Lattice Knots in a Slab

In this paper the number and lengths of minimal length lattice knots confined to slabs of width $L$, is determined. Our data on minimal length verify the results by Sharein et.al. (2011) for the similar problem, expect in a single case, where an improvement is found. From our data we construct two models of grafted knotted ring polymers squeezed between hard walls, or by an external force. In each model, we determine the entropic forces arising when the lattice polygon is squeezed by externally applied forces. The profile of forces and compressibility of several knot types are presented and compared, and in addition, the total work done on the lattice knots when it is squeezed to a minimal state is determined

Manufacturing challenges for custom made solar vehicles in South Africa

Solar challenges are designed to test the reliability and efficiency of solar powered vehicles in endurance races. In the past these manufactured vehicles were technology drivers and led to advances in electric motors and solar cell efficiency. The speed in relation to power consumption is one of the main design considerations, with the only energy source being solar power. In the design and manufacturing of these vehicles a number of requirements need to be met in order to pass the safety standards. The Sasol Solar Challenge (SSC) created an opportunity for South African universities to design and manufacture custom made solar powered vehicles. This paper explores and discusses the challenges for manufacturing solar vehicles in South Africa. Key elements like the communication gap between design and manufacturing, the cost of lightweight solar encapsulation, the shortage of local suppliers and expertise in composite manufacturing are evaluated. These insights can be used as foundation for strategic decisions by future stakeholders

The Compressibility of Minimal Lattice Knots

The (isothermic) compressibility of lattice knots can be examined as a model of the effects of topology and geometry on the compressibility of ring polymers. In this paper, the compressibility of minimal length lattice knots in the simple cubic, face centered cubic and body centered cubic lattices are determined. Our results show that the compressibility is generally not monotonic, but in some cases increases with pressure. Differences of the compressibility for different knot types show that topology is a factor determining the compressibility of a lattice knot, and differences between the three lattices show that compressibility is also a function of geometry.Comment: Submitted to J. Stat. Mec

Clinical and psycho-social profile of child and adolescent mental health care users and services at an urban child mental health clinic in South Africa

Objective: National and international child and adolescent mental healthcare policy and action advocate that the health and well being of children should be increasingly given greater attention. The purpose of this study was to describe the demographic, socio economic and clinical profile of the users at the child and adolescent mental health clinic of the Rahima Moosa Mother and Child Hospital (RMMCH). Method: A descriptive, retrospective clinical audit from users’ clinical files was performed over a one-year period from January to December 2007. Descriptive statistical analyses of demographic and socio-economic variables were made and these variables were compared with the presenting clinical problems. Odds ratios were calculated for variables that showed a statistically significant association (p-value less than 0.05). Results: A total of 303 users attended this clinic. Statistical comparisons between demographic data and disorders revealed that being male increased the likelihood of presenting with AHDH and disruptive behaviourdisorders; being female increased the likelihood of being sexually abused. Race showed a significant association with parent-child relationship difficulties. Regarding socio-economic variables, the identity of the caregiver of the child influenced the risk of disruptive behaviour disorders, sexual abuse, neglect and academic problems. Where the child was placed was a risk factor for disruptive behaviour disorders, sexual abuse, neglect and academic problems. Whether the mother of a user was alive or deceased, was found to be related to ADHD and disruptive behaviour and whether the father of a user was alive or deceased, was found to be related to sexual abuse and academic problems. The education level of the caregiver showed a significant association with sexual abuse, neglectand academic problems; the marital status of the parent (widowed mother) showed a significant association with bereavement. Household income was associated with sexual abuse, neglect and academic problems.Conclusion: This study demonstrated the impact that socio-economic circumstances have on the prevalence of childhood disorders; hence the urgent need for government and social welfare departments to improve the socio-economic status of communities. There is a need to improve psychiatric services for the population served by this hospital, including more clinics in its catchment area, as well as child psychiatry training posts and extended social work services.Keywords: Socio-economic variables; Clinical profile; Child and adolescent mental health services; South Afric

Preparing for solar challenge: critical competences acquired in undergraduate engineering education

