Showing papers by "Simón Bolívar University published in 1980"
402 citations
TL;DR: Species of the ‘bana’ vegetation in the Amazonas region of equatorial South America have scleromorphic leaves which have several features commonly found in xeromorphic plants, including greater leaf and cuticle thickness, pubescent leaves and sunken stomata, and a high incidence of sclerenchyma.
Abstract: Species of the ‘bana’ vegetation in the Amazonas region of equatorial South America have scleromorphic leaves. This leaf type, which characterizes the vegetation of Mediterranean climates, among others, has apparently evolved in this community in response to the oligotrophic soils and widely fluctuating water table. Anatomically, the leaves have several features commonly found in xeromorphic plants, including greater leaf and cuticle thickness, pubescent leaves and sunken stomata, and a high incidence of sclerenchyma. Concentrations of K and P decrease with leaf age, while N remains nearly constant and Ca increases. Concentrations of N and P are lower than in other sclerophyllous species, but the amount of these nutrients recovered before leaf shedding are similar. The correlation between P and N as expressed per unit dry weight is high (r=0.87; p 300 ppm) and Al (>1000 ppm).
130 citations
TL;DR: A broad array of suprageneric groupings reflecting different adaptive types strongly supports the hypothesis that the differentiation of the Sigmodontinae took place in South America from a primitive cricetid immigrant stock which entered South America, probably from North America, not later than during Miocene times.
Abstract: A new genus and species of sigmodontine cricetids, Cholomys pearsonl, from the Lower Pleistocene Vorohue Formation of south-eastern Buenos Aires Province. Argentina, is described. Its closest relative among the extant and extinct cricetids proved to be the living Wiedomys pyrrhorhinus of Brazil. Wiedomys and Cholomys are included in a new tribe of the Sigmodontinae, Wiedomyini. The distinction between the North American and the South American cricetids is stressed, the two groups being postulated to pertain to different subfamilies. The names Neotominae and Sigmodontinae are chosen for these two taxa, respectively. A tribal classification of the Sigmodontinae is advanced. Oryzomyini, Akodontini, Scapteromyini, Phyllotini, Sigmodontini, lehthyomyini and Wiedomyini are recognized as natural tribes of the Sigmodontinae. This broad array of suprageneric groupings reflecting different adaptive types strongly supports the hypothesis that the differentiation of the Sigmodontinae took place in South America from a primitive cricetid immigrant stock which entered South America, probably from North America, not later than during Miocene times.
105 citations
TL;DR: Theorem 2.1 in this paper shows that a diffeomorphism f of a compact riemannian manifold M is Anosov if and only if its tangent map has a non-degenerate Lyapunov quadratic function.
94 citations
TL;DR: In this article, the quantum field theory of electromagnetism in a vacuum is formulated as quantum mechanics in the loop space, and a precise statement of the incompatibility field loop is given in terms of generalized momentum-position uncertainty relations.
Abstract: The quantum field theory of electromagnetism in a vacuum is formulated as quantum mechanics in the loop space. A precise statement of the incompatibility field loop is given in terms of generalized momentum-position uncertainty relations. The loop-dependent wave functions of the basic states are obtained, and a physically satisfactory geometrical interpretation is given.
56 citations
TL;DR: The tentative interpretation is advanced that rapid colonization occurred over most of the present territory by a chromosomically uniform invading stock, which subsequently became differentiated by parapatric chromosome raciation, which formed in unfavorable, dry climatic phases.
