Showing papers by "Simón Bolívar University published in 1984"
TL;DR: In this article, the current transient for three-dimensional nucleation on a finite number of active sites, followed by diffusion controlled growth, has been analyzed and the true nucleation rate per site can be obtained from the current maximum of single-step potentiostatic experiments.
533 citations
TL;DR: In this article, the nucleation of lead onto vitreous carbon electrodes has been investigated and the number density of active sites for nucleation was found to vary with the overpotential but not with the concentration of lead ions in solution.
128 citations
TL;DR: In this article, the relationship between climate, soils, human activities and vegetation along an altitudinal gradient of the Venezuelan paramos is analyzed and interpreted by means of ordination and classification techniques.
Abstract: By means of ordination and classification techniques, the relationships between climate, soils, human activities and vegetation along an altitudinal gradient of the Venezuelan paramos are analyzed and interpreted. The altitudinal gradient chosen is characterized by decrease of temperature, precipitation, soil fertility, soil water-holding capacity, and plant cover as altitude increases. The ordination results suggest vegetation changes to be primarily related to environmental changes occurring with altitude, and secondly to disturbances caused mainly by grazing. Some results point toward a disjunction in the vegetational gradient occurring at ca. 3 500 m.a.s.l. and separating low and high paramo. This disjunction might have been caused by the glacial history of the paramos and the occurrence of frequent night-frosts. The soil samples were kindly analyzed by the Laboratorio de Edafologia, Centro Nacional de Investigaciones Agropecuarias. Help in plant identification was generously obtained from the specialists of Instituto Botanico, Instituto Nacional de Parques, Caracas.
57 citations
45 citations
TL;DR: Ants on their own territory or on territories impregnated with metapleural gland extract from workers of their colony, initiate more intraspecific combats than ants on territories of a different colony or on Territories without the chemical mark.
43 citations
TL;DR: The hypothesis is stated that alarm pheromones are used for nestmate recognition by those ants possessing territorial marking behaviour, and the possible relationship between nestmates recognition systems and territorial behaviour is discussed in an evolutionary context.
Abstract: Camponotus rufipes (Fab.) workers recognize conspecifics from other colonies and ants from different species as aliens. Colony specific recognition is based on odours produced by the mandibular gland which also serve as alarm pheromone. This ant marks its territory with chemicals secreted by an unidentified abdominal gland, which is thus advertised to conspecifics. Marked territories near to the nest induce recruitment or at least prolonged exploration if marked by a foreign conspecific colony. The same territory outside the nest area induces a prolonged permanence of workers from the colony giving the mark. The possible relationship between nestmate recognition systems and territorial behaviour is discussed in an evolutionary context by stating the hypothesis that alarm pheromones are used for nestmate recognition by those ants possessing territorial marking behaviour.
41 citations
TL;DR: In this article, C13 n.m.r. spectroscopy and C, N elementary analysis have been applied to determine the degree of hydrolysis of commercial polyacrilamide samples.
39 citations
TL;DR: The respective patterns of development of the two species have been compared, with reference to such parameters as egg size and number, duration and number of larval stages, and body length of the first zoea.
Abstract: Summary In Venezuela, M. jelskii and M. amazonicum are both found living in fresh waters and sometimes share the same habitat. The respective patterns of development of the two species have been compared, with reference to such parameters as egg size and number, duration and number of larval stages, and body length of the first zoea. Development of M. jelskii exhibits features characteristic of fresh water species, whereas that of M. amazonicum has features usually associated with brackish water species.
37 citations
33 citations
TL;DR: In this article, a procedure was developed which enables the energy consumption of batch food sterilizing processes to be minimized, which is illustrated for pea puree packed in 307 × 409 (mm) cans and heat processed in a pilot-scale retort at six different time-temperature combinations providing the same lethal value.
32 citations
TL;DR: The conclusion is reached that the negentropy content of living systems is a powerful tool in phylogenetic studies, even of small taxonomic groups.
