In this paper,we introduce the censored composite conditional quantile coefficient(cC-CQC)to rank the relative importance of each predictor in high-dimensional censored regression.The cCCQC takes advantage of all usef...In this paper,we introduce the censored composite conditional quantile coefficient(cC-CQC)to rank the relative importance of each predictor in high-dimensional censored regression.The cCCQC takes advantage of all useful information across quantiles and can detect nonlinear effects including interactions and heterogeneity,effectively.Furthermore,the proposed screening method based on cCCQC is robust to the existence of outliers and enjoys the sure screening property.Simulation results demonstrate that the proposed method performs competitively on survival datasets of high-dimensional predictors,particularly when the variables are highly correlated.展开更多
Zn-Al-Cu-TiB2（ZA27-TiB2） in situ composites were fabricated via reactions between molten aluminum and mixed halide salts（K2TiF6 and KBF4） at temperature of 875 °C. The microstructure, mechanical properties an...Zn-Al-Cu-TiB2（ZA27-TiB2） in situ composites were fabricated via reactions between molten aluminum and mixed halide salts（K2TiF6 and KBF4） at temperature of 875 °C. The microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that fine and clean TiB2 particles distribute uniformly through the matrix. The mechanical properties of the composites increase with the increase in TiB2 content. As TiB2 content increases to 5%（mass fraction）, an improvement of HB 18 in hardness and 49 MPa in ultimate tensile strength（UTS） is achieved. The overall results reveal that the composites possess low friction coefficients and the wear rate is reduced from 5.9×10-3 to 1.3×10-3 mm3/m after incorporating 5% TiB2. Friction coefficient and worn surface analysis indicate that there is a change in the wear mechanism in the initial stage of wear test after introducing in situ TiB2 particles into the matrix.展开更多
SiC particles reinforced AZ91 Mg matrix composites （SiCp/AZ91） with SiC volume fractions of 5%, 10% and 15% were fabricated by stir casting. After T4 treatment, these composites were extruded at 350 °C with an ...SiC particles reinforced AZ91 Mg matrix composites （SiCp/AZ91） with SiC volume fractions of 5%, 10% and 15% were fabricated by stir casting. After T4 treatment, these composites were extruded at 350 °C with an extrusion ratio of 12：1. In the as-cast composite, particles segregated at a microscopic scale within the intergranular regions. Hot extrusion almost eliminated this particle aggregation and improved the particle distribution of the composites. In addition, extrusion refined the grains of matrix. The results show that hot extrusion significantly improves the mechanical properties of the composites. In the as-extruded composite, with the increase of SiCp contents, the grain size of the extruded composites decreases, the strength and elastic modulus increase but the elongation decreases.展开更多
The thermophysical properties of the SiC /Al composites mixed with diamond（SiC-Dia/Al） were studied through theoretical calculation and experiments. The thermal conductivity and the thermal expansion coefficient of ...The thermophysical properties of the SiC /Al composites mixed with diamond（SiC-Dia/Al） were studied through theoretical calculation and experiments. The thermal conductivity and the thermal expansion coefficient of the SiC-Dia/Al were calculated by differential effective medium（DEM） theoretical model and extended Turner model, respectively. The microstructure of the SiC-Dia/Al shows that the combination between SiC particles and Al is close, while that between diamond particles and Al is not close. The experimental results of the thermophysical properties of the SiC-Dia/Al are consistent with the calculated ones. The calculation results show that when the volume ratio of the diamond particles to the SiC particles is 3：7, the thermal conductivity and the thermal expansion coefficient can be improved by 39% and 30% compared to SiC/Al composites, respectively. In other words, by adding a small amount of diamond particles, the thermophysical properties of the composites can be improved effectively, while the cost increases little.展开更多
