Physics and Society · Cross-listed from cs.SI
Platform Sorting Drives Ideological Fragmentation in the Social Media Ecosystem
Edoardo Di Martino, Alessandro Galeazzi, Matteo Cinelli et al. (+2 more)
Ideological asymmetries in online political communication are often studied as localized phenomena emerging within communities. Here, we show that fragmentation instead operates at the level of entire platforms, consistent with a process of platform sorting in which users increasingly align with ideologically congruent environments. We analyze political information dynamics across Bluesky, Facebook, Reddit, Truth Social, Twitter/X, and YouTube during the 2020 and 2024 US presidential elections, combining measures of content sharing, engagement allocation, and user-level ideological orientation. Across platforms, ideological fragmentation emerges consistently and persists over time. Platforms exhibit distinct ideological profiles that persist across the two election cycles, ranging from strongly left-leaning to strongly right-leaning environments. Longitudinal analyses further reveal limited ideological variability among persistent user cohorts, indicating that apparent changes within single platforms reflect ecosystem-level sorting rather than convergence toward neutrality. Taken together, our results show that the dynamics of platform sorting is not a transient reaction to political events or moderation interventions, but a persistent structural feature of the social media ecosystem.
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All authors Edoardo Di Martino, Alessandro Galeazzi, Matteo Cinelli, Michele Starnini, Walter Quattrociocchi
General Physics
MeV-GeV Gamma-Ray Astrophysics in the Multimessenger Era
Alessandro De Angelis
Gamma-ray astrophysics probes the most extreme particle accelerators and explosive transients in the Universe. From pioneering theoretical predictions in the 1950s and the first space-borne detections in the 1960s, mostly exploring the sub-MeV region, the field has evolved into a mature, multi-decade enterprise that spans nine orders of magnitude in
photon energy up to PeV energies and interfaces naturally with
neutrino and gravitational-wave astronomy. Yet the energy range from a few hundred keV to a few GeV – the "MeV gap", constraining progress on nucleosynthesis, positron annihilation, transient physics, dark-matter signatures, and electromagnetic counterparts to high-energy
neutrinos and gravitational waves - remains sensitivity-limited. In this paper, we survey the scientific motivations for gamma-ray astrophysics, sketch a concise history from the first ideas to key milestones in space- and ground- based gamma-ray astronomy, and discuss programmatic attempts to close the MeV gap.
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Classical Physics
The emergence of a new sound research methodology in the field of health: designo-therapy ?
Luc Perera and Pierre Jouvelot
Design fits in different fields, and it is given a plurality of titles: thinking, social, ecological, and graphic, space, etc. This discipline crosses the fields of research and engineering, which emancipate themselves from their historic fields and target other areas of public and private services. On the other hand, the sound sector, and more generally the acoustics, is more strictly categorized: musicology, psycho-acoustics or electro acoustics (see figure 1, which gives a relatively comprehensive overview) ). It is in this universe that evolves the discipline of sound design, with accents a priori industrial or environmental. But could it also allies, more unexpectedly, to health design and, if so, in what form\,? To answer this question, we try here, in a few lines, to explain the links between art (s) and health, links that aroused the interest to draw a parallel with the world of design, then to think about its integration. In the medical community. We will conclude, as an illustration, from our own research in sound design, in connection with Indian music.
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Computational Physics · Cross-listed from cond-mat.str-el
Interaction-driven dynamics in graphene flakes as a benchmark for quantum simulation
Fabian Eickhoff, Satoshi Ejima, Lukas Windgätter et al. (+4 more)
We study interaction-driven ultrafast dynamics in finite
graphene flakes following an optical pump quench in an interacting tight-binding model. By comparing exact real-time
evolution with simulations restricted to particle-hole excitation subspaces, we assess when relaxation can be captured by low-order many-body processes and when this is not sufficient. The single-particle orbital
entropy provides a compact diagnostic for dynamic correlation growth. For the systems studied here, periodic
graphene flakes are well described by low-order excitations, whereas confined geometries require substantial higher-order contributions even for relatively small interaction strengths. The quench protocol combines simple initial-state preparation with strongly correlated dynamics, identifying a promising
benchmark problem for future
quantum-computing simulations.
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All authors Fabian Eickhoff, Satoshi Ejima, Lukas Windgätter, Florian G. Eich, Hannah Rittich, Sebastian Zanker, Peter Schmitteckert
Instrumentation and Detectors · Cross-listed from eess.IV
Unsupervised Deep Learning for Limited-Angle STEM-EDX Tomography – Application to 3D Chemical Analysis of Phase-Change Memory Devices
Daniel del Pozo Bueno, Serge Brosset, Theo Monniez et al. (+3 more)
Energy Dispersive X-ray (EDX)
tomography in Scanning Transmission Electron Microscopy (STEM) enables 3D compositional and elemental mapping at the nanoscale, but its use is limited by restricted tilt ranges and low-dose conditions required to avoid beam damage. Limited-angle acquisition introduces missing-wedge artefacts such as elongation and anisotropic resolution, while noisy low-dose data further degrade reconstruction quality and quantitative reliability. Here, we introduce an unsupervised deep learning framework based on Deep Image Prior with total variation regularization (DIP-TV) for limited-angle STEM-EDX
tomography. We extend it to a multi-channel formulation (DIPm-TV) that jointly reconstructs multiple elemental maps by exploiting spatial correlations. Using a synthetic 3-channel phantom, we show that the method compensates for severe missing-wedge artefacts corresponding to approximately $100^\circ$ of missing angular range under moderate noise, outperforming simultaneous iterative reconstruction technique and compressed sensing approaches. We apply the method to 3D chemical analysis of Ge-Sb-Te (GST)
memory devices in virgin (as-fabricated) and SET (crystalline) operational states. Samples were prepared as cross-sectional focused ion beam lamellae and acquired under a limited-angle tilt range from $-40^\circ$ to $+40^\circ$ with $5^\circ$ steps and a dose of $2.0\times10^5$ $e^-/Ang^2$. The multi-channel approach enables voxel-by-voxel elemental reconstruction using only EDX signals without external structural priors such as high-angle annular dark-field imaging. The reconstructed volumes show near-isotropic spatial resolution and reveal compositional heterogeneities associated with device operation. This approach enables 3D chemical characterization in experimentally accessible sample geometries where conventional methods fail due to severe angular limitations.
