SQL语句优化技术分析与探讨

一个成熟的管理信息系统必需建立在一个好的数据库基础之上，由于用户对数据库的查询效率提出很高的要求，因此必须对数据库的查询进行优化。通过介绍有关数据库查询优化技术，从几个方面来具体阐述SQL优化查询的实现方法。     

The empirical distribution of good codes

Let the kth-order empirical distribution of a code be defined as the proportion of k-strings anywhere in the codebook equal to every given k-string. We show that for any fixed k, the kth-order empirical distribution of any good code (i.e., a code approaching capacity with vanishing probability of error) converges in the sense of divergence to the set of input distributions that maximize the input/output mutual information of k channel uses. This statement is proved for discrete memoryless channels as well as a large class of channels with memory. If k grows logarithmically (or faster) with blocklength, the result no longer holds for certain good codes, whereas for other good codes, the result can be shown for k growing as fast as a certain fraction of blocklength     

基于DSP的单相电压型逆变器的研究与实现

介绍了电压型全桥逆变电路的基本结构和工作原理。在此基础上,设计了基于DSP的硬件测试平台,并提出了在DSP中产生SPWM(正弦脉冲宽度调制)的方法,采用了PI调节的闭环控制算法。离线计算参考电压的方法减轻了系统负担。经试验验证,该方法可行,效果较好。     

WDM全光网自适应路由和波长分配算法

研究了无波长转换WDM全光网的路由和波长分配算法（RWA）。通过对已有算法的分析和比较,提出了一种自适应最小跳数路由算法（ADMH）。此算法以最小跳数路由为基础,同时考虑网络状态的变化,因而不仅能尽量少使用网络资源,也能使网络资源的分布保持均衡。计算机模拟仿真的结果表明,这种算法性能在各种网络参数条件下优于或等于已有算法。     

Properties and Algorithms for Unfolding of Probabilistic Data-Flow Graphs

It is known that any selection statement (e.g. if and switch-case statements) in an application is associated with a probability which could either be predetermined by user input or chosen at runtime. Such a statement can be regarded as a computation node whose computation time is represented by a random variable. This paper focuses on iterative applications (containing loops) reflecting those uncertainties. Such an application can then be transformed to a probabilistic data-flow graph.Two timing models, the time-invariant and time-variant models, are introduced to characterize the nature of these applications. Since there can be many unfolding factors associated with each of the possible graph outcomes, for the time-invariant model, we propose a means of selecting a constant minimum rate-optimal unfolding factor for unfolding the probabilistic graph. We demonstrate that this factor guarantees the best schedule length.We also suggest a good estimate for choosing an unfolding factor for a graph under the time-variant model. Experiments show that using our selection scheme results in an iteration period close to the theoretical iteration bound of the experimental graph. Furthermore, this paper discusses an alternative approach which selects a few optimal schedules (with respect to the graph outcomes) to be stored in the system. The other possibilities will be represented by a modified template graph.     

Design of high-Q varactors for low-power wireless applicationsusing a standard CMOS process

New applications such as wireless integrated network sensors (WINS) require radio-frequency transceivers consuming very little power compared to usual mainstream applications, while still working in the ultra-high-frequency range. For this kind of application, the LC-tank-based local oscillator remains a significant contributor to the overall receiver power consumption. This statement motivates the development of good on-chip varactors available in a standard process. This paper describes and compares the available solutions to realize high-Q, highly tunable varactors in a standard digital CMOS submicrometer process. On this basis, quality factors in excess of 100 at 1 GHz, for a tuning ratio reaching two, have been measured using a 0.5-μm process     

Quantitative Analysis of the Target Related to Cash Flow Statement

1IntroductionTheFinancialMinistryofChinaenacted"EnterpriseAccountingStafldards-CashFlowStatement"onMarch20th,1998andrequiredtoimplementitfromJanuarylst,1998.Meanwhile,theStandardspointsoutthattheStatementofchangesinfinancialpositionshallnotbecompiledanymore.ItwasAmericathatfirstdecidedtoreplacestatementofchangesinfinancialpositionwithcashflowstatement.Afterwards,U.K.,AustraliaCanadaHongkong,Taiwanandmanyothercountriesandareasfollowed.Toemphasizecashflowstatementandovercometheshortcomi…     

