Chemical weathering processes in the Yalong River draining the eastern Tibetan Plateau,China

To better understand chemical weathering and controlling processes in the Yalong River of the eastern Tibetan Plateau, this study presents major ion concentrations and stable isotopes of the dissolved loads. The isotopic compositions (δ¹³C-DIC, δ³⁴S and δ¹⁸O-SO₄) of the dissolved loads are very useful to quantify solute sources and define the carbon budget related with chemical weathering in riverine systems. The isotopic composition of sulphate demonstrates that most of the sulphate is derived from sulphide oxidation, particularly in the upper reach of the Yalong River. The correlations between δ¹³C-DIC, water chemistry and isotopes of sulphate, suggest that the carbon dynamics are mainly affected by carbonate weathering by sulphuric acid and equilibration processes. Approximately 13% of the dissolved inorganic carbon in the Yalong River originates from carbonate weathering by strong acid. The CO₂ consumption rates are estimated to be 2.8 × 10⁵ mol/km²/yr and 0.9 × 10⁵ mol/km²/yr via carbonate and silicate weathering in the Yalong River, respectively. In this study, the influence of sulphide oxidation and metamorphic CO₂ on the carbon budget is estimated for the Yalong River draining the eastern Tibetan Plateau.     

Sorption behavior of phenanthrene in Yangtze estuarine sediments: sequential separation

In the present study, phenanthrene was chosen as the probe compound for determining the sorption of PAHs in sediments from Yangtze estuary and nearby coastal area, China. Sorption isotherms were fitted well by the Freundlich and dual models, respectively. Selected sediments were further sequentially separated to remove the carbonate and organic carbon (OC). Calculated OC sorption capacity values based on both H₂O₂ oxidization and 375 °C combustion methods were similar and comparable to the K_oc values estimated by the empirical linear sorption equations. Both sorption models and sorption data using sequentially separated samples achieve the similar conclusions: (1) the partition behavior dominated by OC in sediments with f_oc > 0.01; (2) for sediments with 0.001 < f_oc < 0.01, OC dominated sorption at relatively high aqueous concentration; whereas mineral phase adsorption dominated sorption at lower concentration especially when C_w/S_w was in the range of 0.0001-0.001 in natural aqueous system.     

History matching of enhanced coal bed methane laboratory core flood tests

Enhanced coalbed methane (ECBM) involves the injection of a gas, such as nitrogen or carbon dioxide, into the coal reservoir to displace the methane present. Potentially this strategy can offer greater recovery of the coal seam methane and higher rates of recovery due to pressure maintenance of the reservoir. While reservoir simulation forms an important part of the planning and assessment of ECBM, a key question is the accuracy of existing approaches to characterising and representing the gas migration process. Laboratory core flooding allows the gas displacement process to be investigated on intact coal core samples under conditions analogous to those in the reservoir. In this paper a series of enhanced drainage core floods are presented and history matched using an established coal seam gas reservoir simulator, SIMED II. The core floods were performed at two pore pressures, 2 MPa and 10 MPa, and involve either nitrogen or flue gas (90% nitrogen and 10% CO₂) flooding of core samples initially saturated with methane. At the end of the nitrogen floods the core flood was reversed by flooding with methane to investigate the potential for hysteresis in the gas displacement process. Prior to the core flooding an independent characterisation programme was performed on the core sample where the adsorption isotherm, swelling with gas adsorption, cleat compressibility and geomechanical properties were measured. This information was used in the history matching of the core floods; the properties adjusted in the history matching were related to the affect of sorption strain on coal permeability and the transfer of gas between cleat and matrix. Excellent agreement was obtained between simulated and observed gas rates, breakthrough times and total mass balances for the nitrogen/methane floods. It was found that a triple porosity model improved the agreement with observed gas migration over the standard dual porosity Warren-Root model. The Connell, Lu and Pan hydrostatic permeability model was used in the simulations and improved history match results by representing the contrast between pore and bulk sorption strains for the 10 MPa cases but this effect was not apparent for the 2 MPa cases. There were significant differences between the simulations and observations for CO₂ flow rates and mass balances for the flue gas core floods. A possible explanation for these results could be that there may be inaccuracy in the representation of mixed gas adsorption using the extended Langmuir adsorption model.     

