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  • ASTROPHYSICS  (6)
  • Rhizobia  (3)
  • nitrogen partitioning  (2)
  • 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism  (1)
  • 1
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    Apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite (2008)
    Blackwell Publishing
    Details
    Publication Date: 2012-02-03
    Description: A mixed-polarity zone, representing alternations between remagnetized and non-remagnetized strata, has been documented within the lower few metres of the CRP-1 core (Ross Sea, Antarctica). Detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single-domain particles of a ferrimagnetic iron sulphide mineral, while the reversed-polarity magnetization of non-remagnetized strata is carried by magnetite with a broad range of grain sizes and negligible magnetostatic interactions. Scanning electron microscope observations of polished sections indicate that the ferrimagnetic iron sulphide mineral is greigite (Fe3S4). Based on microtextural relationships, it is not possible to determine the relative timing of formation for much of the greigite. However, a significant proportion of the greigite has grown on the surface of authigenic siderite (FeCO3) grains that occur as microconcretions and as cement surrounding detrital matrix grains. In such cases, microtextural relationships indicate that siderite post-dates early diagenetic pyrite and that greigite post-dates the siderite. Siderite usually forms in environments with abundant dissolved iron and carbonate, but without dissolved pore water H2S. This set of geochemical conditions occurs in methanic settings below the sulphate reduction zone (in which early diagenetic pyrite forms).We interpret the observed remagnetization of the lower part of the CRP-1 core as due to a late diagenetic pore water migration event where abundant iron on the surface of siderite grains reacted with fluids containing limited dissolved sulphide, thereby causing precipitation of greigite. The distribution of siderite (and associated greigite) in the lower part of the CRP-1 core is patchy, which accounts for the apparent alternation of polarities. This study is part of a growing catalogue of remagnetizations involving greigite, which suggests that occurrences of greigite should be treated with caution in palaeomagnetic and environmental magnetic studies.
    Description: Published
    Description: 89-100
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Antarctica ; diagenesis ; greigite ; iron carbonate ; iron sulphide ; remagnetization ; siderite ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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    PAPER (OA)
  • 2
    Electronic Resource
    Electronic Resource
    Numbers of clover rhizobia needed for crown nodulation and early growth of clover in soil (1994)
    Springer
    Biology and fertility of soils 17 (1994), S. 121-124 
    Details
    ISSN: 1432-0789
    Keywords: Clover ; Inoculation ; Nodulation ; Rhizobia ; Soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Low soil populations of Rhizobium leguminosarum biovar trifolii indicate a need for inoculating clovers (Trifolium sp.) at planting. The number of rhizobia in soil varies considerably from field to field and the number needed for nodulation on the upper taproot and for vigorous seedling development is not known. Two experiments were undertaken using arrowleaf clover (T. vesiculosum Savi) and crimson clover (T. incarnatum L.) grown in pots filled with soil. Two soils were used; one contained 10 indigenous rhizobia g-1 and the other contained fewer than three. The treatments consisted of amending each soil with two strains of inoculant rhizobia to contain from 10 to approximately 1×106 rhizobia g-1 followed by planting to clover. The number of nodules near the top of the root increased as the number of rhizobia in the soil increased to the highest inoculum level. A low number (approximately 1×103 to 1×104) of rhizobia was sufficient for maximal N content of seedlings. It seems that soil containing 100 or fewer rhizobia g-1 may respond to inoculation with increased crown nodulation and seedling vigor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00337743
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Distribution of 15N from ammonium fertilizer in field grown Acacia (1993)
    Springer
    Plant and soil 151 (1993), S. 147-150 
    Details
    ISSN: 1573-5036
    Keywords: Acacia ; isotope dilution ; nitrogen fixation ; N15 ; nitrogen partitioning ; tree
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract An experiment was conducted in the field to determine the partitioning of 15N from ammonium sulfate fertilizer in two-year old trees of Acacia mangium and Acacia auriculiformis. For both species, most of the 15N excess was partitioned into woody tissue, green material and root biomass present at the beginning of the experiment. Approximately one third of the 15N excess was contained in leaves that developed during the 60 days of the experiment. The concentration of 15N excess in the newly developed leaves indicated that more than 90% of the N came from a source other than the fertilizer. Based on the large quantity of N applied in the fertilizer and the inherently infertile soil, it appears that much of the N contained in the newly developed leaves came from N remobilized from other tree parts. ei]{gnR O D}{fnDixon}
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010796
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  • 4
    Electronic Resource
    Electronic Resource
    Partitioning of biologically fixed nitrogen in cowpea during pod development (1989)
    Springer
    Plant and soil 116 (1989), S. 129-131 
    Details
    ISSN: 1573-5036
    Keywords: 15N ; nitrogen fixation ; nitrogen partitioning ; translocationVigna unguiculata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two days after exposure of roots to15N labeled N2, partitioning of biologically fixed N into leaves, stems, peduncles, pods, roots and nodules was measured in the early pod development stage of cowpea (Vigna unguiculata (L.). The experimental objective was to determine the quantity of biologically fixed N that is incorporated into vegetative tissue before being mobilized to pods. For the three varieties of cowpea included in the experiment a maximum of 50% of the N, biologically fixed two days earlier, was contained in the pods. The remaining N was distributed throughout the vegetative portion of the plant with at least 30% in stems and leaves which indicates that much of the newly fixed N must cycle through a N pool in these tissues before reaching the pods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02327269
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  • 5
    Electronic Resource
    Electronic Resource
    Competition between siratro and kleingrass for15N labelled mineralized nitrogen (1986)
    Springer
    Plant and soil 96 (1986), S. 327-335 
    Details
