Clostridium difficile causes pseudomenbranous colitis (PMC) and diarrhea in humans. Toxigenic strains of C. difficile produce two toxins. Toxin A is an enterotoxin and cytotoxin, and toxin B is a potent cytotoxin. The gene encoding toxin A has been sequenced and was shown to possess a 2.5 kb region, containing 38 similar repeating amino acid sequences, at the 3' -end of the gene. This region of the toxin A gene codes for the carbohydrate-binding portion of the toxin. The monoclonal antibody PCG-4 (MAb) binds to this portion of toxin A and neutralizes its enterotoxic activity. In addition, this monoclonal antibody has been shown to immunoprecipitate toxin A, suggesting that the MAb PCG-4 is binding to two or more similar epitopes on the toxin. The goal of this research project was to identify the neutralizing epitopes recognized by the MAb PCG-4 on the surface of the toxin A. To map the epitopes bound by the MAb PCG-4, a series of overlapping deletion clones were constructed from a 4.7 kb fragment from the 3'-end of the toxin A gene. The recombinant polypeptides expressed by these clones were tested for reactivity with the MAb PCG-4. By comparing the overlapping polypeptides, defined as either PCG-4 reactive or nonreactive, I localized the PCG-4 epitope to a 44-amino acid sequence situated between the amino acid residues 2098-2141 of toxin A A similarity search of the toxin with the 44-amino acid sequence containing the PCG-4 epitope revealed the presence of two other possible PCG-4 epitopes located between the amino acid residues 2355-2398 and 2459-2502. However, subsequent cloning experiments showed that only the region located between the amino acid residues 2355-2398 contained a PCG-4 reactive epitope. The identification of two similar epitopes within the toxin's structure explains how this monoclonal antibody is able to immunoprecipitate toxin A in the absence of subunits. Furthermore, I found that small recombinant polypeptides, containing the PCG-4 epitope lost reactivity with this monoclonal antibody following denaturation, suggesting that the epitopes recognized by this monoclonal antibody are conformationally dependent. / Master of Science

A methodology and prototype has been developed which enables users of GML and SCRIPT on an IBM 3090 to preview documents on a locally attached personal computer before printing. Currently, no utility exists to accomplish this activity. This new preview process is graphical in nature and provides an absolute picture of the document, exactly as it will be printed on an IBM 3812 laser printer. / Master of Science

El objetivo del documento es presentar un enfoque que evalúa el desempeño de la política monetaria y la política fiscal en una economía pequeña, abierta y parcialmente dolarizada como la peruana, más allá de las reglas o las funciones de reacción de política convencionales. En el período contenido entre el primer trimestre de 1990 y el último trimestre de 2013, se pretende explicar la política monetaria a partir de una Regla de Taylor, y la política fiscal sobre la base de una función de reacción. La Regla de Taylor expone el uso de la tasa de interés como instrumento de política, a partir de las brechas de producto y de inflación, y el efecto de la depreciación cambiaria. Además, en este estudio se propone incorporar el efecto de variables del ámbito internacional (los precios internacionales) y del marco político (la calidad institucional), con el propósito de analizar cómo cambia la eficiencia de las acciones y las decisiones de política. De otro lado, las acciones de política fiscal se enfocarán en el manejo de la brecha de gasto real como indicador de impulso fiscal, a través de una función de reacción, en la que se evalúa el efecto de la brecha de producto. En adición, se repite la estrategia de incorporar el impacto proveniente del entorno mundial (los términos de intercambio) y el desempeño institucional (la restricción política). Por tanto, los resultados muestran que no habría márgenes de maniobra para las acciones de política, puesto que al demostrar la dependencia de éstas al contexto internacional, y al perfil institucional interno, se comprueban las restricciones de política económica.

