The elastic properties of Mo2BC were studied using ab initio calculations. The calculated bulk modulus of 324 GPa is 45% larger than that of Ti0.25Al0.75N and 14% smaller than that of c-BN, indicating a highly stiff material. The bulk modulus (B) to shear modulus (G) ratio is 1.72 at the transition from brittle to ductile behaviour. This, in combination with a positive Cauchy pressure (c12 − c44), suggests moderate ductility. When compared with a typical hard protective coating such as Ti0.25Al0.75N (B = 178 GPa; B/G = 1.44; negative Cauchy pressure), Mo2BC displays considerable potential as protective coating for metal cutting applications. In order to test this proposal, Mo2BC thin films were synthesized using dc magnetron sputtering from three plasma sources on Al2O3(0 0 0 1) at a substrate temperature of ∼900 °C. The calculated lattice parameters are in good agreement with values determined from x-ray diffraction. The measured Young's modulus values of ∼460 ± 21 GPa are in excellent agreement with the 470 GPa value obtained by calculations. Scanning probe microscopy imaging of the residual indent revealed no evidence for crack formation as well as significant pile-up, which is consistent with the moderate plasticity predicted. The apparent contradiction between moderate ductility on the one hand and indentation hardness values of 29 GPa can be understood by considering the electronic structure particularly the extreme anisotropy. The presence of stiff Mo–C and Mo–B layers with metallic interlayer bonding enables this intriguing and unexpected property combination.

A study on the effect of a structured problem-solving strategy on problem-solving skills and conceptual understanding of physics was undertaken with 189 students in 16 disadvantaged South African schools. This paper focuses on the development of conceptual understanding. New instruments, namely a solutions map and a conceptual index, are introduced to assess conceptual understanding demonstrated in students' written solutions to examination problems. The process of the development of conceptual understanding is then explored within the framework of Greeno's model of scientific problem-solving and reasoning. It was found that students who had been exposed to the structured problem-solving strategy demonstrated better conceptual understanding of physics and tended to adopt a conceptual approach to problemsolving.

In any laser skin treatment, the optical properties (absorption and scattering coefficients) are important parameters. The melanin content of skin influences the absorption of light in the skin. The spread in the values of the absorption coefficients for the South African skin phototypes are not known. A diffuse reflectance probe consisting of a ring of six light delivery fibers and a central collecting fiber was used to measure the diffused reflected light from the arms of 30 volunteers with skin phototypes I-V (on the Fitzpatrick scale). The absorption coefficient was calculated from these measurements. This real-time in vivo technique was used to determine the absorption coefficient of sun-exposed and -protected areas on the arm. The range of typical absorption coefficients for the South African skin phototypes is reported. The values for the darker South African skin types were much higher than was previously reported for darker skin phototypes. In the analysis, the contributions of the eumelanin and pheomelanin were separated, which resulted in improved curve fitting for volunteers of southern Asian ethnicity without compromising the other groups.

Integrating indigenous knowledge (IK) into school science teaching is one way of maximising the sociocultural relevance of science education for enhanced learners' performance. The epistemological differences however between the nature of science (NOS) and nature of indigenous knowledge (NOIK) constitute a major challenge for an inclusive IK-science curriculum integration. This article is about the application of a truth-based epistemological framework designed to support teachers to make decisions on how specific pieces of indigenous knowledge (local traditional practices and technologies) may be included in science lessons. First, an attempt was made to develop a truth-based epistemological framework for identifying epistemology(ies) of indigenous knowledge and practices. Second a group of science teachers used the truth-based epistemological framework to examine ways in which some specified IK practices that comprised a coherent set of knowledge themes on health, agriculture and technology could be integrated into the school science curriculum in a valid and legitimate way. The IK practices used in the study were systematically identified and documented by means of personal observations and interviews of key informants in a rural community in Zimbabwe. The main findings of the study showed that the truth-based epistemological framework was useful in providing an epistemological basis for including some IK practices in science teaching and learning. As a tool for pedagogy the framework enabled the science teachers to reconsider and change their valuing of Indigenous knowledge Systems (IKS), more specifically in ways in which local knowledge can validly be incorporated into school science teaching.

An individualised laser skin treatment may enhance the treatment and reduces risks and side-effects. The optical properties (absorption and scattering coefficients) are important parameters in the propagation of laser light in skin tissue. The differences in the melanin content of different skin phototypes influence the absorption of the light. The absorption coefficient at the treatment wavelength for an individual can be determined by diffuse reflectance spectroscopy, using a probe containing seven fibres. Six of the fibres deliver the light to the measurement site and the central fibre collects the diffused reflected light. This is an in vivo technique, offering benefits for near-real-time results. Such a probe, with an effective wavelength band from 450 to 800 nm, was used to calibrate skin-simulating phantoms consisting of intralipid and ink. The calibration constants were used to calculate the absorption coefficients from the diffuse reflectance measurements of three volunteers (skin phototypes, II, IV and V) for sun-exposed and non-exposed areas on the arm.

While Si, C and SiC are very well known materials that have been extensively studied in their multitude of structures and allotropes, there is, surprisingly, a dearth of reliable information for off-50:50 compounds involving Si and C. Do such compounds exist and, if so, what are the plausible structures for these compounds? Using first principles total energy methods, we generally explore these questions before investigating in some detail the structures involving silicon dicarbide. Of the structures considered, our results show that the tetragonal glitter phase is lowest in energy. Of the two higher energy cubic structures that we considered, we note that there is a continuous transition from the high energy fluorite structure to the lower energy pyrite structure. We predict the transition pressure from glitter to pyrite to be 24.7 GPa. We give detailed structural and electronic properties for these systems. Since diamond and SiC are known for their hardness properties, we compute the elastic properties of SiC 2 , and we make an assessment of its hardness properties. We propose the glitter structure to be a plausible phase for SiC 2 .

No abstract

A quasi-experimental study was undertaken to extend first-world research on physics problem solving into disadvantaged South African classrooms. Sixteen urban high schools, involving 189 learners, participated in the study, investigating the effect of a structured problem solving strategy on performance and conceptual understanding. This article focuses on the enhancement of problem solving performance in classroom tests and the midyear examination. The treatment group outperformed the control group by 8% in the midyear examination. Using ANOVA, this increased average score was statistically significant at the .001 level, indicating enhanced problem solving skills. Furthermore, it was demonstrated that the strategy was not transferred successfully to topics studied prior to implementation of the problem solving strategy. A theory is presented to explain the results in terms of the co-development of conceptual understanding and problem solving skill.