Space Physics
The Localized 12-hour Wave Over Alaska: Leveraging Meridional Wind Measurements From the Sodium Lidar
Sophie R. Phillips, Katrina Bossert, Komal Kumari et al. (+3 more)
The 12-h wave in meridional winds in the mesosphere and lower thermosphere (MLT) during the solar minimum 2018-2019 Arctic winter is investigated using sodium
lidar observations at Poker Flat Research Range (PFRR), Chatanika, Alaska (64N,147W). Nightly 12-h wave amplitudes increased significantly during December-January, with amplitudes exceeding 130 m/s above 97 km on several days. This was more than double the 12-h wave amplitudes observed outside this time period. Meteor radar winds over Chatanika also showed significant increase in meridional wind 12-h wave amplitudes at altitudes between 82 and 97 km during this time period with lower amplitudes than
lidar measurements. The strong variation in 12-h wave amplitudes was not correlated with SME index, though the largest amplitudes coincided with the sudden stratospheric warming (SSW) in early January. Measurements were compared to a seasonal WACCM-X model run and four days of HIAMCM. For the four dates of available HIAMCM data, 12-h wave amplitudes over Chatanika were found to be similar between both HIAMCM and WACCM-X and the
lidar below 97 km, with amplitudes measured by
lidar exceeding the models at altitudes between 97-105 km. All measurements followed a similar seasonal trend with increasing amplitudes at the end of December/early January. Fits of SW2 from WACCM-X show the SW2 tidal amplitude following similar seasonal trends to 12-h wave measurements. These high-resolution
lidar measurements indicate that localized 12-h wave amplitudes are larger than previously reported by studies using meteor radar measurements.
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All authors Sophie R. Phillips, Katrina Bossert, Komal Kumari, Erich Becker, Richard L. Collins, Nicholas Pedatella
Biological Physics · Cross-listed from cs.RO
Water Surface Swimming in a Centipede and its Robophysical Model
Zhaochen J. Xu, Delfin Aydin, Abdullah Mustafa et al. (+4 more)
Elongate multi-legged
robots use coordinated body waves and distributed legs to move through cluttered terrestrial environments. However, as housing actuators for independent leg control can require bulky body segments, their non-streamlined body and limb structure makes it difficult to achieve swimming capability comparable to their terrestrial locomotor performance. At the water surface, we found that the multi-legged
robots we tested unexpectedly moved backward: their body waves traveled in the same direction as their displacement, i.e., swimming with a direct wave. We found similar behavior in the centipede Lithobius forficatus, which swims with a direct body wave and periodic leg movement. To study how distributed legs contribute to direct-wave swimming, we analyze animal kinematics and develop a multi-legged robophysical model that allows independent variation of leg morphology and stiffness, body-wave direction, and leg coordination. Robophysical experiments show that direct body waves produce consistent forward motion under the tested conditions and that swimming performance depends on body–leg coordination. Additionally, directionally compliant legs increase displacement from approximately 0.08 to 0.21 body lengths per cycle relative to rigid legs under matched anti-phase actuation. These findings clarify how distributed appendages contribute to surface swimming and establish gait and morphology design principles for extending multi-legged field
robots from terrestrial locomotion into aquatic environments.
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All authors Zhaochen J. Xu, Delfin Aydin, Abdullah Mustafa, Margarita B. Levin, Jianfeng Lin, Tianyu Wang, Daniel I. Goldman
Fluid Dynamics
A catalog of exact steady states in Kolmogorov flow
Matthew Golden
Two-dimensional Kolmogorov flow is a common proving ground for the dynamical systems picture of
turbulence. Hundreds of unstable periodic orbits have been found for this system across many Reynolds numbers and domain sizes, although the most well explored is Re$=40$ on a square $2\pi\times 2\pi$ domain with a forcing wavenumber of $k=4.$ Here I present a catalog of 8952 exact steady states of the flow in this canonical parameter regime. These solutions provide a fixed constellation informing the dynamics of both
turbulence and transients.
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Physics Education
A Simple Miniaturized Stellar Interferometer: Measuring the Angular Diameter of Venus with a Masked Telescope
Eric J. Friedman and Michelle Goman
We describe a simple, visually compelling demonstration/laboratory of astronomical interferometry using a standard planetary
telescope and a thin piece of opaque plastic punched with two small holes. By observing the disappearance of interference fringes as the hole spacing is increased, students can directly estimate the angular diameter of Venus. The demonstration is a tabletop analogue of the landmark 1921 Michelson-Pease measurement of Betelgeuse and scales naturally from that measurement: where Michelson and Pease required a 6.1 m baseline to resolve a disk 47 mas (milli-arcsecond) across, a 15 mm baseline suffices for Venus, when it is approximately 10-15$''$ (arc seconds). The lab works reliably in ordinary atmospheric seeing conditions, and a side-by-side comparison of Venus (or Jupiter) with a bright
star such as Sirius provides an immediate visual demonstration of the difference between extended and point sources. It works equally well as a laboratory at a variety of difficulty levels. Furthermore, it does not require advanced knowledge or skills with optical
telescopes. While the underlying ideas are well known, we are unaware of any source that presents them in an accessible, unified form.
