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Physics Physics

physics Watch Physics

Monday 16 March

Instrumentation and Detectors

Design and operation of a flash lamp for vacuum ultraviolet light production

Silas Bosco, Jonas Bürgi, Livio Calivers et al. (+10 more)

Noble liquids, notably argon and xenon, are utilised as both detector media and as the detector target for dark matter and neutrino physics experiments. When the noble liquid is excited by particles, it scintillates vacuum ultraviolet light, which sensors then detect. A major focus of the detector development community is on producing precision light sensors for noble liquid detectors. We introduce a flash lamp to test VUV-sensitive light sensors with light at wavelengths observed at noble liquid detectors. This paper discusses the design and presents results from a flash lamp prototype operated at room temperature.
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All authors Silas Bosco, Jonas Bürgi, Livio Calivers, Richard Diurba, Johannes Furrer, Jan Kunzmann, Saba Parsa, Sascha Rivera, Nicolas Sallin, Camilla Tognina, Serhan Tufanli, Michele Weber, Dominik Wermelinger

Optics

Resolving Nonequilibrium Gas Kinetics in Supersonic Neutral Flows with Coherent Rayleigh Brillouin Scattering

Atulya Kumar, Gabriel Alfaro, Marios Kounalakis et al. (+2 more)

We present a characterization of high-speed flows in nonequilibrium thermodynamic conditions using single-shot coherent Rayleigh-Brillouin scattering(CRBS). The technique is applied on a highly underexpanded jet using 200ns laser pulses, enabling simultaneous probing of multiple spatial locations. We map the jets average axial velocity and density distributions and resolve local velocity gradients, providing access to parameters relevant to turbulence characterization. The measurements are validated against numerical simulations, showing good agreement overall. We find that in most cases individual single-shot spectra exhibit substantial deviation from the bulk averaged lineshapes, reflecting the non-Maxwellian velocity distributions generated by shock-induced regimes. The results presented here establish single-shot CRBS as an important tool for direct measurements of flow velocity components, velocity gradients, and density in complex, unsteady supersonic environments.
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All authors Atulya Kumar, Gabriel Alfaro, Marios Kounalakis, Stefan Karatodorov, Alexandros Gerakis

Atmospheric and Oceanic Physics

Investigating How the Fractions Skill Score and Brier Divergence Skill Score Reflect Forecast Error

Bobby Antonio

Meaningful scores for forecast verification are essential for developing reliable forecasts, and there has been much effort to develop scores that align well with human perceptions of forecast quality. Whilst many of these scores have intuitive interpretations, relatively little is known about how these scores rank different forecasts, and how scores reflect forecast error. We theoretically explore the behaviour of two scores that fall within the `neighbourhood' paradigm of spatial verification; the Fractions Skill Score (FSS) and Brier Divergence Skill Score (BDnSS). We investigate how each score ranks forecasts with two types of error; errors in the mean frequency (corresponding to intensity or shape errors) and errors in the standard deviation (corresponding to errors in spatial structure, such as blurring or excess noise). We find that under many situations the FSS assigns higher scores to forecasts that over-predict mean frequency, thus theoretically confirming the need to use the FSS with percentile thresholds. Both scores generally assign higher scores to forecasts with lower neighbourhood standard deviation, a reflection of the `double penalty' problem; however, we observe that size of this effect is larger for the BDnSS than the FSS, showing that the FSS under some situations is less susceptible to the double penalty problem than the BDnSS.
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Accelerator Physics · Cross-listed from cond-mat.supr-con

Quench Protection in Insulated REBCO Conductors: Design Optimization and Fast Detection via REBCO SQD

Hajar Zgour, Walid Abdel Maksoud, Bertrand Baudouy et al. (+1 more)

This work was conducted within the framework of the exploratory French project PEPR SupraFusion, which aims to advance the field of fusion energy by developing High-Temperature Superconductor (HTS)-based demonstrators capable of storing significant energy while operating under high magnetic fields and currents. Ensuring a reliable protection during a quench in Insulated REBCO conductors is challenging\,: slow normal-zone propagation and validation delays allow the hotspot's temperature to reach damaging levels. We compare (i) conductor protection via copper-stabilizer optimization and (ii) a co-wound, REBCO superconducting quench detector (SQD) that is electrically isolated yet thermally coupled and intentionally deoxygenated to lower Tc and Ic for an earlier transition. Onedimensional THEA modeling shows that a good choice of stabilizer cross-section makes the protection possible during quench events by keeping the temperature of the hotspot within a safe limit. The simulations also demonstrate that the use of a REBCO SQD enables the quench detection at lower temperatures.
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All authors Hajar Zgour, Walid Abdel Maksoud, Bertrand Baudouy, Antoine Guinet

Plasma Physics

A proof-of-concept for automated AI-driven stellarator coil optimization with in-the-loop finite-element calculations

Alan A. Kaptanoglu and Pedro F. Gil

Finding feasible coils for stellarator fusion devices is a critical challenge of realizing this concept for future power plants. Years of research work can be put into the design of even a single reactor-scale stellarator design. To rapidly speed up and automate the workflow of designing stellarator coils, we have designed an end-to-end “runner” for performing stellarator coil optimization. The entirety of pre and post-processing steps have been automated; the user specifies only a few basic input parameters, and final coil solutions are updated on an open-source leaderboard. Two policies are available for performing non-stop automated coil optimizations through a genetic algorithm or a context-aware LLM. Lastly, we construct a novel in-the-loop optimization of Von Mises stresses in the coils, opening up important future capabilities for in-the-loop finite-element calculations.
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Biological Physics · Cross-listed from cond-mat.stat-mech