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All authors Daniel del Pozo Bueno, Serge Brosset, Theo Monniez, Gabriele Navarro, Philippe Ciuciu, Zineb Saghi
Classical Physics
A phase-field modeling approach to sea-ice fracturing
Laetitia Drumare, Vidar Skogvoll, François Renard et al. (+2 more)
The thin ice that covers the polar oceans is a complex geomaterial that is constantly stressed and fractured by winds and ocean currents. In the central Arctic, this forcing produces deformations in the form of shear bands, within which individual ice plates detach, locally generating a granular medium. Capturing this transition from a continuous to a granular sea-ice cover has implications for the adequate representation of the mechanical and dynamical behavior of sea-ice in regional and large-scale models used for operational and
climate prediction purposes. Our work investigates the feasibility of a phase-field approach to capture this granularization processes and focuses on fracture propagation in the material. The model combines a double-well free-energy formulation with an overdamped displacement response. The governing equations are solved using a spectral method in
Fourier space. The implementation accounts for body forces, representative of the main forcings on sea-ice, and remains computationally tractable despite the highly nonlinear character of the double-well energy formulation. We first validate the framework against a
benchmark problem: the opening of an inclusion embedded into an elastic
matrix under tensile loading. Then, additional simple shear configurations are investigated: an inclusion solicited under plane shear and a cylindrical Couette experiment, for which the analytical solution of the displacement field is known. The resulting fracture patterns and displacement fields demonstrate that our phase-field framework captures key features of tensile and shear fracture propagation, including the linear scaling between crack speed and applied load predicted by the Griffith's theory.
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All authors Laetitia Drumare, Vidar Skogvoll, François Renard, Luiza Angheluta, Véronique Dansereau
Optics
Intrinsic plasmon canalization in the biaxial van der Waals crystal MoOCl$_2$
Farid Aghashirinov, Andrea Mancini, Lin Nan et al. (+4 more)
Anisotropic polaritons in low-
symmetry crystals allow for subwavelength confinement and directional routing of light. The most extreme form of such anisotropy arises at the topological transition between elliptical and
hyperbolic dispersion, where the isofrequency contours collapse into parallel lines and polaritons propagate in a diffractionless, beam-like fashion. This canalization regime has previously been accessed through twisted
heterostructures or engineered metasurfaces. Here we show that natural canalization can be achieved without any fabrication or structuring by exploiting the intrinsic elliptical-to-
hyperbolic transition in the van der Waals
crystal MoOCl$_2$ at room temperature. Using near-field imaging, we directly visualize plasmon-polariton canalization emerging at the low-loss Drude crossing point along the [010]
crystal axis. Owing to the moderate slope of the Drude permittivity, the resulting polaritons remain highly directional across a broad spectral window. This weak dispersion also enables robust thickness-dependent tuning, and we demonstrate, both experimentally and theoretically, that the canalization wavelength can be adjusted by more than 1 {\mu}m simply by varying the flake thickness. This work brings canalized polariton propagation into the 4.5 - 6 {\mu}m range, beyond the frequency limits of
phonon-polariton platforms and overlapping with important molecular vibrations, opening new opportunities for mid-IR nanophotonics and sensing.
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All authors Farid Aghashirinov, Andrea Mancini, Lin Nan, Giacomo Venturi, Bettina Frank, Harald Giessen, Antonio Ambrosio
Atomic Physics
Ytterbium lattice clock with systematic uncertainty of $1.3\times 10^{-18}$ and instability at the $10^{-19}$ level
Qiang Zhu, Jingran Shi, Yuechen Zhang et al. (+8 more)
We report an optical
lattice clock based on $^{171}$Yb atoms with a total systematic uncertainty of $1.3\times 10^{-18}$. An in-
vacuum buildup cavity was employed to enhance the
lattice light power. Differential frequency measurement between two identical clocks facilitates the evaluation of systematic shifts. Synchronous comparison of the two clocks reached a stability level of $2.7\times 10^{-19}$ in an averaging time of 216,000~s. The blackbody radiation (BBR) shield which is placed in
vacuum provides a well-characterized BBR environment, enabling an uncertainty contribution of $8.7\times 10^{-19}$ from the BBR Stark shift.
Lattice light shifts were measured at different
lattice depths $U$, and fitted with a fourth-order
polynomial of $U$. The zero-linear-shift frequency $\nu_{\mathrm{zero}}$ was determined to be 394 798 260.6(3) MHz. The
lattice light shift can be controlled at an uncertainty level of $6.3\times 10^{-19}$ under typical operating conditions. Other systematic shifts have also been evaluated. The two clocks will be used for remote frequency comparisons between Shanghai and Wuhan.
