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452 Matching Results
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Performance Study and Dynamic Optimization Design for Thread Pool Systems
Thread pools have been widely used by many multithreaded applications. However, the determination of the pool size according to the application behavior still remains problematic. To automate this process, in this thesis we have developed a set of performance metrics for quantitatively analyzing thread pool performance. For our experiments, we built a thread pool system which provides a general framework for thread pool research. Based on this simulation environment, we studied the performance impact brought by the thread pool on different multithreaded applications. Additionally, the correlations between internal characterizations of thread pools and their throughput were also examined. We then proposed and evaluated a heuristic algorithm to dynamically determine the optimal thread pool size. The simulation results show that this approach is effective in improving overall application performance.
Date:
December 19, 2004
Creator:
Xu, Dongping
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Phase Transformations in Cast Duplex Stainless Steels
Duplex stainless steels (DSS) constitute both ferrite and austenite as a matrix. Such a microstructure confers a high corrosion resistance with favorable mechanical properties. However, intermetallic phases such as {sigma} and {chi} can also form during casting or high-temperature processing and can degrade the properties of the DSS. This research was initiated to develop time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) diagrams of two types of cast duplex stainless steels, CD3MN (Fe-22Cr-5Ni-Mo-N) and CD3MWCuN (Fe-25Cr-7Ni-Mo-W-Cu-N), in order to understand the time and temperature ranges for intermetallic phase formation. The alloys were heat treated isothermally or under controlled cooling conditions and then characterized using conventional metallographic methods that included tint etching, and also using electron microscopy (SEM, TEM) and wavelength dispersive spectroscopy (WDS). The kinetics of intermetallic-phase ({sigma} + {chi}) formation were analyzed using the Johnson-Mehl-Avrami (MA) equation in the case of isothermal transformations and a modified form of this equation in the case of continuous cooling transformations. The rate of intermetallic-phase formation was found to be much faster in CD3MWCuN than CD3MN due mainly to differences in the major alloying contents such as Cr, Ni and Mo. To examine in more detail the effects of these elements of the phase stabilities; a …
Date:
December 19, 2004
Creator:
Kim, Yoon-Jun
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Photoemission Study of the Rare Earth Intermetallic Compounds: RNi2Ge2 (R=Eu, Gd)
EuNi{sub 2}Ge{sub 2} and GdNi{sub 2}Ge{sub 2} are two members of the RT{sub 2}X{sub 2} (R = rare earth, T = transition metal and X = Si, Ge) family of intermetallic compounds, which has been studied since the early 1980s. These ternary rare-earth intermetallic compounds with the tetragonal ThCr{sub 2}Si{sub 2} structure are known for their wide variety of magnetic properties, Extensive studies of the RT{sub 2}X{sub 2} series can be found in Refs [ 1,2,3]. The magnetic properties of the rare-earth nickel germanides RNi{sub 2}Ge{sub 2} were recently studied in more detail [4]. The purpose of this dissertation is to investigate the electronic structure (both valence band and shallow core levels) of single crystals of EuNi{sub 2}Ge{sub 2} and GdNi{sub 2}Ge{sub 2} and to check the assumptions that the f electrons are non-interacting and, consequently, the rigid-band model for these crystals would work [11], using synchrotron radiation because, to the best of our knowledge, no photoemission measurements on those have been reported. Photoemission spectroscopy has been widely used to study the detailed electronic structure of metals and alloys, and especially angle-resolved photoemission spectroscopy (ARPES) has proven to be a powerful technique for investigating Fermi surfaces (FSs) of single-crystal compounds.
Date:
December 19, 2004
Creator:
Park, Jongik
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Polk County Enterprise (Livingston, Tex.), Vol. 122, No. 102, Ed. 1 Sunday, December 19, 2004
Semi-weekly newspaper from Livingston, Texas that includes local, state and national news along with advertising.
