Architectural plasticity of clonal plants may enhance exploitation of soil moisture heterogeneity by the plants. The plasticity of clonal architecture in response to soil moisture in the stoloniferous herb, Duchesne...Architectural plasticity of clonal plants may enhance exploitation of soil moisture heterogeneity by the plants. The plasticity of clonal architecture in response to soil moisture in the stoloniferous herb, Duchesnea indica Focke, was investigated in an experiment with different soil moisture contents as treatments, i.e. 40%, 60%, 80%, 100% of the maximum moisture content of soil (MMCS). As soil moisture content increased, the spacer length, ramet density, branching intensity and branching angle of D. indica plants changed by quadratic curve. And the optimum habitat for the plants was at 80% of the MMCS. This architectural plasticity in D. indica was simulated through the Dynamic Logistic Model. The imitative effect was statistically satisfactory. Its architectural plasticity observed here may allow the species to show foraging behavior in its habitat where soil moisture is patchily distributed.展开更多
A multi-parameter nonlinear elasto-plastic constitutive model which can fully capture the three typical features of stress-strain response, linearity, plasticity-like stress plateau and densification phases was develo...A multi-parameter nonlinear elasto-plastic constitutive model which can fully capture the three typical features of stress-strain response, linearity, plasticity-like stress plateau and densification phases was developed. The functional expression of each parameter was determined using uniaxial compression tests for aluminum alloy foams. The parameters of the model can be systematically varied to describe the effect of relative density which may be responsible for the changes in yield stress and hardening-like or softening-like behavior at various strain rates. A comparison between model predictions and experimental results of the aluminum alloy foams was provided to validate the model. It was proved to be useful in the selection of the optimal-density and energy absorption foam for a specific application at impact events.展开更多
In order to study the deformation behavior and evaluate the workability of the dual-phase Mg-9Li-3Al-2Sr alloy, isothermal hot compression tests were conducted using the Gleeble-3500 thermal-mechanical simulator, in r...In order to study the deformation behavior and evaluate the workability of the dual-phase Mg-9Li-3Al-2Sr alloy, isothermal hot compression tests were conducted using the Gleeble-3500 thermal-mechanical simulator, in ranges of elevated temperatures (423-573 K) and strain rates (0.001-1 s^-1). Plastic instability is evident during the deformation which is in the form of serrated flow; serrated yielding is attributed to the locking of mobile dislocations by the Mg and Li atoms which diffuse during the deformation. The relationships between flow stress, strain rate and deformation temperature were analyzed and the deformation activation energy and some basic material factors at different strains were calculated using the Arrhenius equation. The effects of temperature and strain rate on deformation behavior were represented using the Zener–Hollomon parameter in an exponent-type equation. To verify the validity of the constitutive model, the predicted values and experimental flow curves under different deformation conditions were compared, the correlation coefficient (0.9970) and average absolute relative error (AARE=4.41%) were calculated. The results indicate that the constitutive model can be used to accurately predict the flow behavior of dual-phase Mg-9Li-3Al-2Sr alloy during high temperature deformation.展开更多
In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six (x=0-0.2) electrode alloys were prep...In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six (x=0-0.2) electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of (La, Mg)2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in (La, Mg)2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.展开更多
The series-wound dashpot of the Burgers model is modified by introducing the strain hardening parameter, and the new model is considered as a combination of the modified dashpot and the Van Der Poel model. The cyclica...The series-wound dashpot of the Burgers model is modified by introducing the strain hardening parameter, and the new model is considered as a combination of the modified dashpot and the Van Der Poel model. The cyclical pulse load consisting of a haversine load time and a rest period is adopted to simulate the actual vehicle load, and the permanent strain model under the repeated load is derived from the rheological and viscoelastic theories. Subsequently, the model is validated by the results of uniaxial repeated load permanent deformation tests of three asphalt mixtures. It is indicated that the proportion of residual viscoelastic strain to permanent strain decreases gradually with the load cycles, and only accounts for 2% to 3% during most of the loading period. If the rest period is long, the residual viscoelastic strain is little. The rest period of the actual vehicle load may be long enough, so the residual viscoelasticity can be ignored and the simplified model can be obtained. The proposed model can well describe the permanent deformation of asphalt mixtures under repeated load.展开更多
