Fluid Dynamics
Vortical similarities across laminar and turbulent extreme gust encounters
Hiroto Odaka, Barbara Lopez-Doriga and Kunihiko Taira
This study uncovers a striking similarity between massively separated laminar and turbulent flows that develop over a square wing during extreme
vortex gust encounters. The evolving large-scale, vortical core structures responsible for significant transient lift variations exhibit remarkable similarity across Re = 600 and 10,000. The formation of these structures is attributed to a substantial gust-induced vorticity flux produced at the wing surface, resulting in shared large-scale topological features between the low- and high-Reynolds-number flows. Although fine-scale vortical structures quickly emerge in the Re = 10,000 case, the large-scale structures identified by scale decomposition of the turbulent flow resemble those observed at Re = 600. These findings suggest that large-scale vortical features present in laminar extreme aerodynamic flows provide key insights into their higher Reynolds number counterparts, potentially reducing the complexity of flow modeling and control for extreme aerodynamics.
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Optics
Wavelength and Polarization Multiplexed Nonlocal Metasurface for Quantitative Phase Microscopy
Haiwei Wang, Shikun Ma, Shaban B. Sulejman et al. (+6 more)
Imaging transparent samples remains an ongoing challenge in the study of unstained biological
cells and material samples. Widely used methods trade off system complexity, cost and bulk, computational efficiency and information content. Here we demonstrate the use of a nonlocal metasurface located in the object plane for obtaining single-shot, low-noise differential phase contrast images visualising phase gradients along orthogonal directions in a sample obtained at wavelengths of 613 nm and 656 nm. Furthermore, we show that these images are sufficient to calculate the quantitative phase introduced into the transmitted optical field by the sample. We find that the recovered phase of an optical field generated by a spatial light modulator is in good agreement with specified values. We also present information-rich differential phase contrast images of unstained HeLa
cells with the recovered phase excursion values consistent with the literature. Our results demonstrate the potential for metasurfaces as a platform for extracting information from an optical field for use in next-generation compact imaging systems with applications in medical diagnostics, biotechnology, and materials science.
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All authors Haiwei Wang, Shikun Ma, Shaban B. Sulejman, Niken Priscilla, Wendy S.L. Lee, Peter Francis Matthew Elango, Lukas Wesemann, Elizabeth Hinde, Ann Roberts
Applied Physics
Phonon controlled mechanical memory via pinning and depinning of transition waves
Samuele Ferracin, Dengge Jin, Vincent Tournat et al. (+1 more)
Multistable mechanical metamaterials enable programmable transitions between discrete stable states through propagating kink transition waves (TWs). Yet controlling these kinks typically requires local actuation or high-energy deformation, limiting scalability. Here we demonstrate a universal strategy for pinning and depinning TWs using local defects and boundary
phonon excitations. Inspired by
phonon-dislocation interactions in crystalline solids, we use pairs of
phonons that form a beating envelope resonant with the pinned kink's translational mode, which lies within a phononic band gap. This resonant coupling efficiently transfers energy to the kink, allowing it to overcome defect barriers and propagate across
impurities. The proposed mechanism enables application of these systems as information processing units in mechanical computing, namely as scalable and more robust mechanical
memory.
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All authors Samuele Ferracin, Dengge Jin, Vincent Tournat, Jordan R. Raney
Plasma Physics
Forced Reconnection in Voigt-Regularized MHD
Andrew Brown, Yi-Min Huang and Amitava Bhattacharjee
Forced reconnection in Voigt-regularized MHD is investigated in the Hahm-Kulsrud-Taylor problem. It is shown that Voigt regularization introduces an early linear phase of reconnection that partially bypasses the ideal current sheet formation phase. Three distinct regimes of Rutherford-like island growth and saturation are elucidated, including the braking effects of regularization and viscosity. It is conjectured, with numerical justification, that the inclusion of drag in the momentum equation does not inhibit the relaxation to steady state in the long-time limit.
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Geophysics · Cross-listed from astro-ph.EP
Mantle Convection and Nightside Volcanism on Lava World K2-141 b
Tobias G. Meier, Claire Marie Guimond, Raymond T. Pierrehumbert et al. (+13 more)
Ultra-short period lava worlds offer a unique window into the coupled
evolution of planetary interior and atmospheres under extreme irradiation. In this study, we investigate the mantle dynamics, nightside volcanism, and volatile outgassing on lava world K2-141 b ($1.54 R_{\oplus}$, $5.31 M_{\oplus}$) using two-dimensional convection models with tracer-based volatile tracking. Our simulations explore a range of interior configurations, including models with and without plastic yielding, basal versus mixed heating, core cooling, and melt intrusion. In models without plastic yielding (i.e. with a strong lithosphere), we find that mantle upwellings form at the substellar and antistellar points, while downwellings form near the day-night terminators at the boundary between the magma ocean and cold, solid nightside. These downwellings facilitate the recycling of crustal material, representing a form of asymmetric, single-lid tectonics. The resulting magma ocean thickness varies from 200 to 300 km depending on the model parameters, corresponding to about 2-3% of the
planet's radius. Continuous nightside volcanism produces a basaltic crust and gradually depletes the mantle of volatiles. We find that over a billion years, volcanic eruptions can outgas tens of bars of CO$_{2}$ and H$_{2}$O. We show that even relatively large volcanic eruptions on the nightside produce thermal emission signals of no more than 1 ppm, remaining below the current detectability threshold in thermal phase curves. However, for most models, outgassing rates are increased near the day-night terminators and future studies should assess whether such localised outgassing could lead to atmospheric signatures in transmission spectroscopy.
