Dimensionality-driven metal-insulator transition in spin-orbit-coupled IrO2.

A metal-insulator transition is observed in spin-orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t ∼ 1.5-2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros-Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator.

A novel fuel cell design foroperandoenergy-dispersive x-ray absorption measurements.

A polymer electrolyte fuel cell has been designed to allowoperandox-ray absorption spectroscopy (XAS) measurements of catalysts. The cell has been developed to operate under standard fuel cell conditions, with elevated temperatures and humidification of the gas-phase reactants, both of which greatly impact the catalyst utilisation. X-ray windows in the endplates of the cell facilitate collection of XAS spectra during fuel cell operation while maintaining good compression in the area of measurement. Results of polarisation curves and cyclic voltammograms showed that theoperandocell performs well as a fuel cell, while also providing XAS data of suitable quality for robust XANES analysis. The cell has produced comparable XAS results when performing a cyclic voltammogram to an establishedin situcell when measuring the Pt LIII edge. Similar trends of Pt oxidation, and reduction of the formed Pt oxide, have been presented with a time resolution of 5 s for each spectrum, paving the way for time-resolved spectral measurements of fuel cell catalysts in a fully-operating fuel cell.

Local structure refinement of disordered material models: ion pairing and structure in YCl3 aqueous solutions.

Hydrogen/deuterium isotopic neutron diffraction techniques have been used to investigate the structure of a 1 m aqueous solution of YCl3 at room temperature. Empirical potential structure refinement (EPSR) has been used to build a three-dimensional model of the solution structure that is consistent with the bulk solvent correlations strongly probed by the neutron scattering technique. Optimization of the local structural environment of the Y3+ ion sites within the model has been performed through calculations of the yttrium K-edge, extended X-ray absorption fine structure (EXAFS) spectrum of the solution, and detailed information has been extracted on the structure of the ion hydration shell and the extent of inner-sphere ion pairing within the solution. The results demonstrate the significant potential of this hybrid data analysis approach to circumvent the limitations of the individual experimental methods, to refine atomic potential models, and to produce accurate, quantitative structural models of the local environment of dilute atomic species within tightly constrained bulk network structures.

Analysis of time-resolved energy-dispersive X-ray absorption spectroscopy data for the study of chemical reaction intermediate states.

Energy-dispersive X-ray absorption spectroscopy is an increasingly powerful tool for the investigation of kinetic processes in chemical systems as an element-specific local structure and electronic-state probe. Advances in synchrotron radiation sources and detector technology are pushing the time resolution of the method to ever shorter periods, currently milliseconds to microseconds, while also providing a concomitant improvement in data quality that now makes feasible the identification of structural and electronic motifs characteristic of intermediate states in chemical processes. To maximize the value of the newly available high-quality time-resolved data, techniques for consistent data normalization and structural component analysis have been developed and here are illustrated in a model study of the electron-transfer reaction between [IrCl6]2- with [Co(CN)5]3-.

The structure of a trimolecular liquid: tert-butyl alcohol:cyclohexene:water.

The structure of the trimolecular liquid mixture of 2:6:1 cyclohexene, tert-butyl alcohol, and water has been investigated using hydrogen/deuterium substitution neutron scattering techniques, and a three-dimensional structural model refined to be consistent with the experimental data has been built using the technique of Empirical Potential Structure Refinement. The model shows a well-mixed solution of the three molecular components where the competing interactions between the nonpolar cyclohexene and polar water molecules are balanced in the solution leading to largely pure-alcohol-like interactions between the tert-butyl alcohol molecules. Cyclohexene molecules favor direct solvation by alcohol methyl groups while water molecules are accommodated, dispersed throughout the solution, via hydrogen bonding interactions with the alcohol molecule hydroxyl groups. Rare occurrences of direct cyclohexene-water interactions are of the classic hydrophobic hydration type and no evidence is found for microscopic heterogeneity in the trimolecular mixture in contrast to the general findings for binary alcohol-water solutions.

