Instrumentation and Detectors
First results of a Monolithic Active Pixel Sensor with Internal Signal Gain Fully Integrated in a 180 nm CMOS Technology
Heinz Pernegger, Emma Kate Anderson, Paula Bartulović et al. (+8 more)
Dense tracking environments in experiments at CERN's High-Luminosity LHC and future FCC experiments call for an increased use of timing information in addition to the position measurement of pixel detectors. This adds one dimension to the information available, and is essential for pile-up mitigation at high luminosity. The CASSIA sensor project (CMOS Active SenSor with Internal Amplification) focuses on the development of pixel
matrices with internal charge multiplication based on monolithic CMOS sensor technologies suitable for application as charged particle tracking and timing detectors. CMOS sensors with in-pixel internal amplification would result in higher signal amplitudes having an improved signal-to-noise ratio, better time resolution and increased sensitivity, making them attractive for high-radiation environments. Their monolithic integration in small pixels reduces the input capacitance of a front-end amplifier and power dissipation making it suitable for fine-pitch low-power detectors. Fast signal rise time due to internal charge amplification improves the response time and timing resolution, all of which makes such a technology attractive for future 4D tracking applications in HEP experiments. This paper presents the first results of the CASSIA sensor, a novel MAPS which uses gain layers fully integrated in a 180nm imaging process to achieve internal signal amplification. In the first measurements presented here we demonstrate the gain behaviour of different pixel implant designs and show that the sensor can be operated with low gain proportional mode as LGAD sensor at lower voltages and as SPAD sensor at higher voltages.
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All authors Heinz Pernegger, Emma Kate Anderson, Paula Bartulović, Ivan Berdalović, Marc Giroux de Foiard Brown, Sebastian Haberl, Matija Jugović, Anastasia Kotsokechagia, Jenny Lunde, Borna Požar, Tomislav Suligoj
Fluid Dynamics
Fluid-inertia torques from particle-shape symmetry
L. Sundberg, F. Candelier, N. Fintzi et al. (+4 more)
Numerical simulation of particle motion in fluids at low particle Reynolds numbers is often based on empirical force and torque models obtained by fitting force and torque from ab-initio computations for simple particle shapes such as spheres, spheroids, or cylindrical disks and fibres. To do the same for more complex particles shapes, one needs to first know how particle shape constrains the dependence of force and torque on flow velocity, its gradient, and on particle orientation. Here we use
symmetry analysis and perturbation theory to determine the form of the hydrodynamic torque on a particle settling in a quiescent fluid at low but non-zero particle Reynolds numbers, for particle shapes with different point-group
symmetries. The
symmetry conclusions are verified by comparing with explicit calculations for nearly spherical particles.
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All authors L. Sundberg, F. Candelier, N. Fintzi, G. Voth, J. L. Pierson, K. Gustavsson, B. Mehlig
Physics and Society
Biswas-Chatterjee-Sen (BChS) kinetic exchange opinion model on modular networks
Hrishidev Unni, Soumyajyoti Biswas and Anirban Chakraborti
We study opinion formation in a society where
agents interact on a modular network generated using a
stochastic block model (SBM). Opinion dynamics is modeled through the Biswas-Chatterjee-Sen (BChS) kinetic exchange model, in which
agents undergo pairwise interactions that could be positive or negative. By tuning the relative strength of intra- and inter-group connectivity inherent to the SBM, as well as the disagreement probability, we identify distinct collective phases. In particular, we observe a robust regime with strong intragroup ordering but no global consensus, in addition to fully ordered and disordered states. In the particular case of two modules, we observe an anti-
ferromagnetic type ordering with the increase of negative interaction between the groups. We show approximate analytical calculations and numerical results of it. These results demonstrate how modular interaction structure can qualitatively alter collective opinion dynamics and hinder consensus formation.
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Fluid Dynamics
The influence of energy-containing scales on the distribution of spectral energy transfers
Arthur Couteau, Panayotis Dimopoulos Eggenschwiler and Patrick Jenny
We present computations of individual mode-to-mode energy transfers from direct numerical simulations of homogeneous isotropic
turbulence. Unlike previous approaches based on shell-filtered velocity fields, this method distinguishes between the energy exchanged by each pair of modes within a triad. We introduce a potential function based on the energy content of the modes involved and show that it predicts the distribution of intense energy transfers in the vicinity of the sampling mode considered. By performing simulations with forcing applied at intermediate wavenumbers, we demonstrate that the region of most intense transfers is determined by the spectral location of the energy-containing scales rather than by the local or nonlocal character of the triad. Direct energy exchanges with the energy-containing range are suppressed by
geometric constraints from the divergence-free condition, but persist as residuals when the sampling mode is close to the energy-containing scales. The comparison with an
estimator derived from EDQNM theory shows good agreement and recovers the forward, scale-local nature of energy transfer consistent with the cascade picture.
