11,728 research outputs found
Lithium in the Hyades L5 brown dwarf 2MASS J04183483+2131275
Aims. From the luminosity, effective temperature and age of the Hyades brown dwarf 2MASS J04183483+2131275 (2M0418), substellar evolutionary models predict a mass in the range 39−55 Jupiter masses (MJup) which is insufficient to produce any substantial lithium burning except for the very upper range >53 MJup. Our goal is to measure the abundance of lithium in this object, test the consistency between models and observations and refine constraints on the mass and age of the object.
Methods. We used the 10.4-m Gran Telescopio Canarias (GTC) with its low-dispersion optical spectrograph to obtain ten spectra of 2277 s each covering the range 6300–10 300 Å with a resolving power of R ~ 500.
Results. In the individual spectra, which span several months, we detect persistent unresolved Hα in emission with pseudo equivalent widths (pEW) in the range 45–150 Å and absorption lines of various alkalis with the typical strengths found in objects of L5 spectral type. The lithium resonance line at 6707.8 Å is detected with pEW of 18 ± 4 Å in 2M0418 (L5).
Conclusions. We determine a lithium abundance of log N(Li) = 3.0 ± 0.4 dex consistent with a minimum preservation of 90% of this element which confirms 2M0418 as a brown dwarf with a maximum mass of 52 MJup. We infer a maximum age for the Hyades of 775 Myr from a comparison with the BHAC15 models. Combining recent results from the literature with our study, we constrain the mass of 2M0418 to 45–52 MJup and the age of the cluster to 580–775 Myr (1σ) based on the lithium depletion boundary method.We thank the referee for a detailed report that improved the
quality of this manuscript. This research has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under the grants AYA2015-
69350-C3-2-P and AYA2015-69350-C3-3-P. We thank Yakiv Pavlenko for his
calculations of equivalent widths at different temperatures, Isabelle Baraffe for
her models, and Eduardo MartÃn for sharing his results prior to publication. This
work is based on observations made with the Gran Telescopio Canarias (GTC),
operated on the island of La Palma in the Spanish Observatorio del Roque de
los Muchachos of the Instituto de AstrofÃsica de Canarias (programme GTC77-
16B led by Pérez Garrido). This research has made use of the Simbad and
Vizier databases, operated at the Centre de Données Astronomiques de Strasbourg (CDS), and of NASA’s Astrophysics Data System Bibliographic Services
(ADS). We thank John Stauffer for kindly providing the optical spectra of the K
and M Hyades members published in 1997 (Stauffer et al. 1997a)
Deep and superficial amygdala nuclei projections revealed in vivo by probabilistic tractography
Copyright © 2011 Society for Neuroscience and the authors. The The Journal of Neuroscience uses a Creative Commons Attribution-NonCommercial-ShareAlike licence: http://creativecommons.org/licenses/by-nc-sa/4.0/.Despite a homogenous macroscopic appearance on magnetic resonance images, subregions of the amygdala express distinct functional profiles as well as corresponding differences in connectivity. In particular, histological analysis shows stronger connections for superficial (i.e., centromedial and cortical), compared with deep (i.e., basolateral and other), amygdala nuclei to lateral orbitofrontal cortex and stronger connections of deep compared with superficial, nuclei to polymodal areas in the temporal pole. Here, we use diffusion weighted imaging with probabilistic tractography to investigate these connections in humans. We use a data-driven approach to segment the amygdala into two subregions using k-means clustering. The identified subregions are spatially contiguous and their location corresponds to deep and superficial nuclear groups. Quantification of the connection strength between these amygdala clusters and individual target regions corresponds to qualitative histological findings in non-human primates, indicating such findings can be extrapolated to humans. We propose that connectivity profiles provide a potentially powerful approach for in vivo amygdala parcellation and can serve as a guide in studies that exploit functional and anatomical neuroimaging.The Wellcome Trust, a Max Planck Research Award and Swiss National Science Foundation
Electrochemical and photo-electrochemical processes of Methylene blue oxidation by Ti/TiO2 electrodes modified with Fe-allophane
Indexación: Scopus.This work reports the degradation of methylene blue (MB) on Ti/TiO2 and Ti/TiO2/Fe-allophane electrodes in a pH 3 using 0.1 M Na2SO4 as support electrolyte. SEM micrographs show a homogeneous distribution of TiO2 over the whole electrode surface forming nanotubes and nanopores. Fe-allophane modified electrode shows the formation of large-grains agglomerate on the electrode surface due to allophane, which provides a greater surface area to the electrode due to meso and micropore structures. Preliminary cyclic voltammetry show that Ti/TiO2 has the typical voltammetric response due to Ti(III)/Ti(IV) pair. Diffusional problems were observed through of the film when the electrode is modified with Fe-allophane modifying the quasi-reversible process Ti(III)/Ti(IV). Different kind of methodologies in the degradation process were used: Electrochemistry (EC), Photochemistry (PC), Photoelectrochemistry (PEC) and Adsorption (Ads). These methods were developing to discard any reaction or interaction that is not of interest. On Ti/TiO2 with PC and Ads methodologies was not observed any activity to MB degradation showing that is not photosensitive and that the interaction between this and surface electrode is low. But with EC and PEC degradation to 55% is reached after 3 hours of electrolysis. With Ti/TiO2-Fe-allophane electrodes are observed a higher activity for all methodologies. The PC and Ads methods show that the MB degradation reaches to ∼20 % of the initial concentration. As mentioned above, the PC and Ads processes no show degradation on Ti/TiO2, therefore the degradation it only due to the adsorption of MB in/on allophane coat behaving as concentrator matrix. A lower improvement is observed with EC process when is incorporated Ti/TiO2-Fe-allophane is due to the barrier of the electrode surface by oxidation products. With PEC is reached the higher degradation value of ∼88 %, showing an improvement of the degradation with the presence of Fe-allophane. The results indicate that the main role of Fe-allophane on the electrode is similar to a concentrator matrix.http://ref.scielo.org/shz7t
Spin-dependent effective interactions for halo nuclei
We discuss the spin-dependence of the effective two-body interactions
appropriate for three-body computations. The only reasonable choice seems to be
the fine and hyperfine interactions known for atomic electrons interacting with
the nucleus. One exception is the nucleon-nucleon interaction imposing a
different type of symmetry. We use the two-neutron halo nucleus 11Li as
illustration. We demonstrate that models with the wrong spin-dependence are
basically without predictive power. The Pauli forbidden core and valence states
must be consistently treated.Comment: TeX file, 6 pages, 3 postscript figure
Verifying black hole orbits with gravitational spectroscopy
Gravitational waves from test masses bound to geodesic orbits of rotating
black holes are simulated, using Teukolsky's black hole perturbation formalism,
for about ten thousand generic orbital configurations. Each binary radiates
power exclusively in modes with frequencies that are
integer-linear-combinations of the orbit's three fundamental frequencies. The
following general spectral properties are found with a survey of orbits: (i)
99% of the radiated power is typically carried by a few hundred modes, and at
most by about a thousand modes, (ii) the dominant frequencies can be grouped
into a small number of families defined by fixing two of the three integer
frequency multipliers, and (iii) the specifics of these trends can be
qualitatively inferred from the geometry of the orbit under consideration.
