Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma

Equations describing the linear evolution of a non-dissipative Langmuir wave in inhomogeneous nonstationary anisotropic plasma without magnetic field are derived in the geometrical optics approximation. A continuity equation is obtained for the wave action density, and the conditions for the action conservation are formulated. In homogeneous plasma, the wave field E universally scales with the electron density N as E ~ N^{3/4}, whereas the wavevector evolution varies depending on the wave geometry

Evidence for pseudogap and phase-coherence gap separation by Andreev reflection experiments in Au/La_{2-x}Sr_{x}CuO_4 point-contact junctions

We present new Au/La_{2-x}Sr_{x}CuO_{4} (LSCO) point-contact conductance measures as a function of voltage and temperature in samples with 0.08 <= x <= 0.2. Andreev reflection features disappear at about the bulk Tc, giving no evidence of gap for T > Tc. The fit of the normalized conductance at any T < Tc supports a (s + d)-wave symmetry of the gap, whose dominant low-T s component follows the Tc(x) curve in contrast with recent angle-resolved photoemission spectroscopy and quasiparticle tunneling data. These results prove the separation between pseudogap and phase-coherence superconducting gap in LSCO at x <= 0.2.Comment: 4 pages, 4 eps figures, 1 table (RevTeX). Labels added to Fig. 1; Fig. 3 resized; references added; short discussion about ballistic contact regime adde

Possibility of local pair existence in optimally doped SmFeAsO(1-x) in pseudogap regime

We report the analysis of pseudogap Delta* derived from resistivity experiments in FeAs-based superconductor SmFeAsO(0.85), having a critical temperature T_c = 55 K. Rather specific dependence Delta*(T) with two representative temperatures followed by a minimum at about 120 K was observed. Below T_s = 147 K, corresponding to the structural transition in SmFeAsO, Delta*(T) decreases linearly down to the temperature T_AFM = 133 K. This last peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of Fe spins. It is believed that the found behavior can be explained in terms of Machida, Nokura, and Matsubara (MNM) theory developed for the AFM superconductors.Comment: 5 pages, 2 figure

Extracción de bases de reglas simples y lingüísticamente interpretables

Comunicación presentada al "XIII ESTYLF'06" celebrado en Ciudad Real del 20 al 22 de Septiembre de 2006.Este artículo presenta una técnica basada en la lógica difusa para extraer bases de reglas a partir de datos numéricos. Permite obtener bases de reglas interpretables lingüísticamente a la vez que simples en cuanto a número de reglas, sencillez en las partes antecedentes y consecuentes y facilidad de implementación hardware/software. Los pasos más significativos de esta técnica son los siguientes: (1) extracción de la base de reglas empleando particiones granulares de las variables del problema, (2) ajuste de las funciones de pertenencia para las variables de salida y posterior simplificación, (3) simplificación tabular de la base de reglas y (4) simplificación de las funciones de pertenencia para las variables de entrada. La técnica puede aplicarse de forma automática mediante las herramientas de CAD integradas en el entorno Xfuzzy 3. Se incluye un ejemplo de aplicación en robótica móvil para ilustrar las ventajas de la técnica propuesta.Peer reviewe