912 resultados para La_(2-x)Nd_xCuO_(4 y)


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Fil: Vizzotti, Martín Miguel. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

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Fil: Cairo, María Emilia. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

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Fil: Vizzotti, Martín Miguel. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

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Fil: Cairo, María Emilia. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

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In this study we investigate benthic phosphorus cycling in recent continental margin sediments at three sites off the Namibian coastal upwelling area. Examination of the sediments reveals that organic and biogenic phosphorus are the major P-containing phases preserved. High Corg/Porg ratios just at the sediment surface suggest that the preferential regeneration of phosphorus relative to that of organic carbon has either already occurred on the suspension load or that the organic matter deposited at these sites is already rather refractory. Release of phosphate in the course of benthic microbial organic matter degradation cannot be identified as the dominating process within the observed internal benthic phosphorus cycle. Dissolved phosphate and iron in the pore water are closely coupled, showing high concentrations below the oxygenated surface layer of the sediments and low concentrations at the sediment-water interface. The abundant presence of Fe(III)-bound phosphorus in the sediments document the co-precipitation of both constituents as P-containing iron (oxyhydr)oxides. However, highly dissolved phosphate concentrations in pore waters cannot be explained, neither by simple mass balance calculations nor by the application of an established computer model. Under the assumption of steady state conditions, phosphate release rates are too high as to be balanced with a solid phase reservoir. This discrepancy points to an apparent lack of solid phase phosphorus at sediment depth were suboxic conditions prevail. We assume that the known, active, fast and episodic particle mixing by burrowing macrobenthic organisms could repeatedly provide the microbially catalyzed processes of iron reduction with authigenic iron (oxyhydro)oxides from the oxic surface sediments. Accordingly, a multiple internal cycling of phosphate and iron would result before both elements are buried below the iron reduction zone.

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EvalCOMIX es un servicio Web de autoría y despliegue de instrumentos que una vez integrado con Moodle permite el uso de dichos instrumentos para la evaluación de distintas actividades realizadas por los alumnos. La evaluación podrá ser realizada tanto por parte del docente como por parte de los propios alumnos a sí mismos o al resto de compañeros. La primera integración de esta herramienta fue realizada para la versión 1.9 de Moodle. Para la integración de la versión 2.X de Moodle se ha decidido realizar mejoras en distintos aspectos. Uno de ellos es la portabilidad de la integración, la cual depende intrínsecamente de su procedimiento de instalación.

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Publication information: Chicago, Ill. : Everts & Stewart, 1874.

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"Curso de legislación y tratados panamericanos. Facultad de derecho y ciencias socvales. Conferencia dada el lunes 6 de octobre de 1919."

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Trägerband: Ms. lat. oct. 26; Ms. lat. oct. 30; Vorbesitzer: Johann Hartmann Beyer

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Numerosos estudios acerca de analgesia postoperatoria arrojan resultados positivos en favor de la administración de opiáceos en el espacio peridural y en general perimedular por la eficacia analgésica y anealgesia prolongada en los pacientes quirúrgicos. La adición de -fentanil- a una dosis única de 2mcg (microgramos)/kg. de peso a la lidocaina en la técnica de punción lumbar (L2-3;L3-4) para anestesia peridural se realizó en 100 pacientes del Hospital Vicente Corral Moscoso de Cuenca. Los pacientes fueron intervenidos por diversos procedimientos que abarcan las especializades de cirugía general, cirugía plástica, cirugía vascular, traumatología y ortopedia, ginecología, obstetricia y urología. A los pacientes se les constituyó aleatoriamente en dos grupos (casos y controles). Los resultados evidencian que si bien todos los pacientes presentaron analgesia postoperatoria la duraciïïon de la misma en el grupo de control se redujo a menos de una hora en comparación con el grupo de estudio en la que se obtuvo una analgesia promedio de siete horas y media. La administración posterior de otros analgésicos evidencia, igualmente, una marcada diferencia entre los grupos, sindo mucho menor en el grupo de estudio. Las compilaciones de esta técnica son leves y se resumen en prurito, naúsea y retención urinaria en porcentajes inferiores al 5. Las pruebas de significación estadística a las que se sometieron los resultados marcan una muy significativa diferencia entre las variables sometidas a estudio, en una muestra muy homogénea

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The L-dopa is the immediate precursor of the neurotransmitter dopamine. Unlike dopamine, L-dopa easily enters the central nervous system and is used in the treatment of Parkinson's disease. A sensitive and selective method is presented for the voltammetric determination of L-dopa in pharmaceutical formulations using a carbon paste electrode modified with trinuclear ruthenium ammine complex [(NH3)(5)Ru-III-O-Ru-IV(NH3)(4)-O-Ru-III(NH3)(5)](6+) (Ru-red) incorporated in NaY zeolite. The parameters which influence on the electrode response (paste composition, potential scan rate, pH and interference) were also investigated. The optimum conditions were found to an electrode composition (m/m) of 25% zeolite containing 6.7% Ru, 50% graphite and 25% mineral oil in acetate buffer at pH 4.8. Voltammetric peak currents showed a linear response for L-dopa concentration in the range between 1.2 x 10(-4) and 1.0 x 10(-2) Mol l(-1) (r = 0.9988) with a detection limit of 8.5 x 10(-5) mol l(-1). The variation coefficient for a 1.0 x 10(-3) mol l(-1) L-dopa (n = 10) was 5.5%. The results obtained for L-dopa in pharmaceutical formulations (tablet) was in agreement with compared official method. In conclusion, this study has illustrated that the proposed electrode modified with Ru-red incorporated zeolite is suitable valuable for selective measurements of L-dopa. (C) 2004 Elsevier B.V. All rights reserved.

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The 1:1 proton-transfer compound of the potent substituted amphetamine hallucinogen (R)-1-(8-bromobenzo[1,2-b; 4,5-b']difuran-4-yl)-2-aminopropane (common trivial name 'bromodragonfly') with 3,5-dinitrosalicylic acid, 1-(8-bromobenzo[1,2-b;4,5-b']difuran-4-yl)-2-mmoniopropane 2-carboxy-4,6-dinitrophenolate, C13H13BrNO2+ C7H3N2O7- forms hydrogen-bonded cation-anion chain substructures comprising undulating head-to-tail anion chains formed through C(8) carboxyl O-H...O(nitro) associations and incorporating the aminium groups of the cations. The intra-chain cation-anion hydrogen-bonding associations feature proximal cyclic R33(8) interactions involving both a N+-H...O(phenolate) and the carboxyl O--H...O(nitro)associations. Also present are aromatic pi-pi ring interactions [minimum ring centroid separation, 3.566(2)A; inter-plane dihedral angle, 5.13(1)deg]. A lateral hydrogen-bonding interaction between the third aminium proton and a carboxyl O acceptor link the chain substructures giving a two-dimensional sheet structure. This determination represents the first of any form of this compound and confirms that it has the (R) absolute configuration. The atypical crystal stability is attributed both to the hydrogen-bonded chain substructures provided by the anions, which accommodate the aminium proton-donor groups of the cations and give cross-linking, and to the presence of cation--anion aromatic ring pi-pi interactions.