Radiation therapy calculations using an on-demand virtual cluster via cloud computing

Computer hardware costs are the limiting factor in producing highly accurate radiation dose calculations on convenient time scales. Because of this, large-scale, full Monte Carlo simulations and other resource intensive algorithms are often considered infeasible for clinical settings. The emerging cloud computing paradigm promises to fundamentally alter the economics of such calculations by providing relatively cheap, on-demand, pay-as-you-go computing resources over the Internet. We believe that cloud computing will usher in a new era, in which very large scale calculations will be routinely performed by clinics and researchers using cloud-based resources. In this research, several proof-of-concept radiation therapy calculations were successfully performed on a cloud-based virtual Monte Carlo cluster. Performance evaluations were made of a distributed processing framework developed specifically for this project. The expected 1/n performance was observed with some caveats. The economics of cloud-based virtual computing clusters versus traditional in-house hardware is also discussed. For most situations, cloud computing can provide a substantial cost savings for distributed calculations.Comment: 12 pages, 4 figure

Very small grains in the Milky Way and external galaxies

These studies of the infrared colors of reflection nebulae, HL HI clouds, HII regions and external galaxies have shown the following results. Different classes of objects locate in different regions on the R vs F sub v (60)/F sub v (100) diagram. This is determined both by differences in dust properties and by differences in the illuminating radiation field. For example, HL clouds and reflection nebulae almost have the same behavior since both are in the diffuse Interstellar Medium (ISM) and can be expected to have similar grain populations; the small difference in their infrared colors can be explained by the difference of the illuminating radiation field. On the other hand, the dramatic difference of R=vF sub v (12)/F sub v (far IR) between HII region and diffuse ISM may be due to the destruction of the Very Small Grain (VSG) component in the HII regions, although radiation transfer effects may play a part as well. The ratio R=vF sub v (12)/F sub v (far IR) is approximately constant in normal spiral galaxies. This implies that the mass ratio b=Mass (VSG)/Mass (dust) does not vary greatly from one galaxy to another

Contact of Single Asperities with Varying Adhesion: Comparing Continuum Mechanics to Atomistic Simulations

Atomistic simulations are used to test the equations of continuum contact mechanics in nanometer scale contacts. Nominally spherical tips, made by bending crystals or cutting crystalline or amorphous solids, are pressed into a flat, elastic substrate. The normal displacement, contact radius, stress distribution, friction and lateral stiffness are examined as a function of load and adhesion. The atomic scale roughness present on any tip made of discrete atoms is shown to have profound effects on the results. Contact areas, local stresses, and the work of adhesion change by factors of two to four, and the friction and lateral stiffness vary by orders of magnitude. The microscopic factors responsible for these changes are discussed. The results are also used to test methods for analyzing experimental data with continuum theory to determine information, such as contact area, that can not be measured directly in nanometer scale contacts. Even when the data appear to be fit by continuum theory, extracted quantities can differ substantially from their true values

Silicon Nitride Deposition, Chromium Corrosion Mechanisms and Source/Drain Parasitic Resistance in Amorphous Silicon Thin Film transistors

Hydrogenated amorphous silicon (a-Si:H) based thin film transistors (TFTs) are finding increased application as switching elements in active-matrix liquid crystal displays (AMLCDs). Extensive research has been focussed on optimizing fabrication conditions to improve materials quality and on reducing channel length to increase device speed. However, the basic physics and chemistry have not yet been fully understood. In addition, little attention has been paid to the significant effect of source/drain parasitics. The work described in this thesis is closely related to the speed and stability issues on the discrete device level. Specifically, the influence of gate nitride deposition and its NH3 plasma treatment has been studied. The competing effects of nitridation reaction and radiation damage were found to cause an interesting trade-off between the device stability and speed. Further effort was devoted to the analysis of an important TFT failure phenomenon. Both electrical and spectroscopic techniques were utilized for gate Cr corrosion studies. It was determined that the corrosion was largely promoted by the CF4 plasma exposure of Cr during the fabrication. Finally, new test structures were designed, fabricated and characterized to study the source/drain parasitic resistance

Lumped-Parameter Model and Nonlinear DSSI Analysis

A 2-.degrees-of-freedom discrete model with 8 constant lumped parameters is developed to equivalently simulate frequency-dependent dynamic impedances of the elastic halfspace. The equations of motion for the nonlinear dynamic soil-structure interaction (DSSI) analysis are established in the time domain and then nonlinear seismic responses of the coupling system are predicted by the proposed iterative procedure. Based on numerical results for three typical shear-type structures, effects of the shear stiffness of underlying soils and different ground motions on dynamic responses are examined

Remission of obesity among a nationally representative sample of US children

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147066/1/ijpo12457.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147066/2/ijpo12457_am.pd

Developmental deep dyslexia in Chinese : a case study

2002-2003 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe