Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains l...Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains limited Accordingly, we measured sap flow velocity of Populus euphratica using the heat ratio method between 2012 and2014. Nocturnal stem sap flow was separated into nighttime and stem refilling using the ‘‘forecasted refilling''method. Nighttime transpiration was observed for each phenophase. The highest value was during the full foliation period but lowest during leaf expansion and defoliation periods. The contribution of nighttime transpiration to daytime transpiration was an average of 15% but this was comparatively higher during the defoliation period. Relationships between nighttime transpiration, vapor pressure deficits, and air temperatures were more closely associated than with wind speed in all phenophases. Moreover, we found that nighttime transpiration linearly correlated to vapour pressure deficit during the first and the full foliation periods, but nighttime transpiration showed exponential correlations to air temperatures during the same phenophases. Additionally, environmental drivers of transpiration were significantly different between nighttime and daytime(P \ 0.05). Driving forces behind nighttime transpiration were characterized by many factors, and integrated impacts between these multiple environmental factors were complex. Future studies should focus on these integrated impacts on nighttime transpiration, and the physiological mechanisms of nighttime transpiration should be investigated, given that this could also influence its occurrence and magnitude during different phenophases.展开更多
为探究环下润滑供油通道滑油流量分配特性,采用volume of fluid(VOF)方法对轴心射流收油环内部两相流动进行了计算,获得了供油通道内油膜形成过程与流场特征,重点讨论了供油温度、主轴转速、供油流量及供油孔径组合对流量分配的影响规律...为探究环下润滑供油通道滑油流量分配特性,采用volume of fluid(VOF)方法对轴心射流收油环内部两相流动进行了计算,获得了供油通道内油膜形成过程与流场特征,重点讨论了供油温度、主轴转速、供油流量及供油孔径组合对流量分配的影响规律,建立了临界孔径比的无量纲关联式。结果表明:滑油射流冲击收油环中心后形成油膜,其边缘断裂形成油带、油矢甩至侧壁面,最终油膜铺满整个端面;计算工况范围内,滑油分配主要受供油流量及孔径影响,各出口流量随供油流量上升均呈线性增加,滑油分配比随供油流量增加而平均降低15.05%;滑油分配比随下游孔径与孔径比的增加而上升;当无量纲供油流量越大且下游无量纲孔径越小时,临界孔径比越高并趋近于1,当无量纲供油流量降低或下游无量纲孔径增大时,临界孔径比则下降。展开更多
基金financially supported by the Key Research Program of Frontier Sciences CAS(QYZDJ-SSWDQC031)Key Project of the Chinese Academy of Sciences(KZZDEW-04-05)+1 种基金the National Natural Science Foundation of China(91025024)the ‘‘Western Light’’ project of the Chinese Academy of Science
文摘Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains limited Accordingly, we measured sap flow velocity of Populus euphratica using the heat ratio method between 2012 and2014. Nocturnal stem sap flow was separated into nighttime and stem refilling using the ‘‘forecasted refilling''method. Nighttime transpiration was observed for each phenophase. The highest value was during the full foliation period but lowest during leaf expansion and defoliation periods. The contribution of nighttime transpiration to daytime transpiration was an average of 15% but this was comparatively higher during the defoliation period. Relationships between nighttime transpiration, vapor pressure deficits, and air temperatures were more closely associated than with wind speed in all phenophases. Moreover, we found that nighttime transpiration linearly correlated to vapour pressure deficit during the first and the full foliation periods, but nighttime transpiration showed exponential correlations to air temperatures during the same phenophases. Additionally, environmental drivers of transpiration were significantly different between nighttime and daytime(P \ 0.05). Driving forces behind nighttime transpiration were characterized by many factors, and integrated impacts between these multiple environmental factors were complex. Future studies should focus on these integrated impacts on nighttime transpiration, and the physiological mechanisms of nighttime transpiration should be investigated, given that this could also influence its occurrence and magnitude during different phenophases.
文摘为探究环下润滑供油通道滑油流量分配特性,采用volume of fluid(VOF)方法对轴心射流收油环内部两相流动进行了计算,获得了供油通道内油膜形成过程与流场特征,重点讨论了供油温度、主轴转速、供油流量及供油孔径组合对流量分配的影响规律,建立了临界孔径比的无量纲关联式。结果表明:滑油射流冲击收油环中心后形成油膜,其边缘断裂形成油带、油矢甩至侧壁面,最终油膜铺满整个端面;计算工况范围内,滑油分配主要受供油流量及孔径影响,各出口流量随供油流量上升均呈线性增加,滑油分配比随供油流量增加而平均降低15.05%;滑油分配比随下游孔径与孔径比的增加而上升;当无量纲供油流量越大且下游无量纲孔径越小时,临界孔径比越高并趋近于1,当无量纲供油流量降低或下游无量纲孔径增大时,临界孔径比则下降。
