Arrays of gas bubbles of uniform size are generated in a liquid and subjected to sound at a frequency of 30 kHz. In a viscous mixture of glycerine and water, sonoluminescence is produced in the absence of cavitation noise or streamer activity. Under relatively low amplitude conditions the light occurs in flashes with the same frequency as the sound field, and with duration less than one-tenth that of the sonic period. The phenomenon is believed to be associated with volume pulsations of the bubbles and, specifically, with dissociation of H2O into the radicals OH and H during the compression phase of each cycle when the temperature is relatively high. Photons are emitted as the radicals recombine. Calculations suggest that about 108 photons/sec might be expected from a single 0.2-mm-diam bubble by this mechanism when the bubble temperature reaches 1800°K. Bremsstrahlung (from accelerated charges) is negligible under these same conditions.

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A new design for an ultrasonic motor operating at a frequency of about 14.5 kHz for generating continuous as well as stepwise angular rotation has been developed. The device uses a magnetostrictive ferrite transducer and a single power amplifier for its operation. A possible mechanism for the operation of the ultrasonic motor has been suggested. The variation of the speed of rotation as a function of frequency, excitation voltage, and load has been studied. The measurement of the performance characteristics reveal that the ultrasonic motor is capable of giving 100 rpm at 34.6-W electric output. The rpm of the rotating disk can be controlled by a slight adjustment of the frequency of the rf signal to the driving transducer. The load capability of the device is 1 kg. Using a tone burst of 10 ms, an angular step of 1.8 deg has been realized.

LETTERS TOTHE EDITOR tions for the neutral vowel/o/. Acoustic analysis shows that F1 and F2 of the neutral vowel may correspond to those of/,x/,/e/, or/•/, depending on context. This is to be expected because the primary function of a neutral vowel is to provide a smooth transition (for the articulators) between two consonants. The main distinguishing feature of/o/, when it is present, is its low amplitude and short duration. These prosodic parameters are best indicated by a stress marker and not by the use of a separate phonemic symbol. These considerations suggest that the so-called neutral vowel/o/is best approximated by an allophone of /e/, or/•/depending on context, with appropriate stress indication. When in doubt, remember that its most common occurrence is as an allophone of/•x/. In transcriptions where stress indication is important, one adds the digit 0, 1, or 2 immediately following the vowel symbol to indicate unstressed, secondary stress, and primary stress. This would make the transcription somewhat unreadable, but stress markers can easily be suppressed from listings when readability is important.Some readers might be concerned that using two characters per phoneme might require 12 to 16 bits of valuable computer storage to represent a phoneme. The notation proposed here is intended only for input to or output from the computer. The internal representation of phonemes might be a fixed six-or seven-bit code or variable length code using Huffman coding.The transcription resulting from the use of the notation can indeed be readable, as illustrated by the following transcription of the example given in Dixon and Maxeyl: ,/AIM SAAREE/YOOV REECHT DHIS AWFIS BAI MISTEIK /PLEEZ KANSALT YAR DAREKTAREE Results are reported of the ultrasonic-absorption coefficient and its variation with frequency in an aqueous mixture of urea with enzyme urease. The probable causes for the observed high absorption are examined. THE ULTRASONIC-ABSORPTION METHOD HAS NOW BECOME A USEFUL tool for the study of rapid and reversible processes in fluids. Some of these studies, such as the equilibrium in rotational isomers, 1 dimerization • in carboxylic acid, and ionic dissociation in dectrolytes 3 are already well recognized. However, there have been only a few applications of this method for the study of biological media. This is presumably because of the fact that the reversible fast step in a biological transformation is very often accompanied The third-order elastic moduli of quartz have been measured using a pulseecho interferometer technique. Values for the constants are given and compared with those of previous workers. TaERE HAS BEEN CONSIDERABLE INTEREST RECENTLY IN TIlE NONlinear elastic properties of solids, especially in relation to the propagation characteristics of ultrahigh-frequency elastic waves. The nonlinear behavior may be conveniently described in terms of "third-order" elastic moduli, so called because they appear in polynomial stored-energy functions as coefficients of third-order 640 Volume 44 Number 2 1968

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