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For many years, a team of physicists at the HTWG Konstanz has been shifting the focus of physics education from teaching “content” to teaching “methods”. An overview is given on the derived state. Several questions are addressed, such as: What are the advantages? Are there constraints and limits? How can a shift be achieved? What are student reactions and how does other teaching staff deal with the new situation

Metal halide perovskites have attracted considerable attention as excellent candidates for application in solar cells. Despite their excellent performance, photovoltaic devices based on perovskite absorber’s wide-scale integration into industrial application is limited by their chemical and electrical instabilities. The central topic of this thesis is therefore to investigate thermodynamic aspects of point defects and the conduction mechanisms along with their implications for current–voltage characteristics i.e.,hysteresis in the solar cells. By application of three different methods, impedance spectroscopy, deep level transient spectroscopy and sweep rate dependent current–voltage characteristics as function of temperature, we show that understanding the fundamental aspects of mobile ionic defects in the material as well as the distribution of these defects in the device is essential for improving the stability and the device performance. We show that halide vacancy-interstitial pairs are present in all investigated perovskite compositions and these defects can lead to a significant reduction in the power conversion efficiency of perovskite solar cells., Metallhalogenid-Perowskite haben erhebliche Aufmerksamkeit als hervorragende Kandidaten für die Anwendung in Solarzellen. Trotz ihrer ausgezeichneten Leistung ist die breite Integration von photovoltaischen Geräten auf der Grundlage von Perowskit-Absorbern in die industrielle Anwendung durch ihre chemische und elektrische Instabilität begrenzt. Das zentrale Thema dieser Arbeit ist daher die Untersuchung der thermodynamischen Aspekte von Punktdefekten und der Leitungsmechanismen sowie deren Auswirkungen auf die Strom-Spannungs-Charakteristik, i.e., die Hysterese in den Solarzellen. Durch die Anwendung von drei verschiedenen Methoden, der Impedanzspektroskopie, der Transientenspektroskopie auf tiefer Ebene und der Sweep-Rate-abhängigen Strom-Spannungs-Charakteristik als Funktion der Temperatur, zeigen wir, dass das Verständnis der grundlegenden Aspekte der mobilen ionischen Defekte im Material sowie der Verteilung dieser Defekte in der Vorrichtung für die Verbesserung der Stabilität und der Leistung der Vorrichtung von wesentlicher Bedeutung ist. Wir zeigen, dass Halogenid-Vakanz-Zwischengitter-Paare in allen untersuchten Perowskit-Zusammensetzungen vorhanden sind und dass diese Defekte zu einer signiőkanten Verringerung der Energieumwandlungseffizienz von Perowskit-Solarzellen führen können.

In der Dissertation werden Aspekte zukünftiger Mobilität mit Methoden aus der theoretischen Physik und der Wissenschaft komplexer Systeme. Dazu werden mathematische Modelle und Simulationen entwickelt, die zentrale Aspekte der Dynamik von Mobilitätssystemen abbilden. Ziel ist es, den Einfluss spezifischer Parameter auf die gesamte systemische Dynamik zu verstehen und vorherzusagen, sowie nichtlineare, kollektive Effekte aufzudecken.

Random matrix theory (RMT) is a mathematical framework that has found profound applications in physics, particularly in the study of many-body systems. Its success lies in its ability to predict universal statistical properties of complex systems, independent of the specific details. This thesis explores the application of RMT to two classes of many-body systems: quantum and stochastic many-body systems. Within the quantum framework, this work focuses on the Bose-Hubbard system, which is paradigmatic for modeling ultracold atoms in optical traps. According to RMT and the Eigenstate Thermalization Hypothesis (ETH), eigenstate-to-eigenstate fluctuations of expectation values of local observables decay rapidly with the system size in the thermodynamic limit at sufficiently large temperatures. Here, we study these fluctuations in the classical limit of fixed lattice size and increasing boson number. We find that the fluctuations follow the RMT prediction for large system sizes but deviate substantially for small lattices. Partly motivated by these results, the Bose-Hubbard model on three sites is studied in more detail. On few sites, the Bose-Hubbard model is known to be a mixed system, being neither fully chaotic nor integrable. We compare energy-resolved classical and quantum measures of chaos, which show a strong agreement. Deviations from RMT predictions are attributed to the mixed nature of the few-site model. In the context of stochastic systems, generators of Markov processes are studied. The focus is on the spectrum. We present results from two investigations of Markov spectra. First, we investigate the effect of sparsity on the spectrum of random generators. Dense random matrices previously used as a model for generic generators led to very large spectral gaps and therefore to unphysically short relaxation times. In this work, a model of random generators with adjustable sparsity — number of zero matrix elements — is presented, extending the dense framework. It

This thesis investigates the mechanically controlled break junctions, with a particular emphasis on elucidating the behaviour of molecular currents at room temperature. The core of this experimental investigation involves a detailed analysis of conductance, examining how it varies over time and with changes in the gap between electrodes. Additionally, this study thoroughly evaluates transmission properties, coupling effects, and current characteristics. A pivotal aspect of the research was the meticulous current measurement, followed by carefully selecting optimal data sets. This process set the stage for an in-depth analysis of resonant tunnelling phenomena observed through a single channel. Notably, these experiments were conducted under open atmospheric conditions at room temperature. A significant finding from this study is the recognition that our current model requires refinement. This adjustment is necessary to more accurately encapsulate a broader spectrum of molecular transport mechanisms. Furthermore, this work significantly advances our comprehension of quantum effects in single-molecule junctions, particularly concerning similar molecules to Corannulene extending to some organometallics. One of the essential disclosures is the identification of deviations in the transport model, primarily attributable to electron-electron interactions. This insight is crucial as it paves the way for developing a more comprehensive and precise model, enhancing our understanding of molecular-scale electronic transport.:List of Figures xi List of Tables xiii Acronyms xiii Terminology xv Symbols xvi Abstract xvii 1 Introduction 1 1.1 Motivation and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Molecular Electronics Background . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 RelatedWork, the State of Art . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4 Structure of the work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Das Beratungsangebot des Sächsischen Landesamtes für Umwelt, Landwirtschaft und Geologie (LfULG) richtet sich an familiär geführte landwirtschaftliche und gartenbauliche Betriebe, bei denen der Generationswechsel ansteht. Es umfasst eine Orientierung zu Gestaltungsmöglichkeiten und zeitlichen Abläufen und unterstützt bei der Kommunikation innerhalb der Familie. Redaktionsschluss: 01.02.2024

Laser-driven plasma accelerators can produce high-energy, high peak current ion beams by irradiating solid materials with ultra-intense laser pulses. This innovative concept attracts a lot of attention for various multidisciplinary applications as a compact and energy-efficient alternative to conventional accelerators. The maturation of plasma accelerators from complex physics experiments to turnkey particle sources for practical applications necessitates breakthroughs in the generated beam parameters, their robustness and scalability to higher repetition rates and efficiencies. This thesis investigates viable optimisation strategies for enhancing ion acceleration from thin foil targets in ultra-intense laser-plasma interactions. The influence of the detailed laser pulse parameters on plasma-based ion acceleration has been systematically investigated in a series of experiments carried out on two state-of-the-art high-power laser systems. A central aspect of this work is the establishment and integration of laser diagnostics and operational techniques to advance control of the interaction conditions for maximum acceleration performance. Meticulous efforts in continuously monitoring and enhancing the temporal intensity contrast of the laser system, enabled to optimise ion acceleration in two different regimes, each offering unique perspectives for applications. Using the widely established target-normal sheath acceleration (TNSA) scheme and adjusting the temporal shape of the laser pulse accordingly, proton energies up to 70 MeV were reliably obtained over many months of operation. Asymmetric laser pulses, deviating significantly from the standard conditions of an ideally compressed pulse, resulted in the highest particle numbers and an average energy gain ≥ 37 %. This beam quality enhancement is demonstrated across a broad range of parameters, including thickness and material of the target, laser energy and temporal intensity contrast. To overcome the energy scaling

In der Teilchenphysik existieren für zentrale Begriffe oftmals Synonyme. Beispielsweise wird für Botenteilchen auch die Bezeichnung Austauschteilchen oder Eichboson genutzt. Im Englischen finden sich analog force carrier, messenger particles oder gauge bosons. Es fehlt bisher an Übersichten über die Nutzung einzelner Termini, wie diese Begriffe im Deutschen und Englischem verwendet werden sowie welche Begründungen und Verstehenskontexte eine Rolle spielen. Aus linguistischer Perspektive zählt nicht nur der einzelne Begriff, sondern insbesondere der Frame (= konzeptuelle Wissenseinheit) der damit evoziert wird. Ziel der vorliegenden Arbeit war es, eine qualitative Inhaltsanalyse bezüglich der Fragestellung, wie vier zentrale Begriffe (Austausch, Wechselwirkung, Umwandlung, Stoß) in der Teilchenphysik genutzt werden, zu erarbeiten. Das Forschungsdesgin orientiert sich dabei an Methoden der qualitativen Forschung. Die Datenerhebung erfolgt auf zwei Wegen: Zum einen über eine computergestützte Dokumentenanalyse ausgewählter Fachbücher der Teilchenphysik in deutscher und englischer Sprache; zum anderen mit leitfadengestützten Expert:inneninterviews, welche am Rande der 26. IPPOG-Tagung 2023 am CERN durchgeführt wurden.

