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A novel imaging modality is introduced, using Radio-Frequency Longitudinally Detected Electron Spin Resonance (RF-LODESR), capable of providing qualitative and semi-quantitative information on a variety of parameters reflecting physiological function, the most significant being tissue oxygenation. Effective spin-lattice (T_1e*) and spin-spin (T_2e*) electronic relaxation time maps of the abdomen of living 200 g rats were generated after intravenous administration of a triarylmethyl free radical (TAM). These maps were used to evaluate oxygen distribution. Differences between the liver, kidneys and bladder were noted. Conclusions were made regarding distribution, perfusion and excretion rate of the contrast medium. Ligature induced anoxia in the kidney was also visualised. LODESR involves transverse ESR irradiation with a modulated excitation and observing oscillations in the spin magnetisation parallel to the main magnetic field. The T_1e* and T_2e* maps were calculated from a set of LODESR signal phase images collected at different detection frequencies. Each phase image also provides qualitative information on tissue oxygen level without any further processing. Additionally, a new method is introduced for measuring T_1e, valid for inhomogeneous spectra, based on measuring the spectral area as a function of detection frequency. These methods present alternatives to the conventional transverse ESR linewidth-based oximetry methods, particularly for animal whole body imaging applications.

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The total transmission probability of an asymmetric Aharonov-Bohm ring with an embedded scattering center in both branches and a magnetic flux passing through its center has been investigated. The transmission is calculated from the overall scattering matrix for the ring structure determined by cascading scattering matrices without the symmetric conditions. In this model, by imposing scattering centers with different strengths to the upper and lower arms of the ring, the effects of coupling between the ring and the leads and the magnetic flux in the total transmission probability as a function of transmission phase have been observed. We find the following results from our model study: 1) in the strong coupling limit, there is no zero transmission; 2) with a constant coupling and scatterer in each branch, the transmission peaks get closer together and the transmission becomes smoother as the magnetic flux increases; and 3) in the weak coupling limit with a constant magnetic flux and elastic scattering in each arm, transmission resonances become sharper due to the localized states in the ring and the magnitude of transmission is enhanced at smaller transmission phases.For the case of a single or double barrier in one arm of the ring, the discrete energy levels of the double barrier well in one branch are controlled by the width of the well and continuous levels in the other branch are controlled by a single scattering barrier. We find a peculiar quantum transport through this system such as a symmetric Breit-Wigner (BW) and an asymmetric Fano transmission resonance. The transition from BW to Fano resonance occurs by tuning either the transmission phase of the electrons through a single barrier or the magnetic AB flux threading through the AB ring. The characteristics of the Fano line-shape resonance will be examined by the asymmetric parameter that is a measure of the degree of coupling between the discrete state and the continuum. / Department of Physics and Astronomy

The electronic transport properties in low dimensional systems have several important features which have attracted a wide range of both experimental and theoretical interests. The quantum ballistic transport regime in these small systems is achieved when dimensions of systems are less than the elastic mean free path and the phase coherent length. We have studied electron transport in a nanochannel, containing repulsive delta impurities. To find the conductance, a recursive Green's function method is used. The study includes finding the transverse eigenvaiues, eigenfunctions, and computing hopping integrals to determine the Green's propagators.The effects of the number, and position of the repulsive delta impurities with various potential strengths on the conductance in a nanostructure have been presented. A FORTRAN program has been used and developed for the numerical calculations. The general practical applications for nanostructures include the ability to make electronic devices smaller, denser and operate at very low voltages. The future electronic devices will utilize the developments of conductance through components having dimensions on the nanometer scale. / Department of Physics and Astronomy

Multiple longitudinal potential barriers affect electron transport in a nanostructure. In addition to a symmetric, aperiodic quantum wire with five potential barriers, a quantum wire containing thirteen potential barriers was modeled based on a quasiperiodic sequence known as the Fibonacci sequence. Conductance of the wires and transmission coefficients of the corresponding one-dimensional systems were calculated and analyzed in this work.Conductance calculations were performed using a FORTRAN computer program, tbgf, which performs the tight-binding, recursive Green's function method. Also Program Tran Coeffwas developed in order to calculate one-dimensional transmission coefficients using the method known as wavefunction matching. This method matches electronic wavefunctions in neighboring regions to determine the one-dimensional transmission coefficients at the electron energy normalized to the barrier strengths. The program uses the data file generated by Program Data Input. / Department of Physics and Astronomy