Ultradeep Infrared Array Camera Observations of sub-L* z~7 and z~8 Galaxies in the Hubble Ultra Deep Field: the Contribution of Low-Luminosity Galaxies to the Stellar Mass Density and Reionization

Ultradeep Ks Imaging in the GOODS-N

Ultrafast effective multi-level atom method for primordial hydrogen recombination

Ultraluminous Star-Forming Galaxies and Extremely Luminous Warm Molecular Hydrogen Emission at z=2.16 in the PKS 1138-26 Radio Galaxy Protocluster

Ultraluminous X-ray sources out to z~0.3 in the COSMOS field

Ultraviolet color-color relation of early-type galaxies at 0.05 < z < 0.12

Ultraviolet Fe II emission in z ~ 2 quasars

Ultraviolet number counts of galaxies from Swift UV/Optical Telescope deep imaging of the Chandra Deep Field South

Ultraviolet Spectroscopy of Supernovae: The First Two Years of Swift Observations

Ultraviolet tails and trails in cluster galaxies: A sample of candidate gaseous stripping events in Coma

Unabsorbed Seyfert 2 galaxies: the case of "naked" AGN

Unburned Material in the Ejecta of Type Ia Supernovae

Uncertainties and Systematic Effects on the estimate of stellar masses in high z galaxies

Uncertainty in 2-point correlation function estimators and BAO detection in SDSS DR7

Unconventional Cosmology

Uncovering delayed patterns in noisy and irregularly sampled time series: an astronomy application

Uncovering Obscured Active Galactic Nuclei in Homogeneously Selected Samples of Seyfert 2 Galaxies

Uncovering strong MgII absorbing galaxies: Imaging below the Lyman limit

Uncovering the formation of ultra-compact dwarf galaxies by multivariate statistical analysis

Uncovering the Spectral Energy Distribution in Active Galaxies Using High Ionization Mid-infrared Emission Lines