Mechanical switches

Overall, the technical complexity of the Deans switch system is considerably greater than that of a mechanical switching valve and it is accepted that reliability and ease of use is reduced as the system complexity increases. For many compound types, however, the completely non-intrusive nature of the Deans method offers sufficient advantages to justify its application. However, the use of modern electronic pressure and flow controls integrated into the overall computer control of the chromatographic system does now make the operation of Deans switches significantly easier or more reliable than has been reported in its earlier applications. 

S. T. Adam, Quality test of a mechanical switching valve for two-dimensional open tubular gas cliromatography , 7. High Resolut. Chromatogr. Chromatogr. Commun. 11 85-89(1988). 

Mechanical switches provide a simple manual interface to operate all sorts of loads, but they suffer from all the drawbacks of manual control, namely in terms of speed of response, and also requiring permanent operator awareness. 

However, the switchover from an A2 to an A1 hydrolysis is a very common mechanistic pathway in strong acid media, probably more common than the pure A2 mechanism. Excess acidity analyses have shown that thioacetic acid, several thiobenzoic acids, and many thiolbenzoate and thionbenzoate esters show this sort of mechanism switch.179 Acylals and thioacylals also show this behavior,116 with thioacylals using two water molecules and acylals one. Many hydroxamic acids react this way,127,216 as do esters of various types,41,217,218 episulfoxides219 and aryloxatriazoles.220 Acylhydrazines can also show a mechanism switch of this sort, although with these substrates the situation is somewhat more complex.221... 

Other types of thermal switches have been built, e.g. mechanical switches which can be turned on and off easily, but which produce heat in the switching and are therefore used at T > IK. Thermal contact is made by pressing together metallic surfaces. Conductance of a few mW/K can be obtained in the on state [14,30,41-45]. Another disadvantage of these switches are the large forces (typically 10 kg) needed to produce a good contact. Nowadays, the use of these switches is not common. 

Mammalian cells contain at least one additional eIF-2-specific kinase, known as the RNA-specific eIF-2 kinase (abbreviated PKR). PKR is induced by interferon and can be activated by minimal concentrations of double-stranded RNA. Activated PKR phosphorylates eIF-2, which, according to the above mechanism, switches off protein biosynthesis. 

The redox-controlled mechanical switching in SAMs of disulfide-functionalized bistable TTF-DMN rotaxanes consisting of cyclophane 124+ and a dumbbell-shaped component containing TTF and DMN stations was also extensively investigated.49... 

In the mechanical switch (See Fig) a thin metal foil in the shape of a square is placed against the "rate stick and this is followed by a thin piece of insulating material (such as mica, Mylar or Nylon) 1/2 mil... 

Positional changes of atoms in a molecule or supermolecule correspond on the molecular scale to mechanical processes at the macroscopic level. One may therefore imagine the engineering of molecular machines that would be thermally, photochem-ically or electrochemically activated [1.7,1.9,8.3,8.109,8.278]. Mechanical switching processes consist of the reversible conversion of a bistable (or multistable) entity between two (or more) structurally or conformationally different states. Hindered internal rotation, configurational changes (for instance, cis-trans isomerization in azobenzene derivatives), intercomponent reorientations in supramolecular species (see Section 4.5) embody mechanical aspects of molecular behaviour. 

The versatility of this approach to interlocked molecules make it very attractive as a means towards nanoscale molecular machines in which the motions of the individual components are beginning to be translated into molecular logic operations and mechanical switches. We will return to this subject in the next chapter. 

Deans, D. R., Huckle, M. T., Peterson, R, M. New combination of columns for gas chromatographic analysis of gases by using a non mechanic switching technique. Chromatographia4, 279(1971). 

Polystyrene capacitors have exceptionally low tan S values (< 10 q, making them well suited for frequency-selective circuits in telecommunications equipment. Polymer capacitors are widely used for power-factor correction in fluorescent lighting units, and in start/run circuitry for medium-type electric motors used in washing machines, tumble-dryers and copying machines for example. They are also used in filter circuits to suppress radio frequencies transmitted along main leads. Such interference noise may originate from mechanical switches, furnace controllers and switch mode power supplies it not only spoils radio and television reception but can also cause serious faults in data-processing and computer equipment. 

Digital computers were first built at Harvard University (Aiken s53 Automatic Sequence Controlled Calculator, Mark I, 1939-1944) and at the University of Pennsylvania by Eckert54 and Mauchly55 (Electronic Numerical Integrator and Calculator, ENIAC, 1946) they used vacuum tubes instead of the cumbersome and slow mechanical switches. ENIAC morphed into an Eckert-Mauchly design of BINAC, which was sold to Remington Rand and became Univac I. 

Figure 5.12. Mechanical switch based on altering the conductivity of a carbon nanotube...

Randl, S., Lucas, N., Connon, S. J., Biechert, S. A mechanism switch in enyne metathesis reactions involving rearrangement influence of heteroatoms in the propargylic position. Adv. Syn. Catal. 2002, 344, 631-633. 

This particular pressure switch is a mechanical switch that works by connecting a bourdon tube to a lever switch. The bourdon tube is a slender... 

The particular sensor/switch that we chose for this project has a bourdon tube to sense pressure and mechanically switch the signal current. It is an electromechanical switch. 

Fig. S.29. Possible pathways for the fragmentation of the tweezer-viologen complexes. Depending on the dendron size, the mechanism switches between Cl and C2 from the upper to the lower pathway. 

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