GaN基白光LED的结温测量

用正向电压法、管脚法和蓝白比法等三种方法测量GaN基白光LED的结温,获得了较为准确的结温,误差可以控制在4℃以内.正向电压法在恒定电流的条件下,得到了正向电压与结温的线性关系;蓝白比法在不同环境温度和不同注入电流两种情况下,都得到了蓝白比与结温较好的线性关系.提出了蓝白比法可能的物理机制,提高环境温度和增大注入电流都会使结温升高,蓝光峰值波长也会改变,这两个因素都会影响荧光粉的激发和发光效率.降低结温需要考虑的主要因素有白光LED的接触电阻、串联电阻和外量子效率,封装材料的热导率,反射杯和管脚的设计,以及空气散热部分的散热面积等.     

基于动态网格的旋翼流场计算

基于无限插值理论,将旋翼按桨叶数分为几个子块,然后在桨叶连续公共界面上对接各子块,形成绕整个旋翼流场的三维多块网格。各桨叶子块的流场信息直接通过连续公共界面相互交换,利用非定常欧拉方程求解出整个旋翼流场。发展的动态网格在前飞流场计算中取得了成功。     

Modulation effects of rotating radiofrequency field in forward nuclear scattering of synchrotron radiation

The quantization of a nuclear angular momentum in the rotating hyperfine (HF) field of any frequency is theoretically studied in resonant forward scattering of synchrotron radiation (SR). The adiabatically slow rotation of the quantization axis does not perturb the multilevel structure of nuclear states created by the static hyperfine interaction. It follows directly from the pattern of quantum beats of a resonant response (RR) to an SR pulse. When the rotation frequency is of the order of the Larmor frequencies, determining the stationary HF sublevels, the pattern of quantum beats of an RR is formed by the nuclear resonant transitions between quasienergy levels. At the rotation frequency much larger than the Larmor frequencies the multilevel structure of nuclear states results from the quadrupole interaction only. This revised version was published online in August 2006 with corrections to the Cover Date.