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31.
Large instrumental mass fractionation (IMF) may occur during measurements of oxygen isotope ratios by SIMS. Part of this fractionation depends on crystal structure and mineral composition. In order to improve the accuracy of SIMS measurements, we gathered 6 commonly used garnet standards and prepared 6 others to adequately cover the composition range Alm0-73, Prp0-99, Grs0-20. Electron microprobe analyses were performed at UBP-Clermont to check the chemical homogeneity of these standards. Oxygen isotope compositions were determined by laser fluorination and mass spectrometry at UW-Madison. Ten SIMS sessions and 336 δ18O measurements at CRPG-Nancy, on a Cameca IMS1270 instrument, demonstrate that the standards are homogeneous with external reproducibility of 0.3‰ (1σ). In terms of δ18O, SIMS measurements indicate that, during a single session, IMF can vary up to 6.3‰ from one garnet standard to another. In most of the sessions, IMF can be correlated with the grossular content. However, for a satisfactory correction scheme, we suggest the combination of the 3 main components (Ca, Fe, Mg). This is done using a simple least square calculation routine. The correction coefficients determined for each session can be used to calculate the IMF and correct the measured isotopic ratio of a garnet of known chemical composition. This way, we were able to reproduce the δ18O values of most of the Fe-Mg-Ca garnet standards within ± 0.6‰. Interestingly, the use of only 3 end-member standards (AlmCMG, PrpMM, GrsSE) plus a standard of intermediate composition (e.g. UWG-2) is sufficient to reproduce δ18O within the same precision. Thus, linear interpolation among end-member standards is satisfactory in the case of the garnet solid-solutions. Two studies carried out on zoned garnets from the Alps and the Pyrenees indicate that matrix effects become significant when variations in grossular contents are important (> 10%). In order to obtain reliable isotope ratio measurements on Fe-Mg-Ca garnets using a SIMS, we suggest a correction scheme using at least 3 reliable end-member standards plus a standard of intermediate composition (a garnet standard closest to the average composition of the analysed garnet). This allows cross-checking and incorporates a correction based on the variations in composition of zoned crystals. 相似文献
32.
奇异值分解及其在北美陆地气温与我国降水遥相关中的应用 总被引:11,自引:7,他引:11
从矩阵理论的奇异值分解(SVD)定理出发,详细地论述了有关数学原理及计算方法,作为SVD的一个应用,计算了北美陆地气温场与我国夏季降水场的奇异值解,并对分离出的主相关区的可靠性及预报蕴示进行了讨论,结果表明:北美陆地气温与我国夏季降不存在明显的线性相关,尤其是冬季、陆地气温场以降江中下游及西北地区夏季降不有很好的指示意义 相似文献
33.
边坡工程加固需求度评价及其应用 总被引:8,自引:6,他引:8
稳定程度不足的边坡通常都需要进行加固。但在加固系统设计时工程师们必须搞清边坡的哪些部位应进行重点加固 ,哪些部位只需要一般加固 ,甚至不需要加固 ,以便合理地布置加固措施。在工程地质力学综合集成方法论 (EGMS)的基础上 ,作者提出了边坡工程加固需求度 (DRD)的概念及其应用方法。 相似文献
34.
针对利用地震道进行相对波阻抗反演中遇到的横向连续性难以保持、初始子波容错度差以及随机噪声干扰影响反演结果等问题,提出了一种基于矩阵Toeplitz稀疏分解的相对波阻抗反演方法.该方法将地震数据剖面的Toeplitz稀疏分解问题分解为两个子反演问题,其一以Toeplitz子波矩阵元素为待反演的参数,用Fused Lasso方法求解,可保证子波具有紧支集且是光滑的;其二以稀疏反射系数矩阵元素为待反演参数,用基于回溯的快速萎缩阈值迭代算法求解,大大降低了目标函数中参数选择的难度.通过交替迭代求解上述两个子反演问题可将地震数据剖面因式分解为一个Toeplitz子波矩阵和一个稀疏反射系数矩阵;然后由反射系数矩阵递推反演可以得到高分辨率的相对波阻抗剖面;利用测井资料加入低频分量后,也可得到高分辨率的绝对波阻抗剖面.Marmousi2模型生成的合成记录算例和实际地震资料算例均表明:本文方法可以从带限地震数据中有效地反演相对波阻抗,反演结果分辨率高并且能够很好地保持地震数据的横向连续性;即使在初始估计子波存在误差和地震数据被随机噪声污染的情况下也能取得较好的效果. 相似文献
35.
