Computational Physics
A Showcase of Using the Partial-Structure R1 to Assemble Small-Molecule Crystal Structures
Xiaodong Zhang
Using a few concrete examples this paper has demonstrated a few observations on using the partial-structure R1 (pR1) to assemble small-molecule
crystal structures. (1) Assembling can start with orienting and/or placing large fragments or small fragments containing heavy atom(s). (2) It is handy to attach a fragment to a partial model as only the orientation needs to be optimized. (3) In a structure containing heavy atoms it is impossible to directly calculate the orientations of a light-atom-only fragment. Instead, it is necessary to use residual reflection intensities in which the contribution of the partial model containing all heavy atoms is deducted away. These observations indicate that pR1 is a useful tool for solving some small-molecule
crystal structures.
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Instrumentation and Detectors
Neural-network-based material identification in photon-counting computed tomography using region-of-interest spectral features
A. Miadzvetski, V. Rozhkov, R. Sotenskii et al. (+2 more)
This work investigates the feasibility of neural-network-based material identification based on
photon-counting computed
tomography (PCCT) data. The input data were spectral vectors extracted from regions of interest (ROIs) in reconstructed tomographic slices of a phantom containing La-, Nd-, and Gd-based samples, as well as air, water, bone, and polymethyl methacrylate (PMMA). The original tomographic slices were acquired at 12 detector threshold settings (THL = 45, 55, 65, 75, 85, 95, 105, 115, 125, 135, 145, 165). For model training, the spectra were interpolated onto a uniform grid from THL 45 to THL 165 with a step of one THL unit. Large ROIs, small ROIs, and their combined
dataset were considered. To avoid an overestimated performance caused by correlated ROIs extracted from the same tomographic slice, the data were split into training, validation, and test subsets at the slice level.
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All authors A. Miadzvetski, V. Rozhkov, R. Sotenskii, D. Shashurin, G. Chelkov
Applied Physics · Cross-listed from quant-ph
Wireless millikelvin interconnects for superconducting quantum hardware
Kristopher Barr, Mingyan Zhong, Euan Parry et al. (+8 more)
Scalable
quantum computing is limited by the dense network of electrical interconnects linking cryogenic
quantum processors to room-temperature control electronics. To overcome this bottleneck, considerable effort has focused on cryogenic CMOS electronics and microwave-to-optical transduction, aiming to reduce wiring complexity and thermal loading. Wireless interconnects have recently emerged as a promising complementary approach, yet their compatibility with superconducting
quantum hardware remains largely unexplored. Here, we demonstrate the wireless excitation of a superconducting microwave resonator of the type routinely employed for
qubit readout, operating at millikelvin temperatures inside a dilution refrigerator. By directly comparing wired and wireless operation within the same cryogenic environment, we show that wireless coupling preserves the intrinsic resonator response while revealing parasitic electromagnetic pathways arising from stray radiation within the cryostat enclosure. These results establish a framework for the co-design of wireless interconnects, cryogenic packaging and superconducting
quantum hardware.
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All authors Kristopher Barr, Mingyan Zhong, Euan Parry, Manoj Stanley, Qusay Al-Taai, Paniz Foshat, Kaveh Delfanazari, Martin Weides, Nick M. Ridler, Chong Li, Alessandro Rossi
Classical Physics · Cross-listed from cond-mat.stat-mech
Cooling rate and glassy behavior in the Fermi–Pasta–Ulam system
Matteo Razza, Andrea Carati and Luigi Galgani
In this work, we numerically studied the cooling process of a
Fermi–Pasta–Ulam system, which occurs when the FPU system is placed in contact with a gas whose temperature $T$ is reduced with a certain cooling rate $\xi$. It was found that the existence of a weak
stochastic threshold has a significant impact on the cooling process, because below such a
stochastic threshold the specific FPU energy is larger than its temperature, i.e., the FPU system falls out of
equilibrium. The difference remains finite in the limit $T \to 0$, so that the FPU system maintains a residual amount of energy $E_0$ at vanishing temperature. Our numerical simulations reveal that this energy exhibits a power–law dependence on both the system size and the cooling rate, scaling approximately as $E_{0} \sim (\xi N)^{2/3}$.
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Accelerator Physics
Robust Betatron-Tune Measurement from Schottky Spectra: Complementary Classical and Deep-Learning Paradigms
Peihan Sun, Manzhou Zhang, Renxian Yuan et al. (+2 more)
Schottky spectra provide key beam diagnostics, with betatron sidebands encoding the fractional tune. Reliable tune measurement is particularly important for third-order resonance slow extraction in compact medical
proton synchrotrons, where low signal-to-noise ratios and limited frequency resolution can compromise conventional peak-detection and curve-fitting methods. This work develops two complementary tune
estimators with a shared spectral front-end but different temporal representations. The classical
estimator coherently pools motion-compensated spectra, detects the sideband using a multi-width matched-filter bank, and performs sub-bin estimation through local argmax and an adaptive MAD-gated centroid. The deep-learning
estimator converts each spectrum into a tune-likelihood map using a convolutional neural network with FFT-based global convolutions, then propagates the posterior with a discrete two-dimensional (q,v)
Bayesian tracker under a Gaussian motion model while also reporting posterior uncertainty. On a synthetic dynamic-tune
benchmark, the deep-learning
estimator outperforms published baselines across the operating range, while the classical
estimator exceeds the latency-compensated baseline and requires neither training data nor GPU acceleration. On near-stationary SAPT beam data, both methods operate end-to-end, with the deep-learning model requiring no retraining. Median per-frame latency remains below 1 ms on commodity hardware, supporting real-time-capable tune measurement in compact medical synchrotrons.
