Computational Physics
Physics-enriched neural solvers for transient ice-flow simulation
Thomas Gregov, Sebastian Rosier, Brandon Finley et al. (+2 more)
Transient glacier simulations with higher-order ice flow require the repeated solution of a nonlinear problem as the geometry evolves. In the online mode of the Instructed Glacier Model, the velocity field is represented by a neural network whose weights are warm-started from the previous time step and updated with a few optimizer iterations. We show that supplying the network with inexpensive input fields derived from low-order ice-flow balances improves this online solver. Unlike residual-based physics-informed neural networks, which incorporate physics through governing-equation penalties in the loss, our approach leaves the governing energy objective unchanged, adding physical structure through the network inputs. Across three real-world glacier configurations, the enriched solver is markedly more robust to solver settings. On the two alpine cases, it also improves the tuned accuracy–runtime trade-off, reducing surface-velocity errors by factors of two to four at fixed runtime and reaching few-percent relative errors with only $10^4$–$10^5$ trainable parameters, far fewer than comparable raw-input baselines. A 300-year Aletsch simulation then completes in under one minute, and the larger Valais domain in about two minutes, on a single GPU—a budget once reserved for much simpler shallow-ice models. Gains are smaller for the fast marine-terminating glacier, where nonlocal stress coupling favors larger or spectral networks. More broadly, the results suggest that enriching a neural solver's inputs with reduced-order physics can make repeated higher-order solves much cheaper, with no training data and no offline training.
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All authors Thomas Gregov, Sebastian Rosier, Brandon Finley, Andreas Vieli, Guillaume Jouvet
Physics and Society
The hierarchical organization of urban social overlap: How shared social spaces diverge from physical mobility
Bibandhan Poudyal, Mariana Macedo, Ronaldo Menezes et al. (+1 more)
Cities are commonly characterized through population density, infrastructure, and mobility flows. These quantities describe where people are and how they move, but movement does not uniquely determine where populations repeatedly encounter one another or whether different locations participate in the same social environments. Here, we construct co-presence overlap networks across 13 Brazilian cities to distinguish these dimensions of urban organization. We introduce two complementary measures: colocation, which quantifies recurrent co-presence activity within individual locations, and co-connectedness, which measures the extent to which locations share the same co-present pairs. We find that the spatial concentration of colocation differs substantially from that of mobility, producing social centers that can differ in both number and location from mobility centers. At the network level, co-connectedness exhibits a non-random hierarchical organization in which locations preferentially share recurrent pairs with locations of similar activity. This hierarchy is systematically weaker and substantially more variable across cities than the corresponding mobility hierarchy, demonstrating that cities with similar mobility organization can differ in how recurrent social overlap is organized across locations. Finally, we show that the spatial proximity of colocation activity to social centers relative to residential centers provides a complementary spatial dimension of urban organization. Together, these results separate three features that are conflated when cities are characterized through mobility alone: movement between locations, local opportunities for social interaction, and the organization of recurrent social overlap across locations.
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All authors Bibandhan Poudyal, Mariana Macedo, Ronaldo Menezes, Gourab Ghoshal
Fluid Dynamics
Physical mechanism of turbulence attenuation by polymers from a timescale perspective
Hayato Masuda, Yusuke Koide, Yutaro Motoori et al. (+1 more)
To elucidate the physical mechanism of
turbulence attenuation by
polymers at each scale, we conduct direct numerical simulations of homogeneous isotropic
turbulence in dilute
polymer solutions. We model
polymers as FENE dumbbells and simulate them using Brownian dynamics. By visualising the hierarchical structures of coherent
vortices, we demonstrate that as the Weissenberg number increases,
polymers progressively suppress
vortices from smaller to larger scales, attenuating their turbulent energy. While inspired by Lumley's theory, we propose a novel timescale-based framework for analysing this attenuation process using the scale decomposition. We define a scale-dependent Weissenberg number, $\mathrm{Wi}_{\mathrm{sd}}(k)$, as the ratio of the
polymer relaxation time to the turnover time of multiscale
vortices at each wave-number. We reveal that when expressed in terms of $\mathrm{Wi}_{\mathrm{sd}}(k)$, the energy attenuation rate at each scale collapses onto a single curve that rises at $\mathrm{Wi}_{\mathrm{sd}}(k) \gtrsim 1$, proving that $\mathrm{Wi}_{\mathrm{sd}}(k)$ successfully describes both the onset and the degree of
turbulence attenuation at any given scale $k^{-1}$. Furthermore, the scale decomposition uncovers that
polymers preferentially align with the turbulent stretching direction at the scale satisfying $\mathrm{Wi}_{\mathrm{sd}}(k) \approx 1$. Based on these results, we establish a physical picture of the
polymer–
turbulence interaction and explicitly link it to the statistics in
turbulence attenuated by
polymers.
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All authors Hayato Masuda, Yusuke Koide, Yutaro Motoori, Susumu Goto
Optics
Multidimensional attosecond clocking near Dirac cones in graphite
Daniel Kroeger, Anna Hassine, Eyal Uzner et al. (+5 more)
Two-color high-harmonic spectroscopy is widely used to access sub-cycle electron dynamics and to retrieve harmonic timing information, including harmonic phases and attochirp across gases, solids, and
liquids. However, the dependence of such timing observables on additional
laser-control parameters remains largely unexplored. Here, we introduce driving intensity as an additional dimension of two-color harmonic spectroscopy in highly oriented pyrolytic graphite (HOPG). The retrieved attosecond two-color delays maximizing the 4th and 5th harmonic yields evolve systematically and differently with driving intensity.