A polycrystal plasticity model was developed to analyze the room-temperature deformation behaviors of Mg-3A1-1Zn alloy(AZ31).The uniaxial tension and compression tests at room temperature were conducted using cast a...A polycrystal plasticity model was developed to analyze the room-temperature deformation behaviors of Mg-3A1-1Zn alloy(AZ31).The uniaxial tension and compression tests at room temperature were conducted using cast and extruded AZ31 rods with different textures and combined with the proposed model to reveal the deformation mechanisms.It is shown that,different flow curves of two specimens under tension and compression tests can be simulated by this model.The flow curves of AZ31 extrusions exhibit different shapes for tension and compression due to different activities of tensile twinning and pyramidalc+a slip.The metallographic and TEM observations showed the equal twinning activities at the initial stage in tension and compression tests and the occurrence of pyramidalc+a slip in compression of as-cast Mg-3A1-1Zn alloy with increasing the strain,which is consistent with the simulated results by the proposed model.展开更多
Remarkable achievements have been made in China's agricultural development since the late 1970s. Nevertheless, deep-rooted problems are arising from inefficient farming practices. From mid- and long-term perspectives...Remarkable achievements have been made in China's agricultural development since the late 1970s. Nevertheless, deep-rooted problems are arising from inefficient farming practices. From mid- and long-term perspectives, migration of China's agricultural labor will slow and large-scale operation of farmland will accelerate. Although grain supply and demand have maintained a tight balance, new potentials still exist in improving grain production. Under the pressures of resource and environmental constraints, advancing the green and efficient transition of agriculture will become a new trend in China's agricultural development. In this context, the treatment of agricultural pollution, supply-side structural reform and innovation of agricultural subsidy policy are of strategic significance to the transition and upgrade of China's agriculture.展开更多
The influences of power spinning process parameters on the mechanical properties of spinning parts were analyzed with an SXD100/3-CNC numerical control power spinning machine.The unidirectional tensile tests were carr...The influences of power spinning process parameters on the mechanical properties of spinning parts were analyzed with an SXD100/3-CNC numerical control power spinning machine.The unidirectional tensile tests were carried out.Based on the experimental data,a ternary quadratic regression equation was established by orthogonal experiment.The Ramberg-Osgood constitutive model of tin-bronze connecting rod bushing was obtained.Referred to the constitutive relation of macroscopic incremental,the incremental elastoplastic constitutive relation of spinning parts was deduced based on the Mises yield criterion and kinematic hardening model.The results can be applied to the elastoplastic analysis in finite element numerical simulation.展开更多
The phase structure and electrochemical properties of La1.7+xMg1.3-x(NiCoMn)9.3(x=0-0.4) alloys were investigated. The XRD analysis reveals that the alloys consist of LaNi5 phase and other phases, such as LaMg2Ni...The phase structure and electrochemical properties of La1.7+xMg1.3-x(NiCoMn)9.3(x=0-0.4) alloys were investigated. The XRD analysis reveals that the alloys consist of LaNi5 phase and other phases, such as LaMg2Ni9 phase (PuNi3 structure) and La4MgNi19 phases (Ce5Co19+Pr5Co19 structure, namely A5B19 type). With the increase of the x value, the LaMg2Ni9 phase fades away and La4MgNi19 phases appear, while the abundance of LaNi5 phase firstly increases and then decreases. At the same time, the cell volume of LaNi5 phase and LaMg2Ni9 phase decreases. The electrochemical measurement shows that alloy electrodes could be activated in 4-5 cycles, and with the increase of the x value, the maximum discharge capacity gradually increases from 330.9 mA-h/g (x=0) to 366.8 mA-h/g (x=0.4), but the high-rate dischargeability (HRD) and cyclic stability (S) decrease somewhat (x=0.4, HRD600=82.32%, S100=73.8%). It is found that the HRD is mainly controlled by the electrocatalytic activity on the alloy electrode surface, and the decline of cyclic stability is due to the appearance of A5B19 type phase with larger hydrogen storage capacity, which leads to larger volume expansion and more intercrystalline stress and then easier pulverization during charging/discharging.展开更多
