Signal crayfish are an internationally widespread invasive species that can have important detrimental ecological impacts. This thesis aims to determine whether signal crayfish have the potential to also impact the physical environment in rivers. A series of experiments were undertaken in purpose-built still-water aquaria using a laser scanner to obtain Digital Elevation Models (DEMs) of narrowly-graded gravel surfaces before and after exposure to crayfish. The difference between DEMs was used to quantify volumetric changes in surface topography due to crayfish activity. Two distinct types of topographic change were identified. The first was the construction of pits and mounds which resulted in an increase in surface roughness and grain exposure. The second was the rearrangement of surface material caused by crayfish brushing past grains when walking and foraging, reorientating grains and altering friction angles. A series of 80 flume runs were undertaken to quantify alterations made by crayfish to water-worked, as well as loose, gravel substrates at low velocity flows. Crayfish significantly altered the structure of water-worked substrates, reversing the imbrication of surface grains to a more random arrangement. Surfaces were entrained at a relatively high velocity flow subsequent to crayfish activity in order to directly link topographic and structural alterations to substrate stability. Nearly twice as many grains were mobilised from surfaces which had been disturbed by crayfish in comparison to control surfaces that were not exposed to crayfish. A field investigation aimed to determine the potential significance of the geomorphic impact of crayfish in rivers. Signal crayfish were tracked through a 20 m reach of a small, lowland alluvial river for 150 days using a Passive Integrated Transponder (PIT) system. Crayfish were active throughout the channel, although their activity became limited as water temperature dropped and flow stage increased. Substrate was not an important determinant of crayfish activity at this scale. Instead, crayfish tended to be found along the inner bank of a meander bend where there was a substantial cover of macrophytes. Consequently, signal crayfish were active for extended periods on substrates of a similar size to those that they could disturb in flume experiments. These results suggest that signal crayfish could have important geomorphic effects in rivers, disturbing bed structures and increasing the mobility of coarse material. This may have important implications for both the management of some rivers and benthic organisms that reside on the river bed.

Imaging mass spectrometry (IMS) in microscope mode allows the spatially resolved molecular constitution of a large sample section to be analysed in a single experiment. If performed in a linear mass spectrometer, the applicability of microscope IMS is limited by a number of factors: the low mass resolving power of the employed ion optics; the time resolution afforded by the scintillator screen based particle detector and the multi-hit capability, per pixel, of the employed imaging sensor. To overcome these limitations, this thesis concerns the construction of an advanced ion optic employing a pulsed extraction method to gain a higher ToF resolution, the development of a bright scintillator screen with short emission lifetime, and the application of the Pixel Imaging Mass Spectrometry (PImMS) sensor with multi-mass imaging and time stamping capabilities. Initial experimental results employing a three electrode ion optic to spatially map ions emitted from a sample surface are presented. By applying a static electric potential a time-of-flight resolution of t/2Δt=54 and a spatial resolution of 20 μm are determined across a field-of-view of 4 mm diameter. While the moderate time-of-flight resolution only allows particles separated by a few Dalton to be distinguished, the instrument is used to demonstrate the multi-mass imaging capabilities of the PImMS sensor when being applied to image grid structures or tissue samples. An improved time-of-flight resolution is achieved by post extraction differential acceleration of a selected range of ions (up to 100 Da) using a newly developed five electrode ion optic. This modification is shown to correct the initial velocity spread of the ions coming off the sample surface, which yields an enhanced time-of-flight resolution of t/2Δt=2000 . The spatial resolution of the instrument is found to be 20 μm across a field-of-view of 4 mm. Adjusting the extraction field strength applied to the ion optic of the constructed mass spectrometer allows the optimised mass range to be tuned to any mass of interest. Ion images are recorded for various samples with comparable spatial and ToF resolution. Hence, studies on tissue sections and multi sample arrays become accessible with the improved design and operational principle of the microscope mode IMS instrument. A fast and efficient conversion of impinging ions into detectable flashes of light, which can consequently be recorded by a fast imaging sensor, is essential to maintain the achievable time-of-flight and spatial resolution of the IMS instrument constructed. In order to find a suitable fast and bright scintillator to be applied in a microchannel based particle detector, various inorganic and organic substances are characterised in terms of their emission properties following electron excitation. Poly-para-phenylene laser dye screens are found to show an outstanding performance among all substances analysed. An emission life time of below 4 ns and a brightness exceeding that of a P47 screen (industry standard) by a factor 2× is determined. No signal degradation is observed over an extended period, and the spatial resolution is found to be comparable to commercial imaging detectors. Hence, these scintillator screens are fully compatible with any ion imaging application requiring a high time resolution. In a further series of mass spectrometric experiments, ions are accelerated onto a scintillator mounted in front of a multi pixel photon counter. The charged particle impact stimulated the emission of a few photons, which are collected by the fast photon counter. Poly-para-phenylene laser dyes again show an outstanding efficiency for the conversion of ions into photons, resulting in a signal enhancement of up to 5× in comparison to previous experiments, which employed an inorganic LYSO scintillator.

