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A. Shamsai - One of the best experts on this subject based on the ideXlab platform.
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A steady-state Saturation model to determine the subsurface travel time (STT) in complex hillslopes
Hydrology and Earth System Sciences, 2010Co-Authors: Touraj Sabzevari, Ali Talebi, Reza Ardakanian, A. ShamsaiAbstract:Abstract. The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature), soil properties and climate conditions. The Saturation Capacity of hillslopes affect the travel time of subsurface flow. The Saturation Capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent), hillslope length, profile curvature (concave, straight or convex) and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all complex hillslopes was presented. This equation is a function of the Saturation zone length (SZL) on the surface. Saturation zone length of the complex hillslopes was calculated numerically by using the hillslope-storage kinematic wave equation for subsurface flow, so an analytical equation was presented for calculating the Saturation zone length of the straight hillslopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsurface travel time, convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hillslopes and their Saturation Capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on Saturation zone extension were investigated.
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A steady-state Saturation model to determine the subsurface travel time (STT) in complex hillslopes
Hydrology and Earth System Sciences Discussions, 2009Co-Authors: Touraj Sabzevari, Ali Talebi, Reza Ardakanian, A. ShamsaiAbstract:Abstract. The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature), soil properties and climate conditions. The Saturation Capacity of hillslopes affect the travel time of subsurface flow. The Saturation Capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent), hillslope length, profile curvature (concave, straight or convex) and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all complex hillslopes was presented. This equation is a function of the Saturation zone length (SZL) on the surface. Saturation zone length of the complex hillslopes was calculated numerically by using the hillslope-storage Boussinesq (hsB) model in the steady state conditions, so an analytical equation was presented for calculating the Saturation zone length of the straight hillslopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsurface travel time, convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hillslopes and their Saturation Capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on Saturation zone extension were investigated.
Touraj Sabzevari - One of the best experts on this subject based on the ideXlab platform.
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A steady-state Saturation model to determine the subsurface travel time (STT) in complex hillslopes
Hydrology and Earth System Sciences, 2010Co-Authors: Touraj Sabzevari, Ali Talebi, Reza Ardakanian, A. ShamsaiAbstract:Abstract. The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature), soil properties and climate conditions. The Saturation Capacity of hillslopes affect the travel time of subsurface flow. The Saturation Capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent), hillslope length, profile curvature (concave, straight or convex) and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all complex hillslopes was presented. This equation is a function of the Saturation zone length (SZL) on the surface. Saturation zone length of the complex hillslopes was calculated numerically by using the hillslope-storage kinematic wave equation for subsurface flow, so an analytical equation was presented for calculating the Saturation zone length of the straight hillslopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsurface travel time, convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hillslopes and their Saturation Capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on Saturation zone extension were investigated.
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A steady-state Saturation model to determine the subsurface travel time (STT) in complex hillslopes
Hydrology and Earth System Sciences Discussions, 2009Co-Authors: Touraj Sabzevari, Ali Talebi, Reza Ardakanian, A. ShamsaiAbstract:Abstract. The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature), soil properties and climate conditions. The Saturation Capacity of hillslopes affect the travel time of subsurface flow. The Saturation Capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent), hillslope length, profile curvature (concave, straight or convex) and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all complex hillslopes was presented. This equation is a function of the Saturation zone length (SZL) on the surface. Saturation zone length of the complex hillslopes was calculated numerically by using the hillslope-storage Boussinesq (hsB) model in the steady state conditions, so an analytical equation was presented for calculating the Saturation zone length of the straight hillslopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsurface travel time, convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hillslopes and their Saturation Capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on Saturation zone extension were investigated.
Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.
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Adsorption mechanism of acids and bases in reversed-phase liquid chromatography in weak buffered mobile phases designed for liquid chromatography/mass spectrometry.
Journal of Chromatography A, 2009Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:Abstract The overloaded band profiles of five acido-basic compounds were measured, using weakly buffered mobile phases. Low buffer concentrations were selected to provide a better understanding of the band profiles recorded in LC/MS analyses, which are often carried out at low buffer concentrations. In this work, 10 μ L samples of a 50 mM probe solution were injected into C 18 -bonded columns using a series of five buffered mobile phases at pH W S between 2 and 12. The retention times and the shapes of the bands were analyzed based on thermodynamic arguments. A new adsorption model that takes into account the simultaneous adsorption of the acidic and the basic species onto the endcapped adsorbent, predicts accurately the complex experimental profiles recorded. The adsorption mechanism of acido-basic compounds onto RPLC phases seems to be consistent with the following microscopic model. No matter whether the acid or the base is the neutral or the basic species, the neutral species adsorbs onto a large number of weak adsorption sites (their Saturation Capacity is several tens g/L and their equilibrium constant of the order of 0.1 L/g). In contrast, the ionic species adsorbs strongly onto fewer active sites (their Saturation Capacity is about 1 g/L and their equilibrium constant of the order of a few L/g). From a microscopic point of view and in agreement with the adsorption isotherm of the compound measured by frontal analysis (FA) and with the results of Monte-Carlo calculations performed by Schure et al., the first type of adsorption sites are most likely located in between C 18 -bonded chains and the second type of adsorption sites are located deeper in contact with the silica surface. The injected concentration (50 mM) was too low to probe the weakest adsorption sites (Saturation Capacity of a few hundreds g/L with an equilibrium constant of one hundredth of L/g) that are located at the very interface between the C 18 -bonded layer and the bulk phase.
