Polytropic spheres in Palatini f(R) gravity

We examine static spherically symmetric polytropic spheres in Palatini f(R) gravity and show that no regular solutions to the field equations exist for physically relevant cases such as a monatomic isentropic gas or a degenerate electron gas, thus casting doubt on the validity of Palatini f(R) gravity as an alternative to General Relativity.Comment: Talk given by EB at the 30th Spanish Relativity Meeting, 10 - 14 September 2007, Tenerife (Spain). Based on arXiv:gr-qc/0703132 and arXiv:0712.1141 [gr-qc

A no-go theorem for polytropic spheres in Palatini f(R) gravity

Non-vacuum static spherically-symmetric solutions in Palatini f(R) gravity are examined. It is shown that for generic choices of f(R), there are commonly-used equations of state for which no satisfactory physical solution of the field equations can be found within this framework, apart from in the special case of General Relativity, casting doubt on whether Palatini f(R) gravity can be considered as giving viable alternatives to General Relativity.Comment: 7 pages, 1 figure. Version accepted for publication as a Fast Track Communication in CQ

A MORE OBJECTIVE PROCEDURE FOR DETERMINING ECONOMIC SUBREGIONS: CLUSTER ANALYSIS

Research Methods/ Statistical Methods,

Food insecurity in veteran households: findings from nationally representative data

OBJECTIVE: The present study is the first to use nationally representative data to compare rates of food insecurity among households with veterans of the US Armed Forces and non-veteran households. DESIGN: We used data from the 2005-2013 waves of the Current Population Survey - Food Security Supplement to identify rates of food insecurity and very low food security in veteran and non-veteran households. We estimated the odds and probability of food insecurity in veteran and non-veteran households in uncontrolled and controlled models. We replicated these results after separating veteran households by their most recent period of service. We weighted models to create nationally representative estimates. SETTING: Nationally representative data from the 2005-2013 waves of the Current Population Survey - Food Security Supplement. SUBJECTS: US households (n 388 680). RESULTS: Uncontrolled models found much lower rates of food insecurity (8·4 %) and very low food security (3·3 %) among veteran households than in non-veteran households (14·4 % and 5·4 %, respectively), with particularly low rates among households with older veterans. After adjustment, average rates of food insecurity and very low food security were not significantly different for veteran households. However, the probability of food insecurity was significantly higher among some recent veterans and significantly lower for those who served during the Vietnam War. CONCLUSIONS: Although adjusting eliminated many differences between veteran and non-veteran households, veterans who served from 1975 and onwards may be at higher risk for food insecurity and should be the recipients of targeted outreach to improve nutritional outcomes

Supporting Career Development and Employment: Benefits Planning, Assistance and Outreach (BPA&O) and Protection and Advocacy for Beneficiaries of Social Security (PABSS)

This training curriculum is dedicated to increasing knowledge and understanding of the Social Security Administration\u27s disability and return to work programs and work incentive provisions as prescribed in the Social Security Act and Ticket to Work and Work Incentives Improvement Act of 1999 as well as other federal benefit programs. These informational resources were compiled and edited to provide continuing education and print materials for benefits specialists and protection and advocacy personnel on the interplay of these benefit programs and impact or employment

Bias Analysis in Entropy Estimation

We consider the problem of finite sample corrections for entropy estimation. New estimates of the Shannon entropy are proposed and their systematic error (the bias) is computed analytically. We find that our results cover correction formulas of current entropy estimates recently discussed in literature. The trade-off between bias reduction and the increase of the corresponding statistical error is analyzed.Comment: 5 pages, 3 figure

Shapes of the Proton

A model proton wave function, constructed using Poincare invariance, and constrained by recent electromagnetic form factor data, is used to study the shape of the proton. Spin-dependent quark densities are defined as matrix elements of density operators in proton states of definite spin-polarization, and shown to have an infinite variety of non-spherical shapes. For high momentum quarks with spin parallel to that of the proton, the shape resembles that of a peanut, but for quarks with anti-parallel spin the shape is that of a bagel.Comment: 8 pages, 5 figures, to be submitted to Phys. Rev. C This corrects a few typos and explains some further connections with experiment

Isomorphic classical molecular dynamics model for an excess electron in a supercritical fluid

Ring polymer molecular dynamics (RPMD) is used to directly simulate the dynamics of an excess electron in a supercritical fluid over a broad range of densities. The accuracy of the RPMD model is tested against numerically exact path integral statistics through the use of analytical continuation techniques. At low fluid densities, the RPMD model substantially underestimates the contribution of delocalized states to the dynamics of the excess electron. However, with increasing solvent density, the RPMD model improves, nearly satisfying analytical continuation constraints at densities approaching those of typical liquids. In the high density regime, quantum dispersion substantially decreases the self-diffusion of the solvated electron. In this regime where the dynamics of the electron is strongly coupled to the dynamics of the atoms in the fluid, trajectories that can reveal diffusive motion of the electron are long in comparison to $\beta\hbar$.Comment: 24 pages, 4 figure