Showing papers by "University of Los Andes published in 1984"
TL;DR: It is suggested that species-specific capacitance in the genus Espeletia is a response to temperature-limited soil water availability and that cold tropical environments with frequent subfreezing temperatures tend to select for high water storage capacity in giant rosette plants.
Abstract: Pith water storage capacity and its role in plant-water relations were studied in seven giant rosette species of the genus Espeletia from the Venezuelan Andes. Readily available water from the pith was calculated to be capable of sustaining mean transpiration for up to 2.5 h. The relative importance of water stored in the pith, however, differed among species. The species that grow in the higher and colder environments tended to have a greater capacitance than the species that grow in the lower and less extreme environments. The pith volume per unit leaf area (PV/LA) was found to be a good indicator of the relative water storage capacity of the adult individuals of each species. Diurnal fluctuations in leaf water potential were not as pronounced in the species with higher PV/LA values. The species-specific PV/LA was highly correlated with the leaf turgor loss point and with the total resistance to water flow from soil to leaves. These results suggested that species-specific capacitance in the genus Espeletia is a response to temperature-limited soil water availability and that cold tropical environments with frequent subfreezing temperatures tend to select for high water storage capacity in giant rosette plants.
79 citations
TL;DR: An expansion of the original version of the model is made to take into account social and organizational factors which are thought to be important in the Colombian case, and preliminary results are presented.
52 citations
TL;DR: In this article, a flow system described, iron(II) is measured spectrophotometrically with 1,10-phenanthroline, and total iron is determined in the same flow line by atomic absorption spectrometry.
32 citations
TL;DR: It is shown that when the first instar nymphs of R. prolixus and R. robustus were infected with T. rangeli, survival of the bugs during the stages of development to the adult stage decreased, indicating that T. Rangeli is pathogenic for both species of triatomine.
Abstract: The pathological effects of Trypanosoma rangeli on Rhodnius prolixus and R. robustus, and the relation of mortality to infection, were studied under laboratory conditions. Frequent observations revealed that when the first instar nymphs of R. prolixus and R. robustus were infected with T. rangeli, survival of the bugs during the stages of development to the adult stage decreased. This decrease was statistically significant when compared with uninfected control-bugs, indicating that T. rangeli is pathogenic for both species of triatomine. In R. prolixus the most affected nymphal stages were the first, second and fifth instars, where a higher mortality was also observed. In R. robustus a progressive increase of the mortality from the first to fifth instars, was observed. The pathogenicity of T. rangeli as measured by overall mortality was the same in R. prolixus and R. robustus. The possible pathogenic mechanism of T. rangeli in triatomine-bugs and its epidemiological implications, are discussed.
32 citations
TL;DR: A molecular emission cavity detector is attached to a flow injection system for the determination of sulphide, sulphite and sulphate in the ranges 2 −130, 3 −150 and 5 −250 ng S, respectively, in 3 −μ1 samples as mentioned in this paper.
26 citations
24 citations
TL;DR: In this article, the electrical properties of as-grown n-type CuInSe, single crystal are studied between 80 and 300 K. The data can be explained by considering the scattering of phonons by boundary, impurities, umklapp, and normal processes.
Abstract: The electrical properties of as-grown n-type CuInSe, single crystal are studied between 80 and 300 K. The sample, which is highly compensated, has a shallow donor level of ionization energy of about 6 meV. The mobility data are analysed by taking into account the scattering by ionized impurities, acoustic and polar optical phonons. The conduction band deformation potential is found to be 19.5 eV. The thermal conductivity of the same sample is measured between 4 and 80 K. The data can be explained by considering the scattering of phonons by boundary, impurities, umklapp, and normal processes. The low value of the correction factor F = 0.34, is interpreted as due to the scattering of phonons by extended defects originating from the large microscale fluctuations in the composition of CuInSe2.
Les propriete electriques d'un cristal simple de CuInSe2 type-n ont ete etudiees entre 80 et 300 K. L'echantillon qui est hautement compense, possede un nivau donneur peu profond d'energie d'ionisation d'environ 6 meV. Les donnees ont ete analisees en tenant compte de la dispersion par impuretes ionisees, l'acoustique et le fonon polaire optique. Le potentiel de deformation de la bande de conduction resulte egal a, 19,5 eV. La conductivitye thermique dans les měmes echantillons a ete mesuree entre 4 et 80 K. Les donnees peuvent s'expliquer en considerant la dispersion des fonons par limitation, impuretes, Umklapp et procedes normaux. La basse valeur du facteur de correction F = 0,34, a ete interprete comme resultant de la dispersion de fonons par les defauts etendus ayant pour origine (en micro-echelle) les grandes fluctuations dans la composition du CuInSe2.
24 citations
TL;DR: In this article, it has been shown that the sharp increase in the absorption coefficient observed around 0.90 eV corresponds to the transition between the shallow acceptor level and the conduction band and not due to the energy gap as reported earlier.
17 citations
TL;DR: In this article, optical absorption and photoconductivity studies were carried out in the semimagnetic semiconductor Cd 1−x Fe x Te for the first time and the results confirmed that the system behaves like diluted alloys according to the Fridal - Anderson model.
17 citations
TL;DR: In this paper, the diphenylzinc-water system was used as catalyst for ethylene oxide polymerization in benzene solution at 60° and the reaction was first order with respect to monomer with kP = 5.7 × 10−5 sec−1 mol−1 l.
17 citations
TL;DR: In this article, the absorption and photoconductivity spectra of p -CuInS 2 single crystals, grown by chemical vapour transport method, were obtained at 76 and 300 K.
TL;DR: In this article, the X-ray photoelectron spectroscopy (XPS) technique is used to investigate properties of various hydrated PdO · nH2O systems.
