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Approximating the shapley value and shapley interactions
Full text linkAlthough the behavior of agents is often led by self-interest, many environments pose an incentive for cooperation by accomplishing a task together and thus be compensated collectively. This naturally leads to the search of a payout mechanism that assigns to each agent a share of the collective benefit which reflects its individual contribution to the completed task. Game theory models such scenarios by the notion of cooperative games in which the agents are the participating players. Within the game-theoretic framework, the Shapley value poses the most prominent solution to the emerging fair division problem, arguably capturing a widespread understanding of fairness.
Over the last decade, the Shapley value has received unprecedented attention within the field of machine learning, attributing importance to entities such as features, datapoints, and structural components of predictive models. Especially the branch of explainable artificial intelligence picked it up as a means to provide understanding of the decision-making of increasingly complex and opaque models. Likewise, Shapley interactions which capture synergies between players have recently attracted attention. Unfortunately, the computational complexity of both quantities, the Shapley value and Shapley interaction, suffers from the exponential blow-up w.r.t. to the number of involved players and thus becomes quickly infeasible in practice. This incentivizes the research on approximation algorithms that return precise estimates while palpating the cooperative game as little as possible.
In this thesis, we develop approximation algorithms that leverage novel representations of the Shapley value and Shapley interactions on the basis of mean estimation and weighted regression which allow for tailored sampling schemes. Given the Shapley value’s richness of applications, our methods are purposefully domain-independent without imposing structural assumptions. Consequently, they can be applied across the entire spectrum of emerging cooperative games. To this end, we place special emphasis on the variance reduction technique of stratification to develop methods that utilize the gathered information from each sample to a richer degree than in other representations possible and derive theoretical guarantees for the estimates’ precision. Empirical evaluations in the context of machine learning confirm the soundness of our propositions and their capability to display an advantage over competing methods
The diffuse soft X-ray background
Full text linkThe diffuse soft X-ray background (SXRB) holds important information about astrophysical processes from a few AU to kpc around us. In this thesis, I go from the solar wind’s interaction with the inflowing interstellar medium (ISM) at AU scales, to the local hot bubble (LHB) in 100 pc scales, and eventually arrive at the possibly >~10 kpc giant X-ray structure stemming from the inner part of the Galaxy, called the eROSITA bubbles (eRObub), using the eROSITA All-Sky Survey data (eRASS).
The Sun dwells in the LHB which is a low-density region containing ~10^6 K gas and emits thermally in the soft X-rays. The determination of the LHB hot gas properties, however, is often ambiguous because of a variable foreground caused by the charge exchange process between the solar wind ions and the inflowing neutral ISM (SWCX). I tackle this problem by choosing sight lines towards giant molecular clouds on the LHB surface, which isolate the foreground and provide calibration points for the LHB density. By the repeating surveys, the spectral analysis reveals a monotonically increasing SWCX contribution that correlates with solar activity, and the SWCX’s dependence on ecliptic latitudes, expected from the ionisation properties of the solar wind. On the other hand, the LHB seems to exhibit a temperature variation in the order of 20 eV. The LHB projected density appears to be consistent with a constant of n_e ~ 4x10^{-3} cm^{-3}, which would argue for a scenario where the hot gas indeed extends to the local bubble wall.
Moving beyond isolated sight lines, I spatially and spectrally decompose the whole western Galactic hemisphere into conventional SXRB components and focus on the LHB aspect. I observe an apparent temperature dichotomy between the northern and southern hemispheres at |b|>30 deg, which could be set up by the most recent supernova explosions in the LHB. The LHB emission measure (EM) generally increases towards the Galactic poles, which is evidence of a larger LHB extent away from the Galactic plane due to less pressure resisting expansion. Comparison with local dust maps shows clear anti-correlation between N_H and EM, supporting a scenario where the hot gas fills cavities in the local bubble. I verify a known and discover a new tunnel of hot gas, potentially linking the LHB to the nearby superbubbles. In this light, I discuss the possibility of a wider interconnected network of hot ISM throughout the Milky Way. The resulting LHB EM map is used to produce a new 3D LHB model to create a latest view of the hot solar neighbourhood by combining known superbubbles in the literature.
