135 research outputs found
On the Interpretation of the l-v Features in the Milky Way Galaxy
We model the gas dynamics of barred galaxies using a three-dimensional,
high-resolution, -body+hydrodynamical simulation and apply it to the Milky
Way in an attempt to reproduce both the large-scale structure and the clumpy
morphology observed in Galactic H\emissiontype{I} and CO diagrams. Owing
to including the multi-phase interstellar medium, self-gravity, star-formation
and supernovae feedback, the clumpy morphology, as well as the large-scale
features, in observed diagrams are naturally reproduced. We identify in
our diagrams with a number of not only large-scale peculiar features such
as the '3-kpc arm', '135-km s arm' and 'Connecting arm' but also clumpy
features such as `Bania clumps', and then link these features in a face-on view
of our model. We give suggestions on the real structure of the Milky Way and on
the fate of gas clumps in the central region.Comment: accepted to PAS
Interplay between Stellar Spirals and the ISM in Galactic Disks
We propose a new dynamical picture of galactic stellar and gas spirals, based
on hydrodynamic simulations in a `live' stellar disk. We focus especially on
spiral structures excited in a isolated galactic disk without a stellar bar.
Using high-resolution, 3-dimensional N-body/SPH simulations, we found that the
spiral features of the gas in galactic disks are formed by essentially
different mechanisms from the galactic shock in stellar density waves. The
stellar spiral arms and the interstellar matter on average corotate in a
galactic potential at any radii. Unlike the stream motions in the galactic
shock, the interstellar matter flows into the local potential minima with
irregular motions. The flows converge to form dense gas clouds/filaments near
the bottom of the stellar spirals, whose global structures resemble dust-lanes
seen in late-type spiral galaxies. The stellar arms are non-steady; they are
wound and stretched by the galactic shear, and thus local densities of the arm
change on a time scale of ~ 100 Myrs, due to bifurcating or merging with other
arms. This makes the gas spirals associated with the stellar arms non-steady.
The association of dense gas clouds are eventually dissolved into inter-arm
regions with non-cirucular motions. Star clusters are formed from the cold,
dense gases, whose ages are less than ~30 Myrs, and they are roughly associated
with the background stellar arms without a clear spatial offset between gas
spiral arms and distribution of young stars.Comment: 13 pages, 12 figures, accepted by ApJ. Higher resolution of ms.pdf is
available at http://d.pr/Nvjk A targzipped Supplementary movies is available
at http://d.pr/TV6
Analysis of H2O Masers in Sharpless 269 using VERA Archival data --- Effect of maser structures on astrometric accuracy
Astrometry using H2O maser sources in star forming regions is expected to be
a powerful tool to study the structures and dynamics of our Galaxy. Honma et
al. (2007) (hereafter H2007) claimed that the annual parallax of S269 is
determined within an error of 0.008 milliarcsec (mas), concluding that S269 is
located at 5.3 kpc +- 0.2 kpc from the sun, and R= 13.1 kpc. They claimed that
the rotational velocity of S269 is equal to that of the sun within a 3% error.
This small error, however, is hardly understood when taking into account the
results of other observations and theoretical studies of galactic dynamics. We
here reanalyzed the VERA archival data using the self-calibration method
(hybrid mapping), and found that clusters of maser features of S269 are
distributed in much wider area than that investigated in H2007. We confirmed
that, if we make a narrow region image without considering the presence of
multiple maser spots, and only the phase calibration is applied, we can
reproduce the same maser structures in H2007. The distribution extent of maser
spots in the feature differs 0.2 mas from east to west between our results and
H2007. Moreover, we found that change of relative positions of maser spots in
the cluster reaches 0.1 mas or larger between observational epochs. This
suggests that if one simply assumes the time-dependent, widely distributed
maser sources as a stable single point source, it could cause errors of up to
0.1 mas in the annual parallax of S269. Taking into account the internal
motions of maser spot clusters, the proper motion of S269 cannot be determined
precisely. We estimated that the peculiar motion of S269 with respect to a
Galactic circular rotation is ~20 km/s. These results imply that the observed
kinematics of maser emissions in S269 cannot give a strong constraint on
dynamics of the outer part of the Galaxy, in contrast to the claim by H2007.Comment: 33 pages, 11 figures, to be published in New Astronom
Myocardial sympathetic denervation prevents chamber-specific alteration of beta-adrenergic transmembrane signaling in rabbits with heart failure
Objectives.The purpose of this study was to assess the effect of myocardial sympathetic denervation on the chamber-specific alteration of beta-adrenergic signaling in left ventricular failure in rabbits.Background.Local abnormalities in sympathetic nerve terminals, including the neuronal reuptake of norepinephrine, are thought to be responsible for the chamber-specific regulation of beta-adrenergic signaling in heart failure.Methods.Sixteen rabbits were given 6-hydroxydopamine, 25 mg/kg body weight intravenously on days 1 and 2 and 50 mg/kg intravenously on days 7 and 8. Another 16 rabbits received vehicle. Aortic regurgitation was induced in eight of the 6-hydroxydopamine—treated and eight of the vehicle-treated rabbits on day 14. Another eight of the 6-hydroxydopamine—treated and eight of the vehicletreated rabbits underwent a sham operation. The hearts were excised for biochemical analysis on day 21.Results.Hemodynamic characteristics on day 21 showed left ventricular failure in both the aortic regurgitation groups. The plasma norepinephrine concentration on day 21 was higher in both the aortic regurgitation groups than in the sham groups. The beta-adrenoceptor densities and isoproterenol plus 5′guanylylimidodiphosphate-, 5′-guanylylimidodiphosphate- and sodium fluoride-stimulated adenylyl cyclase activities were decreased only in the failing left ventricle of the vehicle-pretreated aortic regurgitation group, but in both ventricles of the 6-hydroxydopamine-pretreated aortic regurgitation group. The basal and forskolin-stimulated adenylyl cyclase activities were similar in both the aortic regurgitation groups and in the sham groups.Conclusions.Sympathetic denervation prevented chamberspecific alterations in beta-adrenergic signaling in acute left ventricular failure. Local loss of sympathetic nerve endings, and especially the defective neuronal norepinephrine reuptake, are likely to be responsible for the chamber-specific alteration of the beta-adrenoceptor-G protein-adenylyl cyclase system in heart failure in rabbits
Marylosides A-G, Norcycloartane Glycosides from Leaves of Cymbidium Great Flower ‘Marylaurencin’
Seven novel norcycloartane glycosides, maryloside A–G (1–7), were isolated from the leaves of Cymbidium Great Flower ‘Marylaurencin’, along with a known norcycloartane glycoside, cymbidoside (8). These structures were determined on the basis of mainly NMR experiments as well as chemical degradation and X-ray crystallographic analysis. The isolated compounds (1–6 and 8) were evaluated for the inhibitory activity on lipopolysaccharide (LPS) and interferon-γ (IFN-γ)-stimulated nitric oxide (NO) production in RAW 264.7 cells. Consequently, 1 and 3 exhibited moderate activity
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