78,930 research outputs found
Derivation of chemical abundances in star-forming galaxies at intermediate redshift
We have studied a sample of 11 blue, luminous, metal-poor galaxies at
redshift 0.744 < z < 0.835 from the DEEP2 redshift survey. They were selected
by the presence of the [OIII]4363 auroral line and the [OII]3726,3729 doublet
together with the strong emission nebular [OIII] lines in their spectra from a
sample of around 6000 galaxies within a narrow redshift range. All the spectra
have been taken with DEIMOS, which is a multi-slit, double-beam spectrograph
which uses slitmasks to allow the spectra from many objects to be imaged at the
same time. The selected objects present high luminosities (20.3 < MB < 18.5),
remarkable blue color index, and total oxygen abundances between 7.69 and 8.15
which represent 1/3 to 1/10 of the solar value. The wide spectral coverage
(from 6500 to 9100 angstroms) of the DEIMOS spectrograph and its high spectral
resolution, R around 5000, bring us an opportunity to study the behaviour of
these star-forming galaxies at intermediate redshift with high quality spectra.
We put in context our results together with others presented in the literature
up to date to try to understand the luminosity-metallicity relation this kind
of objects define. The star-forming metal-poor galaxies would be of special
relevance in showing the diversity among galaxies of similar luminosities and
could serve to understand the processes of galaxy evolution.Comment: 22 pages, 7 figures, Master Thesis, Universidad Autonoma de Madri
Partition function based analysis of CMB maps
We present an alternative method to analyse cosmic microwave background (CMB)
maps. We base our analysis on the study of the partition function. This
function is used to examine the CMB maps making use of the different
information embedded at different scales and moments. Using the partition
function in a likelihood analysis in two dimensions (Q_rms,n), we find the
best-fitting model to the best data available at present the COBE--DMR 4 years
data set. By means of this analysis we find a maximum in the likelihood
function for n=1.8 (-0.65 +0.35) and Q_rms-PS = 10 (-2.5 +3) muK (95 %
confidence level) in agreement with the results of other similar analyses
(Smoot et al. 1994 (1 yr), Bennet et al. 1996 (4 yr)). Also making use of the
partition function we perform a multifractal analysis and study the possible
fractal nature of the CMB sky. We find that the measure used in the analysis is
not a fractal. Finally, we use the partition function for testing the
statistical distribution of the COBE--DMR data set. We conclude that no
evidence of non-Gaussianity can be found by means of this method.Comment: 9 pages, 7 figures. To be published in MNRA
Quadratic differentials and asymptotics of Laguerre polynomials with varying complex parameters
In this paper we study the asymptotics (as ) of the sequences of
Laguerre polynomials with varying complex parameters depending on the
degree . More precisely, we assume that and . This study has been carried out previously only for
, but complex values of introduce an asymmetry that
makes the problem more difficult.
The main ingredient of the asymptotic analysis is the right choice of the
contour of orthogonality, which requires the analysis of the global structure
of trajectories of an associated quadratic differential on the complex plane,
which may have an independent interest.
While the weak asymptotics is obtained by reduction to the theorem of
Gonchar--Rakhmanov--Stahl, the strong asymptotic results are derived via the
non-commutative steepest descent analysis based on the Riemann-Hilbert
characterization of the Laguerre polynomials.Comment: 40 pages, 11 figures. To appear in J. Math. Anal. Appl. arXiv admin
note: text overlap with arXiv:math/0204248 by other authors. text overlap
with arXiv:math/0204248 by other author
The Magnetic Fields of the Quiet Sun
This work reviews our understanding of the magnetic fields observed in the
quiet Sun. The subject has undergone a major change during the last decade
(quiet revolution), and it will remain changing since the techniques of
diagnostic employed so far are known to be severely biased. Keeping these
caveats in mind, our work covers the main observational properties of the quiet
Sun magnetic fields: magnetic field strengths, unsigned magnetic flux
densities, magnetic field inclinations, as well as the temporal evolution on
short time-scales (loop emergence), and long time-scales (solar cycle). We also
summarize the main theoretical ideas put forward to explain the origin of the
quiet Sun magnetism. A final prospective section points out various areas of
solar physics where the quiet Sun magnetism may have an important physical role
to play (chromospheric and coronal structure, solar wind acceleration, and
