Spin in a General Time Varying Magnetic Field: Generalization of the Adiabatic Factorization of Time Evolution

An extension of the adiabatic factorization of the time evolution operator is studied for spin in a general time varying magnetic field $B(t)$. When $B(t)$ changes adiabatically, such a factorization reduces to the product of the geometric operator which embodies the Berry phase phenomenon and a usual dynamical operator. For a general time variation of $B(t)$, there should be another operator $N(t)$ in the factorization that is related to non-adiabatic transitions. A simple and explicit expression for the instantaneous angular velocity of this operator is derived. This is done in a way that is independent of any specific representation of spin. Two classes of simple conditions are given under which the operator $N(t)$ can be made explicit. As a special case, a generalization of the traditional magnetic resonance condition is pointed out.Comment: 10 page

Baryogenesis from Symmetry Principle

In this work, a formalism based on symmetry which allows one to express asymmetries of all the particles in terms of conserved charges is developed. The manifestation of symmetry allows one to easily determine the viability of a baryogenesis scenario and also to identity the different roles played by the symmetry. This formalism is then applied to the standard model and its supersymmetric extension, which constitute two important foundations for constructing models of baryogenesis.Comment: 15 pages, 1 figure, 3 tables. Slight modifications to match the published versio

Application of natural commutation technique to an improved cycloconverter type high-frequency link inverter with center-tapped transformer

This thesis presents a new isolated cycloconverter type high frequency (HF) link dc to ac power converter (inverter) that consists of three arms of bidirectional switches at transformer secondary. This topology has the advantage of light weight and reduced switch count, compared to other types of HF link inverter. However, like all HF link inverter topologies, this topology also suffer high voltage surge problem and power device switching loss. In order to overcome these problems, two sets of switching technique, namely the asymmetric bipolar PWM control and edgealigned unipolar PWM control, are introduced. These switching techniques utilize natural commutation technique that enables total soft switching operation and voltage surge reduction. Furthermore, the proposed switching techniques are able to reduce the transistor conduction loss due to the existence of freewheeling period. The research work verifies of the proposed topology and switching techniques by means of SPICE simulations. It also describes the natural commutation mechanism for HF link inverter in detail. An open loop laboratory prototype based on the Infineon C167 fixed-point microcontroller was constructed. The results obtained from the experimental rig were found to be in very close agreement with the theoretical prediction and simulation. The laboratory prototype was able to supply output voltage 340Vrms as well as 120Vrms, with THD less than 2.5%. The total power conversion efficiency reaches 86% when the output power was beyond 300

Impulsive radiation from a horizontal electric dipole above an imperfectly conducting surface

Solutions for the impulsive wave fields generated by a horizontal electric dipole situated above an imperfectly conducting surface are derived. The space-time expressions for the reflected wave fields open the door to analysis of their properties in the far-, intermediate-, and near-field regions, and can serve as benchmark for numerical methods employed to wave simulation with applications in antenna design and radio communication. The EM properties of the conductive material are represented by a surface impedance and translated to the wave motion via employing the local plane wave relation as the boundary condition. At the core of tackling the impedance boundary value problem is the derivation of three space-time reflected-wave Green's functions. In contrast to the vertical electric dipole problem, a coupling term is present in the transform-domain wave solutions, and hinders direct application of the extended Cagniard-De Hoop method. A partial-fraction decomposition of this coupling term is the key to furnishing the transformation back to the time domain. Numerical results illustrate time traces and spectra of the measurable reflected electric field strength