735 research outputs found
The M4 Core Project with HST - IV. Internal Kinematics from Accurate Radial Velocities of 2771 Cluster Members
We present a detailed study of the internal kinematics of the Galactic
Globular Cluster M 4 (NGC 6121), by deriving the radial velocities from 7250
spectra for 2771 stars distributed from the upper part of the Red Giant Branch
down to the Main Sequence. We describe new approaches to determine the
wavelength solution from day-time calibrations and to determine the radial
velocity drifts that can occur between calibration and science observations
when observing with the GIRAFFE spectrograph at VLT. Two techniques to
determine the radial velocity are compared, after a qualitative description of
their advantages with respect to other commonly used algorithm, and a new
approach to remove the sky contribution from the spectra obtained with
fibre-fed spectrograph and further improve the radial velocity precision is
presented. The average radial velocity of the cluster is km s with an average dispersion of km
s. Using the same dataset and the same statistical approach of previous
analyses, 20 additional binary candidates are found, for a total of 87
candidates. A new determination of the internal radial velocity dispersion as a
function of cluster distance is presented, resulting in a dispersion of
km s within 2 from the center of cluster and steadily
decreasing outward. We statistically confirm the small amplitude of the cluster
rotation, as suggested in the past by several authors. This new analysis
represents a significant improvement with respect to previous results in
literature and provides a fundamental observational input for the modeling of
the cluster dynamics.Comment: 17 pages, 17 figures. Accepted for publication in MNRAS on September
15, 201
Sustainability ranking of desalination plants using Mamdani Fuzzy Logic Inference Systems
As water desalination continues to expand globally, desalination plants are continually under pressure to meet the requirements of sustainable development. However, the majority of desalination sustainability research has focused on new desalination projects, with limited research on sustainability performance of existing desalination plants. This is particularly important while considering countries with limited resources for freshwater such as the United Arab Emirates (UAE) as it is heavily reliant on existing desalination infrastructure. In this regard, the current research deals with the sustainability analysis of desalination processes using a generic sustainability ranking framework based on Mamdani Fuzzy Logic Inference Systems. The fuzzy-based models were validated using data from two typical desalination plants in the UAE. The promising results obtained from the fuzzy ranking framework suggest this more in-depth sustainability analysis should be beneficial due to its flexibility and adaptability in meeting the requirements of desalination sustainability
Metallicity evolution, metallicity gradients and gas fractions at z~3.4
We used near-infrared integral field spectroscopic observations from the
AMAZE and LSD programs to constrain the metallicity in a sample of 40 star
forming galaxies at 3<z<5 (most of which at z~3.4). We measure metallicities by
exploiting strong emission line diagnostics. We found that a significant
fraction of star-forming galaxies at z~3.4 deviate from the Fundamental
Metallicity Relation (FMR), with a metallicity up to a factor of ten lower than
expected according to the FMR. This deviation does not correlate with the
dynamical properties of the galaxy or with the presence of interactions. To
investigate the origin of the metallicity deviations in more detail, we also
infer information on the gas content, by inverting the Schmidt-Kennicutt
relation. In agreement with recent CO observational data, we found that, in
contrast with the steeply rising trend at 0<z<2, the gas fraction in massive
galaxies remains constant, with indication of a marginal decline, at 2<z<3.5.
When combined with the metallicity information, we infer that to explain both
the low metallicity and gas content in z~3.4 galaxies, both prominent outflows
and massive pristine gas inflows are needed. In ten galaxies we can also
spatially resolve the metallicity distribution. We found that the metallicity
generally anticorrelates with the distribution of star formation and with the
gas surface density. We discuss these findings in terms of pristine gas inflows
towards the center, and outflows of metal rich gas from the center toward the
external regions. (Abridged)Comment: Replaced to match the published versio
Testing Newtonian gravity with distant globular clusters: NGC1851 and NGC1904
Globular clusters are useful to test the validity of Newtonian dynamics in
the low acceleration regime typical of galaxies, without the complications of
non-baryonic dark matter. Specifically, in absence of disturbing effects, e.g.
tidal heating, their velocity dispersion is expected to vanish at large radii.
