Fluid Dynamics
Assessment of wind energy potential of buildings by CFD simulation in dense urban environments - From Case Studies to a Dendrogram-Based Design Framework
David Serero, Loïc Couton, Jean-Denis Parisse et al. (+1 more)
Building-integrated wind turbines (BIWT) remain under-deployed in dense European urban contexts despite their potential contribution to net-zero energy targets. This paper presents a measurement-validated computational fluid dynamics (CFD) framework to identify optimal locations for micro-wind turbines on the envelopes of dense Parisian Haussmannian blocks. The methodology couples a multi-month on-site anemometry campaign on two case-study buildings, a calibrated steady RANS digital twin using the realisable k-$\epsilon$
turbulence model, and the introduction of an architecturally integrated accelerator wing -termed aerofoil -placed at the envelope edge to amplify and stabilise the local flow. Quantitative validation against year-long anemometer records yields a mean absolute percentage error (MAPE) of approximately 18 % and a hit-rate FAC2 above 0.85, meeting the COST 732 acceptance criteria for urban CFD models. On the École Nationale Supérieure d'Architecture Paris-Val-de-Seine (ENSAPVS) case study, the inter-tower configuration produces a directional speed-up factor of 3.4 (95 % CI 3.18-3.62) for the prevailing north-westerly sector at +70 m above ground; the addition of the aerofoil yields a further +13 % local speed-up, equivalent to +44 % in extractable power. A capacity-factor analysis based on the measured Weibull distribution and the Savonius rotor power curve estimates an annual yield of approximately 69 MWh, offsetting around 6 % of the building's annual electricity consumption -a substantially lower but more realistic figure than the cube-of-mean estimate. The findings are synthesised in a decision dendrogram that maps wind-rose typology, building plan, height and implantation onto recommended device families, providing architects and engineers with a transferable design-stage tool.
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All authors David Serero, Loïc Couton, Jean-Denis Parisse, Robert Le Roy
Fluid Dynamics
Deep Koopman Sensing
Nithin Somasekharan, Yadi Cao and Shaowu Pan
Real-time reconstruction of fluid flows from sparse sensor measurements is important for both physical understanding and flow control. When first-principles models are too expensive for online data assimilation (DA), learned reduced-order models provide an efficient alternative, but are commonly optimized for forward prediction rather than state estimation. We propose Deep Koopman Sensing, a data-driven reduced-order DA framework that combines a nonlinear autoencoder with parameter-conditioned linear latent dynamics approximating the Koopman operator. We compare the proposed model with parametric dynamic mode decomposition (pDMD), a multilayer perceptron (MLP), and xLSTM across four
benchmarks: 1D viscous Burgers, 2D flow past a cylinder, 2D dambreak, and 3D flow past a sphere. Our results reveal a marked distinction between forecasting and sensing: open-loop accuracy does not reliably predict assimilation performance, while Deep Koopman Sensing achieves the lowest assimilation error across all four
benchmarks. More importantly, with an extended Kalman filter, incorporating sensor measurements improves the estimates of both linear latent models across all four
benchmarks, whereas it degrades the nonlinear models, despite their strong open-loop performance. With ensemble filtering, the nonlinear models are no longer degraded by assimilation, while the Koopman model still attains the lowest assimilation error. These results show that latent dynamics should be designed for the downstream estimation task rather than selected solely for forecast accuracy, and demonstrate Koopman-based reduced-order modeling as an effective approach for real-time flow reconstruction from sparse, streaming measurements.
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Optics
Tailoring complex coupling for efficient synchronization of semiconductor lasers
Nathan Vigne, Amit Pando, Li-Li Ye et al. (+6 more)
A grand challenge for
laser synchronization is the intrinsic frequency disorder. We build an experimental platform for programming the complex coupling coefficients of
semiconductor lasers to promote frequency and phase locking. The coupling amplitude between every pair of
lasers in an array is tuned to scale with their frequency difference. Coupling phases are scanned to meet the phase matching conditions for constructive interference of coupled fields. The minimum coupling budget for global synchronization is significantly reduced, as shown experimentally for three vertical-cavity surface-emitting
lasers with intrinsic frequency detuning. The customized coupling offers an efficient approach to stable synchronization of
semiconductor laser arrays for coherent beam combining.
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All authors Nathan Vigne, Amit Pando, Li-Li Ye, Mehmet Bütün, KyeoReh Lee, Ying-Cheng Lai, Nir Davidson, Fan-Yi Lin, Hui Cao
Optics · Cross-listed from cond-mat.mtrl-sci
Twin Domains in Van der Waals Quaternary Oxides
Dorothée S. Mader, Niels Brumby, Xiaosheng Yang et al. (+10 more)
Optical anisotropy is the basis for many intriguing phenomena in van der Waals materials, including
hyperbolic polaritons and extreme birefringence. Stacking and twisting van der Waals materials along the out-of-plane direction emerged as a powerful route to tailor this anisotropy, but designing lateral interfaces remains a challenge. Here, twin domains are reported in the van der Waals quaternary oxides MgTeMoO$_6$, MnTeMoO$_6$, ZnTeMoO$_6$, and CoTeMoO$_6$ - materials that possess strong in-plane optical anisotropy and second-order nonlinearity. The domains naturally form in their orthorhombic
crystal structure and extend over hundreds of micrometers. It is proposed that this stability is achieved by the domain wall acting as a diagonal mirror plane in the
crystal structure, parallel to the (1-10) or (110)
crystal planes, resulting in nearly opposite birefringence between domains. This hypothesis is experimentally confirmed by determining the angle between the
crystal axes of neighboring domains using polarization-resolved optical microscopy, infrared-visible sum-frequency generation microscopy, and transmission electron microscopy. The latter further allowed an estimate of the domain wall thickness. Overall, the observation of twin domains with orthogonal optical anisotropy opens new routes to use van der Waals quaternary oxides for birefringent waveguiding, polariton steering, and frequency conversion applications.
