This female science division ensign was among the crewmember who were evacuated from the habitat ring following an explosion in Miles O'Brien's quarters. She passed Major Kira. (DS9: "The Darkness and the Light")
This female science division officer worked on the bridge of the Defiant during the final attack against the Dominion in the Dominion War. She manned an aft station when her console exploded and she fell over another console. Later, she was working on an aft station of the bridge. (DS9: "What You Leave Behind")
This science officer was played by stunt actress Linda Madalone who received no credit for this appearance.
He served aboard the Defiant during the war between the Dominion and Starfleet and was among the crewmembers who were successful in their mission to destroy a Dominion facility near the Argolis Cluster. (DS9: "Behind the Lines")
He left Quark's and was talking to another man. They stopped their talk when Kira and Odo had their first kiss on the Promenade. (DS9: "His Way")
This Starfleet science officer was wounded during the Dominion attack on Deep Space 9 in 2373. An operations division officer helped him on board the Defiant when Captain Sisko ordered the evacuation of Deep Space 9. (DS9: "Call to Arms")
He attended the official ceremony on the bridge in which AdmiralWilliam Ross gave Captain Sisko the command of the starship. He left the bridge shortly before Ross told Sisko that another point of interest was on the PADD he gave the captain, the name change from Sao Paulo to USS Defiant. (DS9: "The Dogs of War")
This Starfleet officer was played by background actor Stephen Blackehart, who received no credit for his appearance.
On his official site, Blackehart named this officer "Lieutenant Pa'ak". 
This Vulcan Starfleet officer served in the science division on board Deep Space 9 in 2372.
During the strike of the employees of Quark's O'Brien saw her and told Julian Bashir that she'll not join Quark's during the strike. He was right, she passed the establishment. (DS9: "Bar Association")