8,528 research outputs found
A Parametric Framework for the Comparison of Methods of Very Robust Regression
There are several methods for obtaining very robust estimates of regression
parameters that asymptotically resist 50% of outliers in the data. Differences
in the behaviour of these algorithms depend on the distance between the
regression data and the outliers. We introduce a parameter that
defines a parametric path in the space of models and enables us to study, in a
systematic way, the properties of estimators as the groups of data move from
being far apart to close together. We examine, as a function of , the
variance and squared bias of five estimators and we also consider their power
when used in the detection of outliers. This systematic approach provides tools
for gaining knowledge and better understanding of the properties of robust
estimators.Comment: Published in at http://dx.doi.org/10.1214/13-STS437 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Sub-horizon Perturbation Behavior in Extended Quintessence
In the general context of scalar-tensor theories, we consider a model in
which a scalar field coupled to the Ricci scalar in the gravitational sector of
the Lagrangian, is also playing the role of an ``Extended Quintessence'' field,
dominating the energy content of the Universe at the present time. In this
framework, we study the linear evolution of the perturbations in the
Quintessence energy density, showing that a new phenomenon, named here
``gravitational dragging'', can enhance the scalar field density perturbations
as much as they reach the non-linear regime. The possibility of dark energy
clumps formation is thus discussed.Comment: Proceedings of the 5th International UCLA Symposium on Sources and
Detection of Dark Matter and Dark Energy in the Universe (Dark Matter 2002),
Marina del Rey, California, USA, 20-22 February 200
La pesca costera en la Argentina
Se aborda el estudio de la pesca costera en la Argentina (océano Atlántico sudoccidental) teniendo en cuenta los factores económicos, sociales y políticos que promovieron su retraso o desarrollo. Para comprenderlo se analizan las diversas etapas históricas desde la época de la conquista (1580) hasta nuestros días. Se detalla sobre la actualidad de las artes de pesca en pequeña escala, las características de los pescadores, el manejo de las pesquerías costeras y el conflicto por los recursos y perspectivas
Scalar field dark energy and Cosmic Microwave Background
A dynamical scalar field represents the simplest generalization of a pure
Cosmological Constant as a candidate to explain the recent evidence in favour
of the accelerated cosmic expansion. We review the dynamical properties of such
a component, and argue that, even if the background expectation value of this
field is fixed and the equation of state is the same as a Cosmological
Constant, scalar field fluctuations can still be used to distinguish the two
components. We compare predicted spectra of Cosmic Microvave Background (CMB)
anisotropies in tracking scalar field cosmologies with the present CMB data, in
order to get constraints on the amount and equation of state of dark energy.
High precision experiments like SNAP, {\sc Planck} and {\sc SNfactory},
together with the data on Large Scale Structure, are needed to probe this issue
with the necessary accuracy. Here we show the intriguing result that, with a
strong prior on the value of the Hubble constant today, the assumption of a
flat universe, and consistency relations between amplitude and spectral index
of primordial gravitational waves, the present CMB data at give
indication of a dark energy equation of state larger than -1, while the
ordinary Cosmological Constant is recovered at .Comment: 4 pages including 2 figures, Dark Matter 2002 proceedings,
Nucl.Phys.B in pres
Numerical study of halo concentrations in dark-energy cosmologies
We study the concentration parameters, their mass dependence and redshift
evolution, of dark-matter halos in different dark-energy cosmologies with
constant and time-variable equation of state, and compare them with "standard''
Lambda-CDM and OCDM models. We find that previously proposed algorithms for
predicting halo concentrations can be well adapted to dark-energy models. When
centred on the analytically expected values, halo concentrations show a
log-normal distribution with a uniform standard deviation of ~0.2. The
dependence of averaged halo concentrations on mass and redshift permits a
simple fit of the form (1+z) c=c0 (M/M0)^a, with a~-0.1 throughout. We find
that the cluster concentration depends on the dark energy equation of state at
the cluster formation redshift z_{coll} through the linear growth factor
D_+(z_{coll}). As a simple correction accounting for dark-energy cosmologies,
we propose scaling c0 from Lambda-CDM with the ratio of linear growth factors,
c0 -> c0 D_+(z_{coll})/D_{+,Lambda-CDM}(z_{coll}).Comment: 11 pages, submitted to Astronomy & Astrophysic
Astrophysical and Cosmological Information from Large-scale sub-mm Surveys of Extragalactic Sources
We present a quantitative analysis of the astrophysical and cosmological
information that can be extracted from the many important wide-area, shallow
surveys that will be carried out in the next few years. Our calculations
combine the predictions of the physical model by Granato et al. (2004) for the
formation and evolution of spheroidal galaxies with up-to-date phenomenological
