Generating Two-Dimensional Fields of Autocorrelated, Normally Distributed Parameters by the Matrix Decomposition Technique   总被引：1，自引：0，他引：1  

Aly I. El-Kadi  Stan A. Williams 《Ground water》2000,38(4):530-532

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Multifractal versus monofractal analysis of wetland topography   总被引：2，自引：1，他引：1  

I. Tchiguirinskaia  S. Lu  F. J. Molz  T. M. Williams  D. Lavallée 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(1):8-32

The land surface elevation distribution will serve as fundamental input data to any wetland flow model. As an alternative to the traditional smooth function approach to represent or interpolate elevation data, we explore the use of Levy monofractals and universal multifractals as a means for defining a statistically equivalent topography. The motivation behind this effort is that fractals, like natural topography, are irregular, they offer a way to relate elevation variations measured at different scales, and the relationships are of a statistical nature. The study site was a riparian wetland near Savannah, GA, that contained beavers, and a total of four elevation transects were examined. The elevation increments showed definite non-Gaussian behavior, with parameter values, such as the Hurst coefficient and Lévy index (α), depending on the question of presence of beaver activity. It was obvious that the data were highly irregular, especially the transects influenced by beavers. Significantly different α values were obtained depending on whether the entire data set or just the tails were examined, which demonstrated inability of the monofractal model to reflect fully the irregularity of wetland data. Further analysis confirmed definite multifractal scaling, and it is concluded that the multifractal model is superior for this data set. Universal multifractal parameters are calculated and compared to those obtained previously for more typical terrain. Although it is difficult to consider a unique universal multifractal parameter α for the entire wetland, multifractal-like scaling was evident in each transect as reflected by the nonlinear behaviors of the scaling functions. We demonstrate a good agreement between theory and measurements up to a critical order of statistical moments, q _D , close to 3.5 and obtain realistic unconditioned simulations of multifractal wetland topography based on our parameter estimates. Future work should be devoted to conditioning multifractal realizations to data and to obtaining larger data sets so that the question of anisotropy may be studied.  相似文献   

大别山碧溪岭深色榴辉岩和片麻状花岗质岩石SHRIMP分析：晋宁期？…   总被引：64，自引：15，他引：49  

程裕淇  刘敦一  I. S. Williams  简平  庄育勋  高天山 《地质学报》2000,74(3):193-205

本文报道大别山安徽省岳西县碧溪岭深色榴辉岩和片麻状花岗质岩石的锆石SHRIMP分析结果.深色榴辉岩的原岩为基性凝灰岩,锆石在岩石中主要产于石英、石榴子石和绿辉石内,为高压-超高压变质作用的产物,内部主体形成年龄约为757±7 Ma,代表高压-超高压榴辉岩相变质事件的时代;经受了后期流体改造的锆石边部年龄为223±3 Ma.在片麻状花岗质岩石中,发育韵律环带结构的深熔锆石形成于约727±15 Ma,受后期流体改造的锆石边部年龄为219±3 Ma.综合野外地质关系、区域地质背景和锆石的岩相学特征,笔者提出了碧溪岭榴辉岩相岩石高压-超高压变质作用发生于晋宁期,印支期仅代表一次后期流体改造事件的观点.  相似文献   

Excursion to St. Albans,Tyttenhanger and Hill end: Saturday,July 20th, 1918     

Arthur H. Williams 《Proceedings of the Geologists' Association. Geologists' Association》1918,29(3):149

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Geologic and Hydrologic Factors Controlling Radon-222 in Ground Water in Maine   总被引：2，自引：0，他引：2  

Willem F. Brutsaert  Stephen A. Norton  Charles T. Hess  John S. Williams 《Ground water》1981,19(4):407-417

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Erratum     

Northridge  S. P.; Tasker  M. L.; Webb  A.; Williams  J. M. 《ICES Journal of Marine Science》1995,52(6):1005-1012

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Handbook of geostationary orbits     

B. G. Williams 《Celestial Mechanics and Dynamical Astronomy》1996,65(4):459-460

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Shock strengths in clumps impacted by winds of increasing power     

A.J. Lim  T.W. Hartquist  D.A. Williams 《Monthly notices of the Royal Astronomical Society》2001,326(3):1110-1114

We have performed spherically symmetric and axisymetric hydrodynamic simulations of wind–clump interactions in order to determine the conditions under which a wind, impacting upon a clump and increasing in power with time, drives a strong shock into the clump. If the wind ram pressure and the clump thermal pressure are comparable when the impact first occurs, then the wind ram pressure must increase on a time-scale markedly smaller than the sound-crossing time of the clump if it is to drive a shock that becomes strong at any point in the clump. We comment on the possible relevance of this result for the dynamics and chemistry of hot cores in regions of high-mass star formation.  相似文献   

A study of three extraction methods for hydrocarbons in marine sediment     

M.K. Wong  P.J.leB. Williams 《Marine Chemistry》1980,9(3):183-190

Three methods for the extraction of hydrocarbons from surface sediments were studied. The methods were: (1) digestion by methanolic-KOH and extraction with methanol; (2) Soxhlet extraction with chloroform and (3) Soxhlet extraction with carbon tetrachloride. Results are presented and compared.  相似文献   

On the contribution of grain surface reactions to interstellar molecule densities     

M. A. Leitch-Devlin  T. J. Millar  J. Pickles  D. A. Williams 《Astrophysics and Space Science》1976,44(2):385-388

Some recent arguments concerning the relevance of grain surface reactions to interstellar molecule formation are shown to be without foundation. It is probable that surface reactions, gas phase ion-molecule and neutral reactions all contribute to interstellar molecular densities.  相似文献