Poisson-Gumbel joint distribution model uses maximum wind speed corresponding to multiple typhoons to construct sample sequence.Thresholds are usually used to filter sample sequences to make them more consistent with ...Poisson-Gumbel joint distribution model uses maximum wind speed corresponding to multiple typhoons to construct sample sequence.Thresholds are usually used to filter sample sequences to make them more consistent with Poisson distribution.However,few studies have discussed the threshold setting and its impact on Poisson-Gumbel joint distribution model.In this study,a sample sequence based on the data of Qinzhou meteorological station from 2005 to 2018 were constructed.We set 0%,5%,10%,20%and 30%gradient thresholds.Then,we analyzed the influence of threshold change on the calculation results of maximum wind speed in different return periods.The results showed that:(1)When the threshold increases,the maximum wind speed of each return period will decrease gradually.This indicates that the length of the sample series may have a positive effect on the return period wind speed calculation in Gumbel and Poisson-Gumbel methods.Although the augment of the threshold increases the average value of the maximum wind speed of the sample sequence,it shortens the length of the sample sequence,resulting in a lower calculated value of the maximum wind speed.However,this deviation is not large.Taking the common 10%threshold as an example,the maximum wind speed calculation deviation in the 50 a return period is about 1.9%;(2)Theoretically,the threshold is set to make the sample sequence more consistent with Poisson distribution,but this example showed that the effect is worth further discussion.Although the overall trend showed that the increase of the threshold can makeχ2 decrease,the correlation coefficient of linear fitting was only 0.182.Taking Qinzhou meteorological station data as an example,theχ2 of 20%threshold was as high as 6.35,meaning that the selected sample sequence was not ideal.展开更多
Using the data on the maximum wind speed within ten minutes every month in the period 1971-2009 in Zhucheng City of Shandong Province, we conduct statistical analysis of the maximum wind speed in Zhucheng City. The re...Using the data on the maximum wind speed within ten minutes every month in the period 1971-2009 in Zhucheng City of Shandong Province, we conduct statistical analysis of the maximum wind speed in Zhucheng City. The results show that over thirty-nine years, the annual maximum wind speed in four seasons in Zhucheng City tends to decline. The annual maximum wind speed declines at the rate of 1.45 m/s every 10 years. It falls fastest in winter, with decline rate of 1.73 m/s every 10 years; it is close to the average annual maximum wind speed in spring and autumn, with decline rate of 1.44 m/s and 14.8 m/s every 10 years, respectively; it falls slowest in summer, and the extreme value of the maximum wind speed occurs mainly in spring. The curve of changes in the monthly maximum wind speed in Zhucheng City assumes diminishing shape of "two peaks and one trough". We conduct preliminary analysis of the windy weather situation, and put forth specific defensive measures against the hazards of strong winds in the different periods.展开更多
中国气象局陆面数据同化系统(CLDAS)和高分辨率CLDAS(HRCLDAS)实况格点分析资料弥补了海面风观测稀疏的不足,然而其风速极大值与实际存在偏差,例如在狭管效应显著的台湾海峡区域普遍存在低估现象,其中CLDAS低估更严重,不能满足气象服务...中国气象局陆面数据同化系统(CLDAS)和高分辨率CLDAS(HRCLDAS)实况格点分析资料弥补了海面风观测稀疏的不足,然而其风速极大值与实际存在偏差,例如在狭管效应显著的台湾海峡区域普遍存在低估现象,其中CLDAS低估更严重,不能满足气象服务需求。因此本文提出一种基于地面站点观测风速二次融合的格点风场极大值订正技术,即采用反距离权重法将站点风速极大值观测周围一定影响半径区域内的站点风速观测插值到区域内的风场格点上,并综合考虑区域内风场误差和空间平滑程度以确定最优影响半径。利用2021~2023年CLDAS和HRCLDAS数据开展台湾海峡区域分区域(闽东、闽中及闽南渔场)风场极大值订正试验,结果表明:风场极大值订正技术能有效改进CLDAS和HRCLDAS对台湾海峡区域格点风速极大值低估情况,且HRCLDAS改进效果更优。HRCLDAS相较CLDAS出现小值最优影响半径频率增加。极值订正后,CLDAS和HRCLDAS逐小时平均绝对误差(MAE)降低率大多达到70%~85%和90%~95%;不同月份MAE降低率均超过60%,其中10月至次年1月订正效果最优,MAE降低率分别超过85%和90%;订正后误差空间分布与海岸线平行,自西向东减少,位于福建沿海及台湾海峡区域浮标站点区域MAE极值订正后降低至1 m s^(-1)以下。2305号台风“杜苏芮”和2023年1月23~25日典型冷空气大风过程的评估结果进一步表明,风场极大值订正技术对不同类别的大风过程均有效。展开更多
This is a review of high-speed train development in the sense of technology advances all over the world. Three generations of high-speed trains are classified according to their technical characteristics and maximum o...This is a review of high-speed train development in the sense of technology advances all over the world. Three generations of high-speed trains are classified according to their technical characteristics and maximum operating speed. Emphasis is given to the newly developed high-speed train in China, CRH380. The theoretical foundations and future development of CRH380 are briefly discussed.展开更多
Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical sc...Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical scheme for calculating the maximum wind speed radius and wind velocity distribution of a moving tropical cyclone is derived. In addition, the effect of frictional force on the internal structure of the tropical cyclone is discussed. By comparison with observational data, this numerical scheme demonstrates great advantages, i.e. it can not only describe the asymmetrical wind speed distribution of a tropical cyclone reasonably, but can also calculate the maximum wind speed in each direction within the typhoon domain much more accurately. Furthermore, the combination of calculated and analyzed wind speed distributions by the scheme is perfectly consistent with observations.展开更多
AIM: To investigate the effect of age on reading acuity and reading speed in attaining text information in healthy eyes.METHODS: Reading acuity, critical print size, reading speed and maximum reading speed were measur...AIM: To investigate the effect of age on reading acuity and reading speed in attaining text information in healthy eyes.METHODS: Reading acuity, critical print size, reading speed and maximum reading speed were measured in groups of 40 children (8 to 12 years old), 40 teenagers (13 to 19 years old), 40 young adults (20 to 39 years old), and 40 adults (40 years old and above) using the Buari-Chen Malay Reading Chart [contextual sentences (CS) set and random words (RW) set] in a cross-sectional study design.RESULTS: Reading acuity was significantly improved by 0.04 logMAR for both CS set and RW set from children to teenagers, then gradually worsened from young adults to adults (CS set: 0.06 logMAR;RW set: 0.08 logMAR). Critical print size for children showed a significant improvement in teenagers (CS set: 0.14 logMAR;RW set: 0.07 logMAR), then deteriorated from young adults to adults by 0.09 logMAR only for CS set. Reading speed significantly increased from children to teenagers,[CS set: 46.20 words per minute (wpm);RW set: 42.06 wpm], then stabilized from teenagers to young adults, and significantly reduced from young adults to adults (CS set: 28.58 wpm;RW set: 24.44 wpm). Increment and decrement in maximum reading speed measurement were revealed from children to teenagers (CS set: 39.38 wpm;RW set: 43.38 wpm) and from young adults to adults (CS set: 22.26 wpm;RW set: 26.31 wpm) respectively.CONCLUSION: The reference of age-related findings in term of acuity and speed of reading should be incorporated in clinical practice to enhance reading assessment among healthy eyes population.展开更多
基金This work was supported by the Second Tibet Plateau Scientific Expedition and Research Program(STEP)under grant number 2019QZKK0804the National Natural Science Foundation of China“Study on the dynamic mechanism of grassland ecosystem response to climate change in Qinghai Plateau”under grant number U20A2098.
文摘Poisson-Gumbel joint distribution model uses maximum wind speed corresponding to multiple typhoons to construct sample sequence.Thresholds are usually used to filter sample sequences to make them more consistent with Poisson distribution.However,few studies have discussed the threshold setting and its impact on Poisson-Gumbel joint distribution model.In this study,a sample sequence based on the data of Qinzhou meteorological station from 2005 to 2018 were constructed.We set 0%,5%,10%,20%and 30%gradient thresholds.Then,we analyzed the influence of threshold change on the calculation results of maximum wind speed in different return periods.The results showed that:(1)When the threshold increases,the maximum wind speed of each return period will decrease gradually.This indicates that the length of the sample series may have a positive effect on the return period wind speed calculation in Gumbel and Poisson-Gumbel methods.Although the augment of the threshold increases the average value of the maximum wind speed of the sample sequence,it shortens the length of the sample sequence,resulting in a lower calculated value of the maximum wind speed.However,this deviation is not large.Taking the common 10%threshold as an example,the maximum wind speed calculation deviation in the 50 a return period is about 1.9%;(2)Theoretically,the threshold is set to make the sample sequence more consistent with Poisson distribution,but this example showed that the effect is worth further discussion.Although the overall trend showed that the increase of the threshold can makeχ2 decrease,the correlation coefficient of linear fitting was only 0.182.Taking Qinzhou meteorological station data as an example,theχ2 of 20%threshold was as high as 6.35,meaning that the selected sample sequence was not ideal.
