Switching time

Switching speed. Typical switching times for TN devices are 20 to 50ms, which is quite slow and has limited tl television displays. 

Tbe purpose of tbe bydroxyl group is to acbieve some hydrogen bonding with the nearby carbonyl group and therefore hinder the motion of the chiral center. Another way to achieve the chiral smectic Cphase is to add a chiral dopant to a smectic Chquid crystal. In order to achieve a material with fast switching times, a chiral compound with high spontaneous polarization is sometimes added to a mixture of low viscosity achiral smectic C compounds. These dopants sometimes possess Hquid crystal phases in pure form and sometimes do not. 

For determining the off potentials of cathodically protected pipelines, time relays are built into the cathodic protection station to intermpt the protection current synchronously with neighboring protection stations for 3 s every 30 s. The synchronous on and off switching of the protection stations is achieved with a synchronous motor activated by a cam-operated switch. The synchronization of the protection station is achieved as follows a time switch is built into the first protection station. An interruption of the protection current is detectable at the next protection station as a change in the pipe/soil potential. Since the switching time is known, the time switch of the second protection station can be activated synchronously. The switching of further protection stations can be synchronized in the same manner. 

Introducing the dimensionless variables x = and 6 = t/t, where t is the switch time interval, and is the length of one SMB column, the model equations become ... 

Fig. 9-4. Cyclic steady state internal concentration profiles of the more retained component during a switch time interval (start, 25 %, 50 %, 75 %, and at the end of a switch time interval) for SMBS.

Fig. 9-5. Transient evolution (first 5 cycles) of the concentration of the more retained component in the extract for (a) SMB4, (b) SMBS, and (c) SMB 12. Solid line, TMB dotted line, SMB stepped dotted line, SMB approach with average concentration over a switch time interval o, SMB instantaneous concentration evaluated between switchings.

The influence of the switch time interval on the purity is shown in Fig. 9-10. A change on the switch time interval will lead to a change on the equivalent solid flow rate throughout the system. In all runs the inlet and outlet flow rates, as well as the internal liquid flow rates in all the four sections of the SMB unit, are kept constant. 

Increasing the switch time interval is equivalent to decrease the solid flow rate and the net fluxes of components in all sections of the TMB unit will be pushed in the same direction of the liquid phase. This implies that, first, the more retained species will move upwards in section III and will contaminate the raffinate stream and the less retained species will move upwards in section IV, will be recycled to section I, and will contaminate also the extract stream. The decrease of the switch time interval will have similar consequences. The equivalent solid flow rate will increase and the net fluxes of component in all four sections of the TMB unit will be pushed in the opposite direction of the liquid phase. This implies that, first, the less-retained species will move downwards in section II and will contaminate the extract stream and the more retained component will also move downwards in section I, will be recycled with the solid to the section IV, and will contaminate the raffinate stream. It is possible to obtain simultaneously high purities and recoveries in a SMB, but the tuning must be carefully carried out. 

The original optimization problem with five variables was, by choosing the liquid flow rate in section I by pressure-drop limitations and following Equations (35) and (36) to evaluate the switch time interval and the recycling flow rate, reduced to a two-variable optimization problem the choice of liquid flow rates in the two central sections. Table 9-5 summarizes the SMB operating conditions (and equivalent TMB conditions) used in the design of the 7 -711 plot. 

Feed concentration Switch time interval t = 3.3 min Flow rate in section I 2 = 31 mL min ... 

Spectral exchange is considered here as sudden frequency modulation with switching time tc = 0. As a result the spectral periphery is described by a universal power law /(co) = 1/gj4 as in Eq. (2.58) and Eq. (2.62)... 

With reduction in size comes reduction in intrinsic switching time and proportionally higher device speed. Present design speed is in the range of 100 MHz and is expected to reach 300 MHz or higher by the year 2000. 

In addition to the sensitivity to ring structure, slight alterations of the hydrocarbon chain may lead to dramatic differences in electro-optic performance in chiral compounds [43]. For example, in some electroclinic Sm-A materials it has been reported that if the chain is shortened or if a double bond is localised at the end of the hydrocarbon chain, the tilt angle, electroclinic coefficient, and switching time are significantly suppressed [43]. 

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