Optics · Cross-listed from cond-mat.mtrl-sci
Role of quasi-Fermi levels in Si- and Mg-related optical absorption in nitride laser diodes (LDs): material context
Konrad Sakowski, Cyprian Sobczak, Pawel Strak et al. (+5 more)
Optical absorption and reabsorption of light emitted from active regions in nitride
laser diodes (LDs) have been shown to reduce the light extraction efficiency of these devices. It was proven that the presence of Si and Mg may considerably increase the optical absorption. This effect is much stronger in the high-energy (short-wavelength) range of the spectrum. The absorption increase is directly related to the ionization of the Si donor and Mg acceptor levels, which are controlled by the electron and hole quasi-
Fermi levels. It is shown that the absorption may be increased because of the higher ionization of Mg caused by the compensation in the p-type region and the high ionization of Si in the n-type region. It was explained theoretically why optical efficiency is increased by removal of doping in waveguides. It was also shown that good material quality leads to a low absorption level, especially in the Mg-doped p-type part of the device.
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All authors Konrad Sakowski, Cyprian Sobczak, Pawel Strak, Izabella Grzegory, Robert Czernecki, Jacek Piechota, Agata Kaminska, Stanislaw Krukowski
Biological Physics · Cross-listed from q-bio.PE
How adaptation to food resources and death rates shape oscillatory dynamics in a microbial population
Benedetta Ciarmoli and Sophie Marbach
Microbes constantly interact with their environment by depleting and transforming food sources. Theoretical studies have mainly focused on Lotka-Volterra models, which do not account for food source dynamics. In contrast, consumer-resource models, which consider food source dynamics, are less explored. In particular, it is still unclear what physical mechanisms control oscillatory dynamics at a single population level, a phenomenon which can only be captured by a consumer-resource model. Here, we present a minimalistic consumer-resource model of a single microbial population with growth and death dynamics, consuming a continuously replenishing substrate. Our model reveals that decaying oscillations can occur around steady state if and only if the timescale of microbial adaptation to food supply changes exceeds the death timescale. This interplay of timescales allows us to rationalize the emergence of oscillatory dynamics when adding various biophysical ingredients to the model. We find that microbial necromass recycling or complementary use of multiple food sources reduces the parameter range for oscillations and increases the decay rate of oscillations. Requiring multiple simultaneous food sources has the opposite effect. Essentially, facilitating growth reduces the likelihood of oscillations around a fixed point. We further demonstrate that such damped oscillatory behavior is correlated with persistent oscillatory behavior in a noisy environment. We hope our work will motivate further investigations of consumer-resource models to improve descriptions of environments where food source distributions vary in space and time.
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Instrumentation and Detectors
Simulation and optimization of the Active Magnetic Shield of the n2EDM experiment
N. J. Ayres, G. Ban, G. Bison et al. (+47 more)
The n2EDM experiment at the Paul Scherrer Institute aims to conduct a high-sensitivity search for the electric dipole moment of the
neutron.
Magnetic stability and control are achieved through a combination of passive shielding, provided by a magnetically shielded room (MSR), and a surrounding active field compensation system by an Active
Magnetic Shield (AMS). The AMS is a feedback-controlled system of eight coils spanned on an irregular grid, designed to provide
magnetic stability to the enclosed volume by actively suppressing external
magnetic disturbances. It can compensate static and variable
magnetic fields up to $\pm 50$ $\mu$T (homogeneous components) and $\pm 5$ $\mu$T/m (first-order gradients), suppressing them to a few $\mu$T in the sub-Hertz frequency range. We present a full finite element simulation of
magnetic fields generated by the AMS in the presence of the MSR. This simulation is of sufficient accuracy to approach our measurements. We demonstrate how the simulation can be used with an example, obtaining an optimal number and placement of feedback sensors using genetic
algorithms.
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All authors N. J. Ayres, G. Ban, G. Bison, K. Bodek, V. Bondar, T. Bouillaud, G. L. Caratsch, E. Chanel, W. Chen, C. Crawford, V. Czamler, C. B. Doorenbos, S. Emmeneger, S. K. Ermakov, M. Ferry, M. Fertl, A. Fratangelo, D. Galbinski, W. C. Griffith, Z. D. Grujic, K. Kirch, V. Kletzl, J. Krempel, B. Lauss, T. Lefort, A. Lejuez, K. Michielsen, J. Micko, P. Mullan, O. Naviliat-Cuncic, F. M. Piegsa, G. Pignol, C. Pistillo, I. Rienäcker, D. Ries, S. Roccia, D. Rozpędzik, L. Sanchez-Real Zielniewicz, N. von Schickh, P. Schmidt-Wellenburg, E. P. Segarra, L. Segner, N. Severijns, K. Svirina, J. Thorne, J. Vankeirsbilck, N. Yazdandoost, J. Zejma, N. Ziehl, G. Zsigmond
Optics
Inverse Design of the Topology Bandwidth Tradeoff in Valley Photonic Crystals
Devansh Satra, Abhishek Kumar and Anshuman Kumar
Valley photonic
crystals provide a route to broadband domain-wall guiding, but increasing the bulk gap can delocalize Berry
curvature and reduce the non-quantized valley-Chern number. We introduce a mixed-integer particle-swarm framework that searches polygonal VPC unit
cells and maps the Pareto tradeoff between normalized bandgap and valley
topology using the bulk objective $\mathcal{T}=(\Delta f/f_0)^2|C_v|$. The selected designs are then evaluated independently using full-wave transport simulations through disorder-averaged propagation-length extraction in $200a$ domain-wall waveguides with positional disorder $\sigma=0.01a$. Across the studied design ensemble, the extracted propagation length exhibits a positive empirical association with $|C_v|$, providing a direct multi-design connection between the patch-integrated valley-Chern number and quantified disorder-limited transport in this VPC family. The framework therefore treats bandwidth, valley
topology, and device robustness as distinct but connected quantities, enabling balanced inverse design rather than optimization of a single transport metric alone.
