超燃冲压发动机性能的准二维计算方法

为了能在双模态超燃冲压发动机流道方案初步论证中提供一种较快速的发动机性能计算方法,在二维N-S方程基础上,引入一维完全燃烧计算方法,提出了预估超燃冲压发动机性能的准二维计算方法。该方法能够计入激波、边界层分离等对发动机性能的影响,可在较短时间计算出整机推力、比冲性能和沿程热力学参数。通过对自由射流发动机计算,验证了此方法。并在此基础上,初步分析了燃料喷注位置和流道构型对发动机性能的影响。      

H2O/CO2污染对煤油燃料超声速燃烧影响数值研究

在纯净空气与H₂O/ CO₂污染空气来流对比试验结果基础上,采用数值计算方法和化学动力学方法,研究了H₂O和CO₂污染组分对煤油燃料超声速燃烧的影响,获得了试验手段难以得到的燃烧室流场参数和性能数据。完成了相应的煤油燃料超声速燃烧室二维数值计算,其中匹配了进口总温、总压、马赫数、氧气摩尔分数和工作当量油气比。将数值计算结果与相应试验测量值进行了对比分析,并结合燃烧室流场数据、性能参数分析了H₂O和CO₂污染的动力学影响、以及对燃烧室性能的影响。研究表明:(1)数值计算结果与实验测量值总体上吻合,两种手段均体现了纯净空气来流时不同煤油当量油气比的燃烧室性能,并反映了一致的“污染效应”影响趋势;(2) H₂O污染、H₂O+ CO₂污染的存在降低了煤油燃料超声速燃烧室性能,体现在燃烧诱导压升、燃烧效率、流向冲量增量的下降,而且随着污染组分含量的增加,燃烧室性能下降越加显著。      

超燃冲压发动机凹腔内补氧的强化点火试验

在超燃冲压发动机扩张型燃烧室中,对凹腔内局部补氧的点火强化方法进行了试验研究。采用高速摄影手段研究了不同的补氧方式对凹腔内火焰分布特征和燃烧强度的影响,并针对并联双凹腔燃烧室构型,研究了在单侧凹腔补氧条件下向异侧凹腔的火焰传播过程。试验结果表明,采用凹腔内补氧的方式能调节凹腔内的燃料浓度分布、改善凹腔内的燃烧过程,控制燃烧放热强度;稳态燃烧情况下,观察到凹腔驻留火焰的两种存在特征,分别表现为:由回流区热量反馈机制作用下的凹腔局部驻留火焰和燃烧室全局压力反馈影响下的凹腔剪切层火焰。只有在单侧凹腔燃烧建立了全局压力反馈的条件下才能实现凹腔火焰的异侧传播。      

冲压发动机C/SiC喷管承压失效研究

新型三维编织碳/碳化硅复合材料存在较强的各向异性,而各个方向的性能数据积累不足,复合材料的强度计算方法尚不完善,为了发现新型三维编织碳/碳化硅复合材料在冲压发动机喷管中应用可能遇到的问题,并找到相应地解决措施,开展了这种复合材料应用于冲压发动机喷管的承压强度计算和承压实验研究。对承压实验中出现的低压破坏情况进行了分析,分析了低压破裂的原因,提出了改进措施。分析结果表明:C/SiC喷管喉部密度较低,导致强度较低,承载能力下降,是首次强度验证实验过程中该局部破坏的原因;为提高喷管强度,需要通过其形状设计并控制沉积流场,保证其喉部的沉积密度达到1.9g/cm³以上。对改进后的喷管进行了实验验证,实验结果与计算结果基本一致,满足要求。因此,在实际应用中应对喷管喉部和纵向密度的分布进行工业CT无损检测,确保喷管密度的分布均匀。      

环境规制对产业区际转移的影响--基于污染密集型产业的研究

文章在区分正式环境规制与非正式环境规制的基础上,分析了环境规制影响产业区际转移的理论机制,进而选取2003－2013年中国30个省份的面板数据进行了实证研究,并运用门槛回归模型研究了环境规制影响产业转移的门槛特征与空间异质性。研究结果表明,正式环境规制对污染密集型产业的区际转移有显著的影响,且随着正式环境规制强度的提高,会对污染密集型产业区际转移产生先抑制后促进的作用,验证了两者之间存在门槛特征和空间异质性。非正式环境规制整体上推动了污染密集型产业的区际转移,显现了非正式规制的经济效应。     