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All authors Tobias G. Meier, Claire Marie Guimond, Raymond T. Pierrehumbert, Jayne Birkby, Richard D. Chatterjee, Chloe E. Fisher, Gregor J. Golabek, Mark Hammond, Thaddeus D. Komacek, Tim Lichtenberg, Alex McGinty, Erik Meier Valdés, Harrison Nicholls, Luke T. Parker, Rob J. Spaargaren, Paul J. Tackley
Biological Physics · Cross-listed from q-bio.PE
Fluctuating environments are sufficient to drive substantial variability in species abundance across locations
James F. D. Henderson and Andreas Tiffeau-Mayer
Species growing in environments that change in time and space will vary in their abundance across locations, even in the absence of persistent location preferences. Here we quantify this non-
equilibrium effect by studying a minimal model of a spatially compartmentalised community with time-averaged-neutral competition but location-dependent environmental fluctuations. We analytically derive distributions of two-point inequality, defined as the log-ratio of a species' abundance across a pair of locations. We characterise how the balance of relaxation via migration and fluctuation strength determine the bulk and extreme value statistics of these distributions in the two-patch and infinite-patch cases. We demonstrate the existence of a noise-induced transition to bimodal inequality, which depends on the correlation timescale of the environmental fluctuations. Finally, we discuss the evolutionary benefit of finite migration rates in environments with temporal correlations.
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Optics
Electro-optic modulation of coherent and incoherent mid-IR radiation in two-dimensional arrays
Jared Sisler, Phillippe Pearson, Michael Kelzenberg et al. (+2 more)
Light in the mid-infrared (mid-IR) spans wavelengths from 3-8 $\mu$m and is important to many applications such as gas sensing and thermal imaging. Due to materials challenges, there is currently a lack of mid-IR reconfigurable optical elements. Here, we present an electrically addressable metasurface for modulation of coherent and incoherent mid-IR radiation in two spatial dimensions. Our device achieves optical modulation due to the field-effect free-carrier depletion in a lightly doped ($10^{19}$ cm$^{-3}$) film of indium-tin-
oxide (ITO) coupled to a gap plasmon resonator. By addressing 32 individual elements across the metasurface, we first demonstrate tunable diffraction of coherently reflected mid-IR light. Next, we introduce a scalable perimeter-addressed driving scheme for tunable diffraction in two dimensions. Finally, we demonstrate modulated emissivity with spatially reconfigurable two-dimensional patterns at elevated temperatures. This work advances the development of solid-state reflective beam-steering devices in the mid-IR and manipulation of thermally emitted incoherent radiation.
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All authors Jared Sisler, Phillippe Pearson, Michael Kelzenberg, Andrei Faraon, Harry A. Atwater
History and Philosophy of Physics
Activation and Alignment: A Causal Account of the Scientific Revolution
Harry Sticker
Standard historiographical approaches to the Scientific Revolution illuminate background conditions but leave three puzzles unresolved: what triggered the initial escalation of inherited tensions, what made early investigative efforts durable, and why natural philosophy became the locus of transformation rather than theology, law, or classical scholarship. This paper develops a causal account by identifying the mechanisms of activation at the individual level and the institutional
alignment that converted rare psychological drive into durable research traditions. The trigger architecture operates at two levels. At the individual level, activation occurs when investigators experience inherited puzzles as psychologically intolerable; capture stabilizes inquiry through cognitive, material, and social entanglements; and externalization converts methods into transmissible forms. At the institutional level, role expansion embeds elevated standards into positions; succession ratchets prevent regression through competitive selection; and domain channeling directs institutional energy toward particular fields. A systematic comparison across Islamic, Chinese, and European cases demonstrates that each component is necessary, but none is sufficient on its own. The Scientific Revolution occurred when all components aligned at Padua-Venice and Oxford-London, where corporate autonomy, competitive appointments, and state patronage converged with investigative practices. The Galileo case provides decisive evidence: his selective activation across domains demonstrates that activation operates as a specific mechanism rather than a stable dispositional trait.
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Instrumentation and Detectors
Internal Charge Amplification in Germanium at 77K and 4K: From Single-Free-Flight Bounds to a Physics-Informed Ionization Model
Dongming Mei, Kunming Dong, Narayan Budhathoki et al. (+2 more)
Internal charge amplification (ICA) in cryogenic high-purity germanium (HPGe) can lower detection thresholds by providing gain inside the detector
crystal, but reliable operation requires a predictive estimate of the avalanche-onset critical electric field \(E_{\mathrm{crit}}\). We present a compact framework for \(E_{\mathrm{crit}}\) at 77~K and 4~K (typical HPGe operating temperatures) that bridges (i) a mobility-based single-free-flight (SFF) upper bound with (ii) a physics-informed impact-ionization model incorporating energy-dependent scattering, nonparabolic (Kane) dispersion, intervalley transfer, and the high-energy “lucky-drift” tail. This unified treatment yields closed-form, design-useful relations, including \(E_{\mathrm{crit}}^{(\mathrm{PI})}=B(T)/\ln[A(T)d]\), and a practical calibration workflow that maps measured low-field mobility \(\mu(T)\) and gain curves \(M(V)\) (Chynoweth analysis) to device-level bias targets with propagated uncertainty bands. Example electron and hole estimates indicate that realistic transport typically lowers \(E_{\mathrm{crit}}\) relative to SFF and increases the predicted change in \(E_{\mathrm{crit}}\) between 77~K and 4~K. The resulting portable formulas connect materials/transport inputs to geometry, excess noise, and field shaping, providing design-ready guidance for stable, unipolar-favored ICA with controlled quenching in Ge and other cryogenic
semiconductors.
