Metal matrix composites

Works on the west coast of India

RCC structures in marine environment

Aluminium/copper-graphite composite

Aluminium based metal matrix composites

thyristor circuits for various purposes

A Natural Media Filter (NMF) and Constructed Treatment Wetland (CTW) pilot study was performed on an industrial landfill leachate site. The pilot study was designed to test if a NMF and CTW could be a low cost replacement option for the current wastewater treatment system. The main contaminates of concern for the leachate were poly-chlorinated biphenyls (PCBs) and ammonia.The pilot unit consisted of two systems, a subsurface flow CTW and an up-flow NMF that utilize mushroom compost as a media. The two units were run in parallel and were both supplied with untreated leachate. The CTW was operated at a flow rate of 0.3 gpm with a 2.2 day retention time. The goal of the study was to operate the NMF at 0.2 gpm with a half-day retention time, but due to operational issues this flow rate varied throughout the study. The Influent concentration of ammonia varied from non-detectable to 17 mg/l as nitrogen, with effluent concentration from the CTW fluctuating from non-detectable to 16 mg/l. For PCBs, influent concentrations during the majority of the study were non detectable, but during the last few months of the study large spikes in PCBs were recorded. The natural media filter was able to remove PCBs below limits of detection for most of the study, but breakthrough occurred towards the end of the study.For the constructed treatment wetland, removal of ammonia and nitrate/nitrite were modeled using the both the Plug Flow Model and the Tank-in-Series Model. The CTW was considered to be a Plug Flow unit and was oxygen limited. For the Natural Media Filter, the data collected did not allow for a proper evaluation of the adsorption capacity of the unit. A PCB mass balance was performed on the NMF from data collected from core samples of the compost. The unit was successful in removing PCB loading nine times higher than its designed capacity and the failure of the unit is attributed to short circuiting caused by the unit freezing.

The thesis objective is to safeguard power electronics used in modular converter applications. A new fault current limiting and protection circuit is proposed. The system level fault mitigation assemblies take a long time to remove a fault and within this time the IGBTs used in the Flexible AC Transmission System (FACTS) application will undergo high thermal and mechanical stress. Exposure to such conditions over a prolonged period of time will reduce the device lifetime, which is one of the major reasons why power electronics are not very popular in utility applications. Modular converter approach will reduce the device ratings required to mitigate the fault at power electronics level. The fault current limiting and protection circuit is tested using PSPICE simulation tool. The test set up is simple comprising of two IGBTs, one which acts as device under test (DUT) and another which acts as switch regulating fault seen by DUT. The test voltage is 480 Volt and R-L is varied over a range of L – 20nanoHenry, 2microHenry, and 10microHenry and R – 20Ohm, 50Ohm, and 100Ohm. The fault current limiting (FCL) and protection circuit worked accurately in each of the cases described above, thereby safely turning OFF the device within the short circuit withstand capacity (10microseconds) of IGBTs. The FCL and protection circuit can mitigate both Hard Switched Fault and Fault Under Load seen by the IGBT during short circuit condition. The circuit developed is different from the conventional protection gate drives available in the market and there is the possibility of customizing it further for modular blocks.

Acetic acid needs to be removed from a waste stream in the UREX+ process so that nitric acid can be recycled and possible interference with downstream steps can be avoided. Acetic acid arises from acetohydroxamic acid (AHA) used to suppress plutonium in the first step of the UREX+ process. Later, it is hydrolyzed into hydroxyl amine nitrate and acetic acid. Many common separation technologies were examined, and solvent extraction was determined to be the best choice under process conditions. Solvents already used in the UREX+ process were then tested to determine if they would be sufficient for the removal of acetic acid. The tributyl phosphate (TBP)-dodecane diluent, used in both UREX and NPEX, was determined to be a solvent system that gave sufficient distribution coefficients for acetic acid in addition to a high separation factor from nitric acid. This solvent system was tested under various TBP concentrations in the dodecane to create a concentration plot that can be used for further flow sheet development. Each step in the UREX+ process was examined to determine if there was any acetic acid interference in the performance of any step of the UREX+ flow sheet that would make it necessary to remove the acetic acid prior to that step. It was found that no interference with acetic acid was present. Therefore, the acetic acid removal step can be placed essentially anywhere in the process. For simplicity, it has been proposed to place the removal step at the end of the process after TALSPEAK where all desirable metals have already been extracted and the nitric acid waste stream is prepared to be recycled.

A study to assess the utility of an aircraft referenced 3D audio display was undertaken to determine if there could be any improvements to pilot performance when operating under high workload conditions. Test subjects flew a general aviation light twin-engine aircraft under simulated single-pilot instrument flight rule conditions. Workload was elevated by ensuring each test subject had to execute an unexpected missed approach procedure and simultaneously handle a simulated engine failure. Subjective data was gathered using the NASA Task Load Index and a post-flight questionnaire on perceived performance, workload and situational awareness. Objective data on pilot performance was gathered using the research aircraft’s onboard instrumentation system. Within the limitations of having a low number (5) of test subjects available, subjective data results showed a perceived increase in situational awareness, performance, and a statistically significant reduction in workload. Although not statistically significant, the only objective impact to performance was a slight increase in heading control and course intercept. There was no corresponding performance increase in airspeed control, angle of bank control, or improvements to aircraft track. Overall, the results indicate that a 3D audio display would have utility and pilot acceptance as a supplemental navigational display, but would not result in any substantial improvements to pilot performance.