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AIR is the additive increase rate, is the multiplicative decrease factor, and is the threshold for packet loss ratio.


For run B, the decrease factor r was much smaller than for run A.


This decrease factor is often greater than onehalf, and therefore an application using parallel connections is considered an aggressive sender.


This function decreases monotonically since the rate decrease factor is always positive.




 As increasing the embedded objects and the database searching tasks in Web Pages, there is larger difference among the loads of different server in a cluster system, which becomes more difficult for a heterogeneous Web server cluster to achieve high performance. In this paper, the authors present a dynamic load balancing algorithm MDC(Multiplicative Decrease in Critical area). For each of the servers in the cluster, the algorithm can more accurately evaluate the current load state by using the Equivalent Load... As increasing the embedded objects and the database searching tasks in Web Pages, there is larger difference among the loads of different server in a cluster system, which becomes more difficult for a heterogeneous Web server cluster to achieve high performance. In this paper, the authors present a dynamic load balancing algorithm MDC(Multiplicative Decrease in Critical area). For each of the servers in the cluster, the algorithm can more accurately evaluate the current load state by using the Equivalent Load Alternant and can more efficiently restrain the occurring of the reject service phenomenon by using a special MDC operator. Besides, the authors apply a method of random distributing base probability to assign each request to an appropriate server in terms of their weight. All the parameters that will be used in the algorithm can be acquired by simulated test. The authors also provide improved approximation results of above algorithm for the case where documents consist of relatively many embedded objects or database searches and lots of requests arrived the dispatcher synchronously.  针对Web服务器集群系统中负载动态变化特性,提出了一种临界加速递减动态请求负载分配算法.通过负载权值的等效变换更准确地反映集群中单台服务器的当前负载状态;通过临界递减因子来有效抑制服务器可能出现的“拒绝访问”现象;通过随机概率分配方式替代固定转发分配方式,使访问负载的分布更均匀;通过实际测试获取算法中所需的计算参数,使配置操作更为简单.实验结果表明,该算法对较大负载的文件集的大密度访问情况效果明显.  System reliability was always neglected by Equal interval Preventive Maintenance(PM) models,meanwhile longtime expected interval PM models usually couldn't satisfy the system maintenance need in a finite time horizon.From this perspective,a sequential imperfect PM model was proposed with the consideration of optimized maintenance schedule in a finite time horizon.A hybrid hazard rate recursion rule was developed based on the concept of age reduction factor and hazard rate increase factor to predict the evolution... System reliability was always neglected by Equal interval Preventive Maintenance(PM) models,meanwhile longtime expected interval PM models usually couldn't satisfy the system maintenance need in a finite time horizon.From this perspective,a sequential imperfect PM model was proposed with the consideration of optimized maintenance schedule in a finite time horizon.A hybrid hazard rate recursion rule was developed based on the concept of age reduction factor and hazard rate increase factor to predict the evolution of the system reliability in different maintenance phases.The optimized PM schedule was deduced by minimizing the maintenance cost in the finite time horizon with the assumption that the mean cost per unit time for PM was a function of the reliability threshold R and the improvement factors.Simulation results showed that this reliability centered PM model made a decrease of the PM interval and it could provide maintenance decision support for job shop scheduling.  为了克服等周期维护模型忽略设备可靠性要求,以及长期运行期望维护周期模型忽略设备特定阶段维护需求的缺点,通过引入基于役龄递减因子和故障率递增因子的混合式故障率演化规则,建立了有限区间内基于设备可靠性的顺序预防性维护优化模型,并以威布尔分布为例,利用仿真方法对其进行了优化。仿真结果显示,该模型可使设备的维护周期呈递减之势,反映了设备在某一特定阶段的可靠性需求。  Conventional preventive maintenance(PM) often holds a same time interval T and the ageT policy gives unavoidably decreasing reliabilities at the PM actions for the degradation system with imperfect maintenance effect.This study developed a reliabilitycentered sequential preventive maintenance model for a system subject to the degradation due to imperfect maintenance,which is more practical in engineering.It is assumed that whenever the system reliability reaches the threshold R,an imperfect PM action should... Conventional preventive maintenance(PM) often holds a same time interval T and the ageT policy gives unavoidably decreasing reliabilities at the PM actions for the degradation system with imperfect maintenance effect.This study developed a reliabilitycentered sequential preventive maintenance model for a system subject to the degradation due to imperfect maintenance,which is more practical in engineering.It is assumed that whenever the system reliability reaches the threshold R,an imperfect PM action should be performed on the system.In order to predict the evolution of the system reliability in different maintenance cycle,a hybrid hazard rate recursion method was proposed based on the concept of age reduction factor and hazard rate increase factor.The optimal PM schedule was deduced by minimizing the maintenance cost rate in the life cycle of the system.The optimization process is based on the Monte Carlo simulation.The simulation results show that this maintenance model is practical and it can provide decision support for maintenance scheduling.  等周期预防性维护策略不可避免地会使设备的可靠性随着役龄及维护次数的增加而逐步降低.为此,结合役龄递减因子和故障率递增因子的优点,通过引入基于两类调整因子的混合式故障率演化规则,建立了基于设备可靠性的顺序预防性维护优化模型,并以威布尔分布为例,利用蒙特卡罗仿真方法对其进行了优化.结果显示,该模型符合设备的实际维护情况,可为设备的维护决策提供有力的支持.   << 更多相关文摘 
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