Unprecedented modern rates of warming are expected to advance alpine treelines to higher elevations,but global evidence suggests that current treeline dynamics are influenced by a variety of factors.Seasonal snow cove...Unprecedented modern rates of warming are expected to advance alpine treelines to higher elevations,but global evidence suggests that current treeline dynamics are influenced by a variety of factors.Seasonal snow cover has an essential impact on tree recruitment and growth in alpine regions,which may in turn influence current treeline elevation;however,little research has been conducted on its role in regional treeline formation.Based on 11,804treeline locations in the eastern Himalayas,we extracted elevation,climate,and topographic data for treeline and snowline.Specifically,we used linear and structural equation modelling to assess the relationship between these environmental factors and treeline elevation,and the climate-snow-treeline interaction mechanism.The results showed that the treeline elevation increased with summer temperature and permanent or seasonal snowline elevation,but decreased with snow cover days and spring temperature at the treeline positions(P<0.001).Importantly,spring snowline elevation(33.4%)and seasonal snow cover days(21.1%)contributed the most to treeline elevation,outperforming the permanent snowline,temperature,precipitation,and light.Our results support the assertion that the temperature-moisture interaction affects treeline elevation in the eastern Himalayas,but we also found that the effects were strongly mediated by seasonal snow cover patterns.The increasing tendency of snow cover governed by climate humidification observed in the eastern Himalayas,is likely to limit future treeline advancement and may even cause treeline decline due to the mortality of the remaining old trees.Together,our findings highlight the role of seasonal snow cover patterns in determining treeline elevation in the eastern Himalayas,which should be considered when assessing the potential for treeline ascent in snow-mediated alpine systems elsewhere.展开更多
Smart textiles are attracting great interest.Particularly,air-conditioning textiles are highly desired for their merits in energy conservation and personal temperature/humidity management.Currently,air-conditioning te...Smart textiles are attracting great interest.Particularly,air-conditioning textiles are highly desired for their merits in energy conservation and personal temperature/humidity management.Currently,air-conditioning textiles can be fabricated by two strategies.One uses infrared-radiation-adaptive materials,and the other uses moisture-responsive actuators that can regulate temperature and humidity simultaneously.Here,the fabrication of a silk-yarn switch comprising electrospun highly aligned nanofibers is reported and its application in air-conditioning textiles is demonstrated.Silk yarn rotates in contact with liquid,and can be recovered by drying.The different responses and wetting behaviors of the switch to H_(2)O and C_(2)H_(6)O is investigated.It is argued that alignment and surface hydrophilicity of nanofibers play important roles in this term.To elaborate,actuating trait is mainly controlled by reduction of the surface free energy of aligned silk nanofibers,during the wetting process.As proof of concept,the application of the sweat-driven silk-yarn switch in regulating the temperature/humidity of the human body is demonstrated in this work.Considering the large production,versatile processibility,and good biocompatibility,silk actuator may have practical applications in designing smart switches(or valves)for intelligent textiles,artificial muscles,and other application scenarios.展开更多
When a water droplet on a micropillar-structured hydrophobic surface is submitted to gradually increased pressure, the CassieBaxter wetting state transforms into the Wenzel wetting state once the pressure exceeds a cr...When a water droplet on a micropillar-structured hydrophobic surface is submitted to gradually increased pressure, the CassieBaxter wetting state transforms into the Wenzel wetting state once the pressure exceeds a critical value. It has been assumed that the reverse transition(Wenzel-to-Cassie-Baxter wetting state) cannot happen spontaneously after the pressure has been removed.In this paper, we report a new wetting-state transition. When external pressure is exerted on a droplet in the Cassie-Baxter wetting state on textured surfaces with high micropillars to trigger the breakdown of this wetting state, the droplet penetrates the micropillars but does not touch the base of the surface to trigger the occurrence of the Wenzel wetting state. We have named this state the suspended penetration wetting state. Spontaneous recovery from the suspended penetration wetting state to the initial Cassie-Baxter wetting state is achieved when the pressure is removed. Based on the experimental results, we built models to establish the penetration depth that the suspended penetration wetting state could achieve and to understand the energy barrier that influences the equilibrium position of the liquid surface. These results deepen our understanding of wetting states on rough surfaces subjected to external disturbances and shed new light on the design of superhydrophobic materials with a robust wetting stability.展开更多
