Fluid Dynamics
Stability and nonlinear dynamics of three-layer viscous films inside a vertical cylindrical tube
David Halpern and Awa Traore
We investigate the dynamics and stability of three immiscible viscous
liquid layers coating the interior of a vertical cylindrical tube, a configuration relevant to stratified core–annular transport processes. A long-wave asymptotic analysis yields a coupled system of nonlinear
evolution equations governing the motion of the three interfaces. Linear stability analysis predicts a persistent long-wave instability, the capillary (Rayleigh–Plateau) instability of the air–core interface, together with secondary finite-wavenumber instability bands that emerge from interfacial coupling in certain parameter regimes. These stability characteristics depend sensitively on the layer thicknesses, viscosity ratios, and surface tension parameters, and include mode-switching associated with competing maxima in the dispersion relation. Nonlinear simulations reveal three distinct dynamical outcomes: saturation to finite-amplitude travelling waves, air-core closure through plug formation, and rupture of the intermediate
liquid layer while the air core remains open. The intermediate-layer rupture mechanism is unique to the three-layer configuration which has no analogue in one- or two-interface cylindrical film flows. Numerical continuation is used to compute branches of travelling-wave solutions and their associated limit points. Comparison with time-dependent simulations shows that travelling-wave branches successfully predict the transition from saturated waves to plug formation, but do not capture the distinct rupture mechanism associated with collapse of the intermediate layer.
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Classical Physics
Scalar-Longitudinal Radiation in Extended Electrodynamics with Multipole Theory and a Compensated Source Model
Natan Rentzber
Extended electrodynamics (EED) leaves the Lorenz gauge condition unimposed and treats the scalar combination $C=\nabla\cdot\mathbf{A}+c^{-2}\partial\Phi/\partial t$ as a dynamical field. For a conserved source with no scalar initial field, $C=0$ and the theory reduces to classical electrodynamics. A source with a nonzero local continuity anomaly has no Maxwell solution, but EED remains well posed and can support a scalar-longitudinal sector. For each radiating frequency of a localized source, the far field separates into the usual transverse Maxwell channel and a scalar-longitudinal channel with a longitudinal electric field, no
magnetic field of its own, and a co-propagating $C$ field. Under the field-only energy balance used here, the time-averaged fluxes add without interference. The scalar channel depends only on $\Lambda=\partial\rho/\partial t+\nabla\cdot\mathbf{J}$ and radiates when its moments at $k=\omega/c$ are nonzero. An all-orders multipole formula is derived for this flux. Bound polarization and magnetization sources conserve charge identically and cannot excite the scalar channel. A compensated polarized carrier with a globally neutral anomalous surface layer isolates the channel and gives its dipole flux in closed form. The connection between the adopted flux and a physical stress-energy tensor remains unresolved. These results are conditional predictions of EED and do not imply a failure of charge conservation in classical electrodynamics.
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Atomic and Molecular Clusters · Cross-listed from cond-mat.mtrl-sci
Dynamic Ensembles of Phosphine-Stabilized Gold Nanoclusters
Caitlin A. McCandler, Disha Sanwal and Jutta Rogal
Atomically precise phosphine-stabilized gold nanoclusters are commonly characterized by single-
crystal X-ray diffraction, yet the extent to which these static structures represent finite-temperature behavior remains unclear. To explore the free-energy landscapes,
equilibrium populations, and isomerization kinetics of these nanoclusters in the gas phase, we establish a general framework that combines molecular dynamics simulations based on a machine-learned interatomic potential with Markov state models (MSMs). Analysis of the MSMs indicates that experimentally reported
crystal structures frequently correspond to minor metastable states or transient configurations rather than the dominant finite-temperature structures. Increasing ligand coverage systematically alters both the thermodynamics and kinetics of structural rearrangements, driving the transition from planar to three-dimensional gold cores while accelerating isomerization dynamics. Moreover, catalytically accessible geometries are often only minor members of the
equilibrium ensemble, highlighting a trade-off between structural stability and surface accessibility. These results emphasize that ligand-protected nanoclusters need to be viewed as dynamic ensembles and their finite-temperature behavior cannot be fully captured by their corresponding crystallographic structures alone.
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Plasma Physics
Informing spectral models for dense plasmas with K-edge absorption measurements of warm dense copper
T. Cordova, E. V. Marley, D. A. Chin et al. (+14 more)
Warm dense matter remains a challenging regime to characterize experimentally and to model with predictive accuracy. Recent experimental platforms have been developed to generate, characterize, and diagnose uniform warm dense matter, enabling detailed comparisons with models. Here, we present experiments conducted at the OMEGA
laser facility that compress and heat a buried layer target to warm dense matter conditions, where the targets are heated to temperatures of approximately 20 eV and compressed to densities of 25 g/cm^3. We probe the warm dense
plasma using x-ray absorption spectroscopy, using the K-edge and bound-bound absorption features to constrain the temperature and charge state distribution of the
plasma. We compare these measurements with two types of models: collisional-radiative models with detailed electronic structure and ad-hoc density effects, and a multi-ion model based on density functional theory in combination with excited-state projector augmented-wave potentials. Neither approach fully reproduces the observed data, We show that the broad structure and position of the K-edge region can be modeled using density functional theory in combination with excited-state projector augmented-wave potentials. The density functional theory results are contrasted with a collisional-radiative model approach that incorporates ad-hoc density effects, which show incomplete agreement with the experimental observations, highlighting a need for improved density-dependent atomic modeling in warm dense
plasmas.
