Corrections to the classically predicted electrical conductivity in normal metals arise due to the quantum mechanical properties of the conduction electrons. These corrections provide multiple experimental tests of the conduction electrons' quantum phase coherence. I consider if independent measurements of the phase coherence via different corrections are quantitatively consistent, particularly in systems with spin-orbit or magnetic impurity scattering. More precisely, do independent quantum corrections to the classically predicted conductivity depend identically on the ubiquitous dephasing mechanisms in normal metals? I have inferred the coherence lengths from the weak localization magnetoresistance, magnetic field-dependence of time-dependent universal conductance fluctuations, and magnetic field-dependent universal conductance fluctuations, three observable quantum corrections, in quasi one- and two-dimensional AuPd wires and quasi-1D Ag and Au wires between 2 and 20 K. While the coherence lengths inferred from weak localization and time-dependent universal conductance fluctuations are in excellent quantitative agreement in AuPd, the strong quantitative agreement is apparently lost below a critical temperature in both Ag and Au. Such a disagreement is inconsistent with current theory and must be explained. I developed a hypothesis attributing the coherence length discrepancy seen in Ag and Au to a crossover from the saturated to unsaturated time-dependent conductance fluctuation regime. Two experimental tests were then employed to test this hypothesis. One test examined the effects of a changing spin-flip scattering rate in Au while the second examined how passivation of the two level systems responsible for time-dependent conductance fluctuations at the surface of a Au nanowire affects the inferred coherence lengths. The results of the two tests strongly indicate that the observed disagreement in Au (and likely Ag) is indeed due to a crossover from saturated to unsaturated time-dependent conductance fluctuations.

This thesis describes the background behind and early results from an instrument designed to measure atmospheric electrical currents. Preliminary data presented herein (including the marked similarity in the signals from the two arrays, the noticeable Carnegie curve, and the correlation between the measured electric field and current at the same site) demonstrate the proper functioning of the instrument. A description of global circuit theory and Antarctic climate illuminate the deployment decisions. Also presented are a preliminary study suggesting that the instrument is affected by the presence of an electrode layer, and some of the mathematical and theoretical relationships required to determine physical variables from the raw data.

We have successfully trapped $\sp7$Li in a vapor cell magneto-optical trap (MOT). The trap is studied in detail and the parameters are measured from the experiment. The trapping mechanism has been understood in terms of the radiation force and a simple one dimensional model is used in interpreting and predicting the experimental results. The cold-cold atom collision rate coefficient is measured in a beam MOT. The two collision mechanisms, fine structure changing and radiative escape, are discussed in a molecular picture. One of the channels, the fine structure changing channel, can be turned on and off by the experimental conditions, namely the laser intensity in this experiment. The rate coefficient for each mechanism has been determined from the experiment.

The magnetospheric cusp is the principal site of solar wind plasma entry into the magnetosphere, and plasma entry through this region constitutes an important source of plasma in the Earth's magnetosphere. The goal of this dissertation is to understand the dynamics and location of the plasma injection process and the subsequent transport of this plasma throughout the magnetosphere by numerically modeling the cusp in terms of the "zeroth-order" physical processes. A quantitative model of ion injection and number density in the magnetospheric cusp is developed, incorporating mutually consistent electric and magnetic fields. This work extends the method of Onsager et al., who calculated precipitating particle fluxes from quantitative models of magnetosheath flow and ion acceleration at the magnetopause. We have simulated cusp ion energy-latitude spectrograms at mid-altitude. Both the large-scale energy-latitude dispersion and the embedded small-scale energy-pitch-angle V signatures are clearly evident in these simulated spectrograms. Our results show that a much finer V microsignature is obtained when the ion injection source is restricted to a small region. However, the cutoff of the plasma injection at the magnetosheath sonic line also yields relatively narrow V's, even without restricting the injection region to a small locus on the magnetopause. This effect is most noticeable in winter conditions. To explain the frequently observed multiple cusp ion injections that appear to overlap on the same field lines, we present two independent approaches. Our simulations have successfully reproduced the meso-scale cusp ion overlapping structure by firstly incorporating temporal effects of separate bursts of reconnection which last 1.4 min and are 3.6 and 4.6 mins apart; and secondly by introducing a time-dependent magnetosheath plasma density variation along the magnetopause to our cusp model, even with assuming steady interconnection. Our cusp injection model which returns precipitating particle flux also allows us to calculate the number density profile in the cusp. Our result along the noon-meridian cusp demonstrates that the density gradient is sharper on the equatorward edge than the poleward edge, and that the equatorward edge of the density structure shifts to higher latitude at lower altitude.

This investigation explores the connection between the open polar cap magnetic flux phiPCF and interplanetary conditions. phi PCF is determined from GGS/Polar VIS Earth Camera far ultraviolet observations of the aurora borealis. Observations from the GGS/Wind SWE and MFI instruments are used to characterize the interplanetary conditions. Additional observations from the IMP-8 PLA and MAG instruments are used to evaluate solar wind propagation time delay estimation methods so that the GGS/Wind observations can be better associated with the GGS/Polar observations. This allows the GGS/Wind observations to be used to estimate the polar cap potential &phis;PCP values associated with the GGS/Polar phiPCF values. Statistical methods are applied to determine a proxy relationship between &phis;PCP and phiPCF. The Rice Field Model (RFM) is modified to accept phi PCF as a configuration parameter, and RFM polar caps are produced using phi PCF determined both directly from the GGS/Polar images and by the proxy relationship from the GGS/Wind data. The RFM is able to produce polar caps with the same areas and open magnetic fluxes as the GGS/Polar observations, but the agreement in the polar cap shapes and locations leaves opportunities for further improvements.