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All authors Peihan Sun, Manzhou Zhang, Renxian Yuan, Deming Li, Jian Dong
Chemical Physics
jQMC: A JAX-based ab initio quantum Monte Carlo package designed for GPU-accelerated computing
Kousuke Nakano and Michele Casula
We present jQMC, a Python-based computational package for ab initio
Quantum Monte Carlo (QMC) simulations, designed for modern GPU-accelerated computing environments. jQMC implements two well-established QMC
algorithms: Variational Monte Carlo (VMC) and the
lattice-regularized variant of
Diffusion Monte Carlo (LRDMC). The employed wave function is a Jastrow factor combined with the antisymmetrized geminal power with
spin-singlet and
spin-triplet pairings, which contains the single Slater determinant as its special lowest-rank case. The wave function can be initialized from external Hartree-Fock/Density Functional Theory calculations through the TREX-IO library (a common wave-function format across electronic-structure packages) and optimized by
stochastic reconfiguration and linear-method energy minimization. One of the prominent features of jQMC is its use of JAX, which enables automatic differentiation for wave function optimization and atomic force calculations, and allows the main QMC
algorithms to be Just-In-Time (JIT) compiled and portable across CPU and GPU. jQMC is vectorized over walkers at the top level of the QMC
algorithms, providing efficient intra-GPU~(CPU) vectorization. The multi-GPU~(CPU) parallelization is also supported through MPI and JAX sharding. To assess the practical performance of this implementation, we benchmarked jQMC performance on NVIDIA GPUs (A100 and H100) and analyzed CUDA kernels. For the test cases analyzed here, with system sizes up to 160 electrons, the current version of jQMC is faster than TurboRVB, a Fortran90 code implementing the same
algorithms and wave functions, once jQMC is run on GPUs. In terms of wall-time, the gain can reach an order of magnitude for VMC, while it is more moderate for LRDMC.
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Optics
Space-Time Lensing by Accelerated Interfaces in Dispersive Media
Cédric D'Exelle, Klaas De Kinder and Christophe Caloz
We present space-time
lensing by synthetic accelerated interfaces in dispersive media. Frequency-dependent group velocities map spectral components of a pulse onto distinct trajectories in the longitudinal space-time plane, while an accelerated interface reshapes their frequencies through time-dependent Doppler shifts. We develop an inverse-design procedure for the interface trajectory that focuses a quasi-monochromatic wave packet at a prescribed space-time event for an arbitrary dispersion relation, then extend the construction to polychromatic pulses. In its time-reversed form, the operation collimates a broadband pulse into a narrow-band wave. Moreover, cascading the forward and reverse operations enables a broadband pulse to propagate through an otherwise dispersive channel in a spectrally compressed state before being refocused. Full-wave simulations validate the focusing construction and demonstrate dispersion suppression.
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Chemical Physics
Accurate Solvation Properties in supercritical CO$_2$ with Molecular Density Functional Theory
Mohamed Houssein Mohamed, Odette Tannous, Camille Muller et al. (+4 more)
Supercritical CO$_2$ is a highly efficient solvent for the development of more environmentally benign chemical processes. It is crucial to predict its solvation properties – the solvation free energy and the solvation structure – both accurately and at low computational cost. We show here that classical density functional theory (cDFT) can reproduce the solvation properties obtained from conventional molecular simulations, while requiring a computational effort that is several orders of magnitude lower. This excellent agreement is achieved using a molecular cDFT formalism based on a density that depends on both the positions and orientations of CO$_2$ molecules in the vicinity of the solute. We further examine several levels of approximation for the excess free-energy functional in cDFT and demonstrate that the homogeneous reference fluid approximation is sufficient to recover the molecular dynamics (MD)
benchmark results. These findings open the way to extending molecular cDFT to other thermodynamic conditions.
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All authors Mohamed Houssein Mohamed, Odette Tannous, Camille Muller, Daniel Borgis, Francesca Ingrosso, Luc Belloni, Antoine Carof
Atomic Physics · Cross-listed from cond-mat.quant-gas
Momentum Distribution of a mass-imbalanced three-body system across the Efimov-Unatomic transition
D. S. Rosa, R. M. Francisco, T. Frederico et al. (+2 more)
We investigate the single-particle momentum distribution, the two-body contact and three-body tail coefficients of mass-imbalanced three-body systems at the critical dimension $D_c$, where the transition between discrete and continuous scale invariance takes place as the spatial dimension is tuned between three and two dimensions. We show that the asymptotic momentum distribution at $D_c$ is governed by a distinct logarithmic scaling structure, which differs fundamentally from both the log-periodic behavior of Efimov states and the power-law scaling of the unatomic regime. This structure contains an additional quadratic-logarithmic contribution, characterized by the asymptotic coefficient $C_3''$, which leads to a finite and well-defined description of the momentum tail at the transition. The coefficient $C_3''$ depends sensitively on the mass imbalance, changing sign across different mass configurations and vanishing for identical particles. For heavy-light-light configurations, the subleading three-body term vanishes at a characteristic momentum, leaving the leading two-body contribution at the order retained in the asymptotic expansion. The physical accessibility of this cancellation depends on the separation between the trimer size and the interaction range. We further analyze the narrow intermediate region connecting the Efimov and unatomic regimes, here identified as an intermediate scaling regime, whose extent and properties are strongly controlled by the mass ratio. These results establish the critical dimension as a regime with emergent scaling properties and provide quantitative momentum-space signatures for probing the transition between discrete and continuous scale invariance in few-body
quantum systems.
