Fluid Dynamics
Generalised Mixing-Plane Method for Compressible Reacting-Mixture Flows in Steady Multiphysics Turbomachinery Simulations
Yifeng Wang, Lin Shi, Fenglai Huang et al. (+3 more)
The mixing-plane method plays a pivotal role in steady simulations of multiple turbomachinery components. With advances in computational power, a whole-engine gas turbine simulation is no longer an elusive approach. However, whole-engine simulations require simultaneous coupling of the compressor, turbine and combustor. A key challenge is that the working fluid after the combustor can no longer be treated as a perfect gas, since the combustion introduces composition variations and combustion products. Conventional mixing-plane methods based on a fixed-composition gas cannot guarantee a thermodynamically consistent mixed-out state. To overcome the difficulty, this paper extends the classic mixing-plane approach to handle compressible reacting flows. The nonlinearity in the thermodynamic closure is addressed using a novel nested
algorithm combining an outer pressure-root search with an inner enthalpy inversion. Physical state checks and power-law pressure sampling are incorporated to improve numerical robustness at low normal velocities where the pressure root approaches its upper physical bound. The performance of the method is demonstrated in three configurations: a quasi-1D interface test elucidating the thermodynamic stiffness of the proposed mixing-plane formulation for different fuel types and flow conditions; the Darmstadt transonic compressor case that verifies the proposed method reduces to the classic mixing-plane formulation when the mixture fraction reduces to zero; and a whole-engine simulation of the KJ66 micro-turbojet is used to demonstrate the performance of the method for multiphysics turbomachinery simulations. Good agreement with experimental data is observed, and the maximum relative mass-flow error across the mixing planes remains below 0.11%, demonstrating conservative and thermodynamically consistent interface coupling for compressible reacting turbomachinery flows.
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All authors Yifeng Wang, Lin Shi, Fenglai Huang, Rui Wang, Feng Wang, Hui Xu
Atmospheric and Oceanic Physics · Cross-listed from cs.LG
A library for differentiable signal processing and machine learning on the sphere
Thorsten Kurth, Max Rietmann, Mauro Bisson et al. (+6 more)
The two-dimensional sphere embedded in three-dimensional Euclidean space S2, plays a central role in a variety of scientific and engineering domains, including geophysics, planetary science, geodesy, atmospheric physics,
quantum chemistry, cosmology, and virtual reality, among many others. As machine learning increasingly permeates these fields, the demand grows for robust tools that process and model functions on the sphere, while respecting the inherent topological and
symmetry properties of the domain. We present torch-harmonics, a comprehensive library that offers efficient, differentiable implementations of advanced signal processing and machine learning (ML) methods for spherical data. These include the spherical harmonic transform (SHT), the spherical analogue of the
Fourier transform, vector spherical harmonics, discrete-continuous and spectral convolutions, as well as both global and neighborhood spherical
attention mechanisms. Beyond traditional representations, torch-harmonics provides the building blocks for state-of-the-art spherical ML architectures such as spherical
transformers in order to enable scalable, rotationally-aware learning and inference in modern scientific and engineering applications.
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All authors Thorsten Kurth, Max Rietmann, Mauro Bisson, Andrea Paris, Alberto Carpentieri, Jean Kossaifi, Anima Anandkumar, Christian Hundt, Boris Bonev
Optics
Phase-resolved wide-field CARS microscopy with speckle illumination
Federico Vernuccio, Pascal Berto, Baptiste Marthy et al. (+5 more)
Coherent anti-Stokes Raman scattering (CARS) microscopy enables label-free chemical imaging of biological samples and materials. Conventionally, CARS is implemented using a point-scanning approach that probes a single vibrational mode at a time. Hyperspectral CARS enhances chemical specificity by sequentially addressing multiple Raman modes. However, the measured CARS intensity is distorted by an undesired non-resonant background, which broadens and shifts the Raman peaks, thereby hindering the interpretability of hyperspectral images. Here, we introduce a phase-sensitive, wide-field hyperspectral CARS microscopy scheme that suppresses the non-resonant background. The proposed approach combines three key components: a high-power picosecond tunable optical parametric amplifier (OPA), speckle illumination, and quantitative phase imaging based on quadriwave lateral shearing interferometry (QLSI). The high-power OPA provides the peak power required for efficient nonlinear excitation. Speckle illumination distributes the optical energy over the objective back pupil and mitigates coherent imaging artifacts. QLSI enables the simultaneous measurement of the amplitude and phase of the CARS field, thereby allowing separation of resonant and non-resonant contributions, without the need for an external reference beam. This unique combination enables practical phase-resolved CARS imaging over a field of view exceeding $60 \times 60~\text{\textmu m}^2$ at a frame rate of 1.4 Hz. We illustrate the approach by acquiring hyperspectral images of microplastics and liver steatosis across the entire CH-stretching region.
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All authors Federico Vernuccio, Pascal Berto, Baptiste Marthy, Guillaume Baffou, Sandro Heuke, Randy Bartels, Pierre Bon, Hervé Rigneault
Computational Physics
MyTm: An Automated Melting Temperature Calculation Toolkit
Y. S. Huang, H. X. Song, Y. Sun et al. (+7 more)
Melting temperature calculation is one of the important topics in computational materials science. In high-throughput in silico screening and artificial intelligence assisted design of materials, it usually requires a rapid and autonomous assessment of the melting temperature of the target. Unfortunately, molecular dynamics (MD) simulations of the melting point require many cumbersome and manual operations, making large-scale calculation of the melting point challenging. In this work, we introduce MyTm, a toolkit that employs MD to automatically determine the melting point. The method is fully modularized, and by combining these modules, the program enables fully automated melting calculations by using commonly adopted approaches, including the direct-heating method, the void method, the modified void method, the solid-
liquid coexistence method, and the Z method. Moreover, a machine learning (ML) method is proposed and employed to recognize and classify the solid like and
liquid like atoms, which effectively resolve the low accuracy issue in conventional classification approaches, thus making the automated high throughput pipeline of melting-point calculation possible. The robustness and efficacy of MyTm have been demonstrated by several well studied systems.
