Applied Physics
Engineering Spatial Dispersion to Synthesize Arbitrary Spatial Filters Based on Metagratings
Jinyong Kim and Minseok Kim
This paper presents a design framework for synthesizing angularly selective spatial filters using non-uniform metagratings. While traditional metagratings focus on channeling energy into higher-order Floquet modes for a fixed incidence angle, we leverage the fundamental mode as a versatile degree of freedom to engineer spatial dispersion over a continuous angular spectrum. By strategically distributing non-uniformly loaded metallic wires and rigorously modeling their mutual interactions through an impedance-
matrix formulation, we realize prescribed angular transfer functions with high efficiency. In particular, the framework is validated at 3.5 GHz through full-wave simulations of (i) low-pass, (ii) high-pass, and (iii) all-pass spatial filters. The results demonstrate that fundamental-mode engineering in non-uniform metagratins offers a highly efficient platform for advanced spatial wave manipulation.
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Classical Physics · Cross-listed from cond-mat.soft
Multiple charge carrier species as a possible cause for triboelectric cycles
Juan Carlos Sobarzo and Scott Waitukaitis
The tendency of materials to order in triboelectric series has prompted suggestions that contact electrification might have a single, unified underlying description. However, the possibility of triboelectric cycles, i.e. series that loop back onto themselves, is seemingly at odds with such a coherent description. In this work, we propose that if multiple charge carrying species are at play, both triboelectric series and cycles are possible. We show how series arise naturally if only a single charge carrier species is involved and if the driving mechanism is approach toward thermodynamic
equilibrium, and simultaneously, that cycles are forbidden under such conditions. Suspecting multiple carriers might relax the situation, we affirm this is the case by explicit construction of a cycle involving two carriers, and then extend this to show how more complex cycles emerge. Our work highlights the importance of series/cycles towards determining the underlying mechanism(s) and carrier(s) in contact electrification.
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Fluid Dynamics
Development of strongly nonlinear structures at the charged boundary of a non-conducting liquid in an electric field
N.M. Zubarev and E.A. Kochurin
Direct numerical simulation of the strongly nonlinear stages of instability development for a non-conducting
liquid with a charged free surface in a normal electric field is performed. It is demonstrated that two main stages of the instability can be distinguished: an initial stage, during which dimples appear on the surface, and a developed stage, during which these dimples transform into expanding bubbles. The bubble size increases with increasing applied field, despite the fact that the scale corresponding to the dominant mode of the instability decreases.
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Biological Physics
Intermediate physical interactions induce spatiotemporal dynamics in Turing patterns
Cathelijne ter Burg and David Zwicker
Turing patterns are a central paradigm for describing spatial patterns in nature. The corresponding theory of reaction-
diffusion dynamics combines ideal
diffusion with nonlinear reactions, resulting in patterns when species diffuse at different rates and reactions are sufficiently nonlinear. However, real systems are more complex and particularly involve physical interactions between constituents. While such interactions can promote patterns, we here show that they can also induce dynamic, chaotic patterns. These patterns exhibit well-defined length and time scales, which result from cycles of droplet coarsening and fission. The dynamical patterns combine properties of traditional Turing patterns and chemically active droplets, which emerge for strong physical interactions. Our analysis thus reveals three qualitatively different regimes that emerge when two components interact physically and undergo nonlinear reactions.
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Atomic Physics
Spectroscopy of $^4$He at 0.25 ppt Uncertainty and Improved Alpha-Helion Charge-Radius Difference Determination
K. Steinebach, J. C. J. Koelemeij, H. L. Bethlem et al. (+1 more)
High-precision spectroscopy of simple atomic systems can be used to advance the theory of atomic energy levels but can also serve as a sensitive probe of
nuclear charge radii. For this last purpose, we report an improved measurement of the $2\,^3{S}_1 \to 2\,^1{S}_0$ transition frequency in $^4$He with 48 Hz uncertainty (0.25 ppt), using a Bose-Einstein condensed sample confined in a magic-wavelength optical dipole trap. A systematic Doppler shift from condensate motion is suppressed by time-resolved ion detection, and the transition frequency is calibrated via a White Rabbit link to a remote active hydrogen maser clock. Combined with previous $^3$He measurements and improved theory, we obtain the most precise determination to date of the charge-radius difference between the helion and alpha particle ($r_{h}^2 -r_{\alpha}^2$) of $1.0676(10)\text{fm}^2$. This is consistent with other recent determinations and confirms that the current discrepancy between QED theory and experimentally observed ionization energies of excited states in helium is not apparent in the isotope shift.
