Showing papers by "University of Los Andes published in 1980"

Chromosomal speciation in a rassenkreis of venezuelan spiny rats (genus proechimys, rodentia, echimyidae)

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.

Back-and-Forth Systems for Arbitrary Quantifiers

Abstract: L ∞Ω (K) is the logic obtained by adding a Lindstrom's quantifier K 1 … k ( ϕ 1 ( 1 )… ϕ k ( k )) to the logical operations of L Ω . The corresponding finitary logic is L ∞ω ( K ), and L Ω ( K i ) i∉⌉ is obtained by adjoining a family of quantifiers. In this paper, we give back-and-forth systems characterizing elementary equivalence in those logics and their fragments of bounded quantifier rank. This generalizes work of Fraisse and Ehrenfeucht for L ∞ω , Karp for L Ω , Brown, Lipner, and Vinner for cardinal quantifiers, Badger for Magidor-Malitz quantifiers, and others. Our systems apply to higher order quantifiers also.

Lipids and Lipoproteins in Venezuelan and American Schoolchildren: Within and Cross-Cultural Comparisons

Abstract: Summary: This study was designed to focus upon within-culture differences in plasma lipids and lipoproteins in Venezuelan schoolchildren having different socioeconomic and nutritional backgrounds and also to provide cross-cultural comparisons of lipids, lipoproteins, and anthropometric measurements between Venezuelan and American schoolchildren. The study was carried out in 1298 schoolchildren, ages 7 to 12 years, 428 in private and 870 in public schools in Merida, Venezuela, with comparison to 472 public schoolchildren in the (Cincinnati, OH) Princeton School District. Within Venezuelan schools, private schoolchildren were heavier, taller, had marginally higher Quetelet indices, and had considerably higher fasting plasma cholesterol, plasma high-density lipo-protein (C-HDL), and plasma low-density lipoprotein (C-LDL) levels. These lipid-lipoprotein differences were highly significant after adjusting (by covariance analysis) for Quetelet index, sex, and age. Children from private Venezuelan schools ingested more total calories, more protein, more fat, and more carbohydrate. When the diet compositions were calculated as percentage of total calories, the private schoolchildren ingested nearly twice as many calories as fat and a somewhat lower proportion of calories as carbohydrate, with a comparable proportion as protein, when compared to the public Venezuelan schoolchildren. Male-female comparisons within Venezuelan schools revealed patterns of sex-related lipoprotein differences which were qualitatively similar to those in Princeton schoolchildren. Thus, 7- to 12-year-old females had higher total plasma cholesterol and triglyceride, lower C-HDL, and higher C-LDL. Within sex, cross-cultural comparisons of lipids, lipoproteins, and Quetelet indices revealed two major differences. Venezuelan children had significantly higher fasting plasma triglyceride and lower C-HDL levels, differences not attributable to systematic differences in measures of ponderosity, because Quetelet indices in Venezuelan and Cincinnati schoolchildren did not differ appreciably. In regard to total and low-density lipoprotein cholesterol, Venezuelan and Princeton public schoolchildren were remarkably comparable, although Venezuelan private schoolchildren had somewhat higher plasma cholesterol and C-LDL levels than did Princeton public schoolchildren. We speculate that increasing "westernization" and "urbanization" of Venezuelan society is associated with convergence of Venezuelan and American pediatric plasma lipid and lipoprotein levels. Maintenance of comparable total plasma cholesterol and C-LDL levels with lower C-HDL into adulthood in Venezuela would, in fact, suggest augmented risks for coronary heart disease for Venezuela within this lipid-lipoprotein frame of reference. Speculation: We speculate that increasing "westernization" and "urbanization" of Venezuelan society is associated with convergence of Venezuelan and American pediatric plasma lipid and lipoprotein levels. Maintenance of comparable total plasma cholesterol and plasma low-density lipoprotein levels, with lower plasma high-density lipoprotein levels into adulthood in Venezuela would, in fact, suggest augmented risk for coronary heart disease in Venezuelans, within this lipid-lipoprotein frame of reference.

