Showing papers by "University of Los Andes published in 1981"
TL;DR: Zinc (10−100 ng ml -1 and cadmium (20−200 ng ml −1 ) are successively eluted from an ion exchange column and determined by their inhibition of the cobalt-catalyzed chemiluminescence generation from luminol as mentioned in this paper.
57 citations
TL;DR: In this article, Horn's markovian model of forest succession is discussed and different domains of attraction arise when the replacement probabilities are density dependent, and explicit light-gap opening and colonization terms are introduced to make the model useful in tropical rain forests dynamics.
41 citations
29 citations
TL;DR: In this article, a general analysis of the interaction of classical particles with the classical electromagnetic zero-point field (cemzpf) is presented, which provides a possible observational test for stochastic electrodynamics (SED).
Abstract: This article presents a general analysis of some aspects of the interaction of classical particles with the classical electromagnetic zero-point field (cemzpf). The analysis provides a possible observational test for stochastic electrodynamics (SED). A convergence form factor derived semiclassically supports the narrow linewidth and related approximations of SED by introducing a typically sharp frequency cutoff. An extended classical charge monopole can then be shown to perform a simple jiggling motion under the influence of the cemzpf. Besides this motion (same as polarizable particles), monopolar particles also display a random walk in velocity space which leads them to ever-increasing translational kinetic energies. Hence, classical particles under the influence of the cemzpf display a conspicuous behavior because of the following well-known interrelated results: First, no velocity-dependent forces exist for classical particles moving exclusively through the cemzpf. Second, both monopolar and polarizable particles in SED are predicted to perform a random walk in velocity space due to the action of this field. Only collisions may provide a stopping mechanism. An analysis of the work of Boyer and others concerning particle collisions with walls, suggests the idea that collisions transfer energy from an unconfined gas of mutually colliding particles to the random field. Using this, a Fokker-Planck model for an unconfined gas of mutually colliding classical particles is constructed. It displays a universal equilibrium energy spectrum ${E}^{\ensuremath{-}\mathrm{const}}$ for the gas particles under the cemzpf as seen from any point fixed to co-moving coordinates. Primary cosmic rays have such an energy distribution. This motivated the proposal of a zero-point field (zpf) cosmic-ray acceleration mechanism in a previous work. Such a proposal requires a careful examination. However, methodologically speaking, one should first examine the alternative possibility that the behavior predicted in SED for classical particles does not occur in nature. If that would happen to be the case, then SED and the cemzpf concept should be critically revised. That the cemzpf concept may apparently lead to difficulties, is seen by presenting a paradoxical example where a monopolar particle moving through the cemzpf is predicted to suffer an enormous frictional force due to the surrounding zpf. The prediction obviously violates the Lorentz invariance of the cemzpf energy density spectrum. But the paradox is easily resolved by realizing the improper ultrarelativistic behavior of the Lorentz-Dirac equation which is used in the example. Extreme care must then be exerted in the use of the equations of motion of classical charged particles when moving under the influence of a zpf. The search for internal contradictions in SED, not related with the well-known renormalization and other difficulties of classical electrodynamics, has so far been unsuccessful. This and several points of rigor here and elsewhere included, are enough to indicate that the conspicuous behavior of classical particles discussed here is correctly predicted from the assumptions of SED. It is therefore proposed that this predicted behavior may serve as an observational test for the validity of SED.
21 citations
TL;DR: The phenological structure of epigeic animal communities was studied using pit-fall traps along an altitudinal transect in the Peruvian desert, indicating a reliance on perennials for food and shelter rather than on unpredictable annuals.
20 citations
TL;DR: In this article, the photoconductivity spectrum of a single crystal grown both by chemical transport and by the Bridgman method has been studied at 300 K. Splitting of the valance band was clearly observed in both the chaleopyrite and pseudo-wurtzite structures.
19 citations
17 citations
TL;DR: A system approach to handling the solid waste problem in an urban area of Venezuela is described in this paper, where data on garbage production and density is derived from field studies and incorporated into decision models for planning equipment needs and feasible efficient collection policies.
