Keijo Hämäläinen

Learn More
The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and(More)
ERKALE is a novel software program for computing X-ray properties, such as ground-state electron momentum densities, Compton profiles, and core and valence electron excitation spectra of atoms and molecules. The program operates at Hartree-Fock or density-functional level of theory and supports Gaussian basis sets of arbitrary angular momentum and a wide(More)
A novel variant of the level set method is introduced for dynamic two-dimensional X-ray tomography. The target is allowed to change in time while being imaged by one or several source-detector pairs at a relatively high frame-rate. The algorithmic approach is motivated by the results in [Kolehmainen et al., SIAM J. Sci. Comput. 30(3)], showing that the(More)
We present experimental and theoretical results on the momentum distribution and the quasiparticle renormalization factor in sodium. From an x-ray Compton-profile measurement of the valence-electron-momentum density, we derive its discontinuity at the Fermi wave vector. This yields an accurate measure of the renormalization factor that we compare with(More)
  • 1