Release cycles, switches

Fig. 4.2.9 Transient results showing the z position of 4 different points during a switch-release cycle...

Fig. 15.4 A dual-jet cryogenic modulator, a Right-hand-side jet traps analytes eluted from the first column b right-hand-side jet switched off, cold spot heats up rapidly and analyte pulse is released into the second column simultaneously, left-hand-side jet switched on to prevent leakage of first-column material c next modulation cycle is started (adapted from [32])...

The mechanism of the catalytic cycle is outlined in Scheme 1.37 [11]. It involves the formation of a reactive 16-electron tricarbonyliron species by coordination of allyl alcohol to pentacarbonyliron and sequential loss of two carbon monoxide ligands. Oxidative addition to a Jt-allyl hydride complex with iron in the oxidation state +2, followed by reductive elimination, affords an alkene-tricarbonyliron complex. As a result of the [1, 3]-hydride shift the allyl alcohol has been converted to an enol, which is released and the catalytically active tricarbonyliron species is regenerated. This example demonstrates that oxidation and reduction steps can be merged to a one-pot procedure by transferring them into oxidative addition and reductive elimination using the transition metal as a reversible switch. Recently, this reaction has been integrated into a tandem isomerization-aldolization reaction which was applied to the synthesis of indanones and indenones [81] and for the transformation of vinylic furanoses into cydopentenones [82]. 

A chemical process operator taped down the acknowledge button on the instrument cabinet to stop an incessant alarm after a level alarm switch had slipped. The alarm switch slipped down its support into a sump and alarmed every few minutes as the sump pump cycled on and off. The acknowledge button, common to a number of alarms, deactivated the whole system. A critical high temperature alarm was not sounded because of this modification. The operator failed to see the alarm light, and the situation eventually led to a large toxic vapor release. [1]... 

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