Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Bibliography: leaves 161-163.

A complete stochastic theory of relaxation is developed in terms of a homogeneous equation for the averaged density matrix of a system immersed in a thermal bath. This theory is then used as the basis of a new stochastic approach to the phenomenon of collisional broadening of spectral line shapes. Single photon and multiphoton processes are studied. The features of a line shape are linked by simple expressions to the statistical properties of a stochastic hermitian Hamiltonian. The ordinary line shape predicted by Kubo's approach is generalized. The present approach predicts broadening as well as asymmetry and shift. A representation of line shapes in multiphoton processes by diagrams is also developed.

Experimental proof is presented that some of the motions responsible for transverse relaxation (T₂) in deuterium magnetic resonance (²H NMR) experiments on acyl chains of a model membrane in the liquid crystalline phase are extremely slow on the ²H NMR time scale being characterized by a correlation time T₂ > ѡq⁻¹. The experiments used to investigate these slow motions involve a form of the Carr-Purcell-Meiboom-Gill pulse sequence modified so as to be suitable for ²H NMR (q-CPMG). The most plausible mechanism responsible for T₂ relaxation is the gradual change in the average molecular orientation due to lateral diffusion of the phospholipid molecules along curved membrane surfaces. Presence of such diffusion is directly established by a selective inversion recovery experiment in which magnetization transfer across the spectrum is seen. The results of the T₂ relaxation as measured in the q-CPMG experiments are fitted to an average correlation time, T₂ ≈ 62 ms, yielding an estimate of the average effective radius of curvature of 1.2 µm for a typical model membrane system, in good agreement with other methods of measurement. The implications of this main result are examined for a number of model membranes; in particular, considerable changes are seen in the character of molecular motions in systems containing small concentrations of sterols. Similarly, changes caused by the topological differences between the lamellar L∝ and hexagonal H₁₁ phases are examined in a model membrane system which undergoes a L∝ to H₁₁ phase transition. A novel way of quantifying the differences in the orientational order parameters across the phase transition is used; the observed differences are consistent with the different symmetry properties of the two phases. Perdeuteriated polycrystalline hexamethylbenzene is used to demonstrate various methods of measuring ²H NMR relaxation. In addition, some aspects of orientation dependence of the relaxation rates are examined, and found to agree with the theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Electron transport and relaxation may be substantially different in low-dimensional systems compared to that observed in bulk material. In the present work, Monte Carlo models are used for the solution to the Boltzmann transport equation, with scattering rates calculated quantum mechanically for superlattice and quantum wells. Carrier relaxation following optical excitation is examined in multiple quantum well systems. Simulated results of the carrier relaxation process in coupled asymmetric wells and modulation doped wells are in good agreement with published experimental results on similar structures. Scattering rates in superlattices due to polar optical phonons, intervalley phonons, ionized impurities and carrier-carrier scattering are derived. Carrier transport through high energy superlattice minibands is examined in superlattice base hot electron transistors. Additionally, transport in the ballistic limit in periodic quantum wire structures, including geometric superlattices, is examined utilizing a mode matching method. / Graduation date: 1992

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph.D.)--McMaster University (Canada), 1994. / Source: Dissertation Abstracts International, Volume: 56-08, Section: B, page: 4313. Adviser: A. D. Bain.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.