Peer Revenue Impact factor: volatile

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics

physics Watch Physics

Friday 10 October

Optics

Strong coupling of collective optical resonances in dielectric metasurfaces

Izzatjon Allayarov, Vittorio Aita, Diane J. Roth et al. (+5 more)

Dielectric metasurfaces can achieve strong light-matter interaction based on several types of collective (nonlocal) resonances, such as surface lattice resonances (SLRs) and quasi bound states in the continuum (quasi-BICs). Spectral selectivity, field enhancement, and high and controllable Q-factors make these resonances appealing for technological applications in lasing, sensing, nonlinear optics, and quantum photon sources. An emerging challenge focuses on tailoring light-matter interaction via mode coupling and hybridization between the fundamental resonances of a metasurface. While strong coupling phenomena have been demonstrated between various resonant modes, the interplay between collective resonances of different natures has not been observed to date. Here, we theoretically, numerically, and experimentally demonstrate the onset of coupling and hybridization between symmetry-protected quasi-BICs and SLRs in a dielectric metasurface. We show the emergence of anticrossing (or Rabi splitting) in the strong coupling regime with suppression of reflection, observed under TE-polarised excitation, and the manifestation of an accidental BIC under TM-polarised illumination as a result of energy exchange between the participating collective resonances in the weak coupling regime. The first effect is accompanied by hybridized near fields of the modes. The observed coupling mechanisms can be controlled by modifying the angle of incidence, polarisation, and surrounding environment. This foundational study on the coupling and hybridization of collective resonances offers insights that can be leveraged for the design of metasurfaces with targeted quasi-aBIC and collective hybridized resonances. It could also open new possibilities to control the near fields associated with such resonances, with promising applications in tunable nanophotonics and light manipulation.
Read the full abstract

All authors Izzatjon Allayarov, Vittorio Aita, Diane J. Roth, Boaz van Casteren, Anton Yu. Bykov, Andrey B. Evlyukhin, Anatoly V. Zayats, Antonio Calà Lesina

Accelerator Physics

Influence of an external static magnetic field on prebreakdown electron emission and heating

Roni Koitermaa, Marzhan Toktaganova, Andreas Kyritsakis et al. (+4 more)

High magnetic fields can increase the occurrence of vacuum arcing, suggesting that both electric and magnetic fields can play a role in the vacuum arcing process. The mechanism of vacuum arcing in high magnetic fields is believed to involve both the cathode and the anode, with the cathode serving as the originator of field-emitting nanoprotrusions or tips, while the anode serves a secondary role. Significant heating of the anode surface can be achieved by magnetic focusing of the emitted electron beam, leading to increased heat flux due to greater current density. We simulated the emitted electron beam in different configurations of the electric and magnetic fields using the particle-in-cell (PIC) and finite element methods (FEM). The heating caused by the impacting electron beam was simulated for magnetic fields ranging from 0 T to 30 T. The directions of the electric and magnetic fields were found to play a major role in the focusing of the electron beam. We found that a sufficient temperature increase on the anode surface for evaporation can be reached at magnetic fields on the order of 10-30 T, suggesting the possibility of plasma initiation on the anode side.
Read the full abstract

All authors Roni Koitermaa, Marzhan Toktaganova, Andreas Kyritsakis, Tauno Tiirats, Alexej Grudiev, Veronika Zadin, Flyura Djurabekova

Optics

Riemann-Silberstein geometric phase in 4D polarization space

Yuqiong Cheng, Yuan-Song Zeng, Wanyue Xiao et al. (+5 more)

Geometric phase is a far-reaching concept in quantum and classical physics. The first discovered geometric phase, the Pancharatnam-Berry (PB) phase, has profoundly shaped nanophotonics through metasurfaces. However, the PB phase arises from SU(2) polarization evolution and is constrained to a 2D polarization space, failing to capture the full polarization degrees of freedom. We generalize geometric phase to the 4D Riemann-Silberstein (RS) space that simultaneously describes electric, magnetic, and hybrid electric-magnetic polarizations. We show that SU(4) polarization evolution can generate a new geometric phase, the RS phase, alongside the PB phase. Unlike the PB phase that typically manifests in circularly polarized light, the RS phase can emerge in arbitrarily polarized light. Together, they enable a high-dimensional geometric framework for light propagation across general interfaces. We reveal that the phase shifts governed by Fresnel equations are direct manifestations of the RS-space geometric phases, integrating a century-old wave theory into this paradigm. We experimentally validate the framework using metasurfaces and achieve high-dimensional wavefront manipulation. Our work offers fundamental insights into the geometric nature of light-matter interactions, with implications for topological and non-Abelian physics in classical wave systems.
Read the full abstract

All authors Yuqiong Cheng, Yuan-Song Zeng, Wanyue Xiao, Tong Fu, Jiajun Wu, Geng-Bo Wu, Din Ping Tsai, Shubo Wang

