IST Austria: PubRep (Institute of Science and Technology)
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ISTA Thesis
No full textTribocharging, or contact electrification, is the phenomenon in which two initially neutral materials exchange electric charge through contact and subsequent separation. While it is widely observed in everyday life and crucial to numerous natural processes, even the most basic aspects of tribocharging are still a mystery—what are the charge carriers involved and what drives their exchange? This work spans three separate projects that address different aspects of tribocharging. First, we introduce a novel strategy combining Finite Element Method (FEM) simulations with Kelvin Probe Force Microscopy (KPFM) to quantitatively extract surface charge density from surface voltage maps. Second, we present a simple theoretical model that allows for the existence of triboelectric cycles, under the assumption that multiple charge carrying species are involved. Third, we present experimental evidence that identical materials can spontaneously evolve into a triboelectric series, driven by contact history. Modeling this behavior enables the replication of experimental results with simulations, and even experimentally forcing the appearance of a pre-designed series by manipulating contact history. Together, the findings from these projects challenge traditional views on tribocharging, provide new tools for probing it, and open up new avenues of research—all with the hopes of bringing us closer to understanding this puzzling phenomenon
A candidate giant planet companion to the massive, young White Dwarf GALEX J071816.4+373139 informs the occurrence of giant planets orbiting B stars
No full textIt has been suggested that giant planet occurrence peaks for stars with M* ≈ 3 M⊙ at a value a factor of 4 higher than observed for solar-mass stars. This population of giant planets predicted to frequently orbit main-sequence B stars at a ≈ 10 au is difficult to characterize during the few hundred million years while fusion persists in their host stars. By the time those stars become massive, young white dwarfs, any giant planets present would still be luminous as a consequence of their recent formation. From an initial sample of 2195 Gaia-identified massive, young white dwarfs, we use homogeneous Spitzer Infrared Array Camera (IRAC) photometry to search for evidence of unresolved giant planets. For 30 systems, these IRAC data provide sensitivity to objects with M ≲ 10 MJup, and we identify one candidate with M ≈ 4 MJup orbiting the white dwarf GALEX J071816.4+373139. Correcting for the possibility that some of the white dwarfs in our sample result from mergers, we find a giant planet occurrence n GP = 0.11+0.13-0.07 for stars with initial masses M* ≳ 3 M⊙. Our occurrence inference is consistent with both the Doppler-inferred occurrence of giant planets orbiting M* ≈ 2 M⊙ giant stars and the theoretically predicted factor of 4 enhancement in the occurrence of giant planets orbiting M* ≈ 3 M⊙ stars relative to solar-mass stars. Future James Webb Space Telescope NIRCam observations of our sample would provide sensitivity to Saturn-mass planets and thereby a definitive estimate of the occurrence of giant planets orbiting stars with M* ≳ 3 M⊙
Amorphous high entropy alloy nanosheets enabling robust Li–S batteries
No full textHigh-entropy alloys (HEAs) show great potential for catalyzing complex multi-step reactions, but optimizing their parameters, i.e., composition, but also their crystallinity and morphology, remains a significant challenge. In this study, FeCoNiMoW HEAs are synthesized into either amorphous nanosheets (HEANS) or crystalline nanoparticles (HEANP), which are then used to catalyze the lithium–sulfur (Li–S) reaction of Li–S batteries (LSBs). Evaluations in symmetric cells, coin cells, and pouch cells reveal that HEANS significantly enhance LSB performance, achieving initial discharge capacities up to 1632 mAh g−1. The batteries also exhibit excellent cycling stability over 1000 cycles at 3Cand maintain high-rate performance up to 10C with a capacity of 614 mAh g−1. Comprehensive in situ analyses and density functional theory calculations demonstrate that amorphous HEANS provide more active sites, better ionic conductivity and stronger chemical interactions with lithium polysulfides (LiPS). These properties effectively suppress the shuttle effect, promote the complete S8 → Li2S conversion by reducing the impedance of the solid-electrolyte interphase, and accelerate the Li2S4 → Li2S2 step by lowering the nucleation energy barrier. Overall, this study highlights the superior catalytic properties of amorphous 2D HEAs in LSBs and offers new insights into the mechanisms of LiPS conversion
How to construct explicit decay rates for kinetic Fokker–Planck equations?