13 citations
01 Jul 1981
TL;DR: Agarwal et al. as discussed by the authors recuperar la historia de la configuracion del movimiento estudiantil en Colombia, revisible con la primera decada del Frente Nacional, and que tiene antecedentes en el gobierno militar y en la La violencia.
Abstract: Busca recuperar la historia de la configuracion del movimiento estudiantil en Colombia, historia que coincide, con la primera decada del Frente Nacional, y que tiene sus antecedentes en el gobierno militar y en la La violencia". Con el fin de desarrollar el tema senalado, inicialmente se trata el aspecto de la participacion social en la universidad. Luego se ubican los antecedentes inmediatos del movimiento estudiantil, para, luego, enfocar cronologicamente su configuracion, Auge y declinacion, tratando de darle contenidos explicativos al fenomeno. "
10 citations
TL;DR: Results show that OC may affect plasma triglycerides through the influence of apolipoproteins that modulate lipoprotein lipase activity.
7 citations
TL;DR: In this paper, the missing low frequency B1 mode in a single crystal of CuInS2 has been experimentally detected for the first time using Fourier transform spectroscopy.
Abstract: The missing low frequency B1 mode in a single crystal of CuInS2 has been experimentally detected for the first time. This mode is only Raman active; however, it was activated for infrared absorption process by introducing Fe impurity. The missing mode was investigated using Fourier transform spectroscopy. The experimentally observed value (110 cm−1) is in accordance with the theoretically predicted value.
TL;DR: In this article, the sensitivity of the spectral density and the correlation of the harmonic oscillator to the charge distribution were examined in the context of classical stochastic electrodynamics.
Abstract: The sensitivity of the spectral density and the correlation of the harmonic oscillator to the charge distribution is examined in the context of classical stochastic electrodynamics. While the first exhibits some degree of sensitivity, the second exhibits none in the limit of zero charge. Thus a comparison can be made with nonrelativistic quantum mechanics independent of the charge distribution. In the same spirit, the anharmonic oscillator is examined. In the limit of zero charge, it is shown that classical stochastic electrodynamics qualitatively agrees with quantum mechanics, but ambiguities make a quantitative comparison difficult. In an appendix, the oscillator approximation to the hydrogen atom is briefly discussed.
Journal Article•
01 Jan 1981
TL;DR: In this article, the composicion of congruencias in categorias regulares was investigated, and it was shown that the condicion of Lawvere (toda relacion de equivalencia is una congruencia) is equivalent to congruencia in a cualquiera de las siguientes propiedades.
Abstract: Se investiga la composicion de congruencias en categorias regulares y se demuestra, entre otros resultados, que la condicion de Lawvere (toda relacion de equivalencia es una congruencia) es equivalente en tales categorias a cualquiera de las siguientes propiedades: (i) la compuesta de congruencias que conmutan es una congruencia, (ii) un morfismo regular con congruencia r envia toda congruencia que conmuta con r a una congruencia en la imagen, (iii) cualquier par de morfismos regulares con congruencias que conmutan y tienen interseccion trivial posee un "pushout" que es simultaneamente un "pullback" Con lo anterior es posible caracterizar las categorias regulares en las que la compuesta de congruencias es siempre una congruencia, generalizando asi hechos bien conocidos del Algebra Universal
TL;DR: In reserpinized mice the occurrence of goldthioglucose hypothalamic lesions was significantly lower than in control mice, and the protective effect of reserpine was not reversed by serotonergic and dopaminergic agonists, alone or in combination, nor by insulin.
Abstract: In reserpinized mice the occurrence of goldthioglucose hypothalamic lesions was significantly lower than in control mice. Some protection was also conferred by serotonin-receptor blockers and by treatment with nialamide+DL-α-methyldopa, but the protective effect of reserpine was not reversed by serotonergic and dopaminergic agonists, alone or in combination, nor by insulin.
TL;DR: It is found that only some rewarding sites are related to temperature regulation and, that each rewarding site operates as a discrete elementary reinforcing unit with its particular pattern of susceptibilities to distinct drives or substances.
01 Jul 1981
TL;DR: In this paper, the authors describe the evolucion of the economia colombiana and of the politica economica durante a decada, in particular, the sector externo, the proceso inflacionario, the actividad productiva, inversion, and the inversion and its relationship with politica and the coyuntura externa.
