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  • Chemistry  (2)
  • GEOPHYSICS
  • Historic landscape preservation
  • National Park management
  • 1985-1989  (2)
  • 1980-1984
  • 1950-1954
  • 1989  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Characterization of impurities in a synthetic renin substrate peptide by fast-atom bombardment mass spectrometry and hybrid tandem mass spectrometry (1989)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 3 (1989), S. 314-319 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Fast-atom bombardment mass spectrometry of a synthetic renin substrate decapeptide (Pro-His-Pro-Phe-His-Leu-Val-Ile-His-D-Lys) indicated the presence of several of side-products, including a component 12 Da higher in mass. Low-energy collisionally activated decomposition analyses were performed using a hybrid tanden, instrument and demonstrated that the heavier side product had two components, in which the structural modification was either at the N- or the C-terminus. Additional analyses of the N-acetyl derivative indicated that for each component the strucutrual modification blcoked a site of N-acetylation. It is suggested that the formation of these side products is attributable to the generation of formaldehyde, during removal of the histidine protecting group (benzyloxymethyl), which reacts with the N-terminus of the peptide to give an imidazolidinone structure or with the D-lysine ε-amine group to yield an imine. While the precise genesis of the side-products remains speculative, it is clear that the combined strategy of derivatization and tandem mass spectrometry has allowed structural conclusions concerning individual components of an isobaric mixture.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290030912
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  • 2
    Electronic Resource
    Electronic Resource
    The characterization of uniaxial graphite fiber/epoxy composites by mechanical testing and scanning electron microscopy (1989)
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 9 (1989), S. 253-264 
    Details
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The effect of the constituent material on the mechanical properties and on the overall crack propagation behavior of uniaxial graphite/epoxy composites was studied using two different types of graphite fibers, i.e., PAN precursor and pitch precursor fibers in combination with an epoxy known for its toughness. The tensile properties and interlaminar shear strength (ILSS) of composites with various fiber volume fraction were studied using an Instron Universal Testing Machine. The fracture surface of composites was studied using scanning electron microscopy (SEM). The surprising result from the tensile tests is that the percent elongation of AS4/epoxy composites was much higher than that of individual components, i.e., the epoxy and the fiber. The stress-strain curves of AS4 fiber/epoxy composites show yielding. The yielding is interpreted to result from shear stress concentration due to the fiber breakage. Two causes of failure mode were observed in this study: (1) ductile plastic deformation by the PAN-based AS4/epoxy composites; (ii) brittle catastrophic failure shown by the pitch-based VSB-16/epoxy composites. The tensile strengths and moduli of the composites increased as the volume fraction of fibers increased. The principal fracture features of AS4/epoxy composites under tension were fiber pullout (bundles and single fibers) and very rough fracture surface due to the pullout of fiber bundles with epoxy, whereas VSB-16/epoxy composites under tensile and bending loads showed only tensile (or compressive) failure. The composites of epoxy/PAN (polyacrylonitrile)-based fibers (AS4) showed greater ILSS than those of the pitch-based fiber (VSB-16)/epoxy. The most characteristic features of the interlaminar shear failure surface of AS4/epoxy composites are delamination and formation of hackles.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/adv.1989.060090307
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