The Tibetan Plateau(TP)is a prevalent region for convection systems due to its unique thermodynamic forcing.This study investigated isolated deep convections(IDCs),which have a smaller spatial and temporal size than m...The Tibetan Plateau(TP)is a prevalent region for convection systems due to its unique thermodynamic forcing.This study investigated isolated deep convections(IDCs),which have a smaller spatial and temporal size than mesoscale convective systems(MCSs),over the TP in the rainy season(June-September)during 2001–2020.The authors used satellite precipitation and brightness temperature observations from the Global Precipitation Measurement mission.Results show that IDCs mainly concentrate over the southern TP.The IDC number per rainy season decreases from around 140 over the southern TP to around 10 over the northern TP,with an average 54.2.The initiation time of IDCs exhibits an obvious diurnal cycle,with the peak at 1400–1500 LST and the valley at 0900–1000 LST.Most IDCs last less than five hours and more than half appear for only one hour.IDCs generally have a cold cloud area of 7422.9 km^(2),containing a precipitation area of approximately 65%.The larger the IDC,the larger the fraction of intense precipitation it contains.IDCs contribute approximately 20%–30%to total precipitation and approximately 30%–40%to extreme precipitation over the TP,with a larger percentage in July and August than in June and September.In terms of spatial distribution,IDCs contribute more to both total precipitation and extreme precipitation over the TP compared to the surrounding plain regions.IDCs over the TP account for a larger fraction than MCSs,indicating the important role of IDCs over the region.展开更多
On the Loess Plateau, water is the main limiting factors for vegetation growth. Root distribution characters have special ecological meaning as it reflected the utilizations of trees to the environments. Even-aged sta...On the Loess Plateau, water is the main limiting factors for vegetation growth. Root distribution characters have special ecological meaning as it reflected the utilizations of trees to the environments. Even-aged stands ofRobinia pseudoacacia on slope lands facing south and north were selected as sampling plots for root distribution investigation. Investigatiing results showed that indicated that on all sites, root biomass decreased with depth, and the distribution depth of fine root was deeper than that of coarser root. The results of variance analysis indicated that there were great differences in root biomass among different diameter classes, and coarser root was the main sources of variance, and the root biomass, especially fine root (?<3mm) biomass on northern exposition sites was bigger than that on southern exposition sites. Analysis of the vertical root distribution parameters, root extinction coefficient, β indicated that the value of β on northern exposition was more than 0.982, while the value of β on southern exposition was less than 0.982, which indicated that the vertical root distribution depth ofRobinia pseudoacacia on southern exposition was deeper than that on southern exposition. And the distribution depth of fine roots (Φ<1mm) was deeper than that of thicker roots(Φ<3mm), which was in favor of the uptake of water and nutrients from deeper layers, helped the trees to adapt the arid environment, and promoted the growth of the upper parts of the tree. Keywords Root diameter classes - Variance analysis - Root extinction coefficient - Vertical distribution characters - Site conditions - Loess Plateau CLC number S792.27.01 Document code A Foundation Item: This research was supported by National Natural Science Foundation of China (30371150 and 40371075).Biography: LI Peng (1974-) male, post: Ph. D. in Northwest Scientific & Technological University of Agriculture and Forestry, Yangling 712100, Shaanxi Province, P. R. China. Tel: 029-82312651.Responsible editor: Chai Ruihal展开更多
A promising method to improve the attosecond pulse intensity has been theoretically pre- sented by properly adding an ultraviolet pulse into the orthogonal two-color field. The results show that by properly adding a 1...A promising method to improve the attosecond pulse intensity has been theoretically pre- sented by properly adding an ultraviolet pulse into the orthogonal two-color field. The results show that by properly adding a 125 nm ultraviolet pulse to the orthogonal two-color field, not only the harmonic yield is enhanced by 2 orders of magnitude compared with the original orthogonal two-color field case, but also the single short quantum path, which is selected to contribute to the harmonic spectrum, results in an ultrabroad 152 eV bandwidth. Moreover, by optimizing the laser parameters, we find that the harmonic enhancement is not very sen- sitive to the pulse duration and the polarized angle of the assisted ultraviolet pulse, which is much better for experimental realization. As a result, an isolated pulse with duration of 38 as can be obtained, which is 2 orders of magnitude improvement in comparison with the original two-color orthogonal field case.展开更多
A new approach for blind equalization and channel identification is proposed in this paper. The equalization scheme is based on over sampling technique and an independent component analysis network. The equalized seq...A new approach for blind equalization and channel identification is proposed in this paper. The equalization scheme is based on over sampling technique and an independent component analysis network. The equalized sequence and its higher order statistics are used to identify the channel parameters. Compared to traditional equalization methods, the proposed approach is with a simple architecture, and does not need learning sequences. Computer simulations show the validity of the proposed method.展开更多
High quality cubic GaN (c GaN) is grown by metalorganic vapor deposition (MOCVD) at an increased growth temperature of 900℃,with the growth rate of 1 6μm/h.The full width at half maximum (FWHM) of room temperature...High quality cubic GaN (c GaN) is grown by metalorganic vapor deposition (MOCVD) at an increased growth temperature of 900℃,with the growth rate of 1 6μm/h.The full width at half maximum (FWHM) of room temperature photoluminescence (PL) for the high temperature grown GaN film is 48meV.It is smaller than that of the sample grown at 830℃.In X ray diffraction (XRD) measurement,the high temperature grown GaN shows a (002) peak at 20° with a FWHM of 21′.It can be concluded that,although c GaN is of metastable phase,high growth temperature is still beneficial to the improvement in its crystal quality.The relationship between the growth rate and growth temperature is also discussed.展开更多
基金supported by the National Natural Science Foundation of China[grant number 42105064]the Second Tibetan Plateau Scientific Expedition and Research(STEP)program[grant number 2019QZKK0102]the special fund of the Yunnan University“double first-class”construction.
