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

Methods of expressing the radiation patterns of phased arrays in closed form that include the effects of radiated mutual coupling are investigated. The two basic methods considered are the classical array analysis method and the active element pattern methods. The theoretical derivations of the active element pattern methods are presented and the various types of active element patterns are defined. Also, a new method based on active element patterns, the hybrid active element pattern method, is introduced which accurately predicts the patterns of small and moderately-sized arrays of equally-spaced elements. Arrays of center-fed dipoles are considered in this study since dipole arrays can be fully characterized, including mutual coupling, using modem numerical electromagnetic analysis codes, thus allowing verification of the array analysis methods presented here. The results are general, however, and may be applied to arrays of any type of element. The array patterns computed using the classical analysis method and the active element pattern methods are compared to those computed using ideal array analysis and the highly-accurate numerical codes. / Master of Science

Extensive research to determine the strength of steel deck reinforced concrete floor systems has been carried out on single-span, single panel width test specimens. Little of this research has considered the benefits that actual field conditions have on overall strength and stiffness. This experimental study investigates typical field details at intermediate supports and end spans. In particular, the influence of adjacent spans and typical pour stop details are considered. Additionally, this study illustrates the applicability of simple analytical models, which can be used to determine the strength and stiffness of steel deck reinforced concrete floor systems. / Master of Science

In the past forty years, much work has been done in the area of multiple scattering effects on the propagation of electromagnetic waves in a random particulate medium. This work is important to wave propagation in the atmosphere, the planetary sphere, and the ocean. Current research is aimed at high frequencies (gigahertz to terahertz). At these frequencies, multiple scattering effects become very important since the wavelength reduces to the size of a particle. The purpose of this thesis is to augment the Twersky theory of multiple scattering in a random particulate medium. Most applications of Twersky’s work use a far-field approximation and a point-particle assumption. At high frequencies, particle sizes may be large relative to a wavelength; therefore, the point-particle assumption is inaccurate. Under a low-density approximation, this thesis introduces a scattering operator, which defines closed equations for the fields due to multiple scattering. The low-density approximation holds for many media (e.g. clouds and rain). The scattering operator may be solved for various particle shapes, eliminating the need for the point-particle assumption. / Master of Science

Nearly periodic structures exhibit localized modes of vibration depending upon the ex· tent of the coupling and the disorder between their periodic components. These localized modes may cause excessive vibration amplitudes resulting in significantly higher stresses than the ones the structures have been designed to withstand. The Rayleigh-Ritz method, as employed earlier, for dynamic analysis for two-span beams could predict only the lower modes of vibration at prohibitive computational expense. A semi-analytical method which predicts even the higher modes at significantly reduced cost has been applied to the free vibration analysis of two-span beams. This method has been applied to the forced vibration analysis of a couple of mistuned turbine blades modeled as a two- span beam rotating in a turbulent flow field. It is shown that the maximum vibration amplitude of the mistuned structure may increase by several hundred percent as compared to that of the perfectly ordered structure. / Master of Science

Even with the performance of microprocessors expected to double within the next three to five years, the processing power increase offered by parallel processing has made multiprocessor systems very cost-effective. Each module in the multiprocessor systems will typically include a processor, coprocessor, cache, and main memory. This kind of architecture has generated the system-on-aboard distributed-intelligence concept, and the 32-bit multimaster buses thus come into play since these high-performance systems need to communicate with each other. During communication, commands and large blocks of data are transmitted across the bus. Along with the multiprocessor system, the single-CPU system continues to need a fast bus and wide data path to serve as a common I/O interface for terminals, disk storage devices, communication, and memory boards. With the board size limited, the trend toward distributed intelligence increases the need to place more functions on a single board, and therefore bus interface unit (BIU) integrated circuits (ICs) play an important role in the design of new boards. Spaceborn systems must be fault-tolerant due to their high susceptibility to transient faults and the high costs of repair and maintenance. Hence, a gate array fault-tolerant bus-interface IC based on modified NuBus protocols is designed to meet these requirements. The gate array IC design system HIGHLAND from United Technologies Microelectronics Center is used, along with other CAD tools such as the Berkeley VLSI Tool Set and LOGEN to generate a layout for the BIU. Two programs are written to interface the necessary CAD tools. All the circuits are designed and simulated on a VAXstation 3200 (Ultrix-32) and VAX11/785 (VMS). / Master of Science

Many structures are sensitive to initial imperfections, sometimes leading to a great decrease in buckling load. Koiter showed that the effect of initial imperfections is largely determined by the initial post-buckling behavior of the perfect structure. The present work seeks to implement Koiter’s method of asymptotic post-buckling analysis on a finite element program Engineering Analysis Language (EAL). EAL is based on engineering strain measures. It is shown via examples that the predicted post-buckling behavior of a structure for engineering strain measure is approximately the same as that for Green’s strain measure provided the strains are small. To characterize the post-buckling behavior by Koiter’s method in the finite element form, the linear and incremental stiffness matrices are required. These matrices comprise the tangent stiffness matrix. As EAL uses the modified Newton-Raphson procedure to solve nonlinear structures, it calculates the tangent stiffness. The first and second order incremental stiffnesses are extracted by partial differentiation of the tangent stiffness using a second order central difference scheme. The linear stiffness is directly given by the EAL processor ”K”. These stiffnesses are then used to get the post-buckling load-displacement behavior close to the bifurcation point. Numerical results for the initial post-buckling behavior are obtained for truss and frame structures using the Koiter’s analysis procedure on EAL. It is compared to the nonlinear load-displacement behavior of the structures with small initial imperfections. The post-buckling load-displacement behavior for a knee frame is also compared to the behavior obtained experimentally by Roorda [19] and analytically by Koiter [13]. The asymptotic analysis procedure has given good asymptotic post-buckling results. / Master of Science