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All authors Dongming Mei, Kunming Dong, Narayan Budhathoki, Shasika Panamaldeniya, Francisco Ponce
Biological Physics
Extrapolating molecular dynamics simulations to zero time step and across thermodynamic space
Kush Coshic and Gerhard Hummer
The integration time step is a critical determinant of performance in molecular dynamics simulations, governing the trade-off between speed and fidelity. Although 2 fs remains the standard in atomistic biomolecular simulations, the push for performance has popularized a 4 fs time step with hydrogen mass repartitioning, often combined with multiple time stepping or mass rescaling. However, it is often unclear whether a chosen protocol is overly aggressive, as the apparent numerical stability of a trajectory can mask underlying thermodynamic inaccuracies. Increasing the time step will exacerbate systematic discretization errors, inherent to all numerical integration
algorithms. In the widely used Verlet family of integrators, these errors manifest as $\mathcal{O}(\Delta t^2)$ deviations in thermodynamic observables such as potential energy and volume, and for common Langevin splitting schemes, even temperature. We demonstrate that these deviations follow a simple, linear thermodynamic model, allowing for their rigorous removal by extrapolation to the zero time step limit. In turn, the time-step dependence provides us with estimates of the system heat capacity, compressibility, and thermal expansion coefficient. This framework allows us to construct consistent probability distributions of energy and volume across thermodynamic states, effectively recovering Boltzmann-consistent statistics at a target condition independent of time step. These considerations are particularly important for enhanced sampling methods such as replica exchange and umbrella sampling, which rely on rigorous Boltzmann sampling and require accurate energies and temperatures for valid replica exchange probabilities and statistical reweighting.
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Optics
Physics of Dipole and Quadrupole Brewster Angles in Thin Films
Edward H.Krock, Mughaid Ali, Haizhong Weng et al. (+2 more)
The Brewster angle is a well-known-phenomenon that describes the angle at which the intensity of reflection of p-polarized light is zero for a single dielectric interface. We investigate the angle dependent reflection in a simple SiN thin film, with thickness in the hundreds of nanometres, a common thickness used in optical waveguides, Fabry-Perot resonators, sensors and
lasers. We describe the reflection of our SiN thin film in terms of electric and
magnetic multipoles through a multipole expansion of the fields inside our film. Previous theoretical studies on Fabry Perot modes in GaP films have only considered the reflection of unpolarized light at normal incidence. Our investigation expands on this work to s- and p-polarization and angle dependent effects permitting the study of both Fabry Perot and Brewster angle effects together. Our approach allows us to re-derive the well-known Brewster angle equation from the electric dipole term. We then derive several new Brewster angle equations associated with the
magnetic dipole and electric/
magnetic quadrupoles in our model. Our model is then validated by obtaining good agreement between the predicted reflection from our multipoles to the measured reflection of the same thin film. The distinction between the standard electric dipole Brewster angle and our newly discovered Brewster angles is the destructive interference between remaining multipoles. It is this destructive interference which produces the zero in measured and modelled reflection, associated with the Brewster angle. In addition, the Brewster condition of the
magnetic dipole and quadrupoles are only satisfied at specific wavelengths. This multipole model brings additional understanding of how light interacts with thin film dielectric materials.
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All authors Edward H.Krock, Mughaid Ali, Haizhong Weng, C. M. Smith, John F.Donegan
Popular Physics · Cross-listed from stat.OT
Implications of the Pessimistic Lower Limit on the Drake Equation
Max Baak and Hella Snoek
The observation of life on Earth is generally accepted to be uninformative concerning the probability of life on other Earth-like
planets, a belief first formalized by Brandon Carter and based on the selection effect of our existence. In a similar way, the Drake equation is either presented as estimate of the total number of active, communicative, extraterrestrial civilizations in our
Galaxy ($n^g_{\rm civ}$), i.e. excluding humanity, or humanity is included in the estimate but judged to be an uninformative data point. Daniel Whitmire has recently challenged the Carter abiogenesis argument, claiming the logic behind it is flawed, as the conditional likelihoods used by Carter in Bayes'
theorem are not evaluated prior to the occurrence of the evidence of life on Earth, but posterior. Doing so correctly, the anthropic selection effect is removed and the observation of life on Earth is informative after all. Following this argument, we treat the Drake equation as estimate of all technological civilizations in a statistical counting experiment and include the data point of humanity as informative evidence. This allows one to set a pessimistic lower limit on $n^o_{\rm civ}$ for the observable universe, $n^o_{\rm civ} > 0.051$ at 95% C.L., or $n^g_{\rm civ} > 8\times10^{-13}$ at 95% C.L. for the
Galaxy. In particular, this excludes models that predict $n^o_{\rm civ}\ll 1$ for the observable universe and refines the allowable parameter space for hypotheses like Rare Earth. Our analysis substantially reduces the portion of the Drake equation parameter space that predicts humanity is alone; when applying the lower limit this study finds $P(n^o_{\rm civ}>1 |\, {\rm humanity}) = 97.6\%$, making solitude in the observable universe a disfavored outcome. For the low-end estimate of $n^o_{\rm civ}\! =\! 1$ we calculate a probability of 42% for the existence of other communicating civilizations.