    ISSN: 1573-5036
    Keywords: Isotope discrimination ; Macropitilium atropurpureum ; Nitrogen fixation ; Nitrogen transfer ; Panicum coloratum ; Rhizobia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Isotope dilution provides a method for measuring plant competition for mineral N and transfer of biologically fixed N from a legume to a grass. A plant growth medium was enriched with15N, and used to grow Siratro (Macropitilium atropurpureum D.C. Urb.) and Kleingrass 75 (Panicum coloratum L.) in 20 liter pots for 98 days in a glasshouse. The plants were grown in pure stand and in mixtures. When grown in 50∶50 mixture the grass obtained 59% of the labelled N and the legume obtained 41%. The grass produced nearly as much root mass as the legume even though biomass of the shoots were less than half that of the legume. Reducing the proportion of either plant species in the mixture reduced the proportion of the mineralized N absorbed by that species. The shoots of the grass were significantly more enriched (1.166 atom%15N excess) than the roots (1.036). The grass received 12% of its N as biologically fixed N from the legume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375137
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  • 6
    Electronic Resource
    Electronic Resource
    Importance of bacteroid number in nodules and effective nodule mass to dinitrogen fixation by cowpeas (1985)
    Springer
    Plant and soil 87 (1985), S. 223-231 
    Details
    ISSN: 1573-5036
    Keywords: Nitrogen fixation ; Rhizobia ; Vigna unguiculata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Biological nitrogen fixation is considered an important trait of cowpeas (Vigna unguiculata (L.) Walp. var. ‘California Blackeye’ No. 5) for economical production yet the process does not alone provide the quantity of nitrogen required by the plant for maximum productivity. Two experiments were undertaken to determine the potential of an increase in nodule mass and number of bacteroids resulting in increased nitrogen fixation. Cowpeas were grown in a glasshouse for 7 weeks under conditions forcing near total dependence on biological nitrogen fixation for growth. Nodule mass on the roots was varied by inoculating seeds with various ratios of effective and ineffective rhizobia that could be identified serologically and by the color of nodule formed. The results of both experiments demonstrated a linear relationship between total nodule mass formed by the effective rhizobia and quantity of nitrogen fixed. The regression coefficients were high in both experiments (r=0.99** and 0.91**). The relationship between total nitrogen fixed and total number of bacteroids of the effective strain was not consistent. In one experiment the regression coefficient was 0.93** but in the other experiment it was 0.65**. From these results it appears that there is good potential for increasing nitrogen fixation in cowpeas by increasing nodule mass. An increase in nodule mass would also result in an increase in the number of bacteroids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02181861
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  • 7
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    On the formation and confinement of dense clouds in QSOs and active galactic nuclei (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A model for the formation and confinement of dense (at least about 1 billion per cu cm) clouds in QSOs and active galactic nuclei is presented wherein thermal instabilities behind radiative shocks cause the collapse of regions where the preshock density is enhanced over that of the surrounding medium. Such shocks (of total energy around 10 to the 51st ergs) are likely to occur if the frequent optical outbursts observed in many of these objects are accompanied by mass ejections of comparable energy. It is found that clouds quite similar to those thought to exist in QSOs etc. can be created in this manner at radii of the order of 10 to the 17th cm. The clouds can be subsequently accelerated to observed bulk velocities by either radiation pressure or a collision with a much stronger (total energy around 10 to the 53 ergs) shock. Alternatively, their high observed velocities could be caused by gravitational infall or rotation. The mass production required at inner radii by the outflow models can be supplied through a mechanism previously discussed by Shields (1977).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 227
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Consequences of narrow cyclotron emission from Hercules X-1 (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Explanations of the line feature in the hard X-ray (58 keV) spectrum of the compact X-ray source Hercules X-1 are presented. The most important characteristic of the emission (interpreted as a cyclotron emission from a strong magnetic field, i.e., B greater than one trillion Gauss) is that the FWHM is less than 12 keV, with a total observed luminosity in the line of approximately 1% of the total X-ray luminosity. If the source region is only at the magnetic poles of a neutron star, the electrons are confined to a path nearly parallel to the B-field lines, and the angle of emission will be narrow. Photon emission under such circumstances is also discussed; and it is suggested that photons can leave either through holes in the shell formed by the hard X-rays, or can escape through the shell itself. Attention is given to the accretion flow structure near the magnetopause, as a critical parameter of narrow line emission.
    Keywords: ASTROPHYSICS
    Type: Nature; vol2 274
    Format: text
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  • 9
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    Structure of the iron fluorescence line in X-ray binaries (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The paper presents an approximate solution to the iron K alpha line transfer problem in a stellar atmosphere illuminated by an external X-ray source as in a binary X-ray system. The emergent Comptonized line profile can independently yield information on the abundance of heavy elements in the primary atmosphere and on the solid angle subtended by the primary at the X-ray source.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 215
    Format: text
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  • 10
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    A new luminosity limit for spherical accretion onto compact X-ray sources (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Preheating of infalling gas by emergent X-rays can suppress accretion on to a compact X-ray source. For spherically symmetric accretion, the effect results in a new luminosity limit, orders of magnitude less than the Eddington limit, above which steady flow is impossible. The model may apply to the globular-cluster X-ray sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 208; Sept. 1
    Format: text
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