A quadtree-like representation for storing gridded elevation data is described. In its simplest form, the data structure is a pyramid with each node containing a two bit code. The root of the pyramid has associated with it the minimum elevation for the grid and the range (the greatest power of 2 less than or equal to the difference between the minimum and maximum elevation values). Any specified elevation value is determined by traversing a path from the root to a leaf node. As the traversal proceeds, the minimum and range values are refined by interpreting the codes stored at each node along the path. At the leaf level, the final minimum value equals the associated elevation value. Since the total number of nodes in the pyramid is 4/3 the number of elevation grid cells, the amortized storage cost is less than 3 bits per grid cell. When the difference between elevation values is not "too great", this basic representation is quite effective. For data where greater elevation differences occur between neighboring cells, this basic method is modified to improve the representation, but at a cost in storage. Our method is most appropriate for efficient secondary storage archival, such as on CD-ROM. It also allows efficient retrieval of complete elevation data from any subregion, at multiple scales, within the entire elevation database. / Master of Science

A new method for analyzing axisymmetric, high-frequency transformers is presented. The method is based on the simultaneous solution of the coupled, nonlinear thermal and electromagnetic equations using the finite element method. A novel technique for modeling the reluctivity of the soft-ferrite core material permits a time-harmonic transformation of the electromagnetic equations. This eliminates the need to step through time while maintaining the effects of hysteresis losses. Also, a quasi-steady formulation of the heat-conduction equation eliminates the time dependency on the thermal problem. A direct substitution iterative scheme is used in conjunction with the finite element method to compensate for the coupled and nonlinear nature of the equations. To verify the magnetics portion of the finite element code numerically, a linear, uncoupled test case is given which compares the magnetic results from the present method to those from a commercial software package. To investigate the accuracy of the fully coupled and nonlinear model, an example is presented which compares the results from the numerical analysis of an inductor to those obtained by experimental measurement. / Master of Science

Three long-term field experiments were established in the spring of 1978 and continued through 1988 to evaluate corn (Zea <i>mays</i> L.) response to high Cu levels from Cu rich swine manure and CuS0₄ applications. The field research was conducted on soils with diverse properties, i.e., on a Bertie fine sandy loam (Aquic Hapludults), a Guernsey silt loam (Aquic Hapludalfs), and a Starr-Dyke clay loam (Fluventic DystrochreptsTypic Rhodudults). Three treatments in the long-term field experiments on the three soils were a control, annual applications of eu as eu rich swine manure, and annual applications of Cu as CuS0₄ equivalent to that in the manure. After the 11 years, 1109 mt ha⁻¹ of wet Cu rich swine manure were applied for the manure treatment. The Cu rich manure contained an average of 1316 mg Cu kg⁻¹, An average of 325 kg Cu ha⁻¹ added to the soils from the manure application over the 11 years exceeded U.S.E.P.A. guidelines for safe copper loading levels for cropland by 45 kg ha⁻¹. Copper concentrations in corn ear leaves were within the normal range of 3 to 20 mg kg⁻¹ where the 325 kg Cu ha⁻¹ were applied to the soil as either Cu rich manure or CuS0₄. Concentrations of Cu in the grain were also in the normal range of 1 to 5 mg kg⁻¹ where the high level of the two Cu sources was applied to soils. There was no decrease in corn yield on the three soils from application of either Cu source. / Master of Science

An active power factor correction circuit with controlled on-time is proposed. The circuit has a simpler control scheme than the power bc10r correction circuit with hysteresis control, and yet is able to attain high power factor. A very important aspect of this work was the formulation of the design guidelines for the input filter for the power factor correction circuit. Conventional methods of filter design may introduce an unwanted phase shift between the input voltage and current, thereby degrading the power factor. The cause of this phase shift is explained and based upon it, the design guidelines for the input filter are established. The FFT is used to more accurately define the input filter attenuation requirement. A comparison is made between power factor correction circuit with controlled on-time and the power factor correction circuit with hysteresis control (with input filter for both of them) on the basis of their minimum weight. A regulated 100 W, 120 VAC input and 300 V output power factor correction circuit was implemented on a breadboard. Ridley's small signal switch model [10] for the power factor correction circuit with hysteresis control is successful1y app1ied to this control scheme to close the loop. / Master of Science

