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Signal and noise analysis of a-Si:H radiation detector-amplifier system
Hydrogenated amorphous silicon (a-Si:H) has potential advantages in making radiation detectors for many applications because of its deposition capability on a large-area substrate and its high radiation resistance. Position-sensitive radiation detectors can be made out of a 1d strip or a 2-d pixel array of a Si:H pin diodes. In addition, signal processing electronics can be made by thin-film transistors on the same substrate. The calculated radiation signal, based on a simple charge collection model agreed well with results from various wave length light sources and 1 MeV beta particles on sample diodes. The total noise of the detection system was analyzed into (a) shot noise and (b) 1/f noise from a detector diode, and (c) thermal noise and (d) 1/f noise from the frontend TFT of a charge-sensitive preamplifier. the effective noise charge calculated by convoluting these noise power spectra with the transfer function of a CR-RC shaping amplifier showed a good agreement with the direct measurements of noise charge. The derived equations of signal and noise charge can be used to design an a-Si:H pixel detector amplifier system optimally. Signals from a pixel can be readout using switching TFTs, or diodes. Prototype tests of a double-diode readout scheme …
Date:
March 1, 1992
Creator:
Cho, Gyuseong
System:
The UNT Digital Library
Rhetorical Analysis of the Media and History
Thesis written by a student in the UNT Honors College discussing the history and nature of media coverage, including Operation Desert Storm and the Civil Rights Movement. Special attention is paid to the role of television in journalism.
Date:
Spring 1992
Creator:
Schwartz, Cathy
System:
The UNT Digital Library
'A Time of Gifts': Europe Revisited
Colloquium written by a student in the UNT Honors College as a short story that features traveling to Europe and the wisdom of observation.
Date:
Spring 1992
Creator:
Desiderato, Michelle
System:
The UNT Digital Library
The Writing Portion of the TASP Test: Does Instruction Make a Difference?
Thesis written by a student in the UNT Honors College examining whether the teaching of composition affects student performance on the writing portion of the Texas Academic Skills Program (TASP) test.
Date:
Spring 1992
Creator:
Vrba, Susanne G.
System:
The UNT Digital Library
Charged particle spectra in {sup 32}S + {sup 32}S interactions at 200 GeV/nucleon from CCD-imaged nuclear collisions in a streamer chamber
We have measured the transverse momentum spectra 1/p{sub T} dN/dp{sub T} and rapidity distributions dN/dy of negatively charged hadrons and protons for central {sup 32}S + {sup 32}S interactions at 200 GeV/nucleon incident energy. The negative hadron dN/dy distribution is too broad to be accounted for by thermal models which demand isotropic particle emission. It is compatible with models which emphasize longitudinal dynamics, by either a particle production mechanism, as in the Lund fragmentation model, or by introducing one-dimensional hydrodynamic expansion, as in the Landau model. The proton dN/dy distribution, although showing no evidence for a peak in the target fragmentation region, exhibits limited nuclear stopping power. We estimate the mean rapidity shift of participant target protons to be {Delta}y {approximately} 1.5, greater than observed for pp collisions, less than measured in central pA collisions, and much less than would be observed for a single equilibrated fireball at midrapidity. Both the negative hadron and proton dN/dy distributions can be fit by a symmetric Landau two-fireball model. Although the spectrum possesses a two-component structure, a comparison to pp data at comparable center-of-mass energy shows no evidence for enhanced production at low p{sub T}. The two-component structure can be explained by a …
Date:
April 1, 1992
Creator:
Teitelbaum, L. P.
System:
The UNT Digital Library
The effect of rhenium, sulfur and alumina on the conversion of hydrocarbons over platinum single crystals: Surface science and catalytic studies
Conversion reactions of hydrocarbons over Pt-Re model catalyst surfaces modified by sulfur and alumina have been studied. A plasma deposition source has been developed to deposit Pt, Re, and Al on metal substrates variable coverage in ultrahigh vacuum without excessive heating. Conversion of n-hexane was performed over the Re-covered Pt and Pt-covered Re surfaces. The presence of the second metal increased hydrogenolysis activity of both Pt-Re surfaces. Addition of sulfur on the model Catalyst surfaces suppressed hydrogenolysis activity and increased the cyclization rate of n-hexane to methylcyclopentane over Pt-Re surfaces. Sulfiding also increased the dehydrogenation rate of cyclohexane to benzene Over Pt-Re surfaces. It has been proposed that the PtRe bimetallic catalysts show unique properties when combined with sulfur, and electronic interactions exist between platinum, rhenium and sulfur. Decomposition of hydrocarbons on the sulfur-covered Pt-Re surfaces supported that argument. For the conversion of 1-butene over the planar Pt/AlO{sub x}, the addition of Pt increased the selectivity of hydrogenation over isomerization.
