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  • 1990-1994  (4)
  • Chemistry  (3)
  • Chemical Engineering  (1)
  • Ozone uptake  (1)
  • 1
    ISSN: 1432-2285
    Keywords: Ozone uptake ; Stomatal conductance ; Spruce
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The uptake of air pollutants depends both on pollutant concentration and on stomatal conductance. This paper deals with the uptake of ozone (O3) from the air into the needles of Norway spruce [Picea abies (L.) Karst.] under ambient climatic conditions. Regulation of O3 uptake by the stomata is shown and also the difference between the “physiologically active O3 concentration” and the O3 concentration of the ambient air. Data from the sun and shade crown of spruce trees at 1000 m a.s.l. are presented. Analysis of data from three vegetation periods has shown that at low ambient O3 concentrations the O3 uptake is largely regulated by stomatal conductance. Water vapour pressure deficit (VPD) of the atmosphere is the climatic factor which showed the highest positive correlation with O3 concentration. However, a high leaf-air VDP led to stomatal closure, thus reducing the O3 uptake in the needles despite high O3 concentrations in the ambient air. The potential O3 stress caused by high O3 concentrations can be strongly mitigated by this natural closing of the stomata and the simultaneous occurrence of moderate drought stress.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 352-356 
    ISSN: 0749-1581
    Keywords: Separated-local-field NMR ; Chemical-shift tensor orientations ; Poly(ethylene oxide) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C chemical-shift tensor orientations in the OCH2CH2O moieties of poly(ethylene oxide) (PEO) and poly(ethylene terephthalate) (PET) were determined by means of 1H—13C separated-local-field NMR spectroscopy, and the literature values for the shift tensors in polyethylene (PE) and polyoxymethylene (POM) were improved. An angular resolution of ± 4° was attained on standard equipment with 90° pulse lengths exceeding 4 μs. Relatively high uniformity of the methylene tensor orientations, complying with local molecular symmetry, was found.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 13 (1992), S. 197-206 
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: As part of an engineering analysis and experimental methodology to characterize prepreg tack, a compression-to-tension test was optimized to enhance reproducibility and generate intrinsic property data. With the resulting stress-strain compression and tension data, a theoretical model was developed to describe tack as a bulk viscoelastic property of a prepreg laminate stack. Using the viscoelastic analysis, four intrinsic material parameters to characterize prepreg tack could be defined. These were 1) relaxed modulus, 2) unrelaxed modulus, 3) relaxation time, and 4) initial void content of the prepreg stack. Relaxed and unrelaxed moduli of the prepreg stack were independent of temperature, while the relaxation time was highly dependent on temperature and matrix viscosity. In addition, the relaxation time was found to be influenced by resin/fiber content and prepreg surface characteristics, which also influenced the void content of the prepreg stack. Using these measured parameters, good agreement was observed between theory and experimental data for both the stress-strain curve of the tack test and the simplified compression tack index (CTI*), defined as the ratio of output energy of the prepreg stack during tensile unloading to input energy during compressive loading.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two new solid-state NMR methods for measuring orientation distributions in partially ordered solids are applied to high tensile-strength fibre polymers. Both methods use the anisotropy of the carbon-13 chemical shift tensor as a probe for local molecular directions, but they differ in the manner in which the information is extracted and complement one other. The spectral resolution is higher in the ORDER (ORientation Distributions with Enhanced Resolution) experiment, which employs rotor-synchronized three-dimensional magic angle spinning (MAS) NMR, while the angular precision with which the orientation distribution can be determined is higher in the DECODER (Direction Exchange with Correlation of Orientation Distribution Evaluation and Reconstruction) experiment. The utility of the two techniques is demonstrated by their application to the study of industrially produced poly(p-phenyleneterephthalamide) fibres. Both give the same result for the width (χ = 13°) and the order parameters (〈P2〉=0.85, 〈P4〉=0.57, 〈P6〉=0.34, 〈P8〉=0.14) of the orientation distribution.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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