  Kaon production and kaon flow in heavy-ion collisions at SIS energies are
analyzed using the relativistic transport model. The experimental data are
found to be consistent with the scenario that kaon scalar (before being cut
down by the range term) and vector mean field potentials are about 1/3 of that
of nucleons in the Walecka model. This also explains the strong attraction
found for $K^-$ in kaonic atoms, and gives information on the possibility of
$K^-$ condensation in dense matter.
