Applied Physics
Universal scaling of electrochemical information transfer at solid-liquid interfaces
Eikichi Kimura, Ashutosh Rathi, Saki Tsuchiya et al. (+6 more)
Electrochemical potentials at solid-
liquid interfaces govern diverse chemical and energy conversion processes; however, the extent to which their electrochemical influence extends into the solid remains unclear. Here, we show that the maximum accessible electrochemical information is governed by a single dimensionless screening parameter $u$, defined as the ratio of the effective electrostatic separation between the interface and probe to the electrostatic propagation length in the solid. The maximum Fisher information follows a universal inverse-square scaling with this parameter. This relation identifies electrostatic screening as a fundamental constraint on information transfer across solid-
liquid interfaces and provides quantitative design principles for interfacial electrochemical sensing.
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All authors Eikichi Kimura, Ashutosh Rathi, Saki Tsuchiya, El Mustapha Mansouri, Sara Mandić, Kristi Kanya Saikia, Keisuke Oshimi, Masazumi Fujiwara, Keigo Arai
Physics and Society
How large should academic departments be?
Jan Bachmann, Lisette Espín-Noboa, Fariba Karimi et al. (+3 more)
Academic departments are the primary unit of scholarship and education at universities, and they vary vastly in their sizes. However, the consequences and natural dynamics of department size are poorly understood. Small departments face disproportionate teaching and administrative overhead per faculty member, while large ones face coordination costs and thematic incoherence. Here, we characterize and model the dynamics of academic department sizes using $14,000$ U.S.-based departments in eight academic domains. Across all domains, similar broad-tailed distributions reveal a common size range from 4 to 23 faculty members, widening across domains at its upper border. Annual size-dependent closure risks and growth rates indicate that stability is greatest in this size range: below it, small departments either close or grow quickly; within it, closure risk is low and sizes stabilize; above it, large departments can persist, with marginal attrition and minimal closure risk. An analytically tractable model of size-dependent coagulation and fragmentation, informed only by the aggregated size distribution, reproduces department dynamics across the full size range. Rescaling each domain by its most stable size reveals a common regression toward the stable range across most domains. Our results establish academic departments as organizations with natural size dynamics defined by a grow-or-close pattern for the smallest departments, and a weak pressure against unlimited growth for the largest.
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All authors Jan Bachmann, Lisette Espín-Noboa, Fariba Karimi, Daniel B. Larremore, Gerardo Iñiguez, Aaron Clauset
Chemical Physics
Reactivity of Ambident Nucleophiles in Magnetic Fields: a Combined Conceptual DFT and Current-DFT Study
Bang C. Huynh, Meilani Wibowo-Teale, Andrew M. Wibowo-Teale et al. (+2 more)
The influence of strong external
magnetic fields (up to $0.30\,B_0$) on the electronic structure and reactivity of ambident nucleophiles is investigated using the nitrite and thiocyanate anions as prototypical examples. To capture
magnetic-field-induced changes in reactivity, current-density-functional theory (current-DFT) calculations are interpreted through conceptual density-functional theory (conceptual DFT) descriptors, namely global hardness and local softness via Fukui functions, focusing on the
evolution of the electronic structure and associated properties with increasing field strength in different orientations. By extending our previous adiabatic treatment of molecules to include higher-
spin states, in analogy with earlier work on atoms, and by considering the
symmetry properties of relevant
quantum-chemical quantities within full
magnetic groups using the QSym$^2$ framework, we uncover substantial
magnetic-field-induced modulations of both molecular polarity and the shape of the Fukui function. Despite these modulations, the ambident nucleophilicity of both $(\textrm{NO}_2)^-$ and $\textrm{SCN}^-$ is largely preserved, as is the preference for attack by soft electrophiles at the sulfur end of $\textrm{SCN}^-$. At higher field strengths, however, the Fukui functions become increasingly diffuse, reflecting the growing importance of external
magnetic interactions relative to internal electrostatic forces. The resulting redistribution of local reactivity not only predicts reaction pathways with unexpected geometries but also raises the possibility that regioselectivity may become progressively less well-defined in the strong-field regime.
