Medical Physics
CBCT-IQ: A Publicly Available Annotated Cone-Beam CT Dataset for Image Quality Assessment and Benchmarking
Sepideh Hatamikia, Anna Breger, Clemens Karner et al. (+14 more)
Medical image quality plays a critical role in diagnostic accuracy, especially in X-ray-based imaging modalities such as cone-beam computed
tomography (CBCT), where image quality must be balanced against radiation dose. While expert visual evaluation remains the clinical standard for image quality evaluation, it is time-consuming, subjective and affected by inter-observer variability, emphasizing the need for reliable quantitative image quality assessment (IQA) methods. However, the development and validation of such IQA methods have been limited by the lack of publicly available CBCT
datasets with expert image quality annotations. In this study, we provide the first open-access CBCT IQA
dataset containing 1,764 annotated image slices acquired using systematic variations in image acquisition and reconstruction parameters. Three clinical experts graded the overall image quality and a predefined regions of interest (ROI) using a four-level scoring scheme. In addition, we
benchmark 26 full reference- and no reference-based IQA measures against expert annotations and introduce an exploratory IQA measure-based ranking capable of distinguishing subtle image quality differences. This
dataset introduced a standardized
benchmark for future CBCT IQA research and provides a valuable resource for the development and validation of new IQA methods, enabling reproducible research and advancing CBCT IQA.
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All authors Sepideh Hatamikia, Anna Breger, Clemens Karner, Birgit Pohn, Poorya MohammadiNasab, Martin Buschmann, Stephanie Nougaret, Laura Haddad, Ali Abbasian Ardakani, Afshin Mohammadi, Paul Apfaltrer, Wolfgang Birkfellner, Alfred Pohl, Ander Biguri, Gernot Kronreif, Carola-Bibiane Schönlieb, Tess Reynolds
Physics and Society
How null-model constraints affect statistical validation in projected bipartite networks
Alessandro Catalano and Rosario N. Mantegna
Statistical validation of projected bipartite networks depends critically on the null model adopted to describe random co-occurrences. Although several null models have been proposed, their comparison has mainly focused on the validated backbones they produce rather than on the statistical assumptions underlying their construction. Here we compare four widely used null models - the microcanonical configuration model generated by the Curveball
algorithm, the Bipartite Configuration Model (BiCM), the Bipartite Partial Configuration Model (BiPCM), and the Hypergeometric approximation - using three empirical bipartite systems from comparative genomics, international trade and food science. We use the statistically validated links obtained from the microcanonical bipartite configuration model as the reference
benchmark for assessing performances of the other three models. Our central result is that the statistical consequences of relaxing null-model constraints cannot be understood solely from the constraints themselves but must be analyzed through the probability distribution induced for the co-occurrence statistic. In particular, the combined behaviour of the expectation and variance largely explains the observed differences among the statistically validated backbones. We further derive a leading-order sparse approximation for the BiCM expectation, showing that the first correction to the Hypergeometric prediction is controlled by the degree heterogeneity of the non-projected layer. Surprisingly, despite neglecting this heterogeneity, the Hypergeometric model accurately reproduces the co-occurrence variance of the microcanonical ensemble across all
datasets. Our results suggest that null models should be compared not only according to the constraints they preserve but also according to the statistical consequences that these constraints induce on the distribution of the test statistic.
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Plasma Physics
Proof of operation of a micro-hollow cathode discharge driven by a true ns-pulsed high voltage: emission properties and atomic nitrogen production
Nikolaos Chazapis, Dimitrios Stefas, Alexandra Brisset et al. (+5 more)
The implementation of Micro-Hollow Cathode Discharges (MHCDs) for the efficient and controlled dissociation of molecular nitrogen into reactive N-atoms remains a central challenge in the synthesis of strategic materials such as hexagonal boron nitride (h-BN). Traditional MHCDs driven with DC high voltages (HV) can generate N-atoms under low-to-moderate gas pressures. However, they are prone to intrinsic instabilities that eventually induce arcing, increase thermal load and limit significantly their lifetimes. In this work we aim to enhance N2 dissociation efficiency in an Ar/N2 MHCD driven by a true nanosecond (ns) pulsed positive HV which has not been yet considered in MHCDs. A testbed reactor is employed to investigate microplasma behavior under ns-pulsed operation, which is then compared to a conventional DC MHCD. Specifically, we combined optical emission and ns-TALIF diagnostics under suitable operating conditions of each HV regime comprising different gas mixtures, pressures, and electrical parameters. These measurements allowed for the identification of key excited species and mapping of ground-state N-atoms absolute density in the low-pressure chamber of the MHCD reactor. It is demonstrated that ns-pulsed excitation produces a more symmetric discharge expansion on the cathodic surface compared to a standard DC excitation, while generating similar nature of emissive species and consuming up to 2 orders of magnitude lower average power depending on the operating frequency and voltage. Importantly, up to 6-fold enhancement in absolute N-atoms density (maximum value measured: 1.14x10 15 cm -3 ) is achieved with the ns-pulsed MHCD making it very promising for h-BN synthesis.
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All authors Nikolaos Chazapis, Dimitrios Stefas, Alexandra Brisset, Laurent Invernizzi, Noël Girodon-Boulandet, Guillaume Lombardi, Claudia Lazzaroni, Kristaq Gazeli
General Physics
Predicting Radial Velocities from Rossiter-McLaughlin Time Series Observations
Vardan Adibekyan, Olivier Demangeon, Diogo Teixeira et al. (+7 more)
The Rossiter-McLaughlin (RM) effect produces apparent radial velocity (RV) shifts through line-profile distortions caused by a transiting
planet blocking different regions of the rotating
stellar surface. Because the underlying orbital RV trend can be estimated from out-of-transit observations, RM sequences provide a controlled laboratory for studying flux-induced RV variations. We compiled a sample of 1171 ESPRESSO observations of 13 targets obtained during 21 RM observing nights and trained machine-learning models to reconstruct a reference RV trend from observed RVs, line-profile diagnostics, and activity indicators. Predictive performance varied substantially among
stars and depended on both the strength of the RM signal and the similarity of the target
star to the training sample. Applications to Sun-as-a-
star observations and Proxima Centauri recovered known periodicities but did not fully remove the activity-induced variability. Larger and more diverse
datasets will be required to assess the potential of this approach for mitigating activity-induced RV signals.
