Fluid Dynamics
Multi-branch Shell Models of Two-Dimensional Turbulence exhibit Dual Energy-Enstrophy Cascades
Flavio Tuteri, Sergio Chibbaro and Alexandros Alexakis
Classical shell models of
turbulence do not display dual cascade - inverse of energy and direct of enstrophy - because they fail to reproduce the right thermal spectra. We propose here a multi-branch shell model, including a geometry hierarchically organized across scales, in order to overcome this limitation. For this model, we demonstrate numerically both the agreement of the thermal spectra with those of two-dimensional fluid equations and the emergence of a statistically stationary dual cascade. This construction also allows us to study local transfers and to investigate both self-similarity and non-Gaussianity.
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Chemical Physics
Accurate prediction of inverted singlet-triplet excited states using self-consistent spin-opposite perturbation theory
Nhan Tri Tran, Hoang Thanh Nguyen and Lan Nguyen Tran
The violation of Hund's rule, resulting in an inverted singlet-triplet (INVEST) gap, represents a paradigm shift in photophysics with major implications for OLED technology. INVEST molecules facilitate barrierless reverse intersystem crossing, theoretically permitting 100% internal
quantum efficiency without thermal activation. However, accurately predicting negative singlet-triplet energy gaps typically demands prohibitive computational costs. In this study, we evaluate the efficacy of our recently developed one-body Møller-Plesset perturbation theory (OBMP2) and its
spin-opposite variant (O2BMP2) as efficient alternatives. Benchmarking against 30 INVEST molecules reveals that O2BMP2, with appropriate
spin-opposite scaling, achieves the accuracy of ADC(3) and EOM-CCSD. Furthermore, with the possibility of reducing computational complexity to $N^4$, O2BMP2 provides a robust balance of accuracy and efficiency, making it suitable for the high-throughput screening of next-generation INVEST materials.
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Instrumentation and Detectors
Compact sub-10 ps Resolution Radio Frequency Photomultiplier Tube
Sergey Abrahamyan, Simon Zhamkochyan, Hasmik Rostomyan et al. (+16 more)
Experimental measurements of the radial spreading of photoelectrons emitted from a multi-alkali photocathode in a MCP-based photomultiplier tube have shown that, for
photon wavelengths of 455 nm, 515 nm and 625 nm, the maximum initial energies of the emitted photoelectrons are approximately 0.3 eV, 0.2 eV and 0.1 eV respectively. Combining these experimental results with simulations performed using the SIMION simulation package, a compact
radio-frequency photoelectron multiplier tube with a temporal resolution better than 10 ps is proposed. The device would be suitable for applications in several fields, particularly in medical optical instruments employing time-correlated single-
photon counting.
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All authors Sergey Abrahamyan, Simon Zhamkochyan, Hasmik Rostomyan, Amur Margaryan, Hayk Elbakyan, Aram Kakoyan, Artashes Papyan, Anna Safaryan, John Annand, Kenneth Livingston, Rachel Montgomery, Patrick Achenbach, Josef Pochodzalla, Dimiter Balabanski, Satoshi Nakamura, Viatcheslav Sharyy, Dominique Yvon, Ani Aprahamian, Vanik Kakoyan
Optics
Optical parametric multi-pass cell amplifier
Supriya Rajhans, Nikolas Rupp, Esmerando Escoto et al. (+14 more)
Ultrafast
lasers with simultaneously high average and peak power have become indispensable for driving a multitude of applications, including high-harmonic generation, strong-field physics, and particle source applications. Both parametric amplifiers and post-compressed Ytterbium
lasers have emerged as
prime platforms to meet these demands. While multi-pass
cell (MPC) based post-compression offers broadband output with high beam quality, it provides limited wavelength tunability and suffers from temporal contrast degradation. Conversely, optical parametric amplifiers (OPAs) provide spectral tunability and high temporal contrast but they are limited by low pump-to-signal conversion efficiency and spatial beam inhomogeneities. Here, we introduce the Optical Parametric Multi-Pass
Cell Amplifier (OPMPC), a hybrid architecture that overcomes the limitations of both schemes. Our approach utilizes two non-collinearly intersecting MPCs providing broadband parametric amplification of the seed pulses and complete idler removal after each pass through the
crystal, thereby suppressing back-conversion. We experimentally demonstrate a record pump-to-signal power conversion efficiency of 43% using a 1030 nm pump at a 1 kHz repetition rate with a pulse energy of 174 $\mu$J. The amplified signal at 1500 nm exhibits excellent beam quality, power and spectral stability and is compressed to 48 fs, demonstrating a new platform for ultrafast pulse generation.
