Previous quasi-static cyclic tests of shear walls,which routinely used an incremental lateral displacement test protocol with a constant axial load,failed to reflect the character of moment-shear force interaction of ...Previous quasi-static cyclic tests of shear walls,which routinely used an incremental lateral displacement test protocol with a constant axial load,failed to reflect the character of moment-shear force interaction of prototype buildings.To study the effect of the moment-shear force interaction on the seismic performance of shear walls,three identical 2-story shear wall specimens with different loading patterns were constructed at 1/2 scale,to represent the lower portion of an 11-story high-rise building,and were tested under reversed cyclic loads.The axial force,shear force and bending moment were simultaneously applied to simulate the effects of gravity loads and earthquake excitations on the prototype.The axial force and bending moment delivered from the upper structure were applied to the top of the specimens by two vertical actuators,and the shear force was applied to the specimens by two horizontal actuators.A mixed force-displacement control test program was adopted to ensure that the bending moment and the lateral shear were increased proportionally.The experimental results show that the moment-shear force interaction had a significant effect on the failure pattern,hysteretic characteristics,ductility and energy dissipation of the specimens.It is recommended that moment-shear force interaction should be considered in the loading condition of RC shear wall substructures cyclic tests.展开更多
Relationship between biodiversity and ecosystem function is one of the core issues in ecological research.Phytoplankton,as the main producer of aquatic ecosystem,its diversity,productivity,and community stability are ...Relationship between biodiversity and ecosystem function is one of the core issues in ecological research.Phytoplankton,as the main producer of aquatic ecosystem,its diversity,productivity,and community stability are of great signifi cance to reveal ecosystem function.There are signifi cant diff erences in hydrodynamics,water retention time,and phytoplankton community structure between river-type reservoir and newly built lake-type reservoir.The comparative analysis of phytoplankton community stability between the two types of reservoir has not been reported.Jiuquwan Reservoir(river-type)and Taihu Reservoir(lake-type),the two reservoirs in the Dongjiang River source area of Zhujiang(Pearl)River Basin,were selected for comparison in terms of multi-year operation vs.new impoundment,river-type vs.lake-type,and shallow water vs.sub-deep water reservoirs.Samples were collected in dry season(December 2019),normal season(March 2020),and wet season(August 2020),on which the phytoplankton diversity and productivity of the two reservoirs,and the relationship and diff erence of community stability were examined.Results show that(1)the number of phytoplankton species in Jiuquwan Reservoir decreased comparing that before algal bloom and the restoration treatment,while that in Taihu Reservoir increased compared with that before the impoundment of the reservoir.There was no signifi cant diff erence in functional groups and species number between the two reservoirs(P>0.05);(2)the biological stability,diversity,productivity,and resource utilization effi ciency of newly built lake-type reservoir were higher than those of multi-year river-type reservoir.In addition,the utilization effi ciency of phytoplankton resources was the highest in wet season in both reservoirs.The increases in biodiversity,richness,and evenness promoted the stability of the community,while increases in productivity and resource utilization effi ciency weakened the stability of the community;(3)community stability was aff ected by both biotic and abiotic factors,and hydrodynamic index was the main factor.This study is helpful to understand the relationship and diff erences in phytoplankton diversity,productivity and community stability in diff erent types of reservoirs,and provides a guidance for maintaining the stability of reservoir water ecosystem and protecting the biodiversity.The relationships between phytoplankton diversity,productivity,and community stability will be investigated in depth,for which a long-term observation will be conducted on the impact of environmental factors and diversity on the local biostability in diff erent types of reservoirs.展开更多
