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  • Springer  (642)
  • Institute of Physics  (211)
  • American Geophysical Union (AGU)
  • 1975-1979  (853)
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  • 1
    Publication Date: 1977-01-01
    Print ISSN: 0364-152X
    Electronic ISSN: 1432-1009
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Springer
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  • 2
  • 3
  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 53 (1979), S. 345-351 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Population distributions, densities and percentage deaths and individual size variations of the barnacles Chthamalus stellatus and Tetraclita squamosa, and the distribution of the vermetid snail Spirogluphus annulatus are measured to clarify determinants the Florida Keys (USA). The species composition of the pilings community and barnacle population densities correspond to physical gradients dependent on piling distance from shore. Interspecific competition for space is insignificant in determining C. stellatus presence or absence on pilings. Intraspecific crowding in highdensity zones of adult T. squamosa is evidenced by a significant decrease in basal diameter as density increases. The peak percentage of dead C. stellatus coincides with peak densities. The percentage of dead T. squamosa is at a low point at peak densities due to the ability of T. squamosa cyprids to settle and survive on adult shells in high-density regions. Feasible perturbation experiments for testing the importance of interspecific competition in determining the densities and vertical distributions of the species are discussed. The results of such experiments can be used to test the assumptions and predictions of the widely applied competition coefficient measure proposed by Levins (1968). Several theoretical deficiencies of Levins' measure are discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 43 (1977), S. 71-92 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Eighteen species of Candaciidae have been identified from collections made at 339 stations in the Indian Ocean. Most species are zonally distributed; however, on the eastern and western sides of the Indian Ocean, species ranges are extended north or south by boundary currents. Factor analysis was used to cluster phenotypically similar species based on 130 characters taken from the maxilla (a feeding appendage), the first swimming foot, and the fifth foot (a secondary sexual structure). Four morphological clusters were extracted. Clusterings based on separate factor analyses limited to characters from feeding or from sexually adapted appendages are in substantial agreement with the clusters based on composite morphology. Two geographically recurrent groups of species were also identified, one from equatorial waters, one from the central gyre. Each recurrent group is composed of species exceptionally different in body size and belonging to different morphological clusters. Niches of the species are compared using Hutchinson's multidimensional hypervolume as a model. An attempt is made to describe the niche of each species in terms of environmental variables measured at stations where the species was abundant. Environmental variables (dimensions) included in this study are space, time, temperature, food, oxygen and salinity. Mean niche adaptations of most of the species are separable from congeners along at least one niche dimension. It is proposed that community relationships among the Candaciidae developed to prevent both gamete loss and to avoid trophic competition. It is postulated that newly evolving species underwent contemporaneous displacement of both secondary sexual and trophic characters as a condition for sympatry, or diverged in their physiological adaptations to escape sympatric interference.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Planta 137 (1977), S. 259-264 
    ISSN: 1432-2048
    Keywords: Glycolysis ; Lemna ; Nitrogen deficiency ; Protein degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When Lemna is deprived of nitrogen, growth and respiration decrease and the pattern of 14CO2 release from [1-14C]glucose and [6-14C]glucose is consistent with a relatively strong inhibition of glycolysis. Protein degradation is enhanced but the concentration of free amino acid decreases. It is argued that the biological significance of the increased protein degradation does not lie in its contribution to respiration but as a mechanism to replace one set of enzymes adapted to a particular environmental condition (high nitrogen) with another set of enzymes adapted for low nitrogen in the environment. The change in enzyme pattern associated with the change from high to zero nitrogen in the growth medium has been examined for nine enzymes. The changes in activity observed are consistent with the observed apparent inhibition of glycolysis during nitrogen starvation, but do not explain the inhibition of the pentose phosphate pathway.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 8 (1979), S. 301-322 
    ISSN: 1432-1416
