From Now to Timelike Infinity on a Finite Grid

We use the conformal approach to numerical relativity to evolve hyperboloidal gravitational wave data without any symmetry assumptions. Although our grid is finite in space and time, we cover the whole future of the initial data in our calculation, including future null and future timelike infinity.Comment: 15 pages, 14 figures, revtex

On Killing vectors in initial value problems for asymptotically flat space-times

The existence of symmetries in asymptotically flat space-times are studied from the point of view of initial value problems. General necessary and sufficient (implicit) conditions are given for the existence of Killing vector fields in the asymptotic characteristic and in the hyperboloidal initial value problem (both of them are formulated on the conformally compactified space-time manifold)

On the Effect of Constraint Enforcement on the Quality of Numerical Solutions in General Relativity

In Brodbeck et al 1999 it has been shown that the linearised time evolution equations of general relativity can be extended to a system whose solutions asymptotically approach solutions of the constraints. In this paper we extend the non-linear equations in similar ways and investigate the effect of various possibilities by numerical means. Although we were not able to make the constraint submanifold an attractor for all solutions of the extended system, we were able to significantly reduce the growth of the numerical violation of the constraints. Contrary to our expectations this improvement did not imply a numerical solution closer to the exact solution, and therefore did not improve the quality of the numerical solution.Comment: 14 pages, 9 figures, accepted for publication in Phys. Rev.

Femtosecond electron and spin dynamics probed by nonlinear optics

A theoretical calculation is performed for the ultrafast spin dynamics in nickel using an exact diagonalization method. The present theory mainly focuses on a situation where the intrinsic charge and spin dynamics is probed by the nonlinear (magneto-)optical responses on the femtosecond time scale, i.e. optical second harmonic generation (SHG) and the nonlinear magneto-optical Kerr effect (NOLIMOKE). It is found that the ultrafast charge and spin dynamics are observable on the time scale of 10 fs. The charge dynamics proceeds ahead of the spin dynamics, which indicates the existence of a spin memory time. The fast decay results from the loss of coherence in the initial excited state. Both the material specific and experimental parameters affect the dynamics. We find that the increase of exchange interaction mainly accelerates the spin dynamics rather than the charge dynamics. A reduction of the hopping integrals, such as present at interfaces, slows down the spin dynamics significantly. Besides, it is found that a spectrally broad excitation yields the intrinsic speed limit of the charge (SHG) and spin dynamics (NOLIMOKE) while a narrower width prolongs the dynamics. This magnetic interface dynamics then should become accessible to state of art time resolved nonlinear-optical experiments.Comment: 5 pages with 3 figures, to appear in Applied. Phys. B 68, (1999

Nonlinear Magneto-Optics of freestanding Fe monolayers from first principles

The nonlinear magneto-optical Kerr-effect (NOLIMOKE) is determined for freestanding Fe monolayers with several in-plane structures from first principles. Based on the theory of nonlinear magneto-optics by H\"ubner and Bennemann [Phys. Rev. B, {\bf 40}, 5973 (1989)] we calculate the nonlinear susceptibilities of the monolayers using the ab initio FLAPW-method WIEN95 with the additional implementation of spin-orbit coupling and the calculation of the dipole transition matrix elements appropriate for freestanding monolayers. We present results for the spectral dependence of the nonlinear susceptibility tensor elements and the resulting intensities and Kerr angles. Special emphasize is put on the effects of structural changes such as the variation of the lattice constant and different surface orientations. The influence of spin-orbit coupling on the tensor elements for different magnetization directions is presented as well as the azimuthal dependence of the intensities generated by several low index surfaces, showing the pronounced sensitivity of second harmonic generation to lateral structural changes as well as magnetic properties even in the monolayer range

A Scheme to Numerically Evolve Data for the Conformal Einstein Equation

This is the second paper in a series describing a numerical implementation of the conformal Einstein equation. This paper deals with the technical details of the numerical code used to perform numerical time evolutions from a "minimal" set of data. We outline the numerical construction of a complete set of data for our equations from a minimal set of data. The second and the fourth order discretisations, which are used for the construction of the complete data set and for the numerical integration of the time evolution equations, are described and their efficiencies are compared. By using the fourth order scheme we reduce our computer resource requirements --- with respect to memory as well as computation time --- by at least two orders of magnitude as compared to the second order scheme.Comment: 20 pages, 12 figure

Local twistors and the conformal field equations

This note establishes the connection between Friedrich's conformal field equations and the conformally invariant formalism of local twistors.Comment: LaTeX2e Minor corrections of misprints et

Numerical Calculation of Conformally Smooth Hyperboloidal Data

This is the third paper in a series describing a numerical implementation of the conformal Einstein equation. This paper describes a scheme to calculate (three) dimensional data for the conformal field equations from a set of free functions. The actual implementation depends on the topology of the spacetime. We discuss the implementation and exemplary calculations for data leading to spacetimes with one spherical null infinity (asymptotically Minkowski) and for data leading to spacetimes with two toroidal null infinities (asymptotically A3). We also outline the (technical) modifications of the implementation needed to calculate data for spacetimes with two and more spherical null infinities (asymptotically Schwarzschild and asymptotically multiple black holes)

The glucocorticoid receptor in inflammatory processes : transrepression is not enough

Glucocorticoids (GCs) are the most commonly used anti-inflammatory agents to treat inflammatory and immune diseases. However, steroid therapies are accompanied by severe side-effects during long-term treatment. The dogma that transrepression of genes, by tethering of the glucocorticoid receptor (GR) to DNA-bound pro-inflammatory transcription factors, is the main anti-inflammatory mechanism, is now challenged. Recent discoveries using conditional GR mutant mice and genomic approaches reveal that transactivation of anti-inflammatory acting genes is essential to suppress many inflammatory disease models. This novel view radically changes the concept to design selective acting GR ligands with a reduced side-effect profile

Closing the gap between spatial and spin dynamics of electrons at the metal-to-insulator transition

We combine extensive precision measurements of the optically detected spin dynamics and magneto-transport measurements in a contiguous set of n-doped bulk GaAs structures in order to unambiguously unravel the intriguing but complex contributions to the spin relaxation at the metal-to-insulator transition (MIT). Just below the MIT, the interplay between hopping induced loss of spin coherence and hyperfine interaction yields a maximum spin lifetime exceeding 800~ns. At slightly higher doping concentrations, however, the spin relaxation deviates from the expected Dyakonov-Perel mechanism which is consistently explained by a reduction of the effective motional narrowing with increasing doping concentration. The reduction is attributed to the change of the dominant momentum scattering mechanism in the metallic impurity band where scattering by local conductivity domain boundaries due to the intrinsic random distribution of donors becomes significant. Here, we fully identify and model all intricate contributions of the relevant microscopic scattering mechanisms which allows the complete quantitative modeling of the electron spin relaxation in the entire regime from weakly interacting up to fully delocalized electrons