The chromosomes of spiny rats, proechimys trinitatis, from Trinidad and Eastern Venezuela (Rodentia, Echimyidae)

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.

[Diagnosis by non-invasive methods of incipient left ventricular lesions in patients with Chagas' disease. Use of echocardiography and mechanocardiography]

Abstract: In this study, ninety-seven patients with positive complement-fixation reaction for Chagas' disease were submitted to M-mode echocardiograms, fonomechanocardiograms, right and left heart catheterization and left cine-ventriculogram, in an attempt to establish the usefulness of these non-invasive methods for the diagnosis of myocardial damage in Chagasic patients. Only the left ventricular end-diastolic volume determination showed a significant echo-angiographic correlation, as well as a satisfactory sensitivity and specificity to detect early myocardial damage. Therefore, with this parameter it was possible to diagnose 33% of patients which had left ventricular cine-angiographic damage, without clinical, electrocardioangiographic or radiological abnormalities. All other non-invasive parameters measured in this study were useful only in patients with advanced myocardial damage, recognizable by abnormal ECG or clinical signs of congestive heart failure. We recommend to obtain good quality left ventricular ecocardiograms in every chagasic patient, particularly those with normal ECG. This will allow the diagnosis of incipient cardiomyopathy in almost one third of all chagasic patients with early left ventricular abnormalities, recognizable by cine-ventriculograms.

Temperature Variation of Energy Gap Values in CuGa(Se1-xSx)2

Abstract: Single crystal samples of CuGa(Se1-xSx)2 alloys have been grown by an iodine transport method and measurements made of the reflectance spectrum of these samples in the temperature range 4–300 K. For each sample the values of energy gap EA and EB corresponding to the two higher valence bands A and B have been determined but the third gap could not be observed. The variation of EA and EB with temperature has been fitted to the equations proposed by Manoogian and Leclerc, i.e. E-E0=UTs+Vθ(cothθ/2T-1). The variation of the parameters V and θ as a function of composition are discussed. For the case of CuGaS2, EA-EB gives the value crystal field splitting Δcf and the variation of this parameter with temperature is determined. It is shown that the variation in Δcf can be explained in terms of a variation with temperature in the contribution of the upper d orbitals to the valence band, the results being in fair agreement with the values proposed by Yamamoto et al.

A taxonomical monograph of Anemia subgenus Anemiorrhiza (Filicinae)

Abstract: The morphology of the specimens contained in the herbaria B, P, S and US were studied. The subgenus Anemiorrhiza comprise 12 taxa(2 infraspecific) 3 hybrids and have 12 synonyms. Descriptions, keys and distribution by countries are given. A set of characters is postulated as a pattern of variation (state variables) for the genus Anemia. And based on it a numerical classification under information theory is presented. A modified WAGNER'S tree is hypothesised to account for the branching secuence and the amount of divergence between the species of the subgenus Anemiorrhiza. Es wird die Morphologie der Arten untersucht, die in den Herbarien B, P, S und US enthalten sind. Die Untergattung Anemiorrhiza umfast 12 Taxa (2 infraspezifische), 3 Hybriden und 12 Synonyme. Es werden die Beschreibungen, Schlussel und Vorkommen je nach Landern geliefert. Es wird eine Anzahl von Merkmalen als Variationsmoglichkeiten (state variables) der Gattung Anemia beschrieben und die darauf fundierte numerische Klassifizierung als Informationstheorie prasentiert. Ein abgeanderter WAGNERscher Stammbaum wird hypothetisiert zu Erlauterung der Verzweigungsfolge und der Anzahl von Abweichungen zwischen den verschiedenen Arten der Untergattung Anemiorrhiza.