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All authors D. S. Rosa, R. M. Francisco, T. Frederico, G. Krein, M. T. Yamashita
Chemical Physics
Girsanov Reweighting for Uncertainty Propagation in Rare-Event Kinetics
Leonard Moracchini, Thomas Pigeon, Morgane Menz et al. (+3 more)
Machine-learning interatomic potentials (MLIPs) have become a powerful tool for rare event sampling in molecular dynamics, offering near ab initio accuracy at a fraction of the computational cost. However, the uncertainty associated with these models remains a major challenge. Existing uncertainty quantification approaches have largely focused on point-wise quantities, such as energies and forces, or on
equilibrium thermodynamic observables. In this work, we introduce a framework for propagating MLIP uncertainty to the averaged committor probability, a kinetic observable that enables reaction-rate calculations. Our approach combines rare event sampling methods such as Adaptive Multilevel Splitting with Girsanov reweighting to estimate the sensitivity of committor probabilities to variations in MLIP parameters, without requiring the costly resampling of reactive trajectories for each parameter realization. We derive exact and approximate Girsanov-based
estimators for uncertainty propagation and validate them on several
benchmark systems, including a rugged Muller-Brown potential, a dimer in a solvent, and the conformational transition of butane. The proposed framework enables the construction of uncertainty-aware probability distributions for rare event observables and successfully recovers reference rare event probabilities from uncertain surrogate models. Under mild assumptions on the accuracy of the MLIP within metastable basins, the framework can also provide uncertainty bounds on reaction rates through Hill's relation. These results demonstrate that path-space reweighting provides an efficient route for propagating MLIP uncertainty to rare event kinetics.
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All authors Leonard Moracchini, Thomas Pigeon, Morgane Menz, Thibault Faney, Thomas D. Swinburne, Mihai-Cosmin Marinica
Applied Physics · Cross-listed from cond-mat.soft
Microscopic constitutive theory of stress overshoot, yielding, and strain hardening in amorphous materials
Ankit Singh, Valeriy V. Ginzburg and Alessio Zaccone
We develop a microscopic constitutive theory for the nonlinear deformation of metallic and
polymer glasses based on nonaffine elasticity coupled to irreversible many-body relaxation. The theory predicts the full stress–strain response, from linear elasticity through stress overshoot and yielding to steady plastic flow. We show that stress overshoot originates from the competition between a nonaffine elastic instability induced by strain-driven loss of mechanical connectivity at the atomic/molecular level, and viscous dissipation associated with structural relaxation. For
polymer glasses, finite chain extensibility naturally accounts for strain hardening at large deformation. The stretched-exponential relaxation exponent is obtained independently from stress or modulus relaxation measurements and provides the primary dynamical input to the theory. Using a small set of physically meaningful parameters, the model quantitatively reproduces experimental stress–strain curves for metallic glasses, polycarbonate, PMMA, and epoxy resins over a broad range of strain rates. These results establish a unified microscopic framework linking relaxation dynamics, yielding, plastic flow, and strain hardening in amorphous solids.
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Atomic Physics
Rate coefficients for dielectronic recombination of N-like Ne
E.-O. Hanu, M. Lestinsky, E. B. Menz et al. (+16 more)
Dielectronic recombination (DR) for the process Ne$^{3+}$ + e$^{-}$ $\rightarrow$ Ne$^{2+}$ was investigated in a merged-beams arrangement at the heavy-ion storage ring CRYRING@ESR. The energy-dependent DR rate coefficient, $\alpha(E)$ was measured over the electron-ion collision energy range from 0 to 25 eV. The measurements cover the complete set of DR resonance series associated with $2s\to2p$ core excitations. The primary ion beam is estimated to have consisted of $44\%$ of the ions in the ground state, with the remainder distributed among long-lived metastable levels. In addition to the measurements we carried out
quantum mechanical calculations of DR cross sections. The theoretical treatment includes contributions from the ground and excited metastable initial levels, weighted according to the estimated beam composition. From the experimental energy-resolved spectra, we derive a temperature dependent DR
plasma recombination rate coefficient $\alpha_\mathrm{exp}(T)$ (PRRC). In the temperature domain where Ne$^{3+}$ is abundant in collisionally ionized
plasmas, the present results show a good agreement with the present and with previous theoretical predictions. In the low-temperature regime characteristic for photoionized
plasmas, the experimentally derived DR
plasma rate coefficient is slightly larger than the published theoretical ones and does not agree within the experimental uncertainties. Parametrized fits of the experimentally derived DR PRRC are presented in order to facilitate an easy inclusion into astrophysical modelling codes.
