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831.
832.
The dilute-solution behavior of poly(vinyl alcohol) (PVAVTFA), derived from vinyl trifluoroacetate, in water-dimethylsulfoxide (DMSO) mixtures was investigated. With solvent mixtures ranging from 10 to 20 vol % DMSO, the relation between the reduced viscosity ηsp/C and the polymer concentration C was linear for polymer concentrations above 0.2 g/dL, whereas in solutions in mixed solvents of other compositions the dependence was linear for polymer concentrations above 0.1 g/dL. The relation between the intrinsic viscosity [η] obtained for aqueous solutions of PVAVTFA and the molecular weight M estimated from viscosity measurements in solutions of poly(vinyl acetate) (PVAVTFA), obtained by acetylation of PVAVTFA, was given by [η] = 7.34 × 10?4 M0.63. The value of [η] was greatest for the solvent mixture with 10 vol % DMSO and smallest for about 50 vol % DMSO, and Huggins constants k were smallest and greatest for these two cases, respectively. The turbidity of the solutions of low-molecular-weight PVAVTFA, was higher than that of high-molecular-weight PVAVTFA up to 30 vol % DMSO, and the reverse relation held for 40-70 vol % DMSO.  相似文献   
833.
834.
835.
Microwave spectra of SF2 in the first excited states of the three normal modes were observed and analyzed. A comparison of the observed inertia defects in the ν1 and ν3 states with those calculated by omitting the contributions of the Coriolis interaction between the two modes led to a ν?1 - ν?3 vibrational frequency differences of 25.72 ± 0.33 cm?1, with ν1 being definitely higher. The inertia defect in the ground state and our measured values for the inertia defect in the ν2 state and for the ν?1 - ν?3 difference were combined with the centrifugal distortion constants of Kirchhoff et al. [J. Mol. Spectrosc.48, 157–164 (1973)] to improve the harmonic force field. The interaction constant between the two SF stretching coordinates was determined precisely. The third-order and the cubic anharmonic potential constants were calculated from the observed vibration-rotation constants. The equilibrium structure was determined to be re(SF) = 1.58745 ± 0.00012 A? and θe(FSF) = 98.048 ± 0.013°.  相似文献   
836.
Photoluminescence decay was observed with various excitation energies and at various temperatures in amorphous As2S3. The decay at high temperature or with the high excitation energy had the t-32 long time behavior. This decay is concluded to arise from the combination of the tunneling recombination and the variable range hopping of carriers in the band tail.  相似文献   
837.
The rate for hydrolysis, chemoselectivitly toward nucleophiles, and partition property of N-neopentyl-, N-trimethylsilylmethyl-, and N-trimethylgermylmethyl-N-nitrosoureas were compared. The latter two compounds are silicon and germanium analogues of the neopentyl derivative. The substitution effect of Ge in place of Si or C are discussed on the chemical and physicochemical properties.  相似文献   
838.
839.
InGaN/GaN‐based light emitting diodes (LEDs) grown on m ‐plane, a ‐plane and off‐axis between m ‐ and a ‐plane GaN bulk substrates were investigated. A smooth surface was obtained when a ‐plane substrate was applied; however, large amounts of defects were observed. Photoluminescence measurements of the LEDs with a well thickness of 2.5 nm revealed that all the LEDs showed the peak emission wavelength at 389 nm. The PL intensity of the a ‐plane LED is one order of magnitude lower than that of the m ‐plane LED. The a ‐plane LEDs showed significant lower electroluminescence output powers than m ‐plane LEDs, suggesting that excitons are trapped by the defects, which act as non‐radiative recombination centers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
840.
Optical absorption edge in annealed As2S3 films shifts to lower energy after band-gap illumination. In these photodarkened films, polarization memory of photoluminescence was found to increase. In the case of illumination with linearly polarized light, anisotropy is induced in the absorption edge. The polarization memory was larger for larger shift of absorption edge. In contrast with this trend, the memory was smaller in As-rich films, the absorption edge of which was located at lower energy. It is considered that the optical anisotropy of the luminescence centers increases accompanying the reversible photostructural change.  相似文献   
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