The compromise between strength and plasticity has greatly limited the potential application of particles reinforced magnesium matrix composites(MMCs).In this work,the Ti particles reinforced AZ31 magnesium(Mg)matrix ...The compromise between strength and plasticity has greatly limited the potential application of particles reinforced magnesium matrix composites(MMCs).In this work,the Ti particles reinforced AZ31 magnesium(Mg)matrix composites achieved simultaneous improvement in strength,elongation and wear resistance.The Ti particles reinforced AZ31 composites were fabricated by ultrasonic-assisted stir casting with hot extrusion.The results showed that a strong interfacial bonding was obtained at Ti/Mg interface because of the formation of semicoherent orientation relationship of Ti Al/Mg,Ti Al/Al_(2)Ti and Al_(2)Ti/Mg interfaces.The as-extruded 6 wt.%Ti/AZ31 composite presented the best compressive mechanical properties and wear resistance with ultimate tensile strength,elongation and wear rate of 327 MPa,20.4%and 9.026×10^(-3)mm^(3)/m,obviously higher than those of AZ31 alloys.The enhanced mechanical properties were attributed to the grain refinement and strong interfacial bonding.The improved wear resistance was closely related to the increased hardness of composites and the formation of protective oxidation films.展开更多
Ecophysiological responses to drought stress of Populus euphratica in Alashan Desert Eco-hydrology Experimental Research Station were investigated.Results show that under mild and moderate drought stress,stomatal leng...Ecophysiological responses to drought stress of Populus euphratica in Alashan Desert Eco-hydrology Experimental Research Station were investigated.Results show that under mild and moderate drought stress,stomatal length,aperture,area and density is likely to decrease in the early days,but afterwards this is likely to recovery with treatment over the pas‐sage of treatment time.Under severe drought stress,these properties appear to decline continuously.However,after 45 days of drought-stress treatment,the decline is not as noticeable as before,indicating that Populus euphratica could possibly reduce water evaporation by shutting down the stoma,leading to an improvement in its water use efficiency with better survival under drought stress conditions.The leaf area first decreases,and then increases under mild and moderate drought stress conditions,with the average values under different degree of stress found to be approximately 129.52,120.08,116.63 and 107.28 cm2,respectively.Under moderate stress conditions,the leaf water potential appears to show a continuous decline where the average values under different degree of stress are found to be-1.27,-1.85,-4.29 and-4.80 MPa,respectively.In terms of proline content,the results demonstrate that this factor appears to increase significant‐ly under moderate and severe drought stress conditions.Especially under severe drought stress condition,the content is found to be more than 700μg/g.Ranging over average values of 14.64 and 15.90 nmol/g under moderate and severe drought stress,respectively,Malondialdehyde content is found to increase quite rapidly under moderate and severe drought stress conditions at first,which then appears to decrease gradually with the treatment over time.展开更多
The dynamic behavior of entangled poly(methyl methacrylate)(PMMA)chains in both the traditional monocationic ionic liquid(MIL)and synthetic dicationic ionic liquid(DIL)with the same anion bis[(trifluoromethyl)sulfonyl...The dynamic behavior of entangled poly(methyl methacrylate)(PMMA)chains in both the traditional monocationic ionic liquid(MIL)and synthetic dicationic ionic liquid(DIL)with the same anion bis[(trifluoromethyl)sulfonyl]imide([TFSI]−)has been examined over the wide composition range using differential scanning calorimetry and rheological measurements.PMMA/DIL and PMMA/MIL systems exhibit two glass transitions in the midrange of composition due to self-concentration effects.PMMA in DIL shows slower relaxation behavior,however,after the iso-free-volume correction,the terminal relaxation timeτ_(0)of PMMA in both the DIL and MIL presents the power law behaviorτ_(0)∼ϕ^(v)with