As flores das espécies de Moraceae são díclinas (= unissexuais), aclamídeas ou monoclamídeas, pequenas e chama a atenção o gineceu por ser unilocular e uniovulado, mas com aspecto tubular no decorrer do desenvolvimento, resultado de pseudomonomeria. Estas flores estão inseridas em inflorescências consideravelmente diversas em termos estruturais, além de apresentarem síndromes de polinização diferentes. Assim, os objetivos deste trabalho foram esclarecer as vias que originam as diferentes formas de inflorescências e elucidar condições florais enigmáticas como a ausência de perianto e gineceu pseudomonômero, utilizando sete espécies de linhagens diferentes de Moraceae como modelos de estudo: Brosimum gaudichaudii, Castilla elastica, Clarisia ilicifolia, Ficus citrifolia, F. pertusa, Maclura tinctoria e Morus nigra. Inflorescências em vários estádios de desenvolvimento, botões florais e flores foram processados para exames de superfície e anatômico. O meristema da inflorescência é semelhante quanto à forma entre as espécies apenas nos estádios iniciais. Em Ficus pertusa a inflorescência se fecha pelas margens devido à presença de orobrácteas; em Castilla elastica a inflorescência forma uma depressão central (inflorescência pistilada), podendo se tornar bivalvar (inflorescência estaminada), sendo rodeada por brácteas involucrais; em Brosimum gaudichaudii o meristema torna-se plano, e as flores estaminadas e pistiladas ficam imersas no receptáculo e cobertas por brácteas interflorais; em Clarisia ilicifolia e Maclura tinctoria os meristemas das inflorescências estaminadas e pistiladas tornam-se planos e alongam-se, porém, na pistilada adquire uma forma globosa; em Morus nigra o meristema se alonga. Brácteas interflorais estão ausentes apenas em Morus nigra. A morfologia e desenvolvimento florais diferem entre as espécies estudadas em especial quanto ao número de órgãos florais. O perianto é constituído de sépalas robustas, verdes, presentes na maioria das espécies estudadas, com exceção de Brosimum gaudichaudii, cuja flor estaminada exibe uma bractéola que envolve os órgãos florais e a flor pistilada é aclamídea, assim como a flor estaminada de Castilla elastica. Em todas as espécies as sépalas variam em número (dois a cinco), sendo sua iniciação assincrônica. Não há iniciação de primórdios de pétalas, individualizados ou oriundos de divisão dos primórdios de estames. Os primórdios de estames iniciados na flor estaminada (1-5, dependendo da espécie) tornam-se funcionais; portanto, não há aborto de estames na flor estaminada. Na flor pistilada de Castilla elastica raramente iniciam estaminódios. A estrutura anatômica das sépalas e dos estames varia entre as espécies, representando possíveis adaptações à entomofilia ou anemofilia descritas para a família. A epiderme pode apresentar tricomas tectores e secretores, dependendo da espécie. O mesofilo varia em número de camadas nas espécies, e esta variação é refletida na união entre os órgãos. Laticíferos e idioblastos fenólicos e cristalíferos ocorrem no mesofilo das sépalas e conectivo dos estames em todas as espécies, provavelmente atuando na proteção da flor contra herbívoros e radiação UV. Os estames apresentam variação na forma dos filetes e no conectivo. Nas flores estaminadas de Morus nigra e Maclura tinctoria as células do mesofilo são maiores com espaços intercelulares; e na estrutura final da flor, as quatro sépalas são acompanhadas de estames inflexos e um pistilódio, os quais compõem uma complexa estrutura que atua na dispersão dos grãos de pólen. O gineceu pseudomonômero é modificado em pistilódio na flor estaminada de Maclura tinctoria e Morus nigra. Os carpelos são iniciados como um único primórdio central que se divide, originando dois outros, que se alongam assimetricamente. Os próximos estádios diferem entre as espécies e foram resumidos em duas vias ontogenéticas: (1) contribuição total dos dois carpelos na formação do ovário, estilete e estigma, porém, apenas um dos carpelos inicia um óvulo em seu ovário unilocular - encontrado na maioria das espécies. (2) contribuição parcial dos dois carpelos, sendo que o carpelo de maior comprimento participa da formação do ovário, estilete e estigma e inicia um óvulo, enquanto o de menor comprimento participa apenas da formação do ovário - encontrado em Maclura tinctoria. As espécies de Moraceae compartilham estádios iniciais do desenvolvimento da inflorescência, do perianto, androceu e gineceu pseudomonômero, sendo