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All authors Vardan Adibekyan, Olivier Demangeon, Diogo Teixeira, Nuno C. Santos, Khaled Al Moulla, Eduardo Cristo, Andre Silva, Roman Chertovskih, Garik Israelian, Artur Hakobyan
Fluid Dynamics · Cross-listed from cond-mat.soft
Weak-electrolyte diffusiophoresis for rigid colloids
Subrata Majhi and Huanshu Tan
We develop a model for the diffusiophoresis of a chemically inert, rigid spherical colloid with fixed surface charge in a monovalent weak electrolyte, in which a neutral solute reversibly dissociates into ions. A weak far-field gradient is imposed in the neutral-species concentration. In the fast-reaction limit, local mass action and bulk electroneutrality determine the far-field ionic gradients, while the bulk zero-current condition determines the
diffusion-potential gradient. We solve the coupled Nernst-Planck, Poisson and Stokes equations for arbitrary double-layer thickness, linearising in the gradient strength while retaining the nonlinear Poisson-Boltzmann
equilibrium. In the Debye-Hückel limit, the mobility consists of one half of the matched fully dissociated response and a finite-double-layer correction due to neutral-ion coupling; the correction vanishes in both the Hückel and Smoluchowski limits. Beyond this limit, numerical solutions for the representative systems reveal a branch-selective response as the surface potential magnitude increases. When the counterion is slower than the co-ion, dissociation-association weakens a retarding concentration-polarisation layer, allowing the mobility to exceed the fully dissociated value. When the counterion is faster, the response remains close to the one-half scaling set by mass action. This reaction-polarisation coupling cannot be reproduced by adjusting only the bulk ionic strength, and hence the Debye length, in a fully dissociated model.
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Accelerator Physics
Space-charge compensation of a low-energy He2+ beam with fluorine-containing gases
Takashi Nagatomo, Yasuyuki Morita and Osamu Kamigaito
This study investigates the space-charge compensation (SCC) of a low-energy He2+ beam by introducing fluorine-containing gases into the low-energy beam transport line (LEBT) of the RIKEN Heavy-Ion Linear Accelerator. The introduction of SF6, C3F8, and CHF3 improved beam transmission through the LEBT, and the largest improvement was obtained using SF6. In contrast, the increase in the beam current with Kr was relatively small, and its effect was less pronounced than that of the fluorine-containing gases. The introduction of fluorine-containing gases increased the rise time of the chopped beam to approximately 10 ms. Experiments performed without the prebuncher confirmed that the prebuncher was largely responsible for this slow rise. Furthermore, the substantial difference in the rise time between Kr and the fluorine-containing gases suggests that different charge carriers may contribute to the SCC in these two cases. Based on the results, a new grid-type beam chopper was installed immediately upstream of the
radio-frequency quadrupole linac (RFQ). This configuration allows short beam pulses to be generated immediately before the RFQ while maintaining a direct-current beam in the LEBT, thereby achieving both an effective SCC and a fast beam-current rise. In an acceleration test using the new chopper, a 19.3 micro A He2+ beam was successfully and stably accelerated to the radioisotope-production beamline at a duty factor of 10%. This corresponds to approximately 193 micro A in continuous-wave mode operation, demonstrating that the proposed method is effective for realizing the acceleration of a 200 micro A-class He2+ beam.
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Chemical Physics · Cross-listed from cs.LG
Frugal Bayesian Optimization: Scalable Surrogates for Data- and Resource-Limited Discovery
Panagiotis Krokidas, Christoforos Rekatsinas, Vassilis Sioros et al. (+3 more)
Bayesian Optimization (BO) is widely adopted for data-efficient optimization in scientific and engineering applications, yet its computational cost is rarely evaluated alongside optimization performance. Here we present a systematic, compute-aware study of BO that evaluates surrogate models along two axes: optimization quality and computational frugality. Across eight
benchmark functions and nine real-world
datasets spanning materials science, mechanics, robotics, chemistry, and machine learning, we
benchmark four surrogate models: Gaussian Processes, Random Forests, NGBoost, and
Bayesian Adaptive Spline Surfaces. We show that Gaussian Process-based BO consistently incurs the highest time and
memory overhead without delivering superior optimization or sample efficiency. In contrast, scalable alternatives achieve equal or better performance at a fraction of the computational cost. Motivated by these findings, we introduce a surrogate-recommendation framework that predicts the most suitable BO surrogate from inexpensive
dataset characteristics. Together, these results establish FruBO as a reproducible, compute-aware baseline for
Bayesian Optimization and provide practical guidance for surrogate selection under limited computational and experimental budgets.
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All authors Panagiotis Krokidas, Christoforos Rekatsinas, Vassilis Sioros, Grigorios M. Chatziathanasiou, Efi-Maria Papia, George Giannakopoulos
Fluid Dynamics
A global mass-preserving numerical method for low-Mach-number real-gas flows in closed systems
Sanath Kotturshettar, Gonçalo Alcobia, Pietro Carlo Boldini et al. (+2 more)
A mass-preserving low-Mach-number framework is proposed for closed-system real-fluid flows governed by general nonlinear equations of state. The formulation enforces consistency between the spatially uniform thermodynamic pressure, the equation of state, and global mass conservation. Moreover, the numerical
algorithm employs a segregated strategy in which the thermodynamic state is updated before the momentum equations, and the velocity field is advanced using a pressure-correction method. This approach enables an efficient solution procedure by decoupling the thermodynamic and momentum updates and retaining the use of FFT-based solvers for the pressure correction. The resulting formulation is implemented with second-order spatial accuracy. The implementation is first verified using the method of manufactured solutions, in which the thermodynamic state is prescribed through analytical density and thermodynamic-pressure fields, enabling verification of the nonlinear equation of state, thermodynamic-pressure
evolution, and the low-Mach-number divergence constraint. The framework is subsequently validated against
benchmark laminar and turbulent flows for both ideal and real fluids, particularly transcritical CO$_2$ channel flow, demonstrating its accuracy and robustness in the presence of strong thermodynamic nonlinearities.