Metal halide perovskites have attracted considerable attention as excellent candidates for application in solar cells. Despite their excellent performance, photovoltaic devices based on perovskite absorber’s wide-scale integration into industrial application is limited by their chemical and electrical instabilities. The central topic of this thesis is therefore to investigate thermodynamic aspects of point defects and the conduction mechanisms along with their implications for current–voltage characteristics i.e.,hysteresis in the solar cells. By application of three different methods, impedance spectroscopy, deep level transient spectroscopy and sweep rate dependent current–voltage characteristics as function of temperature, we show that understanding the fundamental aspects of mobile ionic defects in the material as well as the distribution of these defects in the device is essential for improving the stability and the device performance. We show that halide vacancy-interstitial pairs are present in all investigated perovskite compositions and these defects can lead to a significant reduction in the power conversion efficiency of perovskite solar cells., Metallhalogenid-Perowskite haben erhebliche Aufmerksamkeit als hervorragende Kandidaten für die Anwendung in Solarzellen. Trotz ihrer ausgezeichneten Leistung ist die breite Integration von photovoltaischen Geräten auf der Grundlage von Perowskit-Absorbern in die industrielle Anwendung durch ihre chemische und elektrische Instabilität begrenzt. Das zentrale Thema dieser Arbeit ist daher die Untersuchung der thermodynamischen Aspekte von Punktdefekten und der Leitungsmechanismen sowie deren Auswirkungen auf die Strom-Spannungs-Charakteristik, i.e., die Hysterese in den Solarzellen. Durch die Anwendung von drei verschiedenen Methoden, der Impedanzspektroskopie, der Transientenspektroskopie auf tiefer Ebene und der Sweep-Rate-abhängigen Strom-Spannungs-Charakteristik als Funktion der Temperatur, zeigen wir, dass das Verständnis der grundlegenden Aspekte der mobilen ionischen Defekte im Material sowie der Verteilung dieser Defekte in der Vorrichtung für die Verbesserung der Stabilität und der Leistung der Vorrichtung von wesentlicher Bedeutung ist. Wir zeigen, dass Halogenid-Vakanz-Zwischengitter-Paare in allen untersuchten Perowskit-Zusammensetzungen vorhanden sind und dass diese Defekte zu einer signiőkanten Verringerung der Energieumwandlungseffizienz von Perowskit-Solarzellen führen können.

Die Arktis erwärmt sich aus noch nicht vollständig geklärten Gründen drei- bis viermal schneller als der Rest der Erde. Wolken, die den Energiehaushalt der Oberfläche und den vertikalen Transport von Wärme und Feuchtigkeit über dem Meereis signifikant beeinflussen, werden durch die oft begrenzte Verfügbarkeit von tröpfchenbildenden Aerosolpartikeln beeinflusst. Diese Aerosol-Wolken-Wechselwirkungen sind schwer zu erfassen, da die untere Troposphäre zumeist komplex geschichtet ist. In dieser Doktorarbeit werden drei neue wissenschaftliche Veröffentlichungen vorgestellt, die unternommenen wurden, um die vertikale Aerosolverteilung über dem arktischen Meereis mit einem Fesselballon zu untersuchen. Im ersten Schritt wurde eine neue Aerosolmessplattform, genannt CAMP, für Fesselballoneinsätze konzipiert. CAMP beinhaltet vier mobile Instrumente in einem Gehäuse, das vor Umwelteinflüssen schützt, zur Messung der Mikrophysik von Aerosolpartikeln. Die Sensoren wurden gründlich kalibriert und charakterisiert und die Leistung der Plattform in Feldtests bewertet. Im zweiten Schritt wurden während einer Forschungsexpedition in der zentralen Arktis Fesselballonmessungen von einer Eisscholle aus durchgeführt. Neben CAMP wurden vier weitere Instrumentenpakete mit dem Ballon geflogen, um die atmosphärische Grenzschicht zu charakterisieren. Die gewonnenen Daten wurden validiert und der wissenschaftlichen Gemeinschaft frei zur Verfügung gestellt. Im dritten Schritt wurden vierunddreißig Aerosolprofile analysiert und die Auswirkungen des Luftmassenursprungs und der Troposphärenstruktur auf die vertikale Aerosolverteilung bewertet. Die Ergebnisse der Studie zeigten, dass die Aerosolpartikel oberhalb der Grenzschicht für Wolken-Wechselwirkung von wesentlicher Bedeutung sind. Eine Analyse der Kopplung zwischen Wolke und Oberfläche zeigte deutlich, dass der vertikale Transport von Aerosolen von der Oberfläche zur Wolkenbasis in entkoppelten Wolkenfällen gehemmt war. Sekundäre Partikelbildu, The Arctic is warming three to four times faster than the rest of the Earth for reasons that are not yet fully understood. Clouds, which significantly affect the surface energy budget and the vertical transport of heat and moisture above sea ice, are influenced by the often limited availability of droplet-forming aerosol particles. However, aerosol-cloud interactions are challenging to assess due to the commonly complex structured lower troposphere. This doctoral thesis presents three novel scientific publications that detail the steps taken to investigate the vertical aerosol distribution above the Arctic sea ice with a tethered balloon. In the first step, the new cubic aerosol measurement platform (CAMP) was designed for tethered balloon deployments. CAMP contains four mobile instruments in an environmentally robust housing for measuring aerosol particle microphysics. The sensors were thoroughly calibrated and characterized, and the platform performance was evaluated in field tests. Secondly, tethered balloon measurements were performed from an ice floe during a research expedition into the central Arctic. CAMP and four other instrument packages were deployed with the balloon to characterize the atmospheric boundary layer. The obtained data were validated and made freely available to the scientific community. Lastly, thirty-four aerosol profiles were analyzed, and the impact of the air mass origin and the lower tropospheric structure on the vertical aerosol distribution was evaluated. The study results showed that the aerosol particles above the boundary layer are essential for interactions with low-level clouds. An analysis of the cloud-surface coupling state clearly demonstrated inhibited vertical transport of aerosols from the surface to the cloud base in decoupled cloud cases. Secondary particle formation initiated by low-level transport of precursor vapors from south of the ice edge caused high concentrations of smaller particles above the boundary layer. In

Active galactic nuclei (AGN) jets are one of the most fascinating objects in the Universe. Since their discovery by Curtis about a hundred years ago, we uncovered many of their secrets, but fundamental mechanisms related to the nature of their launching, evolution and multiwavelength variability are still not perfectly understood. In this dissertation work, I present my research on very long baseline interferometry (VLBI) observations of AGN jets, investigating the above-mentioned of topics. After the introductory chapters describing phenomena related to AGN (Ch. 3), I describe the observational method, VLBI (Ch. 4), which enables radio astronomers to reach unprecedented spatial resolutions to study the central parsec region of AGN. AGN emit radiation throughout the entire electromagnetic spectrum, and the correlation of the activity between the different wavebands is a widely investigated topic. This includes temporal variations in brightness and polarization, ejection of new jet features in connection to elevated flux density states or detection of high-energy astroparticles associated with a given object, as well as common characteristics of astroparticle-emitter sources. In this dissertation, I research the link between the radio and the gamma-ray activity in AGN jets using VLBI imaging techniques. In Chapter 5 I present the first images from the 2.3-GHz monitoring of the TANAMI Collaboration targeting the TeV-emitter AGN of the southern sky. The goal of the study is to prove the viability of such a program, as many of the objects are extremely faint, and more importantly, to investigate the characteristics of TeV-detected objects. When analyzing this biased sample of twenty-four TeV-emitter AGN, I found that the core brightness temperatures shows an inverse relation with synchrotron peak frequency, and a direct relationship with the 0.1-100 GeV gamma-ray flux density. In addition, the median and average core brightness temperature of the sample is a magnitude l

