Accelerating atomic structure search with cluster regularization.

We present a method for accelerating the global structure optimization of atomic compounds. The method is demonstrated to speed up the finding of the anatase TiO2(001)-(1 × 4) surface reconstruction within a density functional tight-binding theory framework using an evolutionary algorithm. As a key element of the method, we use unsupervised machine learning techniques to categorize atoms present in a diverse set of partially disordered surface structures into clusters of atoms having similar local atomic environments. Analysis of more than 1000 different structures shows that the total energy of the structures correlates with the summed distances of the atomic environments to their respective cluster centers in feature space, where the sum runs over all atoms in each structure. Our method is formulated as a gradient based minimization of this summed cluster distance for a given structure and alternates with a standard gradient based energy minimization. While the latter minimization ensures local relaxation within a given energy basin, the former enables escapes from meta-stable basins and hence increases the overall performance of the global optimization.

Step edge structures on the anatase TiO2 (001) surface studied by atomic-resolution TEM and STM.

Low-coordinate surface sites, such as those present on high-index step edges, often exhibit chemical reactivity that markedly differs from more close-packed facets. To understand the site-specific reactivity, insight into the three-dimensional atomic arrangement of step edges is needed. Here, we employ atomic-resolution transmission electron microscopy (TEM) of nanoparticles in combination with scanning tunneling microscopy (STM) of a single crystal surface to uncover the structure of prevalent step edges on the anatase TiO2 (001) surface.

[Efficacy of sodium carboxymethylcellulose in the treatment of dry eye syndrome]. / Eficacia de la carboximetilcelulosa sódica para el tratamiento del síndrome del ojo seco.

AIM: To assess the efficacy of sodium carboxymethylcellulose in the treatment of dry eye. MATERIAL AND METHODS: We carried out a prospective, randomized, masked-observer, control/problem group, single-center clinical assay during a period of 12 months in 19 patients that presented mild or moderate forms of dry eye. Patients were clinically evaluated each 3 months and treated with a 0.5% isotonic solution of sodium carboxymethylcellulose (CMC) or balanced salt solution. Subjective symptoms, functional tests and conjunctival impression cytology were performed according preexistent schedule study visits. To compare data between groups chi squared (chi2) analysis was applied. RESULTS: We observed a significant (p<0.05) decrease in the frequency of subjective symptoms and a significant (p<0.05) improvement of tearfilm interface stability after CMC treatment. There was a tendency to improve the degree of corneal surface wettability and the tearfilm integrity with higher percentage improvements in the CMC group compared to controls. Improved baseline values in at least one of the objective functional tests carried out (p<0.05) was also observed in an elevated percentage of patients in the CMC group (83.3%) compared with controls (34%). Furthermore, we observed a tendency to diminish the frequency of associated subjective symptoms after treatment. Conjunctival impression cytology did not provide significant differences related with therapeutic response. CONCLUSIONS: The results show a significant beneficial effect of CMC to improve clinical parameters in mild and moderate forms of dry eye.