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

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

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 …
Date: May 1999
Creator: Abbott, John C.
System: The UNT Digital Library
The Effect of Presence of Support Systems and Level of Agreement on the Performance of Work Groups (open access)

The Effect of Presence of Support Systems and Level of Agreement on the Performance of Work Groups

In the study of team-based organizations most of the research has focus on the internal make-up and structure of teams. Recently there has been more interest in the effects that environment has on teams. With this new focus Support Systems in organizations have become an area of interest. Examining the perceptions of workers with respect to support systems of organizations could give insight into performance. This study specifically examines the interaction between a team's shared perception of the support in their environment and the level of support in their environment. The interaction between the two does seem to have a strong relationship with perceived performance. How do the two concepts interact, and what does this mean for organizational designers? Both questions are discussed.
Date: May 1999
Creator: Adcock, John R. (John Roger)
System: The UNT Digital Library
Current and Future Trends in Computer Use in Elementary School Settings (open access)

Current and Future Trends in Computer Use in Elementary School Settings

The study examined current and future trends in computer use in elementary school settings. A survey instrument was developed and validated for distribution to a random sample of 200 technology coordinators in the public school districts in the state of Texas from whom 95 responses were received. The survey instrument was used to obtain information about five areas of computer use in elementary schools. These areas are: physical configurations, instructional uses, implementation issues, training and staff development, and Internet use. The study found that all public school districts that participated in the study have acquired computer hardware in their elementary schools. In addition, some other advanced computer technology components are starting to be found in elementary schools, such as teacher workstations, CD-ROM, interactive video, computer multimedia, LCD panels, and laser printers. Respondents reported that elementary school teachers in their districts have incorporated computers into their classrooms as an instructional tool and many changes have occurred in teachers’ teaching styles due to computers. However, there are some problems that hinder the effective use of computers. The major problem is lack of training. A high percentage of respondents, 81.3%, indicated that the majority of their elementary school teachers had completed less than …
Date: August 1999
Creator: Al-Awidi, Hamed M.
System: The UNT Digital Library
A Computer-Based Process Control System for a Target Station in a LINAC Facility (open access)

A Computer-Based Process Control System for a Target Station in a LINAC Facility

An event-driven, sequential, process control system was designed for International Isotopes, Inc., to automate and remotely control a target station at the company's linear accelerator facility. The designed system consisted of two major sections: a software program (virtual instrument), which was developed by LabVIEW, and a hardware interface (FieldPoint Modular Distributed I/O System by National Instrument), which had to be a pre-developed system that did not require customization. The designed virtual instrument was tested on a simulation model that mimed the target station. The result was a valid design.
Date: May 1999
Creator: Al-Shantaf, Abdulraouf O.
System: The UNT Digital Library
Teacher Implementation of a Pretreatment Assessment Procedure in a Public Middle School (open access)

Teacher Implementation of a Pretreatment Assessment Procedure in a Public Middle School

In an attempt to determine the effectiveness of a pretreatment assessment procedure known as the scatter plot (Touchette, MacDonald, & Langer, 1985), direct observational data was collected by 13 middle school teachers on four "problem" students. After four weeks of data collection, interobserver agreement probes were calculated and a visual analysis of the plotted data was performed to ascertain a possible pattern of problem behavior. Additionally, in an attempt to assess the teachers' perceptions of the scatter plot, the 13 teachers were asked to complete a questionnaire. Although a visual analysis of the plotted data suggested a possible pattern of problem behavior, interobserver agreement probes failed to achieve a desired overall reliability of 90% or higher. Despite a low IOA, results of the questionnaire administered to the 13 teachers generally supported the use of the scatter plot as a means of assessing student behavior. Possible reasons for failing to attain an IOA of 90% or higher include the total number of students in a class, the number of subjects observed per period, the teacher's location in the classroom, and the subjects ability to recognize if the teacher was "looking." Recommendations are provided regarding future research concerning the scatter plot and …
Date: May 1999
Creator: Alcala, Angelo L. (Angelo Lee)
System: The UNT Digital Library
The Power Politics of Hells Canyon (open access)

