Fluid Dynamics
Physics-guided surrogate learning enables zero-shot control of turbulent wings
Yuning Wang, Pol Suarez, Mathis Bode et al. (+1 more)
Turbulent boundary layers over aerodynamic surfaces are a major source of aircraft drag, yet their control remains challenging due to multiscale dynamics and spatial variability, particularly under adverse pressure gradients. Reinforcement learning has outperformed state-of-the-art strategies in canonical flows, but its application to realistic geometries is limited by computational cost and transferability. Here we show that these limitations can be overcome by exploiting local structures of wall-bounded
turbulence. Policies are trained in turbulent channel flows matched to wing boundary-layer statistics and deployed directly onto a NACA4412 wing section at $Re_c=2\times10^5$ without additional training on the wing, constituting zero-shot deployment. The transferred policies reduce total drag by 11.1%, while state-of-the-art opposition control reduces it by 8.9%. With the actuation cost taken into account, the corresponding net-energy savings are 10.9% and 8.8%, respectively. Surrogate training provides an estimated improvement of four orders of magnitude in exploration efficiency over direct on-wing training, enabling scalable flow control.
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All authors Yuning Wang, Pol Suarez, Mathis Bode, Ricardo Vinuesa
Fluid Dynamics
HOC simulations of miscible viscous fingering of a finite slice: A new insight
Mijanur Rahaman, Jiten C. Kalita and Satyajit Pramanik
We investigate the dynamics of viscous fingering (VF) in miscible slices in homogeneous, isotropic porous media. The fluid flow is governed by incompressible Darcy's law, whereas the solute transport is described using an advection-
diffusion equation. The viscosity of the miscible system depends on the solute concentration, creating a viscosity contrast between the displacing fluid and the finite sample. When expressed in terms of stream function, the flow is described by a system of nonlinear, two-way coupled advection-
diffusion type equations. We consider three types of boundary conditions: (a) periodic, (b) impermeable (zero normal velocity) and no-flux (solute), and (c) permeable (allowing non-zero normal velocity) and no diffusive flux (solute) transverse boundaries. This initial boundary value problem is solved numerically using a fourth-order compact finite difference method, while the Crank-Nicolson technique is used for time integration. Although the onset of viscous fingering and early time behavior are independent of the choice of boundary types, long-time behavior, solute mixing and spreading depend on the boundary conditions. In particular, it is observed that the permeable boundaries allow solute mass to increase, leading to stronger fingering instabilities, larger mixing lengths and non-trivial
evolution of interfacial lengths. The findings of this study have implications in chromatography separation.
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Fluid Dynamics
Hierarchical Iterative Method in CFD Numerical Solution
Dehong Meng, Hao Yue, Hao Wang et al. (+4 more)
We propose a hierarchical asynchronous iterative method that differs from the traditional synchronous iterative method used across the entire flow field in conventional Computational Fluid Dynamics applications. This method forcibly divides the spatial region of the flow field into three layers: the boundary layer, the inner field, and the outer field. By adopting a novel approach of using different iteration steps for each layer, it significantly enhances computational efficiency. Using the hierarchical iterative method, numerical simulation studies were conducted on three typical
benchmark models with different velocity ranges. Additionally, discussions were held regarding new modes such as using different control equations and computational parameters for each layer. The results based on structured grids indicate that, for the cases studied in this paper, the proposed method can achieve identical simulation results compared to traditional methods while only consuming 53.2% of the computational time of traditional methods, without significantly increasing manpower costs. This paper provides suggestions and discusses on the numerical applications of this novel iterative mode, and offers new insights for follow-up research based on this method.
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All authors Dehong Meng, Hao Yue, Hao Wang, Wei Li, Yuhang Qi, Rui Wang, Junwu Hong
Physics Education
Experimental Skills for Undergraduate Career Preparation in Quantum Information Science and Engineering
Shams El-Adawy, A.R. Piña, Benjamin M. Zwickl et al. (+1 more)
The growth of the
Quantum Information Science and Engineering (QISE) industry has increased interest in how undergraduate programs prepare students for careers in this field. Prior research emphasizes the value of experiential learning as preparation for the
quantum industry, but lacks specificity regarding the experimental skills needed for positions available to bachelor's degree graduates. In this study, we investigate the experimental skills associated with bachelor's-level
quantum industry positions through 44 semi-structured interviews with
quantum industry professionals. Guided by the American Association of Physics Teachers recommendations for the undergraduate physics laboratory curriculum, we characterize the experimental skills associated with positions described as requiring bachelor's-level preparation and thematically synthesize them into four categories: instrumentation, computation and data analysis, experimental and project design, and communication and collaboration. We further examine how these skills cluster across role types and articulate them as learning goals to provide guidance for educators interested in aligning undergraduate instruction with the needs of students wanting to pursue a career in the
quantum industry. Our findings suggest the need to emphasize the discussion of hardware in QISE theory courses, expand experimental training through instructional laboratories, and intentionally integrate professional skills in undergraduate QISE education.
