Optics
Experimental observation of hyperbolic spacetime dynamics
Jonas Himmel, Coraline Bacq, Krishna Chand Maurya et al. (+11 more)
Understanding
quantum dynamics in curved spacetime is a central challenge at the intersection of
quantum mechanics and
gravity. Anti-de-Sitter (AdS) spacetime plays a pivotal role in the context of the AdS/CFT correspondence, which relates gravitational dynamics in the AdS bulk to a conformal field theory (CFT) living on its boundary. Despite its foundational importance, direct experimental access to dynamical
quantum phenomena in Lorentzian AdS spacetime has so far remained out of reach. Here, we report the first experimental emulation of fermionic wave packet dynamics in Lorentzian AdS spacetime using a photonic platform. By mapping the Dirac equation in curved spacetime onto the propagation of light in engineered wave\-guide arrays, we directly observe gravitational confinement of relativistic wave packets and resolve their center-of-mass motion in real time. We identify a characteristic superposition of slow geodesic oscillations governed solely by spacetime
curvature and fast Zitterbewegung arising from relativistic particle–antiparticle interference. While the geodesic frequency is independent of
fermion mass, the Zitterbewegung frequency exhibits a distinct joint dependence on mass and
curvature, revealing a
curvature-induced modification of relativistic
quantum dynamics. Our results provide the first quantitative experimental access to fermionic bulk dynamics in emulated AdS$_2$ spacetime with Lorentzian signature. This establishes a scalable analog platform that may potentially be used for exploring dynamical aspects of holography.
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All authors Jonas Himmel, Coraline Bacq, Krishna Chand Maurya, Max Ehrhardt, Matthias Heinrich, Tom A. W. Wolterink, Pablo Basteiro, Rathindra Nath Das, René Meyer, Tobias Huber-Loyola, Andreas Pfenning, Sven Höfling, Johanna Erdmenger, Alexander Szameit
Medical Physics
Experimental Validation of Skull Acoustic Modelling Strategies for Transcranial Focused Ultrasound Simulation: A Cross-Comparison Study
Han Li, Aidan J Horner, Xinyu Zhang et al. (+1 more)
Accurate acoustic modelling of the skull is essential for simulation-guided transcranial focused ultrasound (tFUS), but commonly used skull parameterisation strategies differ in complexity and reported accuracy. This study experimentally compared five k-Wave skull models: two voxel-wise linear mapping models, two three-layer models, and one single-layer fixed-parameter model. Nineteen regions of interest from five historical and two Thiel-embalmed human skulls were tested at 220 kHz, 680 kHz, and 1000 kHz. Bowl-surface source fields were reconstructed using acoustic holography, and simulated intracranial pressure fields were benchmarked against needle-hydrophone measurements. Across frequencies, mean peak-pressure errors ranged from 20% to 31%, whereas intensity errors reached 41% to 77%. Errors in -6 dB focal volume ranged from 11% to 67%, and focal-position discrepancies were typically several millimetres. Simulations generally predicted smaller insertion losses than measured, indicating a tendency to underestimate skull-related attenuation and overestimate transmitted intracranial exposure. The linear mapping model with fixed attenuation gave the lowest frequency-averaged pressure error, but no model showed a consistent advantage across all metrics. These results show that current skull models can reproduce gross intracranial beam patterns while retaining substantial quantitative uncertainty in exposure, focal coverage, and target localisation.
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All authors Han Li, Aidan J Horner, Xinyu Zhang, Zhihong Huang
Plasma Physics
Collisionless Bulk Electron Heating in Resonant Low-Voltage Capacitively Coupled Plasmas
Sarveshwar Sharma, Igor D. Kaganovich, Animesh Kuley et al. (+3 more)
We investigate collisionless power absorption in resonant, low$-$pressure capacitively coupled
plasmas (CCPs). In these
radio-frequency (RF) discharges, the sheath capacitance almost exactly balances the
plasma inductance, driving the total RF discharge voltage down to just a few volts. However,
plasma persists not only in this ultra$-$low$-$voltage regime; it also generates ions that strike the electrodes with kinetic energies substantially exceeding the amplitude of the applied RF voltage. This counterintuitive behavior arises from the presence of a pronounced electrostatic potential well of approximately 40 V within the
plasma bulk, which confines electrons while simultaneously accelerating ions toward the electrodes. We show that, under these resonant conditions, collisionless electron heating exhibits a fundamentally different behavior from the conventional paradigm of
stochastic sheath heating mediated by electron$-$sheath interactions. Instead, the predominant energy transfer mechanism is bulk electron heating in RF electric fields via a primarily collisionless process that emerges from the synergistic action of: (i) a strongly amplified RF electric field within the
plasma bulk, (ii) electron oscillatory motion (bouncing) within the
plasma potential well, and (iii) electron scattering resulting from collisions with neutral atoms. Collectively, these phenomena give rise to a pronounced high$-$energy tail in the electron energy distribution function and thereby lead to a substantial enhancement of the ionization rates. As the gas pressure rises, the resonance is disrupted. At the same time, the region of maximum power absorption moves from the
plasma core toward the edges and the sheath, which is accompanied by the disappearance of the high$-$energy electron population and a corresponding decrease in ionization rates
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All authors Sarveshwar Sharma, Igor D. Kaganovich, Animesh Kuley, Sudip Sengupta, Alexander V. Khrabrov, Bhooshan Paradkar
Fluid Dynamics
Scaling laws and local enhancements of buoyancy flux in stratified turbulent flows
Gyeongseob Song, Fabio Feraco, Raffaele Marino et al. (+6 more)
In the presence of stratification, turbulent flows exhibit intermittency not only at small scales but also at large scales, comparable to the mean flow, as observed in the atmosphere and oceans. We study such flows through a large parametric exploration using direct numerical simulations of the Boussinesq equations with different forcing types. We examine two Prandtl numbers (1 and 6) and vary the Froude number ($Fr$) over a range of geophysical interest values, $0.01\le Fr \le 1$, corresponding to a variation in terms of the buoyancy Reynolds number ($R_{IB}$) of $0.06\le R_{IB} \le 2300$. We analyze the dependence on $R_{IB}$ of the buoyancy flux ($B_f$), the mixing efficiency, the shear parameters, and the vertical momentum flux. Strongly non-Gaussian tails in the spatio-temporal distribution of the $B_f$ are observed, with kurtosis reaching $\approx 10^2$, indicating the potential for stratified geophysical flows to be characterized by highly variable transport properties along the direction of
gravity even under stable stratification. This is associated with long-time intermittent behavior of vertical velocity and temperature at large scale, which produces local
turbulence and enhances dissipation and transport. We present evidence that the skewness of $B_f$ increases with $R_{IB}$ as a power-law and saturates in the passive-scalar limit. We also show that the domain-averaged $B_f$ exhibits two distinct trends: logarithmic growth with $R_{IB}$ and approach to a small offset as stratification strengthens. A simple model for the temporal
evolution of energy and $B_f$ indicates that the defect between vertical and potential energy drives strong $B_f$ events. This trend directly leads to convective instabilities, the formation of two-dimensional and three-dimensional eddies, and rapid dissipation on a turnover timescale, allowing the energetic cycle to restart-also occurring in bursts.
