期刊文献+
共找到15篇文章
< 1 >
每页显示 20 50 100
时态变量“Now”语义及相应时态关系运算 被引量:18
1
作者 叶小平 汤庸 《软件学报》 EI CSCD 北大核心 2005年第5期838-845,共8页
讨论了时态变量“Now”的基本语义,即Now不仅可以表示当前时间,还能表示过去时间和将来时间.在语义分析的基础上,讨论了带变量时态关系运算中需要解决的基本问题,即变量Now值的确定问题,研究了相应时态关系数据操作,建立了带变量时态关... 讨论了时态变量“Now”的基本语义,即Now不仅可以表示当前时间,还能表示过去时间和将来时间.在语义分析的基础上,讨论了带变量时态关系运算中需要解决的基本问题,即变量Now值的确定问题,研究了相应时态关系数据操作,建立了带变量时态关系代数系统. 展开更多
关键词 时态变量语义 时间变量值确定 变量时态关系代数系统
下载PDF
基于BCDM的含有变量的双时态关系代数研究 被引量:2
2
作者 王路帮 钱省三 《计算机应用研究》 CSCD 北大核心 2010年第6期2071-2074,共4页
在BCDM(双时态概念数据模型)中,时间变元Now和UC的存在解决了时态记录的频繁更新问题;但是时态变元的存在又给数据库的操作带来某种不确定性甚至是错误,同时引起关系代数运算的歧义。基于BC-DM,通过绑定时间变元,用时态映射的集合定义... 在BCDM(双时态概念数据模型)中,时间变元Now和UC的存在解决了时态记录的频繁更新问题;但是时态变元的存在又给数据库的操作带来某种不确定性甚至是错误,同时引起关系代数运算的歧义。基于BC-DM,通过绑定时间变元,用时态映射的集合定义时态关系,由此建立了一种含有时间变元的双时态关系代数体系。该关系代数体系在双时态运算下是封闭的。 展开更多
关键词 时态概念数据模型 时态数据库 时态变量 时态关系代数
下载PDF
用带时钟变量的线性时态逻辑扩充Object-Z 被引量:1
3
作者 文志诚 李长云 满君丰 《计算机应用研究》 CSCD 北大核心 2009年第5期1764-1769,共6页
Object-Z是形式规格说明语言Z的面向对象扩充,适合描述大型面向对象软件规格说明,但它不能很好地描述连续性实时变量和时间限制。线性时态逻辑能够描述实时系统,但不能很好地处理连续时间关系,也不能很好地模块化描述形式规格说明。首... Object-Z是形式规格说明语言Z的面向对象扩充,适合描述大型面向对象软件规格说明,但它不能很好地描述连续性实时变量和时间限制。线性时态逻辑能够描述实时系统,但不能很好地处理连续时间关系,也不能很好地模块化描述形式规格说明。首先用时钟变量扩充线性时态逻辑,接着提出了一个方法——用带时钟变量的时态逻辑(LTLC)来扩充Object-Z。用LTLC扩充的Object-Z是一个模块化规格说明语言,是Object-Z语法和语义的最小扩充,其最大优点在于它能方便地描述和验证复杂的实时软件规格说明。 展开更多
关键词 OBJECT-Z 用带时钟变量时态逻辑 实时系统 形式规格说明 形式验证
下载PDF
偏序时态XML索引TempPartialIndex 被引量:1
4
作者 汤娜 叶小平 +2 位作者 汤庸 彭鹏 杜梦圆 《软件学报》 EI CSCD 北大核心 2016年第9期2290-2302,共13页
时态数据管理是常规数据管理的深化和扩展,具有理论研究的意义与实践应用的价值.时态数据索引是时态数据管理的重要技术支撑,是其中的一个研究热点.首先,提出了一种时态数据结构,通过数据节点间的偏序关系,可将常规的二维时间区间的处... 时态数据管理是常规数据管理的深化和扩展,具有理论研究的意义与实践应用的价值.时态数据索引是时态数据管理的重要技术支撑,是其中的一个研究热点.首先,提出了一种时态数据结构,通过数据节点间的偏序关系,可将常规的二维时间区间的处理转化为基于偏序的时态等价类上的一维的处理,该数据结构可以快速有效地处理时态操作;其次,在该新型时态数据结构基础上研究了时态XML索引Temp Partial Index,其基本特征是将时态数据结构整合到非时态的XML索引中,即,将其整合到语义层之中,通过时态过滤和语义过滤掉大量节点之后,再进行结构连接;另外,着重讨论了基于Temp Partial Index"一次一集合"及其时态变量查询和增量式的动态更新机制.同时,仿真结果表明:Temp Partial Index能够有效地支持时态XML的各类查询及更新操作,技术上具有可行性和有效性. 展开更多
关键词 时态偏序关系 时态数据结构 时态XML索引 时态变量查询 增量式动态更新
下载PDF
有效时间不确定性研究
5
作者 王淯 《中国新技术新产品》 2011年第13期15-16,共2页
时态数据库中的有效时间中引入了时态变量Now。本文主要介绍now产生的复杂语义,进而分析复杂语义带来的查询结果的时态不确定问题以及现有处理模型及其不足,最后建立now复杂语义不确定性时态数据模型。
关键词 时态变量now 不确定性 数据模型
下载PDF
高校教学计划数据库的设计与维护
6
作者 戴祖旭 《武汉化工学院学报》 2003年第4期65-67,共3页
分析了高校教学计划的时态性特征;在设计数据库时采用了水平分解时态关系变量的方法,并给出了教学计划数据库插入、更新维护算法.该方案可减少数据库中表的数量、避免对未来时间属性的定期更新维护工作.
关键词 教学计划数据库 时态关系变量 水平分解 维护算法
下载PDF
Variation Dynamics of Total Nitrogen and Nicotine of Burley Tobacco at Various Growing Stages under Different Nitrogen Nutrition Levels 被引量:2
7
作者 柴家荣 《Agricultural Science & Technology》 CAS 2012年第11期2327-2331,共5页
[Objective] This study aimed to investigate the variation dynamics of total nitrogen and nicotine of burtey tobacco at various growing stages under different ni- trogen nutrition levels to provide reference for optimi... [Objective] This study aimed to investigate the variation dynamics of total nitrogen and nicotine of burtey tobacco at various growing stages under different ni- trogen nutrition levels to provide reference for optimizing fertilization technologies for burley tobacco. [Method] Fresh burley tobacco leaves were collected at various growing stages and dried to measure the content of total nitrogen, protein and nico- tine by using INTEGRAL automated chemical analyzer and analyze the correlation with nitrogen application level. [Result] Regardless of the nitrogen application level, the content of total nitrogen and protein showed a downward trend since root ex- tending stage and reached the minimum at mature stage; the content of nicotine showed an upward trend since early vigorous growing stage and increased to the maximum at mature stage; the content of total nitrogen, protein and nicotine all in- creased after air curing; the content of total nitrogen, protein and nicotine showed positive correlation with nitrogen application level, while total nitrogen/nicotine was negatively correlated. The results indicate that nitrogen level is closely related to the total nitrogen and nicotine of burley tobacco at growing period and post-air curing, rational application of nitrogen is an important measure to regulate the content of total nitrogen and nicotine of tobacco. [Conclusion] This study provides scientific ba- sis for rational fertilization of burley tobacco. 展开更多
