Turning defence into offence? Intrusion of cladoceran brood chambers by a green alga leads to reproductive failure

We observed a novel anti-grazer strategy in the green alga Chlorella vulgaris, where the cells entered the brood chambers of two grazers, Daphnia magna and Simocephalus sp, densely colonized the eggs, and significantly reduced the grazers' reproductive success

Comparisons of sonoluminescence from single-bubbles and cavitation fields: bridging the gap

Sonoluminescence (SL) refers to the generation of light through the energetic pulsations of acoustic cavitation bubbles in a liquid. For years, SL was observed primarily in cavitation fields. These bubbles are believed by many to undergo near-adiabatic compression, resulting in the heating of the bubble contents and the subsequent emission of light. Recently, researchers have discovered a ‘new’ form of sonoluminescence in which light is observed to emanate from a single bubble undergoing very large volume excursions. The mechanism for light production is unknown, but many believe it is due to a rapid heating of the central core by an imploding shock wave. Based in part on the emission time scales, there is a common belief that the two forms of SL are quite distinct. We address this issue by comparing the two phenomena with regards to their light-flash durations and emission spectra-leading to some surprising differences and similarities

Comparisons of sonoluminescence from single-bubbles and cavitation fields: bridging the gap

Sonoluminescence (SL) refers to the generation of light through the energetic pulsations of acoustic cavitation bubbles in a liquid. For years, SL was observed primarily in cavitation fields. These bubbles are believed by many to undergo near-adiabatic compression, resulting in the heating of the bubble contents and the subsequent emission of light. Recently, researchers have discovered a ‘new’ form of sonoluminescence in which light is observed to emanate from a single bubble undergoing very large volume excursions. The mechanism for light production is unknown, but many believe it is due to a rapid heating of the central core by an imploding shock wave. Based in part on the emission time scales, there is a common belief that the two forms of SL are quite distinct. We address this issue by comparing the two phenomena with regards to their light-flash durations and emission spectra-leading to some surprising differences and similarities

Optical pulse width measurements of sonoluminescence in cavitation-bubble fields

Optical pulse width measurements of sonoluminescence from cavitation-bubble fields have been obtained for two well-defined cavitation zones in an aqueous solution of Glycerin using a fast (650 ps rise-time) PMT and a fast (10 GS/S) digitizer. One zone corresponds to cavitation produced from an ultrasonic homogenizer. A lens was used to focus on a particular region of “streaming” sonoluminescence. A second, more localized cavitation zone was produced using a 2-in-diam PZT driving crystal in a rectangular fluid-filled container. Single-bubble sonoluminescence was used to characterize the response of the PMT to low-level light input. The measured rise-time and pulse width for sonoluminescence from cavitation fields is indicative of the response of the PMT and suggests that the pulse width of cavitation-field sonoluminescence is much less than 1.1 ns. </p

Optical pulse width measurements of sonoluminescence in cavitation-bubble fields

Optical pulse width measurements of sonoluminescence from cavitation-bubble fields have been obtained for two well-defined cavitation zones in an aqueous solution of Glycerin using a fast (650 ps rise-time) PMT and a fast (10 GS/S) digitizer. One zone corresponds to cavitation produced from an ultrasonic homogenizer. A lens was used to focus on a particular region of “streaming” sonoluminescence. A second, more localized cavitation zone was produced using a 2-in-diam PZT driving crystal in a rectangular fluid-filled container. Single-bubble sonoluminescence was used to characterize the response of the PMT to low-level light input. The measured rise-time and pulse width for sonoluminescence from cavitation fields is indicative of the response of the PMT and suggests that the pulse width of cavitation-field sonoluminescence is much less than 1.1 ns. </p

Bjerknes force and bubble levitation under single-bubble sonoluminescence conditions

