Near-field effect in optics of small objects composed of dipole atoms

A self-consistent problem of interaction of two dipole atoms separated by an unrestricted distance with the field of a quasi-resonance light wave was solved on the assumption that the investigated atoms are Lorentz linear oscillators and the polarizing fields inside the system consist of the Coulomb and the retarded parts. The solution obtained was investigated for the case where the atoms have the same polarizability and the distance between them is much smaller than the length of the external light wave. Formulas for the electric fields inside a small object and outside it have been obtained. It is shown that inside a small two-atom object there can take place longitudinal and transverse optical vibrations accompanied by corresponding dispersion effects depending on the interatomic distance and the angle between the axis of the system and the direction of propagation of the external light wave. The field outside the small object in the wave zone is linearly polarized when the external wave has linear polarization. However, the direction of polarization of the corresponding waves is largely determined by their frequency. It is also shown that the amplitude of the field outside the small object in the wave zone depends greatly on the frequency of the external field and the interatomic distance. The effects observed are considered as a near-field effect in optics of small objects. This phenomena makes it possible to investigate the structure of small objects with the use of optical radiation. Ul'yanovsk Branch of the Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 48 Goncharov Str., Ul'yanovsk, 432700, Russia; e-mail: gadomsky@quant.univ.simbirsk.su. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 765–770, November–December, 1999.     

Problems of the electronic structure of nonmetals in a wide energy region of fundamental absorption (review)

The article surveys the main unsolved problems of the electronic structure of nonmetals in a wide energy region of fundamental absorption. Udmurtia State University, 71, Krasnogeroiskaya Str., Izhevsk, 426034, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 299–315, May–June, 1999.     

扫描近场光学显微镜光纤锥中导波反射特性

利用局部模耦合模型理论上分析了扫描近场光学显微镜光纤的光场性质,给出光纤维中存在的正,反向传播的基模场微分方程,以及基模反向耦合系数的数值计算结果,其最高反射系数达１％左右。这种反射光可起着光纤维激光器谐振腔输出端镜的作用。     

基于局部Gabor二进制模式的高光谱伪装目标图像分类

为提高光谱伪装目标图像分类精度,提出了一种基于局部Gabor二进制模式（LGBP)的空间分类方法。LGBP作为一种多尺度算法,被用来提取高光谱图像的纹理特征。然后高光谱图像中的每一个像元可以用一个光谱特征向量及一个纹理特征向量表示。通过这种方法,增大类间距离。最后使用多核支持向量机结合光谱信息和空间纹理信息实现对高光谱伪装目标图像的分类。实验证明了该方法的有效性,分类总体精度和Kappa系数分别达到了95.6%和0.937。所提出的方法对于提高分类精度及鲁棒性具有重要意义。     

翼片扰动对COIL超音速平行流混合的影响

氧碘混合过程是化学氧碘激光器(COIL)中的一个重要步骤,氧碘混合质量直接决定着COIL的运行效率和光束质量。采用化学荧光法,研究了两种不同结构的扰动翼片组对COIL超音速平行流混合过程的影响。实验结果表明,1#扰动翼片组对氧碘超音速平行流的混合增强效果明显,其荧光区达到主气流中心线所经历的流向距离大幅缩短,碘解离区内的荧光区与测试区的面积比相对于无混合扰动时提高了4.2倍;采用2#翼片组扰动混合时,流向距离值进一步缩短了40%~60%,碘解离区内的面积比值又提高了20%~40%。氧发生器有/无主载气条件(2#翼片组)下的混合过程比较显示后者混合效果更好。     