Abstract: Describe la evolucion de la economia colombiana y de la politica economica durante la decada. En particular, se examina la evolucion del sector externo, del proceso inflacionario, de la actividad productiva y de la inversion y su relacion con la politica y la coyuntura externa. Tambien aborda el analisis de la evolucion de la politica de endeudamiento externo y de su efectividad. Adicionalmente sintetiza los resultados, identificando los determinantes fundamentales de la politica de endeudamiento externo y de la politica cambiaria.
01 Jan 1981
TL;DR: A hybrid-time approach is suggested for the modeling of ecosystems whose processes unfold continuously in time and which are subject to sudden and repetitive disturbances, i.e. occurring discontinuously at discrete intervals of time.
Abstract: A case is made for the study of ecosystems whose processes unfold continuously in time and which are subject to sudden and repetitive disturbances, i.e. occurring discontinuously at discrete intervals of time. A hybrid-time approach is suggested for the modeling of such systems.
01 Jan 1981
Abstract: During the last year the KN sigma term has been recalculated by several authors (1–4). As we know the sigma term is a quantity which gives an indication of the chiral symmetry breaking terms in the strong interaction Hamiltonian and this evaluation requires that limit of zero mass pseudoscalar meson is taken, and therefore approximations are required in order to use experimental data obtained from physical particle processes.
Journal Article•
TL;DR: The relativistic torque acting on a circuit carrying a current and having a uniform translatory motion in a constant and uniform electric field would seem to suggest the possibility of an acyclic relativistically electric motor as discussed by the authors.
Abstract: The relativistic torque acting on a circuit carrying a current and having a uniform translatory motion in a constant and uniform electric field would seem to suggest the possibility of an acyclic relativistic electric motor. However, the net effect on the side parallel to the rotation axis is exactly balanced by the variation of the angular momentum (in the case of an insulating circuit transporting electric charges) or by the external moment due to the magnetic field (in the case of a conducting circuit) acting on the two sides perpendicular to the rotation axis.
TL;DR: A histochemical study of the ground substance of the cartilage in which these bones develop demonstrated the predominance of acid and neutral mucopolysaccharides.
Abstract: A descriptive study of the maxilla and mandible of Cavia is presented. The study includes gross, histological and histochemical investigation of these bones in fetal and adult animals. Particular attention was given to the organization of cellular detail, and vascularity. Tooth development was examined during both intra and extrauterine life. A histochemical study of the ground substance of the cartilage in which these bones develop demonstrated the predominance of acid and neutral mucopolysaccharides.
TL;DR: In this paper, a small difference in the fundamental energy gap of the blue and colourless crystals was detected by optical absorption spectrometry, and it was suggested that with 450ppm Fe+++ concentration CuAls2 may exhibitzero magnetic susceptibility at room temperature.
Abstract: Blue crystals of CuAlS2 were grown for the first time by the closed tube vapour transport method. Colourless crystals were also grown. A Small difference in the fundamental energy gap of the blue and colourless crystals was detected by optical absorption spectrometry. Absorption peaks characteristic of Fe+++ impurity were detected in the spectra of only blue crystals. Fe+++ concentration in the blue crystals was estimated from the room temperature magnetic susceptibility measurement. Prom the survey of the magnetic susceptibility data of the composition CuFexAl(1-x)S2 it is suggested that with 450ppm Fe+++ concentration CuAls2 may exhibitzero magnetic susceptibility at room temperature.
TL;DR: The finer innervation of the tissues of the lung was studied with several methods of silver impregnation, focussing especially on the fibers and endings of the nerves.
Abstract: The finer innervation of the tissues of the lung was studied with several methods of silver impregnation, focussing especially on the fibers and endings of the nerves. The richest terminal innervation could be found in the epithelial and subepithelial tissue, and was sometimes similar to the situation in the smooth muscles which might indicate that, somehow, secretory and motor innervation are alike morphologically. On the other hand, there were many nerve fibers in the perichondrium of the small nodules and plaques of cartilage too, although they did not enter the cartilaginous tissue. The final nerves ended in different forms, from round or ovoid masses to free “ultraterminal” filaments.