Contrast displays

The more stable cioso-carboranes, by contrast (displayed in Figs. 2 and 3), react with these same reagents at higher temperatures to form other do o-carboranes or to form dilithio-cioso derivatives such as LiaCzBjHj 169). 

Digital x rays can be modified electronically to increase contrast, display certain structures in color or three dimensions, or subtract areas that interfere, allowing clearer pictures of structures such as veins and arteries. Very small differences in density may be amplified for even clearer viewing. This may be important in cases in which a contrast medium is injected into veins or arteries enhancing small differences allows the use of smaller amounts of the contrast medium, lessening the danger to patients. 

The application of an electric field above the threshold value results in a reorientation of the nematic liquid crystal mixture, if the nematic phase is of negative dielectric anisotropy. The optically active dopant then applies a torque to the nematic phase and causes a helical structure to be formed in the plane of the display. The guest dye molecules are also reoriented and, therefore, the display appears coloured in the activated pixels. Thus, a positive contrast display is produced of coloured information against a white background. The threshold voltage is dependent upon the elastic constants, the magnitude of the dielectric anisotropy, and the ratio of the cell gap to the chiral nematic pitch ... 

The Fc fragments lack the regions of variable sequence. Because their (nearly constant) sequences are quite similar to each other, the properties of their surfaces also are quite similar, and they are able to interact with each other to form a regular lattice. The group of Fab fragments, by contrast, display a heterogeneous variety of binding surfaces. 

Some reactions are simply accelerated by application of acoustic waves to a reaction mixture no change in the nature of the products formed is associated with the sonochemical activation. Other reactions, in sharp contrast, display "sonochemical switching", which in a number of instances is a symptom of a class 1 reaction the application of ultrasonic waves may completely change the proportion of products or even cause the appearance of new compounds. 

Helical Poly(phenylacetylenes). The most widely studied helical-substituted polyacetylenes are based on poly(phenylacetylene) with chiral ring substituents. Pol5unerization of chiral phenylacetylenes was first reported in 1995 (72). 4-(-)-Menthoxycarbonylphenylacetylene (41) was subjected to the polymerization with several transition metal catalysts such as [(nbd)RhCl]2 and WCle. The resultant Rh-based polymer shows a large optical rotation and intense CD effects in the electric absorption region of the main chain. The polymer, thus, exists in a helical conformation with an excess of one-handed screw-sense. Poly(phenylacetylene) with small chiral pendants, poly(42), in contrast, displays poorer chiroptical properties. Interestingly, an increase in temperature steeply increases the optical rotation of poly(41) if the polymer is produced with a W catalyst. Such a drastic enhancement of chiroptical properties is not observed in the case of Rh-based poly(41). 

Drzaic, P. S., Wiley, R. C., and McCoy, J., High brightness and colour contrast displays constructed from nematic droplet/polymer films incorporating dichroic dyes, Proc. SPIE, 1080, 41, 1989. 

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