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than that predicted by previous models. In addition, in several instances, 

 resonant frequencies have been measured which are significantly higher than 

 can be accounted for by these models. 



The new model consists of a small, spherical shell, enclosing an air cavity, 

 in water. The shell is a viscous, heat-conducting Newtonian fluid, with the 

 physical properties of fish flesh. The interface between the shell and the 

 cavity supports a surface tension. The shell is insonified by a harmonic 

 plane compressional wave, whose wave-length is large compared to the shell 

 diameter. 



The solution to the problem consists of obtaining the amplitude of the 

 scattered compressional wave. This was accomplished by first determining 

 the appropriate wave equations from the linearized equations of motion. 

 Eigenfuction solutions to these equations were then obtained. However, 

 theoretical evidence indicates that only the fundamental mode is an important 

 contributor to volume reverberation, so that higher modes were neglected. 

 Application of the boundary conditions then led to the required solution for 

 the amplitude of the scattered compressional wave. Due to the complexity of 

 this solution, order of magnitude analyses of the various terms were con- 

 ducted in order to obtain a simplified expression. Equations for both the 

 resonant frequency and acoustic cross section were then determined from this 

 simplified expression. 



A comparison of the results of the new model with experimental data indicates 

 that the new model constitutes a definite improvement over previous models. 

 The new model can predict the high values of damping and elevated resonant 

 frequencies that previous models could not. The comparison indicates that 

 the model is most accurate for fish in which tension in the swimbladder wall 

 has a minor effect on resonant scattering. This includes the fish which are 

 of interest in studies of volume reverberation and therefore, the new model 

 will be of considerable value in such studies. 



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