Medical Physics
Sampling Density Compensation using Fast Fourier Deconvolution
Rui Luo, Peng Hu and Haikun Qi
Density Compensation Function (DCF) is widely used in non-Cartesian MRI reconstruction, either for direct Non-Uniform Fast
Fourier Transform (NUFFT) reconstruction or for iterative undersampled reconstruction. Current state-of-the-art methods involve time-consuming tens of iterations, which is one of the main hurdles for widespread application of the highly efficient non-Cartesian MRI. In this paper, we propose an efficient, non-iterative method to calculate DCF for arbitrary non-Cartesian $k$-space trajectories using Fast
Fourier Deconvolution. Simulation experiments demonstrate that the proposed method is able to yield DCF for 3D non-Cartesian reconstruction in around 20 seconds, achieving orders of magnitude speed improvement compared to the state-of-the-art method while achieving similar reconstruction quality.
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Optics
Non-Diffracting Beams for Near-Field Millimeter-Wave Communications: Advantage Regimes Under Aperture and Blockage Constraints
Yifeng Qin, Jing Chen, Zhi Hao Jiang et al. (+2 more)
Near-field blockage changes the beam-design objective in millimeter-wave links: maximizing the unblocked on-axis gain does not necessarily maximize blocked-link performance. This paper studies when phase-only, aperture-constrained non-diffracting (ND) beams provide a blocked-link advantage over equal-aperture, equal-power conventional reference beams. We develop a unified annular-spectrum framework that generates isotropic Bessel-like and anisotropic Mathieu-like beams under discrete phased-array constraints, and a geometry-aware analysis centered on three propagation landmarks: the peak-intensity distance, the crossover distance, and an effective post-blockage recovery distance. Their relationship yields a recovery-before-crossover condition linking blockage size, depth, cone angle, and usable ND range, and motivates a blocked-link gain ratio that maps directly onto an achievable-rate gap at every operating SNR. The analysis also explains why anisotropic Mathieu-like beams can outperform isotropic ones under direction-dependent blockage. Monte Carlo simulations verify the predicted advantage regimes, an auxiliary comparison against a near-field focusing baseline confirms that the advantage persists against an unblocked-optimal array, and sensitivity studies over cone-angle choice and partial-transmission blockers show that the opaque-screen picture is a conservative reading of the underlying physics. The results identify Bessel-like and Mathieu-like beams as practical candidates for blockage-resilient near-field communications.
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All authors Yifeng Qin, Jing Chen, Zhi Hao Jiang, Zhining Chen, Yongming Huang
Applied Physics
Unidirectional Zero Reflection and Perfect Absorption via Exceptional Points in Active Piezoelectric Willis Metamaterials
Hrishikesh Danawe and Serife Tol
Electro-momentum coupling in piezoelectric metamaterials with broken inversion
symmetry enables asymmetric elastic wave transport by linking macroscopic electric fields to momentum, an effect analogous to Willis coupling in elastic media. A one-dimensional layered piezoelectric metamaterial integrated with shunt
circuits, consisting of a resistor, inductor, and strain-proportional voltage feedback gain, is proposed to achieve dynamic control of frequency-dependent stiffness and damping through electromechanical interactions. Tuning the
circuit parameters yields direction-dependent wave scattering at targeted frequencies. Dynamic homogenization reveals macroscopic constitutive relations exhibiting both Willis and electro-momentum couplings. Non-Hermitian exceptional points are identified, where scattering eigenmodes coalesce and produce extreme asymmetries in wave response. Near these points, the system realizes unidirectional zero reflection (UZR) and unidirectional perfect absorption (UPA), achieving complete absorption from one direction and total reflection from the opposite side. The findings demonstrate a compact and reconfigurable platform for tunable, directional elastic wave control using passive-active hybrid metamaterials, opening new avenues for programmable devices in acoustic isolation, wave-based computing, sensing, and energy manipulation in solid media.
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Accelerator Physics
Obvious and non-obvious aspects of digital Self-Excited-Loops for SRF cavity control
Larry Doolittle, Shreeharshini Murthy, Matei Guran et al. (+3 more)
In 1978, Delayen showed how Self-Excited Loops (SEL) can be used to great advantage for controlling narrow-band SRF cavities. Its key capability is establishing closed-loop amplitude control early in the setup process, stabilizing Lorentz forces to allow cavity tuning and phase loop setup in a stable environment. As people around the world implement this basic idea with modern FPGA DSP technology, multiple variations and operational scenarios creep in that have both obvious and non-obvious ramifications for latency, feedback stability, and resiliency. This paper will review the key properties of a Delayen-style SEL when set up for open-loop, amplitude stabilized, and phase-stabilized modes. Then the original analog
circuit will be compared and contrasted with the known variations of digital CORDIC-based implementations.
