Chemical Physics
From Full Dynamic to Pure Static: A Family of $GW$-Based Approximations
Pierre-François Loos and Johannes Tölle
We introduce a systematic hierarchy of one-body Green's function methods derived from the $GW$ approximation, constructed by progressively reducing the dynamical content of the self-energy. Starting from the fully dynamical Dyson formulation, we generate a family of approximations that interpolates between the standard $GW$ approximation to purely static effective single-particle
Hamiltonians. This framework enables a controlled investigation of the role of dynamical effects and particle-hole coupling in the description of ionization potentials. Within this unified formalism, the hole and particle branches can be selectively decoupled through downfolding strategies into reduced one-particle spaces. By benchmarking the different members of this hierarchy on molecular ionization energies, we assess their accuracy, numerical robustness, and algorithmic complexity. We demonstrate that consistently derived partially static schemes can yield reliable quasiparticle energies while significantly simplifying the underlying
eigenvalue problem. We further introduce a novel static Hermitian self-energy obtained as the static limit of this hierarchy. Despite its conceptually distinct origin, it produces results remarkably close to those of qs$GW$, thereby providing an alternative static route toward partial self-consistency.
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Optics · Cross-listed from quant-ph
Kirkwood-Dirac distributions in classical optics
Alfredo Luis and Lorena Ballesteros Ferraz
We develop a comprehensive analysis of the Kirkwood-Dirac distributions in classical optics, revealing their deep connection with optical coherence as fundamental concept in optics. From their very definition, the Kirkwood-Dirac distributions emerge as generalized mutual coherence functions involving two different bases instead of just one. This perspective provides a unified interpretation of the so-called anomalous values, that are complex and negative values, as direct manifestations of coherence. We show that this interpretation consistently applies across all field variables considered in this work, including polarization, interference and wave propagation. Furthermore, we propose diverse methods of experimental determination of these distributions based on interference, in full agreement with their coherence-based interpretation.
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Fluid Dynamics
Preferential orientation of slender elastic floaters in gravity waves
Wietze Herreman, Basile Dhote and Frederic Moisy
Slender floaters drifting in propagating
gravity waves slowly rotate towards a preferential state of orientation with respect to the angle of incidence. This angular drift arises from a wave-induced, second order mean yaw moment. We develop a diffractionless, hydro-elastic theory to compute this mean yaw moment for a thin, flexible structure whose width and thickness are small compared with the wavelength. For floater lengths smaller than half the wavelength, we derive a simple, predictive criterion for the preferred orientation: Soft, short and heavy floaters prefer the longitudinal state, while stiff, long and light floaters prefer the transverse state. For floaters longer than the wavelength, the orientational dynamics become more intricate and may exhibit multiple
equilibrium states. We discuss the implications of the model for flexible floating structures such as pontoons and inflatable structures.
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Plasma Physics
Anderson Localization of Ion-Temperature-Gradient Modes in Aperiodic Stellarators
Amitava Bhattacharjee
The
geometric coefficients of the ion-temperature-gradient (ITG) eigenmode equation along a
magnetic field line are aperiodic because the line samples the full three-dimensional geometry. Starting from a reduced fluid model for drift waves [Phys. Fluids 26, 880 (1983)], we show that aperiodic stellarator geometry leads to a quasiperiodic Hill equation for the ITG mode structure. In a tight-binding approximation this equation reduces to an Aubry–André–Harper difference equation, suggesting an Anderson-localization mechanism for ITG eigenfunctions. For the continuous equation the localization threshold is identified by the onset of a positive Lyapunov exponent of the transfer
matrix at the drift-wave-resonant
eigenvalue. The result is a structural property of the
eigenvalue problem and is obtained on the drift-wave-resonant branch of the fluid model, at weak global and local
magnetic shear. We discuss what bearing, if any, this transition may have on the observed clamping of the ion temperature in stellarators, a question that is not settled by this theory.
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Biological Physics
Active Transport as a Mechanism of Microphase Selection in Biomolecular Condensates
Le Qiao, Peter Gispert, Lukas S. Stelzl et al. (+1 more)
The size and organization of biomolecular condensates formed by
liquid-
liquid phase separation (LLPS) are set by multiple cellular mechanisms that are not yet fully understood. Here we identify a transport-driven mechanism:
stochastic binding of phase-separating
proteins to cytoskeletal motor
proteins, followed by active redistribution along filament networks, generates an effective long-range repulsion that arrests coarsening and selects a finite condensate size. A minimal
diffusion-transport model, analyzed by linear stability theory and three-dimensional simulations, reveals a transition from macroscopic to microphase separation at remarkably low binding/release fractions, corresponding to minute motor-bound populations. Tuning motor binding rates $b$ or transport velocities enables sublinear control of condensate sizes ($L \sim b^{-1/4}$) from a few hundred nanometres up to the micron scale. The selected length scale is robust to the intrinsic shot noise of the binding–release reactions. In anisotropic cytoskeletal environments, transport asymmetry drives morphological transitions from spherical to cylindrical condensates, independently of the thermodynamic parameters. This mechanism provides a versatile, spatiotemporally programmable route to condensate organization and informs the design of synthetic active emulsions with tunable architectures.
