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An Adaptive Linearization Method for a Constraint Satisfaction Problem in Semiconductor Device Design Optimization

Description: The device optimization is a very important element in semiconductor technology advancement. Its objective is to find a design point for a semiconductor device so that the optimized design goal meets all specified constraints. As in other engineering fields, a nonlinear optimizer is often used for design optimization. One major drawback of using a nonlinear optimizer is that it can only partially explore the design space and return a local optimal solution. This dissertation provides an adaptive optimization design methodology to allow the designer to explore the design space and obtain a globally optimal solution. One key element of our method is to quickly compute the set of all feasible solutions, also called the acceptability region. We described a polytope-based representation for the acceptability region and an adaptive linearization technique for device performance model approximation. These efficiency enhancements have enabled significant speed-up in estimating acceptability regions and allow acceptability regions to be estimated for a larger class of device design tasks. Our linearization technique also provides an efficient mechanism to guarantee the global accuracy of the computed acceptability region. To visualize the acceptability region, we study the orthogonal projection of high-dimensional convex polytopes and propose an output sensitive algorithm for projecting polytopes into two dimensions.
Date: May 1999
Creator: Chang, Chih-Hui, 1967-
Partner: UNT Libraries

Comparative Biochemistry and Evolution of Aspartate Transcarbamoylase from Diverse Bacteria

Description: Aspartate transcarbamoylase (ATCase) catalyzes the first committed step in pyrimidine biosynthesis. Bacterial ATCases are divided into three classes, A, B and C. Class A ATCases are largest at 450-500, are. dodecamers and represented by Pseudomonas ATCase. The overlapping pyrBC' genes encode the Pseudomonases ATCase, which is active only as a 480 kDa dodecamer and requires an inactive pyrC'-encoded DHOase for ATCase activity. ATCase has been studied in two non-pathogenic members of Mycobacterium, M. smegmatis and M. phlei. Their ATCases are dodecamers of molecular weight 480 kDa, composed of six PyrB and six PyrC polypeptides. Unlike the Pseudomonas ATCase, the PyrC polypeptide in these mycobacteria encodes an active DHOase. Moreover, the ATCase: DHOase complex in M. smegmatis is active both as the native 480 kDa and as a 390 kDa complex. The latter lacks two PyrC polypeptides yet retains ATCase activity. The ATCase from M. phlei is similar, except that it is active as the native 480 kDa form but also as 450,410 and 380 kDa forms. These complexes lack one, two, and three PyrC polypeptides, respectively. By contrast,.ATCases from pathogenic mycobacteria are active only at 480 kDa. Mycobacterial ATCases contain active DHOases and accordingly. are placed in class A1 . The class A1 ATCases contain active DHOases while class A2 ATCases contain inactive DHOases. ATCase has also been purified from Burkholderia cepacia and from an E. coli strain in which the cloned pyrB of B. cepacia was expressed. The B. cepacia ATCase has a molecular mass of 550 kDa, with two different polypeptides, PyrB (52 kDa) and PyrC of (39 kDa). The enzyme is active both as the native enzyme at 550 kDa and as smaller molecular forms including 240 kDa and 165 kDa. The ATCase synthesized by the cloned pyrB gene has a molecular weight of 165 kDa composed ...
Date: May 1999
Creator: Hooshdaran, Massoumeh Ziba
Partner: UNT Libraries

The Effect of Quality and Color Visual Aids on Immediate Recall, Attitude Toward Speaker, and Attitude Toward Speech

