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  • Articles: DFG German National Licenses  (2)
  • 1985-1989  (2)
  • 61.70  (1)
  • Chromium
  • Cotransport
  • Electron microscopy
  • Polymer and Materials Science
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  • Articles: DFG German National Licenses  (2)
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  • 1
    ISSN: 1432-0630
    Keywords: 61.70 ; 78.30 ; 72.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Shallow thermal donors are electrically active oxygen-related thermally formed defects observed in oxygen-rich silicon annealed between 300 ° and 600 ° C. Seven donors have been identified with an average central-cell correction of only 5 meV. In view of their molecule-like nature this close agreement to the effective mass theory prediction for a hydrogen-like donor in silicon is of interest. It is shown that these centres are not correlated to the residual impurities phosphorus and boron but rather to the presence of nitrogen. Nitrogen-doped oxygen-rich samples show increased shallow thermal donor growth and a reduction in the growth of other oxygen-related donors in comparison to normally nitrogen-undoped oxygen-rich samples. A reduction in shallow thermal donor concentration at high nitrogen concentrations is reported.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Bradyrhizobium ; Electron microscopy ; Mutants ; Nitrogen fixation ; Nodulation ; Soybean ; Symbiosis ; Transposon Tn5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genome of the slow-growing Bradyrhizobium japonicum (strain 110) was mutagenized with transposon Tn5. A total of 1623 kanamycin/streptomycin resistant derivatives were screened in soybean infection tests for nodulation (Nod) and symbiotic nitrogen fixation (Fix). In this report we describe 14 strains possessing a stable, reproducible Nod+Fix- phenotype. These strains were also grown under microaerobic culture conditions to test them for free-living nitrogen fixation activity (Nif). In addition to strains having reduced Fix and Nif activities, there were also strains that had reduced symbiotic Fix activity but were Nif+ ex planta. Analysis of the genomic structure revealed that the majority of the strains had a single Tn5 insertion without any further apparent physical alteration. A few strains had additional insertions (by Tn5 or IS50), or a deletion, or had cointegrated part of the vector used for Tn5 mutagenesis. One of the insertions was found in a known nif gene (nifD) whereas all other mutations seem to affect different, hitherto unknown genes or operons. Several mutant strains had an altered nodulation phenotype, inducing numerous, small, widely distributed nodules. Light and electron microscopy revealed that most of these mutants were defective in different stages of bacteroid development and/or bacteroid persistence. The protein patterns of the mutants were inspected by two-dimensional gel electrophoresis after labelling microaerobic cultures with l-(35S)methionine. Of particular interest were mutants lacking a group of proteins the synthesis of which was known to be under oxygen control. Such strains can be regarded as potential regulatory mutants.
    Type of Medium: Electronic Resource
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