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All authors Supriya Rajhans, Nikolas Rupp, Esmerando Escoto, Arthur Schönberg, Dominic Laumer, Malte Sumfleth, Issam Abdallah, Bastian Manschwetus, Caroline Juliano, Nikan Javid, Cord L. Arnold, Tais Gorkhover, Markus Drescher, Robert Riedel, Ingmar Hartl, Christoph M. Heyl, Tino Lang
Plasma Physics
Real-time Tomography-based Bayesian Inference from TCV Bolometry Data
D. Hamm, C. Theiler, L. Simons et al. (+3 more)
Radiated power information is crucial to diagnose and optimize the performance of fusion
plasmas. Traditionally, at the TCV tokamak, radiated power analysis has only ever been possible following
plasma discharge termination. However, recently, TCV bolometer data have become available in real-time. This offers the opportunity of integrating the radiated power information into the TCV
plasma control system. In this work, we propose a novel real-time
tomography-based
Bayesian technique allowing estimation of the power radiated from user-defined regions of interest in the
plasma. The real-time estimates are obtained as computationally cheap linear combinations of bolometer measurements, using pre-computed coefficients that are optimized for the specific discharge planned. This method is not, thus, trained on a set of synthetic or tomographically reconstructed emissivity profiles. We detail the derivation of the technique and show its equivalence to traditional tomographic estimates under suitable conditions. We then demonstrate that this technique enables accurate real-time estimation of the total, core, divertor and main chamber radiated power, by its application to a representative and heterogeneous set of TCV discharges. Finally, we discuss the robustness of the technique to faulty detectors, showing that simple precautions allow safe handling of many common issues. The computational routines implementing the described technique are provided as open-source code.
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All authors D. Hamm, C. Theiler, L. Simons, B. P. Duval, U. Sheikh, the TCV team
Fluid Dynamics
Water droplet dynamics and evaporation in airtanker firefighting
Fabian Denner
This study presents the first systematic investigation of the dynamics of individual water droplets in the context of airtanker firefighting. While previous work has focused on ground-deposition patterns measured in standardized field tests, the droplet-scale mechanisms governing evaporation and transport have remained largely unexplored. A tailored model of the coupled momentum, heat, and mass transfer of an isolated water droplet in ambient air is proposed and applied to examine the
evolution of droplets under a wide range of atmospheric conditions. The results demonstrate that droplet size governs the effectiveness of water delivery, the release height emerges as the dominant operational parameter, and relative humidity is the key atmospheric property. Increasing the release height lengthens the flight time and increases evaporative losses, while low relative humidity accelerates evaporation, particularly for droplets smaller than one millimeter. Only droplets within a narrow range of initial radii, $150\,\mu\mathrm{m} \lesssim r_{\mathrm{d},0} \lesssim 3\,\mathrm{mm}$, are able to reach the ground following an airtanker release, with smaller droplets fully evaporating during their fall and larger droplets being subject to secondary atomization. Although airtanker releases involve very large
liquid volumes and complex spray dynamics, the present analysis deliberately isolates droplet-scale behavior and does not resolve collective spray effects, wake interactions, or
turbulence. The findings therefore serve as a physically consistent baseline for droplet evaporation and transport, forming a foundation for spray-resolved modeling efforts aimed at improving airtanker delivery strategies.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Origin and Propagation of Spin-orbit Torques in Pt/Co/Cu/NiFe/Capping Multilayers
Yuming Bai, Rulin Tian, Yue Zhang et al. (+1 more)
Spin-orbit torque (SOT) enables efficient current-driven control of magnetization, offering a promising pathway toward low-power spintronic devices. However, the origin and propagation of both damping-like (DL) and field-like (FL) SOTs in complex multilayers remain unclear. Here, we investigate NiFe thickness-dependent SOT efficiencies in Ta/Pt/Co/Cu/NiFe/Cu/Capping multilayers (x = 15 nm; Capping = Pt, Al, and SiO2). By employing a
spin rotation geometry, the perpendicularly magnetized Pt/Co/Cu stacks serve as a
spin source introducing unconventional
spin polarization orthogonal to the Oersted field, eliminating its contribution and enabling unambiguous separation of SOTs using planar
Hall and polar MOKE measurements. To distinguish bulk and interfacial contributions, we introduce a sample-area-normalized moment m = mNiFe/S, accounting for thickness-dependent magnetization and eliminating uncertainties arising from nominal thickness scaling and
magnetic dead layers. We find that DL-SOT follows nearly linear 1/m scaling, consistent with rapid
spin absorption at the Cu/NiFe interface but exhibits finite beta_SOT when 1/m approaches zero in both Pt- and Al-capped samples, indicating additional interfacial
spin-current contributions at Cu/Pt and Cu/Al interfaces. In contrast, SiO2-capped samples show negligible interfacial contributions. Furthermore, FL-SOT deviates markedly from 1/m scaling and exhibits a significantly longer
spin dephasing length (about 1.7 nm) compared to DL-SOT, implying extended propagation across NiFe. Comparative capping-layer studies further corroborate this behavior through interface-dependent
spin transport. Our findings clarify the origin and distinct propagation characteristics of DL and FL torques, providing guidelines for engineering interfacial
spin-orbit functionalities in ultrathin metallic
heterostructures.
