Elliptical Distance Transforms And Object Splitting

The classical morphological method to separate fused objects in binary images is to use the watershed transform on the complement of the distance transform of the binary image. This method assumes roughly disk-like objects and cannot separate objects when they are fused together beyond a certain point. In this paper we revisit the issue by assuming that fused objects are unions of ellipses rather than mere disks. The problem is recast in terms of finding the constituent primary grains given a boolean model of ellipses. To this end, we modify the well-known pseudo-Euclidean distance transform algorithm to generate arbitrary elliptical distance transforms to reduce the dimension of the problem and we present a goodness-of-fit measure that allows us to select ellipses. The results of the methods are given on both synthetic sample boolean models and real data

An electron Talbot interferometer

The Talbot effect, in which a wave imprinted with transverse periodicity reconstructs itself at regular intervals, is a diffraction phenomenon that occurs in many physical systems. Here we present the first observation of the Talbot effect for electron de Broglie waves behind a nanofabricated transmission grating. This was thought to be difficult because of Coulomb interactions between electrons and nanostructure gratings, yet we were able to map out the entire near-field interference pattern, the "Talbot carpet", behind a grating. We did this using a Talbot interferometer, in which Talbot interference fringes from one grating are moire'-filtered by a 2nd grating. This arrangement has served for optical, X-ray, and atom interferometry, but never before for electrons. Talbot interferometers are particularly sensitive to distortions of the incident wavefronts, and to illustrate this we used our Talbot interferometer to measure the wavefront curvature of a weakly focused electron beam. Here we report how this wavefront curvature demagnified the Talbot revivals, and we discuss applications for electron Talbot interferometers.Comment: 5 pages, 5 figures, updated version with abstrac

Oceanic influence on atmospheric mercury at coastal and inland sites: a springtime noreaster in New England

Continuous measurements of elemental (Hg<sup>0</sup>) and reactive mercury were conducted at two sites in New Hampshire during a powerful April 2007 noreaster. During the most intense period of the storm, enhancements of ~30–50 ppqv in Hg<sup>0</sup> were observed at a coastal and a high elevation inland site. This enhancement occurred simultaneously with elevated mixing ratios of three marine tracers, CH<sub>3</sub>I, CH<sub>2</sub>Br<sub>2</sub> and CHBr<sub>3</sub>. These observations suggest a marine source of Hg<sup>0</sup>, possibly outgassing from the ocean surface during strong turbulence. The Hg<sup>0</sup> enhancement observed 100 km inland suggests that the impact of coastal storms on terrestrial Hg cycling may not be limited to near-shore environments. Combining Hg<sup>0</sup> and marine tracer measurements during the storm with estimates of oceanic tracer fluxes during previous strong storms yields an order-of-magnitude estimate of the oceanic source of Hg<sup>0</sup> during the storm (~7 ppqv h<sup>−1</sup>) which can account for the observed enhancement at the field sites