9,490 research outputs found
A Dynamical Consideration on Earthquake Damages of Bridge Piers : First Report
As was also noted from the results of the Fukui Earthquake of June 1948, it is now quite evident that the earthquake damage of the bridge substructure decisively affects the damage of the whole bridge, directly or indirectly, with almost no exception. In view of this fact, it is attempted in this paper to make a dynamical study from both theoretical and experimental points of view on the mechanism of earthquake damages of the bridge substructure and thereby contribute to the earthquake-proof design and construction of bridge piers
GMC Collisions as Triggers of Star Formation. V. Observational Signatures
We present calculations of molecular, atomic and ionic line emission from
simulations of giant molecular cloud (GMC) collisions. We post-process
snapshots of the magneto-hydrodynamical simulations presented in an earlier
paper in this series by Wu et al. (2017) of colliding and non-colliding GMCs.
Using photodissociation region (PDR) chemistry and radiative transfer we
calculate the level populations and emission properties of CO ,
[CI] at m, [CII] m and [OI]
transition at m. From integrated
intensity emission maps and position-velocity diagrams, we find that
fine-structure lines, particularly the [CII] m, can be used as a
diagnostic tracer for cloud-cloud collision activity. These results hold even
in more evolved systems in which the collision signature in molecular lines has
been diminished.Comment: 10 pages, 7 figures, accepted for publication in ApJ, comments
welcom
High-mass star formation in Orion triggered by cloud-cloud collision II, Two merging molecular clouds in NGC2024
We analyzed the NANTEN2 13CO (J=2-1 and 1-0) datasets in NGC 2024. We found
that the cloud consists of two velocity components, whereas the cloud shows
mostly single-peaked CO profiles. The two components are physically connected
to the HII region as evidenced by their close correlation with the dark lanes
and the emission nebulosity. The two components show complementary distribution
with a displacement of 0.4 pc. Such complementary distribution is typical to
colliding clouds discovered in regions of high-mass star formation. We
hypothesize that cloud-cloud collision between the two components triggered the
formation of the late O stars and early B stars localized within 0.3 pc of the
cloud peak. The collision timescale is estimated to be ~ 10^5 yrs from a ratio
of the displacement and the relative velocity 3-4 km s-1 corrected for probable
projection. The high column density of the colliding cloud 1023 cm-2 is similar
to those in the other massive star clusters in RCW 38, Westerlund 2, NGC 3603,
and M42, which are likely formed under trigger by cloud-cloud collision. The
present results provide an additional piece of evidence favorable to high-mass
star formation by a major cloud-cloud collision in Orion.Comment: 24 pages, 10 figures, submitted for publication in PASJ (cloud-cloud
collision special issue
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