Fluid Dynamics · Cross-listed from cond-mat.soft
Precipitation-dissolution cycling drives intermittent salt creeping
Javier Rodríguez-Rodríguez, Manikuntala Mukhopadhyay, Lijun Thayyil Raju et al. (+3 more)
Salt creeping — the precipitation of salt
crystals away from an evaporating
liquid interface along surrounding surfaces — occurs across settings from geology and cultural-heritage weathering to inkjet printing and carbon sequestration. Yet why its dynamics are sometimes smooth and sometimes violently intermittent has remained unexplained. Here we investigate the confined evaporation of salt solutions from a capillary with unidirectional water loss, and show that intermittent salt creeping is driven by a cycle of precipitation and dissolution sustained entirely by
liquid transport. Time-resolved measurements reveal that each burst of
crystal growth coincides with episodic imbibition of solution into the growing salt deposit on the outer capillary surface, which couples evaporation to crystallization. Combining experiments with a minimal theoretical model, we show that the difference between the supersaturation at which
crystals nucleate and the saturation concentration at which they redissolve — the metastable zone of the salt — is sufficient to generate this cycle. The same mechanism accounts for the cases in which creeping is not intermittent: where the concentration at the capillary exit never reaches the nucleation threshold the
liquid meniscus recedes smoothly, and where it cannot subsequently fall back below saturation the deposit grows continuously, exhibiting self-amplified creeping. Our results recast salt creeping as a relaxation oscillator, and identify precipitation-dissolution cycling as a generic route to intermittency in evaporating multicomponent fluids.
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All authors Javier Rodríguez-Rodríguez, Manikuntala Mukhopadhyay, Lijun Thayyil Raju, Detlef Lohse, Jasper van der Gucht, Uddalok Sen
Fluid Dynamics · Cross-listed from cs.LG
Heuristic Learning for Active Flow Control Using Coding Agents
Paul Garnier, Jonathan Viquerat and Elie Hachem
Active flow control involves nonlinear dynamics, partial observations, and computationally expensive simulations, making controller design particularly challenging. Deep reinforcement learning (DRL) has emerged as a powerful framework for such problems, but its success typically relies on large numbers of simulator interactions and produces neural-network policies whose decision process often remains difficult to interpret. In this work, we investigate a different paradigm: instead of optimizing neural-network parameters, we use modern coding
agents to search directly for explicit executable feedback laws. We introduce a constrained heuristic-learning protocol in which an
agent iteratively proposes, evaluates, and revises controller implementations while interacting exclusively through the public
benchmark interface. The proposed framework is evaluated on 13 active flow-control
benchmarks spanning one, two, and three-dimensional problems and compared against the strongest available DRL baselines under identical simulation budgets. The discovered heuristic controllers match or outperform the best DRL policy in 10 of the 13 environments while remaining compact, interpretable, and directly inspectable. Beyond aggregate performance, the resulting controllers reveal physically meaningful feedback mechanisms, transfer successfully across more challenging configurations, and remain competitive under varying Reynolds and Rayleigh numbers, actuator counts, and observation sparsity. These results suggest that heuristic learning through coding
agents constitutes a credible and complementary alternative to conventional reinforcement learning, combining competitive performance with physically interpretable controller representations.
Prompts and source code are available at https://github.com/DonsetPG/fluid-heuristic-learning.
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Optics
Drill-bit-inspired dynamic focal fields for augmented laser materials processing
Evangelos Skoulas, Pinku Yadav, Justin Hidjam et al. (+8 more)
Laser manufacturing has advanced through increasingly precise control of power, pulse duration, repetition rate and scan trajectory, yet the spatial intensity profile of the beam is still usually fixed during light-matter interaction. This constraint limits how energy can be delivered to matter, particularly in processes where melt flow, material removal and surface morphology evolve on comparable time and length scales. Here we introduce drill-bit-inspired
laser beams that convert the focal intensity distribution from a passive, static spot into an active, programmable processing tool. By combining cylindrical vector beams with rotational vectorial polarization filtering, we create a near diffraction limited two lobe Hermite-Gaussian focus that continuously
spins about the propagation axis and can be reconfigured on demand. We establish two operating regimes, dynamic beam spinning and instantaneous beam-profile shifting, and derive closed-form descriptions of the accumulated fluence and effective pulse number governed by the along-scan pitch l = u/f, where u is the scan speed and f is the
spin frequency. Across continuous-wave and ultrashort-pulse regimes, this dynamic energy deposition enables low-power metal machining with drilling efficiencies about four times higher than static Gaussian, enhances convective melt flow, promotes pore resorption and reduces retained porosity in keyhole welding, as visualized by in situ X-ray imaging, and turns simple linear scans into programmable surface textures. These results show that dynamic focal-profile control can extend
laser processing beyond static beam shaping, opening a broadly applicable route to programmable energy deposition in manufacturing.
