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ItemCharacterizing Single Ventricle Patient-Specific Anatomy Using Segmentation of MRI and 3D Reconstruction to Aid Surgical Planning(Georgia Institute of Technology, 2008-08-01) Jayaprakash, GopinathSingle 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.
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ItemCylindrical beam volume holograms recorded in reflection geometry for diffuse source spectroscopy(Georgia Institute of Technology, 2008-05-06) Jolly, SundeepMultimodal 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.
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ItemDesign 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 ThuyAn 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.
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ItemLow Static Power and High Throughput Wave-Pipelined Global Interconnect Circuits(Georgia Institute of Technology, 2007-12-17) Youngblood, Mark WilliamThis 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.
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ItemOhmic Contacts for Wide Bandgap Devices(Georgia Institute of Technology, 2007-05) Mehra, ZenBipolar devices based on GaN and SiC have gained tremendous popularity as an alternative to Si based devices, primarily due to the ability to sustain high temperature and high voltage operations that can be attributed to their high breakdown field and saturation velocity. Any bipolar device based on wide bandgap technology requires high performing ohmic contacts that have low specific contact resistivity and exhibit linear I-V behavior, as opposed to Schottky characteristics. A range of high work function metals like Ni, Au, Pd, Pt, Al can be used to realize these contacts. Further, annealing under specific conditions is required to ensure extremely high doping in the near surface layer. In this research, the Ni/Au stack for p-type contacts, and the Ti/Al/Ti/Au layer for n-type contacts have been specifically investigated over a range of annealing time periods and temperatures. Control wafers with GaN:Mg (p-type) or GaN:Si and GaN/AlGaN (n-type) formed the basis of this study. The Transmission Line Model (TLM) technique was used to conduct measurements, and obtain the specific contact resistance. Specific contact resistances as low as 9.44*10-3 Ω-cm2 for n-type, and 5.73*10-3 Ω-cm2 for p-type were achieved. These shall form the basis for ultimate fabrication of an InGaN/GaN HBT with a high current gain, breakdown voltage (VBR) and current density (J). The quality of resulting contact is seen to depend on the initial doping/bulk resistance, determination of a unique time-temperature window, and careful process control. A further investigation is conducted into non-linear behavior exhibited by p-type contacts for low separation.