exponent v conforming to experimental results for conventional polymer solutions(v=2.0±0.2).At high ILs concentration(70%),the entanglement molecular weight M_(e)of PMMA/DIL system is lower than that of PMMA/MIL system owing to the formation of additional physical network in DIL,while the difference of M_(e)is reversed at low ILs content.The composition dependence might be related to the fact that the probability of formation of physical cross-linking points in linked double imidazolium ring increases with the increase of DIL content.The recovered creep strain of PMMA/DIL is almost 18 times of PMMA/MIL,exhibiting significantly better viscoelastic behavior.展开更多
In this study,the deformable titanium(Ti)particles reinforced AZ91 composite was successfully prepared by powder metallurgy and subsequent extrusion.The mechanical properties and microstructural evolution of pure AZ91...In this study,the deformable titanium(Ti)particles reinforced AZ91 composite was successfully prepared by powder metallurgy and subsequent extrusion.The mechanical properties and microstructural evolution of pure AZ91 and 5 Ti/AZ91 composite were studied.The yield strength,ultimate tensile strength,and elongation of 5 Ti/AZ91 composite are measured to be 212 MPa,323 MPa,and 10.1%,respectively.Microstructure analysis revealed that Ti particles are elongated along the extrusion direction,forming a discontinuous strip Ti particles,fine precipitated Mg_(17)Al_(12) phase inhibits dynamic recrystallization(DRX)behavior through Zener pinning effect and hinders the growth of matrix grains,resulting in refiner grains of 5 Ti/AZ91 composite.Heterogeneous deformed Ti particles and magnesium(Mg)matrix to generate additional heterogeneous deformation-induced(HDI)strengthening.Heterogeneous deformation-induced strengthening mainly contributed to the increment of yield strength for 5 Ti/AZ91 composite.展开更多
Abstract The overall crystallization kinetics and spherulite morphologies of miscible poly（ethylene oxide） （PEO）/1-butyl-3- methylimidazolium hexafluorophosphate （[BMIM][PF6]） mixtures were studied by differenti...Abstract The overall crystallization kinetics and spherulite morphologies of miscible poly（ethylene oxide） （PEO）/1-butyl-3- methylimidazolium hexafluorophosphate （[BMIM][PF6]） mixtures were studied by differential scanning calorimetry （DSC）, polarized optical microscopy （POM） and rheological measurements. The finer crystal structures were further detected by wide angle X-ray diffraction （WAXD） and small angle X-ray scattering （SAXS）. Crystallization of PEO is largely suppressed by [BMIM][PF6] addition especially at higher ionic liquid （IL） concentrations above 20 wt%. Both the overall crystallization rate and the spherulite growth decrease with the increase of IL content and crystallization temperature; however, the crystallization mechanism keeps unchanged as evidenced by the similar Avrami exponent n and WAXD results. The addition of [BMIM][PF6] could induce more nuclei to some extent, but the induction time of crystallization is evidently prolonged, and a linear to non-linear transition of the spherulite growth （R ∝ t to R ∝t^1/2） can be observed. At higher IL concentration, the spherulite texture changes apparently from particular serrated to branch surface due to the diffusion-controlled growth and the dilution effect, which also as a main factor contributes to the increasing trend of the long period of crystals.展开更多
A new one-step synthesis of 3-hydroxymethylbenzofuran, based on intramolecular cyclization of 2- （methoxymethyl）-2-（2＇-methoxymethyl-4＇-methylphenyl）-butanone I under diluted hydrochloric acid in THF, was develo...A new one-step synthesis of 3-hydroxymethylbenzofuran, based on intramolecular cyclization of 2- （methoxymethyl）-2-（2＇-methoxymethyl-4＇-methylphenyl）-butanone I under diluted hydrochloric acid in THF, was developed. The mechanism for this process was investigated via chemical equilibrium shift of tautomer in acidic conditions. The applicability of this new method was studied further in this paper.展开更多
基金supported by the Basic Research Plan of Yunnan Province,China(No.2019FA020)the Yunling Scholars of Yunnan Province,China(No.KKRC201952012)the Leading Talents of Industrial Technology in Ten Thousand Talents Plan of Yunnan Province,China,and the Scientist Studio of Yunnan Province,China.
