The effect of libration and low-temperature motions

The small amount of deformation made possible by the libration, and evidenced in the P-transition, has a very important technological consequence. The very complex mechanism of fracture is treated in Chapter 9. Here we simply say 

Having looked at the effect of temperature, now we must consider the effect of observation time or rate. This is done in the same way as with the effect of chemical composition on the glass transition. The P-transition is caused by the onset of molecular motion of lower energy barrier than that involved in the fuU rotation 

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