关键词 Burley tobacco Nitrogen nutrition Growth period Total nitrogen NICOTINE
下载PDF
Evolution and Generation of Dynamics of Two-Mode Squeezed States of Time-Dependent Coupled Boson System
8
作者 ZHANG Xue ZHENG Tai-Yu ZHENG Li 《Communications in Theoretical Physics》 SCIE CAS CSCD 2008年第10期955-960,共6页
The system of the Hamiltonian involving a driving part,a single mode part,and a two-mode squeezedone and a two-mode coupled one is discussed using the Lewis-Riesenfeld invariant theory.The time evolution operatoris ob... The system of the Hamiltonian involving a driving part,a single mode part,and a two-mode squeezedone and a two-mode coupled one is discussed using the Lewis-Riesenfeld invariant theory.The time evolution operatoris obtained.When the initial state is a coherent state,the quantum fluctuation of the system is calculated,and it isdependent on the squeezed part and the two-mode coupled part,but not dependent on the driving one. 展开更多
关键词 two-mode squeezed states Lewis Riesenfeld invariant theory time evolution operator
下载PDF
The identification algorithm for commensurate order linear time-invariant fractional systems
9
作者 王振滨 曹广益 朱新坚 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2005年第5期576-580,共5页
An efficient identification algorithm is given for commensurate order linear time-invariant fractional systems. This algorithm can identify not only model coefficients of the system, but also its differential order at... An efficient identification algorithm is given for commensurate order linear time-invariant fractional systems. This algorithm can identify not only model coefficients of the system, but also its differential order at the same time. The basic idea is to change the system matrix into a diagonal one through basis transformation. This makes it possible to turn the system’s input-output relationships into the summation of several simple subsystems, and after the identification of these subsystems, the whole identification system is obtained which is algebraically equivalent to the former system. Finally an identification example verifies the effectiveness of the method previously mentioned. 展开更多
关键词 fractional systems COMMENSURATE linear time-invariant state-space representation system identification
下载PDF
Geom/G_1,G_2/1/1 REPAIRABLE ERLANG LOSS SYSTEM WITH CATASTROPHE AND SECOND OPTIONAL SERVICE 被引量:6
10
作者 Yinghui TANG Miaomiao YU Cailiang LI 《Journal of Systems Science & Complexity》 SCIE EI CSCD 2011年第3期554-564,共11页
This paper studies a single server discrete-time Erlang loss system with Bernoulli arrival process and no waiting space. The server in the system is assumed to provide two different types of services, namely essential... This paper studies a single server discrete-time Erlang loss system with Bernoulli arrival process and no waiting space. The server in the system is assumed to provide two different types of services, namely essential and optional services, to the customer. During the operation of the system, the arrival of the catastrophe will break the system down and simultaneously induce customer to leave the system immediately. Using a new type discrete supplementary variable technique, the authors obtain some performance characteristics of the queueing system, including the steady-state availability and failure frequency of the system, the steady-state probabilities for the server being idle, busy, breakdown and the loss probability of the system etc. Finally, by the numerical examples, the authors study the influence of the system parameters on several performance measures. 展开更多
