Le développement de nanomatériaux à propriétés optiques et fonctionnalisés pour un marquage spécifique est en plein essor dans le domaine de l'imagerie biologique. Parmi les agents de contraste exogènes déjà utilisés, les marqueurs fluorescents tels que les nanocristaux semi-conducteurs (CdSe/ZnS,…) et les molécules organiques naturelles (GFP,…) ou synthétiques (fluorescéine,…) souffrent respectivement de clignotements (blinking) et de photo-blanchiment (bleaching) c'est-à-dire d'une faible tenue au rayonnement lumineux incident. Récemment, la microscopie de Génération de Second Harmonique (GSH) à partir de structures non-centrosymétriques de certains matériaux ou molécules optiquement non linéaires (ONL), s'est révélée un outil particulièrement prometteur. Les inconvénients du clignotement et du photo-blanchiment sont en effet absents pour le processus non linéaire de GSH. De plus, le principe de fonctionnement des marqueurs ONL repose sur un processus non résonant, contrairement aux marqueurs fluorescents, ce qui est un avantage décisif pour le choix de la longueur d'onde d'excitation des nanosondes. Pour des illuminations dans le proche infrarouge, cela permet de limiter l'énergie déposée dans le milieu biologique, d'augmenter la profondeur d'imagerie et enfin de bien séparer spectralement les signaux des marqueurs ONL de l'auto-fluorescence naturelle de certains échantillons. Notre objectif, dans ce contexte, était la synthèse et la caractérisation de nouvelles nanosondes ONL de forme sphérique et de taille inférieure à 100nm. Le matériau de structure cristalline non centrosymétrique retenu est l'iodate de fer (Fe(IO3)3) car ses éléments chimiques sont peu toxiques et que ses propriétés paramagnétiques peuvent également donner un contraste en imagerie par résonance magnétique (IRM) ce qui est potentiellement intéressant par rapport à d'autres cristaux ONL tels que ZnO, KNbO3, BaTiO3 et KTP. D'un point de vue synthèse, les microémulsions inverses sont bien référencées dans la littérature pour leur rôle de gabarit permettant un bon contrôle de la taille et de la morphologie des nanomatériaux obtenus par co-précipitation. Dans ce travail, les nano-réacteurs ont été préparés à partir des systèmes AOT/alcane/eau et Triton/1-hexanol/cyclohexane/eau. De manière très originale et pratique, le développement d'un banc optique de diffusion Hyper-Rayleigh (HRS) a permis de suivre in-situ et en temps réel les cinétiques de cristallisation des nanoparticules de Fe(IO3)3 en fonction de conditions expérimentales variables. Les mécanismes de croissance et de cristallisation des nano-bâtonnets de Fe(IO3)3 ont été élucidés en combinant d'autres techniques physico-chimiques usuelles comme la diffraction des rayons X, la diffusion dynamique de la lumière et la microscopie électronique en transmission. Nous avons démontré que la température et la nature du tensioactif influencent les forces d'interaction à l'interface organique-inorganique ce qui permet, pour certaines conditions expérimentales, de réduire la taille et la polydispersité des nanocristaux en fin de processus. Toutefois, avant d'envisager l'utilisation de ces derniers en tant que marqueurs optiques spécifiques, il est nécessaire d'encapsuler ces nanocristaux en raison de la faible stabilité du composé aux pH physiologiques. Les premiers essais de stabilisation en microémulsions par une couche de silice ont permis d'obtenir des nanoparticules de taille ~ 10 nm avec une forte réponse ONL. La caractérisation complète et la fonctionnalisation de ces nanostructures ainsi qu'une optimisation des interactions à l'interface particules – films de tensioactifs constituent les perspectives de ce travail. / The development of functionalized nanomaterials with optical properties for a site-specific labeling or conjugation has undergone a rapid growth in the biological imaging field. Among the exogenous contrast agents which are already used, fluorescent nanocrystals such as semi-conductor (CdSe / ZnS, ...) and natural organic molecules (GFP, ...) or synthetic molecules (fluorescein, ...) suffer from blinking and photobleaching, respectively. Recently, Second Harmonic Generation (SHG) from acentric structures of some Non-Linear Optical (NLO) materials or organic molecules appeared to be particularly promising. Indeed, the major disadvantages of blinking and photobleaching are absent in the SHG process. Additionally, imaging of NLO probes is based on a non-resonant process, contrary to traditional fluorescent probes, which is key in terms of excitation wavelength. Near infrared illumination can limit the energy deposited in the biological tissues, increase the imaging depth and, finally, the SHG signal can be more readily spectrally resolved from the natural auto-fluorescence. The main objectives of this thesis were the synthesis and characterization of new NLO nanoprobes with a spherical shape and a size lower than 100 nm. The non-centrosymmetric material of interest is iron iodate (Fe(IO3)3). Its chemical elements are non toxic and its paramagnetic response may also provide a contrast in Magnetic Resonance Imaging (MRI) which is not the case of the other NLO crystals such as ZnO, KNbO3, BaTiO3 and KTP. From a synthesis point of view, reverse microemulsions are well documented in the literature as good templates for the size and shape control of nanomaterials obtained by a coprecipitation reaction. In this work, nanoreactors were prepared from the AOT/alkane/water and Triton/1-hexanol /cyclohexane/water systems..A very original and convenient setup based on the Hyper-Rayleigh Scattering (HRS) was implemented so that the real-time crystallization kinetics of the growing acentric iron iodate nanocrystals in microemulsions could be measured according to different experimental conditions. We demonstrate that HRS is a fast, valuable and nondestructive alternative to probe in-situ the crystallization and growth dynamics of Fe(IO3)3 nanorods whereas the growth mechanism was elucidated by a combination of Dynamic Light Scattering, X-ray diffraction and Transmission Electron Microscopy experiments. The binding interaction between surfactant molecules and colloidal particles was studied as a function of the synthesis temperature as well as the surfactant nature. In some experimental conditions the size and polydispersity of the final nanorods can be thus reduced. However, the use of iron iodate as specific NLO optical probes is so far restricted due to its low stability at physiological pH. Preliminary encapsulation tests by a thin silica-coating in reverse microemulsions show the presence of ~ 10nm nanocparticles with a strong NLO response. The complete characterization and functionalization of these nanostructures as well as the optimization of the binding interactions at the organic-inorganic interface are the prospects of this work