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All authors Qiang Zhu, Jingran Shi, Yuechen Zhang, Xiatian Xu, Bing Wang, Dezhi Xiong, Zhuanxian Xiong, Pengcheng Fang, Qunfeng Chen, Lingxiang He, Baolong Lyu
Biological Physics · Cross-listed from cond-mat.soft
Moving backward to go faster: Diatom-inspired sliding reveals efficient modes of locomotion
Julien le Dreff and Blaise Delmotte
Across biological scales, from sperm
cells to whales, locomotion commonly relies on undulatory gaits, in which traveling deformation waves interact with the surrounding fluid to generate thrust opposite to the direction of wave propagation. In viscous environments, microorganism locomotion is classically understood in terms of undulatory bending of slender filaments such as flagella, with optimal propulsion achieved when the deformation wavelength is comparable to the swimmer length. Inspired by diatom colonies, we identify a fundamentally different swimming mechanism based on sliding between neighboring elements within a chain. We show that sliding between stacked elongated
cells generates internal shear that drives propulsion opposite to classical undulatory swimming, while achieving higher speeds and greater energetic efficiency. Remarkably, optimal performance occurs at wavelengths much larger than the chain length and at
cell aspect ratios consistent with those observed in natural diatom colonies, suggesting that hydrodynamic efficiency may constitute an evolutionary selective pressure in diatom chains. Together, these results identify sliding as a previously overlooked mode of locomotion in multicellular assemblies and suggest new design principles for efficient bio-inspired microswimmers and swarm robotic systems.
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Plasma Physics · Cross-listed from astro-ph.SR
Solar flare ribbons structured by uncombed chromospheric loops
L. P. Chitta, E. R. Priest, David Orozco Suárez et al. (+33 more)
A part of the
magnetic energy released during a
flare is transported to the lower atmosphere. High-resolution observations show that
flare ribbons, sites of energy deposition at the footpoints of flaring loops which appear bright in the chromosphere and transition region, are structured on small spatial scales on the order of 100 km. Based on idealized numerical models of
flares it is suggested that the ribbon fine-structures could originate from a tearing instability and the development of plasmoids in current sheets. Here we report on Fe I 5250.6 Å and Mg I b2 5173 Å spectral observations of a
solar flare from the Tunable Magnetograph onboard the SUNRISE III balloon-borne mission that reveal an intricate link between the
flare ribbon structure and the ambient chromosphere. We identified uncombed chromospheric loops and non-flaring fine-structures that are interspersed among brighter
flare ribbon threads. These loops remain stable on timescales of minutes. Spectral lines from these regions show reduced emission or self-reversal in the line core compared with the immediately adjacent
flare ribbons. We discuss the potential role of these structures in the onset of a
flare. Furthermore, we suggest that irrespective of the complexities in the flaring current sheet, uncombed chromospheric loops and nonflaring fine-structure might play a role in spatially modulating the
flare energy deposition in the lower atmosphere.
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All authors L. P. Chitta, E. R. Priest, David Orozco Suárez, Azaymi L. Siu-Tapia, Jose Carlos del Toro Iniesta, Francisco Javier Bailén, Julian Blanco Rodríguez, Alberto Álvarez-Herrero, Maria Balaguer Jiménez, Esteban Sanchis Kilders, Ignacio Torralbo, Christoph Kuckein, Sami K. Solanki, Andreas Lagg, Achim Gandorfer, Yukio Katsukawa, Pietro Bernasconi, Thomas Berkefeld, Alex Feller, Tino L. Riethmüller, Masahito Kubo, H. N. Smitha, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hoelken, Francisco A. Iglesias, Ryohtaroh T. Ishikawa, Yusuke Kawabata, Takuma Matsumoto, Takayoshi Oba, Hanna Strecker, Dušan Vukadinović
Plasma Physics
Systematic comparison of VMEC and HINT equilibrium calculations for finite-beta LHD plasmas
Albert Civit-Bertran, Yasuhiro Suzuki and Shimpei Futatani
A systematic comparison between VMEC and HINT
equilibrium calculations has been carried out for Large Helical Device
plasmas to clarify the influence of the assumption of the nested flux surfaces at finite beta. Three
vacuum magnetic-axis configurations, $R_{\rm axV} = \SI{3.53}{\, m}$, $\SI{3.60}{\, m}$, $\SI{3.85}{\, m}$, are examined for the beta values on the axis in the range $\beta_0 \in [0.0\%, 5.0\%]$. The
magnetic-axis position, the rotational transform on the axis, and the
plasma volume enclosed by the last closed flux surface are compared between the two codes. At low-$\beta_0$, VMEC and HINT give consistent
equilibria, indicating that the nested flux surfaces are largely preserved. Above a configuration-dependent critical $\beta_0$, however, the two solutions begin to diverge, indicating that the nested flux surfaces assumption is compromised. In HINT, the enclosed
plasma volume decreases at higher beta because the
stochastic magnetic field evolves near the
plasma edge, whereas VMEC cannot represent this flux surface breaking due to its assumption of nested flux surfaces. These results show that the 3D
equilibrium responses in LHD
equilibria become increasingly important from inward- to outward-shifted configurations, mainly through Pfirsch-Schlüter current-driven perturbations of the
magnetic field and the resulting edge stochasticity.
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Biological Physics · Cross-listed from cond-mat.soft
Virial stress in systems of active Brownian particles in the presence of translational and rotational inertia
Chandranshu Tiwari, Sunil P. Singh and Roland G. Winkler
We elucidate the stress in a system of active Brownian particles augmented with translational and rotational inertia (ABP+TRI). Stress tensors are derived for periodic systems as well as systems confined between walls by employing Lagrange's equations of motion of the first kind for the rotational motion. Using Langevin simulations of an ideal active gas in two dimensions, we confirm the existence of an equation of state for periodic systems that depends on translational and rotational inertia in general. Confinement implies a strong polarization of the propulsion direction near a wall and an enhanced density, both of which increase with increasing rotational inertia. This affects the local stress tensor normal to the confining walls, leading to a breakdown of the equation of state. Yet the local stress in the bulk part of the confined systems is identical with that of the periodic system. Importantly, for both kinds of boundary conditions, the so-called swim stress is not included in the local stress tensor; thus, in general, the swim stress is not representative of the stress in systems of ABP+TRIs.
