Chemical Physics
Benchmarking mixed quantum-classical dynamics for collective electronic strong coupling
Arun Kumar Kanakati, Oriol Vendrell and Gerrit Groenhof
Experiments indicate that collective coupling of molecular ensembles to confined optical modes can modify excited-state dynamics and photochemical reactivity. To describe such cavity-induced effects at atomic resolution, semi-classical molecular dynamics approaches have been developed that treat
nuclear motion classically while describing the collective light-matter interaction within the Tavis-Cummings framework of
quantum electrodynamics. Here, we
benchmark mixed
quantum-classical approaches, Ehrenfest dynamics and Fewest-Switches Surface Hopping (FSSH), for simulating nonadiabatic dynamics of electronically strongly coupled carbon monoxide molecules. Their predictions are compared against numerically exact
quantum dynamics simulations performed with the multi-configuration time-dependent Hartree (MCTDH) method, which treats both electronic and
nuclear degrees of freedom
quantum mechanically. We find that the semi-classical approaches reproduce the qualitative features of the full
quantum dynamics. Quantitative agreement is best achieved with FSSH when a decoherence correction is included. These results demonstrate that mixed
quantum-classical methods provide a computationally efficient and quantitatively reliable alternative to fully
quantum simulations for investigating nonadiabatic photochemistry under collective electronic strong coupling in systems beyond the reach of exact
quantum treatments.
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Atmospheric and Oceanic Physics · Cross-listed from astro-ph.EP
Detection of C3 in Titan with VLT-ESPRESSO
Rafael Rianço-Silva, Pedro Machado, Pascal Rannou et al. (+3 more)
Titan is regarded as a natural laboratory in the
Solar System for studying atmospheric photochemistry and the abiotic production of organic molecules on cold small
exoplanets. Since the end of the Cassini-Huygens mission,
telescope observations have enabled new detections of increasingly complex carbon-based molecules at infrared and sub-millimetre wavelengths, while the optical regime has been largely overlooked. Following a recent tentative detection of the 405 nm absorption band of C3 in Titan in archived optical VLT UVES spectra at resolving power R = 60000, this work reports an eight sigma detection of the C3 405 nm absorption band in Titan using dedicated ultra high resolution VLT ESPRESSO observations at R = 190000, the highest spectral resolution optical observations of Titan to date. The VLT ESPRESSO spectrum is compared to model spectra of Titan with varying C3 abundances. A chi squared analysis is used to assess the agreement between non
solar spectral features and C3 absorption as the C3 abundance is varied, and a
Bayesian Markov Chain Monte Carlo fit between model and observed spectra is performed. The chi squared analysis yields an eight sigma detection of C3, consistent with a C3 column density of approximately 1.5E13 cm-2, while the MCMC fit retrieves a C3 column density of 1.47E13 cm-2 at five sigma. These values are consistent with the order of magnitude predicted by photochemical models, which reach parts per million levels in the Titan mesosphere. This work demonstrates the usefulness of instruments and techniques originally developed for
exoplanet research when applied to
Solar System targets.
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All authors Rafael Rianço-Silva, Pedro Machado, Pascal Rannou, Jorge Martins, Anthony E. Lynas-Gray, Giovanna Tinetti
Optics
Cubic magneto-optic Kerr effect in Co(111) thin films
Maik Gaerner, Robin Silber, Malte Schäffer et al. (+4 more)
The magneto-optic Kerr effect (MOKE) is often applied as a tool for the
magnetic characterization of thin films. Here, the change in polarization upon reflection from the magnetized sample is mainly regarded as being linearly proportional to the magnetization $\mathbf{M}$ (LinMOKE). MOKE contributions of second order in $\mathbf{M}$, also known as quadratic MOKE (QMOKE), which are proportional to $\mathbf{M}^2$, have also been studied in the past and used in thin film characterization. Recently, we reported on a systematic investigation of third-order MOKE contributions, named cubic MOKE (CMOKE) in Ni(111) thin films. This CMOKE manifests itself as an anisotropic contribution to the MOKE signal (with regard to the crystallographic orientation) measured in longitudinal or transversal configuration in full
magnetic saturation. While LinMOKE (odd in $\mathbf{M}$) and QMOKE (even in $\mathbf{M}$) can easily be separated by methods based on magnetization parity, this no longer holds true for LinMOKE and CMOKE (odd in $\mathbf{M}$). It is therefore crucial to be aware of CMOKE contributions in order to correctly interpret MOKE data. Here, we report on the observation of CMOKE in thin film
heterostructures with structurally twinned and untwinned Co(111) layers, demonstrating that a large CMOKE is not only present in Ni thin films. Additionally, we show that the observed anisotropic contributions cannot stem from LinMOKE by analyzing their dependence on the angle of incidence (AoI) of light. While the QMOKE is almost vanishing in Co(111) using light with wavelengths of 635\,nm and 406\,nm, the CMOKE contributions reach up to about 30% of the LinMOKE contribution at an AoI of 45 degrees and become even more dominant towards normal AoI, which emphasizes the importance of higher-order MOKE effects in magneto-optic experiments.