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All authors Shams El-Adawy, A.R. Piña, Benjamin M. Zwickl, H.J. Lewandowski
Optics
Raman amplification and ISRS in SDM links: Analytical evaluation and closed-form models for optical transmission
Lucas Alves Zischler, Antonio Mecozzi and Cristian Antonelli
In optical communications, the Raman effect is exploited for its lasing properties in distributed Raman amplification (DRA) and leads to spectral distortions through inter-channel stimulated Raman scattering (ISRS). In single-mode fibers, these effects are well understood and modeled, but equivalent closed-form expressions for arbitrarily coupled space-division multiplexing (SDM) links are lacking. In this work, we expand upon previous literature by providing closed-form expressions modelling DRA and ISRS in common SDM fiber designs that support arbitrarily-coupled degenerate mode-groups, incorporate mode coupling, and accounting for inter-modal non-linear effects, showing excellent agreement with simulations. The derived formulas are then applied to representative scenarios, illustrating how distinct pump and fiber configurations influence gain and mode-dependent gain (MDG). Finally, we describe suggested routines for experimentally estimating the Raman response profiles of SDM fibers.
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Biological Physics · Cross-listed from cond-mat.soft
Physical Properties of Dextran Solutions as Model Crowding Media
Giuliano Migliorini, Josipa Cecic Vidos, Josef Hamacek et al. (+2 more)
The role of macromolecular crowding in living systems is widely appreciated, but artificial crowders used to model these effects in vitro are often inadequately characterized. In this work, we examine density, viscosity,
polymer self-
diffusion and water
diffusion in crowded dextran systems. Dextran viscosity and self-
diffusion follow size-dependent trends, collectively described by universal functions of the overlap concentration corresponding to a Flory exponent of 0.44, characteristic of branched
polymers. Viscosity increases with concentration as a power law, with a crossover from dilute to semi-dilute behaviors. Dextran self-
diffusion decays exponentially: this can be interpreted in light of Rosenfeld's excess
entropy scaling hypothesis. Water self-diffusivity and specific volume decrease with concentration, but show no dependence on
polymer size. We show how these results can be used to construct the true volume fraction of crowders, which takes into account bound water. Overall, our findings showcase the power of
polymer physics concepts in macromolecular crowding studies in vitro.
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All authors Giuliano Migliorini, Josipa Cecic Vidos, Josef Hamacek, Anand Yethiraj, Francesco Piazza
Atomic Physics
Association between projectile and target excitation in slow Ar$^{q+}$-CO$_2$ collisions
Akash Srivastav, Sumit Srivastav, Vishnu P et al. (+1 more)
We investigate ionic fragmentation of CO$_2^{n+}$~\mbox{($2\le n\le 4$)} produced in collisions with Ar$^{q+}$~\mbox{($4\le q\le 16$)} projectiles at a collision velocity of $\approx$~0.3~a.u. For most projectile and fragmentation channel combinations, the shape of the kinetic energy release distribution (KERD) differs with the electron capture mediated charge change (\mbox{$\Delta q$}) in the scattered projectile: KERD for \mbox{$\Delta q = 2$} is broader at high KER than for \mbox{$\Delta q =1$}. The difference generally diminishes with increasing projectile charge. Two deviations in this general trend are seen in the fragmentation of CO$_2^{3+}$, one for Ar$^{4+}$ impact in the high KER region and the other for Ar$^{6+}$ impact in the low KER region. The calculated reaction windows for multielectron capture within the framework of the extended classical over-the-barrier model (ECOBM) indicate that while ionization of the target occurs via multielectron capture, the scattered projectile may subsequently undergo multi-fold autoionization. Interpreting projectile autoionization to be a consequence of capture into highly excited states and high fragment KER to be a consequence of excitation of the ionized target to high-lying states, we find a strong dependence between the target and scattered projectile excitations.
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All authors Akash Srivastav, Sumit Srivastav, Vishnu P, Bhas Bapat
Atmospheric and Oceanic Physics
OTProf: estimating high-resolution profiles of optical turbulence ($C_n^2$) from reanalysis using deep learning
Maximilian Pierzyna, Sukanta Basu and Rudolf Saathof
Accurate, high-resolution vertical profiles of optical
turbulence ($C_n^2$), which reflect local meteorology and topography, are crucial for ground-based optical astronomy and free-space optical communication. However, measuring these profiles or generating them with numerical weather models requires substantial operational or computational effort. In this work, we present OTProf, a deep-learning method that estimates high-resolution $C_n^2$ profiles from widely available coarse-resolution ERA5 reanalysis data. OTProf is based on the Squeezeformer architecture, modified for super-resolution by introducing grid-agnostic interpolation in the latent space. We train and evaluate OTProf in the Netherlands using high-resolution $C_n^2$ data obtained from the Weather Research and
Forecasting (WRF) model. The commonly used Hufnagel-Valley model serves as the baseline. Overall, OTProf reproduces the vertical structure of WRF-based $C_n^2$ more accurately than Hufnagel-Valley and yields more accurate estimates of the Fried parameter $r_0$ and the scintillation index $\sigma_I^2$. Out-of-domain performance is assessed using a smaller WRF-based $C_n^2$
dataset covering the Canary Islands. Initial results indicate a performance drop because the orography differs markedly from the training domain. We show that output bias correction based on a few local simulations can help OTProf to adapt, but more work for domain adaptation is needed. OTProf is therefore primarily recommended for in-domain applications, e.g., generating $C_n^2$ climatologies from long ERA5 records.
