Objective:This study aimed to investigate the association of atopic dermatitis(AD)and anxiety/depression behaviors induced by AD with the intestinal microbiota.Additionally,it sought to evaluate the therapeutic potent...Objective:This study aimed to investigate the association of atopic dermatitis(AD)and anxiety/depression behaviors induced by AD with the intestinal microbiota.Additionally,it sought to evaluate the therapeutic potential of mannan oligosaccharide(MOS)in alleviating AD symptoms through the modulation of the gut microbiota and the enhancement of short-chain fatty acids(SCFAs)production.Methods:Female Kunming mice were challenged with 2,4-dinitrofluorobenzene(DNFB)to induce AD-like symptoms.MOS was administered orally daily for 14 days.On the 6th and 11th days post-modeling,the number of scratching bouts in mice was recorded.Following dissection,epidermal thickness,mast cell infiltration,and serum levels of inflammatory cytokines were measured.Meanwhile,cerebral levels of neurotransmitters,including 5-hydroxytryptamine(5-HT)and norepinephrine(NE),were assessed.The abundance of intestinal microbiota and fecal concentrations of SCFAs were also analyzed.Results:MOS significantly reduced AD-like symptoms by reducing inflammatory cytokines,as reflected in a significant decrease in the number of scratching bouts,epidermal thickness,mast cells and inflammatory cytokine levels.MOS intervention up-regulated the expression of 5-HT and NE,and consequently alleviated anxiety and depression-like behaviors.Furthermore,compared with the AD group,MOS intervention increased the gut microbiota abundance of mice,especially beneficial bacteria such as Bifidobacterium,Lactobacillus and Klebsiella.At the same time,these beneficial bacteria significantly increased the fecal contents of SCFAs,especially propionic acid.Correlation analysis indicated that AD amelioration was positively correlated with fecal SCFAs levels and the proliferation of certain intestinal microbes.Conclusion:MOS intervention could offer a novel approach to managing AD and its psychological comorbidities.展开更多
Microstrip traveling wave tubes(TWTs)have garnered significant attention due to their potential applications in communication,defense,and industrial systems.This paper presents a compact W-band dual-channel TWT,utiliz...Microstrip traveling wave tubes(TWTs)have garnered significant attention due to their potential applications in communication,defense,and industrial systems.This paper presents a compact W-band dual-channel TWT,utilizing a U-shaped microstrip meander-line slow-wave structure(SWS).High-frequency characteristics are analyzed through simulation and cold tests.The results demonstrate that adjusting structural parameters effectively optimizes the S-parameters.Particle-in-cell(PIC)simulations with an 18.8 kV,0.1 A electron beam predict an output power of 18 W with a gain of 14 dB.Experimental measurements of S-parameters are conducted using three substrate materials:Rogers 5880,quartz,and diamond.The quartz substrate exhibits the closest agreement with simulation results.The results advance the development of the microstrip-based TWTs for high-data-rate communication systems.展开更多
In the process of protecting ferrous materials,aluminum coating usually forms a dense oxide film on the surface of the iron-based alloy.However,the capacity of the sacrificial anode is rather insufficient.In order to ...In the process of protecting ferrous materials,aluminum coating usually forms a dense oxide film on the surface of the iron-based alloy.However,the capacity of the sacrificial anode is rather insufficient.In order to solve this problem,the microstructure and electrochemical corrosion properties of Al-8Si-3Fe-xIn alloy under low chlorine conditions were studied.The results show that indium(In)dissolves to form In^(3+)and In^(+)reverse plating on the surface of the bare substrate to form a passivation film defect.When the In content is high,the segregated In forms an activation point in the form of a cathode phase.In activatesτ_(6)phase to form a micro-couple,which improves the non-uniform corrosion.The In-containing corrosion products at the phase boundary hinder the diffusion of Cl−.With an increase of In content,the self-corrosion potential(Ecorr)of the alloy shifts negatively,and the self-corrosion current density(Jcorr)decreases from 6.477μA/cm^(2)to 1.352μA/cm^(2),and then increases gradually.However,when the In content is 0.1%,the Ecorr of the alloy changes from−0.824 V to−0.932 V,and the Jcorr decreases from 6.477μA/cm^(2)to 4.699μA/cm^(2),suggesting that the use of sacrificial anode will give the best effect.展开更多
