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DOI: http://dx.doi.org/10.5377/nexo.v24i1.587 Nexo, Vol. 24, No. 1, pp. 1, 2011

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

In this work, we performed the separation of natural organic matter (MON) present in the raw water that supplies two water treatment plants, one from river (Boaco) and one from lake (Juigalpa), in two types: hydrophobic, formed by the fractions very hydrophobic (MH) and slightly hydrophobic (LH); and the hydrophilic type constituted by the charged (CHA) and neutral (NEU) fractions. These waters obtained from each fraction were subjected to a process of coagulation-flocculation-sedimentation on a laboratory scale using aluminum sulfate as a coagulant, wherein the hydrophilic fraction (CHA and NEU) was poorly removed (< 35 %) in comparison with the hydrophobic one (> 65 %). Surrogate parameters were used to characterise this MON such as dissolved organic carbon (COD), colour, ultraviolet absorbance (UV254) and specific ultraviolet absorbance (SUVA). Determination of SUVA values indicates a mixture of hydrophobic and hydrophilic organic matter in both raw waters as their values of specific ultraviolet absorbance (SUVA) were between 2-4 L/mg-m; however the hydrophobic fraction (MH + LH) was the predominant one, 63.6 % and 65 % measured as COD in dry season for Boaco and Juigalpa respectively, in rainy season, the percentage were a little higher (71.2 % and 66.1 %). Finally, it was found that the river water (Boaco) contains higher concentrations of trihalomethanes (89-166 μg/L) than the water lake (Juigalpa) (28-80 μg/L) after being chlorinated. Found that the hydrophobic fraction was the major contributor in 68.5 % (Boaco) and 78.6 % (Juigalpa) to the formation of trihalomethanes for dry season in both treated water. In rainy season, the THMs formation were a little higher. Keywords: Organic matter; Trihalomethanes; Fractionation; Superficial water DOI: http://dx.doi.org/10.5377/nexo.v24i1.596   Nexo, Vol. 24, No. 1, pp. 72-80, 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

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

Introducción: entre 1989 y 2000 se implementaron un grupo de estrategias sociales, económicas y sanitarias en Cuba encaminadas a preservar los niveles de salud de la población. No ha sido suficientemente estudiado la medida, en que los servicios de salud contribuyeron a preservar estos niveles. Objetivos: describir el comportamiento de indicadores de las dimensiones: situación de salud, socio-económica, demográfica, y servicios de salud en el periodo entre 1989 y 2000. Evaluar la relación entre indicadores de situación de salud y el resto de las dimensiones. Método: estudio ecológico a nivel nacional. Se consideraron para las cuatro dimensiones un total de 21 indicadores. Fueron descritas las variaciones relativas entre años para cada indicador, así como las asociaciones entre pares de variables de las diferentes dimensiones a través del coeficiente de correlación de rangos de Sperman. Resultados: el PIB y el salario medio mensual decrecieron entre 1989 y 1993 para luego recuperarse. La tasa de crecimiento poblacional descendió. Los indicadores de servicios de salud se mantuvieron. Se incrementó el gasto en salud por habitante, el número de médicos de familia, de enfermeros por habitante y de unidades del nivel primario de atención de salud. La esperanza de vida se incrementó y la mortalidad infantil decreció. Los incrementos en la incidencia de Tuberculosis y en el índice de bajo peso al nacer fueron mínimos. Conclusiones: La política socio económica y en especial el fortalecimiento de los servicios de salud contribuyó a compensar y en algunos casos revertir los efectos negativos que podrían haberse experimentado en la situación de salud dada la situación económica.

Introducción: El tema de la calidad de la atención sanitaria es tratado cada vez con más frecuencia en el ámbito sanitario. Algunos autores afirman que la falta de calidad representa un treinta porciento de los costos del sector. Objetivos: brindar elementos conceptuales relacionados con los costos de la no calidad, su presencia en el Sistema Nacional de Salud y una propuesta de acciones para evitarlos. Método: Se realizó una revisión bibliográfica y documental a través del modelo BIG 6. Se realizó un grupo de consenso con los 14 profesores del departamento de Economía de la Salud de la ENSAP, donde estuvieron presentes economistas, contadores, médicos, farmacéuticos, abogados, psicólogos, ingenieros industriales, ingenieros informáticos y matemáticos. Resultados: El costo de la no calidad debe reflejarse como cualquier sacrificio en que se incurre por no brindar servicios efectivos y donde la población y los trabajadores queden con un alto nivel de satisfacción. Los costos de la no calidad más frecuentes fueron: los asociados a la insatisfacción de los pacientes y trabajadores, a la mala utilización de la tecnología y las instalaciones, a la mala gestión de las instituciones y a las deficiencias en la atención (errores médicos). Para evitar estos costos se debe mirar la gestión y mejoramiento de la calidad desde la perspectiva de la inversión. Debe quedar bien justificada es la relación entre el costo y los efectos alcanzados a partir de comparar diferentes alternativas de solución. Conclusiones: La sostenibilidad y preservación del sistema de salud cubano van asociados al uso eficiente de los recursos. Evitar los costos de la no calidad será un importante paso en el logro de estos objetivos.