Miniaturization of electronic devices for enhancing their performance is associated with higher heat fluxes and cooling requirements. Surface modifi cation by texturing or coating is the most cost-effective approach to enhance the cooling of electronic devices. Experiments on carbon nanotube coated heater surfaces have shown heat transfer enhancement of 60 percent. In addition, silicon nanotubes etched on the silicon substrates have shown heat flux enhancement by as much as 120 percent. The heat flux augmentation is attributed to the combined effects of increase in the surface area due to the protruding nanotubes (nano- n eff ect), disruption of vapor lms and modi fication of the thermal/mass di ffusion boundary layers. Since the e ffects of disruption of vapor lms and modifi cation of the thermal/mass di ffusion boundary layers are similar in the above experiments, the difference in enhancement in heat transfer is the consequence of dissimilar nano- n eff ect. The thermal conductivity of carbon nanotubes is of the order of 6000 W/mK while that of silicon is 150 W/mK. However, in the experiments, carbon nanotubes have shown poor performance compared to silicon. This is the consequence of interfacial thermal resistance between the carbon nanotubes and the surrounding fluid since earlier studies have shown that there is comparatively smaller interface resistance to the heat flow from the silicon surface to the surrounding liquids. At the molecular level, atomic interactions of the coolant molecules with the solid substrate as well as their thermal-physical-chemical properties can play a vital role in the heat transfer from the nanotubes. Characterization of the e ffect of the molecular scale chemistry and structure can help to simulate the performance of a nano fin in diff erent kinds of coolants. So in this work to elucidate the eff ect of the molecular composition and structures on the interfacial thermal resistance, water, ethyl alcohol, 1-hexene, n-heptane and its isomers and chains are considered. Non equilibrium molecular dynamic simulations have been performed to compute the interfacial thermal resistance between the carbon nanotube and different coolants as well as to study the diff erent modes of heat transfer. The approach used in these simulations is based on the lumped capacitance method. This method is applicable due to the very high thermal conductivity of the carbon nanotubes, leading to orders of magnitude smaller temperature gradients within the nanotube than between the nanotube and the coolants. To perform the simulations, a single wall carbon nanotube (nano-fin) is placed at the center of the simulation domain surrounded by fluid molecules. The system is minimized and equilibrated to a certain reference temperature. Subsequently, the temperature of the nanotube is raised and the system is allowed to relax under constant energy. The heat transfer from the nano- fin to the surrounding fluid molecules is calculated as a function of time. The temperature decay rate of the nanotube is used to estimate the relaxation time constant and hence the e ffective thermal interfacial resistance between the nano-fi n and the fluid molecules. From the results it can be concluded that the interfacial thermal resistance depends upon the chemical composition, molecular structure, size of the polymer chains and the composition of their mixtures. By calculating the vibration spectra of the molecules of the fluids, it was observed that the heat transfer from the nanotube to the surrounding fluid occurs mutually via the coupling of the low frequency vibration modes.

The largest group of plant disease resistance (R) genes that share similar structures contains a predicted nucleotide-binding site (NBS) domain. NBS domains of this class of R genes show highly conserved amino acid motifs, which makes it possible to isolate resistance gene analogs (RGAs) by PCR with degenerate primers and homology searches from public databases. Multiple combinations of degenerate primers were designed from three conserved motifs (one motif was used for a subgroup-specific primer design) in the NBS regions of R genes of various plants. All combinations of primer pairs were used to amplify genomic DNA from sorghum. TIR-specific primer combinations showed no PCR amplification in sorghum. Homology searches identified many NBS-encoding sequences among the expressed or genomic molecular database entries for sorghum. Motif analysis of the sorghum NBS sequences that were identified in this study revealed eight major conserved motifs plus two additional highly conserved motifs, but no TIR-specific motifs. Phylogenetic analysis of sorghum NBS sequences showed tree topology typical of NBS-LRR genes, including clustered nodes and longbranch lengths. Eleven distinct families of NBS sequences, representing a highly diverse sample, were isolated from Sorghum bicolor. With two exceptions, sorghum RGA families appeared to be closely related in sequence to at least one R-gene cloned from other species. In addition, deduced amino acid sequences of sorghum RGAs showed strong sequence similarity to almost all known non-TIR (Toll/Interleukin 1 Receptor)- type R-genes. Mapping with sorghum RGA markers revealed one linkage group containing four out of ten randomly selected markers, suggesting non-random distribution of NBS sequences in the sorghum genome. Rice sequences homologous to sorghum NBS sequences were found from two-way BLAST searches. Some of them were shown to be orthologs, when determined by using phylogenetic approaches which combined five different evolution models and tree-building methods.