The research demonstrated that laser powder bed fusion(LPBF)coupled with controlled annealing at 1200°C,could significantly increase the proportion of coincidence site lattice(CSL)grain boundary,thereby achieving...The research demonstrated that laser powder bed fusion(LPBF)coupled with controlled annealing at 1200°C,could significantly increase the proportion of coincidence site lattice(CSL)grain boundary,thereby achieving an outstanding synergy of enhanced strength and exceptional ductility.The plastic deformation behavior,strain hardening behavior,and fracture behavior of LPBF 316L steel annealing at 1200℃for 20 h were studied through quasi-in-situ tensile process.It was found that LPBF 316L steel formed a certain proportion of deformation twins during the tensile process,and the formation of twins changed the crystal orientation,thus promoting further slip and crystal deformation.The synergistic effect of slip and twin promoted higher plasticity.LPBF process coupled with controlled annealing at 1200°C for 20 h leads to a ultimate tensile strength of 613 MPa and total elongation of 73.8%.展开更多
Pedestrian's road-crossing model is the key part of micro-simulation for mixed traffic at signalized intersection.To reproduce the crossing behavior of pedestrians,the microscopic behaviors of the pedestrians pass...Pedestrian's road-crossing model is the key part of micro-simulation for mixed traffic at signalized intersection.To reproduce the crossing behavior of pedestrians,the microscopic behaviors of the pedestrians passing through the crosswalk at signalized intersection were analyzed.A pedestrian's decision making model based on gap acceptance theory was proposed.Based on the field data at three typical intersections in Beijing,China,the critical gaps and lags of pedestrians were calibrated.In addition,considering pedestrian's required space,a modification of the social force model that consists of a self-deceleration mechanism prevents a simulated pedestrian from continuously pushing over other pedestrians,making the simulation more realistic.After the simple change,the modified social force model is able to reproduce the fundamental diagram of pedestrian flows for densities less than 3.5 m-2 as reported in the literature.展开更多
Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried ou...Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.展开更多
The influence of different ageing processes on the microstructure, corrosion behaviors and mechanical properties of extruded Al-5.6Zn-1.6Mg-0.05Zr(wt.%) alloy was studied in this work. The changes of morphology, size ...The influence of different ageing processes on the microstructure, corrosion behaviors and mechanical properties of extruded Al-5.6Zn-1.6Mg-0.05Zr(wt.%) alloy was studied in this work. The changes of morphology, size and distribution of MgZn_(2)precipitate with ageing temperature and time were revealed by optical and electron microscopy. Intergranular corrosion(IGC) and exfoliation corrosion(EXCO) tests were carried out to assess the changes in corrosion susceptibility of the tempered alloy, and some white spots on the surface of the sample aged for longer time were found to be precursors of pits. Electrochemical cyclic polarization test depicted the corrosion behavior under different tempers. Ageing influences on the mechanical behaviors of the alloy were revealed by evaluating its microhardness and tensile strength. The microscopic features of the strengthening phases determined by the ageing procedure directly affect the corrosion resistance and mechanical properties of the alloy.展开更多
Ni-based alloy coating on 21-4-N heat-resistant steel was prepared using CO2 laser, and the high-temperature abrasion wear was tested. The microstructure of this cladding layer and its abrasion wear behavior at high t...Ni-based alloy coating on 21-4-N heat-resistant steel was prepared using CO2 laser, and the high-temperature abrasion wear was tested. The microstructure of this cladding layer and its abrasion wear behavior at high temperature by changing compositions and temperatures were investigated by means of optical microscope and scanning electron microscope. Among the three compositions of cladding layer, i.e. Ni21+20%WC+0.5%CeO2, Ni25+20%WC+0.5%CeO2 and Ni60+20%WC+0.5%CeO2, the experimental results show that Ni21+20%WC+ 0.5%CeO2 cladding layer is made up of finer grains, and presents the best abrasion wear behavior at high temperature. The wear pattern of laser cladding layer is mainly grain abrasion at lower temperature, and it would be changed to adhesive abrasion and oxide abrasion at higher temperature.展开更多