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All authors E.-O. Hanu, M. Lestinsky, E. B. Menz, M. Looshorn, Z. Andelkovic, A. Biniskos, C. Brandau, A. Braeuning-Demian, M. R. Fogle, W. Geithner, F. Herfurth, P.-M. Hillenbrand, C. Krantz, R. Schuch, M. Tatsch, G. Vorobyev, S.-X. Wang, T. Stoehlker, S. Schippers
Instrumentation and Detectors
Characterisation of a Thick Pixelated Silicon Detector for Electron Spectroscopy of Neutron Beta Decay
Manuel Lebert, Lilli Löbell, Igor Konorov et al. (+1 more)
Silicon detectors are commonly used for spectroscopy of low-energy particles. For electrons in the 1 MeV range, a rather large thickness of 2mm is required to entirely stop the electrons and commercial options are scarce. With the instrument PERC at the FRM II, we aim to measure beta spectra from polarised and unpolarised
neutrons in order to determine the axial-vector coupling constant, the element $V_\textrm{ud}$ of the Cabibbo-Kobayashi-Maskawa
quark-mixing
matrix, and to search for hypothetical scalar and tensor contributions. We present the characterisation of a commercially available, pixelated detector to assess its suitability to measure the entire electron energy spectrum of free
neutron beta decay.
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All authors Manuel Lebert, Lilli Löbell, Igor Konorov, Bastian Märkisch
Physics and Society · Cross-listed from cs.MA
Social Simulations: from Agent-Based Modeling to Digital Twins
Erica Cau, Andrea Failla, Valentina Pansanella et al. (+1 more)
This book chapter covers the
evolution of social simulation from classical
agent-based models, in which
agents interact according to explicitly defined behavioral rules, to AI-enhanced simulations based on Large
Language Models and, ultimately, Social Digital Twins: high-fidelity, data-driven representations of real-world socio-technical systems. Along this trajectory, we discuss the main methodological foundations, applications, advantages, and limitations of each paradigm, highlighting the progressive shift from abstract models designed to investigate general social mechanisms toward increasingly realistic computational representations of specific social systems.
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All authors Erica Cau, Andrea Failla, Valentina Pansanella, Giulio Rossetti
Fluid Dynamics
Drawing with water waves
Taiga Kanehira, James Steer, Laura-Beth Jordan et al. (+4 more)
The deterministic reproduction of complex 3D wave fields remains a significant challenge in ocean engineering. This study proposes a novel methodology for drawing arbitrary 2D curves and 3D volumetric shapes on a water surface using transient multi-directional focused waves. To overcome the limitations of conventional discrete-point focusing methods, our framework integrates Bézier curve parametrisation, equal arc-length sampling, and an Iterative Amplitude Correction (IAC)
algorithm. This effectively mitigates wave height overshoot and enables precise spatial superposition of spectral components. The method's effectiveness was validated through linear wave theory and Smoothed Particle Hydrodynamics (SPH) simulations, successfully reproducing 2D characters and a 3D human face. Physical experiments in the FloWave circular wave basin further demonstrated target shape generation, such as a 2D
star and 3D pyramid. Although further integration of nonlinear wave theories is necessary for high-amplitude accuracy, this technique establishes a deterministic methodology for creating arbitrary 2D and 3D surface geometries. It represents a significant advantage in wave field control for ocean engineering applications.
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All authors Taiga Kanehira, James Steer, Laura-Beth Jordan, Shaun Fraser, Thomas Davey, Hidemi Mutsuda, Samuel Draycott
Atomic Physics · Cross-listed from nucl-ex
Nuclear Charge Radius of $^9$Be from Muonic Atom Spectroscopy Using a Microcalorimeter
Ofir Eizenberg, Shikha Rathi, Andreas Abeln et al. (+34 more)
The $2p\to1s$ transition energy in muonic $^9$Be was measured using a metallic
magnetic calorimeter, resulting in $E_{2p\to 1s}=33\,391.48(34)\,$eV. The result is 30 times more precise than the previous best measurement and enables the extraction of the corresponding
nuclear charge radius $r_c($$^9$Be$)=2.5506(51)\,$fm. It is $2.4$ times more precise than the commonly used value based on electron scattering and differs from it by $2.3$ times the combined uncertainties. This measurement represents the first determination of a
nuclear charge radius using muonic x-ray spectroscopy with microcalorimeters.