Testability of 2-Level AND/EXOR Circuits

It is often stated that AND/EXOR circuits are much easier to test than AND/OR circuits. This statement, however, only holds true for circuits derived from restricted classes of AND/EXOR expressions, like positive polarity Reed-Muller and fixed polarity Reed-Muller expressions. For these two classes of expressions, circuits with good deterministic testability properties are known. In this paper we show that these circuits also have good random pattern testability attributes. An input probability distribution is given that yields a short expected test length for biased random patterns. This is the first time theoretical results on random pattern testability are presented for 2-level AND/EXOR circuit realizations of arbitrary Boolean functions. It turns out that analogous results cannot be expected for less restricted classes of 2-level AND/EXOR circuits. We present experiments demonstrating that generally minimized 2-level AND/OR circuits can be tested as easy (or hard) as minimized 2-level AND/EXOR circuits.     

Remarks on `Comments on field equivalence principles' [and reply]

The commenter asserts that a statement quoted in the above named work (ibid., vol.AP-35, no.2, pp.242-4, 1987) that is said to be incorrect was actually quoted out of context and therefore misunderstood. The statement's validity is demonstrated. In replying, the original author maintains the correctness of his interpretation of the quoted statement     

Ready, aim-write

A methodical audience identification approach called a prewrite is proposed to reduce the need for rewriting a document. To prewrite, the writer must write a statement of the purpose of the document and a statement identifying both the intended audience and the implications of writing to that audience. Five questions the writer must answer about the audience are given, and information on audience identification and the needs of particular audiences is included     

Helpful or Harmful? How Frequent Repetition Affects Perceived Statement Credibility

On the basis of experimental data, we study how repetition of a statement affects perceived statement credibility. We identify 2 counteracting effects: The first effect, known as “truth effect,” describes a positive relationship between repetition and statement credibility. People tend to ascribe higher credibility to messages that they repeatedly encounter. In contrast, the second effect occurs when repetition is taken too far. Here, an indirect and negative effect is identified and participants start to perceive the message as a persuasive attempt. This perception triggers reactance, which in turn considerably reduces participants' trust in the source and leads to a significant decrease in the overall credibility of the message. Our results broaden the understanding of the benefits and harms of repeated persuasive messages.     

基于SQL选择语句的聚类分析

在数据挖掘中SQL语句常用于数据的特征规则,特别是聚类规则。因为仅仅用一些简单的SQL语句就可以同时创建特征规则和聚类规则。把SQL语句和其他应用软件结合起来,将提高创建t-加权和d-加权的能力,特别是在特征规则中进一步归一化的能力,其中t-加权用于衡量每条数据记录的典型性,d-加权用于衡量聚类区分原则中的差异性。基于概念树把层次结构转换成表格结构将影响SQL语句的编写和成功执行,并且把层次结构中的每一个树结构转换为相应的表结构,最终把整个层次结构转换为表结构,才能合理高效地设计查询程序。     

VC实现水晶报表对数据源的动态绑定和历史数据显示查询

为了对在线钢板的温度数据进行实时检测和存储,以VC++6.0作为平台,建立监控点和PC机之间的串口通信,运用ADO技术将数据写入Access数据库。在PC端显示时,采用SQL语句和水晶报表自带的公式语句进行查询,将存储的数据以数据图标的形式进行回放。而传统的VC平台下对水晶报表的使用大多是绑定单一的数据源,这对多数据库的应用来说是不可行的。所以,本文基于在线钢板温度建工系统,阐述了如何在VC下实现对水晶报表的动态绑定数据源和历史数据的显示查询。     

