Showing papers by "Simón Bolívar University published in 1986"
TL;DR: Analysis of tissue water relations and seasonal changes in leaf water potential components of an evergreen tree, Morisonia americana, and two evergreen shrubs, Capparis verrucosa andC.
Abstract: This study compared the tissue water relations and seasonal changes in leaf water potential components of an evergreen tree,Morisonia americana, and two evergreen shrubs,Capparis verrucosa andC aristiquetae, with two deciduous trees,Humboltiella arborea andLonchocarpus dipteroneurus, and the deciduous vineMansoa verrucifera All these species coexist in a tropical dry forest in Venezuela Leaves of the evergreen species are sclerophyllous, while those of the deciduous species are mesophytic Leaf area to leaf weight ratios of fully mature leaves were about 75 and 170 cm2 g-1 in evergreen and deciduous species, respectively Seasonal fluctuations of leaf water content per unit of dry weight, water potential, and turgor pressure were smaller in evergreen than in deciduous species The analysis of tissue water relations using pressurevolume curves showed that evergreen species could develop a higher leaf turgor and lose turgor at lower leaf water potentials than deciduous species This was related to a lower osmotic potential at full turgor in evergreen (≃-30 MPa)_than in deciduous (≃-20 MPa) species, rather than to the elastic properties of leaf tissue The volumetric modulus of elasticity was 14 MPa in evergreen compared with 7-10 MPa in deciduous species Thus, leaf characteristics are important in determining the drought resistance of evergreen species of this tropical dry forest
152 citations
TL;DR: In this paper, three different types of models are analyzed: temporal rainfall models at a point, areal storm rainfall models, and space-time rainfall representations, with a special emphasis on the role of the scale of fluctuation of the process in these characteristics.
Abstract: The role of scale in the rainfall characterizations resulting from different rainfall models is the main issue under study. Three different types of models are analyzed: temporal rainfall models at a point, areal storm rainfall models, and space-time rainfall representations. The perspective is taken that precipitation models need mainly to incorporate those features of the process which lead to an adequate representation under some amount of local averaging either in time or in space or in space and time. Thus the characteristics of the averaged rainfall process resulting from the different models are analyzed with a special emphasis on the role of the scale of fluctuation of the process in these characteristics.
101 citations
TL;DR: It is found that the diffusion constant for vortex motion is given at ${T}_{c}$ by D\ensuremath{\simeq}0.2 (in units of nearest-neighbor distance squared per MC step per spin).
Abstract: We have performed Monte Carlo (MC) simulations on systems of L\ifmmode\times\else\texttimes\fi{}L classical planar unit spins on square lattices, for L=6, 15, 30, 60, 90, and 200. The interaction between any two given spins S${\ensuremath{\rightarrow}}_{1}$ and S${\ensuremath{\rightarrow}}_{2}$ is given by -JS${\ensuremath{\rightarrow}}_{1}$\ensuremath{\cdot}S${\ensuremath{\rightarrow}}_{2}$ if ${S}_{1}$ and ${S}_{2}$ are nearest neighbors and vanishes otherwise. In order to make sure that our results correspond to equilibrium values, we have looked into the time-dependent properties of this model in the vicinity of critical temperature (${T}_{c}$). We have found that the diffusion constant for vortex motion is given at ${T}_{c}$ by D\ensuremath{\simeq}0.2 (in units of nearest-neighbor distance squared per MC step per spin). The values of the relaxation times follow from the value of D. Our computer running times were typically ${10}^{5}$ MC steps per spin, larger than any relaxation time for the system sizes we deal with. We use a procedure based on finite-size scaling to establish the value of ${T}_{c}$=0.89J/${k}_{B}$, the value of \ensuremath{
u}=0.5\ifmmode\pm\else\textpm\fi{}0.1, and the value of ${\ensuremath{\eta}}_{c}$=0.24\ifmmode\pm\else\textpm\fi{}0.03, in agreement with the values predicted by the Kosterlitz-Thouless theory.
82 citations
TL;DR: In this paper, the spatial structure of the depth of rainfall from a stationary storm event is investigated by using point process techniques, where cells are assumed to be stationary and to be distributed in space either independently according to a Poisson process, or with clustering according to the Neyman-Scott scheme.