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Applied Physics · Cross-listed from astro-ph.IM
Searching systematically for coupling of laser and phase-modulation noise in heterodyne interferometry
Kohei Yamamoto, Olaf Hartwig, Lennart Wissel et al. (+3 more)
Heterodyne interferometry for precision science often comes with an optical phase modulation, for example, for intersatellite clock noise transfer for gravitational wave (GW) detectors in space, exemplified by the
Laser Interferometer Space
Antenna (LISA). The phase modulation potentially causes various noise couplings to the final phase extraction of heterodyne beatnotes by a phasemeter. In this paper, in the format of space-based GW detectors, we establish an analytical framework to systematically search for the coupling of various noises from the heterodyne and modulation frequency bands, which are relatively unexplored so far. In addition to the noise caused by the phase modulation, the high-frequency
laser phase noise is also discussed in the same framework. The analytical result is also compared with a numerical experiment to confirm that our framework successfully captures the major noise couplings. We also demonstrate a use case of this study by taking the LISA-like parameters as an example, which enables us to derive requirements on the level of the
laser and phase modulation noises in the high frequency regimes.
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All authors Kohei Yamamoto, Olaf Hartwig, Lennart Wissel, Holly Leopardi, Kenji Numata, Ryan Derosa
Optics
Two-photon light-sheet live imaging at kilohertz frame rate using birefringence-based pulse splitting
Lei Zhu, Dale Gottlieb, Vincent Maioli et al. (+5 more)
Multiphoton microscopy is widely used for live imaging. However, its acquisition speed remains limited by fluorophore emission rates and photodamage. To increase the pixel rate of a two-
photon microscope beyond a few megahertz (MHz), multi-point parallelized schemes have been proposed. Two-
photon (2P) light-sheet microscopy emerges as an effective approach for high-speed multiphoton imaging of live specimens, as it enables parallelized excitation while minimizing the required
laser power. However, optimizing the signal-to-photodamage ratio in 2P light-sheet microscopy requires to precisely control the illumination parameters, including both wavelength and pulse frequency. Since conventional femtosecond
laser sources generally do not allow independent modulation of these parameters, the development of low-cost, efficient and robust strategies to modulate the temporal excitation profile is essential to fully exploit the advantages of 2P light-sheet microscopy. Here, we introduce a compact pulse splitting scheme that meets these criteria. We used cascaded birefringent
crystals to convert each excitation
laser pulse into an adjustable sequence of collinear sub-pulses. We demonstrate its effectiveness in optimizing 2P light-sheet imaging of live zebrafish embryos. We analyze the impact of pulse splitting on photobleaching, nonlinear photodamage, and imaging performance. Additionally, we demonstrate high-speed 2P imaging of the beating heart and
brain calcium dynamics using red fluorophores in live embryos. We achieve kilohertz imaging frame rate, reaching more than 150 MHz pixel rates with fluorescent signal levels above 10 $photons.pixel^{-1}$ using a
laser mean power and a peak intensity in the range of 100 mW and 0.1 $TW.cm^{-2}$ at the sample, respectively. This adjustable pulse-splitting scheme allows full advantage to be taken of light-sheet illumination for fast in vivo 2P imaging.
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All authors Lei Zhu, Dale Gottlieb, Vincent Maioli, Antoine Hubert, Frédéric Druon, Pierre Mahou, Emmanuel Beaurepaire, Willy Supatto
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Mechanistic Origin of Charge Separation and Enhanced Photocatalytic Activity in D-$\pi$-A-Functionalized UiO-66-NH$_2$ MOFs
Anastasiia Kultaeva, Volodymyr Vasylkovskyi, Andreas Sperlich et al. (+4 more)
Donor-$\pi$-acceptor (D-$\pi$-A) functionalization of MOF linkers can enhance visible-light photocatalytic activity, yet the mechanisms responsible for these effects remain unclear. Here we combine EPR spectroscopy, transient photoluminescence, and first-principles calculations to examine how diazo-coupled anisole, diphenylamine (DPA), and N,N-dimethylaniline (NNDMA) groups modify the photophysics of UiO-66-NH$_2$. All donor units introduce new occupied states near the valence-band edge, enabling charge separation through dye-to-framework electron transfer. Among them, the anisole-modified material stands out for facilitating efficient intersystem crossing into a triplet charge-transfer configuration that suppresses fast recombination and yields long-lived charge carriers detectable by photo-EPR. Meanwhile, bulkier donors such as DPA and NNDMA - despite their stronger electron-donating character - also tend to introduce defect-associated trap states. These results underscore the interplay between donor-induced electronic-structure changes, triplet pathways, and defect-mediated recombination, offering a mechanistic basis for tuning photocatalytic response in D-$\pi$-A-modified MOFs.
