Accelerator Physics
Self-Synchronized Terahertz and X-Ray Free-Electron Lasers from a Single Pre-Bunched Electron Beam
Yin Kang, Kaiqing Zhang, Zhen Wang et al. (+27 more)
Ultrafast pump-probe spectroscopy combining intense terahertz (THz) and X-ray pulses is a critical tool for investigating complex structural and electronic dynamics in materials. However, current setups combining THz sources and X-ray free-electron
lasers (FELs) often suffer from high system complexity, inherent timing jitter, or limited THz pulse properties. Here, we experimentally demonstrate the generation of intrinsically synchronized, strong-field, narrow-band THz and X-ray FELs from a single pre-bunched electron beam. Sequentially passing the beam through X-ray and THz amplifiers reveals a highly synergistic process: the initial periodic THz density modulation notably boosts the X-ray FEL pulse energy, while robustly surviving the intense X-ray emission to drive high-power, narrow-band THz radiation. Originating from the same electron bunch, the two pulses inherently maintain a precise, constant time delay. This jitter-free scheme establishes a highly reliable platform tailored for both X-ray-pump/THz-probe and THz-pump/X-ray-probe experiments.
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All authors Yin Kang, Kaiqing Zhang, Zhen Wang, Cheng Yu, Zhangfeng Gao, Wencai Cheng, Hang Luo, Yue Wang, Hanghua Xu, Xiaoqing Liu, Jinguo Wang, Huan Zhao, Yanyan Zhu, Yongmei Wen, Fei Gao, Yangyang Lei, Chengcheng Xiao, Liping Sun, Yongfang Liu, Jiaqiang Xu, Weiyi Yin, Xingtao Wang, Taihe Lan, Zheng Qi, Tao Liu, Zhi Guo, Bin Li, Chao Feng, Bo Liu, Zhentang Zhao
Applied Physics · Cross-listed from cond-mat.mtrl-sci
DINO4DSTEM: A self-supervised framework for structural discovery in 4D-STEM
Daniel Khaykelson, Lothar Houben and Boris Rybtchinski
Nanodiffraction using 4D-STEM has become a key technique for quantitative nanoscale structural mapping in materials research, yet interpreting its high-dimensional
datasets in structurally complex materials remains a major bottleneck. Existing analysis workflows typically rely on structural models, manual annotation, predefined classes, or sample-specific heuristics, limiting their ability to characterize heterogeneous complex materials. Here, we introduce DINO4DSTEM, a self-supervised machine learning framework that automatically discovers structurally meaningful states directly from raw diffraction data. Without structural models, manual labels, a predefined number of classes, or system-specific parameter tuning, the framework learns representations that organize diffraction patterns by their intrinsic structural similarities, transforming large collections of low-dose measurements into quantitative nanoscale structure maps. Across diverse
datasets, DINO4DSTEM consistently identifies the dominant structural degrees of freedom, providing
segmentation without human supervision. We applied the framework to the crystallization of indomethacin, a beam-sensitive, multidomain pharmaceutical system, revealing that crystallinity emerges from a partially ordered precursor and spans a continuous spectrum of structural order. The discovered nanoscale structural states are mapped to reveal the
evolution of order across the specimen quantitatively. By replacing task-specific analysis with general self-supervised representation learning, DINO4DSTEM provides a broadly applicable framework for quantitative nanoscale structural mapping in complex materials, enabling the discovery of emergent structural organization in heterogeneous, beam-sensitive systems.