Abstract: The spatial structure of the depth of rainfall from a stationary storm event is investigated by using point process techniques. Cells are assumed to be stationary and to be distributed in space either independently according to a Poisson process, or with clustering according to a Neyman-Scott scheme. Total storm rainfall at the centre of each cell is a random variable and rainfall is distributed around the centre in a way specified by a spread function that may incorporate random parameters. The mean, variance and covariance structure of the precipitation depth at a point are obtained for different spread functions. For exponentially distributed centre depth and a spread function having quadratically exponential decay, the total storm depth at any point in the field is shown to have a gamma distribution. The probability of zero rainfall at a point is investigated, as is the stochastic variability of model parameters from storm to storm. Data from the Upper Rio Guaire basin in Venezuela are used in illustration.
76 citations
TL;DR: In this paper, the first-order action for self-dual linearized massive gravity in D = 3 is given, and two master actions relevant for this spin-2 case are given, explaining the equivalence between the selfdual formulation and the topological massive one.
64 citations
TL;DR: The bridging acyl complexes [Os 3 H(μ-COC 4 H 3 X)(CO) 10 ] (X = NH, O, or S) have been prepared by oxidative addition of the 2-formyl derivatives of pyrrole, furan, or thiophene (C 4H 3 XCHO) with cleavage of the aldehydic CH bonds as mentioned in this paper.
48 citations
TL;DR: Cytogenetic analysis was performed in Akodon (Akodon) puer, Akodon azarae bibianae,Akodon ( Hypsimys ) budini, Bolomys temchuki elioi, Bolmys tem chuki liciae, Oxymycterus rufus rUFus, Oxy mycterUS ruf us platensis, and OxymyCTerus paramensis.
Abstract: Cytogenetic analysis was performed in Akodon (Akodon) puer (= Akodon coenosus ) , Akodon azarae bibianae, Akodon ( Hypsimys ) budini, Bolomys temchuki elioi, Bolomys temchuki liciae, Oxymycterus rufus rufus, Oxymycterus ruf us platensis , and Oxymycterus paramensis . Diploid numbers, chromosomal morphology, and lengths and banding patterns (G and C) were determined for each taxon. Chromosomal number and gross morphology are also described in topotypical specimens of Akodon ( Akodon ) arenicola (= Akodon ( Akodon ) azarae azarae ) and Oxymycterus nasutus . A 2n = 34 karyotype, similar to one previously reported as Akodon coenosus , was confirmed in Akodon puer. A. budini showed a 2n = 38 karyotype peculiar within the genus as regards chromosomal morphology and C bands. A. a. bibianae has a 2n = 38 karyotype closely related with that of A. a. azarae . The two subspecies of B. temchuki , which differ strikingly in fur color, showed an identical 2n = 34 karyotype, which was quite similar in diploid number, chromosomal morphology, and banding patterns to that reported for B. lasiurus , but was different in the morphology of the Y and in G and C bands when compared with B. obscurus from the south of Buenos Aires Province. The three species of Oxymycterus , which markedly differ in morphometric character states, showed an identical 2n = 54 karyotype, and no banding differences were observed between O. rufus and O. paramensis .
43 citations
TL;DR: In this paper, the density of active sites and the nucleation rates per site for lead onto vitreous carbon from lead ion solutions in the presence of halides (Cl−, Br−, I−) have been investigated.
Abstract: The density of active sites and the nucleation rates per site for the nucleation of lead onto vitreous carbon from lead ion solutions in the presence of halides (Cl−, Br−, I−) have been investigated. Mass transport to growing nuclei was not found to be affected by the formation of soluble complexes of lead with the halides. No systematic variation of the true nucleation rates per site was observed upon addition of halides to the electrolyte. The density of active sites for nucleation, on the other hand, increased in the presence of halides. It is also shown that, in the absence of halide ions, the density of active sites for the nucleation of both lead and silver are equal to and independent of the concentration of metal ions in solution.
