Atmospheric and Oceanic Physics
AI Emulation of Stochastic Sudden Stratospheric Warming with Interpretable Latent Structure
C. Daniel Boscu, Daniel Hernandez, Fabio Alvarez Ventura et al. (+4 more)
Rare weather regime transitions pose a challenge for data-driven modeling due to class imbalance. In this study, we develop a probabilistic deep learning emulator for a prototypical system with regime transitions, the
stochastic Holton–Mass model of stratospheric variability, and analyze the structure of its learned latent space. The Holton–Mass model exhibits two metastable regimes, a strong and a weak polar
vortex, maintained by nonlinear wave–mean flow interactions, with weak
stochastic forcing intermittently triggering rare transitions between these regimes that qualitatively represent SSW events. We employ a ResNet-inspired Conditional Variational Autoencoder with six-layer encoder and decoder layers and explicit current-state conditioning to model the distribution of the system's state at the next time step (one day). The emulator accurately reproduces short-term dynamics, steady-state probability distributions, regime persistence statistics, rare transition rates, the transition committor function, and the transition expected lead time of the physical model. Beyond emulation fidelity, we interrogate the learned latent representation to understand how the model internalizes the underlying metastable structure of the dynamics. Principal Component Analysis of the 32-dimensional latent space reveals a clear and unsupervised separation into four physically interpretable clusters corresponding to strong versus weak
vortex regimes and stable versus transition-prone configurations. Such emergent regime separation in latent space is hard to identify for deep generative models applied to high-dimensional
stochastic systems. Our results show that carefully designed probabilistic emulators can uncover physically meaningful
manifolds governing extreme-event dynamics, potentially aiding the development of improved operational advanced warning systems.
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All authors C. Daniel Boscu, Daniel Hernandez, Fabio Alvarez Ventura, Justin Finkel, Ashesh Chattopadhyay, Pedram Hassanzadeh, Dorian S. Abbot
Atomic Physics
Stark effect of hydrogenic ions as a test of the indefinite-metric formalism of the eight-component relativistic wave equation for spin-$\frac{1}{2}$ particles
Paulus C. Tjiang, Sylvia H. Sutanto and Vincentius E. W. Tjia
The eight-component relativistic wave equation for
spin-$\frac{1}{2}$ particles of Robson and Staudte (FV$\frac{1}{2}$), a Feshbach–Villars linearization of the Feynman–Gell-Mann equation, reproduces the Dirac hydrogenic spectrum with a doubled solution space and an indefinite inner product. Its exact Stark shifts must equal the Dirac ones; whether its indefinite-metric perturbation theory delivers them is not guaranteed. We compute the first- and second-order Stark shifts of the $n=1$–3 levels of hydrogenic ions from H to U$^{91+}$ in the Schrödinger, Dirac and FV$\frac{1}{2}$ theories, evaluating all spectral sums, continuum included, by the Dalgarno–Lewis method. The FV$\frac{1}{2}$ and Dirac shifts coincide level by level, to working precision at first order (closed-form roots) and to 45 significant figures at second order. Both ingredients are needed: without the explicit
spin–field coupling the first-order roots become complex, and without the negative-norm states the $(Z\alpha)^2$ coefficient is wrong. Norm sign and parity are locked in the doubled space: a potential lifting the $2s_{1/2}$–$2p_{1/2}$ degeneracy needs its own
spin–gradient term, and shifts placed by hand on the $\kappa$-labeled states give a spurious imaginary linear Stark shift. The relativistic linear Stark effect is smaller by finite factors, but a second-moment sum rule shows the non-relativistic linear Stark strength is conserved, the missing part reappearing in singular $(Z\alpha)^{-2}$ second-order terms. For levels with a fine-structure partner, an exact intra-shell/regular split of the second-order shift gives the $(Z\alpha)^0$ coefficients analytically and relates the $\pi^2$ terms of the $(Z\alpha)^2$ coefficients to the singular ones. The Dirac weak/strong-field crossover for $n=2$ of hydrogen lies near 2.8~kV cm$^{-1}$, and the perturbative window set by the fine structure grows as $Z^5$.
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Plasma Physics
Analysis of grid instabilities in particle-in-cell codes based on a meshfree approach
J. M. Finn and E. G. Evstatiev
A new method of analyzing grid, or aliasing, instabilities is described, in particle-in-
cell (PIC) codes for
plasma kinetic theory. It starts with a meshfree approach with $N_{p}$ macroparticles, with $N_{p}<\infty$. Linearization of these equations is done about a uniform density non-drifting
equilibrium prescribed by macroparticles on a uniform
lattice. Macroparticle positions perturbations are induced about this
lattice. The resulting linear equations are analyzed for stability and dispersion relations. The linearized equations are then discretized on a grid of $N_{g}$ points with $N_{g} \le N_{p}$, in both momentum conserving (MCP) and energy conserving (ECP) formulations. For a cold stationary
plasma, this leads a dynamical
matrix. For ECP, the
matrix is symmetric and positive definite (SPD) and immediately shows stability. For MCP, the dynamical
matrix is neither symmetric nor positive definite, preventing immediate conclusions on stability. For both MCP and ECP and for a cold stationary
plasma, the resulting
matrix elements vary relative to the meshfree value, a result of aliasing. This deviation is periodic in the displacement of the particle
lattice relative to the grid. In the MCP discretization,
eigenvalues occur in complex conjugate pairs for general placement of the particle
lattice relative to the grid. These conjugate pairs indicate nonnegative growth rates. The nature of the aliasing is studied and shown to be related to the trapezoidal rule error over the grid. The scaling of the linear growth rates with respect to $N_{g}$ and especially with respect to $N_{ppc}$ is studied. These analytical results are compared with PIC simulations and found to be in excellent agreement. The connection with a cold drifting beam is discussed briefly, specifically, grid-induced instabilities for both the MCP and ECP.
