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101.
Ram Mudambi 《Industry and innovation》2012,19(1):1-21
Research on the geographic clustering of economic activity dates back to the early twentieth century. It is recognized that in spite of advances in transportation and communications, clustering remains most critical, and is consequently prevalent, in knowledge-intensive fields. Multinational enterprises (MNEs) that increasingly base their value creation and competitive advantage on knowledge-intensive activities are key participants in clusters, affecting both the nature and intertemporal evolution of local innovative activities. However, the role of MNEs in clusters remains under-researched. This paper traces the origins of research on geographic clusters, identifies the seminal contributions focusing on the role of MNEs, discusses potential problems inherent to this area of inquiry and develops an organizing framework for new research. 相似文献
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103.
The research domain of Multimedia Content Analysis (MMCA) considers all aspects of the automated extraction of knowledge from multimedia data. High-performance computing techniques are necessary to satisfy the ever increasing computational demands of MMCA applications. The introduction of Graphics Processing Units (GPUs) in modern cluster systems presents application developers with a challenge. While GPUs are well known to be capable of providing significant performance improvements, the programming complexity vastly increases. To this end, we have extended a user transparent parallel programming model for MMCA, named Parallel-Horus, to allow the execution of compute intensive operations on the GPUs present in the cluster. The most important class of operations in the MMCA domain are convolutions, which are typically responsible for a large fraction of the execution time. Existing optimization approaches for CUDA kernels in general as well as those specific to convolution operations are too limited in both performance and flexibility. In this paper, we present a new optimization approach, called adaptive tiling, to implement a highly efficient, yet flexible, library-based convolution operation for modern GPUs. To the best of our knowledge, our implementation is the most optimized and best performing implementation of 2D convolution in the spatial domain available to date. 相似文献
104.
Elizabeth A. Mack 《Papers in Regional Science》2014,93(1):3-29
This study evaluates the relationship between the spatial distribution of broadband providers and the presence of knowledge intensive firm clusters in US counties. Results highlight this relationship is heterogeneous and localized. In some places, broadband appears to be an essential link that enables knowledge firms to strategically locate in lower cost counties and in close proximity to major knowledge centres. In other places, the availability of broadband Internet connections are unable the negative externalities associated with locations in more remote areas of the country. From a policy perspective, this suggests that broadband should be viewed as a key component, but not the only component, of comprehensive local economic development plans. 相似文献
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106.
针对低压微电网在不同接地方式下运行的安全稳定性问题,提出了典型微网的接地方案。基于国家/行业标准,结合理论分析和实践应用比较,对低压微电网主变压器接地方式、微源接地方式、低压微网系统接地方式分别进行了比选,给出了不同情况下各种接地方式的适用条件和场合。结合微网系统特点得出了适用低压微网的接地方案,即主变优选用D,yn11连接组别,中性点有效接地,微源并网时中性点不接地,孤岛时仅主电源中性点接地。整个微网系统采用TN-S/TN-C-S与TT混合接地方式,微源和三相用户采用四级开关,单相用户采用两级开关。 相似文献
107.
This article presents an intelligent strategy to achieve appropriate real power sharing among distributed generators in a microgrid. The presented strategy employs two droop-based control methods and automatically adjusts their parameters. The first method is unit power control, which has specifications similar to the conventional droop method, and the second is feeder flow control, showing significant characteristics in both grid-connected and islanded modes operation of a microgrid. A combination of unit power control and feeder flow control methods is used for a multi-distributed generator microgrid. The microgrid operation mode passes from the grid-connected to the islanded through a transition. A new evolutionary algorithm called cuckoo search is employed to coordinate the power management of distributed generators within an on-line droop tuning. In comparison to the predecessor evolutionary algorithms, the cuckoo search algorithm represents more effective random processes with fewer parameters. Using the proposed control strategy, while the distributed generators contribute to load demand provision based on their rated powers, their powers are optimized in terms of overshoot and settling time. Digital time-domain simulation studies are carried out in the MATLAB/SIMULINK (The MathWorks, Natick, Massachusetts, USA) environment to verify the performance of the proposed control system. 相似文献
108.
109.
针对微网友好接入对高性能并网接口的需求,提出了一种新型的柔性变流器并网接口。为了使该并网接口有效地工作,给出了基于瞬时无功功率理论的电流检测方法,深入研究了柔性变流器并网接口直流侧电压和定无功功率控制方法;此外,基于加权电流反馈的思想,提出了谐波和不对称电流综合补偿的滞环电流控制方法。最后应用Matlab/Simulink进行了仿真,仿真结果进一步验证了使用所提并网接口与控制策略实现微网友好接入的有效性和可行性。 相似文献
110.
基于多状态建模的独立型微网优化配置 总被引:1,自引:0,他引:1
针对风速、光照强度和负荷不确定性对独立型微网优化配置的影响,应用三者的概率密度函数对每个月份构造典型日,利用多状态系统理论对典型日各个时刻风光出力和负荷进行了多状态建模。以经济性和环保性为目标,建立了基于多状态建模的独立型微网多目标优化配置模型,并采用改进的非劣排序遗传算法(NAGA-Ⅱ)对模型进行了求解。最后,针对某一算例分别使用所提出的优化配置方法和已有的基于确定历史场景的优化配置方法进行了仿真计算,通过对仿真结果在若干随机场景下的比较分析,验证了所提优化配置模型和方法的合理性和有效性。 相似文献