561975 research outputs found
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Non-Markovian dynamics in nonstationary Gaussian baths: A hierarchy of pure states approach
No full textBuilding on the standard hierarchy of pure states (HOPS) approach, we construct a generalized formulation suitable for open quantum systems interacting with nonstationary Gaussian baths, potentially extending its applicability to nonequilibrium baths. This is achieved by extending the conventional exponential decomposition of a bath-correlation function (BCF) for nonstationary cases. Using our formulation of HOPS, we derive the corresponding hierarchy of master equations and, when each term in the BCF expansion can be associated with an independent physical bath, we show how the formalism connects to the well-known pseudomode representation. We demonstrate the method's performance on two examples of nonstationary squeezed reservoirs generated via uniform squeezing and degenerate parametric amplification in a one-sided cavity. Benchmarking against the hierarchy of master equations shows that HOPS is more efficient under hierarchy truncation. The pseudomode representation is shown to be more efficient in the strongly non-Markovian regime. Our results highlight HOPS as a versatile and powerful tool for simulating open quantum systems in nonstationary baths, with potential applications ranging from squeezed light-matter interactions to driven-quantum materials and dissipative phase transitions
Improved magnetic domain imaging in photoelectron emission microscopy using symmetry analysis and momentum selection
No full textMagnetic circular dichroism in photoemission provides a powerful tool for probing the electronic and magnetic structure of ferromagnets. In the threshold regime, the use of laboratory light sources enables magnetic domain imaging with photoelectron emission microscopy (PEEM), but the achievable magnetic contrast is typically weak, leading to long acquisition times. In this work, we present a theoretical study of contrast enhancement in threshold-photoemission PEEM based on symmetry considerations and relativistic one-step photoemission calculations. We show that surface symmetry imposes specific relations among the fundamental dichroic intensities and the corresponding asymmetries, which can be exploited by momentum selection using an aperture in the PEEM. As a prototype system, we investigate in-plane and perpendicular magnetized Fe(001). Our results demonstrate that sizable magnetic domain contrast can be achieved at low photon energies by selecting appropriate emission directions, providing a practical route toward efficient laboratory-based magnetic domain imaging
Flexible Kompetenzausschlüsse: Zum Umfang der EU-Sozialkompetenzen nach der Mindestlohnentscheidung des EuGH
No full textMit der Mindestlohnrichtlinie 2022/2041 hat sich der Unionsgesetzgeber auf kompetenziell dünnes Eis begeben. Dänemark sah die Kompetenzgrenzen des Art. 153 Abs. 5 AEUV als überschritten an und leitete eine Nichtigkeitsklage vor dem EuGH ein. Der Beitrag untersucht die 2025 ergangene EuGH-Entscheidung in der Rechtssache C-19/23 – Dänemark/Parlament und Rat im Hinblick auf den Umfang der Kompetenzausschlüsse des Art. 153 Abs. 5 AEUV und hinsichtlich der Anforderungen an die rechtmäßige Wahl der Kompetenzgrundlage bei Richtlinien mit multiplen Zielsetzungen. Der Gerichtshof hat die unionsrechtlichen Kompetenzgrenzen elastisch ausgelegt, ohne eine klare Testformel zur Unterscheidung zwischen mittelbaren und unmittelbaren Eingriffen in das Arbeitsentgelt vorzulegen. Im Hinblick auf die doppelte Zielsetzung der Richtlinie verweigert der EuGH eine eingehende Prüfung und attestiert dem Richtliniengeber die Rechtmäßigkeit der alleinigen Berufung auf die Kompetenznorm aus Art. 153 Abs. 1 lit. b) AEUV. In dieser Hinsicht vermag das Urteil Dänemark/Parlament und Rat nicht zu überzeugen
CO Diffusion on Interstellar Amorphous Solid Water: A Computational Study
No full textSurface chemistry on interstellar dust grains is recognized as a central component in astrochemical models, representing a plausible formation route for many of the observed complex molecular species. However, key parameters governing interstellar surface chemistry, such as diffusion energy barriers, remain poorly constrained. In particular, surface diffusion constitutes a fundamental step in the synthesis of complex organic molecules and plays a crucial role in understanding the desorption process. In this paper, the diffusion dynamics of carbon monoxide (CO) on amorphous solid water (ASW) surfaces, representative of interstellar ices, is modeled with quantum-chemical methods. Employing a representative ensemble of water clusters, each made of 22 molecules, diffusion energy barriers between the binding sites are computed using density functional theory. Diffusion rate coefficients are then determined by applying the harmonic approximation of the transition state theory. The results, in agreement with experimental studies, revealed a wide distribution of diffusion energies. This reflects the intrinsic topological heterogeneity of ASW surfaces and highlights how surface mobility significantly influences CO's desorption dynamics and, as a consequence, surface-mediated reactivity in interstellar environments. We show that key parameters commonly employed in astrochemical models, such as the ratio between binding and diffusion energy, should be carefully revised
The ExoGRAVITY survey: A K-band spectral library of giant exoplanet and brown dwarf companions
