The Ti-46A1-6Nb （mole fraction, %） ingots that were directionally solidified by cold crucible were cyclic heat treated at 1330 ℃ in the a phase region. The microstructures and mechanical properties of the ingots be...The Ti-46A1-6Nb （mole fraction, %） ingots that were directionally solidified by cold crucible were cyclic heat treated at 1330 ℃ in the a phase region. The microstructures and mechanical properties of the ingots before and after heat treatment were investigated. The results show that the large columnar grains are changed into equiaxed grains after heat treatment. The grain size decreases with increasing the cyclic times, which is caused by the recrystallization and the transition from the large grain of small lamellae to the small grain of large lamellae. Four times of cyclic heat treatment refines the grain size from 1.33 mm to 0.59 turn, nevertheless the lamellar spacing increases from 0.71 ~tm to 1.38 lim. Extending the holding time and increasing the cyclic times of heat treatment eliminate the fl-segregation at the grain boundary and the interlamellar. The compression testing shows that the compressive strength of the directionally solidified ingot in the parallel and perpendicular directions are 1385.09 MPa and 1267.79 MPa, respectively, which are improved to 1449.75 MPa and 1527.76 MPa after two and four times of cyclic heat treatment, respectively, while that is 1180.64 MPa for the as-cast sample. The fracture mode of the sample after cyclic heat treatment is quasi-cleavage fracture.展开更多
Verlinde has suggested that the gravity has an entropic origin, and a gravitational system could be regarded as a thermodynarnical system. It is well-known that the equipartition law of energy is invalid at very low t...Verlinde has suggested that the gravity has an entropic origin, and a gravitational system could be regarded as a thermodynarnical system. It is well-known that the equipartition law of energy is invalid at very low temperature. Therefore, entropic force should be modified while the temperature of the holographic screen is very low. It is shown that the modified entropic force is proportional to the square of the acceleration, while the temperature of the holographic screen is much lower than the Debye temperature TD. The modified entropic force returns to the Newton＇s law of gravitation while the temperature of the holographic screen is much higher than the Debye temperature. The modified entropic force is connected with modified Newtonian dynamics （MOND）. The constant ao involved in MOND is linear in the Debye frequency WD, which can be regarded as the largest frequency of the bits in screen. We find that there do have a strong connection between MOND and cosmology in the framework of Verlinde＇s entropic force, if the holographic screen is taken to be bound of the Universe. The Debye frequency is linear in the Hubble constant Ho.展开更多
Gateway floor heave control is the key to guarantee mine safe and efficient production. Through analysis of floor instability characteristics and bolting control, gateway floor strata show second level stress under ab...Gateway floor heave control is the key to guarantee mine safe and efficient production. Through analysis of floor instability characteristics and bolting control, gateway floor strata show second level stress under abutment pressure, which causes plastic flow failure in floor strata; gateway floor instability shows mainly shear-break slippage of ＂triangle sliding body＂. Mechanics of floor bolting is mainly a function of connection and combination. Main area of bolting control lies in two gateway floor angles. The paper analyzes mechanics principle of gateway floor instability, constructs stability mechanics model of gateway floor bolting, obtains gateway floor stability criterion of different bolting angles and optimum formula of bolting parameters, carries out the engineering example, and guides better field application. It provides theoretical base for bolting gateway floor instability control.展开更多
Based on our previous paper (Commun.Theor.Phys.39 (2003) 417) we derive the convolution theoremof fractional Fourier transformation in the context of quantum mechanics,which seems a convenient and neat way.Generalizat...Based on our previous paper (Commun.Theor.Phys.39 (2003) 417) we derive the convolution theoremof fractional Fourier transformation in the context of quantum mechanics,which seems a convenient and neat way.Generalization of this method to the complex fractional Fourier transformation case is also possible.展开更多
The elastic-plastic behavior and failure of pipe-on-pipe impact(p-o-p-i)problem is studied through analytical model and numerical simulation in this paper.The impact of a whipping pipe with one end hinged and the othe...The elastic-plastic behavior and failure of pipe-on-pipe impact(p-o-p-i)problem is studied through analytical model and numerical simulation in this paper.The impact of a whipping pipe with one end hinged and the other end free on a simply-supported target pipe at its midpoint is considered.The analytical model based on tubular beam theory is proposed in the study of the deformation and plastic collapse behavior of pipes impacted on different positions and therefore to obtain the various failure modes depending on the material and structural parameters of the pipes.Numerical simulations using the finite element code MSC-Marc are performed and the results are coincident with the theoretical predictions.展开更多
