Optics · Cross-listed from cond-mat.dis-nn
Non-Hermitian Delocalization Realizes Random Dirac Criticality in One Dimension
Bo Li, Shen Zhang and Ren Zhang
Non-Hermitian systems can evade Anderson localization and exhibit delocalized states even in one dimension. Here, we show that such non-Hermitian delocalized states under periodic boundary conditions (PBC) are intrinsically critical, realizing the universality class of one-dimensional random Dirac
fermions. By linking spectral winding to topological Anderson transitions via Hermitization, we demonstrate that the delocalized PBC states exhibit a Dirac-type criticality with universal algebraic correlations. In contrast to Hermitian systems, where this criticality occurs only at fine-tuned transition points, it emerges generically in non-Hermitian systems as a consequence of spectral
topology. These results identify a universal mechanism by which non-Hermiticity promotes criticality, providing a unified description of non-Hermitian delocalization in one dimension.
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Atomic Physics
Limit on the nuclear Schiff moment of europium-153
Bassam Nima, Mingyu Fan, Xubo Wang et al. (+6 more)
The Schiff moment of a
nucleus is a
symmetry-violating
nuclear moment that indicates new physics beyond the Standard Model. We place the limit, $|\mathscr{S}({}^{153}$Eu)$| < 1.7 \times 10^{-8}$ $e\,$fm$^3$ (95% confidence), on the Schiff moment of the $^{153}$Eu
nucleus, using
nuclear spin resonances in two ensembles of oppositely-polarized $^{153}$Eu$^{3+}$ ions in a Y${}_2$SiO${}_5$
crystal. This measurement using octupolar
nuclei in a mm-scale
crystal constrains new physics at the TeV energy-scale.
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All authors Bassam Nima, Mingyu Fan, Xubo Wang, Sen Wang, En Fu Zhou, Andrew M. Jayich, Jiang Ming Yao, Lan Cheng, Amar Vutha
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Multilayer Screening of Double and Conventional Perovskite Solar Cells Using SCAPS-1D and Machine Learning: Optimization of ETL, HTL, and Absorber for High-Efficiency Architectures
Neda Nasiri, Seyed Mahdi Mastoor and Amirhosein Ahmadkhan Kordbacheh
The combinatorial design space of multilayer perovskite
solar cells is vast, yet exhaustive experimental or computational screening of all possible material combinations remains impractical. Here, we integrate SCAPS-1D device simulations with machine learning to systematically explore 125 device architectures constructed from five electron transport layers (ETL), five absorbers (including lead-free double perovskites), and five hole transport layers (HTL). A representative subset of configurations is used to train a machine learning (ML) model, which predicts the power conversion efficiency (PCE) of the remaining unexplored structures. Leave-One-Group-Out cross-validation yields a Spearman rank correlation, demonstrating reliable ranking capability. SHAP (SHapley Additive exPlanations) analysis reveals that the HTL band gap, absorber band gap, and ETL electron affinity are the most influential descriptors, providing physical insights into interfacial recombination and charge extraction. The machine learning model identifies several high-performance configurations that are subsequently verified by full SCAPS-1D simulations. Among them, the device FTO/TiO$_2$/Cs$_2$AgBiBr$_6$/NiO/Ag achieves a PCE of 28.85%, and the ML-suggested structure FTO/SnO$_2$/Cs$_2$AgInBr$_6$/NiO/Ag exhibits 28.62%, outperforming a closely related literature architecture by approximately 4% absolute. Notably, eight of the top-11 structures employ the lead-free double perovskite Cs$_2$AgInBr$_6$. This work demonstrates that a physics-based, data-driven workflow combining SCAPS-1D, ML, and SHAP can accelerate the discovery of high-efficiency, environmentally friendly perovskite
solar cells while providing transparent design rules. The approach is generalizable to other multilayer optoelectronic systems.
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Optics
Low-symmetry lattices of non-chiral meta-atoms for resonant handedness-preserving reflection
Anastasia Pozharkova, Oleg Blokhin, Sergey A. Dyakov et al. (+1 more)
Mirrors that preserve the handedness of optical radiation upon reflection are an essential building block for the design of numerous resonant nanophotonic structures with capabilities for enantiomeric discrimination. Ordinary metallic and Bragg dielectric mirrors are not suitable in these context since they flip handedness of electromagnetic field upon reflection around normal incidence. While there has been considerable progress in the development of such reflecting structures, this research area remains largely unexplored. Here, we present a detailed numerical and theoretical analysis of the potential of low-
symmetry periodic
lattices composed of high-
symmetry non-
chiral meta-atoms for resonant reflection with handedness preservation (HP). Using full-wave numerical simulations, we analyze a family of rhombic and monoclinic (oblique)
lattices of circular dielectric disks and/or holes, and in each identify the regime of near-perfect HP reflection. We study the robustness of these structures to
geometric deviations, material losses, and incidence angle. Finally, we describe the resonant HP response of these structures using the coupled-mode theory formalism.
