Research on the defect structure and g factors for the tetragonal (CrO4)3− impurity center in ZrSiO4: Cr5+ crystal

ABSTRACT

The EPR g factors g// and g⊥ for the tetragonal (CrO₄)^3? impurity center in ZrSiO4: Cr⁵⁺ crystal are studied from the high-order perturbation formulas based on the two-mechanism (the crystal field and charge-transfer mechanisms) model. The studies indicate that differing from the tetragonally-elongated host (SiO4)^4- tetrahedron, the dominant defect structure of the substitutional (CrO₄)^3? tetrahedron is tetragonally- compressed with the ground state |d_z² due to the Jahn-Teller distortion. Furthermore, the agreement of g factors between calculation and experiment requires a small admixture of the first excited state |d_x²_?y² to the ground state |d_z² due to the vibrational motion of ligands, which leads a compressed (CrO₄)^3? tetrahedron to become a twinkling elongated one, These results are discussed.     

Effect of defect configuration on the localization of phonons in two-dimensional phononic crystals

Effects of defect location on the defect frequency and the localization of phonons are investigated in two novel kinds of model, created by moving the location of the native cylinder and inserting an ad-cylinder in the central cellular respectively. The results show that the defect frequency in Model 1 is only related to the distance, while in Model 2, is related not only to the distance, but also to the moving direction. From the pressure distribution, obvious localization phenomenon is found. The position and shape of the localized energy are varied with the position of the defect.     

An efficient statistics-based method for the automated detection of sperm whale clicks

In this paper, we present a new method for the automated detection of sperm whale regular clicks and creaks based on statistical computations. In the first stage, a spectrogram is computed from the input waveform, followed by a noise normalisation process. A frequency domain filter is then applied, and the energy accumulated in each time frame is calculated. Two-second time-windows are then classified as containing either regular clicks, creaks, or noise based on statistical parameters using a neural network classifier. Finally, previously obtained statistical parameters are used to implement an energy-based detection criterion for the classified time-windows. Individual regular clicks and creaks are isolated by linking contiguous detected time frames. The proposed method was tested on five recordings of sperm whale sounds. Comparison of the detection performances to hand-labelled regular clicks and creaks revealed that this method outperforms two recently reported waveform-based methods when working with the same recordings files. An average percentage of detection of 86.97% was attained for the set of files. This method consumes also little computation time.     

贴片电阻表面缺陷自动识别方法

贴片电阻生产过程中的缺陷主要依靠人工在显微镜下检测,速度慢、长期成本高、误检率高.针对贴片电阻单元具有排列整齐、结构简单、图像灰度级少的特点,在贴片电阻图像二值化、边缘提取、直线检测基础上,以相邻电阻单元的相关系数作为电阻缺陷判别依据,提出基于子图投影匹配的快速缺陷检测方法.采用主分量分析法压缩图像数据量,提取缺陷特征,以基于支持向量机对贴片电阻缺陷进行分类并建立实验系统.缺陷检测及识别实验表明,缺陷检测正确率为92.5oo,算法的快速性和识别准确度满足系统快速高精的要求.     

基于激光雷达数据SVM分类的室内环境识别研究

语义地图构建对移动机器人导航与规划具有重要意义,而环境分类是语义地图构建的核心问题。目前所采用的环境分类方法匹配率较低,已成为语义地图构建所面临的主要问题。对此笔者提出了一种基于支持向量机的分类方法,该方法利用激光雷达数据提取环境几何特征,训练SVM分类器对机器人工作空间模式进行识别,并将所提算法用于室内环境的语义分类。实验结果表明,该分类方法具有较高的识别率,可有效地实现语义地图构建。     

