Fluid Dynamics
To stall-cell or not to stall-cell: Variational data assimilation of 3D mean flow past a stalled airfoil
Uttam Cadambi Padmanaban, Craig Thompson, Bharathram Ganapathisubramani et al. (+1 more)
The full-field reconstruction of three-dimensional (3D) turbulent flows from sparse experimental measurements remains a significant challenge, particularly for flows exhibiting complex 3D flow separation. In this work, we address this challenge for the case of stall
cells - spanwise coherent structures that form on the suction surface of wings at post-stall conditions. Planar particle image velocimetry (PIV) experiments are performed on a NACA 0012 wing at a chord-based Reynolds number of $Re_c \approx 450{,}000$ and angle of attack $\alpha = 14^\circ$, acquiring two-component mean velocity data on four spanwise planes. The experimental data show clear spanwise variation in the extent of the separation and flow dynamics, consistent with the presence of stall
cells. Three-dimensional variational (3DVar) data assimilation (DA) within the field inversion framework is then employed to reconstruct the full 3D mean flow field by augmenting these sparse planar measurements with the Spalart–Allmaras (SA) Reynolds-averaged Navier–Stokes (RANS)
turbulence model. The performance of the reconstruction is assessed on planes not used in the assimilation. It is shown that a single plane of sparse experimental data is sufficient to recover the essential features of a stall
cell, including counter-rotating
vortices around focal points on the suction surface. The lowest reconstruction error is obtained when two planes of data that are close together but exhibit markedly different separation extents are used, and the complementary roles of the reference data placement and the computational boundary conditions in shaping the reconstructed stall
cell structure are explained. These results demonstrate the capability of 3DVar DA to reconstruct the full 3D physics of stall
cells from two-component velocity data acquired on select spanwise planes.
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All authors Uttam Cadambi Padmanaban, Craig Thompson, Bharathram Ganapathisubramani, Sean Symon
Biological Physics
Delayed control driven oscillations in plant roots
Riz Fernando Noronha, Kunihiko Kaneko and Koichi Fujimoto
Arabidopsis roots show oscillatory growth patterns on homogeneous agar surfaces, whereas other plants, such as maize, do not. Although several explanations have been proposed, a simple and general model that makes testable predictions across species has been lacking. Roots sense
gravity and correct their growth direction towards the vertical. Motivated by recent evidence for a time delay in this gravitropic correction, we develop a minimal nonlinear model based on the delay hypothesis that predicts whether a root oscillates or grows vertically downwards. The model identifies a fourfold relation between the delay and time period, robust across different response functions. Analysing images of Arabidopsis, we find that the mode of the oscillatory arc length is not significantly different between inclined and vertical growth conditions. The quantitative agreement between the experimentally measured oscillatory arc length and the arc length estimated from estimated root growth speed and response delay supports this fourfold delay-period rule for delay-driven root oscillations. The simplicity of our model allows for a direct comparison with data from diverse plant species.
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Applied Physics · Cross-listed from quant-ph
Observation of attractor transitions in active magnon-polaritons under microwatt drives
Hao Wu, Qichun Liu, Yuanbin Fan et al. (+2 more)
Magnon-polaritons provide a room-temperature platform for investigating nonlinear cavity
quantum electrodynamics in the microwave domain, but experimentally observing controlled transitions among distinct nonlinear attractors remains challenging in conventional passive systems, where strong external driving is usually required. Here we report the observation of attractor transitions in an active
magnon-polariton formed by a self-oscillating microwave cavity coupled to a yttrium iron garne (YIG) sphere. The feedback loop supplies an internal microwave drive, while Kerr frequency pulling and Suhl-mediated
magnon-
magnon scattering produce an enhanced effective nonlinearity. Stability analysis using experimentally calibrated parameters reveals a rich fixed-point (FP) landscape with multiple unstable-FP phases and a triple-point region. By tuning gain across these phases, we observe the first experimental evidence of explosive growth of bistability, followed by transitions to multifrequency limit cycles, comb-like/fractal spectra, and broadband chaotic dynamics at microwatt powers. Near a critical point,
magnetic-field-triggered switching between nonlinear emission states produces spectral shifts up to 162 times the bare gyromagnetic response. By enabling low-power attractor transitions and attractor-switching-amplified spectral response, active
magnon-polaritons open opportunities for nonlinear microwave signal generation, high-precision sensing, and neuromorphic computing.
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All authors Hao Wu, Qichun Liu, Yuanbin Fan, Yulong Liu, Qing Zhao
Medical Physics
Mechanistic driven TCP and NTCP modeling for particle therapy accounting for a broad range of physical irradiation parameters and tissue environmental conditions
Marco Battestini, Jules Morand, Giulio Bordieri et al. (+3 more)
In conventional radiotherapy, the probability of controlling tumor growth is quantified using Tumor Control Probability (TCP) models. Instead, the probability of experiencing a side effect after the irradiation of healthy tissues and organs is typically assessed using the concept of Normal Tissue Complication Probability (NTCP), an additional crucial metric for evaluating and comparing treatment plans. This work is dedicated to the development, implementation, and application of a general mechanistic model to describe the effects of particle therapy (PT) on different tissue organizations beyond Poissonian assumptions, extending the Generalized
Stochastic Microdosimetric Model (GSM2), i.e., a
stochastic radiobiological model that describes the time
evolution of DNA lesions in a
cell nucleus according to microdosimetric principles, to the study of macroscopic biological systems. Specifically, we extend the biological stage of radiation damage of the GSM2 model to larger spatial and temporal scales, involving
cell populations with a specific
geometric and functional architecture. The model's single-
cell resolution allows it to account for energy deposition and tissue heterogeneity, considering different organ volume effects,
cell type distributions, and oxygen gradients for different radiation qualities of the beam, that is, type, energy, and LET of radiation, and various fractionation schemes. We show the interplay between physical and environmental parameters on the induction of side effects on healthy tissues, for different radiation qualities and fractionation schemes, and we highlight the impact of biochemical heterogeneities in the target environment, for tumor response.
