Fluid Dynamics · Cross-listed from math.NA
Fast Solver for the Reynolds Equation on Piecewise Linear Geometries
Sarah Dennis and Thomas G. Fai
The Reynolds equation is derived from the incompressible Navier Stokes equations under the lubrication assumptions of a long and thin domain geometry and a small scaled Reynolds number. The Reynolds equation is an
elliptic differential equation and a dramatic simplification from the governing equations. When the fluid domain is piecewise linear, the Reynolds equation has an exact solution that we formulate by coupling the exact solutions of each piecewise component. We consider a formulation specifically for piecewise constant heights, and a more general formulation for piecewise linear heights; in both cases the linear system is inverted using the Schur complement. These methods can also be applied in the case of non-linear heights by approximating the height as piecewise constant or piecewise linear, in which case the methods achieve second-order accuracy. We assess the time complexity of the two methods, and determine that the method for piecewise linear heights is linear time for the number of piecewise components. As an application of these methods, we explore the limits of validity for lubrication theory by comparing the solutions of the Reynolds and the Stokes equations for a variety of linear and non-linear textured slider geometries.
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Data Analysis and Statistics · Cross-listed from stat.ME
Plotting correlated data
Lukas Koch
A very common task in data visualization is to plot many data points with some measured y-value as a function of fixed x-values. Uncertainties on the y-values are typically presented as vertical error bars that represent either a Frequentist confidence interval or
Bayesian credible interval for each data point. Most of the time, these error bars represent a 68% confidence/credibility level, which leads to the intuition that a model fits the data reasonably well if its prediction lies within the error bars of roughly two thirds of the data points. Unfortunately, this and other intuitions no longer work when the uncertainties of the data points are correlated. If the error bars only show the square root of diagonal elements of some covariance
matrix with non-negligible off-diagonal elements, we simply do not have enough information in the plot to judge whether a drawn model line agrees well with the data or not. In this paper we will demonstrate this problem and discuss ways to add more information to the plots to make it easier to judge the agreement between the data and some model prediction in the plot, as well as glean some insight where the model might be deficient. This is done by explicitly showing the contribution of the first principal component of the uncertainties, and by displaying the conditional uncertainties of all data points.
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Fluid Dynamics
Machine-learning wall model of large-eddy simulation for low- and high-speed flows over rough surfaces
Rong Ma and Adrian Lozano-Duran
We present a wall model for large-eddy simulation that incorporates surface-roughness effects and is applicable across low- and high-speed flows, for both transitional and fully rough conditions. The model, implemented using an artificial neural network, is trained on a direct numerical simulation database of compressible turbulent channel flows over rough walls. The
dataset contains 372 cases spanning a wide range of irregular roughness topographies, including Gaussian and Weibull distributions, Mach numbers 0~3.3, and friction Reynolds numbers 180~2000. We employ an information-theoretic, dimensionless learning method to identify the inputs with the highest predictive power for the dimensionless wall friction and wall heat flux. Predictions are accompanied by a confidence score derived from a spectrally normalized neural Gaussian process, which quantifies uncertainty in regions that deviate from the training
dataset. The model performance is first evaluated a-priori on 110 turbulent channel flow cases, yielding prediction errors below 4%. The model is assessed a-posteriori in wall-modeled large-eddy simulations across diverse test cases. These include over 160 subsonic and supersonic turbulent channel flows with rough walls, a transonic high-pressure turbine (HPT) blade with Gaussian roughness, a high-speed compression ramp with sandpaper roughness, and three hypersonic blunt bodies with sand-grain roughness. Results show that the proposed wall model typically achieves a-posteriori predictive accuracy within 10% for wall shear stress and within 15% for wall heat flux, with high confidence in the channel flows and HPT blade cases. In the rough-wall compression ramp and hypersonic blunt bodies, the model captures the heating augmentation with errors ranging 0%~20%. In the cases with the highest errors, the reduced performance is correctly detected by a drop in the confidence score.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Multiscale Numerical Modelling of Ultrafast Laser-Matter Interactions: Maxwell Two Temperature Model Molecular Dynamics (M-TTM-MD)
Othmane Benhayoun and Martin E. Garcia
In this work, we present a comprehensive numerical framework that couples numerical solutions of Maxwell's equations using the Finite-Difference Time-Domain (FDTD) approach, Molecular Dynamics (MD), and the Two-Temperature Model (TTM) to describe ultrafast
laser-matter interactions in metallic systems at the atomic scale. The proposed Maxwell-Two-Temperature Model-Molecular Dynamics (M-TTM-MD) bridges the gap between electromagnetic field propagation, electron-
phonon energy exchange, and atomic motion, allowing for a self-consistent treatment of energy absorption, transport, and structural response within a unified simulation environment. The calculated electromagnetic fields incorporate dispersive dielectric properties derived using the Auxiliary Differential Equation (ADE) technique, while the electronic and
lattice subsystems are dynamically coupled through spatially and temporally resolved energy exchange terms. The changes in the material topography are then reflected in the updated grid for the FDTD scheme. The developed M-TTM-MD model provides a self-consistent numerical framework that offers insights into
laser-induced phenomena in metals, including energy transport and surface dynamics under extreme nonequilibrium conditions.