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All authors Sanath Kotturshettar, Gonçalo Alcobia, Pietro Carlo Boldini, Rene Pecnik, Pedro Costa
Computational Physics
Multistability and state-switching in series-coupled resonant tunneling diodes
Jannis Waldmann, Jonnel Jaurigue and Kathy Lüdge
Resonant tunneling diodes (RTDs) embedded in an electrical
circuit are known for their
neuron-like response characteristics, which makes them promising candidates for neuromorphic applications. This paper investigates the dynamical response of series-coupled RTDs and systematically analyzes the impact of coupling and inhomogeneities on the solution structure. We further propose a scheme for controlled switching between coexisting stable states which allows to realize tunable
memory elements in these
circuits. The coupled RTD system exhibits a rich bifurcation structure, showing different degrees of multistability between symmetric and antisymmetric solutions. Limit-cycle branches and their dependence on the system parameters are analyzed using numerical continuation methods. A central focus is placed on the role of
symmetry. For two identical RTDs, the system possesses a $\mathbb{Z}_2$ exchange
symmetry, which governs the emergence of
symmetry-breaking bifurcations and multistable states. The analysis is further generalized to $N$ coupled RTDs, revealing the underlying $S_N$
symmetry structure and its influence on the organization of
equilibrium branches, paving the way for neuromorphic network operation.
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Medical Physics
Intestinal peristalsis and wrinkling: A novel paradigm
René Thierry Djoumessi, Christopher Miller, Nipuni D. Nagahawatte et al. (+3 more)
A new computational framework for modeling the intestinal wall as a multi-layered fiber-reinforced continuum is presented. The framework reproduces for the first time physiological motility and overcoming large-displacements limitations (self-contact and volume locking) occurring in classical hyperelastic formulations of soft tissues. We introduce: i) layer-specific functions, segregating active circumferential and longitudinal muscle fibers while maintaining homogeneous passive reinforcement, and ii) a quasi-incompressible volumetric contribution, to handle large peristaltic contractions.
Cell electrophysiology is further extended to reproduce both slow waves and spike bursting activities thus mimicking for the first time a localized neural excitation in a three-dimensional geometry of small intestine segment. We introduce a spatio-temporal modulation of contractility to accurately capture activation driven by both slow waves and spike bursts. The overall coupled nonlinear electromechanical boundary valued problem is modeled following the active strain approach. A robust augmented-Lagrangian contact
algorithm is also embedded to avoid self-penetration and geometrical instabilities under large displacements. The 8-variables nonlinear governing equations are then discretized using in house P1-P2-P4 finite elements codes implemented within the GetFEM library. Numerical experiments demonstrate the ability of the proposed framework to reproduce physiological peristalsis, i.e., wall contraction greater than 80%, thus allowing full occlusion matching in vivo endoscopic images, and naturally generating wrinkling patterns consistent with experimental observations. We show that an active electromechanics anisotropic heterogeneous modeling strategy is critical for a numerically stable and physiologically accurate representation of gastrointestinal motility.
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All authors René Thierry Djoumessi, Christopher Miller, Nipuni D. Nagahawatte, Marco Paggi, Leo K. Cheng, Alessio Gizzi
Fluid Dynamics · Cross-listed from cond-mat.soft
Coalescence-induced alignment of anisotropic particles in drying sessile droplets
Johannes Schöttner, Qingguang Xie and Jens Harting
Alignment of anisotropic particles strongly governs the functional properties of printed materials, yet most studies have focused on particle
alignment in single evaporating droplets. In droplet- based printing, however, neighboring droplets can coalesce, generating rapid capillary flows that redistribute material and markedly affect the final morphology. Here, we use mesoscale simulations to investigate how droplet coalescence and subsequent evaporation jointly determine
alignment and redistribution in sessile droplets with different contact angles and volumes. During the early stages of coalescence, the mean nematic order along the coalescence direction increases for all combinations of contact-angle and volume asymmetries of the droplets. At later times, the mean nematic order either continues to increase or decreases, depending on the droplet geometry. We derive a
geometric scaling based on
curvature and volume asymmetry and show that the simulation results collapse onto a master curve, identifying an effective
geometric asymmetry parameter that governs the mean nematic order at the end of coalescence. During evaporation, the contact angle strongly influences how the coalescence-induced orientational structure is transferred to the final deposit. For small contact angles, the contact line remains pinned for a longer duration, better preserving
alignment. In contrast, larger contact angles promote contact-line motion, which weakens
alignment, as reflected by a reduced mean nematic order, while simultaneously generating stronger concentration gradients in the final deposit.
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Physics and Society
Autocatalytic knowledge dynamics in the AI era
Boris M. Dolgonosov
In the AI era, knowledge is growing at an accelerated rate. The goal of this study is to construct the macrodynamics of knowledge and elucidate the role of AI in this process. An autonomous knowledge production system is examined. The driving force behind the system's development is the disturbance of its homeostasis under the impact of external or internal factors. To solve emerging problems, the system uses available or generates new knowledge. The process is autocatalytic in the sense that knowledge accumulated over the past is used to create new knowledge. Knowledge production is hampered by resource scarcity and environmental disturbances that worsen the system's state. The loss of knowledge, in particular due to its obsolescence, contributes to the process' slowdown. Information noise also inhibits the advancement of knowledge, leading to energy dissipation. The combination of autocatalysis, aimed at generating new knowledge, with counteracting forces caused by resource scarcity, environmental problems, knowledge loss, and information noise provides the basis for building knowledge dynamics. The resulting dynamic equation shows that, depending on the balance of the forces acting, the rate of knowledge production can change as follows: 1) increase, ensuring system's development; 2) decrease to a finite (non-zero) level: the system degrades but survives; and 3) decline to zero: the system collapses. The model was applied to WIPO patent filing data, yielding parameter values. The influence of AI enhances autocatalysis, but counteracting factors also increase. A shift in the balance of forces leads to a phase transition with a change in knowledge dynamics. The system's
evolution can proceed through a series of phase transitions. Key milestones in AI development are compared with the forces represented in knowledge dynamics. Barriers to knowledge growth are discussed.