Description: Thirty years of empirical research on visual aids have produced inconsistent results--perhaps because the quality and color of those visuals were inconsistent. The purpose of this study was to determine what effects quality and color of instructional transparencies used in an informative speech have on listener recall and attitudes toward speaker and speech. A total of 709 community college and university students in 36 intact classes were randomly assigned to one of four visual treatment groups (poor-quality black/white, high-quality black/white, poor-quality color, or high-quality color) or one of two control groups (no-speech or no-visuals). A videotaped speech was projected onto a large screen at the right of the room; visual aids (each shown for approximately 30 seconds) were projected onto another screen set immediately to the left. Recall was measured by a 10-item multiple choice test; attitude toward speech and speaker were each measured by six seven-item semantic differential scales. Analysis of variance indicated that the type of transparencies used in an informative speech have a definite effect on immediate recall and attitude toward the speech, but no effect on attitude toward speaker. All four treatment groups scored significantly higher on recall than the no-speech and no-visual control groups. Log percent of change showed poor color to produce the lowest scores (still 13% better than control) and quality color to produce the highest scores (19.5'% better). Analysis found listeners to have a more positive attitude toward the speech when quality color, quality black/white, or poor black/white visuals were used. It appears that any visual (even a poor quality one) produces better recall than no visuals. Speakers with the time to produce quality visuals should add color; speakers who pay little attention to quality would be advised to use black/white visuals. Implications for future research are suggested.
Date: May 1999
Creator: Hamilton, Cheryl A. (Cheryl Ann)
Partner: UNT Libraries

Isolation and Characterization of a New Capsule-Forming Bacterium

Description: A unique, previously undescribed Gram-negative bacterium was isolated from several soils in Texas and extensively characterized in this study. The cells measured 1-2 by 4-6 μm. The distinguishing characteristic of the bacterium is the extraordinary capsular material which surrounds the cells. The new isolates are aerobic, mesophilic, non motile and have the ability to utilize a variety of organic compounds as the sole source of carbon and energy. The organism grows optimally at 30° C and the optimal pH lies between 7.0-8.0. The isolates produce catalase but oxidase is not produced. They do not produce indole or hydrogen sulfide. The organism can hydrolyze gelatin and Tween 80 but not starch, esculin and casein. The major cellular fatty acid is anteiso 15:0. The guanine and cytosine content is 58-62 mole%. The organism's taxonomic position was further established by specific gene probes, 16S rRNA homology, DNA homology and "ribotyping." These data showed that it was most closely related to members of the genus Paenibacillus, although somewhat divergent from other species classified in this genus. After careful evaluation of the results obtained during this study, it is proposed that this unique bacterium be named Paenibacillus velasolus sp. nov.
Date: May 1999
Creator: Thongmee, Acharawan
Partner: UNT Libraries

The Many Battles of Glorieta Pass: Struggles for the Integrity of a Civil War Battlefield

Description: This study focuses on modern-day attempts to preserve the site where Union volunteers from Colorado defeated a Confederate army from Texas at the 1862 Battle of Glorieta Pass to curtail Confederate expansion westward. When construction workers in 1987 accidently uncovered remains of the war dead, a second battle of Glorieta Pass ensued. Texas and New Mexico officials quarreled over jurisdiction of the war casualties. Eventually Congress authorized the National Park Service to expand the Pecos National Park through purchase and donation of land to include the battlesite. Sources include local records, newspapers, federal and state documents, and interviews with preservation participants.
Date: August 1999
Creator: Hull, William Edward, 1945-
Partner: UNT Libraries

An Analysis of a Title I Inclusive Middle School Program in Texas over a Three Year Period: A Case Study

Description: The purpose of this study was to describe a Title I inclusion program in a north Texas middle school, to evaluate the degree of its success as a high achieving program, and to analyze how closely it met the requirements of the Improving America's Schools Act of 1994. Data were collected from the learning facilitators and teachers at the middle school with the permission of the school district. This study began with extensive research on the nature of adolescents and the beliefs and characteristics of high achieving middle schools. It addressed the steps which were recommended in the literature to improve middle schools and benefit students that are at-risk of failing to master the curriculum at their grade level. The researcher concluded by reporting effective strategies being used in middle school at-risk programs. These are strategies noted by experts as successful in identified programs. The population for this study was seventh and eighth grade Title I students who attended middle school during the 1992-1993, 1993-1994, 1994-1995 and 1995-1996 school years. The data collected by the researcher are presented in two parts: the description of the Title I inclusion program; and the results of the Texas Assessment of Academic Skills tests in reading and math, the Shaw-Hiehle Math Tests, and the Gates-MacGinitie Reading Tests. Findings from this study suggest that the program met the requirements of a Title I program established by the federal government. The test scores for the middle school improved during the three years of the program. The Title I inclusion program met the requirements of the Improving America's Schools Act. Finally, the Title I students were successful working in classrooms with other students on challenging curriculum which met the State's content and performance standards. These findings have implications for other middle schools who are developing Title I ...
Date: May 1999
Creator: Restivo, Janet DiMaria
Partner: UNT Libraries