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All authors K. Steinebach, J. C. J. Koelemeij, H. L. Bethlem, K. S. E. Eikema
Optics
Engineering Photoluminescence with Mie Voids
Yuchao Fu, Ilia Lykov, Sergejs Boroviks et al. (+5 more)
Spontaneous emission, as a fundamental radiative process and a versatile information carrier, plays a vital role in light-emitting devices, optical information modulation and encryption, super-resolution fluorescence imaging. Engineering the photonic environment surrounding
photon emitters enables control over their emission properties. However, simultaneously achieving precise engineering of both excitation enhancement and
quantum-yield modulation at the nanoscale remains elusive, highlighting substantial room for advancing the precise orchestrating of photoluminescence. Here, we introduce silicon Mie voids - air-defined cavities that invert the conventional solid-particle geometry - to achieve independent tuning of photoluminescence within a single subwavelength unit, while minimizing optical losses. Full-wave simulations and experiments on both gradient and uniform Mie-void arrays jointly validate this quantitative framework for spontaneous emission tuning, which disentangles excitation enhancement arising from local field confinement in air and
quantum-yield enhancement resulting from strengthened emitter-resonator coupling, while confirming the accelerated radiative decay enabled by the modified optical LDOS. Leveraging this flexible mechanism, we realize a
multimodal nanophotonic pattern with near-diffraction-limited pixels that encode the EPFL logo in the bright field and the SJTU logo in both dark field and photoluminescence maps. These results establish Mie voids as a powerful platform for high-density
multimodal encrypted displays and open new avenues for advancing state-of-the-art nanophotonic devices.
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All authors Yuchao Fu, Ilia Lykov, Sergejs Boroviks, Nai-Quan Zhu, Tianyue Li, Siarhei Zavatski, Makhlad Chahid, Olivier J. F. Martin
Optics
De-occluding broadband metalens
Seungwoo Yoon, Dohyun Kang, Eunsue Choi et al. (+9 more)
Obstructions such as raindrops, fences, or
dust degrade captured images, especially when mechanical cleaning is infeasible. Conventional solutions to obstructions rely on a bulky compound optics array or computational inpainting, which compromise compactness or fidelity. Metalenses composed of subwavelength meta-atoms promise compact imaging, but simultaneous achievement of broadband and obstruction-free imaging remains a challenge, since a metalens that images distant scenes across a broadband spectrum cannot properly defocus near-depth occlusions. Here, we introduce a learned split-spectrum metalens that enables broadband obstruction-free imaging. Our approach divides the spectrum of each RGB channel into pass and stop bands with multi-band spectral filtering and learns the metalens to focus light from far objects through pass bands, while filtering focused near-depth light through stop bands. This optical signal is further enhanced using a neural network. Our learned split-spectrum metalens achieves broadband and obstruction-free imaging with relative PSNR gains of 32.29% and improves object detection and semantic
segmentation accuracies with absolute gains of +13.54% mAP, +48.45% IoU, and +20.35% mIoU over a conventional
hyperbolic design. This promises robust obstruction-free sensing and
vision for space-constrained systems, such as mobile
robots, drones, and endoscopes.
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All authors Seungwoo Yoon, Dohyun Kang, Eunsue Choi, Sohyun Lee, Seoyeon Kim, Minho Choi, Hyeonsu Heo, Dong-ha Shin, Suha Kwak, Arka Majumdar, Junsuk Rho, Seung-Hwan Baek
Plasma Physics
Sensitivity of External Magnetic Field on the Change in Cross-section of a Toroidal Current
Suman Aich, Joydeep Ghosh, Rakesh L. Tanna et al. (+3 more)
Due to any toroidal current column, the
magnetic field is found to be sensitive as well as insensitive to its cross-sectional area depending on location of subject point, as predicted by numerical approaches [S. Aich, J. Thakkar, and J. Ghosh,
Plasma Fusion Res. 17, 2403055 (2022)], and hence the presence of an angle of invariance is found to be present for any toroidal geometry. Present study aims to validate those numerical observations using the measured
magnetic field due to Aditya Upgrade tokamak
plasma.
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All authors Suman Aich, Joydeep Ghosh, Rakesh L. Tanna, D. Raju, Sameer Kumar, Aditya-U team
Data Analysis and Statistics · Cross-listed from quant-ph
Mikado strategy for the detection of atoms in images of microtrap arrays
Marc Cheneau and François Goudail
Building on top of our recent work [arXiv:2502.08511], we introduce a new strategy to solve the problem of detecting atoms in high-resolution images of microtrap arrays. By alternating estimation and detection steps, we get rid of the need for an explicit model to compute the posterior occupancy probability of each site given its a priori optimal estimate. As direct benefits, we show an improved detection accuracy compared to our previous work when the sites are not optically well resolved, and we expect a greater robustness against real experimental conditions.