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Optics
Cryogenic nonlinear processes in thin-film lithium niobate
Tristan Kuttner, Ulrich Sauter, Robert J. Chapman et al. (+6 more)
Photonic integrated
circuits operating at cryogenic temperatures are necessary for many
quantum technologies such as
quantum transduction, integrated single-
photon emitters and detectors, as well as deep-space communication and sensing devices. Thin-film lithium niobate (TFLN) is an emerging platform that is a strong candidate for fully integrated
quantum photonics, offering low loss, fast electro-optic reconfigurability, nonlinear
quantum light sources, and the ability to host
quantum emitters and single-
photon detectors. To interface TFLN with technologies that require cryogenic operation, like superconducting single-
photon detectors, microwave-to-optical transducers, and solid-state
quantum emitters, it is important to study its optical and electrical properties from room temperature down to cryogenic temperatures. Here, we investigate linear and nonlinear photonic devices, including racetrack resonators, Mach-Zehnder modulators and periodically poled waveguides in TFLN using a cryogenic fiber probe station with full temperature control down to 5 K. We quantify a shift in resonances, a 22% increase in electro-optic modulator half-wave voltage, a blue shift of 18 nm for Type-0 phase-matching as well as a red shift of 64 nm for Type-II phase-matching as the sample temperature decreases. Our study of nonlinear processes in a cryogenic environment will contribute towards developing novel devices for inter-platform
quantum information processing, secure communication, and enhanced sensing.
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All authors Tristan Kuttner, Ulrich Sauter, Robert J. Chapman, Myriam Rihani, Jost Kellner, Alessandra Sabatti, Giovanni Finco, Andreas Maeder, Rachel Grange
Optics
High-Density Monocular 3D Particle Image Velocimetry by Wavefront Shaping and Deep Learning
Dafei Xiao, Jibu Tom Jose, Amit Parizat et al. (+4 more)
Three-dimensional (3D) Particle Image Velocimetry (PIV) measures flow velocities by imaging
laser-illuminated tracer particles seeded in a fluid, and is widely used in both academia and industry. Many applications require a compact setup for optical accessibility, ideally with a single camera, while also demanding high seeding densities for accurate velocimetry. These requirements, however, are typically incompatible:
monocular methods break down at high densities; high-density measurements instead generally rely on multi-camera tomographic systems. Here, we introduce Point-spread-function-Engineering Training-based PIV (PET-PIV), a compact
monocular 3D velocimetry approach that resolves this long-standing compactness-density trade-off through a minimal optical modification and deep-learning-based
algorithms. PET-PIV requires only the insertion of a single thin phase mask to an otherwise conventional PIV setup, beneath the objective in microscopy or at the lens iris in macro-scale imaging, and calibrates the resulting imaging system in situ, making the approach straightforward to implement and readily scalable. Computationally, PET-PIV operates in two complementary regimes: a tracking/Lagrangian mode that localizes and links individual particles, and, more importantly, a field mode for ultra-high densities which directly reconstructs 3D velocity fields from 2D image sequences. In realistic experimental validations using a tomographic PIV system, PET-PIV demonstrates strong agreement with ground-truth references, with correlation coefficients (CC) exceeding 0.97, alongside an order-of-magnitude improvement in computational speed. Notably, PET-PIV enables
monocular 3D macro-scale PIV at densities previously achievable only with multi-camera setups, dramatically expanding the applicability of 3D velocimetry in space-constrained and optically restricted environments.
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All authors Dafei Xiao, Jibu Tom Jose, Amit Parizat, Reut Orange Kedem, Josué Sznitman, Omri Ram, Yoav Shechtman
Classical Physics · Cross-listed from cond-mat.mtrl-sci
Strength-degradation phase-field regularization of cohesive fracture: the antiplane case
Blaise Bourdin and Corrado Maurini
Phase-field approaches to fracture, initially designed as regularization of the Griffith model of brittle fracture, are now commonly viewed as gradient-damage models whose regularization length becomes a material property driving crack nucleation. One weakness of this approach is that the strength surface cannot be arbitrary: its shape is dictated by the elastic energy, and its magnitude by the regularization length. We focus on the antiplane version of the model introduced by Bourdin, Marigo, Maurini and Zolesi (arXiv:2506.22558), which handles crack propagation along unknown paths and nucleation governed by an arbitrary convex strength surface by degrading the strength instead of the stiffness. It can be interpreted as a regularization of softening plasticity in which localization bands obey an equivalent cohesive law set by the strength domain and the toughness, while the role of the regularization length, when small compared to the elasto-cohesive length, is purely numerical. Strength, stiffness, and toughness thus become independent material data, and limit analysis, perfect plasticity, cohesive fracture, and brittle fracture merge into a single variational framework. We derive closed-form solutions for a simple shear problem, propose a numerical scheme combining alternate minimization and conic programming, and numerically verify the equivalent cohesive law, its independence of the regularization, and the size effect governed by the elasto-cohesive length. A "surfing" simulation highlights the structure of the propagating crack while a re-entrant V-notch is used to show how the model bridges small-scale yielding, cohesive fracture, and brittle fracture without a priori hypotheses.
