Two-group decodable distributed differential space-time code for wireless relay networks based on SAST codes 2

Space-time code can be implemented in wireless relay networks when all relays cooperate to generate the code at the receiver. In this case, it is called distributed space-time code. If the channel response changes very quickly, the idea of differential space-time coding is needed to overcome the difficulty of updating the channel state information at the receiver. As a result, the transmitted signal can be demodulated without any knowledge of the channel state information at the relays or the receiver. In this paper, development of new low decoding complexity distributed differential space-time codes is considered. The developed codes are designed using semiorthogonal algebraic space-time codes. They work for networks with an even number of relays and have a two-group decodable maximum likelihood receiver. The performance of the new codes is analyzed via MATLAB simulation which demonstrates that they outperform both cyclic codes and circulant codes

Effects of Various Quenching Media on Mechanical Properties of Annealed 0.509wt%C –0.178wt%Mn Steel

Evaluation of palm kernel oil, cotton seed oil and olive oil as quenching media of 0.509Wt%C medium carbon steel was investigated. To compare the effectiveness of the oils, the samples were also quenched in water and SAE engine oil which are the commercial quenchants. The samples were quenched to room temperature in the quenching media (palm kernel oil, cotton seed oil and olive oil). The machined specimen of the steel was heated at 8800Cthen quenched in water, engine oil, palm kernel oil, cotton seed oil and olive oil. Tensile strength, hardness and impact energy were used to measure the quenching effectiveness of the various media. The microstructures and mechanical properties of the quenched samples were used to determine the quench severity of the oils.  The test of the mechanical properties shows that the hardness of steel quenched in water was (1740.54 HBN), while the hardness of steel quenched in palm kernel oil was (740.34 HBN) which was recorded as the least in all samples quenched. As-received sample absorbed the highest amount of energy (183.10J) before fracture while sample quenched in water absorbs the least energy (28.50J). The microstructure of the samples quenched in the oils under study revealed the formation of low proportions of martensite and in the case of olive oil, there was retained austenite. Hence, olive oil can be used where cooling severity less than that of water and SAE 40 engine oil is required for hardening of plain carbon steels.http://dx.doi.org/10.4314/njt.v34i3.1

Design, Construction and Performance Comparison of Two Solar Stills Having Different Absorber Design

Productivity enhancement of solar stills has been one of the main goals of researchers. In this study, two designs of solar stills absorber plate were conceptualized and developed and their effects on the productivity process were investigated experimentally. A solar still using a submerged flat absorber plate and another solar still without any submerged absorber plate were designed and constructed. The designs were developed by virtue of the comparative analyses to be carried out.  The two still designs were tested under the same conditions. Comparatively, more distilled water was obtained from the solar still without submerged plate at 10litres of inlet raw water during the first day of experiment while the still with submerged flat absorber had more distillate during the second and third day of the experiment with 20 and 30 liters inlet raw water respectively. The efficiencies were 82.35 % and 83.30 % on the first day of experiment, 82.99% and 82.56% on the second day of experiment and 83.82% and 81.98% on the third day of experiment for still with submerged flat plate absorber and still without submerged flat plate absorber respectively.http://dx.doi.org/10.4314/njt.v34i4.1