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All authors Evangelos Skoulas, Pinku Yadav, Justin Hidjam, Aurelien Woher, Rainer Kling, Beat Neuenschwander, Alexander Rack, Xavier Maeder, Patrik Hoffmann, Elia Iseli, Sergey Shevchik
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Synthesis of Ti2B2Clx MBenes in molten salts from theoretical and experimental perspectives
Rodrigo M. Ronchi, Emile Defoy, Andrejs Petruhins et al. (+11 more)
The unique properties and application possibilities of two-dimensional (2D) materials motivates the exploration of different nanolaminated compounds. Here, by using a molten salt approach, we selectively etch Ti2InB2 with ZnCl2 to produce a multilayer (ml) Ti2B2Clx MBene. Scanning transmission electron microscopy, in combination with energy dispersive X-ray, and electron energy loss spectroscopies show that In atoms are completely removed from the precursor upon etching, being replaced by chlorine surface terminations with a coverage 1.1 < x < 1.4. Further, in situ X-ray diffraction indicates a direct biphasic transformation from Ti2InB2 to ml-MBene, with no signs of intermediate phase formation. A computational framework based on density functional theory further corroborates these experimental observations by showing a negative reaction free energy for the formation of ml-MBene, favourable over all competing processes. In addition, A-element substitution into to the 3D Ti2ZnB2 phase is predicted to be endergonic, consistent with the absence of experimental evidence for its formation. Initial Li-ion battery performance evaluation showed a stable discharge capacity similar or better than MAX phases and other borides. Altogether, the theoretical framework combined with materials synthesis and characterization provides a general approach for 2D materials development, for further expansion of the family of 2D materials.
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All authors Rodrigo M. Ronchi, Emile Defoy, Andrejs Petruhins, Justinas Palisaitis, Lianghao Yu, Lan Tang, Solenn Reguer, Dominique Thiaudière, Ningjun Chen, Durga Sankar Vavilapalli, David Portehault, Jonas Björk, Per O. Å. Persson, Johanna Rosen
Optics
NaBiF$_4$: Er$^{3+}$, Yb$^{3+}$ upconversion particle as a multi-functional bio-marker
Atanu Ghosh, Krishna Kumari Swain, Agniva Das et al. (+6 more)
Lanthanide-doped upconversion particles (UCPs) have revolutionized optical bioimaging platforms because of their excellent photostability, non-toxicity, and utilization of near-infrared excitation, which facilitates deep tissue penetration with negligible autofluorescence. However, it remains a challenge to achieve high-contrast and sub-diffraction imaging in noisy biological media, without using a high-power
laser. Here, we report various protocols applied to bismuth-doped UCPs address some of these challenges. Compared to the photoluminescence (PL) emission of the regular Yttrium doped UCPs, we observe a three-fold increment in the
quantum yield of the overall emission of bismuth-UCPs, and a four-fold increment, specifically, in red emission. Leveraging this advantage, we devise a protocol employing two infrared wavelengths, 975 nm and 1064 nm, to selectively control the PL emission. Interestingly, our results reveal two distinct regimes in which PL can be systematically quenched or enhanced, by adjusting the 975 nm
laser power. We model the overall dynamics as a simplified stimulated emission depletion process involving three energy levels. In addition, the particle has a thickness under sub-diffraction, shows optical trapping ability, and potential of surface functionalization to enable specific conjugation with diverse biospecimens. These studies establish bismuth doped UCPs as an excellent candidate in accomplishing advanced biomarker operating with enhanced signal-to-noise ratio and sub-diffraction imaging capabilities.
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All authors Atanu Ghosh, Krishna Kumari Swain, Agniva Das, Mrutyunjaya Rath, Snigdhadev Chakraborty, Bipeen Kumar, Yamini Selvam, Siddharth Dhomkar, Basudev Roy
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Capturing the calendering U-shape in lithium-ion electrode thermal conductivity
Julius Störk
Calendering is a key manufacturing step in lithium-ion electrode production, increasing volumetric energy density by reducing electrode porosity. Its effect on through-plane effective thermal conductivity, however, can be non-monotonic: measurements of graphite-based anodes show an initial decrease in thermal conductivity during early calendering followed by recovery at higher compaction. Conventional porosity-based effective-medium closures cannot reproduce this U-shaped behaviour. We develop a calendering-aware extension of the Zehner–Bauer–Schlünder model that combines a Knudsen-corrected porous-medium baseline with a compression-indexed contact contribution. For graphite electrodes, the model represents the competing effects of increasing particle contact and calendering-induced reorientation of anisotropic graphite particles, which initially reduces favourable through-plane heat-transport pathways. For quasi-isotropic NMC cathodes, the observed response is instead captured through process-dependent contact-network
evolution. Across 27 calendering states spanning thin and thick graphite anodes and NMC622 and NMC811 cathodes, the proposed closure reduces the mean absolute percentage error from 31.1% for the zero-fit reference model to 4.5%. The result shows that incorporating process-dependent microstructural
evolution is necessary to capture the measured conductivity minimum. Validation across additional electrode formulations, thicknesses, and chemistries remains necessary to assess transferability.
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Instrumentation and Detectors · Cross-listed from cond-mat.supr-con
Microscopic equivalence of the vortex-entry current and the depairing current in a superconducting thin-film strip
Takayuki Kubo
The
vortex-entry current density $J_{\rm v}$ of a superconducting strip is usually defined, within phenomenological Pearl–London theory, as the current density at which the edge barrier for
vortex entry disappears. In that approach, $J_{\rm v}$ depends on a short-distance core cutoff introduced by hand, and its temperature dependence cannot be determined within the same framework. To remove this cutoff ambiguity and determine the temperature dependence, one needs a microscopic calculation of the
vortex-entry current. Nevertheless, such a microscopic calculation has never been carried out. Here, we formulate and solve this problem for an ideal homogeneous dirty-limit superconducting thin-film strip at zero applied field, with self-field effects neglected.