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All authors Gyeongseob Song, Fabio Feraco, Raffaele Marino, Jorge L. Chau, Alain Pumir, Leonardo Primavera, Annick Pouquet, Pablo D. Mininni, Duane Rosenberg
Plasma Physics
Experimental validation of a fast control-oriented, physics-informed surrogate model for plasma equilibrium reconstruction in the TCV tokamak
M. Grandin, A. Mele, C. Galperti et al. (+5 more)
Magnetic equilibrium reconstruction provides the
plasma state estimate required for real-time shape control in tokamaks. We present a fast, physics-informed neural network surrogate of the liuqe
equilibrium reconstruction code \cite{liuqe1} for the TCV tokamak at EPFL, achieving inference times below 100~$\bm\mu$s and enabling 10~kHz shape control. The model is trained on around 10,000 TCV discharges spanning the full operational range of
plasma shapes. Its modular branch/trunk architecture decouples
magnetic measurement encoding from spatial coordinate processing, enabling physics-informed regularization via automatic differentiation of the predicted flux map. The surrogate has been compiled and deployed on the TCV real-time control system, and validated both offline and in real time against the models liuqe-rt and lih, showing comparable accuracy. Closed-loop performance assessed with the real-time software in-the-loop fge \cite{fge1} demonstrates control-equivalent behavior across multiple control strategies.
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All authors M. Grandin, A. Mele, C. Galperti, D. Gonzales Castineiras, C. Heiß, A. Cenedese, TCV team, EUROfusion Tokamak Exploitation team
Fluid Dynamics
No need to stay positive: a practical approach to direct numerical simulations of elastic turbulence
Damiano Capocci, Moritz Linkmann and Alexander Morozov
Successfully performing direct numerical simulations of polymeric flows remains a major challenge in computational fluid mechanics. In addition to the velocity field, such simulations must resolve polymeric degrees of freedom, often expressed via the conformation tensor, $\mathbf{c}$, which captures the local stretch of
polymer molecules. A key difficulty here lies in maintaining the physical requirement $\mathrm{Tr}\, \mathbf{c}>3$, which is not explicitly enforced by the governing equations. Consequently, simulations initiated from physical conditions may silently drift into unphysical states with $\mathrm{Tr}\, \mathbf{c}<0$, indicating a loss of positive-definiteness of the conformation tensor. Existing numerical methods to prevent this are costly, making direct numerical simulations of chaotic
polymer flows, such as elastic
turbulence, heavily reliant on high-performance computing. Here, we ask whether simulations that violate $\mathrm{Tr}\, \mathbf{c}>3$ can still yield meaningful physical insight into the underlying dynamics. We simulate a model dilute
polymer solution driven through a plane channel at low Reynolds number and observe the transition to elastic
turbulence. Our simulations exhibit two threshold resolutions: below the first, they become numerically unstable and exhibit a finite-time blow-up; above the second, they maintain positive-definiteness. In between, simulations remain stable and chaotic despite local violations of $\mathrm{Tr}\, \mathbf{c}>3$. Surprisingly, these violations do not affect mid-plane statistics of velocity, its gradients, or
polymer stretch, which match results from fully positive-definite simulations. This suggests that resolving flow structures or key flow statistics may not require the extreme resolutions needed to preserve positive-definiteness, potentially lowering computational barriers for studying elastic
turbulence.
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Physics and Society
Quantifying defensive pressure on the ball carrier in soccer based on minimum arrival time
Takuma Narizuka, Ikuya Sakamoto, Ken Yamamoto et al. (+1 more)
Defensive pressure on the ball carrier is a fundamental component of soccer tactics. Existing pressure measures often involve additional modeling assumptions, which may reduce interpretability. In this study, we quantify defensive pressure as the opponent minimum arrival time to the ball-carrier location, computed from a physics-based motion model. Using synchronized event and tracking data from all 306 matches in the top division of the Japan Professional Football League during the 2023 season, we analyze the statistical characteristics and temporal
evolution of this quantity during ball-possession intervals. The results show that the opponent minimum arrival time tends to decrease during possession and to increase again at the start of the next possession after ball release. We also find that possessions starting under stronger defensive pressure tend to yield smaller ball progression, and that, for intentional open-play passes, possessions ending under stronger pressure are more likely to be lost. These findings indicate that minimum arrival time provides an interpretable and physically grounded measure of immediate defensive pressure on the ball carrier. The proposed framework provides a simple and interpretable baseline for quantifying pressing dynamics from tracking data.
