3,562 research outputs found
Closed Form Expression for the Momentum Radiated from Cosmic String Loops
We modify the recent analytic formula given by Allen and Casper for the rate
at which piecewise linear cosmic string loops lose energy to gravitational
radiation to yield the analogous analytic formula for the rate at which loops
radiate momentum. The resulting formula (which is exact when the effects of
gravitational back-reaction are neglected) is a sum of O(N^4) polynomial and
log terms where, N is the total number of segments on the piecewise linear
string loop. As illustration, we write the formula explicitly for a simple
one-parameter family of loops with N=5. For most loops the large number of
terms makes evaluation ``by hand" impractical, but, a computer or symbolic
manipulator may by used to yield accurate results. The formula has been used to
correct numerical results given in the existing literature. To assist future
work in this area, a small catalog of results for a number of simple string
loops is provided.Comment: 17 pages, RevTex 3.0, 3 postscript figures and C-language computer
code available via anonymous ftp from directory pub/pcasper at
alpha1.csd.uwm.edu, WISC-MILW-94-TH-1
Video conferencing in the classroom: case studies of effective practice, case study one: Lent Rise Combined School
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Waveforms for Gravitational Radiation from Cosmic String Loops
We obtain general formulae for the plus- and cross- polarized waveforms of
gravitational radiation emitted by a cosmic string loop in transverse,
traceless (synchronous, harmonic) gauge. These equations are then specialized
to the case of piecewise linear loops, and it is shown that the general
waveform for such a loop is a piecewise linear function. We give several simple
examples of the waveforms from such loops. We also discuss the relation between
the gravitational radiation by a smooth loop and by a piecewise linear
approximation to it.Comment: 16 pages, 6 figures, Revte
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A highly scalable Met Office NERC Cloud model
Large Eddy Simulation is a critical modelling tool for scien- tists investigating atmospheric flows, turbulence and cloud microphysics. Within the UK, the principal LES model used by the atmospheric research community is the Met Office Large Eddy Model (LEM). The LEM was originally devel- oped in the late 1980s using computational techniques and assumptions of the time, which means that the it does not scale beyond 512 cores. In this paper we present the Met Office NERC Cloud model, MONC, which is a re-write of the existing LEM. We discuss the software engineering and architectural decisions made in order to develop a flexible, extensible model which the community can easily customise for their own needs. The scalability of MONC is evaluated, along with numerous additional customisations made to fur- ther improve performance at large core counts. The result of this work is a model which delivers to the community signifi- cant new scientific modelling capability that takes advantage of the current and future generation HPC machine
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