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  • 1
    ISSN: 1432-1009
    Keywords: Sulfate ; Nitrate ; Critical loads ; Modeling ; Deposition standards
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The critical loads approach is emerging as an attractive means for evaluating the effects of atmospheric deposition on sensitive terrestrial and aquatic ecosystems. Various approaches are available for modeling ecosystem responses to deposition and for estimating critical load values. These approaches include empirical and statistical relationships, steady-state and simple process models, and integrated-effects models. For any given ecosystem, the most technically sophisticated approach will not necessarily be the most appropriate for all applications; identification of the most useful approach depends upon the degree of accuracy needed and upon data and computational requirements, biogeochemical processes being modeled, approaches used for representing model results on regional bases, and desired degree of spatial and temporal resolution. Different approaches are characterized by different levels of uncertainty. If the limitations of individual approaches are known, the user can determine whether an approach provides a reasonable basis for decision making. Several options, including point maps, grid maps, and ecoregional maps, are available for presenting model results in a regional context. These are discussed using hypothetical examples for choosing populations and damage limits.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 57 (1989), S. 1069-1098 
    ISSN: 1572-9613
    Keywords: Block copolymers ; generating function ; Polya's theorem ; gelation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We determine the statistical properties of block copolymer complexes in solution. These complexes are assumed to have the topological structure of (i) a tree or of (ii) a line-dressed tree. In case the structure is that of a tree, the system is shown to undergo a gelation transition at sufficiently high polymer concentration. However, if the structure is that of a line-dressed tree, this transition is absent. Hence, we show the assumption about the topological structure to be relevant for the statistical properties of the system. We determine the average size of the complexes and calculate the viscosity of the system under the assumption that the complexes geometrically can be treated as porous spheres.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1617-4623
    Keywords: Tomato ; Agrobacterium T-DNA ; Inverse PCR ; Activator ; Transposon tagging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We are developing a system for isolating tomato genes by transposon mutagenesis. In maize and tobacco, the transposon Activator (Ac) transposes preferentially to genetically linked sites. To identify transposons linked to various target genes, we have determined the RFLP map locations of Ac- and Dissociation (Ds)-carrying T-DNAs in a number of transformants. T-DNA flanking sequences were isolated using the inverse polymerase chain reaction (IPCR) and located on the RFLP map of tomato. The authenticity of IPCR reaction products was tested by several criteria including nested primer amplification, DNA sequence analysis and PCR amplification of the corresponding insertion target sequences. We report the RFLP map locations of 37 transposon-carrying T-DNAs. We also report the map locations of nine transposed Ds elements. T-DNAs were identified on all chromosomes except chromosome 6. Our data revealed no apparent chromosomal preference for T-DNA integration events. Lines carrying transposons at known map locations have been established which should prove a useful resource for isolating tomato genes by transposon mutagenesis.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 57 (1989), S. 1099-1122 
    ISSN: 1572-9613
    Keywords: Block copolymers ; generating function method ; Polya's theorem ; gelation ; nonnested structures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We determine the statistical properties of block copolymers in solution. These complexes are assumed to have the topological structure of connected graphs with “nonnested” loops and cycles. The generating function method is used to determine the number of topologically different complexes containing a given number of block copolymers. It is shown that at sufficiently high concentration the system undergoes a transition to a gel phase. Furthermore, the average number of polymers per complex is calculated. Finally, the relative increase in viscosity is found under the assumption that the complexes can be treated as porous spheres.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1619-7089
    Keywords: Positron emission tomography ; 11C-amino acids ; 18F-fluorodeoxyglucose ; Prolactinoma ; Salivary gland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Aspects of metabolism in prolactinomas were investigated by positron emission tomography using l-[1-11C]tyrosine, l-[methyl-11C]methionine and 18F-fluorodeoxyglucose (18FDG). Using l-[1-11C]tyrosine, four patients were monitored prior to and 18 h after an injection of 50 mg bromocryptine. At 18 h after bromocryptine intervention, l-[1-11C]tyrosine uptake into tumour was reduced with 28% (P〈0.07). A correlation analysis of the bromocryptine-induced decrease in l-[1-11C]tyrosine uptake and the reduction of serum prolactin levels indicated that the action of bromocryptine on prolactin synthesis and prolactin release is not coupled. In the untreated situation, the four patients were investigated with 18FDG as well, but the prolactinomas could not be visualized. Three untreated patients were studied with l-[methyl-11C]methionine. The tumour-imaging potential of l-[methyl-11C]methionine and l-[1-11C]tyrosine appeared to be nearly equivalent for prolactinomas. Unlike prolactinoma tissue, the salivary glands showed a pronounced preference for l-[1-11C]tyrosine as compared to l-[methyl-11C]methionine. l-[1-11C]tyrosine is a valuable tool to obtain information on the metabolism and treatment of prolactinomas.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-9368
    Keywords: transposon ; Activator ; Dissociation ; cell-autonomous ; spectinomycin ; tomato ; phosphinothricin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cell-autonomous genes have been used to monitor the excision of both endogenous transposons in maize andAntirrhinum, and transposons introduced into transgenic plants. In tobacco andArabidopsis, the streptomycin phosphotransferase (SPT) gene reveals somatic excision of the maize transposonActivator (Ac) as green sectors on a white background in cotyledons of seedlings germinated in the presence of streptomycin. Cotyledons of tomato seedlings germinated on streptomycin-containing medium do not bleach, suggesting that a different assay for transposon excision in tomato is desirable. We have tested the use of the spectinomycin resistance (SPEC) gene (aadA) and a Basta resistance (BAR) gene (phosphinothricin acetyltransferase, or PAT) for monitoring somatic excision ofAc in tobacco and tomato. Both genetic and molecular studies demonstrate that genotypically variegated individuals that carry clones of cells from whichAc orDs have excised from either SPEC or BAR genes, can be phenotypically completely resistant to the corresponding antibiotic. This demonstrates that these genes act non-cell-autonomously, in contrast to the SPT gene in tobacco. Possible reasons for this difference are discussed.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0736-0266
    Keywords: Sulfate ; Cartilage ; Glycosaminoglycans ; Mouse ; Articular ; Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have studied the effect of environmental sulfate concentration on the glycosaminoglycan synthesis of anatomically intact patellar cartilage of the mouse in vitro. Incubation of mouse patellae in medium with sulfate concentrations below 0.5 mM resulted in a diminished incorporation of sulfate but in unaltered incorporation of glucosamine. This suggested the synthesis of undersulfated glycosaminoglycans under these conditions. We characterized glycosaminoglycans synthesized at three different sulfate concentrations: a sulfate concentration physiological for the mouse (1.0 mM), a sulfate concentration in the range where sulfate incorporation was strongly diminished (0.1 mM), and an extremely low sulfate concentration (10 nM). Analysis of glycosaminoglycan disaccharides and DEAE anion chromatography of the glycosaminoglycans could not confirm the synthesis of undersulfated glycosaminoglycans at 0.1 mM. The chromatogram of glycosaminoglycans synthesized in medium containing 10 nM showed the presence of a very low sulfated glycosaminoglycan pool not observed at higher medium sulfate concentrations. Intermediately sulfated glycosaminoglycans were also synthesized during incubation with 10 nM sulfate. So, our data indicate that only very low sulfate concentrations in the medium lead to the synthesis of undersulfated glycosaminoglycans and that the sulfation mechanism of murine patellar cartilage chondrocytes does not seem to fit completely in an “all-or-nothing” pattern.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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