59,170 research outputs found
Tidal stability of giant molecular clouds in the Large Magellanic Cloud
Star formation does not occur until the onset of gravitational collapse
inside giant molecular clouds. However, the conditions that initiate cloud
collapse and regulate the star formation process remain poorly understood.
Local processes such as turbulence and magnetic fields can act to promote or
prevent collapse. On larger scales, the galactic potential can also influence
cloud stability and is traditionally assessed by the tidal and shear effects.
In this paper, we examine the stability of giant molecular clouds (GMCs) in the
Large Magellanic Cloud (LMC) against shear and the galactic tide using CO data
from the Magellanic Mopra Assessment (MAGMA) and rotation curve data from the
literature. We calculate the tidal acceleration experienced by individual GMCs
and determine the minimum cloud mass required for tidal stability. We also
calculate the shear parameter, which is a measure of a clouds susceptibility to
disruption via shearing forces in the galactic disk. We examine whether there
are correlations between the properties and star forming activity of GMCs and
their stability against shear and tidal disruption. We find that the GMCs are
in approximate tidal balance in the LMC, and that shear is unlikely to affect
their further evolution. GMCs with masses close to the minimal stable mass
against tidal disruption are not unusual in terms of their mass, location, or
CO brightness, but we note that GMCs with large velocity dispersion tend to be
more sensitive to tidal instability. We also note that GMCs with smaller radii,
which represent the majority of our sample, tend to more strongly resist tidal
and shear disruption. Our results demonstrate that star formation in the LMC is
not inhibited by to tidal or shear instability.Comment: 18 pages, 10 Figures, Accepted in PAS
Implementation of uniform perturbation method for potential flow past axisymmetric and two-dimensional bodies
The aerodynamic characteristics of potential flow past an axisymmetric slender body and a thin airfoil are calculated using a uniform perturbation analysis method. The method is based on the superposition of potentials of point singularities distributed inside the body. The strength distribution satisfies a linear integral equation by enforcing the flow tangency condition on the surface of the body. The complete uniform asymptotic expansion of its solution is obtained with respect to the slenderness ratio by modifying and adapting an existing technique. Results calculated by the perturbation analysis method are compared with the existing surface singularity panel method and some available analytical solutions for a number of cases under identical conditions. From these comparisons, it is found that the perturbation analysis method can provide quite accurate results for bodies with small slenderness ratio. The present method is much simpler and requires less memory and computation time than existing surface singularity panel methods of comparable accuracy
Heavy Quarkonium Dissociation Cross Sections in Relativistic Heavy-Ion Collisions
Many of the hadron-hadron cross sections required for the study of the
dynamics of matter produced in relativistic heavy-ion collisions can be
calculated using the quark-interchange model. Here we evaluate the low-energy
dissociation cross sections of , , , , and
in collision with , , and , which are important for
the interpretation of heavy-quarkonium suppression as a signature for the quark
gluon plasma. These comover dissociation processes also contribute to
heavy-quarkonium suppression, and must be understood and incorporated in
simulations of heavy-ion collisions before QGP formation can be established
through this signature.Comment: 38 pages, in LaTe
Constraints on Dark Photon from Neutrino-Electron Scattering Experiments
A possible manifestation of an additional light gauge boson , named
as Dark Photon, associated with a group is studied in neutrino
electron scattering experiments. The exclusion plot on the coupling constant
and the dark photon mass is obtained. It is shown
that contributions of interference term between the dark photon and the
Standard Model are important. The interference effects are studied and compared
with for data sets from TEXONO, GEMMA, BOREXINO, LSND as well as CHARM II
experiments. Our results provide more stringent bounds to some regions of
parameter space.Comment: 22 pages, 6 figures, 2 tables, text improved, fig.6 updated,
references adde
Covariant hamiltonian dynamics
We discuss the covariant formulation of the dynamics of particles with
abelian and non-abelian gauge charges in external fields. Using this
formulation we develop an algorithm for the construction of constants of
motion, which makes use of a generalization of the concept of Killing vectors
and tensors in differential geometry. We apply the formalism to the motion of
classical charges in abelian and non-abelian monopole fieldsComment: 15 pages, no figure
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