Dissertations / Theses on the topic 'Stream characterisation'

Ice streams are the dominant drainage pathways of contemporary ice sheets and their location and behaviour are viewed as key controls on ice sheet stability. Identifying palaeo-ice streams is of paramount importance if we are to produce accurate reconstructions of former ice sheets and examine their critical role in the oceanclimate system. Many workers have invoked palaeo-ice streams from a variety of former ice sheets, despite a limited understanding of their glacial geomorphology. This thesis addresses the problem by predicting several diagnostic geomorphological criteria indicative of ice stream activity. These are developed objectively from the known characteristics of contemporary ice streams and can be summarised as: large flow-set dimensions (>20 km wide and >150 km long), highly convergent flow patterns, highly attenuated subglacial bedforms (length:width >10: 1), Boothia-type dispersal plumes, abrupt lateral margins «2 km), ice stream marginal moraines, evidence of pervasively deformed till, and submarine sediment accumulations (marine-terminating ice streams only). Collectively, the criteria are used to construct conceptual landsystems of palaeo-ice stream tracks. Using satellite imagery and aerial photography to map glacial geomorphology, identification of the criteria is used to validate the location of a previously hypothesised ice stream and identify a hitherto undetected palaeo-ice stream from the former Laurentide Ice Sheet. Implications for ice stream basal processes are explored and their ice sheet-wide significance is assessed. On Victoria Island (Arctic Canada) five of the geomorphological criteria are identified and the extent of the marine-based M'Clintock Channel Ice Stream is reconstructed at 720 km in length and 140 km in width. The ice stream (operating between 10,400 and 10,000 yr BP) was located within a broad topographic trough, but internal glaciological processes, rather than properties of the bed controlled the margin locations. It eroded into pre-existing unconsolidated sediments and left a spectacular pattern of subglacially-produced landforms, recording a snapshot view of the bed prior to ice stream shut-down. Sediment availability appears critical to its functioning (deformable bed?) and the debris flux of the ice stream is inferred to have been high. Frictional shut-down occurred once down-cutting through sediments reached hard bedrock close to the terminus. The presence of four of the geomorphological criteria are used to identify a terrestrial ice stream which drained the Keewatin Sector of the Laurentide Ice Sheet between ca. 10,000 and 8,500 yr BP. Its size is reconstructed at over 450 km in length and 140 km in width, and it left behind a subglacial bedform pattern consisting of highly attenuated drumlins (length:width ratios up to 48: 1) displaying exceptional parallel conformity. This represents an isochronous bedform pattern and variations in lineament elongation ratio are thought to be a useful proxy for ice velocity. Highest elongation ratios occur immediately downstream of a topographic step where the ice stream entered a sedimentary basin. It is inferred that the ice stream was triggered by climatic warming which altered the ice sheet configuration and the thermal state of the bed. A switch from cold to warm-based conditions probably triggered rapid basal sliding. The ice stream (and a tributary) shut down when it ran out of ice, causing widespread thinning of the ice sheet and subsequent deglaciation. These ice streams denote considerable ice sheet instability over both hard and soft (deformable) beds and emphasise the enormous effects that ice streams had in controlling the deglaciation of the Laurentide Ice Sheet.

In this thesis the effect of uniform and profiled (non-uniform) steady flows on a scale-model tidal stream turbine (0.5m diameter) are experimentally investigated using the University of Liverpool high-speed recirculating water-channel. The power and thrust coefficients of the turbine with numbers of blades between two and six and various blade-pitch-angles are measured in uniform flow with low levels of turbulence at velocities ranging from 0.45m/s to 1.34m/s. With a three-bladed turbine at optimum blade-pitch-angle the power and thrust coefficients are compared in three different flow conditions of uniform flow with low turbulence intensity (2%), uniform flow with high turbulence intensity (5%) and non-uniform flow with high turbulence intensity (5%). Using an Acoustic Doppler Velocimeter (ADV) measurements of three-dimensional velocities are taken, initially, around the three-bladed turbine with optimum blade-pitch-angle. The velocities at five different heights and up to 7D downstream are probed where the upstream velocity is uniform with low turbulence levels and mean upstream velocity of 0.9m/s. Further ADV measurements are taken downstream of the three-bladed turbine through a horizontal centre-plane at lower velocities of 0.45m/s and 0.68m/s to probe the effect of Reynolds number on the turbine's wake. In addition wake measurements are taken downstream of the two-bladed turbine with optimum and non-optimum blade-pitch-angles to study the effect of differing tip-speed-ratios, thrust and power coefficients. Also the wake of the turbine support structure without blades is investigated. In a flow with high turbulence and mean velocity of 0.9m/s the wake of the three-bladed turbine is studied through a centre-plane equal to the turbine hub height. Further in a profiled flow, representative of a 1/5th velocity power law and upstream integral average velocity of 0.82m/s (over the turbine's swept area), characterisation of the flow downstream of the three-bladed turbine with optimum blade-pitch-angle is taken at five depths up to 5D downstream. These velocities are then compared in detail to those in uniform flow. Finally the ADV technique is used extensively throughout this thesis and, indeed, in most studies concerned with tidal turbine wakes. As issues regarding certain aspects of the ADV came to light during this study, the robustness of this technique is investigated by using two different ADV probe orientations and a comparison to 1D Laser Doppler Velocimetry is made.