39 citations
TL;DR: In this paper, a 2-year period near the mouth of the Caura River, which drains a large watershed on Precambrian shield covered with tropical moist forest, was studied and the concentrations of dissolved organic carbon were essentially static despite a 10-fold seasonal change in discharge.
Abstract: Samples were taken weekly over a 2-year period near the mouth of the Caura River, which drains a large watershed on Precambrian shield covered with tropical moist forest. The concentrations of dissolved organic carbon were essentially static despite a 10-fold seasonal change in discharge. Particulate carbon showed an unexpected but relatively weak inverse relationship to discharge. Yield of total organic carbon (12.3 g C m−2 yr−1) was higher than would have been expected from the literature. Yield can be predicted accurately from discharge because of the strong homeostasis in concentration of dissolved organic carbon.
37 citations
TL;DR: The twoPseudomyrmex species studied have the following communication systems: P. triplarinus informs its nestmates about the presence of food, but not about its location, and P. termitarius does neither.
Abstract: The twoPseudomyrmex species studied have the following communication systems:
a)
P. triplarinus informs its nestmates about the presence of food, but not about its location.P. termitarius does neither.
b)
Both species recognize their territory and/or area around the nest entrance through odours on the substrate.P. triplarinus marks its territory with a pheromone from the thorax, probably from the metapleural gland. This territorial mark lasts less than 1 h, and probably advertises at least part of the home range of the colony. The territorial odour used byP. termitarius, probably works as a nest entrance orientation mark, and lasts over 5 h, but less than 24 h. The origin of the odour is not clear.
c)
P. triplarinus uses a cephalic pheromone as the main signal for nestmate recognition.P. termitarius uses non-identified odours, present on all body parts of the insect, as a nestmate recognition signal.
d)
Both species produce alarm pheromones from the head and the gaster.
20 citations
TL;DR: In this article, the effect of water deficiency on the tissue water relations and leaf growth of six corn cultivars, growing in glasshouse conditions, in order to understand growth responses to drought of tropical corn was reported.
Abstract: This study reports on the effect of water deficit on the tissue water relations and leaf growth of six corn cultivars, growing in glasshouse conditions, in order to understand growth responses to drought of tropical corn. A mild water-stress treatment was imposed slowly; plants reached a minimum pre-dawn leaf water potential of about –1.5 MPa by day 12 after watering was withheld. Analysis of the water relation characteristics of growing leaves using the pressure–volume technique demonstrated that under water deficits all the cultivars changed their moisture-release curves compared with irrigated plants. Osmotic potential at full turgor was lowered in water-stressed plants of all the genotypes and the degree of such change was between 0.34 MPa and 0.58 MPa. Thus, turgor pressure was lost at a lower water potential in water-stressed plants than in irrigated plants of all the varieties. Volumetric elastic moduli were also increased under water deficits and the increase ranged between 10% and 141% among the cultivars. In all the genotypes, the stress imposed led to a reduction of leaf area and dry matter accumulation. Leaf expansion was very sensitive to low turgor pressure and it ceased when turgor reached 0.2 MPa. Thus, varieties able to maintain a higher degree of turgor pressure (i.e. by osmotic adjustment) under water deficits may be able to prolong leaf growth.
TL;DR: In this article, the persistence properties of pseudo-Anosov maps were shown to imply that any co-perturbation of them presents all the dynamical features of the original map.
Abstract: We give a new proof of the existence of analytic models of pseudo-Anosov maps. The persistence properties of Thurston's maps ensure that any Co-perturbation of them presents all their dynamical features. Using Lyapunov functions of two variables we are able to choose certain analytic perturbations which do not add any new dynamical behaviour to the original pseudo-Anosov map.
TL;DR: It is proved that the chromatic uniqueness of the following infinite families of bipartite graphs are chromatically unique: K m,m + k, K r ∪ Km,n + k with m ⩾ 2 and 0⩽ max (5, √2m).
TL;DR: In this paper, a synthesis of α-bromo-α,β-unsaturated esters from tert-butyl α-(trimethylsilyl)-α-βromoacetate and carbonyl compounds is described.
