Quasi-exact solvability beyond the SL(2) algebraization

We present evidence to suggest that the study of one dimensional quasi-exactly solvable (QES) models in quantum mechanics should be extended beyond the usual \sla(2) approach. The motivation is twofold: We first show that certain quasi-exactly solvable potentials constructed with the \sla(2) Lie algebraic method allow for a new larger portion of the spectrum to be obtained algebraically. This is done via another algebraization in which the algebraic hamiltonian cannot be expressed as a polynomial in the generators of \sla(2). We then show an example of a new quasi-exactly solvable potential which cannot be obtained within the Lie-algebraic approach.Comment: Submitted to the proceedings of the 2005 Dubna workshop on superintegrabilit

A conjecture on Exceptional Orthogonal Polynomials

Exceptional orthogonal polynomial systems (X-OPS) arise as eigenfunctions of Sturm-Liouville problems and generalize in this sense the classical families of Hermite, Laguerre and Jacobi. They also generalize the family of CPRS orthogonal polynomials. We formulate the following conjecture: every exceptional orthogonal polynomial system is related to a classical system by a Darboux-Crum transformation. We give a proof of this conjecture for codimension 2 exceptional orthogonal polynomials (X2-OPs). As a by-product of this analysis, we prove a Bochner-type theorem classifying all possible X2-OPS. The classification includes all cases known to date plus some new examples of X2-Laguerre and X2-Jacobi polynomials

A Family of Quasi-solvable Quantum Many-body Systems

We construct a family of quasi-solvable quantum many-body systems by an algebraic method. The models contain up to two-body interactions and have permutation symmetry. We classify these models under the consideration of invariance property. It turns out that this family includes the rational, hyperbolic (trigonometric) and elliptic Inozemtsev models as the particular cases.Comment: 9 pages, REVTeX4, final versio

Nanocrystalline cathodes for PC-SOFCs based on BCZY

Perovskites based on BaCeO3-δ exhibit the highest proton conductivity among this class of materials, however, they are susceptible to hydration and carbonation in presence of water vapor and CO2 [1]. In contrast, the chemical stability of BaZrO3-based protonic conductors is better, but they require sintering temperatures as high as 1700 ºC and suffer from high intrinsic grain boundary resistance, limiting the final performance. Partial substitution of Zr for Ce in Ba(Ce0.9-xZrx)Y0.2O3-δ allows obtaining electrolytes with both high proton conductivity and good chemical stability. The performance of a PC-SOFC at low temperatures depends significantly on the ohmic resistance of the electrolyte, although it can be lowered by reducing the electrolyte thickness. Another important limiting factor is the increase of the cathode polarization resistance due to the thermally activated nature of the oxygen reduction reaction. For this reason, it is essential to obtain high efficiency cathodes operating at reduced temperatures. In this work, BaCe0.6Zr0.2Y0.2O3-δ (BCZY) powders were prepared by freeze-drying precursor method. These powders were mixed with a Zn-containing solution as sintering additive in order to obtain dense pellets with submicrometric grain size at only 1200 ºC. After that, La0.6Sr0.4Co0.8Fe0.2O3 nanocrystalline electrodes were deposited symmetrically onto dense pellets BCZY by conventional spray-pyrolysis [3]. The structure, microstructure and electrochemical properties of these electrodes have been examined by XRD, FE-SEM and impedance spectroscopy. The stability of these electrodes at intermediate temperatures was evaluated as a function of time. These nanocrystalline cathodes exhibit a substantial improvement of the electrode polarization resistance with respect to the same materials prepared by screen-printing method at high sintering temperatures, e.g. 0.7 and 3.2 cm2 at 600 ºC for LSCF cathodes prepared by spray-pyrolysis and screen-printing method respectively (Figure). An anode supported cell with composition LSCF/BCZY/NiO-BCZY was also prepared to test the electrochemical performance.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Ictiólogos de la Argentina: Juana Yolanda Dziekonska de Ciechomski.

This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina

Estructura de la corteza en el centro peninsular mediante el análisis espectral de datos gravimétricos y modelización en 2+1/2D

El análisis espectral de las anomalías de Bouguer del centro peninsular ha puesto de manifiesto la existencia de dos discontinuidades corticales situadas a unas profundidades medias de 29,2±1,7 y 8,2±0,4 km. De acuerdo con los datos sísmicos, la discontinuidad más profunda representa el Moho y la más superficial está situada dentro de la corteza superior. Mediante la inversión en el dominio de las frecuencias de la anomalía regional, se ha elaborado un modelo tridimensional del Moho. Su geometría está caracterizada por una depresión con las mayores profundidades dispuestas según una orientación NO-SE, alcanzando valores próximos a 30 km. Por tanto, la corteza en esta zona se encuentra ligeramente engrosada, descendiendo el Moho bajo las áreas centrales del Sistema Central y sus márgenes con las Cuencas del Duero y del Tajo. Hacia los extremos de la cadena el espesor de la corteza disminuye. En los modelos gravimétricos transversales al Sistema Central realizados, la estructura de la cadena aparece definida como un bloque cortical elevado en el que el límite corteza superior-corteza media asciende en sentido transversal a la cadena, adquiriendo una forma arqueada. El límite con las Cuencas del Duero y del Tajo corresponde a dos fallas inversas de buzamientos próximos a 50°, asociados a gradientes gravimétricos de dirección NE-SO bien marcados. El modelo gravimétrico longitudinal muestra el carácter heterogéneo de la corteza superior en el Sistema Central. Estas heterogeneidades están relacionadas con dominios establecidos en el basamento hercínico de forma que la densidad de los materiales disminuye hacia la zona occidental. Aunque tanto el análisis espectral de los datos gravimétricos como la modelización sugieren la existencia de un engrosamiento bajo el Sistema Central, éste se encuentra circunscrito a la zona central y es menor que el propuesto por los modelos sísmico

Permeabilidad de gases en membranas de zeolita ZSM-5

El trabajo incluido en el presente articulo tiene como objetivo analizar la influencia de la deposición de zeolita ZSM-5 en un tubo de alumina sobre la velocidad de transferencia de materia de distintos gases con el fin de analizar la capacidad de separación. Se ha evaluado la influencia de la presencia de zeolita, así como del caudal de gas alimentado y la temperatura a la que se desarrolla el proceso deseparación