Spalling uniaxial strength of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> at high strain rates

In this article research into the uniaxial tensile strength of Al₂O₃ monolithic ceramic is presented. The experimental procedure of the spalling of long bars is investigated from different approaches. This method is used to obtain the tensile strength at high strain rates under uniaxial conditions. Different methodologies proposed by several authors are used to obtain the tensile strength. The hypotheses needed for the experimental set-up are also checked, and the requirements of the set-up and the variables are also studied by means of numerical simulations. The research shows that the shape of the projectile is crucial to achieve successfully tests results. An experimental campaign has been carried out including high speed video and a digital image correlation system to obtain the tensile strength of alumina. Finally, a comparison of the test results provided by three different methods proposed by different authors is presented. The tensile strength obtained from the three such methods on the same specimens provides contrasting results. Mean values vary from one method to another but the trends are similar for two of the methods. The third method gives less scatter, though the mean values obtained are lower and do not follow the same trend as the other methods for the different specimens.     

起始相位的受限排列

在含重原子晶体结构的测定中,重原子贡献的相位是一个非常重要的信息。利用重原子相位作电子密度逼近或者Karle迭代是求解含重原子晶体结构的重要手段。但是,当重原子的贡献不占主导地位,或者当重原子分布的对称性高于整个结构的对称性时,上述方法就不易奏效。这时的重原子信息是否还可以用来大大简化结构分析的过程?这是一个值得探讨的问题。本文提出利用重原子的相位来限制直接法中起始相位的排列方式。这样可以成倍地缩减起始相位排列的种数。这一方法同作者提出的另一方法相配合可以使直接法在测定含重原子晶体结构方面的效能大为提高。 关键词：     

Cryptographic Algorithm Using Newton-Raphson Method and General Bischi-Naimzadah Duopoly System

Image encryption is an excellent method for the protection of image content. Most authors used the permutation-substitution model to encrypt/decrypt the image. Chaos-based image encryption methods are used in this model to shuffle the rows/columns and change the pixel values. In parallel, authors proposed permutation using non-chaotic methods and have displayed good results in comparison to chaos-based methods. In the current article, a new image encryption algorithm is designed using combination of Newton-Raphson’s method (non-chaotic) and general Bischi-Naimzadah duopoly system as a hyperchaotic two-dimensional map. The plain image is first shuffled by using Newton-Raphson’s method. Next, a secret matrix with the same size of the plain image is created using general Bischi-Naimzadah duopoly system. Finally, the XOR between the secret matrix and the shuffled image is calculated and then the cipher image is obtained. Several security experiments are executed to measure the efficiency of the proposed algorithm, such as key space analysis, correlation coefficients analysis, histogram analysis, entropy analysis, differential attacks analysis, key sensitivity analysis, robustness analysis, chosen plaintext attack analysis, computational analysis, and NIST statistical Tests. Compared to many recent algorithms, the proposed algorithm has good security efficiency.     

Approximate reconstruction of torsional potential energy surface based on voronoi tessellation

Torsional modes within a complex molecule containing various functional groups are often strongly coupled so that the harmonic approximation and one-dimensional torsional treatment are inaccurate to evaluate their partition functions. A family of multi-structural approximation methods have been proposed and applied in recent years to deal with the torsional anharmonicity. However, these methods approximate the exact “almost periodic” potential energy as a summation of local periodic functions with symmetric barrier positions and heights. In the present theoretical study, we illustrated that the approximation is inaccurate when torsional modes present non-uniformly distributed local minima. Thereby, we proposed an improved method to reconstruct approximate potential to replace the periodic potential by using information of the local minima and their Voronoi tessellation. First, we established asymmetric barrier heights by introducing two periodicity parameters and assuming that the exact barrier positions are at the boundaries of Voronoi cells. Second, we used multiplicatively weighted Voronoi tessellation to refine the barrier heights and positions by defining a structure-related distance metric. The proposed method has been tested for a few higher-dimensional cases, all of which show promising improved accuracy.     

Direct mode-shape expansion of a spatially incomplete measured mode by a hybrid-vector modification

A direct estimation method for expanding incomplete experimental mode shapes is presented. The approach adopts a hybrid vector which includes measured data at master degrees of freedom (dofs) and constant values at slave dofs. The constant values are refined by a set of mode-correction factors. Modelling errors between the analytical model and tested structure are also considered by introducing a series of model-correction factors. Initial-guess values of the mode-correction factors are used to decouple the coupled constructed equations, and an iterative technique for solving these equations is proposed. The results from a five-degree-of-freedom mass–spring system indicate that the proposed approach provided a better performance than the commonly used existing expansion methods and can reliably estimate unmeasured components of mode shapes, even in cases with limited modal measurements and severe measurement noise. The performance of the proposed method was also investigated using real measurements from a steel cantilever-beam experiment. Experimental data were measured by 20 accelerometers mounted at the cantilever beam: among these accelerometers, three of these were assumed to be measured, and the others were used to check the estimation accuracy of the proposed method. The results show that the unmeasured components in the mode shapes were properly estimated by implementing the proposed method, even for high-frequency modes.     

