Surface analysis of buna-N-rubber and teflon was performed. Scanning electron microscopy was used to analyze the topography of both materials and x-ray microanalysis identified the elemental chemical composition of the polymers. Teflon was primarily a smooth surface with random irregular spots, while buna-N-rubber had a very rough topography with "caverns" and crevices spread over the surface. The x-ray microanalysis showed that there are no impurities on the surface of teflon; however, calcium, silicone and sulfur were present on the surface of buna-N-rubber. Water contact angle measurements indicated that buna-N-rubber was a more hydrophobic surface than teflon. Qualitative analysis of the attachment of Pseudomonas fragi A TCC 4973, Listeria monocytogenes Scott A and Bacillus cereus ATCC 11778 to buna-N-rubber and teflon was assessed by scanning electron microscopy. These bacteria readily attached to both surfaces. Pseudomonas fragi attached after 2 hours in the presence of this microoorganism and Bacillus cereus and Listeria monocytogenes attached at 12 and 24 hours, respectively. Quantitative analysis of the attachment of Pseudomonas fragi to both surfaces as affected by various milk fat concentrations and temperature, and the availability of nutrients (different dilutions of skim milk, casein, casein and lactose, and whey and lactose) was conducted. Attachment was assessed by impedance microbiology. Milk fat content did not play a significant role in the process of attachment of this organism to either type of surfaces; however, significantly greater numbers attached to buna-N-rubber than to teflon. Overall bacteria attached in higher numbers to both surfaces when grown at 21°C, compared to bacteria grown at 4°C. For buna-N-rubber, bacteria attached in significantly higher numbers when the concentration of nutrients was minimal, while for teflon, the results were, in most cases, opposite to these. / Ph. D.

A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. An experimental investigation using conventional strain gage instrumentation and moire interferometry is performed. A finite element analysis of the Iosipescu shear test for unidirectional and cross-ply composites is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon the strain gage measurements used for the determination of composite shear moduli. From the test results for graphite-epoxy laminates, it is shown that the proximity of the load introduction point to the test section greatly influences the individual gage readings for certain fiber orientations but the effect upon shear modulus measurement is relatively unimportant. A numerical study of the load contact effect shows the sensitivity of some fiber configurations to the specimen/fixture contact mechanism and may account for the variations in the measured shear moduli. A comparison of the strain gage readings from one surface of a specimen with corresponding data from moire interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to eccentric loading which induced twisting and yielded spurious shear stress-strain curves. In the numerical analysis, it is shown that the Iosipescu specimens for different fiber orientations have to be modeled differently in order to closely approximate the true loading conditions. Correction factors are needed to allow for the non uniformity of the strain field and the use of the average shear stress in the shear modulus evaluation. The correction factors, which are determined for the region occupied by the strain gage rosette, are found to be dependent upon the material orthotropic ratio and the finite element models. Based upon the experimental and numerical results, recommendations for improving the reliability and accuracy of the shear modulus values are made, and the implications for shear strength measurement discussed. Further application of the Iosipescu shear test to woven fabric composites is presented. The limitations of the traditional strain gage instrumentation on the satin weave and high tow plain weave fabrics is discussed. Test result of a epoxy based aluminum particulate composite is also presented. A modification of the Iosipescu specimen is proposed and investigated experimentally and numerically. It is shown that the proposed new specimen design provides a more uniform shear stress field in the test section and greatly reduces the normal and shear stress concentrations in the vicinity of the notches. While the fabrication and the material cost of the proposed specimen is tremendously reduced, it is shown the accuracy of the shear modulus measurement is not sacrificed. / Ph. D.

Studies on the activity of femlic, gallic, and vanillic acids on germination and growth of corn (Zea mays L.), radish (Raphanus sativus L.), and peanut (Arachis hypogaea L.) showed that the inhibitory effects of these acids were concentration and growth variable dependent. Ten days after treatment, significant reduction in percent germination of the three species occurred with higher phenolic acid treatments, except that gallic acid did not significantly inhibit peanut germination. Among the growth parameters investigated, root elongation and dry weight were more affected than either germination or shoot length and dry weight. Radish and corn were more sensitive than peanut. In two-combination experiments, the interactive effects of phenolic acids on corn germination and shoot growth were generally not significant, indicating an additive effect. Femlic acid, generally, antagonized higher concentrations of vanillic or gallic acids on corn root length and dry weight, suggesting a differential uptake of phenolic acids by corn roots or a limited uptake of gallic and vanillic acids in the presence of ferulic acid. In a soil system, higher and repeated phenolic acid treatments were required to bring about inhibition of corn growth than those which were effective in petri dishes. All levels of the synthetic auxin, 2,4-D (2,4-dichlorophenoxyacetic acid) were effective in reversing the inhibitory effects of 1 mM ferulic acid on corn root length when these two acids were applied in combination. No 2,4-D treatment counteracted 10 mM of ferulic acid. All levels of 2,4-D combined with 1 mM ferulic acid and the mixture of 0.1 nM 2,4-D with 10 mM ferulic acid were antagonistic for corn shoot length. No significant interactions were obtained on corn germination or seedling growth when 2,4-D was combined with gallic acid. Using manometric techniques, no inhibitory effects of ferulic or gallic acids observed on 02 consumption of germinating corn seeds. Ferulic acid did not interfere with water uptake of corn seeds during imbibition and germination. These findings indicate that the phytotoxicity of these acids observed on corn germination and seedling growth are not due to their interference with water uptake and respiratory activity of germinating seeds. / Ph. D.

