How typical is the Coma cluster?

Coma is frequently used as the archetype z~0 galaxy cluster to compare higher redshift work against. It is not clear, however, how representative the Coma cluster is for galaxy clusters of its mass or X-ray luminosity, and significantly: recent works have suggested that the galaxy population of Coma may be in some ways anomolous. In this work, we present a comparison of Coma to an X-ray selected control sample of clusters. We show that although Coma is typical against the control sample in terms of its internal kinematics (substructure and velocity dispersion profile), it has a significantly high (~3sigma) X-ray temperature set against clusters of comparable mass. By de-redshifting our control sample cluster galaxies star-formation rates using a fit to the galaxy main sequence evolution at z < 0.1, we determine that the typical star-formation rate of Coma galaxies as a function of mass is higher than for galaxies in our control sample at a confidence level of > 99 per cent. One way to alleviate this discrepency and bring Coma in-line with the control sample would be to have the distance to Coma to be slightly lower, perhaps through a non-negligible peculiar velocity with respect to the Hubble expansion, but we do not regard this as likely given precision measurements using a variety of approaches. Therefore in summary, we urge caution in using Coma as a z~0 baseline cluster in galaxy evolution studies.Comment: accepted for publication in MNRA

Conceptual design of an airborne laser Doppler velocimeter system for studying wind fields associated with severe local storms

An airborne laser Doppler velocimeter was evaluated for diagnostics of the wind field associated with an isolated severe thunderstorm. Two scanning configurations were identified, one a long-range (out to 10-20 km) roughly horizontal plane mode intended to allow probing of the velocity field around the storm at the higher altitudes (4-10 km). The other is a shorter range (out to 1-3 km) mode in which a vertical or horizontal plane is scanned for velocity (and possibly turbulence), and is intended for diagnostics of the lower altitude region below the storm and in the out-flow region. It was concluded that aircraft flight velocities are high enough and severe storm lifetimes are long enough that a single airborne Doppler system, operating at a range of less than about 20 km, can view the storm area from two or more different aspects before the storm characteristics change appreciably

Resolved stellar population of distant galaxies in the ELT era

The expected imaging capabilities of future Extremely Large Telescopes (ELTs) will offer the unique possibility to investigate the stellar population of distant galaxies from the photometry of the stars in very crowded fields. Using simulated images and photometric analysis we explore here two representative science cases aimed at recovering the characteristics of the stellar populations in the inner regions of distant galaxies. Specifically: case A) at the center of the disk of a giant spiral in the Centaurus Group, (mu B~21, distance of 4.6 Mpc); and, case B) at half of the effective radius of a giant elliptical in the Virgo Cluster (mu~19.5, distance of 18 Mpc). We generate synthetic frames by distributing model stellar populations and adopting a representative instrumental set up, i.e. a 42 m Telescope operating close to the diffraction limit. The effect of crowding is discussed in detail showing how stars are measured preferentially brighter than they are as the confusion limit is approached. We find that (i) accurate photometry (sigma~0.1, completeness >90%) can be obtained for case B) down to I~28.5, J~27.5 allowing us to recover the stellar metallicity distribution in the inner regions of ellipticals in Virgo to within ~0.1 dex; (ii) the same photometric accuracy holds for the science case A) down to J~28.0, K~27.0, enabling to reconstruct of the star formation history up to the Hubble time via simple star counts in diagnostic boxes. For this latter case we discuss the possibility of deriving more detailed information on the star formation history from the analysis of their Horizontal Branch stars. We show that the combined features of high sensitivity and angular resolution of ELTs may open a new era for our knowledge of the stellar content of galaxies of different morphological type up to the distance of the Virgo cluster.Comment: 21 pages, 17 figures, PASP accepted in pubblicatio

Progress in materials and structures at Lewis Research Center

The development of power and propulsion system technology is discussed. Specific emphasis is placed on the following: high temperature materials; composite materials; advanced design and life prediction; and nondestructive evaluation. Future areas of research are also discussed