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All authors Anastasia Pozharkova, Oleg Blokhin, Sergey A. Dyakov, Denis G. Baranov
Fluid Dynamics · Cross-listed from cond-mat.soft
When and how particles are removed by drops
Abhinav Naga, Franziska Sabath, Doris Vollmer et al. (+1 more)
Particulate contaminants decrease the power output of
solar panels, the transparency of windows, and are detrimental to microelectronics, where even a single particle can induce a short
circuit. Despite significant research on particle adhesion and self-cleaning, it remains unclear when and how a drop can remove a particle from a surface, thus efficiently cleaning the surface. Here, by combining
lattice Boltzmann simulations and confocal microscopy experiments, we show that at least six different scenarios arise from the complex interplay between capillary and friction forces when a drop collides with a particle on a surface. Notably, the capillary force plays a dual role in particle removal: while its tangential component always drives removal, its normal component can also hinder it. We introduce a dimensionless capillary capture parameter that successfully predicts particle removal across a wide range of particle and surface properties. Our results reveal that the design of easy-to-clean surfaces should not focus only on maximizing hydrophobicity, but also on minimizing the particle-surface friction.
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All authors Abhinav Naga, Franziska Sabath, Doris Vollmer, Halim Kusumaatmaja
Instrumentation and Detectors
Modeling of Dark Count Probability in Perimeter-Gated SPADs
Md Sakibur Sajal, Ziyad Alswaidan, Tathagata Srimani et al. (+1 more)
This Letter presents a novel analytical framework showing that the dark count probability (PDC) of perimeter-gated single-
photon avalanche diodes (pg-SPADs) follows a complementary Gompertz function. Specifically, we show that PDC follows a complementary Gompertz form from which we derive a pixel-specific descriptor, the midpoint perimeter gate voltage, which characterizes a pixel's equiprobable operating point. We further show that a perimeter gate voltage compensation rate may be obtained from this descriptor to offset temperature-induced changes in the pixel's activation function. The proposed framework is experimentally validated using 4,096 pg-SPADs arranged in a 64 x 64 array and manufactured in a 0.35 $\mu$m CMOS process. The devices were characterized at temperatures ranging from -5 $^o$C to 55 $^o$C and perimeter gate voltage magnitudes of 0 to 5 V. The measured results demonstrate deterministic bias control of dark count probability across process and temperature variations.
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All authors Md Sakibur Sajal, Ziyad Alswaidan, Tathagata Srimani, Marc Dandin
Optics · Cross-listed from cond-mat.mes-hall
Reflective Metastructure Q-plate for Ultrashort Laser Pulses
Christopher G. O. Weiß, Bert Lägel, Benjamin Stadtmüller et al. (+2 more)
The orbital angular momentum of light is an intriguing property for developing light driven applications. It emerged as an independent degree of freedom by which to manipulate light and, consequently, the interaction of light with matter. Several methods exist for the generation of light carrying orbital angular momentum, mostly employing transmitting or reflecting optical components, which radially modulate the phase profile of the light. As one of such components, transmissive q-plates established themselves as standard elements due to their usability over a broad wavelength range. Here, we present our approach to build a highly reflective q-plate based on a plasmonic metasurface capable of converting orbital angular momentum from the nanostructure to ultrashort
laser pulses without temporal broadening. We highlight its working principle over a wide range of wavelengths for reflection under normal and gracing incidence.
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All authors Christopher G. O. Weiß, Bert Lägel, Benjamin Stadtmüller, Martin Aeschlimann, Tobias Eul
Data Analysis and Statistics · Cross-listed from math.SP
Generalizing Perron–Frobenius theory and eigenvector-based centralities to networks with complex edge weights
Yu Tian, Mason A. Porter and Lucas Böttcher
A fundamental concept in linear
algebra and its applications to network analysis is the Perron–Frobenius (PF)
theorem, which underpins eigenvector-based centrality measures such as eigenvector centrality, PageRank, and hubs and authorities. By invoking the PF
theorem, we know for strongly connected networks with positive edge weights that the eigenvector corresponding to the largest
eigenvalue of the weight
matrix yields a well-defined centrality measure (namely, eigenvector centrality). Traditional formulations of the PF
theorem and associated centrality measures assume that networks have real-valued weights. However, many networks in areas such as
quantum information,
quantum chemistry, electrodynamics, and machine learning have complex-valued edge weights. In this paper, we study generalizations of the PF
theorem to complex-valued
matrices, establish connections between these generalizations, and propose generalized eigenvector-based centrality measures to analyzing node importances in networks with complex edge weights. We also prove results about the existence of complex-weighted networks that satisfy generalized PF properties and calculate associated centrality measures for several examples, which we draw from application areas such as electron transport,
circuit analysis, mathematical chemistry, and communication networks.
