Recent experiments revealed intriguing similarities in the$^{64}$Ni+$^{207}$Pb, $^{132}$Xe+$^{208}$Pb, and $^{238}$U+$^{238}$U reactionsat energies around the Coulomb barrier. The experimental data indicate that forall systems substantial energy dissipation takes place, in the first stage ofthe reaction, although the number of transferred nucleons is small. On theother hand, in the second stage, a large number of nucleons are transferredwith small friction and small consumption of time. To understand the observedbehavior, various reactions were analyzed based on the microscopictime-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 measuredtrends. In addition, the Balian-V\'en\'eroni variational principle is appliedto head-on collisions of $^{238}$U+$^{238}$U, and the variance of the fragmentmasses is compared with the experimental data, showing significant improvement.The underlying reaction mechanisms and possible future studies are discussed.
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