3,144 research outputs found
Simulations of spiral galaxies with an active potential: molecular cloud formation and gas dynamics
We describe simulations of the response of a gaseous disc to an active spiral
potential. The potential is derived from an N-body calculation and leads to a
multi-armed time-evolving pattern. The gas forms long spiral arms typical of
grand design galaxies, although the spiral pattern is asymmetric. The primary
difference from a grand-design spiral galaxy, which has a consistent 2/4-armed
pattern, is that instead of passing through the spiral arms, gas generally
falls into a developing potential minimum and is released only when the local
minimum dissolves. In this case, the densest gas is coincident with the spiral
potential, rather than offset as in the grand-design spirals. We would there
fore expect no offset between the spiral shock and star formation, and no
obvious co-rotation radius. Spurs which occur in grand-design spirals when
large clumps are sheared off leaving the spiral arms, are rare in the active,
time-evolving spiral reported here. Instead, large branches are formed from
spiral arms when the underlying spiral potential is dissolving due to the
N-body dynamics. We find that the molecular cloud mass spectrum for the active
potential is similar to that for clouds in grand design calculations, depending
primarily on the ambient pressure rather than the nature of the potential. The
largest molecular clouds occur when spiral arms collide, rather than by
agglomeration within a spiral arm.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Sex and the preimplantation embryo: implications of sexual dimorphism in the preimplantation period for maternal programming of embryonic development.
201
Epitaxial Growth Kinetics with Interacting Coherent Islands
The Stranski-Krastanov growth kinetics of undislocated (coherent)
3-dimensional islands is studied with a self-consistent mean field rate theory
that takes account of elastic interactions between the islands. The latter are
presumed to facilitate the detachment of atoms from the islands with a
consequent decrease in their average size. Semi-quantitative agreement with
experiment is found for the time evolution of the total island density and the
mean island size. When combined with scaling ideas, these results provide a
natural way to understand the often-observed initial increase and subsequent
decrease in the width of the coherent island size distribution.Comment: 4 pages, 4 figure
Factors Predictive of Outcome after Use of the Ponseti Method for the Treatment of Idiopathic Clubfeet
Use of an intramedullary rod for treatment of congenital pseudarthrosis of the tibia: A long-term follow-up study
Generic User Process Interface for Event Generators
Generic Fortran common blocks are presented for use by High Energy Physics
event generators for the transfer of event configurations from parton level
generators to showering and hadronization event generators.Comment: Physics at TeV Colliders II Workshop, Les Houches, France, May 2001
14 pages, 6 figure
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