The last project explores the morphology and the spectrum of the eRObub as a follow-up to their recent discovery. The 3D morphology of the eRObub is explored using a geometrical model of a blast wave propagating in an ideal Galactic halo from the Galactic centre, which indicates a eRObub horizontal extent of ~6 kpc and demonstrates the large degeneracy revolving the vertical extent due to projection effects inherent in our location on the Galactic plane. The spectral analysis of the eRObub reveals an anomalous Fe XVII 3d/3s line ratio, which is best explained by two temperature components at kT = 0.25±0.03 and 0.56^{+0.04}_{-0.02} keV. We point out the existence of a bright shell surrounding the northern bubble, which is cooler and does not require a two-temperature model to fit. We rule out non-equilibrium ionisation as a possible explanation and discuss the possibility of the cool shell being a foreground structure. The eRObub spectra show a low abundance (Z ~ 0.2 Z_sun) which is consistent with shock-heating of the Galactic halo without significant metal enrichment. The North Polar Spur appears to be significantly higher in metallicity (Z > 0.5 Z_sun) than the eRObub, lending support for a star-formation-related and a separate origin from the eRObub
Pathophysiologische, diagnostische und therapeutische Aspekte neuroinfektiologischer Erkrankungen
Full text linkUnraveling luminescent and enabling photocatalytic processes of double and lead halide perovskite nanocrystals
Full text linkColloidal semiconductor nanocrystals (NCs) have become a key platform in nanomaterial research due to their tunable optoelectronic properties, and advanced synthesis methods that yield uniform, well-defined structures. Their size-dependent behavior—from quantumconfined to bulk-like regimes—makes them highly versatile for both fundamental studies and device applications. Among them, lead halide perovskite (LHP) NCs stand out for their exceptional performance in light absorbing, emitting, and detecting applications, thanks to their high defect tolerance and a simplified band structure. However, their practical use remains limited by poor moisture stability and the high toxicity of lead.
LHP NCs show significant potential for photocatalytic hydrogen production due to their high absorption coefficients and long charge-carrier diffusion lengths. However, their degradation in polar solvents limits the use of LHPs in this application. This thesis proposes a vapor-phase strategy to address this limitation by establishing a solid–gas interface that minimizes direct contact between liquid polar solvents and LHP nanoplatelets (NPls). The sustained high hydrogen evolution rate of LHP NPls/platinum (Pt) over 20 hours under simulated solar light demonstrates the feasibility of the developed vapor-phase approach, characterized by the vapor composition and different types of LHP NPls. To elucidate the charge carrier transfer mechanism from the LHP NPls to Pt cocatalysts, time-resolved photoluminescence (PL) spectroscopy is employed. The results highlight the critical role of exciton diffusion, modeled with an exponential time distribution. The diffusion time distribution is influenced by the size and geometry of NPls and the concentration of Pt nanoclusters. Moreover, transient absorption spectroscopy further reveals ultrafast electron transfer dynamics from LHP NPls to Pt nanoclusters.
On the other hand, Cs2AgBiCl6 double perovskite (DP) NCs offer a potential lead-free alternative to LHPs, showing promise for white light emission. The broad PL spectrum featuring dual emission peaks is observed in Cs2AgBiCl6 NCs with an indirect bandgap, the origins of which have been under debate. The study clarifies their origins using PL excitation and temperature-dependent PL spectroscopy. The red emission comes from excitonic recombination of defect-bound excitons with a giant oscillator strength, explaining the strong absorption peak with an extralarge binding energy. The blue emission closely relates to the surface chemistry of the DP NCs, associated with the synthetic methods. These findings underscore the critical role of silver in determining the optical properties of Cs2AgBiCl6 NCs.
The results in this thesis offer valuable insights for optimizing the performance of perovskite NCs in practical applications, including mitigating moisture instability in photocatalysis and reducing toxicity in white light emission systems.Kolloidale Halbleiter-Nanokristalle (NK) haben sich aufgrund ihrer einstellbaren optoelektronischen Eigenschaften und fortschrittlichen Synthesemethoden, die einheitliche und gut definierte Strukturen ermöglichen, zu einer wichtigen Plattform in der Nanomaterialforschung entwickelt. Ihr größenabhängiges Verhalten macht sie sowohl für die Grundlagenforschung als auch für technologische Anwendungen vielseitig einsetzbar. Unter ihnen zeichnen sich Blei-Halogenid-Perowskit (BHP)-NK durch ihre hervorragende Leistung in lichtabsorbierenden, -emittierenden und -detektierenden Anwendungen aus, was auf ihre hohe Fehlertoleranz
und vereinfachte Bandstruktur zurückzuführen ist. Ihre praktische Anwendung wird jedoch durch geringe Feuchtigkeitsstabilität und die hohe Bleitoxizität eingeschränkt.
