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Efficient methods of exploring the potential energy surface
Full text linkComputational simulations have become indispensable in physics, materials science, and chemistry, enabling deep insights into material properties and molecular behavior. A central challenge in these fields is efficiently exploring the potential energy surface, which is essential for understanding and predicting system behaviors at the atomic level. This thesis aims to develop and enhance computational methods for efficient exploration of the potential energy surface through three key projects.
Firstly, we introduce the symmetry penalty function, a novel approach for global optimization algorithms like Minima Hopping. By applying Pauling's rule of structural parsimony, the method biases the search towards structures with similar atomic environments, effectively reducing the configurational space and improving search efficiency. This approach led to significant computational speedups, achieving up to 25-fold faster discovery of ground states in silicon carbide and 63-fold in C molecules.
Secondly, we develop the mode-based finite difference method for vibrational frequency calculations. The traditional finite difference method in Cartesian coordinates is sensitive to noise in the forces, this is problematic because density functional theory calculations inherently have some noise in the forces. The mode-based method mitigates this by performing finite differences in mode space, reducing the impact of the noise on the forces and enhancing accuracy. Applied to Na clusters and ethanol molecules, the mode-based method achieved mean relative errors up to two orders of magnitude lower than the Cartesian-based method.
Thirdly, utilizing the advancement from our mode-based method for the vibrational analysis, we conducted an extensive global structure search on sodium clusters ranging from 50 to 370 atoms using the Minima Hopping algorithm with a Finnis-Sinclair potential. This study reveals the emergence of body-centered cubic structures in clusters of approximately 276 to 338 atoms, the first observation of bulk-like structural motifs in nanoparticles. Additionally, these findings provide theoretical explanations for experimental anomalies in melting temperatures and photoelectron spectra near 300 atoms, which have been an unsolved scientific problem for sodium clusters for almost two decades.
Collectively, the methods developed in this thesis enhance the efficiency of potential energy surface exploration and the accuracy of vibrational analysis. Additionally, our insights into the structural evolution of sodium nanoparticles provide new insights and contribute to solving a long-standing scientific research gap regarding sodium clusters
Protein engineering to modulate dynamics of molecular machines
No full textProteins are macromolecules that drive nearly every biological process, including cell metabolism, signaling, and structural support. While sequencing genomes has helped decipher the primary amino acid sequences of countless proteins, it is ultimately the three-dimensional fold that determines a protein’s function. Experimental methods and, more recently, computational tools enabled to solve or predict the folds of many proteins, contributing to our understanding of the relationship between protein fold and function. Altering protein function or creating entirely new functions requires generating proteins with new folds, for which the encoding amino acid sequences are unknown. Protein engineering is the discipline that seeks to discover new sequences that fold into proteins with desired function. As methodologies have evolved, moving from evolution-inspired approaches to rational and de novo design, protein engineering has gained significance for fundamental research and therapeutic applications. This thesis explores protein engineering as a tool, both for dissecting bacterial cellular machinery and for probing potential antibacterial mechanisms. It comprises two independent, yet complementary projects that highlight the power and versatility of protein engineering.
The first project centered on the nanomachine Type VI secretion system (T6SS), a dynamic protein complex found in many diderm bacteria that functions as a molecular speargun to inject protein effectors into target cells. T6SS relies on a contractile sheath structure that undergoes significant conformational changes to deliver effectors, followed by disassembly and recycling of the sheath by an unfoldase enzyme. This recycling is highly selective: the unfoldase only recognizes and disassembles the sheath when it is contracted. While it was assumed that this selectivity relies on T6SS structural changes exposing a known recognition motif for the unfoldase, the precise mechanism enabling the unfoldase to distinguish sheath conformations remained unclear.
