Two-Dimensional Supersymmetric Quantum Mechanics: Two Fixed Centers of Force

The problem of building supersymmetry in the quantum mechanics of two Coulombian centers of force is analyzed. It is shown that there are essentially two ways of proceeding. The spectral problems of the SUSY (scalar) Hamiltonians are quite similar and become tantamount to solving entangled families of Razavy and Whittaker-Hill equations in the first approach. When the two centers have the same strength, the Whittaker-Hill equations reduce to Mathieu equations. In the second approach, the spectral problems are much more difficult to solve but one can still find the zero-energy ground states.Comment: This is a contribution to the Proc. of the Seventh International Conference ''Symmetry in Nonlinear Mathematical Physics'' (June 24-30, 2007, Kyiv, Ukraine), published in SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at http://www.emis.de/journals/SIGMA

New Mechanism of Magnetoresistance in Bulk Semiconductors: Boundary Condition Effects

We consider the electronic transport in bounded semiconductors in the presence of an external magnetic field. Taking into account appropriate boundary conditions for the current density at the contacts, a change in the magnetoresistance of bulk semiconductors is found as compared with the usual theory of galvanomagnetic effects in boundless media. New mechanism in magnetoresistance connected with the boundary conditions arises. In particular, even when the relaxation time is independent of the electron energy, magnetoresistance is not vanish.Comment: 7 pages, Elsart macro package (LaTeX2e edition

Habitat computing: Towards the creation of tech-enabled mexican neighborhoods

The use of personal computers and Internet at home is becoming more and more common in some developing countries such as Mexico, where affordable prices and credit plans have contributed to this trend. Undoubtedly, the presence of information technology in the households has effects in the life of families and their communities; however how beneficial these effects are depends on the way technology is contextualized to support domestic and community practices. Achieving a proper contextualization is the goal of what we call habitat computing. This paper presents the case of Real del Sol, a housing community in Mexico where an implementation of habitat computing is being developed. Houses are built with Internet access and personal computers as part of their basic infrastructure. We analyze here the role, usage and development of the Real del Sol community intranet, which is a key element on supporting the vision of the project. © Springer-Verlag Berlin Heidelberg 2007