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All authors Takuma Narizuka, Ikuya Sakamoto, Ken Yamamoto, Yoshihiro Yamazaki
Instrumentation and Detectors
Design and electron optics performance of a MEMS electrostatic electron monochromator
M.J. Adriaans, J. P. Hoogenboom and A. Mohammadi-Gheidari
Monochromators are routinely used in Transmission Electron Microscopy and Electron Energy Loss Spectroscopy, to improve both spatial and energy resolution. State-of-the-art monochromators, however, are complex instruments that typically require additional electron optical correctors, limiting their implementation to the high-end, most expensive microscopes. Miniaturized monochromation relying on purely electrostatic fringe fields has recently been proposed as a means to realize a simpler and thereby more cost-effective and easier to operate high-resolution monochromator. Here, we present a design for such a compact, fully electrostatic fringe-field based monochromator. Our design consists of a superposition of an Einzel lens with a series of electrostatic deflectors and is entirely based on dimensions that can be realized with MEMS fabrication technology. Thanks to mild mechanical and electrostatic potential tolerances, the MEMS-fabricated electrodes can be passively aligned and only need seven regular power supplies. We present an analysis of spectral broadening due to diffraction in our monochromator design as well as particle simulations including
stochastic Coulomb interactions. This analysis shows that our design can achieve a resolution of 19 meV while maintaining 128 pA of beam current and thus potentially achieve energy filtering comparable to state-of-the-art monochromators. Our MEMS monochromator could therefore bring the application of energy filtering into the domain of SEM and specifically allow higher resolution imaging in chromatic-aberration dominated low-voltage SEM.
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Plasma Physics · Cross-listed from astro-ph.HE
Fast Radio Bursts produced during collapse of macroscopic X-mode in magnetized pair plasma
Maxim Lyutikov
We demonstrate that in highly magnetized pair
plasma nonlinear long-wavelength X-modes experience wave collapse/breaking, whereby the wave undergoes severe spatial steepening, driven by nonlinear modifications of the refractive index and strong ponderomotive forces. The collapse/wave breaking occurs in a narrow parameter regime, when the fluctuating part of the
magnetic field exceed the guide field, and
plasma magnetization is close to the current starvation regime. This regime is naturally achieved in highly magnetized
neutron stars, magnetars. Breaking during a fraction of the dynamic timescale, and quickly generates high-k modes. The initial EM energy, spread over large spatial scales, is squeezed into these highly localized, short-wavelength (yet macroscopic) singular pulses. The corresponding electromagnetic “foam” spectrum is red, $E_k \propto k^{-2}$, while the particles' spectrum is exceptionally hard, $f(\gamma) \propto \gamma^0$ The wave collapse produces short bright EM pulses - astrophysical Fast
Radio Bursts. The highest energy particles may produce short contemporaneous high energy bursts.
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Atmospheric and Oceanic Physics · Cross-listed from math.ST
Kling-Gupta linear regression
Hristos Tyralis and Georgia Papacharalampous
Kling-Gupta efficiency ($\mathrm{KGE}$) is a model performance evaluation metric widely used in hydrology, but its properties as a statistical
estimator have remained unexplored. We formalize the Kling-Gupta loss $L_\mathrm{KG} = (1 - \mathrm{KGE})^2$ in an extremum estimation framework (maximizing $\mathrm{KGE}$) for multiple linear regression. We give explicit formulas showing that Kling-Gupta regression scales the ordinary least squares (OLS) coefficient vector by a variance-inflation factor depending on sample variances and covariances. Its predictions reproduce the training set response variance, unlike OLS's variance reduction, while both maintain the response mean and achieve the same sample correlation. We prove that no
estimator simultaneously maximizes Nash-Sutcliffe efficiency ($\mathrm{NSE}$) and $\mathrm{KGE}$: OLS maximizes $\mathrm{NSE}$ but not $\mathrm{KGE}$, whereas Kling-Gupta regression maximizes $\mathrm{KGE}$ at the expense of $\mathrm{NSE}$. We establish almost-sure convergence of the Kling-Gupta
estimator to well-defined population limits. The training and test set performance metrics for both
estimators converge asymptotically to identical limits (different for OLS vs. Kling-Gupta). In a single-predictor model with fixed intercept, we identify conditions where a global minimum of $L_\mathrm{KG}$ does not exist because of discontinuity at zero slope. This work establishes a mathematical foundation for $\mathrm{KGE}$-based estimation and clarifies its effects on predictive performance in hydrologic modeling.
