JGU-Hochschulschriften

Permanent URI for this collectionhttps://openscience.ub.uni-mainz.de/handle/20.500.12030/9264

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    Synthese und Untersuchung der physikalischen Eigenschaften von Verbindungen des FeMo1−xVxO4-Typs
    (2025) Osten, Felix Lukas; Möller, Angela; Tremel, Wolfgang
    In der vorliegenden Arbeit wurden die über Festkörperreaktionen zugänglichen Verbindungen des FeMo1−xVxO4-Typs in Hinsicht auf ihre strukturellen und physikalischen Eigenschaften untersucht und beschrieben. Mittels in-situ und ex-situ Röntgendiffraktion an Pulvern, sowie kalorimetrischen Untersuchungen (DSC) konnte das Phasenverhältnis der (α-/β)-FeMoO4 Polymorphe der FeMo1−xVxO4-Substitutionsreihen und dessen Beeinfl usssung durch Temperatur und chemischen Druck mittels Substitution mit FeVO4 beschrieben werden. Das Phasenverhältnis von Tieftemperatur- (α-Phase) zu Hochtemperaturphase (β-Phase) ist mit diesen Parametern vollständig einstellbar. Anhand der röntgenographischen Charakterisierung ergab sich eine Zuordnung zur bevorzugten Substitution der Mo-Lagen durch Vanadium. Der Frage nach der aus Ladungsgründen (MoO4(2−) / VO4(3−) ) folgenden Gemischtvalenz Fe(II,III) wurde mit Hilfe der Mössbauerspektroskopie nachgegangen werden. Hieraus ließ sich eine Zuordnung zu Fe(II,III)-Lagen bestimmen. Aufgrund der Beobachtung einer Ladungsordnung unterhalb von 200 K wurde ein Polaronenmechanismus angenommen, der an Hand magnetischer Untersuchungen näher analysiert wurde. Ausgehend von Suszeptibilitätsdaten konnten Größe und Moment der Polaronen bestimmt und diese der zweidimensionalen Holstein-Klasse eingeordnet werden. Die Leitfähigkeit der Verbindungen FeMo1−xVxO4 (x=0, 0.11, 0.20) wurde mit Hilfe von Widerstandsmessungen untersucht.
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    Posttranslationale Regulation der Transportaktivität humaner kationischer Aminosäuretransporter (human cationic aminoacid transporter: hCATs)
    (2025) Bender-Sigel, Julia; Langguth, Peter; Efferth, Thomas; Closs, Ellen
    Cells depend on transporters for communication, interaction, and the selective uptake of nutrients and other molecules. Despite their importance, the intricate regulatory mecha-nisms that govern transporter activity and surface expression are not fully understood for many of these vital membrane proteins. This work investigated the post-translational regulation of human cationic amino acid transporters (hCATs) by protein kinase C (PKC) involving Rho-GTPases (Cdc42, Rac1, and RhoA) and other potentially involved proteins. The central finding of the work is that both PKC and Rho-GTPases, especially Cdc42, play a crucial role in modulating the transport activity of all four hCAT isoforms. Activation of PKC leads to a significant reduction in arginine uptake by the hCATs. This effect was demonstrated in Xenopus laevis oocytes as a model system and various human cell lines. Interestingly, the reduced arginine uptake is caused by the altered membrane localization of the transporters (induced endocytosis). An important aspect of this work is the investigation of the interplay of Rho-GTPases in regulating hCAT transporters showing the involvement of these GTPases in adapting transporter activity to meet cellular arginine demand. The results suggest that the simul-taneous activation of PKC and Rho-GTPases could lead to complex regulation of hCAT transporters, involving a reduced localization of the transporters in the plasma mem-brane. The importance of membrane localization for the function of hCAT transporters was par-ticularly emphasized in this work. Understanding the mechanisms that regulate mem-brane proteins, especially transporter proteins, is of central importance, as they represent both targets and sensors for the cell's environment. In summary, this research makes an important contribution to understanding the com-plex regulation of amino acid transporters, especially hCATs. The results show that PKC and Rho-GTPases play a crucial role in modulating transport activity and that membrane localization of the transporters is an important factor for their function. The interaction between PKC and Rho-GTPases could represent a finely tuned system that controls amino acid uptake as needed.
