2,611 research outputs found
Forming first-ranked early-type galaxies through hierarchical dissipationless merging
We have developed a computationally competitive N-body model of a
previrialized aggregation of galaxies in a flat LambdaCDM universe to assess
the role of the multiple mergers that take place during the formation stage of
such systems in the configuration of the remnants assembled at their centres.
An analysis of a suite of 48 simulations of low-mass forming groups (of about
1E13 solar masses) demonstrates that the gravitational dynamics involved in
their hierarchical collapse is capable of creating realistic first-ranked
galaxies without the aid of dissipative processes. Our simulations indicate
that the brightest group galaxies (BGGs) constitute a distinct population from
other group members, sketching a scenario in which the assembly path of these
objects is dictated largely by the formation of their host system. We detect
significant differences in the distribution of Sersic indices and total
magnitudes, as well as a luminosity gap between BGGs and the next brightest
galaxy that is positively correlated with the total luminosity of the parent
group. Such gaps arise from both the grow of BGGs at the expense of lesser
companions and the decrease in the relevance of second-ranked objects in equal
measure. This results in a dearth of intermediate-mass galaxies which explains
the characteristic central dip detected in their luminosity functions in
dynamically young galaxy aggregations. The fact that the basic global
properties of our BGGs define a thin mass fundamental plane strikingly similar
to that followed giant early-type galaxies in the local universe reinforces
confidence in the results obtained.Comment: 25 pages, 14 figures, 3 tables. Accepted to MNRA
Padronização de uma bateria para a avaliação de fatores de risco psicossociais trabalhistas em trabalhadores colombianos
A battery of questionnaires to assess psychosocial risk factors at work was developed in 2010 in response to Resolution 2646 created by the Colombian Ministry of Social Protection. However, this battery presents some theoretical and practical limitations. A new battery of instruments has been designed and validated that includes instruments and risk indicators of the demand-control-social support and the effort-reward imbalance models. Other factors, not included in these models, but that Resolution 2646 suggests should be assessed, have also been added, and with this additional information, the new battery allows us to also calculate a “global indicator” of demand, control, and social support; family and social risk conditions, coping and personality; and health and wellbeing. The new battery was administered to a sample of 16,095 workers from different occupations and representative Colombian regions. An analysis of the various domains indicates that internal consistency of the various scales is high. The new battery has the following properties: it is simple to use in paper format or when administered by computer, it enables comparison between occupations, it offers unified scores for each variable, and provides information to assess the risk factors suggested by Resolution 2646. In addition, it will make it possible to compare the results obtained when analyzing Colombian workers with those obtained from studies of workers from other countries.Em 2010, desenvolveu-se uma bateria de instrumentos para avaliar fatores psicossociais trabalhistas de risco para a saĂşde, em resposta Ă Resolução 2 646 do MinistĂ©rio da Proteção Social da ColĂ´mbia. Contudo, esta conta com algumas limitações que, a partir da construção e da validação de uma nova bateria, neste estudo se pretendem superar. AlĂ©m disso, a nova bateria oferece recursos adicionais para a avaliação desses fatores: a presente bateria incorpora os instrumentos e os indicadores centrais dos modelos demanda-controle-apoio social e desiquilĂbrio esforço-recompensa e os fatores internos do trabalho nĂŁo considerados nesses modelos, mas que a Resolução considera necessários, mediram-se com testes preexistentes ou desenvolvidos pelos autores. Com os dados coletados, Ă© possĂvel calcular indicadores globais de demanda, controle e apoio social; alĂ©m de condições familiares e sociais de risco, enfrentamento, personalidade e indicadores de saĂşde e bem-estar. Para a validação, a bateria foi aplicada a uma amostra de 16 095 trabalhadores de diferentes cargos e municĂpios colombianos. As anál i ses de consistĂŞncia interna e validade permitem afirmar que a bateria Ă© simples de aplicar em papel ou digital, permitirá comparar cargos, obter pontuações unificadas por variável, oferecer um diagnĂłstico de um nĂşmero importante das variáveis sugeridas na Resolução bem como permitirá comparar os resultados dos trabalhadores colombianos com os de outros paĂses. Palavras-chave: fatores trabalhistas de risco psicossocial, Resolução 2 646 de 2008, modelo demanda-controle-apoio social, modelo desiquilĂbrio esforço-recompensa, estresse