Cooling capacity of vortex tubes by changing different characteristics

Published articleThe improvement of the efficiency and cooling capacity of a simple vortex tube is considered. Three Ranque-Hilsch Vortex tubes, with different diameters and lengths, were developed and manufactured. The vortex tube is an unique device with no working parts and has the ability to deliver hot and cold air simultaneously. It is a simple, low cost device, which is easy to manufacture. Different orifice sizes and nozzle configurations are designed and manufactured to investigate the performance of the three vortex tubes. The f 22 mm vortex tube with a f 7, 5 mm orifice and small diameter nozzle gave a better efficiency and an increase in the drop in temperature of the cold air against the different inlet pressures. The maximum efficiency of the f 22 mm diameter vortex tube improved from 8, 9% against a cold fraction of 0, 630 (with the f 6 mm x 2 tangential nozzle block) to 18, 92% against a cold fraction of 0, 644 (with the f 3 mm x 4 tangential nozzle block) at an inlet pressure of 500 kPa. The maximum drop in temperature of the cold air improved from 27, 0 oC against a cold fraction of 0, 120 (with the f 6 mm x 2 tangential nozzle block) to 42, 3 oC against a cold fraction of 0, 284 (with the f 4 mm x 2 tangential nozzle block) at an inlet pressure of 600 kPa

Vachellia (Acacia) karroo Communities in South Africa: An Overview

Vachellia karroo is a useful and widespread tree in Africa. It belongs to the family Fabaceae, which is the third largest woody plant family in southern Africa. This is an ecologically and economically important species as almost all of its parts, including bark, pods, seeds, leaves and thorns, are extremely useful to both humans and animals. Various commercial products are also obtained from the tree, and gum is one of the most important products. V. karroo in South Africa has an extensive distribution range that includes several biomes. It is very adaptable and has wide habitat tolerance, growing under many differing conditions of soil, climate, and altitude. Although it is often associated with heavy, clayey soils on the banks of rivers and streams, it also grows in bushveld, dry thornveld, grassland and woodland. V. karroo is easy to grow and as a result can become an aggressive invader of valuable farming land and grazing areas, a phenomenon usually referred to as bush encroachment. An analysis of historic data comprising 1553 relevés and 2006 species, compiled from all areas of South Africa where V. karroo is known to occur was conducted, and TWINSPAN classification produced five main vegetation types

Why Read (Diffractively)?

Academics should produce quality scholarly research. However, the demands of the marketised, neoliberal higher education institution and the increase in the academic’s bureaucratic and administrative tasks do not allow for adequate engagement with the deep work and slow forms of scholarship that are needed to produce cutting-edge and insightful research. Many academics find it challenging to think critically and creatively under such conditions, yet they are unwilling to fill their time with shallow work instead. Thus, they are torn between producing an institutionally-determined number of research outputs, and striving towards producing quality scholarly work that advances knowledge in the academic’s discipline. Reading groups serve to rework this tension by providing a communal and scheduled place and mind-space for reading major academic works. Reading takes time and persistence. We find that setting aside time and creating creative spaces for reading groups offer an opportunity for silent revolt against the pressures of the higher education institution. In this (post)qualitative inquiry we diffractively read – “through one another” – two autoethnographical accounts to experiment with our experiences of various reading groups over a period of three years while positioning ourselves in relation to Barad’s notion of diffraction. This speculative experimentation entails a myriad of ideas and methods that serve to decentre hegemonic, monolithic knowledge systems through seeking alternative ways of knowing, and recognises the importance of the entanglement of matter and meaning in tracing (and countering) the social relations produced in neoliberalist contexts. Such (re)thinking is thus a vital counterpoint to the neoliberal obsessions of the higher education context, (re)directing the scholar to new non-autonomous and mutable landscapes

ASSESSMENT OF MANUFACTURABILITY AND PERFORMANCE OF POLYURETHANE HEART VALVES PRODUCED THROUGH A LOCALLY DEVELOPED DIP MOULDING PROCESS

