. Each presented manuscript depends on the re- sults published within the previous manuscript, yielding a unitary study of the exoplanet HD189733b. The investigation of the potassium absorption required to account for different effects: The telluric lines removal and the effect of center-to-limb variation (see Manuscript I), the residual Rossiter-Mc-Laughlin effect (see Manuscript II) and the broadening of spectral lines on a translucent atmospheric ring by zonal jet streams (see Manuscript III). This thesis shows that high-resolution transmission spectroscopy is a powerful tool to probe sharp alkali line absorption on giant exoplanet atmospheres and to investigate on the properties and dynamics of hot Jupiter type atmospheres. KW - planets and satellites: atmospheres KW - planets and satellites: composition KW - planets and satellites: gaseous planets KW - exoplanets Y1 - 2021 ER - TY - JOUR A1 - Omel'chenko, Oleh A1 - Ocampo-Espindola, Jorge Luis A1 - Kiss, István Z. T1 - Asymmetry-induced isolated fully synchronized state in coupled oscillator populations JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - A symmetry-breaking mechanism is investigated that creates bistability between fully and partially synchronized states in oscillator networks. Two populations of oscillators with unimodal frequency distribution and different amplitudes, in the presence of weak global coupling, are shown to simplify to a modular network with asymmetrical coupling. With increasing the coupling strength, a synchronization transition is observed with an isolated fully synchronized state. The results are interpreted theoretically in the thermodynamic limit and confirmed in experiments with chemical oscillators. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.L022202 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 2 PB - American Physical Society CY - Melville, NY ER - TY - JOUR A1 - Cherstvy, Andrey G. A1 - Safdari, Hadiseh A1 - Metzler, Ralf T1 - Anomalous diffusion, nonergodicity, and ageing for exponentially and logarithmically time-dependent diffusivity BT - striking differences for massive versus massless particles JF - Journal of physics. D, Applied physics N2 - We investigate a diffusion process with a time-dependent diffusion coefficient, both exponentially increasing and decreasing in time, D(t)=D-0(e +/- 2 alpha t). For this (hypothetical) nonstationary diffusion process we compute-both analytically and from extensive stochastic simulations-the behavior of the ensemble- and time-averaged mean-squared displacements (MSDs) of the particles, both in the over- and underdamped limits. Simple asymptotic relations derived for the short- and long-time behaviors are shown to be in excellent agreement with the results of simulations. The diffusive characteristics in the presence of ageing are also considered, with dramatic differences of the over- versus underdamped regime. Our results for D(t)=D-0(e +/- 2 alpha t) extend and generalize the class of diffusive systems obeying scaled Brownian motion featuring a power-law-like variation of the diffusivity with time, D(t) similar to t(alpha-1). We also examine the logarithmically increasing diffusivity, D(t)=D(0)log[t/tau(0)], as another fundamental functional dependence (in addition to the power-law and exponential) and as an example of diffusivity slowly varying in time. One of the main conclusions is that the behavior of the massive particles is predominantly ergodic, while weak ergodicity breaking is repeatedly found for the time-dependent diffusion of the massless particles at short times. The latter manifests itself in the nonequivalence of the (both nonaged and aged) MSD and the mean time-averaged MSD. The current findings are potentially applicable to a class of physical systems out of thermal equilibrium where a rapid increase or decrease of the particles' diffusivity is inherently realized. One biological system potentially featuring all three types of time-dependent diffusion (power-law-like, exponential, and logarithmic) is water diffusion in the brain tissues, as we thoroughly discuss in the end. KW - anomalous diffusion KW - scaled Brownian motion KW - stochastic processes KW - nonstationary diffusivity KW - water diffusion in the brain KW - nonergodicity Y1 - 2021 U6 - https://doi.org/10.1088/1361-6463/abdff0 SN - 0022-3727 SN - 1361-6463 VL - 54 IS - 19 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Laskin, Gennadii A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3 JF - Structural dynamics N2 - We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Grüneisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime. KW - Thin films KW - Thermodynamic properties KW - Bragg peak KW - Ultrafast X-ray diffraction KW - Thermal effects KW - Phonons KW - Magnetism KW - Lattice