以西北农林科技大学校园内生长良好的耐旱树种刺槐(R obin ia p seud oacacia L.)、元宝枫(A certrunca tum Bge.)、沙棘(H ipp ophae rham noid es L.)、白榆(U lm us pum ila L.)、油松(P inus tabu laef orm is C arr.)、白皮松(P in...以西北农林科技大学校园内生长良好的耐旱树种刺槐(R obin ia p seud oacacia L.)、元宝枫(A certrunca tum Bge.)、沙棘(H ipp ophae rham noid es L.)、白榆(U lm us pum ila L.)、油松(P inus tabu laef orm is C arr.)、白皮松(P inus bung eana Zucc.ex End l.)及中生树种女贞(L igustrum lucidum A it.)和柳树(S a lix m a tsud ana K o idz.f.p endu la Schne id)为研究对象,用压力套在2.5 M Pa下诱导1年生枝条发生木质部栓塞,研究自然条件下木质部栓塞的恢复特性,探讨木质部栓塞恢复特性与PV曲线水分参数间的关系。结果表明,木质部栓塞恢复的快慢,与其小枝的木质部栓塞脆弱性顺序基本一致;栓塞的发生和恢复与树木木质部的结构密切相关。植物木质部栓塞的发生、恢复,与植物耐旱性一样受多种因素控制,虽然与PV曲线水分参数有一定关系,但任何单一水分参数的排序,均与木质部栓塞的脆弱性和恢复速率不完全一致。木质部水势和树木不同部位间的水势梯度是影响木质部栓塞发生和恢复的最主要因素,蒸腾作用、气孔关闭及植物的渗透调节等可能也与木质部栓塞的恢复有关。展开更多
Aims Nocturnal sap flow(E_(night))has been observed in a variety of plant species and environmental conditions.In water-limited environ-ments,E_(night) is important in the regulation of plant water’s physi-ology.This...Aims Nocturnal sap flow(E_(night))has been observed in a variety of plant species and environmental conditions.In water-limited environ-ments,E_(night) is important in the regulation of plant water’s physi-ology.This study was designed to evaluate the way in which E_(night)(defined as sap flow from 20:30 to 06:00)responded to changes in the atmospheric vapor pressure deficit(VPD)and the soil water con-tent(SWC),and explored its potential physiological significance for different plant species in a semi-arid area.Methods We selected three shrub species:Vitex negundo L.(VN),Hippophae rhamnoides L.(HR)and Spiraea pubescens Turcz(SP)in the semi-arid Loess Plateau of China.The plots of the three communities dominated by each of three species were on the same hill slope.Half-hourly sap flow density was measured in six to seven sample stems for each species during the main grow-ing season(June to August 2015).VPD,SWC,leaf water potential(Ψleaf)and stomatal conductance(G_(s))were measured at the same time.Regression analyses were conducted to determine the rela-tionships between E_(night),E_(day),E_(night)/E_(daily),VPD and SWC at half-hourly and daily time scales,as well as between E_(night),E_(day) andΨleaf.Important Findings The mean values of E_(night) and E_(day) were higher,but E_(night)/E_(daily) val-ues were lower for VN compared to HR and SP.The responses of sap flow density to VPD and SWC varied at different temporal scales.VPD was the dominant factor that affected E_(night) and E_(day) at the half-hourly scale for all three species.In contrast,SWC was the key factor that influenced E_(day) at the daily time scale.The values of E_(day) and E_(night)/E_(daily) correlated negatively with SWC because the effect of SWC was stronger on E_(day) than on E_(night).Although the low fraction of E_(night)/E_(daily)(4%-7%)may indicate a minor short-term effect of E_(night) on the standing water balance,E_(night) had eco-physiologically significance to the plants.The discrepancy inΨleaf between sunset and the following 展开更多
Although hydrogen leakage at hydrogen refueling stations has been a concern,less efforts have been devoted to hydrogen leakage during the refueling of hydrogen-powered vehicles.In this study,hydrogen leakage and dilut...Although hydrogen leakage at hydrogen refueling stations has been a concern,less efforts have been devoted to hydrogen leakage during the refueling of hydrogen-powered vehicles.In this study,hydrogen leakage and dilution from the hydrogen dispenser during the refueling of hydrogen-powered vehicles were numerically investigated under different wind configurations.The shape,size,and distribution of flammable gas clouds(FGC)during