Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plan...Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plant community structure,has been tested many times in artificial productivity gradients(fertilization studies),but whether it applies to natural productivity gradients is unclear.Methods To test whether seedling light limitation would increase across a natural productivity gradient,I conducted a cross-site field experi-ment in southwest michigan,USA.A each of six old fields natu-rally varying in productivity,I exposed transplanted seedlings of big bluestem(Andropogon gerardii)to a light addition(tie-back)treat-ment that increased light availability and measured their biomass after one and two growing seasons.Important Findingsseedlings responded positively to the tie-back treatment,but positive responses did not increase across the natural productivity gradient.These results suggest that although light does limit seedling establishment,the strength of light limitation does not depend on variation in productivity in natural systems.Instead,light limitation interacted with a variety of site differences to determine establishment.although the general principle that light limitation increases with productivity is well established,these results indicate that it may not always occur in natural systems.展开更多
针对某轻客车型为提高乘员平躺舒适性而取消安全带锁扣弯钩限位结构的设计变更,评估其在正面碰撞中是否仍满足ECE R 137法规对乘员保护性能的要求。文章选取3套主驾座椅样本,其中2个取消锁扣弯钩限位及护罩结构,配备仪表板、气囊、安全...针对某轻客车型为提高乘员平躺舒适性而取消安全带锁扣弯钩限位结构的设计变更,评估其在正面碰撞中是否仍满足ECE R 137法规对乘员保护性能的要求。文章选取3套主驾座椅样本,其中2个取消锁扣弯钩限位及护罩结构,配备仪表板、气囊、安全带等系统部件,依据ECE R 137法规搭建滑台试验系统,采用Hybrid Ⅲ 50th假人,通过高速摄像与数据采集设备,进行3次重复碰撞试验,系统分析假人关键伤害指标。结果显示,取消弯钩限位后,所有假人伤害指标均符合法规要求,头部伤害值略有降低,颈、胸及大腿部伤害值保持稳定,试验重复性良好,表明约束系统性能未受影响。取消安全带锁扣弯钩限位结构在保障碰撞安全的前提下,可提升乘员舒适性,为该车型设计改进提供了可靠依据。展开更多
基金National Science Foundation[0909942]Lauff and Porter awards from the Kellogg Biological Station+2 种基金an A.L.Rogers Endowed Research Scholarship from Michigan State Universitythe NSF Long-Term Ecological Research Program at KBSMSU AgBioResearch.This is KBS contribution 1705.
文摘Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plant community structure,has been tested many times in artificial productivity gradients(fertilization studies),but whether it applies to natural productivity gradients is unclear.Methods To test whether seedling light limitation would increase across a natural productivity gradient,I conducted a cross-site field experi-ment in southwest michigan,USA.A each of six old fields natu-rally varying in productivity,I exposed transplanted seedlings of big bluestem(Andropogon gerardii)to a light addition(tie-back)treat-ment that increased light availability and measured their biomass after one and two growing seasons.Important Findingsseedlings responded positively to the tie-back treatment,but positive responses did not increase across the natural productivity gradient.These results suggest that although light does limit seedling establishment,the strength of light limitation does not depend on variation in productivity in natural systems.Instead,light limitation interacted with a variety of site differences to determine establishment.although the general principle that light limitation increases with productivity is well established,these results indicate that it may not always occur in natural systems.
文摘针对某轻客车型为提高乘员平躺舒适性而取消安全带锁扣弯钩限位结构的设计变更,评估其在正面碰撞中是否仍满足ECE R 137法规对乘员保护性能的要求。文章选取3套主驾座椅样本,其中2个取消锁扣弯钩限位及护罩结构,配备仪表板、气囊、安全带等系统部件,依据ECE R 137法规搭建滑台试验系统,采用Hybrid Ⅲ 50th假人,通过高速摄像与数据采集设备,进行3次重复碰撞试验,系统分析假人关键伤害指标。结果显示,取消弯钩限位后,所有假人伤害指标均符合法规要求,头部伤害值略有降低,颈、胸及大腿部伤害值保持稳定,试验重复性良好,表明约束系统性能未受影响。取消安全带锁扣弯钩限位结构在保障碰撞安全的前提下,可提升乘员舒适性,为该车型设计改进提供了可靠依据。
