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Physics Physics

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Thursday 8 January

Atomic and Molecular Clusters · Cross-listed from cond-mat.mtrl-sci

Crystal Generation using the Fully Differentiable Pipeline and Latent Space Optimization

Osman Goni Ridwan, Gilles Frapper, Hongfei Xue et al. (+1 more)

We present a materials generation framework that couples a symmetry-conditioned variational autoencoder (CVAE) with a differentiable SO(3) power spectrum objective to steer candidates toward a specified local environment under the crystallographic constraints. In particular, we implement a fully differentiable pipeline to enable batch-wise optimization on both direct and latent crystallographic representations. Using the GPU acceleration, this implementation achieves about fivefold speed compared to our previous CPU workflow, while yielding comparable outcomes. In addition, we introduce the optimization strategy that alternatively performs optimization on the direct and latent crystal representations. This dual-level relaxation approach can effectively escape local minima defined by different objective gradients, thus increasing the success rate of generating complex structures satisfying the target local environments. This framework can be extended to systems consisting of multi-components and multi-environments, providing a scalable route to generate material structures with the target local environment.
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All authors Osman Goni Ridwan, Gilles Frapper, Hongfei Xue, Qiang Zhu

Chemical Physics · Cross-listed from quant-ph

Path Integral Lindblad Dynamics in Presence of Time-Dependent Fields

Amartya Bose

The path integral Lindblad dynamics (PILD) method [A. Bose, J. Phys. Chem. Lett. 15(12), 3363-3368 (2024)] had been introduced as a way of incorporating the impact of certain empirical processes like pumps and drains on the dynamics of quantum systems interacting with thermal environments. The method being based on the time-translational invariance of the Nakajima-Zwanzig memory kernel, however, was not able to account for time-dependent external fields. In this communication, we give an alternate, simpler formulation of PILD, that allows us to go beyond this limitation. It does not require the evaluation of the non-Markovian memory kernel directly, and consequently can be applied to Floquet systems as well.
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Applied Physics

An Adaptive Power Division Strategy for Nonlinear Components in Rectification

Zhongqi He, Liping Yan and Changjun Liu

This letter presents a novel adaptive power division strategy, which uses two rectifying diodes with nonlinear impedance characteristics that are configured in parallel to function optimally at their individual power levels. Through the strategic adjustment of the input admittance, the conductance of the low-power diode decreases progressively with increasing power, while the conductance of the high-power diode increases correspondingly. This conductance-based power allocation method ensures that the power is rectified consistently by the most appropriate diode, regardless of the power level, and, thus, enables efficient rectification across an extended range. This letter presents a rectifier typology to substantiate the proposed strategy. Experimental results confirm the efficiency of the adaptive power division strategy, with the rectifier showing efficiency in excess of 60% from 5 to 29.5 dBm, giving a power dynamic range of 24.5 dB.
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Applied Physics

Reversible vertical positioning of acoustically levitated particle using a spiral reflector

Yusuke Koroyasu, Takayuki Hoshi, Yoshiki Nagatani et al. (+3 more)

Dynamic positioning in acoustic levitation typically depends on active control of the transducers phases, which necessitates complex driving electronics. While mechanically actuated reflectors offer a simpler alternative, achieving reversible transport along the vertical axis solely through mechanical actuation remains challenging. Here, we demonstrate vertical particle translation using a rotating spiral reflector with a half-wavelength pitch. With the rotation axis laterally offset relative to the acoustic focus, the spiral surface functions as a series of translating slopes. Experimental and numerical results confirm stable, bidirectional transport, yielding a vertical displacement of approximately $0.58\lambda$ per revolution and a maximum height of $3.18\lambda$, with radial confinement maintained within $0.24\lambda$. This approach provides a cost-effective solution for non-contact sample handling without active phase control.
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All authors Yusuke Koroyasu, Takayuki Hoshi, Yoshiki Nagatani, Daichi Tagami, Yoichi Ochiai, Tatsuki Fushimi

Fluid Dynamics

Low-wavenumber wall pressure fluctuations in turbulent flows within concentric annular ducts

