79 research outputs found
A parametrization of the growth index of matter perturbations in various Dark Energy models and observational prospects using a Euclid-like survey
We provide exact solutions to the cosmological matter perturbation equation
in a homogeneous FLRW universe with a vacuum energy that can be parametrized by
a constant equation of state parameter and a very accurate approximation
for the Ansatz . We compute the growth index \gamma=\log
f(a)/\log\Om_m(a), and its redshift dependence, using the exact and
approximate solutions in terms of Legendre polynomials and show that it can be
parametrized as in most cases. We then
compare four different types of dark energy (DE) models: CDM, DGP,
and a LTB-large-void model, which have very different behaviors at
z\gsim1. This allows us to study the possibility to differentiate between
different DE alternatives using wide and deep surveys like Euclid, which will
measure both photometric and spectroscopic redshifts for several hundreds of
millions of galaxies up to redshift . We do a Fisher matrix analysis
for the prospects of differentiating among the different DE models in terms of
the growth index, taken as a given function of redshift or with a principal
component analysis, with a value for each redshift bin for a Euclid-like
survey. We use as observables the complete and marginalized power spectrum of
galaxies and the Weak Lensing (WL) power spectrum. We find that, using
, one can reach (2%, 5%) errors in , and (4%, 12%) errors in
, while using WL we get errors at least twice as large.
These estimates allow us to differentiate easily between DGP, models and
CDM, while it would be more difficult to distinguish the latter from a
variable equation of state parameter or LTB models using only the growth
index.}Comment: 29 pages, 7 figures, 6 table
A Multifrequency approach of the cosmological parameter estimation in presence of extragalactic point sources
We present a multifrequency approach which optimizes the constraints on
cosmological parameters with respect to extragalactic sources and secondary
anisotropies contamination on small scales. We model with a minimal number of
parameters the expected dominant contaminations in intensity, such as
unresolved point sources and the thermal Sunyaev-Zeldovich effect. The model
for unresolved point sources, either Poisson distributed or clustered, uses
data from Planck early results. The overall amplitude of these contributions
are included in a Markov Chain Monte Carlo analysis for the estimate of
cosmological parameters. We show that our method is robust: as long as the main
contaminants are taken into account the constraints on the cosmological
parameters are unbiased regardless of the realistic uncertainties on the
contaminants. We show also that the two parameters modelling unresolved points
sources are not prior dominated.Comment: 17 Pages, 15 Figures, Submitted to MNRA
Immunovirological response to combined antiretroviral therapy and drug resistance patterns in children: 1- and 2-year outcomes in rural Uganda
Children living with HIV continue to be in urgent need of combined antiretroviral therapy (ART). Strategies to scale up and improve pediatric HIV care in resource-poor regions, especially in sub-Saharan Africa, require further research from these settings. We describe treatment outcomes in children treated in rural Uganda after 1 and 2 years of ART start
Modelling the correlation between the thermal Sunyaev Zel'dovich effect and the cosmic infrared background
We show how the correlation between the thermal Sunyaev Zel'dovich effect
(tSZ) from galaxy clusters and dust emission from cosmic infrared background
(CIB) sources can be calculated in a halo model framework. Using recent tSZ and
CIB models, we find that the size of the tSZ x CIB cross-correlation is
approximately 20 per cent at 150 GHz. The contribution to the total angular
power spectrum is of order -2 \mu K^2 at ell=3000, however, this value is
uncertain by a factor of two to three, primarily because of CIB source
modelling uncertainties. We expect the large uncertainty in this component to
degrade upper limits on the kinematic Sunyaev Zel'dovich effect (kSZ), due to
similarity in the frequency dependence of the tSZ x CIB and kSZ across the
frequency range probed by current Cosmic Microwave Background missions. We also
find that the degree of tSZ x CIB correlation is higher for mm x sub-mm spectra
than mm x mm, because more of the sub-mm CIB originates at lower redshifts
(z<2), where most tSZ clusters are found.Comment: 16 pages, 5 figures. Accepted for publication in MNRA
Risk factors for virological failure and subtherapeutic antiretroviral drug concentrations in HIV-positive adults treated in rural northwestern Uganda
ABSTRACT: BACKGROUND: Little is known about immunovirological treatment outcomes and adherence in HIV/AIDS patients on antiretroviral therapy (ART) treated using a simplified management approach in rural areas of developing countries, or about the main factors influencing those outcomes in clinical practice. METHODS: Cross-sectional immunovirological, pharmacological, and adherence outcomes were evaluated in all patients alive and on fixed-dose ART combinations for 24 months, and in a random sample of those treated for 12 months. Risk factors for virological failure (>1,000 copies/mL) and subtherapeutic antiretroviral (ARV) concentrations were investigated with multiple logistic regression. RESULTS: At 12 and 24 months of ART, 72% (n=701) and 70% (n=369) of patients, respectively, were alive and in care. About 8% and 38% of patients, respectively, were diagnosed with immunological failure; and 75% and 72% of patients, respectively, had undetectable HIV RNA (<400 copies/mL). Risk factors for virological failure (>1,000 copies/mL) were poor adherence, tuberculosis diagnosed after ART initiation, subtherapeutic NNRTI concentrations, general clinical symptoms, and lower weight than at baseline. About 14% of patients had low ARV plasma concentrations. Digestive symptoms and poor adherence to ART were risk factors for low ARV plasma concentrations. CONCLUSIONS: Efforts to improve both access to care and patient management to achieve better immunological and virological outcomes on ART are necessary to maximize the duration of first-line therapy
Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts
We present constraints on cosmological parameters using number counts as a
function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ
(PSZ) catalogue. The PSZ is selected through the signature of the
Sunyaev--Zeldovich (SZ) effect, and the sub-sample used here has a
signal-to-noise threshold of seven, with each object confirmed as a cluster and
all but one with a redshift estimate. We discuss the completeness of the sample
and our construction of a likelihood analysis. Using a relation between mass
and SZ signal calibrated to X-ray measurements, we derive constraints
on the power spectrum amplitude and matter density parameter
in a flat CDM model. We test the robustness of
our estimates and find that possible biases in the -- relation and the
halo mass function are larger than the statistical uncertainties from the
cluster sample. Assuming the X-ray determined mass to be biased low relative to
the true mass by between zero and 30%, motivated by comparison of the observed
mass scaling relations to those from a set of numerical simulations, we find
that , , and
. The value of
is degenerate with the mass bias; if the latter is fixed to a value
of 20% we find and a
tighter one-dimensional range . We find that the larger
values of and preferred by Planck's
measurements of the primary CMB anisotropies can be accommodated by a mass bias
of about 40%. Alternatively, consistency with the primary CMB constraints can
be achieved by inclusion of processes that suppress power on small scales
relative to the CDM model, such as a component of massive neutrinos
(abridged).Comment: 20 pages, accepted for publication by A&
Planck early results. VIII. The all-sky early Sunyaev-Zeldovich cluster sample
We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from
its six highest frequencies. This early SZ (ESZ) sample is comprised of 189 candidates, which have a high signal-to-noise ratio ranging from 6
to 29. Its high reliability (purity above 95%) is further ensured by an extensive validation process based on Planck internal quality assessments
and by external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 previouslyknown
ESZ clusters. Planck furthermore releases 30 new cluster candidates, amongst which 20 meet the ESZ signal-to-noise selection criterion.
At the submission date, twelve of the 20 ESZ candidates were confirmed as new clusters, with eleven confirmed using XMM-Newton snapshot
observations, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z
below 0.3) and span more than a decade in mass, up to the rarest and most massive clusters with masses above 1 Ă 1015 M
Altimetry for the future: building on 25 years of progress
In 2018 we celebrated 25âŻyears of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
DUACS DT2014: the new multi-mission altimeter data set reprocessed over 20 years
The new DUACS DT2014 reprocessed products have been available since April
2014. Numerous innovative changes have been introduced at each step of an
extensively revised data processing protocol. The use of a new 20-year
altimeter reference period in place of the previous 7-year reference
significantly changes the sea level anomaly (SLA) patterns and thus has a
strong user impact. The use of up-to-date altimeter standards and geophysical
corrections, reduced smoothing of the along-track data, and refined mapping
parameters, including spatial and temporal correlation-scale refinement and
measurement errors, all contribute to an improved high-quality DT2014 SLA
data set. Although all of the DUACS products have been upgraded, this paper
focuses on the enhancements to the gridded SLA products over the global
ocean. As part of this exercise, 21 years of data have been homogenized,
allowing us to retrieve accurate large-scale climate signals such as global
and regional MSL trends, interannual signals, and better refined mesoscale
features.An extensive assessment exercise has been carried out on this data set, which
allows us to establish a consolidated error budget. The errors at mesoscale
are about 1.4âŻcm2 in low-variability areas, increase to an average of
8.9âŻcm2 in coastal regions, and reach nearly 32.5âŻcm2 in high
mesoscale activity areas. The DT2014 products, compared to the previous
DT2010 version, retain signals for wavelengths lower than ââŒââŻ250âŻkm,
inducing SLA variance and mean EKE increases of, respectively, +5.1 and
+15âŻ%. Comparisons with independent measurements highlight the improved
mesoscale representation within this new data set. The error reduction at the
mesoscale reaches nearly 10âŻ% of the error observed with DT2010. DT2014
also presents an improved coastal signal with a nearly 2 to 4âŻ% mean
error reduction. High-latitude areas are also more accurately represented in
DT2014, with an improved consistency between spatial coverage and sea ice
edge position. An error budget is used to highlight the limitations of the
new gridded products, with notable errors in areas with strong internal
tides
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