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.

Responses to drought of five Brachiaria species. II. Water relations and leaf gas exchange

Abstract: Neotropical savannas are exposed to recurrent dry periods of varied duration, and forage grasses must be able to cope with such temporal stresses to maintain productive pastures. This study compared leaf water relations and net photosynthesis under drought of five perennial Brachiaria species: the tufted B. brizantha (CIAT 6780), the semi-stoloniferous B. decumbens (CIAT 606) and B. mutica, and the stoloniferous B. humidicola (CIAT 679) and B. dictyoneura (CIAT 6133). Plants of the five grasses were grown in large pots and subjected to drought by suspending watering until first wilting symptoms (14 days for B. brizantha, B. decumbens and B. mutica, and 29 days for B. humidicola and B. dictyoneura). Afterwards, they were re-watered and a second soil dry cycle was imposed. Time trends in leaf water potential (� l), relative water content (RWC), osmotic potential at full turgor (� 100 ), stomatal conductance (Gs) and net photosynthesis (A) of stressed (DT) plants were compared to those of

Finsler geometry and actions of the p-Schatten unitary groups ∗

Abstract: Let p be an even positive integer and U p (H) the Banach-Lie group of unitary operators u which verify that u — 1 belongs to the p-Schatten ideal B p (H). Let O be a smooth manifold on which U p (H) acts transitively and smoothly. Then one can endow O with a natural Finsler metric in terms of the p-Schatten norm and the action of U p (H). Our main result establishes that for any pair of given initial conditions x ∈ O and X ∈ (TO) x there exists a curve 6(t) = e t z · x in O, with z a skew-hermitian element in the p-Schatten class, such that δ(0) = x and δ(0) = X, which remains minimal as long as t∥z∥ p < π/4. Moreover, δ is unique with these properties. We also show that the metric space (O, d) (where d is the rectifiable distance) is complete. In the process we establish minimality results in the groups U p (H) and a convexity property for the rectifiable distance. As an example of these spaces, we treat the case of the unitary orbit O = {uAu*: u ∈ U p (H)} of a self-adjoint operator A ∈ B(H).

The photocatalytic oxidation of dibenzothiophene (DBT)

Abstract: TiO2/UV solar light degradation of dibenzothiophene (DBT) aqueous solutions readily occurs in neutral and acid media. For instance, at neutral pH, t1/2 = 30 min are found for DBT degradation and mineralization. In neutral and acid media the rate limiting step for mineralization is the same as for degradation and corresponds to the DBT sulfone formation. Benzaldehyde is the major reaction product. In addition, it also acts as an intermediate in the mineralization to CO2 + water + sulfate. The results support the Langmuir–Hinshelwood degradation mechanism. Therefore, instead of pseudo-first-order rate constants, apparent rate constants that depend on concentration are obtained. Only at basic pH these apparent rate constant are independent of the [DBT]0. The solubility of DBT in water is increased by one-order of magnitude when solutions of the surfactant Triton X-100 is used at [Triton X-100] > CMC (critical micelle concentration). Under these conditions DBT is readily degraded without degrading Triton X-100 at t1/2 ca. 120 min. DBT is solubilized into Triton X-100 micelles from where it exchanges with water and becomes available for degradation. Triton X-100 monomers slightly compete with DBT for the TiO2 catalytic site. The degradation method established in this work might be used, for instance, to decontaminate soil contaminated with sulphur-rich heavy oil following a pre-treatment consisting of washing out the solid with Triton X-100 solutions, prior to photolysis.

Chemical composition, antioxidant capacity and functionality of raw and processed Phaseolus lunatus

Abstract: The nutrients, non-nutritional components and bioactive compounds, as well as the antioxidant capacity of raw, cooked, tray and drum-dried Phaseolus lunatus have been quantified. Likewise, the minerals, soluble carbohydrates, total polyphenols and tannins in the soaking and cooking waters were quantified. In addition, the functional properties such as the water and oil absorption indexes and the emulsifying and the foaming capacities were studied. The protein content of the raw beans was 24.98% and decreased, like calcium, magnesium and potassium, with the soaking and cooking processes; these losses are found in the soaking and cooking waters. Drum drying decreased anti-nutritional factors like trypsin inhibitors (66.09%) and cyanhydric acid (50.36%). Similarly, soluble fiber, available starch, total starch, and soluble sugars diminished, while total and insoluble fiber and resistant starch increased. The content of total polyphenols, tannins and antioxidant capacity decreased with thermal processing, being drum drying the process that least diminished antioxidant capacity. Likewise, the water absorption index was increased by 85% and 161.5% with processing. It was shown that P. lunatus is an important source of nutrients and can be consumed in whole bean form or used as a functional ingredient to be added in the development of new products. Copyright © 2007 Society of Chemical Industry