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All authors Marco Battestini, Jules Morand, Giulio Bordieri, Marta Missiaggia, Emanuele Scifoni, Francesco G. Cordoni
Applied Physics
Neuronal arithmetic operators based on Ovonic threshold switches (OTS) for biologically inspired analog computing
Jingyeong Hwang, Jaesang Lee, Jiin Bang et al. (+10 more)
Biological
neurons perform arithmetic computations - including additive integration and divisive gain modulation - through synaptic conductance changes and shunting inhibition, enabling context-dependent information processing that far exceeds simple threshold-and-fire models. Replicating these capabilities in compact hardware remains a fundamental challenge for neuromorphic engineering. Here, we demonstrate artificial
neuron circuits based on Ovonic threshold switches (OTS) that physically implement three arithmetic operations: SUM, PARALLEL, and DIVISION. The SUM and PARALLEL
neurons exploit MOSFET-controlled dendritic conductances, producing output firing rates that collapse onto invariant curves as a function of combined inputs - satisfying the canonical criteria for neuronal addition. The DIVISION
neuron leverages a JFET-based shunting pathway, inspired by GABA_A-mediated inhibition in the cortex, to achieve divisive gain modulation well described by a Hill-type function (R2 ~ 0.95, Hill exponent n ~ 1.3), consistent with nonlinear normalization observed in visual and olfactory
circuits. Applying the DIVISION
neuron to pixel-wise image normalization under non-uniform illumination recovers obscured visual content, mirroring contrast normalization in the visual cortex. Compared to CMOS-based division implementations, the proposed approach offers improvements in energy efficiency and scalability exceeding an order of magnitude, establishing a viable path toward compact,
brain-inspired analog computing.
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All authors Jingyeong Hwang, Jaesang Lee, Jiin Bang, Younghyun Lee, Unhyeon Kang, Seungmin Oh, Kyungmin Lee, Jaehyun Park, Seongsik Park, Hyun Jae Jang, Sangbum Kim, Min Hyuk Park, Suyoun Lee
Biological Physics
A stochastic agent-based extension of the GSM$^2$ model for particle therapy: cell-cycle dynamics, dose-rate dependence, and fractionation effects
Francesco G. Cordoni, Marco Battestini and Marta Missiaggia
We present a
stochastic agent-based extension of the Generalized
Stochastic Microdosimetric Model (GSM$^2$) that links microscopic energy deposition by ionizing radiation to population-scale response. Each
cell is represented as an
agent whose DNA damage,
cell-cycle phase, and fate evolve as a continuous-time Markov process. Particle arrivals, repair, misrepair, division, death, and migration are treated as competing
stochastic events in an event-driven
algorithm, enabling track-structure simulations of spheroids with up to $1.5\times10^5$
cells in minutes on a single workstation. For static populations, the model reproduces the Lea–Catcheside dose-rate dependence of survival for
proton and carbon-ion irradiation over four orders of magnitude in dose rate. Dose-rate sparing decreases with increasing LET and disappears for low-energy carbon ions. After calibration to a single survival curve for aerobic X-ray irradiation of V79 spheroids, the model predicts without further fitting survival under anoxia and after carbon-ion irradiation in aerobic and anoxic conditions, reproducing measured oxygen enhancement ratios and relative biological effectiveness. Applied to three-dimensional tumor spheroids, the framework resolves responses to single, split, and fractionated irradiations, separates the effects of repair, reassortment, and repopulation, and quantifies
stochastic variability between realizations. The model provides a mechanistic single-
cell framework for studying time-dependent effects and uncertainty in particle irradiation.
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Atomic Physics
Long-range states in collisions of ultracold molecules
James F. E. Croft, Brian K. Kendrick and Jeremy M. Hutson
We use coupled-channel calculations to explore the nature of near-threshold bound states in a simplified model of Rb+KRb. This is a prototype for systems with very strong coupling at short range and chaotic behavior for the short-range states. We find that there are states with strong long-range character that exist close to threshold and probably persist to depths at least 100 GHz below each threshold. These states are only weakly coupled to the short-range states and do not form part of the chaotic
manifold. Since they spend little time at short range, they are relatively insensitive to destruction by
laser light. They can thus have long lifetimes that are unrelated to the density of states and can cause narrow Feshbach resonances when the states are shifted across thresholds by external fields.
