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ItemZinc Oxide coated Carbon Nanotubes as Piezoelectric Nanogenerators(Georgia Institute of Technology, 2009-12) Mason, CelestePiezoelectric nanogenerators were created using two designs: coating carbon nanotubes (CNTs) grown on a silicon wafer substrate with a thin film of zinc oxide (ZnO), coupled with an additional gold-coated CNT grown wafer to act as an electrodes and coating carbon nanotubes (CNTs) grown on carbon fiber with each type of coating to form flexible electrodes. The CNTs on all samples were grown using a standard recipe, with thermally evaporated iron as catalyst. ZnO deposition techniques such as RF sputtering and ion-assisted deposition were used. Gold deposition was accomplished by thermal evaporation and RF sputtering. Once electrodes were combined, preliminary electrical testing resulted in measurement of current densities of up to 4.2x10-7 A/cm3. Additional electrical measurements indicated that the current generated was the result of piezoelectric behavior of the ZnO coating. These values may be increased with better penetration of both gold and ZnO coatings during deposition on the CNTs. Improvement of film quality, such as gold adhesion and ZnO crystal orientation, may also increase current generation.
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ItemInvestigation of Physics-Based Approaches for Wind Turbine Modeling and Design(Georgia Institute of Technology, 2009-05-04) Nucci, MichaelRising oil costs have created a need for a new sustainable energy source. Currently wind energy is beginning to fulfill this need. With many financial incentives being offered for clean energy, wind turbines are a promising green energy source. Wind turbine analysis can be difficult and costly. Accurate spanwise pressure distributions are difficult to measure experimentally, and a full-fledged Navier-Stokes analysis is very computationally expensive. A comparison of two separate computer codes was performed. These include PROPID, which uses a blade element momentum theory method and empirical data about the wind turbine airfoil. The second method is a Reynolds Averaged Navier-Stokes (RANS) CFD code called windrotor2 which also was used to predict the performance of the NREL Phase VI rotor. Once the codes were validated they were then used to predict the performance of new rotor designs. This research shows that PROPID can be used as a surrogate model for turbine analysis and design. PROPID can be shown to predict performance that is on par with CFD methods in terms of accuracy, but takes only a fraction of the time to perform the analysis. PROPID can also be shown to accurately predict the performance of new turbine configurations as long as empirical data is readily available.
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ItemEnrichment of Adipose-derived Mesenchymal Stem Cells Using Resveratrol(Georgia Institute of Technology, 2009-05-04) Erdman, Christopher PaulMesenchymal stem cells (MSCs) hold great promise for the application of tissue engineering to orthopedic problems such as critical-size defects. Cell sorting has indicated a benefit to enriching the MSC population, but is undesired for clinical applications. Pharmacological enrichment utilizing adipogenic inhibitors such as resveratrol represent a clinically viable alternative. Cells were isolated from rats, and treated with differentiation media to verify multipotency, and were then treated with 0, 12.5, and 25 µM resveratrol in growth media and osteogenic media. MSC and osteoprogenitor (OPC) populations were measured using flow cytometry and OPC quality was assessed with osteocalcin production, osteoprotegerin production, and alkaline phosphatase activity. Resveratrol increased the population percent and cell number of MSCs in both growth and osteogenic media, but only increased the number of OPCs in growth media. In both media types resveratrol increased alkaline phosphatase activity and osteocalcin levels. Resveratrol enriches ADMSCs for mesenchymal stem cells and osteoprogenitors.
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ItemModeling and Simulation of the Impact Response of Linear Cellular Alloys for Structural Energetic Material Applications(Georgia Institute of Technology, 2009-05-04) Jakus, AdamWe investigate the deformation and fracture as well as stress transfer behavior of 250 maraging steel linear cellular alloys (LCAs) undergoing high velocity impact upon a rigid target. Of paramount importance for application as a ballistic delivery mechanism for thermite powders, is the ability to transfer stress along the inner length of the cell walls. Additionally, outward fragmentation of the LCA body upon impact must be controlled. Parameters for a Johnson-Cook strength model of 250 maraging steel are determined in conjunction with 3-dimensional Lagrangian based finite element analysis on a solid cylinder. These parameters are then applied to four, 25% theoretical density LCA geometries: hollow cylinder, pie, reinforced pie, and 9-cell waffle. Verification of the validity of the Johnson-Cook parameters determined from the solid cylinder experiments and simulations is analyzed through comparison of experiments of the four LCA geometries, produced using a direct reduction technique with corresponding simulations. Upon verification of the Johnson-Cook strength model for maraging steel, the deformation and fracture as well as the stress transfer response of the LCAs during impact is analyzed. Through transient analysis of finite element simulations, it has been determined that the 9-cell waffle geometry displays optimal stress transfer behavior as well as limited outward fragmentation.
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ItemInvestigation of Adjoint Based Shape Optimization Techniques in NASCART-GT using Automatic Reverse Differentiation(Georgia Institute of Technology, 2009-05-04) Verma, SiddharthaAutomated shape optimization involves making suitable modifications to a geometry that can lead to significant improvements in aerodynamic performance. Currently available mid-fdelity Aerodynamic Optimizers cannot be utilized in the late stages of the design process for performing minor, but consequential, tweaks in geometry. Automated shape optimization involves making suitable modifications to a geometry that can lead to significant improvements in aerodynamic performance. Currently available mid-fidelity Aerodynamic Optimizers cannot be utilized in the late stages of the design process for performing minor, but consequential, tweaks in geometry. High-fidelity shape optimization techniques are explored which, even though computationally demanding, are invaluable since they can account for realistic effects like turbulence and viscocity. The high computational costs associated with the optimization have been avoided by using an indirect optimization approach, which was used to dcouple the effect of the flow field variables on the gradients involved. The main challenge while performing the optimization was to maintain low sensitivity to the number of input design variables. This necessitated the use of Reverse Automatic differentiation tools to generate the gradient. All efforts have been made to keep computational costs to a minimum, thereby enabling hi-fidelity optimization to be used even in the initial design stages. A preliminary roadmap has been laid out for an initial implementation of optimization algorithms using the adjoint approach, into the high fidelity CFD code NASCART-GT.High-fidelity shape optimization techniques are explored which, even though computationally demanding, are invaluable since they can account for realistic effects like turbulence and viscocity. The high computational costs associated with the optimization have been avoided by using an indirect optimization approach, which was used to dcouple the effect of the flow field variables on the gradients involved. The main challenge while performing the optimization was to maintain low sensitivity to the number of input design variables. This necessitated the use of Reverse Automatic differentiation tools to generate the gradient. All efforts have been made to keep computational costs to a minimum, thereby enabling hi-fidelity optimization to be used even in the initial design stages. A preliminary roadmap has been laid out for an initial implementation of optimization algorithms using the adjoint approach, into the high fidelity CFD code NASCART-GT.