Papers

Physics-informed surrogate models can accelerate computational fluid dynamics simulations. However, many existing methods reproduce global flow patterns more reliably than localized multiscale structures. This study presents a physics-informed Fourier-wavelet transformer for next-step velocity-field reconstruction in real-world flow benchmarks. The proposed formulation combines hybrid Fourier-wavelet spectral encoding with physics-biased self-attention based on partial differential equation residual diagnostics. It also uses self-supervised pretraining through Masked Physics Prediction and Equation Consistency Prediction. The experiments are conducted on two real benchmark cases: cylinder-wake flow and fluid-structure interaction. All approaches are evaluated under a shared local protocol and compared with spectral, transformer-based, operator-learning, and physics-informed neural-network baselines. On the cylinder-wake benchmark, the proposed model achieves the best aggregate accuracy, with an all-channel normalized mean-squared error of 0.05875 and an all-channel Pearson correlation coefficient of 0.97019. On the fluid-structure-interaction benchmark, it gives the lowest all-channel normalized mean-squared error of $2.70 \times 10^{-4}$, compared with $4.02 \times 10^{-4}$ for the strongest baseline. Component-wise field comparisons and scale-separated diagnostics further show stronger recovery of localized wake structures, including near-body, wake-core, and far-wake features. The results demonstrate improved real-world flow reconstruction while maintaining a practical accuracy-cost tradeoff.

Widely separated optical parametric oscillation (OPO) represents a powerful method for coherent wavelength conversion across infrared and visible spectra. While such generation has been demonstrated in material platforms like silicon nitride and lithium niobate, 4H-SiC remains unexplored despite offering combined strong second-order and third-order nonlinearities with ultralow material loss. Here we demonstrate tunable, widely separated OPO generation in 4H-SiC microresonators through dispersion engineering. By optimizing the resonator geometry to achieve normal dispersion at telecommunication wavelengths and pumping at around 1550 nm, a pair of signal and idler spanning nearly an octave is generated,which represents the first demonstration of widely separated OPO in 4H-SiC. The frequency separation is tuned by varying the pump wavelength, with measured signal and idler wavelengths align well with phase-matching prediction. Leveraging the non-centrosymmetric crystal structure of 4HSiC, the generated OPO signal undergoes cascaded second-harmonic generation (SHG) and sum-frequency generation (SFG) with the pump, yielding coherent visible light at wavelengths below 700 nm. This cascaded upconversion of widely separated OPO signals represents a novel pathway for visible light generation. These results establish 4H-SiC as a promising platform for nonlinear wavelength conversion spanning from visible to 2 um region.

Solar Cycle 25 has run far stronger than the 2019 consensus forecast issued by the NOAA/NASA/ISES prediction panel, with densities in low Earth orbit from 2022-2026 holding at 2-3x the predicted levels. The cumulative drag impulse experienced by LEO satellites reached 5-6 standard deviations beyond the forecast's stated uncertainty. This means that even operators who designed conservatively against the two-sigma worst case fell short of their drag budgets. This paper quantifies a lower bound on the economic cost of that misprediction. Starting from the 13,704 payloads on-orbit below 800 km during 2022-2026, we screen to the 1,597 payloads which we validated with high confidence to be both operational and in ballistic freefall. We estimate each satellite's ballistic coefficient and propagate its trajectory under the forecasted atmosphere versus the observed one. A probabilistic cost model assigns each satellite an annualized mission cost based on direct costs (amortized capital costs plus annual operations), stratified by size class, with bespoke estimates for high value missions. Survival and forward cost discounting is applied at a modal 11% per year. We combine the differences in lifetime with the cost model to estimate the total dollar impact. Against the forecast's two-sigma upper bound which we consider to be a standard engineering design target, these satellites lost 688 cumulative mission years valued at \$0.88 billion. Against the nominal forecast, they lost 2,472 mission years worth \$2.77 billion. These estimates are deliberate lower bounds which exclude propulsive satellites, revenue above direct cost, and downstream economic impact. The results give a quantitative case for the value of accurate decadal-scale space weather forecasting, and show that well-calibrated uncertainties are as valuable to a satellite operator end-user as the accuracy of the central prediction itself.

