977 resultados para Leis orgânicas do ensino


Relevância:

20.00% 20.00%

Publicador:

Resumo:

UANL

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Tesis (Doctorado en Medicina) UANL

Relevância:

20.00% 20.00%

Publicador:

Resumo:

A series of vanadium-niobium oxide catalysts in which the vanadia content varies between 0.3 and 18mol%was prepared by coprecipitation. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and by catalytic testing in the oxidative dehydrogenation reaction of propane. The results of the surface analysis by XPS and LEIS are compared. It is concluded that the active site on the catalyst surface contains 2.0 ± 0.3 vanadium atoms on average. This can be understood byassuming the existenceof two or three different sites:isolated vanadium atoms, pairs of vanadium atoms, or ensembles of three vanadium atoms. At higher vanadium concentration more vanadium clusters with a higher activity are at the surface.LEIS revealed that as the vanadium concentration in the catalyst increases, vanadium replaces niobium at the surface. At vanadium concentrations above 8 mol%, new phases such as P-(Nb, V)20S which are less active because vanadium is present in isolated sites are formed, while the vanadium surface concentration shows a slight decrease

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Spinel ferrites are commercially important because of their excellent magnetic and catalytic properties. The study by Low Energy Ion Scattering (LEIS) can reveal atomic scale information on the surface. The surface of selected spinel ferrites was investigated by LEIS. It has been found that it is the octahedral sites which are preferentially exposed on the surface of the spinel ferrites. So the probable planes which are exposed on spinel ferrite surfaces are D(110) or B(111). This prediction using LEIS gives scope for tailor-making compounds with catalytically active ions on the surface for various catalytic reactions.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Resumen tomado de la publicaci??n. Contiene una tabla de porcentajes y una gr??fica de valoraci??n del software

Relevância:

20.00% 20.00%

Publicador:

Resumo:

La enseñanza secundaria creada por Manuel Passos, casi tres meses después del estallido de la Revolución de Septiembre (1836), no entró en funcionamiento de inmediato. En un principio, los objetivos definidos por la enseñanza escolar secundaria consistian en la preparación para el ingreso en los estudios superiores y en la formación profesional de los alumnos que no podían seguir la formación académica. Con todo, por las materias enseñadas y por la frecuencia de su enseñanza, la enseñanza secundaria nunca concretó los objetivos de la formación profesional . La instalación y el funcionamiento de los Liceos creó la necesidad de adopción de procesos pedagógicos y didácticos más perfeccionados y modernos. En la década de 1860-1870, le corresponde un período de apatía en el funcionamiento de la enseñanza escolar secundaria.