A general technique for solving Maxwell's equations exactly, based on expansion of the solution in a complete set of vector basis functions has been developed. These vector eigenfunctions are derived from the complete set of separable solutions to the scalar Helmholtz equation in a particular coordinate system and are shown to form a complete set. The method is applicable to a variety of problems including the study of near and far field electromagnetic scattering from particles with arbitrary shapes, plasmon resonances in spherical nanoparticles with spherically concentric 'shells' and the calculation of plasmon resonances in the sphere-plane geometry. An exact method for solving the inhomogenous Maxwell's equation (i.e., in the presence of charges and currents) is also outlined.

Low frequency noise in giant magnetoresistive spin valves has been studied as a means of optimizing signal to noise ratios and characterizing device performance. The devices studied were sputter deposited NiFe/Cu/NiFe/FeMn spin valves with D R/R ∼ 4%. Static measurements demonstrated a strong dependence of the magnetic coupling and giant magnetoresistance (GMR) ratio on the thickness and quality of the Cu spacer layer and the bottom NiFe layer (free layer). These parameters were varied to determine how the noise in spin valve sensors would be affected. Noise power spectra were measured in patterned spin valves. The noise was observed to have a 1/f slope at low frequencies. The fluctuation-dissipation relation relating thermal fluctuations in magnetization to the resistance fluctuations was used to explain the origin of the 1/f noise. The noise was found to be sensitive to the anisotropy and defect density of the free layer. The noise was minimized for spin valves operating with parallel anisotropy axes and an applied field aligned along the hard axis of magnetization. Dynamic fields were used to measure the Barkhausen noise in the sense layer of the spin valve. The low frequency noise in the presence of dynamic fields was much greater than the 1/f noise background. Clustering of Barkhausen jumps was used to explain the observed dependence of the noise power on the magnitude and frequency of the applied field. Higher frequency signals resulted in lower Barkhausen noise. The noise was reduced when the applied field was aligned along the hard axis of magnetization.

Electromagnetic levitation, which can provide rapid heating and melting, homogeneity of melt and minimal specimen contamination, is an important branch of containerless processing. The longitudinal electromagnetic levitator is a new type of levitation device, which was invented recently and has a potential to become a containerless manufacturing processing tool. It has some unique advantages, such as good visual access to the sample, capability to support multiple samples, large loads and cylindrical shape sample availability. In this thesis, a brief review of the history and application of electromagnetic levitation is presented. Then the detailed theoretical analysis coupled with experimental work validating the theoretical models of the longitudinal electromagnetic levitator are presented. First, a new electric current model is introduced, which is more appropriate for the computation of the electromagnetic force field in the levitated specimen. Based on this new model, the essential equations for the electromagnetic field and the lifting force field for a cylindrical sample are derived, the current density distribution and the averaged power in the sample are analyzed. Additionally, both lifting force and lifting capacity for the longitudinal levitator are investigated analytically, and compared with experimental data with good agreement. These theoretical predictions can be used to design longitudinal levitators, to select suitable material for levitation, and to provide the framework for further investigation of materials processing using the longitudinal levitator. In addition, temperature distribution simulation for the sample levitated in the longitudinal electromagnetic levitator is implemented by analytical and numerical ways. Isothermal case, steady state and lumped system are discussed respectively as some special cases. The exact solution and numerical simulation of the temperature distribution for the levitated sample are compared with good agreement. The flow motion within the levitated sample and the numerical simulation of the temperature distribution with flow convection has also been investigated. The results provide important information of the levitation phenomena which are very useful for scientific and engineering applications, especially for materials processing.

The plasmon resonance in metallic nanoshells can be used to efficiently harvest solar energy and convert it into thermal or electronic form. Possible applications include improved optical coupling into silicon photodiodes, solar water heaters, and photocatalysis. We use standard optimization algorithms to theoretically determine the best mixture of different nanoshell species ([core, shell] sizes) for two practical scenarios. We show that a mixture of nanoshell species [r1, r2] = [47, 58] nm and [r1, r2] = [28, 42] run in a 6:5 volume ratio is optimal for absorbing AM 1.5 sunlight when deposited on a silicon surface. Surprisingly, we find that a single particle species is very good for scattering AM 1.5 light on a glass surface, and that very little benefit is gained by mixing different shells. Assumptions and approximations made in the analysis are discussed.

The explosive growth in the information technology industry requires high-performance optical sources. In recent years, wavelength-tunable optical pulse sources are of interest for applications in optical instrumentation, communications, and sensing. This thesis demonstrates and analyzes the generation of wavelength tunable, picosecond pulses from mode-locked semiconductor fiber ring lasers. One structure using an intracavity electro-optic modulator and the other an injected optical control signal, are investigated and experimentally characterized. A single or superimposed linearly chirped fiber Bragg gratings are used to provide wavelength selectivity, tunability, and multi-wavelength operation. The semiconductor optical amplifier as the gain media makes it possible to obtain stable simultaneous oscillation of several wavelengths at any wavelength band with very small channel spacing. We have successfully generated picosecond pulses at one or two wavelengths over the reflection bandwidth(s) of the grating(s) by simply changing the modulation frequency.