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Optics
Electric Field Resolved Image Formation in a Widefield Optical Microscope
Arjun Ashoka, Juhwan Lim, Akshay Rao et al. (+1 more)
Visualizing the spatiotemporal
evolution of the electric field of light is fundamental to optics, from designing photonic devices to developing next-generation microscopes. However, we lack the experimental tools to directly access the electric field of light in the sample plane of an optical microscope. Here, we introduce an all-optical imaging modality that resolves the electric field of light in the plane of a traditional widefield transmission optical microscope with 100-attosecond temporal and 200-nanometer spatial resolution. With this we demonstrate the delayed buildup of scattering contrast and pulse broadening through and around a thick MoTe2 flake - dynamics inaccessible via standard simulations. We showcase our technique's versatility by additionally resolving the full in-plane vector electric field lines during photoexcitation as the optical pulse propagates through and around the MoTe2 flake.
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All authors Arjun Ashoka, Juhwan Lim, Akshay Rao, Dmitry A. Zimin
Atomic Physics
Characterization of Feshbach resonances in $^6\mathrm{Li}{-}^7\mathrm{Li}$ using improved interaction potentials
Jing-Chen Zhang, Paul Julienne and Yu Liu
We characterize Feshbach resonances in all isotopologues of the $\mathrm{Li}{-}\mathrm{Li}$ system with improved interaction potentials. Starting from spectroscopically accurate Morse/long-range (MLR) potential-energy curves for the singlet ($X^{1}\Sigma^{+}$) and triplet ($a^{3}\Sigma^{+}$) electronic states of $\mathrm{Li}_2$, we apply small phenomenological inner-wall adjustments (following Julienne and Hutson, Phys. Rev. A 89, 052715 (2014), arXiv:1404.2623v3) and fit the resulting potentials to threshold measurements for the $^{6}\mathrm{Li}{-}^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}{-}^{7}\mathrm{Li}$ isotopologues, including binding energies, scattering lengths, and Feshbach resonance positions. Using the optimized potentials in coupled-channels scattering calculations, we predict and characterize s-wave Feshbach resonances in the $^{6}\mathrm{Li}{-}^{7}\mathrm{Li}$ isotopologue. In its lowest-energy hyperfine channel, all resonances are narrow ($\sim 0.01{-}0.1$ G), strongly closed-channel dominated, and predominantly triplet in electronic
spin character, in marked contrast to the homonuclear systems. These results provide a foundation for designing Raman optical-transfer pathways to produce ultracold $\mathrm{Li}_2$ molecules in deeply bound rovibrational levels of both the $X^1\Sigma^{+}$ and $a^3\Sigma^{+}$ potentials across all three isotopologues.
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Fluid Dynamics
Design Implications of Chord Length and Number of Blades on Self-Starting Process in Vertical-Axis Wind Turbines
Faisa Muhammad and Muhammad Saif Ullah Khalid
Self-starting remains a key limitation of lift-driven vertical-axis wind turbines and is strongly influenced by
geometric design choices that also govern steady-state performance. This work quantifies the roles of chord length and blade number on startup dynamics and the attained steady tip-speed ratio using two-dimensional URANS simulations of freely rotating Darrieus-type rotors. Two configuration families are examined, an equal-chord set in which three and five bladed turbines share the same chord length, and an equal-solidity set in which the chord length is reduced for the five blade turbines to match solidity with the three blade counterparts. Results are analyzed using the time
evolution of tip-speed ratio, reduced-frequency measures to identify sustained unsteady intervals, vorticity-field diagnostics of dynamic stall
vortex formation and detachment, and a torque decomposition into pressure and viscous moments. The results show that increasing number of blades can enhance early stage acceleration but generally lowers the steady tip-speed ratio by intensifying blade-
vortex interaction in the downstream half cycle. Increasing chord length promotes self-starting by strengthening unsteady loading during the transition out of the low-speed regime, but also increases viscous losses and wake interaction, leading to lower the steady tip-speed ratio for self-starting high chord configurations. The role of viscous moments is also analyzed to quantify their contribution to self-starting behavior and to assess their influence on limiting the attainable operating state after self-starting. These findings provide design-relevant guidance on the startup–performance trade-off associated with the chord length and number of blades in freely accelerating vertical-axis wind turbines.
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Classical Physics
Hamilton Revised: The Action Principle for Initial Value Problems
W. A. Horowitz and A. Rothkopf
We present the variational action principle for initial value problems in classical, conservative-force point particle mechanics. We rigorously derive this formulation by taking the classical limit of the Schwinger-Keldysh expression for the time dependence of the expectation value for operators in
quantum mechanics. We clarify the connection between the variation of the position and the variation of the velocity of a particle when implementing Hamilton's Principle in deriving the Euler-Lagrange Equations. We show that both the plus and minus Keldysh paths (of the average and difference of the forward/backward paths) have classical paths and fluctuations – unlike the common perception that the minus path provides the fluctuations around the single classical solution given by the plus path – and that the fluctuations of both paths are crucial for the correct normalization of the classical limit. The classical limit yields "initial conditions" and equations of motion for the minus paths such that the unique classical solution for the minus paths is that they are identically zero, and, fascinatingly, that the minus paths' solution propagates backwards in time; thus one does not need to set the minus paths to zero by hand when taking the classical limit of the Schwinger-Keldysh formalism. We note implications for the classical and
quantum mechanics of non-holonomic constraints and
quantum field theories with gauges dependent on the derivatives of the fields.