que as principais diferenças ocorrem nos estádios intermediários, o que altera a estrutura da flor e inflorescência. Essas vias de desenvolvimento parecem ser estáveis dentro do clado urticoide e contribuem para a redução da estrutura floral neste grupo de rosídeas. / The flowers of the species of Moraceae are diclinous (= unisexual), achlamydeous or monochlamydeous, small, drawing attention the gynoecium for being unilocular and uniovular but with tubular shape in the course of development, a result of pseudomonomery. These flowers are inserted in structurally diverse inflorescences, and show different pollination syndromes. The objectives of this study were to clarify the pathways that cause the different forms of inflorescences, and to elucidate enigmatic floral conditions as the absence of perianth and pseudomonomerous gynoecium in Moraceae, by using seven species of different lineages of the family as study models: Brosimum gaudichaudii, Castilla elastica, Clarisia ilicifolia, Ficus citrifolia, F. pertusa, Maclura tinctoria and Morus nigra. Infllorescences, buds and flowers in several developmental stages were prepared for examination under scanning electron and light microscopies. The meristem of the inflorescence is similar in shape among the species only in the early stages of development. In Ficus pertusa the inflorescence closes along the margins due to the presence of orobracts. The inflorescence of the Castilla elastica forms a central depression (pistillate inflorescence) and may become bivalvar (staminate inflorescence), being surrounded by involucral bracts. In Brosimum gaudichaudii the meristem becomes flat, and the staminate and pistillate flowers are immersed in the receptacle and covered by interfloral bracts; in Clarisia ilicifolia and Maclura tinctoria the meristem of the staminate and pistillate inflorescences becomes flat and lengthens, however, the pistillate inflorescence acquires a globose shape; in Morus nigra the meristem is elongated. Interfloral bracts are absent only in Morus nigra. The floral morphology and development differ among the species studied especially in terms of number of floral organs. The perianth consists of robust green sepals, present in the majority of the species studied, with the exception of Brosimum gaudichaudii, whose staminate flower exhibits a bract involving the floral organs and the pistillate flower is achlamydeous, as well as the staminate flower of Castilla elastica. In all species the sepals vary in number (two to five), and show asynchronous initiation. There is no initiation of petal primordia, individualized or originated from division of stamen primordia. The stamen primordia initiated in the staminate flower (1-5, depending on the species) become functional; so there is no stamen abortion in the staminate flower. The pistillate flower of Castilla elastica rarely initiates staminodes. The anatomical structure of the sepals and stamens varies among species, representing possible adaptations to the entomophily or anemophily described for the family. The epidermis may have glandular and/or non glandular trichomes, depending on the species. The mesophyll varies in number of layers in the species, and this variation is reflected in the union of the organs. Laticifers and crystal and phenolic idioblasts occur in the mesophyll of the sepals and connective of the stamens in all species, probably acting on flower protection against herbivores and UV radiation. The stamens vary in terms of filament and connective shape. In the staminate flowers of Morus nigra and Maclura tinctoria the cells of the mesophyll are larger with intercellular spaces; and in the final structure of the flower, the four sepals are accompanied by inflexed stamens and a pistillode, which compose a complex structure that acts in the pollen grain dispersal. The pseudomonomerous gynoecium is transformed into pistillodes in the staminate flowers of Maclura tinctoria and Morus nigra. The carpel initiates as a single central primordium which divides and originates two others, which elongate asymmetrically. The next stages differ among species and have been summarized in two ontogenetic pathways: (1) the total contribution of the two carpels in the formation of the ovary, style and stigma, however, in only one of the carpels an ovule arises at the single locule - found in most species. (2) Partial contribution of the two carpels, wherein the carpel with greater length participates in the formation of the ovary, style, stigma and ovule, while the carpel with shortest length is only involved in the formation of ovary - found in Maclura tinctoria. The species of Moraceae share early stages of development of the inflorescence, the perianth, androecium and pseudomonomerous gynoecium, and the main differences occur in the intermediate stages, which alters the structure of the flower and inflorescence. These developmental pathways seem to be stable within the urticalean rosids and contribute to the reduction of the floral structure in this group.

