Relative stabilities of sedimentary rearranged sterenes as calculated by molecular mechanics: a key to unravel further steroid diagenesis     

J.W. de Leeuw  H.C. Cox  M. Baas  T.M. Peakman  B. van de Graaf  J.M.A. Baas 《Organic Geochemistry》1993,20(8)

Molecular mechanics calculations of rearranged cholestenes revealed that diacholest-13(17)-enes with 10α stereochemistry are more stable than their 10β counterparts and that a partly rearranged sterene with a Δ⁸ double bond and 10β, 14β stereochemistry (compound 7) is relatively stable at thermodynamic equilibrium. The calculated data are in good agreement with sedimentary and experimental data and thus reinforce recent propositions for early-stage diagenesis of steroids.  相似文献   

A fracture-mechanical cellular automaton model of seismicity     

Jeremy R. Henderson  Ian G. Main  Calum Maclean  Michael G. Norman 《Pure and Applied Geophysics》1994,142(3-4):545-565

We present a cellular automaton model which simulates the process of seismogenesis using rules for evolution which are derived from the field of fracture mechanics, and include an interplay of positive and negative feedbacks. We describe the implementation of this model, and its analysis, in a massively parallel environment using the Connection Machine. Starting from a lattice with a fractal distribution of fracture toughnesses, theb value evolves in a way which closely mimics both the evolutions ofb value observed in the laboratory and derived from earthquake catalogues, reaching a broad and irregular maximum in the period preceding a major event, and declining rapidly during catastrophic failure. We conclude that the processes modelled are a reasonable representation of those occurring in Nature, and that the cellular automaton paradigm is a valuable way of simulating these processes on a large scale in an economical manner.  相似文献   

Analysis of magnetic anomalies due to some two-dimensional bodies using the Mellin transform     

N. L. Mohan  L. Anand Babu  N. Sunderarajan  S. V. Seshagiri Rao 《Pure and Applied Geophysics》1990,133(3):403-428

An interpretation technique using the Mellin transform is suggested for the analysis of magnetic anomalies due to some two-dimensional structures namely (i) a vertical sheet of both finite and infinite depth extent, (ii) a thick dyke and (iii) a horizontal circular cylinder. The Mellin transformed magnetic anomalies resemble gamma functions which are amenable to an easy interpretation. This procedure is illustrated with a small number of synthetic examples in each case. The practicality of the method is exemplified with the well-known vertical magnetic anomalies of Kursk (USSR) in the case of an infinite sheet model and Karimnagar magnetic anomaly (India) in the case of a horizontal circular cylinder. The results are compared with the techniques already available and found to be reliable.  相似文献   

识别多类异常的句法模式识别方法     

韩道范 《吉林大学学报(地球科学版)》1988,(3)

本文介绍识别多类异常的句法模式识别方法。它将异常值分段(或分小区间)并提取特征,根据特征值确定基元,然后将异常表示成链。用已知异常的链设计最近邻分类器,通过它对未知异常进行分类和识别。文章中仅对异常识别给出了特征值的提取,链的形成以及求不同长度链之间距离的算法。  相似文献   

西沙永兴岛附近海域沉积物的环境质量评价     

徐阁  王德鸿  王诗文  石军  袁超  韩留玉 《海洋学报》2022,44(1):137-146

根据2009-2017年9个航次对西沙永兴岛附近海域共6个站位的沉积物重金属监测结果,应用数理统计法估算了该区域7种重金属元素的背景值,分析了重金属的含量及年际变化,采用单因子标准指数法和潜在生态危害指数法对其重金属含量进行了评价.结果表明:研究区域沉积物重金属具有低背景值,均符合海洋沉积物质量第一类标准,沉积物质量为...  相似文献   

The Long‐Term Robustness and Stability of Consensus Values as Composition Location Estimators for a Typical Geochemical Test Material in the GeoPT Proficiency Testing Programme     

Peter C. Webb  Philip J. Potts  Michael Thompson  Stephen A. Wilson  Charles J. B. Gowing 《Geostandards and Geoanalytical Research》2019,43(3):397-408