We report a rapid additive-free synthesis of nanocrystals (NCs) of RHO-type ZIF-71 (1) of composition [Zn(dcim)₂] (dcim = 4,5-dichloroimidazolate) in 1-propanol as solvent at room temperature. NC-1 has a size of 30–60 nm and exhibits permanent microporosity with a surface area (SBET = 970 m² g−¹) comparable to that of microcrystalline material. When kept under the mother solution NC-1 undergoes transformation into a novel SOD-type polymorph (2), which in turn converts into known ZIF-72 (3) with lcs topology. It is shown that microcrystals (MCs) of 2 can be favourably synthesised using 1-methylimidazole as a coordination modulator. NC-2 with size <200 nm was prepared using NC-ZIF-8 as a template with SOD topology in a solvent assisted ligand exchange-related process. DFT-assisted Rietveld analysis of powder XRD data revealed that novel polymorph 2 possesses an unusual SOD framework conformation. 2 was further characterised with regard to microporosity (SBET = 597 m² g−¹) and thermal as well as chemical stability. DFT calculations were performed to search for further potentially existing but not-yet synthesised polymorphs in the [Zn(dcim)₂] system.

Published Article / With the dawn of the new curriculum in this country, namely, Curriculum 2005 (C2005) in 1997, and the Revised National Curriculum Statement (RNCS) in 2002, which are the two major curriculum policy developments in South Africa (Ramsuran & Malcolm, 2006:515), it invited an assortment of reactions from the entire education fraternity. The most obvious and extensive critique of the curriculum was that of the Report of the Ministerial Review Committee, which was established to review it in 2000. The approach adopted in this study is to encompass both processes of initial introduction and the revision stages in its reference to the curriculum. This article however, reveals that despite these implementation challenges, the overwhelming majority (88%) of the teachers have not only begun to embrace it, but are also applying the OBE principles in their lessons.

