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Transformation, deformation, and formation of minerals in the Vredefort and Ries impact structure and implications for magnetic properties of impactites
Get PDFShock effects of rock-forming minerals with a focus on Fe-Ti-oxides from the Ries- and the Vredefort impact structures were studied in relation to the magnetic properties. Therefore, samples were investigated from locations characterized by enigmatic magnetic anomalies attributed to the respective impact events. The main aim is to gain insights into the host rocks' stress, temperature and oxygen fugacity evolution. Based on different shock effects in impact breccias, the emplacement conditions of the rocks are discussed.
Archean basement gneisses within the pronounced magnetic anomaly northwest of the Vredefort impact structure center have quartz (SiO2) grains with shock-generated planar fractures, as documented by two drill cores with ≈10 m depth. Ilmenite (FeTiO3) revealed that shock loading and unloading at relatively low shock pressures (<16 GPa) can result in the formation of mechanical (0001) and {10-11} twins. At re-equilibration temperatures of 600-700°C, exsolution of magnetite (Fe3O4) within ilmenite occurred, forming a few µm-sized magnetite lamellae parallel to the {10-11} twin boundaries and spheroid magnetite along twin and grain boundaries. Furthermore, shearing fractured and locally melted Fe-bearing oxides, which resulted in their intrusion into adjacent shear fractures within neighboring quartz and feldspar. Dauphiné twins associated with shock-induced planar fractures within quartz suggest that the temperatures before the impact event (paleo-depth of 11-23 km resulting in 650-725°C) were higher than the Curie temperature of magnetite (580°C), which is the carrier of the paleomagnetic orientation. Therefore, uplift of the Archean gneiss upon shock-unloading and subsequent cooling in the magnetic field direction present during the Vredefort impact best explains the observed magnetic remanence. The study, furthermore, found no microstructural difference (i.e., phase assemblage, planar fracture abundance and frequency) between samples from the surface and depth of the two drill cores. Lightning strikes heavily influenced the magnetic record of the surficial rocks, however, microstructural products formed from lightning strikes are likely nm-sized and reside below the resolution of the scanning electron microscope.
Ilmenite in the Ries impact breccias recorded that at moderate shock pressures (>16 GPa),
transformation twin lamellae were generated that share a common {11-20} plane with the host and a 109° angle between the c-axes of host and twin. Moreover, new grains with foam structure formed, which are characterized as orientation domains that also share a common {11-20} plane and whose c�axes span 109° or 99° angles. This crystallographic orientation relationship of new grains and the inferred twins indicates the back-transformation from FeTiO3 high-pressure polymorphs (liuite and wangdaodeite). A variety of different high-temperature reactions generated rutile (TiO2; T=850-1050°C) and minerals of the ferropseudobrookite-armalcolite solid-solution [(Fe,Mg)Ti2O5; T>1140°C] from ilmenite. Furthermore, redox reactions recorded variations in oxygen fugacity. At high temperatures, an enrichment of iron, in terms of elevated Fe/Ti ratios at the rims of ilmenite
aggregates, indicates the presence of a reducing agent during the impactite formation, which generated elemental iron. Cooling and subsequent oxidation of iron formed magnetite. Below 700°C at high oxygen fugacity conditions in combination with a leaching agent, pseudorutile (Fe2Ti3O9) was locally created around single ilmenite grains or completely replaced them. A new occurrence of polymict crystalline breccia in the Ries impact structure at the Aumühle quarry exhibits the direct lithological relationship to the underlying Bunte Breccia and overlying suevite. The polymict crystalline breccia consists of ≈50% shocked crystalline clasts from the Variscan basement and ≈50% components from the sedimentary cover sequence, which display no apparent shock effects. Its emplacement likely occurred during the excavation stage of impact cratering. The mathematical Maxwell Z-model describes flow fields during excavation, indicating that shocked material from the crystalline basement was ballistically ejected. A mixture with ballistically ejected sedimentary clasts was subsequently placed on top of Bunte Breccia and then covered by suevite.
Reworking of Bunte Breccia and suevite to form polymict crystalline breccia can be excluded based on the absence of glass fragments, larger clast sizes, and random paleomagnetic directions of polymict crystalline breccia compared to suevite. The proposed emplacement is consistent with observations of polymict crystalline breccias from other impact structures.