[Objective] The aim was to research macrobenthos community structure and its relations with environmental factors in three reservoirs. [Method] Benthic diversity and water quality of Yuqiao Reservoir, Beidagang Reserv...[Objective] The aim was to research macrobenthos community structure and its relations with environmental factors in three reservoirs. [Method] Benthic diversity and water quality of Yuqiao Reservoir, Beidagang Reservoir and Er- wangzhuang Reservoir were investigated in May, July and September 2011, respec- tively. []Result] Of all the 14 sampling sites, 22 species of macroinvertebrates were collected, totally, which included 6 species of aquatic insects, 7 species of Mollusca, 2 species of Crustacean, 7 species of Oligochaeta. The species of macroinverte- brates during May, July and September in Yuqiao reservoir were 11, 8 and 10, respectively. The dominant species were Chironomus sinicus, and Monopylephorus limosus. The average density and biomass of the macrobenthos were 132.43 ind./m2 and 50.09 g/m2. Yuqiao reservoir was mostly at status of premediate polluted, according to the Margalef index, Shannon index and Pielou index. The species of during May, July and September in Beidagang reservoir were 5 5 and 5, respectively. The dominant species were Chironomus sinicus, Penaeus vannamei. The average density and biomass of the macrobenthos were 218 ind./m2 and 2.70 g/m2. Beidagang reservoir was mostly at status of heavy polluted, accord- ing to the Margalef index, Shannon-wiener index, Pielou index. The species of during May, July and September in Erwangzhuang reservoir were 3, 5 and 5, respectively. The dominant species were Monopylephorus limosus, Chi- ronomus sinicus. The average density and biomass of the macrobenthos were 104 ind/m2 and 0.20 g/m2. Erwangzhuang reservoir was mostly at status of intermediate polluted, according to the Margalef index, Shannon index, Pielou index. The density of zoobenthos in Yuqiao Reservoir was positively significantly correlated with TP (P〉 0.05), negatively correlated with NH4+-N (P〉0.05), positively correlated with COD (P〈 0.01), not significantly correlated with other environment factors (P〉0.05). There was no significant correlation between biomass of zoobenthos and environment factors. The density of zoobenthos in Beidagang Reservoir with NH4+-N was positively signif- icantly correlated (P〈0.05), not significantly correlated with other aquatic environment factors (P〉0.05). There was no significant correlation between biomass of zoobenthos and environment factors. The density of zoobenthos in Erwangzhuang Reser- voir with NO3-N was positively significantly correlated (P〈0.05), not significant cor- related with other aquatic environment factors (F〉0.05). The biomass of zoobenthos in Erwangzhuang Reservoir with NH4+-N was positively significantly correlated (P〈 0.05), not significant correlated with other aquatic environment factors (P〉0.05). [Conclusion] It is indicated that this three reservoirs were all eutrophied and polluted, and the eurephication extent change of water in three reservoirs is as follows: Beidagang reservoir〉Erwangzhuang reservoir〉Yuqiao reservoir.展开更多
Five years' (2000-2004) continuous study has been carried out on small mammals such as rodents in seven different sample plots, at three different altitudes and in six different ecological environment types in the ...Five years' (2000-2004) continuous study has been carried out on small mammals such as rodents in seven different sample plots, at three different altitudes and in six different ecological environment types in the eastern part of the Wuling Mountains, south bank of the Three Gorges of Yangtze River in Hubei. A total of 29 297 rat clamps/times were placed and 2271 small mammals such as rodents were captured, and 26 small mammals were captured by other means. All the small mammals captured belonged to 8 families 19 genera and 24 species, of which rodentia accounted for 70.83% and insectivora 29.17%. Through analysis of the data, the results showed that: 1 ) although the species richness had a trend of increasing along different sample plots as altitude increased from south to north, quite a few species showed a wide habitat range in a vertical distribution ( 15 species were dispersed over three zones and two species over two zones) , indicating a strong adaptability of small mammals such as rOdents at lower altitudes in most areas and comparatively less vertical span of entire mountains; 2) whether in seven different sample plots or six different ecological types, Apodemus agrarius and Rattus norvegicus were dominant species below 1200m, and Anourosorex squamipes, Niviventer confucianus and Apodemus draco were dominant above altitudes of 1300m, however, in quantity they were short of identical regularity, meaning they did not increase as the altitude did, or decrease as the ecological areas changed; 3)the density in winter was obviously greater than that in spring, and the distribution showed an increasing trend along with altitude, but the density in different sample plots was short of identical regularity, showing changes in different seasons and