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All authors Y. S. Huang, H. X. Song, Y. Sun, J. L. Li, Y. L. Xu, F. C. Wu, Y. C. Gan, Y. F. Wang, H. Wang, Hua Y. Geng
Computational Physics · Cross-listed from cond-mat.mtrl-sci
An electromechanically coupled multiphase-field model with generalized kinetic relations for ferroelectrics
Hsu-Cheng Cheng and Dennis M. Kochmann
Classical phase-field models typically use the Allen–Cahn
evolution law to model interface motion as a consequence of energy-gradient descent. This implies a linear kinetic relation between the velocity of an interface (e.g., a domain wall in a ferroelectric) and its driving force. When nonlinear kinetic relations are to be modeled, as commonly found in ferroelectric ceramics, an alternative
evolution law and hence an alternative model is needed. Here, we propose an electromechanically (stress-driven) coupled multiphase-field framework with a general kinetic formulation, which integrates a prescribed kinetic relation directly into the
evolution law. We show that this model correctly evolves domain walls with the assigned nonlinear kinetics, e.g., of mixed exponential-power law type, following the so-called Merz–Stadler law. The multiphase formulation further enables distinct kinetic relations and interfacial energies to be assigned to different order-parameter pairs, which reflects the distinguishable properties of the different types of ferroelectric domain walls. The proposed framework is broadly applicable for simulating kinetic relations in materials with applications beyond ferroelectrics.
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Optics
How Shaped Waves Propagate in Scattering Media
David Gaspard and Arthur Goetschy
The radiative transport equation provides a powerful framework for describing wave propagation in scattering media. However, it cannot describe coherent waves whose incident wavefront is deliberately tailored. Here we establish a transport theory for wavefront-controlled waves based on a
matrix transport equation. Unlike conventional radiative transport, which propagates a scalar radiance, our theory propagates a complex two-by-two
matrix that retains phase information and obeys a nonlinear transport equation, despite the underlying wave dynamics being linear. We use this
matrix transport equation to derive the spatial profiles of the energy and current densities of transmission eigenchannels, from closed to open channels, in arbitrary diffusive systems. Remarkably, these profiles can be expressed analytically in terms of the solution of the conventional radiative transport equation for a random wave in the same medium. The theory further extends to energy loss, including absorption and leakage into uncontrolled channels, revealing
symmetry breaking of transmission eigenchannels in complex structures. Validated against numerical solutions of the wave equation, we establish
matrix transport as a framework for describing and controlling coherent wave propagation in complex media.
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Biological Physics
Axonemal bending stiffness of $\mathit{Chlamydomonas}$ cilia implies single-motor forces above $5\,\mathrm{pN}$
Maximilian Kotz, Veikko F. Geyer and Benjamin M. Friedrich
The regular bending waves of cilia and flagella provide an iconic model system for the collective dynamics of molecular motors. The known regular arrangement of dynein motors in a cilium's axoneme allows us to connect mesoscopic cilia properties, such as axonemal bending stiffness, to microscopic motor properties, such as the force exerted by an individual motor. We estimate the active force generated by the collection of dynein molecular motors in $\mathit{Chlamydomonas}$ axonemes using previous estimates of its bending stiffness. Divided by the maximal possible number of active motor heads, this provides a lower bound of ${>}10\,\mathrm{pN}$ for the peak force generated by a motor head, which exceeds typical stall forces ${<}5\,\mathrm{pN}$ of molecular motors. This discrepancy suggests that either the bending stiffness of microtubules and axonemes was previously overestimated, or that collective force generation in dense motor arrays can surpass the sum of expected contributions of individual motors.
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Optics
Judd-Ofelt analysis of holmium-doped alumino-silicate optical glass prepared by MCVD combined with nanoparticle doping
Petr Varak, Michal Kamradek, Pavla Nekvindova et al. (+2 more)
We present a detailed Judd–Ofelt (JO) analysis of Ho$^{3+}$-doped alumino-silicate optical fiber preforms in a wide range of compositions and prepared by both the standard solution doping method as well as the more advanced nanoparticle doping. The absorption spectra were measured, the absorption cross sections were calculated for each observed transition, and the Judd–Ofelt analysis was conducted. The preforms exhibited the values of JO parameters of $\Omega_2 = (7.2--10.6) \times 10^{-20}\,\mathrm{cm}^2$, depending on the Al$_2$O$_3$ content, and $\Omega_4$ and $\Omega_6$ around $2.5$ and $1.2 \times 10^{-20}\,\mathrm{cm}^2$, respectively. The radiative transition parameters, such as transition probabilities, branching ratios, and radiative lifetimes, were calculated. The radiative lifetime of the ${}^5I_7 \rightarrow {}^5I_8$ transition, in the $16.1--17.2\,\mathrm{ms}$ range, combined with a measured value in the $0.9--1.9\,\mathrm{ms}$ range, was used to calculate the
quantum efficiency, which was in the $5--11\,\%$ range. The preforms prepared by nanoparticle doping containing high Al$_2$O$_3$ contents above $8\,\mathrm{mol.}\,\%$ exhibited superior values of measured lifetime (above $1.5\,\mathrm{ms}$) and
quantum efficiency (above $8\,\%$) compared to the standard solution-doped samples. To the best of our knowledge, this work is the first comprehensive report on the JO analysis of Ho$^{3+}$-doped alumino-silicate glass. The calculated parameters may be used in various calculations, simulations, and modelling of holmium-doped fiber
lasers and other devices.