Yaomin Zhao, Taiyang Wang and Benshuai Lyu

Compressible direct numerical simulations of turbulent channel flows in concentric annular ducts of height $2\delta$ are performed to study the low-wavenumber wall pressure fluctuations (WPF) over cylindrical walls at a bulk Mach number $M_b = 0.4$ and bulk Reynolds number $Re_b=3000$. The radius of the inner cylinder $R$ is varied between $0.2\delta$, $\delta$, $2\delta$ and $\infty$. As $R$ decreases, the one-point power spectral density of the WPF decreases at intermediate but increases at high frequencies. When $R$ decreases, the 1D (streamwise) wavenumber-frequency spectrum of the WPF decreases at high wavenumbers. At low wavenumbers, however, as $R$ reduces to $0.2\delta$ the 1D wavenumber-frequency spectrum exhibits multiple spectral peaks whose strengths increase with frequency. Examination of the 2D wavenumber-frequency spectra shows that these represent acoustic duct modes that closely match theoretical predictions. The acoustic modes of higher radial orders exhibit increasingly high amplitude on the inner than on the outer walls. The low-wavenumber components of the $0$th-order (azimuthal) 2D wavenumber-frequency spectrum are of great importance in practice, and their magnitude increases as $R$ reduces; this increase is increasingly pronounced at higher frequencies. Analytical modelling and numerical validation show that this increase appears to arise from the “geometric” effects connected with the Green's function, and they are generated mainly by radial and azimuthal disturbances. Disturbances closer to the wall are shown to be increasingly important in WPF generation as $R$ reduces, which highlights a potential in WPF control using wall treatment on thin cylinders.
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Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci

Spatial resolution(s) in atom probe tomography

Baptiste Gault, Frédéric De Geuser, Christoph Freysoldt et al. (+2 more)

Atom probe tomography (APT) is often quoted to provide "atomic-scale" analysis of materials in three dimensions. Despite efforts to quantify APT's spatial resolution, misunderstanding remain regarding its true spatial performance. If the depth resolution was once reported to be 20 pm, quoting this value outside of its specific context is misleading and should be avoided. The resolution achievable in pure metals, at one specific location within one reconstructed dataset, does not generally apply across materials or analysis conditions, or even throughout a single tomographic reconstruction. Here, we review various efforts at defining and measuring the spatial resolution in the study of single phase and single element materials - i.e. pure metals - in field-ion microscopy (FIM) and APT. We also report on the degradation of the resolution arising from ion optical devices used to improve the mass-resolution. We aim to offer some perspective as to how reported resolutions may be or may not be of any relevance to most of the materials characterisation efforts by APT, including cases of precipitates in a matrix that emphasise the need to consider an effective resolution. Finally, we discuss concepts to improve the spatial accuracy of the technique in a relatively distant future.
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All authors Baptiste Gault, Frédéric De Geuser, Christoph Freysoldt, Benjamin Klaes, François Vurpillot

Classical Physics

On extracting momentum from supports: the bullet in the beam problem

Xiaoyu Zheng, Tianyi Guo and Peter Palffy-Muhoray

To gain insights into momentum transfer from the supporting environment, we consider the simple problem of a bullet, fired from below, into a wooden beam resting on two supports. The resulting upward velocity of the beam strongly depends on where the bullet enters the beam; this dependence is due to upward momentum extracted by the beam from its supports. Our simple example illustrates the momentum transfer mechanism exploited in the remarkable dynamics of the chain fountain.
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Physics and Society

Towards a Sociology of Sociology: Inequality, Elitism, and Prestige in the Sociological Enterprise From 1970 to the Present

Gavin Cook

There is a science of science and an informal economics of economics, but there is not a cohesive sociology of sociology. We turn the central findings and theoretical lenses of the sociological tradition and the sociological study of stratification inward on sociology itself to investigate how sociology has changed since the 1970s. We link two bibliometric databases to trace diachronic relationships between PhD training and publication outcomes, both of which are understudied in the science of science and sociology of science. All of sociology's top 3 journals remained biased against alum of less prestigious PhD programs, and while most forms of bias in elite sociological publishing have ameliorated over time, the house bias of the American Journal of Sociology in favor PhD alumnae of UChicago has intensified.
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Optics

Ultra-high performance microwave spectral filters using optical microcombs

David J. Moss

Microwave photonic (MWP) filters are essential components in microwave systems due to their wide bandwidth, low loss, and immunity to electromagnetic interference. A sharp transition band is critical for precise spectral shaping and interference suppression, yet conventional MWP filters face challenges in achieving both sharp transitions and high reconfigurability. Adaptive MWP filters with sharp transition based on a transversal filter structure using an optical microcomb source are demonstrated in this paper. Four different types of single-band MWP filters with roll-off rates up to ~32.6 dB/GHz and a minimum shape factor of ~1.15 are achieved. In addition, simply through designing tap coefficients, band-pass filters with tunable centre frequencies ranging from 5 GHz to 15 GHz and dual-band MWP filters with various filter response are demonstrated without changing any hardware, where sharp transition is also validated. The adaptive filters with sharp transition presented in this paper offer a stable and highly reconfigurable solution for applications requiring stringent spectral selectivity, such as next-generation wireless networks, high-resolution radar imaging, and advanced biomedical photonic sensing.
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Optics · Cross-listed from quant-ph

Increasing the secret key rates and point-to-multipoint extension for experimental coherent-one-way quantum key distribution protocol

Venkat Abhignan, Mohit Mittal, Aditi Das et al. (+1 more)