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All authors Anastasiia Kultaeva, Volodymyr Vasylkovskyi, Andreas Sperlich, Eugenio Otal, Katsuya Teshima, Wolf Gero Schmidt, Timur Biktagirov
Optics
Irreversible thermalization vs reversible dynamics mediated by anomalous correlators: Wave turbulence theory and experiments in optical fibers
T. Torres, J. Garnier, L. Zanaglia et al. (+8 more)
We theoretically and experimentally investigate spontaneous self-organization in a conservative (
Hamiltonian) turbulent wave system, operating far from thermodynamic
equilibrium. Our system is governed by two coherently coupled nonlinear Schrödinger equations, describing the polarization
evolution of light in a dispersive nonlinear optical fiber. The analysis reveals the emergence of two fundamentally distinct turbulent regimes. In a first regime, the waves undergo a slow, irreversible thermalization process, which is accurately described by the wave
turbulence kinetic equation and the associated H-
theorem of
entropy growth. In stark contrast with this expected irreversible process, we identify a second different regime, where strong phase-correlations spontaneously emerge, giving rise to a fast reversible oscillatory dynamics of the normal correlator and anomalous phase-correlator. Experimental observations confirm the occurrence of both irreversible thermalization and reversible dynamics mediated by the anomalous correlated fluctuations.
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All authors T. Torres, J. Garnier, L. Zanaglia, M. Ferraro, C. Michel, V. Doya, J. Fatome, B. Kibler, S. Wabnitz, A. Picozzi, G. Millot
Computational Physics
Spectral finite-element formulation of the optimized effective potential method for atomic structure in the random phase approximation
Shubhang Krishnakant Trivedi and Phanish Suryanarayana
We present a spectral finite-element formulation of the optimized effective potential (OEP) method for atomic structure calculations in the random phase approximation (RPA). In particular, we develop a finite-element framework that employs a
polynomial mesh with element nodes placed according to the Chebyshev-Gauss-Lobatto scheme, high-order $\mathcal{C}^0$-continuous Lagrange
polynomial basis functions, and Gauss-Legendre quadrature for spatial integration. We employ distinct
polynomial degrees for the orbitals, Hartree potential, and RPA-OEP exchange-correlation potential. Through representative examples, we verify the accuracy of the developed framework, assess the fidelity of one-parameter double-hybrid functionals constructed with RPA correlation, and develop a machine-learned model for the RPA-OEP exchange-correlation potential at the level of the generalized gradient approximation, based on the kernel method and linear regression.
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Biological Physics · Cross-listed from cond-mat.soft
Condensation dynamics of sticky and anchored flexible biopolymers
Adam R. Lamson, Mohammadhossein Firouznia and Michael J. Shelley
Cells regulate gene expression in part by forming DNA-
protein condensates in the
nucleus. While existing theories describe the
equilibrium size and stability of such condensates, their dynamics remain less understood. Here, we use coarse-grained 3D Brownian-dynamics simulations to study how long, end-anchored biopolymers condense over time due to transient crosslinking. By tracking how clusters nucleate, merge, and disappear, we identify two dominant dynamical pathways, ripening and merging, that govern the progression from an uncompacted chain to a single condensate. We show how microscopic kinetic parameters,
protein density, and mechanical constraints shape these pathways. Using insights from the simulations, we construct a minimal mechanistic free-energy model that captures the observed scaling behavior. Together, these results clarify the dynamical determinants of DNA and chromatin reorganization on timescales relevant to gene regulation.
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Chemical Physics
Signatures of coherent energy transfer and exciton delocalization in time-resolved optical cross correlations
Hallmann Óskar Gestsson and Alexandra Olaya-Castro
We investigate how optical second-order cross correlations witness the
quantum features of a prototype donor-acceptor light-harvesting unit. By considering a pair of detuned two-level emitters electronically coupled and incoherently driven to a non-
equilibrium steady-state, we gain insight into how electronic
quantum properties such as
exciton eigenstate delocalization, coherent energy transfer and steady-state electronic coherence, are manifested in the joint probability of emission or optical second-order cross correlation. Specifically, we show that the frequency associated with oscillations present in time-resolved second-order cross correlation functions quantifies not only the time scale of coherent energy transfer but also the degree of delocalization of the
exciton eigenstates. Furthermore, we show that time-resolved cross correlations directly witness steady-state electronic coherence. Our work strengthens the idea that measurements of the intensity
quantum cross correlations can provide distinctive signatures of the
quantum behavior of biophysical emitters.
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Atmospheric and Oceanic Physics
When and where higher-resolution climate data improve impact model performance
Johanna T. Malle, Christopher P.O. Reyer, Yael Amitai et al. (+32 more)
Climate impact assessments increasingly rely on high-resolution
climate and forcing
datasets, under the premise that finer detail enhances both the accuracy and policy relevance of projections. Yet systematic evaluations of when and where higher resolution actually improves impact model outcomes remain limited, and it is unclear whether increasing spatial resolution consistently enhances performance across sectors, regions, and forcing variables. Here we show that gains in
climate input accuracy and impact model performance are largest when moving from coarse (60 km) to intermediate (10 km) resolution, while further refinement to 3 km and 1 km yields more modest and inconsistent benefits. Using cross-sectoral simulations from the Inter-Sectoral Impact Model Intercomparison Project, we find that higher resolution substantially improves model skill in temperature-sensitive impact models and topographically complex regions, whereas precipitation-driven and low-relief systems show weaker and less systematic improvements. For temperature, both
climate inputs and model outputs improve most strongly at the 60 km to 10 km transition, with diminishing gains at finer scales; for precipitation, some models even exhibit reduced performance beyond 10 km. These results highlight that optimal resolution depends on sectoral and regional context, and point to the need for improving model process representation and downscaling techniques so that added spatial detail translates into meaningful skill gains. For data providers, this implies prioritizing resolutions that maximize improvements where they matter most, while for modelling groups and users it underscores the need for explicit benchmarking of resolution choices in
climate impact assessments.
