796 research outputs found
Two-Dimensional Magnetohydrodynamic Simulations of Barred Galaxies
Barred galaxies are known to possess magnetic fields that may affect the
properties of bar substructures such as dust lanes and nuclear rings. We use
two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to
investigate the effects of magnetic fields on the formation and evolution of
such substructures as well as on the mass inflow rates to the galaxy center.
The gaseous medium is assumed to be infinitesimally-thin, isothermal,
non-self-gravitating, and threaded by initially uniform, azimuthal magnetic
fields. We find that there exists an outermost x1-orbit relative to which
gaseous responses to an imposed stellar bar potential are completely different
between inside and outside. Inside this orbit, gas is shocked into dust lanes
and infalls to form a nuclear ring. Magnetic fields are compressed in dust
lanes, reducing their peak density. Magnetic stress removes further angular
momentum of the gas at the shocks, temporarily causing the dust lanes to bend
into an 'L' shape and eventually leading to a smaller and more centrally
distributed ring than in unmagnetized models. The mass inflow rates in
magnetized models correspondingly become larger, by more than two orders of
magnitude when the initial fields have an equipartition value with thermal
energy, than in the unmagnetized counterparts. Outside the outermost x1-orbit,
on the other hand, an MHD dynamo due to the combined action of the bar
potential and background shear operates near the corotation and bar-end
regions, efficiently amplifying magnetic fields. The amplified fields shape
into trailing magnetic arms with strong fields and low density. The base of the
magnetic arms has a thin layer in which magnetic fields with opposite polarity
reconnect via a tearing-mode instability. This produces numerous magnetic
islands with large density which propagate along the arms to turn the outer
disk into a highly chaotic state.Comment: 22 pages, 19 figures, 3 tables; Accepted for publication in the ApJ;
Version with full-resolution figures available at
http://mirzam.snu.ac.kr/~wkim/Bar/mhdbar.pd
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Male New Zealand robins (Petroica longipes) cater to their mate's desire when sharing food in the wild.
In many species that have bi-parental care, food-sharing males provide vital nutritional resources to their mates during reproduction. However, it is currently unknown whether females can signal specific desires to their mates, or if males can cater to female desire in the wild. Here we investigate whether and how wild male North Island robins (Petroica longipes) respond to changes in their mates' desires and nutritional need when sharing food. We demonstrate that wild female robins' desire for particular foods changes over short time periods; when given the choice between two types of insect larvae, females prefer the type they have not recently eaten. In our experiments, wild male robins preferentially shared the larvae type that their mate was most likely to desire and also increased the quantity of food shared if she had begun incubating. Males catered to their mates' desire when female behaviour was the only cue available to guide their choices. This is the first evidence that females may behaviourally communicate their specific food desires to their mates, enabling males to cater to fine-scale changes in their mates' nutritional requirements in the wild. Such a simple behaviour-reading mechanism has the potential to be widespread among other food-sharing species
Memory Performance Influences Male Reproductive Success in a Wild Bird.
