Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics

physics Watch Physics

Sunday 30 August

Physics and Society

Peer Review at Capacity: An editor's view

Yamir Moreno

From the editor's desk, the pressure on peer review is no longer an abstract concern. It appears in the growing number of invitations needed to secure an appropriate report, the repeated reliance on a small group of dependable colleagues, and the duplication of work when manuscripts move between journals. The problem is not simply that science has too few potential reviewers. It is that reviewing labor is unevenly distributed, weakly recognized, and organized through a publication architecture built for a smaller system.
Read the full abstract

Fluid Dynamics

Splashing-regime transitions and secondary-droplet scaling in oblique drop impacts on a deep pool

Ying Xiong, Yang Zhang, Lingling Xie et al. (+1 more)

Oblique drop impact onto a deep liquid pool produces asymmetric crowns, directional jetting, and splashing transitions that cannot be characterized by the total impact inertia alone. We numerically investigate water drops impacting a quiescent deep pool over $41\leq We\leq1790$ and $10^\circ\leq\theta\leq90^\circ$. The simulations reproduce the principal features observed experimentally and identify five post-impact regimes in the $We$–$\theta$ plane: deposition, front splashing, side splashing, side-front splashing, and crown splashing. The deposition–front-splashing transition is described by the tangential-inertial parameter $K_s=We\cos\theta$, with $K_s^c\approx120$. This criterion follows from the competition between downstream crown-rim inertia and capillary retraction at the Taylor–Culick velocity. The transition from front to side-front splashing is instead governed primarily by normal impact inertia, with a critical normal Weber number $We_N^c\approx318$. Beyond these regime transitions, the secondary-droplet statistics reveal fragmentation behavior common to the different splashing regimes. The droplet-size distributions are positively skewed, and the median diameter follows $d_{s,\mathrm{med}}/D\sim We^{-3/5}$. Second-order velocity structure functions support a scale-dependent capillary–inertial description of rim and ligament breakup. Combined with mass conservation, this scaling gives $N_s\sim We^{9/5}$, providing a numerical explanation for the secondary-droplet-number scaling observed experimentally. Thus, directional impact inertia governs the macroscopic selection of splashing regimes, whereas the secondary-droplet populations across these regimes exhibit a common capillary–inertial fragmentation scaling.
Read the full abstract

All authors Ying Xiong, Yang Zhang, Lingling Xie, Xiaolei Li

Data Analysis and Statistics · Cross-listed from astro-ph.IM

A generalized likelihood model for segmented muon counters

Joaquín de Jesús, Juan Manuel Figueira, Federico Sanchez et al. (+1 more)

Measurements of the muonic component of extensive air showers constrain cosmic-ray mass composition and hadronic interactions at energies beyond those accessible at accelerators. Arrays of segmented detectors with binary readout are widely used for this purpose: they sample the muon density at different distances from the shower core to reconstruct the muon lateral distribution function (LDF). Each detector response is summarized by the number of activated segments, $k$, whose probability distribution provides the likelihood relating the observation to the expected muon content. Signal pile-up, detector inefficiency, corner-clipping muons, and background signals shape this distribution, and neglecting them can bias the reconstruction. Existing analytical models include pile-up but otherwise assume an ideal detector response. In this work, we develop a unified statistical framework that incorporates inefficiency, corner clipping, and background through a small set of physically interpretable parameters. We derive exact expressions for the detector response and the likelihood required for muon-LDF reconstruction, together with a simple binomial approximation that preserves the main statistical properties of the exact distribution. Dedicated Monte Carlo simulations are used to assess the impact of the assumptions underlying the analytical treatment and show that it is negligible over the parameter range considered. They also show that the exact and approximate likelihoods yield similar performance in terms of estimator bias and confidence-interval coverage. Although motivated by the Underground Muon Detector of the Pierre Auger Observatory, the framework applies more broadly to segmented particle detectors with binary readout in which particle content is inferred from the number of activated segments.
Read the full abstract

All authors Joaquín de Jesús, Juan Manuel Figueira, Federico Sanchez, Darko Veberic

Space Physics · Cross-listed from astro-ph.SR

Ion-Scale Waves Regulated by Plasma Beta and Cross Helicity: Observational Evidence for the Helicity Barrier in Imbalanced Solar Wind Turbulence

G. Q. Zhao, R. Meyrand, H. Q. Feng et al. (+3 more)

Ion-scale waves are believed to play an important role in heating of the solar corona and wind, though their generation mechanism remains unclear. Based on Parker Solar Probe observations, this Letter investigates the occurrence of ion-scale waves in the near-Sun solar wind with heliocentric distances between 0.1 and 0.2 au. Results show that the occurrence rate of left-handed polarized waves significantly depends on the plasma beta ($\beta$) and cross helicity ($\sigma_c$). The occurrence rate rapidly increases with decreasing $\beta$ and increasing $\sigma_c$. Overall, the occurrence rate exceeds 45$\%$ when $\beta<0.2$ and $\sigma_c > 0.7$ are satisfied. These observations are consistent with the direct predictions of the helicity barrier theory that suggests the generation of ion cyclotron waves via imbalanced magnetized turbulence.
Read the full abstract

All authors G. Q. Zhao, R. Meyrand, H. Q. Feng, H. F. Yang, L. Xiang, Z. Wang

Fluid Dynamics

Lagrangian particles and particle clusters in large-aspect-ratio turbulent Rayleigh-Bénard convection experiment

Prafulla P. Shevkar, Mitanjali, Roshan J. Samuel et al. (+2 more)