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All authors Petr Varak, Michal Kamradek, Pavla Nekvindova, Jan Hrabovsky, Pavel Peterka
Data Analysis and Statistics · Cross-listed from stat.ME
B-GRASP: A Bayesian Framework for Inferring Graph Weights from SPDE-Inspired Dynamics
Christina Schenk and Babak Maboudi Afkham
We present B-GRASP (
Bayesian GRAph inference with SPDE priors), a
Bayesian framework for inferring uncertain edge weights in
stochastic dynamical systems on graphs from noisy observations of nodal states. The unknown edge weights parameterize the graph differential operator and therefore directly govern the
evolution of the graph process. Motivated by connections between differential operators in PDEs and SPDEs and their graph counterparts, we construct
stochastic graph models incorporating
diffusion, reaction dynamics, and
stochastic forcing. The resulting hierarchical formulation jointly represents uncertainty in the graph structure and
stochastic forcing. Latent graph variables determine positive edge weights and the corresponding graph
Laplacian, while latent Brownian variables represent the
stochastic forcing. Conditional on these variables, the graph dynamics define a deterministic forward map from which the likelihood and posterior distribution are constructed. We characterize the posterior using maximum a posteriori estimation and the No-U-Turn Sampler, enabling both point estimation and uncertainty quantification. We demonstrate the framework on a one-dimensional inverse heat-conduction problem, stationary and nonstationary graph reaction-
diffusion systems with nonlinear dynamics, and state-level COVID-19 data in the United States. The numerical results show that posterior uncertainty provides information not captured by point estimates, particularly for weakly identifiable or highly conductive edges, and enables uncertainty in both graph connectivity and
stochastic forcing to be quantified within a
Bayesian framework.
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Applied Physics
Light-driven Modulation of 1-bit Metamaterial Unit Cells and Arrays
Benjamin A Scott, Kieran J Cowan, Fraser Burton et al. (+2 more)
Shape-morphing materials have the potential to realise simple, tunable telecommunication arrays without the need for complex circuitry. However, existing devices either lack individual
cell control, or require an integrated power supply, reducing their beamsteering ability and increasing size, weight and power consumption. This paper presents a simple, photothermally activated 1-bit reflectarray unit
cell requiring no integrated power sources. The unit
cell consists of dimer elements, which are connected or disconnected via a photothermally activated electrical bridge to achieve modulation. The paper discusses the shape
memory materials used for switching, and presents a design for a photothermal switching mechanism. The unit
cell is validated by waveguide experiments, showing strong agreement with simulations at the working frequency of 3.7GHz. Finally, a 4-
cell array is created. Each
cell is activated sequentially, with good agreement between simulation and experiment, demonstrating the ability to control each
cell exclusively. This study therefore demonstrates that a 1-bit unit
cell can be photothermally configured without complicated electronics or an integrated power supply, opening the door to a new class of shape-morphing reflectarray.
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All authors Benjamin A Scott, Kieran J Cowan, Fraser Burton, Ken E Evans, Alexander W Powell
Atmospheric and Oceanic Physics
Mathematical Exploration of Wave Motion due to Earth-Space Force (Ground Action) Consequences
Monday Sunday Adiaha and Oladiran Johnson Abimbola
This study mathematically explores wave motion induced by earth-space forces specifically ground actions. Developing and solving governing differential equations provides insights into intricate propagation dynamics caused by these forces. Numerical simulation modeled wave behavior and results were analyzed to understand ground action impacts. Initial wave generation and subsequent propagation were simulated using COMSOL Multiphysics which models wave dynamics in physical media. Partial differential equations describing wave motion alongside
Fourier transform techniques were applied to analyze the frequency components. Mathematical derivations yielded wave equations while COMSOL's built-in statistical analysis tool analyzed results. Data visualization employed plotting tools within the software to create detailed graphs. The wave amplitude relative to distance km varied at 0.001 at 0 km and 0.001 at 10 km over 10 km. Amplitudes were recorded at intervals 0.05 0.1 0.15 0.2 0.25 1.05 1.1 1.15 1.2 and 1.25 s. The impact of varying amplitude and frequency on the behavior ranges from 1 s at 0.1 amplitude in Case 1 (0.2, 200) to 1 s at 0.2 amplitude in Case 3 (0.2, 300). Outputs indicate: (1) initial energy input significantly influences the propagation characteristics aiding seismic prediction and mitigation design; (2) propagation details underscore the medium properties' importance in shaping behavior vital for earthquake engineering and accurate ground-motion prediction; (3) sensitivity to amplitude and frequency suggests tailoring parameters can optimize wave-based geophysical surveys and environmental monitoring. This study serves as a policy guide for understanding wave dynamics to inform building codes and disaster preparedness strategies for mitigating seismic impacts.
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Fluid Dynamics
Role of flame localization in wavemaker regions on the suppression of combustion instability in turbulent partially-premixed methane flames
Abhishek Kushwaha, Bjarne Lieth and Isaac Boxx
The interaction between flame dynamics & hydrodynamic instabilities plays a fundamental role in determining the stability of swirl-stabilized combustors. In the present study, we investigate the hypothesis that spatial overlap between flame & wavemaker region is a necessary prerequisite for combustion stability in flows characterized by a wavemaker region. To test the hypothesis, a low-momentum secondary methane injection was introduced through circumferential holes located on the centerbody of a swirl-stabilized burner. The injection velocity was maintained below 5% of bulk flow velocity to minimize momentum-induced modifications of flow field while selectively redistributing heat release. In addition, an equivalent amount of fuel was diverted from primary fuel supply to secondary injection ports, known as fuel-staging, to isolate the effects of flame relocation from those of the total fuel flow rate. The introduction of secondary injection produced a transition of the flame from M-shaped to V-shaped structure, while fuel-staging yielded a similar flame response, demonstrating that observed behavior results primarily from redistribution of heat release. Linear stability analysis revealed that wavemaker region remains near inlet of the combustion chamber. Moreover, flame root transitions from a lifted M-flame to attached V-flame and consistently stabilizes at radial position corresponding to the identified wavemaker region. The coincidence of flame attachment & wavemaker location under stable operating conditions provides strong experimental evidence that flame stabilization is governed by their spatial overlap rather than by a modification of the underlying hydrodynamic instability. The proposed framework provides new insight into the coupling between flame stabilization & hydrodynamic instability & offers practical guidance for the design of stable, low-emission combustion systems.
