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91.
本文针对传统直流电机的模型建立问题,基于曲线拟合技术,提出了简洁有效的参数辨识方法。由于实际的直流电机模型正反向参数差别很大,因此本建模方法中对直流电机的正向模型和反向模型分别对待。实验结果验证了所建立的直流电机模型的优越性能。 相似文献
92.
扭曲叶片的绘型常采用的单锥面展开法 ,因是基于局部相似 ,所以 ,存在误差 ,无法分析 ,难以编程。笔者在有关水泵问题研究中 ,对扭曲叶片绘型的单锥面展开法进行了改进 ,给出利用非等变角对数螺旋线进行叶片绘型的新方法。这种方法能够很好地控制β角的变化规律 ,并能对误差进行分析和修正 ,便于编程计算 ,易于操作 ,在水泵设计中有广泛的实用价值。 相似文献
93.
基于可持续发展的国家物质流分析 总被引:24,自引:0,他引:24
210003本文采用物质流分析方法,研究了1995—2002年中国经济系统的物质输入和输出等相关指标,发现经济系统的物质需求总量和物质输出总量巨大,自然环境的生态压力短期内无法得到缓解;人均物质需求量不高,物质生产力也很低;环境库兹涅茨曲线呈现出倒“U”型,最高点出现在人均收入700美元,然后进入下降通道;技术水平是影响物质需求总量变化的关键因素;出口能源中的煤炭存在巨大隐藏流是导致生态贸易赤字的主要原因。 相似文献
94.
传统企业电子商务转型的价值曲线与收支曲线 总被引:2,自引:0,他引:2
本文阐述了传统企业电子商务转型的必要性,提出并分析了传统企业电子商务转型的价值曲线和收支曲线。 相似文献
95.
George P. Boretos Author Vitae 《Technological Forecasting and Social Change》2007,74(3):331-340
One of the fastest growing technologies of our times is that of mobile phones. In this article we use the assumption that the diffusion of mobile technology, as measured by the number of active mobile accounts, follows the well known S-curve of natural growth in competition systems. The accuracy of the logistic fit is tested against actual data for the whole world, Europe, China and the GSM system. Using the produced models predictions concerning the future of mobile business are deliberated.According to these models active mobile accounts around the globe are expected to grow from 1.7 billion in 2004 to approximately 2 billion in 2008, reaching a peak penetration of 29.2%. Growth barriers, apart from the age of the potential user, are also low income and extreme poverty. Europe, early adopter of mobile technology and leader in active mobile accounts against all other regions in the world, has apparently reached a peak with almost every European, apart from the very young or very old, using a mobile phone. The mobile market in China is anticipated to exceed 500 million active accounts and may increase even further depending on the economic and social reform that is currently under way in that part of the world. GSM will most likely remain the leading mobile technology in the future as it is today.The growth process for the world, Europe, and the GSM system is almost completed and during this stage instabilities may occur before the potential emergence of a new wave of growth. 相似文献
96.
Real interest rates fluctuated a great deal since the 1970s. In the 1980s federal deficits accelerated and their impact on both nominal and real interest rates gained lots of attention. Based on monthly and quarterly data from January 1971 to December 1997 it is found that federal deficits had significant positive effect on the real interest rates: Personal income or consumption are found to have significant positive impact on the real interest rates, whereas expected inflation and money supply are found to have negative impact on the real interest rates. These findings are consistent with the conventional economic theory. 相似文献
97.
Monique Reid Gideon du Rand 《The South African journal of economics. Suid-afrikaanse tydskrif vir ekonomie》2015,83(4):506-526
Mankiw and Reis propose the Sticky Information Phillips Curve (SIPC) as an alternative to the standard New Keynesian Phillips Curve to address empirical shortcomings in the latter. A SIPC for South Africa is estimated, and we find estimates of information updating probability between 0.69 and 0.81, somewhat higher than suggested by methods using micro‐evidence. Because the estimation requires data on expectations of current period inflation and output gap conditional on sequences of earlier period information sets, we provide a detailed analysis of the impact on our estimates of alternative proxies available in South Africa. 相似文献
98.
热交换站中的循环泵是整个采暖系统的核心设备,动力之源,重要性如同一个人的心脏,它的选型正确与否,直接关乎整个采暖系统的运转。本文对作者接触到的几个新建、改建的煤矿热交换站在循环泵选型上存在的误区进行分析,指出解决问题的对策。 相似文献
99.
Erling Røed Larsen 《Journal of Consumer Policy》2006,29(3):301-318
Indirect taxes on transportation activities that pollute can correct externalities and close the gaps between private and social costs. However, policy makers often find such Pigou taxes difficult to implement because of political resistance due to possibly adverse affects on equity. For this reason it is important to assess the distributional aspects of environmental levies. This article estimates properties of the demand for transportation in parametric and non-parametric analyses of Consumer Expenditure Surveys for the United States and finds patterns in the resulting set of Engel curves. Private transportation using air flights and new cars has Engel elasticity above unity while public transportation via mass transit has Engel elasticity below unity. The findings can be interpreted in an important way since they show that a differentiated scheme of environmental taxes on transportation may function progressively. A Pigou scheme with larger taxes on modes of transportation that pollute more appears to coincide with larger levies on luxury modes preferred by richer households. 相似文献
100.
基于“学习曲线”效应的长期质量成本模型 总被引:11,自引:1,他引:11
企业质量管理中存在“学习曲线”效应。在传统质量成本模型中引入累积产量和学习率 ,形成了长期质量成本模型。该模型长期质量成本随累积产量的增加而下降 ,而不同时期的最适宜质量水平随累积产量的增加而提高并趋近于零缺陷水平。该模型的结果与六西格玛管理实践一致 相似文献