Medical Physics
On the dynamical stability of skeletal muscle
Javier A. Almonacid, Nilima Nigam and James M.Wakeling
There has been debate for over 70-years about whether active skeletal muscle is dynamically stable at lengths greater than its optimal length. The stability of computational muscle models is a critical issue, as it directly affects our ability to simulate muscle deformation across different operating lengths, especially at lengths where muscles are known to remain functional despite model-predicted instabilities. In this study, we revisit the question of dynamical stability of ODE-based models of skeletal muscle. In particular, we investigate whether activation-independent tissue properties can provide stability to contractions along the dip region of the total force-length curve. First, using a combination of analytical tools (
eigenvalue analysis and non-dimensionalization) and numerical simulations, we confirm that traditional Hill-type muscle models can display divergent dynamics in this region. Then, we propose a stabilized version of a 1D Hill-type muscle model that incorporates the 3D nature of skeletal muscle deformation. This results in a completely convex force-length relationship that can bring robustness to numerical simulations, while preserving the computational efficiency of 1D models. Our findings suggest that activation-independent intrinsic mechanical properties of muscle are sufficient to stabilize contractions even in the dip region, offering new insight into how muscles maintain functional integrity during active stretch.
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Physics and Society · Cross-listed from astro-ph.IM
Sustainable, Local Socio-Economic Development Through Astronomy
Joyful E. Mdhluli and IAU Office of Astronomy for Development
Astronomy, often perceived as a distant or luxury science, holds immense potential as a driver for sustainable local socio-economic development. This paper explores how astronomy can create tangible benefits for communities through education, tourism, technology transfer, and capacity building. Using case studies from South Africa, Chile, Indonesia, and India, we demonstrate how astronomical facilities and initiatives have stimulated local economies, generated employment, supported small enterprises, and enhanced STEM participation, while simultaneously inspiring a sense of shared global heritage. The analysis identifies both successes and challenges, including unequal benefit distribution, limited local ownership, and sustainability gaps once external funding ends. Building on these lessons, we propose a practical framework/guidelines for designing, implementing, and evaluating astronomy-based community initiatives, rooted in participatory engagement and aligned with the UN Sustainable Development Goals (SDGs). This paper positions astronomy as a catalyst for inclusive growth, demonstrating that investment in the cosmos can translate into grounded, measurable benefits for people and places on Earth.
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Medical Physics
Zero-Dimensional Cardiovascular Modeling: A Personalized Approach to Non-Invasive Measurement and Sensitivity Analysis
Pranav Kumar Sasikumar
Zero-dimensional cardiovascular models provide a computationally efficient framework for studying global hemodynamic behavior, yet the influence of model complexity on parameter sensitivity remains insufficiently understood. This work investigates two lumped-parameter cardiovascular models, a simplified single-ventricle configuration and a detailed four-chamber representation, to examine how physiological parameter sensitivities vary with model structure. Time-varying elastance functions are used to represent cardiac dynamics, and global sensitivity analysis is performed using Sobol and Morris methods to quantify the impact of key physiological parameters, including venous return, myocardial contractility, total peripheral resistance, and arterial compliance. The results demonstrate that sensitivity rankings differ substantially between the two models, highlighting the role of model granularity and parameter interactions in shaping cardiovascular responses. These findings support sensitivity-driven model reduction and provide a foundation for scalable, non-invasive cardiovascular simulation frameworks.
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Chemical Physics
The Open Polymers 2026 (OPoly26) Dataset and Evaluations
Daniel S. Levine, Nicholas Liesen, Lauren Chua et al. (+12 more)
Polymers-macromolecular systems composed of repeating chemical units-constitute the molecular foundation of living organisms, while their synthetic counterparts drive transformative advances across medicine, consumer products, and energy technologies. While machine learning (ML) models have been trained on millions of
quantum chemical atomistic simulations for materials and/or small molecular structures to enable efficient, accurate, and transferable predictions of chemical properties,
polymers have largely not been included in prior
datasets due to the computational expense of high quality electronic structure calculations on representative polymeric structures. Here, we address this shortcoming with the creation of the Open
Polymers 2026 (OPoly26)
dataset, which contains more than 6.57 million density functional theory (DFT) calculations on up to 360 atom clusters derived from polymeric systems, comprising over 1.2 billion total atoms. OPoly26 captures the chemical diversity that makes
polymers intrinsically tunable and versatile materials, encompassing variations in monomer composition, degree of polymerization, chain architectures, and solvation environments. We show that augmenting ML model training with the OPoly26
dataset improves model performance for
polymer prediction tasks. We also publicly release the OPoly26
dataset to help further the development of ML models for
polymers, and more broadly, strive towards universal atomistic models.
