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171.
Crosslinks are introduced by γ irradiation into 1,2-polybutadiene while strained in uniaxial extension near Tg with stretch ratio λ0, thereby trapping a proportion of the entanglements originally present. The stress at any subsequent strain λ is accurately given by the sum σN + σx, where σN is the stress contributed by a trapped entanglement network with λ = 1 as reference and a Mooney–Rivlin stress-strain relation, and σx is that contributed by a crosslink network with λ = λ0 as reference and neo-Hookean stress-strain relation. The birefringence is accurately given as δn = ?NσN + ?xσx, where the ?'s are the respective stress-optical coefficients. From measurements at λ = λ0 where σx = 0, ?N can be determined separately. For polymer with 88% 1,2 microstructure, ?N and ?x are nearly equal and independent of irradiation dose, though strongly dependent on temperature. For polymer with (95–96)% 1,2, ?N and ?x are different (even opposite in sign) and dependent on dose. This behavior is associated with a side reaction of cyclization by the γ irradiation, which is inhibited by the 1,4 moiety in the polymer with lesser 1,2 content. It is responsible for residual birefringence in the state of ease (λ = λs) where σN = –σx and the stress is zero. 相似文献
172.
Trevor R. Griffiths S. V. J. Lakshman A. Varada Rajulu 《Journal of chemical crystallography》1984,14(6):559-564
The optical absorption spectrum of the octahedral moiety CoCl4(H2O)2 in single crystal [(CH3)3NH]CoCl3·2H2O has been studied at room and liquidair temperatures. The observed ambient bands at 6800, 16,300, and 19,000 cm–1 have been assigned, respectively, to the transitions4
T
1(F) 4
T
2(F),4
A
2(F), and4
T
1 (P). The crystal field parameters evaluated areD
q
=B=850 cm–1, andC=4.63B. At liquid-air temperatures the4
T
1(P) band is seen to split into the expected four components
7,
8,
8, and
6, due to spin-orbit coupling, and the coupling coefficient was computed to be 525 cm–1. 相似文献
173.
174.
175.
Several aspects of the time-dependent-thermal-lensing (TDTL) technique were explored experimentally, including pressure effects, risetime behavior and falltime behavior. The experiments were performed using azulene vapor excited to high vibrational energies (≈ 17000 cm?1). It was found that the energy appears in translational degrees of freedom at very early times, but the intrinsic limitations of the technique permitted only an estimate of the V-T rate constant for excited azulene deactivation by krypton. The result is discussed in terms of other recent experiments, and it is tentatively concluded that deactivation of excited azulene by unexcited azulene molecules may proceed primarily by a V-V process. 相似文献
176.
Aequationes mathematicae - 相似文献
177.
Hans Peter Weber Trevor J. Petcher Marcel Hensch Conrad Hans Eugster 《Helvetica chimica acta》1975,58(7):2009-2018
The structures of two acid catalysed rearrangement products of taxochinone ( 1 ) have been determined by X-ray analysis. One of the products turned out to be a 20 (10→9) abeo-abietane ( 2 ), the other an optically inactive phenalenone ( 3 ). Crystals of the former compound, C20H26O3, belong to space group P212121 with four molecules per cell and the structure was refined with 879 significant reflexions to R = 0.032. Crystals of the latter compound, C20H22O2, belong to space group P21/c with 12 molecules per cell and the structure was refined with 1823 significant reflexions to R = 0.058. 相似文献
178.
Trevor W. Marshall 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1983,34(2):241-245
The solution is obtained, in the weak-damping approximation, to the problem of the approach to the barometric distribution in Brownian motion. 相似文献
179.
Deutsch D Henthorn T Marvin E Xu H 《The Journal of the Acoustical Society of America》2006,119(2):719-722
Absolute pitch is extremely rare in the U.S. and Europe; this rarity has so far been unexplained. This paper reports a substantial difference in the prevalence of absolute pitch in two normal populations, in a large-scale study employing an on-site test, without self-selection from within the target populations. Music conservatory students in the U.S. and China were tested. The Chinese subjects spoke the tone language Mandarin, in which pitch is involved in conveying the meaning of words. The American subjects were nontone language speakers. The earlier the age of onset of musical training, the greater the prevalence of absolute pitch; however, its prevalence was far greater among the Chinese than the U.S. students for each level of age of onset of musical training. The findings suggest that the potential for acquiring absolute pitch may be universal, and may be realized by enabling infants to associate pitches with verbal labels during the critical period for acquisition of features of their native language. 相似文献
180.
Reingold JA Uk Son S Bok Kim S Dullaghan CA Oh M Frake PC Carpenter GB Sweigart DA 《Dalton transactions (Cambridge, England : 2003)》2006,(20):2385-2398
Coordination of the carbocyclic ring of hydroquinones to electrophilic transition-metal fragments such as Mn(CO)3+ and Rh(COD)+ produces stable pi-bonded eta6-complexes that are activated to facile reversible deprotonation of the -OH groups. The deprotonations are accompanied by electron transfer to the transition metal, which acts as an internal oxidizing agent or electron sink. With manganese as the metal, the resulting eta5-semiquinone and eta4-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal-organometallic coordination networks. With rhodium as the metal, the pi-quinonoid complexes have been demonstrated to play a unique role in multifunctional C-C coupling catalysis and in the synthesis of new organolithium reagents. Both classes of pi-quinonoid complexes appear to have significant applications in nanochemistry by providing an excellent vehicle for templating the directed self-assembly of nanoparticles into functional materials. 相似文献