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Optics
Programmable nonlinearity within nanophotonic waveguides
Benjamin A. Ash, Ryotatsu Yanagimoto, Mandar M. Sohoni et al. (+8 more)
Nonlinear nanophotonics enables the engineering of optical functions using light-matter interactions in nanoscale structures with carefully designed geometries. Phase matching in nonlinear optics is typically essential for realizing high efficiency for desired processes and engineering of sophisticated functions, but it can be challenging to reliably achieve in nanophotonic waveguides. Conventionally, phase matching in nanophotonics is achieved through nanofabrication, e.g., by poling a device's nonlinear material using electrodes with fixed geometry. This approach has two drawbacks: the optical functions a device can perform are fixed at the time of fabrication, and the device's performance can be degraded by fabrication imperfections. Here, we circumvent these limitations by engineering programmable $\chi^{(2)}$ holograms inside nanophotonic waveguides, enabling reconfigurable quasi-phase matching that can be updated after device fabrication in approximately one second. By projecting structured optical illumination onto photoconductive electrodes, we generated spatial patterns of electric-field-induced $\chi^{(2)}$ to exert spectral, modal, and polarization control over three-wave mixing processes. This programmability also allowed us to employ closed-loop in situ optimization to compensate for phase mismatch in complex waveguide structures, such as width-modulated waveguides and spiral waveguides exceeding 10 cm in length. Furthermore, we show that programmable nonlinearity enables powerful in situ diagnostics, including direct dispersion measurements of various transverse modes and on-chip wavefront phase
tomography. Our work opens up the possibility of building cascaded nonlinear nanophotonic systems where yield issues due to fabrication variations can be sidestepped while retaining the benefits of etched waveguides such as confinement and dispersion engineering.
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All authors Benjamin A. Ash, Ryotatsu Yanagimoto, Mandar M. Sohoni, Yang Xu, Yiqi Zhao, Martin M. Stein, Fan O. Wu, Marc Jankowski, Logan G. Wright, Tatsuhiro Onodera, Peter L. McMahon
Applied Physics · Cross-listed from cs.LG
BranchIP: Learning Adaptive Equivariant Computation for Interatomic Potentials
Laura Zichi, Gil Harari, Chuin Wei Tan et al. (+6 more)
Equivariant machine learning interatomic potentials (MLIPs) have revolutionized atomistic modeling, but accurate treatment of complex materials and molecular systems demands expensive models. This limits simulation length- and time-scales, with tensor products a key computational bottleneck. The recent emergence of foundation-scale MLIPs further exacerbates this challenge. We present Branch Interatomic Potential (BranchIP), a single-model framework for learned adaptive tensor product computation, trained with a novel
distillation loss. In our experiments on two systems of physical interest, a heterogeneous catalysis system and a
proton-conducting solid acid electrolyte, BranchIP accelerates MLIPs across model sizes by up to $2.4\times$ while reducing
memory usage by up to $2.6\times$. This is achieved while maintaining physical fidelity. Furthermore, the learned adaptive computation provides model interpretability by revealing which interactions demand deeper computation and showing how computational depth relates to chemical complexity and dynamics.
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All authors Laura Zichi, Gil Harari, Chuin Wei Tan, Marc L. Descoteaux, Albert Zhu, Menghang Wang, Yoel Zimmermann, H.T. Kung, Boris Kozinsky
Fluid Dynamics · Cross-listed from cond-mat.soft
Microscopic origin of the chiral pressure in a two-dimensional fluid
Francisco Vega Reyes
We show that a two-dimensional chiral fluid supports an antisymmetric contribution to the pressure, and determine its microscopic expression. Its origin lies outside the standard kinetic and collisional channels of the normal pressure tensor, stemming instead from the average of a parity-breaking pseudo-scalar. This chiral pressure is set by the rotational (
vortex) viscosity of micropolar hydrodynamics, whose kinetic value for rough disks we compute here, to Gaussian order. Crucially, both the chiral pressure and the rotational viscosity survive at zeroth order in the gradients, meaning they persist even in the fully homogeneous fluid – which we show is not only well defined but steady (the Quiescent Chiral State, QCS). Since this averaged pseudo-scalar does not vanish in a chiral fluid, any expansion of its distribution function must contain terms in this pseudo-scalar variable.
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Physics and Society
The efficacy-competitiveness frontier in the Swiss system
László Csató and Balázs R. Sziklai
An ideal tournament is both efficacious and attractive: it selects the best player as the winner, but only at the end of the tournament in order to maintain suspense as long as possible. We identify and explore the trade-off between these criteria in Swiss-system chess team tournaments via simulations. Organising more rounds is shown to improve efficacy but increase the probability of a stakeless last round. The 2008 reform in the Chess Olympiad ranking is found to be a questionable move, as the previous rule based on board points determines the efficacy-competitiveness frontier, regardless of whether two or three points are awarded for winning a match. Combining board points and match points is better than using match points only. Our results can help optimise the design of the Swiss system, which, besides chess, is also widely used in e-sports.