If such behaviour is not observed, and in particular if, as observed in
elliptical galaxies, the dispersion is found constant at large radii below a
certain threshold acceleration, this might indicate a break down of Newtonian
dynamics.
To minimise the effects of tidal heating in this paper we study the velocity
dispersion profile of two distant globular clusters, NGC 1851 and NGC 1904.
The velocity dispersion profile is derived from accurate radial velocities
measurements, obtained at the ESO 8m VLT telescope. Reliable data for 184 and
146 bona fide cluster star members, respectively for NGC 1851 and NGC 1904,
were obtained.
These data allow to trace the velocity dispersion profile up to ~2r0, where
r0 is the radius at which the cluster internal acceleration of gravity is a0 =
10e-8 cm/s/s. It is found that in both clusters the velocity dispersion becomes
constant beyond ~r0. These new results are fully in agreement with those found
for other five globular clusters previously investigated as part of this
project. Taken all together, these 7 clusters support the claim that the
velocity dispersion is constant beyond r0, irrespectively of the specific
physical properties of the clusters: mass, size, dynamical history, and
distance from the Milky Way. The strong similarly with the constant velocity
dispersion observed in elliptical galaxies beyond r0 is suggestive of a common
origin for this phenomenon in the two class of objects, and might indicate a
breakdown of Newtonian dynamics below a0.Comment: Accepted for publication by A&A main journal. 12 pages, 12 figure
Trans-arterial radioembolization in intermediate-advanced hepatocellular carcinoma: systematic review and meta-analyses.
Published onlineJournal ArticleThis is the final version of the article. Available from Impact Journals via the DOI in this record.Trans-arterial radioembolization (TARE) is a recognized, although not explicitly recommended, experimental therapy for unresectable hepatocellular carcinoma (HCC).A systematic literature review was performed to identify published studies on the use of TARE in intermediate and advanced stages HCC exploring the efficacy and safety of this innovative treatment.Twenty-one studies reporting data on overall survival (OS) and time to progression (TTP), were included in a meta-analysis. The pooled post-TARE OS was 63% (95% CI: 56-70%) and 27% (95% CI: 21-33%) at 1- and 3-years respectively in intermediate stage HCC, whereas OS was 37% (95% CI: 26-50%) and 13% (95% CI: 9-18%) at the same time intervals in patients with sufficient liver function (Child-Pugh A-B7) but with an advanced HCC because of the presence of portal vein thrombosis. When an intermediate and advanced case-mix was considered, OS was 58% (95% CI: 48-67%) and 17% (95% CI: 12-23%) at 1- and 3-years respectively. As for TTP, only four studies reported data: the observed progression probability was 56% (95% CI: 41-70%) and 73% (95% CI: 56-87%) at 1 and 2 years respectively. The safety analysis, focused on the risk of liver decompensation after TARE, revealed a great variability, from 0-1% to more than 36% events, influenced by the number of procedures, patient Child-Pugh stage and treatment duration.Evidence supporting the use of radioembolization in HCC is mainly based on retrospective and prospective cohort studies. Based on this evidence, until the results of the ongoing randomized trials become available, radioembolization appears to be a viable treatment option for intermediate-advanced stage HCC.The present study was funded by ASBM Srl through an unrestricted grant to CERGAS, Bocconi University, Via Roentgen 1, 20136 Milan, Italy
Fast Gibbs sampling for high-dimensional Bayesian inversion
Solving ill-posed inverse problems by Bayesian inference has recently
attracted considerable attention. Compared to deterministic approaches, the
probabilistic representation of the solution by the posterior distribution can
be exploited to explore and quantify its uncertainties. In applications where
the inverse solution is subject to further analysis procedures, this can be a
significant advantage. Alongside theoretical progress, various new
computational techniques allow to sample very high dimensional posterior
distributions: In [Lucka2012], a Markov chain Monte Carlo (MCMC) posterior
sampler was developed for linear inverse problems with -type priors. In
this article, we extend this single component Gibbs-type sampler to a wide
range of priors used in Bayesian inversion, such as general priors
with additional hard constraints. Besides a fast computation of the
conditional, single component densities in an explicit, parameterized form, a
fast, robust and exact sampling from these one-dimensional densities is key to
obtain an efficient algorithm. We demonstrate that a generalization of slice
sampling can utilize their specific structure for this task and illustrate the
performance of the resulting slice-within-Gibbs samplers by different computed
examples. These new samplers allow us to perform sample-based Bayesian
inference in high-dimensional scenarios with certain priors for the first time,
including the inversion of computed tomography (CT) data with the popular
isotropic total variation (TV) prior.Comment: submitted to "Inverse Problems
A mass threshold in the number density of passive galaxies at z2
The process that quenched star formation in galaxies at intermediate and high
redshift is still the subject of considerable debate. One way to investigate
this puzzling issue is to study the number density of quiescent galaxies at
z~2, and its dependence on mass. Here we present the results of a new study
based on very deep Ks-band imaging (with the HAWK-I instrument on the VLT) of
two HST CANDELS fields (the UKIDSS Ultra-deep survey (UDS) field and
GOODS-South). The new HAWK-I data (taken as part of the HUGS VLT Large Program)
reach detection limits of Ks>26 (AB mag). We select a sample of
passively-evolving galaxies in the redshift range 1.4<z<2.5. Thanks to the
depth and large area coverage of our imaging, we have been able to extend the
selection of quiescent galaxies a magnitude fainter than previous analyses.
