Nitrogen fertilization is important in attaining high yielding, quality tobacco. However, practices that use excessive N can be uneconomical, threaten the environment and produce leaves that are high in nitrates. Leaves high in nitrates have been positively correlated with leaves that are high in tobacco specific nitrosamines (TSNA), which are considered potent carcinogens. Competition from cheaper, foreign leaf, increasing costs of fertilizers and new market structures which show purchasers seeking low TSNA leaf demand that producers become more efficient in their N use. The objective of this study is an examination of burley (TN 90) and dark (KY 171) tobacco cultural practices with the hypothesis that optimizing growing conditions will enhance N efficiency. This experiment took place during 2005 and 2006 in the traditional tobacco growing regions of Springfield (Dickson silt loam) and Greeneville, TN (Lindside silt loam). Experimental isolated growing condition variables. Irrigation treatments isolate the importance of soil moisture. Fertigation, while using irrigation practices, isolates the effects of synchronizing crop N demand with N supply. Plasticulture, using fertigation protocol, isolates the importance of soil temperature. Season long measurements of soilwater tension, soil temperature and leaf nitrates were used to evaluate the ability of each practice to keep plants in optimal N uptake and utilization growing conditions. Results showed that the most dramatic and consistent treatment effects were found in the TSNA analysis. Even during a season characterized by precipitation being sufficient in volume and timing to meet plant water demands, irrigation was successfully able to decrease TSNA concentration by about 30%. During drier growing seasons, TSNA was reduced by 50% or more. Measurements of leaf nitrates taken with a Horiba monitor were able to consistently detect treatment and N rate differences. The last sample taken around eight weeks after transplanting correlated strongly with TSNA content (0.81). This tool could prove effective in characterizing optimal N management. Cultural practices that offer control over soil water tension, nitrate content in leaves and soil temperatures can be effective in increasing the ability of the plant to uptake and utilize N towards achieving high yielding, high GRI quality and low TSNA leaf.

Titanium and its alloy (Ti-6Al-4V) are widely used in aerospace industries because of their light weight, high specific strength, and corrosion resistance. This study conducted a comparative experimental analysis of the machinability of Ti-6Al-4V for conventional flood coolant machining and sustainable dry machining. The effect of cutting speed, feed rate, and depth of cut on machining performance has been evaluated for both conditions. The machining time and surface roughness were found to be lower in dry machining compared to flood coolant machining. The tool wear was found to be unpredictable, and no significant difference was observed for dry and coolant machining. In a comparison of all the parameters, sustainable dry machining was found to provide better performance in machining Ti-6Al-4V. This study also investigated the machinability of Ti-6Al-4V using coated and uncoated tungsten carbide tools under dry conditions. Tool wear is a serious problem in the machining of titanium alloys in dry conditions. Heat dissipation from the toolworkpiece interface a difficult challenge in dry machining, resulting in the alloying of the workpiece to the tool surface. Dry machining with the coated tool was comparatively faster, and resulted in less tool wear than uncoated tools. Using the Titanium aluminum nitride TiAlN coated carbide tool during dry machining provided a smoother surface finish with lower average surface roughness. The conclusion, therefore, is that the tool coating was found to be effective for the dry machining of titanium alloys.

The primary object of this investigation is to design a system, including equipment and procedures, that can be used to evaluate the noise characteristics of photoconductive cells. The data once collected must be in a comprehensive and useful form. The secondary object is to use this system to evaluate a large number of cells of various types and to compare their noise profiles in a manner such that definite conclusions can be drawn concerning the absolute noise levels and profiles generated by the various cell types and the relations that may exist between the cells' noise output and the way they were fabricated.

The main objective of this investigation is to study experimentally the behavior of rectangular reinforced concrete frames subject to a combination of low column loads, beam loads, and lateral load. The analytical tool used in this investigation is a computer program which is a generalized computational method for non linear force deformation relationship and secondary forces due to displacement of the joints during loading. In the experimental portion of this investigation, two rectangular frames, one design by the Ultimate Strength Design method and the other by a Limit Design method were prepared and tested to failure with short time loading. Physical tests indicate that frames under the action of low gravity loads and lateral load became unstable after the formation of two hinges in the beams.

