Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The main objective of this study was to determinate the effect of the temperature, methanol concentration and catalyst ratio, in the rate of hydrogen production, using aqueous phase reforming reaction. The catalyst used was impregnated nickel in commercial alumina. The catalyst was produced by the incipient impregnation method. After it, was calcined, and reduced, using hydrogen (5 %), with a flow of 250x10-3 l·min-1, at 723.15 K (450 °C) and for 4 h. The synthesized catalyst was characterized, and the surface area, crystallinity and composition were determined, as well as micrographs were taken to verify its morphology. To find the effect of the variables in the rate of hydrogen production, a Taguchi L8 statistical design was used, with three variables and two levels: temperature 473.15 K y 498.15 K, methanol concentration 2% v/v y 6% v/v; and catalyst fraction used 2,5 % m/m y 5 % m/m.   It was found that the catalyst used has an area of 88 m2/ g, with little crystallinity, being considered amorphous, with a nickel percentage approximately of 3%, as selected in the methodology. According to the statistical design, it was observed that only the temperature is significant in the rate of hydrogen production and the optimal temperature that favors hydrogen production is 498.15 K, while the concentration of methanol or amount of catalyst is not significant in the APR process.

The monitoring of forest characteristics is relevant in the context of climate change. In this study, both vertical and horizontal forest structure as well as carbon stocks were determined for a 28 ha successional forest patch on the Costa Rican Caribbean. This evaluation was performed on the basis of land use and assuming a hypothesis of homogeneity in forest structure. Results indicated that average DBH, tree height and canopy openness were 1.15 m, 20.83 m and 18.5%, respectively. Of the six structural variables determined, DBH and canopy openness were the two most important and results showed a high level of homogeneity in the forest. A calculation of the biomass showed that the forest patch contained between 100-130 T/ha above the ground and a total carbon stock of 1372-1795 T. This investigation represented the first approach to study the forest associated with the experimental station under scrutiny and was relevant to determine baseline data. It is expected that future studies can use the information presented herein for their purposes.

In this work is proposed a methodology for the programming of programmable automatas with TIA Portal from Petri Nets. In order to do it, an industrial application that requires to mix paints is selected, then a simulated process  that involves three tanks with their corresponding valves that activate for each one of them during an amount of time according to the color required in the preparation, three push buttons will select the color of the painting that you want to produce. Initially the Petri net is considered and then using of matrices the states equation is displayed for the trigger of all the transitions until returning to the initial state. The methodology establishes that after it the outputs must be associated to the different states and the transitions are associated to inputs. The Petri network is then translated into the programming language taking care to activate the next state and to deactivate the previous state according to the transition that occurs. Finally, the outputs are activated according to the states in which they were placed. When executing the simulation in the PLC, it was possible to verify the proper behavior of the sequence according to what was planned, thus demonstrating the effectiveness of the presented methodology.  

A series of simulations of moderate magnitude earthquakes were carried out near the Central Valleyof Costa Rica. These simulations were used to calibrate a velocity model and adjust a range of frequencies that would allow to obtain the best fit between the observed and synthetic data. With this information, simulations of scenarios of strong events of different magnitude that could occur in some of the faults surrounding the central region of the country were generated. The results are a series of maps showing the maximum velocities that could be obtained in the rock stratum without taking into account the phenomena of seismic amplification by soft soils.

A power loss analysis of the new 1-FB-1 DC/DC converter is proposed. The resulting model can be used to better predict the real DC-DC conversion rates that will be obtained when practical elements are implemented; as well as, a better heat loss estimation. Four distinct power loses are incorporated to the ideal canonical model: copper power loss at the transformer, transistor conduction power loss, diode conduction power loss and equivalent series resistor power loss at the output capacitor. The loss analysis establishes the framework to determine its feasibility for being used as a power supply in portable computers, hand-held devices, and communication equipment.

The article reflects on the research process, from the formulation of the problem to its materialization in a thesis format. The process of constructing a research problem is analyzed, considering the complex link between the theoretical and the empirical and the reformulations that it supposes. It also analyzes some usual mistakes and common places in the first formulations of the problem. In turn, the article deepens on the potentialities and characteristics of the field work with historical sources and interviews and the writing process that these types of sources suppose. The article seeks to provide learnings and develop advice for the development of a research process and its materialization in thesis format, nurturing from techniques and perspectives from various disciplines.

La fresca tradición oral de los pueblos rurales de Tacna, a cuya escucha se llega al atardecer el día, nos acercan a su historia, a su moral y a sus costumbres convertidas en relatos para ser transmitidos de una generación a otra. En esa cadena de narradores la historia contada sufre cambios, al ganar o perder elementos, dependiendo de la fidelidad de la memoria y de la habilidad del narrador. Ocurre con los cuentos del pueblo lo que con sus remedios para la salud. Aunque son muchos los que saben de las virtudes de una yerba y todos pueden contar los cuentos, hay un diestro curandero para el cuerpo y el alma y un cuentero que conoce mejor las historias del pueblo. Ofrecemos aquí un adelanto de material de que disponemos, captados en distintos momentos y lugares de los altos de Tacna y tratados libremente por el autor. Para resumir en una frase: son historias del pueblo vueltas a contar.

Tacna (Perú) y Arica (Chile) son dos ciudades fronterizas que han conformado históricamente un solo espacio geoeconómico y que mantienen relaciones económicas muy activas; sin embargo, en los últimos años, los gobiernos de ambos países han pugnado por fomentar en sus respectivas zonas fronterizas mejores condiciones de competitividad, dejando en un segundo plano las acciones de complementación económica que podrían generar beneficios recíprocos y coadyuvar al desarrollo de ambas localidades.

La enzima Dextranasacarasa fue producida por fermentación del Leuconostoc Mesentoreoides NRRL B512-F por un sistema “feed batch” de 3 litros de capacidad con un caudal de aereación de 0,5 1/min, una velocidad de agitación de 200 RPM y control de pH. El pH fue mantenido en 6.7 +- 0.2 por la adición de una solución combinada de sacarosa y NaOH a través de la acción de una bomba operada por el controlador.

La metodologí­a configuracionista para la investigación social gathers a serie of contributions produced by De la Garza in social science epistemology's field. The text is a tenacious defense of science that battles equanimously against the postulates of positivism and standard science (going back to the texts that De la Garza produced in the 1980s) and against "anti-epistemology" (or , in other words, the impact that pospositivism and linguistic turn has had on the scientific community). The author deals, in the different chapters, with disarming the ontological and epistemic-methodological assumptions on which these perspectives are based. Then, he provides the basis to found a new social science.