AZT (3'-azido-2’, 3’-dideoxythymidine) has been shown to prolong the survival of patients infected with human immunodeficiency virus (HIV) and decrease the severity of opportunistic infections. Such studies have prompted the use of AZT to treat symptomless individuals infected with HIV in the hope of delaying or even preventing the progression to acquired immunodeficiency syndrome (AIDS). However, before chronic use of AZT in symptomless individuals is initiated, it is important to establish whether this anti-viral drug would directly alter the phenotype and functions of the cells involved in the immune system. In the current study, we observed that AZT when administered orally for 7 -14 days into DBA/2 mice at 500 - 1000 mg/kg body weight induced a dose-dependent decrease in cellularity of the thymus. AZT caused significant alterations in the thymus resulting from a significant decrease in the number of double-positive (CD4⁺CD8​​⁺) cells and an increase in the number of double-negative (CD4⁻CD8⁻) cells. Interestingly, after the i.p. administration of interleukin-2 (IL-2) simultaneously with AZT, the total cellularity of the thymus was completely reconstituted. We also observed that AZT effectively suppressed the in vivo T cell response to conaibumin and gp120 of HIV. Furthermore, the addition of AZT to in vitro cultures caused a dose-dependent decrease in T and B cell proliferative responses to mitogens at 50μM or greater concentrations. Also, AZT inhibited the generation of cytotoxic T lymphocytes when added to the culture and this inhibition was reconstituted by the addition of exogenous IL-2. Together, our studies demonstrate that AZT modulates the phenotype and function of cells of the immune system which, in turn, could have marked repercussions on immune responses of the host toward infections and cancers. Also, our data demonstrating that AZT can suppress T cell responsiveness against HIV antigens caution against chronic use of AZT in asymptomatic HIV-infected individuals. / Master of Science

Research currently being conducted at Virginia Tech has produced a viable pesticide wastewater clean-up procedure using biologically based materials. The system consists of two steps. First, pesticide laden wastewater is mixed with a lignocellulosic sorbent such as peat moss in a demulsification and sorption step. Second, the wastewater filtered rinsate is then passed through a packed column containing the same sorbent in a column sorption and filtration step. Although the system yielded adequate results and performed the tasks commensurate with its design, the original batch demulsification and sorption phase of the process had several operational problems. Namely, the system was large and not very portable, the recirculation system was not very reliable, and the entire step one process was laborious and time consuming to execute. These problems and limitations prompted the redesign of the step one process into a new, more efficient system. The new system consists of a steel frame similar to the old system. However, the new frame is smaller, lighter, more portable, and one person can easily operate and maneuver the new system. In addition, the new system provides a safer work environment for the operator. The frame surrounds the barrel and liner like a cage so that if the hand winch or the cable fails when lifting the liner out of the barrel, the operator is protected. The recirculation system has been automated such that it 1s self priming, and turns off when all the rinsate contained between the inner liner and outer barrel has been pumped dry. The come-a-long has been replaced with a hand wench that makes loading and unloading of the inner liner easier. Finally, the same pump that is used to recirculate the rinsate is used to transfer the rinsate onto the column for the second sorption and filtration step. There is now no need for additional pumps. After the system was designed and developed, it was tested on two pesticides, atrazine and metolachlor, to determine if the new system yielded results comparable to the old system. The atrazine concentration in the rinsate was reduced from an initial 721 mg/kg (ppm) in step one to 2 mg/kg in the step two column sorption and filtration phase. This represents an atrazine reduction of 99.72% over the entire two step process. The metolachlor concentration in the rinsate was reduced from an initial 704 mg/kg in step one to 30 mg/kg in the step two column sorption and filtration phase. This represents a metolachlor reduction of 95.74% over the entire two step process. The percent reduction of pesticide from the rinsate in the new system is comparable to the 99% reductions obtained using the old system. / Master of Science

