Electron-phonon vertex and its influence on the superconductivity of two-dimensional metals on a piezoelectric substrate

We investigate the interaction between the electrons of a two-dimensional metal and the acoustic phonons of an underlying piezoelectric substrate. Fundamental inequalities can be obtained from general energy arguments. As a result, phonon mediated attraction can be proven to never overcome electron Coulomb repulsion, at least for long phonon wavelengths. We study the influence of these phonons on the possible pairing instabilities of a two-dimensional electron gas such as graphene.Comment: 10 pages, 3 figure

La Esencia de la Ingeniería de Software: El Núcleo de Semat

Esta es una traducción del artículo que se publicó en Communications of the ACM en Diciembre de 2012 bajo el título “The Essence of Software Engineering: The SEMAT Kernel” y se realiza debido a la importancia que adquiere el tema para la audiencia de hispanoparlantes, de forma que se pueda generar un acceso a lo que constituye uno de los últimos adelantos en Ingeniería de Software

Supercurrent flow through an effective double barrier structure

Supercurrent flow is studied in a structure that in the Ginzburg-Landau regime can be described in terms of an effective double barrier potential. In the limit of strongly reflecting barriers, the passage of Cooper pairs through such a structure may be viewed as a realization of resonant tunneling with a rigid wave function. For interbarrier distances smaller than $d_0=\pi\xi(T)$ no current-carrying solutions exist. For distances between $d_0$ and $2d_0$, four solutions exist. The two symmetric solutions obey a current-phase relation of $\sin(\Delta\varphi/2)$, while the two asymmetric solutions satisfy $\Delta\varphi=\pi$ for all allowed values of the current. As the distance exceeds $nd_0$, a new group of four solutions appears, each contaning $(n-1)$ soliton-type oscillations between the barriers. We prove the inexistence of a continuous crossover between the physical solutions of the nonlinear Ginzburg-Landau equation and those of the corresponding linearized Schr\"odinger equation. We also show that under certain conditions a repulsive delta function barrier may quantitatively describe a SNS structure. We are thus able to predict that the critical current of a SNSNS structure vanishes as $\sqrt{T'_c-T}$, where $T'_c$ is lower than the bulk critical temperature.Comment: 20 pages, RevTex, to appear in Phys. Rev. B, 6 figures on request at [email protected]

Josephson effect between trapped Bose-Einstein condensates

We study the Josephson effect between atomic Bose-Einstein condensates. By drawing on an electrostatic analogy, we derive a semiclassical functional expression for the three-dimensional Josephson coupling energy in terms of the condensate density. Estimates of the capacitive energy and of the Josephson plasma frequency are also given. The effect of dissipation due to the incoherent exchange of normal atoms is analysed. We conclude that coherent Josephson dynamics may already be observable in current experimental systems.Comment: 4 pages, RevTe

Fenómenos de coherencia cuántica macroscópica

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica de la Materia Condensada. Fecha de lectura: 18-4-199

A first course in software engineering methods and theory

Even though the software engineering curriculum has been designed many times, some problems still remain: the gap between academy and industry, the failure to continuously update the courses, the difficulties for combining theory and practice, and the lack of a sound, widely accepted theoretical basis. The SEMAT (Software Engineering Methods and Theory) initiative has been proposed for addressing some of the aforementioned problems. Based on the main ideas related to SEMAT, in this paper we propose a first course that introduces students to the main issues about SEMAT. This course is planned to be included in the System and Informatics Engineering Program belonging to the Universidad Nacional de Colombia, Medellin Branch. Also, we discuss the way in which this course addresses the previously diagnosed problems.Aunque desde hace años se habla del diseño curricular de la ingeniería de software, algunos problemas aún subsisten: la brecha existente entre la academia y la industria del software, los problemas para mantener actualizados los cursos, las dificultades para combinar la teoría con la práctica y la carencia de una sonora y ampliamente aceptada base teórica para la ingeniería de software. La iniciativa SEMAT (nombrada así por el acrónimo en inglés de Teoría y Métodos de la Ingeniería de Software) se propuso para solucionar algunos de los problemas en mención. Tomando como base las ideas relacionadas con SEMAT, en este artículo se propone un primer curso que suministra a los estudiantes una introducción a los principales tópicos de SEMAT. Se planea incluir este curso en el programa de Ingeniería de Sistemas e Informática de la Universidad Nacional de Colombia, Sede Medellín. También, se discute la manera en que este curso contribuye a solucionar los problemas que se diagnosticaron previamente

A first course in software engineering methods and theory

Even though the software engineering curriculum has been designed many times, some problems still remain: the gap between academy and industry, the failure to continuously update the courses, the difficulties for combining theory and practice, and the lack of a sound, widely accepted theoretical basis. The SEMAT (Software Engineering Methods and Theory) initiative has been proposed for addressing some of the aforementioned problems. Based on the main ideas related to SEMAT, in this paper we propose a first course that introduces students to the main issues about SEMAT. This course is planned to be included in the System and Informatics Engineering Program belonging to the Universidad Nacional de Colombia, Medellin Branch. Also, we discuss the way in which this course addresses the previously diagnosed problems