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Atomic Physics
Hyperfine-resolved laser excitation and detection of nuclear isomer in trapped $^{229}$Th$^{3+}$ ions
Wu Wang, Ke Zhang, Ke-Mi Xu et al. (+2 more)
We present a comprehensive theoretical investigation of hyperfine-resolved excitation and detection of the low-energy isomeric state of $^{229}$Th in trapped $^{229}\mathrm{Th}^{3+}$ ions. Using a
quantum master equation approach, we quantitatively analyze the dependence of the isomeric population on
laser linewidth, detuning, and irradiation time, showing that their proper matching is essential for efficient excitation. Going beyond earlier conceptual discussions of electronic-fluorescence-based
nuclear-state detection, we propose two concrete
nuclear-state detection schemes based on three hyperfine-resolved electronic fluorescence channels at 690, 984, and 1088 nm. Our quantitative analysis shows that, for 50 ions, the 690- and 984-nm scheme yields detectable
photon count rates on the order of $10^3~\mathrm{s}^{-1}$ at 690 nm and $10^4~\mathrm{s}^{-1}$ at 984 nm, whereas the 1088-nm scheme achieves a detectable
photon rate on the order of $10^3~\mathrm{s}^{-1}$. By quantifying the trade-off between irradiation time and scan-step size, we show that the
nuclear transition can be located within one month for a 100-MHz uncertainty using currently available
vacuum-ultraviolet
laser technology. These results provide practical guidance for trapped-ion $^{229}\mathrm{Th}$ spectroscopy and the development of
nuclear clocks.
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All authors Wu Wang, Ke Zhang, Ke-Mi Xu, Jin-Bo Hu, Shan-Gui Zhou
Optics
A Magnetically Switchable Bifocal Metasurface
Alberto Santonocito, Barbara Patrizi, Alessio Gabbani et al. (+2 more)
Tunable flat optics are essential for advancing compact photonic devices. Here we show a numerical study of a reflective magneto-optical metasurface with a dynamically tunable focal length. The structure comprises bismuth iron garnet nanodisks in a Gires-Tournois resonator configuration. The magneto-optical properties of the garnet modulate the reflected phase response via an external
magnetic field, allowing focusing at different focal lengths. Full-wave simulations demonstrate that the metasurface exhibits distinct focusing characteristics depending on the applied
magnetic field direction for a fixed right circularly polarized incident wave at 1.550 {\mu}m. Specifically, switching the external field from +0.2 T to -0.2 T changes the focal length by a factor of approximately two (from 7.16 mm to 13.76 mm). These findings demonstrate that magneto-optical metasurfaces offer a flexible, viable approach for non-mechanical, tunable focusing in compact reflective optical components.
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All authors Alberto Santonocito, Barbara Patrizi, Alessio Gabbani, Francesco Pineider, Guido Toci
Computational Physics · Cross-listed from quant-ph
Magnonic Gottesman-Kitaev-Preskill states
Zi-Xu Lu, Gang Liu, Matteo Fadel et al. (+1 more)
Bosonic
quantum error correction encodes a logical
qubit in an oscillator, avoiding the hardware overhead of large
qubit arrays. Among such encodings, Gottesman-Kitaev-Preskill (GKP) states are paticularly powerful because their phase-space grid structure protects against small displacement errors simultaneously in both conjugate quadratures. Here we provide the first protocol for preparing magnonic GKP states, which involves an ellipsoidal
magnetic crystal effectively coupled to a superconducting
qubit via a microwave cavity. The
geometric anisotropy intrinsically squeezes the
magnon mode, while the cavity-mediated
qubit control realizes an effective conditional-displacement interaction. We show that two rounds of a conditional-displacement interaction and a
qubit projective measurement yield three- and four-component magnonic GKP-like states. We also show how to realize single logical
qubit gate operations, such as Pauli, Hadamard and phase gates, completing the logical Pauli basis of the approximate GKP code. Our results establish hybrid
magnon-
qubit systems as a promising platform for preparing bosonic code states, with applications in magnonic fault-tolerant
quantum computation and
quantum sensing.
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All authors Zi-Xu Lu, Gang Liu, Matteo Fadel, Jie Li
Computational Physics
Computation of frequency- and time-domain Jacobians in optical tomography with Monte Carlo simulations
Pauliina Hirvi, Jaakko Olkkonen, Qianqian Fang et al. (+1 more)
Significance: Jacobians, or spatially resolved sensitivity profiles, are central to image reconstruction in model-based optical
tomography of biological tissue. Although Monte Carlo (MC) simulations are the gold standard for modeling light transport in turbid media, methodology for frequency- and time-domain Jacobians remains incomplete. Aim: This work extends MC to directly compute absorption and scattering Jacobians for frequency-domain (amplitude and phase) and time-domain (intensity and mean time-of-flight) measurements and prism-terminated optical fiber detectors. Approach: Jacobians are derived in the perturbation MC framework and implemented in the high-performance, open-source Monte Carlo eXtreme (MCX) simulator. Results are validated against the
diffusion approximation (DA) solved using the finite element method in neonatal head models. MC with split voxels on curved surfaces is extended to Jacobian computation. The detector model is implemented in post-processing and compared with isotropic reception at surface. Results: MC- and DA-derived Jacobians show excellent agreement only in high-scattering regimes, highlighting the importance of MC for low-scattering domains. The detector model reduces surface sensitivity and marginally increases sensitivity to deeper tissues at short (< 2 cm) source-detector separations. Conclusion: A complete theoretical framework and MC software for computing frequency- and time-domain Jacobians is provided. Realistic detector modeling is encouraged for short-separation channels.
