Showing papers by "University of Los Andes published in 1983"
TL;DR: In this article, the phase inversion locus is represented on a generalized mixed bidimensional scan (formulation-WOR), where the formulation variable may be the salinity, oil ACN, alcohol type or concentration, surfactant parameter such as EON, or temperature.
Abstract: The inversion locus is represented on a generalized mixed bidimensional scan (formulation-WOR), where the formulation variable may be the salinity, oil ACN, alcohol type or concentration, surfactant parameter such as EON, or temperature At near unity water/oil ratio the inversion locus (Phase Inversion Formulation: PIF) approximately matches the optimum formulation for minimum tension and phase behavior. In this region the inversion depends essentially upon physico-chemical factors. At extreme water/oil ratios, the inversion locus depends essentially upon the volumetric proportions of the phases, i.e., a physical factor A general classification of emulsion type is proposed according to the optimum formulation and phase inversion lines The alterations of the inversion locus with surfactant type, oil viscosity and conditions of emulsification, are discussed.
146 citations
57 citations
TL;DR: Patients with T cruzi infection have antibody to GP90, whereas patients with leishmaniasis do not and the two infections can be distinguished in an ELISA system using this antigen, in a mouse model.
50 citations
TL;DR: In this article, the authors found that the viscosity minimum of a MOW 3-phase emulsion is associated with the optimum formulation for three-phase behavior, which is related with the ultra-low interfacial tension exhibited by such systems.
Abstract: Surfactant-oil-water emulsified systems are found to exhibit a sharp change in viscosity near the optimum formulation for three-phase behavior. When the formulation is scanned through the three-phase transition by changing (in turn) brine salinity, oil EACN, surfactant HLB or alcohol concentration, the viscosity passes through a minimum for MOW three-phase emulsions. Bidimensional formulation scans corroborate that the viscosity minimum is associated with the optimum formulation. This minimum is related with the ultra-low interfacial tension exhibited by such systems.
50 citations
TL;DR: A new technique for in vivo neurotransmitter extraction was developed by chronically implanted in the caudate or the thalamus of rats and measurable amounts of dopamine and norepinephrine were recovered from the perfusion fluid.
Abstract: A new technique for in vivo neurotransmitter extraction was developed. Perfusion U shaped cannulae were chronically implanted in the caudate or the thalamus of rats. A segment of the cannula was a piece of dialysis tube of molecular weight cut off 1000. Measurable amounts of dopamine and norepinephrine were recovered from the perfusion fluid. Intraperitoneal amphetamine 10 mg/kg increased dopamine output from the caudate but not from the thalamus. The potential applications of this technique are discussed.
44 citations
TL;DR: Water balance was studied in developing leaves of Curatella americana, Byrsonima crassifolia, Bowdichia virgilioides and Casearia sylvestris, four widespread tropical savanna evergreen woody species that renew their leaves during the dry season, suggesting leaves of the four species were adapted only to short term diurnal water deficits.
Abstract: Water balance was studied in developing leaves of Curatella americana, Byrsonima crassifolia, Bowdichia virgilioides and Casearia sylvestris, four widespread tropical savanna evergreen woody species that renew their leaves during the dry season. Water potential components of leaves of different ages were estimated in the laboratory by determination of pressure-volume (PV) curves. Data from PV curves were used to help interpret the significance of variations in leaf water potential (ΨL) and stomatal conductance observed in leaves of different ages in the field.
34 citations
TL;DR: In this article, it was shown that the recently predicted growing trend of the translational kinetic energy for monopolar classical particles immersed in the CEMZPF should be quenched, when ZPF-induced relativistic oscillations of the centre of charge with respect to the center of mass of classical monopolar particles are considered.