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Physics and Society
Emergent dilemma and periodic oscillation in the nonlinear interplay between epidemic and behavior
Longzhao Liu, Hongwei Zheng, Yajing Hao et al. (+3 more)
Human behaviors, particularly non-pharmaceutical interventions (NPIs), are dynamically coupled with epidemic spreading. While prior studies mainly assume a linear interplay, real-world behavioral
evolution is driven by nonlinear responses and social influence. Here, we incorporate these multifaceted mechanisms into a co-evolutionary model and analytically derive the critical thresholds. Notably, as the infection rate grows, NPI compliance initially rises but then abruptly drops to zero. This paradoxical decline indicates an emergent social dilemma: at high infection rates, abandoning NPIs is individually optimal but detrimentally triggers an explosive surge in epidemic prevalence. We further show that socially induced overestimation of the infection rate can counterintuitively
prompt individuals to abandon NPIs. Moreover, the interplay with social influence induces periodic oscillations, reflecting a tragic cycle of recurrent epidemic waves. Furthermore, we validate the robustness of this NPI-abandonment dilemma in networked population. Our work illustrates rich emergent phenomena in the co-
evolution of epidemic and behavior, challenging traditional views on this coupled dynamics.
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All authors Longzhao Liu, Hongwei Zheng, Yajing Hao, Qun Wang, Xin Wang, Shaoting Tang
Computational Physics · Cross-listed from cs.LG
HAMNO: A Hierarchical Adaptive Multi-scale Neural Operator with Physics-Informed Learning for Dynamical Systems
Mostafa Bamdad, Mohammad Sadegh Eshaghi and Timon Rabczuk
Neural operators provide a powerful framework for learning solution mappings of partial differential equations directly in function space. However, many existing architectures still struggle to represent nonlinear time-dependent systems that involve multi-scale structures, long-range interactions, and stable long-time
evolution. In this work, we introduce the Hierarchical Adaptive Multi-scale Neural Operator (HAMNO), a neural-operator architecture that combines local convolutional representations, global spectral operators, and hierarchical encoder-decoder processing. The central component of HAMNO is a data-dependent gating mechanism that adaptively balances local and global information at each spatial location, allowing the model to resolve fine-scale features while preserving long-range dependencies. We further develop a physics-informed extension, PI-HAMNO, based on a multi-objective loss strategy that combines data fitting with strong- and weak-form physics constraints. The strong-form term penalizes the domain-integrated squared PDE residual in physical coordinates, while the weak-form term is constructed by multiplying the governing residual by finite-element test functions and evaluating the resulting element integrals using centroid-based tetrahedral quadrature. The framework is evaluated on non-periodic Allen-Cahn (AC), Cahn-Hilliard (CH), and Swift-Hohenberg (SH) equations defined on cubic domains. Across long-horizon rollout, data-limited training, out-of-distribution initial-condition shifts, and random-seed variations, HAMNO improves predictive accuracy over standard neural-operator baselines, while PI-HAMNO further enhances stability, physical consistency, and data efficiency. The implementation is publicly available at https://github.com/MBamdad/HAMNO .
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Boron Co-Alloying in AlScN Wurtzite Ferroelectrics: Insights from an 850-Sample Combinatorial Study
Federica Messi, Nathan Rodkey, Manuel Kober-Czerny et al. (+1 more)
AlScN wurtzite ferroelectrics are promising candidates for energy-efficient non-volatile
memory. However, AlScN suffers from a high coercive field and reduced cycling endurance, and the limited tunability of its properties constrains further optimization. Co-doping AlScN with boron offers the promise of independently tailoring the chemical and structural properties, making AlScBN an attractive quaternary system. This material has already been explored for a few selected compositions, however, no systematic study of the full AlScBN compositional space exists. A combinatorial approach consisting of gradient deposition with HiPIMS at low temperatures of 250{\deg}C and automatic analysis of film properties allowed us to analyze a total of 850 unique samples within the AlScBN phase space. In addition to a full screening of the materials' chemical and structural properties, we fabricate and characterize combinatorial device libraries. XPS charge transfer analysis experimentally confirms that bond ionicity correlates with a reduction in the coercive field for AlScN and AlScBN systems, opposite trends are instead observed for AlBN. While the films maintain a high remanent polarization of 130-150 {\mu}C/cm2, Sc and B co-doping reduces the coercive field from 7 MV/cm to 3 MV/cm. Notably, B co-alloying lowers the amount of Sc needed to lower the coercive field, reducing reliance on this scarce element. In addition, we find that co-alloying with B, notably improves cycling endurance, which is related to a reduction in defect density. These results establish AlScBN as a scalable, CMOS-compatible ferroelectric, positioning it as an interesting alternative to AlScN.
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All authors Federica Messi, Nathan Rodkey, Manuel Kober-Czerny, Sebastian Siol
Optics · Cross-listed from quant-ph
Controlled ion-ion interactions and cavity-enhanced emission of a coherent dinuclear Eu$^{3+}$ complex
Evgenij Vasilenko, Vishnu Unni Chorakkunnath, Barbora Brachnakova et al. (+4 more)
Molecular rare-earth-ion complexes offer unique opportunities for
quantum technologies by combining the intrinsic coherence properties of rare-earth ions with chemically tunable molecular environments. A crucial capability is the realization of multi-
qubit architectures with defined
qubit couplings to enable two-
qubit quantum gates. Here, we investigate the optical coherence properties and excitation-induced interactions of two Eu$^{3+}$-based molecular complexes, comparing a mononuclear reference system with a dinuclear analogue in which two Eu$^{3+}$ ions are positioned at a well-defined intramolecular distance of about 7 Angstrom. Using cryogenic ensemble spectroscopy, including spectral hole burning, free-induction decay, and
photon echo measurements at temperatures down to 100 mK, we demonstrate long optical coherence times $T_{2,\text{o}}$ of up to 9 $\mu$s. As a key step toward scalable multi-
qubit architectures, a control-target sequence was implemented to probe conditional ion-ion interactions, revealing a stronger interaction-induced dephasing in the dinuclear complex. Finally, we show the integration of the dinuclear complex into a fiber-based optical microcavity, and observe an 380-fold emission enhancement of the $\mathrm{}^5\mathrm{D}_0\rightarrow\mathrm{}^7\mathrm{F}_0$ transition. Together, these results position molecular rare-earth complexes as versatile and chemically tunable building blocks for scalable
quantum technologies.
