The physical core is crystallized in magnetic iron-nickel alloy-composite. The core is not hollow.

物质核心是磁性铁镍合金复合材料的结晶，其核心不是中空的。

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My Irish visit reminded me once again how critical physical fitness is to our core well being both personally and professionally.

FORBES: Fitness Forever: Three Steps to Take Now

Scientists in Riga at the Institute of Physics at the University of Latvia are continuing to work on a much more physical mock-up of the core.

BBC: Planet Earth

Adapted from an early short story by Elmore Leonard that was previously filmed very capably in 1957 with Glenn Ford and Van Heflin, "3:10 to Yuma" strikes a fair balance between physical action and psychological warfare, but always at its core is the question of how we are to measure these two men.

CNN: Review: '3:10 to Yuma' a classic ride