S-matrix network models for coherent waves in random media: construction and renormalization

Networks of random quantum scatterers (S-matrices) form paradigmatic models for the propagation of coherent waves in random S-matrix network models cover universal localization-delocalization properties and have some advantages over more traditional Hamiltonian models. In particular, a straightforward implementation of real space renormalization techniques is possible. Starting from a finite elementary cell of the S-matrix network, hierarchical network models can be constructed by recursion. The localization-delocalization properties are contained in the flow of the forward scattering strength ('conductance') under increasing system size. With the aid of 'small scale' numerics qualitative aspects of the localization-delocalization properties of S-matrix network models can be worked out.Comment: 10 pages, LaTeX, 8 eps figures included, proceedings PILS98, to be published in Annalen der Physi

Structure and dynamics of the electronically excited C 1 and D 0⁺ states of ArXe from high-resolution vacuum ultraviolet spectra

ISSN:0021-9606ISSN:1089-769

Pushing the button: Why do learners pause online videos?

With the recent surge in digitalization across all levels of education, online video platforms gained educational relevance. Therefore, optimizing such platforms in line with learners’ actual needs should be considered a priority for scientists and educators alike. In this project, we triangulate logfiles of a large German online video platform for educational videos with behavioral data from a laboratory study and the objective characteristics of the selected videos. We aim to understand the potential motives for why participants pause educational videos while watching such videos online. Our analyses revealed that perceived difficulties in comprehension and meaningful structural breakpoints in the videos were associated with increased pausing behavior. In contrast, pausing behavior was not associated with the videos’ formal structural features highlighted in the video platform. Implications of these findings and the potentials of our methodological approach for theory and practice are discussed. © 2021 The Author

Correlation Effects on Transport Through Few-Electrons Systems

We study lateral tunneling through a quantum box including electron-electron interactions in the presence of a magnetic field which breaks single particle degeneracies. The conductance at zero temperature as a function of the Fermi energy in the leads consists of a set of peaks related to changing by one the electron occupancy in the box. We find that the position and heights of the peaks are controlled by many-body effects. We compute the conductance up to 8 electrons for several cases where correlation effects dominate. In the range of intermediate fields spin selection rules quench some peaks. At low and high fields the behavior of the conductance as a function of the number of electrons is very different due to big changes in the many-body ground state wavefunctions.Comment: 9 pages, 2 postscript figures, Latex 3.1

Do a pedagogical agent’s clothing and an animated video’s setting affect learning?

Pedagogical agents are often used to enhance social cues in learning materials. The inclusion of pedagogical agents raises several design questions, for example on what kind of clothing the agent should wear. Further, it is not yet clear how the setting of an animated learning video (i.e., the digitally created background) affects learning. In an online experiment (N = 200), we investigated whether creating thematically appropriate clothing and setting has some added value in that it improves learning outcomes in comparison to more neutral assets. Whereas all participants acquired knowledge from the animated video, there were no main effects of clothing and setting for any of the dependent variables, but an interaction for learning outcomes (ηp2=0.02), indicating that the appropriately dressed agent worked better combined with the inappropriate setting than with the appropriate setting. Overall, given those non-significant main effects and the small effect size of the interaction, there seem to be some degrees of freedom for designers of pedagogical agents in animated learning videos. However, these degrees of freedom may be limited to at least moderate (i.e., neutral) levels of appropriateness

Rituximab induces phenotypical and functional changes of NK cells in a non-malignant experimental setting

Background: Rituximab has broad and increasing application in rheumatic diseases. It is known from lymphoma studies that natural killer (NK) cells can lyse rituximab-coated transformed B cells. However, the role of NK cells in mediating rituximab-induced depletion of non-malignant B cells is unknown. The purpose of this study was to provide fundamental data on rituximab-mediated effects on NK cells in PBMCs without tumor cells, in order to simulate effects that could be relevant in patients with rheumatic disease. Methods: Freshly isolated peripheral blood mononuclear cells (PBMCs) from healthy donors were cultured overnight with therapeutic antibodies. NK cells were isolated using a commercial kit or depleted from PBMCs using anti-CD56 and anti-CD16 monoclonal antibodies and magnetic beads. Cells were analyzed by multicolor flow cytometry. Cytotoxicity assays were performed using 51Cr-labeled K562 target cells. Results: Addition of rituximab to PBMCs resulted in depletion of B cells, which was dependent on NK cells and serum factors. The extent of B cell depletion correlated with the percentage of NK cells. Following incubation with rituximab, NK cells within PBMCs were activated, degranulated and downregulated the low affinitiy Fc-γ-receptor CD16 (FcγRIIIA). The co-activating receptor CD137 (41BB) was upregulated on a fraction of NK cells. NK cell function was altered in some donors in whom we observed rituximab-dependent reduction in NK cell cytotoxicity towards K562 tumor cells. Conclusions: NK cells mediate rituximab-induced B cell depletion. Rituximab induces altered NK cell phenotype and function

