The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform...The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform parachute systems.The projection area of canopy is calculated in the inflation process.The flow field characteristics and the interaction between canopies are analyzed.Results showed that,with free stream velocity of 50m/s,overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system,because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores.Concurrently,compared with the single-cruciform parachute,the vortex motion in the wake of double-cruciform-parachute is more intense.Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°.By comparison,the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50m/s.The results are consistent with those of the wind tunnel test.展开更多
Surface impact treatment was carried out on the cruciform joint weldment of 16MnR steel by using the HJ-II-type ultrasonic impact machine.The ultrasonic impact current is 1.2 A,the impact amplitude is 30?m and ultraso...Surface impact treatment was carried out on the cruciform joint weldment of 16MnR steel by using the HJ-II-type ultrasonic impact machine.The ultrasonic impact current is 1.2 A,the impact amplitude is 30?m and ultrasonic impacting time is 30 and 60 min,respectively.Fatigue experiments were carried out for both treated specimen and un-treated specimen by using EHF-EM200K2-070-1A fatigue testing machine.The fatigue fractures were observed with the scanning electron microscope of 6360LA type and the microstructure of ultrasonic impact treating surface layer was analyzed by using high resolution transmission electron microscope of JEM-2100 type.The experimental results show that the microstructure of ultrasonic impact surface layer has been successfully nanocrystallized.The fatigue life of welded cruciform joints of 16MnR steel can be significantly improved through the ultrasonic impact treatment.The main reasons are that the ultrasonic impact treating can reduces the stress concentration in the weld toe,decrease the tensile stress,and even change to compressive stress in the weldment,the grain size in the welded joint can be refined.The longer the impact time,the greater increasing range of fatigue life will be.Compared to the sample without treatment,its fatigue life was increased 210.37%,362.48%,respectively,when the impact time was 30,60 min,respectively.展开更多
Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of ...Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of load carrying cruciform joints inships is investigated using Effective Notch Stress (ENS) approach. A fictitious notch of 1 mm radius is introduced at theweld root and toe and fatigue stress is evaluated. The effect of weld leg length (l) and weld penetration depth (p) on ENS atweld root and toe are determined. The critical weld leg length (lcr) at which fatigue failure transitions from weld root toweld toe is investigated. An approximation formula for determination of the critical weld leg length considering weldpenetration depth (p) is proposed.展开更多
Using diamine as anchoring group, the self-assembled monolayers（SAMs） based on oligo（phenyleneethynylene）s（OPEs） and cruciform OPEs with an extended tetrathiafulvalene（TTF）（OPE3 and OPE3-TTF）were successfull...Using diamine as anchoring group, the self-assembled monolayers（SAMs） based on oligo（phenyleneethynylene）s（OPEs） and cruciform OPEs with an extended tetrathiafulvalene（TTF）（OPE3 and OPE3-TTF）were successfully formed on the Au substrate. The Uniformity and stability of SAMs were confirmed through cyclic voltammetry（CV） and electrochemical reductive desorption. The investigation of transport properties of SAMs was achieved by conducting-probe atomic force microscopy（CP-AFM） with both Au and Pt tips. The results indicated that the conductance of OPE3-TTF was 17 and 46 times that of OPE3 for Au and Pt tips, respectively. Theoretical calculations are qualitatively consistent with the experimental results, suggesting that the diamine as anchoring group has a great potential in molecular electronics.展开更多
In order to achieve a better understanding of failure behavior of cruciform specimen under different biaxial loading conditions,a three-dimensional finite element model is established with solid and interface elements...In order to achieve a better understanding of failure behavior of cruciform specimen under different biaxial loading conditions,a three-dimensional finite element model is established with solid and interface elements.Maximum stress criterion,two Hashin-type criteria and the new proposed criteria are used to predict the strength of plain woven textile composites when biaxial loading ratio equals 1.Compared with experimental data,only the new proposed criteria can reach reasonable results.The applicability of the new proposed criteria is also verified by predicting the tensile and compressive strength of cruciform specimen under different biaxial loading ratios.Moreover,the introduction of interface element makes it more intuitive to recognize delamination failure.The shape of the predicted delamination failure region in the interface layer is similar to that of the failure region in neighboring entity layers,but the area of delamination failure region is a little larger.展开更多
