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Search Results: 1 - 10 of 9759 matches for " PATRICIA CADENA "
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Effects of Solar UV Radiation on Materials Used in Agricultural Industry in Salta, Argentina: Study and Characterization  [PDF]
Carlos Cadena, Delicia Acosta
Journal of Materials Science and Chemical Engineering (MSCE) , 2014, DOI: 10.4236/msce.2014.24001
Abstract: The current study presents the characterization of three types of materials after exposure to solar UV radiation. The selection of the materials is related to socio-economic aspects and rural activities in the northwest of Argentina (a.k.a. NOA). The objective was to establish a time parameter that allows estimating the durability of the materials according to their use. One of the materials is used as a protective cover (polyethylene film) of greenhouses, which are used for crop cultivation in the area. Another material is used in photovoltaic modules (PVMs), which are used to supply energy in isolated areas and the third material is sunscreen used by people that are exposed to UV radiation during rural activities. Degradation or deterioration of the materials was monitored using different spectroscopic assays: infrared was used to detect any structural changes in the material, X-rays were used for possible changes in the crystalline structure of the material, and spectral transmittance as this property is likely to be affected by changes in the structure of the material. The results showed that degradation of polyethylene seems to be related to the diminution in transparency and the loss of mechanical resistance with increasing exposure time. The decrease in transparency of one of the layers of a PVM caused a considerable decrease in the energy generated, whereas the sunscreens with a low sun protection factor (SPF) rapidly lost their protective properties and changed their photostability properties. Our results revealed a relationship between relative transmittance loss and exposure timse, which allows estimating the stability of different materials.
Diferenciación morfológica y molecular de especies de crisópidos (Neuroptera: Chrysopidae)
CADENA,PATRICIA; áNGEL,FERNANDO; GóMEZ,LUIS A; GONZáLEZ,RANULFO;
Revista Colombiana de Entomología , 2007,
Abstract: in the cauca valley (colombia), the distribution and identification of the most abundant lacewing species were studied in zones where sugar cane (saccharum spp.) is cultivated. it has therefore been possible to determine the species that could be used to counter the effect of the yellow aphid sipha flava (hemiptera: aphididae) on the overall production of sugar cane. although the lacewing species and morphotypes in the current study can be separated using morphological characters, the validity of those characters was studied. to do that, we established a morphological differentiation using internal genitalia and a molecular differentiation using a pcr-rflp analysis of the 18s rdna region of 11 species from three genera of the family chrysopidae (ceraeochrysa, chrysoperla, and leucochrysa), some of whom could be important biological control agents of the yellow sugar cane aphid s. flava. the characters used proved to be useful for distinguishing the species. in the case of internal genitalia, there were different patterns of the structures. in the case of molecular data, the species were differentiated using only one combination of ns primers for the dna amplification, followed by digestion of fragments with a restriction enzyme (ns5-ns6+drai). these results add to the taxonomic understanding of the family, and may help resolve systematic problems within the genera.