TL;DR: In this article, the MINDO/SR method was used to calculate the difference in density of states for a 14-nickel atom cluster, and it was observed that the theoretical curve matches very closely the experimental one.
TL;DR: In this paper, an infrared spectra of the C-H stretch of gas-phase CF/sub 3/C(triple bond)CH was obtained and peak absorption cross sections were obtained for nu/sub 1/ = 1-5 of CH absorptions.
Abstract: Intracavity dye laser photoacoustic spectra have been obtained for overtone excitation of the C-H stretch (deltanu/sub 1/ = 4, 5, and 6) of gas-phase CF/sub 3/C(triple bond)CH. Standard infrared techniques were used to obtain the fundamental and lower overtones (deltanu/sub 1/ = 1, 2, 3). The local-mode model is used to assign prominent peaks. For all transitions in the C-H stretching mode a band close in energy to the main absorption is observed and is assigned as a hot band (nu/sub 1/ = 0, nu/sub 7/ = 1) ..-->.. (nu/sub 1/ = nu, nu/sub 7/ = 1) for nu = 1-6, which shows the strong interaction between the C-H stretching mode (nu/sub 1/) and the C-H bending model (nu/sub 7/). Also the fundamental and lower overtones (..delta..nu/sub 2/ = 1, 2, 3) of the C(triple bond)C stretch are obtained. Harmonic frequencies (omega/sub i/) and anharmonicity constants (X/sub ii/) with i = 1 or 2 for C-H and C(triple bond)C bonds, respectively, are calculated. The off-diagonal local-mode-normal-mode anharmonicity constant X/sub 17/ derived from the interaction between modes nu/sub 1/ and nu/sub 7/ is also reported. Peak absorption cross sections are obtained for nu/sub 1/ = 1-5 of CH absorptions and nu/submore » 1/ = 1-3 of C(triple bond)C absorptions.« less
01 Jan 1986
Journal Article•
TL;DR: The population biology of Sigmodon alstoni in the Venezuelan savanna of Guarico was monitored between October 1982 and September 1984 by Biweekly trapping revealed the existence of a yearly fluctuation in density with an increase phase in the dry season and a decrease phase during the transition into the rainy season as discussed by the authors.
Abstract: The population biology of Sigmodon alstoni in the Venezuelan savanna of Guarico was monitored between October 1982 and September 1984. Biweekly trapping revealed the existence of a yearly fluctuation in density with an increase phase in the dry season and a decrease phase during the transition into the rainy season and throughout most of the rainy season, and dissapeareance of the animals during the transition between the rainy and the dry seasons. Demographic parameters (survival, reproduction, age structure) were associated with the seasonal pattern of rainfall which renders the Danos extremely dry and flooded intermittently. Changes in habitat due to seasonal rainfall may also be important.
Journal Article•
TL;DR: The degree of exposure to mass communication media--television, radio and newspapers--is a determining factor in children's food preferences at all socioeconomic levels, and that television is the media exerting the greatest influence.
Abstract: The main purpose of this study was to determine the effect of mass media advertisement of food products (TV, radio and the press), particularly in pre-school and school-age children, as well as the concomitant impact these age groups have on the family food buying patterns. To test the hypothesis that the impact of mass media advertising on foods varied in the different socioeconomic levels of a community, a stratified sample of all children below 13 years of age, who attended the Francisco Fajardo school in the central coast of Venezuela, was drawn. Mass media contact, food and nutrition knowledge and other socioeconomic characteristics were related to the family's food-buying patterns. More specifically, the age, working status and educational level of the mother in regard to beliefs concerning the nutritional value of advertized food products, were related. A semi-structured questionnaire was designed, tested and applied to the housewife or whoever performed this role within the family. Findings revealed that families of low socioeconomic status are prone to be most influenced by mass media food product advertising. This is reflected not only in food purchasing practices but also in food consumption patterns at the family level. Chocolate drinks, cereals, jello, sausages, and ice cream are the most popular products among pre-school and school-aged children, without social class distinction. Furthermore, results revealed that the degree of exposure to mass communication media--television, radio and newspapers--is a determining factor in children's food preferences at all socioeconomic levels, and that television is the media exerting the greatest influence.
