色噪声对光学双稳态的影响

采用统一色噪声近似构建了由乘法色噪声驱动的纯吸收型光学双稳态状态方程,并分析了色噪声对光学双稳态的影响,将结果与白噪声驱动的光学双稳态进行比较.结果表明:当乘法噪声与加法噪声处在正关联时,增加乘法色噪声的自关联时间r,光学双稳性的区域显著变宽,即磁滞回线面积变大;当乘法噪声与加法噪声处在负关联时,只有乘法噪声较小时,改变乘法色噪声的自关联时间r,光学双稳态才发生改变;当乘法噪声的自相关时间等于零时,本文模型退化为乘法白噪声驱动的光学双稳性状态方程.     

基于宽度可调节的线缺陷平板型光子晶体的空气槽微腔

研究了一种空气槽光子晶体微腔,这种腔是由在平板型光子晶体上引入一条宽度可以调节的线缺陷空气槽形成的.腔模的电场被强烈局限在空气槽中,由于介电常量的不连续性,电场得到很大的提高,同时模体积被大大地降低.数值模拟与分析了微腔的能带结构和场分布,考虑到腔模的谐振频率和对称性,发现一阶偶膜同时具有较高的品质因子和较小的模体积;应用有限时域差分法,得到腔模的品质因子可以高达10⁶,模体积仅为0.02(λ/n)³.计算了一阶偶模谐振波长随空气槽宽度以及空气孔半径的变化,发现随着宽度的增加,波长越来越短.而随着空气孔半径的增加,波长近似线性地减小;当空气孔半径为170 nm时,可以获得最高的腔品质因子.     

分数阶傅里叶变换结合高峰均比抑制算法对CO-OFDM系统的影响分析

针对相干光正交频分复用系统中出现的高峰值平均功率比问题,提出分数阶傅里叶变换与高峰值平均功率比抑制算法相结合的方法.计算表明:随着分数阶傅里叶变换阶数的减小,信号的峰值平均功率比逐渐降低;与抑制算法结合后可进一步降低系统的峰值平均功率比,并解决抑制算法影响系统性能的问题.从结合的兼容性、抑制高峰值平均功率比效果及改善引入抑制算法后对系统的负面影响三方面进行仿真分析,结果表明:采用选择性映射算法与分数阶傅里叶变换结合后,旋转因子同为4时,峰值平均功率比高于6.6dB的概率较单一选择性映射算法低104;选取高峰值平均功率比抑制情况相近时,结合算法的时间复杂度比单一选择性映射算法降低了8倍;采用限幅算法与分数阶傅里叶变换结合的仿真情况也较单一限幅算法有很大提高,表明该算法结合的兼容性良好.     

First-principles study of structural, elastic, electronic and optical properties of SrMO3 (M=Ti and Sn)

We present structural, elastic, electronic and optical properties of the perovskites SrMO₃ (M=Ti, and Sn) for different pressure. The computational method is based on the pseudo-potential plane wave method (PP-PW). The exchange-correlation energy is described in the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters are in reasonable agreement with the available experimental data. This work shows that the perovskites SrTiO₃, and SrSnO₃ are mechanically stable and present an indirect band gaps at the Fermi level. Applied pressure does not change the shape of the total valence electronic charge density and most of the electronic charge density is shifted toward O atom. Furthermore, in order to understand the optical properties of SrMO₃, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient and electron energy-loss are calculated for radiation up to 80 eV. The enhancement of pressure decreases the dielectric function and refractive indices of SrTiO₃ and SrSnO₃.     

Influence of aging time of the starting solution on the physical properties of fluorine doped zinc oxide films deposited by a simplified spray pyrolysis technique

Fluorine doped zinc oxide (FZO) films were fabricated from fresh and aged (4, 8, 12 and 16 days) starting solutions using a simplified and low cost spray pyrolysis technique. The X-ray diffraction study showed that the preferential orientation is along the (0 0 2) plane for all the films irrespective of the age of the solution. The crystallite size calculated using the Scherrer’s formula is comparatively smaller only for the film prepared from the starting solution having aging time 4 days which may be due to the efficient incorporation of fluorine atoms into the ZnO lattice. This phenomenon is confirmed by the minimum resistivity value (3.14 × 10⁻² Ω cm) obtained in this particular case. The visible transmittance and the optical band gap values are found to be in the range of 63–83% and 3.20–3.31 eV, respectively. The optical transmittance is found to decrease gradually as the aging time of the solution increases and the optical band gap is found to be slightly higher in the case of the film prepared from the fourth day solution. The scanning electron microscopy results depicted that the microstructure of ZnO:F films are largely influenced by the aging of the starting solution.     

