Showing papers by "Simón Bolívar University published in 1993"
TL;DR: It is proposed that a complex mix of ethanol, ethyl- acetate, pentane, hexanal, isolamyl-acetate, and/or isopentanol serve as a short-range orientation cue to fresh wounds on the plant and that additional host odors, attracting weevils from a distance, have still to be discovered.
Abstract: Attraction to host plants by adultRhynchophorus palmarum (L.) palm weevils was studied in the field and in the laboratory. Chemical analysis revealed the presence of ethanol and ethyl-acetate in stems of coco palms and in pineapple fruits and of pentane, hexanal, and isopentanol in coco stems. In the olfactometer, the first two compounds and isoamyl-acetate were attractive to the insects and the last three compounds, although not attractive by themselves, increased attractiveness when mixed with the first two compounds. Mixtures of these compounds, in proportions similar to the one occurring in attractive plant tissue, were as attractive as natural coconut tissue. In the field, the chemical compounds, either presented alone or as a mixture, did not attract the weevil. Males produce an aggregation pheromone when smelling ethyl-acetate. Rhynchophorol, 2(E)-6-methyl-2-hepten-4-ol, the known active component of the aggregation pheromone, attracts weevils in the olfactometer and in the field only if plant tissue, ethyl-acetate, or the above-mentioned odor mix are present. We propose that a complex mix of ethanol, ethyl-acetate, pentane, hexanal, isolamyl-acetate, and/or isopentanol serve as a short-range orientation cue to fresh wounds on the plant and that additional host odors, attracting weevils from a distance, have still to be discovered. Rhynchophorol can be considered to be a Synergist, having an anemotactic action at a distance. We recommend the use of retention traps baited with rhynchophorol, ethyl-acetate, and sugar cane as an alternative control method for the pest.
121 citations
TL;DR: The trade-off between xylem water transport capacity and leaf lifespan found in species coexisting in this forest reveals the existence of contrasting but successful adaptations to this environment.
Abstract: Drought-deciduous and evergreen species coexist in tropical dry forests. Drought-deciduous species must cope with greater seasonal leaf water-potential fluctuations than evergreen species and this may increase their susceptibility to drought-induced xylem embolism. The relationship between water transport efficiency and leaf life-span were determined for both groups. They differed in seasonal changes of both, wood water content (W c) and wood specific gravity (G). During the dry season, the W c in drought-deciduous species declined and the minimum value was recorded when leaf fall was complete. At this time, the volumetric fraction of gas (V g) increased indicating air entry into xylem vessels. In contrast, W c, G and V g changed only slightly throughout the year for evergreen species. Maximum hydraulic conductivity of drought-deciduous species was 2-6 times that of the evergreen species. but was severely reduced at leaf fall. In the evergreen species, similar water conductivities were measured during wet and dry seasons. The trade-off between xylem water transport capacity and leaf lifespan found in species coexisting in this forest reveals the existence of contrasting but successful adaptations to this environment. Drought-deciduous species maximize production in the short term with higher water transport efficiency which leads to the seasonal occurrence of embolisms. Conversely, the behaviour of evergreen species with reduced maximum efficiency is conservative but safe in relation to xylem embolism.
103 citations
TL;DR: The diversity of factors that take part in the design of intelligent patient Monitoring and management systems is presented and particular attention is given to intelligent monitoring and management interfaces, and to the use of knowledge-based systems in patient monitoring andmanagement.
Abstract: The diversity of factors that take part in the design of intelligent patient monitoring and management systems is presented. Particular attention is given to intelligent monitoring and management interfaces, and to the use of knowledge-based systems in patient monitoring and management. >
102 citations
TL;DR: The acid fractions of 15 crude oils of different degrees of maturity, biodegradation, and origin, from the Maracaibo Basin, western Venezuela, were analyzed by high-resolution gas chromatography/ mass spectrometry (GC/MS) to determine their usefulness as indicators of biodegradability and oil migration.
