2,992 research outputs found
Constraints on Oscillating Quintom from Supernova, Microwave Background and Galaxy Clustering
We consider in this paper a simple oscillating Quintom model of dark energy
which has two free parameters and an equation of state oscillating and crossing
-1. For low redshifts the equation of state of this model resembles itself
similar to the linearly parameterized dark energy, however differ substantially
at large redshifts. We fit our model to the observational data separately from
the new high redshift supernova observations from the HST/GOODS program and
previous supernova, CMB and galaxy clustering. Our results show that because of
the oscillating feature of our model the constraints from observations at large
redshifts such as CMB become less stringent.Comment: 4 pages, 6 figures Revtex
Optimal strategies : theoretical approaches to the parametrization of the dark energy equation of state
The absence of compelling theoretical model requires the parameterizing the
dark energy to probe its properties. The parametrization of the equation of
state of the dark energy is a common method. We explore the theoretical
optimization of the parametrization based on the Fisher information matrix. As
a suitable parametrization, it should be stable at high redshift and should
produce the determinant of the Fisher matrix as large as possible. For the
illustration, we propose one parametrization which can satisfy both criteria.
By using the proper parametrization, we can improve the constraints on the dark
energy even for the same data. We also show the weakness of the so-called
principal component analysis method.Comment: 7pages, 11 figures, 2 tables, To match the version accepted by AS
Growth and optical properties of GaN/AlN quantum wells
We demonstrate the growth of GaN/AlN quantum well structures by
plasma-assisted molecular-beam epitaxy by taking advantage of the surfactant
effect of Ga. The GaN/AlN quantum wells show photoluminescence emission with
photon energies in the range between 4.2 and 2.3 eV for well widths between 0.7
and 2.6 nm, respectively. An internal electric field strength of
MV/cm is deduced from the dependence of the emission energy on the well width.Comment: Submitted to AP
INTERACTION OF FAST HYDROGEN IONIC CLUSTERS WITH MATTER
Fast ionic clusters Hn+ interact with matter in a specific way which is observed to deviate strongly from the interaction of atomic ions at the same velocity. We present some results obtained at Lyon about foil and gas interactions of hydrogen clusters (5 ≤ n ≤ 23) at projectile velocities close to the Bohr velocity, i.e. dynamics of the cluster fragmentation, charge state of atomic fragments and absolute dissociation cross sections in gas. We also discuss future experiments specially at higher velocities
Robust design of Si/Si3N4 high contrast grating mirror for mid-infrared VCSEL application
A Si/Si3N4 high contrast grating mirror has been designed for a VCSEL
integration in mid-infrared ({\lambda} = 2.65 m). The use of an
optimization algorithm which maximizes a VCSEL mirror quality factor allowed
the adjustment of the grating parameters while keeping large and shallow
grating pattern. The robustness with respect to fabrication error has been
enhanced thanks to a precise study of the grating dimension tolerances. The
final mirror exhibits large high reflectivity bandwidth with a polarization
selectivity and several percent of tolerance on the grating dimensions.Comment: The final publication is available at http://www.springerlink.com,
Optical and Quantum Electronics (2012) Online Firs
Contrôle bactériologique et chimique des extraits de viande
Billon Jean, Cazaillet M., Chevallier R. Contrôle bactériologique et chimique des extraits de viande. In: Bulletin de l'Académie Vétérinaire de France tome 113 n°4, 1960. pp. 225-236
Electronic temperatures, densities and plasma X-ray emission of a 14.5 GHz Electron-Cyclotron Resonance Ion Source
We have performed a systematic study of the Bremsstrahlung emission from the
electrons in the plasma of a commercial 14.5 GHz Electron-Cyclotron Resonance
Ion Source. The electronic spectral temperature and the product of ionic and
electronic densities of the plasma are measured by analyzing the Bremsstrahlung
spectra recorded for several rare gases (Ar, Kr, Xe) as a function of the
injected power. Within our uncertainty, we find an average temperature of ? 48
keV above 100W, with a weak dependency on the injected power and gas
composition. Charge state distributions of extracted ion beams have been
determined as well, providing a way to disentangle the ionic density from the
electronic density. Moreover X-ray emission from highly charged argon ions in
the plasma has been observed with a high-resolution mosaic crystal
spectrometer, demonstrating the feasibility for high-precision measurements of
transition energies of highly charged ions, in particular of the magnetic
dipole (M1) transition of He-like of argon ions
Cosmologies with a time dependent vacuum
The idea that the cosmological term, Lambda, should be a time dependent
quantity in cosmology is a most natural one. It is difficult to conceive an
expanding universe with a strictly constant vacuum energy density, namely one
that has remained immutable since the origin of time. A smoothly evolving
vacuum energy density that inherits its time-dependence from cosmological
functions, such as the Hubble rate or the scale factor, is not only a
qualitatively more plausible and intuitive idea, but is also suggested by
fundamental physics, in particular by quantum field theory (QFT) in curved
space-time. To implement this notion, is not strictly necessary to resort to ad
hoc scalar fields, as usually done in the literature (e.g. in quintessence
formulations and the like). A "running" Lambda term can be expected on very
similar grounds as one expects (and observes) the running of couplings and
masses with a physical energy scale in QFT. Furthermore, the experimental
evidence that the equation of state of the dark energy could be evolving with
time/redshift (including the possibility that it might currently behave
phantom-like) suggests that a time-variable Lambda term (possibly accompanied
by a variable Newton's gravitational coupling G=G(t)) could account in a
natural way for all these features. Remarkably enough, a class of these models
(the "new cosmon") could even be the clue for solving the old cosmological
constant problem, including the coincidence problem.Comment: LaTeX, 15 pages, 4 figure
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