Observing classical nucleation theory at work by monitoring phase transitions with molecular precision.

It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned

Dificultades del profesorado en Educación Física de educación secundaria ante el alumno con discapacidad

En este estudio se pretende determinar las dificultades y problemas que tienen actualmente los profesores de Educación Secundaria en la especialidad de Educación Física, ante la variedad de alumnos con discapacidad que pueden existir en sus clases. Se trata sin duda de uno de los temas más delicados en la educación. Para ello se estudió la zona norte de Madrid tomando una muestra de 30 profesores. Los instrumentos de obtención de información fue un cuestionario de 25 preguntas pasado a todos los profesores, así como la formación de un grupo de discusión. Los resultados evidencian la buena disposición del colectivo docente para integrarlos de la manera más correcta, pero por el contrario se encuentran ante falta de recursos, tantos materiales, humanos y formativos. La poca coordinación entre departamentos, el número excesivo de alumnos o la falta de respaldo por parte de la administración desemboca en muchos casos en una falta de motivación que repercute en una peor calidad de enseñanza

Hitting all Maximal Independent Sets of a Bipartite Graph

We prove that given a bipartite graph G with vertex set V and an integer k, deciding whether there exists a subset of V of size k hitting all maximal independent sets of G is complete for the class Sigma_2^P.Comment: v3: minor chang

Structural analysis, magnetic and transport properties of the (Ru1-xCox)Sr2GdCu2O8 system

The effects of Co substitution on structural and superconducting properties of RuSr2GdCu2O8 compound have been studied. Rietveld refinements of the X-ray diffraction patterns indicate that the cobalt ion progressively replaces ruthenium sites. This replacement induces significant changes on the crystal structure and on the magnetic and superconducting properties. The effects Co substitution on the superconducting behaviour, and more particulary on the changes induce by the hole doping mechanism, were investigated in (Ru1-xCox)Sr2GdCu2O8 by a "bond valence sum" analysis with Co content from x= 0.0 to x = 0.2. The weak ferromagnetic transition at Tm= 138.2 K is shifted to lower temperature, and suppressed at higher Co content. From the crystallographic point of view the Ru-O(1)-Cu bond angle, associated to the rotation of the RuO6 octahedra, around the c-axis remain essetially constant when Ru is substituted by Co. Furthermore, increasing Co content has the effect to increase the weak ferromagnetic moment, which may be interpreted as the main responsible for breaking the delicate balance between magnetic and superconducting ordering.Comment: 21 pages, 8 figure