Date:
December 19, 2004
Creator:
White, Barbara
Object Type:
Newspaper
System:
The Portal to Texas History
Quantum Chemistry, and Eclectic Mix: From Silicon Carbide to Size Consistency
Chemistry is a field of great breadth and variety. It is this diversity that makes for both an interesting and challenging field. My interests have spanned three major areas of theoretical chemistry: applications, method development, and method evaluation. The topics presented in this thesis are as follows: (1) a multi-reference study of the geometries and relative energies of four atom silicon carbide clusters in the gas phase; (2) the reaction of acetylene on the Si(100)-(2x1) surface; (3) an improvement to the Effective Fragment Potential (EFP) solvent model to enable the study of reactions in both aqueous and nonaqueous solution; and (4) an evaluation of the size consistency of Multireference Perturbation Theory (MRPT). In the following section, the author briefly discusses two topics central to, and present throughout, this thesis: Multi-reference methods and Quantum Mechanics/Molecular Mechanics (QM/MM) methods.
Date:
December 19, 2004
Creator:
Rintelman, Jamie Marie
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Rheological Properties of Aqueous Nanometric Alumina Suspensions
Colloidal processing is an effective and reliable approach in the fabrication of the advanced ceramic products. Successful colloidal processing of fine ceramic powders requires accurate control of the rheological properties. The accurate control relies on the understanding the influences of various colloidal parameters on the rheological properties. Almost all research done on the rheology paid less attention to the interactions of particle and solvent. However, the interactions of the particles are usually built up through the media in which the particles are suspended. Therefore, interactions of the particle with the media, the adsorbed layers on the particle surface, and chemical and physical properties of media themselves must influence the rheology of the suspension, especially for the dense suspensions containing nanosized particles. Relatively little research work has been reported in this area. This thesis addresses the rheological properties of nanometric alumina aqueous suspensions, and paying more attention to the interactions between particle and solvent, which in turn influence the particle-particle interactions. Dense nanometric alumina aqueous suspensions with low viscosity were achieved by environmentally-benign fructose additives. The rheology of nanometric alumina aqueous suspensions and its variation with the particle volume fraction and concentration of fructose were explored by rheometry. The adsorptions of …
Date:
December 19, 2004
Creator:
Li, Chuanping
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Sapulpa Daily Herald (Sapulpa, Okla.), Vol. 90, No. 83, Ed. 1 Sunday, December 19, 2004
Daily newspaper from Sapulpa, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 19, 2004
Creator:
Broaddus, Matthew B.
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Solidification at the High and Low Rate Extreme
The microstructures formed upon solidification are strongly influenced by the imposed growth rates on an alloy system. Depending on the characteristics of the solidification process, a wide range of growth rates is accessible. The prevailing solidification mechanisms, and thus the final microstructure of the alloy, are governed by these imposed growth rates. At the high rate extreme, for instance, one can have access to novel microstructures that are unattainable at low growth rates. While the low growth rates can be utilized for the study of the intrinsic growth behavior of a certain phase growing from the melt. Although the length scales associated with certain processes, such as capillarity, and the diffusion of heat and solute, are different at low and high rate extremes, the phenomena that govern the selection of a certain microstructural length scale or a growth mode are the same. Consequently, one can analyze the solidification phenomena at both high and low rates by using the same governing principles. In this study, we examined the microstructural control at both low and high extremes. For the high rate extreme, the formation of crystalline products and factors that control the microstructure during rapid solidification by free-jet melt spinning are examined …
Date:
December 19, 2004
Creator:
Meco, Halim
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Solvation!