Date:
April 1, 1992
Creator:
Kim, C.
System:
The UNT Digital Library
Electronic and structural properties of metallic microclusters
The first part of this thesis presents a first-order pseudopotential calculation at T=O of the total energy of small sodium clusters of size N<800. The calculation is based on a local-pseudopotential scheme and local-density correlation and exchange. A temperature-size (T-N) phase-diagram is then derived using the T=O results and Lindemann`s criterion for melting. The phase-diagram contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line T{sub M}(N) where cluster-stability occurs at electronic magic numbers: (2) a phase related to complete geometrical shells of body-centered-cubic structure at temperatures below the melting line; and (3) a close-packed structure at very low temperatures and sufficiently large N. The melting line drops to T{sub M}(N)=O for N<65, where electronic magic numbers are stable even at T=O. The phase diagram reduces asymptotically to the known phases of sodium as N{yields}{infinity}, including the known martensitic transformation at T{approximately}5 K. The second and the last part of this thesis consists of a study of small-cluster many-body systems by means of an on-site ``local`` chemical potential which allows the continuous variation of local electron-density. This method yields a criterion to distinguish particular features of a small cluster that are likely to survive …
Date:
April 1, 1992
Creator:
Maiti, A.
System:
The UNT Digital Library
Image potential states at metal-dielectric interfaces
Angle-resolved two-photon laser photoemission was used to observe the image potential electronic states on the (111) face of a silver single crystal. The transient image potential states were excited from the occupied bulk bands with photons whose energy was tunable around 4 eV. Photoemission of the image potential states was accomplished with photons of energy tunable around 2 eV. Image potential states were found to persist in the presence of physisorbed adlayers of xenon and cyclohexane. On clean Ag(111), the effective mass of the n=1 image potential state was found to be 1.4{plus_minus}0.1 times the mass of a free electron (m{sub e}). A binding energy of 0.77 eV, measured by earlier workers, was assumed in analysis of the data for the clean surface. On Ag(111), at 75 K covered by one monolayer of xenon, the binding energy of the n=1 image potential state was unchanged relative to its value on the clean surface. An effective mass of (1.00{plus_minus}0.05) {center_dot} m{sub e} was obtained. On Ag(111) at 167 K, covered by one monolayer of cyclohexane, the binding energy of the n=2 member of the image potential series was 0.30{plus_minus}0.05 eV. The energy of the n=1 state was again unchanged by deposition …
Date:
April 1, 1992
Creator:
Merry, W. R. Jr.
System:
The UNT Digital Library
Independent verification and validation of large software requirement specification databases
To enhance quality, an independent verification and validation (IV&V) review is conducted as software requirements are defined. Requirements are inspected for consistency and completeness. IV&V strives to detect defects early in the software development life cycle and to prevent problems before they occur. The IV&V review process of a massive software requirements specification, the Reserve Component Automation System (RCAS) Functional Description (FD) is explored. Analysis of the RCAS FD error history determined that there are no predictors of errors. The size of the FD mandates electronic analysis of the databases. Software which successfully performs automated consistency and completeness checks is discussed. The process of verifying the quality of analysis software is described. The use of intuitive ad hoc techniques, in addition to the automatic analysis of the databases, is required because of the varying content of the requirements databases. The ad hoc investigation process is discussed. Case studies are provided to illustrate how the process works. This thesis demonstrates that it is possible to perform an IV&V review on a massive software requirements specification. Automatic analysis enables inspecting for completeness and consistency. The work with the RCAS FD clearly indicates that the IV&V review process is not static; it must …
Date:
April 1, 1992
Creator:
Twitchell, K. E.