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Computational Physics · Cross-listed from cond-mat.stat-mech
Leveraging Interactions for Efficient Swarm-Based Brownian Computing
Alessandro Pignedoli, Atreya Majumdar and Karin Everschor-Sitte
Drawing inspiration from swarm intelligence, we show that short-range attractive interactions between thermally driven Brownian quasiparticles enable energy-efficient optimization. As quasiparticles can be generated directly within a material, the swarm size can be adjusted with minimal energy overhead. Using an optimization task defined by a spatially varying temperature landscape, we quantitatively show that interacting swarms reliably identify global optima and significantly outperform non-interacting searchers within a well-defined regime of interaction strength and swarm size. This improvement arises from emergent cooperative behavior, where local interactions guide the swarm toward high-quality solutions without central coordination. To link our physical model to experimental realizations, we coarse-grain the quasiparticle dynamics onto a sensor
lattice and generate trajectories emulating particle-tracking measurements. We further show that the interacting swarm adapts robustly to landscapes that evolve over time. These findings establish interacting Brownian quasiparticles as a physical platform for scalable and energy-efficient unconventional computing.
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Chemical Physics · Cross-listed from astro-ph.GA
Millimeter and submillimeter spectroscopy of methylallene, CH$_3$CHCCH$_2$
Holger S. P. Müller, Frank Lewen, Jean-Claude Guillemin et al. (+1 more)
Small polycyclic aromatic hydrocarbons and somewhat larger cyano derivatives were detected in the cold dark cloud TMC-1 recently. Their formation from smaller hydrocarbons is not well understood, in part because abundances of many species are not known. Methylallene, CH$_3$CHCCH$_2$, may be one of the building blocks, but its rotational spectrum was characterized only to a very limited extent. We recorded rotational transitions in the 36$-$501 GHz region to extend the existing line list of methylallene and thus enable searches for the molecule in space.
Quantum-chemical calculations were carried out to evaluate initial spectroscopic parameters. We obtained transition frequencies with $J \le 61$ and $K_a \le 21$ and resolved the internal rotation splitting of the CH$_3$ group at least partially. As a result, a full set of distortion parameters up to sixth order along with two octic ones were determined, as well as parameters describing the internal rotation of the methyl group. The spectroscopic parameters are accurate enough to identify methylallene up to 720 GHz, sufficient for searches even in the warm interstellar medium.
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All authors Holger S. P. Müller, Frank Lewen, Jean-Claude Guillemin, Stephan Schlemmer
Atmospheric and Oceanic Physics · Cross-listed from astro-ph.GA
Rotational Spectroscopy as a Tool to Study Vibration-Rotation Interaction: Investigations of $^{13}$CH$_3$CN and CH$_3$$^{13}$CN up to $v_8 = 2$ and a Search for $v_8 = 2$ Transitions toward Sagittarius B2(N)
Holger S. P. Müller, Arnaud Belloche, Frank Lewen et al. (+1 more)
Methyl cyanide, CH$_3$CN, is present in diverse regions in space, in particular in the warm parts of
star-forming regions where it is a common molecule. Rotational transitions of $^{13}$CH$_3$CN and CH$_3$$^{13}$CN in their $v_8 = 1$ lowest excited vibrational states ($E_{\rm vib} \approx 520$ K) are quite prominent in Sagittarius B2(N). In order to be able to search for transitions of the next higher vibrational state $v_8 = 2$, we recorded spectra of samples enriched in $^{13}$CH$_3$CN and CH$_3$$^{13}$CN up to $v_8 = 2$ in the 35 to 1091~GHz region and reinvestigated existing spectra of CH$_3$CN in its natural isotopic composition between 1085 and 1200 GHz. Perturbations caused by near-degeneracies in $K = 4$ of $v_8 = 2^0$ and $K = 2$ of $v_8 = 2^{-2}$ yielded accurate information on the energy spacing of 22.93 and 21.79 cm$^{-1}$ between the $l$-components of $^{13}$CH$_3$CN and CH$_3$$^{13}$CN, respectively.
Fermi-type interaction between $K = 13$ and 14 of $v_8 = 1^{-1}$ and $v_8 = 2^{+2}$ probe the energy differences between the two states of both isotopomers. In addition, a $\Delta K \pm2$, $\Delta l \mp1$ interaction between the ground vibrational state of $^{13}$CH$_3$CN and $v_8 = 1^{+1}$ provides information on their energy spacing. Furthermore, we obtained improved or extended ground state rotational transition frequencies of $^{13}$CH$_3$$^{13}$CN and extensive data for $^{13}$CH$_3$C$^{15}$N and CH$_3$$^{13}$C$^{15}$N. Finally, we report the results of our search for transitions of $^{13}$CH$_3$CN and CH$_3$$^{13}$CN in their $v_8 = 2$ states toward Sagittarius B2(N).
