Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Iterated Neumann problem for the higher order Poisson equation

Abstract: Rewriting the higher order Poisson equation Δnu = f in a plane domain as a system of Poisson equations it is immediately clear what boundary conditions may be prescribed in order to get (unique) solutions. Neumann conditions for the Poisson equation lead to higher-order Neumann (Neumann-n ) problems for Δnu = f . Extending the concept of Neumann functions for the Laplacian to Neumann functions for powers of the Laplacian leads to an explicit representation of the solution to the Neumann-n problem for Δnu = f . The representation formula provides the tool to treat more general partial differential equations with leading term Δnu in reducing them into some singular integral equations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Monte Carlo simulation of a mixed spin 2 and spin Ising ferrimagnetic system

Abstract: The critical behaviour of a mixed ferrimagnetic Ising system on a square lattice in which the two interpenetrating square sublattices have spins and has been studied. We carried out exact ground state calculations and performed Monte Carlo simulations to obtain the finite-temperature phase diagram of the model. We found that the system that includes only a nearest-neighbour interaction and the crystal field does not have a compensation point. Also, our study seems to indicate that, contrary to effective-field predictions, there is no tricritical point at nonzero temperature for this model; however a more elaborate analysis will be needed to draw a definite conclusion on this point.

Induction of mixed-function oxygenase system and antioxidant enzymes in the coral Montastraea faveolata on acute exposure to benzo(a)pyrene

Abstract: Components of the cytochrome P 450 monooxygenase system (MFO) and antioxidant enzymes were investigated in the coral Montastraea faveolata exposed to the organic contaminant benzo( a )pyrene (B( a )P). For bioassays the corals were exposed to increasing concentrations of B( a )P (0.01 and 0.1 ppm) for 24 and 72 h, with water renewal every 24 h. Enzymatic activity of catalase (CAT), superoxide dismutase (SOD) and glutathione S-transferase (GST) were measured in host (polyp) and hosted (zooxanthellae) cells. NADPH cytochrome c reductase activity and contents of cytochrome P 450 and P 420 were only measured in the polyp. Antioxidant enzymes CAT and SOD in polyps and zooxanthellae and GST in polyps increased significantly at the highest concentration and maximum time of exposure. Cytochrome P 420 was found in all colonies, and the cytochrome P 450 content was greatest in the colonies from the highest concentrations of contaminant. NADPH cytochrome c reductase activity and the concentration of pigments did not vary between treatments. This is the first report of the induction of both detoxifying mechanisms, the MFO system and antioxidant enzymes on acute exposure to an organic contaminant in the reef-constructing coral species M. faveolata .