The thermal diffusivity and conductivity of several ceramic composites were determined experimentally to observe the effect of temperature, heat treatment and orientation on these properties. The thermal conductivity and diffusivity of SiC whisker reinforced Ba-osumilite glass-ceramic exceeded that of SiC fiber reinforced osumilite due to higher thermal conductivity and diffusivity of the whiskers. An anisotropy was observed in thermal conductivity of the whisker composite due to whisker orientation normal to hot-pressing direction. Thermal conductivity of carbon fiber reinforced borosilicate glass parallel to the fiber plane was about twice that of the normal orientation and of the matrix. Heating the composite to above 600°C resulted in permanent decrease in thermal conductivity due to void formation by relaxation of the elastically bent fibers by viscous flow of the matrix. Thermal conductivity of iniaxial carbon fiber reinforced lithia-aluminosilicate glass-ceramic was over ten times higher parallel to the fibers than perpendicular. Permanent decrease of thermal conductivity normal to the fibers was due to matrix cracking caused by relief of internal stresses due to matrix crystallization and thermal gradients during fabrication. Modification of the original theories of Maxwell and Rayleigh permitted derivation of expressions for thermal conductivity of composites of a continuous matrix with dilute concentrations of spherical and cylindrical geometries and of parallel flat plates with thermal resistance at the interfaces. / M.S.

Broccoli is increasingly being grown as an alternate crop in many tobacco producing regions. Many of these regions, especially in Virginia, are quite susceptible to soil erosion losses. In order to reduce erosion and reap the other benefits of conservation tillage, a strip tillage machine named FOR2 was designed, developed and tested. FOR2 prepares the seedbed and places the seed in one pass through the field. This thesis reports the qualitative and quantitative evaluation of FOR2 based on result from two experiments. The first experiment evaluated broccoli emergence under three different tillage treatments, one of which was FOR2. The second experiment assessed the influence of adjustable machine parameters on the prepared soil condition in terms of aggregate size distributions, The parameters that were varied included pre-planting irrigation amount, tiller depth, tiller RPM, and tractor speed. The analysis revealed that the FOR2 machine produced commercially acceptable stands of broccoli with 77% germination. It was also determined that the percentage of aggregates in the seedbed greater than 0.297 mm was significantly influenced by the irrigation level and the tiller RPM. Tiller depth and tractor speed had no significant effect on the response. / M.S.

Tangential slot injection of supersonic air (M_j = 1.70) into a supersonic air freestream (M₁ = 2.93) was investigated. The model used had a slot height of 1.27 cm, which was also approximately the boundary layer thickness in the primary stream, and a thin splitter plate with a thickness of 0.052 cm. Computer controlled measurement systems were used at four streamwise stations, (x/a) = 0.25, 4, 10, 20, to determine cone static pressure, pitot pressure, and stagnation temperature. From this information profiles of M, U, and ρ̅ were also generated. Spark Schlieren and Nano-Shadowgraph pictures were taken of the flowfield. The results showed excellent repeatability and documented the development of the injected flow to beyond the region where the outer shear layer and wall boundary layer had merged. The effect of a weak shock interaction upon the shear layer was also investigated. An oblique shock, generated on the upper wall with a wedge, impinged on the shear layer. The shock wave had a nominal pressure ratio of 1.82, which did not result in separation of the wall boundary layer. The profile distortion caused by this shock/viscous layer interaction was documented. / M.S.