Brief Symptom Inventory: Music and Non-Music Students

Description: The present study is a comparison of music and non-music students with respect to their response patterns on the Brief Symptom Inventory as well as several demographic questions. The sample consisted of 148 non-music students and 141 music students at three levels: (1) freshmen/sophomore; (2) juniors/seniors; and (3) graduate students. Music students consisted of volunteers from several different music classes and non-music students were volunteers from non-music classes. There were no significant differences found among or between groups for the BSI subscales. However, music students were significantly less likely to have gone to counseling in the past and to seek professional counseling for future problems. Recommendations for psycho-educational interventions with musicians are discussed as well as suggestions for future research.
Date: August 1999
Creator: Young, James A. (James Alan), 1968-
Partner: UNT Libraries

Mutagenized HLA DNA Constructs: Tools for Validating Molecular HLA Typing Methodologies

Description: This study describes the development and validation of mutagenized cloned DNA constructs, which correspond to the polymorphic regions of the class II region of the HLA complex. The constructs were used to verify the allelic specificity of primers and probes in polymerase chain reaction (PCR)-based HLA typing assays such as Sequence Specific Primers (SSP) and Sequence Specific Oligonucleotide Probes (SSOP). The constructs consisted of the entire polymorphic region of exon 2 of class II HLA allele sequences that included primer annealing sites or probe hybridization sites. An HLA allele sequence was inserted into a plasmid, cloned, then mutagenized to match a specific HLA allele, and finally, the correct clone was verified by bidirectional sequencing of the insert. Thus, the construct created a cloned reference DNA sample for any specific allele, and can be used to validate the accuracy of various molecular methodologies.
Date: May 1999
Creator: Schulte, Kathleen Q.
Partner: UNT Libraries

Biodiversity of Dragonflies and Damselflies (Odonata) of the South-Central Nearctic and Adjacent Neotropical Biotic Provinces

Description: The south-central United States serves as an important biogeographical link and dispersal corridor between Nearctic and Neotropical elements of western hemisphere odonate faunas. Its species are reasonably well known because of substantial collections, but there has been no concerted effort to document the extent of biodiversity and possible geographic affinities of dragonflies and damselflies of this region. The recent discoveries of Argia leonorae Garrison, Gomphus gonzalezi Dunkle and Erpetogomphus heterodon Garrison from southern and western Texas and northern Mexico suggest that Odonata species remain to be discovered in this area, particularly from far south Texas and northern Mexico. I have documented a total of 12,515 records of Odonata found in 408 counties within the south-central U.S. A total of 73 species of damselflies and 160 species of dragonflies was revealed in the region. The 233 (197 in Texas) Odonata species are distributed among 10 families and 66 genera. Illustrated family, generic, and species-level keys are provided. Since the beginning of this work in the Fall of 1993, one species has been added each to the Louisiana and Oklahoma faunas, and 12 species have been added, previously unreported from Texas, including four new to the U.S. The area of highest Odonata biodiversity overall (161 spp.) is in the Austroriparian biotic province. The greatest degree of faunal similarity between the south-central U.S. and other intra-continental regions was observed for the eastern (64%) United States. Diversity is a function of area, and as expected, the numbers of breeding birds and Odonata, in each contiguous U.S. state are positively correlated (r=0.376, n=33, p=0.031). There is, however, no strong correlation between land area and species diversity within the region, but those natural biotic provinces (Austroriparian, Texan, Balconian) where aquatic systems and topographic heterogeneity are the greatest provide a broader spectrum of potential Odonata habitats and ...
Date: May 1999
Creator: Abbott, John C.
Partner: UNT Libraries

Historical Exposures to Chemicals at the Rocky Flats Nuclear Weapons Plant: A Pilot Retrospective Exposure Assessment