Published Aticle / This article reports on the experiences of Mathematics educators during the implementation of the National Curriculum Statement (NCS) in Grades 10 - 12. The study is contained in five different, but educationally related constructs addressing training, problem areas which challenge or appeal to Mathematics educators, lesson planning, assessment strategies and the effective integration of OBE in the teaching of Mathematics. A mixed methods design was used, with data being collected and collated using questionnaires and semi-structured interviews. The quantitative data employed descriptive data analysis, while the qualitative data was analysed by identifying differences and similarities. The study revealed that educators differed in terms of the problems they encountered with implementing the NCS in Mathematics. They agreed, however, that the implementation was successful and that it contributed to better teaching.

Magister Public Health - MPH / High HIV incidence among young women is a global public health concern with the potential for a huge impact on their lives. Several interventions have been identified to help reduce HIV incidence among young women, including HIV Counselling and Testing (HCT). Lack of knowledge of HIV status is a major barrier to HIV prevention, care and treatment efforts. Therefore, HCT uptake among young women needs to be up-scaled. Early detection and treatment can help cushion the impact of AIDS on the lives of young women. There are various factors that negatively influence young women’s HCT uptake, including psychosocial characteristics. Studies have linked self-esteem to HCT and high levels of HIV risk behaviour practices among young women. The aim of this study was to assess the relationship between self-esteem and HCT uptake among young women (16 to 24 years) in South Africa using data from the 2012, Third National HIV Communication Survey (NCS). This was a quantitative secondary data analysis of cross-sectional data from the 2012 NCS. The participants of this study were young women (n =1922) from all provinces in South Africa. The independent variable was self-esteem and the dependent variable was ever testing for HIV and testing in the last 12 months, with a number of socio-demographic characteristics as covariates. Data was analysed using STATA statistical software (version 13.0, STATA Corp., College Station Texas, USA). Socio-demographic characteristics were described through descriptive statistics. The relationship between independent variables and HIV testing was analysed with Chi-squared tests of association. Logistic regression models were used to examine the relationship between self-esteem and HCT uptake when controlling for confounders.

This thesis reports work in three areas of X-ray crystallography. An initial chapter describes the structure of a protein, the methods based on the use of X-rays and computer analysis of diffraction patterns to determine crystal structure, and the subsequent derivation of the structure of part or all of a protein molecule. Work to determine the structure of the protein cytokine receptor-like factor 3 (CRLF3) leading to the successful generation of a structural model of a significant part of this molecule is then described in Chapter 2. A variety of techniques had to be deployed to complete this work, and the steps undertaken are described. Analysis was performed principally using phaser, using maximum likelihood methods. Areas for improvement in generating non-crystallographic symmetry (NCS) operators in existing programmes were identified and new and modified algorithms implemented and tested. Searches based on improved single sphere algorithms, and a new two-sphere approach, are reported. These methods showed improvements in many cases and are available for future use. In Chapter 4, work on determining the relative importance of low resolution and high intensity data in molecular replacement solutions is described. This work has shown that high intensity data are more important than the low resolution data, dispelling a common perception and helping in experimental design.

Thesis (Ph.D. (Afrikaans en Nederlands)--North-West University, Potchefstroom Campus, 2008.

Der Trend auch für schnelle, zeitkritische Regelungsaufgaben geht zunehmend in Richtung Feldbusse und Industrial Ethernet. Dem unbestreitbaren Nutzen der Kosteneinsparung stehen Probleme gegenüber: Die unsicheren Zeitbedingungen im Netz verschlechtern die dynamischen Eigenschaften digitaler Regelungen in unvorhersehbarer Weise. Diese Arbeit stellt eine praktikable Methodik vor, um die Regelgüte solcher Systeme sicher und aufwandsarm vorherzusagen. / High dynamic, i.e. time-critical automatic feedback control systems are more and more implemented using field bus or industrial ethernet solutions. The cost-efficiency of these approaches is unchallengeable, but they also cause serious technical problems: Uncertain time behavior of data networks so far degrades the dynamic performance of digital closed-loop controls in an unpredictable manner. The research paper introduces a practicable, reliable and straightforward method to forecast the system behavior.

