A numerical approach for process optimization and microstructure evolution of lager-sized forging of aluminium alloy 7050 was proposed, which combined a commercial FEM code Deform 3D with empirical models. To obtain t...A numerical approach for process optimization and microstructure evolution of lager-sized forging of aluminium alloy 7050 was proposed, which combined a commercial FEM code Deform 3D with empirical models. To obtain the parameters of empirical constitutive equation and dynamic recrystallization models for aluminium alloy 7050, the isothermal compression tests of 7050 samples were performed on Gleeble-1500 thermo-simulation machine in the temperature range of 250-450 ℃ and strain rate of 0.01-10 s-1, and the metallograph analysis of the samples were carried out on a Leica DMIRM image analyzer. The simulation results show that the dynamic recrystallization in the central area of the billet occurs more easily than that on the edge. Repetitious upsetting and stretching processes make the billet deform adequately. Among several forging processes e.g. upsetting, stretching, rounding and flatting, the stretching process is the most effective way to increase the effective strain and refine the microstructure of the billet. As the forging steps increase, the effective strain rises significantly and the average grain size reduces sharply. Recrystallized volume fractions in most parts of the final forging piece reach 100% and the average grain size reduces to 10 μm from initial value of 90 μm.展开更多
In this paper,the 16-parameter nonconforming tetrahedral element which has an energy-orthogonal shape function space is presented for the discretization of fourth order elliptic partial differential operators in three...In this paper,the 16-parameter nonconforming tetrahedral element which has an energy-orthogonal shape function space is presented for the discretization of fourth order elliptic partial differential operators in three spatial dimensions.The newly constructed element is proved to be convergent for a model biharmonic equation.展开更多
Recent new technology developments were presented in the field of industrial bending operations,including flexible stretch forming and 3D rotary stretch forming.Attempts were made to give an overview of different mech...Recent new technology developments were presented in the field of industrial bending operations,including flexible stretch forming and 3D rotary stretch forming.Attempts were made to give an overview of different mechanisms that influence dimensional accuracy,including local cross-sectional deformations such as suck-in and volume conservation effects,along with global deformations such as springback.An analytical model was developed to determine the particular influence of different material,geometry and process parameters on dimensional variability of bent components.The results were discussed in terms of overall process capability(Cp) and associated process windows.The results show that different governing mechanisms prevail in various bending operations,meaning that attention has to be placed on controlling those process parameters that really are important to part quality in each specific case.Several strategies may be defined for reducing variability.One alternative may be to design more robust process and tool technology that reduce the effect of upstream parameters on dimensional variability of the formed part.The results show that optimal tool design and technology may in specific cases improve the dimensional accuracy of a formed part.Based on the findings discussed herein,it is concluded that advances in industrial bending operations require focus on improving the understanding of mechanical mechanisms,including models and parameter development,new technology developments,including process,tool,measurement and control capabilities,and process discipline at the shop floor,combined with a basic philosophy of controlling process parameters rather than part attributes.展开更多
A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. Accor...A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. According to the test results, several assumptions were made to deduce the bearing capacity calculation method based on the force balance of the whole section. An optimal dimension relationship for the truss beam chords was proposed and verified by finite element analysis. Results show that the LACFST spatial truss beam failed after excessive deflection. The strain distribution agreed with Bernoulli-Euler theoretical prediction. The truss beam flexural bearing capacity calculation results matched test evidence with only a 3% difference between the two. Finite element analyses with different chord dimensions show that the ultimate bearing capacity increases as the chord dimensions increase when the chords have a diameter smaller than optimal one; otherwise, it remains almost unchanged as the chord dimensions increase.展开更多