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All authors T. Cordova, E. V. Marley, D. A. Chin, R. A. London, S. B. Hansen, S. M. Vinko, J. E. Pask, H. A. Scott, H. P. Le, D. Aberg, M. K. G. Kruse, T. Döppner, F. N. Beg, J. Emig, P. M. Nilson, P. Sterne, M. J. MacDonald
Optics
Black-Box Coherence Matrix Eigen-Spectroscopy with Programmable Photonics
Kevin Zelaya, Jonathan Friedman and Mohammad-Ali Miri
The precise characterization of spatial optical coherence is fundamental to emerging applications in optical communications and computational imaging. However, extracting the full coherence
matrix traditionally requires phase-sensitive interferometry, which is highly vulnerable to environmental noise and poses severe scalability challenges for integrated photonics. Here, we introduce an architecture-agnostic framework for analyzing and controlling partially coherent light on programmable photonic
circuits. By leveraging the Schur-Horn
theorem, our approach systematically diagonalizes the incident coherence
matrix, relying solely on output intensity measurements and entirely circumventing the need for complex phase
retrieval. We experimentally validate this black-box protocol on a low-depth, non-universal photonic integrated
circuit, successfully reconstructing the hidden
eigenvalues of mixed states generated from up to four mutually incoherent sources. Furthermore, we demonstrate active, in-situ statistical light control by introducing non-
unitary amplitude modulation to significantly enhance interference visibility, exposing a fundamental physical trade-off between coherence enhancement and optical loss. Inherently resilient to hardware constraints and experimental noise, this scalable paradigm establishes a robust pathway for realizing ultra-compact, on-chip spatial coherence analyzers.
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Fluid Dynamics
Effect of Microscale Turbulent Structures Dynamics on Forced Convection in Turbulent Porous Media Flow
Ching-Wei Huang, Vishal Srikanth and Andrey V. Kuznetsov
The influence of microscale flow structures (smaller than the pore size) on turbulent heat transfer in porous media has not been yet investigated. The goal of this study is to determine the influence of the micro-
vortices on convection heat transfer in turbulent porous media flow. Turbulent flow in a homogeneous porous medium was investigated using Large Eddy Simulation (LES) at a Reynolds number of 300. We observed that the convection heat transfer characteristics are dependent on whether the micro-
vortices are attached or detached from the surface of the obstacle. There is a spectral correlation between the Nusselt number and the pressure instabilities due to
vortex shedding. A secondary flow instability occurs due to high pressure regions forming periodically near the converging pathway between obstacles. This causes local adverse pressure gradient, affecting the flow velocity and convection heat transfer. This study has been performed for obstacles with shapes of square and circular cylinders at porosities of 0.50 and 0.87. Understanding the dominant modes that affect convection heat transfer can aid in finding an optimum geometry for the porous medium.
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Atomic Physics · Cross-listed from quant-ph
Multipolar Light-Matter Hamiltonians in Symmetry-Breaking Photonic Vacuums
Liu Yang, Jiadu Lin and Qing-Dong Jiang
We show that the conventional multipolar
Hamiltonian is qualitatively modified when the photonic
vacuum breaks inversion or time-reversal
symmetry. By explicitly applying the Power-Zienau-Woolley transformation, we derive the resulting multipolar
Hamiltonians for two idealized
chiral photonic environments: a spatial-
chiral vacuum, which breaks inversion
symmetry, and a temporal-
chiral vacuum, which breaks time-reversal
symmetry. In the spatial-
chiral case, the transformation generates an inversion-breaking self-energy, whereas in the temporal-
chiral case it produces an additional Zeeman-like energy. Using a trapped hydrogen-like atom and a charged harmonic oscillator in cavities as minimal examples, we show that these
symmetry-dependent terms lead to characteristic spectral shifts. Our work provides a general framework for describing light-matter interactions in
chiral quantum electrodynamics and identifying the associated
symmetry-dependent effects on cavity-embedded atoms, molecules, and
quantum materials.
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Chemical Physics · Cross-listed from cond-mat.stat-mech
Quantum Rényi-Jarzynski Equality
Benjamin Bobell, Mert Okyay and Rahul Nandkishore
The Jarzynski equality provides a strict link between nonequilibrium work and
equilibrium free energy changes. Its typical
quantum formulations, however, rely on measurement protocols that destroy coherence. In this Letter, we use the resource-theoretic approach to derive a non-destructive
quantum Jarzynski equality conditioned on the outcomes of an arbitrary bath observable. This yields the Rényi-Jarzynski equality, which quantifies a finite bath's drift from
equilibrium under a non-adiabatic drive via the Rényi $k$-divergence. We further demonstrate that the Rényi-Jarzynski equality provides a tunable cost function for
quantum optimal control problems where minimizing bath drift is desired, such as state preparation and gate design, enabling the minimization of cross-talk in finite
quantum systems. Our toy model exhibits a transition between competing minima for some critical value of $k$, illustrating how the Rényi order tunes sensitivity to different regions of a bath distribution. Strikingly, when drive parameters vary across bath energy levels, minimizing bath drift requires generating system-bath
entanglement.
