基于核四极矩共振原理的炸药探测方法研究与实验

介绍了一种基于核四极矩共振（Nuclear Quadrupole Resonance, NQR）原理的炸药探测方法及其基本原理和其用于炸药探测的依据,提出了一种可行的基于核四极矩共振原理的炸药检测系统,描述了其结构组成、工作原理及实验方法,并给出了对黑索金（RDX）、梯恩梯（TNT）、奥克托今（HMX）、太恩（PETN）和特屈儿（TETRYL）炸药的测试实验结果. 实验表明该方法可行,能实现对以上炸药的探测.     

Analytical solutions for some defect problems in 1D hexagonal and 2D octagonal quasicrystals

We study some typical defect problems in one-dimensional (1D) hexagonal and two-dimensional (2D) octagonal quasicrystals. The first part of this investigation addresses in detail a uniformly moving screw dislocation in a 1D hexagonal piezoelectric quasicrystal with point group 6mm. A general solution is derived in terms of two functions φ ₁, φ ₂, which satisfy wave equations, and another harmonic function φ ₃. Elementary expressions for the phonon and phason displacements, strains, stresses, electric potential, electric fields and electric displacements induced by the moving screw dislocation are then arrived at by employing the obtained general solution. The derived solution is verified by comparison with existing solutions. Also obtained in this part of the investigation is the total energy of the moving screw dislocation. The second part of this investigation is devoted to the study of the interaction of a straight dislocation with a semi-infinite crack in an octagonal quasicrystal. Here the crack penetrates through the solid along the period direction and the dislocation line is parallel to the period direction. We first derive a general solution in terms of four analytic functions for plane strain problem in octagonal quasicrystals by means of differential operator theory and the complex variable method. All the phonon and phason displacements and stresses can be expressed in terms of the four analytic functions. Then we derive the exact solution for a straight dislocation near a semi-infinite crack in an octagonal quasicrystal, and also present the phonon and phason stress intensity factors induced by the straight dislocation and remote loads.      

Spectral behavior of pulsed Bessel beams focused by a dispersive lens

Starting from the Huygens–Fresnel diffraction integral, the analytical expression for the power spectrum of pulsed Bessel beams focused by a dispersive aperture lens is derived and used to study the spectral anomalies of pulsed Bessel beams in the focused field. Numerical calculation results are given to illustrate the dependence of spectral anomalous behavior on the pulse parameters, truncation parameter and material dispersion of the lens. It is shown that near the phase singularities the spectral anomalies may take place. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.     

A novel pose and illumination robust face recognition with a single training image per person algorithm

In the real-world application of face recognition system, owing to the difficulties of collecting samples or storage space of systems, only one sample image per person is stored in the system, which is so-called one sample per person problem. Moreover, pose and illumination have impact on recognition performance. We propose a novel pose and illumination robust algorithm for face recognition with a single training image per person to solve the above limitations. Experimental results show that the proposed algorithm is an efficient and practical approach for face recognition.     

Enhanced spontaneous emission factor for microcavity lasers

The microcavity and the influence of nonradiative recombination can control spontaneous emission. An analytic resolution of rate equation is studied for microcavity lasers. The relationship between output prop- erties and structural parameters of multi-quantum wells (MQWs) is obtained. One of the most important consequences of the incrcased spontaneous emission factor is the reduction of laser threshold. It is found that the characteristic curve of a "thresholdless" laser is strongly nonradiative depopulation-dependent. The light output is increased by the enhanced well number and the reduced width. In particular, there is an optimal well number corresponding to the lowest threshold current density for MQW structure in the microcavity lasers.     

Titanium metallization of alumina ceramics by molten salt reaction

In this work, we reported a novel method that is flexible to metallize alumina ceramics with complex surface. Through Ti²⁺ disproportionation occurred in molten NaCl-KCl-K₂TiF₆ bath, the dense Ti layer was deposited on Al₂O₃ ceramics surface with strong adhesion. The effects of reaction temperature, time and initial K₂TiF₆ concentration on deposition rate were investigated. As-prepared coatings compose of bilayer structure of reactive Ti₂O phase, namely, the outer layer with coarse grains and the inner layer with fine grains. The wettability of eutectic Ag72Cu28 and Pb37Sn63 alloys with metallized Al₂O₃ ceramics was measured by using sessile drop method and compared with that of original ceramics. The results show that the metallized Al₂O₃ surface could be reactively wetted well with Ag72Cu28 and Pb37Sn63 alloys. The contact angles lowered to 35° and 8°, respectively, when temperature rose to 900 °C, showing significant enhancement of wettability after Ti metallization by molten salt reaction.     

Characteristics of guided waves in indefinite-medium waveguides

We have presented a discussion on the guided waves in the indefinite-medium waveguides. The characteristic equations describing TE and TM guided waves have been derived. Aiming mainly at the TE guided waves, we have analyzed the existence conditions for the guided and surface modes for four distinct cases, respectively. A number of exotic properties have been revealed in such waveguides, such as the coexistence of forward and backward modes, the absence of fundamental modes, the existence of surface modes and the relaxed requirements for waveguide core constitutive parameters. Numerical results have confirmed our analyses.     

低温等离子体对塑料表面处理——低温等离子体对高密度聚乙烯表面处理的ESR研究

本文研究了不同处理条件(处理功率、处理时间和处理压力)下等离子体气体(Ar、N₂、O₂和空气等)对高密度聚乙烯表面处理产生的自由基的ESR谱。我们观察到等离子体处理产生的自由基是相当稳定的,它的ESR信号强度随处理功率和处理时间增加而增加。但处理压力对它影响不大。我们证明了紫外线对高密度聚乙烯表面产生自由基作用随处理条件而变化。并初步解释了谱的超精细相互作用。     

基于效用的机会网络缓存替换策略

机会网络具有节点流动性较大、数据时延长、资源有限等特点,如何合理和高效地使用节点提供的缓存资源、增加节点间的协作来减少机会网络时延、节省带宽、防止拥塞是一个关键问题.通过对机会网络缓存策略研究,提出了基于效用的概率缓存替换策略,该策略分别计算数据的流行度和最短机会路径的权重,得出节点的效用值,通过比较效用值确定了节点要缓存的数据.实验结果表明提高了节点获取资源的成功率并减少了协作缓存资源请求的平均响应时间.     

Kohonen网络在电容CT图像重建中的应用

提出一种采用Ｋｏｈｏｎｅｎ网络算法进行１２电极电容ＣＴ系统的图像重建的方法．该网络由输入和输出两层神经元组成,输入为１２电极电容ＣＴ系统测量所得的６６个电容值,输出对应管道介质的空间分布模式．该网络采用竞争算法无监督学习,实验结果证明,该网络有较强的抗噪声能力,可重建出较精确的介质分布图像