In an effort to understand intrinsic grain boundary brittleness, computer simulation of grain boundary structures in ordered NiAl was carried out. The considered boundaries were boundaries of low reciprocal coincident site density Σ. The structural unit model was used to obtain a general picture of the grain boundary features in NiAl. Relation between the grain boundary stoichiometry and the energy was studied and it was found that the grain boundary energy increases with a higher aluminum content in the grain boundary. Thus, excess of aluminum in the grain boundary seems to make the material brittle. The grain boundaries obtained are relatively dense and grain boundary brittleness would not be expected to originate from large interstitial holes. However, the structures computed show a large spread in energy values and it is proposed that the observed brittleness is due to the appearance of high energy structures when dislocations arrive at the boundary. / Master of Science

A water analogy technique was used in this investigation of the flow field in the pulse I motor of a two-pulse solid rocket motor. A full scale model of clear acrylic material was constructed to allow direct visual access of the flow field. The experiment, which was conducted with one of the VPI water analogy rigs, simulated the flow in the spent pulse I motor chamber after the pulse Il motor would have been ignited. The relations between the pattern and angle of the throughflow holes on the bulkhead--which separates the two motor chambers--and the downstream flow pattern in the pulse I chamber were assessed by changing the bulkhead model configuration for each test. Video records of the flow pattern were obtained through flow visualization tests, which used either fluorescein dye or air bubbles as the tracer. Also, hot water tests with thermocouple measurements were conducted as a means of investigating the rate of mixing of the propellent from the pulse Il motor with the gases in the pulse I motor chamber, as well as the migration of the pulse Il propellent along the wall of the pulse I motor casing. The test data show a clear relation between the hole arrangement on the bulkhead and the ensuing downstream flow pattern, as well as the rate of mixing along the wall of the pulse I motor casing. Consequently, the results provide directions for improving the performance of heat transfer insulation material on the wall of the pulse I motor through a prudent choice of the hole arrangement on the bulkhead. / Master of Science

A series of process design and economics models have been created which calculate the process cost for several scenarios in steam-explosion/fractionation of wood. Steam -explosion pulping may prove to be an alternative to currently practiced standard pulping processes which require large capital investments, cause significant environmental problems, and produce a narrow range of products. In addition, steam-explosion/fractionation technology may offer the opportunity to produce chemicals and materials from biomass at a lower raw material and process cost than the alternative petrochemical feedstocks. The models are a series of modular computer simulations, where each module summarizes a particular group of unit operations with respect to mass balance, energy requirements, and process cost including utilities, capital, labor, and other related costs. These modules are compiled into 3 groups of scenarios: 1) unprocessed steam-exploded wood for use as enzyme! acid hydrolysis feedstock, hardboard production, or as unbleached pulp, 2) water extracted steam-exploded wood for recovery of pentosan polysaccharides and a lignocellulosic fiber, and 3) water and aqueous solvent (alkali or ethanol) extracted steam -exploded wood for recovery of pentosan polysaccharides, lignin polymers, and a cellulose -rich, unbleached fiber. For the base case evaluated, the cost of producing a 50% moisture, based on total weight, steam-exploded fiber is the raw material cost, dry basis, plus 3.5 cents! Lb of raw material consumed, dry basis. For Southwestern Virginia hardwoods at 2 cents/Lb ($40 per ton), dry basis, the total process cost is 5.5 cents/ Lb. / Master of Science

Greenhouse and field studies were conducted to determine the effects of shade on photosynthetic, growth and yield responses of "Redchief" strawberries. Plants were exposed to 0 , 30 , 47 and 63 percent shade in the greenhouse. Net photosynthesis (Pn) as measured under the shade treatments demonstrated a curvilinear decrease. Pn as measured under saturating light levels of 790 μ-tmol· m-2 · s·1 began to decrease in plants grown under 30 percent or higher shade levels. Light saturation curves for leaves expanded in full sun and then transferred to shade treatments for seven days showed a decrease in Pn saturation rate and light saturation point at 63 percent shade. Saturation curves for leaves expanded under the shade treatments exhibited a decreasing trend in saturation rate and point at all shade levels. Heavy shade (63%) reduced leaf thickness and depth of the palisade cell layers. Individual leaf area was not affected by shade treatments. As percent shade increased, total plant dry weight decreased linearly as did specific leaf weight. Shade treatments of 0, 30, 63 or 95 percent were applied over field-grown plants either in the fall during flower bud initiation, or in the fall and spring, during flower bud initiation and spring vegetative growth. Berry number was reduced as percent shade increased. Plants shaded only in the fall had higher berry number than plants shaded both in the fall and spring. Berry weight was also reduced as percent shade increased. Sugar concentration, pH and titratable acidity were not affected by shade levels or time of shade application. / Master of Science

