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11.
Accurate simulation of multiphase flow in fractured porous media remains a challenge. An important problem is the representation of the discontinuous or near discontinuous behaviour of saturation in real geological formations. In the classical continuum approach, a refined mesh is required at the interface between fracture and porous media to capture the steep gradients in saturation and saturation‐dependent transport properties. This dramatically increases the computational load when large numbers of fractures are present in the numerical model. A discontinuous finite element method is reported here to model flow in fractured porous media. The governing multiphase porous media flow equations are solved in the adaptive mesh computational fluid dynamics code IC‐FERST on unstructured meshes. The method is based on a mixed control volume – discontinuous finite element formulation. This is combined with the PN+1DG‐PNDG element pair, which has discontinuous (order N+1) representation for velocity and discontinuous (order N) representation for pressure. A number of test cases are used to evaluate the method's ability to model fracture flow. The first is used to verify the performance of the element pair on structured and unstructured meshes of different resolution. Multiphase flow is then modelled in a range of idealised and simple fracture patterns. Solutions with sharp saturation fronts and computational economy in terms of mesh size are illustrated.  相似文献   
12.
The restoration of destroyed connections of epistyles joined together by means of metallic connectors is among the most difficult problems encountered by scientists working for the conservation/restoration of monuments made of marble. The complexity of the geometry and the interaction of three completely different materials (metal-filling material-marble) constituting the connection render the study (either experimental or analytic) extremely complicated. In this direction a numerical analysis is presented here in order to deeply understand the response of a typical ancient connection subjected to axial loads as well as to quantify the influence of some geometric parameters on its response. The parameters studied include the length of the connector, the width of its flanges, the depth of the groove (mortise), the existence or not of relieving space and the filling material’s volume. The numerical model was calibrated and validated according to the results of an earlier experimental study realized on the worksite of the Parthenon Temple. It was concluded that the interventions required to relieve the stress field by changing the size of the connector are disproportional to the respective positive effect on the response of the connection. Moreover it was proved that the most beneficial parameter is the relieving space.  相似文献   
13.
This article aims at presenting and discussing the strategies for updating the finite element numerical modeling of stone masonry arch bridges using operational modal analysis. The study comprehended three bridges: two old ones, the St. Lázaro and the Lagoncinha bridges, and a recently constructed bridge in Vila Fria, Portugal. Updating of the bridge models is performed by comparing the numerical and experimental modal parameters. Three-dimensional detailed numerical models are used to perform modal analysis of the bridges. Experimental modal identification of the bridges is based on the measurement of their acceleration responses during normal operation. The assigned material properties are also based on available results obtained from in situ and laboratory tests and on the results of visual inspection and historical research carried out for both old bridges.  相似文献   
14.
This article presents results of non-destructive Schmidt hammer tests performed on ancient fired clay bricks sampled from historical masonry. These tests were carried out in order to evaluate, and compare, the different degrees of degradation, depending on the bricks’ specific exposures and locations within a wall. The results indicate that this technique is sensitive enough to distinguish sample locations and measure weathering differences, even for different surfaces of a particular sample. For each case study, referenced surfaces were tested for bricks from a facade or interior wall. Each surface was tested with a Schmidt hammer type LB at ten different points of measurement, and these measurements were repeated ten times. For each impact at a particular point, a mean rebound value was calculated to provide an index of the degree of brick-surface microweathering.  相似文献   
15.
JoAnn McGregor  Kudzai Chatiza 《对极》2019,51(5):1554-1580
This article develops the concept of “urban frontier” to explore conflicts over state regularisation of city edge informal settlements in Zimbabwe’s capital Harare. It conceptualises the presence of “lawless” urban frontiers and “illegal” territorial authorities in capital cities as expressions of a permissive form of central statecraft. In so doing, the article takes forward debates over the politics shaping the margins of Africa’s rapidly expanding cities, redressing scholars’ tendency to neglect central party‐state strategic calculations and party politics in their analyses of unregulated settlements. Dominant interpretations generally hinge on state absence or weakness and emphasise localised influences. The case of Harare’s highly politicised city‐edge informal settlements reveals the inadequacy of apolitical approaches particularly clearly, as all were controlled by the ruling ZANUPF party. The conflicts provoked by regularisation provide a lens on disputes within the ruling party, which we interpret as disputes over different forms of clientalist statecraft. Analyses of urban frontiers can thus help move away from generic one‐size‐fits‐all explanations of informality and patronage politics in Africa’s expanding cities.  相似文献   
16.
17.
The chemical compositions and microstructures of some 35 faience objects from Egypt spanning the period from the Middle Kingdom through to the 22nd dynasty are determined using analytical scanning electron microscopy. Replicate faience beads glazed in the laboratory using the efflorescence and cementation methods are similarly investigated. In efflorescence glazing, there appears to be preferential efflorescence of soda over potash, and in cementation glazing, preferential take up of potash over soda into the glaze. These data are then used to try to infer the raw materials and methods of glazing employed in the production of the ancient faience. The glaze/glass phases present in the faience differ significantly in composition from that of New Kingdom glass. This could be due either to the use of different plant ashes or to changes in the composition of the plant ashes during the production of faience and/or glass. Although it is only rarely possible to determine with certainty whether ancient faience was glazed by efflorescence, cementation or application, the observed microstructures provide an indication of the approach adopted to achieve desired performance characteristics such as strength.  相似文献   
18.
雷戈所著《秦汉之际的政治思想与皇权主义》一书,认为从秦朝到汉初的思想史发展阶段是中国思想史上皇权主义意识形态的生成和确立时期,并将其概括为"后战国时代";采用独特的"历史-思想"研究法,从政治制度、官场规则和官吏的政治生活中,挖掘特定时期的政治思想共识,为政治思想史研究开辟了新的路径,并扩大了思想史的资料范围;认为秦汉时期生成的皇权主义秩序,把"天高皇帝远"的制度现实变为"天高皇帝近"的观念实存,实现了对人们思想的可控性,从此,思想成为皇权可以控制和规范的领域,达到了有效的思想专制。这是秦汉以降中国思想史发展的基本特征。该书在研究方法的创新和思想深度的开掘上,都做出了独到的贡献。  相似文献   
19.
姜萌 《史学月刊》2007,(3):79-85
《陈寅恪的最后二十年》、《顾颉刚和他的弟子们》、《束星北档案》等著作,代表了当前历史传记写作的一种趋势。《陈寅恪的最后二十年》的文本近似历史叙事散文;《顾颉刚和他的弟子们》的文本更接近史学论文;而《束星北档案》则类同电视记录片的文稿。这些著作共有的特点是:在修撰方式上,大量运用了第一手材料;在文本风格上,力求作品深入浅出、雅俗共赏;在写作理念上,坚持真实第一,尊重历史。这一趋势非常值得重视。  相似文献   
20.
In the age of post-Fordist flexible production, a consumer realizes her/his identity in part through the act of consumption. The visual aspect of commodity–consumer negotiation acquires importance, as commodities must be visually differentiated to attract the gaze of a particular consuming group. The act of visual differentiation is achieved through symbolic packaging, which creates a cognitive link between commodity and consumer. I draw from Baudrillard, who states that in postmodern consumption the sign value of products becomes more important than their actual usefulness (use value). Baudrillard, however, overlooks the importance of gender, race and space in this visual mediation. Through an empirical study of the packaging of women's skin and hair products in two different stores catering to two different income groups in Worcester, Massachusetts, I indicate how gendered identities that are created are complex, porous and materially rooted in space. The geographic situatedness of the exercise checks overgeneralizations allowing it to be studied as an object–subject mediation in a particular spatial context.  相似文献   
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