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Optics
Optical nonlinearity in a strongly interacting Rydberg atom ensemble
Lu Qin, Zeyun Shi, Xingdong Zhao et al. (+2 more)
Rydberg atoms, characterized by their
giant polarizability and strong long-range interactions, provide an ideal platform for exploring optical nonlinearities. By coupling light to ensembles of Rydberg atoms, one can map the strong and nonlocal interactions between Rydberg atoms and light fields. A particularly important scheme for realizing such nonlinearity is electromagnetically induced transparency (EIT). This article presents a review of the research progress in nonlinear optics based on Rydberg-EIT systems, particularly nonlinear light propagation in Rydberg atomic gases. We first introduce the fundamental properties of Rydberg atoms and the physical mechanism of EIT-enhanced nonlinearity, emphasizing how the Rydberg blockade effect endows the system with a
giant nonlocal Kerr nonlinearity. Subsequently, we discuss some typical nonlinear optical phenomena in such a system with focusing and defocusing nonlocal nonlinearities. In the focusing regime, we discuss spatial
solitons,
vortex solitons,
soliton cloning,
soliton molecules, optical bullets, and self-induced transparency
solitons. Other topics are also discussed. In the defocusing regime, we analyze pattern formation and shock wave dynamics. Finally, we provide an outlook on the future development of this field toward
quantum control, hybrid-system integration, and novel functional devices.
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All authors Lu Qin, Zeyun Shi, Xingdong Zhao, Weibin Li, Guoxiang Huang
Fluid Dynamics · Cross-listed from cond-mat.soft
Skimming transition in flexible granular sweeping
Y. Ochi and H. Katsuragi
A flexible body placed in a steady flow bends to reduce drag. This self-streamlining is a hallmark of fluid-structure interaction (FSI). Granular-structure interaction is equally ubiquitous in nature. However, it remains poorly understood. Thus, we investigate inertial granular-structure interaction (IGSI). Specifically, ejection induced by a flexible plate sweeping a granular bed is experimentally examined. We find that a faster sweep results in less ejection, particularly for a flexible plate. To understand the underlying physics of this behavior, a dimensionless number Sk is introduced as the ratio of the plate elastic timescale to the sweep timescale. At $\mathrm{Sk} \lesssim 1$, the plate deflection follows the self-streamlining law of FSI and induces substantial ejection. At $\mathrm{Sk} \gtrsim 1$, on the other hand, the plate skims the bed and the mass of ejected grains decreases sharply. Sk organizes IGSI as the granular counterpart of FSI.
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Fluid Dynamics · Cross-listed from cond-mat.soft
Time-resolved sedimentation of dense potato-starch suspensions measured by optical coherence tomography
T. Saiki and H. Katsuragi
We demonstrate optical coherence
tomography (OCT) as a measurement technique for dense, optically opaque suspensions. Conventional optical methods cannot access the interior of such suspensions. OCT resolves individual potato-starch particles (${\sim}20~\mathrm{\mu m}$) as distinct scatterers, even though the suspension appears opaque to the eye. By tracking the vertical centroid position of the particle-laden layer $\langle Z \rangle(t)$ and the supernatant boundary $Z_\mathrm{sup}(t)$ in the same OCT image sequence, we obtain the instantaneous settling velocity $V(t)$ and the time-evolving effective volume fraction $\phi_\mathrm{eff}(t)$ simultaneously and continuously in time. To our knowledge, this is the first measurement to combine settling velocity and particle concentration into a single continuous trajectory within one sedimentation run. Conventional batch measurements yield only one velocity value per run. We applied this method to dense potato-starch suspensions, varying the initial volume fraction $\phi_0$ from 0.30 to 0.50 and the solvent density $\rho_\mathrm{L}$ from 1.0 to $1.3{\times}10^3~\mathrm{kg~m^{-3}}$ using aqueous sodium polytungstate solutions. The normalized velocity $V/V_\mathrm{Stokes}$ plotted against $\phi_\mathrm{eff}$ collapses onto a common trend consistent with both the Krieger–Dougherty model and the Richardson–Zaki law over $\phi_\mathrm{eff} \simeq 0.30$–$0.52$, confirming that the method captures physically reasonable hindered-settling behavior. These results establish OCT as a viable tool for probing internal dynamics in dense suspensions that were previously inaccessible to optical measurement.
