Effect of noble gas doping in single-bubble sonoluminescence.

The trillionfold concentration of sound energy by a trapped gas bubble, so as to emit picosecond flashes of ultraviolet light, is found to be extremely sensitive to doping with a noble gas. Increasing the noble gas content of a nitrogen bubble to about 1% dramatically stabilizes the bubble motion and increases the light emission by over an order of magnitude to a value that exceeds the sonoluminescence of either gas alone. The spectrum also strongly depends on the nature of the gas inside the bubble: Xenon yields a spectral peak at about 300 nanometers, whereas the helium spectrum is so strongly ultraviolet that its peak is obscured by the cutoff of water.

Single-Molecule FRET to Measure Conformational Dynamics of DNA Mismatch Repair Proteins.

Single-molecule FRET measurements have a unique sensitivity to protein conformational dynamics. The FRET signals can either be interpreted quantitatively to provide estimates of absolute distance in a molecule configuration or can be qualitatively interpreted as distinct states, from which quantitative kinetic schemes for conformational transitions can be deduced. Here we describe methods utilizing single-molecule FRET to reveal the conformational dynamics of the proteins responsible for DNA mismatch repair. Experimental details about the proteins, DNA substrates, fluorescent labeling, and data analysis are included. The complementarity of single molecule and ensemble kinetic methods is discussed as well.

Observation of bubble dynamics within luminescent cavitation clouds: Sonoluminescence at the nano-scale.

Measurements of acoustically driven cavitation luminescence indicate that this phenomenon is robust over a huge parameter space ranging from 10 kHz to >10 MHz. The minimum bubble radius achieved is an upper bound for the size of the light-emitting region and ranges from about 1 microm at 15 kHz to tens of nm at 11 MHz. Although lines can be discerned in the spectra of some cavitation clouds, they sit on top of a broadband continuum which can have greater spectral density in the ultraviolet than is observed for resonantly driven sonoluminescence from a single bubble.

Comment on "Mie scattering from a sonoluminescing bubble with high spatial and temporal resolution".

A key parameter underlying the existence of sonoluminescence (or SL) is the time dependence of the radius R(t) of the collapsing bubble from which SL originates. With regard to the use of light scattering to measure this quantity, we wish to note that we disagree with the statement of Gompf and Pecha-highly compressed water causes the minimum in scattered light to occur 700 ps before SL-and that this effect leads to an overestimate of the bubble wall velocity. We discuss potential artifacts in their experimental arrangement and reply to their criticisms of our experiments on Mie scattering.

Physical acoustics of ultrasound-assisted lipoplasty.

The acoustic fields generated by probes and cannulas used for ultrasound-assisted lipoplasty (UAL) are sources of cavitation and sonoluminescence. The localized stress fields and heating caused by cavitation are strong enough to lyse cells and, in the authors' opinion, constitute the means of therapeutic action of UAL. The spectrum of sonoluminescence extends into the ultraviolet. Various devices have been calibrated and various issues relating to health risks are discussed.

Sonoluminescence: nature's smallest blackbody.

The transduction of sound into light through the implosion of a bubble of gas leads to a flash of light whose duration is delineated in picoseconds. Combined measurements of spectral irradiance, Mie scattering, and flash width (as determined by time-correlated single-photon counting) suggest that sonoluminescence from hydrogen and noble-gas bubbles is radiation from a blackbody with temperatures ranging from 6000 K (H(2)) to 20,000 K (He) and a surface of emission whose radius ranges from 0.1 microm (He) to 0.4 microm (Xe) . The state of matter that would admit photon-matter equilibrium under such conditions is a mystery.

Blackbody spectra for sonoluminescing hydrogen bubbles.

The dynamical motion of sonoluminescing bubbles formed from a mixture of water and hydrogen gas indicates that these bubbles contain hydrogen. Their spectrum is well matched by an ideal 6000 K blackbody radiating from a surface with a radius less than 1/4 microm. According to this model, the state of matter inside the collapsed bubble is so stressed that the photon mean free path is much smaller than 1 microm. Implications for various theories of the light-emitting mechanism and the role of chemical reactions are discussed.