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All authors Daniel S. Levine, Nicholas Liesen, Lauren Chua, James Diffenderfer, Helgi Ingolfsson, Matthew P. Kroonblawd, Nitesh Kumar, Amitesh Maiti, Supun S. Mohottalalage, Muhammed Shuaibi, Brian Van Essen, Brandon M. Wood, C. Lawrence Zitnick, Samuel M. Blau, Evan R. Antoniuk
Fluid Dynamics
Validating the Boltzmann approach to the Large-Eddy simulations of forced homogeneous incompressible turbulence
Muhammad Idrees Khan, Sauro Succi and Giacomo Falcucci
The simulation of turbulent flows remains a central challenge, as even our most powerful computers cannot resolve the finest scales of motion in many flows of practical interest. As a result, the effects of unresolved scales on large eddies must be modelled via closures and coarse-graining procedures. Large-eddy simulation (LES) traditionally coarse-grains Navier-Stokes equations using Smagorinsky's effective viscosity model. This has the merit of simplicity but fails to account for strong non-
equilibrium effects, as they typically arise in most flows in the vicinity of solid walls, the reason being that the notion of eddy viscosity assumes scale separation between small and large eddies, an assumption that fails for high-Reynolds flows far from
equilibrium. The
lattice Boltzmann method (LBM) offers an alternative by coarse-graining at the kinetic level, potentially capturing non-
equilibrium effects beyond reach of hydrodynamic closures. This paper addresses whether LBM-Smagorinsky LES of forced homogeneous isotropic
turbulence (FHIT) exhibits kinetic behavior. We test whether the turbulent Knudsen number $K_t$, measuring scale separation, reaches order one (kinetic regime) or remains asymptotically small (hydrodynamic regime). Using reference DNS ($800^3$) and iso-Reynolds LES ($100^3$) at $Re = 2 \times 10^4$, we quantify $K_t$ via spatial maps, temporal statistics, energy spectra, and higher-order moments. Results show $K_t \sim O(10^{-3})$, strictly positive without negative excursions, with spectra and flatness following canonical LES behavior. We conclude that despite its kinetic formulation, LBM-Smagorinsky LES operates in the hydrodynamic regime, with small FHIT eddies remaining in local
equilibrium with larger ones, validating Smagorinsky viscosity and confirming that LBM-LES functions as conventional hydrodynamic LES while preserving LBM efficiency and locality.
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Plasma Physics
Breaking seed dormancy in Mediterranean Brassica rapa wild populations: is cold plasma treatment efficient?
M.H. Wagner, T. Dufour, A. Geraci et al. (+11 more)
Turnip (Brassica rapa) is a native species of the Mediterranean area, spread from northwest France to south Algeria. In this study, dormancy and germination traits were assessed for 61 wild Brassica rapa populations collected across the Mediterranean region. Seed dormancy is a key factor influencing germination and seedling establishment. Three dormancy-breaking methods were compared: gibberellic acid, scarification and cold
plasma. The efficiency and selectivity were evaluated through germination ability, time to 10% germination (T10), mean germination time and greenhouse emergence. Five days after imbibition, germination was only 18% for the untreated seeds but 60% for the
plasma-treated seeds. Germination also began 24 hours earlier and mean germination time was reduced across most populations. However, there was a limited effect on seedling emergence, which remained around 55% for both untreated and treated samples. Comparative analysis indicates that cold
plasma was more effective in alleviating embryo dormancy. In addition, histological and scanning electron microscopy showed that the seed coat differed according to the geographical origin of the populations, with a deeper dormancy in seeds from Sicilian populations.
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All authors M.H. Wagner, T. Dufour, A. Geraci, E. Oddo, G.R. Tarantino, F. Scafidi, C. Bailly, H. Hadj Arab, B. Boucenna, M. Tiret, C. Falentin, A. Dupont, S. Ducournau, A.M. Chèvre
Biological Physics
Viral Evolution Under Physical Constraints: Decay, Mutation, and Transmission as a Constrained Optimization Problem
Mohammad Rasoolinejad
Viruses display striking diversity in structure, transmission mode, immune interaction, and evolutionary behavior. Despite this diversity, viral strategies are not unconstrained. Here we present a unifying framework that treats viral
evolution as a problem of constrained optimization governed by physical decay, immune pressure, mutation robustness, and transmission architecture. We model virions as multi-component physical systems subject to irreversible environmental failure and viruses as replicators operating under immune-driven selection and mutation-selection balance. Within this framework, major viral transmission strategies arise as necessary solutions rather than taxonomic accidents. Environmentally transmitted and airborne viruses are predicted to be structurally simple, chemically stable, and reliant on replication volume rather than immune suppression. Structurally complex viruses tolerate rapid environmental decay by encoding immune-modulatory machinery, latency, or persistent replication, at the cost of reduced mutation robustness. Temperature-dependent seasonality emerges naturally from the thermally activated nature of viral decay, without invoking host behavior.