General Physics

Universality of critical behaviors in the three-dimensional (3D) Ising magnets

Zhidong Zhang

This article gives a brief overview on recent advances in experiments of critical exponents in three groups of magnetic materials. Revisiting experimental data verifies that a universality class with the critical exponents beta = 3/8, gamma = 5/4 and delta = 13/3 occurs in the three-dimensional (3D) Ising magnets, such as transition-metal intermetallics, rare-earth transition-metal compounds and manganites. Furthermore, the topological contributions to critical behaviors in the 3D Ising model are estimated by the difference between the exact solutions and the approximation values.
Read the full abstract

Medical Physics

MORSE: Multiple Orthogonal Reference Sensitivity Encoding

Oliver Josephs, Barbara Dymerska, Nadine N. Graedel et al. (+3 more)

Parallel imaging is ubiquitous in MRI, enabling diverse applications such as ultra-high-resolution functional and quantitative imaging with greater temporal resolution or reduced scan times respectively. Successful unfolding is contingent on robust and accurate estimation of the relative coil sensitivities, which often involves computation times that preclude real-time deployment. Here we present a computationally-efficient method of robustly estimating coil sensitivities, and reconstructing under-sampled images using a data-driven regularised SENSE formalism. Our MORSE scheme estimates multiple sensitivities per voxel to address issues such as rapidly varying sensitivities, chemical shift artefact, or insufficient fields of view and provides a data-driven regularisation term for noise control. Exemplar structural and functional image reconstructions at 3T and 7T are presented and compared with a vendor-provided GRAPPA reconstruction as well as state-of-the-art ESPIRiT and LORAKS algorithms. MORSE consistently produced high-quality, artefact-free images with reconstruction times feasible for real-time deployment. It is flexible and robust, and made available to the community in open-source as a library of functions within the vendor-agnostic Gadgetron image reconstruction framework.
Read the full abstract

All authors Oliver Josephs, Barbara Dymerska, Nadine N. Graedel, Yael Balbastre, Nadege Corbin, Martina F. Callaghan

Physics and Society · Cross-listed from cs.AI

Physics-Informed High-order Graph Dynamics Identification Learning for Predicting Complex Networks Long-term Dynamics

Bicheng Wang, Junping Wang and Yibo Xue

Learning complex network dynamics is fundamental to understanding, modelling and controlling real-world complex systems. There are two main problems in the task of predicting the dynamic evolution of complex networks: on the one hand, existing methods usually use simple graphs to describe the relationships in complex networks; however, this approach can only capture pairwise relationships, while there may be rich non-pairwise structured relationships in the network. First-order GNNs have difficulty in capturing dynamic non-pairwise relationships. On the other hand, theoretical prediction models lack accuracy and data-driven prediction models lack interpretability. To address the above problems, this paper proposes a higher-order network dynamics identification method for long-term dynamic prediction of complex networks. Firstly, to address the problem that traditional graph machine learning can only deal with pairwise relations, dynamic hypergraph learning is introduced to capture the higher-order non-pairwise relations among complex networks and improve the accuracy of complex network modelling. Then, a dual-driven dynamic prediction module for physical data is proposed. The Koopman operator theory is introduced to transform the nonlinear dynamical differential equations for the dynamic evolution of complex networks into linear systems for solving. Meanwhile, the physical information neural differential equation method is utilised to ensure that the dynamic evolution conforms to the physical laws. The dual-drive dynamic prediction module ensures both accuracy and interpretability of the prediction. Validated on public datasets and self-built industrial chain network datasets, the experimental results show that the method in this paper has good prediction accuracy and long-term prediction performance.
Read the full abstract

Optics

Performance limit of on-chip speckle spectrometers

Bhupesh Kumar, Graham D. Bruce, Luca Dal Negro et al. (+1 more)

Disorder-driven, integrated speckle spectrometers offer exceptional spectral resolution within a compact design. They benefit from enhanced optical path lengths due to multiple light scattering events, however, often at the cost of low optical throughput. Here, we investigate the relationship between these two figures of merit by systematically varying the scattering strength of random-uniform disorder distributions. Furthermore, we also investigate the temperature stability of such spectrometers. Our study shows that the device resolution can be tuned from 2 nm to 20 pm, while the operating temperature ranges from 1 to more than 6 degrees and throughput can be varied by more than a factor of 10, paving the way for application-tailored design of microscale high-resolution spectrometers.
Read the full abstract

All authors Bhupesh Kumar, Graham D. Bruce, Luca Dal Negro, Sebastian A. Schulz

History and Philosophy of Physics

Two Types of Natural Kind Discovery: Nobel Meets Kuhn

Samuel Schindler

Philosophers have spilled much ink over the discovery of ideas in the classical 'context of discovery'. However, there has been little engagement with the question of what constitutes a discovery of 'things in the world'. A much-overlooked answer to this question is provided by T.S. Kuhn. In this paper, I show that discoveries awarded with a Nobel Prize in Physics in the past 53 years accord with a basic premise of Kuhn's account and his distinction between two types of natural kind discoveries. I also draw normative conclusions for credit attribution in science.
Read the full abstract

