Physical review. E最新文献

In this study, instead of an approximate hard Gaussian overlap model, the effects of confinement on a system of oblate hard ellipsoid (OHE) particles interacting with planar substrates through the hard-disk-wall potential (HDW) were studied via computer simulation. In HDW, the thick oblate molecule with elongation k=a/b<1 is replaced by a thin disk with a diameter D=D_{s}σ_{0}, where σ_{0}=2b. We used NVT Monte Carlo simulations and showed that for small and large D_{s}, planar (edge-on arrangement) and homeotropic (face-on arrangement) anchoring are stable. The molecular volume absorbed by the substrates for each D_{s} is calculated analytically and the critical values of the transition parameter D_{s}^{T} were predicted from planar to homeotropic anchoring. Also, the transition parameters for two particles' elongations, k=0.2 and 0.345, are achieved via simulation. The results are approximately in agreement with the predicted values. Our results for the OHE particles with k=0.345 correspond to the hard Gaussian overlap results of Teixeira et al., qualitatively. We used an NPT Monte Carlo simulation to study the system in the region of D_{s}≈D_{s}^{T} and checked the influence of the packing fraction on the anchoring competition. The system in two cases, maximally penetrable and impenetrable substrates with D_{s}=0 and D_{s}=1.0, are investigated via NPT Monte Carlo simulations, and the isotropic-nematic transition packing fraction was compared. In addition, the orientational structure of k=0.2 and 0.345 OHEs confined between thin symmetry walls was studied as a function of wall separation. In addition, for k=0.2,D_{s}=0, and 1.0, the isotropic-nematic transition packing fraction of confined HGO particles and OHE particles were calculated and compared.

In this paper, a conservative phase-field based lattice Boltzmann equation (LBE) is developed to simulate gas-liquid-solid flows with large fluid density contrasts. In this model, the gas-liquid interface is captured by the conservative Allen-Cahn equation (CACE), where an additional source term is incorporated to realize the wettability of solid structure. Subsequently, a LBE is designed to solve this modified CACE (MCACE), while the two-phase flow field is resolved by using another classical incompressible LBE, and the fluid-solid interaction force is calculated by smoothed-profile method (SPM). Several classical simulations are conducted to demonstrate the capability of the present MCACE-LBE-SPM for simulating gas-liquid-solid flows, including a droplet spreading on a static wettable cylinder, a wettable cylinder floating on the gas-liquid interface without gravity, capillary interactions between two wettable cylinders under gravity, and multiple horizontal cylinders in gas-liquid channel flow. Numerical results indicate that the predictions by present MCACE-LBE-SPM are in good agreement with the theoretical or previous numerical results.

The excessive dendritic development during the electrochemical evolution of the microstructures in rechargeable batteries can ultimately cause a short circuit, thermal instability, or runaway, and loss of active material. We initially develop a computational framework to quantify the bias of the electrodeposition on the roughened interface favoring the convex zones. Subsequently, we impose a countering temperature effect to enhance the diffusion on the trailing concave zones. Consequently, we establish a stability criterion for controlling surface roughening where the visualized space of parameters establishes a relationship between the geometry of the interface, the physical properties of the electrolyte, and the charging conditions. The developed framework could be useful for controlling the propagation of the microstructures and the prevention of runaway, during prolonged cycles, particularly when the surface roughness gets pronounced in the later stage of cycle life.

The well-known Navier-Stokes-Fourier equations of fluid dynamics are, in general, not adequate for describing rarefied gas flows. Moreover, while the Stokes equations-a simplified version of the Navier-Stokes-Fourier equations-are effective in modeling slow and steady liquid flow past a sphere, they fail to yield a nontrivial solution to the problem of slow and steady liquid flow past an infinitely long cylinder (a two-dimensional problem essentially); this is referred to as Stokes' paradox. The paradox also arises when studying these problems for gases. In this paper, we present a way to obtain meaningful solutions for two-dimensional flows of rarefied gases around objects by circumventing Stokes' paradox. To this end, we adopt an extended hydrodynamic model, referred to as the CCR model, consisting of the balance equations for the mass, momentum, and energy and closed with the coupled constitutive relations. We determine an analytic solution of the CCR model for the problem and compare it with a numerical solution based on the method of fundamental solutions. Apart from addressing flow past a circular cylinder, we aim to showcase the capabilities of the method of fundamental solutions to predict the flow past other objects in two dimensions for which analytic solutions do not exist or are difficult to determine. For that, we investigate the problem of rarefied gas flow past an infinitely long semicircular cylinder.

Starting from the reported experimental evidence that the residence time of contacts between the ends of biopolymers is length dependent, we investigate the kinetics of contact breaking in simple polymer models from a theoretical point of view. We solved Kramers equation first for an ideal chain and then for a polymer with attracting ends, and compared the predictions with the results of molecular dynamics simulations. We found that the mean residence time always shows a power-law dependence on the length of the polymer with exponent -1, although it is significantly smaller when obtained from the analysis of a single trajectory than when calculated from independent initial conformations. Only when the interaction is strong (≫kT) and the interaction range is small (of the order of the distance between consecutive monomers) does the residence time converge to that of the Arrhenius equation, independent of the length. We are able to provide expressions of the mean residence time for cases when the exact definition of contact is not available a priori, expressions that can be useful in typical cases of microscopy experiments.

