Biological Physics
Label-free Imaging of Single-Biomolecule Structure and Interaction by Stimulated Raman Photothermal Encoded Scattering
Pin-Tian Lyu, Yifan Zhu, Qing Xia et al. (+8 more)
Current single molecule methods either rely on fluorescence or lack chemical information. Here we report stimulated Raman photothermal encoded scattering (SRPSCAT) microscopy for quantitative bond-selective imaging of single-biomolecule structures and interactions in native environments. In this approach, scattering of the target molecule is modulated by the deposited energy from stimulated Raman gain and loss processes, thereby encoding vibrational spectroscopic information. Leveraging single-molecule sensitivity of interferometric scattering, SRPSCAT can map single
proteins with chemical specificity, determine their mass, and distinguish
protein secondary structures based on their Raman fingerprints. Furthermore, single
protein binding kinetics are quantified and the conformational dynamics of single de novo designed allosteric
proteins are observed. Together, these results highlight the potential of SRPSCAT for label-free structural, functional and dynamic analysis at the single-molecule level.
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All authors Pin-Tian Lyu, Yifan Zhu, Qing Xia, Guangrui Ding, Arvind Pillai, Xinru Wang, Jianpeng Ao, Haonan Lin, Lulu Jiang, David Baker, Ji-Xin Cheng
Fluid Dynamics
Trans-stenotic pressure drop estimation from PC-MRI and ultrasound imaging velocimetry using a modified Bernoulli equation
Ali Amiri, Johan T. Padding, Selene Pirola et al. (+1 more)
Accurate non-invasive estimation of trans-stenotic pressure gradients remains a challenge. In clinical practice, pressure gradients are often estimated from velocity measurements using Bernoulli-based formulas, but these simplified relations do not explicitly account for how pressure losses change with the flow regime. Here, we introduce a modified Bernoulli (MB) formulation that incorporates regime-dependent pressure losses through a Reynolds-number-dependent loss coefficient. Steady in-vitro experiments were performed in an idealized stenosis model over physiologically relevant flow rates (0.65-3.9 L/min), combining direct pressure measurements with ultrasound imaging velocimetry and phase-contrast
magnetic resonance imaging (PC-MRI) to measure velocities. The MB model was calibrated from the measured pressure drops and then evaluated against the simplified Bernoulli (SB) and extended Bernoulli (EB) formulations. Over the tested flow regime, MB agreed best with the measurements. SB and EB showed larger biases, with errors of roughly 10-55% (SB) and -15 to 25% (EB), and overestimated the pressure drop in the clinically relevant range. We additionally quantified the effect of PC-MRI in-plane pixel size on MRI-based pressure estimates. Coarse sampling of the stenosis throat led to systematic underestimation of flow rate and bulk velocity and, consequently, of the MB-predicted pressure drop. In contrast, the peak throat velocity was substantially less sensitive to pixel size, resulting in smaller estimation errors when used as input for the MB. Overall, the results demonstrate that accounting for flow-regime-dependent loss mechanisms enhances pressure drop estimation, and that sufficient sampling of the stenotic throat is crucial for MRI-based flow rate and pressure drop estimation. In addition, peak-velocity-based MB pressure drop estimations are less sensitive to pixel size.
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All authors Ali Amiri, Johan T. Padding, Selene Pirola, Willian Hogendoorn
Chemical Physics
Automating Computational Chemistry Workflows via OpenClaw and Domain-Specific Skills
Mingwei Ding, Chen Huang, Yibo Hu et al. (+8 more)
This work presents a decoupled framework for multi-step computational chemistry automation built on OpenClaw. OpenClaw serves as the general-purpose
agent for task coordination and supervision. Planning skills externalize task descriptions into executable task specifications, domain skills provide computational chemistry procedures, and the DPDispatcher skill grounds computation in heterogeneous HPC environments. In a methane-oxidation reactive MD case study, the framework coordinated cross-tool execution, supported bounded recovery from runtime failures, and extracted reaction networks.
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All authors Mingwei Ding, Chen Huang, Yibo Hu, Yifan Li, Zitian Lu, Xingtai Yu, Duo Zhang, Wenxi Zhai, Tong Zhu, Qiangqiang Gu, Jinzhe Zeng
Computational Physics · Cross-listed from cond-mat.stat-mech
Lattice and PT symmetries in tensor-network renormalization group: Case study of a hard-square lattice gas model
Xinliang Lyu
The tensor-network renormalization group (TNRG) is an accurate numerical real-space renormalization group method for studying phase transitions in both
quantum and classical systems. Continuous phase transitions, as an important class of phase transitions, are usually accompanied by spontaneous breaking of various
symmetries. However, the understanding of
symmetries in the TNRG is well-established mainly for global on-site
symmetries like U(1) and SU(2). In this paper, we demonstrate how to incorporate
lattice symmetries (including reflection and rotation) and the PT
symmetry in the TNRG in two dimensions (2D) through a case study of the hard-square
lattice gas with nearest-neighbor exclusion. This model is chosen because it is well-understood and has two continuous phase transitions whose spontaneously-broken
symmetries are
lattice and PT
symmetries. Specifically, we write down proper definitions of these
symmetries in a coarse-grained tensor network and propose a TNRG scheme that incorporates these
symmetries. We demonstrate the validity of the proposed method by estimating the critical parameters and the scaling dimensions of the two phase transitions of the model. The technical development in this paper has made the 2D TNRG a more well-rounded numerical method.