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All authors Bang C. Huynh, Meilani Wibowo-Teale, Andrew M. Wibowo-Teale, Frank De Proft, Paul Geerlings
Fluid Dynamics
Integral relations for the skin-friction coefficients and other quantities of annular flows
Pierre Ricco
Integral identities relating the skin-friction coefficients and the Reynolds shear stresses in annular cylindrical flows are derived. In the pressure-driven case, an identity for the radial location of the maximum streamwise velocity is obtained and, in the cylinder-driven case, an identity for the bulk velocity is found. The formulas are used to analyse existing numerical and experimental data and simplify to classical channel-flow and pipe-flow identities in the limiting cases of vanishingly small and infinitely large radius ratios.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Levitated nano-trampoline resonators for magnetic field sensing
Xianfeng Chen, Nirmala Raj, Matthew R. Chua et al. (+7 more)
Levitated systems and high-$Q$ membrane nanomechanical resonators have achieved exceptional sensitivity in precision sensing, but functionalizing such resonators for practical applications without degrading their low dissipation remains challenging. Here, we combine diamagnetic levitation with a high-$Q$ nanomechanical resonator to realize a high-precision magnetometer for sensing weak oscillating
magnetic fields. A macroscopic diamagnetically levitated graphite plate acts as a free-floating proof mass that couples strongly to
magnetic fields, converting them into mechanical motion that is resonantly amplified by a low-dissipation nano-trampoline resonator. Operating at room temperature and without
magnetic shielding, we achieve a peak
magnetic-field sensitivity of $4.5\, \mathrm{pT}/\sqrt{\mathrm{Hz}}$ using a resonator with a mechanical quality factor of $Q=6\times10^{6}$ at $443\, \mathrm{kHz}$. The system sensitivity is limited by thermomechanical noise. With further improvements in mechanical $Q$, this hybrid levitated platform offers a pathway toward femtotesla-level AC
magnetic-field sensing, establishing diamagnetically levitated nanomechanical resonators as a new class of high-sensitivity magnetometers at room temperature.
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All authors Xianfeng Chen, Nirmala Raj, Matthew R. Chua, Yi Fan Chen, Chenyue Gu, Minxing Xu, Young-Wook Cho, Syed M. Assad, Lu Ding, Ping Koy Lam
Classical Physics · Cross-listed from cond-mat.soft
Geometric Renormalization and a Chirality Threshold in Recursively Coiled Filaments
Hiroyuki Shima
Repeated coiling creates a filament hierarchy. We formulate helicalization as an iterated map acting on an arbitrary rod compliance, rather than homogenizing one prescribed construction. A marginal Jordan mode yields an outer-radius inverse-square stiffness class, while pitch disorder creates a Lyapunov threshold between amplified and screened extension–twist response. An exact finite-level rate distinguishes representative amplified and screened cases by level three; direct three-dimensional beam calculations validate the response through level four and convergence through level five.
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Chemical Physics
Putting PASPT2 on a Firmer Basis
Chunzhang Liu, Ning Zhang and Wenjian Liu
The recently proposed partial-active-space (PAS) multi-state second-order perturbation theory (PASPT2) [Precis. Chem. 4, 997 (2026)] features connected amplitudes and a connected, closed intermediate
Hamiltonian. Despite these hallmarks, PASPT2 (denoted as PASPT2H from now on) is not strictly size-extensive, as originally thought (and numerically confirmed), albeit strictly size-consistent. Nevertheless, PASPT2 is near-extensive for the states with major projections on the chosen PAS $\mathcal{M}_0$. This becomes more transparent upon introducing PASPT2X, a strictly size-extensive variant. Compared with the intruder-prone PASPT2X, the intruder-free PASPT2H merely neglects the second-order corrections that are important only for those states with major projections on the orthogonal complement $\mathcal{R}_X$ of $\mathcal{M}_0$ within the closed space $\mathcal{M}_X$ ($=\mathcal{M}_0\oplus\mathcal{R}_X$); however, such states are not supported by the chosen finite one-particle basis set. The weak violation of size-extensivity is therefore numerically insignificant for the target states supported by $\mathcal{M}_0$, reinforcing the theoretical basis of PASPT2H.
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Optics
Field-driven nonlinear metasurface: self-adaptive transition between high-selectivity transmission and broadband shielding
Yuan Xu, Hanqing Liu, Shangjing Xi et al. (+4 more)
The escalating complexity of electromagnetic (EM) environment is posing a significant challenge to the reliability of modern electronic information systems. To address the need for the spatial EM safety of electronic devices, we present a field-driven nonlinear metasurface (NMS) that enables effective protection against out-of-band interference and in-band high-intensity radiation. By constructing a reconfigurable hybrid coupling
topology and mapping it to the metasurface geometry, the proposed NMS achieves a self-adaptive transition between its transmission and shielding mode depending on the incident power. The experimental results are in good agreement with theoretical analysis and full-wave simulation. We obtain a highly selective passband with roll-off rate larger than 20.6dB/GHz and a broadband shielding with shielding effectiveness exceeding 23.6dB and 60% bandwidth, demonstrating a significantly enhanced performance relative to the literature. Our findings establish a promising route toward comprehensive EM protection on
radio frequency front-end systems.
