None / Master of Science

Five parametric modeling techniques have been identified to be possible alternatives to the Fast Fourier Transform (FFT) for signature analyses involving short data records. The developments in signal processing that have lead to these techniques are reviewed. Mathematical definitions for parametric models are provided in terms of time-domain stochastic difference equations as well as in terms of frequency-domain rational transfer functions. Computer programs are developed for implementation of each of the five parametric modeling techniques. Results are presented from studies conducted on simulated stochastic signals to characterize the performance of the parametric modeling techniques and to compare the performance of these techniques to the FFT. One of the parametric modeling techniques, Pisarenko Harmonic Decomposition shows outstanding performance in comparison to the FFT and to the other parametric modeling techniques. / Master of Science

The Wiener theory of the minimum mean square error ·criterion is well furnished by knowing the autocorrelation function of the input to the linear system. This input signal is generally an additive mixture of a piecewise continuous message and a noise. The problem considered in this paper is the determination of the autocorrelation function and also their power density spectrum of the noise component for the random base and height modulated square wave whose leading edges are periodic functions of time. We note that the adopted probability density function for heights of random square wave have Gamma-Distribution Density Function. In addition to this distribution function, we consider the rectangular and Beta-density function on the base of square waves. In fact, the leading edges of most periodic-random base function can be simply described by using the rectangular and Beta-Density function. Another matter under consideration is the visualization of the variations noise power density spectrum immersed in the masked signal (mixtured signal) with respect to the variance σ² and s² of Gamma and Beta-distribution, respectively. / M.S.

Performance of a three-phase fluidized-bed biofilm fermenter system, which is used for the production of a secondary metabolite, is analyzed through computer simulation techniques. Penicillin fermentation was chosen for the model system. From the steady-state analysis, it was found that a complete-mixed contacting pattern is superior to a plug flow pattern in terms of productivity, since less inhibitory effect of the substrate is pronounced in that configuration. Optimum biofilm thickness for the fermenter system was found to be a function of various operating parameters, and should be determined from information on the interactions between fermenter productivity and the operating conditions. The dynamic analysis has shown that for a given constant oxygen transfer rate in bulk phase, there exist operating conditions optimal for maximizing the volumetric productivity of the fermenter system. When a constant oxygen transfer rate with a k.e.a of 300 hr 1 was used with a complete-mixed contacting pattern, the optimum inlet substrate con- centration and mean residence time were found to be 20 (g glucose/liter) and 10 (hours), respectively. Production phase could be extended by increasing the substrate concentration in the feed stream, but the optimum increasing rate and initiation time of increase are functions of other operating parameters, such as initial inlet substrate concentration, mean residence time, and oxygen transfer rate in the fermentor. An increasing rate of 0.6 g glucose/liter/hr with the initiation time t 0 = 51 was found to be the optimal, for the operating conditions found in the dynamic analysis. The result has also shown that a high total biomass concentration and a high oxygen transfer rate in the fermentor are the most important factors to achieve a high productivity. / Ph. D.

Agricultural loans issued to farmers in Virginia from the years 1980-1985 are examined to determine the factors which significantly predict repayment ability. Through a review of literature, extension meetings, conferences and informal conversation with agricultural lenders in the state, a list of financial variables and operation characteristics is compiled and analyzed. Results of the analysis are considered in terms of their immediate and potential assistance to lenders in making loan decisions. Using data from various commercial banks, Production Credit Associations and Farmers Home Administrations throughout Virginia, a model is developed to determine repayment ability of a borrower. Results indicate that several factors are significant in determining this process. Financial ratios such as percent equity, current debt, cash flow I and cash expense-cash receipt are important in determining if a borrower will repay his loan as scheduled. A number of operation characteristics were also found significant. These include: the number of creditors of the borrower, the amount of diversification of the operation and the amount of non-farm income. The results of the study should prove to be a significant aid to lenders and implies need for further research in the loan repayment area. / M.S.