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All authors Le Qiao, Peter Gispert, Lukas S. Stelzl, Friederike Schmid
Instrumentation and Detectors
Characterization of afterpulse in SiPMs with single-cell readout as a function of bias voltage and fluence
P. Parygin, E. Garutti, E. Popova et al. (+1 more)
We present a detailed investigation of the afterpulse effect in silicon photomultipliers (SiPMs), using a dedicated structure with single-
cell readout. This enables direct measurement of intrinsic device properties and observation of individual pulses even after irradiation. Three independent analysis methods to quantify afterpulse induced events were developed and validated by Monte Carlo simulations. The first method is based on charge integration, while the other two methods use multiple linear regression to reconstruct transient waveforms and accurately identify individual pulse positions. These positions are then used either as direct event counts or to construct time interval distributions, enabling comprehensive characterization of the afterpulse probability and providing insights into the dynamics of trapping in silicon. Using this framework, we measured three SiPM samples: one fresh reference device and two irradiated devices exposed to reactor
neutron fluences of 2e12 and 1e13 cm^-2. We report systematic measurements of the afterpulse probability and time constant as functions of bias voltage and irradiation fluence. For overvoltages in the range of 3 to 5 V above breakdown, the afterpulse time constant is found to be below 10 ns and the afterpulse probability below 6%. Both quantities show no significant dependence on irradiation fluence.
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All authors P. Parygin, E. Garutti, E. Popova, J. Schwandt
Optics
Electrically-driven chiral emission from plasmonic tunnel junctions
Yuanyang Xie, Alexey V. Krasavin and Anatoly V. Zayats
Chirality plays a crucial role in a broad range of processes including light-matter interactions in physics, chemistry and biology, which opens up new applications in nanophotonics,
quantum technologies and photochemistry.
Quantum tunnelling provides a promising mechanism for light generation at the nanoscale, however the realisation of
chiral light emission has remained elusive. Here, by integrating tunnel junctions with
chiral plasmonic nanohelicoids, we achieve nanoscale generation of
chiral light at a single-particle level. The tunnelling-driven resonant excitation of
chiral dipolar modes of the nanohelicoids results in emission of a
vortex light beam possessing both
spin angular momentum with handedness selectivity of over 0.8 and its orbital counterpart, equal in magnitude and opposite in sign. The developed approach offers a new means for sculpturing
photon spin generation at the nanoscale, highlighting its potential for next-generation optical components in display and AR/VR applications, as well as
quantum information processing and photochemistry.
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Instrumentation and Detectors
SPIROS: Streamlined, Precise, Intuitive, and Rapid Optical Simulator for particle physics detectors
Tatsuya Kikawa
This paper presents SPIROS (Streamlined, Precise, Intuitive, and Rapid Optical Simulator), a dedicated optical simulation tool developed for the design and analysis of particle physics detectors. Unlike general-purpose frameworks such as GEANT4, SPIROS offers a lightweight simulation engine and a user-friendly interface optimized for optical processes, including scintillation, Cherenkov emission, and
photon transport with reflection, refraction, scattering, absorption, and detection. Detector geometries can be directly imported from 3D CAD models, and all configurations including materials, surfaces, sources, and sensors are specified via a single human-readable input file. Validation against GEANT4 shows excellent agreement in
photon generation and propagation behaviors, while
benchmark tests demonstrate that SPIROS runs more than two times faster for typical detector configurations. The software has already been applied to multiple
neutrino experiments, including T2K, NINJA, and AXEL, for detector design, performance studies, and optimization. SPIROS is open-source and freely available at https://github.com/tkikawa/spiros.
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Optics
Yellow whispering-gallery-mode lasing from amorphous fluoride microspheres
Abhishek Sureshkumar, Jonathan Demaimay, Georges Perin et al. (+7 more)
Compact, low-noise coherent light sources in the visible remain challenging due to limited gain platforms and inefficient pumping. We report a new route to visible microlasing based on direct, one-
photon blue pumping and an amorphous fluoride gain material platform. Dysprosium doped fluoride microspheres are fabricated via
plasma-torch-induced, pressureless amorphization of single
crystals, enabling compositions beyond conventional glass-forming limits while ensuring ultrasmooth morphology, low
phonon energy, and homogeneous dopant distribution. We demonstrate the first fiber-coupled whispering-gallery-mode lasing from an amorphous fluoride microsphere in the yellow (573 nm), with an ultralow threshold of $190 \mu$W despite
spin-forbidden Dy$^{3+}$ transitions. Lasing is evidenced by characteristic light-light curve indicating a low spontaneous emission factor, narrow-linewidth emission, and relaxation oscillations yielding a loaded quality factor of $Q = 3.5 \times 10^6$. This platform is readily extendable to other rare-earth emitters, enabling entire visible spectral coverage beyond the limitations of upconversion pumping, with prospects for color-tunable and white-light emission. Finally, fiber-based amplification of the WGM signal demonstrates a pathway toward compact, fiber-integrated visible microlasers with controllable noise and linewidth.
