3,927 research outputs found
Statefinder Revisited
The quality of supernova data will dramatically increase in the next few
years by new experiments that will add high-redshift supernova to the currently
known ones. In order to use this new data to discriminate between different
dark energy models, the statefinder diagnostic was suggested and investigated
by Alam et al. in the light of the proposed SuperNova Acceleration Probe (SNAP)
satellite. By making use of the same procedure presented by these authors, we
compare their analyzes with ours, which shows a more realistic supernovae
redshift distribution and do not assume that the intercept is known. We also
analyzed the behavior of the statefinder pair {r,s} and the alternative pair
{s,q} in the presence of offset errors
The first analytical expression to estimate photometric redshifts suggested by a machine
We report the first analytical expression purely constructed by a machine to
determine photometric redshifts () of galaxies. A simple and
reliable functional form is derived using galaxies from the Sloan
Digital Sky Survey Data Release 10 (SDSS-DR10) spectroscopic sample. The method
automatically dropped the and bands, relying only on , and
for the final solution. Applying this expression to other SDSS-DR10
galaxies, with measured spectroscopic redshifts (), we achieved a
mean and a scatter when averaged up to . The method was
also applied to the PHAT0 dataset, confirming the competitiveness of our
results when faced with other methods from the literature. This is the first
use of symbolic regression in cosmology, representing a leap forward in
astronomy-data-mining connection.Comment: 6 pages, 4 figures. Accepted for publication in MNRAS Letter
ATP-Stimulated, DNA-Mediated Redox Signaling by XPD, a DNA Repair and Transcription Helicase
Using DNA-modified electrodes, we show DNA-mediated signaling by XPD, a helicase that contains a [4Fe-4S] cluster and is critical for nucleotide excision repair and transcription. The DNA-mediated redox signal resembles that of base excision repair proteins, with a DNA-bound redox potential of ~80 mV versus NHE. Significantly, this signal increases with ATP hydrolysis. Moreover, the redox signal is substrate-dependent, reports on the DNA conformational changes associated with enzymatic function, and may reflect a general biological role for DNA charge transport
Cosmological Parameter Estimation from SN Ia data: a Model-Independent Approach
We perform a model independent reconstruction of the cosmic expansion rate
based on type Ia supernova data. Using the Union 2.1 data set, we show that the
Hubble parameter behaviour allowed by the data without making any hypothesis
about cosmological model or underlying gravity theory is consistent with a flat
LCDM universe having H_0 = 70.43 +- 0.33 and Omega_m=0.297 +- 0.020, weakly
dependent on the choice of initial scatter matrix. This is in closer agreement
with the recently released Planck results (H_0 = 67.3 +- 1.2, Omega_m = 0.314
+- 0.020) than other standard analyses based on type Ia supernova data. We
argue this might be an indication that, in order to tackle subtle deviations
from the standard cosmological model present in type Ia supernova data, it is
mandatory to go beyond parametrized approaches
Breaking the color-reddening degeneracy in type Ia supernovae
A new method to study the intrinsic color and luminosity of type Ia
supernovae (SNe Ia) is presented. A metric space built using principal
component analysis (PCA) on spectral series SNe Ia between -12.5 and +17.5 days
from B maximum is used as a set of predictors. This metric space is built to be
insensitive to reddening. Hence, it does not predict the part of color excess
due to dust-extinction. At the same time, the rich variability of SN Ia spectra
is a good predictor of a large fraction of the intrinsic color variability.