No full textWe study time averages for the norm of solutions to kinetic Fokker–Planck equations associated with general Hamiltonians. We provide fully explicit and constructive decay estimates for systems subject to a confining potential, allowing fat-tail, subexponential and (super-)exponential local equilibria, which also include the classic Maxwellian case. The key step in our estimates is a modified Poincaré inequality, obtained via a Lions–Poincaré inequality and an averaging lemma
The recruitment of the A-type cyclin TAM to stress granules is crucial for meiotic fidelity under heat
No full textStress granules (SG) are biomolecular condensates that represent an adaptive response of cells to various stresses, including heat. However, the cell type–specific function and relevance of SG formation, especially during reproductive development, are largely not understood. Here, we show that the meiotic A-type cyclin TARDY ASYNCHRONOUS MEIOSIS (TAM) is recruited to SGs in male meiocytes of Arabidopsis after exposure to heat. We find that the amino terminus of TAM is necessary and sufficient for the localization of proteins to meiotic SGs. Swapping the amino terminus of TAM with the one of its sister protein CYCA1;1 resulted in a separation-of-function allele of TAM, which prevents the partitioning of TAM to SGs while restoring a wild-type phenotype in a tam mutant background under nonheat stress conditions. Notably, plants expressing this TAM version prematurely terminate meiosis under heat resulting in unreduced gametes. Thus, the formation of TAM-containing SGs is necessary for genome stability under heat stress
A Lyman continuum analysis of ∼100 galaxies at z spec∼ 3 in the Abell 2744 cluster field
No full textIdentifying Lyman continuum (LyC) leakers at intermediate redshifts is crucial for understanding the properties of cosmic reionizers because the opacity of the intergalactic medium (IGM) prevents the direct detection of LyC emission from sources during the Epoch of Reionization (EoR). In this study, we confirm two new LyC candidate leakers at z ∼ 3 in the Abell 2744 cluster field, with absolute escape fractions (fesc) of 0.83−0.80+0.15 and 0.74−0.70+0.23, respectively. The LyC emission was detected using HST/WFC3/F275W and F336W imaging. These two candidate leakers appear to be faint (MUV = −17.61 ± 0.06 and −18.22 ± 0.10), exhibit blue UV continuum slopes (β = −2.43 ± 0.05 and −1.92 ± 0.09), have low masses (M★ ∼ 107.51 ± 0.03 and 107.17 ± 0.15 M⊙) and Lyα equivalent widths of 90 ± 3 Å and 28 ± 12 Å, respectively. These two LyC candidate leakers were detected in a catalog of 91 spectroscopically confirmed sources using public spectra from the JWST and/or MUSE. We also analyzed properties that were proposed as indirect indicators of LyC emission, such as Lyα, the O32 ratio, and M★. We created a galaxy subsample that was selected according to these properties, stacked the LyC observations of this subsample, and assessed the limits of the escape fractions in the stacks. We aim to enhance our understanding of LyC escape mechanisms and improve our predictions of the LyC fesc during the EoR by analyzing the individual candidates and the stacks in the context of the currently limited sample of known LyC leakers at z ∼ 3
TMLR
No full textSupervised learning for causal discovery from observational data often achieves competitive performance despite seemingly avoiding the explicit assumptions that traditional methods require for identifiability. In this work, we analyze CSIvA (Ke et al., 2023) on bivariate causal models, a transformer architecture for amortized inference promising to train on synthetic data and transfer to real ones. First, we bridge the gap with identifiability theory, showing that the training distribution implicitly defines a prior on the causal model of the test observations: consistent with classical approaches, good performance is achieved when we have a good prior on the test data, and the underlying model is identifiable. Second, we find that CSIvA can not generalize to classes of causal models unseen during training: to overcome this limitation, we theoretically and empirically analyze \textit{when} training CSIvA on datasets generated by multiple identifiable causal models with different structural assumptions improves its generalization at test time. Overall, we find that amortized causal discovery still adheres to identifiability theory, violating the previous hypothesis from Lopez-Paz et al. (2015) that supervised learning methods could overcome its restrictions
Reduced fitness under drought stress in F1 hybrids of Antirrhinum majus varieties with divergent flower colors
No full textPremise: What maintains trait divergence in the face of gene flow? Two varieties of wild snapdragon (Antirrhinum majus) characterized by divergent flower color hybridize in their native range. Selection on flower color genes is indicated by sharp clines, but the selective agents have not been demonstrated. Although previous work has focused on pollinators, pigmentation genes can also contribute to abiotic stress tolerance. We hypothesized that pigmentation in A. majus mediates stress tolerance, which could contribute to hybrid zone maintenance through parental niche divergence or hybrid maladaptation. Specifically, we tested whether morphotype mediates drought tolerance in an experiment comparing magenta-flowered var. pseudomajus, yellow-flowered var. striatum, and their pink-flowered hybrid cross.