Ballen SiO2 with characteristically curved fractures within impact melt rocks from the Ries impact structure was investigated to elucidate its formation mechanisms and conditions. It likely originated from fluid-inclusion-rich quartz grains in the gneisses of the crystalline basement. Quartz transformed into diaplectic glass upon shock loading, which partly retained structural information about the precursor phase. As a result, the fluid inclusions dissolved into the amorphous phase. Upon shock unloading and subsequent cooling, dehydration caused fracturing of the glass resulting in curved interfaces as similarly observed from volcanic glasses, i.e., perlitic structures. Structural remnants within the diaplectic glass enabled topotactic crystallization, resulting in preferred crystallographic orientations within quartz. In cases without structural information within the amorphous phase, quartz as well as cristobalite (at elevated temperatures) formed with random crystallographic orientations. Dendritic cristobalite only occurs at the rim of the aggregates in correlation with adjacent vesicles and is interpreted to have formed from a fluid-rich melt
Einsatz der Magnetresonanztomographie für die Detektion periapikaler Entzündungsprozesse und assoziierter mukosaler Pathologien
Get PDFContextual modulation of stimulus processing in the mouse visual thalamus
Get PDFIn order to appropriately utilize visual signals from the environment, the brain needs to place this information into a context. Contexts are multifaceted, and can refer to the overall nature of the visual landscape, as well as the goals and behaviours of the animal. The behavioural context can determine the type of visual signals that the animal is likely to encounter, and, simultaneously, the type of behaviours the animal is likely to perform on a moment-to-moment basis. These behaviours may be used to explore the visual scene, and can themselves generate certain types of visual signals. It is therefore unsurprising that visual systems in the brain account for context at the earliest stages of sensory processing. One of these initial processing stages in the mammalian brain is the visual thalamus. This dissertation presents the results of three investigations on the contextual modulation of neural activity in the dorsal lateral geniculate nucleus (dLGN) of the thalamus. To conclude, novel results involving the ventral lateral geniculate nucleus of the thalamus in setting a behavioural context are synthesized. Taken together, it is hoped that these works will contribute to an acknowledgement of the diversity of contextual modulations in vision, and lead to a better understanding of how the brain constructs its own sensory world.
Until the last decade, investigations of sensory processing in the mammalian brain were typically carried out in anaesthetized animals using simple artificial stimuli. However, brains have evolved process complex natural environments while the animal is awake and behaving. These factors must therefore be taken into account when investigating the function of a certain piece of neural circuitry. The research presented in Chapter 2 examines the role of feedback from the visual cortex to the dLGN in awake animals viewing naturalistic video stimuli. The work reveals a robust effect of this feedback on dLGN neurons in the presence of naturalistic stimulation. Furthermore, it was found that cortical feedback produces effects that are similar to locomotion, but that the two influences are statistically independent, suggesting that locomotion operates on dLGN neurons through a different mechanism.
Researchers use behavioural signals like locomotion to infer that the animal is in a behavioural state termed "arousal". Another external marker for arousal is pupil dilation. Previous work examined the effects of arousal on sensory systems by partitioning neural activity into two mutually exclusive groupings based on the level of arousal. The work in Chapter 3, however, extends the notion of behavioural state by showing relationships between dLGN activity and pupil dilation over multiple, nested temporal scales. Some of these modulations, especially at faster timescales, were related to specific behaviours such as locomotion and eye movement. Overall, despite the presence of a robust neural activity pattern characterizing these modulations across temporal scales, there was a diversity in the strength with which individual neurons coupled to a certain temporal component. This pattern of results indicates that, rather than operating in two distinct modes, dLGN neurons are under the continuous influence of a multitude of arousal-related factors.
Modelling plays an important role in neuroscience, allowing the translation between conceptual and quantitative understanding. In Chapter 4, a descriptive model is introduced to assess the additive contributions of locomotion, pupil size, and cortical feedback to the stimulus responses of individual dLGN neurons. This work not only utilizes a novel efficient and robust method for assessing responses to naturalistic visual stimuli, but also provides a unified quantitative account of the various modulatory influences acting on dLGN neurons.
The enclosed research primarily provides descriptive accounts of contextual modulation of activity in the early visual system of mammals. Where it is limited is in the discussion of mechanisms and functional roles. Chapter 5 reviews two findings from other research groups uncovering a novel mechanism, involving the ventral lateral geniculate nucleus (vLGN) of the thalamus, by which mammals might control behavioural responses to visual stimuli. These novel findings highlight the usefulness of asking "how" and "why" in neurobiological research. Thus, in the final chapter, the potential mechanisms underlying dLGN modulations uncovered in Chapters 2 through 4 are discussed, and various proposals for their teleological functions in vision are made
ℤ₂ lattice gauge theories coupled to dynamical matter
Get PDFLattice gauge theories have an important role in understanding strongly correlated systems in particular the problem of confinement. The recent progress in quantum simulation already allows us to study simple building blocks of such systems. A better theoretical understanding of lattice gauge theories and how they could be studied in quantum simulation platforms is thus needed.