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All authors Johanna T. Malle, Christopher P.O. Reyer, Yael Amitai, Andrey L. D. Augustynczik, Yaron Be'eri-Shlevin, Elad Ben-Zur, Peter Burek, Tarunsinh Chaudhari, Jinfeng Chang, Alessio Collalti, Daniela Dalmonech, Shouro Dasgupta, Iulii Didovets, Marc Djahangard, Laura Dobor, Louis François, Simon N. Gosling, Fred F. Hattermann, Shaoshun Huang, Heike Lischke, Thomas Lorimer, Katarina Merganicova, Francesco Minunno, Mats Nieberg, Elizabeth J. Z. Robinson, Martin Schmid, Mikhail Smilovic, Ritika Srinet, Elia Vangi, Xue Yang, Rasoul Yousefpour, Ana I. Ayala, Daniel Mercado-Bettin, Dánnell Quesada-Chacón, Dirk N. Karger
Fluid Dynamics
Design, Testing and Numerical Modelling of a Low-Speed Wind Tunnel Gust Generator
Marinos Manolesos, Christos Ampatis, Dimitris Gkiolas et al. (+2 more)
Understanding and accurately reproducing gust-induced unsteady aerodynamics is essential for improving load prediction, aeroelastic analysis, and control strategies in aircraft, uninhabited aerial vehicles, and wind turbines, particularly in regimes where nonlinear flow phenomena dominate. In this work, a low-speed wind tunnel gust generator based on oscillating vanes is designed, manufactured, and characterised through a combined experimental and numerical investigation. The system is intended to reproduce deterministic gust profiles relevant to aircraft, uninhabited aerial vehicles, and wind-turbine applications, operating in highly unsteady aerodynamic regimes. Experimental measurements using hot-wire anemometry are performed to quantify the generated gust field under a range of free-stream velocities, amplitudes, and forcing frequencies. In parallel, time-accurate CFD simulations are conducted using a deforming-mesh approach to validate the measurements and to analyse the flow physics associated with gust formation and propagation. Particular
attention is given to the negative velocity peaks inherent to classical '1-cos' gust profiles. A modified vane motion protocol is proposed and shown to significantly reduce the negative peak factor while maintaining a substantial gust ratio. Numerical results reveal that secondary flow-angle variations arise from nonlinear interactions between
vortices shed by adjacent vanes.
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All authors Marinos Manolesos, Christos Ampatis, Dimitris Gkiolas, Konstantinos Rekoumis, George Papadakis
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Corrosion-resistant and conductive Ti-Nb-O coatings tailored for ultra-low Pt-loaded BPPs and PTLs in PEM electrolyzers
David Kolenatý, Jiří Čapek, Stanislav Haviar et al. (+6 more)
We develop highly corrosion-resistant and conductive Ti-Nb-O coatings for metallic components – bipolar plates (BPPs) and porous transport layers (PTLs) – in PEM water electrolyzers. Using reactive high-power impulse magnetron sputtering (HiPIMS), we deposit compact 200 nm
bilayer coatings onto SS316L substrates, systematically tailoring their composition. By precisely controlling oxygen partial pressure and Nb/Ti ratio, we adjust stoichiometry and structure, directly affecting electrical resistivity and corrosion resistance. We examine interfacial contact resistance (ICR) and electrochemical parameters before and after accelerated corrosion testing. Optimized coatings exhibit resistivity on the order of 10^-4 Ohmcm and extremely low corrosion current densities (J_corr = 0.01-0.08 uA/cm^2), well below the U.S. DOE 2026 target. Most importantly, these coatings enable the ICR target after accelerated corrosion testing with a Pt overlayer as thin as 5 nm, reducing Pt loading by up to two orders of magnitude compared to conventional approaches.
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All authors David Kolenatý, Jiří Čapek, Stanislav Haviar, Jiří Rezek, Radomír Čerstvý, Akash Kumar, Kalyani Shaji, Mariia Zhadko, Petr Zeman
Atmospheric and Oceanic Physics
Reconstructing Pre-Satellite Tropical Cyclogenesis Climatology Using Deep Learning
Chanh Kieu, Thanh T.N. Nguyen, Duc-Trong Le et al. (+7 more)
A reliable tropical cyclone (TC) climatology is the key to assessing historical and future changes in TC activities. While global TC records have been systematically maintained since the early 1940s, substantial uncertainties remain for the pre-satellite era during which TC observations relied mostly on scattered aircraft reconnaissance and sporadic ship reports. This study presents a deep learning (DL) approach to reconstruct historical TC activity in the western North Pacific (WNP) basin, with a main focus on the pre-satellite era. Using data feature enrichment tailored for tropical cyclogenesis (TCG), we demonstrate that DL can effectively capture the main characteristics and changes in TCG climatology during the post-satellite era. With additional cross-validations, the reconstruction of TCG climatology is then extended to a pre-satellite period (1940-1960) during which TC base-track
datasets are most uncertain. Our DL reconstruction reveals a significant missing of TCG in the current best-track data between September and November during the pre-satellite era. Such a TCG undercount in the best track data occurs mainly around 10-15$^\circ$N in the central WNP, while coastal regions show better consistency with DL reconstruction. These findings not only highlight the potential of DL for improving historical assessments of TC activity, but also advance our understanding of TCG processes by identifying key environmental conditions conducive to TC formation. The DL approach presented herein can be applied to other ocean basins,
climate proxies, or reanalysis
datasets for future TC
climate studies.