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Optics
Coherent Multidimensional Spectroscopy at the Few-Cycle Limit: Accounting for the Pump Spectrum
Jacob S. Higgins, Gerrit N. Christenson and James D. Gaynor
Coherent multidimensional spectroscopy will benefit greatly from near single-cycle pulses through the spectral breadth of states that can be accessed and the high frequency oscillations that can be resolved. However, the necessary cost of working with such pulses is the spectral structure arising from efficient self-phase modulation, which imparts into the signal and complicates interpretation of the molecular response. In this paper, we develop an in-operando approach to characterize and remove pump spectral features from two-dimensional spectroscopic signals. The pump spectrum is retrieved via an interferometric integrated autocorrelation measurement that runs concurrently with the experiment and thereby inherits the same time and frequency domain properties. A deconvolution procedure then suppresses noise and extracts the third-order response from the total signal. The analysis enables correction of spectral intensities and unambiguous assignment of spectral features to the molecular response. This work pushes multidimensional spectroscopy toward the impulsive limit and enables integration with other nonlinear spectroscopies such as attosecond spectroscopy - all without compromising few-cycle pulse properties.
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Physics and Society · Cross-listed from math.DS
Infectious behaviour: Simulating the effects of communication and social influence on pathogen transmission in crowds
Sophia Johanna Wagner, Anne Templeton and Gerta Köster
Public health measures at mass gatherings work only if people follow them, and adherence depends both on how instructions are communicated and what others do. We link these behavioural factors to pathogen transmission in a local-scale,
agent-based exposure model combining pedestrian dynamics with airborne transmission. Rather than fitting a parametric behavioural model,
agents draw their adherence at run time from survey respondents (2,170 attendees of UK sports and music events) who reported the same context: we vary stewards' communication effectiveness and adherence of role models, as well as
agents' shared social identity with each, assuming that strong shared social identity increases their influence. In a ticket-checkpoint queue of 101
agents, effective communication combined with strong shared social identity with stewards reduces the number of highly exposed
agents by 82% for mask wearing. In contrast, strong shared social identity with non-adhering role models gives almost nine times as many highly exposed
agents as with adhering role models. Physical distancing was not monotonically beneficial, because adherence changes how
agents move: an infectious
agent that kept distance moved along the edge of the queue, leading to similar results across conditions. Our pipeline transfers to any survey that includes behavioural measures and contextual variables.
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Optics
Metalens-transparent ultrasound transducer module for extended depth photoacoustic microscopy
Krishnendu Samanta, Myunghoo Lee, Shubham Mirg et al. (+5 more)
Optical-resolution photoacoustic microscopy (ORPAM) provides label-free optical-absorption contrast at millimeter-scale tissue depths with micrometer-scale lateral resolution. However, its volumetric coverage is limited by the short depth of focus of conventional optical lenses, whereas system miniaturization is constrained by bulky optics and ultrasound transducers. Here, we present an extended-depth ORPAM system that combines an ultra-thin metalens for optical excitation with a planar transparent ultrasound transducer (TUT) for photoacoustic detection. Fabricated from piezoelectric lithium niobate, the chip-scale TUT provides ~80% optical transparency and enables coaxial optical excitation with simultaneous acoustic detection at 14.4 MHz center frequency. This architecture eliminates the need for bulky acousto-optic combiners and large-volume acoustic coupling arrangements between the transducer and imaging target. We evaluate three ultra-thin metalens designs as
hyperbolic, quadratic, and extended depth-of-focus (EDOF), which provide effective axial ranges of 0.3, 0.8, and 1.3 mm, respectively, with lateral resolutions of 1.1 micron for
hyperbolic, 1.2 micron quadratic lenses, and 1.5 micron for EDOF across the full axial range. Phantom experiments demonstrate improved visualization of multilayered, inclined, volumetrically distributed targets with the EDOF design compared with the two other metalenses. Label-free imaging in awake, head-fixed mice further demonstrates that EDOF provides extended-depth visualization of subcortical microvasculature without being subjected to anesthesia-induced confounds. This chip-scale metalens-TUT architecture provides a foundation for developing compact photoacoustic microscopy systems.
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All authors Krishnendu Samanta, Myunghoo Lee, Shubham Mirg, Zhihao Zhou, Saniya Patil, Johannes E. Fröch, Arka Majumdar, Sri-Rajasekhar Kothapalli
Chemical Physics
First-Principles Nonadiabatic Dynamics via the Multi-Orbital Anderson-Newns Model
Liwen Ko and Joonho Lee
We develop a first-principles theory for nonadiabatic surface dynamics, providing a fit-free connection between density functional theory (DFT) calculations and the effective multi-orbital Anderson-Newns (AN) theory. Our theory contains two main advances. First, we outline the multi-orbital AN theory with orbital overlap and derive closed-form expressions for the hybridization energy, electronic dynamics, and electronic friction. Second, we describe a procedure to map the DFT
Hamiltonian into the effective AN
Hamiltonian with nuclear-position dependence. We obtain the electronic part of the AN
Hamiltonian solely from the adsorbate-projected density-of-states
matrix. We then define the bare nuclear potential as the difference between the total energy and the hybridization energy. The theory is applied to H and CO on the Cu surface, where widely used assumptions about the hybridization function, including the wide-band limit, semi-elliptical forms, and separability in energy and nuclear coordinate, are found to fail, and the single-orbital description breaks down qualitatively for CO. We expect this work to be broadly useful for first-principles modeling of coupled nuclear-electronic dynamics and chemical reactions at metallic surfaces.