Using quantum key distribution (QKD) protocols, a secret key is created between two distant users (transmitter and receiver) at a particular key rate. Quantum technology can facilitate secure communication for cryptographic applications, combining QKD with one-time-pad (OTP) encryption. In order to ensure the continuous operation of QKD in real-world networks, efforts have been concentrated on optimizing the use of experimental components and effective QKD protocols to improve secret key rates and increase the transmission between multiple users. Generally, in experimental implementations, the secret key rates are limited by single-photon detectors, which are used at the receivers of QKD and create a bottleneck due to their limited detection rates (detectors with low detection efficiency and high detector dead-time). We experimentally show that secret key rates can be increased by combining the time-bin information of two such detectors on the data line of the receiver for the coherent-one-way (COW) QKD protocol with a minimal increase in quantum bit error rate (QBER, the proportion of erroneous bits). Further, we implement a point-to-multipoint COW QKD protocol, introducing an additional receiver module. The three users (one transmitter and two receivers) share the secret key in post-processing, relying on OTP encryption. Typically, the dual-receiver extension can improve the combined secret key rates of the system; however, one has to optimise the experimental parameters to achieve this within security margins. These methods are general and can be applied to any implementation of the COW protocol.
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All authors Venkat Abhignan, Mohit Mittal, Aditi Das, Megha Shrivastava

Fluid Dynamics

Numerical study on fast spectral evolution due to double resonance and applicability of generalized kinetic equation

Mitsuhiro Tanaka

It is known that for a two-layer fluid system, the kinetic equation governing the evolution of the spectrum of the wave field given by the standard wave turbulence theory (WTT) breaks down due to the existence of a "double resonance", and the spectrum can evolve on a time scale much faster than that predicted by the standard WTT. In this study, using a simplified model for a two-layer fluid system, the applicability of the generalized kinetic equation (GKE) for such a situation is examined numerically. It is shown that the GKE can reproduce the appearance of a sharp peak in the surface wave spectrum due to double resonance, but it overestimates the growth of the peak, consequently failing to quantitatively describe the temporal evolution of the spectrum correctly, particularly near the double resonance point.
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Optics

Silicon photonic optical-electrical-optical converters based on load-resistor and current-injection operation

Masaya Arahata, Shota Kita, Akihiko Shinya et al. (+2 more)

Optical-electrical-optical (OEO) converters are key primitives for low-latency, energy-efficient photonic computing because they enable nonlinear activation and optical signal regeneration on chip. We report two monolithically integrated silicon-photonic OEO converters-load-resistor (high-speed variant) and current-injection (high-gain variant) types-fabricated at a silicon photonics foundry. Each device combines a germanium photodetector with a micro-ring modulator (MRM). The converters exhibit reconfigurable nonlinear transfer functions and measurable on-chip RF OEO gain. The RF OEO gain scales linearly with the MRM bias power, with slopes of 0.10 mW^-1 (load-resistor of 10 k{\Omega}) and 1.4 mW^-1 (current-injection), enabling a gain > 1 region at practical bias powers (~10 mW and ~1 mW, respectively). Eye diagrams confirm clear openings up to 4 Gb/s for a high-speed load-resistor variant with a 500-{\Omega} load. To the best of our knowledge, this is the first experimental demonstration of a monolithically integrated, foundry-fabricated silicon-photonic load-resistor type OEO converter exhibiting reconfigurable nonlinear transfer and on-chip RF OEO gain. In the carrier-injection device, the activation slope exceeds unity, yielding 3.9 dB extinction-ratio regeneration. Short-pulse measurements yield 3-dB bandwidths of 1.49 GHz, 160 MHz (load-resistor of 500 {\Omega} and 10 k{\Omega}), and 76 MHz (current-injection), consistent with the RF data. Energy analysis shows an energy-bandwidth trade-off (RC-limited for load-resistor vs. lifetime-limited for injection) and outline routes to sub-pJ/bit operation via reduced capacitance and improved EO efficiency. These results establish silicon-photonic OEO converters as compact, foundry-compatible building blocks for scalable optoelectronic computing and optical neural networks.
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All authors Masaya Arahata, Shota Kita, Akihiko Shinya, Hisashi Sumikura, Masaya Notomi

Fluid Dynamics

Impact force and spreading characteristics of droplet impact on cylindrical surfaces