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Fluid Dynamics
Inertial effects on the interphase drag force and rheology of dilute suspensions of buoyant droplets at low Reynolds number
Nicolas Fintzi and Jean-Lou Pierson
In this work, we compute the hydrodynamic force and the first and second moments of force acting on a translating spherical droplet immersed in a uniform flow using the reciprocal
theorem. We consider the low but finite Reynolds number regime, $Re = a U \rho_f / \mu_f$, and the dilute limit of small droplet volume fraction $\phi$. Here, $U$ denotes the magnitude of the relative velocity between the phases, $a$ the droplet radius, and $\rho_f$ and $\mu_f$ the density and viscosity of the continuous phase, respectively. We show that the $O(Re)$ inertial corrections to the first and second moments of force scale as $O(\rho_f \phi U^2)$ and $O(a\rho_f\phi U^2)$, respectively. Equivalently, in dimensionless form, these corrections scale as O(\phi Re) and O( R a \phi Re), where R denotes the macroscopic length scale. Moreover, the ensemble average of the drag force and the higher-order force moments over the distribution of droplet velocities introduces additional contributions proportional to the velocity variance of the dispersed phase, both in the interphase momentum exchange and in the effective stress of the continuous phase. As a consequence, in dilute emulsions of buoyant droplets, the effective stress depends quadratically on the relative velocity between the phases, on the velocity variance of the dispersed phase, and on the spatial gradients of these quantities. Finally, we consider a steady-state pipe flow to examine how the force moments derived in this study affect the behaviour of the two-phase flow in this particular configuration.
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Physics and Society · Cross-listed from q-fin.TR
Directional Liquidity and Geometric Shear in Pregeometric Order Books
João P. da Cruz
We introduce a structural framework for the geometry of financial order books in which liquidity, supply, and demand are treated as emergent observables rather than primitive
market variables. The
market is modeled as a relational substrate without assumed metric, temporal, or price coordinates. Observable quantities arise only through observation, implemented here as a reduction of relational degrees of freedom followed by a low-dimensional spectral projection. A one-dimensional projection induces a price-like coordinate and a projected liquidity density around the mid price, from which bid and ask sides emerge as two complementary restrictions. We show that directional liquidity imbalances decompose naturally into a rigid drift of the projected density and a
geometric shear mode that deforms the bid–ask structure without inducing price motion. Under a minimal single-scale hypothesis, the shear geometry constrains the projected liquidity to a gamma-like functional form, appearing as an integrated-gamma profile in discrete data. Empirical analysis of high-frequency Level~II data across multiple U.S. equities confirms this geometry and shows that it outperforms standard alternative cumulative models under explicit model comparison and residual diagnostics.
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Fluid Dynamics
Divergence-Free Diffusion Models for Incompressible Fluid Flows
Wilfried Genuist, Éric Savin, Filippo Gatti et al. (+1 more)
Generative
diffusion models are extensively used in unsupervised and self-supervised machine learning with the aim to generate new samples from a probability distribution estimated with a set of known samples. They have demonstrated impressive results in replicating dense, real-world contents such as images, musical pieces, or human
languages. This work investigates their application to the numerical simulation of incompressible fluid flows, with a view toward incorporating physical constraints such as incompressibility in the probabilistic
forecasting framework enabled by generative networks. For that purpose, we explore different conditional, score-based
diffusion models where the divergence-free constraint is imposed by the Leray spectral projector, and autoregressive conditioning is aimed at stabilizing the forecasted flow snapshots at distant time horizons. The proposed models are run on a
benchmark turbulence problem, namely a Kolmogorov flow, which allows for a fairly detailed analytical and numerical treatment and thus simplifies the evaluation of the numerical methods used to simulate it. Numerical experiments of increasing complexity are performed in order to compare the advantages and limitations of the
diffusion models we have implemented and appraise their performances, including: (i) in-distribution assessment over the same time horizons and for similar physical conditions as the ones seen during training; (ii) rollout predictions over time horizons unseen during training; and (iii) out-of-distribution tests for
forecasting flows markedly different from those seen during training. In particular, these results illustrate the ability of
diffusion models to reproduce the main statistical characteristics of Kolmogorov
turbulence in scenarios departing from the ones they were trained on.
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All authors Wilfried Genuist, Éric Savin, Filippo Gatti, Didier Clouteau
Optics
Scaling of broadband Ho:CALGO regenerative amplifier to multi-mJ pulse energy
Anna Suzuki, Michael Müller, Sergei Tomilov et al. (+1 more)
We report on energy scaling of a 2.08-{\mu}m wavelength regenerative amplifier (RA) system based on the broadband gain material Ho:CaAlGdO4 (CALGO) to multi-mJ pulse energy at kHz repetition rates. Compared to previous reports, energy scaling was enabled thanks to an upgraded seed
laser with a higher fluence and better spectral overlap to the gain spectrum of Ho:CALGO, which increased amplification efficiency. Bifurcation-free energy extraction was investigated experimentally and numerically for various repetition rates. A stable output was obtained at 10 W average power for repetition rates of 30 kHz and above. In addition, stable 3.4-mJ energy extraction was achieved at a 1-kHz repetition rate. We discuss the further scaling potential of pulse energy and pulse duration.
