Characterization of cristobalite in ash and dome rock from the Soufriere Hills volcano, Montserrat： Implications for respiratory health hazards     

Ben J. Williamson Claire J. Horwell 《中国地球化学学报》2006,25(B08):224-225

A link between the inhalation of respirable silicas （SiO2） and respiratory diseases such as silicosis is widely recognized. Ash from dome collapse eruptions on Montserrat has been found to contain high levels （〉20%） of silicas in the form of cristobalite, tridymite, quartz and/or amorphous silica. The toxicity of these silica polymorphs varies widely. Cristobalite and quartz （tridymite less well established） are viewed as carcinogenic to humans whereas amorphous silica generally shows a reduced biological response. In assessing the potential health effects of volcanic ash particulates it is vital to determine the types and concentration of silicas as well as their size （respirable fraction）, shape and surface properties. The aim of this study is to develop methods to assess potentially toxic respirable airborne silicas in the dome collapse ash （applicable to a range of ash types） and to develop a model to predict the levels and types of respirable silicas from future eruptions. The model is being developed by comparing dome rock with related ash from a series of previous eruption events. Mineralogical assessment using conventional scanning X-ray diffraction （XRD） was hampered by difficulties in differentiating characteristic peaks for cristobalite and tridymite in complex multi-component ash samples （containing high levels of plagioclase）. These difficulties have been largely overcome using an Enraf-Nonius PDS120 diffractometer with curved （120 degrees 20） position sensitive detector （PSD）. The determination of size, shape and elemental characteristics of ash particulate and dome rock samples has been carried out using automated analytical scanning electron microscopy. The quantification of mineral proportions using PSD-XRD was highly successful with an accuracy of 1 to 2 wt%. However, the determination of phase proportions using automated analytical SEM was problematic due to scattering effects and the multiphase nature of many of the particles.  相似文献   

Computer simulation studies of Crystallization under confinement conditions     

Fernando Bresme  Luis G. Cmara 《Chemical Geology》2006,230(3-4):197-206

Crystallization under confinement conditions is a very important process in geochemistry and geophysics. Computer simulations of fluids in nanometer scale pore spaces can provide a unique microscopic insight into the structure, dynamics and forces arising from the crystallization process. We discuss in this paper molecular dynamics computer simulations of crystallization in pores of nanometer dimensions. The crystallization pressure due to the freezing of a model of Argon in a nanopore is computed using molecular dynamics simulations. We also investigate the influence of pore geometry in determining the dynamics of confined fluids, as well as mass separation in binary mixtures. It turns out that the pore geometry reveals itself as an important variable, leading to 1) new mechanisms for fast diffusion in confined spaces, and 2) accumulation of solute in specific regions inside the pore.  相似文献   

Estimating the minimum in-stream flow requirements via wetted perimeter method based on curvature and slope techniques     

LIU Suxia  MO Xingguo  XIA Jun  LIU Changming  LIN Zhonghui  MEN Baohui  JI Lina 《地理学报》2006,16(2):242-250

Under the assumptions of triangular cross section channel and uniform stable flow, an analytical solution of the minimum ecological in-stream flow requirement (MEIFR) is deduced. Based on the analytical solution, the uncertainty of the wetted perimeter method is analyzed by comparing the two techniques for the determination of the critical point on the relationship curve between wetted perimeter, P and discharge, Q. It is clearly shown that the results of MEIFR based on curvature technique (corresponding to the maximum curvature) and slope technique (slope being 1) are significantly different. On the P-Q curve, the slope of the critical point with the maximum curvature is 0.39 and the MEIFR varied prominently with the change of the slope threshold. This indicates that if a certain value of the slope threshold is not available for slope technique, curvature technique may be a better choice. By applying the analytical solution of MEIFR in the losing rivers of the Western Route South-to-North Water Transfer Project in China, the MEIFR value via curvature technique is 2.5%-23.7% of the multi-year average annual discharge, while that for slope technique is 11%-105.7%. General conclusions would rely on the more detailed research for all kinds of cross-sections.  相似文献   

GPS高程拟合的方式及可靠性分析   总被引：2，自引：1，他引：2  

伍青云 《中国煤田地质》2006,18(3):70-72

在范围不大的区域中，高程异常具有一定的几何相关性，GPS高程拟合就是利用这一原理，求解正常高。在解析法求解过程中，首先用最小二乘法确定拟合数学模型的系数，在此基础上计算出待测点的高程异常值。通过实例验证：GPS高程拟合的精度主要取决于GPS大地高的精度、重合点正常高的精度、重合点的分布及拟模型的选择。一般在重合点数量充足且分布均匀的情况下，GPS高程拟合的精度可达到四等水准网的精度要求。  相似文献   

