Peer Revenue Past citations are no guarantee of future returns

Papers

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

Physics Physics

physics Watch Physics

Tuesday 10 March

History and Philosophy of Physics

The Architecture of Inter-Level Representation

Harry Sticker

Inter-level connections in science routinely require constructs that neither of the connected theories contains. Statistical mechanics requires assumptions such as the Stosszahlansatz to generate thermodynamic irreversibility - assumptions that Hamiltonian mechanics cannot provide. Quantum chemistry offers four incompatible analyses of chemical bonding for the same quantum state, none of which are selected by the Schrodinger dynamics. Molecular genetics has not converged on a stable definition of the gene despite decades of molecular detail. These are not isolated anomalies but instances of a common architectural pattern. The missing apparatus is the bridge theory: a third theoretical role that connects a dynamical theory to an observational theory through a many-to-one inter-level map. That map generates the contingent space - the set of dynamical states compatible with an observational description but not selected by it - whose geometry neither connected theory determines. Completing the bridge theory requires three conditions in order: a Partition that defines observational equivalence classes; a Magnitude that characterizes the geometry and scale of the contingent space; and a Closure that selects or weights its elements. The framework yields an objective distinction between closing and introducing rules, formalized by the Mirror Test, and supports a tripartite taxonomy of emergence. It explains why some inter-level disputes persist and what would be required to resolve them.
Read the full abstract

Fluid Dynamics

Swirl flow in microchannels: patterned slip walls enhance heat transport

L. G. Chej, M. F. Carusela, A. G. Monastra et al. (+2 more)

Microchannel heat sinks (MCHS) are widely used for thermal management in high-power electronics due to their ability to dissipate large heat fluxes with minimal coolant consumption. While numerous strategies - such as geometric modifications, surface disruptions, and enhanced coolant formulations - have been explored to improve heat transfer, many of these approaches increase hydraulic resistance and pumping power requirements. Recent studies have shown that slip/no-slip wall patterns can enhance flow rates and convective heat removal without additional energy input, and that patterned microstructures can induce secondary swirling motions known to promote mixing and heat transfer. Motivated by these findings, we investigate a slip/no-slip pattern specifically designed to generate swirl flow inside a straight microchannel. Building upon prior work on passive chaotic advection and boundary-condition engineering, we assess the hydrodynamic and thermal performance of this patterned configuration under conditions relevant to laminar microchannel cooling. Our results demonstrate that appropriately arranged slip/no-slip regions can induce swirl without geometric perturbations or increased pumping power, ultimately improving heat transfer efficiency at fixed volumetric flow rate. This study highlights the potential of boundary-condition patterning as a simple, energy-neutral strategy for enhancing the performance of microfluidic heat-transfer devices.
Read the full abstract

All authors L. G. Chej, M. F. Carusela, A. G. Monastra, J. Harting, P. Malgaretti

Biological Physics · Cross-listed from q-bio.NC

A Variational Latent Equilibrium for Learning in Neuronal Circuits

Simon Brandt, Paul Haider, Walter Senn et al. (+2 more)

Brains remain unrivaled in their ability to recognize and generate complex spatiotemporal patterns. While AI is able to reproduce some of these capabilities, deep learning algorithms remain largely at odds with our current understanding of brain circuitry and dynamics. This is prominently the case for backpropagation through time (BPTT), the go-to algorithm for learning complex temporal dependencies. In this work we propose a general formalism to approximate BPTT in a controlled, biologically plausible manner. Our approach builds on, unifies and extends several previous approaches to local, time-continuous, phase-free spatiotemporal credit assignment based on principles of energy conservation and extremal action. Our starting point is a prospective energy function of neuronal states, from which we calculate real-time error dynamics for time-continuous neuronal networks. In the general case, this provides a simple and straightforward derivation of the adjoint method result for neuronal networks, the time-continuous equivalent to BPTT. With a few modifications, we can turn this into a fully local (in space and time) set of equations for neuron and synapse dynamics. Our theory provides a rigorous framework for spatiotemporal deep learning in the brain, while simultaneously suggesting a blueprint for physical circuits capable of carrying out these computations. These results reframe and extend the recently proposed Generalized Latent Equilibrium (GLE) model.
Read the full abstract

All authors Simon Brandt, Paul Haider, Walter Senn, Federico Benitez, Mihai A. Petrovici

Fluid Dynamics · Cross-listed from astro-ph.GA

The statistics and structure of dissipation in subsonic and supersonic turbulence

Edward Troccoli and Christoph Federrath

Turbulence plays a critical role in the atmosphere, oceans, engineering, and astrophysics. The dissipation (heating) induced by turbulent flows is particularly important for the thermodynamics and chemistry of interstellar clouds, yet its structure and statistics remain poorly understood. Using high-resolution turbulence simulations with controlled explicit viscosity, we study the kinetic energy dissipation rate, $\varepsilon_{\mathrm{kin}}$, across subsonic and supersonic regimes. We find that dissipation lags large-scale kinetic energy injection events by $1.64\pm0.21$ and $0.48\pm0.07$ turbulent turnover times in subsonic and supersonic turbulence, respectively. Correlations show $\varepsilon_{\mathrm{kin}}\propto\vert\nabla\times\mathbf{v}\vert^2$ (vorticity squared) in the subsonic regime, where density fluctuations are negligible, while in the supersonic regime dissipation is primarily correlated with density, $\varepsilon_{\mathrm{kin}}\propto\rho^{3/2}$. A spectral analysis demonstrates that achieving numerical convergence of $\varepsilon_{\mathrm{kin}}$ across all scales is challenging, especially in the subsonic case, even at $2048^3$ resolution. Nonetheless, subsonic dissipation is clearly localised on small vorticity-dominated scales, while supersonic dissipation spans many scales, combining elongated, thin shocks with small-scale vorticity. Finally, we determine the fractal dimension of $\varepsilon_{\mathrm{kin}}$. In the subsonic regime, intense dissipation is predominantly organised in flattened vortex filaments embedded in thin shearing layers on small scales, becoming more volume-filling at larger scales. In the supersonic regime, $\varepsilon_{\mathrm{kin}}$ exhibits a fractal dimension between 1 and 2 across nearly all scales, likely reflecting shock surfaces and their intersections forming filaments.
Read the full abstract