Methods: We experimentally compared drought tolerance of each morphotype from allopatric crosses within and between varieties using three greenhouse treatments. Control plants were watered as needed, while drought-treated plants were watered half as often, either from the transplant stage (“early” drought), or from flowering onset (“late” drought).
Results: Parental morphotypes responded identically to drought in fitness and most phenotypic traits. However, hybrids had lower survival (14%) under late drought stress than parental morphotypes (70%). All hybrids that flowered in the late drought treatment died, compared to ~20% of flowering parental morphotypes.
Conclusions: Hybrid maladaptation to abiotic stress could potentially contribute to flower color divergence in the face of gene flow in A. majus. Further research should test the relevance of our results to field conditions and explicitly probe the role of flower color genes in drought tolerance
Data for "Aromatic Ring Flips Reveal Reshaping of Protein Dynamics in Crystals and Complexes"
No full textProtein conformational energy landscapes are shaped not only by intramolecular interactions but also by their environment. In protein crystals and protein-protein complexes, intermolecular contacts alter this energy landscape, but the exact nature of this alteration is difficult to decipher. Understanding how the crystal lattice affects protein dynamics is crucial for crystallography-based studies of motion, yet its influence on collective motions remains unclear. Aromatic ring flips in the hydrophobic core represent sensitive probes of such dynamics. Here, we compare the kinetics of aromatic ring flips in the protein GB1 in crystals, in complex with its binding partner IgG, and in solution, combining advanced isotope labeling with quantitative NMR methods. We show that rings in the core flip nearly a thousand times less frequently in crystals than in solution. Enhanced-sampling molecular dynamics simulations, based on a new crystal structure, reproduce these elevated barriers and reveal how the crystal restrains motions
Finite steady-state current defies non-Hermitian many-body localization
No full textNon-Hermitian many-body localization (NH MBL) has emerged as a possible scenario for stable localization in open systems, as suggested by spectral indicators identifying a putative transition for finite system sizes. In this work, we shift the focus to dynamical probes, specifically the steady-state spin current, to investigate transport properties in a disordered, non-Hermitian XXZ spin chain. Through exact diagonalization for small systems and tensor-network methods for larger chains, we demonstrate that the steady-state current remains finite and decays exponentially with disorder strength, showing no evidence of a transition up to disorder values far beyond the previously claimed critical point. Our results reveal a stark discrepancy between spectral indicators, which suggest localization, and transport behavior, which indicates delocalization. This highlights the importance of dynamical observables in characterizing NH MBL and suggests that traditional spectral measures may not fully capture the physics of non-Hermitian systems. Additionally, we observe a noncommutativity of limits in system size and time, further complicating the interpretation of finite-size studies. These findings challenge the existence of NH MBL in the studied model and underscore the need for alternative approaches to understanding localization in non-Hermitian settings