dynamics KW - Lasers KW - Perovskites Y1 - 2020 U6 - https://doi.org/10.1063/4.0000072 SN - 2329-7778 VL - 8 IS - 2 PB - AIP Publishing LLC CY - Melville, NY ER - TY - GEN A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Laskin, G. A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3 T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Grüneisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1144 KW - Thin films KW - Thermodynamic properties KW - Bragg peak KW - Ultrafast X-ray diffraction KW - Thermal effects KW - Phonons KW - Magnetism KW - Lattice dynamics KW - Lasers KW - Perovskites Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-515718 SN - 1866-8372 ER - TY - JOUR A1 - Nakoudi, Konstantina A1 - Stachlewska, Iwona S. A1 - Ritter, Christoph T1 - An extended lidar-based cirrus cloud retrieval scheme BT - first application over an Arctic site JF - Optics express : the international electronic journal of optics / Optica N2 - Accurate and precise characterization of cirrus cloud geometrical and optical properties is essential for better constraining their radiative footprint. A lidar-based retrieval scheme is proposed here, with its performance assessed on fine spatio-temporal observations over the Arctic site of Ny-Alesund, Svalbard. Two contributions related to cirrus geometrical (dynamic Wavelet Covariance Transform (WCT)) and optical properties (constrained Klett) are reported. The dynamic WCT rendered cirrus detection more robust, especially for thin cirrus layers that frequently remained undetected by the classical WCT method. Regarding optical characterization, we developed an iterative scheme for determining the cirrus lidar ratio (LRci) that is a crucial parameter for aerosol - cloud discrimination. Building upon the Klett-Fernald method, the LRci was constrained by an additional reference value. In established methods, such as the double-ended Klett, an aerosol-free reference value is applied. In the proposed constrained Klett, however, the reference value was approximated from cloud-free or low cloud optical depth (COD up to 0.2) profiles and proved to agree with independent Raman estimates. For optically thin cirrus, the constrained Klett inherent uncertainties reached 50% (60-74%) in terms of COD (LRci). However, for opaque cirrus COD (LRci) uncertainties were lower than 10% (15%). The detection method discrepancies (dynamic versus static WCT) had a higher impact on the optical properties of low COD layers (up to 90%) compared to optically thicker ones (less than 10%). The constrained Klett presented high agreement with two established retrievals. For an exemplary cirrus cloud, the constrained Klett estimated the COD355 (LRci355) at 0.28 +/- 0.17 (29 +/- 4 sr), the double-ended Klett at 0.27 +/- 0.15 (32 +/- 4 sr) and the Raman retrievals at 0.22 +/- 0.12 (26 +/- 11 sr). Our approach to determine the necessary reference value can also be applied in established methods and increase their accuracy. In contrast, the classical aerosol-free assumption led to 44 sr LRci overestimation in optically thin layers and 2-8 sr in thicker ones. The multiple scattering effect was corrected using Eloranta (1998) and accounted for 50-60% extinction underestimation near the cloud base and 20-30% within the cirrus layers. Y1 - 2021 U6 - https://doi.org/10.1364/OE.414770 SN - 1094-4087 VL - 29 IS - 6 SP - 8553 EP - 8580 PB - Optical Society of America CY - Washington ER - TY - THES A1 - Antonelli, Andrea T1 - Accurate waveform models for gravitational-wave astrophysics: synergetic approaches from analytical relativity N2 - Gravitational-wave (GW) astrophysics is a field in full blossom. Since the landmark detection of GWs from a binary black hole on September 14th 2015, fifty-two compact-object binaries have been reported by the LIGO-Virgo collaboration. Such events carry astrophysical and cosmological information ranging from an understanding of how black holes and neutron stars are formed, what neutron stars are composed of, how the Universe expands, and allow testing general relativity in the highly-dynamical strong-field regime. It is the goal of GW astrophysics to extract such information as accurately as possible. Yet, this is only possible if the tools and technology used to detect and analyze GWs are advanced enough. A key aspect of GW searches are waveform models, which encapsulate our best predictions for the gravitational radiation under a certain set of parameters, and that need to be cross-correlated with data to extract GW signals. Waveforms must be very accurate to avoid missing important physics in the data, which might be the key to answer the fundamental questions of GW astrophysics. The continuous improvements of the current LIGO-Virgo detectors, the development of next-generation ground-based detectors