Showing papers by "Simón Bolívar University published in 1982"

Breeding systems in a montane tropical cloud forest in Venezuela

Abstract: The breeding systems, reproductive efficacies and population densities of 75 species of trees, shrubs, perennial herbs and vines in a montane tropical cloud forest in Venezuela are investigated. 56.96% and 44.32% of the trees, versus the other life forms considered, respectively possess obligate outbreeding mechanisms. Two shrubs are non-pseudogamous apomicts. The percentage of dioecy among tree species (31%) is among the highest recorded in tropical forests. Reproductive efficacy is similar under all breeding systems in the forest interior. Obligately outbred taxa are slower recolonizers of a disturbed border as compared with non-obligate outbreeders. Explanations are advanced for the high incidence of dioecy combined with a low level of self-incompatibility among hermaphroditic species. It is concluded that the breeding system spectrum reflects an unpredictable pollination pattern, rather than insufficient pollinator servicing.

Massless second-order tetradic spin-3 and higher-helicity bosons

Abstract: The unique, uniform, second-order formulation of massless bosons of helicity ≥3 is presented here in terms of tetradic fields. The actions we find are shown to coincide both with the first-order (tetradic) formulation of Vasiliev and with the symmetric second-order description of Fronsdal. We carefully analyse the gravitational coupling of the spin-3 field and find that tetradic spin-3 matter presents the same translational consistency problem as symmetric matter does. Further, in the curved tetradic case the generalized Lorentz invariance can be restored by the addition of nonminimal terms.

The dependence of drainage density on climate and geomorphology

Abstract: A measure of the kinetic energy per unit mass of effective rainfall is developed as a function of the storm characteristics and the instantaneous unit hydrograph of a basin. The lower the kinetic energy at the outlet for a given potential energy, the larger is the energy expenditure inside the basin and the larger one may expect to find the drainage density. This analysis shows that the drainage density cannot be analysed on the basis of climate alone and that it is necessary to take into account the response characteristics of the basin in any spatial or climatic study of drainage densities.

Patterns of energy content in plants from the venezuelan paramos.

Abstract: Determinations of energy and ash content were made on the organs of some common plant species from an elevational gradient in the Venezuelan paramos. The results indicate differences in energy content among the life forms sampled. Giant rosette plants show the highest values in the roots while woody plants have the highest energy content in the leaves. The reproductive organs show a higher energy content than the vegetative organs. There is a tendency to increase energy content as elevation and environmental stress increase. The adaptive significance of these patterns is discussed. The high average energy value for paramo plants, 20.18 KJ/g ash free dry weight, is similar to values reported for alpine tundra plants and conifer forests.

Cyclic deformation of Nb single crystals III. Temperature and strain-rate dependence of the cyclic flow stress

Abstract: The temperature and strain-rate dependence of the cyclic flow stress of Nb single crystals with two different axial orientations has been studied at temperatures between 175 and 350 K. This dependence is found to be independent of the crystal orientation when the internal stresses are taken into account, and the results are discussed in terms of the theory of thermally activated dislocation glide. A transition temperature can be identified at about 250 K which separates two regions with different thermally activated deformation behaviour. Above this transition temperature the strain rate can be described by a stress power law, and the activation energy can be represented by a logarithmic function of the stress, as in Escaig's model of screw dislocation mobility. In the temperature range 170–250 K the results are also in agreement with the more recent model proposed by Seeger. The large experimental errors inherent in the values of activation enthalpy at low stresses are emphasized and taken into ...

Microflora in pasteurized fruit juices in Venezuela

Abstract: A total of 96 pasteurized fruit juice samples obtained at retail level and packed in pure-pak containers were analyzed, to determine their pH and mould yeasts counts. The isolated microflora were identified by macroscopic and microscopic techniques besides biochemical reactions. The pH rate values were the following: cocktail fruit, pH 2.3-4.3; orange, pH 2.8-3.7; passion fruit, pH 2.3-3.7; and tamarind, pH 2.5-3.7. The yeast and mould counts per ml were: cocktail fruit, 0-8.0 x 10(3), orange, 1.0 x 10(2)-4.5 x 10(3); passion fruit, 0-7.7 x 10(3), and tamarind, 0-6.0 x 10(2). The predominance of yeasts over the fungi in almost all the juices is evident; the only exception was tamarind juice. The genera of the yeasts commonly isolated were: Candida, Rhodotorula, Saccharomyces and Pichia, and among the fungi: Aspergillus, Penicillium and Cladosporium. Yeasts are probably the main cause of spoilage in these pasteurized fruit juices.

Polyhedral polarity defined by a general bilinear inequality

Abstract: LetX andY be finite dimensional vector spaces over the real numbers. LetΩ be a binary relation betweenX andY given by a bilinear inequality. TheΩ-polar of a subsetP ofX is the set of all elements ofY which are related byΩ to all elements ofP. TheΩ-polar of a subset ofY is defined similarly. TheΩ-polar of theΩ-polar ofP is called theΩ-closure ofP andP is calledΩ-closed ifP equals itsΩ-closure. We describe theΩ-polar of any finitely generated setP as the solution set of a finite system of linear inequalities and describe theΩ-closure ofP as a finitely generated set. TheΩ-closed polyhedra are characterized in terms of defining systems of linear inequalities and also in terms of the relationship of the polyhedronP with its recessional cone and with certain subsets ofX andY determined by the relationΩ. Six classes of bilinear inequalities are distinguished in the characterization ofΩ-closed polyhedra.