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All authors Yuming Bai, Rulin Tian, Yue Zhang, Tao Wang
Optics
Design and characterization of a simple polarization grating-based polarimeter
Massimo Santarsiero, J. C. G. de Sande and Gemma Piquero
In undergraduate optics courses, diffraction gratings are studied extensively, generally within the scalar approximation. When the vector nature of light is taken into account, so-called polarization diffraction gratings have been proposed, which are a cutting-edge research topic due to their numerous applications. This paper proposes a simple experiment to introduce students to polarization diffraction gratings and, at the same time, use this device to apply many of the concepts learned about polarimetry. Although current research uses spatial light modulators and metasurfaces, we use a cheap commercial polarization grating. In addition to show how a polarization grating can be characterized, its use as a cheap and easy-to-use Stokes polarimeter is described and demonstrated experimentally. In performing the experiment, issues typical of inverting linear systems will arise, and this will also provide the opportunity to address the problem of finding well-conditioned systems of equations.
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Optics
Strong optical nonreciprocity in a photonic crystal composed of spinning cylinders
Hengzhi Li, Wanyue Xiao, Junho Jung et al. (+2 more)
Moving media break time-reversal
symmetry and exhibit intriguing optical nonreciprocity. This nonreciprocity is usually weak due to the much lower moving speed of media relative to the speed of light. We demonstrate that strong optical nonreciprocity can emerge in a two-dimensional photonic
crystal composed of spinning dielectric cylinders. The photonic
crystal supports two types of
chiral modes at the Brillouin zone center: hybridized multipole modes and
symmetry-protected bound states in the continuum (BICs), both of which carry intrinsic
spin angular momentum. For finite wavevectors near the zone center, the BICs transform into quasi-bound states in the continuum (QBICs). Under oblique incidence of circularly polarized plane waves, the photonic
crystal exhibits nonreciprocal transmission and absorption that are significantly enhanced at the frequencies of these hybridized multipole modes and QBICs. Furthermore, the high quality factors of the QBICs enable sharp transitions in nonreciprocity. Our work uncovers strong
chiral light-matter interactions in periodic moving structures, with potential applications in nonreciprocal light manipulation. The mechanism may also be generalized to other classical wave systems, such as phononic
crystals.
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All authors Hengzhi Li, Wanyue Xiao, Junho Jung, Hao Pan, Shubo Wang
Geophysics · Cross-listed from cs.CV
A Decade of Generative Adversarial Networks for Porous Material Reconstruction
Ali Sadeghkhani, Brandon Bennett, Masoud Babaei et al. (+1 more)
Digital reconstruction of porous materials has become increasingly critical for applications ranging from geological reservoir characterization to tissue engineering and electrochemical device design. While traditional methods such as micro-computed
tomography and statistical reconstruction approaches have established foundations in this field, the emergence of deep learning techniques, particularly Generative
Adversarial Networks (GANs), has revolutionized porous media reconstruction capabilities. This review systematically analyzes 96 peer-reviewed articles published from 2017 to early 2026, examining the
evolution and applications of GAN-based approaches for porous material image reconstruction. We categorize GAN architectures into six distinct classes, namely Vanilla GANs, Multi-Scale GANs, Conditional GANs,
Attention-Enhanced GANs, Style-based GANs, and Hybrid Architecture GANs. Our analysis reveals substantial progress including improvements in porosity accuracy (within 1% of original samples), permeability prediction (up to 79% reduction in mean relative errors), and achievable reconstruction volumes (from initial $64^3$ to current $2{,}200^3$ voxels). Despite these advances, persistent challenges remain in computational efficiency,
memory constraints for large-scale reconstruction, and maintaining structural continuity in 2D-to-3D transformations. This systematic analysis provides a comprehensive framework for selecting appropriate GAN architectures based on specific application requirements.
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All authors Ali Sadeghkhani, Brandon Bennett, Masoud Babaei, Arash Rabbani
Optics
Phase Retrieval using Nonlinear Curvature Sensing within Convergent Beams
Justin R. Crepp, Caleb G. Abbott, James Smous et al. (+2 more)
Path-length diversity methods may be used for adaptive optics (AO) systems to retrieve phase and amplitude information by measuring intensity across multiple planes. Observations that rely on free-space propagation, such as the nonlinear
curvature wavefront sensor (WFS), have been shown to offer excellent sensitivity and robustness to scintillation. However, the default design results in a large opto-mechanical footprint due to unavoidable
geometric-optics and wave-optics effects. Measurements recorded in a convergent beam would improve instrument compactness, while concentrating light into smaller detector regions of interest, improving signal-to-noise ratio and possibly wavefront reconstruction speed. In this paper, we study path-length diversity wavefront sensing using four planes of contemporaneous intensity measurements made in a convergent beam. We develop a physical optics propagation model and validate the model by performing wavefront reconstructions in both simulations and lab experiments. The manuscripts core contribution is a practical, intensity-domain,
Fourier-transform-based recipe to use a conventional multi-plane Gerchberg-Saxton (or comparable) reconstruction pipeline with convergent-beam measurements, enabling a compact optical layout. We find that this approach offers practical benefits over an equivalent free-space wavefront sensor, in particular reducing size, weight, complexity and cost.