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All authors Abhishek Sureshkumar, Jonathan Demaimay, Georges Perin, Christelle Velly, Héléne Ollivier, Yannick Dumeige, Alain Braud, Patrice Camy, Stéphane Trebaol, Pavel Loiko
Optics
Experimental Evidence of Thermal Capillary Waves Excitation on a Microsphere Surface
Abhishek Sureshkumar, Georges Perin, Julien Lapeyre et al. (+7 more)
Whispering-gallery-mode (WGM) microsphere resonators have emerged as a versatile platform across various photonic applications. Despite significant progress, their performance at short wavelengths is fundamentally limited by scattering-induced optical losses that restrict achievable quality factors (Q-factor). Although surface roughness has long been recognised as the leading cause of these losses, its physical origin has remained unclear, with current understanding attributing it to unavoidable fabrication imperfections. Here, we show that thermally excited capillary waves are the fundamental source of scattering losses in microsphere cavities. Using high-resolution atomic force microscopy (AFM) combined with rigorous statistical analysis, we quantitatively identify the characteristic signatures of frozen capillary fluctuations at the sub-nanometre level. The experimentally extracted roughness parameters show close agreement with theoretical predictions based on capillary wave theory. These findings fundamentally revise the prevailing interpretation of surface scattering losses and establish thermodynamic fluctuations, rather than fabrication defects, as the limiting roughness mechanism. By identifying frozen capillary waves as the limiting factor, this work opens new pathways for engineering ultra-high-Q microsphere resonators through fabrication management strategies, particularly for visible- and ultraviolet-photonic applications where scattering losses are most severe.
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All authors Abhishek Sureshkumar, Georges Perin, Julien Lapeyre, Rozenn Bernard, Kelig Terrien, Bertrand Dudoux, Adil Haboucha, Hélène Ollivier, Yannick Dumeige, Stéphane Trebaol
Computational Physics
SMC-AI: Scaling Monte Carlo Simulation to Four Trillion Atoms with AI Accelerators
Xianglin Liu, Kai Yang, Fanli Zhou et al. (+9 more)
The rapid advancement of deep learning is reshaping the hardware design landscape toward AI tasks, posing fundamental challenges for HPC workloads such as atomistic simulation. Here we present SMC-AI, a general algorithmic framework that extends the SMC-X method for efficient canonical Monte Carlo simulation on AI accelerators, including GPUs and NPUs, while maintaining extreme scalability. The implementation of SMC-AI on an NPU cluster reaches unprecedented performance, achieving MC simulation of 4 trillion atoms on 4096 NPU dies. This represents the largest ML-accelerated atomistic simulation reported, delivering 32X system size and 1.3X throughput than previous records, with a relatively small computational budget. Excellent strong and weak scaling efficiency are reached for both the NPU and GPU implementation. By decoupling ML models from simulation, SMC-AI creates an abstraction that facilitates integration and porting of diverse ML models, laying a foundation for the future development of scalable scientific software.
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All authors Xianglin Liu, Kai Yang, Fanli Zhou, Yongxiang Liu, Hao Chen, Yijia Zhang, Dengdong Fan, Wenbo Li, Bingqiang Wang, Shixun Zhang, Pengxiang Xu, Yonghong Tian
Optics
Comparative performance of three optical biosensing platforms for SARS-CoV-2 antibodies detection in human serum
Agostino Occhicone, Alberto Sinibaldi, Peter Munzert et al. (+5 more)
This study presents a rigorous comparative analysis of two label-free optical biosensing platforms, Bloch surface wave (BSW) and microring resonator (MRR), for the detection of SARS-CoV-2 antibodies in human serum. To ensure direct comparability, a new BSW readout system was established alongside an existing MRR platform, allowing assays to be conducted under nearly identical experimental conditions. Both sensors were functionalized with various SARS-CoV-2 Spike and Nucleocapsid
protein variants to capture specific host antibodies. The results demonstrate that both platforms provide rapid, quantitative, and sensitive detection of anti-Spike and anti-Nucleocapsid antibodies without the need for secondary labels. Furthermore, the platforms show excellent agreement with longitudinal serology
benchmarks and high repeatability across different biochip batches. This work establishes both BSW and MRR technologies as powerful, low-cost candidates for next-generation clinical diagnostics and serological surveillance.
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All authors Agostino Occhicone, Alberto Sinibaldi, Peter Munzert, Jordan N. Butt, Ethan P. Luta, Diego M. Arévalo, Francesco Michelotti, Benjamin L. Miller
Classical Physics
Normal contact of metainterfaces: the roles of finite size and microcontact interactions
Donald Zeka, Nawfal Blal, Fatima-Ezzahra Fekak et al. (+3 more)
The design of contact interfaces that meet quantitatively a specified friction law (friction force vs normal force) is challenging due to the multi-scale and multi-physics nature of contact interactions. Recently, a concept was proposed to address this question in the case of dry elastic microarchitected contact interfaces, so-called metainterfaces. These take their macroscopic friction properties from an array of discrete asperities whose geometrical descriptors are optimized through an inverse design phase. Such design is based on the experimentally-observed proportionality between friction force and real contact area under pure compression, reducing the friction problem to a simpler contact mechanics problem of designing the contact area. In this context, the design strategy assumes that asperities are placed on a linear elastic half-space and behave independently from each other. Both assumptions are likely to fail in experimental realizations of metainterfaces, potentially inducing discrepancies between the actual and target behaviours. Here, we use full 3D finite element modelling to critically assess the validity of those two assumptions in existing experimental metainterfaces, and their potential impact on the design quality. The results first confirm the validity of the strategy, in the conditions in which it was used in the literature. Then, by systematically varying the spatial arrangement of asperities, their interdistance and the size of their elastic base, we identify conditions under which the literature assumptions fail. Our findings provide critical insights into the robustness and practical limitations of the metainterface design strategy and guidelines for its future improvements.
