Competitive heavy metals adsorption on natural bed sediments of Jajrood River,Iran   总被引：3，自引：1，他引：2  

Mohsen Saeedi  Majid Hosseinzadeh  Maryam Rajabzadeh 《Environmental Earth Sciences》2011,62(3):519-527

The presence of heavy metal concentrations was examined in natural sediments from four sites along the Jajrood river in northeast of Tehran, the capital of Iran. Besides determination of elemental concentrations (Pb, Cu, Zn, Cd, Ni and Cr), X-ray fluorescence and X-ray diffraction tests were carried out to determine other chemical components in these adsorbents. Also the ability of sediments to adsorb these heavy metal ions from aqueous solutions was investigated. Results show that the extent of adsorption increases with increase in adsorbent concentration. The amount of adsorbed Pb, Cu and Zn in sediments was much greater than that of the other metals, and Cr was adsorbed much less than others. The adsorbabilities of sediments to heavy metals increased in the order of Pb > Cu > Zn > Cd > Ni > Cr. Based on the adsorption data, equilibrium isotherms were determined at selected areas to characterize the adsorption process. The adsorption data followed Freundlich and Langmuir isotherms in most cases. Correlation and cluster analysis was performed on heavy metals adsorption and sediment components at each site to evaluate main adsorbing compounds in sediments for each metal. Results demonstrated that heavy metals sorption is mostly related to load of organic matter in the Jajrood river sediments.  相似文献   

Sorption of lead on Iranian bentonite and zeolite: kinetics and isotherms     

Mohsen Hamidpour  Mahmoud Kalbasi  Majid Afyuni  Hossein Shariatmadari  Gerhard Furrer 《Environmental Earth Sciences》2011,62(3):559-568

This study deals with the use of the natural, low-cost sorbents bentonite and zeolite for the removal of lead from aqueous solutions. The mineral material is from large deposits of bentonite and zeolite that have been discovered recently in Iran. Experimental and modeling data from our kinetic and equilibrium investigations reveal that (1) the pseudo-second-order kinetic model gave the best fit, and (2) the Koble–Corrigan sorption model describes the interaction between Pb(II) and the two mineral materials better than the Freundlich and Langmuir models. However, the sorption of Pb(II) ions by zeolite and bentonite is complex and probably involves several mechanisms. The experimental data show that natural zeolite and bentonite used in this study exhibited a reasonable sorption capacity for Pb(II), and thus may be useful for the immobilization of Pb(II) from polluted sites.  相似文献   

Gravitational instability of discs with dissipative coronae around supermassive black holes     

Fazeleh Khajenabi  Mohsen Shadmehri 《Monthly notices of the Royal Astronomical Society》2007,377(4):1689-1695

We study the dynamical structure of a self-gravitating disc with coronae around a supermassive black hole. Assuming that the magnetorotational instability responsible for generating the turbulent stresses inside the disc is also the source for a magnetically dominated corona, a fraction of the power released when the disc matter accretes is transported to and dissipated in the corona. This has a major effect on the structure of the disc and its gravitational (in)stability according to our analytical and self-consistent solutions. We determine the radius where the disc crosses the inner radius of gravitational instability and forms the first stars. Not only the location of this radius which may extend to very large distances from the central black hole, but also the mass of the first stars highly depends on the input parameters, notably the viscosity coefficient, the mass of the central object and the accretion rate. For accretion discs around quasi-stellar objects (QSOs) and the Galactic Centre, we determine the self-gravitating radius and the mass of the first clumps. Comparing the cases with a corona and without a corona for typical discs around QSOs or the Galactic Centre, when the viscosity coefficient is around 0.3, we show that the self-gravitating radius decreases by a factor of approximately 2, but the mass of the fragments increases with more or less the same factor. The existence of a corona implies a more gravitationally unstable disc according to our results. The effect of a corona on the instability of the disc is more effective when the viscosity coefficient increases.  相似文献   

Formation of Small-Scale Condensations in the Molecular Clouds via Thermal Instability     

Mohsen Nejad-Asghar  Jamshid Ghanbari 《Astrophysics and Space Science》2006,302(1-4):243-251

A systematic study of the linear thermal instability of a self-gravitating magnetic molecular cloud is carried out for the case when the unperturbed background is subject to local expansion or contraction. We consider the ambipolar diffusion, or ion-neutral friction on the perturbed states. In this way, we obtain a non-dimensional characteristic equation that reduces to the prior characteristic equation in the non-gravitating stationary background. By parametric manipulation of this characteristic equation, we conclude that there are, not only oblate condensation forming solutions, but also prolate solutions according to local expansion or contraction of the background. We obtain the conditions for existence of the Field lengths that thermal instability in the molecular clouds can occur. If these conditions establish, small-scale condensations in the form of spherical, oblate, or prolate shape may be produced via thermal instability.  相似文献   

Constraints on star formation from the close packing of protostars in clusters     

B. G. Elmegreen  Mohsen Shadmehri 《Monthly notices of the Royal Astronomical Society》2003,338(4):817-823

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Simulation of Salinity Distribution of Anbar Salt Dome in Gotvand Reservoir in Iran,Using System Dynamics and Proposes a Strategy to Reduce Salinity     