基金Acknowledgments The authors acknowledge the financial support from the Guangdong Major Project of Basic and Applied Basic Research,China(No.2020B0301030006)the National Natural Science Foundation of China(Nos.52171133,52171103)+1 种基金the“111 Project”by the Ministry of Education of China(No.B16007)Fundamental Research Fund of Central Universities in China(No.2018CDJDCL0019)。
基金Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration under Grant No.2019B05the Heilongjiang Provincial Natural Science Foundation of China under Grant No.LH2019E098,the National Natural Science Foundation of China under Grant Nos.51878631 and 51678544the National Key Research and Development Program of China under Grant Nos.2017YFC1500605 and 2018YFC1504602-01。
文摘Previous quasi-static cyclic tests of shear walls,which routinely used an incremental lateral displacement test protocol with a constant axial load,failed to reflect the character of moment-shear force interaction of prototype buildings.To study the effect of the moment-shear force interaction on the seismic performance of shear walls,three identical 2-story shear wall specimens with different loading patterns were constructed at 1/2 scale,to represent the lower portion of an 11-story high-rise building,and were tested under reversed cyclic loads.The axial force,shear force and bending moment were simultaneously applied to simulate the effects of gravity loads and earthquake excitations on the prototype.The axial force and bending moment delivered from the upper structure were applied to the top of the specimens by two vertical actuators,and the shear force was applied to the specimens by two horizontal actuators.A mixed force-displacement control test program was adopted to ensure that the bending moment and the lateral shear were increased proportionally.The experimental results show that the moment-shear force interaction had a significant effect on the failure pattern,hysteretic characteristics,ductility and energy dissipation of the specimens.It is recommended that moment-shear force interaction should be considered in the loading condition of RC shear wall substructures cyclic tests.
基金Supported by the Key Research and Development Program of Guangdong Province(No.2019B110205004)the Science and Technology Foundation of Guizhou Province(Nos.[2020]4Y009,[2020]6009)。
文摘Relationship between biodiversity and ecosystem function is one of the core issues in ecological research.Phytoplankton,as the main producer of aquatic ecosystem,its diversity,productivity,and community stability are of great signifi cance to reveal ecosystem function.There are signifi cant diff erences in hydrodynamics,water retention time,and phytoplankton community structure between river-type reservoir and newly built lake-type reservoir.The comparative analysis of phytoplankton community stability between the two types of reservoir has not been reported.Jiuquwan Reservoir(river-type)and Taihu Reservoir(lake-type),the two reservoirs in the Dongjiang River source area of Zhujiang(Pearl)River Basin,were selected for comparison in terms of multi-year operation vs.new impoundment,river-type vs.lake-type,and shallow water vs.sub-deep water reservoirs.Samples were collected in dry season(December 2019),normal season(March 2020),and wet season(August 2020),on which the phytoplankton diversity and productivity of the two reservoirs,and the relationship and diff erence of community stability were examined.Results show that(1)the number of phytoplankton species in Jiuquwan Reservoir decreased comparing that before algal bloom and the restoration treatment,while that in Taihu Reservoir increased compared with that before the impoundment of the reservoir.There was no signifi cant diff erence in functional groups and species number between the two reservoirs(P>0.05);(2)the biological stability,diversity,productivity,and resource utilization effi ciency of newly built lake-type reservoir were higher than those of multi-year river-type reservoir.In addition,the utilization effi ciency of phytoplankton resources was the highest in wet season in both reservoirs.The increases in biodiversity,richness,and evenness promoted the stability of the community,while increases in productivity and resource utilization effi ciency weakened the stability of the community;(3)community stability was aff ected by both biotic and abiotic factors,and hydrodynamic index was the main factor.This study is helpful to understand the relationship and diff erences in phytoplankton diversity,productivity and community stability in diff erent types of reservoirs,and provides a guidance for maintaining the stability of reservoir water ecosystem and protecting the biodiversity.The relationships between phytoplankton diversity,productivity,and community stability will be investigated in depth,for which a long-term observation will be conducted on the impact of environmental factors and diversity on the local biostability in diff erent types of reservoirs.