In this paper the effects of inertia are explored for the case of a thermal excitation applied on the surface of an infinitely long, solid circular cylinder. The linear uncoupled field equations for a homogeneous, isotropic, thermoelastic medium are used to derive the desired field equations of stress and displacement. The solution procedure included, first, the determination of the thermal boundary value problem from the energy equation which is identically satisfied for the uncoupled condition. Secondly, substitution of the strain-displacement relationships and the previously obtained thermal relation into the equilibrium equation containing inertial effects. The equilibrium equation is the only nonidentically satisfied equation. Thirdly, a solution of this equation is then found in the S-domain by Laplace transformation. Finally, the desired displacement equation is transformed into the time-domain as a function of temperature, time and radius of the cylinder by using inverse Laplace transforms and the calculus of residues.

<p>The photovoltaics (PV) research community is currently pursuing many approaches to reduce the cost of PV and increase the energy conversion efficiency. Single-crystalline silicon (sc-Si) solar cells are able to achieve high efficiency but have a higher cost relative to other technologies. It may be possible to drastically reduce the cost of sc-Si PV by fabricating solar cells which are an order of magnitude thinner than conventional solar cells, i.e. thinner than 30 microns. Aside from new fabrication paradigms, ultra-thin sc-Si solar cells require advanced light-trapping techniques to enhance the absorption of long-wave radiation which is otherwise transmitted through the cell. In this thesis, a novel process flow for the fabrication of ultra-thin sc-Si solar cells in the laboratory was designed and implemented with the aim of testing light-trapping structures in the context of actual ultra-thin sc-Si devices. The process flow uses 10 micron thick sc-Si membranes, 0.95 cm in diameter, fabricated on silicon-on-insulator wafers using double-sided processing. The best fabricated device incorporated a back surface field, a white paint diffuse rear reflector and a silicon nitride antireflection coating. It achieved a fill factor, efficiency, short circuit current and open circuit voltage of 0.67, 9.9%, 27.9 mA cm^-2 and 0.53 V respectively. Simulations suggest the device efficiency can approach 15.4% without light-trapping and 16.5% with a diffuse rear reflector as a light trapping structure. This process flow is intended to be used as a platform on which to test further light-trapping structures with the continuation of this project.</p> / Master of Applied Science (MASc)

<p>Preparing silicon wafers is a tedious multi-step process that includes etching, polishing, and cleaning. The minimum wafer thickness attainable in current high volume wafer production processes is generally 160 to 300 μm, and the kerf loss for these processes is up to 40% of the total volume. Thin silicon wafers (~30 to 100μm) are very expensive to produce and the wafering process is not cost effective due to the high amount of material loss (more than 80% at these dimensions) during the process and the risk of breakage of the wafers during wafering. In this thesis, a new method called Vapour-Liquid Interface Growth (VLIG) is proposed. VLIG is capable of directly growing a sheet of single crystal silicon without wafering with a thickness of about 30 to 50μm. The features of the process are 1) low temperature operation; 2) the resulting silicon sheet is easily detachable and self-supporting; 3) the resulting sheet has uniform thickness and is single crystal. The system operates in a supersaturated growth solution of an indium-silicon melt. A seed line in a substrate facing down is employed. A layer of single crystal silicon grows on the seed line at the melt surface due to surface segregation during the super cooling process. The grown silicon can grow laterally due to the limited thickness of the melt depth that minimizes growth in the vertical growth direction. The grown silicon can be easily peeled off from the seed line substrate due to the presence of a gap between the grown silicon sheet and the oxide layer on the seed line substrate. The self-supporting silicon sheet now comprises a very thin silicon substrate or sheet.</p> <p>VLIG silicon sheet is characterized by X-ray diffraction to determine the crystallinity. Hall Effect measurements are performed to measure the electrical properties. VLIG silicon sheet is (111) oriented single crystal and it exhibits the same orientation as the substrate. The growth temperature is from 975 to 850^oC, and the VLIG silicon is p-type doped with indium. The resistivity is 4.181x10^-3 ohm-cm, and the doping level is around 5.3.0x10¹⁸ /cm3. The measured mobility is ranging from 280 cm²/V.s. In this study, VLIG demonstrates the potential of growing thin sheet of single crystal silicon with qualities that feasible for photovoltaic application.</p> / Master of Applied Science (MASc)

