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991.
采用螺旋线和折叠线技术相结合的方法,设计了一种基于水介质高功率脉冲调制器。该调制器采用了两个开关,通过控制两个开关的导通时刻,可以在两个负载上得到脉冲长度相等的两个脉冲。对该种折叠型传输线的波过程进行了详细分析,给出了过渡段部分阻抗等参数对负载电压的影响;用Pspice电路软件对脉冲形成线的充电电压和二极管电压、电流进行了模拟;最后利用高压同轴电缆,对该种类型调制器进行了低压情况下的验证实验,实验结果与理论分析、模拟研究一致。此种类型的调制器具有结构紧凑、可同时输出两个脉冲的优点。 相似文献
992.
The dispersion relations of the surface polariton in a semi-infinite wire medium with spatial dispersion are analysed. In comparison with the traditional spatial dispersive medium there only exists one branch instead of multibranch for the dispersion curve. The possibility of the experimentally observing the surface polaritons by attenuated total reflection is simulated numerically. 相似文献
993.
The global existence and structures of solutions to multi-dimensional unsteady compressible Euler equations are interesting
and important open problems. In this paper, we construct global classical solutions to the interaction of four orthogonal
planar rarefaction waves with two axes of symmetry for the Euler equations in two space dimensions, in the case where the
initial rarefaction waves are large. The bi-symmetric initial data is a basic type of four-wave two-dimensional Riemann problems.
The solutions in this case are continuous, bounded and self-similar, and we characterize how large the rarefaction waves must
be. We use the methods of hodograph transformation, characteristic decomposition, and phase space analysis. We resolve binary
interactions of simple waves in the process. 相似文献
994.
Pu‐Jun Jin Zheng‐Quan Yao Mao‐Lin Zhang Yu‐Hu Li Hui‐Ping Xing 《Journal of Raman spectroscopy : JRS》2010,41(2):222-225
A blue pigment was identified by micro‐Raman spectroscopy, X‐ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX) and X‐ray diffraction (XRD). The test sample, a funerary lacquer tray, belongs to West Han Dynasty (206 BC–AD 8) of China and was decorated with faint blue patterns. The result from Raman spectroscopy showed that the faint blue is covellite (CuS) due to the presence of a characteristic peak at 474.5 cm−1, which further was confirmed by XRF, SEM–EDX and XRD. This research indicated that CuS had been used as a blue pigment to decorate lacquer wares from the West Han Dynasty in China. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
995.
We report a novel post‐growth microwave treatment approach to selectively modify the surface morphologies of gold (Au) films coated on the polystyrene (PS) bead substrates for effectively improving the surface‐enhanced Raman scattering (SERS) effect on the analytes. The discrete dipole approximation (DDA) model was introduced to evaluate the enhancement effects by calculating the localized electromagnetic field distribution and extinction efficiency based on the sizes of the trenches and voids, and the surface roughness of the modified Au–PS bead substrates. The SERS performance of microwave‐modified Au–PS substrates on rhodamine 6G (Rh 6G) and saliva yields at least 10‐fold improvements in SERS intensities compared to the as‐grown substrates, which is also in agreement with theoretical predictions by DDA modeling. This work demonstrates both experimentally and theoretically the efficacy of the microwave heating treatment on modifying the Au–PS bead substrates for the realization of high SERS performance in biomedical applications. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
996.
C. Chen D.J. Chen Z.L. Xie P. Han R. Zhang Y.D. Zheng Z.H. Li G. Jiao T.S. Chen 《Applied Physics A: Materials Science & Processing》2008,90(3):447-449
Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures were investigated
by X-ray diffraction and Hall effect measurements. AlN passivation induced an additional compressive stress in an AlGaN barrier
layer instead of an additional tensile stress induced by Si3N4 passivation. The change of strain after passivation contributes in a relatively small proportion to the variation of the
carrier concentration in AlGaN/GaN heterostructures compared with the contribution from passivation of surface traps. The
results from Hall effect measurements show that the AlN passivation layer has a better effect on passivation of deep levels
than the Si3N4 film and also results in a remarkable increase in mobility of the two-dimensional electron gas.
PACS 73.40.Kp; 71.55.Eq; 81.65.Rv; 81.05.Ea; 61.05.cp 相似文献
997.
针对低场磁共振成像系统,该文设计了一种紧凑灵活的信号接收方案,实现对多通道磁共振信号的高速采样与直接数字解调. 系统采用高速模数转换器(A/D)对磁共振信号直接采样;以单片数字下变频器(DDC)--AD6636, 完成4路采样信号的数字解调;以数字信号处理器(DSP)作为控制器,实现对AD6636的配置以及I/Q数据的读取. 信号采样频率可达100 MSPS,适用于1 T以下的系统. 实验证明该设计具有结构紧凑,采样速率高,配置方便快速,滤波器设计丰富灵活等特点,为磁共振成像谱仪的研制提供了一种高性能的信号接收方案. 相似文献
998.
首次提出产生局域空心光束(Bottle beam)的另一类新型锥透镜模型.讨论了凹凸两种模型,分别是在传统轴棱锥的底部磨削和胶合圆台结构形成.研究结果表明平面波正入射新型凹锥透镜可产生单个Bottle beam,正入射新型凸锥透镜可形成具有周期性的Bottle beam.通过几何光学分析了产生Bottle beam的原理,计算了Bottle beam的相关参数.由衍射积分理论分析和模拟了新型锥透镜后的光强分布特性,所得分析结果与几何光学分析基本符合.
关键词:
新型锥透镜
Bottle beam
轴棱锥
Bessel光 相似文献
999.
C. T. Zheng C. S. Ma Z. C. Cui X. Yan D. M. Zhang C. W. Tian 《Optical and Quantum Electronics》2011,42(5):327-346
By introducing normalized mode excitation coefficient and total mode excitation coefficient, we improve the 3-D mode propagation
analysis (MPA) method for convenient design and analysis of multimode interference (MMI) coupler. With the improved 3-D MPA
method and point-matching method, we present a novel formulation technique to analyze the low- and high-frequency characteristics
for the impedance-matched polymer Mach-Zehnder interferometer electro-optic (EO) switch based on MMI couplers. As an application,
under 1550 nm, optimization and simulation performed for the designed device reveal low driving voltage of 1.375 V with short
EO region length of 5 mm. The insertion loss and extinction ratio are less than 3.75 dB and more than 42 dB, respectively.
The microwave characteristic impedance is about 49.6 Ω, and due to the less mismatch between lightwave velocity and microwave
velocity, the estimated cutoff switching frequency is up to 263 GHz with the 10–90% rise time and fall time about 1.90 ps
under the operation of step-style square-wave switching signal. This theoretical cutoff switching frequency is almost 1.53
times of that of our previous reported shielded EO switch with similar design technique. 相似文献
1000.
在LF-11和LF-12高功率激光装置上进行的实验中,设计了一些特定的激光束-金腔靶-探测器条件,创造了激光直接加热、准辐射加热和激光、X光混合加热三种物理条件,采用软X光透射光栅能谱时空分辨技术,测量了腔靶、缝靶和双孔靶等高分辨X光能谱,研究了激光等离子体X光辐射非平衡特性。 相似文献