This study aimed to understand the relationship between mobile device screen display size (laptops and smartphones) and text segmentation (continuous text, medium text segments, and small text segments) on learning outcomes, cognitive load, and user perception. This quantitative study occurred during the spring semester of 2015. Seven hundred and seventy-one chemistry students from a higher education university completed one of nine treatments in this 3x3 research design. Data collection took place over four class periods. The study revealed that learning outcomes were not affected by the mobile screen display size or orientation, nor was working memory. However, user perception was affected by the screen display size of the device, and results indicated that participants in the sample felt laptop screens were more acceptable for accessing the digital chemistry text than smartphone screens by a small margin. The study also found that neither learning outcomes, nor working memory was affected by the text segmentation viewed. Though user perception was generally not affected by text segmentation, the study found that for perceived ease of use, participants felt medium text segments were easier to learn from than either continuous or small test segments by a small margin. No interaction affects were found between mobile devices and text segmentation. These findings challenge the findings of some earlier studies that laptops may be better for learning than smartphones because of screen size, landscape orientation is better for learning than portrait orientation in small screen mobile devices, and meaningful text segments may be better for learning than non-meaningful, non-segmented, or overly segmented text. The results of this study suggest that customizing the design to the smartphone screen (as opposed to a one-size-fits-all approach) improves learning from smartphones, making them equal to learning from laptops in terms of learning outcomes and cognitive load, and in some cases, user perspective. / text

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Cyclic nucleotide-gated channels (CNGCs) are non-selective cation channels that were first identified in vertebrate photosensory and olfactory neurons. Although the physiological roles and biophysical properties of animal CNGCs have been well studied, much less is known about these channels in plants. The Arabidopsis genome encodes twenty putative CNGC subunits that are postulated to form channel complexes that mediate various physiological processes involving abiotic and biotic stress responses, ion homeostasis and development. The identification of Arabidopsis autoimmune CNGC mutants, such as defense no death class (dnd1 and dnd2), and the constitutive expressor of pathogenesis related genes 22 (cpr22) implicate AtCNGC2, 4, 11 and 12 in plant immunity. Here, I present a comprehensive study of the molecular mechanisms involved in CNGC-mediated signaling pathways with emphasis on pathogen defense. Previously, a forward genetics approach aimed to identify suppressor mutants of the rare gain-of-function autoimmune mutant, cpr22, identified key residues that are important for CNGC subunit interactions and channel function. First, I present a structure-function analysis of one of these suppressor mutants (S58) that revealed a key residue in the cyclic nucleotide binding domain involved in the stable regulation of CNGCs. Second, I present a new suppressor screen using AtCNGC2 T-DNA knockout mutants that specifically aimed to identify novel downstream components of CNGC-mediated pathogen defense signaling. In this screen, I successfully isolated and characterized the novel Arabidopsis mutant, repressor of defense no death 1 (rdd1), and expanded this study to demonstrate its involvement in AtCNGC2 and AtCNGC4-mediated signal transduction. Additionally, I demonstrated for the first time, the physical interaction of AtCNGC2 and AtCNGC4 subunits in planta. The findings presented in this thesis broaden our current knowledge of CNGCs in plants, and provide a new foundation for future elucidation of the structure-function relationships and signal transduction mediated by these channels.

Cyclic nucleotide-gated channels (CNGCs) are non-selective cation channels that were first identified in vertebrate photosensory and olfactory neurons. Although the physiological roles and biophysical properties of animal CNGCs have been well studied, much less is known about these channels in plants. The Arabidopsis genome encodes twenty putative CNGC subunits that are postulated to form channel complexes that mediate various physiological processes involving abiotic and biotic stress responses, ion homeostasis and development. The identification of Arabidopsis autoimmune CNGC mutants, such as defense no death class (dnd1 and dnd2), and the constitutive expressor of pathogenesis related genes 22 (cpr22) implicate AtCNGC2, 4, 11 and 12 in plant immunity. Here, I present a comprehensive study of the molecular mechanisms involved in CNGC-mediated signaling pathways with emphasis on pathogen defense. Previously, a forward genetics approach aimed to identify suppressor mutants of the rare gain-of-function autoimmune mutant, cpr22, identified key residues that are important for CNGC subunit interactions and channel function. First, I present a structure-function analysis of one of these suppressor mutants (S58) that revealed a key residue in the cyclic nucleotide binding domain involved in the stable regulation of CNGCs. Second, I present a new suppressor screen using AtCNGC2 T-DNA knockout mutants that specifically aimed to identify novel downstream components of CNGC-mediated pathogen defense signaling. In this screen, I successfully isolated and characterized the novel Arabidopsis mutant, repressor of defense no death 1 (rdd1), and expanded this study to demonstrate its involvement in AtCNGC2 and AtCNGC4-mediated signal transduction. Additionally, I demonstrated for the first time, the physical interaction of AtCNGC2 and AtCNGC4 subunits in planta. The findings presented in this thesis broaden our current knowledge of CNGCs in plants, and provide a new foundation for future elucidation of the structure-function relationships and signal transduction mediated by these channels.

