<p> Edge magnetoplasmons (EMPs) and pinning mode resonances in two dimensional electron systems (2DESs) can both be thought of as lower hybrid modes of cyclotron and plasma resonances. This dissertation describes low temperature microwave spectroscopy of both of these modes. EMPs have oscillating charge confined at the 2DES edge by the combination of the perpendicular magnetic field and the electrostatic potential that produces the edge. Pinning mode resonances are from electron solids oscillating against confinement provided by disorder in the bulk of the 2DES. </p><p> The first part of this dissertation concerns the search for a mode similar to an EMP but confined solely by a linear magnetic inhomogeneity in the perpendicular magnetic field (<i>B_z</i>). While we do not observe such an excitation, we do observe a marked reduction in the velocity of an EMP in the presence of a <i>B_z</i>-inhomogeneity. </p><p> In the second part of this dissertation, we investigate pinning modes in &ldquo;wide'' quantum well samples, for which the effective electron-electron interaction is softened at short range due to the vertical extent of the wavefunction. We observe a pinning mode resonance whose peak frequency (<i>f_pk</i>) vs Landau level filling (&nu;) shows an anomalous increase as &nu; moves away from &nu; = 1 under roughly the same conditions as anomalous quantum Hall effects observed previously in DC transport. A region of &nu; with enhanced <i>f_pk</i> is interpreted as evidence for a new electron solid phase.</p>

<p> This dissertation proposes three novel bandpass filter structures to protect systems exposed to damaging levels of electromagnetic (EM) radiation from intentional and unintentional high-power microwave (HPM) sources. This is of interest because many commercial microwave communications and sensor systems are unprotected from high power levels. Novel technologies to harden front-end components must maintain existing system performance and cost. The proposed concepts all use low-cost printed circuit board (PCB) fabrication to create compact solutions that support high integration.</p><p> The first proposed filter achieves size reduction of 46% using a technology that is suitable for low-loss, narrowband filters that can handle high power levels. This is accomplished by reducing a substrate-integrated waveguide (SIW) loaded evanescent-mode bandpass filter to a half-mode SIW (HMSIW) structure. Demonstrated third-order SIW and HMSIW filters have 1.7 GHz center frequency and 0.2 GHz bandwidth. Simulation and measurements of the filters utilizing combline resonators prove the underlying principles.</p><p> The second proposed device combines a traditional microstrip bent hairpin filter with encapsulated gas plasma elements to create a filter-limiter: a novel narrowband filter with integral HPM limiter behavior. An equivalent circuit model is presented for the ac coupled plasma-shell components used in this dissertation, and parameter values were extracted from measured results and EM simulation. The theory of operation of the proposed filter-limiter was experimentally validated and key predictions were demonstrated including two modes of operation in the on state: a constant output power mode and constant attenuation mode at high power. A third-order filter-limiter with center frequency of 870 MHz was demonstrated. It operates passively from incident microwave energy, and can be primed with an external voltage source to reduce both limiter turn-on threshold power and output power variation during limiting. Limiter functionality has minimal impact on filter size, weight, performance, and cost.</p><p> The third proposed device demonstrates a large-area, light-weight plasma device that interacts with propagating X-band (8-12 GHz) microwave energy. The structure acts as a switchable EM aperture that can be integrated into a radome structure that shields enclosed antenna(s) from incident energy. Active elements are plasma-shells that are electrically excited by frequency selective surfaces (FSS) that are transparent to the frequency band of interest. The result is equivalent to large-area free-space plasma confined in a discrete layer. A novel structure was designed with the aid of full-wave simulation and was fabricated as a 76.2 mm square array. Transmission performance was tested across different drive voltages and incidence angles. Switchable attenuation of 7 dB was measured across the passband when driven with 1400 V_pp at 1 MHz. Plasma electron density was estimated to be 3.6 &times; 10¹² cm^-3 from theory and full-wave simulation. The proposed structure has potential for use on mobile platforms.</p>

<p> Electromagnetic equations pertaining to electrically small dipole antennas and electrically small monopole antennas with small circular ground planes are reviewed. Two electrically small antenna designs are analyzed numerically and the results are compared. The first is a frequency agile version of the two-dimensional (2D) planar Egyptian axe dipole (EAD) antenna. The second is its three-dimensional (3D) counterpart. The frequency agile performance characteristics of both the 2D and 3D EAD designs are studied and compared. The potential for non-Foster augmentation to achieve large instantaneous fractional impedance bandwidths is detailed for each antenna. In addition, details are given on how to run frequency agile simulations in both ANSYS HFSS and Agilent's ADS. Details are also provided on how to generate an antenna's non-Foster |S₁₁| and radiation efficiency curves using HFSS, and how to generate an antenna's non-Foster |S₁₁| curve using ADS. </p>

Dielectric losses and dielectric constants at radio frequencies for nitrobenzene, water and xylene. The method of resistance variation was used to measure the phase difference psi and dielectric constant K for frequencies between 2 x 105 and 14 x 105 cycles/sec. Special cells were required. (1) Variation with frequency. The results agree approximately with the equations: For carefully dried nitrobenzene at 30&deg;C, psi = .028&deg; + 6.03 x 104/f; for distilled water at 23.5&deg;, psi = 0.8&deg; + 2.09 x 106/ f. These indicate that in addition to the true dielectric loss there is a leakage through the liquid proportional to 1/f. For xylene, psi was too small to measure, less than .01&deg; at 3 x 10 5 cycles. K was found to be practically independent of the frequency, being 2.24 for xylene and of the order of 100 for water. (2) Variation with temperature, for nitrobenzene. K decreased from 42 at 20&deg; to 24 at 14.2&deg;, while psi increased in the same range in the ratio of 7 to 1. These values were obtained, however, for a sample of nitrobenzene for which psi was 12 times as great as for a carefully dried sample.

Interchange instability is an important dynamic mechanism in plasma physics and has been advanced as an explanation of a variety of phenomena in the magnetospheric physics. This work derives a new instability criterion for interchange motion in a plasma that connects to a finite-conductivity wall. The new criterion is for a arbitrary magnetic &lt;beta> (ratio between thermal pressure and magnetic pressure averaged within flux tube) system, which contains background shear flow, whereas most classical criteria did not consider all of these conditions. Thus this new result is more appropriate to be applied in a real plasma system like the Earth's plasma sheet, which exhibits a wide range of &lt;beta> values and background shear flow. Based on magnetosphere-ionosphere coupling theory and ideal MHD adiabatic theory in the inner plasma sheet, a theoretical model was constructed in the ionosphere region. A finite boundary layer was set up between two regions of uniform-content flux tubes, and a perturbation on the boundary layer was investigated. Both analytical and numerical approaches are used to study the stability of the plasma configuration. The flux tubes are interchange unstable when the angle between the gradient of flux tube volume, defined as V = dsB , and the gradient of adiabatic specific entropy PV 5/3 is larger than arccos&lt;b&gt; 1lnPV5/3 1ln V/ 21+5&lt;b&gt;/6 . Combining this new criterion with the statistical calculation of the plasma sheet characteristics by using the Tsyganenko magnetic field model (the 1996 version) and the Tsyganenko-Mukai plasma model, it is found that, in the Earth's inner plasma sheet, the angle between the two gradients is typically of the order of 15&deg;, which indicates that the statistical-average Earth's plasma sheet is interchange stable. This result is applicable to the study of interchange instability and plasma transport in the global-MHD and other large-scale magnetosphere simulations, and provides a theoretical base for the study of analogous dynamic processes in the magnetospheres of other planets like Jupiter.

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.