热液金刚石压腔在地质流体研究中的应用

热液金刚石压腔(HDAC)是专为模拟地壳温压条件下的地质作用而设计的，它尤其适用于观测水或其它流体与地质物质之间的相互作用。HDAC可时-190～1200℃，0～10GPa的热液体系进行实验，并可在实验的温压条件下．用各种先进的光学方法分析样品，更可以把实验的全程录像存档。充满流体的HDAC本身就可当做是一个人工合成的流体包裹体。因此它可以用来研究流体的状态方程和相关系。它又可时其它流体包裹体样品施加外压力，因此在热分析的过程中可免除包裹体的膨胀或爆破的困境。HDAC可应用到颇为宽广的温压范围，它已被广泛地用来观测各种化学体系的临界现象，包括在地质方面特别有用的含水硅酸盐体系。HDAC也可与同步辐射X光源相结合，而取得各种金属或稀土元素水溶液的x射线吸收精细结构(X-ray absorption fine structure；XAFS)光谱，因而时在热液里的金属或稀土元素络合物的组分和结构提供了最基本的资料。然而，X光的强度在透过金刚石时，因绕射和吸收而大大地减弱，因此应用一般的HDAC来获取那些吸收边在10keV以下的元素的XAFS光谱颇为困难。目前已有两种改良式的HDAC解除了这方面的困难，而时在元素周期表上的第一排过渡性金属元素和稀土元素的水溶液，提供清晰的XAFS光谱。这些资料可用来研究金属或稀土元素络合物在地质热液里的特性，及其在元素迁移和成矿作用方面的效应。而这些元素在地质应用方面特别重要。     

Major sporting events and geographies of disability

Major sporting events for athletes with disabilities have become part of a strategic agenda to create positive social legacies for those typically marginalized in their communities. These events are subject to strict guidelines set forth by the International Paralympic Committee to deliver broad-based accessibility. In some cases, changes to accessibility are temporary, wherein other upgrades remain as permanent fixtures for venues, transportation, and public spaces. However, the temporality at the heart of major event projects can also work against long-term, sustainable improvements to the material conditions persons with disabilities face as they experience the urban realm. In this paper, we draw upon case studies of the Glasgow 2014 Commonwealth Games and the Toronto 2015 Parapan American Games to explore the value of major sporting events in delivering urban accessibility improvements and offer a critical commentary on the limitations of the event project to herald sustainable change.     

强迫流与不稳定流的相互作用

通过数值试验的方法,研究非保守系统中的基流平衡被破坏和重建过程中,产生非平衡中尺度环流与不稳定能量造成的对流关系,着重探索在形成持续时间较长、尺度较大的深厚湿对流的物理过程中,强迫与不稳定的相互作用.研究结果表明:强迫流比不稳定流小一个量级.强迫流虽然本身的量值较小,但是强迫流是不稳定流的触发机制.如果环境场具有深厚的不稳定层(垂直或倾斜方向),并且环境场强迫出一定振幅的呈上升运动的强迫流,则在0～3小时以后,将在强迫流上升运动中心激发出不稳定流上升运动中心,或使已经存在的不稳定流上升运动中心向强迫流上升运动中心移动.     

Experimental and numerical study of current-induced artificial upwelling

The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice.     

Discussion of “experiment and statistical assessment on piping failures in soils with different gradations”

Internal stability assessment methods, such as Kezdi and Kenney and Lau, have some degree of uncertainty and they do not take the effect of soil density in consideration. Analysis show that the internal stability of some granular soils could be stable, transition state, or unstable based on the relative density. All these factors could affect the accuracy of statistical analysis based on the assessment of these methods.     

Closure to discussion of “experiment and statistical assessment on piping failures in soils with different gradations”

This paper responds to the comments from two discussions. The comments related to the uncertainties in the internal stability criteria and the determination of input soil property for prediction models, which affect the accuracy of predicting critical hydraulic gradient, are addressed and discussed.     

甘宁交界地区弧形断裂失稳理论的模拟研究

以１０２°～１０９°Ｅ,３５．５°～４２°Ｎ为界,通过对该区地质构造,地壳结构的归纳总结,采用临界失稳函数的概念及断裂失稳理论,通过有限元法定量地模拟研究了甘、宁交界地区弧形断裂的稳定状态,认为１．在平面上,临界失稳函数的分布具有不均匀性与断裂活动具有一定的相关性。２．中强地震往往发生在临界失稳函数变化较大的地段。３．临界失稳函数在横向上、纵向上分布不均匀区域容易形成应力集中,从而产生地震     

Experimental study on blocking and self-cleaning behaviors of beam dam in debris flow hazard mitigation

