磁流变阀是一种以磁流变液为工作介质的智能控制器件,其进出口压差可调且响应速度快的特点使其在减振抗震系统中具有广泛的应用前景。设计了一种典型的阻尼间隙为圆环流动式的圆环流磁流变阀,对其工作原理进行了阐述,同时推导了圆环流...磁流变阀是一种以磁流变液为工作介质的智能控制器件,其进出口压差可调且响应速度快的特点使其在减振抗震系统中具有广泛的应用前景。设计了一种典型的阻尼间隙为圆环流动式的圆环流磁流变阀,对其工作原理进行了阐述,同时推导了圆环流磁流变阀的压降数学模型。采用有限元法(FEM)和计算流体力学法(CFD)分别对圆环流磁流变阀的电磁场和流场进行了建模仿真,分析了不同电流下磁流变阀压降变化规律,仿真结果表明圆环流磁流变阀的压降随着加载电流的增大而增大,并且逐渐趋于饱和;同时采用FEM方法得到的最大压降为948 k Pa,采用CFD方法得到的最大压降为1 079 k Pa。搭建了圆环流磁流变阀压降性能试验台,对不同电流及不同负载下的磁流变阀压降性能进行了试验分析,并与仿真结果进行了对比,结果表明试验压降变化趋势与两种仿真方法得出的压降变化基本相符,试验测试得到的最大压降为662 k Pa。同时,试验结果表明外加负载对圆环流磁流变阀压降大小变化基本无影响。展开更多
Friction stir welding provides better retention of ductility and plasticity in comparison to fusion welding and it increases the stability against cracking.This study aims to enhance both the ductility and strength of...Friction stir welding provides better retention of ductility and plasticity in comparison to fusion welding and it increases the stability against cracking.This study aims to enhance both the ductility and strength of the welded joints.Tool profile was found to play an important role in retaining ductility,understanding the metal flow behavior and determining the fracture initiating point.The microstructure of different regions in the onion ring was inferred to correlate the strength with the metal flow pattern.The onion ring pattern strengthened the weld nugget.Shoulder and taper threaded profile tool resulted in superior mechanical properties.Microhardness results confirmed that the fracture runs through low hardness areas such as heat affected zone and thermo-mechanically affected zone.The scanning electron microscopic images revealed elongated grains and dimples,justifying ductile mode of fracture.展开更多
Duck circovirus （DuCV）, a potential immunosuppressive virus, was investigated in Southern China from March 2006 to December 2009 by using a polymerase chain reaction （PCR） based method. In this study, a total of 1...Duck circovirus （DuCV）, a potential immunosuppressive virus, was investigated in Southern China from March 2006 to December 2009 by using a polymerase chain reaction （PCR） based method. In this study, a total of 138 sick or dead duck samples from 18 different farms were examined with an average DuCV infection rate of-35%. It was found that ducks between the ages of 40~60 days were more susceptible to DuCV. There was no evidence showing that the DuCV virus was capable of vertical transmission. Farms with positive PCR results exhibited no regularly apparent clinical abnormalities such as feathering disorders, growth retardation or lower-than-average weight. The complete genomes of 91 strains from Fujian Province and 1 from Zhejiang Province were sequenced and analyzed. The 10 DuCV genomes, comlbared with others genomes downloaded from GenBank, ranged in size from 1988 to 1996 base pairs, with sequence identities ranging from 83.2% to 99.8%. Phylogenetic analysis based on genome sequences demonstrated that DuCVs can be divided into two distinct genetic genotypes, Group I （the Euro-USA lineage） and Group II（the Taiwan lineage）, with approximately 10.0% genetic difference between the two types. Molecular epidemiological data suggest there is no obvious difference among DuCV strains isolated from different geographic locations or different species, including Duck, Muscovy duck, Mule duck, Cheery duck, Mulard duck and Pekin duck.展开更多
The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model...The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model of three-dimensional（3D）viscoelastic flow through elliptical ring die for polymer extrusion was investigated.The penalty function formulation of viscoelastic incompressible fluid was introduced to the finite element model to analyze 3D extrusion problem.The discrete elastic viscous split stress（DEVSS）and streamline-upwind PetrovGalerkin（SUPG）technology were used to obtain stable simulation results.Free surface was updated by updating the streamlines which needs less memory space.According to numerical simulation results,the effect of zero-shear viscosity and elongation parameter on extrudate swell was slight,but with the increase of volumetric flow rate and relax time the extrudate swell ratio increased markedly.Finally,the numerical simulation of extrudate swell flow for low-density polyethylene（LDPE）melts was investigated and the results agreed well with others’work.These conclusions provided quantitative basis for the forecasting extrudate swell ratio and the controlling of extrusion productivity shape.展开更多
PCV2 （Porcine circovirus type 2） is considered as the essential infectious agent of PMWS （post weaning multisystemic wasting syndrome） in pigs. Serological studies have shown that the virus is ubiquitous. Currentl...PCV2 （Porcine circovirus type 2） is considered as the essential infectious agent of PMWS （post weaning multisystemic wasting syndrome） in pigs. Serological studies have shown that the virus is ubiquitous. Currently, there are many reports about the epidemiology and genetic characteristics of this virus around the world, but in Mexico it has not been studied. More than 3,500 samples of serum, rectal swabs, tissues and semen of 34 Mexican porcine farms from 10 important producer regions were analyzed by PCR. Results show that 97% of the farms were positive. Both genotypes, PCV2a and PCV2b were detected. It also found that the most prevalent genotype in Mexico is PCV2b. Regarding to amino acid sequence; three major heterogenic regions were present in the positions 59-91,123-136 and 185-210.展开更多
