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Physics Physics

physics Watch Physics

Tuesday 10 February

Instrumentation and Detectors

Conceptual Design of a Novel Highly Granular Crystal Electromagnetic Calorimeter for Future Higgs Factories

Baohua Qi, Fangyi Guo, Shu Li et al. (+9 more)

Next-generation high-energy electron-positron colliders, operating as Higgs factories, require an unprecedented jet energy resolution for precision measurements of Higgs and Z/W bosons. To address this challenge, a conceptual design is presented for a novel high-granularity crystal electromagnetic calorimeter that combines the superior intrinsic energy resolution of a homogeneous calorimeter with the fine segmentation required for particle-flow reconstruction. The crystal electromagnetic calorimeter design is based on orthogonally arranged long scintillating crystal bars read out by silicon photomultipliers (SiPMs) at both ends. Key design specifications were established through comprehensive simulation studies. Critical technical considerations, including crystal choices, photosensors, electronics, mechanical support, and radiation damage, are discussed. A dedicated digitisation framework was developed to realistically model effects from the crystal, SiPMs, and readout electronics. The performance of a single calorimeter module was evaluated using simulated electron showers. Simulation results for a single module demonstrate an excellent electromagnetic energy resolution of $1.12\%/\sqrt{E(\mathrm{GeV})}\oplus0.22\%$ and an energy linearity within $\pm0.5\%$ for electrons from 3 GeV to 100 GeV. The performance significantly exceeds the design requirement of $\leq 3\%/\sqrt{E(\mathrm{GeV})}\oplus1\%$. The results establish the feasibility of the proposed high-granularity crystal calorimeter concept and point to a promising pathway toward the precision calorimetry required for future high-energy electron-positron collider experiments.
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All authors Baohua Qi, Fangyi Guo, Shu Li, Yong Liu, Manqi Ruan, Weizheng Song, Shengsen Sun, Yifang Wang, Yuexin Wang, Haijun Yang, Yang Zhang, Zhiyu Zhao

Plasma Physics

Scaling laws for the cutoff wavenumber of the short-wavelength ion-temperature-gradient mode in a Z-pinch

O. Gupta, M. Barnes, F. I. Parra et al. (+4 more)

We use a heuristic fluid model to predict the dependence of the cutoff wave number for the short-wavelength ion temperature gradient (SWITG) mode on ion density gradient, ion temperature gradient (ITG) and ion-electron temperature ratio. In particular, we predict that the cutoff wave number increases linearly with increasing ITG for sufficiently large values of the ITG. Direct numerical solutions of the gyrokinetic dispersion relation using a purpose-built solver confirm the predicted scalings at large ITG values and find a weaker power-law scaling for intermediate ITG values. Combining these wave number scalings with a simple diffusive estimate for turbulent fluxes produces a scaling prediction for the ITG heat flux in SWITG-driven turbulence. Applying the critical balance conjecture additionally provides scalings for the aspect ratio of the SWITG turbulent eddies.
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All authors O. Gupta, M. Barnes, F. I. Parra, L. Podavini, A. Zocco, T. Adkins, P. G. Ivanov

Optics

Instantaneous modes in dispersive laser cavities

Kristian Seegert, Yi Yu, Mikkel Heuck et al. (+1 more)

We develop a unified instantaneous-mode description for lasers with dispersive cavities, exploiting the separation of timescales between fast cavity fields and slow carrier dynamics. The resulting reduced rate equations retain the essential effects of frequency-dependent mirrors through a dynamic modal gain and an effective confinement factor determined directly by the mirror reflectivity. Applied to a Fano laser, the reduced description captures the essential dynamics, closely reproduces the full-model behavior and clarifies the physical origin of dispersive instabilities. More generally, the approach provides a transparent framework for deriving reduced models and simplifying the stability analysis of dispersive laser cavities.
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All authors Kristian Seegert, Yi Yu, Mikkel Heuck, Jesper Mørk

Physics and Society

Symmetric preferences, asymmetric outcomes: Tipping dynamics in an open-city segregation model

Fabio van Dissel, Tuan Minh Pham and Wout Merbis

Schelling's model of segregation demonstrates that even in the absence of social or governmental interventions, individuals with mild in-group preferences can self-organize into strongly segregated neighborhoods. Many variants of this celebrated model have been proposed by assuming agents tend to increase their satisfaction. Complementary to this traditional, utility-based approach, we model residential moves using satisfaction-independent reaction rates in a spatially extended chemical reaction network. The resulting model exhibits an emergent phenomenon: despite symmetric in-group preferences, the system undergoes a tipping transition at a critical preference level, beyond which one agent type dominates. We characterize this asymmetric phase transition in details using mean-field analysis, numerical simulations and finite size scaling methods. We find that while the transition shares key features with the Ising universality class, such as $\mathbb{Z}_2$ symmetry breaking and similar exponent ratios, the full set of critical exponents does not match any known universality class.
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Geophysics

Variability in Performance of a Machine-Learning Seismicity Catalog: Central Italy, 2016-2017

Jaehong Chung, Yifan Yu, Lauro Chiaraluce et al. (+2 more)