We perform Lagrangian particle-tracking experiments in turbulent Rayleigh-Bénard convection at aspect ratio Gamma = 10, Rayleigh number Ra = 9.3 x 10^7, and Prandtl number Pr = 4.8. Approximately 50,000 neutrally buoyant particles are tracked for durations of up to 150 Kolmogorov times. The resulting trajectories are sufficiently long to capture the mean-square displacement of single particles from the short-time ballistic regime to the long-time diffusive regime. We further analyse Lagrangian velocity structure functions and particle-pair dispersion, both of which exhibit scaling behavior consistent with theoretical expectations in their respective temporal regimes. In the Richardson-like regime, the pair-dispersion exponent exceeds 3, most clearly in the lateral direction. Multi-particle statistics are investigated by analysing particle clouds with initial radii of approximately 8 and 20 Kolmogorov lengths using principal component analysis. The clouds spread more strongly in the lateral directions than in the vertical direction and deform from initially spherical shapes into oblate ellipsoids within approximately 10 Kolmogorov times, revealing pronounced anisotropic dispersion. The dynamics is identified from the particle-connectivity network through a spectral analysis of the graph Laplacian followed by k-means clustering. Furthermore, we examine the probability density functions of all three acceleration components and assess the statistical convergence of their second and fourth moments. The lateral acceleration components are more intermittent than the vertical component, as indicated by their heavier tails. Acceleration statistics conditioned on the bulk region are slightly less intermittent than those obtained over the full measurement volume, which we attribute to the highly intermittent plume-ejection and plume-aggregation events occurring near the walls.
Read the full abstract

All authors Prafulla P. Shevkar, Mitanjali, Roshan J. Samuel, Christian Cierpka, Jörg Schumacher

Applied Physics · Cross-listed from cond-mat.mes-hall

Harnessing the skyrmion Hall effect for low-power skyrmion transport in a tubular synthetic antiferromagnet

Ivan P. Miranda, Grzegorz J. Kwiatkowski, Jacob J. Mankenberg et al. (+4 more)

We show that optimal control can turn the skyrmion Hall effect from a source of typically unwanted transverse motion into a mechanism for reducing Ohmic losses in skyrmion transport. We consider a pair of antiferromagnetically coupled skyrmions confined to a tubular geometry, where their relative transverse displacement becomes a periodic internal coordinate. The skyrmion Hall effect drives this coordinate, while finite interlayer coupling makes the resulting relation between applied current and longitudinal velocity nonlinear, allowing different current protocols to produce the same prescribed average velocity. We determine which of these protocols minimizes Joule heating. Depending on the interlayer coupling and spin-transfer-torque parameters, the optimal current is either constant, with the skyrmion pair maintaining a fixed relative position, or time dependent, with the pair undergoing periodic relative motion around the tube. In either case, the additional internal degree of freedom created by the skyrmion Hall effect and interlayer coupling enables skyrmion transport at a lower power than in the uncoupled limit.
Read the full abstract

All authors Ivan P. Miranda, Grzegorz J. Kwiatkowski, Jacob J. Mankenberg, Cecilia M. Holmqvist, Igor S. Lobanov, Valery M. Uzdin, Pavel F. Bessarab

Physics and Society

Open, Reproducible Per-Bidding-Zone Carbon Intensity for Nordic Power Systems

Eirik Botten Nicolaysen

Carbon-aware scheduling of electrical loads depends on accurate grid carbon-intensity (CI) signals, yet existing tools commonly apply a uniform placeholder emission factor that misrepresents regional variation. This work presents an open, reproducible method for computing per-bidding-zone CI across the Nordic power system. Generation-by-type data from ENTSO-E is combined with IPCC AR5 life-cycle emission factors, duration-weighted per bidding zone, with an explicit materiality threshold for missing data. Applied to nine bidding zones (NO1-NO5, SE1-SE4) for 2025, the method yields CI values ranging from 14.5 to 39.6 gCO2eq/kWh. The results reveal that the uniform 18.0 gCO2eq/kWh placeholder is wrong in both directions: it understates CI for most zones, by a factor of approximately 2.2 for NO4, yet overstates CI for the nuclear-dominated zone SE3, whose production-based CI is the lowest of the nine. Drift is characterised against a pre-registered threshold of 15% year-on-year change, including a borderline case in SE4 and event-driven variation in NO4. Forecasting experiments do not reject the null hypothesis that simple baselines suffice, in either the Norwegian or Swedish zones. The full method, data, and results are released under open licences and archived at DOI 10.5281/zenodo.21042581, with the per-zone values contributed upstream to the codecarbon library. Per-bidding-zone resolution is necessary for accurate carbon accounting in Nordic grids, where country-level averages obscure substantial intra-country variation.
Read the full abstract

Computational Physics

Characteristic Mode Analysis of Composite Nanostructures using a Coupled System of Volume Integral and Hydrodynamic Equations

Meruyert Khamitova, Ran Zhao, Doolos Aibek Uulu et al. (+2 more)

Full-structure and sub-structure characteristic mode analysis (CMA) formulations are developed for composite metallic–dielectric nanostructures based on a coupled system of volume integral equations (VIE) and the hydrodynamic equation (HDE). In the full-structure CMA, the generalized eigenvalue equation (GEE) is constructed from the matrix of the complete coupled system, and the resulting characteristic currents describe the response of the entire composite nanostructure. In the sub-structure CMA, the GEE is constructed from a reduced system, derived from the coupled system by eliminating the dielectric-region unknowns, so that it is expressed only in terms of the metallic-region currents. This isolates the resonances of the metallic region while still incorporating the effect of the dielectric region through the reduced system. Because the reduced system has a smaller dimension, the sub-structure CMA is computationally more efficient than the full-structure CMA and, when the dielectric does not resonate in the frequency range of interest, identifies the same resonances. Both formulations are validated against extinction cross-section (ECS) results and are used to characterize how a dielectric environment reshapes the metallic resonances, including substrate-induced red-shifts and, for high-contrast substrates in direct contact, hybridized modal responses.
Read the full abstract