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All authors Maik Gaerner, Robin Silber, Malte Schäffer, Jaroslav Hamrle, Andrea Ehrmann, Martin Wortmann, Timo Kuschel
Chemical Physics
Impact of scissors-correction schemes on first-principles calculations of second-harmonic generation in ultraviolet nonlinear-optical crystals
YingXing Cheng, Congwei Xie, Zhihua Yang et al. (+1 more)
In this work, we assess two widely used scissors-correction schemes for first-principles calculations of second-harmonic generation in representative borate and phosphate ultraviolet nonlinear-optical (UV-NLO)
crystals, namely scheme-L [Phys.\ Rev.\ Lett.\ 63, 1719 (1989)] and scheme-N [Phys.\ Rev.\ B 72, 045223 (2005)]. To enable controlled and numerically robust comparisons, we derive a unified static-limit formulation that avoids spurious divergences and is applicable to both schemes, thereby extending earlier static-limit treatments that were effectively restricted to scheme-L.
Benchmark calculations show that both schemes largely preserve the spectral line shape while mainly rescaling the overall response. Scheme-N systematically yields 15%–25% larger SHG magnitudes than scheme-L, although for some tensor components and experimental
datasets scheme-L shows closer agreement with experiment. We further show that Kleinman
symmetry is satisfied in the static limit at the level of the formal theory, whereas apparent violations in practical calculations arise mainly from the numerical approximation used to evaluate generalized derivatives.
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All authors YingXing Cheng, Congwei Xie, Zhihua Yang, Shilie Pan
Optics
Pulse-duration-sensitive high harmonics and attosecond locally-chiral light from a chiral topological Weyl semimetal
Alba de las Heras, Ofer Neufeld and Angel Rubio
High harmonic generation (HHG) in solids results from an interplay between intraband acceleration and electron-hole recombination driven by a high-intensity
laser pulse. Here, we theoretically reveal that the driving pulse duration can play a major role in extending HHG to higher
photon energies by promoting higher conduction band excitations. The effect is present in a conventional
semiconductor as Si, restricted in a large-gap
insulator as MgO, and most prominent in RhSi, a prototypical
chiral Weyl semimetal presenting numerous band crossings. Further, we elucidate the HHG selection rules in RhSi required for the synthesis of attosecond locally
chiral light. The
chiral crystal structure enables the generation of a local 3D electric field exhibiting an asymmetric instantaneous torsion on attosecond timescales. A pronounced circular dichroism emerges when the driving helicity is either aligned with or opposite to the
crystal handedness. Our findings motivate future experiments in
chiral Weyl semimetals to track high-energy band crossings and in-situ locally
chiral light, paving the way for
chiral compact light sources and light-wave driven topological electronics.
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Physics and Society
The effect of a toroidal opinion space on opinion bi-polarisation
Frank P. Pijpers, Benedikt V. Meylahn and Michel R.H. Mandjes
Many models of opinion dynamics include measures of distance between opinions. Such models are susceptible to boundary effects where the choice of the
topology of the opinion space may influence the dynamics. In this paper we study an opinion dynamics model following the seminal model by Axelrod, with the goal of understanding the effect of a toroidal opinion space. To do this we systematically compare two versions of the model: one with toroidal opinion space and one with cubic opinion space. In their most basic form the two versions of our model result in similar dynamics (consensus is attained eventually). However, as we include bounded confidence and eventually per
agent weighting of opinion elements the dynamics become quite contrasting. The toroidal opinion space consistently allows for a greater number of groups in steady state than the cubic opinion space model. Furthermore, the outcome of the dynamics in the toroidal opinion space model are more sensitive to the inclusion of extensions than in the cubic opinion space model.
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Fluid Dynamics · Cross-listed from math.NA
Approaching the optimal closure: equivariance, inductive bias, and Reynolds-number generalization in data-driven LES
Syver Døving Agdestein and Benjamin Sanderse
Data-driven closures for large-eddy simulation (LES) are commonly built to respect the
symmetries of the Navier–Stokes equations, on the premise that this improves accuracy and generalization. We test this premise in a controlled comparison of three data-driven LES closures that share a pointwise, Galilean-invariant velocity-gradient construction but span non-equivariant, octahedral-equivariant, and tensor-basis designs: an unconstrained multi-layer perceptron (MLP), a group-convolutional network whose exactly equivariant weights we synthesize in closed form, and a tensor-basis neural network (TBNN). The designs follow from an analysis of which
symmetries survive discretization on a uniform grid, where the continuous orthogonal group reduces to the 48-element octahedral group. Across a range of network sizes the three closures saturate to the same a priori and a posteriori accuracy, and a direct conditional-mean estimate identifies the a priori floor as the one-point optimal closure of Langford and Moser. The equivariant and tensor-basis models reach this floor with $25$ times fewer parameters than the MLP: the inductive bias buys parameter efficiency rather than a lower error floor. Finally, we train the closures across several viscosities and supply the global filter-scale Reynolds number $\operatorname{Re}_\Delta = \Delta^2 \| \nabla \bar{u} \| / \nu$ as an input, a scaling-invariant feature dictated by the same
symmetry analysis. The closures then generalize across Reynolds number: they hold their dissipation calibration at held-out viscosities and filter ratios where Reynolds-blind closures mis-dissipate, and partially correct it on an out-of-distribution Taylor–Green flow. Reynolds-number generalization is thus largely a calibration that the right input feature supplies.