This dissertation consists of two closely related parts: theory development and coding of correlation effects in a model potential for solvation, and study of solvent effects on chemical reactions and processes. The effective fragment potential (EFP) method has been re-parameterized, using density functional theory (DFT), more specifically, the B3LYP functional. The DFT based EFP method includes short-range correlation effects; hence it is a first step in incorporating the treatment of correlation in the EFP solvation model. In addition, the gradient of the charge penetration term in the EFP model was derived and coded. The new method has been implemented in the electronic structure code GAMESS and is in use. Formulas for the dynamic dipole polarizability, C{sub 6} dispersion coefficient and dispersion energy were derived and coded as a part of a treatment of the dispersion interactions in the general solvation model, EFP2. Preliminary results are in good agreement with experimental and other theoretical data. The DFT based EFP (EFP1/DFT) method was used in the study of microsolvation effects on the S{sub N}2 substitution reaction, between chloride and methyl bromide. Changes in the central barrier, for several lowest lying isomers of the systems with one, two, three and four waters, were …
Date:
December 19, 2004
Creator:
Adamovic, Ivana
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Synchrotron Diffraction Studies of Spontaneous Magnetostriction in Rare Earth Transition Metal Compounds
Thermal expansion anomalies of R{sub 2}Fe{sub 14}B and R{sub 2}Fe{sub 17}C{sub x} (x = 0,2) (R = Y, Nd, Gd, Tb, Er) stoichiometric compounds are studied with high-energy synchrotron X-ray powder diffraction using Debye-Schemer geometry in temperature range 10K to 1000K. Large spontaneous magnetostriction up to their Curie temperatures (T{sub c}) is observed. The a-axes show relatively larger invar effects than c-axes in the R{sub 2}Fe{sub 14}B compounds whereas the R{sub 2}Fe{sub 17}C{sub x} show the contrary anisotropies. The iron sub-lattice is shown to dominate the spontaneous magnetostriction of the compounds. The contribution of the rare earth sublattice is roughly proportional to the spin magnetic moment of the rare earth in the R{sub 2}Fe{sub 14}B compounds but in R{sub 2}Fe{sub 17}C{sub x}, the rare earth sub-lattice contribution appears more likely to be dominated by the local bonding. The calculation of spontaneous magnetostrain of bonds shows that the bonds associated with Fe(j2) sites in R{sub 2}Fe{sub 14}B and the dumbbell sites in R{sub 2}Fe{sub 17}C{sub x} have larger values, which is strongly related to their largest magnetic moment and Wigner-Seitz atomic cell volume. The roles of the carbon atoms in increasing the Curie temperatures of the R{sub 2}Fe{sub 17} compounds are …
Date:
December 19, 2004
Creator:
Yang, Ning
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Synthesis of Dihydrobenzofurans via Palladium-Catalyzed Heteroannulations
Palladium-catalyzed heteroannulation of 1,3-dienes with 3-iodo-2-alkenols, and 2-iodo-2-alkenols, as well as their amino analogs, affords the corresponding cyclic ethers and amines respectively. The presence of a {beta}-hydrogen in the vinylic halide results in {beta}-hydride elimination giving the corresponding alkyne. The presence of a bulky group in the {alpha}-position of the vinylic halide results in failure or reduced amounts of annulation products. A chloride source, pyridine base and electron-rich phosphine are essential for this reaction.
Date:
December 19, 2004
Creator:
Rozhkov, Roman Vladimirovich
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
X-Ray Raman Spectroscopy of High-Pressure Phases and Novel Materials derived from Low-Z Compounds
None
Date:
December 19, 2004
Creator:
Evans, W. J.; Eng, P. J.; Maddox, B.; Newville, M.; Baer, B.; Cynn, H. et al.
Object Type:
Report
System:
The UNT Digital Library
15th Street News (Midwest City, Okla.), Vol. 34, No. 11, Ed. 1 Friday, November 19, 2004
Newspaper from Rose State College in Midwest City, Oklahoma that includes national, local, and campus news along with advertising.
