Experiments on the interaction of current channels in a laboratoryplasma: relaxation to the force-free state

A series of experiments on the dynamic interaction of two current channels has been performed in the large plasma device, a laboratory device at UCLA. The two current channels are formed by coating the cathode source nonuniformly and then biasing it with respect to an anode 10 m away. The experiment consists of two phases, one in which a net current is drawn through the plasma, and one in which the net current is zero. The current channels twist about each other, merge, and evolve toward a force-free state when a net current is drawn through the plasma. When the net current is zero the interaction between the channels is greatly reduced. The dynamics of the system are dominated by electron pressure and associated electrostatic fields. However, as the currents twist, a small amount of magnetic helicity is generated. The helicity and its temporal rate of change are computed and found to compare within experimental uncertainty to the predicted rate     

Fluctuation-induced interactions between dielectrics in general geometries

We study thermal Casimir and quantum nonretarded Lifshitz interactions between dielectrics in general geometries. We map the calculation of the classical partition function onto a determinant, which we discretize and evaluate with the help of Cholesky factorization. The quantum partition function is treated by path integral quantization of a set of interacting dipoles and reduces to a product of determinants. We compare the approximations of pairwise additivity and proximity force with our numerical methods. We propose a "factorization approximation" that gives rather good numerical results in the geometries that we study.     

A whistler wave interaction with a density striation: a laboratoryinvestigation of an auroral process

In a laboratory experiment, whistler waves are launched toward a field-aligned density gradient. Characteristic scale length and frequency ratios were carefully scaled to reproduce situations found in the auroral ionosphere. The experiment clearly shows the direct conversion of whistler waves to largely electrostatic lower hybrid waves     

Un détecteur commercial pour contrôler l'éluat des colonnes de chromatographie en phase liquide

Résumé Le détecteur décrit dans ce mémoire apporte une contribution aux progrès de la chromatographie en phase liquide. Avec un appareil de ce genre on peut étudier les paramètres des colonnes afin de pouvoir juger de leurs performances. L'existence de deux méthodes de détection élargit le champ d'application du détecteur à fil mobile. Le modèle à Argon [21] sera finalement te plus sensible de ces détecteurs à cause de sa plus grande efficacité d'ionisation alors que le modèle D.I.F. [22] a l'avantage d'une plus haute température de fonctionnement permettant de réduire le risque de condensation du soluté (ou de ses produits de pyrolyse) pendant l'expérience.     

Fast Algorithms for Finding O(Congestion + Dilation) Packet Routing Schedules

O (c+d) steps using constant-size queues, where c is the congestion of the paths in the network, and d is the length of the longest path. The proof, however, used the Lovász Local Lemma and was not constructive. In this paper, we show how to find such a schedule in time, with probability , for any positive constant β, where is the sum of the lengths of the paths taken by the packets in the network, and m is the number of edges used by some packet in the network. We also show how to parallelize the algorithm so that it runs in NC. The method that we use to construct the schedules is based on the algorithmic form of the Lovász Local Lemma discovered by Beck. Received: July 8, 1996     

A continuum, O(N) Monte Carlo algorithm for charged particles

We introduce a Monte Carlo algorithm for the simulation of charged particles moving in the continuum. Electrostatic interactions are not instantaneous as in conventional approaches, but are mediated by a constrained, diffusing electric field on an interpolating lattice. We discuss the theoretical justifications of the algorithm and show that it efficiently equilibrates model electrolytes and polar fluids. In order to reduce lattice artifacts that arise from the interpolation of charges to the grid we implement a local, dynamic subtraction algorithm. This dynamic scheme is completely general and can also be used with other Coulomb codes, such as multigrid based methods.     

Low-energy modes and Debye behavior in a colloidal crystal

We study the vibrational spectrum and the low-energy modes of a three-dimensional colloidal crystal using confocal microscopy. This is done in a two-dimensional cut through a three-dimensional crystal. We find that the observed density of states is incompatible with the standard Debye form in either two or three dimensions. These results are confirmed by numerical simulations. We show that an effective theory for the projections of the modes onto the two-dimensional cut describes the experimental and simulation data in a satisfactory way.