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Biological Physics
Chesapeake Bay Food Web: Robustness Analysis via Energy Cutoff in Complex Networks
Eduardo M. K. Souza, Rafael N. C. C. Leite and Andre M. C. Souza
The Chesapeake Bay, one of the largest estuaries in the United States, is an ecological system of great complexity and relevance. The food web is composed of thirty-six trophic components, all of which are functionally connected. In this work, the interactions among these components are numerically analyzed using complex network methods. An energy flow cutoff paradigm is applied to a weighted ecological network. The results reveal patterns characteristic of connectivity dynamics, evidencing both the initial robustness of the system and its tendency to fragmentation at higher values of the cutoff. From an applied perspective, the findings underscore the importance of conservation strategies that protect keystone species, such as carnivorous fish, which act as crucial connectors between the two main subnetworks. Although they are positioned at the top of the food web and are often assumed to be less critical to network stability, these species play a pivotal role in regulating populations of lower-level organisms, thereby maintaining the overall integrity of the ecosystem.
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Plasma Physics
Superelastic Heating in Treanor-Gordiets Plasmas: A Unified Analytic Closure
Bernard Parent
In thermally non-
equilibrium plasmas, conventional harmonic models can significantly mispredict superelastic electron heating rates. When the vibrational temperature exceeds the gas temperature ($T_{\rm v}>T_{\rm g}$), these models underestimate energy transfer by several times; conversely, they overestimate heating when $T_{\rm g}>T_{\rm v}$. We show that this discrepancy arises from neglecting the exponential heating from overpopulated, high-lying states in anharmonic Treanor-Gordiets distributions, and their thermodynamic depopulation at high gas temperatures. To resolve this, we derive a closed-form, thermodynamically consistent macroscopic closure based on detailed balance and a second-order Dunham expansion. This unified framework introduces an analytic anharmonic correction factor that captures the kinetic competition between vibrational-vibrational (V-V) up-pumping and vibrational-translational (V-T) relaxation. By predicting the Treanor minimum, this formulation recovers the fidelity of full state-to-state kinetic
benchmarks. Ultimately, this model provides a governing equation for heat exchange between electrons and excited states in non-
equilibrium environments – including
plasma-assisted combustion and hypersonic flows – enabling the development of accurate, rate-limited reduced-order models for macroscopic fluid solvers.
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Physics and Society · Cross-listed from cond-mat.dis-nn
Directionality and node heterogeneity reshape criticality in hypergraph percolation
Yunxue Sun, Xueming Liu and Ginestra Bianconi
Directed and heterogeneous hypergraphs capture directional higher-order interactions with intrinsically asymmetric functional dependencies among nodes. As a result, damage to certain nodes can suppress entire hyperedges, whereas failure of others only weakens interactions. Metabolic reaction networks offer an intuitive example of such asymmetric dependencies. Here we develop a message-passing and statistical mechanics framework for percolation in directed hypergraphs that explicitly incorporates directionality and node heterogeneity. Remarkably, we show that these hypergraph features have a fundamental effect on the critical properties of hypergraph percolation, reshaping criticality in a way that depends on network structure. Specifically, we derive anomalous critical exponents that depend on whether node or hyperedge percolation is considered in maximally correlated, heavy-tailed regimes. These theoretical predictions are validated on synthetic hypergraph models and on a real directed metabolic network, opening new perspectives for the characterization of the robustness and resilience of real-world directed, heterogeneous higher-order networks.
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Biological Physics · Cross-listed from cond-mat.soft
From biting to engulfment: Target mechanics determines modes of phagocytosis through curvature–actin coupling
Shubhadeep Sadhukhan, Caitlin E. Cornell, Mansehaj Kaur Sandhu et al. (+10 more)
Phagocytosis is a core innate immune process that clears targets spanning a wide range of mechanical properties, yet the role of target mechanics in recognition and engulfment remains unclear. Here, we combine theoretical modeling and experiments to reveal how target stiffness governs distinct modes of phagocyte–target interaction. We develop a membrane-based simulation framework in which both the engulfing
cell and its target are deformable and undergo large shape changes, while actin-driven protrusions are regulated by
curvature-sensitive membrane complexes. The model predicts three mechanical regimes with increasing target stiffness: (i) biting (trogocytosis), where part of the target is extracted; (ii) pushing, where the target is displaced rather than engulfed; and (iii) complete engulfment. We validate these predictions in epithelial clearance of apoptotic targets in vivo and macrophage engulfment of
Giant Unilamellar Vesicles (GUVs) and lymphoma
cells. Together, our results identify target mechanics as a key regulator of clearance and
cell–
cell interactions.
