Ultra-Compact Dwarfs in the Fossil Group NGC 1132

Ultra-Compact H II Regions

Ultra-Compact H II Regions and the Early Lives of Massive Stars

Ultra-Compact Stellar Systems in the Fornax Galaxy Cluster

Ultra-Cool and Extra-Vigorous: Rotation and Activity in M and L dwarfs

Ultra-cool Dwarfs from Large Area Surveys

Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

Ultra-deep mid-IR survey of a lensing cluster

Ultra-deep Spitzer Mid-Infrared Spectroscopy of LIRGs and ULIRGs at z ~ 1-2

Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State

Ultra-faint dwarf galaxies as a test of early enrichment and metallicity-dependent star formation

Ultra-faint satellites of the Milky Way

Ultra-fine dark matter structure in the Solar neighbourhood

Ultra-hard fluid and scalar field in the Kerr-Newman metric

Ultra-high angular resolution by gravitational microlensing

Ultra-High Energy Cosmic Particles studies from space: super-EUSO, a possible next-generation experiment

Ultra-High Energy Cosmic Radiation: Current Issues and Future Prospects

Ultra-High Energy Cosmic Ray and Neutrino Observations

Ultra-high energy cosmic ray correlations with Active Galactic Nuclei in the world dataset

Ultra-high energy cosmic ray investigations by means of EAS muon density measurements