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Plasma Physics · Cross-listed from hep-ph
QED cross sections in strong magnetic fields
Olavi Kiuru, Joonas Nättilä, Risto Paatelainen et al. (+1 more)
The magnetospheres of magnetars, a class of highly magnetized
neutron stars, host
magnetic fields exceeding the Schwinger limit, where
Quantum Electrodynamics (QED) becomes nonlinear. In such environments, QED scattering processes are strongly modified, which may affect
plasma dynamics. In this work, we apply a formalism originally developed for the study of
magnetic-field effects in hot
quark-
gluon plasma to strong-field QED. The method resums interactions between virtual electrons and the external
magnetic field, consistently incorporating the finite decay widths of excited Landau levels derived from the
fermion self-energy. Using this framework, we perform the first systematic analysis of tree-level QED scattering processes in strong
magnetic fields, concentrating on the processes of highest relevance for the
plasma dynamics of magnetars. All resulting cross sections are provided in an open-source Python package.
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All authors Olavi Kiuru, Joonas Nättilä, Risto Paatelainen, Aleksi Vuorinen
Instrumentation and Detectors
Cryogenic operation of neutron-irradiated silicon photomultiplier arrays up to 1e14 neq/cm^2
Esteban Currás-Rivera, Guido Haefeli and Federico Ronchetti
In the context of the Scintillating Fibre (SciFi) Tracker for the LHCb Upgrade 2, radiation-induced damage in silicon photomultipliers (SiPMs) has been studied over a wide temperature range, from room temperature down to 100 K. With the LHCb detector Upgrade 1, installed during the LHC's Long Shutdown 2 (LS2) (2019-2021), the first large-scale SciFi tracker read out by multichannel silicon photomultipliers (SiPMs) was constructed, installed, and has been operated ever since. A major challenge for the SciFi tracker is the
neutron radiation at the SiPMs' location. At the end of the lifetime of the Upgrade 1 detector, the expected
neutron fluence for the SiPMs will reach 6e11 neq/cm^2. Cryogenic operation is being investigated to mitigate even higher radiation-induced damage for Upgrade 2, where the total
neutron fluence is expected to reach 3e12 neq/cm^2. A large set of custom SiPM arrays, varying in pixel size, electric field configuration, and doping implant concentration, developed by FBK and Hamamatsu, were tested after
neutron irradiation. Characterisation was performed in a dedicated cryogenic test setup, where the operating temperature was varied over a wide range. Key performance parameters such as breakdown voltage, gain, dark count rate, optical crosstalk, and afterpulsing were characterised as functions of temperature, overvoltage, and
neutron fluence. The result is a precise assessment of radiation damage for state-of-the-art technology from two leading SiPM manufacturers, allowing the results to be transferred to other SiPM applications.
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Optics
Giant Brillouin gain in frozen CS2 capillaries
Simon Seiderer, Andreas Geilen, Luan N. Sliwa et al. (+5 more)
Stimulated Brillouin-Mandelstam scattering offers exceptional capabilities for photonic signal processing, but current platforms demand performance trade-offs between long interaction lengths, high gain, low optical losses, and practical implementation. Here, we demonstrate a novel platform based on the reversible freezing of a carbon disulfide filled
liquid-core optical fiber. This approach delivers a
giant in-fiber Brillouin gain of 434 W-1m-1 with a linewidth of 24 MHz, while maintaining low propagation losses in a fully spliced architecture and providing the potential for meter-scale interaction lengths. Leveraging this gain, as a proof of principle, we realize an optoacoustic
memory operating at sub-nanojoule pulse energies - more than two orders of magnitude lower than state-of-the-art implementations. This power reduction is universal for Brillouin-based fiber applications in general and will enable low-power photonic signal processing and neuromorphic computing, efficient microwave photonics and sensing, as well as in-fiber
quantum optomechanics-based technologies.
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All authors Simon Seiderer, Andreas Geilen, Luan N. Sliwa, Linqiao Gan, Xue Qi, Mario Chemnitz, Markus A. Schmidt, Birgit Stiller
Fluid Dynamics
Universal transport laws in buoyancy-driven porous mixing
Marco De Paoli and Xiaojue Zhu
Buoyancy-driven convection in porous media governs heat and mass transport in a wide range of natural and engineered systems, from groundwater aquifers and geothermal reservoirs to carbon storage in geological formations and flows through planetary interiors. Yet the transient regime, in which fingering flows emerge and transport is strongly enhanced, is still described largely through empirical scaling laws, limiting predictive capability across conditions. Here we show that transient porous buoyancy-driven mixing obeys exact time-dependent balances that couple transport, flow intensity, and scalar dissipation. These balances remain accurate when restricted to the actively mixing layer, revealing that the essential dynamics are localized within a finite region. Leveraging these results, we derive a minimal one-parameter closure for the mean scalar field. The theory we propose predicts self-similar mean profiles, universal second-order statistics, and a linear transport law without case-by-case tuning. Direct numerical simulations up to spatial resolution of $2048\times2048\times16384$ points validate these predictions. Our results place transient porous mixing on a predictive footing, showing how macroscopic transport laws emerge from exact balances and self-similar dynamics, and provide a general framework for buoyancy-driven transport in porous media.