All authors Meruyert Khamitova, Ran Zhao, Doolos Aibek Uulu, Sebastian Celis Sierra, Hakan Bagci

Atomic Physics

Cancellation of $D_2$ line transitions of alkali-metal atoms by magnetic-field values

Artur Aleksanyan, Susanna Petrosyan and Emil Gazazyan

In a previous work the $\pi$ transitions of the $D_1$ line of alkali-metal atoms were shown to cancel at magnetic-field values given by a single closed-form expression. The $D_2$ line has until now resisted the same treatment, because the fixed-$m$ Hamiltonian blocks of the $^2P_{3/2}$ manifold reach the dimension $4\times4$, and the corresponding formulas were considered to be too heavy to be useful. In this work we show that this difficulty is only apparent. Since the Zeeman interaction couples only levels with $\Delta F=\pm1$, every block, whatever its dimension, is tridiagonal; its characteristic polynomial therefore obeys a three-term recursion, and the components of its eigenvectors are polynomials in the eigenvalue. Using these two properties we obtain the eigenvalues in closed form by Ferrari's and Cardano's formulas, the eigenvectors without any further diagonalization, and finally a single relation which gives the magnetic-field value canceling a $D_2$ transition as an explicit function of the excited-state eigenvalue, the nuclear spin $I$, the ground-state hyperfine splitting and the magnetic quantum number. A necessary condition on $m$ and on the polarization is derived, which replaces the selection rule known for the $D_1$ line. All the magnetic-field values canceling $\pi$, $\sigma^+$ and $\sigma^-$ transitions of $^{23}$Na, $^{39}$K, $^{40}$K, $^{41}$K, $^{85}$Rb, $^{87}$Rb and $^{133}$Cs are calculated up to 20~kG and given with their uncertainties; there are 234 of them. Contrary to the $D_1$ line, the $\sigma^{\pm}$ transitions of the $D_2$ line do cancel, and they account for the majority of the values found. The accuracy of the calculated $B$ values is limited only by the uncertainties of the excited-state hyperfine constants.
Read the full abstract

Physics and Society

ButterMamba: Butterworth-Enhanced Spatial-Temporal Mamba for Efficient Traffic Flow Prediction

Limiao Zhang, Yuhui Lu, Jie Gao et al. (+3 more)

Accurate traffic flow prediction is fundamental to intelligent transportation systems, playing a pivotal role in urban mobility optimization and smart city development. While Graph Neural Networks (GNNs) integrated with time series forecasting have emerged as promising solutions, two critical limitations persist: (1) the quadratic complexity of attention-based architectures hinders real-time deployment in large-scale networks, and (2) high-frequency noise in sensor data significantly degrades prediction reliability. These challenges are particularly acute in metropolitan scenarios where both computational efficiency and noise robustness are paramount. To address these limitations, we introduce ButterMamba, a novel and efficient framework based on State Space Models (SSMs). ButterMamba consists of two key components: (1) a Butterworth Spectral Filtering module that preprocesses the data by removing high-frequency noise, allowing the model to focus on significant underlying trends, and (2) a Spatial-Temporal State Mixer that uses a parallel Mamba architecture to efficiently capture both long-range temporal dependencies and complex spatial correlations across the road network. By decoupling noise filtering from spatial-temporal modeling, ButterMamba achieves superior predictive accuracy with linear computational complexity. Extensive experiments on three public datasets demonstrate that ButterMamba not only outperforms existing state-of-the-art models in terms of prediction accuracy but also considerably reduces training time and memory usage.
Read the full abstract

All authors Limiao Zhang, Yuhui Lu, Jie Gao, Hao Jiang, Haiping Ma, Xingyi Zhang

Plasma Physics

Generation of Isolated Collimated Polarized $\gamma$-ray Beams via Spatiotemporal Optical Vortex Modulation

Xinyu Xie, Fengyu Sun, Huai-Hang Song et al. (+2 more)

Attosecond, collimated, bright, polarized $\gamma$-ray sources are in high demand across nuclear physics, astrophysics, and high-energy physics. However, realizing attosecond duration, high collimation, high brilliance, and high polarization simultaneously within a single isolated source remains an outstanding challenge, owing to the inherent trade-offs between beam trapping and radiative dynamics. Here, we propose a novel scheme to generate an isolated, collimated, high-brilliance, polarized attosecond $\gamma$-ray beam from conventional solid foils irradiated by a linearly polarized spatiotemporal optical vortex (STOV) laser pulse accessible in Lab. Three-dimensional spin-resolved particle-in-cell simulations reveal that this relativistic-intensity STOV pulse can trap and accelerate electrons at its spatiotemporal singularity, producing a compact isolated electron bunch. This electron bunch subsequently undergoes head-on collision with the reflected laser pulse, which generates isolated $\gamma$-ray beams through nonlinear Compton scattering. With a peak intensity of $7\times10^{21}$ W/cm$^2$, we observe an isolated collimated ($\sim1.5^{\circ}$) $\gamma$-ray beam with an average linear polarization of $>60\%$ and a duration of $\sim$500 attoseconds. This approach is feasible with current or upcoming laser facilities and robust against variations in laser and target parameters, highlighting the capability of spatiotemporal structured light field modulation to address outstanding problems in plasma physics.
Read the full abstract

All authors Xinyu Xie, Fengyu Sun, Huai-Hang Song, Wei-Min Wang, Wenpeng Wang

Plasma Physics · Cross-listed from astro-ph.SR

Origin of small-scale evaporation flows deep in the chromosphere during a solar flare

