基于波场模型的宽带相干源方位估计优化方法

阵列流形内插方法(AMI)是一种基于波场模型的宽带聚焦方法。它无须角度预估,可以应用于任意已知结构的阵列,但其采样矩阵的截断点数通常选取较大,尤其在均匀线阵列下大大增加了运算量。针对这个问题,提出了一种采样矩阵优化方法,该方法利用贝塞尔函数的性质,重新构造了采样矩阵,使得新的采样矩阵在不损失信号信息的前提下,最大限度地降低运算量,从而有效缩短了运算时间。计算机仿真实验结果表明了该方法只需和阵元个数相同的截断点数就可以有效地实现方位估计,并获得与阵列流形内插方法相当的方位估计性能。

地层温压条件下超声波测试技术

从波动方程式出发 ,证明了波场物理模型实验的比例观测关系式 ,给出简化关系式成立的条件 ,为正确理解和选择实验参数提供了依据。讨论了地层温度、压力条件下物理模型实验的必要性 ,并以MTS超声测试系统为例 ,简要介绍了系统的结构与功能 ,给出了地层温度、压力模拟的方法。

基于边缘分割与改进CNN的CT影像预诊断技术

针对基于图像识别的智能预诊断精确度较低的问题,文中提出了一种融合边缘分割与改进CNN的CT影像预诊断算法。在Bandelet变换的基础上构建WTS-MRF模型,并采用分割递归算法对CT影像的特征区域进行处理,进而设计出基于决策输出补偿的Faster R-CNN预诊断识别算法。同时还利用了脑出血、肺结核和肾结石等典型病例影像的数据样本,通过设置对比实验验证了该算法的预诊断可靠性。相较于同类预诊断识别方法,所提算法的准确率提升了6%,CT影像的分割准确率平均值为90%,预诊断识别精确率的平均值则可达96.9%。故其性能优于同类文献对比算法,能为基于人工智能的CT影像预诊断技术发展提供一定的理论支撑。

Heat transfer model for microwave hot in-place recycling of asphalt pavements

In order to solve for temperature fields in microwave heating for recycling asphalt mixtures, a two-dimensional heat transfer model for the asphalt mixtures within the heating range is built based on the theory of unsteady heat conduction. Four onedimensional heat transfer models are established for the asphalt mixtures outside the heating range, which are simplified into four half-infinite solids. The intensity of the radiation electric field is calculated through experiment by using heating water loads. It is suggested that the mathematical model of boundary conditions can be established in two ways, which are theoretical deduction and experimental reverse. The actual temperature field is achieved by fitting temperatures of different positions collected in the heating experiment. The simulant temperature field, which is solved with the Matlab PDE toolbox, is in good agreement with the actual temperature field. The results indicate that the proposed models have high precision and can be directly used to calculate the temperature distribution of asphalt pavements.

Destruction of Spiral Wave Using External Electric Field Modulated by Logistic Map

Evolution of spiral wave generated from the excitable media within the Barkley model is investigated. The external gradient electric field modulated by the logistic map is imposed on the media （along x- and y-axis）. Drift and break up of spiral wave are observed when the amplitude of the electric field is modulated by the chaotic signal from the logistic map, and the whole system could become homogeneous finally and the relevant results are compared when the gradient electric field is modulated by the Lorenz or Rossler chaotic signal.

SH-wavefield simulation for a laterally heterogeneous whole-Earth model using the pseudospectral method

We present a scheme to simulate SH-wave propagation in a whole-Earth model with arbitrary lateral heterogeneities employing the Fourier pseudospectral method. Wave equations are defined in two-dimensional cylindrical coordinates and the model is taken through a great circle of the Earth. Spatial derivatives in the wave equations are calculated in the wavenumber domain by multiplication, and the transformation between spatial and wavenumber domains is performed via fast Fourier transformation. Because of the high accuracy and high speed of the Fourier pseudospectral method, the scheme enables us to calculate a short-wavelength global SH-wavefield with accurate waveforms and arrival times for models with heterogeneities that can be approximated as azimuthally symmetric. Comparing with two-dimensional simulation methods based on an axisymmetric model, implementing the seismic source in the present scheme is more convenient. We calculated the global SH-wavefield for the preliminary reference Earth model to identify the generation, reflection and refraction of various seismic phases propagating in the Earth. Applications to a heterogeneous global model with low-velocity perturbation above the core-mantle boundary were conducted to analyze the effect of lateral heterogeneity on global SH-wave propagation.

HETEROGENEITY, NONLINEARITY AND ENDOGENOUS MARKET VOLATILITY

This paper aims to contribute to the literature on the explanatory power of behavior models with heterogeneous agents. The authors present a new nonlinear structural stock market model which is a nonlinear deterministic process buffeted by dynamic noise. An exogenous noise is introduced to the model with the assumption of IID normal innovations of the fundamental value in order to investigate how noisy dynamics interacts with deterministic process. The market is composed of two typical trader types： the rational fundamentalists and the boundedly rational traders governed by greed and fear. The interaction between noise and deterministic element determines the evolution process of the system as key parameters are changed. The authors find the model is able to generate time series that exhibit dynamical and statistical properties closely resembling those of the S＆：P500 index, such as volatility clustering, fat tails （leptokurtosis）, autocorrelation in square and absolute return, larger amplitude, crashes and bubbles. The authors also investigate the nonlinear dependence structure in our data. The results indicate that the GARCH-type model cannot completely account for all nonlinearity in our simulated market, which is thus consistent with the results from real markets. It seems that the nonlinear structural model is more powerful to give a satisfied explanation to market behavior than the traditional stochastic approach.