Mengqi Ye, Tianyou Wang and Zhizhao Che

Droplet impact phenomena are ubiquitous in both nature and industry. Existing studies of droplet impact have focused on the kinematics of droplet impact on flat surfaces, whereas research on cylindrical surfaces remains relatively limited, particularly from a force-based perspective. Here, droplet impact on cylindrical surfaces is studied by numerical simulation, with particular attention to the spreading behavior and impact force acting on the wall. In the deposition mode, a single peak appears in the impact force curve, which corresponds to the rapid transfer of the droplet's initial momentum. In the rebound mode, two distinct peaks are observed, and the second peak arises from the reaction force during the retraction process. Increasing the surface wettability causes the asymmetry coefficient, the ratio of the maximum spreading lengths in the azimuthal and axial directions of the cylinder, to first decrease and then gradually approach a constant, while the effect of the surface wettability on the initial impact force is negligible. As the Weber number We increases, the first dimensionless peak of the impact force $F_{p1}^{*}$ approaches a constant, and the relationship can be expressed as $F_{p1}^{*}={\beta}_1+{{\beta}_2}{{We}^{-1}}$ (where ${\beta }_1$ and ${\beta }_2$ are constants). The dimensionless maximum spreading area, dimensionless maximum spreading length, dimensionless maximum spreading angle, and asymmetry coefficient all exhibit power-law relationships with the Weber and Ohnesorge numbers. Furthermore, an increase in the diameter ratio of the cylinder and the droplet leads to a reduction in the asymmetry coefficient and an increase in the first dimensionless peak of the impact force.
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Optics

Self-heterodyne spectroscopy via a non-uniformly spaced frequency comb

Bofeng Zhang, Gang Zhao, Xiaobin Zhou et al. (+4 more)

Frequency comb spectroscopy has significantly advanced molecular spectroscopy across scientific research and diverse applications. Among its key performance metrics especially for time-resolved studies, sensitivity and measurement speed are paramount. However, a long-standing compromise between these parameters arises from the need for noise reduction. Here, we introduce a comb spectroscopy system that overcomes this limitation using a single frequency comb of non-uniformly spaced modes. The comb is generated using an extremely simple setup, composed of a continuous-wave (CW) fiber laser and a single-sideband phase modulator (SSM). Our approach delivers optical-to-radio-frequency conversion comparable to dual-comb spectroscopy (DCS) but through a simplified self-heterodyning architecture. By leveraging the intrinsic mutual coherence of the comb, this design achieves a noise-equivalent absorption coefficient (NEA) of 5.0*10^(-6) Hz^(-1/2)–an order-of-magnitude improvement over state-of-the-art DCS, coupled with long-term stability. The system resolves weak molecular overtone spectra on nanosecond timescales, in a single-shot measurement, at a signal-to-noise ratio of 128. This integration of high sensitivity, resolution, and speed resolves the core trade-off that has long constrained time-resolved spectroscopic analysis.
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All authors Bofeng Zhang, Gang Zhao, Xiaobin Zhou, Xiaojuan Yan, Jiaqi Yang, Weiguang Ma, Suotang Jia

Optics

Photonic Temporal Illusion

Grigorii Ptitcyn, Diego M. Solís, M. S. Mirmoosa et al. (+1 more)

Materials with unusual optical properties are central to advanced control of light. Yet, in nature, such materials may be exceedingly rare and often difficult to obtain. To overcome this limitation, here we introduce the concept of temporal illusion: A temporally dynamic framework in which carefully programmed temporal variations in effective parameters generate responses akin to those of, in principle, any arbitrary time-invariant structure. We theoretically demonstrate that proper modulation of the permittivity of a conventional dielectric in space and time replicates the optical behavior associated with exotic materials. Besides, we reveal that, beyond steady-state effects, temporal illusion also enables control over transient responses, for instance, by effectively lowering the time constant of high-quality-factor resonators, therefore, allowing faster energy accumulation. Moreover, by incorporating detuning between modulation and excitation, we show that the framework unlocks additional functionalities. The temporal illusion paradigm thus broadens the capabilities of space-time varying systems, offering a powerful route to synthesize material responses on demand and paving the way for new theoretical and experimental directions in optics and wave physics.
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All authors Grigorii Ptitcyn, Diego M. Solís, M. S. Mirmoosa, Nader Engheta

Wednesday 7 January

Physics and Society

Computation as Organisation

Kimia Witte

Computation is commonly defined as the execution of abstract algorithms over symbolic representations, with physical systems treated as substrates that realise predefined operations. While effective for engineered machines, this separation becomes problematic when applied to living systems, where persistence, adaptation, and failure occur without symbolic instruction or central control. Here, computation is reformulated as a structural property of organised matter. Organisation is defined as the persistence of relational constraints that delimit admissible state transitions. Information is not encoded content but relational invariance: differences that influence future behaviour by reshaping what transitions remain possible. Computation is identified with the ongoing enactment of such organisation, integrating memory, processing, and execution as inseparable aspects of material dynamics. Within this framework, algorithms correspond to internally embedded regularities enabled by constraint, and computational limits arise from organisation itself. The account provides experimentally accessible criteria for computation based on persistence, recovery, and structural failure under perturbation.
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General Physics

Is it possible to describe an electron by the evolution of a single point?