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Chemical Physics · Cross-listed from quant-ph
Hardware-Efficient Ground-State Preparation using Variational Imaginary-Time Majorana Evolution
Federico Santona, Manuel G. Algaba, Aeishah Ameera Anuar et al. (+3 more)
Compact ground-state preparation
circuits are essential for early fault-tolerant
quantum chemistry. We introduce Variational Imaginary-time Majorana
Evolution (VIME), a classical pre-training
algorithm that extends operator-projected variational
quantum imaginary-time
evolution (OVQITE) to molecular electronic structure using a single compiled Majorana-propagation (MP) surrogate graph. We pair VIME with a compressed tiled
Unitary Product State (c-tUPS) ansatz that we develop to reduce both classical simulation and
quantum state-preparation costs. In the strongly correlated ruthenium complex TLD-1411, active-space calculations requiring up to 52
qubits achieve chemical precision against DMRG reference energies, with energy errors approximately $400\times$ smaller than those from ADAPT-VQE-based variational Majorana-propagation (ADAPT-VMPE). Across the strongly multireference acene series up to heptacene (60
qubits), VIME matches or improves on the MP-reported energy accuracy of the ADAPT-VMPE comparison points with up to $26\times$ fewer CNOTs and $167\times$ lower two-
qubit depth. These results establish imaginary-time classical pre-training of compressed variational ansätze as a promising route to resource-efficient molecular ground-state preparation.
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All authors Federico Santona, Manuel G. Algaba, Aeishah Ameera Anuar, Anna M. Wernbacher, Prachi Sharma, Fedor Šimkovic IV
Medical Physics
Towards 3D fully randomized frequency-domain reconstruction of the speed of sound in breast ultrasound computed tomography
Luca A. Forte
Ultrasound computed
tomography is emerging as a promising diagnostic imaging tool. 2D geometries suffer from notorious out-of-plane scattering artifacts. Image reconstruction can be achieved with frequency-domain full waveform inversion and it can be further accelerated by randomly phase-encoding the elementary sources. In this manuscript, we extend our previous results for the 2D geometry of a ring-array to the 3D cylindrical geometry of multiple rings. In particular, we consider the cases of an elementary source described by a single array element (quasi-omni-directional transmission), a line source and a focused transmission respectively. With differences in image quality, we prove that a fully randomized frequency-domain inversion in 3D is capable to reconstruct portions of a human breast surrounded by the cylindrical geometry and detect mm-size masses of varying contrast in dense breast, in reasonable computing times, thus opening the concrete possibility to the design of 3D imaging devices with high sensitivity levels. The methods are applicable to multiple tomographic geometries in 3D and, in principle, can be integrated into next generation medical ultrasound scanners.
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Fluid Dynamics
Helical pipes homogenize particle transport in pneumatic conveying
Wing To Ku, Patric Mueller and Thorsten Poeschel
Pneumatic conveying at moderate gas velocities can result in strongly heterogeneous particle transport, with slow particles accumulating near the bottom of the pipe while faster particles are transported above. Here, we investigate helical pipes as a passive means of homogenizing particle transport without increasing the gas velocity. CFD-DEM simulations show that the helical pipe induces swirling motion of the gas and particles, continuously redistributing particles across the pipe cross-section. This transforms the heterogeneous transport observed in a straight pipe into a more homogeneous state with a narrower particle-velocity distribution. The results demonstrate that helical pipes can maintain efficient pneumatic conveying at moderate gas velocities while reducing excessive particle velocities.
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Geophysics
Flow-rate controls on trapped hydrogen redistribution in a heterogeneous sandstone: a synchrotron X-ray micro-CT study
Catherine Spurin, Sojwal Manoorkar, Sharon Ellman et al. (+7 more)
Subsurface hydrogen storage in porous geological formations is a promising strategy for balancing temporal mismatches between renewable energy generation and demand. The viability of large-scale hydrogen storage depends on predicting hydrogen distribution, trapping, and recovery during cyclic injection and withdrawal operations. However, these multiphase flow processes are influenced by rock heterogeneity, capillary hysteresis and trapping at the pore-scale. In this work, fast in-situ synchrotron X-ray
tomography was used to directly visualise hydrogen mobilisation during brine imbibition in a heterogeneous sandstone. By systematically varying the brine injection rate, the influence of flow conditions on hydrogen recovery, and the
evolution of trapped hydrogen were quantified. Significant mobilisation of disconnected hydrogen clusters was observed during imbibition, even at low capillary numbers ($< 10^{-6}$). Rock heterogeneity influenced trapping behaviour, particularly during the early stages of imbibition. Our results highlight the importance of incorporating pore-scale heterogeneity and transient trapping mechanisms into hydrogen storage predictions.