    Keywords: Mathematical modelling ; Venereal disease ; Gonorrhoea ; Criss-cross infection ; Nonhomogeneous mixing ; Asymptomatic infections ; Public health control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Summary The continually rising trend in the incidence of venereal diseases, especially gonorrhoea, in a large number of countries, both developed and developing is causing considerable public health concern. There is a disquieting volume of human suffering involved, as well as large economic losses in treatment and hospitalization. The present paper reviews the existing state of development in the mathematical modelling of the relevant disease dynamics. The ‘criss-cross’ nature of the infections, which in heterosexual contacts switch between the male and female populations, together with the nonlinear form of the rate of spread normally occurring in infectious diseases, leads to special types of simultaneous nonlinear differential equations. The simplest deterministic models available entail threshold phenomena connecting the maintenance of endemic states to the contact-rates, the personto-person infection-rates, and the removal-rates. A few stochastic results are also available. Special attention is given to the aspects of nonhomogeneous mixing, analysis of contact-rates, infection without immunity, allowance for asymptomatic infection, the recognition of many different classes of infected individuals, and the problems of public health forecasting and control. In some cases transient solutions of the equations can be used to forecast future trends in disease incidence, depending on appropriate assumptions about alternative public health interventions. It is concluded that further mathematical work should be concentrated on relatively simple models comprising no more than three or four district epidemiological groups for each sex. There should be both (i) more intense mathematical investigations, and (ii) new attempts to assimilate the models directly to public health venereal disease control.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 99 (1975), S. 211-230 
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The physiological effects of two inhibitory axons supplying the stretcher muscles of three crabs (Hyas, Gecarcinus andGrapsus) were investigated, with a view to establishing the relative importance of pre- and postsynaptic inhibition. 2. InHyas, the specific inhibitory (SI) axon and the common inhibitory (CI) axon both exerted powerful presynaptic inhibition on the terminals of the excitatory axon. The effect of the SI axon was generally stronger, but some excitatory terminals were found in which CI axon stimulation was more effective. Thus, inhibition of the excitatory postsynaptic potential recorded intracellularly from the muscle fiber is the statistical result of variable inhibition at different excitatory terminals. 3. InHyas, postsynaptic inhibition was insignificant at low frequencies of stimulation, but increased at higher frequencies, for both SI and CI axons. The SI axon had a stronger postsynaptic effect than the CI axon. 4. InGecarcinus, the CI axon had a more powerful postsynaptic effect than the SI axon, whereas the SI axon was more effective at the presynaptic level. The two axons are specialized for different types of inhibition. 5. InGrapsus, the SI axon was more effective than the CI axon at both pre- and postsynaptic levels. Thus, considerable variation in pre- and postsynaptic connections of the two inhibitor axons occurs in different species of crabs. 6. In all species, the CI axon was least effective in muscle fibers with small, facilitating excitatory postsynaptic potentials. Sometimes the CI axon did not produce any effect at all in such fibers. 7. Presynaptic inhibition in crabs probably occurs mainly at narrow “bottlenecks” of the excitatory axon, where impulses are easily blocked by inhibitory synaptic action.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 4 (1977), S. 303-321 
    ISSN: 1432-1416
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Summary A time-dependent, nonlinear model of neuronal interaction which was probabilistically analyzed in a previous article is shown here to be a natural generalization of the Hartline-Ratliff model of the Limulus retina. Although the primary physical variables in the model are the membrane potentials of neurons, the equations which govern the means and covariances of the membrane potentials are coupled through the average firing rates; as a consequence, the average firing rates control the selective storage and retrieval of covariance information. Motor learning in the cerebellar cortex is treated as a problem of covariance storage, and a prediction is made for the underlying synaptic plasticity: the change in synaptic strength between a parallel fiber and a Purkinje cell should be proportional to the covariance between discharges in the parallel fiber and the climbing fiber. Unlike previous proposals for synaptic plasticity, this prediction requires both facilitation and depression to occur (under different conditions) at the same synapse.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2048
    Keywords: Abscisic acid ; Amylase ; Cereal kernel ; Germination (seeds) ; Gibberellin ; Triticale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Abscisic-acid (ABA) levels were determined in triticale 6A190 kernels at various stages of development from anthesis to maturity. ABA reached a maximum at ca. 22 d post-anthesis and declined rapidly 12 d later. Associated with drying of the kernel at maturity there was a rapid increase in the endogenous level of α-amylase, apparently based upon de-novo synthesis. Simultaneously there were visible signs of degradation of the large starch grains in the starchy endosperm. Regulation of α-amylase production in the kernel by exogenous gibberellic acid (GA3) was only evident in the almost mature kernel (30–40 d after anthesis) and then only if these kernels were first dried artificially. Furthermore, little α-amylase mRNA could be detected prior to kernel maturity and water loss. Thus, the high levels of gibberellin (GA) that have been found early in kernel development in cereals do not appear to control the later production of α-amylase and onset of kernel germination in the ear of triticale. However, the presence of high levels of ABA until maturity could prevent early germination and premature production of α-amylase. Kernels of triticale 6A190 are characteristically shrivelled and non-dormant at maturity. The relevance of changes in the capacity of kernels to respond to and produce GA and ABA is discussed in relation to problems of harvest dormancy in cereals.
    Type of Medium: Electronic Resource
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