5,883 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
The Dwarf Galaxy Population of the Dorado group down to Mv=-11
We present V and I CCD photometry of suspected low-surface brightness dwarf
galaxies detected in a survey covering ~2.4 deg^2 around the central region of
the Dorado group of galaxies. The low-surface brightness galaxies were chosen
based on their sizes and magnitudes at the limiting isophote of 26.0V\mu. The
selected galaxies have magnitudes brighter than V=20 (Mv=-11 for an assumed
distance to the group of 17.2 Mpc), with central surface brightnesses \mu0>22.5
V mag/arcsec^2, scale lengths h>2'', and diameters > 14'' at the limiting
isophote. Using these criteria, we identified 69 dwarf galaxy candidates. Four
of them are large very low-surface brightness galaxies that were detected on a
smoothed image, after masking high surface brightness objects. Monte Carlo
simulations performed to estimate completeness, photometric uncertainties and
to evaluate our ability to detect extended low-surface brightness galaxies show
that the completeness fraction is, on average, > 80% for dwarf galaxies with
and 22.5<\mu0<25.5 V mag/arcsec^2, for the range of sizes
considered by us (D>14''). The V-I colors of the dwarf candidates vary from
-0.3 to 2.3 with a peak on V-I=0.98, suggesting a range of different stellar
populations in these galaxies. The projected surface density of the dwarf
galaxies shows a concentration towards the group center similar in extent to
that found around five X-ray groups and the elliptical galaxy NGC1132 studied
by Mulchaey and Zabludoff (1999), suggesting that the dwarf galaxies in Dorado
are probably physically associated with the overall potential well of the
group.Comment: 32 pages, 16 postscript figures and 3 figures in GIF format, aastex
v5.0. To appear in The Astronomical Journal, January 200
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
Strategies Employed by Community-Based Service Providers to Address HIV-Associated Neurocognitive Challenges: A Qualitative Study
Background: HIV-associated neurocognitive disorders and other causes of neurocognitive challenges experienced by people living with HIV (PLWH) persist as public health concerns in developed countries. Consequently, PLWH who experience neurocognitive challenges increasingly require social support and mental health services from community-based providers in the HIV sector. Methods: Thirty-three providers from 22 AIDS service organizations across Ontario, Canada, were interviewed to determine the strategies they used to support PLWH experiencing neurocognitive difficulties. Thematic analysis was conducted to determine key themes from the interview data. Results: Three types of strategies were identified: (a) intrapersonal, (b) interpersonal, and (c) organizational. Intrapersonal strategies involved learning and staying informed about causes of neurocognitive challenges. Interpersonal strategies included providing practical assistance, information, counseling, and/or referrals to PLWH. Organizational strategies included creating dedicated support groups for PLWH experiencing neurocognitive challenges, partnering with other organizations with services not available within their own organization, and advocating for greater access to services with expertise and experience working with PLWH. Conclusion: Through concerted efforts in the future, it is likely that empirically investigating, developing, and customizing these strategies specifically to address HIV-associated neurocognitive challenges will yield improved social support and mental health outcomes for PLWH
A Multiple System of Radio Sources at the Core of the L723 Multipolar Outflow
We present high angular resolution Very Large Array multi-epoch continuum
observations at 3.6 cm and 7 mm towards the core of the L723 multipolar outflow
revealing a multiple system of four radio sources suspected to be YSOs in a
region of only ~4 arcsecs (1200 AU) in extent. The 3.6 cm observations show
that the previously detected source VLA 2 contains a close (separation ~0.29
arcsecs or ~90 AU) radio binary, with components (A and B) along a position
angle of ~150 degrees. The northern component (VLA 2A) of this binary system is
also detected in the 7 mm observations, with a positive spectral index between
3.6 cm and 7 mm. In addition, the source VLA 2A is associated with extended
emission along a position angle of ~115 degrees, that we interpret as
outflowing shock-ionized gas that is exciting a system of HH objects with the
same position angle. A third, weak 3.6 cm source, VLA 2C, that is detected also
at 7 mm, is located ~0.7 arcsecs northeast of VLA 2A, and is possibly
associated with the water maser emission in the region. The 7 mm observations
reveal the presence of an additional source, VLA 2D, located ~3.5 arcsecs