A mathematical hysteretic model for elastomeric isolation bearings     

J. S. Hwang  J. D. Wu  T.‐C. Pan  G. Yang 《地震工程与结构动力学》2002,31(4):771-789

An analytical model for high damping elastomeric isolation bearings is presented in this paper. The model is used to describe mathematically the damping force and restoring force of the rubber material and bearing. Ten parameters to be identified from cyclic loading tests are included in the model. The sensitivity of the ten parameters in affecting the model is examined. These ten parameters are functions of a number of influence factors on the elastomer such as the rubber compound, Mullins effect, scragging effect, frequency, temperature and axial load. In this study, however, only the Mullins effect, scragging effect, frequency and temperature are investigated. Both material tests and shaking table tests were performed to validate the proposed model. Based on the comparison between the experimental and the analytical results, it is found that the proposed analytical model is capable of predicting the shear force–displacement hysteresis very accurately for both rubber material and bearing under cyclic loading reversals. The seismic response time histories of the bearing can also be captured, using the proposed analytical model, with a practically acceptable precision. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

圆弧状沉积盆地与软土单覆盖层出平面地表运动对比   总被引：2，自引：0，他引：2  

袁晓铭  李雨润  孙锐 《地震工程与工程振动》2002,22(4):16-21

采用解析方法，通过圆弧状沉积盆地与同样参数的软土均匀单覆盖层的对比，研究沉积盆地对平面SH波二维散射效应和其出平面地表运动。数值对比结果表明：（1）波垂直入射时盆地中央地表位移幅值反应，其随频率变化形式与软土单覆盖层的地表运动有较强的对应性，且此时单覆盖层地表位移幅值为其下降；（2）盆地的二维散射效应特点显著波的汇聚作用使盆地中的地表运动显著放大，总体上较软土单覆盖层的地表位移幅值要大，其频域内的最大反应则明显大于单覆盖层情况，但最大反应在盆地表面出现的位置依赖于入射波角度、盆地深宽比和盆地的软硬程度；（3）沉积盆地中地表位移运动有强烈扭转效应，且随盆地变软和入射波频率增高而增强。  相似文献   

From stable dipolar towards reversing numerical dynamos     

C. Kutzner  U.R. Christensen 《Physics of the Earth and Planetary Interiors》2002,131(1):29-45

We are using a three-dimensional convection-driven numerical dynamo model without hyperdiffusivity to study the characteristic structure and time variability of the magnetic field in dependence of the Rayleigh number (Ra) for values up to 40 times supercritical. We also compare a variety of ways to drive the convection and basically find two dynamo regimes. At low Ra, the magnetic field at the surface of the model is dominated by the non-reversing axial dipole component. At high Ra, the dipole part becomes small in comparison to higher multipole components. At transitional values of Ra, the dynamo vacillates between the dipole-dominated and the multipolar regime, which includes excursions and reversals of the dipole axis. We discuss, in particular, one model of chemically driven convection, where for a suitable value of Ra, the mean dipole moment and the temporal evolution of the magnetic field resemble the known properties of the Earth’s field from paleomagnetic data.  相似文献   

Simulation of individual particle movement in a gravel streambed     

J. Mikael Malmaeus  Marwan A. Hassan 《地球表面变化过程与地形》2002,27(1):81-97

A two‐dimensional simulation model of travel distances of individual particles in a gravel‐bed river is presented. The model is based on a number of rules, which include particle size, entrainment, trajectory, distance of movement and entrapment. Particle interactions are controlled by resistance fields defined about each obstacle and critical elevation defined in the model. Resistance fields, particle dropping and critical elevation rules control particle interactions. The interaction rules cause the particles to develop pebble clusters, stone cells and transverse structures (transverse ribs). The simulated travel distances of individual particles are consistent with reported field results. Individual particle travel distances were simulated using two different models; one without interactions between the individual particles and the stationary bed and one with interactions. The case without interactions demonstrates the random nature of sediment transport, and narrow ranges of travel distances. Wider ranges of travel distances, similar to those for natural situations, were obtained for the cases with interactions. The more intense the interaction between the mobile stones and the stationary ones, the wider the range of distances of travel for a given particle size. Modelling the mean travel distance yielded a result similar to that published previously, which was based on empirical data. Well developed bed‐surface structures were obtained for relatively poorly sorted sediment with intense interactions between particles. Transverse structures developed when relatively large particles were allowed to move. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

嵌岩桩与含沉渣桩低应变动力检测曲线理论计算方法与特征研究   总被引：2，自引：3，他引：2  

刘煜洲  刘东甲  王杰英 《物探化探计算技术》2003,25(2):97-104

根据文献[1]、[2]介绍了基桩反射波法动测正演问题的数理模型、计算方法及其通用性，并据此计算了完整嵌岩桩及有不同厚度沉渣的嵌岩桩与摩擦桩的理论曲线。提出了在一定物性参数条件下判断沉渣是否超过规定标准的方法，并给出了数个实例。  相似文献   

3-D rheologic model of earthquake preparation (I)—Displacement field     

宋治平  尹祥础  梅世蓉 《地震学报(英文版)》2003,(6)

Introduction The rock medium shows mainly elastic character under low-temperature, low-pressure and external force for short duration, yet it shows rheologic property under high-temperature, high-pressure and long-time external force. It is reasonable that the rapid earthquake generating process lasted for tens seconds is analyzed by the elastic theory. As for the earthquake generating process for hundreds or thousand years, nevertheless, the rheologic property of rock must be taken into accou…  相似文献