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All authors Larry Doolittle, Shreeharshini Murthy, Matei Guran, Lennon Reyes, Shrividhyaa Sankar Raman, Philip Varghese
Computational Physics · Cross-listed from cond-mat.soft
Grain volume distribution alters the critical phenomena in complex granular systems
Teng Man, Yimin Lu, Zhongrong Wang et al. (+3 more)
The grain size distribution (GSD) plays an important role in the mechanical properties of amorphous disordered systems and complex granular materials. Varying GSD causes segregation issues and alters critical behaviors. This work used the discrete element method (DEM) to investigate the rheological and critical behaviors of sheared granular flows with various GSDs. The results show that, while a unified rheological relation can be obtained, a characteristic length scale, which is associated with the contact probability and can be obtained from any GSD, is embedded within such a polydisperse disordered system. We further acquire a correlation function between critical solid fractions and dimensionless grain volume distributions. This work elucidates the effect of particle volumes on the rheology and micromechanics of dry granular systems and provides further insights in better incorporating the influence of other particle properties into a unified framework, which is helpful and critical for the corresponding engineering and geophysical problems.
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All authors Teng Man, Yimin Lu, Zhongrong Wang, Herbert Huppert, Alessio Zaccone, Honglei Sun
Physics Education
Reflections of quantum educators on strategies to diversify the second quantum revolution
Apekshya Ghimire and Chandralekha Singh
We focus on reflections and suggestions of five college
quantum educators from four different institutions (two from same institution) regarding what can be done to diversify the second
quantum revolution. They are leading QIST researchers, and very passionate about improving
quantum education. The educators were asked about their thoughts on whether the interdisciplinary nature of the field, in which nobody can claim to be an expert in all aspects of QIST, may make it easier to create a better culture from the beginning, supportive of equitable participation of diverse groups unlike physics. This is because disciplines such as physics have an ingrained inequitable culture based on brilliance attribution that is a major impediment to diversity, equity and inclusion. Educators were interviewed on Zoom using a semi-structured think-aloud protocol about various issues related to QIST education including those pertaining to how to diversify the second
quantum revolution. Their suggestions can be invaluable and can help other educators adapt and implement strategies to diversify QIST.
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Optics
Raman-Accelerated Power Depletion of Fundamental Mode in a Few-Mode Fiber in the Visible Spectral Range
Wasyhun A. Gemechu, Guohao Fu and Mario Zitelli
We experimentally and numerically investigate Raman-driven power depletion in the fundamental mode of few-mode fibers (FMFs) excited by visible ultrashort pulses. Using a tunable femtosecond
laser and SMF-28 fibers operated below the single-mode cutoff wavelength, we explore nonlinear mode dynamics through precise coupling,
holographic mode decomposition, and spectral analysis. Experiments on 12-meter and 50-meter fibers reveal significant energy transfer to higher-order modes via intermodal Raman scattering. These findings advance our understanding of nonlinear propagation in FMFs, with important implications for high-power
laser delivery and next-generation optical communication systems.
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Classical Physics · Cross-listed from cond-mat.soft
Aging and configurational memories at rough frictional interfaces
Kasra Farain and Daniel Bonn
Frictional interfaces retain distinct
memories of how they were sheared and how long they have rested, yet rate-and-state descriptions typically compress these histories into a single state variable. Here we combine nanometer-per-second sliding experiments on rough multi-asperity contacts with different protocols to disentangle temporal and configurational
memories at frictional onset. We identify a broad friction force peak associated with shear-driven reorganization of the load-bearing contact network. By contrast, holding a previously sheared system at rest in an arrested configuration produces a much narrower friction force peak that grows approximately logarithmically with hold time and relaxes over nanometer-scale slip distances. Configurational disorder without waiting regenerates only the broad peak, whereas waiting without configurational disorder generates only the aging peak. These results show that aging and configurational disorder write and read experimentally separable frictional
memories, and that static friction is a protocol-dependent quantity rather than a fixed material property.
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Chemical Physics
Herman-Kluk-Like Semi-Classical Initial-Value Representation for Boltzmann Operator
Binhao Wang, Fan Yang, Chen Xu et al. (+1 more)
The coherent-state initial-value representation (IVR) for the semi-classical real-time propagator of a
quantum system, developed by Herman and Kluk (HK), is widely used in computational studies of chemical dynamics. On the other hand, the Boltzmann operator $e^{-\hat{H}/(k_B T)}$, with $\hat{H}$,$k_B$, and $T$ representing the
Hamiltonian, Boltzmann constant, and temperature, respectively, plays a crucial role in chemical physics and other branches of
quantum physics. One might naturally assume that a semi-classical IVR for the
matrix element of this operator in the coordinate representation (i.e., $ \langle \tilde{x} | e^{-\hat{H}/(k_B T)} | x \rangle$, or the imaginary-time propagator) could be derived via a straightforward “real-time $\rightarrow$ imaginary-time transformation” from the HK IVR of the real-time propagator. However, this is not the case, as such a transformation results in a divergence in the high-temperature limit $(T \rightarrow \infty)$. In this work, we solve this problem and develop a reasonable HK-like semi-classical IVR for $ \langle \tilde{x} | e^{-\hat{H}/(k_B T)} | x \rangle$ specifically for systems where either the gradient of the potential energy (i.e., the force intensity) has a finite upper bound, or the potential becomes harmonic in the long-range limit. The integrand in this IVR is a real Gaussian function of the positions $x$ and $\tilde{x}$, which facilitates its application to realistic problems. Our HK-like IVR is exact for free particles and harmonic oscillators, and its effectiveness for other systems is demonstrated through numerical examples.