Vacuum forming is a popular, cost effective method amongst large and small scale applications. The method is used to mold a material to the surface of a mold/pattern in order to create a negative copy for reproduction or an object in positive form. The prototype vacuum forming system developed and documented herein is of a membrane-seal type that consists of three (3) principle parts: radial platen, Hinged Frame and Platen Support Assembly, and a PVC surge tank. Each part is described in detail through design, manufacturing, and testing processes. The design supports functional versatility, small scale molding, and uses readily available materials. Functional prototype testing was performed with the thermoplastic KYDEX® and multiple objects for mold examples. Results include successful proof of concept, design pros and cons, and findings based on functional testing.

Wood composites are widely used in construction applications because of their superior dimensional and structural attributes over raw wood products. However, current wood composite manufacturing practices, which rely on thermal-curing of adhesives, are expensive, energy intensive, time consuming and are prone to manufacturing defects. Use of radiation curable adhesives (RCAs) could potentially answer all of these issues. Specifically, use of electron-beam (e-beam) radiation has been increasing in areas of research and industry where rapid, low-temperature polymerization is required and low energy consumption is desired. For e-beams to be used in wood composites, however, it must be determined whether or not the wood is structurally impacted by irradiation, and to what extent. Maple beams irradiated with a range of e-beam dosages were studied in three-point bend tests to assess the changes in bulk properties of the wood, and were further studied with infrared spectroscopy to identify chemical changes resulting from the radiation treatments. Also, dynamic mechanical analysis (DMA) was performed on maple veneers treated with the same doses of radiation to characterize changes in the viscoelastic properties. Furthermore, while RCAs and their curing have been studied, it is important to understand if the presence of wood will impede the polymerization of these adhesives, and to what extent. Maple veneers impregnated with one of two resins were cured with the same e-beam dosages and investigated by means of DMA and FTIR spectroscopy. Swelling tests were conducted to detect interaction between the resins and the wood, which would indicate good interfacial bonding in the composite matrix. Notable loss of strength was observed in the irradiated wood, especially at 180kGy. Monitoring the glass transition temperature (Tg) and activation energy (Ea) derived from DMA revealed that the most destructive trends in the wood began around 80kGy. Cure of resins in the composites was hindered by the presence of the wood, but both resins did eventually reach complete cure at doses higher than what the neat resins required. Interaction between the resins and the wood was evident. In the end, results indicate that there is a range of radiation dosages in which the resin in a wood composite can be cured without destroying the structural integrity of the wood.

The use of sunlight has always been a major goal in the design and operation of commercial buildings to minimize electrical consumption of artificial lighting systems. Glazing systems designed to allow optimal visible light transmission also allow significant unwanted direct solar heat gain caused by infrared light. Conversely, glazing systems that are designed to reflect unwanted direct solar heat gain significantly reduce the transmittance of visible light through windows. The goal of this research was to characterize the performance of water as gap-fill for double-glazing units in eliminating the compromises that exist in current glazing systems with respect to light and heat transmittance. An in situ test approach and computer simulations were conducted to measure the performance of water-filled glazing units against air-filled glazing units. The thermal transmittance and solar heat gain coefficient values obtained from both the field experiments and computer simulations, glazing units with air-fill proved better than the glazing units with non-flowing water-fill. However, the high convective coefficient and the high thermal mass of the water can be used to its advantage when it is allowed to flow at peak temperatures, thus, maintaining lower temperature swings indoor. This can lead to a reduction of about 50-70% direct solar heat and still maintain high visibility.