Plasma Physics
kobra: a new Vlasov code intended for plasma-wall modeling
Sebastian Konewko, Nathan Maestracci and Sven Van Loo
In a fusion device
plasma-wall interactions \edit{on the sheath scale} can be modeled as a collisionless problem. When modeling these regions particle-in-
cell codes suffer from statistical error originating from undersampling the velocity space. On the other hand, Vlasov codes do not have this issue as they evolve the full distribution function. Here, we present a new finite-volume Vlasov code, kobra, equipped with adaptive-mesh refinement to reduce computational effort. Currently, the code solves the Vlasov-Poisson equations. We validate our code in 1d1v and 1d2v using established
benchmarks, i.e. the two-stream instability, Landau damping, the Dory-Guest-Harris instability, and also a classical electrostatic
plasma sheath. We find that the code reproduces the theoretical properties of these problems well. More importantly, the adaptive grid provides a computational gain that is likely to scale to higher dimensional,
plasma-wall simulations.
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Atomic Physics
Kinetic modeling of molecular beam formation in a cryogenic buffer-gas cell
Ekkehard Steinmacher, Phillip Groß, Franziska Tuttas et al. (+2 more)
Cryogenic buffer-gas
cells are widely used to produce cold molecular beams, but the microscopic dynamics governing beam formation remain challenging to model. Here we present fully kinetic simulations of a cryogenic buffer-gas
cell using the Direct Simulation Monte Carlo method implemented in the PICLas framework, treating the buffer gas and ablated molecules within a single unified model. We capture characteristic features of cryogenic buffer-gas sources, including plume cooling, directed transport toward the aperture, and the formation of a slow molecular beam, while also resolving energy transfer from the hot ablation plume to the helium buffer gas that is inaccessible to existing approaches relying on the background-gas approximation. Our results demonstrate that fully kinetic simulations can provide detailed insights into buffer-gas
cell dynamics and open a route toward a systematic optimization of such sources.
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All authors Ekkehard Steinmacher, Phillip Groß, Franziska Tuttas, Marcel Pfeiffer, Tim Langen
Optics
Antimony for broadband nanophotonics across the ultraviolet, visible and infrared
Fernando Chacón-Sánchez, Jacek Wojcik, Marina García Pardo et al. (+5 more)
Semimetal elemental antimony (Sb) nanostructures show great potential for applications where nanophotonic properties play a key role, such as phase-change optical
memories, non-linear optical elements, photothermal therapy
agents, photodetectors and photocatalysts. However, designing advanced Sb-based photonic devices critically requires an accurate and reliable knowledge of the optical response of bulk and nanoscale Sb. Herein, we report for the first time a fully consistent and accurately measured dielectric function for Sb nanoscale films in a wide spectral range from the ultraviolet to the far infrared (4 - 0.04 eV, i.e. ~ 0.3 - 30 $\mu$m), surpassing previous reports that explored a limited spectral range. It is found that the Sb spectral response is driven exclusively by
giant interband transitions in the visible up to mid infrared (4 - 0.4 eV, i.e. ~ 0.3 - 3 $\mu$m), and that their contribution dominates over that of free carriers down to 0.12 eV (i.e. ~ 10 $\mu$m). Such spectral response enables Sb nanostructures to display spectrally selective and tunable nanophotonic resonances. First, we showcase interband plasmonic resonances in the visible-to-near infrared for Sb nanogratings. Second, we report
giant refractive index dielectric resonances in the mid infrared for nanostructured Sb/dielectric/metal resonant cavities. These findings open a pathway to optimized planar Sb nanoscale designs enabling a tailored light-matter interaction, which will be useful for integrated data, telecom, medical, optoelectronic and energy conversion devices operating in a broad spectral range.
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All authors Fernando Chacón-Sánchez, Jacek Wojcik, Marina García Pardo, Fátima Cabello, Peter Mascher, Fernando Agulló-Rueda, Rosalía Serna, Johann Toudert
Biological Physics
Multiscale retinal flow on a spherical cap of varying aperture
Chang Lin, Zilong Song, Bob Eisenberg et al. (+2 more)
Modelling retinal haemodynamics is crucial for understanding retinal microcirculation but is computationally demanding because it involves coupling between the vasculature and surrounding tissue across multiple scales. This computational burden has been substantially alleviated by a recent analytic solution on the planar disc that enables lumping the capillary bed and surrounding tissue into an effective resistor. However, that formulation treats the retina as a flat surface, whereas the retina is a curved surface with a finite anterior aperture. In this work, we develop a nontrivial and physiologically necessary extension to spherical-cap tissue domains with varying apertures, where surface
curvature and finite-aperture boundaries complicate solving coupled Darcy equations on a curved
manifold. Using a stereographic projection and a decoupling transformation, we derive an analytic solution for the capillary-tissue system on the spherical cap that represents flow in both the capillary bed and interstitial tissue more realistically while retaining the efficient resistor formulation, a key advantage of the planar-disc formulation. This solution is coupled to one-dimensional (1D) arteriolar and venular flows to obtain a multiscale description of retinal haemodynamics. Using a vasculature model designed to capture retinal vascular features, we show that the multiscale model's predictions are consistent with experimental data. We further explore aperture effects using both a fixed hemispherical vasculature and aperture-dependent vasculature. The aperture affects retinal haemodynamics mainly through changes in the constructed vasculature itself, whereas the surface-averaged pressures and relative terminal flow distributions remain nearly unchanged. This framework provides a foundation for studying retinal pathophysiology on more anatomically realistic domains.