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Effect of the temperature on the isotherm parameters of phenol in reversed-phase liquid chromatography.
Journal of Chromatography A, 2004Co-Authors: Hyunjung Kim, Fabrice Gritti, Georges GuiochonAbstract:Adsorption isotherm data of phenol from an aqueous solution of methanol onto a C18-bonded silica (Symmetry-C18) were acquired by frontal analysis (FA) at six different temperatures, in a wide concentration range. The non-linear fitting of these data provided the bi-Langmuir model as best isotherm model, a conclusion further supported by the results of the calculation of the affinity energy distribution (AED). The isotherm parameters were obtained using several methods, the fitting of FA isotherm data, the calculation of the AED, and the inverse method, that uses overloaded elution band profiles. The different values obtained are in close agreement. They allow a quantitative investigation of the separate properties of the low- and the high-energy sites on the adsorbent surface. Increasing the temperature decreases the Saturation Capacity of the low-energy adsorption sites and the adsorption constant of the high-energy sites. In contrast, increasing the temperature does not cause any significant changes in either the Saturation Capacity of the high-energy sites or the adsorption constant of the low-energy sites.
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Accuracy and precision of adsorption isotherm parameters measured by dynamic HPLC methods.
Journal of Chromatography A, 2004Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:Abstract The fluctuations of the column temperature, the composition and the flow rate of the mobile phase affect the accuracy and precision of the adsorption isotherm parameters measured by dynamic HPLC methods. Experimental data were acquired by frontal analysis (FA) for phenol in equilibrium between C 18 -bonded Symmetry and a methanol:water mixture (20:80, v/v), at 303 K and a flow rate of 1 mL/min. The fluctuations of the experimental parameters were 0.1 K for the temperature, 0.1% for the mobile phase composition and 0.001 mL/min for the flow rate. The best isotherm model was shown to be the tri-Langmuir isotherm. Random errors were calculated and shown to agree with experimental results. Overloaded band profiles of phenol were acquired at low (sample size, 100 μL, concentration 3 g/L) and high (same sample size, concentration 60 g/L) loadings, at seven temperatures (298, 300, 302, 303, 304, 306, and 308 K), for seven mobile phase compositions (methanol 16, 18, 19, 20, 21, 22, and 24%), and with seven mobile phase flow rates (0.95, 0.97, 0.99, 1.00, 1.01, 1.03, and 1.05 mL/min), always keeping two experimental parameters at the values selected for the FA runs. Assuming that the isotherm model stays the same, the inverse method (IM) was used to derive the isotherm parameters in each case. Temperature affects the equilibrium constants according to Van’t Hoff law. A temperature change of 1 K around 303 K causes a relative variation of 1.5% of the high-energy adsorption constant b 3 and of 0.6% of the Saturation Capacity q 3 . The isotherm parameters are very sensitive to the mobile phase composition, especially the highest energy mode. Both adsorption constants b 2 and b 3 follow the linear strength solvent model (LSSM). A methanol volume fraction change of 1% causes a relative decrease of 3.2 and 5.0% of b 2 and b 3 , respectively and a 2% decrease of the Saturation Capacity q 3 . Finally, flow rate changes affect only the Saturation capacities. A flow rate change of 1% causes a 2% change in the Saturation Capacity parameters.
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Modeling of the adsorption behavior and the chromatographic band profiles of enantiomers : behavior of methyl mandelate on immobilized cellulose
Journal of Chromatography A, 1993Co-Authors: Frédéric Charton, Stephen C. Jacobson, Georges GuiochonAbstract:Abstract The adsorption isotherms of (−)- and (+)-methyl mandelate from a hexane-isopropanol (90:10) solution were measured on a chromatographic column packed with 4-methylcellulose tribenzoate coated on silica. These isotherms are accounted for by a bi-Langmuir isotherm model, the two Langmuir terms having widely different initial slopes and Saturation capacities, but each term having the same Saturation Capacity for the two enantiomers. The competitive isotherms were also measured. They are in excellent agreement with the prediction of a competitive bi-Langmuir model based on the single-component isotherms. The individual band profiles are in agreement with the profiles calculated from these isotherms. Thus, a simplified competitive isotherm can be used to model a separation on a chiral stationary phase the recognition mechanism of which is not well identified and the adsorption behavior of which is certainly not ideal.