Al-5%Si-AI2O3 composites were prepared by powder metallurgy and in-situ reactive synthesis technology. Friction and wear properties of Al-5%Si-Al2O3 composites were studied using an M-2000 wear tester. The effects of ...Al-5%Si-AI2O3 composites were prepared by powder metallurgy and in-situ reactive synthesis technology. Friction and wear properties of Al-5%Si-Al2O3 composites were studied using an M-2000 wear tester. The effects of load, sliding speed and long time continuous friction on friction and wear properties of Al-5%Si-Al2O3 composites were investigated, respectively. Wear surface and wear mechanism of Al-5%Si-Al2O3 composites were studied by Quanta 200 FE-SEM. Results showed that with load increasing, wear loss and coefficient of friction increased. With sliding speed going up, the surface temperature of sample made the rate of the producing of oxidation layer increase, while wear loss and coefficient of friction decreased. With the sliding distance increasing, coefficient of friction increased because the adhesive wear mechanism occurred in the initial stage, then formation and destruction of the oxide layer on the surface of the sample tended to a dynamic equilibrium, the surface state of the sample was relatively stable and so did the coefficient of friction. The experiment shows that the main wear mechanism of Al-5%Si-Al2O3 composites includes abrasive wear, adhesive wear and oxidation wear.展开更多
A rectangular finite element for laminated plate with bonded and/or embedded piezoelectric sensors and actuators is developed based on the variational principle and the first order shear deformation theory. The elemen...A rectangular finite element for laminated plate with bonded and/or embedded piezoelectric sensors and actuators is developed based on the variational principle and the first order shear deformation theory. The element has four-node, 20-degrees-of-freedom with one potential degree of freedom for each piezoelectric layer to represent the piezoelectric behavior. The higher order derivation of deflection is obtained by using the normal rotation expressions to take the effects of transverse shear deformation into considerations. The finite element can accurately simulate the deformation of both thin and moderately thick plates. A Fortran program is written and a number of benchmark tests are exercised to verify its effectiveness. Results are compared well with the existing data. The unbalanced composite with piezoelectric layers is then analyzed by using the model. Results show that the changes of the ratio between the thickness of positive angle layers and the negative angle layers have an effect on the deformation of the structure under the same electric loading.展开更多
The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets（GNSs） are compared with those of copper-graphite（Gr） composites fabricated by t...The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets（GNSs） are compared with those of copper-graphite（Gr） composites fabricated by the same method.The results show that the Cu-GNSs composites exhibit higher relative density,microhardness and bending strength compared with Cu-Gr composites with the same volume fraction of GNSs and Gr.Moreover,the friction coefficients and wear rates reduce significantly by the addition of GNSs,whereas the limited impact on reducing friction and wear is found on graphite.The abrasive and delamination wear are the dominant wear mechanisms of the composites.It is believed that the superior mechanical and tribological performances of Cu-GNSs composites are attributed to the unique strengthening effect as well as the higher lubricating efficiency of graphene nanosheets compared with those of graphite,which demonstrates that GNS is an ideal filler for copper matrix composites,acting as not only an impactful lubricant but also a favorable reinforcement.展开更多
基金Outstanding Youth Foundation of Hunan Provincial Department of Education(Grant No.22B0911)。
文摘In this paper,we introduce the censored composite conditional quantile coefficient(cC-CQC)to rank the relative importance of each predictor in high-dimensional censored regression.The cCCQC takes advantage of all useful information across quantiles and can detect nonlinear effects including interactions and heterogeneity,effectively.Furthermore,the proposed screening method based on cCCQC is robust to the existence of outliers and enjoys the sure screening property.Simulation results demonstrate that the proposed method performs competitively on survival datasets of high-dimensional predictors,particularly when the variables are highly correlated.
基金Projects(51071035,51274054,51375070)supported by the National Natural Science Foundation of ChinaProject(313011)supported by the Key Project of Ministry of Education of China
文摘Zn-Al-Cu-TiB2（ZA27-TiB2） in situ composites were fabricated via reactions between molten aluminum and mixed halide salts（K2TiF6 and KBF4） at temperature of 875 °C. The microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that fine and clean TiB2 particles distribute uniformly through the matrix. The mechanical properties of the composites increase with the increase in TiB2 content. As TiB2 content increases to 5%（mass fraction）, an improvement of HB 18 in hardness and 49 MPa in ultimate tensile strength（UTS） is achieved. The overall results reveal that the composites possess low friction coefficients and the wear rate is reduced from 5.9×10-3 to 1.3×10-3 mm3/m after incorporating 5% TiB2. Friction coefficient and worn surface analysis indicate that there is a change in the wear mechanism in the initial stage of wear test after introducing in situ TiB2 particles into the matrix.
