Shigeo Hayashi

Effects of dissolved gases and pH on sonolysis of 2,4-dichlorophenol

Ultrasonic degradation of 2,4-dichlorophenol (2,4-DCP) has been studied under oxygen, air, argon, and nitrogen in aqueous solutions for a liquid temperature of 20 degrees C at 489 kHz. The degradation rate increases significantly in the presence of O2, and argon, whereas it remains the lowest under nitrogen, for which a competitive reaction model has been proposed for its non-exponential decay. Experiments have been also performed at three different pHs, 11.0, 6.3, and 2.0. The significant degradation has been achieved at pH 6.3 under O2 (0.86 x 10(-3) s(-1)), which is 1.9 and 4 times higher than acidic (pH 2.0), and basic (pH 11.0) conditions, respectively. The degradation rates have decreased in the order O2 > Ar > air > N2 irrespective of pH.

High‐Intensity Na* Emission During Multibubble Sonoluminescence In Sulfuric Acid

Intense Na* emission in sulfuric acid was observed in different spatial locations from blue emission. The color change from blue to orange observed along the streamer in the filamentous structure of a bubble cloud even with the naked eye. The Na* emission seemed to be generated after bubble coalescing. The intensity of Na* emission increased at lower frequency, where bubbles may grow more easily to lead more energetic surface oscillations.

Improved power series expansion for the time evolution operator: Application to two-dimensional systems

The power series expansion formalism is used to construct analytical approximations for the propagator of the partial differential equation of a generic type. The present approach is limited to systems with polynomial coefficients. Three typical two-dimensional examples, a Henon–Heiles anharmonic resonating system, a system–bath Hamiltonian, and a Fokker–Planck chaotic model are considered. All results are in excellent agreement with those of an established numerical scheme in the field. It is found that the power series expansion method accurately describes the dynamics of very anharmonic processes in the whole time domain.

Electrolysis-assisted single-bubble sonoluminescence in chlorine-doped water

Abstract Seeding bubbles for sonoluminescing single bubbles were created by direct-current electrolysis in 0.1 mol/l-aqueous solutions of potassium chloride for chlorine and potassium nitride for hydrogen. Compared with bubbles in air- and hydrogen-doped water, a bubble in chlorine-doped water evaded trapping in the acoustic field, but it could give luminescence intermittently only for 5–15 s. The luminescence of the bubble in chlorine-doped water was barely discernible to the naked eye, whereas that in hydrogen-doped water was a little brighter than that in air-doped water.

Quantum Statistics of Multidimensional Nonlinear Oscillators

This paper presents two perturbation approaches to calculating the quantum statistics of multidimensional nonlinear oscillators in a simple, economic way. These are the power series expansion formalism and the system-specific split operator method. The former involves a harmonic reference system, while the latter allows for the use of physically motivated (anharmonic) zeroth-order representations. Both approaches are outlined with some improvements, and their possible limitations are discussed. The relative efficacy of the approaches is tested on two typical models that are often used by researchers as benchmarks for different numerical methods. Although no system-specific reference system is involved in the power series expansion of the Boltzmann operator, it quite accurately describes the quantum statistics in the entire temperature range, even though the coupling strength is rather large. Yet another important advantage of this approach is that it is essentially analytical, and therefore its numerical implementation does not require any computational effort. This makes the power series expansion technique particularly attractive for treating many-body problems. In contrast, the split operator method is found to be efficient only in the limit of separable motion. Otherwise, this approach results in a less than optimally efficient approximation for the density matrix, or even one which is worse than the standard Trotter approximation.

A phase‐locked loop based analog simulator for a class of stochastic nonlinear dynamics

An analog simulator has been built for such a class of second‐order Langevin equations that the potential function is given by an integral of the phase angle of admittance for a piezoelectric resonator. It can be applied to the problem of noise induced escape from a potential well since the potential has a minimum at resonance frequency and a surmountable barrier at antiresonance frequency. The design is based on the phase‐locked loop, and the system frequency plays a role of the random variable corresponding to the position of a particle performing a random walk. The modular design makes it possible to adapt the simulator to specific problems.