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All authors Yuan Xu, Hanqing Liu, Shangjing Xi, Xiaodi Zhang, Yanqing Cheng, Wenye Ji, Peiguo Liu
Optics
Self-healing topological streams in space-time
Yudong Ren, Wenhao Li, Yuang Pan et al. (+2 more)
Topological states are renowned for their robustness against perturbations. Recent advances have further introduced momentum-gap (or time)
topology in time-varying media, enabling temporal topological states. However, existing studies for momentum-gap
topology are largely confined to non-propagating interface states; their potential for wave transport, especially at moving boundaries, has yet to be realized. Here, we experimentally demonstrate topological streams in space-time: space-time topological edge states that propagate along a moving boundary in a dynamically modulated time-synthetic photonic
lattice. These streams arise from the coexistence of energy-gap and momentum-gap
topologies and break both spatial and temporal translation
symmetries, conserving neither energy nor momentum. Remarkably, they reconstruct their wave profiles after strong localized spatiotemporal obstacles, enabled by an imaginary quasienergy gap and kinematic decoupling from radiative bulk channels. Our results establish a form of self-healing spatiotemporal non-Hermitian protection, showing that the temporal dimension can transform
topology from pinned states and isolated events into robust, directional and self-restoring wave transport.
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All authors Yudong Ren, Wenhao Li, Yuang Pan, Hongsheng Chen, Yihao Yang
Physics and Society · Cross-listed from econ.GN
Measuring inequality and social stratification with Lorenz curvature
Antti Hippeläinen
We construct a continuous family of inequality and social stratification indices based on the
curvature of the Lorenz curve. We study the inequality axioms of the family and find that they are satisfied only with the so-called stratification-aversion parameter $\alpha$ set to 0 – in all other cases, these constraints cannot be satisfied in a strict sense. With $\alpha = 0$, the index has a very simple closed form and its value can be easily approximated. We study the values of the index on World Bank inequality data and see how the rankings across a wide selection of countries change as $\alpha$ is varied. Spearman and Kendall rank-correlation
matrices with other common indices are also computed and analyzed. We find the
curvature index to deviate consistently from the comparison indices, albeit less so for consumption- than income-based countries.
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Fluid Dynamics
Numerical Validation of Lyapunov-Liouville Theory and Non-Diffusive Closures in Decaying Isotropic Fluid and Scalar Turbulence
Nicola de Divitiis
This work validates the Lyapunov–Liouville framework and its non-diffusive closures in decaying homogeneous isotropic
turbulence (HIT) by numerically integrating the closed von Kármán–Howarth and Corrsin equations via an adaptive solver. Three initial states (Saffman–Birkhoff, Loitsiansky, Gaussian) are analyzed across Prandtl numbers from $Pr=10^{-3}$ to $1000$. The model reproduces the distinct decay paths, with Saffman–Birkhoff yielding velocity and thermal exponents $m \simeq n \simeq -1.25$, while Loitsiansky condition accelerates mechanical decay ($m \simeq -1.51$) and increases thermal persistence ($n \simeq -0.89$). The Gaussian profile induces rapid decay ($m \simeq -2.7$), approaching a critical threshold at $t \simeq 33$ initial Lyapunov times. At $Pr=1000$, the thermal microscale drops below the Kolmogorov scale, with the Batchelor constant settling around $C_B \simeq 3.5$. Calculated Kolmogorov ($C_K \simeq 1.72-1.75$) and Obukhov–Corrsin ($C_{OC} \simeq 1.8$) constants align with
benchmarks. Finally, velocity and temperature increment PDFs successfully capture multi-scale intermittency and non-Gaussian statistics, matching DNS and experimental data.
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Applied Physics · Cross-listed from eess.SP
Noise-Robust Frequency Estimation via Overlapped Sampling-Intervals Zero-Crossing Fitting
Phichai Youplao, Nithiroth Pornsuwancharoen and Yusaku Fujii
The trade-off between noise averaging and temporal resolution fundamentally limits conventional zero-crossing frequency
estimators under dynamic and noisy conditions. This paper presents an overlapped sampling-intervals zero-crossing fitting method (OS-ZFM), which introduces a structured overlapping regression framework that decouples noise averaging from temporal update rate. The method adopts a deterministic closed-form formulation, enabling a unified bias-variance analysis to characterize the statistical behavior of the
estimator and clarify the role of structured data reuse. Numerical results under intensity and background noise at a signal-to-noise ratio (SNR) of 10 dB show that OS-ZFM reduces median estimation error by more than 60% compared to conventional zero-crossing fitting methods at the same temporal resolution. It further achieves up to 90% reduction relative to basic zero-crossing detection and consistently yields lower estimation errors than
Hilbert-transform-based
estimators. Experimental validation utilizing impact-induced transient motion measured by
laser Doppler interferometry demonstrates that OS-ZFM reconstructs smooth and physically consistent trajectories with improved temporal fidelity. Owing to its low computational complexity and deterministic formulation, the proposed method enables accurate real-time frequency and acceleration tracking in resource-constrained measurement systems.
