The mass production of carbon nanotubes (CNTs) by a cost effective process is still a challenge for further research and application of CNTs. This research focussed on the deposition of CNTs on a continuously-fed carbon substrate via arc discharge at atmospheric pressure. In this work, modifications, control and optimization of the available arc-discharge reactor were conducted. New reactor support and new tape feeding mechanisms were added to the reactor for better temperature assessment, longer operating period and better control of the speed of the tape. The influence of inter-electrode gap, substrate velocity and arc current on the surface temperature were investigated. Multiwalled carbon nanotubes (MWNTs) were produced at lower currents (< 20 A) and at larger inter-electrode gaps. Further investigation shows that inter-electrode gap influenced both the arc characteristic and the anode surface temperature (Ts). Here, Ts was measured by an optical pyrometer. The inter-electrode gap was found to indirectly affect the formation of NTs. Anode surface temperature (Ts) varied with gap, reaching a minimum at an intermediate gap. Higher CNTs yield was found at this lowest Ts. This minimum Ts is consistent with the presence of a cloud of nanoparticles ejected by the heated graphite/carbon surfaces. These graphene fragments are thought to later fold and form nanotube “seeds” and then develop into multiwall nanotubes. This cloud of nanoparticles also may affect the electrical conductivity at the front of the anode. Simulation of the arc behaviour, i.e. temperature distributions and flow properties of the plasma, using a computer package Comsol Multiphysics 3.2, was stable only when the electrical conductivity of a dusty plasma near to the electrodes was included. Our experiments show that carbon nanotubes grew better at a Ts range of ~ 3650 K - 3700 K and at the tape speed of 3 mm/s. The results from our work also strongly suggested that tiny carbon crystallites are the main intermediates for CNT growth in an electric arc. The limiting factor for a solid state growth mechanism, therefore, is high temperature annealing of carbon or graphene fragments. Further work should aim to understand the growth mechanism of CNTs, produce comprehensive analysis on the arc plasma composition and also explore the possibility of producing CNTs at higher rates.

No description available.

This paper proposes a diachronic and synchronic analysis of the extensive use of se in Spanish reflexive and passive constructions with se being discussed in relation to the Unaccusative Hypothesis in Arc Pair Grammar.Universals in Arc Pair Grammar, namely the Unaccusative Law, the 1-Advancement Exclusiveness Law and the Final 1-Arc Law will account for the similarities and differences, first between English and Spanish predicates; and second, between ordinary reflexive constructions and reflexive passive constructions.Evidence from Spanish, primarily synchronic, is presented to analyze reflexive constructions that come from an initial unaccusative stratum. A parallel between these constructions and reflexive passives is established to demonstrate that unaccusative predicates and reflexive passive constructions are very closely related.Diachronically the paper claims that there is a logical and clear evolution of se based on corefentiality, anaphoric chains, unspecified arguments, and self-erasing ghost arcs.Finally this paper attempts to explain why in some instances the predicate will not exhibit agreement with the corresponding nominal. The Chomeur relation and the introduction of ghost arcs according to Arc Pair Grammar Laws and Theorems will provide the basis for this explanation.

Interruption of DC is more challenging than that of AC because of the absence of DC zero-crossings. This thesis proposes an alternative counter-voltage (ACV) DC hybrid circuit breaker (DC-HCB). This DC-HCB can interrupt the DC up to 5 kA with the source voltage of up to 1 kV and it can meet the general requirements i.e., interrupting the DC within 5ms, and limiting over-voltages due to the CB operation. The existing/investigated DC circuit breakers, i.e., active mode DC-HCB and the traditional counter-voltage (TCV) DC-HCB are also investigated and compared with the proposed DC-HCB. The investigations are based on the time-domain simulation studies in the PSCAD/EMTDC. The studies show that the ACV DC-HCB is the preferred option to both the existing DC-HCBs. The main features of the proposed ACV DC-HCB include lower capacitance in the commutation path and the need for a smaller dielectric strength for the primary-path circuit breaker.

