Collisions with another person on ski slopes pose a serious risk of injury.Snow-poor winters related to climate change may contribute to an increasing need for artificial snow on slopes,at least in the ski areas of th...Collisions with another person on ski slopes pose a serious risk of injury.Snow-poor winters related to climate change may contribute to an increasing need for artificial snow on slopes,at least in the ski areas of the Alps.As a result,the number of available downhill slopes may be limited,which causes higher traffic on available ski terrain.In addition,artificial snow is often hard and icy,promoting high downhill speeds and is associated with long braking distances.It is therefore not surprising that the number of reported collisions involving skiers and/or snowboarders is increasing.展开更多
Fractal assembly in discrete structures,especially for artificial supramolecular species,has attracted significantly increased interest over the past two decades.In this study,we present the precisely controlled fract...Fractal assembly in discrete structures,especially for artificial supramolecular species,has attracted significantly increased interest over the past two decades.In this study,we present the precisely controlled fractal expanding synthesis of a novel triangular prism supramolecule featuring Sierpiński triangular face,which was achieved through a module-intervened self-expansion strategy.The homoleptic S1 was firstly synthesized through the assembly of ligand L1 with Zn2+ions.Based on the triangular-faced prism S1,we further introduced Sierpiński triangular faces on the section of the heteroleptic supramolecular cage S2 with an expanded inner cavity and more abundant active sites for photocatalytic properties.The topotactic architectures for both S1 and S2 were fully characterized by nuclear magnetic resonance spectroscopy,high-resolution electrospray ionization mass spectrometry,transmission electron microscopy,and atomic force microscopy.Furthermore,the enhanced photocatalytic activity of the fractal expanded S2 was performed via the superior amine oxidative efficiency over S1.This study proposes the unprecedented fractal expanding strategy for three-dimensional supramolecular species with higher complexity,potentially opening new avenues for structural regulation of artificial fractal molecules.展开更多
To address the contradiction between the rapid development of ski tourism and effective protection of the ecological environment,this study constructed the DPSIR-EES(Drive-Pressures-State-Impact-Response-Environment-E...To address the contradiction between the rapid development of ski tourism and effective protection of the ecological environment,this study constructed the DPSIR-EES(Drive-Pressures-State-Impact-Response-Environment-Economy-Society)model and Ski Tourism Destination Ecological Security System(STDESS)framework system.They form an integrated methodology system based on the“entropy weighting-hierarchical analysis-gray correlation projection”composite weighting method that can be used to clarify the intrinsic mechanism of ecological security in ski tourism destinations.Taking Chongli as a case study,this study evaluated the evolution of its ecological security from 1995 to 2023,predicted the ecological security early warning levels from 2024 to 2050,and analyzed the mechanism of influences on regional ecological security.The findings indicate that the ecological security of ski tourism destinations shows a significant“stepped leap–dynamic equilibrium”evolutionary path.The dynamic response mechanism of the subsystems is characterized by significant heterogeneity.The ecological security early warning system revealed the temporal and sequential differentiation of risk transmission.The factors influencing ecological security show the significant dual dominance of policy and climate.This paper enhances the applicability of ecological security systems within ski tourism contexts by analyzing their evolutionary characteristics,predicted future changes and impact factors,and it provides an effective case study for ecological improvement.展开更多
Purpose:This study aimed to compare biomechanical aspects of a novel"running"diagonal stride(DSRUN)with"conventional"diagonal stride(DSCONV)skiing techniques performed at high speed.Methods:Ten eli...Purpose:This study aimed to compare biomechanical aspects of a novel"running"diagonal stride(DSRUN)with"conventional"diagonal stride(DSCONV)skiing techniques performed at high speed.Methods:Ten elite Italian male junior cross-country skiers skied on a treadmill at 10 km/h and at a 10°incline utilizing both variants of the diagonal stride technique.The 3-dimensional kinematics of the body,poles,and roller skis;the force exerted through the poles and foot plantar surfaces;and the angular motion of the leg joints were determined.Results:Compared to DSCONV,DSRUN demonstrated shorter cycle times(1.05±0.05 s vs.0.75±0.03 s(mean±SD),p<0.001)due to a shorter rolling phase(0.40±0.04 s vs.0.09±0.04 s,p<0.001);greater force applied perpendicularly to the roller skis when they had stopped rolling forward(413±190 N vs.890±170 N,p<0.001),with peak force being attained earlier;prolonged knee extension,with a greater range of motion during the roller ski-stop phase(28°±40 vs.16°±3°,p=0.00014);and more pronounced hip and knee flexion during most of the forward leg swing.The mechanical work performed against friction during rolling was significantly less with DSRUN than with DSCONV(0.04±0.01 J/m/kg vs.0.10±0.02 J/m/kg,p<0.001).Conclusion:Our findings demonstrate that DSRUN is characterize by more rapid propulsion,earlier leg extension,and a greater range of motion of knee joint extension than DSCONV-Further investigations,preferably on snow,should reveal whether DSRUN results in higher acceleration and/or higher peak speed.展开更多
Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpin′ ski triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are c...Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpin′ ski triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are constructed in this study by using 1208 V-shaped 4,400-dicyano-1,10:30,100-terphenyl molecules and Fe atoms on Au(1 1 1), and studied in detail by low-temperature scanning tunneling microscopy. Density functional theory calculations are employed to rationalize the invisible Fe atoms in STM images. Monte Carlo simulations are performed to understand the formation mechanism of the surface-supported fractal crystals.展开更多
摘要Collisions with another person on ski slopes pose a serious risk of injury.Snow-poor winters related to climate change may contribute to an increasing need for artificial snow on slopes,at least in the ski areas of the Alps.As a result,the number of available downhill slopes may be limited,which causes higher traffic on available ski terrain.In addition,artificial snow is often hard and icy,promoting high downhill speeds and is associated with long braking distances.It is therefore not surprising that the number of reported collisions involving skiers and/or snowboarders is increasing.