Vortex entry is treated as the loss of local stability of the
vortex-free current-carrying state. The calculation uses the fixed-current Gibbs functional of Usadel theory, which is valid over the full temperature range $0<T<T_c$, and examines both spatially uniform and nonuniform perturbations. The microscopic calculation shows that the condition for disappearance of the
vortex-entry barrier is identical to the depairing condition. The central result is not merely that two current densities have the same value. The criterion for disappearance of the
vortex-entry barrier and the depairing criterion are not independent conditions. Both identify the same loss of local stability of the
vortex-free current-carrying state, namely, the same spinodal. Consequently, $J_{\rm v}(T)=J_{\rm dp}(T)$ for all $0<T<T_c$. This result determines the temperature dependence of $J_{\rm v}$, removes the Pearl–London core-cutoff ambiguity, and establishes the microscopic equivalence of the
vortex-entry and depairing current criteria.
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Optics · Cross-listed from quant-ph
A diode nanocavity for fast, efficient and tunable emission of highly entangled photon pairs and Fourier-transform-limited single photons
Ievgen Brytavskyi, Thomas Oberleitner, Christian Weidinger et al. (+16 more)
Deterministic sources of entangled
photon pairs and indistinguishable
photons are expected to play a key role in photonic
quantum technologies.
Semiconductor quantum dots are promising candidates due to their on-demand emission and compatibility with nanophotonic structures. However, current implementations face trade-offs between extraction efficiency, Purcell enhancement, as well as charge noise that causes blinking and degrades indistinguishability. Here we demonstrate a tunable nano-optoelectronic device based on a
quantum dot embedded in a p-i-n diode circular-Bragg-grating-resonator and featuring extraction efficiencies up to 0.55(6) and Purcell-factor of $\sim$8. The device generates wavelength-tunable entangled
photon pairs with suppressed blinking and raw (corrected) concurrence > 0.89 (0.91) over a range of 1.6 nm. The very same source also emits single, nearly
Fourier-limited and highly indistinguishable
photons with raw (corrected) $\mathcal{V}_{\text{HOM}}$ = 0.951(4) (0.988(6)). These results demonstrate a viable platform for
semiconductor quantum photonics.
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All authors Ievgen Brytavskyi, Thomas Oberleitner, Christian Weidinger, Maximilian Aigner, Gabriel Undeutsch, Tobias Steindl, Johannes Reindl, Ailton Garcia Jr., Melina Peter, Christian Schimpf, Santanu Manna, Michele B. Rota, Quirin Buchinger, Sven Höfling, Tobias Huber-Loyola, Rinaldo Trotta, Tobias M. Krieger, Eva Schöll, Armando Rastelli
Classical Physics
Surface charge density of current-carrying conductors: An exact analytical solution for infinitely thin wires of arbitrary shape
Roberto Merlin
An exact asymptotic expression is derived for the surface charge density associated with a steady current in closed loops or wire segments of infinitesimal cross section connected to a battery. Except for vanishingly thin boundary layers at the ends of the wire, and irrespective of the conductor shape, the charge density varies linearly with arc length, as does the electrostatic potential along the curve. This proportionality generalizes earlier results and provides a clear physical picture of charge accumulation in electrical
circuits.
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Fluid Dynamics · Cross-listed from cond-mat.soft
Colloid recovery from porous structures under ambient flow: enhanced extraction via phoretic and osmotic mechanisms
Jitendra Dhakar, Kapil Upadhyaya and Akash Choudhary
Chemical gradients are widely employed to enhance particle transport in porous media, such as laundry detergency and enhanced oil recovery. Diffusiophoresis and diffusioosmosis refer to the movement of colloid and movement of near-surface fluid in response to electrolyte gradients, respectively. These mechanisms play a crucial role in colloid and drug transport in constricted regions where bulk transport is infeasible. Our earlier work [Tiwari et al., Langmuir 41, 18583 (2025)] has shown that phoretic and osmotic transport in dead-end micro-pores can be controlled by orienting salt gradients into or out of the pores; however, the extent to which this orientation influences large-scale spatiotemporal patterns and colloid extraction is not thoroughly explored. In this work, we study the phoretic and osmotic colloidal extraction from porous structure exposed to an ambient flow. We characterize the impact of solute gradient orientation, such as solute-out (i.e., solute-emitting porous media) and solute-in (i.e., solute-consuming media) modes. The two-dimensional porous structure is made of a number of pillars/fibers arranged in a
lattice ordered hexagonal packing with equal spacing. The results from finite-element simulations show that phoretic colloidal extraction exhibits a qualitatively distinct behavior in the two modes: in the solute-out mode, colloids are extracted from the peripheral region of the porous structure, whereas in the solute-in mode, extraction predominantly occurs from the stagnant core. Diffusioosmotic slip on the internal surface of pillars/fibres further amplifies extraction in both modes, with a relatively larger enhancement in the solute-in mode due to internal spatiotemporal flow patterns. Beyond demonstrating the sensitivity of osmotic transport in porous media, these insights can guide enhanced membrane filtration, laundry detergency, and enhanced oil recovery.