In order to study the anodic behavior and microstmctures of A1/Pb-Ag-Co anode during zinc electrowinning, by means of potentiodynamic investigations, scanning electron microscopy （SEM） and X-ray diffraction （XRD） ...In order to study the anodic behavior and microstmctures of A1/Pb-Ag-Co anode during zinc electrowinning, by means of potentiodynamic investigations, scanning electron microscopy （SEM） and X-ray diffraction （XRD） analyses, the mechanism of the anodic processes playing on the surface of A1/Pb-0.8%Ag and A1/Pb-0.75%Ag-0.03%Co anodes prepared by electro-deposition from methyl sulfonic acid bath for zinc electrowinning from model sulphate electrolytes have been measured. On the basis of the cyclic voltammograms obtained, information about the corrosion rate of the composite in PbO2 region has been concluded. The microstructures were also observed by means of SEM and XRD which showed Pb-0.75%Ag-0.03%Co alloy composite coating has uniform and chaotic orientation tetragonal symmetry crystallites of PbSO4, but Pb-0.8%Ag alloy composite coating has well-organized orientation crystallites of PbSO4 concentrated in the certain zones after 24 h of anodic polarization. It is important that Al/Pb-0.75%Ag-0.03%Co anode oxide film consists of non-conductive dense MnO2 and PbSO4 and a, fl-PbO2 penetrated into which, in fact, are the active centers of the oxygen evolution after 24 h of anodic polarization.展开更多
A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al...A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.展开更多
The effect of temperature in range of 155-175 ℃ on the creep behavior, microstructural evolution, and precipitation of an Al-Cu-Li alloy was experimentally investigated during creep ageing deformation under 180 MPa f...The effect of temperature in range of 155-175 ℃ on the creep behavior, microstructural evolution, and precipitation of an Al-Cu-Li alloy was experimentally investigated during creep ageing deformation under 180 MPa for 20 h. Increasing temperature resulted in a noteworthy change in creep ageing behaviour, including a variation in creep curves, an improvement in creep rate during early creep ageing, and an increased creep strain. Tensile tests indicate that the specimen aged at higher temperature reached peak strength within a shorter time. Transmission electron microscopy(TEM) was employed to explore the effect of temperature on the microstructural evolution of the AA2198 during creep ageing deformation. Many larger dislocations and even tangled dislocation structures were observed in the sample aged at higher temperature. The number of T1 precipitates increased at higher ageing temperature at the same ageing time. Based on the analysed results, a new mechanism, considering the combined effects of the formation of larger dislocation structures induced by higher temperature and diffusion of solute atoms towards these larger or tangled dislocations, was proposed to explain the effect of temperature on microstructural evolution and creep behaviour.展开更多
The effects of hot extrusion and addition of Al_(2)O_(3p) on both microstructure and tribological behavior of 7075 composites were investigated via optical microscopy(OM),scanning electron microscopy(SEM),energy dispe...The effects of hot extrusion and addition of Al_(2)O_(3p) on both microstructure and tribological behavior of 7075 composites were investigated via optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),and transmission electron microscopy(TEM).The experimental consequences reveal that the optimal addition of Al_(2)O_(3p) was 2 wt%.After hot extrusion,the Mg(Zn,Cu,Al)2 phases partially dissolve into the matrix and generate many uniformly distributed aging precipitation particles,the Al_(7)Cu_(2)Fe phases are squeezed and broken,and the Al_(2)O_(3p) become uniform distribution.The microhardness of as-extruded 2 wt%Al_(2)O_(3p)/7075 composites reaches HV 170.34,increased by 41.5%than as-cast composites.The wear rate of as-extruded 2 wt%Al_(2)O_(3p)/7075 composites is further lower than that of as-cast composites under the same condition.SEM-EDS analyses reveal that the reinforced wear resistance of composites can put down to the protective effect of the Al_(2)O_(3p) reinforced transition layer.After hot extrusion,the transition layer becomes stable,which determines the reinforced wear resistance of the as-extruded composites.展开更多
The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),trans...The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.展开更多
The microwave absorbing characteristics of basic cobalt carbonate,cobalt oxide(Co3O4),and the mixture of basic cobalt carbonate and cobalt oxide were investigated by means of microwave cavity perturbation,their temper...The microwave absorbing characteristics of basic cobalt carbonate,cobalt oxide(Co3O4),and the mixture of basic cobalt carbonate and cobalt oxide were investigated by means of microwave cavity perturbation,their temperature increasing curves were measured,and their ability to absorb microwave energy was also assessed based on the temperature increasing behavior of the material exposed to microwave field.Analyses of spectrum attenuation and relative frequency shift show that basic cobalt carbonate has weak capability to absorb microwave energy,while cobalt oxide has very strong capability to absorb microwave energy.It is feasible to thermally decompose basic cobalt carbonate though addition of small amount of cobalt oxide in microwave fields.The capability to absorb microwave energy of sample increases with an increase in mixing ratio of Co3O4.展开更多
