Berry phases and zero-modes in toroidal topological insulator

An effective Hamiltonian describing the surface states of a toroidal topological insulator is obtained, and it is shown to support both bound-states and charged zero-modes. Actually, the spin connection induced by the toroidal curvature can be viewed as an position-dependent effective vector potential, which ultimately yields the zero-modes whose wave-functions harmonically oscillate around the toroidal surface. In addition, two distinct Berry phases are predicted to take place by the virtue of the toroidal topology.Comment: New version, accepted for publication in EPJB, 6 pages, 1 figur

Observações de planetas extrasolares no Observatório Astronómico da Ribeira Grande (Fronteira)

O estudo dos planetas extra-solares tem sido uma das áreas em maior actividade na Astronomia e inclusivamente tem impulsionado estudos em áreas como a Geofísica, para uma melhor compreensão da origem e evolução dos planetas. O projecto TRANSIT, do Centro de Geofísica de Évora, desenvolve uma campanha de acompanhamento de trânsitos de planetas extra-solares, utilizando o Observatório Astronómico da Ribeira Grande (Fronteira), cujos resultados apresentamos neste trabalho. Este tipo de campanhas, ainda que com equipamento modesto (pelos padrões actuais), permitem refinar os elementos orbitais dos planetas já descobertos

Detection of outliers in multivariate data: a method based on clustering and robust estimators

Outlier identification is important in many applications of multivariate analysis. Either because there is some specific interest in finding anomalous observations or as a pre-processing task before the application of some multivariate method, in order to preserve the results from possible harmful effects of those observations. It is also of great interest in supervised classification (or discriminant analysis) if, when predicting group membership, one wants to have the possibility of labelling an observation as does not belong to any of the available groups. The identification of outliers in multivariate data is usually based on Mahalanobis distance. The use of robust estimates of the mean and the covariance matrix is advised in order to avoid the masking effect (Rousseeuw and Leroy, 1985; Rousseeuw and von Zomeren, 1990; Rocke and Woodruff, 1996; Becker and Gather, 1999). However, the performance of these rules is still highly dependent of multivariate normality of the bulk of the data. The aim of the method here described is to remove this dependence

Global Alfven Wave Heating of the Magnetosphere of Young Stars

Excitation of a Global Alfven wave (GAW) is proposed as a viable mechanism to explain plasma heating in the magnetosphere of young stars. The wave and basic plasma parameters are compatible with the requirement that the dissipation length of GAWs be comparable to the distance between the shocked region at the star's surface and the truncation region in the accretion disk. A two-fluid magnetohydrodynamic plasma model is used in the analysis. A current carrying filament along magnetic field lines acts as a waveguide for the GAW. The current in the filament is driven by plasma waves along the magnetic field lines and/or by plasma crossing magnetic field lines in the truncated region of the disk of the accreting plasma. The conversion of a small fraction of the kinetic energy into GAW energy is sufficient to heat the plasma filament to observed temperatures.Comment: Submitted to ApJ, aheatf.tex, 2 figure