It is proposed a class of statistical estimators H = （H1,… ,Hd） for the Hurst parameters H = （H1,… ,Hd） of fractional Brownian field via multi-dimensional wavelet analysis and least squares, which are asymptotic...It is proposed a class of statistical estimators H = （H1,… ,Hd） for the Hurst parameters H = （H1,… ,Hd） of fractional Brownian field via multi-dimensional wavelet analysis and least squares, which are asymptotically normal. These estimators can be used to detect self-similarity and long-range dependence in multi-dimensional signals, which is important in texture classification and improvement of diffusion tensor imaging （DTI） of nuclear magnetic resonance （NMR）. Some fractional Brownian sheets will be simulated and the simulated data are used to validate these estimators. We find that when Hi ≥ 1/2, the estimators are accurate, and when Hi 〈 1/2, there are some bias.展开更多
Based on the collation and statistical analysis of flood and drought information in Baoji area from 1368 to 1911, and in the context of climate change, we investigated the spatio-temporal evolution characteristics of ...Based on the collation and statistical analysis of flood and drought information in Baoji area from 1368 to 1911, and in the context of climate change, we investigated the spatio-temporal evolution characteristics of drought and flood disaster chains in this area during the Ming and Qing dynasties using the methods of moving average, cumulative anomaly and wavelet analysis. The results are as follows:(1) We found a total of 297 drought and flood events from 1368 to 1911 in Baoji. Among these events, droughts and floods occurred separately 191 and 106 times, which accounted for 64.31% and 35.69% of the total events, respectively.(2) We observed distinct characteristics of flood and drought events in Baoji in different phases. The climate was relatively dry from 1368 to 1644. A fluctuant climate phase with both floods and droughts occurred from 1645 to 1804. The climate was relatively wet from 1805 to 1911. Moreover, we observed a pattern of alternating dry and wet periods from 1368 to 1911. In addition, 3 oscillation periods of drought and flood events occurred around 70 a, 110 a and 170 a, which corresponded to sunspot cycles.(3) We also observed an obvious spatial difference in drought and flood events in Baoji. The northern and eastern parts of Weihe River basin were regions with both frequent droughts and floods.(4) The sequential appearance of drought and flood disaster chains in Baoji from 1368 to 1911 was in response to global climate change. Since the 1760s, global climatic deterioration has frequently led to extreme drought and flood events.展开更多
基金supported in part by the National Basic Research Program of China(973 Program,2013CB910200,and 2011CB707802)
文摘It is proposed a class of statistical estimators H = （H1,… ,Hd） for the Hurst parameters H = （H1,… ,Hd） of fractional Brownian field via multi-dimensional wavelet analysis and least squares, which are asymptotically normal. These estimators can be used to detect self-similarity and long-range dependence in multi-dimensional signals, which is important in texture classification and improvement of diffusion tensor imaging （DTI） of nuclear magnetic resonance （NMR）. Some fractional Brownian sheets will be simulated and the simulated data are used to validate these estimators. We find that when Hi ≥ 1/2, the estimators are accurate, and when Hi 〈 1/2, there are some bias.
基金National Natural Science Foundation of China,No.41601016Philosophy and Social Science Research Fund in Shaanxi,No.2017E003Fundamental Research Funds for Key Subject Physical Geography of Baoji University of Arts and Sciences
文摘Based on the collation and statistical analysis of flood and drought information in Baoji area from 1368 to 1911, and in the context of climate change, we investigated the spatio-temporal evolution characteristics of drought and flood disaster chains in this area during the Ming and Qing dynasties using the methods of moving average, cumulative anomaly and wavelet analysis. The results are as follows:(1) We found a total of 297 drought and flood events from 1368 to 1911 in Baoji. Among these events, droughts and floods occurred separately 191 and 106 times, which accounted for 64.31% and 35.69% of the total events, respectively.(2) We observed distinct characteristics of flood and drought events in Baoji in different phases. The climate was relatively dry from 1368 to 1644. A fluctuant climate phase with both floods and droughts occurred from 1645 to 1804. The climate was relatively wet from 1805 to 1911. Moreover, we observed a pattern of alternating dry and wet periods from 1368 to 1911. In addition, 3 oscillation periods of drought and flood events occurred around 70 a, 110 a and 170 a, which corresponded to sunspot cycles.(3) We also observed an obvious spatial difference in drought and flood events in Baoji. The northern and eastern parts of Weihe River basin were regions with both frequent droughts and floods.(4) The sequential appearance of drought and flood disaster chains in Baoji from 1368 to 1911 was in response to global climate change. Since the 1760s, global climatic deterioration has frequently led to extreme drought and flood events.