To address this, I analyzed structural differences between the sheath in its different conformations. These studies pinpointed specific residues of the sheath to interact upon contraction, potentially exposing previously hidden sites necessary for unfoldase recognition. By targeted mutagenesis, I engineered functional T6SS variants that either prevented or allowed unfoldase binding independently of the sheath’s conformation. Using fluorescence microscopy, I tracked the nanomachine’s dynamics in real time, observing whether the unfoldase colocalized with the T6SS sheath. Functional assays provided insights into how these mutations impacted effector delivery efficiency and recycling, while structural analyses indicated specific structural changes essential for unfoldase recognition. Together, these studies allowed me to develop a mechanistic model explaining that certain structural changes beyond exposure of the known unfoldase recognition motif regulate the specific interaction between contracted sheath and unfoldase that allows recycling of sheath.
The second project focused on the design of protein-based binders targeting two critical bacterial proteins that play essential roles in maintenance of cell envelope integrity. The first of these is Penicillin-Binding Protein 2a (PBP2a), a target for antibiotic development in Methicillin-resistant Staphylococcus aureus (MRSA). PBP2a, which enables bacterial resistance to certain β-lactam antibiotics, has traditionally been targeted at its active site. However, my goal was to develop a protein binder that could inhibit the protein by interacting with alternative, previously unexplored sites. Using modern computational protein design methods, I generated and refined binders with nanomolar affinities for PBP2a. In vitro competition assays with traditional antibiotics revealed only minimal competition for the active site, confirming a new mechanism of target binding. In cell-based assays, these binders significantly reduced MRSA viability, indicating a promising treatment approach that differs from traditional active site inhibition.
The second protein target, BamA, is essential in Gram-negative bacteria and is involved in outer membrane protein biogenesis. BamA is challenging to target effectively due to its structural flexibility, which allows it to adopt multiple conformations essential for its function. To inhibit BamA, I computationally designed protein binders intended to stabilize BamA in a non-functional state, which should result in bacterial lysis. Experimental evaluation of these binders is pending.
Taken together, by explaining regulatory mechanisms of bacterial nanomachines and exploring alternative antibacterial strategies, this thesis provides insights into the utility of protein engineering as a research tool to study complex fundamental processes and probe therapeutic strategy. These and other emerging protein engineering methods will provide novel tools to re-engineer native proteins but also design new proteins and protein complexes with advanced functions enabling applications across medicine, biotechnology, and materials science
Endovascular treatment of ischemic stroke due to large-vessel occlusion of the anterior circulation in the 6- to 24-hour time window
Full text linkThe starting point for this dissertation was the observation that in clinical practice some patients with anterior circulation large vessel occlusion (aLVO) receive endovascular treatment (EVT) even if they do not meet the guideline selection criteria in the 6-24 hour time window. This is due to the selective inclusion criteria of the DEFUSE-3 and DAWN trials. Although there have been some retrospective studies of less selected patient groups, these have left many relevant questions unanswered.
The aim of this dissertation was to help fill the research gaps regarding the efficacy and safety of EVT in less selected patient populations from clinical practice.
Based on the identified research gaps, the dissertation encompasses three projects. The first project evaluated the safety and efficacy of EVT compared with best medical treatment in patients with aLVO who did not meet the eligibility criteria of DEFUSE-3 and DAWN. In the second subproject, we aimed to investigate whether fulfillment of the DEFUSE-3 and DAWN inclusion criteria is a predictor of functional outcome at three months in patients who received EVT. In the third project, we investigated the association between different multimodal CT-based surrogate markers of early ischemic changes in patients presenting 6-24 hours after stroke onset and their predictive utility for functional outcomes at 90 days
Das Verhältnis zwischen Wirtschaft und Gesellschaft in Indien
Full text linkZiel dieser Dissertation ist es, die Beziehung zwischen Wirtschaft und Gesellschaft in Indien zu erforschen. Die indische Gesellschaft ist immer noch mit einem hohen Grad an Ungleichheit konfrontiert, während Unternehmen vom wirtschaftlichen Aufschwung bereits seit Jahrzehnten profitieren. Um der Ungleichheit entgegenzusteuern, verfolgte die indische Regierung mit der Einführung des Companies Act 2013 eine innovative Idee. Mit dem Act müssen große Unternehmen einen Teil ihres Gewinns in Projekte zur Unternehmensverantwortung investieren. Mit der Definition von Unternehmensverantwortung, welche die Regierung im Act veröffentlichte, veränderte sich die Dynamik zwischen Wirtschaft und Gesellschaft in Indien. Diese Definition steht ausserdem in vielerlei Hinsicht im Widerspruch mit westlichen Konzepten der Unternehmensverantwortung, die den akademischen Diskurs dominieren.
