The objective of this research is to develop and implement a method for fault simulation that considers bridging faults in CMOS circuits that are tested using supply current monitoring. The discussion is restricted to single fault detection in CMOS combinational circuits. A CMOS circuit is represented by a two-level hierarchy. At the higher level, the circuit is partitioned into modules based on the circuit layout. Each module is represented at the lower level by a switch-level graph. This representation has the advantage of structural accuracy at the lower level and efficient logic propagation at the higher level. Based on a module's switch-level graph, an exhaustive list of bridging faults corresponding to certain physical defects can be derived. Fault collapsing techniques are used to optimize the exhaustive fault list. There are two major processes in this bridging fault simulation program, logic simulation and fault sensitization at switch level. The simulation program uses preprocessing and bit-wise parallelism to minimize computation time. At the end of fault simulation, a fault coverage and fault matrices suitable for test grading and fault diagnosis are produced for each test set. This research also identifies types of CMOS modules and uses them to analyze test generation for bridging faults. The completeness and minimality of switch-level test sets are considered for general series-parallel (GSP) modules. Finally, several single-module circuits are simulated using gate-level, switch-level and random test sets, and their effectiveness is compared. / Master of Science

This paper presents a semi-theoretical computer model that estimates individual and mean ionic activity coefficients in the NaCl-NaOH-HCl-H₂O system at 25°C. This extra thermodynamic model incorporates long-range electrostatic ion-ion interaction (Debye- Hückel effects), short-range ion-ion interactions (ion association), and short-range ion-solvent interactions (hydration). The activity of water in NaCl, NaOH, and HCl solutions is fit with maximum deviations from experimental values of 0.78%, 0.79%, and 2.09%, respectively. Ion size parameters, å, were modified slightly from literature values. Hydration numbers for individual species were chosen on the basis of best fit. Ion pair dissociation constants of 15.0 were chosen for reactions involving NaCl(aq), NaOH(aq), and HCl(aq) ion pairs. The model predicts individual ionic activity coefficients for ions and ion pairs, and predicts mean molal ionic activity coefficients for NaCl, NaOH, and HCl for solutions up to 6.0 m with maximum deviations from experimental values of 0.73%, 1.77%, and 3.86%,respectively. The estimated degree of dissociation varies widely if the ion pair dissociation constants are varied between 5 and 1000. Calculated values for trace activity coefficients, saturation solubility, and vapor pressure compare favorably to experimental data. / Master of Science

Bermuda, settled in l6l2, was the second successful English colony founded in the New World. The islands appeared to provide investors in England with an excellent opportunity to make a profit, but the colony failed to generate the anticipated profits because the investors failed to allow sufficient incentive for the colonists to produce high quality cash crops. Little research has been conducted on the early history of Bermuda, and the little that has been done has focused on political events within the colony and colonizing company. This work uses letters, petitions, contemporary accounts, and other colonial and company documents to examine the interaction between the colonists in Bermuda and the investors in England and to determine the impact of this interaction on the failure of the colony. / Master of Arts

Gödel proved his Incompleteness theorems for any theory 'strong' enough to represent recursive functions. In the process he showed that the provability predicate can be represented in such theories. Modal logics of provability are modal logics which attempt to express the concept of 'provability' and 'consistency' using the modal operators '[]' and '<>' respectively. This is achieved by forcing '[]' to behave like the provability predicate. GL is a modal logic which has been shown to be complete and sound with respect to arithmetic theories (theories which can represent all recursive functions), hence results about concepts such as 'consistency,' 'provability' and 'decidability' in arithmetic theories can be stated and proved in GL. It has also been proved that GL is complete with respect to the class of finite, transitive, reversely well-founded models. This essentially means that the set of theorems of GL is recursive and hence there exists an effective procedure to determine whether a given wff is a theorem of GL or not. We investigate a weaker version of GL called GH and show that GH is not complete with respect to arithmetic theories. We show this by first showing that GH is a proper subset of GL and then showing that the theorems missing from GH are properties of the provability predicate. We finally, show that GH is not complete with respect to the class of transitive, reversely well-founded models and hence not sound and complete with respect to any frame. / Master of Science

The activated sludge wastewater treatment process depends upon the formation of biological floc for effective liquid-solids separation, nutrient stabilization and sludge dewatering. Continued research into floc formation, intrafloc interactions and floc hydrodynamics is necessary for improved understanding of the activated sludge process.The overall goal of this research program was to investigate laser-based methods for characterizing biological flocs. The research objectives included the selection of laser-based methods which are applicable to the wastewater treatment plant environment, design and development of laser-based instrument configurations, measurement of particles with known characteristics, measurement of activated sludge samples and determination of the factors affecting laser-based instrument operation. / Master of Science

Magnesium tetraborate is a candidate phosphor for a laser-heated thermoluminescence (TL) dosimetry system which is under development. Near tissue-equivalent radiation absorption properties and reported sensitivity to low radiation doses offer advantages over commonly employed LiF phosphors. Sintered wafers suitable for routine measurement were prepared. The effects of powder preparation conditions and activator concentration on TL sensitivity were investigated. Samples with additional impurities (co-doped samples) were prepared in order to increase sensitivity through coactivation or sensitization effects. TL emission spectra were employed to evaluate the effects of co-doping. / Master of Science / incomplete_metadata

