数字音频压缩中的变换编码算法

变换编码是音频压缩中的一个重要部分,文中叙述ＭＰＥＧ音频编码标准中的变换编码技术,包括改进余弦变换和反变换（ＭＤＣＴ和ＩＭＤＣＴ）时域混叠抵消与自适应窗选择,详细推导了ＭＤＣＴ和ＩＭＤＣＴ的快速算法。     

MEI方法分析介质光栅对平面波的绕射

本文首次用ＭＥＩ方法分析了任意形状的介质光栅对平面波的绕射作用，针对周期性结构的特点，利用周期空间的Ｇｒｅｅｎ函数完成ＭＥＩ方程的建立。利用有限差分方程处理单元介质分布不均匀的情况，数值结果验证了方法的正确性，几种结构介质光栅的计算说明了方法的准确性和实用性     

Internet收电子邮件的安全机制

近年来，Ｉｎｔｅｒｎｅｔ用户已不满足于简单电子邮件，要求提供多用途的和安全的电子邮件，为此出现了ＭＩＭＥ，ＰＥＭ，ＰＧＰＴ ＭＯＳＳ，Ｓ／ＭＩＭＥ，ＰＧＰ／ＭＩＭＥ，ＭＩＭＥｗｉｔｈＭＳＰ等多种方案。本文综述了这些方案，尤其对安全机制进行了详细的讨论。     

BIM框架指导EDI报文开发与应用的工程化方法

介绍了一种用于ＥＤＩ报文开发与应用的工程化理论，阐述了企业与信息模型化（ＢＩＭ）的概念，说明了用于ＵＮ／ＥＤＩＦＡＣＴ的ＢＩＭ框架的实践要素及ＢＩＭ框架所具备的优点。     

数字图像的评价方法

１前言随着数字信号处理技术、高集成度ＬＳＩ技术等的发展,图像的高效编码技术得到了进一步的提高。如今,它广泛地应用在以盘片、磁带等标准媒体为主的计算机、广播、通信网络等领域。图像、声音的高效编码方式的国际标准化工作是由ＭＰＥＧ（Ｍｏｃｉｎｇ　ＰｉｃｔｕｅｅＣｏｄｉｎｇＥｘｐｅｒｔＧｅｏｕｐ）小组来进行的,它是ＩＳＯ／ＩＥＣＪＴＣ１／ＳＣ２／ＷＧ８的下属组织,１９８８年５月于渥太华召开了第一次会议。其后,ＭＰＥＧ以ＩＳＯ／ＩＥＣＪＴＣ１／ＳＣ２９ＭＧ１１的身份继续开展这方面的活动。ＭＰＥＧ的图像主观…     

ISO／IEC MPEG—2先进音频编码（二）

ＩＳＯ／ＩＥＣＭＰＥＧ－２先进音频编码（二）３滤波器组滤波器组是ＭＰＥＧ－２ＡＡＣ系统的一个重要组成部分。在编码器中，它把输入端的时域信号转变成系统内部的时间－－频率表示形式。在解码器中，这个过程恰恰相反。在编码器中，使用一个正向的ＭＤＣＴ进行变换，...     

基于Internet/MIME的EDI技术研究

本文首先介绍了基于Ｉｎｔｅｒｎｅｔ的ＥＤＩ应用背景，在分析Ｉｎｔｅｒｎｅｔ／ＭＩＭ电子邮件标准的基础上，讨论了有关ＥＤＩ单证封装技术，随后，介绍了基于Ｉｎｔｅｒｎｅｔ／ＭＩＭＥ的ＥＤＩ单证安全传输技术，并展望了基于Ｉｎｔｅｒｎｅｔ／ＭＩＭＥ的ＥＤＩ应用前景。     

多功能Internet邮件扩展

ＭＩＭＥ作为ＲＦＣ８２２的扩展，是一种模块化的、可扩展的消息格式．可以表示多部分／多媒体消息。本文描述了ＭＩＭＥ的四种标题字段．简要介绍了ＭＩＭＥＵＡ的功能和配置，并列举了ＭＩＭＥ的某些应用。     

带有网络分割的CSMA／CD技术

带有网络分割的ＣＳＭＡ／ＣＤ技术范仲春局域网有三种介质访问控制方法：ＣＳＭＡ／ＣＤ、令牌总线和令牌环，这些方法和协议已成为局域网的国际标准系列，它们分别对应于ＩＥＥＥ８０２．３、ＩＥＥＥ８０２．４和ＩＥＥＥ８０２．５，其中ＣＳＭＡ／ＣＤ在轻负载下性能...     