models for the evolution of starburst and normal late-type galaxies and of
radio sources. We compute the expected number counts and the redshift
distributions of these source populations separately and then focus on
proto-spheroidal galaxies. For the latter objects we predict the counts and
redshift distributions of strongly lensed sources at 250, 350, 500, and 850
micron, the angular correlation function of sources detected in the surveys
considered, the angular power spectra due to clustering of sources below the
detection limit in Herschel and Planck surveys. An optimal survey for selecting
strongly lensed proto-spheroidal galaxies is described, and it is shown how
they can be easily distinguished from the other source populations. We also
discuss the detectability of the imprints of the 1-halo and 2-halo regimes on
angular correlation functions and clustering power spectra, as well as the
constraints on cosmological parameters that can be obtained from the
determinations of these quantities. The novel data relevant to derive the first
sub-millimeter estimates of the local luminosity functions of starburst and
late-type galaxies, and the constraints on the properties of rare source
populations, such as blazars, are also briefly described.Comment: 16 pages, 10 figures. Accepted for publication on MNRA
Host lifestyle affects human microbiota on daily timescales
Background:
Disturbance to human microbiota may underlie several pathologies. Yet, we lack a comprehensive understanding of how lifestyle affects the dynamics of human-associated microbial communities.
Results:
Here, we link over 10,000 longitudinal measurements of human wellness and action to the daily gut and salivary microbiota dynamics of two individuals over the course of one year. These time series show overall microbial communities to be stable for months. However, rare events in each subjects’ life rapidly and broadly impacted microbiota dynamics. Travel from the developed to the developing world in one subject led to a nearly two-fold increase in the Bacteroidetes to Firmicutes ratio, which reversed upon return. Enteric infection in the other subject resulted in the permanent decline of most gut bacterial taxa, which were replaced by genetically similar species. Still, even during periods of overall community stability, the dynamics of select microbial taxa could be associated with specific host behaviors. Most prominently, changes in host fiber intake positively correlated with next-day abundance changes among 15% of gut microbiota members.
Conclusions:
Our findings suggest that although human-associated microbial communities are generally stable, they can be quickly and profoundly altered by common human actions and experiences.National Science Foundation (U.S.) (Grant 0821391
A machine learning approach for the estimation of fuel consumption related to road pavement rolling resistance for large fleets of trucks
There remains a level of uncertainty concerning the methodological assumptions and parameters to consider in the estimation of road vehicle fuel consumption due to the condition of road pavements. In fact, recent studies highlighted how existing models can lead to very different results and that because of this, they are not fully ready to be implemented as standard in the life-cycle assessment (LCA) framework. This study presents an innovative approach, based on the application of the Boruta algorithm (BA) and neural networks (NN), for the assessment and calculation of the fuel consumption of a large fleet of truck, which can be used to estimate the use phase emissions of road pavements. The study shows that neural networks are suitable to analyse the large quantities of data, coming from fleet and road asset management databases, effectively and that the developed NN model is able to estimate the impact of rolling resistance-related parameters (pavement roughness and macrotexture) on truck fuel consumption
Genetic characterization of the Bardigiano horse using microsatellite markers
The study was aimed at investigating the genetic structure of the Bardigiano horse and its relationships with the Haflinger, Maremmano and Arabian breeds using 11 microsatellite markers. A total of 94 alleles were detected across the breeds, with a mean of 8.5 alleles per locus and a mean observed heterozygosity of 0.69. Compared to the other breeds, the Bardigiano horse showed quite a high genetic variability, as indicated by the mean number of alleles (7.0 vs 6.1÷7.6) and by the observed heterozygosity (0.72 vs 0.66÷0.71). Moreover, the genotype distributions in the Bardigiano groups of different sex and age were not significantly different. The overall FST value showed that the genetic differences among breeds accounted for 7.8% (P=0.001) of the total variation, and the pairwise FST values were all significant. The assignment test allocated between 96.8 and 98.9% of the individuals to the population they were collected from, with a mean probability of assignment of about 97% for all breeds, except for the Arabian, where it approached 100%. The results have highlighted that the Bardigiano breed has a high within and between breed variability, which is considerably more than could be expected by looking at its evolution history. This justifies the need for the development of additional breeding strategies to preserve the existing genetic variability
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