L. P. Chitta, H. N. Smitha, F. A. Iglesias et al. (+29 more)

Flares are caused by an abrupt release of magnetic energy in the solar atmosphere. Plasma heated to well over 10 MK filling the post-flare corona originates from a rapid heating and ablation of the cooler chromospheric material. This chromospheric evaporation is thought to be facilitated primarily by nonthermal electrons impinging on to the lower atmosphere. Questions on when and where in the chromosphere these upflows originate, however, are not fully resolved. Here we report on unprecedented high-resolution observations of an M-class flare recorded by the Sunrise Ultraviolet Spectropolarimeter and Imager on board the balloon-borne SUNRISE observatory, that reveal highly structured upflows on spatial scales of ~100 km originating deep in the chromosphere. The flows even precede the onset of nonthermal electrons by about 10 minutes and last through the impulsive phase of the flare. Our observations shed new light on the lower atmospheric heating and mass circulation in flares that are challenging to reconcile with the standard solar flare model.
Read the full abstract

All authors L. P. Chitta, H. N. Smitha, F. A. Iglesias, T. L. Riethmüller, A. Feller, W. Chen, A. Lagg, A. Gandorfer, J. Hölken, S. K. Solanki, J. C. del Toro Iniesta, Y. Katsukawa, P. Bernasconi, T. Berkefeld, A. Álvarez-Herrero, M. Kubo, D. Orozco Suárez, B. Grauf, M. Carpenter, A. Bell, Valentín Martínez Pillet, F. J. Bailén, J. Blanco Rodríguez, J. Sebastián Castellanos Durán, E. Harnes, R. T. Ishikawa, Y. Kawabata, T. Matsumoto, T. Oba, A. L. Siu-Tapia, H. Strecker, D. Vukadinović

Instrumentation and Detectors

Toward Ionization Cluster Size Measurements with a Compact Nanodosimeter

Victor Merza, Aleksandr Bancer, Vladimir Bashkirov et al. (+8 more)

Nanodosimetry aims to provide measurable quantities related to the nanoscopic particle track structure, which determines the biological effectiveness of radiation. While simulated nanodosimetry has already demonstrated its potential for radiation treatment planning, the experimental realization of practical nanodosimetric detectors is still in its early stages. In this work, a nanodosimetric prototype operated with low-pressure gas was developed to count ionizations in a nanometer-equivalent sensitive gas volume. Its performance was evaluated experimentally with alpha beams from an Am-241 source in 1 mbar propane gas. The results support the further development of this compact nanodosimeter class, with potential applications in particle therapy, radiation protection, and space radiation dosimetry.
Read the full abstract

All authors Victor Merza, Aleksandr Bancer, Vladimir Bashkirov, Ana Belchior, Beata Brzozowska, Piotr Gasik, Jaroslaw Grzyb, Khaled Katmeh, Marcin Pietrzak, Antoni Ruciński, Reinhard Schulte

Plasma Physics

Unified Gas-Kinetic Wave-Particle Method for Multiscale Simulation of Vlasov-Poisson-Fokker-Planck System

Zhigang Pu, Chang Liu, Yixiao Wang et al. (+1 more)

A unified gas-kinetic wave–particle method with Fokker–Planck collisions (UGKWP-FP) is developed for the Vlasov–Poisson–Fokker–Planck system. The collision operator is modeled by the Lenard–Bernstein operator, whose stochastic representation corresponds to the Ornstein–Uhlenbeck process in velocity space. To extend the UGKWP framework beyond the conventional Bhatnagar–Gross–Krook (BGK) collision model, the Fokker–Planck operator is decomposed into a nonstiff drift–diffusion contribution and a stiff thermalization contribution. The former is retained in the particle dynamics through a modified Ornstein–Uhlenbeck process, whereas the latter is represented by a BGK-type relaxation toward the local Maxwellian. This decomposition enables an adaptive wave–particle representation: the method follows stochastic particle dynamics in rarefied regimes and increasingly represents the rapidly equilibrating distribution by the analytical wave component as the continuum regime is approached. The modified friction coefficient is constructed to recover the original Fokker–Planck dynamics in the rarefied limit while preserving the hydrodynamic limit under strong collisions. Numerical experiments demonstrate that the proposed method captures velocity-space drift and diffusion, recovers the expected kinetic and continuum behavior across a range of Knudsen numbers, and reproduces the characteristic evolution of collisional plasma phenomena.
Read the full abstract

All authors Zhigang Pu, Chang Liu, Yixiao Wang, Kun Xu

Optics · Cross-listed from quant-ph

Thresholdless dynamical instability in transverse $\mathcal{PT}$-symmetric scattering systems: The hidden role of bound states in the continuum

Chao Zheng

The stationary scattering properties of transverse parity-time ($\mathcal{PT}$) symmetric systems have been extensively studied, yet their dynamical stability, a prerequisite for any stationary description, remains largely unexplored. Here we uncover a thresholdless dynamical instability in such systems, driven by symmetry-protected bound states in the continuum (BICs). Without gain and loss, the up-down mirror symmetry of the transverse geometry generically protects a BIC, which manifests as the coalescence of an $S$-matrix pole and zero on the real axis of the complex wave-number plane. A Hermitian symmetry-breaking perturbation shifts the poles into the lower half-plane, converting the BIC into a resonance with a Fermi-golden-rule decay width. An anti-Hermitian $\mathcal{PT}$-symmetric perturbation instead reverses the sign of the second-order energy shift, driving the poles into the upper half-plane and producing a time-growing bound state with $\operatorname{Im}E=\gamma^{2}\Gamma_{V}/2+O(\gamma^{3})$, where $\gamma$ is the gain-loss strength and $\Gamma_{V}$ is the golden-rule coupling of the BIC to the continuum. The instability therefore sets in at arbitrarily small $\gamma$ whenever $\Gamma_{V}>0$. We confirm this mechanism in a three-site side-coupled model that is unstable despite possessing a unitary scattering matrix, and in a four-site rhombic model where transverse and longitudinal gain-loss placements yield vanishing and finite thresholds, respectively. These results establish a microscopic stability criterion and a design principle for stable $\mathcal{PT}$-symmetric scattering devices.
Read the full abstract