Automakers are increasingly using aluminum for structural applications in order to reduce vehicle weight and improve fuel efficiency. However, aluminum bodied cars have largely been confined to lower-volume, niche markets due in part to the number of challenges associated with welding of aluminum in comparison with steel. Therefore, a need exists for new joining processes which can produce high-quality welds in thin aluminum sheet at high production rates and low cost. The recently invented double-sided arc welding (DSAW) process is one such joining process. It has been shown to be capable of producing high quality butt-joint configuration welds in thin aluminum sheet and thick steel plate. In DSAW, an arc is initiated across two torches that are mounted on either side of the workpiece, allowing it to be welded from both sides. The objective of this research was to determine the feasibility and merits of using the DSAW process to produce seam and spot welds in thin aluminum sheet in the lap-joint configuration. The double-sided arc welding (DSAW) apparatus used in the present study was powered by a single square wave alternating current variable polarity power supply to produce an arc across two liquid cooled, plasma arc welding torches. This equipment was used to produce a series of conduction-mode DSAW seam and spot welds in 1 mm thick and 1.5 mm thick AA5182-O and AA6111 sheet in the lap-joint configuration. Metallographic analysis was used to characterize the microstructure of the welds, while microhardness and tensile tests were used to characterize the mechanical properties. Since hydrogen is easily absorbed by molten aluminum, all weld specimens must be cleaned prior to welding in order to produce high quality, pore-free welds. Although previous studies had shown that the specimens could be sufficiently cleaned by degreasing and wire brushing them prior to welding, this cleaning procedure was not found to be adequate for the specimens used in this study and a more aggressive cleaning technique was required. A number of different specimen pre-cleaning techniques were examined, and a combination of degreasing, deoxidizing, and manual wire brushing was found to produce the least amount of porosity in bead-on-plate welds produced in 1.5 mm thick AA5182-O sheet. Further reductions in porosity were accomplished by redesigning the shielding gas cup of the top Thermal Arc torch to promote more laminar gas flow and generate a more evenly distributed shielding gas plume. Using the redesigned shielding gas cup, a shielding gas flow rate of 10 lpm was found to provide good coverage of the weld pool and produce virtually pore-free welds. The feasibility of using the DSAW process to produce spot welds in 1 mm thick AA5182-O sheet in the lap-joint configuration was examined by producing a series of spot welds over a range of welding powers and weld times. Weld nuggets were produced using a welding current as low as 50 A with a cycle time of one second. However, all of the welds exhibited a pinhole at the centre of the nugget which penetrated through the entire thickness of the specimen, regardless of welding current and cycle time used. Solidification shrinkage porosity and crater cracking were also observed near the centerline of the welds. Hydrogen gas porosity and oxide tails were also observed in the welds. These defects were found to decrease the strength and quality of the spot welds made between 1 mm thick AA5182-O sheets in the lap-joint configuration. A series of welds were made to determine if the DSAW process could be used to produce seam welds in 1 mm thick AA5182-O sheet in the lap-joint configuration. Visually acceptable, crack-free welds were produced using welding powers ranging from 2.0 kW to 5.1 kW, at welding speeds between 10 mm/s and 70 mm/s. Welds produced within this range of welding conditions were found to possess excellent cathodic cleaning on both sides of the workpiece, a smooth weld bead, and a columnar-to-equiaxed grain transition. However, transverse cross-sections of the specimens revealed varying amounts of oxide entrainment in the weld metal which was seen most frequently as unbroken interface oxide sheets or tails at the fusion boundaries. Often times, small clusters of porosity were found to nucleate along the oxide tails. This suggested that there was insufficient fluid flow in the weld to disrupt the pre-existing oxide sheets at the interface between the sheets. Careful specimen pre-cleaning using a combination of degreasing, deoxidizing, and manual stainless steel wire brushing was found to reduce, but not eliminate the oxide tails. Microhardness testing revealed that the microhardness was relatively consistent across the weld metal, heat-affected zone (HAZ), and base metal. In a series of tensile-shear tests, all of the welded specimens were observed to fail in the weld metal, within 1 mm of the fusion boundary. Another series of seam welds were produced between 1 mm thick AA6111 and 1 mm thick AA5182 sheets in the lap-joint configuration to explore the nature and intensity of fluid flow in the molten weld pool responsible for breaking oxide tails. The difference in magnesium content between the two alloys produces a different microstructure and response to chemical etching, thereby revealing any effects of fluid motion in the weld pool. Relatively weak buoyancy driven fluid flow was observed when the AA6111 sheet was placed on top of the AA5182 sheet, and some minor stirring was seen between the two sheets. When the slightly less dense AA5182 sheet was placed above the AA6111 sheet, very little fluid flow was observed and the two alloys remained unmixed. Overall, the weld pool formed during DSAW was found to be very quiescent. This suggests that the normally strong Marangoni and Lorentz force induced flow seen in other arc welding processes does not occur in the double-sided arc weld pool. This leaves only a very weak buoyancy driven fluid flow which is incapable of disrupting the pre-existing oxide at the interface between the sheets immediately adjacent to the fusion zone boundary. Overall the DSAW process was found to be capable of producing visually acceptable lap-joint configuration seam welds in AA5182-O sheet over a wide range of welding speeds and welding powers, provided that the pre-existing oxide and any other surface contaminants were chemically removed prior to welding.