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All authors Ofir Eizenberg, Shikha Rathi, Andreas Abeln, Sonia Bacca, Gonçalo Baptista, Nir Barnea, Noam Burger, Thomas Elias Cocolios, Marie Deseyn, Tim Egert, Christian Enss, Andreas Fleischmann, Loredana Gastaldo, César Godinho, Nitzan Goldberg, Michael Heines, Daniel Hengstler, Paul Indelicato, Weiguang Jiang, Klaus Kirch, Andreas Knecht, Daniel Kreuzberger, Jorge Machado, Ulf-G. Meißner, Ben Ohayon, Nancy Paul, Randolf Pohl, Tim Redelbach, Michael Roosa, Katharina von Schoeler, Quentin Senetaire, Shihang Shen, Daniel Unger, Stergiani Marina Vogiatzi, Johanna Walch, Frederik Wauters, Aziza Zendour
Computational Physics · Cross-listed from cs.LG
Microstructure-Conditioned Surrogate Models for Graded Multiscale Optimization of Mycelium Composites
J. Storm, I.B.C.M. Rocha, S. Schyck et al. (+2 more)
Emerging sustainable materials increasingly rely on engineered hierarchy and microstructure to achieve control of their properties and mechanical behavior. Optimizing these materials with controllable microstructures requires efficient multiscale simulations. Data-driven surrogate models for the microscale can accelerate multiscale simulations, but require large amounts of data even for a fixed microstructure. When a range of microstructures is considered, as is the case in multiscale optimization, even more data is needed to train a surrogate. To overcome this challenge, we condition a hybrid physics-data surrogate on microstructural variables using a hypernetwork. This approach enables accurate predictions of multiscale mechanical behavior for a mycelium-woodchip composite material, even when trained on small
datasets. The conditioned surrogate makes multiscale simulations of functionally graded structures tractable, and we validate it against a full FE^2 simulation. We optimize a graded multiscale disk, and reduce the peak stress by 43% compared to one with a random microstructure. Then, we go one step further, conditioning the network directly on manufacturing variables that can have a complex influence on the microstructure. This is a practical route to engineer the microscale for desired macroscale behavior. This contribution highlights the benefits of microarchitectured structures and demonstrates how conditioned surrogate models enable their multiscale optimization, which will accelerate the development and design of future sustainable materials and structures.
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All authors J. Storm, I.B.C.M. Rocha, S. Schyck, K. Masania, F.P. van der Meer
Plasma Physics
Dual-pulse micronozzle acceleration of sub-GeV-class protons
D. Pan and M. Murakami
We propose a dual-pulse micronozzle acceleration scheme that enables phase-locked acceleration of
laser-driven
protons, mitigating the trade-off between maximum
proton energy and
laser-to-
proton conversion efficiency. A delay-tuned synchronization window injects a compact
proton front generated by a shaping prepulse into a quasistatic axial electric field driven by a delayed main pulse in a micronozzle cavity. Phase locking preserves the relative phase between the
proton bunch and the accelerating field, suppresses thermal debunching, and prolongs the acceleration stage. At main-pulse intensities of order 10^21 W/cm^2, sub-GeV
proton cutoff energies are obtained with a total
laser-to-
proton conversion efficiency of about 20%. The efficiency for
protons above 100 MeV exceeds about 13%, indicating preferential energy loading into a compact
proton population. Simulations with an unconfined dual-pulse hydrogen rod show that the improvement results from temporal synchronization and
geometric confinement, which sustain a long-lived axial accelerating channel. An analytical synchronization model agrees with the simulations. Three-dimensional particle-in-
cell simulations confirm that phase locking and spectral hardening are preserved in slit-nozzle geometries, with cutoff energies about 60% higher than those of an unconfined hydrogen rod. These results establish phase-locked acceleration as a practical design principle for compact, high-yield sub-GeV
proton drivers for secondary-particle applications.
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Instrumentation and Detectors · Cross-listed from astro-ph.IM
Proof of concept of heterodyne interferometry at 10.6 um using photonic correlation
Tituan Allain, Jean-Philippe Berger, Guillaume Bourdarot et al. (+2 more)
The task of imaging complex
dust environments such as the inner astronomical units of a
planet-forming disks requires dedicated mid-infrared (MIR) interferometric facilities with kilometric baselines and a large number of
telescopes. Extrapolating technologies from current facilities is not straightforward. We aim to demonstrate the feasibility of using MIR heterodyne interferometry with a photonic correlation approach to recombine MIR signals from distant
telescopes. We want to determine the current technological limits of such systems are. We developed a laboratory demonstration bench that can correlate MIR signals at 10 um with a photonic correlator. The photonic correlator uses commercially available telecom components at 1.5 um to transport and correlate heterodyne signals that could go up to 10 GHz in bandwidth, directly extendable to 40 GHz. We used the demonstration bench to study the noise levels and detection limits of a heterodyne interferometer with a photonic correlation. We confirm the correlation exhibited by wideband MIR signals with the photonic correlator, along with a characterization of the performance of the system and analyzed the noise levels. We show that the photonic correlator does not limit the detection and that it can be used to compensate for free-space delays at 10 um with a fiber delay at 1.5 um. With our current sub-optimal commercial infrared (IR) detectors, we have derived a detection limit of 130 Jy that is coherent flux for 8 m class
telescopes with 1 h of incoherent integration. We discuss the possibility of lowering the detection limit down to typical T-Tauri
stars (approximately 1 Jy) using new detectors and coherent integration based upon local oscillator synchronization with telecom fiber links.