System:
The UNT Digital Library
Investigation of ultrafast photothermal surface expansion and diffusivity in GaAs via laser-induced dynamic gratings
This thesis details the first direct ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples over a wide range of temperatures. By utilizing a 90 fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion due to heating and subsequent contraction caused by cooling provided the dominant influence on the probe. At room temperature a rise due to thermal expansion was observed, corresponding to a maximum net displacement of {approximately} 1 {Angstrom} at 32 ps. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, thus allowing a determination of the rate of expansion as well as the surface thermal diffusivity, D{sub S}. By varying the fringe spacing of the grating, this technique has the potential to separate the signal contributions to the expansion of the lattice in the perpendicular and parallel directions. In the data presented here a large fringe spacing was used, thus the dominant contribution to the rising edge of the signal …
Date:
April 1, 1992
Creator:
Pennington, D. M.
System:
The UNT Digital Library
Studies of fundamental properties of rutherfordium (Element 104) using organic complexing agents
Chemical properties of rutherfordium (Rf) have been investigated with the organic ligands triisooctylamine (TIOA), tributylphosphate (TBP), and thenoyltrifluoroacetone (TTA). The TIOA studies showed that Rf behaves differently than Th and Eu and most similarly to Zr, only Zr and Rf extract from 12 M HCI. This result is further evidence that Rf is a Group 4 element. Studies with TBP showed that Rf chemical behavior differed from the other Group 4 elements. The extraction by TBP at different chloride concentrations showed that Rf at times behaves more like Pu{sup 4+} than Zr or Hf. At high chloride concentrations, Rf and Pu extraction decreased. Under the same conditions, Zr, Hf and Th extraction increased. In addition, Rf extraction by TBP was affected by hydrogen ion concentration, while Zr and Hf extraction was not. TTA extractions were used to determine the K{sub eq}, K{sub hyd}, and the ionic radius of Rf. The of K{sub eq} for Rf with TTA was calculated to be 3.18 {plus minus} 0.90. The first four log K{sub hyd's} for Rf are calculated to be {minus}2.6 {plus minus} 0.7, {minus}5.9 {plus minus} 1.7, {minus}10.2 {plus minus} 2.9, and {minus}14.5 {plus minus} 4.1. These hydrolysis constants indicate that Rf …
Date:
April 1, 1992
Creator:
Czerwinski, K. R.
System:
The UNT Digital Library
Studies of fundamental properties of rutherfordium (Element 104) using organic complexing agents
Chemical properties of rutherfordium (Rf) have been investigated with the organic ligands triisooctylamine (TIOA), tributylphosphate (TBP), and thenoyltrifluoroacetone (TTA). The TIOA studies showed that Rf behaves differently than Th and Eu and most similarly to Zr, only Zr and Rf extract from 12 M HCI. This result is further evidence that Rf is a Group 4 element. Studies with TBP showed that Rf chemical behavior differed from the other Group 4 elements. The extraction by TBP at different chloride concentrations showed that Rf at times behaves more like Pu{sup 4+} than Zr or Hf. At high chloride concentrations, Rf and Pu extraction decreased. Under the same conditions, Zr, Hf and Th extraction increased. In addition, Rf extraction by TBP was affected by hydrogen ion concentration, while Zr and Hf extraction was not. TTA extractions were used to determine the K{sub eq}, K{sub hyd}, and the ionic radius of Rf. The of K{sub eq} for Rf with TTA was calculated to be 3.18 {plus_minus} 0.90. The first four log K{sub hyd`s} for Rf are calculated to be {minus}2.6 {plus_minus} 0.7, {minus}5.9 {plus_minus} 1.7, {minus}10.2 {plus_minus} 2.9, and {minus}14.5 {plus_minus} 4.1. These hydrolysis constants indicate that Rf will not hydrolyze at conditions …
Date:
April 1, 1992
Creator:
Czerwinski, K. R.