Project objectives were to develop an improved plating medium to achieve reproducible colony counts and accurate quantification for growth or survival of Spirillum volutans; and to develop an improved method for selection of S. volutans from nature. Growth enhancement studies began with casein hydrolysate-succinate-salts medium (CHSS). Casein hydrolysate concentration, type of casein hydrolysate, pH, and phosphate concentration optima were determined. Growth of S. volutans doubled after 24 h with the addition of potassium phosphate buffer (1 mM final concentration) to CHSS medium (CHSS-P). Addition of supplements to CHSS-P medium, and modified Bordetella and Brucella media failed to increase the cell yields of S. volutans. Punctiform colonies did form in CHSS-P medium (0.7% agar) pour-plates, yet at a recovery rate much lower than reported by Padgett et at. (1982) for surface growth on spread plates. The role of amino compounds as possible growth factors was investigated. Thin-layer chromatography, gas chromatography, and amino acid analysis were employed to identify those amino compounds (if any) that decreased or disappeared in the medium after 48 h of growth. None could be found. Numbers of viable cells were not greatly increased, however, viability was prolonged by growing S. volutans in dialysis sacs suspended in CHSS-P medium. The tolerances of S. volutans to several antimicrobial compounds were determined. Attempts at using hay infusion, Pringsheim, and CHSS-P media supplemented with various compounds as selective agents did not result in predominance of S. volutans. / M.S.

There is considerable agreement that a basketball team enjoys some type of advantage on the team's home court. This study tried to determine whether that advantage was evident in the team's statistics, and whether that advantage was significant over time. The experimental design consisted of t-tests performed on nine different statistical categories, comparing home and away performances. Those statistics were gathered from 43 home and 43 away Virginia Tech regular season Metro Conference men's basketball contests from 1979 through 1987. Results from the testing indicated that there were significantly more points scored at home than on the road. Also, testing showed that Virginia Tech had a significantly higher winning percentage at home than it did on the road. While testing revealed that there were no significant differences in the other seven categories studied, it was concluded that slightly better performances across several categories may cause greater success at home. Continued research on the home court advantage theory is suggested. / M.S.

In this thesis, the design and performance issues of multicomputer interconnection networks are addressed. Analytic models are used to evaluate the performance of large scale multicomputer networks. Performance is measured as the average end-to-end delay between communicating nodes. The models consider the communication processing queueing delays experienced by packets at each node as well as delays associated with transmission of packets. A comparison study of message switching and cut-through switching is presented. It is shown, conforming to previous studies, that a network has superior performance when cut-through switching is used. Cut-through switching is most advantageous when the network load is low and degenerates to message switching performance under heavy network loads. The network model is used to develop a "Network Analyzer", an interactive program that allows analysis of different network designs and workloads. Torus and spanning bus hypercube networks are then analyzed by the program to study the effect of various network parameters, traffic patterns, and switching techniques on network delay performance. The Network Analyzer is relatively easy to learn and use, and once learned, it is easy to change network parameters to perform a trade-off study of design alternatives. The program can also be used to quickly generate listings and graphics to illustrate the results of the analysis. The program proved to be an efficient design tool. Hypercube topologies are the most popular for large scale parallel computers, particularly for computationally intensive applications. The torus and spanning bus hypercubes are implemented in our program and analyzed in detail. Results show that network topology has a mixed impact on system performance. Networks built of standard modules of spanning bus hypercubes are harder to expand, compared to a torus network, but they have lower connection cost per node. Communication delays are generally higher for spanning bus networks except at very low traffic loads. / M.S.

Present stress analysis of adhesively bonded joints suffers from inadequate adhesive material characterization. The lack of correlation between bulk adhesive properties and the corresponding in-situ behavior has led to numerous adhesive test geometries. The current study was an attempt to predict the nonlinear viscoelastic response of an adhesive in-situ using properties obtained from a pure shear test geometry. Four candidate adhesive test geometries were studied both analytically and experimentally in terms of accurate shear property determination and realistic adhesive bond simulation. The thick adherend joint was chosen as the experimental reference of actual viscoelastic response in-situ; the Arcan specimen provided a pure shear stress state for material viscoelastic characterization. Results of finite element analysis and extensive experimental evidence suggest that residual thermal stresses alter the in-situ adhesive properties compared to the bulk adhesive: Furthermore, preliminary results indicate that the free volume nonlinear viscoelastic theory accounts for the effect of residual strains on the in-situ adhesive mechanical response. / M.S.