78 citations
TL;DR: In this article, it was shown that the set A+ of positive invertible elements of a C*-algebra has a natural structure of reductive homogeneous manifold with a Finsler metric.
Abstract: The set A+ of positive invertible elements of a C*-algebra has a natural structure of reductive homogeneous manifold with a Finsler metric. Because pairs of points can be joined by uniquely determined geodesics and geodesics are "short" curves, there is a natural notion of convexity: C ⊂ A+ is convex if the geodesic segment joining a, b ∈ C is contained in C. We show that this notion is related to the classical convexity of real and operator valued functions. Several results about convexity are proved in this paper. The expressions of these results are closely related to the operator means of Kubo and Ando, in particular to the geometric mean of Pusz and Woronowicz, and they produce several norm estimations and operator inequalities.
68 citations
TL;DR: Investigating whether introduced and native grasses differ in their water relations finds evasion mechanisms and oportunistic use of water by H. rufa contribute to, but only partially explain, the success of this grass in the Neotropical savannas where it displaces native plants from sites with better water and nutrient status.
Abstract: Introduced African grasses are invading Neotropical savannas and displacing the native herbaceous community. This work, which is part of a program to understand the success of the African grasses, specifically investigates whether introduced and native grasses differ in their water relations. The water relations of the native Trachypogon plumosus and the successful invader Hyparrhenia rufa were studied in the field during two consecutive years in the seasonal savannas of Venezuela. The two C4 grasses differed clearly in their responses to water stress. H. rufa consistently had higher stomatal conductance, transpiration rate, leaf water and osmotic potential and osmotic adjustment than the native T. plumosus. Also, leaf senescence occurred much earlier during the dry season in H. rufa. Both grasses showed a combination of water stress evasion and tolerance mechanisms such as stomatal sensitivity to atmospheric or soil water stress, decreased transpiring area and osmotic adjustment. Evasion mechanisms are more conspicuous in H. rufa whereas T. plumosus is more drought tolerant and uses water more “conservatively”. The evasion mechanisms and oportunistic use of water by H. rufa, characteristic of invading species, contribute to, but only partially explain, the success of this grass in the Neotropical savannas where it displaces native plants from sites with better water and nutrient status. Conversely, the higher water stress tolerance of t. plumosus is consistent with its capacity to resist invasion by alien grasses on shallow soils and sites with poorer nutrient and water status.
65 citations
53 citations
TL;DR: In this paper, the molecular mechanism for viscosity enhancement during the flow of poly(ethylene oxide) solutions through porous media has been investigated and the results indicated that the mechanism that causes the increased flow resistance is related to the formation of transient networks of polymer molecules in the flow field.
Abstract: The molecular mechanism for viscosity enhancement during the flow of poly(ethylene oxide) solutions through porous media has been investigated. Random packed beds of uniform-size spheres have been used as porous media. Experiments were conducted for one-dimensional (uniform) flow, as well as for a particular three-dimensional (nonuniform) flow situation. A substantial increase in flow resistance with respect to that exhibited by Newtonian fluids has been observed in both cases. The results obtained suggest that, under the conditions employed in the present work, the mechanism that causes the increased flow resistance is related to the formation of transient networks of polymer molecules in the flow field. The nonuniform flow results indicate that the presence of the polymer induces a change in the macroscopic flow distribution within the porous medium.
47 citations
TL;DR: In this article, the formation of nuclei for polymer growth occurs by precipitation of oligomeric species formed on the electrode surface and accumulated in its vicinity, indicating that the establishment of polymer growth occurred by precipitation.
38 citations
TL;DR: The use of total-reflection X-ray fluorescence (TXRF) for the determination of S, V, Fe and Ni in crude petroleum oil samples is described in this article.
35 citations
TL;DR: The results show that two different evolutionary routes to the complex Attini ant societies may exist, and show that simple optimization models cannot explain experimental data, and that social complexity correlates differently with negentropy at different levels of analysis.