We propose a sequential monomer reaction model for a two-species predator-prey system, in which the aggregates of either species can spontaneously produce or lose one monomer and meanwhile, a type-B aggregate can prey...We propose a sequential monomer reaction model for a two-species predator-prey system, in which the aggregates of either species can spontaneously produce or lose one monomer and meanwhile, a type-B aggregate can prey upon one monomer of a type-A aggregate when they meet. Using the mean-field rate equation approach, we analytically investigate the kinetic behavior of the system. The results show that the evolution of the system depends crucially on the details of the rate kernels. The aggregate size distribution of either species approaches the conventional or modified scaling form in most cases. Moreover, the total size of either species grows exponentially with time in some cases and asymptotically retains a constant quantity in other cases, while it decays with time and vanishes finally in the rest cases.展开更多
The integrating factors and conservation theorems of nonholonomic dynamical system of relative motion are studied. First, the dynamical equations of relative motion of system are written. Next, the definition of integ...The integrating factors and conservation theorems of nonholonomic dynamical system of relative motion are studied. First, the dynamical equations of relative motion of system are written. Next, the definition of integrating factors is given, and the necessary conditions for the existence of the conserved quantities are studied in detail. Then, the conservation theorem and its inverse of system are established. Finally, an example is given to illustrate the application of the result.展开更多
Based on the nonlinear failure criterion and the upper bound theorem, the modified tangential technique method was proposed to derive the expression of supporting pressure acting on shallow tunnel. Instead of the same...Based on the nonlinear failure criterion and the upper bound theorem, the modified tangential technique method was proposed to derive the expression of supporting pressure acting on shallow tunnel. Instead of the same stress state, different normal stresses on element boundaries were used. In order to investigate the influence of different factors on supporting pressures, the failure mechanism was established. The solution of supporting pressure, with different parameters, was obtained by optimization theory. The corresponding failure mechanism and numerical results were presented. In comparison with the results using the single tangential technique method, it is found that the proposed method is effective, and the good agreement shows that the present solution of supporting pressure is reliable.展开更多
基金Project(2011CB605504) supported by the National Basic Research Program of ChinaProject(NCET-12-0153) supported by the Program of New Century Excellent Talents in UniversityProject(51274076) supported by the National Natural Science of Foundation of China
文摘The Ti-46A1-6Nb （mole fraction, %） ingots that were directionally solidified by cold crucible were cyclic heat treated at 1330 ℃ in the a phase region. The microstructures and mechanical properties of the ingots before and after heat treatment were investigated. The results show that the large columnar grains are changed into equiaxed grains after heat treatment. The grain size decreases with increasing the cyclic times, which is caused by the recrystallization and the transition from the large grain of small lamellae to the small grain of large lamellae. Four times of cyclic heat treatment refines the grain size from 1.33 mm to 0.59 turn, nevertheless the lamellar spacing increases from 0.71 ~tm to 1.38 lim. Extending the holding time and increasing the cyclic times of heat treatment eliminate the fl-segregation at the grain boundary and the interlamellar. The compression testing shows that the compressive strength of the directionally solidified ingot in the parallel and perpendicular directions are 1385.09 MPa and 1267.79 MPa, respectively, which are improved to 1449.75 MPa and 1527.76 MPa after two and four times of cyclic heat treatment, respectively, while that is 1180.64 MPa for the as-cast sample. The fracture mode of the sample after cyclic heat treatment is quasi-cleavage fracture.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10525522 and 10875129
文摘Verlinde has suggested that the gravity has an entropic origin, and a gravitational system could be regarded as a thermodynarnical system. It is well-known that the equipartition law of energy is invalid at very low temperature. Therefore, entropic force should be modified while the temperature of the holographic screen is very low. It is shown that the modified entropic force is proportional to the square of the acceleration, while the temperature of the holographic screen is much lower than the Debye temperature TD. The modified entropic force returns to the Newton＇s law of gravitation while the temperature of the holographic screen is much higher than the Debye temperature. The modified entropic force is connected with modified Newtonian dynamics （MOND）. The constant ao involved in MOND is linear in the Debye frequency WD, which can be regarded as the largest frequency of the bits in screen. We find that there do have a strong connection between MOND and cosmology in the framework of Verlinde＇s entropic force, if the holographic screen is taken to be bound of the Universe. The Debye frequency is linear in the Hubble constant Ho.