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All authors Holger S. P. Müller, Arnaud Belloche, Frank Lewen, Stephan Schlemmer
Space Physics · Cross-listed from astro-ph.SR
Ground Level Enhancement (GLE#77) in the gamma-ray component: First observation from Arctic and Antarctic stations
Pranali Thakur, Geeta Vichare and Selvaraj Chelliah
This article presents the observations of the extreme ground-level enhancement (GLE #77) of
Solar Cycle 25 that occurred on 11 November 2025, using ground-based NaI(Tl) gamma-ray detectors deployed at Arctic and Antarctic stations, together with
neutron monitor data and particle measurements from the GOES-18 satellite. The event was associated with an intense X-class
solar flare and a strong
solar energetic
proton event. This paper reports the first ground-based detection of a GLE using gamma-ray detectors operating simultaneously in both polar regions, which are concurrent with increases in
neutron monitor counts. Thus highlights the capability of polar gamma-ray detectors to complement traditional
neutron monitor observations during extreme
solar proton events. A detailed analysis revealed distinct
prompt and delayed responses during the event
evolution. Interestingly, the signature of the
prompt peak of GLE#77 (at 10:38 UT) was observed up to high-
rigidity neutron monitors (low latitudes). However, the delayed peak (at 13:08 UT) was not seen at the stations with
rigidity > 6 GV. The timing of the
prompt and delayed peaks coincided with the
proton flux peaks observed by the GOES-18 satellite at energies > 150 MeV and 12-99 MeV, respectively. It is observed that the GLE amplitude has a strong dependence on geomagnetic cutoff
rigidity and has a weak
solar zenith angle dependence.
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Optics · Cross-listed from quant-ph
Scattering of Squeezed Light by a Dielectric Slab
Ghafoor Pooseh
We develop a
quantum theory for the scattering of squeezed coherent light by a dissipative dielectric slab. Using the Green-function quantization approach, we derive the transformation of the field quadratures and show how dispersion, absorption, and multiple reflections distort the incident squeezing. We find that the slab can selectively attenuate or amplify quadrature noise depending on the slab parameters and provide expressions for the output power spectra.
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Plasma Physics
Batch Bayesian optimization of attosecond betatron pulses from laser wakefield acceleration
Dominika Maslarova, Albert Hansson, Mufei Luo et al. (+4 more)
Laser wakefield acceleration can generate a femtosecond-scale broadband X-ray betatron radiation pulse from electrons accelerated by an intense
laser pulse in a
plasma. The micrometer-scale of the source makes wakefield betatron radiation well-suited for advanced imaging techniques, including diffraction and phase-contrast imaging. Recent progress in
laser technology can expand these capabilities into the attosecond regime, where the practical applications would significantly benefit from the increased energy contained within the pulse. Here we use numerical simulations combined with batch
Bayesian optimization to enhance the radiation produced by an attosecond betatron source. The method enables an efficient exploration of a multi-parameter space and identifies a regime in which a
plasma density spike triggers the generation of a high-charge electron beam. This results in an improvement of more than one order of magnitude in the on-axis time-averaged power within the central time containing half of the radiated energy, compared to the reference case without the density spike.
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All authors Dominika Maslarova, Albert Hansson, Mufei Luo, Vojtěch Horný, Julien Ferri, Istvan Pusztai, Tünde Fülöp
Optics
Fast Eikonal Phase Retrieval for High-Throughput Beamlines
Alessandro Mirone, Theresa Urban, Joseph Brunet et al. (+3 more)
We introduce a fast Eikonal Phase
Retrieval (EPR) formulation that accelerates eikonal phase
retrieval by more than two orders of magnitude while retaining controlled accuracy. The method is derived from a second-order asymptotic expansion in the propagation distance $L$ and complemented by the leading Wentzel–Kramers–Brillouin (WKB) wave-optics correction, yielding an efficient iterative correction scheme preconditioned by FFT-diagonal, energy-dependent inverse operators (Paganin-type filters). To ensure robustness across practical experimental regimes, we combine two complementary solvers: (i) a local $O(L^2)$ closure that is accurate when eikonal shifts remain sub-pixel, and (ii) a non-local formulation for multi-pixel shifts, in which intensity is propagated through an explicit eikonal ray mapping using a mass-conserving bilinear redisribution on the detector grid, and detector residuals are transferred back to the object grid by the corresponding adjoint (transpose), implemented as bilinear interpolation, before applying an approximate FFT-diagonal preconditioner to accelerate convergence. The same framework supports polychromatic data through a compact spectral discretisation, allowing energy-dependent transport and inversion while keeping the iteration GPU/FFT efficient. Overall, this unified approach enables accurate and computationally efficient phase
retrieval across propagation conditions relevant to high-throughput PPC-$\mu$CT experiments.