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Biological Physics · Cross-listed from cond-mat.soft
Finite-Time Orientational Relaxation Restructures Collective Motion in Polar Active Matter
Rajneesh Kumar, Subhransu Sekhar Mishra and Debasish Chaudhuri
We introduce a Langevin formulation of Vicsek-like active particles in which orientations evolve through finite-rate relaxation toward the local mean direction, with
alignment strength $J$ and rotational diffusivity $D_r$, thereby combining Vicsek-type local consensus with XY-like orientational dynamics. Using large-scale numerical simulations, we determine the nonequilibrium phase diagram as a function of activity and
alignment rate. Increasing the
alignment rate drives a sequence of transitions from a homogeneous isotropic state to polar bands, a cross-sea phase of intersecting bands, a homogeneous polar state, and ultimately a micro-clustered regime. The isotropic-to-polar transition is strongly first order, as evidenced by Binder cumulants and bimodal distributions of local polarization and density, indicating coexistence of gas-like and
liquid-like regions. Near the onset of collective motion, band size increases with activity but depends non-monotonically on
alignment rate. Further increasing the
alignment rate drives the system through the cross-sea and homogeneous polar phases before enhanced density fluctuations lead to micro-clustering. Our results demonstrate that finite-time orientational relaxation acts as a control parameter that qualitatively restructures collective behavior in polar active matter.
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Applied Physics
Virtual-Array Operational Modal Analysis of Rolling Tires Using a Single Tire Cavity Accelerometer
Pradosh Pritam Dash and Pablo A Tarazaga
The dynamics of the rolling tire govern structure-borne road noise below 500 Hz.
Laser Doppler vibrometry (LDV) is the established laboratory reference for measuring rolling-tire modes. This paper presents a complementary approach that uses a single wireless tire cavity accelerometer (TCA) mounted on the inner liner and a once-per-revolution encoder on the drum of a tire-on-drum rig fitted with a cleat. Because the drum-to-tire diameter ratio (2.74) is non-integer, successive cleat impacts encounter the TCA at different circumferential positions. The TCA's contact-patch signature locates the sensor at each impact within approximately $1^\circ$, and grouping the impact responses by angular position synthesizes a 36-element virtual array from a single 128 s run. Covariance-driven
stochastic subspace identification (SSI-COV) is applied using a consensus rule across multiple parameter settings, bootstrap resampling over impacts, and a correction for window-induced damping; the complete signal-processing chain is verified on synthetic data with known modes. For a slick 195/65R15 tire rolling at 30 km/h under a 1334 N load, ten modes between 46 and 193 Hz are robustly identified, exhibiting circumferential wavenumbers from 1 to 5, damping ratios of 2.1–4.2%, and strongly complex mode shapes, with three additional modes identified tentatively. The extracted modes follow the wavenumber ladder of a stationary modal test of the same tire. Requiring no optical access and capturing the full virtual array in a single run, the proposed method is well suited to treaded tires and on-road testing, at the expense of in-tire sensor installation.
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History and Philosophy of Physics
At the Origins of Electroculture: A Retrodictive Modelling of Bertholon's 18th-Century Electrovegetometer in the Pre-Corona Regime
Thierry Dufour
Pierre-Nicolas Bertholon's 18th-century electrovegetometer was conceived to harness "atmospheric electricity" for plant growth, yet its physical capabilities have never been quantified within the context of today's understanding of the Earth's atmospheric electric system. This study addresses the lack of quantitative assessment of such historical "electroculture" device and its plausible influence on the near-canopy electrical environment. It aims to reinterpret Bertholon's apparatus using contemporary atmospheric electrodynamics, asking under which realistic fair-weather and storm-like conditions a purely passive collector-distributor could generate fields and ion fluxes of physical significance. A two-dimensional, quasi-steady ohmic model has been developed in which the atmosphere is a resistive column carrying the global conduction current, the metal structure is a floating conductor supported by leaky wooden
insulators and space-charge and corona are excluded so that all results describe pre-onset upper bounds. The simulations show that in fair weather the single upper point and the lower multi-point crown of the electrovegetometer enhance the background field by two to three orders of magnitude, yet only within millimetric-centimetric regions around the tips and with total currents limited to the pA-nA/m^2 range. Under storm-like forcing, peak fields at the crown reach 100-1000 kV/m, approaching or exceeding empirical corona-onset thresholds, while remaining largely insensitive to uncertainties in apex angle or collector geometry as long as an elevated mast is present. These results make Bertholon's reports of luminous "aigrettes" physically plausible, but suggest that any fair-weather agronomic impact was subtle and highly localized and that modern "electroculture" claims require careful, coupled electrostatic and biological studies beyond the pre-corona regime.
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History and Philosophy of Physics
From Electroculture to Plasma Agriculture: A Three-Century Arc Bridging Bertholon's Legacy with Contemporary Farming Advances
Thierry Dufour
This review traces the historical trajectory of electricity in agriculture, from the earliest observations of electrical phenomena to the emergence of cold
plasmas. Looking back to Antiquity and then to the Enlightenment, it underlines Abbé Bertholon's 18th-century efforts to channel atmospheric electricity to stimulate crops, using devices such as the electro-végétomètre. Although these early electroculture experiments relied on neither quantitative dosimetry nor rigorous methodology, they foreshadowed the idea of a controlled transfer of electrical energy to plants. Then the review examines the historical development of galvanism, electrochemistry, and the physics of gaseous discharges throughout the 19th and 20th centuries, which collectively laid the foundations for contemporary cold-
plasma technologies. In the 21st century,
plasma agriculture has emerged as an interdisciplinary approach integrating electrical, chemical, radiative, thermal, and fluid-mechanical effects. Applications include seed treatment (preconditioning, seed priming), stimulation of plant growth, soil and water treatment, and decontamination of agri-food products. The review thus reassesses Abbé Bertholon's contributions as those of a methodological precursor and shows how his intuition of a "vivifying electricity" resonates with modern cold-
plasma science. Finally, it argues that
plasma agriculture can transform an Enlightenment intuition into a reproducible experimental framework for sustainable agriculture and food safety.
