405 research outputs found
Prehistoric Migrations: the Case of the Single Grave and Corded Ware Cultures
Prehistoric Migrations - the Case of the Single Grave and Corded Ware Culture
Rescue Archaeology in Denmark 1970-1982
Rescue Archaeology in Denmark 1970-198
An iterative method for the approximation of fibers in slow-fast systems
In this paper we extend a method for iteratively improving slow manifolds so
that it also can be used to approximate the fiber directions. The extended
method is applied to general finite dimensional real analytic systems where we
obtain exponential estimates of the tangent spaces to the fibers. The method is
demonstrated on the Michaelis-Menten-Henri model and the Lindemann mechanism.
The latter example also serves to demonstrate the method on a slow-fast system
in non-standard slow-fast form. Finally, we extend the method further so that
it also approximates the curvature of the fibers.Comment: To appear in SIAD
Canards in stiction: on solutions of a friction oscillator by regularization
We study the solutions of a friction oscillator subject to stiction. This
discontinuous model is non-Filippov, and the concept of Filippov solution
cannot be used. Furthermore some Carath\'eodory solutions are unphysical.
Therefore we introduce the concept of stiction solutions: these are the
Carath\'eodory solutions that are physically relevant, i.e. the ones that
follow the stiction law. However, we find that some of the stiction solutions
are forward non-unique in subregions of the slip onset. We call these solutions
singular, in contrast to the regular stiction solutions that are forward
unique. In order to further the understanding of the non-unique dynamics, we
introduce a regularization of the model. This gives a singularly perturbed
problem that captures the main features of the original discontinuous problem.
We identify a repelling slow manifold that separates the forward slipping to
forward sticking solutions, leading to a high sensitivity to the initial
conditions. On this slow manifold we find canard trajectories, that have the
physical interpretation of delaying the slip onset. We show with numerics that
the regularized problem has a family of periodic orbits interacting with the
canards. We observe that this family has a saddle stability and that it
connects, in the rigid body limit, the two regular, slip-stick branches of the
discontinuous problem, that were otherwise disconnected.Comment: Submitted to: SIADS. 28 pages, 12 figure
Revised WMAP constraints on neutrino masses and other extensions of the minimal CDM model
Recently, two issues concerning the three-year WMAP likelihood code were
pointed out. On large angular scales (), a sub-optimal
likelihood approximation resulted in a small power excess. On small angular
scales (), over-subtraction of unresolved point sources produced
a small power deficit. For a minimal six-parameter cosmological model, these
two effects conspired to decrease the value of by . In
this paper, we study the change in preferred parameter ranges for more
extensive cosmological models, including running of , massive neutrinos,
curvature, and the equation of state for dark energy. We also include
large-scale structure and supernova data in our analysis. We find that the
parameter ranges for , and are not much altered by the
modified analysis. For massive neutrinos the upper limit on the sum of the
neutrino masses decreases from eV to eV when using
the modified WMAP code and WMAP data only. We also find that the shift of
to higher values is quite robust to these extensions of the minimal
cosmological model.Comment: 7 pages. Matching version published in Physical Review D. Figures
changed, references added, additional comment
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