Showing papers by "Simón Bolívar University published in 1981"
TL;DR: In this paper, the identification of a basic geometric group structure acting on the manifold of paths acting on some manifold of some manifold $M$ enables us to derive all the kinematical elements of a gauge theory from the single postulate of invariance of the formulation under this group.
Abstract: The identification of a basic geometric group structure acting on the manifold of paths $P(M)$ of some manifold $M$ enables us to derive all the kinematical elements of a gauge theory from the single postulate of invariance of the formulation under this group.
73 citations
TL;DR: Three and four generalized Lorentzians in two variables have been obtained to approximate the Voigt function by using the asymptotical Padé method and give a reliable and easily calculable approximation for most of the experimental needs.
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.
62 citations
TL;DR: Networking techniques allow several processors within a multiprocessing system to cooperate efficiently on a single large problem.
Abstract: Networking techniques allow several processors within a multiprocessing system to cooperate efficiently on a single large problem.
61 citations
TL;DR: A review of spray pyrolysis deposition of thin films can be found in this article, where the basic process and apparatus utilized in spray pyrotechnics are described in general and also for particular applications.
61 citations
TL;DR: The object of the work reported in this paper was to find a simple and easy to calculate approximation to the Voigt function using the Padé method, which can be used instead of the exact function in experiments that do not require great accuracy.
Abstract: The object of the work reported in this paper was to find a simple and easy to calculate approximation to the Voigt function using the Pade method. To do this we calculated the multipole approximation to the complex function as the error function or as the plasma dispersion function. This generalized Lorentzian approximation can be used instead of the exact function in experiments that do not require great accuracy.
41 citations
TL;DR: In this paper, the gel system was found to consist of two crystal populations, the gel-forming micellar (B) and the better-developed, presumably lamellar(A) crystals incorporated in the gel.
Abstract: Poly(vinyl chloride), PVC, can be gelled from 10% (w/w) solutions in a number of solvents so as to give model networks where the junctions are directly accessible by crystallographic techniques, and where the extent and properties of the network can be correlated with the nature of these junctions. The resulting network structure has been studied as a function of polymer crystallinity and polymer-solvent interaction, and a correlation between gel-forming ability and solubility parameters was found. As in previous and accompanying work [1, 2], the gel system was found to consist of two crystal populations, the gel-forming micellar (B) and the better-developed, presumably lamellar (A) crystals incorporated in the gel. The thermal behavior of wet and dried gels was followed by DSC and by high-temperature x-ray diffraction, in the course of which the distinctness of the two crystal classes became apparent also as regards thermal stability. The gelation behavior of PVC is discussed in the wider perspe...
33 citations
TL;DR: The hypothesis which attempts to explain the physiopathology of certain behavioral disorders observed after chronic ingestion of alcohol and the possible role of Tetrahydroisoquinolines in these disorders, as well as in the etiology of schizophrenia, is discussed.
Abstract: 1. 1. This article reviews some important aspects concerning the chemistry, biochemistry, and pharmacology of Tetrahydroisoquinolines. 2. 2. Special attention is given to the hypothesis which attempts to explain the physiopathology of certain behavioral disorders observed after chronic ingestion of alcohol. 3. 3. The possible role of Tetrahydroisoquinolines in these disorders, as well as in the etiology of schizophrenia, is discussed.
29 citations
TL;DR: A new algorithm is proposed which, under mild assumptions, generates a sequence{xi} that starting at any point inRn will converge to a setX defined by a mixed system of equations and inequalities.
Abstract: A new algorithm is proposed which, under mild assumptions, generates a sequence{x
i
} that starting at any point inR
n
will converge to a setX defined by a mixed system of equations and inequalities. Any iteration of the algorithm requires the solution of a linear programming problem with relatively few constraints. By only assuming that the functions involved are continuously differentiable a superlinear rate of convergence is achieved. No convexity whatsoever is required by the algorithm.
23 citations
TL;DR: The main body of the present work is a summary of the extensive account in Ref. 1 to which we have to refer the reader for most of the details as mentioned in this paper, and additional material is being included where explicitly stated.
Abstract: The main body of the present work is a summary of the extensive account in Ref. 1 to which we have to refer the reader for most of the details. Additional material is being included where explicitly stated.
23 citations
TL;DR: In this paper, a computer program has been written to analyze ionic-thermal-current (ITC) peaks in the case of the monoenergetic model, the Lorentzian, and the Gaussian energy distribution.