Such metric space is a good predictor of the epoch when the maximum in the B-V
color curve is reached. Multivariate Partial Least Square (PLS) regression
predicts the intrinsic B band light-curve and the intrinsic B-V color curve up
to a month after maximum. This allows to study the relation between the light
curves of SNe Ia and their spectra. The total-to-selective extinction ratio RV
in the host-galaxy of SNe Ia is found, on average, to be consistent with
typical Milky-Way values. This analysis shows the importance of collecting
spectra to study SNe Ia, even with large sample publicly available. Future
automated surveys as LSST will provide a large number of light curves. The
analysis shows that observing accompaning spectra for a significative number of
SNe will be important even in the case of "normal" SNe Ia.Comment: 11 pages, 11 figure
Detectability of the First Cosmic Explosions
We present a fully self-consistent simulation of a synthetic survey of the
furthermost cosmic explosions. The appearance of the first generation of stars
(Population III) in the Universe represents a critical point during cosmic
evolution, signaling the end of the dark ages, a period of absence of light
sources. Despite their importance, there is no confirmed detection of
Population III stars so far. A fraction of these primordial stars are expected
to die as pair-instability supernovae (PISNe), and should be bright enough to
be observed up to a few hundred million years after the big bang. While the
quest for Population III stars continues, detailed theoretical models and
computer simulations serve as a testbed for their observability. With the
upcoming near-infrared missions, estimates of the feasibility of detecting
PISNe are not only timely but imperative. To address this problem, we combine
state-of-the-art cosmological and radiative simulations into a complete and
self-consistent framework, which includes detailed features of the
observational process. We show that a dedicated observational strategy using
per cent of total allocation time of the James Webb Space
Telescope mission can provide us up to detectable PISNe per year.Comment: 9 pages, 8 figures. Minor corrections added to match published
versio
Hubble parameter reconstruction from a principal component analysis: minimizing the bias
A model-independent reconstruction of the cosmic expansion rate is essential
to a robust analysis of cosmological observations. Our goal is to demonstrate
that current data are able to provide reasonable constraints on the behavior of
the Hubble parameter with redshift, independently of any cosmological model or
underlying gravity theory. Using type Ia supernova data, we show that it is
possible to analytically calculate the Fisher matrix components in a Hubble
parameter analysis without assumptions about the energy content of the
Universe. We used a principal component analysis to reconstruct the Hubble
parameter as a linear combination of the Fisher matrix eigenvectors (principal
components). To suppress the bias introduced by the high redshift behavior of
the components, we considered the value of the Hubble parameter at high
redshift as a free parameter. We first tested our procedure using a mock sample
of type Ia supernova observations, we then applied it to the real data compiled
by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we
demonstrate that it is possible to drastically suppress the bias introduced by
the high redshift behavior of the principal components. Applying our procedure
to the real data, we show that it allows us to determine the behavior of the
Hubble parameter with reasonable uncertainty, without introducing any ad-hoc
parameterizations. Beyond that, our reconstruction agrees with completely
independent measurements of the Hubble parameter obtained from red-envelope
galaxies.Comment: Modified to match journal versio
Using gamma regression for photometric redshifts of survey galaxies
Machine learning techniques offer a plethora of opportunities in tackling big
data within the astronomical community. We present the set of Generalized
Linear Models as a fast alternative for determining photometric redshifts of
galaxies, a set of tools not commonly applied within astronomy, despite being
widely used in other professions. With this technique, we achieve catastrophic
outlier rates of the order of ~1%, that can be achieved in a matter of seconds
on large datasets of size ~1,000,000. To make these techniques easily
accessible to the astronomical community, we developed a set of libraries and
tools that are publicly available.Comment: Refereed Proceeding of "The Universe of Digital Sky Surveys"
conference held at the INAF - Observatory of Capodimonte, Naples, on
25th-28th November 2014, to be published in the Astrophysics and Space
Science Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodice,
6 pages, and 1 figur
Lepton-nucleus scattering in the impulse approximation regime
We discuss theoretical calculations of electron- and neutrino-nucleus
scattering, carried out using realistic nuclear spectral functions and
including the effect of final state interactions. Comparison between electron
scattering data and the calculated inclusive cross sections off oxygen shows
that the Fermi gas model fails to provide a satisfactory description of the
measured cross sections, and inclusion of nuclear dynamics is needed. The role
of Pauli blocking in charged-current neutrino induced reactions at low is
also analyzed.Comment: To be published in the Proceedings of NUFACT05 (Nucl. Phys. B,
Proceedings Supplements
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