Pervasive autocorrelation of the chemical index of alteration in sedimentary profiles and its palaeoenvironmental implications

The chemical index of alteration has been used widely for reconstruction of the palaeoclimate. However, the mechanisms and environmental factors controlling the chemical index of alteration of sediments are not yet fully understood. In this study, autocorrelations of the chemical index of alteration in nine sedimentary profiles, from both the land and the sea, spanning different geological times, are discussed. The sediments of these profiles have different origins (dust, fluvial or ocean sediments) and are from various climate situations and sedimentary environments. Autocorrelations of chemical index of alteration series are ubiquitously evident in all profiles. It is suggested here that autocorrelations may be caused by post-depositional changes such as persistent weathering and diagenesis. As a result, the chemical index of alteration may not reflect climatic conditions during the time of sediment deposition. This study strongly recommends the confirmation of the reliability and veracity of the chemical index of alteration before it is adopted to evaluate the weathering degree of parent rocks and to reconstruct the past climate. Significant autocorrelations in loess profiles were specifically observed, suggesting that the existing understanding of loess deposition in terms of climate conditions requires re-examination, and that previous reconstructions of rapid climate changes (for example, in centennial-millennial scales) should be treated with caution.

基于DSP的CANopen通讯协议的实现

CANopen是一种开放的应用层协议,其应用可以进一步提高系统的可靠性、通讯效率及灵活性,而且可以使产品具有很好的兼容性。本文采用CANopen通讯协议实现了CAN总线DSP系统与上位机CAN卡之间的通讯,并通过测试实验验证了信息传递的可靠性,保证了全数字网络化伺服驱动系统中对电机控制的准确性和实时性。