Supersolidity in quantum films adsorbed on graphene and graphite

Using quantum Monte Carlo we have studied the superfluid density of the first layer of $^4$He and H$_2$ adsorbed on graphene and graphite. Our main focus has been on the equilibrium ground state of the system, which corresponds to a registered $\sqrt3 \times \sqrt3$ phase. The perfect solid phase of H$_2$ shows no superfluid signal whereas $^4$He has a finite but small superfluid fraction (0.67%). The introduction of vacancies in the crystal makes the superfluidity increase, showing values as large as 14% in $^4$He without destroying the spatial solid order.Comment: 5 pages, accepted for publication in PR

La intervención en variables afectivas hacia las matemáticas y la resolución de problemas matemáticos. El MIRPM

En el presente trabajo se presenta, en primer lugar, una detallada descripción de diferentes propuestas realizadas por diversos autores, tanto a nivel nacional como internacional, para la intervención en variables afectivas (creencias, actitudes, ansiedad…) hacia las matemáticas y la resolución de problemas matemáticos. En segundo lugar, se describe un programa concreto de control emocional en la resolución de problemas matemáticos para maestros en formación inicial así como el eje central del mismo: un Modelo Integrado de Resolución de Problemas Matemáticos (MIRPM). Igualmente se muestran algunos resultados que evidencian la eficacia de este programa, entre los que cabe destacar una disminución significativa de la ansiedad hacia la resolución de problemas matemáticos, un aumento de la autoconfianza y expectativas de éxito y una modificación de las creencias en torno a la resolución de problemas y su enseñanza y aprendizaje

Hybrid Modelling and Control of a Class of Power Converters with Triangular-Carrier PWM Inputs

In this paper, a new control design procedure for a class of power converters based on hybrid dynamical systems theory is presented. The continuous-time dynamics, as voltage and current signals, and discrete-time dynamics, as the on- off state of the switches, are captured with a hybrid model. This model avoids the use of averaged and approximated models and includes the PWM as well as the sample-and-hold mechanism, commonly used in the industry. Then, another simplified hybrid system, whose trajectories match with the original one, is selected to design the controller and to analyse stability properties. Finally, an estimation of the chattering in steady state of the voltage and current signals is provided. The results are validated through simulation and experiments