N型局部有源忆阻器的神经形态行为

局部有源忆阻器(locally-active memristor,LAM)凭借其高集成度、低功耗和局部有源特性等优点,在神经形态计算领域显示出巨大的潜力.本文提出了一种简单的N型LAM数学模型,通过揭示其非线性动力特性,设计了N型LAM神经元电路.采用Hopf分岔、数值分析等方法定量研究了该电路的动力学行为,成功模拟了多种神经形态行为,包括全或无行为、尖峰、簇发、周期振荡等.并利用该神经元电路结构模拟了生物触觉神经元的频率特性.仿真结果表明:当输入信号幅值低于阈值时,神经元电路输出信号的振荡频率与输入信号强度呈正相关(即兴奋状态),并在阈值处达到最大值.随后,继续增大激励强度,振荡频率则逐渐降低(即保护性抑制状态).最后,设计了N型LAM硬件仿真器,并完成了人工神经元电路的硬件实现,实验结果与仿真结果、理论分析相一致,验证了该N型LAM具备的神经形态行为.     

Local stability analysis of a low-dissipation cyclic refrigerator*

We study the local stability near the maximum figure of merit for the low-dissipation cyclic refrigerator,where the irreversible dissipation occurs not only in the thermal contacts but also the adiabatic strokes.We find that the bounds of the coefficient of performance at a maximum figure of merit or maximum cooling rate in the presence of internal dissipation are identical to those in the corresponding absence of internal dissipation.Using two different scenarios,we prove the existence of a single stable steady state for the refrigerator,and clarify the role of internal dissipation on the stability of the thermodynamic steady state,showing that the speed of system evolution to the steady state decreases due to internal dissipation.     

Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料的上转换发光及其温度传感特性EI北大核心CSCD

采用CO_(2)激光区熔法制备了Lu_(2)O_(3)∶0.5%Er^(3+)/x%Yb^(3+)(x=1,3,5)上转换荧光材料。X射线衍射结果表明,所制备的Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料具有纯Lu_(2)O_(3)晶相。在980 nm激光激发下,样品发出明亮的上转换荧光。光谱测试结果表明,样品上转换荧光强度和荧光中绿光与红光比例随Yb^(3+)离子浓度改变,当Er^(3+)和Yb^(3+)离子浓度分别为0.5%和3%时,样品上转换荧光强度最强。通过荧光强度比(FIR)技术研究了样品Lu_(2)O_(3)∶0.5%Er^(3+)/3%Yb^(3+)在298~873 K温度范围内上转换荧光温度传感特性,在532.8 K时最大绝对灵敏度为0.0060 K^(-1),在298 K时最大相对灵敏度为0.0090 K^(-1)。结果表明,Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料非常适合用于宽温度范围荧光温度传感。     

Laser-induced phase conversion of n-type SnSe2 to p-type SnSe

We report a facile phase conversion method that can locally convert n-type SnSe₂ into p-type SnSe by direct laser irradiation. Raman spectra of SnSe₂ flakes before and after laser irradiation confirm the phase conversion of SnSe₂ to SnSe. By performing the laser irradiation on SnSe₂ flakes at different temperatures, it is found that laser heating effect induces the removal of Se atoms from SnSe₂ and results in the phase conversion of SnSe₂ to SnSe. Lattice-revolved transmission electron microscope images of SnSe₂ flakes before and after laser irradiation further confirm such conversion. By selective laser irradiation on SnSe₂ flakes, a pattern with SnSe₂/SnSe heteostructures is created. This indicates that the laser induced phase conversion technique has relatively high spatial resolution and enables the creation of micron-sized in-plane p-n junction at predefined region.     

Rolling velocity and relative motion of particle detector in local granular flow

The velocity of a particle detector in granular flow can be regarded as the combination of rolling and sliding velocities. The study of the contribution of rolling velocity and sliding velocity provides a new explanation to the relative motion between the detector and the local granular flow. In this study, a spherical detector using embedded inertial navigation technology is placed in the chute granular flow to study the movement of the detector relative to the granular flow. It is shown by particle image velocimetry (PIV) that the velocity of chute granular flow conforms to Silbert's formula. And the velocity of the detector is greater than that of the granular flow around it. By decomposing the velocity into sliding and rolling velocity, it is indicated that the movement of the detector relative to the granular flow is mainly caused by rolling. The rolling detail shown by DEM simulation leads to two potential mechanisms based on the position and drive of the detector.