such as the Einstein Telescope or the Cosmic Explorer, as well as the development of the Laser Interferometer Space Antenna (LISA), demand accurate waveform models. While available models are enough to capture the low spins, comparable-mass binaries routinely detected in LIGO-Virgo searches, those for sources from both current and next-generation ground-based and spaceborne detectors must be accurate enough to detect binaries with large spins and asymmetry in the masses. Moreover, the thousands of sources that we expect to detect with future detectors demand accurate waveforms to mitigate biases in the estimation of signals’ parameters due to the presence of a foreground of many sources that overlap in the frequency band. This is recognized as one of the biggest challenges for the analysis of future-detectors’ data, since biases might hinder the extraction of important astrophysical and cosmological information from future detectors’ data. In the first part of this thesis, we discuss how to improve waveform models for binaries with high spins and asymmetry in the masses. In the second, we present the first generic metrics that have been proposed to predict biases in the presence of a foreground of many overlapping signals in GW data. For the first task, we will focus on several classes of analytical techniques. Current models for LIGO and Virgo studies are based on the post-Newtonian (PN, weak-field, small velocities) approximation that is most natural for the bound orbits that are routinely detected in GW searches. However, two other approximations have risen in prominence, the post-Minkowskian (PM, weak- field only) approximation natural for unbound (scattering) orbits and the small-mass-ratio (SMR) approximation typical of binaries in which the mass of one body is much bigger than the other. These are most appropriate to binaries with high asymmetry in the masses that challenge current waveform models. Moreover, they allow one to “cover” regions of the parameter space of coalescing binaries, thereby improving the interpolation (and faithfulness) of waveform models. The analytical approximations to the relativistic two-body problem can synergically be included within the effective-one-body (EOB) formalism, in which the two-body information from each approximation can be recast into an effective problem of a mass orbiting a deformed Schwarzschild (or Kerr) black hole. The hope is that the resultant models can cover both the low-spin comparable-mass binaries that are routinely detected, and the ones that challenge current models. The first part of this thesis is dedicated to a study about how to best incorporate information from the PN, PM, SMR and EOB approaches in a synergistic way. We also discuss how accurate the resulting waveforms are, as compared against numerical-relativity (NR) simulations. We begin by comparing PM models, whether alone or recast in the EOB framework, against PN models and NR simulations. We will show that PM information has the potential to improve currently-employed models for LIGO and Virgo, especially if recast within the EOB formalism. This is very important, as the PM approximation comes with a host of new computational techniques from particle physics to exploit. Then, we show how a combination of PM and SMR approximations can be employed to access previously-unknown PN orders, deriving the third subleading PN dynamics for spin-orbit and (aligned) spin1-spin2 couplings. Such new results can then be included in the EOB models currently used in GW searches and parameter estimation studies, thereby improving them when the binaries have high spins. Finally, we build an EOB model for quasi-circular nonspinning binaries based on the SMR approximation (rather than the PN one as usually done). We show how this is done in detail without incurring in the divergences that had affected previous attempts, and compare the resultant model against NR simulations. We find that the SMR approximation is an excellent approximation for all (quasi-circular nonspinning) binaries, including both the equal-mass binaries that are routinely detected in GW searches and the ones with highly asymmetric masses. In particular, the SMR-based models compare much better than the PN models, suggesting that SMR-informed EOB models might be the key to model binaries in the future. In the second task of this thesis, we work within the linear-signal ap- proximation and describe generic metrics to predict inference biases on the parameters of a GW source of interest in the presence of confusion noise from unfitted foregrounds and from residuals of other signals that have been incorrectly fitted out. We illustrate the formalism with simple (yet realistic) LISA sources, and demonstrate its validity against Monte-Carlo simulations. The metrics