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All authors Evgenij Vasilenko, Vishnu Unni Chorakkunnath, Barbora Brachnakova, Nicholas Lester Jobbitt, Senthil Kumar Kuppusamy, David Hunger, Mario Ruben
Physics Education
A Thematic Analysis of A-level Physics Examiner Reports on Gravity
Corey McInerney
Examiner reports from six major UK exam boards published between 2017 and 2025 are analysed using a mixed-methods thematic analysis. Focusing on questions relating to
gravity, the objective is to understand where students commonly drop marks. Findings reveal that the source of difficulty is dependent upon topic and question style. Mathematical errors account for the majority of lost marks in calculation-type questions, while a lack of conceptual understanding commonly results in lost marks on questions relating to fields, energy and gravitational potential. Pedagogical strategies for teaching
gravity must emphasise algebraic skills for orbital mechanics topics while prioritising qualitative modelling and precise definitions for field theory.
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Applied Physics
Enhancement of nitride-based solar cells using graphene as transparent contact layer
Miriam Cadenas, Mireia Martínez, Kerly Sánchez et al. (+5 more)
The effect of using a
graphene layer as a semitransparent contact layer is studied in
solar cells based on AlInN on Si (100) substrates. The devices consist of AlxIn1-xN layers deposited on p-type Si (100) substrates incorporating a thin amorphous silicon (a-Si) buffer layer to improve the heterointerface quality. Three aluminum contents are studied, namely: x=0.22, 0.35 and 0.43. Subsequently, a monolayer
graphene film was transferred onto the front surface of the devices using a simple and low-temperature transfer process, acting as a semitransparent conductive contact. The photovoltaic characteristics were then evaluated under illumination and dark conditions in devices with and without the
graphene layer. The results show that the incorporation of
graphene leads to a clear improvement in the short-
circuit current density, fill factor, and overall power conversion efficiency for all studied compositions, while the open-
circuit voltage remains largely unaffected. These findings demonstrate the potential of
graphene as an effective transparent conductive contact for nitride-based
solar cells.
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All authors Miriam Cadenas, Mireia Martínez, Kerly Sánchez, Jordi Ibáñez, Sergi Hernández, Sirona Valdueza-Felip, Ana M. Diez-Pascual, Fernando B. Naranjo
Optics
Self-Pulsing Microring Resonator Networks for Bandwidth-Efficient Event Detection in an Optical Fiber Sensor
Alessio Lugnan, Yonas Seifu Muanenda, Ilya Auslender et al. (+4 more)
The native processing of time-dependent signals from optical sensors by integrated photonic
circuits can potentially bring significant advantages in terms of energy consumption, latency and processing power, as it allows skipping or reducing the use of fast digital electronics and directly exploiting optical degrees of freedom and parallelism. However, due to a short
memory, optical operations usually struggle to directly process optical signals with relatively slow (<MHz) dynamics from optical sensors. In this work, we experimentally show that these limitations can be overcome by exploiting the self-pulsing dynamics in a microring resonator (MRR) network. In particular, we demonstrate that such dynamics can expand and retain information about perturbations sensed by a fiber sensor. This reduces the minimum sampling rate for the digitization of the sensor signal by at least one order of magnitude. The reduction is achieved by combining fiber sensing measurements at two different perturbation locations and frequencies with MRR network measurements at multiple output ports, input power levels and
laser wavelengths. This work represents a first step in bridging time-dependent optical processing and optical sensing at sub-{\mu}s time scales.
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All authors Alessio Lugnan, Yonas Seifu Muanenda, Ilya Auslender, Stefano Biasi, Claudio J. Oton, Fabrizio Di Pasquale, Lorenzo Pavesi
Atomic Physics · Cross-listed from cond-mat.quant-gas
Quantum tidal locking in orbiting Bose-Einstein condensates
Yaoyuan Fan, Shuoyu Shi, Lang Cao et al. (+7 more)
Angular momentum coupling manifests widely in diverse physical systems, underpinning the emergent properties and collective dynamics across different scales. The
tidal locking, which originates from the synchronization of rotational and orbital motions, has far-reaching impacts in celestial mechanics, reflecting fundamental processes of angular momentum transfer, energy dissipation, and
evolution toward dynamical
equilibrium. However, its counterpart in mesoscopic
quantum fluids has remained largely unexplored. Here we demonstrate the emergence of
quantum tidal locking in Bose-Einstein condensates undergoing central force motion in an anharmonic potential. The condensate follows a well-defined orbital trajectory in a static trap and experiences an effective rotating potential induced by the trap anharmonicity. The sustained
geometric squeezing continuously deforms the condensate and drives a self-organized synchronization process, in which the intrinsic rotation gradually locks to the orbital motion. Numerical simulations further reveal the formation of a ring-shaped
vortex array over longer timescales, arising from the coherent
evolution of the rotating matter wave during the locking dynamics. Our findings establish
quantum tidal locking in mesoscopic systems as a robust self-organized mechanism for generating and stabilizing circulating states.
