What is the test for a motion to overturn a conviction for sexual assault in a federal criminal case?

Appellant next argues that the evidence at trial was insufficient to sustain his convictions. In passing on a challenge to the sufficiency of the evidence "this court examines the evidence in the light most favorable to the government in order to determine whether any rational trier of fact could find the defendant guilty beyond a reasonable doubt." United States v. Brannan, 898 F.2d 107, 109 (9th Cir.), cert. denied, 498 U.S. 833 (1990).