Martin Rivas

The answer to the title-question is affirmative. The analysis of the geometry of continuous and differentiable curves in three-dimensional Euclidean space suggests that the point represents the location of the center of charge of the electron, satisfies a system of ordinary differential equations of fourth order, and moves at the speed of light. The center of mass of the electron is a different point and will be determined by the evolution of the center of charge. It is the relative motion of the center of charge around the center of mass that gives rise to the spin and magnetic properties. The invariance of the mass and the absolute value of the spin for the center of mass observer imply that in the interaction of the electron with an external electromagnetic field the particle has to radiate. The analysis of a Poincaré invariant interaction of two electrons implies that the only relevant parameter that characterizes the interaction in a natural system of units, is the fine structure constant. The fundamentals of General Relativity have to be revisited.
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Classical Physics

N-body Systems with Linear Wind Resistance: Analytic Solutions

Joseph West

The attractive and repulsive linear Hookean form of gravity is known to allow for analytic solutions to N-body systems for arbitrary masses and initial conditions. This linear system is very well suited for use in the advanced undergraduate classroom with the position of every particle rj(t) known analytically in terms of only sine, cosine, and exponential functions. Here it is shown that simple analytic solutions are also possible when linear wind resistance is included, provided that the force due to wind resistance force on each particle is proportional to the mass of that particle. Surprising analytic expressions for the behavior of the system if only a single particle in the system is subject to a linear wind resistance are also presented.
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Instrumentation and Detectors

Cyclotron Radiation Signal Characterization in Resonant Cavities for the Project 8 Neutrino Mass Experiment

A. Ashtari Esfahani, S. Bhagvati, H. P. Binney et al. (+60 more)

Many experimental methods in physics require understanding radiation from single particles into non-trivial electromagnetic mode structures. Such characterization is critical for Cyclotron Radiation Emission Spectroscopy (CRES), an advancing new measurement technique that has the potential to greatly benefit fundamental physics measurements. In CRES, charged particles emit cyclotron radiation at frequencies that provide their energy measurement. As a notable example, the Project 8 experiment aims to kinematically infer the neutrino mass by measuring the energies of electrons emitted in tritium beta decay using CRES. In near-term realizations of Project 8, resonant cylindrical cavities will be used for CRES readout, in a configuration with a magnetic field oriented along the symmetry axis, and electrons following helical cyclotron trajectories confined to the cavity interior. The physics of electromagnetic radiation in these environments is complicated, since it involves both the motion of the emitting particle and the mode structure imposed by the cavity. In this work, we derive and validate an analytic model for how an oscillating, trapped electron radiates into cavity modes, and the power and frequency content of the radiation that can be read out from these events. These results can be used to guide the design of cavities for future CRES and other experiments.
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All authors A. Ashtari Esfahani, S. Bhagvati, H. P. Binney, S. Böser, M. J. Brandsema, N. Buzinsky, R. Cabral, M. C. Carmona-Benitez, C. Claessens, L. de Viveiros, A. El Boustani, M. G. Elliott, S. Enomoto, M. Fertl, J. A. Formaggio, B. T. Foust, J. K. Gaison, P. Harmston, K. M. Heeger, B. J. P. Jones, E. Karim, K. Kazkaz, P. T. Kolbeck, A. Kurmus, M. Li, A. Lindman, C.-Y. Liu, T. Luo, C. Matthé, R. Mohiuddin, B. Monreal, B. Mucogllava, R. Mueller, A. Negi, J. A. Nikkel, E. Novitski, N. S. Oblath, M. Oueslati, J. I. Peña, W. Pettus, A. W. P. Poon, V. S. Ranatunga, R. Reimann, A. L. Reine, R. G. H. Robertson, G. Rybka, L. Saldaña, V. Sharma, P. L. Slocum, F. Spanier, J. Stachurska, Y.-H. Sun, P. T. Surukuchi, A. B. Telles, F. Thomas, L. A. Thorne, T. Thümmler, M. Turqueti, W. Van De Pontseele, B. A. VanDevender, T. E. Weiss, M. Wynne, A. Ziegler