Conference ProceedingsPolyurethane heart valves have been widely studied as possible replacement for mechanical and bioprosthetic heart valves. The development of an inexpensive routine production technique for manufacturing of polyurethane valves will greatly benefit a very large number of patients in developing and emerging countries. A polymer heart valve shows favourable physical properties and flow dynamics compared to human heart valves, however, the outcome of producing a polymer heart valve with the required flexibility, durability and hemodynamic function is often difficult to predict. The design of the mould, the selection of the material and the fabrication method used are the key factors that influence the achievement of an acceptable heart valve for use in the human body. From their previous work on developing a repeatable, semi-automated dip moulding process for producing tri-leaflet polyurethane heart valves, the authors have shown that the selection of an appropriate set of dip moulding process parameters and mould material properties could result in achieving polyurethane valve leaflets with the required physical and mechanical properties. This paper reports on the progress made with application of the developed dip moulding process to produce polyurethane heart valves suitable for use in human body. The mould, frame and sewing ring were manufactured in Ti6Al4V(ELI) by using a Direct Metal Laser Sintering (DMLS) process and the valve leaflets were moulded directly onto the sewing ring. The heart valve properties obtained are presented and assessed. Conclusions are drawn regarding the prospects of these valves surviving the extensive in vitro simulation trials required to qualify them for subsequent clinical trials

Distribution and degree of occurrence of aflatoxin in groundnuts and groundnut products

No Abstrac

Degenerate Gaussian factors for probabilistic inference

In this paper, we propose a parametrised factor that enables inference on Gaussian networks where linear dependencies exist among the random variables. Our factor representation is effectively a generalisation of traditional Gaussian parametrisations where the positive-definite constraint of the covariance matrix has been relaxed. For this purpose, we derive various statistical operations and results (such as marginalisation, multiplication and affine transformations of random variables) that extend the capabilities of Gaussian factors to these degenerate settings. By using this principled factor definition, degeneracies can be accommodated accurately and automatically at little additional computational cost. As illustration, we apply our methodology to a representative example involving recursive state estimation of cooperative mobile robots.Comment: Accepted by International Journal of Approximate Reasoning on 17 January 202

The mature female clothing shopper : profiles and shopping behaviour

The original publication is available at http://www.sajip.co.zaCITATION: Visser, E.M., Du Preez, R. & Du Toit, J.B. 1996. The mature female clothing shopper : profiles and shopping behaviour. SA Journal of Industrial Psychology, 22(2):1-6, doi:10.4102/sajip.v22i2.603.This study was designed to profile the mature female clothing shopper. More specifically certain variables that could be attributed to differences in consumer behaviour were investigated. Mature female clothing shoppers were segmented as clothing moderates, clothing enthusiasts and the clothing unconcerned. These three cluster groups significantly differed regarding clothing involvement, clothing orientation, activities, interests, opinions, family orientation, needs and media usage. No significant differences were found among the three groups regarding evaluative criteria for clothing and clothing store attributes. Profiles of the clusters were developed, along with applicable marketing implications. Recommendations for further research are made.Hierdie studie is onderneem ten einde die vroulike kledingverbruikers van 55 en ouer te tipeer. Die veranderlikes wat 'n bydrae kon lewer ten opsigte van die verskille in verbruikersgedrag is ondersoek. Die verbruikers is gesegmenteer as die kledinggematigdes, kleding- entoesiaste en die kleding-onbetrokkenes. Die drie groeperings verskil beduidend van mekaar ten opsigte van die volgende veranderlikes naamlik: kleding-betrokkenheid, kleding-oriëntasie, aktiwiteite belangstellings, opinies, familie oriëntasie, behoeftes en media gebruik. Geen beduidende verskille kon gevind word tussen die drie groeperings ten opsigte van die veranderlikes evalueringskriteria van klere en winkeleienskappe nie. Profiele van die verskillende trosse is ontwikkel en die bemarkingsimplikasies is uitgewys. Aanbevelings vir verdere navorsing word gedoen.Publishers' Versio