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All authors Binhao Wang, Fan Yang, Chen Xu, Peng Zhang
Instrumentation and Detectors
Design optimization of silicon nitride nanomechanical resonators for thermal infrared detectors: a guide through key figures of merit
Paolo Martini, Kostas Kanellopulos and Silvan Schmid
Thermomechanical infrared (IR) detectors have emerged as promising alternatives to traditional
photon and thermoelectric sensors, offering broadband sensitivity and low noise without the need for cryogenic cooling. Despite recent advances, the field still lacks a unified framework to guide the design of these nanomechanical systems. This work addresses that gap by providing a comprehensive design guide for IR thermal detectors based on silicon nitride drumhead and trampolines. Leveraging a validated analytical model, we systematically explore how geometry, tensile stress, and optical properties influence key performance metrics such as thermal time constant, noise-equivalent power, and specific detectivity. The analysis encompasses both bare silicon nitride and structures with broadband absorber layers, revealing how different parameter regimes affect the trade-off between sensitivity and response speed. Rather than focusing on a single device architecture, this study maps out a broad design space, enabling performance prediction and optimisation for a variety of application requirements. As such, it serves not only as a reference for benchmarking existing devices but also as a practical tool for engineering next-generation IR sensors that can operate close to the fundamental detection limit. This work is intended as a foundational resource for researchers and designers aiming to tailor IR detectors to specific use cases.
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Atomic Physics
Impact of rotation on a cold atom interferometer and compensation strategy
Noémie Marquet, Yannick Bidel, Malo Cadoret et al. (+8 more)
Rotations play a detrimental role in achieving ultra-high-performance inertial measurements with an atom interferometer, leading potentially to a total loss of interference contrast and the emergence of dominant phase shift biases. This becomes particularly significant when considering operation in dynamic conditions such as those encountered in Earth orbiting satellites in the perspective of future space
gravity missions on-boarding a cold atom accelerometer. We study in this context the impact of rotation on the phase shift and contrast of an atom interferometer and investigate mitigation strategies. An analytical model is derived and compared to experimental demonstrations carried out using an original setup in which the well-controlled proof-mass of a space electrostatic accelerometer is used as the retro-reflection mirror of a cold atom gravimeter. By properly counter-rotating the electrostatic proof-mass, we demonstrate for instance the possibility of recovering the interferometer contrast, otherwise equal to zero, to a level better than 90%, in both cases of constant angular velocities or in presence of angular accelerations. Our results demonstrate the possibility to perform high performance inertial measurements with a cold atom interferometer in a challenging environments.
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All authors Noémie Marquet, Yannick Bidel, Malo Cadoret, Alexis Bonnin, Sylvain Schwartz, Phuong-Anh Huynh, Alexandre Bresson, Antoine Godard, Franck Pereira Dos Santos, Olivier Carraz, Nassim Zahzam
Chemical Physics
The predictive power of the calculated line lists of carbon monoxide
E. S. Medvedev and V. G. Ushakov
The ability of our semi-empirical irregular dipole-moment functions (2022) and (2025) to predict the intensities of the yet unobserved lines, as well as to describe the observed ones not used in the fitting, is demonstrated by comparison with recent measurements in the 0-0, 1-0, 3-0, and 7-0 bands.
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Optics
Dispersion engineered AlGaAs-on-insulator nanophotonics by distributed feedback
Francesco Rinaldo Talenti, Luca Lovisolo, Zijun Xiao et al. (+9 more)
Technological advances in the fabrication of nanophotonic
circuits have driven the scientific community to increasingly focus on the precise tailoring of their key optical properties, over a broadband spectral domain. In this context, the modulation of the local refractive index can be exploited to customize an effective reflectivity by the use of distributed Bragg mirrors, enabling the on-chip integration of Fabry-Pérot resonators. The resulting cavity length is strongly wavelength-dependent, offering practical solutions to the growing demand of dispersion engineering. Owing to their typically high core-to-cladding refractive index contrast and exceptional nonlinear properties, III-V
semiconductor-based platforms represent promising candidates for the fabrication of Bragg reflectors. In this work, we propose an AlGaAs-on-
insulator linear resonator based on distributed Bragg mirrors. We discuss the first experimental demonstration of a systematic, shape-constrained inverse design technique which tailors a prescribed dispersion profile, showing a strong agreement between simulations and measurements. In perspective, the proposed approach offers an efficient and general response to the challenge of dispersion engineering in integrated optical
circuits.
