199 research outputs found
Molecular Gas in Spiral Galaxies
In this review, I highlight a number of recent surveys of molecular gas in
nearby spiral galaxies. Through such surveys, more complete observations of the
distribution and kinematics of molecular gas have become available for galaxies
with a wider range of properties (e.g., brightness, Hubble type, strength of
spiral or bar structure). These studies show the promise of both
interferometers and single-dish telescopes in advancing our general
understanding of molecular gas in spiral galaxies. In particular, I highlight
the contributions of the recent BIMA Survey of Nearby Galaxies (SONG).Comment: 8 pages, 1 figure. To appear in the proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium, "The Dense Interstellar Medium in Galaxies",
which was held in Zermatt, Switzerland in September 200
Nuclear Bar Catalyzed Star Formation: 13^CO, C18^O and Molecular Gas Properties in the Nucleus of Maffei 2
(Abridged) We present resolution maps of CO, its isotopologues, and HCN from
in the center of Maffei 2. The J=1-0 rotational lines of 12^CO, 13^CO, C18^O
and HCN, and the J=2-1 lines of 13^CO and C18^O were observed with the OVRO and
BIMA arrays. The 2-1/1-0 line ratios of the isotopologues constrain the bulk of
the molecular gas to originate in low excitation, subthermal gas. From LVG
modeling, we infer that the central GMCs have n(H_2) ~10^2.75 cm^-3 and T_k ~
30 K. Continuum emission at 3.4 mm, 2.7 mm and 1.4 mm was mapped to determine
the distribution and amount of HII regions and dust. Column densities derived
from C18^O and 1.4 mm dust continuum fluxes indicate the CO conversion factor
in the center of Maffei 2 is lower than Galactic by factors of ~2-4. Gas
morphology and the clear ``parallelogram'' in the Position-Velocity diagram
shows that molecular gas orbits within the potential of a nuclear (~220 pc)
bar. The nuclear bar is distinct from the bar that governs the large scale
morphology of Maffei 2. Giant molecular clouds in the nucleus are nonspherical
and have large linewidths. Dense gas and star formation are concentrated at the
sites of the x_1-x_2 orbit intersections of the nuclear bar, suggesting that
the starburst is dynamically triggered.Comment: 50 pages, 14 figures, accepted for publication in Ap
An extragalactic supernebula confined by gravity
Little is known about the origins of the giant star clusters known as
globular clusters. How can hundreds of thousands of stars form simultaneously
in a volume only a few light years across the distance of the sun to its
nearest neighbor? Radiation pressure and winds from luminous young stars should
disperse the star-forming gas and disrupt the formation of the cluster.
Globular clusters in our Galaxy cannot provide answers; they are billions of
years old. Here we report the measurement of infrared hydrogen recombination
lines from a young, forming super star cluster in the dwarf galaxy, NGC 5253.
The lines arise in gas heated by a cluster of an estimated million stars, so
young that it is still enshrouded in gas and dust, hidden from optical view. We
verify that the cluster contains 4000-6000 massive, hot "O" stars. Our
discovery that the gases within the cluster are bound by gravity may explain
why these windy and luminous O stars have not yet blown away the gases to allow
the cluster to emerge from its birth cocoon. Young clusters in "starbursting"
galaxies in the local and distant universe may be similarly gravitationally
confined and cloaked from view.Comment: Letter to Natur
The Long-Term Variability of the X-Ray Sources in NGC 6946 and NGC 4485/4490
We analyze data from five Chandra observations of the spiral galaxy NGC 6946
and from three Chandra observations of the irregular/spiral interacting galaxy
pair NGC 4485/4490, with an emphasis on investigating the long-term variability
exhibited by the source populations. We detect 90 point sources coincident with
NGC 6946 down to luminosities of a few times 10^36 erg/s, and 38 sources
coincident with NGC 4485/90 down to a luminosity of ~1x10^37 erg/s. Twenty-five
(15) sources in NGC 6946 (NGC 4485/90) exhibit long-term (i.e., weeks to years)
variability in luminosity; 11 (4) are transient candidates. The single
ultraluminous X-ray source (ULX) in NGC 6946 and all but one of the eight ULXs
in NGC 4485/90 exhibit long-term flux variability. Two of the ULXs in NGC
4485/90 have not been identified before as ultraluminous sources. The
widespread variability in both systems is indicative of the populations being
dominated by X-ray binaries, and this is supported by the X-ray colors of the
sources. The distribution of colors among the sources indicates a large
fraction of high-mass X-ray binaries in both systems. The shapes of the X-ray
luminosity functions of the galaxies do not change significantly between
observations and can be described by power laws with cumulative slopes ~0.6-0.7
(NGC 6946) and ~0.4 (NGC 4485/90).Comment: 26 pages, 9 figures, 15 tables - to appear in the August 2008 issue
of ApJS - new version corrects a few typo
Why Moral Expertise Needs Moral Theory
