Optics
Bloch-Landau-Zener Oscillations in Moiré Lattices
Sergey K. Ivanov, Yaroslav V. Kartashov and Vladimir V. Konotop
We develop a theory of two-dimensional Bloch-Landau-Zener (BLZ) oscillations of wavepackets in incommensurate moiré
lattices under the influence of a weak linear gradient. Unlike periodic systems, aperiodic
lattices lack translational
symmetry and therefore do not exhibit a conventional band-gap structure. Instead, they feature a mobility edge, above which (in the optical context) all modes become localized. When a linear gradient is applied to a moiré
lattice, it enables energy transfer between two or several localized modes, leading to the oscillatory behavior referred to as BLZ oscillations. This phenomenon represents simultaneous tunneling in real space and propagation constant (energy) space, and it arises when quasi-resonance condition for propagation constants and spatial proximity of interacting modes (together constituting a selection rule) are met. The selection rule is controlled by the linear gradient, whose amplitude and direction play a crucial role in determining the coupling pathways and the resulting dynamics. We derive a multimode model describing BLZ oscillations in the linear regime and analyze how both attractive and repulsive nonlinearities affect their dynamics. The proposed framework can be readily extended to other physical systems, including cold atoms and Bose-Einstein condensates in aperiodic potentials.
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Fluid Dynamics
Self-adaptive elastic flaps with bending and torsion for 3D blunt body drag reduction
J. M. Camacho-Sánchez, M. Lorite-Díez, Y. Fan et al. (+2 more)
This study investigates the potential for drag-reduction of low-mechanical-order, self-adaptive control systems, consisting of hinged flaps attached along the edges of the rectangular base of a canonical blunt body. Comparative experiments are conducted in a wind tunnel under crosswind conditions at a Reynolds number of $Re = 2.13 \times 10^5$. The flaps, made of rigid rectangular panels, are mounted in three configurations: rigidly fixed%(RF) , flexibly hinged with a single degree of freedom in bending, and flexibly hinged with two degrees of freedom, allowing both bending and torsion, the latter representing a novel drag-reduction device, easily tunable to ensure a quasi-steady, stable adaptive reconfiguration. Two
geometric arrangements are tested: horizontal flaps attached along the top and bottom (TB) edges, and vertical flaps along the lateral (left and right, LR) edges. The experimental study includes force, pressure, flap deformation and wake velocity measurements at varying yaw angles to simulate crosswind conditions. When the body is aligned with the flow, both arrangements reduce drag due to a rear cavity effect that elongates the recirculating flow. The TB arrangement is found to be much more effective at reducing drag in yawed conditions and its performance is improved using the flexible hinges. In these cases, static deformations correspond to boat-tailing that reduces the induced drag together with the turbulent kinetic energy in the wake. The use of the wind-average drag coefficient (taking into account events of crosswind) to evaluate an effective drag reduction clearly shows the TB arrangement with bending and torsion as the best appendage, with a 7.62% drag reduction compared to the body with no appendages, proving the good performance of simple, two-degrees-of-freedom control systems to adapt to changing three-dimensional wakes.
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All authors J. M. Camacho-Sánchez, M. Lorite-Díez, Y. Fan, J. I. Jiménez-González, O. Cadot
Optics
Structured Random Models for Phase Retrieval with Optical Diffusers
Zhiyuan Hu, Fakhriyya Mammadova, Julián Tachella et al. (+2 more)
Phase
retrieval is a nonlinear inverse problem that arises in a wide range of imaging modalities, from electron microscopy to
Fourier ptychography. In particular, the reconstruction is facilitated when the sensing
matrix is i.i.d. random, enabling strong theoretical guarantees and efficient reconstruction
algorithms. However, its applicability is restricted by excessive computational costs. In this paper, we propose structured random models for phase
retrieval, where we emulate a dense random
matrix by a cascade of structured transforms and random diagonal
matrices. We reduce the complexity from quadratic to log-linear at no cost in reconstruction performance. Through a spectral method initialization followed by gradient descent, robust reconstruction is obtained at an oversampling ratio as low as 2.5. Moreover, we observe that the reconstruction performance is solely determined by the singular-value distribution of the forward
matrix. This class of models can directly be implemented with basic optical elements such as lenses and diffusers, paving the way for large-scale phase imaging with robust reconstruction guarantees.
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All authors Zhiyuan Hu, Fakhriyya Mammadova, Julián Tachella, Michael Unser, Jonathan Dong
Accelerator Physics
Coherent radiation produced by microtron electron bunches
S.V. Anishchenko and P.V. Molchanov
The theory of coherent transition radiation produced by a relativistic electron beam during its extraction from a microtron is established. Expressions for the beam form factor, spectral-angular and angular distribution of coherent transition radiation are obtained in explicit form. Estimates of microwave noise caused by coherent transition radiation are given.