外商直接投资的退出效应与绩效检验

文章摒弃了“从FDI进入研究东道国溢出效应”的传统思路,强调FDI退出对东道国的受益（贡献）情况。文章进一步利用2008-2013年间两位码分类的中国工业动态面板数据,估计了FDI退出对工业全要素生产率的效应。研究发现：FDI退出对中国工业绩效的影响呈现出显著的差异性,以追求研发创新和高端人才优势为战略动机的探索型FDI退出抑制了中国工业绩效的改善,而以国际分工和产业转移为投资目标的利用型FDI退出则有利于整体工业水平的提升,其对工业绩效改善的贡献呈递增之势。     

An Empirical Investigation of Dual Network Effects in Innovation Project Development

As innovation project developers advance their knowledge through more project experience, cross-project learning is likely to enhance project performance. Past research has demonstrated positive contributions of developer networking at the macro (project) level. However, the network effects at the micro (project property) level have not been studied as much. To address this gap, we apply a network model to examine which project properties (e.g., the project's operating system and topic) generate positive or negative network effects in addition to the macro network effect when developers engage in multiple projects. In this dual (developer and property) network model, we theorize that positive network effects take place because of cross-project learning and knowledge exchange, whereas negative network effects can also occur due to time constraints and cognitive overloading. In addition to such dual network effects, we also consider such project success predictors as spatial and temporal reach opportunities for project users (scope of translations and project age) and human resources availability (developer team size). Our empirical application using open source software (OSS) data demonstrates that the presented model can effectively integrate both the dual network effects and non-network variables as factors influencing the commercial success of OSS projects.     

技术性贸易壁垒对出口国的经济效应综合分析

在国际社会不断呼吁贸易自由化的今天,技术性贸易壁垒成为了阻碍贸易的一项重要措施。一般的观点认为,技术性贸易壁垒给出口国带来的只是巨大的负效应,然而笔者以为,这只是一种短期的影响,而从中长期来说,如果处理得当,可能还会存在正的效应。文章分短期和中长期两个阶段,用理论和实证相结合的方法,分析和探讨了技术性贸易壁垒对出口国带来的贸易效应、社会福利效应和产业效应。     

空气隙对矩形微带天线性能的影响

论述了通过引入空气隙来改变矩形微带天线性能。首先，根据修改的微带天线的腔模理论，利用电磁场理论推导了具有空气隙的矩形微带天线的等效介电常数和谐振频率的理论计算公式。然后，考虑了边缘场的影响，引入了有效介电常数，对谐振频率的理论公式进行了修正。同时，应用等效原理和镜像原理推导出辐射方向图。最后，对于空气隙高度为不同数值的情况给出矩形微带天线的谐振频率和辐射方向图的数值结果，与文献实测结果很吻合。     

Performance Heterogeneity in Latin America: An Investigation into the Transient Effects of Country of Origin

The heterogeneity of firm performance has been studied from the perspective of factors, including the firm effect, the industry effect, and the country effect. This study emphasizes the importance of country transient effects in light of the volatility present in Latin American countries. Variance decomposition was carried out for the economic and operational performance of five countries in the period from 1998 to 2007. The results show that country effects matter for Latin America, its transient effects increase in periods of higher turbulence, and have a greater effect on a firms' economic performance than on its operational performance.     

The Effect of Flexibility on Export Venture Performance

Abstract

Although both international marketing theorists and practitioners have been expounding the importance of flexibility little or no research has been done to examine the effect of flexibility on export venture performance. Most of the research to date was directed towards examining the effect of flexibility on performance in the domestic context. Moreover, the studies in the literature also gave exclusive attention to the performance-enhancing effect of flexibility and ignored the moderating effects of organisational and environmental contingencies on the flexibility-performance relationship. This paper will present the results of a study that assessed the effect of flexibility on export performance.

The findings support the proposition that flexibility is significantly related to export performance but that environmental dynamism, legal forms of business ownership, international experience, control mechanism, and exporter-distributor cooperation have a moderating effect on the relationships between flexibility and export venture performance. The study also found that firms that were challenged by intense competitive rivalries, spent a lot of time and effort on monitoring foreign marketing activities, and had substantial cooperation with overseas distributors were more flexible in their manufacturing, marketing, financial, and organizational activities.     

外国直接投资对国内资本“挤出”效应的实证研究——从资本形成角度看FDI对我国经济增长的影响

FDI在直接增加东道国资本流量的同时,还会对国内资本产生一定的“挤出”或“挤入”效应。因此,从资本形成角度看,FDI对东道国经济增长的影响是不确定的,其取决于FDI最终“挤入”还是“挤出”了国内资本。本文利用我国1985年至2003年的相关数据,通过经济计量模型对此进行了实证研究,结果表明,FDI虽然对我国国内资本的“挤出”效应和“挤入”效应并存,但总体上有一个“净挤入”的效果,因此,从资本形成的角度来看,FDI促进了我国的经济增长。本文建议我国应继续扩大利用FDI,并对抑制FDI对国内资本的挤出效应提出了相应的建议。