基金Projects (51101043, 50801017, 51001036) supported by the National Natural Science Foundation of ChinaProject (HIT.NSRIF.201130) supported by the Fundamental Research Funds for the Central Universities, China
文摘SiC particles reinforced AZ91 Mg matrix composites （SiCp/AZ91） with SiC volume fractions of 5%, 10% and 15% were fabricated by stir casting. After T4 treatment, these composites were extruded at 350 °C with an extrusion ratio of 12：1. In the as-cast composite, particles segregated at a microscopic scale within the intergranular regions. Hot extrusion almost eliminated this particle aggregation and improved the particle distribution of the composites. In addition, extrusion refined the grains of matrix. The results show that hot extrusion significantly improves the mechanical properties of the composites. In the as-extruded composite, with the increase of SiCp contents, the grain size of the extruded composites decreases, the strength and elastic modulus increase but the elongation decreases.
文摘The thermophysical properties of the SiC /Al composites mixed with diamond（SiC-Dia/Al） were studied through theoretical calculation and experiments. The thermal conductivity and the thermal expansion coefficient of the SiC-Dia/Al were calculated by differential effective medium（DEM） theoretical model and extended Turner model, respectively. The microstructure of the SiC-Dia/Al shows that the combination between SiC particles and Al is close, while that between diamond particles and Al is not close. The experimental results of the thermophysical properties of the SiC-Dia/Al are consistent with the calculated ones. The calculation results show that when the volume ratio of the diamond particles to the SiC particles is 3：7, the thermal conductivity and the thermal expansion coefficient can be improved by 39% and 30% compared to SiC/Al composites, respectively. In other words, by adding a small amount of diamond particles, the thermophysical properties of the composites can be improved effectively, while the cost increases little.
基金Project(51201143)supported by the National Natural Science Foundation of ChinaProject(SWJTU12BR004)supported by the Fundamental Research Funds for the Central Universities,China
文摘Al-5%Si-AI2O3 composites were prepared by powder metallurgy and in-situ reactive synthesis technology. Friction and wear properties of Al-5%Si-Al2O3 composites were studied using an M-2000 wear tester. The effects of load, sliding speed and long time continuous friction on friction and wear properties of Al-5%Si-Al2O3 composites were investigated, respectively. Wear surface and wear mechanism of Al-5%Si-Al2O3 composites were studied by Quanta 200 FE-SEM. Results showed that with load increasing, wear loss and coefficient of friction increased. With sliding speed going up, the surface temperature of sample made the rate of the producing of oxidation layer increase, while wear loss and coefficient of friction decreased. With the sliding distance increasing, coefficient of friction increased because the adhesive wear mechanism occurred in the initial stage, then formation and destruction of the oxide layer on the surface of the sample tended to a dynamic equilibrium, the surface state of the sample was relatively stable and so did the coefficient of friction. The experiment shows that the main wear mechanism of Al-5%Si-Al2O3 composites includes abrasive wear, adhesive wear and oxidation wear.
文摘A rectangular finite element for laminated plate with bonded and/or embedded piezoelectric sensors and actuators is developed based on the variational principle and the first order shear deformation theory. The element has four-node, 20-degrees-of-freedom with one potential degree of freedom for each piezoelectric layer to represent the piezoelectric behavior. The higher order derivation of deflection is obtained by using the normal rotation expressions to take the effects of transverse shear deformation into considerations. The finite element can accurately simulate the deformation of both thin and moderately thick plates. A Fortran program is written and a number of benchmark tests are exercised to verify its effectiveness. Results are compared well with the existing data. The unbalanced composite with piezoelectric layers is then analyzed by using the model. Results show that the changes of the ratio between the thickness of positive angle layers and the negative angle layers have an effect on the deformation of the structure under the same electric loading.
文摘The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets（GNSs） are compared with those of copper-graphite（Gr） composites fabricated by the same method.The results show that the Cu-GNSs composites exhibit higher relative density,microhardness and bending strength compared with Cu-Gr composites with the same volume fraction of GNSs and Gr.Moreover,the friction coefficients and wear rates reduce significantly by the addition of GNSs,whereas the limited impact on reducing friction and wear is found on graphite.The abrasive and delamination wear are the dominant wear mechanisms of the composites.It is believed that the superior mechanical and tribological performances of Cu-GNSs composites are attributed to the unique strengthening effect as well as the higher lubricating efficiency of graphene nanosheets compared with those of graphite,which demonstrates that GNS is an ideal filler for copper matrix composites,acting as not only an impactful lubricant but also a favorable reinforcement.
