1. Investigación

This article details the assessment process and evaluation results for two categories in the 8th Critical Assessment of Protein Structure Prediction experiment (CASP8). The domain prediction category was evaluated with a range of scores including the Normalized Domain Overlap score and a domain boundary distance measure. Residue-residue contact predictions were evaluated with standard CASP measures, prediction accuracy, and Xd. In the domain boundary prediction category, prediction methods still make reliable predictions for targets that have structural templates, but continue to struggle to make good predictions for the few ab initio targets in CASP. There was little indication of improvement in the domain prediction category. The contact prediction category demonstrated that there was renewed interest among predictors and despite the small sample size the results suggested that there had been an increase in prediction accuracy. In contrast to CASP7 contact specialists predicted contacts more accurately than the majority of tertiary structure predictors. Despite this small success, the lack of free modeling targets makes it unlikely that either category will be included in their present form in CASP9

This work describes the synthesis, structural characterization and electrical properties of solid solutions with the general formula Gd2Hf2−xBxO7, where B = Ti4+, Sn4+ and Zr4+. All samples were successfully prepared in ~ 30 h, via a mechanochemical reaction in a planetary ball mill, using the corresponding elemental oxides as starting chemicals. The XRD and Raman spectroscopy analysis of the title samples revealed that on firing at 1500 °C Hf4+ substitution by Sn4+ and Ti4+ produces better ordered pyrochlore structures and decreases the electrical conductivity of Gd2Hf2O7 by more than two orders of magnitude (from 2.7 × 10−4 at 700 °C to 8.71 × 10−7 and 1.12 × 10−6 Sm cm−1, for Gd2Sn2O7 and Gd2Ti2O7, respectively). By contrast, the Gd2Hf2−xZrxO7 system remains disordered with conductivity increasing by almost an order of magnitude and reaching a value for Gd2Zr2O7 of 1.55 × 10−3 Sm cm−1 at 700 °C, whereas the activation energy for oxygen migration decreases in both, the Sn- and Ti-containing systems, and increases slightly in the Zr-containing solid solution. These changes cannot be only explained when taking into account the cations size ratio criteria; the covalency of the metal bond plays also a key role in determining the structural characteristics and electrical properties of the title three systems.