The potential to precisely control both the linear and nonlinear index of refraction through optical manipulation of the atomic states has recently pushed warm alkali vapors to the forefront of research in the field of quantum sensors, quantum memories, and quantum fluids of light. Rubidium (Rb) vapor in centimeter-scale glass cells or millimeter-scale MEMS cells has proven to be a very promising platform for these applications, yet only a handful of research works have been dedicated to the investigation of the (non)linear refractive index of Rb vapor. We present results of theoretical calculations of the (non)linear refractive index of warm Rb vapor, based on the optical Bloch equations for 6-level Rb atoms interacting with a probe laser. They are compared to the experimental results obtained using an interferometric technique, showing excellent quantitative agreement. A Kerr nonlinear refractive index $n_2$ of up to $10^{-4}$ cm$^2$/W is obtained. Python scripts for all theoretical calculations presented in this work are provided, including the refractive index calculation, that can readily be used in practical implementations for simulating the (non)linear refractive index of Rb vapor including the effects of Doppler broadening, transit time broadening, pressure broadening, saturation, optical pumping, and spin-exchange collisions.

Phase-field models play a central role in the continuum description of phase separation, in which the bulk free-energy density and the interfacial thickness parameter determine pattern formation and microstructural evolution. In practice, these constitutive quantities are rarely known a priori and must be inferred from limited dynamical observations. In this work, an extended pseudo-spectral physics-informed neural network (ESPINN) framework is developed for the inverse identification of phase-field models from transient snapshot data. It enables the simultaneous recovery of both the bulk chemical potential and unknown gradient coefficients. Numerical experiments on the one-dimensional Cahn-Hilliard equation demonstrate accurate and statistically stable reconstruction in the noiseless regime, with substantial constitutive information recoverable from even a single snapshot pair. In the presence of noise, reconstruction accuracy degrades gracefully, and increasing the number of snapshots improves robustness by reducing variance across runs. These results establish ESPINN as a data-efficient and physically consistent approach for learning free-energy structure in continuum models of phase separation.

Nanostructures can be designed to absorb light efficiently at resonance despite their subwavelength footprint, but causality and passivity fundamentally limit the bandwidth over which strong absorption can be maintained. Here we derive fundamental absorption-bandwidth limits for passive, causal, linear, and temporally dispersive subwavelength objects by rigorously casting electromagnetic scattering as an equivalent impedance-matching problem. This mapping yields ultimate Bode-Fano-type constraints for optical absorption and provides rational synthesis guidelines for the material dispersion of passive nanoparticles that can approach the bounds. Our results clarify the ultimate limits for broadband light harvesting and dissipation, with implications for solar-energy conversion, photothermal hyperthermia, thermal management, and related nanophotonic technologies.

This work examines conditionally convergent Coulomb lattice sums under periodic boundary conditions. The recently developed finite lattice sum cleanly decomposes the series into three distinct components: a periodic bulk term $\nu_{\rm pbc}$, a shape-dependent non-periodic boundary term $\nu_{\rm b}$, and a finite-size correction term $\nu_{\rm corr}$. This rigorous formulation explicitly parameterizes the geometry of a finite lattice by its exact shape and size and takes an effective pairwise form. We analyze it in detail and compare it with various derivations of lattice sums in the literature. Perspectives on future applications are discussed, including analytical developments for arbitrarily shaped crystals and numerical mesh-type algorithms for condensed matter simulations.

We introduce the Quantum Split-Step Fourier (QSSF) algorithm for nonlinear optical waveguides, a numerical framework that combines split-step propagation of the nonlinear Schrödinger equation with a commutator-preserving Bogoliubov evolution of Gaussian quantum fluctuations. The method propagates the classical mean field together with the Bogoliubov matrices $U$ and $V$, from which reduced second moments, covariance matrices, symplectic eigenvalues, and entropic measures are constructed for arbitrary spectral windows. Applied to soliton-driven resonant radiation, QSSF shows that the selected radiation band acquires a steadily increasing von Neumann entropy and a corresponding loss of purity, quantifying its entanglement with the rest of the spectrum in the lossless Gaussian setting. The analysis also reveals a surprisingly pronounced low-dimensional structure: although the radiation occupies many Fourier bins, its reduced Gaussian state is dominated by only a few Williamson modes. QSSF therefore provides a practical information-theoretic diagnostic for quantum correlations in nonlinear frequency conversion, supercontinuum generation, and multimode squeezed-light formation in ultrafast waveguide platforms.

