Sadatoshi Koroyasu

Kinetic Analysis of the Growth Rate of the Flagellar Hook in Salmonella typhimurium by the Population Balance Method

The growth rate of flagellar hooks in Salmonella typhimurium was analyzed by computer-aided simulation of the length distributions of mutant hooks of uncontrolled length (polyhooks). The wild-type hook has a relatively well-controlled length, with an average of 55 nm and a standard deviation of 6 nm. Mutations in the fliK gene give rise to polyhooks. A histogram of the lengths of polyhooks from a fliK mutant shows a peak at 55 nm with a long monotonic tail extending out to 1 microm. To analyze the growth rate, we employed the population balance method. Regression analysis showed that the histogram could fit a combination of two theoretical curves. In the first phase of growth, the hook starts with a very fast growth rate (40 nm/min), and then the rate exponentially slows until the length reaches 55 nm. In the second phase of growth, where the hook length is over 55 nm, the hook grows at a constant rate of 8 nm/min. Second mutations in either the fliK or flhB genes, as found in pseudorevertants from fliK mutants, give rise to polyhook filaments (phf). The ratio between the numbers of hooks with and without filament was 6:4. The calculated probability of filament attachment to polyhooks was low so that the proportion of hooks that start filament growth was only 2% per minute. The lengths of polyhooks with and without filaments were measured. A histogram of hook length in phfs was the same as that for polyhooks in single-site fliK mutants, against the expectation that the distribution would shift to a shorter average. The role of FliK in hook length control is discussed.

Generation of Defects Due to Machining of TiAl Intermetallic Compound and Their Effects on Mechanical Strength

The generation of machining defects and their effect on bending strength characteristics are discussed with respect to a TiAl intermetallic compound, which is attracting much attention as a high-temperature structural material because of its high specific strength. The discussion focuses on the mechanism of the formation of edge chipping and machined surface cracks during cutting of a TiAl intermetallic compound. Also, some effects of these machining defects on the bending strength are clarified. The comparison of cutting results with abrasive machining results helps clarify the dependence of strength on undeformed chip thickness during chip generation of machining processes.

Machinability of TiAl Intermetallic Compounds

TiAl intermetallic compounds are cut in order to examine their machinabilty and to clarify the influence of machined defects on the mechanical strength. The main results are as follows: Diamond tools and cemented carbide tools exhibit streakyabrasiyetype damage. Surface and edge defects are formed along the lamellar layer direction. Bending strength is higher when the cutting direction is parallel to the edge. In the case of lower strength specimens, breakouts or cracks are observed at the edge. The average strength is improved by chamfering.

Characteristics and inception of waves on falling liquid films in inclined wetted-wall columns.

線形安定性理論に基づき, 傾斜濡れ壁塔における流下液膜の波の形成と構造を理論的に解析し, 時間的に安定な波の周波数, 波長, 波速, 空間的成長速度および振幅の各無次元数に対する近似理論式を求めた.本理論式によれば. 波動特性値の無次元数は液レイノルズ数, 無次元表面張力, 傾斜角および無次元周波数の関数となり, 液入口で極めて微小な波の振幅は液の流下方向に対して指数関数的に増加する.本研究ではまた, 傾斜濡れ壁塔の平板壁に沿って膜状で流下する水の表面上の波に対する周波数, 波長, 波速と空間的成長速度を実測した.その結果, 波動特性値は流れ方向に変化せず一定値をとるが, 波の振幅は流下距離の増加とともに増し, ある位置すなわち波立ち開始点で直接目で観察できる波が現れることがわかった.さらに理論および実験結果を比較検討することによって, 流動特性値や波立ち開始点が線形安定性理論を用いて定量的に予測できることが明らかになった.