Enhancement of mobilities in a pinned multidomain crystal

Mobility properties inside and around degenerate domains of an elastic lattice partially pinned on a square array of traps are explored by means of a fully controllable model system of macroscopic particles. We focus on the different configurations obtained for filling ratios equal to 1 or 2 when the pinning strength is lowered. These theoretically expected but never observed configurations are degenerated, which implies the existence of a multidomain crystal. We show that the distinction between trapped and untrapped particles that is made in the case of strong pinning is not relevant for such a weaker pinning. Indeed, one ought to distinguish between particles inside or around the domains associated to positional degeneracies. The possible consequences on the depinning dynamics of the lattice are discussed.Comment: 7 pages, 10 figures Version 2 : longer versio

Single File Diffusion enhancement in a fluctuating modulated 1D channel

We show that the diffusion of a single file of particles moving in a fluctuating modulated 1D channel is enhanced with respect to the one in a bald pipe. This effect, induced by the fluctuations of the modulation, is favored by the incommensurability between the channel potential modulation and the moving file periodicity. This phenomenon could be of importance in order to optimize the critical current in superconductors, in particular in the case where mobile vortices move in 1D channels designed by adapted patterns of pinning sites.Comment: 4 pages, 4 figure

Determination of the interactions in confined macroscopic Wigner islands: theory and experiments

Macroscopic Wigner islands present an interesting complementary approach to explore the properties of two-dimensional confined particles systems. In this work, we characterize theoretically and experimentally the interaction between their basic components, viz., conducting spheres lying on the bottom electrode of a plane condenser. We show that the interaction energy can be approximately described by a decaying exponential as well as by a modified Bessel function of the second kind. In particular, this implies that the interactions in this system, whose characteristics are easily controllable, are the same as those between vortices in type-II superconductors.Comment: 8 pages, 8 figure

Boundary sentinels in cylindrical domains

We study a model describing vibrations of a cylindrical domain with thickness e > 0. A characteristic of this model is that it contains “pollution terms” in the boundary data and “missing terms” in the initial data. The “method of sentinels” of J.L. Lions [7] is followed to construct a sentinel using the observed vibrations on the boundary. Such a sentinel, by construction, provides information on pollution terms independent of missing terms. This requires resolution of initial-boundary value problems with nonzero boundary data of mixed type and an exact controllability problem. Further, we characterize so called “stealthy pollution terms” present in the model

Exact controllability of vibrations of thin bodies

In this paper, we address the problem of exact controllability of the wave equation in three dimensional domains which are thin in one direction. We prove the existence of exact controls and analyze their asymptotic behaviour as thickness parameter goes to zero. We characterize their limit as the solution of an exact controllability problem in two dimension

Boundary sentinels in cylindrical domains

We study a model describing vibrations of a cylindrical domain with thickness e > 0. A characteristic of this model is that it contains "pollution terms" in the boundary data and "missing terms" in the initial data. The "method of sentinels'' of J.L. Lions [7] is followed to construct a sentinel using the observed vibrations on the boundary. Such a sentinel, by construction, provides information on pollution terms independent of missing terms. This requires resolution of initial-boundary value problems with non-zero boundary data of mixed type and an exact controllability problem. Further, we characterize so called "stealthy pollution terms" present in the model

Local Symmetries and Order-Disorder Transitions in Small Macroscopic Wigner Islands

The influence of local order on the disordering scenario of small Wigner islands is discussed. A first disordering step is put in evidence by the time correlation functions and is linked to individual excitations resulting in configuration transitions, which are very sensitive to the local symmetries. This is followed by two other transitions, corresponding to orthoradial and radial diffusion, for which both individual and collective excitations play a significant role. Finally, we show that, contrary to large systems, the focus that is commonly made on collective excitations for such small systems through the Lindemann criterion has to be made carefully in order to clearly identify the relative contributions in the whole disordering process.Comment: 14 pages, 10 figure

Configurational entropy of Wigner crystals

We present a theoretical study of classical Wigner crystals in two- and three-dimensional isotropic parabolic traps aiming at understanding and quantifying the configurational uncertainty due to the presence of multiple stable configurations. Strongly interacting systems of classical charged particles confined in traps are known to form regular structures. The number of distinct arrangements grows very rapidly with the number of particles, many of these arrangements have quite low occurrence probabilities and often the lowest-energy structure is not the most probable one. We perform numerical simulations on systems containing up to 100 particles interacting through Coulomb and Yukawa forces, and show that the total number of metastable configurations is not a well defined and representative quantity. Instead, we propose to rely on the configurational entropy as a robust and objective measure of uncertainty. The configurational entropy can be understood as the logarithm of the effective number of states; it is insensitive to the presence of overlooked low-probability states and can be reliably determined even within a limited time of a simulation or an experiment.Comment: 12 pages, 8 figures. This is an author-created, un-copyedited version of an article accepted for publication in J. Phys.: Condens. Matter. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher-authenticated version is available online at 10.1088/0953-8984/23/7/075302.

A sociocognitive approach to social problem solving in patients with traumatic brain injury: a pilot study

PRIMARY OBJECTIVE: Patients with traumatic brain injury (TBI) have difficulty dealing with the social world and may display inappropriate social behavior that negatively affects their social and occupational rehabilitation. This difficulty may be explained by a social problem-solving (SPS) impairment, but little is yet known about the cognitive processes involved in the ability to solve social problems. Several publications have demonstrated that executive functions are related to social problem solving, but the role of social cognition needs to be confirmed. The present pilot study examined the expected relationships between SPS ability and both social cognition and social behavioral skills. RESEARCH DESIGN: We compared the performances of 15 patients with TBI on SPS, theory-of-mind and social behavior tasks with those of 25 matched healthy controls. MAIN OUTCOMES AND RESULTS: Our results showed for the first time that impaired social problem solving is associated with a theory-of-mind deficit, but surprisingly not with executive impairment. There was no evidence that SPS deficits predict social behavioral disorders. CONCLUSIONS: Studying social problem solving in patients with TBI may inform the design of more appropriate methods of social rehabilitation