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All authors Chanh Kieu, Thanh T.N. Nguyen, Duc-Trong Le, Duc Gia-Anh Hoang, Quang-Lap Luu, Binh T. Dang, Truong X. Ngo, Quang-Trung Luu, Tien D. Du, Khiem V. Mai
Computational Physics · Cross-listed from cond-mat.str-el
Revisiting the Broken Symmetry Phase of Solid Hydrogen: A Neural Network Variational Monte Carlo Study
Shengdu Chai, Chen Lin, Xinyang Dong et al. (+4 more)
The
crystal structure of high-pressure solid hydrogen remains a fundamental open problem. Although the research frontier has mostly shifted toward ultra-high pressure phases above 400 GPa, we show that even the broken
symmetry phase observed around 130~GPa requires revisiting due to its intricate coupling of electronic and
nuclear degrees of freedom. Here, we develop a first principle
quantum Monte Carlo framework based on a deep neural network wave function that treats both electrons and
nuclei quantum mechanically within the constant pressure ensemble. Our calculations reveal an unreported ground-state structure candidate for the broken
symmetry phase with $Cmcm$ space group
symmetry, and we test its stability up to 96 atoms. The predicted structure quantitatively matches the experimental equation of state and gives the closest x-ray diffraction peak-position match among the tested candidates. Furthermore, our group-theoretical analysis provides a
symmetry-counting compatibility check between the $Cmcm$ structure and existing Raman and infrared spectroscopic data. Crucially, static density functional theory calculation reveals the $Cmcm$ structure as a dynamically unstable saddle point on the Born-Oppenheimer potential energy surface, demonstrating that a full
quantum many-body treatment of the problem is necessary. These results shed new light on the phase diagram of high-pressure hydrogen and call for further experimental verifications.
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All authors Shengdu Chai, Chen Lin, Xinyang Dong, Yuqiang Li, Wanli Ouyang, Lei Wang, X.C. Xie
Physics Education
Measuring fidelity of implementation of named active learning methods in physics
Ibukunoluwa Bukola, Meagan Sundstrom, Justin Gambrell et al. (+3 more)
Various active learning methods have been developed for introductory physics, and these methods are increasingly being adopted by instructors. However, instructors often do not implement these methods exactly as was originally intended by the developers, as they may face issues related to funding and institutional support for active learning and/or have different instructional contexts (e.g., student populations) and environments (e.g., physical classroom layouts) than the developers. Existing research does not sufficiently capture the range of variation in instructor implementation of established active learning methods, especially in comparison to high-fidelity implementations. In this study, we first identify the critical components (i.e., components without which the active learning method cannot be said to have been implemented) of three named active learning methods: SCALE-UP, ISLE, and Tutorials. We then evaluate the fidelity with which 18 different introductory physics instructors implement these methods by analyzing classroom observations and comparing the extent to which these broader implementations use each critical component in their classroom to high-fidelity implementations. We find across all three active learning methods that broader implementations spend similar amounts of class time on the critical components as high-fidelity implementations. At the same time, we observe substantial variation in the specific styles that broader implementers operationalize these critical components (e.g., doing a few long activities versus many short activities). Finally, we find no clear relationship between fidelity of implementation and student conceptual learning gains for our study's sample of instructors, providing preliminary evidence that different ways of implementing the critical components of active learning method may all effectively improve student understanding.
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All authors Ibukunoluwa Bukola, Meagan Sundstrom, Justin Gambrell, Colin Green, Adrienne L. Traxler, Eric Brewe
Applied Physics
Bound States to the Continuum: Time-varying Spoof Acoustic Surface Waves
E. Paul, G. J. Chaplain, J. Li et al. (+2 more)
We develop a theoretical framework for time-modulated acoustic metasurfaces comprising a line array of modulated cavities, and show that bound acoustic surface waves can undergo temporal diffraction from bound states localised at an interface into bulk waves. The dispersion relation is derived via an operator formalism that captures the spatio-temporal coupling between Floquet sidebands. We show that under periodic modulation of the cavity length sidebands spaced by the modulation frequency are produced (diffraction in time), enabling the coupling of bound surface acoustic waves with bulk radiation i.e. from a bound state to the continuum. We observe the negative-frequency spectra as spatial reflections along the array via time-domain finite element simulations. Spectral $k$-gaps are observed at band crossings, with the width of the gap proportional to the modulation amplitude. The modulation enters solely through a time-dependent reflection phase, such that the framework applies generally to metasurfaces with programmable boundary conditions, beyond purely mechanical modulation.
