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
The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenome...The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.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
Experiments on specimens of mild steel and cast iron have beenperformed under vari- ous loading conditions. A modified formula isput forward to analyze the cruciform specimen which is often used inmagnetic methods for...Experiments on specimens of mild steel and cast iron have beenperformed under vari- ous loading conditions. A modified formula isput forward to analyze the cruciform specimen which is often used inmagnetic methods for calibration. We assume that the relationshipbetween the magnetic output and strain is linear and a newfour-coefficient method is deduced. Finally, the results of practi-cal applications are given.展开更多
Residual antibiotics in food pose a serious long-term threat to human health.Therefore,an on-site visualization method for antibiotic detection is required.However,the requirements of traditional antibiotic testing me...Residual antibiotics in food pose a serious long-term threat to human health.Therefore,an on-site visualization method for antibiotic detection is required.However,the requirements of traditional antibiotic testing methods in terms of operator proficiency and equipment cost hinder the rapid point-of-caretesting detection of suspected samples.Herein,we reported an integrated microfluidic device combining a microfluidic chip containing cruciform valves with immunochromatographic strips for the rapid detection of multiple antibiotics in milk.The rapid qualitative and quantitative analysis of four types of antibiotics(sulfonamides,β-lactams,streptomycin,and tetracyclines)was performed using mobile phone photography and mobile phone application analysis.The detection time was maintained at 10 min.The limits of detection(LODs)for the four antibiotics were 0.15,0.12,0.25,and 0.29 ng/mL,respectively,and the selectivity for the different antibiotics was observed even in a highly complex matrix.This device successfully integrated separation and real-time detection onto a chip and might provide a promising perspective for the detection of multiple antibiotics in milk.展开更多
The thermomechanical fatigue behaviour of different high temperature alloys has been investigated and is under investigation respectively. The creep-fatigue behaviour of heat resistant steels was investigated by long-...The thermomechanical fatigue behaviour of different high temperature alloys has been investigated and is under investigation respectively. The creep-fatigue behaviour of heat resistant steels was investigated by long-term service-type strain cycling tests simulating thermomechanical fatigue (TMF-) loading conditions at the heated surface of e.g. turbine rotors. Single-stage as well as three-stage cycles leads to similar results at the application of the damage accumulation rule. Life prediction which simulates typical combinations of cold starts, warm starts and hot starts has been established successfully for isothermal service-type loading and will be exceeded for thermomechanical loading. Long-term thermomechanical fatigue testing of Thermal Barrier Coating systems show typical delamination damage. An advanced TMF cruciform testing system enables complex multiaxial loading.展开更多
Magnesium alloys are frequently subjected to biaxial stress during manufacturing process,however,the work hardening behavior under such circumstance are not well understood.In this study,the deformation mechanisms and...Magnesium alloys are frequently subjected to biaxial stress during manufacturing process,however,the work hardening behavior under such circumstance are not well understood.In this study,the deformation mechanisms and differential work hardening behavior of rolled AZ31 magnesium alloy sheets under biaxial loading are investigated.The change of plastic work contours with increasing plastic strain indicates the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state,resulting in higher macroscopic work hardening rates of biaxial loading than uniaxial loading,with the elastic-plastic transition part of work hardening extended and stage Ⅲ hardly emerged.Electron backscatter diffraction and Schmid factor analysis confirm the low activation of non-basalslip during biaxial loading tests.While the thickness strain is primarily accommodated by pyramidal<c+a>slip at the initial stage of biaxial deformation,{10–11}contraction twinning is activated at larger plastic strain.The low activation of non-basalslip also retards the dynamic recovery and cross-slip of basal and prismaticslips,leading to the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state.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
Two different types of experimental techniques to perform non-isothermal, uniax-ial and biaxial fatigue tests were described. A new miniaturised electrothermal-mechanical test rig was presented and discussed. It enabl...Two different types of experimental techniques to perform non-isothermal, uniax-ial and biaxial fatigue tests were described. A new miniaturised electrothermal-mechanical test rig was presented and discussed. It enables testing of small specimens under complex thermomechanical loading conditions. In order to cope with the simulation of well defined biaxial proportional and non-proportional loadings with in-phase and out-of-phase superposition of thermal loads a cruciform biaxial fatigue testing machine has been developed. Special design features of both machines, and the specimens tested, as well as typical test results were discussed.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
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
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
Empirical relationship was developed to predict the fatigue life of gas metal arc welded （GMAW） cruciform joints failing from root region. High strength, age hardenable aluminium alloy of AA7075-T6 grade was used as...Empirical relationship was developed to predict the fatigue life of gas metal arc welded （GMAW） cruciform joints failing from root region. High strength, age hardenable aluminium alloy of AA7075-T6 grade was used as the base material. The design of experiments concept was used to optimize the required number of fatigue testing experiments. Fatigue experiment was conducted in a servo hydraulic controlled fatigue testing machine under constant amplitude loading. The empirical relationship was developed. By using the developed empirical relationship, the fatigue life of GMAW cruciform joints failing from root region was predicted at 95% confidence level. The effect of cruciform joint dimensions on fatigue life was discussed in detail.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
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.