TL;DR: The existence of universal connections from which all connections on principal bundles can be induced was proved by Narasimhan and Ramanan as discussed by the authors, who considered the case of smooth vector bundles without additional structure and proved a classification theorem.
TL;DR: In this article, a detailed manner in which the formionic inexact modes enter the calculation of the multi-loop amplitude for type II and heterotic superstrings is analyzed, and the amplitude is written in a holomorphic and modular invariant form in terms of specific functions of the kinematic variables and the moduli of the string world sheet.
TL;DR: The limited presence of flavone glycosides and flavonol diglycosides in certain species can be effectively employed as chemical markers in determining the parentage of these species in fuchsia cultivars of unknown hybrid origin.
Abstract: A comprehensive survey of 225 populations of 80 taxa of Fuchsia showed flavonol monoglycosides, especially quercetin and kaempferol 3-0-glucosides, to be ubiquitous in all species examined. Flavonol diglycosides are unusual, however, and occur in just eight species in five of the nine sections of the genus. Flavone glycosides were found in only nine species belonging to five sections and are associated with primitive taxa, having been lost in more recently derived species or sections. Flavone sulphates are restricted to species of the disjunct sect. Skinnera from New Zealand. The limited presence of flavone glycosides and flavonol diglycosides in certain species can be effectively employed as chemical markers in determining the parentage of these species in fuchsia cultivars of unknown hybrid origin.
TL;DR: Methods are described for the determination of trace levels of calcium in steels by atomic-absorption and atomic-emission spectrometry with a carbon furnace for atomization and excitation with a commercial electrothermal atomic- absorption instrument.
TL;DR: In this article, the reaction of 1-methylpyrrole with N-chloroacetanilide leads to the incorporation of an acetanilides moiety in the pyrrole ring by addition-elimination.
Abstract: Reaction of 1-methylpyrrole with N-chloroacetanilide leads to the incorporation of an acetanilide moiety in the pyrrole ring by addition–elimination.
TL;DR: In this article, two light beams are superimposed in the same region of the film and the deformed region behaves as a mirror whose curvature radius depends on the intensity of the light beam.
Abstract: Light-sensitive liquid films are used to produce cross modulation between light beams in an all-optical setup. Two light beams are superimposed in the same region of the film. The samples are black oils whose physical properties strongly depend on the temperature. The liquid film is deformed by heating with the first light beam, thus changing the divergence of the other one. In the first setup presented in this paper the power concentration per unit area of a laser beam (HeNe, cw, 1 mW) is switched from a maximum to a minimum value and conversely) following the intensity variations of another laser beam (HeNe, cw, 10 mW). The time required to change the power concentration from 0.1 mW/mm2 to 10-3 mW/mmz is about 100 ms. In another setup, large-scale deformations of the liquid film (diameter about 5 mm ) are induced by heating with a white-light beam. The deformed region behaves as a mirror whose curvature radius depends on the intensity of the light beam. This allows one to form the real image of a 3-D object through the mirror and to switch it on and off by chopping the light beam. A typical switching time is about 1 s.
TL;DR: La chloration d'indoles substitues en 5 (OCH 3, CH 3, Br, CN, NO 2 ) par NaOCl est etudiee as mentioned in this paper.
Abstract: La chloration d'indoles substitues en 5 (OCH 3 , CH 3 , Br, CN, NO 2 ) par NaOCl est etudiee. Des melanges de chloro-1 et dichloro-1,3 indoles sont formes
TL;DR: In this article, the experimental aspects of He II are used as a guide toward a comprehensive theory in which nonzero temperature U(1) and SU(2) gauge fields are incorporated into a gauge hierarchy of effective Lagrangians.
Abstract: New experimental aspects of He II are used as a guide toward a comprehensive theory in which nonzero temperatureU(1) andSU(2) gauge fields are incorporated into a gauge hierarchy of effective Lagrangians. We conjecture that anSU(n) gauge-theoretic description of the superfluidity of4He may be obtained in the limitn → ∞. We indicate, however, how experiments may be understood in the zeroth-, first-, and second-order of the hierarchy.