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Optics
Driving Spintronic Terahertz Emitters at GHz Repetition Rates
Thomas A. Gething, Henry De Libero, Morgan T. Hibberd et al. (+3 more)
Spintronic terahertz emitters (STEs) are versatile sources of terahertz (THz) frequency radiation that offer high electric field strengths and gap-free bandwidths covering the THz (0.1-30 THz) band. In addition, they are low-cost to produce and easy to use in a variety of optical setups. However, an obstacle to their wider applicability is the recently reported decrease in optical fluence damage threshold when driven with high-repetition-rate
lasers. Here, we use an asynchronous optical sampling (ASOPS) THz time-domain spectrometer (THz-TDS) to observe the degradation of the THz signal in real-time when driven by a 1 GHz repetition-rate
laser. We demonstrate that the loss of THz emission is permanent and is likely the result of thermal damage to the STE structure. However, by utilizing substrates with high thermal conductivities, an increase of the damage threshold of over three orders of magnitude is observed enabling stable emission from a STE for the first time when driven by a high-repetition-rate
laser.
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All authors Thomas A. Gething, Henry De Libero, Morgan T. Hibberd, Thomas Thomson, Paul W. Nutter, Darren M. Graham
Fluid Dynamics
A macroscopic-shadow-corrected lattice Boltzmann method for fast, time-accurate simulation of low-Reynolds-number transient flows
Yanhui Ding, Yaolong Yu, Yuan Yu et al. (+1 more)
Explicit
lattice Boltzmann simulations of slow transient flows are constrained by the acoustic time step. Dual-time stepping can remove this restriction, but slow inner convergence has limited reported wall-clock gains to roughly four- to tenfold, without a mechanism that strengthens under refinement. We present the macroscopic-shadow-corrected
lattice Boltzmann method (MSC-LBM), which applies defect correction to the unsplit kinetic residual. At each
Fourier wavenumber, a Stokes-like system is solved exactly for the conserved residual moments while preserving the second-order backward-differentiation formula (BDF2) fixed point and temporal accuracy. Along the two-relaxation-time axis $\Lambda=1/4$, $\omega^+=\omega^-=1$ makes one collision eliminate all non-hydrodynamic perturbations; $\eta(\nu)=|6\nu-1|/(6\nu+1)$ vanishes at $\nu=1/6$, leaving hydrodynamic slow modes whose long-wave shadow is inverted by the corrector. In completed timing campaigns, MSC-LBM achieves 27.95- and 52.71-fold wall-clock speedups at $N=256$, $\mathrm{Re}=1$ under matched-accuracy and $1\%$ gates. The matched speedup rises monotonically to 122.02 at $N=1024$, with gains persisting across $\mathrm{Re}=10^{-4}$–$100$. The three-dimensional D3Q19 extension reaches 27.85 and 8.84 under the same gates at $N=128$, $\mathrm{Re}=1$. A bounce-back-consistent kinetic coarse solver with adaptive relinearisation extends MSC-LBM to fully enclosed cavities, yielding setup-excluding physical-march speedups of 26.86 at $\mathrm{Re}=10$ and 3.84 at $\mathrm{Re}=100$ for $N=128$. An exact per-wavenumber symbol inverse establishes the attainable off-design contraction envelope. The contraction, parameter-sweep, and timing results jointly delimit the demonstrated operating regime: low-to-moderate-Reynolds-number transients for which acoustic stepping need not dictate computational cost.
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All authors Yanhui Ding, Yaolong Yu, Yuan Yu, Hao Zhang
Chemical Physics · Cross-listed from quant-ph
From Wavefunction Regularity to Eigenvector Conditioning: Accuracy–Cost Trade-offs of Quantum Algorithms for Non-Hermitian Transcorrelated Hamiltonians
Cheng-Lin Hong, Emiel Koridon, Paul K. Faehrmann et al. (+3 more)
The electron–electron Coulomb singularity forces cusp structure in electronic wavefunctions. This cusp structure limits wavefunction regularity and slows the convergence of expansions in smooth bases, requiring large basis sets to reach a target accuracy. The transcorrelated (TC) method incorporates this short-range behavior into the
Hamiltonian, thereby improving the regularity of the transformed wavefunction and accelerating convergence toward the complete-basis-set limit. The resulting
Hamiltonian is non-Hermitian and non-normal, which limits the direct applicability of standard
quantum algorithms. For such non-normal operators, the complexity of several recent
quantum algorithms depends explicitly on quantities related to eigenvector conditioning and
eigenvalue sensitivity. Understanding these quantities is essential for assessing both algorithmic complexity and
quantum resource requirements. In this work, we address these issues in two stages. We first study a solvable model, which provides a controlled setting for isolating how transcorrelation affects basis convergence and eigenvector conditioning. Within this setting, we investigate two distinct one-parameter Jastrow correlators. We derive the asymptotic energy-error scaling: $N^{-1/2}$ for the bare projection and $N^{-3/2}$ for both TC correlators at generic fixed parameters, with $N$denoting the basis size. Furthermore, we show that this faster convergence can yield a
polynomial improvement in the asymptotic query-complexity upper bound. We then extend the analysis to second-quantized electronic-structure
Hamiltonians and use particle-number-sector diagnostics to distinguish target-sector from auxiliary-sector conditioning. Our work provides a framework for understanding the central accuracy–cost trade-off in TC
Hamiltonians.
