Bubble motions confined in a microspace observed with stroboscopic technique

Dynamic motions of gas bubble confined in a microspace, i.e., in a channel of a microreactor, were observed with a video microscope and stroboscopic technique using a light emitting diode operated in a pulsed mode. There are many important phenomena related to the bubble dynamics synchronized with ultrasonic wave and continued for more than a few minutes. With the stroboscopic technique, the time-expanded bubble motions synchronized with ultrasound wave and the real time background images can be simultaneously observed. A number of interesting phenomena resulting from the dynamic motions of a microbubble in a microspace were observed; nonspherical bubble oscillation, rectified diffusion, emergence of cavitation, and microstreaming of different patterns depending on the input power of ultrasound. The observation technique described in this investigation could be a convenient tool for taming the bubble under a microscope to investigate the bubble dynamics in detail.     

Observation of plasma and magnetoplasma resonances of two-dimensional electrons in a single MgZnO/ZnO heterojunction

The magnetoluminescence of the two-dimensional electron system in a single Mg _x Zn_{1 ? x} O/ZnO hetero-junction (x = 0.02) at a temperature of 0.3 K in magnetic fields up to 14 T has been studied. The concentration of two-dimensional electrons in the structure under study has been determined from the oscillations of the luminescence intensity as a function of the magnetic field. The value thus obtained is close to the one derived from transport measurements. The resonance corresponding to plasma excitations of two-dimensional electrons has been observed using optical detection of microwave absorption. In a magnetic field, the lower branch of magnetoplasma excitations, which corresponds to the propagation of edge magnetoplasmons in a structure with nearly square geometry, has been observed and investigated.     

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.     

Inhibitors of skin-tumor promotion. VIII. Inhibitory effects of euglobals and their related compounds on Epstein-Barr virus activation. (1)

Twelve euglobals from Eucalyptus globulus and their twenty-six related compounds were examined for their inhibitory effects on Epstein-Barr virus activation by a short-term in vitro assay. The results showed that most of the euglobals having monoterpene structures, and euglobal-III (8) had strong inhibitory activity. Grandinol (18), homograndinols (19 and 20), and compounds 26, 27, 28, and 32 showed stronger inhibitory effects. Based on the results, the structural requirements for the activity of these compounds were discussed.