In this thesis we study a paradigmatic one-dimensional ℤ₂ lattice gauge theory (LGT), where dynamical matter is coupled to a gauge field. The hallmark of this ℤ₂ LGT is confinement of particles (partons) into bound dimers (mesons), which is mediated through a non-local gauge interaction. We employ numerical calculations using matrix-product states, complemented by analytical arguments in certain limits.
We provide a general explanation of confinement, and study different probes of confinement numerically. At finite temperature we uncover a smooth crossover from a confined to a thermally deconfined regime. There we discover that mesons are in fact already pre-formed at high temperature, where thermal fluctuations make them incoherent. The ℤ₂ LGT could be implemented in state-of-the-art quantum simulators with cold atoms.
For that reason, we likewise study simple geometric probes of confinement, which are readily accessible in quantum simulation experiments.
Motivated by the prospect of quantum simulation, we also study different phase diagrams of the ℤ₂ LGT and uncover rich physics driven by the interplay of non-local gauge mediated interaction and local repulsion between partons. We show that when matter has a global U(1) symmetry, a parton Mott state can be stabilized at half filling and a meson Mott state can be realized at two-thirds filling. By including superconducting terms, which explicitly break the global U(1) symmetry of the matter, we obtain a system resembling a gauged Kitaev chain. There, a nearly empty or fully filled lattices show similar confined features, since matter fluctuations that dominate the physics in that regime are constituted by parton pairs. We thus demonstrate that the topological transition in Kitaev chains can be understood as a confinement transition.
In addition, we develop a mean-field theory for the ℤ₂ LGT by employing a product ansatz where we decouple matter and gauge fields, but the Gauss law is enforced on the mean-field level via Lagrange multipliers. The mean-field theory qualitatively captures the main features of the exact ℤ₂ LGT, including confinement.
Finally, we study a mixed-dimensional XXZ model, which can be mapped to a ℤ₂ LGT. We show that such systems can exhibit confined mesons at finite temperature, which transition to a deconfined parton gas. Such systems can be simulated with cold atoms with magnetic dipoles.
Our theoretical results pave the way towards a better understanding of ℤ₂ LGTs, in particular confinement. All of this is relevant for future quantum simulations, as we develop new probes suitable for experimental platforms.Gittereichtheorien spielen eine wichtige Rolle zum Verständnis von stark korrelierten Systemen, besonders bei confinement (Einschluss) von Teilchen. Mit neuesten Quantumsimulatoren kann man Bausteine von solchen Systemen bereits untersuchen. Ein besseres theoretisches Verständnis von Gittereichtheorien und die Entwicklung von Methoden zur Untersuchung von solchen Systemen mit Quantumsimulatoren ist also notwendig.
In dieser Arbeit untersuchen wir die paradigmatische eindimensionale ℤ₂ Gittereichtheorie, in welcher dynamische Materie an ein Eichfeld gekoppelt ist. Die Besonderheit dieser ℤ₂ Gittereichtheorien ist der confinement von Teilchen (Partonen) in Dimere (Mesonen), welcher durch eine nicht lokale Eichwechselwirkung vermittelt wird. Wir benutzen numerische Berechnungen und komplementieren diese mit analytischen Argumenten.
Wir entwickeln eine vollständige Erklärung von confinement, und untersuchen mithilfe verschiedener numerischer Methoden den confinement von Teilchen.
Bei endlichen Temperaturen beobachten wir einen glatten crossover zwischen confinement und freien Teilchen.
Die Mesonen formen sich schon bei höheren Temperaturen, allerdings ist Kohärenz durch thermische Fluktuationen zerstört und die Teilchen erscheinen als frei.
Diese ℤ₂ Gittereichtheorie könnte man im Quantumsimulator mit ultrakalten Atomen simulieren. Wir untersuchen deswegen verschiedene geometrische Observablen die in solchen Systemen einfach zugänglich sind.