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Computational Physics · Cross-listed from nlin.SI
Asymmetric integrable turbulence and rogue wave statistics for the derivative nonlinear Schrödinger equation
Ming Zhong, Weifang Weng and Zhenya Yan
We investigate the asymmetric integrable
turbulence and rogue waves (RWs) emerging from the modulation instability (MI) of plane waves for the DNLS equation. The \(n\)-th moments and ensemble-averaged kinetic and potential energy exhibit oscillatory convergence towards their steady-state values. Specifically, the amplitudes of oscillations for these indexes decay asymptotically with time as \(t^{-1.36}\), while the phase shifts demonstrate a nonlinear decay with a rate of \(t^{-0.78}\). The frequency of these oscillations is observed to be twice the maximum growth rate of MI. These oscillations can be classified into two distinct types: one is in phase with ensemble-averaged potential energy modulus $|\langle H_4\rangle|$, and the other is anti-phase. At the same time, this unity is also reflected in the wave-action spectrum \( S_k(t) \) for a given \( k \), the auto-correlation function \( g(x,t) \) for a given \( x \), as well as the PDF \( P(I,t) \). The critical feature of the
turbulence is the wave-action spectrum, which follows a power-law distribution of \( |k+3|^{-\alpha} \) expect for $k=-3$. Unlike the NLS equation, the
turbulence in the DNLS setting is asymmetric, primarily due to the asymmetry between the wave number of the plane wave from the MI and the perturbation wave number.. As the asymptotic peak value of \( S_k \) is observed at \( k = -3 \), the auto-correlation function exhibits a nonzero level as \( x \to \pm L/2 \). The PDF of the wave intensity asymptotically approaches the exponential distribution in an oscillatory manner. However, during the initial stage of the nonlinear phase, MI slightly increases the occurrence of RWs. This happens at the moments when the potential modulus is at its minimum, where the probability of RWs occurring in the range of \( I\in [12, 15] \) is significantly higher than in the asymptotic steady state.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Cryogenic temperature dependence and hysteresis of surface-trap-induced gate leakage in GaN high-electron-mobility transistors
Ching-Yang Pan, Shi-Kai Lin, Yu-An Chen et al. (+1 more)
This work provides a detailed mapping of various mechanisms of surface-trap-induced gate leakage in GaN HEMTs across a temperature range from room to cryogenic levels. Two-dimensional variable-range hopping is observed at small gate bias. Under higher reverse gate bias, the leakage is dominated by the Poole–Frenkel emission above 220 K, but gradually transitions to the trap-assisted tunneling below 220 K owing to the frozen-trap effect. The trap barrier height extracted from the gate leakage current under the upward gate sweep is 0.65 V, which is 12% higher than that from the downward sweep. The gate leakage current as a function of the gate bias exhibits clockwise hysteresis loops above 220 K but counterclockwise ones below 220 K. This remarkable opposite hysteresis phenomenon is thoroughly explained by the trap mechanisms.
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All authors Ching-Yang Pan, Shi-Kai Lin, Yu-An Chen, Pei-hsun Jiang
Geophysics · Cross-listed from cs.LG
Towards geological inference with process-based and deep generative modeling, part 1: training on fluvial deposits
Guillaume Rongier and Luk Peeters
The distribution of resources in the subsurface is deeply linked to the variations of its physical properties. Generative modeling has long been used to predict those physical properties while quantifying the associated uncertainty. But current approaches struggle to properly reproduce geological structures, and fluvial deposits in particular, because of their continuity. This study explores whether a generative
adversarial network (GAN) - a type of deep-learning
algorithm for generative modeling - can be trained to reproduce fluvial deposits simulated by a process-based model - a more expensive model that mimics geological processes. An ablation study shows that developments from the deep-learning community to generate large 2D images are directly transferable to 3D images of fluvial deposits. Training remains stable, and the generated samples reproduce the non-stationarity and details of the deposits without mode collapse or pure memorization of the training data. Using a process-based model to generate those training data allows us to include valuable properties other than the usual physical properties. We show how the deposition time let us monitor and validate the performance of a GAN by checking that its samples honor the law of superposition. Our work joins a series of previous studies suggesting that GANs are more robust that given credit for, at least for training
datasets targeting specific geological structures. Whether this robustness transfers to larger 3D images and
multimodal datasets remains to be seen. Exploring how deep generative models can leverage geological principles like the law of superposition shows a lot of promise.
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Accelerator Physics
A further study on the high-precision optics for HIAF-BRing
Ke Wang, Li-Na Sheng, Tao Li et al. (+6 more)
The High Intensity heavy ion Accelerator Facility (HIAF) successfully accelerated the 18O6+ beam on October 27, 2025. This paper presents a further simulation study on the high-precision optics, namely sliced optics, of the Booster Ring (BRing) at HIAF based on measured
magnetic fields, focusing on three aspects: (1) closed-orbit distortion (COD) and variations in optical parameters induced by errors; (2) closed-orbit correction; (3) dynamic aperture. Specifically, detailed investigations are conducted on COD and optical parameter variations caused by magnet
alignment errors and dipole magnet field errors, alongside simulations of closed-orbit correction and detailed calculations of BRing's dynamic aperture. Results show the sliced optics outperforms the original optics in COD control. Without chromaticity correction, its dynamic aperture is superior to the original; after chromaticity correction, it remains comparable. This study provides valuable insights for accelerator tuning and optimization.
