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Articles 91 - 98 of 98
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 …
Afm And C-Afm Studies Of Gan Films, Katherine Cooper
Afm And C-Afm Studies Of Gan Films, Katherine Cooper
Theses and Dissertations
This thesis uses the techniques of atomic force microscope (AFM) and conductive AFM (C-AFM) to study the conduction properties of n-type GaN films. A total of 16 samples were examined and grouped according to their surface morphologies and conduction behaviors. The most common type of surface morpliology was that of Ga-rich samples having undulating "hillocks" with interspersed holes. Although most of the samples had this common morphology, their local conduction behaviors were not all similar. Local I-V spectra of the tip-sample Schottky contact could be grouped according to three major types: low leakage, high leakage, and "p-type". The highest quality …
Integration Of Vmc++ Into A Commercial Treatment Planning System, Joseph Kingsley Gardner
Integration Of Vmc++ Into A Commercial Treatment Planning System, Joseph Kingsley Gardner
Theses and Dissertations
Recently, there has been interest to integrate VMC++ into the commercial treatment planning system at VCU as another Monte Carlo code option, since it has been shown to increase efficiency dramatically without introducing a significant amount of systematic error. Also, independent validation of VMC++ for photon beams is of interest since this has not been performed previously in literature. This study included several tests required to integrate VMC++. Output factor normalization was performed and found to agree with experiment to within 1% for all field sizes except 1x1 cm2. Geometric validation was successful. Dosimetric validation was performed with respect to …
Stm Studies Of Oxygen Etching Of Silicon Surfaces, Mary L. Willis
Stm Studies Of Oxygen Etching Of Silicon Surfaces, Mary L. Willis
Theses and Dissertations
This study uses atomic force microscopy (AFM) to investigate the oxygen etching behavior of the following silicon surface orientations: (001), (111), (113), (5 5 12) and (112). Most etching was performed at sample temperatures between 650 °C and 800 °C, at pressures of 3.3×10-7 and 1.5×10-7 Torr, and at an exposure of 200 L. Surface orientation strongly influences the morphology resulting from extended etching. The surface orientations that are stable against etching and remain flat include Si(001), Si(111), and Si(113). Such surfaces also include island structures, which result from etching around oxide-induced pinning sites. The density of these islands increases …
Afm, Cafm, And Efm Studies Of The Gan System, John C. Dickinson
Afm, Cafm, And Efm Studies Of The Gan System, John C. Dickinson
Theses and Dissertations
This thesis discusses a variety of techniques based on the atomic force microscope (AFM), and their application to the GaN materials system. In particular, the local conductivity and contact potential of surfaces have been measured using the techniques of Conductive AFM (CAFM) and Surface Potential Electric Force Microscopy (SPEFM), respectively. CAFM studies of GaN surfaces have revealed that prismatic planes around islands and pits on surfaces can lead to enhanced conductivity, which may be related to leakage problems in device applications. With regard to SP-EFM work, the change in surface potential associated with inversion domains on Ga-polar GaN has been …
Einstein's Equations In Vacuum Spacetimes With Two Spacelinke Killing Vectors Using Affine Projection Tensor Geometry, Miles D. Lawrence
Einstein's Equations In Vacuum Spacetimes With Two Spacelinke Killing Vectors Using Affine Projection Tensor Geometry, Miles D. Lawrence
Theses and Dissertations
Einstein's equations in vacuum spacetimes with two spacelike killing vectors are explored using affine projection tensor geometry. By doing a semi-conformal transformation on the metric, a new "fiducial" geometry is constructed using a projection tensor fields. This fiducial geometry provides coordinate independent information about the underlying structure of the spacetime without the use of an explicit form of the metric tensor.
Mechanical Effects Of Acoustic Transients On Tobacco Mosaic Virus, Philip Edward Hamrick
Mechanical Effects Of Acoustic Transients On Tobacco Mosaic Virus, Philip Edward Hamrick
Theses and Dissertations
The mechanical breakage of tobacco mosaic virus (TMV) due to the action of acoustic transients has been investigated. The acoustic transients were produced by transient heating of a Prussian blue dye solution (attenuation coefficient of 1000 per cm) when a ruby laser light (20 x 106 watts) was incident on the dye surface. A quartz piezoelectric transducer was used to determine the amplitude and form of the acoustic wave. The production of acoustic waves by transient heating is discussed, and the theoretical form of the acoustic wave determined for various boundary and initial conditions are compared to the experimentally …