近年来,极端高温干旱等灾害事件频发,给经济和社会带来巨大影响,尤其是2022年夏季,我国中东部地区遭遇了持续性高温和严重干旱,造成了严重经济损失。标准化加权平均降水(Standardized Weighted Average Precipitation,SWAP)指数基于简...近年来,极端高温干旱等灾害事件频发,给经济和社会带来巨大影响,尤其是2022年夏季,我国中东部地区遭遇了持续性高温和严重干旱,造成了严重经济损失。标准化加权平均降水(Standardized Weighted Average Precipitation,SWAP)指数基于简单物理模型,考虑前期降水的累积效应与衰减效应,能够准确地反映当前旱涝状况,并展现对应的演变过程。为了探究此次干旱事件的变化特征,本文将该方法与传统的标准化降水指数(Standardized Precipitation Index,SPI)进行对比,采用该方法对2022年夏季的干旱进行逐日监测,并结合游程理论,对干旱的极端程度进行了量化分析。结果表明:SWAP指数在逐日尺度上的监测效果更优,能够提供更为精确的干旱信息。本次事件中干旱首先出现在华北和东北地区,随后蔓延至西北和华南地区,最终在8月中旬大部分地区都呈现严重干旱的状态。此次干旱是近62 a以来最为极端的干旱事件,在不同阈值下,干旱日数、干旱日SWAP累积量和干旱强度均达到了历史最高水平。本研究为评估干旱事件的极端程度提供了新的方法,为未来干旱的监测、预警及气候灾害的管理与应对提供了科学依据与技术支持。展开更多
On the basis of a macro flow resistance method and the Darcy Theory,a mathematical model is elaborated to characterize the flow resistance of a bag filter serving a coal-fired power plant.The development of the theore...On the basis of a macro flow resistance method and the Darcy Theory,a mathematical model is elaborated to characterize the flow resistance of a bag filter serving a coal-fired power plant.The development of the theoretical model is supported through acquisition of relevant data obtained by scanning the micro structure of the bag filter by means of an electron microscope.The influence of the running time and boiler load on the flow resistance and the impact of the flow resistance on the efficiency of the induced draft fan are analyzed by comparing the results of on-site operation tests.We show that the initial operation time and the table operation time are linearly related to the flow resistance of the bag filter;with the increase of boiler load,the flow resistance of the bag filter rises approximately as a quadratic function;with the rise of resistance,the power consumption of the induced draft fan increases while the efficiency of the induced draft fan decreases.展开更多
As a major agricultural country, China suffers from severe meteorological drought almost every year.Previous studies have applied a single threshold to identify the onset of drought events, which may cause problems to...As a major agricultural country, China suffers from severe meteorological drought almost every year.Previous studies have applied a single threshold to identify the onset of drought events, which may cause problems to adequately characterize long-term patterns of droughts.This study analyzes meteorological droughts in China based on a set of daily gridded(0.5° 9 0.5°) precipitation data from 1961 to 2014. By using a multi-threshold run theory approach to evaluate the monthly percentage of precipitation anomalies index(Pa), a drought events sequence was identified at each grid cell. The spatiotemporal variations of drought in China were further investigated based on statistics of the frequency, duration,severity, and intensity of all drought events. Analysis of the results show that China has five distinct meteorological drought-prone regions: the Huang-Huai-Hai Plain, Northeast China, Southwest China, South China coastal region,and Northwest China. Seasonal analysis further indicates that there are evident spatial variations in the seasonal contribution to regional drought. But overall, most contribution to annual drought events in China come from the winter. Decadal variation analysis suggests that most of China's water resource regions have undergone an increase in drought frequency, especially in the Liaohe, Haihe, and Yellow River basins, although drought duration and severity clearly have decreased after the 1960 s.展开更多
X charts with estimated control limits are commonly used in practice and treated as if the in-control process parameters were known. However, the former can behave quite differently from the latter. To understand the ...X charts with estimated control limits are commonly used in practice and treated as if the in-control process parameters were known. However, the former can behave quite differently from the latter. To understand the differences, it is necessary to study the run length distribution (RLD), its mean (ARL) and standard deviation (SDRL) of the X charts when the control limits are estimated. However, ARL and SDRL are integrals over an infinite region with a boundless integrand, the finiteness has not been proved in literature. In this paper, we show the finiteness and uniform integrability of ARL and SDRL. Furthermore, we numerically evaluate the ARL, SDRL and the RLD using number theory method. A numerical study is conducted to assess the performance of the proposed method and the results are compared with those given by Quesenberry and Chen.展开更多
文摘On the basis of a macro flow resistance method and the Darcy Theory,a mathematical model is elaborated to characterize the flow resistance of a bag filter serving a coal-fired power plant.The development of the theoretical model is supported through acquisition of relevant data obtained by scanning the micro structure of the bag filter by means of an electron microscope.The influence of the running time and boiler load on the flow resistance and the impact of the flow resistance on the efficiency of the induced draft fan are analyzed by comparing the results of on-site operation tests.We show that the initial operation time and the table operation time are linearly related to the flow resistance of the bag filter;with the increase of boiler load,the flow resistance of the bag filter rises approximately as a quadratic function;with the rise of resistance,the power consumption of the induced draft fan increases while the efficiency of the induced draft fan decreases.
基金provided by the National Basic Research Program of China (2012CB955403)the National Natural Science Foundation of China (41425002)the National Youth Top-notch Talent Support Program in China
文摘As a major agricultural country, China suffers from severe meteorological drought almost every year.Previous studies have applied a single threshold to identify the onset of drought events, which may cause problems to adequately characterize long-term patterns of droughts.This study analyzes meteorological droughts in China based on a set of daily gridded(0.5° 9 0.5°) precipitation data from 1961 to 2014. By using a multi-threshold run theory approach to evaluate the monthly percentage of precipitation anomalies index(Pa), a drought events sequence was identified at each grid cell. The spatiotemporal variations of drought in China were further investigated based on statistics of the frequency, duration,severity, and intensity of all drought events. Analysis of the results show that China has five distinct meteorological drought-prone regions: the Huang-Huai-Hai Plain, Northeast China, Southwest China, South China coastal region,and Northwest China. Seasonal analysis further indicates that there are evident spatial variations in the seasonal contribution to regional drought. But overall, most contribution to annual drought events in China come from the winter. Decadal variation analysis suggests that most of China's water resource regions have undergone an increase in drought frequency, especially in the Liaohe, Haihe, and Yellow River basins, although drought duration and severity clearly have decreased after the 1960 s.
基金This research is is partially supported by the National Natural Science Foundation of China.
文摘X charts with estimated control limits are commonly used in practice and treated as if the in-control process parameters were known. However, the former can behave quite differently from the latter. To understand the differences, it is necessary to study the run length distribution (RLD), its mean (ARL) and standard deviation (SDRL) of the X charts when the control limits are estimated. However, ARL and SDRL are integrals over an infinite region with a boundless integrand, the finiteness has not been proved in literature. In this paper, we show the finiteness and uniform integrability of ARL and SDRL. Furthermore, we numerically evaluate the ARL, SDRL and the RLD using number theory method. A numerical study is conducted to assess the performance of the proposed method and the results are compared with those given by Quesenberry and Chen.
