Neil P. Oxtoby

Molecular-Dynamics Simulations of Dynamic Phenomena in Complex Plasmas

Complex plasmas consist of micrometer-sized spheres immersed into an ordinary ion-electron plasma. They exist in solid, liquid, and gaseous states, sustain particle-mediated waves, and exhibit a range of nonlinear and dynamic effects. Here, we present a numerical study of nonlinear-wave steepening (tsunami effect), interaction of solitons, and shock-wave propagation in monolayer complex plasmas. The simulated results are found to be in a good agreement with the experiments. It was also found that the simulation using a tenth-order confinement potential produced more homogeneous lattices with fewer defects than that with the conventional parabolic potential.

Ideal Gas Behavior of a Strongly Coupled Complex (Dusty) Plasma

In a laboratory, a two-dimensional complex (dusty) plasma consists of a low-density ionized gas containing a confined suspension of Yukawa-coupled plastic microspheres. For an initial crystal-like form, we report ideal gas behavior in this strongly coupled system during shock-wave experiments. This evidence supports the use of the ideal gas law as the equation of state for soft crystals such as those formed by dusty plasmas.

Tracking shocked dust: State estimation for a complex plasma during a shock wave

We consider a two-dimensional complex (dusty) plasma crystal excited by an electrostatically-induced shock wave. Dust particle kinematics in such a system are usually determined using particle tracking velocimetry. In this work we present a particle tracking algorithm which determines the dust particle kinematics with significantly higher accuracy than particle tracking velocimetry. The algorithm uses multiple extended Kalman filters to estimate the particle states and an interacting multiple model to assign probabilities to the different filters. This enables the determination of relevant physical properties of the dust, such as kinetic energy and kinetic temperature, with high precision. We use a Hugoniot shock-jump relation to calculate a pressure-volume diagram from the shocked dust kinematics. Calculation of the full pressure-volume diagram was possible with our tracking algorithm, but not with particle tracking velocimetry.

Quantum Filtering One Bit at a Time

In this Letter we consider the purification of a quantum state using the information obtained from a continuous measurement record, where the classical measurement record is digitized to a single bit per measurement after the measurements have been made. Analysis indicates that efficient and reliable state purification is achievable for one- and two-qubit systems. We also consider quantum feedback control based on the discrete one-bit measurement sequences.

Tracking interacting dust: comparison of tracking and state estimation techniques for dusty plasmas

When tracking a target particle that is interacting with nearest neighbors in a known way, positional data of the neighbors can be used to improve the state estimate. Effects of the accuracy of such positional data on the target track accuracy are investigated in this paper, in the context of dusty plasmas. In kinematic simulations, notable improvement in the target track accuracy was found when including all nearest neighbors in the state estimation filter and tracking algorithm, whereas the track accuracy was not significantly improved by higher-accuracy measurement techniques. The state estimation algorithm, involving an extended Kalman filter, was shown to either remove or significantly reduce errors due to pixel-locking. For the purposes of determining the precise particle locations, it is concluded that the simplified state estimation algorithm can be a viable alternative to using more computationally-intensive measurement techniques.

Visualizing a Dusty Plasma Shock Wave via Interacting Multiple-Model Mode Probabilities

Particles in a dusty plasma crystal disturbed by a shock wave are tracked using a three-mode interacting multiple model approach. Color-coded mode probabilities are used to visualize the shock wave propagation through the crystal.

Interacting multiple model estimators for tracking thousands of interacting, small targets in a complex plasma

Tracking a large number of small targets is a challenging task. This work considers tracking approximately 3000 micron-sized particles in a complex plasma. Inter-particle screened-Coulomb interactions increase the complexity of the tracking problem, which is further complicated by highly nonlinear dynamics - a shock wave. Subsets of the particles are tracked concurrently by Interacting Multiple Model estimators, with the results combined off-line. State estimation is performed by an extended Kalman filter. Estimator performance is quantified on synthetic data, with discussion focussing on aspects of the Interacting Multiple Model.

Tracking system to maximize the engagement envelope of a data linked weapon

This paper presents the results of an integrated target tracking, pursuit and intercept strategy. It is designed to maximize the overlap between the engagement envelope of a data linked weapon and the possible predicted locations of an agile target. Once the target track has been initialized, a Markov Model calculates all possible locations of the target up to the time of intercept, approximately 30 seconds from launch. These locations and associated probabilities are updated during the tracking process. This includes target maneuvers, which are detected using an IMM estimator. The engagement envelope is maximized at fixed points in time. In doing so the intercept decision is delayed until, there is a high probability of a successful interception.