Fuzzy state estimation in linear dynamic systems

Abstract: The problem of state estimation in linear dynamic systems with fuzzy initial states and poorly defined perturbation input signals (i.e fuzzy inputs) is considered. A new notion of vector summ of n-dimensional fuzzy sets provides the basis for state and input "imprecision" propagation trough the systems dynamics. Recursive state estimation formulae are developed to obtain a fuzzy set of possible states at each instant of time.

Modelamiento de actitudes nacionalespor medio de historietas cómicas

Abstract: Resumen en: This study measured the infIuence of comic books on the attitudes of 9-12 year-olds toward their country. The data showed that being exposed to a comic...

Echocardiographic evaluation of pulmonary arterial hypertension

Abstract: We performed an echocardiographic and hemodynamic study in 10 patients with cath proven pulmonary arterial hypertension (PAH). The results show that the echocardiographic pattern of PTH such as flat diastolic pulmonary echo, premature closing, flutter, abscense of "A" wave, in creased opening velocity and changes in the right ventricular systolic time intervals, are equivocal. The most common echo finding in our study, was the increased opening velocity. Other echo data could be absent despite the true presence of pulmonary hypertension in a particular case. This report shows similar findings to a recent one published elsewhere (12) with no correlation between echo and hemodynamic data.

Diferenciación histotípica de la corteza cerebelosa in vitro

Abstract: Se estudio la diferenciacion neuronal de la corteza cerebelosa del pollo tanto in situ como in vitro. La maduracion de los elementos principales corticales ocurre en una secuencia de eventos morfologicos por primera vez descrita en el pollo. Este proceso tiene un periodo critico de modelaje neuronal, entre los dias 14-16, cuando las celulas granulosas descienden en un 80% desde la capa plexiforme hasta su region definitiva. Las celulas de Purkinje inician simultaneamente la formacion de su arbol dendritico. In vitro se pudo reproducir los eventos esenciales, manteniendo constante la edad de cultivo y variando la edad del embrion del cual se tomaban las muestras para la preparacion de los cultivos rotatorios. Ademas de lograrse reproducir casi en su totalidad las caracteristicas fenotipicas de las celulas cerebelosas corticales, se analizo el proceso de sinaptogenesis y sus variaciones in vitro. Algunas consideraciones en torno a la plasticidad neuronal in vitro son discutidas.

Fracciones de clase en la burguesia de ciudades intermedias de colombia : un estudio sociologico

Abstract: En la historia clasica del capitalismo tuvieron enorme importancia las fracciones de clase burguesas. El comerciante rompe la economia feudal del terrateniente, los artesanos se proletarizan y dan su trabajo al industrial, el campo sufre un proceso capitalista en agricultura y ganaderia, y la creciente acumulaci6n termina en el financista y el monopolio. Existe una cierta logica econ6mica para que tal cosa ocurra, por lo cual es explicable que quiera verse o analizarse en semejantes terminos el desarrollo capitalista contemporaneo de paises dependientes. Es decir, resulta facil establecer esquemas de contradicci6n y conflicto entre terratenientes e industriales dentro de la clase burguesa, y asi se han querido ver algunos eventos colombianos desde el siglo xix. Pero justo es advertir, una vez mfs, que hay diferencias notables entre el capitalismo como concepto econ6mico y el "capitalismo" como etapa hist6rica en paises europeos ya plenamente capitalistas. Los historiadores colombianos se han preguntado muchas veces si realmente habia en el siglo xix tales alineamientos como latifundistas conservadores y comerciantes del partido liberal, y si realmente hubo alguna vez tal fraccionamiento de clases dentro de la burguesia en los origenes del capitalismo en Colombia. Todavia hoy se especula con tal tema, y es el prop6sito del presente trabajo aportar datos contemporaneos que permi-

Non-standard analysis and generalized functions

Abstract: A preliminary theory of generalized functions as an alternative to distributions is developed using nonstandard analysis. Various of the elementary results in distribution theory areproven using these non-standard generalized functions. In particularj non-stand ard stochastic fields which are alternatives to generalized stochastic processes are introduced.