Experiments were performed with two different helium injector models at different injector transverse and yaw angles in order to determine the mixing rate and core penetration of the injectant and the flow field total pressure losses. when gaseous injection occurs into a supersonic freestream. Tested in the Virginia Tech supersonic tunnel. with a freestream Mach number of 3.0 and conditions corresponding to a freestream Reynolds number of 5.0 x 107 1m. was a single. sonic. 5X underexpanded, helium jet at a downstream angle of 30° relative to the freestream. This injector was rotated from 0° to _28° to test the effects of injector yaw. The second model was an array of three supersonic, 5X underexpanded helium injectors with an exit Mach number of 1.7 and a transverse angle of 15°. This model was tested in the NASA Langley Mach 6.0, High Reynolds number tunnel, with freestream conditions corresponding to a Reynolds number of 5.4 x 10⁷ /m. The injector array as tested at yaw angles of 0° and -15°. Surface flow visualization showed that significant flow asymmetries were produced by injector yaw. Nanosecond exposure shadowgraph pictures were taken, showing the gaseous injection plume to be unsteady, and further studies demonstrated this unsteadiness was related to shock waves orthogonal to the injectant bow shock, that were generated at a frequency of 30 kHz. The primary data technique used, was a concentration probe which measured the molar concentration of helium in the flow field. Concentration data and other meanflow data was taken at several downstream axial stations and yielded contours of helium concentration, total pressure, Mach number, velocity, and mass flux, as well as the static properties. From these contour plots, the various mixing rates for each case were determined. The injectant mixing rates, expressed as the maximum concentration decay, and mixing distances were found to be unaffected by injector yaw, in the Mach 3.0 experiments, but were adversely affected by injector yaw in the Mach 6.0 experiments. One promising aspect of injector yaw was the that as the yaw angle was increased, lateral motion of the injectant plume became significant, and the turbulent mixing region area increased by approximately 34%. Comparisons of the 15° transverse angled injection into a Mach 6.0 flow to previous experiments with 15° injection into a Mach 3.0 freestream, demonstrated that there is a significant decrease in initial mixing, at Mach 6.0, resulting in a much longer mixing distance. From a parametric computational study of the Mach 6.0 experiments, the effects of adjacent injectors was found to decrease lateral spreading while increasing the vertical penetration of the injectant plume, and marginally increasing the injectant core decay rate. Matching of the computational results to the experimental results was best achieved when using the Baldwin-Lomax turbulence model without the Degani-Schiff modification. / Ph. D.

Recently, studies in performance appraisal have focused more on the process of performance appraisal rather than on the mechanics of performance appraisal. This study focused on the individual differences among raters and the effect these differences have on recognition accuracy and rating accuracy. Specifically, individual differences were examined through individual constructs (personal prototypes) of different performance levels and individual levels of knowledge for a particular job. Furthermore, the effect of a competing task on recognition accuracy and rating accuracy were examined. The present study employed a 2 (presence/absence of competing task) X 2 (high family resemblance prototype/low family resemblance prototype) between subjects design with level of knowledge as a covariate. Eighty experienced carpentry workers and construction laborers from Southern Virginia were the subjects. The subjects were tested on their individual level of knowledge with a carpentry knowledge exam. Personal prototypes for each subject were obtained by individual interviews with each subject. The competing task manipulation consisted of subjects in the competing task condition receiving a task to complete while viewing the videotape while subjects in the no competing task condition did not receive a task. After the knowledge exam and prototype interview, the sample viewed a videotape of three carpenters performing four different woodworking tasks (sanding, sawing, hammering and staining) and completed a recognition and performance appraisal measure after observation. It was expected that subjects, regardless of their level of knowledge, with a competing task to perform during observation would make less accurate ratings than subjects with no competing task to perform. It was also hypothesized that raters with higher job knowledge would recognize more behaviors consistent with their personal prototypes and falsely recognize more behaviors from their personal prototypes than lower knowledge raters. Further, it was hypothesized that lower job knowledge raters should be more accurate in their recognition of ratee behaviors than would higher job knowledge raters. Further, it was hypothesized that higher knowledge raters would falsely recognize behaviors consistent with their personal prototype when there was a competing tasks than when was no competing task. There should be no difference for lower knowledge raters. Finally, it was hypothesized that high job knowledge raters would make less accurate performance appraisal ratings because of their reliance of their personal prototypes under increased processing conditions whereas there should be no such differences for lower job knowledge raters. The competing task did serve to divide the subjects attention in viewing the videotape as compared with subjects without a competing task. Little support was obtained for the hypotheses. These findings suggest that the presence/absence of competing task did not significantly effect rater accuracy and that subjects’ personal prototypes did not effect neither their recognition accuracy nor rating accuracy. Future implications for research study will be offered. / Ph. D.

