Atmospheric and Oceanic Physics
Predictability of El Niño from Delayed Observations
Francisco J. Beron-Vera
Using monthly Niño-3.4 anomalies through July 2026, we investigate how much predictive information is contained in delayed observations of the index. Ridge regression identifies informative delays, while multilayer perceptron and sparse identification of nonlinear dynamics (SINDy) models test whether nonlinear complexity provides additional direct forecast skill; gated recurrent unit (GRU) and long short-term
memory (LSTM) networks provide a complementary test in which the temporal representation is learned internally. Delayed observations substantially improve forecasts over persistence and climatology at leads of up to six months, but increasing model complexity provides no systematic improvement. Historical recursive experiments favor a simple explicit SINDy recurrence and select shallow recurrent architectures, with no appreciable gain from learning the temporal representation internally. These results support a compact predictive representation of Niño-3.4
evolution in which the representation of past information is more consequential than model complexity. As a prospective application, the selected models are used to forecast the developing 2026 event beyond the last available observation and to compare its predicted
evolution with completed historical El Niño events.
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Chemical Physics
Quantum Vibronic Dynamics Shape Catalytically Relevant Au-Ligand Interfaces in Atomically Precise Gold Nanoclusters
Mengyuan Cui, Tianrui Chen, Junhua Zhou et al. (+6 more)
Atomically precise gold nanoclusters are versatile for photocatalysis and energy conversion because their electronic structure stems from strong metal-ligand interactions. However, these interactions are mostly discussed statically, leaving dynamic reorganization of Au-ligand interfaces under photoexcitation unclear. We investigate rod-shaped [Au25(PPh3)10(SC2H5)5Cl2]2+ using ultrafast transient-grating spectroscopy, two-dimensional electronic spectroscopy, ab initio calculations, and hierarchical equations-of-motion simulations. The multidimensional spectra resolve multiple electronic relaxation pathways and a hierarchy of coherent structural motions, from localized Au-ligand distortions to collective framework vibrations. Wavelet analysis reveals that high-frequency Au-ligand vibrations emerge immediately after excitation, whereas low-frequency collective modes appear later through interstate vibronic coupling, indicating sequential redistribution of structural coherence. Simulations reproduce the nonlinear response and identify the microscopic vibronic couplings responsible. The results show that photoexcitation drives continuous ultrafast reorganization of the Au-ligand bonding network, transiently reshaping interfacial electronic structure before thermalization. This work establishes dynamic Au-ligand interfaces as the microscopic link between excited-state energy flow and photochemical function in atomically precise nanoclusters.
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All authors Mengyuan Cui, Tianrui Chen, Junhua Zhou, Xiangmei Duan, Vandana Tiwari, Chao Mei, Ajay Jha, Fulu Zheng, Hong-Guang Duan
Plasma Physics
Spatio-Temporal Synchronization of Counter-Propagating Femtosecond Pulses
Tamir Cohen, Moshe Fraenkel and Ishay Pomerantz
Generating intense x-ray radiation via inverse-Compton scattering and exploring the strong-field regime of QED, require precise spatio-temporal synchronization of tightly focused counter-propagating intense
laser pulses. We present a protocol for establishing spatio-temporal synchronization in this geometry that combines microscope-based target positioning, wavefront-sensor-assisted
alignment of off-axis
parabolic mirrors, and a high-resolution temporal delay scan based on interference. We observed an interference window of 72 fs in good agreement with the expected autocorrelation width. The accuracy levels in space and time of using this protocol are discussed.
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Chemical Physics · Cross-listed from cond-mat.soft
Conformation-Mediated Kinetics of Polymer Chain Scission under Tension
Jie Zhu and Laurence Brassart
Chain scission is a key molecular process underlying damage and fracture in
polymer networks. In this Letter, we develop a statistical-mechanical framework for predicting chain-scission kinetics while accounting for three-dimensional (3D) conformational fluctuations. Within transition-state theory, scission is formulated as a multichannel first-rupture problem, with bond-specific rates governed primarily by self-consistent potentials of mean force. In the freely jointed limit, the additional 3D configurational freedom enhances rupture relative to the collinear 1D reference. Finite bending stiffness introduces orientational correlations that can reverse this enhancement and, at high stiffness, reduce rupture rates by orders of magnitude. These correlations also make rupture bond-position dependent, with higher rates near the chain ends and a common interior rate. For sufficiently long chains, the interior contribution dominates, yielding linear scaling of the chain-scission rate with chain length. These molecularly resolved rates provide physically grounded inputs for future network-scale models of
polymer damage and fracture.