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Plasma Physics · Cross-listed from astro-ph.GA
Particle acceleration and pitch-angle evolution in relativistic turbulence
Daniel Humphrey, Cristian Vega, Stanislav Boldyrev et al. (+1 more)
Synchrotron radiation detected from relativistic astrophysical objects such as
pulsar-wind nebulae and {jets from active
galactic nuclei} depends on the
magnetic fields and the distribution functions of energetic electrons in these systems. Relativistic magnetically dominated
turbulence has been recognized as an efficient mechanism for structure formation and non-thermal particle acceleration in these environments. Recent numerical simulations of relativistic
turbulence have provided insights into the energy distribution functions of accelerated electrons. Much less is currently understood about their {pitch angle distributions}, which are crucial for accurately interpreting the spectra of synchrotron radiation. {We perform a detailed case study of} the pitch angle distributions formed during the process of turbulent acceleration {for $B_0/\delta B_0 = 10$ and $\tilde{\sigma}_0 \sim 40$, where $B_0$ is the uniform component of the
magnetic field, $\delta B_0$ is the fluctuating component, and $\tilde{\sigma}_0$ is the
plasma magnetization based on the
magnetic fluctuations. We find that even minimal numerical noise can cause substantial pitch angle scattering, but we demonstrate techniques for overcoming the numerical challenges associated with the
evolution of very small pitch angles. Our numerical results are consistent with the phenomenological model found in \cite[][]{vega2024b,vega2025}.}
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All authors Daniel Humphrey, Cristian Vega, Stanislav Boldyrev, Vadim Roytershteyn
Fluid Dynamics
Interface Fluctuations in a Turbulent Binary Fluid using Data-Driven Methods
Samuel Z Khiangte, Triparna Sanyal, Sumantra Sarkar et al. (+1 more)
Interfacial fluctuations in a two-phase binary fluid mixture reveal signatures of underlying physical processes that occur within each phase and on a range of spatial and temporal scales. In this study, we investigate a model binary fluid system consisting of a single droplet of one phase moving in the background of the second phase. The binary fluid system is subjected to turbulent forcing. We perform extensive direct numerical simulations of the turbulent system to examine how quantities such as interfacial dynamics and droplet acceleration can be systematically decoded. Extensive simulations of binary fluid systems are computationally expensive and time-consuming. In contrast, data-driven models have shown promise in recent times in reducing computational cost. In this work, we build and compare the performances of four interpretable data-driven models, i.e., dynamic mode decomposition (DMD), Hankel DMD, sparse identification of nonlinear dynamics (SINDy), and
Stochastic Langevin regression (SLR), each using dimensionality reduction via proper orthogonal decomposition, to identify simplified dynamical equations governing interfacial dynamics and center-of-mass acceleration. We show how these learned models can be generalized to encode physical properties, such as the interfacial surface tension and droplet size. In particular, we show that SLR predicts the underlying dynamical equations of the binary-fluid system with the greatest accuracy over a wide range of interfacial tension values and droplet sizes. In addition, SLR requires fewer terms compared to SINDy to capture the underlying dynamics, and is thus computationally the most efficient among the four methods. These data-driven techniques can be used in many practical applications, such as the dynamics of biological
cell membranes, thin films, and other industrial applications.
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All authors Samuel Z Khiangte, Triparna Sanyal, Sumantra Sarkar, Nairita Pal
Fluid Dynamics · Cross-listed from astro-ph.SR
Bridging the Prandtl number gap: 3D simulations of thermohaline convection in astrophysical regimes
Adrian E. Fraser
Thermohaline convection (also known as fingering convection or thermohaline mixing) occurs in
stellar radiation zones where a sufficient inversion of the mean molecular weight is present. This process mixes chemicals radially and occurs in a variety of
stars, including near the luminosity bump on the red
giant branch and potentially in polluted white
dwarfs. Previous efforts to characterize this process using 3D simulations have been restricted to regimes far from actual
stars: The Prandtl number $\Pr$–the ratio of the kinematic viscosity to thermal diffusivity–assumes values as low as $10^{-6}$ in
stars, but 3D simulations have been restricted to $\Pr \gtrsim 10^{-2}$. For this reason, disagreements between observations and simulations are routinely dismissed as stemming from this $\Pr$ gap. This letter bridges this gap and demonstrates that 3D simulations of thermohaline convection can be performed in
stellar parameter regimes. Using a suite of simulations spanning previously studied regimes with $\Pr \gtrsim 10^{-2}$ down to $\Pr = 10^{-6}$, we demonstrate that the chemical mixing model of Brown, Garaud, & Stellmach (2013) remains consistent with 3D simulations across both regimes. Therefore, tensions between this model and observations cannot be dismissed as resulting from a $\Pr$ gap, and must be resolved by considering additional physics.
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Chemical Physics · Cross-listed from cond-mat.mes-hall
Jan Kunc, Bohdan Morzhuk, Veronika Stará et al. (+6 more)
The realization of high-fidelity organic-inorganic
quantum emulators is frequently hindered by the interfacial imperfections introduced during device fabrication. Here, we demonstrate a robust nanofabrication protocol that restores the atomic-scale purity of epitaxial
graphene on SiC to UHV-equivalent levels, as confirmed by Low-Energy Electron Diffraction, and Microscopy. This pristine interface enables the emergence of macroscopic excitonic coherence in epitaxial overlayers of 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), a model molecular system characterized by intense electron-
phonon coupling. Through a combination of high-sensitivity
Fourier Transform Photo-current Spectroscopy, photoluminescence, and dynamic Raman mapping, we resolve a complex vibronic
manifold governed by Davydov splitting. We show that the $P6_3/m$ crystalline
symmetry of the HMTP overlayer lifts the degeneracy of the HOMO-LUMO transition, creating discrete bright and dark excitonic branches. Using an analytical tight-binding model parameterized by ARPES-derived intermolecular coupling and Raman vibrational modes validated by molecular dynamics simulations, we quantify the polarization energy, the Huang-Rhys factor, and Herzberg-Teller corrections to the Franck-Condon model. Our results reveal that the dark-state branch dominates the radiative channel, following a polaron-mediated relaxation pathway consistent with Kasha's rule. By reconciling macroscopic device architecture with UHV-level surface science, this work establishes a scalable platform for the study of dark-
exciton dynamics and the development of solid-state molecular
quantum memories.