Any code of which we cannot think is good

A central paradox of coding theory concerns the existence and construction of the best codes. Virtually every linear code is good, in the sense that it meets the Gilbert-Varshamov bound on distance versus redundancy. Despite the sophisticated constructions for codes derived over the years, however, no one has succeeded in demonstrating a constructive procedure that yields such codes over arbitrary symbol fields. Using the theory of Kolmogorov complexity, it is shown that this statement holds true in a rigorous mathematical sense: any linear code that is truly random, in the sense that there is no concise way of specifying the code, is good. Furthermore, random selection of a code that does contain some constructive pattern results, with probability bounded away from zero, in a code that does not meet the Gilbert-Varshamov bound regardless of the block length of the code. In contrast to the situation for linear codes, it is shown that there are effectively random nonlinear codes which have no guarantee on distance. In addition, it is shown that the techniques of Kolmogorov complexity can be used to derive typical properties of classes of codes in a novel way     

一种基于程序可达图的并发程序依赖性分析方法

依赖性分析是一种重要的程序分析手段.针对多线程共享变量通信机制,本文在提出一种新的并发程序表示—线程交互可达图(tIRG)的基础上,从全局分析并发程序的依赖关系,构建了以程序状态和语句二元组为节点的并发程序依赖图(MSDG).与传统的以语句为节点的并发程序依赖图相比,MSDG图中依赖关系不仅精确,且具有可传递性,对其遍历可获得高精度的并发程序切片,精度和效率较其它高精度切片方法有显著提高.     

Myoelectric Signal Processing: Optimal Estimation Applied to Electromyography?Part I: Derivation of the Optimal Myoprocessor

This paper (Part I of II) describes the development of a novel technique for processing the electrical activity of muscle which uses multiple channels of myoelectric activity. A phenomenological mathematical model of myoelectric activity is formulated. From this model, a mathematical statement of the optimal myoelectric signal processor is derived, and some of its properties are investigated. This mathematical statement encompasses and places in perspective almost all single-channel myoprocessor developments to date, as well as specifying the optimal multiple-channel myoprocessor. An experimental demonstration of the efficacy of this processor is presented in a subsequent paper (Part II).     

热断层(TTM)技术对睡眠质量的评估与探讨

本文的目的是探讨利用热断层(TTM)技术对睡眠质量进行评估的方法及其应用价值。采用的方法是对281位体检客人进行睡眠质量评估,以客人详细主述记录为对照。结果,被TTM诊断为有睡眠障碍的有119例,有主诉睡眠障碍的有122例,检出率为97．5％。由此可得出这样的结论:TTM对睡眠质量的评估简单快速,准确率高,具有直观实用的诊断价值。     

Minimum trajectory sensitivity of a linear system

The letter provides a proof for the statement that, for a linear multivariable system, minimum eigenvalue sensitivity guarantees minimum trajectory sensitivity.     

Parametric FE-approach to flip-chip reliability under various loading conditions

In this paper we focus on the thermo-mechanical reliability of flip-chip assemblies which are, in addition to periodic thermal loads, constrained by mechanical boundary conditions caused by the attachment of a heat-spreader. Whereas mechanically unconstrained flip-chip assemblies have been in the focus of reliability studies for a long time, the loading induced by additional mechanical constraints and hence the impact on solder bump reliability is still largely unknown. So a comprehensive study was carried out comprising FE-simulations for lifetime prediction and thermal cycling tests for experimental verification. For this purpose a tool for modular parametric FE-model generation was developed. The experiments do coincide with the simulative prediction with good accuracy, allowing for the first time a distinct statement about the reliability of flip-chip packages with attached heat-spreaders. As a result we have found that in general all additional constraints on the chip do reduce its lifetime. A distinct ranking has be obtained as a function of the specified variables. Eventually design guidelines are given.     

基于MC35的GSM直放站远程监控系统

在对GSM移动通信系统和直放站系统理论分析基础之上,重点介绍了基于MC35的直放站监控系统主控板软硬件的设计、实现。主控板作为监控系统的核心部分有着重要的作用,他要对直放站各功能模块进行监控管理,包括对直放站状态的查询、功放开关及ATT的设置并及时地将直放站的工作状态通过MC35模块主动上报给远端的监控中心。