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Atomic Physics · Cross-listed from quant-ph
Thermal Throttling of Quantum State Transfer
Twesh Upadhyaya, T. C. Mooney, Yifan Hong et al. (+1 more)
Quantum state transfer on
qubit lattices is a crucial step in a panoply of
quantum information processing tasks. Understanding its fundamental limits in the presence of practical imperfections remains a pressing open question. In particular, it is unclear how thermal noise in the intermediate ancilla sites impedes transfer. In this work, we derive tight lower bounds on the necessary growth of commutator norms to achieve approximate state transfer. Specializing to 1D power-law systems with thermal ancilla states, we demonstrate that state transfer runtimes depend sensitively on the scaling of temperature with system size, improving logarithmic bounds to algebraic ones. Our work extends previous results on exact state transfer to the qualitatively different and more practically relevant regime of approximate state transfer.
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All authors Twesh Upadhyaya, T. C. Mooney, Yifan Hong, Alexey V. Gorshkov
Physics and Society
Rural Commute Patterns
Mohamed Khalafalla, Doreen Kobelo, Thobias Sando et al. (+1 more)
Transportation provides access to employment opportunities and essential services such as healthcare services, while urban areas have various transportation options, the situation differs in rural areas. Rural residents often have longer commute distances, limited access to public transit, and extended waiting times for public transportation if they exist, which can significantly impact their access to vital services and job opportunities. This study used data from the 2017 NHTS survey to examine the commuting patterns in rural areas by utilizing multinomial logistic regression to determine how various factors impact the choice of mode of transport in rural areas. Findings from this study revealed a higher dependency, 92.1%, on using personal vehicles when making trips in rural areas. Multinomial logistic regression results showed that socio-demographics, household, and trip characteristics affect the mode of transport used in a trip. Older adults, females, and individuals with higher education levels than high school graduates are less likely to use public transit when making trips. For household characteristics, the availability of vehicles in a household and households with higher income levels have lower probabilities of making a trip using public transit. Longer trip distances reduce the likelihood of a trip using active commuting modes such as walking and biking. These findings provide insights into understanding the transportation behaviors in rural areas and provide knowledge to be used in the planning and developing of transportation projects to promote equitable and accessible transportation in rural areas.
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All authors Mohamed Khalafalla, Doreen Kobelo, Thobias Sando, Janeroza Matyeni
Popular Physics
The 1908 Tunguska event in data of the nearest weather station
Andrei Ol'khovatov
This paper is a continuation of a series of works, devoted to various aspects of the 1908 Tunguska event. In this paper data is discussed from a weather station in the settlement of Kezma. This weather station was the nearest one to the epicenter of the 1908 Tunguska event. The station was about 215 km southwards from the epicenter. Also eyewitness accounts from Kezhma and some places on the Angara River are considered. The paper demonstrates the diversity of optical manifestations of the 1908 Tunguska event reported from Kezhma and its surroundings. A note by the observer of the weather station in Kezhma, concerning, in particular, the appearance of the two huge fiery circles is very important. The weather log of the weather station shows that the Tunguska event occurred during the sharp increase in cloud cover and deteriorating weather. At the beginning of July, rains and thunderstorms, including hail, began according to the weather log. In the opinion of the author, the data of the Kezhma weather station and the eyewitness accounts are in agreement with the geophysical interpretation of the 1908 Tunguska event. In any case, the meteorological factor is an important aspect of the Tunguska event, and so it deserves detailed research.
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Atomic and Molecular Clusters · Cross-listed from cond-mat.quant-gas
Electrostriction in a Bose-Einstein Condensate of Dipolar Molecules
Haneul Kwak, Ian Stevenson, Weijun Yuan et al. (+5 more)
The recent creation of a Bose-Einstein condensate (BEC) of dipolar molecules has opened a new frontier for many-body
quantum systems in which dipolar interactions can drive novel self-organization phenomena. Here, we observe electrostriction in a molecular BEC, an elliptical deformation driven by anisotropic dipolar interactions. We use double microwave dressing, involving $\sigma$- and $\pi$-polarized fields, to control non-axially symmetric dipolar interactions. We compare the experimental observations of electrostriction to a model based on an extended Gross-Pitaevskii equation and find excellent agreement in the regime of weak to moderate interactions. Using electrostriction, we demonstrate that the molecular BEC can be torqued by dynamically changing the orientation of the elliptical $\sigma$ microwave field. This provides a route to setting molecular
quantum gases into rotation, opening opportunities to probe vorticity, superfluidity, and supersolidity in strongly dipolar matter.
