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To recruit to reproductive size in fire-prone savannas, juvenile trees must avoid stem mortality (topkill) by fire. Theory suggests they either grow tall, raising apical buds above the flames, or wide, buffering the stem from fire. However, growing tall or wide is of no advantage without stem protection from fire. In Litchfield National Park, northern Australia, we explored the importance of bark thickness to stem survival following fire in a eucalypt-dominated tropical savanna. We measured bark thickness, prefire height, stem diameter and resprouting responses of small stems under conditions of low to moderate fire intensity. Fire induced mortality was low (<10%), topkill was uncommon (<11% of 5 m to 37% of 1 m tall stems) and epicormic resprouting was common. Topkill was correlated only with absolute bark thickness and not with stem height or width. Thus, observed height and diameter growth responses of small stems are likely different pathways to achieving bark thick enough to protect buds and the vascular cambium. Juvenile height was traded off against the cost of thick bark, so that wide stems were short with thicker bark for a given height. The fire resilience threshold for bark thickness differed between tall (4-5 mm) and wide individuals (8-9 mm), yet tall stems had lower P Topkill for a given bark thickness. Trends in P Topkill reflected eucalypt versus non-eucalypt differences. Eucalypts had thinner bark than non-eucalypts but lower P Topkill . With deeply embedded epicormic buds eucalypts do not need thick bark to protect buds and can allocate resources to height growth. Our data suggest the only 'strategy' for avoiding topkill in fire-prone systems is to optimise bark thickness to maximise stem bud and cambium protection. Thus, escape height is the height at which bark protects the stem and a wide stem per se is insufficient protection from fire without thick bark. Consequently, absolute bark thickness is crucial to explanations of species differences in topkill, resprouting response and tree community composition in fire-prone savannas. Bark thickness and the associated mechanism of bud protection offer a proximate explanation for the dominance of eucalypts in Australian tropical savannas.

To determine the selection of input wave field at the bottom of the viscous-elastic boundary, and study the seismic response of two parallel large-diameter shield tunnels, corresponding numerical models were established for analysis. First, through the study of wave method for seismic motion input of viscous-elastic boundary, several different wave fields selection methods for calculating the equivalent nodal forces at the bottom of the model were compared using free field and scattering field models. Then, using viscous-elastic boundary and the previous seismic motion input method, established soil-tunnels system finite element models with different interval between two large-diameter tunnels and input seismic waves with different spectral characteristics analyzed the dynamic response of the soil-tunnels system. The results show that the simulation accuracy is highest when calculating the equivalent nodal loads by the free wave field, and the seismic input method based on the substructure of artificial bound

Purpose To examine the changes in the pupillary light response after phacoemulsification and to compare the difference in the response among patients in different age categories. Study design Prospective observational study. Methods Four-hundred twenty-two eyes of 422 patients in 3 age categories (60-69 years, 70-79 years, and 80-89 years) scheduled for phacoemulsification were consecutively enrolled. The eyes underwent examinations with an infrared pupillometer to obtain the parameters of the pupillary light response preoperatively and at 1 day and 1 and 3 months postoperatively. Differences in the parameters of the pupillary response were compared among 4 time intervals and the 3 age categories. Results The mean maximum and minimum pupillary diameters significantly decreased at 1 day postoperatively and returned to the preoperative level by 1 month postoperatively ( P <.0001). The mean percentage of pupillary constriction was significantly reduced at 1 and 3 months postoperatively compared with preoperatively and at 1 day postoperatively ( P <.0001). The average pupillary constriction and dilation velocities were significantly lower at 1 and 3 months postoperatively than they were preoperatively and at 1 day postoperatively ( P <.0001). The latency to constriction did not differ significantly among the time intervals. The percentage of pupillary constriction was significantly smaller, and the average constriction and dilation velocities were lower in association with higher age categories at all time intervals ( P ≤.0185). Conclusion The pupillary light response was impaired several months after cataract surgery and worsened with increasing patient age, indicating that cataract surgery may compromise the pupillary constriction and dilation functions in association with age.

S718.5; [目的]研究兴安落叶松生物量增长率对氮沉降是否存在响应,年际间是否存在差异;不同径级是否会影响兴安落叶松生物量增长率对氮沉降的响应.[方法]通过人工氮添加的方法模拟大气氮沉降变化,探究兴安落叶松林连续3年(2014—2016)树木生物量的变化对氮沉降的响应.从2012年开始,共设置4个氮添加水平,分别为对照(CK,0 g·m-2·a-1)、低氮(TL,2.5 g·m-2·a-1)、中氮(TM,5 g·m-2·a-1)和高氮(TH,7.5 g·m-2·a-1),每年的生长季(5—10月)按月将NH4 NO3溶于32 L蒸馏水,利用背喷式喷雾器均匀喷洒于样方内,对照样地喷洒等量纯净水.[结果](1)3年间各施氮处理生物量增长率均显著高于对照组(P<0.05)、各年份生物量增长率均存在显著差异(P<0.05),而且2016年生物量增长率明显高于前两年(P<0.05).(2)2014年各处理间无显著差异;2015年TL处理的生物量增长率显著高于TM和TH处理(P<0.05),2016年TL处理的生物量增长率显著高于TH处理(P<0.05).(3)不同处理对年际间不同径级生物量增长率也产生不同影响.TL处理对2014和2016年的1015 cm径级的兴安落叶松生物量增长率有显著促进作用(P<0.05);TM处理对所有年份1015 cm和1520 cm径级兴安落叶松生物量增长率均有显著促进作用(P<0.05);TH处理对所有年份胸径大于10 cm的3个径级(1015、1520、>20 cm)兴安落叶松生物量增长率均有显著促进作用(P<0.05).[结论](1)长期氮添加有可能导致树木生长率的增量逐渐减少甚至出现抑制,将改变现有北方森林生态系统碳源汇动态;(2)由于不同径级树木对氮沉降的响应不同,为提高氮沉降对北方森林碳库影响的模型预测精度,应按不同径级分别模拟.