A novel method of controlling miniature sensors using Handspring Visor Prism PDA has been implemented. A generic motherboard was developed to map the data and address lines from the Visor onto a Complex Programmable Logic Device (CPLD) to provide basic electrical signals to the sensor board. The sensor board housed the sensor and contained application specific circuitry. The PDA, the motherboard, and the sensor board completed the control mechanism for the sensor. Miniature sensors and PDA based control mechanism scaled down the size of the complete system making the unit portable. This unit facilitated a faster analysis of data on field. Two applications were targeted: Flurometer (bio-sensor) and Corner Cube Retroreflector (CCR-optical sensor for communication). A sensor board was developed to control a thermally regulated fluorometer undergoing the Nuclei Acid Synthesis Based Amplification (NASBA) process, which detected the fluorescence from the solution containing target RNA. NASBA runs were conducted using solution containing K. brevis- Red tide organisms to validate the interface of the PDA with a fluorometer. Real time fluorescence plot over time was obtained on the PDA indicating presence/absence of the target RNA; thus, it successfully interfaced the PDA with the fluorometer. Additionally, a sensor board was developed to control the electrostatic actuation mechanism of the MEMS based CCR. Efforts were made to fabricate the vertical mirrors of CCR using wet and dry fabrication techniques.

Microwave frequency multipliers are very useful and advantageous components in microwave systems, especially, where the generation of high frequency sinusoidal signals is very difficult because of degrading performance of the solid state oscillators with increasing frequency. These components are frequently employed in diverse applications such as commercial wireless communication systems, microwave transmitters and receivers, and military systems. In the following work the basic principles of microwave FET frequency multipliers, specifically concentrated on triplers, are studied presenting theoretical concept and utilizing computerized simulation of piecewise linear FET (PLF) model. The use of PLF model which neglects nonlinear reactances and relies on resistive nonlinearities allows for the theoretical concept and, consequently, the multiplication mechanism in a frequency multiplier to be clearly and easily identified. At the end of this study, after presenting basic considerations on FET frequency multipliers a practical microwave frequency tripler design is presented.

3D seismic reflection data were acquired by the R/V Langseth and used to extract heat flow information using bottom-simulating reflector (BSR) depths across the southern Costa Rica convergent margin. These data are part of the CRISP Project, which will seismically image the Middle America subduction zone in 3D. The survey was conducted in an area approximately 55x11 km, northwest of the Osa Peninsula, Costa Rica. For the analysis presented here, seismic data were processed using a post-stack time migration. The BSR—a reverse polarity seismic reflection indicating the base of the gas hydrate phase boundary—is imaged clearly within the slope-cover sediments of the margin wedge. If pressure is taken into account, in deep water environments the BSR acts as a temperature gauge revealing subsurface temperatures across the margin. Two heat flow models were used in this analysis. In the Hornbach model BSR depth is predicted using a true 3D diffusive heat flow model combined with Integrated Ocean Drilling Program (IODP) thermal conductivity data and results are compared with actual BSR depth observations to constrain where heat flow anomalies exist. In the second model heat flow values are estimated using the heat flow equation. Uniform heat flow in the region should result in a deeper BSR downslope toward the trench due to higher pressure; however results indicate the BSR is deepest at over 325 meters below the seafloor (mbsf) further landward and shoals near the trench to less than 100 mbsf, suggesting elevated heat flow towards the toe of the accretionary prism. Heat flow values also reflect this relation. In addition to this survey-wide trend, local heat flow anomalies appear in the form of both circular patterns and linear trends extending across the survey, which can be related to mounds, thrust faults, folds, double BSRs, and seafloor erosion imaged in the seismic data. I suggest that these areas of higher local heat flow represent sites where advection of heat from deep, upward-migrating, thermogenically-sourced fluids and/or gases may be taking place. These heat flow trends have implications for not only earthquake nucleation, but also methane hydrate reserve stability. / text

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / The tracking modulation index (Km) is a key performance parameter for any autotracking antenna and should especially be considered for classically difficult targets such as missiles and/or fast moving aircraft. Antenna subsystems are typically characterized by their gain to temperature ratio (G/T) to optimize receive data bit error rates (BER) for distant targets. One important parameter often overlooked for telemetry autotracking antennas is a graded value for the available tracking modulation index (Km) that is common in radar autotracking applications. Tracking modulation performance is a major contributor for minimizing the antenna pointing error during an autotrack mission. Autotracking radar antenna specifications typically include tracking modulation as a major design parameter, many receive-only autotrack antennas used for telemetry applications do not consider this important parameter for the intended tracking mission which may result in poor autotracking performance. This paper investigates the effects of tracking modulation levels on system pointing errors for various classes of feed topologies.

