118,785 research outputs found
Sharp bounds on enstrophy growth in the viscous Burgers equation
We use the Cole--Hopf transformation and the Laplace method for the heat
equation to justify the numerical results on enstrophy growth in the viscous
Burgers equation on the unit circle. We show that the maximum enstrophy
achieved in the time evolution is scaled as , where
is the large initial enstrophy, whereas the time needed for
reaching the maximal enstrophy is scaled as . These bounds
are sharp for sufficiently smooth initial conditions.Comment: 12 page
Axial-flow pump design digital computer program
FORTRAN program for computerized design of axial flow pump by blade element analysi
Breaking Symmetries in Graph Representation
There are many complex combinatorial problems
which involve searching for an undirected graph
satisfying a certain property. These problems are
often highly challenging because of the large number
of isomorphic representations of a possible solution.
In this paper we introduce novel, effective
and compact, symmetry breaking constraints for
undirected graph search. While incomplete, these
prove highly beneficial in pruning the search for a
graph. We illustrate the application of symmetry
breaking in graph representation to resolve several
open instances in extremal graph theory
Route planning in a four-dimensional environment
Robots must be able to function in the real world. The real world involves processes and agents that move independently of the actions of the robot, sometimes in an unpredictable manner. A real-time integrated route planning and spatial representation system for planning routes through dynamic domains is presented. The system will find the safest most efficient route through space-time as described by a set of user defined evaluation functions. Because the route planning algorthims is highly parallel and can run on an SIMD machine in O(p) time (p is the length of a path), the system will find real-time paths through unpredictable domains when used in an incremental mode. Spatial representation, an SIMD algorithm for route planning in a dynamic domain, and results from an implementation on a traditional computer architecture are discussed
Identifying the Higgs Spin and Parity in Decays to Z Pairs
Higgs decays to Z boson pairs may be exploited to determine spin and parity
of the Higgs boson, a method complementary to spin-parity measurements in
Higgs-strahlung. For a Higgs mass above the on-shell ZZ decay threshold, a
model-independent analysis can be performed, but only by making use of
additional angular correlation effects in gluon-gluon fusion at the LHC and
gamma-gamma fusion at linear colliders. In the intermediate mass range, in
which the Higgs boson decays into pairs of real and virtual Z bosons, threshold
effects and angular correlations, parallel to Higgs-strahlung, may be adopted
to determine spin and parity, though high event rates will be required for the
analysis in practice.Comment: 14 pages, 2 postscript figure
A Comparison of Intermediate Mass Black Hole Candidate ULXs and Stellar-Mass Black Holes
Cool thermal emission components have recently been revealed in the X-ray
spectra of a small number of ultra-luminous X-ray (ULX) sources with L_X > 1
E+40 erg/s in nearby galaxies. These components can be well fitted with
accretion disk models, with temperatures approximately 5-10 times lower than
disk temperatures measured in stellar-mass Galactic black holes when observed
in their brightest states. Because disk temperature is expected to fall with
increasing black hole mass, and because the X-ray luminosity of these sources
exceeds the Eddington limit for 10 Msun black holes (L_Edd = 1.3 E+39 erg/s),
these sources are extremely promising intermediate-mass black hole candidates
(IMBHCs). In this Letter, we directly compare the inferred disk temperatures
and luminosities of these ULXs, with the disk temperatures and luminosities of
a number of Galactic black holes. The sample of stellar-mass black holes was
selected to include different orbital periods, companion types, inclinations,
and column densities. These ULXs and stellar-mass black holes occupy distinct
regions of a L_X -- kT diagram, suggesting these ULXs may harbor IMBHs. We
briefly discuss the important strengths and weaknesses of this interpretation.Comment: 4 pages, 2 color figures, uses emulateapj.sty and apjfonts.sty, subm.
to ApJ
A fully (3+1)-D Regge calculus model of the Kasner cosmology
We describe the first discrete-time 4-dimensional numerical application of
Regge calculus. The spacetime is represented as a complex of 4-dimensional
simplices, and the geometry interior to each 4-simplex is flat Minkowski
spacetime. This simplicial spacetime is constructed so as to be foliated with a
one parameter family of spacelike hypersurfaces built of tetrahedra. We
implement a novel two-surface initial-data prescription for Regge calculus, and
provide the first fully 4-dimensional application of an implicit decoupled
evolution scheme (the ``Sorkin evolution scheme''). We benchmark this code on
the Kasner cosmology --- a cosmology which embodies generic features of the
collapse of many cosmological models. We (1) reproduce the continuum solution
with a fractional error in the 3-volume of 10^{-5} after 10000 evolution steps,
(2) demonstrate stable evolution, (3) preserve the standard deviation of
spatial homogeneity to less than 10^{-10} and (4) explicitly display the
existence of diffeomorphism freedom in Regge calculus. We also present the
second-order convergence properties of the solution to the continuum.Comment: 22 pages, 5 eps figures, LaTeX. Updated and expanded versio
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