Ion Sizes and Finite-Size Corrections for Ionic-Solvation Free Energies

Free energies of ionic solvation calculated from computer simulations exhibit a strong system size dependence. We perform a finite-size analysis based on a dielectric-continuum model with periodic boundary conditions. That analysis results in an estimate of the Born ion size. Remarkably, the finite-size correction applies to systems with only eight water molecules hydrating a sodium ion and results in an estimate of the Born radius of sodium that agrees with the experimental value.Comment: 2 EPS figure

Ion Pair Potentials-of-Mean-Force in Water

Recent molecular simulation and integral equation results alkali-halide ion pair potentials-of-mean-force in water are discussed. Dielectric model calculations are implemented to check that these models produce that characteristic structure of contact and solvent-separated minima for oppositely charged ions in water under physiological thermodynamic conditions. Comparison of the dielectric model results with the most current molecular level information indicates that the dielectric model does not, however, provide an accurate description of these potentials-of-mean-force. We note that linear dielectric models correspond to modelistic implementations of second-order thermodynamic perturbation theory for the excess chemical potential of a distinguished solute molecule. Therefore, the molecular theory corresponding to the dielectric models is second-order thermodynamic perturbation theory for that excess chemical potential. The second-order, or fluctuation, term raises a technical computational issue of treatment of long-ranged interactions similar to the one which arises in calculation of the dielectric constant of the solvent. It is contended that the most important step for further development of dielectric models would be a separate assessment of the first-order perturbative term (equivalently the {\it potential at zero charge} ) which vanishes in the dielectric models but is generally nonzero. Parameterization of radii and molecular volumes should then be based of the second-order perturbative term alone. Illustrative initial calculations are presented and discussed.Comment: 37 pages and 8 figures. LA-UR-93-420

Affordable Care Act Litigation: The Supreme Court and the Future of Health Care Reform

In Florida v. HHS, a lawsuit brought on behalf of 26 states challenging the constitutionality of the Patient Protection and Affordable Care Act (ACA), the Supreme Court will determine the future direction of health care reform in the United States. During the unprecedented 5-1/2 hours of oral arguments, the Court will hear 4 issues: the individual purchase mandate, severability, the Medicaid expansion and the Anti-Injunction Act. The states challenging the ACA maintain that the purchase mandate uniquely penalizes individuals for failing to purchase insurance. Uninsured individuals, however, rarely do nothing. Instead, they self-insure, rely on family, and cost-shift to hospitals, the insured, and tax payers. Because most uninsured people will eventually require uncompensated care, they impose costs on everyone through higher taxes and insurance premiums. Further, although the ACA’s mandate is unusual, it is not unprecedented. Mandatory worker contributions to Medicare, for example, are a compelled purchase of health insurance. The necessary and proper clause, which permits Congress to pass laws rationally related to the exercise of federal powers, may be the best argument in favor of the mandate because the mandate is necessary for the other insurance market reforms to work. If the Court were to strike down the mandate, it would then have to determine whether the mandate is severable from the rest of the ACA. Although the ACA did not explicitly state that if part of the act were deemed unconstitutional the rest would survive, most ACA reforms are severable because they are unrelated to the mandate, such as funding for public health and community health centers. The more difficult question is whether the mandate is so intertwined with the ACA’s still unimplemented market reforms that the Court must strike them down. The Court will also review the constitutionality of expanding Medicaid to all individuals with household incomes below 138% of the federal poverty level. The states argue that Medicaid expansion is unduly coercive because they could lose all Medicaid funding and not just the funding related to the expansion. The Court, however, is unlikely to uphold the coercion theory because state participation in Medicaid has always been optional and some states have openly discussed exercising their option to discontinue the program. Finally, the Court will hear technical arguments concerning the Anti-Injunction Act (AIA), which prohibits lawsuits “for the purpose of restraining the assessment or collection of any tax.” The Court is unlikely to invoke the AIA because neither the administration nor the states contend that it applies. The ACA will achieve near universal coverage, something that seemed unimaginable just a short time ago. Health reform envisages a social contract in which everyone shares the cost, recognizing that virtually everyone will become ill one day. The ACA and its individual mandate are not unjustified limits on freedom, but rather are vital to a decent society

A Resonant soft x-ray powder diffraction study to determine the orbital ordering in A-site ordered SmBaMn2O6

Soft X-ray resonant powder diffraction has been performed at the Mn L2,3 edges of A-site ordered SmBaMn2O6. The energy and polarization dependence of the (1/2 1/2 0) reflection provide direct evidence for a (x2-z2)/(y2-z2) type orbital ordering in contrast to the single layer manganite. The temperature dependence of the reflection indicates an orbital reorientation transition at 210 K, below which the charge and orbital ordered MnO2 sheets show AAAA type of stacking. The concurring reduction of the ferromagnetic super exchange correlations leads to further charge localization

Circularly polarized resonant soft x-ray diffraction study of helical magnetism in hexaferrite

Magnetic spiral structures can exhibit ferroelectric moments as recently demonstrated in various multiferroic materials. In such cases the helicity of the magnetic spiral is directly correlated with the direction of the ferroelectric moment and measurement of the helicity of magnetic structures is of current interest. Soft x-ray resonant diffraction is particularly advantageous because it combines element selectivity with a large magnetic cross-section. We calculate the polarization dependence of the resonant magnetic x-ray cross-section (electric dipole transition) for the basal plane magnetic spiral in hexaferrite Ba0.8Sr1.2Zn2Fe12O22 and deduce its domain population using circular polarized incident radiation. We demonstrate there is a direct correlation between the diffracted radiation and the helicity of the magnetic spiral.Comment: 4 pages, 4 figure

Novel Negotiation protocol to support CDM process in a layered ATM System

In the SESAR Step 2 concept of operations a RBT is available and seen by all making it possible to conceive a different operating method than the current ATM system based on Collaborative Decisions Making processes. Currently there is a need to describe in more detail the mechanisms by which actors (ATC, Network Management, Flight Crew, airports and Airline Operation Centre) will negotiate revisions to the RBT. This paper introduces a negotiation model, which uses constraint based programing applied to a mediator to facilitate negotiation process in a SWIM enabled environment. Three processes for modelling the negotiation process are explained as well a preliminary reasoning agent algorithm modelled with constraint satisfaction problem is presented. Computational capability of the model is evaluated in the conclusion