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Optics · Cross-listed from cond-mat.mtrl-sci
Domain-Selective Enhancement of Second Harmonic Generation in Monolayer MoS$_2$ via Ferroelectricity-Controlled Photodoping
David Hernández-Pinilla, Line Jelver, María Jesús Martínez-Morillo et al. (+6 more)
Hybrid
heterostructures combining two-dimensional
semiconductors with ferroelectric materials offer a versatile route to actively control light-matter interactions at the nanoscale. Here, we report all-optical, light-induced domain-selective control of second-harmonic generation (SHG) in monolayer molybdenum disulfide (MoS$_2$) integrated with periodically poled lithium niobate (LiNbO$_3$). Spatially resolved SHG imaging reveals a pronounced modulation of the nonlinear optical response of monolayer MoS$_2$ governed by the ferroelectric domain pattern of the underlying substrate. A strong SHG contrast is observed between domains of opposite polarization, with a marked dependence on both the excitation wavelength and the incident optical power. The comparison between ferroelectric domains that either enable or do not exhibit light-driven photodoping in the MoS$_2$ monolayer provides a direct assessment of the role of carrier density in the nonlinear optical response. We find that ferroelectric-polarization-controlled photodoping at the MoS$_2$/LiNbO$_3$ interface enhances the effective second-order susceptibility, $\chi^2$, producing an increase in SHG intensity of up to ~70% under resonant excitation conditions. Ab initio calculations corroborate that charge doping modifies the electronic band structure of MoS$_2$ and strongly affects $\chi^2$ in the resonant regime, providing microscopic support for the experimentally observed modulation. The results highlight the combination of light intensity and ferroelectricity as a powerful knob for band-structure modulation in 2D materials and reconfigurable nonlinear optical responses, opening pathways toward programmable frequency conversion, smart light modulators, and advanced nonlinear photonic functionalities in integrated hybrid platforms.
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All authors David Hernández-Pinilla, Line Jelver, María Jesús Martínez-Morillo, César Hernando-Fuente, Miquel Cherta, Guillermo López-Polin, Joel D. Cox, Luisa E. Bausá, Mariola O Ramírez
Fluid Dynamics · Cross-listed from astro-ph.EP
Tidal dissipation in magnetised, rotating stars and planets: linear calculations exploring various magnetic field configurations
Shijun Chu, Zhao Guo, Aurélie Astoul et al. (+2 more)
We study
tidal flows in the convective envelopes of rotating, magnetised fluid bodies, such as low-mass
stars and
giant planets. In well-mixed convective regions, (magneto-)inertial waves are linearly excited by
tidal forcing, and their dissipation can dominantly drive
spin and orbital
evolution in many close
star-
planet and binary
star systems. We perform linear magnetohydrodynamic calculations of wavelike tides in spherical-shell geometry of a tidally-forced, rotating, incompressible, viscous and non-ideal magnetised fluid. Our calculations consider the widest range of
magnetic field configurations to date (including both aligned and misaligned dipole fields, free-decay dipole and quadrupole fields, azimuthal "Malkus fields" and mixed poloidal-toroidal "Prendergast fields") to analyse the effects of
magnetic fields on the wavelike response and dissipation. We find that the
tidal response at a given frequency depends strongly on both
magnetic field strength and geometry.
Magnetic fields with strong poloidal components modify the flow more efficiently and introduce high-frequency Alfvénic resonances associated with weakly damped eigenmodes. When an enhanced (turbulent) viscosity is adopted, we find that viscous dissipation remains comparable to Ohmic dissipation for strong fields, in contrast to previous studies in which Ohmic dissipation was argued to dominate. We also explore the variation in
magnetic effects as the shell thickness,
magnetic Prandtl and Ekman numbers are varied. Finally, the frequency-averaged
tidal power is found to be largely insensitive to the
magnetic field in most cases, though significant deviations are found for free-decay fields. Our results have important implications for the
tidal evolution of magnetised, rotating
stars and
planets.
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All authors Shijun Chu, Zhao Guo, Aurélie Astoul, Adrian J. Barker, Rainer Hollerbach
Fluid Dynamics · Cross-listed from cond-mat.mes-hall
The stability of electronic Poiseuille flow in two-dimensional materials
Marine Bastida, Alvaro Meseguer and Iacopo Torre
Motivated by the experimental observation of electronic Poiseuille flow in
graphene [J.A. Sulpizio et al. Nature 576, 75 (2019)] we analyze the linear stability of plane-Poiseuille flow of electrons in a two-dimensional material using a modified Orr-Sommerfeld equation. We calculate the critical current needed to make the flow unstable as a function of the experimental parameters and characterize the most favorable situation, that is the one needing the lowest current density, to observe flow instability. We predict the streamwise wavenumber and frequency at which the instability occurs and discuss the difficulties of an experiment aimed at probing this phenomenon.
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Instrumentation and Detectors · Cross-listed from cond-mat.mes-hall
A low-temperature ultra-high-vacuum scanning probe microscope with in situ electronic transport capabilities: from macro to nano in 10 minutes
Diego Exposito, Oscar Custance and Ivan Brihuega
We have developed a low temperature (LT), ultra-high-
vacuum (UHV) system that combines two complementary techniques, scanning probe microscopy (SPM) and electrical transport measurements, within a single platform. By providing simultaneous access to the atomic-scale surface landscape and the macroscopic device response of the same sample, the setup enables direct correlations between local structural/spectroscopic signatures and global electronic transport behavior in two-dimensional (2D) devices. The system allows experiments where atomic-scale modifications or controlled manipulations are performed while continuously monitoring their impact on device-scale performance. The setup consists of two interconnected UHV chambers: a dedicated preparation chamber and a separate measurement chamber that houses a
liquid-helium cryostat and the SPM/transport stage. Base pressure is 1x10^-11 Torr. A key feature is direct optical access to the sample, enabling rapid and reliable tip positioning with an accuracy of 5 microns x 5 microns within 10 minutes. The SPM, operated using custom-built electronics, can track the exact same sample region across a temperature range from 2.9 K to 400 K, with mechanical stability below 1 pm. System performance is demonstrated on
graphene devices, and bulk Pb is used to determine energy resolution. Using superconducting tips, scanning tunneling spectroscopy measures the superconducting gap with an energy resolution of 30 microV. Transport measurements track the temperature dependence of both resistivity and critical current across the superconducting transition of an in-situ prepared Pb nanowire.