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All authors Pauliina Hirvi, Jaakko Olkkonen, Qianqian Fang, Ilkka Nissilä
History and Philosophy of Physics
Lorentz-FitzGerald Contraction as the Unique Closure Condition for Moving Spherical-Harmonic Cavities
Shiva Meucci
We prove that the Lorentz–FitzGerald contraction is the unique deformation of a resonant cavity moving through a mechanical wave medium that preserves spherical-harmonic phase closure. For a cavity moving at speed $v = \beta c$ through a medium supporting nondispersive wave propagation at speed $c$, the round-trip phase of an internal ray at angle $\theta$ to the motion depends on the boundary radius $r(\theta)$ according to $\Phi(\theta) = 2k\,r(\theta)\sqrt{1-\beta^2\sin^2\theta}/(1-\beta^2)$. Requiring $\Phi(\theta)$ to be independent of $\theta$ – the necessary condition for retaining a spherical-harmonic eigenstructure – uniquely fixes the Lorentzian aspect ratio \[ \frac{a_\parallel}{a_\perp} = \frac{1}{\gamma} = \sqrt{1-\beta^2}. \] Substituting this unique boundary into the round-trip time yields the resonant period dilation $T = \gamma T_0$, without additional assumptions. Both results – contraction and dilation – follow from a single mechanical constraint: preservation of eigenstructure under motion. This is the missing uniqueness
theorem of the constructive relativity program initiated by FitzGerald, Lorentz, and Heaviside: the proof that Lorentzian kinematics are not merely consistent with, but uniquely required by, phase closure in a mechanical wave medium.
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Optics · Cross-listed from quant-ph
Observation antibunching with classical light in a linear interferometer
Yu Gu, Yuhan Ma, Yiqi Song et al. (+8 more)
Understanding the boundary between classical and nonclassical phenomena is important for both fundamental researches in
quantum optics and applications in
quantum information. One of the most interesting research directions in this field is exploring nonclassical effects with classical light. In this paper, we will show that it is possible to observe antibunching with thermal light in a Hanbury Brown-Twiss interferometer by treating single-
photon detectors as
photon-number-resolving detectors to perform
photon-number projection measurements. Both temporal and spatial antibunching is observed via the correlation of two detectors detecting one and zero
photon, respectively. By comparing the measured results of thermal and
laser light, it is found that the observed antibunching arises from the combined effect of
photon statistics of thermal light and
photon-number projection measurement.The classical and nonclassical nature of the observed antibunching is analyzed. The results are helpful to understand the connection between classical and nonclassical correlation and may find applications in multiphoton interference and
quantum imaging.
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All authors Yu Gu, Yuhan Ma, Yiqi Song, Meixue Chen, Hui Chen, Huaibin Zheng, Yuchen He, Yu Zhou, Fuli Li, Zhuo Xu, Jianbin Liu
Chemical Physics
Relativistic Exact-Two-Component Core-Valence-Separated Algebraic Diagrammatic Construction Theory For Near L-edge X-ray Absorption Spectra
Somesh Chamoli, Sudipta Chakraborty, Xubo Wang et al. (+1 more)
We present an efficient implementation of the second-order two-component relativistic core-valence-separated algebraic diagrammatic construction method (CVS-ADC(2)) for core-excitation calculations. The approach employs state-averaged frozen natural spinors (SA-FNS) to reduce the number of floating-point operations, together with the Cholesky decomposition (CD) technique, which lowers the storage requirements associated with two-electron integrals. These reductions make the method particularly well-suited for systems containing heavy elements. Systematic benchmarking against four-component reference calculations confirms the reliability and robustness of the two-component (X2CMP/X2CAMF)-based framework. The close agreement with canonical results further demonstrates that the SA-FNS-based CVS-ADC(2) approach achieves comparable accuracy at only a fraction of the computational cost. Moreover,
benchmark studies of L$_{2,3}$-edge spectra for 3$d$ transition-metal compounds demonstrate that CVS-ADC(2) serves as a computationally efficient and reliable alternative to the non-Hermitian EOM-CC method for reproducing experimental spectra. Finally, calculations on a ruthenium complex illustrate the method's applicability to relativistic studies of medium-sized molecular systems.
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All authors Somesh Chamoli, Sudipta Chakraborty, Xubo Wang, Achintya Kumar Dutta
Plasma Physics
Electrothermal Dynamics of Cold Front in Impure Tokamak Plasmas
S. Oshiro, A. Matsuyama and Y. Nakamura
Current density perturbations induced by radiative collapse, which is a possible mechanism governing tokamak
plasma disruptions, have been investigated using a reaction-
diffusion model. The reaction term of the current
diffusion equation, which depends on the first and second radial derivatives of the electrical resistivity profile, produces a strong disturbance in the current density profile in a narrow layer of the cold front. While the current density locally increases in the region where the electron temperature gradient is steep, it decreases behind the cold front in the region where the electron temperature profile exhibits a pronounced concave-down
curvature. The electrothermal dynamics driven by such a shape of the current density perturbation and the competition between Ohmic heating and
impurity radiation are simulated by the tokamak transport code INDEX.