Plasma Physics · Cross-listed from q-bio.OT

Plasma-Activated Zn, Fe, Mn Micronutrient Solutions for Crop Biofortification

Punit Kumar, Priti Saxena and Abhishek Kumar Singh

Micronutrient deficiency in soils limits crop productivity and reduces the nutritional quality of cereals and pulses. Conventional fertilizer supplementation often suffers from low bioavailability and environmental losses. In this study, we investigate the use of Plasma Activated Water (PAW) enriched with divalent micronutrient ions as a sustainable alternative to enhance nutrient uptake, soil fertility, and seed vigor. The PAW was generated using a gliding arc plasma system in air, and ion-enriched solutions were prepared at controlled concentrations. The physicochemical parameters (pH, ORP, conductivity, RONS species) were analyzed to assess the plasma induced reactivity. Treatments were applied to micronutrient deficient soils for wheat (Triticum aestivum) and chickpea (Cicer arietinum) seeds under greenhouse conditions. Results demonstrated significant enhancement in germination index, chlorophyll content, and shoot root biomass compared to controls. PAW and ionic treatments notably increased the micronutrient content in grains, indicating effective biofortification. Soil microbial activity and enzyme assays showed no toxicity and a mild stimulatory effect due to reactive nitrogen species. This study establishes a green, scalable method of delivering micronutrients through plasma-activated irrigation water, linking plasma chemistry with sustainable agronomy and nutritional security.
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Physics and Society

Dynamics of Unemployment with Discouraged Workers: A Nonlinear Mathematical Model

Poushali Das, Shraddha Sachan, Mukul Chauhan et al. (+2 more)

In this article, we formulate and analyze a new non-linear mathematical model to describe the dynamics of unemployment with a discouraged working population. We consider five dynamic variables, namely, unskilled unemployed individuals, skilled unemployed individuals, discouraged individuals, employed persons, and job vacancies. Furthermore, we determine the equilibrium points of the dynamic system and investigate their local stability. To demonstrate the results, we conduct numerical simulations by presenting solution trajectories and analyzing how variations in key parameters influence the states of the dynamical variables.
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All authors Poushali Das, Shraddha Sachan, Mukul Chauhan, Narendra Kumar, Amit K. Verma

Computational Physics · Cross-listed from cs.LG

Data-Driven Reduced-Complexity Modeling of Fluid Flows: A Community Challenge

Oliver T. Schmidt, Aaron Towne, Adrian Lozano-Duran et al. (+2 more)

We introduce a community challenge designed to facilitate direct comparisons between data-driven methods for compression, forecasting, and sensing of complex aerospace flows. The challenge is organized into three tracks that target these complementary capabilities: compression (compact representations for large datasets), forecasting (predicting future flow states from a finite history), and sensing (inferring unmeasured flow states from limited measurements). Across these tracks, multiple challenges span diverse flow datasets and use cases, each emphasizing different model requirements. The challenge is open to anyone, and we invite broad participation to build a comprehensive and balanced picture of what works and where current methods fall short. To support fair comparisons, we provide standardized success metrics, evaluation tools, and baseline implementations, with one classical and one machine-learning baseline per challenge. Final assessments use blind tests on withheld data. We explicitly encourage negative results and careful analyses of limitations. Outcomes will be disseminated through an AIAA Journal Virtual Collection and invited presentations at AIAA conferences.
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All authors Oliver T. Schmidt, Aaron Towne, Adrian Lozano-Duran, Scott T. M. Dawson, Ricardo Vinuesa

Instrumentation and Detectors · Cross-listed from hep-ph

A universal vision transformer for fast calorimeter simulations

Luigi Favaro, Andrea Giammanco and Claudius Krause

The high-dimensional complex nature of detectors makes fast calorimeter simulations a prime application for modern generative machine learning. Vision transformers (ViTs) can emulate the Geant4 response with unmatched accuracy and are not limited to regular geometries. Starting from the CaloDREAM architecture, we demonstrate the robustness and scalability of ViTs on regular and irregular geometries, and multiple detectors. Our results show that ViTs generate electromagnetic and hadronic showers with minimal deviations from Geant4 in multiple evaluation metrics, while maintaining the generation time in the $\mathcal{O}(10-100)$ ms on a single GPU. Furthermore, we show that pretraining on a large dataset and fine-tuning on the target geometry leads to reduced training costs and higher data efficiency, or altogether improves the fidelity of generated showers.
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Plasma Physics

Autonomous Sampling and SHAP Interpretation of Deposition-Rates in Bipolar HiPIMS

Alexander Wieczorek, Nathan Rodkey, Jan Sommerhäuser et al. (+2 more)