基金supported by the Major Science and Technology Projects of Yunnan Province(No.202302AB080016)the National Natural Science Foundation of China(Nos.22101060,22371056,and 52303269)the Science and Technology Research Project of Guangzhou(Nos.202201020201 and 2023A03J0624)。
摘要Fractal assembly in discrete structures,especially for artificial supramolecular species,has attracted significantly increased interest over the past two decades.In this study,we present the precisely controlled fractal expanding synthesis of a novel triangular prism supramolecule featuring Sierpiński triangular face,which was achieved through a module-intervened self-expansion strategy.The homoleptic S1 was firstly synthesized through the assembly of ligand L1 with Zn2+ions.Based on the triangular-faced prism S1,we further introduced Sierpiński triangular faces on the section of the heteroleptic supramolecular cage S2 with an expanded inner cavity and more abundant active sites for photocatalytic properties.The topotactic architectures for both S1 and S2 were fully characterized by nuclear magnetic resonance spectroscopy,high-resolution electrospray ionization mass spectrometry,transmission electron microscopy,and atomic force microscopy.Furthermore,the enhanced photocatalytic activity of the fractal expanded S2 was performed via the superior amine oxidative efficiency over S1.This study proposes the unprecedented fractal expanding strategy for three-dimensional supramolecular species with higher complexity,potentially opening new avenues for structural regulation of artificial fractal molecules.
基金National Natural Science Foundation of China,No.42471284,No.42071199Beijing Social Science Foundation,No.22GLB036。
摘要To address the contradiction between the rapid development of ski tourism and effective protection of the ecological environment,this study constructed the DPSIR-EES(Drive-Pressures-State-Impact-Response-Environment-Economy-Society)model and Ski Tourism Destination Ecological Security System(STDESS)framework system.They form an integrated methodology system based on the“entropy weighting-hierarchical analysis-gray correlation projection”composite weighting method that can be used to clarify the intrinsic mechanism of ecological security in ski tourism destinations.Taking Chongli as a case study,this study evaluated the evolution of its ecological security from 1995 to 2023,predicted the ecological security early warning levels from 2024 to 2050,and analyzed the mechanism of influences on regional ecological security.The findings indicate that the ecological security of ski tourism destinations shows a significant“stepped leap–dynamic equilibrium”evolutionary path.The dynamic response mechanism of the subsystems is characterized by significant heterogeneity.The ecological security early warning system revealed the temporal and sequential differentiation of risk transmission.The factors influencing ecological security show the significant dual dominance of policy and climate.This paper enhances the applicability of ecological security systems within ski tourism contexts by analyzing their evolutionary characteristics,predicted future changes and impact factors,and it provides an effective case study for ecological improvement.
摘要Purpose:This study aimed to compare biomechanical aspects of a novel"running"diagonal stride(DSRUN)with"conventional"diagonal stride(DSCONV)skiing techniques performed at high speed.Methods:Ten elite Italian male junior cross-country skiers skied on a treadmill at 10 km/h and at a 10°incline utilizing both variants of the diagonal stride technique.The 3-dimensional kinematics of the body,poles,and roller skis;the force exerted through the poles and foot plantar surfaces;and the angular motion of the leg joints were determined.Results:Compared to DSCONV,DSRUN demonstrated shorter cycle times(1.05±0.05 s vs.0.75±0.03 s(mean±SD),p<0.001)due to a shorter rolling phase(0.40±0.04 s vs.0.09±0.04 s,p<0.001);greater force applied perpendicularly to the roller skis when they had stopped rolling forward(413±190 N vs.890±170 N,p<0.001),with peak force being attained earlier;prolonged knee extension,with a greater range of motion during the roller ski-stop phase(28°±40 vs.16°±3°,p=0.00014);and more pronounced hip and knee flexion during most of the forward leg swing.The mechanical work performed against friction during rolling was significantly less with DSRUN than with DSCONV(0.04±0.01 J/m/kg vs.0.10±0.02 J/m/kg,p<0.001).Conclusion:Our findings demonstrate that DSRUN is characterize by more rapid propulsion,earlier leg extension,and a greater range of motion of knee joint extension than DSCONV-Further investigations,preferably on snow,should reveal whether DSRUN results in higher acceleration and/or higher peak speed.
基金supported by National Natural Science Foundation of China(Nos.21373020,21403008,61321001,21433011,21522301,21133001,21333001,913000002)Ministry of Science and Technology(Nos.2014CB 239302,2013CB 933404,2011CB808702)the Research Fund for the Doctoral Program of Higher Education(No.20130001110029)
摘要Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpin′ ski triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are constructed in this study by using 1208 V-shaped 4,400-dicyano-1,10:30,100-terphenyl molecules and Fe atoms on Au(1 1 1), and studied in detail by low-temperature scanning tunneling microscopy. Density functional theory calculations are employed to rationalize the invisible Fe atoms in STM images. Monte Carlo simulations are performed to understand the formation mechanism of the surface-supported fractal crystals.