Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions wa...Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions was defined in this paper, which was affected by advancement of science and technology. Based on the new concept of crop yield, the time series techniques relying on past yield data was employed to set up a forecasting model. The model was tested by using average grain yields of Liaoning Province in China from 1949 to 2005. The testing combined dynamic n-choosing and micro tendency rectification, and an average forecasting error was 1.24%. In the trend line of yield change, and then a yield turning point might occur, in which case the inflexion model was used to solve the problem of yield turn point.展开更多
校园用水数据,既有趋势性又有季节性。为了准确地对智能水表收集的用水数据进行异常点分析,从而检测预估管网漏损问题,研究对用水数据进行了相关检验,并选择了合适的自回归差分移动平均模型(Autoregressive Integrated Moving Average M...校园用水数据,既有趋势性又有季节性。为了准确地对智能水表收集的用水数据进行异常点分析,从而检测预估管网漏损问题,研究对用水数据进行了相关检验,并选择了合适的自回归差分移动平均模型(Autoregressive Integrated Moving Average Model,ARIMA)模型。基于Chen-Liu迭代算法,研究利用R软件进行编程,成功识别了用水数据中的异常点位置、类型、异常效应的大小,以及调整后的时间序列等,由此预估管网漏损可能出现的日期和位置。研究发现,基于ARIMA时间序列模型对用水数据进行异常点的检测较为准确,且输出的异常点类型可以区分异常点是人为因素造成还是由管网漏损问题造成,进而预估管网漏损问题,这为供水行业漏损管理模式提供了一种新的方向。展开更多
研究单个感染细胞的细胞毒性T淋巴细胞(cytotoxic T lymphocytes,CTL)免疫反应的HTLV-Ⅰ(人类嗜T细胞病毒)感染模型的稳定性,考虑到细胞被感染和感染细胞被杀死的时间对该模型的影响,利用Schauder不动点定理和泛函微分方程稳定性理论,...研究单个感染细胞的细胞毒性T淋巴细胞(cytotoxic T lymphocytes,CTL)免疫反应的HTLV-Ⅰ(人类嗜T细胞病毒)感染模型的稳定性,考虑到细胞被感染和感染细胞被杀死的时间对该模型的影响,利用Schauder不动点定理和泛函微分方程稳定性理论,得到了在不同时滞下模型平衡点的局部稳定性的产生条件。最后,选取合理参数进行数值模拟,验证了所得结论。展开更多
随着GNSS的不断发展,基于精密单点定位(precise point positioning,PPP)技术的高精度时间传递研究已成为时频领域的关键技术之一.本文以北斗三号系统解算接收机钟差为研究对象,分析了无电离层(ionospheric-free,IF)组合和非组合(uncombi...随着GNSS的不断发展,基于精密单点定位(precise point positioning,PPP)技术的高精度时间传递研究已成为时频领域的关键技术之一.本文以北斗三号系统解算接收机钟差为研究对象,分析了无电离层(ionospheric-free,IF)组合和非组合(uncombined,UC)PPP模型对时间传递的影响.首先推导了两种PPP数学模型差异,选取2024年年积日第79~81天的BRUX和USN7两个外接氢原子钟测站观测数据进行分析.结果表明:两种PPP模型解算的接收机钟差差值在0.15 ns内波动,修正的Allan方差数值接近;对BRUX-USN7时间链路对比分析,3天内时间传递结果均在0.8 ns内波动,两种模型解算钟差修正的Allan方差数值近似.综上,两种PPP模型虽然钟差数值解算的理论模型不同,但在钟差解算和时间传递方面无明显差异,非组合模型可以用来进行时间传递且在保留电离层信息方面更具有优势.展开更多
Historical evidence indicates that dust storms of considerable ferocity often wreak havoc, posing a genuine threat to the climatic and societal equilibrium of a place. A systematic study, with emphasis on the modeling...Historical evidence indicates that dust storms of considerable ferocity often wreak havoc, posing a genuine threat to the climatic and societal equilibrium of a place. A systematic study, with emphasis on the modeling and forecasting aspects, thus, becomes imperative, so that efficient measures can be promptly undertaken to cushion the effect of such an unforeseen calamity. The present work intends to discover a suitable ARIMA model using dust storm data from northern China from March 1954 to April 2002, provided by Zhou and Zhang (2003), thereby extending the idea of empirical recurrence rate (ERR) developed by Ho (2008), to model the temporal trend of such sand dust storms. In particular we show that the ERR time series is endowed with the following characteristics: 1) it is a potent surrogate for a point process, 2) it is capable of taking advantage of the well developed and powerful time series modeling tools and 3) it can generate reliable forecasts, with which we can retrieve the corresponding mean number of strong sand dust storms. A simulation study is conducted prior to the actual fitting, to justify the applicability of the proposed technique.展开更多
基金Supported by Agricultural Poor-helping Monopoly of Graduate University of Chinese Academy of Science (40641002)
文摘Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions was defined in this paper, which was affected by advancement of science and technology. Based on the new concept of crop yield, the time series techniques relying on past yield data was employed to set up a forecasting model. The model was tested by using average grain yields of Liaoning Province in China from 1949 to 2005. The testing combined dynamic n-choosing and micro tendency rectification, and an average forecasting error was 1.24%. In the trend line of yield change, and then a yield turning point might occur, in which case the inflexion model was used to solve the problem of yield turn point.