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All authors Anna Suzuki, Michael Müller, Sergei Tomilov, Clara J. Saraceno
Fluid Dynamics
Physics-Informed Transformer operator for the prediction of three-dimensional turbulence
Zhihong Guo, Sunan Zhao, Huiyu Yang et al. (+2 more)
Data-driven
turbulence prediction methods often face challenges related to data dependency and lack of physical interpretability. In this paper, we propose a physics-informed
Transformer operator (PITO) and its implicit variant (PIITO) for predicting three-dimensional (3D)
turbulence, which are developed based on the
vision Transformer (ViT) architecture with an appropriate patch size. Given the current flow field, the
Transformer operator computes its prediction for the next time step. By
embedding the large-eddy simulation (LES) equations into the loss function, PITO and PIITO can learn solution operators without using labeled data. Furthermore, PITO can automatically learn the subgrid scale (SGS) coefficient using a single set of flow data during training. Both PITO and PIITO exhibit excellent stability and accuracy on the predictions of various statistical properties and flow structures for the situation of long-term extrapolation exceeding 25 times the training horizon in decaying homogeneous isotropic
turbulence (HIT), and outperform the physics-informed
Fourier neural operator (PIFNO). Furthermore, PITO exhibits a remarkable accuracy on the predictions of forced HIT where PIFNO fails. Notably, PITO and PIITO reduce GPU
memory consumption by 79.5% and 91.3% while requiring only 31.5% and 3.1% of the parameters, respectively, compared to PIFNO. Moreover, both PITO and PIITO models are much faster compared to traditional LES method.
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All authors Zhihong Guo, Sunan Zhao, Huiyu Yang, Yunpeng Wang, Jianchun Wang
Chemical Physics · Cross-listed from cond-mat.soft
On the Determination of Gel Points
Kazumi Suematsu, Haruo Ogura, Seiichi Inayama et al. (+1 more)
A critical composition of cross-linked polysiloxanes observed by Scanlan and Winter is reinvestigated in comparison with the theory of gelation. We assume, based on the Scott findings, the
geometric distribution for one of the monomers, divinyl-terminated poly(dimethylsiloxane). Calculation results show that the two theories are in near-consistency, supporting the Scanlan-Winter estimation based on the linear viscoelastic theory. On the other hand, there is a disturbing result that calculation using the mean molecular weight, $M_{n}$, leads to exact agreement between the two theories, suggesting that the distribution is in effect monodisperse, contrary to the assumed
geometric one and also the observed polydispersity, $M_w/M_n=2.1$. Further experimental studies employing monodisperse monomers would be highly valuable to consolidate the bridge between these two fundamental theories.
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All authors Kazumi Suematsu, Haruo Ogura, Seiichi Inayama, Toshihiko Okamoto
Chemical Physics · Cross-listed from quant-ph
Beyond Photon Shot Noise: Chemical Limits in Spectrophotometric Precision
Georg Engelhardt, Dahai He and JunYan Luo
In this work, we investigate precision limitations in spectrophotometry (i.e., spectroscopic concentration measurements) imposed by chemical processes of molecules. Using the recently developed
Photon-resolved Floquet theory, which generalizes Maxwell-Bloch theory for higher-order measurement statistics, we analyze a molecular model system subject to chemical reactions whose electronic and optical properties depend on the chemical state. Analysis of sensitivity bounds reveals: (i) Phase measurements are more sensitive than intensity measurements; (ii) Sensitivity exhibits three regimes:
photon-shot-noise limited, chemically limited, and intermediate; (iii) Sensitivity shows a turnover as a function of reaction rate due to the interplay between coherent electronic dynamics and incoherent chemical dynamics. Our findings demonstrate that chemical properties must be considered to estimate ultimate precision limits in optical spectrophotometry.
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Atomic Physics
Broadband Heterodyne Microwave Detection using Rydberg Atoms with High Sensitivity
Hsuan-Jui Su, Shao-Cheng Fang, Ting-An Li et al. (+3 more)
We present a Rydberg atom-based microwave electric field sensor that achieves extended dynamic range and enhanced sensitivity across a broad bandwidth. By characterizing the Autler-Townes (AT) splitting induced by a single-tone microwave field, we demonstrate a spectroscopic method that simultaneously extracts both the microwave frequency and electric field strength directly from the splitting pattern. We implement dual-tone heterodyne detection, achieving a minimum detectable field strength on the order of uV/cm and a sensitivity in the sub-uV/cm/Hz^1/2 regime, while extending the operational bandwidth up to 3 GHz. Through systematic characterization of frequency and power dependencies, we identify optimal operating conditions to minimize power broadening in the resonant AT regime and maximize sensitivity in the far-off-resonance AC Stark regime. The resulting platform combines high sensitivity, broad bandwidth, and a dynamic range of approximately 90 dB, establishing Rydberg atoms as practical sensors for precision electric field metrology.