基金the financial supports from the Guangdong Major Project of Basic and Applied Basic Research(2020B0301030006)the National Natural Science Foundation of China(Nos.52171103,52171133)+3 种基金the Natural Science Foundation of Chongqing(cstc2019jcyjmsxm X0234)the“111 Project”(B16007)by the Ministry of Educationthe Fundamental Research Funds for the Central Universities(No.2020CDJDPT001)Graduate Research and Innovation Foundation of Chongqing,China(No.CYB21001)。
文摘The compromise between strength and plasticity has greatly limited the potential application of particles reinforced magnesium matrix composites(MMCs).In this work,the Ti particles reinforced AZ31 magnesium(Mg)matrix composites achieved simultaneous improvement in strength,elongation and wear resistance.The Ti particles reinforced AZ31 composites were fabricated by ultrasonic-assisted stir casting with hot extrusion.The results showed that a strong interfacial bonding was obtained at Ti/Mg interface because of the formation of semicoherent orientation relationship of Ti Al/Mg,Ti Al/Al_(2)Ti and Al_(2)Ti/Mg interfaces.The as-extruded 6 wt.%Ti/AZ31 composite presented the best compressive mechanical properties and wear resistance with ultimate tensile strength,elongation and wear rate of 327 MPa,20.4%and 9.026×10^(-3)mm^(3)/m,obviously higher than those of AZ31 alloys.The enhanced mechanical properties were attributed to the grain refinement and strong interfacial bonding.The improved wear resistance was closely related to the increased hardness of composites and the formation of protective oxidation films.
基金the National Natural Science Foundation of China"Nighttime tran-spiration and its eco-hydrological effects in typical desert vegetation"(42001038)the Major special projects of science and technology in Inner Mongolia Autonomous Region(zdzx2018057)+1 种基金the project of CAS innovation cross team(JCTD-2019-19)The authors thank anonymous reviewers for their valuable review and constructive comments on this manuscript.
文摘Ecophysiological responses to drought stress of Populus euphratica in Alashan Desert Eco-hydrology Experimental Research Station were investigated.Results show that under mild and moderate drought stress,stomatal length,aperture,area and density is likely to decrease in the early days,but afterwards this is likely to recovery with treatment over the pas‐sage of treatment time.Under severe drought stress,these properties appear to decline continuously.However,after 45 days of drought-stress treatment,the decline is not as noticeable as before,indicating that Populus euphratica could possibly reduce water evaporation by shutting down the stoma,leading to an improvement in its water use efficiency with better survival under drought stress conditions.The leaf area first decreases,and then increases under mild and moderate drought stress conditions,with the average values under different degree of stress found to be approximately 129.52,120.08,116.63 and 107.28 cm2,respectively.Under moderate stress conditions,the leaf water potential appears to show a continuous decline where the average values under different degree of stress are found to be-1.27,-1.85,-4.29 and-4.80 MPa,respectively.In terms of proline content,the results demonstrate that this factor appears to increase significant‐ly under moderate and severe drought stress conditions.Especially under severe drought stress condition,the content is found to be more than 700μg/g.Ranging over average values of 14.64 and 15.90 nmol/g under moderate and severe drought stress,respectively,Malondialdehyde content is found to increase quite rapidly under moderate and severe drought stress conditions at first,which then appears to decrease gradually with the treatment over time.
基金the National Natural Science Foundation of China(Nos.51873125,52073184 and 51721091)Scientific Research Foundation of International Cooperation and Exchanges of Sichuan Province(No.2019YFH0027).