Spruce-fir ecosystems of the eastern United States interest scientists because of reported changes in population growth. Whether red spruce (Picea rubens Sarg.) populations are declining because of disease, pollution or environmental stress or experiencing natural changes in stand development is unclear. This research examined the growth and physiological responses of red spruce seedlings to changes in atmospheric CO₂ water and nutrient availability to determine the response of this species to potential climatic changes. Red spruce seedlings were grown from seed for 1 year in ambient (374 ppm) or elevated (713 ppm) CO₂ in combination with low or high soil fertility treatment, and well-watered or water-stressed conditions. Red spruce seedlings grown with limited nutrient and water availability increased growth in elevated CO₂ as did seedlings grown with high soil fertility treatment and ample water. At 12 months of age, elevated CO₂-grown seedlings had greater dry weight, height, diameter and specific leaf weight than ambient CO₂-grown seedlings. Seedlings that formed a bud in elevated CO₂ at 5 months of age produced more total fixed growth than seedlings grown in ambient CO₂. Mean relative growth rate was greater in elevated than ambient CO₂-grown seedlings only from 3 to 5 months of age. Growth was greater at 12 months despite a lower photosynthetic rate in elevated CO₂-grown seedlings compared to ambient CO,-grown seedlings. Transplanting seedlings from 175-cm³ pots into 646-cm³ pots at 7 months did not change growth and physiological responses to elevated CO₂ at 12 months. Dry weight allocation patterns to leaf, stem and root were not influenced by growth in elevated CO₂ for 1 year. Drought-conditioning had a greater influence on the physiological responses of red spruce to decreasing water potential than did growth in elevated CO₂. Results from this research suggest that red spruce seedlings will grow bigger faster in a future elevated CO₂ atmosphere even if water and nutrients are limiting. / Ph. D.

Problems of cascade connections (synthesis) and decomposition (analysis) are analyzed for two classes of linear systems with infinite dimensional state spaces, namely, 1) admissible systems in the sense of Bart, Gohberg and Kaashoek and 2) regular systems as recently introduced by Weiss. For the class of BGK-admissible systems, it is shown that the product of two admissible systems is again admissible and that a Wiener-Hopf factorization problem can be solved just as in the finite-dimensional case. For the class of regular systems, it is shown that the cascade connection of a rational stable and antistable system has an additive stable-antistable decomposition; this involves giving a distribution interpretation to the solution of a linear Sylvester equation involving unbounded operator coefficients. As an application, some preliminary work is presented toward obtaining a state space solution of the sensitivity minimization problem for a pure delay plant. / Ph. D.

There has been increasing concern that the cultural imposition of masculine gender role norms contributes to physical and mental health disorders among men. The construct of masculine gender role stress (MGRS) is a gender based perspective of stress which posits that masculine gender role cognitive schemata are employed by men to appraise potential threat in the environment and guide their coping responses. Heavy reliance on these schemata is believed to increase stress and restrict coping behavior. The current study examined the relationship of MGRS to the appraisal and psychophysiological and behavioral responses of males in situations demanding emotional expression. Sixty male college students scoring in the upper and lower third of the MGRS scale distribution responded to role play scenarios designed to elicit angry and tender emotional responses. Subjects rated how stressful they found the tasks to be. Ratings of the level of nonverbal and verbal expressiveness in subjects' responses were also obtained. Cardiovascular reactivity was measured during subjects' verbal and nonverbal responses. / Ph. D.

The synthesis of fluorinated cellulose derivatives was pursued for the purpose of investigating the effects of fluorine on the interfacial properties of cellulose derivatives, in multiphase materials. Synthetic approaches included: 1) the replacement of hydroxyl groups on cellulose with fluorine using fluoride displacement chemistry, or direct, one step fluorination 2) the replacement of hydroxyl groups on hydroxypropyl cellulose, HPC, with direct one step fluorinating agents, or 3) the conventional derivatization of cellulose with prefluorinated agents. Fluoride displacement of cellulose sulfonate esters was plagued low yields, and was therefore ineffective. Direct cellulose fluorination with aminofluorosulfur, and aminofluorocarbon reagents was effective for the surface fluorination of cellulose. However, the bulk, homogeneous fluorination of cellulose was complicated by side reactions that often precluded fluorination. Cellulose dissolved in DMAC/LiCI underwent simultaneous chlorination, and branching reactions when treated with dialkylaminosulfur trifluoride, DAST. Branching resulted from an anhydrous HF catalyzed trans-glycosidation reaction, which produced mainly (3-1,6 branching. Serendipitously, this discovery allows for the first known synthesis of long chain branched cellulose derivatives, with increased molar mass, and increased polydispersity. Treatment of HPC with DAST and FAR gave good levels of fluorination; however, the HF catalyzed gelation was always a complicating factor. The lower reactivity of FAR allowed for partial control of gelation with the use of nonnucleophilic bases. The easiest way to introduce fluorine was to perform conventional derivatization using prefluorinated reagents such as for the synthesis of fluorobenzyl cellulose. Mixed benzyl ethers of controlled fluorine content were made by altering the ratio of pfluorobenzyl chloride to benzyl chloride during reaction. 2-Dimensional NMR techniques were used to identify most proton and carbon resonances of cellulose and amylose fluorobenzyl ethers. Thermal analysis, solution analysis, and l3C spin-lattice relaxation experiments were used to compare the rod-like and coil-like behavior of the fluorobenzyl cellulose and amylose. Polycaprolactone, PCL, was blended with tri-O-benzylated cellulose with different degrees of fluorination. PCL was found to be immiscible with all derivatives, of fluorine contents from 0 % to as high as 11.7%. PCL did display some degree of mechanical compatibility with all derivatives. The greatest compatibility was found with benzylated cellulose having fluorine contents slightly below the maximum. It was found that no specific interactions were occurring between peL and fluorobenzyl cellulose. The enhanced compatibility of the mixed fluorobenzyl/benzyl cellulose ethers was postulated to arise from intramolecular interactions, which served to enhance the mixing of the copolymeric mixed benzyl ethers with PCL. / Ph. D.