Métodos estadísticos de los trabajos publicados en "Rehabilitación" en la década 1989-1999 / Statistical methods used in the works published in "Rehabilitación" in the decade of 1989-1999

Objetivos: Identificar y cuantificar los métodos estadísticos utilizados en los artículos originales publicados en la revista Rehabilitación en los últimos 10 años. Realizamos una comparación de la utilización de estadística en dos períodos 1989-1994 y 1995-1999.Diseño: Estudio descriptivo. Métodos: Todos los artículos originales publicados en la revista Rehabilitación en los últimos 10 años, fueron revisados por dos investigadores independientes para identificar y cuantificar el uso de los métodos estadísticos utilizados. Resultados: De los 376 artículos originales analizados, 238 (63 por ciento) corresponden al primer período (1989-1994) y 138 (37 por ciento) al segundo período (1994-1999). El 59 por ciento eran estudios retrospectivos, el 39 por ciento prospectivos y el 2 por ciento tras la lectura no podíamos determinar si habían sido prospectivos o retrospectivos. En 214 artículos (57 por ciento) solo se utilizó estadística descriptiva (porcentajes) y en los 162 restantes (43 por ciento) se emplearon una o más de una técnica estadística (AU)

Ensayos clínicos publicados en la revista Rehabilitación entre los años 1989-1999 / Clinical trials published in the Rehabilitation journals between 1989-1999

Objetivos: Identificar y describir los ensayos clínicos aleatorizados, publicados en la revista Rehabilitación entre los años 1989-1999. Métodos: Todos los artículos originales publicados en ese período, fueron revisados por dos investigadores independientes y se distribuyeron en cinco grupos: Ensayos Clínicos, estudios básico-experimentales con animales de laboratorio, epidemiológicos, clínico-diagnósticos y otros. Se realizó una descripción de los ensayos clínicos (estudios experimentales en seres humanos). Resultados: Se identificaron 376 artículos originales, de los cuales 44 (12 por ciento) eran del grupo ensayo clínico, 13 (3 por ciento) investigación básica-experimental con animales de laboratorio, 256 (58 por ciento) epidemiológicos, 42 (11 por ciento) clínico-diagnóstico y 21 (6 por ciento) incluidos en otros. El 60 por ciento pertenecen al primer período y el 40 por ciento al segundo. Aleatorizado 20 por ciento, controlado 43 por ciento, enmascaramiento 9 por ciento, consentimiento informado 5 por ciento, con fármacos el 25 por ciento, más de 50 participantes el 30 por ciento. Conclusión: Se realizan y publican pocos ensayos clínicos en nuestra especialidad y encontramos graves deficiencias en la información comunicada (AU)

Geometrical structure of yttrium and metal-bromine complexes in solution: limitations of extended X-ray absorption fine structure analysis (EXAFS).

An extensive study on the appearance of multi-electron features in the X-ray absorption spectra of several yttrium(III)-based compounds has been performed. The existence of a multi-electron transition of non-negligible intensity within the extended X-ray absorption fine structure (EXAFS) region of the Y K-edge spectra has been proven. The impact of such features in the EXAFS analysis is made evident for aqueous solutions of YBr3 x 6H2O in liquid and glassy states in the concentration range 0.005-2.0 M, in which this transition induces an overestimation in the coordination numbers derived from EXAFS. We have performed theoretical computation of cross-sections for the double-electron processes at the K-edge of both Y and Br. These computations have been applied to the experimental EXAFS K-edge spectra of both Y and Br in several solids and in aqueous solutions. While in the case of Y K-edge spectra the presence of such multi-electron transitions was seen to seriously affect the standard EXAFS analysis, its influence in the case of Br K-edge spectra was determined to be negligible.

Importance of multiple-scattering phenomena in XAS structural determinations of [Ni(CN)4]2- in condensed phases.

A quantitative analysis of the XAS spectra of the tetracyanonickelate complex [Ni(CN)4]2- has been carried out. The simultaneous study of the EXAFS and XANES regions yielded complementary information regarding the geometric and electronic structures of the complex. XANES spectra were modeled by applying recently developed self-consistent, full multiple-scattering algorithms in the FEFF8 code (version 8 x 34). XANES spectra for clusters of different sizes (from 9 to 125 atoms) were computed and compared with experimental spectra. This region of the spectra was proportional to a broadened Ni p-density of states diagram above the Fermi level. Although the main features of the XANES spectra were reasonably reproduced by computations, the weak dependence of the theoretical spectra on cluster size contrasts with the close similarity between the experimental spectra of the solid and solution systems. Because of the special geometry of the complex, calculations with polarized light parallel and perpendicular to the molecular plane were carried out, yielding a reasonable reproduction of the experimental data from another report for cluster sizes equal to or higher than 45 atoms. The highly symmetric square planar structure of the complex was found to be responsible for the unusual amplitude of the multiple-scattering (MS) contributions to the EXAFS spectra. Spectra in this region were fitted using the FEFFIT EXAFS analysis program, taking into account only the MS paths that simultaneously have both a high amplitude, as calculated with the ab initio code FEFF, and a small Debye-Waller factor, as estimated by the independent-vibration approximation model. Fitting results yielded very similar structures for the Ni2+ complex in the solid state and in solution, though the larger Debye-Waller factors found for the solid suggest higher static disorder in this state.