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Plasma Physics
Electron Dynamics in a Wakefield Accelerator Driven by Laser Pulses Carrying Orbital Angular Momentum
Q. Qian, M. Li, Y. Ma et al. (+21 more)
Laser pulses carrying orbital angular momentum (OAM) provide a new degree of freedom for controlling
plasma-based accelerators. Here, we experimentally demonstrate OAM-driven
laser wakefield acceleration, producing electron beams with a two-beamlet structure that indicates unique azimuthal dynamics inside the
plasma wake. Particle-in-
cell simulations reproduced the observed spectral features and revealed helical electron trajectories driven by OAM-pulse-driven wakefields. These results show that the
laser driver's phase structure can shape electron acceleration dynamics, opening a route to optimal control of beam structure in compact
laser-driven accelerators.
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All authors Q. Qian, M. Li, Y. Ma, P. T. Campbell, C-H. Chang, E. Denis, N. Ernst, R. Fedosejevs, B. Hou, A. James, M. W. von der Leyen, K. Krushelnick, C. Kuranz, A. Longman, A. Maksimchuk, J. Nees, P. Norreys, T. Nutting, J. B. Ohland, J. Palastro, A. G. R. Thomas, R. Timmis, L. Willingale, M. Burger
Optics
Reconfigurable microwave photonic Fano filters based on optical Kerr microcombs
Qi Zou, Jiayang Wu, Yang Sun et al. (+9 more)
Microwave photonic (MWP) Fano filters, featuring asymmetric filter shapes that enable steep spectral transitions, are attractive for high bandwidth microwave signal processing such as frequency discrimination. However, achieving both steep spectral transitions and a high degree of reconfigurability remains challenging for conventional methods relying on direct mapping of Fano resonances generated by optical filters. Here, we propose and experimentally demonstrate a new way for realizing MWP Fano filters based on a microcomb-driven transversal filter system. Leveraging the large number of comb lines provided by microcombs as discrete taps, the transversal filter system can synthesize filter response that closely resembles Fano resonances, yielding high rolloff rates and slope rates up to 33.8 dB / GHz and 25.7 dB / GHz in our experiments, respectively. In addition, by simply programming the tap coefficients without changing any hardware, highly reconfigurable filter response can be realized. We experimentally demonstrate independent tuning of all three Fano characteristic parameters, including the asymmetry factor, resonance linewidth, and center frequency. These results verify the effectiveness of our approach for implementing highly reconfigurable MWP Fano filters with steep spectral transitions, offering strong versatility for meeting diverse requirements in practical applications.
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All authors Qi Zou, Jiayang Wu, Yang Sun, Yang Li, Guanghui Ren, Thach G. Nguyen, Xingyuan Xu, Bill Corcoran, Sai T. Chu, Roberto Morandotti, Arnan Mitchell, David J. Moss
Optics
Imaginary Gauge Fields for One-Way Transparency and Absorption in a Passive Metasurface
Qingdong Yang, Zhongfu Li, Xinhua Wen et al. (+3 more)
Electromagnetic nonreciprocity enables waves to respond differently when their propagation direction is reversed, forming the basis of isolation, directional routing, and asymmetric energy control. A central challenge is to achieve high transmission in one direction while inducing strong absorption in the opposite direction within a single passive element, as passive material dissipation typically attenuates both propagation channels equally. Here we demonstrate that an imaginary artificial gauge field can redistribute net dissipation between opposite directions in a passive structure. By synthesizing a moving-type magnetoelectric response from gyromagnetic elements and subwavelength metallic resonators, we realize a polarization-independent metasurface in which the forward wave weakly excites the dissipative resonance through destructive current interference, whereas the backward wave strongly activates the same lossy mode through constructive interference. The fabricated metasurface transmits more than 80% of the incident power from one side while absorbing more than 80% from the opposite side, with low reflection from both directions. Near-field mapping of the surface electric field provides direct real-space evidence of this gauge-controlled, direction-dependent charge accumulation and dissipation. This work establishes imaginary gauge fields as a powerful route for engineering dissipative landscapes in open wave systems and opens a pathway toward compact, passive, reflectionless isolators and nonreciprocal absorbers.