Not applicableMarsden Fund (Royal Society of New Zealand
The Fueling of Nuclear Activity: II. The Bar Properties of Seyfert and Normal Galaxies
We use a recent near-infrared imaging survey of samples of Seyfert and normal
galaxies to study the role of bars in the fueling of nuclear activity. The
active galaxy sample includes Seyfert galaxies in the Revised Shapely-Ames
(RSA) and Sandage & Tammann's (1987) extension to this catalog. The normal
galaxies were selected to match the Seyfert sample in Hubble type, redshift,
inclination and blue luminosity. All the galaxies in both samples classified as
barred in the RSA catalog are also barred in the near-infrared. In addition,
~55% of the galaxies classified as non-barred in the RSA show evidence for bars
at 2.1 microns. Overall, ~70% of the galaxies observed show evidence for bar
structures. The incidence of bars in the Seyfert and normal galaxies is
similar, suggesting Seyfert nuclei do not occur preferentially in barred
systems. Furthermore, a slightly higher percentage of normal galaxies have
multiple-bar structures.Comment: aastex 4.0, accepted for publication in the Astrophysical Journal
Letter
La pobreza en Cartagena: un análisis por barrios
En el presente documento se hace un análisis descriptivo de la pobreza urbana enCartagena. El tema se aborda desde dos perspectivas. En la primera, se analiza lapobreza desagregada por los barrios que conforman la cabecera municipal deCartagena. En la segunda, se realiza una comparación de la situaciónsocioeconómica de los habitantes de Cartagena con la de las principales ciudades deColombia. Vale la pena mencionar que este trabajo es pionero no sólo en Cartagenasino en Colombia, en cuanto al nivel de división por barrios al que se analizanindicadores socioeconómicos, tales como la pobreza, el ingreso, los logroseducativos, la migración y el autorreconocimiento racial. Dentro de los principalesresultados se comprobó una focalización espacial de la pobreza en sectoresespecíficos de la ciudad, tales como las laderas del Cerro de la Popa y los barriosaledaños a la Ciénaga de la Virgen. En estas zonas de la ciudad se concentra no sólola población más pobre sino la de menores logros educativos. Otro resultadointeresante, y que está acorde con la literatura internacional, es que en los barrioscartageneros de mayor pobreza existe también una alta proporción de habitantes quese autorreconocen de raza negra.Pobreza urbana, Cartagena, economía regional y urbana
Capacity limitations of visual memory in two-interval comparison of Gabor arrays
The capacity of short-term visual memory (VSTM) was assessed in a two-interval spatial
frequency (SF) discrimination task. The cued Gabor target in a multi-element array either increased or
decreased in SF across a 2s interstimulus interval (ISI). Distracters as well as target were made to
change across ISI so that memory of the individual SF of Gabor elements was required to solve the
discrimination. The dynamics of the information loss from visual memory were analysed by
manipulating the timing of spatial cues and masks. Cueing the target position before the first display
gave thresholds comparable with those for a single Gabor patch. Cues placed after the first display gave
higher thresholds indicating some loss of information. Within the ISI there was little increase in
threshold or set size effect with cue delay. However there was a sharp rise in thresholds for cue
positions after the second display. Gabor masks placed before a mid-ISI cue were more effective than
noise masks or Gabor masks placed after the cue. With a cue placed late in the ISI, preceded by a
Gabor mask, the masking effect decreased with increasing delay of the mask after the first display. This
suggests a selective, dynamic but increasingly durable representation of the initial stimulus is built up
in memory, and there is a graded form of “overwriting” of this representation by new stimuli
Intra-sexual competition alters the relationship between testosterone and ornament expression in a wild territorial bird
Open Access funded by Natural Environment Research Council Under a Creative Commons licensePeer reviewedPublisher PD
Dysregulation of the haem-haemopexin axis is associated with severe malaria in a case-control study of Ugandan children.
BACKGROUND: Malaria is associated with haemolysis and the release of plasma haem. Plasma haem can cause endothelial injury and organ dysfunction, and is normally scavenged by haemopexin to limit toxicity. It was hypothesized that dysregulation of the haem-haemopexin pathway contributes to severe and fatal malaria infections.
METHODS: Plasma levels of haemin (oxidized haem), haemopexin, haptoglobin, and haemoglobin were quantified in a case-control study of Ugandan children with Plasmodium falciparum malaria. Levels at presentation were compared in children with uncomplicated malaria (UM; n = 29), severe malarial anaemia (SMA; n = 27) or cerebral malaria (CM; n = 31), and evaluated for utility in predicting fatal (n = 19) vs non-fatal (n = 39) outcomes in severe disease. A causal role for haemopexin was assessed in a pre-clinical model of experimental cerebral malaria (ECM), following disruption of mouse haemopexin gene (hpx). Analysis was done using Kruskall Wallis tests, Mann-Whitney tests, log-rank tests for survival, and repeated measures ANOVA.