Die Forschung konzentriert sich auf die Verantwortlichkeiten großer Unternehmen und die Erwartungen, die von verschiedenen Akteuren an sie gestellt werden. Die Wirtschaftsethik und damit das Verständnis und die Erwartungen dessen, wofür grosse Unternehmen verantwortlich sind, ist stark mit dem kulturellen Kontext verbunden. Die Dissertation trägt mit einem kultursensiblen Ansatz zur Erforschung von Unternehmensverantwortung in Indien bei und auf diese Weise wird der akademische Diskurs um eine nicht-westliche Perspektive erweitert.
Um Indiens einzigartige Beziehung zwischen Wirtschaft und Gesellschaft besser zu verstehen, wird zunächst eine Auswahl westlicher Theorien vorgestellt, um eine Basis von Denkweisen zu erstellen. Mit dieser Denkbasis wird die westliche Literatur, die im akademischen Diskurs als universell dargestellt wird, in komprimierter Form vorgestellt und anschliessend auf den indischen Kontext angewandt, indem Parallelen und Diskrepanzen aufgezeigt werden. In dieser Dissertation wurde jedoch kein Ländervergleich durchgeführt. Die Denkbasis der westlichen Literatur wird nicht stellvertretend für die Gesamtheit westlicher Theorien herangezogen und auch die indische Regierung wählte mit der Einführung des Act eine ganz bestimmte Herangehensweise, um soziale Herausforderungen zu meistern. Indien kann daher nicht als Repräsentant von über 150 nicht-westlichen Ländern betrachtet werden.
Um Erwartungen im indischen Kontext zu erfassen, wurden zwei gesonderten Studien durchgeführt, welche die wissenschaftliche Perspektive und die gesellschaftliche Perspektive auf Unternehmensverantwortung untersucht. In der ersten Studie wird die wissenschaftliche Perspektive über den akademischen Diskurs in Form einer Literaturanalyse untersucht. In der zweiten Studie wird die gesellschaftliche Perspektive über den medialen Diskurs durch eine Analyse indischer Zeitungsartikel erschlossen. Für beide Analysen wurde die Context Configuration Analysis verwendet, eine qualitative Methode für nicht numerische Daten.
Im akademischen Diskurs wurde eine Typologie von den Vor- und Nachteilen des Act entwickelt und anschliessend Verbesserungsvorschläge erfasst. Die Argumente beziehen sich entweder auf die konzeptionelle oder die Akteursebene. Des Weiteren zeigen die Ergebnisse einen kontroversen Diskurs, indem sich Meinungen teilweise direkt widersprechen. Der akademische Diskurs spiegelt das Spannungsfeld und die Komplexität wider, die durch die Herausforderung entstehen, das Konzept der Unternehmensverantwortung in der Kultur und dem Kontext Indiens zu definieren und zu etablieren. Veränderungsvorschläge konzentrieren sich auf Feinheiten bei der Formulierung des Act und die Implementierung. Interessant ist, dass die Existenz des Act in seinen Grundsätzen nicht in Frage gestellt wird, obwohl die Argumente mehrheitlich negativ sind, was weitgehend auf Akzeptanz des von der Regierung gewählten Kurses hindeutet.
Im medialen Diskurs liegt der Schwerpunkt der Untersuchung einerseits in dem systematischen Erforschen der Erwartungen, welche die Medien an Unternehmen stellen und andererseits wurde untersucht, warum Unternehmen diese Verantwortung haben. Ergebnisse zeigen, dass der Act auch im medialen Diskurs ein Meilenstein ist, der die Erwartungen an Unternehmen hinsichtlich ihrer Verantwortung massgeblich beeinflusst hat. Die soziale Entwicklung soll von Unternehmen vorangetrieben werden. Unter anderem zeigt die Typologie der Verantwortlichkeiten, dass die Erwartungen bereits drei Jahre nach der Implementierung mit dem Act übereinstimmen und dass Unternehmen im medialen Diskurs als ausführende Kraft gesehen werden, welche die Visionen der Regierung umsetzt.