A surface search was made using a small-area four-layer scintillator detector. Slow lightly ionizing particles created in cosmic ray interactions in the atmosphere which arrived within 13 ms of the shower front were searched for. In a live time of 2.55 x 10⁵ s 394,608 showers of two or more muons and 21,038 showers of four or more muons were recorded. No multiple muon events were recorded in which a trailing particle was identified above the expected random background, with a velocity between 7.4 x 10⁻⁵c and 6.7 x 10⁻³c. The detector operated without a trigger and used interplanar timing information to identify potential events, and operated above a threshold of 1/400 of that of a minimum ionizing muon. / Ph. D.

Natural environments are often limiting to plant growth in more than one resource due to the simultaneous fluctuations in resource supply and demand. The mechanisms a species uses to acclimate to simultaneous resource variation may not be uniform among species of the same growth form. Four evergreen ericaceous shrubs responded individualistically to fluctuations in light and water in an experimental garden study. <i>Rhododendron maximum</i> and <i>Kalmia latifolia</i> were able to acclimate photosynthetically to high and low irradiance under both high and low water availability. <i>Rhododendron catawbiense</i> and <i>R. minus</i> showed significantly higher acclimation to high light in high water treatments. All four species were able to reduce their osmotic potential and water deficit at the turgor loss point seasonally, especially in low water treatments. Low soil water availability also reduced midday conductance and water potential in all four species. Rhododendron maximum and <i>R. catawbiense</i> were very conservative in their water use patterns. <i>Rhododendron minus</i> and <i>K. latifolia</i> exercised less stomatal control over water loss but did not appear to experience water stress under these treatment conditions. Rhododendron catawbiense was the most sensitive to low water availability and had the lowest turgor pressure of the four species. Daily carbon dioxide assimilation was highest in high light, high water. treatments and lowest in low light, low water treatments for all four species. During the two years of this study, these species did not show any consistent pattern of increased growth in the high light, high water treatments where carbon dioxide assimilation was highest. Since these species are native to low resource habitats, their abilities to significantly increase growth during periods of high resource availability may be less than that of plants adapted to high resource availability. The results of these experiments indicate that these four species of the same growth form respond differently to simultaneous fluctuations in light and water resources. / Ph. D.

The purpose of this study was to determine the characteristics of effective internships in principal preparation programs. A three-round modified policy Delphi was used. The panel consisted of interns, mentors, and university facilitators from 18 of the 22 Danforth Foundation-funded principal preparation programs. Characteristics of internships were divided into two categories: procedural and experiential. Procedural characteristics were defined as the process and management characteristics of the internship. The procedural characteristics were subdivided into selection, planning, placement, support, and evaluation. Experiential characteristics were defined as the experiences the intern had once placed with the supervising administrator. The experiential characteristics were subdivided into school climate; instructional management; research, evaluation, and planning; resources; staff development; staff evaluation; and community support. From the data base for Round 1, 132 items were selected for subsequent rounds. Panel members were asked to rate the importance of each item on a five-point scale. Items with a mean of 3.75 or greater were considered a characteristic of an effective internship in a principal preparation program. At the completion of Round 3, 114 out of 132 items met this criterion. Consensus by interns, mentors, and university facilitators was reached on 116 out of 132 items. Consensus was defined as no statistically significant difference among the ratings of the three groups. The major conclusions drawn from the study were (a) there are a number of different ways that an internship may be implemented in a principal preparation program, (b) the intern should not have full-time teaching (or other job) responsibilities while completing the internship, and (c) educators are somewhat parochial when it comes to recognizing the benefit of experience outside of education. It was recommended that the characteristics identified in the study be reviewed by those who develop internships in principal preparation programs and that the procedural and experiential characteristics that fit the context of the program be considered for implementation. / Ed. D.