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All authors Yaoyuan Fan, Shuoyu Shi, Lang Cao, Ziyue He, Qiuxin Zhang, Dong Hu, Yu Wang, Qing Wang, Tianwei Zhou, Xiaoji Zhou
Computational Physics · Cross-listed from cond-mat.stat-mech
Universal Information-Theoretic Structure of the Quasi-Stationary Domany–Kinzel Automaton
Hyun-Yong Lee, Kenji Harada and Naoki Kawashima
We characterize the quasi-stationary distribution (QSD) of the bond directed-percolation line of the Domany–Kinzel automaton using a
matrix-product-state representation of the probability distribution, obtained by projecting out the absorbing state and iterating the transfer
matrix. Unlike moment- or sampling-based methods, this yields the full conditional distribution and direct access to information-theoretic diagnostics. The spatial structure of the QSD changes sharply across the transition: the active phase is bulk-like with finite density, whereas in the inactive phase the surviving activity collapses into a single flock – the smallest interval containing all active sites – occupying a vanishing fraction of the chain. Throughout the inactive phase the bipartite mutual information of the QSD equals the
entropy of a single binary choice – whether the flock lies to the left or right of the cut – so the surviving clusters together encode just one bit of positional information, corresponding to a single effective cluster.
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Fluid Dynamics
Thin-film drainage becomes singular at saddles
Simeon Djambov, Alice Marcotte, François Gallaire et al. (+1 more)
From coating curved parts to creeping lava, thin-film gravitational drainage over complex surfaces can produce abrupt accumulation, usually associated with sharp edges or defects. Here, experiments, simulations and asymptotics show that a smooth saddle alone generates a logarithmically singular ridge, regularized within a dynamic region where drainage balances hydrostatic pressure and capillarity. In a Newtonian lubrication picture, this mechanism can inform redistribution in manufacturing and geophysics, motivating extensions to complex rheology and interacting
geometric features.
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All authors Simeon Djambov, Alice Marcotte, François Gallaire, Pier Giuseppe Ledda
Space Physics
Extreme, transient bursts of energy in the auroral ionosphere. II. A magnetotail dipolarization event
Magnus F Ivarsen, Yukinaga Miyashita, Brian Pitzel et al. (+5 more)
We report ground-based coherent VHF radar observations of extreme turbulent field-structures detected in coincidence with a magnetospheric substorm-associated magnetotail dipolarization. The field-structures are observed by the ICEBEAR radar, in the form of Farley-Buneman (FB) waves in the auroral electrojets, and the field-structures themselves move an order of magnitude faster than the saturation speed of the underlying FB waves, implying transient electric field sources up to 330 mV/m in strength. The field-structures are identified and automatically tracked using an unsupervised clustering & tracking
algorithm, applied to clutters of ICEBEAR radar backscatter targets, a method that turns the Doppler radar into a tracking radar capable of measuring the ionospheric ExB-drift by proxy. We place this finding in a coordinated multi-instrument context. Three THEMIS spacecraft observed the dipolarization event in-situ in the near-Earth
plasma sheet. In the ionosphere, Swarm A, crossing through the guilty auroral arc at the onset of the dipolarization event, recorded clear signatures of propagating Alfvén waves threading the relevant flux tube. We interpret the ICEBEAR transients as the natural ionospheric foot signature of a shear Alfvén pulse launched by the bipolar space-charge (
Hall) electric field of the thinned current sheet, with amplification along the converging flux tube, partial reflection at the ionospheric boundary, and spatial sharpening by precipitation-produced Pedersen-conductance gradients on the auroral arc edges. A one-dimensional wave-transmission analysis recovers the observations. Our results elucidate a tightly controlled coupling between magnetotail processes and meter-scale auroral
plasma turbulence, and demonstrate the capability of ICEBEAR to resolve extreme, transient electric-field enhancements in the ionosphere.
