I-V characteristics of in-plane and out-of-plane strained edge-hydrogenated armchair graphene nanoribbons

The effects of tensile strain on the current-voltage (I-V) characteristics of hydrogenated-edge armchair graphene nanoribbons (HAGNRs) are investigated by using DFT theory. The strain is introduced in two different ways related to the two types of systems studied in this work: in-plane strained systems (A), and out-of-plane strained systems due to bending (B). These two kinds of strain lead to make a distinction among three cases: in-plane strained systems with strained electrodes (A1) and with unstrained electrodes (A2), and out-of-plane homogeneously strained systems with unstrained, fixed electrodes (B). The systematic simulations to calculate the electronic transmission between two electrodes were focused on systems of 8 and 11 dimers in width. The results show that the differences between cases A2 and B are negligible, even though the strain mechanisms are different: in the plane case, the strain is uniaxial along its length, while in the bent case the strain is caused by the arc deformation. Based on the study, a new type of NEMS-solid state switching device is proposed.Comment: 22 pages, 7 figure

Charge and spin polarized currents in mesoscopic rings with Rashba spin-orbit interactions coupled to an electron reservoir

The electronic states of a mesoscopic ring are assessed in the presence of Rashba Spin Orbit coupling and a $U(1)$ gauge field. Spin symmetric coupling to an ideal lead is implemented following B\"uttiker's voltage probe. The exact density of states is derived using the reservoir uncoupled eigenstates as basis functions mixed by the reservoir coupling. The decay time of uncoupled electron eigenstates is derived by fitting the broadening profiles. The spin and charge persistent currents are computed in the presence of the SO interaction and the reservoir coupling for two distinct scenarios of the electron filling fraction. The degradation of the persistent currents depends uniformly on the reservoir coupling but nonuniformly in temperature, the latter due to the fact that currents emerge from different depths of the Fermi sea, and thus for some regimes of flux, they are provided with a protective gap. Such flux regimes can be tailored by the SO coupling for both charge and spin currents

Equilibrium currents in a Corbino graphene ring

We address the description of a graphene Corbino disk in the context of a tight binding approach that includes both kinetic and Rashba spin-orbit coupling due to an external out-of-plane electric field. Persistent equilibrium currents are induced by an external magnetic field breaking time reversal symmetry. By direct diagonalization, we compute the spectrum and focus on the dispersion near the $K$ points at the Fermi level. The dispersion keenly reproduces that of a continuum model in spite of the complexity of the boundary conditions. We validate the assumptions of the continuum model in terms of predominant zig-zag boundaries conditions and weak sub-band coupling. The wave functions displaying the lowest transverse modes are obtained, showing the predominance of edge states with charge density at the zig-zag edges. The persistent charge currents, nevertheless, do not follow the traditional argument of current cancellation from levels below the Fermi level, and thus they depart in the tight-binding from those found in the continuum model.Comment: 8 pages, 6 figure

Assessing pedagogical leadership of principals: A review of the frameworks and instruments

El artículo hace una revisión de los enfoques e instrumentos en la evaluación del liderazgo pedagógico de la dirección escolar. El director como líder pedagógico se manifiesta en unas prácticas de éxito que deben tener sus efectos en la mejora de la escuela, de las prácticas docentes y, en último extremo, en los aprendizajes de los alumnos. La evaluación del liderazgo pedagógico se debe inscribir en el marco complejo de la evaluación de la escuela y de los efectos del liderazgo. Se revisan los instrumentos de evaluación y, particularmente, dos que estamos empleando: el Cuestionario Vanderbilt de Liderazgo en Educación (VAL-ED), y el Proyecto Internacional de Dirección Escolar Exitosa (ISSPP). Defendiendo su necesidad, se aboga por una evaluación multidimensional, cuyos resultados puedan contribuir a la mejora escolarThe paper reviews the frameworks and instruments for evaluating the pedagogical leadership of principals. The principal as instructional leader is evidenced by successful practices that should have its effects on school improvement, teaching practices and, ultimately, on student outcomes. In the complex context of school evaluation and the effects of leadership, it should be located the appraisal of school leaders. Assessment tools are reviewed and, particularly, two are using: Vanderbilt Assessment of Leadership in Education (VAL-ED), and the International Successful School Principal Project (ISSPP). It defending your need, it calls for a multidimensional leadership assessment, that can contribute to school improvemen

Educação democrática para a cidadania ativa

Una educación democrática, en el doble sentido de educar para la democracia y en democracia, es a la vez un fin y un medio de la educación. La educación pública debe capacitar a los futuros ciudadanos para poder participar activamente en la esfera pública sin riesgo de exclusión, lo que supone asegurar que toda la población adquiera aquellas virtudes, conocimientos y habilidades necesarios para la participación política y la inserción social. El artículo realiza un análisis y una revisión actual de lo que significa una ciudadanía activa y su construcción tanto en la enseñanza como en la trama organizativa de la escuela. Finalmente, se resalta que educar democráticamente es una tarea comunitaria, por lo que se ha de inscribir local y socialmenteDemocratic education has a double meaning: educating for democracy by exercising democracy, it is –at the same time– a goal and context of education. Public education should train future citizens to actively participating in the public sphere, without risk of exclusion. This includes ensuring that all people acquire virtues, values and skills required in order to become participating citizens, and to insert socially. The article is an analysis and current review of what active citizenship and its construction means both in teaching and in the organizational culture of the school. Finally, it is emphasized that it is a matter to build local and social communityEducação democrática, é tanto um fim como um meio de educação no duplo sentido de educar para a democracia e democracia. A educação pública deve treinar futuros cidadãos a participar ativamente na esfera pública, sem risco de exclusão, o que significa garantir que todas as pessoas adquirem as virtudes, o conhecimento e as habilidades necessárias para a participação política e inclusão social. O artigo analisa e uma avaliação atual do que ativa os meios de cidadania e construção tanto no ensino e tecido organizacional da escola. Finalmente, destaca-se que a educação democrática é uma tarefa da comunidade, por isso tem de registar-se localmente e socialment