Graph-Embedding Empowered Entity Retrieval

In this research, we improve upon the current state of the art in entity retrieval by re-ranking the result list using graph embeddings. The paper shows that graph embeddings are useful for entity-oriented search tasks. We demonstrate empirically that encoding information from the knowledge graph into (graph) embeddings contributes to a higher increase in effectiveness of entity retrieval results than using plain word embeddings. We analyze the impact of the accuracy of the entity linker on the overall retrieval effectiveness. Our analysis further deploys the cluster hypothesis to explain the observed advantages of graph embeddings over the more widely used word embeddings, for user tasks involving ranking entities

Constraints on the equation of state of dark energy and the Hubble constant from stellar ages and the CMB

We place tight constraints on the redshift-averaged, effective value of the equation of state of dark energy, w, using only the absolute ages of Galactic stars and the observed position of the first peak in the angular power spectrum of the CMB. We find w<-0.8 at the 68% confidence level. If we further consider that w > -1, this finding suggests that within our uncertainties, dark energy is indistinguishable from a classical vacuum energy term. We detect a correlation between the ages of the oldest galaxies and their redshift. This opens up the possibility of measuring w(z) by computing the relative ages of the oldest galaxies in the universe as a function of redshift, dz/dt. We show that this is a realistic possibility by computing dz/dt at z~0 from SDSS galaxies and obtain an independent estimate for the Hubble constant, H_0 = 69 \pm 12 km s-1 Mpc-1. The small number of galaxies considered at z>0.2 does not yield, currently, a precise determination of w(z), but shows that the age--redshift relation is consistent with a Standard LCDM universe with $w=-1$.Comment: Submitted to Ap

The life cycle of starbursting circumnuclear gas discs

High-resolution observations from the sub-mm to the optical wavelength regime resolve the central few 100pc region of nearby galaxies in great detail. They reveal a large diversity of features: thick gas and stellar discs, nuclear starbursts, in- and outflows, central activity, jet interaction, etc. Concentrating on the role circumnuclear discs play in the life cycles of galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical simulations with the RAMSES code to self-consistently trace the evolution from a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the formation of clumps and stars and the disc's subsequent, partial dispersal via stellar feedback. Our approach builds upon the observational finding that many nearby Seyfert galaxies have undergone intense nuclear starbursts in their recent past and in many nearby sources star formation is concentrated in a handful of clumps on a few 100pc distant from the galactic centre. We show that such observations can be understood as the result of gravitational instabilities in dense circumnuclear discs. By comparing these simulations to available integral field unit observations of a sample of nearby galactic nuclei, we find consistent gas and stellar masses, kinematics, star formation and outflow properties. Important ingredients in the simulations are the self-consistent treatment of star formation and the dynamical evolution of the stellar distribution as well as the modelling of a delay time distribution for the supernova feedback. The knowledge of the resulting simulated density structure and kinematics on pc scale is vital for understanding inflow and feedback processes towards galactic scales.Comment: accepted by MNRA

A combined theoretical and experimental study of the low temperature properties of BaZrO3

Low temperature properties of BaZrO3 are revealed by combining experimental techniques (X-ray diffraction, neutron scattering and dielectric measurements) with theoretical first-principles-based methods (total energy and linear response calculations within density functional theory, and effective Hamiltonian approaches incorporating/neglecting zero-point phonon vibrations). Unlike most of the perovskite systems, BaZrO3 does not undergo any (long-range-order) structural phase transition and thus remains cubic and paraelectric down to 2 K, even when neglecting zero-point phonon vibrations. On the other hand, these latter pure quantum effects lead to a negligible thermal dependency of the cubic lattice parameter below ~ 40 K. They also affect the dielectricity of BaZrO3 by inducing an overall saturation of the real part of the dielectric response, for temperatures below ~ 40 K. Two fine structures in the real part, as well as in the imaginary part, of dielectric response are further observed around 50-65 K and 15 K, respectively. Microscopic origins (e.g., unavoidable defects and oxygen octahedra rotation occurring at a local scale) of such anomalies are suggested. Finally, possible reasons for the facts that some of these dielectric anomalies have not been previously reported in the better studied KTaO3 and SrTiO3 incipient ferroelectrics are also discussed.Comment: 8 pages, 5 figures, submitted to Physical Review

Dynamics of open quantum systems initially entangled with environment: Beyond the Kraus representation

We present a general analysis of the role of initial correlations between the open system and an environment on quantum dynamics of the open system.Comment: 5 revtex pages, no figures, accepted for publication in Phys. Rev.