How well do South African schools convert grade 8 achievement into matric outcomes?

School retention in South Africa and performance in the major school-leaving matric examination are characterised by significant inequalities on the basis of race and socio-economic status. In order to know at what point in the educational trajectory policy interventions and school improvement programmes will be most effective, it is necessary to trace the development of these educational inequalities to earlier phases of schooling and before. This paper reports on findings from a unique dataset that tracks individuals who participated in TIMSS in 2002 as grade 8 students to matric in 2006 and 2007. This permits an investigation into the extent to which educational inequalities are already evident by the eighth grade, and what if anything is achieved by secondary schools to reduce them. Several noteworthy findings emerge. The overall level of achievement, at both grade 8 and matric, differs widely across the historically different parts of the school system. There are also intriguing differences in the abilities of different parts of the system to convert grade 8 achievement into matric outcomes. What is clear is that inequalities in the cognitive ability of students at the outset of secondary school persist and that there is no observable evidence of a closing of these gaps by matric. This points to the importance of interventions prior to secondary school – at the primary school level and even at the level of early childhood development. Finally, it is also demonstrated that the decision to take mathematics in matric is characterised by a high degree of randomness within the historically black part of the school system. This points to the value of meaningful assessment practices and feedback to students, which serve as an important signal as to whether or not to choose mathematics as a matric subject.South Africa, Socio-economic Status, Education, Educational Achievement, Educational Inequality

Characteristic length of random knotting for cylindrical self-avoiding polygons

We discuss the probability of random knotting for a model of self-avoiding polygons whose segments are given by cylinders of unit length with radius $r$. We show numerically that the characteristic length of random knotting is roughly approximated by an exponential function of the chain thickness $r$.Comment: 5 pages, 4 figure

Topological entropy of a stiff ring polymer and its connection to DNA knots

We discuss the entropy of a circular polymer under a topological constraint. We call it the {\it topological entropy} of the polymer, in short. A ring polymer does not change its topology (knot type) under any thermal fluctuations. Through numerical simulations using some knot invariants, we show that the topological entropy of a stiff ring polymer with a fixed knot is described by a scaling formula as a function of the thickness and length of the circular chain. The result is consistent with the viewpoint that for stiff polymers such as DNAs, the length and diameter of the chains should play a central role in their statistical and dynamical properties. Furthermore, we show that the new formula extends a known theoretical formula for DNA knots.Comment: 14pages,11figure

Abundance of unknots in various models of polymer loops

A veritable zoo of different knots is seen in the ensemble of looped polymer chains, whether created computationally or observed in vitro. At short loop lengths, the spectrum of knots is dominated by the trivial knot (unknot). The fractional abundance of this topological state in the ensemble of all conformations of the loop of $N$ segments follows a decaying exponential form, $\sim \exp (-N/N_0)$, where $N_0$ marks the crossover from a mostly unknotted (ie topologically simple) to a mostly knotted (ie topologically complex) ensemble. In the present work we use computational simulation to look closer into the variation of $N_0$ for a variety of polymer models. Among models examined, $N_0$ is smallest (about 240) for the model with all segments of the same length, it is somewhat larger (305) for Gaussian distributed segments, and can be very large (up to many thousands) when the segment length distribution has a fat power law tail.Comment: 13 pages, 6 color figure

Educational outcomes : pathways and performance in South African high schools

CITATION: Reddy, V., Van der Berg, S., Janse van Rensburg, D. & Taylor, S. 2012. Educational outcomes: pathways and performance in South African high schools. South African Journal of Science, 108(3/4), Art. #620, doi:10.4102/sajs.v108i3/4.620.The original publication is available at http://sajs.co.zaWe analysed the pathways and performances in mathematics of high (secondary) school students in South Africa using a panel-like data set of Grade 8 students who participated in the 2002 Trends in International Mathematics and Science Study (TIMSS) and who were tracked to Grade 12 examination data sets. We examined the relationship between TIMSS mathematics performance and reaching Grade 12, the selection of and performance in Grade 12 mathematics, and success rates in the matriculation examination. The progression of students from schools serving middle-class (Subsystem M) and poorer students (Subsystem P, the majority) was compared. Firstly, mathematics achievement scores in South Africa are low and different performance patterns were shown between the two subsystems. Secondly, students who started with similar Grade 8 mathematics scores had different educational outcomes 4 years later. In Subsystem M schools, Grade 8 mathematics scores were a good indicator of who would pass matric, whilst this relationship was not as strong in Subsystem P schools. Thirdly, there was a stronger association between TIMSS Grade 8 scores and subject choice of matric mathematics in Subsystem M schools than in Subsystem P schools. Fourthly, there was a strong correlation between Grade 8 mathematics performance and matric mathematics achievement. Mathematics performance in the earlier years predicted later mathematics performance. To raise exit level outcomes, mathematics scores need to be raised by Grade 8 or earlier. To improve educational and labour market outcomes, the policy priority should be to build foundational knowledge and skills in numeracy. © 2012. The Authors.http://sajs.co.za/educational-outcomes-pathways-and-performance-south-african-high-schools/reddy-vijay-van-der-berg-servaas-janse-van-rensburg-dean-taylor-stephenPublisher's versio