altitude grades had an important impact on small mammals such as rodents; 4) in species diversity and evenness index, there were obvious changes between the seven different sample plots, probably caused by frequent human interference in this area. Comparatively speaking, there was less human interference at high altitudes where vegetation was rich and had a high diversity and evenness index, and the boundary effect and community stability were obvious. Most ecological types have been seriously interfered with due to excessive assart at low altitudes with singular vegetation and low diversity and evenness index and poor community stability, showing an ecosystem with poor anti-reversion. If human interference can be reduced in those communities at high altitudes with low diversity and evenness index, the biological diversity in the communities will gradually recover to similar levels of other ecological areas.展开更多
The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr (mass fraction, %) alloy (GW104 alloy) cast by metal mould casting (MMC) and lost foam casting (LFC) were evaluated, respectively. It is r...The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr (mass fraction, %) alloy (GW104 alloy) cast by metal mould casting (MMC) and lost foam casting (LFC) were evaluated, respectively. It is revealed that different forming modes do not influence the phase composition of as-cast alloy. In the as-cast specimens, the microstructures are similar and composed of α-Mg solid solution, eutectic compound of α-Mg+Mg 24 (Gd, Y) 5 and cuboid-shaped Mg 5 (Gd, Y) phase; whereas the average grain size of the alloy produced by metal mould casting is smaller than that by lost foam casting. The eutectic compound of the alloy is completely dissolved after solution treatment at 525 ℃for 6 h, while the Mg 5 (Gd, Y) phase still exists after solution treatment. After peak-ageing, the lost foam cast alloy exhibits the maximum ultimate tensile strength of 285 MPa, and metal mould cast specimen 325 MPa at room temperature, while the tensile yield strengths of them are comparable. It can be concluded that GW104 alloy cast by lost foam casting possesses similar microstructure and evidently lower mechanical strength compared with metal mould cast alloy, due to slow solidification rate and proneness to form shrinkage porosities during lost foam casting process.展开更多
The mathematical model of the motion of some plane′s flap mechanism is set up by the method of establishing mathematical model of space mechanism. When the input parameter is given, the theoretical output paramet...The mathematical model of the motion of some plane′s flap mechanism is set up by the method of establishing mathematical model of space mechanism. When the input parameter is given, the theoretical output parameter of the flap mechanism is achieved by the model. The wear and tear volume is introduced into the mathematical model, and if the input parameter is the same, the real output parameter of the flap mechanism worn can be obtained. On the basis of this, it is able to achieve the friction and the wear reliability of the flap mechanism.展开更多
The effect of Mn substitution for partial Fe in RFe 11Ti on structure and magnetic properties of compounds was researched. RFe 7Mn 4Ti samples (R=Y,Tb,Dy,Ho,Er) were prepared by means of vacuum arc-melting and s...The effect of Mn substitution for partial Fe in RFe 11Ti on structure and magnetic properties of compounds was researched. RFe 7Mn 4Ti samples (R=Y,Tb,Dy,Ho,Er) were prepared by means of vacuum arc-melting and subsequent vacuum annealing. The structure and magnetic properties of RFe 7Mn 4Ti compounds were investigated by X-ray powder diffraction and magnetic measurements. The following conclusions were obtained: all the RFe tMn 4Ti compounds crystallize in the ThMn 12-type structure. The lattice constants and the unit-cell volume changed with the increase of atomic number for R=Y, Tb, Dy, Ho, and Er. The compensation characters appear for the DyFe 7Mn 4Ti and HoFe 7Mn 4Ti compounds, and the compensation temperatures were about 123 K and 90 K, respectively. The Curie temperature, the saturation magnetization, and saturation moment of RFe 7Mn 4Ti compounds were given.展开更多
A mechanics system consisting of three mass points on sphere S 2 is considered. The configuration space of the system is a fibre bundle over S 2 . It is proved that first Chern class of the bundle is -2 c 1...A mechanics system consisting of three mass points on sphere S 2 is considered. The configuration space of the system is a fibre bundle over S 2 . It is proved that first Chern class of the bundle is -2 c 1(γ) where γ is the canonical line bundle over the complex projective space CP 1=S 2 , which shows the bundle is non trivial. The information about the first Chern class makes the cohomology groups and homotopy groups of the configuration space worked out. In addition the effects of these topolo gical properties of the configuration space on the behavior in large scale of the system, as the number of equilibrium positions, periodic orbits and reduced phase space, are discussed.展开更多
