Experimental and modeling studies on the synthesis and properties of higher fatty esters of corn starch

This paper describes a systematic study on the synthesis of higher fatty esters of corn starch (starch laurate and starch stéarate) by using the corresponding vinyl esters. The reactions were carried out in DMSO using basic catalysts (Na2HPO4, K2CO3, and Naacetate). The effect of the process variables (vinyl ester to starch ratio, catalyst intake, reaction temperature and type of the catalyst) on the degree of substitution (DS) of the starch laurate and starch stearate esters was determined by performing a total of 54 experiments. The results were adequately modeled using a non-linear multivariable regression model (R2≥0. 96). The basicity of the catalyst and the reaction temperature have the highest impact on the product DS. The thermal and mechanical properties of some representative product samples were determined. High-DS products (DS = 2.26-2.39) are totally amorphous whereas the low-DS ones (DS = 1.45-1.75) are still partially crystalline. The thermal stability of the esterlfied products is higher than that of native starch. Mechanical tests show that the products have a tensile strength (stress at break) between 2.7-3.5 MPa, elongation at break of 3-26%, and modulus of elasticity of 46-113 MPa.

CARTOGRAFÍAS DEL YO. ESCRITURA AUTOBIOGRÁFICA Y MODERNIDAD EN CENTROAMÉRICA, DEL MODERNISMO AL TESTIMONIO.

This dissertation examines some canonical Central American autobiographical works of the 20th Century. The authors studied include Rubén Darío, Rafael Arévalo Martínez, Froylán Turcios, José Coronel Urtecho, César Brañas, Eunice Odio, Roque Dalton, Miguel Mármol and Rigoberta Menchú. The dissertation maintains that autobiographical writing always interpellates the Other's story and that this interpellation is based in the need to incorporate into modern discourse the social sectors considered "pre-modern." Indigenous people, peasants, women, artisans and workers, oral or illiterate cultures, represent a zone of autobiographical fear and desire. These combined impulses are connected to some cultural peculiarities of the Central American region: mainly, the way in which the rhetoric and practice of Liberalism is adapted by the regional elites from the end of 19th Century onward.After a general overview offered in Chapter 1, this dissertation is divided in three parts that correspond to three different cultural epochs—Modernismo (Chapters 2, 3, 4), Vanguardia (Chapters 5 and 6), and Postvanguardia y testimonio (Chapters 7 y 8). In Modernista autobiography the class-racial-ethnic Other appears as something that "haunts" the traditional, representing both an object of fear and a limit to a Eurocentric concept of modernity. In contrast, the Vanguardista autobiography emphasized its desire of the Other. This general desires for "incorporate" the (national) Other is linked to the foundational /nationalist emphasis that the avant-garde showed in Central America. However, Liberalism never incorporated fully the utopian social models of the Vanguardistas. Due to the crisis of both the Liberal rhetoric and Vanguardista cultural projects, during the 1960s and 1980s the aesthetic-ideological project of the Vanguardia suffered a radicalization. One of the main outcomes was the popularization of testimonio, which has become the most analyzed form of Central American autobiographical writing today. In testimonio the Other and his/her cultural model (basically, orality) and the Gemeinschaft of rural community become embodied as a counter-hegemonic voice that seeks to interpellate the cultural models of the "lettered city" and modernity from a subaltern location

Testimonio documental sandinista y narratividad: reflexiones a partir de 'Todas estamos despiertas' de Margaret Randall.

Este artículo propone que en las narrativas testimoniales sandinistas se puede advertir localizaciones de enunciación diversas, por razones de género, clase, o calidad gubernativa de los narradores. De entre tal diversidad, se opta por analizar el testimonio documental de Margaret Randall Todas estamos despiertas para advertir motivos narrativos característicos, que llevan a pensar en “coyunturas testimoniales”. Estas coyunturas resultan, a su vez, fundamentales para el análisis de la cuestión de la memoria de la revolución sandinista en los contextos actuales. Palabras clave: Testimonio, Sandinismo, Memoria, Narratividad, Historia.In this essay, I propose that Sandinista testimonial narratives have diverse points of enunciation, based on writer´s gender, class or localization as members of the revolutionary government. Among a diversity of texts, I opt for analyze the book of documentary narratives by Margaret Randall Todas estamos despiertas, evaluating three narratives motives linked to what I consider “testimonial conjunctures”. Furthermore, I believe that these moments are fundamental to analyze the current question of the memory of the Sandinista revolution. Key words: Testimonio, Sandinista, Memory, Narrative, Histor

Análisis de la Evaluación Educativa y su relación con la Planifcación Docente y el Rendimiento Académico estudiantil durante el primer semestre del año 2008.

Es importante desde el inicio de este documento aclarar, que la Evaluación es un proceso que se desarrolla en todos los ámbitos de la vida cotidiana del hombre y en todos los casos, la utiliza para tomar decisiones. Así por ejemplo, en una familia el padre y/o la madre evalúa el comportamiento y la salud de sus hijos; el director de departamento evalúa el desempeño del profesorado bajo su ámbito de dirección, los Decanos y Directores de centros evalúan los logros alcanzados y las dificultades presentadas, en correspondencia a un periodo determinado y con base a las normativas existentes y en todos los casos, se toman decisiones, para mejorar, en la familia, en la empresa, en la Universidad

Auger electron spectroscopy study of oxidation of a PdCr alloy used for high-temperature sensors

A Pd-13 wt. percent Cr solid solution is a promising high-temperature strain gage alloy. In bulk form it has a number of properties that are desirable in a resistance strain gage material, such as a linear electrical resistance versus temperature curve to 1000 C and stable electrical resistance in air at 1000 C. However, unprotected fine wire gages fabricated from this alloy perform well only to 600 C. At higher temperatures severe oxidation degrades their electrical performance. In this work Auger electron spectroscopy was used to study the oxidation chemistry of the alloy wires and ribbons. Results indicate that the oxidation is caused by a complex mechanism that is not yet fully understood. As expected, during oxidation, a layer of chromium oxide is formed. This layer, however, forms beneath a layer of metallic palladium. The results of this study have increased the understanding of the oxidation mechanism of Pd-13 wt. percent Cr

Nicaragua Indicadores demográficos, estimaciones 2016

El estudio se basa en la estimación de los principales indicadores demográficos de Nicaragua. Es un estudio descriptivo y transversal. Los indicadores corresponden al año 2016. Índices de Friz y Burgdöfer indica que la población en Nicaragua es relativamente joven, la edad media es de 23 años y la mediana de 19 años. Por cada persona activa a punto de salir, hay 6 personas a punto de entrar que lo reemplazara. Existen 6 personas que pueden hacerse cargo de una persona mayor de 65 años