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All authors Catherine Spurin, Sojwal Manoorkar, Sharon Ellman, Ian B. Butler, Aliakbar Hassanpouryouzband, Damien Freitas, Fernando Alvarez-Borges, Robert Atwood, Katriona Edlmann, Eike Thaysen
Chemical Physics · Cross-listed from cond-mat.mes-hall
Symmetry considerations in chirality-induced spin selectivity
Dmitry Budker and Angela Wittmann
The chirality-induced
spin selectivity (CISS) effect, the coupling between structural chirality and electron
spin polarization, has been experimentally observed across many diverse systems. However, despite extensive theoretical effort, a unified mechanistic understanding remains elusive. In this perspective, we demonstrate how some of the basic properties of the fascinating effects of CISS can be understood based on straightforward
symmetry considerations commonly employed in fundamental particle physics. In particular, we show that CISS does not violate any fundamental
symmetries including parity and time-reversal. By anchoring CISS within the universal
language of
symmetry, we offer a robust conceptual foundation for interpreting experiments and guiding future theoretical and experimental designs.
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Fluid Dynamics
Rapid generation of relaxed centimeter-sized drops by capillary auto-ejection
Patric Mueller, Kai Ihrig, Achim Sack et al. (+2 more)
Many microgravity experiments require centimeter-sized spherical
liquid drops. In drop-tower experiments, only a few seconds of microgravity are available, so the drops must be generated and reach a nearly relaxed state within a very short time. We investigate capillary auto-ejection (puddle jumping) as a passive mechanism for producing free-floating drops and investigate how the supporting cavity can be shaped to minimize the relaxation time after ejection. For cavities with a parabolic cross-section filled with a fixed
liquid volume, minimization of the initial
liquid surface area yields a unique shape, and smoothed particle hydrodynamics simulations show that this shape also gives the shortest relaxation time within the parabolic family. Introducing a shallow central depression into the cavity reduces the relaxation time further, despite producing a larger initial
liquid surface area. These results provide design principles for capillary-driven drop generators that enable the rapid production of relaxed centimeter-sized drops during the short microgravity intervals available in drop towers.
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All authors Patric Mueller, Kai Ihrig, Achim Sack, Jonathan E. Kollmer, Thorsten Poeschel
Fluid Dynamics
Direct Modeling of Pore Size Evolution and Microcollapse in Lyophilization by Population Balance
Isaac Stonewall Wheeler, Vivek Narsimhan, Alina A. Alexeenko et al. (+1 more)
In the primary drying step of pharmaceutical freeze drying, it is well known that amorphous excipients are prone to "microcollapse" as they approach their glass transition temperature. Existing modeling approaches for this phenomenon generally entail either avoidance of this regime or an experimentally burdensome empirical assessment of the resulting drop in resistance to mass transfer. In this work, we approach the phenomenon head-on by developing a population balance model for the pore size distribution of a freeze-dried cake during microcollapse and relating the pore size to mass transfer resistance. By treating the population balance with the method of moments and an interpolative closure, we keep the model's computational burden on par with the literature-standard model for primary drying. For a literature example when mass transfer resistance clearly varies as a function of product temperature during drying, we fit the population balance model to cases with high and low product temperature and show that it can then simulate intermediate cases with equal accuracy. The validity of the expression for mass transfer resistance is demonstrated with another literature data set, where pore size distributions were measured after the fact for a formulation without microcollapse; only a single parameter from this model needs to be fit to those cases to yield predictive accuracy in product temperature on par with post-hoc empirical assessment. Finally, a sophisticated multi-experiment fit for one formulation across a range of conditions yields quantitative agreement in product temperatures, suggesting that the rate constant for microcollapse behavior may be a material parameter and independent of the precise porous geometry.
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All authors Isaac Stonewall Wheeler, Vivek Narsimhan, Alina A. Alexeenko, Davide Fissore
Computational Physics
RFBniCS: An open-source simulation framework for redox flow batteries
Amirhossein Aghabarari, Jørgen S. Dokken, Martin T. Horsch et al. (+2 more)
We present RFBniCS, an open-source finite-element framework implemented in FEniCSx for simulating redox-flow-battery (RFB) half-
cells. RFBniCS solves an established macro-homogeneous porous-electrode model accounting for strongly coupled electrolyte flow, multicomponent species transport, ionic and electronic charge conservation, and interfacial Faradaic charge transfer. Different from other open-access tools, RFBniCS can perform transient RFB half-
cell simulations in one-, two-, and three-dimensional geometries while explicitly resolving the transport of both redox-active and supporting-electrolyte species. It also describes electrolyte flow through porous electrodes and, in the three-dimensional formulation, through adjacent flow channels. To verify the implementation, RFBniCS's predictions in parameter-limiting regimes are compared against other published implementations, with RFBniCS generally showing superior accuracy and speed. We further demonstrate RFBniCS's capabilities by a simulation of the transient response of the negative half-
cell of a vanadium redox flow battery, with a moderately concentrated supporting electrolyte. In the current implementation, RFBniCS provides the computational basis for studying redox-flow-battery half-
cells and can be extended to complex flow-field designs, alternative chemistries, full-
cell coupling, detailed membrane transport, and additional multiphysics effects.