文摘校园用水数据,既有趋势性又有季节性。为了准确地对智能水表收集的用水数据进行异常点分析,从而检测预估管网漏损问题,研究对用水数据进行了相关检验,并选择了合适的自回归差分移动平均模型(Autoregressive Integrated Moving Average Model,ARIMA)模型。基于Chen-Liu迭代算法,研究利用R软件进行编程,成功识别了用水数据中的异常点位置、类型、异常效应的大小,以及调整后的时间序列等,由此预估管网漏损可能出现的日期和位置。研究发现,基于ARIMA时间序列模型对用水数据进行异常点的检测较为准确,且输出的异常点类型可以区分异常点是人为因素造成还是由管网漏损问题造成,进而预估管网漏损问题,这为供水行业漏损管理模式提供了一种新的方向。
文摘研究单个感染细胞的细胞毒性T淋巴细胞(cytotoxic T lymphocytes,CTL)免疫反应的HTLV-Ⅰ(人类嗜T细胞病毒)感染模型的稳定性,考虑到细胞被感染和感染细胞被杀死的时间对该模型的影响,利用Schauder不动点定理和泛函微分方程稳定性理论,得到了在不同时滞下模型平衡点的局部稳定性的产生条件。最后,选取合理参数进行数值模拟,验证了所得结论。
文摘随着GNSS的不断发展,基于精密单点定位(precise point positioning,PPP)技术的高精度时间传递研究已成为时频领域的关键技术之一.本文以北斗三号系统解算接收机钟差为研究对象,分析了无电离层(ionospheric-free,IF)组合和非组合(uncombined,UC)PPP模型对时间传递的影响.首先推导了两种PPP数学模型差异,选取2024年年积日第79~81天的BRUX和USN7两个外接氢原子钟测站观测数据进行分析.结果表明:两种PPP模型解算的接收机钟差差值在0.15 ns内波动,修正的Allan方差数值接近;对BRUX-USN7时间链路对比分析,3天内时间传递结果均在0.8 ns内波动,两种模型解算钟差修正的Allan方差数值近似.综上,两种PPP模型虽然钟差数值解算的理论模型不同,但在钟差解算和时间传递方面无明显差异,非组合模型可以用来进行时间传递且在保留电离层信息方面更具有优势.
文摘Historical evidence indicates that dust storms of considerable ferocity often wreak havoc, posing a genuine threat to the climatic and societal equilibrium of a place. A systematic study, with emphasis on the modeling and forecasting aspects, thus, becomes imperative, so that efficient measures can be promptly undertaken to cushion the effect of such an unforeseen calamity. The present work intends to discover a suitable ARIMA model using dust storm data from northern China from March 1954 to April 2002, provided by Zhou and Zhang (2003), thereby extending the idea of empirical recurrence rate (ERR) developed by Ho (2008), to model the temporal trend of such sand dust storms. In particular we show that the ERR time series is endowed with the following characteristics: 1) it is a potent surrogate for a point process, 2) it is capable of taking advantage of the well developed and powerful time series modeling tools and 3) it can generate reliable forecasts, with which we can retrieve the corresponding mean number of strong sand dust storms. A simulation study is conducted prior to the actual fitting, to justify the applicability of the proposed technique.
