Obstacle activation volume

It may seem contradictory that the Peierls stress is on the one hand able to determine the yield strength of a metal and can nevertheless be overcome by thermal activation already at room temperature. The reason for this is that its activation volume is rather small. The stress Tm needed to athermally overcome the barrier is large, but due to the small size of the activation volume, the obstacle energy Q is still small enough to be provided by thermal activation at room temperature. 

If we plot the quotient of the stress a in the polymer and the temperature versus the logarithm of the strain rate, points at constant temperature should fall onto a common line. Figure 8.9 plots this for polycarbonate, thus confirming our considerations. This kind of plot is called Eyring plot. If there is more than one type of obstacle, the slope of the curve is not constant anymore. If, for instance, one type of obstacle is dominant up to one temperature, but another is more important at higher temperatures, the Eyring plot contains a kink because both obstacles differ in the activation volume Ad. ... 

The inhalation exposure level is the amount of substance per m in the breathing zone of the worker, which is the volume of air within 1 metre in any direction of the worker s head). Measuring the exposure level of each activity would be the ideal approach to assess the associated risks. But this is not realistic, not in general and especially not for small-scale situations [45]. The accurate measurement of health risk through atmospheric monitoring requires many samples in order to take into account within, and between, worker sources of variability [46-48]. The cost and practical difficulties associated with atmospheric monitoring represent an often insurmoimtable obstacle for companies, especially for small and medium enterprises (SMEs). A model-based approach remains as a possibility. 

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