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Contribution of ionically immobilized bovine serum albumin to the retention of enantiomers.
Journal of Chromatography A, 1992Co-Authors: Stephen C. Jacobson, Georges GuiochonAbstract:The retention of the enantiomers of mandelic acid and N-benzoylalanine was studied on columns prepared by immobilizing bovine serum albumin (BSA) on an anion exchanger. The amount of BSA fixed on the column is easy to adjust and measure. The adsorption isotherms were determined. For each enantiomer, the isotherm is well accounted for by a bi-Langmuir equation. One term of the isotherm (which is the same for both enantiomers) corresponds to non-selective interactions and the other term to the chiral selective interactions. The column Saturation Capacity of this second term is 8% larger for the less strongly retained enantiomer. This Saturation Capacity corresponds approximately to one enantiomer molecule adsorbed for five BSA molecules immobilized. This result is in agreement with the assumption of the hydrophobic cavity of BSA being the chiral selective site.
Beer Singh - One of the best experts on this subject based on the ideXlab platform.
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Adsorption Behaviour of Diisopropyl Flourophosphate on Whetlerite Carbon
Defence Science Journal, 2013Co-Authors: Suresh Srinivasan, Beer Singh, Naresh Vyas, A. K. Gupta, M.p. KaushikAbstract:Breakthrough behaviour of diisopropyl florophosphate (DFP) vapour on whetlerite carbon has been studied by using modified wheeler equation. The kinetic Saturation Capacity and pseudo first order rate constant with respect to the effect of various parameters such as bed weight, flow rate, concentration and temperature were correlated. The results of this study indicate that breakthrough time is increased with increase of the bed weight of carbon. Rate constant value increases as flow rate increases, while kinetic Saturation Capacity value is invariable. Defence Science Journal, 2013, 63(5), pp.473 -477 , DOI:http://dx.doi.org/10.14429/dsj.63.2512
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Impregnated charcoal cloth for the treatment of air polluted with hydrogen cyanide
Environmental Progress & Sustainable Energy, 2012Co-Authors: G.k. Prasad, J. Praveen Kumar, P.v.r.k. Ramacharyulu, Beer SinghAbstract:Impregnated charcoal cloth was prepared by a novel single-step method using water-soluble salts such as copper nitrate, silver nitrate, and ammonium heptamolybdate. Impregnation was achieved by using simple, user-friendly spraying technique. The obtained cloth samples were characterized by nitrogen adsorption technique. Kinetics of hydrogen cyanide adsorption were explored using charcoal cloth impregnated with copper(II), molybdenum(VI), and silver(I) salts. Modified Wheeler equation was used for analyzing adsorption kinetics, and the data were represented as kinetic Saturation Capacity and kinetic rate constant. Kinetic Saturation Capacity value was found to decrease from 0.01 to 0.003 g/g as the value of inlet concentration increased from 81 to 365 ppm. Kinetic rate constant value increased from 2018 to 5048 min−1 when the flow rate was increased from 400 to 1000 mL/min, whereas kinetic Saturation Capacity value was found to be invariant. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 715–720, 2013
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Sulphur mustard vapor breakthrough behaviour on reactive carbon systems
Journal of Hazardous Materials, 2006Co-Authors: G.k. Prasad, T. H. Mahato, Shilpi Yadav, Beer SinghAbstract:Abstract Breakthrough behaviour of sulphur mustard, the deadliest of persistent chemical warfare agents, on carbon systems such as NaOH/CrO 3 /C, NaOH/CrO 3 /EDA/C and RuCl 3 /C has been studied and the data were compared with that of active carbon. Effects of bed lengths of carbons on breakthrough time have also been correlated. Thereafter, the effects of flow rate of air–sulphur mustard mixture, concentration and temperature on the kinetic parameters such as rate constant ( k v ) and kinetic Saturation Capacity ( W e ) were analyzed and interpreted by means of modified Wheeler equation. Rate constant was found to be increasing while W e was found to be invariable with the increase in air flow rate. Both k v and W e decreased with the increase of temperature, however, no significant effect on W e and k v was observed due to concentration change (0.3–0.6 mg/l). The values of kinetic Saturation Capacity were used to predict the service lives/breakthrough times of carbon beds (when used in filtration systems).
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Breakthrough behavior of sulphur mustard vapor on whetlerite carbon.