A Formal Physical Framework for the Origin of Life: Dissipation-Driven Selection of Evolving Replicators

Shlomo Segal

The emergence of life from inanimate matter presents a thermodynamic challenge: the Second Law of Thermodynamics dictates a global trend towards disorder, yet life constitutes localized pockets of profound organization. This paper presents a formal physical framework for abiogenesis grounded in the statistical physics of non-equilibrium systems. We transition from the established connection between dissipation and process probability (e.g., Crooks Fluctuation Theorem) to a large-deviation framework for the likelihood of system histories. This formalism reveals a probabilistic bias towards histories with greater integrated dissipation. We then demonstrate how this bias leads to the selection of heredity. The core of our argument is a rigorous mathematical proposition showing that while simple autocatalysis leads to an exponential increase in dissipation, template-directed replication, via its capacity for mutation and adaptation (a process from which we derive an effective adaptation rate, alpha), unlocks a super-exponential growth pathway. This translates to a doubly-exponential amplification in the relative probability of its emergence over time, constituting an asymptotically dominant physical bias for its selection. This framework delineates a hierarchical transition from simple dissipative structures to information-bearing replicators, whose stability is contingent upon exceeding critical thresholds of fidelity, kinetic efficiency, and resource supply. We conclude by proposing a refined, quantitative, and falsifiable experiment, defining a precise mathematical signature for identifying the onset of evolutionary processes in synthetic chemical systems.
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Optics

Multi-Plane Spatially Resolved Phase Structuring Using Optical Communication Modes

Vinicius S. de Angelis, Maximilian Jeindl, Leonardo A. Ambrosio et al. (+3 more)

We present a deterministic framework for three-dimensional beam shaping that enables versatile control of intensity and phase, pixel-by-pixel, across multiple axial planes. Conventional multi-plane holographic techniques typically rely on iterative optimization and mitigate inter-plane crosstalk through phase randomization, introducing speckle noise and thereby limiting deterministic phase control. Here, target fields are synthesized as a linear superposition of free-space communication modes obtained from the singular value decomposition of a coupling operator connecting a source plane to multiple target planes. Because these modes form orthogonal and energy-efficient transmission channels between the source and receiving spaces, their superposition yields volumetric wavefields with enforced phase coherence and reduced inter-plane crosstalk, without iterative refinement. We experimentally demonstrate high-fidelity reconstruction of intensity and phase profiles across multiple planes using a single phase-only spatial light modulator, including arbitrary structured phase singularity patterns. The proposed approach establishes communication-mode optics as a practical and physically grounded framework for multi-plane beam shaping, particularly in applications where phase structure and coherence across depth are essential.
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All authors Vinicius S. de Angelis, Maximilian Jeindl, Leonardo A. Ambrosio, David A. B. Miller, Federico Capasso, Ahmed H. Dorrah

General Physics

Informational corrections to the early-Universe radiation sector: CET Omega, WIMP freeze-out, and implications for a possible 20 GeV gamma-ray excess

Christian Balfagon

Recent analyses of Fermi-LAT data have identified a nearly spherical, halo-like excess of gamma rays peaking at E_gamma ~ 20 GeV. If interpreted as dark matter annihilation, the excess directly probes the thermal freeze-out epoch and therefore any non-standard corrections to the early-Universe expansion rate. In this work we examine the implications of this tentative signal for CET Omega, an informational and modular extension of relativistic quantum field theory and cosmology. CET Omega predicts a universal state-dependent modification to the radiation energy density of the early Universe, characterized by a doubly logarithmic correction originating from renormalized modular fluctuations in the spectral triple of the theory. The correction is negligible during Big Bang nucleosynthesis and recombination but becomes relevant during thermal WIMP freeze-out. We derive the correction from the modular two-point function, justify the onset scale associated with the informational sector, and compute its quantitative impact on freeze-out through numerical solutions. We also analyze the evolution of the informational field Phi_Omega(x) and show that it freezes in before the freeze-out epoch and survives to the present time under gravitational advection. The resulting modification induces percent-level shifts in the relic abundance and sub-percent morphological corrections to the annihilation gamma-ray flux. We compare the scenario with Early Dark Energy, kination, and varying N_eff models, and show that the parameter range 10^{-4} < alpha_log < 10^{-2} remains consistent with Planck, BBN, and BAO constraints while predicting potentially observable deviations in the gamma-ray morphology accessible to next-generation MeV-GeV missions.
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Atmospheric and Oceanic Physics

Physically Motivated Knowledge Distillation for Blind Geometric Correction of Side-Scan Sonar Imagery

Can Lei, Hayat Rajani, Valerio Franchi et al. (+4 more)

Side-scan sonar (SSS) imagery is susceptible to geometric distortions caused by platform motion instability, which degrade geometric consistency and limit downstream analyses such as mosaicking and perception. Conventional correction methods typically rely on navigation and attitude measurements, which are often unreliable in real ocean conditions. This unreliability necessitates blind geometric correction from a single distorted image, a highly ill-posed problem. To address this issue, we propose a physically motivated knowledge distillation framework for blind geometric correction of SSS imagery. Specifically, a teacher network is trained using paired distorted and geocoded reference images to learn distortion-related geometric differences, and this knowledge is transferred to a student network that performs correction using only a single distorted image during blind inference. To ensure physically plausible deformation estimation, we design a parametric decoder that represents distortions as row-wise affine transformations consistent with the SSS line-scanning imaging mechanism. To compensate for the absence of reference information during blind inference, a hallucination context module is introduced to approximate the teachers geometric reasoning from distorted features under a multi-level distillation scheme. In addition, a differentiable forward warping strategy is adopted to handle the non-bijective deformation characteristics of SSS imagery in an end-to-end manner. Extensive experiments on multiple datasets show that the proposed method outperforms state-of-the-art baselines and generalizes well across different platforms and acquisition conditions.
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All authors Can Lei, Hayat Rajani, Valerio Franchi, Rafael Garcia, Nuno Gracias, Huigang Wang, Wei Qiang