Abstract: A computer program has been written to analyze ionic-thermal-current (ITC) peaks. The reorientation energy is assumed to have a distribution of width $\ensuremath{\sigma}$ around a mean value ${E}_{0}$. The relaxation parameters ${E}_{0}$, $\ensuremath{\sigma}$, ${\ensuremath{\tau}}_{0}$ and the number of dipoles ${N}_{D}$ are calculated by two different methods. One set is obtained after a least-squares fitting of the experimental data was performed and another set by matching a set of experimental parameters chosen with a certain criterion. The two methods are applied to analyze Sr${\mathrm{F}}_{2}$:La ITC spectra in the cases of the monoenergetic model, the Lorentzian, and the Gaussian energy distribution. The Gaussian distribution for the reorientation energy gives the most credible results, provided that the curves are efficiently cleaned. Only in this case do the two methods converge to the same set of relaxation parameters; the value of $\ensuremath{\sigma}$ is then an increasing function of the nominal concentration and not of ${N}_{D}$. The origin of the curve broadening is discussed in terms of dipole-dipole interaction, and it is shown that this effect alone is not responsible for the energy distribution. Moreover, evidence of the presence of satellite peaks on each side of the main relaxation peak is presented. These satellite peaks explain the need of analyzing only efficiently cleaned curves for obtaining reliable results.
22 citations
TL;DR: In this article, it was shown that the x-ray scattering profile from quenched PVC samples is not representative of the amorphous phase and any crystallinity values derived on the basis of that assumption are therefore open to question.
Abstract: X-ray diffractometer traces obtained from PVC samples maintained at temperatures in the range 180 to 200°C indicate that crystal melting is followed by a state of intermediate order rather than by a truly amorphous state. In addition, this study raises serious doubts regarding the validity of the assumption that the x-ray scattering profile from quenched PVC samples is representative of the amorphous phase. Any crystallinity values derived on the basis of that assumption are therefore open to question.
TL;DR: In this article, a Monte Carlo algorithm was used to simulate the time and space dependence of chemical concentrations in a reacting system, which is used to study the phenomenon of trigger waves in the Oregonator model of the Belousov-Zhabotinskii reaction including the diffusion of species X and Y in one dimension.
Abstract: A Monte Carlo algorithm, capable of simulating numerically the time and space dependence of chemical concentrations in a reacting system, is presented. This method is used to study the phenomenon of trigger waves in the Oregonator model of the Belousov–Zhabotinskii reaction, including the diffusion of species X and Y in one dimension. The results show that a small disturbance in a homogeneous mixture can grow into a chemical (trigger) wave propagating in space at constant velocity. The dependence of this velocity on several factors is studied, namely, initial concentrations, the diffusion of Y, and the stoichiometry of the autocatalytic step of the model. A comparison of the Monte Carlo results with a previous simulation also is discussed.
Journal Article•
TL;DR: A review of trends in height and weight at menarche in Venezuela is presented in this paper using data from studies published during the period 1936 to 1978. Variations by socioeconomic status are identified and discussed.
Abstract: A review of trends in height and weight at menarche in Venezuela is presented using data from studies published during the period 1936 to 1978. Variations by socioeconomic status are identified and discussed. (summary in ENG) (ANNOTATION)
TL;DR: In this article, two types of crossed field separators are described, one with parallel rectangular magnetic poles and the other with tilted poles, and the spectra of equal energy electrons are compared for each of the separators.
Abstract: In the present work two types of crossed field separators are described. The first separator has parallel rectangular magnetic poles and the second has tilted poles. The spectra of equal‐energy electrons are compared for each of the separators. The same is done for protons. Indications of astigmatism elimination are observed at the mass focus using the tilted poles configuration for both the electrons and protons.
TL;DR: Pablo Martin and Julio Puerta Universidad Simon Bolivar, Departamento Fisica, Apdo.
Abstract: Pablo Martin and Julio Puerta Universidad Simon Bolivar, Departamento Fisica, Apdo. 80659, Caracas 1081, Venezuela. Received 19 March 1981. 0003-6935/81/152601-01$00.50/0. © 1981 Optical Society of America. Four errors appeared in this paper. Readers should note the following corrections: 1. Page 259, left-hand column, 18th line, Eq. (3): b = ΔvD (2 ln2) 1 / 2 should read b = ΔvD [2(ln2)/]-; 2. Page 260, left-hand column, 42nd line, Eq. (6): z = d +
TL;DR: An experimental method providing holographic recording of the dispersion curve of any transparent material is presented and it is shown that simultaneous encoding both in the space and time frequency domains is required to record pupil parameters.
