Anomalous direction for skyrmion bubble motion

Magnetic skyrmions are localized topological excitations that behave as particles and can be mobile, with great potential for novel data storage devices. In this work, the current-induced dynamics of large skyrmion bubbles is studied. When skyrmion motion in the direction opposite to the electron flow is observed, this is usually interpreted as a perpendicular spin current generated by the spin Hall effect exerting a torque on the chiral N\'{e}el skyrmion. By designing samples in which the direction of the net generated spin current can be carefully controlled, we surprisingly show that skyrmion motion is always against the electron flow, irrespective of the net vertical spin-current direction. We find that a negative bulk spin-transfer torque is the most plausible explanation for the observed results, which is qualitatively justified by a simple model that captures the essential behaviour. These findings demonstrate that claims about the skyrmion chirality based on their current-induced motion should be taken with great caution

Sorry vs please, accept my apologies: teaching politeness explicitly to first grade high school students

Tesis (Profesor de Inglés para la Enseñanza Básica y Media y al grado académico de Licenciado en Educación)The purpose of this project is to determine how can we help students to develop a more native-like performance. Since Chile has an English Program oriented and based on the communicative approach, teaching pragmatics is something which is not considered in the educational curricula and also there is a limited provision of materials given by the Ministry of Education. For the aforementioned reason, the students of the first-grade high school in a bilingual school were subjects of an intervention that was carried out during four pragmatic lessons in order to analyze the impacts that teaching Pragmatic Competence (PC) in an explicit way has, considering also the self-perception about their skills to communicate themselves using the English language before and after the treatment. To conduct this project a mixed method approach was selected as it gave us the opportunity of combining quantitative and qualitative instruments in order to obtain better and more precise results. The aim of this project is to contribute in a field which currently is not studied deeply; despite the studies that already exist is not common to make an analysis on pragmatics. Most of the students are confident in terms of language proficiency, the majority of the participants evaluated themselves better in receptive than productive skills. In terms of sociopragmatic competence, there was not a statistically significant improvement. However, requests showed a more native-like performance. Regarding pragmalinguistic competence, strategies in the post-test were better applied than in the pre-test. In light of the results obtained in this study, there are some implications that can be recommended for different areas. Mainly, this study has a huge influence in terms of national education policies. Keywords: pragmatic, sociopragmatic, pragmalinguistic, speech acts, teaching pragmatics, pragmatic strategies.El propósito de este proyecto es determinar cómo podemos ayudar a los estudiantes a desarrollar un rendimiento más natural al hablar en inglés. Debido a que en Chile se aplica un programa de inglés orientado y basado en el enfoque comunicativo, la enseñanza de la pragmática es algo que no se considera en los programas educacionales ni tampoco en los materiales entregados por el Ministerio de Educación. Por esta razón, estudiantes de primero medio de una escuela bilingüe fueron sujetos de una intervención que se desarrolló durante cuatro lecciones con el fin de analizar los impactos que tiene enseñar una competencia en pragmática de manera explícita, considerando además la percepción propia acerca de sus habilidades para comunicarse usando el inglés, antes y después del experimento. Para llevar a cabo este proyecto se seleccionó un enfoque de método mixto, que nos dio la oportunidad de combinar instrumentos cuantitativos y cualitativos para obtener resultados mejores y más precisos. El objetivo de este proyecto es contribuir en un campo que actualmente no se estudia profundamente; a pesar de los estudios que ya existen no es común hacer un análisis de la pragmática. La mayoría de los estudiantes se sienten bastante seguros en términos de su nivel de inglés. Muchos de ellos se evaluaron mejor en las habilidades receptivas que en las productivas. En términos de competencia sociopragmática no hubo una mejora significativa. Sin embargo, en la parte de petición, los alumnos mostraron respuestas más nativas. En relación con las estrategias de pragmalingüística, en el post-test, fueron mejor utilizadas que en el pre-test. Los resultados obtenidos en este estudio tienen implicaciones que pueden ser recomendadas para diferentes áreas. Principalmente, este estudio tiene una gran influencia en términos de políticas nacionales educacionales

Suppression of surface barrier in superconductors by columnar defects

We investigate the influence of columnar defects in layered superconductors on the thermally activated penetration of pancake vortices through the surface barrier. Columnar defects, located near the surface, facilitate penetration of vortices through the surface barrier, by creating ``weak spots'', through which pancakes can penetrate into the superconductor. Penetration of a pancake mediated by an isolated column, located near the surface, is a two-stage process involving hopping from the surface to the column and the detachment from the column into the bulk; each stage is controlled by its own activation barrier. The resulting effective energy is equal to the maximum of those two barriers. For a given external field there exists an optimum location of the column for which the barriers for the both processes are equal and the reduction of the effective penetration barrier is maximal. At high fields the effective penetration field is approximately two times smaller than in unirradiated samples. We also estimate the suppression of the effective penetration field by column clusters. This mechanism provides further reduction of the penetration field at low temperatures.Comment: 8 pages, 9 figures, submitted to Phys. Rev.

Driven lattice glass as a ratchet and pawl machine

Boundary-induced transport in particle systems with anomalous diffusion exhibits rectification, negative resistance, and hysteresis phenomena depending on the way the drive acts on the boundary. The solvable case of a 1D system characterized by a power-law diffusion coefficient and coupled to two particles reservoirs at different chemical potential is examined. In particular, it is shown that a microscopic realisation of such a diffusion model is provided by a 3D driven lattice-gas with kinetic constraints, in which energy barriers are absent and the local microscopic reversibility holds.Comment: 12 pages, 4 figures, minor change