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Physics and Society
Declines in research funding and science ecosystem fragility
Anbang Du, Beining Zhang, Rifat Atun et al. (+2 more)
Scientific knowledge advances through within-country and cross-border scientific activities and collaborations, influenced by funding and strength of research enterprise. Sudden declines in research funding, for example from Federal sources in the United States (US) 2024-25, adversely impact on scientific collaboration. How rapid declines in funding affect the science enterprise and the magnitude of impact need to be analysed. Past studies have modelled the global scientific system as complex collaborative networks of entities and studied its
topology and dynamics. However, these studies have not undertaken compensation analysis to real-world shocks that have produced rapid declines in scientific research funding. In this study we examine the effect of the sharp declines in the US Federal funding on cancer science research enterprise globally. We model the cancer science ecosystem as a 5-layer multiplex network of collaborative linkages between 233 countries and territories in grants and clinical trial co-investigations, paper co-authorships, co-inventions and patent co-ownerships. We quantify information flow in the multiplex system through network efficiency. Proposing a framework for compensation analysis, we show that sharp declines in US Federal funding for research degrade global information exchange in science, imposing outsized compensatory burdens on country groups such as the European Union (EU) and BRICS (Brazil, Russia, India, China and South Africa). However, we also show that if other countries provide more support for international collaborations, there is an opportunity to remodel the cancer science system to be more resilient to future shocks.
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All authors Anbang Du, Beining Zhang, Rifat Atun, Michael G Head, Markus Brede
Accelerator Physics
An Introduction to Measurement Uncertainty
Samanta Piano
This chapter introduces the fundamental principles of metrology and the concept of measurement uncertainty. It explains the role of measurement in engineering and manufacturing, outlines the distinction between error and uncertainty, and presents standard methods for evaluating uncertainty, including the GUM framework, uncertainty budgets, and Monte Carlo simulation. Practical examples and industrial standards are discussed to illustrate real-world applications.
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Physics and Society
An Agent-Based Model for Migration Decision-Making Under Higher Frequency of Extreme Climate Events
Valentina Antonaccio Guedes and Rafael Prieto-Curiel
This paper develops an
agent-based model of
climate-related human migration that links repeated environmental shocks to individual migration decision-making through the joint
evolution of perceived risk, aspirations to migrate, and migration capability. Building on the aspirations-capabilities framework, the model represents migration as an emergent outcome of two opposing dynamics: shocks increase perceived risk and raise aspirations to move, while simultaneously eroding wealth and reducing the capability to do so. This interaction generates non-linear mobility patterns, including immobility under rising
climate stress.
Agents are embedded in a spatially heterogeneous shock environment, and their migration capability is further shaped by local conditions and diaspora support. Results show that more frequent shocks can initially increase migration pressure but eventually trap vulnerable
agents in place as resources decline.
Climate shocks amplify existing income inequalities in mobility outcomes, with lower-income
agents more likely to become trapped or remain acquiescently immobile, while higher-income
agents retain greater flexibility to migrate or choose voluntary immobility.
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Atmospheric and Oceanic Physics · Cross-listed from math.NA
Residual Pseudospectra Reveal a Physics-Informed Koopman Backbone for Tropical Pacific Variability and ENSO Prediction
Paula Lorenzo-Sanchez, Matthew J. Colbrook and Antonio Navarra
Tropical Pacific sea-surface-temperature (SST) variability spans interacting timescales, with the ENSO as its dominant interannual expression. Yet the dynamical structure organizing this variability and underpinning extended-range predictability remains difficult to extract from high-dimensional observations. Koopman operator learning offers spectral coordinates for nonlinear dynamics, yet finite geophysical records often produce dense, sampling-sensitive spectra whose physical content is ambiguous. We show that this apparent redundancy reflects coherent operator-level structure. Combining kernel Extended Dynamic Mode Decomposition with residual minimization and pseudospectral analysis, we use the Koopman
eigenvalue relation as a physics-informed consistency test to organize learned spectra. Applied to ERA5 and HadISST tropical Pacific SST anomalies, the residual landscape identifies 19 robust residual-minimum frequencies with coherent spatial modes that persist across products and sampling realizations. Together, these modes define a compact Koopman backbone spanning low-frequency modulation through quasi-biennial components, including ENSO-band variability. The surrounding spectral cloud is structured by integer powers and nonlinear combinations of this backbone, forming a residual-ordered Koopman hierarchy. The backbone reconstructs substantial Nino3.4 variance and enables skillful out-of-sample forecasts, with greatest gains at 8-18-month leads. By
embedding dynamical consistency into physics-informed operator learning, the framework turns opaque spectra into robust, interpretable and predictive representations of tropical Pacific variability.
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Atmospheric and Oceanic Physics
Revisiting urban heat indices in Switzerland using low-cost measurement networks
Martí Bosch and Moritz Burger
Urban populations are increasingly exposed to extreme heat events such as heatwaves, which can be exacerbated in cities due to the urban heat island (UHI) effect. With the aim of developing adaptation strategies, recent years have seen a growing interest in deploying high-resolution measurement networks using low-cost devices (LCDs), which enable the evaluation of intra-urban temperature distribution and its impacts at an unprecedented spatial resolution. However, the reliability of LCD measurements has been called into question, especially regarding potential overheating due to inadequate radiation shielding. In this study, we develop a statistical method to correct temperature biases based on short-wave radiation using a generalized additive model (GAM) and then apply it to LCD measurements in the urban
climate networks of the cities of Bern, Lausanne, Neuchatel and Zurich (Switzerland). To that end, we first calibrate the correction procedure to the LCD models used in each city using an intercomparison field study, in which the LCD models are collocated next to a professional automated weather station (AWS) operated by MeteoSwiss in the rural surroundings of Bern. Then, we evaluate how these corrections can influence two
climate indices, namely the number of tropical nights and the number of heat warnings issued in each city according to MeteoSwiss heat warning system. The findings suggest that the current AWS underestimate the heat warnings, whereas some LCD models likely overestimate them due to radiative errors. Nevertheless, uncorrected LCD measurements still provide a more reliable estimate of urban temperatures than AWS located outside urban settings. The insights can guide selection of LCD models for new monitoring networks and support the application of model-specific radiative bias corrections to existing LCDs, enabling more accurate assessments of heat and its impacts.
