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Cadmium (II) electrode based on plasticized PVC membranes with 1-furoyl-3,3-diethyl thiourea as ionophore and tributylphosphate as plasticizer has been developed. The membrane was applied on a support of conducting epoxy resin. Some parameters of evaluation of the electrode are presented in this work. The constructed electrode showed linear response in the concentration range of 10-6-10-3 mol/dm 3 , had a slope of 28.5 mV/decade, a detection limit (DL) of 2.10-6 mol/dm 3 and a lower limit of lineal range (LLLR) of 4.2.10-6 mol/dm 3. The static response time obtained was less than 20 seconds. The Cd/S relationship in the membrane was 1:1, as was determined by chemical microanalysis of energy dispersive X-ray spectroscopy (EDS). The constructed electrodes had a lifetime of 5 days.

The [Ni-(H(2)O)(n)](2+)(H(2)O)(m) (n ≤ 6, m ≤ 18) complexes were studied by means of first-principles all-electron calculations performed with the BPW91 gradient corrected functional and the 6-311+G(d,p) basis sets for the H, O, and Ni atoms. Triplet states were found as low-lying states for each (n, m) combination. The estimated Ni(2+)-(H(2)O)(n) binding energies (112.8-57.4 kcal/mol for the first layer and 52.0-23.0 kcal/mol for the second one) decreases and the Ni(2+)-OH(2) bond lengths lengthen as n + m increases. With six H(2)O moieties the Ni(2+) ion furnishes its first coordination sphere of octahedral geometry. Further water addition renders the formation of the second layer. The effect of Ni(2+) on the (H(2)O)(n)···(H(2)O)(m) hydrogen bond formation for several "n" and "m" combinations was studied, revealing an enhancement of this kind of bonding, which is of key importance for the stabilization and growth of the clusters. For some n + m isomers the second layer appears before the first octahedral layer is fully formed. For example, the square planar Ni(2+)-(H(2)O)(4) core originates two-dimensional 4 + 2 and 4 + 4 isomers, where each outer water molecule accepts two H-bonds, lying 2.0 kcal/mol above the 6 and 6 + 2 ground states. The clusters were also studied by IR spectra; the OH stretching vibrational frequencies allowed us to identify the outer solvation shells by the presence of red-shifted hydrogen bond regions.

Los datos de entrada, parámetros y la estructura de los modelos matemáticos introducen incertidumbre en los resultados; siendo aconsejable realizar un análisis de sensibilidad cuando se implementan o antes de su uso. Este estudio evaluó la sensibilidad del coeficiente de Manning debido al tipo de cobertura de las planicies y el cauce del río, en el cómputo de los niveles de agua y en la delimitación de las áreas inundadas. El estudio usó el modelo unidimensional [1-D] MIKE 11 para la implementación de un tramo de cinco kilómetros del río Santa Bárbara en el sur de Ecuador. Para el análisis de sensibilidad se realizaron seiscientas simulaciones de Monte Carlo para cada evento de crecida, y los resultados sirvieron para evaluar la robustez del modelo 1-D. Este análisis reveló sensibilidad a los cambios en el coeficiente de Manning; hubo una diferencia de hasta 1,02 m. entre niveles máximos y mínimos de agua. Sin embargo, los resultados de los mapas de inundación revelaron diferencias casi imperceptibles en la extensión del área inundada. Los hallazgos indican que el valor medio de Manning recomendado en la literatura es confiable para estimar mapas de peligro de inundación en ríos de montaña de la región interandina.

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