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Atmospheric and Oceanic Physics · Cross-listed from astro-ph.EP
Hydrodynamic escape from the proto-lunar disk and the origin of the Earth-Moon volatile dichotomy
Kaveh Pahlevan, Andrew N. Youdin and Paolo A. Sossi
Volatile elements - those that vaporize at low temperatures - are depleted in lunar rocks relative to terrestrial rocks. This systematic chemical depletion is evidence for vaporization and preferential removal of vapor from proto-lunar materials during the high-temperature processes accompanying lunar origin. Despite the robustness of these observations, the physical processes by which proto-lunar vapors were removed after the
giant impact are not yet well-understood. Here, we show that toward the end of post-
giant impact cooling history, Earth's atmosphere was dominated by carbon species (e.g., CO) and was spatially compact, behaving as a closed system retaining Earth's volatile inventory, whereas the proto-lunar disk atmosphere was dominated by H and H2 and was spatially extended, developing into a hydrodynamic
outflow analogous to the
solar wind. We find that
equilibrium H2 recombination (2H->H2) in a partially-dissociated disk atmosphere produces a nearly isothermal structure, a feature known to activate
outflows. The expected
outflow was strong enough to propel proto-lunar volatiles from a Roche-interior (r < 3RE) disk out of Earth's
gravity field and to establish a cometary tail composed of volatile elements transporting proto-lunar disk volatiles into interplanetary space. The proposed model suggests that the dichotomy in volatile element abundances between the silicate Earth and Moon is a natural outcome of the hydrodynamical behavior of magma ocean atmospheres and that lunar chemical and isotopic volatile abundances are diagnostic of the radial structure of the proto-lunar disk towards the end of its condensation.
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Chemical Physics
The Angular Localization Function (ALF): a practical tool to measure solvent angular order with Molecular Density Functional Theory
Maïwenn Souetre, Benjamin Rotenberg and Guillaume Jeanmairet
Molecular density functional theory is a powerful technique for efficiently computing the spatially and orientationally dependent
equilibrium density of a molecular solvent around an arbitrary solute. This density encodes the detailed solvent structure, but contains so much information that it is difficult to interpret comprehensively. Although spatial dependence is frequently analyzed through orientationally integrated number density, angular information remains poorly exploited. The present work addresses this gap by introducing a function that provides a local measure of the angular order: the Angular Localization Function (ALF), derived from the ideal free energy functional, which quantifies the
entropy. We discuss the connections between ALF and well known statistical functions. We illustrate the utility of ALF by discussing the solvent structure for three systems immersed in water: water as a solute, an octanol molecule, and three clay minerals (talc, fluorotalc and pyrophyllite) with small differences in their structure leading to subtle effects on their interactions with water. ALF provides information complementary to quantities such as the average polarization or charge density to characterize the local orientational distribution of solvent molecules around solutes and next to surfaces. It also offers a convenient visualization tool akin to the Electronic Localization Function (ELF) used to analyze bonding in
quantum chemistry.
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Chemical Physics
Why Projection-Based DMRG-in-DFT Cannot Be Exact, Even with the Exact Exchange-Correlation Functional
Enzo Monino, Daria Drwal, Michał Hapka et al. (+2 more)
We establish the theoretical foundations for
embedding a correlated wave function in an environment formed by Kohn-Sham orbitals. We show that introducing an approximation which equates two, in principle distinct, kinetic-energy functionals yields an
embedding functional identical to the projection-based wavefunction-in-DFT formulation of Miller and co-workers. We demonstrate that this functional is inherently nonvariational: its minimum is not guaranteed to coincide with the exact ground-state energy and remains bounded from above by it. Building on this formal framework, we analyze the dominant sources of error in projection-based DMRG-in-DFT
embedding with approximate exchange-correlation (xc) functionals. Using molecules with dissociating covalent bonds as a diagnostic example, we demonstrate that the primary source of error is the nonadditive exchange-correlation energy describing the nonclassical coupling between the active subsystem and its environment. Eliminating the fractional-
spin error by employing a pair-density xc functional (PDFT) instead of a semilocal GGA does not remedy this deficiency, because the inaccuracy stems from self-interaction effects at the subsystem-environment interface.
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All authors Enzo Monino, Daria Drwal, Michał Hapka, Libor Veis, Katarzyna Pernal
Fluid Dynamics · Cross-listed from cond-mat.soft
Dynamic Wettability Modulation of Textured, Soft and LIS Interfaces Using Electrowetting
Deepak J., Suman Chakraborty, Shubham S. Ganar et al. (+1 more)
Electrowetting on textured and lubricant infused surfaces is conventionally expected to promote enhanced droplet spreading by reducing apparent contact angles. Contrary to this intuition, we report rapid tangential droplet ejection at applied DC voltages on specific microtextured, lubricant infused surfaces. Using high speed imaging and a precisely controlled electrowetting setup, we reveal the dependence of droplet dynamics on surface
topology, wetting state, and the presence of a lubricant. On densely textured thick PDMS substrates of post spacing 5 to 10 um in a low hysteresis non-wetting Cassie state, and on all lubricant infused textured surfaces, droplets experience sudden lateral motion and eventual detachment. We attribute this counterintuitive phenomenon to unbalanced electrocapillary forces at the contact line combined with minimal pinning, which allows asymmetries in electric stresses to translate directly into net lateral motion. In contrast, Wenzel state droplets or surfaces with larger texture spacing exhibit conventional spreading with strong adhesion. By capturing the fundamental interplay among electrostatic driving forces, contact line pinning, and interfacial mobility, our results provide a new paradigm for controlled droplet transport and ejection in electrowetting systems mediated by dense micro posts and lubricant induced interfaces.
