Acknowledgments I would like to take the opportunity to thank all friends and colleagues that have given me support and encouragement in my thesis work. Thank you! My work has been supervised by Bo Bernhardsson and Björn Witten-mark. During the work they have continuously provided me with enthusiasm , vision, and wisdom. They are outstanding researchers to have as role models for a PhD-student....

We present results of ab initio numerical simulations of time delays in two-photon ionization of the helium atom using the attosecond streaking technique. The temporal shifts in the streaking traces consist of two contributions, namely, a time delay acquired during the absorption of the two photons from the extreme-ultraviolet field and a time delay accumulated by the photoelectron after photoa...

Future large ensembles of time delay lenses have the potential to provide interesting cosmological constraints complementary to those of other methods. In a flat universe with constant w including a Planck prior, LSST time delay measurements for ∼ 4, 000 lenses should constrain h to ∼ 0.007 (∼ 1%), Ωde to ∼ 0.005, and w to ∼ 0.026 (all 1-σ precisions). Similar constraints could be obtained by a...

A general (Volterra-Lotka type) integrodifferential system which describes a predator-prey interaction subject to delay effects is considered. A rather complete picture is drawn of certain qualitative aspects of the solutions as they are functions of the parameters in the system. Namely, it is argued that such systems have, roughly speaking, the following features. If the carrying capacity of t...