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Atomic Physics
Measurement of the O$^{-}$ Photodetachment cross-section in the electrostatic storage ring FLSR
Oliver Forstner, Thorben Niemeyer, Andrey I. Bondarev et al. (+10 more)
The achievable precision of photodetachment studies via tunable
laser light has been investigated on circulating oxygen anions at the room-temperature electrostatic low-energy storage ring of Frankfurt University (FLSR) in preparation of investigations on molecular species. For this purpose, the FLSR, originally designed for reaction dynamics studies on positive ions, was upgraded by a source for anions, by the installation of a tunable high repetition rate
laser system and by implementation of a transversal interaction region between
laser and ion beam. Results on the electron affinity and the ground state fine structure of O$^{-}$, which both serve as a calibration standard, are discussed, exhibiting the performance and accuracy of this new spectroscopic application of the FLSR.
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All authors Oliver Forstner, Thorben Niemeyer, Andrey I. Bondarev, Markus Dworak, Vadim Gadelshin, Raphael Hasse, Lothar Schmidt, Markus Schöffler, Matou Stemmler, Kurt E. Stiebing, Dominik Studer, Klaus Wendt, Patric Ziel
Optics
Nonlocal-nonlinear phonon polaritons
Gonzalo Álvarez-Pérez, Line Jelver, Alexander Paarmann et al. (+1 more)
When light is confined to deeply subwavelength volumes, optical responses can become nonlocal. Yet how nonlocality reshapes nonlinear light-matter interactions remains largely unexplored, particularly in dielectrics. Here, we theoretically uncover a new class of nonlinear optical processes arising from the interplay between optical-
phonon propagation and ionic-bond anharmonicity in polar
crystals. We show that, unlike conventional local nonlinearities, this mechanism enables second-order responses even in centrosymmetric materials. Moreover, these responses can be tuned by the confinement and resonantly enhanced near optical-
phonon resonances. Using density functional perturbation theory, we quantify the resulting nonlocal second-order susceptibilities in representative polar
crystals. Our results establish nonlocal-nonlinear optics as a new regime of light-matter interaction in dielectrics.
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All authors Gonzalo Álvarez-Pérez, Line Jelver, Alexander Paarmann, Simone De Liberato
Plasma Physics
Anomalous Electric Fields in Earth's Turbulent Magnetosheath: Insights From 3D Hybrid Simulations
Jeffersson A. Agudelo Rueda, Julia E. Stawarz, Luca Franci et al. (+3 more)
In both collisional and collisionless
plasmas the presence of a broad range of electromagnetic and
plasma fluctuations provides anomalous electric fields that can be important for the dynamical
evolution of the system as it is the case of
magnetic reconnection,
plasma turbulence and dynamo theory. In the context of
plasma turbulence at scales larger than the ion's inertial length, the
plasma satisfies the frozen-in condition, and the anomalous electric fields are produced by correlations between turbulent velocity and
magnetic fields. Conversely, for collisionless
plasmas and at kinetic scales, the total electric field has additional contributions that arise from kinetic phenomena, namely, charge separation, ambipolar electric fields and electron inertia, and each of these terms presents an anomalous counterpart. In this work we characterize the anomalous electric fields. We present a framework that can explain partial balance between the anomalous resistivity and anomalous transport, and we use it to study anomalous electric fields at kinetic scales. We establish how the different contributions to the anomalous electric field couple to the large-scale electric fields and show that the anomalous terms act back-reacting on
magnetic-field organization and they may contribute to effective turbulent
magnetic diffusion or shielding. Finally, we test two Sub-Grid-Scale models including anisotropic transport coefficients and show that although these models partially recover the spectral information, the phase coherence is not entirely recovered by these models suggesting a more complex non-linear contribution of the anomalous terms to the resolved scales.
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All authors Jeffersson A. Agudelo Rueda, Julia E. Stawarz, Luca Franci, Nobumitsu Yokoi, Camille Granier, Silvio S. Cerri
Fluid Dynamics
Assessment of turbulent fire dynamics and combustion instabilities using a flamelet model
Yunxiao Yan, Fabian Brännström, Christian Hasse et al. (+1 more)
The Sandia one-meter methane fire plume is an established
benchmark for turbulent combustion modeling of large-scale flames. This study investigates the combustion instabilities formed close to the base of the Sandia fire plume. Finite rate chemistry and differential
diffusion are considered using a flamelet/progress variable (FPV) approach. The performance of the FPV approach is assessed by comparing with the eddy dissipation model (EDM) and the experimental data for the large-scale fire plume via large eddy simulations (LES). The effects of radiation modeling and mesh resolution on the predictive capability of the model are systematically investigated by comparing the axial and radical velocities against the experimental data at various locations. Although all models successfully capture the primary flow characteristics of fire plumes, the FPV model with differential
diffusion yields improved predictions in the near-flame-base region. The formation mechanism of cellular flow structures near the flame base is investigated via a budget analysis of the vorticity equation, and the type of instability governing the formation of the cellular structure is clarified. Finally, the individual effects of finite rate chemistry and differential
diffusion on the prediction of the thermo-chemical quantities are quantified. Overall, this study explains the underlying physics governing combustion instabilities at the base of turbulent fire plumes, provides novel insights into the performance of flamelet models for LES of gaseous pool fires, and offers reliable guidance for the high-fidelity numerical simulation of large-scale turbulent buoyancy driven flames.