AISI 4140 alloy steel has been a very common material to be investigated in automotive and aerospace industries for several decades. AISI 4140 alloy steel is chromium, molybdenum, and manganese containing low alloy steel. It has high fatigue strength, abrasion and impact resistance, toughness, and torsional strength. The functional performance is largely determined by the surface states after machining. The aim of the present study is to explore the polishing methods and surface analysis after machining AISI 4140 alloy steel in different cutting speeds and cooling conditions. The surface analysis includes surface roughness, hardness and residual stresses. Compared to traditional polishing, an innovative experimental work was conducted on electro-polishing technology for removing surface layer before subsurface residual stress measurement. The results of this work show that the electro-polishing method is a significant approach for the residual stress analysis. High cutting speed and cooling conditions can improve the surface quality to achieve lower surface roughness, higher microhardness and more compressive residual stresses after machining AISI 4140 alloy steel.

Metal oxides in the atmosphere emitted from various natural and anthropogenic processes alter the chemical balance of the Earth's atmosphere due to heterogeneous and photochemical processes with atmospheric trace gases. Therefore, understanding the heterogeneous chemistry and heterogeneous photochemistry of atmospheric trace gases on these oxide surfaces has become vital to precisely predict the effect of mineral dust loading on the Earth's atmosphere. Among the various components of mineral dust, light absorbing oxides play a significantly important role during the daytime. The work reported herein has focused mainly on TiO2 and Α-Fe2O3. These are light adsorbing components found in atmospheric mineral dust. Apart from being a component of mineral dust, TiO2 is heavily used in a number of industrial applications ranging from uses in self-cleaning, water purification to cosmetics. These applications have led to their presence in the atmosphere as anthropogenic dust particles and in contact with the atmosphere as a stationary phase. Iron-containing particles are transferred to the atmosphere mainly from wind and volcanic activities in the form of iron-containing mineral dust and volcanic ash aerosols. Α-Fe2O3 is the most stable iron containing compound found in the Earths' crust which constitutes in significant amounts in mineral dust. The presence of these oxide surfaces in the atmosphere can play a major role in heterogeneous chemistry and photochemistry. In this dissertation research, transmission FTIR spectroscopy and X-ray photoelectron spectroscopy are used to probe the details of heterogeneous chemistry and photochemistry of CO2, SO2, NO2, HCOOH, and HNO3 on titanium dioxide and hematite surfaces. Adsorption sites, surface speciation and surface species stability have been determined from analysis of FTIR and XPS spectra. Isotope labeling experiments were also carried out in order to obtain mechanistic information about the details of surface hydroxyl group reactivity on these oxide particle surfaces. Furthermore, heterogeneous photochemical reactions of adsorbates from atmospheric trace gas adsorption on TiO2 and Α-Fe2O3 were investigated under the conditions pertinent to troposphere. The role of adsorbed water on the stability of adsorbed species that form as a result of heterogeneous reactions and the effect of relative humidity on photochemistry on these oxide particles surfaces has also been investigated due to its important implications in the atmospheric chemistry of oxide surfaces. The research adds to our overall scientific understanding of the molecular level details of heterogeneous chemistry and photochemistry of light absorbing components in the atmosphere.