the leakage and dilution processes were analyzed.The results showed that the presence of hydrogen-powered vehicles resulted in irregular FGC shapes.Greater wind speeds(v wv)were associated with longer FGC propagation distances.At v_(wv)=2 m·s^(−1)and 10 m·s^(−1),the FGC lengths at the end of the leakage were 7.9 m and 20.4 m,respectively.Under downwind conditions,higher wind speeds corresponded to lower FGC heights.The FGC height was larger under upwind conditions and was slightly affected by the magnitude of the wind speed.In the dilution process,the existence of a region with a high hydrogen concentration led to the FGC volume first increasing and then gradually decreasing.Wind promoted the mixing of hydrogen and air,accelerated FGC dilution,inhibited hydrogen uplifting,and augmented the horizontal movement of the FGC.At higher wind speeds,the low-altitude FGC movements could induce potential safety hazards.展开更多
Cells utilize calcium ions(Ca^2+)to signal almost all aspects of cellular life,ranging from cell proliferation to cell death,in a spatially and temporally regulated manner.A key aspect of this regulation is the compar...Cells utilize calcium ions(Ca^2+)to signal almost all aspects of cellular life,ranging from cell proliferation to cell death,in a spatially and temporally regulated manner.A key aspect of this regulation is the compartmen-talization of Ca^2+in various cytoplasmic organelles that act as intracellular Ca^2+stores.Whereas Ca^2+release from the large-volume Ca^2+stores,such as the endoplasmic reticulum(ER)and Golgi apparatus,are preferred for signal transduction,Ca^2+release from the small-volume individual vesicular stores that are dispersed throughout the cell,such as lysosomes,may be more useful in local regulation,such as membrane fusion and individualized vesicular movements.Conceivably,these two types of Ca^2+stores may be established,maintained or refilled via distinct mechanisms.ER stores are refilled through sustained Ca^2+influx at ER-plasma membrane(PM)membrane contact sites(MCSs).In this review,we discuss the release and refilling mechanisms of intracellular small vesicular Ca^2+stores,with a special focus on lysosomes.Recent imaging studies of Ca2+release and organelle MCSs suggest that Ca^2+exchange may occur between two types of stores,such that the small stores acquire Ca^2+from the large stores via ER-vesicle MCSs.Hence vesicular stores like lysosomes may be viewed as secondary Ca^2+stores in the cell.展开更多
PEGylation is the gold standard for constructing protein resistance surfaces.Herein,grafting mPEG-SH and SH-PEG-SH with varied molecular weights(Mw=5K,10K,and 20K)on a gold chip,and the subsequent lysozyme adsorptions...PEGylation is the gold standard for constructing protein resistance surfaces.Herein,grafting mPEG-SH and SH-PEG-SH with varied molecular weights(Mw=5K,10K,and 20K)on a gold chip,and the subsequent lysozyme adsorptions of the PEG layers are evaluated using quartzcrystal microbalance based on dissipation(QCM-D).The lysozyme resistance depends on the features of grafting density and chain conformation,i.e.,linear and looped conformation.However,long-chain PEG(Mw≥10K)is insufficient to form a dense layer to resist protein due to large steric hindrances.Short-chain PEG(Mw=1K)with linear and looped structures is used to refill onto the long-chain PEG layer to increase the grafting density of PEGs and improve protein resistance.The refilling process and the subsequent protein adsorption depend on conformation rather than the density of the long-chain PEG substrate.Notably,the long-chain PEG looped substrates significantly improve protein resistance,attributing to the high viscoelasticity of the looped substrate and an increase in grafting density after refilling.Thus,refilling short-chain PEG improves protein resistance and the substrate conformation-dependence gives insight into the impact of topology,providing new ideas for how to increase chain density and select suitable topology to resist protein adsorption and demonstrating a potential application in biomedical fields.展开更多
