Site-Selective X-Ray-Excited Thermoluminescence and Fluorescence of Zro2 from the Local Structure of the Zr L3 Edge

The results presented are an investigation of the local structure of a ZrO2 sample using site-selective x-ray, excited fluorescence, and thermoluminescence methods. The experimental results demonstrate that fluorescence and thermoluminescence yield an x-ray absorption near-edge structure at the Zr L3 edge that depends on the x-ray photon energy associated with the transition from a Zr 2p3/2 occupied state to a 4d unoccupied state. Although conventional fluorescence measured by x-ray absorption yields the average structure over all Zr, the thermoluminescence yield measured by x-ray absorption provides information on the local structure of Zr only after a long period of phosphorescence. Furthermore, the x-ray absorption of the ZrO2 sample leads to competitive fluorescence and phosphorescence owing to deexcitation of a core hole

Influence of oxygen on the crystalline : amorphous transition in gallium nitride films

Oxygen is a common impurity in nitride-based materials that affects the properties of technologically important materials such as gallium nitride semiconductors. In this work, the influence of oxygen on the structural evolution of GaN films is investigated using near-edge X-ray absorption fine structure (NEXAFS). The combined spectra of Ga L3-edge, N K-edge, and O K-edge indicate that the gallium coordination, formed by a mixture of oxide and nitride bonds, is directly dependent on the concentration of oxygen in the films. Below 24 atom % oxygen, gallium atoms are tetrahedrally coordinated within the films, while at higher concentrations the octahedral environment persists

Structural order in oxygenated gallium nitride films

Structural order in nanocrystalline, oxygenated GaN thin films (thickness ~ 500 nm) has been examined. The films were grown using low-pressure chemical vapor deposition of (CH₃)₂GaN₃ single source precursor. During deposition, residual oxygen from the vacuum environment was incorporated into the films. Photoemission spectroscopy indicated that oxygen mainly substituted nitrogen during deposition. Long-range X-ray diffraction indicated that the films were oriented along the hexagonal (002) direction when the incorporated concentration of oxygen was lower than 25 atomic % (at. %). Above this, the films were amorphous. The results of angle-dependent near-edge X-ray absorption fine structure facilitated the formation of a short-range structural model, which explained the influences of the oxygen concentration on the long-range order in the films. These studies are useful in understanding the structural evolution in doped-nitride films

groESL Sequence Determination, Phylogenetic Analysis, and Species Differentiation for Viridans Group Streptococci

The full-length sequences of the groESL genes (also known as cpn10/60) of Streptococcus anginosus, Streptococcus constellatus, Streptococcus gordonii, and Streptococcus sanguis and the near full-length sequence of the groESL genes of Streptococcus intermedius, Streptococcus bovis, Streptococcus mitis, Streptococcus mutans, Streptococcus oralis, and Streptococcus salivarius were determined. The lengths of the groES genes from the 10 species listed above ranged from 282 to 288 bp, and the full-length sequences of groEL determined for 4 species (S. anginosus, S. constellatus, S. gordonii, and S. sanguis) revealed that each was 1,623 bp. The intergenic region (spacer) between the groES and groEL genes varies in size (15 to 111 bp) and sequence between species. The variation of the groES sequences among the species tested was greater (62.1 to 95.1% nucleotide sequence identities) than that of the groEL sequences (77.2 to 95.2% nucleotide sequence identities). Phylogenetic analysis of the groES and groEL genes yielded evolutionary trees similar to the tree constructed by use of the 16S rRNA gene. The intraspecies variation of the spacer was minimal for clinical isolates of some species. The groESL sequence data provide an additional parameter for identification of viridans group streptococcal species

High Prevalence of Antimicrobial Resistance in Rapidly Growing Mycobacteria in Taiwan

An increasing number of clinical isolations of rapidly growing mycobacteria (RGM) at the National Taiwan University Hospital were noted from 1992 to 2001. Broth microdilution MICs of 15 antimicrobial agents were determined for 200 clinical isolates of RGM, including the Mycobacterium fortuitum group (69 isolates), M. chelonae (39 isolates), and M. abscessus (92 isolates). Our results showed that the resistance rates of these isolates to the currently available agents were remarkably high. Amikacin was active against nearly all RGM isolates. Clarithromycin was usually active against M. abscessus (79% susceptibility) and the M. fortuitum group (65% susceptibility). The majority of M. fortuitum group isolates were susceptible to ciprofloxacin (62%) and imipenem (61%). The susceptibilities to other conventional anti-RGM agents of these isolates were poor but differed markedly by species. The newer fluoroquinolones (levofloxacin, moxifloxacin, and gatifloxacin) and meropenem showed better in vitro activities against the M. fortuitum group isolates than against the other two species of RGM. Linezolid had fairly good activity against these RGM isolates, particularly against M. chelonae isolates (82% susceptible). Telithromycin had poor activity against these RGM isolates (the MICs at which 50% of the isolates tested are inhibited [MIC(50)s] were 32 to 64 μg/ml, and the MIC(90)s were >64 μg/ml)