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All authors Ke Wang, Li-Na Sheng, Tao Li, Geng Wang, Wei-Ping Chai, You-Jin Yuan, Jian-Cheng Yang, Guo-Dong Shen, Liang Lu
Accelerator Physics
Beam Energy Measurement using a Bayesian Approach with the Stacked Foil Method
Alexander Gottstein, Lorenzo Mercolli, Eva Kasanda et al. (+7 more)
We present a practical method to measure the energy of
proton beams at a medical cyclotron using the stacked foil technique in combination with a
Bayesian inference method. By measuring the $^{48}$V activity induced in a stack of irradiated titanium foils, the
proton energy can be inferred without relying on direct current or charge measurements, making the method suitable even for low-
vacuum environments or air-exposed setups. This technique is further extended to configurations where the beam energy is degraded to levels around 8 MeV. A
Bayesian fit of the measured activity profile allows not only for a robust energy estimation but also for a consistent treatment of uncertainties and nuisance parameters. Monte Carlo simulations are employed to validate the underlying assumptions, including the impact of energy dispersion or cross-section uncertainties. Our results demonstrate that this method provides accurate beam energy measurements across several typical experimental setups used at the Bern Medical Cyclotron. Additionally, we evaluate the sensitivity of the method to the choice of
nuclear cross-section data and assess how the number of foils in the stack affects the uncertainty in the inferred beam energy.
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All authors Alexander Gottstein, Lorenzo Mercolli, Eva Kasanda, Isidre Mateu, Lars Eggimann, Elnaz Zyaee, Gaia Dellepiane, Pierluigi Casolaro, Paola Scampoli, Saverio Braccini
Instrumentation and Detectors
Evaluating plastic scintillator performance as a substitute of LYSO in SiPM based animal PET scanners: A GEANT4 simulation analysis
Davinder Siwal, P. K. Mohanty, D. Bose et al. (+1 more)
A systematic study is conducted to understand the coincident resolving time (CRT) for a pair of Lutetium-yttrium oxyorthosilicate (LYSO) and the plastic scintillation detector bars under the Geant4 framework.
Crystals are coupled to a silicon photomultiplier single pad wafer with an appropriate optical coupling for signal readout. Pad reads the light
photons undergoing optoelectronic conversion at the wafer site and generates electrical pulses with a bi-exponential shape. These signals are used to determine the trigger time stamp of back-to-back gamma-rays emitted from a point source, enabling the evaluation of CRT performance at different plastic scintillator lengths. For the LYSO detector, the simulation yields the CRT response of 174 ps, which aligns to the literature reported value for the dimensions 2 mm x 2 mm x 10 mm. To identify the plastic scintillator dimensions with an integrated gamma-ray detection efficiency comparable to LYSO's photopeak efficiency at 511 keV gamma
photons, various bar lengths of commercial plastic BC404 and TIFR Ooty's in-house developed plastic material are attempted in Geant4. Consequently, for both the plastic scintillators, the equivalent length (for the same cross-sectional area) was found to be 4 times that of LYSO
crystal length at a threshold of 25 keV. CRT value determined for this dimension is found to be $\approx$ 300 ps for both the plastic medium. It suggests that, if an animal preclinical PET scanner is developed with plastic bars, the minimum achievable image resolution (FWHM) of $\approx$ 4.5 cm can be expected for a pair of detection elements.
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All authors Davinder Siwal, P. K. Mohanty, D. Bose, A. Jain
Optics
Electromagnetic Theory of Metasurface Perfect Magnetic Conductor (PMC)
Oscar Céspedes Vicente, Karim Achouri and Christophe Caloz
Artificial
magnetic conductors (AMCs) mimic the idealized boundary condition of a perfect
magnetic conductor (PMC), which reflects electromagnetic waves with a preserved electric field and inverted
magnetic field. Despite their usefulness, existing AMC implementations often rely on complex or impractical designs, and lack a clear electromagnetic theory explaining their behavior, especially under oblique or polarization-diverse incidence. This work addresses these limitations by presenting a rigorous electromagnetic framework for PMC metasurfaces based on dipolar and quadrupolar surface susceptibilities within the generalized sheet transition conditions (GSTCs) formalism. We show that achieving polarization- and angle-independent PMC behavior requires a specific set of heteroanisotropic (nonlocal) susceptibilities, and we derive closed-form expressions for angular scattering that include higher-order multipole contributions. A physically realizable, asymmetric metasurface structure is then designed to satisfy these theoretical conditions. Despite its
geometric asymmetry, the proposed structure exhibits a isotropic PMC response at resonance, confirmed by full-wave simulations and multipolar susceptibility extraction. These results demonstrate how properly engineered surface multipoles can yield angularly independent
magnetic boundary conditions using only thin, passive metallic layers. This work bridges the gap between AMC design and electromagnetic theory, and enables a new class of angle-independent metasurface reflectors for more accurate simulations, optimizations and innovative AMC designs.
