High rate impact, role

The Role of Rubber Modification in Improving High Rate Impact Resistance... 

First, the role of rubber modification in high rate impact is to suppress spallation by inducing the material to yield in the presence of dynamic tensile stresses arising from impact. Second, this yield-spall transition occurs at different strain rates for different rubber contents and may be predictable using quasistatic, low temperature tests of this type. These tests can also provide information concerning the basic nature of the yield process in these materials through the activation parameters which are obtained. Third, the Bauwens-Crowet equation seems to be a good model for the rate and temperature sensitive behavior of the American Cyanamid materials and is therefore a likely candidate for a yield criterion to use in the analytical code work on these materials which we hope to perform as a continuation of this work. 

For many applications the resistance of the material to shock loading is an important property. Here we find ourselves, contrary to the previous section, on the very short side of the time scale. For the impact strength the short-term tensile strength as well as the ultimate strain play a role the impact strength is, in fact, the energy needed for rupture at a high rate of deformation, J impact strength accurately and uniquely. 

Drugs in Class II have low aqueous solubility (but high membrane permeability), and any factor affecting dissolution rate would be expected to have an impact on the absorption of such compounds. Factors that are noted in Fig. 11, such as fluid pH, volume and viscosity, and bile secretion (especially in response to fatty foods), might be expected to play a role in dissolution rate and thereby affect absorption. Compounds that fall into this class include carbamazepine, cyclosporin, digoxin, griseofulvin, and spironolactone. Food would be expected to exert a potentially significant affect on... 

If chelation to a neigbouring group is possible, the use of HMPA is often not required for reduction of the carbonyl and reactions can be carried out under mild conditions. To examine the impact of chelation, Flowers studied the rate of reduction of 2-butanone, methyl acetoacetate and /V,/V-dimethylacetoace-tamide by Sml2.20 Reduction of the (1-keto ester or amide was several orders of magnitude faster than that of the unsubstituted ketone, which is consistent with chelation playing a major role. Further rate and mechanistic studies on the reduction of acetophenone and a series of 2 - and 4 -substituted acetophenone derivatives showed that both chelation and coordination provide highly... 

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