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All authors Qingdong Yang, Zhongfu Li, Xinhua Wen, Oubo You, Yi Wang, Shuang Zhang
Applied Physics
Voltage-Controlled Phosphate Precipitation Gating in Solid-State Nanopore Memristors
Weihong Wang, German Lanzavecchia, Ali Douaki et al. (+9 more)
Nanofluidic memristors preserve a record of electrical activity via ion migration and alterations in conductance that depend on the history of the device s state. These characteristics make them suitable for aqueous, energy efficient, and biologically compatible neuromorphic systems. To establish the viability of fluidic memristors for mimicking the
brain s dynamic behavior, a more thorough understanding of the memristive materials and the underlying switching processes is required. In this study, we systematically examined a recently introduced memristive device based on inpore chemical reactions, where the combined influence of electrolyte composition and pore architecture on precipitation gated
memory remains poorly understood. To address this, we constructed an asymmetric electrochemical system using CaCl2 and phosphate solutions separated by SiNx solid state nanopores. We explored how variations in pH, phosphate concentration, pore geometry, and voltage pulsing regimens affect the electrical characteristics and memristive performance. Comparison of the single pore and the array showed that parallel pores produced smoother pH and concentration dependent hysteresis and pulse responses, whereas the single pore retained larger, nonmonotonic changes.
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All authors Weihong Wang, German Lanzavecchia, Ali Douaki, Shukun Weng, Yanqiu Zou, Huaizhou Jin, Alberto Giacomello, Lorenzo Iannetti, Roman Krahne, Shangzhong Jin, Makusu Tsutsui, Denis Garoli
Biological Physics · Cross-listed from cond-mat.soft
Shear effects in active models of normal and cancer cells
Souvik Sadhukhan, Rajsekhar Das, Lin Zhao et al. (+2 more)
Mechanical properties of biological tissues, driven by passive and active forces, play a vital role in several processes ranging from development to cancer metastasis. However, the dynamical responses of
cells in tissues, subject to mechanical deformations such as shear and the associated rheological properties, are not well characterized. Here, we use three-dimensional
agent-based models for normal and cancer tissues to investigate their responses to simple shear as a function of
cell stiffness and
stochastic active forces. In the normal epithelium, with uniform strength of active force, the yield stress as a function of shear rate follows the Herschel-Bulkley form over a range of
cell volume fraction. Strikingly, the shear rate dependence and the elasticity-dependent changes in the yield stress fall on master curves upon suitable scaling. To model cancer-like behavior, a certain fraction ($N_p$) of
cells was chosen to have enhanced activity and decreased stiffness. As $N_p$ increases, the extent of collective
cell movement decreases, transitioning from affine (collective) to non-affine (individualistic) movement, a finding that is in accord with imaging experiments. Simulations of a model of a stiff solid tumor, with radius $R_s$ embedded in normal tissue, show that as $R_s$ increases, the yield stress increases. Interestingly, the
cells migrate collectively as $R_s$ increases. A Gaussian Mixture Model (GMM) and a mean field theory quantitatively account for the simulation as well as experimental results on cancerous, non-cancerous, and a mixture of these two types. The combined theoretical and experimental study establishes that heterogeneity in stiffness and activity determines non-affine movements in normal and cancer tissues.
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All authors Souvik Sadhukhan, Rajsekhar Das, Lin Zhao, Wolfgang Losert, D. Thirumalai
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Discovering Physically Interpretable Mathematical Expression for Predicting CO2 Adsorption in Metal-Organic Frameworks via Machine Learning-Symbolic Regression
Yimin Shao, Shengluo Ma, Shenghong Ju et al. (+2 more)
This work presents a machine learning-symbolic regression (ML-SR) strategy to develop a physically interpretable formula for predicting low pressure CO2 adsorption capacity in hypothetical metal-organic frameworks (hMOFs). Four ML models were trained on a small
dataset of 1,000 samples, and five key descriptors-largest cavity diameter, pore limiting diameter, void fraction, gravimetric surface area, and number of hydrogen atoms-were identified through SHAP and feature importance analyses. Symbolic regression was then employed to derive a concise adsorption formula, Q=aA, where a represents an adsorption baseline (mmol/g) and A is a dimensionless adsorption number incorporating four structural descriptors. We interpret A as the ratio between an adsorption binding force and a
diffusion driving force, revealing how pore
topology and surface chemistry jointly influence adsorption. Validation against a comprehensive
dataset of 137,652 hMOFs demonstrates that this formula achieves over 70% prediction accuracy for 62,448 structures, confirming strong applicability within defined structural and operational ranges. Unlike conventional black box ML models, the proposed physics-guided expression enables efficient prediction and provides clearer insight into adsorption mechanisms.