Semiconductor Bloch-equation calculations reproduce these trends and reveal a pronounced sensitivity of the intensity-dependent delays to the electronic band dispersion. Our results demonstrate multidimensional attosecond clocking near Dirac cones and establish intensity-dependent two-color delays as a sensitive observable for band-dispersion in
quantum materials.
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All authors Daniel Kroeger, Anna Hassine, Eyal Uzner, Camilo Granados, Marcelo F. Ciappina, Ofer Neufeld, Michael Krüger, Zhaopin Chen
Physics Education
The Force Concept Inventory Across Continents: Testing Q-Matrix Transferability and Cross-Cultural Differences in Mechanics Reasoning
Wade Naylor, Raheeq Tahir, Alan S. Cornell et al. (+1 more)
The Force Concept Inventory (FCI) is one of the most widely used research-based assessments in physics education, yet the assumption that its underlying cognitive structure is transferable across educational contexts remains largely untested. This study investigates the transferability of FCI Q-
matrices using the Generalized Deterministic Inputs, Noisy "And" Gate (G-DINA) cognitive diagnostic applied to two large cohorts: students from the Learning About STEM Student Outcomes (LASSO) online system database in the United States (N = 4,750) and introductory physics students at the University of Johannesburg, South Africa (N = 1,016). Rather than treating the analysis as a local model calibration exercise, we frame the problem as one of cross-context cognitive invariance. Differential Item Functioning (DIF) analyses revealed substantial cross-cultural differences, with 14 of 30 items exhibiting high DIF after controlling for latent skill mastery. These differences were concentrated in force dynamics and contact-force
reasoning and remained invariant under alternative Q-
matrix specifications. The findings suggest that observed differences reflect genuine variations in students' conceptual
reasoning rather than psychometric artifacts, highlighting the importance of validating Q-
matrix structures before deploying cognitive diagnostic and adaptive assessments across diverse non-local educational settings.
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All authors Wade Naylor, Raheeq Tahir, Alan S. Cornell, Xuelan Qiu
Accelerator Physics
Damping Ring Optimization in Natural Emittance and IBS Dominated Regimes
Matthew Andorf, Nigel Lockyer, Emilio Nanni et al. (+2 more)
Linear electron-positron
colliders enable precision measurements of Standard Model observables and beyond. Modern linear
colliders need damping rings wherein the emittance of the source is damped and asymmetrized. A previous work [Phys. Rev. ST Accel. Beams 4, 021001 (2001)] delineated a systematic procedure for damping ring design. In this paper, we apply those principles, and frame damping ring design as a constrained numerical minimization problem when including intrabeam scattering. We use a multi-objective genetic optimization to map the transition from natural- emittance-dominated to intrabeam-scattering-dominated regimes. We compare to analytic results where possible to good agreement. The analysis is applied to parameters for the C$^{3}$
collider concept, but the procedure is fully generalizable to other linac parameters.
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All authors Matthew Andorf, Nigel Lockyer, Emilio Nanni, Caterina Vernieri, Jared Maxson
Optics
Compact, open, and tunable two-dimensional Fabry-Pérot cavity
Bruno Bender, Andrea Bergschneider, Marcel Baer et al. (+2 more)
In order to enhance light-matter interactions, optically active material, like a
semiconductor, can be embedded into an optical cavity. For small cavity mode volumes, which are required for reaching the strong coupling regime, this is typically done by fabrication of microcavities. While guaranteeing a mechanically stable cavity, these systems lack tunability and are difficult to implement for small samples like van der Waals
heterostructures (vdW). Here we present a design for a fully tunable two-dimensional (2D) Fabry-Pérot (FP) cavity which can host any material. The cavity can be freely positioned between two confocal high-NA aspheric lenses which allows for optical transmission microscopy and spectroscopy in real and momentum space. In order to maintain maximal mechanical stability, the cavity mirrors are held in a monolithic titanium frame. A pre-loaded flexure joint allows for manual coarse tuning of the cavity length and mirror parallelism, while three piezo actuators in a tripod layout can be used for fine tuning. We find cavity length fluctuations smaller than 100 pm, measure a finesse of 360 and reach the lowest accessible $m=3$ cavity mode (one electric field antinode within the air gap) at a minimal physical mirror separation of 380 nm. In order to demonstrate the 2D nature of the cavity mode we perform momentum space imaging in transmission as well as spectroscopy to measure the cavity dispersion.
