5,772 research outputs found
Phantom inflation and the "Big Trip"
Primordial inflation is regarded to be driven by a phantom field which is
here implemented as a scalar field satisfying an equation of state
, with . Being even aggravated by the weird properties
of phantom energy, this will pose a serious problem with the exit from the
inflationary phase. We argue however in favor of the speculation that a smooth
exit from the phantom inflationary phase can still be tentatively recovered by
considering a multiverse scenario where the primordial phantom universe would
travel in time toward a future universe filled with usual radiation, before
reaching the big rip. We call this transition the "big trip" and assume it to
take place with the help of some form of anthropic principle which chooses our
current universe as being the final destination of the time transition.Comment: 23 pages, 5 figures, LaTex, Phys. Lett. B (in press
Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST
sources having star-like counterparts in the SDSS DR5 photometric survey
(r<=20.2). We found that simple supervised neural networks, trained on sources
with SDSS spectra, and using optical photometry and radio data, are very
effective for identifying high-z QSOs without spectra. The technique yields a
completeness of 96 per cent and an efficiency of 62 per cent. Applying the
trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO
candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z
QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6
revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None
of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO,
consistently with a high completeness. The initial sample of z>=3.6 QSOs is
increased from 52 to 76, i.e. by a factor 1.46. From the new identifications
and candidates we estimate an incompleteness of SDSS for the spectroscopic
classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.Comment: 16 pages, 9 figures accepted for publication in MNRA
Library Staff Salary Survey Report: A First Thursday Presentation
This presentation was given by the Salary Task Force (STF) members, Jamie Rogers, Annia Gonzalez, and Kelley Rowan at an FIU Libraries First Thursday\u27s Forum. Members of the task force presented the results from two surveys, including cost of living research and SUS salary analysis and comparisons. Afterwards, attendees were invited to ask questions and express their concerns before the task force publishes the final report. The research in this presentation is based on surveys and research conducted by all Salary Task Force members
Meson-exchange currents and quasielastic predictions for charged-current neutrino-12C scattering in the superscaling approach
We evaluate and discuss the impact of meson-exchange currents (MECs) on
charged-current quasielastic neutrino cross sections. We consider the nuclear
transverse response arising from two-particle two-hole states excited by the
action of electromagnetic, purely isovector meson-exchange currents in a fully
relativistic framework based on the work by the Torino Collaboration [A. D.
Pace, M. Nardi, W. M. Alberico, T. W. Donnelly, and A. Molinari, Nucl. Phys.
A726, 303 (2003)]. An accurate parametrization of this MEC response as a
function of the momentum and energy transfers involved is presented. Results of
neutrino-nucleus cross sections using this MEC parametrization together with a
recent scaling approach for the one-particle one-hole contributions (named
SuSAv2) are compared with experimental data (MiniBooNE, MINERvA, NOMAD and T2K
Collaborations).Comment: 16 pages, 19 figure
Pressure dependence of Raman modes in double wall carbon nanotubes filled with α-Fe.
The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in CNTs research. In this work, the capillary effect was used to fill double wall carbon nanotubes with iron. The samples are characterized by Mössbauer and Raman spectroscopy, transmission electron microscopy, scanning area electron diffraction, and magnetization. In order to investigate their structural stability and compare it with that of single wall carbon nanotubes (SWNTs), elucidating the differences induced by the inner-outer tube interaction, unpolarized Raman spectra of tangential modes of double wall carbon nanotubes (DWNTs) filled with 1D nanocrystallin α-Fe excited with 514 nm were studied at room temperature and elevated pressure. Up to 16 GPa we find a pressure coefficient for the internal tube of 4.3 cm−1 GPa−1 and for the external tube of 5.5 cm−1 GPa−1. In addition, the tangential band of the external and internal tubes broadens and decreases in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tubes (at least up 16 GPa). Structural phase transitions were not observed in this range of pressure
The EMPIRE Survey: Systematic Variations in the Dense Gas Fraction and Star Formation Efficiency from Full-Disk Mapping of M51
We present the first results from the EMPIRE survey, an IRAM large program
that is mapping tracers of high density molecular gas across the disks of nine
nearby star-forming galaxies. Here, we present new maps of the 3-mm transitions
of HCN, HCO+, and HNC across the whole disk of our pilot target, M51. As
expected, dense gas correlates with tracers of recent star formation, filling
the "luminosity gap" between Galactic cores and whole galaxies. In detail, we
show that both the fraction of gas that is dense, f_dense traced by HCN/CO, and
the rate at which dense gas forms stars, SFE_dense traced by IR/HCN, depend on
environment in the galaxy. The sense of the dependence is that high surface
density, high molecular gas fraction regions of the galaxy show high dense gas
fractions and low dense gas star formation efficiencies. This agrees with
recent results for individual pointings by Usero et al. 2015 but using unbiased
whole-galaxy maps. It also agrees qualitatively with the behavior observed
contrasting our own Solar Neighborhood with the central regions of the Milky
Way. The sense of the trends can be explained if the dense gas fraction tracks
interstellar pressure but star formation occurs only in regions of high density
contrast.Comment: 7 pages, 5 figures, ApJL accepte
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