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

Versatile, low-cost, computer-controlled, sample positioning system for vacuum applications

A versatile, low-cost, easy to implement, microprocessor-based motorized positioning system (MPS) suitable for accurate sample manipulation in a Second Ion Mass Spectrometry (SIMS) system, and for other ultra-high vacuum (UHV) applications was designed and built at NASA LeRC. The system can be operated manually or under computer control. In the latter case, local, as well as remote operation is possible via the IEEE-488 bus. The position of the sample can be controlled in three linear orthogonal and one angular coordinates

Electrokinetic and hydrodynamic properties of charged-particles systems: From small electrolyte ions to large colloids

Dynamic processes in dispersions of charged spherical particles are of importance both in fundamental science, and in technical and bio-medical applications. There exists a large variety of charged-particles systems, ranging from nanometer-sized electrolyte ions to micron-sized charge-stabilized colloids. We review recent advances in theoretical methods for the calculation of linear transport coefficients in concentrated particulate systems, with the focus on hydrodynamic interactions and electrokinetic effects. Considered transport properties are the dispersion viscosity, self- and collective diffusion coefficients, sedimentation coefficients, and electrophoretic mobilities and conductivities of ionic particle species in an external electric field. Advances by our group are also discussed, including a novel mode-coupling-theory method for conduction-diffusion and viscoelastic properties of strong electrolyte solutions. Furthermore, results are presented for dispersions of solvent-permeable particles, and particles with non-zero hydrodynamic surface slip. The concentration-dependent swelling of ionic microgels is discussed, as well as a far-reaching dynamic scaling behavior relating colloidal long- to short-time dynamics

DESERCIÓN ESTUDIANTIL UNIVERSITARIA, UNAN MANAGUA-FAREM CARAZO

El análisis sobre el fenómeno de la deserción en la Facultad Regional Multidisciplinaria de Carazo, ha sido un interés de las autoridades superiores, dado que si el fenómeno lo analizamos a nivel general de la Universidades del CNU, este alcanza hasta un 40%, a nivel de la UNAN Managua, representa un promedio del 18%, a nivel de la FAREM Carazo, alcanza el 11%, como puede observarse, no se trata de un problema propiamente dicho, lo que no implica descontinuar con las estrategias que se han venido implementando y que los participantes señala como factores motivacionales: ferias vocacionales, clases a la excelencia académica, cursos propedéuticos, visitas a los colegios de secundaria, etc. Más bien considero hay que darles mayor énfasis y seguimiento para medir su impacto en estudios posteriores sobre este mismo tema. En cuanto a la deserción en los centros de educación primaria y secundaria y otras modalidades, el porcentaje es mayor, motivado por otros factores adicionales a los ya expuesto en este estudio. Los factores incidentes en el fenómeno de la deserción según los resultados han sido, los de carácter Exógenos en su gran mayoría y factores endógenos en menor proporción, pero estos son los que nos interesan controlar a los interno, los endógenos resultan difíciles de controlarlos

Reseña: María Cristina Menéndez. Política y medios en la era de la información.

La relación entre los medios y la política representa un amplio núcleo de estudio, dentro de lacomunicación social. Gracias a las investigaciones de comunicación de masas, existe unapreocupación teórica y empírica por estudiar esta relación. Para el análisis de esta relación, entrepolítica, medios y opinión pública, las diversas disciplinas de las ciencias sociales, proponendiversas líneas de investigación

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