Absolute plate motions and true polar wander in the absence of hotspot tracks

The motion of continents relative to the Earth's spin axis may be due either to rotation of the entire Earth relative to its spin axis--true polar wander--or to the motion of individual plates. In order to distinguish between these over the past 320 Myr (since the formation of the Pangaea supercontinent), we present here computations of the global average of continental motion and rotation through time in a palaeomagnetic reference frame. Two components are identified: a steady northward motion and, during certain time intervals, clockwise and anticlockwise rotations, interpreted as evidence for true polar wander. We find approximately 18 degrees anticlockwise rotation about 250-220 Myr ago and the same amount of clockwise rotation about 195-145 Myr ago. In both cases the rotation axis is located at about 10-20 degrees W, 0 degrees N, near the site that became the North American-South American-African triple junction at the break-up of Pangaea. This was followed by approximately 10 degrees clockwise rotation about 145-135 Myr ago, followed again by the same amount of anticlockwise rotation about 110-100 Myr ago, with a rotation axis in both cases approximately 25-50 degrees E in the reconstructed area of North Africa and Arabia. These rotation axes mark the maxima of the degree-two non-hydrostatic geoid during those time intervals, and the fact that the overall net rotation since 320 Myr ago is nearly zero is an indication of long-term stability of the degree-two geoid and related mantle structure. We propose a new reference frame, based on palaeomagnetism, but corrected for the true polar wander identified in this study, appropriate for relating surface to deep mantle processes from 320 Myr ago until hotspot tracks can be used (about 130 Myr ago).     

大叶白麻叶化学成分的研究

从大叶白麻[poacynumhendersonii(Hookf)woodson]叶中分得2个木脂素类化舍物,经理化常数测定和光谱分析,分别鉴定为(-)-丁香脂素[(-)-Syringaresino1]和( )-松脂素-4-O-β-D-葡萄糖甙[( )-Pinoresionol-4-0-β-D-glucopyranoside].     

卫星导航设备时延精密标定方法与测试技术研究

分析和研究了卫星导航设备时延标定的方法,并针对卫星导航设备时延的特点,提出卫星导航设备时延应用统计量和稳定性来表征,并提出了基于射频采样和软件无线电的精密设备时延测量方法（RFSR）,能够准确地分析设备时延和设备时延的稳定性,通过仿真分析验证了方法正确性;通过建立试验验证系统,对可编程延迟线、电缆等设备的模拟测量,验证了该方法的正确性和优越性.