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Plasma Physics
Core-edge integrated modeling of ARC: on the effect of impurity transport and detachment conditions
Marco Muraca, Pablo Rodriguez-Fernandez, Nathaniel T. Howard et al. (+5 more)
Integrated modeling of ARC H-modes has been conducted to assess the feasibility of high-performance scenarios compatible with divertor detachment. The analysis incorporates self-consistent
evolution of
impurity radiation and density profiles, demonstrating that fusion power levels approaching a GW can be achieved while maintaining divertor temperatures below 2 eV with Ar seeding. Sensitivity studies reveal a strong dependence of fusion power on the separatrix density, with performance spanning 750-1000 MW, and a weaker dependence on enrichment factor and pedestal density. Alternative seeding strategies using Neon have also been explored.
Plasmas with Argon seeding consistently access H-mode, providing the highest fusion power and detached divertor operation, whereas Neon seeding leads to lower performance (600-850 MW) and less robust H-mode access, due to excessive core
impurity accumulation. A small W
impurity peaking has been found, with decreasing values at higher Zeff. Further analyses incorporate reduced momentum transport modeling, and sensitivity studies of neoclassical
impurity transport, confirming the robustness of the results. Overall, these findings support the viability of high-performing H-mode operation in ARC, ensuring divertor protection, enabled through Argon and Neon
impurity seeding.
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All authors Marco Muraca, Pablo Rodriguez-Fernandez, Nathaniel T. Howard, Joe Hall, Giovanni Tardini, Davide Silvagni, Thomas Body, Jon Hillesheim
Fluid Dynamics
Studies of PHP with CASCO code and its experimental validation
Vadim Nikolayev, Slaven Bajić, Guillaume Boudier et al. (+5 more)
We discuss here two major issues related to the steady functioning of the pulsating (oscillating) heat pipe (PHP): the effect of the surface properties and stopovers. They are studied with the CASCO simulation software (Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in French) version 4. Its experimental validation against two different prototypes is presented. The first is used also to study the effect of the nucleation barrier (the wall superheating necessary for the bubble nucleation) that reflects the wall wettability and roughness. An optimal value of the nucleation barrier is found where the thermal resistance achieves a minimum for a given evaporator power. The functioning regime is continuous showing pressure waves propagating along all the PHP channel. The stopover regime is observed both for small and large barriers. The second experimental setup (PHP Smart Loop) is used to study the stopover regime. It is found that it is characterized by a chaotically repeating sequence of fast pressure growth (corresponding to oscillations) followed by a slower pressure decay during a stopover. The decrease of the thermal resistance with heating load is explained by a decrease of the stopover time caused by a faster
liquid film shrinking.
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All authors Vadim Nikolayev, Slaven Bajić, Guillaume Boudier, Eric Blondé, Typhaine Coquard, Mauro Abela, Mauro Mameli, Sauro Filippeschi
Fluid Dynamics
A field-equation semi-local transformation for compressible wall turbulence
Zifei Yin and Jing Wang
Compressibility and wall heat transfer change the inner scaling of wall
turbulence through the mean density and viscosity fields. Most semi-local transformations are applied after a wall-normal profile has been selected. Here the transformed coordinate and transformed velocity are defined by wall-anchored field equations before any profile is extracted. Wall density and friction velocity enter as boundary data for auxiliary field equations; the resulting reference density and friction velocity, together with the local density and viscosity, set the viscous scaling in the wall layer. The local logarithmic density contrast is introduced as a bounded correction to the coordinate-stretching factor. For weak density variation the corrected stretch follows the local inverse kinematic-viscosity variation, while the bounded form limits the influence of finite density contrasts. The transformed coordinate $Y^+$ and transformed velocity $\bm{U}^+$ are obtained from field equations using the corrected stretching and the mean viscous shear. In the constant-property limit the density contrast vanishes, $Y^+$ reduces to the ordinary wall coordinate and each transformed velocity component reduces to the conventional mean velocity component in wall units. For channel flows, the field equations are solved with wall boundary data and the extracted profiles retain their own wall origins. A cooled shock/boundary-layer interaction examines the response when the wall density and friction velocity vary in the streamwise direction. Across the cooled high-speed boundary layers considered here, the bounded density correction narrows the inner- and buffer-layer profile spread...
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Crystal Shape and Lattice Deformation in Powder Diffraction
Matteo Leoni and Alberto Leonardi
Accurate modelling of diffraction peak shapes is essential for extracting microstructural information from nanocrystalline materials. Common-volume functions are widely used to describe finite-size and shape broadening in powder diffraction, but analytical expressions are available only for a limited set of ideal geometries. Here, we introduce a generalized
Fourier-based framework in which
crystal-domain shape deformation,
lattice deformation, and relative shape-
lattice misorientation are treated as independently refinable tensor operations within a unified formalism. The approach enables continuous affine transformations of both
crystal shape and
lattice base while preserving analytical evaluation of directional
Fourier coefficients. As a result, complex particle shapes, anisotropic deformations, and arbitrary relative orientations between shape and
lattice can be modelled within a single reciprocal- and real-space framework, including coupled shape-
lattice transformations not accessible using conventional powder diffraction line-profile methods. The formalism can be applied to individual diffraction peaks, full powder patterns, and total-scattering shape corrections. Validation against virtual scattering experiment data demonstrates that
crystal size, shape,
lattice deformation, and relative shape-
lattice orientation can be simultaneously recovered with high accuracy.
