共查询到20条相似文献,搜索用时 12 毫秒
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为描述激光熔覆层质量与工艺参数之间的相互关系,在研究自动送粉激光熔覆过程能量分配规律的基础上,利用金相法检测的不同工艺条件下单道熔覆层的宏观参数,定量计算了L.C.Lim提出的单位质量熔覆材料的比能和单位时间实际输入的比能两个重要参数,并系统地分析了影响因素。在激光参数恒定的条件下,单位质量熔覆材料的比能随送粉速率的增大而减小;单位时间实际输入的比能随扫描速度的增加而减小。对单位质量熔覆材料的比能随扫描速度的变化出现最小值的现象给出了合理的解释。为进一步研究熔覆层的凝固行为、显微组织与工艺参数的关系奠定了理论基础。 相似文献
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Alan G. Thompson 《Journal of Electronic Materials》1973,2(1):47-70
The choice of a window material suitable for high power CO2 lasers emitting at 10.6 μm is discussed. Gallium arsenide was chosen and its preparation is discussed at length. The physical,
electrical and optical properties of GaAs are also discussed with particular reference to the high-resistivity form which
is necessary to reduce free-carrier absorption at 10.6 μm to an acceptable level. The method used to measure the optical absorption
coefficient is a calorimetric one making use of a low power CO2 laser. The variation of the optical absorption coefficient with impurities, different dopants, resistivity, laser beam polarization
and various growth parameters has been examined. It was found that GaAs could be routinely prepared with an absorption coefficient
below 0.02 cm-1 at 10.6 μm, a minimum value of 0.005 cm-1 being the best observed. The prime cause of this absorption has not yet been established, but the need for further theoretical
work is clear. The quality of the GaAs prepared makes it a prime candidate for a window material in high power CO2 lasers and systems.
This work was partially supported by the Office of Naval Research, Physics Branch, under Contract N00014-70-C-0132. 相似文献
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由于尺寸较小,D波段行波管盒型窗对各个参数的影响较为敏感,因此使用CST软件对蓝宝石窗片的盒形窗进行优化设计。从各个工艺参数出发,对窗片金属化层的内径和厚度,以及焊料层的厚度和圆波导高度等的影响进行了软件仿真分析,得到了优化后最佳值为10GHz的带宽,即在133GHz144GHz范围内,驻波比低于1.2。最后加入整个慢波结构和衰减瓷的模型中进行计算,得到了驻波比低于1.4的结果,满足整管指标要求。 相似文献
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为了研究金属激光直接沉积工艺过程中工艺参量对工艺能效的影响,采用自主研发的HCX60五轴激光复合制造机床开展工艺能效田口试验,并对其结果进行了信噪比分析、极差分析以及方差分析,得到激光功率、送粉量、扫描速率、提升量以及搭接率对工艺能效的影响主次关系,提出了工艺因素优化组合。结果表明,送粉量对工艺能效的影响最为显著,最佳参量组合为激光功率P=500W,送粉量f=28g/min,扫描速率v=600mm/min,提升量h=0.6mm和搭接率λ=30%。这为研究增材制造工艺参量对工艺能效的作用及影响规律提供了理论借鉴和实验基础。 相似文献
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《Signal processing》1986,11(2):157-168
The optimum energy criterion continuous and discrete prolate spheroidal wave function windows had a profound effect on the basic understanding and practical optimization of many problems in communication theory, signal processing, and antenna theory. However, in many situations, there is interest in not only packing maximum window energy in some frequency interval, but also interest in imposing precise spectral window values and spectral nulls over some specified frequencies. We have formulated and solved such an optimization problem in an analytical sense as well as in an efficient computational sense. The problem is first expressed as a constrained maximization of a normalized quadratic form w′Aw/w′w, where A is a positive-definite matrix specified by the window energy concentration interval, w is the window weighting vector, and the constraining subspace is specified by the spectral window values and locations. This problem is then transformed to a nonconstrained maximization of a normalized quadratic form w′ PAPw/w′w, where P is a projection operator onto the orthogonal complement of the original constraining subspace. Persymmetric properties of A and PAP are used to reduce the computational complexity of the solution of the optimum window. Numerical maximization can be readily performed using the iterative power method. Specific examples are presented. 相似文献
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基于600 mm口径的某激光发射系统,提出了一种卷帘覆盖压紧式密封方法,卷帘采用卷曲收放结构,通过电机驱动卷轴转动带动同步带运动,同时利用弹性拉紧机构拉紧卷帘,使卷帘在收放运动过程中一直保持紧贴密封平面来达到密封效果。通过理论分析与有限元建模仿真,对其密封特性进行了分析,得出密封平面的结构形式是影响密封性能的主要因素。通过分析比较,选取PVC作为卷帘材料。设计的结构为密封凸起平面形式,卷帘厚度为0.5 mm,结构边缘带有30倒角。对其密封特性进行有限元仿真分析,得出卷帘中心挠度为6.269 mm。在设计指标所允许的的极限载荷下卷帘所受应力远小于材料拉伸强度,不会破坏。满足密封要求。 相似文献
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Triple energy window scatter correction technique in PET 总被引:3,自引:0,他引:3
A practical triple energy window technique (TEW) is proposed, which is based on using the information in two lower energy windows and one single calibration, to estimate the scatter within the photopeak window. The technique is basically a conventional dual-window technique plus a modification factor, which can partially compensate object-distribution dependent scatters. The modification factor is a function of two lower scatter windows of both the calibration phantom and the actual object. In order to evaluate the technique, a Monte Carlo simulation program, which simulates the PENN-PET scanner geometry, was used. Different phantom activity distributions and phantom sizes were tested to simulate brain studies, including uniform and nonuniform distributions. The results indicate that the TEW technique works well for a wide range of activity distributions and object sizes. The comparisons between the TEW and dual window techniques show better quantitative accuracy for the TEW, especially for different phantom sizes. The technique is also applied to experimental data from a PENN-PET scanner to test its practicality. 相似文献