信息窗

ＶＥＲＩＴＡＳＳＡＮＰｏｉｎｔＣｏｎｔｒｏｌ ,构造企业信息化神经中枢在经济全球化的今天 ,现代企业在以服务器、存储、光纤网络为基础的ＩＴ平台之上将业务覆盖范围迅速拓展。２００２年 ,ＶＥＲＩＴＡＳ最新推出了ＳＡＮ ＰｏｉｎｔＣｏｎｔｒｏｌ３．５,ＶＥＲＩＴＡＳＳＡＮ ＰｏｉｎｔＣｏｎｔｒｏｌ的最新版本构建在ＶＥＲＩＴＡＳ适应性软件架构 (ＡｄａｐｔｉｖｅＳｏｆｔｗａｒｅＡｒｃｈｉｔｅｃｔｕｒｅ)之上 ,这是一种新的软件和服务模式 ,用来降低数据中心的复杂性 ,极大改善ＩＴ对不断变化的业务需求和技术响应。它通过更…     

信息窗

ＥＲＩＴＡＳＳＡＮＰｏｉｎｔＣｏｎｔｒｏｌ ,构造企业信息化神经中枢在经济全球化的今天 ,现代企业在以服务器、存储、光纤网络为基础的ＩＴ平台之上将业务覆盖范围迅速拓展。２００２年 ,ＶＥＲＩＴＡＳ最新推出了ＳＡＮ ＰｏｉｎｔＣｏｎｔｒｏｌ３．５,ＶＥＲＩＴＡＳＳＡＮ ＰｏｉｎｔＣｏｎｔｒｏｌ的最新版本构建在ＶＥＲＩＴＡＳ适应性软件架构 (ＡｄａｐｔｉｖｅＳｏｆｔｗａｒｅＡｒｃｈｉｔｅｃｔｕｒｅ)之上 ,这是一种新的软件和服务模式 ,用来降低数据中心的复杂性 ,极大改善ＩＴ对不断变化的业务需求和技术响应。它通过更强…     

两种快速ESPRIT算法

在众多的高分辨谱估计算法中，ＥＳＰＲＩＴ算法由于不需进入谱搜索而具有小得多的运算量。本文提出两种ＥＳＰＲＩＴ算法的加速方法，空分法和时移法，可进一步减少运算量。同时还给出了两种改进算法的运算量和性能分析及模拟的实验结果。     

均匀线列阵下的快速TLS-ESPRIT算法

ＴＬＳ－ＥＳＰＲＩＴ算法是一种方位估计算法,由于采用了全局最小二乘估计,其在低信噪比下的估计性能较ＥＳＰＲＩＴ算法有所提高,但算法略显复杂。本文针对均匀线列阵,构成了ＴＬＳ－ＥＳＰＲＩＴ的简化算法,使其运算量明显减少,同时还可给出源功率的估计。文中给出了算法的结构及计算机仿真结果。     

基于最小冗余线阵的共轭循环ESPRIT算法

本文提出了一种基于最小冗余线阵的共轭循环ＥＳＰＲＩＴ算法,理论分析和计算机仿真实验均表明,算法具有良好的ＤＯＡ估计性能,增大了阵列孔径,抗噪能力强,分辨率高,可以用较少的阵元估计更多的信号源方向,计算机仿真实验验证了算法的有效性,并比较了该算法与共轭循环ＥＳＰＲＩＴ算法的ＤＯＡ估计性能。     

稳定快速收敛的自适应格型IIR滤波

本文提出一种稳定快速收敛的格型自适应ＩＩＲ滤波（ＡＩＩＲＰ）新算法。新的自适应ＩＩＲ滤波结构不同于一般的格型ＡＩＩＲＦ实现结构，它由ＡＩＩＲＦ的分子、分母多项式分别以全零点格型结构综合构成，具有结构简单、计算量少等优点。ＡＩＩＲＦ的格型结构，解决了ＡＩＩＲＦ的系统稳定性问题。新的格型算法可快速收敛于ＡＩＩＲＦ的全局无偏最优解，解决了ＰＥＡ算法的有偏及ＯＥＡ算法的局部极小点问题。计算机模拟实验结果证明了新的ＡＩＩＲＦ格型算法的有效性。     

