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91.
A. Pompei 《Applied Acoustics》2006,67(5):420-431
In the present paper, we simulate focused wave fields generated by a system of plane transducers used in an immersion ultrasonic technique. The ultrasonic beam penetrates into the elastic medium through the fluid-solid boundary. A real-time computer algorithm is proposed to calculate stress components in the solid medium. It is shown that a good focusing wave structure can be provided by a pair of plane rectangular transducers, inclined with respect to each other and to the beam acoustic axis. 相似文献
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Based on scalar diffraction theory, 8-phase-level 256×256 elements diffractive microlens array with element dimension of 50×33 μm2 have been fabricated on the back-side of PtSi(3~5 μm) infrared CCD. The measurement results indicated that the ratio of the signal-to-noise of the infrared CCD with microlens was increased by a factor of 2.8. 相似文献
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红外目标模拟器由红外目标图像发生器和投影光学系统组成。该红外光学系统是一个要求与2个导引光学系统的光学技术参数相匹配的长焦距、大视场和具有像方远心光路的中红外光学系统。叙述用于红外目标模拟器的红外耦合光学系统的设计原理,提出它与导引光学系统一起可组成放大倍率M=4.5×的红外投影光学系统,并指出IR CRT产生的图像通过红外投影光学系统可成像在导引接收器上。针对给出的红外耦合光学系统的设计特点和技术要求,光学材料选取硅(Si) 锗(Ge) 硅(Si),采用简单的柯克三片式结构完成光学系统设计。设计评价结果表明,该系统的光学性能和成像质量均满足设计指标要求。 相似文献
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The composition of thin perovskite films, especially the oxygen content, is a crucial parameter which influences many physical properties, such as conductivity and catalytic activity. Films produced by pulsed laser deposition are normally annealed in an oxygen atmosphere after deposition to achieve a desired oxygen content. In pulsed reactive crossed beam laser ablation, no annealing step is necessary, but a fundamental question regarding this deposition technique is still open: where does the oxygen in the films come from?There are three possibilities, i.e. from the target, from the gas background, or from the gas pulse. To answer this question two experiments were performed: 18O2 was used during the deposition process as background gas with 16O anions in the target and 16O2 gas pulse, and a 18O2 gas pulse with 16O from the target and background. These experiments revealed that the quantification of the oxygen origin is only possible, when no oxygen exchange occurs at the deposition temperature. The films are characterized after deposition by elastic recoil detection analysis (ERDA) to determine the 16O/18O ratio. Experiments with different oxidizing species in the gas pulse (N2O and O2) confirm that the oxidizing potential (N2O > O2) as well as the number of molecules are important. 相似文献
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Starting from the propagation equation of Hermite-cosh-Gaussian (HChG) beams and the intensity moments definition, an analytical expression for the propagation of the kurtosis parameter of unapertured HChG beams passing through paraxial optical ABCD systems is derived and illustrated numerically. Special interesting cases are discussed, in particular, the kurtosis parameter of HChG beams at the waist plane is obtained readily from our general propagation expression. 相似文献