Tatsuyuki Kawakubo

External Noise Effect on the Onset of Williams Domain in Nematic Liquid Crystals

In order to examine the effect of external noise on the electrohydrodynamic instability, we have measured the wave number spectrum of the pattern of Williams domain in nematic liquid crystals MBBA in the presence of external noise superposed to the a c voltage. The threshold voltage for the onset of Williams domain is found to shift to higher values with increasing noise power. Its noise dependence is interpreted in terms of a theory presented by Dubois-Violette et al.

Critical Fluctuation near Threshold of Gunn Instability

The low frequency noise and the oscillatory microwave power spectrum have been simultaneously measured on the Gunn diode in order to investigate the critical phenomenon near the threshold of the Gunn instability. In a rather wide bias range an anomalously large low frequency noise and a noisy power spectrum are observed. The appearance of a wide critical region is discussed with the use of an equation for the negative-resistance oscillator.

High Frequency Conductivity of NiO

The conductivities of 1.2, 7.9 and 12.6 ppm (weight ratio) Li-substituted NiO are measured at high frequencies up to 24 GHz in the temperature range 110° to 450°K. The conductivity at high frequencies can be expressed as the sum of a temperature-dependent conductivity σ 1 and a temperature-independent additive conductivity σ 2 . The former σ 1 is independent of frequency until microwave region but the latter σ 2 is strongly dependent on freqnency. The frequency dependence of σ 2 can be represented by the dispersion formula for the dielectric loss due to the hopping of charge carriers around imperfections. The staying time at a lattice site is determined: τ=2.2×10 10 sec. A lack of temperature dependence of σ 2 implies that the staying time τ does not depend on temperature and further that the holes are not selftrapped. The conduction mechanism in NiO is rather illustrated as something analogous to impurity conduction.

Critical Slowing-Down near Threshold of Electrical Oscillation

The probability distribution and the autocorrelation function of the fluctuating output voltage of a Wien-Bridge oscillator have been measured as a function of the feedback factor β. It has been found that both the variance and the correlation time of the fluctuation which are determined from the probability distribution and the correlation function, respectively, become infinite in a manner like (β c -β) -1 as β approaches the threshold β c of the oscillation. The aspect is analogous to the Curie-Weiss law in the second-order phase transition. The results are discussed within the linear response scheme starting from a simplified kinetic equation for the fluctuating output voltage of the Wien-Bridge oscillator.

Crystal Distortion and Electric and Magnetic Transition in VO2

The semiconductor to metal transition in VO 2 is discussed in connection with the crystal distortion on the basis of a simplified one-dimensional model. It is shown that a localized electron state forming ion pairs will be stabilized at low temperatures when the transfer energy makes a sudden increase for a small contraction of ionic distance. The occurrence of the semiconductor to metal transition is explained by the stabilization of the delocalized state at high temperatures due to the excitation of electrons from the bonding to the antibonding state in each ion pair.

Formation of a vortex around a sink: A kind of phase transition in a nonequilibrium open system

Abstract Measurements of the velocity of vortex flow produced around a sink show that the amount of discharge Q is required to exceed a threshold value Q c for the formation of a vortex and that the vortex velocity is proportional to ( Q − Q c ) 0.5

Fluctuation in Transient Process of Electrical Oscillation

The time-dependent fluctuation with sudden changes in feed-back factor has been measured on a Wien Bridge oscillator. Also have been observed the evolution and decay processes of oscillation in its transient process. The dynamics of oscillation amplitude can be well explained by van der Pol equation. As the oscillation of output voltage corresponds to that of charge on the capacitor which constitutes a part of the bridge of the Wien Bridge oscillator, the theory of system size expansion is applicable. The time dependence of fluctuation has been analysed in terms of the theory of Kubo, Matsuo, and Kitahara. A good agreement between theoretically calculated curves and experimental results has been obtained.

Critical change of ion conductance and self-sustained potential oscillation in artificial membrane systems

A change in conductance of an artificial membrane at a threshold concentration of environmental salt solution was interpreted in terms of a change in adsorptive reaction rate on the interface which was derived from an autocatalytic reaction model. The model also accounted for a self-sustained potential oscillation which was observed when the salt concentration of one side of the membrane was higher than the threshold mentioned above and that of the other side lower.

Convective instability and electric potential oscillation in a water-oil-water system

Abstract A convective instability is observed in an aqueous solution of surfactant which attaches to a nitrobenzene layer. Small convective rolls at first occur

A model simulation of self-sustained electrical oscillations across a water/oil interface

Abstract A self-sustained electrical oscillation observed in a water/oil/water system in which one of the water phases contains sodium oleate as a surfactant is interpreted in terms of the diffusion of oleate anions in water and their absorption into the oil phase by formation of inverted-micelles. The model also accounts for the observed result that the self-sustained oscillation is stable only for a specific range of sodium oleate concentration.