The stability factors W of a self-synchronous vibrating machine, in space motion, are given by formula(21)and (54) as working with single mass and dual mass respectively.

自同步振动机的稳定性指数W，当振动机为空间单质体和空间双质体时其表达式分别为式（21）及式（54）。

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Wei W. -b., Chen Z. -b 2008. Wrist arthrodeses with wrist fusion plate in 21 cases: Biocompatibility and function evaluation.

魏文兵，陈振兵。腕关节融合钢板内固定21例：生物相容性及功能评估。

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Teng J W. Dynamic process of substance and energy exchanges in depths of the earth and formation of mineral resources [J]. Geotectonica et Metallogenia, 2003, 27 (1) : 3 ~ 21.

[8]滕吉文。地球深部物质和能量交换的动力过程与矿产资源的形成[J]。大地构造与成矿学，2003,27 (1)：3 ~ 21。

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And now, to Indiana, a state that went for George W. Bush by 21 points 4 years ago.

NPR: Reliably GOP States Still In Play In Presidential Race

If you receive a form W-2G, Certain Gambling Winnings, you report the amount in box 1 on your form 1040, line 21 (again, no form 1040-EZ).

FORBES: Best Night of Baseball Ever: You Can Bet on It