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Accelerator Physics · Cross-listed from cond-mat.supr-con
Superheating field of clean superconductors near the type-I–type-II boundary: the low-temperature Meissner stability limit of niobium
Takayuki Kubo
We calculate the low-temperature superheating field $B_{\rm sh}$ of clean
superconductors near the boundary between type-I and type-II superconductivity, with particular emphasis on Nb. Ginzburg–Landau theory is not applicable at low temperatures, while previous microscopic calculations have been limited to either the large-$\kappa$ regime or the dirty limit. The clean, low-$\kappa$ regime relevant to Nb has therefore remained unresolved. We solve the self-consistent nonlinear nonlocal Eilenberger problem for the Meissner state and then analyze its stability against small perturbations. For a Nb-like material with $\kappa_{\rm GL}=0.7$, we obtain $B_{\rm sh}\simeq 290\,{\rm mT}$ at $T/T_c=0.2$, using $B_{c0}\simeq 200\,{\rm mT}$. For a TESLA-shaped Nb accelerator cavity, this corresponds to an intrinsic Meissner-stability limit of about $67\,{\rm MV/m}$.
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Medical Physics
Foveated-Imaging Geometry CT Architecture and Seeded Diffusion Model Enabling Global Super-Resolution Reconstruction
Wenxin Mo, Yingxian Xia, Yongle Yan et al. (+3 more)
For X-ray computed
tomography (CT), a smaller detector pixel size generally leads to higher scanner spatial resolution, but inevitably increases system cost as well as data overhead in acquisition and processing. To achieve high-resolution (HR) CT imaging in a more resource-efficient manner, we propose a Foveated-Imaging Geometry CT (FIGCT) architecture, which integrates local HR data into an acquisition scheme dominated by low-resolution (LR) measurements. We further develop a
Diffusion Probabilistic FIGCT Super-Resolution Reconstruction (DPFSR) framework to generate global HR CT images over the full field of view (FOV). The concept of FIGCT is first established, and its typical configurations are characterized according to the arrangement of HR data. Two key indices, namely the HR data fraction (HDF) and the LR-to-HR detector pixel size ratio (LHR), are introduced to describe the FIGCT geometry. The proposed DPFSR incorporates local HR information into intermediate clean-image estimates in both the projection and image domains during the reverse
diffusion process. This additional step not only guides HR image generation from LR data, but also improves data consistency between the clean-image estimates and the originally measured data. Preliminary numerical simulation results on FIGCT show that the proposed architecture provides high-precision CT images within the region of interest (ROI) corresponding to the HR data, while the spatial resolution deteriorates rapidly outside the ROI. With DPFSR, global HR reconstruction is achieved on the AAPM Grand Challenge
dataset and swine lung CT data, outperforming existing SR methods in terms of Learned Perceptual Image Patch Similarity (LPIPS), PSNR, and SSIM.
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All authors Wenxin Mo, Yingxian Xia, Yongle Yan, Hao Zhou, Li Zhang, Hewei Gao
Fluid Dynamics
Baroclinic wave dynamics in the Ekman-free rotating rectangular annulus with localized forced plume
Shivam Swarnakar, Ayan Kumar Banerjee, Sridhar Balasubramanian et al. (+1 more)
We report numerical simulations of a rotating rectangular annulus that isolates the Ekman-free bulk of the cylindrical baroclinic annulus, subjected to bi-directional temperature gradients imposed by a uniformly cooled inner wall and a localized forced heated plume at the outer bottom. The finite-volume OpenFOAM solver is employed across combinations of source Richardson number $Ri_0 = 99, 4, 1$ and Rossby number $Ro = 0.3, 0.1, 0.07$. A non-dimensional scaling of the governing equations identifies geostrophic-hydrostatic balance as the leading-order bulk state, a result confirmed a posteriori by the $x$ and $z-$momentum budgets. Baroclinic waves of mode $m=2$ at $Ro=0.3$ transition to $m=3$ as $Ro$ decreases, consistent with the contraction of the Eady deformation radius $L_\rho = NH/f$; Complex Empirical Orthogonal Function (CEOF) analysis characterizes the wave regime and detects a
Hopf-bifurcated vacillating state at $Ri_0 = 99,~Ro = 0.1$. The plume morphology, classified through the Morton length scale and source flux-balance parameter, transitions from weak, laterally-swept structures at $Ri_0 = 99$ to sustained columnar plumes traversing the full baroclinic depth at $Ri_0 \leq 4$. The plume entrainment coefficient $\Gamma(z)$ shows opposite rotational sensitivities at low and high $Ri_0$, which we organize through a local plume Rossby number $Ro_p = w/(2\Omega b)$. A mixing-length argument predicts a bulk turbulent heat flux $\overline{u'T'} \propto Ri_0^{-1/2}$, anticipating an order-of-magnitude enhancement from $Ri_0 = 99$ to $Ri_0 = 1$, in agreement with the simulations. A regime map in the $(Ri_0, Ro)$ plane reveals that, within the explored range, the plume-regime and wave-selection problems are approximately separable: $Ri_0$ sets the plume regime while $Ro$ selects the dominant baroclinic wave mode.