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All authors Alessandro Mirone, Theresa Urban, Joseph Brunet, Claire L. Walsh, Peter D. Lee, Paul Tafforeau
Classical Physics
Electroactive morphing effects on the aerodynamic performance through wobulation around an A320 wing with vibrating trailing edge at high Reynolds number
C. Rouaix, C. Jiménez-Navarro, M. Carvalho et al. (+9 more)
This study aims to investigate the effects of electroactive morphing on a 70cm chord A320 wing by means of near trailing edge slight deformation and vibration. Wing morphing is performed by Macro Fiber Composites (MFC) mini-piezoelectric actuators distributed along the span of the ”Reduced Scale” (RS) A320 prototype of the H2020 No 723402 European research project SMS, ”Smart Morphing and Sensing for aeronautical configurations”, (https://cordis.europa.eu/project/id/723402 and www.smartwing.org/SMS/EU). The configuration studied corresponds to a low-subsonic regime (Mach number 0.063) with a 10 degree incidence and a Reynolds number of 1 Million. The numerical simulations are carried out with the Navier-Stokes Multi-Block (NSMB) solver, which takes into account the deformation of the rear part of the wing implemented experimentally with the piezoelectric actuators. A detailed physical analysis of the morphing effects on the wake dynamics and on the aerodynamic performance is conducted with a constant amplitude of 0.7cm over a wide range of actuation frequencies [10-600]Hz. Optimal vibration ranges of [180-192]Hz and [205-215]Hz were found to respectively provide a 1% drag reduction and a 2% lift-to-drag ratio increase compared to the non-morphing (static) configuration. The natural frequencies associated with the shear layer Kelvin-Helmholtz (KH)
vortices and the Von-Karman (VK)
vortex shedding were found to play a central role in the modification of the wake dynamics by morphing as well as in the increase of the aerodynamic performance. Actuating at (or close to) the upper shear layer (USL) natural frequency (~185Hz) provides an order of 1% drag reduction and 1% lift-to-drag ratio increase, while actuating at (or close to) the lower shear layer (LSL) natural frequency (~208Hz) provides an order of 8% lift increase and 2% lift-to-drag increase. Furthermore, the linear variation of the actuation frequency over time, called wobulation, was shown to have significant effects. This approach demonstrated, through an appropriate mapping, the ability to quickly and efficiently detect optimal constant actuation frequency ranges providing aerodynamic performance increase and simultaneously reducing the amplitude of the main instability modes.
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All authors C. Rouaix, C. Jiménez-Navarro, M. Carvalho, C. Raibaudo, J. Abou-Khalil, A. Marouf, Y. Hoarau, G. Harran, J.C.R. Hunt, H. Hangan, J.F. Rouchon, M. Braza
Chemical Physics
Femtosecond Nonadiabatic Confinement of Molecular Dication Yield
Carlos Marante, Lina Fransén, Alexie Boyer et al. (+5 more)
Doubly charged molecular cations often carry signatures of electronic correlation and electron-
nuclear entanglement present in the parent cation. Here, we produce ethylene dications using a combination of an extreme ultraviolet pump and near-infrared probe pulses, observing a peak in the dication yield at a pump-probe delay of approximately 15 fs. Ab-initio calculations, which explicitly take into account coupled electron-
nuclear dynamics induced by the pump and the multiphoton nature of the probe-induced ionization step, reproduced the observed delay in the yield. It originates from resonant enhancement of the multiphoton ionization of the electronically excited ethylene cation as the carbon-carbon double bond expands. However, this effect is tempered by rapid nonadiabatic relaxation of the excited ionic states. Our results suggest a general mechanism whereby ultrafast nonadiabatic relaxation of a molecular ion can compete with its strong-field ionization rate, confining the dication yield to a narrow temporal window of a few femtoseconds.
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All authors Carlos Marante, Lina Fransén, Alexie Boyer, Vincent Loriot, Franck Lépine, Luca Argenti, Morgane Vacher, Saikat Nandi
Medical Physics
Combining quasi-static and high frequency experiments for the viscoelastic characterization of brain tissue
Laura Ruhland, Nina Reiter, Silvia Budday et al. (+1 more)
Mechanical models of
brain tissue are a beneficial tool to simulate neurosurgical interventions, disease progression, or
brain development. However, the accuracy and predictive capacity of such a model relies on a precise experimental characterization of the tissue's mechanical behavior. Such a characterization is yet limited by inconsistent or contradictory experimental responses reported in the literature, particularly when measurements are performed in different time or length scales. Although
brain tissue has been extensively investigated in previous studies, the combination of experimental findings from different scales has received limited
attention. In this study, we combine ex vivo mechanical responses of porcine
brain tissue obtained at different time scales in a mechanical model. We investigated the mechanical behavior of three different
brain regions in the quasi-static domain with multi-modal large strain rheometer measurements and at high frequencies with
magnetic resonance elastography (MRE). A comparative analysis of the mechanical parameters obtained from both experimental techniques demonstrated consistent regional variations in the viscoelastic behavior across the two domains. However, the mechanical behavior changes from a higher elasticity in the quasi-static and low frequency domain to a dominating viscosity at high frequencies. Based on the quasi-static and the high frequency behavior, we calibrated a fractional Kelvin-Voigt model and consequently unified the two responses in a single mechanical model to obtain a comprehensive characterization of the tissue's mechanical behavior.
