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  • Articles  (3)
  • 21.10 Hw  (2)
  • free volume  (1)
  • polyimides  (1)
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  • Articles  (3)
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  • 1
    ISSN: 1434-601X
    Keywords: 27.30+t ; 21.10 Hw ; 21.60 Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theγ-decays of levels in26Mg have been investigated up to 12.5 MeV excitation energy by proton-γ-ray coincidence measurements in the23Na(α, pγ) reaction at 14.2 and 16 MeV bombarding energy. Lifetime-measurements, made with the Doppler-shift attenuation method, and proton-γ-ray angular-correlation measurements were performed at Eα=14.2 MeV. Many high-spin states were observed, among them levels at 6,978 (5+), 7,283(4−), 7,395(5+), 7,953(5−), 8,202(6+), 8,472(6+), 9,065(5), 9,112(6+), 9,169(6−), 9,383 (6+), 9,542(5), 9,829(7+), 9,989(6+) and 12,479(8+, 7−) keV excitation energy. The spectrum of positive-parity states and their electromagnetic properties are reproduced with good accuracy by shell-model calculations which employ a unifieds-d shell Hamiltonian and the unrestricted configuration space of the 0d 5/2 1s 1/2 0d 3/2 shell. Members of five inferred rotational bands, withK π=0+, 2+, 3+, 0+ and 3− have been observed up to at leastI=6. TheK π=2+ band shows strong anomalies of excitation energies andE2 transition rates near theI=6 state. The static intrinsic quadrupole moments calculated from the shell model wave functions indicate transitions from prolate to oblate deformation within theK π=2+ band and also the ground state band. The lowest lyingI π=4+ state appears to be “spherical” and cannot be associated with a rotational band.
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  • 2
    ISSN: 1434-601X
    Keywords: 27.30+t ; 21.10 Hw ; 21.60 Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New shell model calculations have predicted several high-spin (I π=5+ and 6+) levels in28Si near 10 MeV excitation energy which are missing from or ambiguous in existing experimental studies. Angular distributions, linear polarizations and Doppler-shifts ofγ-rays have been measured for theγ-decay of theE p=1,911 and 2,073 KeV resonances of the27Al(p, γ) reaction in an attempt to discover these missing states or confirm the discrepancies between experiment and theory. The excitation energies and spin-parities of the resonances were determined as 13,424.4±0.2 keV,I π=5+ and 13,582.3±0.5 keV,I π=6+. States populated in theγ-decay of these resonances were assigned spins and parities as follows: 11,777 keV,I π=5+; 11,331 keV,I π=6+; 10,417 keV,I π=5+; 9,417 keV,I π=4+ and 8,945 keV,I π=5+. On the basis ofγ-ray transition rates T=1 is assigned to the 13,424 keV level and T=0 to the 10,417 and 11,777 keV levels. With the new data excellent agreement is achieved between the experimental spectrum of28Si and the new shell model predictions. These data provide evidence for aK π=3+ rotational band comprised by the 6,276, 6,889, 8,945 and 11,331 keV levels. This band emerges also from the shell model wave functions as do theK π=0+ bands based on the ground state and the 6,691 keV state.
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1855-1868 
    ISSN: 0887-6266
    Keywords: gas permeability ; permselectivity ; activation energies ; free volume ; polyimides ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas transport of helium, hydrogen, carbon dioxide, oxygen, argon, nitrogen, and methane in three soluble poly(phenylene sulfone imide)s based on 2,2-bis(3,4-decarboxyphenyl) hexafluoropropane dianhydride (6FDA) has been investigated. The effects of increasing length of well-defined oligo(phenylene sulfone) units on the gas permeabilities and diffusivities were determined and correlated with chain packing of the polymers. Activation energies of diffusion and permeation were calculated from temperature-dependent time-lag measurements. The influences of the central group in the diamine moiety of 6FDA-based polyimides on physical and gas transport properties are discussed. The incorporation of a long oligo(phenylene sulfone) segment in the polymer backbone decreases gas permeability and permselectivity simultaneously. The decreases in permeability coefficients can be mainly related to decreases in diffusion coefficients. Changing the central group of diamine moiety from —S— to —SO2— leads to a 45-50% decrease in CO2 and O2 permeabilities without appreciable increase in the selectivities. This is considered to be due to the formation of charge transfer complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1855-1868, 1997
    Additional Material: 10 Ill.
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