We have developed an improved recombination calculation of H, He i, and He ii in the early universe that involves a line-by-line treatment of each atomic level. We find two major differences compared with previous calculations. First, the ionization fraction xe is approximately 10% smaller for redshifts &800 because of nonequilibrium processes in the excited states of H. Second, He i recombinat...

In astronomy multiple images are frequently obtained at the same position of the sky for followup co-addition as it helps one go deeper and look for fainter objects. With large scale panchromatic synoptic surveys becoming more common, image co-addition has become even more necessary as new observations start to get compared with co-added fiducial sky in real time. The standard co-addition techn...

Significant observational progress in addressing the question of the origin and early evolution of galaxies has been made in the past few years, allowing for direct comparison of the epoch when most of the stars in the universe were forming to prevailing theoretical models. There is currently broad consistency between theoretical expectations and the observations, but rapid improvement in the d...

This paper examines the central hypothesis of the influential Malthusian theory, according to which improvements in the technological environment during the pre-industrial era had generated only temporary gains in income per capita, eventually leading to a larger, but not significantly richer, population. Exploiting exogenous sources of cross-country variations in land productivity and the leve...

We study the effect of a prolonged epoch of reionization on the angular power spectrum of the Cosmic Microwave Background. Typically reionization studies assume a sudden phase transition, with the intergalactic gas moving from a fully neutral to a fully ionized state at a fixed redshift. Such models are at odds, however, with detailed investigations of reionization, which favor a more extended ...