Lifshitz tails estimate for the density of states of the Anderson model

We prove an upper bound for the (differentiated) density of states of the Anderson model at the bottom of the spectrum. The density of states is shown to exhibit the same Lifshitz tails upper bound as the integrated density of states

Reasoning and Change Management in Modular Ontologies

The benefits of modular representations are well known from many areas of computer science. In this paper, we concentrate on the benefits of modular ontologies with respect to local containment of terminological reasoning. We define an architecture for modular ontologies that supports local reasoning by compiling implied subsumption relations. We further address the problem of guaranteeing the integrity of a modular ontology in the presence of local changes. We propose a strategy for analyzing changes and guiding the process of updating compiled information

Evaluación del impacto de la colaboración internacional sobre el aprendizaje de la geografía

El Center for Global Geography Education (CGGE) (Centro para la Enseñanza de la Geografía Mundial) está constituido por una serie de módulos en línea que investigan temas relacionados con la geografía, permitiendo el análisis y la discusión en grupo entre diversos equipos de estudiantes no licenciados. Mediante la utilización de los datos obtenidos a partir de experimentos llevados a cabo en diez países, hemos evaluado la efectividad de los módulos en la mejora de la compresión de los estudiantes de conceptos geográficos y la valoración de las perspectivas transculturales sobre estos temas. El análisis de los datos cualitativos y cuantitativos puso al descubierto que el CGGE alcanzó sus objetivos de reforzar los conocimientos y las competencias geográficas. El diseño de los módulos y de su colaboración internacional interesó en gran medida a estudiantes y profesores. Establecemos revisiones específicas de sus contenidos a fin de fomentar intercambios más intensos de las perspectivas internacionales entre estudiantes universitarios.The Center for Global Geography Education (CGGE) is a set of online modules exploring geographic issues, which allow collaborative analysis and discussion between international teams of undergraduates. Using data from trials held in 10 countries, we evaluated the modules' effectiveness in improving student understanding of geographic concepts and appreciation for cross-cultural perspectives on the issues. Analysis of qualitative and quantitative data revealed that CGGE achieved its aims of enhancing geographic knowledge and skills. The modules and their international collaboration design inspired high interest among students and professors. We identify specific revisions to their content in order to foster deeper exchanges of international perspectives among university students.El Center for Global Geography Education (CGGE) (Centro para la Enseñanza de la Geografía Mundial) está constituido por una serie de módulos en línea que investigan temas relacionados con la geografía, permitiendo el análisis y la discusión en grupo entre diversos equipos de estudiantes no licenciados. Mediante la utilización de los datos obtenidos a partir de experimentos llevados a cabo en diez países, hemos evaluado la efectividad de los módulos en la mejora de la compresión de los estudiantes de conceptos geográficos y la valoración de las perspectivas transculturales sobre estos temas. El análisis de los datos cualitativos y cuantitativos puso al descubierto que el CGGE alcanzó sus objetivos de reforzar los conocimientos y las competencias geográficas. El diseño de los módulos y de su colaboración internacional interesó en gran medida a estudiantes y profesores. Establecemos revisiones específicas de sus contenidos a fin de fomentar intercambios más intensos de las perspectivas internacionales entre estudiantes universitarios

Comparative Measurements of Inverse Spin Hall and Magnetoresistance in YIG|Pt and YIG|Ta

We report on a comparative study of spin Hall related effects and magnetoresistance in YIG|Pt and YIG|Ta bilayers. These combined measurements allow to estimate the characteristic transport parameters of both Pt and Ta layers juxtaposed to YIG: the spin mixing conductance $G_{\uparrow \downarrow}$ at the YIG$|$normal metal interface, the spin Hall angle $\Theta_{SH}$, and the spin diffusion length $\lambda_{sd}$ in the normal metal. The inverse spin Hall voltages generated in Pt and Ta by the pure spin current pumped from YIG excited at resonance confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we extract the spin diffusion length in Ta, found to be $\lambda_{sd}^\text{Ta}=1.8\pm0.7$ nm. Both the YIG|Pt and YIG|Ta systems display a similar variation of resistance upon magnetic field orientation, which can be explained in the recently developed framework of spin Hall magnetoresistance.Comment: 8 pages, 5 figures, 1 tabl

Detection of the microwave spin pumping using the inverse spin Hall effect

We report electrical detection of the dynamical part of the spin pumping current emitted during ferromagnetic resonance (FMR) using the inverse Spin Hall Effect (ISHE). The experiment is performed on a YIG$|$Pt bilayer. The choice of YIG, a magnetic insulator, ensures that no charge current flows between the two layers and only pure spin current produced by the magnetization dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin pumping. To avoid measuring the parasitic eddy currents induced at the frequency of the microwave source, a resonance at half the frequency is induced using parametric excitation in the parallel geometry. Triggering this nonlinear effect allows to directly detect on a spectrum analyzer the microwave component of the ISHE voltage. Signals as large as 30 $\mu$V are measured for precession angles of a couple of degrees. This direct detection provides a novel efficient means to study magnetization dynamics on a very wide frequency range with great sensitivity

Global existence of a solution to a phase field model for supercooling

In this work, we will derive a macroscopic model of phase field type for supercooling. The phase transition process is described by the evolution of the temperature and the volume fraction of the liquid phase. This phase field model can also be interpreted as the approximation of some generalized Stefan problem. We will prove the existence of solutions to an initial--boundary value problem for the resulting system by using a time discrete scheme

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