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.

Three and four generalized Lorentzian approximations for the Voigt line shape.

Abstract: Three and four generalized Lorentzians in two variables have been obtained to approximate the Voigt function by using the asymptotical Pade method. The accuracy has been greatly improved with respect to the one and two generalized Lorentzian approximations reported in a previous paper. Furthermore, the four Lorentzian function is always positive for all values of the normalized collision width and line separation. This approximation gives an accuracy for most of the values of better than 0.0001, and in the worst region the absolute error is ~0.001. In the limits of low and high pressure adequate limit functions are obtained. A four generalized Lorentzian gives a reliable and easily calculable approximation to the Voigt function for most of the experimental needs.

Breaking of Water-in-Crude Oil Emulsions. 4. Estimation of the Demulsifier Surfactant Performance To Destabilize the Asphaltenes Effect

Abstract: Surfactant molecules are tested as water-in-crude emulsion breakers to attain the quickest separation rate in the so- called "proportional regime". A concept of demulsifier performance is proposed on the basis of the required demulsifier con- centration to offset the effect of a given amount of asphaltenes. The experimental evidence allows one to rank the tested products and relate their performance to their hydrophilicity and molecular weight. Some evidence indicates that the presence of acids in the crudemakesiteasiertobreakemulsionsandsuggeststhatso-called"extendedsurfactants"cansignificantlyshortenthedemulsifying process.

Pollinator limitation and position dependent fruit set in the high Andean orchidMyrosmodes cochleare (Orchidaceae)

Abstract: Myrosmodes cochleare is a terrestrial orchid restricted to high elevations of the northern Andes. It is self-compatible but not autogamous. Flowering begins at the apex of the inflorescence, but flower size increases steadily towards the base. Fruit set of selfed flowers was found to increase significantly from the apex to the base of the inflorescence. Open-pollinated fruit set was significantly lower than hand-pollinated fruit set overall, but the highest levels occurred in the middle of the inflorescence. Eumenid wasps and a calliphorid fly were observed to pollinate the flowers, but visits were rare and occurred only during infrequent warm periods.

Application of spatial Poisson models to air mass thunderstorm rainfall

Abstract: Eight years of summer storm rainfall observations from 93 stations in and around the 154 km2 Walnut Gulch catchment of the Agricultural Research Service, U.S. Department of Agriculture, in Arizona are processed to yield the total station depths of 428 storms. Statistical analysis of these random fields yields the first two moments, the spatial correlation and variance functions, and the spatial distribution of total rainfall for each storm. The sample is then split, and half is used to estimate, for each storm day, the distributions of the three parameters of each of the three conceptual spatial Poisson process models proposed previously by Rodriguez-Iturbe et al. (1986). The absolute and relative worth of the three Poisson models are evaluated by comparing their prediction of the spatial distribution of storm rainfall with observations from the second half of the sample. The effect of interstorm parameter variation is examined.