Optics

Vortex beams with tunable "all-with-visible-light" dye-doped liquid crystal q-plates for broadband application

Adrián Moya, Adriana R. Sánchez-Montes, Sergi Gallego et al. (+4 more)

The photoalignment technique for liquid crystal (LC) device fabrication, despite being a well-established method, remains of significant relevance because of its broad applicability. Among its applications, one of particular interest is the generation of structured light, specifically the manufacturing of Pancharatman-Berry (PB) devices, capable of generating optical vortices with angular momentum. In this work, we propose a thorough theoretical and experimental analysis of the optical response of dye-doped liquid crystal (DDLC) devices by examining their performance in terms of tunability and achromaticity across the whole visible spectrum, considering diattenuation effects and how they affect the efficiency of the devices. We experimentally demonstrate the fabrication of photoaligned devices in the visible range with 532 nm laser light and the robust generation of high-quality optical vortices, achieved by a straightforward and accessible technique using a commercial Variable Spiral Plate (VSP), avoiding the need for complex rotational systems or programmable spatial light modulators. Our results demonstrate that diattenuation effects do not prevent the functionality of the devices across the whole visible spectrum and with extended ranges of achromaticity.
Read the full abstract

All authors Adrián Moya, Adriana R. Sánchez-Montes, Sergi Gallego, Eva M. Calzado, Andrés Márquez, Inmaculada Pascual, Augusto Beléndez

Instrumentation and Detectors

CTPX1: A Highly Integrated and High-Throughput Data-Driven Camera Based on Timepix4

Qicai Li, Hongbin Liu, Xingfen Jiang et al. (+10 more)

The upgrade of the China Spallation Neutron Source (CSNS-II) will raise the proton beam power to 500 kW. Consequently, the existing Timepix3-based detector systems, limited to a count rate of 80 Mhits/s, will encounter severe saturation challenges. To address the demand of the Energy-Resolved Neutron Imaging instrument (ERNI) for next-generation higher count-rate electronics, this paper presents CTPX1, a high-performance data-driven camera system based on the Timepix4 ASIC. The system adopts a compact modular architecture, integrating readout electronics, a precision high-voltage bias unit, and a TEC temperature control subsystem. To fully exploit the readout potential of the Timepix4 ASIC's 16 high-speed serial links, this paper proposes a two-stage parallel processing architecture. This architecture achieves real-time data aggregation with a total bandwidth of up to 81.92 Gbps. Over a continuous 12-hour operation period, temperature fluctuations were kept within 0.1 {\deg}C while the high-voltage output noise remained below 1 mV. High-flux X-ray testing indicates that the system achieves a peak event readout rate of 1.17 Ghits/s, approaching the limit of the configured link speed. In-beam neutron verification at CSNS confirms that the camera successfully resolves fine spatial structures, achieving an imaging performance consistent with the 55 {\mu}m pixel pitch of the sensor. Furthermore, the clear observation of spectral features in the Time of flight (TOF) spectrum of a {\gamma}-Fe sample validates the system's good time resolution. This camera effectively addresses the data readout saturation challenges, validates the feasibility of Timepix4 technology for neutron imaging, and provides a viable solution for next-generation high-performance neutron imaging instruments.
Read the full abstract

All authors Qicai Li, Hongbin Liu, Xingfen Jiang, Jianrong Zhou, Yujie Zhou, Haoran Guo, Dongcheng Cai, Weile Gong, Yimie Yuan, Chengshuo Zhang, Shengxiang Wang, Yubin Zhao, Zhijia Sun

Computational Physics

A fast incompressible Navier-Stokes solver for non-uniform grids

Pedro Costa, Duarte Palancha, Joshua Romero et al. (+2 more)

We present a scalable incompressible Navier–Stokes solver for three-dimensional Cartesian grids with non-uniform spacing. A direct tensor-product–Thomas method solves the constant-coefficient Poisson and Helmholtz equations arising from pressure projection and implicit diffusion, without approximate factorization. On uniform grids, the method recovers the classical eigenfunction-expansion method evaluated with fast Fourier transforms (FFTs). On stretched grids, diagonal scaling symmetrizes the one-dimensional Laplace operators, and the resulting numerical eigenbasis transforms are evaluated as general matrix–matrix multiplications (GEMMs). FFTs and GEMMs can be selected independently in each diagonalized direction while retaining the pencil decomposition, collective transposes, and tridiagonal machinery of an established FFT-based solver. The elliptic solver is verified to round-off accuracy, and the complete flow solver is validated against benchmark flows. Against geometric multigrid and block cyclic reduction with FFT diagonalization, the present method achieves the lowest time-to-solution among the tested approaches; at fixed grid dimensions, its cost is insensitive to grid stretching. CPU and multi-GPU tests show that GEMM-rich variants attain higher strong-scaling efficiency by better amortizing communication. On a single GPU, the fully GEMM-based variant increases the Poisson cost by $2.8\times$ but the complete Navier–Stokes step cost by only $1.8\times$. Weak scaling exposes the trade-off: dense-transform costs grow with the global transform dimension, whereas non-uniform meshes can reduce the required number of grid points. The resulting open-source solver, CaNS-EIGEN, extends an FFT-based Navier–Stokes solver to large-scale simulations on grids stretched in multiple directions.
Read the full abstract