基金Supported by the National Natural Science Foundation of China （50874037）
文摘Gateway floor heave control is the key to guarantee mine safe and efficient production. Through analysis of floor instability characteristics and bolting control, gateway floor strata show second level stress under abutment pressure, which causes plastic flow failure in floor strata; gateway floor instability shows mainly shear-break slippage of ＂triangle sliding body＂. Mechanics of floor bolting is mainly a function of connection and combination. Main area of bolting control lies in two gateway floor angles. The paper analyzes mechanics principle of gateway floor instability, constructs stability mechanics model of gateway floor bolting, obtains gateway floor stability criterion of different bolting angles and optimum formula of bolting parameters, carries out the engineering example, and guides better field application. It provides theoretical base for bolting gateway floor instability control.
基金National Natural Science Foundation of China under Grant No.10775097
文摘Based on our previous paper (Commun.Theor.Phys.39 (2003) 417) we derive the convolution theoremof fractional Fourier transformation in the context of quantum mechanics,which seems a convenient and neat way.Generalization of this method to the complex fractional Fourier transformation case is also possible.
基金National Natural Science Foundation of China(No.11032001)
文摘The elastic-plastic behavior and failure of pipe-on-pipe impact(p-o-p-i)problem is studied through analytical model and numerical simulation in this paper.The impact of a whipping pipe with one end hinged and the other end free on a simply-supported target pipe at its midpoint is considered.The analytical model based on tubular beam theory is proposed in the study of the deformation and plastic collapse behavior of pipes impacted on different positions and therefore to obtain the various failure modes depending on the material and structural parameters of the pipes.Numerical simulations using the finite element code MSC-Marc are performed and the results are coincident with the theoretical predictions.
基金supported by National Natural Science Foundation of China under Grant Nos.10775104 and 10305009Natural Science Foundation of Zhejiang Province of China under Grant No.102067
文摘We propose a sequential monomer reaction model for a two-species predator-prey system, in which the aggregates of either species can spontaneously produce or lose one monomer and meanwhile, a type-B aggregate can prey upon one monomer of a type-A aggregate when they meet. Using the mean-field rate equation approach, we analytically investigate the kinetic behavior of the system. The results show that the evolution of the system depends crucially on the details of the rate kernels. The aggregate size distribution of either species approaches the conventional or modified scaling form in most cases. Moreover, the total size of either species grows exponentially with time in some cases and asymptotically retains a constant quantity in other cases, while it decays with time and vanishes finally in the rest cases.
基金The project supported by Natural Science Foundation of Heilongjiang Province of China under Grant No. 9507
文摘The integrating factors and conservation theorems of nonholonomic dynamical system of relative motion are studied. First, the dynamical equations of relative motion of system are written. Next, the definition of integrating factors is given, and the necessary conditions for the existence of the conserved quantities are studied in detail. Then, the conservation theorem and its inverse of system are established. Finally, an example is given to illustrate the application of the result.
基金Projects(2013CB0360042011CB013800)supported by the National Basic Research Program of China+1 种基金Project(51178468)supported by the National Natural Science Foundation of ChinaProject(2011G013-B)supported by the Science and Technology Development of Railways Department in China
文摘Based on the nonlinear failure criterion and the upper bound theorem, the modified tangential technique method was proposed to derive the expression of supporting pressure acting on shallow tunnel. Instead of the same stress state, different normal stresses on element boundaries were used. In order to investigate the influence of different factors on supporting pressures, the failure mechanism was established. The solution of supporting pressure, with different parameters, was obtained by optimization theory. The corresponding failure mechanism and numerical results were presented. In comparison with the results using the single tangential technique method, it is found that the proposed method is effective, and the good agreement shows that the present solution of supporting pressure is reliable.