Description: In a mortality study of white males who had worked at the Rocky Flats Nuclear Weapons Plant between 1952 and 1979, an increased number of deaths from benign and unspecified intracranial neoplasms was found. A case-control study nested within this cohort investigated the hypothesis that an association existed between brain tumor death and exposure to either internally deposited plutonium or external ionizing radiation. There was no statistically significant association found between estimated radiation exposure from internally deposited plutonium and the development of brain tumors. Exposure by job or work area showed no significant difference between the cohort and the control groups. An update of the study found elevated risk estimates for (1) all lymphopoietic neoplasms, and (2) all causes of death in employees with body burdens greater than or equal to two nanocuries of plutonium. There was an excess of brain tumors for the entire cohort. Similar cohort studies conducted on worker populations from other plutonium handling facilities have not yet shown any elevated risks for brain tumors. Historically, the Rocky Flats Nuclear Weapons Plant used large quantities of chemicals in their production operations. The use of solvents, particularly carbon tetrachloride, was unique to Rocky Flats. No investigation of the possible confounding effects of chemical exposures was done in the initial studies. The objectives of the present study are to (1) investigate the history of chemical use at the Rocky Flats facility; (2) locate and analyze chemical monitoring information in order to assess employee exposure to the chemicals that were used in the highest volume; and (3) determine the feasibility of establishing a chemical exposure assessment model that could be used in future epidemiology studies.
Date: February 1, 1999
Creator: Robertson, Janeen Denise
Partner: UNT Libraries Government Documents Department

Crenulative Turbulence in a Converging Nonhomogeneous Material

Description: Crenulative turbulence is a nonlinear extension of the Bell-Plesset instability, usually observed in a converging system in which there is a nonhomogeneous response of stress to strain and/or strain rate. In general, crenelation occurs in any circumstance in which the mean flow streamlines converge the material more strongly than the compressibility can accommodate. Elements of the material slip past each other, resulting in local fluctuations in velocity from that of the mean flow, producing a type of turbulence that is more kinematic than inertial. For a homogeneous material, crenelation occurs at the atomic or molecular scale. With nonhomogeneous stress response at larger scales, the crenulative process can also occur at those larger scales. The results are manifested by a decrease in the rate of dissipation to heat, and by the configurationally-irreversible mixing of nonhomogeneities across any mean-flow-transported interface. We obtain a mathematical description of the crenulative process by means of Reynolds decomposition of the appropriate variables, and the derivation of transport equations for the second-order moments that arise in the mean-flow momentum and energy equations. The theory is illustrated by application to the spherical convergence of an incompressible fluid with nonhomogeneous distribution of kinematic viscosity.
Date: January 1, 1999
Creator: Romero, C.A.
Partner: UNT Libraries Government Documents Department

A Reduced Grid Method for a Parallel Global Ocean General Circulation Model

Description: A limitation of many explicit finite-difference global climate models is the timestep restriction caused by the decrease in cell size associated with the convergence of meridians near the poles. A computational grid in which the number of cells in the longitudinal direction is reduced toward high-latitudes, keeping the longitudinal width of the resulting cells as uniform as possible and increasing the allowable timestep, is applied to a three-dimensional primitive equation ocean-climate model. This ''reduced'' grid consists of subgrids which interact at interfaces along their northern and southern boundaries, where the resolution changes by a factor of three. Algorithms are developed to extend the finite difference techniques to this interface, focusing on the conservation required to perform long time integrations, while preserving the staggered spatial arrangement of variables and the numerics used on subgrids. The reduced grid eliminates the common alternative of filtering high-frequency modes from the solution at high-latitudes to allow a larger timestep and reduces execution time per model step by roughly 20 percent. The reduced grid model is implemented for parallel computer architectures with two-dimensional domain decomposition and message passing, with speedup results comparable to those of the original model. Both idealized and realistic model runs are presented to show the effect of the interface numerics on the model solution. First, a rectangular, mid-latitude, at-bottomed basin with vertical walls at the boundaries is driven only by surface wind stress to compare three resolutions of the standard grid to reduced grid cases which use various interface conditions. Next, a similar basin with wind stress, heat, and fresh water forcing is used to compare the results of a reduced grid with those of a standard grid result while exercising the full set of model equations. Finally, global model runs, with topography, forcing, and physical parameters similar to those used for ...
Date: December 1, 1999
Creator: Wickett, M.E.
Partner: UNT Libraries Government Documents Department