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Medical Physics
Wave-Equation Migration Velocity Analysis for Multistatic Synthetic Aperture Ultrasound
Rehman Ali, Trevor M. Mitcham, Marvin M. Doyley et al. (+2 more)
Sound speed heterogeneities can create aberrations in B-mode ultrasound images by inducing tissue-dependent delays and diffractive effects that conventional beamforming does not incorporate. By using the
Fourier split-step method to simulate pressure fields in heterogenous sound speed media, reverse-time migration (RTM) can reconstruct the B-mode image by cross-correlating transmitted and received pressure fields. As a result, RTM is differentiable with respect to sound speed. This enables the reconstruction of the sound speed profile that minimizes the aberration in the B-mode image. In seismic imaging, this form of diffraction
tomography, known as wave-equation migration velocity analysis, can roughly be understood as a type of full-waveform inversion (FWI) that acts in the image domain rather than errors in the received channel data. This is the first work applying WEMVA to medical pulse-echo ultrasound imaging. Phantom experiments show dramatic improvements in image quality with measured improvements in point target resolution from 1.22$\pm$1.01 to 0.32$\pm$0.07 mm and lesion contrast from 3.05 to 4.39 dB.
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All authors Rehman Ali, Trevor M. Mitcham, Marvin M. Doyley, Nebojsa Duric, Jeremy J. Dahl
Medical Physics
MAAS-SFRThelper: An Integrated ESAPI Plugin for Structure Generation, Optimization, and Evaluation of Spatially Fractionated Radiation Therapy
Japan K. Patel, Todd A. Wareing, Tenzin Kunkyab et al. (+13 more)
Spatially fractionated radiation therapy (SFRT) planning requires three coordinated tasks: generation of high-dose sphere structures, position-aware optimization, and peak-valley dose ratio evaluation. We present MAAS-SFRThelper, a shared-source Eclipse Scripting Application Programming Interface (ESAPI) plugin that integrates structure generation,
geometric-aware optimization, and peak-valley dose ratio evaluation for SFRT into a single workflow inside Varian's Eclipse treatment planning system. The plugin exposes five task-oriented tabs sharing common services for sphere extraction and objective creation. The SphereLattice tab generates sphere
lattices using five placement patterns. The Optimization tab searches over candidate
lattice positions using a four-metric
geometric surrogate score and triggers VMAT optimization and dose calculation. The Evaluation tab implements four analysis modes; its three-dimensional peak-valley classification recovers sphere centers from the
lattice structure through a
geometric extraction pipeline rather than relying on dose thresholds. We validated all functionality on digital phantoms against analytic ground truth. The plugin is distributed as source code under the Varian Limited Use Software License Agreement. Source code and documentation are publicly available on GitHub.
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All authors Japan K. Patel, Todd A. Wareing, Tenzin Kunkyab, Caleb Raman, Ilias Sachpazidis, Peter Szentivanyi, Ryan Clark, Gregory Gill, Pierre Lansonneur, Arjun Karnwal, Michael Kudla, Sergejs Unterkirhers, Junqi Song, Jun Yang, Anthony Magliari, Matthew C. Schmidt
Optics · Cross-listed from cond-mat.mes-hall
Mobile Exceptional Points Generate Momentum-Space Switching Domains
Jung-Wan Ryu and Chang-Hwan Yi
Exceptional points (EPs), non-Hermitian degeneracies where both
eigenvalues and eigenvectors coalesce, play a central role in the
topology of non-Hermitian spectra. Recent advances have enabled the controlled creation and manipulation of EPs in a wide range of physical systems, raising the question of what new band
topology emerges when EPs become mobile under cyclic modulation. Here we show that mobile EPs generate momentum-space switching domains that partition the Brillouin zone into regions with distinct band-switching behavior. Using a minimal two-band
lattice model, we introduce a band-permutation invariant that determines whether eigenmodes exchange after one modulation cycle. The boundaries between switching regions arise from the projection of EP trajectories in an extended parameter space combining
crystal momentum and the modulation parameter. As the modulation strength increases, the switching domains expand and eventually cover the entire Brillouin zone, resulting in global band switching. The predicted switching-domain structure is further demonstrated in a photonic
crystal with lossy materials. These results open a new avenue within non-Hermitian
topology by enabling the engineering of EP-driven phenomena through their controlled motion.
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Optics
Generalized Optical Theorem for Structured Neutron Beams and Consequences for Forward-Transmission Null Tests of Time-Reversal Invariance
Sepehr Samiei
The simple form of the optical
theorem of scattering theory, $\sigma_{\rm tot}^{\rm pw} = (4\pi/k)\,\Im f(0)$, is valid for an incident plane wave or for a wave packet whose
Fourier components possess azimuthal
symmetry about the incident wave vector $\vec{k}$. Previous work has shown that this expression can break down for structured beams of light which possess orbital angular momentum (OAM), despite the fact that there is clearly no violation of unitarity, and the relevant modifications have been worked out for the case of massless
photons. We present a form of the optical
theorem involving
neutron OAM states for the case of the scattering of massive nonrelativistic particles. We apply this form to Ryndin's
theorem on the application of time reversal
symmetry to forward scattering, indicate how the statement of the null condition for T violation in forward scattering is modified, and show that this effect is negligible compared with other sources of systematic error in
neutron optics transmission experiments.