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Optics · Cross-listed from eess.IV
The Lift Spectrum: How Measurement-to-Space Adaptivity Shapes Robustness in Image-Free Single-Pixel Sensing
Yuyuan Han, Jingwei Li, Xiaoxia Zhang et al. (+9 more)
Single-pixel sensing encodes a scene as a short sequence of coded measurements, and image-free methods infer the task directly from that sequence. We show that removing image reconstruction relocates the central design problem to the lift: how 1D measurements become a 2D task representation. We organize this choice as a lift spectrum from a fixed-physics inverse, through a learned static projection, to content-adaptive
retrieval. These are not interchangeable forms of reconstruction: the fixed-physics route reconstructs an image consumed at inference, whereas our spatiotemporal soft-fusion (STSF) network lifts measurements directly into task features, and task-prioritized loss scheduling (TPLS) uses a separate learned reconstruction branch only as scheduled training supervision. A probe-selected recurrent encoder and a parameter-matched lift ablation identify the STSF design. In simulation, STSF+TPLS exceeds the prior image-free baseline on three
datasets at 3.13% sampling (+3.2 to +9.9 pp foreground mIoU) and remains competitive down to 0.39%. The strongest clean-trained reconstruct-then-segment baseline wins without measurement noise, but measurement noise reverses the ranking: the reconstructed task input carries a 20-70x larger normalized relative perturbation than the measurements themselves. Stressed to failure, the three lift regions exhibit distinct dominant signatures–collapse, imprinting, and coarsening. STSF+TPLS transfers without fine-tuning to a real single-pixel bench, where the reversal reappears as a proof of concept; inference takes about 14 ms per mask on an RTX 4090. Within the tested fixed-acquisition regime, measurement-to-space adaptivity therefore organizes both the clean-to-noisy operating envelope and the failure a system encounters. Code and pretrained weights: https://github.com/Hanyuyuan6/STSF-TPLS.
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All authors Yuyuan Han, Jingwei Li, Xiaoxia Zhang, Long Qiu, Chong Wang, Wenxuan Hao, Jiangyu Han, Xinyu Yao, Yuchen He, Hui Chen, Jianbin Liu, Huaibin Zheng
Instrumentation and Detectors
OASIS-ERIS: Open Acquisition System for IEPE Sensors - Electrically Refined and Inter-device Synchronization
Oliver M. Zobel, Johannes Maierhofer and Daniel J. Rixen
OASIS-ERIS, the Open Acquisition System for IEPE Sensors - Electrically Refined and Inter-device Synchronization, is the successor to the previously released OASIS-UROS. It is based on the Analog Devices AD7606C-18 analog-to-digital converter, offering 18-bit resolution on eight simultaneously sampled channels, and the Espressif ESP32-S3 microcontroller. The laboratory usability of OASIS-ERIS is significantly improved compared to OASIS-UROS due to the added inter-device synchronization. By physically connecting the sample clocks across devices, a truly synchronized data acquisition can be achieved with an arbitrary number of acquisition boards. Additionally, a migration of the firmware to ESP-IDF allows a major increase of the achievable sampling frequency to 100 kHz. This paper documents the hardware and software stack of OASIS-ERIS, and provides all materials necessary for reproduction. Further, the performance of OASIS-ERIS is tested against a commercial measurement system in an Experimental Modal Analysis campaign. The results show that OASIS-ERIS closely matches the performance of the commercial system, making it a viable replacement for academia and projects with tightly constrained budgets.
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Optics · Cross-listed from quant-ph
Optical time travel: proposal for testing Hawking's Chronology Protection Conjecture in an optical analogue
D. Bermudez and U. Leonhardt
Classical general relativity allows time travel, but Hawking [Phys. Rev. D 46, 603 (1992)] conjectured that
quantum mechanics ultimately prevents it. Here we propose a feasible experiment to test Hawking's Chronology Protection
Conjecture in optics. In this scheme, time travel is inherently related to lasing, and the amplified
vacuum fluctuations above
laser threshold establish the
quantum limits of time travel
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Optics · Cross-listed from quant-ph
Norm of resonance states in quantum scattering and electromagnetic systems
Florian Lorenz, Jan Möseritz-Schmidt and Roland Ketzmerick
Resonance states spatially diverge and are thus not square integrable. Instead, their norm is defined by the biorthogonal scalar product of left and right states. We replace the corresponding volume integral by a convenient boundary integral in piecewise homogeneous systems and apply this procedure to diverse physical settings. For a
quantum particle in any number of dimensions we treat hard-wall and piecewise constant potentials. For electromagnetic systems with piecewise homogeneous material properties, we consider three-dimensional and effectively two-dimensional cavities of arbitrary shape. As examples, we treat the spherical scatterer and the circular disk.