Optics

Velocity-tunable exciton-photon hybridization in cathodoluminescence

Sven Ebel, Martin Nørgaard, Christian Nicolaisen Hansen et al. (+2 more)

Exciton-photon hybridization is typically realised in geometrically defined optical cavities, where tunability is achieved by modifying either the cavity or the excitonic medium. Here we investigate transition-radiation interferences in suspended subwavelength films resembling a free-electron-defined resonance and explore their interaction with excitons in transition metal dichalcogenides. We demonstrate that these resonances hybridize with excitonic transitions and can be tuned continuously by varying the electron energy. The resulting detuning depends on both film thickness and electron velocity, establishing the latter as an external and continuous knob for exciton-photon coupling. This approach enables tunable hybridization without structural modification and provides a free-electron-driven nanoscale platform for studying exciton-light interactions.
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All authors Sven Ebel, Martin Nørgaard, Christian Nicolaisen Hansen, N. Asger Mortensen, Sergii Morozov

Biological Physics · Cross-listed from cond-mat.soft

A mechanical bifurcation constrains the evolution of cell sheet folding in the family Volvocaceae

Valens Tribet and Pierre A. Haas

The processes of morphogenesis that give rise to the shapes of organs and organisms during development are often driven by mechanical instabilities. Can such mechanical bifurcations also drive or constrain the evolution of these processes in the first place? We discover an instance of these constraints in the green algae of the family Volvocaceae. During their development, their bowl-shaped embryonic cell sheet turns itself inside out. This inversion is driven by a simple wave of cell wedging in the genus Pleodorina (16-128 cells) and more complex programmes of cell shape changes in Volvox (~400-50000 cells). However, no species with intermediate cell numbers (256 cells) have been described. Here, we relate this gap to a mechanical bifurcation: Focusing on the inversion of Pleodorina californica (64 cells), we develop a continuum model, in which the cell shape changes driving inversion appear as changes of the intrinsic curvature of an elastic surface. A mechanical bifurcation in this model predicts that inversion is only possible in a subset of its parameter space. Strikingly, parameters estimated for P. californica fall into this possible subset, but those that we extrapolate to 256 or more cells using allometric observations and a model of cell cleavage in Volvocaceae do not. Our work thus suggests that the more complex inversion strategies of Volvox are an evolutionary necessity to obviate this bifurcation and indicates more broadly how mechanical bifurcations can drive the evolution of morphogenesis.
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Biological Physics · Cross-listed from cond-mat.soft

Cracking donuts and sorting lipids: Geometry controls archaeal membrane stability and lipid organization

Felix Frey, Miguel Amaral and An{\dj}ela Šarić

Cells are defined by lipid membranes that differ in their structure across the tree of life. While the membranes of most bacteria and eukaryotes consist of single-headed bilayer lipids, the membranes of archaea are composed of mixtures of single-headed bilayer lipids and double-headed bolalipids. Archaeal bolalipids can adopt straight or u-shaped conformations, enabling them - together with bilayer lipids - to control whether membranes form bilayer or monolayer structures. Yet, the physical principles governing archaeal membranes remain largely unexplored, especially how membrane structure couples to externally imposed curvature during membrane remodeling. Here, we perform coarse-grained molecular dynamics simulations of toroidal vesicles to systematically probe the effects of all relevant combinations of mean and Gaussian curvatures on shape stability and lipid organization. We find that soft bilayer membranes can sustain all curvatures induced, whereas rigid bolalipid monolayer membranes either transition to different vesicle shapes or rupture. Bilayer-mimicking u-shaped bolalipids and bilayer lipids are spatially accumulated in regions of high mean membrane curvature independent of Gaussian curvature. Our work identifies curvature-composition coupling as a physical signature of archaeal membrane remodeling.
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Applied Physics

An efficient finite element formulation for Newtonian noise analysis

Pieter Reumers, Xhorxha Kuci, Stijn François et al. (+1 more)

The Einstein Telescope is a third-generation underground gravitational wave observatory designed to achieve an unprecedented sensitivity down to 3 Hz. Waves propagating in the soil due to anthropogenic or natural vibration sources generate density fluctuations which cause gravitational attraction, resulting in motion of the mirrors of the laser interferometer known as Newtonian noise. A finite element formulation is presented, which evaluates the total Newtonian noise, as well as the bulk and surface contributions, from a seismic wave field defined on a finite element mesh, using Gaussian quadrature. Linear and quadratic tetrahedral (4-node and 10-node) and brick (8-node and 20-node) finite elements are supported. The corresponding volume and surface integrals are expressed in terms of finite element coupling matrices that depend only on the geometry and material properties. The formulation is verified for plane P- and S-waves propagating in an elastic homogeneous full space with a mirror suspended in a spherical cavity, assuming that the wavelength is much larger than the radius of the cavity, so that wave scattering can be ignored. Excellent agreement with analytical solutions is obtained. Similar good agreement is reported for the Newtonian noise on a test mass suspended at a finite distance above the free surface of a homogeneous elastic halfspace in which a Rayleigh wave propagates. The methodology has been implemented in the ANNA Newtonian Noise Analysis toolbox which runs in the MATLAB programming and numeric computing platform and is compatible with the open-source GNU Octave Scientific Programming Language; a Python version is also available. The proposed finite element framework provides a physically consistent and computationally efficient approach for computing gravitational-seismic coupling in heterogeneous media.
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All authors Pieter Reumers, Xhorxha Kuci, Stijn François, Geert Degrande