Die Dissertation trägt zu einem kontext- und kultursensitiven Ansatz in Theorie und Forschung bei und gibt praktische Implikationen für die neu eingeführte Politik Indiens. Die konkrete Analyse birgt das Potential, die Zusammenarbeit zwischen Interessengruppen sowohl national als auch international zu erleichtern. Die Teilprojekte wurden in Zusammenarbeit mit verschiedenen Akteuren der indischen Industrie und Wissenschaft durchgeführt
Quantifying bacterial responses to antibiotics at the single-cell level
Full text linkThe emergence of pathogen resistance to antimicrobials is putting modern medicine at risk. One of the main challenges in the treatment of bacterial infections is that current antibiotics often fail to eradicate the whole bacterial population, driven by the constant misuse and overuse of these compounds. Even genetically identical cells can take on highly heterogeneous physiological states resulting in bacterial subpopulations being less susceptible to the treatment. In particular, some cells are in physiological states that allow them to survive antibiotic treatment without any resistance mutations. For instance, slow-growing cells have been reported to be more tolerant to some antibiotics, and this increased tolerance can facilitate the subsequent fixation of resistance mutations. Most methods for the discovery and study of antimicrobial compounds are based on liquid cultures which focus on the antibiotic response at the population level, being blind to single-cell dynamics. Consequently, the determinants of sensitivity to antibiotics are only poorly understood at the single-cell level due to the lack of quantitative data.
In recent years, powerful methods have been developed to quantitatively measure behaviour and responses in single bacterial cells. By combining microfluidics with time-lapse microscopy, it is possible to track growth, gene expression, division, and death within lineages of single cells. An especially attractive microfluidic design is the Mother Machine, a device where bacteria grow within narrow growth channels that are perpendicularly connected to a main flow channel, which supplies nutrients and washes away cells growing out of the growth channels. In this work, we investigate the response of bacterial cells to antibiotics using an integrated microfluidic and computational setup: the dual-input Mother Machine (DIMM). The DIMM allows arbitrary time-varying mixtures of two input media, such that cells can be exposed to a controlled set of varying external conditions. Using the companion image analysis software Mother Machine Analyser (MoMA) we can segment and track cell lineages from phase-contrast images with high throughput and accuracy.
In light of this work, we developed new multiplexed microfluidic designs using the new PyMicrofluidics tool, which facilitates the drawing and handling of complex circuits. These new designs, enable the study of multiple conditions in parallel. Furthermore, we introduced filtering structures in the Mother Machine channels. The media carrying nutrients or antibiotics flows from the main channel through the channels where the cells are trapped, without letting the cells escape. This grants the ability to load cells inside the Mother Machine faster, as well as reduce the nutrient-gradient effect caused by the delivery of media only through diffusion in classical dead-end channels.