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All authors Francesco Rinaldo Talenti, Luca Lovisolo, Zijun Xiao, Zeina Saleh, Andrea Gerini, Carlos Alonso-Ramos, Martina Morassi, Aristide Lemaître, Stefan Wabnitz, Alfredo De Rossi, Giuseppe Leo, Laurent Vivien
Computational Physics · Cross-listed from stat.ME
Loss functions arising from the index of agreement
Hristos Tyralis and Georgia Papacharalampous
We examine the theoretical properties of the index of agreement loss function $L_W$, the negatively oriented counterpart of Willmott's index of agreement, a common metric in environmental sciences and engineering. We prove that $L_W$ is bounded within [0, 1], translation and scale invariant, and estimates the parameter $\Bbb{E}_{F}[\underline{y}] \pm \Bbb{V}_{F}^{1/2}[\underline{y}]$ when fitting a distribution. We propose $L_{\operatorname{NR}_2}$ as a theoretical improvement, which replaces the denominator of $L_W$ with the sum of Euclidean distances, better aligning with the underlying
geometric intuition. This new loss function retains the appealing properties of $L_W$ but also admits closed-form solutions for linear model parameter estimation. We show that as the correlation between predictors and the dependent variable approaches 1, parameter estimates from squared error, $L_{\operatorname{NR}_2}$ and $L_W$ converge. This behavior is mirrored in hydrologic model calibration (a core task in water resources engineering), where performance becomes nearly identical across these loss functions. Finally, we suggest potential improvements for existing $L_p$-norm variants of the index of agreement.
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Fluid Dynamics
Lattice Boltzmann model for non-ideal compressible fluid dynamics
S.A. Hosseini, M. Feinberg and I.V. Karlin
We present a new kinetic model and its
lattice Boltzmann realization for the simulation of compressible, non-ideal fluid flows. The method employs first-neighbour
lattices and introduces a consistent set of correction terms constructed via quasi-
equilibrium attractors, ensuring positive-definite and Galilean-invariant Navier-Stokes dissipation rates. This construction circumvents the need for extended stencils or ad hoc regularization, while maintaining numerical stability and thermodynamic consistency across a broad range of flow regimes. The resulting model accurately reproduces both the Euler- and Navier-Stokes hydrodynamic limits. As a stringent validation, we demonstrate, for the first time within a
lattice Boltzmann framework, quantitatively accurate simulations of shock-drop interactions at Mach numbers up to 1.47. The proposed approach thus extends the applicability of
lattice Boltzmann methods to high-speed, non-ideal compressible flows with a minimal kinetic stencil.
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Data Analysis and Statistics · Cross-listed from math.AT
MCbiF: Measuring Topological Autocorrelation in Multiscale Clusterings via 2-Parameter Persistent Homology
Juni Schindler and Mauricio Barahona
Datasets often possess an intrinsic multiscale structure with meaningful descriptions at different levels of coarseness. Such
datasets are naturally described as multi-resolution clusterings, i.e., not necessarily hierarchical sequences of partitions across scales. To analyse and compare such sequences, we use tools from topological data analysis and define the Multiscale Clustering Bifiltration (MCbiF), a 2-parameter filtration of abstract simplicial complexes that encodes cluster intersection patterns across scales. The MCbiF is a complete invariant of (non-hierarchical) sequences of partitions and can be interpreted as a higher-order extension of Sankey diagrams, which reduce to dendrograms for hierarchical sequences. We show that the multiparameter persistent homology (MPH) of the MCbiF yields a finitely presented and block decomposable module, and its stable
Hilbert functions characterise the topological autocorrelation of the sequence of partitions. In particular, at dimension zero, the MPH captures violations of the refinement order of partitions, whereas at dimension one, the MPH captures higher-order inconsistencies between clusters across scales. We then demonstrate through experiments the use of MCbiF
Hilbert functions as interpretable topological feature maps for downstream machine learning tasks, and show that MCbiF feature maps outperform both baseline features and representation learning methods on regression and classification tasks for non-hierarchical sequences of partitions. We also showcase an application of MCbiF to real-world data of non-hierarchical wild mice social grouping patterns across time.
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Applied Physics
Layered Bimetal Nanoporous Platforms for SERS Sensing
Yanqiu Zou, Anastasiia Sapunova, Tommaso Giovannini et al. (+15 more)
Nanoporous metals are extensively investigated as platforms for applications in plasmonics. They present high surface areas and strong local electric fields that can be tuned at different energies, playing with the choice of the metals and the morphology of the porous layers. Until recently, research in the field of plasmonics has primarily focused on porous metals composed of a single element, with limited
attention given to the impact of
alloy composition. The investigation of bi-metallic systems has only just begun to emerge in the literature. In particular, combining two or more different plasmonic metals, it could be possible to explore the interactions between two metals excited at specific energies. This involves plasmonic coupling, electron transfer, band hybridization at the interface, electromagnetic field interactions, and possibly thermal and electronic energy transfer depending on separation, size, and materials involved. The analysis of bi-metal systems can also be interesting in biomolecule detection, such as in the case of Surface Enhanced Raman Scattering (SERS). Here we report, for the first time, a detailed study (comprising morphological analyses, numerical modelling, and optical spectroscopies) on bi-metal nanoporous platforms prepared with a dry-synthesis method enabling the easy and controllable fabrication of
bilayers combining different metals such as Au, Ag, and Cu.