Fluid Dynamics

Competing instabilities in wide-gap viscoelastic Taylor-Couette flow: Taylor vs. helical vortices

Alexander Proskurin

This paper presents a numerical study of the stability of a polymer solution flow between concentric cylinders with a rotating inner cylinder. The case of a small-radius inner cylinder is considered. The fluid motion is described using a specific case of the Kelvin-Voigt model, often referred to as the Oskolkov model. This model is applicable to very dilute polymer solutions, where the retardation time is much smaller than the characteristic time of the problem and elastic forces are much smaller than viscous forces. The stability of the steady-state motion is investigated using a fully nonlinear approach by means of direct numerical simulation of a perturbation introduced as finite-duration white noise. Depending on the Reynolds number, the perturbation either decays or grows. The critical Reynolds numbers obtained for both Newtonian and non-Newtonian fluids are found to be in agreement with the predictions of the linear theory. It is also shown that an increase in the elastic forces makes helical perturbations more dangerous than their axisymmetric counterparts.
Read the full abstract

Optics

Programmable generation of optical skyrmions on a silicon photonic chip

Mingyuan Zhang, Xiaofu Pan, Wu Zhou et al. (+6 more)

Optical skyrmions, characterized by topologically stable and spatially varying polarization textures, show immense potential for robust optical communications and metrology. However, conventional methods for generating optical Stokes skyrmions rely on bulky free-space optics, strictly constraining both system miniaturization and dynamic reconfigurability. Here, we demonstrate the efficient and programmable generation of optical skyrmions and bimerons using a compact silicon photonic chip. By integrating a programmable Mach–Zehnder interferometer mesh with a multi-dimensional grating emitter, we dynamically control the amplitudes, phases, and polarizations of emitted fundamental and orbital angular momentum modes. This architecture allows on-demand electrical switching among a complete library of optical quasi-particle states, including Néel, Bloch, intermediate, and anti-type skyrmions and bimerons. Experimental full-Stokes polarimetry confirms high-fidelity polarization textures with near-unity skyrmion numbers. Our foundry-compatible platform translates complex topological light generation into simple voltage controls, paving the way for next-generation communication and sensing systems based on optical skyrmions.
Read the full abstract

All authors Mingyuan Zhang, Xiaofu Pan, Wu Zhou, Wenzhang Tian, Zengqi Chen, Yiou Cui, Yijie Shen, Yeyu Tong, Jianqi Hu

Physics and Society

Integrating adaptive human behavior into epidemic models with large language models

Yicheng Mao, Haoyang Li, Rob Deardon et al. (+1 more)

Infectious disease transmission is shaped by patterns of human interaction, which adapt as epidemic conditions change. Capturing these context-dependent behaviors remains a fundamental challenge for epidemic models. Here, we recast this challenge by using large language models (LLMs) to represent adaptive human behavior within mechanistic epidemic models. We operationalize this idea through Generative Adaptive Behavioral Layer for Epidemics (GABLE), which adapts LLMs to infer behavioral responses to epidemic and policy conditions and translates them into age-structured contact matrices coupled to a mechanistic epidemic model. Applied to COVID-19 in France, GABLE reproduced responses in population mixing and age-specific contact structures that remained epidemiologically informative. In short-term forecasting, LLM-generated contact matrices outperformed mobility-driven matrices derived from real-world mobility data, with the largest gains at longer horizons. GABLE also extends beyond forecasting to prospective policy evaluation by projecting behavioral and epidemic responses to candidate interventions before implementation. When supplied with subsequently implemented policies, GABLE reproduced epidemic trajectories and generated distinct responses to alternative policy timing and composition. By leveraging LLMs as a flexible behavioral layer, GABLE provides a framework for coupling context-sensitive behavioral generation with epidemic dynamics.
Read the full abstract

All authors Yicheng Mao, Haoyang Li, Rob Deardon, Hongru Du

Atmospheric and Oceanic Physics

Python-Fortran Hybrid Programming to Fuse AI and Physical Models: Examples of AI-LDA in climate and weather models (Hf2pMDA_v1.0)

Xianrui Zhu, Zikuan Lin, Shaoqing Zhang et al. (+12 more)

AI provides an unprecedented opportunity for advancing physics numerical modeling including data assimilation, which is a highly efficient and critically-important tool for advancing our understanding on Earth system and its applications. At the same time, deep incorporation of AI and physical modeling can make great driving to advance AI by injecting it rich physics from long time physics-based modeling development. However, since such physics models are conventionally coded in Fortran and AI algorithms usually are conveniently designed in Python, difficulties exist to directly incorporate AI algorithms into physics models, vice versa. Here, based on the F2PY protocol, we have developed a procedure that implements an infrastructure which conveniently conducts Hf2pMDA to form a program entity so that AI algorithms and physical models can invoke mutually. As examples, within Hf2pMDA, a climate coupled data assimilation (CDA) system is naturally upgraded to a strongly CDA (SCDA) system, and a 1 km high-resolution weather DA system is conveniently implemented within a multi-layer downscaling model that has multiscale DA in different nesting layers. In the climate SCDA system, a coupled general circulation model (CGCM) and a multiscale filtering algorithm is integrated by a Python main controller (PMC) that calls Fortran CGCM components and Weakly-CDA modules as well as a data-trained SCDA algorithm by latent space autoencoder in Python. In the high-resolution weather DA system, the downscaled model consisting of traditional Fortran DA modules in all mother domains and Python AE DA algorithm in the central child domain is integrated by a PMC that organizes these components. With convenient realization of deep incorporation of any AI algorithm and physics model, the Hf2pMDA has a great potential to make progress on both AI and scientific modeling.
Read the full abstract

