Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtr...Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtropical regions.In this study,a 4-year nitrogen addition experiment explored its eff ects on foliar litter production and carbon,nitrogen and phosphorus in a subtropical Michelia wilsonii forest.A clear seasonal pattern in foliar litterfall was observed,regardless of nitrogen treatments,with a peak in spring and a smaller one in autumn.Foliar litter increased with increasing nitrogen but did not aff ect litter carbon concentrations and often decreased nitrogen and phosphorous concentrations.The eff ect of nitrogen addition was dependent on time(month/year).Carbon,nitrogen and phosphorous return showed similar bimodal seasonal patterns.Nitrogen addition increased carbon and nitrogen return but did not aff ect phosphorous.Our results suggest that the addition of nitrogen stimulates carbon and nutrient return via litterfall.展开更多
Comparative analyses were conducted on the nutrient element content and returning amount of main fractional compositions of litter in Korean pine (KP), Mongolian Scots pine(MSP) and Dahurian larch (DL) plantations in ...Comparative analyses were conducted on the nutrient element content and returning amount of main fractional compositions of litter in Korean pine (KP), Mongolian Scots pine(MSP) and Dahurian larch (DL) plantations in Laoshan Plantation Experiment Station of Maoershan Experiment Forest Farm of Northeast Forestry University. The results are as follows: (1) The nutrient element content and returning amount in litter varies among different fractional compositions and tree species, the total returning amount of all nutrient elements and the returning amount of K, Ca, Mg, N and P are DL>MSP>KP, the returning amount of Cu is DL>KP>MSP, the returning amount of Fe and Mn are MSP>DL>KP, (2) To KP and DL plantations, the main nutrient element returned is dead needles; dead branches, bark scales and dead cones account for a little proportion; whereas to MSP plantation, besides dead needles,dead branches and bark scales also play an important role in the return of nutrient elements; (3)A little deal of dead leaves can provided a great deal of returning amount of nutrient elements.展开更多
火星表面发射起飞是实现火星采样返回任务的关键环节之一。为准确评估火星上升器(Mars Ascent Vehicle,MAV)发射起飞时的动力学响应,基于离散单元法(Discrete Element Method,DEM)构建了模拟火壤颗粒介质模型,研究模拟火壤的承载力学特...火星表面发射起飞是实现火星采样返回任务的关键环节之一。为准确评估火星上升器(Mars Ascent Vehicle,MAV)发射起飞时的动力学响应,基于离散单元法(Discrete Element Method,DEM)构建了模拟火壤颗粒介质模型,研究模拟火壤的承载力学特性。构建了“模拟火壤–着陆器–发射装置–上升器”多要素耦合动力学模型,开展了倾斜热发射动力学仿真。结果表明,在斜坡表面沿不同方向发射时,上升器发射分离时姿态角变化较小,偏航、俯仰、滚转角分别不大于1.0°、3.2°、0.18°;上升器运动将影响模拟火壤对着陆器各足垫支承载荷的幅值,发射过程中着陆器俯仰角与滑移量较小,整体姿态稳定,可有效支撑上升器的发射分离过程。研究方法可用于指导星表发射装置的动力学仿真与稳定性设计。展开更多
本文以斗式提升机为模型,采用DEM(Discrete Element Method)算法对粉料在提升机内运动过程进行离散元模拟仿真,分析粉料颗粒在其内部的运动轨迹,得出粉料粒径以及料斗数对提升机回料率的影响规律,为提升机的结构优化提出理论性的指导。...本文以斗式提升机为模型,采用DEM(Discrete Element Method)算法对粉料在提升机内运动过程进行离散元模拟仿真,分析粉料颗粒在其内部的运动轨迹,得出粉料粒径以及料斗数对提升机回料率的影响规律,为提升机的结构优化提出理论性的指导。结果表明:(1)均匀粉料粒径越小,机尾回料越严重,并得到回料量与粒径之间的关系式;(2)斗数增加可以提高提升机输送效率,降低粉料回料量;(3)随着粉料粒径的增大,料斗填充率呈现先增大后降低的趋势,并在4 mm粉料粒径时得到峰值,填充率达到69%。展开更多
基金supported by the National Natural Science Foundation of China(grants 32071745,32001165,31901295 and 31800519)the Program of Sichuan Excellent Youth Sci-Tech Foundation(2020JDJQ0052)+1 种基金the Applied Basic Research Program of Sichuan of China(2021YJ0340)the National Key Research and Development Program of China(2016YFC0502505 and 2017YFC0505003).