Drug efflux represents an important protection mechanism against antibiotics and environmental toxic compounds in bacteria. Efflux genes constitute from 6% to 18% of all transporters in bacterial genomes, yet their regulation, natural substrates, and physiological functions are poorly understood. Among the 20 chromosomally encoded efflux genes in Escherichia coli K-12, only the AcrAB-TolC efflux system is constitutively expressed under the ordinary laboratory growth of E. coli. To explore conditions and circumstances that trigger the expression of additional efflux genes as well as their physiological functions, I examined the expression of all 20 efflux genes under a physiologically relevant circumstance for E. coli, which is anaerobic condition in this study. I found that expression of an RND type efflux pump MdtEF is up-regulated more than 20 fold when E. coli is cultured under anaerobic conditions. Mutagenesis studies revealed that the anaerobically induced expression of mdtEF is subject to the regulation of the anaerobic global transcription factor ArcA. Direct drug efflux and tolerance assay showed that anaerobically grown E. coli cells display an increased efflux activity and enhanced drug tolerance in an MdtEF dependent manner, confirming the functional up-regulation of the efflux pump MdtEF in the anaerobic physiology of E. coli. Since the up-regulation of mdtEF by anaerobic growth occurs in the absence of antibiotics and drugs, I speculate that MdtEF has physiological functions under the anaerobic growth of E. coli. To explore this, I first compared the viability of ΔmdtEF and WT MG1655 strains and found that ΔmdtEF caused a decreased cell survival during prolonged anaerobic growth of E. coli. Interestingly, this defect became more pronounced when cells grow in the presence of 10 mM nitrate, but no defect was observed in ΔmdtEF strain when cells grow in the presence of 40 mM fumarate under the same anaerobic conditions, suggesting that MdtEF has physiological roles relevant to the anaerobic respiration of nitrate. I further found that E. coli cells harboring the deletion of mdtEF are susceptible to indole nitrosative derivatives, a class of toxic by-products formed and accumulated within E. coli when the bacterium respires nitrate under anaerobic conditions, and deletion of the genes responsible for the biosynthesis of indole, tnaAB, restores the growth defect of the ΔmdtEF strain during anaerobic respiration of nitrate. Taken together, I conclude that the multidrug efflux pump MdtEF expels the nitrosated indole derivatives out of E. coli cells under anaerobic conditions. Since the production and accumulation of nitrosyl indole derivatives is ascribed to the reactive nitrogen species elicited when E. coli consumes nitrate, I propose that the up-regulated multidrug efflux pump MdtEF functions to protect E. coli from nitrosative damage in its anaerobic ecological niches. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

No description available.

TiNi shape memory alloy is characterized by shape memory and superelastic effects which occur due to reversible martensite transformation. It has been recently found that TiNi alloy has superior dent and wear resistance compared to other conventional materials. The stress-induced martensite transformation exhibited by this alloy contributes to its dent and wear resistance. Much work is required to establish the fundamental principals governing the superelastic behavior of TiNi under wear and indentation conditions. Understanding the superelastic behavior helps to employ superelastic TiNi in applications where high impact loading is expected as in gears and bearings. In this study the superelastic behavior of shape memory alloys under reciprocating sliding wear and indentation loading conditions was investigated. The deformation behavior of superelastic Ti-Ni alloys was studied and compared to AISI 304 stainless steel. Dominant wear and deformation mechanisms were identified.

