ABSTRACTS OF TECHNICAL ARTICLES 1513 



which it does not occur. In this paper, the dependence of the yield on the 

 energy just above this threshold is derived. The derivation is not rigorous 

 because it circumvents some of the difficulties of the three-body problem by 

 applying ergodicity, albeit in a weakened form. The result is that, for atoms, 

 the yield rises as the 1 . 1 27th power of the energy excess. For ions the exponent 

 Hes between this number and unity. 



WiLLARD, G. W.' 



Ultrasonically Induced Cavitation in Water : A Step-by-Step Process, 

 J. Acoust. Soc. Am., 25, pp. 669-686, July, 1953. 



A 2.5-mc, barium-titanate, spherically focusing radiator was used to produce 

 cavitation in both degassed and aerated water entirely within the restricted, 

 high intensity focal region, remote from the water boundaries. The sonic 

 intensity rises to 1.8 kw/cm^ and the pressure amplitude to ±70 atmospheres 

 at the focus. High-intensity illumination and an unusual high speed photo- 

 graphic technique permit observation and timing of the step-bj'-step process 

 of cavitation development. 



Feather-shaped cavitation bursts are sporadically produced, being initiated 

 in the insignificant quill portion nearest the radiator, then abruptly expanding 

 to form the catastrophic plume portion. The plume is believed to be formed 

 by myriads of microcavities, too small and close for individual observation. 

 These two fundamental steps are identically produced, and with equal ease, 

 both in degassed and aerated water. The whole action is over in several milli- 

 seconds, except that in the case of aerated water a third bubble step is pro- 

 duced. In aerated water, non-collapsing gas bubbles are generated by and 

 concurrently with, the catastrophic step. These bubbles remain after collapse 

 of the burst, to be blown off down stream by the sonically induced liquid 

 streaming. 



The bubble step is not generated without the presence of the catastrophic 

 step. The latter is generated only if the initiation step reaches a definite degree 

 of development (not always attained). This requires sonic activation for 

 increasing lengths of time for decreasingly smaller sonic intensities. Origina- 

 tion of the initiation step, and hence of the whole cavitation phenomena, is 

 believed to occur whenever a stray nucleus (weak spot) streams into the high 

 intensity sonic field. 



Young, W. R.' 



Comparison of Mobile Radio Transmission at 150, 450, 900 and 3700 

 Mc, I.R.E., Trans., P.G.V.C. 3, pp. 71-83, June, 1953. 



Bell Telephone Laboratories, Inc. 