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All authors Bruno Bender, Andrea Bergschneider, Marcel Baer, Martin Kroner, Wolf Wüster
Computational Physics · Cross-listed from cond-mat.str-el
Diversifying time evolution of matrix product states using BUGs
Kornél Kapás, Dominik Sulz, Charlotte Verhoeven et al. (+3 more)
Time
evolution of tensor-network states is a central tool for studying nonequilibrium dynamics in strongly correlated
quantum systems. In the past decade, using the time-dependent variational principle (TDVP) discretized by projector-splitting has become the gold standard for evolving
matrix product states (MPS) with long-range
Hamiltonians. More recently, a conceptually different class of discretizations of the TDVP, the class of Basis Update and Galerkin (BUG) integrators, has been developed within the framework of dynamical low-rank approximation, offering an alternative, more flexible approach. In this work, we formulate two BUG integrators explicitly for MPS. The BUG integrators result in "single-site" MPS integrators that are robust with respect to small singular values, avoid backward-in-time substeps, and naturally allow for the adaptive choice of bond dimensions. We consider the augmented BUG integrator of first order and the midpoint BUG integrator of second order and clarify their relation to the projector-splitting discretization of the TDVP. Using representative models of strongly correlated
quantum systems, like the XY
spin model with long-range interaction and two-dimensional
lattice models of
fermions and
spins of various lengths, we perform a systematic numerical comparison between BUG and projector-splitting time discretizations of the continuous-time TDVP, focusing on scalability, numerical complexity, and accuracy. We find that BUG integrators, due to their reduced numerical cost and the flexibility of the concept, provide a competitive and, in certain regimes, advantageous alternative to the well-established time-stepping by projector-splitting in TDVP, especially in models with large local dimensions, and in cases where observables are extracted with high temporal resolution.
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All authors Kornél Kapás, Dominik Sulz, Charlotte Verhoeven, Miklós Antal Werner, Örs Legeza, Christian Lubich
Optics · Cross-listed from cond-mat.mes-hall
Superfluorescence in CdS/CdSe/CdS Spherical Quantum Wells Modulated by Excitation Geometry
Chunzheng Bai, Qihao Sun, Yiying Zhu et al. (+6 more)
Superfluorescence (SF) originates from the spontaneous buildup of macroscopic coherence among initially incoherent emitters. Its formation is highly sensitive to dephasing and collective coupling in the system. Here, we observe room-temperature SF in CdS/CdSe/CdS spherical
quantum wells. With increasing excitation fluence, the peak emission intensity shows a nearly quadratic increase, while the emission delay and pulse width decrease. Burnham-Chiao ringing is also observed, revealing the characteristic collective radiation dynamics of SF. Further experiments with stripe excitation show that shortening the excitation length L changes the dominant fast emission from amplified spontaneous emission to SF. More importantly, the threshold for SF under stripe excitation is only about 1/30 of that under spot excitation. This large reduction indicates that the propagating radiation field provided by spatially extended excitation favors the buildup of cooperative coherence. These findings provide direct experimental evidence for understanding ultrafast many-body coherence dynamics and offer a route to actively control collective emission at room temperature.
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All authors Chunzheng Bai, Qihao Sun, Yiying Zhu, Ruilin Xu, Bin Gu, Jinsong Qi, Fengrui Hu, Xiaoyong Wang, Jiayu Zhang
Fluid Dynamics
Newtonian fluid invasion into a Yield-Stress Fluid-Saturated Medium
Nathan Abitbol, Alex Hansen, Alberto Rosso et al. (+2 more)
We investigate pressure imposed two-phase flows in porous media where a Newtonian fluid displaces an immiscible Bingham yield-stress fluid. Using a pore-network model, we identify invasion patterns governed by three dimensionless parameters: the pressure-based capillary number $Ca_P$, the viscosity ratio $M$ , and a number $R_\tau$, the ratio of yield stress to capillary forces. Beyond the classical Lenormand regimes (viscous fingering, capillary fingering, stable displacement), we discover two new regimes: a tree-like pattern at low viscosity ratios and a progressively widening column-like pattern at high viscosity ratios. We characterize all regime transitions and establish a breakthrough condition for the invading fluid.
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All authors Nathan Abitbol, Alex Hansen, Alberto Rosso, Federico Lanza, Laurent Talon
Optics
Full complex wavefunction reconstruction with direct-interference ptychography
A. Ducharme and L. Clark
We demonstrate the separable reconstruction of the sample wavefunction amplitude and phase using direct-interference ptychography in scanning transmission electron microscopy. We reconstruct the sample wavefunction in simulated and experimental data under the Weak Object Approximation (WOA) with an extension of single-sideband (SSB) ptychography using information in the double- and triple-overlap regions. The contrast transfer function for the amplitude information is equivalent to the ideal contrast transfer function of Center of Mass imaging (COM). Our results support reporting the imaginary part of SSB reconstructions.
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Atmospheric and Oceanic Physics
4D Parallelism Unlocks Exascale Bayesian Neural Networks for High-Fidelity Atmospheric Modeling
Deifilia Kieckhefen, Juan Pedro Gutiérrez Hermosillo Muriedas, Lars Helge Heyen et al. (+12 more)
We present BEAST, the first-ever
Bayesian Swin
Transformer for atmospheric
forecasting on 0.25$^\circ$ global resolution able to accurately quantify both aleatoric and epistemic uncertainty. To overcome the associated computational bottlenecks, we devise an orthogonal 4D-parallelization scheme that introduces a unique domain-tensor-parallelism strategy and a novel uncertainty parallel method, enabling us to fully leverage GPU capacity and efficiently scale model training. For a 2.4-billion-parameter model, we achieve a peak performance of 3.96 EFLOP/s on 20,480 NVIDIA GH200 GPUs on the JUPITER supercomputer. We train BEAST as a 700-million-parameter model with 96 random weight samples on 384 nodes on 40 years of data for nearly one million gradient updates. This model achieves predictive skill scores competitive with state-of-the-art probabilistic atmospheric AI models and numerical models, and can predict extreme events with exceptional skill, while generating large ensembles 3 to 4 times faster than the current-best AI model. Our contribution unlocks the potential of high-fidelity uncertainty quantification in atmospheric AI models, heralding a new era for AI-based models in
climate and Earth system sciences.