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Fluid Dynamics
Feature-based manifold model of actuated wakes
Alicia Rodríguez-Asensio, Guy Y. Cornejo Maceda, Bernd R. Noack et al. (+2 more)
We propose a feature-based reduced-order model to predict the transient dynamics of bluff-body wakes under arbitrary time-varying actuation. Starting point is a control-oriented POD Galerkin modeling which is challenged by incorporating time-varying actuations as a free input. Our model includes three key enablers. First, POD modes are replaced by a more accurate feature-based
manifold of same dimension. Second, a state space is distilled from dynamic features which encapsulate time-varying coherent structures. Third, this state space is augmented for the transient actuation response. Thus, a simple analytical
manifold dynamics is obtained. The approach is applied to the fluidic pinball at Re=30, a canonical configuration of three identical circular cylinders arranged in an equilateral triangle and immersed in uniform flow under symmetric actuation. The model is validated against several representative actuation scenarios and accurately reproduces the transient dynamics without requiring unsteady training data, providing an interpretable, observable-based and control-oriented framework. The proposed description of actuated bluff-body flows is expected to be generalisable to other configurations.
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All authors Alicia Rodríguez-Asensio, Guy Y. Cornejo Maceda, Bernd R. Noack, Stefano Discetti, Andrea Ianiro
Optics
Heterogeneous-Gradient Phase–Polarization Alignment and Maximal-Ratio Weight Allocation for Multi-Aperture Coherent FSO Reception
Cheng Chen, Tong Luo, Jiayin Xue et al. (+5 more)
Multi-aperture coherent reception can improve freespace optical (FSO) links by converting spatial diversity into coherent combining gain. In turbulent links, the aperture branches are simultaneously affected by relative phase errors, polarization mismatch, and unequal signal-to-noise ratios (SNRs). Existing methods treat phase/polarization
alignment and branch-weight allocation as separate operations, or absorb all impairments into a high-dimensional
MIMO equalizer that obscures the physical meaning of each aperture's contribution. This paper proposes a structured blind combining method based on heterogeneous gradient sources: phase and per-aperture polarization parameters are updated by closed-form analytical gradients that maximize the combined output power, while aperture weights and an optional global polarization angle are updated by gradients derived from the constellation-radius error. An exponential parameterization pn = eqn/N ensures positivity without clipping. The internal variable qn is adapted by radius-error gradients, thereby allocating maximal-ratio-combining-like weights according to the quality of the already aligned branches.
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All authors Cheng Chen, Tong Luo, Jiayin Xue, Siyu Gong, Qun Zhang, Linsheng Fan, Qi Wu, Yanfu Yang
Atmospheric and Oceanic Physics
HourGlass: A probabilistic data-driven temporal downscaler for global and regional weather forecasting
Magnus Sikora Ingstad, Mariana C. A. Clare, Olav Ersland et al. (+16 more)
Many forecast applications require high frequency temporal resolution, yet most state-of-the-art data-driven weather
forecasting systems operate at 6-hourly resolution. Although direct hourly
forecasting is possible, it suffers from error accumulation and temporal inconsistency. We introduce HourGlass, a probabilistic data-driven temporal downscaling method that reconstructs the
evolution between forecast states. HourGlass is trained using variants of the continuous ranked probability score (CRPS) preserving small-scale spatial variability while encouraging temporal consistency. Unlike existing deterministic temporal downscaling approaches, which tend to produce overly smooth fields, HourGlass generates realistic probabilistic forecasts. Training on forecast trajectories rather than reanalysis or analysis data also avoids the temporal inconsistencies present in
datasets used by previous methods. We evaluate HourGlass in two settings: AIFS-HourGlass, applied globally to ECMWF's AIFS-Single and AIFS-ENS forecast systems, and Bris-HourGlass, applied regionally to MET Norway's high-resolution stretched-grid ensemble model, Bris. Verification against observations shows that both models retain the skill of their underlying
forecasting systems while producing temporally coherent hourly forecasts with realistic small-scale variability. Case studies demonstrate physically consistent
evolution during rapidly developing weather events, including extratropical cyclones and organised convection. Hourly precipitation remains challenging: HourGlass improves the spatial realism of precipitation fields but still underestimates the most intense extremes, a common limitation of data-driven weather
forecasting models. These results demonstrate that HourGlass effectively bridges the gap between 6-hourly data-driven forecasts and the hourly products required for operational regional and global
forecasting.