During World War II the rise of labor to political power in Jamaica, an English Colony since 1655, represented a new and dramatic development that necessitated political reform. In November 1944, the inauguration of limited self-government based upon the Westminster model of government, and for the first time in the history of Jamaica, on universal adult suffrage, brought the Crown Colony period to and end and placed Jamaica securely on the road to self-government. Like most British dependencies, Jamaica began a long period of tutelary democracy under British guidance to achieve statehood. From 1944 to full independence in 1962, periodic constitutional advances took place. By 1959, the island was self-governing with only defense and international relations referred to the Crown. / Master of Arts

Crossbred pigs (n=144, avg age and weight - 28 ± 3 d, 7.5 kg) were used in two 6 wk trials to assess the effects of dietary pH and phosphorus source on performance, gastrointestinal digesta pH and chloride ion concentration (Cl⁻), bone characteristics and body composition. Pigs were blocked according to weight within sex and litters were balanced across groups. Treatments were randomly allotted within blocks to a 3 x 2 factorial arrangement with three dietary pH levels (5.4, 6.0 and 6.7) and two phosphorus sources: dicalcium phosphate (DCP) and defluorinated phosphate (DFP). Pigs fed the pH 6.7 diet had reduced average daily gain (ADG, P < .01) and average daily feed intake (ADFI, P < .001) during wk 1-3 and overall compared with pigs fed the pH 6.0 diet, but ADG and ADFI were not effected when the pH 5.4 diet was fed. There was a dietary pH by phosphorus source interaction (P < .05) for ADFI. DCP fed pigs had increased ADFI as dietary pH was reduced from 6.7 to 5.4, but DFP fed pigs had similar ADFI as dietary pH decreased from 6.0 to 5.4, and decreased ADFI as dietary pH increased from 6.0 to 6.7. Dietary pH had little influence on F:G, and phosphorus source had little effect on either ADG, ADFI or F:G. Dietary pH did not influence the pH and Cl⁻ of the digesta for any gastro-intestinal section measured, except the Cl⁻ in the stomach; both pH 5.4 and 6.7 fed pigs had a higher (P < .01) Cl⁻ than the pH 6.0 fed pigs. Only shear force of the fourth metacarpal and specific gravity of the fourth metatarsal were increased (P < .01) for pigs fed the DCP compared with DFP diets. Neither dietary pH nor phosphorus source influenced backfat or loin muscle area. These results suggest that maintaining the acidifity of the diet during the first 3 wk after weaning at 28 d of age is important with the primary response seen in ADFI. Varying dietary pH from 5.4 to 6.7 had little or no effect on gastrointestinal digesta characteristics, bone development and body composition. / Master of Science

Broccoli (<i>Brassica oleracea</i> L. var. italica) has become an increasingly popular vegetable with American consumers. Much of the attractiveness of fresh broccoli is derived from this vegetable's high nutrition and excellent organoleptic properties. In a consumer response survey, Virginia Master Gardeners indicated a preference for broccoli that has less stalk and more florets by weight. The objectives of this research were to produce single unit broccoli, and to examine vacuum and shrink-film wrapping of single unit and bunching broccoli as alternatives to the standard post harvest practice of top icing in order to preserve post harvest quality attributes: vitamin C, color, odor, and turgidity. Broccoli cv. 'Symphony' was direct seeded and transplanted at two sites in Virginia (within row spacing 20 cm , .9 m centered, 3 row bed). Single unit broccoli was classified as broccoli with head diameters greater than or equal to 20 cm (i.e., equivalent to one bunch of broccoli). Single unit and bunching broccoli for post harvest experimentation was vacuum or shrink-film wrapped with plastic film wraps of varying gauges. The broccoli was held in cold storage from 12 to 22 days with no supplemental ice. Single unit broccoli was produced successfully at one site only. The yields, however, were a fraction of total bunching broccoli yields. There was no significant difference in marketable yields with either planting method (direct seeded vs transplanting) at site 2. Transplants, however, out yielded the direct seeded broccoli at site 1. Vacuum and shrink-film wrapping proved to be very effective in preserving organoleptic attributes of single unit and bunching broccoli even when never receiving ice. Vitamin C and chlorophyll retention were not influenced by wrapping. / Master of Science