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Untersuchung des Zusammenhangs zwischen Klimawandel, menschlicher Sicherheit, Konflikten und Geschlechterdynamiken in Bangladesch
No full textEntwicklung von Nanobody- und Antikörperwerkzeugen zur Untersuchung der purinergen P2X-Signalübertragung bei Entzündungen
No full textBesatz von Europäischen Aalen (Anguilla anguilla) in Küstengewässern der deutschen Ostsee
No full textEstuarine hydrodynamics in arid climates – a case study of the Persian Gulf and its small estuaries
Full text linkUnlike positive estuaries, low-inflow estuaries such as inverse and salt-plug estuaries have received less scientific attention. This thesis aims to investigate the hydrodynamic aspects of these remarkable estuarine systems by example of the Persian Gulf (PG), the Mond River Estuary (MRE), and an idealized funnel-shaped estuary using observations and numerical modeling.
The PG region, characterized by an arid climate, represents an extraordinary environment for studying estuarine hydrodynamics. Classified as an inverse estuary due to higher evaporation than precipitation and river discharges, the PG provides a valuable case study for understanding the dynamics of low-inflow estuaries. The system is studied with a particular focus on the influence of tidal forcing on the exchange flows and salinity. Numerical experiments indicate that tidal forcing significantly increases the annual inflow-outflow rates at the Strait of Hormuz (SOH) to approximately ±0.54 Sv, which is more than double previous estimates. Tides enhance PG salinity through (i) intense landward (entering the PG) salt flux by tidal advection, and (ii) strong tidal mixing in the PG, especially at the SOH. On the northwestern and southern shallow banks of the PG, high salinity values imposed by tides coincide with peak values of the tidal Froude number (FrT) and the formation of amphidromic points in these coastal areas.
The MRE, located on the northern coast of the PG, exhibits a salt-plug estuarine system during warm months, representing another type of low-inflow estuaries. In fact, the MRE transitions from a positive estuary in wet months to inverse and salt-plug estuaries during dry months. Also, the MRE exhibits a highly unsteady estuarine state following heavy rains. The unsteady state is characterized by the formation of a relatively freshwater lens between two high-salinity water masses: one from the PG and another from the hypersaline runoff passing saline soils upstream of the estuary (freshwater lens estuary). The Péclet Number (Pe), calculated from observed salt flux terms, indicates a predominance of strong advective transport imposed by hypersaline runoff over diffusive transport throughout the MRE. Additionally, numerical modeling of the MRE indicates that a sea-level rise of 20 cm can result in an increase in salinity within the freshwater lens and positive estuaries, in contrast to a salinity decrease in inverse and salt-plug estuaries.
Furthermore, a three-dimensional hydrodynamic model is employed to compare various scenarios under different tidal conditions in an idealized funnel-shaped salt-plug estuary. The analysis reveals that when log(FrT) > 3, tidal forcing overcomes the density gradient, reinforcing the salinity maximum zone with a landward displacement. In this idealized estuary, the model demonstrates the development of longitudinal flows in two cells of positive and inverse estuarine circulations, detached by a salinity maximum zone. Meanwhile, two cells of positive estuaries are separated by a mixing maximum zone in the idealized freshwater lens estuary.
The results of these studies provide valuable foundations for understanding biogeochemical processes and sediment dynamics in low-inflow estuarine systems, which can support sustainable development considering water quality and climate change impacts worldwide
Massenspektrometrische und optische Untersuchung der photokatalytischen Wasserstoffproduktion durch kolloidale CdSe/CdS/Pt-Hybridnanostrukturen
Full text linkMultidimensional and Multimodal Soft X-ray Methods for Quantum Materials Research
Full text linkQuantum materials are governed by a complex interplay of spin, orbit, charge and lattice degrees of freedom, resulting in emergent phenomena like high-temperature superconductivity, charge and orbital ordering and insulator-to-metal transitions (IMTs). Often, the interaction of these subsystems results in an energy landscape with multiple local minima favouring different phases. In many cases, two or more distinct phases coexist and the macroscopic property of the material is shaped by the properties of the individual phases as well as their interaction. To understand the complexity that shapes quantum materials, their properties need to be studied in multiple dimensions of space, energy and time.
X-rays are indispensable tools for the study of quantum materials as they enable probing on atomic length scales as well as excitation of electrons bound in specific core levels. Synchrotron radiation sources provide the coherence, spectral brightness, flexible focusing capabilities and tunability of the photon energy to adapt the X-ray beam properties to the requirements of a specific measurement scheme and sample. The photon energy can be tuned to electronic resonances of one element to disentangle its role for macroscopic functionality. Free-electron lasers (FELs) extend this capability in the time domain down to pico- and femtoseconds, the time scales of atomic and electronic motion.