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Optics
Structural Resilience of Space-Time Wave Packets to Volumetric Scattering
Kefu Mu, Hsiao-Chih Huang, Chen-Ting Liao et al. (+1 more)
Optical space-time wave packets (STWPs) can be engineered to sustain tight transverse confinement over long distances. However, whether the requisite precise spatiotemporal correlations underlying this behavior survive volumetric scattering remains unclear. Here, we experimentally demonstrate that STWP light sheets with transverse thicknesses of 11 and 22 microns largely retain their prescribed spatiotemporal structure after transmission through 10 mm thick scattering phantoms (scattering coefficient = 0.84 per mm). Moreover, compared with size-matched Gaussian beams, STWPs exhibit greater preservation of their initial spectral intensity distribution across the prescribed space-time domain following scattering. Additionally, the transmitted STWPs remain tightly confined and preserve on-axis intensity decay rates similar to those of their unscattered counterparts. As the scattering conditions span biologically relevant regimes, the structural and propagation resilience of STWPs to scattering highlights their potential for extended-depth 3D biomedical microscopy.
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All authors Kefu Mu, Hsiao-Chih Huang, Chen-Ting Liao, Hui Min Leung
Biological Physics · Cross-listed from cond-mat.soft
An interdimensional funnel enhances topologically protected oscillations in high-dimensional stochastic systems
Varsha Traynor and Jaime Agudo-Canalejo
Biochemical systems such as
protein complexes often occupy configuration spaces whose dimensionality grows with the number of molecular components. Although usually viewed as an obstacle to coherent dynamics, here we show that high dimensionality can enhance topologically protected oscillations. In the topological regime, a
stochastic system with a $D$-dimensional configuration space develops a steady-state current confined to a one-dimensional edge cycle. The intervening boundary faces between the $D$-dimensional bulk and the one-dimensional cycle form an interdimensional funnel, sequentially pushing the system towards lower dimensional faces, down to the one-dimensional cycle. As a consequence, increasing $D$ enhances the funnel, leading to improved one-dimensional localization and oscillatory coherence. A quantized biorthogonal Zak phase identifies the transition to the topological regime, which additionally exhibits a highly structured non-Hermitian skin effect. In contrast with previous realizations of topological states in
stochastic systems, the phenomena we uncover have no counterpart in
quantum condensed matter or active matter systems.
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Physics Education
Raytracing Black Holes with AI Accelerators
Thomas Fischbacher and Nicholas Kessler
We show how software infrastructure that was mainly built to power AI applications also can be used to great benefit for other purposes – by demonstrating a fully self-contained JAX-based black hole raytracer in under 180+200 lines of Python code plus documentation. Major motivations for showcasing such a construction are (a) to show to professional physicists how Machine Learning (ML) accelerators can greatly simplify building numerical applications for GPU accelerator hardware with very modest coding effort and programming expertise – even if the problems at hand do not involve ML per se, (b) to make a meaningful part of General Relativity (GR) accessible to computer science professionals who might not have realized that mathematical background they developed on Deep Learning problems may have brought this theory within easy reach for them, and (c) to inspire students and educators to explore the potential of an approach that represents physical law, i.e. relations between local differential quantities, not in terms of differentiable symbolic expressions, but in terms of differentiable
algorithms.
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Applied Physics
A Green's-function method for vertical thermal boundary conductance in anisotropic multilayers
Dihui Wang, Troy Munro and Heng Ban
Vertical thermal interfaces occur in both engineered and natural materials. Their vertical thermal boundary conductance can differ from the horizontal counterpart, requiring dedicated characterization. Yet current thermal metrology resolves vertical thermal boundary conductance only in restricted geometries such as two bulk media, for lack of an efficient forward solution that admits anisotropy, multilayers, and depth-dependent vertical thermal boundary conductance together. We present a Green's-function boundary integral equation (GBIE) method that couples transfer-
matrix Green's functions to an interface-only integral equation for depth-dependent $G_v(z)$, supporting dissimilar orthotropic multilayers ($k_x\neq k_y\neq k_z$) on either side and horizontal conductance $G_h$. For anisotropic film-on-substrate multilayers with films from $1~\mu\mathrm{m}$ to $100~\mathrm{nm}$, the GBIE agrees with three-dimensional finite element method (FEM) predictions to within one percent mean normalized phase and amplitude error, while running $29\text{--}210\times$ faster and reducing peak
memory by factors of $120\text{--}450$ in single-core tests; a JIT-compiled JAX implementation reaches up to $4100\times$ on a matched 16-core comparison. The GBIE further reproduces a continuous film over a buried interface, representative of a thermoreflectance measurement, and a finite-depth interface with depth-dependent $G_v(z)$. The GBIE accommodates lateral-to-film-thickness ratios above $10^{5}$, where volumetric FEM can become computationally prohibitive. These results establish an efficient forward solution for vertical-interface heat transport in systems ranging from microelectronic device sidewalls to grain boundaries in polycrystalline solids.