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All authors Haneul Kwak, Ian Stevenson, Weijun Yuan, Siwei Zhang, Asaf Toprakci, Lin Su, Tijs Karman, Sebastian Will
Optics · Cross-listed from astro-ph.IM
Effects of manufacturing tolerances on the performance of metamaterial microwave anti-reflection coatings
Rustam Balafendiev, Miranda Eiben and Jon E. Gudmundsson
Metamaterial anti-reflection coatings (ARC) are used in a variety of applications, including: lenses, filters, and absorbers. Typically, the design of a given ARC is done within an infinite medium approximation, which presupposes that every unit
cell on the interface is identical. However, in realistic applications, the geometry of a given ARC usually has some degree of variability, be it due to the shape of the surface inherent to the application, like in a lens, or manufacturing tolerances. This variation may alter the performance of the optical element in unanticipated ways, by creating additional scattering, enabling diffractive maxima that would normally be absent and, most crucially, changing the transparency of the ARC as a function of frequency. In this work we utilize full-wave modeling of finite samples of plastic which are matched with free space using a metamaterial ARC on both of their interfaces. By adding a degree of randomness to the ARC geometry we attempt to characterize the extent to which a given variation affects the expected performance of an ARC.
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Atmospheric and Oceanic Physics
Interpretable AI predicts a 2026 summer dry anomaly in central China
Anran Wang, Wen Shi, Yong Luo et al. (+5 more)
Seasonal precipitation anomalies are largely regulated by atmospheric circulation, which dynamical models predict with greater reliability than precipitation itself. Here, we employ a deep learning model that translates dynamical circulation predictions into precipitation estimates. Predictions initialized from March to May consistently indicate a dry anomaly over central China in summer 2026. Retrospective evaluations revealed higher predictive skill in the analogue years, which also tended to feature central equatorial Pacific warming persisting from the preceding winter into summer. This warming favors an anomalous cyclonic circulation over the western North Pacific-South China Sea-South China region, which induces northerly winds and moisture divergence that jointly suppress rainfall over central China. Supporting this mechanism, layer-wise relevance propagation (LRP) independently identifies these northerly winds as the dominant driver of the prediction among all model inputs. Perturbation tests supported this attribution: removing LRP-identified features effectively eliminates the dry anomaly. Our framework thus provides physically interpretable explanations for AI-derived regional
climate projections, facilitating evidence-based assessment before observational data become available.
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All authors Anran Wang, Wen Shi, Yong Luo, Jianbin Huang, Lijuan Chen, Junhu Zhao, Weixin Jin, Huihui Yuan
Instrumentation and Detectors
Characterisation of Commercially Available NUV-MT Silicon Photomultipliers
T. Avgitas, Z. Balmforth, I. Manthos et al. (+2 more)
Silicon Photomultipliers (SiPMs) based on NUV-MT technology offer improved photo-detection efficiency and reduced correlated noise compared to earlier designs, making them increasingly attractive for particle and astroparticle physics applications. We present a systematic characterisation of commercially available Broadcom AFBR-S4N series NUV-MT SiPMs over a wide range of temperatures and overvoltages, from -85oC to 23oC and from 10-16V overvoltage (VoV). Key performance parameters are measured, including breakdown voltage, gain, signal-to-noise ratio, dark count rate, afterpulsing probability, and both internal and external optical crosstalk. At 12Vov and 23oC a dark noise of 107.2+/-2.1 kcps/mm^2 is measured, consistent with manufacturer specifications. At 12Vov and -30oC the measurements yielded an average dark noise of 1.69+/-0.12 kcps/mm^2, an average gain of (6.88+/-0.15)x10^6, an average signal to noise ratio of 13.6+/-0.9, an average afterpulsing probability of (0.59+/-0.06)%, an average direct crosstalk probability of (26.49+/-0.28)%, an average delayed crosstalk probability of (0.72+/-0.10)%, and an average external crosstalk probability of (0.10+/-0.04)%.
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All authors T. Avgitas, Z. Balmforth, I. Manthos, K. Nikolopoulos, C. Toukmenidis
Geophysics
Effect of style of faulting on the probabilistic characterization of directionality of horizontal response spectral ordinates
Nathan Girmay and Eduardo Miranda
Horizontal earthquake ground motions exhibit substantial changes in amplitude with changes in orientation. While the effects of style of faulting on central tendency measures of ground motion intensity such as RotD50 are well established in ground motion models, less
attention has been given to how faulting mechanism influences the complete directional characteristics of ground motions. This study addresses this gap by conducting a comprehensive probabilistic characterization of ground motion directionality for strike-slip and reverse-slip earthquakes using 3,862 records with moment magnitudes greater than five. Two directionality parameters were examined across 58 oscillator periods ranging from 0.01 to 10 s. The directionality parameters examined consist of pseudo-acceleration response spectral ordinates at all non-redundant orientations normalized by either RotD100 or RotD50 intensities (denoted as {\eta} and {\nu}, respectively). Nonlinear regression was used to develop mechanism-specific models for the
geometric mean, logarithmic standard deviations, and full probability distributions of these parameters. Results show that strike-slip earthquakes exhibit notably different directionality compared to reverse-slip earthquakes, particularly at longer periods. Strike-slip earthquakes are, on average, 1% to 44% more polarized than reverse-slip earthquakes at periods above 0.5 s, and have RotD100/RotD50 ratios that are 1% to 3.7% larger. The developed models enable engineers and engineering seismologists to obtain mechanism-specific estimates of pseudo-acceleration response spectral ordinates at specific orientations, for applications such as regional seismic risk assessments and orientation-specific probabilistic seismic hazard analyses.