The analogy between the wave equation of liquid and the Navier equations of structural elasticity is examined in detail. By introducing appropriate parameters, the structural counterpart of the liquid sloshing model c...The analogy between the wave equation of liquid and the Navier equations of structural elasticity is examined in detail. By introducing appropriate parameters, the structural counterpart of the liquid sloshing model can be easily built. Therefore, the dynamic analysis of liquid sloshing can be reduced to that of structural elasticity, and the existing FEM structural analysis computer programs can be applied to liquid sloshing analysis without any modification. The present method also reveals the internal relationship between liquid sloshing and structural vibration. The effectiveness and reliability of the method is illustrated by the numerical example.展开更多
文摘Architectural plasticity of clonal plants may enhance exploitation of soil moisture heterogeneity by the plants. The plasticity of clonal architecture in response to soil moisture in the stoloniferous herb, Duchesnea indica Focke, was investigated in an experiment with different soil moisture contents as treatments, i.e. 40%, 60%, 80%, 100% of the maximum moisture content of soil (MMCS). As soil moisture content increased, the spacer length, ramet density, branching intensity and branching angle of D. indica plants changed by quadratic curve. And the optimum habitat for the plants was at 80% of the MMCS. This architectural plasticity in D. indica was simulated through the Dynamic Logistic Model. The imitative effect was statistically satisfactory. Its architectural plasticity observed here may allow the species to show foraging behavior in its habitat where soil moisture is patchily distributed.
基金Projects (90716005, 10802055, 10972153) supported by the National Natural Science Foundation of ChinaProject (2007021005) supported by the Natural Science Foundation of Shanxi Province, China+2 种基金Project supported by the Postdoctoral Science Foundation of ChinaProject supported by the Homecomings Foundation, ChinaProject supported by the Top Young Academic Leaders of Higher Learning Institutions of Shanxi, China
文摘A multi-parameter nonlinear elasto-plastic constitutive model which can fully capture the three typical features of stress-strain response, linearity, plasticity-like stress plateau and densification phases was developed. The functional expression of each parameter was determined using uniaxial compression tests for aluminum alloy foams. The parameters of the model can be systematically varied to describe the effect of relative density which may be responsible for the changes in yield stress and hardening-like or softening-like behavior at various strain rates. A comparison between model predictions and experimental results of the aluminum alloy foams was provided to validate the model. It was proved to be useful in the selection of the optimal-density and energy absorption foam for a specific application at impact events.
基金Projects(CDJZR14130007106112015CDJXY130011)supported by Fundamental Research Funds for the Central Universities,China
文摘In order to study the deformation behavior and evaluate the workability of the dual-phase Mg-9Li-3Al-2Sr alloy, isothermal hot compression tests were conducted using the Gleeble-3500 thermal-mechanical simulator, in ranges of elevated temperatures (423-573 K) and strain rates (0.001-1 s^-1). Plastic instability is evident during the deformation which is in the form of serrated flow; serrated yielding is attributed to the locking of mobile dislocations by the Mg and Li atoms which diffuse during the deformation. The relationships between flow stress, strain rate and deformation temperature were analyzed and the deformation activation energy and some basic material factors at different strains were calculated using the Arrhenius equation. The effects of temperature and strain rate on deformation behavior were represented using the Zener–Hollomon parameter in an exponent-type equation. To verify the validity of the constitutive model, the predicted values and experimental flow curves under different deformation conditions were compared, the correlation coefficient (0.9970) and average absolute relative error (AARE=4.41%) were calculated. The results indicate that the constitutive model can be used to accurately predict the flow behavior of dual-phase Mg-9Li-3Al-2Sr alloy during high temperature deformation.
基金Projects(50961009,51161015)supported by the National Natural Science Foundation of ChinaProject(2011AA03A408)supported by the High-tech Research and Development Program of ChinaProjects(2011ZD10,2010ZD05)supported by the Natural Science Foundation of Inner Mongolia,China
文摘In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six (x=0-0.2) electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of (La, Mg)2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in (La, Mg)2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.
