Xi'an City is an important city of western region, facing the mission of constructing international metropolitan. There are many environmental issues in the city, which should be solved by legal construction. Base...Xi'an City is an important city of western region, facing the mission of constructing international metropolitan. There are many environmental issues in the city, which should be solved by legal construction. Based on the environmental status of the city, the construction content of environmental legal system was analyzed, focusing on conflict resolution, and the corresponding ways of research were proposed.展开更多
On the basis of some studies of elastic pipe conveying fluid, the dynamic behavior and stability of Maxwell viscoelastic pipes conveying fluid with both ends simply supported, which are gyroscopic conservative system,...On the basis of some studies of elastic pipe conveying fluid, the dynamic behavior and stability of Maxwell viscoelastic pipes conveying fluid with both ends simply supported, which are gyroscopic conservative system, were investigated by using the finite difference method and the corresponding recurrence formula. The effect of relaxation time of vis coelastic materials on the variation curve between dimensionless flow velocity and the real part and imaginary part of dimensionless complex frequencies in the first-three-order modes were analyzed concretely. It is found that critical flow velocities of divergence instability of Maxwell viscoelastic pipes conveying fluid with both ends simply supported decrease with the decrease of the relaxation time, while after the onset of divergence instability ( buckling) critical flow velocities of coupled-mode flutter increase with the decrease of the relaxation time. Particularly, in the case of greater mass ratio. with the decrease of relaxation time, the onset of coupled-mode flutter delays, and even does not take place. When the relaxation time is greater than 10(3), stability behavior of viscoelastic pipes conveying fluid is almost similar to the elastic pipes conveying fluid.展开更多
Thermal sprayed Ni-20wt. % Al coating is fabricated on 6061-T6 aluminum alloy substrates by twin-wire arc spraying (TWAS). Experimental results present that the average bonding strength is around 53 MPa and the aver...Thermal sprayed Ni-20wt. % Al coating is fabricated on 6061-T6 aluminum alloy substrates by twin-wire arc spraying (TWAS). Experimental results present that the average bonding strength is around 53 MPa and the average hardness reaches 325 HV. The Vickers microhardness of NiAl and Ni3Al intermetaUic compounds is larger than that of the substrate, which is beneficial for improving the wear property. Wear mechanism exhibits features of adhesive wear. Friction and wear test results indicate that the wet friction coefficient is higher than the coefficient of dry friction after 200 cycles, and variations of the wet friction coefficient are relatively smaller.展开更多
The interaction between precipitation and recrystallization and its effect on t he properties of the Cu-Ni-Si-Cr alloy during aging were discussed.The result s show that the deformation results in much more dispersed...The interaction between precipitation and recrystallization and its effect on t he properties of the Cu-Ni-Si-Cr alloy during aging were discussed.The result s show that the deformation results in much more dispersed precipitation of the phases. The precipitations have accelerating or retarding effects on the recryst allization. On the formation and growth of recrystallization, the precipitated p hases are coarsed or dissolved in front of grain boundaries following a re-prec ipitation in the recrystallization area.展开更多
Splitting modulus variational principle in linear theory of solid mechanics was introduced, the principle for thin plate was derived, and splitting modulus finite element method of thin plate was established too. The ...Splitting modulus variational principle in linear theory of solid mechanics was introduced, the principle for thin plate was derived, and splitting modulus finite element method of thin plate was established too. The distinctive feature of the splitting model is that its functional contains one or more arbitrary additional parameters, called splitting factors, so stiffness of the model can be adjusted by properly selecting the splitting factors. Examples show that splitting modulus method has high precision and the ability to conquer some ill-conditioned problems in usual finite elements. The cause why the new method could transform the ill-conditioned problems into well-conditioned problem, is analyzed finally.展开更多
In this paper, alloy powders mixed with a molar ratio of Fe : P : C of 80 : 13 : 7 were sprayed on Q235 steel by plasma spray method to prepare coating with amorphous phases. The phase composition of the mixed all...In this paper, alloy powders mixed with a molar ratio of Fe : P : C of 80 : 13 : 7 were sprayed on Q235 steel by plasma spray method to prepare coating with amorphous phases. The phase composition of the mixed alloy powders and prepared coating were characterized by X-ray diffraction ( XRD ). The morphology and the composition cf the coating were analyzed by scanning eleetron microscopy (SEM) nnd energy dispersive apectroscopy ( EDS ). In addition, the thermal stability ef the coating with amorphous phases was characterized by differential thermal analyzer ( DTA ). Tile results showed that, usirtg mixed alloy powders with a molar ratio of Fe: P: C of 80:13:7, the coating containing certain amount of amorphous alloys was suceessathlly prepared through atmospheric plasma spray technique. In the coating, the main phases were determined to be Fe, FeP aad Fe2P. The crystallization of the coating started from about 461°. Tile coating was mechanically adhered to the substrate.展开更多