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All authors Dorothée S. Mader, Niels Brumby, Xiaosheng Yang, Nele Stetzuhn, Eduardo Ortega, Christian Carbogno, Katayoun Gharagozloo-Hubmann, Sebastian F. Maehrlein, Martin Wolf, Kirill Bolotin, Peining Li, Niclas S. Mueller, Alexander Paarmann
Optics
Setup and performance of focal-plane characterization benches for high precision astrometry
Fabrice Pancher, Sebastien Soler, Fabien Malbet et al. (+7 more)
Detecting Earth-like
exoplanets requires micro-arcsecond astrometry, which relies on a precisely calibrated focal plane equipped with high-resolution detectors. Accurate calibration depends on characterizing detector imperfections and systematic effects. Optical benches have been developed to assess the sensor's behavior: an integrating-sphere setup for electro-optical parameters, an interferometric bench for pixel-level geometry, and a
star-field projection system for intrinsic distortion. This work presents the characterization benches built for a 46-Megapixels (MP) imaging sensor, based on the same technology as the four 220-MP detectors foreseen for the final focal-plane, and the performance metrics obtained from these setups in the context of NASA's HWO and ESA's M-class missions. Upgrades will bring the test environment closer to operational conditions: a second 46-MP sensor will be added for multi-detector tests, plus an adjustable-angle fringeprojection system and improved
alignment.
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All authors Fabrice Pancher, Sebastien Soler, Fabien Malbet, Hugo Rousset, Manon Lizzana, Alain Leger, Thierry Lépine, Florence Ardellier-Desages, Jerôme Amiaux, Pierre-Olivier Lagage
Optics
Extracting dipole orientations from asymmetric plasmonic nanostructures towards machine-learning-assisted spectropolarimetry
P. Christian Simo, Michaela Zbytovska, Annika Mildner et al. (+4 more)
In this work, nanoparticles with various asymmetries are analyzed for their azimuthal orientations using polarimetric dark-field spectroscopy at different analyzing angles of a linear polarizer. This approach reveals their spectral behavior in terms of electric far-field dipole intensities when modeled with an analytical dipole model. By simultaneously fitting the spectra from a set of analyzer angles, the respective dipole orientations are extracted. In a statistical approach, all non-repeating permutations are further studied with a machine learning
algorithm. The resulting azimuthal distribution of dipole orientations coincides well with the
geometric orientations derived from simulations and electron microscope images. A histogram gradient boosting regressor evaluates the impact of the measurement setup on the simultaneously fitted sets, linking the weights of the analyzer angles to the asymmetry in the plasmonic systems. This comprehensive spectroscopic method improves the accuracy of dipole orientation measurements and enables modern machine learning models to interpret potentially complex features of nanostructures.
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All authors P. Christian Simo, Michaela Zbytovska, Annika Mildner, Lukas Lang, Melanie Sommer, Dieter P. Kern, Monika Fleischer
Atomic Physics
Interactions and excitation blockade of Rydberg macrodimers
Dhiya Varghese, Rejish Nath, Simon Hollerith et al. (+1 more)
We present a theoretical study of interactions between Rydberg macrodimers, molecular bound states of Rydberg atoms, and the largest known neutral homonuclear diatomic molecules. Accounting for the large number of molecular interaction channels from four interacting Rydberg atoms, we show that macrodimer-macrodimer interactions are anisotropic and similar in strength and range to atomic-state Rydberg interactions. Our analysis reveals the presence of two-atom, three-atom, and four-atom contributions in the bimolecular system, and elucidates how these interactions are rooted in the underlying atomic Rydberg-state couplings. Our calculations of the excitation blockade between macrodimers are in reasonable agreement with experimentally observed signals, and pave the way for the exploration of optically controlled collective
quantum dynamics in molecular systems.