一种改进的Elman神经网络的模型

本文首先详细地阐述了Ｅｌｍａｎ神经网络的结构、原理和学习算法。为了进一步提高Ｅｌｍａｎ神经网络的逼近能力和动态特性，我们提出了一种改进的Ｅｌｍａｎ神经网络模型。这种新的Ｅｌｍａｎ神经网络在关联节点与输出节点之间又增加了一组可调权值，利用误差回馈原理推导出了其相应的学习算法。仿真实验结果表明，改进的Ｅｌｍａｎ神经网络比原来的网络具有更好的动态性能，对于贯序输入输出数据的逼近收敛速度更快。     

一种DDLMS和CMA方法相结合的盲均衡算法

本文提出一和种适用于M-PAM和M-QAM的新的盲均衡算法：DDMLS-CMA算法。该算法克服了盲均衡算法Sato、Godrd残余误差大的缺点，又保持了快速收敛特性，并且收敛速率比BG算法快，是一种稳定的盲均衡算法。     

用任意阵实现二维到达角和极化的联合估计

基于四阶累积量和ＥＳＰＲＩＴ算法提出一种新的任意高斯噪声环境上多个独立空间信号二维到达角和极化的联合估计方法。该算法的阵列由和坐标轴方向一致的偶极子对组成,各偶极子对的排列结构任意。计算机模拟结果证实了方法的可行性。     

V5接口上PSTN协议的实现

Ｖ５接口是ＩＴＵ－Ｔ新近提出的一种用于ＡＮ（接入网）和ＬＥ（本地交换机）之间的标准化数字接口。在Ｖ５接口上能够支持多种协议的接入。本文着重讨论了Ｖ５接口上ＰＳＴＮ协议的实现过程。     

静态阻抗断层图像重建新方法

阻抗断层图像重建是一个严重病态的非线性的逆问题,特别是在静态阻抗断层成像中,由于其图像重建模型误差和测量噪声的影响更为严重,因此常用的基于目标函数梯度信息不断迭代的改进的Newton-Raphson类重建算法,即使使用正则化技术,其稳定性仍较差,甚至发散.本文提出一种全新的静态阻抗断层图像重建方法,它利用基于生物自然选择与遗传机理的遗传算法去搜索阻抗图像重建问题的最优解,无需正则化技术,也不会象改进的Newton-Raphson类算法那样易陷入局部最优解.实验结果也表明基于遗传算法的图像重建方法重建的静态阻抗断层图像,其成像精度和空间分辨率都大大好于改进的Newton-Raphson类重建算法.     

Estimation of anomaly location and size using electrical impedance tomography

We developed a new algorithm that estimates locations and sizes of anomalies in electrically conducting medium based on electrical impedance tomography (EIT) technique. When only the boundary current and voltage measurements are available, it is not practically feasible to reconstruct accurate high-resolution cross-sectional conductivity or resistivity images of a subject. In this paper, we focus our attention on the estimation of locations and sizes of anomalies with different conductivity values compared with the background tissues. We showed the performance of the algorithm from experimental results using a 32-channel EIT system and saline phantom. With about 1.73% measurement error in boundary current-voltage data, we found that the minimal size (area) of the detectable anomaly is about 0.72% of the size (area) of the phantom. Potential applications include the monitoring of impedance related physiological events and bubble detection in two-phase flow. Since this new algorithm requires neither any forward solver nor time-consuming minimization process, it is fast enough for various real-time applications in medicine and nondestructive testing.     

