Physical Review E最新文献

Electron heat flux is an important and often dominant mechanism of energy transport in a variety of collisional plasmas in a confined fusion or astrophysical context. While nonlocal conductive heat transport, driven by strong temperature gradients, has been investigated extensively in previous literature, nonlocal regimes of the current-driven heat flow and friction have not received the same attention. In this Letter, a first-principles reduced kinetic method is applied to study nonlocal effects on current-driven transport. In addition to nonlocality due to sharp gradients, sufficiently large currents are found to significantly enhance current-driven heat flux due to a novel nonlocal mechanism, with this enhancement being increasingly prevalent for higher effective ionizations Z^{*}. Introducing the dimensionless number N_{u}≡|u_{e}-u_{i}|/v_{th,e}, these enhancements occur for even relatively weak flows N_{u}≳1/100, analogously to standard nonlocal effects becoming significant for Knudsen numbers N_{K}≳1/100.

The following model is studied analytically and numerically: point particles with masses m,μ,m,⋯ (m≥μ) are distributed over the positive half-axis. Their dynamics is initiated by giving a positive velocity to the particle located at the origin; in its course, the particles undergo elastic collisions. We show that, for certain values of m/μ, starting from the initial state where the particles are equidistant, the system evolves in a hydrodynamic way: (i) the rightmost particle (blast front) moves as t^{δ} with δ<1; (ii) recoiled particles behind the front enter the negative half-axis; and (iii) the splatter-the particles with locations x≤0-moves in the ballistic way and eventually takes over the whole energy of the system. These results agree with those obtained in S. Chakraborti et al., SciPost Phys. 13, 074 (2022)2542-465310.21468/SciPostPhys.13.3.074, for m/μ=2, and random initial particle positions. At the same time, we explicitly found the collection of positive numbers {M_{i},i∈N} such that, for m/μ=M_{i}, i≤700, the following holds: (a) the splatter is absent; (b) the number of simultaneously moving particles is at most three; and (c) the blast front moves in the ballistic way. However, if, similarly as in S. Chakraborti et al., the particle positions are sampled from a uniformly distributed ensemble, for m/μ=M_{i} the system evolves in a hydrodynamic way.

The growth of information scrambling, captured by out-of-time-order correlation functions (OTOCs), is a central indicator of the nature of many-body quantum dynamics. Here, we compute analytically the complete time dependence of the OTOC for an integrable Sachdev-Ye-Kitaev (SYK) model, N Majoranas with random two-body interactions of infinite range, coupled to a Markovian bath at finite temperature. In the limit of no coupling to the bath, the time evolution of scrambling experiences different stages. For t≲sqrt[N], after an initial polynomial growth, the OTOC approaches saturation in a power-law fashion with oscillations superimposed. At t∼sqrt[N], the OTOC reverses trend and starts to decrease linearly in time. The reason for this linear decrease is that, despite being a subleading 1/N effect, the OTOC in this region is governed by the spectral form factor of the antisymmetric couplings of the SYK model. The linear decrease stops at t∼2N, the Heisenberg time, where saturation occurs. The effect of the environment is an overall exponential decay of the OTOC for times longer than the inverse of the coupling strength to the bath. The oscillations at t≲sqrt[N] indicate lack of thermalization-a desired feature for better performance of quantum information devices.

This study investigates the emergence of symmetry-breaking dynamics and the associated bifurcation behavior in an identically coupled Rosenzweig-MacArthur model with fitness-dependent dispersal between patches. We identify the occurrence of a symmetry-breaking (SB) state, characterized by the difference in the amplitude of oscillations across patches, signifying a form of desynchronization that supports species persistence. As the predator dispersal rate is varied, the SB state undergoes a sequence of dynamical transitions, alternating between chaotic symmetry breaking (CSB) and periodic symmetry breaking (PSB) states, and it includes the emergence of periodic windows that occur within chaotic windows across the dispersal rate. The alternating chaotic and periodic nature of SB dynamics is confirmed with the help of Lyapunov exponent analysis. In addition to the SB state, we observed antiphase synchronized (APS) and in-phase synchronized (IPS) states. To further understand the impact of initial conditions on distinct dynamical outcomes, we explore the basins of attraction within multistable regions. Finally, the stability of the APS, PSB, and IPS states is analyzed using Floquet analysis.