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All authors Shubhadeep Sadhukhan, Caitlin E. Cornell, Mansehaj Kaur Sandhu, Marta Batet Palau, Youri Peeters, Stijn Hanssen, Samo Penič, Aleš Iglič, Daniel A. Fletcher, Valentin Jaumouillé, Daan Vorselen, Verena Ruprecht, Nir S. Gov
Optics
Photoacoustic Tensile Imaging
Daohuai Jiang, Xuanxuan Ye, Hengrong Lan et al. (+2 more)
Photoacoustic (PA) imaging combines the high optical absorption contrast of optical imaging with the deep tissue penetration of ultrasound detection, offering great potential for functional imaging and disease diagnosis. However, current PA imaging methods mainly explore optical absorption properties of biological tissue. To the best of our knowledge, tensile measurement based on PA effect is still an untapped area to be explored. In this work, we propose photoacoustic tensile imaging (PATI), a new PA imaging modality enabling quantitative assessment of tensile stress in biological samples. PATI exploits the nonlinear PA response induced by dual-pulse
laser excitation to establish a mapping between the applied tension and the increment of the nonlinear PA signal. By varying the temporal delay between the heating and detecting
laser pulses, the relationship between tensile force and nonlinear PA characteristics is quantitatively analyzed. Phantom experiments demonstrate a strong correlation between the nonlinear PA signal intensity and the applied tensile force. These results confirm the feasibility of the proposed approach for tensile force monitoring, which holds potential in biomedical applications, such as vascular pressure monitoring.
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All authors Daohuai Jiang, Xuanxuan Ye, Hengrong Lan, Xianzeng Zhang, Fei Gao
Applied Physics
Integrated laser heating stage with active geometry modulation for simultaneous in-situ X-ray transmission and evolved gas analysis of molten liquids
Chao Ang, Zhenqi Jiao, Yue Yang et al. (+4 more)
We report the design and development of a compact, integrated
laser heating stage tailored for in situ high-temperature X ray transmission studies of molten
oxides. In horizontal beam geometries, widely used in both laboratory and synchrotron facilities, the natural spreading (wetting) of molten samples on substrates significantly reduces the effective vertical optical path length, detrimental to signal quality in transmission-mode measurements. To overcome this limitation, we introduced a thermocouple assisted active geometry modulation technique. This method mechanically lifts the spreading melt into a
liquid bridge via surface tension, optimizing the transmission path length while simultaneously enabling in situ temperature monitoring. The device features a triple fiber coupled
laser head with high power density, a precision closed loop Proportional Integral Derivative temperature control system, and an atmosphere controlled
vacuum chamber coupled with a mass spectrometer. This integration allows for simultaneous evolved gas analysis, enabling the correlation of structural phase transitions with chemical volatilization or reaction dynamics. Validated by tracking the melting kinetics of a multicomponent glass precursor, this versatile setup provides a comprehensive solution for high quality data acquisition in X ray transmission experiments across various sources.
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All authors Chao Ang, Zhenqi Jiao, Yue Yang, Na Yu, Xuerong Liu, Yi Hu, Zhu-Jun Wang
Chemical Physics
First-Principle-Inspired Reduced-Order Models of Chemical-Kinetics in $\text{H}_2\left(\text{X}^1\Sigma_g^+\right)$+$\text{H}\left({}^2\text{S}\right)$ System
Hye Su Jeong, Tae Woong Jeong and Sung Min Jo
In the present study, two-different reduced-order models are proposed for $\text{H}_2\left(\text{X}^1\Sigma_g^+\right)$+$\text{H}\left({}^2\text{S}\right)$ system by leveraging first-principle quasi-classical trajectory simulations and in-depth master equation analyses. The most recent available ab-initio potential energy surface is adopted to construct a new set of rovibrational state-to-state kinetic database valid over a wide range of temperatures. Firstly, a modified two-temperature model is proposed by incorporating the master equation-informed model parameters, enabling the advanced treatment of the internal energy coupling and the nonequilibrium dissociation predictions. Secondly, a hybrid coarse-graining model is proposed by combining a graph-based approach optimized globally for a wide range of temperatures with a centrifugal-barrier-based coarse-graining method. The proposed reduced-order models offer significantly improved accuracy in predicting the nonequilibrium energy transfer and dissociation dynamics compared to the existing coarse-graining and 2T models in previous studies. In addition, aerothermal heating prediction relevant to Uranus planetary entry reveals 16.5% of convective heat flux discrepancy compared to the present modified 2T approach with the existing 2T, demonstrating the importance of accurate modeling of the chemical-kinetics in the $\text{H}_2\left(\text{X}^1\Sigma_g^+\right)$+$\text{H}\left({}^2\text{S}\right)$ system.
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Biological Physics
What Does FEXI Measure in Neurons?
Valerij G. Kiselev and Jing-Rebecca Li
Exchange between tissue compartments is crucial for interpretation of
diffusion MRI measurements in
brain gray matter. However, reported values of exchange time are broadly dispersed, about two orders of magnitude. We analyze the measurement technique called Filtered Exchange Imaging (FEXI) using numerical solution of Bloch–Torrey equation in digitalized
neurons downloaded from NeuroMorpho.org. The FEXI outcome, which is the recovery of
diffusion coefficient in
cells with impermeable membrane is multiexponential, with the time constants defined by the
eigenvalues of Laplace operator. Fitting the commonly used exponential recovery function results in a strong dependence of the apparent exchange time on the involved mixing time interval and the adjustment or fixation of the
equilibrium diffusivity. To obtain an estimate of membrane permeability, we reinterpret previously published data on preexchange lifetime in neuronal
cell culture. It results in 0.005 micrometer/ms. The corresponding exchange time is approximately 140 ms. We conclude that essentially shorter exchange times are due to fast
geometric exchange inside the ramified
cells.