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All authors Yanqiu Zou, Anastasiia Sapunova, Tommaso Giovannini, Chen Wang, Huaizhou Jin, Vincenzo Caligiuri, Andrea Schirato, Luca Bursi, Alessandro Alabastri, Shukun Weng, Ali Douaki, German Lanzavecchia, Ivan Marri, Roman Krahne, Nicolò Maccaferri, Zhenrong Zheng, Shangzhong Jin, Denis Garoli
Fluid Dynamics · Cross-listed from astro-ph.SR
Diffusion-Free Dynamics in Rotating Spherical Shell Convection Driven By Internal Heating and Cooling
Neil T. Lewis, Tom Joshi-Hartley, Steven M. Tobias et al. (+2 more)
The bulk properties of convection in
stellar and
giant planet interiors are often assumed to be independent of the molecular diffusivities, which are very small. By contrast, simulations of this process in rotating, spherical shells, which are typically driven by conductive boundary heat fluxes, generally yield results that depend on the diffusivity. This makes it challenging to extrapolate these simulation results to real objects. However, laboratory models and Cartesian-box simulations suggest that
diffusion-free dynamics are more readily obtained if convection is driven using prescribed internal heating and cooling instead of boundary fluxes. Here, we apply this methodology to simulations of Boussinesq, hydrodynamic rotating spherical shell convection. We find that this set-up unambiguously yields
diffusion-free behaviour for some bulk properties of the convection, such as the radial temperature contrast and the convective heat transport. Moreover, the transition from prograde to retrograde equatorial zonal flow is
diffusion-free and only depends on the convective Rossby number. The diffusivity dependence of other bulk properties is regime-dependent. In simulations that are rotationally constrained, the convective velocities, and the strength and structure of the zonal flow, are
diffusion-dependent, although the zonal flow appears to approach a
diffusion-free state for sufficiently high supercriticality. In simulations that are uninfluenced by rotation, or are only influenced by rotation at large scales,
diffusion-free convective velocities and zonal flows are obtained. The result that many aspects of our idealised simulations are
diffusion-free has promising implications for the development of realistic
stellar and
giant planet convection models that can access
diffusion-free regimes.
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All authors Neil T. Lewis, Tom Joshi-Hartley, Steven M. Tobias, Laura K. Currie, Matthew K. Browning
Fluid Dynamics
Stability of trapped fluid clusters in two-phase porous media flow
Mathias Klahn, Gaute Linga, Tanguy Le Borgne et al. (+1 more)
A key challenge in multiphase flow through porous media is to understand and predict the conditions under which trapped fluid clusters become mobilized. Here, we investigate the stability of such clusters in two-phase flow and present a simple, quasistatic model that accurately determines the critical Bond number (that is, the critical ratio between the average pressure gradient of the flow and the surface tension) for the onset of cluster mobilization. The model is derived by combining elementary geometrical considerations with mass conservation and a mechanical
equilibrium condition, resulting in a system of coupled differential equations. Our derivation sheds new light on the mechanisms that govern cluster stability. In addition, since the number of equations equals the number of cluster openings, our model is significantly faster than direct numerical simulations of the same problem and enables efficient exploration of the system's parameter space. Using this approach, we highlight a discrepancy with the prediction of current mean-field theories, which predict that the largest stable cluster size scales in proportion to $r/\text{Bo}^\alpha$, where $r$ is a typical pore size, $\text{Bo}$ is the Bond number and $\alpha$ is a fixed exponent. We discuss the mechanisms that explain the breakdown of the mean field theories, and we show that a scaling law of this form can only exist if $\alpha$ is allowed to depend on a broad set of flow and
geometric parameters.
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All authors Mathias Klahn, Gaute Linga, Tanguy Le Borgne, Joachim Mathiesen
Optics
Reconfigurable on-chip vortex beam generation via acoustically stimulated Brillouin nonlinear optical radiation
Ming Li, Xiang Chen, Wen-Qi Duan et al. (+8 more)
The integrated devices that generate structured optical fields with non-trivial orbital angular momentum (OAM) hold great potential for advanced optical applications, but are restricted to complex nanostructures and static functionalities. Here, we demonstrate a reconfigurable OAM beam generator from a simple microring resonator without requiring grating-like nanostructures. Our approach harnesses Brillouin interaction between confined
phonon and optical modes, where the acoustic field is excited through microwave input. The
phonon stimulate the conversion from a guided optical mode into a free-space
vortex beam. Under the selection rule of the radiation, the OAM order of the emitted light is determined by the acousto-optic phase matching and is rapidly reconfigurable by simply tuning the microwave frequency. Furthermore, this all-microwave control scheme allows for the synthesis of arbitrary high-dimensional OAM superpositions by programming the amplitudes and phases of the driving fields. Analytical and numerical models predict a radiation efficiency over 25% for experimentally feasible on-chip microcavities. This work introduces a novel paradigm for chip-to-free-space interfaces, replacing fixed nanophotonic structures with programmable acousto-optic interactions for versatile structured light generation.