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Atomic Physics · Cross-listed from quant-ph
Monolithic Quantum Error Correction in the Presence of Distinguishability
Shubham P. Jain, Eric R. Hudson, Wesley C. Campbell et al. (+2 more)
Quantum error-correcting codes require that the environment cannot distinguish relevant error processes acting on different codewords. In practice, residual Zeeman, Stark, or anharmonic interactions shift the underlying states, making errors distinguishable and weakening the conditions for perfect recovery. We study this effect with an analytically solvable four-level model and a canonical spontaneous-emission noise model for atoms and molecules. Distinguishability raises the effective Kraus rank of the noise channel, lowers the recovered fidelity, and sets an operational checking time that shortens as the frequency separation between the emitted
photons increases. We find that rapid syndrome checking suppresses the buildup of distinguishability and quantify how fast one needs to check to restore near-perfect recovery. Error distinguishability is thus a practical limitation of monolithic error correction, and our analysis identifies fast syndrome extraction as a route to mitigating it.
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All authors Shubham P. Jain, Eric R. Hudson, Wesley C. Campbell, Alexey V. Gorshkov, Victor V. Albert
Applied Physics · Cross-listed from cond-mat.soft
Viscous Dissipation Governs Bubble Morphology and Failure in Soft Matter
Sushma SP, Anshul Shrivastava, Imnatoshi Jamir et al. (+2 more)
Cavitation, the growth of bubbles in fluids and soft matter, plays a central role in tissue damage, ultrasound therapies, and material failure, yet the influence of viscoelastic dissipation on bubble dynamics remains unclear. Here, we investigate cavitation in polyacrylamide hydrogels with identical elastic moduli but different viscous dissipation. We observe a striking
symmetry breaking transition: elastic gels rapidly develop ellipsoidal cavities before rupture, whereas viscoelastic gels sustain large, nearly spherical bubbles. A modified Rayleigh Plesset framework shows that viscous stresses suppress shape instabilities and delay
symmetry breaking, whereas elastic stresses accelerate cavity deformation. Finite element simulations independently validate these findings. The Deborah number (De) further captures the competition between material relaxation and cavity growth, with higher De associated with predominantly elastic growth and lower De with greater relaxation. Together, our results establish viscous dissipation as a key stabilizing mechanism that governs bubble morphology and failure in soft materials. These results have direct implications for understanding cavitation-mediated damage in biological tissues, optimizing therapeutic ultrasound, and advancing mechanical characterization of hydrogels for engineering and food processing applications.
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All authors Sushma SP, Anshul Shrivastava, Imnatoshi Jamir, Aritra Chatterjee, Namrata Gundiah
Medical Physics
Towards Modeling the Hemodynamic Impact of Mitral and Aortic Valve Repair in Patients with Left Ventricular Assist Devices
Mia Bonini, Michael Ferguson, Marc Hirshvogel et al. (+4 more)
Valve dysfunction is a major threat to long-term success in left ventricle assist device (LVAD) therapy, with direct implications for right heart performance. In this study, we apply a patient-specific, image-based computational modeling framework to evaluate the hemodynamic impact of simulated mitral and aortic valve repair in five LVAD-supported patients. Each patient was modeled under four conditions: (patient-specific LVAD-supported state), simulated mitral valve (MV) repair, simulated aortic valve (AV) repair, and simulated combined MV&AV repair. Because validation data for valve repair were unavailable, the simulated repair scenarios are exploratory in silico interventions based on clinically validated patient-specific models. The models integrate dynamic CT imaging, echocardiography, catheterization data, and device-specific LVAD parameters into a coupled 3D-0D simulation pipeline. Valve dynamics are governed by transvalvular pressure and flow, allowing physiological modeling of regurgitant lesions and surgical repair. The right ventricular (RV) was assessed using a combination of model-derived metrics, including right ventricular ejection fraction (RVEF), pulmonary artery pulsatility index (PAPi), and RV-PA coupling. In addition, we performed blood residence time (RT) analysis to evaluate blood stasis within the left heart and aorta. The simulations suggest that valve repair improved cardiac output, reduced pulmonary congestion, and enhanced right ventricular loading conditions. Notably, mitral valve repair restored aortic valve opening during the cardiac cycle, which improved sinus washout and reduced blood residence time within the aortic root-factors associated with lower thrombotic risk. Overall, these findings suggest a potential role for valve repair in LVAD-supported hearts, though larger, validated patient cohorts are needed to confirm these results.
