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  • 1
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The pre-Cambrian granulites of Enderby Land Antarctica, contain coexisting spinel-quartz, sapphirine-quartz, hypersthene-sillimanite-quartz and osumilite on a regional extent. Osumilite is present in a variety of mineral assemblages, most of which are documented in granulites for the first time. The mineral assemblages, reactions and compositional zoning in minerals are discussed in terms of continuous and discontinuous reactions in response to changing conditions of metamorphism. The development of many of the mineral coronas can be explained by continuous rather than discontinuous reactions, due to the effects of Mg-Fe and (Mg,Fe)-2Al exchange equilibria with decreasing temperature. The highest P-T conditions of metamorphism (8–10 kb, 900 °–980 ° C, Ellis, in preparation) were beyond the stability limit of coexisting garnet-cordierite. Secondary cordierite has developed through a large number of mineral reactions in response to cooling of these granulites. A theoretical analysis of the phase relations involving osumilite in the chemical systems K2O-MgO-Al2O3-SiO2 and K2O-MgO-FeO-Al2O3-SiO2 is presented. In the pure Mg-system the lower temperature stability limit of Mg-osumilite is inferred to be defined with increasing pressure by the reactions Os→Cd+En+Kfeld+Qtz, Os→Sa+En+Kfeld+Qtz, Os→Sill+En+Kfeld+Qtz. In iron-bearing systems an important reaction involving osumilite is Os+Gt→Cd+Hy+Kfeld+Qtz. At moderate temperatures and pressures, osumilite is limited to rocks which lie on the Mg-rich side of the Cd-Hy stable tie line on an AFM diagram. At higher pressures and temperatures osumilite occurs in a widerrange of rock compositions because of the stability of coexisting garnet and osumilite. Petrographic data, as well as chemographic relations indicate that for many common rock compositions, garnet, cordierite, hypersthene, sapphirine and sillimanite cannot coexist with both osumilite and K-feldspar.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Key words Nitrogen-fixing bacteria ; Stringent response ; ppGpp ; RelA ; ATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Following amino acid or ammonium starvation, ppGpp is accumulated by Rhizobium meliloti strain 1021 but not by R. meliloti strain 41 or Rhizobium tropici. Azorhizobium caulinodans ORS571 produced ppGpp following amino acid deprivation; however, the free-living nitrogen-fixing bacteria Azotobacter vinelandii and Azomonas agilis did not produce ppGpp. Western blot analysis using anti-RelA antibody demonstrated that R. meliloti strain 1021, Azotobacter vinelandii and Azorhizobium caulinodans cross-reacted under conditions that detected RelA in Escherichia coli CF1648. Cross-reaction was not observed in R. meliloti strain 41, R. tropici, or Azomonas agilis. All strains that accumulated ppGpp also produced high intracellular levels of ATP.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0021-9991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2015-11-27
    Description: The increasingly dense coverage of Europe with broad-band seismic stations makes it possible to image its lithospheric structure in great detail, provided that structural information can be extracted effectively from the very large volumes of data. We develop an automated technique for the measurement of interstation phase velocities of (earthquake-excited) fundamental-mode surface waves in very broad period ranges. We then apply the technique to all available broad-band data from permanent and temporary networks across Europe. In a new implementation of the classical two-station method, Rayleigh and Love dispersion curves are determined by cross-correlation of seismograms from a pair of stations. An elaborate filtering and windowing scheme is employed to enhance the target signal and makes possible a significantly broader frequency band of the measurements, compared to previous implementations of the method. The selection of acceptable phase-velocity measurements for each event is performed in the frequency domain, based on a number of fine-tuned quality criteria including a smoothness requirement. Between 5 and 3000 single-event dispersion measurements are averaged per interstation path in order to obtain robust, broad-band dispersion curves with error estimates. In total, around 63,000 Rayleigh- and 27,500 Love-wave dispersion curves between 10 and 350 s have been determined, with standard deviations lower than 2 per cent and standard errors lower than 0.5 per cent. Comparisons of phase-velocity measurements using events at opposite backazimuths and the examination of the variance of the