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All authors Jan Kunc, Bohdan Morzhuk, Veronika Stará, Devanshu Varshney, Mykhailo Shestopalov, Kryštof Matějka, Martin Rejhon, Jiří Novák, Jan Čechal
Plasma Physics
Comment on "Impact of particle number and cell-size in fully implicit charge- and energy-conserving particle-in-cell schemes" by N. Savard et al., Phys. Plasmas 32, 073903 (2025)
Luis Chacon, Guangye Chen and Lee Ricketson
We take issue with the conclusions in the recent publication by Savard et al. In the study, the authors implement a fully nonlinear charge- and energy-conserving implicit particle-in-
cell method (ECC-IPIC), and use it to study the impact of particle number in the quality of the ECC-IPIC solutions for several problems, including an ion acoustic shockwave (IASW) problem and several sheath problems in bounded
plasmas. From the study, the authors concluded that “to reproduce highly resolved convergent solutions, a higher amount of particles per
cell need to be used in the implicit scheme for both periodic and bounded simulations when the
cell size exceeds the Debye length.” We demonstrate that, according to our analysis for the IASW test, this conclusion does not survive independent scrutiny. We have identified several diagnostics procedural issues that are at the root of their conclusion, which when fixed dramatically change the outcome of the study.
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Atomic Physics
Quantum Scattering of Fullerene 12C60 with Rare Gas Atoms and its selection rules for rotational quenching
Alexander Petrov, Anna Linnik, Jacek Klos et al. (+2 more)
The discovery of the C60 fullerene opened new horizons to design carbon nanostructures with targeted electronic structure as well as transport and optical properties. For example, endohedral 12C60 molecules were proposed as candidates for functional
quantum architectures to store and manipulate encased atomic and molecular
qubits. Recent advances in cryogenic buffer-gas cooling and frequency-comb spectroscopy have enabled rovibrational
quantum-state-resolved measurements of gas-phase 12C60, revealing rotational fine structure reflecting its high icosahedral
symmetry. Here, we present a perturbative
quantum description of the 12C60 molecule interacting with a buffer gas of 40Ar atoms at temperatures of order 100 K, including a detailed analysis of their electronic structure, their interaction anisotropies, and the collision-induced rotational quenching of 12C60 in its vibrational and electronic ground state. The role of the icosahedral
symmetry on the collisional dynamics is emphasized leading to unusual selection rules. Finally, we compute the isotropic and anisotropic static and dynamic dipole polarizability of 12C60 in its absolute ground state in order to evaluate the long-range, van der Waals interaction between 12C60 and 40Ar.
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All authors Alexander Petrov, Anna Linnik, Jacek Klos, Eite Tiesinga, Svetlana Kotochigova
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Unraveling Lithium Dynamics in Solid Electrolyte Interphase: From Graph Contrastive Learning to Transport Pathways
Qiye Guan and Yongqing Cai
Fast lithium transport across the solid-state electrolyte (SSE)/lithium metal anode interface is critical for high-performance all-solid-state batteries. Uncovering the complex lithium dynamics governed by diverse local environments in the solid electrolyte interphase (SEI) is fundamental for performance optimization. However, a general framework for characterizing these distinct local environments and the associated transport mechanisms remains lacking. Here, we develop GET-SEI, a general framework that discovers local atomic environments without predefined labels through Graph contrastive learning (GCL), models lithium transition kinetics via Extended dynamic mode decomposition (EDMD), and quantifies reactive lithium flux through Transition path theory (TPT). Applied to different SSE/Li systems, including sulfides (Li6PS5Cl/Li, Li10GeP2S12/Li) and
oxides (Li7La3Zr2O12/Li), the GET-SEI reveals dominant transport pathways and kinetic bottlenecks in each system, providing quantitative metrics for evaluating lithium transport efficiency. As novel high-performance SSEs continue to emerge, GET-SEI offers a widely applicable, interpretable tool for targeted SEI engineering.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Efficient first-principles modeling of complex molecular crystals at sub-chemical accuracy
Benjamin X. Shi, Kristina M. Herman, Flaviano Della Pia et al. (+5 more)
Molecules can form myriad crystalline polymorphs, each with distinct properties affecting their performance across diverse applications, from pharmaceuticals to functional materials and more. Predicting the thermodynamically most stable polymorph from first principles remains a formidable challenge. It requires methods that scale to large, technologically-relevant molecules while achieving very high accuracy (below 1 kJ/mol) on relative
lattice energies. Such accuracy, often termed sub-chemical accuracy, is generally beyond the reach of the workhorse density functional theory (DFT). In this work, we introduce a framework, combining advances in correlated wavefunction theory (cWFT) and the many-body expansion, to deliver accurate, cost-effective predictions of complex molecular
crystals. For 23 organic molecules and 13 ice polymorphs, we predict
crystal lattice energies to within experimental uncertainties at costs comparable to hybrid DFT, while being several orders of magnitude more efficient than previous cWFT approaches. We extend this approach to a set of large, drug-like molecules including axitinib and ROY, previously inaccessible to cWFT and where DFT is insufficient, achieving sub-chemical accuracy on the relative energies between challenging polymorphs. With the reference data generated throughout this work, we have been able to further parametrize a DFT functional with unprecedented accuracy aligning with our predictions. This cWFT framework as well as DFT functional are made openly available, providing new ranking tools to facilitate efficient high-throughput screening of molecular
crystal polymorphs.
