开关电源的分布式并联均流技术概述

随着大功率和分布式开关电源需求的不断提高,分布式并联均流技术已成为电力电子研究的一个热门问题和发展方向。本文综合阐述了开关电源并联均流技术的应用背景、基本原理、常用方法及其发展趋势。     

Air transport and economic growth: a review of the impact mechanism and causal relationships

ABSTRACT

The impacts of air transport on the economy arise both directly, via activity in the aviation sector; and indirectly, via increased spending and wider economic benefits associated with improved access to resources, markets, technology and economic mass. Economic activity, in turn, supports and generates demand for air transport. Despite its potential importance, the reciprocal nature of the causal relationship between air transport and economic performance has remained somewhat understudied. This paper provides a synthesis review of the channels the aviation sector interacts with regional economy. The review focuses on quantitative studies that contribute to the state-of-the-art understandings of the causality. We find that the reciprocal causal relationship is more likely to prevail in less developed economies. For more developed economies, only one direction of the causality is recognised, which runs from air transport to economic growth. Especially substantial is the effect of airline enplanement on service-related employment. The reverse direction of the relationship is, however, not as significant as believed in a causal sense within the developed world. Therefore, cautions need to be taken when applying income elasticities (such as the elasticity of air passenger demand with respect to GDP) in air travel demand forecasting, which implicitly assumes that economic growth causally leads to air traffic increment. Based on the fundamental links between air transport and economic growth, some typical imperfections and inefficiencies in aviation markets are discussed and promising avenues for future research are proposed.     

预制拼装桥墩体系及其抗震性能研究进展

预制拼装桥墩体系(Pre-fabricated Concrete PierSystem, PCP)抗震性能是影响其推广、应用的关键。为加快PCP在中、高烈度等复杂恶劣工程环境中的设计、施工与建造，首先综述了PCP节点连接的接缝形式、连接构造类型及典型工程示例，指出了PCP常用3种接缝形式和6种连接构造力学性能的研究现状及其优缺点；其次，系统地梳理了PCP抗震性能的研究进展，分析了不同连接条件下PCP的抗震性能，明晰了现有PCP抗震性能研究的不足及未来研究方向；最后，详细地论述了PCP抗震性能提升方法的研究前沿，探究了耗能延性构造的设置、高性能材料的应用、新型装配式节点构造设计以及新型混合预制桥墩体系的提出等PCP抗震性能提升方法的优缺点和发展方向。结果表明：通过对装配式节点的合理设计以及薄弱区域的预处理，预制拼装桥墩体系的抗震性能能够达到“等同现浇”的设计原则。然而PCP在复杂恶劣工程环境中的推广应用仍面临以下关键问题：PCP既有节点连接方式、体系和改进措施的抗震性能研究成果亟需归纳；新型节点连接方式、新体系和新型改进措施亟待提出，相关抗震性能有待验证；既有和新型PCP抗震性能的理论分析及抗震设计方法尚需完善；适用于复杂恶劣环境的预制拼装桥墩设计、施工标准亟需制定。     

The built environment and travel behavior in urban China: A literature review

Interests in studying of the built environment impacts on travel behavior have proliferated from North America to other parts of the world including China. Until very recently, there has been very little research into travel behavior in China. However, during the last decade, there has been a fast growing interest in studying the built environment and travel behavior in Chinese cities, perhaps motivated by China’s unprecedented urbanization and rapid urban transport development. Case studies from China provide new insights into the impacts of built environment on travel behavior that can help to enrich existing scholarship. However, currently there is a generally poor understanding of the role played by Chinese research and how it has enriched the international literature. This paper aims to fill this gap by reviewing studies in and outside China by both Chinese and non-Chinese scholars. The focus is on the contribution of these studies to the international literature. We identify four areas of contribution: how the built environment has been developed and its implications for travel behavior; the importance of housing sources in defining residential built environment and explaining travel behavior; the unique Danwei (or work unit) perspective on jobs-housing relationships and commuting behavior; and the importance of neighborhood types in explaining travel behavior in Chinese cities. The findings from this review should be relevant for researchers interested in developing future studies that will further advance geographic knowledge of the built environment and travel behavior, specifically in China and with broader global contexts.     

竞争中二度价格歧视研究

运用博弈论知识，采用定量分析方法，系统地讨论了二度价格歧视条件下竞争厂商的利润最大化条件．首先讨论了二度价格歧视利润最大化条件，然后将此条件加以推广．接着分别研究了线性需求函数和非线性需求函数情形下的利润最大化问题．针对上述问题，均给出了严谨的理论分析和有关计算公式．     

政府干预与政策竞争:欧盟阻止船舶移籍的经验及其对中国的启示

从政策选择上对如何阻止长期以来困扰国际海运业的船舶移籍问题进行探讨，基于对国内外船舶移籍现状及其发展过程的分析，深入分析了欧盟成员国在阻止船舶移籍方面所采取的政府干预与政策竞争策略，指出了中国改善船舶移籍状况的政策取向。     

国际航运投资决策研究综述

分析了30年来国内外国际航运投资决策问题，认为对国际航运传统的或经典的投资决策方法的研究比较成熟，将定性评价转化为定量评价的投资决策方法的研究有所进行，但基于期权的投资决策方法的研究尚未进行。为此，阐述了这一领域未来的研究重点与前沿问题。     

企业文化建设如何迎接国际化竞争的挑战

从企业文化的内涵入手,结合部分企业成功的经验,对现代企业如何加强企业文化建设,提高企业的核心竞争力,更好的迎接国际化竞争提出了建议和对策。     

关注当代问题:新世纪以来国内科学史研究专题回顾——以五种重要刊物为主

本文选择国内最重要的五种与科学史直接有关的刊物，披阅其上自2000年第1期以来的所有文章，择其论题直接关注当代问题者，归纳为六个方面：中医问题、现代中国科学体制及政策、科学传播、科学主义、李约瑟问题、科学史理论。笔者结合此六方面近年在国内的争议及某些文化背景，缕述数十篇相关论文要旨，给出一个新世纪以来国内科学史研究之专题回顾。由此亦可看出近年国内科学技术史研究者关注方向之演变。     

资源均衡优化的原理

本文应用网络计划技术,论述了资源均衡优化的原理,并给出了优化的具体方法和步骤.文中引用方差σ~2来度量资源均衡的程度,把网络图的优化转换为求σ~2,并使其逐渐变小来获得最优方案.