文摘Using the data on the maximum wind speed within ten minutes every month in the period 1971-2009 in Zhucheng City of Shandong Province, we conduct statistical analysis of the maximum wind speed in Zhucheng City. The results show that over thirty-nine years, the annual maximum wind speed in four seasons in Zhucheng City tends to decline. The annual maximum wind speed declines at the rate of 1.45 m/s every 10 years. It falls fastest in winter, with decline rate of 1.73 m/s every 10 years; it is close to the average annual maximum wind speed in spring and autumn, with decline rate of 1.44 m/s and 14.8 m/s every 10 years, respectively; it falls slowest in summer, and the extreme value of the maximum wind speed occurs mainly in spring. The curve of changes in the monthly maximum wind speed in Zhucheng City assumes diminishing shape of "two peaks and one trough". We conduct preliminary analysis of the windy weather situation, and put forth specific defensive measures against the hazards of strong winds in the different periods.
文摘中国气象局陆面数据同化系统(CLDAS)和高分辨率CLDAS(HRCLDAS)实况格点分析资料弥补了海面风观测稀疏的不足,然而其风速极大值与实际存在偏差,例如在狭管效应显著的台湾海峡区域普遍存在低估现象,其中CLDAS低估更严重,不能满足气象服务需求。因此本文提出一种基于地面站点观测风速二次融合的格点风场极大值订正技术,即采用反距离权重法将站点风速极大值观测周围一定影响半径区域内的站点风速观测插值到区域内的风场格点上,并综合考虑区域内风场误差和空间平滑程度以确定最优影响半径。利用2021~2023年CLDAS和HRCLDAS数据开展台湾海峡区域分区域(闽东、闽中及闽南渔场)风场极大值订正试验,结果表明:风场极大值订正技术能有效改进CLDAS和HRCLDAS对台湾海峡区域格点风速极大值低估情况,且HRCLDAS改进效果更优。HRCLDAS相较CLDAS出现小值最优影响半径频率增加。极值订正后,CLDAS和HRCLDAS逐小时平均绝对误差(MAE)降低率大多达到70%~85%和90%~95%;不同月份MAE降低率均超过60%,其中10月至次年1月订正效果最优,MAE降低率分别超过85%和90%;订正后误差空间分布与海岸线平行,自西向东减少,位于福建沿海及台湾海峡区域浮标站点区域MAE极值订正后降低至1 m s^(-1)以下。2305号台风“杜苏芮”和2023年1月23~25日典型冷空气大风过程的评估结果进一步表明,风场极大值订正技术对不同类别的大风过程均有效。
文摘This is a review of high-speed train development in the sense of technology advances all over the world. Three generations of high-speed trains are classified according to their technical characteristics and maximum operating speed. Emphasis is given to the newly developed high-speed train in China, CRH380. The theoretical foundations and future development of CRH380 are briefly discussed.
基金supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 40425009 and 40730953
文摘Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical scheme for calculating the maximum wind speed radius and wind velocity distribution of a moving tropical cyclone is derived. In addition, the effect of frictional force on the internal structure of the tropical cyclone is discussed. By comparison with observational data, this numerical scheme demonstrates great advantages, i.e. it can not only describe the asymmetrical wind speed distribution of a tropical cyclone reasonably, but can also calculate the maximum wind speed in each direction within the typhoon domain much more accurately. Furthermore, the combination of calculated and analyzed wind speed distributions by the scheme is perfectly consistent with observations.
基金Supported by the Research Grant Scheme 600-IRMI-DANA 5/3/BESTARI(00013/2016)and 600-IRMI/MYRA 5/3/MITRA(007/2017)-2 from the Universiti Teknologi MARA,Malaysia
文摘AIM: To investigate the effect of age on reading acuity and reading speed in attaining text information in healthy eyes.METHODS: Reading acuity, critical print size, reading speed and maximum reading speed were measured in groups of 40 children (8 to 12 years old), 40 teenagers (13 to 19 years old), 40 young adults (20 to 39 years old), and 40 adults (40 years old and above) using the Buari-Chen Malay Reading Chart [contextual sentences (CS) set and random words (RW) set] in a cross-sectional study design.RESULTS: Reading acuity was significantly improved by 0.04 logMAR for both CS set and RW set from children to teenagers, then gradually worsened from young adults to adults (CS set: 0.06 logMAR;RW set: 0.08 logMAR). Critical print size for children showed a significant improvement in teenagers (CS set: 0.14 logMAR;RW set: 0.07 logMAR), then deteriorated from young adults to adults by 0.09 logMAR only for CS set. Reading speed significantly increased from children to teenagers,[CS set: 46.20 words per minute (wpm);RW set: 42.06 wpm], then stabilized from teenagers to young adults, and significantly reduced from young adults to adults (CS set: 28.58 wpm;RW set: 24.44 wpm). Increment and decrement in maximum reading speed measurement were revealed from children to teenagers (CS set: 39.38 wpm;RW set: 43.38 wpm) and from young adults to adults (CS set: 22.26 wpm;RW set: 26.31 wpm) respectively.CONCLUSION: The reference of age-related findings in term of acuity and speed of reading should be incorporated in clinical practice to enhance reading assessment among healthy eyes population.
