矩形大定源层状模型瞬变电磁响应计算

针对矩形大定源介绍了一种层状导电模型瞬变电磁响应的快速计算方法.其基本思想是,将大定源回线源用较少的有限大小方形回线叠加.在频率域,该叠加过程导出矩形大定源回线模型响应可以表示为一个标准的Hankel积分,叠加效应仅仅是相应Bessel函数的空间积分过程.瞬变电磁响应可以利用余弦变换由频率域响应获得.均匀半空间模型计算结果和解析解较为吻合,层状模型模拟结果符合物理规律,不同测点位置感应电动势的视电阻率具有很好的一致性.新方法误差只是来源于圆回线对小方形回线的等效误差.与均匀半空间解析结果比较,只用16个方形回线等效,相对误差就可以小于10^-3.     

Proposed Adsorption–Diffusion Model for Characterizing Chromium(VI) Removal Using Dried Water Hyacinth Roots

Experiments have been carried out to characterize the adsorption of chromium(VI) in the aqueous phase onto dried roots of water hyacinth. Results revealed a very high degree of removal efficiency (∼100%). Theoretical analyzes are also made for describing the sorption and diffusion processes. The effective pore diffusivity of chromium(VI) in the water hyacinth roots is determined by a suitable global optimization technique. The depth of penetration, on the other hand, has been estimated for various initial concentrations of chromium(VI). Theoretically predicted concentration profiles are in excellent agreement with the experimental values.     

Landslides impacting linear infrastructure in west central British Columbia

Destructive landslides are common in west central British Columbia. Landslides include debris flows and slides, earth flows and flowslides, rock falls, slides, and avalanches, and complex landslides involving both rock and soil. Pipelines, hydrotransmission lines, roads, and railways have all been impacted by these landslides, disrupting service to communities. We provide examples of the destructive landslides, their impacts, and the climatic conditions associated with the failures. We also consider future landsliding potential for west central British Columbia under climate change scenarios.     

Investigation of the nature of slip surface using geochemical analyses and 2-D electrical resistivity tomography: a case study from Lapseki area, NW Turkey

The nature and subsurface structure of the slip surface of a landslide was studied on the basis of geochemical analyses and 2-D electrical resistivity tomography (ERT) survey. Head scarp and lateral slip surfaces of the landslide marked by clear slickensided shear planes were composed of the average amounts of clayey silt (32.5%) and sand (67.5%). Energy dispersive X-ray spectroscopy (EDX) data revealed the enrichment of Si (23.24%), Fe (12.2%), Al (9.51%) and C (8.34%) in the elemental composition of the disturbed slip surface. From X-ray diffractometry (XRD) data, six main clay types were determined, such as Volkonskoite, Halloysite, Ferrosilite, Saponite, Illite and Nontronite. The ERT survey displayed that the landslide developed as a reactivation on the upper part of an old landslide body.     

Slope stability analysis on a regional scale using GIS: a case study from Dhading,Nepal

A spatially distributed physically based slope stability model combined with a hydrological model is presented and applied to a 350-km² area located in Dhading district, Nepal. Land slide safety factor maps are generated for five cases, including three steady state conditions assuming either completely dry soils, half saturated soils, or fully saturated soils, and two quasi-dynamic conditions, i.e. soil wetness resulting from storm events with, respectively a 2 or 25-year return period. For the quasi-dynamic cases, two methods are used, one based on accumulation of groundwater flow from upstream areas, and the other on accumulation of soil water from direct infiltration. The methodology delineates areas most prone to shallow land sliding in function of readily available data as topography, land-use and soil types. For the study area only 29% of the soils are unconditionally stable, while 25% of the soils are found to be unstable under fully saturated conditions. The comparison between the methods based on contributing area or on infiltration for quasi-dynamic conditions show that the approach based on infiltration is more reliable for the study area. The proposed methodology for predicting landslide susceptibility on a regional scale, based on basic data in GIS form, may be useful for other remote regions where detailed information is not available.     

四川石棉县科落头滑坡形成机制分析与治理方案建议

科落头滑坡是一个大型老滑坡,近年来受雨季暴雨影响,特别是“5．12”汶川大地震后发生了局部复活变形。在充分论述其滑动机制、稳定性分析的基础上,提出了滑坡治理方案建议。     

降雨滑坡预警的概率分析方法

滑坡启动的降雨临界值是滑坡预警的关键,由于研究区资料数据有限,关键值难以确定,降雨滑坡预警效果受影响。所以应该对预警结果进行概率分析。本文利用作者在已开发的降雨滑坡预警系统,提出采用降雨滑坡预警概率分析方法进行预警。通过对滑坡与雨量相关性、降雨滑坡启动值等对滑坡预警的时间概率、空间概率及预警概率进行分析,计算危险区内已发生滑坡频率和降雨滑坡发生频率,得到降雨滑坡预警概率使得预警系统更加可靠。并以沐川县为例对模型进行了算例检验,为更科学的对降雨滑坡进行预警提供方法借鉴。     

