Degenerations for module variety by U-exact sequence

In module variety, Riedtmann and Zwara have shown that geometric degeneration by orbit closure is equivalent to algebraic degeneration by exact sequence. In this paper, we define the U-algebraic degeneration by the notion U-exact sequence introduced by Davvas and Parnian-Gramaleky, and we give its relation with geometric degeneration. Moreover, we also explain its relation with virtual and homomorphism degenerations.