The Power Politics of Hells Canyon

This study examines the controversy regarding Hells Canyon on the Snake River, North America's deepest gorge. Throughout the 1950s, federal and private electric power proponents wrangled over who would harness the canyon's potential for generating hydroelectricity. After a decade of debate, the privately-owned Idaho Power Company won the right to build three small dams in the canyon versus one large public power structure. The thesis concludes that private development of Hells Canyon led to incomplete resource development. Further, support of private development led to extensive Republican electoral losses in the Pacific Northwest during the 1950s.
Date: August 1999
Creator: Alford, John Matthew
System: The UNT Digital Library
Ion Implantation of In{sub 0.53}Ga{sub 0.47}As (open access)

Ion Implantation of In{sub 0.53}Ga{sub 0.47}As

None
Date: May 14, 1999
Creator: Almonte, Marlene I.
System: The UNT Digital Library
Effect of Operating Parameters and Chemical Additives on Crystal Habit and Specific Cake Resistance of Zinc Hydroxide Precipitates (open access)

Effect of Operating Parameters and Chemical Additives on Crystal Habit and Specific Cake Resistance of Zinc Hydroxide Precipitates

The effect of process parameters and chemical additives on the specific cake resistance of zinc hydroxide precipitates was investigated. The ability of a slurry to be filtered is dependent upon the particle habit of the solid and the particle habit is influenced by certain process variables. The process variables studied include neutralization temperature, agitation type, and alkalinity source used for neutralization. Several commercially available chemical additives advertised to aid in solid/liquid separation were also examined in conjunction with hydroxide precipitation. A statistical analysis revealed that the neutralization temperature and the source of alkalinity were statistically significant in influencing the specific cake resistance of zinc hydroxide precipitates in this study. The type of agitation did not significantly effect the specific cake resistance of zinc hydroxide precipitates. The use of chemical additives in conjunction with hydroxide precipitation had a favorable effect on the filterability. The morphology of the hydroxide precipitates was analyzed using scanning electron microscopy.
Date: August 1, 1999
Creator: Alwin, Jennifer Louise
System: The UNT Digital Library
Development and evaluation of high resolution quadrupole mass analyzer and an inductively coupled plasma-Mach disk (open access)

Development and evaluation of high resolution quadrupole mass analyzer and an inductively coupled plasma-Mach disk

By definition a plasma is an electrically conducting gaseous mixture containing a significant concentration of cations and electrons. The Inductively Coupled Plasma (ICP) is an electrodeless discharge in a gas at atmospheric pressure. This discharge is an excellent one for vaporizing, atomizing, and ionizing elements. The early development of the ICP began in 1942 by Babat and then by Reed in the early 1960s. This was then followed by the pioneering work of Fassel and coworkers in the late 1960s. Commercial ICP spectrometers were introduced in the mid 1970s. A major breakthrough in the area of ICP took place in the early 1980s when the ICP was shown to be an excellent ion source for mass spectrometry.
Date: December 10, 1999
Creator: Amad, Ma'an Hazem
System: The UNT Digital Library

Development of a Coaxiality Indicator

Access: Use of this item is restricted to the UNT Community
The geometric dimensioning and tolerancing concept of coaxiality is often required by design engineers for balance of rotating parts and precision mating parts. In current practice, it is difficult for manufacturers to measure coaxiality quickly and inexpensively. This study examines feasibility of a manually-operated, mechanical device combined with formulae to indicate coaxiality of a test specimen. The author designs, fabricates, and tests the system for measuring coaxiality of holes machined in a steel test piece. Gage Repeatability and Reproducibility (gage R&R) and univariate analysis of variance is performed in accordance with Measurement System Analysis published by AIAG. Results indicate significant design flaws exist in the current configuration of the device; observed values vary greatly with operator technique. Suggestions for device improvements conclude the research.
Date: December 1999
Creator: Arendsee, Wayne C.
System: The UNT Digital Library
Examining the Nature of Interactions which Facilitate Learning and Impact Reading Achievement During a Reading Apprenticeship: A Case Study of At-risk Adolescent Readers (open access)

