Constraining Dark Energy with X-ray Galaxy Clusters, Supernovae and the Cosmic Microwave Background

We present new constraints on the evolution of dark energy from an analysis of Cosmic Microwave Background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state w_0, the early time equation of state w_et and the scale factor at transition, a_t. From a combined analysis of all three data sets, assuming a constant equation of state and that the Universe is flat, we measure w_0=-1.05+0.10-0.12. Including w_et as a free parameter and allowing a_t to vary over the range 0.5<a_t<0.95 where the data sets have discriminating power, we measure w_0=-1.27+0.33-0.39 and w_et=-0.66+0.44-0.62. We find no significant evidence for evolution in the dark energy equation of state parameter with redshift. Marginal hints of evolution in the supernovae data become less significant when the cluster constraints are also included in the analysis. The complementary nature of the data sets leads to a tight constraint on the mean matter density, Omega_m and alleviates a number of other parameter degeneracies, including that between the scalar spectral index n_s, the physical baryon density Omega_bh^2 and the optical depth tau. This complementary nature also allows us to examine models in which we drop the prior on the curvature. For non-flat models with a constant equation of state, we measure w_0=-1.09+0.12-0.15 and Omega_de=0.70+-0.03. Our analysis includes spatial perturbations in the dark energy fluid, assuming a sound speed c_s^2 =1. For our most general dark energy model, not including such perturbations would lead to spurious constraints on w_et which would be tighter by approximately a factor two with the current data. (abridged)Comment: 11 pages, 13 figures, 2 tables. Accepted for publication in MNRAS. Two new figures added: Fig.9 shows the effects of including dark energy perturbations and Fig.10 compares X-ray cluster data with 2dF dat

Electron Shock Waves: Ionization Rate and Solutions to the EFD Equations

This paper describes our numerical investigation into ionizing breakdown waves, primarily antiforce waves. Antiforce waves are waves for which the electric field force on the electronsisin the opposite direction of the wave\u27s propagation. This investigation required us to utilize one-dimensional electron fluid-dynamical equations, which were applied to a pulse wave that transmits into a region of neutral gas and is under the influence of an applied electric field. Two important assumptions were made in applying these equations: electrons were considered to be the main component in the propagation of the pulse wave, and the partial pressure of the electron gas provided the driving force for the wave. The pulse waves were considered to be shock-fronted, and these waves are composed of2 regions: a thin sheath region that exists behind the shock front and a thicker quasi-neutral region that follows the sheath region and in which ionization continues as the electron fluid cools. The set of equations used to investigate these waves consists of the equations of conservation of mass, momentum, and energy coupled with Poisson\u27s equation, which altogether are known as the electron fluid-dynamical (EFD) equations

On a discounted notion of strict dissipativity

Recent results in the literature have provided connections between the so-called turnpike property, near optimality of closed-loop solutions using model predictive control schemes, and strict dissipativity. An important feature of these results is that strict dissipativity provides a checkable condition for the other two properties. These results relate to optimal control problems with undiscounted stage cost. Motivated by applications in economics, we consider optimal control problems with discounted stage cost and define a notion of discounted strict dissipativity. As in the undiscounted case, we show that discounted strict dissipativity provides a checkable condition for various properties of the solutions of the optimal control problem associated with the appropriately defined discounted available storage function

Phylogenetic incongruence through the lens of Monadic Second Order logic

International audienceWithin the field of phylogenetics there is growing interest in measures for summarising the dissimilarity, or incongruence, of two or more phylogenetic trees. Many of these measures are NP-hard to compute and this has stimulated a considerable volume of research into fixed parameter tractable algorithms. In this article we use Monadic Second Order logic to give alternative, compact proofs of fixed parameter tractability for several well-known incongruence measures. In doing so we wish to demonstrate the considerable potential of MSOL - machinery still largely unknown outside the algorithmic graph theory community - within phylogenetics. A crucial component of this work is the observation that many measures, when bounded, imply the existence of an agreement forest of bounded size, which in turn implies that an auxiliary graph structure, the display graph, has bounded treewidth. It is this bound on treewidth that makes the machinery of MSOL available for proving fixed parameter tractability

The Impact of Perspective in Identifying and Responding to Potential Sexual Misconduct: A Study of University Students

Recent events have demonstrated a divergent understanding of sexual harassment and other forms of sexual misconduct. Although sociocultural standards regarding sexual misconduct have changed over time, including improved social and workplace standards and protections, it is clear that not everyone views these events through the same lens. The lens is even less clear when potential misconduct is viewed from the distinct perspectives of a “victim” and a “perpetrator.” We surveyed 424 undergraduate and graduate students at Indiana University Kokomo to identify the impact of perspective and various sociodemographic characteristics that may influence perceptions of what is, and is not, sexual misconduct. In addition, we examined if these factors also influence opinions on the severity of response toward this misconduct. Students completed a gender-neutral survey that presented eight potential sexualmisconduct scenarios in a first-person narrative. In each scenario, the fact pattern was identical, but some surveys were in the perspective of the “victim” and some were in the perspective of the “perpetrator.” We find that perspective matters, as do reported preconceived attitudes toward sexual misconduct. We also find preliminary evidence that the impact of perspective and the severity of the response may depend on whether the misconduct occurs in an organizational setting, in a date setting, or without a distinct victim