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All authors Laura Ruhland, Nina Reiter, Silvia Budday, Kai Willner
Instrumentation and Detectors
A Wide Bandwidth Trans-impedance Amplifier for Picosecond-Scale SiPM Characterization in a Wide Temperature Range
P. Carniti, C. Gotti, G. Pessina et al. (+1 more)
Future high-energy physics experiments using SiPMs as photosensitive elements may require operation at low temperatures (down to 80 K) to measure single
photons with high time resolution in a highly radioactive environment. This calls for a complete characterization of these sensors over a wide temperature range to find the best compromise between detector performance and cooling requirements. This paper presents the design of a transimpedance amplifier featuring high gain ($\sim 7500\ \text{V/A}$), very high speed ($<500\ \text{ps}$ rise time) and low input noise ($\lesssim 20\ \text{pA}/\sqrt{\text{Hz}}$), able to faithfully reproduce all the features of SiPM signals without affecting its noise or jitter performance. These features make the amplifier suitable for precise measurements of the time-of-arrival of single-
photon signals, as well as gain and recovery time. This article provides a detailed and thorough analysis of the
circuit. The network was simulated and measured in two configurations that differ in their open-loop gain and dominant pole frequencies. After selecting the best configuration for our purposes, the amplifier was characterized in detail at ambient temperature and at 80 K. Finally, we evaluated the amplifier using a SiPM operated at low over-voltage. While SiPMs are typically characterized at high over-voltage to enhance gain and minimize timing jitter, testing at low over-voltage allowed us to assess the amplifier's performance under more challenging and realistic conditions for single-
photon timing.
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All authors P. Carniti, C. Gotti, G. Pessina, D. Trotta
Chemical Physics
A Cross-Domain Graph Learning Protocol for Single-Step Molecular Geometry Refinement
Chengchun Liu, Wendi Cai, Boxuan Zhao et al. (+1 more)
Accurate molecular geometries are a prerequisite for reliable
quantum-chemical predictions, yet density functional theory (DFT) optimization remains a major bottleneck for high-throughput molecular screening. Here we present GeoOpt-Net, a multi-branch SE(3)-equivariant geometry refinement network that predicts DFT-quality structures at the B3LYP/TZVP level of theory in a single forward pass starting from inexpensive initial conformers generated at a low-cost force-field level. GeoOpt-Net is trained using a two-stage strategy in which a broadly pretrained
geometric representation is subsequently fine-tuned to approach B3LYP/TZVP-level accuracy, with theory- and basis-set-aware calibration enabled by a fidelity-aware feature modulation (FAFM) mechanism. Benchmarking against representative approaches spanning classical conformer generation (RDKit), semiempirical
quantum methods (xTB), data-driven geometry refinement pipelines (Auto3D), and machine-learning interatomic potentials (UMA) on external drug-like molecules demonstrates that GeoOpt-Net achieves sub-milli-Å all-atom RMSD with near-zero B3LYP/TZVP single-point energy deviations, indicating DFT-ready geometries that closely reproduce both structural and energetic references. Beyond
geometric metrics, GeoOpt-Net generates initial guesses intrinsically compatible with DFT convergence criteria, yielding nonzero “All-YES” convergence rates (65.0% under loose and 33.4% under default thresholds), and substantially reducing re-optimization steps and wall-clock time. GeoOpt-Net further exhibits smooth and predictable energy scaling with molecular complexity while preserving key electronic observables such as dipole moments. Collectively, these results establish GeoOpt-Net as a scalable, physically consistent geometry refinement framework that enables efficient acceleration of DFT-based
quantum-chemical workflows.
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All authors Chengchun Liu, Wendi Cai, Boxuan Zhao, Fanyang Mo
Instrumentation and Detectors
Hybrid MCP-PMT characterisation on a testbeam with Cherenkov setup
G. Romolini, J. Alozy, R. Ballabriga et al. (+12 more)
A novel photodetector based on a MCP-PMT
vacuum tube with encapsulated CMOS ASIC has been tested at the CERN SPS high energy
hadron beam, allowing single
photon Cherenkov detection operating at 10$^4$ gain and with timing resolution of about 280~ps.
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All authors G. Romolini, J. Alozy, R. Ballabriga, N. V. Biesuz, R. Bolzonella, M. Campbell, G. Cavallero, V. Cavallini, A. Cotta Ramusino, M. Fiorini, E. Franzoso, M. Guarise, X. Llopart Cudie, A. Saputi, D. Vincenzi
Fluid Dynamics
Parametric vector flows for registration fields in bounded domains with applications to nonlinear interpolation of shock-dominated flows
Jon Labatut, Jean-Baptiste Chapelier, Angelo Iollo et al. (+1 more)
We present a registration procedure for parametric model order reduction (MOR) in two- and three-dimensional bounded domains. In the MOR framework, registration methods exploit solution snapshots to identify a parametric coordinate transformation that improves the approximation of the solution set through linear subspaces. For each training parameter, optimization-based (or variational) registration methods minimize a target function that measures the
alignment of the coherent structures of interest (e.g., shocks, shear layers, cracks) for different parameter values, over a family of bijections of the computational domain $\Omega$. We consider diffeomorphisms $\Phi$ that are vector flows of given velocity fields $v$ with vanishing normal component on $\partial \Omega$; we rely on a sensor to extract appropriate point clouds from the solution snapshots and we develop an expectation-maximization procedure to simultaneously solve the point cloud matching problem and to determine the velocity $v$ (and thus the bijection $\Phi$); finally, we combine our registration method with the nonlinear interpolation technique of [Iollo, Taddei, J. Comput. Phys., 2022] to perform accurate interpolations of fluid dynamic fields in the presence of shocks. Numerical results for a two-dimensional inviscid transonic flow past a NACA airfoil and a three-dimensional viscous transonic flow past an ONERA M6 wing illustrate the many elements of the methodology and demonstrate the effectiveness of nonlinear interpolation for shock-dominated fields.
