低频时码信号正交解调技术研究

采用正交叠加和正交采样技术，提出了更大程度上数字化的低频时码信号正交解调的设计方案。同时，分析了这种解调方法的虚假抑制和抗镜像干扰能力。分析表明所论述的解调技术易于实现数字化，且成本低廉，具有一定的实用价值。     

Getting the right age? Testing luminescence dating of both quartz and feldspars against independent age controls

When luminescence dating was being developed much scientific effort was invested in showing it could achieve the correct ages, but this is now not routinely carried out for established protocols. This paper focussed on known age deposits from two case studies to explore whether correct ages were achieved. Case study 1 used the Storegga tsunami deposit dated to 8.2 ka sampled both horizontally and vertically and measured with OSL, IRSL and pIRIR. All results, for both quartz and feldspars, returned the correct age for the horizontal sample. Results from the vertical sample were more problematic with issues attributed to ongoing feldspar contamination of quartz and to beta heterogeneity. To agree with the independent age control single aliquot results required combination of >400 palaeodose replicates and in the case of IRSL the use of minimum age models. Measurements of feldspars at the single grain level using pIRIR measurements showed much improvement. Case study 2 used a barchan dune on the Tibet Plateau, China known to have been in position ∼10 years. Both quartz and feldspars returned young ages close to the true age, but the feldspar ages with brighter luminescence signal were more accurate once the luminescence signal to background ratio was optimised. On the basis of this study we advise against sampling vertically. We also recommend measuring feldspars with single grain pIRIR where possible, measuring >150 palaeodose replicates per sample and choosing feldspars rather than quartz for very young samples.     

常见稀有气体采样容器研究进展及意义

稀有气体是地学研究的重要手段之一,在研究成矿流体来源、壳幔相互作用过程中具有重要的研究意义,其组成及同位素比值是研究天体和地质体来源、成岩机理及各种地质和物理化学过程的关键,可作为地球化学示踪剂。如何有效地在大气圈、水圈和岩石圈进行稀有气体同位素样品的提取,是气体同位素研究急需解决的基础科学问题,所以气体采样容器和取样技术显得尤为重要。本文在文献调研的基础上,对常见的采样容器的优缺点进行对比,并总结了不同采样容器对稀有气体取样的优劣性。常见的气体采集容器包括不锈钢瓶、铜管、玻璃瓶、气体采样袋、注射器等,而稀有气体的采集容器常为不锈钢瓶和铜管等;通过对比表明不锈钢瓶具有耐高温、耐高压、抗强腐蚀、不易燃、不易爆等特点和优越性,在气体样品采集和运输过程中稳定性最好,实验效果也最好;铜管采样效果和密封性好,但操作较为复杂;玻璃采样容器效果次之;石英玻璃瓶虽然操作简便,但是运输保存不便;气体采样袋和注射器的采集和运输储存效果较差。因此建议稀有气体样品采集使用不锈钢瓶和铜管以及钠钙材质的玻璃瓶,不建议将石英材质玻璃容器以及注射器和气袋作为稀有气体的采样工具。该工作可为气体地球化学的研究提供新的参考。     

Generalized Hough transform for the stress inversion of calcite twin data

Since the mechanical twinning along calcite e-planes has a critical resolved shear stress, not only principal stress axes but also differential stress can be determined from the orientations of twin lamellae. Based on the five-dimensional stress space that fulfills the principle of coordinate invariance, it is shown in this article that the inversion of twin and untwin data is comparable with fitting a spherical cap to data points on a unit sphere in the space. The principal stress orientations and stress ratio are indicated by the center of the cap, whereas differential stress is denoted by the size of the cap. Based on this geometrical interpretation, the generalized Hough transform was applied to the inversion of the data in this study. The new method is demonstrated to be robust to sampling bias, variability in the critical resolved shear stress. The determination of differential stress was difficult when the differential stress to be detected was ∼10 times larger than the critical resolved shear stress. Stresses were separated by the method from heterogeneous data successfully as long as the spherical caps corresponding to the stresses to be detected had no or a small intersection.     

传感器信号调制脉冲序列抽样频率的确定

通过对传感器输出信号波形有无振荡进行分类 ,依据传感器响应时间的定义 ,分别找到一阶、二阶及理想动态传感器的频带上限与动态响应时间两者间的关系式 ;提出了传感器“受激系数”的概念 ,推导出输出信号波形有无振荡两种传感器之间的比例关系。并通过一个数值例子 ,说明所推导出关系式的应用。     

国产海底地震仪的时间记录与原始数据精细校正

海底地震仪(OBS)的时间记录对数据处理是至关重要的.实践发现,部分国产便携式OBS的数据记录存在较大的内部时间误差,并且实测地震剖面异常的同相轴"断阶"、"倾斜"现象时有发生.我们通过自激自收试验,对这些异常现象进行了验证,确认其来源于OBS数据文件内部时间漂移,以及数据处理程序存在的缺陷.统计表明,A、B型OBS内部时间漂移量在250Hz的预设采样率下为0～40ms,L、S型OBS在100Hz下为0～90ms.这个量级的时间漂移,会对OBS数据处理、计算模拟产生影响.进一步,我们采用计算实际采样间隔、调整采样间隔、数据重采样的方法,对这种误差进行校正,并且改进了相关的OBS数据处理程序.本文的研究加深了对OBS数据时间记录误差的认识,得到了OBS数据文件内部时间漂移的分布规律,使得中等及较大程度的内部时间漂移的精细校正得到重视,进而完善了OBS数据处理步骤和流程,对OBS数据的有效利用进行了重要补充,为国产OBS的广泛使用、仪器研发提供了重要参考.     

