a b s t r a c tThe present work investigates the irradiation hardening of Fe-based model ferritic alloys after Fe-ion irradiation experiments in order to deduce mechanistically based nominal hardness from the nanoindentation tests on the ion-irradiated surface. Ion-irradiation experiments were carried out at 290 • C with 6.4 MeV Fe 3+ ions. The constant stiffness measurement (CSM) was used to obtain the depthprofile of hardness. The results has been analyzed and discussed based on the Nix-Gao model and an extended film/substrate system hardness model. The depth-sensing nano-indentation techniques with CSM revealed that the hardness gradient of the unirradiated Fe-based model alloy can be explained through the indentation size effect (ISE). On the other hand, the gradient of ion-irradiated surface of these samples includes not only the ISE but also softer substrate effect (SSE). We propose a new approach to evaluate a nominal hardness, which may connect to the bulk hardness, from experimentally obtained nano-hardness depth profile data.

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We have developed a simple HPLC assay to measure the activity of S-mephenytoin 4-hydroxylase in human liver microsomes, and have assessed its practical applicability by determining the kinetic parameters of the enzyme in 10 different human liver samples. The recovery of 4-hydroxymephenytoin and phenobarbital (the internal standard) after the precipitation of microsomal protein was almost complete, and the coefficients of variation for the intra- and interassay measurement of S-mephenytoin 4-hydroxylase activity were < 6.4 and 8.0%, respectively. Eadie-Hofstee plots for the formation of 4-hydroxymephenytoin gave a straight line for all of the 10 samples studied. There was large interindividual variability in the kinetic parameters estimated: 4.6- (36 to 166 microM), 11.8- (0.9 to 10.6 nmole/mg protein/h) and 30.1- times (0.10 to 3.01 microliters/mg protein/min) for Km, Vmax and Vmax/Km, respectively. The mean (+/- SD) Km, Vmax and Vmax/Km were 72.4 +/- 40.4 microM, 4.23 +/- 2.88 nmole/mg protein/h and 1.33 +/- 1.02 microliters/mg protein/min, respectively. Thus, the assay was sufficiently accurate and reproducible to permit estimation of the kinetic parameters of S-mephenytoin 4-hydroxylase in human liver microsomes, and it appears to be applicable to an in vitro study of the possible involvement of S-mephenytoin-type oxidation polymorphism in drug metabolism.