自对准硅化物CMOS／SOI技术研究

在ＣＭＯＳ／ＳＩＭＯＸＳＯＩ电路制作中引入了自对准钴（Ｃｏ）硅化物（ＳＡＬＩＣＩＤＥ）技术，研究了ＳＡＬＩＣＩＤＥ工艺对ＳＯＩＭＯＳＦＥＴ单管特性和ＣＭＯＳ／ＳＯＩ电路速度性能的影响．实验表明，采用ＳＡＬＩＣＩＤＥ技术能有效地减小ＭＯＳＦＥＴ栅、源、漏电极的寄生接触电阻和方块电阻，改善单管的输出特性，降低ＣＭＯＳ／ＳＯＩ环振电路门延迟时间，提高ＣＭＯＳ／ＳＯＩ电路的速度特性．     

基于MEI吸收边界条件的导体柱散射问题模拟

首次在圆柱坐标系时域有限差分 (FDTD)法中采用基于时域不变性测试方程 (MEI)方法的吸收边界条件 ,对导体圆柱的电磁散射问题进行了数值模拟研究。在相同计算条件下 ,与应用Bayliss Turkel二阶辐射边界条件的FDTD结果相比较 ,直观地表明MEI方法结果与解析解吻合更好     

时域MEI方法在矩形导体柱散射问题中的应用

本文用时域有限差分法（FDTD）模拟二维矩形导体柱的电磁散射场，采用时域不变性测试方程（MEI）作为吸收边界条件对该散射场进行求解。将所得计算结果与截断边界网格点采用Mur二阶吸收边界条件所得的数值结果相比较，两者吻合很好。结果表明使用时域MEI方法作为吸收边界条件能有效缩短截断边界与物体边界的距离，且能得到足够精确的解。     

基于MEI方法的贴体网格FDTD方法

利用Thompson变换在任意形状的散射体外部产生共形的外部计算网络,并使FDTD计算区域的截断边界与散射体边界形状完全一致,时域不变性测试方程（MEI）方法被作为该截断边界上的局域吸收边界条件,从而大大压缩了FDTD的计算空间。数值试验结果证实,该方法可在不降低计算精度的前提下减少计算机内存需求。     

MEI系数循环卷积的快速解法

提出了一种用于减少不变量测试方程(MEI)法计算时间的快速算法,循环卷积和快速多极子(FMM)技术(CC-FMM)分别用于不同区域对应的MEI系数,可以加速建立不变量测试方程所需系数的计算.由于循环卷积和FMM的计算效率明显高于直接求和,故整个算法的计算时间明显减少.二维验算实例验证了这种算法的有效性和准确度.     

Application of discrete periodic wavelets to measured equation ofinvariance

Recently, the wavelet expansions have been applied in field computations. In the frequency domain, the application is focused on the thinning of matrices arising from the method of moment (MoM). The thinning of matrices can best be done by the measured equation of invariance (MEI), which provides sparsity almost without sacrificing accuracy in that the boundary equation it entails is convertible to that of the MoM. The real power of the wavelet expansions is to give high resolution in convolution integrals. High resolution is also needed in the process of finding the MEI coefficients, which are obtained via an integration process almost identical to that of the MoM. In this paper, it is shown that when the fast discrete periodic wavelets (FDPW) are used as metron currents in the MEI method, the resolutions of the MEI coefficients are improved at high-frequency computations or at geometric extremities. The level of sparsity of the MEI is much more favorable than that achievable by the thinning of MoM matrix using the wavelet expansions. The role of FDPW in the MEI happens to be more fitting than its place in the MoM     

