No description available.

The study of ferroelectric LiNbO<SUB>3</SUB> and LiTaO<SUB>3</SUB> doped with transition metals involves the characterisation of LiNbO<SUB>3</SUB>/LiTaO<SUB>3</SUB> solid solutions in the systems Li<SUB>2</SUB>O-Nb<SUB>2</SUB>O<SUB>5</SUB>-M<SUB>x</SUB>O<SUB>y</SUB> and Li<SUB>2</SUB>O-Ta<SUB>2</SUB>O<SUB>5</SUB>-M<SUB>x</SUB>O<SUB>y</SUB> (M = Cr, Mn, Fe, Co, Ni, Cu). Compounds were made by solid state reaction at temperatures between 1000 and 1500°C, depending on the system studied. The emphasis of this work is on the characterisation of the defect structure of LiNbO<SUB>3</SUB>/LiTaO<SUB>3</SUB> solid solutions using phase diagram determination, X-ray and neutron powder diffraction, EXAFS, ESR and optical spectroscopy. The valence of the incorporated cations was studied by magnetic measurements. The electrical properties of these materials have been investigated using AC impedance spectroscopy. It can be shown that the physical properties of LiNbO<SUB>3</SUB> and LiTaO<SUB>3</SUB> depend strongly on the defects in the structure which can be controlled by purposeful doping with other cations. Structural refinements of the X-ray and neutron powder diffraction data have shown that the defects arising from nonstoichiometry are accommodated by vacancies created on the Li site. This affects the structure when doped with third cations, giving rise to complex substitution mechanisms Spectroscopic studies have shown that the dopants (Cr<SUP>3+</SUP>, Mn<SUP>2+</SUP>/Mn<SUP>3+</SUP>, Co<SUP>2+</SUP>, Ni<SUP>2+</SUP>, Cu<SUP>+</SUP>, Cu<SUP>2+</SUP>) are shifted from the central octahedral position towards the adjacent empty octahedron. The electrical properties of LiNbO<SUB>3</SUB> and LiTaO<SUB>3</SUB>, measured by AC impedance spectroscopy, depend strongly on the dopant content: the conductivity generally rises, whereas the activation energy for the electrical conductivity drops with increasing dopant concentration. The microstructure of electroceramics can also be probed by AC impedance spectroscopy and it was shown that the texture of all samples was bad due to poor sintering of the pellets. Longer sintering times did not improve the quality of the ceramics which exhibit a large pore size distribution. An important aspect for future work would be the quality improvement of LiNbO<SUB>3</SUB>/LiTaO<SUB>3</SUB> based ceramics.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

University of Stellenbosch Business School / ENGLISH ABSTRACT: This study examined the relationship between economic structure and energy intensity in selected developed and developing countries of the world. A methodological and systematic approach was adopted to select the thirty-one countries explored in the study. Therefore, to answer the research questions posed in the study, the Granger Causality Technique and the Augmented Dickey-Fuller (ADF) method were used. This study discovered that the variables examined in the study showed variations. The variations emerged because of differences in methodologies and analytical frameworks adopted. Errorcorrection models were estimated and used to test for the direction of Granger causality. In the model, a high R2 was observed among the six variables (i.e. energy efficiency, per capita income, manufacturing, average energy prices, energy imports, technological developments), which invariably account for 60.8 percent of the variance in the energy intensity. Based on this, the unidirectional Granger causality runs from efficiency, per capita income and manufacturing to energy intensity. Hence, the price effects are relatively less significant in the causal chain. The result is at variance with the hypothesis that the structure of the economy does not determine its energy intensity. Nevertheless, a unidirectional Granger causality running from economic structure to energy intensity indicates that improvement in the economic structure would encourage a decline in energy intensity.

The sodium-calcium exchanger (NCX) is a countertransporter of Na+ and Ca2+ across most cell membranes. It has been identified as an essential component of Ca2+ homeostasis in physiological and disease conditions in both cardiovascular and neurological settings. The exchanger not only transports Na+ and Ca2+, but is also regulated by these ions. Although ionic regulatory profiles differ between NCX isoforms, similar regulatory domains have been identified. Previous structure-function studies have determined key residues within these domains, particularly in the eXchanger Inhibitory Peptide region (XIP) and the Ca2+ binding domains (CBD1/2), which have a direct impact on ionic regulation of the outward exchange currents. Recent structural studies of the Ca2+ binding domains of NCX1 suggest a mechanism by which Ca2+ binding would not only be essential for activation of current but may also influence Na+-dependent inactivation. The alternative splice region is located within the Ca2+ binding domain and may play a role in mediating these regulatory phenotypes. Previous studies have demonstrated that specific combinations of the mutually-exclusive and cassette exons are associated with profound effects on ionic regulation in NCX1. This study focuses on examining the mechanisms by which the alternative splice region, in combination with specific regulatory domains, modulates exchange activity in two isoforms, NCX1 and NCX2. Chimaeric and mutant constructs in the alternative splice region were expressed in Xenopus oocytes and outward Na+-Ca2+ exchange activity was assessed using the giant, excised patch clamp technique. Substitution of the region corresponding to the mutually exclusive exon in either exchanger greatly reduced the extent of Na+-dependent inactivation, independently of intracellular Ca2+ concentrations. However, replacement of both the region corresponding to the mutually exclusive exon A and the XIP region reestablishes a wild-type profile in NCX2. The first mutually exclusive exon is therefore critical in determining Na+ and Ca2+-dependent regulatory properties. Furthermore, non-conserved residues within the XIP region may be essential in maintaining the structural stability of the Na+-dependent inactive state of NCX1, and by interacting with the mutually exclusive exon, may contribute to the structure-function relationship and the distinct regulatory phenotype of each Na+-Ca2+ exchanger variant and isoform.