共查询到20条相似文献，搜索用时 31 毫秒
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David A Williams 《Astronomy& Geophysics》2000,41(3):3.08-3.16
An account of the RAS Presidential Address of 11 February 2000, given by David A Williams , Perren Professor of Astronomy, University College London. 相似文献
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A method to predict aquifer vulnerability to pesticide contamination at the subregional scale was developed. The assessment method was designed to incorporate relevant hydrologic and pesticide-transport information and to use generally available data. The method assumes steady-state advection of pesticides in the vadose zone, including sorption and biological decay. The solution is presented as a vulnerability index (VI) that increases as the aquifer vulnerability increases. The hydrologic input data for the VI model are obtained from the soil survey geographic database. Pesticides were grouped into three leachability classes using a leachability ratio (half-life divided by organic carbon partition coefficient). Pesticide transformation is assumed to occur in the surface layer. The influence of vertical transport in the remainder of the vadose zone has been incorporated by applying a multiplying factor to the VI that varies with depth to ground water. Hydraulic conductivity is used as a surrogate for soil-water velocity for practical purposes. The performance of the VI model is evaluated using ground water data from Weld County, Colorado. The model is demonstrated to be successful at predicting relative vulnerability, defined as the magnitude of pesticide concentration and percent of wells in a unit that exhibit a pesticide detection. Areas of low, medium, and high vulnerability are assigned. Results indicate that the vulnerability classifications are most dependent on the leachability ratio, hydraulic conductivity, and organic carbon content. 相似文献
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1996～2003年全世界灾害地震统计分析 总被引：5，自引：0，他引：5
讨论了1996～2003年8年期间全世界灾害地震的空间分布特征和地震灾情与全球地震活动性、地震震级和地震发震时刻的关系。结果表明：这8年期间地震灾情与全球地震活动性及地震震级无明显的统计相关关系,似乎与发震的国度、地震的发震时刻有一定的关系。 相似文献
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本文对钢筋混凝土框架的地震破坏进行了计算机模拟试验研究，指出了破坏过程中结构瞬态动力特性的变化特征，研究了影响瞬态动力特性的若干因素，明晰了结构整体耗能能力的大小与结构周期的延长之间的关系。作者认为结构瞬态动力特性和地震动的特性是影响结构破坏过程的主要因素，指出结构地震破坏模拟具有广阔的应用前景。 相似文献
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Baldwin BR Peacock AD Park M Ogles DM Istok JD McKinley JP Resch CT White DC 《Ground water》2008,46(2):295-304
Passive multilevel samplers (MLS) containing a solid matrix for microbial colonization were used as in situ microcosms in conjunction with a push-pull biostimulation experiment designed to promote biological U(VI) and Tc(VII) reduction. MLS were deployed at 24 elevations in the injection well and two downgradient wells to investigate the spatial variability in microbial community composition and growth prior to and following biostimulation. The microbial community was characterized by real-time quantitative polymerase chain reaction (Q-PCR) quantification of bacteria, NO(3)(-)-reducing bacteria (nirS and nirK), delta-proteobacteria, Geobacter sp., and methanogens (mcrA). Pretest cell densities were low overall but varied substantially with significantly greater bacterial populations detected at circumneutral pH (t-test, alpha= 0.05), suggesting carbon substrate and low pH limitations of microbial activity. Although pretest cell densities were low, denitrifying bacteria were dominant members of the microbial community. Biostimulation with an ethanol-amended ground water resulted in concurrent NO(3)(-) and Tc(VII) reduction, followed by U(VI) reduction. Q-PCR analysis of MLS revealed significant (1 to 2 orders of magnitude, Mann-Whitney U-test, alpha= 0.05) increases in cell densities of bacteria, denitrifiers, delta-proteobacteria, Geobacter sp., and methanogens in response to biostimulation. Traditionally, characterization of sediment samples has been used to investigate the microbial community response to biostimulation; however, collection of sediment samples is expensive and not conducive to deep aquifers or temporal studies. The results presented demonstrate that push-pull tests with passive MLS provide an inexpensive approach to determine the effect of biostimulation on contaminant concentrations, geochemical conditions, and the microbial community composition and function. 相似文献
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A methodology for improving geopotential models has been developed. Theoretical relations have been derived converting coefficients in harmonic expansions for radial distortions due to geopotential models into geopotential Stokes coefficients. Terms of the order of 10
–10
in magnitude have been retained. 相似文献
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S. E. Serrano T. E. Unny 《Stochastic Environmental Research and Risk Assessment (SERRA)》1987,1(4):281-296
Two methods for the solution of partial differential equations (PDE) for the general case of random in time physical parameters are presented and their application to the solution of unsteady regional groundwater flow equations are illustrated. The first method is the semigroup approach which directly offers a solution without resorting to closure approximations (hierarchy techniques), perturbation techniques, or Montecarlo simulation techniques. The semigroup approach can also handle the general stochastic problem when randomness also appears as initial conditions, boundary conditions or forcing terms. The second method is an approximation scheme to obtain the semigroup solution in complex cases and permits the solution of equations with more than one random coefficient. 相似文献
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Naohiro Nakamura 《地震工程与结构动力学》2006,35(2):217-231
In order to perform time history earthquake response analyses with consideration to both the dynamic soil–structure interaction and the non‐linear behaviour of the structure, it is important to transform the soil impedance in the frequency domain to the impulse response in the time domain. In this paper, a new transform method with high practicality is proposed. First, the formulation of the proposed transform method is described. Next, the validity of the method is examined using an example problem whose impulse response is analytically obtained. Then, the impedance of the rigid foundation on 2‐layered soil is transformed to the time domain, and the characteristics of the impulse response are investigated. Finally, time history earthquake response analyses of a structure on the soil using the obtained impulse response are carried out. The validity and the efficiency of the proposed method are confirmed through these investigations. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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考虑接连两次地震影响的建筑物震害分析方法 总被引：2，自引：1，他引：1
本文通过对建筑物进行静力弹塑性分析(Push-over)和静力循环往复加载分析,分别得到两次地震作用对建筑物所造成的损伤。分析表明,考虑两次地震对建筑物的影响,累积破坏现象明显。最后给出了一个六层钢筋混凝土框架结构的算例。 相似文献
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D.W. King R.A.W. Haddon E.S. Husebye 《Physics of the Earth and Planetary Interiors》1975,10(2):103-127
The results of a theoretical study of the interpretation of precursors to PP (Δ ～ 100°) in terms of scattering by small-scale random irregularities in the crust and uppermost mantle are presented. These results are compared with observational data from two nuclear explosions recorded at the Warramunga array and three earthquakes recorded at the NORSAR array. This comparison reveals that the scattering interpretation offers a plausible and adequate explanation of the detailed observational data, namely: onset times, duration, slowness, azimuth and amplitude variations. The scattering interpretation of PP precursors, along with a similar interpretation of precursors to PKPPKP, removes the need for postulating several sharp-reflecting discontinuities in the uppermost few hundred kilometers of the crust and upper mantle. 相似文献
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