The growth and characterization of GaN grown on an Al2O3 coated (001)Si substrate by metalorganic vapor phase epitaxy

Single crystal GaN films have been grown on to an Al2O3 coated (001)Si substrate in a horizontal-type low-pressure MOVPE system. A thin Al2O3 layer is an intermediate layer for the growth of single crystal GaN on to Si although it is only an oriented polycrystal him as shown by reflection high electron diffraction. Moreover, the oxide was not yet converted to a fully single crystal film, even at the stage of high temperature for the GaN overlayer as studied by transmission electron microscopy. Double crystal X-ray diffraction showed that the linewidth of (0002) peak of the X-ray rocking curve of the 1.3 mu m sample was 54 arcmin and the films had heavy mosaic structures. A near band edge peaking at 3.4 eV at room temperature was observed by photoluminescence spectroscopy. (C) 1998 Elsevier Science B.V. All rights reserved.

Enrichment activities for able and talented children.

Proporciona una gran cantidad de recursos para animar a los niños superdotados a disfrutar de su potencial. Las actividades pueden ser utilizadas dentro y fuera del aula. Todas son fotocopiables y van acompañadas de soluciones y notas para los maestros Los recursos se dividen en varios temas: inglés, alfabetización, matemáticas, ciencias, humanidades, ciudadanía, resolución de problemas, toma de decisiones y procesamiento de la información; lenguas extranjeras, los niños pequeños, el pensamiento lógico, el trabajo de detective y los códigos; pensamiento lateral (forma específica de organizar los procesos de pensamiento, que busca una solución mediante estrategias que normalmente serían ignoradas por el pensamiento lógico), concursos. Cada tema va precedido por un comentario, esboza los vínculos curriculares y dan una orientación general para los maestros.

Vortex lattice and matching fields for a long superconducting wire

We investigate the flux penetration patterns and matching fields of a long cylindrical wire of circular cross section in the presence of an external magnetic field. For this study we write the London theory for a long cylinder both for the mixed and Meissner states, with boundary conditions appropriate for this geometry. Using the Monte Carlo simulated annealing method, the free energy of the mixed state is minimized with respect to the vortex position and we obtain the ground state of the vortex lattice for N=3 up to 18 vortices. The free energy of the Meissner and mixed states provides expressions for the matching fields. We find that, as in the case of samples of different geometry, the finite-size effect provokes a delay on the vortex penetration and a vortex accumulation in the center of the sample. The vortex patterns obtained are in good agreement with experimental results.

Wilma Norman-Neruda, Brustbild, mit Violine

Signatur des Originals: S 36/F01412