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All authors Ming Li, Xiang Chen, Wen-Qi Duan, Yuan-Hao Yang, Jia-Qi Wang, Mai Zhang, Xin-Biao Xu, Chun-Hua Dong, Luyan Sun, Guang-Can Guo, Chang-Ling Zou
Biological Physics · Cross-listed from cond-mat.soft
Modeling Diffusion and Permeation Across the Stratum Corneum Lipid Barrier
Rinto Thomas, Praveen Ranganath Prabhakar, Douglas J. Tobias et al. (+1 more)
Human skin oils are a major sink for ozone in densely occupied indoor environments. Understanding how the resulting volatile and semivolatile organic oxidation products influence indoor air chemistry requires accurate representations not only of their emission into indoor air but also of their transport across the outermost skin barrier, the stratum corneum. Using molecular dynamics simulations, we investigate the passive permeation of acetone, 6-methyl-5-hepten-2-one, and water – two representative products of skin-oil oxidation and a reference compound – through a model stratum corneum lipid membrane. We determine position-dependent diffusivities using two complementary analyses based on the same set of simulations and evaluate their accuracy through a propagator analysis. The two approaches provide upper and lower bounds for the true diffusivity, which, when combined with previously reported free-energy profiles, yield permeabilities relevant for modeling macroscopic skin transport. Our results show that permeation is governed primarily by energetic barriers rather than by molecular mobility, and that the predicted transport coefficients vary by about one order of magnitude depending on the chosen diffusivity
estimator. These findings provide molecular-level constraints for parameters used in indoor air chemistry models and establish a transferable framework for linking atomistic transport mechanisms to large-scale simulations of human exposure and indoor air quality.
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All authors Rinto Thomas, Praveen Ranganath Prabhakar, Douglas J. Tobias, Michael von Domaros
Plasma Physics
Linear damping of magneto-acoustic waves in two-fluid partially ionized plasmas
David Martínez-Gómez
Magneto-acoustic waves in partially ionized
plasmas are damped due to elastic collisions between charged and neutral particles. Here, we use a linearized two-fluid model to describe the influence of this collisional interaction on the properties of small-amplitude waves propagating in a uniform and static background. Mainly focusing on the case of waves generated by a periodic driver, we perform a detailed study of the dependence of the wavenumbers and damping rates on the ionization degree of the
plasma, the strength of the collisional coupling, and the angle of propagation. We describe how the different wave modes (fast, slow, acoustic) are related to the individual properties of each fluid in a wide range of physical conditions. In addition, we derive analytical approximations for the damping rates due to charge-neutral collisions in the limits of weak and strong coupling and check their range of validity in comparison with the exact numerical results. These approximations can be generally applied to a large variety of astrophysical and laboratory partially ionized
plasmas, but here we also discuss the particular application to
plasmas only composed of hydrogen.
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Optics · Cross-listed from quant-ph
Quantization of Polaritons Confined in Dielectric Structures
Amir Rahmani, Dogyun Ko, Maciej Dems et al. (+2 more)
Light-matter interaction in the regime of strong
quantum coupling is usually treated within the framework of the Hopfield model. However, the picture of coupling well-defined modes of light and matter is correct only as long as the shapes of these eigenmodes are not substantially modified by the interaction. Moreover, parameters of theoretical models are usually obtained by fitting to experimental data. To date, there is no straightforward method to determine a
quantum master equation corresponding to a system with specific dielectric structure, which may lead to incompatibility of theoretical descriptions and physical realizations. In this work, a recipe for obtaining a
quantum model in the polariton eigenmode basis is presented, based on Bogoliubov transformation in the conservative case and third quantization technique in the dissipative case. It is shown how this method can be used for boosting interaction strength and engineering nonlocal many-body interactions in carefully designed nanostructures, resulting in strongly nonclassical correlations of emitted light.
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All authors Amir Rahmani, Dogyun Ko, Maciej Dems, Andrzej Opala, Michał Matuszewski
General Physics
Estimation of $\pi$ via experiment
Keiko I. Nagao, Yuga Sakano, Takashi Shinohara et al. (+2 more)
In this study, we conducted an experiment to estimate $\pi$ using body-to-body and body-to-wall collisions. By geometrically analyzing the system's motion, we first review how the collision count corresponds to the digits of $\pi$. This method utilizes the property that the number of collisions corresponds to $\pi$ to the $n$-th decimal place by setting the mass ratio of bodies to $1:100^n$ under ideal conditions. In particular, when the mass ratio is $1:100$ – which is the case we tested experimentally – the number of collisions is 31, and $\pi$ to the tenths decimal place (3.1) can be derived. In the experiments, a suspended apparatus was developed to minimize energy losses such as friction and air resistance. We also devised the shape and material of the colliding bodies' surface and the characteristics of the suspension string, aiming for measurements under stable conditions. Based on the experimental results, we reproduced the number of collisions consistent with the theoretical values and confirmed that estimating $\pi$ to the tenths decimal place is possible under realistic conditions.