Hydrogen production via the electrolysis of water has gained a lot of attention in the last couple of years. Research related to electrolysers is mostly aimed towards decreasing the noble–metal catalyst content. In this study the presently used catalyst application techniques were reviewed and critically examined to find commercially applicable and effective methods. Selected methods were then practically applied to determine their feasibility and to gain “know–how” related to the practical application of these techniques. The selected techniques were the hand paint, inkjet print, screen print and spray paint techniques. Meaningful comparisons were made between the methods in terms of parameters such as practicality, waste of catalyst and microstructure. The results point out that the hand paint and spray paint methods are feasible methods although there are improvements to be made. The hand paint method was improved by applying a carbon micro porous layer to the gas diffusion layer before the painting is carried out. The addition of the carbon layer reduced the soaking of the catalyst–containing ink through the gas diffusion layer. A method not initially investigated was identified an evaluated and showed promising results in lowering the mass of catalyst applied. This method comprised of sputtering a layer of catalyst material onto a prepared gas diffusion layer. It also came to light from the results that electrodes, and therefore membrane electrode assemblies, can be produced at a much lower cost than the commercial available membrane electrode assemblies. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

Hydrogen production via the electrolysis of water has gained a lot of attention in the last couple of years. Research related to electrolysers is mostly aimed towards decreasing the noble–metal catalyst content. In this study the presently used catalyst application techniques were reviewed and critically examined to find commercially applicable and effective methods. Selected methods were then practically applied to determine their feasibility and to gain “know–how” related to the practical application of these techniques. The selected techniques were the hand paint, inkjet print, screen print and spray paint techniques. Meaningful comparisons were made between the methods in terms of parameters such as practicality, waste of catalyst and microstructure. The results point out that the hand paint and spray paint methods are feasible methods although there are improvements to be made. The hand paint method was improved by applying a carbon micro porous layer to the gas diffusion layer before the painting is carried out. The addition of the carbon layer reduced the soaking of the catalyst–containing ink through the gas diffusion layer. A method not initially investigated was identified an evaluated and showed promising results in lowering the mass of catalyst applied. This method comprised of sputtering a layer of catalyst material onto a prepared gas diffusion layer. It also came to light from the results that electrodes, and therefore membrane electrode assemblies, can be produced at a much lower cost than the commercial available membrane electrode assemblies. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