文摘磁流变阀是一种以磁流变液为工作介质的智能控制器件,其进出口压差可调且响应速度快的特点使其在减振抗震系统中具有广泛的应用前景。设计了一种典型的阻尼间隙为圆环流动式的圆环流磁流变阀,对其工作原理进行了阐述,同时推导了圆环流磁流变阀的压降数学模型。采用有限元法(FEM)和计算流体力学法(CFD)分别对圆环流磁流变阀的电磁场和流场进行了建模仿真,分析了不同电流下磁流变阀压降变化规律,仿真结果表明圆环流磁流变阀的压降随着加载电流的增大而增大,并且逐渐趋于饱和;同时采用FEM方法得到的最大压降为948 k Pa,采用CFD方法得到的最大压降为1 079 k Pa。搭建了圆环流磁流变阀压降性能试验台,对不同电流及不同负载下的磁流变阀压降性能进行了试验分析,并与仿真结果进行了对比,结果表明试验压降变化趋势与两种仿真方法得出的压降变化基本相符,试验测试得到的最大压降为662 k Pa。同时,试验结果表明外加负载对圆环流磁流变阀压降大小变化基本无影响。
基金Project(ISRO/RES/3/683/15-16 dt 07.08.2015)supported by Indian Space Research Organization
文摘Friction stir welding provides better retention of ductility and plasticity in comparison to fusion welding and it increases the stability against cracking.This study aims to enhance both the ductility and strength of the welded joints.Tool profile was found to play an important role in retaining ductility,understanding the metal flow behavior and determining the fracture initiating point.The microstructure of different regions in the onion ring was inferred to correlate the strength with the metal flow pattern.The onion ring pattern strengthened the weld nugget.Shoulder and taper threaded profile tool resulted in superior mechanical properties.Microhardness results confirmed that the fracture runs through low hardness areas such as heat affected zone and thermo-mechanically affected zone.The scanning electron microscopic images revealed elongated grains and dimples,justifying ductile mode of fracture.
基金Modern Agri-industry Technology Research System(CARS-43)Science and Technology Innovation Fund of Fujian Academy of Agriculture Science(STIF-02)Science and Technology Innovation Foundation for Young Scientists of Fujian Academy of Agriculture Science(2008QB-6)
文摘Duck circovirus （DuCV）, a potential immunosuppressive virus, was investigated in Southern China from March 2006 to December 2009 by using a polymerase chain reaction （PCR） based method. In this study, a total of 138 sick or dead duck samples from 18 different farms were examined with an average DuCV infection rate of-35%. It was found that ducks between the ages of 40~60 days were more susceptible to DuCV. There was no evidence showing that the DuCV virus was capable of vertical transmission. Farms with positive PCR results exhibited no regularly apparent clinical abnormalities such as feathering disorders, growth retardation or lower-than-average weight. The complete genomes of 91 strains from Fujian Province and 1 from Zhejiang Province were sequenced and analyzed. The 10 DuCV genomes, comlbared with others genomes downloaded from GenBank, ranged in size from 1988 to 1996 base pairs, with sequence identities ranging from 83.2% to 99.8%. Phylogenetic analysis based on genome sequences demonstrated that DuCVs can be divided into two distinct genetic genotypes, Group I （the Euro-USA lineage） and Group II（the Taiwan lineage）, with approximately 10.0% genetic difference between the two types. Molecular epidemiological data suggest there is no obvious difference among DuCV strains isolated from different geographic locations or different species, including Duck, Muscovy duck, Mule duck, Cheery duck, Mulard duck and Pekin duck.
基金Supported by the National Science Foundation for Distinguished Young Scholars of China（50425517） the Shandong Province Natural Science Foundation（Y2007F59）
文摘The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model of three-dimensional（3D）viscoelastic flow through elliptical ring die for polymer extrusion was investigated.The penalty function formulation of viscoelastic incompressible fluid was introduced to the finite element model to analyze 3D extrusion problem.The discrete elastic viscous split stress（DEVSS）and streamline-upwind PetrovGalerkin（SUPG）technology were used to obtain stable simulation results.Free surface was updated by updating the streamlines which needs less memory space.According to numerical simulation results,the effect of zero-shear viscosity and elongation parameter on extrudate swell was slight,but with the increase of volumetric flow rate and relax time the extrudate swell ratio increased markedly.Finally,the numerical simulation of extrudate swell flow for low-density polyethylene（LDPE）melts was investigated and the results agreed well with others’work.These conclusions provided quantitative basis for the forecasting extrudate swell ratio and the controlling of extrusion productivity shape.
文摘PCV2 （Porcine circovirus type 2） is considered as the essential infectious agent of PMWS （post weaning multisystemic wasting syndrome） in pigs. Serological studies have shown that the virus is ubiquitous. Currently, there are many reports about the epidemiology and genetic characteristics of this virus around the world, but in Mexico it has not been studied. More than 3,500 samples of serum, rectal swabs, tissues and semen of 34 Mexican porcine farms from 10 important producer regions were analyzed by PCR. Results show that 97% of the farms were positive. Both genotypes, PCV2a and PCV2b were detected. It also found that the most prevalent genotype in Mexico is PCV2b. Regarding to amino acid sequence; three major heterogenic regions were present in the positions 59-91,123-136 and 185-210.