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All authors Shivam Swarnakar, Ayan Kumar Banerjee, Sridhar Balasubramanian, Amitabh Bhattacharya
Computational Physics · Cross-listed from nlin.AO
Towards Critical Branching Mechanism in Recurrent Neural Networks
Feixiang Ren and Ling Feng
Criticality has been proposed as a key organizing principle in biological neural systems, yet its origin and relevance in artificial neural networks remain unclear. We analyze hidden-state dynamics in trained long short-term
memory (LSTM) networks and show that small networks near their optimal training epochs (steps) exhibit scale-free avalanche statistics and branching parameters close to unity, indicative of near-critical dynamics, while larger models remain subcritical. To explain the coexistence of subcritical branching with robust $1/f^{\beta}$ noise, we introduce a mixture branching process framework that links heterogeneous branching dynamics to long-range temporal correlations. These results identify critical-like behavior in LSTMs as an emergent, capacity-dependent dynamical regime.
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Instrumentation and Detectors · Cross-listed from hep-ex
Agentic Hybrid RAG for Evidence-Grounded Muon Collider Analysis
Ruobing Jiang, Dawei Fu, Cheng Jiang et al. (+6 more)
Muon collider research spans accelerator physics, detector instrumentation, and high-energy phenomenology, with relevant evidence scattered across a rapidly expanding and heterogeneous body of scientific literature. As high-energy physics (HEP) increasingly explores
agent-assisted analysis workflows, efficiently locating, integrating, and verifying scientific evidence becomes an essential capability. While
retrieval-augmented generation (RAG) offers a promising framework for scientific question answering, integrating agentic
reasoning without compromising
retrieval precision remains a key challenge. In this work, we present agentic hybrid RAG, an evidence-grounded RAG framework for
muon collider research. The framework combines a hybrid retriever, integrating sparse lexical and dense semantic
retrieval, with an agentic
reasoning module for query decomposition, evidence expansion, and grounded answer generation. To enable systematic evaluation, we construct the first
benchmark for
retrieval-augmented scientific question answering in the
muon collider domain, comprising a curated literature corpus together with dedicated
retrieval and answer-generation
benchmarks covering major detector and physics research topics. Extensive evaluation shows that hybrid
retrieval provides the strongest
retrieval backbone, while agentic
reasoning is most effective for controlled evidence expansion and answer synthesis. Built on this principle, agentic hybrid RAG consistently outperforms representative
retrieval and RAG baselines in
retrieval effectiveness, answer quality, evidence coverage, and factual grounding. Together, the
benchmark and framework provide a foundation for evidence-grounded scientific question answering and future HEP analysis
agents operating over large-scale scientific literature. Code is available at \href{https://github.com/AItutorialjrb/RAG_
muon_JINST}{this URL}.
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All authors Ruobing Jiang, Dawei Fu, Cheng Jiang, Tianyi Yang, Zijian Wang, Youpeng Wu, Yong Ban, Yajun Mao, Qiang Li
Computational Physics
Flow-based generative models for amortized Bayesian inference in regression and inverse PDE problems
Shaoqian Zhou, Ling Guo and Xuhui Meng
Bayesian inference provides a principled framework for uncertainty quantification in scientific machine learning. However, conventional
Bayesian approaches usually require solving a new inference problem for each observation set, causing substantial computational costs that hinder real-time applications like online monitoring and digital twins. Furthermore, inferring over infinite-dimensional function spaces with varying observation sets poses major challenges for existing amortized inference methods. In this work, we propose Flow-ABI, a flow-based generative framework for amortized
Bayesian inference in regression and inverse partial differential equation (PDE) problems. It consists of two components: (i) a functional prior model that learns expressive priors from historical data and physical knowledge through flow matching, and (ii) a set-conditioned functional posterior sampler mapping observation sets to functional posterior distributions. The learned posterior model naturally accommodates varying, permutation-invariant observation sets, and generalizes across different observation discretizations. Once trained, Flow-ABI enables near-real-time posterior sampling for previously unseen observations without retraining or iterative optimization. The proposed methodology can be seamlessly integrated with a wide class of scientific machine learning frameworks, including physics-informed neural networks and neural operators, for uncertainty-aware inverse PDE modeling. Experiments demonstrate that Flow-ABI accurately captures both Gaussian and non-Gaussian posterior distributions while achieving over two-order-of-magnitude speedups relative to the gold-standard
Bayesian inference method,
Hamiltonian Monte Carlo. These results show Flow-ABI is an effective, scalable, and computationally efficient framework for uncertainty quantification in scientific machine learning.
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Computational Physics
A Physics-Informed B-Spline Framework for Continuous Approximation of Flow Data
Junoh Jung, David Lenz, Emil Constantinescu et al. (+1 more)
Continuous approximations of flow data are useful for downstream analysis, differentiation, and visualization, but purely data-driven reconstructions do not, in general, preserve the governing physics. This limitation becomes particularly important when input data are physically inconsistent, whether due to low-fidelity discretizations or unmodeled discrepancies. In such cases, reconstructed fields may exhibit inaccurate PDE residuals, violated balance laws, or unreliable derived quantities. To address this, we propose a physics-informed B-spline framework that embeds physical constraints directly into the reconstruction process. The method constructs compact, continuously differentiable representations of discrete fields using tensor-product B-splines and determines spline control points by solving an optimization problem balancing data fidelity with residuals of the governing PDEs, alongside initial and boundary conditions. Leveraging exact analytical derivatives of the B-spline basis enables efficient and accurate evaluation of physical residuals without storing full-resolution fields. We refer to this approach as physics-informed multivariate functional approximation (PI-MFA). Numerical studies on the 1D convection-
diffusion, 2D coupled Burgers, and 2D incompressible Navier-Stokes equations show PI-MFA reduces PDE residuals and improves global balance-law consistency. Compared with standard and regularized MFA, PI-MFA produces more physically faithful reconstructions and, for physically inconsistent data, lower approximation errors, while offering computational advantages over tested physics-informed neural networks. Overall, PI-MFA preserves the compactness, local support, and exact differentiability of classical spline spaces while producing reliable continuous flow fields for scientific analysis and visualization.