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All authors Tituan Allain, Jean-Philippe Berger, Guillaume Bourdarot, Carlo Sirtori, Hugues Guillet De Chatellus
Physics and Society
Calming traffic in unsignalized bidirectional streets by introducing one-lane bottlenecks
Victor L. Knoop and Carlos F. Daganzo
A common strategy to calm traffic in an unsignalized, bidirectional street consists in narrowing the street to a single lane at one or more locations. These locations become bottlenecks. Two policies are commonly used there: first-in-first-out (FIFO), and directional priority (DP), which means one of the directions has priority. This paper examines the performance of these two policies on streets with one or more bottlenecks. Two measures of performance are considered: the expected delay (evaluated for typical situations with low demand) and the system capacity. The latter is defined as the pair of flows (d1, d2) that depart the street in the two opposite directions when the system is oversaturated with queues. For a street with a single bottleneck, the capacity under both FIFO and DP is not unique: In both cases, the values of (d1, d2) form a continuous decreasing curve. As expected, we find that arrival flow pairs (a1, a2) below this curve can get through the system without generating queues. Those above cannot. For a single bottleneck it is shown that FIFO yields lower expected delay than DP under low demand. For high demand, DP's capacity exceeds FIFO's when the flows are balanced, but are lower otherwise. For multiple bottlenecks, the expected total delay on the street under low demand is that of a single bottleneck multiplied by the number of bottlenecks. The multi-bottleneck capacity under FIFO turns out to be the same as for a single bottleneck. For DP, traffic near capacity is complex. Capacity points turn out to be numerous and disjointed. Formulas are derived for their values. Higher capacities are typically obtained for longer streets. Curiously, these capacity points are often above the capacity curve of a street with a single FIFO or DP bottleneck, indicating that an extra bottleneck can increase capacity.
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Fluid Dynamics · Cross-listed from quant-ph
The potential of quantum computers for Particle Image Velocimetry
Philipp Pfeffer, Theo Käufer, Julia Ingelmann et al. (+2 more)
Particle Image Velocimetry (PIV) is the
prime image-processing technique to measure and visualize velocity fields of laminar and turbulent flows. The velocity field vectors are obtained with sub-pixelaccuracy by analyzing cross-correlations, empowered by Fast
Fourier Transforms (FFT). Here, we present a
quantum algorithm with multidimensional
quantum Fourier Transforms, termed
Quantum-based PIV (QuPIV), to replace the classical computation of up to millions of velocity vectors. Our end-to-end
quantum algorithm includes a novel state preparation, modified amplitude amplification, and the output extraction. We enhance amplitude amplification by a contracted ground-state projector, which allows a significant reduction of the number of gates in the
quantum circuit. We justify the end-to-end capability with numerical studies on all stages of the
algorithm on both synthetic and experimental data.
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All authors Philipp Pfeffer, Theo Käufer, Julia Ingelmann, Christian Cierpka, Jörg Schumacher
Physics and Society
Measuring What the Crawler Sees: Discovery Curves, Core Persistence, and Shell Dynamics in Longitudinal Web Crawls
Michael Paris, Hande Celikkanat and Luca Foppiano
A longitudinal web crawl is a sequence of partial samples of an evolving URL population. Pairwise containment between two crawls is the standard probe; under a simple urn model of the crawl – each round samples a fraction of the URLs and replaces a fraction – it recovers two interpretable rates, per-round survival $\alpha$ and coverage $c$, but treats the population as uniform and consumes one pair at a time. In this work, we define a formal
language for talking about a crawl. We extend this analysis with the discovery curve $U(s, T)$, the cumulative URL footprint over a sliding window of $T$ crawls starting at $s$, which under the same urn model is also a closed-form function of $(\alpha, c)$. Containment and the discovery curve are then two projections of one process: independent fits agree on $(\alpha, c)$ when the urn is homogeneous, so any disagreement is itself a measurement. Applied to Common Crawl (2020–2025, domain granularity) and to the German Academic Web (GAW, URL granularity), the two projections disagree on both archives, and a two-component urn with a persistent core fraction $\kappa$ alongside shell parameters $(\alpha_\partial, c_\partial)$ reconciles the disagreement. A residual on $c_\partial$ remains, signaling that the shell itself is not homogeneous; $\kappa$ is recorded as the scalar entry point to a rank-resolved generalization, which is left to follow-up work. \keywords{web archive \and crawl coverage \and discovery curve \and urn model \and two-component model \and URL lifetime}
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Fluid Dynamics
Wetting effects on the dynamics of droplets and bubbles at surfaces
Yifan Han, Kerstin Eckert and Gerd Mutschke
Dynamic wetting plays a fundamental role in the dynamics of droplets and bubbles at solid surfaces by influencing contact line motion and interfacial
evolution. In this work, three representative wetting-controlled
benchmarks, namely droplet splashing, bubble coalescence at solid surfaces, and bubble dynamics under shear flow, are investigated using a three-dimensional volume-of-fluid framework coupled with a recently developed dynamic wetting model based on contact line velocity reconstruction method [19]. The model is first validated against experimental observations and literature data for droplet splashing and bubble coalescence. It accurately reproduces the transient contact line
evolution, splashing morphology, and coalescence dynamics. In particular, dynamic wetting suppresses the premature bubble detachment predicted by static wetting models and yields substantially improved agreement with experimental observations. In shear flow, contact angle hysteresis and contact line dissipation strongly influence bubble deformation, sliding, and detachment. These results demonstrate that accurate treatment of dynamic wetting is essential for predicting wetting-controlled droplets and bubbles involving rapid contact line motion, strong interfacial deformation, and
topology changes.