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All authors Deifilia Kieckhefen, Juan Pedro Gutiérrez Hermosillo Muriedas, Lars Helge Heyen, Mathis Bode, Iida Hakulinen, Andreas Herten, Chelsea Maria John, Thorsten Kurth, Anni Moisala, Asena Karolin Özdemir, Kaleb Phipps, Oskar Taubert, Arvid Weyrauch, Markus Götz, Charlotte Debus
Data Analysis and Statistics · Cross-listed from cs.AI
Interpreting the predictions of neural network classification based on a Taylor Coefficient Analysis (TCA)
Markus Klute, Artur Monsch, Lars Sowa et al. (+1 more)
We introduce a rigid and comprehensive taxonomy and paradigm for characterizing the influence of the input feature space $X$ on the predictions $\hat{y}$ of a neural network (NN) used for event classification, based on a Taylor expansion of $\hat{y}$ in $X$. The complete process of introspection we refer to as Taylor Coefficient Analysis (TCA). Based on two simplistic example tasks, which can be easily understood and bencmarked, we illustrate the power of the TCA when it comes to revealing, what properties of $X$ have led to what value of $\hat{y}$, of a given NN model, building up intuition for the method. A more complex application is meant to represent $X$ of a typical classification task at a CERN LHC experiment. Based on this application, we play through the different levels of introspection that the TCA offers and discuss a number of practical aspects for a TCA application typical for the analysis of CERN LHC data. We conclude with a study to support the assumption that those properties of $X$ most relevant for tasks of the complexity typical for a CERN LHC experiment, are usually caught by a TCA up to the second order.
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All authors Markus Klute, Artur Monsch, Lars Sowa, Roger Wolf
Instrumentation and Detectors
Surface Commissioning and Performance of the sMDT Muon Chambers for the ATLAS HL-LHC Upgrade
Jiajin Ge, Elena Voevodina, Hubert Kroha et al. (+21 more)
To improve the first-level
muon trigger efficiency at the HL-LHC, the Monitored Drift Tube (MDT) chambers in the inner small sectors of the ATLAS Barrel
Muon Spectrometer will be replaced with integrated modules of small-Diameter
Muon Drift Tube (sMDT) and Resistive Plate Chambers (RPCs). This paper reports on the surface commissioning of 102 new sMDT chambers at CERN in 2025 following the installation of the final front-end electronics, including the new Amplifier-Shaper-Discriminator (ASD), Time-to-Digital Converter (TDC) chips, and Chamber Service Module (CSM) developed for the HL-LHC. The commissioning included measurements of gas leak rates and high-voltage dark currents, tests of the integrated planarity monitoring system, noise characterization, and measurements of detector efficiency and spatial resolution using
cosmic rays. Fewer than 0.1% of the 49152 tubes were found to be non-functional due to broken sense wires or gas leaks. The chambers exceed the ATLAS design requirements, with gas leak rates a factor of five below the specified limit of $9.3\times 10^{-3}~\mathrm{mbar\cdot liter/s}$ per chamber, dark currents of only around 0.2~nA per tube, average channel noise hit rates below 30~Hz, and average drift tube efficiency and spatial resolution of 99% and $82~\mu\mathrm{m}$, respectively, at an effective threshold of 15 primary electrons.
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All authors Jiajin Ge, Elena Voevodina, Hubert Kroha, Tatiana Azaryan, Kwok Ching Cheung, Tiesheng Dai, Edward Diehl, Claudio Ferretti, Yuxiang Guo, Oliver Kortner, Chihao Li, Chun Kit Lo, Nick Meier, Emmett Salzer, Can Suslu, Cecilia Vanesa Imthurn, Samuel Hugo Venetianer, Curtis Weaverdyck, Chuanshun Wei, Bastian Michael Wesely, Ruslan Yakubovych, Bing Zhou, Junjie Zhu, Jörg Zimmermann
Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci
Agent-authored deposition recipes for X-ray multilayer mirrors: schema-bound LLM control of a magnetron sputtering system with reflectivity-verified outcomes
Oleksiy V. Penkov, Haoyu Fu, Yueying Zhan et al. (+2 more)
Periodic multilayer mirrors for X-rays require a layer period controlled to about 0.1 nm, set by deposition rates held in the laboratory's own notebook. A supervising model session gave a large
language model
agent a target multilayer specification and calibration constants derived from a laboratory archive. The
agent authored recipes in the magnetron sputtering system's native recipe
language and submitted them through a Model Context Protocol bridge of 17 tools in three tiers, with enforcement in the control application. The target was a 30-
bilayer Ru/C multilayer with a period of 6.85 nm, a pair chosen because each period is fitted as two layers. The
agent could read and write only its own working project, so it could alter neither the calibration record nor the measurements that scored it. We scored mirrors by X-ray reflectivity and fixed the 3% acceptance threshold on relative period difference before deposition. Across four scored depositions, the relative period difference fell from 20% on the calibration as given to 2.26% after one measured-feedback iteration and 0.79% after a second. We identified sixteen failure modes of the
agent-facing interface. The result is bounded to the period, pair, and chamber observed.