文摘The Tibetan Plateau(TP)is a prevalent region for convection systems due to its unique thermodynamic forcing.This study investigated isolated deep convections(IDCs),which have a smaller spatial and temporal size than mesoscale convective systems(MCSs),over the TP in the rainy season(June-September)during 2001–2020.The authors used satellite precipitation and brightness temperature observations from the Global Precipitation Measurement mission.Results show that IDCs mainly concentrate over the southern TP.The IDC number per rainy season decreases from around 140 over the southern TP to around 10 over the northern TP,with an average 54.2.The initiation time of IDCs exhibits an obvious diurnal cycle,with the peak at 1400–1500 LST and the valley at 0900–1000 LST.Most IDCs last less than five hours and more than half appear for only one hour.IDCs generally have a cold cloud area of 7422.9 km^(2),containing a precipitation area of approximately 65%.The larger the IDC,the larger the fraction of intense precipitation it contains.IDCs contribute approximately 20%–30%to total precipitation and approximately 30%–40%to extreme precipitation over the TP,with a larger percentage in July and August than in June and September.In terms of spatial distribution,IDCs contribute more to both total precipitation and extreme precipitation over the TP compared to the surrounding plain regions.IDCs over the TP account for a larger fraction than MCSs,indicating the important role of IDCs over the region.
基金This research was supported by National Natural Science Foundation of China (30371150 and 40371075).
文摘On the Loess Plateau, water is the main limiting factors for vegetation growth. Root distribution characters have special ecological meaning as it reflected the utilizations of trees to the environments. Even-aged stands ofRobinia pseudoacacia on slope lands facing south and north were selected as sampling plots for root distribution investigation. Investigatiing results showed that indicated that on all sites, root biomass decreased with depth, and the distribution depth of fine root was deeper than that of coarser root. The results of variance analysis indicated that there were great differences in root biomass among different diameter classes, and coarser root was the main sources of variance, and the root biomass, especially fine root (?<3mm) biomass on northern exposition sites was bigger than that on southern exposition sites. Analysis of the vertical root distribution parameters, root extinction coefficient, β indicated that the value of β on northern exposition was more than 0.982, while the value of β on southern exposition was less than 0.982, which indicated that the vertical root distribution depth ofRobinia pseudoacacia on southern exposition was deeper than that on southern exposition. And the distribution depth of fine roots (Φ<1mm) was deeper than that of thicker roots(Φ<3mm), which was in favor of the uptake of water and nutrients from deeper layers, helped the trees to adapt the arid environment, and promoted the growth of the upper parts of the tree. Keywords Root diameter classes - Variance analysis - Root extinction coefficient - Vertical distribution characters - Site conditions - Loess Plateau CLC number S792.27.01 Document code A Foundation Item: This research was supported by National Natural Science Foundation of China (30371150 and 40371075).Biography: LI Peng (1974-) male, post: Ph. D. in Northwest Scientific & Technological University of Agriculture and Forestry, Yangling 712100, Shaanxi Province, P. R. China. Tel: 029-82312651.Responsible editor: Chai Ruihal
文摘A promising method to improve the attosecond pulse intensity has been theoretically pre- sented by properly adding an ultraviolet pulse into the orthogonal two-color field. The results show that by properly adding a 125 nm ultraviolet pulse to the orthogonal two-color field, not only the harmonic yield is enhanced by 2 orders of magnitude compared with the original orthogonal two-color field case, but also the single short quantum path, which is selected to contribute to the harmonic spectrum, results in an ultrabroad 152 eV bandwidth. Moreover, by optimizing the laser parameters, we find that the harmonic enhancement is not very sen- sitive to the pulse duration and the polarized angle of the assisted ultraviolet pulse, which is much better for experimental realization. As a result, an isolated pulse with duration of 38 as can be obtained, which is 2 orders of magnitude improvement in comparison with the original two-color orthogonal field case.
文摘A new approach for blind equalization and channel identification is proposed in this paper. The equalization scheme is based on over sampling technique and an independent component analysis network. The equalized sequence and its higher order statistics are used to identify the channel parameters. Compared to traditional equalization methods, the proposed approach is with a simple architecture, and does not need learning sequences. Computer simulations show the validity of the proposed method.
文摘High quality cubic GaN (c GaN) is grown by metalorganic vapor deposition (MOCVD) at an increased growth temperature of 900℃,with the growth rate of 1 6μm/h.The full width at half maximum (FWHM) of room temperature photoluminescence (PL) for the high temperature grown GaN film is 48meV.It is smaller than that of the sample grown at 830℃.In X ray diffraction (XRD) measurement,the high temperature grown GaN shows a (002) peak at 20° with a FWHM of 21′.It can be concluded that,although c GaN is of metastable phase,high growth temperature is still beneficial to the improvement in its crystal quality.The relationship between the growth rate and growth temperature is also discussed.