Photonic crystal waveguides (PCWs) are a powerful platform for optical technologies because they can spatially confine light on sub-wavelength scales and manipulate the group velocity of propagation modes, both of which enhance light-matter interactions. Many applications in photonics require a large bandwidth of low-loss and constant-velocity slow light, a significant challenge for previous dispersion and Bloch mode engineering techniques. By combining inverse design with an efficient mode solver and physics based formulas, we reduce the computational time of PCW designs by more than 100 times, allowing for the realization of PCWs with up to an order of magnitude increase in bandwidth and up to 4 times decrease in loss. We then explore the trade-offs between bandwidth, disorder-induce loss, group index, and dispersion. As examples, we apply this approach to two active and practical areas of research for PCWs design: broadband, position-tolerant Purcell enhancement, and compact phase shifters for optical communications. Our results significantly improve state-of-the-art PCW designs and provide a general method to optimize PCWs integrated technologies.

We investigate how the influence of a free surface is transported in turbulent open channel flow by analysing matched open- and closed-channel direct numerical simulations up to $Re_\mathrm{\tau} \approx 900$ in a domain large enough to accommodate very-large-scale motions (VLSMs). The turbulent kinetic energy (TKE) budget shows that the surface influence is communicated primarily through transport terms. Near the free surface, pressure transport supplies energy towards the interface, whereas turbulent transport and dissipation are reduced; the resulting energy surplus is exported away from the surface predominantly by viscous diffusion. The near-surface budget terms do not exhibit a single universal similarity scaling: viscous diffusion is organised over the near-surface viscous scale $\ell_\mathrm{V}$, dissipation over the Kolmogorov sublayer scale $\ell_\mathrm{K}$, and pressure-related terms require the mixed velocity scale $u_\mathrm{b} u_\mathrm{\tau}^2 /h$. The pressure-strain redistribution further reveals outer-inner coupling: although intense pressure-strain events remain small-scale, their magnitude and directional bias are organised by low-velocity VLSM streaks. The free-surface influence is therefore best understood as a coupled multi-scale process involving local kinematic constraints, Reynolds-number-dependent surface layers, and outer-layer coherent motions.

Increasing the resilience of positioning systems that currently rely on Global Navigation Satellite System (GNSS) signals can be achieved by incorporating stable and sensitive measurements of the permanent crustal anomalies in the Earth's magnetic field. We have realised this concept using an in-house-developed, wearable, Free-Induction-Decay Optically Pumped Magnetometer (FID-OPM) to carry out precise and stable measurements of the geomagnetic field in a walking trial. We present an end-to-end validation, including qualification of FID-OPM performance, alongside quantification of improvement in accuracy when data from this sensor is added to a dead-reckoning estimation of position. Using our wearable sensor system we achieve a Beckmann-distributed radial positioning error of 2.24 m over a route exceeding 500 m in length and spanning approximately 360 s.

Stellar toroidal magnetic fields are known to be unstable to the Tayler instability. Here we demonstrate the existence of a complementary current-driven instability of essentially arbitrary toroidal-field configurations in stably stratified nonrotating stars with the following properties: (i) in ideal magneto-hydrodynamics, it grows on the Alfvén timescale $\tau_{\rm A}$; (ii) under certain conditions, it may reveal itself by driving shellular differential rotation about an arbitrary axis perpendicular to the magnetic-field symmetry axis; (iii) it is large-scale in the angular directions $\theta$ and $\varphi$, and develops at radial wave-numbers $k \lesssim \mathcal{N}\tau_{\rm A}/R$, where $\mathcal{N}$ is the Brunt-Väisälä frequency and $R$ is the stellar radius. Thus, unlike the Tayler instability, the proposed instability is intrinsically global. Consequently, it may be less susceptible to dissipative suppression than the Tayler instability and can prevail over it in some regimes. This instability may have broad implications for magnetic field generation in stars and could modify scenarios of magnetic field amplification within the Tayler-Spruit dynamo, contributing to models of efficient angular-momentum transport and chemical mixing in stellar interiors.