Applied Physics · Cross-listed from cond-mat.mtrl-sci

Monolithic integration of diverse crystalline thin films on diamond for near-junction thermal management

Tiancheng Zhao, Tianqi Bai, Yang He et al. (+20 more)

The pursuit of extreme miniaturization and high power in 6G RF front-ends has cast thermal dissipation as the central challenge. Here, we have demonstrated the monolithic integration of functionally distinct single-crystal thin films, including e̱ta}-Ga2O3, Si, GaN, and LiTaO3, onto a single diamond substrate using a multi-step transfer printing technique. Focusing on the critical e̱ta}-Ga2O3/diamond interface, we achieve an exceptional interfacial thermal conductance (ITC) of 149 MW m-2 K-1 through ultra-high vacuum (UHV) annealing, creating an atomically sharp interface featuring covalent bonding. Vibrational electron energy-loss spectroscopy (EELS) analysis combining with molecular dynamics (MD) simulations reveal that distinctive interfacial phonon modes at the e̱ta}-Ga2O3/diamond heterointerface dominate ultrahigh ITC. We experimentally demonstrate that by improving the ITC, the thermal resistance (Rth) of a diamond-based e̱ta}-Ga2O3 MOSFET is driven to a record-low value of 1.58 K mm W-1, underscoring the critical role of interface engineering in near-junction thermal management for diamond-integrated devices. This work demonstrates a scalable, diamond-based monolithic integration platform designed to solve the near-junction thermal challenges in high-power RF front-ends.
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All authors Tiancheng Zhao, Tianqi Bai, Yang He, Wenhui Xu, Xinxin Yu, Ruochen Shi, Zhenyu Qu, Jiaxin Liu, Rui Shen, Haodong Jiang, Yeliang Wang, Jiaxin Ding, Dongchen Sui, Shibin Zhang, Lei Zhu, Ailun Yi, Kai Huang, Min Zhou, Huarui Sun, Zhonghui Li, Peng Gao, Tiangui You, Xin Ou

Atmospheric and Oceanic Physics

A Data-Driven Regional Model for Skillful Medium-Range Typhoon Prediction

Zeyi Niu, Wei Huang, Sirong Huang et al. (+7 more)

Accurate prediction of tropical cyclones remains a major challenge for both numerical weather prediction and emerging artificial intelligence weather prediction systems. While recent global AI models have demonstrated strong skill in large-scale circulation prediction, they often struggle to represent the mesoscale structures critical for tropical cyclone intensity and precipitation. Here we develop the Hybrid Intelligent Typhoon System (HITS), a regional AI forecasting framework for medium-range typhoon prediction over the Asia-Pacific region, trained on a newly constructed 9-km high-resolution typhoon reanalysis dataset. The model combines regional autoregressive prediction with large scale dynamical constraints from the state-of-the-art ECMWF Artificial Intelligence Forecasting System (AIFS), allowing it to remain dynamically consistent with the evolving large-scale circulation while resolving mesoscale structures. HITS is further extended with a structure-aware perceptual training strategy (HITS-LPIPS) that improves the representation of convective and typhoon rainband structures. Experiments show that the hybrid framework substantially improves precipitation structure and typhoon intensity forecasts compared with both purely autoregressive regional AI models and standalone AI downscaling approaches. In particular, HITS-LPIPS reduces intensity errors by up to 47.8% relative to AIFS at a 72 hour lead time and produces a near-unbiased wind-pressure relationship for simulated typhoons. These results demonstrate that dynamically constrained regional AI systems provide a promising pathway for improving medium-range typhoon prediction.
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All authors Zeyi Niu, Wei Huang, Sirong Huang, Zhuo Wang, Mu Mu, Mengqi Yang, Xinhai Han, Haofei Sun, Zhaoyang Huo, Bo Qin

Optics

Broadband temporal localization and delocalized temporal edge states in time photonic crystals

Junkai Jiang, Hao Hu, Yang Long et al. (+4 more)

Time photonic crystals have attracted growing attention in recent years owing to their abilities to enable broadband field enhancements, e.g., free-space electromagnetic waves, dipolar emissions, free-electron radiation, etc. While the non-Hermitian nature of time photonic crystals is primarily attributed to their dependence on external temporal modulations, the constituent materials are oftentimes assumed to be Hermitian. How the material-induced non-Hermiticity interplays with the intrinsic non-Hermitian dynamics of time photonic crystals remains rarely explored. In this work, we demonstrate that the non-Hermiticity arising from the bi-anisotropic electromagnetic response of materials introduces a new mechanism to manipulate the localization of temporal bulk and edge states in time photonic crystals. To be specific, the temporal bulk states in our configurations exhibit remarkable attenuation or amplification, which is theoretically predicted by extending the generalized Brillouin zone framework to the temporal domain. Our analysis reveals that the attenuation or amplification strength, quantified by the temporal penetration depth, is directly governed by electromagnetic constitutive parameters. By appropriately tuning these parameters, we uncover new phenomena including broadband temporal localization, i.e. the collective concentration of energy towards a certain time moment, and delocalized temporal edge states.
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All authors Junkai Jiang, Hao Hu, Yang Long, Liangliang Liu, Songyan Hou, Dongjue Liu, Zhuo Li