profissional, avaliação.En 2010 se desarrollĂł una baterĂa de instrumentos para evaluar factores psicosociales laborales de riesgo para la salud, en respuesta a la ResoluciĂłn 2646 de 2008 del Ministerio de la ProtecciĂłn Social de Colombia. Sin embargo, esta cuenta con algunas limitaciones que, a partir de la construcciĂłn y validaciĂłn de una nueva baterĂa, en el presente estudio se buscan superar. La nueva baterĂa ofrece recursos adicionales para la evaluaciĂłn de estos factores: incorpora los instrumentos e indicadores centrales de los modelos demanda-control-apoyo social y desequilibrio esfuerzo-recompensa, y los factores intralaborales no contemplados en dichos modelos, pero que la ResoluciĂłn considera necesarios, se midieron con pruebas preexistentes o desarrolladas por los autores. Con los datos recolectados es posible calcular indicadores globales de demanda, control y apoyo social; además de condiciones familiares y sociales de riesgo, afrontamiento, personalidad e indicadores de salud y bienestar. Para la validaciĂłn, la baterĂa se aplicĂł a una muestra de 16.095 trabajadores de diferentes ocupaciones y municipios colombianos. Los análisis de consistencia interna y validez permiten afirmar que la baterĂa es sencilla de aplicar en papel o por computador, permitirá comparar ocupaciones, obtener puntuaciones unificadas por variable, ofrecer un diagnĂłstico de un nĂşmero importante de las variables sugeridas en la ResoluciĂłn y comparar los resultados de los trabajadores colombianos con los de otros paĂses
Modeling the Gas Flow in the Bar of NGC 1365
We present new observations of the strongly-barred galaxy NGC 1365, including
new photometric images and Fabry-Perot spectroscopy, as well as a detailed
re-analysis of the neutral hydrogen observations from the VLA archive. We find
the galaxy to be at once remarkably bi-symmetric in its I-band light
distribution and strongly asymmetric in the distribution of dust and in the
kinematics of the gas in the bar region. The velocity field mapped in the
H-alpha line reveals bright HII regions with velocities that differ by 60 to 80
km/s from that of the surrounding gas, which may be due to remnants of
infalling material. We have attempted hydrodynamic simulations of the bar flow
to estimate the separate disk and halo masses, using two different dark matter
halo models and covering a wide range of mass-to-light ratios (Upsilon) and bar
pattern speeds (Omega_p). None of our models provides a compelling fit to the
data, but they seem most nearly consistent with a fast bar, corotation at sim
1.2r_B, and Upsilon_I simeq 2.0 +- 1.0, implying a massive, but not fully
maximal, disk. The fitted dark halos are unusually concentrated, a requirement
driven by the declining outer rotation curve.Comment: 43 pages, 15 figures, accepted to appear in Ap
A ~ 12 kpc HI extension and other HI asymmetries in the isolated galaxy CIG 340 (IC 2487)
HI kinematic asymmetries are common in late-type galaxies irrespective of
environment, although the amplitudes are strikingly low in isolated galaxies.
As part of our studies of the HI morphology and kinematics in isolated
late-type galaxies we have chosen several very isolated galaxies from the AMIGA
sample for HI mapping. Here we present GMRT 21-cm HI line mapping of CIG 340
which was selected because its integrated HI spectrum has a very symmetric
profile, Aflux = 1.03. Optical images of the galaxy hinted at a warped disk in
contrast to the symmetric integrated HI spectrum profile. Our aim is to
determine the extent to which the optical asymmetry is reflected in the
resolved HI morphology and kinematics. GMRT observations reveal significant HI
morphological asymmetries in CIG 340 despite it's overall symmetric optical
form and highly symmetric HI spectrum. The most notable HI features are: 1) a
warp in the HI disk (with an optical counterpart), 2) the HI north/south flux
ratio = 1.32 is much larger than expected from the integrated HI spectrum
profile and 3) a ~ 45" (12 kpc) HI extension, containing ~ 6% of the detected
HI mass on the northern side of the disk. We conclude that in isolated galaxies
a highly symmetric HI spectrum can mask significant HI morphological
asymmetries. The northern HI extension appears to be the result of a recent
perturbation (10^8 yr), possibly by a satellite which is now disrupted or
projected within the disk. This study provides an important step in our ongoing
program to determine the predominant source of HI asymmetries in isolated
galaxies. For CIG 340 the isolation from major companions, symmetric HI
spectrum, optical morphology and interaction timescales have allowed us to
narrow the possible causes the HI asymmetries and identify tests to further
constrain the source of the asymmetries.Comment: 10 page
Computing automorphic forms on Shimura curves over fields with arbitrary class number
We extend methods of Greenberg and the author to compute in the cohomology of
a Shimura curve defined over a totally real field with arbitrary class number.
