湖北省凤凰关地区前寒武纪大别杂岩内地壳冷却速率的估算

本文提出了一个封闭体系的扩散数学模型,用来描述由于化学扩散而导致球状晶体发生的均匀化作用;结合扩散系数和一些岩石物化知识,就可能模拟待定岩石的温度—时间(T-t)史。作者根据斜长石的相图特征并应用该模型,提出了如何确定斜长石扩散初始条件的方法,描述了湖北省凤凰关地区混合岩浅色体中斜长石的均匀化作用;经计算表明:地壳冷却速率(s)为0.75℃/Ma;所提出的数学模型普遍适用于变质岩的冷却问题。     

豫北地区气温、降水变化的时空分布特征

利用中国国家级地面气象站均一化数据集中1971—2010年豫北地区28个测站的温度、降水资料,基于GIS技术对该地区温度和降水变化的时空分布特征进行研究。结果表明:豫北地区气温整体呈升高的趋势,其中冬春季节升温明显。气温变率空间分布表现为北中部增温明显,东部和西部增温幅度较小。降水变化各季节差异较大,春季降水整体呈现增加趋势,其他季节各地降水增减不一;空间变化分布特征为太行山沿线西部山区降水减少趋势明显,东部地区降水略有增加趋势。从整体变化情况来看,豫北地区的气候变化区域间差异加大,局地性变化趋向不稳定。文中用温度与降水的趋势比来分析豫北地区的干旱化发生趋势,结果发现太行山沿线干旱化趋势明显,沿黄河区域干旱化趋势较低,太行山脉和黄河是导致豫北地区气候变化区域性分布的主要地形因子。     

新制度经济学视角下高校周边商业街分异研究——以湖南师范大学和湖南大学本部校区为例

高校扩招带来了其周边商业街的蓬勃发展,已有研究从不同角度对其展开论述,新制度经济学的发展与完善为理解高校周边商业街的分异提供了新的可能性。以湖南师范大学和湖南大学本部校区的4条商业街为例,从新制度经济学的角度解释高校周边商业街分异现象,以期丰富新制度经济学视角微观实证研究的内容。实地调研发现,制度对高校周边商业街的分异具有重要作用,正式制度对不同主体的约束作用不同,进而形成一系列非正式制度,从而共同维系了商业街的发展。最后,从制度的角度对高校周边商业街的发展提出了建议。     

Analysis of the compression behavior of artificial lumpy composite materials

The landfills are dumped without any compaction and have a relatively open structure, which is similar to that of the granular materials. However, the original dumped material might be gradually transformed into a lumpy composite structure because of the influence of the climate. As a result, the lumps are randomly distributed in the reconstituted soil. In the presented study, the compression behavior of the lumpy composite soils was analyzed within the homogenization framework. Firstly, the volume of the composite soil was divided into four individual components. The inter‐lump porosity was introduced to account for the evolution of the volume fractions of the constituents, and it was formulated as a function of the overall porosity and those of its constituents. A homogenization law was then proposed based on the analysis of the lumpy structure together with a numerical method, which gives a relationship for tangent stiffnesses of the lumpy soil and its constituents. Finally, a simple compression model was proposed for the composite lumpy material, which incorporates both the influence of the soil structure and the volume fraction change of the reconstituted soil. The predictions of the model were validated against the test results, and the stress distribution within the lumpy composite was assessed. Copyright © 2016 John Wiley & Sons, Ltd.     

Chloride transfer in cement‐based materials. Part 1. Theoretical basis and modelling

In this first part of the work, we develop macroscopic models for migration and diffusion–migration of ionic species in saturated porous media, based on periodic homogenization. The prior application is chloride transport in cementitious materials. The dimensional analysis of Nernst–Planck equation lets appear to dimensionless numbers characterizing the ionic transfer in the porous medium. Using experimental data obtained from electrodiffusion tests on cement‐based materials (Part II), these dimensionless numbers are linked to the perturbation parameter ?. For a strong imposed electrical field, the asymptotic expansion of Nernst–Planck equation leads to a macroscopic model where the migration is predominant. For a weak imposed electrical field or in natural diffusion, we obtain a macroscopic model coupling diffusion and migration at the same order. In both models, the expression of the homogenized diffusion tensor is identical and only involves the geometric properties of the material microstructure. Copyright © 2012 John Wiley & Sons, Ltd.