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All authors Justin R. Crepp, Caleb G. Abbott, James Smous, Matthew Engstrom, Brian Sands
Optics
Large language models for optical network O&M: Agent-embedded workflow for automation
Shengnan Li, Yidi Wang, Fubin Wang et al. (+7 more)
With the continuous expansion of optical networks and the increasing diversity of services, existing operation and maintenance (O&M) approaches are increasingly challenged to meet the rising demands for intelligence and efficiency. Large
language models (LLMs), endowed with advanced semantic understanding and contextual analysis capabilities, are emerging as a promising enabler for intelligent optical network O&M. Recent studies have demonstrated the feasibility of applying LLMs to optical network management, marking an important step toward intelligent automation. However, systematic investigations into how LLMs can be effectively integrated into existing O&M workflows remain limited. This paper addresses this gap by drawing inspiration from best practices in real-world O&M workflows and systematically identifying scenarios that are well suited for LLM integration. We highlight that
agent-based design is key to improving the executability of tasks, and we propose a multi-
Agent collaborative O&M architecture that integrates LLM capabilities with existing O&M tools. The proposed architecture leverages core LLM-related technologies including
prompt engineering and tool invocation, to build
Agent solutions targeting key tasks such as optical channel management, performance optimization, and fault management. This work presents a conceptual framework for
embedding LLM-based
Agents into optical network O&M workflows, forming agentized processes that demonstrate the feasibility of LLM-assisted task execution and lay the groundwork for future autonomous O&M systems featuring closed-loop perception, decision-making, and action.
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All authors Shengnan Li, Yidi Wang, Fubin Wang, Yujia Yang, Yao Zhang, Yuchen Song, Xiaotian Jiang, Yue Pang, Min Zhang, Danshi Wang
Optics
Temperature-insensitive tunable and stable Fabry-Perot cavity for atomic physics
Joshua Ruelle, Martin Hauden, Francisco S. Ponciano-Ojeda et al. (+1 more)
Optical Fabry-Perot cavities are crucial tools for metrology experiments, where they achieve extreme length stability, and for some atomic physics experiments, where tunability to atomic transitions enables atom-light interactions. However, achieving both frequency stability and tunability in a single cavity has remained a challenge, forcing metrology experiments exploiting atom-cavity interactions to rely on external active feedback systems to stabilize the length of the cavity. Here, we describe a piezoelectrically-tunable cavity with a cancellation of the coefficient of thermal expansion at around $5^\circ\mathrm{C}$, achieving fractional frequency instabilities at the $4\times 10^{-13}$ level for 1~s integration time. This advance eliminates the need for external stabilization in many atom-cavity experiments, making this design ideal for applications such as ultra-stable superradiant
lasers and other cavity
quantum electrodynamics experiments.
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All authors Joshua Ruelle, Martin Hauden, Francisco S. Ponciano-Ojeda, Marion Delehaye
Chemical Physics
ChemFit: A framework for automated high-dimensional model parameter optimization
Moritz Sallermann, Amrita Goswami, Rosana Collepardo-Guevara et al. (+4 more)
The parameterization of simulation-based models is a central yet laborious task in computational chemistry and physics, often driven by human intuition and manual iteration. Automating this task necessitates the definition of suitable objective functions, which tend to be expensive to evaluate, noisy, non-differentiable, or composed of heterogeneous contributions originating from separate sets of simulations. Gradient-free and black-box optimization
algorithms are powerful tools which are particularly well-suited to minimizing such objective functions. Here, we introduce ChemFit, a flexible Python framework for the definition, composition, and massively concurrent evaluation of simulation-based objective functions, which is designed to operate in conjunction with these
algorithms. We demonstrate the broad applicability of this approach by using ChemFit for three representative examples of increasing complexity and real-world relevance. First, we obtain the parameters of the Lennard-Jones potential for
liquid argon from experimental measurements of the density. Second, we parameterize a polarizable and flexible potential energy function to reproduce the structure of small H$_2$O clusters obtained from density functional theory calculations. Finally, we tune a small subset of the parameters of a residue-level coarse-grained
protein force-field, with the goal to reproduce the experimental critical solution temperature of the low complexity domain of the wild-type hnRNPA1 sequence and an arginine-enriched mutant of this
protein. hnRNPA1 is an RNA-binding
protein linked to amyotrophic lateral sclerosis. Together, these examples illustrate how ChemFit enables scalable, reproducible, and optimizer-agnostic parameter fitting for broadly applicable multiscale models.
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All authors Moritz Sallermann, Amrita Goswami, Rosana Collepardo-Guevara, Alberto Ocana, Hannes Jónsson, Elvar Ö. Jónsson, Jorge R. Espinosa
Physics and Society
Unequal changes in commuting patterns across socio-economic strata in response to pandemic restrictions
Cristiano Marinelli, Leo Ferres, Niccolò Comini et al. (+2 more)
Commuting patterns are a central component of urban dynamics and many societal activities. Exogenous shocks, such as a pandemic, might drastically modify them inducing heterogeneous variations across socioeconomic strata. Here, we quantify changes in work commuting patterns in Bogotá, Colombia during three different periods of the COVID-19 pandemic: pre-pandemic (2019), COVID-19 restrictions (2020), and partial reopening (2021). To this end, we use anonymized mobile phone data to infer home and work locations from recurring nighttime and weekday connection patterns, and to build daily commuting metrics. We aggregate mobility flows by administrative boundaries and socioeconomic strata. Additionally, we enrich the
dataset with a range of other variables such as territorial vocation (i.e., urban versus rural), demographic information (i.e., population density) and, as a proxy for digital infrastructure quality, geolocated Speedtest measurements from Ookla. We find a marked reduction of commuting during restrictions in 2020 and a strong recovery in 2021, but with persistent heterogeneity across socioeconomic strata. Indeed, while commuting declined similarly across income groups during restrictions, groups of the population in the lower-income bracket rebounded faster to pre-pandemic levels. On the contrary, we find that groups in the higher-income bracket managed to keep higher stay-at-home behavior. Regression analyses reveal that territorial characteristics and disparities in digital connectivity significantly contribute to these differences, suggesting that infrastructure investments could help mitigate mobility-based inequalities.
