Oxygen vacancies versus fluorine at CeO2(111): a case of mistaken identity?

We propose a resolution to the puzzle presented by the surface defects observed with STM at the (111) surface facet of CeO 2 single crystals. In the seminal paper of Esch et al. [Science 309, 752 (2005)] they were identified with oxygen vacancies, but the observed behavior of these defects is inconsistent with the results of density functional theory (DFT) studies of oxygen vacancies in the literature. We resolve these inconsistencies via DFT calculations of the properties of both oxygen vacancies and fluorine impurities at CeO2(111), the latter having recently been shown to exist in high concentrations in single crystals from a widely used commercial source of such samples. We find that the simulated filled-state STM images of surface-layer oxygen vacancies and fluorine impurities are essentially identical, which would render problematic their experimental distinction by such images alone. However, we find that our theoretical results for the most stable location, mobility, and tendency to cluster, of fluorine impurities are consistent with experimental observations, in contrast to those for oxygen vacancies. Based on these results, we propose that the surface defects observed in STM experiments on CeO2 single crystals reported heretofore were not oxygen vacancies, but fluorine impurities. Since the similarity of the simulated STM images of the two defects is due primarily to the relative energies of the 2p states of oxygen and fluorine ions, this confusion might also occur for other oxides which have been either doped or contaminated with fluorine.

[Tumors of the appendix]

Neoplasms involving the vermiform outgrowth are among the rarely met with conditions, accounting for 0.1 to 0.5 per cent of all gastrointestinal tract tumors. This is a report on personal observation of three patients presenting tumors of the appendix, diagnosed over the period 1987 to 1995. As shown by the results, tumors of the appendix run a clinical course characterized by two distinct forms: clinical picture of acute appendicitis--two cases, and clinical picture of tumor of the colon--one case. It is underscored that intraoperative diagnosis is extremely difficult. The diagnosis is usually made by pathoanatomist, while the therapeutic approach and operative tactics are determined on the ground of histomorphological study results and local operative status. The scope of operative intervention includes appendectomy and right hemicolectomy.

A method for turbulent noise estimation in voiced signals

In this article a new acoustic parameter is introduced and it is shown that it may serve as an indicator of laryngeal function. It is termed the turbulent noise index (TNI) and is defined as 100(1 - Rmax), where Rmax is the mean value of the maximum correlation coefficient between each pair of consecutive glottal cycles in the voiced signal. A method for its calculation is described. Experiments with synthetic and natural voice signals show that TNI is almost independent of frequency modulation noise and amplitude modulation noise. TNI is compared with HNR (harmonic-to-noise ratio) and NNE (normalised noise energy) which require high stationarity of the voice signal and are substantially affected by slow changes of frequency and amplitude. When the parameters HNR and NNE are used to discriminate between normal and pathological voices, the overlap area contains 21.5% and 23.5% of the total number of pathological voices, respectively. Using TNI, the normal and pathological voices overlap is 14.8% of the total number of pathological voices, i.e. compared to the other noise parameters TNI has a significant advantage as a diagnostic parameter.