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All authors Benjamin X. Shi, Kristina M. Herman, Flaviano Della Pia, Venkat Kapil, Andrea Zen, Peter R. Nagy, Sotiris Xantheas, Angelos Michaelides
Atmospheric and Oceanic Physics
Investigating the short-term effects of particulate matter (PM) chemical components on mortality and the potential modifying effect of extreme temperature: A time-series analysis in London
Xiaolu Zhang, Anna Font, Anja Tremper et al. (+5 more)
Particulate matter (PM) is linked to adverse health outcomes, yet the roles of specific PM components and their modification by extreme temperature remain unclear. We examined short-term associations between ten PM chemical components and daily mortality in Greater London (2015-2018). PM components include inorganic aerosols (black carbon from wood burning (BCwb) and traffic exhaust (BCtr), SO4, NO3, and NH4) and organic aerosols (hydrocarbon-like organic aerosol (HOA), biomass burning OA (BBOA), cooking-like OA (COA), more and less oxidized oxygenated OA (MO-OOA and LO-OOA)). We applied quasi-Poisson generalized additive models and weighted
quantile sum (WQS) regression to estimate single-pollutant, multi-pollutant, and mixture effects, respectively, and included interaction terms to test effect modification by heat waves and cold spells. All ten components showed positive associations with all-cause mortality in single-pollutant models with stronger estimated risks for respiratory mortality, particularly for NH4, NO3, SO4. In mixture analyses, the WQS index was significantly associated with all-cause mortality (RR = 1.015, 95% CI: 1.006-1.024 per 25th-percentile increase) and showed a marginally significance with respiratory mortality (RR = 1.018, 95% CI: 0.994-1.042). MO-OOA and COA contributed most to all-cause mortality, while BBOA and BC Wood dominated respiratory effects. Heat waves consistently amplified respiratory risks in both single-pollutant and mixture models with little evidence for cardiovascular mortality. Overall, MO-OOA demonstrated harmful associations across outcomes, suggesting potential toxicity link to secondary atmospheric oxidation processes. These findings support source-specific control strategies and highlight the importance of accounting for extreme temperature in air pollution mitigation policies.
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All authors Xiaolu Zhang, Anna Font, Anja Tremper, Max Priestman, Shawn Y. Lee, David C. Green, Dimitris Evangelopoulos, Gang I. Chen
Fluid Dynamics
Turbulence generation and data assimilation in wall-bounded flows with a latent diffusion model
Fabian Steinbrenner, Baris Turan, Hao Teng et al. (+1 more)
Wall-bounded turbulent flows are chaotic and multiscale, rendering fast prediction at high Reynolds numbers computationally prohibitive in applications such as wind farms. Classical data assimilation is based on repeated solutions of the governing equations and thus inherits this cost. Generative models learn the probability distribution of flow states, enabling scalable probabilistic reconstruction. Our generative framework couples a variational autoencoder with a
diffusion transformer to generate four-dimensional spatiotemporal samples.
Bayesian conditioning enables data assimilation without retraining and allows statistical constraints to be imposed through sampling. The framework is applied to a subdomain of turbulent plane Couette flow, where the corresponding DNS in this generation region requires $O(10^6)$ spatial degrees of freedom. Using $O(10)$ latent spatial degrees of freedom, the model achieves a compression ratio of $O(10^5)$, which is one to two orders of magnitude above prior reports. It reproduces single-point statistics up to fourth order and the energy spectra, as well as the intermittency and phase-sensitive structure captured by velocity-increment and $Q$–$R$ statistics. Two assimilation scenarios demonstrate that, when observations are statistically consistent with the prior, conditional
diffusion models with the proposed sampling strategy preserve complex turbulent statistics in the posterior. However, enforcing these constraints while preserving physical fidelity and sample diversity introduces an inherent trade-off. Excessive conditioning can distort the learned prior, paralleling limitations of classical ensemble-based data assimilation, where this can likewise degrade the prior covariance. These results highlight both the promise of
diffusion models as probabilistic surrogates and the challenges of conditioning them.
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All authors Fabian Steinbrenner, Baris Turan, Hao Teng, Heng Xiao
Physics and Society · Cross-listed from stat.AP
Socio-Spatial Patterns of Suicide Mortality in the United States
Kushagra Tiwari, M. Amin Rahimian, Marie-Laure Charpignon et al. (+2 more)
Suicide causes more than 49,000 deaths annually in the United States, 55% involving firearms. Suicide mortality varies substantially across US counties, but the role of large-scale social networks remains underexplored. We combine county-level suicide mortality data for 2010-2022 with the Facebook Social Connectedness Index (SCI) and measures of exposure to Extreme Risk Protection Orders (ERPOs). In population-weighted two-way fixed effects models adjusting for sociodemographic and economic characteristics, COVID-19, drug-overdose and alcohol-related mortality, poor mental health days, state firearm policies, and geographical proximity, a one-standard-deviation increase in the SCI-weighted suicide mortality rate of socially connected counties was associated with 2.47 additional deaths per 100,000 residents in the focal county (95% CI [0.97, 4.00]). A one-standard-deviation increase in ERPO social exposure was associated with 0.266 fewer deaths per 100,000 (coefficient -0.266; 95% CI [-0.403, -0.128]) after adjustment for geographical proximity and state-by-year fixed effects. The social-proximity association persisted under alternative neighborhood definitions and spatial-error models, and subgroup analyses showed heterogeneity by age. These findings show that both suicide mortality and the lower mortality associated with exposure to firearm-restriction policies are patterned along inter-county social ties beyond what is explained by geographical proximity alone.