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All authors Cheng-Lin Hong, Emiel Koridon, Paul K. Faehrmann, Thomas D. Kühne, Stefano Polla, Werner Dobrautz
Fluid Dynamics
Two-way actuator-line coupling of a geometrically exact finite-volume beam with incompressible and free-surface flow
Amirhossein Taran, Seevani Bali, Željko Tuković et al. (+2 more)
Slender flexible structures such as mooring lines, aquaculture netting, and aquatic vegetation are too thin to be resolved economically by a body-fitted mesh, yet they exchange momentum with the flow in both directions. This paper presents a finite volume actuator-line formulation for the fluid–structure interaction of such structures, in which a geometrically exact Simo–Reissner beam, discretised by
cell-centred finite volumes, is coupled two-way to an incompressible finite volume flow solver through conservative, parallel-consistent transfer operators. The fluid velocity is sampled upstream of each beam control volume, a quasi-steady Morison-type drag closure evaluates the line force, and the equal and opposite reaction is projected into the fluid momentum equation through a normalised Gaussian kernel that conserves force. The two subsystems share a discretisation, time loop, and domain decomposition, so no external structural code is required, and the OpenFOAM implementation is released publicly. The accuracy of the drag-only closure and the conditions over which it holds are quantified against two channel
benchmarks and a wave-flume experiment, with all drag coefficients fixed in advance. In a steady confined channel flow the tip deflection of a wall-mounted cantilever falls within the range of published continuum solutions. For a flexible leaflet in sinusoidal channel flow the peak tip excursion departs from the reference at the longer forcing period. The leaflet then moves further relative to the surrounding fluid, so added-mass and history forces, which the closure omits, become important. In the wave flume the simulated stem reproduces the measured mode shape, intra-wave asymmetry, and base force, and recovers 71–83% of the oscillation range. A quasi-static reconstruction test places the remaining shortfall in omitted fluid inertia rather than in the structural model.
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All authors Amirhossein Taran, Seevani Bali, Željko Tuković, Vikram Pakrashi, Philip Cardiff
Fluid Dynamics
Coupled Rigid-Body Motion and Binary Phase Change: A Sharp Level-Set/Embedded-Boundary Method
Chao-Fan Zhang, Zhong-Han Xue and Jie Zhang
We develop a sharp-interface method for freely moving solid particles undergoing pure or binary melting. A Level-Set representation preserves the particle geometry during long-distance translation and rotation, while an embedded-boundary formulation imposes hydrodynamic, thermal and solutal conditions sharply on a Eulerian Cartesian mesh.
Liquid temperature and solutal concentration are advanced with a conservative moving-cut-
cell discretization, whereas the solid temperature is transported through a geometry-consistent conservative tracer. Hydrodynamic loads, rigid-body motion and phase change are coupled iteratively within each physical time step. The method is validated progressively for rigid-body motion, prescribed-motion pure and binary melting, and fully coupled melting with free particle motion. It reproduces established reference solutions and captures wake-induced rotation of a melting sphere and the simultaneous translation, rotation and thermosolutal melting of a three-dimensional oblate ellipsoid. As a final application, simulations of a floating ice disc reveal how thermoconvective instability,
geometric confinement and melting jointly determine its spontaneous motion, with phase change feeding back on the instability through the evolving particle geometry. Additional tests establish the importance of long-time geometrical fidelity, local scalar conservation and geometry-consistent solid-temperature transport. The resulting framework provides a sharp and conservative approach for strongly coupled moving-body phase-change problems.
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Chemical Physics
Elasticity of polycrystalline davemaoite constrains its grain size in the lower mantle
Peiyu Zhang, Liang Yuan, Rong Huang et al. (+3 more)
Earth's lower mantle hosts large low shear-velocity provinces (LLSVPs) beneath Africa and the Pacific, but their origin remains debated. Davemaoite, a major lower-mantle mineral, has been proposed as a contributor to these anomalies; however, its experimentally measured shear modulus is approximately 30% lower than first-principles predictions, a longstanding discrepancy between theory and experiment. Here, using million-atom machine-learning molecular dynamics simulations, we show that nanoscale grain-boundary disorder, invisible to conventional x-ray diffraction, can reconcile this gap. Introducing 5.8 vol% disordered regions reduces the shear and bulk moduli by 37% and 12%, respectively. This shear-selective softening can reproduce LLSVP-like seismic anomalies in basalt-rich assemblages, but only at disorder levels corresponding to grain sizes smaller than those expected in the lower mantle. Combining the disorder-elasticity relationship with seismic constraints, we derive a minimum davemaoite grain size of approximately 100 nm. This limit is consistent with mantle grain growth models and with attenuation-based evidence for coarse-grained LLSVPs.
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All authors Peiyu Zhang, Liang Yuan, Rong Huang, Yu Ye, Xiang Wu, Junfeng Zhang
Instrumentation and Detectors
Measurement of the $^{39}$Ar specific activity in atmospheric argon with DArT at the Canfranc Underground Laboratory
P. Agnes, H. O. Back, S. Bharat et al. (+41 more)
We report the measurement of the $^{39}$Ar specific activity of atmospheric argon using DArT, a low-background single-phase
liquid-argon detector read out by cryogenic silicon photomultipliers, at the Canfranc Underground Laboratory (LSC) in Spain. DArT was first filled with atmospheric argon and then with a sample of underground argon of known radioactivity from the DarkSide-50 experiment. The underground argon serves as a background reference in this measurement, making the result robust because we do not rely on background simulations. We measure the $^{39}$Ar specific activity with both a cut-and-count method and a binned maximum-likelihood fit, yielding consistent results. We obtain $a_{\text{AAr}}= 0.955 \pm 0.008~\text{Bq}/\text{kg}$. This result agrees with previous measurements from other experiments and provides the most precise determination of the $^{39}$Ar specific activity in atmospheric argon to date. It also validates DArT as a key component of the DArTInArDM experiment at LSC, which aims to measure the $^{39}$Ar activity of the argon extracted from deep underground wells in Colorado (USA) for the Darkside-20k and LEGEND-1000 experiments at Laboratori Nazionali del Gran Sasso in Italy.
