Evaluating the IRI topside model for the South African region: An overview of the modelling techniques

The representation of the topside ionosphere (the region above the F2 peak) is critical because of the limited experimental data available. Over the years, a wide range of models have been developed in an effort to represent the behaviour and the shape of the electron density (Ne) profile of the topside ionosphere. Various studies have been centred around calculating the vertical scale height (VSH) and have included (a) obtaining VSH from Global Positioning System (GPS) derived total electron content (TEC), (b) calculating the VSH from ground-based ionosonde measurements, (c) using topside sounder vertical Ne profiles to obtain the VSH. One or a combination of the topside profilers (Chapman function, exponential function, sech-squared (Epstein) function, and/or parabolic function) is then used to reconstruct the topside Ne profile. The different approaches and the modelling techniques are discussed with a view to identifying the most adequate approach to apply to the South African region’s topside modelling efforts. The IRI-2001 topside model is evaluated based on how well it reproduces measured topside profiles over the South African region. This study is a first step in the process of developing a South African topside ionosphere model

Linear and nonlinear stability analysis of binary viscoelastic fluid convection

The linear and weakly nonlinear stability analysis of the quiescent state in a viscoelastic fluid subject to vertical solute concentration and temperature gradients is investigated. The non-Newtonian behavior of the viscoelastic fluid is characterized using the Oldroyd model. Analytical expressions for the critical Rayleigh numbers and corresponding wave numbers for the onset of stationary or oscillatory convection subject to cross diffusion effects is determined. A stability diagram clearly demarcates non-overlapping regions of finger and diffusive instabilities. A Lorenz system is obtained in the case of the weakly nonlinear stability analysis. The effect of Dufour and Soret parameters on the heat and mass transports are determined and discussed. Due to consideration of dilute concentrations of the second diffusing component the route to chaos in binary viscoelastic fluid systems is similar to that of single-component (thermal) viscoelastic fluid systems. © 2013 Elsevier Inc.

On double-diffusive convection and cross diffusion effects on a horizontal wavy surface in a porous medium

An analysis of double diffusive convection induced by a uniformly heated and salted horizontal wavy surface in a porous medium is presented. The wavy surface is first transformed into a smooth surface via a suitable coordinate transformation and the transformed nonsimilar coupled nonlinear parabolic equations are solved using the Keller box method. The local and average Nusselt and Sherwood numbers are given as functions of the streamwise coordinate and the effects of various physical parameters are discussed in detail. The effects of the Lewis number, buoyancy ratio, and wavy geometry on the dynamics of the flow are studied. It was found, among other observations, that the combined effect of Dufour and Soret parameters is to reduce both heat and mass transfer

Rhabdomyosarcoma of the orbit in a four months old infant in Zimbabwe: a case report

Rhabdomyosacoma, as a medical condition, observed in a four month old infant at a Zimbabwe hospital.Infants younger than one year of age with Rhabdomyosacoma appear to have worse prognosis compared to older children due partly to high rates of local failure. We report a 4 months old infant with orbital rhabdomyosarcoma with poor outcome.. Reluctance to use aggressive local control measures and suboptimal chemotherapy dosing are significant contributory factors. Call is made for need for more studies to determine appropriate local therapy in infants with rhabdomyosarcoma

Patterns of retinoblastoma in Zimbabwe: 2000-2009

A research study on the high incidence of Retinoblastoma eye diseases among children from poor countries like Zimbabwe between the period 2 000 to 2009 .Retinoblastoma is the most common intraocular malignant tumour of childhood but it remains a rare disease. It occurs more commonly in less affluent regions of the world compared to richer regions. The incidence of retinoblastoma within age group 0-4 years varies from country to country. Africa generally has a higher incidence especially in the sub Saharan Africa region ranging from 10.6 to 42.5cases per million. This is in contrast to developed countries where in the USA, the incidence is 11.8 and in Europe it ranges from 6-12. Bulgaria has the lowest incidence of 3.4 cases per million."' In Zimbabwe the incidence of retinoblastoma is estimated at 23.3 per million ranking 3rd highest in the world after Uganda and Mali

Integrated impedance-matching coupler for smart building and other power-line communications applications

Abstract: Power-line communications is a promising technology to help automate buildings, as it utilizes the in-situ power cabling as a communications channel. However, couplers are required to inject and extract the communication signal from the power grid. Most power-line communications couplers make use of a small transformer to adapt impedance levels while also providing galvanic isolation. The cost and size of these transformers have been hindrances in the quest for compact, economic couplers. Previous attempts to eliminate this coupling transformer, while maintaining impedance adaptation, have not been successful in reducing component cost nor physical size. In this paper, a novel approach is followed: (1) a suitable dualfunction band-pass matching circuit is designed as for ordinary electronics, whereafter (2) the specifications of this band-pass matching circuit is upgraded to function safely in the power-grid environment as a coupler. Therefore a matching circuit is transformed into a compact power-line coupler, which further exhibits band-pass filtering and excellent impedance-adapting performance. Simulations as well as laboratory measurements are shown which confirm the accuracy of the design. Finally, practical 220-V measurements in an office block are presented, which prove the versatility of this novel coupler when power-grid conditions fluctuate

The role of the Zimbabwean government in the implementation of management accounting among small and medium enterprises

PURPOSE: This paper aimed to investigate the role of the Zimbabwean government in the implementation of Management Accounting Practices (MAPs) among Small and Medium Enterprises (SMEs). Management accounting is a crucial instrument for success, particularly for SMEs, according to earlier studies. The study noted that there is a dearth of literature on the government's support for the adoption of management accounting SME sector.METHODOLOGY: Semi-structured interviews were used to gather information from 88 participants. Zimbabwe has no SME database, hence, a chain referral sampling technique was used. The data were interpreted using qualitative content analysis.FINDINGS: The study found that there is little that is done by the Zimbabwean government in promoting the use of management accounting among SMEs The areas covered in government-sponsored training for SMEs are bookkeeping, entrepreneurship, and tax preparation; management accounting is not addressed.ORIGINALITY/VALUE: In order to increase public understanding of MAPs, the research advises the Zimbabwean government to conduct seminars, launch awareness-raising campaigns, and establish policies that encourage the use of management accounting.peer-reviewe

Three-dimensional stability of heated or cooled accelerating boundary layer flows over a compliant boundary

In this study we investigate the stability of three-dimensional disturbances imposed on a heated or cooled two-dimensional boundary layer flow with a compliant surface. Such compliant surfaces may delay laminar to turbulent transition and reduce drag and noise levels in fluid flow. We exploit the multi-deck structure of the flow in the limit of large Reynolds numbers to analyse asymptotically the perturbed flow and to derive linear neutral results. A limited parametric study is carried out; the work extends that of Motsa et al. (2002) to three-dimensional disturbances

Nanofluid Flow over a Permeable Surface with Convective Boundary Conditions and Radiative Heat Transfer

We investigate the effects of thermal radiation and convective boundary conditions on heat and mass transfer in nanofluid flow over a permeable flat plate. The mathematical model for the nanofluid incorporates variations in the nanoparticle volume fraction of up to 20%. The performance of two water-based nanofluids, namely, stable suspensions of copper and gold nanoparticles in water was investigated. The governing partial differential equations were transformed into ordinary ones using a similarity transformation and solved numerically. The numerical results were validated by comparison with previously published results in the literature. The main focus of this paper is to study the fluid and surface parameters such as the radiation parameter, and suction/injection parameter, solute concentration profiles, as well as the skin friction coefficient and heat and mass transfer rates were conducted