In this study we examined the differences of performance of various input devices on a steering task. Two paths were created, one easy and one hard, with the harder path having more turning points to navigate with one of three different input devices: mouse and keyboard, Xbox 360 controller, and a joystick. Participants were also exposed to low or high stress conditions. High stress was caused by playing loud short bursts of music over headphones worn by participants during testing. Results indicated the mouse and keyboard performed better in all cases. There was no significant difference between the Xbox controller and joystick. No differences were found in the low and high stress conditions. Differences in sex were found, even when controlling for video game experience. These findings indicate that the mouse and keyboard is the best device to use on a steering task.

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I investigated the use of nitrogen isotopes as a tracer of sewage contamination on coral reefs. Sewage is isotopically distinct from marine nitrogen, allowing its use as a tracer in this environment. Emphasis was placed on sampling modem coral tissues, as modern coral reefs are in a rapid state of decline, possibly as a result of sewage contamination. Samples were collected in Zanzibar for two separate studies. The first study involved sampling over a depth/light gradient on large coral heads. These data, when combined with data from Jamaica, show light is a controlling factor on the nitrogen isotopic composition of coral tissue. Regression of delta15N of coral tissue with depth/light attenuation explains 75-90% of the variance. Results indicate increased fractionation with depth, which is related to the symbiotic nature of corals. Light-sufficient, nitrogen-limited zooxanthellae ( in the coral tissue ) must diffusl! all available nitrogen, and there is little fractionation. At depth, light-limited, nitrogen-sufficient zooxanthellae fractionate nitrogen during assimilation processes. These results have important implications for the use of nitrogen isotopes as a sewage tracer on reefs. In general, increased nutrients to the reef environment result in decreased water clarity, or lowered available light to the coral. This could lower the zooxanthellae's nitrogen requirements and allow fractionation (isotopic depletion). Corals have been shown to become reliant on heterotrophy in non-limiting nutrient conditions, related to loss of control over their zooxanthellae. This suggests the delta15N of their tissues would reflect their diet (and therefore the source of contamination). The counteractive effects of these two factors suggests it may not be possible to resolve the source of eutrophication to corals using the isotopic signatures of their tissue. That is, if the contamination gradient is coincident with a gradient in the symbiotic relationship (i.e. from nutrient limited to nutrient non-limited) or trophic status, there is little possibility of resolution of sewage effects. Results from the second sample suite from Zanzibar and a sample suite from Jepara Bay, Indonesia confirm this hypothesis. Zanzibar samples were collected at a eutrophied and non-eutrophied reef, and show no significant difference between isotopic data. This may be a result of distance from source, or the counter-effects of light. At Jepara Bay, samples were collected along a contamination gradient, from 2 point source discharges. Isotopic data show significant change along the gradient, with the entire bay eutrophied. Without delta15N from all potential nitrogen sources it is impossible to adequately conclude whether sewage was the contaminant using isotopes. Other data collected from these reefs do support the interpretation of anthropogenic contamination. These data include decline in coral and fish communities (determined using biological assays, Zanzibar), and increased heavy metal and chlorophyll-a concentrations (Jepara). One control on nitrogen isotope composition of modern corals was identified, and others suggested. Results will remain enigmatic until sample suites including complete water chemistry, source chemistry, and light regime are interpreted. / Thesis / Master of Science (MSc)

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This dissertation addresses three important open questions in the context of generating random vectors having discrete support. The first question relates to the "NORmal To Anything" (NORTA) procedure, which is easily the most widely used amongst methods for general random vector generation. While NORTA enjoys such popularity, there remain issues surrounding its efficient and correct implementation particularly when generating random vectors having denumerable support. These complications stem primarily from having to safely compute (on a digital computer) certain infinite summations that are inherent to the NORTA procedure. This dissertation addresses the summation issue within NORTA through the construction of easily computable truncation rules that can be applied for a range of discrete random vector generation contexts. The second question tackled in this dissertation relates to developing a customized algorithm for generating multivariate Poisson random vectors. The algorithm developed (TREx) is uniformly fast—about hundred to thousand times faster than NORTA—and presents opportunities for straightforward extensions to the case of negative binomial marginal distributions. The third and arguably most important question addressed in the dissertation is that of exact nonparametric random vector generation on finite spaces. Specifically, it is wellknown that NORTA does not guarantee exact generation in dimensions higher than two. This represents an important gap in the random vector generation literature, especially in view of contexts that stipulate strict adherence to the dependency structure of the requested random vectors. This dissertation fully addresses this gap through the development of Maximum Entropy methods. The methods are exact, very efficient, and work on any finite discrete space with stipulated nonparametric marginal distributions. All code developed as part of the dissertation was written in MATLAB, and is publicly accessible through the Web site https://filebox.vt.edu/users/pasupath/pasupath.htm. / Ph. D.

