| CPC B23K 9/0282 (2013.01) [B21D 41/04 (2013.01); B23P 23/04 (2013.01)] | 7 Claims | 

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               1. A particle having a bulk modulus that varies nonlinearly with changes in pressure, said particle comprising: 
            a solid elastic shell having a tube shape with a closure at both ends and a wall with a circumferentially varying thickness defined by an inner surface and an outer surface; and 
                a core as an entirety of a closed volume defined by the inner surface of said shell, with said core having a bulk modulus less than the bulk modulus of said shell. 
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