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All authors Deepak J., Suman Chakraborty, Shubham S. Ganar, Arindam Das
Physics and Society
Wealth Taxation as a Drift Modification: A Fokker-Planck Approach to Tax Neutrality
Anders G Frøseth
We reformulate the neutral wealth tax framework of Froeseth (2026; arXiv:2603.05264) in the
language of
stochastic dynamics and statistical physics. Individual wealth under
geometric Brownian motion satisfies a Langevin equation with multiplicative noise; the probability density of wealth across a population then evolves according to a Fokker-Planck equation. A proportional wealth tax at
market value enters as a uniform reduction of the drift coefficient, preserving the
diffusion structure and all relative probability currents. This drift-shift
symmetry is the physical content of tax neutrality. Each channel through which neutrality breaks down in practice - book-value assessment, liquidity frictions, forced dividend extraction, migration, and
market impact - corresponds to a specific violation of this
symmetry: a state-dependent, asset-dependent, or flow-dependent modification of the Fokker-Planck equation. The framework clarifies when wealth taxation is a benign rescaling of the dynamics and when it introduces genuinely new physics.
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Plasma Physics
Probing vacuum birefringence in an Ultrastrong Laser Field via High-energy Gamma-ray Polarimetry
Da-Lin Wang, Xian-Zhang Wu, Rui-Qi Qin et al. (+5 more)
Vacuum birefringence (VB), a fundamental prediction of nonlinear
quantum electrodynamics (QED), has eluded direct laboratory detection due to its extreme weakness. We propose a compact, "self-probing" scheme where a GeV electron beam collides head-on with a petawatt
laser pulse. Circularly polarized gamma-ray
photons, generated via nonlinear Compton scattering in the same pulse, then probe the birefringent
vacuum it induces. This integrated design bypasses the stringent synchronization and beam transport requirements of traditional pump-probe setups. Our nonperturbative strong-field QED simulations reveal a clear VB signature: conversion of circular to linear polarization, with the induced Stokes parameter $S_1$ reaching ~0.019 within the selected angular range. This corresponds to a refractive index difference $\Delta n = 1.829 \times 10^{-4}$ over micron-scale paths, directly measurable as a high-contrast "X-shape" asymmetry in $e^+e^-$ pair distributions. The scheme provides a feasible path to first laboratory VB detection with current
laser and accelerator technologies.
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All authors Da-Lin Wang, Xian-Zhang Wu, Rui-Qi Qin, Jiang-Tao Han, Peng-Pei Xie, Bing-Jun Li, Huai-Hang Song, Yan-Fei Li
Physics and Society
Extensions to the Wealth Tax Neutrality Framework
Anders G Frøseth
Frøseth (2026; arXiv:2603.05264) shows that a proportional wealth tax on
market values is neutral with respect to portfolio choice, Sharpe ratios, and
equilibrium prices under CRRA preferences and
geometric Brownian motion. This paper investigates the robustness of that result along two dimensions. First, we extend the neutrality frontier: portfolio neutrality – including all intertemporal hedging demands – is preserved under
stochastic volatility (Heston and general Markov
diffusions) and Epstein-Zin recursive utility, but breaks under non-homothetic preferences such as HARA. Second, we identify four channels through which implemented wealth taxes depart from neutrality even under CRRA: non-uniform assessment across asset classes, general
equilibrium price effects in inelastic
markets, progressive threshold structures, and endogenous labour supply. Each channel is formalised and, where possible, calibrated to the Norwegian wealth tax system. The progressive threshold introduces a tax shield that increases risk-taking near the exemption boundary – an effect opposite in sign to the HARA distortion – and, at the extreme, generates a participation margin at which investors exit the tax jurisdiction entirely. We formalise this tax-induced migration as the extreme response at the progressive threshold and examine the Norwegian post-2022 experience as a case study. The full framework is applied to evaluate the Saez-Zucman proposal for a global minimum wealth tax on billionaires and the related French proposal for a national minimum tax above EUR 100 million.
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Physics and Society
Asset Returns, Portfolio Choice, and Proportional Wealth Taxation
Anders G Frøseth
We analyse the effect of a proportional wealth tax on asset returns, portfolio choice, and asset pricing. The tax is levied annually on the
market value of all holdings at a uniform rate. We show that such a tax is economically equivalent to the government acquiring a proportional stake in the investor's portfolio each period – a form of risk sharing in which expected wealth and risk are reduced by the same factor, while the return per share is unaffected. This multiplicative separability drives four main results. First, the coefficient of variation of wealth is invariant to the tax rate. Second, the optimal portfolio weights – and in particular the tangency portfolio – are independent of the tax rate. Third, the wealth tax is orthogonal to portfolio choice: it induces a homothetic contraction of the opportunity set in the mean-standard deviation plane that preserves the Sharpe ratio of every portfolio. Fourth, both taxed and untaxed investors are willing to pay the same price per share for any asset. The results are derived first under
geometric Brownian motion and then generalised to any return distribution in the location-scale family. A complementary Modigliani-Miller analysis confirms pricing neutrality and identifies an inconsistency in the existing literature regarding the discount rate used for after-tax cash flows. Imposing the CAPM as a special case confirms that after-tax betas equal pre-tax betas and the security
market line contracts uniformly by $(1-\tau_w)$; under CRRA preferences, general-
equilibrium returns and prices are unchanged. This resolves an error in Fama (2021). The neutrality results depend on universal taxation at
market value and frictionless
markets. We formalise three channels – book-value taxation, liquidity frictions, and dividend extraction – through which these conditions break neutrality.
