Biomedical subjects

Ikuo Nakamura

Publications and source records attributed to Ikuo Nakamura.

21 records · Page 2Linked to original sources

PubMed2002

Adaptation and survivors in a random Boolean network.

We introduce the competitive agent with imitation strategy in a random Boolean network, in which the agent plays a competitive game that rewards those in minority. After a long time interval, the worst performer changes its strategy to the one of the best and the process is repeated. The network, initially in a chaotic state, evolves to an intermittent state and finally reaches a frozen state. Time series of survived species (whose strategies are imitated by other agents) in the system depend on the connectivity of each agent. In a system with various connectivity groups, the low connectivity groups win the minority game over the high connectivity groups. We also compared the result with mutation strategy system.

Adaptation, Psychological↗

PubMed2002

Flow pattern exchange in the Taylor-Couette system with a very small aspect ratio.

Numerical investigation is carried out on the flow pattern exchanges found in Taylor-Couette flows between two concentric rotating cylinders. The inner cylinder rotates while the outer cylinder and both end walls are stationary. The aspect ratio (column length/gap width) is small, and its range is from 0.5 to 1.6. Previous experimental results for this range of the aspect ratio showed that the steady flow patterns are classified into three groups: the normal two-cell mode, anomalous one-cell mode and twin-cell mode. All modes found by experiments are predicted in the present numerical calculation. Besides these three flow modes, an unsteady mode is predicted, which is time dependent and fully developed. The existence of the unsteady mode is also confirmed by our experiments. When the inner cylinder starts to rotate from rest, vortices at the corners of the inner cylinder and both end walls develop, and they induce the normal two-cell mode. The flow of the anomalous one-cell mode or twin-cell mode appears after an abrupt breakdown of symmetric two-cell mode flows. During the gradual deceleration of the inner cylinder, the transitions of flow modes occur. We observed mode transitions between the normal two-cell mode and anomalous one-cell mode and mode transitions from the twin-cell mode to the normal two-cell mode, anomalous one-cell mode, and unsteady mode. The critical loci where these mode transitions appear are determined. The numerical confirmation of the twin-cell mode is a different result obtained in the present study.

Journal Article↗

PubMed2002

Accelerated shoot overgrowth of rice mutant ao-1 is epistatic to gibberellin-sensitive and -insensitive dwarf mutants.

A shoot overgrowth mutant of rice ( Oryza sativa L.), accelerated internode overgrowth-1 ( ao-1), is marked by accelerated longitudinal elongation of aerial parts and overgrowth of internodes at the vegetative stage. The physiological properties of ao-1 were similar to those of wild plants treated with a saturating level of exogenous gibberellins (GAs), except for the internode-overgrowth phenotype, which was not mimicked by GA-treated wild plants. The ao-1 mutant was less sensitive to a GA biosynthesis inhibitor, Uniconazole-P, than the wild type. Dwarf alleles of three loci, including two GA-sensitive and one GA-insensitive mutation, were introduced to produce double-mutants with ao-1, but the overgrowth phenotype was not suppressed in double-homozygous mutants. These results suggest that the overgrowth phenotype of ao-1 is caused by abolition of GA signaling rather than by GA overproduction. It is likely that a part of the shoot regulation system of ao-1 is saturated with the GA signal. As a possible model consistent with the results, we propose that AO-1 protein acts as a negative regulator in GA signal transduction.

Journal Article↗