The heart of every galaxy in the universe is home to an awesome monster: a supermassive black hole (SMBH). Reaching masses of millions to billions of times that of our sun, they are among the most powerful sources of energy in the universe. They are surrounded by hot, magnetized plasma, some of which has the unfortunate fate to be accreted and swallowed by the black hole. A small fraction of it is, however, saved by magnetic fields– and is launched thousands of light years into interstellar space, in the form of highly collimated relativistic jets. Such an SMBH-powered system is known as an active galactic nucleus (AGN). Even though AGN have been an active subject of research for almost a century, many aspects of their inner workings remain obscured. What is the nature of the SMBH residing at the center of the AGN? What is the mechanism to launch relativistic jets? How are the emission processes in different parts of the electromagnetic spectrum connected? What is the nature of the commonly observed moving features in relativistic jets, and how general is our established description of AGN? This thesis addresses a number of these questions, in an attempt to incrementally advance the field, having converged into three publications. These are preceded by four introductory chapters describing the methodology of observational radio astronomy, the anatomy of AGN, relevant radiative processes, as well as the basics of numerical simulations. With ongoing advances in observational techniques, direct images of SMBHs can be obtained to extreme resolutions. The first work presented in this thesis is concerned with the interpretation of present and future observational results: Probing the space time and accretion model for the Galactic Center: Comparison of Kerr and dilaton black hole shadows (Röder et al., 2023, A&A vol. 671, A143), investigates the influence of models for the accretion mechanism, emission processes, and the background spacetime, on our ability to determine t

Jupiter’s aurora is the most powerful in our solar system and challenges our understanding due to its variable shape and intensities. The Jupiter magnetosphere, influenced by rapid rotation, a strong magnetic field, and Io’s mass load, was studied extensively by the Juno mission, which arrived in 2016. Juno’s observations of the auroral region, especially its low-altitude polar crossings, revealed diverse phenomena, questioning existing knowledge. The hypothesis that powerful wave-particle interactions cause auroral acceleration is gaining increasing attention while raising questions about the initial assumption that static electron potentials are responsible for intense emission. Measurements supporting this hypothesis are rarely seen, making it difficult to compare them with the auroral features we observe on Earth. This study aims to explore acceleration theories driving Jupiter’s auroras by calculating electron distribution occurrence rates and studying their connection with magnetic field changes and ultraviolet emissions, which is essential for understanding the auroras. Therefore, we combine data from 20 flybys, offering a global perspective by statistically comparing the perijoves observations, rather than focusing on individual local observations. The approach of this is to connect associated various instrument data, combining magnetic fields, electron intensities, and UV emissions, to better understand the electron acceleration mechanisms and processes that generate the intense auroral features. This study found a link between the intense auroras on Jupiter and broadband broad electron energy distributions and azimuthal magnetic field deviations of several 100 nT, indicating field-aligned currents. Thus, stochastic processes might predominantly accelerate intense electron beams, occasionally involving electrostatic structures. Upward and downward beams aligned with the associated currents and bidirectional distributions in downward current regions are obse

Active matter systems show remarkable self-organization across different scales, from micron-size bacteria to meter-size birds. Examples extend beyond biological systems such as flocks of birds, animal herds, and bacterial biofilms, to artificial systems like active colloids and swarms of microrobots. The global patterns and structures often occur purely based on local interactions among neighbors. Emergent properties and functions go beyond what individual components can achieve on their own. Some important features of such systems are active non-equilibrium behavior, non-reciprocal interactions, information processing, and self-steering. In our model of intelligent active Brownian particles (iABPs), information about the position and orientation of neighboring particles obtained through directed visual and isotropic perception, respectively, is used to adjust the propulsion direction. We start with the role of visual perception, where an iABP can sense the instantaneous position of neighboring iABPs within a vision cone (VC) and vision range. Several non-equilibrium structures like motile worms, worm-aggregate coexistence, aggregates, dilute-gas, and compact or dispersed cluster phases are obtained, depending on the system parameters. The maneuverability due to visual signal, activity, density, vision angle, and vision range determine the location and extent of these phases in the phase diagram. The analysis of the particle’s mean-square displacement shows ABP-like dynamics for dilute systems and the worm phase. We then delve into the interplay of visual perception and alignment interactions. The maneuverability due to visual signal and polar alignment determines the selforganization. Various non-equilibrium dynamical aggregates – like motile worm-like swarms and milling, and compact or dispersed clusters – are obtained. Strong polar alignment favors elongated worm-like swarms, which show super-diffusive motion over a much longer time range than individual ABPs. T

This thesis explores the use of high-intensity terahertz (THz) pulses to uncover new physical phenomena in various materials. It investigates the nonlinear conductivity of the transition metal oxide (Sr,Ca)RuO3, revealing strong third harmonic generation linked to electron transport and heavy quasiparticles. In the superconductor MgB2, THz pulses probe the elusive Higgs mode using harmonic generation in magnetic fields. The ferrimagnetic garnet (Gd,Bi)3Fe5O12 displays tunable magnetization dynamics influenced by cavity effects and Zeeman torque. These findings enhance our understanding of THz spectroscopy and its applications in material science.

In einer naturwissenschaftlich geprägten Gesellschaft stellt Teilhabe derzeit und zukünftig einen elementaren Faktor dar. Zur Teilhabe zählen: naturwissenschaftliche Fragestellungen zu erkennen, naturwissenschaftliches Wissen anzuwenden und Schlussfolgerungen zur Entscheidungsfindung zu treffen. Theoretische und praktische Kenntnisse naturwissenschaftlicher Arbeits- und Denkweisen, wie das Experimentieren, sind dafür essenzielle Voraussetzungen. Dementsprechend hat ein inklusiver (Naturwissenschafts-)Unterricht die explizite Aufgabe, eine Teilhabe für alle Lernenden zu ermöglichen. Diese Forderung ist infolge der Ratifizierung der UN-Behindertenrechtskonvention noch stärker in den Fokus gerückt. Es wurden bereits erste Schritte eingeleitet, die eine gleichberechtigte Teilhabe an und durch naturwissenschaftliche Bildung für alle Lernenden realisieren sollen. Da die Thematik Physikunterricht im Bildungsgang Geistige Entwicklung bisher stiefmütterlich behandelt wurde – es gibt nur marginale wissenschaftliche und praktische Beiträge dazu –, stellt sich die Frage, ob die Forderung nach einer Teilhabe für Lernende im Bildungsgang Geistige Entwicklung bislang reine Makulatur ist. Um möglichst vielen von ihnen eine Teilhabe am Physikunterricht – und damit an einer naturwissenschaftlich geprägten Gesellschaft – zu ermöglichen, ist es daher längst überfällig, die Zugangsmöglichkeiten für sie zu optimieren. Dies kann nur durch eine Vernetzung gelingen. Die vorliegende Arbeit nimmt sich dieser Aufgaben an. Im Sinne des Design-Based Research-Ansatzes werden theoretisch und empirisch fundiert Gestaltungsprinzipien zum physikalischen Experimentieren im Bildungshang Geistige Entwicklung erarbeitet und interdisziplinär verknüpft. Darüber hinaus fließen Forschungsergebnisse zu den Themen Teilhabe im Unterricht, Forschendes Lernen, Cognitive Load Theory, barrierearmer Unterrichtsgestaltung, sprachsensible Vermittlung von Bildungsinhalten, Einsatz von Tablets und eBooks im Unterricht s

