共查询到20条相似文献,搜索用时 250 毫秒
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(一)引言激光是一种时间相干性与空间相干性都很好的光.因此,用此种光照射物体可以获得清晰的衍射图样.若在物体后放置一透镜,则在透镜焦面上得到的便是夫琅和费衍射图样即付里叶频谱,如图1所示.每一频谱与物体的某一空间频率相应,即相应于物体的某一信息.这些频谱在像面上重新组合,便复现原物的像.这就是相干成像的机制.但如果照射的光不是相干光,而 相似文献
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莫尔测量法被广泛用于各类流场的结构显示和关键参量测量中,关于相位物体在光路中的放置位置已有不同的报道,针对该问题进行了理论和实验研究。理论分析表明,当相位物体放置于2个光栅前时,偏移量和相位主要取决于2个光栅之间的距离,偏折角取决于相位物体引起的相位扰动与2个光栅之间的间距的比值;而当相位物体放置于2个光栅之间时,偏移量和相位主要取决于相位物体到后面一个光栅之间的距离,偏折角则取决于相位物体引起的相位扰动与其到后面一个光栅之间的距离的比值。为了验证理论结果的正确性和合理性,实验中选取燃烧蜡烛火焰作为对象,对比发现在两种情况下,只要相应的距离选取适当,则相位物体的位置并不影响实验中重建的相位和偏折角等结果。相关研究成果可为莫尔测量法更好地用于各类流场的检测提供一定的参考。 相似文献
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初步认识、理解力的概念十分重要,这是学好初二物理课程力学部分重要的基础,也是进一步学习必不可少的起点.1 力是物体对物体的作用,物体间力的作用是相互的物理学中力这个概念,来源于实际生活中,例如:人推车,人施了力,车受到了力.不但人能够对物体施力,其他物体也能够对别的物体施力,例如:马拉犁,马对犁施加了力;磁铁吸引铁块,磁铁对铁块施加了力.由此可见,力是物体对物体的作用.一个物体受到力的作用,一定有另一个物体对它施加这种作用;力是不能离开施力和受力物体而独立存在的.穿着旱冰鞋的甲、乙两个小孩,当甲用力推乙时,会感到乙也在… 相似文献
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在物理教学中,有一种错误观点:在零势能面上,重力势能为零,也就是说物体在该处没有重力势能.重力势能是由物体所在位置与零势能面间重力势能之差决定的.重力势能的零势能面,是为了能定量地把物体重力势能表示出来,而选取的一个参考面.我们规定:物体处在零势能面上时,重力势能为零,这并不是说物体没有重力势能,而是物体的重力势能可以用零这个数值来表示: 相似文献
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1提出问题题目:选择某一高度为零势面,物体1的重力势能是Ep1=3J,物体2的重力势能是Ep2=-3J,则下列正确的是A.Ep1=Ep2B.Ep1>Ep2C.Ep1相似文献
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两物体间相对滑动时产生的摩擦力叫做滑动摩擦力,滑动摩擦力的产生条件是:(1)两物体间要有压力(接触、形变),(2)两物体间要有相对运动.物体受到与它接触的另一物体对它的滑动摩擦力的大小为f=μN,方向与该物体相对于另一物体的运动方向相反,其中μ为这两物体间的动摩擦因数,μ=f/N,与两个物体材料有关,与接触面的情况(如粗糙程度等)有关. 相似文献
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在讲授静电场时,教师经常从带电体吸引轻小物体引入新课.有心的学生往往会问:带电体为什么会吸引轻小物体?带电体一定会吸引轻小物体吗?就此问题笔者做以下讨论,供参考. 相似文献
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Distortion of optical feedback signals in microchip Nd:YAG lasers subjected to external multi-beam interference feedback 下载免费PDF全文
This paper proposes a theoretical analysis for the characteristics of an external cavity Nd:YAG laser with feedback of multiple-beam interference,which is induced by the multi-reentrance of the light from the external Fabry-Perot cavity.The theoretical model considers the multiple beam interference of the external Fabry-Perot cavity.It is found that the optical feedback signals are distorted to pulse waveforms instead of the sinusoidal ones in conventional feedback.The experimental results are in good agreement with the theoretical analysis.The obtained theoretical and experimental results can advance the development of a laser feedback interferometer. 相似文献
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The thermal effects of the diode end-pumped Nd:YVO4 slab laser crystal are investigated both analytically and numerically. The theoretical model is established with considering the divergence of the pump beam in the slab. A detailed theoretical analysis of the temperature, stress and the focal length of thermal lens are presented. Using 3D finite element analysis, an accurate numerical solution based on the theoretical model is achieved. Our analysis includes the thermal fracture damage of the thermally and optically anisotropic slab and the predicated values are compared with the experimental results. 相似文献
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This paper focuses on the performance analysis and the algorithm development for cooperative wideband spectrum sensing (CWSS) under imperfect reporting channels for cognitive radio (CR). The centralized approach with multiple distributed cooperating secondary users (CSUs) and a fusion center (FC) is considered for CWSS. Nakagami fading is used to model the channel between PUs and the CSUs. The CSUs equipped with multiple diversity antennas are considered to take advantage of both space and antenna diversity. In this work, the reporting channel model under erroneous reporting is proposed. The repetition code-based CWSS (RC-CWSS) algorithm is proposed for performance improvement. First, the modified, improved theoretical analysis of an existing algorithm called partial band Nyquist sampling-based CWSS (PBNS-CWSS) under no reporting errors is given. The theoretical analysis under an imperfect reporting channel is then carried out for the same algorithm. Then, the complete theoretical analysis for the proposed RC-CWSS algorithm is carried out. The theoretical analyses are verified using Monte-Carlo simulations. The analysis shows that the performance of CWSS is greatly affected by the reporting channel errors. Also, the RC-CWSS outperforms recently proposed state-of-the-art algorithms. Finally, the effects of different parameters on the performance of the proposed algorithm are also studied. 相似文献
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A theoretical analysis of phase-locking in a multi-channel radial array CO2 laser is presented. The concepts are based on the theories of injection phase-locking and matrix optics. The mutual optical coupling occurring within the central region is demonstrated by theoretical deduction. Interrelated graphs of the coupling coefficient and the distance between the coupling position and the cavity mirror are calculated by numerical simulation. The results of the analysis are in accord with experimental results. 相似文献
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根据侵彻过程中弹体内部装药的弹性变形假设,利用弹体结构与内部装药的相对位移、摩擦功、热力学原理和热点理论,提出了装药热安定性设计的弹性理论分析方法。计算中,侵彻弹体的响应函数从空穴膨胀理论出发;利用弹塑性材料中应力波Hugoniot跳跃条件以及流体力学动量和质量守恒方程,分析了弹体侵彻混凝土过程中的弹体表面径向应力;结合牛顿第二定律,采用有限差分技术,获得了弹体侵彻过程的轴向阻力。通过弹性理论分析,得到了弹体侵彻过程中影响装药安定性的重要设计参数,为装药安定性设计提供了理论依据。 相似文献