The dissolution behavior of CaO-MgO-SiO2 glass fiber was investigated by scanning electron microscopy （SEM）, Fourier-transform infrared spectrometer （FTIR） and inductively coupled plasma atomic emission spectrosco...The dissolution behavior of CaO-MgO-SiO2 glass fiber was investigated by scanning electron microscopy （SEM）, Fourier-transform infrared spectrometer （FTIR） and inductively coupled plasma atomic emission spectroscopy （ICP-AES） using in-vitro tests. The results show that the soaked fiber is surrounded by an outer calcium-magnesium silicate hydrated layer, and there exists a balancing fimction between the formation and abscission of the hydrated layer during the dissolution process. The concentrations of leached ions increase constantly, and the mass loss of the fibers and pH changes of the solution are found to rise rapidly during the initial dissolution process, then their increasing rates are controlled by the balancing function of the hydrated layer at the subsequent dissolution stages. The dissolution rate constant and time for complete dissolution are estimated to be 274 ng/（cm2.h） and 15.2 d, respectively, presenting preferable biosolubilities.展开更多
A methodology was presented relating the microstructure of asphalt mixtures to their damage behavior. Digital image techniques were used to capture the asphalt mixture microstructure, and the finite element method was...A methodology was presented relating the microstructure of asphalt mixtures to their damage behavior. Digital image techniques were used to capture the asphalt mixture microstructure, and the finite element method was used to simulate the damage evolution of asphalt mixture through splitting test. Aggregates were modeled to be linearly elastic, and the mastics were modeled to be plastically damaged. The splitting test simulation results show that the material heterogeneity, the properties of aggregates and air voids have significant effects on the damage evolution approach. The damage behavior of asphalt mixture considering material heterogeneity is quite different from that of the conventional hypothesis of homogeneous material. The results indicate that the proposed method can be extended to the numerical analysis for the other micromechanical behaviors of asphalt concrete.展开更多
Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) ...Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.展开更多
文摘Objective:This study aimed to investigate the association of atopic dermatitis(AD)and anxiety/depression behaviors induced by AD with the intestinal microbiota.Additionally,it sought to evaluate the therapeutic potential of mannan oligosaccharide(MOS)in alleviating AD symptoms through the modulation of the gut microbiota and the enhancement of short-chain fatty acids(SCFAs)production.Methods:Female Kunming mice were challenged with 2,4-dinitrofluorobenzene(DNFB)to induce AD-like symptoms.MOS was administered orally daily for 14 days.On the 6th and 11th days post-modeling,the number of scratching bouts in mice was recorded.Following dissection,epidermal thickness,mast cell infiltration,and serum levels of inflammatory cytokines were measured.Meanwhile,cerebral levels of neurotransmitters,including 5-hydroxytryptamine(5-HT)and norepinephrine(NE),were assessed.The abundance of intestinal microbiota and fecal concentrations of SCFAs were also analyzed.Results:MOS significantly reduced AD-like symptoms by reducing inflammatory cytokines,as reflected in a significant decrease in the number of scratching bouts,epidermal thickness,mast cells and inflammatory cytokine levels.MOS intervention up-regulated the expression of 5-HT and NE,and consequently alleviated anxiety and depression-like behaviors.Furthermore,compared with the AD group,MOS intervention increased the gut microbiota abundance of mice,especially beneficial bacteria such as Bifidobacterium,Lactobacillus and Klebsiella.At the same time,these beneficial bacteria significantly increased the fecal contents of SCFAs,especially propionic acid.Correlation analysis indicated that AD amelioration was positively correlated with fecal SCFAs levels and the proliferation of certain intestinal microbes.Conclusion:MOS intervention could offer a novel approach to managing AD and its psychological comorbidities.
