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Showing papers by "University of Los Andes published in 1973"


Journal ArticleDOI
TL;DR: In this article, an attempt to differentiate among some of the multiple frequencies due to OH groups was made based on the information obtained from dehydration and deuteration experiments, which indicated the presence of silanol groups.
Abstract: Infrared absorption spectra show important changes in the positions and form of the absorption bands of a film of attapulgite after it has been pumped out. An attempt to differentiate among some of the multiple frequencies due to OH groups is based on the information obtained from dehydration and deuteration experiments. The 1198 cm -~ shoulder, characteristic of attapulgite, is assigned to a Si-O vibration. When attapulgite is refluxed with 5N HCI for 5 hr the octahedral layer is dissolved. The acid attack causes the disappearance of the Si-O-Si absorption bands from attapulgite giving rise to a characteristic vibration at 1090 cm -~, as well as another absorption at 960 cm -1. The latter indicates the presence of silanol groups.

85 citations


Journal ArticleDOI
TL;DR: In this article, the ground state energy and the longitudinal effective mass of magnetic fields of arbitrary strengths were studied in the framework of an improved Landau-Pekar approach, and the correlation effects were reduced when a high magnetic field was switched on.
Abstract: Polaron properties in magnetic fields of arbitrary strengths are studied in the framework of an improved Landau-Pekar approach. General expressions of the ground state energy and longitudinal effective mass are given. It is shown that the introduction of the electron-phonon correlation effects in Landau-Pekar's approximation leads to a 10% lower value of the longitudinal effective mass. The correlation effects are reduced when a high magnetic field is switched on. On etudie les proprietes d'un polarou dans un champ magnetique en tenant compte de l'effet des corrclations electron-phonons a couplage fort. Des expressions de l'energies de l'etat fondamental et de la masse effective longitudinale ont ete obtenues pour des champs d'intensites arbitrages. On montre que l'introduction des correIations electron-phonons dans l'approximation de Landau-Pekar, amene une diminution de 10% de la masse effective. L'application des champs magnetiques intenses entraine une reduction des effets de correlations.

9 citations


Book ChapterDOI
TL;DR: The analysis revealed surprising shifts in the mean viability of homozygotes and a suggestive correlation appeared between rain cycles and the genetic load observed, lending support to the theory that the genetic characteristics of a gene pool reflect the ecological situation of the population.
Abstract: Our comparative genetic study with the second chromosome of Drosophila melanogaster from Hungary and Colombia (25) produced a quantitative appraisal of the detrimental, normal, subvital, and supervital loads. Results such as these lend support to the theory that the genetic characteristics of a gene pool reflect the ecological situation of the population. The most prominent and significant data in this direction were reported for populations of D. pseudoobscura on Mount San Jacinto in California (6,9,16), and of D. pseudoobscura and D. persimilis in Yosemite Park, California (7,8). These pioneering works and our present one detected changes in time. However, while Dobzhansky’s shifts were described in terms of the relative frequencies of various karyotypes for which they were found to be polymorphic, our present report deals with genetic modifications in viability similar to those found in Fusagasuga (26). The profound changes in the organization of the genetic architecture found in Fusagasuga were caused by recurrent cycles of rainfall-bound seasons in the area. Our analysis revealed surprising shifts in the mean viability of homozygotes. Furthermore, a suggestive correlation appeared between rain cycles and the genetic load observed. If maximum and minimum temperatures had been used to describe the climatogical situation, as was done in the past, we would not have detected anything consistent with the cyclic shifts in lethals and semilethals. Other work (27) revealed that even within 7 months significant shifts in the sterility content in the second chromosome of D. melanogaster from Fusagasuga could be effected by the cyclic rainfall-bound seasons. Testing for heterogeneity among homozygotes of the different temporal populations showed the coexistence of a high- and a low-sterility group. Further partitioning of X 2 in contingency tables revealed that through female sterility in the dry season and male sterility in the wet season the local demographic unit is altered. Still other works (21,22) have shown how even reforestation can produce profound genetic changes within a single area.

6 citations



Journal ArticleDOI
01 Mar 1973-Genetica
TL;DR: The so called races of Drosophila pPaulistorum from South America are so deeply isolated ethologically that although still partially bridged by gene flow through hybridization, they should be considered as 6 separate sibling species just as the willistoni group to which D. paulistorum itself belongs.
Abstract: The so called races of Drosophila paulistorum from South America are so deeply isolated ethologically that although still partially bridged by gene flow through hybridization, they should be considered as 6 separate sibling species just as the willistoni group to which D. paulistorum itself belongs. The present article emphasizes the way in which isolation is implemented.

