Masato Takahashi

A crossover operator using independent component analysis for real-coded genetic algorithms

For real-coded genetic algorithms, there have been proposed many crossover operators. The blend crossover (BLX-/spl alpha/) proposed by L.J. Eshelman and J.D. Schaffer (1993) shows a good searching ability for separable fitness functions. However, because of its component-wise operation, BLX-/spl alpha/ faces difficulties in the optimization of non-separable fitness functions. This paper proposes a novel crossover operator that combines the BLX-/spl alpha/ with independent component analysis (ICA). By applying the ICA to the population, the coordinate system of the search space is transformed so as to increase the separability of the fitness function, and then the BLX-/spl alpha/ is applied. A computer simulation shows the good searching ability of the proposed method for non-separable fitness functions.

A Test of the Scaling Law for Structure Function in Phase Separation Process of Polystyrene/Poly (methylphenylsiloxane) Liquid Mixtures

Structure function S ( k , t ) in process of phase separation was investigated by light scattering for polystyrene/poly(methylphenylsiloxane) mixtures to test the scaling law for S ( k , t ) in the late stage. For the critical composition, the structure function obeyed the scaling law of S ( k , t )= k m -3 · S ( k / k m ), where k is the wave number, k m the wave number yielding the maximum intensity, and S ( k / k m ) the scaled structure function independent of time t . However, S ( k , t ) for the off-critical composition gradually changed with t , becoming to have a broader peak, so that the scaling law was only approximately satisfied. The full-width at a half of the maximum intensity increased with increasing quench-depth, being almost the same for the critical and off-critical compositions at comparable quench-depths. The value of exponent h in the power law S ( k / k m )∝( k / k m ) - h at k / k m >1 was around 4 for the off-critical quench, in agreement with the Furukawa theory, while for the cr...

Bimodal behaviour observed by quasi-elastic light scattering in the cross-over region from Θ to critical temperature

Abstract The dynamic behaviour of a polystyrene (Mw = 2.89 × 106)-cyclohexane solution was investigated by quasielastic light scattering in the cross-over region from Θ to critical temperature. The following results were obtained. (1) The time-correlation function of concentration fluctuations showed bimodal decay in the semidilute region (at concentrations C ⩾ 3.32 × 10−2 g polystyrene/g solution. (2) The linewidth Γf for the fast mode had k2-dependence, while Γs for the slow mode exhibited an anomalous angular dependence. As the temperature T approached the critical temperature Tc, however, Γs tended to show the k2-dependence too. (3) In the critical solution, temperature dependences of Γs and Γf were described by Γs∝t0.5 and Γf∝t−1 ( t≡ T − T c | T c ), respectively, suggesting that Γs and Γf correspond to the critical and background parts of average linewidth. As the temperature approached Tc, the amplitude of the slow mode relative to that of the fast mode increased very sharply, and as a result the correlation function approached becoming unimodal. (4) At the Θ-temperature, Γf increased with increasing concentration, whereas Γs decreased. These concentration dependences were qualitatively, but not quantitatively, consistent with the predictions for the gel-mode and the reptation motion, respectively.

Configuration effect of superfluid helium channel on the λ-transition heat flux

Effects of channel of superfluid helium (He II) on heat transport characteristics, especially on the λ-transition heat flux and temperature rise at the channel end, are investigated experimentally and numerically. The ends of the channel are kept open to an He II bath under the atmospheric pressure condition. Supply of heat to the channel results in temperature rise at the channel end. This temperature rise increases with an increase in aspect ratio of the channel. The increase in temperature rise leads to a decrease in the λ-transition heat flux. The temperature rise and the λ-transition heat flux are estimated by solving two-dimensional heat transport equation considering not only the channel but also the He II bath. The results of the present study indicates that the temperature distribution in the He II channel is affected by two- or three-dimensional heat flow around the channel end, especially for a channel having larger aspect ratio.