基金The National Natural Science Foundation of China(No50608006)Program for New Century Excellent Talents in University(NoNCET-07-0120)
文摘The series-wound dashpot of the Burgers model is modified by introducing the strain hardening parameter, and the new model is considered as a combination of the modified dashpot and the Van Der Poel model. The cyclical pulse load consisting of a haversine load time and a rest period is adopted to simulate the actual vehicle load, and the permanent strain model under the repeated load is derived from the rheological and viscoelastic theories. Subsequently, the model is validated by the results of uniaxial repeated load permanent deformation tests of three asphalt mixtures. It is indicated that the proportion of residual viscoelastic strain to permanent strain decreases gradually with the load cycles, and only accounts for 2% to 3% during most of the loading period. If the rest period is long, the residual viscoelastic strain is little. The rest period of the actual vehicle load may be long enough, so the residual viscoelasticity can be ignored and the simplified model can be obtained. The proposed model can well describe the permanent deformation of asphalt mixtures under repeated load.
基金Project(51201092)supported by the National Natural Science Foundation of China
文摘A polycrystal plasticity model was developed to analyze the room-temperature deformation behaviors of Mg-3A1-1Zn alloy(AZ31).The uniaxial tension and compression tests at room temperature were conducted using cast and extruded AZ31 rods with different textures and combined with the proposed model to reveal the deformation mechanisms.It is shown that,different flow curves of two specimens under tension and compression tests can be simulated by this model.The flow curves of AZ31 extrusions exhibit different shapes for tension and compression due to different activities of tensile twinning and pyramidalc+a slip.The metallographic and TEM observations showed the equal twinning activities at the initial stage in tension and compression tests and the occurrence of pyramidalc+a slip in compression of as-cast Mg-3A1-1Zn alloy with increasing the strain,which is consistent with the simulated results by the proposed model.
文摘Remarkable achievements have been made in China's agricultural development since the late 1970s. Nevertheless, deep-rooted problems are arising from inefficient farming practices. From mid- and long-term perspectives, migration of China's agricultural labor will slow and large-scale operation of farmland will accelerate. Although grain supply and demand have maintained a tight balance, new potentials still exist in improving grain production. Under the pressures of resource and environmental constraints, advancing the green and efficient transition of agriculture will become a new trend in China's agricultural development. In this context, the treatment of agricultural pollution, supply-side structural reform and innovation of agricultural subsidy policy are of strategic significance to the transition and upgrade of China's agriculture.
基金Project(2012011023-2)supported by the Natural Science Foundation of Shanxi Province,China
文摘The influences of power spinning process parameters on the mechanical properties of spinning parts were analyzed with an SXD100/3-CNC numerical control power spinning machine.The unidirectional tensile tests were carried out.Based on the experimental data,a ternary quadratic regression equation was established by orthogonal experiment.The Ramberg-Osgood constitutive model of tin-bronze connecting rod bushing was obtained.Referred to the constitutive relation of macroscopic incremental,the incremental elastoplastic constitutive relation of spinning parts was deduced based on the Mises yield criterion and kinematic hardening model.The results can be applied to the elastoplastic analysis in finite element numerical simulation.
基金Project (2008CL068L) supported by the Natural Science Research Project of Higher Education of Jiangsu Province, ChinaProject (50901036) supported by the National Natural Science Foundation of China
文摘The phase structure and electrochemical properties of La1.7+xMg1.3-x(NiCoMn)9.3(x=0-0.4) alloys were investigated. The XRD analysis reveals that the alloys consist of LaNi5 phase and other phases, such as LaMg2Ni9 phase (PuNi3 structure) and La4MgNi19 phases (Ce5Co19+Pr5Co19 structure, namely A5B19 type). With the increase of the x value, the LaMg2Ni9 phase fades away and La4MgNi19 phases appear, while the abundance of LaNi5 phase firstly increases and then decreases. At the same time, the cell volume of LaNi5 phase and LaMg2Ni9 phase decreases. The electrochemical measurement shows that alloy electrodes could be activated in 4-5 cycles, and with the increase of the x value, the maximum discharge capacity gradually increases from 330.9 mA-h/g (x=0) to 366.8 mA-h/g (x=0.4), but the high-rate dischargeability (HRD) and cyclic stability (S) decrease somewhat (x=0.4, HRD600=82.32%, S100=73.8%). It is found that the HRD is mainly controlled by the electrocatalytic activity on the alloy electrode surface, and the decline of cyclic stability is due to the appearance of A5B19 type phase with larger hydrogen storage capacity, which leads to larger volume expansion and more intercrystalline stress and then easier pulverization during charging/discharging.
