Physical Sciences and Mathematics Commons^™

Spectroscopic And Spectro-Astrometric Analysis Of T Tauri Stars, Logan Ryan Brown

Doctoral Dissertations

"To understand our own solar origins, we must investigate the composition of the protoplanetary disk from which the solar system formed. To infer this, we study analogs to the early solar system called T Tauri stars. These objects are low-mass, pre-main sequence stars surrounded by circumstellar disks of material from which planets are believed to form. We present high-resolution, near-infrared spectroscopic data for the T Tauri stars DR Tau and AA Tau using NIRSPEC at the Keck II telescope. For DR Tau, a spectro-astrometric analysis was performed, obtaining sub-seeing spatial information on water emission. Alongside a disk model, we constrained …

Fully Differential Study Of Projectile Coherence Effects In Ionization Of Molecular Hydrogen And Atomic Helium, Thusitha Priyantha Arthanayaka

Doctoral Dissertations

"It has been well established, that projectile coherent properties are important for the study of atomic fragmentation processes. Recent studies of ionization of molecular hydrogen had demonstrated that measured double differential cross sections (DDCS) are very sensitive to the coherent length of the projectile. These measurements have been performed with varied coherence length of the projectiles by controlling the geometry of the collimating slits, which are placed before the target. Later, fully differential cross sections (FDCS) for a coherent and an incoherent projectile beam has been study for the same collision system and the results confirmed the important role of …

Dft Investigations Of Hydrogen Storage Materials, Gang Wang

Doctoral Dissertations

"Hydrogen serves as a promising new energy source having no pollution and abundant on earth. However the most difficult problem of applying hydrogen is to store it effectively and safely, which is smartly resolved by attempting to keep hydrogen in some metal hydrides to reach a high hydrogen density in a safe way. There are several promising metal hydrides, the thermodynamic and chemical properties of which are to be investigated in this dissertation.

Sodium alanate (NaAlH₄) is one of the promising metal hydrides with high hydrogen storage capacity around 7.4 wt. % and relatively low decomposition temperature of …

Unconventional Phase Transitions In Random Systems, Hatem Nuri Barghathi

Doctoral Dissertations

"In this thesis we study the effects of different types of disorder and quasiperiodic modulations on quantum, classical and nonequilibrium phase transitions. After a brief introduction, we examine the effect of topological disorder on phase transitions and explain a host of violations of the Harris and Imry-Ma criteria that predict the fate of disordered phase transitions. We identify a class of random and quasiperiodic lattices in which a topological constraint introduces strong anticorrelations leading to modifications of the Harris and Imry-Ma criteria for such lattices. We investigate whether or not the Imry-Ma criterion, that predicts that random field disorder destroys …

Properties Of Amorphous Transparent Conducting And Semiconducting Oxides From First Principles, Rabi Khanal

Doctoral Dissertations

"Amorphous transparent conducting and semiconducting oxides possess properties superior or comparable to their crystalline counterparts. The structure-property relationship in amorphous oxides is not nearly as well understood as in the case of the crystalline transparent conducting oxides. We have employedab initio molecular dynamics and a liquid quench approach to simulate amorphous oxide structures and performed density functional-based calculations to study the electronic properties of several amorphous conducting and semiconducting oxides with various cation compositions.

The effect of amorphization in oxides was investigated by taking indium oxide as a progenitor of the system. From the thorough study it was confirmed …