A theoretical and numerical analysis of the measured equation ofinvariance

The measured equation of invariance (MEI) has been previously introduced to efficiently and accurately handle the boundary truncation for finite methods. The present authors give a theoretical analysis that provides several important insights into the capabilities of the MEI. From the numerical study, they can explain why the MEI works better than one would expect. Both the theoretical and the numerical analyses demonstrate that the accuracy of the solution is dependent on the electrical size of the geometry as well as the distance between the mesh boundary and the geometry. From the analysis, the authors propose a new set of metrons that is less sensitive to the excitation than the previously proposed sinusoidal metrons     

High frequency loss and electromagnetic field distribution forstriplines and microstrips [MCM packages]

A new three-component measured equation of invariance (MEI) boundary condition is developed and applied to the hybrid edge/nodal vector finite element method. The electric field distribution on the cross section of various lossy transmission lines is calculated. The propagation constant of a lossy transmission line with coated conductor strip is also calculated. The three-component MEI boundary condition simulates the field distribution on the artificial boundary for electromagnetic field excited by the surface charge density and the three vector components of the electric current density. Numerical experiments are performed to test the method by comparing calculated transmission loss with the measured data     

EM scattering analysis of a ferrite cylinder by a FD-FD technique with an effective absorbing boundary condition and MEI

Electromagnetic scattering problem of an arbitrarily shaped ferrite cylinder is analyzed based on the finite difference-frequency domain(FD-FD) method with an effective numerical absorbing boundary condition (ABC) and the measured equation of invariance (MEI) on the terminated boundary. Compared with the method of moments (MoM), both the numerical ABC presented in this paper and the MEI result in dramatic savings in computing time and memory requirement for electrically large objects due to the sparsity of the finite difference equation. The absorbing characteristic of this numerical ABC is demonstrated numerically. The accuracy, memory needs and CPU time of the FD-FD with the numerical ABC or the MEI and the MoM are compared and then result in some important conclusions. Besides, the RCS of some ferrite cylinders are presented.     

Interpolation, extrapolation, and application of the measuredequation of invariance to scattering by very large cylinders

Using the conventional method of moment (MoM) calculations, a cylinder of circumferential dimension of 100 wavelengths is considered to be large. Using the measured equation of invariance (MEI) approach, a cylinder of 10000 wavelengths is within the storage capacity and numerical tolerance of a workstation. Although, the MEI has greatly reduced the storage and solution time of the matrix, its overhead to generate the matrix elements is about the same order as that of the MoM. When the target is very large, that overhead can be very time consuming. This paper presents an interpolation and extrapolation technique such that the boundary equations of the MEI for high frequencies may be predicted from those of low frequencies. It is demonstrated that in the optical limit the same set of coefficients may be used for all frequencies, which is consistent with the concept of geometric optics where the same rule is applied to all frequencies     

An iterative algorithm based on the measured equation of invariancefor the scattering analysis of arbitrary multicylinders

It is known that the measured equation of invariance (MEI) is generally valid for outgoing waves just as other absorbing boundary conditions (ABCs). However, for the scattering problem of multicylinders, the scattered field from one cylinder is just the in-going incident wave to other cylinders. So the MEI cannot be directly applied to the scattering problem of multicylinders. In this paper, an iterative algorithm based on the MEI is first proposed for the scattering problems of multicylinders with arbitrary geometry and physical parameters. Each cylinder is coated with several layers of meshes and the MEIs are applied to the truncated mesh boundaries. It has been demonstrated that the MEI can truncate the meshes very close to the surfaces of the cylinders and then results in dramatically savings in memory requirements and computational time. The MEI coefficients of each cylinder can be stored and reused to form the sparse matrices during each iteration procedure as they are independent of excitations. So more central processing unit (CPU) time is saved as the MEI coefficients are calculated only once in the algorithm. The method can be applied to problems of various kinds of multiple cylinders with arbitrary configurations and cross sections. Numerical results for the scattered fields are in good agreement with the data available. Finally, examples are given to show the iterative algorithm applicable to electrically large multicylinders coated with lossy media