Rare-Earth (RE = Y, Gd, Tb, Dy, Ho, and Er) Chains Bridged with a Triplet Biradical and Magnetic Hysteresis Recorded for RE = Tb.

Complex formation of 5-tert-butyl-1,3-phenylene bis(tert-butyl nitroxide) and rare-earth (RE) metal ions gave a linear chain where each nitroxide O atom is directly bonded to the RE ion. The bridge was proven to be a ground triplet molecule in the complexes. A hysteresis loop was recorded below 2.8 K as a single-chain magnet for the RE = Tb derivative.

Fragmentation of cavitation bubble in ultrasound field under small pressure amplitude.

In the present study, dynamic behavior and fragmentation mechanism of acoustic cavitation bubbles are investigated under relatively small pressure amplitudes of ultrasonic wave through a three-dimensional compressive multiphase flow simulation and experimental observations. It is found that the oscillating bubble takes a non-spherical shape soon after occurring the Rayleigh collapse following the sound pressure distribution around the bubble. Then, the amplitude of non-spherical deformation is enhanced during small high-frequent oscillations after the Rayleigh collapse due to the fluid inertial effect. Finally, the oscillating bubble is fragmented into two smaller ones with the Laplace pressure gradient becoming the final trigger of bubble fragmentation. Besides, the results reveal that the temperature of bubble surface is varied when the non-spherical bubble deformation is large, while during spherical bubble oscillations the surface temperature remains almost unchanged.

Multibubble sonoluminescence enhancement by fluid flow.

Forced fluid flow can cause the enhancement of multibubble sonoluminescence (SL) under suitable conditions. The effect of directional flow with a circulator is similar to that of rotating flow with a stirrer. The mechanism of the enhancement is that both flows prevent cavitation bubbles from coalescing and clustering, which are responsible for the quenching of SL. The intensity of sonochemiluminescence (SCL) in an aqueous luminol solution increases with flow speed at higher ultrasonic powers more significantly than that of SL in distilled water. However, in the range of low ultrasonic power, the intensities of SL and SCL decrease with flow speed. Therefore, an optimum flow speed exists in relation to ultrasonic power and frequency.

Mechanism of O2-accelerated sonolysis of bisphenol A.

The effects of dissolved gases on the sonochemical degradation of bisphenol A (BPA) were studied at a frequency of 500 kHz. BPA degradation rate increased in the order O(2)>Ar>air>N(2). The rate constant for oxygen (2.6 h(-1)) was approximately two fold higher than that for argon (1.2 h(-1)). A primary intermediate (2,3-dihydro-2-methylbenzofuran), a typical intermediate of BPA formed during attack by OH radicals, was detected only in the presence of oxygen, revealing that a different reaction path was responsible for the enhancement of decomposition.

Sonoluminescing single bubble in concentrated alkali halide solutions.

Single-bubble sonoluminescence is generated in concentrated aqueous solutions of LiBr and LiCl. The moving-bubble state, a type of unstable state in which sonoluminescence is still emitted, is observed above the stable-sonoluminescence state similarly to that in aqueous solutions of NaCl and KCl. Luminosity is increased at similar magnitudes for LiBr, LiCl, NaCl and KCl of the same concentration.

Single-bubble sonochemiluminescence in aqueous luminol solutions.

Sonochemiluminescence (SCL) of luminol due to a single bubble is studied through spectral measurement. No SCL was observed from a stable single bubble that emitted high-intensity sonoluminescence (SL). In contrast, SCL was observed under conditions of an unstable dancing bubble, where a bubble grows and ejects tiny bubbles, making it "dance" by counteraction. Furthermore, SCL was observed from dancing bubbles even when SL was not observed, depending on the dissolved gas content. The instability of bubble collapse is the key parameter governing SCL.

Influence of dissolved oxygen content on multibubble sonoluminescence with ambient-pressure reduction.

The efficiency of chemical reactions in the presence of ultrasound at reduced pressures has been monitored using the influence of dissolved oxygen (DO) content on a luminol solution undergoing multibubble sonoluminescence. From these measurements under the condition of constant ultrasonic frequency and constant amplitude of sound pressure, it is shown that the intensity of sonoluminescence is higher at subatmospheric ambient pressure than at atmospheric pressure under the same degree of saturation. Also, it is found that there is an appropriate content of DO to produce the highest intensity of the luminescence and its value varies with ambient pressure.

Influence of bubble clustering on multibubble sonoluminescence.

Influence of clustering of cavitation bubbles on multibubble sonoluminescence (MBSL) in standing wave fields is studied through measurement of MBSL intensity with a photomultiplier tube and observation of corresponding bubble behavior with a high-speed video camera and an intensified charge-coupled device one. It is clarified that, when the SL is quenched suddenly at excessive ultrasonic power, the behavior of bubbles clearly changes; the bubbles which form dendritic branches of filaments change into clusters due to the secondary Bjerknes force. The cluster is composed of several bubbles surrounded by many tiny bubbles, in which bubbles repeatedly coalesce and fragment, and run away from pressure antinodes. When the clusters are broken up by forced fluid motion, the quenching of MBSL is suppressed.

Optimization of a sonochemical reactor using a pulsing operation.

It is known that sonochemical reactions are enhanced by pulsing ultrasound. A method to optimize a sonochemical reactor using a pulsing operation was studied through the measurement of changes in sonoluminescence (SL) intensity from distilled water under various experimental conditions. It was confirmed that pulsing with a constant input power level enhanced SL intensity at lower power levels because of the higher amplitude of ultrasound. In contrast to this, a quenching effect due to excessive sound pressure appeared at higher power levels, and the pulsing operation was not effective under these conditions. Pulsing is more effective at higher frequency than at lower frequency.