To understand how interaction topology and competition affect the diversity of information in the real world, we study the social contagion model introduced by Halvorsen-Pedersen-Sneppen (HPS) [Phys. Rev. E 103, 022303 (2021)2470-004510.1103/PhysRevE.103.022303] on static complex networks. The diversity of the information is measured through the root mean square of the information value W(N,t), which corresponds to the interface width in roughening phenomena. From the numerical simulations, we find that the HPS model on Erdős-Rényi random networks is always in the smooth phase characterized by the roughness exponent α=0. However, it undergoes a transition from a rough phase (α>0) to a smooth phase on scale-free networks as the degree exponent γ increases. When γ=4, we find that the steady-state value of W(N,t) scales as W_{sat}(N)∼logN, indicating that the threshold for the transition is γ^{*}≃4.

Transfer entropy is a widely used measure for quantifying directed information flows in complex systems. While the challenges of estimating transfer entropy for continuous data are well known, it has two major shortcomings for data of finite cardinality: it exhibits a substantial positive bias for sparse bin counts, and it has no clear means to assess statistical significance. By computing information content in finite data streams without explicitly considering symbols as instances of random variables, we derive a transfer entropy measure which is asymptotically equivalent to the standard plug-in estimator but remedies these issues for time series of small size and/or high cardinality, permitting a fully nonparametric assessment of statistical significance without simulation.

We study the dynamics of the Kuramoto model on the sphere under higher-order interactions and an external periodic force. For identical oscillators, we introduce a novel way to incorporate three- and four-body interactions into the dynamics of the order parameter, allowing for a full dimensional reduction of this system. We discuss how such reduction can be implemented in two different ways and how they are related. When restricted to the equator, the dynamics is similar to that of the usual Kuramoto model, up to an interesting renormalization of the coupling constants. Outside this plane, the motion reduces to a two-parameter set of periodic orbits. We also locate the bifurcation curves of the system as functions of different parameters.

We study the local entropy production rate and the local entropy flow in active systems composed of noninteracting run-and-tumble particles in a thermal bath. After providing generic time-dependent expressions, we focus on the stationary regime. Remarkably, in this regime the two entropies are equal and depend only on the distribution function and its spatial derivatives. We discuss in detail two case studies relevant to real situations. First, we analyze the case of space-dependent speed describing photokinetic bacteria, cosidering two different shapes of the speed, namely piecewise constant and sinusoidal. Finally, we investigate the case of external force fields, focusing on harmonic and linear potentials, which allow analytical treatment. In all investigated cases, we compare exact and approximated analytical results with numerical simulations.

Recent studies of two-dimensional polydisperse disk systems have revealed a coordinated self-organization of cell stresses and shapes, with certain distributions collapsing onto a master form for many processes, size distributions, friction coefficients, and cell orders. Here we examine the effects of particle angularity on the indicators of self-organization, using simulations of bidisperse regular N polygons and varying N systematically. We find that the strong correlation between local cell stresses and orientations, as well as the collapses of the conditional distributions of scaled cell stress ratios to a master Weibull form for all cell orders k, is independent of angularity and friction coefficient. In contrast, increasing angularity makes the collapses of the conditional distributions sensitive to changes in the friction coefficient.

The recently proposed macroscopic quantum phenomenon, Temperature-Induced Quantum Migration (TIQM), causes local heating and cooling and significantly affects the local heat capacity of a noninteracting confined Maxwell-Boltzmann gas. TIQM guarantees the non-negativity of local heat capacity at low temperatures, results in a substantial local heat-capacity overshoot, and provides a physical basis for global heat-capacity maxima and thermal confinement energy. We extend this framework here to Bose gases in three different rectangular domains, effectively providing three-dimensional (3D)/two-dimensional (2D)/one-dimensional (1D) confinement at high temperatures while transitioning to 2D/1D/zero-dimensional (0D) at low temperatures, thus inducing dimensional crossovers during temperature changes. We demonstrate that quantum degeneracy enhances the TIQM process, resulting in dimension-dependent effects on local and global heat capacities. For the 3D-2D crossover, TIQM leads to a giant excess local heat capacity and explains the mechanism for the enhancement of the global heat-capacity maximum, which surpasses the unconfined ideal Bose gas limit (1.93), reaching 1.97 at a finite density. Conversely, for the 2D-1D and 1D-0D crossovers, the excess local heat capacity diminishes with increasing quantum degeneracy (density), while it is TIQM alone that becomes responsible for excess global heat capacity. For the 1D-0D crossover, we find that only single-particle ergodic systems can have a global excess heat capacity; otherwise, the maximum behavior disappears completely. TIQM also provides a mechanism for the thermal confinement energy in Bose gases.