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All authors Cristiano Marinelli, Leo Ferres, Niccolò Comini, Nicolò Gozzi, Nicola Perra
Biological Physics
Size-Dependent Fluorescence Kinetics Reveal Contributions of Intrinsic Quenching and Singlet-Triplet Annihilation during LHCII Aggregation
Francois Conradie, Bertus van Heerden, Michal Gwizdala et al. (+1 more)
Aggregation of the main
antenna complex of higher plants, Light-Harvesting Complex II (LHCII), is widely used as an in vitro model for energy-dependent quenching (qE), yet fluorescence reduction in aggregates is frequently interpreted without a quantitative separation of intrinsic quenching from excitation-induced annihilation. Here, we address this ambiguity by directly correlating aggregate size, concentration, steady-state fluorescence intensity, and decay kinetics during controlled, incremental aggregation of isolated LHCII. By combining fluorescence correlation spectroscopy (FCS) with TCSPC in a unified experimental framework, we monitored structural and photophysical changes in real time as detergent removal drives biphasic aggregation. We quantified the aggregate composition from the particle concentrations, enabling direct scaling of the absorption cross-section with aggregate size. The average fluorescence lifetime decreased semi-logarithmically with increases in hydrodynamic radius, whereas steady-state fluorescence intensities deviated strongly from this trend. Intensitydependent measurements and steady-state kinetic modeling reveal that singlet-triplet annihilation (STA) emerges at moderate excitation intensities and rapidly becomes the dominant contributor to fluorescence quenching, even for relatively small aggregates. In contrast, intrinsic quenching increases more gradually with aggregate size. By quantitatively disentangling intrinsic excitation quenching from annihilation processes, this work demonstrates that STA can govern the apparent photophysical response of aggregated LHCII across excitation regimes commonly considered non-annihilating. The size-dependent mechanistic framework presented here provides a basis for distinguishing intrinsic quenching from annihilation effects in aggregation-based studies of photosynthetic
antenna complexes.
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All authors Francois Conradie, Bertus van Heerden, Michal Gwizdala, Tjaart P. J. Krüger
Plasma Physics
Designing A Buildable Optimized Stellarator to Confine Electron-Positron Plasmas
Pedro F. Gil, Jason Smoniewski, Paul Huslage et al. (+7 more)
In this paper, the design of the the
plasma equilibrium and superconducting coils for the Electrons and Positrons in an Optimized Stellarator EPOS experiment is presented. With newly developed stellarator optimization tools, including single-stage and
stochastic optimization, as well as HTS strain, this work demonstrates that it is possible to achieve key metrics for the buildability and confinement properties of the device. In particular, satisfactory quality of quasisymmetry and stellarator robustness is designed, and engineering requirements are met for eight different candidates. A feasibility study is presented that optimizes multiple candidates for different
plasma major radii and coil currents, as well as the best EPOS candidate to date.
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All authors Pedro F. Gil, Jason Smoniewski, Paul Huslage, Rogerio Jorge, Timo Thun, Elisa Buglione-Ceresa, Tristan Schuler, Stefan Fingl, Grégoire-Hubert Ducas, Eve V. Stenson
Biological Physics · Cross-listed from cond-mat.soft
Scaling Laws and Paradoxical Metastable States in Nanofilament Entropic Separation
Jose M. G. Vilar, J. Miguel Rubi and Leonor Saiz
Entropic forces play a fundamental role in nanoscale phenomena, from colloidal self-assembly to biomolecular disaggregation. Here, we develop an exact analytical theory and find general scaling laws for the entropic separation of tether-mediated nanofilament bundles, revealing that a single dimensionless parameter–the ratio of the excluded-volume radius to the tether length–dictates whether filaments are pushed apart or, contrary to the usual expectation, pulled together. This unexpected regime challenges the view that entropic forces invariably promote disaggregation, instead uncovering conditions under which the bundles can remain in attractive metastable states. Brownian dynamics simulations confirm this paradoxical effect, offering predictive insights for applications in biophysics, soft matter physics, and nanotechnology.