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Chemical Physics
Transferable FB-GNN-MBE Framework for Potential Energy Surfaces: Data-Adaptive Transfer Learning in Deep Learned Many-Body Expansion Theory
Siqi Chen, Zhiqiang Wang, Yili Shen et al. (+8 more)
Mechanistic understanding and rational design of complex chemical systems depend on fast and accurate predictions of electronic structures beyond individual building blocks. However, if the system exceeds hundreds of atoms, first-principles
quantum mechanical (QM) modeling becomes impractical. In this study, we developed FB-GNN-MBE by integrating a fragment-based graph neural network (FB-GNN) into the many-body expansion (MBE) theory and demonstrated its capacity to reproduce first-principles potential energy surfaces (PES) for hierarchically structured systems with manageable accuracy, complexity, and interpretability. Specifically, we divided the entire system into basic building blocks (fragments), evaluated their one-fragment energies using a QM model, and addressed many-fragment interactions using the structure-property relationships trained by FB-GNNs. Our investigation shows that FB-GNN-MBE achieves chemical accuracy in predicting two-body (2B) and three-body (3B) energies across water, phenol, and mixture
benchmarks, as well as the one-dimensional dissociation curves of water and phenol dimers. To transfer the success of FB-GNN-MBE across various systems with minimal computational costs and data demands, we developed and validated a teacher-student learning protocol. A heavy-weight FB-GNN trained on a mixed-density water cluster ensemble (teacher) distills its learned knowledge and passes it to a light-weight GNN (student), which is later fine-tuned on a uniform-density (H2O)21 cluster ensemble. This transfer learning strategy resulted in efficient and accurate prediction of 2B and 3B energies for variously sized water clusters without retraining. Our transferable FB-GNN-MBE framework outperformed conventional non-FB-GNN-based models and provided a scalable and accurate route toward interaction energies of large molecular assemblies.
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All authors Siqi Chen, Zhiqiang Wang, Yili Shen, Xianqi Deng, Xi Cheng, Cheng-Wei Ju, Jun Yi, Guo Ling, Dieaa Alhmoud, Hui Guan, Zhou Lin
Optics
Commissioning measurements for a very cold neutron interferometer based on nanodiamond-polymer composite gratings
Roxana H. Ackermann, Sonja Falmbigl, Elhoucine Hadden et al. (+7 more)
Over the past decade,
holographic nanodiamond-
polymer composite gratings have been developed and optimized as high-efficiency diffractive elements for very cold
neutrons (VCN), for use as mirrors and beam splitters in a triple-Laue (LLL) interferometer. We report their optical characterization and, crucially, their
neutron-optical performance, including diffraction efficiency and angular selectivity under VCN conditions. We further demonstrate their integration into a VCN interferometer. The layout of the interferometer and its first implementation at the beamline are described, highlighting practical considerations for long-term operation. We discuss avenues for performance improvement, in particular grating fabrication refinements. These results establish nanodiamond-
polymer composite gratings as viable components for VCN interferometry and pave a way toward precision
neutron phase measurements in the very cold regime.
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All authors Roxana H. Ackermann, Sonja Falmbigl, Elhoucine Hadden, Alexia Dubois Leprou, Hanno Filter-Pieler, Tobias Jenke, Jürgen Klepp, Christian Pruner, Yasuo Tomita, Martin Fally
Optics
Cascade Brilloiun scattering on short-lived phonons for frequency comb generation
Egor R. Verevkin, Ilya V. Doronin, Alexander A. Zyablovsky et al. (+1 more)
We consider Brillouin scattering on short-lived
phonon modes, such that the relative Brillouin shift between propagating and scattered waves is smaller than the relative width of
phonon modes. In this case one
phonon mode facilitates scattering between many pairs of optical modes. We show that in this limit two
phonon modes are sufficient for cascade Brillouin scattering (one forward propagating wave and one counter propagating wave), and that the cascade behavior is qualitatively different from the cascade in conventional Brillouin systems with distinct
phonon modes for each optical mode pair. In particular, our results show that there is a pump threshold above which many optical modes become excited simultaneously, as opposed to a cascade gradually building up. The resulting cascade scattering can be exploited for frequency comb generation with uniform amplitudes and without the need for anomalous dispersion in the medium.