Applied Physics · Cross-listed from cond-mat.supr-con

Probing the Meissner effect in single crystals of $\mathbf{Bi_2Sr_2Ca_2Cu_3O_{10+\delta}}$ via wide-field quantum microscopy under high pressure

Masahiro Ohkuma, Ryo Matsumoto, Shintaro Adachi et al. (+5 more)

We investigated the pressure dependence of the superconducting transition temperature ($T_{\rm c}$) in optimally doped Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ (Bi-2223) single crystals using different pressure-transmitting media. Previous high-pressure studies have reported conflicting behaviors, ranging from a resurgence of $T_{\rm c}$ of optimally doped Bi-2223 in fluid media to an insulating-like transition in solid media. However, a direct comparison of the effects of different pressure-transmitting media is lacking. Here, we employed wide-field quantum microscopy based on nitrogen-vacancy centers to probe the magnetic response under high pressure, utilizing cBN and KBr as media. We observed that a diamagnetic response near 70 K, indicative of the superconducting transition, persisted up to 23 GPa in KBr, whereas it disappeared above 11 GPa and 70 K in cBN. These results demonstrate the high sensitivity of Bi-2223 to the pressure environment and highlight the critical role of hydrostatic pressure in cuprate superconductors.
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All authors Masahiro Ohkuma, Ryo Matsumoto, Shintaro Adachi, Shinobu Onoda, Takao Watanabe, Kenji Ohta, Yoshihiko Takano, Keigo Arai

Optics · Cross-listed from nlin.PS

Propagation of Gaussian beam in strongly nonlocal nonlinear media with inhomogeneous diffraction

K L Mamatha, S Stalin and K Nithyanandan

Solitons in a strongly nonlocal nonlinear medium have attracted considerable attention in recent years due to their unique and distinctive characteristics from those observed in the local nonlinear medium. In this work, we investigate the propagation of a Gaussian beam in strongly nonlocal nonlinear media with spatially varying diffraction. Using analytical and numerical approaches, we examine the propagation dynamics and stability characteristics of the nonlocal soliton. For representative cases of diffraction profiles, our results show that diffraction tailoring strongly influences key beam properties, including amplitude, beam width, phase-front curvature, and phase-space evolution. All diffraction modulation supports the formation of diffraction-managed breather solitons, with excellent agreement between theory and simulations. Furthermore, the modulation instability (MI) studies systematically explored the stability characteristics under various diffraction landscapes. The obtained results demonstrate that by engineering diffraction in such nonlocal media, one can effectively control beam dynamics, thereby opening new possibilities for applications in nonlinear light control, beam shaping, and all-optical system design.
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Medical Physics

Hamiltonian dynamics for stochastic reconstruction in emission tomography

T. Leontiou, A. Frixou, E. Ttofi et al. (+6 more)

Objective: To develop a practical stochastic reconstruction framework for emission tomography that generates ensembles of data-compatible images and enables uncertainty quantification and assessment of forward-model adequacy. Approach: The framework combines stochastic-gradient descent initialization with Hamiltonian Monte Carlo (HMC) sampling directly in high-dimensional voxel space. Beyond point reconstruction, we introduce a spatially resolved operator-weighted diagnostic, the sampled data-visible variance, which quantifies how image fluctuations propagate through the imaging operator and thereby probes the local conditioning of the inverse problem under realistic acquisition physics. The methodology is evaluated using controlled software phantoms, experimental anthropomorphic phantom measurements, and a clinical DATSCAN SPECT acquisition. Main results: Under ideal conditions, the HMC ensemble mean provides point-estimate accuracy comparable to deterministic reconstruction methods, while the sampled ensemble provides additional physically interpretable information. The ensemble analysis helps distinguish uncertainty associated with the intrinsic ill-posedness of the inverse problem from variability linked to forward-model inadequacy. The clinical example demonstrates applicability under realistic acquisition statistics rather than diagnostic performance. Significance: The proposed stochastic reconstruction framework provides a practical ensemble-based approach for emission tomography that extends conventional point reconstruction with model-conditioned uncertainty estimates and spatially resolved diagnostics of forward-model adequacy.
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All authors T. Leontiou, A. Frixou, E. Ttofi, C. Chrysostomou, Y. Parpottas, K. Michael, S. Frangos, E. Stiliaris, C. N. Papanicolas

Fluid Dynamics

Consistent closure modeling in large eddy simulations by direct approximation of the filtered advection term

Max Hausmann and Berend van Wachem

This article addresses the widely overlooked conceptual inconsistency of the large eddy simulation (LES) framework, namely that the commonly used advection term introduces higher wave numbers in the filtered Navier-Stokes equations than consistent with the definition of a filtered equation. It is explained how this inconsistency is the reason that flux limiters, stabilization terms, or dealiasing is often required and that the LES solution is typically mesh dependent. A consistent alternative is the direct approximation of the filtered advection term, for which we derive an exact expression based on an infinite series expansion with terms of increasing order in the filter width. We show that truncating the series expansion after few terms gives an expression that is highly correlated with the filtered advection term and a suitable LES model. A posteriori studies with decaying turbulence and a turbulent shear flow are conducted that reveal that the proposed approximation of the filtered advection term predicts improved kinetic energy spectra and filtered velocity correlations compared to classical LES.
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Physics Education

Low-cost cross-correlation noise setup for measuring the Boltzmann constant and the elementary charge