All authors Xianrui Zhu, Zikuan Lin, Shaoqing Zhang, Zebin Lu, Songhua Wu, Xiangyun Hou, Zhisheng Xiao, Zhicheng Ren, Jiangyu Li, Jing Xu, Yang Gao, Rixu Hao, Xiaolin Yu, Mingkui Li, Guangliang Liu

Saturday 29 August

Optics

Reliable iToF Depth Sensing via Sensor-Intrinsic Uncertainty Modeling and State-Space Restoration

Yansong Du, Yutong Deng, Yuting Zhou et al. (+7 more)

Indirect time-of-flight (iToF) cameras provide compact and cost-effective dense depth measurements, but their ranging accuracy is often degraded by sensor-intrinsic uncertainty under practical imaging conditions. Spatially uniform or range-only Gaussian perturbations cannot accurately reproduce the range-dependent and signal-dependent noise characteristics of real iToF measurements, leading to a synthetic-to-real gap for learning-based restoration. To address this problem, we propose a joint depth-uncertainty modeling and restoration framework for reliable iToF sensing. A sensor-intrinsic depth-uncertainty model is first developed from calibrated tap responses, returned-signal levels, and sensor noise statistics through a depth-oriented weighted least-squares formulation. The resulting pixel-wise uncertainty is used for heteroscedastic depth synthesis and uncertainty-aware restoration supervision. Based on this heteroscedastic data synthesis, we further develop a U-shaped restoration network with Depth Visual State Space (DVSS) blocks, which combine long-range state-space modeling with convolutional spatial-channel refinement for structure-preserving depth recovery. Experiments on synthetic data and measurements captured by an in-house iToF prototype validate the proposed uncertainty model under varying range and returned-signal conditions. Controlled comparisons with fixed and range-aware Gaussian noise, together with evaluations on U-Net, Restormer, and DVSS, further demonstrate that the proposed synthesis consistently benefits different restoration backbones. The complete framework achieves 40.85~dB PSNR and 2.54 mm MAE on the synthetic test set, and 35.42 dB PSNR and 4.87 mm MAE on real iToF measurements.
Read the full abstract

All authors Yansong Du, Yutong Deng, Yuting Zhou, Zhancong Xu, Yingjia Lu, Mengdi Wang, Feiyu Jiao, Bangyao Wang, Zhaoxiang Jiang, Xun Guan

Classical Physics

The Schwitters Memorial Problem: A Car Speeds Across a Triangular Bump

William H. Press

Most drivers slow down for speed bumps, sometimes to almost a stop, as if each speed bump were a stop or yield sign. The late Roy Schwitters and I shared the view (here called the Schwitters Doctrine) that one should take the bumps at a speed of at least 60 or 70 kph (35 to 45 mph), not because we were scofflaws, but because we found, based on informal experiments, that the traverse was less jarring at high speeds than at low. Here, the problem is worked in terms of the geometry of the wheels on the road and two coupled, damped harmonic oscillators representing the suspension of the car and the driver's cushioned seat. The Schwitters Doctrine is recovered, but not in the way that one expects.
Read the full abstract

Classical Physics

Free Precession Revisited: A Vector-Only Analysis of Gyroscopic Dynamic Equilibrium

Dan I. Hariton

This paper presents a self-contained, vector-only formulation of gyroscope precession about a fixed pivot – gravity-driven, not the torque-free Euler-Poinsot case. The analysis uses only vector integrals, dot products, and cross products of intrinsic vectors: no tensor or dyadic formalism, no matrix representation, no Euler angles, and no component decomposition. Inertia enters through two mass integrals alone: the polar second moment of mass $J_0$ about the center of mass, and the vector operator $\vec F(\vec v)$, which carries directional inertia in place of an inertia tensor. Using material time derivatives referenced to the inertial observer, the torque about the pivot is assembled once from the complete acceleration of each mass element, giving an exact, unified vector equation for steady precession. The balance of the gravity torque against this inertia torque reproduces the classical steady-precession relation of the heavy symmetric top exactly at non-vertical tilts, on both the slow and fast branches, with the horizontal-shaft case exact rather than approximate. Closed forms are given for the disk, sphere, and circular and rectangular toruses. The constant tilt angle of dynamic equilibrium is explained as torque equalization: the two torques about the pivot balance exactly at that tilt and unequally on either side of it, treated throughout as a geometric function of the tilt under constant precession and self-spin rates, and never as a function of time. The formulation is informationally equivalent to the classical description; its contribution is methodological: economy of definition, a single algebra throughout, and geometric visualization preserved. The exact steady-precession relation predates this work; Brand obtained it in 1930. First derived by the author in 1975 and re-verified symbolically, it is intended for undergraduate readers, with every step retained.
Read the full abstract

General Physics

Cosmological Perturbations and Observational Constraints on Spinor Field Quintessence Dark Energy