All authors Pedro Costa, Duarte Palancha, Joshua Romero, Roberto Verzicco, Massimiliano Fatica

Atomic Physics

Sensing Low-Frequency Field with Rydberg Atoms via Quantum Weak Measurement

Ding Wang, Shenchao Jin, Xiayang Fan et al. (+5 more)

Recently, Rydberg atom has emerged as an attractive choice to realize quantum sensing of low-frequency electric field. The progress so far has mostly utilized the intensity and phase changes in probe laser and the corresponding detection mechanism still remains classical. Nevertheless, external field acting on the Rydberg state can induce the polarization variation of probe laser in the Rydberg electromagnetically induced transparency (EIT) system embedded in realistic multi-state atoms. We experimentally observe this phenomenon and realize signal extraction by appropriately utilizing the polarization degrees of freedom. Based on such a mechanism, we further design and implement a quantum weak measurement scheme, which clearly suppresses the technical noise and leads to considerable improvement of performance. Evaluation of the sensitivities across different post-selection angles demonstrates that the weak measurement results agree well with the theoretical model predictions. The advantages of our method are analyzed from multiple aspects, including characterizing the responses over different frequencies and comparing the responses of the weak measurement scheme and the traditional transmission-based method. After accounting for the screening effect of a measured ratio 17% where the $^\text{87}$Rb atoms experience a substantially reduced field inside the glass cell, the performance reaches 33 $\mu\text{V}~\text{cm}^\text{-1}~\text{Hz}^\text{-1/2}$ in sensitivity and 1.0 $\mu\text{V/cm}$ in minimal detectable field for an integration time of 1000 s, as perceived by the atoms.
Read the full abstract

All authors Ding Wang, Shenchao Jin, Xiayang Fan, Hongjing Li, Jiatian Liu, Jingzheng Huang, Guihua Zeng, Yuan Sun

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

DFT calculations of magnetocrystalline anisotropy energy with fixed spin moment

Justyn Snarski-Adamski, Joanna Marciniak, Wojciech Marciniak et al. (+2 more)

The development of new-generation permanent magnets is based on experimental efforts and innovative theoretical tools for modeling magnetic properties. Magnetocrystalline anisotropy energy (MAE) - one of the main intrinsic properties of permanent magnets - can be calculated using density functional theory (DFT). However, MAEs determined with different exchange-correlation potentials can vary widely. We show how these seemingly contradictory results can be reconciled using the fully relativistic fixed spin moment (FR-FSM) method. This is because the equilibrium pairs [MAE, $m_s$] calculated with different exchange-correlation potentials overlap with the MAE($m_s$) curve determined from the FR-FSM method ($m_s$ denotes the spin magnetic moment). The FR-FSM method also enables the hypothetical maximum MAE value for a given material to be estimated. In the case of magnetic alloys, MAE(FSM) analysis allows the optimal alloying additions to be determined in order to improve the MAE value. The high independence of the MAE($m_s$) works well for exchange-correlation functionals such as LDA and GGA. However, it is not a universal measure and varies with changes in the value of the U parameter when using LDA+U or GGA+U functionals. Concluding, the framework we describe for MAE versus FSM calculations can be a useful tool in the design of new permanent magnets.
Read the full abstract

All authors Justyn Snarski-Adamski, Joanna Marciniak, Wojciech Marciniak, Justyna Rychły-Gruszecka, Mirosław Werwiński

Instrumentation and Detectors

Development of Readout Electronics for a High-Speed Event-Driven Neutron Imaging Detector Based on Timepix4

Qicai Li, Hongbin Liu, Dongcheng Cai et al. (+9 more)

As the Chinese Spallation Neutron Source enters Phase II, the increase in proton beam power will lead to a further boost in the intensity of pulsed neutron beams. To address the demand for higher event-rate readout electronics for energy-resolved neutron imaging detectors, we have developed a high-performance readout electronics system based on the Timepix4 chip. The prototype electronics system comprises a Timepix4 chip board and a high-performance digital board, which are interconnected through a custom FMC interface. The advantage of this system is its ability to achieve the full bandwidth readout of 160 Gbps for a single Timepix4 chip. The electronics system, based solely on a single ZYNQ-MPSOC chip, is capable of fully meeting the required performance specifications within a compact form factor of 8 cm x 30 cm. Furthermore, the system features a high-capacity external SODIMM memory interface (supporting up to 32 GB), which ensures stable data readout through a single 40 Gbps QSFP+ interface. As of the present moment, notable progress has been achieved, including the successful establishment of 16 data channels between Timepix4 and FPGA that operate error-free and stably at a speed of 5.12 Gbps, which is half of the maximum theoretical speed of 10.24 Gbps. The threshold standard deviation across all pixels is less than 50 e- after equalization. And the clear structural results obtained from X-ray experiments indicate that the functionality is essentially complete, allowing further testing.
Read the full abstract

All authors Qicai Li, Hongbin Liu, Dongcheng Cai, Haoran Guo, Xingfen Jiang, Haiyun Teng, Kai Wang, Xiuku Wang, Shengxiang Wang, Zhijia Sun, Yubin Zhao, Jianrong Zhou