Graduation date: 1999

Thesis (PhD (Metallurgical Engineering))--University of South Australia, 1997

Thesis (PhD (Metallurgical Engineering))--University of South Australia, 1997

The mouse parvovirus designated MPV can infect laboratory mice and affect the humoral and cellular immune response of infected mice, reducing their value for biomedical and medical research. The development and maintenance of MPV-free mouse colonies for biomedical research is therefore essential and requires routine monitoring of the infection status of mice, using serological surveillance procedures. Recent experience in the Animal Resources Centre (ARC), a major supplier of mice to the medical research community in Australia, was that MPV infection was present but was not detectable with the serological tests that were then in routine use. This thesis reports the development of a polymerase chain reaction (PCR) assay for the detection of the MPV in the ARC mouse colonies, the genetic characteristics of the strain of MPV detected, the development of a recombinant virus protein that provided a suitable antigen for enzyme-linked immunosorbent assay (ELISA) and a Western immunoblot (WIB) assay for the detection of MPV antibodies, and use of these various assays to determine aspects of the epidemiology and pathogenicity of the infection that were critical to the eradication of virus infection and future immunological surveillance to ensure the absence of infection. The recombinant protein produced as an antigen was a biotinylated fusion protein, a truncated capsid protein of the strain of MPV detected in the ARC, and was produced using the PinpointTM vector and with expression in Escherichia coli. The protein was produced as an insoluble intracellular product within inclusion bodies and was solubilised using urea and purified. The purified protein was utilised as an antigen for ELISA and the WIB assays to detect virus antibody in infected mice. The outbreak of MPV infection in the ARC was used as an unique opportunity for assessment of the seroprevalence of MPV-1 infection in a large laboratory mouse colony and to utilise this data to determine the sampling size needed to reliably detect MPV-1 infection within such large laboratory mouse colonies. An overall seroprevalence of 16.5% was detected using the developed serological tests, but considerable variation in prevalence was detected in different mouse strains. The response to MPV infection of 4 different but common strains of mice was determined as a basis for developing appropriate surveillance procedures and the selection of appropriate sentinel animals. The effect of infection of these strains at different ages was also investigated. Virus replication was detected in tissues of all the mice strains infected (outbred ARC(s) and inbred C57BL/6JArc, BALB/c and BALB/c-Foxn1nu/Arc) as juveniles and adults, with the exception of C57BL/6JArc inoculated as adults. However, while seroconversion in mice inoculated as juveniles and adults was detected in ARC(s) and C57BL/6JArc mice, it was not detected in BALB/c mice. The high rate of seroconversion to MPV, the early and prolonged development of an immune response, and the lack of age differences in their susceptibility indicated that ARC(s) mice would provide reliable sentinels for the detection of MPV. The genomic nucleotide sequence of the ARC strain, excluding the terminal palindromic regions and the predicted amino acid sequences of the non-structural and structural proteins was determined. This strain was very similar (98-99% nucleotide identity) to the previously described MPV strains MPV-1a, MPV-1b and MPV -1c. The similarity suggested there were unlikely to be significant antigenic differences in the proteins of the ARC strain and those strains of MPV reported previously.

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed February 5, 2008) Includes bibliographical references (p. 29-31).