Relative anisotropy index

Magnetic susceptibility anisotropy has been used to estimate relative aromaticities of some azines <1977JOC897>. If the extent of -electron delocalization for benzene is taken as 1.0, the corresponding values for azines are pyridine 0.7, pyridazine 0.7, pyrimidine 0.5, and 1,3,5-triazine 0.3. Another quantitative magnetic index is the exaltation of the total magnetic susceptibility (A). All aromatic systems reveal large A values, whereas for nonaromatic compounds A is close to zero and it is assumed that aromaticity increases with A. For six-membered monocycles the following values of A have been reported (in units of cm3 mol-1 x —106) benzene (17.9), pyridine (18.3), pyridazine (8.7), pyrimidine (18.2), pyrazine (12.7), l-ethyl-2-pyridone (13.0), and 1,3,5-triazine (19.0). 

Rodriguez Patino et al. [17] presented a method for estimating monolayer thickness (d) from relative intensity of light reflected from the interface. The grey level scale of BAM images was correlated to the relative reflectivity (/) - this allows for the estimation of changes in d upon film compression. The above method can only be applied to monolayers displaying no optical anisotropy, i.e. monolayers for which one value of refractive index can be assumed. For the calculation of surface film... 

Because of the large optical anisotropy of liquid crystals, the relative width A2/2 of this Darwin band is much larger than in X-ray crystallography where the modulation of the refractive index (for X-rays) is of the order of 10 . Experimentally, the measure of the Darwin band in cholesteric liquid crystals requires production of perfectly aligned samples and the use of a spectrometer. This can hardly be done during a lecture. 

As noted earlier, Qa/9 may be equally well-defined in terms of other macroscopic properties such as the refractive index or dielectric tensor. However, the simple relation [Eq. (3.6)] cannot be expected to hold for the dielectric anisotropy Ae and electric polarizability aij. This is due to complicated depolarization effects caused by the relatively large near-neighbor electrostatic interaction. The internal field corrections [3.3] are necessary in the electric case. It has been shown that Qa can be used to describe orientational order both in uniaxial and biaxial phases. Furthermore, measurement of Qa/3 is particularly useful when description of flexible molecules using microscopic order parameters becomes problematic. Experimentally, both magnetic resonance and Raman scattering techniques [3.3] may be employed to monitor the orientational order of individual molecules and to determine microscopic order parameters. 

The role of push-pull molecules in PR systems is to provide refractive index modulation in response to an electric field. In polymers with a low glass transition temperature (Tg), where the molecules are relatively free to rotate due to a higher free volume, the chromophores can reorient in the applied/generated electric field. Because of the anisotropy in polarizability of the chromophores, such a reorientation will induce high refractive index anisotropy termed as orientational birefringence. The ability of a chromophore molecule to induce refractive index change is usually expressed as the figure of merit (FOM) defined by Equation 8.4 [44],... 

The first observation of natural optical anisotropy was made in 1669 by Bartolinius in calcite crystals, in which light travels at different velocities depending on the direction of propagation relative to the crystal structure. The electrooptic effect, electric-field-induced anisotropy, was first observed in glass in 1875 by J. Kerr. Kerr found a nonlinear dependence of refractive index on applied electric field. The term Kerr effect is used to describe the quadratic electrooptic effect observed in isotropic materials. The linear electrooptic effect was first observed in quartz crystals in 1883 by W. Rontgen and A. Kundt. Pockels broadened the analysis of this relationship in quartz and other crystals, which led to the term Pockels effect to describe linear behavior. In the 1960s several developments... 

The delocalization of the skeletal o electrons results in high electronic polarizability of the boron clusters, but, due to molecular geometry, they exhibit low polarizability anisotropy.This results in relatively high isotropic refractive index n and low birefringence (An) of carborane-containing... 

We showed in the discussion of structural anisotropy above, that the core index must greatly exceed the cladding index for the propagation characteristics of the two fundamental modes to differ significantly. Here we show that a relatively small amount of material anisotropy can dramatically influence propagation by removing one of the two possible polarization states of the fundamental mode. This results in a fiber that is truly single moded. 

Polymer spherulites are most frequently studied by polarized optical microscopy because the method is fast, simple, and relatively inexpensive (see Section 1.1.2.1). The remarkable contrast in Figure 3.4 is provided by the birefringent nature of polymer crystals, in which the polarization, expressed as the dimensionless dielectric constant K, and the refractive index n = K - are direction dependent. This anisotropy is represented by the indicatrix, an ellipsoid with semi-axes equal in length to the three principal values of n. Isotropic liquids and glasses are nonbirefringent. Cubic crystals, which are... 

The anisotropic interactions cited above are of broader importance. According to theory, they depend directly on the square of the anisotropy Aa of the polarizability of the particle relative to its mean polarizability a. The anisotropy Aa can be evaluated from depolarized Rayleigh scattering combined with other measurements of optical anisotropy the mean polarizability a can be deduced from the refractive index. The magnitude of the orientation-dependent interaction can be expressed by a characteristic temperature 7 that denotes the magnitude of the interaction for perfect orientation. ... 

Generally, the main principle of behavior of compensators is based on operation of exclusion of any optical parameter. For example, in case of ordinary isotropic phase compensators the thickness and refraction index (n-d ) of optical element have to provide with concrete phase shifting k.X,...°°). Such compensators are used in interferometer tasks. In case of anisotropy compensators the notion of phase shift means not the absolute phase shifting for a given wavelength but rather the relative phase shifting (Ai ) between usual and imusual beams (waves).That is why that the ac-... 

We must not be misled by the examples of MgO, BaTi03 or diamond most ceramics do not crystallize in a cubic group arrd this implies that the many physical properties that are described by a second order terrsor are not isotropic [NYE 87]. Thermal expansion, optical index, electric and thermal conductivities, permittivity and permeability are at first view anisotropic, which can misinform some metallmgists, because the most cormnon metals (irort, alttminum, copper) are cubic. An effect of the anisotropy of thermal expansion is to create residual stress at the grain boundaries of the polycrystals. Beyond the properties described by a second order tensor, low synunetries combine with the properties of iono-covalent bonds to make dislocations rare and relatively immobile, which explains the lack of ductility and the impossibility of plastic deformation. 

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