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All authors Egor R. Verevkin, Ilya V. Doronin, Alexander A. Zyablovsky, Evgeny S. Andrianov
Optics
Tuning Plasmonic Metasurfaces via Phase Change Material Substrates for Modulating Reactivity in Light-Driven Reactions
Ning Lyu, Anjalie Edirisooriya, Dawei Liu et al. (+5 more)
Phase change materials provide a powerful platform for dynamically modulating optical responses in nanophotonic systems. While plasmonic metasurfaces have been widely employed to enhance photocatalytic efficiency and promote particular light-driven reactions, active and dynamical control over reaction pathways within a single device remains challenging. Here, we report a phase-induced tunable metasurface that tailors photoexcited electron populations through mode hybridization, enabling selective control over the reactivity of light-driven chemical processes. By exploiting thermally induced refractive-index switching in a Sb2S3 cavity, the plasmonic resonance strength of Au nanodisks is actively tuned via cavity-plasmon hybridization. This reconfiguration modulates the product yield of methylene blue degradation by a factor of 2.4, suppressing to 0.45 in the crystalline phase and enhancing to 1.09 in the amorphous phase. Importantly, this reconfigurable platform enables dynamic control of the reaction yield using a single metasurface architecture under identical illumination conditions. Our approach establishes a dynamically programmable light-driven reaction platform capable of precisely manipulating reaction reactivity, offering new opportunities for selective photocatalysis in complex multibranch reaction systems.
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All authors Ning Lyu, Anjalie Edirisooriya, Dawei Liu, Zelio Fusco, Shenyou Zhao, Lan Fu, Fiona J. Beck, Christin David
Chemical Physics
Integral-equation analysis of transient diffusion-limited currents at disk electrodes: Asymptotic expansion and compact approximation
Kazuhiko Seki, Yuko Yokoyama and Masahiro Yamamoto
The transient
diffusion-limited current at a disk electrode following a change in interfacial ion concentration induced by a potential step is analyzed with direct relevance to chronoamperometric measurements. The mixed-boundary
diffusion problem is formulated in the Laplace domain and reduced to a Fredholm integral equation that directly determines the Faradaic current. The steady-state limit recovers Saito's equation, while a systematic long-time asymptotic expansion quantifies the approach to steady state. A Padé approximant yields a compact analytical expression in the time domain that accurately describes the current over experimentally relevant time ranges. In contrast to existing high-accuracy numerical procedures based on hybrid asymptotic and
polynomial approximations, the present formulation provides an explicit and compact analytical representation that facilitates interpretation and practical implementation. The short-time response exhibits Cottrell's equation with edge effects characteristic of disk electrodes. Overall, the framework provides practical tools for analyzing transient currents, extracting
diffusion parameters, and assessing the accuracy of widely used analytical approximations in disk-electrode chronoamperometry.
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Biological Physics · Cross-listed from quant-ph
Quadratic Quantum Polarimetry with Entangled Photon Pairs
Jinliang Ren, Vira Besaga, Ivan Lopushenko et al. (+5 more)
Conventional polarimetry, including schemes leveraging entangled light, characterizes optical samples through linear transformations of polarization states. We introduce a two-
photon probing approach in which both
photons of an entangled pair interact with the same depolarizing medium simultaneously. In this regime, the transformation of the two-
photon polarization correlations becomes quadratic in the Mueller
matrix, enabling access to second-order polarization information beyond conventional polarimetry. We develop a theoretical framework linking the Mueller
matrix to the
evolution of the two-
photon polarization correlation tensor and show that depolarization induces quadratic degradation of
entanglement and state purity. Experiments using polarization-entangled
photon pairs transmitted through controlled scattering media confirm the predicted response and reveal enhanced sensitivity to polarization scrambling compared with single-
photon probing. These results establish two-
photon probing as a higher-order
quantum polarimetric modality for characterizing polarization channels.
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All authors Jinliang Ren, Vira Besaga, Ivan Lopushenko, Jinyong Ma, Alexander Bykov, Igor Meglinski, Frank Setzpfandt, Andrey A. Sukhorukov
Physics Education · Cross-listed from astro-ph.IM
Unseen Astronomy
Dr James W. Trayford
The 2025 UK National Astronomy Meeting (NAM) in Durham played host to a session titled "Unseen Astronomy", involving a variety of astronomy researchers in diverse fields. This unique meeting focussed on a number of novel projects exploring alternatives to purely visual means of display in Astronomy, encompassing spheres of education, communication and research, and straddling both accessible and general use applications. The successful inclusion of such a session at a major conference reflects the explosion of interest in
multimodal astronomy in recent years, and hints at its transformative potential. Here, I aim to outline and motivate the topic of multi-modal science and consider its exciting potential. I will discuss this in the context of our own work in the area, the community building being undertaken to bring together researchers considering multi-modality, and efforts to impact astronomy at large.
