Youichi Tokunaga

Magnetoencephalographic analysis of hypsarrhythmia in West Syndrome

Abstract Magnetoencephalography (MEG) was performed in 7 patients with West syndrome (WS). In patients who had localized lesions such as tuberous sclerosis and porencephaly in the cerebral cortex, MEG showed clusters of sources of epileptiform discharges (EDs) of hypsarrhythmia at these lesions. On the other hand, in patients whose underlying cerebral lesions were considered to be distributed, such as hydrocephalus, lissencephaly, and hypoxic encephalopathy, MEG showed wide distribution of sources of EDs of hypsarrhythmia. In patients with cryptogenic WS, estimated sources were distributed over a wide area on the brain in one case, and in the other case, sources converged in 2 foci. MEG allowed estimation of three-dimensional localization of sources of electric currents, and the relationship between cerebral lesions observed by head magnetic resonance imaging (MRI) and sources of electric currents of hypsarrhythmia observed by MEG was clear. In view of the improvements in surgical treatments for epilepsy in WS, MEG is considered an effective method of diagnosis, considering that it allows the accurate evaluation of cerebral lesions associated with hypsarrhythmia by the complementary use of magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and electroencephalography (EEG).

Effects of Carbon Content on Sintering Behavior and Tensile Properties in P/M Martensitic Stainless Steels

SUS410L (Fe-12 wt%Cr) and graphite mixed powder compacts are sintered at 1473 K to 1598 K, followed by heat treatment for controlling the matrix microstructure to martensite. The effects of carbon content on the sintering behavior and tensile properties are discussed, in order to develop the high strength P/M martensitic stainless steels. The results are summarized as follows:The amount of δ-ferrite at sintering temperature decreases and that of austenite increases with increase in carbon content and decrease in temperature. Specimens containing much amount of δ-ferrite undergo densification and pore-rounding during sintering, because of high self-diffusibility of δ-ferrite.0.1 wt% of carbon is necessary at least in order to control the matrix microstructure to martensite through optimum solution treatment.Tensile strength of low temperature tempered specimens increases with increasing carbon content as well as advance in densification. The latter method might be better for strengthening the specimens in view of corrosion resistance.