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Fluid Dynamics
Study of discrete boundary layer suction for transition delay
Mukund R., Pranav Joshi and Ishan Singh
In the present study we have assessed the effect of suction through discrete perforations on the transition of the Blasius boundary layer. In particular, the intermittency and the spectra of the streamwise velocity fluctuations, obtained using hot-wire anemometry, were used to evaluate the optimum suction, i.e., one that provides the greatest delay in transition. The displacement thickness Reynolds number at suction was varied between 1400 and 1600, while the number of rows of holes was either four or ten. The suction holes had diameter of the order of the displacement thickness of the boundary layer, a practical size from manufacturing and maintenance perspectives. As the suction strength was increased the transition front moved downstream, with the maximum delay in transition occurring at the optimum suction. When the suction was increased further, the transition front moved upstream again. The results, supported by a scaling analysis, showed that suction volume flow rate is a better indicator of the effects of suction on the transition delay than suction velocity. In particular, suction through different numbers of rows of perforations produces largely similar effects on the boundary layer transition, provided the suction volume flow rate remains the same. However, suction through fewer rows provided a slightly greater delay in transition in addition to a slightly lower optimum suction volume flow rate. The results also showed that suction applied at a lower Reynolds number provides a substantially greater transition delay but at slightly higher values of the normalized optimum suction volume flow rate.
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Physics and Society
ELSA as an asset to the EU Quantum Act: A position paper
Adrian Schmidt, Pieter Vermaas and Zeki C. Seskir
Europe's expertise in the ethical, legal, and social aspects (ELSA) of emerging technologies is a strategic asset for the successful and sovereign development of
quantum technologies. In this position paper, we argue that this expertise should become a central part of the upcoming EU
Quantum Act. At a time when
quantum technologies are becoming more powerful, economically relevant, and geopolitically contested, European policy should not reduce societal considerations to risk assessment and ex-post regulation. Instead, ELSA expertise can translate European values into technological practices, governance structures, and concrete policy measures, thereby supporting a development which is responsible, socially robust, and competitive. Taking inspiration from the role of concept cars, we present eight aspirational ELSA recommendations that demonstrate what a distinctly European approach to
quantum technologies could offer. These recommendations include setting European policy targets as
quantum moonshots,
embedding European values, addressing the motivations of younger generations, strengthening international cooperation, developing applications globally and inclusively, integrating continuous technology assessment, creating shared sociotechnical repositories, and shaping a European narrative for
quantum technologies. Together, we show that ELSA is not only about mitigating risks. It can also amplify benefits, increase legitimacy and societal acceptance, support economic prosperity, and contribute to a truly sovereign European
quantum future.
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Chemical Physics
Unexpected Collisional Rotational Excitation via Long-Range Capture and Orbiting
Dasarath Swaraj, Guodong Zhang, Siting Hou et al. (+9 more)
Collisional rotational excitation is a fundamental process in many gaseous environments. The textbook hard-sphere model stipulates that high rotational excitation results from head-on collisions, leading primarily to backward scattering, whereas long-range glancing collisions in the forward direction are inefficient for rotational energy transfer. Here, we report rotational state resolved product imaging for a system with strong attractive interaction, the charge-transfer collision between
spin-orbit selected Ar+(2P3/2) ions and para/ortho-H2 molecules. Surprisingly, the H2+ products are rotationally excited and dominated by forward scattering, in sharp contrast to conventional wisdom.
Quantum dynamical calculations on a first-principles diabatic potential energy
matrix reproduce the observations. Trajectory surface hopping analysis further reveals that rotational excitation occurs mostly with large impact parameters, and the captured complex undergoes orbiting motion owing to the strong attractive interaction between the two collision partners before they break up. This novel mechanism should be general for collisional systems featuring strong attractive interactions, which undermine the hard-sphere assumption.
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All authors Dasarath Swaraj, Guodong Zhang, Siting Hou, Dandan Lu, Jerin Judy, Fabio Zappa, Tim Michaelsen, Arnab Khan, Hua Guo, Changjian Xie, Hong Gao, Roland Wester
Biological Physics
Hair is a functionally graded composite, not a uniform fiber
Andrew K. Schulz, Svetlana Griego, Vesna Srot et al. (+11 more)
Hair provides mammals with diverse benefits, including protection, thermoregulation, and enhanced sensory perception. Unlike tendons and teeth, which are biomineralized, hair is hypothesized to accomplish its structure-function relationship purely through keratin, a fibrous
protein that provides structural integrity. Recent research showed that mechanical properties can vary substantially both within and across hair types: the whiskers of Asian elephant (Elephas maximus) exhibit a two-order-of-magnitude material stiffness reduction from base to tip, whereas elephant body hairs are nearly homogenous. Here, we demonstrate that three hierarchical structures vary significantly along the body hairs and whiskers of domestic cat (Felis catus): the layered outer keratin wall, 250-nm-diameter melanosome-like granules in the cortex, and calcium enrichment of these granules. As occasionally described for human hair, the oblong granules are arranged in longitudinal channels, potentially reinforcing the cortex; their prevalence correlates with local mechanical properties along the hair's length. Prolonged chemical treatment of body hairs removes calcium from the granules while breaking down the outer cuticle and internal cortex, hardening bases and splitting tips. Though previously assumed uniform, morphology, composition, and elemental enrichment can change along hairs, producing composite structures with functional gradients.
