  In my talk at the 2nd Galileo-Xu Meeting, I presented several different
topics in 21cm cosmology for which I have done research. These includes the
21cm signature of the first stars[1,2], the 21cm signal from the IGM and
minihalos[3], effect of dark matter annihila- tions on 21cm signal[4], the 21cm
forest by ionized/neutral region[5], and the 21cm forest by minihalo and
earliest galaxies[6,7]. In this conference proceeding I shall not repeat these
discussions, but instead focus on the last part of my talk, i.e. the Tianlai
project, an experiment effort on low redshift 21cm intensity mapping
observation for dark energy measurements.
