Physical Review E最新文献

An analog of nuclear magnetic resonance is realized in a microwave network with symplectic symmetry. The network consists of two identical subgraphs coupled by a pair of bonds with a length difference corresponding to a phase difference of π for the waves traveling through the bonds. As a consequence, all eigenvalues appear as Kramers doublets. Detuning the length difference from the π condition Kramers degeneracy is lifted, which may be interpreted as a Zeeman splitting of a spin 1/2 in a magnetic field. The lengths of another pair of bonds are modulated periodically with frequencies of some 10 MHz by means of diodes, thus emulating a magnetic radio-frequency field. This setup enables the realization of well-known NMR phenomena, such as the transformation from the laboratory to the rotating frame and the observation of Lorentzian-shaped resonance lines.

Generic systems are associated with a mixed classical phase space. The question of the properties of the eigenstates for these systems remains less known, although it plays a key role for understanding several important quantum phenomena such as thermalization, scarring, tunneling, and (de-)localization. In this work, by employing the kicked top model, we perform a detailed investigation of the dynamical signatures of the mixed eigenstates via the out-of-time-order correlator (OTOC). We show how the types of eigenstates get reflected in the short- and long-time behaviors of the OTOC and conjecture that the dynamics of the OTOC can be used as an indicator of the mixed eigenstates. Our findings further confirm the usefulness of the OTOC for studying quantum complex systems and also provide more insights into the characteristics of the mixed eigenstates.

Real-world networks exhibit universal structural properties such as sparsity, small worldness, heterogeneous degree distributions, high clustering, and community structures. Geometric network models, particularly random hyperbolic graphs (RHGs), effectively capture many of these features by embedding nodes in a latent similarity space. However, networks are often characterized by specific connectivity patterns between groups of nodes-i.e., communities-that are not geometric, in the sense that the dissimilarity between groups does not obey the triangle inequality. Structuring connections only based on the interplay of similarity and popularity thus poses fundamental limitations on the mesoscale structure of the networks that RHGs can generate. To address this limitation, we introduce the random hyperbolic block model (RHBM), which extends RHGs by incorporating block structures within a maximum-entropy framework. We demonstrate the advantages of RHBM through synthetic network analyses, highlighting its ability to preserve community structures where purely geometric models fail. Our findings emphasize the importance of latent geometry in network modeling while addressing its limitations in controlling mesoscale mixing patterns.

We investigate a decentralized traffic routing strategy that leverages local traffic load (LTL) information to improve the overall performance of urban transportation networks. Unlike conventional approaches based on static shortest-distance paths or globally optimized travel times, the proposed strategy dynamically balances travel distance with real-time local congestion levels, enabling efficient detour decisions with minimal computational overhead. Using a two-dimensional cellular automaton model, we simulate traffic dynamics under different routing schemes and evaluate key performance indicators, including average velocity, flow, and arrival rate. The results show that the LTL-based strategy significantly enhances system throughput and stability across a broad range of traffic densities. We attribute this improvement to its ability to induce timely, locally informed detours that suppress congestion buildup and spatial heterogeneity. Further analyses of detour statistics, travel distances, and spatiotemporal vehicle density fluctuations elucidate the underlying mechanisms. The robustness of the strategy is also confirmed on real-world urban network topologies. These findings suggest that routing strategies based on localized feedback can provide scalable and adaptive solutions for mitigating congestion in complex traffic systems.

We present the macroscopic dynamics of ferroelectric smectic C, smectic C_{F}, liquid crystals reported recently experimentally by two groups. In this fluid and tilted smectic phase, the macroscopic polarization, P, is tilted with respect to the layer normal, thus giving rise to C_{1h} overall symmetry for this phase in the spatially homogeneous limit. A combination of linear irreversible thermodynamics and symmetry arguments is used to derive the resulting dynamic equations applicable at sufficiently low frequencies and sufficiently long wavelengths. Compared to nonpolar smectic C phases, we find two static cross-coupling terms between compression of the layering and bending of the layers, which do not lead to elastic forces but to elastic stresses. In addition, a number of static cross-coupling terms is elucidated, which can exist in smectic C_{F} but not in the ferroelectric A_{F} phase because of the polar in-plane preferred direction in smectic C_{F}. Due to the fact that the magnitude of the polarization is a slowly relaxing variable, the velocities of the first and second sound both reflect the monoclinic symmetry of the ground state, thus rendering all sound velocities to be biaxial. We also analyze reversible cross-coupling terms between elongational flow and electric fields as well as temperature and concentration gradients, which lend themselves to experimental detection. Such cross-coupling terms have apparently never been considered before for monoclinic symmetry since they are absent without the presence of a polar direction and thus do not exist in nonpolar smectic C phases. Among the dissipative cross-coupling terms characteristic of smectic C_{F}, we find that bending of the layers can couple to temperature gradients. We also address the question how the linear P·E coupling in the energy alters the macroscopic response behavior when compared to usual nonpolar smectic C phases.