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All authors P. Agnes, H. O. Back, S. Bharat, W. M. Bonivento, M. Boulay, M. Caboni, N. Canci, N. Cargioli, P. Castello, S. Cebrián, L. Consiglio, R. Crampton, D. Diaz Mairena, D. Franco, I. Fuente-Ortega, F. Gabriele, D. Gahan, C. Galbiati, P. Garcia Abia, T. Hessel, S. Horikawa, A. Ianni, G. Korga, M. Kuźniak, L. Luzzi, A. Marasciulli, M. Martínez, P. Organtini, A. Ortiz de Solórzano, R. Pavarani, P. Pegoraro, V. Pesudo Fortes, M. Razeti, O. U. Rehman, L. Romero, D. Sablone, E. Sánchez García, R. Santorelli, C. Seoane, J. Sosiak, S. Sulis, C. Tierney, S. Tullio, G. Vera Díaz
Fluid Dynamics
Rigorous vertical averaging for pseudo-3D modeling of precipitation obstructed fluid flow
David Krach, Felix Weinhardt, Holger Class et al. (+2 more)
Computing effective hydraulic properties of porous materials with a dynamically changing pore morphology presents a complex and critical challenge in both theoretical and applied sciences. This paper presents a tool to effectively compute the intrinsic permeability k(x,t) for domains with both temporally and spatially varying pore structures, by utilizing a sample of snapshots of microfluidic experiments with calcium carbonate precipitation. To compute large domains at reasonable cost, a pseudo-3D Stokes solver with an additional viscous drag term is employed. In order to simulate the intricate domains with highly heterogeneous pore space, we derive vertically averaged governing equations including a vertically averaged drag term from scratch and without limiting assumptions. For exemplary precipitates (semi-spheres) of varying sizes within a rectangular channel with fixed solid boundaries, results are compared across multiple modeling approaches, each employing different drag force formulations. In addition, the performance of the derived models is examined for segments of an EICP experiment in terms of accuracy (comparison with 3D solvers) and computational efficiency. Finally, an entire experimental domain is used to demonstrate the capabilities offered by the solver thanks to its efficiency as well as accuracy and the permeability tensor k is computed and compared with experimental results. In all these applications, the vertically averaged drag term proves to be the optimal solution in terms of speed and accuracy, thus allowing for an efficient analysis of the non-uniformity of local fluid flow fluctuations resulting from alterations in the pore space.
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All authors David Krach, Felix Weinhardt, Holger Class, Holger Steeb, Martin Schneider
Atmospheric and Oceanic Physics
Butterfly Effect Confirmed in Global AI Weather Models: Evidence from Tropical Cyclone Forecasting
Jeremy Cheuk-Hin Leung, Daosheng Xu, Weiye Yu et al. (+9 more)
A paradox recently emerged in artificial intelligence (AI) weather prediction research. While some claim AI weather models cannot simulate atmospheric butterfly effect, this conflicts with AI models' limited predictability and advances in AI ensemble forecasting. This study demonstrates via counterexamples that the butterfly effect does exist in AI weather predictions. For Super Typhoon Khanun, AI predictions are constrained by a double-attractor system. Minor initial perturbations confined to two regions trigger state transitions between two local attractors, causing a 1006-km difference in the predicted storm position on Day 7. This behavior is consistent with numerical weather prediction models and observed in ~12% of tropical cyclones in the past 5 years. These findings verify AI's ability to capture atmospheric chaos and provide the physical basis for AI ensemble forecasting.
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All authors Jeremy Cheuk-Hin Leung, Daosheng Xu, Weiye Yu, Shaojing Zhang, Xiaodong Zeng, Gaozhen Nie, Jie Feng, Jingchen Pu, Yi Li, Kaijun Ren, Qingcun Zeng, Banglin Zhang
Plasma Physics
Phase-Space Non-Integrability of Alpha Particles in Near-Omnigeneous Stellarators
A. L. Lachmann, A. R. Knyazev and E. J. Paul
In a burning
plasma, fusion-born alpha particles sustain the fusion reaction by heating the
plasma core. Alpha-particle confinement in stellarators is sensitive to both deviations from omnigeneity and time-dependent Alfvénic perturbations. Traditional Poincaré maps rely on
symmetry assumptions or dimensionality reductions that fail for stellarators with quasisymmetry (QS) error or multi-harmonic Alfvénic perturbations. To address these challenges, we investigate weighted Birkhoff averaging (WBA) as a diagnostic to detect the onset of chaos in guiding-centre trajectories subject to general
magnetic perturbations. WBA exploits the super-convergence of time averages along quasiperiodic orbits, discriminating regular from chaotic trajectories using any smooth observable rather than an exact invariant of motion. Applying WBA to the canonical momentum $P_\eta$, we show that convergence tracks underlying orbit regularity even when quasisymmetry is imperfect and $P_\eta$ is not strictly conserved. Convergence is measured by the digit accuracy of the weighted average along guiding-centre orbits in fields with imperfect omnigeneity, with and without Alfvén eigenmodes computed using AE3D. We use this diagnostic to map phase-space chaos as a function of
equilibrium invariants to identify transport barriers in unperturbed and perturbed stellarator
equilibria. This work demonstrates that chaos induced by many Alfvén harmonics is often not apparent from the largest harmonic alone. We also find evidence that the onset of chaotic behaviour is sensitive to the local radial profile of the wave and not only to its amplitude at the resonance.