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Fluid Dynamics
A time-domain approach for motion-explicit evaluation of loads on floating structures in fully nonlinear waves
Athanasios Dermatis, Henrik Bredmose, Harry B. Bingham et al. (+2 more)
This paper presents a novel method for evaluating second-order consistent hydrodynamic loads, which employs nonlinear wave and body kinematics. The pseudo-spectral formulation of nonlinear potential flow wave solvers is exploited, permitting the application of transfer functions on the nonlinear incident wave field. A closed-form expression is accordingly derived for the potential force component, which constitutes a generalisation of the Pinkster approximation to fully nonlinear waves. Moreover, the quadratic force component is reformulated to account for the total nonlinear body motion and velocity rather than their first-order counterparts. Hence, the traditional assumption that first-order body motions are significantly larger than the second-order components, which is violated in the case of moored floating structures, is circumvented. To this end, the radiation potential is treated in the time domain and is distinguished from the incident and scattering wave contributions, which are considered through wavenumber-domain transfer functions. An important advantage of the proposed approach is that it is established on the output of radiation-diffraction analysis in the frequency domain, and therefore is highly practical and efficient. Finally, the derived force model is coupled with a time-domain motion solver, which permits the consideration of the instantaneous body motion and velocity in the force calculation. The solver is employed to investigate the motions of a moored container ship, and the results demonstrate significant improvements over standard second-order radiation-diffraction theory.
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All authors Athanasios Dermatis, Henrik Bredmose, Harry B. Bingham, Benjamin Bouscasse, Guillaume Ducrozet
Instrumentation and Detectors
Optical readout of MPGDs with solid wavelength shifters
F.M. Brunbauer, A. Cools, M. Cortesi et al. (+20 more)
Optical readout of MicroPattern Gaseous Detectors (MPGDs) makes use of the high granularity of imaging sensors to achieve good spatial resolution for radiation imaging and particle detection. CF4 is widely used as a scintillating gas because its emission lies in the visible range, where optical sensors are most sensitive. However, to reduce reliance on greenhouse gas, such as CF4, which also has limited availability, alternative gas mixtures emitting scintillation light in the ultraviolet range can be used in combination with wavelength shifters. We investigate the spatial resolution achievable with optically read out Gaseous Electron Multipliers (GEMs) and Micromegas when using solid wavelength shifter layers such as Tetraphenyl butadiene (TPB). TPB coatings on the anode of glass Micromegas achieve the best spatial resolution of 0.22 mm owing to the minimal distance between the origin of the scintillation light and the wavelength shifter. Nevertheless, TPB layers were also shown to achieve moderate spatial resolution in combination with optically read out GEMs.
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All authors F.M. Brunbauer, A. Cools, M. Cortesi, E. Fasoula, E. Ferrer-Ribas, K.J. Flöthner, F. Garcia, D. Janssens, M. Lisowska, P. Sviatopolk Mirsky, H. Müller, J. Nummi, E. Oliveri, G. Orlandini, T. Papaevangelou, D. Pfeiffer, E. Pollacco, L. Ropelewski, F. Sauli, J. Samarati, L. Scharenberg, M. van Stenis, R. Veenhof
Chemical Physics
Limitations of MRSF-TDDFT for Applications in Photochemistry
Jiří Janoš, Andrew J. Orr-Ewing, Basile F. E. Curchod et al. (+1 more)
Mixed-reference
spin-flip time-dependent density functional theory (MRSF-TDDFT) has recently emerged as an attractive electronic-structure method for studying photochemical processes, given that it bridges the computational efficiency of single-reference approaches with the versatility of multireference methods. In the following, we critically assess the general applicability of MRSF-TDDFT to photochemistry and identify two important limitations. First, the doubly-excited configurations included in MRSF-TDDFT come at the cost of missing some singly-excited configurations. Second, MRSF-TDDFT provides unreliable excited-state energies when its triplet reference - a cornerstone of the method - abruptly changes its nature, e.g., when the T$_1$ and T$_2$ triplet states become nearly degenerate and exchange electronic character. This change of character of the triplet reference can induce discontinuities or sharp distortions in electronic potential energy curves of the response states in unsuspected regions of the
nuclear configuration space. We propose strategies and diagnostics to detect these limitations in the exploration of potential energy surfaces and nonadiabatic molecular dynamics using MRSF-TDDFT.
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All authors Jiří Janoš, Andrew J. Orr-Ewing, Basile F. E. Curchod, Petr Slavíček
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Linking Calendar and Cycle Ageing in Lithium-Ion Batteries through Consistent Parameterisation of an Electrochemical-Thermal-Degradation Model
Ganesh Madabattula
Parameterisation of coupled degradation mechanisms in lithium-ion batteries is a major challenge. Interactions between the mechanisms depend on usage conditions: C-rate, rest state-of-charge (SoC), depth-of-discharge (DoD) and temperature. This work presents a framework to consistently parameterise key degradation modes–solid-electrolyte interphase (SEI) growth, lithium plating, and active material loss in both electrodes–using insights derived from degradation mode analysis data. The work predicts capacity fade trajectories of a NMC-based lithium-ion
cell under both calendar and combined calendar-cyclic ageing, using a P2D electrochemical-thermal-degradation model. The work predicts state-of-health (SoH), remaining-useful-life (RUL) and internal degradation modes of the
cell–under 81 combinations of temperature (10$^o$C, 25$^o$C, 40$^o$C), C-rate (0.1 C, 0.3 C and 1.0 C), rest SoC (10%, 60%, and 100%) and DoD (50%, 70%, and 90%)–using PyBaMM. The predicted cycle-life varies between 0.8 to 14 years to reach 75% of SoH. The work provides mechanistic insights into competing effects between calendar and cyclic ageing, during cycling. The model demonstrates sub-linear, linear, and sup-linear/accelerated capacity fade based on the usage conditions. The simulated
dataset for all the cases is made available.
