Stokes＇ first problem has been investigated for a Maxwell fluid in a porous half-space for gaining insight into the effect of viscoelasticity on the start-up flow in a porous medium. An exact solution was obtained by...Stokes＇ first problem has been investigated for a Maxwell fluid in a porous half-space for gaining insight into the effect of viscoelasticity on the start-up flow in a porous medium. An exact solution was obtained by using the Fourier sine transform. It was found that at large values of the relaxation time the velocity overshoot occurs obviously and the system exhibits viscoelastic behaviours. On the other hand, for short relaxation time the velocity overshoot disappears and the system exhibits viscous behaviours. A critical value of the relaxation time was obtained for the emergence of the velocity overshoot. Furthermore, it was found that the velocity overshoot is caused by both the viscoelasticity of the Maxwell fluid and the Darcy resistance resulting from the structure of the micropore in the porous medium.展开更多
The semiclassical transport equations are used to study the high frequency performance of AlGaAs / GaAs HBTs. Electron velocity overshoot effect and its influence on the cut off frequency characteristics of AlGaAs / G...The semiclassical transport equations are used to study the high frequency performance of AlGaAs / GaAs HBTs. Electron velocity overshoot effect and its influence on the cut off frequency characteristics of AlGaAs / GaAs HBTs with different collector design parameters are analyzed and discussed.展开更多
An ensemble Monte Carlosimulation is used to compare high field electron transport in bulk GaAs, InAs and In0.3Ga0.7As. In particular, velocity overshoot and electron transit times are examined. We find the steady sta...An ensemble Monte Carlosimulation is used to compare high field electron transport in bulk GaAs, InAs and In0.3Ga0.7As. In particular, velocity overshoot and electron transit times are examined. We find the steady state velocity of the electrons is the most important factor determining transit time over distances longer then 0.2 μm. Over shorter distances velocity overshoot effects in InAs and In0.3Ga0.7 As at high fields are comparable to those in GaAs. We estimate the minimum transit time across a 1 μm InAs sample to be about 4.2 ps. Similar calculations for In0.3Ga0.7As yield 6 ps (for GaAs yield 10 ps). Calculations are made using a nonparabolic effective mass energy band model, Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models.展开更多
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10372007 and 10572006） and the New , Century Training Programme Foundation for the Talents by Chinese Ministry of Education.
文摘Stokes＇ first problem has been investigated for a Maxwell fluid in a porous half-space for gaining insight into the effect of viscoelasticity on the start-up flow in a porous medium. An exact solution was obtained by using the Fourier sine transform. It was found that at large values of the relaxation time the velocity overshoot occurs obviously and the system exhibits viscoelastic behaviours. On the other hand, for short relaxation time the velocity overshoot disappears and the system exhibits viscous behaviours. A critical value of the relaxation time was obtained for the emergence of the velocity overshoot. Furthermore, it was found that the velocity overshoot is caused by both the viscoelasticity of the Maxwell fluid and the Darcy resistance resulting from the structure of the micropore in the porous medium.
文摘The semiclassical transport equations are used to study the high frequency performance of AlGaAs / GaAs HBTs. Electron velocity overshoot effect and its influence on the cut off frequency characteristics of AlGaAs / GaAs HBTs with different collector design parameters are analyzed and discussed.
文摘An ensemble Monte Carlosimulation is used to compare high field electron transport in bulk GaAs, InAs and In0.3Ga0.7As. In particular, velocity overshoot and electron transit times are examined. We find the steady state velocity of the electrons is the most important factor determining transit time over distances longer then 0.2 μm. Over shorter distances velocity overshoot effects in InAs and In0.3Ga0.7 As at high fields are comparable to those in GaAs. We estimate the minimum transit time across a 1 μm InAs sample to be about 4.2 ps. Similar calculations for In0.3Ga0.7As yield 6 ps (for GaAs yield 10 ps). Calculations are made using a nonparabolic effective mass energy band model, Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models.