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Fluid Dynamics
Imperfect bifurcations in a laminar 3D bluff body wake: effect of pitch and yaw
Atharva Lagwankar, Alessandro Chiarini, François Gallaire et al. (+1 more)
We study the effect of pitch and yaw on the bifurcations of the laminar flow past an Ahmed body, a bluff body of width-to-height ratio $W/H=1.2$ and length-to-height ratio $L/H=3$. When perfectly aligned with incoming flow, its wake first undergoes pitchfork bifurcations leading to a static vertical or horizontal deflection, and becomes oscillatory via a secondary Hopf bifurcation at larger Reynolds number $Re$. As commonly observed for imperfect pitchfork bifurcations, any small misalignment preselects one of the steady states, referred to as the "primary" branch, at low $Re$. At larger $Re$, a disconnected "secondary" branch is born via a saddle-node bifurcation. Here, we investigate the effect of misalignment using three-dimensional computations. We first focus on pure pitch and pure yaw with linear stability analysis. In both cases, the secondary branch becomes unstable as soon as the incidence exceeds a small value. In the pure yaw case, the primary branch becomes unstable via a horizontal Hopf bifurcation, destabilised by yaw. In the pure pitch case, the primary branch sees the crossover of vertical Hopf and horizontal pitchfork bifurcations, destabilised and stabilised by pitch, respectively. This motivates use of DNS to study this nonlinear competition, already observed for aligned Ahmed bodies in ground proximity. We then study the effect of simultaneous yaw and pitch with a weakly nonlinear analysis. The competition between the two stationary modes gives rise to rich bifurcation diagrams, allowing us to predict the number of stable solutions and phase space trajectories between different states
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All authors Atharva Lagwankar, Alessandro Chiarini, François Gallaire, Edouard Boujo
Geophysics
Iterative separation of coherent blended signals in common shot gathers using synchrosqueezed curvelet-Radon constraints
Zifei Li, Shaohuan Zu and Haojun Chen
Blended data acquired via simultaneous-source seismic exploration conventionally require post-acquisition deblending, which typically relies on the coherence differences introduced by firing time delays (time dithering). To reduce the dependency of the deblending process on these time dithers, a novel joint constraint based on the synchrosqueezed transform and the Radon transform is proposed, operating directly in the common-shot gather (CSG) domain. Specifically, by exploiting the differences in propagation directions of the blended signals within CSGs, the synchrosqueezed transform is first employed for an initial iterative separation to extract individual sources directly from the continuous records. Once the majority of the valid signals are separated, the Radon transform is subsequently applied in further iterations to suppress the residual blending interference, thereby preventing amplitude damage to the effective signals. Compared to conventional non-CSG deblending methods, this approach bypasses the reliance on time-delay coherence differences, thus enabling real-time quality monitoring of individual sources during field acquisition. Furthermore, compared to other existing CSG-based separation techniques, the proposed joint-constraint iterative framework demonstrates superior performance when handling complex data. Applications on both synthetic and field blended
datasets demonstrate that high-fidelity data separation can be successfully achieved independently of the time-dithering constraints. Finally, because the proposed method operates completely independently across different CSG slices, it is highly amenable to parallel computing, facilitating the efficient processing of massive
datasets within a short timeframe.
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Biological Physics · Cross-listed from cond-mat.soft
Fully developed active turbulence defined through a non-equilibrium phase transition
Lasse Bonn, Tianxiang Ma, Olga Bantysh et al. (+7 more)
Non-
equilibrium systems challenge the standard definitions of phases and phase transitions from
equilibrium statistical physics. For example, in active fluids continuous energy injection at the microscale drives the system intrinsically out of
equilibrium. This process gives rise to collective turbulent-like flows whose onset remains poorly defined. Here we show that the onset corresponds to an activity-driven phase transition, marked by the emergence of a system-spanning critical backbone of vorticity nodal lines. Combining two independent experiments, microtubule kinesin active nematics and dense suspensions of swimming bacteria, with large-scale simulations of active nematics and fluctuating nematohydrodynamics, we show that this transition occurs at a critical activity threshold. Below this threshold, vorticity structures are fragmented and
vortex centres form only finite, mechanically floppy networks. Above this threshold, the nodal lines of the vorticity field percolate and the
vortex centres form a rigid, system-spanning cluster. The
geometric transition is characterised by the emergence of critical percolation statistics for the vorticity nodal lines, while the mechanical transition reflects the emergence of a
vortex configuration that shows rigidity percolation statistics for
vortex centres. We show that both transitions are absent in
equilibrium systems that obey detailed balance, demonstrating that the transition is intrinsically non-
equilibrium. These results establish an experimentally accessible definition of fully developed active
turbulence, linking microscopic activity to macroscopic geometry, and mechanics of living systems.
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All authors Lasse Bonn, Tianxiang Ma, Olga Bantysh, Wei Feng, Martin Cramer Pedersen, Guangyin Jing, Jordi Ignés-Mullol, Francesc Sagués, Nuno A. M. Araujo, Amin Doostmohammadi
Atomic Physics
Radiative Data for As III, Se III, Hf IV, and Tl IV: HFR and MCDHF Calculations for Hot Subdwarf Spectroscopy
Jérôme Deprince, Lucas Maison, Solène Beauraind et al. (+3 more)
Accurate oscillator strengths for doubly and triply ionised heavy elements are required for quantitative spectroscopy of hot subdwarfs, but available data remain sparse. We present new radiative data for As III, Se III, Hf IV and Tl IV, calculated with the pseudo-relativistic Hartree-Fock (HFR) method including core-polarization effects and semi-empirical adjustment of radial parameters to experimental energy levels. Independent multiconfiguration Dirac-Hartree-Fock (MCDHF) computations were also performed for As III, Hf IV and Tl IV, while published MCDHF data were adopted for Se III to assess the reliability of the HFR oscillator strengths. The largest discrepancies between the two approaches are mainly associated with weak transitions, strong cancellation effects, or significant gauge disagreement. For strong transitions satisfying the adopted reliability criteria, we found a good agreement between the oscillator strengths obtained by both methods. The new data have already been applied to the spectra of the heavy-metal hot subdwarfs LS IV-14$^\circ$116 and EC 22536-5304, enabling abundance determinations for As, Se, Hf, and Tl and providing additional lines for future spectroscopic studies.