Examining the Nature of Interactions which Facilitate Learning and Impact Reading Achievement During a Reading Apprenticeship: A Case Study of At-risk Adolescent Readers

The purpose of this qualitative case study was to explore the interactions that take place during a reading apprenticeship which facilitate the learning of reading strategies by adolescent students who are at the middle school level and are still at-risk for reading failure and to investigate how a reading apprenticeship affects reading achievement in the areas of fluency, vocabulary development, comprehension, and the self-perception of the reader. The case study was descriptive and interpretive in nature, and examined two students, each of whom was part of a one-to-one reading apprenticeship. The researcher served as participant observer in both cases and was the teacher in each of the one-to-one reading apprenticeships. The primary data set was qualitative in nature, and elements of quantitative data were also considered. Sessions included pretesting and posttesting using the Classroom Assessment of Reading Processes (Swearingen & Allen, 1997), reading from narrative or expository books, working with words, writing, and dialoguing about the reading. Reading strategies were directly taught, modeled, and reinforced by the teacher/researcher with the goal of the students internalizing the strategies and improving their reading in the areas of fluency, vocabulary development, and comprehension, as well as improving their attitudes toward reading and their …
Date: December 1999
Creator: Arthur, Mary L.
System: The UNT Digital Library
Adjustment of Kindergarten Children through Play Sessions Facilitated by Fifth Grade Students Trained in Child-Centered Play Therapy Procedures and Skills (open access)

Adjustment of Kindergarten Children through Play Sessions Facilitated by Fifth Grade Students Trained in Child-Centered Play Therapy Procedures and Skills

This research study investigated the effectiveness of the application of child-centered play therapy procedures and skills by trained fifth grade students in play sessions with kindergarten children who had adjustment difficulties. Specifically, this research determined if play sessions with trained fifth grade students facilitated change in kindergarten children's self concept, internalizing behavior, and externalizing behavior and their parents' stress level.
Date: May 1999
Creator: Baggerly, Jennifer N. (Jennifer Nalini)
System: The UNT Digital Library
Vicarious Traumatization, Secondary Traumatic Stress, and Burnout in Sexual Assault and Domestic Violence Agency Staff and Volunteers (open access)

Vicarious Traumatization, Secondary Traumatic Stress, and Burnout in Sexual Assault and Domestic Violence Agency Staff and Volunteers

Two constructs, vicarious trauma (VT) and secondary traumatic stress (STS), describe therapists’ reactions to clients’ traumatic material. VT (TSI Belief Scale [BSL]), emphasizes cognitive belief system changes resulting from cumulative exposure to survivors. STS, (Compassion Fatigue Self-test for Psychotherapists [CFST]) combines PTSD and burnout symptomatology explaining sudden adverse reactions to survivors. Burnout (BO; Maslach Burnout Inventory [MBI]), links emotional exhaustion, depersonalization, and deficient personal accomplishment to inadequate institutional supports in interpersonally demanding work. This study investigated BSL and CFST validity, counselor trauma history, and client exposure-related VT, STS, and BO in 105 trauma counselors. Results demonstrate concurrent validity between BSL and CFST; other results dispute adequate validity. BO, and client exposure were related. Traumatized counselors scored higher than non-traumatized counselors on CFST, BSL, and SCL-90-R.
Date: August 1999
Creator: Baird, Stephanie
System: The UNT Digital Library
Everything and Nothing at the Same Time (open access)

Everything and Nothing at the Same Time

This paradoxically titled collection of poems explores what the blues and blindness has come to mean to the author.
Date: May 1999
Creator: Ballenger, Hank D.
System: The UNT Digital Library
Genetic algorithms applied to nonlinear and complex domains (open access)