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All authors Andrew K. Schulz, Svetlana Griego, Vesna Srot, Giulia Ballardini, Natalia Gonzalez-Vazquez, Devin Sheehan, Felicitas Predel, Cem Balda Dayan, Deepti S. Philip, Helena Vrencev, Jelena Lazovic, Peter A. van Aken, Gunther Richter, Katherine J. Kuchenbecker
Computational Physics · Cross-listed from math.NA
PIML-OFEM: A New Large-Scale Structural Analysis Method Based on Problem-Independent Machine Learning and Overlapping Finite Element Technique
Yilin Guo, Chang Liu, Zongliang Du et al. (+7 more)
High-resolution analysis and design of large-scale heterogeneous structures require accurate reduced-order models and efficient online computation. Existing multiscale methods must repeatedly construct local basis functions for different material distributions, whereas substructure-based problem-independent machine learning (PIML) methods can be limited by prescribed boundary displacement interpolation. We propose PIML-OFEM, an overlapping finite element method accelerated by problem-independent machine learning. Each substructure retains only its corner-node degrees of freedom. Oversampled numerical basis functions are constructed by solving local elasticity problems on extended domains and restricting the solutions to the target substructure, eliminating prescribed displacement interpolation on its boundary. Independently constructed local bases are blended through a partition-of-unity overlapping formulation to obtain a globally continuous displacement field. A U-Net learns the mapping from local Young's modulus distributions to numerical basis functions, replacing repeated online local solves and allowing the model to be reused across load cases and global boundary conditions. Numerical examples show close agreement with fine-scale finite element results in displacement and elemental strain energy. PIML-OFEM reduces online computational cost relative to direct finite element analysis and improves accuracy over PIML substructure models based on linear boundary interpolation. In
topology optimization, the method supports stable high-resolution iterations with small filter radii and preserves fine-scale features, including local patterns resembling rank-2 microstructures. The framework provides an efficient physics-data approach for large-scale heterogeneous structural analysis and high-resolution
topology optimization.
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All authors Yilin Guo, Chang Liu, Zongliang Du, Jin Liu, Jingyu Feng, Xinyang Zhang, Yang Li, Tianxing Yang, Changyu Shen, Xu Guo
Instrumentation and Detectors
Gamma spectrometry with CsI(Tl), NaI(Tl) and CdWO4 scintillation crystals using a silicon photomultiplier
R. Yu. Chaplynskyi, F. A. Danevich, D. V. Kasperovych et al. (+6 more)
This study investigated using of silicon photomultiplier (SiPM) for scintillation {\gamma}-spectrometry with CdWO4, CsI(Tl), and NaI(Tl)
crystal scintillators. At room temperature, CsI(Tl)
crystal scintillator provides the best performance, while the achievable energy resolution is lower compared to that obtained with conventional photomultiplier tube (PMT) with green-enhanced photocathode. These findings highlight the potential of SiPMs as a compact and cost-effective alternative to PMTs in
nuclear physics applications, particularly for light portable spectrometers, such as radiation monitoring systems based on small unmanned aerial vehicles.
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All authors R. Yu. Chaplynskyi, F. A. Danevich, D. V. Kasperovych, V. R. Klavdiienko, V. V. Kobychev, E. E. Petrosian, A. R. Podviianiuk, R. B. Podviianiuk, O. G. Polischuk
Geophysics
Diffusion-guided optimization for full waveform inversion
Yiran Shen, Yangkang Chen and Björn Engquist
We present a
diffusion-guided full waveform inversion (FWI) study in which pretrained
diffusion generative models are used as learned regularizers inside a PDE-constrained seismic inversion loop. We compare three training-free guidance strategies:
Manifold-Preserving Guided
Diffusion (MPGD), SDEdit-based initialization, and Split Gibbs
Diffusion Sampling (SGDS), which alternates between FWI likelihood updates and
diffusion-prior denoising. The proposed workflow keeps wave-equation modeling in the inversion loop and uses a geological prior to stabilize model components that are weakly constrained by the seismic data. Controlled GeoFWI experiments,
benchmark-scale Marmousi and Overthrust tests, a difficult Sigsbee2A salt test, and noise-degradation studies show that SGDS improves reconstruction quality relative to conventional L2 and total-variation regularized FWI in clean and moderately noisy synthetic settings. Overall, these experiments demonstrate that
diffusion-guided optimization can serve as a practical learned regularization strategy for synthetic FWI
benchmarks while preserving the wave-equation modeling loop.
