Physical Review E最新文献

We analyze a generalization of Zöttl and Stark's model of active spherical particles [Phys. Rev. Lett. 108, 218104 (2012)0031-900710.1103/PhysRevLett.108.218104] and prolate spheroidal particles [Eur. Phys. J. E 36, 4 (2013)1292-894110.1140/epje/i2013-13004-5] suspended in cylindrical Poiseuille flow, to particle dynamics in an arbitrary unidirectional steady laminar flow through a straight duct geometry. Our primary contribution is to describe a Hamiltonian formulation of these systems and provide explicit forms of the constants of motions in terms of the arbitrary fluid velocity field. The Hamiltonian formulation provides a convenient and robust approach to the computation of particle orbits while also providing new insights into the dynamics, specifically the way in which orbits are trapped within basins defined by a potential well. In addition to considering spherical and prolate spheroidal particles, we also illustrate that the model can be adapted to oblate spheroidal particles.

We show that norm-conserving spin models driven by temporally hyperuniform noise exhibit a sharp ergodicity-breaking transition in the absence of interactions. In the nonergodic phase, the dynamics freeze into configurations determined by the initial condition. Our analysis demonstrates that such interaction-free ergodicity breaking arises generically whenever a global constraint is imposed and the driving noise is class-I hyperuniform, the strongest form in Torquato's classification. The transition can also be interpreted as a condensation of fluctuations into the zero-frequency mode, reminiscent of Bose-Einstein condensation in an ideal gas.

In complex systems, accurately predicting the critical points of first-order phase transitions, such as explosive death, is crucial for early warning and risk management. This study constructs a parameter-aware next-generation reservoir computing (PNGRC) framework to achieve accurate prediction of critical transition. The framework embeds control parameters into the nonlinear vector autoregressive model to generate high-order nonlinear feature vectors that jointly encode system states and parameter information. The forward and backward trajectories under parameter variations are captured in the training stage, and the bidirectional parameter-aware model is constructed to effectively identify the bistable structure and transition paths within hysteresis regions. We evaluate the PNGRC framework on three representative coupled oscillator systems, highlighting its capability to identify first-order critical points across complex dynamical regimes. The results show that the PNGRC framework not only accurately reconstructs system trajectories under training parameters, but also generalizes well to unseen conditions, effectively capturing the period-doubling bifurcation structure and hysteresis phenomena. Compared to traditional parameter-aware reservoir computing, the PNGRC framework substantially reduces data requirements and training time. This work provides an efficient data-driven paradigm for predicting first-order phase transitions.

Granular materials exhibit complex behavior because of their nonequilibrium nature and dissipative mechanism. This study investigates the role of granular potential in bidisperse granular packings and its influence on thermodynamic properties such as entropy, compactivity, and density of states. Experimental tests using x-ray tomography were performed to examine the microstructure and volume fluctuations of bidisperse mixtures with varying composition ratios. Using a statistical mechanics approach and the fluctuation equation framework, the free-volume index and granular potential for an ensemble were quantified, revealing their direct correlation with packing structure and jamming behavior. The results show that granular potential significantly contributes to excess free volume, thereby influencing packing efficiency and stability. The findings offer insights into the implications of granular thermodynamics for natural and engineered systems, such as soil stability, landslides, and vascular flow regulation.

A transport equation is derived from microscopic considerations, aimed at modeling fractional radial transport in cylindrical-like geometries. The procedure generalizes existing work on one-dimensional Cartesian systems. The transport equation emerges as the fluid limit of an underlying continuous-time random walk (CTRW) that preserves the required symmetries and conservation laws. In the process, appropriate radial fractional operators are identified and defined through their Hankel transforms, providing a smooth interpolation between standard radial differential operators. Finally, propagators for the radial fractional transport equation are obtained in terms of Fox H functions.