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Optics
Exceptional-point-constrained locking of boundary-sensitive topological transitions in chiral non-Hermitian SSH-type lattices
Huimin Wang, Yanxin Liu, Zhijian Li et al. (+1 more)
Topological transitions in non-Hermitian systems are generally boundary sensitive: a point-gap winding transition under periodic boundary condition (PBC) and a non-Bloch bulk real-line-gap transition under open boundary condition (OBC) at $\mathrm{Re}(E)=0$ are governed by different spectra and therefore need not coincide. Here we show, for a class of
chiral non-Hermitian Su–Schrieffer–Heeger (SSH)-type
lattices, that these two criticalities can be locked by an exceptional-point-constrained (EP-constrained) parameter
evolution. The key requirement is not the occurrence of isolated exceptional points, but the persistence of a zero-energy Bloch degeneracy along the entire sweep, which is generically exceptional in the non-Hermitian regime. In an analytically tractable limit of an extended non-Hermitian SSH chain, the EP-constrained
manifolds and both transition boundaries are obtained in closed form, making the locking explicit. Away from this limit, numerical generalized-Brillouin-zone (GBZ) calculations confirm the correspondence for representative constrained sweeps, whereas unconstrained paths show that isolated exceptional points or Hermitian degeneracies do not enforce locking. We further verify the mechanism in a spinful four-band extension with branch-resolved GBZs, including strongly branch-imbalanced regimes. These results establish a path-dependent diagnostic principle: along EP-constrained sweeps in this SSH-type class, changes in PBC point-gap winding can indicate OBC non-Bloch bulk real-line-gap transitions and the corresponding changes in zero-energy boundary modes.
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All authors Huimin Wang, Yanxin Liu, Zhijian Li, Zhihao Xu
Biological Physics
Interfacial Permeability, Reflectivity and Preferential Internal Mixing of Phase-Separated Condensates
Oihan Joyot, Zoé Ferrand, Fernando Muzzopappa et al. (+2 more)
Biomolecular condensates organize biochemical processes by spatially concentrating molecules while allowing for dynamic exchange with their surroundings. However, transport across their interface can be strongly attenuated, leading to enhanced retention and preferential internal mixing. Two key mechanisms have been proposed to describe this behavior: biased interfacial reflectivity, which compares how strongly particles are reflected at the interface when attempting to enter or leave the condensate, and interfacial resistance, which sets the kinetic rate at which particles can cross the interface. Quantifying these parameters experimentally has remained challenging. Here, we present a theoretical and experimental framework to address this issue, extending our previously developed half-FRAP approach. We solve the spherical
diffusion problem with a semipermeable interface by spectral decomposition. By evaluating the information content of the integrated recovery curves, we show that they encode sufficient information to recover interfacial parameters over extended regions of parameter space. Applying our framework to tunable coacervates composed of poly-lysine and hyaluronic acid, we find that their interfaces exhibit strongly biased reflectivity and substantial resistance, both driving preferential internal mixing. These parameters depend on salt concentration, linking interfacial transport to intermolecular interaction strength and position in the phase diagram. Our results establish a quantitative connection between interfacial properties and condensate dynamics, revealing how their interplay gives rise to distinct transport regimes.
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All authors Oihan Joyot, Zoé Ferrand, Fernando Muzzopappa, Pierre Weiss, Fabian Erdel
Classical Physics · Cross-listed from q-bio.NC
The Reward Function and the Least Cost Principle for Gravitation and other Laws of Physics
Rubén Moreno-Bote
If the universe follows a specific design, then a central question is which cost function is optimized by the observed forces. This is the problem of inverse optimal control, or inverse reinforcement learning, in which a reward function is inferred from the dynamics of the observed system. We first establish the least cost principle, whereby the laws of motion can be derived from minimization of a time-discounted integral of the acceleration cost minus a state-dependent reward function. After determining the functional form of the acceleration cost from basic principles, we infer the reward function from the laws of motion governing classical gravitation and Coulomb forces. The inferred reward function is high when pairs of particles have high relative velocities and when their relative motion is orthogonal to their distance vectors. All in all, our work suggests that relative motion and quasi-circular orbits are the dynamical and static features optimized by central forces in nature.
