5,379 research outputs found
Weyl Expansion for Symmetric Potentials
We present a semiclassical expansion of the smooth part of the density of
states in potentials with some form of symmetry. The density of states of each
irreducible representation is separately evaluated using the Wigner transforms
of the projection operators. For discrete symmetries the expansion yields a
formally exact but asymptotic series in , while for the rotational
symmetries the expansion requires averaging over angular momentum as
well as energy. A numerical example is given in two dimensions, in which we
calculate the leading terms of the Weyl expansion as well as the leading
periodic orbit contributions to the symmetry reduced level density.Comment: Four of the five figures are appended as a postscript file. The fifth
figure is available by snail mail
Engineering a Conformant Probabilistic Planner
We present a partial-order, conformant, probabilistic planner, Probapop which
competed in the blind track of the Probabilistic Planning Competition in IPC-4.
We explain how we adapt distance based heuristics for use with probabilistic
domains. Probapop also incorporates heuristics based on probability of success.
We explain the successes and difficulties encountered during the design and
implementation of Probapop
Geometric and Diffractive Orbits in the Scattering from Confocal Hyperbolae
We study the scattering resonances between two confocal hyperbolae and show
that the spectrum is dominated by the effect of a single periodic orbit. There
are two distinct cases depending on whether the orbit is geometric or
diffractive. A generalization of periodic orbit theory allows us to incorporate
the second possibility. In both cases we also perform a WKB analysis. Although
it is found that the semiclassical approximations work best for resonances with
large energies and narrow widths, there is reasonable agreement even for
resonances with large widths - unlike the two disk scatterer. We also find
agreement with the next order correction to periodic orbit theory.Comment: Written in RevTeX. After \end{document} comes a uuencoded .ps file
with two figure
First Direct Simulation of Brown Dwarf Formation in a Compact Cloud Core
Brown dwarf formation and star formation efficiency are studied using a
nested grid simulation that covers five orders of magnitude in spatial scale
(10^4 - 0.1AU). Starting with a rotating magnetized compact cloud with a mass
of 0.22 M_sun, we follow the cloud evolution until the end of main accretion
phase. Outflow of about 5 km/s emerges about 100 yr before the protostar
formation and does not disappear until the end of the calculation. The mass
accretion rate declines from 10^-6 M_sun/yr to 10^-8 - 10^-12 M_sun/yr in a
short time (about 10^4 yr) after the protostar formation. This is because (1) a
large fraction of mass is ejected from the host cloud by the protostellar
outflow and (2) the gas escapes from the host cloud by the thermal pressure. At
the end of the calculation, 74% (167 M_Jup) of the total mass (225 M_Jup) is
outflowing from the protostar, in which 34% (77 M_Jup) of the total mass is
ejected by the protostellar outflow with supersonic velocity and 40% (90 M_Jup)
escapes with subsonic velocity. On the other hand, 20% (45 M_Jup) is converted
into the protostar and 6% (13 M_Jup) remains as the circumstellar disk. Thus,
the star formation efficiency is epsilon = 0.2. The resultant protostellar mass
is in the mass range of brown dwarfs. Our results indicate that brown dwarfs
can be formed in compact cores in the same manner as hydrogen-burning stars,
and the magnetic field and protostellar outflow are essential in determining
the star formation efficiency and stellar mass.Comment: 13 pages, 3 figures. Accepted for publication in ApJL. For high
resolution figures, see
http://www2-tap.scphys.kyoto-u.ac.jp/~machidam/astro-ph/BD.pd
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