The equations and numerics necessary for the analysis of dense-gas boundary-layer flows over arbitrarily shaped two-dimensional bodies are developed. The governing equations are derived from the Navier-Stokes-Fourier equations for a general fluid. A numerical method based on the second-order Davis-coupled scheme is employed to solve for mean flows over flat plates. Flows of nitrogen, sulfur hexafluoride, and toluene over adiabatic walls are examined; in addition, flows of nitrogen over heated and cooled walls are studied. Results indicate a breakdown of the standard correlations for the recovery factor and the Nusselt number due primarily to the substantial variations of the Prandtl number and the Chapman-Rubesin parameter throughout the boundary layer. The stability equations for two-dimensional inviscid disturbances in a general fluid are derived. The temporal stability of the mean flows of nitrogen is subsequently examined using the generalized inflection-point criterion extracted from these equations. Results reveal significant variations from standard ideal-gas predictions including the existence of flows for which neither heating nor cooling of the wall has a stabilizing effect. / Master of Science

In this study, a method is developed to solve general stochastic programming problems. The method is applicable to both linear and nonlinear optimization. Based on a proper linearization, a set of probabilistic constraints (performance functions) can be transformed into a corresponding set of deterministic constraints. this is accomplish by expanding all the constraints about the most probable failure point. The use of the proposed method allows the simplification of any stochastic programming problems into a standard linear programming problem. Numerical examples are applied to the area of probability- based optimum structural design. / Master of Science

Undoped and doped Pb(Zr_xTi_1-x)O₃, i. e. PZT, ferroelectric thin films were prepared by chemical solution deposition and spin-coating method. The precursors for making the undoped PZT films were derived from lead acetate, zirconium n-propoxide, and titanium iso-propoxide. In addition, lanthanum acetylacetonate, neodymium acetate, and niobium ethoxide were introduced into the precursor solution to accomplish doping of the corresponding elements. Both doped and undoped PZT films were coated onto Pt/Ti/SiO₂/Si, RuO_x and single-crystal sapphire substrates of various thickness and annealed at a range of temperatures and times. The effects of dopants were studied in terms of the Curie temperature, crystal distortion, transformation temperature, microstructure, optical properties, and electrical properties. In addition to the dopant effect, the effects of substrates were also investigated with regard to crystallization and preferred orientation. The Curie temperature of the doped and undoped PZT films was determined by in-situ hot-stage transmission electron microscope (TEM) and compared with those of bulk ceramics. Lattice distortion and phase transformation were determined by x-ray diffraction (XRD). Microstructure of the films was characterized by using optical microscopy, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). Optical properties were characterized by a UV-VIS-NIR scanning spectrophotometer and electrical properties and fatigue testing were measured on a standardized RT66A using a Virtual-Ground circuit. It was observed that the addition of Nd and La dopants tends to enhance perovskite phase formation and improve electrical properties of PZT films. Higher refractive indices in La and Nd-doped PZT films imply that packing densities of PZT films are improved by adding dopants. Furthermore, the lower leakage currents and improved fatigue properties in PZT films were also observed by the addition of Nb dopants. / Master of Science

During the thickening process of sludges with intermediate to high solid concentrations three settling regimes are typically encountered, namely, zone, transition, and compression regimes. Recent studies have indicated that the validity of Kynch's formulation, which is the most widely used for sizing settling basins, is limited to the zone settling regime. His formulation is based on the solids mass balance equation and does not consider the role of the rising sediment at the bottom of the settling basin. This limitation is rectified in this study by using a dynamic equation, a second order non - linear partial differential equation for the effective pressure of the solid particles. The equation is solved by using the finite element method. The so obtained effective pressure is used with an appropriate constitutive relation for the volume fraction of solids, to determine the variation of the solids content within the deposited material, and the height of the falling mudline. / Master of Science