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All authors Chang Lin, Zilong Song, Bob Eisenberg, Shixin Xu, Huaxiong Huang
Computational Physics · Cross-listed from cond-mat.mtrl-sci
A Community-Developed Domain Ontology for Magnetic Materials
Wilfried Hortschitz, Santa Pile, Claas Fillies et al. (+18 more)
Magnetic materials play a crucial role in energy-related technologies, mobility, and sensing, but their complex multiscale behaviour and the coexistence of multiple unit systems pose persistent challenges for data exchange and interpretation. This paper presents a domain ontology for
magnetic materials, developed within the European Union funded
Magnetic Multiscale Modelling Suite (MaMMoS) project and aligned with the Elementary Multiperspective Material Ontology (EMMO). The ontology formalises intrinsic, hysteretic, and microstructural properties across multiple length scales and supports semantic interoperability between simulation tools, databases, and experimental workflows. One key feature of the ontology is its code-based and human-readable structure, enabled through the EMMOntoPy framework, which allows for direct manipulation and versioning without relying on opaque .owl or .ttl files. This facilitates collaborative development and improves transparency. The ontology supports FAIR (Findable, Accessible, Interoperable, Reusable) principles and is openly available for extension by the community. The aim of the MaMMoS project is to foster reproducibility, improve traceability, and promote the adoption of ontology in the magnetism domain. The ontology that has been developed already serves as the foundation for multiple software tools that handle all kinds of
magnetic material data.
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All authors Wilfried Hortschitz, Santa Pile, Claas Fillies, Harald Oezelt, Alexander Kovacs, Hans Fangohr, Samuel J. R. Holt, Martin Lang, Andrea Petrocchi, Swapneel Pathak, Michael P. Adams, Jonas Winkler, Thomas G. Woodcock, William Rigaut, Pierre Le Berre, Nora M. Dempsey, Alena Vishina, M. Nur Hasan, Georgia A. Marchant, Heike C. Herper, Thomas Schrefl
Data Analysis and Statistics
Combinations of measurements that are simultaneous fits of parameters of interest and systematic uncertainties using the BLUE method
Tomas Dado, Mark Owen and Michele Pinamonti
Combining estimates of the same physics parameter obtained from different measurements improves the precision and robustness of the parameter determination. Modern particle physics measurements are often performed using likelihood fits that include the physics parameter(s) of interest together with nuisance parameters representing systematic uncertainties. In high-statistics analyses, typical of many analyses at the Large
Hadron Collider, these nuisance parameters can be constrained in the likelihood fits. We describe how the Best Linear Unbiased
Estimator method for combinations can be applied to both the estimates of the parameters of interest and the estimates of the nuisance parameters. We show with concrete example combinations that including the nuisance parameters can improve the precision on the parameters of interest. We show with pseudo-experiments that the uncertainty reported by the combination is reliable and that the approximate likelihood combination proposed in a previous publication and implemented in the Convino software reports an underestimated uncertainty. The method is implemented in an open-source software tool, Combiner.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Bottom-up Synthesis of Metastable 2D Hexagonal Copper(I) Iodide on Monolayer and within Bilayer Graphene
David Kaiser, Guobin Jia, Janis Köster et al. (+9 more)
Copper(I) iodide (CuI) is a wide-bandgap
semiconductor crystallizing in the 3D $\gamma$-phase under ambient conditions; its layered van der Waals bulk phase $\beta$-CuI is stable only between 643 and 673 K. The two-dimensional (2D) h-CuI form has been obtained via
liquid-phase exfoliation of mechanochemically prepared precursors and via encapsulation between
graphene sheets, whereas bottom-up growth of 2D h-CuI on open surfaces has not yet been demonstrated. Here, we report a vapor-phase synthesis of h-CuI directly on low-defect, large-area monolayer and within
bilayer reduced oxo-
graphene (r-oxo-G) at low temperatures. Using a copper TEM grid as the solid-state precursor for copper, HI-vapor exposure at 40 $\deg$C initiates nucleation, while annealing at 180 $\deg$C promotes the growth of extended h-CuI domains. Aberration-corrected HRTEM resolves the atomic structure, local twist angles, and
lattice anisotropy of the CuI/r-oxo-G nanohybrid, while STEM-EDX yields a Cu:I ratio consistent with 1:1. First-principles calculations show that van der Waals adhesion to
graphene stabilizes the supported hexagonal layer. Under the presented low-temperature precursor conditions, pathways for nucleation of the $\gamma$-phase are not available, allowing the hexagonal phase to form selectively at the
graphene interface. Ab initio molecular dynamics simulations show that the
heterostructure retains its hexagonal
lattice order at 600 K, including on an open monolayer
graphene support. The lateral extent of the growth is limited mainly by remaining interfacial adsorbates. These results establish a route to metastable 2D h-CuI on a chemically inert
graphene template, which may be useful for wide-bandgap electronic and optoelectronic devices.