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Fluid Dynamics
Impact of Forest Canopy Structure on Buoyant Plume Dynamics During Wildland Fires
Antonio Quim Cervantes, Ajinkya Desai and Tirtha Banerjee
This study investigates the influence of forest canopy heterogeneity on buoyant plume dynamics resulting from surface thermal anomalies representing wildland fires, utilizing Large Eddy Simulation (LES). The Parallelized Large-Eddy Simulation Model (PALM) was employed to simulate six canopy configurations: no canopy, homogeneous canopy, external plume-edge canopy, internal plume-edge canopy, 100 m gap canopy, and 200 m gap canopy. Each configuration was analyzed with and without a static surface heat flux patch of 5000 $\mathrm{W \cdot m^{-2}}$, resulting in a resting buoyant plume. Simulations were conducted under three crosswind speeds: 0, 5, and 10 $\mathrm{m \cdot s^{-1}}$. Results show that canopy structure significantly modifies plume behavior, mean flow, and turbulent kinetic energy (TKE) budgets. Plume updraft speed and tilt varied with canopy configuration and crosswind speed. Pressure gradients associated with plume updrafts were modified based on the canopy configuration, resulting in varying crosswind speed reductions at the plume region. Strong momentum absorption was observed above the canopy for the crosswind cases, with the greatest enhancement in the gap canopies. Momentum injection from below the canopy due to the heat source was also observed, resulting in plume structure modulation based on canopy configuration. TKE was found to be the largest in the gap canopy configurations. TKE budget analysis revealed that buoyant production dominated over shear production. At the center of the heat patch, the gap canopy configurations showed enhanced buoyancy within the gap. Spatial distributions demonstrated increased shear production at the interface between the plume and crosswind.
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Instrumentation and Detectors
Nanodiamond photocathodes for MPGD-based single photon detectors
F.M. Brunbauer, C. Chatterjee, G. Cicala et al. (+11 more)
This study investigates the suitability of Hydrogenated NanoDiamond (HND) materials as an alternative for CsI in MPGD-based
photon detectors. The research focuses on characterizing HND photocathodes coupled with THGEM + Micromegas-based detectors. The HND grains were prepared via hydrogenation and stored in water for more than two years. They were then coated on PCB discs or THGEMs using a pulsed spray technique. The resulting
quantum efficiency (QE) values (~4% at 122 nm) were found to be within a factor of 10 of the best freshly hydrogenated samples reported in the literature ( ~40% at 120 nm). The robustness of reflective HND photocathodes against ion bombardment was measured to be about 10 times larger than the corresponding CsI one after the same charge accumulation. Furthermore, THGEM characterization indicates minimal alteration in response after HND coatings. These results suggest that HND holds potential as a more robust photocathode for gaseous detectors, offering improved performance in single-
photon detection applications.
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All authors F.M. Brunbauer, C. Chatterjee, G. Cicala, D. D'Ago, S. Dalla Torre, M.S. Leone, S. Levorato, T. Ligonzo, M. Lisowska, R. Rai, F. Tessarotto, Triloki, A. Valentini, L. Velardi
Applied Physics
A combined thermal-resistance-capacity and finite-element model for very fast and accurate short- and medium-term simulations of single U-tube borehole heat exchangers
Enzo Zanchini, Francesco Zanchini and Claudia Naldi
An accurate design of a ground-coupled heat pump system requires the knowledge of the outlet fluid temperature from the borehole heat exchangers (BHEs), both in the short and long term. This paper fucuses on the short and medium term. In this time range, either 3D finite-element simulations or Thermal Resistance Capacity Models (TRCMs) can be applied. The former can yield very accurate results but require long computation times. The latter are much faster but cannot be fully precise, because they require simplifying assumptions. In this paper, we present a new method for the short-term and medium-term simulation of single U-tube BHEs, which combines the speed of TRCMs and the accuracy of finite-elements simulations. The method uses a TRCM to estimate the thermal response of the BHE, then corrects the results by interpolation with a
dataset, which has been produced by running 54 finite-element simulations in various configurations. The model is implemented in a C++ program, available at the open-source online data repository of the University of Bologna. The program provides, within two seconds, the time
evolution of the inlet, outlet and mean fluid temperature, of the mean BHE surface temperature, of the 3D and the effective borehole thermal resistance. It can be easily connected to long-term simulation tools to obtain the full-time-scale thermal response of a bore field.
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Optics
Investigation of intrinsic properties of high-quality fiber Fabry–Perot resonators
Germain Bourcier, Stephane Balac, Safia Mohand-Ousaid et al. (+8 more)
Fiber Fabry–Perot (FFP) resonators of a few centimeters are optimized as a function of the reflectivity of the mirrors and the dimensions of the intra-cavity waveguide. Loaded quality factor in excess of 10^9, with an optimum of 4___x___10^9, together with an intrinsic quality factor larger than 10^10 and intrinsic finesse in the range of 10^5 have been measured. An application to the stabilization of
laser frequency fluctuations is presented.
