Asymptotic Behavior of an Age-Structured Population Model and Optimal Maturation Age

AbstractA continuous age-structured population model with two population groups, juveniles and adults, and with a dynamics for the resource, is considered. The only density dependence is through a uniform increase of the death rates. A complete description of the asymptotic behavior of the population dynamics system is obtained showing under natural hypotheses the existence of a nontrivial (“ecological”) equilibrium which attracts any initial nonzero population with nonzero initial amount of resources. Assuming that the offspring production rate is an increasing function of the maturation age, the evolutionarily stable value of this variable is briefly discussed

Growth performance and biochemical composition of nineteen microalgae collected from different Moroccan reservoirs

Macro- and microalgae have recently received much attention due to their valuable chemical constituents. In order to increase existing data, the authors studied nineteen microalgae species isolated from different reservoirs in the Fez region (northern Morocco), undertaking experiments to determine for each species the specific growth rate, their total amounts of proteins, carbohydrates and lipids and the influence of the growth phase on these chemical constituents. Conditions of cultivation were as follows: light intensity equal to 300 μmol photons m-2 s-1, with a temperature regime of 25/20°C (day/night) and a 16/8 (light/dark) photoperiod cycle. The growth rates of the nineteen studied species of microalgae showed a wide variation between species, ranging from 0.27 g l-1 d-1 for Chlamydomonas ovalis to 3.64 g l-1 d-1 for Chlorococcum wemmeri. Protein, carbohydrate and lipid contents varied greatly between taxa and within genera. Ankistrodesmus falcatus, Chlamydomonas ovalis, Chlorococcum sp., Hyaloraphidium contortum, Scenedesmus protuberans, and Synechocystis aquatilis tended to synthesize proteins, the concentrations exceeding 20% dry weight (DW). Ankistrodesmus falcatus, Ankistrodesmus sp., Chlorococcum wemmeri, Coenocystis sp., Isocystis sp., Lyngbya bergei, Oscillatoria amphibia, Polytoma papillatum, Scenedesmus protuberans, Scenedesmus sp. and Synechocystis aquatilis showed a high capacity for lipid storage, greater than 20% DW. For carbohydrate contents, only Scenedesmus protuberans and Scenedesmus quadricauda showed an excessive level compared to other scanned species with 29.21% and 24.76% DW, respectively

Elaboration and characterization of Co-Zn2 SiO4 pigments

In this communication, we reports results on the synthesis of Zn2-xCoxSiO4 (0≤x≤1) ceramic pigments by sol-gel method with the main aim of achieving high purity at lower temperatures. The second objective is to obtain a variety of colours (turquoise, purple, violet and blue) with a minimum quantity as possible as of cobalt. The materials were investigated by X-ray diffraction, infra-red spectroscopy, UV-visible spectroscopy, Lab-colour measurements and Scanning Electron Microscopy (SEM).In this communication, we reports results on the synthesis of Zn2-xCoxSiO4 (0≤x≤1) ceramic pigments by sol-gel method with the main aim of achieving high purity at lower temperatures. The second objective is to obtain a variety of colours (turquoise, purple, violet and blue) with a minimum quantity as possible as of cobalt. The materials were investigated by X-ray diffraction, infra-red spectroscopy, UV-visible spectroscopy, Lab-colour measurements and Scanning Electron Microscopy (SEM)

Dielectric characterization of hydrothermally PREPARED (Cu,Sb)-doped BaTi1-xZrxO3

Powders of copper-doped BaTi1-xZrxO3 have been synthesized using the hydrothermal process. The starting materials were powders of BaO and TiO2, ZrO2.xH2O gel, and an aqueous solution of Cu2+ / Sb5+. The obtained powders were cold compacted and sintered at 1280°C. Impedance spectroscopy measurements have been performed on these ceramics and the results were analyzed using the empiric Cole-Cole model. A procedure to evaluate the electric properties of the grain boundary and bulk grain has been developed based on electric polarization model of double layered dielectrics.Powders of copper-doped BaTi1-xZrxO3 have been synthesized using the hydrothermal process. The starting materials were powders of BaO and TiO2, ZrO2.xH2O gel, and an aqueous solution of Cu2+ / Sb5+. The obtained powders were cold compacted and sintered at 1280°C. Impedance spectroscopy measurements have been performed on these ceramics and the results were analyzed using the empiric Cole-Cole model. A procedure to evaluate the electric properties of the grain boundary and bulk grain has been developed based on electric polarization model of double layered dielectrics