基金National Natural Science Foundation of China(62471097,62471115,62471101)Natural Science Foundation of Sichuan Province(2025ZNSFSC0537)Stable Support Porject of 12th Research Institute of China Electronics Technology Group Corporation。
文摘Microstrip traveling wave tubes(TWTs)have garnered significant attention due to their potential applications in communication,defense,and industrial systems.This paper presents a compact W-band dual-channel TWT,utilizing a U-shaped microstrip meander-line slow-wave structure(SWS).High-frequency characteristics are analyzed through simulation and cold tests.The results demonstrate that adjusting structural parameters effectively optimizes the S-parameters.Particle-in-cell(PIC)simulations with an 18.8 kV,0.1 A electron beam predict an output power of 18 W with a gain of 14 dB.Experimental measurements of S-parameters are conducted using three substrate materials:Rogers 5880,quartz,and diamond.The quartz substrate exhibits the closest agreement with simulation results.The results advance the development of the microstrip-based TWTs for high-data-rate communication systems.
基金Projects(52171003,52271005)supported by the National Science and Technology Major Project of ChinaProject(KYCX23_3032)supported by the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China。
文摘In the process of protecting ferrous materials,aluminum coating usually forms a dense oxide film on the surface of the iron-based alloy.However,the capacity of the sacrificial anode is rather insufficient.In order to solve this problem,the microstructure and electrochemical corrosion properties of Al-8Si-3Fe-xIn alloy under low chlorine conditions were studied.The results show that indium(In)dissolves to form In^(3+)and In^(+)reverse plating on the surface of the bare substrate to form a passivation film defect.When the In content is high,the segregated In forms an activation point in the form of a cathode phase.In activatesτ_(6)phase to form a micro-couple,which improves the non-uniform corrosion.The In-containing corrosion products at the phase boundary hinder the diffusion of Cl−.With an increase of In content,the self-corrosion potential(Ecorr)of the alloy shifts negatively,and the self-corrosion current density(Jcorr)decreases from 6.477μA/cm^(2)to 1.352μA/cm^(2),and then increases gradually.However,when the In content is 0.1%,the Ecorr of the alloy changes from−0.824 V to−0.932 V,and the Jcorr decreases from 6.477μA/cm^(2)to 4.699μA/cm^(2),suggesting that the use of sacrificial anode will give the best effect.
基金Project(52474418)supported by the National Natural Science Foundation of ChinaProject(YDZJSX2022A012)supported by the Central Guiding Local Science and Technology Development Foundation,China。
文摘The research demonstrated that laser powder bed fusion(LPBF)coupled with controlled annealing at 1200°C,could significantly increase the proportion of coincidence site lattice(CSL)grain boundary,thereby achieving an outstanding synergy of enhanced strength and exceptional ductility.The plastic deformation behavior,strain hardening behavior,and fracture behavior of LPBF 316L steel annealing at 1200℃for 20 h were studied through quasi-in-situ tensile process.It was found that LPBF 316L steel formed a certain proportion of deformation twins during the tensile process,and the formation of twins changed the crystal orientation,thus promoting further slip and crystal deformation.The synergistic effect of slip and twin promoted higher plasticity.LPBF process coupled with controlled annealing at 1200°C for 20 h leads to a ultimate tensile strength of 613 MPa and total elongation of 73.8%.
基金Project(70972041)supported by the National Natural Science Foundation of ChinaProject(20100009110010)supported by the PhD Programs Foundation of Ministry of Education of ChinaProject(2011YJS246)supported by Fundamental Research Funds for the Central Universities of China
文摘Pedestrian's road-crossing model is the key part of micro-simulation for mixed traffic at signalized intersection.To reproduce the crossing behavior of pedestrians,the microscopic behaviors of the pedestrians passing through the crosswalk at signalized intersection were analyzed.A pedestrian's decision making model based on gap acceptance theory was proposed.Based on the field data at three typical intersections in Beijing,China,the critical gaps and lags of pedestrians were calibrated.In addition,considering pedestrian's required space,a modification of the social force model that consists of a self-deceleration mechanism prevents a simulated pedestrian from continuously pushing over other pedestrians,making the simulation more realistic.After the simple change,the modified social force model is able to reproduce the fundamental diagram of pedestrian flows for densities less than 3.5 m-2 as reported in the literature.
基金Projects(51375269,51675307) supported by the National Natural Science Foundation of China
文摘Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.