Motiviert durch die Entwicklung von Quantumsimulatoren, untersuchen wir zudem auch verschiedene Phasendiagramme von ℤ₂ Gittereichtheorien und entdecken dabei interessante Physik, die durch das Zusammenspiel von Eichfeld und lokalen Wechselwirkungen entsteht. Wir entdecken eine Mott-Isolator-Phase von Partonen bei halber Füllung, und eine Mott-Isolator-Phase von Mesonen bei zwei drittel Füllung, wenn die Materie eine globale U(1) Symmetrie hat. Wenn wir zusätzlich supraleitende Terme berücksichtigen, welche die globale U(1) Symmetrie zerstören, erhalten wir ein System, was der Kitaev-Kette ähnelt. In diesem Regime, enthält die fast volle oder fast leere Kette ähnliche confinement-Eigenschaften, weil die Teilchenfluktuationen, welche die Physik dominieren, von Partonpaaren ausgeht.
Wir zeigen daher, dass man den topologischen Übergang in Kitaev Ketten als confinement-deconfinement Übergang in diesen ℤ₂ Gittereichtheorien verstehen kann.
Wir entwickeln zusätzlich eine mean-field Theorie für die ℤ₂ Gittereichtheorien, in welchen wir einen Produktansatz wählen und damit die Materieteilchen von dem Eichfeld entkoppeln. Das Gauss Gesetz wird durch Lagrange-Multiplikatoren eingesetzt. Die mean-field Theorie kann wichtige Eigenschaften von exakten ℤ₂ Gittereichtheorie erfassen, einschließlich von confinement.
Schließlich erforschen wir auch das mixed-dimensional XXZ Model, welches zu einer ℤ₂ Gittereichtheorie transformiert werden kann. Wir zeigen nun, dass sich in diesem System auch Mesonen bei niedrigen Temperaturen formen, die einen Übergang zu freien Partonen bei höheren Temperatur haben. Ein solches System kann man mit kalten Atomen mit magnetischem Dipol simulieren.
Unsere theoretischen Ergebnisse ebnen den Weg für ein besseres Verständnis über die ℤ₂Gittereichtheorien, insbesondere confinement. Damit sind unsere Ergebnisse auch relevant für zukünftige Quantensimulationen, weil wir auch neue Methoden entwickeln um die ℤ₂ Gittereichtheorien in Experimenten zu untersuchen
Reading gender
Get PDFDie drei ??? und Die drei !!! sind nicht nur Klassiker der Kinderkrimiserien, sondern auch mit Inhalt und Vermarktung immer wieder Gegenstand der Kritik in Bezug auf (Geschlechter-)Stereotype. Wie lassen sich diese Anfragen einordnen und wissenschaftlich fassen? Welche Entwicklungen und Tendenzen, welche Ambiguitäten sind zu beobachten? Und wie kann auch oder gerade durch Medienwelten mit teils problematischen Darstellungen Geschlechterreflexion angeregt werden?
Die vorliegende Forschungsarbeit bietet einerseits einen theoretisch fundierten Rahmen zum Umgang mit medialen Geschlechterdarstellungen, andererseits ein didaktisches Analysemodell sowie eine ausführliche Untersuchung zu beiden Serien und Anregungen zur wertschätzenden methodischen Umsetzung geschlechterreflexiver Arbeit (nicht nur) im Deutschunterricht.
Sophie Schuhmacher studierte Deutsch, Geschichte, Politik und Gesellschaft und Deutsch als Zweitsprache für das gymnasiale Lehramt an der LMU München, wo sie auch promoviert wurde. Ihre Interessensgebiete umfassen neben genderreflexiver Deutschdidaktik fächerübergreifende Überlegungen zur Werteerziehung und Bildung für nachhaltige Entwicklung.Die drei ??? and Die drei !!! are not only classics of children's crime fiction, but also repeatedly the subject of criticism with regard to (gender) stereotypes. But how can these be apprached scientifically? What developments and tendencies, what ambiguities can be observed? And how can gender reflection be stimulated by fictional worlds with sometimes problematic representations and marketing strategies?
This dissertation offers a theoretically sound framework for dealing with gender representations in media, a didactic analysis model, a detailed examination of the two series and suggestions for the appreciative methodical implementation of gender-reflective work (not only) in literature lessons.