Electromagnetic impedance tomography (EMIT): a new method for impedance imaging

We propose a new impedance imaging method, electromagnetic impedance tomography (EMIT), in which the boundary electric potential measurements in electrical impedance tomography (EIT) are augmented by measurements of the exterior magnetic field induced by the currents excited in the object by the standard EIT procedures. These magnetic measurements can be obtained reliably and inexpensively by simple pickup coils located around the imaged cross section. We derive expressions for the forward problem and for the Jacobian of the measurements, and propose an iterative reconstruction algorithm using a squared error cost function. The performance of EMIT and EIT is compared in numerical simulations using a finite-element model for the conductivity distribution of several phantoms. Evaluation of the rank and condition of the Jacobian demonstrates that the additional magnetic measurements provided by a few pickup coils in EMIT turn an underdetermined EIT problem into a well-posed one with reasonable condition, or significantly improve the conditioning of the EIT problem when it is already fully determined. Reconstructions of various phantoms reveal that EMIT provides particularly significant visual and quantitative improvement (threefold to tenfold reduction in the root-mean-squared error) in the sensitivity at the center of the object, which is the area most difficult to image using EIT.     

Electrical impedance tomography of complex conductivitydistributions with noncircular boundary

Electrical impedance tomography (EIT) uses low-frequency current and voltage measurements made on the boundary of a body to compute the conductivity distribution within the body. Since the permittivity distribution inside the body also contributes significantly to the measured voltages, the present reconstruction algorithm images complex conductivity distributions. A finite element model (FEM) is used to solve the forward problem, using a 6017-node mesh for a piecewise-linear potential distribution. The finite element solution using this mesh is compared with the analytical solution for a homogeneous field and a maximum error of 0.05% is observed in the voltage distribution. The boundary element method (BEM) is also used to generate the voltage data for inhomogeneous conductivity distributions inside regions with noncircular boundaries. An iterative reconstruction algorithm is described for approximating both the conductivity and permittivity distributions from this data. The results for an off-centered inhomogeneity showed a 35% improvement in contrast from that seen with only one iteration, for both the conductivity and the permittivity values. It is also shown that a significant improvement in images results from accurately modeling a noncircular boundary. Both static and difference images are distorted by assuming a circular boundary and the amount of distortion increases significantly as the boundary shape becomes more elliptical. For a homogeneous field in an elliptical body with axis ratio of 0.73, an image reconstructed assuming the boundary to be circular has an artifact at the center of the image with an error of 20%. This error increased to 37% when the axis ratio was 0.64. A reconstruction algorithm which used a mesh with the same axis ratio as the elliptical boundary reduced the error in the conductivity values to within 0.5% of the actual values     

A robust image reconstruction algorithm and its parallel implementation in electrical impedance tomography

An efficient and robust image reconstruction algorithm for static impedance imaging using Hachtel's augmented matrix method was developed. This improved Newton-Raphson method produced more accurate images by reducing the undesirable effects of the ill-conditioned Hessian matrix. It is demonstrated that the electrical impedance tomography (EIT) system could produce two-dimensional static images from a physical phantom with 7% spatial resolution at the center and 5% at the periphery. Static EIT image reconstruction requires a large amount of computation. In order to overcome the limitations on reducing the computation time by algorithmic approaches, the improved Newton-Raphson algorithm was implemented on a parallel computer system. It is shown that the parallel computation could reduce the computation time from hours to minutes.     

Temperature dependence of tissue impedivity in electrical impedance tomography of cryosurgery

The temperature-dependent impedivity of rat liver, transverse abdominal muscle and full skin was determined in vitro as a function of frequency across the temperature range 5 degrees C to 37 degrees C and from 100 Hz to 10 kHz. This study was motivated by an increasing interest in using electrical impedance tomography (EIT) for imaging of cryosurgery and a lack of applicable data in the hypothermic range. Using a controlled-temperature impedance analyzer, it was found that as the temperature is reduced the resulting increase in tissue impedivity is more pronounced at low frequencies and that the beta dispersion, resulting from cell membrane polarization, shifts to lower frequencies. With these new data a simple case study of EIT of liver cryosurgery was examined, using a finite-element model incorporating the Pennes bio-heat equation, to determine the impact of this behavior on imaging accuracy. Overestimation of the ice-front position was found to occur if the EIT system ignored the effects of the low-temperature zone surrounding the frozen tissue. This error decreases with increasing blood perfusion and with higher measurement frequencies.     