North Pakistan represents a highly favourable area for a variety of mineral deposit types, including arc-related porphyry Cu, Au and Mo and arc and backarc epithermal precious metal deposits (Sweatman et al., 1995; PMDC, 2001). However, few deposits have been discovered in the area, mainly due to its remote nature and inaccessibility, and because of a lack of exploration tools for high altitude terrains. From stream sediment sampling campaigns by local and international organizations, including a large dataset provided by the Pakistan Mineral Development Corporation (PMDC), a significant amount of geochemical data now exists for the region. This data has been incorporated into an Arc-GIS 9.2 database, along with stream catchment and geological information, and detail of all known areas of mineralisation. From this, spatial catchment maps together with multi-element geochemical associations have been studied to delineate areas showing anomalous values for Au and base metals. The two most prospective areas were found to be the Shyok Suture Zone and northern Kohistan, with the dominant control on mineralisation being structural rather than lithological. These areas were targeted for detailed stream sediment sampling and mineralogical and geochemical analysis. From studies of Au and Au pathfinder elements in different size fractions of the stream sediments and heavy mineral concentrates (HMC), the catchments of Teru, Asheriat and Pakora (in order of decreasing rank) were identified as most prospective. Morphological and geochemical analyses of native Au grains from panned concentrates has given an indication of proximity to bedrock source (<10 km) and the possible styles of mineralisation in these catchments; porphyry Cu-type in Asheriat and Pb-Sb quartz veins in Teru and Pakora. Automated mineralogical analysis of the stream sediments (<180 µm fraction) and HMC (<180 µm), using a QEMSCANÒ system, confirmed this interpretation. The effectiveness of the developed methodologies for exploration in remote and high altitude terrains of North Pakistan is discussed, and recommendations made for future exploration.

The mechanisms underlying stretch-induced signalling in the human myometrium are poorly understood. Previous work in the group has demonstrated that in vitro stretch of human myometrial cells leads to increased expression of the pro-labour factors COX-2 and IL-8 via activation of the ERK-1/2 MAPK cascade, however the identities of components upstream in this pathway have yet to be elucidated. I over expressed constitutively active Ras in human myometrial cells, leading to increased ERK-1/2 phosphorylation and elevated COX-2 and IL-8 mRNA expression. I then inhibited Ras using both the chemical inhibitor manumycin A and transfection with dominant-negative mutant Ras. Each resulted in decreased ERK-1/2 phosphorylation and COX-2 expression in response to stretch. I performed immunoprecipitations to investigate which factors associated with Ras and found that stretch increased its association with SOS-1 and Grb-2. I then confirmed that Grb-2 was essential for the propagation of the stretch signal to ERK-1/2 by using siRNA to silence Grb- 2 and found that this resulted in decreased phosphorylation of ERK-1/2 and COX-2 and IL-8 protein synthesis. Silencing of SOS-1 decreased COX-2 protein expression but had little effect on ERK-1/2 phosphorylation. I then investigated the role of FAK, a constituent of stretch sensing focal adhesions, in the transduction of the stretch signal. First I used the inhibitors Y-27632 and PF-573,228, however neither inhibited the stretch-induced increase in ERK-1/2 phosphorylation or COX-2 and IL-8 mRNA expression In contrast, using siRNA to silence FAK expression reduced both the stretch-induced increase in ERK-1/2 phosphorylation and COX-2 and IL-8 protein synthesis. Moreover, transfection with dominant-negative FRNK reduced ERK-1 phosphorylation and COX-2 protein synthesis. Cells were also treated with the Src family kinase inhibitor PP-2 resulting in a decrease in stretch-induced ERK-1/2 phosphorylation and COX-2 protein synthesis. These data suggest that Ras, Grb-2 and FAK all act upstream of ERK-1/2 to mediate stretchinduced up-regulation of COX-2 and IL-8 in human myometrial cells, the role of SOS-1 is less clear, but also appears to be involved in stretch-induced expression of COX-2.

Cette thèse s'inscrit dans un ensemble de travaux ayant pour objectif d'étudier les matériels des sapeurs-pompiers et l'effet de leurs actions de lance sur leur environnement. Ce domaine d'étude est encore nouveau avec une première étape essentielle pour les travaux présentés dans ce manuscrit effectué en 2016 avec l'approche performantielle. Nous proposons dans les trois premiers chapitres une étude comparative entre un nouveau matériel de lutte contre l'incendie, la lance diphasique, et les lances utilisées actuellement. Des expérimentations ont permis de déterminer les caractéristiques géométriques mais également l'évolution en fonction de la distance de la taille et de la vitesse des gouttes constituant le jet. Les deux derniers chapitres complètent cette approche par une étude à échelle intermédiaire des phénomènes d'interaction entre un spray et une couche de fumée en utilisant une approche couplée expérimentation/modélisation. Les essais en maquette servent à vérifier la pertinence des simulations numériques du logiciel Fire Dynamics Simulator. L'approche numérique permet de quantifier les échanges thermiques entre le jet et le milieu environnant. Une perspective de ses travaux est l'utilisation des bilans énergétiques, qui ont été établi, pour chercher à optimiser le mode d'action des sapeurs-pompiers
This thesis is part of work that aims to study firefighters' equipment and the effect of their fire hose actions on their environment. This field of study is still new with a first essential step for the work presented in this manuscript carried out in 2016 with the performantial approach. In the first three chapters, we propose a comparative study between a new firefighting equipment, the twin-fluid hose, and the currently used hoses. Experiments have made it possible to determine the geometric characteristics and also the evolution of the size and speed of the drops making up the jet as a function of distance. The last two chapters complete this approach with an intermediate-scale study of the interaction phenomena between a spray and a smoke layer using a coupled experimental/modelling approach. The model tests will be used to verify the relevance of the numerical simulations of the Fire Dynamics Simulator software. The numerical approach makes it possible to quantify the heat exchange between the spray and the surrounding environment. One perspective of this work is the use of energy balances, which have been established, to seek to optimise the mode of action of firefighters