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All authors Germain Bourcier, Stephane Balac, Safia Mohand-Ousaid, Julien Lumeau, Antonin Moreau, Vincent Crozatier, Pierre Sillard, Marianne Bigot, Laurent Bigot, Olivier Llopis, Arnaud Fernandez
Geophysics
Design and Implementation of a 25-Yr Pseudoprospective Earthquake Forecasting Experiment in China (AoyuX)
Jiawei Li, Qingyuan Zhang and Didier Sornette
Forecast models in statistical seismology are commonly evaluated using log-likelihood (LL) scores for the full distribution $P(n)$ of earthquake counts. However, fat tails and out-of-range observations (realized counts exceed all simulations) can bias model rankings. We develop a tail-aware framework that estimates
cell-wise $P(n)$ using adaptive Gaussian kernel density estimation and compares three treatments of out-of-range counts: power-law extrapolation, a fixed minimum probability, and exclusion. Using the AoyuX platform, we conduct a 25-year (2000–2023) month-by-month pseudoprospective experiment in the China Seismic Experimental Site. We compare an epidemic-type aftershock sequence model with a homogeneous background, ETAS$\mu$, with a spatially heterogeneous variant, ETAS$\mu(x,y)$, across six spatial resolutions and five magnitude thresholds, using 100,000 simulations per forecast window. Count distributions follow power laws, $P(n) \sim n^{-(1+a)}$, with $a \approx 1.02 \pm 0.23$, yielding a productivity exponent $\alpha = 0.83 \pm 0.19$ for $b = 0.85 \pm 0.002$. Model rankings depend on tail treatment: power-law extrapolation is theoretically justified and empirically most robust, whereas occasional advantages of the fixed-probability approach in coarse, low-magnitude settings are attributable to noise. Cumulative information gain shows that ETAS$\mu(x,y)$ outperforms ETAS$\mu$ in data-rich configurations, especially for $M_t = 3.0$–$3.5$ and whole-region tests. Positive mean information gain is concentrated where earthquakes with $M \geq 5$ occurred, whereas
stochastic fluctuations dominate data-poor settings. A coefficient-of-variation analysis distinguishes genuine upward trends from noise. The framework supports statistically grounded evaluation of earthquake
forecasting models.
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Optics
Research Progress of Terahertz Technology in Microbiology
Ding Cao, Guangyou Fang and Xuequan Chen
Microorganisms are ubiquitous in nature, and microbial activities are closely intertwined with the entire life cycle system and human life. Developing novel technologies for the detection, characterization and manipulation of microorganisms promotes their applications in clinical, environmental and industrial areas. Over the last two decades, terahertz (THz) technology has emerged as a new optical tool for microbiology. The great potential originates from the unique advantages of THz waves including the high sensitivity to water and inter-/intra-molecular motions, the non-invasive and label-free detecting scheme, and their low
photon energy. THz waves have been utilized as a stimulus to alter microbial functions, or as a sensing approach for quantitative measurement and qualitative differentiation. This review specifically focuses on recent research progress of THz technology applied in the field of microbiology, including two major parts of THz biological effects and the microbial detection applications. In the end of this paper, we summarize the research progress and discuss the challenges currently faced by THz technology in microbiology, along with potential solutions. We also provide a perspective on future development directions. This review aims to build a bridge between THz photonics and microbiology, promoting both fundamental research and application development in this interdisciplinary field.
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Fluid Dynamics
Wetted-Area Minimum and Inlet-Outlet Reciprocity in Optimal Manifolds of Rarefied Gas Flows
Ruifeng Yuan and Lei Wu
While flow optimization has been extensively studied in the continuum regime, its extension to rarefied gas flows remains less explored. Here, based on the Boltzmann model equation, an adjoint
topology optimization method is employed to design two-dimensional single inlet multi outlet
manifolds, aiming to maximize the total mass flow rate while maintaining
outflow uniformity. Two key findings are revealed. (1) analogous to the Knudsen minimum in mass flow rate in the transition regime, a wetted-area minimum is identified, but in the slip flow regime. This phenomenon arises from the competition between flow bend loss and surface friction loss, with the latter being affected by velocity slip at the solid surface. (2) the inlet outlet reciprocity emerges in the free molecular flow regime, where the optimal design becomes invariant to inlet outlet orientation and pressure ratio. Additional insights are gained regarding the channel
curvature, compressibility effects, and the constraint of
outflow uniformity. These findings elucidate the mechanisms governing rarefied gas transport and offer design guidance for
manifolds operating in
vacuum environments.
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Optics · Cross-listed from cond-mat.mtrl-sci
Laser-Induced Heating in Diamonds: Influence of Substrate Thermal Conductivity and Interfacial Polymer Layers
Md Shakhawath Hossain, Jiatong Xu, Thi Ngoc Anh Mai et al. (+9 more)
Diamonds hosting color centers possess intrinsically high thermal conductivity; therefore,
laser-induced heating has often received little
attention. However, when placed on substrates with low thermal conductivity, localized heating of diamonds under
laser excitation can become significant, and the presence of an interfacial
polymer layer between substrate and diamond further amplifies this effect. Yet, the relationship between substrate thermal conductivity,
polymer thickness, and
laser heating remains to be established. Here, a systematic investigation is presented on
laser-induced heating of silicon-vacancy diamond on substrates with varying thermal conductivity and interfacial
polymer thickness. Results reveal that even at a low excitation power of 737~$\mu$W/$\mu$m$^2$, thin amorphous holey carbon – the lowest-conductivity substrate ($\sim$0.2~W~m$^{-1}$~K$^{-1}$) studied – exhibits substantial heating, while glass ($\sim$1.4~W~m$^{-1}$~K$^{-1}$) and polydimethylsiloxane (PDMS, $\sim$0.35~W~m$^{-1}$~K$^{-1}$) show noticeable heating only above 2.95~mW/$\mu$m$^2$. For
polymer interlayers, a thickness of just 2.2~$\mu$m induces significant heating at 2.95~mW/$\mu$m$^2$ and above, highlighting strong influence of both substrate and
polymer thickness on local heating response. Experimental findings are further validated using COMSOL Multiphysics simulations with a steady-state 3D heat transfer model. These results provide practical guidance for substrate selection and sample preparation, enabling optimization of conditions for optical thermometry and
quantum sensing applications.