The boundary element method in the forward and inverse problem of electrical impedance tomography

In this paper, a new formulation of the reconstruction problem of electrical impedance tomography (EIT) is proposed. Instead of reconstructing a complete two-dimensional picture, a parameter representation of the gross anatomy is formulated, of which the optimal parameters are determined by minimizing a cost function. The two great advantages of this method are that the number of unknown parameters of the inverse problem is drastically reduced and that quantitative information of interest (e.g., lung volume) is estimated directly from the data, without image segmentation steps. The forward problem of EIT is to compute the potentials at the voltage measuring electrodes, for a given set of current injection electrodes and a given conductivity geometry. In this paper, it is proposed to use an improved boundary element method (BEM) technique to solve the forward problem, in which flat boundary elements are replaced by polygonal ones. From a comparison with the analytical solution of the concentric circle model, it appears that the use of polygonal elements greatly improves the accuracy of the BEM, without increasing the computation time. In this formulation, the inverse problem is a nonlinear parameter estimation problem with a limited number of parameters. Variants of Powell's and the simplex method are used to minimize the cost function. The applicability of this solution of the EIT problem was tested in a series of simulation studies. In these studies, EIT data were simulated using a standard conductor geometry and it was attempted to find back this geometry from random starting values. In the inverse algorithm, different current injection and voltage measurement schemes and different cost functions were compared. In a simulation study, it was demonstrated that a systematic error in the assumed lung conductivity results in a proportional error in the lung cross sectional area. It appears that our parametric formulation of the inverse problem leads to a stable minimization problem, with a high reliability, provided that the signal-to-noise ratio is about ten or higher.     

A unified approach for EIT imaging of regional overdistension and atelectasis in acute lung injury

Patients with acute lung injury or acute respiratory distress syndrome (ALI/ARDS) are vulnerable to ventilator-induced lung injury. Although this syndrome affects the lung heterogeneously, mechanical ventilation is not guided by regional indicators of potential lung injury. We used electrical impedance tomography (EIT) to estimate the extent of regional lung overdistension and atelectasis during mechanical ventilation. Techniques for tidal breath detection, lung identification, and regional compliance estimation were combined with the Graz consensus on EIT lung imaging (GREIT) algorithm. Nine ALI/ARDS patients were monitored during stepwise increases and decreases in airway pressure. Our method detected individual breaths with 96.0% sensitivity and 97.6% specificity. The duration and volume of tidal breaths erred on average by 0.2 s and 5%, respectively. Respiratory system compliance from EIT and ventilator measurements had a correlation coefficient of 0.80. Stepwise increases in pressure could reverse atelectasis in 17% of the lung. At the highest pressures, 73% of the lung became overdistended. During stepwise decreases in pressure, previously-atelectatic regions remained open at sub-baseline pressures. We recommend that the proposed approach be used in collaborative research of EIT-guided ventilation strategies for ALI/ARDS.     

Electromagnetically induced transparency induced by a 100% amplitude-modulated coupling field

We present a study of electromagnetically induced transparency(EIT) under the excitation of a 100% amplitude-modulated(AM) coupling field.The EIT feature is associated with a Λ type three-level configuration where a coupling and probe field couples two separate optical transitions and it is well-known that the spectrum of the swept probe field gives a simple single transparency feature induced by the single mode coupling field.It is shown that when a 100% AM coupling field is applied,there is an EIT doublet...     

基于理论弹道速度匹配的飞行器测控记忆跟踪算法

针对遥测设备现有记忆跟踪存在速度跳变和外推误差大的问题,提出了一种基于理论弹道速度匹配的记忆跟踪算法。分析了遥测设备记忆跟踪算法原理与不足,对原记忆跟踪算法进行改进,同时将Neville算法用于记忆跟踪数据插值。仿真结果表明新算法外推10 s、5 s和3 s的均方根误差比原算法平均减小44.9％。新算法在设备应用的测试结果同样证明了其优越性。