Using microscience kits to address a student-teacher misconception in electric circuits: At the interface between chemistry and electricity

A test of education students’ understanding of electric circuits, written before their lectures on the topic began, led to practical work with micro-scale circuit apparatus that was designed to further probe and challenge the students’ misconceptions. Response data from one of the lab pracs revealed one very common misconception, that the current through a component was the cause of the potential difference across it. A practical activity based upon the Volta pile was designed to show that current is not the cause of voltage, and that voltage is to be traced to the chemical reaction inside the cells. While some aspects of the activity were successful in a workshop at 10th ISMC, others were not. Our reflections on the outcome lead us to the conclusion that it is necessary to engage with the chemical events inside the cell, in order to understand how it works. Systems-thinking may be the way forward

Pre-service teachers’ misconceptions about current and potential difference in electric circuits – using microscience kits in a POE activity

Third year BEd students in a Physical Sciences content course answered a questionnaire about basic concepts of electric circuits, prior to attending lectures and practicals on the subject. Several well-known misconceptions were found to be prevalent. This led us to design a PredictObserve-Explain (POE) practical activity, using microscience kits. The results from this activity confirmed the prevalence of misconceptions, but also the reluctance of the student-teachers to change them. Our discussion of one important misconception, namely the confusion between current and potential difference, suggests that treating the cell as simply a store of energy and a source of energy without explanation may be the cause of the confusion. A chemist’s approach to this part of physics could avoid the misconception

Densification behavior of spark plasma sintered duplex stainless steel reinforced with TiN nanoparticles

Abstract: Duplex stainless steel (SAF 2205) reinforced with titanium nitride (TiN) nanoparticles ranging from 0 to 8 wt% were fabricated in vacuum via spark plasma sintering (SPS) using optimized SPS process parameter of 1150 oC, 10 min and 100 oC/min. The influence of TiN addition on the densification and shrinkage mechanism of the fabricated duplex stainless steel composite were evaluated. The results indicate even dispersion of the TiN nanoparticles in the steel matrix during tubular mixing. The displacement and shrinkage rates showed three densification stages relating to micro-nano particles rearrangement, plastic deformation of the particles and rapid densification of the composite. The steel composite samples displayed relatively high densities in the range of 96-99 % of the calculated theoretical density but were noted to decrease with TiN content

A correlation between nano and micro-hardness properties of TiN nanoparticles strengthened SAF 2205

Abstract : This work studied the correlation between Vickers and nano-hardness of SAF 2205 reinforced with TiN nanoparticles for the convenience of assessing its mechanical properties. Spark plasma sintering was used to fabricate the composites. Micro and nanoindentations were performed to determine micro and nanohardness values of the fabricated composite. Optical microscope was used to assess the microstructure. The microstructure revealed that the TiN dominated the ferrite/ferrite, ferrite/austenite and austenite/austenite grain boundaries. The micro and nanohardness at the TiN dominated grain boundaries were higher compared to the grain hardness. Hardness also increased considerably as the TiN nanoparticles increases. This is also owed to the strengthening effect played by TiN at the grain boundaries by disrupting dislocation motion in the composite. The determined Vickers hardness was plotted as a function of the corresponding nanohardness, a good linear relation was found between Vickers hardness and nanohardness. A linear relationship (HV = 215.15 + 15.03Hnano) was established which indicates that there is no difference in behavior for the Vickers hardness and nano- hardness

HBV/HIV co-infection: The dynamics of HBV in South African patients with AIDS

Objective. As sub-Saharan Africa is highly endemic for hepatitis B virus (HBV) and human immunodeficiency virus (HIV) infections, and their co-infection requires special management, we aimed to assess the serological and molecular characteristics of HBV in patients with AIDS. Design. This was a cross-sectional, case control study, which enrolled 200 patients with AIDS and 200 HIV-negative controls. HBV serology was done in all participants and HCV serology in participants with a hepatitis B core antibody (anti-HBc) only serological pattern. Nested HBV polymerase chain reaction (PCR) and HBV viral load assays were used for HBV molecular detection. Results. Hepatitis B surface antigen (HBsAg) prevalence was 3-fold higher while the ‘anti-HBc only’ pattern was 6-fold higher in the AIDS group compared with the controls. Mean HBV viral load was significantly higher in HBsAg-positive patients with CD4+ cell count

Variability of the preC/C region of hepatitis B virus genotype A from a South African cohort predominantly infected with HIV

ABSTRACT Hepatitis B virus (HBV) is a serious global health problem, and HBV genotype is an important determinant of disease progression and treatment outcome. The aim of this study was to assess variations of the precore/core (preC/C) region in HBV genotype A. Sequencing of the preC/C and surface (S) genes of HBV was performed on plasma samples from 20 HBV/HIV co-infected and 5 HBV mono-infected individuals. All preC/C study sequences clustered with subgenotype A1, except for 2 which clustered with subgenotype D4 reference strains. The nucleotide and amino acid variability was far higher in the preC/C region than in the S region. Mutations associated with reduction or failure of HBV e-antigen (HBeAg) production were observed, with a preC start codon mutation being common (24%). Other mutations (e.g. P5H/L and I97L) associated with severe liver disease were also noticed, some of which were located in the major histocompatibility restricted sites. PreC/C intergenotype nucleotide divergence was >7%, while subgenotypes differed by 2.5 -7%. Several study sequences were highly divergent from other African subgenotype A1 strains. This study showed that HBeAg-negative chronic hepatitis B is underestimated in subgenotype A1, and also highlighted the variant South African A1 strains. The major advantage of preC/C sequencing is that it informs patient management as HBeAgnegative chronic hepatitis B responds poorly to conventional interferon-α therapy, and some guidelines treat HBeAg-negative chronic hepatitis B differently from HBeAg-positive chronic hepatitis B. These data suggest that subgenotype A1 may be more involved in severe HBVrelated diseases

Evaluation of letsoku and related Southern African clayey soils

The nature of letsoku and related clayey soils, traditionally used by indigenous Southern African communities for a wide range of purposes, was explored. Thirty nine samples were collected from Botswana, Lesotho, Swaziland, South Africa and Zimbabwe. They were analyzed to determine their composition and physical properties. Analyses involved BET surface area determinations, pH measurements, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Structured interviews were used to establish the purpose of use and the location of sourcing sites. Most of the samples were in powder form and some were supplied as dry clay balls. Cosmetic applications were almost universally indicated. However, other functions, related to artwork, medicinal use, cultural symbolism and traditional beliefs were also mentioned. The letsoku samples covered a wide range of colors ranging from bright red to yellow but also from off-white to black with some having a light grey color. It was therefore not surprising that the mineral composition of the letsoku samples also varied widely. A black sample, and the yellow and reddish pastel colored samples, contained significant quantities of the corresponding, color imparting, iron oxides. As expected, clay minerals featured prominently although kaolinite was more often encountered than smectites as the dominant minerals. All samples contained silica and in some instances the content exceeded 90% m/m SiO2. The presence of high contents (40% m/m) of gibbsite in samples from Venda represents a new finding for clayey soils in traditional usage.Supplementary Material 1a. Acquired XRD patterns.Supplementary Material 1b. XRD Mineral composition.Tshwane University of Technology (TUT) in the form of a sabbatical stay; TUT DHET RDG funding travel and chemical expenses. Financial support from the Institute of Material Science, University of Pretoria.http://www.elsevier.com/locate/catena2019-12-01hj2018Chemical EngineeringGeologySchool of Health Systems and Public Health (SHSPH