Sugarcane bacilliform virus (SCBV) is an economically important pathogen of sugarcane in Australia which limits access to foreign sugarcane germplasm. Although SCBV is present in the major cane growing regions worldwide, very little is known about its variability, virulence and the yield losses resulting from infection. The limited information on SCBV has resulted in quarantine measures being introduced to protect the Australian sugarcane industry, with a major consequence being restricted access to imported sugarcane germplasm for breeding programs. Foreign sugarcane germplasm plays an important role in breeding of new commercial varieties for the Australian sugar industry and is essential for the long term productivity, profitability and sustainability of the sugar industry. This study was aimed at characterising Australian isolates of SCBV to enable the development of reliable and robust molecular and/or antibody-based diagnostic tests which could be used to not only assess the impact of SCBV on the Australian sugarcane industry, but could also be used to screen imported sugarcane germplasm for the virus. SCBV virions (SCBV-IM) were purified from the sugarcane accession "Ireng Maleng" and the dsDNA genome was cloned and sequenced. The genome of SCBV-IM comprised 7687 bp with an organisation typical of other badnaviruses. When the entire nucleotide sequence of SCBV-IM was compared to that of the Moroccan SCBV isolate (SCBV-Mo), less than 75% similarity was present. Within the coding regions, ORF I, ORF II and ORF III had 83%, 71% and 73% nucleotide similarity to SCBV-Mo, respectively. At the amino acid level, ORFs I, II and III from SCBV-IM showed 91%, 84% and 85% similarity to the equivalent regions in SCBV-Mo, respectively. To further investigate the level of sequence variability within Australian SCBV isolates, virions were purified from three further sugarcane accessions and a 220 bp fragment of the reverse transcriptase-coding region was amplified. Five clones from each sub-population were selected and sequenced. Analysis of these sequences revealed considerable variability in the virus population with variability within one plant as great as it was between isolates. However, since the use of specific primers could also be selecting for a sub-population of SCBV sequences, it was possible that the variability may actually be greater than that reported. These results indicated that SCBV isolates are complex and variable and may represent a continuum of genetic variability. High molecular weight DNA species larger than the SCBV 7.6 kbp unit-length genome were found in DNA extracted from purified SCBV-IM virions. We confirmed that these high molecular weight nucleic acids were virus-specific and open circular in conformation. Using field inversion gel electrophoresis (FIGE), the SCBV-IM DNA was separated into four discrete bands with sizes ranging from between 1 to 4 genome copies. The DNA was shown to comprise overlapped individual genome-length molecules and not covalently-bonded continuous DNA strands. We presume that these DNA molecules are concatamers formed during replication as a result of a terminal overlap on the sense strand. The presence of these concatamers within virions may explain the observation of particles with lengths corresponding to one, two or three times the modal length of 130 nm. Four SCBV-infected Saccharum officinarum plants were examined for the presence of integrated viral DNA. Southern blot analysis of viral DNA and total DNA extracted from the same plant source were compared with, or without, restriction digestion. The resulting restriction patterns from viral and total DNA were almost identical suggesting that there were no integrated SCBV sequences in the sugarcane cultivars tested. Although larger-than-single-genome copy bands were detected in both the viral and the total DNA samples, this was probably due to the presence of genomic concatamers. SCBV integration studies using Southern analyses were further complicated by high sequence variability which precluded the restriction digestion of all viral DNA species. As such, some of the SCBV DNA species remain as concatamers which appear as larger-than-unit-length SCBV products. An antiserum derived from a mixture of purified SCBV isolates has been used routinely in the past to screen for SCBV infection, but the heterogeneity reported for badnaviruses has cast doubt on the ability of this antiserum to detect all SCBV isolates. We attempted to determine whether antiserum generated against proteins other than the viral capsid could be used to detect SCBV infections, thus improving the reliability and robustness of SCBV diagnosis. The complete coding regions of SCBV ORF I and ORF II were bacterially expressed and used as antigens for antiserum production. Both ORF I and II proteins were found to be highly immunogenic and generated high-titre antisera, designated AS-I and AS-II, respectively. The diagnostic utility of both antisera to detect SCBV in six different infected sugarcane plants was tested using both immunosorbent electron microscopy (ISEM) and western blots. The currently used SCBV antiserum (AS-V), generated against a mixture of purified SCBV isolates, was included for comparison. In western analyses, neither AS-I nor AS-V was able to conclusively detect SCBV in any of the six infected plants due to reactivity with numerous non-specific proteins. In contrast, AS-II reacted specifically with a protein of the expected size (~13.5 kDa) in 2/6 infected plants. When compared using ISEM, AS-V, AS-I and AS-II trapped virions from 6/6, 6/6 and 2/6 SCBV-infected plants, respectively. However, the number of virions trapped using AS-V was approximately 30-fold more than that trapped using either AS-I or AS-II. These results highlight the variability between SCBV isolates and suggest that ISEM with antisera raised against mixtures of viral proteins may be a useful tool for the detection of viral isolates.

