Browsing by Author "Dr. Jason A. Osborne, Committee Member"

Now showing 1 - 4 of 4

Analyzing Software Artifacts through Singular Value Decomposition to Guide Development Decisions
(2007-09-25) Sherriff, Mark Stephen; Dr. Jason A. Osborne, Committee Member; Dr. Thomas L. Honeycutt, Committee Member; Dr. Mladen A. Vouk, Committee Member; Dr. Laurie A. Williams, Committee Chair
Atlantic Bluefin Tuna (Thunnus thynnus) Feeding Ecology and Potential Ecosystem Effects During Winter in North Carolina.
(2007-04-30) Butler, Christopher Matthew; Dr. Jeffrey A. Buckel, Committee Chair; Dr. John M. Miller, Committee Member; Dr. Jason A. Osborne, Committee Member
Atlantic bluefin tuna (Thunnus thynnus) occupy North Carolina waters during winter months. Their potential impact on prey populations during this time has largely been unexplored. Diet, prey-size selectivity, predator-prey size relationships, gastric evacuation rates, daily ration, and population-level predatory demand were estimated for Atlantic bluefin tuna in North Carolina during winter. Quantitative analyses of bluefin tuna stomachs collected from commercial fishers during two winters (2004-2005) were examined. Bluefin tuna diet was dominated by Atlantic menhaden with other teleosts, portunid crabs, and squid being of mostly minor importance. By weight, I found no major inter-annual differences in diet; however, intra-seasonal diet variability was evident with more diverse diets in late-fall and less diverse diets (predominantly Atlantic menhaden) during winter for one out of two years examined. Lengths of Atlantic menhaden collected from bluefin tuna stomachs were compared with lengths of Atlantic menhaden captured from the Atlantic menhaden purse seine fishery; no significant differences were observed suggesting no prey size selection. Minimum and median-sized Atlantic menhaden prey increased with increased bluefin tuna size, while maximum-sized Atlantic menhaden did not change. Diel patterns in mean gut fullness values were used to estimate the first known field derived gastric evacuation rate for this species. Daily ration from mean gut fullness values and gastric evacuation rates were used along with a range of bluefin tuna population sizes and residency to estimate population-level consumption by bluefin tuna on Atlantic menhaden. I found that, at current population levels, bluefin tuna predation on Atlantic menhaden is minimal relative to consumption of Atlantic menhaden by other known predators and commercial harvest. This was corroborated with an independent estimate of Atlantic menhaden consumption using an Ecopath model. Bluefin tuna appear to occupy coastal waters in North Carolina to prey upon Atlantic menhaden; thus, changes in the Atlantic menhaden stock status or distribution could alter winter foraging locations of bluefin tuna. This study has helped fill a gap in the knowledge of bluefin tuna natural history and provided data necessary for implementing multispecies fisheries management.
Formation and Characterization of Electrospun Nonwoven Webs
(2003-02-06) Mohan, Abhay; Dr. Jason A. Osborne, Committee Member; Dr. Tushar K. Ghosh, Committee Co-Chair; Dr. Abdelfattah M. Seyam, Committee Co-Chair
It is known that not all polymers can be melted and extruded to form polymer fibers. Electrospinning process involves a direct method to produce fibers in nanometer range by dissolving the polymer in solvent(s) to form the spinning solution. In this work, the spinning solution was prepared by dissolving Poly (ethylene terephthalate) polymer in triflouroacetic acid and methylene chloride. Charging the solution to a very high potential initiated the process to produce electrospun fibers. With increasing voltage, a critical point is reached and a charged jet of the solution is ejected. As this charged jet moves in the air, the solvent evaporates, leaving behind a charged polymer fiber that collects on a targeted source (rotating drum). Equipment to form electrospun fiberwebs on a rotating drum was designed and successfully built. The equipment for this process is relatively simple and small since this process lend itself to the production of fibers/fiberwebs from small quantity of polymer solution. An experiment was designed to investigate the influence of polymer concentration in the spinning solution and the electric field level on fiber and fiberweb response of interest. Electrospun fibers and fiberwebs were characterized for fiber diameter and its distribution, orientation distribution function, and pore size and its distribution. The results showed that an increase in the electric field resulted in a decrease of the average diameter of the electrospun fibers. It has also been observed that there was concentration/electric field interaction effect on fiber diameter. As the electric field increased keeping polymeric concentration constant, the fibers orientation in machine direction increased. It was observed that as the electric field was increased, the average pore diameter decreased. The decrease in average pore size with increase in electric field was explained in terms of fiber diameter as well as fiberweb structural parameters (orientation and basis weight).