The impact of ionic impurities on the fundamental properties of nematic liquid crystals (LC) has long been observed; however, their influence on fundamental material parameters remains quantitatively unclear. Here we develop and validate a predictive theoretical framework that integrates ionic Coulomb self-energy into the Landau-de Gennes formalism, revealing how free ions nonlinearly suppress the dielectric anisotropy. Additionally, we propose a model that clarifies how electrostatic ion drag contributes to an increase in the rotational viscosity of the nematic phase. We experimentally verify both the dielectric anisotropy model and rotational viscosity model using a dual-frequency nematic LC doped with controlled concentrations of monolayer graphene flakes, which effectively modulates the ionic environment. The experimental results exhibit strong agreement with the theoretical predictions across both positive and negative dielectric regimes, as well as for the ion-modulated rotational viscosity of the LC. Dynamic optical switching measurements further corroborate the rotational viscosity results. This work establishes a self-consistent link between microscopic ionic screening and macroscopic rheo-optic behavior in soft anisotropic media, advancing the fundamental understanding of ion-related electrostatics in complex fluids.

Loopy tensor networks have internal correlations that often make their compression inefficient. We show that even local bond optimization can make better use of the insight it has locally into relevant loop correlations. By cutting the bond, we define a set of states whose linear dependence can be used to truncate the bond dimension. The linear dependence is eliminated with zero modes of the states' metric tensor. The method is illustrated by a series of examples for the infinite pair-entangled projected state (iPEPS) and for the periodic matrix product state (pMPS) that occurs in the tensor renormalization group (TRG) step. In all examples, it provides better initial truncation errors than standard initialization.

Active cholesterics are chiral in both their structure, which has continuous screw symmetry, and their active stresses, which include contributions from torque dipoles. Both expressions of chirality give rise to curl forces in the hydrodynamics, which we derive from the active Ericksen-Leslie equations using a geometric approach. This clarifies the hydrodynamics of continuous screw symmetry and provides an example of generalized odd elastic forces that originate from an equilibrium free energy. We also discuss the nonlinear structure of the active hydrodynamics in terms of the Eulerian displacement field of the cholesteric pseudolayers. For the active instability, screw symmetry generates a contribution of chiral activity to the linearized pseudolayer hydrodynamics that is absent in materials with chiral activity but achiral structure. When the two forms are sufficiently antagonistic, this term produces a new active instability with a threshold and a characteristic wave vector distinct from those of the active Helfrich-Hurault instability in chiral active smectics. Finally, we comment on the isotropic chiral hydrodynamics of materials with three-dimensional screw symmetry.

Active Brownian particles (ABPs) serve as a minimal model of active matter systems. When ABPs are sufficiently persistent, they undergo a liquid-gas phase separation and, in the presence of obstacles, accumulate around them, forming a wetting layer. Here, we perform simulations of ABPs in a quasi-one-dimensional domain in the presence of a wall, studying the dynamics of the polarization field. Over the course of time, we observe a transition from a homogeneous (where all particles are aligned) to a heterogeneous (where particles align only at the interface) polarization regime. We propose coarse-grained equations for the density and polarization fields based on microscopic and phenomenological arguments that correctly account for the observed phenomena.

We develop an operator-description for the linear stability in finite networks of Kuramoto oscillators on circulant graphs. This mathematical approach offers analytical predictions for the linear stability of q-states, which include phase synchronization (q=0) and phase-locked states with different spatial frequencies (|q|>0). This approach seamlessly incorporates the presence of time delays (represented by phase lags in the coupling). With this, we are able to determine the specific combination of connectivity and time delays (phase lags) that leads to any given q-state to be linearly stable. We apply our framework to a variety of networks, including k-ring graphs, distance-dependent graphs, and random circulant graphs. This approach offers a geometric perspective of linear stability in finite networks in terms of the connectivity and delays (phase lag), and it opens a path to designing and controlling the spatiotemporal dynamics of individual and finite oscillator networks.