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / A new common aperture autotracking C-band feed, specifically designed to accurately track fast moving targets such as the Lance missile, is reviewed. Measured data demonstrates exceptional tracking modulation required for good tracking performance while simultaneously providing excellent data channel performance for high G/T over the entire 4.40-5.25 GHz band. The new patent applied for feed design allows users to maintain existing L/S-band capability with a cost effective field upgrade which adds high performance C-band capability to an existing telemetry tracking system.

Many places where natural gas hydrate occurs have a regionally extensive, bottom-simulating seismic reflector (BSR) at the base of the gas hydrate stability zone (GHSZ). This reflection marks the top of an underlying free-gas zone (FGZ). Usually, hydrate recycling (that produces gas as the stability field moves upward relative to sediments) is invoked to explain the presence and properties of the sub-BSR FGZ. However, this explanation is not always adequate: FGZs are often thicker in passive-margin environments where hydrate recycling is relatively slow, than in convergent-margin environments where hydrate recycling is relatively fast (e.g. Blake Ridge compared with Cascadia). Furthermore, some areas with thick FGZs and extensive BSRs (e.g. west Svalbard) have similar rates of hydrate recycling to northern Gulf or Mexico, yet the latter has no regional BSR. Here we discuss a gas-forming mechanism that operates in addition to hydrate recycling, and which produces a widespread, regional, BSR when gas is transported upward through the liquid phase; this mechanism is dominant in tectonically passive margins. If the gas-water solubility decreases downward beneath the GHSZ (this occurs where the geothermal gradient and the pressure are relatively high), low rates of upward fluid flow enable pore water to become saturated in a thick layer beneath the GHSZ. The FGZ that this produces achieves a steady-state thickness that is primarily sensitive to the rate of upward fluid flow. Consequently, geophysical observations that constrain the thickness of sub-BSR FGZs can be used to estimate the regional, diffuse, upward fluid flux through natural gas-hydrate systems.

Selectively-transparent and conducting photonic crystals (STCPCs) made of alternating layers of sputtered indium-tin oxide (ITO) and spin-coated silica (SiO2) nanoparticle films have potential applications in micromorph solar cells and building integrated photovoltaics (BIPVs). In this work, theoretical calculations have been performed to show performance enhancement of the micromorph solar cell upon integration of the STCPC an intermediate reflector. Thin semi-transparent hydrogenated amorphous silicon (a-Si:H) solar cells with STCPC rear contacts are demonstrated in proof-of-concept devices. A 10% efficiency increase in a 135nm thick a-Si:H cell on an STCPC reflector with Bragg peak at 620nm was observed, while the transmitted solar irradiance and illuminance are determined to be 295W/m2 and 3480 lux, respectively. The STCPC with proper Bragg peak positioning can boost the a-Si:H cell performance while transmitting photons that can be used as heat and lighting sources in building integrated photovoltaic applications.

This research focuses on modelling reflectors in typical material testing reactors (MTRs). Reflectors present some challenges to the usual approach to full-core calculational models. Diffusion theory is standardly used in full-core calculations and is known to be inaccurate in regions where the flux is anisotropic, for example within the reflectors. Thus, special consideration should be given to reflector models. In this research, normalised generalised equivalence theory is used to homogenise cross-sections and calculate equivalent nodal parameters and albedo boundary conditions for the reflector surrounding a typical MTR reactor. Various studies have shown that equivalence theory can be used to accurately generate equivalent nodal parameters for the core and reflector regions of large reactors, such as pressurised and boiling water reactors, in one dimension and for two neutron energy groups. This has not been tested for smaller reactors where leakage, environment sensitivity and multi-group spectrum dependency are much larger. The SAFARI-1 MTR reactor is modelled in this work. A thirty day operational cycle is simulated for this reactor, using the nodal diffusion code MGRAC. NGET reflector equivalent nodal parameters are calculated using the codes NEWT and EQUIVA. The impact of different reflector models are evaluated, based on their effect on the core power, flux distribution, reactivity and neutron leakage over the duration of the operational cycle. It is found that homogenisation introduces some environment dependencies in the reflector parameters, particularly in the corners of the reactor core. In full-core calculations, the reflector parameters show some sensitivity to the in-core reflector structures, but not the fuel composition. A practical reflector model for SAFARI-1 is proposed, which proves that NGET equivalence theory can be used for multi-group reflector modelling in a small MTR reactor. This approach to reflector modelling simplifies the core model, increases the accuracy of a diffusion calculation, and increases the efficiency (shorter calculational time and better convergence behaviour) of computer simulations. / Thesis (MSc (Engineering Sciences in Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013.