we describe pave the way for more realistic studies to quantify the biases with future ground-based and spaceborne detectors. N2 - Wenn zwei kompakte Objekte wie Schwarze Löcher oder Neutronensterne kollidieren, wird der Raum und die Zeit um sie herum stark gekrümmt. Der effekt sind Störungen der Raumzeit, sogenannte Gravitationswellen, die sich im gesamten Universum ausbreiten. Mit den leistungsstarken und präzisen Netzwerken von Detektoren und der Arbeit vieler Wissenschaftler rund um den Globus kann man Gravitationswellen auf der Erde messen. Gravitationswellen tragen Informationen über das System, das sie erzeugt hat. Insbesondere kann man erfahren, wie sich die kompakten Objekte gebildet haben und woraus sie bestehen. Daraus lässt sich ableiten, wie sich das Universum ausdehnt, und man kann die Allgemeine Relativitätstheorie in Regionen mit starker Gravitation testen. Um diese Informationen zu extrahieren, werden genaue Modelle benötigt. Modelle können entweder numerisch durch Lösen der berühmten Einstein-Gleichungen oder analytisch durch Annäherung an deren Lösungen gewonnen werden. In meiner Arbeit haben wir den zweiten Ansatz verfolgt, um sehr genaue Vorhersagen für die Signale zu erhalten, die bei kommenden Beobachtungen durch Gravitationswellendetektoren verwendet werden können. KW - gravitational waves KW - Gravitationswellen KW - general relativity KW - allgemeine Relativitätstheorie KW - data analysis KW - Datenanalyse Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-576671 ER - TY - JOUR A1 - Grebenkov, Denis S. A1 - Metzler, Ralf A1 - Oshanin, Gleb T1 - A molecular relay race: sequential first-passage events to the terminal reaction centre in a cascade of diffusion controlled processes JF - New Journal of Physics (NJP) N2 - We consider a sequential cascade of molecular first-reaction events towards a terminal reaction centre in which each reaction step is controlled by diffusive motion of the particles. The model studied here represents a typical reaction setting encountered in diverse molecular biology systems, in which, e.g. a signal transduction proceeds via a series of consecutive 'messengers': the first messenger has to find its respective immobile target site triggering a launch of the second messenger, the second messenger seeks its own target site and provokes a launch of the third messenger and so on, resembling a relay race in human competitions. For such a molecular relay race taking place in infinite one-, two- and three-dimensional systems, we find exact expressions for the probability density function of the time instant of the terminal reaction event, conditioned on preceding successful reaction events on an ordered array of target sites. The obtained expressions pertain to the most general conditions: number of intermediate stages and the corresponding diffusion coefficients, the sizes of the target sites, the distances between them, as well as their reactivities are arbitrary. KW - diffusion KW - reaction cascade KW - first passage time Y1 - 2021 U6 - https://doi.org/10.1088/1367-2630/ac1e42 SN - 1367-2630 VL - 23 PB - IOP - Institute of Physics Publishing CY - Bristol ER - TY - GEN A1 - Grebenkov, Denis S. A1 - Metzler, Ralf A1 - Oshanin, Gleb T1 - A molecular relay race: sequential first-passage events to the terminal reaction centre in a cascade of diffusion controlled processes T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We consider a sequential cascade of molecular first-reaction events towards a terminal reaction centre in which each reaction step is controlled by diffusive motion of the particles. The model studied here represents a typical reaction setting encountered in diverse molecular biology systems, in which, e.g. a signal transduction proceeds via a series of consecutive 'messengers': the first messenger has to find its respective immobile target site triggering a launch of the second messenger, the second messenger seeks its own target site and provokes a launch of the third messenger and so on, resembling a relay race in human competitions. For such a molecular relay race taking place in infinite one-, two- and three-dimensional systems, we find exact expressions for the probability density function of the time instant of the terminal reaction event, conditioned on preceding successful reaction events on an ordered array of target sites. The obtained expressions pertain to the most general conditions: number of intermediate stages and the corresponding diffusion coefficients, the sizes of the target sites, the distances between them, as well as their reactivities are arbitrary. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1159 KW - diffusion KW - reaction cascade KW - first passage time Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-521942 SN - 1866-8372 ER -