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Optics
Dynamical control of light-matter interaction through coherent multipolar scattering in broken symmetry metasurfaces
Mohammed Ashahar Ahamad and Faraz Ahmed Inam
Achieving control over spontaneous emission by tailoring light-matter interactions is a key objective in
quantum nanophotonics. Metasurfaces composed of high-refractive-index resonators like silicon (Si) provide a low-loss platform that supports a variety of strong electric and
magnetic multipolar resonances, offering new opportunities to tailor the local density of optical states (LDOS). This work employs phase-resolved multipolar analysis to investigate spontaneous-emission control in
symmetry-broken dielectric metasurfaces composed of Si cuboid and disk resonators. Controlled in-plane geometrical asymmetry enables hybridization between
magnetic dipole (MD) and
magnetic quadrupole (MQ) modes, whose coherent interaction modifies the local density of optical states (LDOS).
Symmetry-broken dielectric metasurfaces are closely related to quasi-bound states in the continuum (quasi-BICs) and Fano-resonant systems, where geometrical perturbations promote coupling between weakly radiative and bright resonances. From this perspective, the observed MD-MQ hybridized states may be understood as a near-field and multipolar manifestation of
symmetry-broken quasi-BIC physics. The resulting coherent
magnetic multipolar interaction produces strong near-field localization and substantial spontaneous-emission enhancement for embedded emitters. For Erbium ions in broken-
symmetry Si metasurfaces operating near 1.54 um, the analysis reveals pronounced enhancement associated with resonant
magnetic multipolar coupling. These results establish
magnetic multipolar interference as a physically transparent mechanism for emission control in low-loss dielectric metasurfaces and provide useful design guidelines for integrated
quantum photonic devices.
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Data Analysis and Statistics
Learning transferable event representations for charmed baryon physics at BESIII
Kaixuan Huang, Yangu Li, Junpeng Zhao et al. (+6 more)
Deep learning has become an essential tool in high-energy physics, where the ability to learn transferable event representations can significantly improve model generalization across related physics processes. In this work, we present a Particle
Transformer-based framework for learning such representations for charmed
baryon physics in the BESIII experiment. The framework is implemented through large-scale pre-training on Monte Carlo simulation samples and subsequent fine-tuning for downstream analyses. Using the production and decays of the charmed
baryon $\Lambda_c^+$ as a
benchmark, we develop pre-trained models for both event classification and momentum-direction regression. The classification model learns discriminative event representations for the dominant physics categories, rejecting 97.0% of background events at a signal efficiency of 90.0%. Across 12
benchmark $\Lambda_c^+$ decay channels, fine-tuning from the pre-trained model achieves performance comparable or better than training from scratch, with particularly clear improvements in low-statistics regimes. For the regression task, the pre-trained model improves the momentum-direction prediction across the same
benchmark channels. Further improvement is obtained after fine-tuning in the representative semileptonic decay $\Lambda_c^+ \to p K^- e^+ \nu_e$. This strategy provides a scalable solution for a wide range of physics cases at BESIII and can be extended to other high energy experiments.
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All authors Kaixuan Huang, Yangu Li, Junpeng Zhao, Peilian Li, Peirong Li, Xiaorui Lyu, Yunxuan Song, Shengsen Sun, Yangheng Zheng
Atomic Physics
Strontium ${}^{1}S_{0}\!\rightarrow\!{}^{1}P_{1}$ transition frequency measurements assisted by a photonic grating chip
Jaewhan Lee, Hyun Gyung Lee, Won-Kyu Lee et al. (+15 more)
We measure the absolute frequency of the ${}^{1}S_{0}\!\rightarrow\!{}^{1}P_{1}$ transition in strontium using two methods: fluorescence spectroscopy of a thermal atomic beam source from a compact low-power oven and velocity measurements of a slow atomic beam from a two-dimensional grating magneto-optical trap (2D gMOT). The measurements for both methods are performed in the same ultra-high
vacuum chamber containing a diffraction grating chip which is placed below the strontium atoms that are being interrogated. The first method uses a probe
laser beam incident on the grating chip such that the grating acts as an end mirror, with the first-order diffracted beam providing a retro-reflected probe beam. The counter-propagating
laser beams traverse an atomic beam emitted from an oven, enabling spatially resolved fluorescence spectroscopy through CCD imaging and hyperfine-constrained multi-isotope fitting. The second method relies on a large profile cooling
laser beam normally incident onto the grating chip which
laser cools strontium atoms for a slow atomic beam source. The velocity of the atoms exiting the 2D gMOT is measured as a function of the
laser detuning and intensity from which the resonance frequency can be estimated. The two methods are consistent within their quoted uncertainties. Using three
datasets based on retro-beam spectroscopy measurements, and one
dataset using slow atom beam velocity measurements, we determine the ${}^{1}S_{0}\!\rightarrow\!{}^{1}P_{1}$ transition frequency to be $650.503\,815(5)~\mathrm{THz}$. Our result provides a re-evaluation of this $461$ nm transition demonstrated on a compact
laser cooling apparatus based on a diffraction grating platform.
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All authors Jaewhan Lee, Hyun Gyung Lee, Won-Kyu Lee, Huidong Kim, Dohyeon Kwon, Sang-Bum Lee, Meungho Seo, Taeg Yong Kwon, Sangwon Seo, Hyun-Gue Hong, Seji Kang, Sang Eon Park, Young-Ho Park, Jongcheol Park, Yeeun Na, Il-Suk Kang, Sangsik Kim, Jae Hoon Lee
Optics
Broadband Control of Light through Complex Media via Automatic Self-Referencing Transmission Matrix Characterisation
Marcos Maestre Morote, Mickael Mounaix, Andrew Komonen et al. (+2 more)
Light propagation through complex media underpins critical optical technologies, from imaging distant
stars and ground-to-space communication to imaging inside biological tissue with hair-thin multimode fibre endoscopes. Central to controlling light through such disordered media lies the transmission
matrix. Inaccessible to accurate modelling, the transmission
matrix must be measured experimentally$-$yet this conventionally relies on techniques involving an external phase reference. For low-coherence or broadband sources, the stringent coherence, mode-matching, temporal-overlap, and stability requirements of that external reference can make such characterisation prohibitively difficult or fundamentally infeasible. Alternatively, existing self-referencing techniques use algorithmically fragile global optimisation methods, relying on fixed preselected internal reference(s), whose incomplete overlap with the transmitted field can create measurement blind spots. Here, we introduce an automatic self-referencing measurement technique based on spatial state
tomography that circumvents these coherence and algorithmic limitations. Rather than relying on a preselected reference or complex phase
retrieval, our approach systematically leverages the local interference among all propagating modes as distributed phase references without prior assumptions. We demonstrate this framework experimentally for a multimode fibre across coherent, low-coherence, and broadband regimes, recovering its complete optical transmission
matrix and performing high-fidelity spatial and polarisation beam shaping in each case. By enabling robust, source-matched, self-referencing transmission-
matrix measurement, our method extends light control through complex media into broadband illumination regimes relevant to biomedical imaging, optical communications, and high-power
laser applications.