A new mechanical characterization method for thin film microactuators and its application to NiTiCi shape memory alloy

Description: In an effort to develop a more full characterization tool of shape memory alloys, a new technique is presented for the mechanical characterization of microactuators and applied to SMA thin films. A test instrument was designed to utilize a spring-loaded transducer in measuring displacements with resolution of 1.5 pm and forces with resolution of 0.2 mN. Employing an out-of-plane loading method for freestanding SMA thin films, strain resolution of 30{mu}{epsilon} and stress resolution of 2.5 MPa were achieved. This new testing method is presented against previous SMA characterization methods for purposes of comparison. Four mm long, 2 {micro}m thick NiTiCu ligaments suspended across open windows were bulk micromachined for use in the out-of-plane stress and strain measurements. The fabrication process used to micromachine the ligaments is presented step-by-step, alongside methods of fabrication that failed to produce testable ligaments. Static analysis showed that 63% of the applied strain was recovered while ligaments were subjected to tensile stresses of 870 MPa. In terms of recoverable stress and recoverable strain, the ligaments achieved maximum recovery of 700 MPa and 3.0% strain. No permanent deformations were seen in any ligament during deflection measurements. Maximum actuation forces and displacements produced by the 4 mm ligaments situated on 1 cm square test chips were 56 mN and 300 {micro}m, respectively. Fatigue analysis of the ligaments showed degradation in recoverable strain from 0.33% to 0.24% with 200,000 cycles, corresponding to deflections of 90 {micro}m and forces of 25 mN. Cycling also produced a wavering shape memory effect late in ligament life, leading to broad inconsistencies of as much as 35% deviation from average. Unexpected phenomena like stress-induced martensitic twinning that leads to less recoverable stress and the shape memory behavior of long life devices are addressed. Finally, a model for design of microactuators using shape memory alloys ...
Date: June 1, 1999
Creator: Seward, K P
Partner: UNT Libraries Government Documents Department

Surface structures of Al-Pd-Mn and Al-Cu-Fe icosahedral quasicrystals

Description: In this dissertation, the author reports on the surface structure of i-Al-Pd-Mn twofold, threefold, fivefold and i-Al-Cu-Fe fivefold surfaces. The LEED studies indicate the existence of two distinct stages in the regrowth of all four surfaces after Ar{sup +} sputtering. In the first stage, upon annealing at relatively low temperature: 500K--800K (depending on different surfaces), a cubic phase appears. The cubic LEED patterns transform irreversibly to unreconstructed quasicrystalline patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically-identical, but symmetrically-inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. These results may be general among Al-rich, icosahedral materials. STM study of Al-Pd-Mn fivefold surface shows that terrace-step-kink structures start to form on the surface after annealing above 700K. Large, atomic ally-flat terraces were formed after annealing at 900K. Fine structures with fivefold icosahedral symmetry were found on those terraces. Data analysis and comparison of the STM images and structure model of icosahedral Al-Pd-Mn suggest that the fine structures in the STM images may be the pseudo Mackay (PMI) clusters which are the structure units of the structure model. Based upon his results, he can conclude that quasicrystalline structures are the stable structures of quasicrystal surfaces. In other words, quasicrystalline structures extend from the bulk to the surface. As a result of the effort reported in this dissertation, he believes that he has increased his understanding of the surface structure of icosahedral quasicrystals to a new level.
Date: February 12, 1999
Creator: Shen, Z.
Partner: UNT Libraries Government Documents Department

Gas atomization processing of tin and silicon modified LaNi{sub 5} for nickel-metal hydride battery applications

