The formation of super-star clusters in disk and dwarf galaxies

Super-star clusters are probably the largest star-forming entities in our local Universe, containing hundreds of thousands to millions of young stars usually within less than a few parsecs. While no such systems are known in the Milky Way (MW), they are found especially in pairs of interacting galaxies but also in some dwarf galaxies like R 136 in the Large Magelanic Cloud (LMC). With the use of SPH calculations we show that a natural explanation for this phenomenon is the presence of shear in normal spiral galaxies which facilitates the formation of low-density loose OB associations from giant molecular clouds (GMC) instead of dense super-star clusters. In contrast, in interacting galaxies and in dwarf galaxies, regions can collapse without having a large-scale sense of rotation. This lack of rotational support allows the giant molecular clouds to concentrate into a single, dense and gravitationally bound system.

S240 – Human Cochlear Implant Histopathology

Objectives 1) To exam the histopathology of multichannel cochlear implant temporal bones. 2) To evaluate the relationship of residual spiral ganglion cell counts to clinical hearing performance. Methods 8 temporal bones from 4 cochlear implant patients were examined histologically. Paired comparisons were made between implanted and nonimplanted temporal bones. Clinical performance data was obtained from patient charts. Results There were varying amounts of inflammation (fibrosis and ossification) in the basal turn of the cochlear in all implanted temporal bones. Trauma to the facial nerve at facial recess site was noticed in 1 case. Compared with nonimplanted ears, 2 implanted bones with less than 10-year duration of implantation had no significant changes of spiral ganglion cell population. One case with prolong implant duration (15 years) showed about 36% decrease of spiral ganglion cells at the implanted site. The case with best speech recognition (89% with CID sentence) had the highest residual spiral ganglion cells (30% of normal spiral ganglion cell population). 2 cases with poor clinical performance (< 10% with CID sentence) had the residual spiral ganglion cells at 11% and 22%. The case with moderate clinical performance (30% with CID sentence) had 14% of normal spiral ganglion cell population. Surviving dendrites varied from 5% to 30% among 4 cases with no relationship to clinical performance. Conclusions Our findings suggest prolonged implantation may affect spiral ganglion cell population. There is no reverse relationship between residual spiral ganglion cells in implanted temporal bones to clinical speech performance observed from our limited cases.