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All authors David Kaiser, Guobin Jia, Janis Köster, Sadegh Ghaderzadeh, Christian E. Halbig, Siegfried Eigler, Andrey Turchanin, Benjamin Dietzek-Ivanšić, Arkady V. Krasheninnikov, Jonathan Plentz, Elena Besley, Ute Kaiser
Geophysics · Cross-listed from astro-ph.EP
Lava Tube Exploration with LunarLeaper
Anna Mittelholz, Simon C. Stähler, Valentin T. Bickel et al. (+9 more)
Lunar pits, some of which are interpreted as collapse features into underlying lava tubes, expose otherwise inaccessible stratigraphy and may provide entry points to subsurface voids that preserve records of lunar volcanism and offer potential sites for future human exploration. We synthesize the current state of knowledge on lunar pits and lava tubes, covering their morphological characteristics, classification, proposed formation mechanisms, mechanical stability, and detection from orbit. We then review the open science questions that pit and pit-wall investigation is uniquely placed to address, spanning the volcanic stratigraphy of the lunar maria, the structure and lateral variability of the regolith, and the dimensions and accessibility of subsurface conduits. To evaluate how these questions can be tackled in situ, we assess the feasibility and expected performance of geophysical and remote-sensing investigations for subsurface voids and surface exposures, mainly focusing on
gravity measurements, ground-penetrating radar, high-resolution imaging, and spectroscopy. Building on this, we present LunarLeaper, a small legged
robot mission concept combining a gravimeter, ground-penetrating radar, high-resolution imager, spectrometer, and leg-based geomechanical experiments to deliver the first in situ investigation of a mare pit. The concept targets the Marius Hills Pit and its associated rille, with a mobility architecture optimized for the rugged terrain encountered at pit edges and funnel slopes.
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All authors Anna Mittelholz, Simon C. Stähler, Valentin T. Bickel, Jordan Aaron, Aurelie Cocheril, Alessandro Ghirotto, Matthias Grott, Svein-Erik Hamran, Ozgur Karaketin, Alessandro Maturilli, Birgit Ritter, Alexis Shakas
Geophysics · Cross-listed from eess.SP
Optimizing GEDI Simulator Configuration for European Temperate Forests
Selim Behloul, Nikola Besic, Steven Hancock et al. (+5 more)
Accurate estimation of aboveground biomass density is essential for quantifying forest carbon stocks. NASA's GEDI mission provides valuable canopy structure data, but its sparse sampling necessitates the use of simulators to calibrate biomass models at field inventory locations. The widely used simulator of Hancock et al. (2019) emulates GEDI waveforms from airborne
LiDAR point clouds, yet it has never been validated over European temperate forests. Here, we compare approximately 9,500 pairs of observed and simulated GEDI relative height (RH) profiles across French forests using the national airborne
LiDAR program as input. We separate two sources of error: waveform modeling differences, assessed by referencing both simulated and real RH metrics to a common ALS-derived ground elevation, and ground detection bias, evaluated by comparing each GEDI L2A processing
algorithm against the ALS reference. Under the baseline configuration, the mean absolute bias across the full RH profile reaches 0.69 m in leaf-on and 1.28 m in leaf-off conditions. Switching to intensity-based return weighting and selecting the a3 L2A
algorithm reduces these biases to 0.44 m and 0.40 m respectively. The a3
algorithm also achieves near-unbiased ground detection (-0.03 m versus -0.88 m for the default), directly reducing a previously overlooked source of error. We also show that leaf-off acquisitions and low-sensitivity shots, both typically excluded from standard biomass products, are simulated as reliably as their counterparts, substantially expanding the potential calibration and inference
datasets.
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All authors Selim Behloul, Nikola Besic, Steven Hancock, Cedric Vega, Sylvie Durrieu, Jean-Pierre Renaud, Ibrahim Fayad, Philippe Ciais
Fluid Dynamics
DiffSWE2d: a differentiable Shallow Water Equations solver for end-to-end flood and tsunami modelling
Zhonghou Xu
Solving inverse and optimisation problems with traditional shallow water equations (SWE) solvers can be computationally expensive, particularly when gradients with respect to model inputs or parameters must be estimated through repeated forward simulations. In this paper, we introduce DiffSWE2d, an open-source differentiable shallow water equations solver for end-to-end flood and tsunami modelling implemented in PyTorch. By leveraging automatic differentiation, DiffSWE2d represents the time-marching physics as a differentiable computational graph, enabling gradients to be propagated directly through the numerical solver. We validate the solver against two established
benchmark cases and demonstrate its application to tsunami waveform inversion, showing its ability to infer model inputs through gradient-based optimisation. DiffSWE2d provides a flexible framework for integrating physics-based hydrodynamic modelling with modern optimisation and machine learning methods. The source code and reproducible examples are publicly available at: https://github.com/ZhonghouXu/DiffSWE2d
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Optics · Cross-listed from quant-ph
The Quantum Plumber's Problem
Nicolas G. Underwood, Holger F. Hofmann and Jonte R. Hance
Recent work quantified the notion of
quantum counterfactual gain for an extended Elitzur-Vaidman bomb test style scenario, through a connection to the negativity of the Kirkwood-Dirac quasiprobability distribution. We here extend this work to identifying
quantum advantage in a new scenario, which we term the “
Quantum Plumber's Problem”. In this scenario, we imagine a “
quantum plumber”, who knows that one path of an interferometer is blocked, and wants to find the optimal strategy for identifying with certainty which path this is. We discuss various strategies for a generalised path-encoded interferometer, as well as for the specific case of Hofmann's three-path interferometer, introduced in a recent analysis of the relationship between states in five measurement contexts of a three level system. We support our arguments on the relative merit of competing strategies with data collected over many simulated attempts at locating blockages. We also present results for a variant of the game in which the blockage is replaced by a non-demolition detector.