This work focuses on the relationship between flexibility of molecular chains and thermal properties of polyurethane elastomer(PUE), which laid the foundation of further research about how to improve thermal propert...This work focuses on the relationship between flexibility of molecular chains and thermal properties of polyurethane elastomer(PUE), which laid the foundation of further research about how to improve thermal properties of PUE. A series of PUE samples with different flexibility of molecular chains was prepared by using 1,4-butanediol(1,4-BDO)/bisphenol-a(BPA) blends with different mole ratios including9/1, 8/2, 7/3, 6/4 and 5/5. As comparison, PUE extended with pure 1,4-BDO and BPA was also synthesized.These samples were characterized by differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), dynamic mechanical analysis(DMA), etc. The results showed that with the decrease in flexibility of molecular chains the glass transition temperature(Tg) increased and low-temperature properties became worse. Besides, all samples had a certain degree of microphase separation, and soft segments in some samples were crystallized, i.e. the decreasing flexibility of molecular chains led to the impossibility of chains tightly packing and crystalline domains forming so that the degree of microphase separation decreased and the thermal properties became worse.展开更多
Loss of function of large tissues is an urgent clinical problem. Although the artificial microfluidic network fabricated in large tis- sue-engineered constructs has great promise, it is still difficult to develop an e...Loss of function of large tissues is an urgent clinical problem. Although the artificial microfluidic network fabricated in large tis- sue-engineered constructs has great promise, it is still difficult to develop an efficient vessel-like design to meet the requirements of the biomimetic vascular network for tissue engineering applications. In this study, we used a facile approach to fabricate a branched and multi-level vessel-like network in a large muscle scaffolds by combining stereolithography (SL) technology and enzymatic crosslinking mechanism. The morphology of microchannel cross-sections was characterized using micro-computed tomography. The square cross-sections were gradually changed to a seamless circular microfluidic network, which is similar to the natural blood vessel. In the different micro-channels, the velocity greatly affected the attachment and spread of Human Umbilical Vein Endothelial Cell (HUVEC)-Green Fluorescent Protein (GFP). Our study demonstrated that the branched and multi-level microchannel network simulates biomimetic microenvironments to promote endothelialization. The gelatin scaffolds in the circular vessel-like networks will likely support myoblast and surrounding tissue for clinical use.展开更多
基金Xi’an Science and Technology Bureau Fund Project ( No. HJ1106 ( 2) )The Shaanxi Science and Technology Department Fund Project ( No. 2009KRM34)
文摘Xi'an City is an important city of western region, facing the mission of constructing international metropolitan. There are many environmental issues in the city, which should be solved by legal construction. Based on the environmental status of the city, the construction content of environmental legal system was analyzed, focusing on conflict resolution, and the corresponding ways of research were proposed.
文摘On the basis of some studies of elastic pipe conveying fluid, the dynamic behavior and stability of Maxwell viscoelastic pipes conveying fluid with both ends simply supported, which are gyroscopic conservative system, were investigated by using the finite difference method and the corresponding recurrence formula. The effect of relaxation time of vis coelastic materials on the variation curve between dimensionless flow velocity and the real part and imaginary part of dimensionless complex frequencies in the first-three-order modes were analyzed concretely. It is found that critical flow velocities of divergence instability of Maxwell viscoelastic pipes conveying fluid with both ends simply supported decrease with the decrease of the relaxation time, while after the onset of divergence instability ( buckling) critical flow velocities of coupled-mode flutter increase with the decrease of the relaxation time. Particularly, in the case of greater mass ratio. with the decrease of relaxation time, the onset of coupled-mode flutter delays, and even does not take place. When the relaxation time is greater than 10(3), stability behavior of viscoelastic pipes conveying fluid is almost similar to the elastic pipes conveying fluid.
文摘Thermal sprayed Ni-20wt. % Al coating is fabricated on 6061-T6 aluminum alloy substrates by twin-wire arc spraying (TWAS). Experimental results present that the average bonding strength is around 53 MPa and the average hardness reaches 325 HV. The Vickers microhardness of NiAl and Ni3Al intermetaUic compounds is larger than that of the substrate, which is beneficial for improving the wear property. Wear mechanism exhibits features of adhesive wear. Friction and wear test results indicate that the wet friction coefficient is higher than the coefficient of dry friction after 200 cycles, and variations of the wet friction coefficient are relatively smaller.