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All authors Amirhossein Aghabarari, Jørgen S. Dokken, Martin T. Horsch, Eirik Valseth, Mathijs Janssen
Atmospheric and Oceanic Physics
Varda-single-1.0: deterministic data-driven weather forecasting at 1 km resolution over Switzerland's complex topography
Alberto Pennino, Francesco Zanetta, Michele Cattaneo et al. (+28 more)
We present Varda-single-1.0, a medium-range data-driven weather prediction system built for the Alpine domain. It provides hourly deterministic regional forecasts on a mesh of 1 km resolution and global forecasts on a 31 km mesh. The system comprises two independently trained stretched-grid Graph
Transformer models with encoder-processor-decoder architecture, developed in the Anemoi framework: a 6-hourly autoregressive forecaster and a temporal downscaler reconstructing hourly forecasts between the forecaster's steps. Its training curriculum includes pre-training on ERA5 reanalysis data, followed by training on a 20-year kilometre-scale regional reanalysis, and finally fine-tuning on operational kilometre-scale analyses. Verified over one year against operational analyses and surface station observations, Varda-single is competitive with or improves on MeteoSwiss' operational numerical weather prediction baselines for most headline scores and variables. It broadly matches the skill of the high-resolution 1 km ICON-CH1-EPS control at lead times up to +33 h and generally outperforms the 2 km ICON-CH2-EPS control at lead times up to +120 h. Despite competitive aggregate scores, Varda-single underestimates some local wind maxima and produces overly smooth convective precipitation fields, consistent with the smoothing associated with squared-error training. To gain insight into the model's behaviour, we investigate three case studies beyond the aggregated headline scores, and find particular weaknesses in Varda-single's representation of local winds over complex terrain. Varda-single represents an important step in the development of high-resolution ML forecasting over complex terrain, in complementing the operational regional numerical weather prediction models of MeteoSwiss with data-driven models and in providing a pretrained model for researchers and user-specific applications.
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All authors Alberto Pennino, Francesco Zanetta, Michele Cattaneo, Claire Merker, Radi Radev, Jonas Bhend, Louis Frey, Hugues de Laroussilhe, Ophélia Miralles, Carlos Osuna, Daniele Nerini, Andreas Pauling, Daniel Hupp, Ulrich Hamann, Mary McGlohon, Marti Bosch, Luca Lanzilao, Marco Arpagaus, Lukas Jansing, Daniel Leuenberger, Mark A. Liniger, Katrin Ehlert, Matthew Chantry, Håvard Homleid Haugen, Gert Mertes, Ana Prieto Nemesio, Mario Santa Cruz, Jasper Wijnands, Gabriel Moldovan, Harrison Cook, Oliver Fuhrer
Chemical Physics
Nonadiabatic Quantum Dynamics of Hexatriene via the Extended Hubbard-Peierls Model and Time-Dependent DMRG
Timothy N. Georges, Darren J. Valentine and William Barford
Propagating the electronic and nuclear degrees of freedom of a molecule simultaneously is a challenging task, because the number of vibronic states grows exponentially with system size. We use the adaptive time-dependent density
matrix renormalization group to perform simulations of the extended Hubbard-Peierls
Hamiltonian, in which both the electronic and nuclear degrees of freedom are quantized. We describe our approach, and demonstrate it through converged calculations of the nonadiabatic dynamics of hexatriene. This simulation predicts a lifetime of the `bright' $\mathrm{1B_u}$ electronic state of approximately 40 fs. Our predictions for the population of the $\mathrm{1B_u}$ electronic state are in qualitative agreement with those obtained using the linear vibronic coupling model derived from the extended Hubbard-Peierls
Hamiltonian in previous work.
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Fluid Dynamics
On the transmission of floating-point perturbations in flow-dependent filter-width formulations in Large-Eddy Simulation
Valerio D'Alessandro, Alessio Piccolo, Matteo Falone et al. (+1 more)
Heterogeneous high–performance computing architectures expose numerical
algorithms to perturbations arising from the non–associativity of floating–point arithmetic. In Large–Eddy Simulation (LES), similar numerical effects may become relevant when they affect the filter–width entering the subgrid scale (SGS) model. This work investigates this mechanism for the least–squares (LSQ) based filter–width formulation, focusing on how floating–point effects are generated, transmitted, and coupled with the resolved flow. We show that, for fixed resolved kinematics, the LSQ filter–width is logarithmically non-expansive but not strictly contractive with respect to perturbations of the mesh metrics. Consequently, small disturbances may be transmitted with little attenuation through strongly directional filter-width responses. To mitigate this sensitivity, we introduce a scalar max–min compression of the directional mesh scales together with a bounded modulation based on the resolved velocity gradient. The resulting formulation reroutes floating–point perturbations through the filter-width operator, improving robustness while preserving the flow–dependent character of the original LSQ construction. The framework is assessed on heterogeneous CPU and GPU architectures for flow past a circular cylinder at Re=3900 and the Taylor–Green
vortex at Re=1600. In the former, nearly one–to–one transmission of relative metric disturbances can become relevant when the transmitted perturbations interact with shear-layer transition. By contrast, on orthogonal Taylor–Green
vortex grids, the accumulation pathway is structurally absent and no comparable macroscopic response develops. These results suggest floating–point sensitivity matters for LES filter–width formulations in heterogeneous computing environments.