Swarmalators are entities that combine the swarming behavior of particles with the oscillatory dynamics of coupled phase oscillators and represent a novel and rich area of study within the field of complex systems. Unlike traditional models that treat spatial movement and phase synchronization separately, swarmalators exhibit a unique coupling between their positions and internal phases, leading to emergent behaviors that include clustering, pattern formation, and the coexistence of synchronized and desynchronized states, etc. This paper presents a comprehensive analysis of a two-dimensional swarmalator model in the presence of a predatorlike agent that we call a contrarian. The positions and the phases of the swarmalators are influenced by the contrarian and we observe the emergence of intriguing collective states. We find that swarmalator phases are synchronized even with negative coupling strength when their interaction with the contrarian is comparatively strong. Through a combination of analytical methods and simulations, we demonstrate how varying these parameters can lead to transitions between different collective states.

We empirically investigated how pedestrians rotate through bottlenecks to avoid collisions. Shoulder data was found to be more reliable and accurate for measuring rotation compared to head trajectories. An angle exceeding 30^{∘} is used to identify the rotation state, with a false identification rate below 2.5%. Two types of rotation are observed: type I, where pedestrians actively rotate, gradually shifting their orientations away from the desired direction to adapt to confined space, and type II, where pedestrians rotate back. Statistical evidence indicates that the difference in blocking by opposite pedestrians and obstacles between the two sides of a square region in front of the pedestrian, is the potential mechanism triggering rotation behaviors, with a critical value of 20%. As blocking in that region and angular velocity increase, the rotation axis moves closer the pedestrian body center. The spatial distribution of rotation axes can be explained by the maximization of both short-term and long-term rotational yields. Additionally, in confined spaces, pedestrians need two or more step durations to complete the rotation, resulting in a longer rotation time. This paper enhances the understanding of the mechanisms behind human rotation through bottlenecks and provides empirical support for pedestrian rotation modeling.

Statistical thermodynamics of particles having a spectrum of topological correlated states and observing statistical exclusion is developed to describe mixtures of species of arbitrary size and shape. A generalized statistical distribution is obtained through a configuration space ansatz recently introduced for single species accounting for the multiple exclusion statistical phenomena, where spatially correlated particle states can be simultaneously excluded by more than one particle. Statistical exclusion on a correlated states spectrum is characterized by exclusion statistical parameters β_{cij} which are self-consistently determined within the multiple exclusion from thermodynamic boundary conditions. Self-exclusion and cross-exclusion frequency functions e_{ij}(n) and average cumulative exclusion functions G_{ij}(n) are introduced to characterize the state exclusion spectrum as density varies. Haldane's statistics and Wu's distribution for statistically independent excluding species are recovered in the limit of uncorrelated states for single species as well as for mixtures of self- and cross-excluding species with constant mutual statistical exclusion. The multiple exclusion statistics formalism is applied to the k-mer problem on a square lattice rationalized as a mixture of two differently oriented self-excluding and cross-excluding pseudospecies. An isotropic-nematic and a high-density nematic-isotropic (disordered) phase transitions is predicted only for k≥7. The isotropic-nematic transition is continuum as expected, but the high-density transition results in a first-order one. The formalism provides phase coexistence lines and the chemical potential dependence of the low- and high-density branches in the nematic regime. The theoretical approach to lattice gases presented in this work offers a unique general framework applicable to mixtures of entropy-complex lattice gases. From this framework, k-mer phase transitions can be reproduced, and significant configuration features can be derived from the state exclusion spectrum functions.

Self-propelled particles that are subject to noise are a well-established generic model system for active matter. A homogeneous alignment field can be used to orient the direction of the self-propulsion velocity and to model systems like phoretic Janus particles with a magnetic dipole moment or magnetotactic bacteria in an external magnetic field. Computer simulations are used to predict the phase behavior and dynamics of self-propelled Brownian particles in a homogeneous alignment field in two dimensions. Phase boundaries of the gas-liquid coexistence region are calculated for various Péclet numbers, particle densities, and alignment field strengths. Critical points and exponents are calculated and, in agreement with previous simulations, do not seem to belong to the universality class of the 2D Ising model. Finally, the dynamics of spinodal decomposition for quenching the system from the one-phase to the two-phase coexistence region by increasing the Péclet number is characterized. Our results may help to identify parameters for optimal transport of active matter in complex environments.

A quasi-irrotational approximation for the linear Rayleigh-Taylor instability in elastic solids with finite thickness has been developed for the case in which the slab is in contact with a rigid wall. The approximation yields simple but still reasonably accurate expressions for the instability growth rate. They have the same character as the completely irrotational approximations already developed for semi-infinite media, and they recover its results in the limit for very thick slabs. The model is applied to an analysis of the boundary of stability and the boundary for the elastic to plastic transition in elastic-plastic media. The approach allows for consideration of the presence of a viscous fluid beneath the elastic-plastic slab, extending previous results for ideal fluids.