Machine learning (ML) catalogs contain many more earthquakes than routine catalogs, but their performance in phase picking and earthquake detection has not been fully evaluated. We develop station-level detection probabilities using logistic regression and combine them across a seismic network to compute spatial magnitude-of-completeness fields. We apply this approach to two catalogs from the 2016-2017 Central Italy sequence that were constructed from the same seismic network, one routine and one ML based. At the station level, the ML picker increases detection sensitivity by identifying smaller magnitude events and detecting earthquakes at greater distances. Spatially, the magnitude-of-completeness decreases substantially, with median values shifting from 1.6 to 0.5 for P waves and from 1.7 to 0.5 for S waves. However, the ML catalog also shows greater variability in station-level performance than the routine catalog. These results demonstrate that ML-based improvements in detectability are widespread but spatially non-uniform, highlighting their benefits, their limitations, and the potential for further improvements.
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All authors Jaehong Chung, Yifan Yu, Lauro Chiaraluce, Maddalena Michele, Gregory C. Beroza

Chemical Physics

Multilevel DFT Response Theory

Alberto Barlini, Julien Bloino, Henrik Koch et al. (+1 more)

We present a general computational protocol for the evaluation of extensive molecular response properties in complex environments within a polarizable quantum embedding framework. The approach extends multilevel density functional theory (MLDFT) to response theory by formulating the coupled-perturbed Kohn-Sham (CPKS) equations for the MLDFT Hamiltonian. The method is further coupled to an additional polarizable molecular mechanics layer based on the fluctuating-charge (FQ) force field, which allows an accurate yet computationally efficient description of long-range interactions. We apply this new protocol to compute static and frequency-dependent linear polarizabilities and first hyperpolarizabilities of para-nitroaniline (PNA) in 1,4-dioxane and 3-hydroxybenzoic acid (HBA) in aqueous solution. The framework enables physicochemical insight into solute-solvent interactions by disentangling the competing roles of electrostatics, mutual polarization, and quantum confinement (Pauli repulsion). The results match available experiments, demonstrating the reliability and robustness of the proposed approach and providing a viable route for response properties within quantum embedding methods.
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All authors Alberto Barlini, Julien Bloino, Henrik Koch, Tommaso Giovannini

Applied Physics · Cross-listed from eess.IV

Intensity-based Segmentation of Tissue Images Using a U-Net with a Pretrained ResNet-34 Encoder: Application to Mueller Microscopy

Sooyong Chae, Dani Giammattei, Ajmal Ajmal et al. (+6 more)

Manual annotation of the images of thin tissue sections remains a time-consuming step in Mueller microscopy and limits its scalability. We present a novel automated approach using only the total intensity M11 element of the Mueller matrix as an input to a U-Net architecture with a pretrained ResNet-34 encoder. The network was trained to distinguish four classes in the images of murine uterine cervix sections: background, internal os, cervical tissue, and vaginal wall. With only 70 cervical tissue sections, the model achieved 89.71% pixel accuracy and 80.96% mean tissue Dice coefficient on the held-out test dataset. Transfer learning from ImageNet enables accurate segmentation despite limited size of training dataset typical of specialized biomedical imaging. This intensity-based framework requires minimal preprocessing and is readily extensible to other imaging modalities and tissue types, with publicly available graphical annotation tools for practical deployment.
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All authors Sooyong Chae, Dani Giammattei, Ajmal Ajmal, Junzhu Pei, Amanda Sanchez, Tananant Boonya-ananta, Andres Rodriguez, Tatiana Novikova, Jessica Ramella-Roman

Applied Physics

A large scale multi-modal workflow for battery characterization: from concept to implementation

François Cadiou, Cinthya Herrera, Duncan Atkins et al. (+32 more)

The development of material acceleration platforms in battery research requires integrating complementary techniques and correlating heterogeneous experimental datasets. Here, this challenge is tackled in a large-scale multimodal program involving fifteen laboratories and facilities across Europe. Coordinated multi-site experiments are performed on state-of-the-art graphite / LiNiO2 Li-ion full cells to address two archetypal scientific questions: is the electrolyte composition impacting electrode properties, and how do electrode materials evolve when cells are cycled to their end-of-life? A fully standardized and centralized workflow is demonstrated, from sample production and delivery, to metadata and data handling, generating seventy-five concatenated datasets shared among all partners. Their integrated analysis shows that scientific conclusions depend critically on both the observable chosen to describe electrode properties, and the measurement technique employed. Individual experiments provide detailed information into specific aspects, such as crystal structures, redox activity, surface processes, morphology, etc., but can also function as binary diagnostic tool. Two-dimensional observable-technique patterns are introduced, in which each pixel encodes a yes, no or uncertain answer to a given scientific question. These patterns serve as multi-property metaviews, e.g. visual genotypes, enabling to classify material behavior and technique suitability according to predefined user demand and criteria, highlighting the interdependencies between measurement choices, extracted parameters and scientific interpretation. This multimodal workflow establishes a proof-of-concept for correlative analysis and underscores challenges toward fully integrated, automated and holistic approaches in energy material science.
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All authors François Cadiou, Cinthya Herrera, Duncan Atkins, Elixabete Ayerbe, Giorgio Baraldi, Stéphanie Belin, Anass Benayad, Didier Blanchard, Federico Capone, Ennio Capria, Isidora Cekic Laskovic, Robert Dominko, Kristina Edström, Ajay Gautam, Lukas Helfen, Antonella Iadecola, Quentin Jacquet, Gregor Kapun, Xinyu Li, Aleksandar Matic, Nataliia Mozhzhukhina, Andrew J Naylor, Poul Norby, Chris O Keefe, Alexandre Ponrouch, Jean Pascal Rueff, Elena Tchernykova, Deyana Tchitchekova, Israel Temprano, Nikita Vostrov, Marnix Wagemaker, Martin Winter, Christian Wölke, Tejs Vegge, Sandrine Lyonnard

