Recent results in compressed sensing or compressive sampling suggest that a relatively small set of measurements taken as the inner product with universal random measurement vectors can well represent a source that is sparse in some fixed basis. By adapting a deterministic, non-universal and structured sensing device, this paper presents results on using the annihilating filter to decode the in...

PURPOSE MR measurements from an echo-planar imaging (EPI) sequence produce Nyquist ghost artifacts that originate from inconsistencies between odd and even echoes. Several reconstruction algorithms have been proposed to reduce such artifacts, but most of these methods require either additional reference scans or multipass EPI acquisition. This article proposes a novel and accurate single-pass E...

Beyond reionization epoch cosmic hydrogen is neutral and can be directly observed through its 21 cm line signal. If dark matter (DM) decays or annihilates the corresponding energy input affects the hydrogen kinetic temperature and ionized fraction, and contributes to the Lyα background. The changes induced by these processes on the 21 cm signal can then be used to constrain the proposed DM cand...

An integral approach to phase measurement is presented. First, the use of a high-resolution technique for the pixelwise detection of phase steps is proposed. Next, the robustness of the algorithm that is developed is improved by incorporation of a denoising procedure during spectral estimation. The pixelwise knowledge of phase steps is then applied to the Vandermonde system of equations for ret...

We have applied positron annihilation spectroscopy to study in-grown vacancy defects in bulk aluminium nitride (AlN) crystals grown by physical vapor transport. We interpret the lowest lifetime value of about 155ps, measured at low temperatures, to represent the annihilations from the free state of the positron in the crystal lattice. The increased lifetime at high temperatures is an indication...

Note: This paper is the full version of Blath, Etheridge & Meredith (2007). It has also successfully undergone the peer-reviewing process of Annals of Applied Probability, but proved too long to be published in its entirety. It contains full technical details and additional remarks. We propose two models of the evolution of a pair of competing populations. Both are lattice based. The first is a...

A theory for calculating the momentum distribution of annihilating positron-electron pairs in solids is presented. To test the theory, momentum distributions are measured by the Doppler broadening of the annihilation radiation for several bulk metals and semiconductors, as well as for semiconductor alloys and for positrons trapped at vacancies in semiconductors. The theory is based on a two-par...