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All authors Yunxiao Yan, Fabian Brännström, Christian Hasse, Xu Wen
Optics · Cross-listed from astro-ph.IM
Quantum-optimal instruments for high-contrast imaging with multi-plane light converters
Sebastiaan Y. Haffert, Yinzi Xin and Rico Landman
Spatial Mode Demultiplexers (SPADE) are devices that split an incoming wavefront into a particular set of electric field modes. SPADEs have been shown to be
quantum-optimal for many measurement problems including coronagraphy, wavefront sensing and interferometric (nulling) beam combiners. We will show how
quantum optimal SPADEs can be implemented using Multi Plane Light Converters (MPLC). MPLCs are devices that use several phase plates in sequence to achieve arbitrary
unitary transformations. The phase plates themselves are implemented using
liquid-
crystal technology that allows us to create high-quality broadband phase plates. The accurate control of the local phase through the direct write method results in MPLCs with minimal background scatter. We will show the designs and simulated performance for each of the proposed use cases for the ELTs, HWO and LIFE and show how they improve over current concepts.
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Optics
Metalens stereoscopic optical palpation for imaging cancer mechanics
Haoyi Yu, Rhys Jones, Chi Li et al. (+13 more)
Accurate intraoperative margin assessment is critical for complete resection of solid tumours. However, surgeons routinely rely on manual palpation, which is highly subjective and fundamentally limited by poor spatial resolution, and pre-operative imaging lacks real-time feedback. While emerging optical elastography techniques offer quantitative mechanical contrast, their reliance on bulky optical components necessitates cumbersome
alignment and hinders integration into miniaturised
surgical instruments. Here, we report metalens stereoscopic optical palpation (MSOP), a nanophotonic imaging platform leveraging a binocular metalens integrated with a single CMOS sensor to achieve high-fidelity, self-aligned elastography. By replacing complex bulk optics with a compact stereoscopic architecture, MSOP enables robust, high-contrast mapping of tissue surface stress. Following validation in heterogeneous silicone phantoms, we demonstrate MSOP's translational potential by characterising the mechanical signatures of malignancies in fresh mouse pancreatic cancer models, as well as excised human breast and liver specimens. By providing reliable, label-free mechanical contrast across diverse oncological landscapes, MSOP offers a compact tool for precise intraoperative margin delineation to reduce re-excision rates and improve
surgical outcomes.
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All authors Haoyi Yu, Rhys Jones, Chi Li, Bo He, Renate Zilkens, Louise N. Winteringham, Laura Gale, Mireille Hardie, Fiona Bellamy, Saud Hamza, Christobel M. Saunders, Liver Cancer Collaborative, Stefan A. Maier, Brendan F. Kennedy, Haoran Ren, Qi Fang
Optics
Design and numerical performance analysis of efficient Ag3TaX4 (X = S, Se, Te) thin film solar cells
Md. Nahid Hasan, Tanvir Ahmed, Md. Abdur Rashid et al. (+3 more)
Silver-based ternary chalcogenides have recently emerged as promising absorber materials for thin film photovoltaics. Nevertheless, their photovoltaic performance in complete device architectures has not yet been systematically explored. In this work, three-dimensional (3D) n-CdS/p-Ag3TaX4 (X = S, Se, Te)/p+-GeS thin-film
solar cells have been designed and numerically investigated using the
Semiconductor Module of COMSOL Multiphysics. Herein, the various performance
matrices of the proposed devices have been analysed in accordance with the changing of depth, carrier, and defect concentration in each layer of the structures. The optimized Ag3TaS4-based device delivers a power conversion efficiency, PCE of 24.66%, open
circuit voltage, VOC of 1.4V, short
circuit current density, JSC of 20.68 mA/cm2, and fill factor, FF of 85.16%. The Ag3TaSe4-based
solar cell exhibits the PCE of 28.1% with VOC = 1.19V, JSC = 27.0 mA/cm2, and FF = 87.44%. The Ag3TaTe4
solar device shows a PCE of 27.56% with a VOC of 0.88 V, JSC of 36.14 mA/cm2, fill factor of 86.65%. These results provide a deeper insight into device operation and offer practical design guidelines for fabricating efficient Ag3TaX4 (X = S, Se, T e)-based novel next-generation
solar cells.