Instrumentation and Detectors

A 4D-STEM Tomographic Framework Assisted by Object Tracking for Nanoparticle Structure Determination

Saleh Gholam, Arno Annys, Irina Skvortsova et al. (+6 more)

Three-dimensional electron diffraction (3D ED) has emerged as a powerful method for solving the structures of sub-micron-sized particles down to nanoparticles. However, it faces technical challenges when applied to beam-sensitive samples or agglomerated nanoparticles. This study presents a novel approach that combines 4D-STEM tomography with object tracking and segmentation algorithms to overcome these limitations and achieve single-crystalline 3D ED datasets from nanopowder samples. The method and data quality are assessed on brookite TiO2 nanorods and beam-sensitive CsPbBr3 nanoparticles. To finely sample the reciprocal-space, the data acquisition was automated to acquire hundreds of 4D-STEM scans at fine tilt steps using a slightly convergent beam (0.6 to 1 mrad). Compared to conventional 3D ED methodologies, the proposed method provides enhanced signal-to-noise ratio, low illumination time for reducing beam damage, and the ability to analyze multiple particles from a single tomographic dataset. The procedure is optimized to be feasible using commercially available desktops and detectors. This extends the method applicability to systems and samples that were very challenging for conventional 3D ED methods, by eliminating several technical challenges for the data acquisition.
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All authors Saleh Gholam, Arno Annys, Irina Skvortsova, Erica Cordero Oyonarte, Amirhossein Hajizadeh, Philippe Boullay, Johan Hofkens, Johan Verbeeck, Joke Hadermann

Fluid Dynamics

Wave Particle Turbulent Simulation of Spatially Developing Round Jets Using a Non Equilibrium Transport Model with a Mixing Length Characteristic Time Closure

Xiaojian Yang and Kun Xu

In this paper, the wave-particle turbulent simulation (WPTS), a recently developed multiscale, non-equilibrium turbulence modeling approach, is coupled with a turbulence characteristic-time closure derived from Prandtl mixing-length hypothesis and applied to spatially developing round jets. In WPTS, fluid elements in strongly turbulent regions are represented by Lagrangian particles that travel a finite distance before interacting with the background flow field represented in a wave-like (Eulerian) form. This mechanism bears conceptual similarity to the discrete fluid parcels invoked in the Prandtl mixing-length picture. WPTS differs from conventional mixing-length-based turbulence models in two key respects. First, particle evolution follows a non-equilibrium transport mechanism, rather than the equilibrium assumptions typically embedded in eddy-viscosity closures. Second, WPTS advances the wave and particle components in a coupled manner, with the particle fraction governed primarily by the modeled turbulence characteristic time, enabling laminar and turbulent regimes to be represented within a unified framework. Because spatially developing jets provide a canonical test case with well-established similarity behavior, they are used here for evaluation. Specifically, this work (1) develops a mixing-length-based characteristic-time model tailored to jet flows and (2) incorporates it into WPTS to assess predictive performance. The resulting WPTS framework accurately reproduces the jet similarity solution and other characteristic features at Reynolds numbers of 5,000 and 20,000, demonstrating the promise of WPTS as a practical tool for turbulence modeling and simulation.
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Fluid Dynamics

Comprehensive Study of 3D Liquid Flow Fields in Additive Manufactured Structures for SMART Reactors Using Large-Scale Vertical Magnetic Resonance Imaging and Computational Fluid Dynamics

Timo Merbach, Muhammad Adrian, Christoph Wigger et al. (+12 more)

Triply Periodic Minimal Surface (TPMS) structures have emerged as a new class of porous materials with variable geometries and favourable transport properties, making them promising for reactor internals in chemical engineering. However, experimental data on internal TPMS flow behaviour are still limited. To address this gap, the flow behaviour in additively manufactured TPMS structures is analysed using three-dimensional Magnetic Resonance Imaging (MRI) velocimetry in a large-bore vertical 3 T MRI system, in cylindrical columns of 38 mm diameter and Reynolds numbers between 50 and 300. Three different TPMS geometries are investigated, and consistency between Computational Fluid Dynamics (CFD) simulations and experimentally measured MRI velocity fields is established through cross-validation. The MRI system provides fully three-dimensional velocity fields with a divergence deviation below 6 %. MRI revealed distinct flow features: the Gyroid TPnS exhibited pronounced channelling, while the Schwarz-Diamond TPSf showed merge-split behaviour, achieving a 46 % increase in lateral mixing compared to the Gyroid TPnS structures. Numerical simulations reproduce the flow features and show agreement with the MRI data. The combined methodology demonstrates the suitability of MRI velocimetry for the experimental validation of CFD simulations and establishes a robust foundation for future studies of heat and mass transfer, as well as reactive flow, in structured reactor systems.
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All authors Timo Merbach, Muhammad Adrian, Christoph Wigger, Selma Iraqi Houssaini, Benedict Bayer, Artyom Tsanda, Serhan Acikgöz, Christian Weiland, Felix Kexel, Dirk Herzog, Marko Hoffmann, Ingomar Kelbassa, Tobias Knopp, Alexander Penn, Michael Schlüter