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All authors Magnus Sikora Ingstad, Mariana C. A. Clare, Olav Ersland, Vera Gahlen, Håvard Homleid Haugen, Ophélia Miralles, Even M. Nordhagen, Thomas N. Nipen, Ivar A. Seierstad, John Bjørnar Bremnes, Michael Maier-Gerber, Zied Ben Bouallègue, Harrison Cook, Christian Lessig, Gert Mertes, Cathal O'Brien, Florian Pinault, Ana Prieto Nemesio, Matthew Chantry
Physics and Society
Charting the life of Billboard hits through memory, turnover, and predictability
Arthur A. B. Pessa, Angelo A. Flores, Matjaz Perc et al. (+1 more)
Rankings shape the visibility and success of cultural products, yet their temporal dynamics remain underexplored when comparing distinct ranked objects within the same domain. Here, we use nearly seven decades of Billboard Hot 100 songs and six decades of Billboard 200 albums to investigate how success emerges, persists, and differs between songs and albums. We find that albums exhibit a heavier-tailed permanence distribution and reenter the charts more often than songs, whereas songs typically have longer uninterrupted runs. Similarity between successive charts decays much faster for songs than for albums, suggesting that individual hits reflect shorter-lived collective
attention, while albums retain longer cultural
memory. Rank-
turbulence divergence shows that consecutive charts are similar, but that top positions are dominated more by rank reshuffling than by turnover.
Entropy-based analyses reveal high uncertainty in rank movements, with distinct historical patterns for songs and albums and a strong dependence on trajectory length. Clustering of trajectories shows that chart success is organized into a small number of typical pathways, including canonical rise-and-fall trajectories, high-end persistence, and monotonic decline. Together, these results show that musical charts are not merely records of popularity, but dynamic
memory systems in which
attention, turnover, and predictability interact differently for songs and albums.
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All authors Arthur A. B. Pessa, Angelo A. Flores, Matjaz Perc, Haroldo V. Ribeiro
Chemical Physics
Efficient, direct calculation of reaction rate coefficients based on a partially rearranged rovibrational Hamiltonian. A full-dimensional case study of the H$_2$ + D $\rightarrow$ HD + H reaction
Gábor A. Ecseri, Attila G. Császár and Csaba Fábri
It is shown that an efficient, direct, and fully
quantum mechanical calculation of thermal reaction rate coefficients requires a new, partially rearranged form of the numerically-constructed exact kinetic energy part of the rovibrational
Hamiltonian expressed in internal coordinates. Using this
Hamiltonian and an accurate, full-dimensional potential energy surface characterizing the H$_2$ + H exchange reaction, developed by Mielke, Garrett, and Peterson (J. Chem. Phys. 2002, 116, 4142), reaction rate coefficients in the temperature range of $75-800$ K have been computed for the H$_2$ + D $\rightarrow$ HD + H reaction. The paper puts particular emphasis on the exact treatment of overall molecular rotation and on
nuclear spin symmetry.
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Physics Education
Generative AI in Higher Education Laboratory Learning: A Qualitative Case Study of Epistemic Scaffolding and Assessment Boundaries
Matteo Tuveri and Alessandro Riggio
Advanced physics laboratories require students to integrate disciplinary knowledge, experimental practice and scientific argumentation across complex observational and analytical tasks. The increasing availability of generative artificial intelligence (GenAI) adds complexity to this coordination, since AI systems may function as conceptual explainers, operational assistants, artefact reviewers or apparently authoritative evaluators. This exploratory qualitative case study examines AstroTutor, a constrained GenAI tutor introduced as an optional support resource in a Master's-level advanced astrophysics laboratory. The study investigates how students framed the tutor within a broader GenAI-mediated learning ecology that included the instructor, peers, course materials, observations, measurements, data analysis and final assessed reports. Seven students attended the course, five used the tutor, and three groups produced a final report. The analysis combined content analysis, thematic analysis and frame analysis. Drawing on chat logs, final reports and limited post-use reflective responses, the results identify five principal GenAI functions: interface interpreter, warrant organiser, report scaffold, unstable authority and resource whose traces may appear in downstream reports. These findings extend previous research on GenAI in education to the context of advanced physics laboratories, showing that its use requires explicit design boundaries, guidance on legitimate and prohibited practices, verification routines, and assessment requirements that preserve students' epistemic responsibility. The educational implications of a GenAI-mediated learning ecology in advanced physics laboratories are also discussed.
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Accelerator Physics
Beam based undulator trajectory alignment at European XFEL
Winfried Decking, Frank Brinker, Lars Froehlich et al. (+2 more)
Precise
alignment of the undulator trajectory onto a straight line is a per-requisite for high fidelity SASE operation, which in turn also enables non-standard operation modes like self-seeding or two-color operation. At European XFEL electron and
photon beam-based method are combined with a step-by-step performance-based optimization to ensure that the trajectory is on a straight line over most of the length of the about 250 m long undulator system.
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All authors Winfried Decking, Frank Brinker, Lars Froehlich, Matthias Scholz, Wolfgang Freund
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Amorphous materials as a frontier challenge for universal interatomic potentials
Natascia L. Fragapane and Volker L. Deringer
Pre-trained or 'foundational' machine-learned interatomic potentials (MLIPs) are now widely used in materials modelling. However, early pre-trained models and
benchmarks have largely focused on ordered, crystalline structures, and their transferability to non-crystalline solids remains unclear. Here, we show that the amorphous state is indeed a central challenge for future universal MLIPs, based on a systematic evaluation of current mainstream models in this domain. We introduce a benchmarking framework built on a curated reference
dataset of canonical amorphous systems, as well as validation for structures and properties. Our study identifies limitations in the transferability of many current pre-trained models and investigates fine-tuning strategies tailored to disordered phases. Together, our results can facilitate future applications of MLIPs in the fast-growing field of amorphous functional materials, and they provide guidance for designing next-generation training
datasets and transferable atomistic models.
