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464 Matching Results
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Mixed Field Dosimetry Using Focused and Unfocused Laser Heating of Thermoluminescent Materials
The incidents at the Three Mile Island and Chernobyl have triggered the need for better personnel dosimetry methods in mixed radiation fields. This thesis presents a detailed computational study of a new method for mixed radiation field dosimetry using single-element TL dosimeters with pulsed laser heating schemes. The main objective of this study was to obtain an optimum heating scheme so that the depth-dose distribution in a thick TL dosimeter could be accurately determined. The major parts of the study include: (a) heat conduction calculations for TL dosimeters with various heating schemes, (b) glow curve calculations for TL dosimeters based on a first-order kinetic model, (c) unfolding of the depth-dose distribution based on the glow curve data, and (d) estimation of shallow and deep doses from the unfolded depth-dose distribution. Two optimum heating schemes were obtained in this study. The first one was obtained for a focused laser beam, and the second one was obtained for a uniform laser beam. Both heating schemes consist of two processes: top surface heating and bottom surface heating, and each process in turn consists of a sequence of laser pulses with various heating durations and power levels. Compared to the ``true`` depth-dose distribution obtained …
Date:
March 1, 1994
Creator:
Han, Seungjae
System:
The UNT Digital Library
Perceptions of Social Support among Children with Attention Deficit Hyperactivity Disorder, Pre- and Post-Parent Training
The literature demonstrates that children with Attention Deficit Hyperactivity Disorder (ADHD) often experience peer rejection as a result of their difficulties with interpersonal interactions. The manner in which children with ADHD process social information and the extent to which social difficulties may adversely impact these children has remained unclear. In the first part of the study, the perceptions of social support between boys (ages 7 to 11 years) with and without ADHD were compared. An analysis of variance procedure (ANOVA) was performed and children with ADHD were found to perceive significantly lower levels of social support from their classmates than normal peers at pretreatment. The groups did not differ significantly with regard to perceptions of parent, teacher, and close friend support. In the second part of the study, the role of ADHD parent training and its effectiveness in decreasing problem-behaviors, ameliorating social problems, and enhancing perceptions of social support was examined. Repeated measures MANOVAs revealed a significant rater (mother and teacher) by time (pretreatment and posttreatment) interaction effect for total behavior problems, externalizing behavior problems, internalizing behavior problems, and social problems. On each scale, mothers reported more behavior problems than teachers at pretreatment, but fewer problems than teachers at posttreatment …
Date:
August 1994
Creator:
Askins, Martha Ann
System:
The UNT Digital Library
Determination of toxic material penetrations for wildland respirator filters
Thousands of wildland firefighters are exposed to high levels of toxic materials every year. Carbon monoxide, formaldehyde and acrolein gases, along with high particulate concentrations, are the major toxics encountered. Currently, the only respiratory protection wildland firefighters use is a bandanna over the mouth and nose. In this study, a modem activated carbon cartridge with an electrostatic prefilter was compared to a typical bandanna for its ability to filter wildland smoke toxics such as formaldehyde and particulates. The results of the tests were disappointing; neither filter performed very well. The activated carbon cartridge and prefilter efficiently collected formaldehyde gas for up to 60 minutes; however, it only collected 85 percent of the challenge particulate. ]Me bandanna, as expected, was only partially effective at collecting smoke particulate and filtered no toxic gases.
Date:
May 1, 1994
Creator:
Foote, Kenneth Lawrence
System:
The UNT Digital Library
Plasma destruction of North Carolina`s hazardous waste based on hazardous waste generated between the years of 1989 and 1992
The purpose of this research is to analyze the applicability of the plasma waste destruction technology to North Carolina hazardous waste streams. This study outlines the current regulations, existing technologies, and innovative technologies being considered as hazardous waste treatment alternatives. From this foundation, the study proceeds to identify the superiority of the plasma waste destruction technology. Specific areas of discussion include: temperature capabilities, waste residence time requirements, destruction removal efficiencies, operational efficiencies, economic issues, safety, and maintenance. This study finds the plasma destruction technology to be fully effective and superior to conventional facilities. The technology completely destroys hydrocarbons and can reduce the volume of many other hazardous wastes on the order of one part per million. The required residence time of waste in a plasma facility for effective destruction is a fraction of a second, while the rotary kiln incinerator maintains an average residence time of approximately 5 seconds. Also mass and heat balance calculations are performed to quantify the effectiveness and efficiency of this technology. It is found that one day`s average amount of hazardous waste generated in the state of North Carolina can be destroyed in approximately thirty seconds using a standard one megawatt power source. Yet, before …
Date:
December 31, 1994
Creator:
Williams, D.L.
System:
The UNT Digital Library
Measurements of granular flow dynamics with high speed digital images
The flow of granular materials is common to many industrial processes. This dissertation suggests and validates image processing algorithms applied to high speed digital images to measure the dynamics (velocity, temperature and volume fraction) of dry granular solids flowing down an inclined chute under the action of gravity. Glass and acrylic particles have been used as granular solids in the experiment. One technique utilizes block matching for spatially averaged velocity measurements of the glass particles. This technique is compared with the velocity measurement using an optic probe which is a conventional granular flow velocity measurement device. The other technique for measuring the velocities of individual acrylic particles is developed with correspondence using a Hopfield network. This technique first locates the positions of particles with pattern recognition techniques, followed by a clustering technique, which produces point patterns. Also, several techniques are compared for particle recognition: synthetic discriminant function (SDF), minimum average correlation energy (MACE) filter, modified minimum average correlation energy (MMACE) filter and variance normalized correlation. The author proposes an MMACE filter which improves generalization of the MACE filter by adjusting the amount of averaged spectrum of training images in the spectrum whitening stages of the MACE filter. Variance normalized correlation …
Date:
December 31, 1994
Creator:
Lee, J.
System:
The UNT Digital Library
A Study of the Processing Properties of Hard-Particle Reinforced Composite Solders
The microstructural, mechanical and thermal properties of various composite solder formulations were investigated. Special interest was given in observing the processing properties, microstructural characteristics, fatigue behavior, tensile strength, and the effect of environmental ageing on the composite solder formulations. The solderability parameters wetting and speed of soldering, reflow temperature, and the thermal stability of the resulting composite solder were also examined.
Date:
May 1994
Creator:
Calderon, Jose Guadalupe
System:
The UNT Digital Library
The Study of Hydration of Fly Ash in the Presence of Calcium Nitrate and Calcium Formate
This research was designed to investigate the hydration reaction of fly ash when exposed to water. The effects that calcium nitrate and calcium formate have on the hydration reactions were also examined.
Date:
May 1994
Creator:
Hill, Russell L. (Russell Lee)
System:
The UNT Digital Library
Imagery and Form
This paper discusses the integration of imagery and form in the author's works, wheel thrown pottery intended to make an individualized statement. Steven L. Phillips discusses the process of making these forms and the imagery they contain, drawing connections to philosophical concepts.
Date:
May 1994
Creator:
Phillips, Steven L.
System:
The UNT Digital Library