Description: Numerous researchers have studied the relevant material properties of so-called AB{sub 5} alloys for battery applications. These studies involved LaNi{sub 5} substituted alloys which were prepared using conventional cast and crush alloying techniques. While valuable to the understanding of metal hydride effects, the previous work nearly ignored the potential for alternative direct powder production methods, like high pressure gas atomization (HPGA). Thus, there is a need to understand the relationship between gas atomization processes, powder particle solidification phases, and hydrogen absorption properties of ultra fine (< 25 {micro}m) atomized powders with high surface area for enhanced battery performance. Concurrently, development of a gas atomization nozzle that is more efficient than all current designs is needed to increase the yield of ultrafine AB{sub 5} alloy powder for further processing advantage. Gas atomization processing of the AB{sub 5} alloys was demonstrated to be effective in producing ultrafine spherical powders that were resilient to hydrogen cycling for the benefit of improving corrosion resistance in battery application. These ultrafine powders benefited from the rapid solidification process by having refined solute segregation in the microstructure of the gas atomized powders which enabled a rapid anneal treatment of the powders. The author has demonstrated the ability to produce high yields of ultrafine powder efficiently and cost effectively, using the new HPGA-III technology. Thus, the potential benefits of processing AB{sub 5} alloys using the new HPGA technology could reduce manufacturing cost of nickel-metal hydride powder. In the near future, the manufacture of AB{sub 5} alloy powders could become a continuous and rapid production process. The economic benefit of an improved AB{sub 5} production process may thereby encourage the use of nickel-metal hydride rechargeable batteries in electrical vehicle applications in the foreseeable future.
Date: February 12, 1999
Creator: Ting, J.
Partner: UNT Libraries Government Documents Department

The analysis of aqueous mixtures using liquid chromatography-electrospray mass spectrometry

Description: The focus of this dissertation is the use of chromatographic methods coupled with electrospray mass spectrometry (ES-MS) for the determination of both organic and inorganic compounds in aqueous solutions. The combination of liquid chromatography (LC) methods and ES-MS offers one of the foremost methods for determining compounds in complex aqueous solutions. In this work, LC-ES-MS methods are devised using ion exclusion chromatography, reversed phase chromatography, and ion exchange chromatography, as well as capillary electrophoresis (CE). For an aqueous sample, these LC-ES-MS and CE-ES-MS techniques require no sample preparation or analyte derivatization, which makes it possible to observe a wide variety of analytes as they exist in solution. The majority of this work focuses on the use of LC-ES-MS for the determination of unknown products and intermediates formed during electrochemical incineration (ECI), an experimental waste remediation process. This report contains a general introduction to the project and the general conclusions. Four chapters have been removed for separate processing. Titles are: Chapter 2: Determination of small carboxylic acids by ion exclusion chromatography with electrospray mass spectrometry; Chapter 3: Electrochemical incineration of benzoquinone in aqueous media using a quaternary metal oxide electrode in the absence of a soluble supporting electrolyte; Chapter 4: The determination of electrochemical incineration products of 4-chlorophenol by liquid chromatography-electrospray mass spectrometry; and Chapter 5: Determination of small carboxylic acids by capillary electrophoresis with electrospray mass spectrometry.
Date: February 12, 1999
Creator: Johnson, S.
Partner: UNT Libraries Government Documents Department

Calibration of laser ablation inductively coupled plasma mass spectrometry using dried solution aerosols for the quantitative analysis of solid samples

Description: Inductively coupled plasma mass spectrometry (ICP-MS) has become the method of choice for elemental and isotopic analysis. Several factors contribute to its success. Modern instruments are capable of routine analysis at part per trillion levels with relative detection limits in part per quadrillion levels. Sensitivities in these instruments can be as high as 200 million counts per second per part per million with linear dynamic ranges up to eight orders of magnitude. With standards for only a few elements, rapid semiquantitative analysis of over 70 elements in an individual sample can be performed. Less than 20 years after its inception ICP-MS has shown to be applicable to several areas of science. These include geochemistry, the nuclear industry, environmental chemistry, clinical chemistry, the semiconductor industry, and forensic chemistry. In this introduction, the general attributes of ICP-MS will be discussed in terms of instrumentation and sample introduction. The advantages and disadvantages of current systems are presented. A detailed description of one method of sample introduction, laser ablation, is given. The paper also gives conclusions and suggestions for future work. Chapter 2, Quantitative analysis of solids by laser ablation inductively coupled plasma mass spectrometry using dried solution aerosols for calibration, has been removed for separate processing.
Date: February 12, 1999
Creator: Leach, J.
Partner: UNT Libraries Government Documents Department