Abstract: Extension of space-time optics to objects whose transparency is a function of the temporal frequency nu = c/lambda is examined. Considering the effects of such stationary pupils on white light waves, they are called temporal pupils. It is shown that simultaneous encoding both in the space and time frequency domains is required to record pupil parameters. The space-time impulse response and transfer functions are calculated for a dispersive nonabsorbent material. An experimental method providing holographic recording of the dispersion curve of any transparent material is presented.
TL;DR: In this paper, the authors investigated the magnitude of the local temperature variance along an extended surface arising from the influence of stochastic ambient temperatures, where the mean and variance of the ambient temperature were used as the input for calculation of the resulting variance.
Abstract: The principal objective of this investigation was to determine the magnitude of the local temperature variance along an extended surface arising from the influence of stochastic ambient temperatures. The supporting data for the ambient temperature are given by two statistical quantities, the mean and the variance. An analysis of the problem is performed, the special feature of which is the accounting of the ambient temperature variance. This parameter serves as the input for calculation of the resulting variance of the local temperature along the extended surface. Results are given as plots of the temperature band vs position in terms of the participating thermal parameters. From numerical calculations, the values of. both maximum and minimum heat rejection to the ambient are presented concurrently. Under certain limiting conditions the present solutions are found to reduce to the classic results based upon deterministic analysis.
Journal Article•
TL;DR: The purpose of this work was the production of a beverage with a nutritive value similar to that of milk, but available at a lower cost, and in the school-snack program of the National Institute of Nutrition, milk is now being replaced by this Chicha.
Abstract: The purpose of this work was the production of a beverage with a nutritive value similar to that of milk, but available at a lower cost. A traditional beverage in Venezuela, "Chicha de Arroz" (Rice Chicha), was chosen. The various formulas studied were based on rice, non-fat milk and different kinds of soy flour, in addition to sugar, vegetable oil, vitamins, ferrous sulfate and different flavors. A product with protein and caloric values similar to those of milk was obtained. Twenty formulas were prepared and submitted to physico-chemical, microbiological and sensorial evaluations with respect to flavor, color, viscosity and stability during period of refrigeration. The most adequate formula was prepared on a pilot-plant scale. Rat assays gave the same PER results as those of casein. Consumer acceptability was tested on 1,080 school children, and showed to be greater than 95%. The stability was superior to that of milk and the cost, approximately three-fourths that of the latter. In the school-snack program of the National Institute of Nutrition, milk is now being replaced by this Chicha.
Journal Article•
TL;DR: In this article, the rheological behavior of three commercially processed baby foods and four purees made from different tropical fruits was studied, utilizing a coaxial-cylinder viscometer at three temperature levels (20 degrees C, 40 degrees C and 60 degrees C).
Abstract: The rheological behavior of three commercially processed baby foods and four purees made from different tropical fruits was studied, utilizing a coaxial-cylinder viscometer at three temperature levels (20 degrees C, 40 degrees C and 60 degrees C). An analysis of variance was applied to the sample exhibiting more variability between tests, which, having resulted non significant, allowed to obtain average flow curves from all the available experimental data. The flow curves obtained were adequately described by means of the general power law, and were fitted to a pseudoplastic flow behavior by a regression. The consistency coefficient showed a decrease with increasing temperature, represented by a modified Arrhenius equation, whereas the flow behavior index did not vary significantly with temperature.
Journal Article•
01 Jan 1981
01 Jan 1981
01 Jan 1981
TL;DR: In this article, a polynomial P(X 1, X 1, N, X N ) ∈ R [ X ] is shown to have a subspace G p of the linear space generated by the indeterminates which is minimal with respect to the property P∈ R ∈ G p ] (the algebra generated by G p ).
TL;DR: In this paper, a bimetallic complex of bis(triphenyl-phosphine) iminium u-peroxopentacyano cobaltate (III) oxohydroxo-pentacyano molybdate (VI) monohydrated was obtained by ion exchange of a surface modified silica gel.
Abstract: Heterogenization of a bimetallic complex of bis(triphenyl-phosphine) iminium u-peroxopentacyano cobaltate (III) oxohydroxo-pentacyano molybdate (VI) monohydrated was obtained by ion exchange of a surface modified silica gel. Cyclohexene was oxidized over this solid at 150° the main reaction product being the cyclohexene oxide.