圆周的

On the basement of conventional direct fan-beam reconstruction, this paper gives a newly improved algorithm-"fast filtering-backprojection". This method utilizes the symmetrical circle geometry to sample projection data, and reconstructs image on the Polarcoordinate firstly, then translates this reconstructed image onto the cartesian coordinate system with two interpolating operations so that the computer can show the result image on the VGA screen. This algorithm rebates the calculating backprojection greatly, and shortens a few times of reconstructing time than same kinds of means. With the size of image enlarging, the reconstructing time abates with 2 exponent times. In addition, according to the idea of parallel-beam, we rearrange the fan-beams and reconstruct image using parallel-beam method fastly. The rearranging constraint condition is given here.

本文首先在传统的扇束直接重建方法的基础上，提出了一个改进的快速滤波反投影重建算法，它利用旋转采集投影数据的圆周对称的几何关系，先在极坐标系统内进行图象的重建，然后通过两次内插运算再将图象转换到计算机显示方式下的笛卡尔坐标系中去，该方法将以往的直接重建方法中的反投影时所需的运算大大降低，并将重建时间比同类方法缩短了几倍，而且随着重建图象的尺寸的增大，重建时间以2的指数次方倍相对缩短，并获得了较好质量的重建图象；另外，又根据平行束投影重建图象的思想，对扇形射束进行了重排，然后利用平行束重建图象的方法进行扇束的重建，并推导了&扇束重排重建图象&方法的约束条件。

We performed a simulative test, which confirms that wavelet analysis can separate annual wobble and Chandler wobble. Our results show that this method can be used in astronomical geodynamies effectively. This paper is divided into two parts. The first is about statistic characteristic of polar motion. Polar motion includes secular motion, long period fluctuations, Chandler wobble, annual wobble and high frequency wobble. The secular motion is 3.4mas/year and towards 760W meridian. Long period fluctuations have difference periods in x-axis and y-axis. They are 31.7-year and 24-year in x-axis and 28.5-year and 22.9-year in y-axis. These 2~? decades fluctuations have an amplitude of about 30 mas , and are very nearly linearly polarized, with the observed motion of pole being almost entirely along a line between 360E and 1440W. There is a 55.4-year wobble whose amplitude is 9 mas. The amplitude of the interannual fluctuations is about 4? mas. The amplitude of long period fluctuations decreased after 1970. The annual wobble is a steady wobble. It retrograde wobble is only 1/20 of prograde wobble in amplitude.

本文的工作主要分为两部分：第一部分是通过分析POLE97序列，我们对极移的统计特性有了一个较全面的认识，极移主要包括趋势项、长周期项、Chandler项、周年项和高频项：趋势项的方向是西经76°，速度为每年3.4mas；长周期项中Markowitz 项在X、Y两个方向有不同的周期，它们分别是：X方向的两个周期是31.7年和24 年，Y方向的两个周期为28.5年和22.9年它们叠加在一起是一个线偏振运动，最大振幅约为30mas，偏振方向在西经144°和东经36°之间；极移的长周期波动中还存在一个 55.4年周期的圆周运动，振幅约为9mas；十年尺度变化的振幅在4～6mas之间，在Y 方向十年尺度的成份比较多，它们的周期在X方向和Y方向不是对应的；从七十年代年开始长周期变化的振幅明显降低；周年项是一个振幅稳定的摆动，在X、Y两个方向的振幅略有差别，逆向运动振幅大约为顺向运动振幅的1/20；Chandler摆动的振幅自1900年以来经历了几次较大的变化，其中包括1915年和1955年两次极大值，振幅分别达到0&。25和0&。28，以及1925～1940期间小于0.09的过程，Chandler项在X、Y 两个方向的振幅几乎完全相等，其逆向运动振幅不到顺向运动振幅的1/50。

Neither the killing of Mr Zarqawi nor any breakthrough on the political front will stop the insurgency and the fratricidal murders in their tracks.

在对危险的南部地区访问时，他斥责什叶派民兵领导人对中央集权的挑衅行为。

In fact,I've got him on the satellite mobile right now.

实际上 我们已接通卫星可视电话了