Date:
November 19, 2004
Creator:
Delaney, Darcy
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 106, No. 192, Ed. 1 Friday, November 19, 2004
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
November 19, 2004
Creator:
Andrews, Mike
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Aviation Security: Preliminary Observations on TSA's Progress to Allow Airports to Use Private Passenger and Baggage Screening Services
A letter report issued by the Government Accountability Office with an abstract that begins "Beginning on November 19, 2004, the Transportation Security Administration (TSA) is required by law to begin allowing commercial airports to apply to use private contractors to screen passengers and checked baggage. A federal workforce has performed this work since November 2002, in response to a congressional mandate that the federal government take over screening services after the terrorist attacks of September 11, 2001. A 2-year pilot program at five airports testing the effectiveness of private sector screening in a post-September 11 environment concluded on November 18, 2004. This report contains GAO's preliminary observations related to TSA's progress in developing a private-sector screening program that allows airports to apply to opt out of using federal screeners. GAO assessed: (1) the status of TSA's efforts to develop policies and procedures for the opt-out program, including operational plans and guidelines for selecting airports and contractors that may participate; (2) guidance about the opt-out program that TSA has provided to airport operators and other stakeholders, or plans to develop, and how the information is communicated; and (3) TSA's efforts to develop performance measures for evaluating the opt-out program and contractor …
Date:
November 19, 2004
Creator:
United States. Government Accountability Office.
Object Type:
Report
System:
The UNT Digital Library
The Baytown Sun (Baytown, Tex.), Vol. 83, No. 351, Ed. 1 Friday, November 19, 2004
Daily newspaper from Baytown, Texas that includes local, state, and national news along with advertising.
Date:
November 19, 2004
Creator:
Cash, Wanda Garner
Object Type:
Newspaper
System:
The Portal to Texas History
Boerne Star & Hill Country Recorder (Boerne, Tex.), Vol. 98, No. 81, Ed. 1 Friday, November 19, 2004
Semiweekly newspaper from Boerne, Texas that includes local, state, and national news along with advertising.
Date:
November 19, 2004
Creator:
Cartwright, Brian & Barboza, Kerry
Object Type:
Newspaper
System:
The Portal to Texas History
Brady Standard-Herald and Heart O' Texas News (Brady, Tex.), Ed. 1 Friday, November 19, 2004
Semiweekly newspaper from Brady, Texas that includes local, state, and national news along with advertising.
Date:
November 19, 2004
Creator:
Stewart, James E.
Object Type:
Newspaper
System:
The Portal to Texas History
China's Trade with the United States and the World
This report provides a quantitative framework for policy considerations dealing with U.S. trade with China. It provides basic data and analysis of China’s international trade with the United States and other countries. Since Chinese data differ considerably from those of its trading partners (because of how entrepot trade through Hong Kong is counted), data from both PRC sources and those of its trading partners are presented. Charts showing import trends by sector for the United States highlight China’s growing market shares in many industries and also show import shares for Japan, Canada, Mexico, the European Union, and the Association for Southeast Asian Nations (ASEAN ).
Date:
November 19, 2004
Creator:
Lum, Thomas & Nanto, Dick K.
Object Type:
Report
System:
The UNT Digital Library
The Clifton Record (Clifton, Tex.), Vol. 109, No. 56, Ed. 1 Friday, November 19, 2004
Weekly newspaper from Clifton, Texas that includes local, state, and national news along with advertising.