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All authors Magnus F Ivarsen, Yukinaga Miyashita, Brian Pitzel, Jean-Pierre St-Maurice, Jaeheung Park, Devin R Huyghebaert, Yangyang Shen, Glenn C Hussey
Biological Physics · Cross-listed from cond-mat.soft
Pinned Boundaries Delay Contraction and Shape Stress Relaxation in Active Gels
Aniket Marne, James Clarke, Aravind Rao et al. (+6 more)
Cells dynamically generate, transmit, and dissipate stress. Central to these processes is the actomyosin cortex, an active contractile material that drives cellular mechanical behavior. While prior studies have focused on freely contracting actomyosin systems, the role of mechanical constraints such as adhesion to boundaries remains less explored. To address this, we employ reconstituted actomyosin gels to investigate cellular contractility. We study contraction dynamics under pinned boundary conditions, where the gel is adhered transversely to two opposing surfaces, mimicking supracellular actomyosin networks in tissues and embryos. We find that pinned contraction leads to stress buildup, delaying contraction, producing intermittent dynamics, and generating spatially nonuniform strain fields. Stress is relieved through several pathways, including active-stress-driven symmetric constriction and defect-driven processes such as boundary detachment and internal rupture. We develop a hydrodynamic model incorporating elastic, viscous, and active stress contributions that distinguishes between stress-accumulation and stress-release phases and links variations in active stress to the observed intermittent dynamics. The model predicts distinct energy relaxation rates before and after detachment events, providing insight into stress dissipation. We compare experiments with numerical simulations, which reproduce the observed behavior and reveal how internal energy is generated and dissipated during stress buildup and relaxation. Together, our results demonstrate how boundary conditions and spatial heterogeneity govern the mechanical behavior of contractile active gels. These findings provide insight into stress regulation in cellular and tissue-scale systems and may inform the design of adaptive soft materials and bioinspired robotic systems.
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All authors Aniket Marne, James Clarke, Aravind Rao, Hyunjae Lee, Kyla Wong, Aditya Sriram, Rae Robertson-Anderson, Moumita Das, José Alvarado
Geophysics
Breakdown of the classical rupture theory and earthquake propagation in the "forbidden" super-Rayleigh range
Anna Pomyalov, Fabian Barras and Eran Bouchbinder
Earthquakes propagating faster than the shear wave-speed are commonly thought to undergo a super-shear transition upon which they discontinuously jump from the sub-Rayleigh regime to the super-shear one. The super-Rayleigh regime, i.e., the range of propagation speeds between the Rayleigh and shear wave-speeds, is regarded as "forbidden" by the two-dimensional classical rupture theory. Here, we revisit the assumptions underlying the classical theory and develop a rupture theory that takes into account the dependence of the fault strength (frictional resistance) on the slip rate. The theory quantitatively agrees with numerical simulations nearly up to the Rayleigh wave-speed. Yet, very close to the latter, two-dimensional rupture solutions change their character due to frictional rate nonlinearity and rupture continuously propagates through the "forbidden" super-Rayleigh range into the super-shear regime, without a sharp super-shear transition. These results demonstrate that frictional rate dependence, generically observed in experiments, can have profound implications for fast earthquake propagation.
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Classical Physics · Cross-listed from cond-mat.soft
Nonlinear Mechanics and Predictable Bifurcation of Multi-Cell Kresling Origami Chains
Songlin Yue, Leo de Waal, David Garcia Cava et al. (+1 more)
Meta-structures that display axial-twist coupling can be achieved through the emerging kinematics in Kresling origami patterns. A central challenge in these structures is understanding their nonlinear mechanical behaviour, specifically their
equilibrium branches and bifurcation diagrams. This involves identifying relationships between desired responses and the
geometric variables that define the design space, including the Kresling polygon count, initial twist angle, height, radius, and crease lengths. As the number of constituent units increases in an n-layer chain, we track complex
equilibrium branches extending into the post-critical regime under successive instabilities, including branch-point bifurcations and limit-point instabilities. This work begins by establishing the relationship between the
geometric design variables and the response curves of the assembled chain by modelling the crease lines as axial-load-carrying elements. Subsequently,
equilibrium branches and instabilities are systematically investigated via continuation and bifurcation analysis, beginning with the single-layer system and progressively extending to two- and three-layer configurations. Finally, a generalisation strategy is proposed to extend these findings to an n-layer Kresling chain. This strategy enables the predictive construction of
equilibrium paths and the inverse design of multi-layer meta-structures, using prescribed critical points to control post-critical behaviour. It provides a foundation for the inverse design and optimisation of architected mechanical metamaterials with programmable responses.
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All authors Songlin Yue, Leo de Waal, David Garcia Cava, Marcelo A. Dias
Plasma Physics
VEQ: a fast parametric Grad–Shafranov solver for fixed-boundary tokamak equilibria with flexible source profiles
Ruohan Zhang, Huasheng Xie, Yueyan Li et al. (+3 more)
Veloce
EQuilibrium (VEQ) is a compact parametric framework for tokamak modeling workflows that repeatedly query continuous fixed-boundary
equilibria at low latency. The VEQPy implementation evaluated here is an axisymmetric fixed-boundary Grad-Shafranov solver whose main solve enforces a variationally induced projected residual. Its active unknowns are MXH-type flux-surface harmonics and shifted-Chebyshev coefficients for radial profile and source closures. Six input routes accept pressure-gradient, toroidal-field-function, poloidal-flux-gradient, enclosed toroidal current, current-density and safety-factor information through route-specific closures, while all routes map to the same finite-dimensional residual operator. Controlled tests show route consistency for smooth, mutually compatible inputs generated from a common reference
equilibrium. For Pareto-selected reduced configurations in three G-EQDSK cases, the most accurate selected rows correspond to a D-shaped case (9 active parameters, minor-radius-normalized shape error 1.4e-3, solve-only median 1.6 ms), an H-mode case (65, 1.1e-3, 19 ms), and an X-point case treated as a smoothed fixed-boundary representation of a diverted boundary (94, 1.9e-3, 15 ms). Sampled pointwise strong-form Grad-Shafranov diagnostics show that enriching the active representation mainly improves interior force balance, whereas the global RMS and maximum values for the H-mode and X-point cases remain dominated by near-boundary contributions. In an isolated one-dimensional transport-geometry coupling test against the target geometry read from G-EQDSK, the temperature-profile response remains below about one percent. These results support using VEQ for repeated
equilibrium-geometry queries, provided that pointwise diagnostics are retained to screen cases requiring boundary refinement, local correction or higher-fidelity
equilibrium solves.
