COPENHAGEN, Denmark— A German-Iranian professor at a Norwegian technical university was charged Wednesday with violating sanctions on Iran by inviting four guest researchers from the Islamic Republic and giving them access to a laboratory. A Norwegian prosecutor said the visiting researchers had access to knowledge that could be useful to Iran’s nuclear program. Norwegian broadcaster NRK reported that during the period from February 2018 to 2019, the professor, who was not identified, invited four Iranian researchers to NTNU university in Trondheim, the Scandinavian country’s third-largest city. The duration of the guests’ stay varied. “The serious thing here is that people from Iran had access to knowledge, and this is the knowledge that could be useful to Iran’s nuclear program. We do not say that it is, but it is the potential danger here that is serious,” prosecutor Frederik Ranke told NRK. Ranke said the professor was charged with violating the …