Plasmonic photocatalysis with tunable light absorption has aroused significant attention in so-lar-to-chemical energy conversion.However,the energy conversion efficiency of plasmonic photo-catalysts is impeded by inef...Plasmonic photocatalysis with tunable light absorption has aroused significant attention in so-lar-to-chemical energy conversion.However,the energy conversion efficiency of plasmonic photo-catalysts is impeded by ineffective charge separation and the lack of highly active sites for redox reactions.In this work,the Au nanoparticle size and Au-TiO2 interaction of the Au/TiO2 plasmonic photocatalyst were adjusted simultaneously using a post-calcination treatment.The visi-ble-ight-induced water oxidation activity exhibited a volcano-like relationship with the calcination temperature;the treated photocatalyst at 600°C manifested the highest activity.Characterization with UV-visible spectra,XRD,SEM,and XPS revealed that the effect of the Au nanoparticle size and Au-TiO2 interaction were both responsible for the increase in plasmon-induced water oxidation activity.展开更多
This paper studied the residents' level of satisfaction in public housing units in Shenyang of China which aimed to identify how each housing unit feature correlates with the residents' overall satisfaction and impl...This paper studied the residents' level of satisfaction in public housing units in Shenyang of China which aimed to identify how each housing unit feature correlates with the residents' overall satisfaction and implication on policy and design. The discussion is based on a questionnaire survey conducted in 2011. This research concluded that more residents were satisfied with the housing unit features than those who were dissatisfied, while some remarkable differences could be observed if comparative analysis between two different public housing types in China were studied. The affordable housing residents are generally more satisfied with housing unit features than those living in low-rent housing. The most dissatisfying feature is the living room, followed by unit size and the floor plan. Additionally, the living room and the floor plans were features which were highly and positively correlated to the residents' overall satisfaction of housing unit features. Consequently, improving the living room size and the design of housing unit floor plans would clearly be beneficial to alleviating residents' dissatisfaction to the housing units.展开更多
Road surface condition evaluation involves the collection of data over pavement surface for different types of distresses. The exercise consumes a lot of resources if the whole road section length is surveyed and may ...Road surface condition evaluation involves the collection of data over pavement surface for different types of distresses. The exercise consumes a lot of resources if the whole road section length is surveyed and may be prone to errors as a result of surveyors' fatigue. It is therefore important to develop a representative sample to be used when evaluating road condition manually. This study aimed at determining an adequate sample size for section level as well as a way forward for network level condition evaluation of highways in Nepal. Again the study was conducted to quantify the effects of altering the sample unit size for performing a distress survey according to the PCI (pavement condition index) and SDI (surface distress index) method separately for asphalt surfaced roads. The effect of reducing/increasing sample unit size was investigated adopting visual examination through field survey by eight teams in July, 2015, along the section of Banepa-Bardibas highway. The PCI was then calculated for each sample unit using standard deduct curves and PCI calculation methodology as per SHRP (Strategic Highway Research Program) recommendations and the computation of SDI was done as per DoR (Department of Roads) guidelines. The results show that 13% sample unit are needed for SDI and 21% for PCI computation, however, the results are out of the significant level. This is higher than DoR and SHRP guidelines. Again no strong relationship is observed between SDI and PCI values.展开更多
This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-re...This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-resolution grain-size variation, sensitive population, geochemical indexes and magnetic susceptibility. The core covers a time span of 120 years by 21~pb dating and was sampled at 1-2 cm intervals. Grain size, geochemical elements, and physical parameters were analyzed. The results indicate that the sediment of the core is mainly composed of silt and clay, as well as groups of interbedded silt, clay silt, and clay. Vertically, the grain size pattern was controlled by seasonal variations in water discharge and by the sediment input in winter from the abandoned Huanghe River delta. River flooding caused extreme values in all our measured parameters. We identified more than 20 flood events that occurred since 1887 using the physical parameter analysis method. The environmentally sensitive component of sediment grain size (14.32-96.39 gm) contribution〉30%, Zr/Rb ratio〉l.5, and magnetic susceptibility〉16 were selected as the criteria for flood identification generally. We also found that floods that had taken place in the upstream, midstream, or downstream parts of the river were clearly identified by these indexes while the large-scale floods that covered the whole drainage area did not leave clear indications in the sediment record. This study for identification of flood events is of great significance for understanding hyperpycnal current sedimentation as well as for forecasting of floods.展开更多