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Computational Physics
Kolmogorov-Sinai entropies identify optimal observables for prediction and dynamics reconstruction in chaotic systems
Maximilian Topel
Choosing the optimal observable to model dynamical systems for which we do not know the driving equations is nearly always an ad hoc art. Takens' Delay
Embedding Theorem guarantees a diffeomorphism between delay-coordinate vectors built from generic scalar observables and the underlying invariant attractor, but is agnostic to optimal observable choice, and formal bounds on reconstruction quality across observables are not known. Here we prove that, under modest technical conditions, the Kolmogorov-Sinai
entropy of an observable predicts its reconstruction error of the underlying dynamics in chaotic, ergodic systems. Using the Oseledets Multiplicative Ergodic
Theorem, we show that the tangent bundles of reconstructed
manifolds admit an invariant Oseledets filtration diffeomorphically related across admissible observables, with Lyapunov exponents controlling the propagation of perturbations. We bound reconstruction error by a quantity monotonically related to the sum of positive Lyapunov exponents and, by the Ruelle inequality, the Kolmogorov-Sinai
entropy. We validate this empirically on the Lorenz-63 attractor, the Hastings-Powell food chain, and a tetracosane molecular-dynamics trajectory, recovering Spearman rank correlations between $h^{KS,UB}$ and reconstruction RMSE up to $\rho=+0.89$ ($p=5.5\times 10^{-8}$) for the realistic tetracosane case, sharpening to $\rho=+0.97$ under added measurement noise. This provides a rigorous foundation for observable selection in chaotic systems, applicable as an a priori data-selection criterion for any data-driven modeling pipeline.
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Instrumentation and Detectors
Optical effects in Gaseous Electron Multipliers (GEMs)
D. Edgeman, F.M. Brunbauer, M. Gardner et al. (+9 more)
Optical time projection chambers (OTPCs) are well suited for applications that require the highest spatial resolution for particle track reconstruction. The MIGDAL experiment uses a glass GEM-based OTPC and observes a systematic excess in both the intensity and width of particle tracks in its optical readout, when compared with charge readout simulations. One hypothesis is that scintillation light produced inside a GEM hole during the avalanche propagates through the GEM substrate and exits neighboring holes. We present lab measurements testing this hypothesized optical broadening effect in three types of GEM substrates: glass, ceramic, and FR4. Our observations quantify this optical broadening and demonstrate it to be strongest in glass GEMs. Additionally, we use Geant4 simulations to both reproduce our observations and quantify optical broadening effects in realistic charge avalanches. Applying our glass GEM effects to simulated particle tracks yields increases of track intensity and widths by up to approximately 26% and 31%, respectively. This may explain the larger-than-expected track intensities and widths observed in the MIGDAL OTPC. This effect may be relevant to GEM-based OTPCs, with its magnitude depending on the GEM structure and detector-specific optical configuration.
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All authors D. Edgeman, F.M. Brunbauer, M. Gardner, D. Loomba, P.A. Majewski, T. Marley, L. Millins, T. Neep, K. Nikolopoulos, J. Schueler, E. Tilly, W. Thompson
Plasma Physics
Self-consistent modelling and qualitative comparison of mildly relativistic runaway electron dynamics with a closed flux surface formation model during tokamak startup
Y. Lee, H.-T. Kim, P.C. de Vries et al. (+14 more)
A model for mildly relativistic Runaway Electrons (REs) is developed in a reduced-kinetic form and qualitatively compared with radiation characteristics observed in KSTAR ohmic startup. The mildly relativistic correction not only alleviates runaway current overestimation but also accounts for the partial parallel confinement of the initial runaway seed under an open-field configuration during early burn-through. The model is self-consistently integrated in the state-of-the-art predictive
plasma initiation code DYON (Hyun-Tae Kim et al 2022 Nucl. Fusion 62 126012), hereafter referred to as DYON-RE. DYON-RE provides an improved RE confinement model during the transition from an open to a closed
magnetic configuration by employing a model-based description of closed flux surface formation validated in multi machines. We show prediction capability of DYON-RE in two representative discharges among KSTAR ohmic startups. DYON-RE reliably predicts key
plasma parameters such as
plasma current, density, and temperature and also implies the characteristic behavior of the radiative temperature measured by electron cyclotron emission diagnostics in agreement with experimental results. The proposed model offers a framework for designing runaway-free ohmic startup scenarios in CPD and ITER. Future experimental validation will further refine its predictive capabilities and broaden its practical application.
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All authors Y. Lee, H.-T. Kim, P.C. de Vries, P. Aleynikov, J. Lee, K. Park, T. Park, J. Gwak, G. Nam, W. I. Jeong, K.-D. Lee, J.-G. Bak, J. Jang, J.-W. Juhn, Y.-S. Lee, J.-K. Park, Y.-S. Na
Fluid Dynamics
Asymmetric freezing of a sliding droplet on an inclined surface
Sivanandan Kavuri, George Karapetsas, Chander Shekhar Sharma et al. (+1 more)
We investigate the asymmetric freezing of a
liquid droplet sliding on an inclined cold surface using numerical simulations based on the lubrication approximation. The combined effects of
gravity, capillarity, and solidification kinetics on droplet motion, interfacial deformation, and the resulting frozen morphology are examined through systematic variations in substrate inclination, wettability, effective Bond number, and Stefan number. Our results show that sliding prior to and during the early stages of freezing plays a dominant role in governing the asymmetry of the frozen droplet. A tilted ice cusp forms at the droplet tip due to the competition between gravitational forces and capillary resistance, with its orientation and magnitude strongly dependent on substrate wettability and inclination. Greater inclination and increased wettability enhance asymmetry in droplet morphology. Further, highly wetting substrates favor capillary-driven retraction and induce transient
liquid motion opposite to
gravity during freezing. The
evolution of contact-angle hysteresis at both the solid surface and the
liquid-ice interface underscores the importance of early-time dynamics, when the unfrozen
liquid remains mobile and gravitational effects are most pronounced. Decomposition of the
liquid motion into capillary and
gravity-driven contributions provides physical insight into contact-line pinning, receding-edge thinning, and the development of asymmetric
liquid-ice contact angles. Increasing the Stefan number accelerates freezing, limits sliding-induced deformation, and reduces both the cusp angle and the post-freezing contact-angle contrast. Overall, this study establishes a physical framework for understanding the morphology of frozen droplets on inclined substrates.