System:
The UNT Digital Library
Study of the Mn-binding sites in photosystem II using antibodies raised against lumenal regions of the D1 and D2 reaction center proteins
The experiments discussed in this thesis focus on identifying the protein segments or specific amino acids which provide ligands to the Mn cluster of photosystem II (PS II). This Mn cluster plays a central role in the oxygen-evolving complex (OEC) of PS II. The Mn cluster is thought to be bound by lumenal regions of the PS II reaction center proteins known as D1 and D2. First, several peptides were synthesized which correspond to specific lumenal segments of the D1 and D2 proteins. Next, polyclonal antibodies were successfully elicited using three of these peptides. The peptides recognized by these antibodies correspond to protein segments of the spinach reaction center proteins: Ile-321 to Ala-344 of D1 (D1-a), Asp-319 to Arg-334 of D1 (D1-b), and Val-300 to Asn-319 of D2 (D2-a). These antibodies were then used in assays which were developed to structurally or functionally probe the potential Mn-binding regions of the D1 and D2 proteins.
Date:
April 1, 1992
Creator:
Dalmasso, E. A.
System:
The UNT Digital Library
African-American Senior Administrators of Colleges and Universities in American Higher Education: Identification of Characteristics in Their Career Progression
This study identified and compared characteristics in the career progression of African-American college presidents of institutions in the continental United States. The study was concerned with personal, educational and professional characteristics of these senior level administrators. From a population of 141 individuals, 73 presidents participated in this study. Frequencies, means, percentages, chi-square, crosstabulations and analysis of variance (ANOVA) were employed in the analysis of data. The level of significance was set at 0.05.
Date:
May 1992
Creator:
Marbury, R. Kevin (Robert Kevin)
System:
The UNT Digital Library
An analysis of multiple particle settling for LMR backup shutdown systems
Backup shutdown systems proposed for future LMRs may employ discreet absorber particles to provide the negative reactivity insertion. When actuated, these systems release a dense packing of particles from an out-of-core region to settle into an in-core region. The multiple particle settling behavior is analyzed by the method of continuity waves. This method provides predictions of the dynamic response of the system including the average particle velocity and volume fraction of particles vs. time. Although hindered settling problems have been previously analyzed using continuity wave theory, this application represents an extension of the theory to conditions of unrestrained settling. Typical cases are analyzed and numerical results are calculated based on a semi-empirical drift-flux model. For 1/4-inch diameter boron-carbide particles in hot liquid sodium, the unrestrained settling problem assumes a steady-state solution when the average volume fraction of particles is 0.295 and the average particle velocity is 26.0 cm/s.
Date:
May 1, 1992
Creator:
Brock, R. W.
System:
The UNT Digital Library
Aortic Baroreceptor Reflex Control of Blood Pressure: Effect of Fitness
Aortic baroreflex (ABR) control of blood pressure was examined in 7 untrained (UT) and 8 endurance exercise trained (EET) young men. ABR control of blood pressure was determined during a steady state phenylephrine infusion to increase mean arterial pressure 10-15 mmHg, combined with positive neck pressure to counteract the increased carotid sinus transmural pressure, and low levels of lower body negative pressure to counteract the increased central venous pressure. Functioning alone, the ABR was functionally adequate to control blood pressure. However, ABR control of HR was significantly diminished in the EET subjects due solely to the decrease in the ABR sensitivity. The persistent strain from an increased stroke volume resulting from endurance exercise training could be the responsible mechanism.
Date:
May 1992
Creator:
Andresen, Jean M.
System:
The UNT Digital Library
The Association between Attitudes toward Computers and Understanding of Ethical Issues Affecting Their Use
This study examines the association between the attitudes of students toward computers and their knowledge of the ethical uses of computers. The focus for this research was undergraduate students in the Colleges of Arts and Sciences (Department of Computer Science), Business and Education at the University of North Texas in Denton, Texas.
Date:
May 1992
Creator:
Gottleber, Timothy Theodore
System:
The UNT Digital Library
The Association Between Attributional Styles and Academic Performance of Students in a Program of Religious Studies
The problem addressed in this study was to determine if a significant association exists between attributions and academic achievement among students in a program of religious training at a Bible college. The research was designed to ascertain if optimistic attributions are more frequently associated with students in programs of religious education than with students in a public state-supported university environment. No significant correlation was found between optimistic explanatory styles and the academic achievement of Bible college students. A significant positive difference was found to exist between the explanatory styles of students at The Criswell College and students at the University of North Texas. Students in religious courses of study tended toward attributions for negative events that were external, unstable, and specific. The University of North Texas students tended toward attributions for negative events that were internal, stable, and global.
