El presente estudio experimental fue conducido para evaluar y comparar la estabilidad dimensional de las ceras para registro interoclusal Aluwax, Cavex Up y Koriwax en diferentes tiempos, estos materiales comúnmente utilizados en las facultades de odontología para obtener las relaciones intermaxilares céntricas o excéntricas antes y durante el tratamiento odontológico. Se utilizo un aparato para simular el maxilar y la mandíbula. Se prepararon 30 registros interoclusales en cada una de las ceras, estos fueron sometidos a los procedimientos indicados por el fabricante previo al registro. Se coloco un peso de un kg sobre el aparato para simular la fuerza ejercida durante el registro. Las diferencias verticales se midieron con ayuda micrómetro manual, los registros se midieron después de 10seg, 1hora, 24 horas y 48 horas estas fueron conservados a temperatura ambiente. Para el análisis estadístico se utilizó la prueba T-Student. Los resultados mostraron variaciones de hasta 1mm en las ceras Aluwax en las superficies empinadas, y de 0.1 mm en superficies cóncavas, mientras que Cavex y Koriwax presentaron valores similares en ambos tipos de superficies 0.5mm ± 0.2. dentro de las 24 horas. Se concluyó que Las diferencias encontradas son de interés clínico en ambos tipos de superficies y en los tres tipos de cera para registro interoclusal, presentando mayor variación en superficies empinadas la cera aluwax y en superficies cóncavas la cera cavex Palabras Clave: Estabilidad Dimensional, ceras de Registro, Ceras patrón, ceras de impresión / --- This experimental study was conducted to evaluate and compare the dimensional stability of the wax interocclusal record Aluwax, Cavex Up and Koriwax at different times, these materials commonly used in dental schools for the centric or eccentric jaw relations before and during the dental treatment. A custom made metal apparatus with upper and lower members simulating maxillary and mandibular prepared was fabrited. 30 interocclusal records in each of the waxes, underwent these procedures specified by the manufacturer prior to registration were prepared. Weighing one kg on the apparatus to simulate the force exerted during registration. Vertical differences were measured with manual micrometer, records were measured after 10 sec, 1 hour, 24 hours and 48 hours, Its were at room temperature. For statistical was used analysis t-Student's. The results showed variations of up to 1mm in Aluwax waxes on steep surfaces and concave surfaces 0.1 mm, while Koriwax, Cavex and had similar values for both types of surfaces 0.2 ± 0.5mm, within 24 hours. It was concluded that the differences are of clinical interest in both types of surfaces and in all three types of wax interocclusal record, showing greater variation in the Aluwax steep surfaces wax and wax Cavex concave surfaces Keywords: Dimensional stability, Registration waxes, waxes pattern, wax printing

Master of Science / Department of Statistics / Gary Gadbury / High-dimensional data (HDD) have been encountered in many fields and are characterized by a “large p, small n” paradigm that arises in genomic, lipidomic, and proteomic studies. This report used a simulation study that employed basic block diagonal covariance matrices to generate correlated HDD. Quantities of interests in such data are, among others, the number of ‘significant’ discoveries. This number can be highly variable when data are correlated. This project compared randomization tests versus usual t-tests for testing of significant effects across two treatment conditions. Of interest was whether the variance of the number of discoveries is better controlled in a randomization setting versus a t-test. The results showed that the randomization tests produced results similar to that of t-tests.

Mimicking the biological olfactory systems that consist of olfactory receptor arrays with large surface area and massively-diversified chemical reactivity, three dimensional (3D) metal oxide nanowire arrays were used as the active materials for gas detection. Metal oxide nanowire arrays share similar 3D structures as the array of mammal's olfactory receptors and the chemical reactivity of nanowire array can be modified by surface coatings. In this dissertation, two standalone gas sensors based on metal oxide nanowire arrays prepared by microfabrication and in-situ micromanipulation, respectively, have been demonstrated. The sensors based on WO3 nanowire arrays can detect 50 ppb NO2 with a fast response; well-aligned CuO nanowire array present a new detection mechanism, which can identify H2S at a concentration of 500 ppb. To expand the material library of 3D metal oxide nanowire arrays for gas sensing, a general route to polycrystalline metal oxide nanowire array has been introduced by using ZnO nanowire arrays as structural templates. The effectiveness of this method for high performance gas sensing was first investigated by single-nanowire devices. The polycrystalline metal oxide coatings showed high performance for gas detection and their sensitivity can be further enhanced by catalytic noble metal decorations. To form electronic nose systems, different metal oxide coatings and catalytic decorations were employed to diversify the chemical reactivity of the sensors. The systems can detect low concentrated H2S and NO2 at room temperature down to part-per-billion level. The system with different catalytic metal coatings is also capable of discriminiating five different gases (H2S, NO2, NH3, H2 and CO).