TL;DR: With the methods and media compared, sampling by the whole carcass rinse method and enrichment in RAP (43°C) and plating on BSA provide optimal conditions for detection of Salmonella in raw chicken.
TL;DR: In this paper, the asymptotic behavior of several increment processes, obtained from W and a σ − 1/2 σ σ, is investigated in terms of their upper classes.
01 Jan 1984
01 Sep 1984-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the standard free energies of formation of Cr7C3 and Cr3C2 have been obtained from emf measurements on the following galvanic cells with BaF2-BaC2 solid solutions as the electrolyte.
Abstract: The standard free energies of formation of Cr7C3 and Cr3C2 have been obtained from emf measurements on the following galvanic cells with BaF2-BaC2 solid solutions as the electrolyte: Cr,Cr23C6∣BaF-BaC2∣Cr23C6,Cr7C3 (920 to 1250 K) (A) Cr23C6, Cr7C3 ∣BaF2-BaC2∣W, WC (900 to 1200 K) (B) WC, W∣BaF2-BaC2∣Cr3C2, Cr7C3 (973 to 1173 K) (C) Combining the results of this study with a previous work15 and those of Kulkarniet al. and Dawsonet al., the following equations for ΔGfℴ of Cr7C3 and Cr3C2 have been determined: from cell (A): ΔGCr7C3o(±2300) = −155410(±173) − 35.8(±0.1)T joules; from cell (B): ΔGCr7C3o(±2000) = −155585(±385) − 35.8(±0.4)T joules for the reaction 7Cr + 3C = Cr7C3; from cell (C): ΔGCr3C2o, (±1200) = −92860(±210) − 19.4(±0.2)T joules for the reaction 3Cr + 2C = Cr3C2.
TL;DR: In this article, an analysis of the response of a model of hydrophobic pollutants in sedimentation ponds is presented, where a Latin hypercube sampling scheme for model response analysis simultaneously to nine model parameters was used.
TL;DR: In this article, a natural geometric asymptotic approximation for the eigenstates of the Hamiltonian was developed to identify the phase diagram of the theory. But this was performed in the case of √ Z √ 2.
Abstract: The Hamiltonian formulation is analyzed in a basis of gauge-invariant loop states. A natural geometric asymptotic approximation for the eigenstates of the Hamiltonian is developed to identify the phase diagram of the theory. Satisfactory explicit calculations are performed in the case of ${Z}_{2}$.
01 Jan 1984
TL;DR: In this paper, an integrated on-line order determination and a parameter estimation algorithm for a storage plant is presented, based on testing recursively the significance of the reduction in the prediction error variance when increasing the model order by means of a modified F-test.
Abstract: The experimental application of an integrated on-line order determination and a parameter estimation algorithm to a storage plant is presented. The experiments are carried out on different operating points around which the plant can be modeled as a linear, discrete-time, stochastic and S.I.S.O. system. A simple algorithm for the determination of the order is proposed. The experiment is based on testing recursively the significance of the reduction in the prediction error variance when increasing the model order, by means of a modified F-test. The results of three well-known identification procedures, used to perform the parameter estimation in different conditions, are also reported for comparison purposes.
TL;DR: The hydrido cluster Os 3 H 2 (CO) as mentioned in this paper reacts with neat methyl vinyl ether to give two isomers of the insertion product Os 3H(μ-MeCHOMe)(CO) 10 which are stabilised by ether coordination in the 1methoxyethyl bridge but slowly revert to the dihydride on standing in solution.
TL;DR: Injections of arginine and morphine increased the voltage of electric shocks necessary to induce a defensive reaction in the Praying Mantis, and the effect of both was inhibited by naloxone.
Abstract: Injections of arginine and morphine increased the voltage of electric shocks necessary to induce a defensive reaction in the Praying Mantis. The effect of both was inhibited by naloxone.
