Page 49 - Fall 2006

Scanning the Journals
“splash jet” discloses a remarkable broadening. Shock waves induce a strong form of secondary cavitation due to the particular shock wave confinement, which offers a way to estimate integral shock wave energies in isolated vol- umes. Bubble lifetimes in drops are shorter than in extend- ed volumes in remarkable agreement with herein derived corrective terms for the Rayleigh-Plesset equation. These observations, made on board an aircraft flying in parabolic arcs to create near-weightless conditions, would be diffi- cult, if not impossible, in normal gravity.
􏰀 A mathematical system for organizing the 12 tones of the Western scale that makes use of a topological structure called an orbifold is described in the 7 July issue of Science. Chords are points in the topological space, and the segments connecting them indicate how chords progress. The work described in this paper is part of an ambitious project to characterize musical composition in great gener- ality by means of mathematical music theory.
􏰀 Language is largely symbolic, but how we say some- thing can be as important as what we say, according to an article in the 21 July issue of Science Now Daily News. Twenty four college students were asked to describe a dot moving across a screen. The students were told to use one of two sentences: “It is going up” or “It is going down.” The team found that when students described the dots going up, the pitch of their voice was, on average, 6 hertz higher than that of those describing the dot going down. The same thing happened when another 24 students read the sentences from a computer screen, indicating people change the sound of their voice according to directional information contained within words. Listeners readily caught these cues.
􏰀 To a person who suffers from hyperacusis, even the sound of their own voice can be intolerable, according to an article in the 15 July issue of New Scientist. Nobody knows exactly what causes hyperacusis, but it can be brought on by head injuries, exposure to extremely loud sounds, Lyme disease or autism. It has also been linked with tinnitus. The main question puzzling researchers is whether it results from structural damage to the ear or flaws in the way the brain interprets sound signals.
The most successful treatment is a therapy using gradual desensitization with “pink noise,” sound in which the amplitude decreases with increasing frequency.
􏰀 Two-way communication over gas pipelines using multi- carrier modulated sound waves is the topic of a paper in the July issue of Acoustical Science and Technology. Conventional acoustic communication technology is limit- ed by the effect of reverberant signals, but the use of multi- carrier frequencies which change cyclically avoids this. Using this method, a transmission rate of 3840 bps was achieved.
􏰀 A portable navigational aid for the blind transmits soft, low-pitched beeps directly to the inner ear, according to an article in the 19 August issue of New Scientist. The system
guides users with beeps that appear to come from whatever direction the person needs to head in. The user simply walks towards the sound. The device uses a processor in a backpack to combine GPS location readings with data from cameras and motion sensors attached to a headband or hel- met. This information is fed into a virtual 3D model of the streetscape or building the person is navigating to calculate which direction the person should walk. To make the beeps appear to come from a particular direction, the system varies the timing and intensity of the vibrations transmitted to each earpiece to vibrate the skull.
􏰀 The pattern of the sound waves viewed by the Wilkinson Microwave Anisotropy Probe satellite, which show the abundance of hydrogen and helium in the universe, are another evidence for the large amount of dark matter in the universe according to an article in the August 29 Scientific American Newsletter online. These measurements are in agreement with other measurements which show that at most, 5 percent of the mass-energy density of the universe is in the form of atoms. Many physicists and astronomers think dark matter is probably a new particle that so far has eluded detection during particle accelerator experiments or discovery among cosmic rays. In order to behave as dark matter, it must be heavy and weakly interacting with nor- mal matter.
􏰀 The April issue of Acoustics Australia is a special issue on Mechanisms of Hearing Damage. The articles are presented in a “top down” order beginning with the psychoacoustics of sound localization using head- related transfer functions. Another article reviews neural organization with particular emphasis on the signals which descend to the cochlea to either control the processing of sound via the outer hair cells or the excitability of primary neurons carrying the frequency analysis upward. Two papers deal with the genetics of hearing loss. The special issue attempts to draw attention to the cross-fertilization
between psychoacoustics and physiological acoustics.
􏰀 Taiwan’s high-speed train, scheduled to open in October, has raised new questions about the level of noise and vibration, according to a story in the August issue of IEEE Spectrum. The latest twist in this tale began three years ago, when the government solicited design concepts for reducing vibration from passing bullet trains. Taipei-based Sheus Technologies Corp. proposed to stiffen the rail bed’s foundation and install barrier walls containing elastic rub- ber pellets. However, the design is not predicted to meet the National Science Council’s goal, which reportedly was to limit noise from a train passing 200 meters from the track at 300 kilometers per hour to 48 decibels. Some observers fear that semiconductor manufacturing in Tainan Industrial Park may be affected by the vibrations.
􏰀 “Our atmosphere is filled with sounds that we cannot hear,” begins an article on infrasound in the August issue of Physics World. “From listening in on volcanoes to detect- ing nuclear explosions, a global network of infrasound
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