The stellar correlation function from SDSS - A statistical search for wide binary stars

We study the statistical properties of the wide binary population in the Galaxy field with projected separations larger than 200 AU by constructing the stellar angular two-point correlation function (2PCF) from a homogeneous sample of nearly 670'000 main sequence stars. The selected stars lie within a rectangular region around the Northern Galactic Pole and have apparent r-band magnitudes between 15 and 20.5 mag and spectral classes later than G5 (g-r > 0.5 mag). The data were taken from the Sixth Data Release of the Sloan Digital Sky Survey. We model the 2PCF by means of the Wasserman-Weinberg technique including several assumptions on the distribution of the binaries' orbital parameters, luminosity function, and density distribution in the Galaxy. In particular, we assume that the semi-major axis distribution is described by a single powerlaw. The free model parameters - the local wide binary number density and the power-law index of the semi-major axis distribution - are inferred simultaneously by least-square fitting. We find the separation distribution to follow Oepik's law up to the Galactic tidal limit, without any break and a local density of 5 wide binaries per 1'000 cubic parsec with both components having spectral type later than G5. This implies that about 10% of all stars in the solar neighbourhood are members of such a late-type wide binary system. With a relative statistical (2 sigma) error of about 10%, our findings are in general agreement with previous studies of wide binaries. The data suggest that about 800 very wide pairs with projected separations larger than 0.1 pc exist in our sample, whereas none are found beyond 0.8 pc.Comment: 18 pages, 14 figures, 7 tables; added reference for section

Stark Ionization of Atoms and Molecules within Density Functional Resonance Theory

We show that the energetics and lifetimes of resonances of finite systems under an external electric field can be captured by Kohn--Sham density functional theory (DFT) within the formalism of uniform complex scaling. Properties of resonances are calculated self-consistently in terms of complex densities, potentials and wavefunctions using adapted versions of the known algorithms from DFT. We illustrate this new formalism by calculating ionization rates using the complex-scaled local density approximation and exact exchange. We consider a variety of atoms (H, He, Li and Be) as well as the hydrogen molecule. Extensions are briefly discussed.Comment: 5 pages, 5 figures. This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in J.Phys.Chem.Lett., copyright (c) American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/jz401110

The knowledge domain of chain and network science

This editorial paper aims to provide a framework to categorise and evaluate the domain of Chain and Network Science (CNS), and to provide an envelope for the research and management agenda. The authors strongly feel that although considerable progress has been made over the past couple of years in the development of the CNS domain, a number of important and exciting challenges are still waiting to be tackled. This paper provides a definition of the object of study of CNS, its central problem area, the organisation and governance of chain and network co-operation, and the relationships between chain organisation and technology development, market dynamics, and the economy and society at large. It indicates relevant sources of knowledge among the various academic disciplines. It touches upon CNS problem solving by identifying areas for knowledge development and CNS tool construction

Statistical equilibrium and ion cyclotron absorption/emission in strongly magnetized plasmas

We calculate the transition rates between proton Landau levels due to non-radiative and radiative Coulomb collisions in an electron-proton plasma with strong magnetic field B. Both electron-proton collisions and proton-proton collisions are considered. The roles of the first-order cyclotron absorption and second-order free-free absorption and scattering in determining the line strength and shape as well as the continuum are analysed in detail. We solve the statistical balance equation for the populations of proton Landau levels. For temperatures \sim 10^6-10^7 K, the deviations of the proton populations from LTE are appreciable at density \rho < 0.1 B_{14}^{3.5} g cm^{-3}, where B_{14}=B/(10^{14} G). We present general formulae for the plasma emissivity and absorption coefficents under a wide range of physical conditions. Our results are useful for studying the possibility and the conditions of proton/ion cyclotron line formation in the near vicinity of highly magnetized neutron stars.Comment: 17 pages, 8 figures, MNRAS, accepte

On the Relevance of the Bayesian Approach to Statistics

In this essay, I argue about the relevance and the ultimate unity of the Bayesian approach in a neutral and agnostic manner. My main theme is that Bayesian data analysis is an effective tool for handling complex models, as proven by the increasing proportion of Bayesian studies in the applied sciences. I thus disregard the philosophical debates on the meaning of probability and on the random nature of parameters as things of the past that ultimately do a disservice to the approach and are irrelevant to most bystanders.Bayesian inference, Bayes model choice, foundations, testing, non-informative prior, Bayes factor, computational statistics