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All authors Marcos Maestre Morote, Mickael Mounaix, Andrew Komonen, Martin Plöschner, Joel Carpenter
Chemical Physics
An anharmonic liquid-entropy functional from the Mori-Zwanzig memory kernel
Ricardo Buarque, Mauro Gascon and Tod A. Pascal
We utilize the Mori-Zwanzig
memory kernel to separate the density of states of a
liquid into gas, cage, and harmonic-solid components. The cage
entropy is computed self-consistently as the non-Markovian excess of the full velocity response over its Markovian counterpart, and is assigned an excluded-volume
entropy reference rather than a harmonic one. Employing physically motivated constraints, the resulting Three-Phase Explicit Anharmonic Thermodynamics (3PT) method reproduces thermodynamic-integration
entropies of
liquid metals and aligns two water models with independent free-energy perturbation
benchmarks. For monoatomic Lennard-Jones
liquids, 3PT's accuracy follows a universal efficiency curve governed by the kernel's non-Markovianity. We thus establish a direct, trajectory-level mapping between
memory, transient cage dynamics, and
liquid entropy.
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Medical Physics
MWF-MIMOSA for efficient simultaneous relaxometry and myelin water fraction mapping
Yuting Chen, Yohan Jun, Hyeong-Geol Shin et al. (+15 more)
Quantitative
magnetic resonance imaging (qMRI) provides improved sensitivity and specificity to tissue composition and pathological alterations compared with conventional contrast-weighted imaging. Among various qMRI biomarkers, myelin water imaging is of particular interest because myelin plays a central role in
brain function and its alteration is closely associated with many neurological diseases. However, conventional myelin water fraction (MWF) mapping techniques are often limited by long scan times, low spatial resolution, reduced signal-to-noise ratio (SNR), and high specific absorption rate (SAR). Here, we propose MWF-MIMOSA for efficient simultaneous T1, T2, T2* mapping,
magnetic susceptibility source separation, and MWF estimation. To achieve this, multi-contrast and multi-slice zero-shot self-supervised learning (MZS-SSL) was used to jointly reconstruct whole-
brain complex-valued images. To improve computational efficiency of the parameter estimation step, a multilayer perceptron (MLP) was trained within the GACELLE GPU-accelerated parameter estimation framework to circumvent the computationally intensive Bloch simulation process, resulting in a >100-fold computational speed-up in MWF estimation. Numerical simulations were performed to evaluate the accuracy and precision of MWF-MIMOSA, and in-vivo results further demonstrated its robustness. Comparison with existing myelin water imaging methods showed that MWF-MIMOSA is highly correlated with established approaches, while providing complementary quantitative parameter maps at higher spatial resolution and with shorter scan times. Notably, simultaneous multi-parametric mapping was achieved in 5 min at 1 mm isotropic resolution, and in 10 min at 0.7 mm isotropic resolution. These results demonstrate the potential of MWF-MIMOSA for fast, high-resolution simultaneous relaxometry and myelin water imaging.
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All authors Yuting Chen, Yohan Jun, Hyeong-Geol Shin, Shizhuo Li, Shohei Fujita, Xingwang Yong, Jiye Kim, Jongho Lee, Gian Franco Piredda, Tom Hilbert, Aneri Bhatt, Susie Y. Huang, Huafeng Liu, Huihui Ye, Shahin Nasr, Borjan Gagoski, Kwok-Shing Chan, Berkin Bilgic
Computational Physics · Cross-listed from nlin.CD
Extrapolating the emergence of Hamiltonian chaos with random-feature Hamiltonian neural networks
Jaesung Choi
Machine learning of
Hamiltonian dynamics has driven growing interest in
Hamiltonian neural networks (HNNs), which encode Hamilton's equations of motion into the learning architecture. Despite this progress, it remains unknown whether such networks can predict dynamical regimes absent from their training data, in particular the broad chaotic sea that emerges beyond the observed parameter interval. We address this question using a parameter-aware random-feature
Hamiltonian neural network (RF-HNN). Trained using data from only a small number of control-parameter values at which invariant
tori dominate, the RF-HNN predicts autonomous long-time dynamics at unseen parameter values where mixed phase space develops and chaotic regions expand, with no data from that regime used in training or model selection. The method is demonstrated across four two-degree-of-freedom
Hamiltonian families, including the Hénon-Heiles system. Using Poincaré-section geometry and finite-time Lyapunov exponents, we show that the RF-HNN reproduces the breakup of regular structures and the emergence and growth of chaotic regions, whereas conventionally trained HNNs with the same
Hamiltonian structure remain too regular. These results show that what decides parameter extrapolation is not
Hamiltonian structure alone but how the fitted
Hamiltonian continues in the control parameter. To our knowledge, this is the first demonstration that a learned
Hamiltonian can qualitatively extrapolate from predominantly regular dynamics into a broad chaotic sea absent from training.
