Exciton trapping in magnetic wire structures

The lateral magnetic confinement of quasi two-dimensional excitons into wire like structures is studied. Spin effects are take into account and two different magnetic field profiles are considered, which experimentally can be created by the deposition of a ferromagnetic stripe on a semiconductor quantum well with magnetization parallel or perpendicular to the grown direction of the well. We find that it is possible to confine excitons into one-dimensional (1D) traps. We show that the dependence of the confinement energy on the exciton wave vector, which is related to its free direction of motion along the wire direction, is very small. Through the application of a background magnetic field it is possible to move the position of the trapping region towards the edge of the ferromagnetic stripe or even underneath the stripe. The exact position of this 1D exciton channel depends on the strength of the background magnetic field and on the magnetic polarisation direction of the ferromagnetic film.Comment: 10 pages, 7 figures, to be published in J. Phys: Condens. Matte

Experimental demonstration of a mu=-1 metamaterial lens for magnetic resonance imaging

In this work a mu=-1 metamaterial (MM) lens for magnetic resonance imaging (MRI) is demonstrated. MRI uses surface coils to detect the radiofrequency(RF) energy absorbed and emitted by the nuclear spins in the imaged object. The proposed MM lens manipulates the RF field detected by these surface coils, so that the coil sensitivity and spatial localization is substantially improved. Beyond this specific application, we feel that the reported results are the experimental confirmation of a new concept for the manipulation of RF field in MRI, which paves the way to many other interesting applications.Comment: 9 pages, 3 figure

Teaching and critically reflective practice in Freire

Few of the many books written by Freire drew particular, and extended, attention to the teacher in the way Pedagogy of Freedom (1998) was able to do. While this entry draws on many other important works by Freire, it specifically probes elements of this book to place before readers some of the salient qualities and attributes Freire believed teachers, educators and thinkers of education ought to aspire to

La formación de educadores ambientales : consideraciones a partir de un curso

Esta investigación, tiene el objetivo de comprender qué y cómo los participantes de un curso para formación de educadores ambientales consideran aspectos de la educación ambiental importantes para su formación. El referencial teórico y metodológico utilizado en esta investigación es el Análisis Crítico del Discurso. El corpus de la investigación consistió en análisis de textos transcritos después de grabados en video. Participaron 7 personas que trabajan de profesores, en Brasil. Este trabajo nos permitió demostrar que algunas cuestiones escogidas no fueron enseñadas a lo largo del curso. Por supuesto, algunos textos utilizados fueron relacionados a discusiones del curso, en lo que concierne al aspecto político de la educación ambiental, el educador como un agente movilizador de grupos sociales y a la importancia del conocimiento teórico y práctico