Abstract Not Available.

Abstract Not Available.

This paper is an account of an experiment designed to determine the binding energy of the deuteron by a method which is relatively insensitive to uncertainties in the energy-range relation for protons of low energy. The protons, produced by the disintegration of deuterium by Th C″ gamma-radiation, were observed in a low-pressure cloud chamber in a strong magnetic field. The curvatures of the tracks allowed the calculation of the corresponding kinetic energies. The final value of the binding energy as got by this experiment is VB=2.17+/- 0.05x106 electron-volts, which is in excellent agreement with the values previously got by Bethe (from the data of Chadwick, Feather and Bretscher) and by J. R. Richardson and Emo.

Abstract Not Available.

Studies were performed to determine the mechanism whereby carbon nanotubes form in an electric arc. Various experimental parameters including cathode cooling, composition, and diameter were varied. It was found that tube-tube sintering is a primary reason for tube defects, and that this effect can be minimized by reducing the temperature of the cathode where the tubes grow. The investigations also led to the pseudo-convection growth model, which explains many features of the cathode deposits in which tubes form. Various other means of nanotube growth were studied. Possible uses for these nanotubes were also explored.

In complex robotic operating environments in which robots must cooperate in a flexible and event-driven manner, a cooperative distributed environment for intelligent control is required. We develop a realistic technique for going beyond the model of a central controller for a multi-robot environment and replacing it with a schema of interacting, reconfigurable, cooperating robots. This schema provides the following main features: an open model of cooperation capable of supporting a wide variety of representations and algorithms for planning and executing tasks, a dynamic environment in which physical and reasoning capabilities can be added, removed, and reconfigured while performing tasks to best utilize limited resources, the capability of detecting and correcting errors and failures, a rich interaction model capable of handling the complexity and variety of communications and cooperation necessary between intelligent agents, and a realistic method of achieving global goals from localized actions. We formulate this model of interacting robots as a social system. We define this social system by specifying the members of the society, the interactions of these members, and the fundamental guidelines of the society used to judge the actions of the members. We successfully implement a prototype system that incorporates these concepts, and demonstrate it on some example situations involving multiple cooperating robots. Using the results of these examples, we also develop a qualitative analysis of this model against two other common models of intelligent control for multi-robot systems.

In this thesis we propose methods for preconditioning Krylov subspace methods for solving the integral equation formulation of the Helmholtz partial differential equation for modeling scattered waves. An advantage of using an integral formulation is that only the scattering obstacle is discretized and the outgoing boundary conditions are automatically satisfied. Furthermore, convergence is dictated by the wave number kappa with only a mild dependence on the discretization. However such methods are increasingly computationally expensive for increasing values of kappa. This cost is due to GMRES iteration counts that increase like O(kappa2), for a linear system that is dense with dimension N = O(kappa 4). GMRES is slow due to a small subset of the spectrum that is well separated, a part of which approaches the origin as kappa increases. The troublesome subset corresponds to low frequency eigenfunctions which can be approximated using coarse meshes. We propose a preconditioner based on deflating this subset of the spectrum which we evaluate by interpolating coarse mesh approximations of the spectrum. We show that for discretizations of less than one node per wavelength, we can effectively precondition the full problem over a sufficiently resolved mesh.

The optical properties of plasmon resonant metallic nanoparticles are of great interest because of their ability both to control optical fields on the nanometer scale and to function as sensitive indicators of their local environment. I investigate the relationship between the dielectric function of a metal and the optical properties of the constituent metallic nanoparticle. Using a Drude shell - silica core nanoshell geometry, I examine how systematic changes in the parameters of the Drude dielectric function affect the near and far field properties of the nanoparticle. The nanoshell geometry allows separation of intrinsic properties and extrinsic phase retardation, or finite size, effects.

No description available.

HF-waves incident on an overdense (HF-frequency < penetration frequency) ionosphere are known to produce large scale electron density irregularities. It is predicted that similar irregularities are formed during underdense HF-modification. The propagation of UHF radio waves originating from radio stars will be affected by such irregularities in the ionosphere. The interest in a scintillation experiment is twofold. One may obtain information on the electron density irregularies and one may learn about the propagation of radio waves through such a perturbed medium. A thin screen (diffractive) theory is derived which allows to draw conclusions on the electron density irregularities from the intensity fluctuations measured on the ground if the phase perturbations are much less than one radian. Since radio stars suitable for scintillation measurements at UHF are very faint an antenna with a large collection area is required. The observations reported in this dissertation were performed with the 300m diameter spherical reflector of the Arecibo Observatory. Successful observations were performed at 430 MHz and at 1400 MHz. Intensity fluctuations at such high frequencies measured with a large antenna suffer severe filtering in the thin phase screen regime. The theory presented in this dissertation includes these filtering effects. Many observations agree with the predictions of that theory. Some observations indicate that refraction effects have to be included to explain the data. HF-induced electron density irregularities were only observed during overdense heating. Several attempts to detect irregularities at an observing frequency of 430 MHz during underdense heating (HF-frequencies 1.1 to 2 times penetration frequency) failed. All the measurements reported in this dissertation are therefore during overdense heating except for the measurement on the 22 September 1980 whichs shows a transition from underdense to overdense HF-modification. Attempts were made to measure electron density irregularities at an observing frequency of 2380 MHz due to overdense heating but the fluctuations were too weak to be discriminated against instrumental uncertainties. The formation time for the irregularities after the HF-power was turned on was (TURN)25 seconds. Their lifetime after the HF-power was turned off was on the order of hours. The electron density perturbations appear to exceed 1% at times. One observation on 11/12 September 1980 reveals that the density perturbation actually corresponds to a depletion.