Mahendra Goray

We investigate the linear perturbation cosmology of a spinor-field realization of quintessence dark energy by implementing the model in the Einstein–Boltzmann solver CLASS. The model parameters are constrained using a Markov Chain Monte Carlo analysis with Pantheon$^{+}$ Type Ia supernovae, cosmic chronometers, DESI DR2 baryon acoustic oscillations, redshift-space distortions, and Planck 2018 CMB distance-prior data. For the full combined dataset, we obtain $w_{\rm de}=-0.9710^{+0.0206}_{-0.0206}$, $\Omega_{m0}=0.2939^{+0.0047}_{-0.0047}$, and $H_0=66.23^{+0.55}_{-0.53},\mathrm{kms^{-1}Mpc^{-1}}$. The corresponding perturbation quantities are $\sigma_8=0.7537^{+0.0076}_{-0.0075}$ and $S_8=0.7459^{+0.0067}_{-0.0065}$. We find that the spinor-quintessence model closely reproduces the predictions of a phenomenological constant-$w$ model in the matter power spectrum, growth-rate observable $f\sigma_8$, growth index, and CMB temperature anisotropy spectrum, with deviations generally below the percent level. A comparison with $\Lambda$CDM and $w$CDM shows statistically indistinguishable fits, although the Bayesian information criterion favors the simpler $\Lambda$CDM model. Our results demonstrate that the spinor-field quintessence scenario remains consistent with current expansion-history and structure-growth observations when its perturbation evolution is treated consistently, providing a field-theoretically motivated realization of constant-$w$ dark energy at the background and linear perturbation levels.
Read the full abstract

Fluid Dynamics · Cross-listed from math-ph

Fock-Space Formulation of the Boltzmann Collision Operator for Maxwell Molecules

Ilya Karlin

We develop a representation-independent symmetric-Fock formulation of the nonlinear Boltzmann collision operator for Maxwell molecules. Starting from the standard velocity-space operator, we give a short derivation of Bobylev's Fourier identity and isolate its characteristic structure: two linearly related Fourier arguments followed by multiplication. We then prove, independently of collision geometry and of any coordinate realization, a canonical lift–fusion intertwining theorem: one-particle linear maps lift to the two incoming Fock legs and symmetric-algebra multiplication fuses them into a single outgoing state. Bargmann coordinates make this intrinsic construction especially transparent, but do not define it; Bobylev's collision maps subsequently select the Maxwell vertex from the already graded lift–fusion class. The resulting bilinear map obeys the exact grading \[ \widehat{\mathcal Q}(\mathscr H_p,\mathscr H_q)\subseteq\mathscr H_{p+q}, \] which gives an intrinsic origin for the triangular structures of Maxwell kinetics. Its one-vacuum restriction yields the complete Wang Chang–Uhlenbeck spectrum, while moment adaptation makes the nonequilibrium hierarchy strictly triangular and every finite compatible Fock jet an exact autonomous factor with global exponential relaxation. For the inhomogeneous problem, we extend realization covariance to the nonlinear two-leg vertex and evaluate the moving-frame connection independently through Hermite-function and Fourier realizations. The two routes give the same abstract Fock propagation and the same first Chapman–Enskog source; its traceless level-$2$ and vector level-$3$ sectors are relaxed by the exact Maxwell rates, giving $\Pr=2/3$. This provides an explicit computational demonstration that coordinate realizations may be chosen for economy without entering the structural Fock formulation.
Read the full abstract

Atmospheric and Oceanic Physics

Is the Atmosphere Really Such a Good Blanket?

Slavoljub Mijovic

The incorrect application of the current methodology for treating and averaging Earth's surface temperatures has contributed to contradictions and misinterpretations in different scientific disciplines, particularly in climate change and global warming research. The methodology previously proposed by the author addresses these shortcomings and provides a physically based framework for further analysis. This paper demonstrates that the contribution attributed to the atmosphere in determining the warming of the Earth's surface may be substantially overestimated, with the estimated effect differing by approximately 10 degrees Celsius from the conventional interpretation. The analysis is based on the ERA5 reanalysis dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), using hourly skin temperature data for 1950-2025 on a global grid of approximately 1.04 million cells representing the Earth's surface. The proposed method enables an absolute assessment of global warming, confirms the long-term warming trend, and provides a comparative analysis with results obtained using the conventional methodology.
Read the full abstract

Optics

Artificial Intelligence in a Photonic Temporal Processor

Youlve Chen, Jinlong Xiang, Yimin Hu et al. (+13 more)

Optical neural networks (ONNs) promise high-throughput and energy-efficient artificial intelligence, yet essentially all implementations so far encode information across space either in free-space arrays or in integrated waveguide meshes, tying the number of neurons to the number of physical components and fixes the routing topology at fabrication. Here we show that moving the computation into time decouples computational dimension from hardware dimension. Exploiting space-time duality, we implement optical diffraction and interference entirely in time domain, using thin-film lithium niobate modulators as time lenses and temporal masks, with chromatic dispersion providing the coupling between successive temporal neurons. We experimentally verify high-order, complex-valued matrix-matrix multiplications using just a single optical input/output port, scaling the computational dimensions far beyond the channel count. By incorporating optical feedback, we extend this platform into versatile neural networks, where the network layers, neuron numbers, and synaptic connections are fully programmable and in-situ trainable. Our temporal diffractive neural networks are successfully validated on various classification benchmarks, alongside image and video generation tasks. Notably, using this platform we demonstrate an all-analogue generative pipeline in which the latent variable is drawn directly from amplified spontaneous emission, so that no digital sampling or electronic modulation appears anywhere in the generative path. Furthermore, high-resolution images and videos are generated at high frame rates, outperforming state-of-the-art modulator-refresh-limited optical generative systems. These results establish a unified photonic temporal computing framework, providing a scalable and deployable pathway toward next-generation machine intelligence.
Read the full abstract

All authors Youlve Chen, Jinlong Xiang, Yimin Hu, Yuchen Yin, Chaojun Xu, Zhengshun Lei, Xin Wang, Yufeng Zhang, Yixiao Zhu, Qunbi Zhuge, Junwen Zhang, Wei Chu, Tao Lin, Yikai Su, Zhipei Sun, Xuhan Guo