Aryl cyclopropyl ketones have often been employed as diagnostic probes for single electron transfer (SET) in organic chemical reactions. The implicit assumption in such studies is that the formation of rearranged product(s) can be ascribed to the intermediacy of a ketyl anion. Through a detailed examination of the decay of electrolytically generated aryl cyclopropyl] ketyl anions, we have shown that the assumptions made in the use of these substrates as SET probes are not necessarily valid. Using derivative cyclic and linear sweep voltammetry it was discovered that the ketyl anions of alkyl- and unsubstituted aryl cyclopropyl ketones (class I), including phenyl cyclopropyl ketone (28a), 1-benzoyl-2-methylcyclopropane (28b), 1-benzoyl-2,2-dimethylcyclopropane (28c), p-tolyl cyclopropyl ketone (28d), and 1-benzoyl-1-methylcyclopropane (28e), undergo a slow and reversible cyclopropyl carbinyl type rearrangement followed by dimerization of the ring-opened and ring-closed radical anions. The equilibrium constant for the reversible ring opening lies highly in favor of the ring closed form. For (28a^·⁻) in anhydrous N,N-dimethylformamide containing 0.5 M n-Bu₄NBF₄ at 23 °C, the equilibrium constant was estimated at K ≈ 4.6 x 10⁻⁸ with a maximum rate constant for ring opening and a minimum rate constant for ring closing at 2.0 s⁻¹ and 4.3 x 10⁷ s⁻¹ respectively; the rate constant for dimerization was placed at 8.4 x 10⁷ M⁻¹s⁻¹. Semiempirical molecular orbital calculations (AM1) complement the above observations. Similar results were obtained for all class I compounds. The ketyl anions of aryl cyclopropyl ketones with good radical stabilizing groups on the cyclopropane ring (class ID), including trans-1-benzoyl-2-phenylcyclopropane (66), and 1-benzoyl-2-vinylcyclopropane (76) undergo rapid unimolecular ring opening. The rate constants for opening of (66^·⁻) and (76^·⁻) are greater than 10³ s⁻¹ but probably less than 10⁷ s⁻¹ and 10⁵ s⁻¹ respectively. Based upon our findings, class I ketones are extremely unreliable probes for SET; class II ketones may prove to be useful SET probes, but since absolute rate constants for their rearrangement are not yet known, they should be used only with extreme caution. The implications of these results are discussed in light of utilizing aryl cyclopropyl ketones as probes for SET. / Ph. D.

In this dissertation a simplified nondimensional approach for the thermal analysis of power hybrid circuits is presented. The new technique uses only the metallization and the substrate as layers and represents everything below the substrate by an external thermal resistance (expressed as an equivalent convective heat transfer coefficient, h). In this study, the impact on thermal management of thick film metallization and copper cladding on alumina, aluminum nitride, and beryllia ceramic substrates is compared. The thermal conductivity of the substrate material, the thickness of the copper layer, the thermal resistance of the heat sink system, the size of the device, and the spacing between two heat dissipating devices are considered. The model results show that increasing the thickness of the copper layer can significantly decrease the device temperatures on alumina but may increase temperatures on high thermal conductivity substrates. Moreover, the model results show that increasing the thickness of the copper layer requires that the devices be placed farther apart to prevent thermal interaction. The results also demonstrate that the external heat sink resistance can have a significant impact on the heat flow paths and temperatures in the substrate. As the external resistance increases, the spacing required to prevent thermal interaction also increases. In addition to the above, a series of experiments were conducted on various hybrid circuits samples for a low and high heat sink external resistance, i.e., large and small convective heat transfer coefficients, respectively. These samples were constructed using thick film resistors as heat sources on alumina and beryllia substrates. The temperature rise was measured using infrared thermal imaging technique. These experimental results were compared to results predicted by the thermal model. In general, the model underpredicts or overpredicts the experimental temperature rise by 0-2 ·C and the agreement is within the experimental uncertainty of ±2°C. / Ph. D.

