17,690 research outputs found
On the accretion of phantom energy onto wormholes
By using a properly generalized accretion formalism it is argued that the
accretion of phantom energy onto a wormhole does not make the size of the
wormhole throat to comovingly scale with the scale factor of the universe, but
instead induces an increase of that size so big that the wormhole can engulf
the universe itself before it reaches the big rip singularity, at least
relative to an asymptotic observer.Comment: 4 pages, LaTex, to appear in Phys. Lett.
The oxygen abundance in the IFU era
Spatially-resolved information of gas-phase emission provided by integral
field units (IFUs) are allowing us to perform a new generation of emission-line
surveys, based on large samples of HII regions and full two-dimensional
coverage. Here we present two highlights of our current studies employing this
technique: 1) A statistical approach to the abundance gradients of spiral
galaxies, which indicates an -universal- radial gradient for oxygen abundance;
and 2) The discovery of a new scaling relation of HII regions in spiral
galaxies, the "local" mass-metallicity relation of star-forming galaxies.Comment: 6 pages, to appear in Highlights of Spanish Astrophysics VII,
Proceedings of the X Scientific Meeting of the Spanish Astronomical Society
held on July 9-13, 2012, in Valencia, Spai
The entangled accelerating universe
Using the known result that the nucleation of baby universes in correlated
pairs is equivalent to spacetime squeezing, we show in this letter that there
exists a T-duality symmetry between two-dimensional warp drives, which are
physically expressible as localized de Sitter little universes, and two
dimensional Tolman-Hawking and Gidding-Strominger baby universes respectively
correlated in pairs, so that the creation of warp drives is also equivalent to
spacetime squeezing. Perhaps more importantly, it has been also seen that the
nucleation of warp drives entails a violation of the Bell's inequalities, and
hence the phenomena of quantum entanglement, complementarity and wave function
collapse. These results are generalized to the case of any dynamically
accelerating universe filled with dark or phantom energy whose creation is also
physically equivalent to spacetime squeezing and to the violation of the Bell's
inequalities, so that the universe we are living in should be governed by
essential sharp quantum theory laws and must be a quantum entangled system
Synchronization in a ring of pulsating oscillators with bidirectional couplings
We study the dynamical behavior of an ensemble of oscillators interacting
through short range bidirectional pulses. The geometry is 1D with periodic
boundary conditions. Our interest is twofold. To explore the conditions
required to reach fully synchronization and to invewstigate the time needed to
get such state. We present both theoretical and numerical results.Comment: Revtex, 4 pages, 2 figures. To appear in Int. J. Bifurc. and Chao
Inner and outer star forming regions over the disks of spiral galaxies. I. Sample characterization
Context. The knowledge of abundance distributions is central to understanding
the formation and evolution of galaxies. Most of the relations employed for the
derivation of gas abundances have so far been derived from observations of
outer disk HII regions, despite the known differences between inner and outer
regions. Aims. Using integral field spectroscopy (IFS) observations we aim to
perform a systematic study and comparison of two inner and outer HII regions
samples. The spatial resolution of the IFS, the number of objects and the
homogeneity and coherence of the observations allow a complete characterization
of the main observational properties and differences of the regions. Methods.
We analyzed a sample of 725 inner HII regions and a sample of 671 outer HII
regions, all of them detected and extracted from the observations of a sample
of 263 nearby, isolated, spiral galaxies observed by the CALIFA survey.
Results. We find that inner HII regions show smaller equivalent widths, greater
extinction and luminosities, along with greater values of
[NII]{\lambda}6583/H{\alpha} and [OII]{\lambda}3727/[OIII]{\lambda}5007
emission-line ratios, indicating higher metallicites and lower ionization
parameters. Inner regions have also redder colors and higher photometric and
ionizing masses, although Mion/Mphot is slighty higher for the outer regions.
Conclusions. This work shows important observational differences between inner
and outer HII regions in star forming galaxies not previously studied in
detail. These differences indicate that inner regions have more evolved stellar
populations and are in a later evolution state with respect to outer regions,
which goes in line with the inside-out galaxy formation paradigm.Comment: 16 page
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