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Plasma Physics · Cross-listed from astro-ph.SR
The Effect of Expansion and Instabilities in the Thermodynamic Regulation of the Young Solar Wind Plasma
Matilde Coello-Guzmán, Víctor A. Pinto, Roberto E. Navarro et al. (+1 more)
Using Parker
Solar Probe measurements of the
solar wind, we demonstrate that $\beta_{\parallel}$ is the main driver that determines which instabilities limit
proton temperature anisotropy. At radial distances from 10 to 30
solar radii, $\beta_{\parallel}<1$ drives electromagnetic ion-cyclotron and parallel firehose instabilities, in contrast to the situation at 1 astronomical unit, where, due to most $\beta_{\parallel}>1$, mirror and oblique firehose modes are dominant instead. Furthermore, we show that the temperature anisotropy radially evolves following the semi-empirical anti-correlation $T_\perp/T_\parallel\sim\beta_\parallel^{-0.55}$, consistent with observations at larger distances from the Sun.
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All authors Matilde Coello-Guzmán, Víctor A. Pinto, Roberto E. Navarro, Pablo S. Moya
Instrumentation and Detectors
Real-Time Wiener Deconvolution for feature reconstruction in JUNO
L. Lastrucci, M. Grassi, A. Triossi et al. (+74 more)
In particle physics, experiments generate substantial amounts of data that can be difficult to process without preliminary scaling. To avoid losing potentially crucial data, experimental collaborations are studying novel techniques for real-time data processing to extract features for further physics analysis. A common approach, especially in
neutrino physics, is to use FPGAs for data acquisition and pre-processing. This paper presents an advanced Real-Time Wiener deconvolution
algorithm designed to leverage the processing capabilities of the FPGA integrated into the readout boards of the Jiangmen Underground
Neutrino Observatory (JUNO). The goal is to enable real-time reconstruction of the signal generated by photomultiplier tubes (PMTs) when
neutrino interactions are detected. By exploiting online reconstruction of the signal generated by PMTs, we expect to improve the detection of low-energy depositions, such as those produced by transient astrophysical phenomena. These depositions are usually not saved because of the significant background that affects the low end of the energy spectrum, which would result in a large trigger rate, hence a large amount of data required for storage. This paper presents the features of the
algorithm, including its ability to manage high-throughput data streams with minimal latency, adaptability, and resilience in discerning the characteristics of input data. Performance is evaluated on a JUNO electronic board. This study further demonstrates the potential of FPGA-based solutions for
neutrino physics.
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All authors L. Lastrucci, M. Grassi, A. Triossi, J. Hu, X. Jiang, R. Brugnera, A. Garfagnini, V. Cerrone, L. V. D'Auria, A. Gavrikov, R. M. Guizzetti, A. Serafini, G. Andronico, V. Antonelli, A. Barresi, D. Basilico, M. Beretta, A. Bergnoli, M. Borghesi, A. Brigatti, R. Bruno, A. Budano, B. Caccianiga, A. Cammi, R. Caruso, D. Chiesa, C. Clementi, C. Coletta, S. Dusini, A. Fabbri, G. Felici, G. Ferrante, M. G. Giammarchi, N. Giudice, N. Guardone, F. Houria, A. Islam, C. Landini, I. Lippi, L. Loi, P. Lombardi, F. Mantovani, S. M. Mari, A. Martini, L. Miramonti, M. Montuschi, M. Nastasi, D. Orestano, F. Ortica, A. Paoloni, L. Pelicci, E. Percalli, F. Petrucci, E. Previtali, G. Ranucci, A. C. Re, B. Ricci, A. Romani, C. Sirignano, M. Sisti, L. Stanco, E. Stanescu Farilla, V. Strati, M. D. C. Torri, C. Tuvè, C. Venettacci, G. Verde, L. Votano, G. Dong, J. Dong, L. Fan, S. Hou, Z. Ning, Y. Sun, Y. Wang, Z. Wang, X. Yan
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Self-thermometry measurements of the adiabatic temperature change in first-order phase transition magnetocaloric materials
Daniela O. Bastos, André M. R. Soares, Leonor Andrade et al. (+8 more)
Accurately measuring the magnetocaloric effect is necessary to foster the development of
magnetic refrigeration devices. However, current methods are inconvenient, requiring different instruments to measure each individual property or a custom-made setup. By measuring the time-varying magnetization in a commercially available VersaLab\textsuperscript{\textregistered} PPMS\textsuperscript{\textregistered} from
Quantum Design, we have determined the adiabatic temperature change ($\Delta$T$_{\textrm{ad}}$) of the first-order phase transition material Gd$_5$Si$_2$Ge$_2$, for a
magnetic field change of 0 to 1 T, under high
vacuum ($<$ 0.1 mTorr). For each temperature and
magnetic field, the
equilibrium magnetization is used as the magnetization-to-temperature conversion curve, allowing us to extend the validity of a previously proposed technique to the first-order phase transition material Gd$_5$Si$_2$Ge$_2$, which exhibits significant hysteresis. Our method thus enables full characterization (
magnetic entropy change, adiabatic temperature change, and heat capacity) of any magnetocaloric material, whether it has a first-order or a second-order phase transition, using a single instrument. Comparing to a directly measured $\Delta$T$_{\textrm{ad}}$, our method resulted in a peak $\Delta$T$_{\textrm{ad}}$ value of 4.47 K, within 1% of the directly measured value for a sample of the same composition.