Discussions of the nature or possibility of moral expertise have largely proceeded in atheoretical terms, with little attention paid to whether moral expertise depends on theoretical knowledge of morality. Here I argue that moral expertise is more theory-dependent than is commonly recognized: Moral expertise consists, at least in part, in knowledge of the correct or best moral theory, and second, that knowledge of moral theory is essential to moral experts dispensing expert counsel to non-experts. Moral experts would not be moral experts absent knowledge of moral theory, nor could they play the testimonial role we would expect them to play in moral inquiry and deliberation absent such knowledg
Food allergy alters jejunal circular muscle contractility and induces local inflammatory cytokine expression in a mouse model
<p>Abstract</p> <p>Background</p> <p>We hypothesized that food allergy causes a state of non-specific jejunal dysmotility. This was tested in a mouse model.</p> <p>Methods</p> <p>Balb/c mice were epicutaneously sensitized with ovalbumin and challenged with 10 intragastric ovalbumin administrations every second day. Smooth muscle contractility of isolated circular jejunal sections was studied in organ bath with increasing concentrations of carbamylcholine chloride (carbachol). Smooth muscle layer thickness and mast cell protease-1 (MMCP-1) positive cell density were assayed histologically. Serum MMCP-1 and immunoglobulins were quantified by ELISA, and mRNA expressions of IFN-γ, IL-4, IL-6 and TGFβ-1 from jejunal and ileal tissue segments were analyzed with quantitative real-time PCR.</p> <p>Results</p> <p>Ovalbumin-specific serum IgE correlated with jejunal MMCP-1<sup>+ </sup>cell density. In the allergic mice, higher concentrations of carbachol were required to reach submaximal muscular stimulation, particularly in preparations derived from mice with diarrhoea. Decreased sensitivity to carbachol was associated with increased expression of IL-4 and IL-6 mRNA in jejunum. Smooth muscle layer thickness, as well as mRNA of IFN-γ and TGF-β1 remained unchanged.</p> <p>Conclusion</p> <p>In this mouse model of food allergy, we demonstrated a decreased response to a muscarinic agonist, and increased levels of proinflammatory IL-6 and Th2-related IL-4, but not Th1-related IFN-γ mRNAs in jejunum. IgE levels in serum correlated with the number of jejunal MMCP-1<sup>+ </sup>cells, and predicted diarrhoea. Overall, these changes may reflect a protective mechanism of the gut in food allergy.</p
Development of competences while solving real industrial interdisciplinary problems: a successful cooperation with industry
The development of projects in industrial context constitutes an exceptional opportunity for engineering students to develop competences expected by the labour market. Therefore, the adoption of this type of interaction within engineering curricula is highly recommended, not only at the end of the degree, but also in the previous years. The main purpose of this paper is to present and analyse a Project-Based Learning (PBL) semester in which six teams of Industrial Engineering and Management (IEM) students integrate different areas of knowledge, while solving real problems of five companies, emphasizing the technical solutions developed by the students and the feedback provided by the companies. Students' feedback will be also addressed. The main outcomes of this study reveal that most of the technical solutions lie in areas of Lean applications and ergonomic improvement of workplaces. Companies were very pleased with the results of this type of University-Business Cooperation (UBC).This work was funded by COMPETE-POCI-01-0145-FEDER-007043 and FCT-UID-CEC-00319-2013info:eu-repo/semantics/publishedVersio
Modeling Light Adaptation in Circadian Clock: Prediction of the Response That Stabilizes Entrainment
Periods of biological clocks are close to but often different from the rotation period of the earth. Thus, the clocks of organisms must be adjusted to synchronize with day-night cycles. The primary signal that adjusts the clocks is light. In Neurospora, light transiently up-regulates the expression of specific clock genes. This molecular response to light is called light adaptation. Does light adaptation occur in other organisms? Using published experimental data, we first estimated the time course of the up-regulation rate of gene expression by light. Intriguingly, the estimated up-regulation rate was transient during light period in mice as well as Neurospora. Next, we constructed a computational model to consider how light adaptation had an effect on the entrainment of circadian oscillation to 24-h light-dark cycles. We found that cellular oscillations are more likely to be destabilized without light adaption especially when light intensity is very high. From the present results, we predict that the instability of circadian oscillations under 24-h light-dark cycles can be experimentally observed if light adaptation is altered. We conclude that the functional consequence of light adaptation is to increase the adjustability to 24-h light-dark cycles and then adapt to fluctuating environments in nature
Embracing ambiguity in management control and decision-making processes:On how to design data visualizations to prompt wise judgement
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