Age and growth of three species of Ariidae (Siluriformes) in coastal waters of Guinea

The growth of three West African marine catfish, #Arius heudeloti, #A. parkii, #A. latiscutatus (Siluriformes, #Ariidae), was studied in Guinea by examining sections of the first dorsal spine. Age and growth interpretations were possible for fish up to 40 cm and the three species reveal a similar biology. A single annulus is formed each year at the beginning of the rainy season. Growth seems to be slow, and 40 cm fork length individuals are about 6 years old. Three ariids can reach large sizes (80 cm or larger), which may indicate that the natural mortality is low. This adaptativeness is probably related to their strong body protection against predators, their low fecundity and egg incubation. (Résumé d'auteur

Structure and Thermodynamical Properties of Zirconium hydrides from first-principle

Zirconium alloys are used as nuclear fuel cladding material due to their mechanical and corrosion resistant properties together with their favorable cross-section for neutron scattering. At running conditions, however, there will be an increase of hydrogen in the vicinity of the cladding surface at the water side of the fuel. The hydrogen will diffuse into the cladding material and at certain conditions, such as lower temperatures and external load, hydrides will precipitate out in the material and cause well known embrittlement, blistering and other unwanted effects. Using phase-field methods it is now possible to model precipitation build-up in metals, for example as a function of hydrogen concentration, temperature and external load, but the technique relies on input of parameters, such as the formation energy of the hydrides and matrix. To that end, we have computed, using the density functional theory (DFT) code GPAW, the latent heat of fusion as well as solved the crystal structure for three zirconium hydride polymorphs: \delta-ZrH1.6, \gamma-ZrH, and \epsilon-ZrH2.Comment: 9 pages, 9 figures, 15th Int. Conf. Environmental Degradation of Materials in Nuclear Power Systems-water reactors Uses graficx, subfigure, threeparttable (2012