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All authors Jon Labatut, Jean-Baptiste Chapelier, Angelo Iollo, Tommaso Taddei
Fluid Dynamics
Fluid transport by a single active filament in a three-dimensional two-phase flow
Qian Mao, Umberto d'Ortona and Julien Favier
Micro-scale cilia play a vital role in mucociliary clearance (MCC) in the human respiratory airways. In this numerical study, we examine fluid transport driven by the active beating of a single filament immersed in a three-dimensional two-phase flow. The cilium is modeled as an elastic filament actuated by a time-varying basal angle. The two-phase flow is resolved using the Shan-Chen model in a
lattice Boltzmann solver, while the two-way coupling between the filament and the fluid is treated by the immersed boundary method. Pathological conditions such as cystic fibrosis and chronic obstructive pulmonary disease are associated with drastic alterations of MCC properties, including changes in periciliary layer (PCL) thickness and the viscosity ratio between the PCL and the mucus layer (ML). Here, we systematically investigate the effects of these parameters, along with filament bending stiffness, on the beating pattern and fluid transport. Within the parameter ranges investigated, a moderate PCL thickness and viscosity ratio, together with high bending stiffness, tend to yield higher net flow rate and transport efficiency. The underlying hydrodynamic mechanisms are characterized through analyses of the beating pattern, filament dynamics, energy partition, and flow-field
evolution. Two competing mechanisms are identified: the drag-elastic force balance and the viscous
diffusion of momentum. Furthermore, quantitative relationships are established between flow rate and beating pattern, expressed in terms of tip amplitude and beating asymmetry.
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Atomic Physics · Cross-listed from quant-ph
Unconventional Distance Scaling of Casimir-Polder Force between Atomic Arrays
Qihang Ye, Qihang Ye, Bing Miao et al. (+1 more)
Conventionally, dispersion forces mediated by
quantum vacuum fluctuations are known to exhibit universal distance scalings, with retardation typically leading to a faster decay of the interaction. Here, we show that this expectation fails for intrinsically discrete systems. Using the microscopic scattering approach, we study the Casimir-Polder interaction between two atomic arrays, and uncover an unconventional distance scaling in which the force crosses over from a faster decay at short separations to a slower decay in the retarded regime. This behavior originates from the discrete
lattice structure and can be consistently understood within the scattering picture. Extending our analysis to Rydberg atomic arrays, we predict an even stronger deviation from conventional scaling and propose an experimentally feasible scheme for direct measurement. Our results provide a new platform for exploring dispersion forces beyond the continuum limit.
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All authors Qihang Ye, Qihang Ye, Bing Miao, Lei Ying
Geophysics
Sculpting of Martian brain terrain reveals the drying of ancient Mars
Shenyi Zhang, Lei Zhang, Yutian Ke et al. (+1 more)
The Martian
brain terrain (MBT), characterized by its unique
brain-like morphology, is a potential geological archive for finding hints of paleoclimatic conditions during its formation period. The morphological similarity of MBT to self-organized patterned ground on Earth suggests a shared formation mechanism. However, the lack of quantitative descriptions and robust physical modeling of self-organized stone transport jointly limits the study of the thermal and aqueous conditions governing MBT's formation. Here we established a specialized quantitative system for extracting the morphological features of MBT, taking a typical region located in the northern Arabia Terra as an example, and then employed a numerical model to investigate its formation mechanisms. Our simulation results accurately replicate the observed morphology of MBT, matching its key
geometric metrics with deviations <15%. Crucially, however, we find that the self-organized transport can solely produce relief <0.5 m, insufficient to explain the formation of MBT with average relief of 3.29 \pm 0.65 m. We attribute this discrepancy to sculpting driven by late-stage sublimation, constraining cumulative subsurface ice loss in this region to ~3 meters over the past ~3 Ma. These findings demonstrate that MBT's formation is a multi-stage process: initial patterning driven by freeze-thaw cycles implying
liquid water followed by vertical sculpting via sublimation requiring a dry environment. This
evolution provides physical evidence for the transition of the ancient Martian
climate from a wetter period to a colder hyper-arid state.
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All authors Shenyi Zhang, Lei Zhang, Yutian Ke, Jinhai Zhang
Biological Physics
Cross-feeding yields high-dimensional chaos and coexistence of species beyond exclusion principle
Takashi Shimada and Kunihiko Kaneko
Species interactions through cross-feeding via leakage and uptake of chemicals are important in microbial communities, and play an essential role in the coexistence of diverse species. Here, we study a simple dynamical model of a microbial community in which species interact by competing for the uptake of common metabolites that are leaked by other species. The model includes coupled dynamics of species populations and chemical concentrations in the medium, allowing for a variety of uptake and leakage networks among species. Depending on the structure of these networks, the system exhibits different attractors, including fixed points, limit cycles, low-dimensional chaos, and high-dimensional chaos. In the fixed-point and limit-cycle cases, the number of coexisting species is bounded by the number of exchangeable chemicals, consistent with the well-known competitive exclusion principle. In contrast, in the low-dimensional chaotic regime, the number of coexisting species exhibits noticeable but limited excess over this limit. Remarkably, in the high-dimensional chaotic regime, a much larger number of species beyond this limit coexist persistently over time. In this case, the rank-abundance distribution is broader than exponential, as often observed in real ecosystems. The population dynamics displays intermittent switching among quasi-stationary states, while the chemical dynamics explore most of the high dimensions. We find that such high-dimensional chaos is ubiquitous when the number of uptake chemicals is moderately larger than the number of leaked chemicals. Our results identify high-dimensional chaos with intermittent switching as a generic dynamical mechanism that stabilizes coexistence in interacting systems. We discuss its relevance to sustaining diverse microbial communities with leak-uptake cross-feeding.