Bubble levitation in an acoustic standing wave is re-examined here for the case of single-bubble sonoluminescence. The equilibrium position of the bubble is calculated by equating the average Bjerknes force with the average buoyancy force. The predicted values, as a function of pressure amplitude, are compared with experimental measurements. Our measurements indicate that the equilibrium position of the bubble shifts away from the pressure antinode as the drive pressure increases, in qualitative agreement with calculations, but unexpected when only linear theory is considered [A. Eller, J. Acoust. Soc. Am. 43, 170 (1968)]. The Bjerknes force also provides an upper limit to the drive pressure in which a bubble can be levitated near (and above) a pressure antinode, even in the absence of shape instabilities. </p

Effect of surfactants on inertial cavitation activity in a pulsed acoustic field

It has previously been reported that the addition of low concentrations of ionic surfactants enhances the steady-state sonoluminescence (SL) intensity relative to water (Ashokkumar; et al. J. Phys. Chem. B 1997, 101, 10845). In the current study, both sonoluminescence and passive cavitation detection (PCD) were used to examine the acoustic cavitation field generated at different acoustic pulse lengths in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A decrease in the SL intensity was observed in the presence of low concentrations of SDS and short acoustic pulse lengths. Under these conditions, the inhibition of bubble coalescence by SDS leads to a population of smaller bubbles, which dissolve during the pulse “off time”. As the concentration of surfactant was increased at this pulse length, an increase in the acoustic cavitation activity was observed. This increase is partly attributed to enhanced growth rate of the bubbles by rectified diffusion. Conversely, at long pulse lengths acoustic cavitation activity was enhanced at low SDS concentrations as a larger number of the smaller bubbles could survive the pulse “off time”. The effect of reduced acoustic shielding and an increase in the “active” bubble population due to electrostatic repulsion between bubbles are also significant in this case. Finally, as the surfactant concentration was increased further, the effect of electrostatic induced impedance shielding or reclustering dominates, resulting in a decrease in the SL intensity

Effect of surfactants on inertial cavitation activity in a pulsed acoustic field

It has previously been reported that the addition of low concentrations of ionic surfactants enhances the steady-state sonoluminescence (SL) intensity relative to water (Ashokkumar; et al. J. Phys. Chem. B 1997, 101, 10845). In the current study, both sonoluminescence and passive cavitation detection (PCD) were used to examine the acoustic cavitation field generated at different acoustic pulse lengths in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A decrease in the SL intensity was observed in the presence of low concentrations of SDS and short acoustic pulse lengths. Under these conditions, the inhibition of bubble coalescence by SDS leads to a population of smaller bubbles, which dissolve during the pulse “off time”. As the concentration of surfactant was increased at this pulse length, an increase in the acoustic cavitation activity was observed. This increase is partly attributed to enhanced growth rate of the bubbles by rectified diffusion. Conversely, at long pulse lengths acoustic cavitation activity was enhanced at low SDS concentrations as a larger number of the smaller bubbles could survive the pulse “off time”. The effect of reduced acoustic shielding and an increase in the “active” bubble population due to electrostatic repulsion between bubbles are also significant in this case. Finally, as the surfactant concentration was increased further, the effect of electrostatic induced impedance shielding or reclustering dominates, resulting in a decrease in the SL intensity

Bjerknes force and bubble levitation under single-bubble sonoluminescence conditions

Bubble levitation in an acoustic standing wave is re-examined here for the case of single-bubble sonoluminescence. The equilibrium position of the bubble is calculated by equating the average Bjerknes force with the average buoyancy force. The predicted values, as a function of pressure amplitude, are compared with experimental measurements. Our measurements indicate that the equilibrium position of the bubble shifts away from the pressure antinode as the drive pressure increases, in qualitative agreement with calculations, but unexpected when only linear theory is considered [A. Eller, J. Acoust. Soc. Am. 43, 170 (1968)]. The Bjerknes force also provides an upper limit to the drive pressure in which a bubble can be levitated near (and above) a pressure antinode, even in the absence of shape instabilities. </p