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Flavio F. Contreras-Torres

Publications and source records attributed to Flavio F. Contreras-Torres.

2 recordsLinked to original sources

Determination of contrast factors for cubic slip-systems and their application in the microstructural characterization of binary Fm$\bar{3}$m materials

The stress-strain anisotropy -including both elastic properties and dislocation distributions- of crystalline systems can be studied using a dislocation model proposed by Ungár and Borbély. However this model requires fundamental parameters (i.e., contrast factors), which take into account both the elastic properties and symmetry for each system. In this study, such contrast factors were calculated from first principles for cubic slip-systems through the evaluation of the distortion tensor in a dislocation-dependent coordinate set. Moreover, a straightforward expression for the computation of contrast factors is provided. Further analysis of the microstructural parameters was carried out using the modified Williamson-Hall method to characterize rock-salt materials.

cond-mat.mtrl-sci↗

A Stellar Wind Origin for the G2 Cloud: Three-Dimensional Numerical Simulations

We present 3D, adaptive mesh refinement simulations of G2, a cloud of gas moving in a highly eccentric orbit towards the galactic center. We assume that G2 originates from a stellar wind interacting with the environment of the Sgr A* black hole. The stellar wind forms a cometary bubble which becomes increasingly elongated as the star approaches periastron. A few months after periastron passage, streams of material begin to accrete on the central black hole with accretion rates $\dot{M} \sim 10^{-8}$ M$_\odot$ yr$^{-1}$. Predicted Br$γ$ emission maps and position-velocity diagrams show an elongated emission resembling recent observations of G2. A large increase in luminosity is predicted by the emission coming from the shocked wind region during periastron passage. The observations, showing a constant Br$γ$ luminosity, remain puzzling, and are explained here assuming that the emission is dominated by the free-wind region. The observed Br$γ$ luminosity ($\sim 8 \times 10^{30}$ erg s$^{-1}$) is reproduced by a model with a $v_w=50$ km s$^{-1}$ wind velocity and a $10^{-7}$ M$_\odot$ yr$^{-1}$ mass loss rate if the emission comes from the shocked wind. A faster and less dense wind reproduces the Br$γ$ luminosity if the emission comes from the inner, free wind region. The extended cometary wind bubble, largely destroyed by the tidal interaction with the black hole, reforms a few years after periastron passage. As a result, the Br$γ$ emission is more compact after periastron passage.

astro-ph.GA↗