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    Reception of anglicisms by beginning readers – an eye tracking study
    (2024) Linsel, Stefanie; Hansen-Schirra, Silvia; Kranich, Svenja; Schaeffer, Moritz
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    Quantum effects in the search for new physics
    (2024) Lo Chiatto, Prisco
    Quantum field theory is the backbone of modern particle physics. As the name implies, it is based on quantum mechanics, of which it is the consistent expansion to include special relativity. However, its quantum nature is not as evident when performing calculations for observables at collider experiments. Indeed, by construction, perturbation theory at leading order coincides with a classical theory, and quantum effect act as a parametrically small correction. Trying to bridge this gap, this thesis explores purely quantum phenomena as a discovery tool for new physics. We start with an account of entanglement at colliders, focusing on the concrete example of 4-fermion scattering in the electroweak theory and including new physics dipole moments. We show that angular correlations of the fermions' decay products can restore (“resurrect”) interference contributions that are otherwise suppressed by small masses in cross sections, thus unlocking a quantum phenomenon. We also critically evaluate the new physics sensitivity of entanglement markers, by interpreting the angular correlations as spin correlation of the parent fermions; we show that there is no advantage in using entanglement markers, and the angular correlations perform equally or better. We then move to a scenario where quantum interference plays an even more dramatic role. We study a new gauge boson that is nearly degenerate with the Standard Model $Z$ boson and show how interference between the two fundamentally alters predictions. We correct inconsistent treatments in older works, which worked in an uncontrolled approximation that suppressed interference. Surprisingly, we find that the quantum Zeno effect is critical to understanding the phenomenology of this system. This effect, which is not widely known in the particle physics community, is due to the mismatch of unitary evolution and the non-unitary nature of particle decay. Finally, we shift our attention to nonrelativistic quantum mechanics, specifically exploring the connection between the quantum vacuum and the classical limit. Here, we uncover a surprising relationship between large-multiplicity scattering amplitudes and tunneling, offering new insights into how quantum effects persist even as systems approach classical behavior. This finding provides a fresh perspective on the interaction between quantum and classical mechanics in high-energy physics.
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    Feasibility studies of an inverse compton scattering based gamma source at MESA
    (2024) Lorey, Christoph Lukas; Meseck, Atoosa
    Recent years saw a number of accelerator projects attempt to utilize Inverse Compton Scattering (ICS) as gamma sources and beam diagnostic tools. With it's low cross section, ICS is a prospective pairing with energy recovery linacs (ERL) as they require low impact experiments for energy recovery efficiency to be high.\\ At the Johannes Gutenberg-University Mainz, the Mainz Energy Recovering Superconducting Linear Accelerator (MESA) is under construction. To investigate the potential of an ICS experiment at MESA, the task was given to conduct a feasibility study for ICS at MESA. In this thesis, the mathematical foundation of ICS as a relativistic particle collision between fermions and photons is summarized and derived. On this foundation, a semi-analytical numerical ICS simulation code named Comparse was written. It's principles and focus on performance are described in a chapter of it's own. Three positions in the accelerator layout possibly suitable for an ICS experiment were identified in the plans and beam line simulations according to which MESA is currently under construction. Using beam parameters in these locations, a number of ICS performance studies were conducted with Comparse. Through various investigated implementation scenarios, a detailed picture of MESA's potential as the driver for a ICS gamma source is formed. We have shown that with minimal effort, MESA can drive a E_ph' > 200 keV or lambda < 6.2 pm photon source with a flux of at least F >14.000 ph/s. At the other end of the scale, assuming moderate modifications to the MESA beamline and an amplified lambda = 193 nm laser, we project the potential for a F > 5*10^8 ph/s gamma source above 1 MeV photon energy. Finally, we present various aspects of ICS experiment that impact the performance, including polarization effects. With this thesis, we have thus provided a rare comprehensive review of the interdependence of the ICS behavior between polarization, scattering and incident angles as well as recoil and momentum distribution.