Biological Physics · Cross-listed from cond-mat.soft

Impact of magnetic fields on polaron dynamics in low-dimensional systems

Larissa Brizhik and B.M.A.G. Piette

We study the impact of an external magnetic field on the long-range electron transport in quasi-one-dimensional materials, such as polypeptides, (semi-) conducting polymers and macromolecules, taking into account the electron-lattice interaction. At relatively strong electron-lattice interaction extra electrons get self-trapped in the deformation potential well and form stable bound states, called large polarons which in the continuum approximation are known as solitons. Here we do not use the continuum approximation but solve the system of discrete nonlinear equations numerically. We show that the impact of a magnetic field on polaron dynamics depends not only on the field strength, but also on the parameter values of the system which define the properties of solitons such as their energy, amplitude and width of localisation. We also study the impact of a magnetic field on a polaron created by a donor complex on a chain.
Read the full abstract

Instrumentation and Detectors

Optical calibration systems of the Pacific Ocean Neutrino Experiment

M. Agostini, A. Alexander Wight, M. Altomare et al. (+89 more)

This work presents the design and performance characterization of the optical calibration systems produced for the Pacific Ocean Neutrino Experiment (P-ONE), which target gain, energy and time calibration in the detector. These systems include novel light-pulse driver circuitry based on gallium nitride field-effect transistor technology and its application to directional and isotropic, self-monitoring optical calibration instruments. A total of 330 directional light pulsers and two isotropic, 17-inch calibration modules (P-CALs) were produced for the first P-ONE line. We present the designs and performance of both the directional and isotropic calibration devices and perform detailed optical characterizations of both full-production batches. In a wavelength range of $365 - 520\,$nm, our developed driver circuits achieve emission intensities up to $10^{11}\,$photons and pulse widths as small as $1.4\,$ns, respectively. Light-pulse drivers and self-monitoring electronics in the P-CAL were characterized using the same experimental setup, and the instrument's optical-isotropy design was optimized in combination with a dedicated GEANT4-based simulation framework. The optimized P-CAL achieves a simulated isotropy grade of $1.00 \pm 0.01$ across the entire $4\pi\,$solid angle range. These simulation investigations were explicitly confirmed by dedicated measurements in both air and water using two independent experimental setups, and we report the results. With this, a detailed performance estimate for deployed P-CAL modules in P-ONE was possible.
Read the full abstract

All authors M. Agostini, A. Alexander Wight, M. Altomare, K. Baş, N. Baily, P. S. Barbeau, A. J. Baron, S. Bash, C. Bellenghi, M. Boehmer, M. Brandenburg, P. Bunton, N. Cedarblade-Jones, B. Crudele, M. Danninger, T. DeYoung, A. Gärtner, J. Garriz, D. Ghuman, L. Ginzkey, T. Glukler, V. Gousy-Leblanc, D. Grant, A. Grimes, C. Haack, R. Hall, R. Halliday, D. Hembroff, F. Henningsen, M. Herle, O. Janik, H. Johnson, W. Kang, S. Karanth, T. Kerscher, S. Kerschtien, K. Kopański, C. Kopper, P. Krause, C. B. Krauss, N. Kurahashi, C. Lagunas Gualda, A. Lam, T. Lavallee, K. Leismüller, R. Li, S. Loipolder, C. Magee, S. Magel, P. Malecki, T. Martin, A. Maunder, C. Miller, N. Molberg, R. Moore, B. Nührenbörger, B. Nichol, W. Noga, R. Ørsøe, L. Papp, V. Parrish, P. Pfahler, J. Pflanz, B. Pirenne, E. Price, A. Rahlin, M. Rangen, E. Resconi, S. Robertson, M. F. Rodriguez-Pilco, D. Salazar-Gallegos, A. Scholz, L. Schumacher, S. Sharma, B. R. Smithers, C. Spannfellner, J. Stacho, I. Taboada, K. Tchiorniy, J. P. Twagirayezu, M. Un Nisa, B. Veenstra, M. Velazquez, L. von der Werth, C. Weaver, N. Whitehorn, B. Winnicky-Lewis, L. Winter, R. Wroński, J. P. Yañez, S. Yun-Cárcamo, A. Zaalishvili

Fluid Dynamics

Butter on a hot pan: self-regulating dynamics of melt-lubricated sliding

Edoardo Bellincioni, Simon Biermann, Jacco H. Snoeijer et al. (+2 more)

When solids melt while sliding down heated inclines, their motion is governed by a complex coupling between heat transfer, phase change, gravity and viscous dissipation. Despite relevance across a variety of domains, like kitchen physics, geophysics, tribology, and manufacturing, this coupled problem lacks understanding and quantitative experimental validation. Here we report experiments with ice and paraffin wax on a temperature-controlled ramp that achieve terminal velocities from 0.01 m/s to 2 m/s across wide parameter ranges. We develop a theoretical model that captures the self-regulating feedback between melt-layer thickness, sliding velocity, and heat transfer. Without any adjustable parameters, our model collapses all measurements, validating the fundamental mechanism and enabling predictions for analogous systems.
Read the full abstract

All authors Edoardo Bellincioni, Simon Biermann, Jacco H. Snoeijer, Leen van Wijngaarden, Sander G. Huisman

Physics and Society · Cross-listed from cs.SI

Stable Boundaries of Opinion Dynamics in Heterogeneous Spatial Complex Networks

Mats Bierwirth and Johannes Lengler

We investigate majority-vote opinion dynamics on Geometric Inhomogeneous Random Graphs (GIRGs), a powerful model for spatial complex networks. In contrast to classic coarsening dynamics where a single opinion typically achieves global consensus, our simulations reveal that sufficiently large, localized opinion domains do not disappear. Instead, they stabilize, leading to a persistent coexistence of competing opinions. To understand the mechanism behind this arrested coarsening, we develop and analyze a tractable mean-field model of the interface between two opinion domains. Our main theoretical result rigorously establishes the existence of a stable, non-trivial limiting distribution for the interface profile in a mean-field analysis. This demonstrates that the boundary between opinions is stationary, providing a mathematical explanation for how complex network geometry can support robust opinion diversity in social systems.
Read the full abstract