A theoretical model is derived to study the point-wise stress variations which occur in the constituents of a hybrid 3-D short fiber composite subjected to arbitrary homogeneous loading conditions. The model includes the capability to analyze composites containing different types of fibers, different aspect ratios of fibers (as well as continuous fibers), and different fiber orientations. The composite’s stiffness tensor is developed by volume averaging the point-wise stress field in each constituent present in the material system. Validation of the model is accomplished by comparing predicted stiffness properties to experimental data and other accepted models presently available in the literature for PMC’s, MMC’s, and BMC’s. A derivation of a theoretical model describing the resulting point-wise stress redistribution which occurs in the matrix and the fibrous regions caused by fiber-fiber interaction at the ends of finite length fibers or fractured fibers is also presented. This theoretical development includes the significant dependence of stress redistribution on fiber volume fraction, constituent properties, and crack size. Therefore, its use is not limited to polymeric composites but is also applicable to metal matrix and ceramic matrix systems. The model is extended to include one of the first quantitative analyses of variable fiber spacing which occurs in virtually every composite manufactured. A novel fiber discount method is proposed to study multiple fiber fractures which are of extreme importance when attempting to predict tensile strength of fiber dominated composite laminates. A test methodology employing a macro-model composite with embedded strain gauges is presented which can be used to validate (or invalidate) micro-mechanical models currently being developed and used by the scientific community. Results obtained with the embedded resistance gauges and the embedded fiber optic strain sensors (FP-FOSS) are validated with classical test and analytical techniques. These techniques include model composites subjected to thermal effects and mechanical loading sequences. The ability to vary specific physical parameters in the experimental model, such as fiber aspect ratio, fiber volume fraction, interphase/interface, and constituent properties (i.e. model PMC’s and MMC’s), in a systematic fashion enables this technique to study various physical aspects present in actual composite systems. The capability to initiate a fiber fracture at a specific location and load level is demonstrated. It is revealed that significantly different strain concentration exists in PMC composites which contain different fiber volume fractions and crack sizes. By varying fiber spacing between neighbors, a study is initiated on composites containing eccentrically located fibers. These results demonstrate that an asymmetric stress state exists in composites containing variable fiber spacing and fiber fractures. The fact that multiple fiber fracture is achieved in a methodical fashion demonstrates the versatility of the model. These studies show that this experimental technique can model various physical phenomena which occur in actual composite systems. / Ph. D.

Durability of a variety of sheet molding compounds (SMC)/ adhesive /metal systems involving steel, aluminum, phase α-SMC, Budd SMC, and polyurea adherends and polyurethane and epoxy adhesives has been investigated. Three specimen geometries with different modes of stress were employed: lap shear, wedge, and butt torsion. Specimens were exposed to an environmental cycle or to fixed conditions of temperature and humidity with or without load. For phase α-SMC/urethane/ELPO steel adhesive bonds, all visually determined adhesive failure occurs at the SMC/adhesive interface, and it is in reality a mixture of interfacial failure and near surface SMC debonding. The near surface SMC material and the thin layer of primer on the SMC surface are the weak links in the bond. An improvement in durability of phase α-SMC/urethane/ELPO steel adhesive bonds requires an increase in the strength of the outer layer of the SMC material. The metal surface pretreatment proved to be very important for the durability of phase α-SMC /urethane/aluminum adhesive bonds. The adhesive bonds prepared with solvent cleaned aluminum primed with epoxy or phenolic primer displayed poor durability. This is attributed to the contaminants on the aluminum surface after solvent cleaning which hinder the interactions of aluminum surface species with primers. The use of alkaline cleaned aluminum primed with diisocyanate primer improved durability only in dry air conditions. This can be explained by the high susceptibility of the NCO functionality to water, which can rapidly weaken the primer/aluminum bonds. Priming alkaline cleaned aluminum adherends with phenolic or epoxy primers improved dramatically the adhesive bond durability under all testing conditions. Enhanced durability is attributed to chemical and hydrogen bonds established between components of phenolic and epoxy primers and aluminum surface species. Reflection absorption FTIR studies of the interactions between identical or similar compounds that exist in the primers, e.g. diglycidyl ether of bisphenol A, phenol, and methylene diphenyl diisocyanate, and alkaline cleaned aluminum surface species indicated chemical processes. Exposure of bonded samples at 60°C for up to seven days did not reduce the residual strength. Some loaded samples failed during durability tests, indicating that loading is a significant factor in durability. Butt torsion samples proved to be much more sensitive to stress and temperature than the lap shear and wedge samples, showing the important role of the mode of stress in durability. Humidity had a detrimental effect on durability for all systems investigated. For the system Budd SMC/adhesive/ELPO steel an epoxy adhesive exhibited better durability than a polyurethane adhesive. Enhanced durability is explained by higher cohesive strength, a lower moisture absorption rate and higher resistance to hydrolysis of the epoxy adhesive. An increase in bondline thickness proved to be beneficial for adhesive durability, a fact attributed to a more uniform stress distribution in thicker bonds. / Ph. D.