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Instrumentation and Detectors
Identifying Cost-Favorable Locations for Cosmic Explorer
Laurence Datrier, Geoffrey Lovelace, Tooba Ansar et al. (+19 more)
Cosmic Explorer (CE) is a proposed next-generation gravitational-wave observatory that aims to extend our gravitational-wave
vision to the edge of the observable universe. With a foundation of technology proven by the National Science Foundation's
Laser Interferometer Gravitational-Wave Observatory (LIGO), CE will observe black holes and
neutron stars across
cosmic time, explore the nature of extreme matter with high fidelity, and probe the nature of
gravity and fundamental physics. CE's reference design consists of two widely separated L-shaped detectors to be located in the conterminous United States, one with 20 km arms and one with 40 km arms. As of 2026, CE is in its design and site evaluation phase, with plans to begin observing in the early 2040s together with the Einstein
Telescope in Europe. The size of CE observatories—up to an order of magnitude larger than the 4 km LIGO observatories—presents a significant challenge for identifying suitable candidate sites where CE will achieve its science goals, be built within cost boundaries, attract and retain a workforce, and align with community values. In this paper, we report on the design and use of a Python package, the
Cosmic Explorer Location Search (CELS) package, to identify cost-favorable sites for CE. For a specified detector location and L-shaped geometry in the conterminous United States, CELS estimates site-preparation costs associated with excavation, land clearing, and land acquisition, while accounting for the scientific effects of detector tilt, arm length, and arm opening angle. After describing the package's methods, we present results for a national-level cost and positioning analysis that complements a recent national suitability analysis. We also discuss how future improvements to CELS will allow deeper, more local studies as the
Cosmic Explorer team narrows its list of potential locations.
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All authors Laurence Datrier, Geoffrey Lovelace, Tooba Ansar, Lance Blagg, Warren Bristol, Matthew Evans, Chris Lukinbeal, Vuk Mandic, Kiet Pham, Jocelyn Read, Sarmad Rameez, Amber Romero, Oscar Romero, Babatunde Isaac Rotimi, Joshua B. Russell, Andrew Saenz, Francois Schiettekatte, Robert Schofield, David H. Shoemaker, Bretton Simpson, Bram J.J. Slagmolen, Joshua R. Smith
Biological Physics
Elongation suppresses rheotaxis and enables microfluidic enrichment of e̱ta}-lactam-resistant bacteria
Ran Tao, Nathaniel C. Esteves, Jay Zhu et al. (+1 more)
Antimicrobial resistance (AMR) complicates the treatment of diseases including lung and urinary tract infections (UTIs), which are among the most common bacterial infections worldwide. Motile pathogens can use rheotaxis to swim upstream against fluid flows, potentially promoting access to upper regions of anatomical tracts. However, it remains unclear how antibiotic exposure and resistance influence this transport process. Here, using single-
cell tracking microscopy, we investigate how elongation induced by e̱ta}-lactam antibiotics affects the rheotactic migration of E. coli in confined microfluidic channels. Remarkably, we find that rheotaxis can be inhibited 100-fold by antibiotics, even if the susceptible elongated
cells remain fully motile. However, resistant bacteria remain short and retain upstream migration under the same conditions. Using genetically engineered bacteria with tunable
cell length, we show that the underlying mechanism that governs rheotaxis is the coupling between
cell morphology and flow vorticity, where elongated
cells are rapidly rotated downstream. Finally, we exploit this length-dependent transport difference to separate short and elongated
cells under flow and enrich ampicillin-resistant
cells from mixed populations. Together, these results establish bacterial elongation as a key control parameter for rheotactic transport, and provide a proof-of-concept strategy for enriching e̱ta}-lactam-resistant bacteria for potential use in rapid AMR detection.
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All authors Ran Tao, Nathaniel C. Esteves, Jay Zhu, Arnold J. T. M. Mathijssen
Chemical Physics · Cross-listed from math.AG
Equations of Tree Tensor Network Varieties
Serkan Hoşten, Niharika Chakrabarty Paul, Otto T. P. Schmidt et al. (+1 more)
We show that tree tensor network varieties, including tensor train varieties, are general Markov models associated to spaced trees. This allows us to prove that the
prime ideals of these varieties are generated by minors of
matrix flattenings. In the case of tensor train varieties, we discuss whether these minors form a Gröbner basis and provide a combinatorial method to compute the degree for order $3$ tensor trains.
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All authors Serkan Hoşten, Niharika Chakrabarty Paul, Otto T. P. Schmidt, Dmitry Skurt
Applied Physics · Cross-listed from hep-ex
Exploring the limits of high-energy proton-pion separation in granular calorimeters
Andrea De Vita, Abhishek, Tommaso Dorigo et al. (+1 more)
Highly granular calorimeters provide detailed information about hadronic-shower development that may enable particle identification beyond their conventional role in energy measurement. We investigate how well this information can distinguish
protons from positively charged pions and how the achievable discrimination depends on detector
segmentation and particle energy. The study uses Geant4 simulations of isolated particles with energies from 10 to 100 GeV in a homogeneous lead-tungstate calorimeter. A Deep Sets model operating directly on
cell positions and detected energy and time outperforms a boosted decision tree based on reconstructed shower observables. With
cells measuring $3 \times 3 \times 6$ mm$^3$, Deep Sets achieves an accuracy of 93.8% at 10 GeV, decreasing to 67.2% at 100 GeV. Shower
topology is independently informative, deposited energy provides the largest additional contribution, and timing supplies complementary information. Coarser
segmentation reduces discrimination, with performance more sensitive to longitudinal than transverse granularity. These results provide an encouraging
benchmark for calorimeter-based
hadron identification and motivate its inclusion among the optimization targets for future highly granular calorimeters.