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All authors Ruohan Zhang, Huasheng Xie, Yueyan Li, Weiqi Meng, Feng Wang, Zhengxiong Wang
Optics
Multi-pulse accumulation of gas molecular coherence enables gigahertz ultrafast frequency conversion
Yazhou Wang, Marcello Meneghetti, Ian Davidson et al. (+8 more)
Frequency conversion of ultrafast
lasers is fundamentally constrained by the trade-off between pulse energy and repetition rate. Here, we demonstrate a frequency conversion mechanism in which molecular coherence accumulates across ultrafast pulse trains in gas-filled hollow-core fibers. Unlike conventional nonlinear interactions initiated by individual high-energy pulses, this mechanism relies on the collective buildup of coherent molecular oscillations driven by successive pulses. Using this approach, we achieve Raman frequency conversion at repetition rates up to 3 GHz with nanojoule pulse energies. The results demonstrate that accumulated molecular coherence can govern nonlinear frequency conversion, revealing a domain of light-matter interaction whose physical limits remain largely unexplored.
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All authors Yazhou Wang, Marcello Meneghetti, Ian Davidson, Timothy Bate, J. E. Antonio-Lopez, Qiang Fu, Jaroslaw Rzegocki, Gregory T. Jasion, Rodrigo Amezcua-Correa, Francesco Poletti, Christos Markos
Chemical Physics
Symplectic and Thermodynamically Consistent Molecular Dynamics in the Frequency Domain
Kyunghoon Han, Alexandre Tkatchenko and Joshua T. Berryman
We introduce
Fourier integrator molecular dynamics (FIMD), a method for propagating selected vibrational motion of
Hamiltonian systems stably and reversibly in time while analyzing and controlling dynamics in the frequency domain. This makes band selection and vibrational analysis features of the integrator rather than post-processing steps. We demonstrate the method with classical force fields, a machine-learned force field trained on
quantum data, and semi-empirical
quantum chemistry for CO$_2$ and the capped Ace–Phe–Tyr–NMe peptide. The method reproduces spectra within the chosen band, suppresses out-of-band response, reveals mode coupling, and demonstrates force-field dependence of spectral features, especially for the thermodynamically important low frequencies. FIMD offers an efficient and transparent way to probe the vibrational physics underlying spectroscopic and calorimetric observables.
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Accelerator Physics
Two-dimensional beam compression for sub-femtosecond electron beam generation
Weihang Liu, Shimin Jiang, Xiao Li et al. (+3 more)
Sub-femtosecond electron beams are powerful probes of ultrafast electronic, atomic, and
nuclear dynamics, and promising drivers for ultrashort radiation generation from the extreme-ultraviolet to gamma-ray regimes. However, producing such beams at hundred-MeV energies with pC-level charge remains challenging. Here we develop a two-dimensional beam-compression scheme based on transverse–longitudinal coupling, in which dispersive beam optics convert the small transverse emittance of modern electron beams into an ultrashort bunch length. Linear analysis and particle tracking show that, after the dominant longitudinal and energy-spread contributions are cancelled, the compressed bunch length is governed primarily by transverse beam quality and collective-effect growth. We further derive and verify a scaling model that captures collective-effect-induced bunch-length degradation and provides a charge–energy operating map for sub-femtosecond compression. Start-to-end simulations of a realistic injector-to-compressor beamline produce a 200 MeV, pC-level bunch with a bunch length of 0.45 fs and a peak current of about 3.5 kA. Jitter studies over a broad range of beam energies show that the output bunch-length distribution narrows and then varies only weakly with increasing energy. These results suggest a feasible route toward compact, high-energy attosecond electron beam sources and may provide a basis for future sub-femtosecond radiation sources based on undulator emission or inverse Compton scattering.
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All authors Weihang Liu, Shimin Jiang, Xiao Li, Xingguang Liu, Yi Jiao, Sheng Wang
Atmospheric and Oceanic Physics · Cross-listed from cs.LG
Scalable Deep Learning Framework for Global High-Resolution Land Use Reconstruction
Amirpasha Mozaffari, Marina Castaño, Stefano Materia et al. (+7 more)
Uncertainty in the terrestrial carbon cycle remains a major constraint in
climate projections, partly driven by the uncertainties affecting the land surface representation and variability in Earth system models. To address this limitation, we present a data-driven framework AI4Land, for generating high-resolution historical reconstructions and future projections of key land surface variables. The framework follows a two-phase approach using a U-Net architecture. In the first phase, which is the focus of this work, it reconstructs annual land use and land cover by integrating coarse-resolution scenario data with static geophysical features. In a planned second phase, the resulting high-resolution maps will be used to predict dynamic biophysical variables, particularly leaf area index, at finer temporal scales. Trained on Earth observation data, the models learn to reproduce spatially explicit and physically consistent land surface patterns, extending temporal coverage to periods lacking direct observations. AI4Land was developed and trained on MareNostrum5, demonstrating how GPU-accelerated HPC infrastructure enables global-scale
climate AI pipelines. The final product is a suite of open-source emulators designed for real-time coupling with digital twin platforms, such as those developed under the Destination Earth initiative. By delivering realistic and evolving land surface conditions on demand, this work aims to reduce critical uncertainties and improve the predictive power of next-generation
climate simulations.