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Atomic Physics
Non-stick vacuum wall collisions with a laser-coolable molecule
P. Kukreja, L. A. Rautenberg, J. C. Blumenstock et al. (+3 more)
Molecular species that are suitable for direct
laser cooling are typically considered lost or destroyed if they collide with an ambient temperature
vacuum wall. Here, we study surface collisions with aluminum monofluoride (AlF), a
laser-coolable molecule that survives this process with unusually high probability. We detect the outgoing AlF molecules from a single wall collision via Doppler-sensitive
laser-induced fluorescence spectroscopy, using incoming supersonic (pulsed) and thermochemical (continuous) molecular beams. The angular, velocity and rovibrational level distributions of the outgoing molecules show near-complete thermalisation to the wall in a single collision event. We determine an upper limit to the surface residence time of about 5$~\mu$s, and by monitoring the decay in density of pulses of molecules loaded into a small storage volume, we deduce the surface sticking probability for different materials. For a siloxane-coated metallic surface, the sticking probability of AlF is about 0.015, allowing us to accumulate molecules from the thermochemical source into an ambient temperature storage vessel at densities near $10^{8}~$cm$^{-3}$. This provides a route to compact, portable traps for neutral molecules.
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All authors P. Kukreja, L. A. Rautenberg, J. C. Blumenstock, S. Kray, G. Meijer, S. C. Wright
Computational Physics · Cross-listed from cond-mat.str-el
Instabilities in self-consistent diagrammatic approaches and how to cure them
Marcel Gievers, Herbert Eßl, Stefan Rohshap et al. (+2 more)
While self-consistent diagrammatic approaches are widely used to compute the physical properties of correlated
quantum materials, their applicability may get severely hindered precisely in the parameter regions where the most exciting physics is observed. One of the major issues, referred to as "misleading convergence", is the tendency of iterative schemes to converge to unphysical fixed points for intermediate-to-strong electronic interactions, regardless of the numerical accuracy of the computation. Here, we explicitly verify that the origin of this problem in several established self-consistent many-electron approaches, defined in the general diagrammatic framework of the
boson-exchange formalism, resides exclusively in the stability condition of the respective iteration schemes, and not in an intrinsic breakdown of their self-consistent diagrammatic description. This insight enables a simple and general remedy, as recently proposed in Phys. Rev. Lett. 137, 016502 (2026): The redefinition of the iterative procedure, by inverting the unstable eigendirections of the Jacobian associated with the fixed point of the self-consistent
algorithm. We illustrate the successful outcome of this procedure by means of systematic calculations performed on exactly solvable testbed models. Our results demonstrate that the physical fixed point of the diagrammatic schemes we considered can be stabilized, de facto, across the entire parameter range, including the most challenging nonperturbative/strong-coupling regimes.
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All authors Marcel Gievers, Herbert Eßl, Stefan Rohshap, Anna Kauch, Alessandro Toschi
Applied Physics
Influence of magnetic fields on the performance of spin-orbit torque magnetic random-access memory
Jiaxin Liu, Yuqing Zhou, Guoyi Shi et al. (+1 more)
Spin-orbit torque
magnetic random-access
memory (SOT-MRAM) offers high speed, ultrahigh endurance, and compatibility with advanced
semiconductor processes, making it a promising candidate for next-generation nonvolatile
memory. However, intrinsic bias fields in
magnetic tunnel junctions (MTJs), originating from reference-layer stray fields and interlayer coupling, cause asymmetric critical switching currents and increased energy consumption. Existing compensation approaches usually introduce additional
magnetic layers into the MTJ stack, which increases fabrication complexity and limits wafer-scale integration. Here, we propose a bias-compensation strategy without modifying the MTJ stack by engineering local stray
magnetic fields through
magnetic filling materials in vertical interconnect access (VIA) channels during the back-end-of-line process. Micromagnetic simulations show that the proposed
magnetic filling layer can provide the required auxiliary field for deterministic switching and significantly suppress write-current asymmetry. By optimizing the MTJ position relative to the
magnetic filling structure, the write-current bias ratio is reduced from 21.6% in the conventional design to 1.3%. The approach is also applicable to in-plane
magnetic anisotropy SOT-MTJs, reducing the bias ratio from 19.8% to -0.2%. Scaling analysis further demonstrates that the compensation effect remains effective when the device size is reduced to 20% of the original dimension (MTJ diameter approximately 10 nm), indicating its potential for high-density SOT-MRAM integration.
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All authors Jiaxin Liu, Yuqing Zhou, Guoyi Shi, Kaiming Cai
Plasma Physics
Modeling of plasma transport during edge-localized mode in tokamak using a kinetic Vlasov-Poisson code
Ce Wang, Sven Van Loo and Geert Verdoolaege
A kinetic parallel transport code KOBRA based on a finite-volume method is developed to study edge localized mode (ELM)
plasma transport from the mid-plane to divertor targets. The large scale separation between the Debye length (~cm) and the connection length (~10-20 m) leads to prohibitive computational cost in full 6D simulations. To alleviate this, an adaptive-mesh refinement (AMR) strategy is employed. Comparisons with uniform-grid simulations show that AMR accurately reproduces the characteristic ELM dynamics, including the rapid rise and slow decay of divertor fluxes, as well as the early-time peak induced by fast electrons. Analysis of the electron distribution and self-consistent electric field reveals that AMR efficiency is closely linked to phase-space
evolution. Overall, AMR achieves comparable physical accuracy while reducing
memory usage by 30-40% and accelerating computations by up to a factor of two, demonstrating its effectiveness for high-dimensional kinetic ELM simulations.