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All authors Md Shakhawath Hossain, Jiatong Xu, Thi Ngoc Anh Mai, Nhat Minh Nguyen, Trung Vuong Doan, Chaohao Chen, Qian Peter Su, Yongliang Chen, Evgeny Ekimov, Toan Dinh, Xiaoxue Xu, Toan Trong Tran
Optics
A 2-bit Ku-band Digital Metasurface with Infinitely Scalable Capability
Xiaocun Zong, Hao Shi, Fan Yang et al. (+3 more)
In this letter, we present the design and implementation of a 2-bit digaital metasurface operating in the Ku-band, engineered to exhibit advanced polarization conversion characteristics and support dual-polarization control for both X- and Y-polarizations. To address the challenge of array size scalability hindered by extensive DC control routing in 2-bit metasurfaces, we propose a novel RF-DC separation architecture. This approach integrates the metasurface and DC control circuitry onto separate printed
circuit boards (PCBs), interconnected via pin cascading, enabling theoretically unlimited two-dimensional array expansion. To validate this design, a ${4\times16 \times 16}$ metasurface prototype was fabricated and experimentally evaluated, which can achieve a gain of 28.3dB and an aperture efficiency of 21.02%, confirming the scalability and performance of the proposed architecture. The developed 2-bit high-gain metasurface offers significant reference value for applications in long-distance communication and radar detection. Furthermore, the RF-DC separation architecture introduces a pioneering framework for large-scale metasurface deployment in practical engineering scenarios, enhancing design flexibility and scalability.
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All authors Xiaocun Zong, Hao Shi, Fan Yang, Yong Liu, Shenheng Xu, Maokun Li
Fluid Dynamics
Thermocapillary migration of an odd viscous droplet on a uniformly heated surface: A lattice Boltzmann study
Shan Jiang, He Yan, Chenxia Xie et al. (+1 more)
In this study, the thermocapillary actuation behavior of an odd viscous droplet on a uniformly heated surface is numerically investigated using a phase-field-based
lattice Boltzmann method. The numerical results reveal that unlike a conventional viscous droplet that remains stationary on a uniformly heated surface, the presence of odd viscosity converts tangential Marangoni stresses into asymmetric normal stresses along the interface, thereby inducing spontaneous droplet motion. Specifically, when the odd viscosity coefficient is positive (negative), the droplet migrates toward the right (left). Additionally, due to the enhanced interfacial temperature gradient, the droplet migration velocity consistently increases with the contact angle. Further, it is observed that the droplet's migration velocity decreases with an increasing viscosity ratio between the surrounding fluid and the droplet. Finally, as the droplet is placed on an inclined surface, its migration direction and velocity are governed by the interaction between
gravity and the odd viscosity-induced force, and in certain cases, the droplet can even climb upward against
gravity.
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All authors Shan Jiang, He Yan, Chenxia Xie, Lei Wang
Computational Physics
Anti-Interference Communication Using Computational Antenna
Xiaocun Zong, Fan Yang, Shenheng Xu et al. (+1 more)
This letter proposes a novel anti-interference communication method leveraging computational
antennas, utilizing time averaging and 1-bit reconfigurable intelligent surfaces (RIS) to achieve robust signal modulation with minimal hardware complexity. We develop a communication model for computational
antennas and propose an efficient signal processing
algorithm optimized for temporal modulation. A USRP-based experimental platform is established to validate the approach under strong interference conditions (e.g., 5 dB jamming-to-signal ratio). Experimental results reveal up to an 80.9% reduction in bit error rate (BER) and effective restoration of distorted images in transmission tests. Compared to conventional techniques like spread spectrum or frequency hopping, which require significant spectral resources, our method offers superior anti-interference performance without additional spectral overhead. This research provides valuable insights for radar detection, military communications, and next-generation wireless networks.
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All authors Xiaocun Zong, Fan Yang, Shenheng Xu, Maokun Li
Accelerator Physics
High-brightness Graphite Photocathodes
Po-Hsun Wu, Yu-Chieh Lo and Yen-Chieh Huang
A robust and infrared
laser-excited photocathode with high
quantum efficiency, high brightness, and low cost, operating under a moderate
vacuum, has long been sought by the accelerator and microscopy communities. This study investigates various types of graphite photocathodes, including bulk, sheet, and flake graphite, in the regime of thermionically assisted photoemission by an irradiating infrared
laser. Our experiment reveals that, under space-charge-limited photoemission, the flake-graphite photocathode with a dense population of nano-
graphene fins on its surface exhibits the highest
quantum efficiency, which is 770 times greater than that of a copper photocathode irradiated by the same infrared
laser at 1064 nm. With our theory considering both thermionic and multiphoton emissions, we determine that the flake graphite photocathode is 200 times brighter than a copper photocathode irradiated by an infrared
laser and is as bright as a LaB6 field emitter.
