Cloud cavitation shows an unsteady periodic tendency under a certain flow condition. In a cavitating water jet flow with cavitation clouds, the cavities or the clouds produce high impact at their collapse. In order to make clear a mechanism of the periodic cavity behavior, we experimentally examine the behavior in a transparent cylindrical convergent-divergent nozzle using a high-speed video camera. An effect of upstream pressure fluctuation due to a plunger pump is investigated from a viewpoint of unsteady behavior in a cavitating water jet. As a result, it is found that the cavitating flow has two kinds of oscillation patterns in the cavity length (cavitation cloud region). One is due to the upstream pressure fluctuation caused by the plunger pump. The other is much shorter periodic motion related to the characteristic oscillation of cavitation clouds accompanied with the shrinking (reentrant), growing and shedding motion of the clouds.

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We report the results of an ultrastructural study of Pick bodies (PB). A histogram constructed with the maximal width of each filamentous component in PB revealed a wide range of sizes among the filaments, in contrast to the unique composition of the paired helical filaments (PHF) seen in the neurofibrillary tangle of Alzheimer type (NFT-AT). Morphologically, three groups of filaments could be distinguished. The first group consisted of straight smooth-surfaced filaments of 10-14 nm diameter, which were presumably altered neurofilaments. The second one was of straight smooth-surfaced "tubules" of 15-22 nm diameter, smaller than normal microtubules. The third one was of PHF thought to be formed by a pair of filaments of the first group. The PHF found in PB differed from PHF of NFT-AT in the distance between crossovers, and rather resembled the loosely interwinding PHF reported in NFT of progressive supranuclear palsy.

Although it is well known that cloud cavitation shows unsteady behavior with the growing motion of an attached cavity, the shedding motion of a cloud, the collapsing motion of the cloud shed downstream and a reentrant motion in flow fields such as on a 2-D hydrofoil and in a convergentdivergent channel with a rectangular cross-section, observations for the periodic behavior of cloud cavitation in a cylindrical nozzle with a convergent-divergent part, which is mainly used in an industrial field, have hardly been conducted. From engineering viewpoints, it is important to elucidate the mechanism of periodic cavitation behavior in a cylindrical nozzle. In this study, a high-speed observation technique with an image analysis technique was applied to the cloud cavitation behavior in the nozzle to make clear the mechanism of unsteady behavior. As a result, it was observed in the nozzle that the periodic behavior occurs in the cloud cavitation and pressure waves form at the collapse of clouds shed downstream. Also, it was found through the image analysis based on the present technique that the pressure wave plays a role as a trigger mechanism to cause a reentrant motion at the downstream end of an attached cavity.

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