Via the Jacquet-Langlands correspondence, we thereby compute systems of Hecke
eigenvalues associated to Hilbert modular forms of arbitrary level over a
totally real field of odd degree. We conclude with two examples which
illustrate the effectiveness of our algorithms.Comment: 15 pages; final submission to ANTS I
Halo Geometry and Dark Matter Annihilation Signal
We study the impact of the halo shape and geometry on the expected weakly
interacting massive particle (WIMP) dark matter annihilation signal from the
galactic center. As the halo profile in the innermost region is still poorly
constrained, we consider different density behaviors like flat cores, cusps and
spikes, as well as geometrical distortions. We show that asphericity has a
strong impact on the annihilation signal when the halo profile near the
galactic center is flat, but becomes gradually less significant for cuspy
profiles, and negligible in the presence of a central spike. However, the
astrophysical factor is strongly dependent on the WIMP mass and annihilation
cross-section in the latter case.Comment: 5 pages, 4 figures, PR
Setting the normalcy level of HI properties in isolated galaxies
Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring
Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP
Conference Serie
Exploring the Effect of G6PC2 Single Nucleotide Polymorphisms on Enzyme Activity and Human Health
G6PC2 encodes a glucose-6-phosphatase catalytic subunit that is highly expressed in pancreatic islet beta cells. Genome wide association studies (GWAS) have shown that single nucleotide polymorphisms (SNPs) in the G6PC2 gene are associated with variations in fasting blood glucose (FBG), a parameter linked with risk for type 2 diabetes (T2D). Studies in mice have complemented these GWAS data by showing that deletion of G6pc2 abolishes islet glucose-6-phosphatase activity and lowers FBG. We hypothesize that G6pc2 forms a substrate cycle with glucokinase that determines the sensitivity of glucose-stimulated insulin secretion (GSIS) to glucose. In support of this hypothesis we have previously shown that deletion of G6pc2 enhances GSIS at sub-maximal glucose concentrations and abolishes glucose cycling in isolated islets. More recently we have demonstrated that deletion of G6pc2 enhances glycolysis in isolated mouse islets, and that high rates of glucose cycling are also detected in human islets. Our broad hypothesis is that the results of these studies will strongly suggest that G6PC2 inhibition should be considered as a novel therapeutic strategy for lowering FBG and thereby preventing T2D. To extend these observations we have developed a novel intact cell assay for G6PC2 activity. This assay relies on the observation that CREB and ChREBP bound to the rat G6PC1 promoter are highly glucose responsive in the rat islet-derived 832/13 cell line and the fact that endogenous G6PC2 is absent. In the presence of catalytically-dead G6PC2, glucose stimulates G6PC1-luciferase fusion gene expression. However, this induction is blunted in the presence of wild type G6PC2. We are using this assay to determine the effect of non-synonymous G6PC2 SNPs on G6PC2 activity and then examining the association between SNPs that markedly affect G6PC2 activity with their effects on human health as assessed using Vanderbilt’s BioVU biobank. These data will reveal whether SNPs in G6PC2 are associated with only altered FBG or whether G6PC2 affects other aspects of human health
STIS Longslit Spectroscopy Of The Narrow Line Region Of NGC 4151. I. Kinematics and Emission Line Ratios
Longslit spectra of the Seyfert galaxy NGC 4151 from the UV to near infrared
have been obtained with STIS to study the kinematics and physical conditions in
the NLR. The kinematics show evidence for three components, a low velocity
system in normal disk rotation, a high velocity system in radial outflow at a
few hundred km/s relative to the systemic velocity and an additional high
velocity system also in outflow with velocities up to 1400 km/s, in agreement
with results from STIS slitless spectroscopy (Hutchings et al., 1998, Kaiser et
al., 1999, Hutchings et al., 1999) We have explored two simple kinematic models
and suggest that radial outflow in the form of a wind is the most likely
explanation. We also present evidence indicating that the wind may be
decelerating with distance from the nucleus.
We find that the emission line ratios along our slits are all entirely
consistent with photoionization from the nuclear continuum source. A decrease
in the [OIII]5007/H-beta and [OIII]5007/[OII]3727 ratios suggests that the
density decreases with distance from the nucleus. This trend is borne out by
the [SII] ratios as well. We find no strong evidence for interaction between
the radio jet and the NLR gas in either the kinematics or the emission line
ratios in agreement with the results of Kaiser et al. (1999) who find no
spatial coincidence of NLR clouds and knots in the radio jet. These results are
in contrast to other recent studies of nearby AGN which find evidence for
significant interaction between the radio source and the NLR gas.Comment: 32 pages, 13 figures, accepted for publication in The Astrophysical
Journa
DNA-dependent Protein Kinase Activity Is Not Required for Immunoglobulin Class Switching
Class switch recombination (CSR), similar to V(D)J recombination, is thought to involve DNA double strand breaks and repair by the nonhomologous end–joining pathway. A key component of this pathway is DNA-dependent protein kinase (DNA-PK), consisting of a catalytic subunit (DNA-PKcs) and a DNA-binding heterodimer (Ku70/80). To test whether DNA-PKcs activity is essential for CSR, we examined whether IgM+ B cells from scid mice with site-directed H and L chain transgenes were able to undergo CSR. Although B cells from these mice were shown to lack DNA-PKcs activity, they were able to switch from IgM to IgG or IgA with close to the same efficiency as B cells from control transgenic and nontransgenic scid/+ mice, heterozygous for the scid mutation. We conclude that CSR, unlike V(D)J recombination, can readily occur in the absence of DNA-PKcs activity. We suggest nonhomologous end joining may not be the (primary or only) mechanism used to repair DNA breaks during CSR
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