Fluid Dynamics

Bubble entrainment in turbulent jets leaping from liquid surface

Fangye Lin and Mingbo Li

We investigate the phenomenon of air entrainment in turbulent water jets exiting a pool near the free surface. Our experimental results reveal that bubble entrainment occurs only within a specific region close to the point where the jet exits the water and is dictated solely by the jet's exit velocity, rather than the Reynolds number. The morphology of the jet above the pool surface, influenced predominantly by the Froude number or the injection angle, classifies the flow into two regimes: curtain jet and column jet. However, variations in jet morphology have minimal impact on the critical velocity required for bubble entrainment. Our findings suggest that bubble entrainment is driven by the dynamic interplay of shear forces and instabilities. As the jet exits the nozzle, it interacts with the surrounding fluids, amplifying instabilities through Kelvin-Helmholtz mechanisms. These disturbances generate intense fluctuations on the jet surface, creating localized low-pressure zones that trap air and entrain bubbles. As the jet progresses further into the air, capillary forces dampen surface instabilities, diminishing the jet's capacity to sustain bubble entrainment at longer distances. This study offers new insights into the mechanics of air entrainment in turbulent water jets, emphasizing the role of injection velocity and instabilities in the entrainment process.
Read the full abstract

Optics

Polarization Dependence of Excess Loss of Amorphous Coating Supermirror in Optical Region for Cavity Ringdown Spectroscopy

Mitsunori Araki and Kohsuke Suma

A long optical path length is critical in achieving sensitive spectroscopy. For cavity ringdown spectroscopy, a cavity consisting of two supermirrors provides a long path length, where high reflectance of the supermirrors results from their slight excess loss. In the case of a crystal coating supermirror, the excess loss has been suggested to depend on polarization. On the other hand, an amorphous coating supermirror was expected to have a negligible polarization dependence. In this work, we measured the excess loss as a function of mirror rotation around its optical axis in the optical region at 681.2 nm for the three amorphous coating supermirrors produced simultaneously by vapor deposition in the same furnace. The back mirror of the cavity was rotated, and the ringdown time as a function of rotational angle was measured every 10 degrees. As a result, sinusoidal variations in excess loss were observed depending on the rotation. The difference in excess loss between the best and worst rotational angles during the rotation of the back mirror reached a maximum of 5.8 +- 1.2 ppm. This difference demonstrates the importance of optimizing the rotational angle alignment of supermirrors to achieve high sensitivity via a long path length in cavity ringdown spectroscopy.
Read the full abstract

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

Atomistic origin of low thermal conductivity in quaternary chalcogenides Cu(Cd, Zn)$_2$InTe$_4$

Nirmalya Jana, Amit Agarwal and Koushik Pal

Crystalline semiconductors with intrinsically low lattice thermal conductivity ($\mathcal{K}$) are vital for device applications such as barrier coatings and thermoelectrics. Quaternary chalcogenide semiconductors such as CuCd$_2$InTe$_4$ and CuZn$_2$InTe$_4$ are experimentally shown to exhibit low $\mathcal{K}$, yet its microscopic origin remains poorly understood. Here, we analyse their thermal transport mechanisms using a unified first-principles framework that captures both the Peierls (particle-like propagation, $\mathcal{K}_P$) and coherence (wave-like tunneling, $\mathcal{K}_C$) mechanisms of phonon transport. We show that extended antibonding states below the Fermi level lead to enhanced phonon anharmonicity and strong scattering of heat-carrying phonon modes, suppressing $\mathcal{K}$ in these chalcogenides. We show that $\mathcal{K}_P$ dominates the total thermal conductivity, while $\mathcal{K}_C$ remains negligible even under strong anharmonicity of the phonon modes. The heavier Cd ions in CuCd$_2$InTe$_4$ induce greater acoustic-optical phonon overlap and scattering compared to CuZn$_2$InTe$_4$, further lowering thermal conductivity of the former. Additionally, grain boundary scattering in realistic samples contributes to further suppression of thermal transport. Our findings establish the atomistic origins of low $\mathcal{K}$ in quaternary chalcogenides and offer guiding principles for designing low-thermal-conductivity semiconductors.
Read the full abstract

Optics

Topologically-protected superluminal pair annihilation in photonic time crystals

Liang Zhang, Chenhao Pan, Jinze He et al. (+4 more)

Photonic time crystals (PTCs) - dielectric media whose permittivity is periodically modulated in time - map to a Dirac equation with an imaginary mass, opening a momentum gap (k-gap) where modes grow or decay exponentially. Here, we introduce a sequence of temporal Jackiw-Rebbi kinks that act as a programmable flip of the Dirac mass, exchanging the amplifying and decaying in-gap modes. By launching two seeded pulses with a controlled relative phase, we demonstrate topological pair annihilation in spacetime domain, the phase-selective cancellation of counter-propagating, k-gap-amplified modes. The resulting spatiotemporal cascade appears superluminal, yet causality is preserved because the cascaded pattern carries no net energy flux. To facilitate implementation, we construct a minimal time-varying non-Hermitian lattice model and reproduce the phase-selective pair annihilation behavior, establishing a direct continuum-lattice correspondence. Our results identify topological kinks as temporal gating to manipulate the growth and wave propagation of time-varying media.
Read the full abstract

