18,229 research outputs found
Searching for a dipole modulation in the large-scale structure of the Universe
Several statistical anomalies in the CMB temperature anisotropies seem to
defy the assumption of a homogeneous and isotropic universe. In particular, a
dipole modulation has been detected both in WMAP and Planck data. We adapt the
methodology proposed by Eriksen et al. (2007) on CMB data to galaxy surveys,
tracing the large-scale structure. We analyse the NRAO VLA Sky Survey (NVSS)
data at a resolution of ~2 degrees for three different flux thresholds: 2.5,
5.0 and 10.0 mJy respectively. No evidence of a dipole modulation is found.
This result suggests that the origin of the dipole asymmetry found in the CMB
cannot be assigned to secondary anisotropies produced at redshifts around z =
1. However, it could still have been generated at redshifts higher or lower,
such as the integrated Sachs-Wolfe effect produced by the local structures.
Other all-sky surveys, like the infrared WISE catalogue, could help to explore
with a high sensitivity a redshift interval closer than the one probed with
NVSS.Comment: 6 pages, 2 figures. Some minor changes have been done from the
original manuscript. This paper is accepted by MNRA
Non-homogeneous polygonal Markov fields in the plane: graphical representations and geometry of higher order correlations
We consider polygonal Markov fields originally introduced by Arak and
Surgailis (1989). Our attention is focused on fields with nodes of order two,
which can be regarded as continuum ensembles of non-intersecting contours in
the plane, sharing a number of features with the two-dimensional Ising model.
We introduce non-homogeneous version of polygonal fields in anisotropic
enviroment. For these fields we provide a class of new graphical constructions
and random dynamics. These include a generalised dynamic representation,
generalised and defective disagreement loop dynamics as well as a generalised
contour birth and death dynamics. Next, we use these constructions as tools to
obtain new exact results on the geometry of higher order correlations of
polygonal Markov fields in their consistent regime.Comment: 54 page
Visco-hyperelastic model with damage for simulating cyclic thermoplastic elastomers behavior applied to an industrial component
In this work a nonlinear phenomenological visco-hyperelastic model including damage consideration is developed to simulate the behavior of Santoprene 101-73 material. This type of elastomeric material is widely used in the automotive and aeronautic sectors, as it has multiple advantages. However, there are still challenges in properly analyzing the mechanical phenomena that these materials exhibit. To simulate this kind of material a lot of theories have been exposed, but none of them have been endorsed unanimously. In this paper, a new model is presented based on the literature, and on experimental data. The test samples were extracted from an air intake duct component of an automotive engine. Inelastic phenomena such as hyperelasticity, viscoelasticity and damage are considered singularly in this model, thus modifying and improving some relevant models found in the literature. Optimization algorithms were used to find out the model parameter values that lead to the best fit of the experimental curves from the tests. An adequate fitting was obtained for the experimental results of a cyclic uniaxial loading of Santoprene 101-73
Distorted Heisenberg Algebra and Coherent States for Isospectral Oscillator Hamiltonians
The dynamical algebra associated to a family of isospectral oscillator
Hamiltonians is studied through the analysis of its representation in the basis
of energy eigenstates. It is shown that this representation becomes similar to
that of the standard Heisenberg algebra, and it is dependent of a parameter
. We name it {\it distorted Heisenberg algebra}, where is the
distortion parameter. The corresponding coherent states for an arbitrary
are derived, and some particular examples are discussed in full detail. A
prescription to produce the squeezing, by adequately selecting the initial
state of the system, is given.Comment: 21 pages, Latex, 3 figures available as hard copies upon request from
the first Autho
Characterization of Carbon-Contaminated B4C-Coated Optics after Chemically Selective Cleaning with Low-Pressure RF Plasma
Boron carbide (B4C) is one of the few materials that is expected to be mostly
resilient with respect to the extremely high brilliance of the photon beam
generated by free electron lasers (FELs) and is thus of considerable interest
for optical applications in this field. However, as in the case of many other
optics operated at modern light source facilities, B4C-coated optics are
subject to ubiquitous carbon contaminations. These contaminations represent a
serious issue for the operation of high performance FEL beamlines due to severe
reduction of photon flux, beam coherence, creation of destructive interference,
and scattering losses. A variety of B4C cleaning technologies were developed at
different laboratories with varying success. We present a study regarding the
low-pressure RF plasma cleaning of carbon contaminated B4C test samples via
inductively coupled O2/Ar, H2/Ar, and pure O2 RF plasma produced following
previous studies using the same IBSS GV10x downstream plasma source. Results
regarding the chemistry, morphology as well as other aspects of the B4C optical
coating before and after the plasma cleaning are reported. We conclude from
these comparative plasma processes that pure O2 feedstock plasma only exhibits
the required chemical selectivity for maintaining the integrity of the B4C
optical coating.Comment: 27 pages, 15 figure
Consequences of spontaneous reconnection at a two-dimensional non-force-free current layer
Magnetic neutral points, where the magnitude of the magnetic field vanishes
locally, are potential locations for energy conversion in the solar corona. The
fact that the magnetic field is identically zero at these points suggests that
for the study of current sheet formation and of any subsequent resistive
dissipation phase, a finite beta plasma should be considered, rather than
neglecting the plasma pressure as has often been the case in the past. The
rapid dissipation of a finite current layer in non-force-free equilibrium is
investigated numerically, after the sudden onset of an anomalous resistivity.