Detections using triperiodic analytic templates modeled on these general
properties would constitute a verification of radiation from an adiabatic
sequence of black hole orbits and would recover the evolution of the
fundamental orbital frequencies. In an analogy with ordinary spectroscopy, this
would compare to observing the Bohr model's atomic hydrogen spectrum without
being able to rule out alternative atomic theories or nuclei. The suitability
of such a detection technique is demonstrated using snapshots computed at
12-hour intervals throughout the last three years before merger of a kludged
inspiral. Because of circularization, the number of excited modes decreases as
the binary evolves. A hypothetical detection algorithm that tracks mode
families dominating the first 12 hours of the inspiral would capture 98% of the
total power over the remaining three years.Comment: 18 pages, expanded section on detection algorithms and made minor
edits. Final published versio
Equalization in hard disk drive read channels
This paper presents a comprehensive non-exhaustive comparative study of hard disk drive read-channel equalization techniques used in the readback process of magnetically stored information. The main read channel architectures: partial-response maximum likelihood (PRML) and decision feedback equalization (DFE) based systems, are compared in power consumption, layout area, data signalling rate and data density. This work focuses on the key component of the read channel, presenting a continuous-time analog solution for the pulse-slimming equalizer capable of reducing power consumption and die area by a factor of ten, whilst showing equivalent response to a FIR filter implementation.info:eu-repo/semantics/acceptedVersio
A low-cost smart parking solution for smart cities based on open software and hardware
Traffic management and car parking on modern cities continues to be a problem both for citizens and for city officials. The increasing number of vehicles flowing into the city drain the existing scarce parking resources, and the increase in time spent looking for a parking spot leads to more congestions, parasitic traffic, whilst augmenting fuel consumption and air pollution. In this paper we present an integrated flexible solution developed to help address this issue, using open hardware and software components to develop a low-cost smart parking system suitable for contemporary metropolitan cities. The smart parking solution is based on Arduino boards for the sensors network and on Raspberry Pi single-board computers for the gateway devices, integrated through specific developed software components and a mobile application for the end-users.info:eu-repo/semantics/acceptedVersio
Three-body structure of low-lying 12Be states
We investigate to what extent a description of 12Be as a three-body system
made of an inert 10Be-core and two neutrons is able to reproduce the
experimental 12Be data. Three-body wave functions are obtained with the
hyperspherical adiabatic expansion method. We study the discrete spectrum of
12Be, the structure of the different states, the predominant transition
strengths, and the continuum energy spectrum after high energy fragmentation on
a light target. Two 0+, one 2+, one 1- and one 0- bound states are found where
the first four are known experimentally whereas the 0- is predicted as an
isomeric state. An effective neutron charge, reproducing the measured B(E1)
transition and the charge rms radius in 11Be, leads to a computed B(E1)
transition strength for 12Be in agreement with the experimental value. For the
E0 and E2 transitions the contributions from core excitations could be more
significant. The experimental 10Be-neutron continuum energy spectrum is also
well reproduced except in the energy region corresponding to the 3/2- resonance
in 11Be where core excitations contribute.Comment: 16 pages, 9 figures. Accepted for publication in Physical Review
Structure and decay at rapid proton capture waiting points
We investigate the region of the nuclear chart around from a
three-body perspective, where we compute reaction rates for the radiative
capture of two protons. One key quantity is here the photon dissociation cross
section for the inverse process where two protons are liberated from the
borromean nucleus by photon bombardment. We find a number of peaks at low
photon energy in this cross section where each peak is located at the energy
corresponding to population of a three-body resonance. Thus, for these energies
the decay or capture processes proceed through these resonances. However, the
next step in the dissociation process still has the option of following several
paths, that is either sequential decay by emission of one proton at a time with
an intermediate two-body resonance as stepping stone, or direct decay into the
continuum of both protons simultaneously. The astrophysical reaction rate is
obtained by folding of the cross section as function of energy with the
occupation probability for a Maxwell-Boltzmann temperature distribution. The
reaction rate is then a function of temperature, and of course depending on the
underlying three-body bound state and resonance structures. We show that a very
simple formula at low temperature reproduces the elaborate numerically computed
reaction rate.Comment: 4 pages, 3 figures, conference proceedings, publishe
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