Conventional radio-frequency (rf) transverse deflecting structures provide high-resolution longitudinal beam diagnostics, but require externally generated high-power rf, waveguide distribution, synchronization and input coupling at the operating frequency. We propose design criteria for a beam-driven resonant passive transverse deflector that does not require an external rf source. A leading drive bunch excites long-range wakefields in an off-axis periodic copper structure and a delayed witness bunch experiences the transverse wake near a zero crossing. The concept is based on the large temporal slope available from high-frequency wake components. A structure designed for installation after the second bunch compressor in the three-bunch-compressor layout of the European XFEL is optimized to place the zero crossing of the drive-bunch-induced transverse wake potential approximately one rf-bucket spacing of the 1.3 GHz linac, behind the drive bunch. The selected geometry produces a multi-mode transverse kick dominated by TM-like modes. We use time-domain wake simulations, frequency-domain decomposition, cell-number scaling, mechanical-tolerance scans, orbit-offset studies and uniform thermal scaling to determine the operating point and its sensitivity. For this geometry, the zero crossing occurs at s0 = 230.6 mm, with a per-cell temporal slope of Scell = 1.186 mV/(pC fs cell). For a compact 1 m structure operated with a 250 pC drive bunch and a 700 MeV witness beam, the estimated temporal resolution is about 33 fs.

Turbulent fluxes in the atmospheric boundary layer (ABL) govern exchanges of momentum, heat, and mass between the surface and atmosphere, shaping boundary layer structure and influencing weather, climate, and engineering applications. Yet their representation in coarse resolution models remains challenging, particularly under unstable conditions with strongly nonlocal transport and stable conditions with intermittent turbulence. Here, we develop a data driven turbulent flux parameterization in which nondimensional fluxes are represented by a linearized convolution operator acting on nondimensional mean state profiles. We train and evaluate the closure using high resolution large eddy simulations (LES) of idealized flow over homogeneous surfaces spanning multiple stability regimes. Several first order closure variants are constructed from different combinations of mean temperature and velocity profiles to predict heat and momentum fluxes, and the best model is selected by minimizing mean squared error across training and unseen test cases. The resulting parameterization improves predictive skill relative to a standard K-profile closure while retaining an interpretable operator form. Its learned kernels expose the locality and nonlocality of turbulent transport across stability regimes, linking empirical performance to physically inspectable flux–profile relationships. In a posteriori single column simulations, the closure remains stable and produces state profiles that closely match LES, demonstrating its potential as an accurate and transparent ABL flux parameterization.

This document presents a deliverable of the project Innovate for Sustainable Accelerating Systems (iSAS), funded by the EU under its program HORIZON-INFRA-2023-TECH-01 via grant agreement n{\deg}101131435 (deliverable D16, WP5). It contains an analysis on elliptical cryomodules developed for the European Spallation Source (ESS) and a benchmark of high-beta cryomodules across six leading international facilities.

This paper presents a method for fabricating acrylic lenses that simulate the gravitational deflection of light. The fabricated lenses reproduce key features of strong gravitational lensing, while the simulation is further extended to the weak- and microlensing regimes with images analogous to modern astronomical observations. The simulated mass of the lens is measured from the quantitative analysis of the lensed images in each gravitational lensing regime. These independently measured masses are mutually consistent and agree with the values predicted from the machined lens curvature.

Freestanding all-diamond color-center photonics is a promising platform for optical integration of spin-based quantum defects. Within this geometry, we realize a key building block for quantum-network interconnects: a directional coupler that acts as an on-chip beam splitter. We design and simulate directional couplers with triangular cross sections using eigenmode and finite-difference time-domain simulations and target near-50:50 splitting at visible wavelengths. We fabricate the devices directly from bulk single-crystal diamond by angled oxygen reactive-ion-beam etching followed by a dry post-release hard-mask removal process. Room-temperature measurements at $\lambda_0\approx 637 \mathrm{nm}$ yield a mean coupling ratio of $C^\mathrm{meas}=46(16) \%$. Finally, we integrate SnV$^{-}$ centers into the nanophotonic structures and observe near-lifetime-limited optical linewidths and coherent optical Rabi oscillations without post-fabrication annealing, identifying the platform as a viable route towards integrated diamond quantum photonics.

