International Journal of Engineering Research in Africa Vol. 9

Abstract: Cold-pressed pellets were prepared from the mixtures SrTiO₃ - 0.03MF₂ - 0.12LiF, M = Ca, Sr or Ba, then air-fired at 950 °C for 2 hours. The obtained samples were investigated by X-ray diffraction and scanning electron microscopy. Each ceramic is a perovskite single phase and the relative density reaches 95% for all ceramics. The addition of 3 mol. % of the eutectic composition 1MF₂ - 4LiF (T_m ~ 760 °C) to SrTiO₃ lowers the sintering temperature of pure strontium titanate from 1400 °C to 950 °C and induces a strong modification in the SrTiO₃ cubic phase: superlattice reflections are detected and the unit cell symmetry becomes orthorhombic. Dielectric measurements were performed between - 150 °C and 200 °C in the frequency range 20 Hz - 10⁹ Hz. The dielectric permittivity ε_r showed no maximum in the temperature range investigated and is almost frequency independent. At room temperature, the dielectric losses tanδ are less than 0.1 %. Moreover, the frequency dependence of the complex permittivity exhibits a resonance in the microwave region. These fluorinated ceramics could be of interest in piezoelectric devices and are promising dielectrics for class I capacitors manufactured at low temperature.

Abstract: The optimal allocation of reliability to the components of complex systems to maximise their reliability is posed as multi-criteria optimisation. The minimum cut-sets leading to series-parallel reduction of such systems were constituted into criteria and their reliability maximised while minimising cost of improving the systems reliability. Consequently, the system reliability expression is made redundant, which simplifies the problem. The resultant nonlinear optimisation model was solved by the Weighted Sum method for the Pareto optimal component reliability values. The model was applied to a life support system. The results show that higher components/ systems reliability can be achieved using the approach.

Abstract: The advent of wireless computing and massive processing power available within portable devices provides organizations with an unprecedented ability to provide flexible computing services on-demand to enable business initiatives and this development has increased the demand for wireless network security, which if unaddressed enables the theft of data, lowers productivity, and causes quantifiable financial losses. Flaws arising from wireless protocol with networking design and implementation errors present challenges to the Wireless Fidelity (Wi-Fi) community of users. In this paper, we attempt to document and classify the flaws in Wi-Fi Protected Setup (WPS), then proving the existence of this flaw with a WPS Pin Cracking Method, and presenting a Reverse Engineering countermeasure to eliminating WPS from an Access Point firmware, including other recommendations to helping the network administrators not repeat the errors that are the root causes of flaws of wireless networking in general from being exploited. By implementing the various techniques discussed in this paper, a better and more secure wireless network will be developed.

Abstract: A novel cassava peeling machine that operates on the principle of the lathe was designed, fabricated and tested. The unique peeling principle uses a self-loading, self-adjusting single point cutting tool that can follow the contour of the cut cassava tuber sections or sized lots. The single point cutting tool allows the peeler to peel both freshly harvested cassava tubers and cassava tubers that are up to four days old effectively and efficiently. Test results show a peeling efficiency of over 70% for all categories of tubers and a minimal loss of flesh.

Abstract: A vertical livestock feed mixer with spring-controlled packaging unit was designed, constructed and tested. This design had in focus a weighing and gauging mechanism which made possible a semi-automatic packaging in conjunction with feed mixing and discharge operations. The main components of the machine included a double-wall cylindrical mixing chamber consisting of recycling gate, discharge gate, evacuating gate, window and a screw conveyor inside an inner cylinder. The packaging mechanism is attached to the discharge gate and the base of the frame with the frame serving as the structural support for the machine and its contents. The main design parameters included screw conveyor features such as helix angle, fill ratio, normal pressure due to bulk load on screw shaft, axial force per pitch, total screw torque, capacity and power requirements of the screw conveyor. The design concept of the packaging mechanism involved determination of free length of spring, total active length, pitch of spring, spring index, stiffness of spring, maximum shear stress and total spring rate. In a hitch-free operation, the machine was designed to package 25 kg of mixed feed ingredients at a time. In operation, the feed ingredients are scooped and moved upward by the rotary movement of the screw conveyor and then sprayed back into the smaller cylinder without passing through the internal tube. A preliminary testing was carried out on the machine to determine the actual discharge rate and hence the performance of the packaging mechanism. Results revealed that an average discharge rate of 0.356 kg/s was obtained. Powered by a 2 hp single phase electric motor, the machine has a mixing capacity of 4.124 m³/h with a production cost of $470.

Abstract: This study is concerned with the performance analysis and comparison of air standard Diesel and Diesel-Atkinson cycles with heat-transfer loss, friction like term loss and variable specific-heat ratio of the working fluid based on finite-time thermodynamics. Also numerical examples are detailed to show the relations between the output power and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the output power and the thermal efficiency of both cycles. Furthermore, the effects of variable specific-heat ratio of the working fluid, heat transfer and the friction-like term loss on the performance of both irreversible cycles are analyzed. Comparison of the performance of cycles shows that the heat efficiency and the output power of an air standard Diesel-Atkinson are higher than the Diesel ones and the points of maximum output power and thermal efficiency of Diesel-Atkinson cycle occur at the lower compression ratio. Reduction of No_x is another advantage of Diesel-Atkinson cycle. The results obtained in this paper provide guidance for the design of Diesel and Diesel-Atkinson engines.

Abstract: This paper presents a statistical analysis of the performance of organizations and countries in the development, implementation and certification of the international standard SA 8000 on social accountability in their operations. Data obtained from the international organization SAAS (Social Accountability Accreditation Services) were analyzed using bar charts, percentages and Pareto (ABC) analysis. The results showed that the highest number of organizations having certified management system in conformity with the requirements of SA 8000, and also the highest number of personnel in certified organizations were concentrated in Asia, and that the most widespread branches of industry in regard to the certification of their management systems in conformity with the requirements of this standard are such branches as construction, apparel, and textiles industries.