Dynamical correlations and collective excitations of Yukawa liquids

In dusty (complex) plasmas, containing mesoscopic charged grains, the grain-grain interaction in many cases can be well described through a Yukawa potential. In this Review we summarize the basics of the computational and theoretical approaches capable of describing many-particle Yukawa systems in the liquid and solid phases and discuss the properties of the dynamical density and current correlation spectra of three- and two-dimensional strongly coupled Yukawa systems, generated by molecular dynamics simulations. We show details of the $\omega(k)$ dispersion relations for the collective excitations in these systems, as obtained theoretically following the quasilocalized charge approximation, as well as from the fluctuation spectra created by simulations. The theoretical and simulation results are also compared with those obtained in complex plasma experiments.Comment: 54 pages, 31 figure

Correlational Origin of the Roton Minimum

We present compelling evidence supporting the conjecture that the origin of the roton in Bose-condensed systems arises from strong correlations between the constituent particles. By studying the two dimensional bosonic dipole systems a paradigm, we find that classical molecular dynamics (MD) simulations provide a faithful representation of the dispersion relation for a low- temperature quantum system. The MD simulations allow one to examine the effect of coupling strength on the formation of the roton minimum and to demonstrate that it is always generated at a sufficiently high enough coupling. Moreover, the classical images of the roton-roton, roton-maxon, etc. states also appear in the MD simulation spectra as a consequence of the strong coupling.Comment: 7 pages, 4 figure

Frequency Locking of an Optical Cavity using LQG Integral Control

This paper considers the application of integral Linear Quadratic Gaussian (LQG) optimal control theory to a problem of cavity locking in quantum optics. The cavity locking problem involves controlling the error between the laser frequency and the resonant frequency of the cavity. A model for the cavity system, which comprises a piezo-electric actuator and an optical cavity is experimentally determined using a subspace identification method. An LQG controller which includes integral action is synthesized to stabilize the frequency of the cavity to the laser frequency and to reject low frequency noise. The controller is successfully implemented in the laboratory using a dSpace DSP board.Comment: 18 pages, 9 figure

Robust filtering for a class of nonlinear stochastic systems with probability constraints

This paper is concerned with the probability-constrained filtering problem for a class of time-varying nonlinear stochastic systems with estimation error variance constraint. The stochastic nonlinearity considered is quite general that is capable of describing several well-studied stochastic nonlinear systems. The second-order statistics of the noise sequence are unknown but belong to certain known convex set. The purpose of this paper is to design a filter guaranteeing a minimized upper-bound on the estimation error variance. The existence condition for the desired filter is established, in terms of the feasibility of a set of difference Riccati-like equations, which can be solved forward in time. Then, under the probability constraints, a minimax estimation problem is proposed for determining the suboptimal filter structure that minimizes the worst-case performance on the estimation error variance with respect to the uncertain second-order statistics. Finally, a numerical example is presented to show the effectiveness and applicability of the proposed method

Higher order structure in a complex plasma

The direct experimental determination of the 3-point static structure function S(3)(k1, k2, k0) of a 2- dimensional dusty plasma liquid is presented. The measurements are complemented by molecular dynamics simulations of the system, using parameters (dust charge, plasma frequency, coupling and screening coefficients), which are derived from the experimentally obtained 2-point static structure function S(2), as well as the dynamic structure function and current-current fluctuation spectra. The experimental results of S(3) are in good agreement with those of the simulations, including the (low wavenumber) domain, where S(3) acquires negative values. The “Convolution Approximation” (giving S(3) in a factorized form of S(2) functions) clearly breaks down in this domain; however, it is found to be a useful aid for explaining the main features of the S(3)(k1, k2, k0) functions, for which (experimental and simulation) maps are presented at selected values of one of its arguments

Three Dimensional Monocular Human Motion Analysis in End-Effector Space

Abstract. In this paper, we present a novel approach to three dimen-sional human motion estimation from monocular video data. We employ a particle filter to perform the motion estimation. The novelty of the method lies in the choice of state space for the particle filter. Using a non-linear inverse kinematics solver allows us to perform the filtering in end-effector space. This effectively reduces the dimensionality of the state space while still allowing for the estimation of a large set of motions. Preliminary experiments with the strategy show good results compared to a full-pose tracker.

Excited states of heavy baryons in the Skyrme model

We obtain the spectra of excited heavy baryons containing one heavy quark by quantizing the exactly-solved heavy meson bound states to Skyrme soliton. The results are comparable to the recent experimental observations and quark model predictions, and are consistent with the heavy quark spin symmetry. However, somewhat large dependence of the results on the heavy quark mass strongly calls for the incorporation of the soliton-recoil effects.Comment: 24 pages, REVTeX, epsf.sty, 7 figures in uuencoded fil