Thermodynamics of Associated Electrolytes in Water: Molecular Dynamics Simulations of Sulfate Solutions.

A polarizable force field for the sulfate anion SO4(2­) has been developed and extended from nonpolarizable force fields in order to reproduce its structural and thermodynamics properties in aqueous solution. Two force fields with different atomic partial charges on S and O have been tested and used with molecular dynamics with explicit polarization. The results obtained with our developed force field are in good agreement with the experimental hydration properties of the sulfate anion. In addition to molecular dynamics simulations of the sulfate anion in aqueous solution, potentials of mean force of sulfate electrolytes have been calculated via umbrella-sampling molecular dynamics simulations, i.e., MgSO4, EuSO4(+), and UO2SO4. These potentials allow for calculating pair association constants directly comparable to the experimental ones. In the case of monoatomic cations such as Mg(2+) and Eu(3+), the association constants calculated are in very good agreement with the experimental values, i.e., pKcalc = 2.21 (vs 2.21 experimentally) and 3.86 (vs 3.56­3.78 experimentally) for MgSO4 and EuSO4(+), respectively. In the case of purely molecular electrolyte (UO2SO4), the association constant calculated (pKcalc = 1.58­2.07) is in agreement with the range of values available in the literature (pKexp = 1.17­3.14).

Multi-scale modelling of uranyl chloride solutions.

Classical molecular dynamics simulations with explicit polarization have been successfully used to determine the structural and thermodynamic properties of binary aqueous solutions of uranyl chloride (UO2Cl2). Concentrated aqueous solutions of uranyl chloride have been studied to determine the hydration properties and the ion-ion interactions. The bond distances and the coordination number of the hydrated uranyl are in good agreement with available experimental data. Two stable positions of chloride in the second hydration shell of uranyl have been identified. The UO2(2+)-Cl(-) association constants have also been calculated using a multi-scale approach. First, the ion-ion potential averaged over the solvent configurations at infinite dilution (McMillan-Mayer potential) was calculated to establish the dissociation/association processes of UO2 (2+)-Cl(-) ion pairs in aqueous solution. Then, the association constant was calculated from this potential. The value we obtained for the association constant is in good agreement with the experimental result (KUO2Cl(+) = 1.48 l mol(-1)), but the resulting activity coefficient appears to be too low at molar concentration.

The making and transnationalization of an ethnic niche: Vietnamese manicurists.

The article addresses how Vietnamese immigrant women developed an urban employment niche in the beauty industry, in manicuring. They are shown to have done so by creating a market for professional nail care, through the transformation of nailwork into what might be called McNails, entailing inexpensive, walk-in, impersonal service, in stand-alone salons, nationwide, and by making manicures and pedicures de riguer across class and racial strata. Vietnamese are shown to have simultaneously gained access to institutional means to surmount professional manicure credentializing barriers, and to have developed formal and informal ethnic networks that fueled their growing monopolization of jobs in the sector, to the exclusion of non-Vietnamese. The article also elucidates conditions contributing to the Vietnamese build-up and transformation of the niche, to the nation-wide formation of the niche and, most recently, to the transnationalization of the niche. It also extrapolates from the Vietnamese manicure experience propositions concerning the development, expansion, maintenance, and transnationalization of immigrant-formed labor market niches.