Abstract: A series of populations of spiny rats (Proechimys) of NW and N Central Venezuela were found to belong to a circle of species and subspecies which surrounds the Andes of M6rida-CordiUera de la Costa mountain axis. This 'Rassenkreis' consists of 6 successive karyomorphs which exhibit a stepped-dine distribution (2n = 42, 44, 46, 48, 50 and 62). Each of the karyomorphs occupies a discrete subarea in an almost continuous territory. Polymorphism is very rare and no intermediate karyotypes have been found in the borders of each subarea. Although contact zones have not been studied in detail, the distribution seems to be mostly parapatric. Areas are 12-100 km apart, in most cases without effective barrier between them. Only 1 Robertsonlan rearrangement accounts for each of the steps from 2n = 44 to 2n = 50. The transition from 2n = 42 to 2n = 44 involves 1 Robertsonian change and 3 pericentric inversions. The transition from 2n = 50 to 2n = 62 requires 6 Robertsonian rearrangements and 2 pericentric inversions. It is inferred that successive populations of the 2n = 44 2n = 50 series may be at an incomplete stage of reproductive isolation by partial reproductive failure of the FI hybrids. Reproductive isolation may be almost complete between the 2n = 42 and 2n = 44 and the 2n = 50 and 2n = 62 karyomorphs. This 'Rassenkreis' is classified as a superspecies, Proechimys [guairae], comprising three allospecies: P. poliopus, P. guairae, and a new unnamed species (Barina's~ sp. n.). Within P. guairae 4 subspecies (or semispecies) are recognized, 2 of which are named (P. guairae guairae and P. guairae ochraceus). It is postulated that differentiation within this superspecies occurred during the Late Pleistocene. The tentative interpretation is advanced that rapid colonization occurred over most of the present territory by a chromosomically uniform invading stock, which subsequently became differentiated by parapatric chromosome raciation. This was followed by further chromosome differentiation in peripheral isolates which formed in unfavorable, dry climatic phases. During humid climatic phases the ranges expanded and zones of secondary contact with the original populations were established.
38 citations
TL;DR: In this article, a model was developed to predict the retention of nutrients with first order kinetics of thermal degradation in foods packaged in reportable pouches and sterilized by thermal conduction.
Abstract: A model was developed to predict the retention of nutrients with first order kinetics of thermal degradation in foods packaged in reportable pouches and sterilized by thermal conduction. The validity of the model was verified experimentally on a simulated food. The model was effective in predicting the temperature at the center of the container at the end of the heating period and, to a lesser extent, at the end of the cooling period. The prediction of the fraction of nutrient retained at the end of processing compared favorably to the fraction obtained experimentally, and they were within the 90% confidence intervals of the experimental fractions.
21 citations
TL;DR: The photovoltaic behavior of a CdS/ZnIn2Se4 vacuum-evaporated thin film solar cell is reported for the first time in this article, where the combination of semiconductor materials seems to be suitable for use as one of the junctions in tandem solar cell configurations.
19 citations
TL;DR: A detailed description of the karyotype of Proechimys trinitatis, (2n = 62, FN = SO), based on specimens from Trinidad, is given in this article.
Abstract: A detailed description of the karyotype of Proechimys trinitatis, (2n = 62, FN = SO), based on specimens from Trinidad, is given. It differs from the karyotype of Proechimys guyannensis (2n = 40) which is interpreted as an indication of the need of giving full species status to P. trinitatis. It also differs from the karyotype of P. urichi, a montane form living in Eastern Venezuela, and it is remarkably different from the karyotypes of members of the superspecies P. guairae from north-western and north-central Venezuela. Specimens from a sample of Cachipo, in the lowlands of Monagas State, proved to have a karyotype identical to that of the studied specimens of P. trinitatis from Trinidad. This is interpreted as an indication that P. trinitatis is also represented on the continent. Differences in size and in cranial characters of the Venezuelan specimens uggest hat the Cachipo sample might be separated as a distinct subspecies of P. trinitatis. ability is interpopulational (Reig et al., 1979). Therefore, when karyotypic differences are large enough as to imply postzygotic reproductive isolation by a high level of gametic aneuploidy in the F, hybrids (Capanna et al., 1977; Reig et al., 1979) these differences make a good tool for species recognition, even when this recognition is hard to make on morphological grounds. Consequently, chromosome investigations may contribute to the understanding of the confusing systematics of this genus, and help to gain further knowledge on the role played by karyotypic rearrangements in the speciation process, a subject which is becoming a point of primary attention in modem theory of speciation (White, 1978). We now report the karyotype of Proechimys trinitatis (Allen & Chapman) 1893, the type species of Proechimys (Allen, 1899), but which has been alleged (Ellerman, 1940) not to be separable at the species level from the earlier proposed Proechimys guyannensis (E. Geoffroy) 1803.
12 citations
TL;DR: In this article, the surface profile of a thermocapillary liquid submitted to heating by a nonuniform light beam undergoes a time-dependent deformation, and the profiles corresponding to illumination with (a) a Gaussian laser beam, (b) a point source, (c) a fringe system, and (d) a circular Gaussian speckle pattern are calculated.
