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91.
利用BASS模型对国内博客的扩散模式进行了探讨。梳理了博客的有关概念,简单介绍了BASS模型及其发展,利用博客规模统计数确定模型参数,并进行拟合检验。在此基础上,对中国未来博客规模的发展进行了预测。 相似文献
92.
Accurate aircraft trajectory predictions are necessary to compute exact traffic demand figures, which are crucial for an efficient and effective air traffic flow and capacity management. At present, the uncertainty of the take-off time is one of the major contributions to the loss of trajectory predictability. In the EUROCONTROL Maastricht Upper Area Control Centre, the predicted take-off time for each individual flight relies on the information received from the Enhanced Traffic Flow Management System. However, aircraft do not always take-off at the times reported by this system due to several factors, which effects and interactions are too complex to be expressed with hard-coded rules. Previous work proposed a machine learning model that, based on historical data, was able to predict the take-off time of individual flights from a set of input features that effectively captures some of these elements. The model demonstrated to reduce by 30% the take-off time prediction errors of the current system one hour before the time that flight is scheduled to depart from the parking position. This paper presents an extension of the model, which overcomes this look-ahead time constraint and allows to improve take-off time predictions as early as the initial flight plan is received. In addition, a subset of the original set of input features has been meticulously selected to facilitate the implementation of the solution in an operational air traffic flow and capacity management system, while minimising the loss of predictive power. Finally, the importance and interactions of the input features are thoroughly analysed with additive feature attribution methods. 相似文献
93.
94.
Regular business survey data are published as percentages of firms predicting higher, equal or lower values of some reference variable. Time series of such percentages do not fit production data too well. Univariate models often produce forecasts which are just as accurarate. Still, surveys contain anticipative judgement which, when combined with univariate modeling and proper filtering, may produce a good indicator for business cycle turning points. The way survey data are transformed so as to fit statistics on production seems not to be of much importance. A case study of the Finnish forest industry is offered as an example. 相似文献
95.
We study the problem of forecasting volatility for the multifractal random walk model. In order to avoid the ill‐posed problem of estimating the correlation length T of the model, we introduce a limiting object defined in a quotient space; formally, this object is an infinite range log volatility. For this object and the nonlimiting object, we obtain precise prediction formulas and we apply them to the problem of forecasting volatility and pricing options with the MRW model in the absence of a reliable estimate of σ and T. 相似文献
96.
水泥土搅拌桩复合地基承载力的灰色预测 总被引：3，自引：0，他引：3
详细阐述灰色模型的建立及调整过程,利用复合地基沉降实测数据,根据灰色系统理论,建立(1,1)模型,可模拟复合地基的P~s曲线,预测地基沉降的发展趋势,分析水泥土搅拌桩复合地基的承载性能。 相似文献
97.
根据77处雨量站1956-2000年降水量同步系列资料,对唐山市降水变化的周期性、阶段性、不稳定性、降水倾向等特征进行分析,并利用灰色预测模型,预测了降水变化趋势。 相似文献
98.
《American journal of agricultural economics》2001,83(3):785-802
Books reviewed:
Singer, S. Fred. Hot Talk Cold Science: Global Warming's Unfinished Debate
Hogg, Dominic, ed. Technological Change in Agriculture: Locking in to Genetic Uniformity
Ingersent, Ken A., and A. J. Rayner. Agricultural Policy in Western Europe and the United States
Smil, Vaclav. Feeding the World: A Challenge for the Twenty-First Century
Yang, Yongzheng and Tian, Weiming, eds. China's Agriculture at the Crossroad
Lal, Deepak. Unintended Consequences: The Impact of Factor Endowments, Culture, and Politics on Long-Run Economic Performance
Opschoor, J(Hans). B., Kenneth Button, and Peter Nijkamp, eds. Environmental Economics and Development
Hamilton, James T., and W. Kip Viscusi. Calculating Risks? The Spatial and Political Dimensions of Hazardous Waste Policy 相似文献
Singer, S. Fred. Hot Talk Cold Science: Global Warming's Unfinished Debate
Hogg, Dominic, ed. Technological Change in Agriculture: Locking in to Genetic Uniformity
Ingersent, Ken A., and A. J. Rayner. Agricultural Policy in Western Europe and the United States
Smil, Vaclav. Feeding the World: A Challenge for the Twenty-First Century
Yang, Yongzheng and Tian, Weiming, eds. China's Agriculture at the Crossroad
Lal, Deepak. Unintended Consequences: The Impact of Factor Endowments, Culture, and Politics on Long-Run Economic Performance
Opschoor, J(Hans). B., Kenneth Button, and Peter Nijkamp, eds. Environmental Economics and Development
Hamilton, James T., and W. Kip Viscusi. Calculating Risks? The Spatial and Political Dimensions of Hazardous Waste Policy 相似文献
99.
100.
The current financial reporting of cash flows from operations does not present individual sources of these cash flows, making it difficult for investors to assess a firm’s future performance. I hand-collect individual cash flows from unusual operations and examine their characteristics for predicting future cash flows. The results show that the unusual individual cash flow items contain a significant incremental predictive ability for future cash flows. Additional return tests show that stock prices fail to fully reflect their predictive value, suggesting that the current reporting practice may mislead investor perceptions of a firm’s cash generating ability and investors could benefit from a more explicit presentation of cash flows from operations. 相似文献