Friction spot welding （FSpW） was successfully used to produce joints of LY12 aluminum alloy. The effects of refilling time on microstructure and mechanical properties of FSpW joints were systematically studied. Resu...Friction spot welding （FSpW） was successfully used to produce joints of LY12 aluminum alloy. The effects of refilling time on microstructure and mechanical properties of FSpW joints were systematically studied. Results show that the cross-section of FSpW joint presents a basin-like morphology. A white bonding ligament exists in the center of the joint. The stir zone can be clarified into sleeve affected zone and pin affected zone based on different grain sizes. With increasing the refilling time from 2. 0 s to 3.5 s, grains in the stir zone become coarser, microhardness of the joint decreases and tensile shear failure load of the joint firstly increases and then decreases. The maximum tensile shear failure load of 8 130 N is attained when the refilling time is 3.0 s. Shear-plug fracture mode and shear fracture mode can be observed in the tensile shear tests. The maximum hardness of 169. 7 HV is attained in the joint center when the refilling time is 2. 0 s.展开更多
Based on the practices of construction supervision to cement grouting at the reservoir emptying and power tunnels of the TSQ stage Ⅰ Hydropower station, some issues on quality control of cement grouting of hydraulic ...Based on the practices of construction supervision to cement grouting at the reservoir emptying and power tunnels of the TSQ stage Ⅰ Hydropower station, some issues on quality control of cement grouting of hydraulic tunnel are discussed, and corresponding suggestions are put forward for revision of current standard (SL62-94). It is regarded that the refilling grouting could not be used for remedying the thickness of concrete lining; the end sealing of refilling grouting section should not be neglected; higher grouting pressure would be used. For the consolidation grouting, grout return pipe should be placed at the grout hole top for pure pressure type grouting; five-grade water cement ratio of grout mix is suggested; a certain standard should be specified for changing the grout to thicker mix by skipping the intermediate grade; the standard for ending the grouting should be relaxed. In current grouting standard, some terms should be complemented for contact grouting of steel penstock and spiral case and for plug grouting of circular-anchor hole.展开更多
文摘以西北农林科技大学校园内生长良好的耐旱树种刺槐(R obin ia p seud oacacia L.)、元宝枫(A certrunca tum Bge.)、沙棘(H ipp ophae rham noid es L.)、白榆(U lm us pum ila L.)、油松(P inus tabu laef orm is C arr.)、白皮松(P inus bung eana Zucc.ex End l.)及中生树种女贞(L igustrum lucidum A it.)和柳树(S a lix m a tsud ana K o idz.f.p endu la Schne id)为研究对象,用压力套在2.5 M Pa下诱导1年生枝条发生木质部栓塞,研究自然条件下木质部栓塞的恢复特性,探讨木质部栓塞恢复特性与PV曲线水分参数间的关系。结果表明,木质部栓塞恢复的快慢,与其小枝的木质部栓塞脆弱性顺序基本一致;栓塞的发生和恢复与树木木质部的结构密切相关。植物木质部栓塞的发生、恢复,与植物耐旱性一样受多种因素控制,虽然与PV曲线水分参数有一定关系,但任何单一水分参数的排序,均与木质部栓塞的脆弱性和恢复速率不完全一致。木质部水势和树木不同部位间的水势梯度是影响木质部栓塞发生和恢复的最主要因素,蒸腾作用、气孔关闭及植物的渗透调节等可能也与木质部栓塞的恢复有关。
基金This work was supported by the National Natural Science Foundation of China(No.41390462 and 41230745)the Project of Social Science Youth Foundation of Beijing Municipal(No.15JGC148).