Quantum feedback control is a field of research that deals with the manipulation of quantum systems towards a goal, based on continuous observation of the systems. These control strategies have been identified as an essential part of the development of future quantum technologies. An example of this is the formulation of quantum error correction strategies for fault-tolerant quantum computing. The design of control strategies is a challenging task, however, as incomplete descriptions of the quantum system at hand and external noise factors often introduce uncertainties into the system, leading to performance degradation. In this thesis, we focus on the use of machine learning based approaches to find quantum control feedback strategies. These approaches have demonstrated the ability to find near-optimal and robust strategies. In a first study, we develop a control strategy for quantum error correction on topological surface codes in the form of a hierarchical decoder. Using a combination of machine learning and combinational decoding, we were able to demonstrate scalable decoding. We achieved nearly linear-time scaling, while still maintaining a high precision decoding comparable to state-of-the-art conventional decoding strategies. The robustness of the decoding strategies is demonstrated through performing tests on different error models including depolarizing noise and faulty syndrome measurements, as well as by changing the underlying error correction code to the rotated surface code. Analyzing the correction applied by the hierarchical decoder provides us with insight into the learned strategies and identifies possible strengths and weaknesses of the decoder, allowing for possible further developments of machine learning and algorithmic decoders based on these findings. In a second study, we investigate the use of reinforcement learning for quantum feedback control. Since reinforcement learning encompasses model-free approaches, it is a prime candidate for find

Significance Cerebrospinal fluid (CSF) rhinorrhea (leakage of brain fluid from the nose) can be difficult to identify and currently requires invasive procedures, such as intrathecal fluorescein, which requires a lumbar drain placement. Fluorescein is also known to have rare but significant side effects including seizures and death. As the number of endonasal skull base cases increases, the number of CSF leaks has also increased for which an alternative diagnostic method would be highly advantageous to patients. Aim We aim to develop an instrument to identify CSF leaks based on water absorption in the shortwave infrared (SWIR) without the need of intrathecal contrast agents. This device needed to be adapted to the anatomy of the human nasal cavity while maintaining low weight and ergonomic characteristics of current surgical instruments. Approach Absorption spectra of CSF and artificial CSF were obtained to characterize the absorption peaks that could be targeted with SWIR light. Different illumination systems were tested and refined prior to adapting them into a portable endoscope for testing in 3D-printed models and cadavers for feasibility. Results We identified CSF to have an identical absorption profile as water. In our testing, a narrowband laser source at 1480 nm proved superior to using a broad 1450 nm LED. Using a SWIR enabling endoscope set up, we tested the ability to detect artificial CSF in a cadaver model. Conclusions An endoscopic system based on SWIR narrowband imaging can provide an alternative in the future to invasive methods of CSF leak detection.

Articulatory synthesis generates speech sounds by simulating the physical phenomena involved in speech production. The accuracy of the physical modelling is expected to affect the naturalness of the synthesis: the more realistic the description is, the greater the naturalness is expected to be. In this work, the accuracy of acoustic wave propagation in the vocal tract was evaluated with two perceptual experiments. Sustained vowels generated using a one-dimensional acoustic model, a three-dimensional acoustic model and an artificial bandwidth extension algorithm (without a physical basis) were compared. Since the difference between the acoustic methods tested affects mainly the frequencies above 4 kHz, we ensured that the low frequency part of the stimuli, up to 4 kHz, was similar. Thus, the participants' responses were based only on the differences at high frequency. The first experiment was a pair comparison, in which the participants had to select the more natural sounding stimuli. In the second experiment, the participants had to rate the naturalness of the stimuli on a linear scale. The results confirmed that a more accurate physical modeling leads to greater naturalness. However, this was limited to the phonemes /o/ and /u/, for which transverse resonances in the anterior vocal tract may play an important role that only a 3D acoustic simulation can accurately represent. It was also found that male stimuli were perceived as significantly more natural than female ones. However, voice quality did not affect naturalness.

Complex and networked dynamical systems characterize the time evolution of most of the natural and human-made world. The dimension of their state space, i.e., the number of (active) variables in such systems, arguably constitutes their most fundamental property yet is hard to access in general. Recent work [Haehne et al., Phys. Rev. Lett. 122, 158301 (2019)] introduced a method of inferring the state space dimension of a multi-dimensional networked system from repeatedly measuring time series of only some fraction of observed variables, while all other variables are hidden. Here, we show how time series observations of one single variable are mathematically sufficient for dimension inference. We reveal how successful inference in practice depends on numerical constraints of data evaluation and on experimental choices, in particular the sampling intervals and the total duration of observations. We illustrate robust inference for systems of up to N = 10 to N = 100 variables by evaluating time series observations of a single variable. We discuss how the faithfulness of the inference depends on the quality and quantity of collected data and formulate some general rules of thumb on how to approach the measurement of a given system.

The development of an organism starting from a fertilized egg involves the self-organized formation of patterns and the generation of shape. Patterns and shapes are characterized by their geometry, i.e. angles and distances between features. In this thesis, we set out to understand how the given geometry of pattern and shape of a living system feeds back into the evolution of this geometry. We focus on two fundamental developmental processes: axis specification and gastrulation. Both processes rely on the directed movements of cells and molecules driven by molecular force generation. Here, we ask how the geometry of an embryo guides such active flows. Active flows are often confined to the surface of a cell or embryo which is usually curved. We use the hydrodynamic theory of active surfaces to investigate how this curvature impacts on flows that are driven by patterns of mechanical activity. Using a minimal model of the cell cortex, we find that active cortical stresses can drive a rotation of the cell that aligns the chemical pattern of the stress regulator with the geometry of the cell surface. In particular, we find that active tension in the cytokinetic ring ensures that a cell divides along its longest axes, a common phenomenon known as Hertwig’s rule. As a consequence, the body axes of the C. elegans embryo are aligned with the geometry of the egg shell. We next set out to understand the impact of surface geometry on flows and patterns in more complex geometries. We focus in particular on localized sources of mechanical activity in curved fluid films. Such active particles act as sensors of the surface geometry, as the viscosity relates the local flow field to the large-scale geometry of the fluid film. We find that the impact of an anisotropic surface geometry on the flow field can generally be understood in terms of effective gradients of friction and viscosity. With this, we show that contractile points in a fluid film are attracted by protrusions and saddl

In diesem Bericht werden die Ergebnisse einer Online-Befragung dargelegt, die das Wissen über, die Nutzung von und die Hindernisse bei der Implementierung von evidenzbasierten Lehrkonzepten von Dozierenden im Fach Physik an deutschen Hochschulen und Universitäten abfragte. Zeitraum der Erhebung war Oktober 2023 bis November 2023, wobei ca. 1950 Personen angeschrieben wurden und 269 vollständige Fragebögen zur Auswertung vorlagen. Die in Selbstauskunft benannten Haupthindernisse liegen vor allem im Faktor Zeit (zusätzliche Vorbereitungszeit, generell hohe Arbeitslast) und zum zweiten auf der Seite der Studierenden, denen eine zu geringe Anwesenheit und Lernbereitschaft zugeschrieben wird. Neben der detaillierten Auswertung der Umfrage werden verschiedene Gruppenvergleiche präsentiert, die eine weitergehende Interpretation der Umfrageergebnisse erlauben.:1 Einführung 2 Forschungsstand 2.1 Wissen über und Nutzung von evidenzbasiertes Lehrkonzepte 2.2 Allgemeine Hindernisse bei der Umsetzung evidenzbasierter Konzepte 2.3 Hindernisse bei der langfristigen Etablierung evidenzbasierter Lehrkonzepte 3 Methodik 3.1 Fragebogenerstellung 3.2 Zielgruppe 3.3 Datenerhebung 3.4 Datenanalyse 4 Ergebnisse 4.1 Rücklaufquote und abgebrochene Teilnahmen 4.2 Demographie, Breite des Felds der Befragten 4.3 Aktuelle Gestaltung von Lehrveranstaltungen 4.3.1 Teilnehmerzahl 4.3.2 Zeitanteile Lehrenden-/Lernendenaktivität 4.4 Wissen über und Nutzung von evidenzbasierten Lehrkonzepten 4.4.1 Peer Instruction 4.4.2 Interactive Lectures 4.4.3 Think-Pair-Share 4.4.4 Just In Time Teaching 4.4.5 Studio Style Classrooms 4.4.6 Problem Based Learning 4.4.7 Vergleich Bekanntheit, Nutzer- und Abbrecherzahlen der Lehrkonzepte 4.5 Hindernisse bei der Nutzung von evidenzbasierten Lehrkonzepten 4.6 Bedarf für Unterstützungsangebote und Weiterbildungsmöglichkeiten 4.7 Freitextkommentare 4.8 Vergleich von Teilnehmer-Gruppen 4.8.1 Teilnehmende mit vollständigem Fragebogen und Abbrecher der Umfrage 4.8.2 Nutzer