All authors Liang Zhang, Chenhao Pan, Jinze He, Danni Chen, Zirui Zhao, Qingqing Cheng, Yiming Pan

Medical Physics

A pilot cohort study of a microfluidic-based point-of-care bilirubin measurement system

Jean Pierre Ndabakuranye, Inge W.G. Last, Kay Weng Choy et al. (+6 more)

Objective The concentration of bilirubin in blood or serum is useful for assessing liver function as well as monitoring treatment. This study evaluates the clinical performance of a novel point-of-care (PoC) device for the detection of bilirubin in serum. The PoC device incorporates an integrated miniature optoelectronic sensing module and a microfluidic test cartridge. Methods Patients' serum total bilirubin concentrations, ranging from 2 {\mu}mol/L to 480 {\mu}mol/L, were measured using the PoC device and the standard laboratory method (n=20). Bland-Altman analysis and regression analysis using Passing-Bablok method were used to benchmark the PoC device against the standard laboratory measurements. The diagnostic capability of the PoC device in categorising the serum samples within clinically relevant bilirubin concentration thresholds of 200, 300, and 450 {\mu}mol/L was assessed using receiver operating characteristic (ROC) analysis. Results The mean difference between the PoC device and the standard laboratory method was -5.6 {\mu}mol/L, with a 95% confidence interval (CI) of -45.1 {\mu}mol/L to 33.9 {\mu}mol/L. The coefficient of determination (R2) was 0.986. The PoC device achieved a detection sensitivity of 90% and specificity of 97% in categorising bilirubin concentrations within bands used in clinical decision-making. Conclusions This study demonstrates that the proposed PoC device is capable of measuring bilirubin levels in patient samples with clinically acceptable accuracy.
Read the full abstract

All authors Jean Pierre Ndabakuranye, Inge W.G. Last, Kay Weng Choy, Peter Thurgood, Jason C. Steel, Genia Burchall, Stella Stylianou, Khashayar Khoshmanesh, Arman Ahnood

Applied Physics

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott et al. (+9 more)

In this work, we demonstrate a passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT on a sapphire substrate for W-band operation, featuring a 5.5 nm Al0.35Ga0.65N barrier under the gate and a 31 nm Al0.35Ga0.65N barrier in the gate access regions. The device achieves a drain current density of 1.8 A/mm, a peak transconductance of 750 mS/mm, and low gate leakage with a high on/off ratio of 10^7. Small-signal characterization reveals a current-gain cutoff frequency of 127 GHz and a maximum oscillation frequency of 203 GHz. Continuous-wave load-pull measurements at 94 GHz demonstrate an output power density of 2.8 W/mm with 26.8% power-added efficiency (PAE), both of which represent the highest values reported for Ga-polar GaN HEMTs on sapphire substrates and are comparable to state-of-the-art Ga-polar GaN HEMTs on SiC substrates. Considering the low cost of sapphire, the simplicity of the epitaxial design, and the reduced fabrication complexity relative to N-polar devices, this work highlights the potential of recessed-gate Ga-polar AlGaN/GaN HEMTs on sapphire as a promising candidate for next-generation millimeter-wave power applications.
Read the full abstract

All authors Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert, Jiahao Chen, Rafael A. Choudhury, Kyudong Kim, Yu-Chun Wang, Ahmad E. Islam, Andrew J. Green, Shubhra S. Pasayat, Chirag Gupta

Chemical Physics · Cross-listed from stat.ML

Gradient-Guided Furthest Point Sampling for Robust Training Set Selection

Morris Trestman, Stefan Gugler, Felix A. Faber et al. (+1 more)

Training set sampling methods are used to improve model performance and lower data costs in machine learning problems relevant to chemistry. We introduce Gradient Guided Furthest Point Sampling (GGFPS), a simple extension of Furthest Point Sampling (FPS) that leverages molecular force norms to guide efficient sampling of configurational spaces of molecules. Numerical evidence is presented for a toy system (the Styblinski-Tang function) as well as for molecular dynamics trajectories from the MD17 dataset. Our numerical results indicate superior data efficiency and model robustness when using GGFPS compared to FPS and uniform random sampling (URS), as well as established supervised FPS-style selectors, PCov-FPS and PCov-CUR. Distribution analysis of the MD17 data suggests that FPS systematically under-samples equilibrium geometries, resulting in large test errors for relaxed structures. GGFPS cures this artifact and (i) enables up to twofold reductions in training cost without sacrificing predictive accuracy compared to FPS in the 2-dimensional Styblinski-Tang system, (ii) systematically lowers prediction errors for equilibrium as well as strained structures in MD17, and (iii) systematically decreases prediction error variances across all of the MD17 configuration spaces. These results suggest that gradient-aware sampling methods hold great promise as effective training set selection tools, and that naive use of FPS may result in imbalanced training and inconsistent prediction outcomes.
Read the full abstract