双能CT的基本原理、应用和未来展望(英文)

断层影像(CT)的图像对比度与扫描所用的X光源能谱分布有很大关系。传统CT使用具有能谱分布的一个光源进行成像,有时会出现信息模糊致使两种不同材料在CT图像上完全相同。双能CT使用两个不同分布的能谱对物体进行成像,能够消除单能谱情况下的信息模糊。虽然双能CT的基本概念由来已久,但最近商业系统的出现使双能CT迅速成为一个热点。我们首先概述了双能CT的基本物理原理和双能信号处理方法,包括促使双能CT进入现代医学成像的关键技术。其次,双能CT的应用已非常广泛,本文从其在临床应用角度进行了详细介绍使读者有所了解。最后,我们简要探讨了当前的两个技术发展领域:光子技术探测器和技术合成CT。     

基于RBF和PSO的双喉道气动矢量喷管优化设计

本文探索了一种能多变量综合优化的方法,即对喷管进行参数化设计后,用均匀试验设计(UED)将试验样本均匀散布在设计区间内,求出各性能参数后,利用径向基神经网络(RBF)对试验样本进行拟合,再用粒子群算法(PSO)对训练好的神经网络进行寻优,找出了更好的双喉道气动矢量喷管设计参数组合。数值模拟结果显示,优化后的双喉道气动矢量喷管的矢量角有了明显提高。试验表明这种优化方法具有很好的优化能力,可以用来对喷管几何外形进行参数优化。      

Rocking vibration of a rigid strip footing on saturated soil

The dynamic response of a rigid strip footing lying on saturated soil is greatly affected by the pore pressure induced by a rocking moment. To consider the complex behavior of the soil under the rocking load, an analytical solution for a rigid strip foundation on saturated soil under a rocking moment is developed under the framework of Biot’s coupling theory. The boundary-value problem for the governing coupling equations for saturated soil is solved using a Fourier transform to yield a pair of dual integral equations. These dual integral equations are transformed into a set of linear equations using an infinite series of orthogonal Jacobi polynomials to yield the compliance functions. In addition, a parametric study has been carried out to examine the influence of: (1) the dimensionless frequency, (2) the dynamic permeability and (3) the Poisson’s ratio on saturated soil under a rocking rigid strip footing.     

用正演数值计算方法开展双侧向测井对裂缝的响应研究

采用有限元分析软件ANSYS对裂缝的双侧向测井视电阻率与裂缝孔隙度、泥浆电阻率、裂缝倾角和基岩电阻率的关系进行了计算. 在大量正演数据的基础上得出双侧向测井响应反演公式和裂缝孔隙度计算公式,提出更为精细的裂缝倾角的弹性划分模型,用双侧向视电阻率值近似估算裂缝倾角的方法,提高了利用双侧向测井求裂缝产状与裂缝孔隙度（裂缝宽度）的精度.     

桩贯入地基过程的动画仿真

本文通过三维显式有限元计算结果，对混凝土桩打基的过程进行了三堆动力反应分析，褡完成了此过程的动画仿真研究，研制成可携带的录相带工匠仿真动画，形象，生动，直观地再现了桩贯入地基过程中撞击波在桩体，地基中的传播，桩体与地基间的相对接触，滑移及桩锤与桩头部间的接触撞击过程。     

边坡稳定性二元指标体系与应用研究

边坡稳定性影响因素如:强度参数、降雨、地下水、人类工程活动等都具有很高的离散性、变异性、相关性,对安全系数的影响不是确定不变的,而是服从一定统计规律的概率分布。在每个影响因素的置信区间内,取对称的几个值作为不同水平,如三水平取值等,组合不同因素和水平,计算得到系列的安全系数值。取影响因素的平均值,计算得到传统的安全系数(中值安全系数),同时由安全系数的变异性,求出安全系数的可靠性。选择典型的安全系数及相对应的可靠性,基于工程经验丰富的安全系数,初步建立传统安全系数与可靠性耦合的边坡稳定性二元指标体系,由安全系数和可靠性共同度量边坡系统的稳定性。传统安全系数与可靠性耦合的边坡稳定二元体系的初步建立,可有效地考虑边坡系统内实际存在的不确定性和相关性,使边坡的稳定性评价更加客观精确,为边坡安全和滑坡灾害的风险性管理提供理论和方法。论述了边坡稳定性二元指标体系研究意义、研究内容、研究方法和研究趋势。