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All authors Oleksiy V. Penkov, Haoyu Fu, Yueying Zhan, Pengyuan Wu, Jiong Jin
Optics
Interplay between growth conditions and formation of localized light emitters in epitaxial AlN thin films
Meysam Saeedi, Duc V. Dinh, Andrey N. Anisimov et al. (+3 more)
AlN is a promising material for integrated
quantum photonics due to its broad transparency window, its compatibility with CMOS technology, and the possibility to host localized light emitters acting as single
photon sources. However, little is understood yet about the microscopic nature and formation mechanisms of these light emitters. In this contribution, we demonstrate that their formation efficiency depends significantly on the growth conditions of the AlN thin film. We reveal that localized light emitters with distinct zero-
phonon lines in the 600–800~nm range can be efficiently formed in epitaxial AlN thin films grown under N-rich conditions by exposing the AlN to a post-growth treatment consisting in a
proton irradiation followed by an annealing process. In contrast, the density of light emitters formed in AlN grown under Al-rich conditions remains low, even after the thin films have been exposed to the post-growth treatment. These results open a pathway toward a better understanding of the microscopic nature of these light emission centers, as well as their engineered integration as
quantum light sources in AlN-based optomechanical platforms.
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All authors Meysam Saeedi, Duc V. Dinh, Andrey N. Anisimov, Mingyun Yuan, Georgy V. Astakhov, Alberto Hernández-Mínguez
Fluid Dynamics
Gas-liquid stratified MHD flows in inclined rectangular ducts
Subham Pal, Ilya Barmak, Arseniy Parfenov et al. (+2 more)
This study investigates fully developed stratified gas/
liquid magnetohydrodynamic (MHD) flow of an electrically conducting
liquid and a nonconducting gas in inclined rectangular ducts subjected to a vertical
magnetic field. Analytical and numerical solutions for the velocity and induced
magnetic fields are obtained in terms of the governing dimensionless parameters for concurrent upward, concurrent downward, and countercurrent flows. Unlike single-phase MHD flow, duct inclination strongly affects two-phase flow by altering the
liquid holdup and the relative contributions of gravitational, frictional, and electromagnetic forces. The results reveal a complex interplay among
gravity, Lorentz forces, and wall and interfacial shear stresses. These interactions govern the
liquid holdup, pressure gradient, multiple steady solutions, flooding limits, local backflow, jet-like velocity structures, and pumping requirements. Wall conductivity critically affects the induced
magnetic field and Lorentz force distribution and therefore cannot be neglected, even at very small
magnetic Reynolds numbers. Fully insulating ducts generally exhibit the weakest electromagnetic effects and behavior closest to non-MHD flow. Configurations with a conducting bottom wall exhibit substantially stronger electromagnetic effects and greater sensitivity to side-wall conductivity, leading to pronounced changes in the velocity field,
liquid holdup, pressure gradient, gas-lubrication effect, and overall pumping-power requirements.
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All authors Subham Pal, Ilya Barmak, Arseniy Parfenov, Alexander Gelfgat, Neima Brauner
Physics Education
A Framework for Characterizing Learning Contributions Across the Initial Achievement Spectrum
Tianlong Zu
Conceptual assessments are widely used in physics education research to evaluate changes in student understanding, yet class average measures can obscure how those changes are distributed across students with different levels of initial achievement. We introduce a Learning Contribution Framework that characterizes this distribution through the Learning Contribution Curve (LCC) and Learning Contribution Profile (LCP). For a general contribution measure G, the LCC represents cumulative contribution across students ranked by initial achievement, whereas the LCP describes the local mean contribution relative to the population mean of the individual G values. We apply the framework to the individual Hake normalized gain and develop a statistical model linking LCC and LCP behavior to the joint structure of pretest and posttest scores. Under the central assumption that the conditional mean of the subsequent score is linear in the initial score, we identify a score structure parameter $\beta$ and a critical score structure parameter $\beta_c$. Whether $\beta$ is greater than, less than, or equal to $\beta_c$ determines whether the expected LCP increases, decreases, or remains constant across initial achievement. Given the pretest distribution, the model further yields analytical predictions for the complete LCP and LCC that closely reproduce simulation results. Application to classroom concept-assessment data illustrates how the framework reveals local and cumulative patterns of learning contribution that are not evident from an overall class average revealed by the traditional Hake's normalized gain.
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Fluid Dynamics
Diffusion Enhancement and Directional Suppression Induced by Reciprocal Flows
Yuki Koyano, Hiroyuki Kitahata and Takeshi Ooshida
Reciprocal flows repeatedly return fluid elements to their initial positions, producing no net advective transport on time average. Nevertheless, their interplay with
diffusion gives rise to nontrivial transport. To describe this phenomenon, we develop a general theory of effective
diffusion under two-dimensional linear flows with arbitrary time dependence. By analyzing the advection-
diffusion equation, we derive exact expressions for the mean square displacement and the effective
diffusion coefficients for extensional, simple shear, and rotational flows within a single framework. We show that the reciprocal flows universally induce
diffusion enhancement. The
diffusion tensor exhibits pronounced anisotropy, which can result in directional
diffusion suppression in spite of the direction-averaged
diffusion enhancement. Our results provide a general framework for
diffusion control by time-dependent flows and can provide new strategies for transport manipulation in microfluidic and biological systems.