All authors Morris Trestman, Stefan Gugler, Felix A. Faber, O. A. von Lilienfeld

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

Simulating dynamic bonding in soft materials

Tyla R. Holoman, B. P. Prajwal, Glen M. Hocky et al. (+1 more)

Dynamic bonding is an essential feature of many soft materials. Molecular simulations have proven to be a powerful tool for modeling bonding kinetics and thermodynamics in these materials, providing insights into their properties that cannot be obtained by experiments alone. Here, we review recent advances in modeling dynamic bonding in soft matter via molecular dynamics, Monte Carlo, and hybrid simulation methods, highlighting outstanding challenges and future directions.
Read the full abstract

All authors Tyla R. Holoman, B. P. Prajwal, Glen M. Hocky, Thomas M. Truskett

Thursday 9 October

Applied Physics

Intermediate Resistive State in Wafer-Scale MoS${_2}$ Memristors through Lateral Silver Filament Growth for Artificial Synapse Applications

Yuan Fa, Milan Buttberg, Ke Ran et al. (+17 more)

Memristors based on two-dimensional materials (2DMs) have garnered significant attention due to their fast resistive switching (RS) behavior and atomic-level thickness, which enables low power consumption, making them promising candidates for neuromorphic computing. Among these, memristors based on molybdenum disulfide (MoS${_2}$) have been extensively studied. Their RS has been attributed to the formation and rupture of conductive filaments (CFs). However, the underlying mechanism of filament formation remains underexplored, and the inherently stochastic nature of RS leads to high variability and limited reproducibility. Additionally, the lack of scalable fabrication techniques for 2DM-based memristors restricts their integration into standard semiconductor technology. Here, we demonstrate memristors based on metal-organic chemical vapor-deposited MoS${_2}$ on the wafer-scale. Our devices exhibit volatile and nonvolatile RS behavior, tunable by modulating the current compliance. Notably, we observe stable RS characteristics in an intermediate resistive state (IRS), featuring set and reset voltages within $\pm$1 V, an endurance exceeding 2500 cycles in direct current mode, and a state retention over 10${^6}$ s. The experimental data, complemented with simulations, suggest that the IRS originates from the lateral growth of the CF within the MoS${_2}$ layer. Furthermore, the devices successfully emulate synaptic plasticity with current responses on the microsecond timescale, highlighting their potential for large-scale integration in neuromorphic computing architectures.
Read the full abstract

All authors Yuan Fa, Milan Buttberg, Ke Ran, Rana Walied Ahmad, Dennis Braun, Lukas Völkel, Jimin Lee, Sofía Cruces, Bart Macco, Bárbara Canto, Holger Lerch, Thorsten Wahlbrink, Holger Kalisch, Michael Heuken, Andrei Vescan, Joachim Mayer, Zhenxing Wang, Ilia Valov, Stephan Menzel, Max C. Lemme

Physics and Society

The geography of novel and atypical research

Qing Ke, Tianxing Pan and Jin Mao

The production of knowledge has become increasingly a global endeavor. Yet, location related factors, such as local working environment and national policy designs, may continue to affect what kind of science is being pursued. Here we examine the geography of the production of creative science by country, through the lens of novelty and atypicality proposed in Uzzi et al. (2013). We quantify a country's representativeness in novel and atypical science, finding persistent differences in propensity to generate creative works, even among developed countries that are large producers in science. We further cluster countries based on how their tendency to publish novel science changes over time, identifying one group of emerging countries. Our analyses point out the recent emergence of China not only as a large producer in science but also as a leader that disproportionately produces more novel and atypical research. Discipline specific analysis indicates that China's over-production of atypical science is limited to a few disciplines, especially its most prolific ones like materials science and chemistry.
Read the full abstract

Computational Physics

Interpolative separable density fitting on adaptive real space grids

Hai Zhu, Chia-Nan Yeh, Miguel A. Morales et al. (+3 more)

We generalize the interpolative separable density fitting (ISDF) method, used for compressing the four-index electron repulsion integral (ERI) tensor, to incorporate adaptive real space grids for potentially highly localized single-particle basis functions. To do so, we employ a fast adaptive algorithm, the recently-introduced dual-space multilevel kernel-splitting method, to solve the Poisson equation for the ISDF auxiliary basis functions. The adaptive grids are generated using a high-order accurate, black-box procedure that satisfies a user-specified error tolerance. Our algorithm relies on the observation, which we prove, that an adaptive grid resolving the pair densities appearing in the ERI tensor can be straightforwardly constructed from one that resolves the single-particle basis functions, with the number of required grid points differing only by a constant factor. We find that the ISDF compression efficiency for the ERI tensor with highly localized basis sets is comparable to that for smoother basis sets compatible with uniform grids. To demonstrate the performance of our procedure, we consider several molecular systems with all-electron basis sets which are intractable using uniform grid-based methods. Our work establishes a pathway for scalable many-body electronic structure simulations with arbitrary smooth basis functions, making simulations of phenomena like core-level excitations feasible on a large scale.
Read the full abstract