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Computational Physics · Cross-listed from cs.LG
An Empirical Investigation of Neural ODEs and Symbolic Regression for Dynamical Systems
Panayiotis Ioannou, Pietro Liò and Pietro Cicuta
Accurately modelling the dynamics of complex systems and discovering their governing differential equations are critical tasks for accelerating scientific discovery. Using noisy, synthetic data from two damped oscillatory systems, we explore the extrapolation capabilities of Neural Ordinary Differential Equations (NODEs) and the ability of Symbolic Regression (SR) to recover the underlying equations. Our study yields three key insights. First, we demonstrate that NODEs can extrapolate effectively to new boundary conditions, provided the resulting trajectories share dynamic similarity with the training data. Second, SR successfully recovers the equations from noisy ground-truth data, though its performance is contingent on the correct selection of input variables. Finally, we find that SR recovers two out of the three governing equations, along with a good approximation for the third, when using data generated by a NODE trained on just 10% of the full simulation. While this last finding highlights an area for future work, our results suggest that using NODEs to enrich limited data and enable symbolic regression to infer physical laws represents a promising new approach for scientific discovery.
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Optics
Quantum Squeezing Enhanced Photothermal Microscopy
Pengcheng Fu, Xiao Liu, Siming Wang et al. (+10 more)
Label-free optical microscopy through absorption or scattering spectroscopy provides fundamental insights across biology and materials science, yet its sensitivity remains fundamentally limited by
photon shot noise. While recent demonstrations of
quantum nonlinear microscopy show sub-shot-limited sensitivity, they are intrinsically limited by availability of high peak-power squeezed light sources. Here, we introduce squeezing-enhanced photothermal (SEPT) microscopy, a
quantum imaging technique that leverages twin-beam
quantum correlations to detect absorption induced signals with unprecedented sensitivity. SEPT achieves 3.5 dB noise suppression beyond the standard
quantum limit, enabling a 2.5-fold increase in imaging throughput or 31% reduction in pump power, while providing an unmatched versatility through the intrinsic compatibility between continuous-wave squeezing and photothermal modulation. We showcase SEPT applications by providing high-precision characterization of nanoparticles and revealing subcellular structures, such as cytochrome c, that remain undetectable under shot-noise-limited imaging. By combining label-free contrast,
quantum-enhanced sensitivity, and compatibility with existing microscopy platforms, SEPT establishes a new paradigm for molecular absorption imaging with far-reaching implications in cellular biology, nanoscience, and materials characterization.
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All authors Pengcheng Fu, Xiao Liu, Siming Wang, Nan Li, Chenran Xu, Han Cai, Huizhu Hu, Vladislav V. Yakovlev, Xu Liu, Shi-Yao Zhu, Xingqi Xu, Delong Zhang, Da-Wei Wang
Instrumentation and Detectors
Trigger Optimization and Event Classification for Dark Matter Searches in the CYGNO Experiment Using Machine Learning
F. D. Amaro, R. Antonietti, E. Baracchini et al. (+40 more)
The CYGNO experiment employs an optical-readout Time Projection Chamber (TPC) to search for rare low-energy interactions using finely resolved scintillation images. While the optical readout provides rich topological information, it produces large, sparse megapixel images that challenge real-time triggering, data reduction, and background discrimination. We summarize two complementary machine-learning approaches developed within CYGNO. First, we present a fast and fully unsupervised strategy for online data reduction based on reconstruction-based anomaly detection. A convolutional autoencoder trained exclusively on pedestal images (i.e. frames acquired with GEM amplification disabled) learns the detector noise morphology and highlights particle-induced structures through localized reconstruction residuals, from which compact Regions of Interest (ROIs) are extracted. On real prototype data, the selected configuration retains (93.0 +/- 0.2)% of reconstructed signal intensity while discarding (97.8 +/- 0.1)% of the image area, with ~25 ms per-frame inference time on a consumer GPU. Second, we report a weakly supervised application of the Classification Without Labels (CWoLa) framework to data acquired with an Americium–Beryllium
neutron source. Using only mixed AmBe and standard
datasets (no event-level labels), a convolutional classifier learns to identify
nuclear-
recoil-like
topologies. The achieved performance approaches the theoretical limit imposed by the mixture composition and isolates a high-score population with compact, approximately circular morphologies consistent with
nuclear recoils.