关键词 CATASTROPHE discrete supplementary variable technique Erlang loss system repairable queueing system second optional service.
原文传递
Further results on existence-uniqueness for stochastic functional differential equations 被引量:8
11
作者 XU DaoYi WANG XiaoHu YANG ZhiGuo 《Science China Mathematics》 SCIE 2013年第6期1169-1180,共12页
The aim of this paper is to develop some basic theories of stochastic functional differential equations (SFDEs) under the local Lipschitz condition in continuous functions space C. Firstly, we establish a global exist... The aim of this paper is to develop some basic theories of stochastic functional differential equations (SFDEs) under the local Lipschitz condition in continuous functions space C. Firstly, we establish a global existence-uniqueness lemma for the SFDEs under the global Lipschitz condition in C without the linear growth condition. Then, under the local Lipschitz condition in C, we show that the non-continuable solution of SFDEs still exists if the drift coefficient and diffusion coefficient are square-integrable with respect to t when the state variable equals zero. And the solution of the considered equation must either explode at the end of the maximum existing interval or exist globally. Furthermore, some more general sufficient conditions for the global existence-uniqueness are obtained. Our conditions obtained in this paper are much weaker than some existing results. For example, we need neither the linear growth condition nor the continuous condition on the time t. Two examples are provided to show the effectiveness of the theoretical results. 展开更多
关键词 stochastic functional differential equations EXISTENCE UNIQUENESS
原文传递
Subspace-based identification of discrete time-delay system
12
作者 Qiang LIU Jia-chen MA 《Frontiers of Information Technology & Electronic Engineering》 SCIE EI CSCD 2016年第6期566-575,共10页
We investigate the identification problems of a class of linear stochastic time-delay systems with unknown delayed states in this study. A time-delay system is expressed as a delay differential equation with a single ... We investigate the identification problems of a class of linear stochastic time-delay systems with unknown delayed states in this study. A time-delay system is expressed as a delay differential equation with a single delay in the state vector. We first derive an equivalent linear time-invariant(LTI) system for the time-delay system using a state augmentation technique. Then a conventional subspace identification method is used to estimate augmented system matrices and Kalman state sequences up to a similarity transformation. To obtain a state-space model for the time-delay system, an alternate convex search(ACS) algorithm is presented to find a similarity transformation that takes the identified augmented system back to a form so that the time-delay system can be recovered. Finally, we reconstruct the Kalman state sequences based on the similarity transformation. The time-delay system matrices under the same state-space basis can be recovered from the Kalman state sequences and input-output data by solving two least squares problems. Numerical examples are to show the effectiveness of the proposed method. 展开更多