Quantum technology and devices, from mobile phones to autonomous vehicles, have become integral to our daily lives. Ongoing developments aim to enhance the performance of these quantum systems through fundamental and applied research. For example, creating a quantum photonic integrated circuit (QPIC) in silicon will bring us closer to a practical quantum computer. A single-photon telecom emitter in silicon was the missing link for practically realising QPICs. To address this, we have overcome the challenge of integrating single-photon emitters into silicon nanopillars. In this work, I present a scalable and industry-friendly fabrication protocol using metal-assisted chemical etching, which allows the fabrication of smooth and anisotropic nanostructures. Additionally, spectroscopic measurements confirm that the fabrication protocol does not create any colour centres emitting in the telecommunication band. Next, we use carbon broad-beam ion implantation to create telecom-photon emitting G-centres in silicon nanopillars. We measure a 20% enhancement in the photoluminescence signal from pillars compared to the bulk Si due to the waveguiding effect and a Debye-Waller factor of 12%. In addition, we have developed a wafer-scale broad beam ion irradiation protocol to create G-centres and W-centres in silicon. The second part presents the concept of a hybrid spin-mechanical system based on silicon carbide to enhance magnetic field sensitivity. In this work, the envisioned hybrid quantum system requires the spin associated with a silicon vacancy (V_Si) to be coupled with the phononic modes of a nanomechanical resonator or strings in 4H-SiC. For such high-optical-quality resonators, photoelectrochemical dopant-selective etching is the only viable method and is in progress. To contribute to the realisation of such a hybrid quantum system, we study high-mechanical-quality (Q∼10^4) 3C-SiC strings. We fabricate the strings using a standard top-down nanofabrication approach. Afterw

The main purpose of this thesis is to study quantum-electrodynamics (QED) in the presence of external background fields. We address this purpose by computing the Delbrück scattering amplitudes in the low-energy limit, the low-energy N-photon amplitudes in the presence of a constant field, the low-energy four-photon amplitudes in the presence of a constant magnetic field, the forward Compton scattering amplitudes in a constant magnetic field and the one-loop vertex correction in an arbitrary plane-wave field. In most cases, except for the vertex correction, we employ the worldline formalism to perform all calculations simultaneously for both scalar and spinor QED. We utilize the previously obtained result of the off-shell four-photon amplitude with two low- energy photons to calculate the circularly polarized amplitudes for the leading-order contributions to Delbrück scattering, assuming that the incoming and outgoing photons have low-energy. We compute the one-loop N-photon amplitudes in a constant background field considering off- shell low-energy photons in various field configurations. Assuming parallel magnetic and electric components of the background field enables us to obtain compact representations for these amplitudes involving only simple algebra and a single global proper-time integral with trigonometric integrands. Similarly, assuming a constant crossed field, we derive compact expressions for these amplitudes, represented by a single proper-time integral. The outcome of this integral, for fixed parameters, takes the form of a factorial function. The latter case is further refined by employing the spinor helicity formalism, where the helicity components are expressed solely in terms of Bernoulli numbers and spinor products. Moreover, for an arbitrary constant field, we obtain another representation of these amplitudes as series expansions in the external field. As an application, we compute the one-loop four-photon amplitudes in the presence of a pure ma

The transition dynamics in silicon rubber based isotropic magnetorheological (MR) elastomers in terms of the normal force induced by an external homogeneous magnetic field is experimentally addressed. The primary goal was to evaluate dynamic performances of the MR elastic isotropic composite using a transparently presented measuring system with known characteristics in contrast to few previous studies on the topic. It was found that an increase in the magnetic field leads to an increase in the induced force and a decrease in the response time of the MR elastomer. At the same time, both the use of coarse particles as magnetic filler and a significant reduction in the stiffness of the polymer matrix reduce the response time of the MR elastomer under study. The analysis carried out takes into account the dynamics of the electromagnetic coil and the eddy currents induced in the magnet circuit. The shortest response times obtained for various MR elastomer samples are in the range of 27–72 ms for the maximal used magnetic field with an induction of 230 mT. These times correspond to the fastest previously reported ones for MR elastomers and MR elastomer based systems. In addition, the obtained results indicate the presence of different mechanisms responsible for the measured magnetodeformational effect observed in MR elastomers.

The paper reports on a composite based on a polydimethylsiloxane matrix filled with liquid metal and magnetic hard microparticles. The effect of the concentration of such a complex filler on the elasticity and relative permittivity of the composite has been investigated. Inclusions of liquid metal provide improved permittivity compared to the unfilled matrix, while the stiffening effect is not as high as when the matrix is filled with solid particles alone. On the other hand, magnetic hard fillers allow the functionalisation of the composite in terms of its magnetic properties. It is also shown that changing the residual magnetisation of the composite has no significant effect on the elasticity and relative permittivity.

Zusammenfassung Die vorliegende Dissertation ist eine Monografie über die Entwicklung eines kostengünstigen, marktfähigen Magnetometers, welches als magnetisch sensitive Elemente Farbzentren („NV-Zentren“) in Diamantkristallen verwendet. Die Besonderheit dieser NV-Zentren ist, dass sie optisch angeregt und über ihre Photolumineszenzantwort ausgelesen werden können. Die Intensität der Photolumineszenz ist dabei das Maß für die Feldstärke eines äußeren Magnetfelds. Der besondere Reiz dieser Anwendung liegt in der Entwicklung eines sehr kompakten Messkopfs in der Form einer Strahler-Empfängereinheit, welche einen Diamantkristall mit einem Ensemble aus NV-Zentren beinhaltet. Die im Sensorkopf integrierte LED regt die Photolumineszenzantwort der NV-Zentren an, welche mit Hilfe der integrierten Photodioden ausgelesen wird. Ein zwischengeschaltetes Filter unterdrückt das Anregungslicht der LED. Diamant besitzt als Schmuckelement ungebrochen große Attraktivität und wird mit technisch aufwändigen Mitteln und Energieaufwand synthetisiert, sodass hohe Preise für optisch und elektronisch reine Diamantkristalle üblich sind. Einerseits die hohen Preise und andererseits die Unsicherheiten hinsichtlich der Qualitätsmerkmale der Diamantmaterialien können als Markteintrittsbarrieren für diamantbasierte Sensorprodukte gewertet werden. Daher wurden die durchgeführten Arbeiten in zwei technisch verknüpfte wissenschaftliche Untersuchungsfelder unterteilt, die beide die Skalierfähigkeit vereint. Im ersten Teil wurden erstmals Diamantproben aus dem Massenmarkt des kostengünstigen Diamantschleifpulvers auf die Eignung als magnetisch sensitives Element hin untersucht. Hierzu wurden in stickstoffhaltigen HPHT-Diamantschleifkörnern durch Bestrahlung mit hochenergetischen Elektronen hochkonzentrierte Ensembles der NV-Zentren generiert. Die Charakterisierung erfolgte vor dem Hintergrund der Nutzung in einem Magnetometer hinsichtlich der lateralen Verteilung im Kristall und der Sensitivität der N, This dissertation is a monograph on the development of a low-cost, marketable magnetometer that uses color centers ('NV centers') in diamond crystals as magnetically sensitive elements. The special feature of these NV centers is that they can be optically excited and read out via their photoluminescence response. The intensity of the photoluminescence is the measure of the field strength of an external magnetic field. The particular appeal of this application lies in the dessssssssssvelopment of a very compact measuring head in the form of a radiator-receiver unit, which contains a diamond crystal with an ensemble of NV centers. The LED integrated in the sensor head excites the photoluminescence response of the NV centers, which is read out with the aid of the integrated photodiodes. An intermediate filter suppresses the excitation light of the LED. The work carried out was therefore divided into two technically linked scientific fields of investigation, both of which combine scalability. On the one hand, diamond samples from the mass market of low-cost diamond grinding powder were analyzed for the first time with regard to their suitability as a magnetically sensitive element. For this purpose, highly concentrated ensembles of NV centers were generated in nitrogen-containing HPHT diamond abrasive grains by irradiation with high-energy electrons. The characterization was carried out against the background of the use in a magnetometer with regard to the lateral distribution in the crystal and the sensitivity of the NV ensembles to external magnetic fields. In this context, the following conflict of objectives became clear: On the one hand, low NV densities in the ppb to ppm range in an otherwise interference-free diamond volume are necessary to optimize the sensitivity to external magnetic fields, which leads to high decoherence times. On the other hand, high NV densities are advantageous for efficient detection of the photoluminescent light and for improving the sig