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All authors Md. Nahid Hasan, Tanvir Ahmed, Md. Abdur Rashid, Tanzina Rahman, Dinesh Pathak, Jaker Hossain
Medical Physics
Validation of HRV Studio: A Transparent and Quality-Control-Aware Platform for Heart Rate Variability Analysis
Cyrus Mexon Evrard Djindot, Faliang Liu, Sylvain Laborde et al. (+6 more)
Reproducibility of heart rate variability (HRV) analysis is limited by differences in preprocessing and computational conventions across software platforms. We developed HRV Studio, an open-source PyQt6-based desktop application integrating transparent HRV analysis with automated quality-control (QC) diagnostics. Validation included large-scale agreement with NeuroKit2, targeted Kubios benchmarking, spectral-method comparison, synthetic perturbation testing, recording-duration sensitivity analysis, and arrhythmia-focused QC stress testing. HRV Studio showed near-identical agreement for the widely used time-domain indices RMSSD and SDNN under matched conditions. In the primary five-minute NeuroKit2 comparison, frequency-domain median relative errors were 1.35% for LF, 0.18% for HF, and 1.41% for LF/HF, while VLF remained more convention-sensitive (37.79%). Nonlinear Poincaré indices also demonstrated high consistency. Sequence-harmonized Kubios benchmarking confirmed near-identical agreement for time-domain and nonlinear indices and strong agreement for most frequency-domain measures. Extended ten-minute analyses reproduced the same overall pattern with lower disagreement for some convention-sensitive spectral outputs. Synthetic and arrhythmia stress tests maintained 100% numerical stability while consistently triggering QC warnings. Overall, HRV Studio provides a transparent and reproducible platform for HRV research, with strong cross-platform consistency when NN sequences, preprocessing, and analytical conventions are harmonized. Stress-test results indicate computational robustness rather than clinical validation.
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All authors Cyrus Mexon Evrard Djindot, Faliang Liu, Sylvain Laborde, Yinjia Zhang, Jessie Chen, Ming Li, Congrong Wang, Weixiong Rao, Qinpei Zhao
Chemical Physics · Cross-listed from cond-mat.stat-mech
A Minimal Thermodynamically Consistent Chemical Oscillator
Benedikt Remlein, Luca Monari, Beatrice Bartolomei et al. (+3 more)
Inspired by the chemical reaction network considered as the smallest system featuring a
Hopf bifurcation and its reversible extension, we introduce an even more minimal reaction network that is thermodynamically consistent and exhibits autonomous oscillations under nonequilibrium driving. The model combines three features that are rarely realized simultaneously in compact oscillator networks: a chemically plausible structure restricted to uni- and bimolecular reactions, reversibility of such reactions, and analytical tractability. The system consists of three internal species coupled to two chemostatted species and still undergoes a supercritical
Hopf bifurcation when a chemostat concentration is varied. To analyze the dynamics and thermodynamics near the onset of oscillations, we employ the mathematical technique of normal-form reduction, which allows obtaining a controlled irreversible approximation that preserves the leading phase-space structure of the full reversible network while enabling explicit calculations. This framework provides analytical access to the bifurcation structure and the leading contributions governing thermodynamic observables. Within this setting, we use the onset of oscillations to characterize the thermodynamic response of the system. In particular, we offer an analytical description of key thermodynamic quantities such as the semi-grand Gibbs free energy and the non-conservative work rate, which exhibit a kink-like discontinuity at the
Hopf bifurcation. We thus provide an analytical description of a phenomenon previously characterized only through numerical simulations of more complex networks.
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All authors Benedikt Remlein, Luca Monari, Beatrice Bartolomei, Giulio Ragazzon, Massimiliano Esposito, Emanuele Penocchio
Optics
An Ab initio Framework for Simulating Ultrafast Nonlinear Cavity Quantum Electrodynamics Spectra
Luis Vasquez, Kewei Sun, Haibo Ma et al. (+1 more)
In this letter we introduce a theoretical framework for the simulation of ultrafast transient absorption pump-probe spectra of molecular polaritons. We derive and implement the cavity
quantum electrodynamics (QED)
evolution equations of polaritonic states within the framework of the quasi-classical doorway-Window pproximation, hereto referred cQUEDA /sikeda/. This framework uses outputs from mixed
quantum-classical dynamics simulations in the absence of the cavity. Then by including cavity parameters accounting for cavity rate loss, coupling strength, and frequency detuning, we simulate transient absorption pump-probe spectra. Consequently, we address one of the main standing problems of cavity QED, the simulation of polaritons ultrafast dynamics and nonlinear optical properties. We demonstrate the performance of our method by computing the ground-state bleach (GSB), stimulated emission (SE), and excited-state absorption (ESA) contributions of transient absorption pump-probe spectra of pyrazine strongly coupled to a cavity. The cQUEDA is an on-the-fly computationally efficient framework with low computer requirements: the pyrazine calculations, for example, took minutes on modern laptops. cQUEDA offers wide-ranging applicability and can be generalized to model diverse nonlinear spectroscopic signals and
quantum optics responses.
