Page 51 - Summer 2006

Scanning the Journals
story. In January 2005 dozens of pilot whales began to run themselves onto the sand beach along North Carolina’s Outer Banks. The U. S. Navy had been conducting a train- ing exercise in the area around the time of the event, and an initial report by the National Marine Fisheries Service listed sonar as a possible cause for the incident. The Navy stated that the exercise took place about 100 kilometers from where the whales beached, too far to have had any effect. More than a year after the stranding, doubts still linger. The sonar controversy has also focused attention on a broader issue: oceans everywhere are getting noisier because of commercial shipping, underwater oil and gas exploration, and other human activity, and scientists have no clear idea what harm these noises have on whales and other sea creatures.
􏰀 Solitons have been observed in solid crystals for the first time according to a paper in the 29 March issue of Physical Review Letters. Solitons are stable localized waves that propagate through a medium with spreading. They were first observed by the Scottish scientist John Russell in 1834 when he was watching horses drag a barge along a canal. When the boat suddenly stopped, a wave of water contin- ued along the canal without changing shape or slowing down. Now solitons have been observed in crystals of ura- nium when firing beams of neutrons and X-rays into the material. Vibrations, which have wavelengths as small as the spacing between atoms in the crystal, form randomly throughout the material.
􏰀 “Nanomechanics of the subtectorial space caused by electromechanics of cochlear outer hair cells” is the title of a paper in the February 14 issue of Proceedings of the National Academy of Sciences. The electromechanical properties of the soma of the outer hair cells in a guinea- pig cochlea was used to generate mechanical force over the
entire functionally relevant range of 50 kHz. Vibration responses were measured with a laser Doppler vibrometer. For frequencies up to about 3 kHz, the apical surface of the inner hair cells and the opposing surface of the tectorial membrane were found to vibrate with similar amplitudes but opposite phases. At high frequencies there was little relative motion between these surfaces. For frequencies up to at least 3 kHz there appears to be direct fluid coupling between outer and inner hair cells.
􏰀 Songbirds may be able to learn grammar, according to a letter in the 27 April issue of Nature. European starlings learned to recognize acoustic patterns defined by a recur- sive, self-embedding, context-free grammar. The simplest grammar, long thought to be one of the skills that separate man from beast, can be taught to a common songbird, the study suggests.
􏰀 French physicists say they have cracked the riddle of “singing sand dunes” and they are compiling a CD of sand music, according to a note in the 17 September issue of New Scientist. Using sand from Moroccan singing dunes shipped to their laboratory, they found that they could play notes by pushing the sand by hand or with a metal handle. After a month of singing, however, the sands seemed to lose their voice. The singing grains were round with a smooth coating of silicon, iron and manganese, which probably formed on the sand when the dunes once lay beneath an ancient ocean, the researchers said. But in muted grains this coat had been worn away, which explains why only some dunes can sing. What determines frequency is the grain size. However, the role of the coat- ing on the grains is still not well understood. (Ed’s. note: some of the sounds can be heard at www.lps.ens.fr/~douady/SongofDunes/ArticleJduC/CD_ CNRS/CD_piste3.html).
Acoustics in the news
􏰀 “Risks Fall, Hopes Rise for Hearing Implants” is the com- forting headline of a story in the March 7 issue of The New York Times. Earlier a high incidence of meningitis was found in deaf children with cochlear implants, but this was mainly in children with an implant type that is no longer on the market. Deaf children already stand a higher than nor- mal chance of contracting meningitis, an infection of the fluid surrounding the brain and spinal cord, because they often have abnormalities in their inner ears. On the other hand, early implantation is important. Kids who are implanted by age 3 or 4 have language that is pretty normal and can be educated in mainstream classes rather than in special schools for the deaf. In the past 20 years, it is esti- mated that 11,000 American children have received implants. Early implantation is encouraged so that children can hear in the crucial years to learn language.
􏰀 In an attempt to give the public audible evidence of what is normally invisible, artist Carrie Bodle created a multi- speaker sound installation on the Green Building at MIT, according to a story in the September 12 issue of The Boston Globe. The speakers broadcast audio representa- tions of sound waves embedded in the Earth’s upper atmosphere each day from noon to 1:00 pm for a week in September. In another story about the “Sonification/Listening Up” installation, the September 16 issue of the MIT newspaper The Tech reported that some listeners likened the experience to an airplane circling overhead while others described it as a “big didgeridoo.” 􏰀 The debate over whether the Navy’s use of sonar to detect submarines is harming whales and other sound- sensitive species is back again, according to an editorial in the March 7 issue of The New York Times. This time the
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