Based on our previously pulse-coupled integrate-and-fire neuron model in small world networks, we investigate the effects of different connectivity topologies on complex behavior of electroencephalographic-like signal...Based on our previously pulse-coupled integrate-and-fire neuron model in small world networks, we investigate the effects of different connectivity topologies on complex behavior of electroencephalographic-like signals produced by this model. We show that several times series analysis methods that are often used for analyzing complex behavior of electroencephalographic-like signals, such as reconstruction of the phase space, correlation dimension, fractal dimension, and the Hurst exponent within the rescaled range analysis (R/S). We lind that the different connectivity topologies lead to different dynamical behaviors in models of integrate-and-fire neurons.展开更多
A new method of forming a four-port multi-antenna by a two-unit patch antenna array is proposed to design a high isolation low correlation stroll size multi-antenna. Dual polarization is real-ized by the method of fee...A new method of forming a four-port multi-antenna by a two-unit patch antenna array is proposed to design a high isolation low correlation stroll size multi-antenna. Dual polarization is real-ized by the method of feeding in two ports. Defec-ted Ground Structure (DGS) is used to eliminate the coupling between the two antenna units. The test results show that the isolation between two ports reaches around 20dB, and that the antenna correlation coefficients is less than 0. 5, which meets the requirements of future mobile communi-cation systems and provides a solution to multi-antenna of MIMO terminals.展开更多
To develop AZ91D alloys with fine microstructure, effects of the addition of rare earth (RE), Sr and RE + Sr on the dendrite growth and phase precipitation in AZ91D magnesium alloy were studied, respectively. The resu...To develop AZ91D alloys with fine microstructure, effects of the addition of rare earth (RE), Sr and RE + Sr on the dendrite growth and phase precipitation in AZ91D magnesium alloy were studied, respectively. The results show that the microstructure is refined and the morphology of β-Mg17A112 phase is modified with RE or Sr addition, especially with the RE+Sr composite addition which can reduce the average grain size of AZ91D alloy obviously to 141 μm. The needle-like or block-like new phases adhering to β-Mg17A112 phase form at interdendrites during solidification. The enrichment of RE or/and Sr elements in front of the solidification interface, especially at the tips of α-Mg dendrite, which restricts the growth of α-Mg dendrite, changes the preferential growth of α-Mg and finally results in the grain refinement and the blunting of α-Mg dendrite.展开更多
Particle size distribution of coarse aggregates through mechanical sieving gives results in terms of cumu- lative mass percent. But digital image processing generated size distribution of particles, while being fast a...Particle size distribution of coarse aggregates through mechanical sieving gives results in terms of cumu- lative mass percent. But digital image processing generated size distribution of particles, while being fast and accurate, is often expressed in terms of area function or number of particles. In this paper, a mass model is developed which converts the image obtained size distribution to mass-wise distribution, mak- ing it readily comparable to mechanical sieving data. The concept of weight/particle ratio is introduced for mass reconstruction from 2D images of particle aggregates. Using this mass model, the effects of several particle shape parameters (such as major axis, minor axis, and equivalent diameter) on sieve-size of the particles is studied. It is shown that the sieve-size of a particle strongly depend upon the shape param- eters, 91% of its variation being explained by major axis, minor axis, bounding box length and equivalent diameter. Furthermore, minor axis gives an overall accurate estimate of particle sieve-size, error in mean size (D-50) being just 0.4%. However, sieve-size of smaller particles (〈20 ram) strongly depends upon the length of the smaller arm of the bounding box enclosing them and sieve-sizes of larger particles (〉20 mm) are highly correlated to their equivalent diameters. Multiple linear regression analysis has been used to generate overall mass-wise particle size distribution, considering the influences of all these shape parameters on particle sieve-size. Multiple linear regression generated overall mass-wise particle size distribution shows a strong correlation with sieve generated data. The adjusted R-square value of the regression analysis is found to be 99 percent (w.r,t cumulative frequency). The method proposed in this paper provides a time-efficient way of producing accurate (up to 99%) mass-wise PSD using digital image processing and it can be used effectively to renlace the mechanical sieving.展开更多