Abstract: According to the current general ideas on the zitterbewegung and if we assume the existence of a universal classical electromagnetic zeropoint field (CEMZPF) in the manner of stochastic electrodynamics (SED), it can be shown that the recently predicted growing trend of the translational kinetic energy for monopolar classical particles immersed in the CEMZPF should be quenched, when ZPF-induced relativistic oscillations of the centre of charge with respect to the centre of mass of classical monopolar particles are considered. This should occur in such a way that, if proper values of the parameters are assumed, absolutely no translational kineticenergy growth occurs. This is consistent with the fact that protons and other composite particles (nuclei) are found at very high energies (up to 1021 eV and beyond), while primary cosmic-ray electrons do not show up beyond (1012÷1013) eV and only in a e/p=1/100 ratio. That no total quenching occurs for polarizable particles,e.g. protons, is consistent with expectations in astrophysics for a highly excited X-ray-emitting and very rarefied intergalactic neutral plasma. Previous astrophysical speculations on a CR ZPF acceleration mechanism and on the associated very hot intergalactic gas are briefly looked at from this perspective. It is finally conjectured that this concept of a CEMZPF-induced zitterbewegung may be relevant for making further progress in well-known unsolved problems in SED (hydrogen atom, anharmonic oscillator, etc.).
23 citations
TL;DR: In this paper, a method for the rapid determination of cadmium in human urine by extraction with dithizone and flow injection analysis (f.i.a.) is described.
22 citations
TL;DR: In this paper, Lazer, Landesman & Meyer (L.L.M.) extended these results to the following situation: if X and Y are two closed subspaces of H, such that X is finite dimensional and Y is not necessarily orthogonal, then there exists a unique subspace H such that Vf (ug) = 0.
Abstract: @‘f(u) w, 4 2 milwl12 (1) then there exists a unique uo E H such that Vf (ug) = 0. Furthermoref (uO) =min f (u). In 1975 UEH Lazer, Landesman & Meyer (L.L.M.) [3] extended these results to the following situation. Let X and Y be two closed subspaces of H, such that H = X @ Y, X is finite dimensional and X and Y are not necessarily orthogonal. Let T = Vf, then T: H-+ H and is a C’ mapping. Its Frechet derivative at u E His given by T’(rc) = D’f (u). Let ml and ml be two positive constants such that Vu E H, Vx E X, and Vy E Y we have
21 citations
TL;DR: The morphological sequence of Trypanosoma rangeli development in the body cavity of Rhodnius prolixus is described and the epidemiological importance of the developmental pattern of T. Rangeli in the vectors haemolymph and the host-response to the parasite are considered.
Abstract: The morphological sequence of Trypanosoma rangeli development in the body cavity of Rhodnius prolixus is described. The metacyclic trypanosome is the product of successive division and transformation during the intra and extracellular development in the haemocoele. The significance of the early invasion of T. rangeli into the haemolymph is discussed. The epidemiological importance of the developmental pattern of T. rangeli in the vectors haemolymph and the host-response to the parasite are considered.
19 citations
TL;DR: In this article, a systematic study was made on the effects of annealing CuGaTe2 single crystals in vacuum, under reduced pressure, and in the presence of Cd and Zn.
Abstract: A systematic study is made on the effects of annealing CuGaTe2 single crystals in vacuum, under reduced pressure, and in the presence of Cd and Zn. From the variation of hole concentration with temperature, the acceptor state ionization energy is found to lie between 18 and 37 meV. This energy state is associated with Ga vacancy. There is some indication that Zn acts as donor in this compound. The mobility data are explained by taking into account the scattering of the charge carriers by ionized and neutral impurities, acoustic-mode phonon, and space charge effects. The valence-band deformation potential is found to be 4.32 eV.
Une etude systematique a ete faite sur les effets de recuit des cristaux simples de CuGaTe2 dans le vide, sous pression reduite et en presence des elements Cd et Zn. La variation de la concentration des trous avec la temperature a ete etablie et l'energie d'ionisation des etats de l'accepteur a ete trouvee comprise entre 18 et 37 meV. Cet etat d'energie est associe avec la vacance de l'element Ga. C'est une indication que le Zn a joue le rǒle de donneur dans ce compose. Les donnees relatives a la mobilite ont ete obtenues et expliquees en prenant compte les differents mechanismes de dispersion des porteurs de charges y compris les impuretes ionisees et neutres, les phonons de mode acoustique et les effets d'espace de charge. Le potentiel de deformation de la bande de valence trouve est egal a 4,32 eV.
