90 research outputs found
Improved model for the topological soliton-potential interaction in Phi^4 Model
An improved model for the soliton-potential interaction is presented. This
model is constructed with a better approximation for adding the potential to
the lagrangian through a space-time metric. The results of the model are
compared with other models and the differences are discussed.Comment: 8 pages, 11 figure
Why not a di-NUT? or Gravitational duality and rotating solutions
We study how gravitational duality acts on rotating solutions, using the
Kerr-NUT black hole as an example. After properly reconsidering how to take
into account both electric (i.e. mass-like) and magnetic (i.e. NUT-like)
sources in the equations of general relativity, we propose a set of definitions
for the dual Lorentz charges. We then show that the Kerr-NUT solution has
non-trivial such charges. Further, we clarify in which respect Kerr's source
can be seen as a mass M with a dipole of NUT charges.Comment: 20 pages. v2: minor clarifications in section 4, version to appear in
PR
Interaction of topological solitons with defects: using a nontrivial metric
By including potential into the flat metric, we study interaction of
sine-Gordon soliton with potentials. We will show numerically that while the
soliton-barrier system shows fully classical behaviour, the soliton-well system
demonstrates non-classical behaviour. In particular, solitons with low
velocities are trapped in the well and emit energy radiation.Comment: 10 pages, 11 figure
Analytical formulation for soliton-potential dynamics
An analytical model for the soliton-potential interaction is presented, by
constructing a collective coordinate for the system. Most of the characters of
the interaction are derived analytically while they are calculated by other
models numerically. We will find that the behaviour of the soliton is like a
point particle living under the influence of a complicated potential which is a
function of soliton velocity and the potential parameters. The analytic model
does not have a clear prediction for the islands of initial velocities in which
the soliton may reflect back or escape over the potential well.Comment: 12 pages, 10 figure
Electromagnetic Casimir piston in higher dimensional spacetimes
We consider the Casimir effect of the electromagnetic field in a higher
dimensional spacetime of the form , where is the
4-dimensional Minkowski spacetime and is an -dimensional
compact manifold. The Casimir force acting on a planar piston that can move
freely inside a closed cylinder with the same cross section is investigated.
Different combinations of perfectly conducting boundary conditions and
infinitely permeable boundary conditions are imposed on the cylinder and the
piston. It is verified that if the piston and the cylinder have the same
boundary conditions, the piston is always going to be pulled towards the closer
end of the cylinder. However, if the piston and the cylinder have different
boundary conditions, the piston is always going to be pushed to the middle of
the cylinder. By taking the limit where one end of the cylinder tends to
infinity, one obtains the Casimir force acting between two parallel plates
inside an infinitely long cylinder. The asymptotic behavior of this Casimir
force in the high temperature regime and the low temperature regime are
investigated for the case where the cross section of the cylinder in is
large. It is found that if the separation between the plates is much smaller
than the size of , the leading term of the Casimir force is the
same as the Casimir force on a pair of large parallel plates in the
-dimensional Minkowski spacetime. However, if the size of
is much smaller than the separation between the plates, the leading term of the
Casimir force is times the Casimir force on a pair of large parallel
plates in the 4-dimensional Minkowski spacetime, where is the first Betti
number of . In the limit the manifold vanishes, one
does not obtain the Casimir force in the 4-dimensional Minkowski spacetime if
is nonzero.Comment: 22 pages, 4 figure
Rapport fra igangværende forskningsprojekt om alt det vi ikke ved, men burde vide om de sidste 20 års regel-udvikling i Danmark
Det er kendetegnende for debatten om regeludviklingen både i dag og tidligere, at den mere bygger på fornemmelser og oplevede udviklinger end på en systematisk afdækning af den faktiske udvikling. Der er derfor behov for en mere præcis beskrivelse af udviklingen i regelomfanget i Danmark over tid og på tværs af forskellige politikområder samt ikke mindst mere helhjertede og systematiske forsøg på at forklare, hvilke faktorer der driver denne udvikling. Et nyt forskningsprojekt beskriver systematisk den faktiske udvikling i regelomfanget i Danmark
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