Educational outcomes: Pathways and performance in South African high schools

We analysed the pathways and performances in mathematics of high (secondary) school students in South Africa using a panel-like data set of Grade 8 students who participated in the 2002 Trends in International Mathematics and Science Study (TIMSS) and who were tracked to Grade 12 examination data sets. We examined the relationship between TIMSS mathematics performance and reaching Grade 12, the selection of and performance in Grade 12 mathematics, and success rates in the matriculation examination. The progression of students from schools serving middle-class (Subsystem M) and poorer students (Subsystem P, the majority) was compared. Firstly, mathematics achievement scores in South Africa are low and different performance patterns were shown between the two subsystems. Secondly, students who started with similar Grade 8 mathematics scores had different educational outcomes 4 years later. In Subsystem M schools, Grade 8 mathematics scores were a good indicator of who would pass matric, whilst this relationship was not as strong in Subsystem P schools. Thirdly, there was a stronger association between TIMSS Grade 8 scores and subject choice of matric mathematics in Subsystem M schools than in Subsystem P schools. Fourthly, there was a strong correlation between Grade 8 mathematics performance and matric mathematics achievement. Mathematics performance in the earlier years predicted later mathematics performance. To raise exit level outcomes, mathematics scores need to be raised by Grade 8 or earlier. To improve educational and labour market outcomes, the policy priority should be to build foundational knowledge and skills in numeracy

EDTA as a chelating agent in quantitative 1H-NMR of biologically important ions

Biologically important ions (Ca, K, Mg, Fe, and Zn) play major roles in numerous biological processes, with their homeostatic balance being necessary for the maintenance of cellular mechanisms. Sudden and severe loss in homeostasis of just one biologically important ion can cause cascading negative effects. Being able to quickly, accurately and reliably quantify biologically important ions in human bio-fluid samples is something that has been sorely lacking within the field of metabolomics. 1H-NMR is a well-known analytical platform in metabolomics but ions are invisible on 1H-NMR spectra. The foundation of our investigation was based upon a priori knowledge that free EDTA produce two clear single peaks on 1H-NMR spectra, and that EDTA chelated to different ions produce unique 1H-NMR spectral patterns due to 3D conformational changes in the chemical structure of chelated-EDTA and varying degrees of electronegativity. The aim of this study was to develop and test a 1H-NMR-based method, with application specifically to the field of metabolomics, to quantify biologically important ions within the physiological pH range of 6.50-7.50 using EDTA as a chelating agent. Our method produced linear, accurate, precise and repeatable results for Ca, Mg and Zn; however, K and Fe did not chelate with EDTAThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Risk for HIV-1 infection associated with a common CXCL12 (SDF1) polymorphism and CXCR4 variation in an African population

CXC chemokine ligand 12 (CXCL12), or stromal cell–derived factor 1 (SDF1), is the only known natural ligand for the HIV-1 coreceptor, CXC chemokine receptor 4 (CXCR4). A single nucleotide polymorphism (SNP) in the CXCL12 gene (SDF1-3'A) has been associated with disease progression to AIDS in some studies, but not others. Mutations in the CXCR4 gene are generally rare and have not been implicated in HIV-1/AIDS pathogenesis. This study analyzed the SDF1-3'A SNP and performed mutation screening for polymorphic markers in the CXCR4 gene to determine the presence or absence of significant associations with susceptibility to HIV-1 infection. The study consisted of 257 HIV-1–seropositive patients and 113 HIV-1–seronegative controls representing a sub-Saharan African population belonging to the Xhosa ethnic group of South Africa. The SDF1-3'A SNP was associated with an increased risk for HIV-1 infection (P = 0.0319) whereas no significant association was observed between the occurrence of the SDF1-3'A SNP and increased or decreased plasma levels of CXCL12. Comprehensive mutation analysis of the CXCR4 gene confirmed a high degree of genetic conservation within the coding region of this ancient population.The authors thank Lehana Breytenbach for sample collection and maintenance of the HIV database; Heather Money for the coordination of blood specimens from the Western Province Blood Transfusion Service; all clinicians and nursing staff at the HIV clinics and blood transfusion services of the Western Cape; and the study participants