基金Supported by Tianjin Aquatic Species Diveristy Surveying,Monitoring and Evaluation Proejct~~
文摘[Objective] The aim was to research macrobenthos community structure and its relations with environmental factors in three reservoirs. [Method] Benthic diversity and water quality of Yuqiao Reservoir, Beidagang Reservoir and Er- wangzhuang Reservoir were investigated in May, July and September 2011, respec- tively. []Result] Of all the 14 sampling sites, 22 species of macroinvertebrates were collected, totally, which included 6 species of aquatic insects, 7 species of Mollusca, 2 species of Crustacean, 7 species of Oligochaeta. The species of macroinverte- brates during May, July and September in Yuqiao reservoir were 11, 8 and 10, respectively. The dominant species were Chironomus sinicus, and Monopylephorus limosus. The average density and biomass of the macrobenthos were 132.43 ind./m2 and 50.09 g/m2. Yuqiao reservoir was mostly at status of premediate polluted, according to the Margalef index, Shannon index and Pielou index. The species of during May, July and September in Beidagang reservoir were 5 5 and 5, respectively. The dominant species were Chironomus sinicus, Penaeus vannamei. The average density and biomass of the macrobenthos were 218 ind./m2 and 2.70 g/m2. Beidagang reservoir was mostly at status of heavy polluted, accord- ing to the Margalef index, Shannon-wiener index, Pielou index. The species of during May, July and September in Erwangzhuang reservoir were 3, 5 and 5, respectively. The dominant species were Monopylephorus limosus, Chi- ronomus sinicus. The average density and biomass of the macrobenthos were 104 ind/m2 and 0.20 g/m2. Erwangzhuang reservoir was mostly at status of intermediate polluted, according to the Margalef index, Shannon index, Pielou index. The density of zoobenthos in Yuqiao Reservoir was positively significantly correlated with TP (P〉 0.05), negatively correlated with NH4+-N (P〉0.05), positively correlated with COD (P〈 0.01), not significantly correlated with other environment factors (P〉0.05). There was no significant correlation between biomass of zoobenthos and environment factors. The density of zoobenthos in Beidagang Reservoir with NH4+-N was positively signif- icantly correlated (P〈0.05), not significantly correlated with other aquatic environment factors (P〉0.05). There was no significant correlation between biomass of zoobenthos and environment factors. The density of zoobenthos in Erwangzhuang Reser- voir with NO3-N was positively significantly correlated (P〈0.05), not significant cor- related with other aquatic environment factors (F〉0.05). The biomass of zoobenthos in Erwangzhuang Reservoir with NH4+-N was positively significantly correlated (P〈 0.05), not significant correlated with other aquatic environment factors (P〉0.05). [Conclusion] It is indicated that this three reservoirs were all eutrophied and polluted, and the eurephication extent change of water in three reservoirs is as follows: Beidagang reservoir〉Erwangzhuang reservoir〉Yuqiao reservoir.
基金National Natural Science Foundation of China(30070679)the Natural Science Foundation of Hubei Province(2004ABA138)+1 种基金the Key Technology R&D Programme Foundation of Hubei Province(2002AA301C43)the Hubei Health Bureau Research Programme Foundation(NX200427)
文摘Five years' (2000-2004) continuous study has been carried out on small mammals such as rodents in seven different sample plots, at three different altitudes and in six different ecological environment types in the eastern part of the Wuling Mountains, south bank of the Three Gorges of Yangtze River in Hubei. A total of 29 297 rat clamps/times were placed and 2271 small mammals such as rodents were captured, and 26 small mammals were captured by other means. All the small mammals captured belonged to 8 families 19 genera and 24 species, of which rodentia accounted for 70.83% and insectivora 29.17%. Through analysis of the data, the results showed that: 1 ) although the species richness had a trend of increasing along different sample plots as altitude increased from south to north, quite a few species showed a wide habitat range in a vertical distribution ( 15 species were dispersed over three zones and two species over two zones) , indicating a strong adaptability of small mammals such as rOdents at lower altitudes in most areas and comparatively less vertical span of entire mountains; 2) whether in seven different sample plots or six different ecological types, Apodemus agrarius and Rattus norvegicus were dominant species below 1200m, and Anourosorex squamipes, Niviventer confucianus and Apodemus draco were dominant above altitudes of 1300m, however, in quantity they were short of identical regularity, meaning they did not increase as the altitude did, or decrease as the ecological areas changed; 3)the density in winter was obviously greater than that in spring, and the distribution showed an increasing trend along with altitude, but the density in different sample plots was short of identical regularity, showing changes in different seasons and altitude grades had an important impact on small mammals such as rodents; 4) in species diversity and evenness index, there were obvious changes between the seven different sample plots, probably caused by frequent human interference in this area. Comparatively speaking, there was less human interference at high altitudes where vegetation was rich and had a high diversity and evenness index, and the boundary effect and community stability were obvious. Most ecological types have been seriously interfered with due to excessive assart at low altitudes with singular vegetation and low diversity and evenness index and poor community stability, showing an ecosystem with poor anti-reversion. If human interference can be reduced in those communities at high altitudes with low diversity and evenness index, the biological diversity in the communities will gradually recover to similar levels of other ecological areas.