All authors Hai Zhu, Chia-Nan Yeh, Miguel A. Morales, Leslie Greengard, Shidong Jiang, Jason Kaye

Optics

Exact formulation of Huygens' principle in terms of generalized spatiotemporal-dipole secondary sources

Gavin R. Putland

A "spatiotemporal dipole" wave source, as defined by D.A.B. Miller (1991), differs from an ordinary ("spatial") dipole source in that the inverted monopole is delayed relative to the uninverted monopole, the delay being equal to the propagation time from one monopole to the other. A "generalized" spatiotemporal dipole (GSTD), as defined here, is generalized in two ways: first, the delay may be smaller in absolute value (but not larger) than the propagation time, so that the radiated waves cancel at a certain angle from the axis of the dipole; second, one monopole may be attenuated relative to the other, so that the cancellation is exact at a finite distance - on a circle coaxial with the dipole. I show that the Kirchhoff integral theorem, for a single monopole primary source, gives the same wave function as a certain distribution of GSTD secondary sources on the surface of integration. In the GSTDs, the "generalized" delay allows the surface of integration to be general (not necessarily a primary wavefront), whereas the attenuation allows an exact match of the wave function even in the near field of the primary source. At each point on the surface of integration, the circle of cancellation of the GSTD secondary source passes through the primary source, which therefore receives no backward secondary waves, while the direction of specular reflection of the primary wave passes through the same circle, giving a geometrical-optical explanation of the suppression of backward secondary waves at any field point.
Read the full abstract

Biological Physics

Control of Neuronal Survival and Development Using Conductive Diamond

Samira Falahatdoost, Yair D. J. Prawer, Danli Peng et al. (+13 more)

This study demonstrates the control of neuronal survival and development using nitrogen-doped ultrananocrystalline diamond (N-UNCD). We highlight the role of N-UNCD in regulating neuronal activity via near-infrared illumination, demonstrating the generation of stable photocurrents that enhance neuronal survival and neurite outgrowth and foster a more active, synchronized neuronal network. Whole transcriptome RNA sequencing reveals that diamond substrates improve cellular-substrate interaction by upregulating extracellular matrix and gap junction-related genes. Our findings underscore the potential of conductive diamond as a robust and biocompatible platform for noninvasive and effective neural tissue engineering.
Read the full abstract

All authors Samira Falahatdoost, Yair D. J. Prawer, Danli Peng, Andre Chambers, Hualin Zhan, Leon Pope, Alastair Stacey, Arman Ahnood, Hassan N. Al Hashem, Sorel E. De Leon, David J. Garrett, Kate Fox, Michael B. Clark, Michael R. Ibbotson, Steven Prawer, Wei Tong

Data Analysis and Statistics · Cross-listed from cond-mat.mtrl-sci

Ensemble-Based Data Assimilation for Material Model Characterization in High-Velocity Impact

Rong Jin, Guangyao Wang and Xingsheng Sun

High-fidelity simulations are essential for predicting material behavior under high-velocity impact (HVI), but their accuracy depends on material models and parameters that are often calibrated by manual fitting to multiple costly experiments. In this study, we develop an ensemble-based data assimilation framework for automatic calibration of selected plasticity, fracture, and equation-of-state (EOS) parameters in HVI simulations using data from a single HVI test. The framework combines Smoothed Particle Hydrodynamics, the ensemble Kalman filter (EnKF), and adaptive covariance inflation to mitigate variance collapse. A simple benchmark first shows that the framework is at least one order of magnitude more computationally efficient than Markov chain Monte Carlo at comparable identification accuracy. We then use synthetic back-face deflection data for an AZ31B magnesium plate to identify representative parameters in the Johnson-Cook plasticity and fracture models and the Mie-Gruneisen EOS. Results under under-biased, over-biased, and limited-observation cases show that parameters to which the data are sufficiently sensitive can be accurately recovered within about five iterations, with convergent ensemble standard deviations. In contrast, insensitive parameters tend to converge to incorrect values and retain large ensemble spreads. With fewer observations, convergence is still achieved for sensitive parameters but requires more iterations. Under extreme prior bias, a parameter rejuvenation strategy drives sensitive parameters toward the true values even when the truth lies outside the initial ensemble spread. These results show that ensemble standard deviation provides a practical diagnostic for parameter sensitivity, identifiability, and potential non-uniqueness. Overall, the proposed framework offers an efficient and robust approach for material model characterization in HVI problems.
Read the full abstract

Physics and Society

Combining Blotto Networks and Voter Models to Simulate Voter Behavior in Response to Competitive Election Spending

Renee Jerome

In the past, the Voter Model has been explicitly used to model the impact of propaganda on a dynamic, interconnected population, and certain factors have been identified that influence the behavior of voters when under outside influence. The Blotto Game has also been explicitly used to study information wars between two opposing parties, whether in regards to a political issue or advertising war. Both the graph theory behind the Voter Model and the game theory aspects of the Blotto Game are relevant to the behavior of voters or consumers when they are under the influence of competing propaganda campaigns, and for this reason both are useful to understand the most effective spending strategy. In this project, we seek to combine the two problems into a Voter-Blotto Game and examine what components of the graph most effect its value in the eyes of the competing players.
Read the full abstract