Libby Prison ranked as one of the most notorious of Civil War compounds. Used as a transitory depot and hospital as well as a permanent place of confinement, over 125,000 Federal prisoners passed through Libby's doors. The Confederate States Military Prison headquarters located in Libby Prison made it the focal point of Richmond's spindly prison system. Prisoners' diaries tell of depravations suffered during captivity. Insufferable living conditions, poor food rations, inadequate hospital facilities and harsh punishment composed a majority of the prisoners' complaints. Daily newspaper accounts reflected the lifestyles of Richmond's population and residents' attitudes toward the presence of Federal captives in their city. A majority of the time, prisoners had access to the daily papers. Yet very few of them attempted to draw a correlation between the type of existence that they endured within Libby Prison versus the civilian population's struggle to sustain itself in likewise unsuitable circumstances. The Official Records of the Civil War round out the picture of the difficulties faced by the Confederate government in trying to maintain large numbers of prisoners with proper shelter and food. Added to this was the continual desire of Confederate authorities to establish an exchange system to alleviate their burden and Federal prisoners' suffering. This thesis attempts to draw these major sources of information together. Prisoners' reminiscences used in this study were critically evaluated for their validity. To establish the diarists' retention in Libby Prison for the period indicated in the diary, Roll Call Books located at the National Archives were consulted. Newspapers and official correspondence balanced out the interpretation of Libby life. Throughout the Civil War, the Confederate government did not attempt intentionally to deprive Federal prisoners of adequate provisions. A majority of the time, circumstances dictated the actions disliked by captor and prisoner alike. / Master of Arts

The interaction of oblique shocks and oblique compression waves with a laminar boundary layer on an adiabatic flat plate is analyzed by solving the Navier-Stokes equations in conservation-law form numerically. The numerical scheme is based on the Beam and Warming’s implicit method with approximate factorization. We examine the flow of Bethe-Zel’dovich-Thompson (BZT) fluids at pressures and temperatures on the order of those of the thermodynamic critical point. A BZT fluid is a single-phase gas having specific heat so large that the fundamental derivative of gas dynamics, Γ, is negative over a finite range of pressures and temperatures. The equation of state is the well-known Martin-Hou equation. The main result is the demonstration that the natural dynamics of BZT fluids can suppress boundary layer separation. Physically, this suppression can be attributed to the decrease in adverse pressure gradients associated with the disintegration of compression discontinuities in BZT fluids. / Ph. D.

This study investigated the effects of contract grading on motivation and mathematics achievement of underprepared college students. The study also examined the relationship between motivation and mathematics achievement. The expectancy theory of motivation containing the five components anticipated effort, valence of first level, valence of second level, expectancy, and instrumentality provided the theoretical basis for this research. This investigation provided answers to the following questions: Is there a difference in mathematics achievement of students using contract grading as compared to students not using contract grading? Is there a difference in the motivation of students using contract grading and students not using contract grading? Is there a relationship between motivation and mathematics achievement? There were seventy-four students enrolled in the basic skills arithmetic course involved in this study. These students were in attendance at a small, historically black college. The study took place during the fall semester, 1984. Analysis of covariance techniques were used with pretest scores as covariates for posttest achievement and motivation means. Pearson correlation was computed for determining a relationship between motivation and mathematics achievement. Contract grading had a significant effect (p≤.02) on mathematics achievement scores in this study. There was a significant difference between groups on the components of valence of second level (p≤.01) and instrumentality (p≤.03) in favor of contract grading students. There were no significant differences between groups on the components of anticipated effort (p≤-42), valence of first level (p≤.07), and expectancy (p≤.76). Pearson correlation computations found no significant relationship between motivation and mathematics achievement for the contract grading group. Expectancy was significantly correlated with achievement for the noncontract grading group, while the other components were not significant. / Ed. D.

Intra-urban office location research has traditionally described office location patterns in large metropolises. Research is needed to determine whether these findings accurately describe locational patterns in average-sized American cities, such as Roanoke, Virginia. The pattern of insurance office location in Roanoke, Virginia, was examined from 1960 to 1983. It was determined that research in large metropolises accurately described certain trends in Roanoke but inaccurately described others, particularly with regards to office construction and office migration patterns. Insurance offices in Roanoke were stratified on the basis of their affiliation, or the way the office marketed its products. Four common types of insurance offices were identified: independent agencies, general agencies, captive agencies, and indirect writers. Questionnaires were distributed to a random stratified sample of each office type. Chi-square tests revealed significant differences in the organizational features, contact patterns, and locational characteristics of independent agencies, general agencies, captive agencies, and indirect writers. Future research should attempt to understand the structure of other office industries and identify industry-specific factors affecting the locational characteristics of each industry segment. / M.S.