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Fluid Dynamics
Flow Reversal in Low-Prandtl-Number Convection via Lateral Confinement
Zhi-Han Wu, Long Chen, Yan-Wu Cao et al. (+4 more)
A prevailing consensus holds that flow reversals of the large-scale circulation (LSC) are suppressed in low-Prandtl-number (Pr) fluids, as high thermal diffusivity rapidly dissipates the energy required to fuel the corner-
vortex mechanisms. Here, we report Direct Numerical Simulations of
liquid metal convection (Pr=0.029) revealing that strong lateral confinement defies this consensus, enabling sustained LSC reversals. We show that confinement triggers a “plume condensation" transition, reorganizing chaotic thermal plumes into highly coherent, quasi-linear structures. A thermal dissipation analysis demonstrates that this coherence drastically reduces heat loss during transport, allowing plumes to deliver sufficient buoyancy to corner
vortices to drive reversals. We map a distinct “island of reversal" in the parameter space, establishing lateral confinement as a control parameter capable of overcoming the stabilizing effects of high thermal diffusivity.
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All authors Zhi-Han Wu, Long Chen, Yan-Wu Cao, Liang Xue, Ming-Zhu Ai, Juan-Cheng Yang, Ming-Jiu Ni
Physics and Society · Cross-listed from cs.SI
Cross-country structure of a sexual contact network derived from a commercial-sex review platform
Hiromu Ito, Keiko Shigeta, Toshiaki R. Asakura et al. (+1 more)
Sexual contact networks are fundamental to understanding the spread of sexually transmitted infections (STIs), yet their large-scale structure remains difficult to observe because of technical, ethical, and
privacy constraints. Here, we analyze a large bipartite commercial-sex contact network comprising 1,436,738 client-sex worker links, constructed from reviews posted between 1999 and 2024 on The Erotic Review (TER), a review platform covering sex workers listed across 97 countries and territories. We examine the network's cross-country structure, focusing on how clients, sex workers, locations, and time periods are connected. The network formed a
giant connected component containing most clients and sex workers and exhibited small-world-like properties, including short average path lengths, high bipartite clustering, and disassortative degree correlations. Although most reviews were associated with the United States, a small fraction of clients reviewed sex workers in multiple countries or territories, creating spatial bridges between otherwise distant regions. Long-term users created temporal bridges, making the aggregated network more compact than networks built from shorter time windows. Contacts involving transgender female sex workers were structurally concentrated: clients who reviewed both cisgender and transgender female sex workers represented a small minority but accounted for a large share of transgender-related reviews and showed higher cross-country activity. These findings show how a small number of highly connected clients with cross-country review activity can shape the large-scale connectivity of commercial-sex contact networks. More broadly, our results demonstrate the value and limitations of digital trace data for studying cross-country contact structures relevant to STI transmission.
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All authors Hiromu Ito, Keiko Shigeta, Toshiaki R. Asakura, Satoru Morita
Atmospheric and Oceanic Physics
Anomalous Diffusion of Tropical Cyclones Observed in Huge Ensembles of Hindcasts
Abdoul R. Zeba, William D. Collins, Ankur Mahesh et al. (+5 more)
We examine whether tropical cyclones (TCs) obey ordinary Brownian or anomalous
diffusion using a huge ensemble (HENS) of hindcasts for summer 2023. Anomalous
diffusion has been inferred for actual TCs from the fluctuations in their tracks from the shortest paths between the initiation and termination of each cyclone. We reproduce the same anomalous
diffusion power laws connecting spatial position and time using HENS. In addition, we show that the variance in the position of a single TC across HENS since initiation follows a scaling law with time that, in some cases, corresponds to ballistic motion of the TC through the background atmospheric flow. This determination was enabled by the exceptional statistics determined from thousands of plausible yet counterfactual recreations of 34 individual TCs. HENS consists of 7424 15-day hindcasts initiated from observed atmospheric conditions each day from June 1, 2023 to August 31, 2023 using the ECMWF ERA5 meteorological reanalysis. The hindcasts were generated using NVIDIA's Spherical
Fourier Neural Operator (SFNO) machine-learning-based weather and
climate emulator. We identify tropical cyclones in HENS using a variant of the Tempest Extremes detection and tracking frameworks for TCs with adjustments to the disposable parameters to minimize the numbers of false positives and negatives relative to the International Best Track Archive for
Climate Stewardship (IBTrACS) records for TCs observed in summer 2023. We conclude with the implications of our findings for the predictability of TC tracks and landfall locations on lead times of days to weeks.