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All authors Jérôme Deprince, Lucas Maison, Solène Beauraind, Hélène Dupuis, Matti Dorsch, Pascal Quinet
Classical Physics
Automated Sailboat Navigation using Controllabilty-Aware Nonlinear Model Predicitive Control under Stochastic Winds
Junzhuo Wu, Ya-Jun J Pan, Chao Shen et al. (+2 more)
This paper presents a systematic approach to plan and execute a time-efficient sailboat trajectory under the challenging
stochastic wind conditions for automated sailboat. Unlike deterministic scenarios,
stochastic wind disturbances introduce challenges such as gust unpredictability, directional shifts, and fluctuating apparent wind speeds. These characteristics render traditional planning methods, such as Line-of-Sight (LoS) and waypoint approaches, to be ineffective and not applicable, as they often rely on static or deterministic environmental models. This paper proposed a new path planner and controller based on nonlinear model predictive control method. It is compared with a baseline planner and controller. A Lie-algebraic analysis of the sailboat dynamics is carried out to identify the operating conditions under which the vessel loses first-order control authority in surge, and these conditions are embedded as constraints in the NMPC. Finally, simulation results are provided to validate the proposed framework.
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All authors Junzhuo Wu, Ya-Jun J Pan, Chao Shen, Sean Smith, Emmanuel Witrant
Optics
Bias-resolved comb-formation regimes in a simple two-section quantum-dot mode-locked laser for isolator-free, terabit-scale O-band interconnects
Ying Shi, William He, Xiangpeng Ou et al. (+4 more)
Practical O-band
quantum-dot (QD) mode-locked comb sources must combine wide flat-top bandwidth, low
radio-frequency (RF) timing noise, error-correctable bare-line modulation, and feedback tolerance, yet these functions are usually optimized separately and their relation to comb-formation dynamics remains unclear. Here we map the gain-current/saturable-absorber-bias plane of a simple two-section InAs/GaAs QD mode-locked
laser to resolve distinct application-specific regimes. A low-injection, high-reverse-bias regime produces 0.80 ps pulses, consistent with amplitude-modulated operation, whereas a high-injection, intermediate-bias regime yields a 16.16 nm (2.75 THz) flat-top comb with 110 lines and a 14.98 ps extended waveform, consistent with a stronger frequency-modulated contribution. To our knowledge, this is the broadest reported 3 dB bandwidth among QD mode-locked comb sources. At a separate low-noise bias, the beatnote exhibits a 0.58 kHz Lorentzian linewidth and a 41.6 fs integrated timing jitter over the 4 to 80 MHz range, to our knowledge the lowest reported for a high-channel-count O-band QD passive comb. In isolator-free 25 Gb/s NRZ transmission, all 94 carriers across a 13.73 nm 3 dB band remain below the 7 percent HD-FEC threshold. Using all 110 carriers at the maximum-bandwidth bias gives a projected aggregate rate of 2.75 Tb/s. At a separate feedback-test bias, broadband mode locking is preserved and, beyond approximately -28 dB feedback, the RF beatnote enters a feedback-stabilized regime whose linewidth is reduced 42-fold. Thus, short-pulse, broadband, low-noise, transmission-ready, and feedback-stabilized operation occupy distinct selectable regions rather than a single universal optimum. This regime-resolved map links QD comb-formation physics to isolator-free, terabit-scale O-band interconnects.
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All authors Ying Shi, William He, Xiangpeng Ou, Defan Sun, Weiping Li, Xin Yao, Yating Wan
Fluid Dynamics · Cross-listed from cs.LG
Physics-Informed Method of Group Data Handling: Adaptive Construction of Functional Representations with an Application to the Navier-Stokes Equations
Mykhailo Minin
Physics-informed computational methods usually optimize parameters within a functional representation whose structure is fixed in advance. This work proposes a Physics-Informed Method of Group Data Handling (PI-GMDH), in which representations of coupled physical fields are progressively constructed during solution. Candidate functional directions are evaluated through the first variation of the complete physical and observational objective, introduced in packages, and followed by block-coordinate damped Gauss-Newton coefficient optimization. The framework is demonstrated with tensor-product Chebyshev functions on the incompressible Navier-Stokes equations using a two-dimensional time-dependent Taylor-Green
benchmark. Under the tested configuration, adaptive PI-GMDH reached validation and held-out test losses of 5.299e-19 and 5.296e-19 with 204, 201, and 175 active functions for u, v, and p. Complete degree-by-degree and all-terms PI-GMDH variants, together with selected PINN and KAN reference configurations, are used to examine the effect of structural construction policy. The results show that, for this controlled synthetic
benchmark, selective progressive construction can provide a favorable combination of accuracy, representation size, and wall-clock time. The comparison is illustrative rather than a claim of universal superiority over alternative physics-informed approaches.
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Applied Physics
Exchange-mediated directional coupling of short-wavelength spin waves
Zhen Zhu, Roman Verba, Philipp Pirro et al. (+2 more)
Miniaturizing magnonic
circuits and increasing their processing speed require
spin waves with progressively shorter wavelengths. However, conventional directional couplers rely on the dynamic dipolar interaction between spatially separated waveguides, which rapidly weakens in the exchange-dominated regime. As a result, their coupling length increases as the
spin-wave wavelength decreases, limiting further device miniaturization. Here, we introduce an exchange-mediated directional coupler by replacing the nonmagnetic gap between two waveguides with a magnetically modified YIG spacer. The spacer provides a continuous exchange pathway and preserves the splitting between the symmetric and antisymmetric modes at large wavenumbers. We develop an analytical model to describe this mechanism and verify it using micromagnetic simulations. Based on this concept, we design a straight coupler without curved access waveguides, with a footprint of only 400 nm * 30 nm. For a
spin-wave wavelength of approximately 100 nm, the device transfers approximately 98% of the normalized output power to the target waveguide. Its performance remains nearly unchanged even when the damping of the spacer is strongly increased. These results overcome the short-wavelength limitation of dipolar couplers and provide a route toward highly integrated magnonic
circuits for information processing.
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All authors Zhen Zhu, Roman Verba, Philipp Pirro, Andrii V. Chumak, Qi Wang