9,967 research outputs found
Delayed Recombination and Cosmic Parameters
Current cosmological constraints from Cosmic Microwave Background (CMB)
anisotropies are typically derived assuming a standard recombination scheme,
however additional resonance and ionizing radiation sources can delay
recombination, altering the cosmic ionization history and the cosmological
inferences drawn from CMB data. We show that for recent observations of CMB
anisotropy, from the Wilkinson Microwave Anisotropy Probe satellite mission
5-year survey (WMAP5) and from the ACBAR experiment, additional resonance
radiation is nearly degenerate with variations in the spectral index, n_s, and
has a marked effect on uncertainties in constraints on the Hubble constant, age
of the universe, curvature and the upper bound on the neutrino mass. When a
modified recombination scheme is considered, the redshift of recombination is
constrained to z_*=1078\pm11, with uncertainties in the measurement weaker by
one order of magnitude than those obtained under the assumption of standard
recombination while constraints on the shift parameter are shifted by 1-sigma
to R=1.734\pm0.028. Although delayed recombination limits the precision of
parameter estimation from the WMAP satellite, we demonstrate that this should
not be the case for future, smaller angular scales measurements, such as those
by the Planck satellite mission.Comment: 9 pages, 9 figure
Calculation of minor hysteresis loops under metastable to stable transformations in vortex matter
We present a model in which metastable supercooled phase and stable
equilibrium phase of vortex matter coexist in different regions of a sample.
Minor hysteresis loops are calculated with the simple assumption of the two
phases of vortex matter having field-independent critical current densities. We
use our earlier published ideas that the free energy barrier separating the
metastable and stable phases reduces as the magnetic induction moves farther
from the first order phase transition line, and that metastable to stable
transformations occur in local regions of the sample when the local energy
dissipation exceeds a critical value. Previously reported anomalous features in
minor hysteresis loops are reproduced, and calculated field profiles are
presented.Comment: 9pages, 7 figure
Comparing Infrared Dirac-Born-Infeld Brane Inflation to Observations
We compare the Infrared Dirac-Born-Infeld (IR DBI) brane inflation model to
observations using a Bayesian analysis. The current data cannot distinguish it
from the \LambdaCDM model, but is able to give interesting constraints on
various microscopic parameters including the mass of the brane moduli
potential, the fundamental string scale, the charge or warp factor of throats,
and the number of the mobile branes. We quantify some distinctive testable
predictions with stringy signatures, such as the large non-Gaussianity, and the
large, but regional, running of the spectral index. These results illustrate
how we may be able to probe aspects of string theory using cosmological
observations.Comment: 54 pages, 13 figures. v2: non-Gaussianity constraint has been applied
to the model; parameter constraints have tightened significantly, conclusions
unchanged. References added; v3, minor revision, PRD versio
Vector magnetic hysteresis of hard superconductors
Critical state problems which incorporate more than one component for the
magnetization vector of hard superconductors are investigated. The theory is
based on the minimization of a cost functional
which weighs the changes of the magnetic field vector within the sample. We
show that Bean's simplest prescription of choosing the correct sign for the
critical current density in one dimensional problems is just a particular
case of finding the components of the vector . is
determined by minimizing under the constraint , with a bounded set. Upon the selection of
different sets we discuss existing crossed field measurements and
predict new observable features. It is shown that a complex behavior in the
magnetization curves may be controlled by a single external parameter, i.e.:
the maximum value of the applied magnetic field .Comment: 10 pages, 9 figures, accepted in Phys. Rev.
Cosmological constraints in the presence of ionizing and resonance radiation at recombination
With the recent measurement of full sky cosmic microwave background
polarization from WMAP, key cosmological degeneracies have been broken,
allowing tighter constraints to be placed on cosmological parameters inferred
assuming a standard recombination scenario. Here we consider the effect on
cosmological constraints if additional ionizing and resonance radiation sources
are present at recombination. We find that the new CMB data significantly
improve the constraints on the additional radiation sources, with
and at
95% c.l. for resonance and ionizing sources respectively. Including the
generalized recombination scenario, however, we find that the constraints on
the scalar spectral index are weakened to , with the
case now well inside the 95% c.l.. The relaxation of constraints on
tensor modes, scale invariance, dark energy and neutrino masses are also
discussed.Comment: 6 Pages, 7 Figure
Cosmon dark matter?
We investigate if the fluctuations of the scalar field mediating quintessence
-- the cosmon -- can play an important role in cosmology. Small fluctuations
with short wavelength behave similar to a relativistic gas. In contrast, the
contribution to the energy density from horizon size fluctuations may decrease
less rapidly than radiation. We discuss the possibility that the cosmon
fluctuations grow nonlinearly, form lumps and constitute the clustering dark
matter of the universe. Cosmon dark matter would lead to interesting
consequences for the equation of state and the coupling between quintessence
and dark matter.Comment: Published version,correction in appendix A, 43 pages, LaTe
Autonomous clustering using rough set theory
This paper proposes a clustering technique that minimises the need for subjective
human intervention and is based on elements of rough set theory. The proposed algorithm is
unified in its approach to clustering and makes use of both local and global data properties to
obtain clustering solutions. It handles single-type and mixed attribute data sets with ease and
results from three data sets of single and mixed attribute types are used to illustrate the
technique and establish its efficiency
Charge Fluctuations on Membrane Surfaces in Water
We generalize the predictions for attractions between over-all neutral
surfaces induced by charge fluctuations/correlations to non-uniform systems
that include dielectric discontinuities, as is the case for mixed charged lipid
membranes in an aqueous solution. We show that the induced interactions depend
in a non-trivial way on the dielectric constants of membrane and water and show
different scaling with distance depending on these properties. The generality
of the calculations also allows us to predict under which dielectric conditions
the interaction will change sign and become repulsive
Enhancement of Critical Current Density in low level Al-doped MgB2
Two sets of MgB2 samples doped with up to 5 at. % of Al were prepared in
different laboratories using different procedures. Decreases in the a and c
lattice parameters were observed with Al doping confirming Al substitution onto
the Mg site. The critical temperature (Tc) remained largely unchanged with Al
doping. For 1 - 2.5 at.% doping, at 20K the in-field critical current densities
(Jc's) were enhanced, particularly at lower fields. At 5K, in-field Jc was
markedly improved, e.g. at 5T Jc was enhanced by a factor of 20 for a doping
level of 1 at.% Al. The improved Jcs correlate with increased sample
resistivity indicative of an increase in the upper critical field, Hc2, through
alloying.Comment: 17 pages, 4 figures, to be published in Superconductor Science and
Technolog
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