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题目甲、乙、丙三人传球,第一次球从甲传出,到第六次球又回到甲手中的传球方式有种.思路1画出树状图,即可得到答案,有22种,图略.图1图2思路2如图1和图2所示,甲、乙、丙三人传球,可以发现,当且仅当在六次传球中,按顺时针方向的传递次数与按逆时针方向的传递次数之差 相似文献
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Space-charge limiting currents for magnetically focused intense relativistic electron beams
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The self-consistent differential equations, which describe a
laminar-flow equilibrium state in a magnetically focused intense relativistic
electron beam propagating inside a conducting waveguide, are presented. The
canonical angular momentum, $p_{\theta }$, defined under the conditions at the
source, uniquely determines the possible solutions of these equations. By
numerically solving these equations, the space-charge limited current and
the externally applied magnetic field are obtained in a solid beam
and a hollow beam in two cases of $p_{\theta }=0$ (magnetically shielded source)
and $p_{\theta }=$~const. (immersed source) separately. It is shown that the hollow beam
is more beneficial to the propagation of the intense relativistic beam
through a drift tube than the solid beam. 相似文献
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