We investigate the transport properties of active particles undergoing a three-state run-and-tumble dynamics in one dimension, induced by nonreciprocal transition rates between self-propelling velocity states {-v,0,+v} that explicitly break microscopic reversibility. Departing from conventional reciprocal models, our formulation introduces a minimal yet rich framework for studying nonequilibrium transport driven by internal state asymmetries. Using kinetic Monte Carlo simulations and analytical methods, we characterize the particle's transport properties across the transition-rates space. The model exhibits a variety of nonequilibrium behaviors, including ballistic transport, giant diffusion, and Gaussian or non-Gaussian transients, depending on the degree of asymmetry in the transition rates. We identify a manifold in transition-rate space where long-time diffusive behavior emerges despite the absence of microscopic reversibility. Exact expressions are obtained for the drift, effective diffusion coefficient, and moments of the position distribution. Our results establish how internal-state irreversibility governs macroscopic transport, providing a tractable framework to study nonequilibrium active motion beyond reciprocal dynamics.

We study the correlation function of the one-dimensional Ising model at fixed magnetization. Focusing on the scaling limit close to the zero-temperature fixed point, we show that this correlation function, in momentum space, exhibits surprising oscillations as a function of the magnetization. We show that these oscillations have a period inversely proportional to the momentum and give an interpretation in terms of domain walls. This is in sharp contrast with the behavior of the correlation function in constant magnetic fields and sheds light on recent results obtained by Monte Carlo simulations for the correlation functions of the critical two-dimensional Ising model at fixed magnetization.

Laser-generated, transient toroidal helium plasma at atmospheric pressure is studied experimentally. Tomographically reconstructed cross-sectional images reveal the gas flow responsible for the formation of the toroidal structure. A splitting of the toroidal plasma during the final phase of its evolution is observed. The plasma dynamics is induced by a two-lobed plasma kernel resulting from a single, focused laser pulse. This kernel generates two shocks that join to form an enhanced third shock, a so-called Mach reflection, in the plane perpendicular to the optical axis. This shock pattern determines the gas flow, which deforms the plasma into a disk, then transforms it into a nonrotating toroid, and finally splits it into two parallel rings. Schlieren imaging, a novel laser scanning-probe imaging technique, thermodynamic modeling, and a deliberately broken flow symmetry confirm this formation mechanism. This study is of interest for the generation of compact toroidal plasma structures in free space, with potential applications in chemical reactors, laser ignition of internal combustion engines, plasma medicine, and linked magnetic field line plasma confinement.

Magnetic thin films and two-dimensional (2D) arrays of magnetic nanoparticles exhibit unique physical properties that make them valuable for a wide range of technological applications. In such systems, dipolar interactions play a crucial role in determining their physical behavior. However, due to the anisotropic and long-range nature of dipolar interactions, conventional Monte Carlo (MC) methods face challenges in investigating these systems near criticality. In this study, we examine the critical behavior of a triangular lattice of XY dipoles using the optimized Tomita MC algorithm tailored for dipolar interactions. We employ two independent computational approaches to estimate the critical temperature and exponents: equilibrium MC simulations with histogram reweighting and the nonequilibrium relaxation method. Notably, both approaches demonstrate that this XY dipolar system might be in a new universality class very close to the 2D Ising universality class.

We study the two-dimensional extension of the energy or charge transfer problem in the long-wave limit along a mechanical lattice of oscillators for the interplay between linear longitudinal and periodic on-site interactions in the Holstein approach [S. Reza-Mejía and L. A. Cisneros-Ake, Wave Motion 130, 103382 (2024)0165-212510.1016/j.wavemoti.2024.103382]. It is found that the coupling between the linear Schrödinger and sine-Gordon equations, governing the modeling, holds coupled localized and traveling solutions radially symmetric in shape, contrary to the well-known decoupled case where solutions collapse in finite time. We then use the variational description of the problem to find the parameters regime where localization and further propagation take place. For the steady-state scenario, we find a decreasing and oscillatory branch of solutions for the wave function's power, as depending on the frequency of the phase, and then obtain an extension of the Vakhitov-Kolokolov stability criterion that predicts the bifurcation points. We validate these findings by solving the reduced coupled system in the stationary state by means of the Newton method and the Townes soliton condition in the polar coordinates. Finally, we extend our variational approach to the moving case to find the appropriate model and wave parameters where radial motion and the existence of a critical ratio for the strength between longitudinal and on-site interactions take place. These findings are numerically confirmed by solving the full coupled system with the help of the pseudospectral method.