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.     

基于经验模态分解和小波阈值的冲击信号去噪

冲击信号是非线性的并且容易受到噪声污染。为研究冲击信号去噪的问题,本文针对经验模态分解(Empirical Mode Decomposition,EMD)去噪和小波阈值去噪方法存在的不足,提出了基于EMD的小波阈值去噪方法。单纯的EMD去噪方法会在去除高频噪声的同时压制高频的有效信息。本文将EMD与小波阈值去噪相结合,利用连续均方误差准则确定含噪较多的高频固有模态函数(Intrinsic Mode Function, IMF),对高频IMF分量进行小波阈值去噪,以分离并保留这些分量中的有效信息,同时保持低频IMF分量不变。对模拟数据和实际冲击信号进行去噪处理,结果表明,基于EMD的小波阈值去噪方法的去噪效果优于单纯的EMD去噪方法和小波阈值去噪方法。     

可向量计算的块预条件迭代算法

提出一种类似于PE算法的实用并行迭代算法(VPE),可以克服M^-1r^(s)向量或并行化处理的困难.这种算法格式简单明了,收敛速度快.并证明了当矩阵A是M-阵和H-阵时,该算法是收敛的。计算实例显示该算法很有效.     

图像局部熵用于小目标检测研究

分析了局部熵用于小目标检测时造成目标范围扩散等问题的原因,并提出了熵增长方法.该方法用于点目标检测可避免发生目标范围扩散现象.由于边缘纹理和点目标在熵增长处理过程中表现出截然相反的属性,故可避免边缘纹理对于小目标检测产生的严重干扰.该方法也可用于不受噪声干扰的边缘检测.针对相同信噪比目标在不同背景亮度中具有不同熵值和增长量的问题,提出用方差增长替代熵增长,使相同信噪比目标在不同背景亮度中表现出相同的增长量值,降低了后续目标分割的难度.试验表明,熵增长方法和方差增长方法能够有效检测1或2像素大小的点目标,并不受背景中边缘纹理的干扰.对算法的复杂度进行了分析,并提出采用双通道并行流水线方式实现工程化的设计思路.     

Newton-conjugate-gradient methods for solitary wave computations

In this paper, the Newton-conjugate-gradient methods are developed for solitary wave computations. These methods are based on Newton iterations, coupled with conjugate-gradient iterations to solve the resulting linear Newton-correction equation. When the linearization operator is self-adjoint, the preconditioned conjugate-gradient method is proposed to solve this linear equation. If the linearization operator is non-self-adjoint, the preconditioned biconjugate-gradient method is proposed to solve the linear equation. The resulting methods are applied to compute both the ground states and excited states in a large number of physical systems such as the two-dimensional NLS equations with and without periodic potentials, the fifth-order KdV equation, and the fifth-order KP equation. Numerical results show that these proposed methods are faster than the other leading numerical methods, often by orders of magnitude. In addition, these methods are very robust and always converge in all the examples being tested. Furthermore, they are very easy to implement. It is also shown that the nonlinear conjugate gradient methods are not robust and inferior to the proposed methods.     

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.     

Intrinsic Loop Regularization and Renormalization in QED

We show how to regularize and renormalize the QED at the one-loop order by means of the intrinsic loop regularization method proposed by the authors. All the results are the same as those derived by means of other regularization methods.     

提升小波变换与中值滤波结合的红外光谱消噪

在光谱数据的定量分析中,噪声的存在常常会影响结果的准确性。为提高红外光谱分析精度,需要对光谱数据进行去噪处理。将一种光滑阈值函数和一种分层阈值选取方法应用到提升小波域光谱信号的去噪处理中,并对提升小波重构信号进行中值滤波。对某小麦品种的实测光谱信号,添加信噪比为21.17 dB的噪声后采用该方法进行去噪处理,并利用信噪比(SNR)、均方根误差(RMSE)、峰值平均相对误差(AREPV)以及峰位平均误差(AEPP)四项指标对去噪效果进行评价。结果表明,与软阈值法与硬阈值法相比,该方法能更有效地去除光谱信号中的噪声,保留光谱中的有用信息,提高光谱信噪比,降低均方根误差、峰值平均相对误差以及峰位平均误差,提高光谱的分析能力。     

