The electrostatic potential and plasma density variations around a pointlike charged object in a plasma flow are studied. These objects can represent small charged dust particles, for instance. The radiation patterns can be interpreted as the result of sound waves being radiated by the obstacle. Two limits are considered: one where the electron-ion temperature ratio is large, $T_e⪢T_i$, and one where $T_e∕T_i\approx 1$. The former limit can be described by a simple model based on geometrical optics, while the latter requires a kinetic model in order to account for the effects of ion Landau damping. The results are illustrated by numerical simulation using a particle-in-cell code, where the electrons are treated as an isothermal massless fluid, giving a nonlinear Poisson equation. The analytical results are in good agreement with the numerical simulations.

We study the effect of clustering on the organization of cooperation by analyzing the evolutionary dynamics of the “Prisoner’s Dilemma” on scale-free networks with a tunable value of clustering. We find, on the one hand, that a high value of the clustering coefficient produces an overall enhancement of cooperation in the network, even for a very high temptation to defect. On the other hand, high clustering homogenizes the process of invasion of degree classes by defectors, decreasing the chances of survival of low densities of cooperators in the network.

We suggest a control based method to uncover the structure (i.e., the dynamics of each system, the coupling direction, and coupling functions) of coupled systems. We show that driving a coupled system to steady states can reveal the underlying controlled coupling structure. An example of interacting quantum dots is presented to illustrate the structure identification method suggested.

We present a quantitative model for the evolution of single and multiple bubbles in the Richtmyer-Meshkov (RM) instability. The higher-order solutions for a single-mode bubble are obtained, and distinctions between RM and Rayleigh-Taylor bubbles are investigated. The results for multiple-bubble competition from the model shows that the higher-order correction to the solution of the bubble curvature has a large influence on the growth rate of the RM bubble front. The model predicts that the bubble front of RM mixing grows as $h\sim t^{\theta }$ with $\theta \sim \left(0.3–0.35\right)\pm 0.02$.

A stochastic generalization of renormalization-group transformation for continuous-time random walk processes is proposed. The renormalization consists in replacing the jump events from a randomly sized cluster by a single renormalized (i.e., overall) jump. The clustering of the jumps, followed by the corresponding transformation of the interjump time intervals, yields a new class of coupled continuous-time random walks which, applied to modeling of relaxation, lead to the general power-law properties usually fitted with the empirical Havriliak-Negami function.

The hydrodynamic solutions based on Maxwell’s boundary conditions include an empirical slip coefficient (SC), which depends on properties of the adsorbate and adsorbent. Existing kinetic theory derivations of the SC are usually formulated for half-space flow and do not include finite-size effects, which dominate the flow in nanopores. We present an expression for the SC applicable to flow in nanoscale pores, which has been verified by nonequilibrium molecular-dynamics simulation. Our results show that the slip coefficient depends strongly on the pore width for small pores tending to a constant value for pores of width $>20$ molecular diameters for our systems, in contrast to the linear scaling predicted by Maxwell’s theory of slip.

We investigate coupled identical phase oscillators with scale-free distribution of coupling strength. It is shown that partially locked states can occur due to the inhomogeneity in coupling and some properties of the coupling function. Various quantities of the partially locked states are computed through a self-consistency argument and the values show good agreement with simulation results.

The classical and quantum irregular spin dynamics of atomic spinor Bose-Einstein condensates in an optical lattice, where light-induced and static magnetic dipole-dipole interactions originate the interplay of the condensate at each site, are investigated. Classical-quantum correspondence in the large-spin limit is studied. Quantum chaotic features are studied through analysis of the irregular spectrum and time evolution of the Shannon entropy of wave packets. We show how the optical lattice strength influences the system dynamics, and is responsible for a transition from regular to irregular bahavior.

We model a shock wave in an ideal gas by combining the Burnett approximation and Holian’s conjecture. We use the temperature in the direction of shock propagation rather than the average temperature in the Burnett transport coefficients. The shock wave profiles and shock thickness are compared with other theories. The results are found to agree better with the nonequilibrium molecular dynamics (NEMD) and direct simulation Monte Carlo (DSMC) data than the Burnett equations and the modified Navier-Stokes theory.

We consider the percolation aspect of random sequential adsorption of extended particles onto a two-dimensional lattice using computer Monte Carlo simulations. We investigate how the composition of the particles influences the value of the percolation threshold. Two regimes can be distinguished: one for almost linear particles (with the composition of straight segments reaching 85–100 %) and the second one for more bent (flexible) ones. For more bent particles we found a high correlation between the percolation threshold and the structure of an adsorbate at percolation. We also observe that there is no difference in the conclusions for both kinds of lattice considered (square and triangular).

We extend the analysis of a thermal Brownian motor reported by Van den Broeck et al. [Phys. Rev. Lett. 93, 090601 (2004)] to a three-dimensional configuration. We calculate the friction coefficient, diffusion coefficient, and drift velocity as functions of shape and present estimates based on physically realistic parameter values.

Flexoelectric effects are studied in the domain walls of a nematic liquid crystal device showing the Freedericksz transition. Walls parallel to the alignment direction have a strong twist distortion and an electro-optic effect dominated by $e_1-e_3$ is seen. Walls perpendicular to the alignment direction have a strong splay-bend distortion and an electro-optic effect dominated by $e_1+e_3$ is seen. This allows the study of both flexoelectric coefficient combinations in a single device.