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Atomic Physics
Delay-engineered dynamical phases in a programmable non-Markovian spin oscillator
L. M. Ellis, L. M. Rushton, J. D. Zipfel et al. (+4 more)
Non-Markovian dynamics offer a new route towards engineering non-
equilibrium matter, where
memory and feedback act as programmable resources for controlling order in time. Here we report the realization of a non-Markovian
spin oscillator in a hot vapour $^{129}$Xe-Cs co-magnetometer with programmable feedback delay and gain. By tuning these parameters, we observe a hierarchy of dynamical phases, including time-crystalline response, nonlinear bifurcations, and frequency-comb formation. The measured spectra and phase boundaries are captured by linear stability analysis of delayed Bloch equations, revealing these phenomena as different manifestations of the same
memory-induced instability structure. These results establish time-delayed feedback as a powerful strategy for controlling non-
equilibrium phases, enabling
quantum sensing, frequency referencing, and synchronization within a single
spin-based platform.
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All authors L. M. Ellis, L. M. Rushton, J. D. Zipfel, P. Bevington, M. Jayaseelan, W. Chalupczak, V. Guarrera
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Interface-Controlled Phase Stability in Polymorphic HfO$_2$ Revealed by Machine-Learning Atomistic Simulations
Xudong Zhu, Junhong Li and Lixin He
HfO$_2$ exhibits rich polymorphism, and competition among different phases underpins many of its functional properties. Yet bulk free-energy relations alone cannot explain phase selection at mixed-phase boundaries, where interface orientation and structural continuity constrain collective rearrangements. Here, using machine-learning atomistic simulations and a Hf-centered local phase classification scheme, we show that crystallographic interface matching redirects phase competition and accessible transformation pathways. The M(100)/T(100) interface remains pinned as an M/T mixture throughout 3 ns simulations from 300 to 1800 K. M/PO, M/AO, and PO/AO interfaces retain two-phase coexistence up to 900 K, whereas all T/PO interfaces become PO-dominant. At 1800 K, all non-M interfaces become T-dominant, while M-containing interfaces retain a monoclinic majority. Nudged elastic band calculations reveal lower-barrier routes through interface states. For M(100)$\rightarrow$T(100), the interface-mediated route in a long
cell ($\sim$12 nm) yields a barrier of 136.03 meV/f.u., 29.2 % lower than the direct route in a short
cell ($\sim$3 nm). This difference is associated with sequential phase-front motion absent from the short
cell. These results identify phase boundaries as active participants in phase stability and transformation and establish interface orientation and crystallographic matching as variables for stabilizing metastable polymorphs and directing phase conversion in HfO$_2$.
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Optics
A Two-Mirror Faceted Projection System for EUV Lithography
Vasiliy A. Es'kin, Egor V. Ivanov and Olga V. Martynova
We propose an all-reflective two-mirror projection system for extreme ultraviolet (EUV) lithography operating at exposure wavelengths of $13.5$~nm (Mo/Si) and $11.2$~nm (Ru/Be), delivering a fourfold ($4\times$) demagnification of the periodic mask pattern at a numerical aperture approaching unity ($\mathrm{NA}_{\max} \approx 0.993$). In contrast to conventional EUV projection objectives that incorporate 6–10 aspheric mirrors with an overall optical throughput of less than $15\%$, the proposed design redirects each accepted discrete spatial diffraction order scattered by the mask onto the wafer via a dedicated pair of planar mirror facets. The number of reflections is strictly fixed at two for all accepted orders, retaining $50$–$60\%$ of the power leaving the mask in each accepted order. We derive a spatial geometry providing rigorous optical path length equalization across all diffraction orders, thereby removing order-dependent propagation phase shifts. Individually optimized 30-
bilayer Bragg multilayer coatings are designed for each facet using the transfer
matrix method combined with global evolutionary optimization
algorithms. The architecture is generalized to a three-dimensional vector formulation with a two-dimensionally periodic mask. Utilizing inverse lithography technology,
Fourier parameterization, and a differentiable electromagnetic modal waveguide solver, we solve the synthesis problem for binary absorber masks (La absorber on a Ru/Be/Sr multilayer mirror). We demonstrate simulated aerial images of sub-10-nm features on the wafer (isolated peaks with a full width at half maximum (FWHM) of approximately $5.4$~nm and line pairs with a critical dimension of $6$~nm) and find that the two peaks remain resolved for the tested wafer defocus values from $0$ to $5$~nm along the $z$-axis.
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History and Philosophy of Physics
Scientific Promise
Enno Fischer
Scientists constantly face decisions about what lines of research to pursue. This Element introduces the philosophical debate about scientific pursuitworthiness. It explains how it can be rational to pursue a theory even if the theory is less well supported than its rivals, and it discusses existing philosophical frameworks for guiding pursuit decisions. The Element also develops a new perspective. Existing accounts focus predominantly on theories, while experiments are largely neglected. This is an important shortcoming. Theoretical promise depends on experimental promise, and experimental promise raises questions of its own. Drawing on the epistemology of experimentation, the Element advances an account of experimental pursuitworthiness. It is argued that such pursuitworthiness depends on experimental virtues like a clear signal and simplicity of design. Moreover, the kinds of uncertainty that constrain the assessment of scientific pursuits are examined. Finally, the Element highlights open questions in the philosophy of scientific pursuitworthiness.
