95 research outputs found
The ISW-tSZ cross correlation: ISW extraction out of pure CMB data
If Dark Energy introduces an acceleration in the universal expansion then
large scale gravitational potential wells should be shrinking, causing a
blueshift in the CMB photons that cross such structures (Integrated Sachs-Wolfe
effect, [ISW]). Galaxy clusters are known to probe those potential wells. In
these objects, CMB photons also experience inverse Compton scattering off the
hot electrons of the intra-cluster medium, and this results in a distortion
with a characteristic spectral signature of the CMB spectrum (the so-called
thermal Sunyaev-Zel'dovich effect, [tSZ]). Since both the ISW and the tSZ
effects take place in the same potential wells, they must be spatially
correlated. We present how this cross ISW-tSZ signal can be detected in a
CMB-data contained way by using the frequency dependence of the tSZ effect in
multi frequency CMB experiments like {\it Planck}, {\em without} requiring the
use of external large scale structure tracers data. We find that by masking low
redshift clusters, the shot noise level decreases significantly, boosting the
signal to noise ratio of the ISW--tSZ cross correlation. We also find that
galactic and extragalactic dust residuals must be kept at or below the level of
~0.04 muK^2 at l=10, a limit that is a factor of a few below {\it Planck}'s
expectations for foreground subtraction. If this is achieved, CMB observations
of the ISW-tSZ cross correlation should also provide an independent probe for
the existence of Dark Energy and the amplitude of density perturbations.Comment: submitted to MNRA
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
The Roles of the S3MPC: Monitoring, Validation and Evolution of Sentinel-3 Altimetry Observations
The Sentinel-3 Mission Performance Centre (S3MPC) is tasked by the European Space Agency (ESA) to monitor the health of the Copernicus Sentinel-3 satellites and ensure a high data quality to the users. This paper deals exclusively with the effort devoted to the altimeter and microwave radiometer, both components of the Surface Topography Mission (STM). The altimeters on Sentinel-3A and -3B are the first to operate in delay-Doppler or SAR mode over all Earth surfaces, which enables better spatial resolution of the signal in the along-track direction and improved noise reduction through multi-looking, whilst the radiometer is a two-channel nadir-viewing system. There are regular routine assessments of the instruments through investigation of telemetered housekeeping data, calibrations over selected sites and comparisons of geophysical retrievals with models, in situ data and other satellite systems. These are performed both to monitor the daily production, assessing the uncertainties and errors on the estimates, and also to characterize the long-term performance for climate science applications. This is critical because an undetected drift in performance could be misconstrued as a climate variation. As the data are used by the Copernicus Services (e.g., CMEMS, Global Land Monitoring Services) and by the research community over open ocean, coastal waters, sea ice, land ice, rivers and lakes, the validation activities encompass all these domains, with regular reports openly available. The S3MPC is also in charge of preparing improvements to the processing, and of the development and tuning of algorithms to improve their accuracy. This paper is thus the first refereed publication to bring together the analysis of SAR altimetry across all these different domains to highlight the benefits and existing challenges
Randomised pharmacokinetic trial of rifabutin with lopinavir/ritonavir-antiretroviral therapy in patients with HIV-associated tuberculosis in Vietnam.
BACKGROUND: Rifampicin and protease inhibitors are difficult to use concomitantly in patients with HIV-associated tuberculosis because of drug-drug interactions. Rifabutin has been proposed as an alternative rifamycin, but there is concern that the current recommended dose is suboptimal. The principal aim of this study was to compare bioavailability of two doses of rifabutin (150 mg three times per week and 150 mg daily) in patients with HIV-associated tuberculosis who initiated lopinavir/ritonavir-based antiretroviral therapy in Vietnam. Concentrations of lopinavir/ritonavir were also measured. METHODS: This was a randomized, open-label, multi-dose, two-arm, cross-over trial, conducted in Vietnamese adults with HIV-associated tuberculosis in Ho Chi Minh City (Clinical trial registry number NCT00651066). Rifabutin pharmacokinetics were evaluated before and after the introduction of lopinavir/ritonavir -based antiretroviral therapy using patient randomization lists. Serial rifabutin and 25-O-desacetyl rifabutin concentrations were measured during a dose interval after 2 weeks of rifabutin 300 mg daily, after 3 weeks of rifabutin 150 mg daily with lopinavir/ritonavir and after 3 weeks of rifabutin 150 mg three times per week with lopinavir/ritonavir. RESULTS: Sixteen and seventeen patients were respectively randomized to the two arms, and pharmacokinetic analysis carried out in 12 and 13 respectively. Rifabutin 150 mg daily with lopinavir/ritonavir was associated with a 32% mean increase in rifabutin average steady state concentration compared with rifabutin 300 mg alone. In contrast, the rifabutin average steady state concentration decreased by 44% when rifabutin was given at 150 mg three times per week with lopinavir/ritonavir. With both dosing regimens, 2 - 5 fold increases of the 25-O-desacetyl- rifabutin metabolite were observed when rifabutin was given with lopinavir/ritonavir compared with rifabutin alone. The different doses of rifabutin had no significant effect on lopinavir/ritonavir plasma concentrations. CONCLUSIONS: Based on these findings, rifabutin 150 mg daily may be preferred when co-administered with lopinavir/ritonavir in patients with HIV-associated tuberculosis. TRIAL REGISTRATION: ClinicalTrials.gov NCT00651066
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
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
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