Recently, an interesting phenomenon of spatial localization of optical modes along periodic ray trajectories near avoided resonance crossings has been observed [Wiersig, Phys. Rev. Lett. 97, 253901 (2006)]. For the case of a microdisk cavity with elliptical cross section, we use the Husimi function to analyze this localization in phase space. Moreover, we present a semiclassical explanation of this phenomenon in terms of the Goos-Hänchen shift, which works very well even deep in the wave regime. This semiclassical correction to the ray dynamics modifies the phase-space structure such that modes can localize either on stable islands or along unstable periodic ray trajectories.

We provide a general condition for the occurrence of a sudden transition to synchronization in an array of oscillators mutually coupled via the nearest neighbors. At the onset of synchronization a specific constraint must be fulfilled: precisely, the response time of a single system to signals from the adjacent sites must be smaller than the refractory period. We verify this criterion in some models for neuronal dynamics, namely, in excitable systems driven by noise as well as in chaotic oscillators.

By realizing the insufficient degree of Galilean invariance of the traditional multiple-relaxation-time collision operators, Geier et al. [Phys. Rev. E 73, 066705 (2006)] proposed to relax differently the moments shifted by the macroscopic velocity, leading to the so-called cascaded lattice Boltzmann method (LBM). This paper points out that (a) the cascaded LBM essentially consists in adopting a generalized local equilibrium in the frame at rest; (b) this new equilibrium does not affect the consistency of LBM; and finally (c) if the raw moments are relaxed in the frame at rest as usual and the number of relaxation frequencies is reduced, the proposed derivation leads to the two-relaxation-time collisional operator with proper polynomial equilibrium.

We report experimental measurements of particle dynamics on slowly sheared granular matter in a three-dimensional Couette cell. A closely packed ensemble of transparent spherical beads is confined by an external pressure and filled with fluid to match both the density and refractive index of the beads. This allows us to track tracer particles embedded in the system and obtain three-dimensional trajectories $\left[r\left(t\right),\theta \left(t\right),z\left(t\right)\right]$ as a function of time. We study the probability distribution function of the vertical and radial displacements, finding Gaussian and exponential distributions, respectively. For slow shear rates, the mean-square fluctuations in all three directions are found to be dependent only on the angular displacement of the Couette cell, $\Delta {\theta }_e$, $⟨\Delta z^2⟩\sim \Delta {\theta }_e$, $⟨\Delta r^2⟩\sim \Delta {\theta }_e^{\alpha }$, $⟨\Delta {\theta }^2⟩\sim \Delta {\theta }_e^{\beta }$, where $\alpha$ and $\beta$ are constants. With $\Delta {\theta }_e$ proportional to the time between measurements, the values of the constants, $\alpha$ and $\beta$, are found to be subdiffusive and superdiffusive, respectively. ThFe linear relation between $⟨\Delta z^2⟩$ and angular displacement implies a diffusive process, from which we can calculate an “effective temperature,” $T_{\text{eff}}$, in the vertical direction, through a fluctuation-dissipation relation. It is of interest to determine whether these systems can be described by analogous equilibrium statistical mechanics concepts such as “effective temperature” and “compactivity.” By studying the dynamics of tracer particles, we find the effective temperature defined by the Stokes-Einstein relation to be independent of the tracer particle characteristic features, such as density and size, and dependent only on the packing density of the system. For slow shear rate, both the diffusivity and mobility of tracer particles are proportional to the shear rate, giving rise to a constant effective temperature, characteristic of the jammed system. We finally discuss the significance of the existence of $T_{\text{eff}}$ for a statistical mechanics formulation of granular matter.

The physical mechanism of colloidal gelation remains inadequately understood, particularly for intermediate to high volume fractions. Experiments to directly probe the complex evolution of structural and viscoelastic properties of gels have been few despite their fundamental importance in elucidating the physical mechanisms responsible for gelation. In this study, we use a home-built micron-gap rheometer combined with confocal microscopy to directly investigate the coupled structural and dynamic properties of colloidal gelation transition by spatial confinement. We observe that confinement-induced gelation proceeds by a spinodal decomposition route where strongly confined colloidal suspensions evolve into “colloid-rich” and “colloid-poor” regions; the propagation of the “colloid-rich” region in three dimensions is responsible for structural arrest and strong viscoelastic enhancement when a critical film thickness approaches 16–25 particle layers.

The influence of clustering on the collision rate of inertial particles in a smooth random velocity field, mimicking the smaller scales of a turbulent flow, is analyzed. For small values of the ratio between the relaxation time of the particle velocity and the characteristic time of the field, the effect of clusters is to make more energetic collisions less likely. The result is independent of the flow dimensionality and is due only to the origin of collisions in the process of caustic formation.

By detailed analytical treatment of the shock dynamics in the Burgers turbulence with large scale forcing we calculate the velocity structure functions between pairs of points displaced both in time and space. Our analytical treatment verifies the so-called Taylor's frozen-flow hypothesis without relying on any closure and under very general assumptions. We discuss the limitation of the hypothesis and show that it is valid up to time scales smaller than the correlation time scale of temporal velocity correlation function. We support the analytical calculation by performing numerical simulation of the periodically kicked Burgers equation.