Re‐issuing the same test material, its true identity unknown to participants, in two rounds of the GeoPT proficiency testing programme 18 years apart has demonstrated remarkable similarity, and therefore stability, of consensus values independently estimated for over fifty measurands in each round. A comparison of the two data sets, GeoPT5 (AMH‐1) from 1999 and GeoPT41 (ORA‐1) from 2017, shows that corresponding consensus values, rigorously derived by current procedures for complete compatibility, are for the most part statistically indistinguishable when account is taken of their associated uncertainties. Inferences that may be drawn from this exceptional agreement include: (a) the consensus estimation procedure was robust and gave consistent results; (b) overall, the balance of the contributed data was unaffected by significant changes in: (i) the populations of laboratories participating, (ii) the proportions of laboratories producing results by different techniques, (iii) the manner in which systems were calibrated, or (iv) the aspirations of laboratories to attain higher quality results over time; and (c) unsurprisingly perhaps, that the test material itself had remained stable and unchanged during that time. Additionally, a statistical comparison of the original values for AMH‐1 with consensus values derived by current procedures demonstrates that they are also effectively indistinguishable.  相似文献   

地磁台站数字与模拟观测报告一致性分析及影响因素初探     

李永华  杨冬梅  赵永芬  张素琴 《地震地磁观测与研究》2004,25(1):57-62

对2002年度地磁台站模拟观测系统和数字观测系统观测报告中的D、H、Z三分量日均值的一致性进行了分析,并对其影响因素进行了初步探讨,将有助于模拟观测系统向数字观测系统的顺利过渡。  相似文献   

Analysis of inter-gauge dependence by Kendall’s τK, upper tail dependence coefficient, and 2-copulas with application to rainfall fields   总被引：1，自引：1，他引：0  

Francesco Serinaldi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):671-688

  相似文献   

Geochronological characterization and petrogenesis of granitoids in the Ryoke belt, Southwest Japan Arc: constraints from K–Ar, Rb–Sr and Sm-Nd systematics     

Masaki Yuhara  Hiroo Kagami and  Keisuke Nagao 《Island Arc》2000,9(1):64-80

Abstract Rb–Sr and K–Ar chronological studies were carried out on granitic and metamorphic rocks in the Ina, Awaji Island and eastern Sanuki districts, Southwest Japan to investigate the timing of intrusion of the granitoids in the Ryoke belt. Intrusions of 'younger' Ryoke granitic magmas took place in the Ina district between 120 Ma and 70 Ma, and cooling began immediately after the emplacement of the youngest granitic bodies. Igneous activity in Awaji Island was initiated at 100 Ma and continued to 75 Ma. Along-arc variations of Rb–Sr whole-rock isochron ages suggest that magmatism began everywhere in the Ryoke and San-yo belts at almost the same time ( ca 120 Ma). The last magmatism took place in the eastern part of both belts. Rb–Sr and K–Ar mineral ages for the granitoids young eastwards. The age data suggest that the Ryoke belt was uplifted just after the termination of igneous activity. Initial Sr and Nd isotopic ratios for the Ryoke granitoids indicate that most were derived from magmas produced in the lower crust and/or upper mantle with uniform Sr and Nd isotopic compositions. Several granitoids, however, exhibit evidence of assimilation of Ryoke metamorphic rocks or older Precambrian crustal rocks beneath the Ryoke belt.  相似文献   

核心型钢混凝土柱的轴压比限值试验研究   总被引：2，自引：0，他引：2  

刘阳  郭子雄  张志伟 《地震工程与工程振动》2008,28(3):82-86

基于界限破坏时的内力平衡条件,推导了核心型钢混凝土柱轴压比限值的理论计算公式,计算分析了配钢率、混凝土强度等级、柱截面尺寸等因素对核心型钢混凝土柱轴压比限值的影响。进行了5个1/2比例模型柱试件的低周反复加载试验,验证了配置核心型钢对提高混凝土柱的抗震性能和轴压比限值的有效性。计算和试验结果表明,在混凝土柱中配置一定数量的核心型钢,可以有效提高轴压比限值。本文建议的方法可以较为合理地确定核心型钢混凝土柱的轴压比限值,供工程实践参考。  相似文献