Zitong Peng, Jie Zheng and Xiaokai Yue

We present a low-cost experimental setup to measure the Boltzmann constant (kB) and the elementary charge (e) through thermal and shot noise, achieving relative accuracies of up to 1%. The system utilizes a cost-effective ADC module integrated with a carefully selected low-noise audio operational amplifier, resulting in a simple and compact circuit design that better satisfies experimental requirements. Furthermore, the approach employs a dual-channel sampling method to measure cross-correlation noise, thereby significantly reducing the uncorrelated background noise of the device and improving the signal-to-noise ratio. The noise measurement methodology offers an intuitive demonstration of microscopic fluctuations, making it a valuable teaching tool. In addition, the experimental setup employs standard electronic components, is low cost and robust, making it well-suited for widespread adoption in university and even high school laboratories.
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Fluid Dynamics

A convolutional autoencoder and neural ODE surrogate modeling framework applied to transient counterflow flames

Mert Yakup Baykan, Weitao Liu, Mohammad Rafi Malik et al. (+4 more)

A novel convolutional autoencoder and neural ODE (CAE-NODE) framework is proposed for a reduced-order model (ROM) applied to transient 2D counterflow flames, as an extension of AE-NODE methods in homogeneous reactive systems to spatially resolved flows. The multidimensional thermochemical fields (256 x 256 grid, 21 variables) obtained from direct numerical simulations (DNS) are used in training the CAE, where convolutional layers learned the underlying spatial correlations, allowing the CAE to construct an unsupervised 3D latent manifold that is physically meaningful, smooth, and continuous in time. This results in a compression ratio of over 400,000 times. The NODE then subsequently learns the continuous-time dynamics on the latent manifold, enabling the prediction of the full temporal evolution of the flames by integrating forward in time from an initial condition. The results demonstrate that the CAE-NODE can accurately capture the entire transient process, including ignition, flame propagation, and the gradual transition to a non-premixed condition, with excellent agreement with the DNS, while adhering to conservation principles at virtually no computational cost compared to the reference DNS. Predictions remain accurate at strain rates outside the training range. Moreover, despite being unsupervised, the learned latent manifold is highly correlated with the flame-state descriptors such as the progress variable, mixture fraction, and the scalar dissipation rate. This study, for the first time, highlights the potential of CAE-NODE for surrogate modeling of unsteady dynamics of multi-dimensional reacting flows.
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All authors Mert Yakup Baykan, Weitao Liu, Mohammad Rafi Malik, Thorsten Zirwes, Andreas Kronenburg, Hong G. Im, Dong-hyuk Shin

Computational Physics · Cross-listed from cond-mat.mtrl-sci

Loss of altermagnetic order and smooth restoration of Kramers' spin degeneracy with increasing temperature in CrSb and MnTe

Christopher D. Woodgate, Nabil Menai, Arthur Ernst et al. (+1 more)

We describe how thermally induced spin fluctuations modify the electronic structures of two prototypical altermagnets, CrSb and MnTe, via application of the disordered local moment picture. For both materials, our self-consistent, ab initio calculations demonstrate that local magnetic moments persist on Cr and Mn atoms in their paramagnetic states, necessitating a spin-polarised description of the electronic structure even above the Néel temperature, $T_\mathrm{N}$. Moreover, Kramers' spin degeneracy, which is broken for both materials in their altermagnetic ground states, is shown to be smoothly restored - on the average - as the local moments thermally disorder. In metallic CrSb, this occurs at temperatures well below $T_\mathrm{N}$ and the signature effects of its altermagnetism are lost as the magnetic disorder induces heavy smearing of strongly dispersive electronic states around the Fermi energy. By contrast, in semiconducting MnTe, with its band gap largely unaffected by magnetic disorder, the spin degeneracy only returns at temperatures close to and above $T_\mathrm{N}$. We quantify the temperature dependence of the altermagnetic order parameter and the underlying electronic structures of both materials, with implications for their spin transport and spectroscopic properties.
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All authors Christopher D. Woodgate, Nabil Menai, Arthur Ernst, Julie B. Staunton

Atomic Physics · Cross-listed from cond-mat.other

Measuring impurity-induced shifts in Coulomb crystallization

Mingyao Xu, Aaron A. Smith, Leonid Prokhorov et al. (+2 more)

We report a laboratory measurement of how impurities shift Coulomb crystallization in a strongly interacting ionic system. This is achieved by using laser cooled Ca$^+$ crystals doped with a controlled number of Xe$^{12+}$ highly charged ions. We find that the crystallization threshold is unchanged at low impurity concentration, but shows a clear crossover once the impurity content becomes sufficiently large, after which the shift grows approximately linearly. Complementary measurements reveal that this global effect originates from a local pinning of the crystal around the impurities. We further show how the measured shift could impact standard models of crystallization in white dwarfs and neutron stars. Our results provide an experimental route to incorporating impurity effects into models of multicomponent Coulomb matter, relevant to stellar crystallization and strongly coupled plasmas.
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All authors Mingyao Xu, Aaron A. Smith, Leonid Prokhorov, Vera Guarrera, Giovanni Barontini

Instrumentation and Detectors

Decay-Resolved Charge Changes from Radioactive Decays in Levitated Microparticles

Jiaxiang Wang, T. W. Penny, Yu-Han Tseng et al. (+2 more)

We measure event-by-event discrete changes in the net electric charge of an optically levitated silica microsphere arising from individual radioactive decays within the sphere, in coincidence with energy depositions in a nearby scintillation detector. The net charge of the levitated sphere is continuously monitored by measuring its driven response to an oscillating electric field, allowing individual charge-change events to be resolved on millisecond timescales with precision below an elementary charge. Simultaneously, $\alpha$ and $\beta$ particles emitted during decays of implanted $^{212}$Pb and its daughters are detected using a scintillator read out with an array of silicon photomultipliers. By correlating reconstructed charge-change times with the scintillator response, we can directly attribute abrupt changes in the sphere's net charge to individual nuclear decays, and identify differences in the distribution of charges ejected for $\alpha$ and $\beta$ decays. These results establish a new approach for studying low energy charged particles emitted by radioactive decays at the single-decay level, and identify showers of radiogenically produced low-energy electrons emitted by $\alpha$-decaying radon daughters implanted near solid surfaces.
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All authors Jiaxiang Wang, T. W. Penny, Yu-Han Tseng, Benjamin Siegel, David C. Moore