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    Zellfreie DNA als Biomarker in der Sepsis Eine systematische Übersichtsarbeit
    (2025) Schoos, Laura; Schäfer , Michael
    Trotz enormer Fortschritte der Diagnostik und Therapie der Sepsis in den letzten Jahrzehnten ist die Notwendigkeit der Forschung auf diesem Gebiet weiterhin unerlässlich. Als weiteres Puzzleteil einer verbesserten Diagnose des Krankheitsbildes könnte cfDNA als Biomarker dienen. In dieser Metaanalyse konnte durch eine systematische Auswertung der bisherigen Studien auf diesem Gebiet gezeigt werden, dass cfDNA als Biomarker signifikant zwischen einem positiven und einem negativen Outcome differenzieren und septische von nicht septischen Patienten trennen kann. Dabei sollte die cfDNA jedoch keinesfalls als alleiniger Parameter herangezogen, sondern stets in Kombination mit bisher etablierten Biomarkern und Scores betrachtet werden. Um die freie DNA jedoch in der klinischen Praxis etablieren zu können muss ein einheitliches Messverfahren gefunden werden, um die Vergleichbarkeit der Ergebnisse zu gewährleisten. Es werden zudem mehr Studien mit einer größeren Anzahl an Probanden benötigt, um die Ergebnisse zu festigen. Insgesamt lässt sich jedoch festhalten, dass die cfDNA ein großes Potenzial auf dem Gebiet der Sepsis-Diagnostik und Therapie bietet.
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    Eulers Horizonte : Möglichkeiten und Grenzen seiner Arbeitsweise in der Mathematik
    (2025) Aycock, Alexander
    Die Dissertation hat im weitesten Sinne verschiedene Beiträge des Mathematikers und Physikers Leonhard Euler (1707--1783) zum Gegenstand. Die behandelten Themen reichen von der Herausarbeitung seiner Mathematikphilosophie, über die Illustration seiner Arbeitsweise anhand ausgewählter Beispiele, weiter über von ihm vorweggenommene -- bewiesene sowie unbewiesene -- Entdeckungen bis hin zur Eruierung seiner mathematischen Grenzen und der Applikation seiner Ideen auf unterschiedlichste verwandte Fragestellungen.\\ Grundlage waren dabei zahlreiche Euler'sche Abhandlungen selbst, welche vom Verfasser von lateinischer und französischer Sprache ins Deutsche und Englische übertragen worden sind. Eulers Vorbild widerspiegelnd ist die Art der Präsentation eine, welche anderes als die heutzutage vorherrschende synthetisch--deduktive eher induktiv und explanatorisch vorgeht. Es war eines der Hauptanliegen der Arbeit, den Euler'schen Schaffensprozess zu präsentieren und anschließend kritisch zu evaluieren, was auf diese Weise erreicht wurde. \\ Neben bereits hinlänglich bekannten Euler'schen Ergebnissen wie der Lösung des Baseler Problems wurden auch in der Literatur weniger bis gar nicht diskutierte Aspekte wie etwa seine Auflösung der einfachen Differenzengleichung vermöge einer Differentialgleichung unendlicher Ordnung vorgestellt und diskutiert. Überdies sind gänzliche neue Ergebnisse wie die heuristische Derivation des Primzahlsatzes aus den Euler'schen Vorgaben und die psychologisch begründete Nicht--Entdeckung der komplexen Analysis von Euler in der Dissertation zu finden. \\ Insgesamt bietet die Arbeit eine Auswahl von Eulers bemerkenswerten Errungenschaften, mit welchen er die Mathematik bereichert hat, mitsamt ihrer Entstehungs-- bzw. Entdeckungsgeschichte, sodass ein neuer Beitrag zum tieferen Verständnis des Euler'schen Opus erreicht wurde. Zugleich ist mit dem Aufwerfen der Frage nach den Grenzen Leonhard Eulers ein bislang noch kaum in der Literatur besprochenes Themenfeld aufgeworfen worden.\\
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    Design and mechanism of thermally activated delayed fluorescent (TADF) and efficient room temperature phosphorescent (RTP) molecules
    (2023) Dou, Dehai
    In recent years pure organic photoluminscent materials have been shown to possess great potential for applications in the fields of sensors, optoelectronic devices, bio-imaging, data encryption, etc.. Especially thermally activated delayed fluorescent (TADF) and room temperature phosphorescent (RTP) materials received extensive attention from researchers around the world. Currently, organic electroluminescent devices based on TADF materials have achieved some success in small-size displays, but blue materials still suffer from device transport imbalance and low device lifetime. For RTP materials, the triplet state excitons are very susceptible to the influence of the external environment. Efficient and stable room temperature phosphorescent materials that are purely organic have been a challenge. The main studies of this thesis is divided into 3 parts which are summarized as follows: Firstly, TADF and RTP materials need a fast intersystem crossing (ISC) process and a small singlet triplet splitting (ΔEST). Model emitters were designed and synthesised with simultaneous fluorescence, delayed fluorescence, and room temperature phosphorescence. It was proven experimentally and theoretically