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All authors F. D. Amaro, R. Antonietti, E. Baracchini, L. Benussi, C. Capoccia, M. Caponero, L. G. M. de Carvalho, G. Cavoto, I. A. Costa, A. Croce, M. D'Astolfo, G. D'Imperio, G. Dho, E. Di Marco, J. M. F. dos Santos, D. Fiorina, F. Iacoangeli, Z. Islam, E. Kemp, H. P. Lima Jr, G. Maccarrone, R. D. P. Mano, D. J. G. Marques, G. Mazzitelli, P. Meloni, A. Messina, C. M. B. Monteiro, R. A. Nobrega, G. M. Oppedisano, I. F. Pains, E. Paoletti, F. Petrucci, S. Piacentini, D. Pierluigi, D. Pinci, F. Renga, A. Russo, G. Saviano, P. A. O. C. Silva, N. J. Spooner, R. Tesauro, S. Tomassini, D. Tozzi
Space Physics
Sunward Streaming 3He-rich SEP Events Observed by Solar Orbiter and Parker Solar Probe during Perihelion Passage
Samuel T. Hart, George C. Ho, Michael R. Terres et al. (+7 more)
We report on two 3He-rich
solar energetic particle (SEP) events observed by
Solar Orbiter (SO) and Parker
Solar Probe (PSP) during the April 1 - 4, 2024 conjunction when both spacecraft are within 0.3 AU near their respective perihelion passage. The two 3He-rich SEP events, originating from active region (AR) 13615, exhibit two key anomalies: (1) sunward streaming SEPs and (2) SEP travel path lengths exceeding 2 - 8 times the nominal Parker spiral expectations. Remote observations suggest these SEPs have been redirected by a slow coronal mass ejection (CME) that also originated from AR 13615 two days prior on March 30, 2024 at 21:04 UT. Using the near-Sun CME speed and width measurements, we estimate its size and location at the onset time of the first 3He-rich SEP event. Based on our estimates, SEPs propagating around the ICME front have travelled between 0.76 - 0.95 AU when they arrive at SO, increasing to 0.94 - 1.1 AU at PSP, consistent with our observed SEP arrival times. These findings constitute the first multi-spacecraft observation of sunward streaming 3He-rich SEPs. We discuss the implications of this phenomenon on 3He-rich seed material and the rare widespread 3He-rich SEP events (see Section 5.4).
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All authors Samuel T. Hart, George C. Ho, Michael R. Terres, Gabriel C. Muro, Robert C. Allen, Maher A. Dayeh, Radoslav Bučík, Glenn M. Mason, Athanasios Kouloumvakos, Abdullah A. Shmies
Atomic Physics
Development of a Quantum Blackbody Thermometer toward Primary On-orbit Thermometry
Peter J. Beierle, Denis Tremblay, Noah Schlossberger et al. (+3 more)
We present a roadmap to a deployable, intrinsically calibrated thermometer with long-term accuracy of 30 mK, exceeding existing on-orbit resistance-based thermometers. Our
quantum blackbody thermometer is based on measuring fluorescence ratios of optically excited rubidium atoms in microfabricated vapor
cells. The key advantage of the
quantum blackbody thermometer is that long-term stability of the fluorescence ratios is guaranteed by the immutable physical properties (transition strengths) of the rubidium atom. This should be compared against resistance-based thermometers, such as platinum resistance thermometers, which may be calibrated with exceptional accuracy but are susceptible to temporal drift and shifts due to improper handling.
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All authors Peter J. Beierle, Denis Tremblay, Noah Schlossberger, Christopher L. Holloway, Stephen P. Eckel, Eric B. Norrgard
Optics · Cross-listed from quant-ph
A Hybrid Jump-Diffusion Model for Coherent Optical Control of Quantum Emitters in hBN
Saifian Farooq Bhat, Michael K. Koch, Sachin Negi et al. (+2 more)
Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional host for stable single-
photon emission owing to its wide bandgap, high photostability, and compatibility with nanophotonic integration. We present a simulation-based study of temperature-dependent spectral dynamics and optical coherence in a mechanically decoupled
quantum emitter in hBN. Employing a hybrid
stochastic framework that combines Ornstein–Uhlenbeck detuning fluctuations with temperature-dependent, Gaussian-distributed discrete frequency jumps, motivated by experimentally observed spectral
diffusion and blinking, we reproduce the measured
evolution of inhomogeneous linewidth broadening and the progressive degradation of
photon coherence across the relevant cryogenic range (5-30K). The model captures
phonon-related spectral
diffusion with a cubic temperature dependence and the onset of jump-like spectral instabilities at higher temperatures. By calibrating the hybrid
diffusion, jump parameters to the experimentally measured full width at half maximum (FWHM) of the emission line and analyzing the second-order correlation function $g^{(2)}(\tau)$ under resonant driving, we establish a unified phenomenological description that links
stochastic detuning dynamics to the decay of optical coherence in a resonantly driven emitter. Analysis of $g^{(2)}(\tau)$ under resonant driving reveals an additional dephasing rate $\gamma_{\mathrm{sd+j}}$ that rises monotonically with temperature and drive strength, leading to a predicted critical crossover to overdamped dynamics at $T_{\mathrm{crit}} \approx 25.91$~K. This hybrid framework provides a quantitative connection between accessible spectroscopic observables and the dominant noise mechanisms limiting coherent optical control in mechanically decoupled
quantum emitters, exemplified in hBN and generalizable to similar emitters in other materials.
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All authors Saifian Farooq Bhat, Michael K. Koch, Sachin Negi, Alexander Kubanek, Vibhav Bharadwaj
Fluid Dynamics
Effective longitudinal slip over grooves encapsulated by a nearly inviscid lubricant
Ory Schnitzer and Ehud Yariv
We calculate the effective slip length for a rectangularly grooved periodic surface encapsulated (i.e., fully wetted) by a lubricant fluid and subjected to exterior shear flow parallel to the grooves. Our focus is the limit of a nearly-inviscid lubricant, where the ratio $\mu$ of the lubricant viscosity to that of the exterior fluid is small. This limit is singular for an encapsulated surface, indicating a dominant lubricant-flow effect - a stark contrast to superhydrophobic surfaces where the role of the lubricant is typically negligible.