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All authors Valerio D'Alessandro, Alessio Piccolo, Matteo Falone, Simone Bnà
Atomic Physics
A Compact, High-Data-Rate, High-Sensitivity GMOT-Based Light-Pulse Atom Interferometer toward Time-Multiplexed, Multi-Axis Inertial Sensing
Benjamin Smith, Adrian Orozco and Jongmin Lee
Light-pulse atom interferometry has emerged as a promising approach for developing
quantum inertial and
gravity sensors for real-world applications, but achieving robust operation in dynamic environments without sacrificing sensitivity remains challenging. To mitigate performance degradations resulting from vibration-induced noise and mismatches in the spatial overlap between free-falling atoms and light pulses, we demonstrate a first-of-a-kind high-data-rate, high-sensitivity grating magneto-optical trap (GMOT)-based light-pulse atom interferometer (LPAI). This system uses a compact, rugged GMOT architecture, based on an in-
vacuum microfabricated grating chip and a single
laser-cooling beam, to enable high-data-rate GMOT-based cold-atom generation with sub-Doppler cooling. Our GMOT-based LPAI operates at high data rates (up to 100 Hz), while simultaneously achieving both high acceleration sensitivity (550 ng/rt-Hz at 20 Hz, 1.49 ug/rt-Hz at 45 Hz, and 6.31 ug/rt-Hz at 70 Hz) and good bias stability (71 ng). This compact, rugged architecture paves the way for field-deployable
quantum inertial and
gravity sensors in high dynamics and for time-multiplexed, multi-axis inertial sensing.
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Chemical Physics
PyCDFT: A Python-scriptable library for analytical evaluation of orbital conceptual density (matrix) functional theory
Bin Wang, Paul Geerlings, Paul W. Ayers et al. (+1 more)
Conceptual density functional theory (CDFT) defines chemical reactivity descriptors as derivatives of the electronic energy with respect to the number of electrons and the external potential, or combinations thereof; in practice, however, researchers almost always replace these derivatives with finite-difference and frontier-orbital approximations, and no common software exists for their analytical evaluation. We present PyCDFT, to our knowledge, the first standardized, open-source, and scriptable code that analytically computes the descriptors of conceptual density (
matrix) functional theory for ground and excited states up to second order, including the orbital hardness, the Fukui function and Fukui
matrix, and the linear response function, from a single converged mean-field wavefunction imported from virtually any electronic-structure package. The descriptors are obtained from
matrix-free, preconditioned Krylov-subspace solutions of the coupled-perturbed self-consistent-field equations for both
spin-unpolarized and
spin-polarized references, with the work distributed over MPI ranks and all data flowing through a single HDF5 checkpoint file that supports restart, post-processing, and the export of real-space descriptors as cube files for visualization. The design delegates integrals, grids, and exchange-correlation kernels to PySCF and Libxc, keeping the library compact, user-friendly, and interoperable. Worked examples on the ground state of H$_2$O and a broken-
symmetry $\Delta$SCF excited state of NH$_3$ show that a complete second-order CDFT analysis requires only a few lines of user code.
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All authors Bin Wang, Paul Geerlings, Paul W. Ayers, Frank De Proft
Chemical Physics
State-selective molecular orientation by vibrational Autler-Townes adiabatic passage
Meng-Yi Yu, Ya-Nan Lv, Cun-Feng Cheng et al. (+1 more)
Control of molecular angular momentum orientation enables state-resolved studies of molecular interactions and provides a basis for
quantum information processing. Here we propose all-optical Autler-Townes state-selective adiabatic passage (ASAP) to prepare molecules in a single $|J,M\rangle$ sublevel. An Autler-Townes branch created by a strong coupling field is selectively populated and adiabatically mapped onto the target vibrational state. We resolve detuning-dependent rovibrational Autler-Townes splitting in $^{13}$CO$_2$, establishing the spectroscopic basis for the selective excitation of the target dressed branch. The density-
matrix model calibrated by these spectra predicts transfer approaching 90%. The scheme can exploit millisecond vibrational radiative lifetimes within the electronic ground state and extend to polar and nonpolar molecules with infrared-active vibrational modes.
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All authors Meng-Yi Yu, Ya-Nan Lv, Cun-Feng Cheng, Shui-Ming Hu
Optics · Cross-listed from gr-qc
Analogue black hole lightring and its resonances in an optical fiber
R. Terrier, J. Fatome, B. Kibler et al. (+1 more)
We demonstrate the complete observation of a black-hole lightring resonance in an optical analogue. To do so, we generalize the concept of the
photon sphere to non-stationnary systems by showing that the lightring is associated to a spatiotemporal caustic and that its complex frequency is determined by the propagation and divergence of this caustic. For an optical
soliton acting as an analogue black-hole potential, we predict a characteristic spectral plateau whose boundaries are set by the real part of the lightring frequency, while its spectral decay is governed by the imaginary part. Using a pump-probe experiment in a 5-km-long dispersion-shifted fiber, we observe these signatures for two distinct pump wavelengths. The measured spectra agree with numerical simulations and with the predicted lightring-mode profile, providing direct access to both the oscillatory and decay properties of the resonance. Our results establish a direct experimental connection between black-hole lightrings, spacetime caustics, and quasinormal-mode spectroscopy in a dispersive analogue system.
