The Multi-wavelength Extreme Starburst Sample of Luminous Galaxies Part I: Sample Characteristics

This paper introduces the Multi-wavelength Extreme Starburst Sample (MESS), a new catalog of 138 star-forming galaxies (0.1 < z < 0.3) optically selected from the SDSS using emission line strength diagnostics to have high absolute SFR (minimum 11 solar masses per year, with median SFR approx 61 solar masses per year based on a Kroupa IMF). The MESS was designed to complement samples of nearby star-forming galaxies such as the luminous infrared galaxies (LIRGs), and ultraviolet luminous galaxies (UVLGs). Observations using the multiband imaging photometer (MIPS; 24, 70, and 160{\mu}m channels) on the Spitzer Space Telescope indicate the MESS galaxies have IR luminosities similar to those of LIRGs, with an estimated median LTIR ~ 3e11 solar luminosities. The selection criteria for the MESS suggests they may be less obscured than typical far-IR selected galaxies with similar estimated SFRs. 20 out of 70 of the MESS objects detected in the GALEX FUV band also appear to be UV luminous galaxies. We estimate the SFRs based directly on luminosities to determine the agreement for these methods in the MESS. We compare to the emission line strength technique, since effective measurement of dust attenuation plays a central role in these methods. We apply an image stacking technique to the VLA FIRST survey radio data to retrieve 1.4 GHz luminosity information for 3/4 of the sample covered by FIRST including sources too faint, and at too high a redshift, to be detected in FIRST. We also discuss the relationship between the MESS and samples selected through alternative criteria. Morphologies will be the subject of a forthcoming paper.Comment: 59 pages, 19 figures, accepted for publication in A

Radio AGN in 13,240 galaxy clusters from the Sloan Digital Sky Survey

We correlate the positions of 13,240 Brightest Cluster Galaxies (BCGs) with 0.1 <= z <= 0.3 from the maxBCG catalog with radio sources from the FIRST survey to study the sizes and distributions of radio AGN in galaxy clusters. We find that 19.7% of our BCGs are associated with FIRST sources, and this fraction depends on the stellar mass of the BCG, and to a lesser extent on the richness of the parent cluster (in the sense of increasing radio loudness with increasing mass). The intrinsic size of the radio emission associated with the BCGs peaks at 55 kpc, with a tail extending to 200 kpc. The radio power of the extended sources places them on the divide between FR I and FR II type sources, while sources compact in the radio tend to be somewhat less radio-luminous. We also detect an excess of radio sources associated with the cluster, instead of with the BCG itself, extending out to ~1.4 Mpc.Comment: 14 pages, 6 figures, accepted for publication in ApJ

Influence of grain boundary misorientation on hydrogen embrittlement in bi-crystal nickel

Computational techniques and tools have been developed to understand hydrogen embrittlement and hydrogen induced intergranular cracking based on grain boundary (GB) engineering with the help of computational materials engineering. This study can help to optimize GB misorientation configurations by identifying the cases that would improve the material properties increasing resistance to hydrogen embrittlement. In order to understand and optimize, it is important to understand the influence of misorientation angle on the atomic clustered hydrogen distribution under the impact of dilatational stress distributions. In this study, a number of bi-crystal models with tilt grain boundary (TGB) misorientation angles (θ) ranging between 0°≤ θ ≤ 90° were developed, with rotation performed about the [001] axis, using numerical microstructural finite element analysis. Subsequently, local stress and strain concentrations generated along the TGB (due to the difference in individual neighbouring crystals elastic anisotropy response as functions of misorientation angles) were evaluated when bi-crystals were subjected to overall uniform applied traction. Finally, the hydrogen distribution and segregations as a function of misorientation angles were studied. In real nickel, as opposed to the numerical model, geometrically necessary dislocations are generated due to GB misorientation. The generated dislocation motion along TGBs in response to dilatational mismatch varies depending on the misorientation angles. These generated dislocation motions affect the stress, strain and hydrogen distribution. Hydrogen segregates along these dislocations acting as traps and since the dislocation distribution varies depending on misorientation angles the hydrogen traps are also influenced by misorientation angles. From the results of numerical modelling it has been observed that the local stress, strain and hydrogen distributions are inhomogeneous, affected by the misorientation angles, orientations of neighbouring crystal and boundary conditions. In real material, as opposed to the numerical model, the clustered atomic hydrogens are segregated in traps near to the TGB due to the influence of dislocations developed under the effects of applied mechanical stress. The numerical model predicts maximum hydrogen concentrations are accumulated on the TGB with misorientation angles ranging between 15°&#60; θ &#60; 45°. This investigation reinforces the importance of GB engineering for designing and optimizing these materials to decrease hydrogen segregation arising from TGB misorientation angles

Finite element microstructural homogenization techniques and intergranular, intragranular microstructural effects on effective diffusion coefficient of heterogeneous polycrystalline composite media

Microstructural intergranular and intragranular effects play a vitally important role in mass transport within heterogeneous polycrystalline composite media. Full scale macroscopic specimen or component modelling of heterogeneous polycrystalline composite media is complex, time consuming and computationally expensive. Consequently it is important to develop a homogenous model to predict the effective diffusion coefficient of the heterogeneous polycrystalline composite media. It is also important to investigate the effect of intergranular and intragranular microstructure on effective diffusivity of heterogeneous polycrystalline composite media. A two dimensional finite element microstructural representative volume element (FEMRVE) model with different intergranular and intragranular microstructures has been developed using the well-known Voronoi tessellation technique. The effective diffusivity predicted by the FEMRVE model with various intergranular and intragranular microstructures of heterogeneous polycrystalline composite media agrees well with the results of various effective medium theories