Atomic Physics

Testing Exotic Electron-Electron Interactions with the Helium Ionization-Energy Anomaly

Lei Cong, Filip Ficek, Rinat Abdullin et al. (+2 more)

Precision atomic spectroscopy provides a sensitive probe of physics beyond the Standard Model. A recently reported $9\sigma$ theory-experiment discrepancy in the ionization energy of metastable helium has motivated the hypothesis of a new boson mediating exotic electron-electron interactions. Using a model-independent sign-consistency analysis of the induced energy shifts, we show that the sign requirement alone excludes vector-vector and pseudoscalar-pseudoscalar interactions as possible explanations of the anomaly. Incorporating existing constraints together with improved limits obtained here further excludes axial-vector scenarios. Within the single-boson framework considered in this work, only a narrowly constrained scalar-mediated interaction remains viable. The remaining parameter space could be probed, for example, by modest improvements in the determination of the electron gyromagnetic ratio.
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All authors Lei Cong, Filip Ficek, Rinat Abdullin, Mikhail G. Kozlov, Dmitry Budker

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

How Geometry Tames Disorder in Lattice Fracture

Matthaios Chouzouris, Leo de Waal, Antoine Sanner et al. (+3 more)

We investigate the fracture behavior of pre-cracked triangular beam-lattices whose elements have failure stresses drawn from a Weibull distribution. Through a statistical analysis and numerical simulations, we identify and verify the existence of three distinct failure regimes: (i) disorder is effectively suppressed, (ii) disorder manifests locally near the crack tip, modifying the crack morphology, and (iii) disorder manifests globally, leading to initially diffuse failure. Our model naturally reveals the key parameters governing this behavior: the Weibull modulus, quantifying the spread in failure thresholds, and a geometric quantity termed the Slenderness Ratio. We also reproduce the disorder-induced toughening reported in previous experimental and numerical studies, further demonstrating that its manifestation depends non-monotonically on disorder. Crucially, our results indicate that this toughening cannot be simply connected to the amount of damage in the lattice, challenging interpretations that attribute increased fracture energy solely to enhanced crack tortuosity or diffuse failure. Overall, our results establish geometry as a powerful control parameter for regulating how disorder is expressed during fracture in beam-lattices, with broader implications for the disorder-induced toughening in engineered materials.
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All authors Matthaios Chouzouris, Leo de Waal, Antoine Sanner, Alessandra Lingua, David S. Kammer, Marcelo A. Dias

Optics

The mixture of glycerin with tartrazine: a solution to reversibly increase tissue transparency for in vitro quantitative phase imaging

Mikolaj Krysa, Anna Chwastowicz, Malgorzata Lenarcik et al. (+3 more)

Thick tissue sections strongly scatter and absorb light, which limits transmission-based label-free examination via quantitative phase imaging (QPI) modalities. Here we introduce a simple, room-temperature optical clearing medium - glycerol and tartrazine solution (GTS; 60 percent glycerol, 10 percent tartrazine) - that increases the transparency of 50-80 micron murine liver and kidney slices while preserving tissue morphology and enabling rapid, label-free quantitative phase imaging. Using Fourier ptychographic microscopy (FPM) and lensless digital holographic microscopy with pixel super-resolution (LDHM-PSR), we demonstrate markedly improved high-throughput visualization of microstructural features after GTS immersion compared with phosphate-buffered saline (PBS). The improvement is confirmed quantitatively by a significant increase in the one-pixel-lag autocorrelation of phase-gradient values, indicating reduced scattering-driven phase artifacts and enhanced structural continuity in reconstructed phase maps. We further show that GTS is stable for months at room temperature, provides instant yet durable clearing that improves over time, and can be removed by brief PBS washing, enabling downstream multimodal analyses on the same specimen. Finally, we benchmark GTS against the state-of-the-art clearing agent Ce3D, highlighting GTS as a low-cost, safe, operationally straightforward alternative with strong potential for routine, high-throughput QPI-based histopathology workflows.
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All authors Mikolaj Krysa, Anna Chwastowicz, Malgorzata Lenarcik, Pawel Matrybak, Piotr Zdankowski, Maciej Trusiak

Physics and Society

Topology and higher-order global synchronization on directed and hollow simplicial and cell complexes

Runyue Wang, Timoteo Carletti and Ginestra Bianconi

Higher-order networks encode the many-body interactions of complex systems ranging from the brain to biological transportation networks. Simplicial and cell complexes are ideal higher-order network representations for investigating higher-order topological dynamics where dynamical variables are not only associated with nodes, but also with edges, triangles, and higher-order simplices and cells. Global Topological Synchronization (GTS) refers to the dynamical state in which identical oscillators associated with higher-dimensional simplices and cells oscillate in unison. On standard unweighted and undirected complexes this dynamical state can be achieved only under strict topological and combinatorial conditions on the underlying discrete support. In this work we consider generalized higher-order network representations including directed and hollow complexes. Based on an in depth investigation of their topology defined by their associated algebraic topology operators and Betti numbers, we determine under which conditions GTS can be observed. We show that directed complexes always admit a global topological synchronization state independently of their topology and structure. However, we demonstrate that for directed complexes this dynamical state cannot be asymptotically stable. While hollow complexes require more stringent topological conditions to sustain global topological synchronization, these topologies can favor both the existence and the stability of global topological synchronization with respect to undirected and unweighted complexes.
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Accelerator Physics