We use this integrated setup to quantify how the antibiotic response of individual bacteria depends on their physiological state at the time the treatment commences. The time resolution achieved with such technology allows to track how the bacteria evolve during treatment and after the treatment to assess survival. For this, we focus on treating Escherichia coli (E. coli) with a variety of clinically relevant antibiotics at different concentrations. The methods we present in this work will allow the identification of antimicrobial compounds that specifically target these resistant subpopulations, which could in the future complement existing treatment strategies and have a potential impact on antimicrobial drug discovery and treatment design
Convergence of the Euler-Voigt equations to the Euler equations in two dimensions
Full text linkIn this paper, we consider the two-dimensional torus and we study the convergence of solutions of the Euler-Voigt equations to solutions of the Euler equations, under several regularity settings. More precisely, we first prove that for weak solutions of the Euler equations with vorticity in the approximating velocity converges strongly in . Moreover, for the unique Yudovich solution of the Euler equations we provide a rate of convergence for the velocity in . Finally, for classical solutions in higher-order Sobolev spaces we prove the convergence with explicit rates of both the approximating velocity and the approximating vorticity in
Deploying online instruments to evaluate oxidative properties of combustion and atmospheric aerosols
Full text linkOutdoor air pollution is one of the greatest environmental risks to public health according to the World Health Organization. As 99% of the world’s population lives in areas which do not meet the recommended limit values, 6.7 million premature deaths per year can be attributed to the adverse health effects caused by the exposure to particulate matter (PM). This is comparable to the effects of direct tobacco use. While the link between adverse health effects and PM has been clearly established after decades of epidemiological studies the exact mechanism, sources and PM properties responsible are still poorly understood. Oxidative stress has been identified as one of the main possible toxicity pathways which is caused by an imbalance of the oxidant-to-antioxidant ratio that favours the former. PM can introduce particle-bound oxidants like reactive oxygen species (ROS) as well as compounds that can produce ROS in situ in the human body after particle inhalation, which is defined as the oxidative potential (OP). OP has been suggested as potential metric that could provide a link between PM with its specific toxicity-relevant composition and negative health effects. ROS and OP are commonly quantified using acellular assays that simulate oxidation reactions in the lungs using surrogate reductants. Conventionally, offline methods with time delays between sample collection and analysis are applied which can lead to significant underestimations. Due to long time delays between sample collection and measurement highly reactive compounds can decompose before analysis. Online adaptations avoid this by extracting PM directly into the reagents. Two recently published instruments applying different online assays have been deployed for several laboratory measurement campaigns investigating interactions of specific PM constituents as well as the effect of atmospheric processes of different anthropogenic combustion emissions (car, ship, aircraft, wood stove). Additionally, ambient measurements near a heavily congested road site and suburban background site as well as in an underground subway station in London, UK, were performed. In between campaigns, technical developments to improve the instrument’s reliability, user friendliness, and limit of detection were implemented. Significant and highly dynamic changes in ROS and OP activity of combustion PM were observed depending on combustion source and conditions (engine type, load, fuel) as well as photochemical ageing. In most cases an increase of ROS and OP with higher ages has been measured compared to primary emissions. This showed that these sources can also play a role
after atmospheric transport beyond the immediate emission. Even in a seemingly stable and isolated environment like an underground public transport system, dynamic changes of OP and ROS were observed in combination with changing physical and chemical properties of PM. These observations were made possible by applying high time resolution instruments that minimize sample degradation. Furthermore, after several deployments their operation as well as data management was streamlined and simplified
Biosynthesis of the bacterial antibiotic 3,7-dihydroxytropolone and its potential role for iron-acquisition
Full text linkNatural products serve as promising drug leads due to their manifold and potent bioactivities. Tropone natural products with their unusual seven-membered aromatic ring exhibit antibacterial, antiviral and anticancer activities and therefore mark a promising group of compounds for further investigation. In the past, their biosynthesis in bacteria has been linked to phenylacetic acid degradation, where a shunt product was identified as putative universal precursor for tropone natural products such as 3,7-dihydroxytropolone (3,7-DHT). Since then, considerable efforts have been made to elucidate the downstream processing of this precursor, and although the involvement of a few individual enzymes has been demonstrated, a complete biosynthetic pathway for such a tropone natural product had so far not been elucidated.