BHP NK zeigen großes Potenzial für die photokatalytische Wasserstoffproduktion, da sie hohe Absorptionskoeffizienten und lange Ladungsträger-Diffusionslängen besitzen. Ihre Zersetzung in polaren Lösungsmitteln begrenzt jedoch die Einsatzmöglichkeit für diese Anwendung. In dieser Arbeit wird eine Dampfphasenstrategie vorgestellt, die eine Feststoff-GasGrenzfläche etabliert, um den Kontakt zwischen polaren Flüssigkeiten und BHP-Nanoplättchen (NPl) zu minimieren. Die über 20 Stunden unter simuliertem Sonnenlicht aufrechterhaltene Wasserstoffentwicklungsrate der BHP NPl/Platin (Pt)-Katalysatoren bestätigt die Machbarkeit des Ansatzes. Zur Untersuchung des Ladungsträgertransfers von BHP NPl zu PtCokatalysatoren wird zeitaufgelöste Photolumineszenz (PL)-Spektroskopie eingesetzt. Die Ergebnisse verdeutlichen die zentrale Rolle der Exzitonen-Diffusion, modelliert mit exponentieller Zeitverteilung, welche durch Größe, Geometrie und Konzentration der NPl und Pt-Nanocluster beeinflusst wird. Transiente Absorptionsspektroskopie zeigt zudem ultraschnellen Elektronentransfer von BHP NPl zu Pt-Nanoclustern.
Cs₂AgBiCl₆-Doppelperowskit (DP)-NK bieten eine vielversprechende bleifreie Alternative zu BHP und zeigen Potenzial für weiße Lichtemission. Das breite PL-Spektrum mit zwei Emissionspeaks wird bei Cs₂AgBiCl₆-NK mit indirekter Bandlücke beobachtet, deren Ursprünge bislang umstritten waren. Mittels PL-Anregungs- und temperaturabhängiger PL-Spektroskopie werden diese in dieser Arbeit aufgeklärt. Die rote Emission stammt von defektgebundenen
Exzitonen mit hoher Oszillatorstärke, was den starken Absorptionspeak mit hoher Bindungsenergie erklärt. Die blaue Emission steht in engem Zusammenhang mit der Oberflächenchemie und hängt stark von der Synthesemethode ab. Diese Ergebnisse unterstreichen die zentrale Rolle von Silber für die optischen Eigenschaften der Cs₂AgBiCl₆-NK.
Die Ergebnisse dieser Arbeit liefern wertvolle Erkenntnisse zur Optimierung von PerowskitNK in praktischen Anwendungen, insbesondere hinsichtlich der Verbesserung der Feuchtigkeitsstabilität in der Photokatalyse und der Reduzierung der Toxizität bei Weißlichtemission
On the fighting forms of shapes and echoes
Full text linkThis dissertation—"On the Fighting Forms of Shapes and Echoes: Reading Esemplasticity in the Metasonnetry of E. A. Robinson as a Poetics of Ecstasy"—develops a new, comprehensive theory for how poetic artifice induces a state of ecstasyin the reader. The study focuses on a close reading of a single metasonnet by E. A. Robinson , arguing that the ecstatic experience is the result of linguistic dyads, or duplexities, which are pairings of appositional features of language and artifice. Drawing on models from quantum physics and biology, the dissertation posits that these dynamic duplexities, upon breaking symmetry, lead to the emergence of novel, complex, and synesthetic poetic forms. Framed by the philosophy of dialogue articulated in Martin Buber's I and Thou, the three-part analysis (Duplexity, Dynamics, Dialogue) demonstrates how this continuous, esemplastic interanimation between the artifice of the text and the mind of the reader culminates in a profound, transcendent state of lyrical bliss, which is a merging of reader and writer.Diese Dissertation mit dem Titel „On the Fighting Forms of Shapes and Echoes: Reading Esemplasticity in the Metasonnetry of E. A. Robinson as a Poetics of Ecstasy“ entwickelt eine neue, umfassende Theorie darüber, wie poetische Kunstgriffe beim Leser einen Zustand der Ekstase hervorrufen. Die Studie konzentriert sich auf eine eingehende Lektüre eines einzelnen Metasonetts von E. A. Robinson und argumentiert, dass das ekstatische Erlebnis das Ergebnis sprachlicher Dyaden, oder Duplexitäten, ist, bei denen es sich um Paarungen appositioneller Merkmale von Sprache und Kunstgriff handelt. Aufbauend auf Modellen aus der Quantenphysik und der Biologie postuliert die Dissertation, dass diese dynamischen Duplexitäten nach einer Symmetriebrechung zur Emergenz neuartiger, komplexer und synästhetischer poetischer Formen führen. Gerahmt von der in Martin Bubers Ich und Du artikulierten Dialogphilosophie demonstriert die dreiteilige Analyse (Duplexität, Dynamik, Dialog), wie diese kontinuierliche, esemplastische Wechselwirkung zwischen dem Kunstgriff des Textes und dem Geist des Lesers in einem tiefgreifenden, transzendenten Zustand lyrischer Glückseligkeit gipfelt, der eine Verschmelzung von Leser und Autor darstellt
Analyse von Determinanten der Immunantwort nach SARS-CoV-2-Infektion bzw. -Impfung im Hinblick auf Risikofaktoren für Seropositivität