Abstract: Optimization of energy use by evolving organisms, predicted by theoretical extensions of the neo-Darwinian theory, i. contrasted with that of irreversible thermodynamics, which predicts an increase in orderliness and thus an increase in energy consumption per unit of biomass. We compared this index with estimates of social complexity among ant genera and species. Our results show that simple optimization models cannot explain experimental data, and that social complexity correlates differently with negentropy at different levels of analysis. Comparing the genera among Formicidae, workers (not colonies) from genera with highly social species are less negentropic than those of socially primitive ones. At the sub-generic level, social complexity correlated positively with negentropy among species, for major workers inAcromyrmex and for minor workers inAtta. The results illustrate the complexity of thermodynamic criteria in the study of evolution but also hint at their usefulness. In this case, they show that two different evolutionary routes to the complex Attini ant societies may exist.
TL;DR: In this article, a set of coordinates in the non-parametric loop space is introduced, and it is shown that these coordinates transform under infinite dimensional linear representations of the diffeomorphism group.
Abstract: A set of coordinates in the non-parametric loop-space is introduced. We show that these coordinates transform under infinite dimensional linear representations of the diffeomorphism group. An extension of the group of loops in terms of these objects is proposed. The enlarged group behaves locally as an infinite dimensional Lie group. Ordinary loops form a subgroup of this group. The algebraic properties of this new mathematical structure are analyzed in detail. Applications of the formalism to field theory, quantum gravity and knot theory are considered.
TL;DR: For Bayesian inference in one-parameter contexts where either the likelihood or the prior has an exponential family form, relationships are derived for posterior moments and cumulants of (functions of) both the canonical and the expectation parameters as discussed by the authors.
Abstract: For Bayesian inference in one-parameter contexts where either the likelihood or the prior has an exponential family form, relationships are derived for posterior moments and cumulants of (functions of) both the canonical and the expectation parameters. The identities exhibited generalize the simple relationships well known in the conjugate analysis case. Applications of these results are indicated in the areas of Bayesian robustness and approximation. In particular, results are obtained on the behavior of the posterior distribution for a large observation, generalizing work of Meeden and Isaacson.
TL;DR: Time-resolved experimental records show that the bubbles's images follow rectilinear trajectories at an approximately constant speed, which is explained by using the theoretical expression of velocity distribution in thermocapillary liquid flow.
Abstract: A liquid film of black oil is heated by a cw Gaussian laser beam. This process gives rise to a time-increasing, axisymmetric temperature distribution with a maximum in the laser-beam axis. Because the surface tension is decreasing function of temperature, a centrifugal stress gradient and concurrent liquid flow build up in the liquid surface. This phenomenon (known as laser-induced thermocapillary liquid flow) is visualized in the far field of the reflected laser beam, where images of microscopic bubbles traveling with the liquid appear as bright spots. Time-resolved experimental records show that the bubbles’s images follow rectilinear trajectories at an approximately constant speed. This result is explained by using the theoretical expression of velocity distribution in thermocapillary liquid flow.
01 Jan 1993
TL;DR: In this paper, a set of coordinates in the non parametric loop space is introduced, and these coordinates transform under infinite dimensional linear representations of the diffeomorphism group, and an extension of the group of loops in terms of these objects is proposed.
Abstract: A set of coordinates in the non parametric loop-space is introduced. We show that these coordinates transform under infinite dimensional linear representations of the diffeomorphism group. An extension of the group of loops in terms of these objects is proposed. The enlarged group behaves locally as an infinite dimensional Lie group. Ordinary loops form a subgroup of this group. The algebraic properties of this new mathematical structure are analized in detail. Applications of the formalism to field theory, quantum gravity and knot theory are considered.
TL;DR: In 6 h of non-intensive labour, this rapid and sensitive assay can detect as few as two to five clostridial cells or spores in experimentally contaminated soft drinks.
