Blind Admission? The ability of NSC maths to signal competence in university commerce courses as compared to the former SC Higher Grade maths

Mathematics is an important signal used for admission into commerce courses in South African universities. In 2008 the new National Senior Certificate replaced the former Senior Certificate. This new exam no longer had different grades and thus created a structural break in the ability of the mathematics mark to signal preparedness for university. Although the Department of Education provided a “translation” key between the two Certificates, the University of the Witwatersrand (and other universities) admitted many more students in 2009 that met the entry requirements than previously. However, this cohort has lower average test and exam scores than previous years. This suggests that marks obtained for mathematics in the new National Senior Certificate are inflated when compared to the former Senior Certificate. This paper uses similar tests, for two commerce subjects, written by students in 2008 and 2009 to create a comparison between the mathematics marks under the two different certificates. The results suggest that marks in the range of 40-100% for Higher Grade mathematics for the Senior Certificate are now compressed into the 70-95% range for the new National Senior Certificate. This significantly weakens the ability of the school-leaving mathematics mark to signal the ability of students to cope with first year commerce courses.Mathematics, National Senior Certificate, Economics 1, first year, Commerce courses, South Africa

Vibrio vulnificus and Proteus vulgaris Co-infection Associated with High Mortality in a Flock of Turkey in Ado Ekiti, Nigeria

The study reports bacteriological investigations carried out on a case of high mortality (10%) reported over a period of one week in a flock of turkey, 450 in number, aged 16 weeks old, in a poultry farm in Ado-Ekiti, Nigeria. Clinical signs were those of weakness, recumbence, diarrhoea (yellowish to greenish in colour) and weight loss. Post morterm examination was that of enteritis and mild liver enlargement, with no major pathognomonic lesions. Bacteriological investigations were carried out on clinical (Blood, Liver, Heart Muscles and Bile) and environmental (feed, drinking water and litter) samples. Bacteriological studies of the clinical samples obtained from dead birds revealed a co-infection of Vibrio vulnificus and Proteus vulgaris. The clinical bacterial isolates showed highest susceptibility to Ofloxacin (75%), with varied levels of susceptibility to other antibiotics tested. Mortality on the farm was curtailed following an oral medication with norfloxacin. A variety of bacteria, including Vibrio vulnificus and Proteus vulgaris, were isolated from the environmental samples. The bacterial isolates from the environmental samples were resistant to multiple drugs. Since the bacteria implicated in the clinical infection were isolated from environmental samples, an adequate biosecurity measures is needful in poultry farm for profitability. Keywords: Antibiotic-resistance, Bacteria, Co-infection, Mortality and Turke

Crucial role of sidewalls in velocity distributions in quasi-2D granular gases

Our experiments and three-dimensional molecular dynamics simulations of particles confined to a vertical monolayer by closely spaced frictional walls (sidewalls) yield velocity distributions with non-Gaussian tails and a peak near zero velocity. Simulations with frictionless sidewalls are not peaked. Thus interactions between particles and their container are an important determinant of the shape of the distribution and should be considered when evaluating experiments on a tightly constrained monolayer of particles.Comment: 4 pages, 4 figures, Added reference, model explanation charified, other minor change

A lattice model for the line tension of a sessile drop

Within a semi--infinite thre--dimensional lattice gas model describing the coexistence of two phases on a substrate, we study, by cluster expansion techniques, the free energy (line tension) associated with the contact line between the two phases and the substrate. We show that this line tension, is given at low temperature by a convergent series whose leading term is negative, and equals 0 at zero temperature

Autonomous photovoltaic lighting system

This paper introduces a comparison between the conventional and Photovoltaic (PV) lighting systems. A simple sizing procedure for a PV stand-alone system was advised. The paper also proposes a novel PV lighting system. The proposed system is simple, compact and reliable. The system operation was investigated by thoroughly mathematical and simulation work.Postprint (published version

Simple maximum power point controller for single-phase grid-connected PV system

This paper proposes a simple and efficient PI controller for single-phase grid-connected PV generator. The controller ensures the system operation at maximum power point (MPP) irrespective to atmospheric conditions. A detailed design of the controller and DC capacitor were carried out. An averagevalue model was developed to facilitate the design of the controller and to study the system performance under different operation conditions. The results were validated by rigorous simulation.Peer ReviewedPostprint (published version