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All authors Keiko I. Nagao, Yuga Sakano, Takashi Shinohara, Yuji Matsuda, Hisashi Takami
Fluid Dynamics
Analysis and prediction of noise from installed subsonic chevron jets
Hasan Kamliya Jawahar, Benshuai Lyu and Mahdi Azarpeyvand
An experiment is conducted to investigate the effects of chevrons on installed subsonic jet noise at a Mach number of 0.5 using the NASA SMC000 (round) and SMC006 (chevron) nozzles. The jets are of a diameter D=16.93 mm and placed near a flat plate, with a horizontal separation distance L=6.5D between the plate's trailing edge and the nozzle exit. The vertical separation distance H varies between 1.5D, 2D, 2.5D and 3D. Far-field sound is measured at various observable angles ranging from $\theta=60^\circ$ to $150^\circ$ to the downstream jet axis on the reflected side. The measured sound spectra are compared to the near-field scattering model developed by Lyu et al, together with the isolated near-field pressure spectra inputs from corresponding large eddy simulations for both nozzles. Results show that jet installation results in a strong noise amplification at low frequencies for both nozzles due to the scattering of the near-field pressure fluctuations and a mild noise increase at high frequencies due to surface reflection (reflected side). The low-frequency amplification is strongest at H=1.5D and has a dipolar directivity. A secondary spectral hump appears within this low-frequency amplification hump, which is hypothesised due to the interference between the sound generated by the large coherent structures directly and that by their scattering at the plate's trailing-edge. The use of chevrons reduces the low-frequency noise for isolated jets, but leads to even stronger noise amplification for installed jets; this is likely due to enhanced jet mixing resulting in stronger near-field pressure fluctuations at a fixed radial distance. Results show that the scattering model can predict the low-frequency noise amplification well at various observer angles for both nozzles, suggesting the validity of the instability-wave scattering mechanism and modelling for both round and chevron jets.
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Instrumentation and Detectors
Design and simulation of a 4H-SiC low gain avalanche diode with trench-isolation
Sebastian Onder, Philipp Gaggl, Jürgen Burin et al. (+6 more)
We present the design and simulation of a 30 $\mathrm{\mu m}$ thick 4H-SiC Low Gain Avalanche Diode (LGAD) optimized for high-voltage operation. A 2.4 $\mathrm{\mu m}$ thick epitaxially grown gain layer enables controlled internal amplification up to 1 kV reverse bias, while maintaining full depletion below 500 V. Electrical characteristics, including I-V, C-V, and gain behavior, were simulated in Synopsys Sentaurus Technology Computer-Aided Design (TCAD) using a quasi-1D geometry and verified across process-related variations in gain layer parameters. To ensure high-voltage stability and proper edge termination, a guard structure combining deep etched trenches and deep $p^+$ junction termination extension (JTE) implants was designed. TCAD simulations varying the guard structure dimensions yielded an optimized design with a breakdown voltage above 2.4 kV. A corresponding wafer run is currently processed at IMB-CNM, Barcelona.
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All authors Sebastian Onder, Philipp Gaggl, Jürgen Burin, Andreas Gsponer, Matthias Knopf, Simon Waid, Neil Moffat, Giulio Pellegrini, Thomas Bergauer
Plasma Physics · Cross-listed from astro-ph.SR
Influence of kinetic effects in large-scale magnetic reconnection with multi-hierarchy simulation code KAMMUY
Keita Akutagawa, Shinsuke Imada and Munehito Shoda
Magnetic reconnection is a multiscale phenomenon where fluid- and particle-scale processes interact. The particle-in-
cell (PIC) method, capable of resolving kinetic (particle-scale) physics, is extensively used to study the kinetic effects in
magnetic reconnection. Meanwhile, because of the high computational cost, PIC simulations cannot capture the interaction between kinetic and fluid dynamics, which poses a major obstacle to understanding
magnetic reconnection in large-scale phenomena such as
solar flares. A multi-hierarchy simulation that combines Magnetohydrodynamics (MHD) and PIC provides a promising means to overcome these spatial and temporal scale gaps. We developed a multi-hierarchy simulation code KAMMUY (Kinetic And Magnetohydrodynamic MUlti-hierarchY simulation code), in which an ideal MHD simulation for a large domain and a PIC simulation for a smaller domain are solved in parallel with mutual information exchange. To validate the code, we conducted test simulations of MHD wave propagation and the shock tube problem. The results demonstrate that short-wavelength, high-frequency waves generated in the PIC region do not propagate into the MHD region, whereas MHD-scale structures propagate smoothly into the PIC region, highlighting the capability of our code for numerical studies of
magnetic reconnection. By applying the KAMMUY code to
magnetic reconnection while varying the PIC domain size, we find that the reconnection rate remains unchanged, regardless of the extent of the PIC region where the
Hall magnetic field is present. It suggests that the spatial extension of the
Hall magnetic field on the scale of $10 \sim 100 \lambda_i$ does not influence the reconnection rate.