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All authors R. Terrier, J. Fatome, B. Kibler, T. Torres
Medical Physics
AnatomIQ: An Open-Source Toolkit for Automated Background Detection in Medical Imaging
Rafael Carballeira, Hayley A. Cash and Marthony L. Robins
Manual background selection for contrast-to-noise ratio (CNR) calculations in CT image quality assessment is time-consuming, operator-dependent, and compromises reproducibility. Advanced metrics such as Noise Power Spectrum (NPS) and Task Transfer Function (TTF) traditionally require dedicated phantom acquisitions, adding cost, radiation exposure, and workflow disruption. We developed AnatomIQ, an open-source Python toolkit that automates background detection and performs phantom-free NPS and TTF analysis directly on patient anatomy. Automated background detection uses tissue-specific Hounsfield unit thresholding and morphological filtering, paired with a web interface for click-to-select lesion identification from PACS screenshots. Reported metrics include CNR, signal-to-noise ratio, detectability indices, and dose-normalized figures of merit with automated optimization recommendations. NPS quantifies noise texture from automatically detected uniform tissue regions, while TTF leverages natural circular anatomical structures (e.g., trachea, vessels) as edge phantoms, together characterizing the resolution-noise trade-off without dedicated phantom scans. Analysis takes 2-3 minutes per case, with CNR computed in under 10 seconds and NPS/TTF available on demand. Automated detection reliably identified valid regions across anatomical sites, including head-and-neck scans, a near-worst-case test of uniform-region availability. Both NPS and TTF pipelines were validated against phantom-derived references, confirming that in vivo measurements reflect genuine anatomical texture and resolution rather than pipeline artifacts. By eliminating operator variability and phantom requirements, AnatomIQ enables practical continuous quality monitoring and evidence-based reconstruction optimization. The toolkit is open-source, with optional commercial licensing for academic and clinical use.
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Atmospheric and Oceanic Physics · Cross-listed from math.DS
From trends to optimized forecasts: Quantifying the skill and advancing the utility of dynamics-based early warnings for tipping events
Franco Du Plessis, Victoria Volodina, Chris A. Boulton et al. (+5 more)
In this paper we explore and extend the state of the art for understanding the skill and utility of early warnings of critical transitions (tipping points) in forced nonlinear systems. We highlight some of the challenges and opportunities of transforming estimates of a dynamics-based early warning system, based on trends in stability or resilience into forecasts with high skill. We highlight the importance of (a) quantifying consequences of possible actions in response to warnings that may be false negatives or positives (b) considering finite time horizon predictions to give verifiable predictions (c) assumptions necessary for valid extrapolations of trends. We evaluate approaches to improving the skill and utility of the forecast.
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All authors Franco Du Plessis, Victoria Volodina, Chris A. Boulton, Muhammed Fadera, Sneha Kachhara, Timothy M. Lenton, Paul D. L. Ritchie, Peter Ashwin
Chemical Physics
Relativistic Hirshfeld atoms in a molecule: An information-theoretic view, with application to Drude oscillator dispersion models
Keegan Paice and John M. Herbert
Several ad hoc dispersion models for density-functional theory are based on the use of Hirshfeld (or "stockholder") partition of a molecular charge density, which provides an in situ definition of atomic size. We show that a recently introduced "optimized"
quantum Drude oscillator model for dispersion admits a closed-form solution in terms of the Lambert $W$ function, whose branches identify the compact and diffuse oscillator solutions. The compact solution determines the $C_8$ (dipole-quadrupole) dispersion coefficient analytically from the free-atom polarizability, $C_6$ coefficient, and van der Waals radius, without any reference $C_8$ data. Next, we provide a formal basis for a relativistic version of the atoms-in-molecule Hirshfeld partition. Using four-component Dirac-Hartree-Fock densities for isolated atoms defines a strictly positive deformation field that carries the relativistic changes in atomic density into the Hirshfeld partition. A uniqueness
theorem for the non-relativistic case is extended to relativistic Hirshfeld atoms and admits an asymptotic expansion through quadratic order in the fine-structure constant. Normalization requires the relativistic density correction to reshape the reference atom while preserving its population. Finally, four-component polarizabilities and C6 coefficients are reported for closed-shell atoms and ions, which supply the reference data required to extend atoms-in-molecules dispersion models into the heavy-element regime. Periodic trends are observable in a scalar contraction factor that measures relativistic effects.
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Accelerator Physics
From Simulation to Fabrication: Realizing Silicon Crystalline Undulators with Silicon Nitride Stressor Layer Patterning
L. Malagutti, L. Bandiera, F. Bonafè et al. (+14 more)
A crystalline undulator is a
crystal exhibiting periodic deformations that cause channeled particles to oscillate, generating coherent electromagnetic waves. In this study, stressor layer patterning has been employed to induce the desired deformations on a silicon substrate. Finite element method simulations were performed to optimize the
geometric parameters of the undulator. The primary focus was on achieving sinusoidal deformation with sub-millimeter period and amplitude exceeding 1~nm, utilizing the silicon (110) plane for its superior channeling properties. Key parameters, such as substrate thickness and undulator period, were meticulously refined to ensure uniform deformation while minimizing the impact of higher harmonics, which could degrade performance. Based on the simulation results, a crystalline undulator, 160 $\mu$m thick and consisting of 10 periods with a period length of 334 $\mu$m, has been successfully fabricated. The final device demonstrates structural integrity and a uniform deformation extending up to 20 $\mu$m from the surface. Specifically designed for use with 5-30 GeV particle beams, the undulator is capable of generating gamma
photons in the 5-15 MeV range. This work effectively integrates advanced simulation techniques with precise fabrication methods, demonstrating the feasibility of crystalline undulators as high-performance devices for generating gamma radiation.