Adaptive control and parameter estimation in Markov chains: A linear case

Abstract: We consider a controlled Markov chain with finite state space, whose transition probabilities are assumed to depend linearly upon an unknown real parameter α. In particular, we study the asymptotic behavior of the maximum likelihood estimate of α under an arbitrary realizable control when α is known to belong to a given bounded interval on the line. We show that the estimate converges with probability one and characterize those realizations for which convergence does not lead to the true value. We also suggest corrections to the control policy which guarantee almost sure convergence to the true value. For the adaptive situation, where the control depends only on the current estimate of α and the present state, we show that the maximum likelihood estimate converges to a value α*indistinguishable from the true one under the feedback law induced by α*.

Formule de Rice en dimension d

Abstract: Let {x(t): t∈R d} a stochastic process with parameter in R d, and u a fixed real number. Denote by C u, Au, Bu respectively the random sets {t: x(t)= u}, {t: x(t) u}. The paper contains two main results for processes with continuously differentiable paths plus some additional requirements: First, a formula for the expectation of Q T(Au) and Q T(Bu), where for a given bounded open set T in R d, QT(B) denotes the “perimeter of B relative to T” and second, sufficient conditions on the process, so that it does not have local extrema on the barrier u. The second result can also be used to interpret the first in terms of C u.

De Sitter and conformal field theories

Abstract: After a brief review of conformal gravity and conformal anomalies in field theories, this paper deals with elementary particles and quantum field theories in 3 + 2 de Sitter space and in conformal space. The importance of working in realistic space-time rather than Euclidean or spherical models, is demonstrated. The “parton-like” representations Di and Rac give rise to gauge theories of scalar and spinor fields, and a theory of interacting massless particles with all spins. This theory (in 4-dimensional de Sitter space) is constructed on the basis cf a conformally invariant field theory in 3-dimensional space-time. Conformally invariant field theories in 3 and 4 dimensional are reviewed and examined, and new proposals are made for the interpretation of massless field theories in general.

Identification of a heat transfer system using the Galerkin method

Abstract: This paper is concerned with the identification problem of a heat transfer system using the Galerkin method. The output from the system is discretely measured in contamination with random noise. A known random excitation is inserted into the system for improving the identification accuracy. The algorithm for identifying unknown parameters in the system is derived using the output error method. Numerical results denote that the identification accuracy is much improved with a few terms in the approximation to the exact solution and also is improved by the random excitation.

Estimate of the transient conduction of heat in materials with linear thermal properties based on the solution for constant properties

Abstract: A method of analysis is described which yields quasianalytical solutions for one and multidimensional unsteady heat conduction problems with linearly dependent thermal properties, such as thermal conductivity and volumetric specific heat The method accomodates rather general thermal boundary conditions including arbitrary variations in surface temperature or in surface heat flux or a convective exchange with a fluid having even varying temperature Once the solution for the identical problem but with constant properties has been developed, its practical realization is rather direct, being facilitated by a reduced number of iterations The four applied examples given in this work show that a wide variety of nonlinear heat conduction problems can be tackled by this procedure without much difficulty These simple solutions compare favorably with more laborious results reported in the archival heat transfer literature

The Reality of Biological Species: A Conceptualistic and a Systemic Approach

Abstract: Publisher Summary This chapter discusses that the name “species” is applied in biology to three different kinds of objects—namely, (1) the species, one of the taxonomic categories of the Linnean hierarchy, (2) the taxa of species rank or taxonomic species, and (3) supraorganismal evolutionary units, distinguished in this paper as biospecies. As with all taxonomic categories, the category species is a class of classes; it is a classificatory concept, the extension of which is made up of other classificatory concepts. The chapter explains that biospecies are more than sheer aggregates of individual organisms; they are cohesive and discrete evolutionary and ecological units with the attributes of supraorganismal individual entities. Once it is accepted that taxonomic species are concepts referring to natural entities that behave in the world of nature as integrated biosystems of individual organisms, it would seem that the long-lasting controversy between nominalists and realists on the nature of biological species can be solved under the tenets of an epistemic conceptualism and a systemic ontology.

Temperature and Strain Rate Dependence of the Flow Stress of Fatigued Niobium Single Crystals

Abstract: The variation of the cyclic stress with temperature and strain rate of Nb single crystals with two axial orientations has been studied in the temperature range between 175K and 350K A transition temperature can be identified at about 250K which separates two regions with different thermally activated deformation behaviour Above this temperature the activation energy can be represented by a logarithmic function of the stress, as in Escaig's (1968) model of the screw dislocation mobility In the temperature range 170–250K the results are also in agreement with the more recent model of Seeger (1981)

Behavioral Team-Building in a Third-World Steelworks: Efficiency and Ethics

Abstract: The following article is a progress report and behavioral analysis of progress. The progress reported and analyzed is the collective achievement of an interdisciplinary team of professors and students of the Universidad Simon Bolivar and teams of workers, technicians and engineers employed by the SIDOR Steelworks. If credit is to be given for this progress, it belongs to all of the individuals involved. The authors' task here is primarily to report and interpret the project and its results using the proper behavioral vocabulary.