The purpose of this study was to assess the extent to which selected demographic characteristics and academic variables of graduates from an urban. postsecondary practical nursing program could predict students' performance on the National Council Licensure Examination for Practical Nursing (NCLEX-PN). The research questions were: (1) what proportion of the variance in NCLEX-PN performance is associated with a combination of academic variables and demographic variables? (2) What proportion of the variance in NCLEX-PN performance is associated with academic variables? (3) What proportion of the variance in NCLEX-PN was explained by demographic characteristics? (4) What set of variables provide the best prediction of the NCLEX-PN scores? The population, N= 261, used for this ex post facto study consisted of postsecondary practical nursing graduates who wrote the NCLEX-PN examination between 1982 and 1987. There was one dependent (criterion) variable for this study, student scores on the NCLEX-PN. There were seven independent (predictor) demographic characteristics and five independent (predictor) academic variables. The data were obtained from student records between February and May 1992. Data were analyzed using the Number Cruncher Statistical System (NCSS), an advanced statistical analysis software package. Multiple linear regression analysis was considered appropriate for this study because the approach was consistent with professional and research literature and this study used dichotomous and continuous predictor variables. Results of the data analysis indicated the following: Based on the data analysis, demographic variables as a set were not predictors of success on the NCLEX-PN. However, with this population, the number of minor children under sixteen years of age in the students' families accounted for 6% of the variance in the NCLEX-PN. The academic set of variables accounted for the greatest amount of variance in the NCLEX-PN. Sixty-nine percent (69%) of the variance in NCLEX-PN performance is explained by scores on the PNEE and four NLN Achievement Tests: Mental Health, Pharmacology, Maternity Nursing and Nursing of Children. Recommendations for further study included investigations into the relationships between specific content examinations in the NLN Achievement Tests and performance on the NCLEX-PN and further data analysis be conducted to determine if there are academic variables or demographic variables that stand alone as predictors of success on NCLEX-PN. / Ed. D.

Master of Science

Master of Engineering

The feasibility of neural networks to control dynamic systems is examined. Control of a one-dimensional problem is initially investigated to develop an understanding of the structure and simulation of the neural networks. A nondimensional problem is also explored to apply a single neural network design to controlling a class of systems with a wide variety of modeling parameters. Finally, these techniques are applied to control a space vehicle to transfer, intercept, and rendezvous with another orbiting vehicle using the Clohessy-Wiltshire equations of relative motion in two dimensions. A combination of open-loop and closed-loop neural network controllers is shown to work effectively for this problem. Noise is added to the neural network inputs to demonstrate the robustness of these networks. / Ph. D.

M.S.

Amino acids were determined in two types of chinchilla fur (chewed and normal), using three methods for analyses The methods included microbiological assays of Barton-Wright(5) and two column chromatography techniques of Moore and Stein (7, 8). The data obtained from this investigation indicate that of the 16 amino acids analyzed, only one (lysine) was forum to be significantly lower in the chewed fur, as indicated by the "t" test. This difference between the normal and chewed fur was significant at the 2.5% 1evel. Also, arginine was lower and histidine was higher in the chewed fur than in the normal fur, but these difference: were not as conspicuous. In general, the microbioligical analyses were more time consuming end less reproducible than the chromatographic analysis. With the exception of proline, glycine, and leucine, higher values were obtained fer the mine acids using the microbiological methods than with the column fractions. The greatest difficulty was encountered in analyzing the basic amino acids. / Master of Science