Genetic algorithms applied to nonlinear and complex domains

The dissertation, titled ''Genetic Algorithms Applied to Nonlinear and Complex Domains'', describes and then applies a new class of powerful search algorithms (GAS) to certain domains. GAS are capable of solving complex and nonlinear problems where many parameters interact to produce a ''final'' result such as the optimization of the laser pulse in the interaction of an atom with an intense laser field. GAS can very efficiently locate the global maximum by searching parameter space in problems which are unsuitable for a search using traditional methods. In particular, the dissertation contains new scientific findings in two areas. First, the dissertation examines the interaction of an ultra-intense short laser pulse with atoms. GAS are used to find the optimal frequency for stabilizing atoms in the ionization process. This leads to a new theoretical formulation, to explain what is happening during the ionization process and how the electron is responding to finite (real-life) laser pulse shapes. It is shown that the dynamics of the process can be very sensitive to the ramp of the pulse at high frequencies. The new theory which is formulated, also uses a novel concept (known as the (t,t') method) to numerically solve the time-dependent Schrodinger equation Second, …
Date: June 1, 1999
Creator: Barash, D & Woodin, A E
System: The UNT Digital Library
Genetic algorithms applied to nonlinear and complex domains (open access)

Genetic algorithms applied to nonlinear and complex domains

The dissertation, titled ''Genetic Algorithms Applied to Nonlinear and Complex Domains'', describes and then applies a new class of powerful search algorithms (GAS) to certain domains. GAS are capable of solving complex and nonlinear problems where many parameters interact to produce a final result such as the optimization of the laser pulse in the interaction of an atom with an intense laser field. GAS can very efficiently locate the global maximum by searching parameter space in problems which are unsuitable for a search using traditional methods. In particular, the dissertation contains new scientific findings in two areas. First, the dissertation examines the interaction of an ultra-intense short laser pulse with atoms. GAS are used to find the optimal frequency for stabilizing atoms in the ionization process. This leads to a new theoretical formulation, to explain what is happening during the ionization process and how the electron is responding to finite (real-life) laser pulse shapes. It is shown that the dynamics of the process can be very sensitive to the ramp of the pulse at high frequencies. The new theory which is formulated, also uses a novel concept (known as the (t,t') method) to numerically solve the time-dependent Schrodinger equation Second, …
Date: June 1, 1999
Creator: Barash, D & Woodin, A E
System: The UNT Digital Library
Media Effects on the Body Shape Ideal and Bulimic Symptomatology in Males (open access)

Media Effects on the Body Shape Ideal and Bulimic Symptomatology in Males

This study investigates the impact of sociocultural mediators in relation to eating disorders among male undergraduates. Literature on eating disorders has demonstrated that a thin body shape ideal depicted in the media directly contributes to eating pathology among females, but little research has investigated the direct effects of ideal body shape images among men. The focus of the present investigation was to assess the direct effects of exposure to the ideal male body shape on men’s affect, self esteem, body satisfaction, and endorsement of U. S. societal ideals of attractiveness. In addition, the relation of these variables to bulimic symptomatology was examined. Modeling a study conducted on women (Stice & Shaw, 1994), male undergraduates between the ages of 18 to 25 participated in premeasure (N = 169) and post measure (N = 95) conditions. Participants in the post measure were randomly exposed to pictures from magazines containing either male models depicting the ideal body shape, an average body or pictures of clothing without models. Results from repeated mulitvariate analysis indicated that exposure to the ideal body shape condition did not demonstrate significant negative changes in men’s affect, self esteem, body satisfaction or endorsement of U. S. societal ideals of attractiveness. …
Date: December 1999
Creator: Barta, Jonna Lee
System: The UNT Digital Library

A Descriptive Study of Students Who Were Accepted for Admission at West Texas A&M University But Did Not Enroll