文摘The dynamic behavior of entangled poly(methyl methacrylate)(PMMA)chains in both the traditional monocationic ionic liquid(MIL)and synthetic dicationic ionic liquid(DIL)with the same anion bis[(trifluoromethyl)sulfonyl]imide([TFSI]−)has been examined over the wide composition range using differential scanning calorimetry and rheological measurements.PMMA/DIL and PMMA/MIL systems exhibit two glass transitions in the midrange of composition due to self-concentration effects.PMMA in DIL shows slower relaxation behavior,however,after the iso-free-volume correction,the terminal relaxation timeτ_(0)of PMMA in both the DIL and MIL presents the power law behaviorτ_(0)∼ϕ^(v)with exponent v conforming to experimental results for conventional polymer solutions(v=2.0±0.2).At high ILs concentration(70%),the entanglement molecular weight M_(e)of PMMA/DIL system is lower than that of PMMA/MIL system owing to the formation of additional physical network in DIL,while the difference of M_(e)is reversed at low ILs content.The composition dependence might be related to the fact that the probability of formation of physical cross-linking points in linked double imidazolium ring increases with the increase of DIL content.The recovered creep strain of PMMA/DIL is almost 18 times of PMMA/MIL,exhibiting significantly better viscoelastic behavior.
基金financially supported by the Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030006)the National Natural Science Foundation of China(Nos.52171133 and 52171103)the“111 Project”(B16007)by the Ministry of Education and Fundamental Research Fund of Central Universities in China(No.2018CDJDCL0019)。
文摘In this study,the deformable titanium(Ti)particles reinforced AZ91 composite was successfully prepared by powder metallurgy and subsequent extrusion.The mechanical properties and microstructural evolution of pure AZ91 and 5 Ti/AZ91 composite were studied.The yield strength,ultimate tensile strength,and elongation of 5 Ti/AZ91 composite are measured to be 212 MPa,323 MPa,and 10.1%,respectively.Microstructure analysis revealed that Ti particles are elongated along the extrusion direction,forming a discontinuous strip Ti particles,fine precipitated Mg_(17)Al_(12) phase inhibits dynamic recrystallization(DRX)behavior through Zener pinning effect and hinders the growth of matrix grains,resulting in refiner grains of 5 Ti/AZ91 composite.Heterogeneous deformed Ti particles and magnesium(Mg)matrix to generate additional heterogeneous deformation-induced(HDI)strengthening.Heterogeneous deformation-induced strengthening mainly contributed to the increment of yield strength for 5 Ti/AZ91 composite.
基金financially supported by the National Natural Science Foundation of China(Nos.51573115 and 51421061)
文摘Abstract The overall crystallization kinetics and spherulite morphologies of miscible poly（ethylene oxide） （PEO）/1-butyl-3- methylimidazolium hexafluorophosphate （[BMIM][PF6]） mixtures were studied by differential scanning calorimetry （DSC）, polarized optical microscopy （POM） and rheological measurements. The finer crystal structures were further detected by wide angle X-ray diffraction （WAXD） and small angle X-ray scattering （SAXS）. Crystallization of PEO is largely suppressed by [BMIM][PF6] addition especially at higher ionic liquid （IL） concentrations above 20 wt%. Both the overall crystallization rate and the spherulite growth decrease with the increase of IL content and crystallization temperature; however, the crystallization mechanism keeps unchanged as evidenced by the similar Avrami exponent n and WAXD results. The addition of [BMIM][PF6] could induce more nuclei to some extent, but the induction time of crystallization is evidently prolonged, and a linear to non-linear transition of the spherulite growth （R ∝ t to R ∝t^1/2） can be observed. At higher IL concentration, the spherulite texture changes apparently from particular serrated to branch surface due to the diffusion-controlled growth and the dilution effect, which also as a main factor contributes to the increasing trend of the long period of crystals.
基金supported by the National Mega-Project for Innovative Drugs (No. 2012zx09301002-002)State Key Laboratory of Bioactive Substance and Function of Natural Medicines
文摘A new one-step synthesis of 3-hydroxymethylbenzofuran, based on intramolecular cyclization of 2- （methoxymethyl）-2-（2＇-methoxymethyl-4＇-methylphenyl）-butanone I under diluted hydrochloric acid in THF, was developed. The mechanism for this process was investigated via chemical equilibrium shift of tautomer in acidic conditions. The applicability of this new method was studied further in this paper.