The effect of thermo-mechanical processing by deformation and annealing on the grain boundary configuration of commercially pure Ni-200 is reported in this thesis. Ni-200 is unalloyed, thus avoiding the complex effects associated with alloying elements on the formation and development of different types of grain boundaries. One step strain-recovery with strain levels in the range of 3% to 7.5% (with 1.5% intervals) and annealing temperatures in the range of 800ºC to 1000ºC (with 100ºC intervals) were used in processing. The effects of parameters such as strain level, annealing temperature, annealing time and grain growth on grain boundary configurations were studied. Using Orientation Image Microscopy (OIM) it was found that the Fsp (fraction of special grain boundaries) value of strained samples annealed in the range of 800ºC to 1000ºC began to increase after a critical length of time, after which the Fsp value increased quickly and becoming a maximum in 2~4 minutes. The length of the critical annealing time for the increase of Fsp was shorter in the material with the higher levels of strain at a constant annealing temperature. Also the critical annealing time was shorter when annealed at higher temperatures under a fixed level of strain. The Fsp value increased to 80% from an as received value of about 30% in the samples with varying strain levels. However, the Fsp values only increased from 30% to 45% in the material without strain. Due to grain boundary migration, the Fsp values increased with grain size and became a maximum during the heat treatment of the strained material. In the material without strain however even when grain growth occurred, limited improvement in Fsp values occurred showing that contribution of strain is very important to the formation of special boundaries. By varying the strain levels, annealing temperatures and times, material with high Fsp values in a wide range of grain size can be obtained. Under the present processing conditions used however, multi-cycle was not helpful to the improvement of Fsp. TEM observations indicated dislocation tangles occurred near the grain boundary of the 1x6% strained samples. These dislocation tangles decreased with time at 800˚C and were reduced considerably after 20 minutes. Thermodynamic and kinetic models were used in the calculations of twin density-grain size relationships. The results indicated that the contribution of strain is equivalent to the increase of grain boundary energy, which provided an extra driving force and improved probability of twin embryo formation.

The effect of thermo-mechanical processing by deformation and annealing on the grain boundary configuration of commercially pure Ni-200 is reported in this thesis. Ni-200 is unalloyed, thus avoiding the complex effects associated with alloying elements on the formation and development of different types of grain boundaries. One step strain-recovery with strain levels in the range of 3% to 7.5% (with 1.5% intervals) and annealing temperatures in the range of 800ºC to 1000ºC (with 100ºC intervals) were used in processing. The effects of parameters such as strain level, annealing temperature, annealing time and grain growth on grain boundary configurations were studied. Using Orientation Image Microscopy (OIM) it was found that the Fsp (fraction of special grain boundaries) value of strained samples annealed in the range of 800ºC to 1000ºC began to increase after a critical length of time, after which the Fsp value increased quickly and becoming a maximum in 2~4 minutes. The length of the critical annealing time for the increase of Fsp was shorter in the material with the higher levels of strain at a constant annealing temperature. Also the critical annealing time was shorter when annealed at higher temperatures under a fixed level of strain. The Fsp value increased to 80% from an as received value of about 30% in the samples with varying strain levels. However, the Fsp values only increased from 30% to 45% in the material without strain. Due to grain boundary migration, the Fsp values increased with grain size and became a maximum during the heat treatment of the strained material. In the material without strain however even when grain growth occurred, limited improvement in Fsp values occurred showing that contribution of strain is very important to the formation of special boundaries. By varying the strain levels, annealing temperatures and times, material with high Fsp values in a wide range of grain size can be obtained. Under the present processing conditions used however, multi-cycle was not helpful to the improvement of Fsp. TEM observations indicated dislocation tangles occurred near the grain boundary of the 1x6% strained samples. These dislocation tangles decreased with time at 800˚C and were reduced considerably after 20 minutes. Thermodynamic and kinetic models were used in the calculations of twin density-grain size relationships. The results indicated that the contribution of strain is equivalent to the increase of grain boundary energy, which provided an extra driving force and improved probability of twin embryo formation.