Access: Use of this item is restricted to the UNT Community
Each year, institutions of higher education devote valuable financial and personnel resources in the hope of enhancing student recruitment and matriculation. The purpose of this study was to examine the demographic characteristics, the factors that influenced students’ decisions to apply for admission to a university, their educational intentions, and their reasons for not enrolling after they had been admitted. The subjects of the study were first-time freshmen accepted for admission to a mid-size, public, southwestern university who did not enroll for the fall 1997 semester. Statistically significant differences were found when comparing no-shows and enrolled students by gender, ethnicity, age, ACT/SAT score, and distance of their hometown from the university. There were more female no-shows, and more males enrolled than females; a greater percentage of no-shows reported the distance of their hometown to be more than 200 miles; and the mean test score for no-shows was higher. Factors important in the college selection process found to be statistically significant among the groups were: a greater percentage of Minorities than Caucasians reported the importance of the financial aid award or a scholarship offer; students living within 100 miles of the campus reported the proximity of the university as important, advice received …
Date: December 1999
Creator: Barton, Mary Edna
System: The UNT Digital Library

The Effect of Increased Collaboration Among the Library Media Specialist and School Personnel on Perceptions of the Roles and Responsibilities of the Library Media Specialist

Access: Use of this item is restricted to the UNT Community
This study measured and explored changes in perceptions of the roles and responsibilities of the library media specialist when the level of collaboration increased. Seven library media specialists targeted four members of their educational communities with whom to increase collaborative activities. Before and after the collaboration began, the library media specialists, the teachers with whom they chose to collaborate, other members from the same educational community, and a control group that did not participate in increased collaboration were given a roles and responsibilities rank-order form. This form was used to measure changes in perceptions regarding the importance of the three roles and selected responsibilities related to the three roles before and after the collaborative experience. The library media specialists and the targeted teachers also kept reflection logs to record factors that enhanced collaboration, factors that inhibited collaboration, and any changes in their teaching style as a result of the collaborative experience. Results indicate that the participating library media specialists themselves experienced the most change. Role identification remains a problem as library media specialists seek to become teaching partners with classroom teachers yet still must keep the library media center aligned with school and district goals and move toward making it …
Date: August 1999
Creator: Beaird, Marilyn Miller
System: The UNT Digital Library
A Performer's Analysis of Benjamin Britten's Phaedra, Dramatic Cantata for Mezzo Soprano and Small Orchestra, op. 93: a Lecture Recital, Together with Three Recitals of Selected Works of H. Purcell, R. Schumann, R. Vaughan Williams, P. Tchaikovsky, G. Fauré, K. Löwe, G. Menotti, S. Barber and Others (open access)

A Performer's Analysis of Benjamin Britten's Phaedra, Dramatic Cantata for Mezzo Soprano and Small Orchestra, op. 93: a Lecture Recital, Together with Three Recitals of Selected Works of H. Purcell, R. Schumann, R. Vaughan Williams, P. Tchaikovsky, G. Fauré, K. Löwe, G. Menotti, S. Barber and Others

A little-known chamber work by Benjamin Britten is the dramatic cantata Phaedra, op.93, for mezzo-soprano and small orchestra. Among his chamber works, the solo cantata was a musical form used only once by Britten, thus making Phaedra unique among Britten's oeuvre. Britten chose a genre that flourished in the seventeenth and eighteenth centuries the cantata - as a vehicle for the story of Phaedra. He employs clear allusions to Baroque music in Phaedra by the use of harpsichord and continuo in the recitatives, ornamentation, and word painting. The text for Britten's setting of Phaedra is a translation of Jean Racine's Phedre by the American poet Robert Lowell. From Lowell's complete play, Britten extracted Phaedra's key speeches that deal with her three confessions of incestuous love for her stepson, Hippolytus. These monologues are set in a series of recitatives and arias that make up the entirety of this chamber cantata. In order to gain complete understanding of Phaedra, this document will begin with an investigation into the historical background of Racine's Phedre and the conventions of French tragedy from which it arose. Lowell's translation method will then be explored in comparison to Racine's play. In turn, Britten's extractions from Lowell's translation …
Date: May 1999
Creator: Beard-Stradley, Cloyce (Cloyce May)
System: The UNT Digital Library
Characterization of electrical resistivity as a function of temperature in the Mo-Si-B system (open access)

