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  • 1
    ISSN: 1432-0630
    Keywords: 61.14 ; 61.16 ; 61.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We report on high-resolution experiments by Scanning Force Microscopy (SFM) indicating the tight folding of neighbouring molecular chains in Poly(Ethylene) (PE) crystals. Ultradrawn PE films were prepared in the stacked lamellar morphology exhibiting crystalline lamellae and amorphous parts. The [001] direction of the lamellae is aligned parallel to the substrate surface resulting in {hk0} planes perpendicular to the symmetry axis of the probing tip. This preparation technique allows the direct observation of the molecular arrangement in polymeric crystals as well as an investigation of the crystalline/amorphous interface by SFM: at lower magnification, crystalline and amorphous parts of the film can be distinguished clearly. High-resolution imaging on the crystalline lamellae reveals a PE pitch height of 0.26±0.02 nm while the interchain spacing measures 0.50±0.02 nm consistent with (100) lattice planes aligned parallel to the substrate surface. Finally, the molecular folding at the edges of the lamellae has been studied. Evidence is found for the adjacent reentry of individual molecules at the edge of (100) surfaces.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Archives of toxicology 51 (1982), S. 197-220 
    ISSN: 1432-0738
    Keywords: Acute toxicity ; LD50 method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 170 acute toxicity determinations, carried out in rats, mice, and guinea pigs after oral and parenteral administration during the past 5 years, using 5 ♂/5 ♀ animals per dose, were evaluated with respect to the possibility of a reduction of animals necessary for obtaining LD50 values with limits of confidence. Calculations were performed on existing data; no additional animal experiments were initiated for the purpose of this paper. For the majority of substances 3 ♂/3 ♀ animals per dose would have sufficed for the determination of a LD50 value with limits of confidence. Even when using 2 ♂/2 ♀ animals per dose, in most cases sufficently acceptable LD50 values can be determined, if the period of observation — conventionally 4 weeks — would be doubled. Using this procedure, 75% of the animals could be saved. The reduced number of animals and the labor saved thereby would allow for a more individualized observation of single animals thus optimizing the evaluation of acute toxicity testing.
    Type of Medium: Electronic Resource
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