that multiple excited states are involved in the luminescence process. By adjusting the molecular structure, emitters with RTP quantum yield of more than 30% were obtained. Secondly, we designed and studied molecules for achieving phosphorescence emission in neat films. By changing the intramolecular steric hindrance, the phosphorescence radiation lifetime can be improved, also enhancing the quantum yield of phosphorescence emission in neat films. Our experimental data show that lifetimes up to 40 ms and phosphorescence quantum yields of 6.3% are achievable in neat films. All molecules have a lifetime of over 30 ms under ambient conditions. Thirdly, the introduction of fluorine atoms at the donor lowers the HOMO and LUMO energies but also affects the packing pattern of the molecules. Molecules without fluorine atoms pack more tightly compared to molecules with fluorine atoms. The molecules with tighter molecular packing achieved nearly trap-free electron transport in blue emitting molecules. We have gained a deep understanding of how to design trap-free blue luminescent materials.
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    The psychological dynamics of hybrid work - exploring the role of work location, basic need satisfaction, and contextual aspects of telework in daily employee well-being
    (2025) Bantz, Theresa Maria; Rigotti, Thomas
    The COVID-19 pandemic has significantly accelerated the adoption of hybrid-work models, where employees regularly alternate between working from home and the office. This shift has transformed telework from an exception to a norm, fundamentally changing the modern work landscape and raising critical questions regarding its psychological implications. Existing research on telework presents mixed findings regarding its impact on employee well-being, highlighting the need to explore the mediating and moderating factors. Given the widespread adoption of hybrid-work models with frequent transitions between work locations, it is also crucial to shift the focus from between-person to within-person effects. To address these research gaps, this dissertation investigates the within-person effects of hybrid work on employee well-being through three empirical daily diary studies. Drawing on the job demands-resources theory, challenge-hindrance stressor framework, and self-determination theory, this dissertation is guided by three research objectives. First, the direct effects of hybrid work on daily employee outcomes are examined, focusing on within-person variability. Second, the mediating role of basic psychological need satisfaction (autonomy, competence, and relatedness) is explored to explain the relationship between work location and employee well-being. Third, the moderating role of key telework aspects in the hybrid-work context is investigated. These include the time spent teleworking (telework intensity), the prevalence and acceptance of telework within organizations (telework normativeness), and the perceived voluntariness of daily work location choice (daily telework voluntariness), as well as the moderating role of work location in stressor-outcome relationships. Study 1 examined the direct effect of work location on emotional exhaustion and its indirect effect on perceived performance, using daily diary data from 151 employees (N = 876 observations). Multilevel structural equation modeling (MSEM) revealed that employees experienced lower emotional exhaustion and, in turn, higher perceived performance on days when they worked from home compared to days when they worked in the office. Furthermore, telework intensity, telework normativeness, and daily telework voluntariness were examined as potential moderators, reflecting key characteristics of the evolving hybrid work. Conditional indirect effects indicate that these effects were more pronounced when employees rarely worked from home (low telework intensity), belonged to organizations where telework was uncommon (low telework normativeness), or had limited choice over their work location (low daily telework voluntariness). Study 2 investigated the mediating mechanisms through which work location affects work engagement and cognitive stress, focusing on the role of basic need satisfaction. Based on daily data from 114 employees (N = 744 observations), multilevel mediation models revealed that working from home was associated with higher autonomy- and competence-need satisfaction, which positively affected work engagement and reduced cognitive stress. Conversely, working from home was associated with lower relatedness-need satisfaction, which contributed to increased work engagement and reduced cognitive stress. Multilevel moderated mediation models further indicated that telework normativeness weakened the indirect effects of autonomy- and relatedness-need satisfaction. Study 3 shifted the focus to the moderating effect of work location on the relationship between time pressure (a challenge stressor), professional isolation (a hindrance stressor), and work engagement and emotional exhaustion. MSEM analysis of daily data from 124 employees (N = 609 observations) revealed a significant two-way interaction effect only of work location and professional isolation on emotional exhaustion. As in Studies 1 and 2, this study also explored the moderating role of telework normativeness, revealing significant three-way interactions among work location, telework normativeness, and stressors. These interactions influenced the relationships between time pressure and work engagement and emotional exhaustion, and professional isolation and work engagement, with mixed interaction patterns. Overall, these studies comprehensively examined the psychological dynamics inherent in hybrid work. The findings underscore the importance of within-person effects and the need to consider both mediating factors, such as basic need satisfaction, and moderating factors, such as telework intensity, normativeness, and voluntariness, in shaping employee outcomes. The practical implications of these findings are significant for organizations navigating the future of work, offering valuable insights into the promotion and design of hybrid-work arrangements. This dissertation highlights the importance of encouraging flexible work arrangements that enhance employees’ autonomy and competence while actively mitigating negative effects such as isolation. It is crucial to consider the prevalence of telework within organizations and strike a balance between the advantages of home-based and office-based work to ensure a supportive and productive hybrid-work environment.
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    Controlled supramolecular assembly of peptides via chemical reactions
    (2025) Ren, Yong; Weil, Tanja
    Peptide-based bioresponsive systems have gained significant attention in supramolecular chemistry and biomaterials. These systems have enabled the development of synthetic platforms within living cells, providing valuable insights into how structural formation influences cellular processes. This thesis investigates the design, synthesis, and characterization of different stimulus-responsive peptide systems for the in situ formation of intracellular nanostructures, and examines their consequent effects on cellular processes. In the first chapter, a platinum (II)-containing tripeptide was engineered to aggregate into intracellular fibrillar nanostructures, disrupting metabolic functions such as aerobic glycolysis and oxidative phosphorylation, consequently instigating apoptosis systematically. This system offers insights into novel building blocks for the construction of peptide-assembling platforms and elucidates the biological mechanisms of action and biochemical profiles associated with nanostructure formation, which implicates system-level effects, such as the regulation of energy and redox homeostasis. In the second chapter, the development of pH/oxidative stress-responsive isopeptide system was described, including the real-time tracking of the assembling processes and illustration of formed nanostructures, hollow spherical nanofibers, in epithelial cells (MDA-MB 231 cells). Phasor-fluorescence lifetime imaging (FLIM) was utilized to map the transformation form monomers to supramolecular assemblies and correlative light-electron microscopy/tomography (CLEM) revealed formation of nanofibers and their fusion with endosomes to finally form hollow fiber clusters. Spatiotemporal splicing of the assembly events shows time-correlated metabolic dysfunction. This study paves the way to understand and visualize the supramolecular processes of nanostructure formation in biology to ultimately address aggregation-based dysfunction in diseases. Finally, the construction of two amphiphilic pro-assembling peptide sequences protected by a visible light-sensitive cage group was presents. The peptides underwent a cascade of visible light-induced molecular and supramolecular transformations to form nanofibers in living cells. The irradiation with light enable full control over the reaction cascade where the monomer generation and concentration in turn regulates the assembly kinetics. Phasor-FLIM traced the formation of various assembly states in cells and revealed subsequent out-of-equilibrium dynamics associated with monomer activation and consumption. This study facilitates precise control over supramolecular events at discrete time points, and the new imaging technologies offer deeper insights into the dynamic assembly processes with native cells. In summary, this thesis introduces a range of methodologies for controlling and imaging intracellular peptide assembly processes and their associated cellular effects. These findings provide valuable insights into supramolecular assembly mechanisms within complex cellular environments and the role of aggregation-based dysfunction in disease.