The solidification microstructures and hardness of Mg-2%Zn (mass fraction) based alloys with addition of 0.4%Ce, 0.4%Gd, 0.4%Y or 0.4%Nd (mass fraction) were investigated, and the effects of the rare earth elements on...The solidification microstructures and hardness of Mg-2%Zn (mass fraction) based alloys with addition of 0.4%Ce, 0.4%Gd, 0.4%Y or 0.4%Nd (mass fraction) were investigated, and the effects of the rare earth elements on the microstructures and mechanical properties of these alloys extruded at 310℃ were also compared. The results indicate that the trace rare earth Ce, Gd, Y or Nd in the Mg-2%Zn alloy has obviously different grain refinement effects on its solidification microstructures, and the as-cast and hot-extruded alloy with 0.4%Ce has the smallest average grain size and the highest strength. However, the extruded alloys containing 0.4%Nd or 0.4%Y with the elongation of 26.6% and 30%, respectively, show higher plasticity in spite of lower strength as compared with the alloy containing 0.4%Ce.展开更多
The influence of the change of structure plane size on seismic response was studied for a soil-structure interaction system.Based on the finite element method,a soil-structure interaction calculation model was establi...The influence of the change of structure plane size on seismic response was studied for a soil-structure interaction system.Based on the finite element method,a soil-structure interaction calculation model was established to analyze the seismic response by changing the structure plane size and choosing different earthquake waves for different soil fields.The results show that when the natural periods of vibration for different structure plane sizes are close,under the same earthquake wave,the total displacement on the top layer of the structure and the foundation rotation displacement decrease with the increase of structure plane size,and the proportion of superstructure elastic selfdeformation displacement to the total displacement increases with the increase of structure plane size.While for different types of sites and seismic waves,under the horizontal and vertical seismic waves,the seismic responses of different plane sizes have a similar change rule.展开更多
This paper presents finite element results of ceramic masonry prisms and walls under concentric compression. Four different hole geometries of ceramic units were studied (called Types A, B, C and D). The A-type unit...This paper presents finite element results of ceramic masonry prisms and walls under concentric compression. Four different hole geometries of ceramic units were studied (called Types A, B, C and D). The A-type unit had two rectangular hollows, B-type and C-type units have two rounded hollows and different net areas, mad the D-type unit had two rectangular hollows and a double central web. This study analyzed units, prisms and structural walls joined by bedding mortar. The objective was to verify the stress distribution in units and mortars. The results showed that the distribution of compressive stress along the length and width of those units was uniform, but lateral tensile stress along the length was distinct for different geometries. In addition, this study observed that hollow shapes have an important influence in stress distribution. The D-type unit was the one that showed more uniform tension distribution, without peaks of stress concentration. This indicates that a D-type unit is the most efficient unit for use in masonry structures.展开更多
In this study fat-tail weight was estimated by external fat-tail dimensions. External fat-tail dimensions included upper, middle and lower width, length, length of gap, depth, upper and middle circumference recorded o...In this study fat-tail weight was estimated by external fat-tail dimensions. External fat-tail dimensions included upper, middle and lower width, length, length of gap, depth, upper and middle circumference recorded on 1,482 head of Lori-Bakhtiari lambs at 6 months. Of these about 311 lambs were slaughtered at the age of six months. Prediction equations were derived for fat-tail weight by multiple regression analyses with two methods. The results showed that the measure of middle circumference fat-tail was as most important measure in estimation of fat-tail weight. The measure of middle circumference fat-tail accounted for 76 percent of variation in fat-tail weight. The regression equations for predicting fat-tail weight using external fat-tail dimensions obtained from stepwise regression procedure can be estimated only with using from the lower width, length, middle circumference fat-tail and body weight with high acc, uracy (0.92). Average of fat-tail weight estimated in the age of six months in lambs was 2.39 kg. The highest regression coefficient of external fat-tail dimensions on fat-tail weight observed for the length of fat-tail (0.095 kg). Results of the present investigation showed that fat-tail weight in live sheep of Lori-Bakhtiari, could be estimated by measuring external fat-tail dimensions.展开更多