文摘The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.
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Experiments on specimens of mild steel and cast iron have beenperformed under vari- ous loading conditions. A modified formula isput forward to analyze the cruciform specimen which is often used inmagnetic methods for calibration. We assume that the relationshipbetween the magnetic output and strain is linear and a newfour-coefficient method is deduced. Finally, the results of practi-cal applications are given.
基金This work was supported financially by the National Natural Science Foundation of China(Nos.82073816 and 21727814)Advanced Talents of Beijing Technology and Business University(No.19008021179).
文摘Residual antibiotics in food pose a serious long-term threat to human health.Therefore,an on-site visualization method for antibiotic detection is required.However,the requirements of traditional antibiotic testing methods in terms of operator proficiency and equipment cost hinder the rapid point-of-caretesting detection of suspected samples.Herein,we reported an integrated microfluidic device combining a microfluidic chip containing cruciform valves with immunochromatographic strips for the rapid detection of multiple antibiotics in milk.The rapid qualitative and quantitative analysis of four types of antibiotics(sulfonamides,β-lactams,streptomycin,and tetracyclines)was performed using mobile phone photography and mobile phone application analysis.The detection time was maintained at 10 min.The limits of detection(LODs)for the four antibiotics were 0.15,0.12,0.25,and 0.29 ng/mL,respectively,and the selectivity for the different antibiotics was observed even in a highly complex matrix.This device successfully integrated separation and real-time detection onto a chip and might provide a promising perspective for the detection of multiple antibiotics in milk.
基金supported by the Deutsche Forschungsgemeinschaft(DFG),Project No.BE1890,16-1the Forschungs-vereinigung der Arbeitsgemeinschaften der Eisen und Metall verarbeitenden Industrie e.V.(AVIF),Project No.A166+1 种基金the FKM Forschungskuratorium Maschinenbau e.V.Project No.052510the Arbeitsgemeinschaft industrieller Forschungsvereinigungen(AiF)and the VDEh-Gesellschaft zur Forderung der Eisenforschung mbH,Project No.11200 N.
文摘The thermomechanical fatigue behaviour of different high temperature alloys has been investigated and is under investigation respectively. The creep-fatigue behaviour of heat resistant steels was investigated by long-term service-type strain cycling tests simulating thermomechanical fatigue (TMF-) loading conditions at the heated surface of e.g. turbine rotors. Single-stage as well as three-stage cycles leads to similar results at the application of the damage accumulation rule. Life prediction which simulates typical combinations of cold starts, warm starts and hot starts has been established successfully for isothermal service-type loading and will be exceeded for thermomechanical loading. Long-term thermomechanical fatigue testing of Thermal Barrier Coating systems show typical delamination damage. An advanced TMF cruciform testing system enables complex multiaxial loading.
基金the financial support from the National Key R&D Program of China(2018YFC0808800)the National Natural Science Foundation of China(Nos.51875398 and 51471116)the Sichuan Science and Technology Program(2019ZDZX0001).
文摘Magnesium alloys are frequently subjected to biaxial stress during manufacturing process,however,the work hardening behavior under such circumstance are not well understood.In this study,the deformation mechanisms and differential work hardening behavior of rolled AZ31 magnesium alloy sheets under biaxial loading are investigated.The change of plastic work contours with increasing plastic strain indicates the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state,resulting in higher macroscopic work hardening rates of biaxial loading than uniaxial loading,with the elastic-plastic transition part of work hardening extended and stage Ⅲ hardly emerged.Electron backscatter diffraction and Schmid factor analysis confirm the low activation of non-basalslip during biaxial loading tests.While the thickness strain is primarily accommodated by pyramidal<c+a>slip at the initial stage of biaxial deformation,{10–11}contraction twinning is activated at larger plastic strain.The low activation of non-basalslip also retards the dynamic recovery and cross-slip of basal and prismaticslips,leading to the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state.
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Two different types of experimental techniques to perform non-isothermal, uniax-ial and biaxial fatigue tests were described. A new miniaturised electrothermal-mechanical test rig was presented and discussed. It enables testing of small specimens under complex thermomechanical loading conditions. In order to cope with the simulation of well defined biaxial proportional and non-proportional loadings with in-phase and out-of-phase superposition of thermal loads a cruciform biaxial fatigue testing machine has been developed. Special design features of both machines, and the specimens tested, as well as typical test results were discussed.
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 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.
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.
文摘Empirical relationship was developed to predict the fatigue life of gas metal arc welded （GMAW） cruciform joints failing from root region. High strength, age hardenable aluminium alloy of AA7075-T6 grade was used as the base material. The design of experiments concept was used to optimize the required number of fatigue testing experiments. Fatigue experiment was conducted in a servo hydraulic controlled fatigue testing machine under constant amplitude loading. The empirical relationship was developed. By using the developed empirical relationship, the fatigue life of GMAW cruciform joints failing from root region was predicted at 95% confidence level. The effect of cruciform joint dimensions on fatigue life was discussed in detail.
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.