This thesis presents the development of multidimensional and multimodal soft X-ray methods that can be tailored to address specific scientific challenges posed by quantum materials. Multidimensional studies of incident and emitted photon energies and spatial and temporal dependencies as well as the dependence on fluence of a pump laser that drives e.g. an IMT are discussed. Multimodal studies allow observing quantum materials from the point of view of different experimental techniques, like X-ray imaging, X-ray absorption spectroscopy, X-ray emission spectroscopy, (resonant) X-ray diffraction, resonant inelastic X-ray scattering (RIXS) and angle-resolved photoemission spectroscopy (ARPES).
First, the RIXS imaging method, which utilizes a transmission Fresnel zone plate to combine soft X-ray absorption spectroscopy with microscopy with a resolution of 1.8 µm, is presented. This method is applied in a study of the IMT of VO2 microsquares measuring 30 µm × 30 µm. Imaging X-ray absorption spectroscopy (XAS) shows that the phase transition temperature at the edges of the squares is lower in comparison to the centres by 1.2 K. This implies that bulk properties of quantum materials may change upon structuring on the microscale.
Second, this method is transferred to imaging X-ray diffraction (XRD) to investigate the doped titanate Y1−xCaxTiO3 with x = 0.37, revealing insulating and metallic phases which coexist in curved, striped domains across unusually large temperature regions. This observation is related to a varying chemical inhomogeneity of about x ± 0.01, likely arising during crystal growth.
Next, excitation of the electronic subsystem in quantum materials with femtosecond infra-red laser pulses also drives insulator-to-metal transitions. For the study of ultrafast dynamics of magnetite (Fe3O4) at an FEL, zone plates can also be used for time-to-space mapping, recording a delay range of several picoseconds as well as an extended fluence range simultaneously. This time-to-space mapping setup combines temporal, spatial and pump fluence information and may be developed to record single-shot experiments in the future.
Lastly, a method, termed photoelectron spectrometry for the analysis of X-rays (PAX), which converts RIXS photons to photoelectrons via the photoelectric effect, is developed towards high energy resolution to investigate a sample from the family of high-temperature superconducting cuprates. PAX enables simultaneous recording of a range of photon-sample momentum transfer, corresponding to a significant part of the first Brillouin zone in the investigated system. In comparison to grating-based RIXS spectrometers, a PAX instrument is much more compact, saving money and experimental space. The success of the PAX method resulted in the development of a dedicated ultra-high vacuum chamber, soon to be commissioned, which promises a significant improvement in photon count rate and energy resolution, as well as the combination with ARPES.
In summary, this thesis presents experimental developments that enable the study of quantum materials through the utilisation of diverse soft X-ray methods in conjunction with a spatial resolution on the micrometer level, temporal resolution on the level of 100 fs and energy resolution on the level of 100 meV. Furthermore, it outlines concepts to improve this energy and spatial resolution by approximately one order of magnitude. The advancement of the experimental tools described in this thesis will facilitate a deeper comprehension of the complexity of quantum materials and enable us as a society to harness phenomena occurring in quantum materials.Quantenmaterialien werden durch ein komplexes Zusammenspiel von Spin, Orbit, Ladung und Kristallgitter charakterisiert, was emergente Phänomene wie Hochtemperatursupraleitung, Ladungs- und Orbitalordnung und Isolator-Metall-Übergänge hervorrufen kann. Häufig erzeugt die Wechselwirkung dieser Freiheitsgrade eine Energielandschaft mit mehreren lokalen Minima, welche verschiedene Phasen begünstigen. Dies kann dazu führen, dass zwei oder mehr unterschiedliche Phasen koexistieren und die makroskopische Eigenschaft des Materials durch die Eigenschaften der einzelnen Phasen sowie deren Wechselwirkung bestimmt wird. Um diese Komplexität, welche Quantenmaterialien charakterisiert, zu verstehen, müssen ihre Eigenschaften in den Dimensionen von Raum, Energie und Zeit untersucht werden.
Röntgenstrahlen sind unverzichtbare Werkzeuge für die Untersuchung von Quantenmaterialien, da sie die Untersuchung auf atomaren Längenskalen sowie die Anregung von Elektronen, gebunden in spezifischen Kernniveaus, ermöglichen. Synchrotronstrahlungsquellen bieten die Kohärenz, spektrale Helligkeit, flexible Fokussierungsmöglichkeiten und Durchstimmbarkeit der Photonenenergie, welche nötig sind um die Eigenschaften des Röntgenstrahls an die Anforderungen eines bestimmten Messschemas und einer bestimmten Probe anzupassen. Die Photonenenergie kann auf elektronische Resonanzen eines Elements eingestellt werden, um dessen Beitrag zu der makroskopischen Funktionalität zu untersuchen. Freie-Elektronen-Laser (FELs) erweitern diese Möglichkeiten hin zu den Zeitskalen von Piko- und Femtosekunden, auf welchen sich Atome und Elektronen bewegen.