The present study assesses the uncertainty of flow and radionuclide transport in the unsaturated zone at Yucca Mountain using a Monte Carlo method. Matrix permeability, porosity, and sorption coefficient are considered random. Different from previous studies that assume distributions of the parameters, the distributions are determined in this study by applying comprehensive transformations and rigorous statistics to on-site measurements of the parameters. The distribution of permeability is further adjusted based on model calibration results. Correlation between matrix permeability and porosity is incorporated using the Latin Hypercube Sampling method. After conducting 200 Monte Carlo simulations of three-dimensional unsaturated flow and radionuclide transport for conservative and reactive tracers, the mean, variances, and 5th, 50th, and 95th percentiles for quantities of interest (e.g., matrix liquid saturation and water potential) are evaluated. The mean and 50th percentile are used as the mean predictions, and their associated predictive uncertainties are measured by the variances and the 5th and 95th percentiles (also known as uncertainty bounds). The mean predictions of matrix liquid saturation and water potential are in reasonable agreement with corresponding measurements. The uncertainty bounds include a large portion of the measurements, suggesting that the data variability can be partially explained by parameter uncertainty. The study illustrates propagation of predictive uncertainty of percolation flux, increasing downward from repository horizon to water table. Statistics from the breakthrough curves indicate that transport of the reactive tracer is delayed significantly by the sorption process, and prediction on the reactive tracer is of greater uncertainty than on the conservative tracer because randomness in the sorption coefficient increases the prediction uncertainty. Uncertainty in radionuclide transport is related to uncertainty in the percolation flux, suggesting that reducing the former entails reduction in the latter. 相似文献
36.
许志文 《华东地质学院学报》2000,23(1):87-89
介绍了对稀疏矩阵进行压缩存储时,稀疏矩阵相乘运算的基本思想和算法.在此基础上,探讨了避免矩阵中零元素相乘的无效操作,奠定了该算法的矩阵变换基础. 相似文献
37.
Mahmoud F. Maghrebi Amirreza Kavousizadeh Reza Faghfour Maghrebi Arash Ahmadi 《水文研究》2017,31(22):3859-3870
For various hydrological applications such as flood control projects, a knowledge of stage–discharge relationship is of particular interest to river engineers. Stage–discharge curves in compound channels cannot be easily predicted in comparison with single channels due to their 3D characteristics of flow. In this paper, the concept of cross‐sectional isovel contours is used for estimation of stage–discharge curves in compound channels. The multivariate Newton's method is applied to the difference between the observed and estimated data to optimize the exponent values of the governing parameters. The accuracy of the proposed model is tested successfully against available experimental results, which are taken from the Flood Channel Facility (FCF) laboratory. Then the results are compared with the Single and Divided Channel Methods (SCM and DCM, respectively), the Weighted Divided Channel Method (WDCM), the exchange discharge method (EDM), and the Coherence Method (COHM). The average values of mean absolute percentage error (MAPE) and normalized root mean square error (NRMSE) in discharge estimation based on each referenced section at any level for 6 sections of the experimental cases are within 3.1% and 0.023, respectively. The biggest advantage of the proposed method is its inherent simplicity, which does not need any calibration. 相似文献
38.
Hyperspectral Unmixing (HU) has received increasing attention in the past decades due to its ability of unveiling information latent in hyperspectral data. Unfortunately, most existing methods fail to take advantage of the spatial information in data. To overcome this limitation, we propose a Structured Sparse regularized Nonnegative Matrix Factorization (SS-NMF) method based on the following two aspects. First, we incorporate a graph Laplacian to encode the manifold structures embedded in the hyperspectral data space. In this way, the highly similar neighboring pixels can be grouped together. Second, the lasso penalty is employed in SS-NMF for the fact that pixels in the same manifold structure are sparsely mixed by a common set of relevant bases. These two factors act as a new structured sparse constraint. With this constraint, our method can learn a compact space, where highly similar pixels are grouped to share correlated sparse representations. Experiments on real hyperspectral data sets with different noise levels demonstrate that our method outperforms the state-of-the-art methods significantly. 相似文献
39.
40.