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All authors Daniela O. Bastos, André M. R. Soares, Leonor Andrade, Randy K. Dumas, João S. Amaral, Kyle Dixon-Anderson, Yaroslav Mudryk, Victorino Franco, João P. Araújo, Rafael Almeida, João H. Belo
Physics and Society
Homogeneous Boltzmann-type equations on graphs: A framework for modelling networked social interactions
Andrea Tosin
Homogeneous Boltzmann-type equations are an established tool for modelling interacting multi-
agent systems in sociophysics by means of the principles of statistical mechanics and kinetic theory. A customary implicit assumption is that interactions are "all-to-all", meaning that every pair of randomly sampled
agents may potentially interact. However, this legacy of classical kinetic theory, developed for collisions among gas molecules, may not be equally applicable to social interactions, which are often influenced by preferential connections between
agents. In this paper, we discuss ongoing research on incorporating graph structures into homogeneous Boltzmann-type equations, thereby accounting for the "some-to-some" nature of social interactions.
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History and Philosophy of Physics · Cross-listed from quant-ph
From Complementarity to Quantum Properties: An Operational Reconstructive Approach
Philip Goyal
Quantum theory brings into question the compatibility of the twin desiderata of exact knowability of the present state of the physical world and perfect predictability of its future states. Bohr's coordination-causality complementarity principle transforms this tension into one between properties (as ordinarily understood in classical physics) and deterministic causality. Here, we develop an explicit model of
quantum properties which accommodates this essential tension. Our approach integrates operational, reconstructive, and metaphysical standpoints. In particular, we make use of an operational framework employed in a recent operational reconstruction of Feynman's formulation of
quantum theory; base our property model on an analysis of property types; and use the notions of actuality and potentiality to frame the model. We show that this
quantum property model provides a natural resolution of Zeno's paradox of motion, and provides reliable intuitions about phenomena such as electron diffraction and the non-local behaviour of entangled states of non-identical particles.
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Computational Physics
Physics-Informed Neural Operator for Electromagnetic Inverse Scattering Problems
Q. C. Dong, Zi-Xuan Su, Qing Huo Liu et al. (+2 more)
This paper proposes a physics-informed neural operator (PINO) framework for solving inverse scattering problems, enabling rapid and accurate reconstructions under diverse measurement conditions. In the proposed approach, the dielectric property is represented as a learnable tensor, while a neural operator is employed to predict the induced current distribution. A hybrid loss function, consisting of the state loss, data loss and total-variation (TV) regularization, is constructed to establish a fully differentiable formulation for a joint optimization of network parameters and dielectric property. To demonstrate the framework's generality and flexibility, PINO is implemented using three representative neural operators, i.e., the
Fourier Neural Operator (FNO), the enhanced
Fourier Neural Operator (U-FNO) and the Factorized
Fourier Neural Operator (F-FNO). Compared with conventional approaches, the proposed framework offers a simpler formulation and universal modeling capability, making it readily applicable to various measurement scenarios, including multi-frequency and phaseless inversion. Numerical simulations demonstrate that the proposed PINO achieves high accuracy and robust reconstruction across samples with and without phase information, under single-frequency and multi-frequency settings in the presence of noise. The results demonstrate that PINO consistently outperforms conventional contrast-source inversion (CSI) methods and provides an efficient, unified solution to complex electromagnetic inverse-scattering problems.
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All authors Q. C. Dong, Zi-Xuan Su, Qing Huo Liu, Wen Chen, Zhizhang Chen
Chemical Physics
Enabling ab initio geometry optimization of strongly correlated systems with transferable deep quantum Monte Carlo
P. Bernát Szabó, Zeno Schätzle and Frank Noé
A faithful description of chemical processes requires exploring extended regions of the molecular potential energy surface (PES), which remains challenging for strongly correlated systems. Transferable deep-learning variational Monte Carlo (VMC) offers a promising route by efficiently solving the electronic Schrödinger equation jointly across molecular geometries at consistently high accuracy, yet its
stochastic nature renders direct exploration of molecular configuration space nontrivial. Here, we present a framework for highly accurate ab initio exploration of PESs that combines transferable deep-learning VMC with a cost-effective estimation of energies, forces, and Hessians. By continuously sampling
nuclear configurations during VMC optimization of electronic wave functions, we obtain transferable descriptions that achieve zero-shot chemical accuracy within chemically relevant distributions of molecular geometries. Throughout the subsequent characterization of molecular configuration space, the PES is evaluated only sparsely, with local approximations constructed by estimating VMC energies and forces at sampled geometries and aggregating the resulting noisy data using Gaussian process regression. Our method enables accurate and efficient exploration of complex PES landscapes, including structure relaxation, transition-state searches, and minimum-energy pathways, for both ground and excited states. This opens the door to studying bond breaking, formation, and large structural rearrangements in systems with pronounced multi-reference character.