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Physics and Society · Cross-listed from cs.SI
Dorota Celinska-Kopczynska and Eryk Kopczynski
Network theoreticians hypothesize that the structure of real-world networks has a
geometric origin. Especially,
hyperbolic geometry was proven insightful in representing and modeling of scale-free networks. Embedders are
algorithms used to find a
geometric representation of a network. In this study, we introduce a fast lossless graph compression
algorithm based on modern
hyperbolic embedders. Experimental validation on real-world and generated networks shows that our
algorithm beats state-of-the-art by up to 42% on real-world graphs.
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Atmospheric and Oceanic Physics · Cross-listed from math-ph
Beyond Critical Slowing Down: Slow Modes, Extreme Tails, and Field Decoherence in Tipping Transitions
Mickaël D. Chekroun and Valerio Lucarini
Tipping transitions are abrupt reorganizations between statistical regimes, usually anticipated through critical slowing down: recovery slows, autocorrelation and variance rise, and spectral power shifts toward low frequencies. In noisy, spatially extended systems, however, these signatures alone cannot distinguish weakening resilience, increasingly likely excursions toward a competing state, and spatial reorganization. We address these questions in the
stochastic Ghil-Sellers energy balance model, whose ice-albedo feedback supports warm and snowball metastable regimes, through three viewpoints. Reduced Ruelle-Pollicott resonances and Kolmogorov modes diagnose relaxation and response in physically interpretable observables; Extreme Value Theory probes the accessibility and persistence of tail excursions; and Data-Adaptive Harmonic Modes diagnose the frequency-resolved organization of the temperature field. Near tipping, several reduced decay rates slow together and their modes become geometrically harmonized along a common transition direction, while Green functions show delayed recovery and enhanced low-frequency susceptibility only when the response residues are nonzero. Cold extremes become less sharply bounded and more clustered, and the full field becomes less compressible as its phase distribution broadens, even as a dominant low-frequency component emerges. Read jointly, these diagnostics reconcile apparently contrasting signatures and connect statistical indicators to the physical geometry of competing
climate states. We further show that a small localized albedo change can create an additional pair of folds, so that a distance to tipping may carry structural as well as statistical uncertainty. The results provide a framework for interpreting early warnings that distinguishes changes in the system's dynamics from uncertainty in the model's bifurcation structure.
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Applied Physics · Cross-listed from quant-ph
Controlling the Inhomogeneous Broadening and Impedance Matching of a Spin Ensemble
Mathieu Couillard, Debdip Guchait, Hiroki Takahashi et al. (+1 more)
We control the spectral distribution of a
spin ensemble by applying a
magnetic field gradient using an anti-Helmholtz coil inside a dilution refrigerator, and demonstrate impedance matching between the ensemble and a transmission line, achieving -50 dB absorption of incident radiation. This represents a first step toward a
spin-ensemble-based
quantum memory for itinerant microwave
photons. We further model the spectral distribution under the applied gradient to predict the
spin-resonator response, and use the device to systematically tune the weak-to-strong coupling transition in both continuous-wave and time-domain pulsed measurements.
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All authors Mathieu Couillard, Debdip Guchait, Hiroki Takahashi, Yuimaru Kubo
Computational Physics
Toward AI-Agent-Driven Particle Transport Simulations: Implementation of AI-Assisted Workflows for PHITS
Tatsuhiko Sato, Shintaro Hashimoto, Tatsuhiko Ogawa et al. (+5 more)
Monte Carlo particle transport codes are powerful tools, but their use requires substantial knowledge of input preparation, execution, and result analysis. In this study, we present a code-side strategy for applying existing AI assistants and AI
agents to PHITS. Two complementary sets of AI-ready resources were prepared from manuals, lecture materials, sample inputs, utility information, and developer-curated cautions: a bundled knowledge base for
retrieval-augmented generation (RAG)-based assistants and a compact
agent reference for direct use by AI
agents. The knowledge base was loaded into Gemini Notebook to provide conversational PHITS support, while the
agent reference was combined with PHITS-specific policies and execution rules to enable AI
agents to edit input files, execute calculations, inspect errors, analyze results, and assist with source-code modification and compilation. To evaluate the
agent-driven workflow, five demonstration tasks were executed ten times with different AI
agents and computing environments. The results showed that AI
agents could handle complex PHITS workflows when appropriate resources and rules were provided. Practical lessons included precise
prompts, human verification, well-documented sample files, explicit execution policies, and command-line-accessible tools. These findings support bundling AI-ready resources with particle transport codes to enable the use of general-purpose AI tools without requiring dedicated code-specific applications.
