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Skeletonema costatum was grown in an outdoor mesocosm to test the hypothesis that fluctuations in irradiance brought about by changes in mixing time and depth can reduce diatom growth and biomass in the turbulent mixed layer. The light environment and mixing regime within the mesocosm were comparable to those in shallow lakes and coastal waters. Experiments showed no significant differences for 24-h mean and 7-day mean chlorophyll a and carbon-specific growth for mixed depths of 1 m and 3 m, and mixing times between 4 min and 65 min. Fluctuations in irradiance brought about by turbulent mixing had no significant effect on specific growth. The relationship between mixed depths and critical depths for S. costatum was therefore independent of fluctuations in irradiance in the turbulent mixed layer. The results indicated that to control growth of S. costatum mixed depths would have to exceed photic depths by a factor of 15, instead of the conventionally accepted factor of 5. Thus, it is likely that artificial mixing of shallow (< 10 m) eutrophic waters will be more effective in controlling 'slow-growing' summer biomass than 'fast-growing' spring blooms dominated by diatoms., Introduction Although the relationship between light and phytoplankton growth in laboratory cultures is well researched, the effect of variability in light experienced by plankton cells in the mixed layer is [...]

Byline: Adel F. Antippa (1) Keywords: Langmuir; monolayer; domain; lattice; structure Abstract: We make a mathematical analysis of the structure of the two dimensional lattice formed by the centers of parallely aligned and arbitrarily oriented spherocylindrical phospholipidic molecules hexagonally packed in cylindrical domains forming a monomolecular Langmuir film at the liquid--gas interface. The analysis is carried out as a function of the tilting angle I, and the tilting azimuth I. We give a number of expressions for the lattice radius vector, and introduce the Lattice Generating Operator. We also present a number of theorems dealing with the existence and characteristics of the common points of tangency, the double stationary points, the locus circles, and the envelop circles, related to the lattice sites. Author Affiliation: (1) Departement de Physique, Universite du Quebec a Trois-Rivieres, 3351 Boul. des Forges, Trois-Rivieres, Quebec, Canada, G9A 5H7 Article History: Registration Date: 08/10/2004

Byline: A.F. Antippa (1), J.-J. Max (2), C. Chapados (2) Keywords: molecular; organization; Langmuir; films; gas; liquid; interface; boundary effects; hexagonal; packing; orientation; spherocylindrical; rod-like; molecules Abstract: We study the organization of spherocylindrical molecules inside a freely rotating right circular cylindrical domain at the gas/liquid interface. The analysis is made under the assumption that the molecules are rigid and close packed, and that they are oriented parallel to each other. The direction and angle of their common orientation are completely arbitrary. We obtain exact analytic expressions for the lattice of molecular centers and its boundaries as a function of molecular dimensions, molecular orientation, and domain size. As a first application, we derive the number of molecules in a domain, and the packing fraction. The results obtained are essential when attempting to analytically model a Langmuir film where the global order of the film is less than the local order of the domains. Author Affiliation: (1) Departement de Physique, Universite du Quebec a Trois-Rivieres Trois-Rivieres, Quebec, Canada, G9A 5H7 (2) Departement de Chimie-Biologie, Universite du Quebec a Trois-Rivieres Trois-Rivieres, Quebec, Canada, G9A 5H7 Article History: Registration Date: 08/10/2004