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All authors Mia Bonini, Michael Ferguson, Marc Hirshvogel, Maximilian Balmus, Paul C. Tang, Francis Pagani, David Nordsletten
Optics
Temporal Interfaces in Metamaterials with Shape-Varying Inclusions
Ishtiaque Rahman, Mohamed Hesham Mostafa and Viktar Asadchy
Temporal modulation of metamaterials is commonly achieved by varying constituent material properties, while changes in meta-atom geometry offer an additional means of controlling their effective response. Here, we develop an analytical and numerical framework for temporal scattering in metamaterials composed of cylindrical inclusions undergoing abrupt
geometric transformations. Changing the radius of circular cylinders modifies the filling fraction and scalar in-plane effective permittivity, enabling temporal reflection, field amplification or attenuation, and frequency conversion. An area-preserving transformation from circular to elliptical cross sections introduces anisotropy, producing angle-dependent temporal scattering and redirecting the energy flow while conserving the wavevector. We derive these effects using effective-medium theory and temporal boundary conditions and compare the predictions with full-wave time-domain simulations. The simulations reproduce the main scattering and temporal-aiming trends, with larger angular deflections than predicted by the quasistatic model at higher permittivity contrasts. This suggests that moving toward the resonant regime may offer opportunities for stronger temporal aiming. These results identify inclusion geometry as a means of controlling wave amplitude, frequency, and energy-flow direction at temporal interfaces.
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Atmospheric and Oceanic Physics · Cross-listed from cs.LG
PR-Smoother: Simulator-Preserving Non-Gaussian Smoothing for Data Assimilation
Yuta Tarumi
Many physical data assimilation (DA) workflows require smoothing methods that represent non-Gaussian posteriors over physical state variables, scale to high-dimensional simulators, train from observation windows alone, and remain compatible with calibration of the prescribed simulator. We introduce PR-Smoother, a simulator-preserving amortized smoother designed for this prescribed-simulator DA regime. Its key design principle is to keep the prescribed simulator explicit in both the evidence lower bound and the variational family: rather than learning replacement dynamics or a learned trajectory prior, PR-Smoother learns only future-conditioned corrections around the prescribed rollout. This yields an explicit non-Gaussian smoothing distribution over physical trajectories and supports joint state, parameter, and sensor-bias learning from observations alone. The variational family contains the exact smoother in deterministic and linear-Gaussian limits. Empirically, PR-Smoother captures
multimodal posteriors in 4-dimensional Lorenz-96, remains accurate under ambiguous nonlinear observations and process noise in 40-dimensional Lorenz-96, and scales to joint state-parameter-bias inference in 16,384-dimensional Kolmogorov flow.
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Atomic Physics · Cross-listed from quant-ph
Deterministic photon waveform adaptation for quantum connectivity
Jeffrey Mohan, Jérémy Berroir, Filippo Borselli et al. (+9 more)
The scalability of
quantum technologies will depend on the ability to interconnect independent
quantum systems through photonic channels. However, heterogeneous
quantum platforms emit and absorb
photons with widely differing properties, severely limiting inter-node interference and modular connectivity. Here we demonstrate a cold-atom optical
quantum memory that simultaneously achieves near-unity storage-and-
retrieval efficiency and deterministic temporal adaptation of single
photons between arbitrary and programmable input and output pulse waveforms. Operating at high optical depth and within a fully integrated architecture, the system can store
photons with durations spanning over three orders of magnitude and reshape them arbitrarily without compromising efficiency, achieving compatibility with many current platforms. By augmenting the role of a
quantum memory from a passive storage element to an active programmable photonic interface, our results establish a key building block for scalable
entanglement-based
quantum networks and modular
quantum computing architectures.
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All authors Jeffrey Mohan, Jérémy Berroir, Filippo Borselli, David Libault, Ferhat Loubar, Kilian Müller, Jed Rowland, Félix Hoffet, Eleni Diamanti, Tom Darras, Tommaso Mazzoni, Julien Laurat
Biological Physics · Cross-listed from cond-mat.soft
Experimental Characterization of the Passive Mechanical Behavior of Rat Pelvic Floor Muscles: Effects of Test Conditions and Pregnancy
Jose L. Monclova, Matthew Shankel, Ava M. English et al. (+2 more)
Purpose: Pelvic floor muscles undergo large deformations during vaginal delivery, yet the passive tensile behavior of pregnant and non-pregnant pelvic floor muscle and the influence of testing protocols remain incompletely characterized. This study evaluated how pregnancy, loading rate, preconditioning, and storage affect passive tensile mechanics of rat pelvic floor muscle. Methods: Levator ani samples from pregnant and non-pregnant rats were tested in uniaxial tension to failure across multiple preconditioning amplitudes, two loading rates, and fresh or frozen storage conditions. Peak and transition metrics, strain energy density, toe-region stiffness, and high-strain stiffness were extracted using automated region-detection methods. Rat properties were also compared with digitized human cadaver levator ani data. Results: Pregnant rat samples reached greater peak strains than controls, although the difference was not significant. Preconditioning affected peak strain in a loading-rate-dependent manner: responses tapered near 2% preconditioning strain at 0.5% strain/s, whereas no comparable tapering occurred through 15% at 1% strain/s. Compared with human cadaver data, rat samples reached substantially larger peak strains and lower high-strain stiffness. Conclusion: This study provides one of the first direct experimental comparisons of passive pelvic floor muscle mechanics between pregnant and non-pregnant tissue, while systematically evaluating how multiple testing-protocol variables influence the measured response. Distinguishing protocol-dependent variability from biological differences provides a more reproducible basis for cross-study comparison and constitutive model calibration. Rat pelvic floor muscle is a useful model for pregnancy-associated adaptation, but absolute mechanical values should be translated to human tissue cautiously.
