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Full-Text Articles in Physics
Approaching The Singularity In Gowdy Universes, Bartlett Douglas Edmonds Jr.
Approaching The Singularity In Gowdy Universes, Bartlett Douglas Edmonds Jr.
Theses and Dissertations
It has been shown that the cosmic censorship conjecture holds for polarized Gowdy spacetimes. In the more general, unpolarized case, however, the question remains open. It is known that cylindrically symmetric dust can collapse to form a naked singularity. Since Gowdy universes comprise gravitational waves that are locally cylindrically symmetric, perhaps these waves can collapse onto a symmetry axis and create a naked singularity. It is known that in the case of cylindrical symmetry, event horizons will not form under gravitational collapse, so the formation of a singularity on the symmetry axis would be a violation of the cosmic censorship …
Silicon Oxide Nanoparticles Reveal The Origin Of Silicate Grains In Circumstellar Environments, Peneé Armaize Clayborne
Silicon Oxide Nanoparticles Reveal The Origin Of Silicate Grains In Circumstellar Environments, Peneé Armaize Clayborne
Theses and Dissertations
The processes leading to the widespread presence of crystalline silicates throughout the galaxy and the origin of silicon nanoparticles thought to be responsible for the observed extended red emission in diffuse galactic background are still far from being understood. One of the most abundant oxygen bearing species in molecular astronomical regions is SiO. It has been conjectured that silicate formation probably proceeds via the agglomeration of these molecular species; however there are no studies to reveal the microscopic mechanism. We have used a synergistic approach combining experiments in molecular beams and first principles theoretical calculation to demonstrate that the passage …
Determination Of The Band Gap Bowing Parameter Of A1xga1-Xn With Contactless Electroreflectance, Laura C. Mcglinchey
Determination Of The Band Gap Bowing Parameter Of A1xga1-Xn With Contactless Electroreflectance, Laura C. Mcglinchey
Theses and Dissertations
Contactless electroreflectance (CER), a modulation spectroscopy (MS) technique, has been used to study the A and C exciton transitions in A1xGa1-xN layers for a composition range of 0 ≤ x ≤ 0.48 at room temperature. Taking the entire composition range (0 ≤ x ≤ 1) into account by incorporating a previously reported band gap energy for AlN, the dependence of the A-exciton transition on composition showed a downward bowing from linearity. A bowing parameter of b = 1.7 eV was found. Analysis of the lower composition range 0 ≤ x ≤ 0.48 resulted in a linear fit, as did the …