Diferenciación morfológica y molecular de especies de crisópidos (Neuroptera: Chrysopidae) Morphological and molecular differentiation of lacewing species (Neuroptera: Chrysopidae)
PATRICIA CADENA,FERNANDO áNGEL,LUIS A GóMEZ,RANULFO GONZáLEZ
Revista Colombiana de Entomología , 2007,
Abstract: En el Valle del Cauca (Colombia), se estudió la distribución e identificación de las especies más abundantes de crisópidos en zonas donde se cultiva la ca a de azúcar (Saccharum spp.) con mayor intensidad. Así, se han determinado las especies que podrían ser utilizadas para contrarrestar el efecto del pulgón amarillo Sipha flava (Hemiptera: Aphididae) sobre la producción total de la ca a de azúcar. Aunque las especies y morfotipos del presente estudio son separados utilizando caracteres morfológicos, se evaluó la validez de dichos caracteres. Para esto, se realizó una diferenciación morfológica mediante genitalia interna y una diferenciación molecular, empleando la técnica PCR-RFLP sobre la región 18S del ADN ribosomal, de 11 especies de tres géneros de la familia Chrysopidae (Ceraeochrysa, Chrysoperla y Leucochrysa), algunas de las cuales podrían ser importantes como agentes de control biológico del pulgón amarillo de la ca a de azúcar, S. flava. Los caracteres empleados resultaron ser útiles para distinguir las especies. En el caso de la genitalia interna, mostraron diferentes patrones de las estructuras. En el caso de los datos moleculares, las especies fueron diferenciadas utilizando solo una combinación de iniciadores NS para la amplificación del ADN y la digestión del amplificado producida con una enzima de restricción (NS5-NS6+DraI). Esta información se adiciona al conocimiento taxonómico que se tiene sobre la familia, además puede ayudar a resolver problemas sistemáticos al interior de los géneros. In the Cauca Valley (Colombia), the distribution and identification of the most abundant lacewing species were studied in zones where sugar cane (Saccharum spp.) is cultivated. It has therefore been possible to determine the species that could be used to counter the effect of the yellow aphid Sipha flava (Hemiptera: Aphididae) on the overall production of sugar cane. Although the lacewing species and morphotypes in the current study can be separated using morphological characters, the validity of those characters was studied. To do that, we established a morphological differentiation using internal genitalia and a molecular differentiation using a PCR-RFLP analysis of the 18S rDNA region of 11 species from three genera of the family Chrysopidae (Ceraeochrysa, Chrysoperla, and Leucochrysa), some of whom could be important biological control agents of the yellow sugar cane aphid S. flava. The characters used proved to be useful for distinguishing the species. In the case of internal genitalia, there were different patterns of the structures. In the case
Revisiting extensions of regularly varying functions
Meitner Cadena
Mathematics , 2015,
Abstract: Relationships among the classes ${\cal M}$, ${\cal M}_\infty$, and ${\cal M}_{-\infty}$ and the class of \emph{O}-regularly varying functions are shown. These results are based on two characterizations of ${\cal M}$, ${\cal M}_\infty$, and ${\cal M}_{-\infty}$ provided by Cadena and Kratz in [7] and a new one given in this note.
A note on Tauberian Theorems of Exponential Type
Meitner Cadena
Mathematics , 2015,
Abstract: Tauberian Theorems of exponential type provided by Kohlbecker, de Bruijn, and Kasahara are proved in only one Tauberian theorem. To this aim, the structure of those classical tauberian theorems is identified and, using a relationship recently proved by Cadena and Kratz, the relationships among its components are given.
A simple estimator for the $\mathcal{M}$-index of functions in $\mathcal{M}$
Meitner Cadena
Statistics , 2015,
Abstract: An estimator for the $\M$-index of functions of $\mathcal{M}$, a larger class than the class of regularly varying (RV) functions, is proposed. This index is the tail index of RV functions and this estimator is thus a new one on the class of RV functions. This estimator satisfies, assuming suitable conditions, strong consistency. Asymptotic normality of this estimator is proved for a large class of RV functions, showing a better performance than some well-known estimators. Illustrations with simulated and real life datasets are provided.
Mortality Models based on the Transform $\log(-\log x)$
Meitner Cadena
Statistics , 2015,
Abstract: A new stochastic method for describing mortality is proposed and explored. It is based on differences of observed times series of the transform $\log(-\log x)$ of survival probabilities which seem to follow simple patterns over the years. These common structures are gathered by a representation based on age-constants and time-stochastic processes. From the projection of the time-processes the mortality forecasting is straigthforward. Comparisons of the new model with the well-known Lee-Carter and Cairns-Blake-Dowd models employing sex-based mortality data of some countries are provided. Some in-sample and out-of-sample goodness-of-fit criteria show that in some situations the new model performs better than the ones mentioned above. Assessments of the performance of these models using rates of mortality improvement are discussed.