Abstract: We have developed a rapid and sensitive assay for the detection of clostridial cells or spores in liquid food samples. The method recognizes Clostridium 16S (small ribosomal subunit RNA) rDNA (ribosomal DNA) sequences by a polymerase chain reaction-digoxigenin-labelling protocol, coupled to a capture oligonucleotide immobilized on a microtitre plate. The positive results are revealed by means of a colour reaction. In 6 h of non-intensive labour, we can detect as few as two to five clostridial cells or spores in experimentally contaminated soft drinks.
TL;DR: In this paper, the interaction of a pyridine molecule on a modelled MoS 2 surface by a Mo 3 S 8 cluster was investigated and the results showed that π-aclsorption is more energetically favored than σ-one.
TL;DR: Ionic thermal current (ITC) techniques were used to study the behavior of water in two low-rank coals of two coal coals in this paper, and the results showed that water behaved differently in the two coals.
TL;DR: Ascorbic acid was determined indirectly by spectrophotometry at 666 nm based on the photochemical reduction of methylene blue using flow-injection analysis as discussed by the authors, which allowed determination of ascorbic acid in the range 0.18-6.12 μgml−1 with relative standard deviations of 2.09 and 0.31% for 1.97 and 4.92 μgml −1 samples, respectively, and a sampling frequency of 50-55 h−1.
Abstract: Ascorbic acid was determined indirectly by spectrophotometry at 666 nm based on the photochemical reduction of methylene blue using flow-injection analysis. The carrier stream was 12.7 μgml−1 methylene blue in phthalate-HCl buffer solution at pH 3.2. The reactor was irradiated with a 500-Watt halogen lamp to facilitate the development of the photochemical reaction. The system allows determination of ascorbic acid in the range 0.18–6.12 μgml−1 with relative standard deviations of 2.09 and 0.31% for 1.97 and 4.92 μgml−1 samples, respectively, and a sampling frequency of 50–55 h−1. The proposed method was applied successfully to the determination of ascorbic acid in vitamin C tablets.
TL;DR: Aliphatic and aromatic hydrocarbons, fatty acids and heavy metals (Pb, Cu, Ni, Zn, Fe and Cd) were analyzed in atmospheric particulate matter in the city of Caracas, Venezuela as discussed by the authors.
Abstract: Aliphatic and aromatic hydrocarbons, fatty acids and heavy metals (Pb, Cu, Ni, Zn, Fe and Cd) were analyzed in atmospheric particulate matter in the city of Caracas, Venezuela. Samples were taken from 6 stations within the metropolitan area of Caracas, characterized as industrial (one), urban (two), suburban (two) and rural (one). In addition, the concentration and composition of the organic compounds was monitored over a 5 month period at an urban site to determine seasonal and temporal variabilities. In general terms, the concentrations of pollutants decreased from industrial and urban sites to suburban to rural. A similar trend was observed for preliminary toxicity tests carried out on the particulate extracts. The concentration levels of most of the pollutants were high for the industrial and urban sites, and comparable with those of other major cities worldwide.
Journal Article•
TL;DR: Six polypeptide bands, p20, p25, p28, p31, p37 and p38, were specifically detected in epimastigote crude extracts, using polyclonal antibodies directed against transducin (T) or the alpha-subunit of transducIn (T alpha).