Instrumentation and Detectors

Recent application studies of an INTPIX4NA SOIPIX detector-based X-ray camera using an SiTCP-XG 10GbE-based high-speed readout system at KEK facilities

Ryutaro Nishimura, Noriyuki Igarashi, Daisuke Wakabayashi et al. (+10 more)

The Silicon-On-Insulator PIXel (SOIPIX) detector is a unique monolithic structure imaging device currently being developed by the SOIPIX group, led by the High Energy Accelerator Research Organization (KEK). Our detector team at the KEK Photon Factory (PF) has developed an X-ray camera based on the INTPIX4NA SOIPIX detector. This detector provides a sensitive area of 14.1 $\times$ 8.7 $\mathrm{mm^2}$, with 425,984 pixels arranged in an 832-column $\times$ 512-row matrix and a pixel size of 17 $\times$ 17 $\mathrm{\mu m^{2}}$, and offers high spatial resolution and excellent sensitivity under low-intensity X-ray conditions. The readout system used in the X-ray camera is developed at the PF. It is equipped with SiTCP-XG, a 10 Gb Ethernet network controller implemented on a field-programmable gate array, enabling high-frame-rate imaging at several hundred hertz. We are currently investigating the applicability of this X-ray camera in several experiments at KEK. Herein, we report three recent application studies: (1) X-ray zooming microscope optics using two Fresnel zone plates at PF AR-NE1A; (2) phase-contrast X-ray imaging system using a two-crystal X-ray interferometer at PF BL-14C; and (3) nondestructive lithium detection in Li-ion battery electrode materials using muonic X-rays at J-PARC MLF Muon D2.
Read the full abstract

All authors Ryutaro Nishimura, Noriyuki Igarashi, Daisuke Wakabayashi, Yuki Shibazaki, Yoshio Suzuki, Keiichi Hirano, Hiromi Miki, Akio Yoneyama, Hiroshi Sugiyama, Kazuyuki Hyodo, Izumi Umegaki, Koichiro Shimomura, Yasuo Arai

Optics

High-Resolution Multi-Target DOA Estimation for Resonant Beam Systems

Guangkun Zhang, Mingqing Liu, Wen Fang et al. (+3 more)

Direction of arrival (DOA) estimation technology offers a promising solution to address the sensing and positioning demands of Internet of Things (IoT) devices. Optical resonant beam systems (RBS), owing to their inherent characteristics of self-alignment, self-established energy focusing, and passive target sensing, make them naturally suited for {\color{blue}DOA} estimation in IoT scenarios. However, RBS suffer from limited angular resolution and a narrow field of view (FoV) in multi-target environments. To overcome these limitations, this paper proposes a high-resolution wide-field-of-view resonant beam DOA estimation system (RB-HWDOA). The RB-HWDOA integrates an optical spectrum-based DOA estimation algorithm (OSB-DOA), which leverages amplitude information in the two-dimensional Fourier spectrum of the resonant beam, {\color{blue}overcoming the resolution limit imposed by the beam size in spatial-domain methods}. Furthermore, we designed a {\color{blue}telescope} modulation (TM) structure to correct phase and direction mismatches, enabling a multi-Tx framework that focuses beams onto a common sensing module, thereby extending the effective FoV. Combined with the OSB-DOA algorithm, this design supports high-resolution DOA estimation for {\color{blue}multiple targets simultaneously over a wide FoV}. Simulation results show that OSB-DOA resolves angular separations down to $0.1^{\circ}$ across multiple resonant beams, remains robust under noise, {\color{blue}and the TM architecture enables multi-Tx integration for wide-FoV coverage}, making RB-HWDOA a scalable and efficient solution for passive multi-target DOA estimation in complex IoT environments.
Read the full abstract

All authors Guangkun Zhang, Mingqing Liu, Wen Fang, Mingliang Xiong, Yunfeng Bai, Qingwen Liu

Geophysics

Modeling resonance characteristics of the Chang'e-7 lander modulated by solar panel rotation under lunar south-pole thermal environment

Lei Zhang and Jinhai Zhang

The Chang'e-7 (CE-7) mission will deploy the first seismometer at the lunar south pole to detect moonquakes and probe lunar interior structures in 2026 winter. However, the lander's vibration response to the extreme temperature cycles of the polar environment remains unclear, complicating the analysis of noise sources in seismic records. Here, we developed a high-fidelity finite-element model of the CE-7 lander to characterize its resonant behavior under the coupled influence of solar panel rotation and extreme thermal variations. Numerical results reveal that the lander's fundamental frequency (~0.76 Hz) at room temperature drifts significantly between 0.64 Hz and 0.87 Hz when the outside temperature varies from -180 to +80 {\deg}C. This frequency drift is primarily driven by thermally induced stiffness changes in the solar array supporting bracket, whereas geometric reconfiguration due to rotation plays a secondary role. Crucially, this resonance band directly overlaps with the primary seismic observation window (usually <1.0 Hz). Sensitivity analysis further confirms that the fundamental mode remains structurally robust despite material property uncertainties. These findings establish an essential theoretical baseline for identifying and filtering lander-induced resonant noise, which will be immediately applicable upon the acquisition of the first in-situ seismic datasets from the south pole of the Moon, ensuring the high fidelity of accurate lunar interior detection.
Read the full abstract