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Optics
Single-Shot Multispectral Mid-Infrared Imaging with Incoherent Light via Adiabatic Upconversion
Daniel Beitner, Ziv Abelson, Eyal Hollander et al. (+2 more)
Multispectral mid-infrared (2-5 ${{\mu}m}$) imaging is a critical capability across science and technology, offering a window into the vibrational and thermal landscape of matter that is inaccessible to visible sensors. It bridges the microscopic world of molecular interactions with macroscopic sensing technologies, with applications in environmental sensing, defense and molecular diagnostics. However, current mid-IR cameras require cryogenic cooling and exhibit limited pixel resolution, high cost, and restricted spectral access. Optical up-conversion provides a pathway to overcome these limitations, but existing systems typically rely on narrowband phase matching, mechanical scanning, or angular tuning, limiting imaging speed and practicality. Here, we demonstrate the first single-shot, room-temperature multispectral mid-IR imaging of incoherent thermal light enabled by adiabatic sum-frequency conversion. Our system simultaneously converts the entire (2-5 ${{\mu}m}$) region into the visible domain, capturing the image on a Silicon detector with spatial resolution below 20 ${{\mu}m}$ and high angular tolerance. We validate full-field imaging using a USAF resolution target and demonstrate spectroscopic contrast imaging in dielectric metamaterials by resolving wavelength and polarization dependent scattering resonances, all achieved without scanning, thermal control, or cryogenic operation. This compact and robust approach bridges the gap between laboratory-grade infrared sensors and scalable Silicon-based detection technologies suitable for real-world deployment.
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All authors Daniel Beitner, Ziv Abelson, Eyal Hollander, Omri Meron, Haim Suchowski
Instrumentation and Detectors
Improvements of the ALICE GPU TPC tracking and GPU framework for online and offline processing of Run 3 Pb-Pb data
David Rohr
ALICE is the dedicated heavy ion experiment at the LHC at CERN and records lead-lead collisions at a rate of up to 50 kHz in LHC Run 3. To cope with such collision and data rates, ALICE uses a new GEM TPC with continuous readout and a GPU-based online computing farm for data compression. Operating the first GEM TPC of this size with large space charge distortions due to the high collision rate has many implications for the track reconstruction
algorithm, both anticipated and unanticipated. With real Pb-Pb data available, the TPC tracking
algorithm needed to be refined, particularly with respect to improved cluster attachment at the inner TPC region. In order to use the online computing farm efficiently for offline processing when there is no beam in the LHC, ALICE is currently running TPC tracking on GPUs also in offline processing. For the future, ALICE aims to run more computing steps on the GPU, and to use other GPU-enabled resources besides its online computing farm. These aspects, along with better possibilities for performance optimizations led to several improvements of the GPU framework and GPU tracking code, particularly using Run Time Compilation (RTC). The talk will give an overview of the improvements for the ALICE tracking code, mostly based on experience from reconstructing real Pb-Pb data with high TPC occupancy. In addition, an overview of the online and offline processing status on GPUs will be given, and an overview of how RTC improves the ALICE tracking code and GPU support.
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Fluid Dynamics
Impact-induced viscoelastic bungee-jumper jets with uniform extension and stress
Kyota Kamamoto, Asuka Hosokawa and Yoshiyuki Tagawa
We investigate the dynamics of a "bungee-jumper" jet induced by an impulsive force, which retracts after reaching its peak extension. Despite the strongly extensional and highly nonequilibrium nature of this motion, the jet exhibits simple and uniform rheological responses. To elucidate its extensional behavior in a highly extensional regime quantified by large Deborah and Reynolds numbers ($De \approx 2.1 \times 10^1 - 3.3 \times 10^3$, $Re \approx 2.8 \times 10^1 - 4.6 \times 10^2$), we use high-speed velocimetry and polarization-based stress imaging to measure the spatial distribution of velocity and stress throughout jets made of dilute polyethylene
oxide (PEO) solutions. The bungee-jumper jets are found to exhibit two uniform characteristics despite the extreme $De$ conditions: a consistent spatial distribution of the extensional rate and a nearly uniform stress distribution during the jetting motion. These uniformities indicate that the seemingly complex jet dynamics can in fact be effectively represented using a constitutive model with spatially uniform coefficients. Comparison of several viscoelastic models shows that the Voigt model provides the best agreement with the measured dynamics, while the single-spring model captures the essential behavior when elasticity dominates.