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All authors Dhiya Varghese, Rejish Nath, Simon Hollerith, Valentin Walther
Fluid Dynamics
Fluctuation-dissipation relations in isotropic turbulence from Kraichnan's fully resolved DIA closure
Elias Kohler and Matthias Fuchs
Kraichnan's Direct Interaction Approximation (DIA) provides a classical closure framework for homogeneous
turbulence, yet its quantitative predictions across all scales remain incompletely understood. We present a fully resolved numerical solution of the forced DIA equations without additional modelling assumptions, enabling a consistent analysis of stationary spectral properties and temporal dynamics across all wavenumbers. The main focus is on the fluctuation-dissipation relation between the normalised velocity correlation function and the Green function of linear response. This relation holds only at large scales and is systematically violated in the inertial and dissipation ranges. The non-Gaussian nature of this violation is encoded in the DIA through its non-Markovian equations, even though the DIA can be derived using a Gaussian mean-field approximation in the
stochastic field functional. In the inertial range, characteristic decay times agree quantitatively with those obtained from direct numerical simulations, while deviations arise in the dissipation range. These results highlight the ability of the DIA to capture temporal dynamics despite its limitations in predicting spectral scaling.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Beyond binary at submicron dimensions: crossed-ellipse MTJ free layers as multi-state cells for spintronic crossbars
Arup Ghosh, Ariel Zaig, Colin Ducarme et al. (+3 more)
Spintronic crossbars are promising hardware platforms for energy-efficient neuromorphic computing, but conventional
magnetic tunnel junctions (MTJs) are binary, limiting the information density and synaptic precision of each crosspoint. Here, MuMax3 micromagnetic simulations are used to investigate how size and aspect ratio control the switching and remanent-state landscape of crossed-ellipse MTJ free layers, with permalloy as the main model system and CoFeB checks for transferability. At fixed 8:1 aspect ratio, shrinking the device from 16 micron x 2 micron to 80 nm x 10 nm lowers the absolute switching current but raises the switching field from about 11 Oe to about 301 Oe and increases the SOT current density. At fixed major axis 1.6 micron, aspect-ratio tuning produces a low-field four-state regime, while lower aspect ratios stabilize additional remanent states with lower switching fields and current densities. A 1.6 micron x 0.8 micron device exhibits twelve accessible remanent plateaus in its angle-resolved planar Hall response, with the resolved state count depending on both aspect ratio and absolute size. Projected MTJ readout gives multiple electrical levels, while minimum-energy-path calculations show that the twelve configurations are not all thermally independent. Independent MuMax+ calculations reproduce the multistate
topology and reveal lower-barrier multistep escape pathways between nominally distant states. These results define a geometry-dependent design window for scalable multistate spintronic crossbar
cells.
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All authors Arup Ghosh, Ariel Zaig, Colin Ducarme, Thomas Coppée, Flavio Abreu Araujo, Lior Klein
Geophysics
Three dimensional non-singular mollified elastic dislocation theory for extended width fault zones and inhomogeneous boundary element models
Brendan Meade
Classical elastic dislocation theory (CEDT) has two challenges when applied to faulting problems: 1) fictitious on-fault stresses not defined by ordinary integration and 2) the
geometric unreality of infinitely thin fault zones. We show that both can be resolved by a mollified elastic dislocation theory (MEDT) built on Cortez blob (Cortez, 2001) mollified displacement discontinuity Green's functions, which represent deformation across spatially distributed fault zones of finite scale epsilon and produce singularity-free displacements and stresses everywhere. Analytical integration of the mollified source solution over arbitrary planar triangular elements is done with AI, and the resulting closed-form solutions allow for the calculation of non-singular stresses across geometrically complex fault systems. Further, we demonstrate the decoupling of the fault-zone width scale epsilon from the mesh length scale h, the elasticity analog of a result established for regularized viscous flow Stokeslets (Ferranti and Cortez, 2024). We use these mollified kernels to demonstrate numerically stable collocation boundary element models including spatially extended fault zones, material property variations and non-planar topography.
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Optics · Cross-listed from quant-ph
Bell-inequality violation in light transmitted through disordered emitter ensembles
Ruolin Guan, Vineesha Srivastava, Kasper J. Kusmierek et al. (+2 more)
We show that light transmitted through a disordered ensemble of weakly coupled two-level emitters can violate a Bell inequality in a continuous-wave Franson-type measurement. The Bell signal is determined by two steady-state output-field correlations, the equal-time intensity correlation $g^{(2)}(0)$ and the phase-sensitive two-
photon coherence $R$. We compute these quantities for bidirectional propagation through disordered emitter ensembles using a fourth-order cumulant expansion of the many-body master equation. The resulting Bell inequality violation appears in two distinct regimes, an antibunched regime where equal-time coincidences are suppressed and a bunched regime where
photon pairs remain phase coherent. Extrapolating the numerics to a representative weak single-emitter coupling $\beta=0.01$ predicts violation in the antibunched regime for atom numbers $N\simeq75$-$220$, and in the bunched regime for $N\gtrsim250$.
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All authors Ruolin Guan, Vineesha Srivastava, Kasper J. Kusmierek, Ivan Vybornyi, Klemens Hammerer
Classical Physics
Increase of the electromechanical coupling of piezoelectric vibration harvesters through lateral bars
David Gibus, Grégoire Forges, Hélène Debéda et al. (+2 more)
To enhance the performance of vibration energy harvesters, it is essential to maximise the electromechanical coupling coefficient k${}^2$ of piezoelectric devices. This enables sufficient harvested power and tuning capability of the resonant frequency through electrical methods. While much literature treats the optimisation of piezoelectric cantilevers, the optimisation range is usually limited by the transverse coupling coefficient k31${}^2$ of the material. This work introduces an innovative solution to extend the optimisation range and increase the coupling coefficient of piezoelectric cantilevers. This is achieved by minimising lateral strain in the beam using lateral bars to maximise the equivalent material coupling coefficient. The theoretical basis of this innovation is demonstrated through the exploitation of the constitutive equations of piezoelectric materials. The interest of the addition of lateral bars to increase the coupling coefficient is demonstrated and studied with simulations based on the finite elements method. Finally, a proof of concept is realised using a aluminum cantilever prototype integrating a lead-free KNaNbO3 (KNN) piezoelectric material. It is tested under vibration at 0.1 m/s${}^2$ with variable resistive loads. The results show that the coupling coefficient increases by 30% and the relative frequency bandwidth by 32% with resistive tuning of the resonant frequency, by fixing eight steel bars to the cantilever. The designed prototype is a highly performant leadfree vibration energy harvester. It produces a maximum power of 49.9 $\mu$W at resonance, and its normalised power density is equal to 16.5 mW/G${}^2$/cm${}^3$. Its relative frequency bandwidth is equal to 3.1%.