solar elemental abundances).Comment: Review talk presented to the 6th Solar Polarization Workshop held in
Maui HI, USA, May-June 201
Efficient phase-tunable Josephson thermal rectifier
Josephson tunnel junctions are proposed as efficient phase-tunable thermal
rectifiers. The latter exploit the strong temperature dependence of the
superconducting density of states and phase-dependence of heat currents flowing
through Josephson junctions to operate. Remarkably, large heat rectification
coefficients up to 800% can potentially be achieved using conventional
materials and standard fabrication methods. In addition, these devices allow
for the in-situ fine tuning of the thermal rectification magnitude and
direction.Comment: 4 pages, 5 color figure
Comment on "Thermal fluctuations of magnetic nanoparticles" [arXiv:1209.0298]
We comment on some misleading and biased statements appearing in the
manuscript arXiv:1209.0298 ("Thermal fluctuations of magnetic nanoparticles")
about the use of the damped Landau-Lifshitz equation and the kinetic Langer
theory for the calculation of the relaxation rate of magnetic nanoclusters. We
reiterate simple scientific arguments, part of which is well known to the whole
community, demonstrating that the authors' criticisms are unfounded and that
they overstate the issue of damping in the Landau-Lifshitz equation with no
unanimous experimental evidence.Comment: 3 page
Indirect searches for SUSY Dark Matter with the MAGIC Cherenkov Telescope
Neutralinos are the natural well-motivated candidates to provide the
non-baryonic dark matter of the universe which may produce detectable signals
through their annihilation into neutrinos, photons or positrons. Due to its
high flux sensitivity and low energy threshold, the MAGIC Cherenkov telescope
could potentially detect the neutralino annihilation high energy photon
products. In the framework of minimal supergravity, the neutralino SUSY
parameter space can be scanned in different benchmark scenarios defined after
accelerator and cosmology constraints. Moreover, the neutralino density
profiles in galaxy halos and sub-halos have to be understood to infer which is
the optimal observation region to be explored by the MAGIC telescope for the
detection of neutralino photon signatures within our Galaxy and our Local
Group.Comment: 4 pages, proceedings of the conference "Satellites and tidal streams
The Anomalous Chromomagnetic Dipole Moment of the Top Quark
We calculate the one loop corrections to the chromomagnetic dipole moment of
the top quark in the framework of the Standard Model, the two Higgs doublet
model and the Minimal Supersymmetric Standard Model. In the Standard Model we
consider the QCD and the electroweak corrections generated by gluon and Higgs
boson exchanges, respectively. In the Minimal Supersymmetric Standard Model, we
calculate the SUSY- QCD corrections, including the mixing effects between the
stop coming from the left- and right-handed sectors. We obtain that the
Standard Model contribution is of the order of -0.004< delta kappa_g^t <
-0.001, and the values for diferents scenarios are of the order of -0.001 <
\delta \kappa_g^t < -0.01.Comment: Latex file, 15 pages, 5 ps figure
B meson decay anomaly with a non-universal U(1)' extension
We propose an extension of the standard model with an extra U(1)' abelian
symmetry, three Higgs doublets and one Higgs singlet, where the new U(1)'
charges are flavour non-universal. As a result, the model introduces an
enlarger particle spectrum in the TeV scale with large new physics
possibilities. The model reproduces the mixing angles and mass structures of
the quarks, charged and neutral leptons. We found that the observed anomaly of
the decay can be explained due to the
existence of couplings with new extra fermions at the TeV scale.Comment: 10 captioned figure
Topological dynamics and current-induced motion in a skyrmion lattice
We study the Thiele equation for current-induced motion in a skyrmion lattice
through two soluble models of the pinning potential. Comprised by a Magnus
term, a dissipative term and a pinning force, Thiele's equation resembles
Newton's law but in virtue of the topological character of the first two, it
differs significantly from Newtonian mechanics and because the Magnus force is
dominant, unlike its mechanical counterpart, the Coriolis force, skyrmion
trajectories do not necessarily have mechanical counterparts. This is important
if we are to understand skykrmion dynamics and tap into its potential for
data-storage technology. We identify a pinning threshold velocity for the
one-dimensional potential and for a two-dimensional potential we find a pinning
point and the skyrmion trajectories toward the point are spirals whose
frequency (compare Kepler's second law) and amplitude decay depends only on the
Gilbert constant and potential at the pinning point.Comment: 14 pages, 5 figure
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