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All authors Donald Zeka, Nawfal Blal, Fatima-Ezzahra Fekak, Arnaud Duval, Anthony Gravouil, Julien Scheibert
Instrumentation and Detectors · Cross-listed from hep-ph
Probing Majoron Dark Matter with Gravitational Wave Detectors
Ippei Obata and Tsutomu T. Yanagida
The Majoron is a hypothetical (pseudo) Nambu-Goldstone
boson arising from the spontaneous breaking of a global
lepton number
symmetry, and is known as a candidate for dark matter in our Universe. In this paper, we investigate the possibility of probing the Majoron dark matter with a linear optical cavity used in the interferometric gravitational wave detectors. We consider a scenario in which the Majoron dark matter couples to
photons through a QED anomaly, leading to an oscillatory
photon birefringence induced by the coherent dark matter background. The anomaly coefficient is fixed by requiring the model to simultaneously reproduce the electroweak
Higgs scale and a typical right-handed Majorana
neutrino mass scale, and the resulting dark matter-
photon coupling naturally falls within the sensitivity range of optical interferometers. By incorporating additional optics to extract the birefringence signal, we find that ground-based
laser interferometers such as Advanced LIGO, KAGRA, as well as future detectors, can probe a region of the parameter space of Majoron dark matter.
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Atomic Physics
A vacuum-ultraviolet spectropolarimeter for an electron beam ion trap
Nobuyuki Nakamura, Ryohko Ishikawa and Motoshi Goto
We have developed a
vacuum-ultraviolet spectropolarimeter for an electron beam ion trap (EBIT) to measure the linear polarization of emission lines from multiply charged ions around the Lyman-$\alpha$ wavelength. The main components for polarimetry are a rotatable MgF$_2$ waveplate and a SiO$_2$/MgF$_2$ multilayer-coated fused silica plate that functions as a reflective polarizer. A grazing-incidence grating is mounted between them to provide wavelength dispersion. The polarization is determined from the intensity modulation of the spectral line as the waveplate is rotated. The performance of the spectropolarimeter was demonstrated by measuring the polarization of the $2s$–$2p_{3/2}$ transition in Li-like N$^{4+}$ (124~nm) excited by a 1000~eV electron beam in an EBIT. Clear modulation of the line intensity was observed as a function of the waveplate rotation angle. From the measured modulation amplitude, the degree of linear polarization was determined to be $P=-(0.178^{+0.014}_{-0.005})$, with the negative sign indicating that the emission is polarized predominantly perpendicular to the electron beam. This result demonstrates the capability of the present spectropolarimeter to determine polarizations with an absolute uncertainty $\Delta P$ on the order of $0.01$. This instrument provides a useful tool for benchmarking
magnetic-sublevel-resolved collision theories through polarization measurements of multiply charged ions excited by a unidirectional electron beam.
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Fluid Dynamics
Ultimate regimes in horizontal and internally heated convection
Olga Shishkina and Detlef Lohse
We derive asymptotic models for the ultimate regimes in horizontal convection (HC) and pure internally heated convection (IHC), in analogy with our recent (2024) extension of the ultimate-regime model for Rayleigh-Benard convection (RBC). To derive the corresponding models for HC and IHC, we combine turbulent boundary-layer relations with the exact dissipation balances for these two systems. For HC, the resulting scaling relations are consistent with the rigorous transport bound of Siggers et al. (2004). For pure IHC, they are consistent with the exact HC-IHC balance analogy of Wang et al. (2021) and with the rigorous bounds on the convective-flux asymmetry in the equal-temperature-plates configuration (Arslan et al 2021). The main difference between RBC and HC/IHC is that, in the latter two cases, the global kinetic-energy balance does not contain the additional response factor (dimensionless convective heat flux in HC or inverse bulk temperature in IHC), whereas it does in RBC. As a consequence, for fixed Pr, the ultimate-regime scaling exponent is 1/3 for both HC and IHC, rather than 1/2 as in RBC.
