“…Domain adversarial learning further employs a domain discriminator to achieve the same goal [20,46,26,85,67,77,76,74] and achieves remarkable results. Other effective techniques for UDA include entropy minimization [21,15,60], contrastive learning [30,27], domain normalization [71,8], semantic alignment [38,72,16,75], meta-learning [44], self-supervision [57], curriculum learning [80] and self-training [10,86,58]. Despite their effectiveness, they require the access to the source domain data and therefore invoke privacy and portability concerns.…”