Probing nuclear bubble configuration by the $\pi^{-}/\pi^{+}$ ratio in   heavy-ion collisions
  It is theoretically and experimentally argued that there may exist bubble or toroid-shaped configurations in some nucleus systems. Based on the nuclear transport model, it is shown that compared with the collision of normal nuclei, there is a depletion of central density of compression with bubble configurations in projectile and target nuclei. This depletion of central compression density may affect some observables in heavy-ion collisions. 
Gao-Chan Yong
nucl-th nucl-ex