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51.
A variety of mathematical expressions that describe changes over time (t) in the extent of amino acid racemisation (AAR, expressed as the ratio of d- to l-amino acid isomers or epimers) have been used in Quaternary geochronology. The integrated rate equation was first used to estimate fossil age from D/L but its geochronological utility is disadvantaged by uncertainties regarding the conformity of AAR in fossil protein to apparent reversible first-order kinetics for the entire reaction history. ‘Non-linear’ models have subsequently been used to relate D/L to t. The logarithmic equation successfully applied to Atlantic Coastal Plain research has not achieved widespread application, perhaps due to the regional calibration required if sensitivity to temperature is to be modelled, or the difficulties encountered when extending the model to include fossils with D/L<0.1. Success producing a linear correlation between D/L transformed with a power function and t has seen this approach emerge as one of the most commonly applied in AAR geochronology in recent years. Like parabola curve fitting, which has been applied to trends in D/L versus t in a variety of fossils and geographic settings, power transformations may not be suitable for geochronological modelling during the latter stages of amino acid diagenesis. Several studies have demonstrated the utility of simple and contingent linear equations for relating D/L to t. Future research should aim to reduce reliance on independent calibration and explore the geochronological benefits of AAR in pools other than the total hydrolysable amino acids. 相似文献
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A six-step practical approach to semivariogram modeling 总被引:3,自引:2,他引:3
Geostatistical prediction and simulation are being increasingly used in the earth sciences and engineering to address the imperfect knowledge of attributes that fluctuate over large areas or volumes—pollutant concentration, electromagnetic fields, porosity, thickness of a geological formation. Central to the application of such techniques is the need to know the spatial continuity, knowledge that is commonly condensed in the form of covariance or semivariogram models. Their preparation is subdivided here into the following steps: (1) Data editing, (2) Exploratory data analysis, (3) Semivariogram estimation, (4) Directional investigation, (5) Simple modeling, (6) Nested modeling. I illustrate these stages practically with a real data set from a geophysical survey from Elk County, Kansas, USA. The applicability of the approach is not limited by the physical nature of the attribute of interest. 相似文献
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研究数字化核探测器输出脉冲信号的幅度提取问题。根据闪烁探测器的电路特性,推导了其脉冲信号理想曲线方程。综合利用三和值法、最小二乘法、试探法等方法,设计了该理想曲线拟合算法。由脉冲信号采样点数据,通过曲线拟合,计算出曲线的极大值,该值即为闪烁探测器输出脉冲信号的幅度。正反演数据结果对比表明,采用曲线拟合算法提取闪烁探测器输出脉冲信号幅度,其方案可行,计算结果更准确。相较于数字滤波和数字脉冲成形方法提取核探测器输出脉冲幅度,该算法更简单,对仪器的硬件处理速度要求更低。该方法开辟了核探测器脉冲幅度提取的新途径。 相似文献
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圆柱状构件广泛存在于古建筑仿真中,为了提高古建筑深度图像圆柱拟合的精度,针对古建筑仿真3维建模的特点,提出基于高斯图获取圆柱拟合参数初始值,然后利用圆柱距离函数参数化法进行非线性最小二乘拟合的圆柱拟合方法。实验证明,该方法不仅具有较高的精度,而且拟合结果稳定可靠。 相似文献
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ZHANG Yi YAN Li 《地球空间信息科学学报》2007,10(4):276-281
A scheme for an automatic road surface modeling from a noisy point cloud is presented. The normal vectors of the point cloud are estimated by distance-weighted fitting of local plane. Then, an automati... 相似文献
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针对三维激光测高拟合问题,本文采用BP神经网络进行拟合,该方法可以有效地消除或减弱数据中的系统误差影响,提高计算精度。实际算例证明,在数据无粗差情况下,BP神经网络的内符合与外符合精度优于传统的二次曲面拟合的精度。 相似文献
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