X-ray reflection: a FLUKA model and its application in the design of synchrotron light beamlines and CERN's Future Circular Collider

Giuseppe Mazzola, Sunil Chitra, Arnaud Devienne et al. (+10 more)

Relying on atomic scattering factors from evaluated databases, a new model for the reflectivity of x rays on solid surfaces has been developed for FLUKA v4-6.0. This model accounts for the variation of reflectivity as a function of the photon energy, its incidence angle, and linear polarisation; surface roughness effects are also taken into account. FLUKA reflectivities agree well with those obtained from state-of-the-art codes used for the characterization of optical devices, both for homogeneous solids and for multilayer mirrors. This new capability renders FLUKA a nearly one-stop shop for synchrotron radiation simulations: emission from bending magnets and wigglers, photon transport and interaction, electromagnetic (and hadronic when applicable) shower development in complex geometries, as well as x-ray reflection at designated solid surfaces can now be all accounted for in a single FLUKA run. This streamlined FLUKA simulation workflow greatly simplifies the plethora of simulation tools that Monte Carlo practitioners previously needed to rely on. Two application scenarios of this new reflectivity model are showcased: first, the use of a multilayer mirror to deflect x rays from an optical hutch onto an experimental hall at the MINERVA beamline of the ALBA synchrotron and, second, the assessment of the photon flux near the interaction point at the CERN's Future Circular Collider (in its electron-positron stage) as a result of upstream x-ray reflections.
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All authors Giuseppe Mazzola, Sunil Chitra, Arnaud Devienne, Alessandro Frasca, María José García Fusté, Dominique Heinis, Anton Lechner, Giuseppe Lerner, Luca Rebuffi, Manuel Sanchez del Rio, David L. Windt, Eugeni Graugés, Francesc Salvat Pujol

Optics

Gas Line Absorption Mitigation in Hollow-Core Fibre using Spectral Pre-Equalisation

Eric Sillekens and Ronit Sohanpal

We study the impact of CO 2 absorption on hollow-core fibre transmission. Using spectral pre-equalisation, we digitally post-compensate gas-line absorption and show a 5.5 dB reduction in Q-factor penalty, outperforming a 383-tap equaliser by 1.3 dB.

Classical Physics · Cross-listed from astro-ph.GA

Global statistical entropy and its implications for the main sequences of stars and galaxies

David Elbaz

In a dissipative system such as star or a galaxy, the emitted photons are decoupled from matter particles and may therefore be considered as part of a closed system to which the Second Law of Thermodynamics applies. In the present paper, we define a global entropy using a statistical approach that accounts for the contributions of both matter particles and photons. The statistical contribution of radiation is described as a photon gas in the definition of this global entropy. The increase in global entropy can foster structure formation – rather than disorder – because structures such as stars and galaxies are efficient at dissipating energy in the form of photons, and thus at producing entropy. We show that stars generate a nearly equal amount of specific entropy, and therefore a comparable number of photons per unit mass, over their lifetime on the main sequence of the Hertzsprung-Russell (HR) diagram. This suggests that the main sequence of the HR diagram constitutes a locus of convergence toward a universal specific entropy production by stars. We then examine the implications of this approach for the star-formation main sequence in galaxies, and find a similar result. The emergence of organized structures in cosmic history reflects the second law, as organized matter is efficient at generating entropy through the slicing of energy into lower-frequency photons. This is also reflected in the dominant contribution of low-frequency photons to the extragalactic background light. Finally, we briefly discuss how this perspective may inform us on the possibility of the existence of life elsewhere in the universe.
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Chemical Physics · Cross-listed from astro-ph.GA

Organic Acid Chemistry in ISM: Detection of Formic Acid and its Prebiotic Chemistry in Hot Core G358.93$-$0.03 MM1

Arijit Manna, Sabyasachi Pal, Sekhar Sinha et al. (+1 more)

In the interstellar medium, formic acid (HCOOH) plays a significant role in the synthesis of the simplest amino acid, glycine (NH$_{2}$CH$_{2}$COOH). The presence of HCOOH suggests that oxygen-bearing molecules may be directly involved in the chemical and physical evolution of star formation regions, particularly in hot molecular cores. This paper presents the first detection of the rotational emission lines of the $trans$-conformer of HCOOH toward the hot molecular core G358.93$-$0.03 MM1, located in the massive star formation region G358.93$-$0.03. This study employed high-resolution observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7. The column density and excitation temperature of $t$-HCOOH are determined as $(8.13\pm0.72)\times10^{15}$ cm$^{-2}$ and $120\pm15$ K, respectively. The fractional abundance of $t$-HCOOH relative to H$_{2}$ is $(2.62\pm 0.29)\times 10^{-9}$. The column density ratios of $t$-HCOOH/CH$_{3}$OH and $t$-HCOOH/H$_{2}$CO are $(1.56 \pm 0.12)\times 10^{-2}$ and $(1.16 \pm 0.12)$, respectively. We computed a three-phase warm-up chemical model of HCOOH using the gas-grain chemical code UCLCHEM. We found that the observed and modelled abundances of HCOOH are almost identical, within a factor of 0.89. Based on chemical modelling, we showed that HCOOH may be formed through the reaction between HCO and OH on the grain surface, which is further released in the gas-phase.
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All authors Arijit Manna, Sabyasachi Pal, Sekhar Sinha, Sushanta Kumar Mondal