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History and Philosophy of Physics
Event Horizons, Spacetime Geometry, and the Limits of Integrated Consciousness
Jonathon Sendall
What happens to a unified conscious field when its physical implementation straddles a black hole event horizon? This paper addresses that question for integration-based theories, including Integrated Information Theory, Global Workspace Theory, and Predictive Processing. These views share a structural commitment: unity requires a single strongly connected component (SCC) in an effective causal graph over a finite integration window $\tau$. Using the standard black hole causal structure, I show that no SCC can span an event horizon. Any theory that ties unity to strong connectivity must therefore accept that a single conscious field cannot remain numerically identical and unified across such a configuration. From the perspective of the theories themselves, the outcome is bifurcation: each causally connected subsystem continues to satisfy the very structural criteria the theory declared necessary for a unified field. On any such view, the number and boundaries of unified conscious fields are therefore fixed not by the substrate alone but by the conjunction of its internal architecture with the relativistic causal structure of the spacetime it occupies, a dependency that ordinary spacetime conceals by supplying it so abundantly, but which an event horizon abruptly withdraws.
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Biological Physics
Mutation in DNA: A quantum mechanical non-adiabatic model
Hossien Hossieni
We propose a new analytical potential function to model
proton transfer in the adenine-thymine base pair and develop a non-adiabatic
quantum mechanical framework to calculate genetic mutation probabilities. This potential has been used to calculate the probability of mutation in a non-adiabatic process. The results of the new model have been shown to be consistent with the findings of other researchers.
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Chemical Physics
QSAR-Guided Generative Framework for the Discovery of Synthetically Viable Odorants
Tim C. Pearce and Ahmed Ibrahim
The discovery of novel odorant molecules is key for the fragrance and
flavor industries, yet efficiently navigating the vast chemical space to identify structures with desirable olfactory properties remains a significant challenge. Generative artificial intelligence offers a promising approach for de novo molecular design but typically requires large sets of molecules to learn from. To address this problem, we present a framework combining a variational autoencoder (VAE) with a quantitative structure-activity relationship (QSAR) model to generate novel odorants from limited training sets of odor molecules. The self-supervised learning capabilities of the VAE allow it to learn SMILES grammar from ChEMBL database, while its training objective is augmented with a loss term derived from an external QSAR model to structure the latent representation according to odor probability. While the VAE demonstrated high internal consistency in learning the QSAR supervision signal, validation against an external, unseen ground truth
dataset (Unique Good Scents) confirms the model generates syntactically valid structures (100% validity achieved via rejection sampling) and 93.9% unique structures. The latent space is effectively structured by odor likelihood, evidenced by a Frechet ChemNet Distance (FCD) of ~6.96 between generated molecules and known odorants, compared to ~21.6 for the ChEMBL baseline. An ablation of the property head shows that its contribution lies in the density of retrievable structures near an odorant seed – a 4.3-fold increase in distinct novel compounds per seed – rather than in the odor-likeness of any individual compound. Bemis-Murcko analysis shows 2,499 of 6,765 ring-containing candidates, spanning 1,429 distinct core frameworks, absent from all training sets, while a further 294 molecules...
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Plasma Physics
Thermodynamically Consistent Vibrational-Electron Heating: Generalized Model for Multi-Quantum Transitions
Bernard Parent and Felipe Martin Rodriguez Fuentes
Accurate prediction of electron temperature ($T_{\rm e}$) is critical for non-
equilibrium plasma applications ranging from hypersonic flight to
plasma-assisted combustion. We recently proposed a thermodynamically consistent model for vibrational-electron heating [Phys. Fluids 37, 096141 (2025)] that enforces the convergence of $T_{\rm e}$ to the vibrational temperature ($T_{\rm v}$) at
equilibrium. However, the original derivation was restricted to single-
quantum transitions, limiting its validity to low-temperature regimes ($T_{\rm e} \lesssim 1.5$ eV). In this Letter, we generalize the model to include multi-
quantum overtone transitions, extending its applicability to high-energy regimes. We demonstrate that previous models neglecting hot-band transitions incur a systematic heating error of $\exp(-\theta_{\rm v}/T_{\rm v})$, where $\theta_{\rm v}$ is the characteristic vibrational temperature. This error exceeds 40% when $T_{\rm v}$ is greater than $\theta_{\rm v}$, effectively preventing thermal relaxation. To correct this, we derive a formulation where the total heating rate is a summation of channel-specific cooling rates $Q_{\rm e-v}^{(m)}$, each associated with a
quantum jump $m$, scaled by a thermodynamic factor $\exp(m\theta_{\rm v}/T_{\rm e}-m\theta_{\rm v}/T_{\rm v})$. This generalized model preserves thermodynamic consistency by ensuring zero net energy transfer at
equilibrium.