基金Project(2007CB613704)supported by the National Basic Research Program of China
文摘The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr (mass fraction, %) alloy (GW104 alloy) cast by metal mould casting (MMC) and lost foam casting (LFC) were evaluated, respectively. It is revealed that different forming modes do not influence the phase composition of as-cast alloy. In the as-cast specimens, the microstructures are similar and composed of α-Mg solid solution, eutectic compound of α-Mg+Mg 24 (Gd, Y) 5 and cuboid-shaped Mg 5 (Gd, Y) phase; whereas the average grain size of the alloy produced by metal mould casting is smaller than that by lost foam casting. The eutectic compound of the alloy is completely dissolved after solution treatment at 525 ℃for 6 h, while the Mg 5 (Gd, Y) phase still exists after solution treatment. After peak-ageing, the lost foam cast alloy exhibits the maximum ultimate tensile strength of 285 MPa, and metal mould cast specimen 325 MPa at room temperature, while the tensile yield strengths of them are comparable. It can be concluded that GW104 alloy cast by lost foam casting possesses similar microstructure and evidently lower mechanical strength compared with metal mould cast alloy, due to slow solidification rate and proneness to form shrinkage porosities during lost foam casting process.
文摘The mathematical model of the motion of some plane′s flap mechanism is set up by the method of establishing mathematical model of space mechanism. When the input parameter is given, the theoretical output parameter of the flap mechanism is achieved by the model. The wear and tear volume is introduced into the mathematical model, and if the input parameter is the same, the real output parameter of the flap mechanism worn can be obtained. On the basis of this, it is able to achieve the friction and the wear reliability of the flap mechanism.
文摘The effect of Mn substitution for partial Fe in RFe 11Ti on structure and magnetic properties of compounds was researched. RFe 7Mn 4Ti samples (R=Y,Tb,Dy,Ho,Er) were prepared by means of vacuum arc-melting and subsequent vacuum annealing. The structure and magnetic properties of RFe 7Mn 4Ti compounds were investigated by X-ray powder diffraction and magnetic measurements. The following conclusions were obtained: all the RFe tMn 4Ti compounds crystallize in the ThMn 12-type structure. The lattice constants and the unit-cell volume changed with the increase of atomic number for R=Y, Tb, Dy, Ho, and Er. The compensation characters appear for the DyFe 7Mn 4Ti and HoFe 7Mn 4Ti compounds, and the compensation temperatures were about 123 K and 90 K, respectively. The Curie temperature, the saturation magnetization, and saturation moment of RFe 7Mn 4Ti compounds were given.
文摘A mechanics system consisting of three mass points on sphere S 2 is considered. The configuration space of the system is a fibre bundle over S 2 . It is proved that first Chern class of the bundle is -2 c 1(γ) where γ is the canonical line bundle over the complex projective space CP 1=S 2 , which shows the bundle is non trivial. The information about the first Chern class makes the cohomology groups and homotopy groups of the configuration space worked out. In addition the effects of these topolo gical properties of the configuration space on the behavior in large scale of the system, as the number of equilibrium positions, periodic orbits and reduced phase space, are discussed.
文摘The analogy between the wave equation of liquid and the Navier equations of structural elasticity is examined in detail. By introducing appropriate parameters, the structural counterpart of the liquid sloshing model can be easily built. Therefore, the dynamic analysis of liquid sloshing can be reduced to that of structural elasticity, and the existing FEM structural analysis computer programs can be applied to liquid sloshing analysis without any modification. The present method also reveals the internal relationship between liquid sloshing and structural vibration. The effectiveness and reliability of the method is illustrated by the numerical example.