Monte Carlo simulations were used to study the translocation of a flexible polymer through a pore in a membrane, assuming an attractive interaction between the monomers and the membrane on the trans side of the membra...Monte Carlo simulations were used to study the translocation of a flexible polymer through a pore in a membrane, assuming an attractive interaction between the monomers and the membrane on the trans side of the membrane and no interaction on the cis side. For the case T〈Tc （the temperature corresponding to the minimum in the translocation time τ）, the value of τdecreases with increasing temperature, whereas for T〉Tc, τ increases with increasing temperature. The translocation time depends on the absorbed energy uo in a nontrivial way. The value of τ increases initially upon increasing uo before it begins to decrease. The variation of the translocation time with respect to the solvent quality was also studied. It showed that there is a transition, as the solvent quality improves from ＂poor＂ to ＂good＂： when εAB〈εc （the interaction energy corresponding to the minimum in τ）, τdecreases with increasing the value of εAB; when εAB〉εc, τincreases with increasing εAB- When the chain length was changed, it was found that when the absorbed energy uo was greater than uc,τ was proportional to N1.602; for uo〈uc, τ∝N2.248. As the solvent quality improved from ＂poor＂ to ＂good,＂ the translocation probability increased initially before becoming stable.展开更多
Clay-rich subsoils are added to sandy soils to improve crop yield and increase organic carbon （C） sequestration; however, little is known about the influence of clay subsoil properties on organic C sorption and deso...Clay-rich subsoils are added to sandy soils to improve crop yield and increase organic carbon （C） sequestration; however, little is known about the influence of clay subsoil properties on organic C sorption and desorption. Batch sorption experiments were conducted with nine clay subsoils with a range of properties. The clay subsoils were shaken for 16 h at 4 ℃with water-extractable organic C （WEOC, 1 224 g C L-1） from mature wheat residue at a soil to extract ratio of 1：10. After removal of the supernatant, the residual pellet was shaken with deionised water to determine organic C desorption. The WEOC sorption was positively correlated with smectite and illite contents, cation exchange capacity （CEC） and total organic C, but negatively correlated with kaolinite content. Desorption of WEOC expressed as a percentage of WEOC sorbed was negatively correlated with smectite and illite contents, CEC, total and exchangeable calcium （Ca） concentrations and clay content, but positively correlated with kaolinite content. The relative importance of these properties varied among soil types. The soils with a high WEOC sorption capacity had medium CEC and their dominant clay minerals were smectite and illite. In contrast, kaolinite was the dominant clay mineral in the soils with a low WEOC sorption capacity and low-to-medium CEC. However, most soils had properties which could increase WEOC sorption as well as those that could decrease WEOC sorption. The relative importance of properties increasing or decreasing WEOC sorption varied with soils. The soils with high desorption had a low total Ca concentration, low-to-medium CEC and low clay content, whereas the soils with low desorption were characterised by medium-to-high CEC and smectite and illite were the dominant clay minerals. We conclude that WEOC sorption and desorption depend not on a single property but rather a combination of several properties of the subsoils in this study.展开更多
基金This work was supported by the Outstanding Youth Fund （No.20525416）, the National Natural Science Foundation of China （No.20490220, No.20374050, and No.90403022）, and the National Basic Research Program of China （No.2005CB623800）.
文摘Monte Carlo simulations were used to study the translocation of a flexible polymer through a pore in a membrane, assuming an attractive interaction between the monomers and the membrane on the trans side of the membrane and no interaction on the cis side. For the case T〈Tc （the temperature corresponding to the minimum in the translocation time τ）, the value of τdecreases with increasing temperature, whereas for T〉Tc, τ increases with increasing temperature. The translocation time depends on the absorbed energy uo in a nontrivial way. The value of τ increases initially upon increasing uo before it begins to decrease. The variation of the translocation time with respect to the solvent quality was also studied. It showed that there is a transition, as the solvent quality improves from ＂poor＂ to ＂good＂： when εAB〈εc （the interaction energy corresponding to the minimum in τ）, τdecreases with increasing the value of εAB; when εAB〉εc, τincreases with increasing εAB- When the chain length was changed, it was found that when the absorbed energy uo was greater than uc,τ was proportional to N1.602; for uo〈uc, τ∝N2.248. As the solvent quality improved from ＂poor＂ to ＂good,＂ the translocation probability increased initially before becoming stable.
文摘Clay-rich subsoils are added to sandy soils to improve crop yield and increase organic carbon （C） sequestration; however, little is known about the influence of clay subsoil properties on organic C sorption and desorption. Batch sorption experiments were conducted with nine clay subsoils with a range of properties. The clay subsoils were shaken for 16 h at 4 ℃with water-extractable organic C （WEOC, 1 224 g C L-1） from mature wheat residue at a soil to extract ratio of 1：10. After removal of the supernatant, the residual pellet was shaken with deionised water to determine organic C desorption. The WEOC sorption was positively correlated with smectite and illite contents, cation exchange capacity （CEC） and total organic C, but negatively correlated with kaolinite content. Desorption of WEOC expressed as a percentage of WEOC sorbed was negatively correlated with smectite and illite contents, CEC, total and exchangeable calcium （Ca） concentrations and clay content, but positively correlated with kaolinite content. The relative importance of these properties varied among soil types. The soils with a high WEOC sorption capacity had medium CEC and their dominant clay minerals were smectite and illite. In contrast, kaolinite was the dominant clay mineral in the soils with a low WEOC sorption capacity and low-to-medium CEC. However, most soils had properties which could increase WEOC sorption as well as those that could decrease WEOC sorption. The relative importance of properties increasing or decreasing WEOC sorption varied with soils. The soils with high desorption had a low total Ca concentration, low-to-medium CEC and low clay content, whereas the soils with low desorption were characterised by medium-to-high CEC and smectite and illite were the dominant clay minerals. We conclude that WEOC sorption and desorption depend not on a single property but rather a combination of several properties of the subsoils in this study.