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Optics · Cross-listed from quant-ph
Photon pairs, squeezed light and the quantum wave mixing effect in a cascaded qubit system
R. D. Ivanovskikh, W. V. Pogosov, A. A. Elistratov et al. (+6 more)
We develop a theoretical description of
quantum wave mixing (QWM) in a cascaded waveguide-QED system of two superconducting
qubits, where the probe is driven by an external coherent tone and by the resonance fluorescence of a strongly driven source
qubit. Starting from the field correlation functions of the source emission, we derive an effective master-equation treatment for the probe and identify the regime in which the incident fluorescence is characterized by anomalous correlations. When the coherent Rayleigh component of the source spectrum is suppressed, the probe equations of motion become equivalent to those for a
qubit driven by a coherent tone and broadband squeezed light, although the ligt emitted by the source is non-Gaussian and antibunched. This equivalence implies a selection rule for the peaks of the QWM spectrum, with a strong suppression of sidebands associated with processes involving an odd number of
photons taken from the source field. Numerical simulations of the full cascaded two-
qubit model for different ratios of radiative decay rates unambiguously confirm the participation of correlated
photon pairs in QWM processes. The current research illustrates that the analysis of peak amplitudes can be used to probe
photon statistics in the incident nonclassical field.
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All authors R. D. Ivanovskikh, W. V. Pogosov, A. A. Elistratov, S. V. Remizov, A. Yu. Dmitriev, T. R. Sabirov, A. V. Vasenin, S. A. Gunin, O. V. Astafiev
Chemical Physics
Crossing Seam Blockade
Ruoxi Liu, Xiaotong Zhu and Bing Gu
Electronic degeneracies and near-degeneracies including conical intersections and avoided crossings, typically accompanied by strong vibronic couplings and nonadiabatic transitions, play fundamental roles in photochemical, photophysical and photobiological processes. However, its implications on excited-state chemical reactivities are not fully understood. In this theoretical study, we report a surprising phenomena that an open reaction channel can be completely blocked by a crossing seam in the molecular configuration space. Specifically, by numerically exact ab initio nonadiabatic full
quantum geometrical molecular dynamics simulations, we show that the singlet fission channel in the hydrogen chain H4, previously identified as a minimal model for singlet fission, is blocked due to electronic
quantum geometry. We provide a chemically intuitive picture to understand this effect. Our results not only reveal a new mechanism for controlling photochemical reactions, but may also elucidate the mechanism of singlet fission.
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Optics
Spatiotemporal Co-reflection with Spacetime Discontinuities at Moving Interfaces
Yongge Wang, Jingfeng Yao, Chengxun Yuan et al. (+1 more)
The control of reflection and refraction at interfaces using engineered media is central to numerous optical technologies, with negative refraction and the suppression of backscattering representing two prominent research frontiers. In this work, we demonstrate that an effective negative refraction accompanied by an absence of backscattering can be realized at a moving spatiotemporal interface when temporal and spatial reflections occur concurrently. While such spatiotemporal co-reflection is prohibited in one-dimensional linear dispersive media, we show that it becomes permissible under oblique incidence within a specific range of traveling-wave modulation velocities. Leveraging this mechanism, we propose a spatiotemporal flat lens capable of nonreciprocal electromagnetic wave focusing. These findings provide a framework for developing advanced spatiotemporal metamaterials and time-varying metasurfaces.
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All authors Yongge Wang, Jingfeng Yao, Chengxun Yuan, Zhongxiang Zhou
Computational Physics
Direction-aware topological descriptors for elastic stiffness tensor prediction in porous materials
Rafał Topolnicki, Michał Bogdan, Jakub Malinowski et al. (+3 more)
Classical topological descriptors used in topological data analysis (TDA) are invariant under permutations of spatial axes and therefore cannot represent the loading direction, which is essential for modeling anisotropic mechanical response. Here, this limitation is addressed by introducing a direction-aware TDA framework in which the loading axis is explicitly embedded into filtration functions used to compute both persistent homology and Euler characteristic profile descriptors. We apply this framework to predict the full elastic stiffness tensor of porous microstructures using non-directional as well as direction-aware descriptors of the structures as well as convolutional neural networks trained directly on the voxelized structure. We show that the performance of all those are comparable on the diagonal uniaxial, Poisson, and shear components. However for the twelve off-diagonal, normal shear coupling components - which govern elastic anisotropy and are the hardest to predict - only direction-aware
topology retains meaningful predictive power, with all baselines, non-directional descriptors and the CNN collapsing to near-chance accuracy. When used as inputs to gradient-boosted tree models, the proposed descriptors match or exceed the accuracy of the convolutional neural network specifically on these hardest-to-predict coupling terms, despite relying on a compact, physically interpretable representation that is orders of magnitude smaller than the raw voxel grid. Overall, the results establish direction-aware TDA as a practical route for linking porous microstructure to the full anisotropic elastic response, capturing coupling terms that conventional descriptors and end-to-end deep learning models fail to resolve.
