Carbon nanotube-reinforced 2009Al （CNT/2009Al） composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing （FSP） and FSP-rolling, respectively. The CNT/2009A1 composites wit...Carbon nanotube-reinforced 2009Al （CNT/2009Al） composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing （FSP） and FSP-rolling, respectively. The CNT/2009A1 composites with aligned CNTs showed much better tensile properties at room temperature and elevated temperature compared with those with the randomly oriented CNTs, which is mainly attributed to larger equivalent aspect ratio of the CNTs and avoidance of preferential fracture problems. However, much finer grain size was not beneficial to obtaining high strength above 473 K. The aligned CNTs resulted in tensile anisotropy, with the best tensile properties being achieved along the direction of CNT aligning. As the off-axis angle increased, the tensile properties were reduced due to the weakening of the load transfer ability. Furthermore, aligned CNTs resulted in much lower coefficient of thermal expansion compared with randomly oriented CNTs.展开更多
This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the prop...This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the propeller and intermediate shafts, under the influence of propeller-induced static and variable hydrodynamic excitations are also studied. The transfer matrix method related to the constant coefficients of differential equation solutions is used. The advantage of the latter as compared with a well-known method of transfer matrix associated with state vector is the possibility of reducing the number of multiplied matrices when adjacent shaft segments have the same material properties and diameters. The results show that there is no risk of buckling and confirm that the strength of the shaft line depends on the value of the static tangential stresses which is the most important component of the stress tensor.展开更多
The global gravitational model can be expressed as a series of spherical harmonic coefficients computed up to a certain degree and order.The main ordering characteristic can depend on the degree,order,or type of coeff...The global gravitational model can be expressed as a series of spherical harmonic coefficients computed up to a certain degree and order.The main ordering characteristic can depend on the degree,order,or type of coefficient.When determining the spherical harmonic coefficients using the least squares method,it is essential to analyze the ordering pattern of these coefficients and their positions(e.g.,indices)in the vector or matrix.A systematic analysis on the type of coefficient arrangement is presented in this paper.Moreover,the index algorithm for each coefficient ordering pattern is provided.Additionally,the structure of the normal equation matrix with different coefficient arrangement patterns is analyzed.Based on the analysis and the algorithm presented in this paper:(1)we can calculate the index of each coefficient in the vector or matrix of the normal equation;(2)we can change the structure of the normal equation matrix of the Earth’s gravity field from one type of coefficient arrangement to another.Furthermore,(3)we can directly combine different structures of the normal equation matrix,calculated from different types of gravity satellite missions,to form combined normal equations.This approach is beneficial for the determination of Earth’s gravitational model using multi-type observation data.展开更多
Coal bed methane(CBM),the high-quality and efficient fuel,has caught the interest of many nations as they strive for environmentally friendly development.Therefore,the efficient exploitation and utilization of CBM has...Coal bed methane(CBM),the high-quality and efficient fuel,has caught the interest of many nations as they strive for environmentally friendly development.Therefore,the efficient exploitation and utilization of CBM has become one of the international focal research problems.A significant factor affecting the mining of CBM is coal permeability.To better capture the changes that occur during the extraction of CBM,the internal swelling coefficient of matrix(ISCM)has been gradually in permeability introduced into the permeability models,and such models have become an important type of the development of permeability models.The goal is to find out more precisely the evolution mechanism of the ISCM and its influence on the permeability models.In this paper,the selection of coal structure,determination of boundary conditions and influencing factors of permeability for were first analyzed.Then,according to the research process of ISCM,the permeability models including the ISCM were reviewed and divided into four phases:proposal phase,development phase,evaluation phase and display of internal structure phase.On the basis of the ISCM values in the current coal permeability models,the primary influencing factors and evolutionary laws of the ISCM are explored.The results obtained provide guidance for future theoretical refinement of permeability models with the ISCM.展开更多
In this paper, we study the large time behavior of solutions of the parabolic semilinear equation δtu-div（a（x）△↓u） = -｜u｜^αu in （0,∞） × R^N, where α 〉 0 is constant and a∈ Cb^1（R^N） is a symmetr...In this paper, we study the large time behavior of solutions of the parabolic semilinear equation δtu-div（a（x）△↓u） = -｜u｜^αu in （0,∞） × R^N, where α 〉 0 is constant and a∈ Cb^1（R^N） is a symmetric periodic matrix satisfying some ellipticity assumptions.Considering an integrable initial data u0 and α ∈ （2/N, 3/N）, we prove that the large time behavior of solutions is given by the solution U（t, x） of the homogenized linear problem δtU-div（a^h△↓U）=0,U（0） = C, where a^h is the homogenized matrix of a（x）, C is a positive constant and δ is the Dirac measure at 0.展开更多
Motivation of this paper is an open problem exposed by B. Beauzamy .Let M be a 3×3 matrix and d(M) is the distance to the diagonal algebra. Let α(M)= sup {‖P ⊥MP‖∶P is a projection in the diagonal algeb...Motivation of this paper is an open problem exposed by B. Beauzamy .Let M be a 3×3 matrix and d(M) is the distance to the diagonal algebra. Let α(M)= sup {‖P ⊥MP‖∶P is a projection in the diagonal algebra} and then call K(M)=d(Μ)α(M) the distance coefficient of M. The following results are obtained: (1) If M has two zero entries apart from its diagonal, then K(M)322; (2) If M has one zero entry apart from its diagonal, then K(M)4132; (3) If M is arbitrary, then K(M)32.展开更多