Geophysics

Real-time probabilistic tsunami forecasting in Cascadia from sparse offshore pressure observations

Stefan Henneking, Fabian Kutschera, Sreeram Venkat et al. (+2 more)

Near-field tsunami early warning in the Cascadia Subduction Zone is limited by sparse offshore observations. We investigate whether a hypothetical network of 175 ocean-bottom pressure sensors can support real-time Bayesian inference of the full spatiotemporal seafloor velocity field and probabilistic tsunami forecasting for a margin-wide and a partial fully-coupled Cascadia earthquake dynamic rupture-tsunami scenario. The simulated oceanic acoustic, Rayleigh, and tsunami wavefields are similar during the first two minutes after nucleation but diverge thereafter, enabling rapid earthquake scenario discrimination. Using an acoustic-gravity inversion with assimilation of pressure data, tsunami wave height forecasts are obtained in less than a second. We leverage a Bayesian inversion-based framework that splits the computations into an offline precomputation phase performed with large-scale computing facilities, and an online phase that computes forecasts and can be executed on a laptop. Forecast errors remain low at 22.1% for the margin-wide and 19.6% for the partial rupture.
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All authors Stefan Henneking, Fabian Kutschera, Sreeram Venkat, Alice-Agnes Gabriel, Omar Ghattas

Fluid Dynamics

Linear Kelvin Wave Predictions in the $z\to 0$ Limit

Gabriel D Weymouth

Linear wave theory captures the essential physics of free-surface flows at a fraction of the computational cost of nonlinear and viscous methods, making it attractive for design, real-time control, and surrogate modeling applications. However, the Kelvin Green's function for a translating point-source generates unbounded wave energy in the $z\to 0$ limit, causing both numerical difficulties and physical inconsistencies. This paper develops a modified kernel for the Kelvin potential incorporating an elliptic spanwise line integration that naturally resolves this ill-posedness, yielding finite wave energy over the entire free surface. We then present a fast evaluator for both point and line kernels using contour deformation adapted to the non-analytic Kelvin phase, achieving $10^4$-$10^5$ speedup over direct quadrature while preserving the wake asymptotics. Predictions on the most challenging $z=0$ limit demonstrate physically consistent wave patterns and wave resistance trends. An open-source Julia implementation is provided.
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Optics

Inverse Design Validated Optimization of Lead-Free Cs$_3$Cu$_2$Cl$_5$ Visible-Light Microring Resonators Using a Coupled DFT-FDTD Framework

Shoumik Debnath and Sudipta Saha

Microring resonators are indispensable for wavelength filtering, sensing, and on-chip signal routing in photonic integrated circuits, yet visible-wavelength implementations using environmentally benign materials remain scarce. We report a numerical design study of add-drop MRRs employing cesium copper chloride (Cs$_3$Cu$_2$Cl$_5$), a lead-free all-inorganic halide with favorable visible-band optical properties. Wavelength-resolved refractive index ($n$) and extinction coefficient ($k$) of Cs$_3$Cu$_2$Cl$_5$, computed via density functional theory (DFT), serve as direct input to finite-difference time-domain (FDTD) modeling: 2.5D variational FDTD (varFDTD) for the parametric sweeps, and full three-dimensional FDTD for validation of the selected geometry. Independent parametric scans cover ring waveguide width (500–900~nm), coupling gap (150–300~nm), and bend radius (5–20~$\mu$m). At the balanced operating point of 600~nm ring width, 200~nm gap, and 10~$\mu$m radius, we obtain a loaded quality factor ($Q$) of ${\sim}5{,}386$, a free spectral range (FSR) of 11.3~nm, a drop-port extinction ratio (ER) of 32.2~dB, and a finesse of 95.8. The gap sweep traces the full trajectory from over-coupled through critically coupled to under-coupled operation, with the critical point near 200~nm. A sharp bending-loss cliff emerges between 5 and 10~$\mu$m, below which all figures of merit collapse. These sweeps yield a systematic geometry–performance map for Cs$_3$Cu$_2$Cl$_5$-based MRRs, the first reported for this compound to our knowledge. Cross-platform validation in Tidy3D reproduces the spectral fingerprint of the optimized device, and inverse design of the bus coupling region delivers a 3% gain in drop-port power transfer, indicating that the sweep-derived geometry sits close to the coupling optimum.
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Instrumentation and Detectors

