DZW重力仪非线性零漂的贝叶斯估计方法

提出一种利用重力观测数据得到DZW重力仪非线性零漂的新方法。该方法核心算法为贝叶斯公式,原理为以零漂的连续性作为先验约束条件,考虑重力观测数据浮动产生的偏差,将每个采样点零漂的均值和方差作为超参数进行求解。该算法可以重复运算,随着计算次数的增加,超参数会趋向于收敛极限,从而得到最优解。经过数据验证,该算法可以精准得到非线性零漂曲线。零漂校正后重力观测值的方差为1.595 53×10^-10 μGal²,可为DZW重力仪的测量精度提供保证。     

统计同步算法原理及在局域网中的应用

针对局域网中计算机间的时间同步问题,分析了统计同步算法PCS的基本原理,介绍了局域网中网络延迟精确测定的方法,提出了利用一台时统设备实现局域网中PCS算法精度测试的方法,给出了频率漂移的修正公式,并在局域网中对算法性能进行了测试.测试结果表明,计算机时钟的漂移是影响算法精度的主要因素.经过频漂修正,PCS算法性能得到了很大的改善,同步周期较设计周期大大增加,算法同步精度在20min内优于1 ms.     

The role of damping in seismic isolation

In the current code requirements for the design of base isolation systems for buildings located at near-fault sites, the design engineer is faced with very large design displacements for the isolators. To reduce these displacements, supplementary dampers are often prescribed. These dampers reduce displacements, but at the expense of significant increases in interstorey drifts and floor accelerations in the superstructure. An elementary analysis based on a simple model of an isolated structure is used to demonstrate this dilemma. The model is linear and is based on modal analysis, but includes the modal coupling terms caused by high levels of damping in the isolation system. The equations are solved by a method that avoids complex modal analysis. Estimates of the important response quantities are obtained by the response spectrum method. It is shown that as the damping in the isolation system increases, the contribution of the modal coupling terms due to isolator damping in response to the superstructure becomes the dominant term. The isolator displacement and structural base shear may be reduced, but the floor accelerations and interstorey drift are increased. The results show that the use of supplemental dampers in seismic isolation is a misplaced effort and alternative strategies to solve the problem are suggested. Copyright © 1999 John Wiley & Sons, Ltd.     

Holocene reworking of drift‐mantled hillslopes in the Scottish Highlands

Episodic erosion and resedimentation of valley‐side glacigenic drift is evident at three sites in the Scottish Highlands in the form of buried in situ palaeosols intercalated with stacked sediment units. Radiocarbon dating of 10 palaeosols exposed in sections in debris cones suggests that gully erosion and redeposition of drift represents asynchronous debris flow and slopewash activity within the past 6⋅5 cal.kyr. Palynological and charcoal analyses confirm that reworking was unrelated to burning of vegetation, and post‐dated the main phase of anthropogenic woodland clearance at two sites, although the possibility that recent debris flow activity in Glen Docherty may have been associated with removal of woodland cover cannot be dismissed. However, the collective evidence points to discrete, extreme storm‐generated events of random occurrence as the most likely cause of episodes of enhanced slope reworking at the sites investigated. Evidence for periodic climatic deterioration is more equivocal. By implication, the accumulation of substantial debris cones in upland Britain may reflect primarily the reworking of sediment during extremely rare, intense rainstorms, essentially independent of progressive climate changes. Consequently, caution is necessary in using debris flow stratigraphies alone as a means of reconstructing former long‐term climatic changes. Copyright © 2000 John Wiley & Sons, Ltd.     

攀枝花南山台伸缩仪数字与模拟观测结果比较

利用攀枝花南山地震台伸缩模拟和数字仪器并行观测数据,用三次多项式函数进行回归计算,将三次多项式系数作为分析探讨数字和模拟两套仪器的长期漂移变化、线性变化、突跳性变化以及不规则变化等方面的差异性指标。结果表明,数字和模拟仪器的观测结果在长期漂移变化、线性变化方面不存在显著差异;突跳性变化以及不规则变化方面存在一些差异性。数字化与模拟观测结果在突跳性变化以及不规则变化方面差异的原因是数据采集率存在差异所致,数字化数据采集率高意味着所包含的信息更为丰富。模拟观测结果的变化形态与三次多项式函数曲线形态要接近些,相对来讲表现出模拟观测数据变化的单调性,这可能是仅仅读取整点时数据的局限性所致。     

Uranium/thorium dating of ferricretes from mid- to late pleistocene glacial sediments,western Tasmania,Australia

The uranium/thorium (U/Th) dating method was applied to pedogenic/diagenic ferricretes developed within glacial drifts from the northern West Coast Ranges of Tasmania. The dates derived from the method are, by definition, minima for the sediments, with the ferricretes being secondary mineral deposits which appear in the form of bands, horizons or nodules comprised of indurated masses of iron oxy(hydr)oxides developed post-depositionally within the host sediment or soil. The absence of such deposits in well-identified drift sediments of the last glaciation suggests the development of ferricrete horizons in glacial drifts occurred during earlier interstadials and interglacials. This has been confirmed by the uranium/thorium dating of ferricrete bands within glacigenic sediments obtained from three drill cores from the Boco Valley. The ages derived were found to be consistent with estimates for the timing of glaciation derived from palaeomagnetic analyses, radiocarbon dating and relative dating techniques. The results show that the uranium/thorium method can be used to successfully date ferricretes obtained from within glacial sediments of ages <350000 yr and provides valuable information regarding the minimum age of the host sediment. © 1997 John Wiley & Sons, Ltd.     