Blocking is one of the important features when a beam dam intercepts debris flow, while self-cleaning is another when managing suspended debris flow. Both features determine the debris flow control benefits of beam dam but the latter often is not considered in practical engineering design. In this paper, a series of specially designed flume experiments were done to simulate blocking and self-cleaning processes. The blocking ratio and deposition features were measured to contrast the blocking and self-cleaning performance before and after artificial self-cleaning. The experimental results reveal that the beam dam net opening, particle diameter of sediment, sediment concentration, and gradient of the channel are the main factors affecting blocking performance. A new criterion of blocking performance of beam dams that considers the interaction of multiple factors and can provide guidance to practical project design is proposed. For all three types of blocking, sediment deposited upstream of a beam dam can be effectively transported downstream by erosion from post-debris-flow floods, Self-cleaning performance is most efficient for temporary blocking, followed by partial-blocking, and total-blocking. The efficiency of self-cleaning largely depends on the change of the sediment deposit due to erosion. Finally, a discussion is given for the optimal design of an open-type check dam and the feasibility of synergistic effects of self-cleaning in combination with artificial cleaning. Some supporting artificial silt-cleaning should be implemented in practice. A beam dam will, thus, have more storage capacity with which to control the next debris flow event.     

Which way do you lean? Using slope aspect variations to understand Critical Zone processes and feedbacks

Soil‐mantled pole‐facing hillslopes on Earth tend to be steeper, wetter, and have more vegetation cover compared with adjacent equator‐facing hillslopes. These and other slope aspect controls are often the consequence of feedbacks among hydrologic, ecologic, pedogenic, and geomorphic processes triggered by spatial variations in mean annual insolation. In this paper we review the state of knowledge on slope aspect controls of Critical Zone (CZ) processes using the latitudinal and elevational dependence of topographic asymmetry as a motivating observation. At relatively low latitudes and elevations, pole‐facing hillslopes tend to be steeper. At higher latitudes and elevations this pattern reverses. We reproduce this pattern using an empirical model based on parsimonious functions of latitude, an aridity index, mean‐annual temperature, and slope gradient. Using this empirical model and the literature as guides, we present a conceptual model for the slope‐aspect‐driven CZ feedbacks that generate asymmetry in water‐limited and temperature‐limited end‐member cases. In this conceptual model the dominant factor driving slope aspect differences at relatively low latitudes and elevations is the difference in mean‐annual soil moisture. The dominant factor at higher latitudes and elevations is temperature limitation on vegetation growth. In water‐limited cases, we propose that higher mean‐annual soil moisture on pole‐facing hillslopes drives higher soil production rates, higher water storage potential, more vegetation cover, faster dust deposition, and lower erosional efficiency in a positive feedback. At higher latitudes and elevations, pole‐facing hillslopes tend to have less vegetation cover, greater erosional efficiency, and gentler slopes, thus reversing the pattern of asymmetry found at lower latitudes and elevations. Our conceptual model emphasizes the linkages among short‐ and long‐timescale processes and across CZ sub‐disciplines; it also points to opportunities to further understand how CZ processes interact. We also demonstrate the importance of paleoclimatic conditions and non‐climatic factors in influencing slope aspect variations. Copyright © 2017 John Wiley & Sons, Ltd.     

Frequency-dependent PP and PS reflection coefficients in fractured media

When a porous layer is permeated by mesoscale fractures, wave-induced fluid flow between pores and fractures can cause significant attenuation and dispersion of velocities and anisotropy parameters in the seismic frequency band. This intrinsic dispersion due to fracturing can create frequency-dependent reflection coefficients in the layered medium. In this study, we derive the frequency-dependent PP and PS reflection coefficients versus incidence angle in the fractured medium. We consider a two-layer vertical transverse isotropy model constituted by an elastic shale layer and an anelastic sand layer. Using Chapman's theory, we introduce the intrinsic dispersion due to fracturing in the sand layer. Based on the series coefficients that control the behaviour of velocity and anisotropy parameters in the fractured medium at low frequencies, we extend the conventional amplitude-versus-offset equations into frequency domain and derive frequency-dependent amplitude-versus-offset equations at the elastic–anelastic surface. Increase in fracture length or fracture density can enlarge the frequency dependence of amplitude-versus-offset attributes of PP and PS waves. Also, the frequency dependence of magnitude and phase angle of PP and PS reflection coefficients increases as fracture length or fracture density increases. Amplitude-versus-offset type of PP and PS reflection varies with fracture parameters and frequency. What is more, fracture length shows little impact on the frequency-dependent critical phase angle, while the frequency dependence of the critical phase angle increases with fracture density.