Through extensive simulations we demonstrate, for the first time, that the
observed turn-over in the number of quiescent galaxies at K>22 is real. This
has enabled us to establish unambiguously that the number counts of quiescent
galaxies at z~2 flatten and slightly decline at magnitudes fainter than
Ks~22(AB mag.). We show that this trend corresponds to a stellar mass threshold
below which the mechanism that halts the star
formation in high-redshift galaxies seems to be inefficient. Finally we compare
the observed pBzK number counts with those of quiescent galaxies extracted from
four different semi-analytic models. We find that none of the models provides a
statistically acceptable description of the number density of quiescent
galaxies at these redshifts. We conclude that the mass function of quiescent
galaxies as a function of redshift continues to present a key and demanding
challenge for proposed models of galaxy formation and evolution.Comment: Accepted for publication on Astronomy and Astrophysic
Constraints on the star-formation rate of z~3 LBGs with measured metallicity in the CANDELS GOODS-South field
We analyse 14 LBGs at z~2.8-3.8 constituting the only sample where both a
spectroscopic measurement of their metallicity and deep IR observations
(CANDELS+HUGS survey) are available. Fixing the metallicity of population
synthesis models to the observed values, we determine best-fit physical
parameters under different assumptions about the star-formation history and
also consider the effect of nebular emission. For comparison we determine the
UV slope of the objects, and use it to estimate their SFR_UV99 by correcting
the UV luminosity following Meurer et al. (1999). A comparison between SFR
obtained through SED-fitting (SFR_fit) and the SFR_UV99 shows that the latter
are underestimated by a factor 2-10, regardless of the assumed SFH. Other SFR
indicators (radio, far-IR, X-ray, recombination lines) coherently indicate SFRs
a factor of 2-4 larger than SFR_UV99 and in closer agreement with SFR_fit. This
discrepancy is due to the solar metallicity implied by the usual beta-A1600
conversion factor. We propose a refined relation, appropriate for sub-solar
metallicity LBGs: A1600 = 5.32+1.99beta. This relation reconciles the
dust-corrected UV with the SED-fitting and the other SFR indicators. We show
that the fact that z~3 galaxies have sub-solar metallicity implies an upward
revision by a factor of ~1.5-2 of the global SFRD, depending on the assumptions
about the age of the stellar populations. We find very young best-fit ages
(10-500 Myrs) for all our objects. From a careful examination of the
uncertainties in the fit and the amplitude of the Balmer break we conclude that
there is little evidence of the presence of old stellar population in at least
half of the LBGs in our sample, suggesting that these objects are probably
caught during a huge star-formation burst, rather than being the result of a
smooth evolution.Comment: 16 pages, 13 figures, A&A in press. Matched to the published versio
Numerical cubature on scattered data by adaptive interpolation
We construct cubature methods on scattered data via resampling on the support
of known algebraic cubature formulas, by different kinds of adaptive
interpolation (polynomial, RBF, PUM). This approach gives a promising
alternative to other recent methods, such as direct meshless cubature by RBF or
least-squares cubature formulas
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