Geochemical comparison of K-T boundaries from the Northern and Southern Hemispheres

Closely spaced (cm-scale) traverses through the K-T boundary at Stevns Klint (Denmark), Woodside Creek (New Zealand) and a new Southern Hemisphere site at Richards Bay (South Africa) were subjected to trace element and isotopic (C, O, Sr) investigation. Intercomparison between these data-sets, and correlation with the broad K-T database available in the literature, indicate that the chemistry of the boundary clays is not globally constant. Variations are more common than similarities, both of absolute concentrations, and interelement ratios. For example, the chondrite normalized platinum-group elements (PGE) patterns of Stevns Klint are not like those of Woodside Creek, with the Pt/Os ratios showing the biggest variation. These differences in PGE patterns are difficult to explain by secondary alteration of a layer that was originally chemically homogeneous, especially for elements of such dubious crustal mobility as Os and Ir. The data also show that enhanced PGE concentrations, with similar trends to those of the boundary layers, occur in the Cretaceous sediments below the actual boundary at Stevns Klint and all three the New Zealand localities. This confirms the observations of others that the geochemistry of the boundary layers apparently does not record a unique component. It is suggested that terrestrial processes, eg. an extended period of Late Cretaceous volcanism can offer a satisfactory explanation for the features of the K-T geochemical anomaly. Such models would probably be more consistent with the observed stepwise, or gradual, palaeontological changes across this boundary, than the instant catastrophe predicated by the impact theory

Field observations on conditions condusive to the contamination of groundnuts with the mould Aspergillis flavus Link ex Fries

No Abstrac

Coherent bremsstrahlung, boherent pair production, birefringence and polarimetry in the 20-170 GeV energy range using aligned crystals

The processes of coherent bremsstrahlung (CB) and coherent pair production (CPP) based on aligned crystal targets have been studied in the energy range 20-170 GeV. The experimental arrangement allowed for measurements of single photon properties of these phenomena including their polarization dependences. This is significant as the theoretical description of CB and CPP is an area of active theoretical debate and development. With the theoretical approach used in this paper both the measured cross sections and polarization observables are predicted very well. This indicates a proper understanding of CB and CPP up to energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to determine the polarization parameters in our measurements. New technologies for high energy photon beam optics including phase plates and polarimeters for linear and circular polarization are demonstrated in this experiment. Coherent bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger enhancement for hard photons than CB for the channeling orientations of the crystal. Our measurements and our calculations indicate low photon polarizations for the high energy SOS photons.Comment: 23 pages, 27 figures, 2 tables, REVTeX4 two column

The analysis of clay materials for use in a ceramic studio

M.Tech. (Industrial Design)The research project entitled: The Analysis of Clay Materials for use in a Ceramic Studio was undertaken in order to give a quantitative base to the understanding of clay materials and their role in clay bodies. The project consists of analysing the clay materials as they are supplied, using technically sophisticated equipment. A set of data for each of the nine chosen clays was assembled and then correlated for easier comparison. The clay materials were then mixed into clay bodies using a set proportion in order that a comparison of the nine clay bodies could be made and related to the data assembled for the clay materials. The data collected, as well as the ceramic calculations used in the research project were entered into the "Insight" Ceramic software programme for use in the studio. This data base will be the foundation for ongoing research into ceramic materials

Isotopic Production Cross Sections in Proton-Nucleus Collisions at 200 MeV

Intermediate mass fragments (IMF) from the interaction of $^{27}$Al, $^{59}$Co and $^{197}$Au with 200 MeV protons were measured in an angular range from 20 degree to 120 degree in the laboratory system. The fragments, ranging from isotopes of helium up to isotopes of carbon, were isotopically resolved. Double differential cross sections, energy differential cross sections and total cross sections were extracted.Comment: accepted by Phys. Rev.