Mathematical Modeling of High Intensity Infrared Heating of a Food Matrix
(2006-08-07) Yaniv, Yifat R; Dr. Jason A. Osborne, Committee Member; Dr. Kevin M. Keener, Committee Co-Chair; Dr. Brian E. Farkas, Committee Co-Chair
Infrared heating has been used by the food industry for many years. Some of the advantages of infrared heating are its high intensity, ability to penetrate the product, and precise control. While infrared heating has unique advantages over convective and conductive heating, the complex mathematics and lack of optical property data associated with the radiant process have hindered extensive numerical simulation for process design and optimization. The objectives of this research were to develop a mathematical model to predict temperature change and crust formation during high intensity infrared heating of a food matrix, and to perform parametric analysis of process variables. A series of equations for unsteady state heat transfer, internal heat generation, and a moving boundary demarked by a phase change interface were developed. Beer's law was assumed to describe subsurface radiant energy absorption. The equations were solved numerically using explicit finite differences and MATLAB. Russet potato was used in a series of radiant heating experiments designed to test the output of the mathematical model. Surface and center temperatures and crust thickness were measured for a range of radiant flux intensities, and the data compared to the simulation output. Simulated surface temperatures agreed well with measured surface temperature during the initial 150 s of heating. Towards the end of the heating time, higher incident radiant flux (26,900 and 22,500 W⁄m2) resulted in higher simulated surface temperature than laboratory data. A lower flux setting (17,500 W⁄m2) resulted in lower simulated temperatures than measured. The model was able to predict center temperature for the first 150 s of heating for the higher flux settings, followed by higher measured temperature for 26,900 W⁄m2 incident flux. Measured center temperature for the lowest flux setting was lower than simulated temperatures throughout the duration of heating. Experimental crust thickness determination was based on sample mass loss. The model did not account for evaporation of moisture at temperatures less than 100 °C, resulting in lower crust thickness predictions for initial stages of heating. It was hypothesized that variable optical and thermal properties of the matrix, as well as moisture diffusion, and internal pressure build up, were possible causes for deviation of predicted temperatures and crust thickness from laboratory data. The simulation was used as a tool to evaluate parameters that affect radiant heating of products. The affects of radiant flux intensity, matrix reflectance and dissipation coefficient, ambient air temperature, and convective heat transfer coefficient on matrix temperature and crust thickness were tested. Radiant flux intensity and surface reflectance were found to have a large affect on surface temperature, center temperature, and crust thickness. Ambient air temperature and convective heat transfer coefficient were shown to have a direct affect on surface temperature and crust thickness, and an indirect affect on center temperature. Dissipation coefficient parametric analysis revealed the large affect long wavelength dissipation coefficient had on surface temperature. It was concluded that short wavelength radiation had a relatively small affect on simulated temperatures and crust thickness. This was due to the small percentage of short wavelength infrared energy emitted by a 2,000 K emitter, high reflectance, and small generation term associated with short wavelengths infrared energy. Future work should include measurements of optical properties as a function of wavelength, matrix composition, and sample thickness; an addition of a mass diffusion term and an internal pressure term as a function of temperature and time; and expansion of the model to a two-dimensional configuration with variable radiant flux.