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Optics · Cross-listed from gr-qc
Gravitational wave detection via photon-graviton scattering and quantum interference
K. Hari and S. Shankaranarayanan
We present a fully
quantum field-theoretic framework for gravitational wave (GW) detection, describing the interaction as inelastic
photon-graviton scattering. We demonstrate that for a coherent graviton state, this microscopic model explicitly reproduces the standard classical
geometric-optics time delay, providing a rigorous consistency test of the correspondence limit. We propose a detection scheme based on Hong-Ou-Mandel interference, where the GW-induced spectral shifts render entangled
photon pairs distinguishable. This encodes the gravitational signal into the modulation of
photon coincidence rates — a
quantum observable robust against
laser intensity noise. Furthermore, we show that non-classical graviton states, such as squeezed states, induce unique decoherence signatures, establishing theoretical bounds on gravitational decoherence and defining the operational limits for probing the
quantum nature of
gravity.
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Chemical Physics
HEOM-Based Numerical Framework for Quantum Simulation of Two-Dimensional Vibrational Spectra in Molecular Liquids (HEOM-2DVS)
Ryotaro Hoshino and Yoshitaka Tanimura
The multi-mode anharmonic Brownian motion model provides a universal framework for simulating molecular vibrations in condensed phases. When vibrational energy surpasses thermal excitation,
quantum effects become significant, necessitating a rigorous treatment of system-bath
entanglement. The hierarchical equations of motion (HEOM) provide a powerful methodology for simulating such open
quantum systems. In this context, two-dimensional vibrational spectroscopy (2DVS) constitutes a powerful probe for elucidating the complex dynamics of molecular processes, both experimentally and theoretically. This work introduces a computational implementation, HEOM-2DVS, for treating non-Markovian open
quantum dynamics that encompass energy relaxation, dephasing, thermal excitation, and related processes arising from non-perturbative and nonlinear interactions between selected vibrational modes and their thermal environments. To validate the theoretical framework, we computed 2D correlation infrared spectra for three coupled intramolecular vibrational modes of water. The HEOM-2DVS program developed for both CPU and graphics processing unit (GPU) is provided as supplementary material.
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Medical Physics
Multicenter Comparison of Radionuclide Calibrators and SPECT/CT Protocols for Quantitative 177Lu Imaging in Clinical Practice
Wies Claeys, Kristof Baete, Laurence Beels et al. (+8 more)
Purpose: Following the clinical success of 177Lu-based therapies, accurate quantification of 177Lu using radionuclide calibrators (RNCs) and SPECT/CT is gaining importance as prerequisite for accurate treatment delivery and dosimetry. However, the lack of standardization can introduce inter-system variability, compromising multi-center clinical trials. This study aimed to assess the accuracy and variability of 177Lu measurements using RNCs and SPECT/CT across different systems and hospitals. Methods: A uniform cylindrical phantom and a NEMA phantom with hot spheres were prepared using traceable activities and imaged at 8 different hospitals using 13 SPECT/CT systems (9 conventional and 4 3D CZT). Acquisitions and reconstructions were performed using both site-specific and standardized protocols. The cylindrical phantom images were used to evaluate the system calibration and establish image calibration factors (ICFs), the NEMA images to evaluate effective resolution by calculating recovery coefficients (RCs). In parallel, two vials were measured to test RNC accuracy. Results: RNC measurements differed up to 11% between centers, while SPECT quantification of the cylindrical phantom differed up to 20%. While ICFs were consistent for systems of the same type, image quality varied strongly when using clinical protocols (36% difference in RCs in the largest sphere). Standardized reconstruction reduced variability in RCs for each system type (maximum 12% difference), regardless of acquisition protocol, but differences between system types persisted when standardizing acquisition and reconstruction (33% difference). Conclusion: Current 177Lu measurement practices yield significant variability in quantification and image quality. Harmonization efforts should prioritize standardized calibration and reconstruction protocols to improve multicenter reproducibility of quantitative 177Lu-SPECT/CT.
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All authors Wies Claeys, Kristof Baete, Laurence Beels, Claire Bernard, Rachele Danieli, Yves D' Asseler, An De Crop, Michel Hesse, Victor Nuttens, Bruno Vanderlinden, Michel Koole
Biological Physics · Cross-listed from cond-mat.soft
Ion-Modulated Polyelectrolyte Complexation of DNA and Polyacrylic Acid from Molecular Dynamics Simulations
Sisem Ektirici, Vagelis Harmandaris, Christos N. Likos et al. (+1 more)
The formation of complexes between like-charged polyelectrolytes challenges conventional electrostatic intuition and highlights the central role of ions in mediating macromolecular organization. Here, we investigate the salt-dependent association of DNA with poly(acrylic acid) (PAA) using atomistic molecular dynamics simulations in NaCl, MgCl$_2$, and CaCl$_2$ solutions. A time-resolved state classification scheme, based on heavy-atom distance and hydrogen-bond formation, was applied to distinguish bound and unbound configurations, enabling quantitative analysis of how ion valency modulates complex stability and structure. The results reveal a clear hierarchy of association strength with Ca$^{2+}$ promoting persistent complex formation through direct inner-sphere coordination between DNA phosphates and PAA carboxylates, Mg$^{2+}$ mediating weaker, transient bridging interactions and Na$^+$ exhibiting only electrostatic screening action with negligible bridge formation. Structural analysis shows that multivalent ions not only enhance complex stability but also reshape the molecular organization of both macromolecules. Ca$^{2+}$ induces expansion of DNA and compaction of PAA within a strongly bridged complex characterized by directional
alignment and backbone-dominated binding, whereas Mg$^{2+}$ promotes more transient groove associations and Na$^+$ supports flexible, weakly correlated contacts. Our findings provide molecular-level insight into ion-specific mechanisms underlying polyelectrolyte organization and inform the design of responsive biomaterials and nucleic acid-based assemblies in multivalent ionic environments.
