Modeling Biogeochemistry,the Key for Understanding Environmental Chemistry of a Semi－Arid Soil in Egypt     

Ahmed A. Melegy 《中国地球化学学报》2003,22(2):150-155

1IntroductionThecomponentsoftheenvironmentaredamagedbyagriculturalpractices.Soilslosstheirfer tilityandwaterdeterioratesduetopollution .Chemicalweatheringofmineralandsoiloccursattheinterfacesbetweentheliquidandsolidphases;consequentlythesurfaceareaandcompositionofthemineralsplayanimportantroleinthisprocess.GarrelsandMackenzie ( 1 96 7)suggestedthatincon gruentweatheringreactionswouldproducedissolvedspeciesandnewsolidsthataremorestableintheweatheringenvironmentthantheoriginalbedrockminerals.Ro…  相似文献   

Single-Column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer   总被引：2，自引：15，他引：2  

J. Cuxart  A. A. M. Holtslag  R. J. Beare  E. Bazile  A. Beljaars  A. Cheng  L. Conangla  M. Ek  F. Freedman  R. Hamdi  A. Kerstein  H. Kitagawa  G. Lenderink  D. Lewellen  J. Mailhot  T. Mauritsen  V. Perov  G. Schayes  G-J. Steeneveld  G. Svensson  P. Taylor  W. Weng  S. Wunsch  K-M. Xu 《Boundary-Layer Meteorology》2006,118(2):273-303

The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.  相似文献   

Controlling factors of groundwater hydrochemistry in a small island’s aquifer   总被引：3，自引：0，他引：3  

A. Z. Aris  M. H. Abdullah B.Sc.  M.Sc.  Ph.D.  A. Ahmed B.Sc.  M.Sc.  Ph.D.  K. K. Woong B.Sc.  M.Sc.  Ph.D. 《International Journal of Environmental Science and Technology》2007,4(4):441-450

Factor analysis was applied to the hydrochemical data set of Manukan Island in order to extract the principal factors corresponding to the different sources of variation in the hydrochemistry. The application of varimax rotation was to ensure the clear definition of the main sources of variation in the hydrochemistry. The geochemical data of dissolved major, minor and trace constituents in the groundwater samples indicates the main processes responsible for the geochemistry evolution. By using Kaiser normalization, principal factors were extracted from the data for each location. The analysis reveals that there are four sources of solutes: (1) seawater intrusion; (2) leaching process of underlying rock mediated by pH; (3) minerals weathering process and (4) dissolution of carbonate minerals characterized by high loadings of Ca, Zn and Mg. Such processes are dominated by the significant role of anthropogenic impact from the over abstraction of fresh water from the aquifer. Those factors contributed to the changes of the groundwater geochemistry behavior explain the effect of rising extraction of freshwater from the aquifer.  相似文献   

Evaluation of Electro-Oxidation of Textile Effluent Using Response Surface Methods     

R. Saravanathamizhan  N. Mohan  N. Balasubramanian  V. Ramamurthi  C. Ahmed Basha 《洁净——土壤、空气、水》2007,35(4):355-361

In the present investigation, treatment of textile effluent using an electrochemical technique was designed and analyzed using the Box-Behnken method. The influence of individual parameters on electro-oxidation of textile effluent has been critically examined using the response surface method (RSM), and a quadratic model for chemical oxygen demand (COD) reduction has been developed. It has been observed from the present analysis that the predicted values are in good agreement with experimental data with a correlation coefficient of 0.945.  相似文献   

Longitudinal vibration of non-homogeneous earth dams     

Ahmed M. Abdel-Ghaffar  Aik-Siong Koh 《地震工程与结构动力学》1981,9(3):279-305

Two-dimensional analytical elastic models are developed for evaluating dynamic characteristics, namely natural frequencies and modes of vibration of a wide class of earth dams in a direction parallel to the dam axis. In these models the non-homogeneity of the dam materials is taken into account by assuming a specific variation of the stiffness properties along the depth (due to the continuous increase in confining pressure). In addition, both shear and normal (axial) deformations are considered. Cases having constant elastic moduli, linear and trapezoidal variations of elastic moduli, and elastic moduli increasing as the one-half, one-third, two fifths, and a general (l/m)th powers of the depth are studied. Dynamic properties of three real earth dams in a seismically active area (Southern California) estimated from their earthquake records (input ground motion and crest response in the longitudinal direction) as well as results from full-scale dynamic tests on one of these dams (including ambient and forced vibration tests) are compared with those from the suggested models. It was found that the models in which the shear modulus and the modulus of elasticity of the dam material vary along the depth are the most appropriate representations for predicting the dynamic characteristics. The agreement between the experimental and earthquake data and the theoretical results from some of the models is reasonably good.  相似文献   