The growth of the low-altitude economy has led to an increase in the number of small aircraft and aviation equipment,thereby intensifying the demand for small-scale parachutes.Considering the limited attention to smal...The growth of the low-altitude economy has led to an increase in the number of small aircraft and aviation equipment,thereby intensifying the demand for small-scale parachutes.Considering the limited attention to small parachutes in existing research,this paper explores specialized parachutes with practical application value in framework of low-altitude economy.The Arbitrary Lagrangian–Eulerian(ALE)method was employed to analyze fluid-structure interaction(FSI)between parachute canopy and the surrounding air.The dynamic load curves demonstrate that at an inflow velocity of 10 m/s,the dynamic load peaks rapidly in less than 0.1 s during parachute opening,whereas at 50 m/s and 100 m/s,the time to peak is less than 0.03 s.The high-tension regions on the canopy's central surface exhibit an“X”-shaped distribution,with their area influenced by inflow velocity and inflation time,which informs the targeted reinforcement design for cruciform parachutes created by the simulation results in this study.A parachute airdrop test was conducted,and a combination of simplified model and drag coefficient correction is proposed to simulate the steady descent lift force.The relative error between simulation results of drag coefficient and the test data was found to be 4.49%.Simulation results show that the small-scale cruciform parachute in this study can carry an object with a mass of up to 10.18 kg,provided that the descent velocity is less than or equal to 10 m/s.The findings of this paper can provide a reference for the design and optimization of small-scale parachutes and help to assess their potential application in areas such as low-altitude economy.展开更多
It is a common phenomenon for organic semi- conductors to crystallize in two or more polymorphs, leading to various molecular packings and different charge transport properties. Therefore, it is a crucial issue of tun...It is a common phenomenon for organic semi- conductors to crystallize in two or more polymorphs, leading to various molecular packings and different charge transport properties. Therefore, it is a crucial issue of tuning molec- ular crystal polymorphs （i.e., adjusting the same molecule with different packing arrangements in solid state） towards efficient charge transport and high performance devices. Here, the choice of solvent had a marked effect on con- trolling the growth of a-phase ribbon and β-phase platelet during crystallization for an indenofluorene （IF） π-extended tetrathiafulvalene （TTF）-based cruciform molecule, named as IF-TTF. The charge carrier mobility of the a-phase IF-TTF crystals was more than one order of magnitude higher than that of β-phase crystals, suggesting the importance of reasonably tuning molecular packing in solid state for the improvement of charge transport in organic semiconductors.展开更多
Although camouflage as an effective antipredator defense strategy is widespread across animals,highly conspicuous color patterning is not uncommon either.Many orb-web spiders adorn their webs with extra bright white s...Although camouflage as an effective antipredator defense strategy is widespread across animals,highly conspicuous color patterning is not uncommon either.Many orb-web spiders adorn their webs with extra bright white silk.These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs,camouflaging spiders,acting as a decoy,or intimidating predators by their apparent size.The decorations may also deflect predator attacks from spiders.However,empirical evidence for this deflection function remains limited.Here,we tested this hypothesis using the X-shaped silk cruciform decorations built by females of Argiope minuta.We employed visual modeling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators.Then,we determined actual predation risk on spiders using naïve chicks as predators.Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems.Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs,thus reducing predation risk.When both spiders and decorations were present,chicks also attacked the spider main bodies and their legs or decorations,and not randomly:they attacked the legs or decorations sooner and more frequently than they attacked the main bodies,independent of the ratio of the surface area between the decoration and spider size.Despite the increase in detectability,incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack toward the decoration or leg,but not by camouflaging or intimidating,thus,supporting the deflection hypothesis.展开更多
In the half century since the discovery of the double-helix structure of DNA, it has become increasingly clear that DNA functionality is based on much more than its sequence in a double-helical structure. Further adva...In the half century since the discovery of the double-helix structure of DNA, it has become increasingly clear that DNA functionality is based on much more than its sequence in a double-helical structure. Further advances have highlighted the importance of additional aspects of DNA structure： its packaging in the higher order chromatin structure, positioning of nucleosomes along the DNA, and the occurrence of non-helical DNA structures. Of these, the latter has been problematic to prove empirically. Here, we describe a method that uses non-denaturing bisulfite sequencing on isolated Arabidopsis thaliana nuclei to determine the location of cytosines positioned outside the double helix as a result of non-B-form DNA structures. We couple this with computational methods and S1 nuclease digest to reliably identify stable, non-B-form, cruciform structures. This enables us to identify a palindrome in the promoter of FLOWERING LOCUS T that forms a stable non-B-form structure. The stronger conservation of the ability to form a nonhelical secondary structure than of the sequence suggests that this structure is biologically relevant.展开更多
基金supported in part by the Aeronautical Science Foundation of China(No.20172952031)the Aeronautical Science Foundation of China (No.20142952026)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform parachute systems.The projection area of canopy is calculated in the inflation process.The flow field characteristics and the interaction between canopies are analyzed.Results showed that,with free stream velocity of 50m/s,overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system,because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores.Concurrently,compared with the single-cruciform parachute,the vortex motion in the wake of double-cruciform-parachute is more intense.Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°.By comparison,the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50m/s.The results are consistent with those of the wind tunnel test.