No full textContext. Direct observations of exoplanet and brown dwarf companions with near-infrared interferometry, first enabled by the dualfield mode of VLTI/GRAVITY, provide unique measurements of the objects' orbital motions and atmospheric compositions. Aims. Here we compile a homogeneous library of all exoplanet and brown dwarf K-band spectra observed by GRAVITY thus far. This ExoGRAVITY Spectral Library is made publicly available online. Methods. We re-reduced all the available GRAVITY dual-field high-contrast data in a uniform and highly automated way and, where companions were detected, extracted their similar to 2.0-2.4 mu m K-band contrast spectra. We then derived stellar model atmospheres for all the employed flux references (either the host star or the swap calibrator), which we used to convert the companion contrast into companion flux spectra. Solely from the resulting GRAVITY K-band flux spectra, we extracted spectral types, spectral indices, and bulk physical properties for all the companions. Finally, and with the help of age constraints from the literature, we also derived isochronal masses for most of the companions using evolutionary models. Results. The resulting library contains R similar to 500 GRAVITY K-band spectra of 39 substellar companions from late M to late T spectral types, including the entire L-T transition. Throughout this transition, a shift from CO-dominated late M- and L-type dwarfs to CH4-dominated T-type dwarfs can be observed in the K-band. The GRAVITY spectra alone constrain the objects' bolometric luminosity to typically within +/- 0.15 dex. The derived isochronal masses agree with dynamical masses from the literature where available, except for HD 4113 c for which we confirm its previously reported potential underluminosity. Conclusions. Medium-resolution spectroscopy of substellar companions with GRAVITY provides insight into the carbon chemistry and the cloudiness of these objects' atmospheres. It also constrains these objects' bolometric luminosities, which can yield measurements of their formation entropy if combined with dynamical masses, for instance from Gaia and GRAVITY astrometry
Magnetic fields in the Shapley Supercluster core with POSSUM: Challenging model predictions
No full textContext. Faraday rotation measure (RM) grids provide a sensitive means to trace magnetized plasma across a wide range of cosmic environments. Aims. We study the RM signal from the Shapley Supercluster core (SSC) in order to constrain the magnetic field properties of its gas. The SSC region consists of two galaxy clusters, A3558 and A3562, and two galaxy groups between them, at z similar or equal to 0.048. Methods. We combined RM Grid data with thermal Sunyaev-Zeldovich effect data, obtained from the POlarisation Sky Survey of the Universe's Magnetism (POSSUM) pilot survey, and Planck, respectively. To robustly determine the gas density, its magnetic field properties, and their correlation |B| proportional to n(e)(eta), we studied the RM scatter in the SSC region (& Sfr;(RM)) and its behavior as a function of distance to the nearest cluster and/or group (d(nrst)). We compared observational results with semi-analytic Gaussian random field models and more realistic cosmological magnetohydrodynamical (MHD) simulations. Results. With a sky-density of 36 RMs/deg(2), we detect an excess RM scatter of 30.5 +/- 4.6 rad/m(2) in the SSC region. When we compare with models, we find an average magnetic field strength of similar to 1-3 mu G (in the groups and clusters). The & Sfr;(RM)(d(nrst)) profile, derived from data ranging from similar to 0.3-1.8 r(500) for all objects, is systematically flatter than expected compared to the models, with eta < 0.5 being favored. Despite this discrepancy, we find that cosmological MHD simulations matched to the SSC structure most closely align with scenarios where the magnetic field is amplified by the turbulent velocity (v(turb)) in the intercluster regions B-& Fouriertrf; proportional to n(e)(1/2)v(turb) on scales d(nrst) less than or similar to 0.8. Conclusions. The dense RM grid and precision provided by POSSUM allows us to probe magnetized gas in the SSC clusters and groups on scales within and beyond their r(500). Flatter-than-expected RM scatter profiles reveal a significant challenge in reconciling observations with even the most realistic predictions from cosmological MHD simulations in the outskirts of interacting clusters
Isotopes reveal a plant-consuming multi-cultural community in Late Antique Sicily
No full textLate Antiquity in the Mediterranean region and its border areas marks a period of significant historical change characterised by large-scale population movements and intense cultural interactions that are not yet fully understood. To offer new insights into these local-scale interactions, we employed stable isotope analyses of carbon, nitrogen, and oxygen to reconstruct diet and spatial mobility for 17 individuals from the rural Sicilian sites of Scorrione (Modica) and Cisternazzi (Ragusa). Stable carbon and nitrogen isotope results reveal that most of the analysed individuals relied predominantly on plant protein for their diets. Stable oxygen isotope data indicate that some of the buried individuals likely originated from Central Europe or Northern Africa. By combining the archaeological evidence with scientific analyses, the study contributes to our understanding of the dietary habits and cultural interactions in Sicily during Late Antiquity.Methods Material Pre-treatment andanalyticalmeasurements of collagen samples Pre-treatment and analytical measurements of carbonate samples Radiocarbon dating Statistical methods and Bayesian modelling ZooMS and osteological analysis Results Radiocarbon measurements Reconstruction of human diets Spatial mobility Discussio
Microbubble-Mediated Synthesis of Smart Spindle Microfibers for Fog Harvesting
No full textFog has significant potential as a water resource, offering a solution for alleviating the global risk of freshwater scarcity. Spindle-knotted microfibers are highly effective for fog collection, though the complexity of fabricating such structures remains a significant challenge. In this study, a simple microfluidic method using microbubbles is introduced for the fabrication of smart spindle microfibers (SSMs). The combination of microbubbles of varying sizes, induced by pulses from a peristaltic pump, and thermo-responsive poly(N-isopropylacrylamide) (PNIPAm)-based materials facilitated the formation of periodic knots and joint structures with enhanced structural stability and hydrophilic rough surfaces. The spindle-knotted structure, featuring textured hydrophilic surfaces, extends the three-phase contact line and maximizes the volume of the collected water droplets. This promotes the rapid detachment of large droplets formed within a short time, thereby enhancing fog harvesting efficiency. This approach achieves a collection rate of 0.046 g min−1, representing 161% of the previously reported fog collection efficiency. Moreover, SSMs adjust their wettability across different temperature cycles owing to the thermo-responsive properties of PNIPAm, ensuring consistent and reliable fog collection efficiency, even under changing environmental conditions. This adaptability provides practical insights that enable efficient large-scale water harvesting, addressing the urgent need for effective water collection solutions