6,095 research outputs found
The Mass of the Convective Zone in FGK Main Sequence Stars and the Effect of Accreted Planetary Material on Apparent Metallicity Determinations
The mass of the outer convective zone in FGK main sequence stars decreases
dramatically with stellar mass. Therefore, any contamination of a star's
atmosphere by accreted planetary material should affect hotter stars much more
than cool stars. If recent suggestions that high metal abundances in stars with
planets are caused by planetesimal accretion are correct, then metallicity
enhancements in earlier-type stars with planets should be very pronounced. No
such trend is seen, however.Comment: Submitted ApJ Letters March 26th; accepted April 30th. 12 pages, 2
figure
Compact groups from semi-analytical models of galaxy formation -- V: their assembly channels as a function of the environment
We delved into the assembly pathways and environments of compact groups (CGs)
of galaxies using mock catalogues generated from semi-analytical models (SAMs)
on the Millennium simulation. We investigate the ability of SAMs to replicate
the observed CG environments and whether CGs with different assembly histories
tend to inhabit specific cosmic environments. We also analyse whether the
environment or the assembly history is more important in tailoring CG
properties. We find that about half of the CGs in SAMs are non-embedded
systems, 40% are inhabiting loose groups or nodes of filaments, while the rest
distribute evenly in filaments and voids, in agreement with observations. We
observe that early-assembled CGs preferentially inhabit large galaxy systems (~
60%), while around 30% remain non-embedded. Conversely, lately-formed CGs
exhibit the opposite trend. We also obtain that lately-formed CGs have lower
velocity dispersions and larger crossing times than early-formed CGs, but
mainly because they are preferentially non-embedded. Those lately-formed CGs
that inhabit large systems do not show the same features. Therefore, the
environment plays a strong role in these properties for lately-formed CGs.
Early-formed CGs are more evolved, displaying larger velocity dispersions,
shorter crossing times, and more dominant first-ranked galaxies, regardless of
the environment. Finally, the difference in brightness between the two
brightest members of CGs is dependent only on the assembly history and not on
the environment. CGs residing in diverse environments have undergone varied
assembly processes, making them suitable for studying their evolution and the
interplay of nature and nurture on their traits.Comment: 13 pages, 8 figures. Accepted for publication in MNRA
B-physics computations from Nf=2 tmQCD
We present an accurate lattice QCD computation of the b-quark mass, the B and
Bs decay constants, the B-mixing bag-parameters for the full four-fermion
operator basis, as well as estimates for \xi and f_{Bq}\sqrt{B_q} extrapolated
to the continuum limit and the physical pion mass. We have used Nf = 2
dynamical quark gauge configurations at four values of the lattice spacing
generated by ETMC. Extrapolation in the heavy quark mass from the charm to the
bottom quark region has been carried out using ratios of physical quantities
computed at nearby quark masses, having an exactly known infinite mass limit.Comment: 7 pages, 4 figures, presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
HDAC inhibitors in acute myeloid leukemia
Acute myeloid leukemia (AML) is a hematological malignancy characterized by uncontrolled
proliferation, differentiation arrest, and accumulation of immature myeloid progenitors. Although
clinical advances in AML have been made, especially in young patients, long-term disease-free
survival remains poor, making this disease an unmet therapeutic challenge. Epigenetic alterations
and mutations in epigenetic regulators contribute to the pathogenesis of AML, supporting the
rationale for the use of epigenetic drugs in patients with AML. While hypomethylating agents have
already been approved in AML, the use of other epigenetic inhibitors, such as histone deacetylases
(HDAC) inhibitors (HDACi), is under clinical development. HDACi such as Panobinostat, Vorinostat,
and Tricostatin A have been shown to promote cell death, autophagy, apoptosis, or growth arrest in
preclinical AML models, yet these inhibitors do not seem to be effective as monotherapies, but rather
in combination with other drugs. In this review, we discuss the rationale for the use of different
HDACi in patients with AML, the results of preclinical studies, and the results obtained in clinical
trials. Although so far the results with HDACi in clinical trials in AML have been modest, there are
some encouraging data from treatment with the HDACi Pracinostat in combination with DNA
