二维磁结构的扫描隧道显微术研究

文章介绍了近年来利用扫描隧道显微术（STM）对表面和薄膜磁结构的研究进展。二维或表面磁结构可以通过在非磁性单晶上外延磁性单原子层薄膜形成，也可以在清洁的磁性单晶表面形成。利用磁性的STM针尖可以观测到原子分辨的表面磁结构。这将增进人们从纳米尺度对磁性的理解，并推动磁电子学的发展。     

Fusion of infrared polarization and intensity images using support value transform and fuzzy combination rules

Infrared polarization and intensity imagery provide complementary and discriminative information in image understanding and interpretation. In this paper, a novel fusion method is proposed by effectively merging the information with various combination rules. It makes use of both low-frequency and high-frequency images components from support value transform (SVT), and applies fuzzy logic in the combination process. Images (both infrared polarization and intensity images) to be fused are firstly decomposed into low-frequency component images and support value image sequences by the SVT. Then the low-frequency component images are combined using a fuzzy combination rule blending three sub-combination methods of (1) region feature maximum, (2) region feature weighting average, and (3) pixel value maximum; and the support value image sequences are merged using a fuzzy combination rule fusing two sub-combination methods of (1) pixel energy maximum and (2) region feature weighting. With the variables of two newly defined features, i.e. the low-frequency difference feature for low-frequency component images and the support-value difference feature for support value image sequences, trapezoidal membership functions are proposed and developed in tuning the fuzzy fusion process. Finally the fused image is obtained by inverse SVT operations. Experimental results of visual inspection and quantitative evaluation both indicate the superiority of the proposed method to its counterparts in image fusion of infrared polarization and intensity images.     

基于激光诱导偏振光谱与激光诱导荧光技术的CH4/AIR火焰参数测量

建立了激光诱导偏振光谱（LIPS）和激光诱导荧光（LIF）联合的燃烧流场诊断系统,测量了CH4/AIR预混火焰中心不同高度处的OH荧光光谱和激光诱导偏振光谱,计算了OH的浓度及燃烧场温度分布。分析了燃烧炉表面对荧光收集效率的影响,并对两种技术的测量数据进行了分析比对,获得了火焰中心OH密度的分布规律。实验结果表明,联合LIPS和LIF两种技术测量CH4/AIR预混火焰参数是可行的,两种技术测量结果的一致性较好,OH浓度的相对偏差小于5%,温度的相对偏差小于8%。     

基于BP算法神经网络的物理实验曲线拟合

介绍了人工神经元网络的基本原理和BP算法神经网络。将BP算法神经网络应用于物理实验中的幅频特性曲线拟合，在MATLAB下通过训练和仿真验证了应用BP算法神经网络拟合实验曲线的优越性。     

Effect of the chiral chain length on structural and phase properties of ferroelectric liquid crystals

Studies of structural and phase properties obtained on several ferroelectric liquid crystalline materials with 2-alkoxypropionate group used as a chiral centre and without any lateral substitution are presented. In dependence on the chiral chain length these compounds exhibit the cholesteric N* phase, the ferroelectric smectic C* and a low-temperature SmX phase. Values of the spontaneous polarization and spontaneous tilt angle have been determined within the whole range of the SmC* phase. A low-temperature SmX phase has been identified as the orthogonal hexatic SmB* phase. The molecular parameters, namely the layer spacing in the SmC* and SmB* phases and the average intermolecular distances (D) between neighbouring parallel molecules in all investigated phases have been determined using the results of the X-ray diffraction obtained on non-oriented samples. The effect of the chiral chain length on mesomorphic, structural and physical properties of the studied ferroelectric liquid crystalline materials is discussed.     

Proposed interpretation of the transverse magnetic field dependence of the melting temperature T m(B) of a two-dimensional one-component plasma driven by logarithmic interactions

We propose an approximate scaling property of the classical partition function of a two-dimenisional one-component plasma in a high magnetic field based on the molecular dynamics simulations of dubey and Gumbs     

液晶相位可变延迟器对自旋极化电子束极化方向的调制

讨论了液晶相位可变延迟器（liquid crystal variable retarder, LCVR）在自旋极化电子产生方面的应用.LCVR控制入射光子的偏振度，从而实现对自旋极化电子束极化方向的调制.采用LCVR代替1/4波片和Pockels盒的优点在于其对入射光方向不敏感，传输直径大，不需要机械转动即可大波长范围的延迟，且易于校准.另外，还研制了旋转检偏器，通过示波器读出，对光子偏振性进行检测并对LCVR进行校准. 关键词： 自旋极化电子源 液晶相位可变延迟器 极化方向     

纳米银线波导中表面等离极化波激发和辐射的偏振特性研究术

在可见光波段（λ=750nm）,实验研究了在端面辅助情况下,细纳米银线波导中表面等离极化波激发和辐射的偏振特性．实验发现在细纳米银线中,不同偏振态的入射光对应的表面等离极化激元的激发和传输效率有明显不同,但对应的出射光始终为方向恒定的线偏振光．对于化学合成的纳米银线,端面的轴对称性普遍比较好,对此类纳米银线进行激发时,如果入射光偏振态与纳米线近似平行,则激发和传输表面等离极化激元的效率最高;如果正交,激发和传输效率则最低．对于某些端面轴对称性较差的纳米银线,如端面为尖端或类斜面,当入射光偏振态与纳米线有一定夹角时,激发和传输表面等离极化激元的效率最高．在入射光偏振改变的过程中出射光的偏振方向始终与纳米银线平行．最后结合有限元差分方法理论解释了纳米银线中这种偏振特性的物理机理．利用纳米银线中表面等离极化激元激发和辐射的偏振特性,可以在亚波长尺寸上实现对光强和偏振态的调控．     

A new method for information retrieval in two-dimensional grating-based X-ray phase contrast imaging

Grating-based X-ray phase contrast imaging has been demonstrated to be an extremely powerful phase-sensitive imaging technique.By using two-dimensional(2D) gratings,the observable contrast is extended to two refraction directions.Recently,we have developed a novel reverse-projection(RP) method,which is capable of retrieving the object information efficiently with one-dimensional(1D) grating-based phase contrast imaging.In this contribution,we present its extension to the 2D grating-based X-ray phase contrast imaging,named the two-dimensional reverseprojection(2D-RP) method,for information retrieval.The method takes into account the nonlinear contributions of two refraction directions and allows the retrieval of the absorption,the horizontal and the vertical refraction images.The obtained information can be used for the reconstruction of the three-dimensional phase gradient field,and for an improved phase map retrieval and reconstruction.Numerical experiments are carried out,and the results confirm the validity of the 2D-RP method.     

Generation of a mid-infrared broadband polarized supercontinuum in As₂Se₃ photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber(PCF) is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power(i.e.,37 mW),which indicates that the polarization state is well maintained.