southeast of VLA 2A, and with a 1.35 mm counterpart. All these radio continuum
sources have a positive spectral index, compatible with them being YSOs. We
also propose that the high velocity CO emission observed in the region could be
the superposition of multiple outflows (at least three independent bipolar
outflows) excited by the YSOs located at the core, instead of the previous
interpretations in terms of only one or two outflows.Comment: Accepted for publication in The Astrophysical Journal (2007 December
6
Improved faulted phase selection algorithm for distance protection under high penetration of renewable energies
The high penetration of renewable energies will affect the performance of present protection algorithms due to fault current injection from generators based on power electronics. This paper explains the process followed for analyzing this effect on distance protection and the development of a new algorithm that improves its performance in such a scenario. First of all, four commercial protection relays were tested before fault current contribution from photovoltaic system and full converter wind turbines using the hardware in the loop technique. The analysis of results obtained, jointly with a theoretical analysis based on commonly used protection strategy of superimposed quantities, lead to a conclusion about the cause of observed wrong behaviors of present protection algorithms under a high penetration of renewables. According to these conclusions, a new algorithm has been developed to improve the detection of faulted phase selection and directionality on distance protection under a short circuit current fed by renewable energy sources. © 2020 by the author
Avaliação do comportamento de ligações estruturais em madeira lamelada colada por meio de parafusos autoperfurantes
Neste artigo é avaliado o comportamento de ligações autoperfurantes em madeira glulam, utilizando a metodologia de cálculo preconizada pelo Eurocódigo 5 para o cálculo da força estimada e para a identificação dos modos de rotura. O programa experimental e os cálculos para o coeficiente de deslizamento foram definidos pela Norma Europeia EN 26891:1991. Os resultados experimentais obtidos são discutidos e comparados com a metodologia proposta por Tomasi. Os resultados indicam que o modo de rotura, neste tipo de ligação, é o modo f. Os valores de capacidade de carga obtidos pelo Eurocódigo 5, quando comparados com os experimentais, são conservadores e os obtidos pelo método proposto por Tomasi superestima.In this paper we evaluated the behavior of self-drilling wood glulam connections, using the calculation methodology recommended by the Eurocode 5 for calculating the estimated strength and the identification of failure modes. The experimental program and the calculations for the coefficient of slip defined by the European standard EN 26891:1991. The experimental results are discussed and compared with the methodology proposed by Tomasi. The results indicate that the mode of failure in this type of connection is the way f. The load capacity values obtained by the Eurocode 5 when compared with the experimental, are conservative and those obtained by the method proposed by Tomasi overestimates
Bright galaxies at Hubble's redshift detection frontier: Preliminary results and design from the redshift z~9-10 BoRG pure-parallel HST survey
We present the first results and design from the redshift z~9-10 Brightest of
the Reionizing Galaxies {\it Hubble Space Telescope} survey BoRG[z9-10], aimed
at searching for intrinsically luminous unlensed galaxies during the first 700
Myr after the Big Bang. BoRG[z9-10] is the continuation of a multi-year
pure-parallel near-IR and optical imaging campaign with the Wide Field Camera
3. The ongoing survey uses five filters, optimized for detecting the most
distant objects and offering continuous wavelength coverage from
{\lambda}=0.35{\mu}m to {\lambda}=1.7{\mu}m. We analyze the initial ~130
arcmin of area over 28 independent lines of sight (~25% of the total
planned) to search for z>7 galaxies using a combination of Lyman break and
photometric redshift selections. From an effective comoving volume of (5-25)
Mpc for magnitudes brighter than in the
-band respectively, we find five galaxy candidates at z~8.3-10
detected at high confidence (S/N>8), including a source at z~8.4 with mAB=24.5
(S/N~22), which, if confirmed, would be the brightest galaxy identified at such
early times (z>8). In addition, BoRG[z9-10] data yield four galaxies with . These new Lyman break galaxies with m are
ideal targets for follow-up observations from ground and space based
observatories to help investigate the complex interplay between dark matter
growth, galaxy assembly, and reionization.Comment: Accepted for publication on ApJ. 21 pages, 11 figures, 4 table
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