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Computational Physics
A Geometrically Parameterized Quasi-Stationary 3D Model for High-Frequency Induction Tube Welding
Dmitry Ivanov, John Inge Asperheim, Bjørnar Grande et al. (+1 more)
A three-dimensional multiphysics finite element model for the simulation of high-frequency induction welding of tubes is presented. The model couples a time-harmonic $h-\phi$ formulation with a stabilized quasi-stationary advection-
diffusion heat transport equation, enabling accurate prediction of electromagnetic and thermal fields under industrial operating conditions. The model incorporates parameterized geometry generation and semi-automated, physics-tailored mesh construction and is implemented using the open-source tools GetDP and Gmsh. Validation against measurements from a commercial induction welding line for AISI 304 stainless steel tubes demonstrates good agreement with operating data. The validated model is subsequently applied to investigate the influence of impeder material by comparing a conventional FeNiZnV ferrite with the soft
magnetic composite Ferrotron 559H for the induction welding of AISI 304 stainless steel tubes.
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All authors Dmitry Ivanov, John Inge Asperheim, Bjørnar Grande, Prerana Das
Atmospheric and Oceanic Physics
KiloDA: Reconstructing kilometer-scale near-surface wind states from sparse station observations
Yihan Zheng, Ya Wang, Gang Huang et al. (+3 more)
Accurate kilometer-scale near-surface winds are important for understanding atmospheric processes over complex terrain, yet remain difficult to reconstruct from sparse and unevenly distributed observations. Here we introduce KiloDA, a
diffusion framework for hourly kilometer-scale wind reconstruction from surface stations. KiloDA learns the statistical distribution and spatial structure of wind fields from historical 3-km Weather Research and
Forecasting (WRF) model forecasts. At each reconstruction time, no contemporaneous WRF field is used. Instead, station observations provide the only constraints on the current atmospheric state and guide posterior sampling from the learned prior. In idealized WRF experiments, KiloDA recovers localized wind structures when only 0.24% of grid
cells are observed and shows an overall advantage over conventional interpolation across terrain conditions and wind speed regimes. This capability largely transfers to real observations. In a fully withheld region, KiloDA reduces the median wind speed root mean square error (RMSE) by 19% relative to ERA5 reanalysis, using only observations outside the region, with the largest improvements over high-elevation and high-relief terrain. A random station holdout further confirms that this advantage extends across different complex-terrain locations and holdout configurations. These results show that historical model archives can provide useful structural knowledge for reconstructing kilometer-scale wind fields from sparse observations without requiring an accurate model estimate of the current atmospheric state.
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All authors Yihan Zheng, Ya Wang, Gang Huang, Shenming Fu, Haijie Li, Yujiang Cai
Chemical Physics · Cross-listed from cond-mat.soft
Kinetics of ferritin crystal formation and melting in acoustically levitated droplets
Anita Girelli, Iason Andronis, Aigerim Karina et al. (+5 more)
Understanding
protein crystallization pathways is essential for controlling crystallization in structural biology, materials science, and pharmaceutical applications. Classical nucleation theory does not fully capture crystallization processes for several
proteins, including ferritin. Here, we combine acoustic levitation with small- and wide-angle X-ray scattering (SAXS and WAXS) to monitor ferritin crystallization in evaporating aqueous polyethylene glycol (PEG) solutions. Acoustic levitation rapidly drives the droplets through a broad range of
protein and
polymer concentrations, enabling time-resolved measurements of crystallization during evaporation. The scattering data show that ferritin
crystals form during evaporation and subsequently lose their crystalline order upon further dehydration. Varying the PEG molecular weight switches between distinct crystallization pathways: one dominated by attractive
protein-
protein interactions and another dominated by repulsive interactions and excluded-volume effects. Furthermore, we find that lower molecular weight PEG (1000 g/mol) suppresses the dehydration-induced loss of crystalline order observed for higher molecular weight PEG (6000 g/mol), providing a simple strategy for improving
protein crystal stability.
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All authors Anita Girelli, Iason Andronis, Aigerim Karina, Sampad Bag, Lennart Bergström, Tomás Plivelic, Felix Roosen-Runge, Fivos Perakis
Optics
Two-step high-accuracy microwave frequency measurement and time-frequency analysis based on optical frequency combs
Wentao Ma, Taixia Shi, Chi Jiang et al. (+1 more)
Broadband microwave frequency measurement and time-frequency analysis are crucial for applications such as electronic warfare. However, when it comes to ultra wideband signal analysis, traditional electronic methods have high analysis accuracy, but intrinsic electronic bottlenecks limit their real-time analysis. Here, we propose and experimentally demonstrate a two-step microwave frequency measurement and time-frequency analysis method based on optical frequency combs. The system first performs coarse frequency localization over the 0-40 GHz range using stimulated-Brillouin-scattering-assisted frequency-to-time mapping (FTTM) and dual-comb channelized reception. The dual-comb is then reapplied for downconverting the signal under test, followed by digital signal processing to achieve high-accuracy unambiguous frequency extraction. Experimental results show that the system achieves mean single-tone frequency measurement errors of less than 10 kHz over 0-40 GHz. We further experimentally measure multi-tone, linearly frequency-modulated, and V-shaped frequency-modulated signals, demonstrating the proposed method's capability for analyzing complex signals.