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Atomic Physics
Experimental Ni II Oscillator Strengths for Transitions from $3d^84d$ to $3d^84p$ Levels Measured Using High-resolution Fourier Transform Spectroscopy
Ruijie Chen, Christian P. Clear, Gillian Nave et al. (+1 more)
We present the first experimentally measured oscillator strengths for Ni II 3d$^8$4d - 3d$^8$4p transitions. High-resolution
Fourier transform spectra were recorded of Ni-He hollow cathode lamps, and intensity calibrated using deuterium standard lamps to determine relative intensities of Ni II emission lines between 200 and 395 nm. Branching fractions were determined for observed lines from 35 3d$^8$4d upper levels in total, and account for at least 95% of the predicted transition probability for 31 of these levels, with sufficient completeness to give reliable branching fractions. Combining our measured branching fractions with four experimental and 27 theoretically calculated energy level lifetimes provided absolute oscillator strengths for 174 lines, for which no previous experimental values exist. We compare the results with three sets of previously published theoretical calculations, illustrating the improvement of laboratory measurements for these atomic data. Please note: The transition probability
datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.
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All authors Ruijie Chen, Christian P. Clear, Gillian Nave, Juliet C. Pickering
Computational Physics
Physics Based Triple Debye Dielectric Modeling and Multi Layer ADE FDTD Simulation of Terahertz Pulse Reflection for Breast Cancer Detection
Ali Asghar Molavi Choobini and Mehran Shahmansouri
Terahertz (THz) imaging has emerged as a promising non-ionizing modality for breast cancer assessment owing to its intrinsic sensitivity to tissue hydration. However, existing dielectric descriptions of biological tissue, largely restricted to single- or double-Debye models, fail to capture the multiscale relaxation dynamics governing broadband THz dispersion and absorption, thereby limiting the quantitative interpretation of reflected pulse signatures.Here, a physics based triple Debye dielectric framework is developed to quantitatively predict broadband THz-tissue interactions. The proposed model explicitly incorporates three physically distinct relaxation processes associated with free-water rotational dynamics, bound-water relaxation ({\tau}_2), and ultrafast interfacial/macromolecular polarization ({\tau}_3). Model parameters are obtained by nonlinear least-squares fitting to experimentally measured refractive-index data digitized from published THz time-domain spectroscopy measurements of ex vivo human breast tissue. Compared with conventional Debye formulations, the proposed model substantially improves the fitting accuracy, reducing the root-mean-square error from 0.7773 (single Debye) and 0.2976 (double Debye) to only 0.0199 for the triple-Debye model. Fullwave FDTD ADE simulations of realistic multilayer breast structures further demonstrate that reflected THz pulses encode tissue hydration through reproducible temporal signatures, including increased reflection amplitude, delayed pulse arrival, and enhanced waveform broadening in malignant tissue. Polarization and angle resolved Fresnel analysis further indicates that hydration-dependent pseudo-Brewster minima provide an additional contrast mechanism by selectively suppressing reflections from low hydration normal and adipose tissues.
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Physics and Society
Global maps of travel time to emergency and tertiary hospitals
Johan Emilsson
Global estimates of access to health care treat every facility alike. Drive time was routed on the OpenStreetMap network from all 217,841 of its hospitals and 15-, 30- and 60-minute isochrones dissolved for nested capability tiers, weighted with GHS-POP 2025. 96.2% of the world's population lives within an hour's drive of a hospital, 78.5% of a hospital with a documented emergency department, and 40.3% of one with a helipad or university name marking tertiary care. The 1.45 billion people within an hour of a hospital but not of an emergency hospital live mainly in South and East Asia and Nigeria; the 312 million beyond an hour of any hospital lie in a belt from the Sahel to Madagascar. Defining the tertiary tier by helipad alone leaves its estimate unchanged, and the isochrone construction shifts the 60-minute figures by a few percent. Counting every facility as equivalent overstates access to time-critical care.
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Biological Physics · Cross-listed from cond-mat.stat-mech
Chirality enhances diffusion in disordered environments
Joshua Uhlig, Jan Wójcik, Ralf Metzler et al. (+1 more)
Chirality, a systematic rotational bias in the motion of a particle, arises in a wide range of physical and biological systems, from charged colloids in
magnetic fields to swimming bacteria near surfaces. While its effects in homogeneous environments are well understood, the interplay between chirality and structural disorder has remained largely unexplored. Here we investigate the
chiral random walk on two-dimensional percolation clusters above the percolation threshold, combining numerical simulations with an analytically tractable annealed-disorder approximation. We find that the long-time
diffusion coefficient depends non-monotonically on both the chirality parameter and the obstacle density: for every obstacle density above the percolation threshold, there exists an optimal chirality that enhances
diffusion relative to the achiral walk. We show that the optimal chirality is set by an edge-adhering mechanism: maximum
diffusion is achieved when the persistence length of the wall-adhering motion matches half the typical obstacle cluster perimeter. This yields a closed-form prediction for the optimal chirality in terms of
geometric properties of the medium alone, which we verify across the full range of obstacle densities studied. The enhancement extends to first-passage statistics, where chirality shortens typical search times at strong disorder while lengthening them at weak disorder, with direct implications for biological
navigation in disordered environments.