文摘Aims Nocturnal sap flow(E_(night))has been observed in a variety of plant species and environmental conditions.In water-limited environ-ments,E_(night) is important in the regulation of plant water’s physi-ology.This study was designed to evaluate the way in which E_(night)(defined as sap flow from 20:30 to 06:00)responded to changes in the atmospheric vapor pressure deficit(VPD)and the soil water con-tent(SWC),and explored its potential physiological significance for different plant species in a semi-arid area.Methods We selected three shrub species:Vitex negundo L.(VN),Hippophae rhamnoides L.(HR)and Spiraea pubescens Turcz(SP)in the semi-arid Loess Plateau of China.The plots of the three communities dominated by each of three species were on the same hill slope.Half-hourly sap flow density was measured in six to seven sample stems for each species during the main grow-ing season(June to August 2015).VPD,SWC,leaf water potential(Ψleaf)and stomatal conductance(G_(s))were measured at the same time.Regression analyses were conducted to determine the rela-tionships between E_(night),E_(day),E_(night)/E_(daily),VPD and SWC at half-hourly and daily time scales,as well as between E_(night),E_(day) andΨleaf.Important Findings The mean values of E_(night) and E_(day) were higher,but E_(night)/E_(daily) val-ues were lower for VN compared to HR and SP.The responses of sap flow density to VPD and SWC varied at different temporal scales.VPD was the dominant factor that affected E_(night) and E_(day) at the half-hourly scale for all three species.In contrast,SWC was the key factor that influenced E_(day) at the daily time scale.The values of E_(day) and E_(night)/E_(daily) correlated negatively with SWC because the effect of SWC was stronger on E_(day) than on E_(night).Although the low fraction of E_(night)/E_(daily)(4%-7%)may indicate a minor short-term effect of E_(night) on the standing water balance,E_(night) had eco-physiologically significance to the plants.The discrepancy inΨleaf between sunset and the following
基金the National Natural Science Foundation of China(Grant No.:52176070).
文摘Although hydrogen leakage at hydrogen refueling stations has been a concern,less efforts have been devoted to hydrogen leakage during the refueling of hydrogen-powered vehicles.In this study,hydrogen leakage and dilution from the hydrogen dispenser during the refueling of hydrogen-powered vehicles were numerically investigated under different wind configurations.The shape,size,and distribution of flammable gas clouds(FGC)during the leakage and dilution processes were analyzed.The results showed that the presence of hydrogen-powered vehicles resulted in irregular FGC shapes.Greater wind speeds(v wv)were associated with longer FGC propagation distances.At v_(wv)=2 m·s^(−1)and 10 m·s^(−1),the FGC lengths at the end of the leakage were 7.9 m and 20.4 m,respectively.Under downwind conditions,higher wind speeds corresponded to lower FGC heights.The FGC height was larger under upwind conditions and was slightly affected by the magnitude of the wind speed.In the dilution process,the existence of a region with a high hydrogen concentration led to the FGC volume first increasing and then gradually decreasing.Wind promoted the mixing of hydrogen and air,accelerated FGC dilution,inhibited hydrogen uplifting,and augmented the horizontal movement of the FGC.At higher wind speeds,the low-altitude FGC movements could induce potential safety hazards.
文摘Cells utilize calcium ions(Ca^2+)to signal almost all aspects of cellular life,ranging from cell proliferation to cell death,in a spatially and temporally regulated manner.A key aspect of this regulation is the compartmen-talization of Ca^2+in various cytoplasmic organelles that act as intracellular Ca^2+stores.Whereas Ca^2+release from the large-volume Ca^2+stores,such as the endoplasmic reticulum(ER)and Golgi apparatus,are preferred for signal transduction,Ca^2+release from the small-volume individual vesicular stores that are dispersed throughout the cell,such as lysosomes,may be more useful in local regulation,such as membrane fusion and individualized vesicular movements.Conceivably,these two types of Ca^2+stores may be established,maintained or refilled via distinct mechanisms.ER stores are refilled through sustained Ca^2+influx at ER-plasma membrane(PM)membrane contact sites(MCSs).In this review,we discuss the release and refilling mechanisms of intracellular small vesicular Ca^2+stores,with a special focus on lysosomes.Recent imaging studies of Ca2+release and organelle MCSs suggest that Ca^2+exchange may occur between two types of stores,such that the small stores acquire Ca^2+from the large stores via ER-vesicle MCSs.Hence vesicular stores like lysosomes may be viewed as secondary Ca^2+stores in the cell.