Doctor of Philosophy / Radiographic film/screen (F/S) images have a narrow latitude or dynamic range. The film’s ability to record and view all the anatomy within the x-ray field is limited by this narrow dynamic range. The advent of digital radiographic means of storing and displaying radiographic images has improved the ability to record and visualise all of the anatomy. The problem still exists in digital radiography (DR) when radiographic examinations of certain anatomical regions are undertaken. In this work, the value of anatomically shaped radiographic contrast-enhancement masks (RCMs) in improving image contrast and reducing the dynamic range of images in DR was examined. Radiographic contrast-enhancement masks are digital masks that alter the radiographic contrast in DR images. The shape of these masks can be altered by the user. Anatomically shaped RCMs have been modelled on tissue compensation filters (TCFs) commonly used in F/S radiographic examinations. The prime purpose of a TCF is to reduce the dynamic range of photons reaching the image receptor and hence improve radiographic contrast in the resultant image. RCMs affect the dynamic range of the image rather than the energy source of the image, that of the x-ray photons. The research consisted of three distinct phases. The first phase was to examine physical TCFs and their effects on F/S radiographic images. Physical TCFs are used in radiographic F/S examinations to attenuate the x-ray beam to compensate for varying patient tissue thicknesses and/or densities. The effect of the TCF is to reduce resultant radiographic optical density variations in the image, allowing the viewer to observe a range of densities within the image which would otherwise not be visualised. Physical TCFs are commonly aluminium- or lead-based materials that attenuate the x-ray beam. A TCF has varying physical thickness to differentially attenuate the iii beam and is shaped for specific anatomical situations. During this project, various commonly used physical TCFs were examined. Measurements of size and thickness were made. Characteristics of linear attenuation coefficients and half-value thicknesses were delineated for various TCF materials and at various energies. The second phase of the research was to model the physical TCFs in a digital environment and apply the RCMs to DR images. The digital RCMs were created with similar characteristics to mimic the shapes to the physical TCFs. The RCM characteristics can be adjusted by the viewer of the image to suit the anatomy being imaged. Anatomically shaped RCMs were designed to assist in overcoming a limitation when viewing digital radiographic images, that of the dynamic range of the image. Anatomically shaped RCMs differ from other means of controlling the dynamic range of a digital radiographic image. It has been shown that RCMs can reduce the range of optical densities within images with a large dynamic range, to facilitate visualisation of all anatomy within the image. Physical TCFs are used within a specific range of radiographic F/S examinations. Digital radiographic images from this range of examinations were collected from various clinical radiological centres. Anatomically shaped RCMs were applied to the images to improve radiographic contrast of the images. The third phase of the research was to ascertain the benefits of the use of RCMs. Various other methods are currently in use to reduce the dynamic range of digital radiographic images. It is generally accepted that these methods also introduce noise into the image and hence reduce image quality. Quantitative comparisons of noise within the image were undertaken. The anatomically shaped RCMs introduced less noise than current methods designed to reduce the dynamic range of digital radiographic images. It was shown that RCM methods do not affect image quality. Radiographers make subjective assessment of digital radiographic image quality as part of their professional practice. To assess the subjective quality of images enhanced with anatomically shaped RCMs, a survey of radiographers and other iv qualified people was undertaken to ascertain any improvement in RCM-modified images compared to the original images. Participants were provided with eight pairs of image to compare. Questions were asked in the survey as to which image had the better range of optical densities; in which image the anatomy was easiest to visualise; which image had the simplest contrast and density manipulation for optimal visualisation; and which image had the overall highest image quality. Responses from 123 participants were received and analysed. The statistical analysis showed a higher preference by radiographers for the digital radiographic images in which the RCMs had been applied. Comparisons were made between anatomical regions and between patient-related factors of size, age and whether pathology was present in the image or not. The conclusion was drawn that digital RCMs correctly applied to digital radiographic images decrease the dynamic range of the image, allowing the entire anatomy to be visualised in one image. Radiographic contrast in the image can be maximised whilst maintaining image quality. Using RCMs in some digital radiographic examinations, radiographers will be able to present optimised images to referring clinicians. It is envisaged that correctly applied RCMs in certain radiographic examinations will enhance radiographic image quality and possibly lead to improved diagnosis from these images.

This thesis is a biosystematic study focusing on the taxonomy and variability of selected taxa of the genus Sorbus, one of the most diverse and taxonomically complicated plant groups in Europe. Classical and modern biosystematic methods - comparative study, chromosome counting, analysis of nuclear microsatellite markers, flow cytometry, and traditional multivariate and outline morphometric analyses were used to assess the morphological, karyological and genetic variability of the genus. The final synthesis of these approaches led to the description of several new taxa (species, hybrids and a subgenus) and the correction of several taxonomic misinterpretations. To reveal ongoing evolutionary processes responsible for the generation of the observed variability, the reproductive modes of 42 Sorbus taxa were examined using flow-cytometric seed and pollen screens. Apart from revealing major trends, the study estimates the frequency of rare events and provides several novel conclusions that are relevant both specifically to Sorbus/Rosaceae and to apomixis in general.

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