基金Project(2021zzts0152) supported by the Fundamental Research Funds for the Central Universities,ChinaProject(U1837207) supported by the National Natural Science Foundation of China。
文摘The influence of different ageing processes on the microstructure, corrosion behaviors and mechanical properties of extruded Al-5.6Zn-1.6Mg-0.05Zr(wt.%) alloy was studied in this work. The changes of morphology, size and distribution of MgZn_(2)precipitate with ageing temperature and time were revealed by optical and electron microscopy. Intergranular corrosion(IGC) and exfoliation corrosion(EXCO) tests were carried out to assess the changes in corrosion susceptibility of the tempered alloy, and some white spots on the surface of the sample aged for longer time were found to be precursors of pits. Electrochemical cyclic polarization test depicted the corrosion behavior under different tempers. Ageing influences on the mechanical behaviors of the alloy were revealed by evaluating its microhardness and tensile strength. The microscopic features of the strengthening phases determined by the ageing procedure directly affect the corrosion resistance and mechanical properties of the alloy.
文摘Ni-based alloy coating on 21-4-N heat-resistant steel was prepared using CO2 laser, and the high-temperature abrasion wear was tested. The microstructure of this cladding layer and its abrasion wear behavior at high temperature by changing compositions and temperatures were investigated by means of optical microscope and scanning electron microscope. Among the three compositions of cladding layer, i.e. Ni21+20%WC+0.5%CeO2, Ni25+20%WC+0.5%CeO2 and Ni60+20%WC+0.5%CeO2, the experimental results show that Ni21+20%WC+ 0.5%CeO2 cladding layer is made up of finer grains, and presents the best abrasion wear behavior at high temperature. The wear pattern of laser cladding layer is mainly grain abrasion at lower temperature, and it would be changed to adhesive abrasion and oxide abrasion at higher temperature.
基金Project(51004056)supported by the National Natural Science Foundation of China
文摘In order to study the anodic behavior and microstmctures of A1/Pb-Ag-Co anode during zinc electrowinning, by means of potentiodynamic investigations, scanning electron microscopy （SEM） and X-ray diffraction （XRD） analyses, the mechanism of the anodic processes playing on the surface of A1/Pb-0.8%Ag and A1/Pb-0.75%Ag-0.03%Co anodes prepared by electro-deposition from methyl sulfonic acid bath for zinc electrowinning from model sulphate electrolytes have been measured. On the basis of the cyclic voltammograms obtained, information about the corrosion rate of the composite in PbO2 region has been concluded. The microstructures were also observed by means of SEM and XRD which showed Pb-0.75%Ag-0.03%Co alloy composite coating has uniform and chaotic orientation tetragonal symmetry crystallites of PbSO4, but Pb-0.8%Ag alloy composite coating has well-organized orientation crystallites of PbSO4 concentrated in the certain zones after 24 h of anodic polarization. It is important that Al/Pb-0.75%Ag-0.03%Co anode oxide film consists of non-conductive dense MnO2 and PbSO4 and a, fl-PbO2 penetrated into which, in fact, are the active centers of the oxygen evolution after 24 h of anodic polarization.
基金Project(2017YFB0306300) supported by the National key R&D Program of ChinaProjects(51675538, 51905551)supported by the National Natural Science Foundation of ChinaProject(ZZYJKT2019-11) supported by Free Exploration Project of State Key Laboratory of High performance Complex Manufacturing,China。
文摘A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.
基金Project(2017YFB0306300)supported by the National Key R&D Program of ChinaProjects(51601060,51675538)supported by the National Natural Science Foundation of China。
文摘The effect of temperature in range of 155-175 ℃ on the creep behavior, microstructural evolution, and precipitation of an Al-Cu-Li alloy was experimentally investigated during creep ageing deformation under 180 MPa for 20 h. Increasing temperature resulted in a noteworthy change in creep ageing behaviour, including a variation in creep curves, an improvement in creep rate during early creep ageing, and an increased creep strain. Tensile tests indicate that the specimen aged at higher temperature reached peak strength within a shorter time. Transmission electron microscopy(TEM) was employed to explore the effect of temperature on the microstructural evolution of the AA2198 during creep ageing deformation. Many larger dislocations and even tangled dislocation structures were observed in the sample aged at higher temperature. The number of T1 precipitates increased at higher ageing temperature at the same ageing time. Based on the analysed results, a new mechanism, considering the combined effects of the formation of larger dislocation structures induced by higher temperature and diffusion of solute atoms towards these larger or tangled dislocations, was proposed to explain the effect of temperature on microstructural evolution and creep behaviour.