High-power impulse magnetron sputtering (HiPIMS) offers considerable control over ion energy and flux, making it invaluable for tailoring the microstructure and properties of advanced functional coatings. However, compared to conventional sputtering techniques, HiPIMS suffers from reduced deposition rates. Many groups have begun to evaluate complex pulsing schemes to improve upon this, leveraging multi-pulse schemes (e.g. pre-ionization or bipolar pulses). Unfortunately, the increased complexity of these pulsing schemes has led to high-dimensionality parameter spaces that are prohibitive to classic design of experi-ments. In this work we evaluate bipolar HiPIMS pulses for improving deposition rates of Al and Ti sputter tar-gets. Over 3000 process conditions were collected via autonomous Bayesian sampling over a 6-dimensional parameter space. These process conditions were then interpreted using Shapley Additive Explanations (SHAP), to deconvolute complex process influences on deposition rates. This allows us to link observed var-iations in deposition rate to physical mechanisms such as back-attraction and plasma ignition. Insights gained from this approach were then used to target specific processes where the positive pulse components were expected to have the highest impact on deposition rates. However, in practice, only minimal improve-ments in deposition rate were achieved. In most cases, the positive pulse appears to be detrimental when placed immediately after the neg. pulse which we hypothesize relates to quenching of the afterglow plasma. The proposed workflow combining autonomous experimentation and interpretable machine learning is broad-ly applicable to the discovery and optimization of complex plasma processes, paving the way for physics-informed, data-driven advancements in coating technologies.
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All authors Alexander Wieczorek, Nathan Rodkey, Jan Sommerhäuser, Jason Hattrick-Simpers, Sebastian Siol

Instrumentation and Detectors

Detector characterization for a new $^{12}$C+$^{12}$C reaction study at LUNA

R. M. Gesùè, S. Turkat, J. Skowroński et al. (+50 more)

The $^{12}$C+$^{12}$C fusion reaction plays a crucial role in stellar evolution, including the occurrence of supernova explosions, and in the synthesis of the chemical elements. However, our understanding of its cross section remains severely deficient, particularly below $E_\textrm{cm}=2.5$\,MeV, the energy range of interest for astrophysics. To address these unresolved issues, the LUNA collaboration will conduct a dedicated study of the $^{12}$C+$^{12}$C reaction at the Bellotti Ion Beam Facility (Bellotti IBF) located deep underground within the Gran Sasso National Laboratory (LNGS) in Italy. Based on the combination of passive and active shields, this campaign aims to achieve unprecedented sensitivity in measuring the cross sections of the two key reaction channels, $^{12}$C($^{12}$C,$\alpha$)$^{20}$Ne and $^{12}$C($^{12}$C,$p$)$^{23}$Na in the low-energy regime via $\gamma$-ray detection. Here, we report on a sensitivity study for the upcoming campaign with a focus on the characterization of two detectors, namely a HPGe detector and a NaI(Tl) array. Furthermore, their intrinsic contamination is thoroughly investigated since this could potentially influence the overall sensitivity. Assuming typical beam intensities of the Bellotti IBF, we will be able to investigate reaction rates significantly below 100 counts per day. In case of the $^{12}$C+$^{12}$C reaction we therefore expect to acquire experimental data well below the current limit of $E_\textrm{cm}=2.1\,$MeV. The results are supported by simulations to highlight the advantageous low-background environment, essential for high-precision nuclear astrophysics studies.
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All authors R. M. Gesùè, S. Turkat, J. Skowroński, M. Aliotta, L. Barbieri, F. Barile, D. Bemmerer, A. Best, A. Boeltzig, C. Broggini, C. G. Bruno, A. Caciolli, M. Campostrini, F. Casaburo, F. Cavanna, T. Chillery, G. F. Ciani, P. Colombetti, A. Compagnucci, P. Corvisiero, L. Csedreki, T. Davinson, D. Dell'Aquila, R. Depalo, A. Di Leva, Z. Elekes, F. Ferraro, A. Formicola, Zs. Fülöp, G. Gervino, A. Guglielmetti, C. Gustavino, Gy. Gyürky, G. Imbriani, M. Junker, M. Lugaro, P. Marigo, J. Marsh, E. Masha, R. Menegazzo, D. Mercogliano, V. Paticchio, D. Piatti, P. Prati, D. Rapagnani, V. Rigato, D. Robb, L. Russell, R. S. Sidhu, B. Spadavecchia, O. Straniero, T. Szücs, S. Zavatarelli

Biological Physics · Cross-listed from q-bio.NC

Irreversible behavior drives neural flows in the hippocampus

Kaiyue Shi and Christopher W. Lynn

In the brain, neural activity undergoes directed flows between states, thus breaking time-reversal symmetry. At the same time, animals also exhibit irreversible flows between behavioral states. Yet it remains unclear whether – and how – irreversibility in the brain relates to irreversibility in behavior. Here, we explore this connection in the hippocampus, where neural activity encodes physical location. We show that hippocampal irreversibility can be quantified using the time-delayed cross-correlations between neurons. As a mouse moves along a virtual track, we find that physical flows through the animal's environment generate neural flows through its cognitive map. Strikingly, this neural irreversibility is explained by a minimal model with only three parameters: the average velocity of the mouse, the variance in this velocity, and the resolution of the neural encoding. Together, these results provide a mechanistic understanding of irreversibility in the hippocampus and shed light on the links between symmetry breaking in the brain and behavior.
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Optics

