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991.
J. S. Vrentas D. C. Venerus C. M. Vrentas 《Journal of Polymer Science.Polymer Physics》1991,29(5):537-545
An integral constitutive equation which includes strain-coupling effects is proposed. The constitutive equation is more general than the K-BKZ equation, and it is shown that this equation can explain various important aspects of double-step stress-relaxation data. 相似文献
992.
993.
P. Ila 《Journal of Radioanalytical and Nuclear Chemistry》1991,148(2):415-422
Total oxygen, in fourteen rock standards and three ores, was determined with an experimental set up employing cyclic activation analysis using a 14 MeV neutron generator gamma-spectroscopy and NaI(T1) detectors. 相似文献
994.
P. G. Kosky 《Journal of polymer science. Part A, Polymer chemistry》1991,29(1):101-111
Cyclic oligocarbonates are synthesized by two-phase interfacial reactions of aryl bischloroformates in the presence of an amine phase transfer catalyst and an alkali: nClOCOArOCOCl + 4nNaOH → (OArOCO)n + 2nNaCl + nNa2CO3 + 2nH2O. The organocarbonate product may be a macrocyclic oligomer or a linear chain polymer. A qualitative mechanism for this behavior has been proposed by Brunelle, Boden, and co-workers. Four steps are identifiable: activation of the aryl bischloroformate by the amine catalyst, hydrolysis of a portion of this intermediate at the aqueous/organic phase interface, oligomerization between activated and hydrolyzed moieties also at the interface, and chain terminating carbamate formation that leads to polymer. An important modification is made within the framework of the Brunelle and Boden mechanism. While the intramolecular cyclization reaction is formally second-order overall, it behaves as a first-order process. The kinetic constants for both this pseudo-first-order cyclization step and the corresponding second-order linearization step are simply related. It is speculated that the above relationship can be generalized for a whole class of pseudo-first- and second-order rate constants for similar macrocyclic reactions. 相似文献
995.
A E Abdel-Megied P Hansen E B Pedersen C M Nielsen 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(10):1060-1063
The 3'-iodonucleoside 4 and the 3'-O-methylsulfonylthymidine 9 have been synthesized by condensation of silylated uracils 2 with methyl 5-O-tert-butyldiphensilyl-2,3-dideoxy-3-iodo-D-threo-pentofuran oside (3) and methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-3-methylsulfonyl-D-erythro- pentofuranoside (8), respectively. The nucleoside 4 and 9 produced the corresponding 2',3'-didehydro-2',3'-dideoxynucleosides 5 in an elimination reaction on treatment with sodium methoxide. The compounds 5b showed no antiviral activity against HIV-1. 相似文献
996.
F. I. Vybornov E. E. Mityakova A. V. Rakhlin N. D. Krupenya 《Radiophysics and Quantum Electronics》1997,40(12):980-986
We present the results of analysis of the data of vertical ionospheric sounding at the Zimenki test site (Nizhny Novgorod).
The January and July ionograms are used to plot the dependences of the number of “sickle” type disturbances on the time of
the day for the period from 1996 to 1992. A comparison with the scattering in an ionospheric F-layer for the same period is
performed. A trend in the time series of the phenomenon observed is recorded.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 40, No. 12, pp. 1455–1462, December, 1997. 相似文献
997.
A three-phase model of a hybrid chiral quark bag is proposed. In addition to the phases of asymptotically free current quarks
and of totally colorless mesons, the model contains the intermediate phase of massive constituent quarks. A self-consistent
solution with an account for the “Dirac sea” contribution is found in the (1+1)-dimensional case. The dependence of the bag
parameters on the parameters of the theory is investigated analytically and numerically.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 117, No. 2, pp. 263–299, November, 1998. 相似文献
998.
Muonium in liquid SiCl has been observed for the first time at low temperature (−65°C) The observed polarization of muonium
is as much as 25% of the total spin polarization and shows a fast relaxation rate. 相似文献
999.
Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06
μm radiation are reported. We observep
−0.8 scaling ofI
th at 1.06 μm and a weak scaling ofp
−0.4 at 0.532 and 0.355 μm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure
is observed. 相似文献
1000.
Summary An attempt is made to explain the masses of Z and W± bosons by means of a screening mechanism analogous to charge screening in metals. It considers the effect of the electroweak
force on the distribution of negativekinetic-energy neutrinos, which fills the whole universe (neutrino Fermi sea). The large
weak-boson masses appear to be a direct consequence of the vanishing neutrino mass. 相似文献