University of South Africa

About: University of South Africa is a education organization based out in Pretoria, South Africa. It is known for research contribution in the topics: Context (language use) & Population. The organization has 8478 authors who have published 19960 publications receiving 237688 citations. The organization is also known as: Unisa.

Origin and control of high-temperature ferromagnetism in semiconductors.

Abstract: The extensive experimental and computational search for multifunctional materials has resulted in the development of semiconductor and oxide systems, such as (Ga,Mn)N, (Zn,Cr)Te and HfO2, which exhibit surprisingly stable ferromagnetic signatures despite having a small or nominally zero concentration of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and the associated magnetooptical and magnetotransport functionalities, are dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these nanocrystals can be controlled by manipulating the charge state of the Cr ions during the epitaxy. The findings provide insight into the origin of ferromagnetism in a broad range of semiconductors and oxides, and indicate possible functionalities of these composite systems. Furthermore, they demonstrate a bottom-up method for self-organized nanostructure fabrication that is applicable to any system in which the charge state of a constituent depends on the Fermi-level position in the host semiconductor.

The effect of retention factors on organisational commitment : an investigation of high technology employees

Abstract: The objective of the present study was to investigate specific retention factors that induced the organisational commitment of high technology employees. A sample of 94 professional technicians from a South African owned telecommunications company based in the Gauteng province participated. The Organisational Commitment Scale and a retention factor measurement scale were administered. The most relevant explanatory factors were compensation, job characteristics, supervisor support, and work/life policies, which appeared to have a statistically significant influence on the development of organisational commitment in high technology employees. The implications of the findings are discussed.

Improving Predictions for Helium Emission Lines

Abstract: We have combined the detailed He I recombination model of Smits with the collisional transitions of Sawey & Berrington in order to produce new accurate helium emissivities that include the effects of collisional excitation from both the 2 3S and 2 1S levels. We present a grid of emissivities for a range of temperature and densities along with analytical fits and error estimates. These grids eliminate the necessity of making corrections for collisional enhancements as in the work of Clegg or Kingdon & Ferland for lines with upper levels below n=5. For densities greater than ne≈106 cm-3, inclusion of collisional excitation from the 2 1S level is also necessary if accuracies of greater than a few percent are required. Atomic data for a model atom with 29 levels (nmax=5) are presented that match the recombination model of Smits to within 5% over the temperature range T=5000-20,000 K. Collisional effects are calculated self-consistently using the algorithm of Almog & Netzer. This model atom will be useful in models of radiative transfer. A notable feature of this technique is an algorithm that calculates the indirect recombination rates, the recombination to individual levels that go through n>nmax first. Fits accurate to within 1% are given for the emissivities of the brightest lines over a restricted range for estimates of primordial helium abundance. We characterize the analysis uncertainties associated with uncertainties in temperature, density, fitting functions, and input atomic data. We estimate that atomic data uncertainties alone may limit abundance estimates to an accuracy of ~1.5%; systematic errors may be greater than this. This analysis uncertainty must be incorporated when attempting to make high-accuracy estimates of the helium abundance. For example, in recent determinations of the primordial helium abundance, uncertainties in the input atomic data have been neglected. Finally, we compare our theoretical calculations to the measured strengths of a few dozen helium emission lines in three nebulae, Orion (NGC 1976) and the planetary nebulae NGC 6572 and IC 4997. Incorporation of collisional effects yields noticeable improvements for some lines, but some notable discrepancies remain.