Methods development for separation of inorganic anions, organic acids and bases, and neutral organic compounds by ion chromatography and capillary electrophoresis

Description: A novel anion-exchange resin containing three amine groups was prepared by reaction of a chloromethylated polystyrene-divinylbenzene (PS-DVB) resin with diethylenetriamine. After being protonated by contact with an aqueous acid, this resin can be used for ion chromatographic separation of anions. The charge on the resins can be varied from +1 to +3 by changing the mobile phase pH. The selectivity of the new ion exchangers for various inorganic anions was quite different from that of conventional anion exchangers. The performance of this new anion exchanger was studied by changing the pH and the concentration of the eluent, and several different eluents were used with some common anions as testing analytes. Conductivity detection and UV-visible detection were applied to detect the anions after separation. The new resin can also be used for HPLC separation of neutral organic compounds. Alkylphenols and alkylbenzenes were separated with this new polymeric resin, and excellent separations were obtained under simple conditions. This report contains Chapter 1: General introduction and Chapter 6: General conclusions.
Date: April 1, 1999
Creator: Li, J.
Partner: UNT Libraries Government Documents Department

Human Rights & U.S. Foreign Aid, 1984-1995: The Cold War and Beyond...

Description: This study attempts to cast empirical light on the traditionalist-revisionist debate regarding the impact of the Soviet Union's collapse on U.S. foreign policy decision-making. To accomplish this goal, the relationship between human rights and U.S. foreign aid decision-making is examined before and after the Cold War. In doing so, the author attempts to determine if "soft" approaches, such as the use of a country's human rights records when allocating aid, have garnered increasing attention since the end of Cold War, as traditionalists assert, or declined in importance, as revisionists content.
Date: December 1999
Creator: Miller, Brian Lawrence
Partner: UNT Libraries

Factors Influencing How Students Value Asynchronous Web Based Courses

Description: This dissertation discovered the factors influencing how students value asynchronous Web-based courses through the use of qualitative methods. Data was collected through surveys, observations, interviews, email correspondence, chat room and bulletin board transcripts. Instruments were tested in pilot studies of previous semesters. Factors were identified for two class formats. The asynchronous CD/Internet class format and the synchronous online Web based class format. Also, factors were uncovered for two of the instructional tools used in the course: the WebCT forum and WebCT testing. Factors were grouped accordingly as advantages or disadvantages under major categories. For the asynchronous CD/Internet class format the advantages were Convenience, Flexibility, Learning Enhancement, and Psychology. The disadvantages included Isolation, Learning Environment, and Technology. For the synchronous online Web based class format the advantages were Convenience, Flexibility, Human Interaction, Learning Enhancement and Psychology, whereas the disadvantages included Isolation, Learning Environment and Technology. Concurrently, the study revealed the following factors as advantages of the WebCT Forum: Help Each Other, Interaction, Socialization, Classroom News, and Time Independent. The disadvantages uncovered were Complaints, Technical Problems and Isolation. Finally, advantages specified for the WebCT testing tool were Convenience, Flexibility and Innovations, and its disadvantages were Surroundings Not Conducive to Learning, and Technical Problems. Results indicate that not only classroom preference, learning style and personality type influence how students value a Web based course, but, most importantly, a student's lifestyle (number of personal commitments, how far they live, and life's priorities). The WebCT forum or bulletin board, and the WebCT testing or computerized testing were seen mostly by students, as good tools for encouraging classroom communication and testing because of the convenience and flexibility offered. Still, further research is needed both quantitatively and qualitatively to ascertain the true weight of the factors discovered in this study.
Date: December 1999
Creator: Pérez Cereijo, Maria Victoria
Partner: UNT Libraries

Chiral separation of pharmaceutical compounds using electrochemically modulated liquid chromatography (EMLC)

