Short pitch

Thermotropic cholesterics have several practical applications, some of which are very widespread. Most of the liquid crystal displays produced use either the twisted nematic (see Figure 7.3) or the supertwisted nematic electrooptical effects.6 The liquid crystal materials used in these cells contain a chiral component (effectively a cholesteric phase) which determines the twisting direction. Cholesteric LCs can also be used for storage displays utilizing the dynamic scattering mode.7 Short-pitch cholesterics with temperature-dependent selective reflection in the visible region show different colors at different temperatures and are used for popular digital thermometers.8... 

Note 3 With chiral nematic substances forming chiral nematic mesophases of short pitch (<700 nm), up to three blue phases occur in a narrow temperature range between the chiral nematic phase and the isotropic phase. 

Note 2 In the case of a short pitch, when P is less than the wavelength X, the macroscopic extraordinary axis for the refractive index is orthogonal to the director. 

Figure 5.7. A screw conveyor assembly and some of the many kinds of screws in use. (a) Screw conveyor assembly with feed hopper and discharge chute, (b) Standard shape with pitch equal to the diameter, the paddles retard the forward movement and promote mixing, (c) Short pitch suited to transfer of material up inclines of as much as 20°. (d) Cut flight screws combine a moderate mixing action with forward movement, used for light, fine, granular or flaky materials, (e) Ribbon flights are suited to sticky, gummy or viscous substances.

Various types of screws are used for modern conveyors. These include short-pitch, variable-pitch, cut flights, ribbon, and paddle screws. The Procedure given above also applies to these screws. 

The chiral side chain polymers derived from asymmetric esters of terephthalic acid and hydroquinone can form (in a broad temperature range, including ambient temperature) an unusual mesophase (the isotropic smectic phase, IsoSm ) characterized by high transparency and optical isotropy within the visible wavelength range, combined with a hidden layered smectic ordering and some elements of helical superstructure at shorter dimensions of 10 to 250 nm. The short-pitch TGB A model seems to be the most adequate for the mesophase structure. 

Buckets for continuous elevators are V-shaped in cross-section and carry their maximum load when the inclination of the elevator is such that the front and rear of the buckets are inclined equally to the vertical. Single-chain and belt elevators usually are operated at about double the speed of continuous bucket elevators so their inclination does not have to be so pronounced. Double-chain elevators when run in a vertical plane have their buckets suspended between the chains, to permit the required snubbing, but inchned elevators of the standard type, when inclined, have their buckets attached to the chains on their backs. Chains should be of the short-pitch variety to avoid pulsations as they pass about the end sprockets and when handhng abrasive material likely to raise dust they should be bushed. Supporting sprockets and rollers are used on inclined elevators to prevent the loaded side sinking and interfering with the return run of the elevator. 

Similar to short pitch, except pitch is reduced to 1/2 standard pitch. Useful for vertical or inclined applications and for extremely fluid materials. 

FIGURE 52.2 Screw feeder configurations (a) multiple-diameter feeder (b) short-pitch feeder (c) variable-pitch, twin-tapered feeder (d) live-bottom feeder. (From Screw Conveyor Corporation, Hammond, IN.)... 

Sticky or very cohesive materials can build up in short-pitch sections and conveying wiU cease. In this simation, special screw configurations should be used. 

Short-pitch screws allow conveyors to work more efficiently at moderate inclinations, but inclinations above 35 degrees are unusual for gravity... 

This structure, when it is present, appears always as the first stable tilted phase below the orthogonal SmA phase. Tilts in all layers are equal and also all phase differences a are equal. From this point of view the phase is equal to the SmC and the SmC phase. The main difference in the macroscopic properties is the magnitude of the angle a, which is neither close to zero nor close to tt (Fig. 5.4c and d). The structure is helicoidally modulated but has a very short pitch, which extends from a few tens of layers to shorter periods than four layers. Due to the short pitch, the structure optically does not differ from the orthogonal phase and does not exhibit other properties like optical rotatory power, typical for other helicoidally modulated structmes. 

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