Next steps: learning a disentangled gait representation for versatile quadruped locomotion

Quadruped locomotion is rapidly maturing to a degree where robots now routinely traverse a variety of unstructured terrains. However, while gaits can be varied typically by selecting from a range of pre-computed styles, current planners are unable to vary key gait parameters continuously while the robot is in motion. The synthesis, on-the-fly, of gaits with unexpected operational characteristics or even the blending of dynamic manoeuvres lies beyond the capabilities of the current state-of-the-art. In this work we address this limitation by learning a latent space capturing the key stance phases of a particular gait, via a generative model trained on a single trot style. This encourages disentanglement such that application of a drive signal to a single dimension of the latent state induces holistic plans synthesising a continuous variety of trot styles. In fact properties of this drive signal map directly to gait parameters such as cadence, footstep height and full stance duration. The use of a generative model facilitates the detection and mitigation of disturbances to provide a versatile and robust planning framework. We evaluate our approach on a real ANYmal quadruped robot and demonstrate that our method achieves a continuous blend of dynamic trot styles whilst being robust and reactive to external perturbations

PERTURBATIONS IN THE SPECTRA OF HIGH RYDBERG STATES: CHANNEL INTERACTIONS, STARK AND ZEEMAN EFFECTS

Author Institution: Laboratorium fur Physikalische Chemie, ETH-Zurich, 8093 Zurich, SwitzerlandRydberg states of principal quantum number $n\gg50$ have been prepared by irradiation of an atomic beam of xenon with vacuum ultraviolet (VUV) radiation. Narrowband submillimeter-wave (THz) radiation was then used to record spectra of transitions from these Rydberg states to higher or lower-lying Rydberg states. The transitions were detected by selective field ionization and recording either the electrons or the ions, the latter offering the advantage of mass selection. Rydberg states of high principal quantum number are extremely sensitive to their environment, which can be exploited to characterize the experimental conditions under which the spectroscopic measurements are carried out nderline{\textbf{21}}, 385, (2002).}. The high resolution achieved in the experiments (better than 100~kHz) enabled the study of the spectral lineshapes and line positions in dependence of weak electric (down to below $100\mu$V/cm) and magnetic fields (down to a few $\mu$T), and of the density of Rydberg atoms and ions generated in the experimental volume. The experiments rely on the use of a pulsed, broadly tunable, laser-based source of THz radiation nderline{\textbf{93}}, 131105, (2008).} for survey scans, and of a phase- and frequency-stabilized submillimeter-wave backward-wave oscillator-based radiation source nderline{\textbf{39}}, 831, (2006).} for precision measurements. To illustrate the use of these sources, we present the results of the spectroscopic investigations of the hyperfine structure of $^{129}$Xe Rydberg states in spectral regions where s-d interactions are expected to play a role

VAE-Loco: versatile quadruped locomotion by learning a disentangled gait representation

Quadruped locomotion is rapidly maturing to a degree where robots are able to realize highly dynamic maneuvers. However, current planners are unable to vary key gait parameters of the in-swing feet midair. In this article, we address this limitation and show that it is pivotal in increasing controller robustness by learning a latent space capturing the key stance phases constituting a particular gait. This is achieved via a generative model trained on a single trot style, which encourages disentanglement such that application of a drive signal to a single dimension of the latent state induces holistic plans synthesizing a continuous variety of trot styles. We demonstrate that specific properties of the drive signal map directly to gait parameters, such as cadence, footstep height, and full-stance duration. Due to the nature of our approach, these synthesized gaits are continuously variable online during robot operation. The use of a generative model facilitates the detection and mitigation of disturbances to provide a versatile and robust planning framework. We evaluate our approach on two versions of the real ANYmal quadruped robots and demonstrate that our method achieves a continuous blend of dynamic trot styles while being robust and reactive to external perturbations