The ubiquitous nature of antibiotic resistance and antibiotic resistance genes (ARGs) among environmental pathogens from a variety of wastewater effluents, suggests that the aquatic environment, and specifically alternative wastewater treatment systems, may act as reservoirs for drug resistant bacteria and ARGs, thereby contributing to the widespread dissemination of antibiotic resistance. More research is necessary to contribute to our understanding of the occurrence, fate, and mobility of antibiotic resistance and ARGs among bacterial indicators of faecal contamination as well as pathogenic bacteria within Canadian wastewater treatment systems. The primary objective of this research was to determine the prevalence, fate, and potential transfer of bacterial resistance and ARGs among selected environmental pathogens exposed to alternative wastewater treatment systems, while considering the impact of treatment strategies on the expression of antibiotic resistance. A detailed analysis was initially conducted with respect to the characterization and quantification of microbial populations (including antibiotic resistant bacteria) in a variety of treatment systems and waste effluent sources. Traditional culture-based screening techniques in combination with molecular characterization (through colony or multiplex PCR), and molecular quantification using real-time quantitative PCR were utilized in order to help establish a preliminary environmental assessment of selected pathogens (Escherichia coli, Enterococcus spp., Salmonella spp.) and ARGs (tetA, blaSHV, & ampC) within a variety of wastewater treatment systems (lab-scale mesocosms, constructed wetland, constructed lagoon system, and pilot-scale biological nutrient removal (BNR) system). Overall, the level of multiple antibiotic resistance (MAR) among culturable indicator (E. coli & Enterococcus spp.) and environmental bacteria was high (reaching 100% in several instances) within different types of wastewater treatment systems and effluent sources (poultry waste effluent, municipal wastewater, aquaculture wastewater). Common antibiotic resistance profiles among E. coli isolates included simultaneous resistance to between three and five antimicrobials, whereas common MAR profiles among Enterococcus spp. isolates showed resistance to ten or more antibiotics. Real time quantitative PCR was used to determine the concentration of three bacterial pathogens; E. coli, Enterococcus faecalis, and Salmonella spp., and three ARGs; tetA, ampC, and blaSHV, within a variety of wastewater samples. Based on the results, it was concluded that high concentrations of ARGs were present in the treated effluent (10⁴- 10⁶ target gene copies/100 mL), regardless of system type (i.e. constructed lagoon, pilot-scale BNR, or constructed wetland), which may ultimately serve as a potential route for entry of ARGs and antibiotic resistant bacteria into the natural environment. Water is considered an important medium for transfer of resistance genes and resistant bacteria to the broader environment. Few studies have examined the transferability via conjugation of ARGs in E. coli and Salmonella spp. isolated from wastewater. Identification of three resistance determinants (tetA, strA, strB) conferring resistance to tetracycline and streptomycin was performed on selected multi-drug resistant Salmonella spp. and E. coli isolates. The potential for transfer of tetracycline and streptomycin resistance genes was demonstrated through broth conjugation experiments using multi-drug resistant Salmonella spp. and E. coli isolates as donors, and E. coli K12 as the recipient. Conjugation was successfully observed in 75% (9/12) of donor isolates, occurring in both Salmonella spp. and E. coli isolates. Six strains (50%) were capable of transferring their tetA, strA, and strB genes to the recipient strain, resulting in 58.5% (38/65) of total transconjugant strains acquiring all three resistance determinants. The results confirm the role of environmental bacteria (isolated from wastewater treatment utilities) as a reservoir of antibiotic resistance and ARGs, containing mobile genetic elements, which are capable of disseminating and transferring ARGs. As concerns about water quality and environmental contamination by human and agricultural effluents have increased, it has become increasingly more important to consider the prevalence and transferability of ARGs to opportunistic and human pathogens. As observed in this research, the ubiquitous nature of multi-drug resistant bacteria in water and wastewater effluents, the presence of diverse ARGs of human and veterinary health significance, as well as the transfer of resistance determinants through conjugative plasmids to recipient bacteria, suggests that environmental exposure through contact or consumption with contaminated water is probable. However, a lack of critical information still exists regarding the movement of resistance genes within and between microbial populations in the environment. In addition, the extent of human exposure to ARGs and antibiotic resistant bacteria is still not well understood, and future studies on human exposure to these resistant contaminants are necessary.

The global threat from antibiotic resistant organisms and the effect on human and animal health is now well acknowledged. One measure to control the emergence and dissemination of antibiotic resistant organisms is to monitor bacterial populations and examine the epidemiology of antibiotic resistance genes in naturally occurring bacteria. This study examines antibiotic resistant bacteria of human and animal origin and compares resistance gene transfer in the intestinal tract of animal models to that which occurs in vitro. / The study provides information about tetracycline resistance as it occurs in wild-type bacteria within the environment of the normal flora of an animal. The transfer of tetracycline resistance genes in vitro between E. coli isolates from different origins was found to be occurring at lower levels than that which occurred in vitro. The co-transfer of unselected spectinomycin, streptomycin and sulfadiazine resistance in animal models was also demonstrated. / The study has provided important information regarding the nature and epidemiology of antibiotic resistance in naturally occurring strains of E. coli and enterococci from Australia. This should form part of a larger study, which monitors commensal bacteria and collects data regarding antibiotic resistance in natural populations of bacteria. This evidence can then be used to reduce the levels of antibiotic resistance in the environment and reduce the risk to human and animal health. / Thesis (PhD)--University of South Australia, 2006.

Appendix included in back. / Errata posted on back end cover. / Bibliography: leaves 236-268. / xxii, 268, [7] leaves, [41] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A contribution to the knowledge of multidrug resistance and its role in acute leukaemia. / Thesis (Ph.D.)--University of Adelaide, Dept. of Cytogenetics and molecular genetics, 1997