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All authors Yimin Shao, Shengluo Ma, Shenghong Ju, Yijun Shi, Wei Li
Chemical Physics
Quantum Boltzmann Equation Self-Consistent-Field for the Entropic Regularization of Mean-Field Singularities
Romit Chakraborty
We present a
Quantum Boltzmann Equation self-consistent-field (QBE-SCF) formulation for molecular electronic structure in which the one-electron reduced density
matrix is propagated in an atomic orbital basis and relaxed by a Bhatnagar-Gross-Krook collision operator toward a
Fermi-Dirac
equilibrium defined by the instantaneous Fock
matrix. At stationarity, the converged density and Fock
matrices satisfy $[\mathbf{F},\mathbf{P}]=0$, the Hartree-Fock condition. While the zero-temperature
equilibrium target reduces to the integer Aufbau projector, the damped collision operator ensures the steady-state density
matrix is not necessarily idempotent. This kinetic relaxation affords a dual pathway to resolve mean-field singularities. For spatial degeneracies, such as H$_3$ symmetric dissociation, zero-temperature kinetic ergodicity fractionalizes the active space to recover the Generalized Valence Bond (GVB) limit. For the conical intersection in BeH$_2$ and the H$_4$ structural distortion ($D_{2h} \rightarrow D_{4h} \rightarrow D_{2h}$), finite-temperature entropic regularization recovers correlated adiabatic surfaces from a real-valued single-reference density. By maintaining stable numerical convergence across basis-set hierarchies and resolving static correlation without multi-reference wavefunctions, these results establish kinetic relaxation as a synthesis of single-reference electronic structure and
quantum statistical mechanics.
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Biological Physics · Cross-listed from nlin.CD
An Idealized Delay-Differential Model of Scuba Diver Porpoising and Runaway Ascent
Sandy Hardian Susanto Herho, Faizal Ade Rahmahuddin Abdullah, Iwan Pramesti Anwar et al. (+5 more)
A scuba diver holding constant depth balances on an unstable
equilibrium: the gas carried in the suit and buoyancy compensator compresses with depth, so the buoyant force falls as the diver sinks and rises as the diver ascends. We represent the diver as a proportional-derivative controller that regulates this compressible-buoyancy saddle after a finite reaction delay, and we derive the governing delay differential equation from the vertical force balance and the isothermal gas law, reducing it to a damping ratio, two control gains, and a dimensionless delay. The characteristic spectrum, obtained by pseudospectral collocation of the
semigroup generator and checked against a direct Newton solution of the characteristic equation, locates the
Hopf boundary that separates stable hovering from sustained porpoising; for the baseline diver the critical reaction delay is 3.36 s and the onset period is 28.8 s. The bifurcation is supercritical, and because the saturating force is the quadratic hydrodynamic drag, the limit-cycle amplitude grows in proportion to the delay excess rather than as its square root. The safe-operating envelope shows that runaway ascent is triggered by saturation of the compensator, not by loss of linear stability, so a stable and an unstable diver can share the same escape threshold. As onset is approached, the lag-one autocorrelation and variance rise while the fitted recovery rate falls and matches the spectral abscissa, giving an
eigenvalue-exact early warning of the transition.