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All authors Rafał Topolnicki, Michał Bogdan, Jakub Malinowski, Bartosz Naskręcki, Maciej Harańczyk, Paweł Dłotko
Computational Physics
Reinforcement learning with reputation-based adaptive exploration promotes cooperation
An Li, Wenqiang Zhu, Chaoqian Wang et al. (+5 more)
Reinforcement learning provides a framework for studying how individuals adjust their behavior through repeated interaction and feedback in social dilemmas. In Q-learning, exploration controls how often
agents choose actions other than those favored by their current learned Q-values. Yet existing models usually treat the exploration rate as a constant parameter. In systems with social evaluation, however, trial-and-error behavior carries different costs and opportunities for
agents with different reputations, making exploration dependent on social standing rather than uniform across
agents. Herein, we develop a spatial prisoner's dilemma model in which Q-learning
agents adapt their exploration rates according to local reputation differences, while reputation is updated through an asymmetric, state-dependent rule. Results show that adaptive exploration and asymmetric reputation updating each promote cooperation, but their combination produces a stronger reinforcing effect than either mechanism alone. Low-reputation
agents explore more and can recover reputation through cooperation, while high-reputation
agents explore less and avoid reputation losses caused by defection. This mechanism also reorganizes cooperation in space, producing a stable checkerboard-like coexistence at intermediate reputation concern. In addition, cooperation is most vulnerable at intermediate baseline exploration rates, whereas stronger asymmetric reputation updating mitigates this exploration-induced disruption. These results suggest that reputation can act not only as a record of past behavior, but also as a dynamic signal that regulates exploratory behavior during learning and thereby stabilizes cooperation.
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All authors An Li, Wenqiang Zhu, Chaoqian Wang, Longzhao Liu, Hongwei Zheng, Yishen Jiang, Xin Wang, Shaoting Tang
Medical Physics
Predicting Mesoscopic Larmor Frequency Shifts in Ex Vivo Porcine Optic Nerve
Anders Dyhr Sandgaard, André Pampel, Roland Müller et al. (+7 more)
Larmor frequency shifts in white matter (WM) vary with fiber orientation due to anisotropic microstructure. Since clinical voxels are significantly larger than these microscopic frequency variations, the measured signal represents a bulk average of local shifts. Accurate estimation of
magnetic susceptibility therefore requires accounting for these underlying frequency distributions that exist below the imaging resolution. We evaluated whether Microstructure-informed Quantitative Susceptibility Mapping ({\mu}QSM) can predict orientation-dependent sub-voxel frequency shifts from orientationally dispersed hollow cylinders and spherical inclusions.
Diffusion-weighted and multi-gradient-echo images were acquired from ex vivo pig optic nerves at multiple orientations relative to the main
magnetic field using a 3T Siemens Connectom scanner. We also analyzed de-ironed optic nerves to try and separate the effects of myelin and iron on susceptibility. The estimated sub-voxel frequency shifts closely matched {\mu}QSM predictions, consistent with mesoscopic field perturbations generated by uniformly magnetized axons. De-ironing had minimal effect on the frequency shifts, indicating negligible iron contribution. {\mu}QSM accurately reproduces the orientation dependence of Larmor frequency shifts in optic nerve WM, providing new insight into their microstructural origin and supporting improved estimation of tissue
magnetic susceptibility in Quantitative Susceptibility Mapping.
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All authors Anders Dyhr Sandgaard, André Pampel, Roland Müller, Niklas Wallstein, Toralf Mildner, Carsten Jäger, Markus Morawski, Aage Kristian Olsen Alstrup, Harald E. Möller, Sune Nørhøj Jespersen
Computational Physics · Cross-listed from cs.CV
Tensor-Augmented Convolutional Neural Networks: Enhancing Expressivity with Generic Tensor Kernels
Chia-Wei Hsing and Wei-Lin Tu
Convolutional Neural Networks (CNNs) excel at extracting local features hierarchically, but their performance in capturing complex correlations hinges heavily on deep architectures, which are usually computationally demanding and difficult to interpret. To address these issues, we propose a physically-guided shallow model: tensor-augmented CNN (TACNN), which replaces conventional convolution kernels with generic tensors to enhance representational capacity. This choice is motivated by the fact that an order-$N$ tensor naturally encodes an arbitrary
quantum superposition state in the
Hilbert space of dimension $d^N$, where $d$ is the local physical dimension, thus offering substantially richer expressivity. Furthermore, in our design the convolution output of each layer becomes a multilinear form capable of capturing high-order feature correlations, thereby equipping a shallow multilayer architecture with an expressive power competitive to that of deep CNNs. On the Fashion-MNIST
benchmark, TACNN demonstrates clear advantages over conventional CNNs, achieving remarkable accuracies with only a few layers. In particular, a TACNN with only two convolution layers attains a test accuracy of 93.7$\%$, surpassing or matching considerably deeper models such as VGG-16 (93.5$\%$) and GoogLeNet (93.7$\%$). These findings highlight TACNN as a promising framework that strengthens model expressivity while preserving architectural simplicity, paving the way towards more interpretable and efficient deep learning models.