Computational Physics · Cross-listed from cs.LG

Multi-fidelity Batch Active Learning for Gaussian Process Classifiers

Murray Cutforth, Yiming Yang, Tiffany Fan et al. (+2 more)

Many science and engineering problems rely on expensive computational simulations, where a multi-fidelity approach can accelerate the exploration of a parameter space. We study efficient allocation of a simulation budget using a Gaussian Process (GP) model in the binary simulation output case. This paper introduces Bernoulli Parameter Mutual Information (BPMI), a batch active learning algorithm for multi-fidelity GP classifiers. BPMI circumvents the intractability of calculating mutual information in the probability space by employing a first-order Taylor expansion of the link function. We evaluate BPMI against several baselines on two synthetic test cases and a complex, real-world application involving the simulation of a laser-ignited rocket combustor. In all experiments, BPMI demonstrates superior performance, achieving higher predictive accuracy for a fixed computational budget.
Read the full abstract

All authors Murray Cutforth, Yiming Yang, Tiffany Fan, Serge Guillas, Eric Darve

Atmospheric and Oceanic Physics · Cross-listed from astro-ph.EP

Constraining exoplanet interiors using observations of their atmospheres

Tim Lichtenberg, Oliver Shorttle, Johanna Teske et al. (+1 more)

Astronomical surveys have identified numerous exoplanets with bulk compositions that are unlike the planets of the Solar System, including rocky super-Earths and gas-enveloped sub-Neptunes. Observing the atmospheres of these objects provides information on the geological processes that influence their climates and surfaces. In this Review, we summarize the current understanding of these planets, including insights into the interaction between the atmosphere and interior based on observations made with the James Webb Space Telescope (JWST). We describe the expected climatic and interior planetary regimes for planets with different density and stellar flux and how those regimes might be observationally distinguished. We also identify the observational, experimental, and theoretical innovations that will be required to characterize Earth-like exoplanets.
Read the full abstract

All authors Tim Lichtenberg, Oliver Shorttle, Johanna Teske, Eliza M.-R. Kempton

Instrumentation and Detectors

Burnup Measurement using Bent Crystal Diffraction Spectrometers for Pebble Bed Reactors

Ian Kolaja, Lee Bernstein, Ludovic Jantzen et al. (+3 more)

Burnup measurement is essential for monitoring and controlling pebble bed reactors (PBRs), where fuel pebbles circulate rapidly through the core. However, conventional gamma spectroscopy using high purity germanium (HPGe) detectors is difficult due to high activity levels in discharge pebbles, leading to excessive dead time and Compton scattering. This study explores the use of bent crystal diffraction (BCD) spectrometers to filter the emitted gamma spectrum and isolate key peaks for improved measurement accuracy and speed. Pebble wise depletion calculations were performed and the resulting spectra were analyzed using ray tracing (SHADOW3) and gamma response modeling (GADRAS). Key isotopes, $^{137m}$Ba/$^{137}$Cs, $^{239}$Pu, $^{144}$Ce, $^{148m}$Pm, and $^{140}$La, were found to strongly correlate with burnup, residence time, core passes, plutonium production, and fluence. Machine learning regression models applied to simulated spectra achieved a coefficient of determination ($R^2$) as high as 0.995 for burnup prediction. Among various BCD configurations, mosaic silicon crystals in the (440) orientation combined with an HPGe detector provided optimal performance for $^{137m}$Ba, while (220) and (440) configurations paired with scintillators were effective for the remaining isotopes.
Read the full abstract

All authors Ian Kolaja, Lee Bernstein, Ludovic Jantzen, Eleanor Tubman, Tatiana Siaraferas, Massimiliano Fratoni

Optics

Experimental observation of energy-band Riemann surface

Dali Cheng, Heming Wang, Janet Zhong et al. (+3 more)

Non-Hermiticity naturally arises in many physical systems that exchange energy with their environment. The presence of non-Hermiticity leads to many novel topological physics phenomena and device applications. In the non-Hermitian energy band theory, the foundation of these physics and applications, both energies and wavevectors can take complex values. The energy bands thus become a Riemann surface, and such an energy-band Riemann surface underlies all the important signatures of non-Hermitian topological physics phenomena. Despite a long history and recent theoretical interests, the energy-band Riemann surface has not been experimentally studied. Here we provide a photonic observation of the energy-band Riemann surface of a non-Hermitian system. This is achieved by applying a tunable imaginary gauge transformation on the platform of the photonic synthetic frequency dimension. From the measured topology of the Riemann surface, we reveal the complex-energy winding, the open-boundary-condition spectrum, the generalized Brillouin zone, and the branch points. Our findings demonstrate a unified framework in the studies of diverse effects in non-Hermitian topological physics through an experimental observation of energy-band Riemann surfaces.
Read the full abstract

All authors Dali Cheng, Heming Wang, Janet Zhong, Eran Lustig, Charles Roques-Carmes, Shanhui Fan