Theoretical Characterization of the Interface in a Nonequilibrium Lattice System

The influence of nonequilibrium bulk conditions on the properties of the interfaces exhibited by a kinetic Ising--like model system with nonequilibrium steady states is studied. The system is maintained out of equilibrium by perturbing the familiar spin--flip dynamics at temperature T with completely--random flips; one may interpret these as ideally simulating some (dynamic) impurities. We find evidence that, in the present case, the nonequilibrium mechanism adds to the basic thermal one resulting on a renormalization of microscopic parameters such as the probability of interfacial broken bonds. On this assumption, we develop theory for the nonequilibrium "surface tension", which happens to show a non--monotonous behavior with a maximum at some finite T. It ensues, in full agreement with Monte Carlo simulations, that interface fluctuations differ qualitatively from the equilibrium case, e.g., the interface remains rough at zero--T. We discuss on some consequences of these facts for nucleation theory, and make some explicit predictions concerning the nonequilibrium droplet structure.Comment: 10 pages, 7 figures, submitted to Phys. Re

Performance Improvement of Air-cooled Battery Thermal Management System using Sink of Different Pin-Fin Shapes

One of the most important influences on battery safety, capacity, and cell ageing is heat generation and temperature inhomogeneity, which cause unbalanced ageing, resulting in cell performance decline. A well-developed temperature management module is required to avoid such undesirable actions. In this study, an air-cooled temperature management module was developed by coupling a unique heat sink of different pin-fin geometries/shapes to prismatic Li-ion cells and a 3D transient analysis was conducted to simulate the cooling performance of this heat sink under the effect of inlet airflow velocities and temperatures at a discharge rate of 2C for three cases. The results in the form of maximum temperature and temperature homogeneity inside the battery were derived and compared to the commonly used circular pin-fin heat sink. The overall result indicates that case 2, which consists of uniform height, shows better promise than others, taking into consideration the geometry employed. After 600 s and at a constant inlet air velocity of 0.412 m/s across a range of 20 oC to 35 oC, it was found that this heat sink performed better, providing an average of 1.87% and 1.93% improvement in temperature homogeneity and battery maximum temperature, respectively. Also, at a constant inlet air temperature of 27 oC across the range of inlet air velocity of 0.206 m/s to 0.824 m/s, this heat sink provides an average of 1.77% and 0.27% improvement in temperature homogeneity and battery maximum temperature, respectively. Doi: 10.28991/ESJ-2022-06-04-013 Full Text: PD

In situ visualization of Ni-Nb bulk metallic glasses phase transition

We report the results of the Ni-based bulk metallic glass structural evolution and crystallization behavior in situ investigation. The X-ray diffraction (XRD), transmission electron microscopy (TEM), nano-beam diffraction (NBD), differential scanning calorimetry (DSC), radial distribution function (RDF) and scanning probe microscopy/spectroscopy (STM/STS) techniques were applied to analyze the structure and electronic properties of Ni63.5Nb36.5 glasses before and after crystallization. It was proved that partial surface crystallization of Ni63.5Nb36.5 can occur at the temperature lower than for the full sample crystallization. According to our STM measurements the primary crystallization is originally starting with the Ni3Nb phase formation. It was shown that surface crystallization drastically differs from the bulk crystallization due to the possible surface reconstruction. The mechanism of Ni63.5Nb36.5 glass alloy 2D-crystallization was suggested, which corresponds to the local metastable (3x3)-Ni(111) surface phase formation. The possibility of different surface nano-structures development by the annealing of the originally glassy alloy in ultra high vacuum at the temperature lower, than the crystallization temperature was shown. The increase of mean square surface roughness parameter Rq while moving from glassy to fully crystallized state can be caused by concurrent growth of Ni3Nb and Ni6Nb7 bulk phases. The simple empirical model for the estimation of Ni63.5Nb36.5 cluster size was suggested, and the obtained values (7.64 A, 8.08 A) are in good agreement with STM measurements data (8 A-10 A)

Cluster expansion for abstract polymer models. New bounds from an old approach

We revisit the classical approach to cluster expansions, based on tree graphs, and establish a new convergence condition that improves those by Kotecky-Preiss and Dobrushin, as we show in some examples. The two ingredients of our approach are: (i) a careful consideration of the Penrose identity for truncated functions, and (ii) the use of iterated transformations to bound tree-graph expansions.Comment: 16 pages. This new version, written en reponse to the suggestions of the referees, includes more detailed introductory sections, a proof of the generalized Penrose identity and some additional results that follow from our treatmen