TL;DR: The findings indicate that Chagas disease is a diffuse cardiomyopathy in which the left ventricularle seems to be affected earlier and to a greater extent than the right ventricle.
TL;DR: A new way to dissociate amphetamine and fenfluramine anorexia is demonstrated, as others have done with lateral hypothalamic lesions or DA depletion.
Abstract: Rats were made hyperphagic by 6-hydroxydopamine (6-OHDA) injected bilaterally into the ventral midbrain; then they were restricted to a 6h/day feeding schedule and tested for appetite suppression with amphetamine and fenfluramine in randomized order. Amphetamine anorexia was diminished while fenfluramine anorexia was enhanced (both P<0.001). The opposite effect on fenfluramine anorexia shows that the effect of 6-OHDA on amphetamine anorexia was not due to hyperphagia masking the anorexia. Norepinephrine in the forebrain was 90% depleted, but DA and serotonin levels were within 9% of normal. These results demonstrate a new way to dissociate amphetamine and fenfluramine anorexia, as others have done with lateral hypothalamic lesions or DA depletion. The 6-OHDA injections, which were of a type that cause hyperphagia, apparently destroyed a substrate for amphetamine anorexia and also facilitated a substrate for fenfluramine anorexia.
Journal Article•
TL;DR: Die vorliegende Studie gibt cine Beschreibung der post-embryonalen Entwicklung von Heterocypris bogotensis Roessler, die die Morphologie des Prenauplius einschliesst.
Abstract: Die vorliegende Studie gibt cine Beschreibung der post-embryonalen Entwicklung von Heterocypris bogotensis Roessler, die die Morphologie des Prenauplius einschliesst. Auf phylogenetische Fragestellungen wird kurz emgegangen.
TL;DR: The morphological sequence of Trypanosoma rangeli development in the alimentary canal of Rhodnius prolixus, is described, with observation made in dissected guts from 6 hours to 45 days post-infection.
Abstract: The morphological sequence of Trypanosoma rangeli development in the alimentary canal of Rhodnius prolixus, is described, with observation made in dissected guts from 6 hours to 45 days post-infection. No metacyclic-forms are produced in the digestive tract at any time, and transmission by the contaminative route must be considered atypical. Amastigotes appear to be an essential stage in the development of T. rangeli in the gut of R. prolixus. The epidemiological importance of the developmental pattern of T. rangeli in the vector´s gut is discussed, and its usefulness for aging infection is considered.
TL;DR: In this paper, the splittings of the uppermost valence bands in orthorhombic AgInS2 have been determined from the photoconductivity spectrum, and the lattice parameters, the energy gap, the magnetic suceptibility and the melting point of all the materials are presented.
Abstract: AgInS2 and AgInSe2 single crystals have been prepared by chemical transport with iodine and by the Bridgman method. Syntheses of the quaternary alloys AgInSe2(1−x)S2x have also been carried out. The splittings of the uppermost valence bands in orthorhombic AgInS2 have been determined from the photoconductivity spectrum. The lattice parameters, the energy gap, the magnetic suceptibility and the melting point of all the materials are presented.
01 Jan 1983
TL;DR: A pesar de esta información, se ignoran la prevalencia e incidencia reales de la enfermedad en cualquier parte del territorio venezolano.
Abstract: Las encuestas epidemiologicas de leishmaniasis cutanea en Venezuela han sido siempre sobre brotes focales (I-6). El mayor esfuerzo colectivo para conocer la extension territorial de la leishmaniasis cutanea en Venezuela ha sido realizado por la Division Nacional de Dermatologia; alli se registra la dolencia en 21 de las 23 entidades territoriales del pais, con 13 600 casos atendidos entre 1955 y 1977, periodo durante el cual la poblacion crecio desde seis hasta doce millones de habitantes. A pesar de esta informacion, se ignoran la prevalencia e incidencia reales de la enfermedad en cualquier parte del territorio venezolano. La situacion es similar a la de Colombia (71, donde la infeccion, que probablemente es conocida desde fines del siglo pa-
TL;DR: A population of Tropidurus peruvianus was studied using Barber traps along an elevational transect in the Lomas of southern Peru from April 1974 to May 1975; the more important items in the diet were adult and larval beetles, ants, and flies.