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All authors Sivanandan Kavuri, George Karapetsas, Chander Shekhar Sharma, Kirti Chandra Sahu
Atomic Physics
Intermediate-state Coulomb-corrected strong-field approximation for rescattering processes
Chunli Miao, Jiarui Qin, Chan Li et al. (+3 more)
We analytically derive the all-order strong-field S-
matrix series incorporating intermediate-state Coulomb-Volkov corrections (ICSFA). Focusing on rescattering processes described by the second-order term, we systematically investigate the impact of intermediate-state Coulomb interactions on above-threshold ionization (ATI) spectra of atomic hydrogen in linearly polarized
laser fields. Crucially, ICSFA spectra demonstrate superior agreement with the results obtained by numerically solving the time-dependent Schrödinger equation compared to the standard strong-field approximation (SFA) and final-state Coulomb-corrected SFA (FCSFA). Our analysis reveals that intermediate-state Coulomb corrections enhance the yield of the third- and fourth-return-recollision trajectories while modifying interference patterns in the energy spectrum. The observed enhancement of the multi-return-recollision trajectories can be attributed to modifications of the ionization yield and scattering cross-section, which are induced by intermediate-state Coulomb effects. These effects are equivalent to the so-called Coulomb focusing effect.
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All authors Chunli Miao, Jiarui Qin, Chan Li, Xiaolei Hao, Weidong Li, Jing Chen
Optics
Nonlinear exceptional points in an integrated acoustic-wave oscillator for longwave infrared sensing
Linbo Shao, Zichen Xi, Zengyu Cen et al. (+8 more)
Exceptional points (EP) featuring enhanced responsivity and rich dynamics have attracted extensive attentions in device developments and sensing applications. However, it remains debated whether employing EP systems is beneficial in practical sensing applications. Here, we demonstrate that a nonlinear EP in our microwave-frequency acoustic-wave oscillator improves longwave infrared (LWIR) detection under practical conditions. By phase tuning the nonlinear gain, our detector can be operated at different conditions with respect to the nonlinear EP. Compared with operation away from EP, our detector at EP shows a 33-fold improvement in responsivity and an 8.75-fold extension of 3-dB bandwidth. We observe a 6-fold enhancement in signal-to-noise ratio at an input modulation frequency of 6.2 kHz. At the incident LWIR wavelength of 9.6 um, our detector at EP exhibits a noise equivalent power (NEP) of 310 pW*Hz^-1/2 at input frequency of 10 kHz, yielding a figure of merit, product of NEP and time constant, of 9.87*10^-3 pW*Hz^-3/2, a 10-fold improvement over operation away from EP. Our integrated acoustic devices offer a versatile platform for exploring noise dynamics and developing practical sensors that exploit non-Hermitian nonlinearities.
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All authors Linbo Shao, Zichen Xi, Zengyu Cen, Joseph G. Thomas, Dongyao Wang, Tanmay Singh, Liyan Zhu, Honghu Liu, Jun Ji, Yu Yao, Yizheng Zhu
Fluid Dynamics · Cross-listed from cond-mat.soft
Propulsion and far-field hydrodynamics of linked-sphere microswimmers with viscoelastic deformability
Vimal Singh and Akash Choudhary
Viscoelasticity governs the locomotion strategies of deformable microorganisms, rendering it a fundamental mechanical property of microbial motility and an integral component in the design of envisioned microbots. Recent studies have shown that it can enable effective propulsion through non-reciprocal body deformations, even under time-reversible actuation. In this work, we investigate the dynamics of model microswimmers driven by reciprocal actuation, wherein the passive body exhibits viscoelastic deformability. We consider two linked-sphere designs, distinguished by the location of actuation: applied at one end (3-sphere design) or at the midpoint of the swimmer body (4-sphere design). Adopting Kelvin-Voigt deformability, we characterize the kinematic performance of both designs: the three-sphere swimmer possesses an optimal actuation frequency, while the four-sphere swimmer exhibits a critical frequency at which the locomotion direction reverses. We examine the swimmer's far-field hydrodynamic signature and find that resulting flow field is characterized by dominant dipolar and quadrupolar contributions, whose magnitudes are sensitive to the relative length of the actuator segment.