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All authors Luis Vasquez, Kewei Sun, Haibo Ma, Maxim F. Gelin
Physics and Society
Spatiotemporal organization in bike-sharing systems using gravity model parameters
Hanbo Zhang, Qi Rao and Bo Yang
Gravity models describe bike-sharing origin-destination (OD) flows as increasing with origin and destination activity and decreasing with distance. Yet how these relationships change within a day and across observation areas remains unclear. We examine temporal and spatial variation in origin, destination and distance exponents $\alpha$, $\beta$, and $\gamma$, together with $R^2$ and mean absolute error (MAE), across eight bike-sharing systems. Temporal modeling uses sliding windows, while spatial modeling expands a circular area and separates intra-zonal, cross-zonal
outflow, cross-zonal inflow and extra-zonal trips. We find recurring patterns across cities: morning and evening peaks differ in origin and destination dependence, while cross-zonal
outflow and inflow across the same boundary show opposite changes in their relative origin and destination dependence as radius increases. Model performance and distance dependence also vary with time and radius. A full-day, citywide fit therefore combines time periods and flow types with different
gravity relationships.
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Classical Physics
Electromagnetic Radiation from a Neutralized Polarized Sphere with Two Conserved Currents for One Charge History
Natan Rentzber
Can a source radiate when its total charge density vanishes identically? Consider a uniformly polarized sphere coated with free surface charge that cancels the bound surface charge at every point and time. Then $\rho_{\mathrm{tot}}=0$, so every electric charge multipole vanishes. Continuity determines only $\nabla\cdot\mathbf{J}$, which allows the same charge history to be supported by different conserved currents. A compensating interior current gives $\mathbf{J}_{\mathrm{tot}}=\mathbf{0}$ and produces no $\mathbf{E}$ or $\mathbf{B}$ at any frequency. The minimum-norm tangential sheet current instead leaves $\mathbf{J}_{\mathrm{tot}}$ nonzero and divergence-free. Its radiation-zone field is exact in $kR$ and proportional to $j_2(kR)$. At long wavelength the radiated power is suppressed by $(kR)^4/100$, and it vanishes exactly at the positive roots of $j_2$. The same calculation gives the interior field and a closed-form energy balance. The average work supplied by driving equals the radiated power and falls to zero at those roots even though interior fields remain. For comparison, the bare sphere has the factor $3j_1(kR)/(kR)$ and is silent at the roots of $j_1$.
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Data Analysis and Statistics · Cross-listed from astro-ph.GA
Decoupling candidate dual AGN from chance superpositions in the GOTHIC survey via a deep-learning framework
Bhavesh Mukheja, Snehanshu Saha, Anwesh Bhattacharya et al. (+3 more)
Dual active
galactic nuclei (DAGN) mark a critical phase in the
evolution of merging
galaxies and the pairing of supermassive black holes, yet they remain difficult to identify in large imaging surveys because of projection effects and limited spatial resolution. Compact foreground
stars and unresolved substructure can mimic dual
nuclei through chance superposition, complicating automated detection. We revisit the 46,061
galaxies flagged but rejected as DAGN candidates by the GOTHIC pipeline, primarily because the two
nuclei fell within the SDSS fibre aperture or exceeded its separation threshold. We train a supervised deep-learning framework based on the YOLOv11 oriented-bounding-box architecture on annotated SDSS imaging to separate genuine dual
nuclei from foreground
stellar contaminants and other spurious
alignments. The final model attains a validation precision of 0.919, recall of 0.905, and $F_1$ of 0.912, and yields 29,605 dual-
nucleus candidates after removing
star-dominated and blended detections. Structured visual inspection indicates that $54.5$–$62\%$ are consistent with genuine dual
nuclei, implying $\sim(1.4$–$1.8)\times10^{4}$ plausible systems. Cross-calibrating the YOLO separation against the deterministic GOTHIC centroid measurement and restricting to the compact regime ($d \le 6.87''$) gives a conservative subset of $\sim 13{,}672$ candidates, reaching calibrated separations of $\sim 0.56''$. Spectroscopy of the most compact ($\le 1$~kpc) systems shows spectra dominated by
stellar absorption, with no resolved double-peaked emission, so confirmation requires higher-resolution follow-up. The catalogue is a statistically refined list of candidates, not confirmed DAGN. Nonetheless, deep-learning detection substantially reduces contamination and expands the plausible DAGN census.