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All authors L. Malagutti, L. Bandiera, F. Bonafè, N. Canale, D. De Salvador, P. Fedeli, V. Guidi, A. V. Korol, F. Mancarella, R. Negrello, Gianfranco Paternò, M. Romagnoni, F. Sgarbossa, A.V. Solov'yov, A. Sytov, D. Valzani, A.Mazzolari
Chemical Physics
Numerical integration of intracule pair densities with optimized multicenter grids
Markel Ylla, Jesus M. Ugalde, Eduard Matito et al. (+1 more)
Intracule pair densities provide insight into electron correlation, but their routine analysis in extended systems is limited by the cost of numerical integration and the restriction of analytical methods to Gaussian basis functions. We present an efficient multicenter integration scheme for intracule densities and their moments. By adapting the topological fuzzy Voronoi
cell formalism, we partition intracule space around interatomic displacement vectors, concentrating quadrature points near secondary density maxima that standard single-center grids poorly resolve.
Benchmarks on linear alkanes show improved convergence with increasing molecular size, achieving relative errors below 0.02% in electron-electron repulsion energies with fewer quadrature points than single-center methods. The partitioning also enables the decomposition of global two-electron properties into spatial contributions associated with short- and long-range electron-pair separations. Coupling the multicenter grid with kernel density estimation reconstructs smooth radial intracule distributions at large interelectronic distances without the dense angular grids required by conventional surface integration. Validation on the S22
dataset supports the reliability of the method across diverse molecular systems. These developments facilitate intracule analysis in polyatomic systems and the investigation of electron correlation and dispersion interactions.
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All authors Markel Ylla, Jesus M. Ugalde, Eduard Matito, Eloy Ramos-Cordoba
Fluid Dynamics
Femtosecond laser-induced cavitation seeds liquid-jet breakup beyond the Rayleigh-Plateau stability limit
Sourabh Singh, Tamanna, S. Sree Harsha et al. (+1 more)
The Rayleigh-Plateau instability predicts that infinitesimal perturbations of a
liquid jet grow only for kR < 1, with kR = 1 marking the classical stability boundary. Here, we show that femtosecond-
laser-induced cavitation generates a localized, impulsive recoil perturbation on a flowing
liquid jet, enabling a two-dimensional map of jet breakup across the (kR, epsilon/R) plane. The perturbation's spacing (wavelength) and strength (amplitude) are set independently by the
laser repetition rate and pulse energy, respectively. At low amplitudes, tuning the repetition rate recovers the classical Rayleigh-Plateau dispersion relation and its kR = 1 cutoff, while increasing the wavelength enables controlled generation of monodisperse droplet trains, bidisperse droplet populations, and ultimately isolated single droplets. Along the amplitude axis, low pulse energies produce a seed that amplifies only the imposed wavenumber, whereas above a critical energy Ec, the seed broadens to excite many wavenumbers simultaneously. At still higher amplitudes, we demonstrate deterministic breakup for kR > 1, extending to kR = 1.9, with
laser-synchronized droplet production rates up to 0.2 MHz. These results establish localized femtosecond-
laser-induced cavitation as a route to controlled Rayleigh-Plateau breakup both within and beyond the classical linear-stability boundary.
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All authors Sourabh Singh, Tamanna, S. Sree Harsha, Prashant Kumar Singh
Fluid Dynamics
An unstructured finite-volume Helmholtz method with perfectly matched layers for heterogeneous two-phase acoustics
Chuanchao Xu, Jun Liu, Jan Helge Dörsam et al. (+3 more)
This paper presents a
cell-centred unstructured finite-volume method for time-harmonic two-phase acoustics. A volume-fraction representation supplies density and acoustic compressibility. Face fractions average available neighbouring planar interface cuts independently of velocity direction, retaining the established one-field face-density closure. Cartesian complex-coordinate stretching provides perfectly matched layers (PMLs). Real-imaginary splitting yields a real-valued block system, discretized with corrected non-orthogonal fluxes and consistent boundary contributions. Verification covers homogeneous waves, layered gas-
liquid transmission with PML truncation, baffled-piston radiation with Kirchhoff far-field reconstruction, and resolved rigid-sphere radiation forces. Homogeneous-wave pressure converges at approximately second order on orthogonal meshes and on meshes with non-orthogonal interiors and orthogonal boundary
cells. Reconstructed velocity converges at approximately second order on orthogonal meshes and with an observed order of about 1.7 on the latter mesh family. Under aligned refinement, the layered case's relative whole-domain complex-pressure $L_2$ error decreases to $2.657\times10^{-4}$. The resolved-sphere force differs from the Gorkov prediction by at most 1.5% over the tested Rayleigh size range. The results quantify the accuracy and current limitations of the heterogeneous Helmholtz-PML formulation.
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All authors Chuanchao Xu, Jun Liu, Jan Helge Dörsam, Mario Kupnik, Tomislav Maric, Dieter Bothe
Fluid Dynamics
Total Collision Energy model for surface processes in the DSMC method
Yevgeniy A. Bondar and Alexandra N. Molchanova
The total collision energy (TCE) approach originally developed for taking into account gas-phase chemistry in the direct simulation Monte Carlo method is applied to surface chemistry modeling. In the proposed surface TCE (sTCE) model probability of the impact process as a function of the translational energy of the molecule is found analytically from the finite-rate Arrhenius data. This probability function lacks some mathematical drawbacks typical of previous models. Effects of surface temperature, incident angle and internal energy can be taken into account in the sTCE model. Additionally the model is generalized to the specified reaction efficiency formulation.
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