The in vitro hepatic 5'-monodeiodination of thyroxine (T4) to triiodothyronine (T3) in Oreochromis mossambicus, Channa striata, Clarias batrachus, Cyprinus carpio and Oxyeleotris marmorata was found to be time, pH and temperature dependent, and related to the amount of substrate (T4) and homogenate introduced into the reaction vessel, in a manner which was consistent with Menton-Michaelis kinetics, and thus indicative of an enzyme-regulated process. Dithiothreitol introduced into the reaction vessel stimulated T3 production in a dose-related manner.Hepatic 5'-monodeiodinase activity was also detected in a further 28 species of teleosts suggesting that the peripheral monodeiodination of T4, which is well-documented in salmonids, is also widespread amongst other teleost fishes. All species examined exhibited evidence of enzymatic deiodination, but there were marked differences in Km and Vmax values between the species. There was no apparent phylogenetic or environmental relationships to explain the widely divergent Km and/or Vmax values, nor was there a correlation between Km and Vmax when the species were considered together.
Exact analytical expressions for the switching delay of an inverter driving an RC load, taking into account the velocity saturation, are obtained. Modified expressions to include theeffectofsource resistance arethen presented.Owing to the limitation on switching current imposed by the velocity saturation mechanism, the switching delay is substantially increased for identical width-io-length ratios of the MOSFET in a complementary MOS logic circuit. Obviously, it is important to increase the saturation velocity by miniband engineering or otherwise to improve the performance. However, it is found that the improvements in the time delay are marginal after a saturation velocity of 2.4 x lO'cm s-' is reached. The effect of technologies aimed at circumventing the hot-electron and other deleterious effects is a longer delay time of the circuit due to increased series resistance. However, the effect of increased series resistance is substantially damped due to velocity safuration. These results are particularly important in designing CMOS circuits with submicrometre MOSFET dimensions
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