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随着国民经济的发展和科学技术的进步,露天采矿先后出现了全境界、分期、边采边扩和综合开采四种开采方式。分期开采克服了全境界开采生产剥采比大、基建周期长、投资大和投产达产时间长的缺点;边采边扩开采是从分期开采演变发展来的,它克服了分期开采在过渡时期剥离洪峰高的缺点,妥善地解决了分期开采扩帮过渡的一些复杂问题,是采矿科学技术发展的必然趋势。 相似文献
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In the plasma sheath a narrow plasma channel generated by ultraintense laser pulses is simplified as a special cylindrical and hollow plasma waveguide with the infinite thickness of the plasma cladding.The electromagnetic wave (EM) propagation properties of the plasma channel near the cutoff and far from the cutoff are considered.Theoretical analysis shows that TE 0m and TM 0m and hybrid modes emerge in the plasma channel,which is influenced by the normalized frequency parameter B and numerical aperture NA.The cutoffs of the various modes are approximated.Single-mode operation is possible without a high-frequency limitation in the channel. 相似文献
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