Covering around 30-40 % of the terrestrial surface, grasslands provide essential ecosystem functions vital for human well-being. Despite their importance, these ecosystems are under constant pressure from human intervention, leading to a tremendous decline in biodiversity. Consequently, monitoring and management efforts are urgently needed in order to preserve their biodiversity and ecological functions. Traditional biodiversity monitoring through in-situ vegetation surveys are the foundation of comprehensive biodiversity assessments. While these surveys provide detailed information on specific local plant communities, the resulting data are spatially confined to discrete sampling areas and repetitions are usually limited due to financial constraints. Nevertheless, the rapid ecosystem changes and the dramatic global biodiversity decline demand techniques that support large-scale biodiversity assessments at frequent intervals. Data collected by different remote sensing techniques, such as optical remote sensing, offer the potential to fulfill this need and significantly contribute to large-scale biodiversity monitoring. In optical remote sensing, sensors detect and analyze electromagnetic solar radiation reflected, emitted, or scattered from the Earth's surface. Plants interact with incident light by transmitting, absorbing, or reflecting it in different regions of the electromagnetic spectrum, creating a spectral reflectance pattern distinguishable from other surfaces on Earth. However, detecting grassland diversity from remote sensing data is particularly challenging due to the small size of individual grassland species, making them difficult to disaggregate even in high spatial resolution remote sensing data. Spectral pixel-to-pixel variability has been proposed as an approach to describe grassland diversity in remote sensing imagery. The fundamental premise, known as the Spectral Variability Hypothesis (hereafter SVH), suggests that increased spectral variability

Im Vergleich zum Rest der Erde erfährt die Arktis eine signifikant schnellere Klimaerwärmung, die unter dem Begriff Arktische Verstärkung bekannt ist und mit zahlreichen sich verstärkenden Prozessen und Mechanismen einhergeht. Wolken spielen aufgrund ihrer Mitwirkung in verschiedenen, gegensätzlichen Effekten eine zwiespältige und eine der unsichersten Rollen für die Veränderung des arktischen Klimasystems. Daher ist die Untersuchung arktischer Wolken und ihrer Effekte von essenzieller Bedeutung, um den arktischen Klimawandel besser zu verstehen und in Modellen repräsentieren zu können. Diese Arbeit quantifiziert den bodennahen Strahlungseffekt von Wolken (engl. cloud radiative effect, CRE) aus einer Kombination von flugzeuggetragenen Breitbandstrahlungsmessungen während tiefer Flugabschnitte unter meist bewölkten Bedingungen und Strahlungstransfersimulationen für wolkenlose Bedingungen. Die Flugzeugmessungen wurden über den gegensätzlichen offenen Ozean- und Meereisoberflächen während dreier jahreszeitlich unterschiedlicher Kampagnen in der Umgebung von Spitzbergen aufgenommen. Ziel dieser Arbeit ist die Untersuchung des Einflusses von Oberflächen-, Wolken- und thermodynamischen Eigenschaften sowie Sonnenzenitwinkel (SZW) auf Unterschiede des solaren, thermisch-infraroten (TIR) und gesamten (solar+TIR) CRE, in Bezug auf die verschiedenen Kampagnen und Oberflächentypen. Die Unterschiede des solaren CRE werden überwiegend vom Kontrast der Oberflächenalbedo und vom jahreszeitlich variierenden SZW angetrieben. Der stärkste Abkühlungseffekt wurde im Frühsommer festgestellt und die über offenem Ozean beobachtete Abkühlung war stärker als über Meereis (-259 W m-2 vs. -65 W m-2 im Frühsommer, -108 W m-2 vs. -17 W m-2 im Frühjahr). Außerdem beeinflussen von Wolken ausgelöste Veränderungen der Oberflächenalbedo den solaren CRE je nach SZW und Oberflächentyp. Der TIR CRE zeigte aufgrund der vorherrschenden opaken Wolken und einer Kompensierung von Effekten sich ändernder Temp, Compared to the rest of the globe, the Arctic experiences a significantly more rapid climate warming, which is called Arctic amplification and linked to numerous intensifying processes and mechanisms. Due to their contribution to and modification of various counteracting effects, clouds play one of the most ambiguous and uncertain roles in the change of the Arctic climate system. Thus, the investigation of clouds and their effects in the Arctic is essential to better understand and represent the Arctic climate change. This thesis quantifies the near-surface cloud radiative effect (CRE), which is obtained from a combination of airborne broadband radiation measurements during low-level flight sections under mostly cloudy conditions and radiative transfer simulations for cloud-free conditions. The airborne measurements were acquired over the contrasting open ocean and sea ice surfaces during three seasonally distinct campaigns in the vicinity of Svalbard. The objective of this thesis is to analyze the impact of surface, cloud, and thermodynamic properties as well as solar zenith angle (SZA) on differences of the solar, thermal-infrared (TIR), and total (solar+TIR) CRE with respect to the particular campaigns and surface types. The difference of the solar CRE is found to be predominantly driven by the contrasting surface albedo and the seasonally varying SZA. The strongest solar cooling effect was detected in early summer and the cooling observed over open ocean was stronger compared to sea ice (-259 W m-2 vs. -65 W m-2 in early summer, -108 W m-2 vs. -17 W m-2 in spring). Additionally, modifications of the surface albedo induced by the cloud-related illumination changes affect the solar CRE depending on SZA and surface type. The TIR CRE varied only weakly between campaigns and surface types (around 75 W m-2) due to the predominant opaque clouds and a compensation effect of changing temperature and humidity. Consequently, the variability of the total CRE is driven by th

The estimates of global black carbon direct radiative forcing are still subject to substantial uncertainties ranging between 0.20 and 0.42 Wm-2 . In order to reduce these uncertainties, we must improve the representation of complex black carbon mixing state when simulating their optical properties and applying in global models. The main motivation behind this thesis is to gain a better understanding of the current state of the art when it comes to accurately modeling the radiative properties of BC-containing aerosols. We investigated how the optical properties of BC fractal aggregates are affected by the physiochemical properties that change during their ageing cycle, such as the fractal dimension, organic fraction, and particle size. Findings from the numerical study showed that the radiative forcings of black carbon particles can vary by as much as 61% depending on the particle's morphology and chemical composition. This influence of morphology and composition is particularly relevant to polluted urban environments with high mass concentrations of BC. Starting with soot from laboratory-based soot generators, representative for freshly emitted soot in the atmosphere, different morphological representations of BC and their modelling techniques were extensively tested. For BC particles with mobility diameters ³ 70nm and coating fractions £ 60%, the morphological representation as fractal aggregates performed well for modeling their optical properties. Our findings indicate that the use of the volume mean diameter of BC-containing particles, rather than the number mean diameter, is beneficial for calculating their optical properties. In addition, considering the particles to be fractal aggregates for the entire size distribution significantly reduced the uncertainty in optical simulations to nearly ten percent. Investigations conducted in Delhi, a polluted Asian urban environment, confirmed that fractal morphology plays a critical role in reducing the overestimation o, Die Abschätzungen des Strahlungsantriebs von Schwarzem Kohlenstoff (engl. Black Carbon, BC) sind immer noch mit erheblichen Unsicherheiten behaftet, die zwischen 0.20 und 0.42 Wm-2 liegen. Um diese Unsicherheiten zu verringern, müssen wir die Darstellung des komplexen Mischungszustands von schwarzem Kohlenstoff bei der Simulation seiner optischen Eigenschaften in globalen Modellen verbessern. Die Hauptmotivation für diese Arbeit ist es, ein besseres Verständnis des aktuellen Stands des Wissens zu erlangen, wenn es um die genaue Modellierung der Strahlungseigenschaften von BC-haltigen Aerosolen geht. Es wurde ein grundlegendes Verständnis dafür geschaffen, wie die optischen Eigenschaften fraktaler BC-Aggregate durch die physiochemischen Eigenschaften beeinflusst werden, die sich während ihres Alterungszyklus ändern, wie die fraktale Dimension, der organische Anteil und der Partikelgröße. Die Ergebnisse der numerischen Studie zeigen, dass die Strahlungsantriebe von schwarzem Kohlenstoff je nach Morphologie und chemischer Zusammensetzung der Partikel um bis zu 61 % variieren können. Dieser Einfluss von Morphologie und Zusammensetzung ist besonders relevant für verschmutzte städtische Umgebungen mit hohen Massenkonzentrationen von BC. Ausgehend von Labormessungen mit Ruß-Generatoren, deren Emissionen frisch emittierten Ruß in der Atmosphäre entsprechen, wurden verschiedene morphologische Darstellungen von BC und deren Modellierungstechniken in umfassend getestet. Für BC-Partikel mit Mobilitätsdurchmessern ³ 70 nm und Beschichtungsanteilen £ 60% erwies sich die morphologische Darstellung durch fraktale Aggregate für die Modellierung ihrer optischen Eigenschaften als gut geeignet. Unsere Ergebnisse deuten darauf hin, dass die Verwendung des mittleren Volumendurchmessers von BC- haltigen Partikeln anstelle des mittleren Größendurchmessers für die Berechnung optischer Eigenschaften von Vorteil ist. Wenn die Partikel für die gesamte Größenverteilung als fraktale Aggregate be