Efficient approximations of the multi-sensor labelled multi-Bernoulli filter

In this paper, we propose two efficient, approximate formulations of the multi-sensor labelled multi-Bernoulli (LMB) filter, which both allow the sensors' measurement updates to be computed in parallel. Our first filter is based on the direct mathematical manipulation of the multi-sensor, multi-object Bayes filter's posterior distribution. Unfortunately, it requires the division of probability distributions and its extension beyond linear Gaussian applications is not obvious. Our second filter is based on covariance intersection and it approximates the multi-sensor, multi-object Bayes filter's posterior distribution using the geometric mean of each sensor's measurement-updated distribution. This filter can be used for distributed fusion under non-linear conditions; however, it is not as accurate as our first filter. In both cases, we approximate the LMB filter's measurement update using an existing loopy belief propagation algorithm, which we adapt to account for object existence. Both filters have a constant complexity in the number of sensors, and linear complexity in both number of measurements and objects. This is an improvement on an iterated-corrector LMB filter, which has linear complexity in the number of sensors. We evaluate both filters' performances on simulated data and the results indicate that the filters are accurate

The reliability of physical examination in diagnosing arterial injury in penetrating trauma to extremities: A first look at different anatomical regions and injury mechanisms

Background. The accuracy of physical examination to exclude arterial injury in penetrating trauma to extremities has been well established. Objectives. To determine whether the accuracy of physical examination to exclude arterial injury is similar to that of a computed tomography arteriogram (CTA) for different anatomical regions and mechanisms of injury, and in patients with concomitant fractures compared with those without. Methods. A retrospective review was conducted on all patients who underwent CTA for penetrating injuries to an extremity between 1 June 2016 and 30 June 2017. The presence of arterial injuries was noted, and these were grouped into anatomical areas. Clinical notes were reviewed for the presence of hard signs of arterial injury at initial examination. Results. A total of 220 lower limb and 133 upper limb CTAs were included. The mean patient age was 28.9 years (range 11 - 68). The overall sensitivity of physical examination in detecting a CTA-confirmed arterial injury was 95.3% (95% confidence interval (CI) 88.4 - 98.7), with a specificity of 93.9% (95% CI 90.2 - 96.4). Physical examination of the thigh had the highest specificity of 96.4% (95% CI 91.8 - 98.8), followed by the lower leg at 94.4% (95% CI 81.3 - 99.3), the upper arm at 89.6% (95% CI 79.7 - 95.7) and the forearm at 77.8% (95% CI 40.0 - 97.2). For gunshot wounds the specificity was 96.1% (95% CI 92.4 - 98.3), while for stab wounds it was 86.8% (95% CI 74.7 - 94.5). Conclusions. This study agrees with current literature indicating that physical examination has high specificity in detecting arterial injury in the setting of penetrating trauma to an extremity. However, it shows that the specificity is not equal for all anatomical regions or mechanisms of injury

The reliability of physical examination in diagnosing arterial injury in penetrating trauma to extremities: A first look at different anatomical regions and injury mechanisms

Background. The accuracy of physical examination to exclude arterial injury in penetrating trauma to extremities has been well established.Objectives. To determine whether the accuracy of physical examination to exclude arterial injury is similar to that of a computed tomography arteriogram (CTA) for different anatomical regions and mechanisms of injury, and in patients with concomitant fractures compared with those without.Methods. A retrospective review was conducted on all patients who underwent CTA for penetrating injuries to an extremity between 1 June 2016 and 30 June 2017. The presence of arterial injuries was noted, and these were grouped into anatomical areas. Clinical notes were reviewed for the presence of hard signs of arterial injury at initial examination.Results. A total of 220 lower limb and 133 upper limb CTAs were included. The mean patient age was 28.9 years (range 11 - 68). The overall sensitivity of physical examination in detecting a CTA-confirmed arterial injury was 95.3% (95% confidence interval (CI) 88.4 - 98.7), with a specificity of 93.9% (95% CI 90.2 - 96.4). Physical examination of the thigh had the highest specificity of 96.4% (95% CI 91.8 - 98.8), followed by the lower leg at 94.4% (95% CI 81.3 - 99.3), the upper arm at 89.6% (95% CI 79.7 - 95.7) and the forearm at 77.8% (95% CI 40.0 - 97.2). For gunshot wounds the specificity was 96.1% (95% CI 92.4 - 98.3), while for stab wounds it was 86.8% (95% CI 74.7 - 94.5).Conclusions. This study agrees with current literature indicating that physical examination has high specificity in detecting arterial injury in the setting of penetrating trauma to an extremity. However, it shows that the specificity is not equal for all anatomical regions or mechanisms of injury