No abstract

En el artículo se determinan los usos y apropiaciones que dan los adolescentes de la Facebook y las prácticas comunicativas que surgen de estos usos y apropiaciones. Se enmarcó en un enfoque mixto de carácter descriptivo, aplicando una encuesta a adolescentes que permitió comprender los elementos de comunicación que son afectados por el uso del Facebook, y una entrevista para conocer cuáles son las apropiaciones. Se encontró que los adolescentes utilizan Facebook para la socialización y para la definición de su identidad, sin importar el espacio y tiempo. Los adolescentes establecen interacciones sociales, a través del uso de Facebook, que se apropia debido a diferentes actividades y prácticas comunicativas que están correspondidas en la construcción de signos y códigos comunicacionales que se producen en las interacciones.

El propósito de esta investigación, fue identificar los nexos socio-relacionales del uso de las TIC en el entorno escolar de los adolescentes. La investigación tuvo un enfoque mixto, con una muestra de 40 adolescentes, con edades entre 14 y 17 años, pertenecientes a los grados 9 a 11 de una institución educativa colombiana. La información se recolectó a través del mapa socio-relacional, que consistió en graficar las relaciones e interacciones de la población objetivo, en los ámbitos virtual y presencial. Los resultados indican que el número de relaciones que tienen los adolescentes en el medio virtual, son diferentes a las del medio presencial. Esto se debe a que existe mayor conectividad comunicativa. Se concluye que las interacciones sociales mediadas por TIC, se presentan de dos formas: la interacción conectiva de costumbre, con los mismos sujetos del ámbito presencial, y la conectiva ampliada, que se da con individuos diferentes a los de costumbre.

In order to improve the cultivation and conservation of orchid species, it is important to assess the physiological quality of orchid seeds. One of the most traditional tests for analysing seed quality is the tetrazolium test, whose effectiveness is known to improve with pre-treatment of the seeds. As a result, this study compared various pre-treatments to determine how efficient they were at optimising the tetrazolium test in seeds belonging to Cyrtochilum aemulun, Elleanthus aurantiacus and Lephantes sp. The experiment was based on five different pre-treatment solutions, after which the seeds were exposed to tetrazolium at two different concentrations and for three different exposure times. First, the seeds were soaked for ten minutes in one of five pre-treatment solutions: chlorine 0.5%, chlorine 1%, deionised water, sucrose solution 10% (w/v) or a control in which no pre-treatment was applied. After pre-treatment, the seeds were soaked in the dark in a tetrazolium solution, either at 0.25% concentration or at 1.0% concentration, and for either 6, 24 or 48 hours. The control seeds exposed to no pre-treatment showed an increase in the viability of Lephantes sp. at significant difference from the pre-treated seeds. Similarly, pre-treatment with 10% sucrose produced an increase in the tetrazolium test’s effectiveness in E.aurantiacus seeds, with significant differences from the control in most treatments. Therefore, the use of sucrose as a pre-treatment is recommended, in addition to increasing the concentration and exposure time of the seeds.

The research aimed to design a teaching strategy and analyze benefits of its implementation in the use of technologies like GeoGebra and interactive materials that offers the web as enabling tools and teaching as mediation is aimed at students in grade 11 middle education. Tests pre-test and post-test and two experimental groups were applied control. It was verified that the teaching strategy has a positive influence on learning the experimental group improved the level of understanding of the concept of derivative and thus academic performance, in contrast to the control group to which is applied the traditional methodology.

Diffraction, scanning electron microscope and helium porosimetry techniques have been shown to be suitable for obtaining physical and mineralogical properties in soil samples. The X-ray fluorescence spectroscopy allows obtaining the elemental composition of the sample, while the X-ray diffraction technique permits obtaining a qualitative and quantitative composition of the soil minerals. On the other hand, scanning electron microscope shows the microstructure of the soil and the helium porosimetry measures the pore size, volume, distribution, density and other porosity-related characteristics of the material. This document presents the characterisation of three different clayey soils by an experimental plan that included mineralogical, microstructural and porosimetric tests. The soils used were bentonite, kaolin and a natural clay retrieved near to Bogotá city, Colombia. Results obtained from this study allow providing a better understanding of soil behaviour, which traditional mechanical tests do not explain.

Numerous research works have studied the stress distribution in sections with geometric discontinuities and the relationship with the theoretical factor of stress concentration using the finite element method. These works have dealt with topics such as the influence of the length of pieces on the factor in rectangular orthotropic plates; The behavior of the stress concentration factor on short shafts with section changes under bending loads; The theoretical factor of stress concentration in flat parts subjected to tension with "U" grooves; The estimation of the theoretical stress concentration factor for a flat plate with two holes subjected to tension loads. Other studies have compared the stress distribution by applying three methods: elasticity theory, finite element analysis and experimental techniques. Results show that the finite element method is effective in solving the problem. The goal of this research is to determine the theoretical stress concentration factor for a flat plate with two holes subjected to bending applying the finite element method. The modeling of the plate, the application of the loads, the mesh generation and the simulation of the stress distribution were made using the software 4870 Carlos Acevedo Peñaloza et al. ANSYS® Workbench. Four holes with different sizes were worked and for each of them 10 different values of the distance between centers were taken. In this way the relationship between the factor , the size of the holes and the distance between centers was found. This information is of great importance for the design of mechanical elements that are under these conditions.

This paper analyzes the impact of the Thomson effect on the performance of thermoelectric modules. For this, different mathematical models are carried out that involves the relationship between temperature and the seebeck coefficient. These mathematical models are based on the equations that describe thermoelectric effects and are solved using finite element methods. Through linear and polynomial functions of the seebeck coefficient, the different behaviors that can occur in the Thomson coefficient and their effect on the power and efficiency of thermoelectric modules are analyzed. The results show that by not considering the Thomson effect, there is a variation of 31% and 32% in the power and efficiency of the thermoelectric module when the temperature conditions change, which makes it difficult to estimate the performance of the module. This problem can be solved by considering the Thomson effect since it predicts an approximately constant value of electrical power and efficiency for a wide temperature range. For the analyzed conditions, power and efficiency of 5.25 W and 13%, respectively, were observed. The proposed methodology allows an adequate estimation to determine the performance of the modules. Therefore, it could be implemented to search for materials that provide better thermoelectric characteristics.