RESUMEN
Light scattering measurements were done close to the double critical point of the isotropic boundary of the lyotropic liquid crystal potassium laurate, 1-decanol, and heavy water. From scaling analysis we find susceptibility and correlation length exponents that are clearly higher than the mean-field values usually found in other studies on this and similar systems. In order to recover mean-field analysis, we use a parabolic version of the Landau-de Gennes free energy in account of the convex nature of the phase diagram. We also observe pretransitional characteristic domain sizes greater than the correlation length. Furthermore, we show that the transition goes into a new two-phase coexistence region, between the convex tips of pure isotropic and discotic nematic boundaries.
RESUMEN
An attempt was made to determine more accurately the density of molluskan populations in the Pampulha reservoir, using the quadrate method, intending to detect the fluctuation of the populations density, the habitat conditions and the possible competitive interactions among Biomphalaria tenagophila, Melanoides tuberculata, Pomacea haustrum and Biomphalaria glabrata, through the analysis of populational parameters. Among the most significative facts observed in the reservoir it has to be mentioned: the almost disappearance of B. glabrata; the invasion, colonization, fixation and fast growing of M. tuberculata population until reaching about 11,000 individuals/[square metre]; the density fluctuations of B. tenagophila, P. haustrum and M. tuberculata alives and deads; differences on the habitat preference of these three molluskan species at the edge (at the limit earth-water, at 0.70m and 1.40m from the shore line); monthly mortality rates and reproduction seasons of the species.