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  • 1
    Electronic Resource
    Electronic Resource
    The metabolism of leucine in tissue culture of skin fibroblasts of maple-syrup-urine disease
    Amsterdam : Elsevier
    BBA - Biochimica et Biophysica Acta 77 (1963), S. 523-524 
    Details
    ISSN: 0006-3002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0006-3002(63)90536-5
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Generation cycles in stage structured populations (1990)
    Springer
    Bulletin of mathematical biology 52 (1990), S. 375-396 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Some insect populations exhibit cycles in which successive population peaks may correspond to effectively discrete generations. Motivated by this observation, we investigate the structure of matriarchal generations in five simple, continuous-time, stage structure models in order to determine the proportion of individuals in one population peak who are the offspring of individuals in the pervious peak. We conclude that in certain models (including a model of Nicholson's blowflies) successive population peaks do not correspond to discrete generations, whereas in others (including some models of uniform larval competition) successive peaks may well approximate discrete generations. In all models, however, there is eventually significant overlap of generations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458578
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Incorporation of hypoxanthine by PHA-stimulated HPRT-deficient lymphocytes
    Amsterdam : Elsevier
    Experimental Cell Research 88 (1974), S. 289-294 
    Details
    ISSN: 0014-4827
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0014-4827(74)90243-2
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Hair root analysis in X-linked ichthyosis (1983)
    Springer
    Journal of inherited metabolic disease 6 (1983), S. 173-177 
    Details
    ISSN: 1573-2665
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Hair roots have been analysed in a large kindred with X-linked ichthyosis associated with steroid sulphatase deficiency. Enzyme activity in individual hair roots was assayed for the steroid sulphatase: neutral α-glucosidase ratio, the latter serving as an indicator of the general metabolic activity of the hair root. The distribution of the enzyme ratios in the individual hair roots in the heterozygotes described a normal curve suggesting origin from a single population of cells. The results differed strikingly from the irregular distribution of enzyme activities in hair roots of Lesch-Nyhan disease, where mosaicism occurs. It is suggested that the maternal and paternal genes for steroid sulphatase remain activein vivo in each cell in the hair root in apparent contradiction to the Lyon hypothesis. The observation is consistent with that previously reported for skin fibroblastsin vitro. Sulphatase activity in female controls was minimally greater than in males but the difference was not statistically significant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02310876
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of dispersal in a tri-trophic metapopulation model (1995)
    Springer
    Journal of mathematical biology 34 (1995), S. 195-224 
    Details
    ISSN: 1432-1416
    Keywords: Food chain ; Uniform persistence ; Bistability ; Induced outbreaks ; Bifurcation structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The aim of this paper is to understand how dispersal in a patchy environment influences the stability properties of tri-trophic metapopulations. Differential equation models for tri-trophic metapopulations are formulated and analysed. The patchy nature of the metapopulations is incorporated through dispersal phases. Two variants are studied: one with a dispersal phase for the top and one with a dispersal phase for the middle level. A complete characterisation of stable and unstable equilibria is given and the possibility of invasion in these food chains is studied. A dispersal phase for the middle level can destabilize the bottom level-middle level interaction, because of the delay that dispersal causes in the reaction to the resource. When the middle level is not efficiently controlled by the top level, the unstable bottom level-middle level pair can destabilize the entire food chain. Dispersal for the top level can destabilize in the same way. A characterisation of the long term behaviour of the models is given. Bistability with a stable three species equilibrium and a stable limit cycle is one of the possibilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00178773
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  • 6
    Electronic Resource
    Electronic Resource
    Prey dispersal and predator persistence (1992)
    Springer
    Experimental and applied acarology 14 (1992), S. 215-231 
    Details
    ISSN: 1572-9702
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To understand how patchiness influences population dynamics of a tri-trophic interaction, a tractable model is formulated in terms of differential equations. Motivated by the structure of systems such as plants, phytophagous mites and predatory mites, the model takes dispersal into account at the middle trophic level. The effect of dispersal for the middle level in a tri-trophic system could be either stabilising or destabilising since the middle level acts both as prey and as predator. First a simple model with logistic growth for the lowest level is formulated. A model with logistic growth for the lowest level and instantaneous dispersal has a globally stable three-species equilibrium, if this equilibrium exists. Addition of a middle level dispersal phase of non-negligible duration influences equilibrium stability. In the absence of the top trophic level a limit cycle can occur, caused by the delay that exists in the reaction of the middle level to the changes in the lowest level. With low predator efficiency, it is also possible to have an unstable three-species equilibrium. So addition of a middle level dispersal phase of non-negligible duration can work destabilising. Next the persistence of the third trophic level is studied. Even when the three-species equilibrium exists, the third trophic level need not be persistent. A two-species limit cycle can keep its stability when a three-species equilibrium exists; the system is then bistable. It is argued that such a bistability can offer an alternative explanation for pesticide-induced outbreaks of spider mites and failure of predator introduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01200565
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    Paper (German National Licenses)
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