基金National Natural Science Foundations of China(51065010)Science Foundations of Jiangxi(2009GZC0016)
文摘Surface impact treatment was carried out on the cruciform joint weldment of 16MnR steel by using the HJ-II-type ultrasonic impact machine.The ultrasonic impact current is 1.2 A,the impact amplitude is 30?m and ultrasonic impacting time is 30 and 60 min,respectively.Fatigue experiments were carried out for both treated specimen and un-treated specimen by using EHF-EM200K2-070-1A fatigue testing machine.The fatigue fractures were observed with the scanning electron microscope of 6360LA type and the microstructure of ultrasonic impact treating surface layer was analyzed by using high resolution transmission electron microscope of JEM-2100 type.The experimental results show that the microstructure of ultrasonic impact surface layer has been successfully nanocrystallized.The fatigue life of welded cruciform joints of 16MnR steel can be significantly improved through the ultrasonic impact treatment.The main reasons are that the ultrasonic impact treating can reduces the stress concentration in the weld toe,decrease the tensile stress,and even change to compressive stress in the weldment,the grain size in the welded joint can be refined.The longer the impact time,the greater increasing range of fatigue life will be.Compared to the sample without treatment,its fatigue life was increased 210.37%,362.48%,respectively,when the impact time was 30,60 min,respectively.
文摘Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of load carrying cruciform joints inships is investigated using Effective Notch Stress (ENS) approach. A fictitious notch of 1 mm radius is introduced at theweld root and toe and fatigue stress is evaluated. The effect of weld leg length (l) and weld penetration depth (p) on ENS atweld root and toe are determined. The critical weld leg length (lcr) at which fatigue failure transitions from weld root toweld toe is investigated. An approximation formula for determination of the critical weld leg length considering weldpenetration depth (p) is proposed.
基金financially supported by the National Natural Science Foundation of China (Nos. 61571415, 61622406, 51502283)the National Key Research and Development Program of China (Nos. 2017YFA0207500, 2016YFB0700700)the "Hundred Talents Program" of Chinese Academy of Sciences (CAS)
文摘Using diamine as anchoring group, the self-assembled monolayers（SAMs） based on oligo（phenyleneethynylene）s（OPEs） and cruciform OPEs with an extended tetrathiafulvalene（TTF）（OPE3 and OPE3-TTF）were successfully formed on the Au substrate. The Uniformity and stability of SAMs were confirmed through cyclic voltammetry（CV） and electrochemical reductive desorption. The investigation of transport properties of SAMs was achieved by conducting-probe atomic force microscopy（CP-AFM） with both Au and Pt tips. The results indicated that the conductance of OPE3-TTF was 17 and 46 times that of OPE3 for Au and Pt tips, respectively. Theoretical calculations are qualitatively consistent with the experimental results, suggesting that the diamine as anchoring group has a great potential in molecular electronics.
基金supported by the National Natural Science Foundation of China(No.51205190)the Jiangsu Province Key Laboratory of Aerospace Power System(No.NJ20140019)
文摘In order to achieve a better understanding of failure behavior of cruciform specimen under different biaxial loading conditions,a three-dimensional finite element model is established with solid and interface elements.Maximum stress criterion,two Hashin-type criteria and the new proposed criteria are used to predict the strength of plain woven textile composites when biaxial loading ratio equals 1.Compared with experimental data,only the new proposed criteria can reach reasonable results.The applicability of the new proposed criteria is also verified by predicting the tensile and compressive strength of cruciform specimen under different biaxial loading ratios.Moreover,the introduction of interface element makes it more intuitive to recognize delamination failure.The shape of the predicted delamination failure region in the interface layer is similar to that of the failure region in neighboring entity layers,but the area of delamination failure region is a little larger.
基金supported by Shanghai Central Government Leading Local Science and Technology Development Funds(No.YDZX20233100004008).
文摘The growth of the low-altitude economy has led to an increase in the number of small aircraft and aviation equipment,thereby intensifying the demand for small-scale parachutes.Considering the limited attention to small parachutes in existing research,this paper explores specialized parachutes with practical application value in framework of low-altitude economy.The Arbitrary Lagrangian–Eulerian(ALE)method was employed to analyze fluid-structure interaction(FSI)between parachute canopy and the surrounding air.The dynamic load curves demonstrate that at an inflow velocity of 10 m/s,the dynamic load peaks rapidly in less than 0.1 s during parachute opening,whereas at 50 m/s and 100 m/s,the time to peak is less than 0.03 s.The high-tension regions on the canopy's central surface exhibit an“X”-shaped distribution,with their area influenced by inflow velocity and inflation time,which informs the targeted reinforcement design for cruciform parachutes created by the simulation results in this study.A parachute airdrop test was conducted,and a combination of simplified model and drag coefficient correction is proposed to simulate the steady descent lift force.The relative error between simulation results of drag coefficient and the test data was found to be 4.49%.Simulation results show that the small-scale cruciform parachute in this study can carry an object with a mass of up to 10.18 kg,provided that the descent velocity is less than or equal to 10 m/s.The findings of this paper can provide a reference for the design and optimization of small-scale parachutes and help to assess their potential application in areas such as low-altitude economy.