Chlorophenols represent a class of organic contaminants that are commonly used and widely distributed in the environment. Adsorption to soils may inhibit the transport of these chemicals, while slow desorption rates can create a potential source for long-term contamination of groundwater supplies. Microbial degradation of these compounds may also play an important role in their environmental fate. The purpose of this study was to investigate how the processes of sorption, desorption, and biodegradation interact to affect the distribution of pentachlorophenol (PCP) and 4-monochlorophenol (4-MCP) in two soils with different soil organic matter (SOM) content. Batch soil microcosms were used to measure the sorption of both test compounds at three concentrations for each, exposed to two soils with different SOM levels. An ultrafiltration study was designed to quantify partitioning to dissolved organic matter (DOM), while batch desorption experiments were performed to measure chemical release from the soils. Finally, biodegradation experiments were carried out under aerobic conditions to evaluate microbial interactions with PCP and 4-MCP in both the liquid and solid phases. Sorption of both compounds was rapid, with 60-80% occurring within one day, but the process appeared to continue at a slower rate over several months. Statistical analysis showed that there were no differences in sorption due to SOM content or chemical concentration, for the two silty loam soils used in this study. Desorption followed a similar pattern of a fast and then a slow stage, and a significant difference was measured between the two soils. Higher levels of SOM resulted in slower desorption and a lower total release of the contaminants, but both soils retained a large percentage of unextractable compounds. Contact time was found to have the greatest effect on the amount of this nondesorbable fraction. The ultrafiltration study suggested that DOM polymerized into larger molecules after sufficient mixing time (3 months) in solution, which also increased the amount of 4c compounds that were bound to these humic substances. The biodegradation study suggested that natural soil microbes could utilize PCP and 4-MCP from both the liquid and solid phases, and that sorption to dissolved organics and colloidal matter could protect these chlorophenols from microbial degradation. Some data also indicated a possible correlation between desorption rates and bioavailability. / Master of Science

E_h-pH diagrams were constructed from mass-balanced, computer calculations for the copper-sulfur-water system involving different Cu/S ratios that pertain to chalcocite, djurleite, anilite and covellite. Calculations were completed for cases where oxidation of the sulfur proceeded to i) elemental sulfur, ii) thiosulfate, iii) sulfate and iv) destabilized sulfate. Stability regions for each copper sulfide were shown to be dependent on both the Cu/S ratio in the system and the sulfur oxidation state. E_h-pH diagrams were also constructed for chalcocite oxidation to metastable copper sulfides, both with and without xanthate. Stability regions for copper xanthates were also shown to be dependent on the sulfur oxidation state. As oxidation proceeded from elemental sulfur to sulfate, the copper xanthate stability region extended to lower potentials, directly dependent on the sulfide ion concentration. IGP experiments at pH 1.1 suggested that chalcocite oxidation produced metastable nonstoichiometric copper sulfides while cyclic voltammetry indicated they formed at pH 1.1, 4.6, 6.8 and 9.2. XPS implied that copper sulfides may be solid solutions of chalcocite with variable amounts of copper disulfide: CU₂S·xCUS₂. The presence of djurleite in the chalcocite samples was confirmed by X-ray diffraction and may be responsible for the reduction reaction which occurred just prior to the reduction of chalcocite to metallic copper. Reinterpreting cyclic voltammograms from a previous study indicated chalcocite reacted with xanthate to form cuprous xanthate and a nonstoichiometric copper sulfide near 0 mV. Chemisorbed xanthate formed at -295 mV which correlated well with the lower flotation edge determined in this and other studies. The standard free energy of the chemisorbed xanthate was determined to be -13.08 kcal/mole. / Master of Science

M.S.

During the past several years thirteen cows have died in the dairy herd at the Virginia Polytechnic Institute of malignant tumors of the lymphoid type. In view of research with respect to cancers of various types in man, any information relating to tumors acquired in this study should be of value not only to animal industry but also to similar conditions in in man A problem such as this requires long study, probably several years. This paper is a preliminary report on early fundamental steps of the cancer problem in dairy cattle as applied to local conditions. Because spontaneous cases of neoplasms in dairy cattle do not occur with any regularity, other phases of cancer research were instituted for investigation during the interval between cases. From the results of the previously described experiments, the following conclusions were drawn: 1. There was no evidence whatever of the neoplasms occurring in the rats about the dairy bards. 2. The attempts to produce neoplasms in dairy cattle due to foreign bodies implanted in the rumen were unsuccessful. 3. Attempts to transplant some of the tumors occurring naturally in the dairy cattle were unsuccessful. 4. Attempts to produce neoplasms in dairy cattle by weekly injections of four per cent solution or tar and lard were unsuccessful. 5. Attempts to produce tumors in fowl by weekly injections of four per cent solution or tar and lard were successful in five of the nine birds. Attempts to transplant two of these tumors were unsuccessful. 6. Occurrence of tumors in the members or the two families indicates possible genetic relationship. / Master of Science