The aim of this study is to determine how the energy is redistributed during
the initial diffusion phase, and what is the nature of the outward transmission
of information and energy. The resistivity rapidly diffuses the current at the
null point. The presence of a plasma pressure allows the vast majority of the
free energy to be transferred into internal energy. Most of the converted
energy is used in direct heating of the surrounding plasma, and only about 3%
is converted into kinetic energy, causing a perturbation in the magnetic field
and the plasma which propagates away from the null at the local fast
magnetoacoustic speed. The propagating pulses show a complex structure due to
the highly non-uniform initial state. It is shown that this perturbation
carries no net current as it propagates away from the null. The fact that,
under the assumptions taken in this paper, most of the magnetic energy released
in the reconnection converts internal energy of the plasma, may be highly
important for the chromospheric and coronal heating problem
The spatially-resolved star formation histories of CALIFA galaxies: Implications for galaxy formation
This paper presents the spatially resolved star formation history (SFH) of
nearby galaxies with the aim of furthering our understanding of the different
processes involved in the formation and evolution of galaxies. To this end, we
apply the fossil record method of stellar population synthesis to a rich and
diverse data set of 436 galaxies observed with integral field spectroscopy in
the CALIFA survey. The sample covers a wide range of Hubble types, with stellar
masses ranging from to . Spectral
synthesis techniques are applied to the datacubes to retrieve the spatially
resolved time evolution of the star formation rate (SFR), its intensity
(), and other descriptors of the 2D-SFH in seven bins of
galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and five bins of stellar
mass. Our main results are: a) Galaxies form very fast independently of their
current stellar mass, with the peak of star formation at high redshift (). Subsequent star formation is driven by and morphology, with less
massive and later type spirals showing more prolonged periods of star
formation. b) At any epoch in the past the SFR is proportional to ,
with most massive galaxies having the highest absolute (but lowest specific)
SFRs. c) While nowadays is similar for all spirals, and
significantly lower in early type galaxies (ETG), in the past scales well with morphology. The central regions of today's ETGs are
where reached the highest values (Gyrpc), similar to those measured in high redshift
star forming galaxies. d) The evolution of in Sbc systems
matches that of models for Milky-Way-like galaxies, suggesting that the
formation of a thick disk may be a common phase in spirals at early epochs.Comment: 21 pages, 11 figures, 1 table, accepted for publication in Astronomy
& Astrophysics, abstract abridged for arXiv submissio
The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales
This paper presents the mass assembly time scales of nearby galaxies observed
by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record
method of the stellar populations to the complete sample of the 3rd CALIFA data
release, with a total of 661 galaxies, covering stellar masses from 10
to 10 M and a wide range of Hubble types. We apply spectral
synthesis techniques to the datacubes and process the results to produce the
mass growth time scales and mass weighted ages, from which we obtain temporal
and spatially resolved information in seven bins of galaxy morphology and six
bins of stellar mass (M) and stellar mass surface density
(). We use three different tracers of the spatially resolved
star formation history (mass assembly curves, ratio of half mass to half light
radii, and mass-weighted age gradients) to test if galaxies grow inside-out,
and its dependence with galaxy stellar mass, , and morphology.
Our main results are as follows: (a) The innermost regions of galaxies assemble
their mass at an earlier time than regions located in the outer parts; this
happens at any given M, , or Hubble type, including
the lowest mass systems. (b) Galaxies present a significant diversity in their
characteristic formation epochs for lower-mass systems. This diversity shows a
strong dependence of the mass assembly time scales on and
Hubble type in the lower-mass range (10 to 10), but a very
mild dependence in higher-mass bins. (c) All galaxies show negative
log age gradients in the inner 1 HLR. The profile
flattens with increasing values of . There is no significant
dependence on M within a particular bin, except for
the lowest bin, where the gradients becomes steeper.Comment: 15 pages, 13 figures, 3 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
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