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.

The Supermembrane with Central Charges on a G2 Manifold

Abstract: We construct an 11D supermembrane with topological central charges induced through an irreducible winding on a G2 manifold realized from the T7/Z32 orbifold construction. The Hamiltonian H of the theory on a T7 target has a discrete spectrum. Within the discrete symmetries of H associated with large diffeomorphisms, the Z2 × Z2 × Z2 group of automorphisms of the quaternionic subspaces preserving the octonionic structure is relevant. By performing the corresponding identification on the target space, the supermembrane may be formulated on a G2 manifold, preserving the discreteness of its supersymmetric spectrum. The corresponding 4D low energy effective field theory has N = 1 supersymmetry.

Numerical Study of a Three-Dimensional Mixed Ising Ferrimagnet in the Presence of an External Field

Abstract: We present a numerical study based on a Monte Carlo algorithm of the magnetic properties of a mixed Ising ferrimagnetic model on a cubic lattice where spins a = ±1/2 and spins S = 0, ±1 are in alternating sites on the lattice. We carried out exact ground state calculations and employ a Monte Carlo simulation to obtain the finite-temperature phase diagram of the model. A compensation point appears when the next-nearest-neighbor interaction between the spins a = ±1/2 exceeds a minimum value. We found a strong dependence of the compensation temperature with the interactions in the Hamiltonian, particularly the crystal and the external field. An applied field can change the range of values of the compensation temperature from zero up to a maximum value that depends on the field.

Hydraulic Properties of a Mangrove Avicennia Germinans as Affected by NaCl

Abstract: Water transport was assessed in seedlings of the mangrove Avicennia germinans L. grown at 171 and 684 mol m−3 NaCl. Leaf specific conductivity declined by 25 % at high salinity. This was related to low specific conductivity, because Huber values remained similar. Leaves of A. germinans featured low internal conductance to water transport. This was lowered further under high salinity. Water transport constrains imposed by whole shoot and leaf blade at high salinity were balanced by stomatal regulation of water loss, which possibly maintain stem water potentials above embolisms levels.

Population structure of the corals Orbicella faveolata and Acropora palmata in the Mesoamerican Barrier Reef System with comparisons over Caribbean basin-wide spatial scale

Abstract: Studies of genetic diversity and population genetic structure in marine organisms are relevant to understanding populations’ variability, and therefore their ability to withstand environmental perturbations, their potential for resistance to local extinction and their natural rate of recovery. Population structure and genetic diversity were assessed at a regional spatial scale (i.e., Mesoamerican Barrier Reef System, MBRS) in two major reef building coral species Orbicella (formerly Montastraea) faveolata and Acropora palmata, and at a larger spatial scale (i.e., Caribbean-wide; MBRS, Panama, Venezuela and Puerto Rico) for A. palmata only. The most significant findings were as follows: (1) high genetic diversity and low clonality were found for both species, which is expected for O. faveolata but not for A. palmata, (2) both species showed low-to-moderate, yet significant population structure among populations along the MBRS; in particular, O. faveolata and A. palmata from Ambergris (Belize) and O. faveolata from Calabash (Belize) and A. palmata from Puerto Morelos (Mexico) showed some genetic differentiation from the rest of the MBRS populations, and (3) A. palmata from MBRS, Panama, Puerto Rico and Venezuela were grouped into four subregions that could be considered as management units. A more spatially detailed sampling program and the inclusion of recruits will be necessary to get a comprehensive understanding of coral population structure and current gene flow patterns in these two species.