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Computational Physics · Cross-listed from cond-mat.str-el
Understanding the sign problem from an exact Path Integral Monte Carlo model of interacting harmonic fermions
Siu A. Chin
This work shows that the recently discovered operator contraction identity for solving the discreet Path Integral of the harmonic oscillator can be applied equally to
fermions in any dimension. This then yields an exactly solvable model for studying the sign problem where the Path Integral Monte Carlo energy at any time step for any number of
fermions is known analytically, or can be computed numerically. It is found that the sign problem is primarily a property of the free
fermion propagator, but repulsive/attractive pairwise interaction can shift the sign problem to larger/smaller imaginary time but does not make it more severe than the non-interacting case. More surprisingly, one can prove analytically that the first closed-shell state in $D$ dimension, with $n=D+1$
fermion, has no sign problem at large imaginary time. Direct numerical simulations confirm that this is also true for higher closed-shell states in two and three-dimension. Fourth-order and newly found variable-bead
algorithms are used to compute ground state energies of
quantum dots with up to 110 electrons and compared to results obtained by modern neural networks.
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Optics
Strong Coupling Between RF Photons and Plasmons of Electrons on Liquid Helium
Asher Jennings, Ivan Grytsenko, Thomas Giovansili et al. (+6 more)
Plasmons, arising from the collective motion of electrons, can interact strongly with electromagnetic fields or
photons; this capability has been exploited across a broad range of applications, from chemical reactivity to biosensing. Recently, there has been growing interest in plasmons for applications in
quantum information processing. Electrons floating on
liquid helium provide an exceptionally clean, disorder-free system and have emerged as a promising platform for this purpose. In this work, we establish this system as a tunable plasmon-
photon hybrid platform. We demonstrate strong coupling between floating-electron plasmons and
radio-frequency (RF)
photons confined in an LC resonator. Time-resolved measurements reveal coherent oscillatory energy exchange between the plasmonic and photonic modes, providing direct evidence of their coherent coupling. These results represent a step towards cavity
quantum electrodynamics with a floating-electron plasmon coupled to a resonator. Furthermore, the LC resonator serves as a sensitive probe of electron-on-helium physics, enabling the observation of the Wigner
crystal transition and a quantitative study of the temperature-dependent plasmon decay arising from ripplon-induced scattering.
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All authors Asher Jennings, Ivan Grytsenko, Thomas Giovansili, Itay Josef Barabash, Oleksiy Rybalko, Yiran Tian, Jun Wang, Hiroki Ikegami, Erika Kawakami
Atmospheric and Oceanic Physics
Track-Dependent Links between Tropical Cyclones and Extratropical Predictability in Physical and AI Models
Gan Zhang
Global medium-range weather forecasts suffer occasional failures, often linked to tropical cyclones (TCs). We investigate TC influences on extratropical predictability by comparing forecasts from a physics-based model (ECMWF-IFS) and an AI-hybrid model (Google-NGCM) initialized near TC genesis. Analyzing 108 out-of-sample Northern Hemisphere cases reveals similar extratropical error growth patterns and comparable performance between the models. This suggests that the NGCM is capable of predicting the bulk upscale effects of tropical convection without directly representing convective processes. Leveraging the NGCM's computational efficiency, we compare forecasts initialized with and without TC genesis to isolate track-dependent forecast impacts. For Week-2 extratropical forecasts, TC impacts are highly time-, metric-, and track-dependent. The analysis confirms that some poleward-moving TCs degrade Week-2 US and European forecasts and suggests significant impacts from westward-moving TCs. The findings highlight the utility of the AI-hybrid model in predictability research and complex tropical-extratropical teleconnections that warrant future research.
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Optics
Observation of Janus Chirality for Coherent Thermal Emission from Metasurfaces
Kaili Sun, Yangjian Cai, Maxim V. Gorkunov et al. (+2 more)
Metasurfaces emerged as a powerful tool for controlling thermal radiation, yet achieving coherent emission with opposite circular handednesses remains a highly challenging problem. Here, we demonstrate experimentally the Janus
chiral thermal emission from metasurfaces with opposite circular handednesses on either side of a single device. We employ anisotropic metasurfaces supporting high-Q resonances with photonic flatbands enabling near-unity circular dichroism through in-plane
symmetry control. Our experiments confirm the Janus coherent emission, and they are validated by the results of the coupled-mode theory. The flatband resonant metasurfaces enabling a control of
chiral thermal emission provide an efficient platform for
spin-controlled light-matter interaction.