基金Project(2005CB724105) supported by the National Basic Research Program of ChinaProject (IRT0549) supported by the Program for Changjiang Scholars and Innovative Research Team in University
文摘A numerical approach for process optimization and microstructure evolution of lager-sized forging of aluminium alloy 7050 was proposed, which combined a commercial FEM code Deform 3D with empirical models. To obtain the parameters of empirical constitutive equation and dynamic recrystallization models for aluminium alloy 7050, the isothermal compression tests of 7050 samples were performed on Gleeble-1500 thermo-simulation machine in the temperature range of 250-450 ℃ and strain rate of 0.01-10 s-1, and the metallograph analysis of the samples were carried out on a Leica DMIRM image analyzer. The simulation results show that the dynamic recrystallization in the central area of the billet occurs more easily than that on the edge. Repetitious upsetting and stretching processes make the billet deform adequately. Among several forging processes e.g. upsetting, stretching, rounding and flatting, the stretching process is the most effective way to increase the effective strain and refine the microstructure of the billet. As the forging steps increase, the effective strain rises significantly and the average grain size reduces sharply. Recrystallized volume fractions in most parts of the final forging piece reach 100% and the average grain size reduces to 10 μm from initial value of 90 μm.
文摘In this paper,the 16-parameter nonconforming tetrahedral element which has an energy-orthogonal shape function space is presented for the discretization of fourth order elliptic partial differential operators in three spatial dimensions.The newly constructed element is proved to be convergent for a model biharmonic equation.
文摘Recent new technology developments were presented in the field of industrial bending operations,including flexible stretch forming and 3D rotary stretch forming.Attempts were made to give an overview of different mechanisms that influence dimensional accuracy,including local cross-sectional deformations such as suck-in and volume conservation effects,along with global deformations such as springback.An analytical model was developed to determine the particular influence of different material,geometry and process parameters on dimensional variability of bent components.The results were discussed in terms of overall process capability(Cp) and associated process windows.The results show that different governing mechanisms prevail in various bending operations,meaning that attention has to be placed on controlling those process parameters that really are important to part quality in each specific case.Several strategies may be defined for reducing variability.One alternative may be to design more robust process and tool technology that reduce the effect of upstream parameters on dimensional variability of the formed part.The results show that optimal tool design and technology may in specific cases improve the dimensional accuracy of a formed part.Based on the findings discussed herein,it is concluded that advances in industrial bending operations require focus on improving the understanding of mechanical mechanisms,including models and parameter development,new technology developments,including process,tool,measurement and control capabilities,and process discipline at the shop floor,combined with a basic philosophy of controlling process parameters rather than part attributes.
基金Project(51208176)supported by the National Natural Science Foundation of ChinaProjects(2012M511187,2013T60493)supported by the China Postdoctoral Science FoundationProject(2015B17414)supported by the Fundamental Research Funds for the Central Universities,China
文摘A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. According to the test results, several assumptions were made to deduce the bearing capacity calculation method based on the force balance of the whole section. An optimal dimension relationship for the truss beam chords was proposed and verified by finite element analysis. Results show that the LACFST spatial truss beam failed after excessive deflection. The strain distribution agreed with Bernoulli-Euler theoretical prediction. The truss beam flexural bearing capacity calculation results matched test evidence with only a 3% difference between the two. Finite element analyses with different chord dimensions show that the ultimate bearing capacity increases as the chord dimensions increase when the chords have a diameter smaller than optimal one; otherwise, it remains almost unchanged as the chord dimensions increase.