The antigenic relationship between T. denticola, T. socranskii subsp. Socranskii, T. socranskii subsp. Buccale, T. socranskii subsp. paredis, Treponeme D, T. vincentii, T. phagedenis biotype Reiter, T. minutum, and T. refringens was studied using fluorescent antibody staining and those organisms were found to contain a group of common antigens. The cross-reactivity was removed when the antisera was absorbed with Reiter cells. There was a second group of common antigens that were shared by the subspecies of T. socranskii, Treponeme D, and T. pectinvorum. Triton-extracts from different treponemal species were found to contain very few cross-reacting antigens as demonstrated by immunodiffusion, crossed immunoelectrophoresis, ELISA, and Western blots. An immunodiffusion test using treponemal Triton-extracts and antisera against five treponeme species was developed for the routine identification of oral treponemes that were in either pure or mixed cultures. T. denticola cells were found to bind to fibronectin-coated microscope slides. Proteins, that bind fibronectin, in the Triton-extracts of T. denticola, were detected in a fibroectin-captured ELISA. The Triton-extracts also reacted with rabbit fibronectin antiserum and rabbit albumin antiserum in immunodiffusion and ELISA assays. Three proteins with molecular weight of 60K, 47K, and 21K, were eluted from a agarose-gelatin-fibronectin column and reacted in Wester blots with T. denticola antiserum. / M.S.

The subject of corporate bankruptcy has been of interest to financial academicians and practitioners alike. Researchers have directed most of their attention to accounting-based models for predicting bankruptcy filings. Although some research has attempted to estimate the probability and costs of bankruptcy, a very limited amount is centered around the outcome of bankruptcy proceedings. Specifically, little is known about the circumstances that determine whether the firm will liquidate, successfully reorganize, or become an acquisition of another firm after filing for court protection. Given the potentially large losses to both creditors and stockholders, the determinants of bankruptcy outcome should be of considerable interest. The focus of this research is threefold. First, the factors that should have an effect on the disposition of the firm after the bankruptcy filing are examined for their influence on the disposition. Second, since there is some dispute as to the appropriate classification of acquired firms, the correct classification of acquired (or merged) firms is determined. Third, the effect of a major change in the bankruptcy law is examined. / Ph. D. / incomplete_metadata

The planar entry flow behavior of polystyrene, LDPE, and HDPE has been observed experimentally. The purpose of the work was to determine the cause of vortex growth and explain why this phenomenon occurs in some polymers but not in others. To accomplish this a die was constructed in which nearly any flow geometry could be formed by means of inserts. Flow visualization and flow birefringence experiments were performed using this die with 4:1 and 8:1 abrupt planar contraction geometries for τ_12w up to 7x10⁴ Pa and γ from 1 to 80 sec⁻¹. From these experiments it was determined that vortex growth in a polymer is caused by the resistance to flow under the influence of extensional strain. Although extensional viscosity measurements give an indication of whether or not vortices will form, the flow behavior is best correlated by the ratio of the centerline extensional stress to the downstream wall shear stress, τ₁₁ - τ₂₂ / τ_12w, measured in the entry region. The magnitude of this ratio was approximately 2 for LDPE, which exhibited vortex growth, but was approximately 1 for polystyrene, which did not exhibit vortex growth. Based on the experimental results, the numerical work was directed towards the use of a constitutive equation which could predict the extensional properties of the polymers being modelled. The Phan-Thien Tanner model was found to give adequate rheological property predictions and was used with the penalty finite element method to simulate the entry flow behavior of LDPE and polystyrene. Both qualitative (streamline patterns) and quantitative (extensional stress ratio) agreement was found between the experimental and numerical results. Vortex growth was predicted for LDPE, but incorporation of a zero relaxation time at the corner elements was necessary to increase the limit of convergence to the point where vortex growth was predicted. Support for the relation between vortex growth and extensional properties was given by the numerical results. lt was found that, holding all other rheological properties the same, an increase in the predicted extensional viscosity of a fluid results in the prediction of larger vortices. / Ph. D.