Page 48 - January 2006

Scanning the journals
􏰀 The male cub-winged manakin, a tiny red-headed bird, lit- erally sings with its wings, according to an article in the 29 July issue of Science (see also “Acoustics in the News” in the Fall issue of ECHOES). In an effort to attract the attention of females, the bird rakes its feathers back and forth over one another, using an acoustic trick that also allows crickets to sing. While the technique is common among insects, it has never been documented before in vertebrates. When the bird raises its wings over its back, it shakes them back and forth over 100 times a second. The frequency of the sound by raking the feathers, however, is around 1400 Hz. The rapid pronation and adduction of the wings and the collision between the right and left secondaries is thought to produce an impulsive mechanical excitation that induces the enlarged, hollow sixth and seventh feathers to resonate. The sound is reported to be loud and clear, not unlike the sound of a violin.
􏰀 Scanning near-field ultrasound holography (SNFUH), a non- destructive imaging technique, is described in the 7 October issue of Science. SNFUH provides depth information as well as spatial resolution at the 10- to 100-nameter scale. It has a finer resolution than the scanning acoustic microscope and is especially valuable in subsurface imaging, whether integrated circuits or biological systems. Typical frequencies are in the 2-MHz range. In SNFUH, acoustic waves are launched on both the probe tip and the sam- ple at slightly different frequencies, and the interference of these two waves forms a surface acoustic standing wave which is altered by subsurface features such as voids.
􏰀 The July issue of Acoustical Science and Technology includes a tutorial on “Expressive speech: Production, perception and applications to speech synthesis.” It discusses some of the cur- rent problems with data collection, labeling, techniques for analyzing voice quality and applying speech synthesis as an analysis tool. Directions for future work in order to improve synthesis of expressive speech are suggested.
􏰀 When a dry strand of spaghetti is bent beyond its limit of curvature, it does not usually break in half but instead into sev- eral pieces, from as few as three to as many as ten, according to a paper in Phys. Rev. Lett. 95 095505. Apparently flexural waves travel along the length of the rod just after the initial break. These waves increase the local curvature of the rod and trigger an avalanche of new breakages, which in turn initiate more waves, thus causing the rod to fragment. This phenome- non, which has been confirmed by high-speed images of indi- vidual strands of spaghetti as they break, can be applied to other materials such as fiberglass.
􏰀 Continuing analysis of sound recordings made in Arkansas (see “Acoustics in the News” in the Fall issue of ECHOES) have not yet settled the question of whether the ivory-billed woodpecker is alive or extinct, according to a news feature in the 8 September issue of Nature. A team of ornithol- ogists from Cornell University published an article in Science 308, 1460 (2005) stating that the woodpecker was alive and well, and the Secretaries of the Interior and Agriculture held a press conference on April 28 hailing the rediscovery as a rare
Thomas D. Rossing
piece of good news for the Bush administration, smarting from criticism over its environmental policies. There are doubters, however. “Remote sound recordings are notoriously deceptive,” one of them points out. The team was scheduled to return to the Arkansas woods in November with more observers, more acoustic recorders and an expected $200,000 in federal funds.
􏰀 Baryonic acoustic oscillations are a promising way to study dark energy in the universe, according to an article in the 2 September issue of Science. Like sound waves in a slide whis- tle that shift to lower pitches as the whistle’s plunger descends, the wavelength of light increases more quickly if space is stretching faster. So to accumulate a given amount of stretch or redshift, light would have had to travel longer and farther if the universe had expanded more slowly billions of years ago than if the universe had always expanded at its current rate. Because of baryon acoustic oscillations, galaxies show a slight tendency to space themselves at a specific distance. That distance, about 500 million light years, is determined by how far sound waves traveled in the plasma that filled the primordial universe before atoms formed (see ECHOES, Fall 2004). Prior to recombina- tion, the baryons in the universe were locked to photons of the cosmic microwave background, and the photon pressure inter- acting against the gravitational instability produced a series of sound waves in the plasma.
􏰀 A single-molecule torsional pendulum is described in the 2 September issue of Science. The molecule is a single-wall car- bon nanotube grown on a silicon substrate by chemical vapor deposition. The resonance frequency for the torsional oscilla- tions is calculated to be 0.1 MHz.
􏰀 Audio information stored in the grooves of cylinder or disk phonograph records can be reconstructed, without con- tact using optical metrology methods (see “Acoustics in the News” in the Fall 2004 issue of ECHOES), according to a paper in the June issue of the Journal of the Audio Engineering Society. The first three-dimensional reconstruction of record- ed sound from a mechanical carrier is reported. The source material, a celluloid cylinder, was scanned using color-coded confocal microscopy techniques. Three-dimensional meas- urement is required in order reconstruct vertically modulat- ed carriers such as a cylinder.
􏰀 Pitch perception is critical for identifying and segregating auditory objects in both music and speech. Pitch is not unique to humans and has been demonstrated in several animal species as well. A paper in the 25 August issue of Nature reports finding neurons in the auditory cortex of marmoset monkeys that respond to both pure tones and missing fundamental harmon- ic complex sounds having the same fundamental frequency. These pitch-selective neurons are located in near the anterolat- eral border of the primary auditory cortex, which is consistent with the location of a pitch-selective area in humans.
􏰀 Small drops can bounce indefinitely on a bath of the same liquid if the container is oscillated vertically at a sufficiently high acceleration. According to a brief communication in the 8 September issue of Nature, these bouncing droplets can be
46 Acoustics Today, January 2006