基金supported by the National Natural Science Foundation of China (21633010)the National Basic Research Program of China (973 pro‐gram, 2014CB239400)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB01020300)~~
文摘Plasmonic photocatalysis with tunable light absorption has aroused significant attention in so-lar-to-chemical energy conversion.However,the energy conversion efficiency of plasmonic photo-catalysts is impeded by ineffective charge separation and the lack of highly active sites for redox reactions.In this work,the Au nanoparticle size and Au-TiO2 interaction of the Au/TiO2 plasmonic photocatalyst were adjusted simultaneously using a post-calcination treatment.The visi-ble-ight-induced water oxidation activity exhibited a volcano-like relationship with the calcination temperature;the treated photocatalyst at 600°C manifested the highest activity.Characterization with UV-visible spectra,XRD,SEM,and XPS revealed that the effect of the Au nanoparticle size and Au-TiO2 interaction were both responsible for the increase in plasmon-induced water oxidation activity.
文摘This paper studied the residents' level of satisfaction in public housing units in Shenyang of China which aimed to identify how each housing unit feature correlates with the residents' overall satisfaction and implication on policy and design. The discussion is based on a questionnaire survey conducted in 2011. This research concluded that more residents were satisfied with the housing unit features than those who were dissatisfied, while some remarkable differences could be observed if comparative analysis between two different public housing types in China were studied. The affordable housing residents are generally more satisfied with housing unit features than those living in low-rent housing. The most dissatisfying feature is the living room, followed by unit size and the floor plan. Additionally, the living room and the floor plans were features which were highly and positively correlated to the residents' overall satisfaction of housing unit features. Consequently, improving the living room size and the design of housing unit floor plans would clearly be beneficial to alleviating residents' dissatisfaction to the housing units.
文摘Road surface condition evaluation involves the collection of data over pavement surface for different types of distresses. The exercise consumes a lot of resources if the whole road section length is surveyed and may be prone to errors as a result of surveyors' fatigue. It is therefore important to develop a representative sample to be used when evaluating road condition manually. This study aimed at determining an adequate sample size for section level as well as a way forward for network level condition evaluation of highways in Nepal. Again the study was conducted to quantify the effects of altering the sample unit size for performing a distress survey according to the PCI (pavement condition index) and SDI (surface distress index) method separately for asphalt surfaced roads. The effect of reducing/increasing sample unit size was investigated adopting visual examination through field survey by eight teams in July, 2015, along the section of Banepa-Bardibas highway. The PCI was then calculated for each sample unit using standard deduct curves and PCI calculation methodology as per SHRP (Strategic Highway Research Program) recommendations and the computation of SDI was done as per DoR (Department of Roads) guidelines. The results show that 13% sample unit are needed for SDI and 21% for PCI computation, however, the results are out of the significant level. This is higher than DoR and SHRP guidelines. Again no strong relationship is observed between SDI and PCI values.
基金Supported by the National Natural Science Foundation of China(Nos.41206073,41376079,41206051,41206052)the China Geological Survey(Nos.1212010611401,200900501)
文摘This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-resolution grain-size variation, sensitive population, geochemical indexes and magnetic susceptibility. The core covers a time span of 120 years by 21~pb dating and was sampled at 1-2 cm intervals. Grain size, geochemical elements, and physical parameters were analyzed. The results indicate that the sediment of the core is mainly composed of silt and clay, as well as groups of interbedded silt, clay silt, and clay. Vertically, the grain size pattern was controlled by seasonal variations in water discharge and by the sediment input in winter from the abandoned Huanghe River delta. River flooding caused extreme values in all our measured parameters. We identified more than 20 flood events that occurred since 1887 using the physical parameter analysis method. The environmentally sensitive component of sediment grain size (14.32-96.39 gm) contribution〉30%, Zr/Rb ratio〉l.5, and magnetic susceptibility〉16 were selected as the criteria for flood identification generally. We also found that floods that had taken place in the upstream, midstream, or downstream parts of the river were clearly identified by these indexes while the large-scale floods that covered the whole drainage area did not leave clear indications in the sediment record. This study for identification of flood events is of great significance for understanding hyperpycnal current sedimentation as well as for forecasting of floods.
