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1.
“7”是多少? 对于这个问题,正确的回答应是:不知道。因为字符“7”给出的信息还不够,要知道它的意义,必须知道它在数字中的位置,还要知道这个数字是按什么进位制进位的。基数和进位制表示事物个数的数叫做基数,如1,2,3等。以什么基数作为进位的标准呢?丰富多采的生活,产生了丰富多采的进位法,如以基数10为标准时,是“逢十进一”这就是我们举的十进制,同理有二进制、三进制、十六进制、六十进制等。这些进位制都来自生活,又在生活中演变,承担着不同的角色。  相似文献   

2.
光正交码是一种具有良好自相关性和互相关性的(0,1)序列,被广泛的运用于光码分多址(OCDMA)系统.由于光正交码中所有码字的码重都固定不变,使得码字的容量不大.我们提出了变码重光正交码,并对其进行了理论分析.最后,给出了数值仿真结果.结果表明,采用变码重光正交码的系统无论是在可接入用户数还是在系统误码率上都优于采用固定码重光正交码的系统.研究结果对OC-DMA系统参数的选取具有一定的参考价值.  相似文献   

3.
介绍了用集成超前进位全加器设计码制转换电路的理论和方法,并举例说明其应用。  相似文献   

4.
为了减小直接扩频CDMA系统中各用户的多址干扰,研究了一种特殊的扩频序列--完全互补码.介绍了完全互补码的概念和性质,给出了一种完全互补码的生成方法,提出了一种新的扩展完全互补码的方法,讨论了基于完全互补码的CDMA系统模型.对该模型在加性高斯白噪声信道和瑞利衰落信道中的性能进行了仿真,并与基于Gold序列和m序列的CDMA系统的性能进行了分析比较.结果表明,基于完全互补码的CDMA系统具有很好的抗多址干扰性能.  相似文献   

5.
Kasami扩频序列的研究   总被引:1,自引:0,他引:1  
介绍了扩频序列的研究、发展情况和Kasami扩频序列的生成方法 .提出了当移位寄存器的级数n =2 (模 4 )时 ,一种新的序列构造方法 ,所得到的两个集合与Kasami大集合序列的相关特性一致 .并与Gold码、Kasami小集合序列码进行了比较分析 ,进一步拓展了扩频码的生成方法 .  相似文献   

6.
为了缩短多通道直接序列扩频信号的捕获时间,提出了一种新的多通道并行捕获算法.该算法将多个通道的伪码序列进行叠加,形成一个新的伪码序列,由新的伪码序列和多通道直扩信号进行相关,检测到信号后再判决具体通道.分析和仿真结果均表明,提出的算法在不增加实现资源的情况下,以少量降低相关信噪比为代价缩短了捕获时间,适用于多通道直扩信号的快速捕获.  相似文献   

7.
数字与数码     
数字与数码在一般情况下常常不加区别而混用,本文从记数法角度对它们进行区分,对数字与数码的起源,记数的表达形态,进位基数的选择,进位的表示方式以及数字与数码的相互影响和发展趋势等方面作了阐述,指出区别数字与数码在数学史研究中的作用,并以中外有代表性的记数方法为例加以说明。  相似文献   

8.
为了提高舰载相控阵雷达波束指向捷变能力,设计了一种分布式波控系统,其中传输方式采用串行RapidIO,波控主机采用PowerPC矢量运算处理器,子阵运算模块为FPGA。重点推导了舰载相控阵雷达波控码的公式,实现了RapidIO的初始化编程,以及波控主机的波控任务编程。测试波控码的计算和RapidIO通信时间,设计方案能够满足舰载相控阵雷达的波束切换时间指标。  相似文献   

9.
田可  周继 《应用科技》2008,35(3):1-3
根据系统提出的接口以及模块化设计要求,文中提出了一种基于FPGA的波控系统设计方案,并且设计了波控码计算和波束控制软件,软件仿真和实际运行都验证了该方案的可行性,实现了对波控码的高速并行计算和对各单元通道的并行同步控制.  相似文献   

10.
一般地我们需要将抽象的实数以一种具体的形式来表示,通常实数都采用十进位小数的形式来表示,但在实际应用中也需要将实数以其它形式的进位制小数来表示。本文给出将任意实数在通常情形下的十进位小数表示转化为更一般的P进位小数表示形式的数位换算公式及性质。  相似文献   

11.
Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.  相似文献   

12.
何延凌 《科技信息》2008,(4):258-258
Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women's language from these perspectives: pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women's language, more attention should be paid to language use in social context. What's more, the linguistic phenomena in a speaking community can be understood more thoroughly.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。  相似文献   

16.
In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.  相似文献   

17.
As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.  相似文献   

18.
王慧 《科技信息》2008,(10):240-240
Wuthering Heights, Emily Bronte's only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.  相似文献   

19.
The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.  相似文献   

20.
The non-orthogonal localized molecular orbital(NOLMO)is the most localized representation of electronic degrees of freedom.As such,NOLMOs are thus potentially the most efficient for linear scaling calculations of electronic structures for large systems.However,direct ab initio calculations with NOLMO have not been fully implemented and widely used,partly because of the slow convergence issue in the optimization of NOLMO.We devel-  相似文献   

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