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Fluid Dynamics
Sequential water wave reconstruction in VOF-based numerical wave tanks with the EnKF approach
Liwen Yan, Linyuan Che and Jing Li
Existing phase-resolved wave reconstruction methods are mostly based on potential flow theory, which limits their ability to capture strongly nonlinear phenomena such as wave breaking dynamics. In such cases, the importance of multiphase incompressible Navier–Stokes solvers becomes particularly evident. These solvers form the foundation of the widely used numerical wave tanks in marine, ocean, and coastal engineering. However, the high dimensionality of the state variables in such systems often hinders the efficiency of data assimilation. The POD method is applied to reduce the order of the state vector in ensemble-based data assimilation, where instantaneous snapshots are naturally available. Given the unsteady nature and random phase combinations of irregular waves, the effectiveness of single data assimilation is limited. Sequential data assimilation is thus adopted to continuously update the wave profile as it evolves, ensuring that the wave field matches the real-world conditions. Therefore, inflation is needed to mitigate the ensemble collapse. Unlike single-phase flows without any interface, where the background error covariance can be inflated directly, to preserve physical constraints, when inflating for the phase field, the velocity field is simultaneously updated by incorporating potential flow formulas. Three representative cases-regular waves, irregular waves, and plunging waves-are used to validate the proposed method and assess its performance. The effect of assimilation parameters is also examined. The results demonstrate that the sequential data assimilation strategy achieves accurate free-surface reconstruction for a VOF-based numerical wave tank.
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Medical Physics · Cross-listed from cs.CL
CURE: Confidence-driven Unified Reasoning Ensemble Framework for Medical Question Answering
Ziad Elshaer and Essam A. Rashed
High-performing medical Large
Language Models (LLMs) typically require extensive fine-tuning with substantial computational resources, limiting accessibility for resource-constrained healthcare institutions. This study introduces a confidence-driven multi-model framework that leverages model diversity to enhance medical question answering without fine-tuning. Our framework employs a two-stage architecture: a confidence detection module assesses the primary model's certainty, and an adaptive routing mechanism directs low-confidence queries to Helper models with complementary knowledge for collaborative
reasoning. We evaluate our approach using Qwen3-30B-A3B-Instruct, Phi-4 14B, and Gemma 2 12B across three medical
benchmarks; MedQA, MedMCQA, and PubMedQA. Result demonstrate that our framework achieves competitive performance, with particularly strong results in PubMedQA (95.0%) and MedMCQA (78.0%). Ablation studies confirm that confidence-aware routing combined with multi-model collaboration substantially outperforms single-model approaches and uniform
reasoning strategies. This work establishes that strategic model collaboration offers a practical, computationally efficient pathway to improve medical AI systems, with significant implications for democratizing access to advanced medical AI in resource-limited settings.
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Applied Physics
A Novel Beam Tracking Approach for Preventing Beam Collapse
Xiaocun Zong, Fan Yang, Shenheng Xu et al. (+1 more)
To address the issue of beam collapse resulting from instantaneous instability during switch transitions in beam tracking, this paper proposes a novel beam switching method based on a row-by-row switching code table. The paper first establishes an abstract model of the beam tracking application scenario and introduces the reconfigurable intelligent surface (RIS) employed in this paper. Subsequently, simulations are conducted to compare the conventional direct beam switching method with the proposed row-by-row switching code table approach, thereby elucidating the advantages and limitations of the new method. In parallel, a RIS hardware platform is constructed in a microwave anechoic chamber for experimental validation. Both simulation and experimental results show that, by incorporating intermediate state transitions, the approach achieves beam tracking without beam collapse while incurring no significant gain loss. Finally, the paper discusses the applicability scope and potential scenarios for the proposed method. This research provides valuable insights for applications in mobile communications and radar detection.
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All authors Xiaocun Zong, Fan Yang, Shenheng Xu, Maokun Li
General Physics
MOND Theory and Thermodynamics of Spacetime
Ahamd Sheykhi and Leila Liravi
Starting from the Modified Newtonian Dynamics (MOND) theory and using an inverse approach, we construct a general form of the
entropy expression associated with the horizon based on the entropic nature of
gravity. Using the thermodynamics-
gravity correspondence in the cosmological setup, we apply the corrected
entropy expression and find the modified Friedmann equation by three methods, namely, (i) the first law of thermodynamics, (ii) the entropic force scenario and (iii) the emergence nature of
gravity. We confirm that our model guaranties the generalized second law of thermodynamics for the universe enveloped by the apparent horizon. Our studies reveal that the MOND theory of
gravity may be naturally deduced from the modification of the horizon
entropy. These results may fill in the gap in the literatures, understanding the theoretical origin of the MOND theory from thermodynamics-
gravity conjecture.
