6,028 research outputs found
Dynamical analysis of the cluster pair: A3407 + A3408
We carried out a dynamical study of the galaxy cluster pair A3407 \& A3408
based on a spectroscopic survey obtained with the 4 meter Blanco telescope at
the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122
member galaxies brighter than . Our main goal is to probe the galaxy
dynamics in this field and verify if the sample constitutes a single galaxy
system or corresponds to an ongoing merging process. Statistical tests were
applied to clusters members showing that both the composite system A3407 +
A3408 as well as each individual cluster have Gaussian velocity distribution. A
velocity gradient of was identified around
the principal axis of the projected distribution of galaxies, indicating that
the global field may be rotating. Applying the KMM algorithm to the
distribution of galaxies we found that the solution with two clusters is better
than the single unit solution at the 99\% c.l. This is consistent with the
X-ray distribution around this field, which shows no common X-ray halo
involving A3407 and A3408. We also estimated virial masses and applied a
two-body model to probe the dynamics of the pair. The more likely scenario is
that in which the pair is gravitationally bound and probably experiences a
collapse phase, with the cluster cores crossing in less than 1
Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature,
and some signs of galaxy evolution in A3408 suggests a post-merger scenario,
with cores having crossed each other Gyr ago, as an
alternative solution.Comment: 17 pages, 12 figures, submitted to MNRAS, accepted 2016 May 9.
Received 2016 May 9; in original form 2016 April 1
GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle
Physical properties were derived for the candidate open cluster La Serena 94,
recently unveiled by the VVV collaboration. Thanks to the exquisite angular
resolution provided by GeMS/GSAOI, we could characterize this system in detail,
for the first time, with deep photometry in JHK - bands. Decontaminated
JHK diagrams reach about 5 mag below the cluster turnoff in H. The locus
of red clump giants in the colour - colour diagram, together with an extinction
law, was used to obtain an average extinction of . The
same stars were considered as standard - candles to derive the cluster
distance, kpc. Isochrones were matched to the cluster colour -
magnitude diagrams to determine its age, , and
metallicity, . A core radius of pc was
found by fitting King models to the radial density profile. By adding up the
visible stellar mass to an extrapolated mass function, the cluster mass was
estimated as M, consistent with an
integrated magnitude of and a tidal radius of
pc. The overall characteristics of La Serena 94 confirm that
it is an old open cluster located in the Crux spiral arm towards the fourth
Galactic quadrant and distant kpc from the Galactic centre. The
cluster distorted structure, mass segregation and age indicate that it is a
dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo
Assessment of van der Waals inclusive density functional theory methods for layered electroactive materials
Computational-driven materials discovery requires efficient and accurate methods.
Density functional theory (DFT) meets these two requirements for many classes of materials.
However, DFT-based methods have limitations.
One significant shortcoming is the inadequate treatment of weak van der Waals (vdW) interactions, which are crucial for layered materials.
Here we assess the performance of various vdW-inclusive DFT approaches for predicting the structure and voltage of layered electroactive materials for Li-ion batteries, considering a set of 20 different compounds.
We find that the so-called optB86b-vdW density functional improves the agreement with experimental data, closely followed by the latest generation of dispersion correction methods.
These approaches yield average relative errors for the structural parameters smaller than 3 %.
The average deviations for redox potentials are below 0.15 V.
Looking ahead, this study identifies accurate methods for Li-ion vdW bound systems, providing enhanced predictive power to DFT-assisted design for developing new types of electroactive materials in general.MINECO MTM2013-46553-C3-1-P
MINECO ENE2016-81020-
Detection of the Ammonium Ion in Space
We report on the detection of a narrow feature at 262816.73 MHz towards Orion
and the cold prestellar core B1-bS, that we attribute to the 1(0)-0(0) line of
the deuterated Ammonium ion, NH3D+. The observations were performed with the
IRAM 30m radio telescope. The carrier has to be a light molecular species as it
is the only feature detected over 3.6 GHz of bandwidth. The hyperfine structure
is not resolved indicating a very low value for the electric quadrupolar
coupling constant of Nitrogen which is expected for NH3D+ as the electric field
over the N nucleus is practically zero. Moreover, the feature is right at the
predicted frequency for the 1(0)-0(0) transition of the Ammonium ion, 262817(6)
MHz (3sigma), using rotational constants derived from new infrared data
obtained in our laboratory in Madrid. The estimated column density is
1.1(0.2)e12 cm-2. Assuming a deuterium enhancement similar to that of NH2D, we
derive N(NH4+) sim 2.6e13 cm-2, i.e., an abundance for Ammonium of a few
1e(-11).Comment: Accepted for publication in the Astrophysical Journal Letters 04 June
201
Revealing the Mechanism of Sodium Diffusion in NaxFePO4 Using an Improved Force Field
Olivine NaFePO4 is a promising cathode material for Na-ion batteries. Intermediate
phases such as Na0.66FePO4 govern phase stability during intercalation-deintercalation
processes, yet little is known about Na+ diffusion in NaxFePO4 (0 < x < 1). Here
we use an advanced simulation technique, Randomized Shell Mass Generalized Shadow
Hybrid Monte Carlo Method (RSM-GSHMC) in combination with a specifically developed
force field for describing NaxFePO4 over the whole range of sodium compositions,
to thoroughly examine Na+ diffusion in this material. We reveal a novel mechanism
through which Na+/Fe2+ antisite defect formation halts transport of Na+ in the main
diffusion direction [010], while simultaneously activating diffusion in the [001] channels.
A similar mechanism was reported for Li+ in LiFePO4, suggesting that a transition from
one- to two-dimensional diffusion prompted by antisite defect formation is common to
olivine structures, in general.MTM2013-46553-C3-1-P
ENE2016-81020-R
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