Sub-surface Oxygen and Surface Oxide Formation at Ag(111): A Density-functional Theory Investigation

To help provide insight into the remarkable catalytic behavior of the oxygen/silver system for heterogeneous oxidation reactions, purely sub-surface oxygen, and structures involving both on-surface and sub-surface oxygen, as well as oxide-like structures at the Ag(111) surface have been studied for a wide range of coverages and adsorption sites using density-functional theory. Adsorption on the surface in fcc sites is energetically favorable for low coverages, while for higher coverage a thin surface-oxide structure is energetically favorable. This structure has been proposed to correspond to the experimentally observed (4x4) phase. With increasing O concentrations, thicker oxide-like structures resembling compressed Ag2O(111) surfaces are energetically favored. Due to the relatively low thermal stability of these structures, and the very low sticking probability of O2 at Ag(111), their formation and observation may require the use of atomic oxygen (or ozone, O3) and low temperatures. We also investigate diffusion of O into the sub-surface region at low coverage (0.11 ML), and the effect of surface Ag vacancies in the adsorption of atomic oxygen and ozone-like species. The present studies, together with our earlier investigations of on-surface and surface-substitutional adsorption, provide a comprehensive picture of the behavior and chemical nature of the interaction of oxygen and Ag(111), as well as of the initial stages of oxide formation.Comment: 17 pages including 14 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Screening Low-Income Women of Reproductive Age for Cardiovascular Disease Risk Factors

Identifying and treating chronic diseases, their precursors, and other cardiovascular disease (CVD) risk factors during family planning visits may improve long-term health and reproductive outcomes among low-income women. A cross-sectional study design was used to describe the prevalence of chronic diseases (hypertension, high cholesterol, and diabetes), their precursors (pre-hypertension, borderline high cholesterol, and pre-diabetes), and related CVD risk factors (such as obesity, smoking, and physical inactivity) among low-income women of reproductive age

Pure hydroxyapatite as a substitute for enamel in erosion experiments.

OBJECTIVES The study evaluated the suitability of pure crystalline hydroxyapatite (HA) as a substitute for human (H) and bovine (B) enamel in erosion experiments. METHODS Human and bovine enamel and hydroxyapatite specimens (n = 18 each) were submitted to demineralisation by HCl at pH values of 3.0, 2.6 and 2.0 (1.0, 2.5, and 10 mmol/l concentration). Specimens were eroded in a superfusion chamber for 7 min (flow rate: 1 μl/s). Multiple fluid samples were taken per specimen throughout the exposure period. The dissolved calcium content was measured using a colorimetric assay with Arsenazo III reagent, to serve as surrogate for erosive substance loss. Additionally, erosive tissue loss was quantified by profilometry. Differences in erosive substance loss were assessed by the Kruskal-Wallis and Conover's posthoc test. RESULTS Good agreement in erosive substance loss between HA and human specimens was found at pH 2.6, as no statistically significant difference and considerable overlap of their respective interquartile ranges was observed. At pH 2.0 and 3.0, a statistically significant difference between HA and human and bovine enamel was determined. HA consistently tended to have lower mean dissolution rates, with a maximum deviation from human enamel of -16% at pH 3. It displayed lower specimen variability with an average coefficient of variation of 17%, compared to 25% (H) and 25% (B), respectively. CONCLUSIONS Crystalline hydroxyapatite may not be suitable for full substitution of biologic enamel in erosion experiments focusing on absolute measurement values, but is useful for establishing consistent relative trends between erosive agents due to biosimilar erosion behavior and lower experimental variability. This is especially true for preliminary studies where approval for use of biological samples is restricted. CLINICAL SIGNIFICANCE Crystalline hydroxyapatite is a useful substitute of human or bovine enamel in experiments studying chemical aspects of dental erosion

False consensus in situational judgment tests: What would others do?

We introduce an alternative response instruction to reduce the fakability of situational judgment tests. This novel instruction is based on the false consensus effect, a robust social psychological bias whereby people infer that the majority of other people's thoughts, attitudes, and behaviors are aligned with their own. In four studies, including both field and laboratory data (total N = 882), we demonstrate that participants show a false consensus bias when asked what others would do in situational judgment tests. Furthermore, the situational judgment test based on the false consensus effect turned out to relatively difficult to be fake, and produced scores that were meaningfully correlated with conceptually related traits, as well as both self-reported and behavioral outcomes