Rainfall rate characteristics for microwave systems in tropical and equatorial areas

The wave propagation at frequencies from about 10 GHz can suffer rain effects such as attenuation, scattering and depolarization. The magnitude of these effects depends on rain characteristics. This paper presents results of the propagation experiments undertaken in Douala (Cameroon) and in Brazzaville (Congo) under the auspices of the ITU (Geneva) with the collaboration of CNET (France Telecom). Data based on five months measurements of rain rates in Douala with a network of four rain-gauges are presented with reference also to some results of a propagation campaign in Brazzaville. The rain measurement period in Douala includes all of the rainy season. The measurement data are used to investigate the rain effect characteristics of the low latitude tropical regions of Africa and are discussed in relation to the influence of rain on microwave system performances in the region.     

Recovery of Fine and Ultrafine Mineral Particles by Electroflotation – A Review

Fine and ultrafine particles are successfully recovered by flotation when fine bubbles are present. Electroflotation is a technique in which fine bubbles are generated by the electrolysis of water. This article reviews the experimental studies into mineral recovery by electroflotation and the potential application of electrolytic bubbles in the recovery of fine and ultrafine mineral particles. The literature reveals that electroflotation resulted in better recoveries of ultrafine particles (e.g. dolomite, magnesite, and pyrite) as compared with dispersed-air flotation because electrolytic bubbles are smaller in size and are more active than those generated during dispersed-air flotation.     

Lipase‐catalysed biodiesel production from Jatropha curcas oil

Biodiesel as fatty acid alkylesters has become attractive because of its environmental benefits. A non‐edible oil as starting material for biodiesel production appears desirable and does not compromise the edible oils used mainly for food and feed. The present article discusses the enzymatic alcoholysis of crude Jatropha curcas oil in solvent free medium for the production of valuable fatty acid alkyl esters for use as biodiesel. Among various microbial lipases commonly tested in the literature, the highest initial rate (>18 μmol h^–1 mg^–1) with different alcohols was observed with immobilized lipase from Pseudomonas cepacia, but the activity depends on the amount of water. The best conversion (93%) to produce ethyl esters was achieved with lipase immobilized on the polypropylene carrier Accurel 1282 after 16 h at low enzyme concentration (3% w/w). Moreover, the transesterification could be conducted for at least 160 h during 10 batch runs without significant loss of activity. This reduces the costs for immobilized lipase and can thus make the enzymatic biodiesel production commercially more viable, especially starting from a non‐edible plant oil.