Refractive index studies

Despite the above observation, we discovered only a slight gradation in composition from top to bottom in the sample via refractive index studies. The eutectic microstructures we present below are observed throughout their respective specimens with only minor variations in scale and primary-phase abundance. 

Refractive index studies allow measurements of the birefringence, but also of the polarisability. The mean polarisability (a) can be determined using an isotropic liquid solution, whereas the polarisability anisotropy (Aa) is measured in the mesophase. Polarisability studies have been made on palladium, platinum, iridium and silver metallomesogens, and show a higher polarisability for the metal complexes than for their parent ligands. ... 

Mahler, D.T., Scott, A.S., Walsh. J.R. and Haynic, G. (1970). A study of trace metals in finger nails and hair using neutron activation analysis. J.Nucl. Med. 11,739-742 Malik. S.R. and Fremlin, J.H. (1974). A study of lead distribution in human teeth using charged particle activation analysis. Caries Res. 8, 283-292 Manly, R.S. and Hodge, H.G. (1939). Density and refractive index studies of dental hard tissue, J. Dent. Res. 18,133-141... 

Kharat SJ (2008) Density, viscosity, conductivity, ultrasonic velocity, and refractive index studies of aqueous solutions of citric acid at different temperatures. Int J Appl Chem (UAC)... 

In an early study, Greenleaf et al. [4] reported reconstructions of ultrasonic velocity from time-of-flight profiles. Since then there has been periodic activity in using ultrasound to determine the transmission properties attenuation or refractive index. 

Solvents exert their influence on organic reactions through a complicated mixture of all possible types of noncovalent interactions. Chemists have tried to unravel this entanglement and, ideally, want to assess the relative importance of all interactions separately. In a typical approach, a property of a reaction (e.g. its rate or selectivity) is measured in a laige number of different solvents. All these solvents have unique characteristics, quantified by their physical properties (i.e. refractive index, dielectric constant) or empirical parameters (e.g. ET(30)-value, AN). Linear correlations between a reaction property and one or more of these solvent properties (Linear Free Energy Relationships - LFER) reveal which noncovalent interactions are of major importance. The major drawback of this approach lies in the fact that the solvent parameters are often not independent. Alternatively, theoretical models and computer simulations can provide valuable information. Both methods have been applied successfully in studies of the solvent effects on Diels-Alder reactions. 

Theoretical and structural studies have been briefly reviewed as late as 1979 (79AHC(25)147) (discussed were the aromaticity, basicity, thermodynamic properties, molecular dimensions and tautomeric properties ) and also in the early 1960s (63ahC(2)365, 62hC(17)1, p. 117). Significant new data have not been added but refinements in the data have been recorded. Tables on electron density, density, refractive indexes, molar refractivity, surface data and dissociation constants of isoxazole and its derivatives have been compiled (62HC(17)l,p. 177). Short reviews on all aspects of the physical properties as applied to isoxazoles have appeared in the series Physical Methods in Heterocyclic Chemistry (1963-1976, vols. 1-6). 

With liquids, the refractive index at a specified temperature and wavelength is a sensitive test of purity. Note however that this is sensitive to dissolved gases such as O2, N2 or CO2. Under favourable conditions, freezing curve studies are sensitive to impurity levels of as little as 0.(X)1 moles per cent. Analogous fusion curves or heat capacity measurements can be up to ten times as sensitive as this. With these exceptions, most of the above methods are rather insensitive, especially if the impurities and the substances in which they occur are chemically similar. In some cases, even an impurity comprising many parts per million of a sample may escape detection. 

As shown in Fig. 7, a large increase in optical absorption occurs at higher photon energies above the HOMO-LUMO gap where electric dipole transitions become allowed. Transmission spectra taken in this range (see Fig. 7) confirm the similarity of the optical spectra for solid Ceo and Ceo in solution (decalin) [78], as well as a similarity to electron energy loss spectra shown as the inset to this figure. The optical properties of solid Ceo and C70 have been studied over a wide frequency range [78, 79, 80] and yield the complex refractive index n(cj) = n(cj) + and the optical dielectric function... 

The relatively simple study of fluorescence and phosphorescence (based on the action of colour centres) has nowadays extended to nonlinear optical crystals, in which the refractive index is sensitive to the light intensity or (in the photorefractive variety (Agullo-Lopez 1994) also to its spatial variation) a range of crystals, the stereotype of which is lithium niobate, is now used. 

Gel permeation chromatography studies using both refractive index and UV(260 nm) absorption detections have confirmed that both Acacia Senegal and Acacia seyal gums consist of three main components (Islam et al., 1997, Idris et al., 1998, Williams Phillips, 2000, Al Assaf 2006) ... 

In this study, four Styragel columns were utilized one column had a nominal porosity rating of 10, two colvtmns of 10, and the fourth column of 10 A. The refractometer was maintained at 37°C. A 5 ml syphon was used to monitor a solvent flow rate of 1 ml/min. The instrviment was run at the highest sensitivity setting because the refractive index difference between our solvent and polymer was only moderate and because a number of samples analyzed had a broad molecular weight distribution (MWD). 

Ikegami Imai (1962) made a study of precipitation and hydration using turbidity, conductance, refractive index and viscosity measurements. The following account is based on their description. 

Ellipsometry is used to study film growth on electrode surfaces. It is possible to study films at the partial monolayer level and all the way up to coverage of thicknesses of thousands of angstroms while doing electrochemical measnrements. To get nseful data it is important to determine A and j/ for the bare electrode snrface and the surface with a film. These data are processed to derive the film thickness, d, and the refractive index, h, which consists of a real (n) and imaginary part (k), h = n- ik. So ellipsometry gives information on the thickness and refractive index of snrface hlms. 

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