Scanning electrochemical microscopy (SECM) was used for the study and characterization of catalytic and electrocatalytic processes occurring at electrodes. The Surface Interrogation mode (SI-SECM) was introduced for the detection and quantification of adsorbed intermediates and products of catalyzed chemical and electrochemical reactions at noble metals (Pt, Au). In SI-SECM two micro electrodes (i.e. an SECM tip and a substrate of the desired material) are aligned concentrically at a micrometric distance where SECM feedback effects operate. A contrast mechanism based on feedback effects allows for the detection of reactive adsorbed intermediates at the substrate: the SECM tip generates a reactive homogeneous species that “micro-titrates” the substrate adsorbates to yield an electrochemical signal that contains information about the amount of intermediate and about its kinetics of reaction with the redox mediator. The technique was used for the study of the reactivity of three model small adsorbates: 1) the reactivity of adsorbed oxygen on Au and Pt with a reducing mediator was explored and suggested the detection of “incipient oxides” at these surfaces; kinetic parameters of the reactivity of Pt oxides with mediators were obtained, fit to theory and used to explain observations about the electrocatalytic behavior of Pt under anodizing conditions; 2) the reactivity of oxidizing mediators with adsorbed hydrogen on Pt was studied and showed the cation of N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) to be a successful interrogation agent, the detection of hydrogen generated by the decomposition of formic acid on Pt at open circuit was investigated; 3) electrogenerated bromine was used to catalytically interrogate carbon monoxide at Pt, this reaction was previously unreported. The mentioned applications of SECM were validated through the use of digital simulations of diffusion in the complex SECM geometry through flexible commercial finite element method software. / text

Paleochannels are a major cause of roof failure in underground coal mines in southeastern Kentucky. Models that predict the location and geometry of paleochannels are essential to assist in mine planning and development. Data from approximately 506 coal exploration drill holes were subjected to second-order trend-surface analysis to identify stacking or offsetting relationships between sandstone bodies in adjacent stratigraphic intervals. The stacking of sandstone bodies within adjacent intervals suggests the presence of synsedimentary faulting. This model suggests that continued movement along the faults created topographic lows attracted paleodrainages and accommodated thick accumulations of sandstone in approximately the same areas through time. Trend-surface residuals analysis successfully located areas of potential synsedimentary faulting within the study area. An additional 7,189 elevation data points for the top of the Newman Limestone, interpreted from oil and gas records, were utilized to locate sub-Pennsylvanian System faults within the study area. The correlation between faults associated with the coal measures identified using second-order trend-surface analysis and faults affecting the Newman Limestone suggests Pennsylvanian synsedimentary faults were preceded by older Paleozoic fault movement. The greater availability of oil and gas subsurface data makes this relationship an important tool for predicting locations of fault-controlled coal measure paleochannels.

