As mentioned above using caffeine rich drinks and stimulants will help but u might get addicted....tho u know that if u keep ur body hydrated u can stay wake as much as u need,using only a bottle of water, and taking breaks between intervals help the brain process and save what u have studied [10 min break is enough, do 15 pushups, go to the toilet, take a walk or sth] ...its a healthier way and am using this technique and it works