Abstract: Engineers are expected to function in a highly competitive environment, which demands that projects are developed in increasingly efficient and cost-effective ways, across various disciplines. This trend necessitates multidisciplinary collaboration which requires both traditional engineering skills and so called ‘soft skills’, such as good communicative competences and working cooperatively in teams. In this paper it is described how these skills were developed in the course of the University of Johannesburg’s preparation for participation in the biannual Solar Challenge

Understanding the impact of engineering through appropriate technology development

Abstract: This research describes a pilot project which aimed to introduce CDIO-type (Conceive-Design-Implement-Operate), project-based learning through a community-based project in a third year Material Science module. The project formed part of an agriculture research initiative, and relied on interdisciplinary research collaboration between engineering, social sciences, management, entrepreneurship, and industrial arts. The initiative seeks to develop an agribusiness solution that will create an open-market, growth-oriented food economy. As part of the initiative, engineering students, participating in teams, worked alongside a community of urban farmers, most of whom are working poor, so as to develop appropriate, intermediate technology/ies that could support the farmers. This was informed by the need to have students demonstrate high level understanding of disciplinary content, but also to engage in human-centered design thinking and practice

Experimental analysis of damage development in carbon fiber reinforced composites under cyclic loading

Abstract: There is a global need to design low weight structures for strategic, business, and social purposes. Reducing weight is critical for improving energy consumption as well as addressing range, performance, size, and cost challenges associated with structural design, especially in the automotive and aerospace industries. In recognition of this need, advances are being made in replacing high strength steels, magnesium and aluminum alloys with carbon fiber reinforced epoxy composites. These have many merits which include weight reduction for lower fuel consumption, resistance to environmental degradation and better aesthetic appeal. For most applications, the carbon fiber reinforced epoxy composites are exposed to cyclic loading leading to fatigue failure. High cycle fatigue in metals usually evolves by the single crack initiation which propagates until catastrophic failure. In contrast to metals, damage development in carbon fiber reinforced epoxy composites occurs in a complex global fashion which occupies an under-researched field. To enable better design, there is a need for a better understanding of carbon fiber reinforced epoxy composites, in particular, damage progression during cyclic loading. The aim of this paper is to investigate damage development during fatigue loading in carbon fiber reinforced epoxy composites. To this end, carbon fiber/epoxy composites produced from a bi-axial carbon material with a fiber volume fraction of 30% were investigated. The specimens were prepared using a hand layup molding technique. The results showed the first two of the three common stages observed during fatigue damage development. The first stage involved rapid damage, followed by stage two which is gradual, and the final stage which is rapid was not observed. The obtained results clearly show the fatigue damage mechanisms in carbon fiber reinforced epoxy composite materials

An overview of anti-allergic drug therapy and the histamine-1 antihistamines

Allergic disease decreases the daily quality of life of many people, and can increase the number of working days lost owing to sick leave. Associated symptoms with allergic disease depend on the origin of the disease, and can either be allergic, non-allergic and purulent, or can cause rhinitis as a result of a common cold. Treatment depends on the origin of the rhinitis. However, an antihistamine is indicated in most instances. Combination treatment includes sympathomimetic drugs (either local or systemic) and corticosteroid medication (when indicated, and in most instances, used locally). The article provides an overview of the nature and the management of allergic disease and the histamine 1 antihistamines.Keywords: anti-allergic drug therapy, H1 antihistamines, histamine receptors, allergic rhinoconjunctivitis, allergy healt

Investigating the effects of composite materials in solar cell encapsulation

In the past few decades our society’s increasing demands for energy have naturally resulted in increased utilization of renewable resources such as solar energy. Due to this strong demand the solar car endurance race was established to challenge researchers in this field. A competitive vehicle needs around six square meters of solar cells that produce approximately one kilowatt of power. This equates to 514 monocrystalline silicon half cells. The manufacturing challenge is to protect these cells from the terrestrial elements over a prolonged period of time. In this research study a composite encapsulation method was developed for solar cells and tested. Experiments were conducted to assess the processing of composite materials to improve the mechanical strength of the fragile solar cells. The effects of composites on reinforcement, electrical efficiency and thermal efficiency of the photovoltaic (PV) cells were evaluated. Impact testing to simulate a hailstone shows that the fibreglass sandwich panel structure will protect the surface of the cells, whilst reducing their efficiency by less than 5%