4,309 research outputs found
Decaying shock studies of phase transitions in MgOSiO2 systems: implications for the Super-Earths interiors
We report an experimental study of the phase diagrams of periclase (MgO),
enstatite (MgSiO3) and forsterite (Mg2SiO4) at high pressures. We investigated
with laser driven decaying shocks the pressure/temperature curves of MgO,
MgSiO3 and Mg2SiO4 between 0.2-1.2 TPa, 0.12-0.5 TPa and 0.2-0.85 TPa
respectively. A melting signature has been observed in MgO at 0.47 TPa and 9860
K, while no phase changes were observed neither in MgSiO3 nor in Mg2SiO4. An
increasing of reflectivity of MgO, MgSiO3 and Mg2SiO4 liquids have been
detected at 0.55 TPa -12 760 K, 0.15 TPa - 7540 K, 0.2 TPa - 5800 K,
respectively. In contrast to SiO2, melting and metallization of these compounds
do not coincide implying the presence of poor electrically conducting liquids
close to the melting lines. This has important implications for the generation
of dynamos in Super-earths mantles
Stellar Archaeology in the Galactic halo with the Ultra-Faint Dwarfs: VI. Ursa Major II
We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf
satellite Ursa Major II (UMa II), spanning the magnitude range from V ~ 15 to V
~ 23.5 mag and extending over a 18 {\times} 18 arcmin2 area centered on the
galaxy. Our photometry goes down to about 2 magnitudes below the galaxy's main
sequence turn-off, that we detected at V ~ 21.5 mag. We have discovered a
bona-fide RR Lyrae variable star in UMa II, which we use to estimate a
conservative dereddened distance modulus for the galaxy of (m-M)0 =
17.70{\pm}0.04{\pm}0.12 mag, where the first error accounts for the
uncertainties of the calibrated photometry, and the second reflects our lack of
information on the metallicity of the star. The corresponding distance to UMa
II is 34.7 {\pm} 0.6 ({\pm} 2.0) kpc. Our photometry shows evidence of a spread
in the galaxy subgiant branch, compatible with a spread in metal abundance in
the range between Z=0.0001 and Z=0.001. Based on our estimate of the distance,
a comparison of the fiducial lines of the Galactic globular clusters (GCs) M68
and M5 ([Fe/H]=-2.27 {\pm} 0.04 dex and -1.33 {\pm} 0.02 dex, respectively),
with the position on the CMD of spectroscopically confirmed galaxy members, may
suggest the existence of stellar populations of different metal abundance/age
in the central region of UMa II.Comment: To appear in Ap
PARP inhibition: a promising therapeutic target in ovarian cancer
Ovarian cancer is burdened by the highest mortality rate among gynecological cancers. Gold standard is represented by the association of platinum-taxane -based chemotherapy and radical surgery. Despite several adjustments occurred in cytotoxic drug in last decades, most patients continue to relapse, and no significant enhancement has been reached in the overall survival. The development of drug resistance and the recurrence of disease have prompted the investigations of other targets that can be used in the treatment of ovarian cancers. Among such targets, polyadenosine diphosphate-ribose polymerase (PARP) represents a novel way to target specific patways involved in tumor growth. PARP accelerates the reaction of the polyADP-ribosylation of proteins implicated in DNA repair. PARP inhibitors have shown activity in cancers with BRCA mutations, with other deficient DNA repair genes or signaling pathways that modulate DNA repair, or in association with DNA damaging agents not involved in DNA repair dysfunction. A number of inhibitors for PARP has been developed, and such drugs are under investigation in clinical trials to identify their impact in the treatment of ovarian cancers. This review aims to summarize the recent researches and clinical progress on PARP inhibitors as novel target agents in ovarian cancer
Incentivare il benessere e rafforzare le basi del Welfare State: Il Sistema delle Opere Pie nell’Italia del XIX secolo
Calibration of the distance scale from galactic Cepheids: I Calibration based on the GFG sample
New estimates of the distances of 36 nearby galaxies are presented based on
accurate distances of galactic Cepheids obtained by Gieren, Fouque and Gomez
(1998) from the geometrical Barnes-Evans method.
The concept of 'sosie' is applied to extend the distance determination to
extragalactic Cepheids without assuming the linearity of the PL relation. Doing
so, the distance moduli are obtained in a straightforward way.
The correction for extinction is made using two photometric bands (V and I)
according to the principles introduced by Freedman and Madore (1990). Finally,
the statistical bias due to the incompleteness of the sample is corrected
according to the precepts introduced by Teerikorpi (1987) without introducing
any free parameters (except the distance modulus itself in an iterative
scheme).
The final distance moduli depend on the adopted extinction ratio {R_V}/{R_I}
and on the limiting apparent magnitude of the sample. A comparison with the
distance moduli recently published by the Hubble Space Telescope Key Project
(HSTKP) team reveals a fair agreement when the same ratio {R_V}/{R_I} is used
but shows a small discrepancy at large distance.
In order to bypass the uncertainty due to the metallicity effect it is
suggested to consider only galaxies having nearly the same metallicity as the
calibrating Cepheids (i.e. Solar metallicity). The internal uncertainty of the
distances is about 0.1 magnitude but the total uncertainty may reach 0.3
magnitude.Comment: 12 pages, 4 figures, access to a database of extragalactic Cepheids.
Astronomy & Astrophysics (in press) 200
Beam test evaluation of electromagnetic calorimeter modules made from proton-damaged PbWO crystals
The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO(4) crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO(4) crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 10(13) and 1.3× 10(14) cm(−)(2). These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb(−)(1) and 3000 fb(−)(1) respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.Peer Reviewe
First spectroscopic investigation of Anomalous Cepheid variables
Anomalous Cepheids (ACEPs) are intermediate mass metal-poor pulsators mostly
discovered in dwarf galaxies of the Local Group. However, recent Galactic
surveys, including the Gaia DR3, found a few hundreds of ACEPs in the Milky
Way. Their origin is not well understood. We aim to investigate the origin and
evolution of Galactic ACEPs by studying for the first time the chemical
composition of their atmospheres. We used UVES@VLT to obtain high-resolution
spectra for a sample of 9 ACEPs belonging to the Galactic halo. We derived the
abundances of 12 elements, including C, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Ni, Y,
and Ba. We complemented these data with literature abundances for an additional
three ACEPs that were previously incorrectly classified as type II Cepheids,
thus increasing the sample to a total of 12 stars. All the investigated ACEPs
have an iron abundance [Fe/H] dex as expected from theoretical
predictions for these pulsators. The abundance ratios of the different elements
to iron show that the ACEP's chemical composition is generally consistent with
that of the Galactic halo field stars, except the Sodium, which is found
overabundant in 9 out of the 11 ACEPs where it was measured, in close
similarity with second-generation stars in the Galactic Globular Clusters. The
same comparison with dwarf and ultra-faint satellites of the Milky Way reveals
more differences than similarities so it is unlikely that the bulk of Galactic
ACEPs originated in such a kind of galaxies which subsequently dissolved in the
Galactic halo. The principal finding of this work is the unexpected
overabundance of Sodium in ACEPs. We explored several hypotheses to explain
this feature, finding that the most promising scenario is the evolution of
low-mass stars in a binary system with either mass transfer or merging.
Detailed modelling is needed to confirm this hypothesis.Comment: 15 Figures, 4 Tables, Accepted for publication on Astronomy &
Astrophysic
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