In this work, the biosynthetic pathway for 3,7-DHT of the Gram-positive Actinobacterium Streptomyces cyaneofuscatus Soc7 could be reconstituted in vitro for the first time. Furthermore, in a collaborative effort, some insights into the biosynthesis of 3,7-DHT in Gram-negative Pseudomonas sp. Ps652 could also be obtained, which surprisingly proceeds via a different enzymatic route. Additionally, a siderophore-interacting protein (SIP), that likely facilitates iron-acquisition using tropone natural products and/or grants self-resistance against these compounds could be identified and characterized. Structural and biochemical properties of all enzymes were investigated using a combination of methods including high-performance liquid chromatography (HPLC), mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy and protein X-ray crystallography, leading to the main findings that are summarized below:
- Enzymes encoded by genes from the trl gene cluster of Gram-positive Streptomyces cyaneofuscatus Soc 7 including the putative enoyl-CoA hydratase TrlA, thioesterase TrlF, NADH- and FAD-dependent two-component flavoprotein monooxygenase (FPMO) TrlCD and NADPH- and FAD-dependent FPMO TrlE were heterologously produced in Escherichia coli BL21 pL1SL2 and subsequently purified via affinity chromatography. A protein crystal structure of TrlE could be obtained, which allowed further structural characterization. (Part I)
- HPLC and MS-measurements as well as NMR spectroscopy allowed the identification of reaction intermediates and products from in vitro assays with these enzymes. This enabled the full reconstitution of the 3,7-DHT biosynthetic pathway. Accordingly, TrlF cleaves the CoA-ester bond of the tropone natural product precursor from PAA catabolism. TrlE performs an ipso-substitution of a carboxylic acid group with a hydroxyl group (decarboxylation coupled to hydroxylation) and further catalyzes a ring-oxidation to yield tropolone. TrlCD then performs two subsequent ring-hydroxylations of tropolone to afford 7-hydroxytropolone (7-HT) and finally 3,7-DHT. Only TrlA showed no enzymatic activity in vitro under the tested conditions and was therefore substituted by a previously characterized enoyl-CoA hydratase (PaaZ-E256Q variant) from PAA catabolism. (Part I)
- In a collaboration with the group of Prof. Dr. Truman from the John Innes Center in Norwich, UK, the biosynthesis of tropone natural products in Gram-negative Pseudomonas sp. Ps652 was investigated. The results revealed that Pseudomonas sp. Ps652 is able to produce 3,7-DHT and that enzymes encoded in the tpo gene cluster play crucial roles in the biosynthesis. My contribution to this study, assisted by a master student, included the heterologous expression of the FPMO TpoE and the thiosterase TpoD from Pseudomonas sp. Ps652 in Escherichia coli BL21 and the subsequent purification via affinity chromatography. Furthermore, I conducted HPLC- and MS-measurements of the in vitro assays, which revealed that these enzymes work together to convert the tropone precursor from PAA catabolism to a likely on-pathway intermediate for 3,7-DHT biosynthesis. (Part II)
- During the investigation of the genomic environment of the trl gene cluster in Actinobacteria, a co-located gene encoding a predicted SIP could be identified in multiple bacteria. The SIP from the Gram-positive Actinobacterium Amycolatopsis regifaucium was heterologously produced in Escherichia coli BL21 pL2SL2 and subsequently purified via affinity chromatography. Thermal shift measurements as well as photometric assays revealed that this enzyme is able to reduce (di)hydroxytropolone- Fe3+ complexes and thereby provide Fe2+ for the cell. Moreover, a protein crystal structure of this SIP could be obtained and allowed further structural investigation. The combined findings from the enzymatic assays and the protein structure suggests that the current categorization of SIPs should be revisited, as the investigated enzyme showed unusual properties regarding cofactor specificity and structural composition, which do not fit the in the current categorization system similar to other recently reported SIPs. (Part III)
In summary this thesis provides insights into the biosynthesis of tropone natural products, especially 3,7-DHT, for both Gram-negative and Gram-positive bacteria. In particular, the biosynthesis in Gram-positive bacteria could be elucidated by reconstituting the complete pathway in vitro starting from phenylacetyl-CoA. Furthermore, the identification and characterization of a SIP associated with tropone natural product biosynthesis will facilitate future studies on the ecological role of 3,7-DHT and related compounds in iron-acquisition and possibly self-resistance
Exploring two-dimensional magnetism by scanning nitrogen-vacancy magnetometry
Full text linkQubits represent the fundamental building blocks of emerging quantum technologies. Their properties are highly sensitive to the environment, making them well suited for sensing applications and enabling the exploration of new physics at the frontiers of current research. The nitrogen-vacancy (NV) is a particularly promising qubit for quantum sensing applications because its spin ground state can be manipulated, initialized, and read out in a simple setup, its Zeeman splitting allows for quantitative magnetic field measurements, its long spin coherence enables highly sensitive measurements, and diamond, as a host material, provides a robust framework for the fabrication of nanoscale sensors. Embedded in an all-diamond atomic force microscopy tip, the NV can be brought into close contact with a magnetic surface. This enables the quantitative recording of the arising stray magnetic field with high sensitivity and spatial resolution. Thus, scanning NV magnetometry (S-NVM) is a viable tool for studying various phenomena in solid state physics.