demethylating agents
Precision scans of the pixel cell response of double sided 3D pixel detectors to pion and x-ray beams
hree-dimensional (3D) silicon sensors offer potential advantages over standard planar sensors for radiation hardness in future high energy physics experiments and reduced charge-sharing for X-ray applications, but may introduce inefficiencies due to the columnar electrodes. These inefficiencies are probed by studying variations in response across a unit pixel cell in a 55μm pitch double-sided 3D pixel sensor bump bonded to TimePix and Medipix2 readout ASICs. Two complementary characterisation techniques are discussed: the first uses a custom built telescope and a 120GeV pion beam from the Super Proton Synchrotron (SPS) at CERN; the second employs a novel technique to illuminate the sensor with a micro-focused synchrotron X-ray beam at the Diamond Light Source, UK. For a pion beam incident perpendicular to the sensor plane an overall pixel efficiency of 93.0±0.5% is measured. After a 10o rotation of the device the effect of the columnar region becomes negligible and the overall efficiency rises to 99.8±0.5%. The double-sided 3D sensor shows significantly reduced charge sharing to neighbouring pixels compared to the planar device. The charge sharing results obtained from the X-ray beam study of the 3D sensor are shown to agree with a simple simulation in which charge diffusion is neglected. The devices tested are found to be compatible with having a region in which no charge is collected centred on the electrode columns and of radius 7.6±0.6μm. Charge collection above and below the columnar electrodes in the double-sided 3D sensor is observed
Hickson-like compact groups inhabiting different environments
Although Compact Groups of galaxies (CGs) have been envisioned as isolated
extremely dense structures in the Universe, it is accepted today that many of
them could be not as isolated as thought. In this work, we study Hickson-like
CGs identified in the Sloan Digital Sky Survey Data Release 16 to analyse these
systems and their galaxies when embedded in different cosmological structures.
To achieve this goal, we identify several cosmological structures where CGs can
reside: Nodes of filaments, Loose Groups, Filaments and cosmic Voids. Our
results indicate that 45 per cent of CGs do not reside in any of these
structures, i.e., they can be considered non-embedded or isolated systems. Most
of the embedded CGs are found inhabiting Loose Groups and Nodes, while there
are almost no CGs residing well inside cosmic Voids. Some physical properties
of CGs vary depending on the environment they inhabit. CGs in Nodes show the
largest velocity dispersions, the brightest absolute magnitude of the
first-ranked galaxy, and the smallest crossing times, while the opposite occurs
in Non-Embedded CGs. When comparing galaxies in all the environments and
galaxies in CGs, CGs show the highest fractions of red/early-type galaxy
members in most of the absolute magnitudes ranges. The variation between
galaxies in CGs inhabiting one or another environment is not as significant as
the differences caused by belonging or not to a CG. Our results suggest a
plausible scenario for galaxy evolution in CGs in which both, large-scale and
local environments play essential roles.Comment: 16 pages, 9 figures, 1 table, accepted for publication in MNRA
Far Ultraviolet Absolute Flux of alpha Virginis
We present the far ultraviolet spectrum of alpha Virginis taken with EURD
spectrograph on-board MINISAT-01. The spectral range covered is from ~900 to
1080 A with 5 A spectral resolution. We have fitted Kurucz models to IUE
spectra of alpha Vir and compared the extension of the model to our wavelengths
with EURD data. This comparison shows that EURD fluxes are consistent with the
prediction of the model within 20-30%, depending on the reddening assumed. EURD
fluxes are consistent with Voyager observations but are ~60% higher than most
previous rocket observations of alpha Vir.Comment: 13 pages, 4 figures. Submitted to The Astrophysical Journa
matching coefficients for the =2 operators in the lattice static theory
We present the perturbative matching coefficient to which
relates the =2 operator in the continuum to that of the lattice
static theory, which is important in the accurate extraction of the continuum
value of the from lattice simulations. The coefficients are obtained by
the one-loop calculations in both of the continuum and lattice theory. We find
that two new dimension seven operators appear at the with the
O(1) coefficients. We also discuss the possible cancellation of
correction in the ratio
qualitatively.Comment: 14 pages, no figures, uses REVTeX; added references, corrected typo
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