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  • 1
    Electronic Resource
    Electronic Resource
    15N natural abundances and N use by tundra plants (1996)
    Springer
    Oecologia 107 (1996), S. 386-394 
    Details
    ISSN: 1432-1939
    Keywords: Arctic ; 15N abundance ; N cycle ; Nitrate reductase ; Tundra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plant species collected from tundra ecosystems located along a north-south transect from central Alaska to the north coast of Alaska showed large and consistent differences in 15N natural abundances. Foliar δ15N values varied by about 10% among species within each of two moist tussock tundra sites. Differences in 15N contents among species or plant groups were consistent across moist tussock tundra at several other sites and across five other tundra types at a single site. Ericaceous species had the lowest δ15N values, ranging between about −8 to −6‰. Foliar 15N contents increased progressively in birch, willows and sedges to maximum δ15N values of about +2‰ in sedges. Soil 15N contents in tundra ecosystems at our two most intensively studied sites increased with depth and δ15N values were usually higher for soils than for plants. Isotopic fractionations during soil N transformations and possibly during plant N uptake could lead to observed differences in 15N contents among plant species and between plants and soils. Patterns of variation in 15N content among species indicate that tundra plants acquire nitrogen in extremely nutrient-poor environments by competitive partitioning of the overall N pool. Differences in plant N sources, rooting depth, mycorrhizal associations, forms of N taken up, and other factors controlling plant N uptake are possible causes of variations in δ15N values of tundra plant species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328456
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Beta-particle dosimetry in radiation synovectomy (1995)
    Springer
    European journal of nuclear medicine 22 (1995), S. 977-988 
    Details
    ISSN: 1619-7089
    Keywords: Dosimetry ; Radiation synovectomy ; Monte Carlo simulation ; Rheumatoid arthritis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Beta-particle dosimetry of various radionuclides used in the treatment of rheumatoid arthritis was estimated using Monte Carlo radiation transport simulation coupled with experiments using reactor-produced radionuclides and radiachromic film dosimeters inserted into joint phantoms and the knees of cadavers. Results are presented as absorbed dose factors (cGy-cm2/MBq-s) versus depth in a mathematical model of the rheumatoid joint which includes regions of bone, articular cartilage, joint capsule, and tissue (synovium) found in all synovial joints. The factors can be used to estimate absorbed dose and dose rate distributions in treated joints. In particular, guidance is provided for those interested in (a) a given radionuclide's therapeutic range, (b) the amount of radioactivity to administer on a case-by-case basis, (c) the expected therapeutic dose to synovium, and (d) the radiation dose imparted to other, nontarget components in the joint, including bone and articular cartilage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808408
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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