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All authors Andrea De Vita, Abhishek, Tommaso Dorigo, Pietro Vischia
Medical Physics
A Reference System for Open Source Portable Low-Field MRI
David Schote, Helge Herthum, Umberto Zanovello et al. (+8 more)
Despite its renewed
attention, the pathway to point-of-care portable low-field MRI systems remains challenging, limiting adoption across research groups. Incomplete documentation limits reproducibility, causing redesign and complicating cross-system comparison. Moreover, non-standardized testing and characterization complicates ethical approval for clinical studies. We present an open-source reference system for portable low-field MRI designed to support replication, reproducibility, benchmarking, and quantitative comparison. The system is fully open source, based on a ~50 mT permanent magnet, and integrated with a cloud-native acquisition platform. Pulseq-based calibration, characterization, and imaging sequences assessed noise level, eddy currents, image-based SNR, and
geometric accuracy. Quantitative T1, T2, and B0 mapping sequences were developed and evaluated against reference values. Initial results from independent replications at two sites were compared. The system reached a noise level of 1.4 relative to the thermal noise floor and short eddy-current decay constants of 27-32 us across all gradient channels.
Geometric deviations were below 2 mm over the field of view. Image-based SNR were consistent between the independent replications. Measured T1 values closely matched specified values, with an average absolute error of 3.1(1.8)%, while T2 values were overestimated by 10.4(5.8)%. Simulations showed only marginal errors for both quantities, suggesting experimental error sources for T2 mapping. The reference system combines openly documented hardware, software, calibration procedures, phantoms, quantitative MRI, and simulation tools in a reproducible ecosystem, aiming to support cross-site comparability, reproducible research, and collaborative development of future portable low-field MRI technologies.
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All authors David Schote, Helge Herthum, Umberto Zanovello, Julia Pfitzer, Ivo Jutte, Jan Gregor Frintz, Ilia Kulikov, Sebastian Littin, Frank Seifert, Christoph Kolbitsch, Lukas Winter
Classical Physics · Cross-listed from math.DS
Activated switching between coexisting limit cycles
Gabriel Margiani, Orjan Ameye, Oded Zilberberg et al. (+1 more)
Noise-activated switching between coexisting stable states is a fundamental mechanism underlying
stochastic dynamics in systems ranging from chemical reactions to neural networks. While this phenomenon is well understood for stationary attractors, it remains largely unexplored for limit cycles, whose periodic motion cannot be described by a static potential landscape. Here we experimentally demonstrate activated switching between two coexisting limit-cycle attractors in a driven nonlinear system of coupled resonators. Specifically, we introduce controlled fluctuations to directly observe the rare
stochastic transitions between two limit cycles and measure their dependence on noise intensity and driving strength. The measured switching rates are well described by a large-deviation theory, which replaces the conventional activation barrier by the action along the most probable transition path. Our results extend the concept of activated dynamics from stationary to limit-cycle attractors and establish a framework for modeling
stochastic transitions between limit cycles in driven-dissipative systems.
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All authors Gabriel Margiani, Orjan Ameye, Oded Zilberberg, Alexander Eichler
Computational Physics · Cross-listed from quant-ph
Distinct Modes of Quantum Information Transfer in Power-Law Long-Range Spin Networks
E.E. Marshall, C.C. Nelmes, T.J.G. Apollaro et al. (+2 more)
We identify different regimes of
quantum state transfer in long-range coupled
spin-$\frac{1}{2}$ systems, where naturally occurring power-law interactions enable rapid, high-fidelity transfer with minimal engineering. Across a broad range of interaction profiles, from effectively nearest-neighbour coupling to Coulomb interactions, we show how long-range connectivity fundamentally reshapes the mechanisms underlying information propagation within such systems. For effectively short-range interactions, transfer follows familiar ballistic transfer dynamics: an initially localised excitation spreads across many eigenmodes concentrated within the approximately linear region of the spectrum, enabling robust wavepacket motion. In contrast, increasing long-distance interactions via lowering the power-law exponent $\alpha$ ($\alpha=1-2$) drives a striking transformation, where the initial state becomes confined to progressively fewer eigenmodes, ultimately reducing the dynamics to the coherent participation of only a few states corresponding to the highest eigenenergies. This spectral localization gives rise to emergent long-range oscillations between distant sites, revealing a distinct – and faster – transfer mechanism arising from the intrinsic structure of long-range
quantum interactions rather than from full-system engineering pathways.
