Multiscale poro‐creep model for cement‐based materials     

Shui‐Tao Gu  Benoît Bary  Qi‐Chang He  Minh‐Quan Thai 《国际地质力学数值与分析法杂志》2012,36(18):1932-1953

Experimental observations clearly show that the relative humidity (h_r) conditions influence significantly the creep behavior of cement‐based materials, indicating that the water present within these materials plays a crucial role. This work presents a creep model for hardened cement pastes (HCP), based on a multiscale homogenization approach. It takes into account both free and adsorbed water contained in the porosity and investigates their effects on the HCP macroscopic creep behavior. The calcium silicate hydrate phase is assumed to be linear viscoelastic, and the Mori–Tanaka scheme is applied in the Laplace–Carson space to the composite formed of porosity, calcium silicate hydrate, and the other main hydrated compounds (which behavior is linearly elastic) by making use of the correspondence principle. With this model, estimations of the evolution of the macroscopic creep behavior of HCP submitted to constant external loading are examined under different h_r and compared with available experimental data. Finally, a method for implementing the model in a finite element code is proposed, and simulations of standard creep tests are performed to assess its validity. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

GIS在移动蜂窝网络中的应用研究     

陈晓勇  吴华玲  Tran Minh Tri 《测绘科学》2012,37(2):133-137

GIS在移动蜂窝网络规划中有重要应用,本文旨在研究以最低的投资和维护费用,确定GIS最佳解决方案用以改善蜂窝网络的传播质量。本文利用GIS能将蜂窝网络数据库中空间与非空间数据相结合的优势,提供必要的参数,更准确地预测蜂窝网络的覆盖范围。本文研究对象为越南胡志明市的部分区域,实验成功开发出预测移动蜂窝网络覆盖范围的基础地理信息系统模型,实现了预测信号强度的可视化,分析了场强覆盖范围,并显示了研究区域中每个小区站的可能切换区域。实验结果表明,GIS模型在移动通信尤其对小区站覆盖范围预测是非常有用的。  相似文献   

豫西地区秦岭造山带武当群Nd-Hf同位素组成及其物源特征   总被引：1，自引：0，他引：1  

祝禧艳  陈福坤  杨力  王伟  HIEU Pham Trung  苗来成  张福勤 《岩石学报》2009,25(11):3017-3028

武当群变质沉积-火山岩组合是南秦岭地体中重要的基底岩石,其形成时代和地球化学特征可以为理解秦岭造山带的构造演化提供重要的证据.本文报道豫西地区武当群上部沉积岩和下部中-酸性火山岩Sm-Nd同位素和锆石Lu-Hf同位素组成,探讨火山岩成因和沉积岩物源的同位素特征.上部沉积岩的碎屑锆石初始ε_(Hf)值变化在-30～+10之间,对应的模式年龄值t_(DM2)在1.0Ga至3.2Ga之间,初始ε_(Nd)值在-4.0至-6.0之间.沉积物源表现为主要与扬子陆块有亲缘关系的地壳物质和近源的下部火山岩混合的特征.火山岩的锆石初始εHf值变化在-35～+15之间,对应的模式年龄值t_(DM2)在0.8Ga至3.5Ga之间,集中于1.5～1.8Ga和2.2～2.4Ga两个峰值.2个变质石英角斑岩样品初始ε_(Nd)值分别为-9.2和-10.7,而报道的湖北武当群的玄武-安山质熔岩的初始ε_(Nd)值以正值为主.因此,武当群不同类型的火山岩可能存在着成因差异.具有低初始ε_(Nd)值和ε_(Hf)值特征的火山岩可能由地壳物质的重熔而形成的;有些火山岩具有初始ε_(Hf)值变化范围较大(-35～+15)或正初始ε_(Nd)值的特点,可能是壳、幔物质混合成因,有显著的幔源或新生地壳物质的贡献.武当群Nd-Hf同位素组成和碎屑锆石年龄分布特征表明,与扬子陆块有亲缘关系的南秦岭地体在元古代期间可能经历多期地壳增生和再造作用.  相似文献   

Remarkably uniform oxygen isotope systematics for co-existing pairs of gem-spinel and calcite in marble,with special reference to Vietnamese deposits     

Anthony E. Fallick  Gaston Giuliani  Thomas Rigaudier  Adrian J. Boyce  Van Long Pham  Vincent Pardieu 《Comptes Rendus Geoscience》2019,351(1):27-36

Oxygen isotope systematics for co-existing pairs of gem-spinel and calcite in marble from Vietnam and other worldwide deposits have been determined in order to characterize the O-isotope fractionation between calcite and spinel. In Vietnam, the Δ¹⁸O_cc–sp (= 3.7 ± 0.1‰ for six samples from the An Phu and Cong Troi deposits) is remarkably constant. The combination of these data with those obtained on calcite–spinel pairs of Paigutan (Nepal, n = 2), Ipanko (Tanzania, n = 1), and Mogok (Myanmar, = 2) are also consistent with an overall Δ¹⁸O_cc–sp of 3.6 ± 0.3‰ for all the spinel samples (n = 11). The straight line correlation δ¹⁸O_cc = 0.96 δ¹⁸O_sp + 4.4 is excellent despite their worldwide geographic spread. The increment method of calculating oxygen isotope fractionation gave a geologically unreasonable temperature of formation for both minerals at 1374 °C when compared to temperatures obtained by mineral assemblage equilibrium of these marble type deposits, between 610 and 750 °C. The constant Δ¹⁸O_cc–sp reflects a constant temperature for this amphibolite facies assemblage, whose current best estimate is calculated at 620 ± 40 °C, but unquantified uncertainties remain.  相似文献   