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Fluid Dynamics
Effects of Soret diffusion on the intrinsic instability of premixed hydrogen/air flames
Qizhe Wen, Yan Wang, Linlin Yang et al. (+4 more)
Hydrogen flames exhibit multiple intrinsic instabilities. The low molar masses of H and H2 lead to significant Soret
diffusion near the flame front; however, its influence on hydrogen flame instabilities remains to be quantified. This study investigates the effect of Soret
diffusion on instability
evolution dynamics via one-dimensional counterflow analysis and two-dimensional, high-fidelity direct numerical simulations covering both the linear growth regime and the fully developed nonlinear regime over a wide range of equivalence ratios (phi). In the linear regime, Soret
diffusion increases the perturbation growth rate at phi < 1.7, especially under lean conditions, but reduces the growth rate at phi > 1.7. A similar sensitivity reversal is observed in the Markstein length near the peak equivalence ratio of unstretched laminar flame speed. In the nonlinear regime, Soret
diffusion accelerates the formation of small-scale wrinkles in lean hydrogen flames and reduces the characteristic size of large-scale finger structure by one-third. An interesting observation is that, although Soret
diffusion promotes preferential
diffusion and increases the local flame displacement speed, the global fuel consumption rate decreases due to a reduction in the overall flame surface area. In addition,
curvature-based flame segment analysis reveals a synergistic effect between Soret
diffusion and Fickian
diffusion that enhances/reduces the local equivalence ratio in positively/negatively curved regions of the flame front. The probability distributions of the Karlovitz number and the density-weighted displacement speed are also analyzed; results suggest that, for lean hydrogen flames, Soret
diffusion broadens the distributions for both parameters, particularly on the positive side. These findings promise to advance the fundamental understanding of hydrogen flame dynamics under complex differential transport.
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All authors Qizhe Wen, Yan Wang, Linlin Yang, Youhi Morii, Thorsten Zirwes, Shengkai Wang, Zheng Chen
Atmospheric and Oceanic Physics
Dissipating the correlation smokescreen: Causal decomposition of the radiative effects of biomass burning aerosols over the South-East Atlantic
Emilie Fons, Isabel L. McCoy, Tom Beucler et al. (+2 more)
Biomass burning aerosols (BBAs) from Southern Africa seasonally overlie the semi-permanent South-East Atlantic (SEA) stratocumulus deck, impacting the region's energy budget through complex aerosol-cloud-radiation-meteorology interactions.
Climate model intercomparison initiatives, like the Aerosol Comparisons between Observations and Models (AeroCom), have highlighted the large inter-model variability for BBA radiative effects, especially over the SEA, due to parameterization of emission modeling and smoke properties. Observational constraints are needed to reduce these uncertainties, but correlative observational studies are typically affected by confounding meteorological influences. We propose a physically informed statistical approach, based on causal graphs applied to satellite observations, to disentangle BBA influences on shortwave radiation over the SEA and identify the main sources of statistical biases plaguing observational studies. We find that, during the fire season, BBAs cause a regional shortwave cooling of -2.5 W m$^{-2}$, which can be decomposed into equal contributions from three physical pathways: aerosol-radiation interactions (ARI), adjustments to ARI, and aerosol-cloud interactions (ACI). We also perform ablation experiments with graph variants to investigate the main sources of confounding - like large-scale winds, humidity-biased
retrievals or spatial aggregation of data - and show that they result in biased radiative effect estimates (between -50 $\%$ and +15 $\%$). Once free of such biases, our derived causal estimates of smoke radiative effects can be used as observational constraints to improve
climate models.
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All authors Emilie Fons, Isabel L. McCoy, Tom Beucler, David Neubauer, Ulrike Lohmann
Fluid Dynamics
Cavity-Stabilized Rotating Flames in a Circular Hele-Shaw Burner
Xiangyu Nie and Shengkai Wang
We report direct experimental observations of self-organized rotating flames of premixed CH4 and air in an open circular Hele-Shaw burner equipped with an annulus cavity flame holder. These flames formed spontaneously at sufficiently low flow rates, where flame flashback was counteracted by thermal quenching, resulting in a dynamic balance between the local flame speed and flow velocity. Unlike flames propagating in closed micro-channels, these flames exhibited stable traveling-wave patterns with heads gliding along the leading edge of the cavity, where rapid expansion created a low-speed zone that facilitated flame stabilization. At low flow rates, the rotating flames were single-headed, with their rotation frequencies roughly proportional to the laminar flame speeds, suggesting that the flame fronts traveled in a nearly constant-shape fashion. As the flow rate increased, the rotating flames split into multiple heads at approximately equal spacing, and the number of heads and rotation frequency increased with the flow rate, until these rotating flames transitioned into steady ring-shaped flames anchored at the cavity leading edge. Blow-off or extinction occurred at sufficiently high flow rates, where the flame front was pushed out of the rear side of the cavity. Parametric measurements were conducted over a wide range of equivalence ratios and flow rates, from which a regime diagram of different flame modes and their transition boundaries was obtained. Additional experiments were conducted on C3H8 and DME. It was found that the critical total mass flow rate at the rotating-steady flame transition boundary is insensitive to equivalence ratio, gap distance, and fuel type. These results should be useful not only for the fundamental understanding of flame dynamics in micro-channels but also for the practical design of micro-combustors and the application of micro-combustion technologies.
