Prof. Dr. Constantin R. Schrade: „Next-Generation Qubits in Superconducting Circuits”
Niels Bohr Institute, University of Copenhagen, Denmark - Seminar@HHUD: 25.5.23 16:30 s.t., Lecture hall 25.31 O0.5J

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Prof. Dr. Gerhard Kahl: „Microswimmers learning chemotaxis”
Institut für Theoretische Physik, TU Wien, Austria - Seminar@HHUD: 20.4.23 16:30 s.t., Lecture hall 25.31 O0.5J

Microorganisms which are abundant in nature and which play a key role in many biological phenomena have developed a huge variety of strategies which help them in nutrient uptake, to reproduce, to escape from predators, or to hunt prey. These strategies are realized via different manners, such as shape deformations or by the use of appendages. In an effort to understand the locomotion of these microswimmers under low Reynolds number conditions, models have been proposed, which are based on fixed swimming strategies. However, models of such organisms that adapt their swimming strategies to the ever changing surroundings have rarely been investigated, so far. I will report about a project where a simple microswimmer model is trained to swim and to uptake nutrients by combining the equations-of-motion with modern tools of machine learning. Using genetic algorithms optimized neural networks are developed which control the shape deformations of the microswimmers and allow them to navigate in static and time-dependent chemical environ-ments. By introducing noisy signal transmission in the neural networks the well-known biased run-and-tumble motion emerges, as it is known for many swimming microorganisms. Extensions of the simple model in use to more realistic microswimmers are discussed.

Prof. Dr. Martin Müser: „Contact mechanics and its relation to empirical friction laws”
Universität des Saarlandes, Saarbrücken - Seminar@HHUD: 02.02.2023 16:30 s.t., Lecture hall 25.31 O0.5J

Empirical laws describing the friction between solids are simple, however, the microscopic origin of solid friction is generally quite complex, involving the concerted action of many degrees of freedom. Over the centuries, many different processes have been identified causing solid friction to occur, however, for most processes, it is generally difficult to argue why they would lead to the frequently observed (a) proportionality between solid friction and load and (b) irrelevance of the apparent contact area. Moreover, when several mechanisms act in parallel, as is usually the case, it is difficult to predict simple trends like whether more roughness increases or decreases friction: More roughness generally leads to more plastic and viscoelastic deformation and thus to higher friction but roughness also reduces true, microscopic contact and adhesive or capillary forces thereby lowering friction. Given the diversity of mechanisms, it is clear that there can be no universal reason for the empirical laws describing solid friction. Nonetheless, it turns out that the surface topography of the solids in contact and their change with load and sliding turns out crucial.

In my talk, I will present recent advances in contact mechanics, which describes contact-induced deformations and stresses, and explore how the newly gained insights benefit the explanation of the validity of empirical friction laws as well as reasons for their breakdown.

Prof. Dr. Roel Dullens: „Emergence of interparticle friction in attractive colloidal matter”
Radboud University Nijmegen - Seminar@HHUD: 26.01.2023 16:30 s.t., Lecture hall 25.31 O0.5J

Interparticle friction plays a governing role in the mechanics of particulate materials. However, virtually all experimental studies to date rely on measuring macroscopic responses, and as such it remains largely unknown how frictional effects emerge at the microscopic level. This is particularly challenging in systems subject to thermal fluctuations due to the transient nature of interparticle contacts. Here, we directly relate particle-level frictional arrest to local coordination in an attractive colloidal model system. We reveal that the orientational dynamics of particles slows down exponentially with increasing coordination number due to the emergence of frictional interactions, the strength of which can be tuned simply by varying the attraction strength. Using a simple computer simulation model, we uncover how the interparti-cle interactions govern the formation of frictional contacts between particles. Our results establish quantitative relations between friction, coordination and interparticle interactions. This is a key step towards using interparticle friction to tune the mechan-ical properties of particulate materials.