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Ultrafast pulse metrology
Full text linkThe investigation of ultrafast light-matter interaction requires precise control and metrology of ultrashort laser pulses, experimental setups, and related parameters. Connected with recent developments in attosecond physics, new requirements arise for laser technology, its characteri- zation, and the necessary experimental methods. These requirements are driven, for example, by the scaling of the energies of high-harmonics toward the so-called water window – the Energy range between the carbon and oxygen K-edges (284 to 543 electron volts) – or by the develop- ment of petahertz electronics. In addition, new perspectives for the investigation of elementary processes open up. In the context of this work, the underlying physical and experimental aspects of modern attosecond physics are examined in more detail. Starting with a measurement method based on petahertz electronics to determine the carrier-envelope phase (CEP) in a single-shot experiment, it is demonstrated that a robust and versatile measurement method can be achieved with a simple experimental setup. This method takes advantage of elementary electron dynamics in gas and plasma and is distinguished by its applicability across various wavelengths. Furthermore, by utilizing solitonic propagation dynamics in waveguides, it is demonstrated that laser pulses in the short-wave infrared range can be simultaneously spectrally broadened and temporally compressed. This approach circumvents complicated light-field synthesis, as well as the need for dispersive optics and the associated limitations. Attention is given to the stability of output power and the CEP, along with the resulting waveform stability. Temporal characterization reveals a waveform with a duration of a single optical cycle, consisting of spectral components spanning two optical octaves. This bandwidth enables the control of sub-cycle electron dynamics, which manifests as a spectral effect in the field-resolved measurement method. Measuring this effect allows for in-situ CEP calibration. The demonstrated spectral broadening sets new standards in the generation of high-intense ultrashort pulses, particularly regarding the achieved peak power of 0.26 terawatts, high average power, and excellent stability. Such systems are particularly well-suited for generating high-energy high-harmonics. The high average power allows for an increased interaction volume to compensate for the poor con- version efficiency. However, this results in a higher thermal load on the experimental setup and on the filters, necessitating new approaches to withstand it. At the same time, precise stabilization of the temporal delay line is essential to ensure high temporal resolution in experiments.
Therefore, a method has been developed that allows for the filtering of the driving laser and the generated harmonics while also stabilizing the temporal delay between two pulses in an interfer- ometer. It is ultimately demonstrated that this method can withstand high average power and achieve a stable interferometer throughout the duration of typical measurement campaigns.Die Untersuchung ultraschneller Licht-Materie-Wechselwirkung erfordert präzise Kontrolle und Metrologie ultrakurzer Laserpulse, experimenteller Aufbauten und zugehöriger Parameter. Verbunden mit jüngsten Entwicklungen in der Attosekundenphysik entstehen neue Anforderungen an die Lasertechnologie, deren Charakterisierung, aber auch an die erforderlichen experimentellen Methoden. Diese Anforderungen werden beispielsweise von der Skalierung der Energien hoher Harmonischer hin zum sogenannten Wasserfenster – dem Energiebereich zwischen den Kohlenstoff und Sauerstoff K-Kanten (284 bis 543 Elektronenvolt) – oder von der Entwicklung von Petahertzelektronik angetrieben. Darüber hinaus eröffnen sich neue Perspektiven für die Untersuchung elementarer Prozesse. Im Rahmen dieser Arbeit werden die zugrundeliegenden physikalischen und experimentellen Aspekte moderner Attosekundenphysik genauer untersucht. Beginnend mit einer auf Petahertzelektronik basierenden Messmethode zur Bestimmung der Träger-Einhüllenden-Phase (CEP) im Einzelschussexperiment wird gezeigt, dass mit einem einfachen experimentellen Aufbau und dem Ausnutzen elementarer Elektronendynamik in Gas und Plasma eine robuste und vielseitige Messmethode erzielt werden kann, die durch ihre Einsetzbarkeit bei verschiedenen Wellenlängen überzeugt.