An evaluation of the effect of a computer-related participatory ergonomics intervention programme on adolescents in a school environment: A randomised controlled trial

A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, 2015Computer use is increasing among children and thus the potential for related musculoskeletal pain and postural changes is increasing concomitantly. From an early age children are spending more time in front of computers and television, which encourages a static and passive lifestyle. The cumulative effect of this technology-induced, sedentary lifestyle leads to improper posture as well as pain, repetitive strain injury and dysfunctional movement patterns that can potentially carry into adult life. For this reason, there is a need for designing, implementing and assessing the effectiveness of a participatory ergonomics intervention programme in a school environment in South Africa. This study consisted of two phases: the main objective of phase one comprised a cross-sectional study to determine the prevalence of musculoskeletal pain and pain catastrophising in grade eight learners working on computers in a school environment; and to determine the body areas most commonly affected by pain among learners routinely exposed to computers; and to measure the observed posture of adolescents working on computers in a school environment; and to establish the attitude of the teachers and principals towards ergonomics in schools. Phase two was a randomised control trial, with the objective to determine the effect of a participatory computer-related ergonomics intervention programme on grade eight learners in terms of the effect on musculoskeletal pain while working on a computer, pain catastrophising, and postural change and ergonomic behaviour. Sample Selection: a) School sample Private independent schools were selected to participate in the study because they have principally similar socio-economic ecologies. The particular populations of learners selected for this study were exposed more frequently and with higher intensity to computer use, both at home and at school than is currently the case in less privileged socio-economic environments. Two schools were chosen using randomised cluster sampling from a population of 27 independent co-educational secondary schools in the greater Johannesburg region (Appendix D). b) Learner Sample The learner sample included all grade eight learners from all three classes at the two randomly selected private schools in the greater Johannesburg region who were invited to participate in the study (n=127). Consecutive sampling was done according to specific inclusion and exclusion criteria. c) Teacher and Principal sample A convenience sample (n=18) of teachers and principals who responded to the questionnaire was used in this study. Procedure: Phase one: A self-report questionnaire was used to obtain demographic data and to measure pain. Pain catastrophising levels were measured with a pain catastrophising scale for children (PCS-C) and observed posture was measured using the Rapid Upper Limb Assessment tool (RULA). The ergonomics of the computer laboratories of the two schools was assessed using the Computer Workstation Design Assessment form (CWDA). The attitude of the teachers and principals of the schools were measured using a self-report questionnaire. Phase two: A single blind randomized control trial was conducted (pre and post intervention assessment). School A and school B were randomly allocated to either a control group or an intervention group. Allocation into groups was done using concealed allocation with assessor blinding and therefore, the researcher and the research assistant were blinded to group allocation as well as to the delivery of the ergonomic intervention programme to the participants so as to limit assessment bias. The study was conducted over a period of six months. The intervention and control groups were assessed at baseline prior to the intervention and then at three months and six months post-intervention. The control group and the intervention group were required to answer a validated Computer Usage Questionnaire (CUQ) (Smith, 2007) and the Pain catastrophising questionnaire (PCS-C) (Vervoort et al., 2008) at baseline and at three and six month intervals post-intervention. All the participants underwent biometric measurements of person height, weight, school bag weight and postural analysis using the RULA (Rapid Upper Limb Assessment) (McAtamney and Corlett, 1993) method of observation. The learners from the control and intervention group had their postures assessed with RULA while they were using a computer at school during a computer lesson at baseline, three months and six months. The computer-related ergonomic intervention programme was developed with reference to the literature from the few intervention studies that have been done (Ismail et al., 2010; Robbins et al., 2009; Heyman and Dekel, 2009) and it was evaluated by four educators, eight learners and an expert in the field of ergonomics during the pilot study and modified accordingly. The intervention was delivered by a physiotherapy lecturer who was trained in the delivery of the intervention programme. The intervention group received a 45 minute participative intervention programme comprising an educational ergonomic component on posture and workstation set-up and a component of stretches for the neck, shoulders and lower back. This was in the format of a visual power point presentation with planned activities for the participants. A poster demonstrating correct workstation set-up and a variety of stretches was put in the computer classroom of the intervention group. Thereafter, each learner participant was given a sticker to place on their computer screen at home and at school. This sticker, in the form of a red dot, acted as a reminder to the learner participants to adjust their posture and to do their stretches during the time that they spent on the computer. A free web-based link was given to each participant to download onto their home computer to reinforce the reminder of doing stretches and taking regular short breaks from computer use when at home. All participants were given a short multiple choice questionnaire test immediately after the intervention to test their comprehension and understanding of the ergonomic concepts that they had been taught during the intervention programme. The control group participants were not exposed to any ergonomic intervention programme as they were in a different school. At three months and six months post-intervention, the research assistant repeated all the biometric measurements of the learners with regards to height, weight and school bag weight. In addition, the researcher repeated the RULA analysis of the learners’ posture and all the learners who had agreed to participate in the study answered the same questionnaires that they had answered in phase one of the study. The