Characterization to species level of Mycobacterium avium complex strains from human immunodeficiency virus-positive and -negative patients

Forty human clinical Mycobacterium avium-M. intracellulare complex strains isolated in Greece were characterized to the species level by PCR with three sets of primers specific for one or both species. M. avium predominated in both human immunodeficiency virus-positive and -negative patients, but the frequency of M. intracellulare isolation appeared to be higher in the latter.     

The effect of hydrogen on boron diffusion in SiO2

The diffusivity of boron in silicon dioxide may be increased by the introduction of hydrogen into the annealing atmosphere. In this paper we report on the diffusion characteristics of boron ion-implanted into thermally grown SiO₂. A sensitive technique was used in which the boron atoms redistributed into the substrate are characterized by electrical methods. The diffusivity of boron in thermal SiO₂ was measured over the temperature range of 950-1150°C with hydrogen partial pressure from 0 to 0.2 atm. It was found that the diffusion coefficient of boron in oxide at 1150° C increases as the square root of the hydrogen partial pressure. At fixed pressure the temperature dependence of the diffusion coefficient obeys a single-activation-energy exponential rule. At 0.1 atm partial pressure of H₂ the activation energy is 3.0 eV and the preexponential factor is 6 x 10⁵ [cm²/sec.].     

Quantification of historical dust exposures in the diatomaceous earth industry

Quantitative estimates of dust exposure in a diatomaceous earth (DE) mining and milling operation have been derived based on air sampling records for the period 1948-1988. A total of 6395 records was included in the analysis. Conversion of results obtained by particle counting, expressed as millions of particles per cubic feet (mppcf) of gravimetrically from a filter cassette and expressed as mg m-3 total, were converted to mg m-3 respirable dust using a conversion factor derived from data obtained during the same periods at the plant. Conversion factors were calculated as the average difference of means on the log scale in order to provide stable and consistent conversions and as a ratio of arithmetic means so that the results could be compared with similar studies. After converting the available data to mg m-3 respirable dust, geometric mean (geometric standard deviation) concentrations were 0.37 (2.43) during the 1950s and 0.17 (2.35) during later periods. Exposures were estimated using two linear models, one estimating the changes in concentration over time, and the other providing job-specific mean exposures during the more recent period. Extrapolation of the estimates to periods prior to the availability of any data was done using a subjectively-determined scaling factor. The average estimated respirable dust concentrations for 135 jobs were 3.55 (+/-1.25), 1.37 (+/-0.48), 0.47 (+/-0.16) and 0.29 (+/-0.10) mg m-3 prior to 1949, 1949-1953, 1954-1973 and 1974-1988, respectively. Despite the limitations of the available data, the estimation procedures used are expected to provide reasonable quantitative estimates of silica-containing dust exposure for subsequent exposure-response analyses.     

Blue LED growth from 2 inch to 8 inch

Growth of blue InGaN based LED structures on sapphire wafers from 2 inch to 8 inch in diameter was investigated using the Veeco K465 MOCVD platform. Our results indicate that the same pressure,rotation rate and hydride flows can be used for all wafer sizes. AFM and X-ray studies reveal that all wafer sizes have comparable high-quality crystallinity and defect levels for GaN and InGaN/GaN MQW growth. Although the larger diameter wafers exhibit larger wafer bow due to lattice and thermal mismatch,with proper ...