Applied Physics

Field-material coupled neural network: A novel prior-free and data-free inverse problem solver for extracting complex dielectric constant in terahertz band

Pengfei Zhu, Stefano Sfarra, Elena Pivarciova et al. (+2 more)

Accurate extraction of the complex dielectric constant in the terahertz (THz) band is essential for material characterization and non-destructive evaluation yet remains challenging due to the ill-posed nature of electromagnetic inverse problems and the limited availability of reliable reference data. In this work, a field-material couple neural network (FMCNN) is proposed to retrieve the complex dielectric constant directly from THz measurements. The FMCNN consists of a field neural network and a material neural network that are strongly coupled through the frequency-domain Maxwell equations in the form of a Helmholtz equation, with the governing physics enforced by partial differential equation (PDE) and boundary condition constraints. This formulation enables prior-free and data-free inversion, requiring only measured test data as input. The extracted dielectric constants are validated by comparison with results from a one-dimensional normal-incidence model and the Drude-Lorentz model, showing good agreement over a broad frequency range, particularly above 0.2 THz. These results demonstrate that the FMCNN provides a physics-consistent and data-efficient approach for material parameter extraction in the THz band, offering an alternative to conventional model-based methods.
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All authors Pengfei Zhu, Stefano Sfarra, Elena Pivarciova, Carlo Santulli, Xavier Maldague

Physics and Society

Impact of Market Reforms on Deterministic Frequency Deviations in the European Power Grid

Philipp C. Böttcher, Carsten Hartmann, Andrea Benigni et al. (+2 more)

Deterministic frequency deviations (DFDs) are systematic and predictable excursions of grid frequency that arise from synchronized generation ramps induced by electricity market scheduling. In this paper, we analyze the impact of the European day-ahead market reform of 1 October 2025, which replaced hourly trading blocks with quarter-hourly blocks, on DFDs in the Central European synchronous area. Using publicly available frequency measurements, we compare periods before and after the reform based on daily frequency profiles, indicators characterizing frequency deviations, principal component analysis, Fourier-based functional data analysis, and power spectral density analysis. We show that the reform substantially reduces characteristic hourly frequency deviations and suppresses dominant spectral components at hourly and half-hourly time scales, while quarter-hourly structures gain relative importance. While the likelihood of large frequency deviations decreases overall, reductions for extreme events are less clear and depend on the metric used. Our results demonstrate that market design reforms can effectively mitigate systematic frequency deviations, but also highlight that complementary technical and regulatory measures are required to further reduce large frequency excursions in low-inertia power systems.
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All authors Philipp C. Böttcher, Carsten Hartmann, Andrea Benigni, Thiemo Pesch, Dirk Witthaut

Fluid Dynamics

Assessment of jet inflow conditions on the development of supersonic jet flows

Diego F. Abreu, Joao Luiz F. Azevedo and Carlos Junqueira-Junior

In the present work, large-eddy simulations of free supersonic jet flows are performed to investigate the influence of inflow conditions on the jet flow field and its turbulent properties. A high-order nodal discontinuous Galerkin method is employed to solve the governing equations on the generated mesh. Three different inflow profiles are evaluated to represent the nozzle-exit conditions, namely, inviscid, steady viscous, and unsteady viscous profiles. Velocity and shear stress tensor component profiles obtained from the simulations are compared with experimental data. Among the investigated profiles, the steady viscous inflow shows the most significant deviation from the inviscid case, particularly in the near-field region of the jet inlet. The steady viscous profile also leads to reduced peak velocity fluctuations, showing better agreement with experimental results. Further downstream, the influence of the inflow condition diminishes, with all three profiles converging toward the experimental reference. In addition, power spectral density analyses of streamwise velocity fluctuations reveal that the inflow conditions have little effect on spectral distributions, with numerical results showing consistent agreement with experimental data within the accessible Strouhal range. Beyond these findings, the study provides a highly detailed, high-fidelity database of supersonic jet flow simulations, encompassing six large-eddy computations with different meshes, polynomial refinements, and inflow conditions. The database includes high-frequency data in relevant regions of the jet flow field and is openly available in the Zenodo repository, ensuring accessibility and reusability for the scientific community.
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Chemical Physics

Macroscopic Spin-Orbit Interaction through Strong-Field Pumping of Inhomogeneously Aligned Molecular Ensemble

Uriel Zanzuri, Sharly Fleischer, Tamar Seideman et al. (+3 more)