Des Weiteren wird unter Ausnutzung von solitonischer Propagationsdynamik in Wellenleitern gezeigt, dass sich Laserpulse im kurzwelligen Infrarotbereich simultan spektral verbreitern und zeitlich komprimieren lassen. Damit werden die komplizierte Lichtfeldsynthese sowie die Notwendigkeit dispersiver Optiken und die damit verbundenen Einschränkungen umgangen. Hierbei liegt ein Augenmerk auf der Stabilität von Ausgangsleistung und CEP und der damit einhergehenden Wellenformstabilität. Die zeitliche Charakterisierung zeigt eine Wellenform von der Dauer eines einzelnen optischen Zyklus, bestehend aus Spektralkomponenten zweier optischer Oktaven. Diese Bandbreite ermöglicht es, Subzyklen-Elektronendynamik zu kontrollieren, was sich als spektraler Effekt in der feldaufgelösten Messmethode äußert. Die Vermessung dieses Effekts erlaubt eine in-situ CEP Kalibrierung. Die demonstrierte spektrale Verbreiterung setzt dabei neue Maßstäbe in der Erzeugung hochintensiver ultrakurzer Pulse, besonders hinsichtlich der erzielten Spitzenleistung von 0,26 Terawatt, der hohen mittleren Leistung und der ausgezeichneten Stabilität. Solche Systeme eignen sich hervorragend zur Erzeugung hoher Harmonischer mit hohen Energien. Durch die hohe mittlere Leistung kann das Interaktionsvolumen gesteigert werden, um die schlechte Konversionseffizienz zu kompensieren. Die dadurch entstehende höhere thermische Belastung des experimentellen Aufbaus und der Filter erfordert neue Wege, dieser standzuhalten. Gleichzeitig ist eine präzise Stabilisierung der zeitlichen Verfahrstufe vonnöten, um die hohe zeitliche Auflösung in Experimenten zu gewährleisten. Daher wurde eine Methode entwickelt, die sowohl die Filterung von treibendem Laser und erzeugten Harmonischen erlaubt als auch der Stabilisierung des zeitlichen Versatzes zweier Pulse eines Interferometers dient. Es wird abschließend demonstriert, dass damit zum einen der hohen mittleren Leistung standgehalten wird, zum anderen aber auch ein stabiles Interferometer über die Dauer typischer Messkampagnen erzielt werden kann
On the relationship between science and religion
Full text linkWhile some people may prefer to think of a conflict between science and religion, others may believe that it is not necessarily the case. Drawing on Ian G. Barbour’s taxonomy of the science-religion relationship, this dissertation offers an examination through three pillars: theoretical integration, measurement practice, and mechanistic testing. The first pillar integrates theoretical work and empirical evidence from various scientific disciplines to illustrate the psychological process of relating these domains via a flowchart. This process can lead people to adopt one of five conceptualizations: Conflict, Compartment, Context-Switch, Complementary, or Consonance. The second pillar aims to develop a measure that captures these conceptualizations by assuming that the construct is unidimensional and bipolar, and that people respond to the scale items according to an unfolding response process. The third pillar experimentally tests how these mental models affect people’s evaluation of the utility of scientific or religious explanations. The results show that perceptions of conflict and religiosity predict evaluations of religious, but not scientific, explanations. This asymmetry suggests that scientific explanations are primarily evaluated on their epistemic merits, while religious explanations are filtered through pre-existing beliefs. This dissertation, which consists of one theoretical paper and four empirical studies, offers novel insights into how people navigate competing belief systems and has some practical implications for science communication