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All authors Jose L. Monclova, Matthew Shankel, Ava M. English, Mona Eskandari, Heidi P. Feigenbaum
Physics and Society
Network-based modeling of cocaine trafficking flows and displacement effects
H.A. Peters, Frederike Oetker, Robby Roks et al. (+3 more)
The worldwide cocaine
market is undergoing an extraordinary surge. Insights on how cocaine is trafficked from production countries to consumer
markets are limited, and often based on observed trafficking routes (e.g., seizures) alone. In this paper, we introduce a network-based model of actual transnational cocaine flows, beyond flows seized. In this model, cocaine is routed through an international transportation network of land and sea connections, where each link is assigned an interception risk metric for containerized transport. This interception risk metric combines features related to law enforcement inspections, containerized trade, and transport connectivity into three key driving components of interception risk using Principal Component Analysis (PCA). The interception risk metric on each link is then constructed from these driving components, where the importance of each component is characterized by a strength parameter. Given a set of strength parameters, cocaine is assumed to be routed from production countries to consumption countries via routes that minimize the total risk of interception, subject to country-specific supply and demand constraints. In the end, the strength parameters are calibrated by comparing the corresponding flow outcomes with known trafficking activity. From these final trafficking flows associated with the calibrated parameters, we are able to identify `blind spots' (e.g., nonzero flows on links with small or none observed trafficking activity) and provide more evidence of the waterbed effect (e.g., changing routes as a result of increased interdiction efforts by law enforcement).
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All authors H.A. Peters, Frederike Oetker, Robby Roks, Roy Lindelauf, Robbert Fokkink, Huijuan Wang
Atomic Physics
Quantum Chemistry in a Novel Hybrid Dipolar Atom-Ion Mixture
Claudia Galantini, Mateo Londoño, Luc Verwaal et al. (+3 more)
Merging trapped ions with cold atomic clouds offers intriguing prospects for
quantum chemistry and many-body
quantum simulations. Especially when going beyond the standard alkali atomic baths by using lanthanide atoms, opportunities arise to study the interplay between the intermediate-range atom-ion interaction and the tunable long-range dipolar atom-atom interactions. However, the high total angular momentum of the ground-state of open-shell lanthanides, e.g. $^{5}I_{8}$ for dysprosium, affects the atom-ion potential. Here, we discuss the implications for long- and short-range atom-ion interactions and present a novel apparatus which combines an ytterbium ion (Yb$^{+}$) with dipolar dysprosium (Dy) atoms. We highlight the consequences of this novel Dy-Yb$^{+}$ mixture for observing buffer gas cooling, (non-) radiative charge transfer, and three-body recombination. While the energy-averaged rates are dominated by radiative charge transfer, particularly radiative association, we find that three-body recombination can compete with molecular-ion formation at Dy densities $n\gtrsim 10^{12}$ cm$^{-3}$. This competition is further enhanced by the expected non-thermal distribution of ion energies. These processes could be experimentally characterised through controlled variation of the atom-ion interaction parameters, providing a direct test of our theoretical predictions.
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All authors Claudia Galantini, Mateo Londoño, Luc Verwaal, Edgar J. D. Vredenbregt, Jesús Pérez-Ríos, Rianne S. Lous
Atomic Physics
A Cryogenic Penning Trap Based on Permanent Magnets
F. Völksen, K. K. Anjum, R. P. Czampiel et al. (+30 more)
We report on a Penning trap based on NdFeB permanent magnets operated at 4\,K with a
magnetic field strength of 280\,mT. Reliable loading and confinement of
protons, H$_2^+$ ions, and electrons was demonstrated with non-destructive single-particle detection sensitivity of
protons and H$_2^+$ ions using superconducting image-current
circuits. The axial frequency of individual particles reaches a shot-to-shot stability of 47 parts-per-billion comparable to that of state-of-the-art precision Penning-trap experiments. Measurements of the
proton modified-cyclotron frequency show a shot-to-shot scatter of $0.14$ parts per million (p.p.m.), presently limited by millikelvin-level temperature fluctuations of the permanent-magnet assembly. We outline a route towards improving this performance by more than an order of magnitude. This development offers broad potential for axial-mode-related precision measurements and cost-efficient Penning-trap experiments, and represents an important step towards compact, scalable, and transportable antiproton-trap systems.