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Data Analysis and Statistics · Cross-listed from q-fin.ST
Extreme Value Analysis for Finite, Multivariate and Correlated Systems with Finance as an Example
Benjamin Köhler, Anton J. Heckens and Thomas Guhr
Extreme values and the tail behavior of probability distributions are essential for quantifying and mitigating risk in complex systems of all kinds. In multivariate settings, accounting for correlations is crucial. Although extreme value analysis for infinite correlated systems remains an open challenge, we propose a practical framework for handling a large but finite number of correlated time series. We develop our approach for finance as a concrete example but emphasize its generality. We study the extremal behavior of high-frequency stock returns after rotating them into the eigenbasis of the correlation
matrix. This separates and extracts various collective effects, including information on the correlated
market as a whole and on correlated sectoral behavior from idiosyncratic features, while allowing us to use univariate tools of extreme value analysis. This holds even for high-frequency data where discretization effects normally complicate analysis. We employ a peaks-over-threshold approach and thereby fully avoid the analysis of block maxima. We estimate the tail shape of the rotated returns while explicitly accounting for nonstationarity, a key feature in finance and many other complex systems. Our framework facilitates tail risk estimation relative to larger trends and intraday seasonalities at both
market and sectoral levels.
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Medical Physics · Cross-listed from eess.IV
ICHOR: A Robust Representation Learning Approach for ASL CBF Maps with Self-Supervised Masked Autoencoders
Xavier Beltran-Urbano, Yiran Li, Xinglin Zeng et al. (+10 more)
Arterial
spin labeling (ASL) perfusion MRI allows direct quantification of regional cerebral blood flow (CBF) without exogenous contrast, enabling noninvasive measurements that can be repeated without constraints imposed by contrast injection. ASL is increasingly acquired in research studies and clinical MRI protocols. Building on successes in structural imaging, recent efforts have implemented deep learning based methods to improve image quality, enable automated quality control, and derive robust quantitative and predictive biomarkers with ASL derived CBF. However, progress has been limited by variable image quality, substantial inter-site, vendor and protocol differences, and limited availability of labeled
datasets needed to train models that generalize across cohorts. To address these challenges, we introduce ICHOR, a self supervised pre-training approach for ASL CBF maps that learns transferable representations using 3D masked autoencoders. ICHOR is pretrained via masked image modeling using a
Vision Transformer backbone and can be used as a general-purpose encoder for downstream ASL tasks. For pre-training, we curated one of the largest ASL
datasets to date, comprising 11,405 ASL CBF scans from 14 studies spanning multiple sites and acquisition protocols. We evaluated the pre-trained ICHOR encoder on three downstream diagnostic classification tasks and one ASL CBF map quality prediction regression task. Across all evaluations, ICHOR outperformed existing neuroimaging self-supervised pre-training methods adapted to ASL. Pre-trained weights and code will be made publicly available.
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All authors Xavier Beltran-Urbano, Yiran Li, Xinglin Zeng, Katie R. Jobson, Manuel Taso, Christopher A. Brown, David A. Wolk, Corey T. McMillan, Ilya M. Nashrallah, Paul A. Yushkevich, Ze Wang, John A. Detre, Sudipto Dolui
Physics and Society
The role of spatial scales in assessing urban mobility models
Rakhi Manohar Mepparambath and Hoai Nguyen Huynh
Urban mobility models are essential tools for understanding and
forecasting how people and goods move within cities, which is vital for transportation planning. The spatial scale at which urban mobility is analysed is a crucial determinant of the insights gained from any model as it can affect models' performance. It is, therefore, important that urban mobility models should be assessed at appropriate spatial scales to reflect the underlying dynamics. In this study, we systematically evaluate the performance of three popular urban mobility models, namely
gravity, radiation, and visitation models across spatial scales. The results show that while the visitation model consistently performs better than its
gravity and radiation counterparts, their performance does not differ much when being assessed at some appropriate spatial scale common to all of them. Interestingly, at scales where all models perform badly, the visitation model suffers the most. Furthermore, results based on the conventional admin boundary may not perform so well as compared to distance-based clustering. The cross examination of urban mobility models across spatial scales also reveals the spatial organisation of the urban structure.
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Optics
Self-organization of cavity solitons in Brillouin-Kerr ring resonators
Corentin Simon, Matteo Conforti, Loïc Van Bellinghen et al. (+4 more)
We report on the interaction between stimulated Brillouin scattering and temporal cavity
solitons in doubly resonant ring resonators. Our experiments are performed in coherently driven passive optical-fibre resonators. We demonstrate that the interplay between four-wave mixing and cascade Brillouin lasing spontaneously generates patterns of CSs on a temporal grid at twice the Brillouin-shift. These patterns are shown to be highly stable owing to a long-range locking mechanism mediated by the acoustic oscillation generated by the
solitons. We introduce a unified mean-field model of the cavity to describe the dynamics between the coupled forward and backward waves under coherent driving. This model reproduces very well the experiments and explains the paracrystalline structures of the
soliton pattern. Our findings significantly advance the understanding of hybrid Brillouin-Kerr optical frequency combs.