This research focuses on modelling reflectors in typical material testing reactors (MTRs). Reflectors present some challenges to the usual approach to full-core calculational models. Diffusion theory is standardly used in full-core calculations and is known to be inaccurate in regions where the flux is anisotropic, for example within the reflectors. Thus, special consideration should be given to reflector models. In this research, normalised generalised equivalence theory is used to homogenise cross-sections and calculate equivalent nodal parameters and albedo boundary conditions for the reflector surrounding a typical MTR reactor. Various studies have shown that equivalence theory can be used to accurately generate equivalent nodal parameters for the core and reflector regions of large reactors, such as pressurised and boiling water reactors, in one dimension and for two neutron energy groups. This has not been tested for smaller reactors where leakage, environment sensitivity and multi-group spectrum dependency are much larger. The SAFARI-1 MTR reactor is modelled in this work. A thirty day operational cycle is simulated for this reactor, using the nodal diffusion code MGRAC. NGET reflector equivalent nodal parameters are calculated using the codes NEWT and EQUIVA. The impact of different reflector models are evaluated, based on their effect on the core power, flux distribution, reactivity and neutron leakage over the duration of the operational cycle. It is found that homogenisation introduces some environment dependencies in the reflector parameters, particularly in the corners of the reactor core. In full-core calculations, the reflector parameters show some sensitivity to the in-core reflector structures, but not the fuel composition. A practical reflector model for SAFARI-1 is proposed, which proves that NGET equivalence theory can be used for multi-group reflector modelling in a small MTR reactor. This approach to reflector modelling simplifies the core model, increases the accuracy of a diffusion calculation, and increases the efficiency (shorter calculational time and better convergence behaviour) of computer simulations. / Thesis (MSc (Engineering Sciences in Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013.

It is a great challenge in the design of the PBMR to accurately predict gas flow and heat transfer in the reactor. Understanding the heat transfer at the core-reflector interface in particular is a very important aspect as the reactivity of the control rods housed in the reflectors is highly temperature dependent. It is also very important because the core-reflector interface is on the critical path for heat removal during accident conditions. PBMR has developed an OECD/NEA coupled neutronic/thermal-hydraulic benchmark to aid in the understanding of the different modelling approaches currently employed at PBMR. A comparison of THERMIX-KONVEK and DIREKT results showed large temperature differences at the core-reflector interfaces. Further investigation showed that these differences are as a result of the numerical methods used i.e. Cell-Centred (CC) vs. Vertex-Centered (VC). The present study extended this comparison to Star-CD (CC) and Flownex (VC) which are also used to simulate the reactor at PBMR. An ID MATLAB program that mimics the CC and VC numerical methods was verified against Star-CD and Flownex. This program was then used to model an ID version of the OECD/NEA benchmark. Results were compared with DIREKT and THERMIX-KONVEK. Although the results compared well, there were significant errors at the core-reflector interfaces. The findings of this study were that different numerical methods will predict different temperatures, heat fluxes and (temperature-dependent) sink terms. It was also shown that in addition to the differences resulting from numerical methods, differences were seen between Star-CD and DIREKT and Flownex and THERMIX-KONVEK in the region of the core-reflector boundary. In general, for complicated simulations like that of the pebble bed, the numerical basis of software used to simulate the problem needs to be understood for the problem to be correctly modelled. / Thesis (M.Sc. Engineering Sciences (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.