Switching, phase role

It is possible to switch the roles of the phases during a run. The mobile phase becomes the stationary phase and vice versa (see the entry Measurement of Pqw by CCC). The combination of these three points produces the following advantages. 

Epoxy (EP)-PCL conetworks were produced by the group of Hartwig [71, 72]. Crystalline PCL domains, overtaking the role of switch phase, were covalently integrated into the cationically polymerized EP network. The EP/PCL ratio was varied between 85/15 and 60/40. After deformation at = 70°C and fixing at r = 20 °C, of 100% was measured. In the companion paper, the authors addressed the nucleation of the PCL phase [72]. 

Dual-mode is an eluting mode applicable to CCC because only liquid phases are involved. It consists in switching the mobile and stationary liquid phase roles at a certain point within the experiment. This approach permits to ensure the complete elution of all components in complex mixtures comprising a broad range of... 

The role of SCRs is to vary the supply parameters, which require frequent changes in V, i.e. du/df and in /, i.e. di/di in an energized condition. Becau.se of momentary phase-to-phase short-circuit, dv/di occurs during switching OFF and d 7df during switching ON sequences. Both are transient conditions and may damage the semiconductor devices used in the circuit. To protect the devices, the transient conditions can be dealt with as follows ... 

Most importantly, later genetic experiments, using conditional knockout technique to delete all forms of CREB in either the entire forebrain or hippocampus, showed that these conditional knockout mice have normal hippocampal early- and late-phase LTP, and normal performance in hippocampal-dependent memory tasks [13]. Therefore, those newer findings cast significant doubt on the role of CREB as a central switch for long-term plasticity. 

Several mechanisms have been previously proposed for oscillations. Due to the fact that oscillations exist for Lewis numbers both less and greater than 1, it seems that the thermodiffusive mechanism alone cannot explain these oscillations. To study the role of the heat of reaction, a numerical experiment is performed by switching off the heat of the gas-phase reactions (squares in Fig. 26.2). HBs are found between 75% and 85% H2 in air, but the HBs lie within the multiplicity regime IiEi in Fig. 26.2 and oscillations are not stable. 

In chapter 12 we discussed a model for a surface-catalysed reaction which displayed multiple stationary states. By adding an extra variable, in the form of a catalyst poison which simply takes place in a reversible but competitive adsorption process, oscillatory behaviour is induced. Hudson and Rossler have used similar principles to suggest a route to designer chaos which might be applicable to families of chemical systems. They took a two-variable scheme which displays a Hopf bifurcation and, thus, a periodic (limit cycle) response. To this is added a third variable whose role is to switch the system between oscillatory and non-oscillatory phases. 

Like in other chiroptical switches (Section 5.3.1), solvent polarity was found to play an important role. Diastereoselective cyclization was observed in THF and toluene, but not in nonpolar solvents such as n-hexane. Upon photoexcitation, diarylethenes 24 (Scheme 11) can adopt a planar and a twisted conformation, and photocyclization only proceeds through the planar conformation. In the case of chiral diarylethene 27a, there are two diastereomeric planar conformations leading to the diastereomers of the cyclic product 27b. The stereoselectivity in the photocyclization process is enhanced because of a decrease in the excited state energy of the unreactive twisted form, providing a relaxation pathway for the less favorable planar diastereoisomer in more polar solvents. Chiral photochromic diarylethenes are among the most prominent photoswitches known today, featuring nondestructive read-out, excellent reversibility, and the potential for construction of switchable molecular wires and modulation of liquid crystalline phases (see Section 5.5.3).[40,411... 

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