三峡库区巴东新城区库岸三叠系巴东组层间软弱带

摘要 巴东新城区发育有黄土坡滑坡、赵树岭滑坡、太矶头滑坡、童家坪滑坡等多处大型古滑坡,研究库岸斜坡岩体结构特征对滑坡的治理有着至关重要的作用。本文基于巴东新城区白土坡和西壤坡两段库岸深300余米监测剖面的地质勘探资料,根据岩芯颜色、岩性和结构将巴东组第三段划分为24段;通过薄片鉴定、X射线衍射和岩芯精细测量分析库岸斜坡岩体处于滨海环境的海陆过渡相,岩性组合、岩层厚度、矿物组成及强度具有复杂的垂向分带特征;探讨了层间软弱带和大型滑坡的关系。研究表明:巴东新城区库岸斜坡巴东组第三段内发育有13层贯通的软弱带,表现为为富含泥质、结构破碎的泥质软弱夹层、构造碎裂岩、溶蚀改造带和软岩软弱带。在沉积成岩时经历了滨海相反复的海浸海退,软弱带多分布在沉积环境动荡的开阔台地（陆棚泻湖）和局限台地（潮间带）。巴东组第二、三段岩性及沉积环境属缓慢过渡,在构造作用下未发生明显的滑脱。沉积结构和后期构造共同作用形成了贯通软弱带,为大型滑坡发生提供了有利条件。三峡水库全面蓄水后,软弱带在地下水长期作用下必将加剧库岸斜坡的深部形变。     

The zonal E×B plasma drift effects on the low latitude ionosphere electron density at solar minimum near equinox

The F2-layer peak density, NmF2, and peak altitude, hmF2, which were observed by 12 ionospheric sounders during the 20 September 1964 geomagnetically quiet time period at solar minimum are compared with those calculated by the three-dimensional time-dependent theoretical model of the Earth's low and middle latitude ionosphere and plasmasphere. The modeled NmF2 are also compared with those measured during the geomagnetically quiet time periods of 12–15, 18–21, and 26 September 1964 to take into account observed day-to-day ionospheric variability. Major features of the data are reproduced by the model if the corrected HWM90 neutral wind is used. The changes in NmF2 due to the zonal E×B plasma drift are found to be less than 20% in the daytime low latitude ionosphere. The model, which does not take into account the zonal E×B plasma drift, underestimates night-time NmF2 up to the maximum factor of 2 at low geomagnetic latitudes. The night-time increase of NmF2 caused by the zonal E×B plasma drift is less pronounced at −20° and 20° geomagnetic latitudes in comparison with that between −10° and 10° geomagnetic latitude. The longitude dependence of the calculated night-time low latitude influence of the zonal E×B plasma drift on NmF2 is explained in terms of the longitudinal asymmetry in B (the eccentric magnetic dipole is displaced from the Earth's center and the Earth's eccentric tilted magnetic dipole moment is inclined with respect to the Earth's rotational axis), and the variations of the wind induced plasma drift and the meridional E×B plasma drift in geomagnetic longitude. The difference between the hmF2 values calculated by including the effect of zonal E×B drift and that obtained when it is excluded does not exceed 19 km in the low latitude ionosphere. Over the geomagnetic equator the zonal E×B plasma drift produces the maximum increase in the electron density by a factor of 1.06–1.48 and 1.05–1.30 at 700 and 1000 km altitude, respectively, and this increase is not significant above about 1500 km. Changes in the vertical electron content, VEC, caused by the zonal E×B plasma do not exceed 16% during the day, while the value of the night-time VEC is increased up to a factor of 1.4 due to this drift. The maximum effects of the zonal E×B plasma drift on the night-time electron density derived from the model results corresponding to solar minimum and maximum are quite comparable.     

Pulsating of the generalized ion and neutral polar winds

A three-dimensional, time-dependent model of the ion and neutral polar winds was used to study their dynamic evolution during the May 4, 1998 magnetic storm. The simulation tracked the dynamics of five species (O⁺, H⁺, H_s, O_s, and electrons) and covered a 9-h period. During the storm, D_st decreased to −210 nT, Ap reached 300, and K_p was elevated. The IMF B_z component was southward at the start of the storm and for several hours thereafter and then turned northward. However, the magnetospheric energy input to the ionosphere exhibited a 50-min oscillation, with the plasma convection and particle precipitation patterns expanding and contracting in a periodic manner. As a consequence, the ion and neutral polar winds pulsated with an approximate 50-min period. The H⁺ and O⁺ ions displayed cyclic upflows and downflows in the topside ionosphere as well as a highly structured spatial distribution that varied with time. The vertical flux of the neutral H_s atoms was upward at the top of the ionosphere, but the magnitude varied in a cyclic manner in response to the oscillating stormtime energy input. The vertical flux of neutral O_s atoms was downward at the top of the ionosphere and varied significantly with the stormtime energy input. For H⁺, O⁺, and H_s, the maximum total (integrated) vertical flux during the storm was upward at the top of the ionosphere, with values of 8–9×10²⁵ particles/s for H⁺, 2–4×10²⁶ particles/s for O⁺, and 2–3×10²⁷ particles/s for H_s. The corresponding total vertical O_s flux was predominately downward, with only localized areas with positive fluxes.