Fault Tree Reliability Analysis for Passive Medium Pressure Safety Injection System in Nuclear Power Plant

Modern nuclear power plants, both newly designed generation 3 and existing generation 2 reactors, make use of passive safety systems for significant and measurable improvements in safety and reliability. Medium Pressure Safety Injection System (MP-SIS) in Tianwan Nuclear Power Plant is a typical and very important nuclear safety passive system. This paper discusses the reliability of MP-SIS on the basis of Fault Tree Analysis (FTA) with unavailability and Minimal Cut Set (MCS) calculated as two important indicators. The result illustrates that the passive MP-Safety Injection Tank barely contributes to the system’s unavailability and human interactions with Manual Valves and Motor Operated Valves have great negative impact on the reliability.

Statistics and Analysis on Reliability of HVDC Transmission Systems of SGCC

Reliability level of HVDC power transmission systems becomes an important factor impacting the entire power grid.The author analyzes the reliability of HVDC power transmission systems owned by SGCC since 2003 in respect of forced outage times,forced energy unavailability,scheduled energy unavailability and energy utilization eff iciency.The results show that the reliability level of HVDC power transmission systems owned by SGCC is improving.By analyzing different reliability indices of HVDC power transmission system,the maximum asset benef its of power grid can be achieved through building a scientif ic and reasonable reliability evaluation system.

A condition based power system operational risk assessment method

In this paper, some key problems about operational risk assessment are well analyzed. The time-varying and condition-based component outage model was proposed, which can reflect the changes of weather and other operation conditions. A rank enumeration based system state selection method was used to perform risk assessment. Then, the problem of operational risk index was also addressed. In the last part of paper, two groups of numeral tests were presented. The first one showed that the risk assessment results using component instantaneous unavailability, are quite different from the results using steady unavailability, and proves that component outage model with instantaneous unavailability should be used for operational risk assessment; The other one shows that the proposed time-varying component outage model can reflect the operation conditions＇ influences on the risk assessment results.

An Alternative-Service Recommending Algorithm Based on Semantic Similarity

With the development of the Internet of Things(Io T), people's lives have become increasingly convenient. It is desirable for smart home(SH) systems to integrate and leverage the enormous information available from IoT. Information can be analyzed to learn user intentions and automatically provide the appropriate services. However, existing service recommendation models typically do not consider the services that are unavailable in a user's living environment. In order to address this problem, we propose a series of semantic models for SH devices. These semantic models can be used to infer user intentions. Based on the models, we proposed a service recommendation probability model and an alternative-service recommending algorithm. The algorithm is devoted to providing appropriate alternative services when the desired service is unavailable. The algorithm has been implemented and achieves accuracy higher than traditional Hidden Markov Model(HMM). The maximum accuracy achieved is 68.3%.

手机碰到病毒咋办?

病毒对手机的攻击不外乎三个层次:第一,通过攻击WAP服务器使WAP手机无法接收到正常信息。第二,通过攻击、控制“网关”,向手机用户发送大量垃圾信息。第三,直接对手机本身进行攻击,有针对性地对其操作系统和运行程序进行攻击,使手机无法提供服务。下面介绍一些对付手机病毒的方法。

RELIABILITY INDICES OF DISCRETE-TIME Geo^X/G/1 QUEUEING SYSTEM WITH UNRELIABLE SERVICE STATION AND MULTIPLE ADAPTIVE DELAYED VACATIONS

This paper considers the discrete-time GeoX/G/1 queueing model with unreliable service station and multiple adaptive delayed vacations from the perspective of reliability research. Following problems will be discussed： 1） The probability that the server is in a ＂generalized busy period＂ at time n; 2） The probability that the service station is in failure at time n, i.e., the transient unavailability of the service station, and the steady state unavailability of the service station; 3） The expected number of service station failures during the time interval （0, hi, and the steady state failure frequency of the service station; 4） The expected number of service station breakdowns in a server＇s ＂generalized busy period＂. Finally, the authors demonstrate that some common discrete-time queueing models with unreliable service station are special cases of the model discussed in this paper.

Some Reliability Problems Arising in the M^x/G(M/G)/1 Repairable Queueing System with Single Delay Vacation

On the basis of Ref.\, the M x/G(M/G)/1 repairable queueing system with single delay vacation is discussed again. The following reliability problems of the service station are studied: (a) The probability that it fails at time t , i.e. its unavailability; (b) The expected failure number during the time interval (0,t\];; (c) The expected failure number during the ″server busy period″; (d) The expected downtime during the time interval (0,t\]. Some reliability results of the service station are obtained. These results would be interest to reliability analysts.

Heuristics for the Identical Machine Scheduling Problem with Preventive Maintenances

In this paper, two mixed integer programming models integrating production scheduling and preventive maintenances are proposed to derive the optimal solutions for the identical machine scheduling problem with unavailability constraints. In the first model, the maintenance activities are performed periodically and the objective is to minimize the makespan. In the second model, the maintenance activities are flexible and the machines' continuous working time cannot exceed a maximum allowed time T; the objective is to minimize the total completion time of jobs. For the first problem, we propose a heuristic longest batch time(LBT) and prove that the worst case error bound of LBT is 2. For the second problem, we develop a heuristic modified smallest processing time(MSPT) based on some properties of the optimal solutions. Computational experiments show that both of the heuristics are effective and efficient compared with the results obtained by CPLEX and the other algorithms.

Makespan Minimization in Two-Machine Flow-Shop Scheduling under No-wait and Deterministic Unavailable Interval Constraints

This paper systematically studies the two machine flow-shop scheduling problems with no-wait and deterministic unavailable interval constraints.To minimize the makespan,three integer programming mathematical models are formulated for two-machine flow-shop with no-wait constraint,two-machine flow-shop with resumable unavailable interval constraint,and two-machine flow-shop with no-wait and non-resumable unavailable interval constraints problems,respectively.The optimal conditions of solv-ing the two-machine flow-shop with no-wait constraint problem by the permutation schedules,the two-machine flow-shop with resumable unavailable interval constraint problem by the Johnson algorithm,and two-machine flow-shop with no-wait and non-resumable unavailable interval constraints problem by the Gilmore and Gomory Algorithm(GGA)are presented,respectively.And the tight worst-case performance bounds of Johnson and GGA algorithms for these problems are also proved to be 2.Several instances are generated to demonstrate the proposed theorems.Based on the experimental results,GGA obtains the optimal solution for the two-machine flow-shop with no-wait constraint problem.Although it cannot reach the optimal solution for the two-machine flow-shop with resumable unavailable interval constraint problem,the optimal gap is 0.18%on average when the number of jobs is 100.Moreover,under some special conditions,it yields the optimal solution for the two-machine flow-shop with no-wait and non-resumable unavailable interval constraints problem.Therefore,GGA is an efficient heuristic to solve these problems.

Belisana cas, a new spider species from Xishuangbanna Tropical Botanical Garden, China(Araneae, Pholcidae)

A new species, Belisana cas sp. nov. is reported based on description of B. ＂xtbg＂. B. ＂xtbg＂ mentioned by Yao et al.（2018） is unavailable after the ICZN（article 11.3）.