介绍

And then, we review the history, development and actuality of the discrete differential geometry and subdivision method.

第一章介绍了古典微分几何的思想、历史与发展等情况；回顾了离散微分几何的思想起源与发展情况；介绍了细分的思想、历史与发展情况。

First the traditional non-optical detection technology for gas concentrations is briefly introduced, such as ultra-sound technology, gas sensing, catalytic thermal, gas chromatography, interferometry applications, and then the spectral analysis based on the concentration of gas detection is discussed. The latest technological developments on the differential absorption spectroscopy, Fourier transform infrared spectroscopy, tunable laser diode laser absorption spectroscopy, laser radar and differential absorption Raman scattering laser radar, laser-induced fluorescence spectroscopy, laser Photoacoustic Spectroscopy are reviewed in detail.

首先对传统的非光学气体浓度检测技术作出了简单的介绍，包括超声波技术、气敏法、热催化法、气相色谱法、干涉法应用技术，被动检气管法，然后重点阐述了基于光谱学分析气体浓度检测技术的最新发展动态，其中分别对差分吸收光谱技术、傅里叶变换红外光谱技术、可调谐激光二极管激光吸收光谱技术、差分吸收激光雷达和拉曼散射激光雷达、激光诱导荧光光谱技术、激光光声光谱技术进行了详细介绍，最后提出了现代气体浓度检测技术的发展方向。

In this article, the fundamental knowledge of cryptography are introduced first. The author introduces the message digest algorithm, digital signature and X.509 certificate which are the foundations of authentication in public-key systems.

本文首先介绍了密码学方面的基础知识，接着介绍了身份认证中的消息摘要算法和数字签名的原理以及X.509证书，这些是公钥加密体系中身份认证的基础。

In this paper, the concept of network security and security structures of OSI and Internet is introduced, and various threats confronting the computer network are also discussed. Several kinds of network information security technologies, including firewall technology, virtual private network, intrusion detection system, data encryption technology, identity authentication and security protocol etc. are also examined. The security of internal network is the biggest problem in the construction of each network. The solution to this problem lies in setting up a firewall. The theory of a firewall and the approach to its actualization is studied. Intrusion detection system, an important part of the computer network security system, has gained extensive attention. IDS monitors the computer and network traffic for intrusion and suspicious activities. It not only detects the intrusion from the extranet hacker, but also the intranet users. The emergence of virtual private network paves the way for realizing secure connection of LAN quickly and at a relatively low cost. The concept, function, key techniques, including the tunnel technology, and the ways to realize VPN are expounded in this paper. Also introduced is the data encrypt network technology, which is called the soul of computer network security, such as digital digest, digital signature, digital certificate, digital encrypt arithmetic and so on. At the same time, the principle and the process of implementing network security by digital certificate and digital signature, the basic principle and characters of security protocols, and finally, three of the security protocols, concerning the security problems in network, IPsec, SLL and SET are analyzed in detail Computer network system should be a system of dynamic defence, both dynamic and static, passive as well as active, and even offensive, combined with management and technology.

本文系统地介绍了网络安全的概念、OSI及Internet的安全体系结构，并讨论了计算机网络面临的各种安全威胁；内部网络的安全问题是每个建网单位面临的最大问题，可以认为防火墙技术是解决网络安全的一个主要手段，本文研究了防火墙的原理及其实现手段；作为一种主动的防御措施，入侵检测系统作为网络系统安全的重要组成部分，得到了广泛的重视，TDS对计算机和网络资源上的恶意使用行为进行识别和响应，不仅检测来自外部的入侵行为，也监督内部用户的未授权活动；虚拟专用网技术的出现，为实现网络间的连接提供了快速安全但又相对便宜的手段，本文较深入的探讨了实现VPN的隧道技术，并对VPN的概念、功能、实现途径、基本构成、关键技术及发展前景等问题进行了全面论述；数据加密技术是网络安全核心技术之一，本文从数据加密算法、数字摘要、数字签名及数字证书等几方面简要介绍了数据加密技术，并分析用数字证书和数字签名实现网络安全的原理和过程；对安全协议的基本原理、主要特点进行了较为深入的研究，并就网络的安全性问题剖析了三种安全协议：IPsec协议、SLL协议和SET协议。

The paper firstly introduces several ways of designing the system,then the principle of digital recording, and then the main architecture of the system and the devising of the hardware and software.

本文首先介绍了实现嵌入式录音的几种技术，然后介绍了数字录音的原理，在这之后进行了系统的总体结构设计和详细的软硬件设计，给出了系统调试过程和实验结果。

This article introduces a design principle and implementation method of a high-speed digitizer based on PXI bus technology. It describes the system composition from two sides of the hardware and software.

介绍了一种基于PXI总线的高速数字化仪的设计理论和实现方法，从硬件和软件两个方面详细介绍了系统的设计方法。

The main purpose of dimethyl ether was introduced,Thetechnical developing trends was suggested.

扼要地介绍了二甲醚的主要用途和下游产品的开发方向，详细介绍了二甲醚的科技开发动态。

This paper is devoted to studying the linear diophantine equation systematically under the ABS environment.

本文的研究工作分三个部分，首先介绍了ABS算法的研究进展和ABS软件的概况，其次对线性丢番图方程组的解法作了系统的阐述，最后给出了求解线性丢番图方程组的整隐式LU算法和整隐式LX算法并介绍了在ABS软件方面的部分工作。

In this paper, a carrier frequency synchronization algorithm based on autocorrelation has been introduced and realized in FPGA firstly, especially the Cordic algorithm and its realization. Secondly, two symbol synchronization algorithm based on crosscorrelation and autocorrelation are introduced and implemented in FPGA, then the comparison between them is made in the view of realization. Besides, the methods of area diplex and pipelining are embodied in implementation scheme of FPGA.

本文首先介绍了一种基于自相关的载波频率同步算法，给出了它的FPGA实现方案，重点讲述了其中用到的Cordic算法及其实现；然后介绍了分别基于互相关和自相关的两种符号同步算法，给出了各自的FPGA实现方案，从实现的角度比较了两种算法的优缺点，并且在FPGA设计中体现了面积复用和流水线操作的设计思想。

The quaternion calculation for spacecraft attitude determination is investigated in this paper,including the transformation between quaternion and the direction cosine matrix,the quaternion differential equation,the selection of time steps for integrating the quaternion equation,and the compensation methods for the noncommutativity error in high dynamic motion.

介绍了四元数计算中的相关问题，包括四元数与方向余弦阵之间的转换、四元数运动方程、求解四元数运动方程时积分步长的选取和高动态应用中非互易误差的补偿，此外还介绍了对偶四元数的发展。

However, as the name（read－only memory）implies, CD disks cannot be written onorchanged in any way.

然而，正如其名字所指出的那样，CD盘不能写，也不能用任何方式改变其内容。

Galvanizes steel pallet is mainly export which suits standard packing of European Union, the North America. galvanizes steel pallet is suitable to heavy rack. Pallet surface can design plate type, corrugated and the gap form, satisfies the different requirements.

镀锌钢托盘多用于出口，替代木托盘，免薰蒸，符合欧盟、北美各国对出口货物包装材料的法令要求；喷涂钢托盘适用于重载上货架之用，托盘表面根据需要制作成平板状、波纹状及间隔形式，满足不同的使用要求。