The diffusion of C4-24 alkanes, aromatics and cycloalkanes in FAU and MFI zeolites were studied systemati- cally by molecular simulation. The basic data on diffusion energy barriers and the diffusion characteristics o...The diffusion of C4-24 alkanes, aromatics and cycloalkanes in FAU and MFI zeolites were studied systemati- cally by molecular simulation. The basic data on diffusion energy barriers and the diffusion characteristics of alkanes, cyclo- alkanes and aromatics in FAU and MFI zeolites were obtained. It was found out that the 12-member-ring openings between the two adjacent super cages limited the diffusion of hydrocarbons in FAU zeolites, and the hydrocarbon molecules diffused more easily in the intersections of MFI zeolite channels than in the straight channels between the intersections. It was more difficult for the molecules to diffuse in the sinusoidal channel of the MFI zeolite than in the straight channel because of the atoms at the comer of sinusoidal channel. The diffusion of three kinds of C6 alkanes was studied by gravity sorption method. The simulation results were well consistent with the experimental results, indicating that the simulation results were con- vincing.展开更多
A physical model of sinusoidal function was established. It is generalized that the force is directly proportional to a power function of the distance in a classical spring-oscillator system. The differential equation...A physical model of sinusoidal function was established. It is generalized that the force is directly proportional to a power function of the distance in a classical spring-oscillator system. The differential equation of the generalized model was given. Simulations were conducted with different power values. The results show that the solution of the generalized equation is a periodic function. The expressions of the amplitude and the period(frequency) of the generalized equation were derived by the physical method. All the simulation results coincide with the calculation results of the derived expressions. A special function also was deduced and proven to be convergent in the theoretical analysis. The limit value of the special function also was derived. The generalized model can be used in solving a type of differential equation and to generate periodic waveforms.展开更多
With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fad...With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fading waveforms.Compared with the existing stochastic models,the proposed simulator needs only one trial to obtain the desired statistical properties even if the number of samples is not large enough.Moreover,the proposed simulation model can directly generate multiple uncorrelated waveforms for different fading scenarios,such as single-input single-output frequency selective channels and multiple-input multiple-output channels.The performance evaluation and comparison show that the proposed simulator is efficient and accurate.展开更多
In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without r...In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.展开更多
基金the key Project of Chinese National Programs for Fundamental Research and Development (973 Program) (No.2010CB732301) for financial supports
文摘The diffusion of C4-24 alkanes, aromatics and cycloalkanes in FAU and MFI zeolites were studied systemati- cally by molecular simulation. The basic data on diffusion energy barriers and the diffusion characteristics of alkanes, cyclo- alkanes and aromatics in FAU and MFI zeolites were obtained. It was found out that the 12-member-ring openings between the two adjacent super cages limited the diffusion of hydrocarbons in FAU zeolites, and the hydrocarbon molecules diffused more easily in the intersections of MFI zeolite channels than in the straight channels between the intersections. It was more difficult for the molecules to diffuse in the sinusoidal channel of the MFI zeolite than in the straight channel because of the atoms at the comer of sinusoidal channel. The diffusion of three kinds of C6 alkanes was studied by gravity sorption method. The simulation results were well consistent with the experimental results, indicating that the simulation results were con- vincing.
基金Funded by the National Natural Science Foundation of China (No. 50375113).
文摘A physical model of sinusoidal function was established. It is generalized that the force is directly proportional to a power function of the distance in a classical spring-oscillator system. The differential equation of the generalized model was given. Simulations were conducted with different power values. The results show that the solution of the generalized equation is a periodic function. The expressions of the amplitude and the period(frequency) of the generalized equation were derived by the physical method. All the simulation results coincide with the calculation results of the derived expressions. A special function also was deduced and proven to be convergent in the theoretical analysis. The limit value of the special function also was derived. The generalized model can be used in solving a type of differential equation and to generate periodic waveforms.
基金Supported by the Science and Technology Innovation Foundation of Tianjin (No.10FDZDGX00400)
文摘With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fading waveforms.Compared with the existing stochastic models,the proposed simulator needs only one trial to obtain the desired statistical properties even if the number of samples is not large enough.Moreover,the proposed simulation model can directly generate multiple uncorrelated waveforms for different fading scenarios,such as single-input single-output frequency selective channels and multiple-input multiple-output channels.The performance evaluation and comparison show that the proposed simulator is efficient and accurate.
基金supported by the National Natural Science Foundation of China(Grant No.51475294)
文摘In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.