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All authors E. Paul, G. J. Chaplain, J. Li, T. A. Starkey, S. A. R. Horsley
Fluid Dynamics · Cross-listed from cond-mat.soft
Internal Waves Control Bulk Flow in Silos
David Luce, Adrien Gans, Nicolas Vandewalle et al. (+1 more)
We experimentally measure paticle acceleration within the bulk during the discharge of a granular silo. We highlight the existence of a deceleration wave emerging at the outlet level near the dead zone and propagates toward the top of the medium. The wave emission frequency is extracted from spatiotemporal diagrams of the Eulerian instantaneous acceleration profiles. Surprisingly, we find that this frequency decreases with the cohesion of the medium and is independent of the outlet size.
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All authors David Luce, Adrien Gans, Nicolas Vandewalle, Sébastien Kiesgen de Richter
Physics and Society · Cross-listed from gr-qc
Networks as the fundamental constituents of the universe
Carlo A. Trugenberger
We review an approach that uses binary relations as the fundamental constituents of the universe, utilizing them as building blocks for both space and matter. The model is defined by an ultraviolet continuous fixed point of a statistical model on random networks, governed by the combinatorial Ollivier-
Ricci curvature, which acts as a network analogue of the Einstein-
Hilbert action. The model exhibits two distinct phases separated by this fixed point, a
geometric and a random phase, representing space and matter, respectively. At weak coupling and on large scales, the network organizes into a
holographic surface whose collective state encodes both an emergent 3D space and the matter distributed in it. The Einstein equations emerge as constitutive relations expressing matter in terms of fundamental network degrees of freedom while dynamics in a comoving frame is governed by relativistic
quantum mechanics.
Quantum mechanics, however is an effective theory breaking down at the scale of the radius of
curvature of the
holographic network. On smaller scales, not only relativistic invariance is lost but also the Lorentzian signature of space-time. Finally, the
manifold nature of space-time breaks down on the Planck length, where the random character of the fundamental network on the smallest scales becomes apparent. The network model seems to naturally encode several of the large-distance features of cosmology, albeit still at a qualitative level. The
holographic property of black holes arises intrinsically from the expander nature of random regular graphs. There is a natural mechanism to resolve the cosmological constant problem and dark matter appears naturally as a metastable allotrope in the network fabric of space-time. In this model, both
gravity and
quantum mechanics are macroscopic statistical effects reflecting the free energy minimization of fundamental binary degrees of freedom.
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Physics and Society
Statistical field theory for dialectology
James Burridge
Is it possible to develop a `physics of
language' which can explain the spatial, temporal and social patterns we see, and which can predict future change like we forecast the weather? Such a theory is likely to involve ideas from statistical physics. A substantial literature already applies these ideas to
language. However, we lack a model which can match the spatial-temporal detail of historical changes at the level of individual linguistic features, and which offers a principled mechanism to predict the future. Here we present a statistical field theory for the
evolution of linguistic variables which takes steps to fill this gap. Linguistic variant frequencies are represented as a
stochastic state field with spatial interaction and social conformity, coupled to a latent bias field with Onsager Machlup action that reduces overfitting to data. We derive parameter inference procedures and demonstrate them using examples of large-scale dialect survey data from the twentieth century United States. The bias field has a characteristic half-life, which determines the horizon over which linguistic change can be predicted. Inferred model parameters provide evidence for surface-tension-driven coarsening of dialect regions, with population-density gradients exerting systematic forces on interfaces.
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Computational Physics · Cross-listed from cs.LG
Learning-Based Estimation of Spatially Resolved Scatter Radiation Fields in Interventional Radiology
Felix Lehner, Pasquale Lombardo, Susana Castillo et al. (+2 more)
We present three variants of a lightweight, fully connected artificial neural network, suited for interactive estimation of three-dimensional, spatially resolved volumes of scattered radiation fields and a corresponding training pipeline for radiation protection dosimetry in medical radiation fields, such as those found in interventional radiology and cardiology. Accompanying, we present three different synthetically generated
datasets with increasing complexity for training, generated using RadField3D, a Monte Carlo simulation application based on Geant4. As the primary scatter object, we employed the torso of a male Alderson RANDO phantom. On those
datasets, we evaluate convolutional and fully connected architectures of neural networks to demonstrate which design decisions work well for reconstructing the fluence and spectra distributions over the spatial domain of such radiation fields. All our
datasets, as well as our training pipeline, are published as open source in separate repositories. To evaluate the presented neural networks, we define and assess several metrics. Across these measures, the model variants demonstrate good spatial agreement between predicted and ground-truth radiation fields, particularly within specific regions of interest within the radiation field. Of particular relevance for potential application in out-of-field dosimetry is the SMAPE of the scatter radiation field, which represents the most challenging metric and was consistently above 84 %.