A note on the best attainable rates of convergence for estimates of the shape parameter of regular variation
Meitner Cadena
Statistics , 2015,
Abstract: Hall and Welsh gave in 1984 the lowest bound so far to rates of convergence for estimates of the shape parameter of regular variation. We show that this bound can be improved.
Validación de la encuesta de comportamiento alimentario en adolescentes escolarizadas de Bucaramanga, Colombia* Validation of the Eating Behavior Questionnaire in Adolescent School Girls of Bucaramanga, Colombia.
Germán Eduardo Rueda-Jaimes,Laura del Pilar Cadena Afanador,Luis Alfonso Díaz-Martínez,Diana Patricia Ortiz Barajas
Revista Colombiana de Psiquiatría , 2005,
Abstract: Objetivo: determinar la consistencia interna y la validez de criterio de la encuesta de comportamiento alimentario (ECA) en adolescentes, para el tamizaje de trastornos de la conducta alimentaria (TCA). Dise o: estudio de validación con muestreo naturalístico. Se seleccionaron 243 estudiantes al azar entre 1.595 elegibles de tres colegios en Bucaramanga, Colombia, a las que se les aplicó la ECA y se les realizó la entrevista semiestructurada CIDI de forma independiente y enmascarada. Mediciones principales: características demográficas, análisis de factores, prueba alfa de Cronbach, análisis de sensibilidad, especificidad y valores predictivos, prueba kappa media de Cohen, y curva ROC. Resultados: la prevalencia de TCA en la población estudiada es de 30,0%. Para 24 o más puntos, la sensibilidad encontrada de la ECA es 91,8%, la especificidad 52,4%, la kappa media de Cohen 0,341, y el área bajo la curva ROC 0,841. Se hallaron tres dominios que explican 72,6% de la varianza. El alfa de Cronbach para las once preguntas de los tres dominios fue de 0,636. Conclusiones: la ECA es una alternativa aceptable para tamizar grupos de población adolescente. Objective: To determine internal consistency and criterion validity of the Eating Behavior Questionnaire (ECA) among adolescents, for the screening of eating disorders (ED). Design: Study of validation with naturalistic sampling. 243 students were selected at random from 1595 eligible from three schools of Bucaramanga, Colombia, and were evaluated with ECA and CIDI independently and blindly. Main measurements: Demographic characteristic, factors analysis, Cronbach’s alpha, sensitivity analysis, specificity and forecast values, Cohen mean kappa test, and ROC curve. Results: The prevalence of the ED in the studied population is 30.0%. For 24 or more points, sensitivity found was 91.8%, specificity 52.4% , the Cohen mean kappa was 0.341, the area under the ROC curve was 0.841. Three domains were found that explain the 72.6% of the variance, the Cronbach’s alpha for the eleven questions of the three domains was 0.636. Conclusions: The ECA is an acceptable alternative for screening groups of adolescents.
SOBRE UNA NUEVA PROPUESTA DEL PROCESO EVOLUTIVO
CADENA MONROY,LUIS ALVARO;
Acta Biológica Colombiana , 2009,
Abstract: some pitfalls of three currently accepted evolutionary approaches are discussed: gradualism, neutralism and punctuated equilibrium. though two of them refer to change rates, and the other one (neutralism) refers to the absence of selection at the microscopic level, these three proposals are considered due to the relevancy that they have in the context of the bibliography on evolution. an approach is sketched that integrates them and solves the weaknesses of each one. i suggest that the evolutionary process has two fundamental phases. in the first one, organisms create their ecological niche. this is a period of -reverse selection-; in which organism have the initiative. later, a second phase of -normal selection- is set up, and it is the newly created niche that selects among variant organisms (normal selection). this latter process is possible, only if the period of -reversed selection- can be framed into a more general trend of evolutionary change. i discuss two proposals in which the notion of -reverse selection- is applied: the evolutionary origin of chordata and the evolution towards homo sapiens.
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