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

En este trabajo se estudió el comportamiento de las capas deformadas por el desgaste en los pasadores de esteras enlos equipos de laboreo minero. Los datos experimentales se obtuvieron utilizando pasadores desgastados y deformes. Las muestras se cortaron bajo refrigeración constante para evitar cambio en su estructura. Para el análisis de la composición química se utilizó un espectrómetro cuántico. Además, se empleó el método de microscopía óptica para analizar el efecto del endurecimiento por deformación utilizando los perfiles de microdureza. Se encontró que los pasadores tiene una composición química de un acero tipo AISI 1045. Además, se determinó que poseen una microestructura martensítica, la cuál disminuye debido a la deformación por el efecto de la rodadura.Palabras claves: deformación; desgaste; endurecimiento; estructura; pasadores

Nuestra universidad actualmente se encuentra inmersa en sendos procesos de transformación académica, los que incorporan los últimos ajustes de su nuevo modelo educativo institucional (MEI), donde el mismo, a través sus distintas componentes, expresa con claridad meridiana, el rol de la Investigación en el desarrollo de sus nuevos planes; esto, por supuesto representa un desafíoimportante; por un lado de carácter organizativo y por otro una ruptura total de cómo enfrentar la docencia, desde una perspectiva sustentada en una práctica Investigativa y en la aplicación de los resultados de la Investigación, todo ello deberá establecerse en los distintos niveles de la formación profesional;

No tiene resumenDOI: http://dx.doi.org/10.5377/nexo.v22i2.424

The purpose of this paper is to describe most of the procedures to follow in deciding whether you should transfer a tanker wrecked in a "refuge zone". In reaching this decision, it should consider different procedures, in order to objectify the best decision. It is important to know very well the features and infrastructures of the different coastal areas, which can be considered as possible "refuge zones". Based on the foregoing analysis, it has developed a program consisting of several modules to permit compute data of great importance, among which include matrices of environmental and infrastructural values that allow for the calculation of certain factors for transfer actions and preparation of the tanker (transfer time of the tanker, berthing time and connection time to the pumping systems, time of emptying the oil in storage tanks, transfer to another tanker, etc). In addition, this program allows us to estimate the costs of cleaning and restoration, as well as losses in the tourism sector. Keywords: Hydrocarbons; Place of refuge; Oil spills DOI: http://dx.doi.org/10.5377/nexo.v24i1.590   Nexo, Vol. 24, No. 1, pp. 11-19, 2011

In this work, an experimental study for the rheological characterisation of sugar solutions in the process of sugar production was performed. The main purpose was the characterisation of sugar solutions in order to model its rheological behaviour for optimising the evaporation-crystallisation process at a later stage. In the experiments, a 3k factorial design of experiment was used, where it considers the interaction of three factors in determining the response variable, in this case the factors are: the concentration (°Bx), the temperature and revolutions per minute (shear rate), each one with three levels, taking as response variable viscosity. The experimental development and analysis of results lead to the determination of the rheological model for the test solutions in the study range of the factors of interest, and it is proposed a type Ostwald-de Waele model for dilatant fluids. Keywords: Rheological model; Shear rate; Viscosity DOI: http://dx.doi.org/10.5377/nexo.v24i1.595 Nexo, Vol. 24, No. 1, pp. 61-71, 2011

In this work, numerical analysis was used to determine temperature distribution, density and both vertical as horizontal velocities applying engineering simulation software ANSYS. This was conduct for a closed cavity with geometrical relations height/width (H/E) of 0.5, 1 and 2. Likewise, constant temperatures in the left-right vertical walls of 50 and 20 °C and adiabatic boundary condition for the horizontal walls were considered. This activity was done considering Prandtl and Rayleigh numbers of 4.83 and 5.84x107, respectively. When results were compared for H/E = 2 and H/E = 1, it was found that the positive maximum value for the vertical velocity increased 26.29 %, horizontal velocity decreased 72.75 % and the central zone temperature in the cavity decreased 2.46 %. On the other hand, when the results for H/E = 0.5 and H/E = 1 were compared, it was found that the positive maximum value for the vertical velocity increased 7.24 %, horizontal velocity increased 34.08 % and the central zone temperature in the system decreased 3.70 %. Keywords: Natural convection; Closed cavity; ANSYS DOI: http://dx.doi.org/10.5377/nexo.v24i1.589 Nexo, Vol. 24, No. 1, pp. 3-10, 2011