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All authors Wentao Ma, Taixia Shi, Chi Jiang, Yang Chen
Medical Physics
Phase-contrast micro-CT for intra-operative breast tumour margin assessment using a microfocus x-ray source and photon-counting detector
Michelle K. Croughan, Timur E. Gureyev, Jane Fox et al. (+5 more)
Objective: Intra-operative tumour margin assessment during breast-conserving surgery requires rapid, high-resolution imaging of excised tissue, allowing the
surgical team to take appropriate action within a single operation. This study evaluates a custom propagation-based phase-contrast micro-computed
tomography (micro-CT) system designed to meet these clinical constraints without specialised optical elements. Methods: The experimental setup pairs a microfocus x-ray source with a
photon-counting detector in a cone-beam geometry. We explore how the spatial coherence of the source can provide propagation-based phase contrast – with no additional specialised optical elements – and balance this against maximising the x-ray flux of the cone-beam geometry. System performance was evaluated across two anode target materials and filtration configurations at various tube power settings. Imaging capabilities were validated using anthropomorphic breast tissue phantoms and a formalin-fixed paraffin-embedded (FFPE) breast tissue specimen, with reconstructions compared against gold-standard histology. Results: An unfiltered tungsten target operated at 40 kVp yielded optimal image quality. The optimised system achieved high-resolution CT reconstructions of a 5 cm diameter sample with an isotropic voxel size of 40.7 $\upmu\text{m}$ in a scan time of 12 minutes. Reconstructed volumes demonstrated strong visual correlation with corresponding histology slides. Conclusion: Combining a microfocus source with a
photon-counting detector enables high-resolution, phase-contrast micro-CT within a clinically viable timeframe, demonstrating strong potential for intra-operative margin assessment.
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All authors Michelle K. Croughan, Timur E. Gureyev, Jane Fox, Mikkaela McCormack, James A. Pollock, Dominic Jurkschat, Stephanie A. Harker, Marcus J. Kitchen
Applied Physics
Scattering-robust Imaging of Azimuthal Features with Enhanced Resolution
Nilakshi Senapati, Abhinandan Bhattacharjee and Anand K Jha
Imaging through scattering media remains a long-standing challenge in numerous real-world applications, ranging from medical imaging to long-distance sensing. Recently, illumination consisting of a single orbital angular momentum (OAM) mode, which is structured in the azimuthal coordinate, has been shown to provide enhanced resolution for imaging objects with azimuthal features, with the resolution becoming maximum at an optimal OAM value. However, in the presence of scattering, single-mode fields, which are spatially fully coherent, cause the imaging resolution to decrease significantly due to speckle formation. In this work, we employ azimuthally partially coherent fields and experimentally demonstrate imaging of azimuthal features with enhanced resolution in the presence of scattering. We show that lower degree of azimuthal coherence in such illumination leads to increased robustness against scattering while the azimuthal structure of the illumination ensures enhanced resolution. We derive the condition for best imaging resolution, and we report increase of imaging contrast in scattering from about 7% to 50% as the illumination is changed from a single-mode fully coherent field to that of an azimuthal partially coherent field.
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Fluid Dynamics
A Novel Multi-fidelity Surrogate for Efficient Turbine Design Optimization
Qineng Wang, Liming Song, Zhendong Guo et al. (+2 more)
To solve the turbine design optimization problems efficiently, surrogate-based optimization (SBO)
algorithms are frequently used. To further reduce the cost of turbine design, the multi-fidelity surrogate (MFS) based optimization is proposed by the researchers, who resort to augmenting the small number of expensive high-fidelity (HF) samples by a large portion of low-fidelity (LF) but cheap samples in surrogate modeling and optimization process. Nonetheless, according to our observations, the MFS based optimization sometimes can only have better convergence rate at the early stage of optimization process, but yielding worse final solution than the single-fidelity surrogate (SFS) based optimization that uses high-fidelity samples alone. The reason behind can be explained as follows. With the increase of HF samples in the optimization process, the LF samples can cause negative effect and therefore misleading the optimization search. To address the above issue, an ensemble weighted multi-fidelity surrogate (EMFS) is proposed. Specifically, the density-based spatial clustering of applications with noise (DBSCAN) is used to detect the region where the MFS cannot build a more accurate surrogate, and a local SFS is built there. Then, an EMFS is built by combining the MFS and SFS with adaptive weights, which is used to guide the optimization process. The related
algorithm is named as multi- and single-fidelity surrogate fused optimization, i.e., MSFO. Through tests on GE-E3 blade optimization and the film cooling layout design of a turbine endwall, the effectiveness of proposed MSFO is well demonstrated.
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All authors Qineng Wang, Liming Song, Zhendong Guo, Jun Li, Zhenping Feng
Fluid Dynamics
A Novel Multi-fidelity Surrogate for Turbomachinery Design Optimization
Qineng Wang, Liming Song, Zhendong Guo et al. (+2 more)
Turbomachinery design optimization involves expensive black-box problems. Sample-efficient multi-fidelity optimization (MFO) offers an efficient solution. By utilizing multi-fidelity surrogates (MFS), the MFO
algorithm can use fewer high-fidelity samples aided by low-fidelity samples to establish an accurate surrogate model. However, when MFS is used in sequential sampling optimization, it has been observed that the final optimal solution obtained by single-fidelity optimization (SFO) is better than that of MFO, even though MFO performs better at the early stages. This can be attributed to the assumption of an even and nested distribution of samples, which is incorrect when using a sequential adding strategy. To address these issues, we propose a novel
algorithm called multi-single-fidelity optimization (MSFO) to overcome the limitations of the conventional MFO procedures. In the surrogate establishment of MSFO, we use the density-based spatial clustering of applications with noise (DBSCAN) method to detect local areas where low-fidelity samples are no longer effective. A combination of both global MFS and local single-fidelity surrogate model, built using high-fidelity samples alone, is used to establish an ensemble, which improves the anti-interference ability of the
algorithm against misleading low-fidelity data. The effectiveness of the MSFO
algorithm is verified first on numerical
benchmark functions. Then, the
algorithm is used to optimize the aerodynamic profile of a turbine and the film cooling layout design of a turbine endwall. Here, high-fidelity sample sources are obtained from fine-mesh CFD simulations, whereas low-fidelity sample sources are obtained from the same simulations run on a coarser mesh. The results demonstrate that our MSFO
algorithm performs significantly better than the conventional SFO and MFO processes, with a higher level of robustness.