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All authors David Gibus, Grégoire Forges, Hélène Debéda, Pierre Gasnier, Adrien Badel
Classical Physics
Sliding contact fraction in gravity-driven dense cohesionless granular flows
Patrick Richard, Riccardo Artoni, Clovis Lambert et al. (+2 more)
Using large-scale, three-dimensional discrete element simulations, we investigate the kinematic properties of granular chute flows of cohesionless grains, together with the
evolution of the coordination number and the fraction of sliding contacts. Our results reveal that, under certain conditions, increasing the grain–grain friction coefficient leads to a decrease in the global dissipation of the system. This finding highlights that the overall dissipation is not solely governed by the energy lost during sliding contacts, but also by the probability that such contacts occur, a probability that decreases markedly as the friction coefficient increases. Together, these effects demonstrate the subtle and nontrivial interplay between grain-scale frictional interactions and macroscopic flow behavior in dense and cohesionless granular materials.
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All authors Patrick Richard, Riccardo Artoni, Clovis Lambert, Raphaël Maurin, Pascal Fede
Physics and Society
The life and death of football team runs: survival of collective modes shapes Lévy-like transport
Guillermo Herrera Sánchez, Daniel Gradeci, Daniele Ramsay et al. (+1 more)
Broad run-length distributions and short-lag superdiffusion have recently been reported in football players and team centroids, prompting a collective-foraging interpretation. The mechanism linking these player- and team-level signatures remains unclear. Using SoccerMon GPS data from 66 tracked team-match records across 62 fixtures in the Norwegian women's top-flight Toppserien, we asked whether player transport is inherited from a translating team mode and what controls the lifetime of that mode. We decomposed player displacement into centroid translation and motion within the formation, then modelled the switching and termination of directional centroid runs. At longer lags, centroid translation carried an increasing share of player displacement. Run lifetimes were broad but finite: termination was highest near onset, declined with age and rose modestly later. After accounting for speed and directional persistence, collective order added only limited predictive information. At the population level, an age-dependent switching-and-termination model predicted, on held-out match dates, the early enrichment and later depletion of high-order states among surviving runs. These results link player- and team-level Lévy-like movement through a finite-lived collective mode whose age and internal state shape its survival. Long displacements need not be selected in advance; they can emerge when transient collective modes persist, reorganise and selectively survive. More broadly, trajectory statistics may record which dynamical histories survive, not only the rules by which
agents move.
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All authors Guillermo Herrera Sánchez, Daniel Gradeci, Daniele Ramsay, Safe Khan
Optics
Automatic control of gold nanoparticle clustering in plasmonic nanopores based on Raman spectroscopic feedback
Iuliia Sheinman, Yingqi Zhao, Zhendai Huang et al. (+5 more)
Plasmonic nanopores have been used to trap single nanoparticles using electric bias for single-molecule surface enhanced Raman spectroscopic (SM-SERS) detection and sequencing. While they exhibit high sensitivity, removal of nanoparticle clusters in the nanopore is so labor intensive that it hampers biosensing applications. Here, our approach is to use a microcontroller to change the electric voltage to remove the nanoparticle clusters in the nanopore with feedback by the Raman spectra. The SM-SERS spectra of the molecules adsorbed on nanoparticle surface can be acquired over a sufficiently long period, so that the microcontroller can analyze them with <100 ms and trigger the voltage change to remove the nanoparticle cluster. Our system is promising for automatic and high-throughput SM-SERS detection and analysis of DNA and
proteins.