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All authors Kushagra Tiwari, M. Amin Rahimian, Marie-Laure Charpignon, Philippe J. Giabbanelli, Praveen Kumar
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
High-quality, high-information datasets for universal atomistic machine learning
Cesare Malosso, Filippo Bigi, Paolo Pegolo et al. (+7 more)
The quality, consistency, and information content of training data is often what determines the practical value of machine-learning models for atomistic simulations. Yet, many widely used electronic-structure databases are assembled having materials screening as primary goal rather than robust force-field learning, are limited in their scope to a specific class of chemical compounds, and/or employ inconsistent DFT functionals and settings. Here we introduce MAD-1.6, a highly curated
dataset designed explicitly for training broadly applicable atomistic models across the periodic table at high levels of theory. MAD-1.6 extends the MAD
dataset with targeted enrichment strategies that improve the coverage of chemical space to 102 elements while keeping the total number of configurations compact. All structures are computed with a single, standardized all-electron DFT workflow using the r$^2$SCAN meta-GGA functional and consistent convergence settings, ensuring uniformity across chemically heterogeneous systems. The
dataset encompasses molecules, clusters, bulk
crystals, surfaces, and low-dimensional structures, and its quality and consistency are further enhanced by outlier removal using uncertainty quantification. We demonstrate the high accuracy that can be achieved with the proposed
dataset by training PET-MAD-1.6, a generally applicable r$^2$SCAN interatomic potential that covers 102 elements in the periodic table and achieves exceptional levels of
benchmark accuracy and stability in challenging simulation protocols.
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All authors Cesare Malosso, Filippo Bigi, Paolo Pegolo, Joseph W. Abbott, Philip Loche, Mariana Rossi, Tiago J. Goncalves, Sandip De, Michele Ceriotti, Arslan Mazitov
Computational Physics · Cross-listed from cond-mat.mes-hall
Anisotropic two-dimensional magnetoexciton with exact center-of-mass separation
Dang-Khoa D. Le, Hoang-Viet Le, Dai-Nam Le et al. (+4 more)
Excitons in anisotropic two-dimensional (2D) materials, defined by direction-dependent effective masses, are of pronounced interest for their roles in excitonic and magneto-optical phenomena. A perpendicular
magnetic field complicates the separation of center-of-mass (c.m.) and relative motions, especially when electron and hole masses are comparable. Conventional theories often employ an approximate c.m. separation using factorized wave functions, modifying
magnetic Hamiltonian terms and possibly introducing inaccuracies in magnetoexciton energy predictions. This work develops an exact analytical framework for c.m. and relative motion separation in anisotropic 2D magnetoexcitons, without resorting to the stationary-c.m. approximation. Starting from the full electron-hole
Hamiltonian in a homogeneous
magnetic field, the formalism uses the conserved pseudomomentum to derive a relative-motion
Hamiltonian, revealing new anisotropy-dependent couplings and
magnetic coefficients absent in approximate models. The resulting Schrödinger equation is treated via the Feranchuk-Komarov operator method and Levi-Civita transformation, allowing non-perturbative, systematically convergent solutions. Application to monolayer black phosphorus and titanium trisulfide, both freestanding and encapsulated in hexagonal boron nitride, yields magnetoexciton energies, diamagnetic coefficients, and probability densities for the ten lowest states across considerable
magnetic-field ranges. The results demonstrate the significant influence of anisotropy-dependent coupling on
magnetic response in systems with strong mass anisotropy. This formalism is generalizable to other anisotropic 2D
semiconductors, establishing a foundation for advanced magneto-optical studies.
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All authors Dang-Khoa D. Le, Hoang-Viet Le, Dai-Nam Le, Duy-Anh P. Nguyen, Thanh-Son Nguyen, Ngoc-Tram D. Hoang, Van-Hoang Le
Biological Physics · Cross-listed from cond-mat.soft
Ionic Liquid-Driven Modulation of DNA Brush Morphology on Nanoparticle Surfaces
Anuj Chhabra, Sandip Mandal, Yugang Zhang et al. (+3 more)
The morphology of DNA is strongly influenced by its surrounding environment, including factors such as pH, salt type and valency, and the presence of
polymers. Inorganic salts are known to reduce the DNA chain length through mechanisms like electrostatic screening and ion bridging. In contrast, ionic
liquids, a new class of organic salts, have previously been found to increase the DNA chain length, indicating a distinct mode of interaction between the ionic
liquid and DNA chains. This study utilizes self-assembled DNA-AuNPs as a model system to examine changes in the DNA chain morphology and the nanoscale interaction mechanisms in ionic
liquid environment. The DNA chain lengths are measured in solution using X-ray scattering measurements at varying concentrations of two imidazolium ([BMIM] acetate and [EMIM] acetate) based ionic
liquids. Additionally, Molecular Dynamics (MD) simulations are performed mimicking the experimental system. Our results suggest an interplay of electrostatic and groove-binding interactions governing the DNA chain morphology, which depends on IL concentration and the composition of the DNA chains. It has been found that for DNA chains with majority ssDNA, electrostatic interaction dominate, however with increasing composition of double strands, the DNA chains exhibits compaction due to non-electrostatic hydrophobic groove-binding mechanism.
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All authors Anuj Chhabra, Sandip Mandal, Yugang Zhang, Oleg Gang, Prabal K. Maiti, Sunita Srivastava