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All authors Qineng Wang, Liming Song, Zhendong Guo, Jun Li, Zhenping Feng
Fluid Dynamics
Correlative effects of induced magnetic field-buoyancy on reactive solute dispersion dynamics in couple-stress fluids
Aritra Roy, Debabrata Das and Pranab Kumar Mondal
We investigate the dispersion of a reactive solute in a couple-stress fluid flowing between two parallel plates under the combined effects of pressure-driven flow, buoyancy, and an induced
magnetic field. The model incorporates first-order heterogeneous reactions at both channel walls alongside a bulk reaction. Using Mei's multiscale homogenization technique accurate to third order, we develop a higher-order asymptotic formulation to determine the effective longitudinal dispersion coefficient and concentration field. Analytical predictions are complemented by Brownian dynamics simulations and finite-difference solutions, while the Aris method of moments quantifies transient mean displacement, spatial variance, and effective dispersivity. The hydrodynamic analysis reveals a singular branch in the velocity solution when the Hartmann number equals half the couple-stress parameter and identifies a characteristic quarter-power scaling between the Hartmann number and couple-stress parameter, separating couple-stress- and magnetically dominated regimes. The model recovers classical Taylor-dispersion behavior in the non-reactive Newtonian limit and agrees well with experimental measurements. Couple-stress rheology and
magnetic damping suppress shear-induced dispersion, whereas buoyancy enhances dispersion through additional transverse velocity gradients. A distinct saturation regime of the dispersion coefficient emerges with an increasing couple-stress parameter, while unequal wall absorption induces persistent transverse asymmetry, and stronger absorption enhances solute removal near the source. Numerical and
stochastic results validate the analytical framework while resolving higher-order concentration structures and particle-scale wall adsorption.
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Optics · Cross-listed from quant-ph
On-chip squeezed light in the audio frequency band
Xuezhi Zhu, Yunyun Cao, Rui Liu et al. (+7 more)
Squeezed light in the audio-frequency band is a key resource for
quantum metrology and
quantum sensing. However, realizing stable audio-frequency squeezed light on integrated photonic platforms remains challenging due to technical noise and the difficulty of scalable phase referencing. Here, we demonstrate on-chip generation of audio-band two-mode squeezed states down to 60 Hz in a silica microcavity. To enable phase-stable operation without directly locking fragile
quantum modes, we develop a coherent-comb control method in which a weak electro-optic reference comb co-propagates with the
vacuum at the
quantum frequency modes in an orthogonal polarization. This scheme provides quadrature measurement and long-timescale phase stability, thereby enabling covariance-
matrix reconstruction. We verify the
entanglement with the positive partial transposition criterion, which confirms inseparability via a minimum
symplectic eigenvalue of 0.395 ($<0.5$). Our results establish an experimentally accessible route toward on-chip phase-stable audio-band squeezing and support the scalable framework for continuous-variable
quantum information processing with integrated photonics.
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All authors Xuezhi Zhu, Yunyun Cao, Rui Liu, Yaya He, Fan Zhang, Yaqing Zhang, Shiwei Du, Meihong Wang, Xiaoshun Jiang, Xiaolong Su
Applied Physics
Janus Dipoles: Fundamentals, Realizations, and Emerging Applications
Bo Xue, Qiuyang Li, Yuqiong Cheng et al. (+10 more)
The Janus dipole - featuring orthogonally oriented electric and
magnetic dipoles with a 90-degree phase difference - has emerged as a powerful paradigm for wave manipulation. Unlike traditional Huygens dipoles used for directional control, this unique configuration exhibits strongly asymmetric, face-selective near-field behavior while maintaining a quasi-isotropic far-field radiation pattern. These remarkable properties make the Janus dipole an essential platform for directional wave shaping, with wide-ranging applications in on-chip photonics,
quantum interactions, and wireless power transfer. This review systematically traces the rapid development of the Janus dipole from its foundational theoretical inception to its diverse implementation platforms across optical, microwave, and acoustic frequencies. In this paper, we explore the governing principles, classify realization strategies into passive Janus dipoles, active Janus dipoles, and advanced near-field coupling control, and highlight emerging frontiers. By bridging foundational electrodynamics with advanced device engineering, this paper serves as an essential reference and roadmap for researchers designing next-generation, highly integrated, and compact wave-manipulation systems.
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All authors Bo Xue, Qiuyang Li, Yuqiong Cheng, Wenbo Ma, Xuhuinan Chen, Wanting Tong, Junho Jung, Runqi Jia, Ke Chen, Yijun Feng, Xiao Lin, Shubo Wang, Alex M. H. Wong