Sophie Schuhmacher studied German, history, politics and society and German as a second language for secondary school teaching at LMU Munich, where she also completed her doctorate. Her areas of interest include gender-reflective literature didactics, interdisciplinary values education and education for sustainable development
Physiologically adaptive systems across the Mixed Reality continuum
Get PDFAs Mixed Reality (MR) technologies progressively enter our daily lives, blending digital information seamlessly with our physical world, they unlock new potential for enhancing productivity and engagement across various activities, from sketching to typing and object manipulation. However, this fusion of virtual and physical elements also elevates the complexity of our visual environments, challenging our capacity to navigate and process an increasingly congested information space without becoming overwhelmed. This thesis contends that the dynamic nature of MR systems, which blurs the lines between the real and virtual worlds, necessitates the development of adaptive MR environments. Such environments are designed to intelligently modulate and tailor content in real-time, responding to users’ cognitive states and environmental contexts to optimize user engagement and minimize cognitive strain.
Centered on the premise that effective interaction within these richly blended settings hinges on users’ ability to manage attentional resources efficiently, this research explores the integration of physiological computing into MR. By leveraging real-time monitoring of physiological signals, MR systems can gain implicit insights into the user’s attentional state and cognitive load, enabling them to adapt dynamically to support the user’s immediate needs and objectives. By examining how various degrees of virtuality affect users’ engagement, attentional allocation, and workload, this thesis systematically investigates the potential of adaptive MR systems to enhance user experience without compromising productivity.
The investigation extends to designing, evaluating, and implementing physiological computing systems within MR environments, offering novel insights into supporting task engagement and managing attentional load. Moreover, it tackles the technical challenges of embedding physiological sensors within MR hardware, proposing a groundbreaking approach to unobtrusive user state monitoring.
This thesis makes significant strides in bridging the gap between physiological computing and MR, laying the groundwork for future research in ubiquitous computing, pervasive computing, and affective computing. Its findings highlight the critical role of interdisciplinary collaboration in understanding and realizing implicit interaction in adaptive MR systems, where intelligent environments enhance our daily lives by being responsive, intuitive, and seamlessly integrated
Expression and function of Transient Receptor Potential channels in murine lung interstitial macrophages, alveolar epithelial cells and fibroblasts
Get PDFExploring the human-swine interface of influenza A viruses
Get PDFThe COVID-19 pandemic has highlighted the significance of closely monitoring emerging infectious diseases, as 75% of them originate from animals. Influenza A viruses (IAV) have repeatedly proven to be an imminent global health threat over the last century by provoking five human pandemics, that have been mostly traced down to originate from an animal source. In general, IAVs are host specific, but remain genetically highly flexible due to their error-prone RNA polymerase (genetic drift) and their segmented genome structure, which can lead to reassortment between different IAV strains (genetic shift). Thus, IAVs are able to overcome host-restriction factors and evade innate immune response of novel host environments, which leads to frequent inter-species spillover events.
Swine influenza A virus (swIAV) is present in pig populations globally, causing harm to animal welfare and resulting in economic losses as a part of the porcine respiratory disease complex (PRDC). The subtypes H1N1, H1N2 and H3N2 circulate enzootically in pig herds, leading to respiratory disease and, indirectly, reproductive losses. After suspecting pigs as a reservoir for zoonotic IAV, the emergence of the H1N1pdm09 “Swine flu” in 2009 in Mesoamerica became the latest human pandemic and underlined this assumption. H1N1pdm09 as well as other seasonal human IAV were repeatedly introduced by humans into pig populations worldwide by reverse zoonosis. These events have led to a drastic increase of genetic swIAV diversity, with the establishment of potential zoonotic reassortants in pig holdings. The industrialization of pork production and the increasing cross-border trade in recent decades have created a growing interface between humans and swine, which may facilitate reciprocal transmissions of IAV. Sporadic and clustered outbreaks of zoonotic swIAV have been observed regularly worldwide, but without establishing sustained human-to-human transmission chains yet. However, it was observed, that persons with occupational exposure to swine have a heightened seroprevalence for swIAV compared to the general human population, considering them to have an increased risk to exposure of potential zoonotic swIAV.
To gain a comprehensive understanding of the complexity of host-specific factors and disease dynamics of interspecies transmission of IAV at the human-swine interface, a One Health approach was employed in this thesis. Therefore, (i) we revised the role of pigs as reservoirs for zoonotic IAVs and analyzed the latest zoonotic spillover events globally, (ii) updated diagnostic tools to improve swIAV surveillance and analyzed swIAV sequences to track the ongoing genomic diversification and identify zoonotic markers and (iii) explored the human-swine interface to determine the actual frequency of interspecies transmission and analyzed the potential of farm workers and children to spread swIAV in the society