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All authors F. Völksen, K. K. Anjum, R. P. Czampiel, N. Daehnhardt, S. Gavranovic, J. Hoentges, L. Kürschner, J. D. Regier, D. Schweitzer, 1, 2, P. Schöps, A. M. Thomas, S. Wienhues, B. Arndt, T. Imamura, S. Endoh, B. M. Latacz, M. Leonhardt, P. Micke, J. Morgner, D. Natakala, S. Stahl, H. Yildiz, K. Blaum, J. A. Devlin, Y. Matsuda, C. Ospelkaus, W. Quint, A. Soter, J. Walz, C. Smorra, S. Ulmer
Atomic Physics
Optical Ion Clock with Engineered Immunity to Motion-Induced Frequency Shifts
Mark Lide, Wesley Hardin and Christian Sanner
Spectroscopic frequency shifts due to residual motion of the probed atoms significantly contribute to the uncertainty budgets of state-of-the-art optical ion clocks. For clock transitions with second-order Doppler and quadratic Stark shifts of opposite signs, it is possible to configure electrodynamic ion confinement such that these two shift effects become anticorrelated causing zero net shift. Here, we introduce a spectroscopic interrogation protocol which leads, for systems with unknown and varying motional energy gain rates, to first-order auto-suppression of corresponding frequency shifts without requiring the opposite-sign configuration. We experimentally demonstrate the proposed method on a new ytterbium ion optical clock probing the 467 nm electric octupole (E3) transition, where the combined fractional uncertainty contribution from motion-induced frequency shifts is reduced from $1.3\times10^{-18}$ to $0.3\times10^{-18}$. An interleaved optical frequency ratio measurement against ytterbium's electric quadrupole transition (E2) at 435 nm delivers an E3/E2 frequency ratio of $0.932 \,829 \,404 \,530 \,965 \, 340 (39)$. Combined with previously published ratio data this leads to a limit for a potential fractional temporal variation of the fine-structure constant of $2.4 (2.7) \times 10^{-19}/$yr, in agreement with existing bounds.
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Fluid Dynamics · Cross-listed from cs.RO
Underwater Navigation in Unsteady Flows Using Measurement Histories from a Single Sensing Unit
Linhao Jin, Qimin Feng, Peter Gunnarson et al. (+1 more)
Spatial flow measurements support underwater navigation, but distributed sensing is constrained by
robot size and sensor layout. We use a causal observer to estimate current lateral velocities from a finite history of measurements collected by a single sensing unit, supplying the inputs of a fixed navigation controller. In two-dimensional wake simulations with access to body-frame ambient velocity, this virtual sensing interface reduces simultaneous flow sampling from three points to the
robot center. Trained only in a circular-cylinder wake at Re = 100, the flow-history observer achieves 84.4% and 80.6% success at held-out Re = 205 and 240 without retraining. These rates are 7.4 and 4.6 percentage points below direct spatial sensing and more than 30 points above a matched current-only observer. Past flow remains beneficial when past goal and yaw information is available. Across obstacle geometries, performance remains close to direct sensing in square-prism wakes but declines in triangular-prism wakes. Component replacement identifies the lateral velocity difference as control-relevant, while controlled perturbations reveal sensitivity to error persistence. The results demonstrate the closed-loop utility of single-point flow histories under the assumed observation model.
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All authors Linhao Jin, Qimin Feng, Peter Gunnarson, Qiang Zhong
Plasma Physics
Analytic toroidal 3D MHD equilibria and steady Euler flows with invariant surfaces
Matt Landreman
Families of explicit analytic solutions of the magnetohydrodynamic
equilibrium equations are presented, equivalent to steady incompressible Euler flow. The solutions are non-axisymmetric and possess exact nested toroidal flux surfaces. No expansion is made in inverse aspect ratio or in the deviation from axisymmetry. The
magnetic field and flux surfaces are given explicitly in Cartesian coordinates using elementary functions. The field, current density, and scalar pressure are smooth over the toroidal domain. The pressure gradient vanishes only on the
magnetic axis. One family of solutions has uniform rotational transform $\iota=2$, while another family has a sheared $\iota$ profile. These counterexamples to Grad's
conjecture are valuable for understanding the existence and regularity of 3D
equilibria and for testing numerical codes.