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All authors Junoh Jung, David Lenz, Emil Constantinescu, Tom Peterka
Optics · Cross-listed from quant-ph
Optomechanical system with tunable dissipative and dispersive couplings
Quansen Wang, Yuefan Wu, Doudou Wang et al. (+4 more)
We demonstrate an optomechanical system with tunable dissipative and dispersive couplings using a Fabry-Perot cavity and a string mechanical resonator. By varying the diameter and material of the mechanical resonator, and the relative location between the mechanical resonator and the cavity, the relative strengths of dissipative and dispersive coupling could be tuned continuously from dissipation-dominated regime to dispersion-dominated regime. In our experiments, the dissipative-to-dispersive coupling ratios of 1.3 and 0.6 are achieved by using two different mechanical resonators, corresponding to a transition from dissipation-dominated to dispersion-dominated optomechanical system. Theoretically, the coupling ratio could be tuned from 25 to 0.02 by optimizing the mechanical resonator, spanning over three orders of magnitude. These two distinct coupling regimes are achieved with the same experimental platform. The capability to freely adjust the coupling ratio provides a versatile platform for exploring
quantum effects of massive mechanical resonators and
quantum-limited measurements.
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All authors Quansen Wang, Yuefan Wu, Doudou Wang, Genyuan Xu, Jiawei Liang, Qiang Zhang, Yongmin Li
Plasma Physics
DKEKAN: A single-parameterized KAN surrogate for Drift Kinetic Equation Toward Fast Neoclassical Toroidal Viscosity Torque Modeling in Tokamaks
Jinpeng Huang, Xingting Yan, Mingyu Zhang et al. (+5 more)
The neoclassical toroidal viscosity (NTV) torque is a critical driver of toroidal rotation in tokamaks, profoundly influencing
plasma stability and performance. Consequently, incorporating NTV effects is essential for modern integrated modeling frameworks that aim to self-consistently unify multiple physical processes. However, the high computational cost of NTV modeling precludes its self-consistent integration within such frameworks. This bottleneck arises because NTV calculation requires solving its governing equation–the drift kinetic equation (DKE)–in high-dimensional phase space. To address this issue, this study develops DKEKAN, a single-parameterized Kolmogorov-Arnold Network (SKAN) surrogate for solving DKE, to realize fast NTV modeling in tokamaks. The research process consists of the following steps: Firstly, a large
dataset mapping DKE equation parameters to solutions is generated based on first-principle simulations under
plasma parameters of the Experimental Advanced Superconducting Tokamak (EAST); Secondly, a surrogate model for solving DKE is developed based on the SKAN framework, which also incorporates a modular expert network design; Finally, the DKEKAN surrogate model is integrated with the NTV modeling framework to realize fast NTV calculation. With its physics-grouped expert layer and SKAN backbone, DKEKAN outperforms the tested MLP, KAN, and neural-operator baselines in overall prediction accuracy, while reducing the standalone DKE-solving time from 35.85s to 3.74s, corresponding to a speedup of approximately 9.6x, and reducing the total coupled NTVTOK runtime from 38.24s to 5.58s, corresponding to an overall speedup of approximately 6.9x. This work effectively overcomes the computational bottleneck in NTV simulations, thus supporting further integrated modeling that incorporates NTV effects.
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All authors Jinpeng Huang, Xingting Yan, Mingyu Zhang, Nana Bao, Zixuan Song, Yuetao Meng, Weiyong Zhou, Youwen Sun
Computational Physics · Cross-listed from cs.LG
LLM-Guided Neural Architecture Search for Robust Co-Design of Physical Neural Networks
Tyler King and Timothee Leleu
Deploying neural networks on unconventional hardware demands architectures that co-optimize task accuracy and platform-specific constraints such as energy cost, physical non-idealities, and numerical precision. Existing neural architecture search (NAS) methods are typically tailored to a single hardware family, limiting cross-platform comparison and generalization. We introduce Unconventional Hardware Neural Architecture Search (UH-NAS), a hardware-agnostic, LLM-guided NAS framework that integrates
language models as evolutionary operators to co-optimize accuracy and inference energy. By exposing hardware as a swappable backend with per-platform energy models, physical constraints, and non-ideality simulators, UH-NAS enables fair system-level comparisons across various backends without modifying the search
algorithm. Tested on optical MZI hardware, UH-NAS discovers more diverse, robust architectures than conventional baselines while outperforming existing LLM-to-NAS approaches. Additional ablations on architecture robustness under non-idealities and the role of system
prompts highlight the importance of architecture-hardware co-design for emerging computing platforms.
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Optics
Unidirectional-like Edge Transport Induced by Non-Hermitian Skin Effects
Junyi Rao, Jinting Ding, Qinghua Guo et al. (+2 more)
Non-Hermitian skin effects (NHSEs) enable dramatic boundary accumulation of waves, yet their experimental realization typically demands engineered nonreciprocity or spatially patterned loss. Here we demonstrate theoretically and experimentally that uniform loss provides a simple and previously overlooked mechanism for enforcing unidirectional-like edge transport in photonic
crystals (PhCs) that breaks time-reversal
symmetry in the presence of nonchiral edge states. Using a core cladding geometry where domains share identical Chern numbers but possess distinct bulk polarizations, we show that uniform loss activates NHSEs that reshape the spectral
topology of edge bands, giving rise to point gap windings that dictate a one way propagation. Near field measurements confirm that loss converts intrinsically bidirectional interface states into a unidirectional-like circulation around the entire domain wall, showing excellent agreement with theory. Our results establish uniform loss as a universal and structurally simple route for achieving unidirectional-like wave transport.