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All authors E.E. Marshall, C.C. Nelmes, T.J.G. Apollaro, T.P. Spiller, I. D'Amico
Optics
Transversality Locks Longitudinal Gradients in Structured-Light Quadrupole Transitions
Kayn A. Forbes, Dale Green, Abdullah F. Alharbi et al. (+1 more)
Electric quadrupole absorption is driven by optical field gradients, not by field amplitudes alone. This distinction is crucial for structured light, where a paraxially small longitudinal field can generate a leading-order longitudinal gradient. For fully vectorial Laguerre-Gaussian modes, Maxwell transversality locks this longitudinal gradient to the transverse structured gradient of the leading paraxial field. This locking is therefore a general electromagnetic constraint, not a focusing-dependent correction that can be removed independently. Decomposing the symmetric-traceless optical field-gradient tensor into spherical components reveals a strongly channel-selective response: the $\Delta m=0$ transition requires the longitudinal gradient at the retained order, the $\Delta m=\pm1$ channels receive scalar and vectorial nonparaxial corrections on top of the carrier-scale longitudinal derivative of the transverse field, and the $\Delta m=\pm2$ channels remain transverse at the same order. These results show that longitudinal optical structure can enter structured-light quadrupole transitions as an indispensable leading-gradient contribution, even when the longitudinal field amplitude itself is paraxially small.
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All authors Kayn A. Forbes, Dale Green, Abdullah F. Alharbi, Akbar Salam
Instrumentation and Detectors
The Radioactive Background of the JUNO Calibration System
Rui Li, Youhui Yun, Zhangming Chen et al. (+13 more)
The Jiangmen Underground
Neutrino Observatory (JUNO) experiment is a reactor antineutrino detector employing 20 kton of ultra-pure
liquid scintillator to determine the
neutrino mass ordering and to precisely measure oscillation parameters. The total singles background rate from radioactivity is required to be below 10 Hz in the energy range of 0.7-12 MeV within the fiducial volume for reactor
neutrino analysis. The calibration system is designed to characterize the detector energy and position responses, while several of its components are located close to the target and may contribute to the background budget. Therefore, extensive material screening and selection are required to construct a low-background calibration system and to ensure that its contribution remains within the design requirements. In this work, a comprehensive study of the radioactive background induced by the calibration system is presented, including material radioactivity measurements using high-purity germanium detectors and
neutron activation analysis techniques, detailed Monte Carlo simulations to evaluate the background, and comparisons with in-situ detector data to validate the predictions. In this data analysis, dedicated spatial selection methods are developed to isolate calibration-related contributions and to suppress the
liquid scintillator background. The total radioactivity contribution from the calibration system is estimated to be less than 76 mHz, which satisfies the requirement of 200 mHz (2% of the total background budget). The results from in-situ data are found to be consistent with the expectations based on material assay and simulation within uncertainties. These results demonstrate that the calibration-induced background is well understood, in agreement between data and simulation, and negligible for reactor antineutrino measurements in JUNO.
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All authors Rui Li, Youhui Yun, Zhangming Chen, Junting Huang, Jiaqi Hui, Haojing Lai, Jianglai Liu, Yankai Liu, Yue Meng, Akira Takenaka, Ziqian Xiang, Feiyang Zhang, Ping Zhang, Qingmin Zhang, Tao Zhang, Yuanyuan Zhang
Chemical Physics
Universal Machine-learning Molecular Dynamics at the Speed of Empirical Potentials
Tiancheng Li, Jianming Xue, Linfeng Zhang et al. (+2 more)
No interatomic potential has offered universality across chemistry, near-first-principles accuracy and the speed of empirical potentials at once. Here we introduce DPA4C, an equivariant potential whose architecture and compressed CUDA operators are co-designed under deployment constraints to pursue accuracy and efficiency together. Five variants spanning a 49-fold parameter range form the high-throughput end of the measured accuracy–throughput frontier. The largest variant approaches the accuracy of the MACE-Omat models at about two orders of magnitude higher measured throughput. The most compact reduces the energy, force and stress errors of the fastest existing universal MLIP by 61.4%, 48.1% and 34.3% at 1.92 times its saturated throughput. All five variants complete multimillion-atom simulations on a single GPU and run molecular dynamics for 2.048 billion atoms on 1,024 16-GB NVIDIA V100 GPUs at 83.3–91.2% weak-scaling efficiency. Compared with the MEAM empirical potential, DPA4C-Nano reaches 1.8 and 2.5 times the saturated throughput in single-GPU scans on the same V100 hardware for diamond carbon and FCC copper, respectively. DPA4C therefore brings
quantum-trained universal accuracy into a regime of speed and system size previously associated with empirical potentials.