Abstract: Palladium oxide systems, both pure and supported on various substrates such as alumina, zinc oxide, silica and titania, are of interest because of both their semiconducting behaviour and their catalytic activity, and they have been the subject of a number of X-ray photoelectron spectroscopy (XPS) investigations. The XPS technique is used here to investigate properties of various hydrated PdO · nH2O systems prepared both by a single impregnation method on various supports and by various impregnation treatments on the same support. XPS data for supported palladium oxide show that the intensity of interaction with the support is very weak, if indeed it exists. The processes occurring during the impregnation of the supports by the precursors are discussed; the nature of the species obtained depends on the activity of the support.
TL;DR: In this paper, the first diffractometric X-ray structural study of a quaternary semiconductor compound was performed using full matrix anisotropic-isotropic least squares technique using data taken at room temperature with MoK α radiation.
Journal Article•
TL;DR: Diagnostic patterns and figures allow correct identifications of those crabs; also coloration, ecology and their distribution are given.
Abstract: Diagnostic patterns and figures allow correct identifications of those crabs; also coloration, ecology and their distribution are given. The following crabs are reported for Colombia: Gecarcinus (Gecarcinus) ruricola (Linnaeus, 1758), G. (G.) lateralis lateralis (Freminville, 1835), G. (G.) lateralis quadratus Saussure, 1835, G. (lohngarthia) malpilensis Faxon, 1893, Cardisoma guanhumi Latreille, 1825, C. crassum Smith, 1870, Ucides cordatus cordatus (Linnaeus, 1763) and U. cordatus occidentalis. (Ortman, 1898).
TL;DR: In this paper, the lattice thermal conductivity of three II-VI compounds, ZnS and ZnTe, was analyzed on the basis of full Callaway's formalism by considering the scattering of phonons by boundary, point defects, normal, and Umklapp processes.
TL;DR: In this article, a formulation of quantum theory that yields the same experimental predictions as those obtained from von Neumann's formulation is presented. But it is accomplished in such a manner as to obviate the need for observer intervention.
Abstract: Relying on some concepts introduced in a companion paper, we set foth in this article a formulation of quantum theory that yields the same experimental predictions as those obtained from von Neumann's formulation. Moreover, this is accomplished in such a manner as to obviate the need for observer intervention.
TL;DR: A new interpretation of quantum theory is proposed in this paper, which coincides in a number of points with the orthodox interpretation, the main difference being that the projection of the state vector can occur without the intervention of any observer.
Abstract: A new interpretation of quantum theory is proposed. It coincides in a number of points with the orthodox interpretation, the main difference being that the projection of the state vector can occur without the intervention of any observer.
TL;DR: In this article, the absorption spectra of as-grown and copper-annealed n-CuInSe 2 samples were obtained at room temperature, and a shift of the absorption edge to higher energy for the annealed sample as compared to its value in the as grown sample was observed in the measurements.
TL;DR: The interference effect of some organic compounds is described and emissions of p-benzoquinone by hydrogen peroxide in an alkaline medium can be used for the determination of microg amounts of the quinones.
TL;DR: In this paper, a systematic study related to the growth, electrical, and optical properties of CuInTe 2 crystals grown from near-stoichiometric compositions by the Bridgman method has been made.
TL;DR: In this paper, a generalization of the chargedC metric to the nonstationary case is given and the possibility of associating the energy-momentum tensor with the electromagnetic or neutrino field is discussed.
Abstract: A generalization of the chargedC metric to the nonstationary case is given. The possibility of associating the energy-momentum tensor with the electromagnetic or neutrino field is discussed. It is shown that, for a specific choice of the time-dependent parameters, the metric admits at least a two-parameter group of proper Ricci collineations.
01 Jan 1984
TL;DR: In this paper, the authors derived a general expression for the drag force on an anharmonic oscillator with quartic potential moving through random electromagnetic radiation, and showed that the force cancels to all orders in the ODE in the case of motion through the zero-point field (ZPF) radiation.
Abstract: After deriving a general expression for the drag force on an anharmonic oscillator with quartic potential moving through random electromagnetic radiation, we specialize for the thermal and for the zero-point field (ZPF) radiation cases. It is explicitly shown that, as should be physically expected because of ZPF Lorentz invariance, the drag force cancels to all orders in $\ensuremath{\beta}$ and in the oscillator coupling parameter $\ensuremath{\eta}$ for the case of motion through the ZPF. This provides a simple positive test on the self-consistency of the usual techniques of stochastic electrodynamics under nonlinear potentials.
TL;DR: The aerial parts of Lourteigia ballotaefolia afforded, in addition to three known flavonoids, two furanoheliangolides, as the 8- and 9-acetylsarracinoyl esters of 1-keto-8β-9β-dihydroxygermacra-2,4,11(13)-trien-3, (10β)-oxo-6α,12-olide.
TL;DR: In this paper, a model based on the transition of electrons from the oxygen "adsorbate surface states" is proposed to explain the strong photoquenching observed on the high energy side of the band gap value.
TL;DR: Phylogenetic trees of transfer RNA specific for phenylalanine, methionine initiator glycine and valine are constructed and some conclusions can be drawn about the evolution of this molecule.
Abstract: Phylogenetic trees of transfer RNA specific for phenylalanine, methionine initiator glycine and valine are constructed. Although the exact relationships between taxa cannot be obtained from the mere analysis of the sequences some conclusions can be drawn about the evolution of this molecule.
TL;DR: In this paper, the absorption spectra of as-grown and copper-annealed samples of n-CuInSe 2, were obtained at room temperature, and the results showed a shift of the optical absorption edge to higher energy for the annealed sample (E g ≅ 0.977 eV) as compared to its value in the as grown sample.