8,887 research outputs found
Bifurcations and Complete Chaos for the Diamagnetic Kepler Problem
We describe the structure of bifurcations in the unbounded classical
Diamagnetic Kepler problem. We conjecture that this system does not have any
stable orbits and that the non-wandering set is described by a complete trinary
symbolic dynamics for scaled energies larger then .Comment: 15 pages PostScript uuencoded with figure
Analysis of stochastic time series in the presence of strong measurement noise
A new approach for the analysis of Langevin-type stochastic processes in the
presence of strong measurement noise is presented. For the case of Gaussian
distributed, exponentially correlated, measurement noise it is possible to
extract the strength and the correlation time of the noise as well as
polynomial approximations of the drift and diffusion functions from the
underlying Langevin equation.Comment: 12 pages, 10 figures; corrected typos and reference
The Energy-Momentum tensor on manifolds
On manifolds, we study the Energy-Momentum tensor associated with a
spinor field. First, we give a spinorial Gauss type formula for oriented
hypersurfaces of a manifold. Using the notion of generalized
cylinders, we derive the variationnal formula for the Dirac operator under
metric deformation and point out that the Energy-Momentum tensor appears
naturally as the second fundamental form of an isometric immersion. Finally, we
show that generalized Killing spinors for Codazzi Energy-Momentum
tensor are restrictions of parallel spinors.Comment: To appear in IJGMMP (International Journal of Geometric Methods in
Modern Physics), 22 page
Clusters under strong VUV pulses: A quantum-classical hybrid-description incorporating plasma effects
The quantum-classical hybrid-description of rare-gas clusters interacting
with intense light pulses which we have developed is described in detail. Much
emphasis is put on the treatment of screening electrons in the cluster which
set the time scale for the evolution of the system and form the link between
electrons strongly bound to ions and quasi-free plasma electrons in the
cluster. As an example we discuss the dynamics of an Ar147 cluster exposed to a
short VUV laser pulse of 20eV photon energy.Comment: 8 pages, 9 figure
Numerical treatment of the hyperboloidal initial value problem for the vacuum Einstein equations. I. The conformal field equations
This is the first in a series of articles on the numerical solution of
Friedrich's conformal field equations for Einstein's theory of gravity. We will
discuss in this paper why one should be interested in applying the conformal
method to physical problems and why there is good hope that this might even be
a good idea from the numerical point of view. We describe in detail the
derivation of the conformal field equations in the spinor formalism which we
use for the implementation of the equations, and present all the equations as a
reference for future work. Finally, we discuss the implications of the
assumptions of a continuous symmetry.Comment: 19 pages, LaTeX2
On the existence of Killing vector fields
In covariant metric theories of coupled gravity-matter systems the necessary
and sufficient conditions ensuring the existence of a Killing vector field are
investigated. It is shown that the symmetries of initial data sets are
preserved by the evolution of hyperbolic systems.Comment: 9 pages, no figure, to appear in Class. Quant. Gra
3D simulations of Einstein's equations: symmetric hyperbolicity, live gauges and dynamic control of the constraints
We present three-dimensional simulations of Einstein equations implementing a
symmetric hyperbolic system of equations with dynamical lapse. The numerical
implementation makes use of techniques that guarantee linear numerical
stability for the associated initial-boundary value problem. The code is first
tested with a gauge wave solution, where rather larger amplitudes and for
significantly longer times are obtained with respect to other state of the art
implementations. Additionally, by minimizing a suitably defined energy for the
constraints in terms of free constraint-functions in the formulation one can
dynamically single out preferred values of these functions for the problem at
hand. We apply the technique to fully three-dimensional simulations of a
stationary black hole spacetime with excision of the singularity, considerably
extending the lifetime of the simulations.Comment: 21 pages. To appear in PR
A semiclassical analysis of the Efimov energy spectrum in the unitary limit
We demonstrate that the (s-wave) geometric spectrum of the Efimov energy
levels in the unitary limit is generated by the radial motion of a primitive
periodic orbit (and its harmonics) of the corresponding classical system. The
action of the primitive orbit depends logarithmically on the energy. It is
shown to be consistent with an inverse-squared radial potential with a lower
cut-off radius. The lowest-order WKB quantization, including the Langer
correction, is shown to reproduce the geometric scaling of the energy spectrum.
The (WKB) mean-squared radii of the Efimov states scale geometrically like the
inverse of their energies. The WKB wavefunctions, regularized near the
classical turning point by Langer's generalized connection formula, are
practically indistinguishable from the exact wave functions even for the lowest
() state, apart from a tiny shift of its zeros that remains constant for
large .Comment: LaTeX (revtex 4), 18pp., 4 Figs., already published in Phys. Rev. A
but here a note with a new referece is added on p. 1
Improvement of lung preservation - From experiment to clinical practice
Background. Reperfusion injury represents a severe early complication following lung transplantation. Among the pathogenetic factors, the high potassium content of Euro-Collins(R) solution is discussed. Material and Methods: In a pig model of orthotopic left-sided lung transplantation we investigated the effect of Euro-Collins solution (EC: n=6) versus low potassium dextran (LPD: Perfadex(R): n = 6). Sham-operated (n = 6) animals served as control. Transplant function, cellular energy metabolism and endothelial morphology served as parameters. In a clinical investigation, 124 patients were evaluated following single (EC: n = 31; LPD n = 37) or double (EC: n = 17; LPD n = 39) lung transplantation, whose organs where preserved with EC (n = 48) or LPD (n = 76). Duration of ischemia, duration of ventilation and stay on ICU were registered. Primary transplant function was evaluated according to AaDO(2) values. Cause of early death (30 days) was declared. Results: Experimental results: After flush with EC and 18 h ischemia, a reduction of tissue ATP content (p < 0.01 vs inital value and LPD) was noted. Endothelial damage after ischemia was severe (p < 0.05 vs control), paO(2) was significantly decreased. Clinical results: In the LPD group, duration of ischemia was longer for the grafts transplanted first (SLTx and DLTx: p = 0.0009) as well as second (2. organ DLTx: p = 0.045). Primary transplant function was improved (day 0: SLTx: p = 0.0015; DLTx: p = 0.0095, both vs EC). Duration of ventilation and stay on ICU were shorter (n.s.). Reperfusion injury-associated death was reduced from 8% (EC) to 0 (LPD). Conclusion: In experimental lung preservation, LPD lead to an improved graft function. These results were confirmed in clinical lung transplantation. Clinical lung preservation, therefore, should be carried out by use of LPD. Copyright (C) 2002 S. Karger AG, Basel
Numerical evolution of axisymmetric, isolated systems in General Relativity
We describe in this article a new code for evolving axisymmetric isolated
systems in general relativity. Such systems are described by asymptotically
flat space-times which have the property that they admit a conformal extension.
We are working directly in the extended `conformal' manifold and solve
numerically Friedrich's conformal field equations, which state that Einstein's
equations hold in the physical space-time. Because of the compactness of the
conformal space-time the entire space-time can be calculated on a finite
numerical grid. We describe in detail the numerical scheme, especially the
treatment of the axisymmetry and the boundary.Comment: 10 pages, 8 figures, uses revtex4, replaced with revised versio
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