  Solar ultraviolet (UV) bursts are small-scale compact brightenings in
transition region images. The spectral profiles of transition region lines in
these bursts are significantly enhanced and broadened, often with chromospheric
absorption lines such as Ni~{\sc{ii}} 1335.203 and 1393.330 {\AA} superimposed.
We investigate the properties of several UV bursts using a coordinated
observation of the Interface Region Imaging Spectrograph (IRIS), Solar Dynamics
Observatory (SDO), and \textit{Hinode} on 2015 February 7. We have identified
12 UV bursts, and 11 of them reveal small blueshifts of the Ni~{\sc{ii}}
absorption lines. However, the Ni~{\sc{ii}} lines in one UV burst exhibit
obvious redshifts of $\sim$20 km s$^{-1}$, which appear to be related to the
cold plasma downflows observed in the IRIS slit-jaw images. We also examine the
three-dimensional magnetic field topology using a magnetohydrostatic model, and
find that some UV bursts are associated with magnetic null points or bald
patches. In addition, we find that these UV bursts reveal no obvious coronal
signatures from the observations of the Atmospheric Imaging Assembly (AIA) on
board SDO and the EUV Imaging Spectrometer (EIS) on board \textit{Hinode}.
