内可逆空气制冷机制冷率密度分析与优化

以制冷率密度作为热力性能目标,对内逆空气制冷机进行分析与优化,得到了不同于以制冷率为目标的优化结果,并由数值计算分析了压比和热导率分配对制冷率密度的影响特点。     

Owner’s Risk Allocation and Contractor’s Role Behavior in a Project: A Parallel-mediation Model

Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties.     

无源光网络标准发展及关键技术研究

无源光网络(Passive Optical Network,PON)作为当今接入网的主要技术解决方案,具有带宽使用效率高、传输距离远、抗干扰能力强等特点.通过研究PON技术的发展动态,本文首先归纳了各种PON技术的产生背景和应用特点,整理出各技术间的连接关系及主要标准;其次介绍了PON技术的帧结构,并对带宽、波长、传输模式等PON技术的主要参数进行了汇总;然后将国内外研究热点进行划分,围绕媒体访问控制协议、帧结构、动态带宽分配算法、节能机制等关键技术,阐述了其研究现状及在PON中的重要作用;最后对PON技术的发展趋势进行了展望.     

A synchronized design technique for efficient data distribution

One of the important features of database fragmentation and allocation techniques is the fact that they depend not only on the entries of a database relation, but also on their empirical frequencies of use. Distributed processing is an effective way to improve performance of database systems. However, for a Distributed Database System (DDBS) to function efficiently, fragments of the database need to be allocated carefully at various sites across the relevant communications network. Therefore, fragmentation and proper allocation of fragments across network sites is considered as a key research area in distributed database environment. However, fragments allocation to the most appropriate sites is not an easy task to perform. This paper proposes a synchronized horizontal fragmentation, replication and allocation model that adopts a new approach to horizontally fragment a database relation based on attribute retrieval and update frequency to find an optimal solution for the allocation problem. A heuristic technique to satisfy horizontal fragmentation and allocation using a cost model to minimize the total cost of distribution is developed. Experimental results are consistent with the hypothesis and confirm that the proposed model can efficiently solve dynamic fragmentation and allocation problem in a distributed relational database environment.     

RER： A Replica Efficiency Based Replication Strategy

The technology of replication is often used in the unstructured Peer-to-peer （P2P） systems to allocate more replicas for the hot spots in order for a higher search performance. But the questions that what is the optimal number of copies for each file and what is the practicable approach to the optimal number are seldom answered in the related works. In terms of success rate, this paper firstly investigates the optimal allocation of copies for each file according to query rate with the routing algorithm of random walks. Then a practicable method is proposed to approach the optimal allocation in the unstructured P2P systems. Our results offer a new understanding of replication and our work contributes much to the content distribution in the Internet environment.     

Distributed computer system design: An interactive procedure

This paper presents an overview of an interactive system for the design of a distributed computer system. The system helps the designer in finding the optimal combination of processors of varying power to be located at various nodes of the system. It also helps in finding the optimal allocation of data files or databases. The system allows the designer to trade-off between the conflicting objectives: low investment and operating cost and high availability of data. Reasonable relative weights are assigned to each data file, and design objectives can be assigned priorities. A value added network such as TELENET is assumed for data communication. Also, multiple copies of the data file or database may exist in the system to achieve higher data availability and better response time.     

Upgrading automation for nuclear fuel in-core management: From the symbolic generation of configurations, to the neural adaptation of heuristics

FUELCON is an expert system in nuclear engineering. Its task is optimized refueling-design, which is crucial to keep down operation costs at a plant. FUELCON proposes sets of alternative configurations of fuel-allocation; the fuel is positioned in a grid representing the core of a reactor. The practitioner of in-core fuel management uses FUELCON to generate a reasonably good configuration for the situation at hand. The domain expert, on the other hand, resorts to the system to test heuristics and discover new ones, for the task described above. Expert use involves a manual phase of revising the ruleset, based on performance during previous iterations in the same session. This paper is concerned with a new phase: the design of a neural component to carry out the revision automatically. Such an automated revision considers previous performance of the system and uses it for adaptation and learning better rules. The neural component is based on a particular schema for a symbolic to recurrent-analogue bridge, called NIPPL, and on the reinforcement learning of neural networks for the adaptation.     

油田递减阶段配产方法研究

目前我国大多数油田已进入开发后期,都存在不同程度的产量递减现象。对产量配产进行分析必须对产量构成有清楚的认识。本文将产量分成老井自然产量、老井增产措施产量、新井产能三个部分,引入无量纲量,针对每一部分产量进行相应的分析,这种方法完善了仅凭总产量便对油田产量进行配产的方法,更具有科学性、实用性和可操作性,在油田年度部署中能够发挥积极的作用。     

访问特征驱动的副本存储策略自动生成框架

大规模分布式数据存储是云计算和大数据时代的重要支撑技术.在分布式存储系统中,数据副本如何放置是一个基本问题.然而,现有可实用的算法或忽略应用具体的访问特征而牺牲效率,或拘泥于单一应用而不具备泛化能力.通过建立副本存储策略的统一描述模型以及提取应用的关键访问特征参数,定义出副本存储策略自动生成算法的输出和输入;通过机器学习的方法获得访问特征参数和最优副本存储策略参数之间的一般性关系,从而形成自动生成机制的核心算法.在提高存储系统访问性能及节约能耗等成本的同时,有效降低副本存储策略设计过程中的人工干预程度.     

以太网无源光网络中的QoS研究

在分析以太网无源光网络系统MAC协议的基础上,研究基于QoS的动态带宽分配机制,提出一种新的支持业务的QoS的动态带宽分配算法。该算法采用限制性带宽分配方法和基于优先级的调度方式,基于业务的通信量特征对各类业务预分配传输带宽。仿真结果表明该算法在时延和吞吐量性能上优于现有算法。