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All authors Sisem Ektirici, Vagelis Harmandaris, Christos N. Likos, Terpsichori S. Alexiou
Atomic Physics · Cross-listed from cond-mat.quant-gas
Three-body scattering area of identical bosons in two dimensions
Junjie Liang, Hongye Yu and Shina Tan
We study the wave function $\phi^{(3)}$ of three identical
bosons scattering at zero energy, zero total momentum, and zero orbital angular momentum in two dimensions, interacting via short-range potentials with a finite two-body scattering length $a$. We derive asymptotic expansions of $\phi^{(3)}$ in two regimes: the 111-expansion, where all three pairwise distances are large, and the 21-expansion, where one particle is far from the other two. In the 111-expansion, the leading term grows as $\ln^3(B/a)$ at large hyperradius $B=\sqrt{(s_1^2+s_2^2+s_3^2)/2}$. At order $B^{-2}\ln^{-3}(B/a)$, we identify a three-body parameter $D$ with dimension of length squared, which we term the three-body scattering area. This quantity should be contrasted with the three-body scattering area previously studied for infinite or vanishing two-body scattering length. If the two-body interaction is attractive and supports bound states, $D$ acquires a negative imaginary part, and we derive its relation to the probability amplitudes for the production of two-body bound states in three-body collisions. Under weak modifications of the interaction potentials, we derive the corresponding shift of $D$ in terms of $\phi^{(3)}$ and the changes of the two-body and three-body potentials. We also study the effects of $D$ and $\phi^{(3)}$ on three-body and many-body physics, including the three-body ground-state energy in a large periodic volume, the many-body energy and the three-body correlation function of the dilute two-dimensional Bose gas, and the three-body recombination rates of two-dimensional ultracold atomic Bose gases.
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History and Philosophy of Physics · Cross-listed from quant-ph
Revisiting the Interpretations of Quantum Mechanics: From FAPP Solutions to Contextual Ontologies
Philippe Grangier
This note presents a concise and non-polemical comparison of several major interpretations of
quantum mechanics, with a particular emphasis on the distinction between FAPP-solutions ("For All Practical Purposes”) versus ontological solutions to the measurement problem. Building on this distinction, we argue that the Contexts-Systems-Modalities (CSM) framework, supplemented by the operator-algebraic description of macroscopic contexts, provides a conceptually complete, non-FAPP ontology that naturally incorporates irreversibility and the physical structure of measurement devices. This approach differs significantly from other ontological interpretations such as Bohmian mechanics, spontaneous collapse, or many-worlds, and highlights the major role of contextual quantization in shaping
quantum theory.
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Optics
Temporal Paraxial Optics under Adiabatic Modulations
Antonio Alex-Amor and Carlos Molero
This paper presents a temporal paraxial formulation for the propagation of ultrashort optical pulses in time-modulated media with slowly varying refractive index. By deriving the paraxial wave equation directly in the time domain from the Helmholtz equation under an adiabatic approximation, the model remains analytically tractable while extending paraxial optics beyond time-invariant backgrounds commonly treated by frequency-domain expansions. The resulting equation preserves a Schrödinger-like structure in the presence of explicit temporal modulation and admits closed-form solutions for ultrashort Gaussian pulses. The framework supports a Green's-function description and an operator-based
Hamiltonian formalism, from which an ABCD
matrix representation for temporal propagation in time-varying media is obtained. The results demonstrate that temporal modulation provides a dynamic means to control ultrashort pulse dynamics, enabling tailored
evolution of pulse characteristics such as temporal width and chirp, with potential applications in ultrafast pulse shaping and a direct connection to temporal wave-packet dynamics.
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Biological Physics · Cross-listed from cond-mat.soft
Nonequilibrium noise emerging from broken detailed balance in active gels
Ashot Matevosyan, Frank Jülicher and Ricard Alert
In thermodynamic
equilibrium, the fluctuation-dissipation
theorem links thermal fluctuations and dissipation. Biological systems, however, are driven out of
equilibrium by internal processes that produce additional, active fluctuations. Despite being relevant for biological functions such as intracellular transport, predicting the statistical properties of active fluctuations remains challenging. Here, we address this challenge in a minimal model of an active gel as a network of elastic elements connected by transient crosslinks. The crosslinkers' binding and unbinding rates break detailed balance, which drives the system out of
equilibrium. Through coarse-graining, we derive fluctuating hydrodynamic equations including an active noise term, which emerges explicitly from the breaking of detailed balance. Finally, we provide predictions for the
stochastic motion of a tracer particle embedded in the active gel, which enables comparisons with microrheology experiments both in synthetic active gels and in
cells. Overall, our work provides an explicit link between the statistical properties of active fluctuations and the molecular breaking of detailed balance. Thus, it paves the way toward complementing the fluctuation-dissipation
theorem with a fluctuation-activity relation in active systems.
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