Photocatalysis is a process to convert light energy into chemical energies. This advanced process has been extensively applied in different areas, such as water splitting to evolve hydrogen, organic/ inorganic pollutants decomposition, artificial photosynthesis (CO2 reduction), disinfection, heavy metal recovery, organic synthesis and nitrogen fixation (reduction). The difficulty for photocatalysis applied in practical is primarily due to the low quantum yield as for the high recombination of photogenerated charge carriers. Various strategies have been implemented to overcome these challenges. As recently developed advanced materials, two dimensional materials have attracted lots of attentions as for their superiorities such as large specific surface area and high conductivity. These advantages for two dimensional materials make them be promising cocatalysts in enhance catalytic activity. In this thesis, various two dimensional materials (such as MoS2, SnS, BN as well as C3N4) other than graphene were prepared and investigated in the promotion of photocatalytic activity. Specifically, the focus of present work is on two dimensional materials enhanced photocatalysis in environmental remediation, including organic pollutants detoxification as well as bacteria inactivation. It was found that two dimensional materials, including MoS2, SnS, BN, may be excellent candidates as cocatalysts to enhanced visible-light-driven photocatalytic activity. And g-C3N4 as an effective photocatalyst exhibited excellent photocatalytic oxidation activity, and its activity can be further enhanced with surface modification by hydroxyl functional groups (a modification method reported in the thesis). Suggestions for future work were also proposed in this thesis.

A dissertation submitted for the fulfilment of the requirements of the degree of Master of Science to the Faculty of Science, Witwatersrand University, Johannesburg. June 2016. / The combination of effective numerical techniques and scientific intuition to find new and novel types of materials is the process used in the discovery of materials for future technologies. Adding to that, being able to calculate the radiative lifetimes of excitons, exciton properties, and the optical properties by using efficient numerical techniques gives an estimation and identification of the best candidate materials for a solar cell. This approach is inexpensive and stable. Present ab initio methods based on Many-body perturbation theory and density functional theory are capable of predicting these properties with a high enough level of accuracy for most cases. The electronic properties calculated using GaAs as a reference system and the 3D hybird perovskite CH3NH3PbI3 are based on density functional theory. The optical properties are investigated by calculating the dielectric function. The theoretical framework of the radiative lifetime of excitons and calculating the exciton properties are based on Wannier model of the exciton and the Bethe-Salpeter equation. / MT2017

A dissertation submitted to the Faculty of Arts, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Arts May 2016 / The technology of 3-D Printing is afforded extensive coverage in the media. Discourses surrounding this technology are charged with ideas of revolutions in manufacturing, democratisation of technology, and the potential to change the face of consumption and production. This technology is being marketed to the consumer and hobbyist. The consumer-grade 3-D printer is a result of the labour of a loose-knit worldwide community of hobbyists known as the "Maker movement". This movement, a convergence of the traditional "Hacker" culture and Do It Yourself (DIY) is constructed around ideas of affective labour. That is, labour performed for the sole purpose of enjoyment of doing so, and for a sense of well-being and community. The explosion of "affordable" 3-D printing as a technology is a result of this affective labour, yet little mention is made of any forms of labour in popular media discourses surrounding this technology. In this paper I construct a history of the Maker movement while theorising the forms of labour inherent to this movement using the Autonomist Marxism of Michael Hardt and Antonio Negri as a framework. Then, working within the field of Cultural Studies, and drawing on Actor-Network Theory (ANT), I perform Multimodal Critical Discourse Analysis (MCDA) on a small sample of texts to illustrate the occlusion and obfuscation of labour within these discourses of the consumer 3-D printer

Modern semiconductor fabrication techniques allow for the fabrication of semiconductor heterostructures which host electron transport with a minimum of scattering sites. In such devices, electrons populate a two-dimensional electron gas (2DEG) in which electrons propagate in exactly two dimensions, and may be further confined by potential barriers to form electron billiards. At sub-Kelvin temperatures, electron trajectories are determined largely by reflections from the billiard walls, while net conduction through the device depends on quantum mechanical wave interference. Measurements of magnetoconductance fluctuations (MCF) serve as a probe of dynamics within the electron billiard. Many prior studies have utilized heterostructures employing the modulation doping architecture, in which the 2DEG is spatially removed from the donor atoms to minimize electron scattering. Theoretical studies have claimed that MCF will be fractal when the confinement potential defining the billiard is soft-walled, regardless of the presence of smooth potentials within the billiard such as those introduced by remote ionized donors. The small-angle scattering sites resulting from these potentials are often disregarded as negligible; we use MCF measurements to investigate such claims. To probe the effect of remote ionized donor scattering on the phase space in electron billiards, we compare MCF measured on billiards in a modulation-doped heterostructure to those measured on billiards in an undoped heterostructure, in which this potential landscape is believed to be absent. Fractal studies are performed on these MCF traces, and we find that MCF measured on the undoped billiards do not exhibit measurably different fractal characteristics than those measured on the modulation-doped billiards. Having confirmed that the potential landscapes in modulation-doped heterostructures do not affect the electron phase space, we then investigate the effect of these impurities on the distribution of electron trajectories through the billiards. By employing thermal cycling experiments, we demonstrate that this distribution is highly sensitive to the precise potential landscape within the billiard, suggesting that modulation-doped heterostructures do not support fully ballistic electron transport. We compare our MCF correlation data with the dynamics of charge transfer within heterostructure systems to make qualitative conclusions regarding these dynamics.

