A、及时支护顶板
B、有利于运输物料
C、有利于通风
D、控顶宽度小
第2题
光时域反射法(OTDR)Optical time domain reflection method (OTDR) 基本原理:光源发出的光在沿光纤向前传输的过程中产生后向散射,后向散射光强在向后传播过程中随着距离增长而按一定规律衰减,在光速不变的情况下,距离与时间成正比。因此,根据探测器探测到的后向散射光强及其到达探测器的时间,就可以知道沿光纤路径上任一点的初始后向散射光强。Basic principle: the light emitted by the light source will generate backscattering in the process of forward transmission along the optical fiber, and the intensity of backscattered light will decrease in a certain rule as the distance increases in the process of backward propagation. Under the condition that the speed of light remains unchanged, the distance is proportional to time. Therefore, the initial backscattered light intensity at any point along the fiber path can be known based on the backscattered light intensity detected by the detector and the time it took to reach the detector. 光的后向散射包括瑞利散射、喇曼散射和布里渊散射3种形式。The backscattering of light includes Rayleigh scattering, Raman scattering and brillouin scattering.
第8题
A、夯实全民健身在体育强国建设中的基础地位。
B、以制度构建为措施,营造全民健身国家战略的法治环境。
C、以智慧服务为目标,推动“互联网+”助力全民健身发展。
D、以稳中求进为基调,促进全民健身工作模式与方法创新
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