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All authors Tatsuhiko Sato, Shintaro Hashimoto, Tatsuhiko Ogawa, Takuya Furuta, Yuho Hirata, Seiki Ohnishi, Yasuhito Sakaki, Nobuhiro Shigyo
Optics
Twist tunable resonances in photonic bilayer for second harmonic generation
Egor S. Vyatkin and Sergey A. Tarasenko
Moiré structure emerging in photonic
bilayers stacked with a twist enables the controllable frequency selective resonant response. Here, we employ twist tunable resonances to boost second harmonic generation (SHG) at a desired frequency in twisted photonic
bilayers integrated with two-dimensional nonlinear
crystals. We develop an analytical theory relating the resonance frequencies and the SHG enhancement factor to the material parameters of the dielectric layers and the twist angle. The theory reveals a critical twist angle separating two distinct regimes of photonic
bilayer operation: with open and closed moiré diffraction channels. Above the critical angle, the
photon leakage from the guided mode is suppressed and the SHG enhancement factor rises by orders of magnitude. The paper offers a compact route to nonlinear conversion in moiré photonic structures efficient and tunable over a wide spectral range.
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Medical Physics
Multi-Catheter Digitization in Brachytherapy via Few-Shot Synthetic-to-Real Learning and Structure-Aware Tracking
Zhuo Xiao, Bo Liu, Jingjing Wang et al. (+6 more)
Accurate catheter digitization in CT-guided interstitial brachytherapy is a critical but time-consuming task, especially for complex implant configurations. We developed a data-efficient, physics-guided framework for automated multi-catheter digitization with minimal clinical annotation. The pipeline consists of two stages. First, an implant region-aware network was pretrained on synthetic CT volumes with simulated metallic signatures and then fine-tuned using only 10 clinical cases. Second, a structure-aware reconstruction module combined a direction-constrained 3D Hough transform with synchronous physics-constrained inward tracking to separate adherent catheter trajectories. The method was evaluated by patient-level five-fold cross-validation on 203 treatment fractions from 38 patients. The fine-tuned network achieved an HD95 of 0.853 +/- 0.362 mm. End-to-end evaluation yielded an F1 score of 0.891 +/- 0.178, with shaft and tip errors of 0.334 +/- 0.367 mm and 0.896 +/- 0.680 mm, respectively. In cases with severe catheter adhesion, the tracking F1 score remained 0.843 +/- 0.190. The complete workflow required approximately 11.6 s per case. These results indicate that combining few-shot synthetic-to-real learning with physics-guided structural tracking can provide robust and efficient multi-catheter digitization for time-sensitive clinical workflows.
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All authors Zhuo Xiao, Bo Liu, Jingjing Wang, Qinglong Yao, Haitao Sun, Fugen Zhou, Junjie Wang, Qiuwen Wu, Ping Jiang
Optics · Cross-listed from cond-mat.mes-hall
Mode-locking instability and multiple soliton formation in GaN polariton waveguide cavities
O. Bahrova, V. Develay, H. Souissi et al. (+10 more)
We study the emergence of multi-
soliton regimes in 1D ridge polariton waveguides of two different lengths. We show that by varying the position of the gain, which in out-of-
equilibrium polariton systems is provided by the pumping
laser and its associated excitonic reservoir, it is possible to tune the regime of
soliton formation between single and multiple
solitons. This
soliton dynamics can be quantitatively reproduced by solving the Gross-Pitaevskii equations of the coupled
exciton-
photon system, which show that the
soliton splitting mechanism is governed by the
exciton reservoir dynamics.
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All authors O. Bahrova, V. Develay, H. Souissi, C. Brimont, L. Doyennette, B. Alloing, E. Cambril, S. Bouchoule, T. Ackemann, J. Zuniga-Perez, D. Solnyshkov, G. Malpuech, T. Guillet
Optics · Cross-listed from cond-mat.mes-hall
Tellurium Metasurface Beam Splitter with Pulse Laser-Controlled Anisotropy
Takuto Hiraoka, Mizuho Matoba, Yuta Kobayashi et al. (+5 more)
Laser-programmable optical anisotropy offers a new route to developing reconfigurable metasurfaces without conventional nanofabrication processes. Here, we demonstrate a lithography-free approach based on spatial control of the crystallographic $c$ axis orientation in tellurium (Te) using pulse
laser irradiation. As a proof of concept, we demonstrate a Te metasurface beam splitter by
laser-written optical-axis patterning and experimentally confirm that its optical response is in good agreement with theoretical predictions and numerical simulations. By directly programming the local optical anisotropy, this method enables a simple fabrication process while offering the possibility of rewriting and dynamically reconfiguring device functionality. These features make this approach a promising platform for non-resonant active metasurfaces and other reconfigurable flat-optics applications.
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All authors Takuto Hiraoka, Mizuho Matoba, Yuta Kobayashi, Arata Mitsuzuka, Masashi Kawaguchi, Haruyuki Sakurai, Kuniaki Konishi, Masamitsu Hayashi
Optics
Geometry-Optimized Complex-Domain error-diffusion encoding for Fourier Single-Pixel Imaging
Chongwu Shao, Yue Cao, Wei Zhang et al. (+4 more)
This work proposes a geometry-optimized complex-domain error-
diffusion encoding method for
Fourier single-pixel imaging. Instead of independently binarizing multiple grayscale phase-shifting patterns, the proposed method directly represents each complex-valued
Fourier basis pattern using K (K >= 3) weighted binary patterns while diffusing the residual error in the complex domain. A
geometric interpretation is further established, revealing that the encoding process can be viewed as approximating the
Fourier-basis unit circle by a regular polygon in the complex plane. Based on this
geometric interpretation, practical optimization strategies are developed for K = 3, K = 4, and K = 7. Both numerical simulations and real-object experiments demonstrate consistently superior reconstruction quality compared with conventional phase-shifting dithering.