phase-velocity curves are parts of the quality control. With the automated procedure, large data sets can be consistently and repeatedly measured using varying selection parameters. Comparison of average interstation dispersion curves obtained with different degrees of smoothness shows that rough perturbations do not systematically bias the average dispersion measurement. They can, therefore, be treated as random but they do need to be removed in order to reduce random errors of the measurements. Using our large new data set, we construct phase-velocity maps for central and northern Europe. According to checkerboard tests, the lateral resolution in central Europe is ≤150 km. Comparison of regional surface-wave tomography with independent data on sediment thickness in North-German Basin and Polish Trough confirms the high-resolution potential of our phase-velocity measurements. At longer periods, the structure of the lithosphere and asthenosphere around the Trans-European Suture Zone (TESZ) is seen clearly. The region of the Tornquist-Teisseyre-Zone in the southeast is associated with a stronger lateral contrast in lithospheric thickness, across the TESZ compared to the region across the Sorgenfrei-Tornquist-Zone in the northwest.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Habitat International 6 (1982), S. 441-457 
    ISSN: 0197-3975
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geography , Sociology
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0031-9422
    Keywords: Chenopodium quinoa ; gas chromatography-mass spectrometry ; triterpenes.
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 17 (1964), S. 313-313 
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 22 (1989), S. 3969-3973 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We have developed statistical models of upper and middle crustal seismic velocity heterogeneity based on geologic maps and petrophysical data from the Lewisian gneiss complex, Scotland. the level of heterogeneity we have measured is relevant to seismic exploration of the crystalline crust using conventional reflection and refraction techniques. We digitized two 1:10560 geologic maps of Laxfordian (Archean) age Lewisian rocks on a 26.8m grid. Both maps are believed to be representative of the upper and middle crust in north-western Scotland, and both are believed to provide cross-sectional views of parts of the crust. the digital maps were characterized by the statistics of their lithologic populations and by their 2-D spatial autocorrelation functions. Different lithologies were assigned seismic velocities appropriate for the mid-crust using petrophysical data. Three lithologies are dominant: silicic gneisses (Vp∼6.2 km s−1), mafic amphibolites (Vp— 6.75 kms−1), and intermediate composition schists (Vp—6.5kms−1). Both maps have self-affine spatial fabrics.The first map covers the core of a syncline. Its autocorrelation function defines a medium with a fractal dimension of 2.78, a horizontal characteristic length of about 244m and a vertical correlation of about 133m (aspect ratio is 2:1). It has an essentially trimodal velocity (lithology) population consisting of 37 per cent silicicgneiss, 43 per cent mafic amphibolites, and 20 per cent schists. This map is representative of 30-40 per cent of Laxfordian rocks. the second map is a plan view which can be rotated 90° about an axis perpendicular to strike to give a cross-section. This map is characterized by a fractal dimension of 2.55, with a horizontal correlation length of about 111m and a vertical correlation of about 38m (aspect ratio 3:1). It has a nearly bimodal population consisting of 77 per cent silicic gneisses and 22 per cent mafic amphibotites. It is representative of 60-70 per cent of Laxfordian rocks.Lastly we examine the seismic response of an upper to middle crust based on our statistical models using acoustic and elastic 2-D finite-difference synthetic seismograms. Short-offset shot records demonstrate that a Lewisian upper crust produces scattered waves which significantly disrupt signals reflecting from deeper levels. Measurements of transmission scattering Q, and coda decay rates confirm that seismic scattering in Lewisian-type crust is strong. the migrated CMP response of a Lewisian crustal model shows the characteristic ‘salt and pepper’ pattern often observed in the upper crust, and described, incorrectly, as ‘transparent'. We suggest that ‘translucent’ is a more appropriate descriptor.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-0972
    Keywords: Clavulanic acid ; ppGpp ; Streptomyces clavuligerus ; transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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