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All authors Corentin Simon, Matteo Conforti, Loïc Van Bellinghen, Maxime Fournier, Arnaud Mussot, François Leo, Simon-Pierre Gorza
Chemical Physics
Escaping the Hydrolysis Trap: An Agentic Workflow for Inverse Design of Durable Photocatalytic Covalent Organic Frameworks
Iman Peivaste, Nicolas D. Boscher, Ahmed Makradi et al. (+1 more)
Covalent organic frameworks (COFs) are promising photocatalysts for
solar hydrogen production, yet the most electronically favorable linkages, imines, hydrolyze rapidly in water, creating a stability–activity trade-off that limits practical deployment. Navigating the combinatorial design space of nodes, linkers, linkages, and functional groups to identify candidates that are simultaneously active and durable remains a formidable challenge. Here we introduce Ara, a large-
language-model (LLM)
agent that leverages pretrained chemical knowledge, donor–acceptor theory, conjugation effects, and linkage stability hierarchies, to guide the search for photocatalytic COFs satisfying joint band-gap, band-edge, and hydrolytic-stability criteria. Evaluated against random search and
Bayesian optimization (BO) over a space consisting of candidates with various nodes, linkers, linkages, and r-groups, screened with a GFN1-xTB fragment pipeline, Ara achieves a 52.7% hit rate (11.5$\times$ random, p = 0.006), finds its first hit at iteration 12 versus 25 for random search, and significantly outperforms BO (p = 0.006). Inspection of the
agent's
reasoning traces reveals interpretable chemical logic: early convergence on vinylene and beta-ketoenamine linkages for stability, node selection informed by electron-withdrawing character, and systematic R-group optimization to center the band gap at 2.0 eV. Exhaustive evaluation of the full search space uncovers a complementary exploitation–exploration trade-off between the
agent and BO, suggesting that hybrid strategies may combine the strengths of both approaches. These results demonstrate that LLM chemical priors can substantially accelerate multi-criteria materials discovery.
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All authors Iman Peivaste, Nicolas D. Boscher, Ahmed Makradi, Salim Belouettar
Biological Physics · Cross-listed from cond-mat.stat-mech
Waiting-time based entropy estimators in continuous space without Markovian events
Jonas H. Fritz and Udo Seifert
Estimating
entropy production in continuous systems that can only be observed with a limited resolution remains an open problem in
stochastic thermodynamics. Existing
estimators based on the measurement of waiting-time distributions require either the detection of Markovian events, which uniquely determine the state of the system, or assume a discrete underlying dynamics. We present a novel
estimator that relies solely on the detection of a single particle leaving or entering regions, or crossing
manifolds, in continuous space. This
estimator is based on the frequency and the duration of transitions between such events. We derive this bound by introducing two kinds of discretization of space. Finally, we compare our novel bound to the thermodynamic uncertainty relation improved by correlations using simulations of a Brownian
vortex and discuss its relation to other lower bounds to
entropy production.
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Applied Physics
Foil-Mediated Mutual-Impedance in Microwave Cavities with Enhanced Phase Response
Michael T. Hatzon, Graeme R. Flower, Robert C. Crew et al. (+4 more)
We formulate and validate an equivalent
circuit model describing mutual coupling between three microwave cavity resonators interconnected via thin metallic foils. Each cavity is represented as a lumped LCR
circuit, while the foils act as interfaces that mediate energy exchange via mutual impedance. This coupling mechanism produces interference effects and a controllable antiresonance when the input resonators are amplitude- and phase-balanced, while enabling coupling across a continuous metallic interface without direct
antenna or aperture coupling. All three resonators operated in the TM$_{010}$ mode, where two input resonators each excited the third via a thin copper foil. Analytical expressions are derived for the mutual impedance and coupling coefficient of these foils in this geometry. Under balanced conditions, a sharp antiresonance emerges with a several-fold enhanced phase sensitivity at the resonant frequency of the output cavity, consistent with model predictions. The experimentally extracted normalised mutual coupling coefficients, $\Delta_{13}=(10.8\pm0.3)\times10^{-6}$ and $\Delta_{23}=(8.6\pm0.2)\times10^{-6}$, fall within the calculated range $\Delta_{n3}\approx(7\text{--}17)\times10^{-6}$ derived from the foil's electromagnetic properties, where the spread is dominated by the estimated foil thickness uncertainty of $(8.9\pm0.4)\,\mu\mathrm{m}$. These results demonstrate a foil-mediated physical implementation of weak mutual coupling across a metallic interface spanning multiple skin depths, providing a distinct route for engineering controlled interference in three-dimensional multi-resonator systems.
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All authors Michael T. Hatzon, Graeme R. Flower, Robert C. Crew, Ethan Han, Ben T. McAllister, Jeremy F. Bourhill, Michael E. Tobar
Optics
Integrated Microcomb-Driven Vortex Electromagnetic Waves for Broadband Forward-looking Sensing
Guanqun Sun, Zhekai Zheng, Jiacheng Guo et al. (+6 more)
Microwave sensing is a critical enabler for all-weather perception, yet its resolution is fundamentally capped by the diffraction limit of the physical
antenna aperture. While
vortex electromagnetic (EM) waves offer a route to bypass this barrier, practical deployment is constrained by the trade-off between bandwidth, mode purity, and hardware complexity. Here, we propose a microwave photonic architecture enabled by a chip-scale dissipative Kerr
soliton (DKS) microcomb that resolves these constraints. The microcomb provides a grid of over 270 optical lines with linewidths below 30 kHz, which are modulated and optically processed to synthesize
vortex waves covering 8 GHz (18-26 GHz) with 15 programmable orbital angular momentum (OAM) modes. In contrast to conventional parallel-
laser systems, our approach reduces phase error and improves OAM mode purity, while condensing the multi-wavelength source onto a monolithic chip. We demonstrate superior forward-looking imaging performance, clearly resolving both point targets and complex scenes. This work establishes a scalable framework bridging integrated
soliton physics with broadband microwave processing, paving the way for next-generation compact smart sensors.