Computational Physics

Infrared spectroscopy of protonated water clusters via the quantum thermal bath method and highly accurate machine-learned potentials

T. Baird, R. Vuilleumier and S. Bonella

The spectral features of water clusters provide important information on their structure and dynamics and can assist in deciphering the nature of the local environment of aqueous solutions in a variety of different conditions. Accurately capturing these features via numerical simulations is a non-trivial task that typically requires a sophisticated combination of high-level electronic structure methods and costly quantum dynamics techniques. We present results of molecular dynamics simulations of the IR spectra of protonated water clusters, ranging from the monomer to the tetramer, obtained via the combination of highly accurate machine-learned potential energy surfaces (PES) and dipole moment surfaces (DMS), and the quantum thermal bath (QTB) methodology which facilitates cost-effective inclusion of NQEs in molecular dynamics simulations. We compare our results with previous theoretical and experimental studies and show that this combination provides a significantly cheaper, yet still suitably accurate, alternative to more traditional computational approaches.
Read the full abstract

Atomic Physics

Commissioning of a fast fine-step electron-energy-scan system for electron-ion crossed-beams experiments

B. Michel Döhring, Alexander Borovik Jr., Kurt Huber et al. (+2 more)

We report on the commissioning of a fast electron-energy scan system for measurements of electron-impact ionization cross sections. The Giessen crossed-beams experiment employs a high-power electron gun which has been developed over recent years and which permits wide variations of the beam parameters. A multi-electrode design enables the decoupling of the electron energy from the electron density. The newly implemented control system, which governs the various electrode potentials, is described together with the salient technical features.
Read the full abstract

All authors B. Michel Döhring, Alexander Borovik Jr., Kurt Huber, Alfred Müller, Stefan Schippers

Optics

Probing mesoscopic nonlocal screening in van der Waals heterostructures with polaritons

Xuezhi Ma, Zhipeng Li, Ruihuan Duan et al. (+17 more)

Predictive optical modelling of van der Waals (vdW) heterostructures is critical for meta-optics, near-field photonics and quantum technologies. At their buried interfaces, charge transfer and spatially extended screening challenge local descriptions based on layer-by-layer stacking of fixed permittivity tensors. However, such nonlocal corrections have been established mainly for plasmonic systems at ångström-nanometre scales and are often assumed negligible on optical-wavelength scales. Here we challenge this view by uncovering a mesoscopic nonlocal screening regime, extending up to ~140 nm, at buried charge-transfer interfaces in transition-metal dichalcogenide/{\alpha}-molybdenum trioxide (TMDC/{\alpha}-MoO3) phonon-polaritonic heterostructures. Using phonon polaritons as an ultrasensitive probe, we quantify charge transfer from polariton-wavelength shifts and find a thickness-independent saturated response as {\alpha}-MoO3 is thinned. Rather than merely complicating optical modelling, this nonlocal saturation turns a design-level correction into an opportunity by yielding a transferable cross-material metric. Across more than 120 devices, this metric scales linearly with the work-function difference between the TMDC and {\alpha}-MoO3. We further identify a lattice-mismatch-set energy threshold for charge transfer, revising Anderson-type band alignment for vdW interfaces.
Read the full abstract

All authors Xuezhi Ma, Zhipeng Li, Ruihuan Duan, Zeyu Deng, Hao Hu, Mengting Jiang, Yueqian Zhang, Xiaoyuan He, Qiushi Liu, Qiyao Liu, Yuan Ma, Fengxia Wei, Jiayu Shi, Chunqi Zheng, Guangwei Hu, Ping Koy Lam, Chengwei Qiu, Yu Luo, Zheng Liu, Qian Wang

Fluid Dynamics

Flow Field Reconstruction via Voronoi-Enhanced Physics-Informed Neural Networks with End-to-End Sensor Placement Optimization

Renjie Xiao, Bingteng Sun, Yiling Chen et al. (+3 more)

(short version abstract, full in article)High-fidelity flow field reconstruction is important in fluid dynamics, but it is challenged by sparse and spatiotemporally incomplete sensor measurements, as well as failures of pre-deployed measurement points that can invalidate pre-trained reconstruction models. Physics-informed neural networks (PINNs) alleviate dependence on large labeled datasets by incorporating governing physics, yet sensor placement optimization, a key factor in reconstruction accuracy and robustness, remains underexplored. In this study, we propose a PINN with Voronoi-enhanced Sensor Optimization (VSOPINN). VSOPINN enables differentiable soft Voronoi construction for sparse sensor data rasterization, end-to-end fusion of centroidal Voronoi tessellation (CVT) with PINNs for adaptive sensor placement, and unified layout optimization for multi-condition flow reconstruction through a shared encoder-multi-decoder architecture. We validate VSOPINN on three representative problems: lid-driven cavity flow, vascular flow, and annular rotating flow. Results show that VSOPINN significantly improves reconstruction accuracy across different Reynolds numbers, adaptively learns effective sensor layouts, and remains robust under partial sensor failure. The study clarifies the intrinsic relationship between sensor placement and reconstruction precision in PINN-based flow field reconstruction.
Read the full abstract

All authors Renjie Xiao, Bingteng Sun, Yiling Chen, Lin Lu, Qiang Du, Junqiang Zhu

Applied Physics

Interface Engineered Moiré Graphene Superlattices: Breaking the Auger Carrier Multiplication Limit for Infrared Single-Photon Detection

Sichao Du, Ning Li, Zhufeng Pan et al. (+15 more)