Due to the diversity of work requirements and environment,the number of degrees of freedom(DOFs)and the complexity of structure of industrial robots are constantly increasing.It is difficult to establish the accurate ...Due to the diversity of work requirements and environment,the number of degrees of freedom(DOFs)and the complexity of structure of industrial robots are constantly increasing.It is difficult to establish the accurate dynamical model of industrial robots,which greatly hinders the realization of a stable,fast and accurate trajectory tracking control.Therefore,the general expression of the constraint relation in the explicit dynamic equation of the multi-DOF industrial robot is derived on the basis of solving the Jacobian matrix and Hessian matrix by using the kinematic influence coefficients method.Moreover,an explicit dynamic equation with general constraint relation expression is established based on the Udwadia-Kalaba theory.The problem of increasing the time of establishing constraint relationship when the multi-DOF industrial robots complete complex task constraints is solved.With the SCARA robot as the research object,the simulation results show that the proposed method can provide a new idea for industrial robot system modeling with complex constraints.展开更多
In many applications, such as in multivariate meta-analysis or in the construction of multivariate models from summary statistics, the covariance of regression coefficients needs to be calculated without having access...In many applications, such as in multivariate meta-analysis or in the construction of multivariate models from summary statistics, the covariance of regression coefficients needs to be calculated without having access to individual patients’ data. In this work, we derive an alternative analytic expression for the covariance matrix of the regression coefficients in a multiple linear regression model. In contrast to the well-known expressions which make use of the cross-product matrix and hence require access to individual data, we express the covariance matrix of the regression coefficients directly in terms of covariance matrix of the explanatory variables. In particular, we show that the covariance matrix of the regression coefficients can be calculated using the matrix of the partial correlation coefficients of the explanatory variables, which in turn can be calculated easily from the correlation matrix of the explanatory variables. This is very important since the covariance matrix of the explanatory variables can be easily obtained or imputed using data from the literature, without requiring access to individual data. Two important applications of the method are discussed, namely the multivariate meta-analysis of regression coefficients and the so-called synthesis analysis, and the aim of which is to combine in a single predictive model, information from different variables. The estimator proposed in this work can increase the usefulness of these methods providing better results, as seen by application in a publicly available dataset. Source code is provided in the Appendix and in http://www.compgen.org/tools/regression.展开更多
The impregnated radar absorbing material(RAM) honeycomb is often used to fabricate parts of the war plane for reducing radar cross section. The incident wave vector may be divided into two components: one perpendicula...The impregnated radar absorbing material(RAM) honeycomb is often used to fabricate parts of the war plane for reducing radar cross section. The incident wave vector may be divided into two components: one perpendicular to its hole and the other to its side wall. Until now, there has not been a program to calculate the input impedance or its equivalent electromagnetic parameters for the later case. In this paper, an approach for analyzing the reflection characteristics of the impregnated honeycomb when its side wall faces the incident plane wave is proposed. Experiments prove it an effective, accurate and fast solution to this subject.展开更多
Milled form of mesophase pitch-based graphite fibers were coated with a titanium layer using chemical vapor deposition technique and Ti-coated graphite fiber/Cu composites were fabricated by hot-pressing sintering. Th...Milled form of mesophase pitch-based graphite fibers were coated with a titanium layer using chemical vapor deposition technique and Ti-coated graphite fiber/Cu composites were fabricated by hot-pressing sintering. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopies, and by mea- suring thermal properties, including thermal conductivity and coefficient of thermal expansion （CTE）. The results show that the milled fibers are preferentially oriented in a plane perpendicular to the pressing direction, leading to anisotropic thermal properties of the composites. The Ti coating reacted with graphite fiber and formed a continuous and uniform TiC layer. This carbide layer establishes a good metallurgical interracial bonding in the composites, which can improve the thermal properties effectively. When the fiber content ranges from 35 vol% to 50 vol%, the in-plane thermal conductivities of the composites increase from 383 to 407 W.（m.K）-~, and the in-plane CTEs decrease from 9.5 x 10-6 to 6.3 10-6 K-1.展开更多
基金financially supported by the National Basic Research Program of China (Nos.2011CB932603 and 2012CB619600)the National Natural Science Foundation of China (No.51331008)
文摘Carbon nanotube-reinforced 2009Al （CNT/2009Al） composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing （FSP） and FSP-rolling, respectively. The CNT/2009A1 composites with aligned CNTs showed much better tensile properties at room temperature and elevated temperature compared with those with the randomly oriented CNTs, which is mainly attributed to larger equivalent aspect ratio of the CNTs and avoidance of preferential fracture problems. However, much finer grain size was not beneficial to obtaining high strength above 473 K. The aligned CNTs resulted in tensile anisotropy, with the best tensile properties being achieved along the direction of CNT aligning. As the off-axis angle increased, the tensile properties were reduced due to the weakening of the load transfer ability. Furthermore, aligned CNTs resulted in much lower coefficient of thermal expansion compared with randomly oriented CNTs.