Journal of Hazardous Materials, 2006Co-Authors: G.k. Prasad, Beer SinghAbstract:Abstract Sulphur mustard vapor breakthrough behavior on whetlerite carbon has been studied by using modified Wheeler equation. The values of pseudo-first-order rate constant (kv) and kinetic Saturation Capacity (We) were calculated and the effects of various parameters such as bed height, air flow rate, concentration and temperature on the above parameters have also been studied. Rate constant is found to be increasing with air flow rate, while We is found to be invariable. Both kv and We decrease with the increase of temperature, however, no significant effect on We and kv is observed due to concentration change. The values of kinetic Saturation Capacity are used to predict the service lives/breakthrough times of carbon beds (when used in filtration systems).
G.k. Prasad - One of the best experts on this subject based on the ideXlab platform.
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Impregnated charcoal cloth for the treatment of air polluted with hydrogen cyanide
Environmental Progress & Sustainable Energy, 2012Co-Authors: G.k. Prasad, J. Praveen Kumar, P.v.r.k. Ramacharyulu, Beer SinghAbstract:Impregnated charcoal cloth was prepared by a novel single-step method using water-soluble salts such as copper nitrate, silver nitrate, and ammonium heptamolybdate. Impregnation was achieved by using simple, user-friendly spraying technique. The obtained cloth samples were characterized by nitrogen adsorption technique. Kinetics of hydrogen cyanide adsorption were explored using charcoal cloth impregnated with copper(II), molybdenum(VI), and silver(I) salts. Modified Wheeler equation was used for analyzing adsorption kinetics, and the data were represented as kinetic Saturation Capacity and kinetic rate constant. Kinetic Saturation Capacity value was found to decrease from 0.01 to 0.003 g/g as the value of inlet concentration increased from 81 to 365 ppm. Kinetic rate constant value increased from 2018 to 5048 min−1 when the flow rate was increased from 400 to 1000 mL/min, whereas kinetic Saturation Capacity value was found to be invariant. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 715–720, 2013
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Breakthrough behavior of sulphur mustard vapor on activated carbon
Journal of Scientific & Industrial Research, 2007Co-Authors: G.k. Prasad, T. H. Mahato, K. Ganesan, B. SinghAbstract:Active carbon (surface area, 1250 m 2 /g) was used to study vapor breakthrough behavior of sulphur mustard (2, 2'-dichlorodiethyl sulphide). Effect of length of carbon bed on vapor breakthrough time has been examined. Rate constant (k v ) is found to increase while kinetic Saturation Capacity (W c ) is invariable with increase in airflow rate. Both k and W c decrease with the increase of temperature, however, no significant effect on W and k v was observed due to concentration change (0.3-0.6 mg/1). Values of kinetic Saturation Capacity are used to predict service lives/breakthrough times of carbon beds (when used in filtration systems).
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Sulphur mustard vapor breakthrough behaviour on reactive carbon systems
Journal of Hazardous Materials, 2006Co-Authors: G.k. Prasad, T. H. Mahato, Shilpi Yadav, Beer SinghAbstract:Abstract Breakthrough behaviour of sulphur mustard, the deadliest of persistent chemical warfare agents, on carbon systems such as NaOH/CrO 3 /C, NaOH/CrO 3 /EDA/C and RuCl 3 /C has been studied and the data were compared with that of active carbon. Effects of bed lengths of carbons on breakthrough time have also been correlated. Thereafter, the effects of flow rate of air–sulphur mustard mixture, concentration and temperature on the kinetic parameters such as rate constant ( k v ) and kinetic Saturation Capacity ( W e ) were analyzed and interpreted by means of modified Wheeler equation. Rate constant was found to be increasing while W e was found to be invariable with the increase in air flow rate. Both k v and W e decreased with the increase of temperature, however, no significant effect on W e and k v was observed due to concentration change (0.3–0.6 mg/l). The values of kinetic Saturation Capacity were used to predict the service lives/breakthrough times of carbon beds (when used in filtration systems).
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Breakthrough behavior of sulphur mustard vapor on whetlerite carbon.
Journal of Hazardous Materials, 2006Co-Authors: G.k. Prasad, Beer SinghAbstract:Abstract Sulphur mustard vapor breakthrough behavior on whetlerite carbon has been studied by using modified Wheeler equation. The values of pseudo-first-order rate constant (kv) and kinetic Saturation Capacity (We) were calculated and the effects of various parameters such as bed height, air flow rate, concentration and temperature on the above parameters have also been studied. Rate constant is found to be increasing with air flow rate, while We is found to be invariable. Both kv and We decrease with the increase of temperature, however, no significant effect on We and kv is observed due to concentration change. The values of kinetic Saturation Capacity are used to predict the service lives/breakthrough times of carbon beds (when used in filtration systems).
