Biomedical subjects

Katrin Heitmann

Publications and source records attributed to Katrin Heitmann.

3 recordsLinked to original sources

PubMed2005

Inverse-scattering theory and the density perturbations from inflation.

We show how to use inverse-scattering theory as the basis for the inflationary reconstruction program, the goal of which is to gain information about the physics which drives inflation. Inverse-scattering theory provides an effective and well-motivated procedure, having a sound mathematical basis and being of sufficient generality that it can be considered the foundation for a nonparametric reconstruction program. We show how simple properties of the power spectrum translate directly into statements about the evolution of the background geometry during inflation.

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PubMed2004

Nonlinear and nonequilibrium dynamics in geomaterials.

The transition from linear to nonlinear dynamical elasticity in rocks is of considerable interest in seismic wave propagation as well as in understanding the basic dynamical processes in consolidated granular materials. We have carried out a careful experimental investigation of this transition for Berea and Fontainebleau sandstones. Below a well-characterized strain, the materials behave linearly, transitioning beyond that point to a nonlinear behavior which can be accurately captured by a simple macroscopic dynamical model. At even higher strains, effects due to a driven nonequilibrium state, and relaxation from it, complicate the characterization of the nonlinear behavior.

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PubMed2002

The inflationary perturbation spectrum.

Motivated by the prospect of testing inflation from precision cosmic microwave background observations, we present analytic results for scalar and tensor perturbations in single-field inflation models, based on the application of uniform approximations. This technique is systematically improvable, possesses controlled error bounds, and does not rely on assuming the slow-roll parameters to be constant. We provide closed form expressions for the power spectra and the corresponding scalar and tensor spectral indices.

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