4,200 research outputs found
Very large scale structures in growing neutrino quintessence
A quintessence scalar field or cosmon interacting with neutrinos can have
important effects on cosmological structure formation. Within growing neutrino
models the coupling becomes effective only in recent times, when neutrinos
become non-relativistic, stopping the evolution of the cosmon. This can explain
why dark energy dominates the universe only in a rather recent epoch by
relating the present dark energy density to the small mass of neutrinos. Such
models predict the presence of stable neutrino lumps at supercluster scales
(~200 Mpc and bigger), caused by an attractive force between neutrinos which is
stronger than gravity and mediated by the cosmon. We present a method to follow
the initial non-linear formation of neutrino lumps in physical space, by
integrating numerically on a 3D grid non-linear evolution equations, until
virialization naturally occurs. As a first application, we show results for
cosmologies with final large neutrino average mass ~2 eV: in this case,
neutrino lumps indeed form and mimic very large cold dark matter structures,
with a typical gravitational potential 10^{-5} for a lump size ~10 Mpc, and
reaching larger values for lumps of about 200 Mpc. A rough estimate of the
cosmological gravitational potential at small k in the non-linear regime,
Phi_nu = 10^{-6} (k/k_0)^{-2}, 1.2x10^{-2} h/Mpc < k_0 < 7.8x10^{-2} h/Mpc,
turns out to be many orders of magnitude smaller than an extrapolation of the
linear evolution of density fluctuations. The size of the neutrino-induced
gravitational potential could modify the spectrum of CMB anisotropies for small
angular momenta.Comment: 17 pages, 16 figures, accepted for publication in Physical Review D,
minor changes and correction
Klein-Gordon oscillator in a topologically nontrivial space-time
In this study, we analyze solutions of the wave equation for scalar particles
in a space-time with nontrivial topology. Solutions for the Klein--Gordon
oscillator are found considering two configurations of this space-time. In the
first one, it is assumed the space where the metric is
written in the usual inertial frame of reference. In the second case, we
consider a rotating reference frame adapted to the circle S1. We obtained
compact expressions for the energy spectrum and for the particles wave
functions in both configurations. Additionally, we show that the energy
spectrum of the solution associated to the rotating system has an additional
term that breaks the symmetry around
Phase Transition and Monopoles Densities in a Nearest Neighbors Two-Dimensional Spin Ice Model
In this work, we show that, due to the alternating orientation of the spins
in the ground state of the artificial square spin ice, the influence of a set
of spins at a certain distance of a reference spin decreases faster than the
expected result for the long range dipolar interaction, justifying the use of
the nearest neighbor two dimensional square spin ice model as an effective
model. Using an extension of the model presented in ref. [Scientific Reports 5,
15875 (2015)], considering the influence of the eight nearest neighbors of each
spin on the lattice, we analyze the thermodynamics of the model and study the
monopoles and string densities dependence as a function of the temperature.Comment: 11 pages, 8 figure
The pinewood nematode, Bursaphelenchus xylophilus, in Madeira Island
The environmental conditions in Madeira Island are favorable
for the presence and dissemination of the pinewood
nematode (PWN), Bursaphelenchus xylophilus. Five hundred
Pinus pinaster wood samples were collected in several
forest areas and PWN was detected in 22.8 % of the
samples. Bursaphelenchus xylophilus isolates from Madeira
Island displayed the species-specific diagnostic characters.
A morphological variation in the female tail terminus was
detected. In most females, the tail presented a broadly
rounded terminus and, occasionally, a digitate terminus with
a terminal nipple-like extension resembling a mucro. PCR
ITS-RFLP analysis revealed that Madeira Island isolates
exhibited patterns specific to the species B. xylophilus and
similar to virulent isolates. Amplified ITS regions were
further sequenced and no genetic diversity was found for
this genomic region among 17 Portuguese isolates (Madeira
Island and Continental Portugal). Phylogenetic analysis
revealed that Portuguese isolates grouped with isolates from
China, Korea and one isolate from Japa
Compressed Sensing With Prior Information: Strategies, Geometry, and Bounds
We address the problem of compressed sensing (CS)
with prior information: reconstruct a target CS signal with the
aid of a similar signal that is known beforehand, our prior
information. We integrate the additional knowledge of the similar
signal into CS via 1-1 and 1-2 minimization. We then
establish bounds on the number of measurements required by
these problems to successfully reconstruct the original signal.
Our bounds and geometrical interpretations reveal that if the
prior information has good enough quality, 1-1 minimization
improves the performance of CS dramatically. In contrast,
1-2 minimization has a performance very similar to classical
CS, and brings no significant benefits. In addition, we use
the insight provided by our bounds to design practical schemes
to improve prior information. All our findings are illustrated
with experimental results
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