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Chemical Physics
Experimental proof of strong $\Pi$-$\Sigma$ mixing in the Renner-Teller and Pseudo-Jahn-Teller affected CCH$^+$ ($^3\Pi$) ion
Kim Steenbakkers, P. Bryan Changala, Weslley G. D. P. Silva et al. (+8 more)
The ethynyl radical cation, CCH$^+$ ($^3\Pi$), offers a unique system for fundamental spectroscopic studies of non-adiabatic effects due to its open-shell linear structure and the presence of a low-lying $^3\Sigma^-$ state, which induces notable perturbations in the (ro-)vibrational spectrum. To probe these effects, we recorded the broadband vibrational spectrum of CCH$^+$ from 350-3450 cm$^{-1}$ using leak-out spectroscopy. The spectrum reveals a complex splitting pattern in the CCH bending mode, attributed to Renner-Teller and pseudo-Jahn-Teller coupling effects between the $^3 \Pi$ and $^3 \Sigma^-$ electronic states. A three-state diabatic model, validated here against high-resolution IR data of the CH stretching mode, facilitated assignments within the broadband infrared (IR) spectrum, including an additional $\Pi$ vibronic feature observed in the aforementioned high-resolution spectrum. Our results highlight a pronounced sensitivity of the splitting pattern to the $\Pi$-$\Sigma$ energy gap, with couplings so large that even the zero-point vibrational motion of the bending vibration is sufficient to disrupt the vibronic structure of this ion. This compact ion, with strong coupling effects and high-quality spectroscopic data, serves as an exemplary system for evaluating non-adiabatic models.
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All authors Kim Steenbakkers, P. Bryan Changala, Weslley G. D. P. Silva, John F. Stanton, Filippo Lipparini, Jürgen Gauss, Oskar Asvany, Gerrit C. Groenenboom, Britta Redlich, Stephan Schlemmer, Sandra Brünken
Plasma Physics
Pressure gradient-driven plasma flows and magnetogenesis
Zain H. Saleem and Hamid Saleem
We present a self-consistent two-fluid theory demonstrating that pressure gradients simultaneously generate
plasma flows and
magnetic fields. We show that compatibility between ion momentum balance and mass conservation imposes a previously unrecognized constraint on
plasma evolution: the total pressure must satisfy the Laplace equation, $\nabla^2 p = 0$. This condition yields a class of exact analytical solutions in which pressure-driven flows and Biermann-type
magnetic fields emerge together. Application of the model to a
galactic gas clump reveals that, under thermal pressure, electrons and ions move almost together, giving rise to weak currents and consequently very small seed
magnetic fields. Ion dynamics are also important for determining the seed
magnetic-field generation time $\tau_B$ and for estimating the ion flow velocity. The model is further applied to
laser-produced
plasma to describe its short-time
evolution. The present theory provides a unified, self-consistent description of pressure-driven flow generation and magnetogenesis in both astrophysical and laboratory
plasmas.
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Fluid Dynamics
Role of particle volume fraction on particulate suspension droplet evolution, transition and Hysteresis
Kishorkumar Sarva
We study the transitional dynamics of the non-Brownian particulate Newtonian
liquid jet for different particle volume fractions ($\phi$). We focus on the influence of particle volume fraction on the critical inflow velocity at which the dripping-jetting (i.e., dripping to jetting and jetting to dripping) transition occurs for the ratio of the nozzle diameter to the particle diameter ($D_n/D_p$=20). The experiments were conducted by increasing (forward sweep) and decreasing (reverse sweep) the flow rate. These experiments were repeated for different volume fractions. We observe, with an increase in particle volume fraction, the transition from the dripping to the jetting regime occurs through a chaotic dripping regime. With an increase in the particle volume fraction, the jetting regime has occurred at early flow rates during dripping to jetting transition (in forward sweep), and the jetting to dripping transition (reverse sweep) occurred at a lower flow rate than the forward sweep. The particle volume fraction impacts the hysteresis observed for the Newtonian fluid. Due to the changes in the critical flow rate where transition occur, the widening of the hysteresis loop of flow rate with the pinchoff length is observed. The transition from dripping to jetting is observed to have the recurrent escape of the pinchoff mechanism as the jet length changes, influencing the droplet size distribution. The frequency of droplet pinchoff and droplet size have decreased as the particle volume fraction has increased. As the particle volume fraction increases, the size distribution between the dripping and jetting regimes decreases.