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Instrumentation and Detectors
High-Efficiency Broadband Mid-Infrared Absorption in Asymmetrically Matched Metallic Meanders: Development of Ti40V60 Alloy based LEKIDs for Mid-Far IR
Shilpam Sharma, Shekhar Chandra Pandey, Anudeep Singh et al. (+3 more)
Fast, highly sensitive, and broadband detectors operating in the mid-to-far-infrared (MIR-FIR) spectral region are essential for applications ranging from astrophysics to time-resolved spectroscopy using laboratory-based sources and beamlines at Infrared Free-Electron
Laser (IR-FEL) facilities. Conventional Lumped Element Kinetic Inductance Detectors (LEKID) achieve high optical efficiency using resonant quarter wavelength ({\lambda}/4) backshort cavities. However, this cavity-based approach is inherently narrowband and becomes optomechanically challenging at the mid to far infrared (MIR-FIR) wavelengths. Here, we present a completely backshort-free LEKID absorber architecture that achieves broadband absorption exceeding 50%. The meander absorbers were fabricated from a superconducting Ti-V
alloy and characterized using IR radiation from the IR-FEL at RRCAT, India. By illuminating through the silicon substrate and matching the meander's sheet resistance to the silicon substrate's wave impedance, the front-side reflection is strongly suppressed. Simultaneously, the sub-wavelength periodicity of the dense meander inhibits propagating transmission into free space via evanescent wave confinement. This combined mechanism drives efficient Ohmic dissipation within the metallic meander, yielding an experimental absorption efficiency ranging from 50% to 90% across the 12.5-30 micrometer wavelength range. The cavity-free design greatly simplifies the fabrication of the focal plane array while providing the broadband response required for next-generation detectors. To assess the suitability of the Ti40V60
alloy as an active superconducting detector material, a test LEKID resonator was also designed, fabricated, and experimentally characterized.
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All authors Shilpam Sharma, Shekhar Chandra Pandey, Anudeep Singh, Shankar Lal, R. S. Saini, M. K. Chattopadhyay
Space Physics
Are the Parker and Focused Transport Equations Equivalent for Galactic Cosmic Ray Modulation?
J. P. van den Berg, N. E. Engelbrecht and R. D. Strauss
The Parker transport equation (TPE) has been the equation of choice for the past 60 years in studies of
galactic cosmic ray (GCR) modulation. Conversely, the focused TPE describes the same processes on a more fundamental level than the Parker TPE by modelling an anisotropic distribution rather than an isotropic one. It is usually assumed that the Parker TPE is valid for modelling GCRs, but the two TPEs have not been tested against each other in this context. We conduct a first-of-its-kind comparison of these TPEs without particle drifts to test whether they produce the same results under identical
diffusion conditions. A new model for
protons during
solar minimum conditions is developed to numerically solve the TPEs using
stochastic differential equations. The TPEs are designed to be as consistent as possible for
diffusion by normalising the pitch-angle-dependent
diffusion coefficients (DCs) used in the focused TPE to the isotropic DCs used in the Parker TPE. The Parker TPE overestimates the GCR intensity at Earth's orbit for low energies by ~30%, and by ~40% over the poles. This stems from a small first-order anisotropy caused by particle fluxes over the poles. Particles gain easier access to the inner heliosphere by streaming in over the poles, where pitch-angle scattering is generally weaker, and the
magnetic field is typically less wound. The focused TPE also yields nearly identical results for different pitch-angle dependencies of the DCs. The description of particle streaming and weak pitch-angle scattering as effective parallel
diffusion in the Parker TPE makes it overly diffusive. This suggests that DCs derived from fitting the Parker TPE to observations are likely underestimated. Furthermore, GCR spectral and anisotropy data alone cannot distinguish between scattering theories with similar mean free paths but different pitch-angle dependencies.
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Geophysics
Satellite gravity constraints on inner core viscosity and LLVPs density anomalies
Yachong An, Hao Ding, Fred D. Richards et al. (+3 more)
Constraining the physical properties of Earth's deep interior, particularly the viscosity of the solid inner core and the density structure of large low-velocity provinces (LLVPs), remains a major challenge in geophysics. Here we develop a unified dynamical framework that combines mantle-inner core gravitational coupling (MICG) with torsional oscillations in the fluid outer core and show that their interaction can produce a distinct and testable geodetic signature. Guided by this prediction, we analyze satellite
gravity observations together with independent corrections for surface mass variability. We identify a robust approximately 6-year signal in the Stokes coefficient Delta S22, while no corresponding stationary signal is detected in Delta C22. A signal with the same periodicity is independently detected in length-of-day variations (Delta LOD), and the two signals exhibit a near anti-phase relationship. Interpreting this coupled signature within the proposed framework allows us to constrain the inner core viscosity to approximately 4.6 (+/- 1.8) x 10^16 Pa s and the equatorial relief of the inner core boundary to a semi-axis difference of about 200 +/- 70 m. The inversion further indicates mean density anomalies of +5.5 (+/- 0.6) per mil at the base of LLVPs. These results indicate that satellite gravimetry provides a direct observational window into deep-Earth dynamics and the physical properties of Earth's deep interior.