We study the strong-field interaction of a helical bi-chromatic pump with an anisotropic and inhomogeneous molecular system in the form of planar distribution of radially aligned molecular ensemble. This setting gives rise to macroscopic spin-orbit interaction where High Harmonic radiation is emitted while imbued with Orbital Angular Momentum (OAM) whose sign is directly dictated by the helicity of the pump field. We demonstrate this phenomenon in ensembles of $H_2^+$ and $N_2$ molecules with Time-Dependent Density Functional Theory (TDDFT) simulations.
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All authors Uriel Zanzuri, Sharly Fleischer, Tamar Seideman, Eldad Yahel, Amir Natan, Alon Bahabad

Medical Physics

Inter-Electrode Pulse Wave Velocity: A Direct Method for Maternal Arterial Stiffness Assessment During Pregnancy Using Multi-Channel ECG

Nicolas B. Garnier, Marlene J.E. Mayer, Clara Becker et al. (+3 more)

Objective: To validate a novel inter-electrode pulse wave velocity (PWV) method that measures pulse propagation between ECG electrodes without left ventricular ejection time (LVET) estimation. Methods: We analyzed 43 three-channel ECG recordings (1000 Hz) from the FELICITy 2 cohort (approximately 19 and 35 weeks gestation). R-peaks were independently detected per channel using an ensemble approach. Time lags (Delta t) between matched R-peaks across electrode pairs were used to compute PWV as PWV = L / Delta t, where L is effective inter-electrode distance. Three channel pairs yielded independent PWV estimates. Temporal stability was assessed using sliding windows (1-15 minutes). To test whether Delta t reflects morphology or vascular propagation, we evaluated three QRS fiducials (R-peak, QRS onset, maximum dV/dt) and two bandpass filters (0.5-40 and 0.5-100 Hz). Longitudinal changes were compared between control (n=24) and yoga (n=20) groups. Results: PWV values were physiologically plausible and consistent with aortic PWV (5-10 m/s): control 7.40 +/- 1.51 vs 6.98 +/- 1.63 m/s; yoga 7.10 +/- 2.15 vs 8.16 +/- 0.91 m/s (early vs late pregnancy). PWV stabilized at 5 minutes (coefficient of variation 12.3 percent), with 2.6- to 5.2-fold lower variability than heart rate and heart rate variability. Inter-electrode delays (15-27 ms) persisted across fiducials and were minimally affected by filter settings (change -8.5 percent, not significant), arguing against purely morphological distortion; PWV remained within 6.8-9.1 m/s. Preliminary group trends differed (control -5.7 percent, yoga +14.9 percent; interaction p=0.07). Conclusions: Inter-electrode PWV enables direct spatial assessment of pulse propagation with physiologically valid values, is robust to fiducial and filtering choices, and shows promise for pregnancy-related arterial stiffness assessment with standard multi-channel ECG.
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All authors Nicolas B. Garnier, Marlene J.E. Mayer, Clara Becker, Marta C. Antonelli, Silvia M. Lobmaier, Martin G Frasch

Optics

Emergence of transverse optical spin in a subwavelength grating ring resonator

Nikita Iukhtanov, Chao Sun, Georgiy Kurganov et al. (+3 more)

The local polarization of the electromagnetic field plays a crucial role in the interaction of light with spin- and valley-polarized quantum sources. Unlike free-space electromagnetic waves, whose polarization degeneracy enables flexible polarization manipulation, planar integrated optical structures lack such degree of freedom owing to intrinsic structural anisotropy. Here, we propose a planar optical ring resonator based on a subwavelength grating waveguide that supports two quasi-degenerate modes. We demonstrate that coupling of these modes in the ring resonator leads to the formation of the resonances with a predominant direction of electric-field rotation in the vicinity of the resonator, resulting in the non-zero transverse optical spin. The average degree of circular polarization in the proposed structures reaches values of up to 70%. The theoretical predictions are corroborated by experimental validation in the microwave spectral range. Our findings suggest a viable route toward realization of on-chip optical spintronic and valleytronic interfaces.
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All authors Nikita Iukhtanov, Chao Sun, Georgiy Kurganov, Dmitry Zhirihin, Andrey Bogdanov, Roman Savelev

Optics · Cross-listed from quant-ph

Device-independent quantum key distribution over 100 km with single atoms

Bo-Wei Lu, Chao-Wei Yang, Run-Qi Wang et al. (+15 more)

Device-independent quantum key distribution (DI-QKD) is a key application of the quantum internet. We report the realization of DI-QKD between two single-atom nodes linked by 100-km fibers. To improve the entangling rate, single-photon interference is leveraged for entanglement heralding, and quantum frequency conversion is used to reduce fiber loss. A tailored Rydberg-based emission scheme suppresses the photon recoil effect on the atom without introducing noise. We achieved high-fidelity atom-atom entanglement and positive asymptotic key rates for fiber lengths up to 100 km. At 11 km, 1.2 million heralded Bell pairs were prepared over 624 hours, yielding an estimated extractable finite-size secure key rate of 0.112 bits per event against general attacks. Our results close the gap between proof-of-principle quantum network experiments and real-world applications.
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All authors Bo-Wei Lu, Chao-Wei Yang, Run-Qi Wang, Bo-Feng Gao, Yi-Zheng Zhen, Zhen-Gang Wang, Jia-Kai Shi, Zhong-Qi Ren, Thomas A. Hahn, Ernest Y.-Z. Tan, Xiu-Ping Xie, Ming-Yang Zheng, Xiao Jiang, Jun Zhang, Feihu Xu, Qiang Zhang, Xiao-Hui Bao, Jian-Wei Pan