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Physics and Society · Cross-listed from econ.GN
The Geoeconomics of Venture Capital An Economic Complexity Approach to Emerging Technological Sovereignty
Benjamin Leroy, Davi Marim, El Ghali Benjelloun et al. (+2 more)
We explore a quantitative approach to emerging technological sovereignty and geoeconomic power by assessing the relative positioning of countries with economic complexity methods applied to the structure of national venture-capital (VC) portfolios and their associated Revealed Venture Advantage (RVA) metrics. Using Crunchbase firm- and deal-level data, we map venture-backed startups to 18 emerging technology domains via a probabilistic multi-label large-
language-model classifier, and construct an RVA-based country-technology specialization
matrix for the 17 countries with the highest aggregate VC funding. From this
matrix, we derive two eigenvector-based measures: a Geoeconomic Complexity Index (GCI) that ranks countries by the composition of their venture specializations, and an Emerging Technology Geoeconomic Complexity Index (ETGCI) that ranks domains by the extent to which specialization is concentrated among high-GCI countries. Empirically, Cloud Computing, Cybersecurity Tools, and Medtech exhibit the highest ETGCI values, reflecting concentration of specialization in a small set of leading countries. The United States and Israel consistently occupy a marked "high-diversity/low-ubiquity" position and lead the GCI ranking, followed by China, France, Japan, and Germany; both country and domain rankings are stable from 2021-2024. Finally, relatedness-based simulations identify, when it exists, for each country the Simplest Single Sovereignty Enhancing Technology (SSSET), i.e., the most feasible single new technological direction associated with the largest expected improvement in relative geoeconomic positioning.
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All authors Benjamin Leroy, Davi Marim, El Ghali Benjelloun, Arthur Rozan Debeaurain, Jean-Michel Dalle
Computational Physics · Cross-listed from math.NA
Restoring Convergence Order in Explicit Runge-Kutta Integration of Hyperbolic PDE with Time-Dependent Boundary Conditions
Giorgio Maria Cavallazzi, Miguel Pérez Cuadrado and Alfredo Pinelli
Explicit Runge-Kutta (RK) integration of
hyperbolic initial-boundary value problems with time-dependent Dirichlet data often displays order reduction: the observed convergence order falls below the nominal order because the stage structure interacts with asymmetric near-boundary spatial closures. This paper develops a purely spatial remedy that preserves the time integrator while redesigning only the first two boundary-adjacent derivative operators. For an arbitrary explicit $s$-stage RK method applied to linear advection, the one-step truncation error at the boundary-adjacent nodes is shown to admit a tableau-dependent decomposition whose cancellation yields explicit algebraic conditions on the boundary weights. A solvability coefficient $R(\mathbf{b},\mathbf{c},A)$ determines whether a spatial compensation mechanism exists; the result is specialised to SSP-RK3, for which closed-form conditions are derived. Constrained differential
evolution then identifies 5-point closures that, coupled to a 5th-order upwind interior stencil, recover third-order convergence from the degraded second-order behaviour of classical Taylor closures. A stability-aware variant augments the optimisation with an
eigenvalue penalty, exposing the trade-off between order recovery and CFL robustness. Validation covers linear advection, manufactured-solution Burgers flow, and dimensionally split two-dimensional advection. The analysis clarifies why weak-stage-order temporal fixes do not resolve the finite-difference boundary problem, and indicates how the framework extends to non-uniform meshes.
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Medical Physics
A Fast and Generic Energy-Shifting Transformer for Hybrid Monte Carlo Radiotherapy Calculation
Chi-Hieu Pham, Didier Benoit, Vincent Bourbonne et al. (+3 more)
We introduce a novel learning framework for accelerated Monte Carlo (MC) dose calculation termed Energy-Shifting. This approach leverages deep learning to synthesize highly complex polyenergetic dose distributions directly from simple monoenergetic inputs under identical beam configurations. Unlike conventional denoising techniques, which rely on noisy low-count dose maps that compromise beam profile integrity, our method achieves superior cross-domain generalization on unseen
datasets by integrating high-fidelity anatomical textures and source-specific beam similarity into the model's input space. Furthermore, we propose a novel 3D architecture termed TransUNetSE3D, featuring
Transformer blocks for global context and Residual Squeeze-and-Excitation (SE) modules for adaptive channel-wise feature recalibration. Hierarchical representations of these blocks are fused into the network's latent space alongside the primary dose-map parameters, allowing physics-aware reconstruction. This hybrid design outperforms existing UNet and
Transformer-based
benchmarks in both spatial precision and structural preservation, while maintaining the execution speed necessary for real-time use. Our proposed pipeline achieves a Gamma Passing Rate exceeding 98% (3%/3mm) compared to the MC reference, evaluated within the framework of a treatment planning system (TPS) using 6MV TrueBeam Lineac Accelerator (LINAC) for prostate radiotherapy. These results offer a robust solution for fast volumetric dosimetry in adaptive radiotherapy.
