8,084 research outputs found
Crystal image analysis using synchrosqueezed transforms
We propose efficient algorithms based on a band-limited version of 2D
synchrosqueezed transforms to extract mesoscopic and microscopic information
from atomic crystal images. The methods analyze atomic crystal images as an
assemblage of non-overlapping segments of 2D general intrinsic mode type
functions, which are superpositions of non-linear wave-like components. In
particular, crystal defects are interpreted as the irregularity of local
energy; crystal rotations are described as the angle deviation of local wave
vectors from their references; the gradient of a crystal elastic deformation
can be obtained by a linear system generated by local wave vectors. Several
numerical examples of synthetic and real crystal images are provided to
illustrate the efficiency, robustness, and reliability of our methods.Comment: 27 pages, 17 figure
A Submillimeter Study of the Star-Forming Region NGC7129
New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps
of the NGC7129 star forming region are presented, complemented by C18O J=3-2
spectra at several positions within the mapped region. The maps include the
Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and
several other pre-stellar sources embedded within the molecular ridge.
The SCUBA maps help us understand the nature of the pre-main sequence stars
in this actively star forming region. A deeply embedded submillimeter source,
SMM2, not clearly seen in any earlier data set, is shown to be a pre-stellar
core or possibly a protostar. The highest continuum peak emission is identified
with the deeply embedded source IRS6, a few arcseconds away from LkHalpha 234,
and also responsible for both the optical jet and the molecular outflow. The
gas and dust masses are found to be consistent, suggesting little or no CO
depletion onto grains. The dust emissivity index is lower towards the dense
compact sources, beta ~1 - 1.6, and higher, beta ~ 2.0, in the surrounding
cloud, implying small size grains in the PDR ridge, whose mantles have been
evaporated by the intense UV radiation.Comment: Accepted by Ap
A model for the condensation of a dusty plasma
A model for the condensation of a dusty plasma is constructed by considering
the spherical shielding layers surrounding a dust grain test particle. The
collisionless region less than a collision mean free path from the test
particle is shown to separate into three concentric layers, each having
distinct physics. The method of matched asymptotic expansions is invoked at the
interfaces between these layers and provides equations which determine the
radii of the interfaces. Despite being much smaller than the Wigner-Seitz
radius, the dust Debye length is found to be physically significant because it
gives the scale length of a precipitous cut-off of the shielded electrostatic
potential at the interface between the second and third layers. Condensation is
predicted to occur when the ratio of this cut-off radius to the Wigner-Seitz
radius exceeds unity and this prediction is shown to be in good agreement with
experiments.Comment: 29 pages, 4 figures, 1 table, to appear in Physics of Plasmas.
Manuscript revised on May 1, 2004 to take into account accuracy of Mie
scattering dust grain diameter measurement method used in Hayashi/Tachibana
experiment. Model now compared to Hayashi/Tachibana experiment using measured
rather than fitted dust grain diameter and using higher estimate for Te/Ti
(two new references added; revisions made to two paragraphs in Sec. VII, to
bottom plot of Fig. 3, and to right-most column of Table 1
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