椭圆目标的亚像素边缘定位方法研究

分析和比较了三种常见的基于矩的亚像素边缘定位方法,得出三种方法获取的边缘角度以及OFMM法与ZOM法获取的亚像素边缘相同的结论。提出了一种针对椭圆目标的亚像素边缘定位方法。在ROI提取和SOBEL算子初步检测边缘的基础上,利用初步获取的椭圆目标的几何信息,将参与计算的模板个数减少至一个,从而大大减少了运算时间,提高了算法的运算速度。同时实验结果表明,与其他基于矩的亚像素边缘定位方法相比,新方法不仅有更高的运算速度,而且精度和抗噪性能都有很大地提高。     

块多分裂方法与预条件子空间迭代方法

提出一种块多分裂并行PE迭代算法(MPPE),可以克服M^-1r^(s)并行化处理的困难。这种算法格式简单明了,收敛速度快。并证明了当矩阵A是M-阵和H-阵时,该算法是收敛的。同时把这种分裂作为预处理矩阵,对子空间方法类进行了预处理,并给出的计算实例显示该算法很有效,对子空间方法类的余量光滑和加速都起到了比较好的作用。     

用直接法处理Patterson法中的多解问题

测定含重原子晶体的结构,通常都利用Patterson法或以其为基础的重原子法、同晶型法、反常散射法等。此类方法往往会出现多解的情况。作者之一在1965年提出了用直接法消除多解问题的方法。多年来国际上在这方面也一直有类似的探讨。这类方法不仅在分析小分子晶体时有其特点,而且其进一步发展将有助于扩大直接法在生物大分子晶体结构分析中应用的领域,为提高生物大分子晶体结构分析的技术水平作出贡献。作者之一在文献[7]中已用实例说明了此类方法在中心对称情况下的应用。本文则提供非中心对称情况下的成功例子。虽然本例只处理了含重原子晶体Patterson函数的双解问题,但所用手段同样适用于处理同晶型法和反常散射法的双解。     

A study of the pointed observation methods and sensitivity of HXMT

The Hard X-ray Modulation Telescope (HXMT) is an X-ray astronomy satellite consisting of three slat-collimated instruments, the High Energy X-ray Instrument (HE), the Medium Energy X-ray Instrument (ME), and the Low Energy X-ray Instrument (LE). HXMT will carry out an all sky survey and make pointed observations in the 1-250 keV energy band. In order to get the source and background fluxes simultaneously in the pointed observations, two methods, i.e., the combined field of view (FOV) method and the off-axis pointing method are proposed in this paper. Comprehensive analyses of the sensitivities of the three instruments by using these two methods are presented, respectively. It is found that the off-axis pointing method has a higher sensitivity for HE and ME but a lower sensitivity for LE. Since the axes of the three instruments are aligned along the same direction, the off-axis pointing method is recommended as the main method in the pointed observation for HXMT; the combined FOV method can be used when LE is the most relevant instrument in order to satisfy the scientific objective of the observation.     

一种改进的随机检验法用于主成分选择以避免光谱分析校正模型的过拟合或欠拟合

为了避免主成分个数选择不当引起的校正模型过拟合或欠拟合,提出了一种改进的随机检验法,应用该方法对样品复杂程度递增的三组近红外光谱数据进行了实验研究,并与交互验证法进行了比较,分析了模型复杂程度对光谱定量校正模型预测能力的影响,讨论了该方法对复杂样品的适用性问题。结果显示,该方法可避免交互验证法剔除样本的过程,考虑了全部训练样本的信息,可客观地选择主成分,有助于避免过拟合或欠拟合,提高校正模型的预测精度;该方法不同于一般随机检验法的统计检验过程,简化了判据,易实现,选择过程可视化、可交互;在三组实验中,分别选择4,5和8个主成分建模,其外部独立预测集的预测结果最优;该方法适用于小样本复杂样品建模。     

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

Abstract

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.     

蔡氏电路的功能全同电路与拓扑等效电路及其设计方法

基于经典蔡氏电路方程的电容电压与电感电流变量及其状态方程归一化特点,提出了三种标度化、优化的电路设计方法:一种是方程变量都为电压的5运放电源限幅蔡氏电路,便于大规模集成;两种二极管非线性构成的功能全同蔡氏电路,与限幅非线性电路优势互补,可供大规模集成的细胞神经网络系统设计;同时,给出了与蔡氏电路为微分同胚电路的优化三次方蔡氏电路.各电路设计方法适用于以三折线为主的三次型混沌电路.最后,将本文提出的电路设计方法应用于混沌保密通信,实验表明该方法具有实用性和一定的应用价值.