Contraction-extension cycles

It is also seen that the gel repeats the contraction-extension cycles in response to stepwise magnetic field changes. Neither phase shift nor magneto-elastic relaxation can be observed at this frequenqr within the experimental accuraqr. 

In muscle there is an extensive endoplasmic reticulum called the sarcoplasmic reticulum. It seems to be primarily concerned with regulating Ca " ion fluxes during the contraction-relaxation cycle. The components of the sarcoplasmic reticulum are in contact with invaginations of the cell membrane which conduct the wave of depolarization into the interior of the muscle cell and to the myofibrils. Relaxation of muscle is brought about by accumulation of calcium within the sarcoplasmic reticulum, whereas contraction occurs as a consequence of an increase in calcium released from the sarcoplasmic reticulum secondary to an... 

Muscles use energy to contract and expand in response to stimuli. They may act as an unconscious knee jerk reaction, as a consequence of neural activity arising from touching a hot surface, or in any number of conscious movements. Regardless of the reason for muscle activity the fundamental mechanism is a cycle between contraction and extension. 

Consider a cycle consisting of a reversible extension of the surface by unit area at a temperature T+dT and a contraction at T. At T- -dT the quantity of heat put into the system is q8- -dq8, and the surroundings do work on it y dy. At T the system does work on its surroundings y, and gives up the heat q8. The net work done by the system on its surroundings is —dy, and a quantity of heat q8 has fallen from T+dT to T. Therefore, by Carnot s theorem, ... 

O Grady and McBreen performed an extensive study of the nickel oxide electrode employing the cell shown in Fig. 8 in a transmission mode. The study of nickel oxide is complicated by the numerous species present and their interconversion. They found that the as-prepared jS-Ni(OH)2 has the same structure within the x y plane as that determined by x-ray diffraction experiments but with a significant degree of disorder along the c-axis. Oxidation to the trivalent state results in contraction of the Ni—O and Ni—Ni distances along the x-y plane. Re-reduction of this material yields a structure similar to that of the freshly prepared Ni(OH)2. Repeated oxidation-reduction cycles resulted in an increased disorder which is believed to be responsible for facilitating the electrochemical oxidation to the trivalent state. 

Cell locomotion in tissue culture clearly involves a rolling cycle of cell process extension, adhesion, cytoplasmic contraction (or flow) in the direction of adhesion, and de-adhesion (see Newgreen,... 

Figure 74 Reversible conformational transition caused by variation in the ethanol vapor pressure in the surrounding atmosphere, as visualized by AFM. When the extended, tightly adsorbed PnBA brush molecules are exposed to ethanol vapor, the macromolecules swell and contract to form compact globules. Exposure to a humid atmosphere caused the molecules to extend again to a worm-like 2D conformation. The sequence of phase images demonstrates two cycles (first a-d second e-h) of collapse and subsequent extension for three individual PnBA brush molecules on mica in vapors saturated with humidified ethanol (80vol.%) and water. Reprinted from Gallyamov, M. 0. Tartsch, B. Khokhlov, A. R. etal. Chem. Eur. J. 2004,70(18), 4599-4605, with permission from Wiley-VCH. " ...

The stretch sensing behavior of PEDOT-coated yams is shown in Fig. 28.10. It was concluded that even after several extension—contraction cycles, the knitted stmctures preserved their stretch recovery and electrical properties [35]. 

What methods can measure Text In practice, the most convenient approach has been to study situations of relatively strong shear (s t 1), choosing transverse shears to ensure that the molecule rotates and experiences a periodic extension/contraction cycle. - The main parameters measured were nonlinear features in the viscosity and in the flow birefringence— the latter being slightly simpler to interpret. All these nonlinear corrections finally determine the product SText- The measurements... 

Extensive worldwide experience exists for providing fuel supply services under commercial contracts. Certain experience in spent fuel return to the originating country does exist for example, the former Soviet Union received spent fuel returns from affiliated republics and some countries of the Eastern Europe, and the Russian Federation continues to do so currently. At the same time, none of the countries in the world has so far agreed to shoulder the disposal of final waste originating from back-end fuel cycle services being provided by companies operated at its territory [4]. 

A capture thread of Araneus diadematus under increasing magnification. The windlass mechanism is seen in the lower picture where the core fibres after a large extension-contraction cycle have been reeled into a droplet (for details see ref. 12). 

However, an alternative concept arises if the action on the polymer is carried out in a periodic, cyclical way. In this section we are concerned with mechanical properties, so we could apply a deforming stress in an alternating push-pull fashion. The resulting strain would also be periodic, being extension during the pull and contraction on the push. Then the most convenient measurement of the time or rate of the stress/strain observation is the frequency of the applied stress. High frequencies correspond to stress applied over short times, while low frequencies correspond to stress applied over long times. In this way the time of the experiment as experienced by the molecules is the time of one cycle of the periodic stress/strain, and not the total time over... 

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