RESULTS: In Ugandan children presenting with P. falciparum malaria, haemin levels were higher and haemopexin levels were lower in SMA and CM compared to children with UM (haemin, p \u3c 0.01; haemopexin, p \u3c 0.0001). Among all cases of severe malaria, elevated levels of haemin and cell-free haemoglobin at presentation were associated with subsequent mortality (p \u3c 0.05). Compared to ECM-resistant BALB/c mice, susceptible C57BL/6 mice had lower circulating levels of haemopexin (p \u3c 0.01), and targeted deletion of the haemopexin gene, hpx, resulted in increased mortality compared to their wild type littermates (p \u3c 0.05).
CONCLUSIONS: These data indicate that plasma levels of haemin and haemopexin measured at presentation correlate with malaria severity and levels of haemin and cell-free haemoglobin predict outcome in paediatric severe malaria. Mechanistic studies in the ECM model support a causal role for the haem-haemopexin axis in ECM pathobiology
Double-Barred Galaxies: I. A Catalog of Barred Galaxies with Stellar Secondary Bars and Inner Disks
I present a catalog of 67 barred galaxies which contain distinct, elliptical
stellar structures inside their bars. Fifty of these are double-barred
galaxies: a small-scale, "inner" or "secondary" bar is embedded within a
large-scale, "outer" or "primary" bar. I provide homogenized measurements of
the sizes, ellipticities, and orientations of both inner and outer bars, along
with with global parameters for the galaxies. The other 17 are classified as
"inner-disk" galaxies, where a large-scale bar harbors an inner elliptical
structure which is aligned with the galaxy's outer disk. Four of the
double-barred galaxies also possess inner disks, located in between the inner
and outer bars. While the inner-disk classification is ad-hoc -- and
undoubtedly includes some inner bars with chance alignments (five such probable
cases are identified) -- there is good evidence that inner disks form a
statistically distinct population, and that at least some are indeed disks
rather than bars. In addition, I list 36 galaxies which may be double-barred,
but for which current observations are ambiguous or incomplete, and another 23
galaxies which have been previously suggested as potentially being
double-barred, but which are probably *not*. False double-bar identifications
are usually due to features such as nuclear rings and spirals being
misclassified as bars; I provide some illustrated examples of how this can
happen.Comment: LaTeX, 25 pages, 6 EPS figures. Typos fixed and title slightly
altered; accepted by Astronomy & Astrophysics. Version with full-resolution
figures available at http://www.iac.es/galeria/erwin/research
The Molecular Interstellar Medium of the Local Group Dwarf NGC6822
Do molecular clouds collapse to form stars at the same rate in all
environments? In large spiral galaxies, the rate of transformation of H2 into
stars (hereafter SFE) varies little. However, the SFE in distant objects (z~1)
is much higher than in the large spiral disks that dominate the local universe.
Some small local group galaxies share at least some of the characteristics of
intermediate-redshift objects, such as size or color. Recent work has suggested
that the Star Formation Efficiency (SFE, defined as the SFRate per unit H2) in
local Dwarf galaxies may be as high as in the distant objects. A fundamental
difficulty in these studies is the independent measure of the H2 mass in
metal-deficient environments. At 490 kpc, NGC6822 is an excellent choice for
this study; it has been mapped in the CO(2-1) line using the multibeam receiver
HERA on the 30 meter IRAM telescope, yielding the largest sample of giant
molecular clouds (GMCs) in this galaxy. Despite the much lower metallicity, we
find no clear difference in the properties of the GMCs in NGC 6822 and those in
the Milky Way except lower CO luminosities for a given mass. Several
independent methods indicate that the total H2 mass in NGC 6822 is about 5 x
10^6 Msun in the area we mapped and less than 10^7 Msun in the whole galaxy.
This corresponds to a NH2/ICO ~ 4 x 10^{21} cm^-2 /(Kkm/s) over large scales,
such as would be observed in distant objects, and half that in individual GMCs.
No evidence was found for H2 without CO emission. Our simulations of the
radiative transfer in clouds are entirely compatible with these NH2/ICO values.
The SFE implied is a factor 5 - 10 higher than what is observed in large local
universe spirals.Comment: 16 pages, 13 figures. Accepted for publication in Astronomy and
Astrophysic
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