Identity of defect causing nonideality in nearly ideal Au/n-Si Schottky barriers

We have proposed a mechanism of nonideality, i.e., the temperature dependence of the ideality factor, in nearly ideal Au/n-Si Schottky barriers. Because of the nature of metal-induced gap states, positively ionized defects close to the interface are considered to cause local lowering of the Schottky barrier height (SBH) due to downward bending of the energy band. These positively charged defects become neutralized in equilibrium with the Fermi level due to the band bending, when they are very close to the interface. However, because the SBH lowering disappears by the neutralization of donor, the energy level of donor with a usual energy level scheme rises above the Fermi level after the neutralization. This contradiction to the equilibrium neutralization is resolved by Si self-interstitial with a large negative-U property, which is generated by the fabrication process. The energy level of the donor estimated from the SBH lowering is in good agreement with that of theoretical calculation of Si self-interstitial. Thus, the defect is concluded to be the Si self-interstitial, which is distributed to more than 10 Å depth from the interface.     

一维光子晶体缺陷模的偏振特性研究

利用周期结构的布洛赫定理推导了一维无限光子晶体缺陷模方程,研究了缺陷模的偏振特性,以及在不同入射角和缺陷层厚度下缺陷模位置的变化.利用传输矩阵方法对有限周期数光子晶体也进行了研究,分别对应一维无限光子晶体和有限周期数光子晶体给出了数值计算结果.通过比较这两者的数值结果得出了缺陷模随入射角和缺陷层厚度变化的一般规律.     

Robust infrared target tracking using discriminative and generative approaches

The process of designing an efficient tracker for thermal infrared imagery is one of the most challenging tasks in computer vision. Although a lot of advancement has been achieved in RGB videos over the decades, textureless and colorless properties of objects in thermal imagery pose hard constraints in the design of an efficient tracker. Tracking of an object using a single feature or a technique often fails to achieve greater accuracy. Here, we propose an effective method to track an object in infrared imagery based on a combination of discriminative and generative approaches. The discriminative technique makes use of two complementary methods such as kernelized correlation filter with spatial feature and AdaBoost classifier with pixel intesity features to operate in parallel. After obtaining optimized locations through discriminative approaches, the generative technique is applied to determine the best target location using a linear search method. Unlike the baseline algorithms, the proposed method estimates the scale of the target by Lucas-Kanade homography estimation. To evaluate the proposed method, extensive experiments are conducted on 17 challenging infrared image sequences obtained from LTIR dataset and a significant improvement of mean distance precision and mean overlap precision is accomplished as compared with the existing trackers. Further, a quantitative and qualitative assessment of the proposed approach with the state-of-the-art trackers is illustrated to clearly demonstrate an overall increase in performance.     

Defect structure and optical damage resistance of Hf:Fe:LiNbO3 crystals

A series of Hf:Fe:LiNbO₃ crystals were grown by the Czochralski technique with various doping concentrations of HfO₂. Their defect structures were analyzed by the UV-visible absorption spectra and infrared absorption spectra. The optical damage resistance of Hf:Fe:LiNbO₃ crystals was measured by the photo-induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO₃ crystals enhances remarkably with the HfO₂ concentration increasing when the HfO₂ concentration is lower than its threshold concentration (4 mol%). However, when the HfO₂ concentration exceeds its threshold concentration, the optical damage resistance ability of the crystals returns to decrease. This unusual behavior is explained by using the photovoltaic field produced in the crystals.     

Investigation on thermal conductivity of graphene/Si heterostructure with different defect ratios and sizes

The thermal conductivity (TC) of graphene/Si heterostructures with different defect ratios and sizes was investigated using the molecular dynamics method. As the defect ratio of heterostructure increased, the TC decreased first sharply and then slowly under a high temperature stage. The TC of heterostructure also showed a significant size effect. This phenomenon was explained by phonon dispersion and flip competition. The phonon density of states for the graphene heterostructure with different defect ratios and sizes was obtained to understand the thermal transport mechanism. Analysis showed that with the increase in the defect ratio and when the flexural modes of the heterostructure became weak, the longitudinal and transverse modes gradually dominated the phonon transport. This phenomenon can be explained that the Si atom vibration was harder in the vertical plane than that of graphene. The vibration mode hindered the heat carrier of graphene and affected heat transport to the heterostructure.