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Biological Physics
Living Capillary Bridges
Tytti Kärki, Senna Luntama, Yasamin Modabber et al. (+5 more)
Biological tissues exhibit complex behaviors with their dynamics often resembling inert soft matter such as
liquids,
polymers, colloids, and
liquid crystals. These analogies enable physics-based approaches for investigations of emergent behaviors in biological processes. A well-studied case is the spreading of cellular aggregates on solid surfaces, where they display dynamics similar to viscous droplets. In vivo, however,
cells and tissues are in a confined environment with varying geometries and mechanical properties to which they need to adapt. In this work, we compressed cellular aggregates between two solid surfaces and studied their dynamics using microscopy, and computer simulations. The confined cellular aggregates transitioned from compressed spheres into dynamic living capillary bridges exhibiting bridge thinning and a convex-to-concave meniscus
curvature transition. We found that the stability of the bridge is determined by the interplay between
cell growth and
cell spreading on the confining surfaces. This interaction leads to bridge rupture at a critical length scale determined by the distance between the plates. The force distributions, formation and stability regimes of the living capillary bridges were characterized with full 3D computer simulations that included
cell division, migration and growth dynamics, directly showing how mechanical principles govern the behavior of the living bridges; cellular aggregates display jamming and stiffening analogously to granular matter, and
cell division along the long axis enhances thinning. Based on our results, we propose a new class of active soft matter behavior, where cellular aggregates exhibit
liquid-like adaptation to confinement, but with self-organized rupturing driven by biological activity.
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All authors Tytti Kärki, Senna Luntama, Yasamin Modabber, Saila Pönkä, Gonca Erdemci-Tandogan, Mikko Karttunen, Grégory Beaune, Jaakko V. I. Timonen
Optics
Resonate-and-Fire Photonic-Electronic Spiking Neurons for Fast and Efficient Light-Enabled Neuromorphic Processing Systems
Andrew Adair, Dafydd Owen-Newns, Giovanni Donati et al. (+7 more)
Neuromorphic computing seeks to replicate the spiking dynamics of biological
neurons for
brain-inspired computation. While electronic implementations of artificial spiking
neurons have dominated to date, photonic approaches are attracting increasing research interest as they promise ultrafast, energy-efficient operation with low-crosstalk and high bandwidth. Nevertheless, existing photonic
neurons largely mimic integrate-and-fire models, but neuroscience shows that
neurons also encode information through richer mechanisms, such as the frequency and temporal patterns of spikes. Here, we present a photonic-electronic resonate-and-fire (R-and-F) spiking
neuron that responds to the temporal structure of high-speed optical inputs. This is based on a light-sensitive resonant tunnelling diode that produces excitable spikes in response to nanosecond, low-power (100 microwatt) optical signals at infrared telecom wavelengths. We experimentally demonstrate control of R-and-F dynamics through inter-pulse timing of the optical stimuli and applied bias voltage, achieving bandpass filtering of both analogue and digital inputs. The R-and-F
neuron also supports optical fan-in via wavelength-division multiplexed inputs from four vertical-cavity surface-emitting
lasers (VCSELs). This electronic-photonic
neuron exhibits key functionalities - including spike-frequency filtering, temporal pattern recognition, and digital-to-spiking conversion - critical for neuromorphic optical processing. Our approach establishes a pathway toward low-power, high-speed temporal information processing for light-enabled neuromorphic computing.
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All authors Andrew Adair, Dafydd Owen-Newns, Giovanni Donati, Joshua Robertson, José Figueiredo, Eduard Wasige, Qusay Al-Taai, Bruno Romeira, Matěj Hejda, Antonio Hurtado
Popular Physics · Cross-listed from astro-ph.IM
SETI Post-Detection Protocols: Progress Towards a New Version
Michael A. Garrett, Kathryn Denning, Leslie I. Tennen et al. (+1 more)
The International Academy of Astronautics (IAA) SETI Committee has long provided guiding principles for responding to a potential detection of a SETI signal. The foundational Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence, first formulated in 1989, has been widely recognised by the international scientific community. A supplemental set of draft protocols addressing the possibility of a reply to an extraterrestrial signal was prepared in 1995 by the IAA SETI Permanent Committee, with both documents presented in a position paper to the UN Committee on the Peaceful Uses of Outer Space in 2000. In keeping with the evolving landscape of SETI research, the IAA Declaration of Principles was streamlined and updated in 2010. Recognising the need for continued adaptation, the IAA SETI Committee established a Task Group in 2022 to re-examine the protocols in light of recent advances in search methodologies, the expansion of international participation in SETI, and the increasing complexity of the global information environment. The Group recognises the living document nature of the protocols, which will require ongoing refinement to remain relevant and effective in a rapidly changing world. A draft revised Declaration of Principles was presented at the IAC 2024 in Milan, and initial feedback was received from the community, particularly members of the IAA SETI Committee. Since then, we have continued to seek broader community input in a structured process, refining the proposed updates based on further discussions and consultations. A Revised Declaration of Principles, is presented here.
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All authors Michael A. Garrett, Kathryn Denning, Leslie I. Tennen, Carol Oliver