HAS URBAN LIVABILITY CHANGED DRAMATICALLY? A COMPARISON OF THE PLACES RATED ALMANACS

We examine changes in the livability rankings of U.S. metropolitan areas as measured by 1981 and 1985 editions of Places Rated Almanac. The bonus point system of the 1985 Almanac arbitrarily rewards PMSA status in four of the nine indices used to measure urban livability, thus giving 76 metropolitan area a decided advantage over 253 “stand alone”MSAs. A Student's t-test of thirteen comparably measured vaiables in both editions reveals many counterintuitive results. Metropolitan areas gaining in rank have higher rates of violent crime and housing costs and provide less public transportation and health care than their declining counterparts. The changes in rankings reflect changed measurement criteria and metropolitan delimitation rather than any substantive change in the U.S. urban system. Alternative mechanisms allocating bonus points, including a gravity model and the daily urban system, are suggested.     

导航卫星历书参数拟合改进算法

该文对导航卫星历书拟合问题进行了综合研究,结合J2项分析解,提出了一种新的卫星历书拟合方法和用户算法.该方法只需下列参数表示历书: Week、Toa、a、e,i、Ω0、ω0、M0,比正常的GPS卫星历书参数少一个:Ω.用户算法可以根据一阶摄动理论,由新历书参数a、e、i计算Ω,并对MEO、IGSO、GEO卫星的历书参数近地点角进行改进.通过多组模拟轨道和IGS精密轨道的历书拟合实验,结果表明采用新方法具有参数少、计算量少、迭代收敛快、拟合MEO卫星历书精度高等优点,同样适用于高轨GEO、IGSO卫星.