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All authors Junyi Rao, Jinting Ding, Qinghua Guo, Jun He, Xiang Ni
Plasma Physics
First Principles Magnetohydrodynamical Theory for the Expanding Box Model: Effects on Expansion-Induced Alfvén Wave Reflection
Sebastián Saldivia, Nicolás Villarroel-Sepúlveda, Sebastián Echeverría-Veas et al. (+2 more)
The Expanding Box Model (EBM) has been widely employed to simulate multiscale
plasma phenomena in the expanding
solar wind by transforming the MHD equations to a co-moving, non-inertial frame. However, traditional formulations have suffered from historical ambiguity regarding the physical separation between the co-moving and inertial reference frames, primarily arising from a classical approximation of an invariant
magnetic field between them. To resolve this inconsistency, we reformulate the EBM from first principles using a fully covariant approach. Here, we model the expanding
solar wind frame as an anisotropic expanding spacetime metric, allowing us to incorporate radial acceleration profiles and differential transverse expansion, ensuring that all physical fields are correctly transformed by expansion. We demonstrate that asymmetries identified in previous EBM-MHD literature are direct consequences of neglecting the tensorial scaling of the
magnetic field. Our covariant treatment eliminates these residues, restoring
symmetry in the co-moving frame. Projecting our system back into the inertial frame clarifies the distinction between local
plasma dynamics and
plasma expansion, revealing the anisotropy of the Parker spiral as a
geometric projection. Furthermore, linear wave analysis using Elsässer variables reveals that
plasma expansion induces a low-frequency cutoff and
geometric damping. Numerical integration demonstrates that expansion drives the reflection of Alfvén waves, generating counter-propagating modes primarily at low frequencies relative to the expansion rate, while high frequencies converge to the WKB approximation. This provides a consistent foundation for simulations, establishing that expansion can serve as a source of counter-propagating waves necessary to drive
solar wind
turbulence at low frequencies.
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All authors Sebastián Saldivia, Nicolás Villarroel-Sepúlveda, Sebastián Echeverría-Veas, Felipe A. Asenjo, Pablo S. Moya
Atomic and Molecular Clusters
Rainbow RABBITT as a Probe of Coherent Rabi Dynamics
Vladislav V. Serov and Anatoli S. Kheifets
Attosecond pulse trains interacting with a resonantly dressed atom generate a pronounced intra-sideband phase structure that remains hidden in conventional spectrally integrated RABBITT measurements. Using ab initio time-dependent Schrödinger equation calculations for lithium near the resonant $2s\to2p$ transition, we show that the phase extracted within a single sideband can vary by nearly $\pi$ across its spectral width. The resulting intra-sideband phase dispersion exhibits a characteristic dependence on the IR detuning, pulse duration, intensity, and sideband order. Most strikingly, exact resonant Rabi flopping flattens the intra-sideband phase dispersion, whereas a small detuning generates a pronounced phase modulation despite weaker population transfer. This counterintuitive behavior demonstrates that rainbow RABBITT probes the dynamical phase accumulated by a Rabi-dressed wave packet rather than the instantaneous populations of the participating states. A simple analytical model captures the principal features of the numerical calculations and provides physical insight into the emergence of the intra-sideband phase structure. These results establish intra-sideband phase dispersion as a new interferometric observable for mapping coherent Rabi dynamics.
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Applied Physics
Fast-Neutron Irradiation Effect in Heteroepitaxial $\beta$-Ga$_2$O$_3$ Schottky Diodes Fabricated on Low-Cost Sapphire Substrates
Saleh Ahmed Khan, Ahmed Ibreljic, Sourav Sarker et al. (+2 more)
In this work, we investigate the response of Ni/$\beta$-Ga$_2$O$_3$ Schottky barrier diodes fabricated on c-plane sapphire to fast-
neutron irradiation up to a fluence of $1\times10^{15}$ n$\cdot$cm$^{-2}$. The LPCVD-grown heteroepitaxial structure consists of an unintentionally doped buffer, an n$^{+}$ contact layer, and an n-type drift layer, with mesa isolation realized by
plasma-free Ga-assisted LPCVD etching. Prior to irradiation, the devices exhibit a turn-on voltage of 1.20 V, specific on-resistance of 8.43 m$\Omega\cdot$cm$^2$, ideality factor of 1.32, and Schottky barrier height of 1.29 eV. Following irradiation, the devices remain operational, although the forward current decreases, the turn-on voltage increases to 2.40 V, and the barrier height increases to 1.34 eV. Capacitance-voltage measurements reveal a $\sim$50% reduction in net donor concentration, corresponding to a carrier-removal rate of $\sim$105 cm$^{-1}$. Temperature-dependent measurements from 25 to 250 $^\circ$C confirm that thermionic emission remains the dominant transport mechanism and show significant suppression of reverse leakage current after irradiation. The breakdown voltage increases from 101 to 135 V, consistent with
neutron-induced donor compensation. TCAD simulations show a more uniform electric-field distribution and reduced field crowding at the Schottky edge after irradiation. These results provide insight into
neutron-induced donor compensation in heteroepitaxial $\beta$-Ga$_2$O$_3$ and demonstrate the ability of LPCVD-grown $\beta$-Ga$_2$O$_3$ Schottky diodes on sapphire to maintain stable operation under high-fluence
neutron environments relevant to space and
nuclear electronics.
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All authors Saleh Ahmed Khan, Ahmed Ibreljic, Sourav Sarker, Stephen Margiotta, Anhar Bhuiyan