Recent experiments revealed intriguing similarities in the $^{64}$Ni+$^{207}$Pb, $^{132}$Xe+$^{208}$Pb, and $^{238}$U+$^{238}$U reactions at energies around the Coulomb barrier. The experimental data indicate that for all systems substantial energy dissipation takes place, in the first stage of the reaction, although the number of transferred nucleons is small. On the other hand, in the second stage, a large number of nucleons are transferred with small friction and small consumption of time. To understand the observed behavior, various reactions were analyzed based on the microscopic time-dependent Hartree-Fock (TDHF) theory. From a systematic analysis for $^{40,48}$Ca+$^{124}$Sn, $^{40}$Ca+$^{208}$Pb, $^{40}$Ar+$^{208}$Pb, $^{58}$Ni+$^{208}$Pb, $^{64}$Ni+$^{238}$U, $^{136}$Xe+ $^{198}$Pt, and $^{238}$U+$^{238}$U reactions, we find that TDHF reproduces well the measured trends. In addition, the Balian-Veneroni variational principle is applied to head-on collisions of $^{238}$U+$^{238}$U, and the variance of the fragment masses is compared with the experimental data, showing significant improvement. The underlying reaction mechanisms and possible future studies are discussed.
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