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Computational Physics
A Scattered-Field Formulation for Coupled Geometric Wakefield and Space Charge Field Simulations in Particle Accelerators
J. Christ, E. Gjonaj and H. De Gersem
We propose a self-consistent simulation model for particle beams in accelerators, which includes the impact of electromagnetic wakefields caused by the geometry of the accelerator chamber. The method is based on a scattered-field formulation for the beam-driven Maxwell's equations. The total electromagnetic field seen by the particles is obtained as the solution of two coupled problems: a purely wakefield problem and a space charge field problem, where for each of these problems, specialized and numerically efficient approaches can be used. To assess the accuracy of the method, we compare simulation results with the analytical solution for a relativistic beam in a uniform accelerator pipe. The numerical efficiency of the method is, furthermore, demonstrated in the beam dynamics study of the multi-
cell RF photo-gun installed at the SuperKEK
collider facility. We show that electromagnetic wakefields have a non-negligible impact on the quality of the generated beam and, therefore, should be taken into account in the design of high-brilliance electron sources.
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Geophysics
Linearised versus Nonlinear Estimates of Uncertainty in Full Waveform Inversion
Xuebin Zhao and Andrew Curtis
Seismic full waveform inversion (FWI) is a powerful technique to generate high resolution images of the Earth's interior. However, significant uncertainty exists in all FWI solutions due to imperfect acquisition geometries, inherent noise in the data, and nonlinearity of the forward problem. Probabilistic
Bayesian FWI addresses this non-uniqueness by estimating the entire family of possible model solutions described by the posterior probability density function (pdf). The posterior pdf can be estimated using nonlinear inversion methods to quantify full uncertainties. Alternatively, by linearising the physics relating parameters and observations around the maximum a posteriori solution, the posterior pdf is usually approximated by a Gaussian pdf. This is referred to as the linearised method. In this work, we apply both nonlinear and linearised methods to 2D acoustic
Bayesian FWI problems. We use a variational inference
algorithm for the nonlinear case, in which a transformed Gaussian is optimised to approximate the posterior pdf. The results can be compared with those from a linearised, locally-Gaussian based method. We also apply Stein variational gradient descent for comparison. The results show that while both the linearised and nonlinear methods recover the posterior mean models accurately, they exhibit significantly different posterior uncertainty structures, especially around layer interfaces, due to the linearisation of wave physics. Linearised uncertainty estimates are shown to be significantly less accurate: they provide far less accurate fits to observed waveform data, and yield biased estimates of inferred meta-properties such as volumes of geological bodies. This work therefore motivates the application of fully nonlinear inversion methods in
Bayesian FWI if accurate uncertainty estimates over parameters, or inferred or interpreted meta-properties are important.
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Classical Physics
Mpemba Effect in Many-Body Systems Near Equilibrium
Philippe Ben-Abdallah
The Mpemba effect, in which a system initially farther from
equilibrium relaxes faster than a closer one, has been observed in a wide variety of linear and nonlinear systems. Here we develop a unified framework for the Mpemba effect in many-body systems near
equilibrium based on the spectral geometry of the relaxation operator. We distinguish a non-uniform Mpemba effect, associated with a crossing of global distances to
equilibrium, from a strict componentwise Mpemba effect, in which the initially hotter state remains larger in every degree of freedom yet relaxes faster. We show that reciprocal systems admit only the former, whereas reciprocity breaking renders the relaxation operator non-normal and can enable the latter. These results identify reciprocity and non-normality as key ingredients governing anomalous relaxation in linear many-body systems.
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Plasma Physics
Stochastic single-stage stellarator optimization using fixed-boundary equilibria
Pedro F. Gil, Jason Smoniewski, Rogerio Jorge et al. (+2 more)
In this paper, single-stage stellarator optimization is combined with
stochastic coil optimization to improve the robustness of the stellarator as compared to deterministic methods. The
plasma boundary, solved with an MHD solver in fixed-boundary mode, is linked to a set of randomly perturbed coils via the squared flux. The optimizer avoids sharp local minima and can reach improved configurations. Two different configurations obtained with our method, one quasi-axisymmetric and one quasi-helically symmetric, are compared against both the standard
stochastic stage II method and the single-stage method. The new configurations shown here yield improved squared flux, quasisymmetry, and particle loss following a posteriori perturbation of the coils.
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All authors Pedro F. Gil, Jason Smoniewski, Rogerio Jorge, Paul Huslage, Eve V. Stenson
Applied Physics · Cross-listed from cond-mat.mes-hall
Non-volatile Multistate Magnetic Switching via Spin-orbit Torque and Intrinsic Anisotropy
Fei Ye, Chunzheng Wang, Xue Zhang et al. (+6 more)
While current-induced bistate
spin-orbit torque (SOT) switching has been well established, deterministic electrical control of multiple
magnetic states remains a central challenge in spintronics. Here, we realize a conceptually new multistate SOT device in a SrIrO_3/SrRuO_3
bilayer, hosting four intrinsically stable yet electrically distinguishable
magnetic states, including two in-plane canted (IP_c^$\pm$) and two out-of-plane canted (OP_c^$\pm$) states. Pulsed current excitations fully map all twelve deterministic transitions among the four states, establishing a robust switching protocol defined by two characteristic current densities. In-situ scanning nitrogen-vacancy (NV) center magnetometry provides direct real-space evidence for the previously unobserved IP_c^$\pm$ states, and
spin dynamics simulations uncover a two-step switching pathway, driven by the concerted action of
spin torques and the effective anisotropy field within the fourfold anisotropy landscape. Our demonstration of the intrinsic multistate SOT device directly addresses the density bottleneck of conventional bistate SOT technology, establishing a powerful paradigm for compact, high-speed, and energy-efficient multistate spintronics.
