Reversible force generation

Dantzig, J.A., Goldman, Y.E., Millar, N.C., Lacktis, J., Homsher, E. (1992). Reversal of the cross-bridge force-generating transition by photogeneration of phosphate in rabbit psoas muscle fibers. J. Physiol. 451,247-278. 

Since it is relatively easy to transfer molecules from bulk liquid to the surface (e.g. shake or break up a droplet of water), the work done in this process can be measured and hence we can obtain the value of the surface energy of the liquid. This is, however, obviously not the case for solids (see later section). The diverse methods for measuring surface and interfacial energies of liquids generally depend on measuring either the pressure difference across a curved interface or the equilibrium (reversible) force required to extend the area of a surface, as above. The former method uses a fundamental equation for the pressure generated across any curved interface, namely the Laplace equation, which is derived in the following section. 

Most gas separation processes require that the selective membrane layer be extremely thin to achieve economical fluxes. Typical membrane thicknesses are less than 0.5 xm and often less than 0.1 xm. Early gas separation membranes [22] were adapted from the cellulose acetate membranes produced for reverse osmosis by the Loeb-Sourirajan phase separation process. These membranes are produced by precipitation in water the water must be removed before the membranes can be used to separate gases. However, the capillary forces generated as the liquid evaporates cause collapse of the finely microporous substrate of the cellulose acetate membrane, destroying its usefulness. This problem has been overcome by a solvent exchange process in which the water is first exchanged for an alcohol, then for hexane. The surface tension forces generated as liquid hexane is evaporated are much reduced, and a dry membrane is produced. Membranes produced by this method have been widely used by Grace (now GMS, a division of Kvaemer) and Separex (now a division of UOP) to separate carbon dioxide from methane in natural gas. 

The interaction of actin and myosin is key to the generation of contractile forces in skeletal muscles. Skeletal muscles are composed of thick and thin filaments the thick filaments are composed primarily of myosin and thin filaments contain actin. The interaction between the two is a reversible self-assembly process that is followed by disassembly that separates actin from myosin. This separation initiates movement of myosin with respect to actin and results in shortening of the muscle, causing force generation. It is the assembly and disassembly process that we are interested in in this section. 

Fig. 7. Thermomagnetic recording, (a) A focused laser beam generates a thermal profile in the magnetic layer, (b) The coercive force in the layer is reduced and its magnetisation can be reversed by a small magnetic field, here 30 kA/m. At room temperature, the coercive force is high and the written domains are...

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