Electrochemical studies of sulphides,I. The electrocatalytic activity of galena,pyrite and cobalt sulphide for oxygen reduction in relation to xanthate adsorption and flotation     

S.M. Ahmed 《International Journal of Mineral Processing》1978,5(2):163-174

The electrocatalytic activity of galena, pyrite and Co₃S₄ for oxygen reduction has been studied by potentiostatic methods. Open circuit potentials of the sulphide electrodes have also been measured as a function of pH in nitrogen, air and oxygen atmospheres and also in the presence of H₂O₂ and ethyl xanthate. The adsorption of xanthate on sulphides was followed by observing bubble attachment to the electrodes.The catalytic activity for oxygen (or H₂O₂) reduction (the cathodic currents), the electrode potentials and the xanthate adsorption as shown by bubble attachment within certain pH limits, all varied as $\text{Co}{}_3\text{S}{}_4\text{> pyrite (≈ PbS in H}{}_2\text{O}{}_2\text{) ? PbS}$ indicating considerable dependence of the redox processes in flotation on the d - electron character of the sulphides.In the absence of oxygen, xanthate is probably bonded to the water structure of the surface through hydrogen-bonding, thus keeping the surface hydrophilic. Such adsorption reduces the electrode potential and inhibits oxygen reduction.  相似文献   

Evidence of the impacting body of the Ries crater — the discovery of Fe-Cr-Ni veinlets below the crater bottom     

Ahmed El Goresy  E.C.T. Chao 《Earth and Planetary Science Letters》1976,31(3):330-340

Fe-Cr-Ni particles and veinlets have been discovered in the top 15 m of the compressed zone with abundant shatter cones below the bottom of the Ries crater. The metallic particles are less than a few microns across. They occur in various minerals along healed intergranular and locally in intragranular microfractures in quartz diorite, amphibolite and chloritized granite of the basement crystalline rocks.The particles consist of major Fe, Cr, and Ni with minor Si and Ca. Origin due to contamination is absolutely ruled out. We believe that these Fe-Cr-Ni particles are probably condensed from the vaporized impacting body which produced the Ries crater. These particles were injected with high velocity into microfractures near the top of the compressed zone, implanted in and across various minerals before these microfractures were resealed. The presence of Si and Ca as well as the fact that the Cr content is nearly twice that of Ni, led us to conclude that the Ries impacting body is very likely not an iron meteorite but a stony meteorite.  相似文献   

The Arab gulf states — geographic change     

Ahmed A. A. Babikir 《GeoJournal》1986,13(3):194-196

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Intellectual property rights and the transfer of climate change technologies: issues,challenges, and way forward     

Ahmed Abdel-Latif 《Climate Policy》2015,15(1):103-126

The role of intellectual property rights (IPRs) in the development and transfer of climate change technologies has been a contentious issue in negotiations under the United Nations Framework Convention on Climate Change (UNFCCC). Irreconcilable differences seem to oppose those who believe IPRs are an inherent barrier to the transfer of climate change technologies and those who argue they are an essential incentive to innovation. After providing an overview of the polarized debate on this issue, this article reviews the existing literature and empirical evidence and looks into some practical initiatives and recent developments. Finally, it seeks to identify a way forward that could help overcome the current stalemate in international deliberations by suggesting a number of parameters to structure the discussion on this complex issue.  相似文献   

Potential impact of climate change on cereal crop yield in West Africa     

Kazi Farzan Ahmed  Guiling Wang  Miao Yu  Jawoo Koo  Liangzhi You 《Climatic change》2015,133(2):321-334

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