Chemical Physics

Revealing Light-Driven Dynamics at Nanostructured Solid-Liquid Interfaces with In-Situ SHG

Tarique Anwar, Diana DallAglio, Milad Sabzehparvar et al. (+1 more)

Light and heat drive interfacial chemistry at solid-liquid interfaces, underpinning processes central to sustainable energy conversion, including photoelectrochemical and hydrovoltaic systems. Yet, non-invasive probing of light-induced interfacial dynamics remains challenging due to the weak and spatially complex nature of optical signals. Here, we introduce a nanophotonic platform that enhances second harmonic generation (SHG) from nanostructured interfaces by over two orders of magnitude, enabling real-time, all-optical access to interfacial processes. We develop a rigorous overlap-integral formalism that provides a general quantitative framework for SHG in nanostructured geometries. By accounting for spatially inhomogeneous electromagnetic fields, this approach links the nonlinear response to geometry-dependent near-field and reveals new degrees of freedom, namely independent control of attenuation and phase, which are absent in planar systems. This enables deterministic tuning of surface and electric-field-induced contributions through nanophotonic design. Using in situ SHG at silicon-oxide-electrolyte interfaces, we resolve subtle spectral shifts of ~1.3 nm with electrolyte concentration, indicating coupling between electrical double layer potential and semiconductor polarizability. Under controlled optical excitation, we observe reversible, intensity-dependent modulation of interfacial susceptibility, with a decrease at low intensities consistent with photocharging and an increase at higher intensities due to photothermal effects. These results establish nanophotonic-enhanced SHG as a quantitative and tunable probe of interfacial phenomena, providing a unified framework linking optical response, electrostatics, and geometry, and opening new avenues for controlling interfacial charge and potential with light for applications in energy conversion, catalysis, and nanophotonic devices.
Read the full abstract

All authors Tarique Anwar, Diana DallAglio, Milad Sabzehparvar, Giulia Tagliabue

Fluid Dynamics

Intelligent backpropagated neural networks application on Couette-Poiseuille flow of variable viscosity in a composite porous channel filled with an anisotropic porous layer

Timir Karmakar and Amrita Mandal

This study examines Couette-Poiseuille flow of variable viscosity within a channel that is partially filled with a porous medium. To enhance its practical relevance, we assume that the porous medium is anisotropic with permeability varying in all directions, making it a positive semidefinite matrix in the momentum equation. We assume the Navier-Stokes equations govern the flow in the free flow region, while the Brinkman-Forchheimer-extended Darcy's equation governs the flow inside the porous medium. The coupled system contains a nonlinear term from the Brinkman-Forchheimer equation. We propose an approximate solution using an iterative method valid for a wide range of porous media parameter values. For both high and low values of the Darcy number, the asymptotic solutions derived from the regular perturbation method and matched asymptotic expansion show good agreement with the numerical results. However, these methods are not effective in the intermediate range. To address this, we employ the artificial Levenberg-Marquardt method with a back-propagated neural network (ALMM-BNN) paradigm to predict the solution in the intermediate range. While it may not provide the exact solutions, it successfully captures the overall trend and demonstrates good qualitative agreement with the numerical results. This highlights the potential of the ALMM-BNN paradigm as a robust predictive tool in challenging parameter ranges where numerical solutions are either difficult to obtain or computationally expensive. The current model provides valuable insights into the shear stress distribution of arterial blood flow, taking into account the variable viscosity of the blood in the presence of inertial effects. It also offers a framework for creating glycocalyx scaffolding and other microfluidic systems that can mimic the biological glycocalyx.
Read the full abstract

Plasma Physics

Nonlinear evolution of perturbatively driven kinetic instabilities far from marginal stability

Emma G. Devin and Vinícius N. Duarte

Kinetic instabilities develop when a system's distribution function deviates from thermal equilibrium in such a way that allows free energy from that distribution to drive resonant modes. These instabilities occur in many systems, such as fusion and astrophysical plasmas, neutral fluids, and self-gravitating systems. Motivated by the case of Alfvénic instabilities driven by minority populations of energetic particles in tokamak plasmas, we consider a kinetic instability in the presence of sources and sinks and with perturbative drive far from its instability threshold, where a theoretical description of the time evolution has not yet been established. In cases with steady-state saturation levels, we find that the mode first evolves linearly, driven by the positive distribution gradient, then undergoes a fast, strongly nonlinear transition where the distribution function slope is completely flattened around the resonance. The system then evolves in a weakly nonlinear regime driven by the balance of the wave drive and dissipation until reaching saturation. The strongly nonlinear transition is sufficiently fast that it can be treated as occurring instantaneously, and by considering a time-local approximation for the distribution after the flattening has occurred, we find a closed-form analytical solution for the mode amplitude in the weakly nonlinear phase. A compact piecewise-continuous solution for the entire time evolution of the mode amplitude is therefore constructed. This result is shown to agree closely with nonlinear kinetic simulations and is derived within a framework common to other physical systems such as galactic discs and viscous fluids.
Read the full abstract