Description: This research explores the application of a new technique, termed electrochemically modulated liquid chromatography (EMLC), to the chiral separations of pharmaceutical compounds. The introduction section provides a literature review of the technique and its applications, as well as brief overview of the research described in each of the next two chapters. Chapter 2 investigates the EMLC-based enantiomeric separation of a group of chiral benzodiazepines with {beta}-cyclodextrin as a chiral mobile phase additive. Chapter 3 demonstrates the effects of several experimental parameters on the separation efficiency of drug enantiomers. The author concludes with a general summary and possible directions for future studies. Chapters 2 and 3 are processed separately.
Date: February 12, 1999
Creator: Wang, S.
Partner: UNT Libraries Government Documents Department

Structure sensitive adsorption of hydrogen on ruthenium and ruthenium-silver catalysts supported on silica

Description: Supported metal catalysts typically consist of particles with sizes less than 10 nm, and because of the small crystallite size, low coordination number sites (edges and corners) represent a significant fraction of all surface sites. Furthermore, it has been demonstrated that adsorption rates can be much greater at these low coordination sites than on basal plane sites. What has not been generally appreciated, however, is that preferential adsorption at edge and corner sites may explain the mechanism by which a promoter, or the addition of a second metal to form a bimetallic, can alter the selectivity and rate of reaction. For example, the measurements of hydrogen adsorption onto supported Ru-Ag catalysts show marked decreases in the amount of hydrogen adsorbed relative to the amount adsorbed on Ru catalysts. Although it is known that Ag does not dissociatively adsorb hydrogen, this decrease cannot be explained by a simple one-to-one site blocking mechanism unless Ag preferentially populates edges and corners, thereby reducing the number of Ru edge sites. Indeed, Monte Carlo simulations of Ru-Group IB metal catalysts predict that Group IB metal atoms preferentially populate corner and edge sites of ruthenium crystals. This evidence, taken together, suggests that adsorption occurs preferentially at Ru corner and edge sites, which act as portals onto basal planes. A model based on this portal theory for hydrogen adsorption onto supported ruthenium bimetallic catalysts has been developed using a rate equation approach. Specifically, the model accounts for the following features: (1) preferential adsorption through portals, (2) basal plane site-energy multiplicity, and (3) hydrogen spillover onto the support. A comparison of model predictions with experiment is presented for different concentration of Ag in Ru-Ag catalysts. The portal model of hydrogen adsorption can explain the observed decreased in the amount of hydrogen adsorbed on Ru-Ag catalysts. The model can ...
Date: February 12, 1999
Creator: Kumar, N.
Partner: UNT Libraries Government Documents Department

Collision-induced dissociation reactions and pulsed field ionization photoelectron

Description: This report summarized the four parts of the research study and describes the general conclusions. Individual chapters have been removed for separate processing. The chapter titles are: A study of the dissociation of CH{sub 3}SH{sup +} by collisional activation: Observation of non-statistical behavior; High resolution vacuum ultraviolet pulsed field ionization photoelectron band for OCS{sup +}(X{sup 2}{Pi}): An experimental and theoretical study; Rotationally resolved pulsed field ionization photoelectron bands of H{sub 2}{sup +} ({Chi}{sup 2}{Sigma}{sup +}{sub g}, v{sup +} = 0--18); and Rotationally resolved pulsed field ionization photoelectron bands of HD{sup +} ({Chi}{sup 2}{Sigma}{sup +}, v{sup +} = 0--21).
Date: February 12, 1999
Creator: Stimson, S.
Partner: UNT Libraries Government Documents Department

Optically detected magnetic resonance studies on {pi}-conjugate polymers and novel carbon allotropes

Description: This report describes the following: introduction to photoluminescence detected magnetic resonance (PLDMR); introduction to {pi}-conjugated systems; PLDMR measurements on poly(p-phenylene)-type ladder polymers; PLMDR measurements on poly(p-phenylene ethylene); and PLDMR measurements on C{sub 70}, polythiophene, poly(p-phenylene vinylene) and Dan-40. Appendices to this report describe: Operation of ODMR (optically detected magnetic resonance) spectrometer; ODMR system parameters; and Special purpose circuitry.
Date: February 12, 1999
Creator: Partee, J.
Partner: UNT Libraries Government Documents Department