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Undergraduate Research Opportunities Program

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Now showing 1 - 10 of 13

Zinc Oxide coated Carbon Nanotubes as Piezoelectric Nanogenerators

(Georgia Institute of Technology, 2009-12) Mason, Celeste

Piezoelectric 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.
Investigation of Physics-Based Approaches for Wind Turbine Modeling and Design

(Georgia Institute of Technology, 2009-05-04) Nucci, Michael

Rising 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.
Enrichment of Adipose-derived Mesenchymal Stem Cells Using Resveratrol

(Georgia Institute of Technology, 2009-05-04) Erdman, Christopher Paul

Mesenchymal 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.
Modeling and Simulation of the Impact Response of Linear Cellular Alloys for Structural Energetic Material Applications

(Georgia Institute of Technology, 2009-05-04) Jakus, Adam

We 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.
Investigation of Adjoint Based Shape Optimization Techniques in NASCART-GT using Automatic Reverse Differentiation

(Georgia Institute of Technology, 2009-05-04) Verma, Siddhartha

Automated 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.
Characterizing Single Ventricle Patient-Specific Anatomy Using Segmentation of MRI and 3D Reconstruction to Aid Surgical Planning

(Georgia Institute of Technology, 2008-08-01) Jayaprakash, Gopinath

Single ventricle congenital heart defects occur 2 per every 1000 live births in the USA. In these cases, cyanosis occurs due to the mixing of venous deoxygenated blood and oxygenated blood from the lungs. These defects are surgically treated by the total cavo-pulmonary connection (TCPC), where the superior and inferior vena cavae are connected to the pulmonary arteries routing the systemic venous return directly to the lungs. However, this Fontan repair results in high energy losses and therefore the optimization of this connection prior to the surgery could significantly improve post-operative performance. In this paper, the in-house segmentation and 3D reconstruction scheme is used in the following studies. First, 3D geometrical analysis of the TCPCs is used to determine the advantages and disadvantages of two commonly performed TCPC palliations intra-atrial and extra-cardiac configurations. Then, a surgical planning outline is proposed with segmentation of pre and post surgical Magnetic Resonance Imaging (MRI) data followed by the 3D reconstruction with emphasis on extracting surrounding vessels and structures. A pediatric surgeon performs a virtual surgery on the reconstruction of the patient s pre-Fontan anatomy prior to the actual surgery. A segmentation of the heart, aorta and surrounding vessels superimposed with the Glenn, when used with the SURGEM® tool, simulates the actual Fontan operation. This outline allows the surgeon to envision numerous scenarios of possible surgical options, and accordingly to predict the post operative procedures. The segmentation tool is improved upon to increase the accuracy and efficiency of the process and enhance the quality of the anatomical reconstructions.
Cylindrical beam volume holograms recorded in reflection geometry for diffuse source spectroscopy

(Georgia Institute of Technology, 2008-05-06) Jolly, Sundeep

Multimodal multiplex spectroscopy (MMS) has been demonstrated to increase the optical throughput of a spectrometer as opposed to that of conventional optical spectrometers and has been implemented using three-dimensional photonic crystals and spherical-beam volume holograms recorded in the transmission geometry as spectral diversity filters. While such efforts have resulted in compact and sensitive Fourier-transform holographic spectrometers, there still remains much room for performance improvements. Previous studies [6,7,9] have proven the utility of spherical-beam volume holograms recorded in the transmission geometry as spectral diversity filters for spectrometers. The role of the recording geometry in the performance of cylindrical-beam volume holograms as spectral diversity filters is investigated here. The transmission recording geometry is compared to the reflection recording geometry on the basis of the spectral operating range of the resultant spectral diversity filters.
Design and development of a novel compact soft-surface structure for performance improvement and size reduction of a microstrip Yagi array antenna

(Georgia Institute of Technology, 2008-05-05) Thai, Trang Thuy

An new antenna structure based on a microstrip Yagi array antenna and a soft surface (SS) ring is designed and developed, which enables a highly directional gain in addition to an improved front-to-back (F/B) ratio of more than 20 dB. The SS ring is shown to be capable of greatly improving the performance while miniaturizing the design s size by half. The implementation of the SS ring to a microstrip Yagi array antenna is demonstrated for different ground sizes to verify its functionality in suppressing surface waves, showing that an improvement of at least 3 dB in the F/B ratio can be obtained. The design is investigated at the center frequency of 5.8 GHz, however, the structure can be easily scaled to other frequency ranges. A parametric analysis is performed to give insight into the operational mechanism of the SS ring and on the critical dimensions that affect the SS structure surrounding the antenna array. In addition, measurements are presented to validate the results obtained via simulation. The principles established in this paper are applicable to other planar antenna designs.
Image Analysis of Acoustically Excited Bluff Body Flames

(Georgia Institute of Technology, 2007-12-17) Plaks, Dmitriy Vital

This thesis analyzes the effects of various bluff bodies on the downstream flow field. Bluff bodies, for example, those typically found in jet engine augmentors, are objects designed to impede the flow in order to stabilize a flame. The effects of different bluff body shapes (cylindrical and triangular), size (6.35 mm, 9.53 mm, 12.7 mm, and 19.1 mm) and heat release are examined with respect to their influence on downstream vorticity strength, vortex separation distance, and vorticity divergence angle. Particle Image Velocimetry (PIV) is used to obtain the velocity field data from which the vorticity field is calculated. The mean flow velocity, U∞ is 2.7 m/s, and the flow is acoustically excited at 300 Hz with a normalized acoustic velocity of u'/U∞ = 0.8. The vorticity divergence angle increases with increasing bluff body size, is not affected by bluff body shape, and has a non-linear correlation with heat release. Downstream vorticity strength is affected by all three parameters (bluff body shape, size and heat release) in a non-linear manner. Vortex separation distance is a function primarily of bluff body size, increasing for larger bodies; however, the separation distance decreases with increasing heat release. Bluff body shape also has an effect on vortex separation distance as the cylindrical bluff body creates a larger separation distance between vortices.
Low Static Power and High Throughput Wave-Pipelined Global Interconnect Circuits

(Georgia Institute of Technology, 2007-12-17) Youngblood, Mark William

This research project will explore a low-power, high-throughput design using high threshold voltage transistors in combination with wave-pipelining techniques across global interconnect circuits.