753 research outputs found
Strong lensing in the MareNostrum Universe II: scaling relations and optical depths
The strong lensing events that are observed in compact clusters of galaxies
can, both statistically and individually, return important clues about the
structural properties of the most massive structures in the Universe.
Substantial work is ongoing in order to understand the degree of similarity
between the lensing cluster population and the population of clusters as a
whole, with members of the former being likely more massive, compact, and
substructured than members of the latter. In this work we exploit synthetic
clusters extracted from the {\sc MareNostrum Universe} cosmological simulation
in order to estimate the correlation between the strong lensing efficiency and
other bulk properties of lensing clusters, such as the virial mass and the
bolometric X-ray luminosity. We found that a positive correlation exist between
all these quantities, with the substantial scatter being smaller for the
luminosity-cross section relation. We additionally used the relation between
the lensing efficiency and the virial mass in order to construct a synthetic
optical depth that agrees well with the true one, while being extremely faster
to be evaluated. We finally estimated what fraction of the total giant arc
abundance is recovered when galaxy clusters are selected according to their
dynamical activity or their X-ray luminosity. Our results show that there is a
high probability for high-redshift strong lensing clusters to be substantially
far away from dynamical equilibrium, and that of the total amount of
giant arcs are lost if looking only at very X-ray luminous objects.Comment: 15 pages, 10 figures. Accepted by A&
Cisplatin, 5-fluorouracil and interferon alpha 2b for recurrent or metastatic head and neck cancer.
On the basis of preclinical data suggesting the possibility of maximising the efficacy of 5-fluorouracil and cisplatin by interferon, a pilot clinical trial was initiated in recurrent and/or metastatic head and neck cancer. Thirty-four patients were treated with cisplatin at 100 mg m-2, followed by 5-fluorouracil at 1,000 mg m-2 by continuous infusion for 5 days. Interferon alpha 2b was administered at the dose of 3 million U i.m. daily for 7 days, beginning the day before chemotherapy. Courses were repeated every 3 weeks. Two patients achieved a complete remission, six a partial response, 14 had stable disease and 12 progressed on therapy, for an overall response rate of 23% (95% confidence interval 10-36%). Median survival time was 5 months. Toxicity was severe. Stomatitis, diarrhoea and myelosuppression were the most common side-effects. Because of the poor response rate and the presence of severe toxicity, in our opinion further clinical trials in head and neck cancer should be attempted only after a better definition in preclinical studies of interactions among 5-fluorouracil, cisplatin and interferon
Charged di-boson production at the LHC in a 4-site model with a composite Higgs boson
We investigate the scope of the LHC in probing the parameter space of a
4-site model supplemented by one composite Higgs state, assuming all past,
current and future energy and luminosity stages of the CERN machine. We
concentrate on the yield of charged di-boson production giving two
opposite-charge different-flavour leptons and missing (transverse) energy,
i.e., events induced via the subprocess
+ , which enables the production in the intermediate step of all
additional neutral and charged gauge bosons belonging to the spectrum of this
model, some of which in resonant topologies. We find this channel accessible
over the background at all LHC configurations after a dedicated cut-based
analysis. We finally compare the yield of the di-boson mode to that of
Drell-Yan processes and establish that they have complementary strengths, one
covering regions of parameter space precluded to the others and vice versa.Comment: 36 pages, 13 figures, 13 table
Macroscopic contact angle and liquid drops on rough solid surfaces via homogenization and numerical simulations
We discuss a numerical formulation for the cell problem related to a homogenization
approach for the study of wetting on micro rough surfaces. Regularity properties of the solution are
described in details and it is shown that the problem is a convex one. Stability of the solution with
respect to small changes of the cell bottom surface allows for an estimate of the numerical error, at least
in two dimensions. Several benchmark experiments are presented and the reliability of the numerical
solution is assessed, whenever possible, by comparison with analytical one. Realistic three dimensional
simulations confirm several interesting features of the solution, improving the classical models of study
of wetting on roughness
Testing of a new lightweight radar system for tomographical reconstruction of circular structures
Strong lensing in the MareNostrum Universe: biases in the cluster lens population
Strong lensing is one of the most direct probes of the mass distribution in
the inner regions of galaxy clusters. It can be used to constrain the density
profiles and to measure the mass of the lenses. Moreover, the abundance of
strong lensing events can be used to constrain the structure formation and the
cosmological parameters through the so-called "arc-statistics" approach.