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All authors Bhavesh Mukheja, Snehanshu Saha, Anwesh Bhattacharya, Mousumi Das, Françoise Combes, Sudhanshu Barway
Fluid Dynamics · Cross-listed from quant-ph
Efficient Treatment of Non-Linearity in Quantum Computational Fluid Dynamics Using Hybrid Tensor Networks
Pia Siegl, Nis-Luca van Hülst, Maximilian Mandelt Buxadé et al. (+2 more)
Nonlinear terms present a fundamental challenge for
quantum computational fluid dynamics, as their implementation on inherently linear
quantum hardware typically requires resource-intensive workarounds that limit scalability to large-scale simulations. We present a hybrid
quantum-classical tensor network
algorithm that addresses this bottleneck by combining variational time-stepping with
quantum tensor programming to efficiently compile operators and time-dependent fields into
quantum circuits. Within a probabilistic framework, we replace prior state-based nonlinear implementations with tensor-based block encodings, stabilizing success probabilities that otherwise decay exponentially with system size. Benchmarking on turbulent flow fields demonstrates that the
algorithm maintains high success probabilities and moderate measurement overhead across increasing Reynolds numbers and grid resolutions. Compared to fully classical tensor network solvers, our hybrid approach yields substantial reductions in both
memory footprint and computational cost, establishing a scalable pathway toward practical
quantum advantage in scale-resolving CFD simulations.
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All authors Pia Siegl, Nis-Luca van Hülst, Maximilian Mandelt Buxadé, Tomohiro Hashizume, Dieter Jaksch
Optics
Mesa Orientation Engineering for Polarization Locking in VCSELs
Zifeng Yuan, Wenkai Shan, Tingting Chen et al. (+2 more)
While polarization stability is common in many optical systems, intentional polarization bi-stability is also important for polarization-encoded computing. We propose a mesa orientation strategy to engineer the polarization switching of vertical-cavity surface-emitting
lasers (VCSELs). Further experiments demonstrate improved polarization locking performance.
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All authors Zifeng Yuan, Wenkai Shan, Tingting Chen, Beibei Lin, Aaron Danner
Computational Physics
A sharp-diffuse interface model for intermittent and isolated topological transitions
Raaghav Ramani
We propose a hybrid sharp-diffuse interface representation for modeling intermittent and isolated topological transitions during Cahn-Hilliard phase coarsening. Away from topological events, the
evolution is approximated by the Mullins-Sekerka sharp-interface limit system and computed using a boundary integral formulation. When diffuse transition layers overlap, a novel interface surgery
algorithm resolves
topology changes through a localized Cahn-Hilliard pseudo-time
evolution, after which the sharp-interface calculation is resumed. We develop the mathematical formulation underlying this decomposition, present a simple two-dimensional numerical implementation, and simulate a mass-exchange problem with interface coalescence. By localizing the diffuse
evolution to topological events, the method achieves a speedup of two to three orders of magnitude over conventional diffuse-interface simulations.
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Biological Physics
Quantifying the Biophysical Properties of Red Blood Cells in Gaucher Disease
Zhaojie Chai, Marine de Person, Pierre A. Buffet et al. (+2 more)
Gaucher disease (GD), the most common lysosomal storage disorder, alters red blood
cell (RBC) mechanics and circulation, contributing to vascular occlusions, bone infarcts, and splenomegaly. However, the individual roles of GD-RBC biophysical properties in these processes remain unclear. Here, we present a combined computational-experimental investigation to quantitatively characterize GD-RBC biophysical properties and determine how specific mechanical parameters drive abnormal RBC behavior. Informed by experimental data, we independently quantify key RBC properties, including shear modulus (mu), surface-to-volume ratio (S/V), and bending modulus (k_c). Based on these parameters, we construct three GD-RBC subtypes (GD-RBC1-3) to systematically isolate their individual contributions. At the single-
cell level, optical tweezers simulations show up to ~27% reduction in axial diameter and ~42% reduction in transverse compression. Tank-treading dynamics exhibit non-monotonic behavior, with rotation frequencies increasing by up to ~70% or decreasing under elevated bending
rigidity. In confined flow, traversal times through microchannel constrictions increase by more than a factor of two, while splenic slit passage times rise from ~250 ms (control) to >1200 ms for the severe GD-RBC subtype, approaching a functional no-passage threshold. At the population level, viscosity simulations demonstrate that these alterations collectively elevate blood viscosity, with small fractions (~4.0%) of highly rigid
cells disproportionately increasing flow resistance. Overall, this study provides a quantitative and mechanistic framework that disentangles the contributions of key RBC parameters to abnormal behavior in GD, linking cellular-scale biophysics to hematologic dysfunction and microvascular occlusion.
