常温下LED串接放大实现QND光学测量

利用高效率的发光二极管(LED)串接放大,采用大面积高效光电探测器面对面耦合,在常温下从实验上实现了被调制的光子数的光学QND测量,获得量子传输系数T=Ts+Tm=18,态制备能力Vs/m=092的测量结果 关键词：     

不同电磁脉冲对细导线的耦合

 采用时域有限差分法,结合细线处理方法,分别对超宽带电磁脉冲、快前沿电磁脉冲和核电磁脉冲在自由空间细导线上耦合的电流进行了数值计算,得出了不同前沿和脉宽的电磁脉冲在细导线上的感应电流。     

利用二次谐波过程产生532?nm强度压缩光的实验研究

理论分析了当抽运激光具有高于标准量子极限的经典噪声时,在单共振条件下,由倍频腔 输出的532?nm绿光光场的强度噪声起伏,并从实验上获得稳定的强度噪声低于散粒噪声极 限的绿光压缩光,实测的绿光最高强度噪声压缩度为20%(考虑到探测器效率及光路损耗,实 际压缩度达30%).实验结果与理论预测基本一致. 关键词：     

压缩态光场的四阶量子干涉

采用半经典理论讨论了同一抽运源抽运的两个独立光学参量振荡腔(OPO)所产生的压缩态光场的四阶量子干涉效应．结果表明：在OPO振荡阈值处,输出光场压缩度最高但四阶量子干涉最弱,条纹可见度为33.3%,远离阈值时干涉越来越强. 关键词：     

Enhanced Correlation of Electron-Positron Pair in Two and Three Dimensions

Early time electron-positron correlation in vacuum pair-production in an external field is investigated. The entangled electron and positron wave functions are obtained analytically in the configuration and momentum spaces. It is shown that, relative to that of the one-dimensional theory, two- and three-dimensional calculations yield enhanced spatial correlation and broadened momentum spectra. In fact, at early times the electron and positron almost coincide spatially. The correlation also depends on the direction of the applied field. For the spatial correlation, the transverse correlation is stronger than the longitudinal correlation.     

Near-zero thermal expansion in β-CuZnV2O7 in a large temperature range

We report a new type of near-zero thermal expansion material β-CuZnV₂O₇ in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in β-CuZnV₂O₇ is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.     

Improving sound diffusion in a reverberation tank using a randomly fluctuating surface

Underwater reverberation environments that satisfy the conditions of uniformity and isotropy of the diffuse field can be used to measure the acoustic characteristics of underwater targets. This study combines two practical indicators — the standard deviation of the absolute sound pressure field (to indicate uniformity) and the analysis of the wavenumber spectrum in the spherical harmonics domain (to indicate isotropy) — for an accurate evaluation of the diffusion of the sound field in a reverberation tank. A method is proposed that can improve the narrow-band diffusion of the sound field by employing a randomly fluctuating surface. An acoustic experiment was performed in a reverberation water tank (1.2 m×1 m×0.8 m), where a randomly fluctuating surface was generated by making waves. The experimental results show that as the wave motion contributes effectively to the random reflection of sound rays in all directions, the uniformity and isotropy are improved significantly when the surface is fluctuating randomly. This work helps to ensure accurate measurements of the characteristics of underwater targets in reverberation tanks.     

Robustness measurement of scale-free networks based on motif entropy

As a classical complex network model, scale-free network is widely used and studied. And motifs, as a high-order subgraph structure, frequently appear in scale-free networks, and have a great influence on the structural integrity, functional integrity and dynamics of the networks. In order to overcome the shortcomings in the existing work on the robustness of complex networks, only nodes or edges are considered, while the defects of high-order structure in the network are ignored. From the perspective of network motif, we propose an entropy of node degree distribution based on motif to measure the robustness of scale-free networks under random attacks. The effectiveness and superiority of our method are verified and analyzed in the BA scale-free networks.     

Theoretical Studies on the Fe-M Interactions and 31P NMR in Fe(CO)3(EtPhPpy)2MX2 (X=NCS, SCN, Cl; M=Zn, Cd, Hg)

采用密度泛函理论PBE0方法,计算了单核配合物[Fe(CO)3(EtPhPpy)2] (1)、双核配合物[Fe(CO)3(EtPhPpy)2M(NCS)2] (2:M=Zn,3: M=Cd,4: M=Hg) 和[Fe(CO)3(EtPhPpy)2CdX2] (5:X=Cl,6: X=SCN)的几何构型和电子结构,研究了Fe-M相互作用及其对31P化学位移的影响. 结果表明：配合物的稳定性(S)为S(2)>S(3)>S(4),S(3)≈S(6)>S(5).在[Fe(CO)3(EtPhPpy)2CdX2]体系中,含[SCN]-配合物的稳定性大于含Cl-的. Fe-M相互作用的强度(I )顺序为I (2)≈I (3)相似文献   

Spatial Characteristics of Head-Related Transfer Function

The spatial characteristics of head-related transfer functions (HRTFs) are studied by a spatial Fourier analysis.A law of the HRTF spatial sampling in different elevation planes is obtained, and the corresponding spatial interpolating method used to recover the continuous HRTF is proposed. The method is valid, for the average error between the measured and interpolated HRTFs in the horizontal plane is about 0.5%. These results provide guidance for the discrete spatial measurement of HRTFs.