With the growth of wireless networks and the increase in personal internet use for a wide diversity of applications, the importance of the quality of service (QoS) delivered to clients has become of great importance. In order to evaluate QoS, this study explores the application of the linear response surface analysis (LRSA) technique as an evaluation tool for QoS factors such as Throughput and Delay. An 802.11n prototype wireless network is constructed in order to capture QoS data that is then used to construct LRSA models in order to evaluate the QoS factors. The LRSA models are maximised and minimised while constraining specific measured QoS factors and the subsequent results are analysed. Based on this analysis, recommendations for the improvement of wireless networks are made as well as the use of the LRSA technique to evaluate QoS within a wireless network. / Thesis (MSc (Computer Science))--North-West University, Potchefstroom Campus, 2013

With the growth of wireless networks and the increase in personal internet use for a wide diversity of applications, the importance of the quality of service (QoS) delivered to clients has become of great importance. In order to evaluate QoS, this study explores the application of the linear response surface analysis (LRSA) technique as an evaluation tool for QoS factors such as Throughput and Delay. An 802.11n prototype wireless network is constructed in order to capture QoS data that is then used to construct LRSA models in order to evaluate the QoS factors. The LRSA models are maximised and minimised while constraining specific measured QoS factors and the subsequent results are analysed. Based on this analysis, recommendations for the improvement of wireless networks are made as well as the use of the LRSA technique to evaluate QoS within a wireless network. / Thesis (MSc (Computer Science))--North-West University, Potchefstroom Campus, 2013

Physical, chemical and corrosion properties of a hexavalent chromium conversion coating (CCC) and that of a commercial third generation trivalent chromium system; Tripass LT1500, on zinc electrodeposited steel has been studied. Moreover, the role of additives has been studied to elucidate film formation and corrosion resistance mechanisms. Micro-cracking and self-repair corrosion protection behaviour commonly associated with hexavalent CCCs has also been investigated. Scanning Electron Microscopy (SEM) studies showed that for both hexavalent and trivalent CCCs were in general, flat with a spherical-like structure and in the case of the former microcracked beyond 122 nm conversion coating thickness. In general, the micro-crack pattern observed e.g. a dense crack network, depended upon the underlying zinc substrate morphology. The study has also demonstrated the effect of SEM imaging and prior specimen preparation conditions on hexavalent CCC micro-cracking and blistering. X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Infrared (IR) data has indicated that the hexavalent CCC film formation appears to be a electrochemical/sol-gel mechanism given the lack of zinc content at surface and subsurface regions within the conversion coating, presence of H2O and in particular the contribution of Cr(OH)3 as opposed to Cr2O3. An alternative film formation mechanism may exist for trivalent CCC given a higher proportion of zinc at surface and sub-surface regions, IR data analysis indicating that chromium is possibly deposited from a chromium (III) complex ion such as [CrC2O4(H2O)4] + , moreover as Cr(OH)3 and Cr2O3 compounds as indicated by XPS data analysis. The role of cobalt nitrate during film formation is unclear given that cobalt was not detected within the trivalent CCC from XPS and AES data. Electrochemical LPR measurements, polarisation curves and XPS data has shown in general, self-repair corrosion protection properties for hexavalent CCC to be lacking. Instead, it is proposed that the corrosion protection behaviour for hexavalent and trivalent CCC to be barrier. Polarisation curves and LPR data showed that the corrosion resistance performance for trivalent CCC was higher than hexavalent CCC, in general. LPR data showed that the omission of cobalt nitrate and increased addition of sodium molybdate content within the Tripass LT1500 treatment solution formulation was found to overall decrease corrosion resistance within the trivalent CCC. In addition, silica based topcoat and black trivalent CCCs was also investigated and characterised using AES, SEM and LPR. Zinc whiskers was also observed from zinc electrodeposits following exposure to thermal treatment (150°C for 1 h). Elemental analysis and grain pattern investigations failed to help determine the cause of zinc whisker initiation. Zinc whiskers was seen to protrude out of hexavalent and trivalent CCCs, with the latter requiring a longer thermal exposure time.