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All authors Chongwu Shao, Yue Cao, Wei Zhang, Xiaopeng-Jin, Yingran Shen, Shijian Li, Xu-Ri Yao
Applied Physics · Cross-listed from cs.CV
A Nearable Soft Mat Based on Distributed Optical Fiber Sensing for Physiological Monitoring
Vincenzo Lavorgna, Martina Pulcinelli, Andrea Polimadei et al. (+5 more)
Distributed optical fiber sensing (DOFS) combines the advantages of fiber optic sensors, including flexibility, small size, immunity to electromagnetic interference, and high metrological performance, with the capability to transform a single optical fiber into a continuous sensing element for spatially resolved mechanical measurements. Optical frequency domain reflectometry (OFDR), based on Rayleigh backscattering, enables high spatial resolution DOFS measurements, broadening the range of potential sensing applications. However, OFDR based DOFS remains largely unexplored for biomedical applications, despite the need for sensitive, spatially resolved, and conformable sensing interfaces. This study presents a soft DOFS based mat as a large-area interface for physiological monitoring. A single-mode optical fiber was embedded in a flexible silicone
matrix and arranged in a serpentine layout to distribute sensing over the mat surface. With a gage pitch of 2.6 mm, the system provided 2250 sensing sites across the active area at a sampling frequency of 50 Hz. The mat was assessed on six healthy volunteers in a seated nearable configuration on the backrest of a standard office chair. The distributed output enabled two dimensional mapping of the mat response, reflecting back mat mechanical coupling and cardiorespiratory induced perturbations. Respiratory rate and heart rate were therefore estimated and compared with a reference wearable system. The maps revealed physiologically coherent spatial and temporal patterns, while the estimated rates showed good agreement with the reference measurements. These results demonstrate the feasibility of combining large area distributed sensing, spatial mapping, and quantitative cardiorespiratory monitoring within a DOFS based soft nearable interface.
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All authors Vincenzo Lavorgna, Martina Pulcinelli, Andrea Polimadei, Rosaria D Amato, Carlo Massaroni, Michele Arturo Caponero, Emiliano Schena, Daniela Lo Presti
Geophysics
Pore pressure change during nucleation and slip along experimental faults
Nicolas Brantut, François X. Passelègue and Pierre Dublanchet
In order to clarify the main controlling factors influencing fluid pressure changes in fault zones during the seismic cycle, we conducted laboratory rock friction experiments where fluid pressure was monitored in situ during sequences of quasi-static loading followed by dynamic slip events. The simulated fault was a 30$^\circ$ saw-cut in a Westerly granite cylinder, saturated with water, tested under triaxial conditions. Pore pressure was held constant at the boundaries of the block, but the low hydraulic diffusivity of Westerly granite made the fault hydraulically disconnected from the boundaries. During quasi-static loading while the fault was locked, we observed pore pressure increases which we interpret as poroelastic closure of the fault. During dynamic slip events, pore pressure systematically dropped by amplitudes commensurate to the normal stress drop. A large contribution to the pore pressure drop is interpreted as poroelastic opening of the fault. Deviations from the poroelastic effects are observed: in small events, pore pressure dropped further than anticipated, indicating inelastic dilation. In a few large events, pore pressure dropped less than anticipated, which could be the sign of compaction or thermal pressurisation. Prior to macroscopic slip events, we detect systematic pore pressure decreases by up to around 1 MPa, correlated to the occurrence of inhomogeneous preslip along the fault. Slip nucleation, inferred by kinematic inversion of local strain gauge data, is linked to local slip magnitudes of the order of 1 to 10 $\mu$m, and appears to lead to inelastic dilation. A stability analysis of fault slip including dilatant and poroelastic effects shows that poroelastic coupling tends to compensate normal stress variations, leading to faults operating under mostly constant effective normal stress if conditions are undrained.
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Optics
Chiral lasing via broken parity-time symmetry in bound-state-in-the-continuum metasurfaces
Matthew Parry, Daria A. Smirnova, Andrey A. Sukhorukov et al. (+1 more)
We propose a concept for
chiral lasing from planar metasurfaces that obviates the need for traditional out-of-plane
symmetry breaking by exploiting spatial gain-loss modulation to break parity-time
symmetry. We explain the underlying non-Hermitian physics of this design principle using a coupled-mode model of a four-site plaquette. The
symmetry requirements for such
chiral emission are explained with a general
symmetry analysis based on projection operator
matrices, implemented algorithmically for automated evaluation. This method enables the design of planar metasurfaces capable of emitting nearly-pure circularly polarized light. We apply our analysis to simulations of both symmetric and asymmetric versions of a Fylfot metasurface design and demonstrate that the gain mode at the parity-time symmetric exceptional point exhibits
chiral emission. Lastly, we present a readily manufacturable metasurface made from an InGaAs slab, showing that such a metasurface
laser can be actively tuned from linear to circular polarization.
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All authors Matthew Parry, Daria A. Smirnova, Andrey A. Sukhorukov, Dragomir N. Neshev