Processing-Dependent Near-Field Radiative Heat Transfer at Au/SiC Interfaces

A. Márquez and R. Esquivel-Sirvent

Thermal annealing is a widely used thin-film processing technique for modifying interfacial optical losses and electronic scattering in plasmonic materials. Here, we investigate how thermal annealing of gold thin films deposited on silicon carbide substrates influences interfacial near-field radiative heat transfer across nanoscale vacuum gaps. Using experimentally measured dielectric functions for annealed and unannealed Au films, we evaluate the spectral and total radiative heat flux between Au/SiC interfaces within a fluctuational electrodynamics framework. We show that annealing-induced changes in the low-frequency dielectric losses of Au significantly alter evanescent electromagnetic coupling at the interface, leading to enhancements of up to ~40% in the total near-field radiative heat transfer at separations of tens of nanometers. Mode-resolved analysis reveals that this enhancement originates from strengthened coupling of overdamped plasmonic surface modes, which are highly sensitive to thin-film processing and interfacial microstructure. These results demonstrate that standard thermal annealing provides a practical route for tuning interfacial radiative heat transfer in metallic thin-film systems without modifying material composition or geometry, offering guidance for the design and interpretation of nanoscale thermal and plasmonic interfaces.
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Computational Physics · Cross-listed from nlin.AO

Self-Organized Criticality from Protected Mean-Field Dynamics: Loop Stability and Internal Renormalization in Reflective Neural Systems

Byung Gyu Chae

The reflective homeostatic dynamics provides a minimal mechanism for self-organized criticality in neural systems. Starting from a reduced stochastic description, we demonstrate within the MSRJD field-theoretic framework that fluctuation effects do not destabilize the critical manifold. Instead, loop corrections are dynamically regularized by homeostatic curvature, yielding a protected mean-field critical surface that remains marginally stable under coarse-graining. Beyond robustness, we show that response-driven structural adaptation generates intrinsic parameter flows that attract the system toward this surface without external fine tuning. Together, these results unify loop renormalization and adaptive response in a single framework and establish a concrete route to autonomous criticality in reentrant neural dynamics.
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Physics and Society

Reconstructing MSM Sexual Networks to Guide PrEP Distribution Strategies for HIV Prevention

João Brázia, István Z. Kiss, Alexandre P. Francisco et al. (+1 more)

Men who have sex with men (MSM) remain disproportionately affected by HIV, yet optimizing Pre-exposure Prophylaxis (PrEP) distribution remains a public health challenge. Current guidelines and most modelling studies do not incorporate sociodemographic or network-level factors that shape transmission. While network reconstruction from egocentric data has been studied, the relative importance of demographic mixing dimensions remains uncertain. Using data from 4,667 MSM participants, we show that uncertainty in network reconstruction from egocentric survey data - specifically whether assortativity by age or race is incorporated - affects simulated HIV prevalence under the same observed PrEP uptake. We simulate HIV transmission over 50 years across this structural space and evaluate whether empirically observed uptake reaches transmission-critical network positions. Network structure strongly influences outcomes: assortative by degree networks show 17% lower equilibrium prevalence due to hub isolation within communities. Targeted PrEP strategies based on degree or k-shell centrality achieved the highest prevalence reductions, particularly in assortative by age and race networks where hubs bridge demographic groups. PrEP uptake from data is suboptimal in assortative by age and race networks, underperforming compared with network-based strategies. Results demonstrate that uncertainty in network reconstruction affects intervention design and highlight the need for robust prevention strategies under structural ambiguity.
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All authors João Brázia, István Z. Kiss, Alexandre P. Francisco, Andreia Sofia Teixeira

Fluid Dynamics

JAX-Shock: A Differentiable, GPU-Accelerated, Shock-Capturing Neural Solver for Compressible Flow Simulation

Bo Zhang

Understanding shock-solid interactions remains a central challenge in compressiblefluiddynamics. WepresentJAX-Shock: afully-differentiable,GPU-accelerated, high-order shock-capturing solver for efficient simulation of the compressible Navier-Stokes equations. Built entirely in JAX, the framework leverages automatic differentiation to enable gradient-based optimization, parameter inference, and end-to-end training of deep learning-augmented models. The solver integrates fifth-order WENO reconstruction with an HLLC flux to resolve shocks and discontinuities with high fidelity. To handle complex geometries, an immersed boundary method is implemented for accurate representation of solid interfaces within the compressible flow field. In addition, we introduce a neural flux module trained to augment the numerical fluxes with data-driven corrections, significantly improving accuracy and generalization. JAX-Shock also supports sequence-to-sequence learning for shock interaction prediction and reverse-mode inference to identify key physical parameters from data. Compared with purely data-driven approaches, JAX-Shock enhances generalization while preserving physical consistency. The framework establishes a flexible platform for differentiable physics, learning-based modeling, and inverse design in compressible flow regimes dominated by complex shock-solid interactions.
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