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221.
Shear deformation of hot pressed plagioclase–olivine aggregates was studied in the presence and absence of mineral reaction. Experiments were performed at 900 °C, 1500 MPa, and a constant shear strain rate of 5×10−5 s−1 in a solid medium apparatus. Whether the mineral reaction between plagioclase and olivine takes place or not is controlled by choosing the appropriate plagioclase composition; labradorite (An60) does not react, anorthite (An92) does. Labradorite–olivine aggregates deformed without reaction are very strong and show strain hardening throughout the experiment. Syndeformational reaction between olivine and anorthite causes a pronounced strain weakening. The reaction produces fine-grained opx–cpx–spinel aggregates, which accommodate a large fraction of the finite strain. Deformation and reaction are localised within a 0.5-mm-wide sample. Three representative samples were analysed for their fabric anisotropy R* and shape-preferred orientation α* (fabric angle with the shear plane) using the autocorrelation function (ACF). Fabric anisotropy can be calibrated to quantify strain variations across the sheared samples. In the deformed and reacted anorthite–olivine aggregate, there is a strong correlation between reaction progress and strain; regions of large shear strain correspond to regions of maximum reaction progress. Within the sample, the derived strain rate variations range up to almost one order of magnitude. 相似文献
222.
Lake-Sediment Records of Recent Environmental Change on Svalbard: Results of Diatom Analysis 总被引:7,自引:1,他引:7
Surface sediments from 23 lakes on Svalbard were analysed for diatoms. About 182 taxa were found but samples generally have a low richness, with the majority of sites dominated by benthic genera such as Fragilaria, Navicula, and Achnanthes. Centric Cyclotella species occur at only three sites. Modern relationships between diatom abundance and water chemistry and other environmental variables were explored numerically and a preliminary transfer function for pH was developed. Lakes fell into three groups on the basis of their diatom assemblages: (1) high pH, high cation, high conductivity sites characterised by Amphora libyca, (2) shallow sites with relatively high nutrient values characterised by Fragilaria species, and (3) more acid and dilute sites with high amounts of snow cover in the catchments characterised by small Achnanthes species and Navicula digitulus. Five sediment cores representing the recent past were also analysed for diatoms. Three shallow sites were dominated by Fragilaria species throughout the period represented by the cores and no shifts in inferred pH were found. At two deeper sites (Arresjøen, Birgervatnet) major assemblage shifts are found which are unrelated to independent evidence for atmospheric contamination. Early (ca. 1200 AD) changes found at both sites are possibly related to the onset of the ‘Little Ice Age’. Later changes are neither synchronous nor similar in nature and might be best explained as individual responses to the recovery from the ‘Little Ice Age’ and subsequent climatic warming. 相似文献
223.
Seraphim Alvanides 《Area》2004,36(1):41-49
Local taxation reform is back on the agenda in the light of the recent Local Government Bill. In reviewing the literature on the council tax, it is noted that researchers tend to view this from one of two perspectives: either as a fiscal policy, focusing on the tax burden, or as a housing policy, focusing on the property price valuations. Recent debate on council tax reform has gone as far as suggesting that there are regional inequities in the council tax, but what tends to be neglected remains the council tax incidence at the local scale. A research agenda is proposed here as a means of promoting geographically conscious inter-disciplinary research on local taxation. 相似文献
224.
用GPS秒信号锁定高频振荡器的方法研究 总被引:1,自引:0,他引:1
对用远距离传输的GPS秒信号锁定本地高频晶体振荡器的方法进行了探讨。介绍了高精度的时间数字转换器TDC(Time to Digital Converter)和对滤波的方法进行了探讨。为了降低成本又能够满足设计要求的精度,还考虑了双D/A转换的方法。有关的硬件系统已经通过了调试和一系列的测试和实验,在测量和控制精度方面,能达到设计的要求。此外,提出了这个系统有待解决的问题,如双D/A转换的非线性问题,Kalman滤波抗野值及继续提高精度的问题。 相似文献
225.
226.
通过实例推导幂函数对建筑物沉降进行回归分析,并且得出较为精确的结果,同时也说明在选择回归函数的时候,还会受到很多条件影响。 相似文献
227.
Data Fusion in Distributed Multi-sensor System 总被引:5,自引:0,他引:5
GUOHang YUMin 《地球空间信息科学学报》2004,7(3):214-217
This paper presents a data fusion method in distributed multi-sensor system including GPS and INS sensors“ data processing. First, a residual X^2-test strategy with the corresponding algorithm is designed.Then a coefficient matrices calculation method of the information sharing principle is derived. Finally, the federated Kalman filter is used to combine these independent, parallel, real-time data. A pseudolite (PL) simulation example is given. 相似文献
228.
229.
基于灰关联分析的GPS高程拟合加权平均函数模型权函数优选 总被引:6,自引:0,他引:6
基于灰色系统理论的灰关联分析方法,提出了权函数的优选方法,实例分析表明其具有较好的实用价值. 相似文献
230.
地图数字化位置误差的协方差函数 总被引:3,自引:1,他引:3
针对数字化地图的精度 ,利用平稳随机过程的理论来估计位置数据的不确定性 ,提出了一套计算方法 ,主要内容包括运用平稳随机过程的各态历经性 ,对任意点坐标的X、Y按距离拟合求定其协方差 ,其特点是应用了统计估计原理 ,使得到的结果更为合理和简便。 相似文献