WIND ENERGY VARIATIONS IN THE SOUTHWESTERN KALAHARI DESERT AND IMPLICATIONS FOR LINEAR DUNEFIELD ACTIVITY

The southwestern Kalahari linear dunefield, which displays marked morphological variability, possesses a partial but temporally and spatially variable vegetation cover and has frequently been described as a palaeodunefield. Palaeo status has been ascribed on the basis of several criteria including the presence of vegetation, but also because dunes are thought to be out of alignment with modern resultant potential sand-moving wind directions and because present-day wind energy is regarded as low. For the period 1960–1992, wind data from eight dunefield meteorological stations are analysed in detail to examine these assertions. Potential sand transport directions, including spatial and temporal variations, and potential drift directions for the windiest three month periods, are calculated and explained. It is concluded that the present-day potential sand transport environment is markedly variable from year to year and from place to place. While periods of low sand transport energy do occur, it is also noted that the 1980s possessed considerable potential for sand transport in the dunefield. Directional variability is also relatively high, perhaps exceeding that under which linear dunes can be expected to form. Because linear dune aeolian activity has a number of states, however, the present-day wind environment may allow dune surface aeolian activity to occur which does not alter the overall pattern of the dunes.     

塔克拉玛干沙漠高大复合纵向沙垄区路面沙害情势的变化特征

为了探讨机械防护体系人工防护工作停止后,公路路面沙害的形成和发育过程,分别于2003年和2007年对塔中地区一段井场路的路面沙害进行了实地测量和卫片室内量测,研究发现在塔克拉玛干沙漠公路复合型纵向沙垄区段,公路芦苇机械防沙体系极度衰竭后,路面沙害情势变化呈现一定的规律性:(1)2003年-2007年四年间公路沙害发展迅速,路面沙害程度进一步加重.路面沙害路段长度以年均2%的比例增加,沙害路段数也快速增加;路面沙害面积以每年平均10%的面积比例快速发展;沙丘前移压埋类型发展速度明显高于积沙类型.(2)沙垄区路面沙害发生频率和路面沙害程度的发展速率要远高于垄间区,在沙垄区次级地貌单元中,垄顶>背风坡>迎风坡;各地貌部位的沙丘前移压埋类型发展速率高于积沙类型.(3)路风夹角在83°～89°之间的路段沙害演化速率最大,其他小夹角沙害演化规律不明显;路面沙害强度的发展速率与路风夹角的关系不明显.     

钢筋混凝土框架结构层间位移角与构件变形关系研究

层间位移角已作为检验建筑结构抗震性能的主要指标之一而被广泛应用。为实现该指标在钢筋混凝土框架结构基于位移的抗震设计中的应用,研究了层间位移角与构件变形之间的关系。首先,采用对部分子结构的弹性理论分析得到了弹性阶段梁变形对层间位移角贡献比例的计算公式。接着,采用对15层钢筋混凝土框架整体结构的非线性地震反应计算结果的统计分析得到了在塑性阶段梁变形对层间位移角的贡献比例回归计算公式。所建立的计算公式反映了梁与柱的相对刚度和强度比例、层闽塑性变形程度的影响。最后,应用该方法进行了一算例分析,计算结果和试验结果比较一致。利用本文提出的计算方法可以方便地把对框架结构的层间位移需求转变为对梁、柱构件的变形要求。     

非洲磁异常对地磁场结构及其长期变化的控制作用

地球非偶极磁场在主磁场结构及其长期变化中起着重要作用.非偶极磁场主要表现为行星尺度磁异常,它们是南大西洋磁异常、非洲磁异常、欧亚大陆磁异常、澳洲磁异常和北美磁异常.在这5块磁异常中,非洲磁异常对磁赤道的形状和位置以及全球长期变化特征有极大的影响.非洲磁异常的重要性主要表现在3方面：第一,由于异常区位于赤道这一特殊的地理位置,所以它极大地影响磁赤道的形状和位置.相对于偶极场的地磁赤道而言,异常区所在的中北非洲和中大西洋地区的磁赤道向北移动,最大移动量可达约15°.第二,非洲磁异常的快速西漂对全球长期变化的分布起着决定性作用,它在该异常区西边的中美洲形成了全球最主要的长期变化区,在1900~2005年期间,最大年变率Z_max超过200 nT/a.第三,非洲负磁异常区与其南面的南大西洋正磁异常区相结合,〖HJ〗它们的变化使西半球地磁场强度大大减弱,也使全球磁场发生显著畸变.这两块磁异常与深部的反极性斑区有着成因联系.