18,264 research outputs found
The Serpens filament: at the onset of slightly supercritical collapse
The Serpens filament, as one of the nearest infrared dark clouds, is regarded
as a pristine filament at a very early evolutionary stage of star formation. In
order to study its molecular content and dynamical state, we mapped this
filament in seven species. Among them, HCO, HNC, HCN, and CS show
self-absorption, while CO is most sensitive to the filamentary
structure. A kinematic analysis demonstrates that this filament forms a
velocity-coherent (trans-)sonic structure, a large part of which is one of the
most quiescent regions in the Serpens cloud. Widespread CO depletion is
found throughout the Serpens filament. Based on the Herschel dust-derived
H column density map, the line mass of the filament is
36--41~M~pc, and its full width at half maximum is
0.170.01~pc, while its length is ~1.6~pc. The inner radial column density
profile of this filament can be well fitted with a Plummer profile with an
exponent of 2.20.1, a scale radius of pc, and a central
density of ~cm. The Serpens filament appears
to be slightly supercritical. The widespread blue-skewed HNC and CS line
profiles and HCN hyperfine line anomalies across this filament indicate radial
infall in parts of the Serpens filament. CO velocity gradients also
indicate accretion flows along the filament. The velocity and density
structures suggest that such accretion flows are likely due to a longitudinal
collapse parallel to the filament's long axis. Both the radial infall rate and
the longitudinal accretion rate along the Serpens filament are lower than all
previously reported values in other filaments. This indicates that the Serpens
filament lies at an early evolutionary stage when collapse has just begun, or
that thermal and non-thermal support are effective in providing support against
gravity.Comment: 22 pages, 14 figures, 4 tables, accepted for publication in A&A; for
the draft showing figures with full resolution, see
http://gongyan2444.github.io/pdf/absfil.pd
Steady Vibration of Flexible Circular Plate on an Elastic Half Space
The steady vibration of a flexible circular plate with finite rigidity resting on an elastic half space and subjected to harmonic vertical loads on the surface of the plate is studied in the present paper. The contact between the plate and the half space is assumed to be frictionless. Three types of load are considered: 1. the load uniformly distributed over the entire surface of the plate, 2. the load uniformly distributed over a ring zone of the surface of the plate, 3. the concentrated load applied at the center of the plate. By expanding the distribution of the contact stress between the plate and the half space into a series of the Jacobi polynomials, the problem is reduced to solve a system of simultaneous algebraic equations. The numerical results show that: when the rigidity of the plate is rat her large, the plate behaves like a rigid one, on the other hand, when the flexibility of the plate is rather large, the dynamic behavior of the plate is dependent of the type of the applied load
Non-Gaussianity from false vacuum inflation: Old curvaton scenario
We calculate the three-point correlation function of the comoving curvature
perturbation generated during an inflationary epoch driven by false vacuum
energy. We get a novel false vacuum shape bispectrum, which peaks in the
equilateral limit. Using this result, we propose a scenario which we call "old
curvaton". The shape of the resulting bispectrum lies between the local and the
false vacuum shapes. In addition we have a large running of the spectral index.Comment: 13 pages, 3 figures; v2 with minor revison; v3 final version to
appear on JCA
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