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All authors Chi-Hieu Pham, Didier Benoit, Vincent Bourbonne, Ulrike Schick, Dimitris Visvikis, Julien Bert
Computational Physics · Cross-listed from cs.LG
EquiformerV3: Scaling Efficient, Expressive, and General SE(3)-Equivariant Graph Attention Transformers
Yi-Lun Liao, Alexander J. Hoffman, Sabrina C. Shen et al. (+3 more)
As $SE(3)$-equivariant graph neural networks mature as a core tool for 3D atomistic modeling, improving their efficiency, expressivity, and physical consistency has become a central challenge for large-scale applications. In this work, we introduce EquiformerV3, the third generation of the $SE(3)$-equivariant graph
attention Transformer, designed to advance all three dimensions: efficiency, expressivity, and generality. Building on EquiformerV2, we have the following three key advances. First, we optimize the software implementation, achieving $1.75\times$ speedup. Second, we introduce simple and effective modifications to EquiformerV2, including equivariant merged layer normalization, improved feedforward network hyper-parameters, and
attention with smooth radius cutoff. Third, we propose SwiGLU-$S^2$ activations to incorporate many-body interactions for better theoretical expressivity and to preserve strict equivariance while reducing the complexity of sampling $S^2$ grids. Together, SwiGLU-$S^2$ activations and smooth-cutoff
attention enable accurate modeling of smoothly varying potential energy surfaces (PES), generalizing EquiformerV3 to tasks requiring energy-conserving simulations and higher-order derivatives of PES. With these improvements, EquiformerV3 trained with the auxiliary task of denoising non-
equilibrium structures (DeNS) achieves state-of-the-art results on OC20, OMat24, and Matbench Discovery.
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All authors Yi-Lun Liao, Alexander J. Hoffman, Sabrina C. Shen, Alexandre Duval, Sam Walton Norwood, Tess Smidt
Accelerator Physics
Markus Zerlauth and Oliver Brüning
In this paper we will provide an overview of the
hadron colliders built to date and the design and operational challenges that each of these machines has faced. Many of these are inherent to the ongoing effort to optimise the instantaneous and integrated luminosity of the machines, which inevitably lead to many technological challenges that must be met and overcome. We will summarise how these challenges have been successfully met in the past and present machines and outline the role they could play in ambitious future accelerator projects such as the HL-LHC upgrade and the FCC project.
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Optics · Cross-listed from cond-mat.quant-gas
Ultrafast All-Optical Switching via a Supersolid Phase Transition of Light
J. L. Figueiredo, J. T. Mendonça and H. Terças
We propose ultrafast all-optical switching exploiting the bistability between a spatially uniform
photon superfluid and a spontaneously ordered supersolid in a driven-dissipative microcavity. The key ingredient is a tunable nonlocal
photon–
photon interaction engineered by
embedding a high-mobility two-dimensional electron gas (2DEG) inside the cavity. A drift current displaces the
Fermi disk, imparting a negative region to the Lindhard interaction kernel at finite wavevectors and triggering a roton instability. The resulting bistable $S$-curve supports a write–hold–erase protocol in which short optical pulses toggle the system between branches with a switching contrast of order 120~dB in our simulations. The hysteretic ON state persists under a constant sub-threshold drive after the write pulse is removed, realizing an all-optical bistable
memory. Since the
photon field couples additively to each embedded
quantum well, stacking layers with distinct drift angles allows the roton profile to be engineered with higher-order
symmetries, imprinting richer spatial order on the supersolid and enabling nonbinary generalizations of the switch. Operating in the ultrafast, sub-fJ regime, this platform outperforms most existing all-optical switches in contrast and reconfigurability.
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Instrumentation and Detectors
Controlled beams of cryo-cooled protein-like nanoparticles
Jingxuan He, Karol Długołecki, Hubertus Bromberger et al. (+2 more)
We report a cryogenic buffer-gas-
cell-aerodynamic-lens-stack setup that enables the generation of shock-frozen, dense, and controllable beams of various nanoparticles in the gas phase, including small and low-density species such as isolated
proteins. We demonstrate characterization of the setup using strong-field ionization combined with velocity-map imaging, allowing the unambiguous detection of nanoparticles in the
protein-size range and full reconstruction of the particle beams including determination of particle flux and number density. The generation and characterization workflow presented here provides a valuable approach for
protein-like sample preparation and delivery in single-particle diffractive imaging, microscopy, and low-temperature nanoscience.
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All authors Jingxuan He, Karol Długołecki, Hubertus Bromberger, Amit K. Samanta, Jochen Küpper
Optics
Spectra of laser diodes
Bjarne Tromborg and Palle Jeppesen
This paper provides an introduction to the theory of
semiconductor laser diodes, with special focus on their noise properties. It may be considered an additional chapter to the textbook [1]. As such, it will also refer to equations in that book.