The buffer gas cooling process and the properties of the cooled beam in a novel rf quadrupole ion beam guide with axial field was studied. The operation principle of the axial field quadrupole ion beam guide is similar to the quadrupole mass filter operating in AC only mode but the rods were segmented and differential DC biases were applied to produce the axial field. It was operated in buffer gas. / A Monte Carlo simulation was developed and the simulation results were compared with the experimental results. The beam distribution in a thermal equilibrium was assumed as the thermal equilibrium distribution in a simple harmonic motion with rf distortion and the assumption was confirmed by the Monte Carlo simulation. / The temperature of the cooled beam was measured with a beam profile, measurement system which consists of a miniature quadrupole ion beam guide aid a rotating semi-circular Faraday plate. The temperature of the cooled beam was measured to be 0.0424 +/- 0.0026 eV in the experiment while that of the simulated beam was 0.0372 +/- 0.0009 eV. The variation of beam temperature with beam current was 0.0153 +/- 0.0026 eV/nA. The maximum achieved ion transmission was 80%. The transmitted ion beam's energy spread was measured with a retarding potential energy analyzer to be less than 0.1 eV. The cooling time was 0.7 ms with 1V/ cm axial field and was observed to be very dependent on the ion current when there was no axial field.

Here a temperature stable optical fiber current sensor based on the Sagnac loop interferometer and a cavity formed from two Faraday rotation mirrors is developed and tested. To the best of the author's knowledge a cavity composed of two Faraday rotation mirrors has never been used for the measurement of alternating currents. For the first time, it is shown that the maximum Faraday rotation angle for a long, static optical fiber is input polarization insensitive. Also, linear birefringence is shown to quench this angle in long optical fiber. The polarization dynamics in an optical ground wire network, for a summer period and a fall period, are reported for the first time. The highest-speed polarization changes are attributed to the high-voltage power line, i.e., the electrical current. A novel spectral analysis polarization optical time domain reflectometry method, that uses an induced birefringent event, is shown to work in long optical fiber.

Abstract not available.

Weakly electric fish use a unique sensory modality in order to help them communicate, navigate and find prey. These fish emit electric discharges that are monitored by electroreceptors located in the fish's skin. Surrounding objects perturb these baseline transdermal potentials and create electric images. The study of these images has led to a better understanding of general sensory processing principles; however, many aspects of these fish's natural electrosensory environment remain unknown. To this end, a two-dimensional finite element model of Apteronotus leptorhynchus was created. Using this model, we suggest new ways by which electric fish are able to locate objects and propose that it is possible for these fish to extract useful information from their environment using their natural scanning behaviour. Our results also reveal important limitations in standard experimental paradigms that aim to mimic the effects of conspecifics. Alternative paradigms that will enable more realistic stimulation are suggested.

No description available.

No description available.

No description available.

I have investigated the influence of an ultra-thin Au interface layer on the magnetic anisotropy of Co-Pd and Co-Cu structures. Sandwich structures of the form X/Co/Y/Cu/Si(111), with (X, Y) = (Pd, Pd), (Au, Pd), (Pd, Au), (Cu, Cu), (Au, Cu), and (Cu, Au) were studied. For each structure, a Au layer of systematically varied thickness (t(Au)) was inserted at one Co interface. I also investigated Co/Pd and Co/Cu multilayer systems. For each Co-Pd sandwich structures a maximum is observed in the magnetic anisotropy for t(Au) = 1 to 1.5 atomic monolayer (ML). For the Co/Pd multilayer system, a maximum in coercivity occurs with tAu = 0.5 ML. For each Co-Cu sandwich structure except (X, Y) = (Cu, Au), a minimum in magnetic anisotropy is observed at t(Au) = 1 ML. For the Co/Cu multilayer system, a decrease in magnetoresistance was seen with increased tAu except in multilayers with a relatively thin Co layer thickness (∼3 ML) which display a peak in magnetoresistance is seen at tAu = 1 ML. I have also investigated the strain, surface alloying, and surface (interface) roughness of these systems using RHEED, XPS, and LAXD. Analysis of these measurements reveals some correlation between magnetic anisotropy and both strain and surface roughness. Based on my investigations, I conclude that the most likely cause for the non-monotonic changes seen in anisotropy is changes in the surface magnetocrystalline anisotropy. While strain and surface roughness may also play a role, I believe that the influence of the ultra-thin Au interlayer on the orbital hybridization and electronic environment at the interface is dominant.

In this thesis, the surface wave propagation along a periodically perforated conducting ground plane with dielectric coating has been studied for frequencies low enough for the ground plane to be approximated accurately by two bonded wire arrays. The field components have been obtained by using the z-directed electric and magnetic Hertz potentials which greatly simplify the application of the boundary conditions at the interfaces. The application of the appropriate boundary conditions on both sides of the plane of the wire mesh has resulted in a doubly infinite system of equations which, when truncated, can be solved for the wire currents and the propagation characteristics of the surface wave supported by the perforated ground plane. The plane is then modeled by a tensor impedance matrix relating the tangential components of the electric field to the components of the current density in the plane of the mesh. It has been shown that the surface wave propagation constant and the impedance matrix do not significantly depend on the direction of propagation for electrically small wire spacings. For such cases, it is shown that the components of the electric field can be directly related to the second order derivatives of the components of the current density flowing along the perforated ground plane.

The problem of electromagnetic scattering by a sphere on a layered substrate is treated and numerical results are presented. Initially, the Rayleigh limit, where the sphere radius is small compared to the wavelength, is considered. Closed-form expressions for the far-zone scattered fields are derived from the radiation of the induced dipoles in the sphere in the presence of the substrate, and these incorporate in a rather explicit manner the various parameters of the problem. The general case, where the ratio sphere radius/wavelength is arbitrary, is also considered. A rigorous formulation is used based on the Mie solution for the scattering by a sphere in a homogeneous medium and an extension of Weyl's method for dipole radiation in the presence of a flat surface. Numerical results obtained using the rigorous formulation for electrically small spheres are in very good agreement with those obtained using the Rayleigh approximate method.