Cellulose “waxy” (long-chain aliphatic) tri-esters of lauric (C₁₂), myristic (C₁₄), stearic (C₁₈), and eicosanoic (C₂₀) acids; mixed esters of lauric and acetic acids; and fluorinated mixed esters of 2,2,2-trifluoroethoxyacetic (TFEA) and acetic acids were synthesized in homogeneous DMAc/LiCl solution. Degree of substitution (DS) was conveniently controlled via stoichiometry, and fully-substituted cellulose derivatives were produced with little depolymerization. Thermal analysis of the C₁₂ - C₁₄ waxy tri-esters revealed separate melting transitions (T_m,L and T_{m, H}) for ester substituents and main cellulose chains, providing evidence for the existence of a separate (crystalline) phase formed by the ester substituents. Main-chain T_mS of waxy esters converged with the melting transition of the side-chain phase and/or disappeared as substituent length reached C₁₈. The effectiveness of melting point depression at low DS of large substituents increased with increasing substituent length for n-alkyl substituents up to lauryl (C₁₂); at mid-DS of large substituent, increasing the substituent length had no further effect in melting point depression above a length of C₆ (hexanoyl). The preferential sorption of ethanol from aqueous solution by cellulose (CE) and cellulose acetate trifluoroethoxyacetate (CATA) of varying DS was measured by liquid chromatography (LC); the preferential sorption of ethanol did not change when acetate substituents were replaced by trifluoroethoxyacetate substituents. The preferential sorption of ethanol by unmodified cellulose was stronger than the preferential sorption by cellulose acetate and trifluoroethoxyacetate esters. / Master of Science

Two mathematical models are applied to the study of a flight performance problem for an air-superiority fighter aircraft. The first model considers the body axes angular rates as control variables and is accordingly referred to as the body rate model. The second model is a rigid body model featuring rotational dynamics governed by the primary control surface deflections. The body rate model is intermediate between a point-mass model and rigid body model and accordingly, useful for preliminary design applications. Comparisons between the two models are made to determine the utility of each when applied to a particular flight problem. The integral flight performance problem combines notions of roll and pitch agility in a roll reversal maneuver. The flight problem is formulated as an optimal control problem for each of the models. Parameter variations in the initial flight condition specified by the load factor, and in the available roll and pitch control powers were studied and used to compare the models. The results indicate deficiencies in the body rate model as an accurate predictor of agile aircraft characteristics. / Master of Science

Three models are presented which predict frequencies and mode shapes of transverse vibration for a continuous prismatic Bernoulli-Euler beam on elastic supports, subjected to a compressive axial load. The first model, which approximates support stiffnesses by an equivalent elastic foundation, is found to be inaccurate for wave lengths close to the support spacing. A discrete mass model is formulated which accounts for axial load by stability functions which modify the element stiffness matrices. A continuous model is formulated which yields an exact solution for Bernoulli-Euler beam theory. The frequencies predicted by the discrete mass model and continuous model are in excellent agreement. A method of predicting axial compressive load and support stiffness based on measured frequency and phase data is presented which can be used for either the discrete mass model or the continuous model. A frequency reduction factor is derived which accounts for the effects of shear deformation and rotatory inertia. Tests are performed on an eight span beam with compressive axial load. Test results show that the models accurately predict frequencies and mode shapes of vibration. Results indicate that the method formulated can be used to determine compressive axial load and support stiffness. / Master of Science

This study was designed to compare the financial attitudes, financial behaviors, and financial satisfaction of limited income households and middle income households. Deacon and Firebaugh’s family resource management systems theory was used as the theoretical model for this study. Measures of financial attitudes concerned the areas of planning, credit, spending, saving, insurance, financial responsibility, and expectations. Measures of financial behaviors concerned the areas of planning, spending, saving, credit, insurance, taxes, and financial responsibility. Measures of financial satisfaction concerned satisfaction with standard of living and amount of money saved or invested. The respondents were a sub-set of an existing data base, Financial Attitudes and Practices of Virginia Citizens, Form A, (N=529). Forty-one respondents who reported a 1989 income below 125% of the poverty guidelines were included as the limited income sample. One hundred eight respondents who reported an income in 1989 between $30,000 and $44,999 were included as the middle income sample. Descriptive statistics were used for demographic items. T-tests and chi-square tests were used to compare responses to the individual measures by income group. A t-test compared the mean summed scores for the measures of financial attitudes using a Likert type response scale. There was a significant difference in the financial attitudes of limited income households and middle income households (p = .00). Using the same method for the measures of financial behaviors and financial satisfaction, it was found that there also were significant differences in the financial behaviors (p = .00) and financial satisfaction of limited income households and middle income households (p = .00). / Master of Science