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All authors Hsuan-Jui Su, Shao-Cheng Fang, Ting-An Li, Chen-Hao Chang, Yu-Chi Chen, Yi-Hsin Chen
Atmospheric and Oceanic Physics
Spread/Error relationship and spatial error structure of precipitation ensemble nowcasting: Comparison of STEPS and generative AI
Martin Bonte, Lesley De Cruz, Fabian Debal et al. (+1 more)
The predictability of the generative AI-based nowcasting model LDCast (trained on another region) is evaluated over Belgium, together with the pysteps implementation of the nowcasting
algorithm STEPS. STEPS and LDCast are slightly underdispersive, but the ensemble spread provides an estimation of the error at almost all scales. Both models adapt the properties of their ensembles to the type of event, either convective or stratiform. The spatial scores of the STEPS and LDCast ensembles are compared with those of surrogate ensembles having some key properties, revealing that both STEPS and LDCast have very little ability to spatially localise the ensemble mean error vector through their ensemble members. This suggests that the content of STEPS and LDCast ensembles is informative in terms of statistics, but not in terms of dynamics.
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All authors Martin Bonte, Lesley De Cruz, Fabian Debal, Stéphane Vannitsem
Optics · Cross-listed from cond-mat.mes-hall
Ultrastrong light-matter coupling in near-field coupled split-ring resonators revealed by photocurrent spectroscopy
Jing Huang, Jinkwan Kwoen, Yasuhiko Arakawa et al. (+2 more)
Landau polaritons arising from the coupling between cyclotron resonance and terahertz split-ring resonators (SRRs) have served as a central platform for exploring ultrastrong light-matter interaction for more than a decade. Over this period, a wide variety of SRR architectures, differing in size, geometry, and even material composition, have been investigated. However, the regime of near-field coupled SRRs has remained largely unexplored. Here, we demonstrate ultrastrong coupling using photocurrent spectroscopy in two prototypical near-field configurations: a SRR dimer and a topological SRR chain. The measurements reveal hybridization not only with bright resonant modes but also with optically dark modes and topological edge modes, highlighting the exceptional sensitivity of the photocurrent spectroscopy. Moreover, the engineered near-field interactions allow the study of multi-mode ultrastrong coupling and the interplay between topological band structure and cavity
quantum electrodynamics.
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All authors Jing Huang, Jinkwan Kwoen, Yasuhiko Arakawa, Kazuhiko Hirakawa, Kazuyuki Kuroyama
Plasma Physics
Magnetic Compression of Compact Tori Experiment and Simulation
Carl Dunlea
The
magnetic compression experiment at General Fusion was a repetitive non-destructive test to study
plasma physics applicable to
magnetic target fusion compression. A compact
torus (CT) is formed with a co-axial gun into a containment region with an hour-glass shaped inner flux conserver, and an insulating outer wall. External coil currents keep the CT off the outer wall (radial levitation) and then rapidly compress it inwards. The optimal external coil configuration greatly improved both the levitated CT lifetime and the recurrence rate of shots with good compressional flux conservation. As confirmed by spectrometer data, the improved levitation field profile reduced
plasma impurity levels by suppressing the interaction between
plasma and the insulating outer wall during the formation process. Significant increases in
magnetic field, electron density, and ion temperature were routinely observed at
magnetic compression in the final external coil configuration tested, despite the prevalence of an instability, thought be an external kink mode, at compression. Matching the decay rate of the levitation currents to that of the CT currents resulted in a reduced level of MHD activity associated with unintentional compression by the levitation field, and a higher probability of long-lived CTs. The DELiTE (Differential Equations on Linear Triangular Elements) framework was developed for spatial discretisation of partial differential equations on an unstructured triangular grid in axisymmetric geometry. The framework is based on discrete differential operators in
matrix form, which are derived using linear finite elements and mimic some of the properties of their continuous counterparts. A single-fluid two-temperature MHD model is implemented in this framework.
