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51.
Siegel R Dupré N Quarton M Hirschinger J 《Magnetic resonance in chemistry : MRC》2004,42(12):1022-1026
51V magic angle spinning NMR was applied to the alpha(II), beta and gamma phases of VOPO4 at three magnetic field strengths (4.7, 7.1, and 11.7 T). The 51V quadrupole and chemical shift tensors were determined by iterative fitting of the NMR lineshapes at the three magnetic field strengths. The applicability of the method is illustrated by comparison with literature data. Although determined chemical shift tensors are completely axially symmetric and of the same magnitude, all studied phases can clearly be distinguished by their quadrupole coupling tensor. Relationships between the 51V NMR data and structural characteristics such as crystal symmetries are discussed. 相似文献
52.
53.
Abstract Examination of the Rayleigh line of a lyotropic cholesteric polypeptide liquid crystal by the techniques of quasielastic light scattering spectroscopy reveals the presence of two new purely dissipative low frequency light scattering modes of comparable intensity. Angular and electric field dependences of the deconvoluted spectra are consistent with the identification of the mechanism as due to twist and viscous-splay normal modes recently predicted theoretically. Analysis of the narrow mode on this basis yields a value of γ1, the twist viscosity coefficient of the medium. The broader mode results in an estimate of the value of the ratio of the splay to bend elastic moduli, K 11/K 33 ~ 10?5, which is shown to be in accord weith mean field theoretical calculations for a system of such highly elongated macromolecules. 相似文献
54.
The ordinary and extraordinary refractive indices have been measured for lyotropic liquid crystal solutions of poly-γ-benzyl-L-glutamate. The onset of the liquid crystal formation is noted as an abrupt jump in the sample birefringence in the biphasic region. The concentration dependence is otherwise unremarkable. The polymer is found to add a small, anisotropic increment to the refractivity of the supporting solvent. Both n o and n e can thus be measured in an ordinary Abbé refractometer for the low refractive solvents common to these liquid crystal solutions. The optical birefringence does not depend significantly on polymer molecular weight. Data is also included for the wavelength dependence (dispersion) of n o, n e, and Δn. 相似文献
55.
A detailed kinetic model devoted to the hydrazine vapor detonation has been built. It consists of 33 reversible reactions
and 13 species. A reduced kinetic model has been proposed by using the Principal Component Analysis of matrix F (PCAF) method
as implemented in KINALC. It is constituted of 26 reactions and 11 species. This model has been shown to be valid over a pressure
range of 0.1 to 10 atm. However, the predictions of the models are significantly affected by changes in the enthalpy of formation
of NH. With the help of the full kinetic model, a value of A, the proportionality factor in the ZND model between the induction
distance in the detonation wave and the detonation cell size, of has been derived if one considers that the collision efficiency of NH on the thermal decomposition of hydrazine is equal to the one of N. The value of A for pure hydrazine detonation is shown to be strongly dependent on the value of the collision efficiency
of NH.
Received 24 December 2000 / Accepted 11 April 2001 相似文献
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57.
The authors show a nondestructive method for obtaining the isochromatic and isoclinic fringes in a three-dimensional photoelastic
specimen. The basic idea is to delimit a slice between two plane laser beams. The properties of polarization of the scattered
light (Rayleigh's law) and the interference possibilities of the diffused beams are used. By introducing speckle pattern properties,
the correlation factor of the two scattered beams is similar to the illumination given in a plane polariscope for the investigation
of a slice (in a classical frozen-stress technique). The authors use a monochromatic laser beam, a CCD camera and a personal
computer. Because they cannot obtain the correlation factor directly, they do a statistical analysis of the speckle patterns.
The variance (function of the correlation factor) is computed from the light intensities of three images corresponding to
the speckle pattern for plane 1 alone, plane 2 alone, and both planes together. 相似文献
58.
59.
[reaction: see text] In the presence of catalytic amount of NiBr(2) as catalyst precursor, organic halides are reductively coupled at 70 degrees C with acrolein diethyl acetal to give (Z)- and (E)-enolethers by allylic deplacement of an alkoxy group. Subsequent hydrolysis affords beta-arylated aldehydes. 相似文献
60.
Quasielastic light scattering provides a direct probe of the diffusional mobility of large particles in solution. Analysis of the light scattering spectra of natural lecithin as a function of scattering angle and concentration in hydrophilic and lipophilic solvents supports the conclusion that the second critical micelle transition is associated with the elongation of spherical molecular aggregates into cylindrical or ellipsoidal particles. The effective radius of the scattering entity below the second critical point is significantly less in nonpolar solvents. The latter result is explained in terms of amphiphilic lipid-solvent interactions. 相似文献