Sampling efficiency in Monte Carlo based uncertainty propagation strategies: Application in seawater intrusion simulations

The implementation of Monte Carlo simulations (MCSs) for the propagation of uncertainty in real-world seawater intrusion (SWI) numerical models often becomes computationally prohibitive due to the large number of deterministic solves needed to achieve an acceptable level of accuracy. Previous studies have mostly relied on parallelization and grid computing to decrease the computational time of MCSs. However, another approach which has received less attention in the literature is to decrease the number of deterministic simulations by using more efficient sampling strategies. Sampling efficiency is a measure of the optimality of a sampling strategy. A more efficient sampling strategy requires fewer simulations and less computational time to reach a certain level of accuracy. The efficiency of a sampling strategy is highly related to its space-filling characteristics.This paper illustrates that the use of optimized Latin hypercube sampling (OLHS) strategies instead of the widely employed simple random sampling (SRS) and Latin hypercube sampling (LHS) strategies, can significantly improve sampling efficiency and hence decrease the simulation time of MCSs. Nine OLHS strategies are evaluated including: improved Latin hypercube sampling (IHS); optimum Latin hypercube (OLH) sampling; genetic optimum Latin hypercube (GOLH) sampling; three sampling strategies based on the enhanced stochastic evolutionary (ESE) algorithm namely φ_p-ESE which employs the φ_p space-filling criterion, CLD-ESE which utilizes the centered L₂-discrepancy (CLD) space-filling criterion, and SLD-ESE which uses the star L₂-discrepancy (SLD) space-filling criterion; and three sampling strategies based on the simulated annealing (SA) algorithm namely φ_p-SA which employs the φ_p criterion, CLD-SA which uses the CLD criterion, and SLD-SA which utilizes the SLD criterion. The study applies SRS, LHS and the nine OLHS strategies to MCSs of two synthetic test cases of SWI. The two test cases are the Henry problem and a two-dimensional radial representation of SWI in a circular island. The comparison demonstrates that the CLD-ESE strategy is the most efficient among the evaluated strategies. This paper also demonstrates how the space-filling characteristics of different OLHS designs change with variations in the input arguments of their optimization algorithms.     

关于全国地震重点监视防御区制度实施现状、成效之调查、设计的说明

为评估全国地震重点监视防御区制度的实施现状、成效,课题组对相关问题进行了定性和定量研究,定量研究以系列问卷调查为主,包括政府、社区和公众问卷等。本文重点说明了系列问卷调查的设计、抽样以及回收情况,并对问卷调查发现的问题做了简单介绍。     

Recent Developments in Marine Diamond Mining

The marine diamond deposits of southern Africa owe their existence to fluvial transport down the Orange River to the South Atlantic. On the coast, they were moved, sorted and concentrated by high-energy sea and wind conditions to create a veneer of diamondiferous gravels on the sea floor. Large scale, offshore production by De Beers Marine commenced in 1989 in Namibian waters. The company now acts as a contractor for Namdeb, a corporation owned jointly with the Namibian governments. Some junior public companies also produce diamonds by large-scale mechanized means and conduct extensive exploration programs. Two important developments have occurred recently. Firstly, equipment for the recovery of diamonds from the seabed has been successfully borrowed from other industries. Large drills from onshore civil engineering have been modified for marine sampling and mining. Remotely controlled, seabed-mounted, excavational systems have assumed a major role. The new systems allow both evaluation sampling and subsequent mining to be undertaken by similar or the same equipment, making the results compatible. They permit highly selective extraction and enhanced recovery of the gravels from irregular bedrock in water approaching 200 m deep. But none is universally applicable offshore, each being the preferred system under different conditions. Secondly, the total output of sea diamonds from Namibian waters has increased to 0.8 million carats annually and now exceeds that from all the country's onshore sources. An industry has become established. Corporate and individual perseverence, government encouragement, new technology, shareholders' risk finance, and De Beers' diamond marketing have all played a role in the success. Future diamond production may increase as companies meet the challenge of working lower grade, higher volume deposits, which will require new approaches to the mining process. With a decrease in the physical risk of marine mining, the most variable inputs in operational planning and production forecasting are recovered grade and throughout rate, together with equipment availability. The importance of reliable grade estimation from sufficient sampling density is widely perceived, but the greatest performance risk can involve the predicted excavation rate and ''mineability'' of the seabed sediments. Published reserve statements would benefit from a requirement to specify the planned mining method, the consequent cutoff grade to be employed, and whether or not test mining has been undertaken.     

Book review

The Control of the Sea‐bed: A New International Issue by Evan Luard. Taplinger Publishing Co., Inc., New York, 1974. 309 pp. $14.95.