文摘This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the propeller and intermediate shafts, under the influence of propeller-induced static and variable hydrodynamic excitations are also studied. The transfer matrix method related to the constant coefficients of differential equation solutions is used. The advantage of the latter as compared with a well-known method of transfer matrix associated with state vector is the possibility of reducing the number of multiplied matrices when adjacent shaft segments have the same material properties and diameters. The results show that there is no risk of buckling and confirm that the strength of the shaft line depends on the value of the static tangential stresses which is the most important component of the stress tensor.
基金supported by The National Natural Science Foundation of China(42374004).
文摘The global gravitational model can be expressed as a series of spherical harmonic coefficients computed up to a certain degree and order.The main ordering characteristic can depend on the degree,order,or type of coefficient.When determining the spherical harmonic coefficients using the least squares method,it is essential to analyze the ordering pattern of these coefficients and their positions(e.g.,indices)in the vector or matrix.A systematic analysis on the type of coefficient arrangement is presented in this paper.Moreover,the index algorithm for each coefficient ordering pattern is provided.Additionally,the structure of the normal equation matrix with different coefficient arrangement patterns is analyzed.Based on the analysis and the algorithm presented in this paper:(1)we can calculate the index of each coefficient in the vector or matrix of the normal equation;(2)we can change the structure of the normal equation matrix of the Earth’s gravity field from one type of coefficient arrangement to another.Furthermore,(3)we can directly combine different structures of the normal equation matrix,calculated from different types of gravity satellite missions,to form combined normal equations.This approach is beneficial for the determination of Earth’s gravitational model using multi-type observation data.
基金Financial support is provided by the Research Funds for Key Laboratory of Safe and Effective Coal Mining(Anhui University of Science and Technology)Ministry of Education(JYBSYS2021209)+2 种基金National Science Foundation of China(51804176,51974169 and 51904270)Natural Science Foundation of Shandong Province(ZR2023ME031 and ZR2020QE124)China Postdoctoral Science Foundation(2019M652346 and 2018M 642632).
文摘Coal bed methane(CBM),the high-quality and efficient fuel,has caught the interest of many nations as they strive for environmentally friendly development.Therefore,the efficient exploitation and utilization of CBM has become one of the international focal research problems.A significant factor affecting the mining of CBM is coal permeability.To better capture the changes that occur during the extraction of CBM,the internal swelling coefficient of matrix(ISCM)has been gradually in permeability introduced into the permeability models,and such models have become an important type of the development of permeability models.The goal is to find out more precisely the evolution mechanism of the ISCM and its influence on the permeability models.In this paper,the selection of coal structure,determination of boundary conditions and influencing factors of permeability for were first analyzed.Then,according to the research process of ISCM,the permeability models including the ISCM were reviewed and divided into four phases:proposal phase,development phase,evaluation phase and display of internal structure phase.On the basis of the ISCM values in the current coal permeability models,the primary influencing factors and evolutionary laws of the ISCM are explored.The results obtained provide guidance for future theoretical refinement of permeability models with the ISCM.
基金Supported by CNPq-Conselho Nacional de Desenvolvimento Cient'fico e Tecnológico
文摘In this paper, we study the large time behavior of solutions of the parabolic semilinear equation δtu-div（a（x）△↓u） = -｜u｜^αu in （0,∞） × R^N, where α 〉 0 is constant and a∈ Cb^1（R^N） is a symmetric periodic matrix satisfying some ellipticity assumptions.Considering an integrable initial data u0 and α ∈ （2/N, 3/N）, we prove that the large time behavior of solutions is given by the solution U（t, x） of the homogenized linear problem δtU-div（a^h△↓U）=0,U（0） = C, where a^h is the homogenized matrix of a（x）, C is a positive constant and δ is the Dirac measure at 0.