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All authors Iuliia Sheinman, Yingqi Zhao, Zhendai Huang, Kuo Zhan, Zuyan Chen, Ilkka Nissinen, Shuai Li, Jianan Huang
Data Analysis and Statistics · Cross-listed from cond-mat.stat-mech
Sharp Bounds on the Mean Efficiency of a Fluctuating Machine
Badr Farih
The efficiency of a machine at the scale of thermal fluctuations is random, and the conventional ratio $-W/Q_h$ has no moment of any order: its input heat fluctuates through zero. We work instead with the exergetic ratio $\eta=W/(W+T_0S)$, which lies in $[0,1]$ pointwise for non-negative dissipation, and ask what the energy budget alone determines about its mean. With $\alpha=T_0\langle S\rangle/W$ and $\sigma^2$ the relative variance of the dissipation, $1/(1+\alpha)<\langle\eta\rangle\le\sigma^2/(1+\sigma^2)+1/\{(1+\sigma^2)[1+\alpha(1+\sigma^2)]\}$, both ends sharp, with no distributional assumption. The floor is Jensen's inequality: fluctuating dissipation raises the mean efficiency above its deterministic value, and the mean alone gives nothing more. The ceiling is attained by an intermittently reversible law, dissipating nothing in a fraction $\sigma^2/(1+\sigma^2)$ of realisations, a prediction testable on trajectories. A third moment lifts the floor. Fixed delivered work is not required: when it too fluctuates, the bounds hold with the moments taken on $T_0S/W$, and the thermodynamic uncertainty relation on the work current converts the ceiling into a precision-efficiency frontier, whose zero-variance member is the known bound on a motor's ratio-of-means efficiency, shown here to be unsafe for the mean of the fluctuating ratio. Inside the interval lies the maximum-
entropy benchmark $\alpha^{-1}e^{1/\alpha}E_1(1/\alpha)$. Finally the bounds are worked out for a motor with futile cycles, observed until a fixed number of steps is delivered. There the dissipation cannot fall below the reversible cost of that work, and this floor $b$ sharpens the ceiling to $q/(1+\alpha b)+(1-q)/(1+\alpha c)$, $q=\sigma^2/[\sigma^2+(1-b)^2]$, $c=1+\sigma^2/(1-b)$, removing 40-67 per cent of the width. It is saturated when slips are rare: the extremal law is an operating regime, not an idealisation.
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Data Analysis and Statistics
Online local learning for generative thermodynamic computing
Huilin Wang and Weibing Deng
Generative thermodynamic computers turn thermal noise into structured data through Langevin dynamics. We train these systems with a local update at each integration step. The reverse-path Onsager-Machlup objective yields a coupling gradient that is a symmetric sum of local residual-state correlations. We apply this gradient immediately rather than accumulating it over a full trajectory. In digital simulations using MNIST prototypes, online and trajectory-batch training reach similar validation losses on fixed noising paths. Models trained online release less heat on average in all five independently seeded pairs, with both models' parameters held fixed during sampling. Auxiliary classifier and nearest-prototype measures change modestly, while pairwise diversity decreases. The response to noise depends strongly on where the errors enter: independent zero-mean errors in the formed updates produce little heat change over a finite range of noise amplitudes, whereas residual offset and temporal correlation have much larger effects. Storing trained couplings requires substantially less precision than resolving deterministic updates during training. Together, these results establish a local online training method and show how update timing, noise structure, and precision affect generative thermodynamic computing.
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Computational Physics · Cross-listed from cs.LG
Single-condition neural solvers encode transferable response spaces for parametric differential equations
Wenbo Cao and Weiwei Zhang
Operator learning for parametric partial differential equations (PDEs) typically builds global models over prescribed domains, requiring cross-condition data or costly physics-constrained training. Here we show that the output Jacobian of a neural solution model trained at one condition defines a reusable response space for cross-condition solution variations. We introduce Linearized Subspace Transfer (LST) to exploit this space and recover target solutions by minimizing the target PDE-system residual over response-space coordinates. Because any single response space has finite coverage, Active Transfer Modeling (ATM) uses post-transfer residuals as coverage indicators to selectively acquire response spaces from additional single-condition models. Across six systems, single-condition response spaces supported cross-condition transfer, with enrichment improving accuracy when added spaces expanded representation capacity. Relative to evaluated physics-informed operator baselines, ATM reduced error and offline construction cost, with orders-of-magnitude accuracy gains in representative cases and millisecond-to-second target adaptation. These results establish neural solvers as reusable local parametric models.
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Atomic Physics
Second-order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core-valence Correlations
G. Gaigalas, P. Rynkun and L. Kitovienė
The General Relativistic Atomic Structure package [Grasp2018, C. Froese Fischer, G. Gaigalas, P. Jönsson, J. Bieroń, Comput. Phys. Commun. (2019), DOI: 10.1016/j.cpc.2018.10.032], is based on multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction (RCI) methods for energy structure calculations. Atomic state function used in the program is built from the set of configuration state functions (CSFs). The valence-valence, core-valence and core-core correlations are explicitly included through expansions over CSFs in RCI. We present a combination of RCI and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in irreducible tensorial form to account for electron core-valence correlations when an atom or ion has any number of valence electrons. This newly developed method, which offers two ways of use, allows a significant reduction of the CSF space for complex atoms and ions. We also demonstrate how the method and program works for energy structure calculation of Cl III element.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Effect of Near-surface Thermal Spikes on Radiation Hardness of Gallium Oxide
Tomás Fernández Bouvier, Umutcan Bektas, Alexander Azarov et al. (+10 more)
Gallium oxide (Ga$_{2}$O$_{3}$) stands out as an extraordinary high radiation-tolerant
semiconductor, because its
lattice displacements induce polymorph transitions, holding material crystalline instead of leading to amorphization. Meanwhile, under extremely severe irradiation conditions many
crystals become amorphous, often starting from surfaces where the translation
symmetry breaks. Here, we show that the surface amorphization may prevail over the crystallisation in Ga$_{2}$O$_{3}$, however only if the mass and energy of irradiated ions produce sufficiently dense heat spikes in the immediate vicinity of the free surface. Applying machine-learned molecular dynamics simulations together with experimental broad-beam and focused ion-beam irradiations, we conclude that the presence of the free surface enables asymmetric displacements of Ga and O atoms, leading to a local non-stoichiometry. Consequently, when the affected cascade volume is sufficiently large, this compositional imbalance suppresses recrystallization and promotes amorphization. As such, our results are ready to use for tailoring irradiation conditions to either prevent or induce surface amorphization, depending on the requirements of the intended applications in Ga$_{2}$O$_{3}$ or other compound
semiconductors.