基金financially supported by the National Natural Science Foundation of China(No.52073276)Changchun Science and Technology Development Program(No.21ZY07)the Innovation and Entrepreneurship Talent Project of Jilin Province.
文摘PEGylation is the gold standard for constructing protein resistance surfaces.Herein,grafting mPEG-SH and SH-PEG-SH with varied molecular weights(Mw=5K,10K,and 20K)on a gold chip,and the subsequent lysozyme adsorptions of the PEG layers are evaluated using quartzcrystal microbalance based on dissipation(QCM-D).The lysozyme resistance depends on the features of grafting density and chain conformation,i.e.,linear and looped conformation.However,long-chain PEG(Mw≥10K)is insufficient to form a dense layer to resist protein due to large steric hindrances.Short-chain PEG(Mw=1K)with linear and looped structures is used to refill onto the long-chain PEG layer to increase the grafting density of PEGs and improve protein resistance.The refilling process and the subsequent protein adsorption depend on conformation rather than the density of the long-chain PEG substrate.Notably,the long-chain PEG looped substrates significantly improve protein resistance,attributing to the high viscoelasticity of the looped substrate and an increase in grafting density after refilling.Thus,refilling short-chain PEG improves protein resistance and the substrate conformation-dependence gives insight into the impact of topology,providing new ideas for how to increase chain density and select suitable topology to resist protein adsorption and demonstrating a potential application in biomedical fields.
基金This work is supported by the National Natural Science Foundation of China （No. 51204111 ）, the Natural Science Foundation of Liaoning Province （ No. 2013024004 and No. 2014024008）.
文摘Friction spot welding （FSpW） was successfully used to produce joints of LY12 aluminum alloy. The effects of refilling time on microstructure and mechanical properties of FSpW joints were systematically studied. Results show that the cross-section of FSpW joint presents a basin-like morphology. A white bonding ligament exists in the center of the joint. The stir zone can be clarified into sleeve affected zone and pin affected zone based on different grain sizes. With increasing the refilling time from 2. 0 s to 3.5 s, grains in the stir zone become coarser, microhardness of the joint decreases and tensile shear failure load of the joint firstly increases and then decreases. The maximum tensile shear failure load of 8 130 N is attained when the refilling time is 3.0 s. Shear-plug fracture mode and shear fracture mode can be observed in the tensile shear tests. The maximum hardness of 169. 7 HV is attained in the joint center when the refilling time is 2. 0 s.
文摘Based on the practices of construction supervision to cement grouting at the reservoir emptying and power tunnels of the TSQ stage Ⅰ Hydropower station, some issues on quality control of cement grouting of hydraulic tunnel are discussed, and corresponding suggestions are put forward for revision of current standard (SL62-94). It is regarded that the refilling grouting could not be used for remedying the thickness of concrete lining; the end sealing of refilling grouting section should not be neglected; higher grouting pressure would be used. For the consolidation grouting, grout return pipe should be placed at the grout hole top for pure pressure type grouting; five-grade water cement ratio of grout mix is suggested; a certain standard should be specified for changing the grout to thicker mix by skipping the intermediate grade; the standard for ending the grouting should be relaxed. In current grouting standard, some terms should be complemented for contact grouting of steel penstock and spiral case and for plug grouting of circular-anchor hole.