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All authors Sandy Hardian Susanto Herho, Faizal Ade Rahmahuddin Abdullah, Iwan Pramesti Anwar, Faruq Khadami, Alfita Puspa Handayani, Karina Aprilia Sujatmiko, Rusmawan Suwarman, Dasapta Erwin Irawan
Biological Physics · Cross-listed from q-bio.PE
Social Discounting Enables Fast and Reliable Collective Escape
Zachary P Kilpatrick
Solitary animals face a tradeoff when detecting threats: faster detection means accepting more false alarms. We show that groups can manage this tradeoff better by treating an undisturbed neighbor as evidence against a threat, becoming both faster and more accurate than lone individuals. Modeling each animal as a noisy evidence-accumulator that flees when its belief crosses a threshold, we find that a neighbor's flight signals danger while its stillness signals safety. A naive responder reacts only to flights and inflates false alarms as the group grows; a
Bayesian responder weighs both, approximated by a single social discounting rate that interpolates between these limits. This yields closed-form expressions for group performance, including cascade branching ratios that stay strongly subcritical in safety and turn supercritical under threat, so the rate at which an animal discounts a threat while its neighbors stay still can be inferred from behavior alone, and it sets a ceiling on how many neighbors an animal can attend before discounting alone can no longer hold its false-alarm rate. Wild sulphur molly shoals under bird attack are best described by discounting rates well above what individually
Bayesian updating supplies over any neighborhood they could plausibly attend, and the same model, at the inferred value, predicts a false-alarm rate that stays constant as shoals grow.
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Chemical Physics · Cross-listed from astro-ph.GA
Infrared Spectroscopy of Cyanonaphthalenes under Interstellar Relevant Conditions and Their Potential Connection with Astronomical Aromatic Infrared Bands
Jiaqi Xin, Jianzhi Xu, Piero Ferrari et al. (+1 more)
Context. Aromatic infrared bands (AIBs) are widely observed in diverse astrophysical environments and are generally attributed to vibrational emission from polycyclic aromatic hydrocarbons (PAHs). The recent interstellar detection of 1-cyanonaphthalene (1-CNN) and 2-cyanonaphthalene (2-CNN) has motivated detailed infrared spectroscopic studies of cyano-substituted PAHs. Aims. We aim to characterize the infrared spectra and vibrational modes of neutral 1-CNN and 2-CNN under cold and gas-phase conditions and to assess their possible spectroscopic relevance to the astronomical AIBs. Methods. The gas-phase infrared spectra of neutral 1-CNN and 2-CNN were measured in a cold molecular beam using ion-dip spectroscopy. The observed bands were assigned with the aid of harmonic and anharmonic calculations at the B3LYP/N07D level. Infrared emission spectra were subsequently simulated from the experimental spectra within a single-
photon approximation framework. Results. We report the infrared spectra of neutral 1-CNN and 2-CNN measured under cold and gas-phase conditions relevant to the interstellar medium. Their vibrational features were assigned in detail, including fundamental vibrations as well as overtone and combination bands. The simulated emission spectra exhibit features in several wavelength regions associated with prominent AIBs, including the aromatic CH stretching region near 3.3 micron, the CC stretching region near 6.2 micron, the mixed CH in-plane bending and CC stretching region at 8.6-8.9 microns, and the CH out-of-plane bending region between 10 and 15 microns. Conclusions. The present spectra provide laboratory reference data for small cyano-substituted PAHs and offer useful clues for interpreting selected AIB regions. These results suggest that cyanonaphthalene molecules are promising contributors to the aromatic infrared bands.