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Optics
Parity-Lifted Radiative Degeneracy: Orthogonal Dipoles over Parallel Dipoles in Achiral Dielectric Cavities
Zhong-Jian Yang, Ya-Pei Wang, Lin Ma et al. (+3 more)
Parity
symmetry enforces radiative degeneracy of parity-conjugated emitters in free space. We selectively lift this degeneracy in an achiral dielectric cavity via coupling-induced global parity breaking: the cavity and individual dipoles each preserve parity, while their fixed relative orientation breaks global parity, enabling differential decay. This mechanism exhibits a structure-function trend in marked contrast to the Rosenfeld rule: orthogonal electric-
magnetic dipoles yield radiative asymmetry approaching the theoretical limit of 2, whereas parallel ones show negligible differentiation. A semi-analytical model, validated across multiple modes, confirms generality. These findings establish a new paradigm for
symmetry engineering without intrinsic chirality.
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All authors Zhong-Jian Yang, Ya-Pei Wang, Lin Ma, Jian-Hua Liang, Yue You, Jun He
Medical Physics
Using backscattered thermal neutrons to monitor boron concentration during BNCT: a Monte Carlo feasibility study
Zirui Ye, Yuxin Wang, Meitong Wei et al. (+1 more)
Boron
neutron capture therapy (BNCT) requires knowledge of patient-specific $^{10}$B concentration for accurate dose estimation, yet no established method provides real-time boron-sensitive information during irradiation. Backscattered thermal
neutrons carry a $^{10}$B-dependent intensity modulation through the $^{10}$B(n,$\alpha$)$^{7}$Li reaction, documented in BNCT treatment rooms for three decades but not yet developed as a measurement signal. This paper uses Monte Carlo simulation to assess the feasibility of backscattered thermal
neutrons as a measurement channel for $^{10}$B concentration. A thin $^{nat}$LiF-converter detector placed at the beam exit captures the composite forward-plus-backscatter field; differential imaging against a $^{10}$B-free baseline isolates the $^{10}$B-dependent component, quantified by the fractional reduction in the $^{6}$Li capture rate, termed Relative Detector Signal Reduction (RDSR). In homogeneous phantoms, RDSR shows linear concentration dependence ($R^2 = 0.997$) with a practical depth limit of approximately 6 cm. Edge-response analysis yields a
diffusion-limited FWHM of 32-176 mm over 1-5 cm depth, with weak concentration dependence. In a voxelized patient phantom across 12 boron configurations, the $^{6}$Li capture cross-section provides intrinsic thermal
neutron energy selectivity that preferentially weights the band where $^{10}$B absorption is concentrated. Region-of-interest integration achieves counting-statistics sensitivity below 10 ppm; the systematic detection floor (~22-28 ppm at $\pm$1% baseline uncertainty) identifies baseline-reference precision as the dominant constraint. The modeled detector produces limited dose perturbation (+11.6% treatment-time increase). These results establish the physical basis for a boron-sensitive backscattered
neutron measurement concept in BNCT.
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All authors Zirui Ye, Yuxin Wang, Meitong Wei, Xie George Xu
Plasma Physics
Neutron-source fidelity for laser-driven D–D lithium-blanket tritium-breeding tests
Chengqi-Zhang, Yang He, Mamat Ali Bake et al. (+1 more)
Compact deuterium–deuterium (D–D)
neutron sources can provide controllable irradiation fields for lithium-blanket studies, although their broad joint energy and angle distributions differ from the conventional $2.45$~MeV isotropic representation. We couple particle-in-
cell (PIC) simulations of target-normal-sheath-accelerated deuterons with a thick-target $D(d,n)^{3}$He source model and Monte Carlo
neutron transport. For natural lithium, the seven two-dimensional sources change tritium production per source
neutron by $-2.5\%$ to $+54.1\%$ relative to the ideal source. The matched three-dimensional calculation gives an increase of $43.5\%$ and lowers the corresponding ratio from $1.5406$ to $1.4350$. Source substitutions show that the difference is predominantly spectral, since the real spectrum alone gives a factor of $1.4199$, while using the real
neutron emission directions in place of isotropic emission adds only a further factor of $1.0106$ in the three-dimensional case. The real spectrum lowers the $^{6}$Li contribution by $6.9\%$, but the accessible $^{7}$Li$(n,Xt)$ response exceeds this loss. Enrichment to $90\%$ $^{6}$Li keeps the total change within $\pm1.5\%$. In the matched three-dimensional converter and blanket calculation, direct $D(d,p)$T production is $0.8458$ tritons per source
neutron and accounts for $98.1\%$ and $86.9\%$ of the combined production for natural and enriched lithium, respectively. High-density polyethylene moderation raises tritium production by about one order of magnitude but first weakens and then reverses the increase in blanket tritium production. The analysis quantifies source-model effects in compact breeding tests.
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All authors Chengqi-Zhang, Yang He, Mamat Ali Bake, Baisong-Xie
Optics
Imprinting topology on thermal light
Tianle Chen, Kelsey Everts, Andrew Forbes et al. (+1 more)
Topological structuring of light inevitably leverages on optical coherence to ensure that the imparted spatial phases are preserved, requiring highly coherent sources or coherence engineering embedded in the design. Now we show that thermal light can be spatially engineered to carry optical
topologies in the form of Skyrmions. Such
topologies are immune to time averaged decoherence, a fact we leverage on in reverse to create metasurface mediated incoherent
topologies from a thermal source. The pristine nature of our measured Skyrmions validates the approach, while simulations reveal how coherence management in the metasurface design would further enhance the functionality. Remarkably, the generation stage inherits robustness from the
topology, remaining immune to material and fabrication defects. Our work reports the first
topologies from purely thermal light, opening a path to exploiting
topology in ubiquitous everyday light sources.