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All authors Tomás Fernández Bouvier, Umutcan Bektas, Alexander Azarov, Ru He, Nico Klingner, René Hübner, Paul Chekhonin, Aleksi Leino, Kai Nordlund, Javier García Fernández, Andrej Kuznetsov, Gregor Hlawacek, Flyura Djurabekova
Computational Physics · Cross-listed from cond-mat.stat-mech
Shannon Entropy as an Order Parameter for the Two-Dimensional Confined Coulomb Systems: Exact Balance Law, Topological Charge Sum Rule, and Boundary Saturation
Georgiy K. Lavrov and Eduard G. Nikonov
We establish a complete information-theoretic framework for the known minimum-energy configurations of the two-dimensional Thomson problem on a hard-wall disk, based on the Shannon
entropy of the Voronoi topological charge distribution. Two exact results are proven and hold for all studied systems of size $N=12$-$10^5$. First, an
entropy balance law decomposes the total
entropy into bulk, boundary, and mixing contributions without approximation. Second, a topological charge sum rule fixes the total charge at twice the number of boundary particles plus six; together with the observed separation of bulk and boundary coordination numbers, it yields exact relations between the populations of three- and four-coordinated boundary particles and the bulk charge. We further prove that the boundary
entropy is bounded by the binary maximum and that saturation of this bound is equivalent to the bulk charge per boundary particle approaching minus one half, a regime that the framework itself restricts to boundaries of at least twelve particles. All identities are verified numerically to machine precision, locating bulk nucleation at $56$ particles, the maximum of global disorder at $146$, and the onset of boundary saturation beyond about $1000$. The framework carries over to closed spherical geometry, where the total charge is fixed at twelve.
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Optics
A nonlinear hydrodynamic theory of ultrafast laser self-organization
Jean-Philippe Colombier, Emeric Gandon, Quentin Fornasiero et al. (+1 more)
Ultrashort
laser pulses can induce order out of chaos. A femtosecond pulse melts a metal surface for about a hundred picoseconds; under photoexcitation with no net polarization axis, the resolidifying film nonetheless organizes into regular nanoscale patterns. Here we derive from first principles the nonlinear hydrodynamics responsible for it and show it accounts for the full phase diagram of morphologies from measurable
laser and material parameters. Starting from the Navier-Stokes equations in the lubrication limit, the molten film obeys a damped Kuramoto-Sivashinsky equation that reduces to a Swift-Hohenberg formalism near threshold, with every coefficient fixed by the
laser fluence, melt thickness, optical skin depth, and thermocapillary response. The ratio of melt depth to optical skin depth sets the pattern wavelength, while the inter-pulse delay, via post-pulse damping, gates the route from flat surface to ordered pattern to chaos. We validate the phase diagram (hexagonal cavity arrays, bistable mixed states, labyrinths) numerically and confront it with pulse-resolved experiments on two metals, Ni and Fe3Cr. The agreement between theory and experiment quantitatively links the microscopic
laser-material response to the macroscopic pattern selected after many pulses. This order is self-limiting: the same corrugation the instability builds scatters the modes that build it, and simulations, with every scale fixed by material parameters, place the coherence breakdown near a roughness of 30 nm after a few tens of pulses, a finite window confirmed by pulse-by-pulse measurements of orientational order on the experimental surfaces; at stronger coupling, disorder does not destroy the pattern but saturates and pins it instead. This yields a closed, predictive description of
laser-driven self-organization, from single-pulse melt dynamics to the arrest of nanoscale order.
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All authors Jean-Philippe Colombier, Emeric Gandon, Quentin Fornasiero, Eduardo Brandao
Classical Physics · Cross-listed from cond-mat.mtrl-sci
From bending to stretching driven peeling of heterogeneous adhesives
Laurent Ponson
We study theoretically the peeling behavior of adhesives. Adopting a fracture mechanics approach, we derive the equation of motion of the adhesion front propagating at the interface between the adhesive and the substrate from which the peel strength is inferred. The originality of our approach lies in the description of the interplay during peeling between the stretching and the bending modes of deformation of the adhesive that is described as a F{\”o}ppl-Von Karman's thin film. Considering first a straight adhesion front, we retrieve the most salient feature of homogeneous adhesives, namely a peeling angle dependent peel strength driven by bending at large angles and by stretching at low angles. We also derive the shape of the adhesive that can be described using a single bending length scale derived from our model. We then investigate the impact of adhesion heterogeneities. We evidence that the deformations of the adhesion front are governed by a non-local interface elasticity the strength of which decreases with the peeling angle. This phenomenon reflects the transition between a stretching dominated peeling at low angle to a bending driven peeling at large angles that is captured in our model. This transition impacts the stability of adhesive fronts that relaxe more slowly from perturbations and gives rise to a stronger toughening effect in presence of a disorder distribution of adhesion energy at low peeling angles. Overall, this study sheds light on the central role played the elastic deformations of adhesives on their peeling behavior. The proposed framework unfolds the complex interplay between the deformation of adhesives and the peeling driving force that may be leveraged to engineer heterogeneous adhesives with enhanced properties. It also provides rich insights on the mechanisms underlying the emergence of non-local elasticity in interface problems.