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All authors Fei Ye, Chunzheng Wang, Xue Zhang, Sihai Jiao, Zhongjie Wang, Long Cheng, Zhifeng Zhu, Chunlei Gao, Xiaofang Zhai
Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci
Unlocking nanoscale microstructural detail in aluminium alloys through differential phase contrast segmentation in STEM
Matheus A. Tunes, Martin Hasenburger, Rostislav Daniel et al. (+5 more)
Differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM) maps projected electric fields through the phase sensitivity of segmented low-angle detectors. Although typically applied to atomic-resolution imaging at low beam currents, STEM-DPC is here demonstrated as a rapid micro- and nanoscale image-
segmentation tool for materials characterization in advanced aluminium
alloys. Decomposition of false-colour DPC micrographs in hue-saturation-value space enables simultaneous identification and quantification of nanoclusters, GP zones, intermediate precipitate phases, dislocation cores, and associated strain fields within a single field of view. The method is demonstrated across multiple
alloy systems, including clustering and strain-field mapping in a deformed AlMgZn(Cu) crossover
alloy, precipitate identification in a paint-baked automotive sheet
alloy, phase-variant
segmentation in overaged AA7075-T7, and nanopore and nanoparticle detection in an anodic coating on AA2024-T3. Coupling DPC with neural-network
segmentation further enables automated grain-boundary delineation and quantification in nanocrystalline aluminium thin films. Combined with STEM-EDX, DPC-based
segmentation enables correlative microstructural analysis, establishing DPC as a rapid complement to techniques such as SPED and 4D-STEM.
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All authors Matheus A. Tunes, Martin Hasenburger, Rostislav Daniel, Oscar M. Prada-Ramirez, Philip Aster, Sebastian Samberger, Thomas M. Kremmer, Johannes A. Österreicher
Optics
Reconfigurable plasmonic hot spots enabled by composite VO2-gold plasmonic antennas
Rostislav Řepa, Jiří Kabát, Tomáš Šikola et al. (+1 more)
We theoretically investigate the formation of electric and
magnetic hot spots with reconfigurable plasmonic
antennas. We consider three material systems offering different levels of reconfigurability: gold with the static response, vanadium dioxide which allows for ON/OFF switching, and composite gold-vanadium dioxide material platform which offers a possibility to switch between the electric and
magnetic hot spot within a single
antenna. Using bowtie and diabolo
antennas as a case study, we evaluate optical response functions (scattering and absorption cross-sections, electric and
magnetic field enhancement). We demonstrate that the composite material system brings, in addition to enhanced reconfigurability, also novel features of plasmonic
antennas, such as strong optical absorption and a joint electric-
magnetic hotspot.
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All authors Rostislav Řepa, Jiří Kabát, Tomáš Šikola, Vlastimil Křápek
Optics
Enhancement of signal-to-noise ratio at a high-order exceptional point of coherent perfect absorption
Zi-Qi Wang, Yi-Ming Sun, Yao-Dong Hu et al. (+4 more)
Exceptional points (EPs) in non-Hermitian systems offer a remarkably strong response to weak perturbations, but the nonorthogonal nature of the corresponding eigenvectors causes noise to diverge, hindering EPs practical application. Here, we report a twelve-fold enhancement of signal-to-noise ratio (SNR) in
magnetic field sensing enabled by a third-order EP of coherent perfect absorption (CPA EP3) in a passive cavity magnonic system. This non-Hermitian magnonic platform comprises two identical yttrium iron garnet (YIG) spheres coherently coupled to a cavity mode, in which the CPA EP3 is realized by engineering the three-mode loss to form a pseudo-Hermitian absorption
Hamiltonian. By independently tailoring the absorption EP apart from the resonance EP, the system circumvents the noise divergence caused by eigenbasis collapse. Notably, we harness the sensitivity of the minimum output intensity near CPA to perturbations, yielding a seventyfold SNR improvement and a 400-fold increase in responsivity compared with non-CPA system. A comprehensive noise analysis over one hundred repeated measurements confirms the suppression of frequency noise near the CPA EP3. This demonstrates that our scheme not only avoids the noise divergence plaguing conventional higher-order EP sensors but also provides a general strategy to exploit both CPA and EP for SNR enhancement in passive non-Hermitian systems.
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All authors Zi-Qi Wang, Yi-Ming Sun, Yao-Dong Hu, Yi-Pu Wang, Rui-Chang Shen, Wei-Jiang Wu, J. Q. You
Fluid Dynamics
Multipoint Statistical Turbulent Dynamics from Hopf Equation Closures
Mark Warnecke
Obtaining accurate multipoint statistics of
turbulence is computationally very expensive and therefore these statistics have remained largely unexplored from a theoretical standpoint. In this paper, (i) a first-principles-based closure of the $n$th-order structure function governing equation proposed by Sreenivasan & Yakhot (2021) is generalized to a closure of the velocity increment
Hopf equation itself. Then (ii) the closure is further generalized to the $N$-point
Hopf equation. Finally, (iii) an example of the method is provided to analytically determine the $3$-point structure function transition between the known $2$-point structure function and the $3$-point fusion rules from the closed $(N=3)$-point velocity increment
Hopf equation. The analytical solution takes the form of a Batchelor interpolation and shows promising agreement with preliminary DNS data for the cases examined. Since the $N$-point velocity increment
Hopf equation is closed, its solution can be numerically approximated. It is expected that similar methods, applied here to obtain the $2$-point structure function and $3$-point structure function transition, can be used to obtain further analytical predictions of various multipoint quantities to deepen our understanding of
turbulence.
