SUPPRESSION OF BALLISTIC ELECTRON TRANSMISSION THROUGH A SEMICONDUCTOR Π-STRUCTURE BY AN EXTERNAL TRANSVERSE ELECTRIC FIELD

We have conducted numerical studies of ballistic electron transport in a semicon-ductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.     

一种基于恒星光线偏折的大气折射率估计方法

基于标准大气环境的大气折射率理论模型不能反映实际大气折射率的波动性,针对该问题,提出了一种基于恒星光线偏折的大气折射率估计方法。基于光学卫星的恒星观测数据,分析恒星光线经大气折射发生偏折的现象,建立恒星光线经大气折射后进入光学卫星传感器的光路模型,在分层球形大气的假设下证明该光路模型的对称性。研究一种利用恒星实测光线和恒星理论光线迭代前向反馈的方法,用以估计分层大气折射率。最后,利用光学卫星的恒星观测数据进行有效性验证,计算出的大气折射率与理论大气折射率相符,且能够反映短期波动性。对测试用的恒星实测数据进行处理,结果表明:88%以上的恒星理论视线与实测视线的估计值相差不超过1%,其余部分观测数据估计偏差基本不超过20%。     

SUPPRESSION OF BALLISTIC ELECTRON TRANSMISSION THROUGH A SEMICONDUCTOR Π-STRUCTURE BY AN EXTERNAL TRANSVERSE ELECTRIC FIELD

We have conducted numerical studies of ballistic electron transport in a semicon-ductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.     

低轨双星无源定位算法及定位精度分析

针对空间电子侦察卫星对地面固定辐射源进行无源定位的问题，研究并提出了一种通过低轨双星联合利用到达时间差（TDOA）和到达频率差（FDOA）无源定位的解析计算方法。通过公式推导和替换，该算法将原本复杂的时差、频差定位方程组化简为简单的6次实系数多项式方程，极大地降低了原方程组的计算复杂度。文章还推导了目标的定位误差几何稀度（GDOP）与时差测量精度、频差测量精度的关系。仿真结果表明，当参数测量的精度很高时，该算法能够准确地对地面目标定位；对比GDOP与参数测量精度的关系还发现，测频误差对低轨双星定位误差的影响较大。