same venue at each school was used at each measurement interval to ensure consistency of environment for accurate measurement purposes. The RULA (postural assessment) measurements were conducted during the week after the biometric measurements and questionnaires were completed. RULA measurements were conducted by the researcher during the Information technology and design lesson in the computer laboratory of each school. RULA measurements were done by observing each learner for one minute while they worked on a computer during their computer lesson. The computer lesson was 45 minutes in length and the observation process started 10 minutes after the start of the computer lesson. The learners were observed from the dominant hand side and from a side-view during the RULA measurement process. Results: Results showed a high prevalence of musculoskeletal pain (77%) in the adolescents in a school environment. A prevalence of rate of 34% was found for learners experiencing musculoskeletal pain while working on computers and a significant percentage (31.4%) of the learners were observed to be in a category 4 action level. In phase two of this study, there was a significant difference (p<0.05) in the prevalence rate of musculoskeletal pain relating to computer use between the control (25.8%) and the intervention (42.6%) groups at baseline. After six months, there was no significant difference (p<0.52) between the control and intervention groups which may be due to the positive effect of the intervention. However, the withinin group analysis of the prevalence rate of musculoskeletal pain while working on a computer in the intervention group had reduced significantly (p<0.000) from 42.6% to 18% over a period of six months, compared to the control group which only had a small reduction in symptoms from 25.8% to 24.2% (p<0.39). This suggests that the computer-related ergonomic intervention programme had a positive clinical effect on musculoskeletal pain in learners in the intervention group, but no statistically significant effect was found in the between group analysis over a period of six months. The results indicated that more than one body area was affected by pain in some of the learners. In the intervention group 21.5% of the learners experienced musculoskeletal symptoms in their right shoulder, 18.6% in their lower back, 16.8% in their left shoulder, 9.3% in their neck and 9.3% in their upper-mid back area. Pain catastrophising scores for the total sample of learners (Mean=25.12, SD = 8.1) were measured using the PCS-C survey. A PCS score of 30 refers to the 75 percentile and is clinically relevant in terms of predicting the risk for developing chronic pain. A large portion of learners (73.2%) scored below the clinically significant 75th percentile (a score >30) and 26.8% scored above a score of 30, indicating that this percentage of learners had clinically significant catastrophising scores. The average PCS score of both the control and intervention groups decreased over a period of six months and within each group there was a significant decrease in the total PCS score from baseline over a period of six months (p<0.00). In order to determine if the intervention programme had an effect on pain catastrophising in learners, pain catastrophising for the two groups was tested using the statistical test, repeated measures of analysis of variance (ANOVA) to show between group changes. The findings showed that over a period of time, between baseline and three months, there was a significant change in pain catastrophising between the control group and intervention group (p<0.001), however, there was no significant change in pain catastrophising between the two groups at six months (p<0.68), which indicates that the intervention had a positive effect on pain catastrophising in the learner intervention group. The within group changes were significant (p<0.001) for both groups for pain catastrophising between baseline and six months. This similarity of findings of within group changes between the two groups means one cannot determine if these changes were because of the intervention or because of the Hawthorne effect (an observational bias which occurs when human subjects change their behaviour because they think that they are being observed during an experiment) (Gale, 2004) from the researcher’s presence. None of the learners from this study adopted a posture to qualify for action level 1 (AL 1) in either the control or intervention groups. The majority of learners from both groups (40.9% control and 42.6% intervention) were found to be in AL 2 and Al 4 (36.4% for the control and 26.2% for the intervention group). A large percentage of learners from the schools in this study were found to sit in awkward postural positions that could put them at risk of developing musculoskeletal pain. In this current study there was a significant improvement in the number of learners in the intervention group who shifted from AL 4 to AL 2 and AL 3. At six months post-intervention, there were no learners in AL 4 and the number of learners in AL 3 had reduced from 26.2% at baseline to 14.8% (p<0.001) at six months. The control group RULA scores worsened over the period of six months. Although the learners were still not in an “acceptable” range of postural positions, there was a significant improvement on the pre-intervention stage compared with the post-intervention stage, possibly because of the Hawthorne effect. In terms of determining risk factors for developing musculoskeletal pain during computer use, the results showed that only the learners at baseline who worked for more than or equal to 2.5 hours per week on a computer were more at risk for developing pain (OR 2.7, p=0.02) compared to those who worked for less than 2.5 hours per week on a computer. Furthermore, only the learners with pain catastrophising scores ≥30 at three months were found to be at risk for developing musculoskeletal pain (OR 3.34,p<0.001). The set -up of the computer workstation environment in both the control and intervention schools were found to be inadequate. There were non-standardised and non-adjustable desks and chairs in both schools’ computer laboratories and the workspace area of the desk in the intervention school laboratory was compromised. The monitors in both schools were non-adjustable in terms of their height and angle of inclination. With regards to the knowledge of ergonomics amongst teachers from the study, only 13% of the teachers (n=18) had undergone training in ergonomics skills and none of the teachers were satisfied with their knowledge relating to computer-related ergonomics. Finally, the computer-related ergonomics programme in terms of its content was found to be valid and feasible for the South African context. Conclusion: This study showed that an ergonomic intervention programme can be effective in reducing the impact of the poor posture in adolescents using computers in schools

Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons

We present the first experimental results on the use of a thick aligned Si crystal acting as a quarter wave plate to induce a degree of circular polarisation in a high energy linearly polarised photon beam. The linearly polarised photon beam is produced from coherent bremsstrahlung radiation by 178 GeV unpolarised electrons incident on an aligned Si crystal, acting as a radiator. The linear polarisation of the photon beam is characterised by measuring the asymmetry in electron-positron pair production in a Ge crystal, for different crystal orientations. The Ge crystal therefore acts as an analyser. The birefringence phenomenon, which converts the linear polarisation to circular polarisation, is observed by letting the linearly polarised photons beam pass through a thick Si quarter wave plate crystal, and then measuring the asymmetry in electron-positron pair production again for a selection of relative angles between the crystallographic planes of the radiator, analyser and quarter wave plate. The systematics of the difference between the measured asymmetries with and without the quarter wave plate are predicted by theory to reveal an evolution in the Stokes parameters from which the appearance of a circularly polarised component in the photon beam can be demonstrated. The measured magnitude of the circularly polarised component was consistent with the theoretical predictions, and therefore is in indication of the existence of the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for publicatio

Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence

The cross section for coherent pair production by linearly polarised photons in the 20-170 GeV energy range was measured for photon aligned incidence on ultra-high quality diamond and germanium crystals. The theoretical description of coherent bremsstrahlung and coherent pair production phenomena is an area of active theoretical debate and development. However, under our experimental conditions, the theory predicted the combined cross section and polarisation experimental observables very well indeed. In macroscopic terms, our experiment measured a birefringence effect in pair production in a crystal. This study of this effect also constituted a measurement of the energy dependent linear polarisation of photons produced by coherent bremsstrahlung in aligned crystals. New technologies for manipulating high energy photon beams can be realised based on an improved understanding of QED phenomena at these energies. In particular, this experiment demonstrates an efficient new polarimetry technique. The pair production measurements were done using two independent methods simultaneously. The more complex method using a magnet spectrometer showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for publicatio

Mineral-PET: Kimberlite sorting by nuclear-medical technology

A revolutionary new technology for diamond bearing rock sorting which has its roots in medical-nuclear physics has been taken through a substantial part of the R&D phase. This has led to the construction of the technology demonstrator. Experiments using the technology demonstrator and experiments at a hospital have established the scientific and technological viability of the project