We report the observation of anomalously long-delayed afterpulses in photomultipliers of the Baksan Large Neutrino Telescope project$~-$ 10-inch R7081-100, 8-inch R5912-100, 20-inch R12860 photomultipliers produced by Hamamatsu Photonics, and 20-inch N6205 photomultipliers produced by NNVT. The mean delay times relative to the main pulses are approximately $85~\mu$s, $73~\mu$s, $260~\mu$s, and $90~\mu$s, respectively. The probability of such afterpulses does not exceed 0.1% per photoelectron, and their amplitudes are strictly confined to the single-photoelectron level, regardless of the amplitude of the main pulse. The delay time of these afterpulses shows no significant dependence on the PMT operating voltage.

We construct the Hermitian vector and canonical components of the momentum operator in 3D Euclidean space spanned by general curvilinear coordinates (GCC's) using a simple, natural and unified approach based on identifying the momentum operator in any coordinate system as mass times the velocity operator. When this latter is calculated by applying the Heisenberg equation of motion, it returns ($-i\hbar$ times) the gradient operator plus an additional zero-valued sum, which when distributed among the components of the gradient, it makes each the Hermitian vector component of the momentum operator in GCC's. The canonical components follow immediately upon symmetrizing each of these vector components in the corresponding base vector. For accessability by wider audiences, we first develop the formalism for the simple polar coordinates and then we develop the case for GCC's.

Sparse-view computed tomography (SVCT) reduces radiation exposure and acquisition time, but the limited number of projection views makes the reconstruction problem severely ill-posed and leads to streak artifacts when analytical methods are used. Plug-and-Play (PnP) methods combine data fidelity with learned image priors, while stochastic PnP methods use re-noising to reduce the mismatch between denoiser training inputs and reconstruction iterates. However, these methods often require many iterations, which limits their practical efficiency. In this work, we propose multilevel (ML) Stochastic Plug-and-Play (ML-SPnP), a ML stochastic PnP method for SVCT reconstruction formulated on wavelet multiresolution analysis (MRA) approximation spaces. The method combines coarse-to-fine initialization with a finite sequence of ML corrections using resolution-specific denoisers. Under suitable assumptions, the fine-level iterations following the finite ML phase inherit the convergence guarantees of the underlying stochastic PnP algorithm. Experiments on two CT datasets with 20-50 projection views show that ML-SPnP achieves reconstruction quality comparable to the evaluated stochastic PnP methods, while generally requiring less reconstruction time. These results support ML acceleration as an effective strategy for reducing the computational cost of stochastic PnP reconstruction. The code will be made publicly available at https://github.com/antoinedepaepe/ml-spnp.

A novel stochastic parametrization scheme representing organized convection is described. The effects of mesoscale convective systems (MCSs) are represented in an observationally constrained manner, by probabilistically triggering an MCS scheme in regions of enhanced environmental total column water vapour. In combination with the probabilistic trigger, patterns with given spatiotemporal scales determine where and when the scheme is active. Our scheme builds on the multiscale coherent structure parametrization (MCSP), which represents the top-heavy heating structure associated with MCSs. The original and new MCSP schemes are tested in a numerical weather prediction (NWP) ensemble. Both MCSP schemes improve the spatiotemporal scales of tropical precipitation compared to a control. When the spread-error relationship of tropical precipitation is analysed, the new scheme successfully boosts spread compared to original MCSP, improving the underdispersion of the ensemble seen with the original MCSP.

Intelligent active particles are characterized by self-propulsion, directional sensing of their environment, information processing, decision making and goal-oriented self-steering. This implies, in particular, the prevalence of non-reciprocal interactions, and the importance of information propagation through agent groups. Examples include biological systems (cells, insects, birds, fish, pedestrians) as well as engineered systems (nano- and microbots). As many agents move in an aqueous medium, hydrodynamic interactions strongly affect the dynamics. The emergent dynamics includes the formation of swarms and flocks, predator-prey behavior, and the navigation in complex environments.