Hot electrons undergo Auger scattering during their relaxation process has a multiplication effect,which can generate more electrons above the Fermi level, thus improving the efficiency of photoelectric signal conversion.However,the photo-current gain brought by the Auger carrier multiplication is generally limited with a value less than 5,due to the rapid recombination of photo-generated charge-carriers and the inherently low light absorption of two-dimensional materials.Herein,by twisting graphene to an interlayer angle of 10<sub>o</sub>,we report a layer-dependent electronic correlations leading to an efficient carrier multiplication gain of 10<sup>3</sup>.This is primarily offered by the additional localized density-of-states at interface of the bi-layer 10<sub>o</sub>,moire graphene,and the enhanced interlayer coupling of electron waves in a five-layer moire graphene superlattice structure.Therefore,we can harvest the hot electrons during their energy relaxation through a thermalized optical phonon bottleneck effect.It is this effect that promotes the accumulated hot electrons to achieve a maximum Auger scattering rate ~ 10<sup>10</sup>*ps<sup>-1</sup>*cm<sup>-2</sup>.Furthermore,the ballistic transport of these hot electrons and Schottky barrier from a 90 nm thick silicon-on-insulator (SOI) silicon effectively block the thermal noise,thus leading to a highly sensitive near-infrared detection characteristic.At a low incident light power of ~ 10<sup>-13</sup> W/cm<sup>2</sup>,the resulting signal-to-noise ratio is more than 100 dB.The strengthened electromagnetic interaction from highly thermalized optical phonon in stacked moire graphene is utilized in this work.The hot electron multiplication suggests the applicability of Van der Waals moire superlattice architecture for harvesting charge carriers,thus paving the pathway to design infrared single-photon avalanche detectors.
Read the full abstract

All authors Sichao Du, Ning Li, Zhufeng Pan, Munir Ali, Hengrui Zhang, Duokai Chang, Yuehang Zhang, Qiang Wen, Shuo Zhang, Hao Wu, Yunlei Sun, Qiuting Wang, Hao Xie, Chaohao Chen, Zhenyi Ni, Qiangbing Guo, Duo Xiao, Wen-Yan Yin

Atomic Physics

High-Order Matrix Numerov for Singular Potentials

Nir Barnea

The matrix Numerov method provides an efficient framework for solving the time-independent Schrödinger equation as a matrix eigenvalue problem. However, for singular potentials such as the Coulomb interaction, the expected fourth-order convergence deteriorates for low angular momenta due to the behavior of the potential near the origin. We show that this loss of accuracy originates from an implicit boundary assumption in the standard formulation. By incorporating analytic near-origin information into the discretized Hamiltonian, we derive simple boundary corrections that restore fourth-order convergence and can even produce higher convergence rates for $s$- and $p$-wave energies. The resulting scheme preserves the simplicity and computational efficiency of the original method while significantly improving its accuracy for singular potentials.
Read the full abstract

Fluid Dynamics · Cross-listed from astro-ph.SR

$\Lambda$ effect in rotating hydrodynamic convection

P. J. Käpylä

Context: Rotating anisotropic convection generates differential rotation in stellar convection zones. Aims: The main aim is to compute the non-diffusive contribution ($\Lambda$ effect) to angular momentum transport, described by Reynolds stress, from rotating turbulent convection. Methods: Rotating hydrodynamic convection is simulated in Cartesian geometry at different latitudes and rotation rates. Large-scale flows are suppressed such that the Reynolds stress is due to non-diffusive effects. Results: The radial angular momentum flux is downward (outward) for slow (fast) rotation. This is in contrast in prevailing theories in mean-field hydrodynamics where the radial transport is always downward. The outward transport at rapid rotation is due to thermal Rossby waves that manifest as elongated large-scale convection cells near the equator. The horizontal angular momentum flux is always equatorward, with increasing concentration toward the equator as in earlier Cartesian studies. The magnitudes of the $\Lambda$ effect coefficients are roughly an order of magnitude lower than in the case of anisotropically forced turbulence or in analytic theories. Conclusions: The current results highlight the tension between numerical simulations, widely used mean-field models, and solar observations. The mean-fields models have been remarkably successful in reproducing solar differential rotation but underlying assumptions regarding turbulence in these models seem to be at odds with 3D simulations. The current simulation results for the vertical (radial) angular momentum transport are in accordance with spherical shell simulations, where thermal Rossby waves are responsible for the generation of equatorial acceleration or solar-like differential rotation. Thermal Rossby waves are absent in the turbulence models of current mean-field theories and they have not been unambiguously detected in the Sun.
Read the full abstract

Atomic Physics

Saturated absorption and electromagnetically induced transparency of residual rubidium in dense cesium vapor

Armen Sargsyan, Anahit Gogyan and David Sarkisyan

In the sealed-off cesium vapor cell studied in this work, a residual rubidium fraction of approximately $\sim$1% was observed. We investigate the optical response of these trace Rb atoms in a sealed 1~cm long Cs-filled vapor cell. Despite the low concentration, laser excitation at 795~nm allows the observation of saturated absorption and electromagnetically induced transparency (EIT) resonances. The surrounding Cs vapor effectively acts as a buffer medium, reducing the Rb atomic velocity and increasing the interaction time with the laser field, which improves the EIT signal. The experiments are performed in an all-sapphire cell that can be heated up to 500$^{\circ}$C without window blackening, unlike conventional glass cells. From the measured spectra, Cs–Rb collisional cross sections are estimated. These results show that residual atomic species in high-temperature vapor cells can be exploited for spectroscopic and nonlinear-optical studies.
Read the full abstract

