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131.
一款宽光谱鱼眼镜头的设计 总被引:2,自引:1,他引:1
讨论了一款用于监控侦查的鱼眼镜头设计.首先根据使用要求,选择了可以由图像直接提取出目标方位信息的等距离投影方式;又由系统对目标分辨率的要求,选择了焦距相对较长的全帧成像形式.通过合理布局系统结构及材料选择,使各种像差得到较好的校正,并通过加大光阑慧差改善系统照度均匀性.最终设计出工作波段486~900nm,视场180°,F/2.8的宽光谱鱼眼镜头,设计结果系统全视场在乃奎斯特频率63lp/mm处的调制传递函数大于0.3,边缘视场照度大于中心视场照度的50%,f-θ畸变小于3%,各项指标满足系统要求. 相似文献
132.
133.
Modelling of spall damage in ductile materials and its application to the simulation of the plate impact on copper 下载免费PDF全文
A statistical model of dynamic spall damage due to void nucleation and growth is proposed for ductile materials under intense loading, which takes into account inertia, the elastic-plastic effect, and initial void size. To some extent, void interaction could be accounted for in this approach. Based on this model, the simulation of spall experiments for copper is performed by using the Lagrangian finite element method. The simulation results are in good agreement with experimental data for the free surface velocity profile, stress record behind copper target, final porosity, and void concentrations across the target. The influence of elastic-plastic effect upon the damage evolution is explored. The correlation between the damage evolution and the history of the stress near the spall plane is also analyzed. 相似文献
134.
135.
Difference-frequency ultrasound generation from microbubbles under dual-frequency excitation 下载免费PDF全文
The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging. 相似文献
136.
新显色剂PAPC光度法测定Zn(Ⅱ)的研究 总被引:1,自引:0,他引:1
研究了新显色剂4-(2-吡啶偶氮)-邻苯二酚(PAPC)与Zn(II)的显色反应,在pH9.5缓冲溶液中,该试剂与Zn(II)反应生成稳定的登色配合物,其最大吸收 长为494nm,表观摩尔吸光数为6.66*10^4L.mol^-1,cm^-1,锌含量在0-25ug/25ml范围内服从比耳定律,该方法应用于铝合金和钢样中锌的测定,结果满意。 相似文献
137.
138.
Quantum circuits for realizing deterministic and exact teleportation via two partially entangled pairs of particles 下载免费PDF全文
Deterministic and exact teleportation can be achieved via two partially
entangled pairs of particles [Gu Y J 2006 {\em Opt. Comm.} {\bf 259} 385]. The key point of the protocol is a generalized measurement described by a positive operator-valued measure, which can be realized by performing a unitary operation in the extended space and a conventional Von Neumann orthogonal measurement. By decomposing the evolution process from the initial state to the final state, we construct the quantum circuits for realizing the unitary operation with quantum Toffoli gates, and thus provide a physical means to realize the teleportation. Our method for constructing quantum circuits differs from the usual methods based on decomposition of unitary matrices, and is convenient for a large class of quantum processes involving generalized measurements. 相似文献
139.
Characteristics of selective oxidation during the fabrication of vertical cavity surface emitting laser 下载免费PDF全文
Taking into account oxidation temperature, N2 carrier gas flow, and the
geometry of the mesa structures this paper investigates the characteristics of
selective oxidation during the fabrication of the vertical cavity surface emitting
laser (VCSEL) in detail.
Results show that the selective oxidation follows a
law which differs from any reported in the literature. Below 435℃
selective oxidation of Al0.98Ga0.02As follows a linear growth law for the
two mesa structures employed in VCSEL. Above 435℃ approximately increasing
parabolic growth is found, which is influenced by the geometry of the mesa
structures. Theoretical analysis on the difference between the two structures for
the initial oxidation has been performed, which demonstrates that the geometry of
the mesa structures does influence on the growth rate of oxide at higher
temperatures. 相似文献
140.
微量元素示踪法在古代青铜器铜矿料来源研究中的应用 总被引:1,自引:1,他引:0
青铜模拟熔铸实验表明,利用ICP-AES法测定的青铜中亲铜元素的成分数据,通过聚类分析,可以较好地区分不同产地的铜矿料及其青铜产物。文章将这一方法具体应用于盘龙城商代遗址和鄂州出土青铜器的微量元素数据的分析,以考察其可行性和应用价值。多元统计分析结果显示:青铜模拟熔铸实验所得结论,亦可应用于盘龙城和鄂州青铜器铜矿料的区分,进一步验证了微量元素示踪古代青铜器铜矿料来源的可行性。 相似文献