基金Funded by the National High Technology Research Project (No.2002AA331112) and by the Major Science and Technology Projectof Henan Province of China(No.0122021300)
文摘The interaction between precipitation and recrystallization and its effect on t he properties of the Cu-Ni-Si-Cr alloy during aging were discussed.The result s show that the deformation results in much more dispersed precipitation of the phases. The precipitations have accelerating or retarding effects on the recryst allization. On the formation and growth of recrystallization, the precipitated p hases are coarsed or dissolved in front of grain boundaries following a re-prec ipitation in the recrystallization area.
文摘Splitting modulus variational principle in linear theory of solid mechanics was introduced, the principle for thin plate was derived, and splitting modulus finite element method of thin plate was established too. The distinctive feature of the splitting model is that its functional contains one or more arbitrary additional parameters, called splitting factors, so stiffness of the model can be adjusted by properly selecting the splitting factors. Examples show that splitting modulus method has high precision and the ability to conquer some ill-conditioned problems in usual finite elements. The cause why the new method could transform the ill-conditioned problems into well-conditioned problem, is analyzed finally.
文摘In this paper, alloy powders mixed with a molar ratio of Fe : P : C of 80 : 13 : 7 were sprayed on Q235 steel by plasma spray method to prepare coating with amorphous phases. The phase composition of the mixed alloy powders and prepared coating were characterized by X-ray diffraction ( XRD ). The morphology and the composition cf the coating were analyzed by scanning eleetron microscopy (SEM) nnd energy dispersive apectroscopy ( EDS ). In addition, the thermal stability ef the coating with amorphous phases was characterized by differential thermal analyzer ( DTA ). Tile results showed that, usirtg mixed alloy powders with a molar ratio of Fe: P: C of 80:13:7, the coating containing certain amount of amorphous alloys was suceessathlly prepared through atmospheric plasma spray technique. In the coating, the main phases were determined to be Fe, FeP aad Fe2P. The crystallization of the coating started from about 461°. Tile coating was mechanically adhered to the substrate.
基金supported financially by the National Natural Science Foundation of China (Grant No. 51372200)Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-12-1045)+2 种基金Special Program for local serving from Education Department of Shaanxi Provincial Government (Grant No. 2013JC19)Program for Innovation Team in Xi’an University of Technology (Grant No. 108-25605T401)Ph.D. Innovation Fund Projects of Xi’an University of Technology (Fund No. 310-252071501)
文摘This work focuses on the relationship between flexibility of molecular chains and thermal properties of polyurethane elastomer(PUE), which laid the foundation of further research about how to improve thermal properties of PUE. A series of PUE samples with different flexibility of molecular chains was prepared by using 1,4-butanediol(1,4-BDO)/bisphenol-a(BPA) blends with different mole ratios including9/1, 8/2, 7/3, 6/4 and 5/5. As comparison, PUE extended with pure 1,4-BDO and BPA was also synthesized.These samples were characterized by differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), dynamic mechanical analysis(DMA), etc. The results showed that with the decrease in flexibility of molecular chains the glass transition temperature(Tg) increased and low-temperature properties became worse. Besides, all samples had a certain degree of microphase separation, and soft segments in some samples were crystallized, i.e. the decreasing flexibility of molecular chains led to the impossibility of chains tightly packing and crystalline domains forming so that the degree of microphase separation decreased and the thermal properties became worse.
基金This work was supported by National Natural Science Foundation of China (Grant No. 51375371) and the High-Tech Projects of China (Grant Nos. 2015AA020303 and 2015AA042503).
文摘Loss of function of large tissues is an urgent clinical problem. Although the artificial microfluidic network fabricated in large tis- sue-engineered constructs has great promise, it is still difficult to develop an efficient vessel-like design to meet the requirements of the biomimetic vascular network for tissue engineering applications. In this study, we used a facile approach to fabricate a branched and multi-level vessel-like network in a large muscle scaffolds by combining stereolithography (SL) technology and enzymatic crosslinking mechanism. The morphology of microchannel cross-sections was characterized using micro-computed tomography. The square cross-sections were gradually changed to a seamless circular microfluidic network, which is similar to the natural blood vessel. In the different micro-channels, the velocity greatly affected the attachment and spread of Human Umbilical Vein Endothelial Cell (HUVEC)-Green Fluorescent Protein (GFP). Our study demonstrated that the branched and multi-level microchannel network simulates biomimetic microenvironments to promote endothelialization. The gelatin scaffolds in the circular vessel-like networks will likely support myoblast and surrounding tissue for clinical use.