Sugarcane bacilliform virus (SCBV) is an economically important pathogen of sugarcane in Australia which limits access to foreign sugarcane germplasm. Although SCBV is present in the major cane growing regions worldwide, very little is known about its variability, virulence and the yield losses resulting from infection. The limited information on SCBV has resulted in quarantine measures being introduced to protect the Australian sugarcane industry, with a major consequence being restricted access to imported sugarcane germplasm for breeding programs. Foreign sugarcane germplasm plays an important role in breeding of new commercial varieties for the Australian sugar industry and is essential for the long term productivity, profitability and sustainability of the sugar industry. This study was aimed at characterising Australian isolates of SCBV to enable the development of reliable and robust molecular and/or antibody-based diagnostic tests which could be used to not only assess the impact of SCBV on the Australian sugarcane industry, but could also be used to screen imported sugarcane germplasm for the virus. SCBV virions (SCBV-IM) were purified from the sugarcane accession "Ireng Maleng" and the dsDNA genome was cloned and sequenced. The genome of SCBV-IM comprised 7687 bp with an organisation typical of other badnaviruses. When the entire nucleotide sequence of SCBV-IM was compared to that of the Moroccan SCBV isolate (SCBV-Mo), less than 75% similarity was present. Within the coding regions, ORF I, ORF II and ORF III had 83%, 71% and 73% nucleotide similarity to SCBV-Mo, respectively. At the amino acid level, ORFs I, II and III from SCBV-IM showed 91%, 84% and 85% similarity to the equivalent regions in SCBV-Mo, respectively. To further investigate the level of sequence variability within Australian SCBV isolates, virions were purified from three further sugarcane accessions and a 220 bp fragment of the reverse transcriptase-coding region was amplified. Five clones from each sub-population were selected and sequenced. Analysis of these sequences revealed considerable variability in the virus population with variability within one plant as great as it was between isolates. However, since the use of specific primers could also be selecting for a sub-population of SCBV sequences, it was possible that the variability may actually be greater than that reported. These results indicated that SCBV isolates are complex and variable and may represent a continuum of genetic variability. High molecular weight DNA species larger than the SCBV 7.6 kbp unit-length genome were found in DNA extracted from purified SCBV-IM virions. We confirmed that these high molecular weight nucleic acids were virus-specific and open circular in conformation. Using field inversion gel electrophoresis (FIGE), the SCBV-IM DNA was separated into four discrete bands with sizes ranging from between 1 to 4 genome copies. The DNA was shown to comprise overlapped individual genome-length molecules and not covalently-bonded continuous DNA strands. We presume that these DNA molecules are concatamers formed during replication as a result of a terminal overlap on the sense strand. The presence of these concatamers within virions may explain the observation of particles with lengths corresponding to one, two or three times the modal length of 130 nm. Four SCBV-infected Saccharum officinarum plants were examined for the presence of integrated viral DNA. Southern blot analysis of viral DNA and total DNA extracted from the same plant source were compared with, or without, restriction digestion. The resulting restriction patterns from viral and total DNA were almost identical suggesting that there were no integrated SCBV sequences in the sugarcane cultivars tested. Although larger-than-single-genome copy bands were detected in both the viral and the total DNA samples, this was probably due to the presence of genomic concatamers. SCBV integration studies using Southern analyses were further complicated by high sequence variability which precluded the restriction digestion of all viral DNA species. As such, some of the SCBV DNA species remain as concatamers which appear as larger-than-unit-length SCBV products. An antiserum derived from a mixture of purified SCBV isolates has been used routinely in the past to screen for SCBV infection, but the heterogeneity reported for badnaviruses has cast doubt on the ability of this antiserum to detect all SCBV isolates. We attempted to determine whether antiserum generated against proteins other than the viral capsid could be used to detect SCBV infections, thus improving the reliability and robustness of SCBV diagnosis. The complete coding regions of SCBV ORF I and ORF II were bacterially expressed and used as antigens for antiserum production. Both ORF I and II proteins were found to be highly immunogenic and generated high-titre antisera, designated AS-I and AS-II, respectively. The diagnostic utility of both antisera to detect SCBV in six different infected sugarcane plants was tested using both immunosorbent electron microscopy (ISEM) and western blots. The currently used SCBV antiserum (AS-V), generated against a mixture of purified SCBV isolates, was included for comparison. In western analyses, neither AS-I nor AS-V was able to conclusively detect SCBV in any of the six infected plants due to reactivity with numerous non-specific proteins. In contrast, AS-II reacted specifically with a protein of the expected size (~13.5 kDa) in 2/6 infected plants. When compared using ISEM, AS-V, AS-I and AS-II trapped virions from 6/6, 6/6 and 2/6 SCBV-infected plants, respectively. However, the number of virions trapped using AS-V was approximately 30-fold more than that trapped using either AS-I or AS-II. These results highlight the variability between SCBV isolates and suggest that ISEM with antisera raised against mixtures of viral proteins may be a useful tool for the detection of viral isolates.