The extraction of chitin from crustacean waste involved the deproteinisation and demineralisation of crustacean shells using lactic acid fermentation with whey and sucrose as culture medium and carbon source, respectively. The fermentation process was carried out in a vertical Pyrex reactor of 4 L by 2 and 3 weeks at room temperature. The results showed that a good deproteinisation and demineralisation was obtained; however, the product still contained traces of proteins and pigments. Therefore, it was necessary to apply a chemical process with sodium hydroxide and sodium hypochlorite, to completely remove the proteins and pigments from the structure of crustacean shell. A recovery of 85 % was obtained. The comparison of FT-IR spectra of chitin produced and a sample of commercial chitin showed a correlation rate of 93-95 %, indicating that chitin produced using the combined method has a high degree of purity. Keywords: Chitin; Shrimp shell; Sucrose; Vertical reactor; Whey DOI: http://dx.doi.org/10.5377/nexo.v24i1.592   Nexo, Vol. 24, No. 1, pp. 33-42, 2011

In this work, the adsorption kinetic of Cu(II) and Hg(II) onto chitosan was studied from a binary solution at different initial concentration of metallic ions, at different particle sizes and agitation rate. Chitosan was obtained from shrimp shells. Solutions of 1 L of Cu(II) and Hg(II) were placed in contact with 2 g of chitosan and the mixture was agitated by 8 h. Afterwards, the samples were analysed by atomic absorption. The experimental data were tested by application of kinetic models of pseudo-first order and pseudo-second order. The results of adsorption process showed that in the most cases, both ions were effectively adsorbed by chitosan. The percentage of adsorption was 43-100 % and 94-100 % for Cu(II) and Hg(II), respectively. The results also showed that at low concentrations, experimental data were better adjusted by pseudo-first order models; meanwhile, at high concentration, the data were well described by the pseudo-second model. Therefore, the rate-limiting step is the adsorption reaction and not mass transfer. Keywords: Adsorption kinetics; Binary solution; Chitosan; Kinetic models; Shrimp shell DOI: http://dx.doi.org/10.5377/nexo.v24i1.591   Nexo, Vol. 24, No. 1, pp. 20-32, 2011

In this work, the Surire salt marsh was analysed from the viewpoint of biodiversity and its implications caused by the climate change. As result, it is predicted that the following years will be dry and temperatures could rise, which will considerably affect the flora and fauna of the plateau. The Surire salt marsh is a salt body located in the Andean highlands of Chile, in a geological environment of volcanic features. The actual dryness does not allow an accumulation of surface water with large volume; thus, it is possible to identify three main types of water: drainage contributions, accumulation of external water or wetlands, and the thermal springs and brines. These hydrological conditions affect abiotic factors such as soil anaerobiosis, availability of nutrients and salinity, factors determining the development of flora and fauna. Keywords: Surire salt marsh; Andean biodiversity; Climate change; Andean ecosystem DOI: http://dx.doi.org/10.5377/nexo.v24i1.593   Nexo, Vol. 24, No. 1, pp. 43-49, 2011

An experimental methodology was generated for understanding the theoretical and practical concepts inherent to cold flat rolling. Aluminium slabs about 100 mm length, 9 mm thickness with different widths: 10 and 30 mm were rolled. A constant 0.3 mm thickness reduction step was performed in order to achieve a thickness reduction greater than 80 %. In the Abaqus® commercial software, a mathematical model was implemented in order to obtain a greater understanding concerning how the process variables affect the fields of stresses and strains that are not observed experimentally. It was found, by mathematical simulation, that a superficial hardening in the plates was produced and the deformation obtained is heterogeneous, which is corroborated physically. Keywords: Flat rolling; 6063 Aluminium; Data acquisition system; Simulation DOI: http://dx.doi.org/10.5377/nexo.v24i1.594   Nexo, Vol. 24, No. 1, pp. 50-60, 2011