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All authors Tiancheng Li, Jianming Xue, Linfeng Zhang, Duo Zhang, Han Wang
Chemical Physics
Molecular Implementation of the Machine-Learned Skala Exchange-Correlation Functional in CP2K through GauXC
Franz Pöschel, Johann Pototschnig, Frederick Stein et al. (+6 more)
Machine-learned exchange–correlation (XC) functionals offer a route to improve Kohn–Sham density-functional theory without incurring the cost of explicitly correlated electronic-structure methods. Their use in production simulation codes, however, requires a well-defined mapping between the learned model and the host-code density representation. We formulate and implement a Skala-1.1 interface in CP2K through the external GauXC library. CP2K supplies the geometry, Gaussian basis,
spin-resolved atomic-orbital density
matrix, and communicator, while GauXC evaluates the XC energy, atomic-orbital potential
matrix, and available
nuclear derivatives. The interface accepts both all-electron and valence-only density
matrices. The latter may arise from separable dual-space pseudopotentials or molecular effective-core potentials. Implementation errors are isolated from functional differences by comparing the Perdew–Burke–Ernzerhof (PBE) functional evaluated through GauXC with native CP2K PBE. The resulting interface gives consistent energies, forces validated against finite-difference total-energy checks, and force-based molecular-virial diagnostics for representative molecular cases. The dietGMTKN55
benchmark suite is evaluated with an all-electron Gaussian augmented plane-wave treatment for elements up to bromine and def2 effective-core potentials for the heavier elements. The resulting aggregate mean absolute deviation of 1.255 kcal/mol is within 0.012 kcal/mol of the corresponding Skala reference value of 1.243 kcal/mol. This work establishes a validated molecular implementation of Skala in CP2K through GauXC.
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All authors Franz Pöschel, Johann Pototschnig, Frederick Stein, Andreas Knüpfer, Thijs Vogels, Stefano Battaglia, Sebastian Ehlert, Jürg Hutter, Thomas D. Kühne
Computational Physics · Cross-listed from cond-mat.mtrl-sci
The role of weak interfaces in the tensile deformation and fracture of particle-filled polymers studied by phase-field model
Xu Chen, Ya Duan, Xiaoying Zhuang et al. (+1 more)
Weak particle-
matrix interfaces play a critical role in the tensile fracture of particle-filled
polymer composites, but how they govern progressive debonding, fracture localization, and the resulting changes in macroscopic mechanical properties remains insufficiently understood. In this study, a cohesive-zone phase-field model incorporating a hyperelastic
polymer matrix and a smeared interface is employed to investigate the coupled
evolution of interfacial debonding and
matrix fracture in particle-filled
polymer composites. The model is calibrated against and compared with uniaxial tensile responses of particle-filled polyurethane composites and then used to study how interfacial strength, interfacial fracture energy, and
matrix fracture properties affect the macroscopic stress-strain response and damage
evolution. The results show that weak interfaces can induce an intermediate softening regime in the stress-strain response, characterized by a reduced effective tangent stiffness and associated with distributed interfacial damage. Interfacial strength mainly controls the initiation of debonding, whereas interfacial fracture energy affects whether debonding can develop progressively in a distributed manner or rapidly localizes into a dominant crack band. Comparisons with well-bonded reference systems further demonstrate that weak interfaces may reduce the maximum stress but increase the strain at break by promoting distributed debonding around particles and delaying the formation of a dominant crack band. These findings clarify the dual role of weak interfaces and provide a mechanistic understanding of interface-controlled tensile failure in particle-filled
polymer composites.
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All authors Xu Chen, Ya Duan, Xiaoying Zhuang, Timon Rabczuk
Computational Physics · Cross-listed from cond-mat.str-el
Sign-problem-resilient singular-value probe in determinant quantum Monte Carlo
Wen Chen and Rubem Mondaini
The sign problem limits determinant
quantum Monte Carlo studies of strongly correlated
fermion systems. In the
spin-channel Hubbard-Stratonovich decoupling,
spin correlations are exactly related to auxiliary-field correlations. This relation implies that an
antiferromagnetic transition reorganizes auxiliary-field configurations and thereby changes the statistical structure of the resulting
fermion matrices. We use the adjacent gap ratio of low-lying singular values of the space-time
fermion matrix to probe interaction-driven transitions in two half-filled honeycomb-
lattice Hubbard models. In the sign-free honeycomb Hubbard model, the statistic tracks the established transition from a Dirac semimetal to an
antiferromagnetic Mott
insulator. In the complex-weight Haldane-Hubbard model, the transition-sensitive feature remains visible in the phase-quenched reference ensemble and occurs near previous estimates of the transition. Moreover, phase reweighting only weakly modifies the gap ratio over the regimes investigated, despite the rapid suppression of the average phase. These results establish singular-value statistics as a sign-problem-resilient probe of interaction-driven transitions in determinant
quantum Monte Carlo.
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Optics
Influence of metal nanoparticles on whispering gallery modes of a microcavity
Tulika Agrawal, Venkata Dantham, Shubhayan Bhattacharya et al. (+3 more)
Photonic microcavities offer high energy density and low mode volume and attract special
attention due to wide range of applications. Subsequent developments in the area of plasmonic nanocavities have also opened up applications despite their high absorptive properties. In the last two decades, photonic-plasmonic hybrid microcavities have been investigated extensively. In this article, we have conducted a review of the literature on photonic and plasmonic systems individually as well as in hybrid systems. Along with the underlying physics, applications such as cavity
quantum electrodynamics, lasing, sensing, nonlinear optics and Raman spectroscopy have been reviewed. The outputs of the systems for each applications have been discussed and compared for photonic and hybrid systems. This review will provide a thorough understanding of the effects of optical cavities and plasmonics and their applications.
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All authors Tulika Agrawal, Venkata Dantham, Shubhayan Bhattacharya, Aneesh Veluthandath, Stephen Arnold, Prem Bisht