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Computational Physics
Exponential divided differences via Chebyshev polynomials
Itay Hen
Exponential divided differences arise in numerical linear
algebra,
matrix-function evaluation, and
quantum Monte Carlo simulations, where they serve as kernel weights for time
evolution and observable estimation. Efficient and numerically stable evaluation of high-order exponential divided differences for dynamically evolving node sets remains a significant computational challenge. We present a Chebyshev-
polynomial-based
algorithm that addresses this problem by combining the Chebyshev-Bessel expansion of the exponential function with a direct recurrence for Chebyshev divided differences. The method achieves a computational cost of ${\cal O}(qN)$, where $q$ is the divided-difference order and $N$ is the Chebyshev truncation length. We show that $N$ scales linearly with the spectral width through the decay of modified Bessel coefficients, while the dependence on $q$ enters only through structural
polynomial constraints. We further develop an incremental update scheme for dynamic node sets that enables the insertion or removal of a single node in ${\cal O}(N)$ time when the affine mapping interval is held fixed. A full C++ reference implementation of the
algorithms described in this work is publicly available.
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Computational Physics
Reconstructing Relativistic Magnetohydrodynamics with Physics-Informed Neural Networks
Corwin Cheung, Marcos Johnson-Noya, Michael Xiang et al. (+2 more)
We construct the first physics-informed neural-network (PINN) surrogates for relativistic magnetohydrodynamics (RMHD) using a hybrid PDE and data-driven workflow. Instead of training for the conservative form of the equations, we work with Jacobians or PDE characteristics directly in terms of primitive variables. We further add to the trainable system the divergence-free condition, without the need of cleaning modes. Using a novel
MUON optimizer implementation, we show that a baseline PINN trained on early-time snapshots can extrapolate RMHD dynamics in one and two spatial dimensions, and that posterior residual-guided networks can systematically reduce PDE violations.
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All authors Corwin Cheung, Marcos Johnson-Noya, Michael Xiang, Dominic Chang, Alfredo Guevara
Computational Physics · Cross-listed from cs.LG
PI-MFM: Physics-informed multimodal foundation model for solving partial differential equations
Min Zhu, Jingmin Sun, Zecheng Zhang et al. (+2 more)
Partial differential equations (PDEs) govern a wide range of physical systems, and recent
multimodal foundation models have shown promise for learning PDE solution operators across diverse equation families. However, existing multi-operator learning approaches are data-hungry and neglect physics during training. Here, we propose a physics-informed
multimodal foundation model (PI-MFM) framework that directly enforces governing equations during pretraining and adaptation. PI-MFM takes symbolic representations of PDEs as the input, and automatically assembles PDE residual losses from the input expression via a vectorized derivative computation. These designs enable any PDE-encoding
multimodal foundation model to be trained or adapted with unified physics-informed objectives across equation families. On a
benchmark of 13 parametric one-dimensional time-dependent PDE families, PI-MFM consistently outperforms purely data-driven counterparts, especially with sparse labeled spatiotemporal points, partially observed time domains, or few labeled function pairs. Physics losses further improve robustness against noise, and simple strategies such as resampling collocation points substantially improve accuracy. We also analyze the accuracy, precision, and computational cost of automatic differentiation and finite differences for derivative computation within PI-MFM. Finally, we demonstrate zero-shot physics-informed fine-tuning to unseen PDE families: starting from a physics-informed pretrained model, adapting using only PDE residuals and initial/boundary conditions, without any labeled solution data, rapidly reduces test errors to around 1% and clearly outperforms physics-only training from scratch. These results show that PI-MFM provides a practical and scalable path toward data-efficient, transferable PDE solvers.