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All authors Felix Lehner, Pasquale Lombardo, Susana Castillo, Oliver Hupe, Marcus Magnor
Atomic Physics
$\Lambda$-Enhanced Gray Molasses Cooling of $^{85}$Rb Atoms in Tweezers Using the D$_2$ Line
Deon Janse van Rensburg, Rogier Venderbosch, Yuri van der Werf et al. (+5 more)
We demonstrate the implementation of $\Lambda$-enhanced gray molasses cooling on the D$_2$ line of $^{85}$Rb atoms in an optical tweezer array. This technique yields lower atomic temperatures of 4.0(2) $\mu$K compared to red-detuned polarization gradient cooling, and consequently extends the $T_2^*$ coherence time of the hyperfine clock
qubit by a factor of 1.5. The method is
alignment-free and can be readily implemented on
laser beams used for magneto-optical trapping, as it only requires frequency and phase modulation control. Our experimental observations are corroborated by a numerical model based on a semi-classical force approach extended to a four-level system, including two hyperfine states of the upper
manifold that are 120 MHz apart.
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All authors Deon Janse van Rensburg, Rogier Venderbosch, Yuri van der Werf, Jesus del Pozo Mellado, Marijn Venderbosch, Rianne Lous, Edgar Vredenbregt, Servaas Kokkelmans
Optics
Hyperbolic-enhanced Raman scattering in van der Waals MoOCl2: from Fano resonances to picomolar detection
Anton Minnekhanov, Gleb Tikhonowski, Georgy Ermolaev et al. (+13 more)
Natural van der Waals (vdW)
crystals with
hyperbolic dispersion challenge artificial metamaterials but remain confined to the mid-infrared. The emergence of MoOCl2, a quasi-one-dimensional metal with in-plane hyperbolicity, overcomes this spectral limit, shifting the focus to the practical visible range. Here, using angle-resolved polarized Raman spectroscopy, we uncover pronounced polarization-dependent Fano lineshapes that reveal coupling between
phonons and the anisotropic metallic continuum, together with strong wavelength-dependent reshaping of the Raman polarization patterns governed by the anisotropic optical response of MoOCl2. Harnessing this optical anisotropy, we demonstrate "
Hyperbolic-Enhanced Raman" (HypER) scattering, where MoOCl2 provides polarization-tunable analytical enhancement factors exceeding 10^7 and picomolar-level detection of Rhodamine 6G down to 100 pM, without deliberate surface nanostructuring. These results establish air-stable MoOCl2 as a simple, wafer-compatible platform for visible-range
hyperbolic nanophotonics and lithography-free sensing.
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All authors Anton Minnekhanov, Gleb Tikhonowski, Georgy Ermolaev, Konstantin V. Kravtsov, Gleb Tselikov, Adilet Toksumakov, Aleksandr Slavich, Ivan Kazantsev, Ilia Fradkin, Andrey Vyshnevyy, Ivan Kruglov, Ilya Radko, Zdenek Sofer, Aleksey Arsenin, Kostya S. Novoselov, Valentyn Volkov
Optics
High-purity amplification of circularly polarized orbital angular momentum modes in an active spun ring-core tapered fiber
Iuliia Zalesskaia, Hassan Asgharzadeh B., Zahra Eslami et al. (+9 more)
Structured light, optical fields engineered in their spatial, polarization, or phase degrees of freedom, has become a key resource across advanced communication, sensing, imaging, and
quantum technologies. Optical fibers nowadays play an essential role in this landscape, providing stable and scalable platforms for guiding, and amplifying complex modes such as vector and orbital angular momentum (OAM) beams. In this work, we demonstrate an active spun ring-shaped tapered fiber as a gain medium for efficient amplification of OAM modes preserving their modal purity and polarization
topology. OAM beams with topological charges l = 1 and l = 2 carrying 60 ps pulses at 15 MHz repetition rate at 1030 nm wavelength are amplified over 1.2 W average power with modal purity over 95%. The spatially resolved measurement of the OAM beam polarization
topology revealed small distortion due to the coupling in to neighbour modes. These results demonstrate the high potential of active spun ring-shaped tapered fibers for power scaling of complex beams, preserving their phase and polarization structure simultaneously.
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All authors Iuliia Zalesskaia, Hassan Asgharzadeh B., Zahra Eslami, Hossein Fathi, Evgenii Gribanov, Andrey Grishchenko, Florian Lindner, Katrin Wondraczek, Evgeny Savelyev, Marco Ornigotti, Valery Filippov, Regina Gumenyuk
Optics
Simulating vacuum birefringence with a diffractive beam propagation code
Aimé Matheron, Michal Šmíd, Matt Zepf et al. (+1 more)
Ninety years after their prediction,
quantum vacuum nonlinearities in macroscopic electromagnetic fields still await a direct experimental verification in the laboratory. A particularly promising route towards their first measurement is the collision of counter-propagating
laser beams in a pump-probe type experiment. Here, the key challenge is to separate the small
quantum vacuum signal at the oscillation frequency of the probe that is mainly emitted in the vicinity of its forward cone from the large probe background. While quantitatively accurate predictions of the associated
quantum vacuum signals are available, to date there is no framework that combines these predictions with a diffractive beam propagation code. Such codes are designed to holistically model optical experiments and can reliably account for diffraction and absorption losses of optical devices, like lenses and apertures. The latter inevitably influence and modify both the induced signal and background components prior to their detection in experiment. The present work addresses this topical issue and reports on the first implementation of a
quantum vacuum signals emission module in an established diffractive beam propagation toolkit designed for the realistic modelling of optical experiments.