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All authors Joshua Uhlig, Jan Wójcik, Ralf Metzler, Erik Kalz
Optics
Prior-information based super-resolution optical metrology of 2D nanoscale objects
Jin-Kyu So, Eng Aik Chan, Carolina Rendón-Barraza et al. (+2 more)
Previous work has shown that optical metrology of one-dimensional objects, such as slit width, can achieve improved accuracy by using prior information from similar objects to train the metrology
estimator. Here, we demonstrate single-shot optical metrology of nanoscale elliptical particles by analysing their diffraction patterns to retrieve length, width and in-plane orientation using a neural-network
estimator trained on prior information from nano-ellipses with varied dimensions and orientations. Fisher-information flow analysis was used to optimise the physical parameters of the metrology apparatus and maximise measurement accuracy. Using a 633 nm
laser, we measure the dimensions of elliptical particles with accuracy down to ${\lambda}$/128, corresponding to 4.9 nm, and recover their orientation with 5${\deg}$ accuracy. Our results demonstrate the practicality of optical, deep-super-resolution, single-shot, multiparameter measurements of two-dimensional subwavelength objects, with potential relevance to microbiology and nanotechnology applications.
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All authors Jin-Kyu So, Eng Aik Chan, Carolina Rendón-Barraza, Giorgio Adamo, Nikolay I. Zheludev
Fluid Dynamics
Single-eddy contributions to streamwise velocity variance in turbulent pipe flow. Part 1. The single-eddy intensity function
Jinyul Hwang
Townsend's attached-eddy hypothesis explains the asymptotic statistics of wall
turbulence through a superposition of self-similar attached eddies. At a given observation location, active portions contribute to momentum transfer, whereas inactive portions retain only wall-parallel fluctuations. Since this distinction depends on the observation height relative to the eddy height $y_l$, we extract single-eddy intensity functions from DNS of turbulent pipe flow at $Re_\tau\simeq930$–$6000$. Spectral linear
stochastic estimation and differencing isolate wall-coherent contributions at prescribed $y_l$, yielding the streamwise and wall-normal intensity functions $I_{uu}$ and $I_{vv}$. When expressed in $y^*=y/y_l$, both collapse across $y_l$ and share a peak at $y_a^*$, close to the von K'arm'an constant. Near $y_a^*$, both components remain significant, whereas for $y^*\ll y_a^*$, $I_{vv}$ diminishes while $I_{uu}$ remains finite, identifying active and inactive portions. Over the self-similar range, both peak intensities scale as $y_l^{-1}$, and $I_{uu}$ retains this scaling in both portions. Integrating the active portion yields an approximately constant contribution, while the inactive portion recovers the classical near-wall logarithmic variation. An outer logarithmic tendency with a slope close to the Townsend–Perry constant arises from integrating active contributions up to their outer cutoff. At the near-wall peak of $\langle uu\rangle^+$, the scaling steepens to $I_{uu}\sim y_l^{-(1+\beta)}$ with $\beta\simeq1/4$, yielding a finite asymptote with a $Re_\tau^{-1/4}$ defect. The additional exponent is attributed to viscous attenuation of inactive footprints associated with a $y_l$-dependent dissipative scale. Wall-coherent motions also produce a broad outer shoulder, while a localized wall-incoherent residual may contribute to a secondary peak.
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Chemical Physics
Fast and Accurate Excitation Energies from Density Matrix Renormalization Group Calculations Improved by Machine Learning
Pavlo Golub and Libor Veis
An estimation of optoelectronic properties is a crucial necessity and an ongoing challenge in modern functional material science. This involves accurate accessing of ground and excited states in systems with complex electronic structure that are often too computationally expensive for accurate many-body methods. Building on our previous work on ground states [J. Phys. Chem. Lett. 2025, 16, 3295-3301], we present an efficient and cost-effective approach for evaluating electronic excitations in functional materials, combining the density
matrix renormalization group method as a complete active space solver with machine learning techniques. We demonstrate its performance on {\pi}-electron-correlated systems, namely polycyclic aromatic compounds. The transferability and effectiveness of the derived machine learning model are demonstrated on a number of challenging examples with up to 34 {\pi}-electrons.
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Biological Physics · Cross-listed from cond-mat.stat-mech
Certifying Hidden Dissipation from Observed Current Fluctuations
Ahmed Roman
A single-molecule experiment on a driven enzyme or motor resolves only a few of the transitions the machine makes, yet one would like to know how much free energy it dissipates in total, including on the steps that stay hidden. The mean and the fluctuations of the currents on the watched transitions are shown to certify this hidden dissipation, with no knowledge of the transition rates and no access to the hidden transitions: when the watched transitions span the cycles of the network, the observed-current covariance recovers the full density-contracted quadratic current geometry, including the contribution of transitions that are never seen. The mechanism is that fluctuations are set by the dynamical activity, or traffic, the symmetric partner of the current. Contracting the large-deviation cost of empirical currents over density fluctuations identifies the observed-current covariance with a traffic-weighted metric, and turns partial observation into a minimum-energy completion problem over the unseen cycles, whose solution is the certified hidden cost. Existing current-fluctuation uncertainty relations bound dissipation from chosen currents but do not say when partial observation fixes the hidden contribution; the cycle-observability condition derived here does. The statements concern long-time means and fluctuations; finite-time estimates require separate error control.