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All authors Min Zhu, Jingmin Sun, Zecheng Zhang, Hayden Schaeffer, Lu Lu
Optics
Toward Human-Aligned Luminance Measurement for Large-Format LED Displays
Xi Mou, Xiaopeng Peng and Tongsheng Mou
Direct-view LED displays are widely adopted in large-format applications due to their high luminance and reliability. However, visual comfort and accurate performance evaluation remain challenging due to the complex interaction between pixel luminance, human visual perception, and measurement artifacts. In this work, we introduce a novel 2D imaging luminance meter that replicates key optical parameters of the human eye, including entrance pupil size and angular resolution, to assess perceived pixel luminance. We report comprehensive measurements across various visual field angles and distances and establish a refined luminance metric that aligns with foveal
vision standards (1/120 degree). Furthermore, a new method to quantify and mitigate stray light effects significantly improves measurement precision by reducing luminance overestimation from 7% to 2%. Our findings provide a foundation for optimizing LED display design for perceptual comfort and advancing standardization in pixel luminance evaluation.
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Atmospheric and Oceanic Physics
Using a rare event sampling technique to quantify extreme El Niño event statistics
Sarah Packman, Justin Finkel, Dorian S. Abbot et al. (+1 more)
Extreme El Niño events, such as occurred in 1997–1998, can induce severe weather on a global scale, with significant socioeconomic impacts that motivate efforts to understand them better. However, extreme El Niño events are rare, and even in a very long direct numerical simulation (DNS) occur too infrequently for robust statistical characterization. This study seeks to generate extreme El Niño event model data at a lower cost, while preserving statistical fidelity, using a rare event sampling technique, which preferentially devotes computational resources toward extreme events by generating a large, branched ensemble of interrelated trajectories through successive targeted perturbations. We specifically use the “trying-early adaptive multi-level splitting” (TEAMS)
algorithm, which is well-suited for El Niño's relative timescales of predictability and event duration. We apply TEAMS to the Zebiak-Cane model, an intermediate-complexity ENSO model for which it is feasible to run a long DNS (500000 years) for validation. We compare extreme El Niño event return time estimates from TEAMS to those from the long DNS to assess TEAMS' accuracy and efficiency. We find that TEAMS accurately reproduces the return time estimates of the DNS at about one fifth the computational cost. Therefore, TEAMS is an efficient approach to study rare ENSO events that can be plausibly applied to full-complexity
climate models.
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All authors Sarah Packman, Justin Finkel, Dorian S. Abbot, Eli Tziperman
Plasma Physics
Treatment of sunflower seeds by cold atmospheric plasma enhances their tolerance to water stress during germination and early seedling development
L. Taras, C. Bailly and T. Dufour
The aim of this study was to investigate the impact of ambient air
plasma treatment on both sunflower seed germination and early steps of seedling development under water stress. Dry seeds were exposed to a cold atmospheric
plasma (CAP) generated in a dielectric barrier device where excited molecular nitrogen and ozone were detected by optical emission spectroscopy and mass spectrometry respectively. Interestingly, we explain the crucial role of gap's accuracy when treating seeds with CAP, especially to improve interaction between seeds and
plasma and therefore ensure an efficient treatment. CAP significantly improved the germination rates of seeds of dormant and non-dormant sunflower genotypes under water stress, demonstrating its efficiency in alleviating seed dormancy and in improving germination under suboptimal conditions. Furthermore, greenhouse experiments demonstrated that
plasma treatment also stimulated seedling development under water stress conditions. These findings highlight the potential of CAP treatment as an effective approach to promote the whole process of emergence of crop species.
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Computational Physics
Masgent: An AI-assisted Materials Simulation Agent
Guanghen Liu, Songge Yang and Yu Zhong
Density functional theory (DFT) and machine learning potentials (MLPs) are essential for predicting and understanding materials properties, yet preparing, executing, and analyzing these simulations typically requires extensive scripting, multi-step procedures, and significant high-performance computing (HPC) expertise. These challenges hinder reproducibility and slow down discovery. Here, we introduce Masgent, an AI-assisted materials simulation
agent that unifies structure manipulation, automated VASP input generation, DFT workflow construction and analysis, fast MLP-based simulations, and lightweight machine learning (ML) utilities within a single platform. Powered by large
language models (LLMs), Masgent enables researchers to perform complex simulation tasks through natural-
language interaction, eliminating most manual scripting and reducing setup time from hours to seconds. By standardizing protocols and integrating advanced simulation and data-driven tools, Masgent lowers the barrier to performing state-of-the-art computational methodologies, enabling faster hypothesis testing, pre-screening, and exploratory research for both new and experienced practitioners.
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