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1.
Mineral precipitation in an open fracture plays a crucial role in the evolution of fracture permeability in rocks, and the microstructural development and precipitation rates are closely linked to fluid composition, the kind of host rock as well as temperature and pressure. In this study, we develop a continuum thermodynamic model to understand polycrystalline growth of quartz aggregates from the rock surface. The adapted multiphase‐field model takes into consideration both the absolute growth rate as a function of the driving force of the reaction (free energy differences between solid and liquid phases), and the equilibrium crystal shape (Wulff shape). In addition, we realize the anisotropic shape of the quartz crystal by introducing relative growth rates of the facets. The missing parameters of the model, including surface energy and relative growth rates, are determined by detailed analysis of the crystal shapes and crystallographic orientation of polycrystalline quartz aggregates in veins synthesized in previous hydrothermal experiments. The growth simulations were carried out for a single crystal and for grain aggregates from a rock surface. The single crystal simulation reveals the importance of crystal facetting on the growth rate; for example, growth velocity in the c‐axis direction drops by a factor of ~9 when the faceting is complete. The textures produced by the polycrystal simulations are similar to those observed in the hydrothermal experiments, including the number of surviving grains and crystallographic preferred orientations as a function of the distance from the rock wall. Our model and the methods to define its parameters provide a basis for further investigation of fracture sealing under varying conditions. 相似文献
2.
本文从人文地理学的角度剖析了地理环境对于中国历史上国家统一与分裂的重大影响,暨阐述了通常所说的自然与人文的历史的辩证的关系。高山大川的“长城效应”与各区域民族个性差异形成对国家统一的威胁。但同时也是多民族国家统一体的再造与地域文化发展的前提条件之一。 相似文献
3.
Jon W. Carroll 《Midcontinental journal of archaeology, MCJA》2019,44(2):181-206
The original ceramics typology developed for Younge/Western Basin Tradition Springwells phase (ca. AD 1160–1420) assemblages included three variants known as Macomb Linear, Macomb Interrupted Linear, and Springwells Net Impressed ceramics. This discussion considers how subregional variation in Springwells decorative styles reflects participation in a larger regional social network. 相似文献
4.
The Emerald site, also known as the Emerald Acropolis, was an early Mississippian pilgrimage center key to Cahokia’s development. This paper presents the hitherto unpublished results of two archaeological projects conducted at the site, one led by Howard Winters and Stuart Struever in 1961 and the other by Robert Hall in 1964. These investigations produced the most comprehensive information on Emerald’s Moorehead phase (1200–1300 CE) occupation, during which two of its mounds were capped, a secondary mound was constructed on the central mound, and a mound-top structure was erected on this secondary mound. Similar activities took place throughout the region during the thirteenth century, a time marked by dramatic social, political, and religious change in Greater Cahokia. Based on these data, we argue that people returned to Emerald to memorialize or draw on the powers inherent there and thus reincorporate this place into the newly imagined thirteenth century Cahokian world. 相似文献
5.
本文依据已发表的考古学资料,对河南出土的汉代陶阙进行了分类分期研究,并对其中一类陶阙在汉墓中的位置、寓意、双阙中间的“罘罳”及其上面的浮雕像内容进行了探讨。 相似文献
6.
Alexander Tymczuk 《Children's Geographies》2013,11(4):490-503
Ukraine has experienced a wave of labor migration after the dissolution of the Soviet Union. A large number of Ukrainian children have been directly affected as they grow up in transnational households with one or both parents working abroad. In this article, I aim to describe how Ukrainian children and youth conceptualize migration, homeland and abroad in a context of societal, economic and political change. The analysis is mainly based on a qualitative reading of 143 texts written by Ukrainian children. I argue that Ukrainian children and youth place homeland and abroad on a moral map of belonging, and that migration is conceptualized within such a framework as a morally ambiguous movement. 相似文献
7.
日本右翼势力对“台独”的支持大体经历了三个时期:战后初期,日本右翼势力是“台独”逆流的始作俑者和首开“台独”运动先河的罪魁祸首;冷战时期,日本右翼势力不仅在中日复交前使本国成为“台独”势力的大本营,而且在中日复交后仍一如既往、不遗余力地支持“台独”;后冷战时期,日本右翼势力支持“台独”不仅变本加厉,而且呈现出民间与政界配合、右翼与政府呼应之特点。 相似文献
8.
战后,日本通过《日本国宪法》确立了资产阶级民主制度的三权分立之原则和形式,但由于世界范围内的趋势、日本政体的问题和自民党的"一党独大"等原因,遂造成三权失衡即行政权急剧膨胀和立法权与司法权遭到严重削弱诸问题。 相似文献
9.
本文对姜寨第一期房屋遗迹进行初步考察,确认了构成姜寨第一期聚落的5组房屋群之间的分界、各组房屋群的数量,每组房屋群皆由大型、中型和小型的房屋组成,且以小型房屋数量最多,中型和大型房屋数量较少.同时了解到各组的房屋建筑形式均以圆形地上和方形半地穴为主,而且房屋呈向心分布,门向均朝向聚落中心的中央广场.姜寨第一期聚落俨然是一个完整的史前社会组织. 相似文献
10.
Two‐phase flow and near‐critical phenomena are likely to enhance energy transport in high‐temperature hydrothermal systems. We present a series of two‐dimensional simulations of two‐phase flow of pure water at near‐critical conditions. The results show that at near‐critical conditions, two‐phase convection can be more efficient in transporting energy than single‐phase convection. The highest heat fluxes are attained when two‐phase heat‐pipes form near the bottom boundary, recharging the root of the upflow zone and thereby enabling the formation of broad upflow regions. When the system becomes more vapor‐dominated, it loses this ability, upflow zones become narrower and the energy efficiency drops to more moderate values. 相似文献