Abstract: It has been experimentally shown in recent papers that the surface profile of a thermocapillary liquid submitted to heating by a nonuniform light beam undergoes a time-dependent deformation. The profiles corresponding to illumination with (a) a Gaussian laser beam, (b) a point source, (c) a fringe system, and (d) a circular Gaussian speckle pattern are calculated. This study sets some theoretical bases for practical utilization of highly viscous liquid films as transient photographic receivers.
12 citations
01 Mar 1980
TL;DR: In this article, a single correlation of general form is constructed employing both limiting equations in conjunction with additional values of the Nusselt number at intermediate Rayleigh numbers, which is valid for both laminar and turbulent regimes.
Abstract: Natural convective heat transfer from isothermal spheres to air or water is studied. The limiting equations for the Nusselt numbers at very small and large values of the Rayleigh number respectively are developed using a collection of theoretical and experimental results obtained by several investigators. A single correlation of general form is constructed employing both limiting equations in conjunction with additional values of the Nusselt number at intermediate Rayleigh numbers. This single correlation interpolates the limiting equations and is valid for both laminar and turbulent regimes. The computed results agree very well with those given by individual equations for subintervals of the Rayleigh number spectrum.
TL;DR: In this article, self-focusing of laser radiation reflected from the surface of liquid heavy hydrocarbons is reported, and the focus appears at 40 cm of the sample surface after 1 s of irradiation at 350 mW.
01 Sep 1980-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a study of the BaF2-BaC2 system for use as a solid electrolyte applicable to measurements of the chemical potential of carbon was made and from lattice parameter studies of annealed specimens it was concluded that only a limited solid solubility exists; rising from about 0.8 to 1.0 wt pct BaC2 in the temperature interval 973 to 1173 K.
Abstract: A study has been made of the BaF2-BaC2 system for use as a solid electrolyte applicable to measurements of the chemical potential of carbon. From lattice parameter studies of annealed specimens it is concluded that only a limited solid solubility exists; rising from about 0.8 to 1.0 wt pct BaC2 in the temperature interval 973 to 1173 K. Hydrolysis of the solid solutions produced gases containing two carbon atoms with no evidence of single carbon hydrocarbons. This is taken as evidence that the acetylide ion,C
2-
2, of BaC2 is conserved in the solid solution. Galvanic cell studies with Mo-Mo2C and Cr-Cr23C6 electrodes in the temperature range 890 to. 1105 K with electrolytes of differing composition gave results in excellent accord with the most recent measurements of the stabilities of the carbides. Lack of reversibility to graphite indicates a limited application of the electrolyte.
TL;DR: In this article, a gaussian laser beam reflected from a thermocapillary liquid surface self-focuses at a distance L from the sample surface at a time-instant t s after the beginning of the irradiation.
TL;DR: In this paper, a new procedure for the synthesis of 2,3-diaryl-3,4-dihydro-4-hydroxy-1 (2 H )-isoquinolones is described in which the cis -isomer predominates.
TL;DR: In this article, a tight-binding approximation for one-dimensional binary alloys is presented, which is an extension of work by Faulkner and Korringa and handles spatial correlations by restricting the number of allowed configurations in the ensemble over which averages are taken.
Abstract: A new technique to treat one-dimensional binary alloys, described in tight-binding approximation, capable of incorporating short-range correlations in a simple way is presented. The method is an extension of work by Faulkner and Korringa and handles spatial correlations by restricting the number of allowed configurations in the ensemble over which averages are taken. The density of electron states thus calculated exhibits rich structure, which is known to exist but is lost in treatments which neglect local correlation effects. A detailed study of the stoichiometric case with an equal number of atoms of both chemical species is presented, including up to next-nearest-neighbor correlations.
TL;DR: In this paper, the stomach contents of 153 specimens of Tethyaster vestitus and 981 specimens of Astiopecten riensis were analyzed on the basis of samples obtained at depths between 21 and 63m by trawling in Golfo Triste.
Abstract: This research has been done on the basis of samples obtained at depths between 21 and 63m by trawling in Golfo Triste. The stomach content of 153 specimens of Tethyaster vestitus and 981 specimens of Astiopecten riensis were analyzed. A.riensis seems to be an important element within the trophic structure of the community under study, constituting the second and third level of consumers. T.verstitus is, within the above-mentioned community one of the rare constitiuents of the 4th level consumers despite the fact that it takes part in the 3rd level as well.