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Biological Physics · Cross-listed from cond-mat.soft
Interfacial Packing of DNA Nanostars Regulates Dynamics on Synthetic Cell Membranes
Kazutoshi Masuda, Takahiro Yokoyama, Miho Yanagisawa et al. (+1 more)
DNA nanostructures are emerging as programmable components for engineering synthetic
cell membranes, yet how their collective packing and deformability regulate molecular dynamics at membrane interfaces remains poorly understood. Here, we investigate the packing and mobility of DNA nanostars with tunable stiffness on lipid-coated droplets. The negatively charged nanostars spontaneously adsorb onto cationic membranes, and their interfacial packing is changed by the bulk DNA concentration and droplet size, which together determine the number of encapsulated nanostars. Combining fluorescence recovery after photobleaching experiments with coarse-grained simulations, we reveal distinct packing-dynamics relationships for rigid and soft nanostars. For rigid nanostars,
diffusion first decreases gradually and then drops sharply with increasing interfacial packing, approaching a dynamically arrested state consistent with jamming-like behavior. In contrast, at equivalent experimental conditions, soft nanostars systematically reach lower interfacial packing fractions and show a weaker decrease in apparent mobility. This behavior is consistent with their weaker membrane affinity, which facilitates adsorption-desorption with the bulk. When this exchange is suppressed in simulations, crowding reduces the lateral
diffusion of both nanostar types, but produces distinct dense configurations: soft nanostars become strongly deformed, whereas rigid nanostars largely retain their shape and form interlocked, gear-like arrangements. Nanostar adsorption also impedes lipid
diffusion, while differences in membrane affinity result in distinct lipid mobile fractions. These findings reveal how the interplay between nanostar packing and deformability regulates molecular transport at membrane interfaces, providing a physical design principle for tuning lateral fluidity and crowding in artificial
cells.
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All authors Kazutoshi Masuda, Takahiro Yokoyama, Miho Yanagisawa, Arash Nikoubashman
Optics
Autonomous multifunctional image processing via programmable multimode lasing
Jiawei Wu, Yue Yin, Jianqi Hu et al. (+3 more)
Optical image processing offers a promising pathway to overcome the latency and energy limitations of conventional electronic image processors. However, existing approaches based on passive photonic devices are often constrained by signal attenuation, lack of nonlinearity, fixed functionality, and heavy training overhead. Here, we introduce a programmable image processor based on a highly multimode degenerate cavity
laser (DCL), shifting the computational framework from passive extracavity transformation to active intracavity
evolution. By manipulating the intracavity loss distribution and exploiting the nonlinear lasing dynamics, we map computational tasks to the spontaneous mode selection within the DCL, realizing image processing directly at the source. We experimentally demonstrate that by simply altering the encoding scheme of input images, the platform can be flexibly reconfigured for multifunctional tasks, including high-fidelity edge detection and robust image denoising. The computation proceeds autonomously without
dataset training, featuring an intrinsically low latency ($\sim$90 $\mu\mathrm{s}$) with $\mathcal{O}(1)$ complexity. Furthermore, the high intensity sustained within the resonator enables intracavity nonlinear upconversion of the processed image. This work extends the frontiers of
laser applications, providing a compelling candidate for next-generation optical processors.
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All authors Jiawei Wu, Yue Yin, Jianqi Hu, Hao Wang, Xing Fu, Qiang Liu
Applied Physics · Cross-listed from cond-mat.mes-hall
Efficient non-volatile electric control of magnetosensing in CrSBr
Bálint Fülöp, Yeonsu Jeong, Sofia Ferreira-Teixeira et al. (+10 more)
In two-dimensional
crystals, electrostatic gating can modulate the charge carrier density, thereby tuning their electrical properties. In
magnetic materials such as CrSBr, this approach can also enable direct electrical control of magnetoresistance. Non-volatile gating is particularly attractive since it allows the carrier density to be maintained at a desired level without the need for a continuous gate bias, offering significant advantages for technological applications. Here, we demonstrate a simple device architecture in which a solution-processed ferroelectric P(VDF-TrFE) layer is integrated directly onto a CrSBr channel, enabling non-volatile control of its magnetoresistance. We investigate the magnetotransport response over a broad temperature range and demonstrate a reproducible and robust gate dependence. Notably, the ferroelectric gate achieves a gating efficiency approximately one order of magnitude higher than that of a conventional SiO$_2$ dielectric, highlighting the potential of ferroelectric gating for electrical control of 2D
magnetic materials.
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All authors Bálint Fülöp, Yeonsu Jeong, Sofia Ferreira-Teixeira, Covadonga Álvarez-García, Tamás Prok, Xiaomin Guo, Endre Tóvári, Jong Hoon Jung, Luis Hueso, Paolo Samori, Marco Gobbi, Péter Makk, Szabolcs Csonka