Reply     

V. N. Pham 《Geophysical Journal International》2005,162(2):337-338

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Climate Strategy with Co2 Capture from the Air     

David W. Keith  Minh Ha-Duong  Joshuah K. Stolaroff 《Climatic change》2006,74(1-3):17-45

It is physically possible to capture CO₂ directly from the air and immobilize it in geological structures. Air capture differs from conventional mitigation in three key aspects. First, it removes emissions from any part of the economy with equal ease or difficulty, so its cost provides an absolute cap on the cost of mitigation. Second, it permits reduction in concentrations faster than the natural carbon cycle: the effects of irreversibility are thus partly alleviated. Third, because it is weakly coupled to existing energy infrastructure, air capture may offer stronger economies of scale and smaller adjustment costs than the more conventional mitigation technologies. We assess the ultimate physical limits on the amount of energy and land required for air capture and describe two systems that might achieve air capture at prices under 200 and 500 $/tC using current technology. Like geoengineering, air capture limits the cost of a worst-case climate scenario. In an optimal sequential decision framework with uncertainty, existence of air capture decreases the need for near-term precautionary abatement. The long-term effect is the opposite; assuming that marginal costs of mitigation decrease with time while marginal climate change damages increase, then air capture increases long-run abatement. Air capture produces an environmental Kuznets curve, in which concentrations are returned to preindustrial levels.  相似文献   

Water volume change in the lower Mekong from satellite altimetry and imagery data     

F. Frappart  K. Do Minh  J. L'Hermitte  A. Cazenave  G. Ramillien  T. Le Toan  N. Mognard-Campbell 《Geophysical Journal International》2006,167(2):570-584

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Bagging based Support Vector Machines for spatial prediction of landslides     

Binh Thai Pham  Dieu Tien Bui  Indra Prakash 《Environmental Earth Sciences》2018,77(4):146

A hybrid Bagging based Support Vector Machines (BSVM) method, which is a combination of Bagging Ensemble and Support Vector Machine (SVM) classifier, was proposed for the spatial prediction of landslides at the district of Mu Cang Chai, Viet Nam. In the present study, 248 past landslides and fifteen geo-environmental factors (curvature, elevation, distance to rivers, slope, aspect, river density, plan curvature, distance to faults, profile curvature, fault density, lithology, distance to roads, rainfall, land use, and road density) were considered for the model construction. Different evaluation criteria were applied to validate the proposed hybrid model such as statistical index-based methods and area under the receiver operating characteristic curve (AUC). The single SVM and the Naïve Bayes Trees (NBT) models were selected for comparison. Based on the AUC values, the proposed hybrid model BSVM (0.812) outperformed the SVM (0.804) and NBT (0.8) models. Thus, the BSVM is a promising and better method for landslide prediction.  相似文献   

Influence of hydraulic characteristics on stability of unsaturated slope under transient seepage conditions     

Khanh Pham  Hyobum Lee  Dongku Kim  In-Mo Lee  Hangseok Choi 《Landslides》2018,15(9):1787-1799

This paper examines the current procedure for determining the soil-water characteristic curve (SWCC) model with a particular focus on its application to slope stability analysis under transient unsaturated seepage conditions. A series of laboratory experiments was performed to determine the SWCC of different soils, ranging from high plasticity clay to silty sand, found across the Korean Peninsula. The experimental results were utilized to identify the suitable SWCC model for each soil type based on the fitting criterion. Also, this paper developed a numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions. The significant advantage of the proposed framework, from the practical viewpoint, is to directly predict the timing of failure and potential failure plane based on rainfall recording. The effect of choice of SWCC models on predictability in stability analysis was evaluated by adopting the present framework along with the identified SWCC models. Furthermore, a case study of landslides after a 3-month rainfall in Pohang, Korea, was revisited to assess the performance of the proposed framework. The obtained results demonstrate the significant role of SWCC model on the results of slope stability analysis. The analysis using the SWCC model satisfying the fitting criterion could still not capture the real behavior of unsaturated soil. The comprehensive transient analysis is strongly suggested as a complementary means to the current fitting criterion for determining the suitable SWCC model for stability analysis under transient seepage conditions.  相似文献   

Rainfall-induced catastrophic landslide in Quang Tri Province: the deadliest single landslide event in Vietnam in 2020     

Van Tien  Pham  Luong  Le Hong  Duc  Do Minh  Trinh  Phan Trong  Quynh  Dinh Thi  Lan  Nguyen Chau  Thuy  Dang Thi  Phi  Nguyen Quoc  Cuong  Tran Quoc  Dang  Khang  Loi  Doan Huy 《Landslides》2021,18(6):2323-2327

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