The discovery of two-dimensional (2D) magnets has opened a new field of research that requires novel imaging techniques to characterize them. S-NVM is a suitable technique to study these materials due to its sensitivity to detect the weak magnetic signals from even a single atomic layer, typically without perturbing the fragile magnetic state of these materials. Despite the constraints imposed by the photophysics and the quantization axis of the NV, S-NVM is able to operate over the full temperature and external field range relevant to 2D magnets.
S-NVM is applied to study the nanoscale magnetism of single-layer EuGe2 grown by molecular beam epitaxy on a pre-patterned substrate. It is found that its average magnetization is described by a disordered 2D magnet with easy-plane anisotropy and low uniaxial in-plane anisotropy with a paramagnetic contribution. The disorder manifests itself in a complex magnetic texture on the film and can be described by a grain structure with a different critical temperature for each grain, replicating the observed statistics of the texture. Notably, the paramagnetic contribution is a property of each grain, indicating an internal structure below the spatial resolution of the technique.
S-NVM is also used to investigate the origin of the exchange bias in a MnPS3/Fe3GeTe2 heterostructure observed in anomalous Hall effect transport measurements. Although MnPS3 exhibits the magnetic structure of an ideal Heisenberg antiferromagnet with a perfectly compensated magnetic moment, a phase transition occurs below 40 K, giving rise to an uncompensated moment in the bulk crystal. This moment persists down to a few atomic layers and induces the exchange bias in the heterostructure.
These two examples demonstrate the great potential of S-NVM in exploring the rich physics of 2D magnetism. Thereby, it will contribute to new discoveries in the field and support the integration of 2D magnets into novel architectures for innovative spintronic devices
Dog walk encounters: openings between unacquainted persons walking their dog in public space
Full text linkThis thesis presents a comprehensive investigation into chance encounters between people walking their dogs in open spaces. These unplanned interactions occur as dog-guardian formations converge, resulting in inherently mobile encounters that are intertwined with the progression and coordination of the walk. Rooted in ethnomethodology (EM) and conversation analysis (CA), the study explores the gradual development of interactional openings, focusing on what constitutes a ‘proper’ beginning to such encounters.
During dog walks, guardians engage in multiple courses of action, monitoring and instructing their dogs while also preparing for safe interactions with oncoming walkers. The development of an interactional space between mutually approaching dog-guardian formations is crucial for negotiating how the encounter will unfold. This also considers the conditions of possible contact between the dogs since the type of action initiated by guardians also depends on their assessment of whether the dogs are compatible. Moreover, the study examines how guardians publicly display their expertise and make relevant their dogs’ competence, revealing normative and moral aspects associated with walking a dog.
The interactional order and public accountability in these encounters are shaped by methodic practices achieving normativity, orderliness, and intersubjectivity. Adopting a praxeological approach within EMCA, the study transcends traditional ontological divisions between animal and human. The embodied manifestations of dogs interacting with humans are treated as significant phenomena, revealing how intelligibility and understanding emerge during the everyday activity of dog walking. The analysis of dog walk encounters thus highlights the active participation of dogs as ratified participants in interactions with humans.
This thesis enriches our understanding of human-dog interactions and offers valuable insights into the dynamics of chance encounters during dog walks in open spaces. It contributes to the broader field of interspecies interaction and provides a deeper understanding of the interactional intricacies that shape social encounters between individuals and their canine companions. The findings advance our knowledge of how humans and dogs engage with each other within the context of walking, illuminating the complex and nuanced ways in which interspecies communication and coordination take place