Cryogenic phase-change phenomena play an important role in a wide range of engineering applications, including cryogenic cooling systems, superconducting technologies, and space propulsion systems. In particular, the three-phase contact line is recognized as a key region governing evaporation and heat transfer. However, direct measurements of temperature distributions near cryogenic three-phase contact lines remain limited because conventional infrared thermography becomes increasingly difficult at extremely low temperatures. In this study, a two-color temperature-sensitive paint (2C-TSP) technique was applied to visualize the temperature field around a liquid-nitrogen three-phase contact line. A temperature-sensitive dye and a temperature-insensitive reference dye were incorporated into a single coating, enabling robust temperature measurements based on luminescence intensity ratios by compensating for changes in optical intensity caused by refraction and reflection at the liquid-gas interface. Temperature distributions were measured under three heating conditions with heat fluxes of 110, 430, and 900 W/m2. The measured temperature fields revealed a localized temperature minimum at the observed three-phase contact line, suggesting localized cooling associated with phase change. Quantitative analysis showed that the average temperature in the liquid region remained nearly constant, whereas the temperature in the gas region increased with increasing heat flux. These observations reveal a non-uniform thermal structure around the cryogenic three-phase contact line. The present results demonstrate that 2C-TSP is a promising technique for direct visualization of temperature fields around cryogenic three-phase contact lines and provides new insights into phase-change phenomena in liquid nitrogen.

Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radiopure forms, titanium is a suitable material for structural elements in rare-event searches. In such applications, a chemical etching stage is typically performed to remove surface contamination or to prepare the surface for further treatment. However, due to its chemical resistance, the etching of titanium conventionally requires hydrofluoric acid, posing serious health and safety concerns that are further exacerbated in deep underground laboratory settings. An alternative approach is proposed, which uses sulphuric acid. Grade 1 titanium samples were etched in 20% and 40% sulphuric acid solutions at 20$^\circ$C and 40$^\circ$C for up to 24\,h. The effects of etching were quantified through mass change measurements, surface roughness analysis, and scanning electron microscopy. Sulphuric acid effectively etches titanium, with up to $3.5\,\pm\,0.3$ mg/cm$^2$ of titanium removed for an unagitated solution of 40% sulphuric acid at $40^\circ$C for 24\,h. Furthermore, sulphuric acid is shown to be effective at etching at lower concentration and temperature. The formation of a passivation layer during the etching may enable control of the total mass removed.

Frequency-dependent linear and quadratic response functions are implemented for a cavity quantum electrodynamics (QED) generalization of Hartree-Fock (HF) theory. Dynamic electric dipole polarizability, optical rectification hyperpolarizability, and second harmonic generation hyperpolarizability tensors are evaluated for molecules strongly coupled to a single-mode optical cavity, and the results are benchmarked against the same tensors obtained from real-time time-dependent QED-HF simulations. Substantial cavity-induced changes to the frequency-dependent properties are observed for certain perturbing frequencies at large electron-photon coupling strengths. We also find special perturbing frequencies at which there is no cavity effect, regardless of the coupling strength.

Fractal topology–achieved by integrating nontrivial topology into fractal geometries with self-similarity and non-integer dimensions–has opened new avenues for exploring topological phases of matter. Recent theoretical advances revealed a counterintuitive fractal topology: fractality itself can induce nontrivial topology in an otherwise trivial system. Here, we report the first experimental observation of fractality-induced topology in a tight-binding-like photonic crystal, without relying on traditional driving mechanisms such as magnetic fields, staggered hopping, or spin-orbit coupling. We demonstrate that fractality alone is sufficient to lift the degeneracy of Kagome lattice band structure and induce topological corner states within the bandgap of the resulting fractal Kagome photonic crystal, which is a photonic higher-order topological insulator. This work experimentally reveals a novel mechanism for realizing nontrivial topological states, expanding both the fundamental frontier and potential application of topological physics.

Operators of large visitor attractions routinely sort their guests into intuitive behavioral types, from relaxed wanderers to single-minded maximizers, and use this informal typology to guide spatial design and to set the parameters of pedestrian and agent-based simulations. Yet the typology is seldom tested against how people actually move, and it is usually assumed to transfer unchanged between sites. We examine both assumptions with individual-level movement data: volunteers carried GPS trackers through several theme parks operated by different chains and completed a short exit survey, letting us compare what guests do with what they say. Each visit is summarized by a small set of interpretable movement features, and visitors are grouped within each site using a deliberately demanding, multi-criteria validation protocol rather than a single clustering run. The picture that emerges is nuanced. Behavioral groups recur reliably but without sharp boundaries, pointing to a continuum rather than to discrete categories; what people do diverges from how they describe themselves, so self-report is a weak proxy for observed behavior; and, most consequentially, the relationships among movement features reverse from site to site, so behavioral parameters calibrated at a given location cannot be carried elsewhere. A complementary agent-based experiment locates the origin of each group's spatial signature in where visitors choose to go and in what order, rather than in how fast or how directly they walk. The work reframes a familiar industry heuristic as a geographical, site-dependent phenomenon, contributes a reproducible and critically validated pipeline for segmenting movement data, and connects empirical tracking to simulation. Its central message is that human movement behavior must be calibrated in place, not borrowed across contexts.

