The first discovery of point sources

efl students gender and socioeconomic status: the use of politeness strategies in the first and second languages

within the components of communicative competence, a special emphasis is put on the “rules of politeness,” specifically the politeness strategies (brown and levinson, 1978) that speakers deploy when performing the request speech act. this is because the degree of imposition that making a request places upon one’s interlocutor(s) has been seen to be influenced by several factors among which, as ...

Discovery of Point Sources in the Helmholtz Equation Posed in Unknown Domains with Obstacles

We consider an inverse source problem for the Helmholtz equation in domains with possibly unknown obstacles, which are much larger than the wavelength. The inverse problem is to determine the number and locations of point sources in the domain based on sparse measurements of the wave field. Our proposed strategy relies on solving a local inverse scattering problem to obtain the incoming directi...

Detection of point sources

Photometry of individual sources requires an initial phase of detection. The detection process can be separated into two phases: (1) preprocessing of the image, and (2) actual detection, yielding a list of discrete sources. Given a distribution of background intensities, the probabilityof intensitydeviations for light sources as a result of the background can be calculated. Setting a maximum ac...

Point Sources of Pollution

The First Sources of Light

I review recent progress in understanding the formation of the first stars and quasars. The initial conditions for their emergence are given by the now firmly established model of cosmological structure formation. Numerical simulations of the collapse and fragmentation of primordial gas indicate that the first stars formed at redshifts z ≃ 20 − 30, and that they were predominantly very massive,...