Superplasticity and superionic conductivity (SIC), both thermally activated processes, have been independently observed in certain materials with a high diffusion coefficient in high temperature ranges. Intuitively, this observation leads one to the idea that both types of behavior may be inter-related with one another. Therefore, it is the purpose of this research to investigate, specifically, the deformation characteristics of two SIC's, Bi₂O₃ and YSZ (yttria-stabilized zirconia), and to attempt a correlation of their behavior. Compressive deformation of these two materials was conducted over a wide range of temperatures and at various strain rates in an effort to characterize the temperature and/or strain-rate dependences of any observed superplasticity. Steady-state flow stress values were utilized to calculate the strain-rate sensitivity, m, of the materials, as well as the activation energies (Q_C) of superplasticity. Next, the obtained values of Q_C. were compared to SIC activation energies from the literature. Bi₂O₃ exhibited structural superplasticity within the range of test conditions utilized. However, published values of SIC activation energy were lower than experimentally derived Q_C by a factor of four. Therefore, one is not able to state whether or not there is any correlation between the two behaviors. Unfortunately, YSZ exhibited brittle behavior over the entire temperature and strain-rate ranges, so the same analysis could not be performed. Furthermore, SEM micrographs showed that YSZ samples, as processed, did not possess the proper microstructure required for superplasticity. Hence, no final conclusions on YSZ can be drawn from this study. / Master of Science

Noise and distortion limit the channel capacity and degrade the system performance in AM-VSB SCM CATV Distribution Networks. The use of star couplers and fiber amplifiers is an approach to overcome these problems and meet the increasing demand for large capacity and high quality. The capacity and performance analyses of three different network configurations are compared based on the results of computer modeling. In practice, the best configuration depends on the optical amplifiers and the pump lasers used in the system as well as the requirement on the number of channels and the number of subscribers. It is found that in a two-stage star network the largest improvement in the capacity and performance may be achieved when the optical amplifiers between the stages are individually pumped. For example, a capacity of 200 channels and 572 output nodes may be obtained. There is an optimal length of the erbium-doped fiber amplifier (EDFA) and there is also an optimal position where the EDFA is located between the two star couplers. The modeling is based on an extensive analysis of noise and distortion in the system. A discrepancy in the power behavior of laser relative intensity noise (RIN) is pointed out. A previous analysis on reflection-induced noise is extended to include the effect of quadruply-reflected light and optical amplifiers. Since chirp-dispersion distortion and gain tilt distortion are found to be negligible, clipping distortion is the main limitation on the system capacity. Optical amplifier noise provides an additional limitation to the system. Because the gain and amplified spontaneous noise depend on the input signal power and pump power, the gain and spontaneous emission factor are modeled for the comparison of the different systems. / Master of Science

Being held accountable for one's views in an ambiguous situation has been found to increase cognitive processing and reduce possible biases often pervasive in performance appraisals (Tetlock, 1983a). The present study examined the effects of making raters more accountable for their performance ratings through expectations of a supervisory review. Two types of accountability were manipulated. Interpersonal accountability induced subjects to believe that they would receive feedback based on their justifications of their ratings. Reward accountability subjects expected that they would receive a reward based on the quality of their ratings compared to true performance scores. Half of the subjects were also told that the supervisor gave the ratee a negative performance rating. 191 female subjects rated an interviewer's performance after receiving accountability and view manipulations. Results indicated that subjects who received accountability manipulations in conjunction with the view gave more unfavorable ratings and were less accurate on Cronbach's (1955) elevation component of accuracy than no accountability and/or no view groups. Accountable subjects who did not receive the view were expected to increase cognitive processing. These hypotheses pertaining to increases in cognitive complexity and dimensional accuracy were not supported. Although unexpected, interpersonal accountability in conjunction with reward accountability prevented a decrement in processing when given the view. A biased versus unbiased vigilant processing hypothesis was proposed to explain these results. Possible limitations are also proposed as well as implications for future research. / Master of Science

Metal matrix composites have two important interfacial problems between the matrix and the reinforcement which can reduce its desirable mechanical properties. Chemical differences between the matrix and the reinforcement can lead to reactions and deterioration of the reinforcement. Secondly, structural differences between the matrix and the reinforcement lead to bonding conditions which are far from ideal. By using a reinforcement which has a similar chemistry and local atomic structure to that of the matrix, these critical problems can be reduced. A crystalline matrix reinforced with an amorphous form of the matrix is a possible solution to the problem. Composites of amorphous Fe-W alloy particles reinforcing an Fe matrix were produced using mechanical alloying. Bulk samples were produced and their properties were studied. After analyzing the results, the amorphous alloys were determined to be effective strengtheners. However, porosity in the composites led to a reduction of the strengthening imparted by the reinforcement. / Master of Science