Prof. Dr. Ulf Wiedwald: „Magnetic Nanoparticles: From Physical Design to Medical Applications”
Universität Duisburg-Essen - Seminar@HHUD: 19.01.2023 16:30 s.t., Lecture hall 25.31 O0.5J

The application of magnetic nanoparticles (MNPs) in biomedicine and theranostics is one of the most dynamic and promising fields of nanoparticles research. In my presentation, several examples for the use of multifunctional hybrid MNPs in theranostics are discussed. We designed, synthesized and tested various MNPs like ferrites [1], core-shell architectures [2], and magnetite-gold (Fe₃O₄-Au) hybrids [3] for optimized performance, e.g. in magnetic resonance imaging (MRI), magnetic particle hyperthermia (MPH) or DNA splitting [4]. The multidisciplinary approach allows us to address the entire research chain from the chemical synthesis, over the physical properties to cancer treatment methodologies [5] and toxicity screening [6].

References

1. E. Myrovali et al., Sci. Rep. 6, 37934 (2016).
2. S. Liébana-Viñas et al., RSC Advances 6, 72918 (2016).
3. M. V. Efremova et al., Sci. Rep. 8, 11295 (2018).
4. A. Nikitin et al., ACS Applied Materials & Interfaces 13, 14458–14469 (2021).
5. A. Garanina et al., Nanomedicine: Nanotechnol., Biol. and Med. 25, 102171 (2020).
6. A. Garanina et al., Nanomaterials 12, 38 (2022).

Dr. Francesco Buccheri: „Transport in Topological materials”
Institut für Theoretische Physik IV, Heinrich-Heine-Universität Düsseldorf - Seminar@HHUD: 12.1.23 16:30 s.t., Lecture hall 25.31 O0.5J

The notion of topology applied to the band theory of crystalline solids has become a paradigm to complement our understanding of phases of matter and opens the possibility of important technological advances in the fields of quantum computation and electronic control. In this talk, I will introduce two paradigmatic models, a quasi-one-dimensional supercon-ductor and a three-dimensional semimetal, and review some of their recent experimental realization. I will characterize the associated topologically non-trivial states and their robustness against electron-phonon interaction, a key step toward their detection. I will also investigate the signatures in thermoelectric transport, highlighting the contribution of the edge or surface states.

Prof. Dr. Reinhard Werner: „Geschichten über Quantenkorrelationen”
Leibniz Universität Hannover - Seminar@HHUD: 1.12.2022 16:30 s.t., Lecture hall 25.31 O0.5J

Verschränkung ist ein Schlüsselbegriff der Quantentheorie und allermodernen Quantentechnologien. In diesem Vortrag betrachte ich die Meilensteine der Entwicklung und was die jeweiligen Forscher umgetrieben hat. Von Einstein-Podolsky-Rosen über Bell und Tsirelson läuft eine Theorie-Entwicklung, für deren experimentelle Bestätigung es den dies-jährigen Physik-Nobelpreis für Clauser, Aspect und Zeilinger gab. Dies wird wieder eine Flut von wohlmeinenden Erklärungen auslösen, die Verschränkung zu einem mysteriösen Spuk vernebeln. Diesen Nebel ein wenig transparenter zu machen, ist das Hauptanliegen meines Vortrags.

Julia Sammet: „Physik-Lernzentrum: Von Studierenden für Studierende”
Goethe-Universität Frankfurt am Main - Seminar@HHUD: 20.10.22 16:30 s.t., Lecture hall 25.31 O0.5J

Außercurriculare Unterstützungsstrukturen sind in den letzten Jahren immer populärer geworden. Bei der Einrichtung solcher Strukturen stellt sich die Frage der organisatorischen und finanziellen Ausgestaltung. Das Physik-Lernzentrum in Frankfurt wurde von fünf Fachschaften aus verschiedenen Fachbereichen für mehrere Preise nominiert und wurde neben dem universitätseigenen 1822-Preis für exzellente Lehre auch mit dem Ars Legendi Fakultäten Preis 2022 ausgezeichnet. Im Vortrag stellen wir das Konzept unseres Lernzentrums und der Physik Vorkurse vor und diskutieren die Notwendigkeit/Sinnhaftigkeit solcher außercurricularen Lernstrukturen.