TL;DR: In this paper, a couplage serre and a quadruple quadruple approximation is used to obtenir les taux d'excitation d'impact electronique for les transitions entre les niveaux de la configuration la plus basse de Ne 2+
Abstract: On utilise une approximation a couplage serre et a etat quadruple pour obtenir les taux d'excitation d'impact electronique pour les transitions entre les niveaux de la configuration la plus basse de Ne 2+
TL;DR: In this paper, the Green function of a particle that performs a random-walk on the Bethe lattice in the presence of the Coulomb potential is obtained in terms of the incomplete beta function.
TL;DR: By using a gauge-invariant quantization procedure in the loop-space previously proposed by the authors, a simple realization of 't Hooft's algebra is obtained which suggests that the dynamics of the system singles out the permanent confinement region as discussed by the authors.
TL;DR: In this article, the utility of a sodium acyloxyborohydride, derived from sodium borohydride and tartaric acid, in stereoselective reductions of cyclic ketones is demonstrated.
TL;DR: In this paper, the (exp −4) model of van Kranendonk was used to calculate the binary absorption coefficients for the fundamental vibrational bands of N2 and O2 at temperatures from 70 to 340 K.
TL;DR: In this paper, a simple manual procedure for the prediction of the retention of nutrients with first order kinetics of thermal degradation, during thermal processing of conduction-heating foods packed in rectangular containers was developed and evaluated.
Abstract: The objective of this research work was to develop and evaluate simple manual procedure for the prediction of the retention of nutrients with first order kinetics of thermal degradation, during thermal processing of conduction-heating foods packed in rectangular containers. An equation was developed that permits the estimation of the integrated nutrient retention over the volume by means of Stumbo's formula method. The procedure was compared with literature data for thiamin retention in various thermal processes. Results obtained from the application of the method were within the 90% confidence interval of the experimental values.
Journal Article•
TL;DR: The block diagram with the description of the traditional process is presented, together with labor and time requirement studies of the different stages of the process, in order to improve the efficiency and yield of the product.
Abstract: A quantitative study of the traditional process for making "chiga" flour was performed. The "chiga" flour is obtained from the seed of the "chigo" (Campsiandra comosa, Benth) and is utilized as a human food in areas of Venezuela in the Orinoco basin, especially in the State of Apure and in the Territorio Federal Amazonas. The block diagram with the description of the traditional process is presented, together with labor and time requirement studies of the different stages of the process. The yields as well as the requirements for raw materials are also discussed. This research work was carried out to study and provide quantitative information that may allow the duplication of the process, in order to improve the efficiency and yield of the product.
TL;DR: In this paper, the possibility of using spray deposited ZnO layers is explored to fabricate the zinc oxide/p-Si heterojunction solar cells, which have resistivity value 10−Ω cm and optical transmission of solar radiation about 70% have been obtained.
TL;DR: The activities of phosphofructokinase and lactic dehydrogenase found in non-infected bovine erythrocytes were fifty times greater than the previously reported values.
Abstract: The glycolytic process in non-infected and A. marginale-infected bovine erythrocytes was studied. The study included four enzymes: hexokinase, phosphofructokinase, pyruvic kinase and lactic dehydrogenase, and the intracellular concentrations of glucose, ATP and 2,3 diphosphoglyceric acid (DPG). The activities of phosphofructokinase and lactic dehydrogenase found in non-infected bovine erythrocytes were fifty times greater than the previously reported values. Glucose and DPG concentrations, hexokinase, pyruvic kinase and lactic dehydrogenase specific activities did not change significantly during experimental anaplasmosis. Phosphofructokinase activity in A. marginale-infected erythrocytes increased to values 300% of those found in intact bovine red cells. ATP concentration in infected erythrocytes decreased to values of 40% of those found in non-infected cells: from 1.60 +/- 0.40 to 0.70 +/- 0.08 mumole per gram of hemoglobin.