中国户籍制度改革困境:从国家"退出"角度的分析

当前中国户籍制度改革难以进一步推进,文章将户籍制度看作是国家与地方之间的一个长期隐含契约以分析其原因.由于国家不能自由退出这一契约使得中国户籍制度改革不能深入.通过剥除由户籍派生出的特权能将“退出权“还与国家,最终能达到户籍制度改革的目标.     

Effects of compressibility and Knudsen number on the aero optics in hypersonic flow fields

Tsien summarized the similarity in hypersonic flows, and related Knudsen number to Mach number and Reynolds number. Recently, a path-based problem, aero-optical effect, arises in hypersonic flows, and it concerns about the compressibility and the Knudsen number of the gas flows, which differs from the Tsien’s focus to some extent. In this paper, the similarity of hypersonic aero optics is theoretically studied, and both flow fields and induced aero-optical effect after flows pass through a cylinder are predicted by a well-accepted particle-based method, direct simulation Monte-Carlo (DSMC) method. The results show that the optical distortions are inversely proportional to the Knudsen number, while the compressibility plays an important role in the optical degradations. Hence, it is confirmed that the effects of Mach number and Knudsen number on the aero-optical effect induced by hypersonic flows are of great significance. Besides, since the Knudsen number is defined straightforwardly based on the optically active region, the physics is clearer than any other similarity criteria.