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All authors Kaili Sun, Yangjian Cai, Maxim V. Gorkunov, Yuri Kivshar, Zhanghua Han
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Synthesis of Monolayer Ice on a Hydrophobic Metal Surface
Qiaoxiao Zhao, Meiling Xu, Dong Li et al. (+10 more)
Understanding water-metal interactions is central to disciplines spanning catalysis, electrochemistry, and atmospheric science. Monolayer ice phases are well established on hydrophilic surfaces, where strong water-substrate interactions stabilize ordered hydrogen-bond networks. In contrast, their formation on hydrophobic metals has been deemed ther-modynamically unfavourable, with water typically assembling into amorphous films, three-dimensional crystallites, or interlocked
bilayer ice. Here, we demonstrate the synthesis of a monolayer ice phase on the hydrophobic Au(111) surface using a low-energy-electron-assisted growth method. Combined experimental characterizations including low-energy electron diffraction, angle-resolved photoemission spectroscopy, and X-ray photoelectron spectroscopy, complemented by first-principles calculations, prove that the monolayer ice phase composes of intact water molecules. This approach provides a generalizable strategy for stabilizing ordered two-dimensional ice on inert substrates and offers new insight into the interplay between water and low-energy electrons at hydrophobic interfaces.
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All authors Qiaoxiao Zhao, Meiling Xu, Dong Li, Zhicheng Gao, Yudian Zhou, Wenbo Liu, Jingyan Chen, Peng Cheng, Sheng Meng, Kehui Wu, Yanchao Wang, Lan Chen, Baojie Feng
Physics and Society
Correlation-Based Diagnostics of Social Contagion Dynamics in Multiplex Networks
Joan Hernàndez Tey and Emanuele Cozzo
Multiplex contagion dynamics display localization phenomena in which spreading activity concentrates on a subset of layers, as well as delocalized regimes where layers behave collectively. We investigate how these regimes are encoded in temporal correlations of node activity. By deriving a closed-form mean-field expression for node autocorrelations in a contact-based social contagion multiplex model and validating it through simulations, we show that lag-one autocorrelations act as sensitive indicators of both activation and localization transitions. Our results establish temporal correlations as lightweight, structure-agnostic probes of multiplex spreading dynamics, particularly valuable in partially observable systems.
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Atmospheric and Oceanic Physics
AI Decodes Historical Chinese Archives to Reveal Lost Climate History
Sida He, Lingxi Xie, Xiaopeng Zhang et al. (+1 more)
Historical archives contain qualitative descriptions of
climate events, yet converting these into quantitative records has remained a fundamental challenge. Here we introduce a paradigm shift: a generative AI framework that inverts the logic of historical chroniclers by inferring the quantitative
climate patterns associated with documented events. Applied to historical Chinese archives, it produces the sub-annual precipitation reconstruction for southeastern China over the period 1368-1911 AD. Our reconstruction not only quantifies iconic extremes like the Ming Dynasty's Great Drought but also, crucially, maps the full spatial and seasonal structure of El Ni$\~n$o influence on precipitation in this region over five centuries, revealing dynamics inaccessible in shorter modern records. Our methodology and high-resolution
climate dataset are directly applicable to
climate science and have broader implications for the historical and social sciences.
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All authors Sida He, Lingxi Xie, Xiaopeng Zhang, Qi Tian
Physics Education
Active Learning vs Traditional Lecturing in Introductory Mechanics: A Pooled Pass-Rate Benchmark Under Common Departmental Assessments from a Latin American Institutional Change Initiative
Isaac Pérez Castillo, Lidia Jiménez Lara, Orlando Guzman et al. (+6 more)
Improving student success in introductory physics remains a persistent challenge despite substantial progress from research-based instructional practices. Evidence from the Latin American context remains limited, where resources for instructional change are often constrained. This study reports a transparent
benchmark of student passing outcomes in Elementary Mechanics I at a large public university in México, comparing sections using Active Learning (AL) with those using Traditional Lecturing (TL). The labels AL and TL are operational, referring to section-level implementations by individual instructors rather than standardized protocols. Using aggregated counts from coordinator reports and common departmental assessments – written by a committee independent of instructional modality – we estimated pooled student-level pass probabilities for the first and second midterm exams, the global exam, and the final mark. Modality differences are summarized primarily by the risk difference, $RD_a=p_{\mathrm{AL},a}-p_{\mathrm{TL},a}$ (percentage points), with uncertainty quantified using Wilson confidence intervals and a
Bayesian reference analysis with Jeffreys priors for binomial proportions. Across assessments, pooled pass rates were higher under AL than under TL, with the strongest separation observed for the global exam and the final mark. For these outcomes, the $95\%$ confidence intervals excluded zero, including under a random-intercept
Bayesian model. We emphasize a constrained interpretation: the results provide a student-weighted
benchmark of “AL as implemented” versus “TL as implemented” in this setting, without isolating the causal effect of individual instructional techniques. Implications are discussed for departmental decision-making and feasible next steps in evaluation, including improved student data collection and more robust qualitative analysis.
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All authors Isaac Pérez Castillo, Lidia Jiménez Lara, Orlando Guzman, Juan Ernesto Chavero Amador, Juan Miguel Carrillo Gil, Luis Alberto González Flores, Miguel Angel Morales Olvera, Oscar Enrique Bonfil Urbalejo, Eric Burkholder