I studied loggerhead shrikes (Lanius ludovicianus) in the Shenandoah Valley in Virginia from April 1987 to April 1988; factors affecting mortality rates wring the breeding season, fall dispersal, and winter were investigated., The high reproductive,success in this study was similar to that reported by other researchers in the United States. Reproductive success was different among varying grass heights and varying amounts of bare soil areas within 100 m of shrike nests; success was highest in habitats with numerous bare soil areas and medium grass. I radio-harnessed fledglings at a mean age of 56 days to document dispersal, fall home-range areas, and survival rates. During the postfledging dispersal period, survival rates were 100% fledglings dispersed at a minimum of 78 days of age, and fall home-ranges typically contained medium grass and numerous bare soil areas. These habitat characteristics may provide shrikes with increased invertebrate availability. Winter negatively affected the loggerhead shrike population in Virginia; raptor predation was the primary cause of subadult and adult mortality, and road kill was secondary. Shrikes moved from grassland areas to shrub-forest areas during inclement weather and preyed on small birds. Home-range sizes were larger during the winter than at other times of the year. I documented the occurrence of low levels of organochlorine and organophosphates in all birds analyzed for pesticide contamination. Also, I present statistical models to predict age and sex of loggerhead shrikes; wing chord and tail white on rectrix 5 were the most useful variables in discriminating sexes and wing chord was used in discriminating ages. More research is needed on the effects of raptors on shrike populations and on the role of foraging habitat on winter areas. / Master of Science

This research quantifies specific cash price premiums and discounts associated with various characteristics of slaughter cattle in Virginia. Econometric models of Virginia slaughter cattle basis were developed for each practical combination of sex and market by differentials in weight, grade, breed, lot size, order of sale of a particular lot, number of cattle in a particular sale, and a seasonal indicator based on the Chicago Mercantile Exchange (CME) live cattle futures contract month. Explanatory models were found to account for 41 to 64 percent of the variation in slaughter cattle basis for steers and 35 to 47 percent of the variation in slaughter cattle basis for heifers. Results explain over 30 percent more of basis variation than previous research. These basis estimates reduce basis error and hedging risk and potentially offer Virginia cattlemen the means to initiate effective slaughter cattle hedging programs. Furthermore, the implementation of a forward pricing agency which uses estimated basis values may provide alternatives to facing basis risk when selling slaughter cattle in Virginia. An analysis of basis risk provides some indication of the magnitude of possible exposure facing the average Virginia cattleman when making hedging decisions based on estimation procedures as defined herein. The formation of a forward pricing agency should be contingent upon further analyses of basis risk as outlined in this research. Investigation of basis estimate residuals concluded that more variability is present as time to contract maturity increases. This information should prove valuable for those involved in trading options on live cattle futures as options expire one month prior to their respective futures contracts. / Master of Science

A new compact double-notched specimen for in-plane shear testing of isotropic, anisotropic and composite materials was developed. A preliminary test of the specimen was performed on a cross-ply laminate. High sensitivity moire interferometry was used to determine the shear and normal strains on the entire face of the specimen. The results of the test were compared to those of the Iosipescu specimen on the same material. The compact specimen produced a more uniform and more pure shear distribution than the Iosipescu specimen. Stiffness measurements of the composite material were made. A detailed investigation of the specimen was performed and it revealed important attributes and deficiencies of the specimen. Recommendations for future work are cited. The interlaminar shear response of a cross-ply composite was investigated. Shear strains on a ply-by-ply basis were measured using moire interferomety. Qualitative and quantitative information of the interlaminar shear characteristics of the material were obtained. The interlaminar shear modulus of individual plies and the effective modulus for the laminate were determined. Variations of nominally equal plies were observed. / Master of Science

Groundwater contamination by man-made chemicals is increasingly being reported in the United States. The potential for detrimental health effects is substantial and has been addressed by the environmental engineering profession. Typically, contaminated groundwater is pumped to the surface and treated in a variety of methods including air stripping, carbon adsorption, and biodegradation. In situ biodegradation is increasingly being considered as an alternative to pump-and-treat technology. The primary goal of this research was to determine the fate of an organic chemical adsorbed to a subsurface soil when exposed to acclimated bacteria. Toluene was chosen as a representative compound because it is a major constituent of groundwater contaminated by gasoline. In addition, toluene is known to be both biodegradable and adsorbable. Sybron Biochemical, Inc. supplied the aerobic bacteria Psgudomonas gutjga known to readily transform toluene. Soil microcosms were established in test-tubes and conditions simulated those of a saturated, aerobic aquifer. Gas chromatography was used to quantify changes in toluene concentration due to adsorption and biodegradation. The addition of an aqueous toluene solution to sterile microcosms resulted in the rapid and extensive adsorption of toluene to the soil. Subsequent analysis revealed the slow adsorption of an additional small fraction of toluene. Biodegradation studies entailed the addition of acclimated bacteria to sterile soil microcosms in which substantial toluene adsorption had occurred. Addition of small doses of hydrogen peroxide effectively maintained aerobic conditions for biodegradation. As a result, E, putjda was able to transform all measurable toluene in the microcosms. Additional desorption studies revealed that a "resistant" component of toluene remained adsorbed to the soil during biodegradation. This component was neither acted upon by bacteria nor readily extractable by methylene chloride. However, slow desorption of toluene was shown to occur at a rate comparable to slow adsorption. To achieve complete removal, groundwater treatment methods must address the rate-controlled desorption of the resistant toluene component. / Master of Science