基金Project(51965040)supported by the National Natural Science Foundation of ChinaProject(20181BAB206026)supported by the National Science Foundation of Jiangxi Province,China。
文摘The effects of hot extrusion and addition of Al_(2)O_(3p) on both microstructure and tribological behavior of 7075 composites were investigated via optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),and transmission electron microscopy(TEM).The experimental consequences reveal that the optimal addition of Al_(2)O_(3p) was 2 wt%.After hot extrusion,the Mg(Zn,Cu,Al)2 phases partially dissolve into the matrix and generate many uniformly distributed aging precipitation particles,the Al_(7)Cu_(2)Fe phases are squeezed and broken,and the Al_(2)O_(3p) become uniform distribution.The microhardness of as-extruded 2 wt%Al_(2)O_(3p)/7075 composites reaches HV 170.34,increased by 41.5%than as-cast composites.The wear rate of as-extruded 2 wt%Al_(2)O_(3p)/7075 composites is further lower than that of as-cast composites under the same condition.SEM-EDS analyses reveal that the reinforced wear resistance of composites can put down to the protective effect of the Al_(2)O_(3p) reinforced transition layer.After hot extrusion,the transition layer becomes stable,which determines the reinforced wear resistance of the as-extruded composites.
基金Project(2016YFB0300802)supported by the National Key Research and Development Program of China。
文摘The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.
基金Project(50734007) supported by the National Natural Science Foundation of ChinaProject(2007GA002) supported by Project of Scienceand Technology of Yunnan Province,ChinaProject(2008-16) supported by the Analysis and Testing Foundation of Kunming Universityof Science and Technology,China
文摘The microwave absorbing characteristics of basic cobalt carbonate,cobalt oxide(Co3O4),and the mixture of basic cobalt carbonate and cobalt oxide were investigated by means of microwave cavity perturbation,their temperature increasing curves were measured,and their ability to absorb microwave energy was also assessed based on the temperature increasing behavior of the material exposed to microwave field.Analyses of spectrum attenuation and relative frequency shift show that basic cobalt carbonate has weak capability to absorb microwave energy,while cobalt oxide has very strong capability to absorb microwave energy.It is feasible to thermally decompose basic cobalt carbonate though addition of small amount of cobalt oxide in microwave fields.The capability to absorb microwave energy of sample increases with an increase in mixing ratio of Co3O4.
基金Projects(50872098, 51004080) supported by the National Natural Science Foundation of ChinaProject(B0903) supported by the Opening Fund of Research Center of Green Manufacturing and Energy-saving & Emission Reduction Technology of Wuhan University of Science and Technology, China
文摘The dissolution behavior of CaO-MgO-SiO2 glass fiber was investigated by scanning electron microscopy （SEM）, Fourier-transform infrared spectrometer （FTIR） and inductively coupled plasma atomic emission spectroscopy （ICP-AES） using in-vitro tests. The results show that the soaked fiber is surrounded by an outer calcium-magnesium silicate hydrated layer, and there exists a balancing fimction between the formation and abscission of the hydrated layer during the dissolution process. The concentrations of leached ions increase constantly, and the mass loss of the fibers and pH changes of the solution are found to rise rapidly during the initial dissolution process, then their increasing rates are controlled by the balancing function of the hydrated layer at the subsequent dissolution stages. The dissolution rate constant and time for complete dissolution are estimated to be 274 ng/（cm2.h） and 15.2 d, respectively, presenting preferable biosolubilities.
基金Project(50808086) supported by the National Natural Science Foundation of China
文摘A methodology was presented relating the microstructure of asphalt mixtures to their damage behavior. Digital image techniques were used to capture the asphalt mixture microstructure, and the finite element method was used to simulate the damage evolution of asphalt mixture through splitting test. Aggregates were modeled to be linearly elastic, and the mastics were modeled to be plastically damaged. The splitting test simulation results show that the material heterogeneity, the properties of aggregates and air voids have significant effects on the damage evolution approach. The damage behavior of asphalt mixture considering material heterogeneity is quite different from that of the conventional hypothesis of homogeneous material. The results indicate that the proposed method can be extended to the numerical analysis for the other micromechanical behaviors of asphalt concrete.
基金Project(51271012)supported by the National Natural Science Foundation of China
文摘Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.