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Biological Physics · Cross-listed from cond-mat.soft
Entropy-Driven Initiation and Cytoskeletal Viscoelasticity in Endocytosis: An Onsager Variational Framework
Jinjie Liu, Zhongcan Ouyang and Hao Wu
Receptor-mediated endocytosis requires a particle to approach the
cell membrane to within a few nanometers before ligand–receptor binding can occur. Existing continuum models often start from an already established contact and do not explicitly describe how crowding particles on the extracellular side influence the distribution of the particle near the membrane. We examine entropic depletion forces as one possible nonspecific contribution to this initial approach. For ideal depletants, the Asakura–Oosawa excluded-volume construction gives an exact depletion potential for the planar geometry before contact. The potential and force vanish continuously at the onset of excluded-volume overlap. This interaction provides a possible contribution to membrane proximity before specific binding, while its extension to curved wrapping geometries requires additional approximation. Within a reduced continuum model, we combine depletion attraction, ligand–receptor binding, membrane deformation, and cytoskeletal viscoelastic dissipation. The viscoelastic contact is formulated through a hereditary integral and a standard linear solid. The kinetic model gives a conditional minimum ligand density for complete engulfment, a finite particle-size window, and a stiffness-dependent upper limit. When the stationary radius lies inside the domain of finite positive wrapping times, the estimated wrapping time has a minimum at a radius that decreases with increasing binding energy density. At fixed viscosity and other independent parameters, the same time approximation predicts slower wrapping as
cell stiffness increases. The two positive roots defining the size window merge at a limiting parameter value, which characterizes closure of the admissible size interval. Depletion attraction is interpreted as one possible contribution to particle-membrane association
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Space Physics
First Observation of a Polar Coronal Hole-like Fast Solar Wind Stream in the Sub-Alfvénic Solar Corona: an Analysis of Turbulence Properties
Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus et al. (+2 more)
Parker Solar Probe, near its 23rd perihelion in March 2025, sampled an extended interval of sub-Alfvénic solar wind likely originating from a large equatorial coronal hole. At heliocentric distances of approximately 10 solar radii, with speed mostly above 400 km/s, this interval is a first example of “polar coronal hole-like (PCH-l) fast" solar wind observed in the sub-Alfvénic solar corona. We characterize the
turbulence properties of this unique interval using Parker Solar Probe measurements. Despite being sampled well inside the nominal Alfvén surface, the
turbulence appears to be already well developed while remaining strongly transverse and highly imbalanced, exhibiting a large cross helicity. These observations provide new constraints on the development and
evolution of solar wind
turbulence within the lower corona.
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All authors Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus, Yeimy J. Rivera, Samuel T. Badman
Physics and Society
Normalized fractional Hirsch Index and Modified Pareto Law
Asim Ghosh and Bikas K. Chakrabarti
The Hirsch index (introduced in 2005) has been a very successful scientometric author-level measure for the publication impact inequalities among the authors. However, it does not have any upper bound and statistically it grows in proportion to the square root of the number of publications by the author. Social scientists, on the other hand, measure the economic performance of different countries (having different wealth amounts and populations etc.) using inequality indices like the Gini index (since 1912) etc., which are normalized quantities (independent of the country's total wealth or the population size). We show here that a normalized fractional Hirsch index, giving the fraction of total citations earned by fraction of those successful papers published by the author, can even indicate that typically about $14\%$ of the top cited papers earn about $86\%$ of citations for very successful scientists (like the 95 Nobel Laureates considered here). This is similar to Pareto's 80-20 law (since 1896) and agrees more precisely with those observed for self-organized sandpile models, where typically $86\%$ of the avalanche masses are dissipated through $14\%$ of the largest avalanches as the piles approach their respective self-organized critical points.
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Optics
Structured detection beyond spatial imaging
Bruno K. Nowak and Shu-Wei Huang
In a point-scanning microscope, detection through a pinhole improves resolution and replacing the pinhole with a detector array provides redundant encoding of the object spectrum, enabling correction of nonidealities in the imaging system or further resolution improvements, for instance. Here, we show that the mathematical principles underlying structured detection are not intrinsically spatial and therefore structured detection may be used for imaging distributions in other physical domains, such as time, frequency, and velocity space. We numerically illustrate this generality by applying structured detection to an electromagnetic distribution in time using four-wave mixing (FWM). The resulting image reconstructions outperform the temporal equivalent of confocal detection, even as the FWM models are made more realistic and shot noise is considered.
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Fluid Dynamics
Experimental observations of sub-threshold triadic resonances in internal wave beams
Laura J. Irvine, Katherine M. Grayson, Andrew G. W. Lawrie et al. (+1 more)
This work examines sub-threshold triadic responses to a
vortex-ring-induced perturbation of an internal
gravity-wave field, using sparsity-promoting dynamic mode decomposition (spDMD) to diagnose wave structures from experimental observations. Compared with a standard approach to dynamic mode decomposition (DMD) that selects modes by truncation of the singular value spectrum, spDMD, an alternative approach that instead seeks to minimise reconstruction error, is shown here to robustly identify previously indistinguishable oscillatory signals of high frequency in cases of both triadic resonance instability (TRI) and sub-threshold sustained triadic response (STR). These signals are consistent with wave–wave interaction products composed of a primary internal wave with frequency $\omega_0$, and secondary TRI waves with frequencies $\omega_1$ and $\omega_2$ respectively, leading to signals with frequencies $\omega_3 = \omega_0 + \omega_1$ and $\omega_4 = \omega_0 + \omega_2$. We show that these signals satisfy conditions for resonance, but fail to satisfy the dispersion relation for internal waves, indicating that they are confined, non-propagating oscillatory signals rather than freely propagating internal waves. A hierarchical analysis of wave–wave interactions provides evidence that feedback between both branches of the TRI secondary waves gives rise to these signals. Whilst we expect our observations to generalise to many classes of wave–wave interaction, we cannot exclude the possibility that the particular observations we make in the laboratory may arise due to reflections of the primary wave from a free surface. However, beneath strongly density-stratified regions of the ocean we would expect to find these interaction pathways faced with the same
geometric configuration, so we are confident our findings will transfer directly to the natural environment.
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All authors Laura J. Irvine, Katherine M. Grayson, Andrew G. W. Lawrie, Stuart B. Dalziel