基金*The project supported by National Natural Science Foundation of China under Grant No. 90203008 and the Doctoral Foundation of the Ministry of Education of China
文摘Based on our previously pulse-coupled integrate-and-fire neuron model in small world networks, we investigate the effects of different connectivity topologies on complex behavior of electroencephalographic-like signals produced by this model. We show that several times series analysis methods that are often used for analyzing complex behavior of electroencephalographic-like signals, such as reconstruction of the phase space, correlation dimension, fractal dimension, and the Hurst exponent within the rescaled range analysis (R/S). We lind that the different connectivity topologies lead to different dynamical behaviors in models of integrate-and-fire neurons.
基金supported by Program for New Century ExcellentTalents in University
文摘A new method of forming a four-port multi-antenna by a two-unit patch antenna array is proposed to design a high isolation low correlation stroll size multi-antenna. Dual polarization is real-ized by the method of feeding in two ports. Defec-ted Ground Structure (DGS) is used to eliminate the coupling between the two antenna units. The test results show that the isolation between two ports reaches around 20dB, and that the antenna correlation coefficients is less than 0. 5, which meets the requirements of future mobile communi-cation systems and provides a solution to multi-antenna of MIMO terminals.
基金Project(50774075) supported by the National Natural Science Foundation of ChinaProject(2007CB613705) supported by the National Basic Research Program of China
文摘To develop AZ91D alloys with fine microstructure, effects of the addition of rare earth (RE), Sr and RE + Sr on the dendrite growth and phase precipitation in AZ91D magnesium alloy were studied, respectively. The results show that the microstructure is refined and the morphology of β-Mg17A112 phase is modified with RE or Sr addition, especially with the RE+Sr composite addition which can reduce the average grain size of AZ91D alloy obviously to 141 μm. The needle-like or block-like new phases adhering to β-Mg17A112 phase form at interdendrites during solidification. The enrichment of RE or/and Sr elements in front of the solidification interface, especially at the tips of α-Mg dendrite, which restricts the growth of α-Mg dendrite, changes the preferential growth of α-Mg and finally results in the grain refinement and the blunting of α-Mg dendrite.
基金Indian Institute of Technology,Kharagpur in India for supporting this work
文摘Particle size distribution of coarse aggregates through mechanical sieving gives results in terms of cumu- lative mass percent. But digital image processing generated size distribution of particles, while being fast and accurate, is often expressed in terms of area function or number of particles. In this paper, a mass model is developed which converts the image obtained size distribution to mass-wise distribution, mak- ing it readily comparable to mechanical sieving data. The concept of weight/particle ratio is introduced for mass reconstruction from 2D images of particle aggregates. Using this mass model, the effects of several particle shape parameters (such as major axis, minor axis, and equivalent diameter) on sieve-size of the particles is studied. It is shown that the sieve-size of a particle strongly depend upon the shape param- eters, 91% of its variation being explained by major axis, minor axis, bounding box length and equivalent diameter. Furthermore, minor axis gives an overall accurate estimate of particle sieve-size, error in mean size (D-50) being just 0.4%. However, sieve-size of smaller particles (〈20 ram) strongly depends upon the length of the smaller arm of the bounding box enclosing them and sieve-sizes of larger particles (〉20 mm) are highly correlated to their equivalent diameters. Multiple linear regression analysis has been used to generate overall mass-wise particle size distribution, considering the influences of all these shape parameters on particle sieve-size. Multiple linear regression generated overall mass-wise particle size distribution shows a strong correlation with sieve generated data. The adjusted R-square value of the regression analysis is found to be 99 percent (w.r,t cumulative frequency). The method proposed in this paper provides a time-efficient way of producing accurate (up to 99%) mass-wise PSD using digital image processing and it can be used effectively to renlace the mechanical sieving.
