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  • Polymer and Materials Science  (3)
  • ASTROPHYSICS  (2)
  • Chemical Engineering  (1)
  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 403-408 
    ISSN: 0887-6266
    Keywords: gas permeability ; selectivity ; barrier membranes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Diffusion, solubility, and permebility coefficients were measured for He, Co2, Ar, and CH4 in polybutadiene (PB) and in polybutadiene reacted in the solid state to various extents with aqueous bromine. Analysis of the sorption curves and X-ray emission spectra showed that the bromination created a heterogeneous membrane with an outer brominated skin and an unreacted core. At relatively low extent of bromination, the diffusion and permeability coefficients for CO2, Ar, and CH4 decreased by two orders of magnitude, while the transport coefficients for He were virtually unchanged. The permeability coefficients for CO2, Ar, and CH4 became immeasurably small after about 3% bromination. The ideal separation factor for gas pairs with different molecular size increased with bromination, suggesting applications in gas separation processes. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 1223-1227 
    ISSN: 0021-8995
    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 , Physics
    Notes: Over the temperature range of 20 to 90°C, the equilibrium solubility of methane or argon in a star-branched polystyrene-polybutadiene (SB) block copolymer can be reliably estimated from a volume-fraction-weighted average of the homopolymer solubilities; the value of heat of solution for SB block copolymer lies between the two values associated with the constituent homopolymers. Diffusion coefficients for gases in the block copolymer are bracketed by the homopolymer values over the range of temperature employed, but the activation energies for diffusion in SB are higher than either of the homopolymer values. The anomalous temperature dependence and the inability of a computer simulation to reproduce experimental diffusion coefficients supported the concept of a temperature-dependent restriction on chain mobility in the polybutadiene regions of the block copolymer. This β factor embodies the relative reduction in the rate of gas diffusion through the B regions of the copolymer compared to B homopolymer; β has a value of about 2-3 at room temperature but decreases to unity when the polystyrene chains become mobile at the polystyrene Tg.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 14 (1992), S. 69-73 
    ISSN: 0193-7197
    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 , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fatigue resistance of 6 inch Schedule 40 PVC solvent-bonded pipe fittings was investigated. It has often been assumed that the performance of PVC fittings is comparable to that of the corresponding pipe. The results of this study indicate that the fatigue performance of PVC fittings is much lower than that of the pipe. Several fittings were exposed to a repetitive surge cycle of 90 to 180 psig at a rate of 0.111 hertz. Failures of several tees occurred between 13,000 and 16,000 cycles, much sooner than the predicted lifetime of pipe under these conditions.
    Additional Material: 4 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 45 (1994), S. 301-307 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new “Durham” polyacetylene precursor monomer (substituted tricyclo[4.2.2.02,5]deca-3,7,9-triene) was synthesized, and improved synthetic pathways to two existing precursor monomers were developed. Polymers of these three precursor monomers, as well as a bis-trifluoro substituted precursor monomer, were synthesized using ring opening metathesis polymerization (ROMP) with a tungsten alkylidine initiator. The kinetics of conversion (precursor polymer to polyacetylene) were studied for each of the four precursor polymers using differential scanning calorimetry (DSC). Percent age conversion vs. time data were fit to the Avrami expression often used to describe the kinetics of bulk of crystallization of polymers. The parameter K of the Avrami expression was assumed to depend on temperature according to an Arrhenius expression. In this way, an equation with three constants was obtained that completely describes the kinetics of conversion of a particular polyacetylene precursor polymer. Values for the constants depended on the type of substituent on the precursor polymer. Because the kinetics are well described by the Avrami expression, it is proposed that “nucleation” and “propagation” processes are involved in the conversion of the precursor polymers to polyacetylene.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2019-08-28
    Description: We report on the results of a continuation of a large monitoring program of optical spectroscopy of the Seyfert 1 galaxy NGC 5548. The new observations presented here were obtained between 1990 December and 1992 October, and extend the existing database to nearly 1400 days, dating back to 1988 December. The continuum variations are generally smooth and well-resolved, except during the third year of this 4 year project, when the variations were apparently more rapid and of lower amplitude than observed at other times. The broad H(beta) emission line is found to vary in response to the continuum variations with a lag of about 18 days, but with some changes from year to year. The H(beta) transfer functions for each of the 4 yr and for the entire 4 yr database are derived by using a maximum entropy method.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 425; 2; p. 622-634
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  • 6
    Publication Date: 2019-07-12
    Description: Seven rovibrational transitions of the (01/1/0)-(00/0/0) fundamental bending band of C3 have been measured with high precision with the use of a tunable far-infrared laser spectrometer. The C3 molecules were produced by laser vaporization of a graphite rod and cooled in a supersonic expansion. The astrophysically important nu-2 fundamental frequency is determined to be 63.416529(40)/cm. These measurements provide the basis for studies of C3 in the interstellar medium with far-infrared astronomy.
    Keywords: ASTROPHYSICS
    Type: Science (ISSN 0036-8075); 249; 897-900
    Format: text
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