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Physics and Society · Cross-listed from cs.AI
Can AI systems have free will?
Christian List
While there has been much discussion of whether AI systems could function as moral
agents or acquire sentience, there has been very little discussion of whether AI systems could have free will. I sketch a framework for thinking about this question, inspired by Daniel Dennett's work. I argue that, to determine whether an AI system has free will, we should not look for some mysterious property, expect its underlying
algorithms to be indeterministic, or ask whether the system is unpredictable. Rather, we should simply ask whether we have good explanatory reasons to view the system as an intentional
agent, with the capacity for choice between alternative possibilities and control over the resulting actions. If the answer is "yes", then the system counts as having free will in a pragmatic and diagnostically useful sense.
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Computational Physics
A Symmetry-Constrained Fourier–Morse Framework for Compact Anisotropic Interaction Potentials
Hadis Ghodrati, Sibylle Gemming, Florian Günther et al. (+1 more)
Large-scale coarse-grained simulations of anisotropic particles require compact interaction models that retain orientation-dependent energetics. We present a
symmetry-constrained
Fourier–Morse framework in which the radial interaction is described by a Morse potential and its orientational dependence by
Fourier expansions. The representation converges systematically with harmonic resolution, allows known orientational
symmetries to be imposed directly, and supports further reduction through harmonic truncation and coefficient
pruning. Its explicit
Fourier structure also provides a natural basis for constructing or modifying model interactions with prescribed orientational
symmetries. The parameterization requires only a sampled interaction landscape and is therefore independent of the method used to generate the reference data. We demonstrate the approach for four interaction classes of chiral $\alpha$-polyalanine helices, representing more than \num{300000} reference energy values with tens to a few hundred coefficients while reproducing
equilibrium interaction features with meV- and mÅ-level errors. As a proof of concept, molecular-dynamics simulations using the reduced analytical potentials produce stable low-temperature configurations exhibiting local ordering motifs qualitatively consistent with those identified previously by Monte Carlo simulated annealing.
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All authors Hadis Ghodrati, Sibylle Gemming, Florian Günther, Jeffrey Kelling
Computational Physics · Cross-listed from cs.CE
A Non-intrusive Approach for the Imposition of Strong Dirichlet Boundary Conditions in Unfitted Boundary Meshes
J.I. Camarotti, R. Aristio, R. Rossi et al. (+2 more)
The enforcement of essential boundary conditions is a fundamental challenge in unfitted boundary methods. This paper presents a non-intrusive, black-box strategy for imposing such conditions in unfitted meshes. The approach is intended for situations where the user does not have access to the solver's source code or its mathematical formulation, which is often the case when using commercial software. The proposed
algorithm allows solvers originally designed for body-fitted meshes to be used in unfitted cases, provided that four conditions are satisfied: (i) the solver must support user customization by means of scripting, (ii) allow the imposition of Dirichlet boundary conditions at the node level through scripting, (iii) permit the deactivation of elements outside the physical domain, and (iv) provide access to the solution gradient within active elements. The last condition can also be satisfied by externally reconstructing the gradient from nodal values and connectivity information, provided the element formulation is known, making it optional in practice. These requirements are very fair demands and are satisfied by the vast majority of production-ready, possibly commercial, codes. In the current work, we show the application of this non-intrusive
algorithm in the context of the Finite Element Method (FEM) and Isogeometric Analysis (IGA) discretizations, demonstrating optimal $L^2$-norm error convergence. This is demonstrated using the Kratos Multiphysics code (release v10.1) from the user API, simply leveraging the capabilities mentioned above.
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All authors J.I. Camarotti, R. Aristio, R. Rossi, R. Zorrilla, R. Wüchner
Classical Physics
Contact mechanics and friction of soft materials: an apparatus combining multi-axes dynamical actuation/measurement and in situ/in operando visualisation
Matthieu Guibert, Antoine Aymard, Cristobal Oliver et al. (+8 more)
The mechanics and friction of contact interfaces involving soft materials like gel, rubber or human skin are of both fundamental and applied interest. Recent insights have been made into this field thanks to in situ observations of the contact interface. However, current soft-material-oriented tribometers enable only few degrees of freedom for the actuation of the contact, far from covering the richness of the loading conditions relevant to real tribological contacts. Here, we introduce an apparatus dedicated to the study of the contact mechanics and friction of soft materials which, in addition to in situ / in operando optical monitoring of the interface, enables simultaneous actuation along five degrees of freedom: three translations and two rotations. While all three translations feature large velocity/large stroke motion, the one responsible for normal contact loading can also apply high frequency/small amplitude vibrations. The contact's dynamical response is monitored using both a 6-axes force/torque sensor and a 6-axes displacement/rotation sensor. We first describe the structure of the apparatus, its implementation,
alignment, calibration and resolutions. We then illustrate its capabilities through a series of experiments on elastomer contacts. Our apparatus will be useful to investigate the mechanics of a wide range of soft interfaces submitted to rich, tribology-relevant kinematic or dynamic stimuli.