Abstract: Guanine nucleotide binding proteins (GTP-binding proteins) function as transducers of signals in different cellular processes. We have identified several GTP-binding proteins in Trypanosoma cruzi by Western blot analyses. Six polypeptide bands, p20, p25, p28, p31, p37 and p38, were specifically detected in epimastigote crude extracts, using polyclonal antibodies directed against transducin (T) or the alpha-subunit of transducin (T alpha). Four of these bands, p28, p31, p37 and p38, were found in both the soluble and the particulate epimastigote fractions. On the other hand, two of the polypeptides, p20 and p25, were observed only in the particulate fraction, and were not solubilized using 0.2% Triton X-100 and 0.2% Nonidet P-40. A rat monoclonal antibody directed against the ras oncogene, immunorecognized a band with molecular mass of 20,000 daltons, in epimastigote homogenates. In view of their identical apparent molecular weight and solubilization properties, p20, recognized by anti-T or anti-T alpha antibodies, and the 20 KDa band, recognized by anti-ras antibodies, seem to correspond to the same polypeptide. [3H] GDP and [3H] GMP-PNP binding experiments revealed the presence of guanine nucleotide binding proteins in total epimastigote crude extracts, as well as, in the soluble, detergent soluble, and particulate fractions. A primary screening of a T. cruzi cDNA library with anti-T alpha antibodies, followed by secondary and tertiary screenings with anti-ras antibodies yielded six positive clones. One of these clones (Tc-ras1) contains a 600 bp insert which we believe encodes for the ras protein from T. cruzi. On a Northern blot, this cDNA hybridizes to a unique mRNA band of 2.0 Kilobases in epimastigotes.
TL;DR: In this paper, the generalized canonical approach to constrained systems is applied to metric independent classical actions, and the quantum analysis of non-abelian quantum field theories in four dimensions is performed on these lines; their off-shell nilpotent BRST charge is constructed and a new direct proof of the topological nature of associated quantum theories is presented.
Patent•
17 Dec 1993TL;DR: An antimony and tin containing compound for passivating contaminant metals to which a catalyst is exposed during fluid catalytic cracking of hydrocarbons containing said contaminants is described in this article.
Abstract: An antimony and tin containing compound for passivating contaminant metals to which a catalyst is exposed during fluid catalytic cracking of hydrocarbons containing said contaminant metals, said compound having a composition as follows (R*)x Sb(OSn(R**)3)n wherein R* and R** are aryl compounds having between 6 to 13 carbon atoms, wherein n=1, 2 or 3 and x=4 when n=1, x=3 when n=2, and x=0 when n=3.
TL;DR: In this article, the robustness of a base prior distribution with respect to the shape of the prior tails is investigated in the e-contamination model of prior distributions, where the posterior inference is highly sensitive to changes of λ.
Journal Article•
TL;DR: In the following study, dietary fiber, insoluble (IDF), soluble (SDF) and total (TDF) were determined in cereals and by-products and in commercial cereals products which are found in the national market and promoted as a source of fiber.
Abstract: In the following study, dietary fiber, insoluble (IDF), soluble (SDF) and total (TDF) were determined in cereals and by-products and in commercial cereals products which are found in the national market and promoted as a source of fiber. The Prosky's enzimatic-gravimetric method was used. Results were expressed as g/100g wet basis. Total dietary fiber in cereals and by-products showed a range from 1.18% (poshed rice) to 89.10% (corn bran). For the commercial cereal products, the TDF values varied from 3.73% (rice-sesame cookies) to 34.96% (Breakfast cereal named All Bran). The FDI values always were greater than the SDF values. Based on this fact, FDI values were compared with NDF (Neutral Detergent Fiber) values reported in the scientific literature and in the Venezuelan Food Composition Tables using a regression analysis. FDI values were always greater than NDF values and the correlation factor (r) was high and statistical significance to P < 0.05 for both food groups in study.
01 Jan 1993
TL;DR: In this paper, it was shown that the space of spectral measures on a W*-algebra is a smooth Banach manifold in a natural way and that the action of the group of invertible elements of the algebra by inner automorphisms makes it into a reductive homogeneous space.
Abstract: We prove that the space of spectral measures on a W*-algebra is a smooth Banach manifold in a natural way and that the action of the group of invertible elements of the algebra by inner automorphisms makes it into a reductive homogeneous space. This gives a geometric structure for the set of normal operators with the same spectrum.