Crystal field parameters and energy level structure of the MnO4 tetroxo anion in Li3PO4, Ca2PO4Cl and Sr5(PO4)3Cl crystals

A comparative study concerning the electronic structure of the Mn⁵⁺ ion in the Li₃PO₄, Ca₂PO₄Cl, Sr₅(PO₄)₃Cl host lattices has been carried out in the framework of the exchange charge model. The crystal field parameters have been evaluated using the structural data as the only input information. The 10 K absorption spectra of the investigated compounds have been measured in order to verify the correspondence between experimental and calculated energy levels. A systematic trend of the crystal field splitting of the most intense transitions has been evidenced and discussed by considering the symmetry properties of the coordination polyhedra around Mn⁵⁺.     

Characterization of new-layered Cr(III)-doped chlorocadmiumphosphate, Cd(HPO4)Cl·[H3N(CH2)6NH3]0.5 crystal by EPR and optical studies

Cr(III)-doped Cd(HPO₄)Cl·[H₃N(CH₂)₆NH₃]_0.5, a new-layered cadmium phosphate, is synthesized in acidic condition at room temperature. EPR and optical studies are carried out at room temperature. Polycrystalline EPR spectrum reveals the presence of two sites of Cr(III) ions in this layered phosphate lattice with zero-field splitting values of 24.24 and 7.65 mT, indicating that Cr(III) ions are in distorted octahedral sites. The optical absorption spectrum of the sample indicates near octahedral symmetry for the dopant ions. Crystal field, inter-electronic and bonding parameters are evaluated by collaborating EPR and optical data. The evaluated parameters suggest the mode of entry of Cr(III) ion into the layered phosphate as interstitial site, and bonding between the metal and ligand is partially covalent.     

Securing multiplexed information by in-plane rotation of random phase diffusers constituting a sandwich diffuser placed in the Fourier plane of a double random phase encoding system

We propose the encryption and multiplexing of two-dimensional input images by rotating the constituent diffusers of a sandwich random phase diffuser kept in the Fourier plane of a double random phase encoding system. Successive recording of encrypted images is done by taking the input images one by one. The results of multiplexing in encryption and decryption due to different sets of rotation of one or both of the random constituent phase masks have been presented. The use of an aperture system in addition to the rotation of one or both of the random phase masks enhances the multiplexing capability and security of the system avoiding the generation of cross-talk images at the time of decryption. Simulation results are presented in support of the proposed techniques. The decrypted images obtained from a multiplexed encrypted image have been recorded successfully. Mean square-error (MSE) and signal-to-noise ratio (SNR) values as a function of the number of multiplexed images have been calculated.     

食用香料的太赫兹时域光谱

食用香料是人们在烹饪过程中必不可少的调味品,对食用香料的鉴别和食用安全性检测也尤为重要.本文利用太赫兹时域光谱技术对食用香料进行测试,得到了黑胡椒、白胡椒、花椒、大料、姜粉、甘草、香叶以及五香粉、十三香等香料在太赫波段的吸收谱和折射率谱.结果表明,不同种类的香料都有其独特的特征吸收光谱,样品的吸收谱在0.2～1.25THz频段内以不同的斜率单调递增,在1.25～2.0THz频段呈现出不同的吸收峰.样品的折射率值在1.3～1.8之间变化,并且,样品的折射率在其吸收峰所对应的频率处出现了反常色散.通过对吸收系数的斜率、峰值位置以及折射率进行定标分析,太赫兹时域光谱技术可以用于不同种香料的定性检测.实验数据为食用香料的鉴别提供了依据,可以用于建立食用香料的太赫兹波谱数据库.     

Total reaction and fusion cross sections at sub- and near-barrier energies for the system 7Li + 28Si

Fusion cross sections are extracted for the ⁷Li$ + $²⁸Si system, via reaction cross section and transfer measurements at sub- and near-barrier energies ( E _lab = 5.7 to 14MeV). The energy evolution of transfer to reaction cross section ratios is determined with the aid of CDCC calculations, which subsequently allows the deduction of fusion cross sections at sub- and near-barrier energies. It is shown that fusion can be well represented in a BPM context. Fusion cross sections are compared for the systems ⁷Li$ + $²⁸Si and ⁶Li$ + $²⁸Si, the latter studied previously, and are found to exhibit different strengths. Last, the direct channels determined at 13MeV, are found to be dominated by a 2n -transfer mechanism.