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All authors Matthieu Guibert, Antoine Aymard, Cristobal Oliver, Thibaut Durand, Baptiste Boulet, Djibril Gabriel Kashala, Antoine Mille, Mathieu Leocmach, Loïc Vanel, Davy Dalmas, Julien Scheibert
Optics
Micro-transfer Printed Blue InGaN Lasers on Silicon Nitride Photonic Integrated Circuits
Konstantinos Akritidis, Krzysztof Gibasiewicz, Han Wang et al. (+8 more)
Expanding integrated photonics into the blue spectral range requires high-performance light sources, making the gallium nitride (GaN) material family indispensable. While silicon nitride (SiN) platforms offer a robust, CMOS compatible passive ecosystem for visible wavelengths, seamlessly integrating GaN
lasers remains a major bottleneck. Conventional heterogeneous integration methods present distinct trade-offs: full-wafer bonding achieves high throughput but requires careful management of thermal and
lattice mismatches across large areas, whereas flip-chip bonding ensures high yield through pretesting but is constrained by sequential processing speed. In this landscape, micro-transfer printing (MTP) emerges as a disruptive, material-efficient alternative, bypassing these limitations by combining high-density parallel integration with known-good-die selection. Applying MTP to GaN, however, presents a significant material challenge: due to its chemical inertness and strong III-N bonds, device release typically relies on electrochemical etching, which can compromise material quality. Here, we overcome this hurdle and demonstrate the first micro-transfer printed blue
lasers on a SiN platform. Using a heavily doped n-type sacrificial layer together with optimized electrochemical etching conditions, we release smooth-surfaced thin-film light sources from bulk GaN substrates. Following release, the devices are integrated and butt-coupled to SiN fork-shaped edge couplers, achieving high current densities exceeding 20 kA$/$cm$^2$ alongside lasing at 455 nm. These results expand the visible integrated photonic toolkit and establish a framework for multi-wavelength integration, opening new avenues for next-generation technologies including flow cytometry,
quantum computing, optical communications, and augmented/virtual reality.
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All authors Konstantinos Akritidis, Krzysztof Gibasiewicz, Han Wang, Iryna Levchenko, Max Kiewiet, Maximilien Billet, Mikołaj Chlipała, Karolina Peret-Malessa, Pol Van Dorpe, Henryk Turski, Bart Kuyken
Computational Physics · Cross-listed from cs.CE
Partitioned Co-Simulation for CAD-integrated Vibroacoustic Problems in Unbounded Domains
J. I. Camarotti, P. Le, Y. Cai et al. (+4 more)
Vibroacoustic analysis often requires coupling structural and acoustic solvers based on different numerical formulations and discretizations, making monolithic implementations intrusive and limiting software modularity and reuse. This work presents a partitioned co-simulation framework for exterior vibroacoustic analysis that couples an Isogeometric boundary representation analysis (IBRA) structural solver with an isogeometric boundary element method (IGA-BEM) acoustic solver. The methodology operates directly on the computer-aided design (CAD) boundary representation, preserving the exact geometry throughout the analysis and supporting both weak and strong coupling between non-conforming discretizations. A key contribution is the extension of the Aitken dynamic relaxation and Interface Quasi-Newton with Inverse Least-Squares (IQN-ILS) convergence accelerators to complex-valued interface quantities, allowing the coupling iterations to account directly for both amplitude and phase information. The approach is validated using one-way and two-way coupled vibroacoustic
benchmark problems involving thin-shell structures and exterior acoustic domains. The results show excellent agreement with monolithic reference solutions, while the proposed complex-valued convergence accelerators improve the robustness and convergence behavior of the strongly coupled solution procedure without compromising solution accuracy. These results demonstrate that the proposed approach provides an accurate, robust, and modular approach for CAD-integrated frequency-domain vibroacoustic analysis.
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All authors J. I. Camarotti, P. Le, Y. Cai, R. Aristio, D. Panagiotopoulos, R. Wüchner, E. Deckers
Computational Physics · Cross-listed from cond-mat.mes-hall
Unified contact-free formulation of linear-response transport theory
Ziqian Wang and Ji Feng
Thermal Hall transport is conventionally formulated as a current–current Kubo response supplemented by an energy-magnetization correction obtained through an auxiliary pseudogravitational
magnetic field. Motivated by this structure, we develop a unified contact-free moment formulation of linear response to scalar sources. For channels whose source contributions vanish in the dc limit, the transport coefficient is the low-frequency residue of a retarded moment–moment correlator, with equal-time endpoint contributions incorporated before the dc limit is taken. The formulation uses only scalar sources, requires no separate magnetization subtraction, is independent of the local-current gauge, and is invariant under admissible redistributions of bond or interaction energy. It organizes particle, grand-energy, and specified
spin-density channels within a common source–moment response
matrix. Quadratic Landau–Lifshitz
spin waves illustrate the method: the secular growth of polarization-moment correlations isolates the finite Hall residue and yields the
magnon thermal Hall and
spin Nernst coefficients from the same paraunitary band geometry. The formulation provides a unified operator framework that simplifies the organization of particle, thermal, and
spin transport and can streamline calculations by eliminating separate contact and magnetization corrections.
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