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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 316 (1985), S. 424-427 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] At the time of the MERIT, intensive campaign, the IRIS (international radio interferometric surveying4) project was already operating 24-h VLBI observing sessions every 5 days to monitor polar motion and ?t?. To determine ?t? on the intervening 4 days, 1-h observing sessions were scheduled each day ...
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  • 2
    ISSN: 1617-4623
    Keywords: Transposable elements ; Mutation ; Mutator ; Maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The mutagenic activity of the maize transposable element system Mutator can be lost by outcrossing to standard, non-Mutator lines or by repetitive intercrossing of genetically diverse Mutator lines. Lines losing Mutator mutagenic activity in either manner retain high copy numbers (10–15 per diploid genome) of the Mutator-associated Mu transposable elements. Frequent transposition of Mu1-related elements is observed only in active Mutator lines, however. The loss of Mutator activity on intercrossing is correlated with an increase in the copy number of Mu1-like elements to 40–50 per diploid genome, implying a self-encoded or self-activated negative regulator of Mu1 transposition. The outcross loss of Mutator activity is only weakly correlated with a low Mu element copy number and may be due to the loss of a positive regulatory factor encoded by a subset of Mu1-like elements. Transposition of Mu elements in active Mutator lines generates multiple new genomic positions for about half the elements each plant generation. The appearance of Mu1-like elements in these new positions is not accompanied by equally high germinal reversion frequencies, suggesting that Mu1 may commonly transpose via a DNA replicative process.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The vein-type gold deposits of middle to late Archean age constitute one of the major sources of gold production in the world. These deposits are highly diverse in character, but are invariably found in proximity to mafic and ultramafic volcanic rocks, and closely associated with tectonically disturbed zones, or ‘breaks’, in the ancient crust. Using the Larder Lake ‘break’ of northern Ontario and Quebec as a model, a general theory of genesis for such deposits is proposed. The Larder Lake ‘break’ is of linear configuration, up to four miles wide, and extending over a distance of approximately 150 miles. Many rich and extensive vein-type gold deposits are associated with it. This ‘break’ is recognized as a highly folded and faulted, dominantly sedimentary stratigraphic unit, formed as part of the development of the Blake River geosyncline of the Abitibi greenstone belt. Faulting is pervasive within the ‘break’ but it is non-continuous. Under an oxygen-poor, somewhat acidic weathering regime believed extant in Archean time, gold and associated constituents, derived as weathering products from mafic and ultramafic volcanics, appear to have been concentrated as solutions and sols in muddy surficial accumulations along a paleo-continental margin. On transfer to a shallow marine environment, the gold-bearing solutions became concentrated mainly as cherty and pyritic evaporitic residues. These residues, infolded and variably metamorphosed and remobilized during ensuing geosynclinal development, formed the numerous and apparently heterogeneous gold deposits of the Larder Lake ‘break’. Mode of redistribution of gold-bearing residues and metamorphism of their host rocks varies widely. In mild form, little vein development is present and original sedimentary features of the host rock are often preserved. In more extreme cases, true hydrothermal veining is evident and complete recrystallization of the host rock has taken place, sometimes to the extent of formation of a melt with intrusive capabilities. In any case, the gold and related vein constituents remain closely associated with the primary host material and alteration effects are largely derived from the recrystallization of original host rock constituents. The suggested mode of genesis clarifies the relationship between various types of ‘break’-related, vein-type gold deposits and offers an explanation of the complex stratigraphy and structure of the ‘break’ environment. It also suggests a penecontemporaneous relationship between the Larder Lake ‘break’ and other auriferous ‘breaks’, of varying configuration, within the Superior Province of the Canadian Shield. The concept can be used advantageously in exploration for new ‘breaks’ and new deposits.
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  • 6
    Publication Date: 2019-07-12
    Description: The 5.5 years of VLBI observations primarily collected under project IRIS are used to search for evidence of the free-core nutation (FCN). The observations are consistent with an irregular excitation process, and a model which assumes a step excitation in the FCN amplitude to about 2.0 milliseconds of arc in late 1985 fits the data well. Theoretical analysis appears to rule out the strong Mexican earthquake of September 19, 1985, as a cause of the excitation.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 949-952
    Format: text
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  • 7
    Publication Date: 1986-07-01
    Description: The vein-type gold deposits of middle to late Archean age constitute one of the major sources of gold production in the world. These deposits are highly diverse in character, but are invariably found in proximity to mafic and ultramafic volcanic rocks, and closely associated with tectonically disturbed zones, or ‘breaks’, in the ancient crust. Using the Larder Lake ‘break’ of northern Ontario and Quebec as a model, a general theory of genesis for such deposits is proposed. The Larder Lake ‘break’ is of linear configuration, up to four miles wide, and extending over a distance of approximately 150 miles. Many rich and extensive vein-type gold deposits are associated with it. This ‘break’ is recognized as a highly folded and faulted, dominantly sedimentary stratigraphic unit, formed as part of the development of the Blake River geosyncline of the Abitibi greenstone belt. Faulting is pervasive within the ‘break’ but it is non-continuous. Under an oxygen-poor, somewhat acidic weathering regime believed extant in Archean time, gold and associated constituents, derived as weathering products from mafic and ultramafic volcanics, appear to have been concentrated as solutions and sols in muddy surficial accumulations along a paleo-continental margin. On transfer to a shallow marine environment, the gold-bearing solutions became concentrated mainly as cherty and pyritic evaporitic residues. These residues, infolded and variably metamorphosed and remobilized during ensuing geosynclinal development, formed the numerous and apparently heterogeneous gold deposits of the Larder Lake ‘break’. Mode of redistribution of gold-bearing residues and metamorphism of their host rocks varies widely. In mild form, little vein development is present and original sedimentary features of the host rock are often preserved. In more extreme cases, true hydrothermal veining is evident and complete recrystallization of the host rock has taken place, sometimes to the extent of formation of a melt with intrusive capabilities. In any case, the gold and related vein constituents remain closely associated with the primary host material and alteration effects are largely derived from the recrystallization of original host rock constituents. The suggested mode of genesis clarifies the relationship between various types of ‘break’-related, vein-type gold deposits and offers an explanation of the complex stratigraphy and structure of the ‘break’ environment. It also suggests a penecontemporaneous relationship between the Larder Lake ‘break’ and other auriferous ‘breaks’, of varying configuration, within the Superior Province of the Canadian Shield. The concept can be used advantageously in exploration for new ‘breaks’ and new deposits. ©1986 Springer-Verlag
    Print ISSN: 0026-4598
    Electronic ISSN: 1432-1866
    Topics: Geosciences
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  • 8
    Publication Date: 1986-10-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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