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All authors Abdoul R. Zeba, William D. Collins, Ankur Mahesh, Boris Bonev, Karthik Kashinath, Thorsten Kurth, Michael S. Pritchard, Shashank Subramanian
Atmospheric and Oceanic Physics
MAPCast: A Convection Allowing MPAS Emulator for Ensemble-based Background Error Covariance Estimation Toward Multi-Scale Data Assimilation
Yongming Wang and Xuguang Wang
Machine learning (ML) emulators offer a cost-efficient alternative to numerical weather prediction models for generating convection-allowing background ensembles in ensemble-based data assimilation (DA). However, few studies have explored ML-based surrogate background ensembles for estimating background-error covariances (BECs). This study develops a convection-allowing emulator, MAPCast, trained on historical convection-allowing simulations from the Model for Prediction Across Scales (MPAS), and evaluates its ability to estimate BECs, paving the way toward multiscale DA. The evaluation uses 10 retrospective convective cases at 15- and 60-min forecast lead times corresponding to subhourly and hourly DA. MAPCast reproduces MPAS forecasts with good fidelity, including realistic storm coverage, temporal
evolution, and similar spatial and spectral characteristics of state variables. Discrepancies are primarily confined to small spatial scales near sharp gradients and convective-scale features and variables. For BEC statistics, MAPCast captures ensemble spread magnitude and spatial distribution for most variables, although larger errors occur for storm-related fields that are vertical velocity and reflectivity. Correlation structures are reproduced most faithfully at mesoscale and above, followed by at convective scales, whereas cross-variable correlations are less accurately represented than univariate correlations, indicating that multivariate coupling remains the principal limitation. MAPCast shows weaker replication of full-scale versus decomposed large and small-scale correlations. BEC estimates derived from 15-min forecasts consistently outperform those from 60-min forecasts, suggesting that shorter lead times better preserve flow-dependent error structures.
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Data Analysis and Statistics · Cross-listed from stat.ME
Estimating dynamic models by matching random features
Michael Wieck-Sosa and Cosma Rohilla Shalizi
Scientists increasingly express their ideas as dynamic models of complex processes. It is often much easier to simulate these models than to calculate the probability of their generating a particular outcome, making likelihood-based estimation infeasible. Existing likelihood-free approaches rely either on manually chosen summary statistics or on representations learned by neural networks. The former is error-prone and laborious, while the latter is computationally intensive, leaving many scientists in a difficult position. We show that, for a large class of dynamic models, parameters can be estimated by matching a small number of random features of the observed and simulated data. In particular, we show that models with a $p$-dimensional parameter can be identified from just $2p+1$ generic random
Fourier features. We introduce two
estimators for stationary and nonstationary processes, respectively, and we establish their consistency under mild regularity conditions. More broadly, our results serve as the foundation for a new class of methods for simulation-based inference.
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Physics and Society
A Knowledge-Grounded Behavioral Reasoning Framework for Training-Free Urban Healthcare OD Prediction
Linzhen Yang, Xueliang Liu, Chengbo Zhang et al. (+1 more)
Understanding urban healthcare mobility is essential for healthcare resource allocation, hospital capacity planning, and resilient urban governance. Existing healthcare origin-destination (OD) prediction methods primarily rely on supervised deep learning, requiring expensive model training while providing limited interpretability into the behavioral mechanisms of hospital choice. This paper presents a training-free urban healthcare OD prediction framework based on knowledge-grounded behavioral
reasoning, replacing gradient-based neural network learning with collaborative LLM
reasoning over structured urban knowledge. The framework organizes heterogeneous urban information, including healthcare resources, population characteristics, transportation accessibility, weather conditions, and historical mobility, into a unified knowledge graph, enabling evidence
retrieval, urban context understanding, behavioral
reasoning, preference ranking, and
Bayesian verification through a multi-
agent reasoning pipeline. Experiments on a real-world Shenzhen
dataset containing 137 hospitals and 6,341 prediction tasks demonstrate that the proposed framework achieves CPC = 0.5449, Top-1 = 66.19%, Top-5 = 68.03%, and Top-10 = 74.03%, consistently outperforming conventional deep learning baselines on all Top-K metrics (e.g., Top-5 improves by 22.1% over MLP). Compared with Direct LLM using the same backbone without structured
reasoning, the proposed framework improves CPC by 87.5% and Top-1 accuracy by 141%, demonstrating that knowledge-grounded behavioral
reasoning, rather than raw LLM capability, is the key to accurate, interpretable, and training-free healthcare OD prediction. These findings highlight the potential of urban intelligence to move healthcare mobility modeling beyond data fitting toward knowledge-driven behavioral
reasoning.
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All authors Linzhen Yang, Xueliang Liu, Chengbo Zhang, Meng Meng
Plasma Physics · Cross-listed from hep-th
Momentum anisotropy from Resistive Magnetohydrodynamics
Khwahish Kushwah and Gabriel S. Denicol
We derive relativistic resistive magnetohydrodynamics framework for a two-component ultrarelativistic
plasma of massless, oppositely charged particles directly from the Boltzmann-Vlasov equation using the 14-moment approximation. The resulting second-order equations couple the net-charge
diffusion current to the shear-stress tensor through the electric field, with all transport coefficients given in closed microscopic form. In the homogeneous limit, the charge-current dynamics is well described by relaxation-type Ohm's law for moderate field strengths, while large viscosity drives the system into an underdamped oscillatory regime absent from the standard Israel-Stewart formulation. Most strikingly, a purely electric field generates sizable momentum anisotropy even without any underlying flow gradient. Under Bjorken expansion this field-induced anisotropy persists but becomes subleading to the hydrodynamic expansion source.
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