关键词 Identification problems Time-delay systems Subspace identification method Alternate convex search Least squares
原文传递
Adaptive Feedback Stabilization with Quantized State Measurements for a Class of Chaotic Systems 被引量:1
13
作者 王银河 范永清 +1 位作者 王青云 章云 《Communications in Theoretical Physics》 SCIE CAS CSCD 2012年第5期808-816,共9页
We investigate asymptotical stabilization for a class of chaotic systems by means of quantization measurements of states.The quantizer adopted in this paper takes finite many values.In particular,one zoomer is placed ... We investigate asymptotical stabilization for a class of chaotic systems by means of quantization measurements of states.The quantizer adopted in this paper takes finite many values.In particular,one zoomer is placed at the input terminal of the quantizer,and another zoomer is located at the output terminal of the quantizer.The zoomers possess a common adjustable time-varying parameter.By using the adaptive laws for the time-varying parameter and estimating boundary error of values of quantization,the stabilization feedback controller with the quantized state measurements is proposed for a class of chaotic systems.Finally,some numerical examples are given to demonstrate the validity of the proposed methods. 展开更多
关键词 chaotic system STABILIZATION quantization measurement adaptive laws
原文传递
Approximate Controllability of Neutral Functional Differential Systems with State-Dependent Delay 被引量:1
14
作者 Xianlong FU Jialin ZHANG 《Chinese Annals of Mathematics,Series B》 SCIE CSCD 2016年第2期291-308,共18页
This paper deals with the approximate controllability of semilinear neutral functional differential systems with state-dependent delay. The fractional power theory and α-norm are used to discuss the problem so that t... This paper deals with the approximate controllability of semilinear neutral functional differential systems with state-dependent delay. The fractional power theory and α-norm are used to discuss the problem so that the obtained results can apply to the systems involving derivatives of spatial variables. By methods of functional analysis and semigroup theory, sufficient conditions of approximate controllability are formulated and proved. Finally, an example is provided to illustrate the applications of the obtained results. 展开更多
关键词 Approximate controllability Neutral functional differential system State-dependent delay Analytic semigroup Fractional power operator
原文传递
A SINGLE SERVER RETRIAL QUEUE WITH GENERAL RETRIAL TIMES AND TWO-PHASE SERVICE
15
作者 Jinting WANG Jianghua LI 《Journal of Systems Science & Complexity》 SCIE EI CSCD 2009年第2期291-302,共12页
An M/G/1 retrial queue with a first-come-first-served (FCFS) orbit,general retrial time,two-phase service and server breakdown is investigated in this paper.Customers are allowed to balkand renege at particular times.... An M/G/1 retrial queue with a first-come-first-served (FCFS) orbit,general retrial time,two-phase service and server breakdown is investigated in this paper.Customers are allowed to balkand renege at particular times.Assume that the customers who find the server busy are queued inthe orbit in accordance with an FCFS discipline.All customers demand the first 'essential' service,whereas only some of them demand the second 'optional' service,and the second service is multi-optional.During the service,the server is subject to breakdown and repair.Assume that the retrialtime,the service time,and the repair time of the server are all arbitrarily distributed.By using thesupplementary variables method,the authors obtain the steady-state solutions for both queueing andreliability measures of interest. 展开更多
关键词 BALKING BREAKDOWNS retrial queue two-phase service.
原文传递
上一页 1 下一页 到第
使用帮助 返回顶部