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All authors Tianle Chen, Kelsey Everts, Andrew Forbes, Yungui Ma
Plasma Physics · Cross-listed from astro-ph.SR
Ion-Scale Current Sheets Embedded in Reconnection Jet Shear Layer of the Near-Sun Heliospheric Current Sheet
Dae-Young Lee, Dooyoung Choi, Kyung-Eun Choi et al. (+1 more)
Context.
Magnetic reconnection in the heliospheric current sheet (HCS) plays an important role in restructuring the
solar wind
magnetic topology and generating
plasma jets and
magnetic islands. While large-scale signatures of HCS reconnection have been reported in many observational studies, the kinetic-scale structure embedded within reconnection regions remains less well understood. Aims. We investigate the ion-scale currents sheets (CSs) embedded within an HCS reconnection region and their relationship to the flow-shear layer at the edge of a reconnection jet. Methods. We analyzed an HCS crossing observed by the Parker
Solar Probe on March 29, 2024, using high-time-resolution
magnetic field measurements. We focused on ion-scale
magnetic transitions within two brief intervals of flow-shear layer at the edges of the reconnection jet and examined them in a local LMN coordinate system. Results. Twelve representative CSs are identified, whose duration is on average $\sim$0.06 sec, corresponding to spatial scales of only a few ion inertial lengths. They are classified into three types based on the behavior of the out-of-plane
magnetic component $B_{M}$: (1) CSs showing clear bipolar $B_{M}$ variations without bifurcation in reconnecting-field ($B_{L}$), (2) CSs with both bipolar $B_{M}$ variations and bifurcated $B_{L}$ profiles characterized by a plateau structure, and (3) CSs where strong fluctuations obscure an otherwise expected bipolar signature. Conclusions. The reconnection jet shear layer in the HCS may serve as an active site that hosts a chain of ion-scale CSs. This provides new insight into the multiscale structure of HCS reconnection and suggests that flow shear layers may play an important role in generating secondary kinetic-scale structures.
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All authors Dae-Young Lee, Dooyoung Choi, Kyung-Eun Choi, Sung Jun Noh
Space Physics
Influence of Magnetospheric Plasma Environment on Surface Charging of the Lunar South Pole
Yaqi Xiao, Xiaoman Wang and Ronghui Quan
The lunar south pole is a key candidate region for future lunar exploration and base construction, but its charging characteristics under real topographic conditions and dynamic
plasma environments remain insufficiently understood. A high-fidelity terrain model of the lunar south pole spanning 86{\deg}S-90{\deg}S was constructed from optimized LRO/LOLA elevation data. Surface charging
evolution over half a lunar orbital cycle was then simulated with a finite element-BP neural network scheme, using lunar-phase-dependent
plasma inputs encompassing
plasma parameters of
solar wind and diverse Earth magnetospheric zones. The results show that south polar topography strongly regulates surface charging. Higher potentials appear on windward terrains, whereas lower potentials occur in shielded leeward regions, leading to enhanced local electric fields at the tops of uplands and crater floor-wall boundaries. Significant potential differences between the crests and the middle of the downstream walls of various craters indicate that these regions are highly terrain-sensitive. When the Moon passes through Earth's magnetosphere, surface potential and electric field are roughly symmetric around 0{\deg} lunar phase. From the
solar wind to the
plasma sheet, surface potential generally decreases while electric field magnitude rises. Only in the narrow magnetotail lobe adjacent to the
plasma sheet does the potential temporarily increase and the electric field weaken. In the
plasma sheet, the surface potential can decrease to approximately -1000 V, and the domain's peak electric field reaches about 5 V/m. These findings provide references for landing site selection, rover path planning, and electrostatic protection of lunar surface equipment.
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Computational Physics
$\lambda$PIC: A callback-centric particle-in-cell framework
Xuesong Geng, Yunwei Cui, Lingang Zhang et al. (+1 more)
We present $\lambda$PIC, a Python-based electromagnetic particle-in-
cell framework built around a callback-centric architecture. Existing PIC codes typically tie high performance to static, pre-compiled timestep loops, hindering implementation of custom physics, diagnostics, or output logic. $\lambda$PIC breaks this coupling by exposing every stage of the loop as a named stage (hook), permitting attaching arbitrary Python functions that operate on the full simulation state, enabling custom
algorithms and in-situ analysis without modifying the core
algorithms. Under this flexible framework, performance-critical kernels are written in C extensions and Numba, fields and particles are stored in NumPy arrays, and MPI parallelism is paired with graph partitioning to support dynamic load balancing and non-rectangular domains. Although $\lambda$PIC is designed as general-purpose, it has special focus on intense
laser-
plasma interactions. Future work will extend the framework to GPU acceleration and additional physics modules including implicit solvers and
nuclear physics.
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All authors Xuesong Geng, Yunwei Cui, Lingang Zhang, Liangliang Ji