Applied Physics · Cross-listed from cs.LG

Training deep physical neural networks with local physical information bottleneck

Hao Wang, Ziao Wang, Xiangpeng Liang et al. (+8 more)

Deep learning has revolutionized modern society but faces growing energy and latency constraints. Deep physical neural networks (PNNs) are interconnected computing systems that directly exploit analog dynamics for energy-efficient, ultrafast AI execution. Realizing this potential, however, requires universal training methods tailored to physical intricacies. Here, we present the Physical Information Bottleneck (PIB), a general and efficient framework that integrates information theory and local learning, enabling deep PNNs to learn under arbitrary physical dynamics. By allocating matrix-based information bottlenecks to each unit, we demonstrate supervised, unsupervised, and reinforcement learning across electronic memristive chips and optical computing platforms. PIB also adapts to severe hardware faults and allows for parallel training via geographically distributed resources. Bypassing auxiliary digital models and contrastive measurements, PIB recasts PNN training as an intrinsic, scalable information-theoretic process compatible with diverse physical substrates.
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All authors Hao Wang, Ziao Wang, Xiangpeng Liang, Han Zhao, Jianqi Hu, Junjie Jiang, Xing Fu, Jianshi Tang, Huaqiang Wu, Sylvain Gigan, Qiang Liu

Optics

Background-free Tracking of Ultrafast Hole and Electron Dynamics with XUV Transient Grating Spectroscopy

Vincent Eggers, Rafael Quintero-Bermudez, Kevin Gulu Xiong et al. (+1 more)

Extreme ultraviolet (XUV) transient absorption (TA) and transient reflectivity (TR) spectroscopies enable element-specific insights into attosecond-timescale processes in solids. XUV transient grating spectroscopy (TGS) is an emerging tool that combines the advantages of both absorption and reflectivity while offering intrinsically background-free detection. Here, we implement XUV-TGS by generating a transient grating in germanium solid using two few-cycle near-infrared pulses and probing it with an attosecond XUV pulse, produced via tabletop high-harmonic generation. The spectrally resolved, diffracted XUV pulses directly visualize the separate ultrashort decay times of both photoexcited electrons and holes, without the need for iterative deconvolution. By combining XUV-TA and -TG spectroscopy, we extract the evolution of the complex refractive index, ñ, without the need for Kramers-Kronig reconstruction, as required in XUV-TR, allowing us to extract the roots of the induced optical response. We find reflectivity changes of up to 34% via the real part of ñ, whereas changes in the imaginary part only result in a variation in reflectivity of around 0.5%.
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All authors Vincent Eggers, Rafael Quintero-Bermudez, Kevin Gulu Xiong, Stephen R. Leone

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

Modeling bacterial flow field with regularized singularities

Yaochen Yang, Daiki Matsunaga, Da Wei et al. (+1 more)

The flow field generated by a swimming bacterium serves as a fundamental building block for understanding hydrodynamic interactions between bacteria. Although the flow field generated by a force dipole (stresslet) well captures the fluid motion in the far field limit, the stresslet description does not work in the near-field limit, which can be important in microswimmer interactions. Here we propose the model combining an anisotropically regularized stresslet with an isotropically regularized source dipole, and it nicely reproduces the flow field around a swimming bacterium, which is validated by the experimental measurements of the flow field around E. coli and our boundary-element-method simulations of a helical microswimmer, in both cases of the free space and the confined space with a no-slip wall. This work provides a practical tool for obtaining the flow field of the bacterium, and can be utilised to study the collective responses of bacteria in dense suspensions.
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All authors Yaochen Yang, Daiki Matsunaga, Da Wei, Fanlong Meng

General Physics

Observational Constraints and Geometric Diagnostics of Barboza-Alcaniz and Logarithmic Dark Energy Parametrizations

Archana Dixit, Saurabh Verma, Anirudh Pradhan et al. (+1 more)

This study investigates and compares two prominent two-dimensional dark energy (DE) parameterizations: Barboza-Alcaniz (BA) and Logarithmic forms by comparing them with a comprehensive set of observational data comprising Type Ia Supernovae (SNe Ia) from the Pantheon compilation, Baryon Acoustic Oscillations (DESI BAO), and Cosmic Chronometers (CC). The primary objective was to explore the constraining power and cosmological implications of each parameterization in light of the current data. After formulating the theoretical framework and background equations governing cosmic expansion, we employ Markov Chain Monte Carlo (MCMC) techniques using the emcee Python package to constrain the free parameters of each model. The best-fit values for parameters $\omega_0$, $\omega_a$, and $H_0$ were extracted for each model using individual and combined datasets. The results include confidence contours at the levels $1\sigma$ and $2\sigma$. Our findings demonstrate that both parameterizations are consistent with observational data, with logarithmic parameterization showing slightly better constraints in terms of parameter evolution. Furthermore, we employed a statefinder diagnostic to analyze the geometric behavior of the models, providing an effective distinction between the two DE scenarios. This study contributes to a deeper understanding of DE evolution and its constraints in light of current cosmological data.
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All authors Archana Dixit, Saurabh Verma, Anirudh Pradhan, M. S. Barak