The Super Fine-Grained Detector for the T2K neutrino oscillation experiment

S. Abe, H. Alarakia-Charles, I. Alekseev et al. (+169 more)

The magnetised near detector ND280 of the long-baseline neutrino experiment T2K has been upgraded to improve its detection performance and, consequently, enhance our understanding of neutrino-nucleus interactions, reducing the systematic uncertainties in measurements of the neutrino oscillation parameters. A key component of the upgrade is a novel segmented plastic scintillator detector, called the Super Fine-Grained Detector (SuperFGD), made of approximately 2 million optically isolated 1 cm$^3$ cubes read out by three orthogonal wavelength-shifting (WLS) fibres. Scintillation photons are detected by 55,888 Hamamatsu Multi-Pixel Photon Counters (MPPCs). The SuperFGD provides 3D images of neutrino interactions by tracking the final-state charged particles produced isotropically, including protons down to a threshold of around 330 MeV/$c$. The high light yield of SuperFGD greatly improves particle identification and the sub-nanosecond time resolution provides an excellent identification of Michel electrons. The SuperFGD is also able to detect neutrons from neutrino interactions and, for the first time in a neutrino experiment, to reconstruct their kinetic energy using a fine detector segmentation and by measuring the time-of-flight with sub-nanosecond precision. In this article the details of the detector design, construction and performance are described. The detector was installed in ND280 and successfully commissioned with cosmic data in 2023 and, later, with the T2K neutrino beam. The detector response has been characterised with the 2023 and 2024 data and the results are reported in this article.
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All authors S. Abe, H. Alarakia-Charles, I. Alekseev, T. Arai, T. Arihara, S. Arimoto, A. M. Artikov, Y. Awataguchi, N. Babu, V. Baranov, G. Barr, D. Barrow, L. Bartoszek, A. Beliakova, L. Bernardi, L. Berns, S. Bhattacharjee, A. V. Boikov, A. Blondel, A. Bonnemaison, F. Cadoux, S. Cap, A. Cauchois, J. Chakrani, P.S. Chong, A. Chvirova, M. Danilov, C. Davis, V. Davouloury, Yu. I. Davydov, A. Dergacheva, C. Domangue, D. Douqa, T. A. Doyle, O. Drapier, A. Eguchi, J. Elias, G. Erofeev, Y. Favre, D. Fedorova, S. Fedotov, D. Ferlewicz, Y. Fujii, R. Fujita, Y. Furui, F. Gastaldi, A. Gendotti, A. Germer, L. Giannessi, C. Giganti, V. Glagolev, R. Guillaumat, I. Heitkamp, J. Hu, C. Husi, A. K. Ichikawa, T. H. Ishida, A. Izmaylov, K. Iwamoto, M. Jakkapu, C. Jesús-Valls, J. Y. Ji, J. Juneau, C. K. Jung, H. Kakuno, M. Kawaue, P. T. Keener, M. Khabibullin, N. V. Khomutov, A. Khotjantsev, T. Kikawa, H. Kikutani, N. V. Kirichkov, H. Kobayashi, T. Kobayashi, L. Koch, S. Kodama, A. O. Kolesnikov, M. Kolupanova, T. Koto, Y. Kudenko, S. Kuribayashi, T. Kutter, M. Lachat, K. Lachner, M. Lamers James, D. Last, N. Latham, D. Leon Silverio, B. Li, W. Li, C. Lin, M. Louzir, T. Lux, K. K. Mahtani, S. Manly, D. A. Martinez Caicedo, N. Mashin, T. Matsubara, C. Mauger, K. S. McFarland, C. McGrew, J. McKean, A. Mefodiev, E. Miller, O. Mineev, A. Minamino, A. L. Moreno, A. Muñoz, T. Nakadaira, K. Nakagiri, T. Nakaya, J. Nanni, L. Nicolas, V. Nguyen, E. Noah Messomo, T. Nosek, H. M. O'Keeffe, T. Ogawa, W. Okinaga, L. Osu, V. Paolone, G. Pelleriti, L. Pickering, M. A. Ramírez, M. Reh, G. Reina, C. Riccio, A. Rubbia, F. Saadi, K. Sakashita, N. Sallin, F. Sanchez, T. Schefke, C. Schloesser, D. Sgalaberna, A. Shaikovskiy, N. Shvarev, A. Shvartsman, Y. Shiraishi, N. Skrobova, A. Speers, M. Smy, D. Svirida, S. Tairafune, M. Tani, H. Tanigawa, A. Teklu, S. Tereshchenko, V. V. Tereshchenko, T. Tsushima, M. Tzanov, R. Van Berg, I. I. Vasilyev, T. Vladisavljevic, D. Wakabayashi, H. Wallace, A. Weber, N. Whitney, C. Wret, Y. Xu, Y. Yang, N. Yershov, A. J. P. Yrey, M. Yokoyama, Y. Yoshimoto, X. Y. Zhao, H. Zheng, H. Zhong, T. Zhu, E. D. Zimmerman, M. Zito

Instrumentation and Detectors

A modular datalogger and slow-control platform for physics experiments with time-series telemetry and web dashboards

D. Tagnani, N. Toniolo, B. Gongora Servin et al. (+2 more)

We present a NIM 2U slow-control system designed for continuous monitoring of environmental and facility parameters during data taking in nuclear-physics experiments. The architecture integrates a base controller board with eight channels for PT100/PT1000 probes and up to three plug-in extension boards, each providing SMA connections on the front panel. All boards adopt a 16-bit SAR ADC (AD7689) with an external 2.5 V reference, yielding an LSB of 38.15 microV and ensuring metrological uniformity across heterogeneous channel types. The operating range for PT100/PT1000 probes spans -200 degrees C to 300 degrees C, with a design accuracy at the 1% level. The system includes modules dedicated to standard industrial signals 4-20 mA and 0-10 V (manual per-channel selection) and a module for current measurement in the 10 nA-150 microA range with automatic gain-range selection. The software chain publishes time series to Graphite and provides visualization through Grafana over Ethernet. Representative performance measurements are reported for the RTD and Current Reader chains, including long-term stability tests with reference elements and calibration measurements over the operating range. A complete metrological characterization of all industrial input configurations remains part of future work.
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All authors D. Tagnani, N. Toniolo, B. Gongora Servin, T. Marchi, A. Goasduff