Colour systems approach

A technically more appropriate approach is to separate reversible organic thermochromism into intrinsic systems, where heat is the sole cause of the colour change, from indirect systems, in which the colour variation involves changes in... 

The prospective applications ofmolecular assemblies seem so wide that their limits are difficult to set. The sizes of electronic devices in the computer industry are close to their lower limits. One simply cannot fit many more electronic elements into a cell since the walls between the elements in the cell would become too thin to insulate them effectively. Thus further miniaturization of today s devices will soon be virtually impossible. Therefore, another approach from bottom up was proposed. It consists in the creation of electronic devices of the size of a single molecule or of a well-defined molecular aggregate. This is an enormous technological task and only the first steps in this direction have been taken. In the future, organic compounds and supramolecular complexes will serve as conductors, as well as semi- and superconductors, since they can be easily obtained with sufficient, controllable purity and their properties can be fine tuned by minor adjustments of their structures. For instance, the charge-transfer complex of tetrathiafulvalene 21 with tetramethylquinodimethane 22 exhibits room- temperature conductivity [30] close to that of metals. Therefore it could be called an organic metal. Several systems which could serve as molecular devices have been proposed. One example of such a system which can also act as a sensor consists of a basic solution of phenolophthalein dye 10b with P-cyciodextrin 11. The purple solution of the dye not only loses its colour upon the complexation but the colour comes back when the solution is heated [31]. 

In a binary approach the image is processed in white and black colours—which may be called two levels quantization . It provides information in the most compact form, and so is used widely in practical systems where high speed and low costs are requirements. 

GHS is based on standardized approaches to make it easier for companies to comply with and for countries to implement the system. Standardisation can be applied to certain label elements - symbols, signal words, statements of hazard, precautionary statements - and to label format and colour and to SDS format. 

The MacAdam optical sensitivity chart shown in Fig. 26.21 does not take luminence into account and Silberstein (Phil. Mug., 1946, 37, 126) showed that when these ellipses were transferred to the three-dimensional version of the ehromatieity chart they would be ellipsoid as shown in Fig. 26.23. In order that a really satisfactory universally applieable speei-fieation for tolerances in colour matching can be established it is desirable that these ellipsoids should be spherical. This, unfortunately, is not possible and the nearest approach is the Simon and Goodwin system whieh takes the form of about 100 different charts in which, by alteration of the angle of the eo-ordinates of the ehromatieity chart the ellipses are COn-verted to eireles. The scale is such that each half-inch is equivalent to a threshold value of discrimination Fig. 26.24 (Shiot and Goodnih, Amer. Dyes Rep., 19.58, 105). 

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