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  • 1
    Electronic Resource
    Electronic Resource
    The effect of annealing on stretched trans-1,4-polyisoprene networks (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 290-300 
    Details
    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: Variations of stress with temperature for stretched networks of trans-polyisoprene networks in the crystallization region are reported. Such profiles are characteristically U-shaped with the stress at lower temperatures often climbing to high levels. Valley widths of the profiles narrow as annealing temperature increases to about 50°C, then widen at yet higher temperatures. The degree of crystallization at 22°C is 37% and independent of deformation and annealing temperature. The β crystal form is overwhelmingly present with traces of other crystal forms appearing only at high deformations. The theory of stress-induced crystallization provides a good description of experimental results provided the nucleation parameter σ is dependent upon deformation. Therefore, the data provide good qualitative support for the theory in its current form.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340410
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  • 2
    Electronic Resource
    Electronic Resource
    The breaking strength of perfect polymer fibersThis paper was presented at the American Chemical Society Meeting in Dallas Texas, April 1989, in the Polymer Science Award Symposium Honoring W. R. Krigbaum. (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 437-443 
    Details
    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 breaking strength, strain at break, and work to rupture of perfect fibers prepared with polymers of finite molecular weight are calculated by treating the perfect fiber as a stressed crystal undergoing a crystal-melt phase transition. In this view, a tensile load destabilizes the crystal and depresses its melting point. When the load is sufficient to lower the melting temperature to the ambient condition the fiber melts - i.e., fails. The theoretical equations (extremely simple) are applied to several common polymer fibers. The maximum tensile strength of polyethylene, for example, is calculated to be 7 to 9 GPa, in good agreement with current experimental results.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760300802
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  • 3
    Electronic Resource
    Electronic Resource
    Resonance Raman spectroscopy of non-planar nickel porphyrins (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 23 (1992), S. 523-529 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Non-planar conformational distortions have recently been implicated in the biological activity of porphyrins and related tetrapyrroles in proteins, and several studies have used highly substituted porphyrins to model these nonplanar conformational distortions. Several aspects of non-planarity in the highly substituted metalloporphyrins are discussed, focusing on resonance Raman spectroscopy as a technique for investigating these structural issues. First, different non-planar distortions cause characteristic changes in the Raman spectrum. Specifically, the decreases in frequency of several Raman lines when compared with planar porphyrin analogs are shown to be similar for several classes of non-planar highly substituted porphyrins. Second, the effect of the central metal ion [ M = Ni(II), Co(II), Cu(II), Zn(II), Co(III), Fe(III)] on the conformation of the sterically constrained non-planar porphyrin octaethyltetraphenylporphyrin is considered. Responding to the conformational adjustments resulting from different metal size, the frequency of the structure-sensitive Raman line v2 correlates with several structural parameters obtained from either mechanics calculations or crystallographic studies. The parameters include Cβ—Cβ bond length, core size and Cα—N—Cα angle. Finally, an effect of electron-withdrawing substituents on the Raman frequencies is evident for the different classes of highly substituted porphyrins.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250231004
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  • 4
    Electronic Resource
    Electronic Resource
    Confocal microscopy and three-dimensional reconstruction of electrophysiologically identified neurons in thick brain slices (1991)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 18 (1991), S. 11-23 
    Details
    ISSN: 0741-0581
    Keywords: Fluorescent microscopy ; Light microscopy ; Confocal light microscopy ; Neurobiology ; Hippocampus ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Three-dimensional morphology and electrophysiology were correlated from individual neurons in a thick brain slice preparation. The hippocampal formation from immature and adult rats was cut transverse to the longitudinal axis into 500 μ Um-thick slices which were maintained under physiologic conditions. Individual neurons were impaled and physiologically characterized using microelectrodes. Recordings were made from the soma and in some cases from a dendrite. The impaled neurons were filled through the microelectrode with the fluorescent dye lucifer yellow and imaged by confocal scanning laser microscopy using an analog preprocessor. As many as 180 optical sections were recorded as a function of depth through the slices. Images are presented as a series of optical sections, stereo pairs, or three-dimensional reconstructions. Both stereo contouring and volume rendering methods were employed, and the reconstructions were viewed from any arbitrary perspective. Dendritic and axonal fields were separated from each other and displayed separately or as different pseudocolors. The three-dimensional reconstructions provided perspectives that were difficult or impossible to appreciate by viewing the optical sections or conventionally formed stereo pairs.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060180104
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