We show that by integrating out the electric field and incorporating proper boundary conditions,a Boltzmann equation can describe electron transport properties,continuously from the diffusive to ballistic regimes.Gene...We show that by integrating out the electric field and incorporating proper boundary conditions,a Boltzmann equation can describe electron transport properties,continuously from the diffusive to ballistic regimes.General analytical formulas of the conductance in D = 1,2,3 dimensions are obtained,which recover the Boltzmann–Drude formula and Landauer–B ¨uttiker formula in the diffusive and ballistic limits,respectively.This intuitive and efficient approach can be applied to investigate the interplay of system size and impurity scattering in various charge and spin transport phenomena,when the quantum interference effect is not important.展开更多
Interplanetary meteoroids and space debris can impact satellites orbiting the Earth or spacecraft traveling to the Moon.Targeting China Space Station(CSS),7 satellites selected from the constellation of Beidou Navigat...Interplanetary meteoroids and space debris can impact satellites orbiting the Earth or spacecraft traveling to the Moon.Targeting China Space Station(CSS),7 satellites selected from the constellation of Beidou Navigation Satellite System Phase III(BDS-3),and 3 spacecraft orbiting the Moon,we have adopted in the paper the Meteoroid Engineering Model 3,Divine-Staubach meteoroid environment model,and Jenniskens-McBride meteoroid steam model to analyze the meteoroid environment with the mass range of 10–6~10 g.Orbital Debris Engineering Model 3.1 space debris model is used to analyze the orbital debris environment faced by these satellites.The flux of space debris with a size larger than 100μm is compared with that of the meteoroids.The results show that the space debris flux encountered by China Space Station is much higher than that of the meteoroids with sizes in the above range.And quite the opposite,the meteoroids flux impacting the 7 satellites from the BDS-3 is higher.Upon adopting the double-layer Whipple protection measure,the catastrophic collision flux of these satellites encountering meteoroids is about 10–6 times of that without protection,or even less,implying that the Whipple protection effectively guarantees the safety of the satellites in orbit.Besides,it is also found that the flux of the high-density meteoroid population encountered by each satellite is greater than that of the low-density population,whereas the impact velocity is lower for each satellite.These results can aid the orbit selection and the protection design for satellites and spacecraft.展开更多
Due to requests on high rotary velocity of novel smart empennage-stable projectiles, the rolling characteristics under wide-angle oblique angles are studied. Since the wind tunnel tests performed verify numerical simu...Due to requests on high rotary velocity of novel smart empennage-stable projectiles, the rolling characteristics under wide-angle oblique angles are studied. Since the wind tunnel tests performed verify numerical simulation, so that the latter method can be applied to study the rolling characteristics widely combining theoretical models. In the theoretical part, the rolling dynamics equations are established considering the span, taper ratio and oblique angle of the empennages, and are further solved combing ballistic equations. For the simulation, the rolling moment coefficients under various rotary velocities are solved based on rotating coordinate system methods, so that the balance rotary velocity can be obtained using interpolation. The results indicate that shorter span, higher taper ratio and especially larger oblique angle can bring higher projectile rotary velocity;the balance rotary velocity is approximately linear to the oblique angle in a certain range.展开更多
基金Project supported by the National Basic Research Program of China(Grant Nos.2015CB921202 and 2014CB921103)the National Natural Science Foundation of China(Grant No.11225420)
文摘We show that by integrating out the electric field and incorporating proper boundary conditions,a Boltzmann equation can describe electron transport properties,continuously from the diffusive to ballistic regimes.General analytical formulas of the conductance in D = 1,2,3 dimensions are obtained,which recover the Boltzmann–Drude formula and Landauer–B ¨uttiker formula in the diffusive and ballistic limits,respectively.This intuitive and efficient approach can be applied to investigate the interplay of system size and impurity scattering in various charge and spin transport phenomena,when the quantum interference effect is not important.
基金the National Natural Science Foundation of China(42074224)Key Research Program of the Chinese Academy of Sciences(ZDRE-KT-2021-3)Pandeng Program of National Space Science Center,Chinese Academy of Sciences。
文摘Interplanetary meteoroids and space debris can impact satellites orbiting the Earth or spacecraft traveling to the Moon.Targeting China Space Station(CSS),7 satellites selected from the constellation of Beidou Navigation Satellite System Phase III(BDS-3),and 3 spacecraft orbiting the Moon,we have adopted in the paper the Meteoroid Engineering Model 3,Divine-Staubach meteoroid environment model,and Jenniskens-McBride meteoroid steam model to analyze the meteoroid environment with the mass range of 10–6~10 g.Orbital Debris Engineering Model 3.1 space debris model is used to analyze the orbital debris environment faced by these satellites.The flux of space debris with a size larger than 100μm is compared with that of the meteoroids.The results show that the space debris flux encountered by China Space Station is much higher than that of the meteoroids with sizes in the above range.And quite the opposite,the meteoroids flux impacting the 7 satellites from the BDS-3 is higher.Upon adopting the double-layer Whipple protection measure,the catastrophic collision flux of these satellites encountering meteoroids is about 10–6 times of that without protection,or even less,implying that the Whipple protection effectively guarantees the safety of the satellites in orbit.Besides,it is also found that the flux of the high-density meteoroid population encountered by each satellite is greater than that of the low-density population,whereas the impact velocity is lower for each satellite.These results can aid the orbit selection and the protection design for satellites and spacecraft.
文摘Due to requests on high rotary velocity of novel smart empennage-stable projectiles, the rolling characteristics under wide-angle oblique angles are studied. Since the wind tunnel tests performed verify numerical simulation, so that the latter method can be applied to study the rolling characteristics widely combining theoretical models. In the theoretical part, the rolling dynamics equations are established considering the span, taper ratio and oblique angle of the empennages, and are further solved combing ballistic equations. For the simulation, the rolling moment coefficients under various rotary velocities are solved based on rotating coordinate system methods, so that the balance rotary velocity can be obtained using interpolation. The results indicate that shorter span, higher taper ratio and especially larger oblique angle can bring higher projectile rotary velocity;the balance rotary velocity is approximately linear to the oblique angle in a certain range.