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  • 1
    ISSN: 1432-136X
    Keywords: Cardiovascular system ; Chemosensitivity ; Oxygen stores ; Submergence asphyxia ; Aquatic birds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Maximum submergence time of Canada geese was 18% of that of similarly sized Pekin ducks. Due to a smaller respiratory system volume the oxygen store of Canada geese was 82% of that of Pekin ducks, accounting for approximately 33% of the difference in underwater survival times. The respiratory properties and volume of the blood were similar in both species. Both species utilised approximately 79% of the respiratory oxygen store and 90% of the blood oxygen store. Therefore, most of the species difference in survival times was due to a less effective oxygen-conserving cardiovascular response (bradycardia, peripheral vasoconstriction) in Canada geese. Duck cardiac chronotropic sensitivity to hypoxia during submergence was twice that observed in geese. Furthermore, a lower hypoxic ventilatory response was observed in geese than in ducks. Density of monoamine varicosities in hindlimb artery walls was lower in geese than ducks. However, electrical stimulation of the hindlimb muscles did not cause ascending vasodilation during submergence in either species, perhaps due to higher levels of catecholamines in submerged geese. We conclude that the major difference between species is higher oxygen chemosensitivity in ducks which effects a much more rapid and efficacious oxygen-conserving response during forced submergence.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The load-bearing capabilities of short-fiber reinforced thermoplastics composites can be evaluated, in principle, by the methods known to be satisfactory for unreinforced thermoplastics, but in practice the cost of a comprehensive evaluation of a composite would be prohibitive because of the anisotropy of the properties and its variation from point to point. For the same reasons the properties measured on a specimen cut from a molding may have little relevance to its overall performance. This paper describes recent experiments that could lead to a radical change in testing strategy. Instead of the classical method in which standard specimens cut from moldings are assumed to provide the various stiffness coefficients needed for anisotropic stress analysis, simple moldings such as discs or plaques are tested directly. The sacrifice of precision in the measurements and the loss of rigor in the definition of the measured quantities is more than compensated for by a gain in the general utility of the data and the substantial reduction in the cost of evaluations. The mechanical properties of shortfiber thermoplastics composites are particularly sensitive to mold geometry and the new methods of testing enable the effects to be assessed readily, whereas the information generated by the classical method is virtually indecipherable in that context. Examples are given in the paper.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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