2 citations


Journal ArticleDOI
TL;DR: Since there was no evidence that these granulomas were due to allergy or to parasites, they are assumed to have been produced by microfilariae (larva migrans, visceral) and it is proposed to call the entity visceral eosinophilicgranulomas.
Abstract: Summary Ninety-six specimens of liver, appendix, ileum, and other viscera with eosinophilic granulomas were studied at autopsy and in surgical tissue preparations from a tropical country. Since there was no evidence that these granulomas were due to allergy or to parasites, they are assumed to have been produced by microfilariae (larva migrans, visceral) and it is proposed to call the entity visceral eosinophilic granulomas.

2 citations



Journal Article
TL;DR: Una valoracion pronostica del infarto agudo del miocardio en nuestro medio con 15 variables, denominadas X, de facil obtencion se revisaron 115 historicas clinicas codificados bajo el numero 410, de la Seccion de Estadistica del Hospital Universitario San Juan de Dios, correspondientes a 2 anos consecutivos.
Abstract: Intentamos una valoracion pronostica del infarto agudo del miocardio en nuestro medio con 15 variables, denominadas X, de facil obtencion. Se revisaron 115 historicas clinicas codificados bajo el numero 410, de la Seccion de Estadistica del Hospital Universitario San Juan de Dios, correspondientes a 2 anos consecutivos, de los cuales se seleccionaron finalmente 80. Las variables consideradas fueron: Edad, valor absoluto en ano, X-1. Localizacion del infarto por electrocardiograma: Anterior Transmural X-2, Posterior Transmural X-3, al cual se le sumo un caso de infarto subendocardico que sobrevivio. Tension Arterial Sistolica X-4, Tension Arterial Diastolica X-5. Tamano de la Silueta Cardiaca evaluada radio logicamente asi: Normal X-6, Dudosa X-7 y definitivamente aumentada X-8. Tambien desde el punto de vista radiologico, se valoraron los campos pulmonares en: Normales X-9, derivacion de la circulacion pulmonar hacia los vertices X-10, edema intersticial X-II y edema pulmonar X-12. Ademas se tuvieron en cuenta los antecedentes coronarios X-13, de hipertension arterial X-14 y diabeticos X-15. Al analizar las variables vimos que las personas mas jovenes sobrevivieron mas, pero el analisis discriminativo no le dio significancia a este hecho. Asi ocurrio tambien con la localizacion y las cifras tensionales. Encontramos que los dates de mayor valor para predecir el riesgo de muerte en los pacientes con infarto agudo del miocardio fueron el edema agudo del pulmon y la cardiomegalia. Al suministrar las 15 variables al computador, este clasifico correctamente al 85% de les pacientes, mientras que al azar, solo hubiese podido ubicarse correctamente el 54.5%. Finalmente el analisis de la informacion del computador dice que los pacientes con indices inferiores a menos 1 mueren en el 78% de les cosos, los ubicados entre menos 1 y mas 1 tienen una mortalidad de 48.0%, mientras que los situados por encima de 1, tienen solo una mortalidad de 7.0%.

Journal ArticleDOI
TL;DR: In this paper, a single crystal of CdSe was created by bombardment with Mo Kα X-ray radiation, and the traps were studied by the relaxation curves of photoconductivity, obtained at 6000 A and after two dosages of radiation.

Journal ArticleDOI
TL;DR: In this article, the effects of electron-phonon interaction in a system of hot electrons are discussed and the effect associated with the generation of a temperature gradient in the phonon system is given.
Abstract: The effects of electron-phonon interaction in a system of hot electrons are discussed. Particular consideration is given to the effect associated with the generation of a temperature gradient in the phonon system. An expression for this gradient as a function of the electric field is obtained and some experimental implications are discussed. Dans cet article on etudie les effets de l'interaction electron—phonon dans un systeme d'electrons chauds. En particulier on considere l'effet associe avec la generation d'un gradient de temperature dans le systeme de phonons. On a obtenu une expression de ce gradient en fonction du champ electrique et on discute quelques implications experimentales.

Journal ArticleDOI
TL;DR: In this paper, the direct exciton splitting of a zinc blende crystal under uniaxial stress was calculated and the simultaneous application of stress and a magnetic field will allow a precise determination of the electron and hole gyromagnetic factors.