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All authors Zhaojie Chai, Marine de Person, Pierre A. Buffet, Melanie Franco, George Em Karniadakis
Plasma Physics
First-Principles Simulation of Electron-Ion Collisional Transport in Magnetized and Unmagnetized Plasmas
Keheng Zhu, Jian Liu, Chaozhou Mou et al. (+2 more)
Accurate electron-ion collision models are central to predicting transport in fusion and space
plasmas, yet most practical formulations rely on binary-collision assumptions and impact-parameter cutoffs whose quantitative accuracy is difficult to assess directly. We develop a first-principles simulation framework for collisional transport by solving the Newton-Lorentz equations for test electrons in the many-body electric field of a Debye-screened ion background, without imposing binary-collision closures or artificial lower cutoffs. The method combines explicit force summation within a Debye sphere, a volume-preserving particle pusher, and adaptive time stepping, enabling stable and scalable simulations in both unmagnetized and magnetized
plasmas. Using simulation-based measures of momentum relaxation and cross-field
diffusion, we recover the classical scalings for the electron-ion collision frequency and perpendicular
diffusion coefficient, namely $\nu_{ei} \propto v_{th}^{-3}$ and $D_\perp \propto B^{-2}$. Within the parameter range studied, both simulated coefficients are lower than their corresponding classical estimates by approximately 15-25%. These regime-specific
benchmark results indicate that classical transport theory captures the leading scaling behavior, but that the corresponding quantitative prefactors can remain sensitive to many-body and near-field effects in the simulated regime. The framework therefore provides a computational
benchmark for testing and improving reduced collision operators and transport models.
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All authors Keheng Zhu, Jian Liu, Chaozhou Mou, Senran Lin, Wei Zhang
Fluid Dynamics
Backflow-Induced Inertial Arrest of Velocity Fluctuations in Sedimenting Suspensions
Hsien-Hung Wei
A self-contained hydrodynamic theory is proposed to reconcile the discrepancy between divergent Stokesian velocity fluctuations and finite experimental measurements in sedimenting suspensions. We show that the compensating backflow induces non-negligible inertia, giving rise to an emergent screening length $\xi \sim a\phi^{-1/3}Re_p^{-1/3}$ far exceeding the mean interparticle spacing $a\phi^{-1/3}$ even at vanishingly small particle Reynolds numbers. This backflow inertial screening, together with finite-time viscous
diffusion, arrests the indefinite spatiotemporal growth of large-scale velocity fluctuations. The resulting velocity fluctuations scale as $\delta u \sim \phi^{1/3}V_sRe_p^{-1/6}$, together with the viscous correlation time $\tau_c=\xi^2/\nu$, reproducing the well-known hydrodynamic self-diffusivity scaling $D_H\sim V_s a$. The theory predicts the prefactors of these scaling laws without adjustable parameters, in good quantitative agreement with experimental measurements. It also successfully captures the experimentally observed crossover from the finite-correlation regime to the finite-system regime as the screening length becomes comparable to the system size.
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Plasma Physics
An Inverse Grad-Shafranov Neural Network Approach to Tokamak Magnetic Control
Allen M. Wang, Adriano Mele, Cosmas Heiß et al. (+12 more)
A new approach to tokamak
magnetic control enabling high-precision
plasma shaping and novel real-time adaptability is experimentally demonstrated on the Tokamak a Configuration Variable (TCV). The method is motivated by the insight that, under appropriate assumptions, a real-time inverse Grad-Shafranov solver approximates an optimal control policy for
plasma boundary regulation. Building on this, a control architecture is developed in which classical controllers enforce operational constraints while a fast surrogate model provides a real-time inverse mapping from the desired
plasma boundary to Poloidal Field Coil currents. Experimental results on TCV demonstrate improved
plasma shaping with respect to the standard discharge preparation procedure — albeit without explicit real-time shape feedback — while enabling flexible response to asynchronous events. It is shown that a single network provides satisfactory performance across a range of
plasma magnetic configurations. Real-time adaptivity is demonstrated in simulation, and partially in experiment, through adaptive strike point motion and early termination in response to a real-time trigger. These results suggest a viable path toward
magnetic control architectures that reduce reliance on dense diagnostic coverage while maintaining high-accuracy
plasma shaping, with potential relevance for future fusion power plant operation.
