Nonsteady condensation and evaporation waves

We study motion of a phase transition front at a constant temperature between stable and metastable states in fluids with the universal Van der Waals equation of state (which is valid sufficiently close to the fluid's critical point). We focus on a case of relatively large metastability and low viscosity, when it can be shown analytically that no steadily moving phase-transition front exists. Numerically simulating a system of the one-dimensional Navier-Stokes and continuity equations, we find that, in this case, the nonsteady phase-transition front emits acoustic shocks in forward and backward directions. Through this mechanism, the front drops its velocity and eventually comes to a halt. The acoustic shock wave may shuttle, bouncing elastically from the system's edge and strongly inelastically from the phase transition front. Nonsteady rarefaction shock waves appear in the shuttle process, despite the fact that the model does not admit steady rarefaction waves propagating between stationary states. If the viscosity is below a certain threshold, an instability sets in, driving the system into a turbulent state. This work was supported by the Japan Society for Promotion of Science.Comment: revtex text file and four eps files with figures. Physical Review Letters, in pres

HYDROCHEMICAL SOLITON : EXPERIMENTAL STUDY OF A CHEMICAL WAVE COUPLED WITH MARANGONI INSTABILITY IN BELOUSOV-ZHABOTINSKY REACTION(Session IV : Structures & Patterns, The 1st Tohwa University International Meeting on Statistical Physics Theories, Experiments and Computer Simulations)

この論文は国立情報学研究所の電子図書館事業により電子化されました。It has been known the existence of the Big Wave (BW), which is a peculiar chemical wave, in a quasi 2-dimensional shallow layer of unstirred excitable Belousov-Zhabotinsky (BZ) reaction [1]. The specific feature of BW is the fact that it causes a single large solitary wave on the solution surface [1-3]. Therefore BW may belong to the category of the so-called "dissipative soliton" [3]. It has been made clear by some experimental studies that the physical mechanism of BW is due to the hydrodynamic instability coupled with chemical reactions [2-5]

Stochastic Resonance in Electrical Circuit(Session I : Cross-Disciplinary Physics, The 1st Tohwa University International Meeting on Statistical Physics Theories, Experiments and Computer Simulations)

この論文は国立情報学研究所の電子図書館事業により電子化されました。We studied experimentally on SR using electrical circuits. to investigate effects of the potential profile as well as the superposition of two different periodic signals as a modulation signal. Results are summarized as follows : (1) Asymmetric potential profile strongly influences the aspect of SNR. (2) SR suppresses the mode coupling which produces harmonics. As no theoretical work has been done in this direction, the detail will be reported in the near future. This work is partially supported by the Grant in Aid for Scientific Research from the Ministry of Education, Science and Culture in Japan

Noise-Induced Entrainment between Two Coupled Chemical Oscillators in Belouzov-Zhabotinsky Reactions

Abstract. The entrainment dynamics of two chemical-oscillators in an excitable medium separated by some distance d was experimentally studied in the light-sensitive BelousovZhabotinsky reaction under application of external noise. Two chemical-oscillators were always spontaneously synchronized at sufficiently small d or frequency difference in the absence of noise. For insufficient distance to entrain each other, however, the frequency and phase were self-synchronized by application of noise. Increasing the noise intensity the entrainment frequency area between two oscillators increased and showed a maximum at a certain noise intensity, that is, an optimum noise intensity existed. We call this the noise-synchronaization phenomenon

Soft Neurological Signs in Childhood by Measurement of Arm Movements Using Acceleration and Angular Velocity Sensors

Soft neurological signs (SNS) are evident in the motor performance of children and disappear as the child grows up. Therefore SNS are used as criteria for evaluating age-appropriate development of neurological function. The aim of this study was to quantify SNS during arm movement in childhood. In this study, we focused on pronation and supination, which are arm movements included in the SNS examination. Two hundred and twenty-three typically developing children aged 4–12 years (107 boys, 116 girls) and 18 adults aged 21–26 years (16 males, two females) participated in the experiment. To quantify SNS during pronation and supination, we calculated several evaluation index scores: bimanual symmetry, compliance, postural stability, motor speed and mirror movement. These index scores were evaluated using data obtained from sensors attached to the participants’ hands and elbows. Each score increased as age increased. Results obtained using our system showed developmental changes that were consistent with criteria for SNS. We were able to successfully quantify SNS during pronation and supination. These results indicate that it may be possible to use our system as quantitative criteria for evaluating development of neurological function

Acceleration of chemical reaction fronts

Chemical fronts and waves travelling in reaction-diffusion systems frequently induce hydrodynamic flow. This adds an additional transport process to the mechanism of spatio-temporal structure formation and can lead to an acceleration of the chemical (reaction) front. We report on the acceleration of travelling chemical fronts elicited by convection, as caused by the Marangoni effect in the monostable iodate-arsenous acid reaction in a thin liquid film. At a stoichiometric excess of iodate over arsenous acid, the reaction produces a large amount of iodine, which is surface-active. At the reaction front, iodine is transferred from the bulk to the surface inducing spatio-temporal gradients of surface tension that lead to capillary flows. These flows, in turn, promote further iodine adsorption at the surface through hydrodynamic mixing effects. As a consequence, an acceleration of the chemical fronts is observed, even if the concentration difference across the front is constant. After the transient acceleration of the reaction front, it settles at a constant propagation velocity, which is assumed to be regulated by a balance in the mass transfer between the bulk and the surface

Acceleration of chemical reaction fronts

The propagation of reaction-diffusion fronts in an open liquid solution layer is critically affected by mass transfer between the liquid solution and the adjacent gas phase. This is the case in the iodate–arsenous acid (IAA) reaction when run under stoichiometric excess of iodate. Here, iodine is the reaction product, which has a low solubility in the liquid phase, hence, excess iodine rapidly evaporates. In the gas phase, it diffuses and overtakes the reaction front propagating in the liquid medium because its diffusion coefficient in the gas phase is considerably larger than that in aqueous solution. Evaporated iodine is re-dissolved into the reaction medium ahead of the reaction front. Since iodine is the autocatalytic species of the IAA reaction, this additional gas-phase transport may lead to an acceleration of the propagating reaction front