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The purpose of this study has been to construct two accelerating tubes with small beam apertures for the Van de Graaff, modifying the prototype tube designed and tested by Wiley (20), to design and construct a vacuum system for evacuating the tubes, and to determine the characteristics of the tube under operating conditions while installed in the generator.

This thesis is an investigation of the vacuum uv spectra of the phosphorus, phosphoryl, and thiophosphoryl trichlorofluorides in the region 1250 to 3000A. Assignments for absorption bands are made utilizing results from photoelectron spectra and ab initio calculations, oscillator strengths for absorption bands, and CNDO/2 molecular orbital calculations. Results from CNDO/2 calculations are compared with theoretical calculations, and experimental data are discussed with regard to the bonding in the compounds.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2015 / Electrical utilities are tasked with managing large numbers of assets that have long useful lives and are fairly expensive to replace. With emphasis on medium voltage vacuum circuit breakers, a key challenge is determining when circuit breakers are close to their end-of-life and what the appropriate action at that point in time should be. Condition-based maintenance, intended to “do only what is required, when it is required,” has been reported as the most effective maintenance strategy for circuit breakers. This dissertation provides an overview, together with laboratory measurements, on non-intrusive technologies and analytics that could reduce maintenance costs, unplanned outages, catastrophic failures and even enhance the reliability and lifetime of circuit breakers by means of a real-time condition monitoring and effective failure prevention maintenance approach. The key areas of research are the condition assessment of the mechanical mechanism based on coil current signature diagnosis, degradation detection of the main interrupting contacts through thermal monitoring and interrupter vacuum integrity assessment based on magnetron atmospheric condition (MAC) testing. The information from test results allows both immediate onsite analysis and trending of key parameters which enables informed asset management decisions to be taken. / GS2016

Silicon is widely used in optoelectronic devices, including solar cells. In recent years new forms of silicon have become available, including amorphous, microcrystalline and nano-crystalline material. These new forms have great promise for low cost, thin film solar cells and the purpose of this work is to investigate their preparation and properties with a view to their future use in solar cells. A Hot Wire-Deposition Chemical Vapour Deposition CVD (HW-CVD) system was constructed to create a multi-chamber high vacuum system in combination with an existing Plasma Enhanced Chemical Vapour Deposition (PECVD) system; to study the amorphous to crystalline transition in silicon thin films. As the two chambers were linked by a common airlock, it was essential to construct a transfer mechanism to allow the transfer of the sample holder between the two systems. This was accomplished by the incorporation of two gate valves between the two chambers and the common airlock as well as a rail system and a magnetic drive that were designed to support the weight of, and to guide the sample holder through the system. The effect of different deposition conditions on the properties and structure of the material deposited in the combined HW-CVD:PECVD system were investigated. The conditions needed to obtain a range of materials, including amorphous, nano- and microcrystalline silicon films were determined and then successfully replicated. The structure of each material was analysed using Transmission Electron Microscopy (TEM). The presence of crystallites in the material was confirmed and the structure of the material detected by TEM was compared to the results obtained by Raman spectroscopy. The Raman spectrum of each sample was decoupled into three components representing the amorphous, intermediate and crystalline phases. The Raman analysis revealed that the amorphous silicon thin film had a dominant amorphous phase with smaller contribution from the intermediate and crystalline phase. This result supported the findings of the TEM studies which showed some medium range order. Analysis of the Raman spectrum for samples deposited at increasing filament temperatures showed that the degree of order within the samples increased, with the evolution of the crystalline phase and decline of the amorphous phase. The Selected Area Diffraction (SAD) patterns obtained from the TEM were analysed to gain qualitative information regarding the change in crystallite size. These findings have been confirmed by the TEM micrograph measurements. The deposition regime where the transition from amorphous to microcrystalline silicon took place was examined by varying the deposition parameters of filament temperature, total pressure in the chamber, gas flow rate, deposition time and substrate temperature. The IR absorption spectrum for ƒÝc-Si showed the typical peaks at 2100cm-1 and 626cm-1, of the stretching and wagging modes, respectively. The increase in the crystallinity of the thin films was consistent with the evolution of the 2100cm-1 band in IR, and the decreasing hydrogen content, as well as the shift of the wagging mode to lower wavenumber. IR spectroscopy has proven to be a sensitive technique for detecting the crystalline phase in the deposited material. Several devices were also constructed by depositing the ƒÝc-Si thin films as the intrinsic layer in a solar cell, to obtain information on their characteristics. The p- layer (amorphous silicon) was deposited in the PECVD chamber, and the sample was then transferred under vacuum using the transport system to the HW-CVD chamber where the i-layer (microcrystalline silicon) was deposited. The sample holder was transferred back to the PECVD chamber where the n-layer (amorphous silicon) was deposited. The research presented in this thesis represents a preliminary investigation of the properties of ƒÝc-Si thin films. Once the properties and optimum deposition characteristics for thin films are established, this research can form the basis for the optimization of a solar cell consisting of the most efficient combination of amorphous, nano- and microcrystalline materials.

Porous tin oxide nanotubes were obtained by vacuum infiltration of tin oxide nanoparticles into porous aluminum oxide membranes, followed by calcination. The porous tin oxide nanotube arrays so prepared were characterized by FE-SEM, TEM, HRTEM, and XRD. The nanotubes are open-ended, highly ordered with uniform cross-sections, diameters and wall thickness. The tin oxide nanotubes were evaluated as a substitute anode material for the lithium ion batteries. The tin oxide nanotube anode could be charged and discharged repeatedly, retaining a specific capacity of 525 mAh/g after 80 cycles. This capacity is significantly higher than the theoretical capacity of commercial graphite anode (372 mAh/g) and the cyclability is outstanding for a tin based electrode. The cyclability and capacities of the tin oxide nanotubes were also higher than their building blocks of solid tin oxide nanoparticles. A few factors accounting for the good cycling performance and high capacity of tin oxide nanotubes are suggested. / Singapore-MIT Alliance (SMA)

FVP of 2-methoxy-N-(arenylidene)anilines gave benzoxazoles¡Fboth FVP and photolysis of 2-thiomethoxy-N-(arenylidene)anilines gave benzothiazoles.

Pyrolysis of 3- (o-methoxyphenyl)-1-phenylprop-2-en-1-one(49) ¡B1- (o-methoxyphenyl)-3-phenylprop-2-en-1-one (50) and 1-(o-methoxyphenyl)-3-phenylprop -2-yn-1-one (51) gave the expected cyclic products 2-phenylbenzo[b]furan (11) and flavone (73). Furthermore, compounds 49-51 gave phenanthrene-9,10-dione (71)¡Bfluoren-9-one (14) and others as the minor products at high temperture. Under photolytic condition, compounds 49-51 gave photocyclic product (73) all in low yields and recovered mostly the starting materials.