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Plasma Physics
Pulse Shaping Increases Efficiency in Pulsed Plasma Accelerators
Patrick W. Schools, Mammadbaghir Baghirzade, Ryan Heiser et al. (+3 more)
The performance of a gas-fed pulsed electromagnetic thruster is governed by the ability to deposit electrical energy while propellant is available for acceleration. Current pulsed-power systems require tradeoffs between high-current discharges that produce high exhaust velocities and longer pulses that overlap the energy deposition with more of the gas injection. This limited control restricts the specific impulse and mass utilization of these thrusters. This work introduces programmable pulse shaping as a method to increase control over energy deposition and expand the accessible operating space. We use solid-state integrated power modules to vary the discharge delay, pulse width, peak current, and the shape of the current waveform as propellant is injected. Experiments varying pulse widths from 30 to 500 $\mu$s and peak currents from 3 kA to 16 kA show that short, high-current pulses produce higher exhaust velocities and greater impulse bits than longer, lower-current pulses at comparable discharge energy. The switches also enable multiple discharges of arbitrary positioning and duration during a single gas injection. This micro-burst operation is shown to increase specific impulse in air by 278% from 840 to 3177 s through improved propellant utilization. This same pulse shaping ability is found to increase thrust efficiency from 0.2% in single-shot operation to 3.3% in micro-burst operation while operating with air.
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All authors Patrick W. Schools, Mammadbaghir Baghirzade, Ryan Heiser, Adrian Woodley, Laxminarayan L. Raja, Thomas C. Underwood
Geophysics
Ocean Surface Gravity Waves Excited by the 2022 Eruption of Hunga Tonga-Hunga Ha'apai Volcano
Kiwamu Nishida, Mie Ichihara, Tatsuya Kubota et al. (+1 more)
On 15 January 2022, a massive
underwater eruption occurred at the Hunga Tonga-Hunga Ha'apai Volcano. The plume reached the mesosphere, and the eruption excited a significant atmospheric Lamb wave, which forced the tsunami. The complicated tsunami waveforms due to ocean-atmosphere coupling prevented inferring the force history of the excitation. To address this, we analyze ocean surface
gravity waves (OSWs) from 15 to 40 mHz, which are decoupled from the Lamb wave due to their slower phase velocities. Modeling these OSWs, we infer that the excitation started at 4:00 UTC with an amplitude of $10^{10}$ N and lasted for 5 hr, followed by a sub-event at 8:40 UTC. The observations suggest an initial blowout of seawater above the summit and a subsequent
outflow that excited a tsunami below 5 mHz. The 2 hr delayed OSW excitation from 6 to 15 mHz may indicate seawater inflow into the crater.
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All authors Kiwamu Nishida, Mie Ichihara, Tatsuya Kubota, Takashi Tonegawa
Fluid Dynamics · Cross-listed from cond-mat.soft
Covariance-Driven Momentum Rectification at Liquid-Vapor Interfaces Near Wetting Transitions
Nelson Bolívar, Gabriel Abellán and Ivaylo Vasilev
Zero-mean forcing can generate directed transport when a medium responds in a spatially structured way and the relevant
symmetries are broken.
Liquid-vapor interfaces are a useful setting for this problem because surface-tension gradients, wetting dynamics, vapor exchange, capillary and acoustic waves, electro-ionic screening, thermal noise, and boundary compliance can all carry momentum. We develop a conservative continuum model in which the central object is the covariance between a local response field and a zero-mean tangential drive, $\langle Mf\rangle-\langle M\rangle\langle f\rangle$, embedded in an explicit momentum ledger. In a minimal diffuse-interface realization, this covariance gives the phase-selective drift law $U\propto\epsilon_h\Theta\sin\varphi$ for a Marangoni-driven
liquid-vapor interface above a structured wall, with exact nulls when the
symmetry is restored. Wetting susceptibility then acts as a bounded gain factor: first-order spinodal conditions provide the useful amplification regime, critical wetting saturates because interfacial unbinding removes the short-range drive, and bulk criticality suppresses the channel as the interface disappears. Additional reservoirs - phase change, waves, thermal transport, electro-ionic coupling, compliance, and fluctuations - are treated as compensating channels to be isolated by sign reversals, scaling laws, and budget closure. The result is neither a new microscopic force nor an apparatus-level claim, but a
symmetry-constrained accounting scheme for rectified momentum transfer in water-based interfacial systems. Reduced numerical calculations illustrate the phase-selection rules, bounded spinodal gain, momentum-budget closure, transverse chirality, and grid convergence.
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Fluid Dynamics
Coupled Rayleigh–Taylor and Faraday instabilities in vertically vibrated cylindrical containers
Tianyi Chu, Benjamin Wilfong, Timothy Koehler et al. (+2 more)
Interfacial instabilities govern the mixing in confined multiphase flows. Yet, the two mechanisms that drive them are usually studied independently: the pressure-gradient-driven Rayleigh–Taylor (RT) instability, which amplifies long-wavelength modes, and the parametrically forced Faraday instability, which selects shorter-wavelength harmonic or subharmonic modes. When an adverse density contrast and vertical vibration act together, the two compete, and neither alone describes the response. We use Floquet analysis to characterize the onset, growth, modal structure, and velocity fields of Faraday–RT waves in a vertically vibrated cylinder, resolved by azimuthal wavenumber, radial (Bessel) mode, and Floquet harmonic. The formulation recovers the classical RT and Faraday limits and reproduces the instability onset at the frequencies measured experimentally. For a free-sliding interface, increasing the vibration amplitude shifts the dominant instability mechanism from RT growth to subharmonic and then harmonic Faraday responses. Lateral confinement can also stabilize individual RT modes, which is not possible in an unbounded domain, although other Faraday modes may remain unstable. Pinning the contact line couples radial modes that otherwise evolve independently, allowing the unstable mode to be a superposition of RT-unstable and Faraday-stable components. This superposition alters the instability mechanism, producing a richer radial pattern. Reconstruction of the unstable modes shows the (linear) velocity fields that imaging cannot access and demonstrates how the instabilities can change the flow more broadly.
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All authors Tianyi Chu, Benjamin Wilfong, Timothy Koehler, Ryan M. McMullen, Spencer H. Bryngelson