Diese Dissertation beschreibt die Entwicklung von multidimensionalen und multimodalen Weichröntgenmethoden, welche auf die spezifischen wissenschaftlichen Herausforderungen von Quantenmaterialien angepasst werden. Multidimensionale Studien von einfallender und emittierter Photonenenergie, von räumlichen und zeitlichen
Abhängigkeiten sowie von der Abhängigkeit der Fluenz eines Pumplasers, welcher einen Isolator-Metallübergang anregt, werden diskutiert. Multimodale Studien ermöglichen die Beobachtung von Quantenmaterialien mit verschiedenen experimentellen Techniken, wie Röntgenbildgebung, Röntgenabsorptionsspektroskopie, Röntgenemissionsspektroskopie, (resonanter) Röntgendiffraktion, resonanter inelastischer Röntgenstreuung (RIXS) und winkelaufgelöster Photoemissionsspektroskopie (ARPES).
Zunächst wird eine abbildende RIXS Methode vorgestellt, welche eine Transmissions-Fresnel-Zonenplatte verwendet um Weichröntgenabsorptionsspektroskopie mit Mikroskopie mit einer Auflösung von 1.8 μm zu kombinieren. Diese Methode wird in einer Studie des Isolator-Metallübergangs von Mikroquadraten, welche 30 μm×30 μm klein sind und aus Vanadiumdioxid (VO2) bestehen, angewendet. Abbildende Röntgenabsorptionsspektroskopie (XAS) zeigt, dass die Phasenübergangstemperatur an den Rändern der Quadrate im Vergleich zu den Zentren um 1.2K verringert ist. Dies deutet darauf hin, dass sich die Eigenschaften von Quantenmaterialien durch Strukturierung auf der Mikroskala ändern können.
Weiterhin wird diese Methode auf abbildende Röntgenbeugung (XRD) übertragen, um das dotierte Titanatsystem Y1 − xCaxTiO3 mit x = 0.37 zu untersuchen. Hierbei werden isolierende und metallische Phasen beobachtet, welche in gekrümmten, streifenförmigen Domänen über ungewöhnlich große Temperaturbereiche hinweg koexistieren. Diese Beobachtung steht in Zusammenhang mit einer variierenden chemischen Inhomogenität von etwa x±0.01, die wahrscheinlich während des Kristallwachstums entstanden ist.
Auch Femtosekunden-Infrarot-Laserpulse können genutzt werden, um das elektronische System in Quantenmaterialien anzuregen und Isolator-Metall-Übergänge zu treiben. Für die Untersuchung der ultraschnellen Dynamik von Magnetit (Fe3O4) an einem FEL können Zonenplatten auch für die Methode des Time-to-Space Mapping verwendet werden, wobei eine Spanne des Zeitversatzes zwischen Pumplaser und FEL von mehreren Pikosekunden sowie eine Verteilung von Fluenzen gleichzeitig aufgezeichnet werden. Diese Methode kombiniert Informationen über Zeit, Raum und Pumpfluenz und kann in Zukunft für die Aufzeichnung von Einzelschussexperimenten entwickelt werden.
Schließlich wird die Methode der Photoelektronenspektrometrie zur Analyse von Röntgenstrahlung (PAX) weiterentwickelt. Diese Methode wandelt RIXS-Photonen mit Hilfe des photoelektrischen Effekts in Photoelektronen um. Sie wird genutzt um eine Probe aus der Familie der Hochtemperatursupraleiter mit hoher Energieauflösung zu untersuchen. Weiterhin ermöglicht PAX die simultane Messung einer Verteilung von Impulsüberträgen von Photonen auf die Probe. Der Bereich der Verteilung
entspricht einem signifikanten Teil der ersten Brillouin-Zone in dem hier untersuchten System. Im Vergleich zu Gitterspektrometern ist ein PAX-Instrument viel kompakter, was Geld und Experimentierfläche spart. Der Erfolg der PAX-Methode führte zur Entwicklung einer speziellen Ultrahochvakuumkammer, die demnächst in Betrieb genommen wird und eine erhebliche Verbesserung der Photonenzählrate und der Energieauflösung sowie die Kombination mit ARPES verspricht.