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Chemical Physics
Complementary Eigen-Zundel Interpretation Reconciles Thermodynamics and Spectroscopy of Excess Protons in Aqueous HF Solutions
Louis Lehmann, Florian N. Brünig, Jonathan Scherlitzki et al. (+4 more)
Aqueous solutions of HF and HCl behave very differently at intermediate concentrations: HCl dissociates completely, whereas HF remains only partially dissociated and forms bifluoride (HF$_2^-$). This should lead to markedly different excess-
proton spectra in HF and HCl solutions, in contrast to experimental reports. Using ab-initio molecular dynamics, we show that in HF the
proton is not firmly bound to F$^-$, as suggested by textbook chemistry, but dynamically shared with a hydrating water molecule. This is rationalized by a modified Eigen-picture description which also explains the formation of HF$_2^-$. The similar vibrational spectra of HF and HCl solutions are explained by a complementary Zundel picture in terms of almost identical excess
proton transfer free-energy profiles for HF and HCl. These results reconcile thermodynamic and spectroscopic observations and provide a unified microscopic picture of excess
protons in aqueous solution.
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All authors Louis Lehmann, Florian N. Brünig, Jonathan Scherlitzki, Morten Lehmann, Martin Kaupp, Beate Paulus, Roland R. Netz
Classical Physics
A note on Gurzadyan theorem
Christian Carimalo
The issue and proof of Gurzadyan
theorem are presented concisely, avoiding tedious and unnecessary calculations that would mask what is essential. The goal is to provide a good mathematical and physical understanding of the
theorem, making you want to learn more about its use in cosmology.
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Geophysics · Cross-listed from astro-ph.EP
Interaction between vegetation and Snowball phases in the late Proterozoic Earth
Erica Bisesi, Giuseppe Murante, Antonello Provenzale et al. (+3 more)
Between 2.4 and 0.6 Gy ago, our
planet underwent several episodes of global glaciations, including the Snowball Earth case that ended 635 My ago. Causes of this last Snowball event presumably included a decreased greenhouse gas concentration and high continental albedo, both associated with the passage of the super-continent Rodinia at equatorial latitudes. When large continental masses are in equatorial regions, silicate weathering is enhanced, leading to decreased atmospheric CO2 concentration, while the bare continental masses, which at the time hosted no vegetation, enhanced reflection of
solar radiation. Since then, no other Snowball episodes were recorded. Here we numerically explore the climatic dynamics of a rocky
planet for different values of
solar output, continental configuration (current and Rodinia-like), CO2 concentration and continental albedo, simulating the effects of land vegetation. We found that for the
solar input typical of 600-700 My ago (95% of the current value), the presence of bare continents with albedo 0.35 (granite) in the position estimated for Rodinia was sufficient to trigger a Snowball state for CO2 concentrations up to at least 1000 ppm. When bare continents are located in modern positions, Snowball could be triggered only for values of CO2 concentration below 400 ppm. At current
solar input values, Snowball states appear only at or below 100 ppm. Thus, we found: a lower
solar output is an essential component of the transition to Snowball; the presence of land vegetation is crucial and reduces the probability of entering a Snowball state; a low CO2 concentration was not needed for triggering a Snowball in bare Rodinia-like conditions and reduced
solar output; current
solar luminosity does not allow Snowball states, even for equatorial continents, unless continental albedo is that of granite and CO2 concentration is 100 ppm or less. [Abridged]
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All authors Erica Bisesi, Giuseppe Murante, Antonello Provenzale, Jost von Hardenberg, Michele Maris, Laura Silva
Geophysics
Transdimensional Data Assimilation for dynamic model selection problems
Márk Somogyvári and Sebastian Reich
In this paper we combine the non-linear filtering capabilities of particle filters with the transdimensional inference of the reversible-jump Markov chain Monte Carlo method for a data assimilation methodology over dynamic problems with variable dimensionality. By using transdimensional MCMC steps for the rejuvenation of the particle filter, the
algorithm could change the number of state space parameters on the fly and can be applied for transdimensional data assimilation purposes. Classic inversion methodologies use pre-defined models, and only changes the individual parameter values during interpretation. This is often not feasible when the optimal model parametrization is not known a priori or when the model resolution needs to change with time. The proposed transdimensional particle filter
algorithm, combines the advantages of particle filters and the transdimensional MCMC methods, and provides an easily implementable data assimilation
algorithm that could tackle such problems. The methodology could also improve the computational efficiency of particle filters as it could inherently optimize the model complexity in a data-driven way. We demonstrate the capabilities of the enhanced
algorithm on two simple model examples.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
A High-Flux Source of Cold Strontium with a Loading Rate of $4 \times 10^{10}$ atoms/s for Open Release
Thomas Walker, Anna L. Marchant, Elliot Bentine et al. (+17 more)
We present a high-flux source of cold strontium atoms based on a two-dimensional magneto-optical trap (2D MOT) and a Zeeman slower. We use the source to load a 3D MOT in a separate science chamber, observing a loading rate of $4 \times 10^{10}$ atoms/s – to our knowledge, the highest reported loading flux for strontium. To characterise the
vacuum pressure in the science chamber, we load the atoms into a
magnetic trap and measure a lifetime of between 8 and 24 seconds, depending on oven temperature. Finally, we characterise the atom flux and velocity distributions from the oven and from the 2D MOT source, finding reasonable agreement with models in the free molecular flow regime. Our results show it is possible to readily produce a cold strontium flux at comparable levels to alkali species, at oven temperatures compatible with long-term operation, and at
vacuum pressures suitable for state-of-the-art
quantum experiments. We make our design available at no cost, to benefit researchers in the
quantum community.
