直接序列扩频信号快速捕获

提出一种新的基于频域并行搜捕法的改进型快捕电路结构.该结构利用设计复用技术实现FFT单元和IFFT单元的复用;通过软件计算本地伪码FFT,并将其结果存储在ROM中,使硬件规模大幅减少;采用并行设计提高系统的运算速度;采用块浮点算法提高动态范围和运算精度.整个快捕电路由一块FPGA XC2V3000-5实现,工作时钟为29 ns,精度为1/4码片情况下,伪码捕获仅需4.145 ms.仿真和测试结果验证了设计的正确性.     

基于CORDIC算法的直接数字频率合成器

在传统的直接频率合成器（DDS）中，相位到幅度的转化是通过相位码寻址只读存储器（ROM）来实现的。随着微电子技术的进步，用实时计算来代替ROM查找表已成为可能。文章讨论了应用CORDIC算法计算正弦值时旋转方向的确定方法以及CORDIC算法在DDS中的应用，为基于可编程器件设计DDS系统提供了有益的参考。     

基于CORDIC算法的直接数字频率合成器实现方法

提出了一种基于CORDIC算法的改进直接数字频率合成DDFS的实现方法，应用CORDIC算法替代了庞 大的传统正弦函数ROM输出高质量的信号，该方法使DDFS易于在FPGA等器件内实现.     

基于脉冲多重化的数字SPWM技术

为有效降低SPWM逆变波形的谐波含量,提出了一种新颖的脉冲多重化数字SPWM逆变控制技术.与SPWM电平多重化技术不同,脉冲多重化是在每个逆变PWM周期,将SPWM脉冲在时间轴上进行的时间多重化.算法直接以数字正弦序列为基础,省去了以往SPWM脉宽计算的大量复杂过程,有效降低了系统的脉宽计算量.对脉冲多重化SPWM逆变波形频谱进行了理论计算与分析,证明了该技术可以在不增加系统现有开关频率的基础上,进一步降低SPWM逆变波形的谐波含量.最后,给出了该算法的工程实现方法,通过构建实验平台,对该算法进行了实验验证.实验结果证明了该技术的有效性,文中理论分析结果与实际情况完全一致.     

基于FPGA的时间数字转换器的编码器

时间数字转换器的编码器需要把温度计码转换1-0(0-1)跳变处的二进制位置码。针对FPGA的查找表结构,实现了处理任意2m位温度计码的3种行为级编码器(顺序查找法、折半查找法和累加法)和4种数据流级编码器(wallace树、胖树、MUX和ROM)的算法描述,并在EP3C25E144I7中实现。通过对比编码器的LUT使用个数、最短路径延时、最长路径延时和毛刺,发现在FPGA上性能相近且最优的是胖树结构和ROM结构的编码器。ROM结构比胖树结构更易于被编程实现和移植。     

一种单层BOM到多层BOM转化算法的实现

研究当前主要的两种BOM表结构--单层BOM结构和多层BOM结构,分析它们各自的优缺点.提出一种基于存储过程的单层BOM结构到多层BOM结构转化的方法,并给出部分实现代码.该算法是基于存储过程的,因此,相对于一般的算法具有更好的计算性能.     

基于DSP的AM/FM调制器实验模块的实现

采用DDS技术实现了基于DSP的模拟调制实验模块。包括系统的硬件和软件设计,模拟调制原理,DSP实现模拟调制的方法,同时采用单象限正弦波形存储器结构对DDS模块进行了改进,提高调制器的性能。最后对系统功能和性能进行了测试,结果满足设计要求,非常适合学生对DDS和模拟调制原理的学习以及进一步的开发。     

一种高精度可调频调相的正弦信号源的实现方法

介绍了一种应用于电度表校表系统中的高精度的可调频调相正弦信号源的实现方法.以单片机作为控制器件,EPROM存储数据,利用大规模可编程逻辑器件设计实现大部分外围电路,通过D/A转换器实现两路正弦波形的输出,达到校表系统对频率和相位差调节的要求.     

基于图像压缩的PDF417条码数据存储

分析了PDF417二维条码的结构及压缩模式,要将静态图像存储在PDF417条码中就要对其进行高效的压缩,重点阐述了JPEG2000标准的核心算法的实现及优化.实验证明该方法完成了优质高效的压缩任务,从而达到了在PDF417条码内存储静态图像的目的.     

基于网络编码的多媒体云存储系统单节点修复算法

针对现有多媒体云存储系统单节点修复算法中,有限域大,编解码复杂度高,磁盘I/O开销大,存储开销与修复带宽开销不均衡等问题,基于网络编码提出一种多媒体云存储系统单节点修复算法.该算法将系统中节点已分组的多媒体文件数据进行分组存储,并将组内数据在GF(2)有限域上进行异或编码,当部分节点失效时,新生节点只要连接同组中2~3个未失效节点即可精确修复失效节点中的数据.理论分析与仿真实验结果表明:该算法可减小编解码与修复的复杂度,降低磁盘I/O开销;在相同条件下,该算法存储开销与基于最小存储再生码(minimum storage regeneration codes,MSR)算法的存储开销一致,而修复带宽开销与最小带宽再生码(minimum bandwidth regeneration codes,MBR)算法接近.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to