This thesis is in an attempt to realistically model a real-time digital generator which interfaces to an analog system simulator and which consists of the synchronous machine and its peripheral controllers such as the exciter and the governor-turbine subsystems. In this work, the exciter, the synchronous machine, the machine dynamics and the governor are modeled in detail while a simplified model of the turbine is used. The synchronous machine, the main component of this simulation, solves the discretized Park's machine equations which include flux derivative tenns and tenns pertaining to the two amortisseur windings. Treatment of saturation effects in the mutual inductances is also discussed. The Park's model is arranged to obtain a field voltage and machine armature cutTent input - machine tenninal voltage output structure, where the armature current and terminal voltage are rotor based quantities (i.e. in d-q domain). In order to interface the Park's machine model to the analog system model, the Park's and inverse Park's transformation are implemented by software modules. The implementation of a prototype model generator using a Motorola 68020 microprocessor and fast computer peripherals is discussed. The results of the digital computer simulation in real-time for the generator model under various operating conditions are presented. / Master of Science

To provide quality benchmark data (that can be used in numerical simulation comparisons) and to examine the effects of combustion on a typical ramjet engine flowfield, a water-cooled, stainless steel dump combustor model was developed. A two-component Laser Doppler Anemometer (LOA) was used to measure the mean and turbulent velocities in the axial and tangential directions and provide a comparison between combusting and isothermal flows. However, before any LOA measurements could be taken, the combustor had to be configured to run in a suitably stable mode. Stability was identified by the pressure spectra obtained under various running conditions using piezoelectric pressure transducers wired to a spectrum analyzer. Operational parameters such as fuel composition, fuel injection location, acoustic configuration, and equivalence ratio were varied until instabilities were minimized. The optimal configuration ran with upstream fuel injection (premixed mode) at the duct center line and an orifice plate installed immediately upstream of the fuel injectors, with propane as the fuel. Once stability was achieved, LOA data was taken. The results showed some significant differences between the reacting and nonreacting flows. The most significant effect was the difference between the inherent recirculation regions for each case. Combustion decreased the length of the region by approximately 50 percent, while increasing the maximum negative velocities. This made for a more compact, but stronger, recirculation region. Since the recirculation region acts as the main flame holder and is a major source of turbulence, the changes in this region significantly altered the dump combustor flowfield. / Master of Science

The thesis contains a series of ideas & conclusions: The introductory statement suggests four criteria for the pursuit of producing good architecture. These criteria are not in the realm of problem solving. But rather address issues of the heart & mind. It is through a struggle with these measures that architecture becomes true and encompasses a realization larger than the problems at hand. It is only then that architecture exists in a continuum across time. The projects in this book make a meager attempt to begin to understand a pedagogy for spirit. responsibility. making & judgement. / Master of Architecture

Intuition is so often right, but so seldom observed, Reno, Nevada. / Master of Architecture

node monument edge genius loci / Master of Architecture

Following the U.S. Environmental Protection Agency’s specifications for pesticide registration tests, 12 experimental ponds were constructed in Blackstone, VA at VPI&SU Southern Piedmont Agricultural Experiment Station. Colonization and succession of the ponds’ phytoplankton communities were investigated during the first year after filling. Taxa richness and densities, biomass as chlorophyll a, and primary productivity (in situ oxygen method) were measured. In addition, water quality data were collected and analyzed. The dominant taxonomic groups were the Cyanophyceae, Chlorophyceae (with Desmidiaceae dominating), Dinobryon (in the Chrysophyceae), Dinophyceae, and Bacillariophyceae. Similar successional patterns in all 12 ponds occurred, however, the community structure between ponds was not similar at any given time. Although the ponds had statistically similar environmental characteristics, they varied in their community structure indicating that, after one year, they were not mature enough for use as replicate test systems. No structural parameter could be measured with reasonable precision using a three replicate pond scheme recommended by the USEPA. Taxa richness could be measured with a precision of approximately 25% over the year; and was ≤11% during the peak growing months. Taxa densities could usually be measured with a precision of <100% during these months. The in situ oxygen method for measuring primary productivity was found to be to insensitive during early colonization. The heterogeneity of the ponds’ phytoplankton communities indicate that mesocosms will need to be managed to produce replicate experimental units. / Master of Science