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S Tasaki

Publications and source records attributed to S Tasaki.

12 recordsLinked to original sources
PubMed2003

Level spacing statistics of classically integrable systems: investigation along the lines of the Berry-Robnik approach.

By extending the approach of Berry and Robnik, the limiting level spacing distribution of a system consisting of infinitely many independent components is investigated. The limiting level spacing distribution is characterized by a single monotonically increasing function mu(S) of the level spacing S. Three cases are distinguished: (1) Poissonian if mu(+ infinity)=0, (2) Poissonian for large S, but possibly not for small S if 0<mu(+infinity)<1, and (3) sub-Poissonian if mu(+infinity)=1. This implies that, even when energy-level distributions of individual components are statistically independent, non-Poissonian level spacing distributions are possible.

Journal Article↗
PubMed2001

Liouvillian dynamics of the Hopf bifurcation.

Two-dimensional vector fields undergoing a Hopf bifurcation are studied in a Liouville-equation approach. The Liouville equation rules the time evolution of statistical ensembles of trajectories issued from random initial conditions, but evolving under the deterministic dynamics. The time evolution of the probability densities of such statistical ensembles can be decomposed in terms of the spectrum of the resonances (i.e., the relaxation rates) of the Liouvillian operator or the related Frobenius-Perron operator. The spectral decomposition of the Liouvillian operator is explicitly constructed before, at, and after the Hopf bifurcation. Because of the emergence of time oscillations near the Hopf bifurcation, the resonance spectrum turns out to be complex and defined by both relaxation rates and oscillation frequencies. The resonance spectrum is discrete far from the bifurcation and becomes continuous at the bifurcation. This continuous spectrum is caused by the critical slowing down of the oscillations occurring at the Hopf bifurcation and it leads to power-law relaxation as 1/square root of [t] of the probability densities and statistical averages at long times t-->infinity. Moreover, degeneracy in the resonance spectrum is shown to yield a Jordan-block structure in the spectral decomposition.

Journal Article↗
PubMed1979

Release of active and inactive renin by the human kidney.

1. Active and inactive renin were assayed in plasma of the renal veins and the inferior vena cava below the kidney in eight patients with hypertension and unilateral renal abnormalities, 20 min after the patients had resumed the upright position. 2. The concentration of active renin on the affected side was significantly higher than that on the non-affected side. The concentration of inactive renin on the affected side was significantly lower than that on the non-affected side and in the inferior vena cava. 3. These findings suggest either that the affected kidney mainly secretes active renin, which is then converted into inactive renin in the extrarenal circulation, or that the affected kidney activates inactive renin.

Enzyme Activation↗
PubMed1978

Primary aldosteronism aggravated during peripartum period.

Two cases are reported of a 30-year-old and of a 28-year-old Japanese women with primary aldosteronism in whom metabolic and blood pressure abnormalities were aggravated during peripartum period. The characteristic findings in 2 present cases are as follows; 1) lower blood pressure during pregnancy, 2) elevated blood pressure during peripartum period, and 3) after parturition, serum potassium decreased, and the blood pressure elevated. The reason why the hypertension and hypokalemia associated with primary aldosteronism were ameliorated during pregnancy was thought to be due to the increased secretion of progesterone. Furthermore, the rapid recurrence of symptoms, increase in blood pressure, and hypokalemia in the post-partum period could be related to elevated prolactin and decreased progesterone levels.

Adenoma↗