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All authors Guanqun Sun, Zhekai Zheng, Jiacheng Guo, Wenjun Qi, Hao Zhang, Jijun He, Fangzheng Zhang, Yiping Wang, Shilong Pan
Chemical Physics
Particle-Guided Diffusion for Gas-Phase Reaction Kinetics
Andrew Millard and Henrik Pedersen
Physics-guided sampling with
diffusion model priors has shown promise for solving partial differential equation (PDE) governed problems, but applications to chemically meaningful reaction-transport systems remain limited. We apply
diffusion-based guided sampling to gas-phase chemical reactions by training on solutions of the advection-reaction-
diffusion (ARD) equation across varying parameters. The method generates physically consistent concentration fields and accurately predicts outlet concentrations, including at unseen parameter values, demonstrating the potential of
diffusion models for inference in reactive transport.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Inverse-design of two-dimensional magnonic crystals via topology optimization with frequency-domain micromagnetics
Ryunosuke Nagaoka, Takahiro Yamazaki, Chiharu Mitsumata et al. (+2 more)
Magnonic
crystals (MCs) are emerging spintronic metamaterials capable of manipulating transmission properties of
magnons, the quanta of
spin waves. Due to the complex relationship between
lattice geometry and magnonic band dispersion, it remains challenging to establish general design strategies for optimizing targeted properties in MCs. In this study, we demonstrated an inverse-design framework for two-dimensional MCs to explore unconventional
lattice structures with large magnonic band gaps. We employed genetic
algorithms to enable global exploration of structures with a complete band gap as the objective property, and used frequency-domain micromagnetic simulations for computationally efficient band gap evaluation. Our established inverse-design method successfully discovered several previously unreported designs of MCs, whose performance was validated using time-domain micromagnetic simulations. Furthermore, we observed that the design landscape becomes increasingly non-convex at high-order bands, suggesting the existence of multiple design solutions. The overall inverse-design framework is expected to be broadly applicable to experimentally accessible material systems and device dimensions, facilitating the formulation of design rules for MCs.
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All authors Ryunosuke Nagaoka, Takahiro Yamazaki, Chiharu Mitsumata, Yuma Iwasaki, Masato Kotsugi
Fluid Dynamics
Lagrangian dispersion in experimental stratified turbulence
Maelys Magnier, Costanza Rodda, Clément Savaro et al. (+5 more)
Lagrangian measurements of tracer particle dispersion in stratified
turbulence are presented from a large-scale experiment achieving both high buoyancy Reynolds numbers and low Froude numbers – a regime characteristic of oceanic conditions. Stratification has a pronounced effect on the vertical particle dispersion, which is observed to be constrained to distances on the order of the buoyancy scale $w_{\mathrm{std}}/N$, where $w_{\mathrm{std}}$ is the standard deviation of the vertical velocity and $N$ is the Brunt-Väisälä frequency. As expected in strongly nonlinear, stratified
turbulence, the frequency spectrum of the Lagrangian velocity becomes isotropic at frequencies higher than $N$. The spectral decay follows a $1/f^3$ scaling, which contrasts with the $1/f^2$ behavior typical of homogeneous isotropic
turbulence. At time scales corresponding to internal waves, the statistics of velocity increments remain Gaussian, consistent with the weakly nonlinear regime of wave
turbulence. At smaller scales, however, the flow exhibits strongly non-Gaussian statistics, indicative of fully nonlinear turbulent dynamics driven by wave breaking.
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All authors Maelys Magnier, Costanza Rodda, Clément Savaro, Pierre Augier, Nathanael Machicoane, Thomas Valran, Samuel Viboud, Nicolas Mordant
Optics · Cross-listed from astro-ph.IM
Simultaneous Misalignment and Mode Mismatch Sensing in Optical Cavities Using Intensity-Only Measurements
Liu Tao, Eleonora Capocasa, Yuhang Zhao et al. (+3 more)
Precise sensing and control of spatial mode content is essential for the performance of precision optical systems, particularly interferometric gravitational-wave detectors, where misalignment and mode mismatch can lead to significant optical losses and degraded
quantum noise suppression. Conventional approaches, including heterodyne wavefront sensing and phase camera techniques, are effective but can be limited by hardware complexity and systematic uncertainties arising from restricted reference-beam overlap. This paper presents a novel two-step deep learning pipeline for robust beam diagnostics based solely on beam intensity images. In the first stage, a multi-intensity-image convolutional neural network (CNN) performs accurate mode decomposition, recovering the complex modal content of distorted beams. In the second stage, the predicted mode coefficients are fed into a downstream regression network that simultaneously estimates all eight degrees of freedom (DoFs) associated with misalignment and mode mismatch, including beam tilt, lateral offset, and waist size and position mismatches in both transverse directions. The proposed CNN-based framework achieves a mean absolute error (MAE) of 0.0034 in the mode decomposition stage, which propagates to a total MAE of 0.0062 in the recovered beam imperfection parameters at the final stage. This corresponds to an average residual optical loss of 39 ppm per DoF (310 ppm total). This approach relies only on standard CCD imaging and is robust to random intensity noise, eliminating the need for complex interferometric hardware. The results demonstrate that the proposed deep learning pipeline enables real-time, high-accuracy wavefront sensing and mode-mismatch diagnostics, providing a scalable and hardware-efficient tool for improving the stability and sensitivity of precision optical systems.
