7,085 research outputs found
A Survey of Irradiated Pillars, Globules, and Jets in the Carina Nebul
We present wide-field, deep narrowband H, Br, H, [S II],
[O III], and broadband I and K-band images of the Carina star formation region.
The new images provide a large-scale overview of all the H and Br
emission present in over a square degree centered on this signature star
forming complex. By comparing these images with archival HST and Spitzer images
we observe how intense UV radiation from O and B stars affects star formation
in molecular clouds. We use the images to locate new candidate outflows and
identify the principal shock waves and irradiated interfaces within dozens of
distinct areas of star-forming activity. Shocked molecular gas in jets traces
the parts of the flow that are most shielded from the intense UV radiation.
Combining the H and optical images gives a more complete view of the jets,
which are sometimes only visible in H. The Carina region hosts several
compact young clusters, and the gas within these clusters is affected by
radiation from both the cluster stars and the massive stars nearby. The Carina
Nebula is ideal for studying the physics of young H II regions and PDR's, as it
contains multiple examples of walls and irradiated pillars at various stages of
development. Some of the pillars have detached from their host molecular clouds
to form proplyds. Fluorescent H outlines the interfaces between the ionized
and molecular gas, and after removing continuum, we detect spatial offsets
between the Br and H emission along the irradiated interfaces.
These spatial offsets can be used to test current models of PDRs once synthetic
maps of these lines become available.Comment: Accepted in the Astronomical Journa
Deuteron Momentum Distribution in KD2HPO4
The momentum distribution in KD2PO4(DKDP) has been measured using neutron
Compton scattering above and below the weakly first order
paraelectric-ferroelectric phase transition(T=229K). There is very litte
difference between the two distributions, and no sign of the coherence over two
locations for the proton observed in the paraelectric phase, as in KH2PO4(KDP).
We conclude that the tunnel splitting must be much less than 20mev. The width
of the distribution indicates that the effective potential for DKDP is
significantly softer than that for KDP. As electronic structure calculations
indicate that the stiffness of the potential increases with the size of the
coherent region locally undergoing soft mode fluctuations, we conclude that
there is a mass dependent quantum coherence length in both systems.Comment: 6 pages 5 figure
Comment on ``Structure of exotic nuclei and superheavy elements in a relativistic shell model''
A recent paper [M. Rashdan, Phys. Rev. C 63, 044303 (2001)] introduces the
new parameterization NL-RA1 of the relativistic mean-field model which is
claimed to give a better description of nuclear properties than earlier ones.
Using this model ^{298}114 is predicted to be a doubly-magic nucleus. As will
be shown in this comment these findings are to be doubted as they are obtained
with an unrealistic parameterization of the pairing interaction and neglecting
ground-state deformation.Comment: 2 pages REVTEX, 3 figures, submitted to comment section of Phys. Rev.
C. shortened and revised versio
Dewetting of thin polymer films near the glass transition
Dewetting of ultra-thin polymer films near the glass transition exhibits
unexpected front morphologies [G. Reiter, Phys. Rev. Lett., 87, 186101 (2001)].
We present here the first theoretical attempt to understand these features,
focusing on the shear-thinning behaviour of these films. We analyse the profile
of the dewetting film, and characterize the time evolution of the dry region
radius, , and of the rim height, . After a transient time
depending on the initial thickness, grows like while
increases like . Different regimes of growth are
expected, depending on the initial film thickness and experimental time range.Comment: 4 pages, 5 figures Revised version, published in Physical Review
Letters: F. Saulnier, E. Raphael and P.-G. de Gennes, Phys. Rev. Lett. 88,
196101 (2002
- …