Fibre recruitment plays an important role in tendon. Due to their large water content, a popular modelling approach for tendons is poroelasticity. Within this framework some tendon studies have included fibres, though none have included crimped fibre recruitment. We present a one dimensional poroelastic model in which the solid skeleton is composed of a soft neo-Hookean background matrix and crimped fibrils which do not bear load (FIB model). As the tissue is stretched, fibrils are straightened and contribute to load bearing. The fibre-reinforced tissue is compared to a tissue with a purely neo-Hookean (NH) skeleton in response to a uniaxial constant applied load (loading) and release of the load (unloading). The system dynamics are governed by a diffusion equation where the diffusion coefficient depends on stiffness. Within tendon parameter ranges, the FIB model is softer than the NH model, and so approaches steady state more slowly during loading. The presence of stiff, crimped fibrils increases bulk extension without excessively straining the fibrils, providing a natural protection mechanism for the tendon's structural components to load, in agreement with experiments. During unloading, the FIB model is much slower to relax as the tissue softens due to fibril re-crimping. This asymmetry in loading and unloading manifests as a hysteresis loop in the stress-strain curve averaged over the tendon. The hysteresis is reduced with increasing applied load. To the authors' knowledge, the finding of hysteresis within this framework is novel. The inclusion of fibrils allows for clearer biological interpretation and potential comparison to data. While the stress law employed in this study is bespoke for the application at hand by accounting for crimp and fibril recruitment, other fibril constitutive laws can readily be considered and incorporated into this framework.

Ultra-high dose rate (UHDR) irradiation used in FLASH radiotherapy can lead to significant reductions in charge collection efficiency (CCE) in plane-parallel ionisation chambers (PPICs) due to enhanced ion recombination, while the high charge densities involved can also induce strong space-charge-induced electric-field distortions. To investigate these coupled effects, we extended the Garfield++ Monte Carlo particle-transport framework by implementing ion–ion recombination and self-consistent space-charge electric field calculations. The developed Monte Carlo model couples particle transport, electron attachment, recombination processes, and dynamic electric-field distortions. The implementation was validated against analytical and numerical models from the literature. Excellent agreement was obtained for the free electron fraction (FEF), CCE, induced current, and electric field evolution under UHDR conditions. The simulations show that space charge can locally increase the electric field by more than a factor of four or reduce it to nearly zero in some regions of the chamber. The results further suggest that the reduction of the CCE under UHDR conditions is mainly driven by the decrease of the FEF caused by electric-field-dependent electron attachment. This finding indicates that the complex problem of recombination under UHDR conditions may be largely governed by the evolution of the FEF, opening promising perspectives for the development of improved analytical models and real-time correction methods for ionisation chamber dosimetry under UHDR irradiation conditions. This work provides a flexible and self-consistent Monte Carlo framework for investigating recombination phenomena and improving dosimetry models for FLASH radiotherapy.

Tidal modulation of tectonic tremors provides a sensitive measure of fault response to small stress perturbations, yet how this response varies in a mixed fast and slow earthquake system remains unclear. Here we present the first systematic investigation of tremor tidal sensitivity in such a system, focusing on tectonic tremors along the northeastern Japan subduction zone. Using a tremor catalog from 2016 to 2024, we show that the southern end of the Kuril Trench, characterized by tremor migration and relatively weak seismicity, exhibits the strongest tidal sensitivity, whereas the northern Japan Trench shows the weakest response. Spatial analysis further reveals that areas with weaker tidal sensitivity tend to coincide with more earthquakes ($M_j \geq 4$) and denser tremor activity. In addition, tidal sensitivity at the southern end of the Kuril Trench increases from the early to later stages in tremor migration, potentially reflecting changes associated with underlying slow slip processes. Together, these spatial and temporal patterns suggest that tremor tidal sensitivity may be influenced by the relative contribution of other ongoing perturbations. These results highlight tidal sensitivity as a useful probe of the underlying perturbation environment and provide insight into the possible influence of slow slip processes, earthquakes, and other stress changes on tremor-generating regions.