采用电阻测量和X-射线衍射研究了Ti-54.91wt%Ni合金发生R相变的固溶和有序化处理条件。比较了不同残余应变量下经过 R 相变和只经过熟知的马氏体相变两种试样间的形状记忆特性。在近似等原子的 Ni-Ti 合金中 R 相变的发生取决于热处理...采用电阻测量和X-射线衍射研究了Ti-54.91wt%Ni合金发生R相变的固溶和有序化处理条件。比较了不同残余应变量下经过 R 相变和只经过熟知的马氏体相变两种试样间的形状记忆特性。在近似等原子的 Ni-Ti 合金中 R 相变的发生取决于热处理条件。除非在最有利的固溶和有序化组合条件下,通常并不存在 R 相变。延长有序化时间总是促进 R 相变。随着马氏体应变量的增大,不论是否附加 R 相变,形状回复温区加宽,单程形状回复率增高并出现极大值,而双程记忆效应单调地升高。在该合金中 R 相变的发生对于单程回复是有益的,但对于双程记忆则稍有削弱。形成 R相的热处理条件可以用声子形核的概念来解释。R 相变在单程和双程记忆上的不同效果可归因于加热(仅 M→B_2)和冷却(B_2→R 和 R→M)中经历不同的相变。展开更多
The shock wave standoff distances of near space hypersonic vehicles, which execute missions mainly at the altitude of 25 km to 55 km, are vital in aerothermodynamic analysis. The implicit finite volume schemes are der...The shock wave standoff distances of near space hypersonic vehicles, which execute missions mainly at the altitude of 25 km to 55 km, are vital in aerothermodynamic analysis. The implicit finite volume schemes are derived from axisymmetric Navier-Stokes equations for chemical equilibrium flow, and programmed in FORTRAN. Taking a sphere cone for example, the effects of Much numbers （from 22 to 36） on the shock wave standoffdistance and the average density behind the shock are simulated at different altitudes from 25km to 55km. The numerical results illustrate that the turning point of the standoff distance is corresponding to that of the average density with the variation of Mach numbers. Based on the numerical results, we propose a formula for shock wave standoff distance, which is the function of the radius of the blunt body, the Mach number and the altitude in the atmosphere. Compared with previous correlations, the new formula can overcome the drawbacks of larger relative errors and complex calculations of the average density.展开更多
By solving the total energy equation, we obtain the formula of exchange-correlation functional for the first time. This functional is usually determined by fitting experimental data or the numerical results of models....By solving the total energy equation, we obtain the formula of exchange-correlation functional for the first time. This functional is usually determined by fitting experimental data or the numerical results of models. In the uniform electron gas limit, our exchangecorrelation functional can exactly reproduce the results of Perdew-Zunger parameterization from the jellium model. By making use of a particular solution, our exchange-correlation functional could take into accotmt the case of non-uniform electron density, and its validity can be confirmed through comparisons of the band structure, equilibrium lattice constant, and bulk modulus of aluminum and silicon. The absence of mechanical prescriptions for the systematic improvement of exchange-correlation functional hinders further development of density-functional theory （DFT）, and the formula of exchange-correlation functional given in this study might provide a new perspective to help DFT out of this awkward situation.展开更多
文摘采用电阻测量和X-射线衍射研究了Ti-54.91wt%Ni合金发生R相变的固溶和有序化处理条件。比较了不同残余应变量下经过 R 相变和只经过熟知的马氏体相变两种试样间的形状记忆特性。在近似等原子的 Ni-Ti 合金中 R 相变的发生取决于热处理条件。除非在最有利的固溶和有序化组合条件下,通常并不存在 R 相变。延长有序化时间总是促进 R 相变。随着马氏体应变量的增大,不论是否附加 R 相变,形状回复温区加宽,单程形状回复率增高并出现极大值,而双程记忆效应单调地升高。在该合金中 R 相变的发生对于单程回复是有益的,但对于双程记忆则稍有削弱。形成 R相的热处理条件可以用声子形核的概念来解释。R 相变在单程和双程记忆上的不同效果可归因于加热(仅 M→B_2)和冷却(B_2→R 和 R→M)中经历不同的相变。
基金supported by the National Natural Science Foundation of China(Grant Nos.11472037,11272042&51506008)
文摘The shock wave standoff distances of near space hypersonic vehicles, which execute missions mainly at the altitude of 25 km to 55 km, are vital in aerothermodynamic analysis. The implicit finite volume schemes are derived from axisymmetric Navier-Stokes equations for chemical equilibrium flow, and programmed in FORTRAN. Taking a sphere cone for example, the effects of Much numbers （from 22 to 36） on the shock wave standoffdistance and the average density behind the shock are simulated at different altitudes from 25km to 55km. The numerical results illustrate that the turning point of the standoff distance is corresponding to that of the average density with the variation of Mach numbers. Based on the numerical results, we propose a formula for shock wave standoff distance, which is the function of the radius of the blunt body, the Mach number and the altitude in the atmosphere. Compared with previous correlations, the new formula can overcome the drawbacks of larger relative errors and complex calculations of the average density.
基金supported by the National High Technology Research and Development Program of China(Grants Nos.2014CB920903 and 2011CBA00100)the National Natural Science Foundation of China(Grant Nos.11021262,107212303,10372107,11174337 and 11225418)+1 种基金the National Basic Research Program of China(Grants No.2012CB937500)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grants No.20121101110046)
文摘By solving the total energy equation, we obtain the formula of exchange-correlation functional for the first time. This functional is usually determined by fitting experimental data or the numerical results of models. In the uniform electron gas limit, our exchangecorrelation functional can exactly reproduce the results of Perdew-Zunger parameterization from the jellium model. By making use of a particular solution, our exchange-correlation functional could take into accotmt the case of non-uniform electron density, and its validity can be confirmed through comparisons of the band structure, equilibrium lattice constant, and bulk modulus of aluminum and silicon. The absence of mechanical prescriptions for the systematic improvement of exchange-correlation functional hinders further development of density-functional theory （DFT）, and the formula of exchange-correlation functional given in this study might provide a new perspective to help DFT out of this awkward situation.