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All authors Jiaqi Xin, Jianzhi Xu, Piero Ferrari, Gao-Lei Hou
Instrumentation and Detectors
Development of a 10 mol% Rubidium-doped CsI Crystal for $^{87}$Rb Beta-Spectroscopy and Sterile Neutrino Searches
W. K. Kim, K. W. Kim, L. T. Truc et al. (+3 more)
The third-forbidden non-unique beta-decay of $^{87}$Rb to $^{87}$Sr (Q$_\beta = 282.275(6)$ keV) has long served as an important
benchmark for understanding forbidden beta-decay. To investigate this, we have developed a novel CsI scintillator with a 10 mol% Rb concentration using the Bridgman method. The incorporated $^{87}$Rb serves as an intrinsic radioactive source, enabling a source-in-detector configuration with high detection efficiency and minimal energy loss for low-energy electrons from beta-decay. We investigated both Rb doped and Tl co-doped CsI
crystals and characterized their scintillation properties, including light yield, energy resolution, and non-linear response. We report distinct scintillation characteristics for the CsI:Rb and CsI:Tl,Rb
crystals, with light yields of $1.38\pm0.01$ and $4.73\pm0.13$ PE/keV, respectively. Using the measured $^{87}$Rb beta-spectrum, we search for a keV-scale sterile
neutrino admixture through the characteristic kink-like distortion induced by a heavy
neutrino mass eigenstate. This study provides a basis for future sterile
neutrino searches using rubidium doped CsI
crystal.
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All authors W. K. Kim, K. W. Kim, L. T. Truc, H. S. Lee, H. J. Kim, Y. D. Kim
Atmospheric and Oceanic Physics
Generative data assimilation highlights fronts as key regulators of ocean energy cascade
Scott A. Martin, Georgy E. Manucharyan and Patrice Klein
Mesoscale eddies are fundamental to the ocean circulation, yet the extent to which submesoscale motions, a few kilometers across, influence mesoscale eddy energetics through a kinetic energy cascade remains uncertain. High-resolution simulations predict that submesoscale fronts are key regulators of the cascade, transferring energy both downscale towards dissipation and upscale to sustain and shape the seasonality of mesoscale eddies. Testing these predictions has remained difficult because existing observations and state estimates cannot resolve submesoscale currents over sufficiently broad domains. Here we map the ocean's submesoscale energy cascade by combining multi-source satellite observations with a generative deep learning framework, reconstructing gap-free, kilometer-scale surface currents with physically plausible dynamics learned from simulations. Applying this to the eddy-rich Agulhas Current system, we find that submesoscales energize the mesoscale through an upscale energy cascade above 10 km, contributing to the seasonality of mesoscale eddies. Below 10 km, convergence at submesoscale fronts drives a downscale cascade towards dissipation. Both upscale and downscale pathways concentrate within fronts, where cross-scale transfer is up to an order of magnitude more efficient. Despite their limited extent, fronts account for a substantial fraction of the domain-integrated cascade, establishing them as key regulators of the cascade and targets for next-generation eddy parameterizations.
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Fluid Dynamics
Domain-filling rolls in two-dimensional fixed-flux Rayleigh-Bénard convection
Mathew D. B. Lewis, Zehan Zheng and David Goluskin
Rayleigh-Bénard convection of large horizontal extent sometimes self-organizes into domain-filling structures. In two dimensions, domain-filling rolls persist - from some but not all initial conditions - when velocity boundary conditions are stress-free. When velocity boundary conditions are no-slip, domain-filling rolls are not found with fixed-temperature thermal boundary conditions, but they have not been sought with fixed-flux thermal boundary conditions. Here we explore the latter missing case, which is hard to predict because no-slip boundaries do not encourage domain-filling rolls, but fixed-flux boundaries give domain-filling structures in three dimensions for either boundary condition on velocity. We simulate convection with fixed-flux, no-slip boundaries in two-dimensional domains with horizontal period 20 times their height and at various combinations of the fixed-flux Rayleigh number R and Prandtl number Pr. Domain-filling rolls, which are easily found when they are weakly nonlinear at small R, are continued to other (R,Pr) by changing these parameters slowly in time. The (R,Pr) regime where we find domain-filling rolls is substantial but has a boundary. When R is too large or Pr too small, relative to each other, a domain-filling roll pair breaks up into two pairs. These findings contrast with other combinations of dimension and boundary conditions, where scale selection has not been seen to depend strongly on parameter values. The present case helps disentangle competing effects of dimension and boundary conditions, and it offers a more stringent test for explanations of scale selection that have been proposed.
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