A micromechanical finite element model for linear and damage‐coupled viscoelastic behaviour of asphalt mixture

This study presents a finite element (FE) micromechanical modelling approach for the simulation of linear and damage‐coupled viscoelastic behaviour of asphalt mixture. Asphalt mixture is a composite material of graded aggregates bound with mastic (asphalt and fine aggregates). The microstructural model of asphalt mixture incorporates an equivalent lattice network structure whereby intergranular load transfer is simulated through an effective asphalt mastic zone. The finite element model integrates the ABAQUS user material subroutine with continuum elements for the effective asphalt mastic and rigid body elements for each aggregate. A unified approach is proposed using Schapery non‐linear viscoelastic model for the rate‐independent and rate‐dependent damage behaviour. A finite element incremental algorithm with a recursive relationship for three‐dimensional (3D) linear and damage‐coupled viscoelastic behaviour is developed. This algorithm is used in a 3D user‐defined material model for the asphalt mastic to predict global linear and damage‐coupled viscoelastic behaviour of asphalt mixture. For linear viscoelastic study, the creep stiffnesses of mastic and asphalt mixture at different temperatures are measured in laboratory. A regression‐fitting method is employed to calibrate generalized Maxwell models with Prony series and generate master stiffness curves for mastic and asphalt mixture. A computational model is developed with image analysis of sectioned surface of a test specimen. The viscoelastic prediction of mixture creep stiffness with the calibrated mastic material parameters is compared with mixture master stiffness curve over a reduced time period. In regard to damage‐coupled viscoelastic behaviour, cyclic loading responses of linear and rate‐independent damage‐coupled viscoelastic materials are compared. Effects of particular microstructure parameters on the rate‐independent damage‐coupled viscoelastic behaviour are also investigated with finite element simulations of asphalt numerical samples. Further study describes loading rate effects on the asphalt viscoelastic properties and rate‐dependent damage behaviour. Copyright © 2006 John Wiley & Sons, Ltd.     

舟山国家石油储备基地堆载预压加固效果分析

介绍了舟山国家石油储备基地试验区软基堆载预压大型现场试验结果,根据现场试验测得的数据,分析了软土地基堆载预压下沉降变化规律、分层沉降变化规律、深层土体位移变化规律、超静孔隙水压力变化规律,进一步探讨了根据应力和应变分析得到的地基固结性状,其中通过应变分析得到适用于储备基地的沉降经验系数m。结果表明,打设塑料排水板结合堆载预压处理软弱地基具有良好的效果。     

基于神经网络的平底结构砰击压力预报

对利用神经网络预报平底结构入水砰击压力的方法进行了探讨。首先利用仿真软件计算各种情况下平底结构入水所产生的砰击压力，以此形成训练神经网络的数据集。其次利用数据集对三层反馈式网络进行了训练，讨论了不同隐含层节点数对该非线性系统的拟合能力，并且对梯度下降法、动量修正法和基于优化的LM算法的有效性和精度进行了比较，最后得出了适合平底结构入水砰击系统的网络结构。     

GPS signal acquisition using the repeatability of successive code phase measurements

This paper introduces a new method for GPS signal acquisition, which is based on the repeatability of successive code phase measurements and the M-of-N search algorithm. The performance of the proposed method in terms of probability of signal detection is similar to that of traditional methods, except that the calculation of the probability of detection does not rely on the noise distribution or the Carrier-to-Noise ratio (C/N₀). The code phase repeatability-based method is presented along with equations for probability of detection and probability of false detection. If the distribution of the noise is known, it also provides an estimate of the C/N₀. The proposed method is illustrated for coherent and non-coherent acquisition and C/N₀ estimation.     

生物炭对磷石膏中磷的固化作用

磷石膏中的磷在雨水淋滤作用下浸出,将污染堆场附近水体。本研究采用生物炭固化磷石膏中的磷,以减少其对周遭水体的污染。主要通过模拟固化实验和对照浸出实验,分析生物炭用量、反应时间和温度、初始pH值对固化效果的影响,通过XRD、SEM-EDS分析固化后的生成物。实验结果显示,在生物炭用量为25 mg时,单位固化量达到最大值13.20 mg/g;在反应温度T=293 K、初始pH=7条件下,反应平衡时间72 h时浸出液的磷平衡浓度C_e= 1.40 mg/L;温度提升有助于提高生物炭的固化效果,当T=308 K时,浸出液的磷平衡浓度C_e=0.167 mg/L;碱性条件有利于固化反应持续进行,在pH=11条件下,浸出液的磷平衡浓度C_e=0.153 mg/L。实验结果表明生物炭对磷石膏中的磷具有明显的固化效果。磷石膏中的二水硫酸钙溶解后,Ca²⁺与表面带负电的生物炭结合,在生物炭显微结构的凹陷处,化学吸附溶液中的磷酸根生成了絮状、团簇状的羟基磷灰石(HAP)沉淀,从而使浸出磷得到有效控制。     

冰芯记录中末次间冰期-冰期旋回气候突变事件的研究进展

冰芯记录中的气候变化是古气候研究中的重要组成部分. 极地、中低纬度和热带地区的冰芯记录表明, 在冰期间冰期旋回大尺度气候变化背景下, 全球经历了一系列数百年至千年时间尺度的快速气候突变事件, 诸如末次间冰期的干冷事件、末次冰期的DansgaardOeschger事件、 Heinrich事件和Younger Dryas事件等, 虽然这些穿插在冰阶中的暖湿气候事件、间冰阶中的干冷气候事件的成因、机制和影响范围还存在明显的不确定性. 主要介绍不同区域冰芯记录中末次间冰期冰期旋回这些气候突变事件发生的时间、过程和机制等的研究进展.     

云南矿业支柱产业建设的重点、难点及对策研究

云南矿业发展现状尤其是磷化工和有色金属等优势资源的调研和分析结果表明，矿业已成为云南工业的主体产业群体，影响云南矿业发展的难点主要是企业规模偏小，产品结构不合理，企业整体经济效益下降，国有企业困难面大，地质勘探投入少，矿山建设落后等，并据此讨论了矿业作为云南省支柱产业发展的思路和重点，提出相应的对策和建议。     

慕士塔格冰芯钻孔温度测量结果

2002年8月对慕士塔格冰川累积区海拔6300m左右的两根冰芯钻孔(其中—根达到冰川底部基岩)进行了温度测量，揭示了该处冰川的温度分布特征．结果表明：慕士塔格冰芯的冰温是目前中低纬地区山地冰川中最低的，达-21．79℃，该最低温度出现的位置在35m以下；冰床底部的温度为-20．76℃，也远低于其它山地冰川的冰床温度，极低的温度对成冰过程有重要影响，并有利于获得可靠的冰芯记录。     

混合岩中斜长石的交代净边结构和倒转双晶研究——以大别罗田黄土岭长英片麻岩为例

湖北罗田黄土岭长英片麻岩是与紫苏石榴黑云片麻岩共生的浅色片麻岩，成分上近于Ａ型花岗岩．受到浅混合岩化，钾交代现象显著．在斜长石与钾长石新成体接触处有清楚的交代净边结构，背散射电子探针分析表明，净边成分为钠长石（Ａｂ８９～９７）．在净边结构上，发现叠加倒转双晶．净边结构产生于长英片麻岩部分熔融的高温条件下，与整个大别地体隆升过程和Ａ型花岗岩的生成有成因联系