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All authors Yachong An, Hao Ding, Fred D. Richards, Weiping Jiang, Jiancheng Li, Wenbin Shen
Medical Physics · Cross-listed from cs.CV
A practical probabilistic framework for deformable image registration uncertainty in radiotherapy dose propagation
Stefan Heldmann, Sven Kuckertz, Nasim Givehchi et al. (+4 more)
Deformable image registration (DIR) is widely used in radiotherapy for dose propagation and accumulation, but uncertainty in the underlying deformation can substantially affect clinically relevant dose estimates. We present a practical probabilistic framework for propagating DIR uncertainty to voxel-wise dose statistics and dose-volume histograms (DVHs). The method models the mapped correspondence at each voxel as a random variable governed by a transparent local certainty map that can be defined by simple safety margins, structure-boundary mismatch, or structure-wise conservative uncertainty values. This yields interpretable quantities such as dose probabilities, expected dose, confidence bounds, and induced DVH envelopes. The framework is designed to remain lightweight and interpretable: it avoids complex biomechanical or ensemble-based uncertainty models and instead emphasizes simple parameterization, computational feasibility, and transparent dose metrics. We further introduce a structure-guided in/out strategy as an optional refinement that restricts mapping probabilities to anatomically plausible target regions. The approach is demonstrated on a prostate radiotherapy case study and used to compare different certainty-map strategies and probability kernels. The experiments show that the certainty-map design has a stronger effect on resulting dose and DVH uncertainty bounds than the specific kernel choice, while the additional benefit of the in/out strategy is case-dependent and modest in the present example. Overall, the proposed framework provides a transparent way to incorporate DIR uncertainty into radiotherapy dose assessment and to study how modelling choices affect propagated dose metrics.
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All authors Stefan Heldmann, Sven Kuckertz, Nasim Givehchi, Thomas Coradi, Mikel Byrne, Ben Archibald-Heeren, Nils Papenberg
Medical Physics
Slice-Profile-Enabled Phase Distribution Graphs for MRI Simulation
Snawar Hussain, Daniel C. Hoinkiss, Jörn Huber et al. (+2 more)
MRI simulation often separates two descriptions that are both essential for realistic sequence analysis: Bloch dynamics for waveform-resolved radiofrequency (RF) excitation, and phase-graph methods for coherence-pathway
evolution. Extended Phase Graph (EPG) models provide pathway tracking, and Phase–Distribution Graphs (PDG) extend this idea to spatially resolved $k$-space simulation, but existing PDG formulations rely on hard-pulse RF mixing that is order-local: the RF pulse mixes $F_n^+$, $F_n^-$, and $Z_n$ at a fixed coherence order $n$, without coupling different $k_z$ orders. This work introduces a unified Bloch-resolved PDG framework for slice-profile-aware MRI simulation. A scanner-rasterized sequence is partitioned into RF-sensitive Bloch spans and non-RF phase-graph spans. For each unique RF span, Bloch dynamics are solved on a slice grid to obtain a spatially varying propagator $R(z)$. Its
Fourier coefficients $\mathcal{R}_{\Delta}$, indexed by slice-order offset $\Delta$, are compiled into the PDG state graph as sparse cross-order coupling in $k_z$. Graph growth is controlled by retaining the dominant
Fourier coefficients and
pruning low-contribution PDG states. This retains PDG pathway history and voxel-wise image formation while incorporating shaped slice-selective and off-resonant RF behavior. Experiments show close agreement with direct one-dimensional Bloch slice-profile
evolution through repeated excitations, while retaining only a few hundred active PDG states. Image simulations further illustrate slice-position dependence, fat-suppression behavior, measured three-dimensional $B_0$ field maps, and comparison with scanner data. The proposed framework enables sequence-consistent simulation and signal formation understanding in regimes where RF physics, spatial encoding, object heterogeneity, and echo-pathway formation interact.
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All authors Snawar Hussain, Daniel C. Hoinkiss, Jörn Huber, Vincent Kuhlen, Matthias Günther
Optics
Absolute Length Sensing in a Long-Baseline, High-Finesse Optical Cavity
Todd Kozlowski, Henry Frädrich and Aaron D. Spector
The relative phase between two
lasers in transmission of an optical cavity can be used to continuously measure its absolute length with sub-micron precision. The first
laser is kept on resonance with the cavity, while a second
laser is phase-locked to the first with a frequency separation equal to an integer multiple of the cavity's initial free spectral range. As the free spectral range frequency changes due to cavity length changes, the second
laser detunes slightly from resonance and gains an additional phase offset in transmission of the cavity. The cavity length changes can be calibrated in terms of this phase offset. This technique is applied to a high-finesse optical cavity with a length of 123 meters, transforming it into a strainmeter with nanostrain sensitivity to long-term and transient seismic events. We report absolute length changes associated with anthropogenic noise, a distant earthquake, and the diurnal and semidiurnal earth tides.
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Instrumentation and Detectors
An investigation of fast simulation techniques for pion showers using kernel density estimators with the CALICE AHCAL Technological Prototype
CALICE Collaboration: A. Wilhahn, J. Utehs, Z. Ghafoor et al. (+28 more)
In this article, the development and investigation of fast
hadron shower simulation methods is presented. A test beam
dataset has been recorded in 2018 at CERN with the AHCAL Technological Prototype of the CALICE Collaboration, where the calorimeter prototype was exposed to electron,
muon, and negatively charged pion beams of various initial energies. The pion shower
dataset, covering energies between 10 GeV and 200 GeV, has been used to develop a data-driven fast simulation
algorithm of the AHCAL response to pion showers. The resulting shower model demonstrates excellent agreement with measured shower observables. In addition, a method for simulating pion showers at arbitrary energies is introduced, based upon interpolation between simulated showers at neighbouring beam energies.
