165 research outputs found
Current lookback time-redshift bounds on dark energy
We investigate observational constraints on dark energy models from lookback
time (LT) estimates of 32 old passive galaxies distributed over the redshift
interval . To build up our LT sample we combine the age
measurements for these 32 objects with estimates of the total age of the
Universe, as obtained from current CMB data. We show that LT data may provide
bounds on the cosmological parameters with accuracy competitive with type Ia
Supernova methods. In order to break possible degeneracies between models
parameters, we also discuss the bounds when our lookback time versus redshift
sample is combined with with the recent measurement of the baryonic acoustic
oscillation peak and the derived age of the Universe from current CMB
measurements.Comment: 6 pages, 4 figures, LaTe
Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers
In antiferromagnetically coupled superlattices grown on (001) faces of cubic
substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or
Fe/Cr, the magnetic states evolve under competing influence of bilinear and
biquadratic exchange interactions, surface-enhanced four-fold in-plane
anisotropy, and specific finite-size effects. Using phenomenological
(micromagnetic) theory, a comprehensive survey of the magnetic states and
reorientation transitions has been carried out for multilayer systems with even
number of ferromagnetic sub-layers and magnetizations in the plane. In
two-layer systems (N=2) the phase diagrams in dependence on components of the
applied field in the plane include ``swallow-tail'' type regions of
(metastable) multistate co-existence and a number of continuous and
discontinuous reorientation transitions induced by radial and transversal
components of the applied field. In multilayers (N \ge 4) noncollinear states
are spatially inhomogeneous with magnetization varying across the multilayer
stack. For weak four-fold anisotropy the magnetic states under influence of an
applied field evolve by a complex continuous reorientation into the saturated
state. At higher anisotropy they transform into various inhomogeneous and
asymmetric structures. The discontinuous transitions between the magnetic
states in these two-layers and multilayers are characterized by broad ranges of
multi-phase coexistence of the (metastable) states and give rise to specific
transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio
Observational tests for \Lambda(t)CDM cosmology
We investigate the observational viability of a class of cosmological models
in which the vacuum energy density decays linearly with the Hubble parameter,
resulting in a production of cold dark matter particles at late times.
Similarly to the flat \Lambda CDM case, there is only one free parameter to be
adjusted by the data in this class of \Lambda(t)CDM scenarios, namely, the
matter density parameter. To perform our analysis we use three of the most
recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the
current measurements of distance to the BAO peaks at z = 0.2 and z = 0.35 and
the position of the first acoustic peak of the CMB power spectrum. We show that
in terms of statistics both models provide good fits to the data and
similar results. A quantitative analysis discussing the differences in
parameter estimation due to SNe light-curve fitting methods (SALT2 and MLCS2k2)
is studied using the current SDSS and Constitution SNe Ia compilations. A
matter power spectrum analysis using the 2dFGRS is also performed, providing a
very good concordance with the constraints from the SDSS and Constitution
MLCS2k2 data.Comment: Revised version, to appear in JCA
EVALUATION OF NITROGEN MONITORING, BUD FERTILITYAND âTHOMPSON SEEDLESSâ GRAPEVINE PRODUCTION ON DIFFERENT ROOTSTOCKS
Calcium levels and calcium: available phosphorus ratios in diets for white egg layers from 42 to 58 weeks of age
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InfluĂȘncia do nĂșmero de gemas, presença ou ausĂȘncia de folhas e posição do explante na multiplicação in vitro da batata
CARACTERIZAĂĂO DE ESTAĂĂES DE BOMBEAMENTO EM LAVOURAS DE ARROZ DO RIO GRANDE DO SUL
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