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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 29 (1989), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary. Bud sprouting, shoot height, and fresh and dry weights of plants arising from single-node stem segments of Paspalum distichum L. decreased as the depth of burial in the soil increased. Sprouting, rooting and shoot growth of single-node segments submerged in 5–15 cm of water were reduced significantly in the dark. Light alleviated this water-induced reduction in 1-, 3- and 7-node segments. Submergence actually promoted sprouting of the proximal bud and shoot growth from the distal bud in 3-node segments, and shoot growth of the first two buds from the distal end in 7-node segments, Flooding the roots of 3-week -old plants for one month had no effect, but markedly reduced tiller production and dry weights after 2 and 3 months. Treatment at 100% relative humidity promoted new shoot production in 4-month old plants only if all shoots were decapitated (clipped) but not in plants with 6 shoots left intact. Submergence of the whole plant in water drastically reduced new shoot production regardless of clipping treatment. Effects of flooding varied with its duration. It is concluded that though P. distichum, a wetland perennial weed, survives root flooding and submergence conditions, these conditions do not support maximum growth of the plants.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 29 (1989), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary. When sequential single-node shoot segments (third to fifteenth node, counting from the apex) of the perennial grass weed Paspalum distichum L. were buried in soil, new shoot growth was significantly correlated with initial segment length. Growth from the youngest segment (third), which was about 2 cm long, was only half as great as that from segments 8 to 15, which were initially 2–3·5 times longer. When 14-node shoot segments were buried in soil, the apical bud exerted a dominating influence on shoot emergence and new shoot growth of axillary buds. The degree of suppression increased gradually up to node 8 and then decreased as the distance from the apex increased. A similar result was obtained in these shoot segments following decapitation. However, the degrees and patterns of apical and bud dominance varied in shoots collected during different seasons and also in shoots with different node numbers, node position, cutting and chilling treatments. A possible role of apical and bud dominance in P. distichum in keeping aerial shocks in reserve under adverse conditions, thus providing a survival mechanism for this weed, is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 27 (1989), S. 373-398 
    ISSN: 1432-1416
    Keywords: Acquired immunodeficiency syndrome (AIDS) ; Distributed delays ; Human immunodeficiency virus (HIV) ; Sexually transmitted diseases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In this study, we investigate systematically the role played by the reproductive number (the number of secondary infections generated by an infectious individual in a population of susceptibles) on single group populations models of the spread of HIV/AIDS. Our results for a single group model show that if R ⩽ 1, the disease will die out, and strongly suggest that if R 〉 1 the disease will persist regardless of initial conditions. Our extensive (but incomplete) mathematical analysis and the numerical simulations of various research groups support the conclusion that the reproductive number R is a global bifurcation parameter. The bifurcation that takes place as R is varied is a transcritical bifurcation; in other words, when R crosses 1 there is a global transfer of stability from the infection-free state to the endemic equilibrium, and vice versa. These results do not depend on the distribution of times spent in the infectious categories (the survivorship functions). Furthermore, by keeping all the key statistics fixed, we can compare two extremes: exponential survivorship versus piecewise constant survivorship (individuals remain infectious for a fixed length of time). By choosing some realistic parameters we can see (at least in these cases) that the reproductive numbers corresponding to these two extreme cases do not differ significantly whenever the two distributions have the same mean. At any rate a formula is provided that allows us to estimate the role played by the survivorship function (and hence the incubation period) in the global dynamics of HIV. These results support the conclusion that single population models of this type are robust and hence are good building blocks for the construction of multiple group models. Our understanding of the dynamics of HIV in the context of mathematical models for multiple groups is critical to our understanding of the dynamics of HIV in a highly heterogeneous population.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Human evolution 4 (1989), S. 87-92 
    ISSN: 1824-310X
    Keywords: Biface ; China
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract More and more archaeological discoveries show that bifaces are not absent from China, South and East Asia. Bifaces played a very important role in early Paleolithic industries here. The tool assemblage of this industry is similar to those of biface cultures in Africa and Europe. These discoveries will increasingly fill and level up the ≪gap≫ between the cultures of the East and West.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 14 (1989), S. 469-476 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Sputtering of noble metals and an Au-Ag alloy with low keV ion bombardment is investigated by means of measuring angular distribution of sputter-deposited material and by analysing the bombarded target with low energy. Auger electron spectroscopy (LEAES). The measurement provides information on the angular-resolved sputtering yields and the compositional variation of the bombarded surface. The angular distributions of the sputtered particles vary with the measurement conditions: the energy and the type of bombarding ions, the crystallity of the bombarded surface and the vacuum conditions during sputtering. The measurement gives evidence of ion bombardment induced surface segregation on sputtering of the Au-Ag alloy.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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