文摘Motivation of this paper is an open problem exposed by B. Beauzamy .Let M be a 3×3 matrix and d(M) is the distance to the diagonal algebra. Let α(M)= sup {‖P ⊥MP‖∶P is a projection in the diagonal algebra} and then call K(M)=d(Μ)α(M) the distance coefficient of M. The following results are obtained: (1) If M has two zero entries apart from its diagonal, then K(M)322; (2) If M has one zero entry apart from its diagonal, then K(M)4132; (3) If M is arbitrary, then K(M)32.
基金the Beijing Municipal Scienceand Technology Project (No.KM202111417006)the Academic Research Projects of Beijing Union University (Nos.ZK10202305 and ZK80202004)the Beijing Municipal Science and Technology Project (No.KM202111417005)。
文摘Due to the diversity of work requirements and environment,the number of degrees of freedom(DOFs)and the complexity of structure of industrial robots are constantly increasing.It is difficult to establish the accurate dynamical model of industrial robots,which greatly hinders the realization of a stable,fast and accurate trajectory tracking control.Therefore,the general expression of the constraint relation in the explicit dynamic equation of the multi-DOF industrial robot is derived on the basis of solving the Jacobian matrix and Hessian matrix by using the kinematic influence coefficients method.Moreover,an explicit dynamic equation with general constraint relation expression is established based on the Udwadia-Kalaba theory.The problem of increasing the time of establishing constraint relationship when the multi-DOF industrial robots complete complex task constraints is solved.With the SCARA robot as the research object,the simulation results show that the proposed method can provide a new idea for industrial robot system modeling with complex constraints.
文摘In many applications, such as in multivariate meta-analysis or in the construction of multivariate models from summary statistics, the covariance of regression coefficients needs to be calculated without having access to individual patients’ data. In this work, we derive an alternative analytic expression for the covariance matrix of the regression coefficients in a multiple linear regression model. In contrast to the well-known expressions which make use of the cross-product matrix and hence require access to individual data, we express the covariance matrix of the regression coefficients directly in terms of covariance matrix of the explanatory variables. In particular, we show that the covariance matrix of the regression coefficients can be calculated using the matrix of the partial correlation coefficients of the explanatory variables, which in turn can be calculated easily from the correlation matrix of the explanatory variables. This is very important since the covariance matrix of the explanatory variables can be easily obtained or imputed using data from the literature, without requiring access to individual data. Two important applications of the method are discussed, namely the multivariate meta-analysis of regression coefficients and the so-called synthesis analysis, and the aim of which is to combine in a single predictive model, information from different variables. The estimator proposed in this work can increase the usefulness of these methods providing better results, as seen by application in a publicly available dataset. Source code is provided in the Appendix and in http://www.compgen.org/tools/regression.
文摘The impregnated radar absorbing material(RAM) honeycomb is often used to fabricate parts of the war plane for reducing radar cross section. The incident wave vector may be divided into two components: one perpendicular to its hole and the other to its side wall. Until now, there has not been a program to calculate the input impedance or its equivalent electromagnetic parameters for the later case. In this paper, an approach for analyzing the reflection characteristics of the impregnated honeycomb when its side wall faces the incident plane wave is proposed. Experiments prove it an effective, accurate and fast solution to this subject.
基金financially supported by the National Natural Science Foundation of China(No.51274040)the Fundamental Research Funds for the Central Universities(FRF-TP-10-003B)
文摘Milled form of mesophase pitch-based graphite fibers were coated with a titanium layer using chemical vapor deposition technique and Ti-coated graphite fiber/Cu composites were fabricated by hot-pressing sintering. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopies, and by mea- suring thermal properties, including thermal conductivity and coefficient of thermal expansion （CTE）. The results show that the milled fibers are preferentially oriented in a plane perpendicular to the pressing direction, leading to anisotropic thermal properties of the composites. The Ti coating reacted with graphite fiber and formed a continuous and uniform TiC layer. This carbide layer establishes a good metallurgical interracial bonding in the composites, which can improve the thermal properties effectively. When the fiber content ranges from 35 vol% to 50 vol%, the in-plane thermal conductivities of the composites increase from 383 to 407 W.（m.K）-~, and the in-plane CTEs decrease from 9.5 x 10-6 to 6.3 10-6 K-1.