Thesis (PhD (Physics))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: Ultrafast Electron Diffraction (UED) is a rapidly maturing field which allows investigation of the evolution of atomic arrangement in solids on timescales comparable to the vibrational period of their constituent atoms (~10-13 s). The technique is an amalgamation of conventional high energy electron diffraction methods and pump-probe spectroscopy with femtosecond (1 fs = 10-15 s) laser pulses. Ultrafast pulsed electron sources generally suffer from limitations on the attainable electron number per pulse (brightness) due to Coulomb repulsion among the electrons. In this dissertation, the design and construction of a compact UED source capable of delivering sub-300 fs electron pulses suitable for diffraction experiments and containing about 5000 electrons per shot is described. The setup has been characterised by measurement of the transverse beam size and angular spread, and through recording and analyzing an electron diffraction pattern from a titanium foil. Measurement of the temporal duration of fs electron pulses is not trivial, and a specialised compact streak camera operating in accumulation mode has been developed as part of this study. A sub-200 fs temporal resolution has been achieved, and the dependence of temporal duration on electron number per pulse was investigated for the current UED source. The observed trends correlate well with detailed electron bunch simulations. In order to investigate ultrafast processes on samples that cannot be probed repeatedly, it becomes necessary to significantly increase the brightness of current state of the art compact sources such as the one constructed in the present study. UED sources employing electron pulse compression techniques offer this possibility. Traditional pulse compression schemes based on RF cavities, while simple in principle, pose significant technical challenges in their realisation. The current thesis describes two novel UED pulse compression methods developed by the author: achromatic reflectron compression and pulsed cavity compression. Both concepts are expected to be easier to realise than conventional RF compression. Detailed simulations predict that such sources can attain a brightness improvement of more than one order of magnitude over compact sources that do not employ compression techniques. In addition, such sources show much promise for the attainment of pulse durations in the sub-100 fs range.
AFRIKAANSE OPSOMMING: Ultra vinnige elektron diffraksie is ‘n meettegniek wat tans in die proses is om vinnige ontwikkeling te ondergaan. Die tegniek het ten doel om strukturele omsettingsprosesse op ‘n lengteskaal van atoombindings en ‘n tydskaal van die vibrasie periode van atome in materie, ongeveer 10-13 s, te ondersoek. Dit word bewerkstellig deur die spasieresolusievermoë van gewone hoë energie elektron diffraksie met die tydresolusievermoë van femtosekonde (1 fs = 10-15 s) laserspektroskopie te kombineer. Die aantal elektrone per puls (intensiteit) van ultravinnige gepulsde elektronbronne word beperk deur die Coulomb afstootingskragte tussen die elektrone. Hierdie dissertasie beskryf die ontwerp en konstruksie van ‘n kompakte ultravinnige elektron bron. Die elektronpulse wat geproduseer word bevat tot 5000 elektrone per puls met ‘n tyd durasie van minder as 300 fs, en is geskik vir diffraksie eksperimente. Die aparaat is gekarakteriseer deur die volgende metings: elektronpulsdiameter, straaldivergensie, en ‘n titaan foelie se statiese diffraksie patroon. Dit is nie triviaal om die durasie van femtosekonde elektronpulse te meet nie, en n spesiale kompakte akkumulerende “streak camera” is vir die doeleindes van hierdie projek onwikkel. Die tydresolusie van hierdie “streak camera” is beter as 200 fs, en die afhanklikheid van die pulsdurasie wat deur die ultravinnige elektron bron geproduseer word as n funksie van die elektrongetal per puls is met behulp van hierdie toestel bepaal. Die resultate klop redelik goed met gedetaileerde simulasies van die elektron puls dinamika. Die karakterisasie van monsters wat nie herhaaldelik gemeet kan word nie vereis verkieslik ‘n nog hoër pulsintensiteit as wat met huidige bronne bereik kan word. ‘N verdere doelstelling is dus om ultravinnige elektron bronne te ontwikkel wat pulse met meer elektrone per puls kan genereer. Dit kan bewerkstellig word deur bronne wat van elektron puls kompressie tegnieke gebruik maak. Die tradisionele manier waarop dít gedoen word is deur middel van n kontinu gedrewe radio frekwensie holte. Hierdie metode gaan egter gepaard met aanmerklik hoë tegniese uitdagings. Om hierdie rede het die outeur twee alternatiewe puls kompressie konsepte ontwikkel: akromatiese reflektron kompressie and gepulsde holte kompressie. Albei konsepte sal waarskeinlik makliker wees om te realiseer as die tradisionele radio frekwensie kompressie, en is deur middel van gedetaileerde simulasies geverifiseer. Hierdie simulasies voorspel dat die intensiteit van genoemde bronne met ten minste n grooteorde meer kan wees as wat tans met kompakte ultravinnige elektron bronne moontlik is. Verder blyk dit dat sulke bronne n pulsdurasie van minder as 100 fs kan bereik.

Residual stresses are the stresses which are present within a component without any external load. They can be introduced through any number of manufacturing processes and in-service conditions, meaning that they are almost ubiquitous in engineering components. The characterisation of residual stress is an important field of research particularly in an engineering context since the effects of residual stress sum with the loads. As a result, the performance of a component can be greatly enhanced, or significantly reduced, by the presence of residual stress depending on the sign of the stress and the applied load. In this EngD thesis the focus has been on the development of residual stress through the manufacturing processes of aero-engine forgings, specifically the turbine disc. The forgings studied were sub-scale geometries of the disc, forged from the nickel-base superalloy RR1000. The overall aim of this work is to improve the understanding of the residual stress generation and relaxation through implementation of advanced experimental characterisation techniques, with a view to improving current stress predicting process modelling capabilities. With this in mind the work has focussed on the use of neutron diffraction and the contour method to characterise residual stress experimentally, while residual stress predictions have been made using finite element modelling. The findings of this research indicated that very large residual stresses were generated as a result of the quenching process, and that these stresses were then relaxed and redistributed by ageing heat treatments and material removal by machining. The results obtained through the two experimental techniques exhibited very strong agreement, indicated a robust experimental process. Comparisons to the finite element predictions highlighted some issues with the current model; in particular it was found that the simulation of quenching could be improved by better definition of the heat transfer at the surface. Furthermore, the level of stress relaxation during ageing was consistently over predicted in the model. This result is thought to be the result of an over-prediction of the level primary creep in the alloy. Subsequent studies will investigate this behaviour further using the newly developed in-situ heat treatment capabilities which have developed as part of this research.

This study developed a GC-MS method for the simultaneous detection of piperazines and congeners in street samples of amphetamine type stimulants. This research investigated the clandestine routes of synthesis and chemical profiles of phenylpiperazines, represented by 1- (4-fluorophenyl)piperazine (4-FPP) and 1-(3-trifluoromethylphenyl)piperazine (3-TFMPP). These drugs are part of the increasingly prevalent illicit new psychoactive substances. The presence of (2, 3, 4) FPP and (2, 3, 4) TFMPP positional isomers has been identified by other researchers as a limitation due to their similar chemical profiles. The method was optimized and confirmed as compliant with the International Conference on Harmonisation and the Center for Drug Evaluation and Research guidelines on validation. 4- FPP and 3-TFMPP were synthesised using potential routes for clandestine laboratories. Simple extraction and analysis of 11 street samples was conducted using the method developed. Furthermore, the stability of 22 drugs during analysis was investigated. Limits of detection were in the range 5 – 1.95ng/mL free base on column. The synthesised samples were identified as 4-FPP and 3-TFMPP. Several impurities were observed in the synthesised samples, which were identified and categorised as residual reactants, isomers of 4-FPP and of 3-TFMPP and by-products of synthesis. The percentage yields of the synthesised samples obtained were up to 82.4% 4-FPP and 78.7% 3-TFMPP. The street samples were found to contain MDMA, 3-TFMPP, BZP, caffeine, ephedrine and other impurities. The analytical method simultaneously separates 19 of the most common drugs found in piperazine samples and achieves for the first time the GC-MS separation of (i) 2-FPP, 3-FPP and 4-FPP and (ii) 2-TFMPP, 3-TFMPP and 4-TFMPP at the same time from a sample matrix containing all the 19 compounds. This method provides operational laboratories with a more effective method for the chemical characterisation of street samples of piperazines and also provides novel stability data.