Monjezi  Sara  Najarchi  Mohsen  Mo’meni  Mansour  Monjezi  Narges  Hassuninezade  Houshang 《Water Resources》2021,48(6):1013-1022

Water Resources - To water quality management of the Gotvand Reservoir, this paper attempts to determine to what extent the negative impacts of Anbar salt domes dissolution can be reduced...  相似文献   

Validation of soil moisture simulation with a distributed hydrologic model (WetSpa)     

Mohsen Tavakoli  Florimond De Smedt 《Environmental Earth Sciences》2013,69(3):739-747

The objective of this paper is to test the ability of a spatially distributed hydrologic model (WetSpa) to simulate soil moisture. The test is conducted in the Baron Fork river basin (Oklahoma, USA), where soil moisture has been recorded on a daily basis at the WEST site soil moisture monitoring station of the Oklahoma Mesonet. The model is calibrated by comparing hourly simulated and observed river flows at Eldon gaging station from October 1, 1995 to December 31, 1996. The model performance to predict hourly river flows is verified by comparing model estimates and observations from January 1, 1997 to December 31, 2000. Next, the model predictions of soil moisture are compared with observations of WEST site soil moisture monitoring station for the same validation period. The observations are well reproduced by the model with errors that are within range of the observation accuracy, although the predictions show somewhat more abrupt temporal fluctuations as the whole root zone is considered to react instantaneously to precipitation events. The good performance compared to other studies is especially attributed to the quality of the rainfall data provided by weather radars. It is concluded that the performance of the model to predict soils moisture is promising, although spatial patterns still have to be verified.  相似文献   

Effects of cations and anions on iron and manganese sorption and desorption capacity in calcareous soils from Iran     

Somayeh Moharami  Mohsen Jalali 《Environmental Earth Sciences》2013,68(3):847-858

This study investigated the effect of cations and anions on the sorption and desorption of iron (Fe) and manganese (Mn) in six surface calcareous soil samples from Western Iran. Six 10 mM electrolyte background solutions were used in the study, i.e., KCl, KNO₃, KH₂PO₄, Ca(NO₃)₂, NaNO₃, and NH₄NO₃. NH₄NO₃ and NaNO₃ increased the soil retention of Fe and Mn, whereas Ca(NO₃)₂ decreased the soil retention of Fe and Mn. Iron and Mn sorption was decreased by NO₃ ^? compared with H₂PO₄ ^? or Cl^?. The Freundlich equation adequately described Fe and Mn adsorption, with all background electrolytes. The Freundlich distribution coefficient (K _F) decreased in the order H₂PO₄ ^? > Cl^? > NO₃ ^? for Mn and H₂PO₄ ^? > NO₃ ^? > Cl^? for Fe. The highest sorption reversibility was for Fe and Mn in competition with a Ca²⁺ background, indicating the high mobility of these two cations. A MINTEQ speciation solubility model showed that Fe and Mn speciation was considerably affected by the electrolyte background used. Saturation indices indicated that all ion background solutions were saturated with respect to siderite and vivianite at low and high Fe concentrations. All ion background solutions were saturated with respect to MnCO_3(am), MnHPO₄, and rhodochrosite at low and high Mn concentrations. The hysteresis indices (HI) obtained for the different ion backgrounds were regressed on soil properties indicating that silt, clay, sand, and electrical conductivity (EC) were the most important soil properties influencing Fe adsorption, while cation exchange capacity (CEC), organic matter (OM), and Mn-DTPA affected Mn adsorption in these soils.  相似文献   

Effect of vapor pressure of grains in formation of planetesimals through the accretion disc     

Mahmoud Gholipour  Mohsen Nejad-Asghar 《Astrophysics and Space Science》2013,344(2):365-369

The role of grains in evolution of accretion disc is an important issue in astrophysics. In this paper, we study the effect of vapor pressure of grains in the dead zones of protoplanetary discs. Our study is limited to some particular observed cases in which evaporation of grains would be important and their vapor gas are constrained to an approximately isolated case. Here, we use the Einstein model to investigate the thermodynamics of vapor pressure. The results show that there is a critical temperature as a function of oscillation frequency and binding energy of particles. For temperatures greater than this critical value, the system goes into unstable mode. We show that the dead zone of the disc may reach to enough conditions to condense via instability caused by vapor pressure of grains. This mechanism may play an important role in the formation of planetesimals through protoplanetary disc.  相似文献   

Translating Bertin into Arabic today: new hidden facets of Semiology of Graphics     

Mohsen Dhieb 《制图学和地理信息科学》2013,40(2):163-175

ABSTRACT

Semiology of Graphics is a seminal work of contemporary cartography. Published in 1967 by Jacques Bertin, the book attracted as much mistrust as it did interest even if some claims seem obsolete or outdated with the advent of GIS. This article discusses some underlying perspectives regarding an Arabic translation of Sémiologie Graphique. First, one may question the usefulness and the language of translation, and what issues readers should learn or be aware of before reading the book. In the Arab world, little research has engaged graphical semiology and its paradigms are rarely encountered. Second, only a limited number of graphical procedures have been experimented or implemented by digital means. There is a gap between some theoretical statements and their practical applications. Third, many other semiological aspects remain, in substance, little known in detail. This article considers whether these should be revisited by visualization and graphical analytics.  相似文献