High pressure effects on the superconductivity of beta-pyrochlore oxides AOs2O6

High pressure effects on the superconducting transitions of beta-pyrochlore superconductors AOs2O6 (A = Cs, Rb, K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature Tc first increases with increasing pressure in all the compounds and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for A = Cs, Rb and K, respectviely. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the coefficinet A of the T2 term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in Tc. It is suggested that electron correlations and certain quantum fluctuations play important roles in the occurrence or suppression of superconductivity in the beta-pyrochlore oxides.Comment: 6 pages, 4 figure

Violation of Kohler's Rule in the Magnetoresistance near the Lower Charge-Density-Wave Instability in NbSe 3

This paper reports the measurements of resistance (R) and magnetoresistance of NbSe 3 near the critical pressure (P c ¼ 7:5 kbar), where the lower charge-density-wave (CDW) phase is on the verge of destruction. For P ¼ 7:6 kbar, the temperature dependence of dR=dT exhibits a weak anomaly at T Ã ¼ 15 K and the superconducting transition is observed at T c ¼ 2:8 K. From the observation of a large magnetoresistance due to an imperfect nesting of Fermi surface, we show that the weak anomaly is closely related to the lower CDW phase. Moreover, an excess conductance and violation of Kohler's rule are found below $T Ã . The origins of the excess conductance and the violation of Kohler's rule are discussed in terms of charge fluctuation associated with the lower CDW state

Diseño de sistema de alcantarillado sanitario y ampliación del sistema de agua potable del Barrio Villa Vallarta en la Ciudad de Managua

El presente estudio monográfico denominado "DISEÑO DEL SISTEMA DE ALCANTARILLADO SANITARIO Y AMPLIACIÓN DEL SISTEMA DE AGUA POTABLE EN EL BARRIO VILLA VALLARTA'', tiene como propósito mejorar las condiciones higiénico-sanitarias de la población, djsminuir el índice de mortalidad infantil y promover cambios de comportamientos en los miembros de las familias beneficiadas, para que mejoren su nivel de vida. EI Barrio Villa Vallarta se encuentra ubicado en la parie Nor-Este de la ciudad de Managua, localizándose en la zona alta del Acueducto de Managua; específicamente está ubicado en el Distrito No. Vl de la municipalidad de Managua. Se caracteriza por ser una zona de alta densidad debido que en dicho Barrio se encuentran construcciones sencillas y lotes con dimensiones y áreas homogéneas, de aproximadamente | 05 m2. Esta conformado por 393 viviendas,13 manzanas, 9 calles y 3 avenidas, alcanzando un área total de aproximadamente 67, 327.81 m2, incluyendo calles, avenidas y un área comunal de 1,575.45 m2 La calles miden aproximadamente 750.45 m2 Para formular el estudio monográfico, primeramente se realizó un diagnóstico situacional a través de ntrevistas y encuesta dirigidas. a funcionarios, líderes comunales y familias del Barrio. Posteriormente se efectuará el estudio topográfico y el estudio de suelo para conocer las características del terreno y la clasificación o tipo de suelo que predomina en el Barrio. Además se realizó la valoración del Sistema de Alcantarillado Sanitario y Sistema de Agua Potable existente

Hydrostatic pressure effects on superconducting transition of nanostructured niobium highly strained by high-pressure torsion

We study the effects of hydrostatic pressure (HP) compression on the superconducting transition of severely strained Nb samples, whose grain sizes are reduced to the submicrometer level. Engineered granularity by high-pressure torsion (HPT) treatment changes the strength of coupling between submicrometer-scale grains and introduces lattice strain. We attempt to utilize the initially accumulated shear strain in the starting material for increasing the superconducting transition temperature Tc under HP compression. The HP effects on non-strained Nb have already been investigated in the pressure regime over 100 GPa by Struzhkin et al. [Phys. Rev. Lett. 79, 4262 (1997)], and Tc reportedly exhibited an increase from 9.2 to 9.9 K at approximately 10 GPa. (1) Slightly strained Nb in the HPT treatment exhibits the increase in Tc under HP due to the strengthening of the intergrain coupling, so the pressure scale of the pressure response observed by Struzhkin et al. is reduced to approximately one-seventh at the maximum. (2) Prominently strained Nb in the HPT treatment exhibits the increase in Tc under HP due to a reduction in structural symmetry at the unit-cell level: In a Nb sample subjected to HPT (6 GPa, 10 revolutions), Tc exceeds 9.9 K at approximately 2 GPa. According to our first-principle calculations, the reduction in the structural symmetry affords an increase in the density of states at the Fermi energy, thereby yielding a prominent increase in Tc at low pressures