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All authors Thomas Walker, Anna L. Marchant, Elliot Bentine, Oliver Buchmueller, Katherine Clarke, Christopher Foot, Leonie Hawkins, Kenneth M. Hughes, Kamran Hussain, Ludovico Iannizzotto-Venezze, Alice Josset, Hamza Labiad, Dillen Lee, Timothy C. Thornton-Sparkes, Tristan Valenzuela, Maurits van der Grinten, Andrew Vick, Mark G. Bason, Charles F. A. Baynham, Richard Hobson
Fluid Dynamics
Real-time control of multiphase processes with learned operators
Paolo Guida and Didier Barradas-Bautista
Multiphase flows frequently occur naturally and in manufactured devices. Controlling such phenomena is extremely challenging due to the strongly non-linear dynamics, rapid phase transitions, and the limited spatial and temporal resolution of available sensors, which can lead to significant inaccuracies in predicting and managing these flows. In most cases, numerical models are the only way to access high spatial and temporal resolution data to an extent that allows for fine control. While
embedding numerical models in control
algorithms could enable fine control of multiphase processes, the significant computational burden currently limits their practical application. This work proposes a surrogate-assisted model predictive control (MPC) framework for regulating multiphase processes using learned operators. A
Fourier Neural Operator (FNO) is trained to forecast the spatiotemporal
evolution of a phase-indicator field (the volume fraction) over a finite horizon from a short history of recent states and a candidate actuation signal. The neural operator surrogate is then iteratively called during the optimisation process to identify the optimal control variable. To illustrate the approach, we solve an optimal control problem (OCP) on a two-phase Eulerian bubble column. Here, the controller tracks piecewise-constant
liquid level setpoints by adjusting the gas flow rate introduced into the system. The results we obtained indicate that field-level
forecasting with FNOs are well suited for closed-loop optimization since they have relatively low evaluation cost. The latter provide a practical route toward MPC for fast multiphase unit operations and a foundation for future extensions to partial observability and physics-informed operator learning.
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Optics
Nonlocal Optomechanics: Hybrid Anapole Opens a New Route to Optical Tweezing
Susanna R. Rozental, Denis A. Kislov, Ilia M. Fradkin et al. (+13 more)
Optical tweezers confine a particle in an intensity-defined potential well by engaging its local multipoles. In this picture, eliminating far-field scattering from the particle should cancel the optical force, as the multipole moments underpinning the conventional optomechanical response vanish. We show that certain resonant states, such as, e.g., the hybrid anapole state, enable qualitatively different optical manipulation, nonlocal by nature, where the optical force exhibits nontrivial spatial variations absent in conventional tweezing, establishing a new framework for manipulating resonant nanoparticles.
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All authors Susanna R. Rozental, Denis A. Kislov, Ilia M. Fradkin, Nikita S. Babich, Vasiliy Fedotov, Sergey Novikov, Vjaceslavs Bobrovs, Shangran Xie, Oleg Minin, Igor Minin, Lei Gao, Yu-Ling Wu, Lei Gong, Alexey Bolshakov, Alexey Arsenin, Alexander S. Shalin
Physics and Society
Uncovering Functional Blocks in Interregional Production Networks: Evidence from Input-Output Linkages in Japan
Shota Fujishima
This paper examines the latent functional block structure of Japan's production network using interregional input-output data. To isolate non-trivial production linkages, we first estimate a structural
gravity model to account for spatial frictions and economic scale, and then apply a weighted
stochastic blockmodel (SBM) to the resulting residual network. Because these residual linkages often connect distant regions, the SBM is well suited to grouping region-industry pairs based on their shared macroeconomic roles. The results reveal that even after explicitly filtering out the mechanical effects of geographic proximity, the network is organized into functional blocks that maintain a high degree of regional coherence. Beyond this baseline spatial clustering, we find evidence of cross-regional integration, a structural bifurcation between manufacturing and urban services in metropolitan areas, and broadly spanning primary sectors. These findings provide a network-based perspective on regional coordination, offering guidance for how structurally defined production blocks-rather than simple geographic proximity-can inform wide-area policy design.