This thesis examines the economic impact of two alternative canning plant sizes in Scott County, Virginia. The impacts of a community cannery as well as a commercial cannery are analyzed with respect to changes in output, employment, and income. Several uses for the commercial cannery are considered, such as specialization in different product categories. In both cases, an input-output model is used to evaluate the effects of the operation of the cannery in the county. The results indicate that the impact of the commercial cannery is significantly larger than the community cannery. Specialization of the commercial cannery in the Canned Specialties sector has the largest impact with respect to industry output and labor income while specialization in the Sausages and Other Prepared Meats sector has the largest impact with respect to employment. / Master of Science

The L2 gain of a nonlinear time-dependent system measures the maximal gain in the transfer of energy from admissible input signals to the output signals, in which both the input and output signals are measured with the L2 norm. For general nonlinear systems, obtaining a sharp estimate of the L2 gain is challenging both theoretically and numerically. In this thesis, we explore a computationally efficient way to obtain numerical estimations of L2 gains for systems with quadratic nonlinearity. The approach utilizes a recently developed method that solves a class of Hamilton-Jacobi-Bellman equations via a Taylor series-based approximation, which is scalable to high-dimensional problems given the utilization of linear tensor systems. The ideas are demonstrated through a few concrete examples that include a one-dimensional problem with an explicit energy function and several Galerkin approximations of the viscous Burgers equation. / Master of Science / With nonlinear systems that are of the form of input-output models, questions often arise as to how to measure the energy that passes through such systems and determine strategies to look for specific signals that allow the designer freedom to explore certain system behaviors. The energy comes in the form of a signal. For general nonlinear systems, obtaining a sharp estimate of such energy gain is challenging both theoretically and numerically. In this thesis, we explore a computationally efficient way to obtain numerical estimations of these gains for systems with quadratic nonlinearity. The approach combines fundamental theoretical understandings established in the literature with scalable software recently developed in approximating the solution of the underlying partial differential equation, called the Hamilton-Jacobi-Bellman (HJB) equation. In this approach, the energy gain is linked to a single scalar parameter in the HJB equation. Roughly speaking, the energy gain is the lower bound of this scalar parameter above which the HJB equation always admits a non-negative solution. Thus, it boils down to approximating the HJB solution using the software while changing this scalar parameter. We will present the theoretical foundation of the approach and illustrate the foundation through several academic examples ranging from low to relatively high dimensions.

An investigation of the pattern of structural change in a static input-output system is considered, when a series of operational optimizations are performed in one or more subsystems. Specifically, changes in the relative price of each commodity in an economy, along with their implications for the quantities associated, are analyzed. By operationally optimizing a sector, a production process is selected in such a way that the input requirements from other sectors in the economy do not exceed the current equilibrium level as specified by the input-output economy. When the new optimal process is substituted for the current equilibrium process, the input-output structure may be perturbed and a new equilibrium solution needs to be sought. For the multi-sectoral problems, the system would be considered stable if the necessity for the further perturbation ceases, while an equilibrium solution exists to the current input-output system. Three different price models are developed in trying to obtain a new stable system. Depending upon three distinct sets of economic reasons behind, these models are named as the acquisition, the consolidation, and the appreciation model. This study concludes that under all the normal circumstances, a static input-output system does reach a stable state, if the sectoral optimization is conducted through linear programming. This study also investigates the effects of operational optimization of sectors on the quantity side of the economy. / Master of Science