TL;DR: In this article, the photoconductivity spectrum of a single crystal of p type of CuGaTe2 was examined at 300K and 77K. Structural details, which appeared on the high energy side of The band gap transition, are attributed to the valance band structure.
TL;DR: In this article, the profile of the physical variable of a contracting sphere is obtained from the static solutionV of Tolman, and it is shown that bouncing of the surface is impossible in this model.
Abstract: The application of a general method to obtain the profile of the physical variable of a contracting sphere is presented. The model is obtained from the static solutionV of Tolman. It is shown that bouncing of the surface is impossible in this model.
TL;DR: In this paper, the absorption spectrum near the fundamental absorption edge of an-type CuInSe2 single crystal grown by the Bridgman method has been studied at 100 and 300 K. An absorption edge corresponding to the direct-band gap transition is observed at about 1 eV.
Abstract: The absorption spectrum near the fundamental absorption edge of an-type CuInSe2 single crystal grown by the Bridgman method has been studied at 100 and 300 K. An absorption edge corresponding to the direct-band-gap transition is observed at about 1 eV. An additional absorption is observed at lower energies ((0.93÷0.95) eV) and is attributed to direct transitions assisted by long-wave-length optical phonons.
TL;DR: The demonstration of the regular existence of synaptic-like junctions in tissue cultures prepared from different regions of chick central nervous system as well as the occurrence of such intercellular contacts in the cerebellum of adult and normal frogs seem to indicate that those types of neuron-glia relationships are not a simple biologic error.
TL;DR: The temporal samples of Torobarroso, one of the local populations identified, demonstrate genetic “resourcefulness” and selective opportunism by fluctuating mortality, suggesting that both balanced selection and mutational origin are necessary to account for the frequencies of drastic genes encountered.
Abstract: There are several Colombian populations of Drosophila pseudoobscura which have begun to show divergence. The temporal samples of Torobarroso, one of the local populations identified, demonstrate genetic "resourcefulness" and selective opportunism by fluctuating mortality. The data suggest that both balanced selection and mutational origin are necessary to account for the frequencies of drastic genes encountered. In genetic isolates there seems to exist alternatively a mutational component and a balanced - selection component. These components overcome the damage in the first instance and in the second instance, profit from the recessive load.
TL;DR: Among distinct types of hypothalamic rewarding loci a few might be specifically related to temperature regulation, and the effects of the cold and warm environments on self-stimulation on the other appear to be independent one from another.
TL;DR: Prevalence of infection increases with size of molluse and is highest in those 4 to 5 mm long, however, Lymnaea as small as 3 mm produce cercariae and molluscicide treatments should be begun as soon as forms of this size appear.
Abstract: Dans le foyer de distomatose etudie, situe dans l’Etat de Trujillo a plus de 1000 m d’altitude, ou presque 100 % des Bovins sont parasites, le vecteur est Lymnaea cubensis ; le quart des mollusques est infecte et heberge en moyenne 20 redies, capables d’emettre chacune 16 cercaires. La frequence du parasitisme des mollusques augmente avec leur taille et est maximale chez les limnees de 4-5 mm de long, mais les limnees de 3 mm produisent deja des cercaires et les traitements par mollusquicides doivent etre effectues des qu’apparaissent des formes de cette taille.
TL;DR: In this article, the variation of the lattice parameters, from the room temperature to the melting point of the chalcopyrite semiconductor CuGaSn□Se4 by using a high-temperature X-ray camera was studied.
Abstract: The variation of the lattice parameters, from the room temperature to the melting point of the compound, has been studied for the chalcopyrite semiconductor CuGaSn□Se4 by using a high-temperature X-ray camera. The compound shows an increase in the tetragonal of thermal expansionαc. The results are interpreted in terms of expansion of the bonds. The DTA measurement, that has shown a peak at 590°C, has been associated with the decomposition of the quaternary into two phases. At the temperature of 590°C extra lines appeared in the X-ray measurements of θ values of 15.3133o, 18.8235o, 21.0230o, 24.5633o, 26.3712o and 34.7926o. These new extra lines (second phase)_are probably from SnSe2.