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Accelerator Physics
Beam-commissioning-oriented optics study of HFRS Phase-I based on measured magnetic field data
Ke Wang, Li-Na Sheng, Xue-Heng Zhang et al. (+14 more)
The construction of the first phase of the High energy FRagment Separator (HFRS Phase-I) has already been completed and it is anticipated to start beam commissioning in autumn 2025. This paper presents the first order and higher order beam optics calculations for the HFRS Phase-I, using measured magnet data, and evaluates its experimental performance in preparation for beam commissioning. The first order optics of HFRS is calculated based on the sliced
magnetic fields and the higher order aberrations are corrected using a self-compiled program. Monte Carlo particle tracking is employed to analyze the beam phase spaces on the focal planes. The experimental performance of the machine is evaluated through Monte Carlo simulations. The beam phase spaces on the focal planes are thoroughly examined, demonstrating that the higher order aberrations have been well corrected. Moreover, the experimental performance of HFRS is evaluated based on the corrected higher order optics, yielding satisfactory results: the secondary beams of interest can be well separated and exhibit high transmission efficiency. This work provides valuable insights for the upcoming beam commissioning of HFRS Phase-I. The effective correction of higher order aberrations and optimized magnet settings lay a solid foundation for future experiments.
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All authors Ke Wang, Li-Na Sheng, Xue-Heng Zhang, Bei-Min Wu, Ming-Bang Lü, Dong-Sheng Ni, Jing Yang, Xiang Zhang, Fu-Qiang Liu, Qing-Gao Yao, Xiao-Wei Xu, Ya-Jun Zheng, Guo-Dong Shen, Geng Wang, You-Jin Yuan, Jian-Cheng Yang, Liang Lu
Plasma Physics
Dust-ion-acoustic solitons in an ion-beam-driven dusty magnetoplasma with adiabatic and nonadiabatic dust charge variations
N. P. Acharya, S. Basnet, A. P. Misra et al. (+1 more)
We study the characteristics of small-amplitude nonlinear
dust-ion-acoustic (DIA) solitary waves in active magnetized positive-ion-beam-driven dusty
plasmas with the effects of nonadiabatic and adiabatic
dust charge variations. In the model, we consider the ion-neutral collision and thereby consider the collision enhanced ion current to the
dust-charging process and
dust charge fluctuations. We show that the streaming of the positive-ion beam significantly affects the
dust-charging process in which the
dust charge number decreases (increases) with an increased beam velocity (number density). Using the standard reductive perturbation technique, we derive the
evolution equations in the form of Korteweg-de Vries (KdV) equations for DIA solitary waves for two different cases: nonadiabatic and adiabatic
dust charge variations. We study the effect of positive ion beam,
dust charge variation,
magnetic field, ion creation, and ion-neutral collision enhanced current on the wave characteristics. We find that the
soliton energy decays with time and is affected by the beam velocity. Also, the solitary waves get damped by the effects of ion creation, ion loss, ion-neutral collision enhanced current, and
dust charge variation. Although the ion beam does not change the polarity of solitary waves in the case of adiabatic
dust charge variation, a transition from rarefactive to compressive solitary waves occurs in the presence of an ion beam with nonadiabatic
dust charge variation.
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All authors N. P. Acharya, S. Basnet, A. P. Misra, R. Khanal
Fluid Dynamics
Comparative Analysis of the Flow in a Realistic Human Airway
Mario Rüttgers, Julian Vorspohl, Luca Mayolle et al. (+7 more)
Accurate simulations of the flow in the human airway are essential for advancing diagnostic methods. Many existing computational studies rely on simplified geometries or
turbulence models, limiting their simulation's ability to resolve flow features such shear-layer instabilities or secondary
vortices. In this study, direct numerical simulations were performed for inspiratory flow through a detailed airway model which covers the nasal mask region to the 6th bronchial bifurcation. Simulations were conducted at two physiologically relevant Reynolds numbers with respect to the pharyngeal diameter, i.e., at Re_p=400 (resting) and Re_p=1200 (elevated breathing). These values characterize resting and moderately elevated breathing conditions. A
lattice-Boltzmann method was employed to directly simulate the flow, i.e., no
turbulence model was used. The flow field was examined across four anatomical regions: 1) the nasal cavity, 2) the naso- and oropharynx, 3) the laryngopharynx and larynx, and 4) the trachea and carinal bifurcation. The total pressure loss increased from 9.76 Pa at Re_p=400 to 41.93 Pa at Re_p=1200. The nasal cavity accounted for the majority of this loss for both Reynolds numbers, though its relative contribution decreased from 81.3% at Re_p=400 to 73.4% at Re_p=1200. At Re_p=1200, secondary
vortices in the nasopharyngeal bend and turbulent shear-layers in the glottis jet enhanced the local pressure losses. In contrast, the carinal bifurcation mitigated upstream unsteadiness and stabilized the flow. A key outcome is the spatial correlation between the pressure loss and the onset of flow instabilities across the four regions. This yields a novel perspective on how the flow resistance and
vortex dynamics vary with
geometric changes and flow rate.
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All authors Mario Rüttgers, Julian Vorspohl, Luca Mayolle, Benedikt Johanning-Meiners, Dominik Krug, Michael Klaas, Matthias Meinke, Sangseung Lee, Wolfgang Schröder, Andreas Lintermann