Die Entwicklung und Herstellung neuer Materialsysteme gehört seit jeher zu den Triebkräften des technischen Fortschritts. Eine neue Klasse im Bereich der Legierungen, welche als Hochentropielegierungen (HEA) bezeichnet wird, gewinnt dabei seit etwa zehn Jahren zunehmend an Interesse. Konventionelle Legierungen besitzen einen Hauptbestandteil, welcher üblicherweise den Großteil der molaren Zusammensetzung ausmacht, wie z.B. Eisen im Stahl. Eine HEA hingegen zeichnet sich dadurch aus, dass mindestens vier verschiedene Elemente in ungefähr gleichen Volumenanteilen vorliegen. In diesem Fall kommt es zu einer deutlichen Zunahme der namensgebenden Mischungsentropie gegenüber der Enthalpie, was wiederum zur präferierten Bildung einphasiger, fester Lösungen anstelle von geordneten Metallphasen führt. Durch die nahezu unbegrenzte Anzahl möglicher Element- und Anteilskombinationen zur Bildung von HEAs ergibt sich ein mindestens ebenso großer Raum an potentiellen Anwendungen. Auf dem Gebiet der Materialwissenschaften wurden beispielsweise bereits HEAs mit herausragenden Verschleiß- und Korrosionseigenschaften demonstriert. Auch hinsichtlich Härte, Zug- und Umformfestigkeit oder Strahlungsbeständigkeit existieren vielversprechende Arbeiten, welche die hohe Anwendungsrelevanz von HEAs untermauern. Zahlreiche Herstellungsmethoden konnten dabei bereits erfolgreich auf HEAs angewandt werden, wobei alle Dimensionen, von wenige nm dünnen Schichten bis zu gegossenen oder gesinterten Volumenkörpern im cm-Bereich, abgedeckt werden. Der Einsatz moderner 3D-Drucktechnik erlaubt zudem die Kombination der herausragenden Materialeigenschaften von HEAs in komplex geformten Bauteilen. Trotz des hohen und noch immer rapide zunehmenden Forschungsinteresses an HEAs gibt es nur eine sehr überschaubare Anzahl an Arbeiten, die sich mit der gezielten Untersuchung struktureller, chemischer oder elektronischer Aspekte kristalliner HEA-Oberflächen auseinandersetzen. Ein Grund dafür ist die unzureichende, The development and fabrication of new material systems has always been one of the driving forces of technical progress. A new class in the field of alloys, known as high entropy alloys (HEA), has been gaining a rising interest since about ten years. Conventional alloys have one main component, which usually makes up the majority of the molar composition, such as iron in steel. A HEA, on the other hand, is characterized by the fact that at least four different elements are present in approximately equal volume proportions. In this case, there is a significant increase in the eponymous mixing entropy compared to the enthalpy, which in turn leads to the preferential formation of single-phase solid solutions instead of well ordered metallic phases. The almost unlimited number of possible element and proportion combinations to form HEAs results in at least an equally large range of potential applications. In the field of materials science, for example, HEAs with outstanding wear and corrosion properties have already been demonstrated. There is also promising work with regard to hardness, tensile and yield strength or irradiation resistance, which underlines the high applicational relevance of HEAs. Numerous manufacturing methods have already been successfully applied to HEAs, covering all dimensions, from layers as thin as a few nm to cast or sintered solids in the cm range. The use of modern 3D printing technology also allows the combination of the outstanding material properties of HEAs with complex shaped components. Despite the high and still increasing research interest in HEAs, there is only a very limited number of works that deal with the investigation of structural, chemical or electronic aspects of crystalline HEA surfaces. One reason for this is the insufficient availability of such systems, as the production of large crystals with high order usually requires very slow and well-controlled growth processes. One way to overcome this bottleneck is the deposition

Laser-driven plasma accelerators can produce high-energy, high peak current ion beams by irradiating solid materials with ultra-intense laser pulses. This innovative concept attracts a lot of attention for various multidisciplinary applications as a compact and energy-efficient alternative to conventional accelerators. The maturation of plasma accelerators from complex physics experiments to turnkey particle sources for practical applications necessitates breakthroughs in the generated beam parameters, their robustness and scalability to higher repetition rates and efficiencies. This thesis investigates viable optimisation strategies for enhancing ion acceleration from thin foil targets in ultra-intense laser-plasma interactions. The influence of the detailed laser pulse parameters on plasma-based ion acceleration has been systematically investigated in a series of experiments carried out on two state-of-the-art high-power laser systems. A central aspect of this work is the establishment and integration of laser diagnostics and operational techniques to advance control of the interaction conditions for maximum acceleration performance. Meticulous efforts in continuously monitoring and enhancing the temporal intensity contrast of the laser system, enabled to optimise ion acceleration in two different regimes, each offering unique perspectives for applications. Using the widely established target-normal sheath acceleration (TNSA) scheme and adjusting the temporal shape of the laser pulse accordingly, proton energies up to 70 MeV were reliably obtained over many months of operation. Asymmetric laser pulses, deviating significantly from the standard conditions of an ideally compressed pulse, resulted in the highest particle numbers and an average energy gain ≥ 37 %. This beam quality enhancement is demonstrated across a broad range of parameters, including thickness and material of the target, laser energy and temporal intensity contrast. To overcome the energy scaling

Diese Arbeit befasst sich mit der sogenannten Doppelkopie, welche erstmals im Rahmen von Streuamaplituden formuliert wurde und eine Beziehung zwischen Yang-Mills-Theorie und der Gravitation herstellt. Yang-Mills-Streuamplituden tragen sowohl kinematische Informationen als auch Informationen, die mit einer Eigenschaft namens Farbe verbunden sind. Die Doppelkopie besagt, dass die Ersetzung der Farbinformation in Yang-Mills-Amplituden durch eine andere Kopie ihrer kinematischen Information zu Gravitationsamplituden führt, sofern bestimmte algebraische Bedingungen erfüllt sind. Die algebraischen Bedingungen, die für die Doppelkopie erforderlich sind, deuten auf die Existenz einer Algebra hin, die der Kinematik der Yang-Mills-Theorie zugrunde liegt und die kinematische Algebra genannt wird. In den letzten fünfzehn Jahren hat die Doppelkopie die Art und Weise, wie Streuungsberechnungen in der Gravitation durchgeführt werden, revolutioniert, und dennoch bleibt ein grundsätzliches Verständnis der Doppelkopie und der kinematischen Algebra schwer zu fassen. In dieser Arbeit verlassen wir den Rahmen der Streuamplituden und behandeln dieses Problem mit Hilfe von Homotopie-Algebren, den mathematischen Strukturen, die perturbativen Feldtheorien, einschließlich ihrer Off-Shell Struktur, zugrunde liegen. Insbesondere die der Yang-Mills-Theorie zugrunde liegende Algebra lässt sich in algebraische Strukturen für Farbe und Kinematik faktorisieren. Unter Verwendung dieser Faktorisierung konstruieren wir explizit eine kinematische Algebra für die Yang-Mills Theorie bis zur quartischen Ordnung in der Störungstheorie. Dann ersetzen wir die Farbalgebra durch eine zweite Kopie der kinematischen Algebra und erhalten eine Gravitationstheorie bis hinzu und einschließlich der quartischen Wechselwirkungen. Außerdem erklären wir, inwiefern die kinematische Algebra die Struktur ist, die für die Konsistenz der resultierenden Gravitationstheorie verantwortlich ist. Unsere algebraische Herangehenswei, This thesis deals with a relation between Yang-Mills theory and gravity called the double copy, which was first formulated in the framework of scattering amplitudes. Yang-Mills scattering amplitudes carry kinematic information as well as information associated with a property called color. The double copy states that, provided that certain algebraic conditions are met, replacing the color information of Yang-Mills amplitudes with another copy of their kinematic information yields gravitational amplitudes. The algebraic conditions required by the double copy hint at the existence of an algebra underlying the kinematics of Yang-Mills called the kinematic algebra. In the last fifteen years, the double copy has revolutionized the way that scattering computations are performed in gravity, and, yet, a first principle understanding of the double copy and the kinematic algebra remains elusive. In this thesis we divert from scattering amplitudes and address this problem in the framework of homotopy algebras, which are the mathematical structures underlying perturbative field theories, including their off-shell structure. In particular, the algebra underlying Yang-Mills theory factorizes into color and kinematic algebraic structures. Using this factorization, we construct explicitly a kinematic algebra for Yang-Mills theory to quartic order in perturbation theory. Then, following the double copy, we replace the color algebra with a second copy of the kinematic algebra and we obtain gravity up to and including quartic interactions. Moreover, we explain how the kinematic algebra is responsible for the consistency of the resulting gravity theory. Our algebraic approach to the double copy is completely off-shell, gauge independent and local, and provides a novel perspective on the algebraic foundations and origins of the double copy.