Zusammenfassend werden in dieser Arbeit experimentelle Entwicklungen vorgestellt, welche die Untersuchung von Quantenmaterialien durch den Einsatz verschiedener Weichröntgenmethoden in Verbindung mit einer räumlichen Auflösung im Mikrometerbereich, einer Zeitauflösung im Bereich von 100 fs und einer Energieauflösung im Bereich von 100 meV ermöglichen. Darüber hinaus werden Konzepte zur Verbesserung dieser Energie- und Ortsauflösung um etwa eine Größenordnung vorgestellt. Die Weiterentwicklung der in dieser Arbeit beschriebenen experimentellen Werkzeuge wird ein tieferes Verständnis der Komplexität von Quantenmaterialien ermöglichen und uns als Gesellschaft in die Lage versetzen, Phänomene, die in Quantenmaterialien auftreten, nutzbar zu machen
Morphologie und Phylogenie der Priapulida
Full text linkPriapulida is a small phylum of marine worms with only 21 described species across seven genera. Although priapulidans are long-known, standardized documentations of their morphology are still lacking for many species. Some of the morphological structures are only superficially described, if at all, making comparisons among priapulidans difficult. Interestingly for Priapulida is the occurrence of two adult size classes, microscopic (<3.5 μm) and macroscopic (up to 40 cm), differing from related phyla (Kinorhyncha and Loricifera) that are exclusively of microscopic size. Due to the two size classes in Priapulida and contradicting reports of potential fossils among the three related phyla, the ancestral body size of Priapulida remains uncertain. Internal phylogenetic relationships of priapulidans have only been inferred from morphological data, as molecular data from priapulidans are scarce. Proposed phylogenies support both an ancestrally microscopic and macroscopic body size. Phylogenetic analyses based on molecular data may help to clarify the relationships in Priapulida and their ancestral body size.
In this thesis, the following macroscopic species are examined and morphological structures are described in detail using light microscopy, scanning electron microscopy and, for some species, histology: Priapulus caudatus, Priapulus tuberculatospinosus, Priapulopsis bicaudatus, Priapulopsis australis, Halicryptus spinulosus and Halicryptus higginsi. Larval and postlarval stages, as well as adult specimens were collected during multiple field trips or obtained from museum collections. Additionally, molecular data (transcriptomic and genomic) was gathered from these species and analyzed together with publicly available data. Microscopic species were not available for morphological examinations, however, few Tubiluchus specimens could be used for molecular analyses. The morphological investigations conducted in this thesis describe almost all structures of these species in detail. Key findings include newly described structures on the circumoral fields of P. caudatus and P. tuberculatospinosus, as well as on the trunks of H. spinulosus and H. higginsi. Additionally, asymmetric growth of the caudal appendages and the bipartition process of first-ring teeth during postlarval development were observed in P. bicaudatus. The larval stages of P. bicaudatus were also described in greater detail compared to a previous study. While examining P. australis specimens, two individuals exhibit unique morphological characters, resulting in the description of a new macroscopic species, Priapulopsis papillatus.
Furthermore, this thesis presents the first phylogenomic analysis of Priapulida, integrating transcriptomic data from seven species across four genera (including six newly assembled transcriptomes) and conserved genomic loci from ten species across five genera. The positions of rare genera Acanthopriapulus and Maccabeus, which lack molecular data, were inferred through morphological analysis. The topology of this combined phylogenetic tree corresponds almost entirely with those of previous studies that only analyzed morphological data. Key findings include microscopic Meiopriapulus as sister group to all remaining priapulidans, and microscopic Maccabeus that exhibits morphological characters of both size classes as sister group to all macroscopic species. Ancestral state reconstructions of morphological traits on the newly conducted phylogenetic tree suggest an ancestrally small body size and an internal fertilization in extant Priapulida. These traits are consistent with their microscopic sister groups, Kinorhyncha and Loricifera
Searches for new physics in final states with multiple top quarks with the ATLAS detector and upgrade of the ATLAS tracking detector
Full text linkThe Standard Model's known limitations drive the search for new physics, a major focus of modern experimental particle physics. This thesis presents two searches for Beyond the Standard Model physics in the four-top-quark final state at the ATLAS experiment. The first search focuses on final states with a single lepton. The mass of the resonance is explicitly reconstructed by using the products of its fully-hadronic decay. The presence of the signal is investigated both for a simplified vector top-philic boson model, and without model dependence by identifying localized deviations in data compared to the background. The data was found to be compatible with the background-only hypothesis, and exclusion limits were set. The second search investigates final states with at least two reconstructed leptons with the same-sign electric charge. This thesis presents the algorithm for reconstruction of the resonance in this final state and shows its potential application for obtaining model-independent results for final states with multiple leptons.
Before the next LHC phase, the current ATLAS tracking detector will be replaced by a new one, called the ITk. The outer part of the ITk is made using silicon strip sensors, and in the forward regions the tracking is performed in the endcaps. This thesis describes the work on production and quality control of ITk silicon strip endcap modules, the single sensitive units in the ITk strip endcaps. A tool for monitoring module production is presented, which allows to identify deviations in the production process in time and quickly mitigate them in order to ensure excellent quality of the produced modules. The most demanding module quality control step is thermal cycling, requiring a specific setup and dedicated software, both of which are described in this work