文摘Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtropical regions.In this study,a 4-year nitrogen addition experiment explored its eff ects on foliar litter production and carbon,nitrogen and phosphorus in a subtropical Michelia wilsonii forest.A clear seasonal pattern in foliar litterfall was observed,regardless of nitrogen treatments,with a peak in spring and a smaller one in autumn.Foliar litter increased with increasing nitrogen but did not aff ect litter carbon concentrations and often decreased nitrogen and phosphorous concentrations.The eff ect of nitrogen addition was dependent on time(month/year).Carbon,nitrogen and phosphorous return showed similar bimodal seasonal patterns.Nitrogen addition increased carbon and nitrogen return but did not aff ect phosphorous.Our results suggest that the addition of nitrogen stimulates carbon and nutrient return via litterfall.
文摘Comparative analyses were conducted on the nutrient element content and returning amount of main fractional compositions of litter in Korean pine (KP), Mongolian Scots pine(MSP) and Dahurian larch (DL) plantations in Laoshan Plantation Experiment Station of Maoershan Experiment Forest Farm of Northeast Forestry University. The results are as follows: (1) The nutrient element content and returning amount in litter varies among different fractional compositions and tree species, the total returning amount of all nutrient elements and the returning amount of K, Ca, Mg, N and P are DL>MSP>KP, the returning amount of Cu is DL>KP>MSP, the returning amount of Fe and Mn are MSP>DL>KP, (2) To KP and DL plantations, the main nutrient element returned is dead needles; dead branches, bark scales and dead cones account for a little proportion; whereas to MSP plantation, besides dead needles,dead branches and bark scales also play an important role in the return of nutrient elements; (3)A little deal of dead leaves can provided a great deal of returning amount of nutrient elements.
文摘火星表面发射起飞是实现火星采样返回任务的关键环节之一。为准确评估火星上升器(Mars Ascent Vehicle,MAV)发射起飞时的动力学响应,基于离散单元法(Discrete Element Method,DEM)构建了模拟火壤颗粒介质模型,研究模拟火壤的承载力学特性。构建了“模拟火壤–着陆器–发射装置–上升器”多要素耦合动力学模型,开展了倾斜热发射动力学仿真。结果表明,在斜坡表面沿不同方向发射时,上升器发射分离时姿态角变化较小,偏航、俯仰、滚转角分别不大于1.0°、3.2°、0.18°;上升器运动将影响模拟火壤对着陆器各足垫支承载荷的幅值,发射过程中着陆器俯仰角与滑移量较小,整体姿态稳定,可有效支撑上升器的发射分离过程。研究方法可用于指导星表发射装置的动力学仿真与稳定性设计。
文摘本文以斗式提升机为模型,采用DEM(Discrete Element Method)算法对粉料在提升机内运动过程进行离散元模拟仿真,分析粉料颗粒在其内部的运动轨迹,得出粉料粒径以及料斗数对提升机回料率的影响规律,为提升机的结构优化提出理论性的指导。结果表明:(1)均匀粉料粒径越小,机尾回料越严重,并得到回料量与粒径之间的关系式;(2)斗数增加可以提高提升机输送效率,降低粉料回料量;(3)随着粉料粒径的增大,料斗填充率呈现先增大后降低的趋势,并在4 mm粉料粒径时得到峰值,填充率达到69%。
