A correlation-function-based scheme is proposed for calculating the osmotic second virial coefficient B for solutes that dissolve very little in a solvent. The short-distance contribution to B, a ...volume integral of the solute–solute pair correlation function h(r) from 0 to some finite distance r c, is evaluated with h(r) obtained by molecular simulation. The remaining contribution to B from r c to ∞ is calculated with an asymptotic form of h(r) (Evans, R.; et al. J. Chem. Phys. 1994, 1 0 0, 591). It is shown here that B for a model system of methane in water is obtained accurately in the temperature range between 238 and 373 K at 1 bar, with a result that B is a monotonically decreasing function of temperature, and the hydrophobic interaction between methane molecules measured by B is repulsive (B > 0) in supercooled water, virtually null (B ≃ 0) at around 0 °C, and attractive (B < 0) at higher temperatures. It is also remarked that a nearly linear relation holds between B and the first-peak height of the solute–solute radial distribution function.
•Effects of compaction and organic matter on gas and water transport were examined.•Compaction reduced soil gas and water transport properties.•We supposed organic matter blocked pores for gas ...diffusivity and air permeability.•The blocked pores by organic matter yet allowed water to be permeated.
Operation of farm machinery in agricultural fields is the main cause of soil compaction, which may have detrimental effects on soil gas and water transport. However, application of organic matter (OM) reduces the adverse effects of compaction and improves transport properties of soil gases and water. To date, experimental data on the effect of compaction on those transport properties and its relationship to the presence of applied OM remains scarce. The effect of compaction on relative gas diffusivity (Dp/D0)100 and air permeability (ka100) at a soil matric suction of −100cm H2O (soil pF 2.0), and saturated hydraulic conductivity (ks) were investigated using disturbed soil sample taken from 0–15cm layer mixed with rice husk, rice straw, compost, sawdust, and wood bark at a rate of 20% of the soil volume. The common compaction caused by farm machinery in agricultural fields was simulated in the laboratory using a static compression load of 150, 225, and 300kPa. The effect of compaction on total porosity (f) and air content at soil pF 2.0 (ɛ100) was also examined. Compaction reduced f, ɛ100, (Dp/D0)100, ka100, and ks, with the more pronounced significant difference between 150 and 300kPa compactions. The decrease in (Dp/D0)100 was likely attributable to a reduced air content, and the decrease in ka100 and ks was likely attributable to a reduced volume of macropores, as indicated by reduced ɛ100 values. Compared with the control, addition of sawdust and wood bark seemed to have the most positive effect on (Dp/D0)100, ka100, and ks in term of resistance to compaction, while rice straw had the opposite effect. The presence of OM was likely to block the soil pores and increase capillary water in the bottle-neck, leading to lower values of (Dp/D0)100 and ka100 for a given value of ɛ100 (“blockage effect”). These pores blocked by OM, however, seemed to allow the water to flow through the soil matric (“ceramic filter effect”). Further studies on the prolonged application of OM at field scale, taking into account the decomposition process, should be conducted.
Temperature-, pressure-, and salt-concentration-induced variations in the solubility of small nonpolar solutes in aqueous solution and the corresponding variations in the solvent-induced pair ...attraction between such solute molecules are investigated. The variations in the solvation free energy of a solute and those in the solvent-induced pair attraction are well reproduced by a mean-field approximation in which the repulsive cores of solute molecules are treated as hard spheres and the mean-field energy of a solute molecule is taken to be the average potential energy that the solute molecule feels in solution. The mechanisms of variation in the solvation free energy and those of variation in the solvent-induced pair potential, with increasing temperature, pressure, and salt concentration, are clarified. Correlations between the solvation free energy and the solvent-induced pair potential at a contact distance in temperature, pressure, and salt concentration variations are near linear in any mode of variation, but the slope of the linear relation is dependent on the mode of variation and is determined by a ratio of the solvation thermodynamic quantities characteristic of each mode of variation.
Examination of an extensive major and trace element database for about 700 whole rocks from the Ecuadorian Andes reveals series of local trends typified by three volcanoes: Iliniza and Pichincha from ...the Western Cordillera and Tungurahua from the Eastern Cordillera. These local trends are included in a more scattered global trend that reflects typical across-arc chemical variations. The scatter of the global trend is attributed to greater crustal contributions or decreasing melt fractions. Trace element modelling shows that the local trends are consistent with mixing, and not with any fractional crystallization or progressive melting dominated processes. These local trends are extendable to include samples from other Ecuadorian volcanoes, suggesting that mixing processes are dominant throughout the region. Mixing model using trace and major element analyses identifies two end-members: low-silica, basaltic and high-silica, dacitic magmas. It also shows that mixing occurred between magmas after their segregation, rather than earlier mixing between the solid sources prior to melting. As a consequence, there must exist efficient magma-mixing processes that can overcome the obstacles to mixing magmas with contrasting physical properties, and can produce series of hybrid liquids over regional-scale. Model calculations show that estimated silicic end-members are primary magmas and are not co-magmatic derivatives of the corresponding mafic end-members. Lavas of Ecuadorian volcanoes are likely originated from magmas of contrasting origins, such as basaltic magmas generated by fluxed melting of peridotites in the mantle wedge and dacitic, adakite-type magmas originating from the slab or the mafic lower crust.