This study developed a GC-MS method for the simultaneous detection of piperazines and congeners in street samples of amphetamine type stimulants. This research investigated the clandestine routes of synthesis and chemical profiles of phenylpiperazines, represented by 1- (4-fluorophenyl)piperazine (4-FPP) and 1-(3-trifluoromethylphenyl)piperazine (3-TFMPP). These drugs are part of the increasingly prevalent illicit new psychoactive substances. The presence of (2, 3, 4) FPP and (2, 3, 4) TFMPP positional isomers has been identified by other researchers as a limitation due to their similar chemical profiles. The method was optimized and confirmed as compliant with the International Conference on Harmonisation and the Center for Drug Evaluation and Research guidelines on validation. 4- FPP and 3-TFMPP were synthesised using potential routes for clandestine laboratories. Simple extraction and analysis of 11 street samples was conducted using the method developed. Furthermore, the stability of 22 drugs during analysis was investigated. Limits of detection were in the range 5 – 1.95ng/mL free base on column. The synthesised samples were identified as 4-FPP and 3-TFMPP. Several impurities were observed in the synthesised samples, which were identified and categorised as residual reactants, isomers of 4-FPP and of 3-TFMPP and by-products of synthesis. The percentage yields of the synthesised samples obtained were up to 82.4% 4-FPP and 78.7% 3-TFMPP. The street samples were found to contain MDMA, 3-TFMPP, BZP, caffeine, ephedrine and other impurities. The analytical method simultaneously separates 19 of the most common drugs found in piperazine samples and achieves for the first time the GC-MS separation of (i) 2-FPP, 3-FPP and 4-FPP and (ii) 2-TFMPP, 3-TFMPP and 4-TFMPP at the same time from a sample matrix containing all the 19 compounds. This method provides operational laboratories with a more effective method for the chemical characterisation of street samples of piperazines and also provides novel stability data.

The present work was produced as part of the MUZIC consortium, a collaboration between a multi-university team from the UK and industrial partners working on the field of nuclear energy, fabrication of alloys and nuclear research. The aim of the project is to establish a multidiscipline mechanistic understanding of the corrosion and breakaway processes of zirconium alloys used as fuel cladding materials in the nuclear industry. A better understanding of the corrosion mechanism of zirconium alloys will not only aid the development of better performing alloys, but will also allow more accurate models to be developed to reliably predict the service life of existing alloys. This could lead to higher burn-up, increase of energy production and reduction of nuclear waste produced.This work seeks to provide a better understanding of the role of residual stresses in the oxide, which are produced during oxidation due to high Pilling-Bedworth ratio and their impact on oxide phase transformation and oxidation kinetics by employing high energy synchrotron X-ray diffraction techniques. This is achieved by observing how stresses change as oxide growth approaches and passes through transition of the corrosion kinetics, their evolution across the oxide thickness, in situ characterising stresses and phase growth early in oxidation process and how stress changes can affect corrosion properties.It was found that relatively high compressive stresses in the two oxide crystal structures are present. The stresses relax with time up to moments before transition where a possible threshold stress magnitude is reached to aid an extensive tetragonal to monoclinic phase transformation. This generalised tetragonal to monoclinic transformation is believed to produce highly stressed monoclinic crystal structure grains and cause defects in the oxide. The above observation is further supported by a decrease of the tetragonal zirconia content. This is the moment that the oxide looses its protective character and a transition of the corrosion kinetics occurs. By comparing different materials it was observed that the minimum magnitude of the tetragonal phase is lower in better performing alloys while the tetragonal content is some cases was relatively low. It is suggested that the amount of the tetragonal phase, in the oxide layer, is not as important as the rate of it transforming into monoclinic. The extent of tetragonal to monoclinic transformation, that introduces defects in the oxide, defines how protective an oxide layer is. The present work provides a contribution to the available knowledge of the importance of residual stresses in the oxide layer and metal substrate of zirconium alloys and how they can affect corrosion rates or act as a precursor to the corrosion transition.

This research has investigated the conditions necessary for atmospheric-induced stress corrosion cracking to occur in material taken from an intermediate level nuclear waste storage container by means of experiments in a humidity chamber. It has also characterised the residual stresses associated with the container welds by modelling and measurement. Based on the work conducted in this research, the major findings can be summarised as follows:• Deliquescence of salt particles is dependent on relative humidity but independent of the quantity of salt present.• The time to initiate cracking may be sensitive to temperature, getting longer as the temperature decreases, but the timeframe of work as not long enough to establish this conclusively.• AISCC can occur at a stress (residual or applied) of 400MPa (0.2% strain) or more if the other necessary conditions are present. While AISCC was not observed when no stress was present, the threshold of stress below which AISCC will definitely not occur has not been determined in this work.

This practice-led novel and exegesis explores the characterisation of an anecdotal 1980s Wall Street junket on Queensland's Gold Coast in terms of Foucauldian power and discourse. Problematising the subject's decentred ontology implied by the life sciences, Foucault's theories are adapted to illustrate characterisation as a site of discursive interpellation and contest in neoliberal fiction. Decentred, the subject as a scape of discursive practice reveals the struggle between 'personal discourse' and the organisational power of corporations. This has implications not only for character intentionality and artificial subjects, but provides a framework where humanism and organisational agency can be approached as an ontology of the self.