Computational Physics · Cross-listed from cond-mat.mtrl-sci

Elastic properties of amorphous LiTaCl$_6$ solid-state electrolyte

Xiaolin Liu and De-en Jiang

Amorphous solid-state electrolytes are attractive candidates for safe, high-energy-density all-solid-state batteries, yet their mechanical properties remain poorly understood from a computational perspective. Here, we investigate the elastic behavior of the recently discovered amorphous superionic Li-ion conductor LiTaCl$_6$ using density-functional-theory (DFT)-based methods, including unrelaxed static, relaxed static, and strain fluctuations from molecular dynamics (MD) simulations in the isobaric–isothermal (NPT) ensemble with DFT-trained machine-learning force fields (MLFFs). While the unrelaxed static method predicts a Young's modulus an order of magnitude higher than the experiment, the relaxed static method—commonly applied to crystalline electrolytes—still overestimates the modulus by more than 170%. In contrast, the MD approach using MLFFs yields a Young's modulus of $2.84 \pm 0.26$ GPa, which quantitatively agrees with the experimental value of $2.91 \pm 0.32$ GPa. Using the MLFF-MD approach, we further predict bulk modulus (4.44 GPa), shear modulus (1.02 GPa), and Poisson's ratio (0.39) for amorphous LiTaCl$_6$ and conclude that elastically it behaves like a soft polymer or gel. These results demonstrate that amorphous superionic materials possess some unique elastic properties and that, among the methods examined, only the MLFF-MD approach yields quantitative agreement with experiment, highlighting the necessity of a dynamical treatment to simulate their elastic response, consistent with recent findings for crystalline superionic conductors.
Read the full abstract

Plasma Physics · Cross-listed from astro-ph.HE

Rapid Energy Dissipation by Colliding Waves in Strongly Magnetized Plasmas

Tianshu Wu, Xinyu Li and Yangyang Cai

Rapid dissipation of magnetic energy in highly magnetized environments around neutron stars and black holes is a key open question in high-energy astrophysics. We develop a general kinetic picture of counter-propagating wave collisions in magnetized pair plasmas for arbitrary polarizations and find that magnetic energy can be dissipated on the wave-crossing timescale. The two magnetohydrodynamical conditions on the field invariants, $I_1\equiv B^2-E^2>0$ and $I_2\equiv \mathbf{E}\cdot\mathbf{B}=0$, can be spontaneously violated during the collision. Parallel electric fields develop to screen nonzero $I_2$ with little energy loss, consistent with the evolution described by Force-Free Electrodynamics. When magnetic dominance is lost, strong particle energization is triggered, dissipating magnetic energy on the wave-crossing timescale. This dynamical process yields a rapid dissipation channel of magnetic energy and provides a kinetic pathway to high-energy emission.
Read the full abstract

Classical Physics · Cross-listed from quant-ph

Quantum Mechanics as a Relativistic Statistical Theory: A Mass-Shell Factorisation Approach

Mark Everitt

Spinor structure is usually introduced as part of relativistic quantum theory. We show that its underlying algebra can instead emerge without quantisation from a covariant statistical description of a massive relativistic particle subject to an explicit finite-dimensional linear factorisation of the complete massive mass-shell constraint motivated by requiring the theory retain both sheets of the massive mass shell. A finite-dimensional factorisation of the complete mass-shell constraint, linear in all four momentum components, forces a Clifford algebra. In (3+1) dimensions its minimal complex representation is four-dimensional, while each on-shell factor selects a rank-two sector; in this representation statistical completeness requires an arbitrary $2\times2$ matrix distribution within that sector before quantisation. Projecting the Weyl-ordered matrix Liouvillian gives relativistic transport while preserving all internal populations and coherences. For universal deformations on flat canonical phase space satisfying the stated covariance, matrix-neutrality, homogeneity and associativity assumptions, the resulting product is the matrix Weyl–Moyal product. Its parameter has dimensions of action and, when identified with $\hbar$, supplies the scale of physical spin-$\tfrac12$. Requiring all-order constraint preservation gives a vanishing star commutator, while preservation of the selected star-spectral sector yields the two-sided Dirac–Wigner equations. Our central conclusion is therefore that relativistic mass-shell factorisation supplies spinor structure, while completion of the constraint-preservation hierarchy within the stated deformation class leads to the Weyl–Moyal phase-space formulation of quantum mechanics.
Read the full abstract

Chemical Physics

Transition states and dynamical bottlenecks in the Li-NC <-> Li-CN isomerizing reaction with the Lagrangian betweenness

P. García-Cuadrillero, F. Revuelta, R. M. Benito et al. (+1 more)

We study the vibrational dynamics that is responsible for Li-NC <-> Li-CN isomerization reaction using the Lagrangian betweenness, a tool recently developed to identify dynamical bottlenecks in the context of oceanographic transport. Following the spirit of the betweenness-centrality metric, which efficiently identifies the nodes that act as bottlenecks in complex networks, the Lagrangian betweenness is similarly capable to identify bottlenecks in dynamical systems. On the one hand, in this paper we show the ability of the Lagrangian betweenness to identify transition states, which are short-lived states that are formed at the top of the energetic barrier that the system must surpass in order to transition the reaction from the (initial) reactants to the (final) products. On the other hand, we also demonstrate that the Lagrangian betweenness is also able to identify other dynamical bottlenecks, and phase-space invariant structures such as manifolds, chains of islands and invariant tori, which are also responsible for the intricate vibrational dynamics of the system.
Read the full abstract

All authors P. García-Cuadrillero, F. Revuelta, R. M. Benito, F. Borondo