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All authors Amirpasha Mozaffari, Marina Castaño, Stefano Materia, Etienne Tourigny, Oscar Molina-Sedano, Jordi Varela-Agrelo, Dario Garcia-Gasulla, Miguel Castrillo Melguizo, Mario Acosta, Amanda Duarte
Fluid Dynamics
Geometry-induced self-excited dynamo in a regular tetrahedron
Akira Kageyama
We present a rotation-free magnetohydrodynamic dynamo driven by laminar thermal convection in a regular tetrahedral cavity. The tetrahedral boundaries organize the convective flow into a robust pattern of helical convection
cells without global rotation or
turbulence. Direct numerical simulations demonstrate exponential amplification of a weak seed
magnetic field followed by nonlinear saturation. In the reference calculation, the saturated
magnetic energy exceeds the kinetic energy. The velocity field develops $D_4$ dihedral
symmetry, while the self-generated
magnetic field exhibits a corresponding signed $D_4$
symmetry, including antisymmetry under $\pi$ rotations about the two horizontal axes. Analysis of the velocity and
magnetic-field structures reveals a closed induction cycle sustained by geometry-induced helical convection. This system provides a conceptually simple setting for isolating and understanding the fundamental physical processes underlying magnetohydrodynamic dynamo action.
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Applied Physics
Intercoupling of bulk acoustic streaming and acoustothermal effect: A high-frequency focused beam example
Shiyu Li and Zhixiong Gong
High-frequency focused acoustic beams are promising for selective trapping of
cells in fluids, but the related acoustic absorption may generate large acoustothermal effect which could cause thermal heating on
cells or microparticles and bring extra acoustic body force due to the thermal gradient. The theory of the bulk acoustic streaming and acoustic radiation force in a focused-beam for the three-dimensional selective trapping of a
cell has been developed [Li and Gong, Phys. Rev. Fluids, 11, 054201 (2026)], however, the acoustothermal effect and its feedback on the acoustic field at high frequency with strong absorption remain weakly understood. To solve this issue, we develop a theoretical and numerical model that couples acoustic propagation, bulk acoustic streaming, and acoustothermal effect in water. The acoustic body force is decomposed into a viscous-attenuation-induced acoustic body force $\mathbf{f}_{\mathrm{E}}$ and a temperature-gradient-induced acoustic body force $\mathbf{f}_{\mathrm{T}}$, while the temperature field is fed back to the frequency-domain acoustic calculation through the temperature-dependent material properties. Taking the single focused beam for example, within the pressure range constrained by the mechanical index, $\mathbf{f}_{\mathrm{T}}$ remains weaker than $\mathbf{f}_{\mathrm{E}}$, whereas streaming-induced convection can markedly reduce the temperature rise when the thermal Peclet number ($Pe_T$) exceeds unity. This work establishes a theoretical basis for predicting and controlling the intercoupling of bulk acoustic streaming and acoustothermal effec of high-frequency focused beams which will be helpful for the design of single-beam acoustical tweezers.
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Optics
Polarization-Selective Near-Perfect Absorption via Mie-Type Resonance in van der Waals Anisotropic ReS$_2$/$\alpha$-MoO$_3$/Au Heterostructure
Shoumik Debnath and Sudipta Saha
We investigate polarization-selective absorption in a visible-wavelength
heterostructure consisting of a ReS$_2$ stripe grating, an $\alpha$-MoO$_3$ spacer, and an Au back-reflector using finite-difference time-domain simulations. For an optimized geometry with a grating period of 500 nm, stripe width of 250 nm, and ReS$_2$ thickness of 80 nm, the structure exhibits near-unity absorption of 99.99% at 650.5 nm under TE-polarized illumination. The resonant field is concentrated near the outer edges of the ReS$_2$ stripe, while absorption power density is localized in the same region, consistent with a localized edge mode. The absorption response depends strongly on polarization, producing a TE–TM resonance separation of 16.2 nm. Replacing either the biaxial ReS$_2$ layer or the anisotropic $\alpha$-MoO$_3$ spacer with isotropic equivalents substantially modifies the spectral response and reduces the polarization-dependent wavelength separation. In addition, rotating the
crystal orientation of the ReS$_2$/$\alpha$-MoO$_3$ stack shifts both the resonance wavelength and peak absorption without changing the device geometry. The results show that the combination of anisotropic resonator and spacer layers provides an effective means of controlling resonant absorption and polarization selectivity in van der Waals photonic structures.
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