The interest in studying droplet related phenomena has been increasing over the last decades. In the fluid dispensing equipment industry, a major problem is to minimise droplet diameter and to eject droplets in a controlled manner with a low-cost device. Micro-droplet generation has gained its popularity for its multiple applications, such as biotechnology, manufacturing engineering, and fuel dispensing. Taking all this into account, a new low-cost droplet stream generator was designed and fabricated. The material used to manufacture the stream droplet generator structure was PLA, since it is a 3D printable material, which allowed to minimise the device cost. This structure has three separated components: lid, fluid chamber, and pinhole holder. In order to simplify the disturbance mechanism, it was decided that the disruption waves should be applied directly to the fluid. To achieve that, a piezoelectric cell that vibrates through the variation of waveform parameters was placed above the liquid chamber, creating disturbances directly onto the liquid surface in a parallel direction, making this device a push mode generator. The interchangeable nozzle used was a round stainlesssteel high precision optical pinhole with three different sizes: 100 µm, 150 µm, and 200 µm. Jet attribute properties (droplet diameter, droplet velocity, and distance between droplets) were measured as the different conditions changed (piezoelectric diaphragm frequency, outlet pressure, and nozzle size). The present work studied the spray characteristics for water, jet fuel and a jet fuel and biofuel mixture, and different monodisperse regimes were found. A full characterisation of them is presented and discussed in detail. It was found that the range of droplet diameter for a pinhole size of 200 µm that can be used for all three fluids is 401 µm to 472 µm and a range of velocity of 1.24 m/s to 2.48m/s, while for a pinhole size of 150 µm the droplet diameter range that can be obtained is 287 µm to 340 µm and a range of velocity of 2.04 m/s to 4.38 m/s for all three fluids. For a pinhole size of 100 µm the droplet diameter range for all three fluids is 206 µm to 258 µm and the velocity range is 2.36 m/s to 5.99 m/s. It was found that both droplet diameter and spacing decrease with the increase of inlet flow rate and frequency, and the most important property in the jet formation is the nozzle size. The jet velocity is also highly influenced by the flow rate and nozzle size. When compared, the three fluids behave in a different manner, resulting in different droplet diameter and velocity values. This can be explained by the fluids properties, where the mixture of jet fuel and biofuel presents higher viscosity than the other two fluids.
O interesse em estudar fenómenos relacionados com as gotas tem vindo a aumentar nas últimas décadas. Na indústria de equipamentos de ejeção de fluidos, um grande problema é minimizar o diâmetro das gotas e ejetá-las de forma controlada utilizando um dispositivo de baixo custo. A geração de micro-gotas ganhou popularidade pelas suas múltiplas aplicações, como biotecnologia, engenharia de fabricação e ejeção de combustível. Tendo tudo isto em conta, um novo gerador de gotas contínuas, de baixo custo, foi projetado e fabricado. PLA foi o material usado para fabricar a estrutura do gerador de gotas dado que é um material de impressão 3D, o que permite minimizar o custo do dispositivo. Esta estrutura tem três componentes separados: tampa da célula piezoelétrica, câmara de fluido e suporte do pinhole. A fim de simplificar o mecanismo de perturbação, foi decidido que as ondas de perturbação devem ser aplicadas diretamente no fluido. Para conseguir isso, uma célula piezoelétrica foi colocada acima da câmara de fluido. O ”nozzle” utilizado é um pinhole óptico redondo de alta precisão, feito de de aço inoxidável e com três tamanhos diferentes: 100 µm, 150 µm e 200 µm. As propriedades do jato (diâmetro da gota, velocidade da gota e distância entre gotas) foram medidas de para diferentes propriedades (frequência da célula piezoelétrica, pressão de fluído e tamanho do ”nozzle”). O presente trabalho estudou as características do spray para três fluidos diferentes (àgua, jet fuel e mistura de biocombustível) e diferentes regimes monodispersos foram encontrados. Uma caracterização destes parametros é apresentada e discutida com detalhe. Verificou-se que o intervalo do diâmetro das gotas para um ”nozzle” com tamanho de 200 µm, que pode ser usado para todos os três fluidos, é de 401 µm até 472 µm e o intervalo de velocidade é de 1, 24 m/s até 2, 48 m/s, enquanto que para um ”nozzle” com um tamanho de 150 µm, a gama de diâmetros que pode ser obtido é de 287 µm até 340 µm e um intervalo de velocidade de 2, 04 m/s até 4, 38 m/s, para os três fluidos. Para um tamanho de pinhole de 100 µm, o intervalo de diâmetros das gotas para todos os três fluidos é de 206 µm a 258 µm e o intervalo de velocidade é 2, 36 m/s a 5, 99 m/s. Verificou-se que, tanto o diâmetro da gota como o espaçamento, diminuem com o aumento da fluxo da entrada e frequência, e a propriedade mais importante na formação do jato é o tamanho do ”nozzle”. A velocidade do jato é muito influenciada pela velocidade do fluxo e pelo tamanho do ”nozzle”. Quando comparados, os três fluidos comportam-se de uma forma diferente, resultando em diferentes diâmetro de gotas e velocidade do jato. Isto pode ser explicado pelas propriedades dos fluidos, onde a mistura de biocombustível apresenta maior viscosidade do que os outros dois fluídos.