TL;DR: The article as mentioned in this paper focuses on Colombia and Venezuela vis-a-vis their next-door neighbors, engaged as they are in trying to delimit marine and submarine areas off the northwestern corner of the Gulf of Venezuela, where oil and gas may be found.
Abstract: Since the Informal Composite Negotiating Text (ICNT) has practically enshrined the Exclusive Economic Zone in the emerging law of the sea, several Caribbean nations—both continental and insular—have not only advanced unilateral claims in rapid succession but have been attempting the uneasy task of delimiting their respective zones. The article focuses on Colombia and Venezuela vis‐a‐vis their next‐door neighbors, engaged as they are in trying to delimit marine and submarine areas off the northwestern corner of the Gulf of Venezuela, where oil and gas may be found. While Colombia stresses equidistance lines as the foremost delimitation method, Venezuela advocates equitable principles. With the help of maps drawn to show how much has been already delimited, the article discusses at length three recent Venezuelan agreements: a fishing agreement with Trinidad and Tobago (1977), plus two EZ delimitation treaties concluded almost simultaneously in 1978: one with the United States (Puerto Rico and Virgi...
TL;DR: In this article, a self-dual Lagrangian formulation of magnetic monopoles is proposed. But the problem of finding a vector potential free from anomalous singularities is not solved.
Abstract: There are some subtle features associated with the quantum theory of magnetic monopoles. In order to describe the wave function of an electron in the field of a magnetic monopole, a vector potential A is needed. However it is well known (1,2) that there does not exist any vector potential free from anomalous singularities. There have been a number of Lagrangian formulations (1.3) intended to overcome this basic problem. Dirac's formulation is built up in terms of a vector potential which exhibits au unphysical string singularity. The formulation of WL~ and YANG is based on the observation (4) that a nonsingular vector potential can only be given on each of a set of overlapping regions of space-time. In both formulations there are somc important disadvantages. In the formulations a la Dirac the Lagrangian is highly singular due to the string-string terms. In the Wu-Yang formulation the second Maxwell equation cannot be obtained from the action and must be considered as a kinematical constraint. In addition, in both formulations, a completely asymmetrical t reatment to the electric and magnetic charges is given. Due to the dual symmetry one is allowed to write these Lagrangians with the role of the electric and magnetic charges exchanged, but a direct self-dual Lagrangian formulation has not been given yet. I t is a nontrivial problem to produce a, fully covariant formulation of electromagnetism with magnetic charges. However, a reduced noncovariant Lagrangian in terms of the dynamical degrees of freedom, may easily be written. To do this let us start from ordinary electromagnetism with the usual Lagrangian
Journal Article•
TL;DR: In this article, the absence of field copies in a very general class of gauges is proven in a rather obvious geometric way, and the introduction of path-dependent potentials, as new relevant objects, allows us to relate in a natural way the pathdependent formulation of gauge theories to other point function formulations.
Abstract: The introduction of path-dependent potentials, as new relevant objects, allows us to relate in a natural way the path-dependent formulation of gauge theories to other point-function formulations. The absence of field copies in a very general class of gauges is proven in a rather obvious geometric way.
TL;DR: In this paper, the authors extended the model of anisotropic superfluidity of hadronic matter by giving it an analytic formulation in terms of the Ginzburg-Landau macrowave functions.
Abstract: We extend the model of anisotropic superfluidity of hadronic matter previously developed, by giving it an analytic formulation in terms of the Ginzburg-Landau macrowave functions. Analytic solutions of the coupled differential equations of a generalized Ginzburg-Landau type are used to estimate physically measurable parameters. Our work allows us to understand some qualitative aspects of hadronic matter.
01 Jan 1980
TL;DR: In this paper, the authors considered the strong-gravity theory of Isham, Salam and Strathdee in the limit of vanishing f-meson mass, and formulated the problem of the existence of short-range potential.
Abstract: We consider the strong-gravity theory of Isham, Salam and Strathdee in the limit of vanishing f-meson mass, in order to formulate the problem of the existence of short-range potential. Unlike the type-I solutions (in the Salam-Strathdee classification) found in the last two years by some authors, we succeed in incorporating, from the start, some type-II solutions, previously found as asymptotic spherically symmetric solutions by Aragone and one of us. Some unexpected features of density, pressure and one nonclassical potential are discussed.