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)program of China(No.2019QZKK0301)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA26010101)the National Natural Science Foundation of China(Nos.31860123,31560153)。
文摘Unprecedented modern rates of warming are expected to advance alpine treelines to higher elevations,but global evidence suggests that current treeline dynamics are influenced by a variety of factors.Seasonal snow cover has an essential impact on tree recruitment and growth in alpine regions,which may in turn influence current treeline elevation;however,little research has been conducted on its role in regional treeline formation.Based on 11,804treeline locations in the eastern Himalayas,we extracted elevation,climate,and topographic data for treeline and snowline.Specifically,we used linear and structural equation modelling to assess the relationship between these environmental factors and treeline elevation,and the climate-snow-treeline interaction mechanism.The results showed that the treeline elevation increased with summer temperature and permanent or seasonal snowline elevation,but decreased with snow cover days and spring temperature at the treeline positions(P<0.001).Importantly,spring snowline elevation(33.4%)and seasonal snow cover days(21.1%)contributed the most to treeline elevation,outperforming the permanent snowline,temperature,precipitation,and light.Our results support the assertion that the temperature-moisture interaction affects treeline elevation in the eastern Himalayas,but we also found that the effects were strongly mediated by seasonal snow cover patterns.The increasing tendency of snow cover governed by climate humidification observed in the eastern Himalayas,is likely to limit future treeline advancement and may even cause treeline decline due to the mortality of the remaining old trees.Together,our findings highlight the role of seasonal snow cover patterns in determining treeline elevation in the eastern Himalayas,which should be considered when assessing the potential for treeline ascent in snow-mediated alpine systems elsewhere.
基金This work was supported by the NSF of China(51672153,51422204,21975141)the National Key Basic Research and Development Program(No.2016YFA0200103)the National Program for Support of Top-notch Young Professionals.
文摘Smart textiles are attracting great interest.Particularly,air-conditioning textiles are highly desired for their merits in energy conservation and personal temperature/humidity management.Currently,air-conditioning textiles can be fabricated by two strategies.One uses infrared-radiation-adaptive materials,and the other uses moisture-responsive actuators that can regulate temperature and humidity simultaneously.Here,the fabrication of a silk-yarn switch comprising electrospun highly aligned nanofibers is reported and its application in air-conditioning textiles is demonstrated.Silk yarn rotates in contact with liquid,and can be recovered by drying.The different responses and wetting behaviors of the switch to H_(2)O and C_(2)H_(6)O is investigated.It is argued that alignment and surface hydrophilicity of nanofibers play important roles in this term.To elaborate,actuating trait is mainly controlled by reduction of the surface free energy of aligned silk nanofibers,during the wetting process.As proof of concept,the application of the sweat-driven silk-yarn switch in regulating the temperature/humidity of the human body is demonstrated in this work.Considering the large production,versatile processibility,and good biocompatibility,silk actuator may have practical applications in designing smart switches(or valves)for intelligent textiles,artificial muscles,and other application scenarios.
基金supported by the National Natural Science Foundation of China (Grant Nos.11632009,and 11872227)。
文摘When a water droplet on a micropillar-structured hydrophobic surface is submitted to gradually increased pressure, the CassieBaxter wetting state transforms into the Wenzel wetting state once the pressure exceeds a critical value. It has been assumed that the reverse transition(Wenzel-to-Cassie-Baxter wetting state) cannot happen spontaneously after the pressure has been removed.In this paper, we report a new wetting-state transition. When external pressure is exerted on a droplet in the Cassie-Baxter wetting state on textured surfaces with high micropillars to trigger the breakdown of this wetting state, the droplet penetrates the micropillars but does not touch the base of the surface to trigger the occurrence of the Wenzel wetting state. We have named this state the suspended penetration wetting state. Spontaneous recovery from the suspended penetration wetting state to the initial Cassie-Baxter wetting state is achieved when the pressure is removed. Based on the experimental results, we built models to establish the penetration depth that the suspended penetration wetting state could achieve and to understand the energy barrier that influences the equilibrium position of the liquid surface. These results deepen our understanding of wetting states on rough surfaces subjected to external disturbances and shed new light on the design of superhydrophobic materials with a robust wetting stability.
