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991.
992.
993.
A simple model of semimetals in a strong magnetic field is studied in the Hartree-Fock approximation by taking into account both the excitonic and liquid-gas type transitions simultaneously. 相似文献
994.
Stress, strain, and birefringence measurements have been carried out on swollen and unswollen networks of ′cis-1,4-polybutadiene polymers. Neither stress-strain nor birefringence-strain relations of unswollen specimens obey the Gaussian network theory, but both can be fitted by the Mooney-Rivlin equation. On the contrary, data on specimens swollen in tetralin, decalin, benzene, and carbon tetrachloride strictly obey the Gaussian network theory. Existing methods for evaluating the temperature coefficient of the unperturbed dimensions, d In 〈r2〉/dT, from the stress-temperature relation are applied to the present data and discussed in some detail. It is concluded that reliable values of d In 〈r2〉/dT are not obtainable from data on unswollen samples because of the pronounced non-Gaussian effect. The value 7.5 Å3 for the optical anisotropy Å3 (an alternative to the stress-optical coefficient) for unswollen specimens is markedly larger than values (5.8 Å3 on the average) for swollen specimens. This is interpreted as due to the shortrange orientational order among polymer segments. The quantities 〈r2〉, ΔΓ, and their temperature coefficients are calculated for both cis-1,4-polybutadiene and cis-1,4-polyisoprene chains, on the basis of the rotational isomeric state approximation for bond rotations. Values of ΔΓ for cis-1,4-polybutadiene calculated using Clément and Bothorel's set of anisotropic bond polarizabilities are in good agreement with observed values for swollen specimens. Those for cis-1,4-polyisoprene obtained using the same set of anisotropic bond polarizabilities are somewhat smaller than observed values for unswollen specimens. This departure is in the direction expected from the behavior of ΔΓ upon swelling (i.e., a decrease in ΔΓ upon swelling). 相似文献
995.
996.
In order to elucidate the relations between morphological habits and chemical structure of polymers, poly(ethylene sebacate), poly(hexamethylene sebacate) and poly(decamethylene 1,16-hexadecanedicarboxylate) were crystallized from dilute solutions in n-hexanol, isoamyl acetate etc., and were studied with the electron microscopy and x-ray diffraction. The crystal structure of these polyesters are tentatively determined. Morphological “regularity” and “simplicity” of the single crystals are correlated with the chemical structure of the polymers. The crystallization conditions under which “regular” and “simple” single crystals are obtained are relaxed with increase of methylene sequence length in chemical repeat unit. The Bragg extinction bands in the single crystals of poly(hexamethylene sebacate) and poly(decamethylene 1,16-hexadecanedicarboxylate) suggest nonplanar nature of these crystals. The molecular chains in the poly(ethylene sebacate) single crystals are inclined from the normal of the basal plane; the fold surface corresponds to the (001) plane. 相似文献
997.
998.
The stoichiometry of the reaction between lead dioxide suspension and EDTA was studied by derivative polarographic titration and determination of the products. Four moles of Pb(IV) are reduced per mole of EDTA with moderate speed at room temperature in sulphuric acid solutions. Four moles of carbon dioxide and 3 moles of formaldehyde are the products of the oxidation of 1 mole of EDTA. One mole of N-hydroxymethylethylenediamine is also thought to be produced. The overall reaction may be written as 4Pb(IV) + EDTA + 4H(2)O-->4Pb(II) + 4CO(2) + 3HCHO + H(2)NCH(2)CH(2)NHCH(2)OH + 8H(+). Ethylenediamine is also partly produced if a large excess of lead dioxide is used. 相似文献
999.
Hideyuki Matsumoto Miyuki Kasahara Ikuya Matsubara Masatoshi Takahashi Takeshi Arai Minoru Hasegawa Taichi Nakano Yoichiro Nagai 《Journal of organometallic chemistry》1983,250(1):99-107
This paper describes the facile dechlorinative silylation of benzylic chlorides of types XC6H4CH2Cl (X = H, Me and Cl) and ClCH2C6H4CH2Cl (o-, m- and p-isomers) with methylchlorodisilanes ClMe2SiSiMe2Cl, ClMe2SiSiMeCl2 and Cl2MeSiSiMeCl2 in the presence of Pd(PPh3)4 to give the corresponding benzylmethylchlorosilanes in good to high yields. 相似文献
1000.
K. Nagai 《Surface science》1984,136(1):L14-L18
An explanation for the phase diagram of the H/Ni(111) system is proposed, where the existence of the p(2 × 2) phase is assumed in addition to the (2 × 2) phase. Using the position-space renormalization-group theory with prefacing transformation, a lattice gas on a honeycomb lattice, including up to 6th nearest neighbor interactions, is treated. Another explanation previously put forward by Domany et al. is also examined, where the occurrence of the (2 × 2) ordered phase and the gas + p(2 × 2) coexistence phase is assumed. The phase diagrams thus obtained for these two cases are exhibited and discussed. 相似文献