However, several issues related to the usage of strong lensing clusters in
cosmological applications are still controversial, leading to the suspect that
several biases may affect this very peculiar class of objects. With this study
we aim at better understanding the properties of galaxy clusters which can
potentially act as strong lenses. We do so by investigating the properties of a
large sample of galaxy clusters extracted from the N-body/hydrodynamical
simulation MareNostrum Universe. We explore the correlation between the cross
section for lensing and many properties of clusters, like the mass, the
three-dimensional and projected shapes, their concentrations, the X-ray
luminosity and the dynamical activity. We find that the probability of strong
alignments between the major axes of the lenses and the line of sight is a
growing function of the lensing cross section. In projection, the strong lenses
appear rounder within R200, but we find that their cores tend to be more
elliptical as the lensing cross section increases. We also find that the
cluster concentrations estimated from the projected density profiles tend to be
biased high. The X-ray luminosity of strong lensing clusters is higher than
that of normal lenses of similar mass and redshift. This is particular
significant for the least massive lenses. Finally, we find that the strongest
lenses generally exhibit an excess of kinetic energy within the virial radius,
indicating that they are more dynamically active than usual clusters.Comment: 22 pages, 18 figures, accepted for publication on A&
Next Generation Cosmology: Constraints from the Euclid Galaxy Cluster Survey
We study the characteristics of the galaxy cluster samples expected from the
European Space Agency's Euclid satellite and forecast constraints on
cosmological parameters describing a variety of cosmological models. The method
used in this paper, based on the Fisher Matrix approach, is the same one used
to provide the constraints presented in the Euclid Red Book (Laureijs et
al.2011). We describe the analytical approach to compute the selection function
of the photometric and spectroscopic cluster surveys. Based on the photometric
selection function, we forecast the constraints on a number of cosmological
parameter sets corresponding to different extensions of the standard LambdaCDM
model. The dynamical evolution of dark energy will be constrained to Delta
w_0=0.03 and Delta w_a=0.2 with free curvature Omega_k, resulting in a
(w_0,w_a) Figure of Merit (FoM) of 291. Including the Planck CMB covariance
matrix improves the constraints to Delta w_0=0.02, Delta w_a=0.07 and a
FoM=802. The amplitude of primordial non-Gaussianity, parametrised by f_NL,
will be constrained to \Delta f_NL ~ 6.6 for the local shape scenario, from
Euclid clusters alone. Using only Euclid clusters, the growth factor parameter
\gamma, which signals deviations from GR, will be constrained to Delta
\gamma=0.02, and the neutrino density parameter to Delta Omega_\nu=0.0013 (or
Delta \sum m_\nu=0.01). We emphasise that knowledge of the observable--mass
scaling relation will be crucial to constrain cosmological parameters from a
cluster catalogue. The Euclid mission will have a clear advantage in this
respect, thanks to its imaging and spectroscopic capabilities that will enable
internal mass calibration from weak lensing and the dynamics of cluster
galaxies. This information will be further complemented by wide-area
multi-wavelength external cluster surveys that will already be available when
Euclid flies. [Abridged]Comment: submitted to MNRA
Comparison of an X-ray selected sample of massive lensing clusters with the MareNostrum Universe LCDM simulation
A long-standing problem of strong lensing by galaxy clusters regards the
observed high rate of giant gravitational arcs as compared to the predictions
in the framework of the "standard" cosmological model. Recently, few other
inconsistencies between theoretical expectations and observations have been
claimed which regard the large size of the Einstein rings and the high
concentrations of few clusters with strong lensing features. All of these
problems consistently indicate that observed galaxy clusters may be
gravitational lenses stronger than expected. We use clusters extracted from the
MareNostrum Universe to build up mock catalogs of galaxy clusters selected
through their X-ray flux. We use these objects to estimate the probability
distributions of lensing cross sections, Einstein rings, and concentrations for
the sample of 12 MACS clusters at presented in Ebeling et al. (2007)
and discussed in Zitrin et al. (2010). We find that simulated clusters produce
less arcs than observed clusters do. The medians of the
distributions of the Einstein ring sizes differ by between
simulations and observations. We estimate that, due to cluster triaxiality and
orientation biases affecting the lenses with the largest cross sections, the
concentrations of the individual MACS clusters inferred from the lensing
analysis should be up to a factor of larger than expected from the
CDM model. The arc statistics, the Einstein ring, and the
concentration problems in strong lensing clusters are mitigated but not solved
on the basis of our analysis. Nevertheless, due to the lack of redshifts for
most of the multiple image systems used for modeling the MACS clusters, the
results of this work will need to be verified with additional data. The
upcoming CLASH program will provide an ideal sample for extending our
comparison (abridged).Comment: 11 pages, 9 figures, accepted for publication on A&
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