This study is an attempt at consolidating in a single source the inclusive history of the development of Afrikaans since 1652, as well as the various perspectives on the origins of Afrikaans put forward from the eighteenth to the twenty-first century. As a consequence of sociopolitical circumstances in South Africa, the various role-players involved in the origins and development of Afrikaans have not all been adequately taken account of in the description of the history of the Afrikaans language. This has contributed to the prevalence of inaccurate perceptions about the origins of Afrikaans. Amongst others, these misperceptions have let to the teaching of the history of Afrikaanspredominantly focusing on the (white) historical Eastern variety and on standard Afrikaans, minimising the existence of any possible Creole influences on the language. For purposes of this study, the inclusive history of the development of Afrikaans since 1652 was rewritten in order to take account of the influence of all the role players (the Europeans from the West, the indigenous Koina from Africa, and the slaves brought from Asia) on the origins and development of Afrikaans. A further aim of this rewriting was to evaluate and consolidate, chronologically, the approximately 40 perspectives on the origins of Afrikaans against the background of the socio-political milieu within which these perspectives developed. Some aspects of this rewritten history of Afrikaans were taught by means of a series of lessons to learners in regions representative of areas where sub-varieties of the three historical Afrikaans varieties are spoken and heard. The aim was to determine whether series of lessons, similar to the one used in this study, could be regarded (and recommended) as an appropriate presentation method to disseminate the inclusive history of the development of Afrikaans among the school-going youth. Knowledge of and insight in the inclusive history of the development of Afrikaans may contribute to the process of reconciliation in South Africa, because this history suggests that Afrikaans is the collective creation of Afrikaans-speaking citizens' ancestors: Europeans from the West, indigenous Koina from Africa, and slaves brought from the East. / Thesis (Ph.D. (Afrikaans en Nederlands)--North-West University, Potchefstroom Campus, 2008.

This study is an attempt at consolidating in a single source the inclusive history of the development of Afrikaans since 1652, as well as the various perspectives on the origins of Afrikaans put forward from the eighteenth to the twenty-first century. As a consequence of sociopolitical circumstances in South Africa, the various role-players involved in the origins and development of Afrikaans have not all been adequately taken account of in the description of the history of the Afrikaans language. This has contributed to the prevalence of inaccurate perceptions about the origins of Afrikaans. Amongst others, these misperceptions have let to the teaching of the history of Afrikaanspredominantly focusing on the (white) historical Eastern variety and on standard Afrikaans, minimising the existence of any possible Creole influences on the language. For purposes of this study, the inclusive history of the development of Afrikaans since 1652 was rewritten in order to take account of the influence of all the role players (the Europeans from the West, the indigenous Koina from Africa, and the slaves brought from Asia) on the origins and development of Afrikaans. A further aim of this rewriting was to evaluate and consolidate, chronologically, the approximately 40 perspectives on the origins of Afrikaans against the background of the socio-political milieu within which these perspectives developed. Some aspects of this rewritten history of Afrikaans were taught by means of a series of lessons to learners in regions representative of areas where sub-varieties of the three historical Afrikaans varieties are spoken and heard. The aim was to determine whether series of lessons, similar to the one used in this study, could be regarded (and recommended) as an appropriate presentation method to disseminate the inclusive history of the development of Afrikaans among the school-going youth. Knowledge of and insight in the inclusive history of the development of Afrikaans may contribute to the process of reconciliation in South Africa, because this history suggests that Afrikaans is the collective creation of Afrikaans-speaking citizens' ancestors: Europeans from the West, indigenous Koina from Africa, and slaves brought from the East. / Thesis (Ph.D. (Afrikaans en Nederlands)--North-West University, Potchefstroom Campus, 2008.