基金supported by Beijing NOVA Programme(Z131101000413038)Beijing Local College Innovation Team Improve Plan(IDHT20140512)+2 种基金the National Natural Science Foundation of China(91433115,91222203,91233205 and 51222306)the Ministry of Science and Technology of China(2013CB933403 and 2013CB933504)the University of Copenhagen
文摘It is a common phenomenon for organic semi- conductors to crystallize in two or more polymorphs, leading to various molecular packings and different charge transport properties. Therefore, it is a crucial issue of tuning molec- ular crystal polymorphs （i.e., adjusting the same molecule with different packing arrangements in solid state） towards efficient charge transport and high performance devices. Here, the choice of solvent had a marked effect on con- trolling the growth of a-phase ribbon and β-phase platelet during crystallization for an indenofluorene （IF） π-extended tetrathiafulvalene （TTF）-based cruciform molecule, named as IF-TTF. The charge carrier mobility of the a-phase IF-TTF crystals was more than one order of magnitude higher than that of β-phase crystals, suggesting the importance of reasonably tuning molecular packing in solid state for the improvement of charge transport in organic semiconductors.
基金supported by grants from National Natural Science Foundation of China(31801979 and 31872229)from Singapore Ministry of Education(MOE)AcRF Tier 1 grant(R-154-000-B18-114).
文摘Although camouflage as an effective antipredator defense strategy is widespread across animals,highly conspicuous color patterning is not uncommon either.Many orb-web spiders adorn their webs with extra bright white silk.These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs,camouflaging spiders,acting as a decoy,or intimidating predators by their apparent size.The decorations may also deflect predator attacks from spiders.However,empirical evidence for this deflection function remains limited.Here,we tested this hypothesis using the X-shaped silk cruciform decorations built by females of Argiope minuta.We employed visual modeling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators.Then,we determined actual predation risk on spiders using naïve chicks as predators.Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems.Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs,thus reducing predation risk.When both spiders and decorations were present,chicks also attacked the spider main bodies and their legs or decorations,and not randomly:they attacked the legs or decorations sooner and more frequently than they attacked the main bodies,independent of the ratio of the surface area between the decoration and spider size.Despite the increase in detectability,incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack toward the decoration or leg,but not by camouflaging or intimidating,thus,supporting the deflection hypothesis.
文摘In the half century since the discovery of the double-helix structure of DNA, it has become increasingly clear that DNA functionality is based on much more than its sequence in a double-helical structure. Further advances have highlighted the importance of additional aspects of DNA structure： its packaging in the higher order chromatin structure, positioning of nucleosomes along the DNA, and the occurrence of non-helical DNA structures. Of these, the latter has been problematic to prove empirically. Here, we describe a method that uses non-denaturing bisulfite sequencing on isolated Arabidopsis thaliana nuclei to determine the location of cytosines positioned outside the double helix as a result of non-B-form DNA structures. We couple this with computational methods and S1 nuclease digest to reliably identify stable, non-B-form, cruciform structures. This enables us to identify a palindrome in the promoter of FLOWERING LOCUS T that forms a stable non-B-form structure. The stronger conservation of the ability to form a nonhelical secondary structure than of the sequence suggests that this structure is biologically relevant.
文摘为研究承载型60°斜十字全熔透焊接接头(oblique cruciform full-penetration welded joints,OCFWJs)局部应力分布及疲劳性能,设计3个试验模型完成3种名义应力幅水平下的疲劳试验,得到试件疲劳破坏时的循环次数.利用ABAQUS软件建立60°OCFWJs有限元模型,计算得到焊趾处热点正应力、热点剪应力及等效热点应力.基于规范中的名义应力S-N曲线和热点应力S-N曲线,分别采用名义主应力法、等效热点应力法和相互作用方程方法对拉—剪联合作用下60°OCFWJs疲劳寿命进行了评估.结果表明,采用名义应力幅、名义拉应力幅或名义剪应力幅均无法对60°OCFWJs疲劳寿命进行可靠评估.依据国际焊接学会(International Institute of Welding,IIW)规范无论采用热点拉应力幅或热点剪应力幅也无法对60°OCFWJs疲劳寿命进行可靠评估.按欧洲钢结构设计规范Eurocode3相互作用方程方法预测的疲劳寿命远低于试验值,按等效热点应力方法预测的疲劳寿命与试验值符合良好.
