Effects of Vacancies near Substitutional Implants on Trapping and Desorption of Helium - A Simulation

Trapping of He by vacancies and drainage of He from substitutional implants (Ag and Kr in W) to nearby vacancies are investigated using static lattice calculations. The calculations indicate that drainage of He will occur to vacancies within a radius of 2.5 lattice units from the implant. Furthermore the trapping probability of substitutional and interstitial random walkers on a bcc lattice by substitutional traps or vacancies is calculated. When implantation-produced vacancies are present in the vicinity of the observed trap a shielding effect occurs. Trapping constants are calculated with two random walk models for both the unshielded and the shielded defect. For the latter several configurations were taken. The results show that shielding of a defect by one vacancy at a distance of three lattice units leads already to a reduction of He trapping by that defect of 30% to 40%.

Multidrug-resistant tuberculosis in prison inmates, Azerbaijan.

In a tuberculosis (TB) program in the Central Penitentiary Hospital of Azerbaijan, we analyzed 65 isolates of Mycobacterium tuberculosis by IS6110-based restriction fragment-length polymorphism (RFLP) and spoligotyping. From 11 clusters associated with 33 patients, 31 isolates had an IS6110-based banding pattern characteristic of the Beijing genotype of M. tuberculosis. In addition, 15 M. tuberculosis isolates with similar RFLP patterns constituted a single group by spoligotyping, matching the Beijing genotype. Multidrug resistance, always involving isoniazid and rifampin, was seen in 34 (52.3%) of 65 isolates, with 28 belonging to the Beijing genotype

p-type delta-doped layers in silicon: structural and electronic properties

We report on the properties of p-type delta-doped layers prepared in molecular beam epitaxy-Si by growth interruption and evaporation of elemental B. Secondary-ion mass spectrometry measurements at several primary ion energies have been used to show that the full width at half maximum is ~2 nm. Hall measurements confirm that the layers are completely activated at 300 K with a mobility of 30±5 cm2/V s for a carrier density of (9±2)×1012 cm−2. At temperatures below 70 K nonmetallic behavior is observed which we have attributed to conduction between impurity states. It is concluded that the critical acceptor separation for the Mott metal-insulator transition in this system is significantly less than the value found in uniformly doped Si:B

A Catalogue and Analysis of Local Galaxy Ages and Metallicities

We have assembled a catalogue of relative ages, metallicities and abundance ratios for about 150 local galaxies in field, group and cluster environments. The galaxies span morphological types from cD and ellipticals, to late type spirals. Ages and metallicities were estimated from high quality published spectral line indices using Worthey & Ottaviani (1997) single stellar population evolutionary models. The identification of galaxy age as a fourth parameter in the fundamental plane (Forbes et al. 1998) is confirmed by our larger sample of ages. We investigate trends between age and metallicity, and with other physical parameters of the galaxies, such as ellipticity, luminosity, and kinematic anisotropy. We demonstrate the existence of a galaxy age-metallicity relation similar to that seen for local galactic disk stars, whereby young galaxies have high metallicity, while old galaxies span a large range in metallicities. We also investigate the influence of environment and morphology on the galaxy age and metallicity, especially the predictions made by semi-analytic hierarchical clustering models (HCM). We confirm that non-cluster ellipticals are indeed younger on average than cluster ellipticals as predicted by the HCM models. However we also find a trend for the more luminous galaxies to have a higher [Mg/Fe] ratio than the lower luminosity galaxies, which is opposite to the expectation from HCM models.Comment: 17 pages, Latex, 16 figures, 4 tables, submitted to MNRA

Quantitative thermal desorption spectrometry of noble gases in solids

Applied Science