Maize is the staple food for a majority of people in Southern Africa, but plant diseases are responsible for at least 10% of crop production losses. Bacterial leaf streak (BLS) of maize was first reported in South Africa in 1949 and has not been reported elsewhere. Very little is known about the pathogen involved and therefore it is deemed necessary to compile a characteristic profile for the pathogen to prevent the possibility of major crop losses as a result of this disease. This study aimed to use biochemical and phenotypic methods to determine the specific characteristics of the causal agent of BLS. Diseased plant material showing symptoms of BLS were collected during the maize production seasons of 2012 and 2013 within South Africa’s maize production regions namely the North West, Free State, Gauteng and Northern Cape provinces. To prevent contamination, maize leaves were surface sterilised thoroughly before bacterial isolation commenced. Sections of the infected maize leaves were placed on GYC agar plates on which yellow, mucoid bacterial colonies after incubation for 24 to 48 hrs. The isolated bacteria were purified and the molecular identification of the bacteria was conducted in a related study. Although literature indicates that Xanthomonas campestris pv. zeae is the causal agent of BLS, pure cultures obtained from maize leaves showing characteristic symptoms of BLS were identified as species of Xanthomonas, Pantoea, and Enterobacter. To elucidate the pathogenicity of the isolated strains, pathogenicity tests based on Koch’s postulates were performed. Results from the pathogenicity tests confirmed that only the isolate Xanthomonas species was capable of inducing the characteristic BLS symptoms when healthy maize plants were inoculated with the suspected pathogens. It is important to inoculate the maize seedlings at the correct age (four-leaf stage) and the spray method is recommended. Re-isolation was repeated from the same plant material used during the initial isolation process but the isolation method was amended. The optimised isolation method involved the use of a dilution range and spread plate method. Colonies from this isolation technique grew as bright yellow colonies that were identified as Xanthomonas spp. This outcome indicates the importance of surface sterilisation, pulverisation and subsequent dilution of plant materials for isolation of bacterial pathogens from diseases plants. These isolates were used to create protein profiles with SDS-PAGE electrophoresis and carbon utilisation patterns with the Biolog® GN2 system. Protein profiling banding patterns was assessed based on presence/absence criteria. Highly similar protein profiles were observed among the X. campestris pv. zeae isolates but groupings of different protein profiles were determined when minor differences in the protein profiles was taken into account. Xanthomonas campestris pv. zeae was successfully distinguished from the X. axonopodis pv. vasculorum reference strain through unique SDS banding patterns. Banding patterns obtained from cultures grown in a liquid medium (tryptic soy broth) were of a higher quality than the banding patterns obtained from bacteria harvested from solid media (CYG agar plates). Carbon source utilisation data was used to evaluate the average well colour development obtained from each isolate. Statistically significant differences were found among some of the isolates, with some isolates being metabolically more active than other isolates. Substrate utilisation patterns produced by the isolates corresponded to previously published studies on various Xanthomonas species. The cell count of the samples used during carbon utilisation patterns must be standardised in order to obtain reliable results. During this study, the application of Koch’s postulates and two inoculation techniques confirmed that Xanthomonas campestris pv. zeae is the pathogen responsible for bacterial leaf streak of maize. Members of the Pantoea and Enterobacter genera were found on the leaf surface of maize plants infected with BLS but inoculations of healthy maize plants with these bacteria did not result in bacterial leaf streak symptoms on the maize plants. These bacteria were not pathogenic and were considered endophytes. The identified pathogen was characterised through protein and metabolic profiling. The protein profiles of the pathogen obtained through analysis of the major bands of the SDS-PAGE gels were highly similar and distinguishable from the Xanthomonas reference culture. Groupings within the X. campestris pv. zeae group was found when major and minor bands were considered, this may however be altered when the intensities of the bands are used during analysis. Carbon utilisation patterns were assessed using Biolog® GN2 plates. A metabolic fingerprint was created for the pathogen of BLS, it was possible to distinguish between X. campestris pv. zeae and other Xanthomonas strains based on the fingerprint. This fingerprint could be used to identify the pathogen.
MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

All members of the genus Xanthomonas are considered to be plant pathogenic, with specific pathovars infecting several high value agricultural crops. One of these pathovars, X. campestris pv. zeae (as this is only a proposed name it will further on be referred to as Xanthomonas BLSD) the causal agent of bacterial leaf steak of maize, has established itself as a widespread significant maize pathogen within South Africa. Insufficient information about the present distribution of the pathogen is available. The main aim of the study was thus to isolate and characterise the pathogen using molecular methods. Results demonstrated that the causal agent of bacterial leaf streak disease (Xanthomonas BLSD: potentially X. campestris pv. zeae) was widely distributed within the major maize cultivation regions of South Africa. Most of the isolates collected originated from the Highveld maize production provinces (North West, Free State, Gauteng and Mpumalanga provinces) as well as from irrigated maize fields in the Northern Cape province. The XgumD gene marker was used to determine if the isolates belonged to the genus Xanthomonas. The gumD gene fragment is located within the gumB-gumM region of the operon and is conserved among Xanthomonas species. This gene fragment is partially responsible for xanthan production. This marker was amplified from all isolates and a selected number were sequenced. The marker was only able to confirm that the causal agent was a member of the genus Xanthomonas. PCR methods were used for the characterisation of the isolates. This included PCR and sequencing of ribosomal RNA- gyraseB and gumD genes. A fingerprinting method BOX-PCR was also employed. Good quality DNA of sufficient quantities was obtained from the various isolates. Amplification produced no non-specific amplification products. This resulted in good quality sequences that could be analysed using bioinformatics tools. Phylogenetic analyses of the ribosomal RNA and gyraseB genes could not detect differences amongst the 47 Xanthomonas BLSD isolates. However, these genes were able to distinguish between the type strain of these isolates and various Xanthomonas species and pathovars. From all three neighbour joining trees the Xanthomonas BLSD isolates had close association with X. axonopodis pv. vasculorum strain ATCC 35938. For the 16S rRNA gene there exists no sequence differences between Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938. A single nucleotide difference was observed between Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938 for the 23S rRNA gene. The gyraseB gene detected a total of six nucleotide variations between these two Xanthomonas species. For all of the phylogenetic trees there was no clustering of Xanthomonas BLSD with X. campestris pathovars. Genetic profiling (via BOX-PCR) based on present/absent analysis revealed no variations amongst the Xanthomonas BLSD isolates. All isolates shared an identical pattern produced by 12 distinct PCR products. This profiling technique did differentiate between the isolates of Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938. Their profiles shared common bands, but differed in the number and overall pattern of the bands. These results suggest two main conclusions: (i) Xanthomonas BLSD has a clonal origin with geographical separation not impacting genetic variation. The fact that all the isolates appear to be clonal may imply that when resistant maize cultivars are developed these should be resistant to all isolates of the pathovar irrespective of their geographical origin. This is a suggestion that will have to be corroborated using more isolates and additional genetic fingerprinting techniques (ii) the Xanthomonas BLSD isolates from this study may not belong to X. campestris. Further studies using other markers should be conducted to determine the real identity of Xanthomonas BLSD.
MSc Environmental Sciences, North-West University, Potchefstroom Campus, 2015