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Atomic Physics
Radiative Association of Ag and H: Formation of AgH from Ab Initio Calculations
Lin Jiang, Yu Wang, Yukun Yang et al. (+6 more)
Radiative association processes leading to the formation of AgH in cold astrophysical environments are investigated for the first time using full
quantum scattering theory. High accuracy potential energy curves and transition dipole moments for the low-lying electronic states (X$^1\Sigma^+$, A$^1\Sigma^+$, $1^1\Pi$, $3^1\Sigma^+$, $2^1\Pi$) are computed employing the internally contracted multireference configuration interaction method with Davidson correction. Vibrationally and rotationally resolved radiative association cross sections are calculated for transitions from these initial states to the ground X$^1\Sigma^+$ state. Prominent shape resonances arising from quasi-bound rovibrational levels behind centrifugal barriers are identified, with the $2^1\Pi \to$ X$^1\Sigma^+$ channel exhibiting the strongest contribution at low collision energies. Stimulated radiative association under blackbody radiation fields (up to $T = 20\,000$ K) produces modest enhancements, predominantly in the ground-state channel. Thermal rate coefficients computed over 10$^{-1}$–$10^4$~K reveal a general decreasing trend with temperature for all channels. The results provide essential kinetic data for astrochemical models of transition-metal hydride formation in low-temperature interstellar and circumstellar environments.
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All authors Lin Jiang, Yu Wang, Yukun Yang, Xuanbing Qiu, Yali Tian, Guqing Guo, Ling Liu, Chuanliang Li, Yong Wu
Atomic Physics
Binding Energy of Muonic Beryllium: Perturbative versus All–Order Calculations
Shikha Rathi, Ulrich D. Jentschura, Paul Indelicato et al. (+1 more)
We compute the ground-state binding energy of muonic $^9$Be in two ways: first, the fully perturbative treatment of the
nuclear-size effect often employed in light systems, and second, an approach that accounts for the finite-
nuclear-size to all orders (and is inspired by calculations otherwise employed for heavy muonic ions). The results are compared term by term and show that both approaches agree to better than one part-per-million of the total energy. The objective of this work is twofold. The first is practical: to provide a parametrization that allows the extraction of the $^9$Be charge radius from recent and forthcoming experiments with high precision. The second is more conceptual: to act as a bridge between the community working on calculations for light systems and those focusing on heavy systems, demonstrating that the fully relativistic approach otherwise chosen for heavy systems can be enhanced to cover theoretical predictions for all charge numbers.
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All authors Shikha Rathi, Ulrich D. Jentschura, Paul Indelicato, Ben Ohayon
Atomic Physics
Portable laser-cooled ytterbium beam clock based on an ultra-narrow optical transition
R. F. Offer, E. Klantsataya, A. P. Hilton et al. (+9 more)
The highest performance atomic clocks are based on interrogation of ultra-narrow optical transitions. There is now significant interest in developing these systems as a source of GNSS-independent time in deployed, dynamic environments. We report on the development and field trial of a portable optical atomic clock interrogating the 10mHz wide $^1$S$_0\rightarrow ^3$P$_0$ transition in ytterbium-171. To enable measurement of this ultra-narrow transition in a deployed setting we combine an atom-vapor based pre-stabilization reference with all-digital control and continuous clock spectroscopy of a transversely-cooled thermal atomic beam. Characterization of the short-term frequency stability within the lab demonstrates a modified Allan deviation of $2\times 10^{-14}/\sqrt{\tau}$ for integration times up to 100s, reaching a best performance of $1.9\times 10^{-15}$ at 200s. The clock demonstrated the same performance after transport and install aboard a ship for field trial, and operated uninterrupted for multiple days whilst at sea. These results show a pathway towards truly portable optical frequency references based on the interrogation of ultra-narrow transitions.
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All authors R. F. Offer, E. Klantsataya, A. P. Hilton, A. Strathearn, N. Bourbeau Hébert, C. J. Billington, S. Watzdorf, S. K. Scholten, B. White, M. Nelligan, T. M. Stace, A. N. Luiten
Classical Physics · Cross-listed from cond-mat.soft
Jacopo Bilotto, Martin Trulsson and Jean-François Molinari
Athermal elongated particles are well-known to follow Jeffery orbits when sheared in viscous fluids. It is less clear if similar orbits appear in dense granular flows. We show that when sheared for long enough, sufficiently elongated frictionless granular rods, rather than following noisy Jeffery-like orbits, exist in a quasi-
equilibrium state, whose orientational statistics are quantitatively described by classical
liquid crystal theory, where the noise is provided by collisions due to shear. At the same time, we demonstrate a systematic breakdown of this
equilibrium analogy at two distinct limits: at low aspect ratios, where the
equilibrium theory incorrectly predicts an isotropic state, and as inter-particle friction is introduced, where the system moves from steric screening to frictional gearing. Even within this frictionally geared state, the rotational dynamics remain distinct from classical Jeffery orbits. We link this frictional breakdown directly to the system being driven far from
equilibrium, as quantified by an effective Ericksen number that compares non-
equilibrium rotational driving to steric ordering. Our results provide a quantitative map of the transition from a quasi-
equilibrium to a far-from-
equilibrium steady state in a dense, driven system, defining the limits of applicability for thermal
liquid crystal theory in athermal matter.
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