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All authors CALICE Collaboration: A. Wilhahn, J. Utehs, Z. Ghafoor, G. Eigen, S. Lai, O. Bach, E. Brianne, K. Gadow, D. Heuchel, K. Krüger, J. Kvasnicka, A. Laudrain, O. Pinto, M. Reinecke, F. Sefkow, M. De Silva, E. Garutti, G. Kasieczka, S. Martens, J. Rolph, F. Hummer, F. Simon, A. Brogna, V. Büscher, L. Masetti, A. Rosmanitz, C. Schmitt, Q. Weitzel, W. Ootani, T. Suehara, A. Irles
Fluid Dynamics
On the spatial statistics of free-surface turbulence and the complementarity of 'dimples' and 'scars'
Daniel R. Kjellevold, Jørgen R. Aarnes, Omer M. Babiker et al. (+2 more)
The air–water interface governs the exchange of heat and gas between natural water bodies and their surrounding environment.
Turbulence beneath the free surface imprints characteristic features: near-circular depressions (`dimples') and elongated indentations (`scars'). Recent studies have shown that these are linked to sub-surface flow features in a temporal sense. For instance, rapid increases in mean-square surface divergence due to upwelling events, precede dimple count surges. Yet the spatial structure of these connections remains unquantified. We employ spatial statistics to consider the spatial and temporal correlations between dimples and scars and two key velocity-derived fields, surface divergence $\beta=\partial_x u+\partial_y v$ and vertical vorticity $\omega=\partial_x v-\partial_y u$. The dimples and scars are modelled as inhomogeneous Poisson point-processes, with intensity fields driven by the local variance of $\beta$ and $\omega$. Parameters, including spatial support radius $r$ and time lag $\tau$, are estimated by maximum likelihood against six DNS
datasets, quantifying the spatial and temporal connection between dimples, scars, surface divergence and vorticity. Our results demonstrate a clear complementarity: Dimples show strong local connection to the vertical vorticity field but has weak spatial connection with surface divergence and a spatially “global” model is required for dimples to work as
estimators of surface divergence; scars, in a similar but opposite manner, couple locally to surface divergence but globally to the vertical vorticity. The complementarity sheds new light on the way dimples and scars may be used to infer fluxes across the surface, e.g., in remote sensing contexts.
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All authors Daniel R. Kjellevold, Jørgen R. Aarnes, Omer M. Babiker, Simen Å. Ellingsen, Ingelin Steinsland
Optics
Compact Optical-Resolution Photoacoustic Microscopy System with Reflective Objective-Based Transducer Integration
Albano Tabacchi, Bhanu Pratap Singh, Michael Jaeger et al. (+5 more)
We present an optical-resolution photoacoustic microscopy (OR-PAM) system designed to overcome key limitations in conventional transducer integration within a compact microscopy configuration, while preserving high optical performance and improving acoustic detection efficiency. The system uses a reflective objective that reduces spatial constraints within the optical pathway, enabling the integration of a large-area PVDF transducer within the optical obscuration zone. The system performance was characterized through spatial resolution analysis,
laser pulse energy measurement at the sample plane, and evaluation of photoacoustic signal dependence on
laser pulse energy. For biological validation, OR-PAM imaging of sections from B16F10 tumors implanted in mice was performed and compared with optical microscopy and H&E stained histological sections. The results demonstrate strong spatial correlation between photoacoustic signal intensity and melanin rich regions, confirming label-free sensitivity to endogenous optical absorbers at 532 nm. This work establishes a compact OR-PAM imaging setup with improved optical-acoustic integration for high resolution biomedical imaging applications, with potential for future extension to multi-wavelength
laser excitation.
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All authors Albano Tabacchi, Bhanu Pratap Singh, Michael Jaeger, Damien Guignet, Mirjam Schenk, Pavel Subochev, Martin Frenz, Andre Stefanov
Classical Physics · Cross-listed from cond-mat.soft
Quantitative measurement of fluid inertial effects in confined Brownian motion
Quentin Ferreira, Pablo Palacios-Alonso, Harshit Joshi et al. (+3 more)
The hydrodynamic response of Brownian particles in
liquids is fundamentally altered by inertial forces arising from unsteady momentum transport in the surrounding fluid. These forces are of two distinct types: the added mass and the history effect. While both are well understood in bulk and weakly-confined geometries, under deterministic driving, their respective behaviours under strong confinement and thermal fluctuations remain scarcely addressed, unclear and often entangled together. The goal of the present study is thus to fill this fundamental gap. The confinement-induced variations of the two distinct inertial contributions are separately investigated in the vicinity of a flat, rigid wall, using a combination of broadrange thermal colloidal-probe atomic-force-microscopy experiments, advanced numerical simulations and theoretical arguments. Specifically, the separation of the added-mass and history-force contributions is achieved through their different frequency-scaling signatures within the assumed form of the generalized dissipation coefficient. Our results pave the way towards a complete picture of Brownian motion at interfaces, in the lubrication regime, with direct relevance to nanofluidics and interfacial biophysics.
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All authors Quentin Ferreira, Pablo Palacios-Alonso, Harshit Joshi, Rafael Delgado-Buscalioni, Yacine Amarouchene, Thomas Salez
Plasma Physics
Conservative Charge and Current Deposition on Nonuniform 3D Cylindrical PIC Meshes with Residual Self-Field Diagnostics
Zhe Liu, Zhijun Zhou and Yinjian Zhao
Particle-in-
cell simulations on nonuniform cylindrical meshes require deposition schemes that respect cylindrical metrics while controlling numerical self-fields. This work develops cylindrical-volume-weighted charge and current deposition using nodal control volumes and swept-volume factors on logically structured stretched grids. Uniform-density and controlled-transport tests demonstrate accurate charge recovery, well-controlled current-density errors, and continuity residuals substantially lower than the corresponding current-density errors. Single-particle diagnostics show that charge-transport consistency alone does not ensure self-field cancellation; face-centered electric fields give the smallest residual, whereas
cell-centered and shifted
cell-centered layouts produce larger residuals.
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