Date:
November 19, 2004
Creator:
Smith, W. Leon
Object Type:
Newspaper
System:
The Portal to Texas History
The Core of NGC 6240 from Keck Adaptive Optics and HST NICMOS Observations
We present results of near infrared imaging of the disk-galaxy-merger NGC 6240 using adaptive optics on the Keck II Telescope and reprocessed archival data from NICMOS on the Hubble Space Telescope. Both the North and South nuclei of NGC 6240 are clearly elongated, with considerable sub-structure within each nucleus. In K' band there are at least two point-sources within the North nucleus; we tentatively identify the south-western point-source within the North nucleus as the position of one of the two AGNs. Within the South nucleus, the northern subnucleus is more highly reddened. Based upon the nuclear separation measured at 5 GHz, we suggest that the AGN in the South nucleus is still enshrouded in dust at K' band, and is located slightly to the north of the brightest point in K' band. Within the South nucleus there is strong H{sub 2} 1-0 S(1) line emission from the northern sub-nucleus, contrary to the conclusions of previous seeing-limited observations. Narrowband H{sub 2} emission-line images show that a streamer or ribbon of excited molecular hydrogen connects the North and South nuclei. We suggest that this linear feature corresponds to a bridge of gas connecting the two nuclei, as seen in computer simulations of …
Date:
November 19, 2004
Creator:
Max, C. E.; Canalizo, G.; Macintosh, B. A.; Raschke, L.; Whysong, D.; Antonucci, R. et al.
Object Type:
Article
System:
The UNT Digital Library
Dallas Voice (Dallas, Tex.), Vol. 21, No. 28, Ed. 1 Friday, November 19, 2004
Weekly newspaper from Dallas, Texas that includes local, state, and national news and advertising of interest to the Lesbian, Gay, Bisexual, and Transgender (LGBT) community.
Date:
November 19, 2004
Creator:
Vercher, Dennis
Object Type:
Newspaper
System:
The UNT Digital Library
Direct FuelCell/Turbine Power Plant Annual Technical Progress Report: 2004
This report includes the progress in development of Direct Fuel Cell/Turbine. (DFC/T.) power plants for generation of clean power at very high efficiencies. The DFC/T power system is based on an indirectly heated gas turbine to supplement fuel cell generated power. The DFC/T power generation concept extends the high efficiency of the fuel cell by utilizing the fuel cell's byproduct heat in a Brayton cycle. Features of the DFC/T system include: electrical efficiencies of up to 75% on natural gas, 60% on coal gas, minimal emissions, simplicity in design, direct reforming internal to the fuel cell, reduced carbon dioxide release to the environment, and potential cost competitiveness with existing combined cycle power plants. FCE successfully completed testing of the pre-alpha sub-MW DFC/T power plant. This power plant was constructed by integration of a 250kW fuel cell stack and a microturbine. Following these proof-of-concept tests, a stand-alone test of the microturbine verified the turbine power output expectations at an elevated (representative of the packaged unit condition) turbine inlet temperature. Preliminary design of the packaged sub-MW alpha DFC/T unit has been completed and procurement activity has been initiated. The preliminary design of a 40 MW power plant including the key equipment layout …
Date:
November 19, 2004
Creator:
Ghezel-Ayagh, Hossein
Object Type:
Report
System:
The UNT Digital Library
DSNF AND OTHER WASTE FORM DEGRADATION ABSTRACTION
Several hundred distinct types of DOE-owned spent nuclear fuel (DSNF) may potentially be disposed in the Yucca Mountain repository. These fuel types represent many more types than can be viably individually examined for their effect on the Total System Performance Assessment for the License Application (TSPA-LA). Additionally, for most of these fuel types, there is no known direct experimental test data for the degradation and dissolution of the waste form in repository groundwaters. The approach used in the TSPA-LA model is, therefore, to assess available information on each of 11 groups of DSNF, and to identify a model that can be used in the TSPA-LA model without differentiating between individual codisposal waste packages containing different DSNF types. The purpose of this report is to examine the available data and information concerning the dissolution kinetics of DSNF matrices for the purpose of abstracting a degradation model suitable for use in describing degradation of the DSNF inventory in the Total System Performance Assessment for the License Application. The data and information and associated degradation models were examined for the following types of DSNF: Group 1--Naval spent nuclear fuel; Group 2--Plutonium/uranium alloy (Fermi 1 SNF); Group 3--Plutonium/uranium carbide (Fast Flux Test Facility-Test Fuel …
Date:
November 19, 2004
Creator:
CUNNANE, J.
Object Type:
Report
System:
The UNT Digital Library