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Atmospheric and Oceanic Physics
Continued activity of the 25th cycle: largest in 20 years. Ground-level enhancement and Forbush decrease
B.Sargsyan and A.Chilingarian
After a very calm 24th
solar activity cycle, the 25th cycle has already seen several interesting events. A Ground Level Enhancement GLE77 was observed on 11 November 2025 following an X5.1 class
solar flare. A strong Forbush decrease occurred on 19 and 20 January 2026 during one of the most intense geomagnetic storms of
Solar Cycle 25. Events were recorded coherently by the global
neutron monitor network and by SEVAN detectors at multiple altitudes. Using spectrometric capabilities, we reconstruct energy spectra of missing
neutrons and
muons during the FD and compare them with corresponding spectra measured during GLE77. The analysis demonstrates that FD and GLE signatures are intrinsically asymmetric. FDs selectively suppress the preexisting
galactic cosmic ray population, whereas GLEs introduce an additional, harder particle component.
Neutron and
muon channels exhibit markedly different spectral behavior, particularly at higher deposited energies, reflecting their sensitivity to different primary energy ranges. These results show that combined NM and SEVAN observations provide robust, complementary diagnostics of
rigidity dependent
cosmic ray modulation during extreme heliospheric disturbances.
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Atmospheric and Oceanic Physics · Cross-listed from hep-ex
Cosmic Rays as an Interdisciplinary Earth Observation Tool: From Particle Physics and Atmospheric Processes to Geosciences and Urban Science
Bugra Bilin and Nuhcan Akçit
The exploration of
cosmic rays, which are high-energy particles originating from space and the atmosphere, has historically been associated with particle physics and astrophysics. In the last 20 years, these particles have evolved into valuable tools for observing Earth's systems. This review compiles the use of
cosmic rays in three primary areas: (1) particle physics and atmospheric processes, which include
cosmic- ray-induced cascades, ionization, and their impact on atmospheric chemistry and radiation; (2) geosciences, where cosmogenic radionuclides assist in the dating of geological materials and
cosmic-ray
neutrons are used for large-scale monitoring of soil moisture and snow water equivalents; and (3) urban science, where
cosmic- ray
muons are employed for non-invasive subsurface imaging and, when paired with distributed sensors, serve as the basis for smart city monitoring. This review places particular emphasis on integrating these methods with remote sensing and geographic information systems (GIS), which helps close the persistent scale gap between point measurements and satellite observations, thereby enabling three-dimensional digital representations of subsurfaces. This review concludes by discussing data standards, their integration into operational Earth observation workflows, and future research directions.
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Medical Physics · Cross-listed from eess.IV
Magnetic Resonance Simulation of Effective Transverse Relaxation (T2*)
Hidenori Takeshima
Purpose: To simulate effective transverse relaxation ($T_2^*$) as a part of MR simulation. $T_2^*$ consists of reversible ($T_2^{\prime}$) and irreversible ($T_2$) components. Whereas simulations of $T_2$ are easy, $T_2^{\prime}$ is not easily simulated if only magnetizations of individual isochromats are simulated. Theory and Methods: Efficient methods for simulating $T_2^{\prime}$ were proposed. To approximate the Lorentzian function of $T_2^{\prime}$ realistically, conventional simulators require 100+ isochromats. This approximation can be avoided by utilizing a linear phase model for simulating an entire Lorentzian function directly. To represent the linear phase model, the partial derivatives of the magnetizations with respect to the frequency axis were also simulated. To accelerate the simulations with these partial derivatives, the proposed methods introduced two techniques: analytic solutions, and combined transitions. For understanding the fundamental mechanism of the proposed method, a simple one-isochromat simulation was performed. For evaluating realistic cases, several pulse sequences were simulated using two phantoms with and without $T_2^{\prime}$ simulations. Results: The one-isochromat simulation demonstrated that $T_2^{\prime}$ simulations were possible. In the realistic cases, $T_2^{\prime}$ was recovered as expected without using 100+ isochromats for each point. The computational times with $T_2^{\prime}$ simulations were only 2.0 to 2.7 times longer than those without $T_2^{\prime}$ simulations. When the above-mentioned two techniques were utilized, the analytic solutions accelerated 19 times, and the combined transitions accelerated up to 17 times. Conclusion: Both theory and results showed that the proposed methods simulated $T_2^{\prime}$ efficiently by utilizing a linear model with a Lorentzian function, analytic solutions, and combined transitions.
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Computational Physics · Cross-listed from cs.LG
Contrast-Source-Based Physics-Driven Neural Network for Inverse Scattering Problems
Yutong Du and Zicheng Liu
Deep neural networks (DNNs) have recently been applied to inverse scattering problems (ISPs) due to their strong nonlinear mapping capabilities. However, supervised DNN solvers require large-scale
datasets, which limits their generalization in practical applications. Untrained neural networks (UNNs) address this issue by updating weights from measured electric fields and prior physical knowledge, but existing UNN solvers suffer from long inference time. To overcome these limitations, this paper proposes a contrast-source-based physics-driven neural network (CSPDNN), which predicts the induced current distribution to improve efficiency and incorporates an adaptive total variation loss for robust reconstruction under varying contrast and noise conditions. The improved imaging performance is validated through comprehensive numerical simulations and experimental data.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Symmetry Adapted Analysis of Screw Dislocation: Electronic Structure and Carrier Recombination Mechanisms in GaN
Yuncheng Xie, Haozhe Shi, Menglin Huang et al. (+3 more)
As fundamental one-dimensional defects, screw dislocations profoundly reshape the energy landscape and carrier dynamics of crystalline materials. By restoring the exact
algebra of the screw dislocation group, we unveil the latent
symmetry constraints that govern the electronic structure, providing a more rigorous physical picture than the conventional treatments. When applied to GaN, the method yields a band-connectivity constraint and rigorous dipole selection rules for polarization-resolved transitions. Combined with computed
Hamiltonian matrix, the approach gives
symmetry-filtered radiative and dielectric calculations and reveals a piezoelectrical effect at the dislocation core that strongly suppresses radiative recombination. The pronounced dominance of non-radiative capture over radiative recombination highlights the detrimental impact of screw dislocations on the luminous efficiency of GaN, providing a theoretical foundation for optimizing dislocation-limited optoelectronic devices.
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All authors Yuncheng Xie, Haozhe Shi, Menglin Huang, Weibin Chu, Shiyou Chen, Xin-Gao Gong
Fluid Dynamics
A new form of mixing in turbulent sedimentation
Simone Tandurella, Marco Edoardo Rosti, Stefano Musacchio et al. (+1 more)
We study the sedimentation of finite-size inertial particles in a Rayleigh-Taylor-like setup using state-of-the-art direct numerical simulations. The falling particles are observed to produce two distinct regions: a leading mixing layer with a linear concentration profile followed by a bulk region of uniform density. Unlike classical RT
turbulence, the mixing layer extension accelerates with an anomalous, non-integer exponent, while the bulk region moves at a constant velocity. A one-dimensional model based on a local hindered settling law accurately captures the observed dynamics and its dependence on the particle-to-fluid density ratio. The present work identifies a new regime of convective mixing which develops at the front of particle suspensions in sedimentation processes.
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All authors Simone Tandurella, Marco Edoardo Rosti, Stefano Musacchio, Guido Boffetta
Optics
Electrically pumped AlGaN edge-emitting UV-B laser diodes grown by molecular beam epitaxy
Huabin Yu, Shubham Mondal, Rui Shen et al. (+11 more)
Mid and deep ultraviolet (UV)
laser diodes remain among the least explored devices in
semiconductor optoelectronics, despite their importance for spectroscopy, biochemical sensing, disinfection, and emerging
quantum photonics. Here, we demonstrate an electrically pumped AlGaN-based
laser diode operating in the UV-B band (280-315 nm). The device is grown by molecular beam epitaxy (MBE) on single-
crystal AlN substrate and fabricated in a ridge-waveguide geometry. The
laser diode operates at 298.5 nm and exhibits a relatively low threshold current density of 3.4 kA/cm$^2$. Clear nonlinear light-current characteristics and pronounced spectral narrowing with a full-width-at-half-maximum (FWHM) of 0.2 nm are measured above threshold.
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All authors Huabin Yu, Shubham Mondal, Rui Shen, Md Tanvir Hasan, David He, Jiangnan Liu, Samuel Yang, Minming He, Omar Alkhazragi, Danhao Wang, Mackillo Kira, Parag Deotare, Di Liang, Zetian Mi
Instrumentation and Detectors · Cross-listed from astro-ph.IM
Development of Electroformed X-ray Optics Bridging Synchrotron Technology and Space Astronomy
Ryuto Fujii, Koki Sakuta, Kazuki Ampuku et al. (+21 more)
We have developed X-ray
telescope mirrors using an original electroforming replication technique established through the fabrication of millimeter-aperture, ultra-short-focal-length nanofocusing mirrors for synchrotron X-ray microscopy. This paper presents detailed results of X-ray illumination tests of a 60-mm-diameter, full-circumference, double-reflection monolithic electroformed nickel mirror and its Mirror Module Assembly (MMA). The experiments were conducted at the 1-km beamline BL29XUL at SPring-8. To simulate a parallel X-ray beam from celestial sources, we constructed a dedicated evaluation system, the High-Brilliance X-ray Kilometer-long Large-Area Expanded-beam Evaluation System (HBX-KLAEES). Owing to the high
photon flux and the quasi-point-like source with a small divergence provided by HBX-KLAEES, the imaging performance was evaluated with high fidelity, resolving both the sharp core and large-angle components of the Point Spread Function (PSF). The results show an extremely sharp core with a Full Width at Half Maximum (FWHM) of 0.7 arcsec and a Half Power Diameter (HPD) of 14 arcsec, even after integration into the MMA. In addition, a positive correlation was found between angular resolution and axial figure error in both the primary and secondary mirror sections, indicating that axial figure errors contribute to image degradation. Based on these results, the MMA was selected as one of the hard X-ray optics for the FOXSI-4 sounding rocket experiment, which performs high-resolution soft and hard X-ray imaging spectroscopy of
solar flares and was successfully launched. These results demonstrate the potential for further improvements in angular resolution and the development of high-resolution, ultra-short focal length X-ray optics for small satellites, including CubeSats.