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All authors Liu Tao, Eleonora Capocasa, Yuhang Zhao, Jacques Ding, Isander Ahrend, Matteo Barsuglia
Geophysics
Quantifying Salt Precipitation During CO2 Injection: How Flow Rate, Temperature, and Phase State Control Near-Wellbore Crystallization
Karol M. Dąbrowski, Mohammad Nooraiepour and Mohammad Masoudi
Salt precipitation near injection wells can reduce permeability, induce excess pressure buildup, and reduce injectivity within days to weeks of CO2 injection, yet the pore-scale mechanisms coupling multiphase flow, evaporation, and crystallization warrant further detailed quantification across variable phase states and flow regimes. We present high-resolution microfluidic experiments that systematically quantify the dynamics of halite crystallization during CO2-driven brine evaporation across
liquid, gaseous, and supercritical phases (50-80 bar, 20–60 C, Pe = 50–1440). Crystallization kinetics are controlled by transport, with the Avrami rate constant (K) increasing by two orders of magnitude with the Peclet number and exhibiting the dependence of the temperature of Arrhenius (Ea = 58.6 kJ/mol. Supercritical CO2 achieves superior displacement efficiency (residual saturation 0.22-0.36, fractal dimension D = 1.79-1.82) and the fastest evaporation (Sherwood numbers 2-3x higher than the
liquid phase), reducing the nucleation time from 57 min (20C,
liquid) to <1 min (40-60 C, gas/supercritical). The final fractions of
crystal increase 10-fold from
liquid (0.008) to gas-phase conditions (0.08–0.12), confirming that convective transport and phase state dominate over
diffusion-limited mechanisms. Despite probabilistic nucleation, final
crystal distributions are spatially rather uniform with no systematic inlet-outlet bias. These quantitative relationships between dimensionless parameters (Pe, Sh), kinetic constants (K, Ea) and phase-dependent displacement patterns provide critical
benchmarks for validating pore-scale models and predicting near-wellbore permeability impairment in geological storage of saline and hypersaline CO2.
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Chemical Physics
Viscosity as a Smoking Gun for Complex Formation in Solution: Fe$^{2+}$ and Mg$^{2+}$ Chlorides as Examples
Amrita Goswami, Samuel Blazquez, Lucía Fernández-Sedano et al. (+4 more)
Electrolyte solutions at high concentration are indispensable and yet poorly understood. In particular, the extent of speciation – the formation of complexes composed of multiple species – in concentrated ionic solutions is very challenging to obtain theoretically and experimentally, but can have a strong effect on solution properties. The literature is rife with contradictory estimates of speciation from experiments. We find that speciation affects transport properties, and is therefore, a prerequisite to accurately model concentrated solutions. We turn this to our advantage by showing that the viscosity can be used to determine the extent of complexation in concentrated aqueous solutions. Results of simulations as well as experimental measurements are presented. The atomistic Madrid-2019 force-field is extended to model FeCl$_2$. Solutions of FeCl$_2$ and MgCl$_2$ are compared and the observed difference in viscosity explained by more complexation in the former, a conclusion supported by recently reported X-ray absorption and
neutron scattering experiments.
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All authors Amrita Goswami, Samuel Blazquez, Lucía Fernández-Sedano, Eva González Noya, Hannes Jónsson, Jacobo Troncoso, Carlos Vega
Chemical Physics
Enhanced Third-Order Optical Nonlinearity in a Dipolar Carbene-Metal-Amide Material with Two-Photon Excited Delayed Fluorescence
Ikechukwu D Nwosu, Lujo Matasović, Tárcius N Ramos et al. (+11 more)
Advanced photonic materials showing two-
photon absorption (2PA) have been widely explored to develop three-dimensional imaging, micro and nanofabrication, all-optical switching, lithography on a nanoscale and many other enabling technologies. These all require nonlinear absorption chromophores with intrinsic 2PA cross-sections and long-term photo-and thermal stability. Here, we disclose the very first example of the dipolar carbenemetal-amide (CMA) material showing a enhanced 2PA cross-section up to 105 GM. Overall molecular design considerations such as extended $\pi$-conjugation (to increase polarizability), minimizing the singlet-triplet energy gap ($\Delta$E ST ), and using heavy metal atoms are the first design principles to obtain bright one-and two-
photon excited thermally activated delayed fluorescence (TADF) material, showing one of the highest radiative rate of 2.18$\bullet$10 6 s -1 across CMA materials. Bright red CMA 2P-TADF material shows excellent photostability (LT 50 = 3 h) to 20 mW femtosecond pulsed
laser excitation at 1000 nm, encouraging further CMA exploration for future applications in advanced photonic technologies requiring third-order nonlinear optical properties.
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All authors Ikechukwu D Nwosu, Lujo Matasović, Tárcius N Ramos, Nguyen Le Phuoc, Giacomo Londi, Alexander J Gillett, Daniel T W Toolan, Charles T Smith, George F S Whitehead, Mireille Blanchard-Desce, Jonathan Daniel, Mikko Linnolahti, Yoann Olivier, Alexander S Romanov