Characterization of electrical resistivity as a function of temperature in the Mo-Si-B system

Measurements of electrical resistivity as a function of temperature from 25 to 1,500 C were conducted on polycrystalline samples in the Mo-Si-B system. Single phase, or nearly single phase, samples were prepared for the following phases: Mo{sub 3}Si, Mo{sub 5}SiB{sub 2}, Mo{sub 5}Si{sub 3}B{sub x}, MoB, MoSi{sub 2}, and Mo{sub 5}Si{sub 3}. Thesis materials all exhibit resistivity values within a narrow range(4--22 x 10{sup {minus}7}{Omega}-m), and the low magnitude suggests these materials are semi-metals or low density of states metals. With the exception of MoSi{sub 2}, all single phase materials in this study were also found to have low temperature coefficient of resistivity(TCR) values. These values ranged from 2.10 x 10{sup {minus}10} to 4.74 x 10{sup {minus}10}{Omega}-m/{degree} C, and MoSi{sub 2} had a TCR of 13.77 x 10{sup {minus}10}{Omega}-m/{degree} C. The results from the single phase sample measurements were employed in a natural log rule-of-mixtures model to relate the individual phase resistivity values to those of multiphase composites. Three Mo-Si-B phase regions were analyzed: the binary Mo{sub 5}Si{sub 3}-MoSi{sub 2} system, the ternary phase field Mo{sub 5}Si{sub 3}B{sub x}MoB-MoSi{sub 2}, and the Mo{sub 3}Si-Mo{sub 5}SiB{sub 2}-Mo{sub 5} Si{sub 3}B{sub x} ternary region. The experimental data for samples in each of …
Date: December 10, 1999
Creator: Beckman, Sarah E.
System: The UNT Digital Library

The Effects of Task-Based Documentation Versus Online Help Menu Documentation on the Acceptance of Information Technology

Access: Use of this item is restricted to the UNT Community
The objectives of this study were (1) to identify and describe task-based documentation; (2) to identify and describe any purported changes in users attitudes when IT migration was preceded by task-based documentation; (3) to suggest implications of task-based documentation on users attitude toward IT acceptance. Questionnaires were given to 150 university students. Of these, all 150 students participated in this study. The study determined the following: (1) if favorable pre-implementation attitudes toward a new e-mail system increase, as a result of training, if users expect it to be easy to learn and use; (2) if user acceptance of an e-mail program increase as expected perceived usefulness increase as delineated by task-based documentation; (3) if task-based documentation is more effective than standard help menus while learning a new application program; and (4) if training that requires active student participation increase the acceptance of a new e-mail system. The following conclusions were reached: (1) Positive pre-implementation attitudes toward a new e-mail system are not affected by training even if the users expect it to be easy to learn and use. (2) User acceptance of an e-mail program does not increase as perceived usefulness increase when aided by task-based documentation. (3) Task-based documentation …
Date: May 1999
Creator: Bell, Thomas
System: The UNT Digital Library
Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous Fowler-Nordheim I-V Plots with Field Emission Energy Distributions (open access)

Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous Fowler-Nordheim I-V Plots with Field Emission Energy Distributions

The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated. Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous …
Date: August 1999
Creator: Bernhard, John Michael
System: The UNT Digital Library

Cure Kinetics and Processing Parameters of Neat and Reinforced High Performance Epoxy Resins: Evaluation of Techniques

Access: Use of this item is restricted to the UNT Community
Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4’-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Conditions
Date: December 1999
Creator: Bilyeu, Bryan
System: The UNT Digital Library