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Accelerator Physics
Phase-Stable Self-Modulation for GHz Continuous-Wave Ultrafast X-Ray Free-Electron Lasers
Junhao Liu, Zhen Wang, Lanpeng Ni et al. (+3 more)
High-brightness femtosecond-to-attosecond pulses are indispensable for probing electron dynamics on their fundamental temporal scales. X-ray free-electron
lasers (XFELs) at high repetition rates will facilitate high-statistics measurements and time-resolved studies that were previously inaccessible. Although energy recovery linacs (ERLs) are well suited for high-repetition-rate operation, their relatively low peak current poses a major challenge for generating intense ultrashort X-ray pulses. Here, we propose a completely
laser-free scheme that fundamentally overcomes this bottleneck through a continuous, phase-stable self-modulation process. By interacting with its own coherently emitted terahertz radiation within a helical wiggler, the electron bunch naturally accumulates a robust, few-cycle energy modulation in its core, even when starting with the intrinsically low peak current typical of ERLs. A downstream dispersion chicane subsequently converts this energy modulation into an isolated, exceptionally sharp current spike. Start-to-end simulations based on a 1~GeV ERL light source demonstrate the feasibility of generating isolated soft X-ray pulses with an average peak power exceeding 4~GW and a pulse duration of about 1~fs at an unprecedented 1.3~GHz repetition rate. The proposed scheme offers a highly practical pathway for advancing ultrafast X-ray generation into the true continuous-wave regime, with transformative implications for the development of next-generation coherent light sources.
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All authors Junhao Liu, Zhen Wang, Lanpeng Ni, Yujie Lu, Chao Feng, Zhentang Zhao
Physics and Society · Cross-listed from cs.SI
Twitter climate discourse as a signal of pro-environmental behaviors
Edoardo Maggioni, Diego Garlaschelli, Rossana Mastrandrea et al. (+1 more)
Fostering coordinated pro-environmental behaviors at scale is a key challenge for
climate mitigation. Individual actions only generate meaningful impact when they diffuse widely and become socially coordinated, yet monitoring such processes remains difficult with traditional survey-based tools alone. In this study, we examine whether large-scale online
climate discourse is associated with differences in offline pro-environmental behavior across European regions. We combine geolocated Twitter data from the
Climate Change Twitter
Dataset (2017-2019) with survey-based measures from the 2019 Special Eurobarometer, focusing on the regional density of
climate-related tweets and the average number of self-reported pro-environmental actions. We find a strong positive association between tweet density and pro-environmental behavior that remains robust to socio-economic controls, alternative spatial aggregations, and a wide range of robustness checks. To move beyond aggregate volume, we further decompose online discourse using Natural
Language Processing tools that capture distinct social dimensions. While knowledge exchange shows no clear relationship with offline behavior, the prevalence of activism- and social support-related expressions is negatively associated with pro-environmental actions. Overall, our results suggest that online
climate discourse can serve as an informative,
attention-related signal of regional differences in pro-environmental behavior, but that different forms of online engagement relate to offline action in markedly different ways. More broadly, the study highlights the potential of integrating large-scale digital traces with survey data to investigate collective behavior in socio-environmental systems, while remaining explicitly observational in scope.
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All authors Edoardo Maggioni, Diego Garlaschelli, Rossana Mastrandrea, Luca Maria Aiello
Optics · Cross-listed from quant-ph
High-key-rate Fully-Passive Quantum Access Network with Thermal Source
H.W. Yin, B.D. Zhu, H. Peng et al. (+4 more)
To accommodate classical communication systems with progressively increasing transmission rates,
quantum access networks (QAN) have undergone systematic and protocol-level optimizations in recent years, where
quantum passive optical network (QPON) architectures are gaining significant
attention due to their simple structure. It is challenging for the previous QAN based on active protocols or Stokes operator coding protocols to achieve high-speed linear modulation with high extinction ratio and stability under practical conditions. In this work, we propose and experimentally demonstrate a downstream fully passive
quantum access network protocol using passive state preparation (PSP) with free-space and single-mode fiber hybrid channels, and the final key generation rate is up to a record-breaking 19.48 Mbps per
quantum network unit. The proposed PSP-QPON scheme extends the scope of PSP-CVQKD from point-to-point to point-to-multi-point networks, which enables high-key-rate, high-stability, and low-resource-consumption implementation. Moreover, the network channel in this experiment is fully compatible with access networks in classical optical communications, which allows integration with existing optical infrastructure without the need for additional modifications, providing a promising solution for local area network
quantum access network at home or a mobile terminal.
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All authors H.W. Yin, B.D. Zhu, H. Peng, T. Wang, X.Q. Jiang, Y.K. Xu, G.H. Zeng
Plasma Physics
Improved n=1 Empirical Error Field Penetration Threshold Scaling with Ohmic and L-Mode Conventional Tokamak Plasma Discharges
E.M. Bursch, J.K. Park, N.C. Logan et al. (+12 more)
This paper presents an updated n=1 error field penetration threshold scaling, which increases fit quality compared to previous error field scaling laws, is produced from an expanded database, and exhibits reduced uncertainty in projections to future conventional tokamaks. It improves confidence in tokamak engineering tolerances, which are a significant driver of cost and time constraints on device construction. We add J-TEXT data, new JET data, and create the scaling using only conventional tokamak Ohmic and L-mode experiments. Since H-mode
plasmas are more resilient to error field penetration, this scaling predicts what is likely the most dangerous regime of error field penetration for new tokamak designs. These decisions improve confidence in the error field penetration threshold scaling and its application in the construction and design decisions of any future conventional tokamak or FPP.
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All authors E.M. Bursch, J.K. Park, N.C. Logan, F. Mao, N. Wang, C.F.B. Zimmermann, R.J. Buttery, C. Paz-Soldan, M. Pharr, L. Piron, G. Szepesi, H. Wang, S.M. Yang, JET Contributors, EUROfusion Tokamak Exploitation Team