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Optics
On-Chip Interferometric Excitation of an Infinity-Loop Microresonator
Davide Olivieri, Bülent Aslan, Stefano Biasi et al. (+2 more)
Integrated photonics is a powerful platform for exploring Hermitian and non-Hermitian physics. Beyond device geometry, controlling how resonators are driven is crucial to access and tailor their modes. Coherent excitation via multiple input ports (interferometric excitation) enables such control, but its accurate description requires extending standard temporal coupled-mode theory to include interference between excitation pathways. Experimental realizations have so far been limited by phase-unstable, off-chip interferometers. Here we implement a fully integrated, phase-stable interferometric excitation scheme for an infinity-loop microresonator, an established structure operating on an exceptional surface, and use it to test the extended theory. Phase-dependent measurements in the linear and thermo-optic nonlinear regimes show that the relative phase between inputs governs the intracavity energy distribution, enabling up to a twofold increase of the circulating power compared to single-port excitation. This integrated platform enables reproducible studies of phase-dependent effects and coherent-control schemes in non-Hermitian photonic devices.
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All authors Davide Olivieri, Bülent Aslan, Stefano Biasi, Riccardo Franchi, Lorenzo Pavesi
Fluid Dynamics
Spatiotemporally Resolved Multi-Scalar Measurements of Methane Tulip Flames in a Square Channel
Zeyu Yan and Shengkai Wang
Understanding the propagation dynamics of premixed flames in confined spaces is important for fire safety in gas pipelines and for optimizing modern internal combustion engines. In sufficiently long channels, premixed flames routinely develop tulip flame structures, yet the dominant mechanism remains elusive, and quantitative data on the
evolution of flame morphology and key scalar fields are critically needed to improve the explanation, characterization, and modeling of tulip flame dynamics. In this study, premixed flames of a stoichiometric methane/air mixture were investigated in a square channel at a reduced pressure of approximately 0.3 atm. Time-synchronized, multi-plane, dual-color PLIF measurements yielded a spatiotemporally resolved 3-D
dataset of key scalar fields, including temperature and OH concentration, throughout the formation and
evolution of the tulip structure. Significant heat loss across the walls counteracted the heat released by combustion, producing a near-constant-pressure environment throughout the experiment. A super-
equilibrium distribution of OH concentration was observed in the thermal boundary layers, suggesting that thermal cooling dominated over chemical relaxation in those regions. Additionally, the flame-front morphology at five representative times was determined using a 3-D reconstruction
algorithm, from which the flame surface area was extracted. The results of this study should aid theoretical modeling and numerical simulations of premixed flame propagation dynamics in confined spaces under realistic boundary conditions.
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Fluid Dynamics
Porosity and Material Disorder Drive Distinct Channelization Transition
André F. V. Matias, Rodrigo C. V. Coelho, Humberto A. Carmona et al. (+2 more)
Flow through porous media can reshape the medium through erosion and deposition, producing preferential flow channels across a wide range of natural and industrial systems. Yet the mechanisms by which spatial disorder triggers channelization remain unclear. Here we derive a continuum description for the coupled
evolution of flow and porosity by coarse-graining pore-scale dynamics and validating the resulting model with pore-scale simulations. Using this framework, we show that different sources of disorder lead to qualitatively distinct behaviors. Disorder in erosion resistance produces a discontinuous transition to localized flow, with permanent channels appearing only above a finite disorder strength. In contrast, even extremely weak fluctuations in the initial porosity destabilize homogeneous flow and trigger persistent channelization. These results reveal an unexpected sensitivity of evolving porous media to structural heterogeneity, suggesting that channelization can arise generically even in nearly uniform materials.
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All authors André F. V. Matias, Rodrigo C. V. Coelho, Humberto A. Carmona, José S. Andrade Jr., Nuno A. M. Araújo
Space Physics · Cross-listed from astro-ph.SR
Chromospheric turbulence as a regulator of stellar wind mass flux
Munehito Shoda, Tom Van Doorsselaere and Allan Sacha Brun
The mass flux of
solar and
stellar winds is a key quantity for
stellar evolution and space weather, yet its physical regulation mechanism remains an unsolved problem. In particular, conventional Alfvén wave–driven models that self-consistently connect the
stellar surface to the
stellar wind fail to reproduce the observed scaling between
stellar X-ray flux and mass-loss rate, a discrepancy that can be largely attributed to the dissipation of a substantial fraction of the wave energy by chromospheric
turbulence. To address this issue, we aim to clarify the role of chromospheric
turbulence in regulating the
stellar wind mass flux. We perform one-dimensional wave-driven wind simulations, comparing cases with and without chromospheric
turbulence suppression to assess its impact on coronal and wind properties. We find that suppressing chromospheric
turbulence leads to a systematic increase in the coronal particle flux, and hence the wind mass flux, by up to an order of magnitude, particularly in regions of moderately strong
magnetic field. This behavior arises from a combination of changes in the Poynting flux at the coronal base and in the asymptotic wind speed. Furthermore, the model with chromospheric
turbulence suppression reproduces the observed empirical scaling between coronal
magnetic field strength and mass flux without invoking additional energy input mechanisms such as interchange reconnection. These results identify the chromospheric
turbulence as a key factor in regulating
stellar wind mass flux and highlight the importance of incorporating its effects in models that connect the
stellar surface and the
stellar wind.
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