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". It is concluded that the significant extra complexity and computational expense to achieve these relatively small improvements are likely to be unwarranted for many situations. 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.Comment: 11 pages, 6 figures, Conference paper: Signal and Data Processing of Small Targets 2010 (SPIE

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.Comment: 5 pages, 5 figures, 5 authors, published versio

icet - A Python library for constructing and sampling alloy cluster expansions

Alloy cluster expansions (CEs) provide an accurate and computationally efficient mapping of the potential energy surface of multi-component systems that enables comprehensive sampling of the many-dimensional configuration space. Here, we introduce \textsc{icet}, a flexible, extensible, and computationally efficient software package for the construction and sampling of CEs. \textsc{icet} is largely written in Python for easy integration in comprehensive workflows, including first-principles calculations for the generation of reference data and machine learning libraries for training and validation. The package enables training using a variety of linear regression algorithms with and without regularization, Bayesian regression, feature selection, and cross-validation. It also provides complementary functionality for structure enumeration and mapping as well as data management and analysis. Potential applications are illustrated by two examples, including the computation of the phase diagram of a prototypical metallic alloy and the analysis of chemical ordering in an inorganic semiconductor.Comment: 10 page

Convection-induced nonlinear-symmetry-breaking in wave mixing

We show that the combined action of diffraction and convection (walk-off) in wave mixing processes leads to a nonlinear-symmetry-breaking in the generated traveling waves. The dynamics near to threshold is reduced to a Ginzburg-Landau model, showing an original dependence of the nonlinear self-coupling term on the convection. Analytical expressions of the intensity and the velocity of traveling waves emphasize the utmost importance of convection in this phenomenon. These predictions are in excellent agreement with the numerical solutions of the full dynamical model.Comment: 5 page

Oscillateurs paramétriques optiques (instabilités spatio-temporelles et solitons dynamiques)

Les travaux effectués durant cette thèse apportent une contribution à l'étude de la dynamique spatio-temporelle des solitons optiques, candidats à de futures applications de transmission et de stockage d'informations. Tout d'abord, un modèle analytique d'Amplification Paramétrique Optique en régime nanoseconde, dans lequel la déplétion de la pompe est prise en compte, a permis de retrouver la structuration annulaire des profils transverses des champs en interaction, observée expérimentalement. Ce travail analytique a été complété par une étude numérique tenant compte d'effets transverses secondaires, comme la diffraction des faisceaux et la biréfringence du cristal non linéaire. Celle-ci s'est révélée cruciale quant à la détermination de zones de paramètres assurant une amélioration de la conversion d'énergie de la pompe vers les champs signal et complémentaire. Ensuite, nous avons mis en évidence dans un Oscillateur Paramétrique Optique (OPO) dégénéré pompé en continu et dans une valve à cristal liquide avec contre-réaction, une instabilité marquée par l'apparition d'un nouveau type de solitons spatiaux en réseau. Enfin, dans une configuration d'OPO contrapropagatif, nous avons démontré que l'association de l'amplification paramétriqueet de la contrapropagation des champs générait, à partir d'un pompage continu, des impulsions de type solitons temporels stables d'une durée de l'ordre de la picoseconde. Ce travail théorique ouvre la voie à la génération d'impulsions ultracourtes sans avoir recours à un milieu actif comme c'est actuellement le cas.LILLE1-BU (590092102) / SudocSudocFranceF

Discrete wavelength generation using modal interference in a diode-laser-pumped Tm³⁺-doped few-mode fibre

By employing a few-mode core fibre in a symmetric cladding-pumped fibre laser arrangement, intermodal interference occurs between the first two symmetric modes that are excited simultaneously. In free-running mode, without the placement of dielectric mirrors, the Tm³⁺-doped silica fibre laser oscillates on a number of fringes simultaneously. In a grating-tuned arrangement, the tuning curves comprise of a number of discrete fringes consistent with the theory associated with interference between the two excited symmetric modes propagating the length of the fibre.4 page(s