Acceleration of particles from the interaction of ultraintense laser pulses up to 5×10^{21} W cm^{-2} with thin foils is investigated experimentally. The electron beam parameters varied with ...decreasing spot size, not just laser intensity, resulting in reduced temperatures and divergence. In particular, the temperature saturated due to insufficient acceleration length in the tightly focused spot. These dependencies affected the sheath-accelerated protons, which showed poorer spot-size scaling than widely used scaling laws. It is therefore shown that maximizing laser intensity by using very small foci has reducing returns for some applications.
The osmotic virial coefficients, which are measures of the effective interactions between solute molecules in dilute solution, may be obtained from expansions of the osmotic pressure or of the solute ...activity in powers of the solute concentration. In these expansions, the temperature is held fixed, and one additional constraint is imposed. When the additional constraint is that of fixed chemical potential of the solvent, the coefficient of the second-order term yields directly the second osmotic virial coefficient itself. Alternative constraints, such as fixed pressure, fixed solvent density, or the specification of liquid–vapor equilibrium, yield alternative measures of the solute–solute interaction, different from but related to the osmotic virial coefficient. These relations are summarized and, where new, are derived here. The coefficient in question may be calculated from equations of state in which the parameters have been obtained by fitting to other experimental properties. Alternatively, the coefficients may be calculated from direct experimental measurements of the deviations from Henry’s law based on measurements of the activity of the solute in a coexisting gas phase. It is seen for propane in water as a test case that with the latter method, even with what appear to be the best available experimental data, there are still large uncertainties in the resulting second osmotic virial coefficient. With the former method, by contrast, the coefficient may be obtained with high numerical precision but then depends for its accuracy on the quality of the equation of state from which it is derived.
•We introduced an empirical index of soil macropore volume relative to solid volume.•We introduced an empirical index of macropore continuity for water transport.•Compaction reduced macropore ...continuity in terms of soil air and water transport.•Soil air transport was more sensitive to compaction with organic matter addition.•Soil water transport was less sensitive to compaction with organic matter addition.
Experimental data on the effects of compaction and applied organic matter (OM) on macropore structure indices, more particularly on pore continuity, have yet rarely been documented. In this study, static compaction was simulated in the laboratory at 150, 225, and 300kPa upon rice husk, rice straw, compost, sawdust, and wood bark-mixed soils and control. Measurements of relative gas diffusivity (Dp/D0)100 and air permeability (ka100) were conducted at −100cm H2O soil matric suction after measurement of saturated hydraulic conductivity (ks). Corresponding dry bulk density (ρd), total porosity (f), and air content (ɛ100) values were also determined. Volume of macropores (ϕ≥30μm) and micropores (ϕ<30μm) were expressed as volume of air and water at −100cm H2O soil matric suction, respectively, relative to the volume of soil solid. Specific gas diffusivity (SD100) and specific air permeability (Ska100) were calculated as (Dp/D0)100/ɛ100 and ka100/ɛ100, respectively. Analogous to the SD100 and Ska100, specific hydraulic conductivity (Sks) was defined as ks/ɛ100. The results showed that compaction significantly increased ρd, which was followed by a reduction in f, and the mixed OM resulted in a significantly lower ρd and higher f than the control. The volume of macropores was reduced by compaction whereas the volume of micropores remained unaffected, for which the mixed OM tended to result in a higher volume of macropores than the control. Compaction resulted in more tortuous macropores for gas diffusion (lower SD100) and less continuous macropores for gas convection (lower Ska100) for which a significant difference was more pronounced between the 300 and 150kPa compactions. Compaction also resulted in fewer continuous macropores for water movement as indicated by lower Sks. The mixed OM was likely to result in a lower SD100, but except for rice straw tended to result in a higher Ska100 than the control. In addition, the mixed OM also seemed to result in a higher Sks than the control. Of the OM-mixed soils, the decrease in (Dp/D0)100 and ka100 was more sensitive to compaction (i.e., decrease in ɛ100) than that of the control whereas the decrease in ks acted conversely. Discussion of the measured (Dp/D0)100, ka100, and ks is presented in the companion paper.
We treat two different density-functional models of the structures and tensions of the interfaces between phases on approach to the tricritical point of three-phase equilibrium. The major objective ...is to account for some of the results of earlier experimental measurements of these tensions. The thermodynamic background is first reviewed, including representations of the properties near the critical endpoints and tricritical point and of the wetting transitions that may occur on approach to those critical points. The first of the models treated is analytically soluble. Its properties are illuminating but at the price of some artificiality paid for its analytical solubility. The second model, called model T, is in a class of those treated in the past and analyzed numerically. Some of its properties are obtained with sufficient precision to allow one to conclude with near certainty what the analytically exact results would be. This model, too, illuminates the experimental measurements. It is noted where its properties are in accord with those of the analytically soluble model and where the two differ.
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