A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4is developed,which realizes the effective beam quality management in high-power lasers.Because of the severe thermal effect caused by h...A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4is developed,which realizes the effective beam quality management in high-power lasers.Because of the severe thermal effect caused by high-power end pumping,both the appropriate crystal and beam filling factor(the ratio of the laser beam radius to the pump beam radius)are important in the amplifier.The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality.To study the thermal effect in the end-pumped crystal,the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4are theoretically calculated.In the experiment,a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals,respectively,and the experimental results are in good agreement with the theoretical results.In the power amplification,a seed laser is employed in the experiment.The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient,beam quality,and power extraction efficiency.Based on the reasonable layout of the power amplification for each stage amplifier,the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of M_(x)^(2)=1.28 and M_(y)^(2)=1.32.展开更多
A high grain moisture content at harvest has been an important problem in the high latitude region of Northeast China, and it is closely related to the genotypes of varieties, local meteorological factors and planting...A high grain moisture content at harvest has been an important problem in the high latitude region of Northeast China, and it is closely related to the genotypes of varieties, local meteorological factors and planting management. However, delayed harvest at a low temperature could not effectively reduce the grain moisture content. In this study, we continuously observed the grain drying during the late stage of different maturing types of maize varieties in Daqing, Heilongjiang Province, China in 2016 and 2017. A two-segment linear model was used to analyze the different stages of the drying processes: 1) Twosegment linear model fitting can divide the grain drying process of all varieties into two separate linear drying processes with different slopes. 2) During the rapid drying stage, the drying was faster at a higher temperature. The rate of slow drying was influenced by air vapor pressure. 3) The moisture content and meteorological factors when the drying rate turns from one stage into the other were not consistent between varieties and years. After entering the frost period, temperatures below 0℃ will significantly reduce the rate of grain drying. 4) Due to the short growth period of early-maturing varieties, the drying time was prolonged, and the grain moisture content was lower than that of the mid-late maturing varieties. Local meteorological conditions do not allow the drying of mid-late maturing varieties to achieve a lower moisture content. When the temperature falls below 0℃, the drying rate of grain decreases markedly. Therefore, one feasible way to solve the problem of high moisture content is to replace the early-maturing varieties and implement the corresponding cultivation techniques.展开更多
The shortcomings of an adaptive Sage filter are analyzed in this paper.An improved adaptive Sage filter is developed by using a weighted average quadratic form of the historical residuals of observations and predicted...The shortcomings of an adaptive Sage filter are analyzed in this paper.An improved adaptive Sage filter is developed by using a weighted average quadratic form of the historical residuals of observations and predicted states to evaluate the covariance matrices of observations and dynamic model errors at the present epoch.The weight function is constructed based on the variances of observational residuals or predicted state residuals and the space distance between the previous and the present epoch.In order to balance the contributions of the measurements and the dynamic model information,an adaptive factor is applied by using a two-segment function and predicted state discrepancy statistics.Two applications,orbit determination of a maneuvered GEO satellite and GPS kinematic positioning,are conducted to verify the performance of the proposed method.展开更多
基金supported by the National Natural Science Foundation of China(No.62105179)the National Key R&D Program of China(No.2023YFE0199000)the Baima Lake Laboratory Joint Funds of the Zhejiang Provincial Natural Science Foundation of China(No.LBMHZ24F050001)。
文摘A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4is developed,which realizes the effective beam quality management in high-power lasers.Because of the severe thermal effect caused by high-power end pumping,both the appropriate crystal and beam filling factor(the ratio of the laser beam radius to the pump beam radius)are important in the amplifier.The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality.To study the thermal effect in the end-pumped crystal,the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4are theoretically calculated.In the experiment,a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals,respectively,and the experimental results are in good agreement with the theoretical results.In the power amplification,a seed laser is employed in the experiment.The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient,beam quality,and power extraction efficiency.Based on the reasonable layout of the power amplification for each stage amplifier,the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of M_(x)^(2)=1.28 and M_(y)^(2)=1.32.
基金financially supported by the National Key Research and Development Program of China(2016YFD0300110)the National Natural Science Foundation of China(31971849)+1 种基金the China Agriculture Research System of MOF and MARA(CARS-02-25)the Agricultural Science and Technology Innovation Program(CAAS-ZDRW202004)。
文摘A high grain moisture content at harvest has been an important problem in the high latitude region of Northeast China, and it is closely related to the genotypes of varieties, local meteorological factors and planting management. However, delayed harvest at a low temperature could not effectively reduce the grain moisture content. In this study, we continuously observed the grain drying during the late stage of different maturing types of maize varieties in Daqing, Heilongjiang Province, China in 2016 and 2017. A two-segment linear model was used to analyze the different stages of the drying processes: 1) Twosegment linear model fitting can divide the grain drying process of all varieties into two separate linear drying processes with different slopes. 2) During the rapid drying stage, the drying was faster at a higher temperature. The rate of slow drying was influenced by air vapor pressure. 3) The moisture content and meteorological factors when the drying rate turns from one stage into the other were not consistent between varieties and years. After entering the frost period, temperatures below 0℃ will significantly reduce the rate of grain drying. 4) Due to the short growth period of early-maturing varieties, the drying time was prolonged, and the grain moisture content was lower than that of the mid-late maturing varieties. Local meteorological conditions do not allow the drying of mid-late maturing varieties to achieve a lower moisture content. When the temperature falls below 0℃, the drying rate of grain decreases markedly. Therefore, one feasible way to solve the problem of high moisture content is to replace the early-maturing varieties and implement the corresponding cultivation techniques.
基金supported by the Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No.2007B51)the National Natural Science Foundation of China (Grant Nos.41174008 and 41020144004)+1 种基金China Postdoctoral Science Foundation (Grant Nos.20080430148 and 200902444)the Junior Scientist Exchange Program between the China Scholarship Council and the Helmholtz Association of German Research Centers Council
文摘The shortcomings of an adaptive Sage filter are analyzed in this paper.An improved adaptive Sage filter is developed by using a weighted average quadratic form of the historical residuals of observations and predicted states to evaluate the covariance matrices of observations and dynamic model errors at the present epoch.The weight function is constructed based on the variances of observational residuals or predicted state residuals and the space distance between the previous and the present epoch.In order to balance the contributions of the measurements and the dynamic model information,an adaptive factor is applied by using a two-segment function and predicted state discrepancy statistics.Two applications,orbit determination of a maneuvered GEO satellite and GPS kinematic positioning,are conducted to verify the performance of the proposed method.