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All authors Ryuto Fujii, Koki Sakuta, Kazuki Ampuku, Yusuke Yoshida, Makoto Yoshihara, Ayumu Takigawa, Keitoku Yoshihira, Tetsuo Kano, Naoki Ishida, Noriyuki Narukage, Keisuke Tamura, Kikuko Miyata, Gota Yamaguchi, Hidekazu Takano, Yoshiki Kohmura, Shutaro Mohri, Takehiro Kume, Yusuke Matsuzawa, Yoichi Imamura, Takahiro Saito, Kentaro Hiraguri, Hirokazu Hashizume, Hidekazu Mimura, Ikuyuki Mitsuishi
Plasma Physics · Cross-listed from astro-ph.HE
Maximum Energy of Particles Accelerated in Gamma-Ray Burst Afterglow Shocks
Zhao-Feng Wu, Sofía Guevara-Montoya, Paz Beniamini et al. (+3 more)
Particle acceleration in relativistic collisionless shocks remains an open problem in high-energy astrophysics. Particle-in-
cell (PIC) simulations predict that electron acceleration in weakly magnetized shocks proceeds via small-angle scattering, leading to a maximum electron energy significantly below the Bohm limit. This upper bound on electron energy manifests observationally as a characteristic synchrotron cutoff, providing a direct probe of the underlying acceleration physics. Gamma-ray burst (GRB) afterglows offer an exceptional laboratory for testing these predictions. Here, we model the spectral
evolution of GRB afterglows during the relativistic deceleration phase, incorporating PIC-motivated acceleration prescriptions and self-consistently computing synchrotron and synchrotron self-Compton emission. We find that low-energy bursts in low-density environments, typical of short GRBs, exhibit a pronounced synchrotron cutoff in the GeV band within minutes to hours after the trigger. Applying our framework to GRB 190114C and GRB 130427A, we find that current observations are insufficient to discriminate between PIC-motivated acceleration and the Bohm limit, primarily due to poor
photon statistics in the
Fermi-LAT band. Nevertheless, future MeV-TeV afterglow observations can break model degeneracies and place substantially tighter constraints on the mechanisms responsible for particle acceleration in relativistic shocks. To this end, we simulate a fiducial nearby short GRB as a promising probe of the cutoff location, for which the two acceleration scenarios are cleanly distinguishable and the detection of such an event in the near future remains feasible.
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All authors Zhao-Feng Wu, Sofía Guevara-Montoya, Paz Beniamini, Dimitrios Giannios, Daniel Grošelj, Lorenzo Sironi
Optics
Passive Daytime Radiative Cooling Enabled by Bio-Derived Ceramic-Polymer Coatings on Rapid-Curing Fiberglass Casts
Xuguang Zhang, Hexiang Zhang, Hanqing Liu et al. (+6 more)
Passive daytime radiative cooling (PDRC) provides an energy-free approach to suppress surface temperatures by reflecting
solar irradiation while emitting thermal radiation through the mid-infrared atmospheric window. Despite rapid progress in optical performance, most PDRC systems remain limited by rigid, fragile, or planar substrates, restricting their use on flexible, curved, or wearable surfaces. Here, we report a biocompatible and structurally robust PDRC system integrated onto a commercial rapid-curing fiberglass cast, a conformal substrate widely used in orthopedic and industrial applications. The cooling architecture adopts a
bilayer polymer design consisting of a polyvinyl alcohol (PVA) adhesion layer and a polymethyl methacrylate (PMMA) protective layer, both embedded with calcium pyrophosphate (CPP) ceramic particles derived from processed animal bone waste. The bio-derived CPP simultaneously enables broadband
solar scattering and high mid-infrared emittance, while offering sustainability and biocompatibility advantages. The resulting composite exhibits over 90%
solar reflectance and achieves up to 15 C sub-ambient cooling under direct outdoor sunlight.
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All authors Xuguang Zhang, Hexiang Zhang, Hanqing Liu, Xiaoli Li, Mu Ying, Yutian Yang, Marilyn L. Minus, Ming Su, Yi Zheng