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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparative study of electron cyclotron resonance (ECR) and radio frequency (rf) plasma as a nitrogen source for molecular-beam epitaxy GaN was carried out. The effects of differences in the excited nitrogen species on the optical signals during GaN growth were investigated by 77 K photoluminescence (PL). For epitaxial layers grown at optimum V/III ratio using ECR and rf plasma, the PL spectra were dominated by near band-edge emission at 3.47 eV. However, when the V/III ratio was less than the optimum V/III ratio, a broad emission band at about 3.2–3.3 eV was observed in the PL spectrum for the GaN epilayer grown using rf plasma, while in the case of growth using ECR plasma, a deep level emission at about 2.2 eV appeared. These characteristics in PL spectra can used to identify differences in the chemical species in the nitrogen plasma. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-0832
    Keywords: Versicolorin A ; hemiacetal ; reductase ; Aspergillus ; versicolorin C ; dihydrosterigmatocystin ; aflatoxin G2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Versicolorin A hemiacetal was converted to versicolorin C in cell-free systems fromAspergillus parasiticus. The rate of reaction catalyzed by the 35–70% ammonium sulfate fraction was 0.43 nmol min−1 mg−1 with NADPH as cosubstrate and 0.17 nmol. min−1 mg−1 with NADH at 25°C at pH 7.4. The product from incubation of 17-hdyroxy-16,17-dihydrosterigmatocystin with the 35–70% ammonium sulfate fraction and NADPH was a polar compound which was converted to dihydrosterigmatocystin by 0.4 M HCl. The olar comound is proposed to be the 14,17-hydrated open-chain derivative of dihydrosterigmatocystin. Aflatoxin G2a was also reduced in this system to a polar product tentatively identified as the 13,16-hydrated open-chain derivative of AFG2. The reductase activity may be involved in the formation of reduced intermediates and aflatoxins in cultures ofA. parasiticus.
    Type of Medium: Electronic Resource
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