Date:
May 1992
Creator:
Ward, Charles W.
System:
The UNT Digital Library
Atmospheric Visibility Assessment for Urban Areas Using Photographic Slides and Optical Densitometry
The factors involved in calculating Standard Visual Range (SVR) are discussed, and a comparison is made between the visibility reported by airport observers and the photographic slide/ optical densitometer method of calculating SVR. Using slides of Houston, Texas, from the fall and winter of 1988-89, it was found that the altitude at which the contrast measurements are made significantly affects the SVR. Also an index for predicting high and low humidity was developed using the blue/red ratio of the log exposure of the sky, and sun/shade target condition.
Date:
May 1992
Creator:
Jacob, Mary Katherine
System:
The UNT Digital Library
Attitudes of Faculty Members in Rajamangala Institute of Technology, Thailand, Toward the Implementation of Computers
This study explored the attitudes and perceptions of faculty members in Rajamangala Institute of Technology (RIT), Thailand. The purpose of this study was to (a) determine which demographic variables are associated with faculty members attitudes toward the implementation of computers in higher education in Thailand, and (b) determine perceptions among faculty members toward barriers to the widespread use of computers.
Date:
May 1992
Creator:
Cheamnakarin, Pornpimon
System:
The UNT Digital Library
Background Characteristics and Matriculation Rationale of Hispanic and Non-Hispanic Students in Selected Two-Year Colleges
The research was designed to test the hypothesis that significant differences exist between Hispanic and non-Hispanic students respecting background characteristics and reasons for enrollment in selected two-year colleges. The findings led to firm conclusions regarding the need for educational institutions to provide remedial and tutorial services, liberal financial aid, culturally sensitive institutional ambience, diversity in faculty, counselors, and staff, and instructional and student development programs responsive to the cultural diversity of all students.
Date:
May 1992
Creator:
Dexter, R. Parker (Rawlins Parker)
System:
The UNT Digital Library
Bearclaw: a Novel
Written in the tradition of American political suspense thrillers such as "Fail-Safe" and "Seven Days In May," "Bearclaw" uses their idealistic and nationalistic elements to tell a story of an American President eager to lead the world's peoples in a quest to achieve man's "highest destiny," the conquest of space. Believing that this common goal will cause mankind to come together in a spirit of brotherhood, he misreads the historical purpose of the United States and, in the end, refuses to recognize the obvious truths of human frailty and ambition even though he has been victimized by them. The Introduction is a brief survey of the sociopolitical and literary forces which combined to create the American political suspense thriller and an attempt to define its place in the literary canon.
Date:
May 1992
Creator:
Elston, James C. (James Cary)
System:
The UNT Digital Library
Blood Pressure Regulation During Simulated Orthostatism Prior to and Following Endurance Exercise Training
Cardiovascular responses and tolerance to an orthostatic stress were examined in eight men before and after eight months of endurance exercise training. Following training, maximal oxygen consumption and blood volume were increased, and resting heart rate reduced. Orthostatic tolerance was reduced following training in all eight subjects. It was concluded that prolonged endurance training decreased orthostatic tolerance and this decrease in tolerance appeared associated with attenuated baroreflex sensitivity and alterations in autonomic balance secondary to an increased parasympathetic tone noted with training.
Date:
May 1992
Creator:
Stevens, Glen Harold John
System:
The UNT Digital Library
A Case Study of Interpersonal Influences in a Band Music Setting: Bohumil Makovsky (1878-1950) and His Association with Selected Individuals Involved in Instrumental Music in the State of Oklahoma
The purpose of this study was to investigate the interpersonal influences which Bohumil Makovsky, Director of Bands and Chairman of the Music Department at Oklahoma A&M College from 1915 to 1943, had on his students and peers, as confirmed through the perceptions of selected individuals, and to determine what personal characteristics and means he drew upon to induce changes in his students and peers.
Date:
May 1992
Creator:
Dugger, Richard Charles
System:
The UNT Digital Library