En este estudio se evaluó la adaptación de una cepa compatible con Acidithiobacillus ferrooxidans a altas densidades de pulpa de calcopirita, esfalerita y galena, con dos distribuciones de tamaño de partícula, -200 y -325 serie Tyler de tamices. Los microorganismos fueron adaptados por la disminución gradual de la fuente principal de energía, sulfato ferroso, y el aumento en el contenido de mineral, para finalmente realizar un subcultivo sin la adición de fuente de energía externa. La realización de subcultivos en serie resultó ser una estrategia eficaz para la adaptación a altas densidades de pulpa de esfalerita, calcopirita y galena indicando que el protocolo empleado es adecuado. Los resultados muestran que la cepa compatible con Acidithiobacillus ferrooxidans es más resistente a altas concentraciones de esfalerita, seguido por calcopirita y finalmente por galena. El tamaño de partícula juega un papel fundamental en la adaptación de los microorganismos al mineral.

In this study the adaptation of Acidithiobacillus ferrooxidans-like to high concentrations of chalcopyrite, sphalerite and galena were evaluated with two mineral-particle sizes: 200 and 325 Tyler mesh. The strain was adapted using two simultaneous processes. The first one consisted in a gradual decreasing of the main energy source, ferrous sulphate. The second one consisted in a gradual increasing of the mineral content. Finally, a test was made without ferrous sulphate. The serial subculturing was found to be an efficient strategy to adapt Acidithiobacillus ferrooxidans-like to higher concentrations of chalcopyrite, sphalerite and galena. This indicates that a suitable protocol was employed. The results showed that Acidithiobacillus ferrooxidans-like is more resistant to high concentration of sphalerite, chalcopyrite and galena in descendant order. The particle size played an important role in the adaption of microorganism to the mineral.

Seasonal variability of the sea surface temperature (SST) in the Eastern Tropical Pacific were studied. For this purpose the following data were analyzed: SST and wind data from the Comprehensive Ocean-Atmosphere Data Set from 1978 to 1997, temperature and salinity fields from the LEVITUS climatology and sea surfac heights from TOPEX/Poseidon from 1993 to 2002. Various locally important factors that modulate this variability were identified: (1) the influence of the Gulf of California with the seasonal variability of the California Current, which extend about 200 km from the mouth towards the south and west, and about 300 km from the peninsula's west side toward the north; (2) the influence of the Gulfs of Tehuantepec and Papagayo where, due to the behavior of the winds, a local cooling of the surface during winter is generated; (3) upwelling at the Equator, off Cabo Corrientes, and off the west coast of Baja California; (4) spatial and temporal variation of the Inter-Tropical Convergence Zone and its relation with the thermal equator; (5) remote propagating signals in the zone; and (6) seasonal variations of the Equatorial Current System.

Se estudiaron los principales factores que modulan la variabilidad estacional de la temperatura superficial del mar (TSM) en el Pacífico Tropical Oriental. Para ello se analizaron las siguientes bases de datos: TSM y viento de la base Comprehensive Ocean-Atmosphere Data Set de 1978 a 1997, campos climatológicos de temperatura y salinidad de LEVITUS y alturas del nivel del mar de los altímetros TOPEX/Poseidon de 1993 a 2002. Como factores locales importantes que modulan esta variabilidad se identificaron: (1) la influencia del Golfo de California junto con el desplazamiento estacional de la Corriente de California, que se extiende desde la boca del Golfo hacia el sur y oeste unos 200 km y por el lado occidental de la península de Baja California hacia el norte aproximadamente 300 km; (2) la influencia del Golfo de Tehuantepec y del Golfo de Papagayo, donde, debido al comportamiento de los vientos, se genera un enfriamiento local de la superficie durante el invierno; (3) surgencias en el Ecuador, frente a Cabo Corrientes y frente a las costas de Baja California; (4) la variación espacial y temporal de la Zona de Convergencia Intertropical y su relación con el ecuador térmico; (5) la propagación de señales remotas y (6) la variación estacional del sistema de corrientes ecuatoriales.

The hydrostatic-pressure and applied electric field dependencies of the binding energy and the optical-absorption spectra, associated with transitions between the n = 1 valence subband and the donor-impurity band, in symmetrical and asymmetrical GaAs-Ga1-xAl xAs double quantum-well structures are calculated using a variational procedure within the effective-mass approximation. Results are obtained for different well and barrier widths, shallow-donor impurity positions, hydrostatic pressure, and applied electric field.

Using the effective-mass approximation and the variational method, we have calculated the effects of hydrostatic pressure on the donor- and acceptor-related optical absorption spectra in symmetrical GaAs double quantum well structures. A central finite potential barrier and two infinite external barriers constitute the profile of the potential barrier considered for the wells. Our results are presented as a function of the well and barrier widths and hydrostatic pressure. For the pressure dependence we consider the gamma-X mixing in the central barrier layer. For symmetrical and infinite-external-barrier quantum wells, and depending on the sizes of the structure and the hydrostatic pressure, the donor-related spectra show three special structures, whereas for the acceptor one only two structures appear.