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All authors Allen M. Wang, Adriano Mele, Cosmas Heiß, Cristian Galperti, Zander Keith, Alessandro Pau, Antoine Merle, Olivier Sauter, Daniel Gonzalez Castiñeiras, Francesco Carpanese, Federico Felici, Mark Dan Boyer, Cristina Rea, TCV Team, EUROfusion Tokamak Exploitation Team
Fluid Dynamics
Momentum-scalar coupled turbulence with anomalous momentum and scalar diffusions. Part 2: With short-range external force and implementation in electrokinetic turbulence
Wei Zhao
We extend the generalized anomalous
diffusion framework established in Part I to the short-range forcing regime ($\beta > 2/3$), where the multiscale-force dominated (MFD) subrange is intercalated after the inertial subrange, competing directly with the dissipation ranges. Focusing on electrokinetic (EK)
turbulence as the prototypical example with $\beta=1$, we derive the relations for the velocity and scalar dissipation wavenumbers, $k_{MD}$ and $k_{SD}$, across all four subranges of the Quad-cascade process (inertial, constant-$\Pi_u$, constant-$\Pi_s$, and variable flux). By incorporating Golestanian's predicted anomalous
diffusion regimes for electrolytes, we construct comprehensive phase diagrams showing how the relative magnitudes of $k_{MD}$ and $k_{SD}$ are governed by the scale-dependent anomalous Schmidt number $Sc_Z$. We identify two new spectral subranges that emerge exclusively in this short-range forcing regime: (i) the convective-viscous subrange ($k_{MD} \ll k \ll k_{SD}$) of velocity spectrum for $Sc_Z \gg 1$, where the scalar field drives a viscous flow yielding $E_u \sim k^{-\left(\frac{3}{2} + \frac{\xi_s}{2}\right)}$ with a stretched-exponential cutoff; and (ii) the diffusive-forcing subrange ($k_{SD} \ll k \ll k_{MD}$) of scalar spectrum for $Sc_Z \ll 1$ and $\gamma \leq \alpha$, where the scalar dissipation range determines the electric forcing, leading to $E_s \sim k^{\xi_u - 2\alpha}$. These results provide a complete analytical map of EK
turbulence under anomalous
diffusion, revealing how external parameters such as electric field strength and ionic diffusivity determine the cascade
topology.
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Fluid Dynamics
Momentum-scalar coupled turbulence with anomalous momentum and scalar diffusions. Part 1: Without external force and with long-range external force
Wei Zhao
We present a theoretical model for momentum–scalar coupled
turbulence in which both fields undergo anomalous
diffusion, described by fractional biharmonic operators of orders $\gamma/4$ and $\alpha/4$, respectively. Focusing on the long-range external forcing or unforced
turbulence, we derive analytical expressions for the kinetic energy spectrum $E_u(k)$, the scalar spectrum $E_s(k)$, and the characteristic wavenumbers $k_K = \left( \frac{\epsilon_u^{1/3}}{c_u} \right)^{1/(\gamma - 2/3)}$ (reciprocal of Kolmogorov scale) and $k_S = \left( \frac{\epsilon_u^{1/3}}{c_s} \right)^{1/(\alpha - 2/3)}$ (reciprocal of scalar dissipation scale) as functions of $\gamma$, $\alpha$, turbulent dissipation rate $\epsilon_u$, diffusivities of momentum ($c_u$) and scalar ($c_s$), respectively. An anomalous Schmidt number $Sc_Z = k_0^{\gamma - \alpha} \frac{c_u}{c_s}$ is defined to governs the cascade
topology. It describes the ratio of
diffusion times of scalar and momentum on the minimum wavenumber $k_0$. Superdiffusion ($\gamma<2$ or $\alpha<2$) is shown to counter-intuitively enlarge $k_K$ and $k_S$, broadening the inertial range. The theory unifies the classical Kolmogorov–Obukhov–Corrsin–Batchelor scalings as special cases when $\gamma=\alpha=2$, and provides a foundation for understanding non-Fickian transport in complex turbulent systems.
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Instrumentation and Detectors
Photogrammetry for Precise, Rapid Module Alignment in the Mu2e Tracker
Dylan Palo, Mamta Jangra, Aseet Mukherjee et al. (+1 more)
We discuss a photogrammetry technique to measure the inter-module
alignment in the Mu2e tracker. The tracker consists of 216 modules each with 96 straw tubes. The relative
alignment of the straw tubes in a module was previously measured by an X-ray technique, which tied the straw tube measurements to three fiducials per module. The photogrammetry technique uses an array of 15 cameras to make precise position measurements of the module fiducials in a global tracker coordinate system. Measurements of the fiducial position and radius on the camera's CCD yield ~$25 \mu m$ resolution in the transverse directions and < $300 \mu m$ along the camera axis. In addition, we describe a procedure to combine the images with "local" mechanical measurements to yield $<100 \mu m$ precision along the camera axis. The technique offers a touch-less, rapid (~1 hour), and affordable metrology approach within the requirements of the tracker.
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All authors Dylan Palo, Mamta Jangra, Aseet Mukherjee, Klara Northrup