基金Projects(2007CB613701 2007CB613702) supported by the National Basic Research Program of China+2 种基金Project(NCET-08-0098) supported by the Program for New Century Excellent Talents in UniversityProject(50974037) supported by the National Natural Science Foundation of ChinaProject(90209002) supported by the Special Fund for Basic Scientific Research of Central Colleges in China
文摘The solidification microstructures and hardness of Mg-2%Zn (mass fraction) based alloys with addition of 0.4%Ce, 0.4%Gd, 0.4%Y or 0.4%Nd (mass fraction) were investigated, and the effects of the rare earth elements on the microstructures and mechanical properties of these alloys extruded at 310℃ were also compared. The results indicate that the trace rare earth Ce, Gd, Y or Nd in the Mg-2%Zn alloy has obviously different grain refinement effects on its solidification microstructures, and the as-cast and hot-extruded alloy with 0.4%Ce has the smallest average grain size and the highest strength. However, the extruded alloys containing 0.4%Nd or 0.4%Y with the elongation of 26.6% and 30%, respectively, show higher plasticity in spite of lower strength as compared with the alloy containing 0.4%Ce.
基金Supported by National Natural Science Foundation of China(No.51178308 and No.51278335)
文摘The influence of the change of structure plane size on seismic response was studied for a soil-structure interaction system.Based on the finite element method,a soil-structure interaction calculation model was established to analyze the seismic response by changing the structure plane size and choosing different earthquake waves for different soil fields.The results show that when the natural periods of vibration for different structure plane sizes are close,under the same earthquake wave,the total displacement on the top layer of the structure and the foundation rotation displacement decrease with the increase of structure plane size,and the proportion of superstructure elastic selfdeformation displacement to the total displacement increases with the increase of structure plane size.While for different types of sites and seismic waves,under the horizontal and vertical seismic waves,the seismic responses of different plane sizes have a similar change rule.
文摘This paper presents finite element results of ceramic masonry prisms and walls under concentric compression. Four different hole geometries of ceramic units were studied (called Types A, B, C and D). The A-type unit had two rectangular hollows, B-type and C-type units have two rounded hollows and different net areas, mad the D-type unit had two rectangular hollows and a double central web. This study analyzed units, prisms and structural walls joined by bedding mortar. The objective was to verify the stress distribution in units and mortars. The results showed that the distribution of compressive stress along the length and width of those units was uniform, but lateral tensile stress along the length was distinct for different geometries. In addition, this study observed that hollow shapes have an important influence in stress distribution. The D-type unit was the one that showed more uniform tension distribution, without peaks of stress concentration. This indicates that a D-type unit is the most efficient unit for use in masonry structures.
文摘In this study fat-tail weight was estimated by external fat-tail dimensions. External fat-tail dimensions included upper, middle and lower width, length, length of gap, depth, upper and middle circumference recorded on 1,482 head of Lori-Bakhtiari lambs at 6 months. Of these about 311 lambs were slaughtered at the age of six months. Prediction equations were derived for fat-tail weight by multiple regression analyses with two methods. The results showed that the measure of middle circumference fat-tail was as most important measure in estimation of fat-tail weight. The measure of middle circumference fat-tail accounted for 76 percent of variation in fat-tail weight. The regression equations for predicting fat-tail weight using external fat-tail dimensions obtained from stepwise regression procedure can be estimated only with using from the lower width, length, middle circumference fat-tail and body weight with high acc, uracy (0.92). Average of fat-tail weight estimated in the age of six months in lambs was 2.39 kg. The highest regression coefficient of external fat-tail dimensions on fat-tail weight observed for the length of fat-tail (0.095 kg). Results of the present investigation showed that fat-tail weight in live sheep of Lori-Bakhtiari, could be estimated by measuring external fat-tail dimensions.