Optics

Trifolium nanocavity metasurfaces on single-crystal Au(111) for depth-tunable optical-variable reflection

Amos Sospeter Kiyumbi

Symmetry-broken plasmonic nanocavities provide a simple route to engineer reflective optical response in continuous-metal metasurfaces. Here, we report an experimental study of trifolium-shaped nanocavity arrays milled into single-crystal Au(111) microplates and characterized by white-light reflection spectroscopy in the visible–near-infrared. The structured Au surfaces exhibit broad but well-defined reflection bands and pronounced low-reflectance regions that differ strongly from flat gold. We show that the optical response is highly sensitive to groove depth: increasing the cavity depth from $300$ nm to $350$ nm induces a clear redshift ($\sim 63$ nm) of the dominant long-wavelength minimum band ($\lambda = 700-800$ nm) and reshapes the intermediate spectral profile. In addition, the trifolium geometry shows a measurable azimuth-dependent response under sample rotation, unlike the azimuthally invariant behaviour often associated with circular groove cavities. These experimentally demonstrated properties directly support application directions in reflective structural colour, compact colour filtering, frequency-selective reflective surfaces, and optical-variable anti-counterfeiting features.
Read the full abstract

Fluid Dynamics

Modelling wetting-bouncing transitions of droplet impact on random rough surfaces

Huihuang Xia, Yixiang Gan and Wei Ge

Droplet impact on rough surfaces is of critical importance to various applications, yet remains incompletely understood. The present work aims to uncover droplet impact dynamics on random hydrophobic surfaces using volume of fluid simulations. Random fractal surfaces with RMS roughness ranging from 2 to 50 micrometers were generated using the Weierstrass-Mandelbrot function. Three identifiable impact outcomes including no bouncing, complete bouncing, and bouncing with breakup have been identified as Weber number varies between 5.7 and 12.9 and RMS roughness varies between 0 and 50 micrometers. We examine the spreading, retraction, re-spreading, and breakup stages of the impact events under different velocity and surface morphologies conditions. Numerical simulations show that the maximum spreading factor decreases linearly as surface roughness increases. Two scaling laws have been proposed for droplet impact on surfaces with small and large roughness values, respectively. A key finding is that the droplet contact time remains constant, independent of both Weber number and surface roughness. The joint effect of Weber number and surface roughness governs the wetting-bouncing transition, with larger roughness delaying the transition. This work elucidates the mechanisms governing droplet impact dynamics on random rough surfaces, thereby providing new insights directly relevant to droplet-based applications.
Read the full abstract

Chemical Physics · Cross-listed from eess.SY

Safe or Slow? The Illusion of Thermal Stability Under Reduced-Velocity Nail Intrusion

Eymen Ipek, Oliver Korak, Georg Gsellmann et al. (+1 more)

This study investigates the effects of nail penetration speed on the safety outcomes of large-format automotive lithium-ion pouch cells. Through six controlled tests varying the speed of nail insertion, we observed that lower penetration speeds did not induce thermal runaway; instead, the cells exhibited self-discharge while the nail remained embedded. These findings suggest that penetration speed is a critical factor in the onset of thermal runaway, providing valuable insights for the development of safer battery systems and more effective safety testing protocols.
Read the full abstract

All authors Eymen Ipek, Oliver Korak, Georg Gsellmann, Andrey Golubkov

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

Ab initio simulation of the first-order proton-ordering transition in water ice

Qi Zhang, Sicong Wan and Lei Wang

Proton ordering in water ice is a paradigmatic order-disorder transition in a locally constrained system. The ice rules require exactly two hydrogens close to each oxygen, restricting the disorder to an exponentially large yet strongly correlated manifold of hydrogen-bond configurations. Within this constrained space, meV-scale energy differences drive the transition from disordered ice Ih to ordered ice XI, while distinct configurations are separated by eV-scale barriers. These barriers hinder equilibration in experiments, and efficient sampling of this space with the required energy accuracy has remained a long-standing challenge in simulation. We address this by combining a machine learning interatomic potential with loop updates that preserve the ice rules and continuous updates of atomic coordinates, enabling equilibrium sampling with ab initio accuracy and capturing configurational entropic effects. In systems of up to 360 water molecules, with over 10^6 samples retained per temperature point, the simulations reveal clear first-order transition signatures at 83 K: a negative Binder cumulant, a bimodal potential energy distribution, and a sharp step in the lattice aspect ratio. Nuclear quantum effects are estimated to lower the transition temperature by approximately 20 K, bringing the prediction closer to the experimental value of 72 K.
Read the full abstract

Physics and Society

Optimality as a Generative Principle for Network Structure

Guram Mikaberidze, Beso Mikaberidze and Dane Taylor

Most real-world networks have evolved or been engineered to optimize some function, yet a unified framework for studying optimal networks across domains is lacking. We introduce GradNet, an AI-enabled framework that treats network topology as a continuously differentiable object, enabling the design and study of networks that optimize structural and dynamical objectives amenable to automatic differentiation under realistic constraints. We derive general optimality conditions, including an equimarginal principle for linear budgets, that make optimized networks analytically tractable. Canonical network features emerge spontaneously from constrained optimization: maximizing Kuramoto synchronization under coupling budgets yields sparse, bipartite, frequency-disassortative networks; minimizing social tension in opinion dynamics reproduces the factional split in Zachary's karate club; and maximizing communication capacity in spatial quantum networks under distance-dependent costs recovers minimum spanning trees. GradNet thus serves both as a network design tool scalable beyond $10^5$ nodes and as a scientific probe of structure-function relationships.
Read the full abstract