Development of sustainable and environmentally friendly chemical processes is of vital importance nowadays. Although there is a palette of different synthetic methods for the formation of epoxides, sulphoxides and sulphones, from both economic and environmental points of view, a direct oxidation with a simple oxidant is highly appreciated. The main goals of the thesis were design and synthesis of novel titanium containing zeolitic materials with the ability to catalyse selective oxidation of sterically demanding organic compounds, particularly epoxidation of cyclic olefins and terpenes and oxidation of bulky thioethers to corresponding sulphoxides and sulphones with hydrogen peroxide as the oxidant. Two novel extra-large pore titanosilicates were prepared by means of hydrothermal synthesis (Ti-CFI, Ti-UTL), three large-pore titanosilicates (Ti-CON, Ti-AFI, Ti-IFR) were prepared using two step deboronation - liquid phase titanium impregnation procedure and two groups of lamellar materials were prepared. One group was based on modified nanosheet TS-1; the other was prepared from Ti-IPC- 1P lamellar precursor, which was prepared by means of top-down transformation of Ti-UTL. Last but not least, the Ti-UTL was transformed into new titanosilicates Ti-IPC-2 (OKO structure) and Ti-IPC-4 (PCR structure) by...

The internalizing and externalizing dimensions of psychopathology have been shown to effectively identify groups that are at higher risk for experiencing certain forms of psychopathology. Many studies have shown that chronic physical health conditions are a risk factor for psychological distress, yet there has been very little research examining the association between chronic physical health conditions and dimensional models of psychopathology to date. In the present study we examined the factor structure of internalizing and externalizing symptoms in a sample of adults with postural orthostatic tachycardia syndrome (POTS; n =172) and in a sample of adults without any chronic illness diagnoses (n = 199). Confirmatory factor analyses suggested that psychological distress in individuals with POTS can be effectively characterized by an internalizing dimension composed of distress and fear subcomponents as well as an externalizing dimension. Tests of measurement invariance allowed for the examination of latent means, which showed that individuals with POTS tend to have higher scores on the internalizing dimension and lower scores on the externalizing dimension than healthy controls. Regression analyses suggested that within the sample of people with POTS, those who were more accepting of their illness and had higher health related quality of life tended to have lower scores on the internalizing dimension. Findings suggest that individuals with POTS are at heightened risk for experiencing internalizing symptoms of psychopathology. A dimensional conceptualization of psychopathology seems like an effective way to identify symptoms of psychopathology that are separate from symptoms of autonomic nervous system dysfunction.

Neste trabalho apresentamos uma nova abordagem para a exploração de fibras neurais a partir de imagens de tensores de difusão. A estratégia combina técnicas de visualização de informação e visualização científica para obter uma rápida e precisa interpretação das fibras. Para isto fazemos uma transformação das fibras para vetores, e utilizamos uma nova técnica de projeção multi-dimensional (P-LSP), para trabalhar com conjuntos grandes de dados. A exploração do espaço das fibras é feita através desta projeção. Além disso, é apresentada a extensão das técnicas LSP e P-LSP para criar projeções em 3D, assim como estratégias que permitem interagir com pontos em 3D. Outra contribuição deste trabalho é a modificação de um método apresentado para criar superfícies de densidade fechadas sobre pontos esparsos. Esta modificação torna possível criar superfícies sobre conjuntos de pontos maiores com uma qualidade aceitável, o que é utilizado para representar conjunto de fibras como uma superfície. Esta nova abordagem é comparada com trabalhos similares mostrando nossas vantagens em termos de tempo de processamento, qualidade e funcionalidades para analisar esta categoria de dados / This work presents a novel approach for the exploration of neural fibers extracted from Diffusion Tensor Images. The developed strategy combines techniques from information and scientific visualization in order to attain a fast and precise interpretation of fiber sets. The approach transforms fibers into vectors from which a new multidimensional projection technique (PLSP) capable of handling large data sets. The fiber space is explored through the projection. Additionally this work extends P-LSP and LSP projections to 3D, and defines strategies to interact with 3D sparse points. Another contribution of this work is the extension of a method to create close density surfaces over the sparse space generated by the projections. The visualization approach is compared with other similar work showing advantages in processing time, quality and exploration capability to analyze this type of data sets