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Optics
Quantitative 3D imaging of highly distorted micro-crystals using Bragg ptychography
Peng Li, David Yang, Christoph Rau et al. (+3 more)
Bragg coherent diffraction imaging (BCDI) fails to reliably retrieve phases in micro-
crystals exhibiting strong strain inhomogeneities, which restricts its applicability. Here we show that three-dimensional Bragg ptychography (3DBP) overcomes this limitation by enabling stable inversion for large
lattice distortions. Using a combination of experimental measurements and numerical tests, we compare the performance limits of the two approaches and demonstrate that 3DBP tolerates
lattice distortions more than six times larger than BCDI. We also establish the sensitivity of both methods on a weakly distorted
crystal, for which 3DBP yields smoother amplitude and phase fields with reduced short-length-scale artifacts. 3DBP thus provides a reliable route for imaging micro-
crystals with large
lattice distortions, expanding the scope of coherent X-ray Bragg microscopy to strongly deformed systems.
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All authors Peng Li, David Yang, Christoph Rau, Marc Allain, Felix Hofmann, Virginie Chamard
Fluid Dynamics
On the deformation of a shear thinning viscoelastic drop in a steady electric field
Sarika Shivaji Bangar and Gaurav Tomar
The deformation of viscoelastic drops under electric fields plays a crucial role in applications such as microfluidics, inkjet printing, and electrohydrodynamic manipulation of complex fluids. This study examines the deformation and breakup dynamics of a linear Phan-Thien-Tanner (LPTT) drop subjected to a uniform electric field using numerical simulations performed with the open-source solver Basilisk. Representative combinations of conductivity ratio ($\sigma_r$) and permittivity ratio ($\epsilon_r$) are chosen from six characteristic regions of the ($\sigma_r$, $\epsilon_r$) phase space, $PR_A^+$, $PR_B^+$, $PR_A^-$, $PR_B^-$, $OB^+$, and $OB^-$. In regions where the first- and second-order deformation coefficients have the same sign ($PR_A^-$, $PR_B^-$, $OB^+$), the LPTT drops exhibit deformation dynamics that negligibley deviate from the Newtonian behavior. In the $PR_A^+$ region, drops deform into prolate spheroidal shapes below a critical electric capillary number and transition to stable multi-lobed shapes or breakup beyond this threshold. Increasing elasticity of drop opposes the deformation, thereby reducing deformation and increasing critical $Ca_E$ with the Deborah number ($De$). In the $PR_B^+$ region, drops form prolate shapes below critical $Ca_E$ and develop conical ends above it. The steady-state deformation exhibits a non-monotonic dependence on $De$, increasing at low $De$ and decreasing at higher values. A similar non-monotonic variation is also observed in critical $Ca_E$. In the $OB^-$ region, LPTT drops attain oblate shapes below critical $Ca_E$ and undergo breakup beyond it. The deformation magnitude shows a non-monotonic variation with $De$, increasing initially and decreasing at higher elasticity.
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Applied Physics
Metasurface Tape for Efficient Millimeter-Wave Power Transfer via Surface-Wave Propagation
Phuc Toan Dang, Kota Suzuki, Yoshiki Ashikaga et al. (+3 more)
Millimeter-wave technologies are essential for future high-speed wireless communications. However, a fundamental challenge remains in the form of severe free-space path loss, where the power density decreases inversely with the square of the distance r (i.e., proportional to r^{-2}) as a spherical dependence. To overcome this limitation, we propose a flexible metasurface tape that is designed to guide electromagnetic energy as surface waves. Unlike conventional free-space propagation, this engineered metasurface confines the field to a subwavelength interface, thereby altering the power decay law to a circular dependence (i.e., proportional to r^{-1}). We numerically and experimentally, for the first time, demonstrate this concept using a periodic grounded-patch array fabricated on a flexible substrate and operated at approximately 100 GHz. The measurement results show that the metasurface tape significantly increases the transmitted power, yielding an average rate of improvement of approximately 40 per meter in received power relative to the free-space baseline in our measurement geometry (e.g., 29-dB increase at 2 m). This increase is realized over a broad bandwidth from 95 GHz to 105 GHz (i.e., approximately 10 %), accommodating wideband modulation schemes required for high-data-rate applications. The flexible, lightweight nature of the tape allows it to be easily installed on diverse surfaces. Our demonstration indicates that the metasurface tape is a promising platform for extending the effective range of millimeter-wave systems, thus offering a robust solution to the path-loss bottleneck in next-generation wireless networks.
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All authors Phuc Toan Dang, Kota Suzuki, Yoshiki Ashikaga, Yasushi Tsuchiya, Sendy Phang, Hiroki Wakatsuchi