The study at hand introduces a newapproach to characterize fatigue crack growth in small strain linear viscoelastic solids by configurational mechanics. In this study, Prony series with n-Maxwell elements are used to describe the viscoelastic behavior. As a starting point in this work, the local balance of energy momentum is derived using the free energy density. Moreover, at cyclic loading, the cyclic free energy substitutes the free energy. Using the cyclic free energy, the balance of cyclic energy momentum is obtained. The newly derived balance law at cyclic loading is appropriate for each cycle. In the finite element framework, nodal material forces and cyclic nodal material forces are obtained using the weak and discretized forms of the balance of energy momentum and cyclic energy momentum, respectively. The crack driving force and the cyclic crack driving force are determined by the nodal material forces and the cyclic nodal material forces, respectively. Finally, numerical examples are shown to illustrate path-independence of the domain integrals using material forces and cyclic material forces. The existence of the balance of energy momentum and cyclic energy momentum are also illustrated by numerical examples.

Die Entwicklung und Herstellung neuer Materialsysteme gehört seit jeher zu den Triebkräften des technischen Fortschritts. Eine neue Klasse im Bereich der Legierungen, welche als Hochentropielegierungen (HEA) bezeichnet wird, gewinnt dabei seit etwa zehn Jahren zunehmend an Interesse. Konventionelle Legierungen besitzen einen Hauptbestandteil, welcher üblicherweise den Großteil der molaren Zusammensetzung ausmacht, wie z.B. Eisen im Stahl. Eine HEA hingegen zeichnet sich dadurch aus, dass mindestens vier verschiedene Elemente in ungefähr gleichen Volumenanteilen vorliegen. In diesem Fall kommt es zu einer deutlichen Zunahme der namensgebenden Mischungsentropie gegenüber der Enthalpie, was wiederum zur präferierten Bildung einphasiger, fester Lösungen anstelle von geordneten Metallphasen führt. Durch die nahezu unbegrenzte Anzahl möglicher Element- und Anteilskombinationen zur Bildung von HEAs ergibt sich ein mindestens ebenso großer Raum an potentiellen Anwendungen. Auf dem Gebiet der Materialwissenschaften wurden beispielsweise bereits HEAs mit herausragenden Verschleiß- und Korrosionseigenschaften demonstriert. Auch hinsichtlich Härte, Zug- und Umformfestigkeit oder Strahlungsbeständigkeit existieren vielversprechende Arbeiten, welche die hohe Anwendungsrelevanz von HEAs untermauern. Zahlreiche Herstellungsmethoden konnten dabei bereits erfolgreich auf HEAs angewandt werden, wobei alle Dimensionen, von wenige nm dünnen Schichten bis zu gegossenen oder gesinterten Volumenkörpern im cm-Bereich, abgedeckt werden. Der Einsatz moderner 3D-Drucktechnik erlaubt zudem die Kombination der herausragenden Materialeigenschaften von HEAs in komplex geformten Bauteilen. Trotz des hohen und noch immer rapide zunehmenden Forschungsinteresses an HEAs gibt es nur eine sehr überschaubare Anzahl an Arbeiten, die sich mit der gezielten Untersuchung struktureller, chemischer oder elektronischer Aspekte kristalliner HEA-Oberflächen auseinandersetzen. Ein Grund dafür ist die unzureichende, The development and fabrication of new material systems has always been one of the driving forces of technical progress. A new class in the field of alloys, known as high entropy alloys (HEA), has been gaining a rising interest since about ten years. Conventional alloys have one main component, which usually makes up the majority of the molar composition, such as iron in steel. A HEA, on the other hand, is characterized by the fact that at least four different elements are present in approximately equal volume proportions. In this case, there is a significant increase in the eponymous mixing entropy compared to the enthalpy, which in turn leads to the preferential formation of single-phase solid solutions instead of well ordered metallic phases. The almost unlimited number of possible element and proportion combinations to form HEAs results in at least an equally large range of potential applications. In the field of materials science, for example, HEAs with outstanding wear and corrosion properties have already been demonstrated. There is also promising work with regard to hardness, tensile and yield strength or irradiation resistance, which underlines the high applicational relevance of HEAs. Numerous manufacturing methods have already been successfully applied to HEAs, covering all dimensions, from layers as thin as a few nm to cast or sintered solids in the cm range. The use of modern 3D printing technology also allows the combination of the outstanding material properties of HEAs with complex shaped components. Despite the high and still increasing research interest in HEAs, there is only a very limited number of works that deal with the investigation of structural, chemical or electronic aspects of crystalline HEA surfaces. One reason for this is the insufficient availability of such systems, as the production of large crystals with high order usually requires very slow and well-controlled growth processes. One way to overcome this bottleneck is the deposition

Spontaneous Raman spectroscopy (SR) is a versatile method for analysis and visualization of ferroelectric crystal structures, including domain walls. Nevertheless, the necessary acquisition time makes SR impractical for in situ analysis and large scale imaging. In this work, we introduce broadband coherent anti-Stokes Raman spectroscopy (B-CARS) as a high-speed alternative to conventional Raman techniques and demonstrate its benefits for ferroelectric domain wall analysis. Using the example of poled lithium niobate, we compare the spectral output of both techniques in terms of domain wall signatures and imaging capabilities. We extract the Raman-like resonant part of the coherent anti-Stokes signal via a Kramers–Kronigbased phase retrieval algorithm and compare the raw and phase-retrieved signals to SR characteristics. Finally, we propose a mechanism for the observed domain wall signal strength that resembles a Cerenkov-like behavior, in close analogy to domain wall signatures obtained by secondharmonic generation imaging.We, thus, lay here the foundations for future investigations on other poled ferroelectric crystals using B-CARS.

This doctoral thesis presents an extensive study on the applications of generalized coherent states (GCS) for the quantum dynamics of many-body systems. The research starts with exploring the fundamental properties of generalized coherent states, which are created by generators of the SU($M$) group acting on an extreme state, and demonstrating their role in representing ideal quantum condensates. A significant feature is the relationship between generalized coherent states and the more standard Glauber coherent states (CS). Similarities in their overcomplete and non-orthogonal nature are shown, alongside crucial differences with respect to $U(1)$ symmetry and entanglement properties, which generalized coherent states solely adhere to. Furthermore, this thesis delves into the nonequilibrium dynamics of GCS as well as Glauber CS under nonlinear interactions. Combining analytical analysis and numerical calculations, it is found that while their two-point correlation functions are equivalent in the thermodynamic limit, their autocorrelation functions exhibit distinctly different characteristics. It is proven analytically that the autocorrelation functions of the evolved GCS relate to the ones of the corresponding Glauber CS through a Fourier series relation, which arises due to the $U(1)$ symmetry of the GCS. A substantial part of this thesis is dedicated to investigating the dynamics of the Bose-Hubbard model, incorporating both nonlinear interaction and tunneling term. This investigation introduces a novel approach which employs an Ansatz for the wave function in terms of a linear combination of GCS, where the differential equations of all the variables are determined by the time-dependent variational principle without truncation. This innovative method is adeptly applied to the nonequilibrium dynamics in various scenarios, from the bosonic Josephson Junction model where some fundamental quantum effects can be revealed by a handful of GCS basis functions, to large sys