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All authors Aimé Matheron, Michal Šmíd, Matt Zepf, Felix Karbstein
Chemical Physics
Dual-LAO for calculating fast and robust relative binding free energies of simple and complex transformations
Narjes Ansari, Félix Aviat, Jérôme Hénin et al. (+2 more)
Relative Binding Free Energy (RBFE) calculations are a cornerstone of rational hit-to-lead and lead optimization in modern drug discovery. However, the high computational cost and limited reliability in tackling large or complex molecular transformations often prevent their routine, high-throughput use. Here we introduce dual-LAO, a novel, highly efficient method for calculating RBFE. Building on the Lambda-ABF-OPES framework, this method combines a dual-
topology setup and suitable restraints to dramatically accelerate free energy convergence. We demonstrate that dual-LAO, in combination with the AMOEBA polarizable force field, achieves an unprecedented acceleration factor of 15 to 30 times compared to current state-of-the-art methods on standard drug targets. Crucially, the approach maintains high accuracy and successfully tackles previously prohibitive molecular changes, including scaffold-hopping, buried water displacement, charge changes, ring-opening, and binding pose perturbations. This significant leap in efficiency allows for the widespread, routine integration of predictive molecular simulations into the rapid optimization cycles of drug discovery, enabling chemists to confidently model historically challenging systems in timescales compatible with real-world project deadlines.
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All authors Narjes Ansari, Félix Aviat, Jérôme Hénin, Jean-Philip Piquemal, Louis Lagardère
Geophysics · Cross-listed from cond-mat.stat-mech
Earthquake Dynamics as a Benchmark for Scale-Invariant Behavior
Kilian Duplat, German Varas and Osvanny Ramos
We analyze regional earthquake energy statistics from the Southern California and Japan seismic catalogs and find scale-invariant energy distributions characterized by an exponent $\tau \simeq 1.67$. To quantify how closely scale-invariant dynamics with different exponent values resemble real earthquakes, we generate synthetic energy distributions over a wide range of $\tau$ under conditions of constant activity. Earthquake-like behavior, in a broad sense, is obtained for $1.5 \leqslant \tau < 2.0$. When energy variations are further restricted to be within a factor of ten relative to real earthquakes, the admissible range narrows to $1.58 \leqslant \tau \leqslant 1.76$. We identify the physical mechanisms governing the dynamics in the different regimes: fault dynamics characterized by a balance between slow energy accumulation and release through scale-free events in the earthquake-like regime; externally supplied energy relative to a slowly driven fault for $\tau < 1.5$; and dominance of small events in the energy budget for $\tau > 2$
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Optics
A generalized perturbative approach for the computation of nonlinear scattering problems
Jérémy Itier, Gilles Renversez and Frédéric Zolla
We present a perturbative technique for modeling the scattering of light by a nonlinear material. This approach eliminates the need for an iterative
algorithm to solve the fully coupled nonlinear problem. We demonstrate its effectiveness in the cases of a nonlinear anisotropic slab and a nonlinear periodic
crystal, both illuminated by a plane wave under conical incidence and arbitrary polarization. Quantitative comparisons of the accuracy and computational time with our previously published rigorous model are provided.
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Biological Physics · Cross-listed from q-bio.MN
Design of a minimal, allosteric, and ATPase-like machine using mechanical linkages
Tosan Omabegho
ATPases cyclically convert chemical energy in the form of ATP gradients into directed motion inside
cells. To function, ATPases rely on allosteric communication between at least two binding sites, an internal signaling mechanism that is not well understood. Here, we model an ATPase-like machine by using a system of mechanical linkages to recreate negative allosteric coupling between two binding sites and generate cycles in which the sites alternate occupancy. The ATPase analog has two mechanical degrees of freedom and two discretized binding sites: one for the ATP, Pi and ADP analogs, and one for an allosteric effector analog. The geometry of the ATPase analog allows stepwise binding reactions at each site to capture the two degrees of freedom in a mutually exclusive way. Consequently, the enzyme interconverts between multiple rigid and partially rigid forms, such that neither site can be fully bound when both sites are occupied. Two mechanisms work together to generate an enzymatic cycle: one, in which the tighter-binding ATP analog can bind and displace the effector from the enzyme; and a second, in which flexibility introduced by splitting the ATP analog into two pieces (catalysis) allows the effector to rebind and displace the products (ADP analog). We show that cleavage (forward catalysis) and ligation (reverse catalysis) alter the
rigidity of the enzyme complex equivalently to binding and dissociation, respectively, but must do so more slowly for effective cycling to take place. Simple designs for synthetic systems that mimic ATPase monomers can be derived from this work.
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