The 2011 NFL combine came to a close on Tuesday as the defensive backs were the final group of players to take the field at Lucas Oil Stadium. As was the case during the prior three days of workouts there were a number of outstanding performances which truly impressed the scouts and coaches that remained in Indianapolis. Here's a look at the risers and sliders from the group:

Prince Amukamara/CB/Nebraska: Amukamara's speed was the big question entering the day and the former Cornhusker proved he has plenty of it. His first 40 broke 4.4 seconds on a number of watches and his second attempt was equally impressive as he timed 4.42 seconds. Later in drills Amukamara proved why he's one of the most polished cornerbacks available in April's draft. Amulamara leaves Indianapolis as a top ten pick.

Patrick Peterson/CB/LSU: Despite tipping the scales at 219 pounds, heavier than expected, Peterson still ripped through his workout. His first 40 clocked 4.31 seconds even with the extra weight and Peterson did an admirable job in position drills. The junior needs to loosen up his footwork and backpedal yet there's no denying his upside is unlimited.

Chris Culliver/DB/South Carolina: The versatile defensive back that started at both safety and cornerback in college was fast and fluid in his workout. He twice timed under 4.35 seconds in the 40 then displayed solid fundamentals during position drills. Culliver even worked through some leg cramps and finished all the drills, which impressed several onlookers.

Buster Skrine/CB/Tennessee Chattanooga: Skrine leaves Indianapolis as the fastest man from the 2011 combine. His first 40 time was clocked as low as 4.27 seconds on a number of watches. His second was slightly slower, primarily due to a bobble at the 20-yard mark which knocked Skrine off balance. Though he still needs a bit of work on his position skills, Skrine showed enough to make people think he can contribute at the next level as a rookie.

DeMarcus Van Dyke/CB/Miami: Van Dyke finished up a phenomenal two months with a terrific workout. After a terrific performance at the Shrine Game in January, then a solid showing two weeks later in the Senior Bowl, he gave scouts more to think about with his combine effort. Van Dyke never ran slower than 4.30 seconds in the 40 then displayed quickness, explosion and balance in the position drills. He's gone from backup with the Hurricanes last season to potential top-100 pick in the draft.

Curtis Brown/CB/Texas: After running a pair of 40's which averaged just under 4.5 seconds, Brown put on a clinic in position drills. His backpedal was extremely quick, hip turn smooth and Brown showed the ability to immediately reverse course and drive to the action.

Brandon Burton/CB/Utah: The little known junior from Utah showed why scouts must quickly get acquainted with him. Burton ran solid times in the 40, posting marks of 4.40 and 4.42 seconds in his attempts. During position drills he was incredibly smooth and showed the ability to quickly drive forwards to the football out of his backpedal. He'll move toward the draft as a top-100 choice.

Cortez Allen/CB/The Citadel: The small-school corner, who received a late invitation to the combine, proved his worth on the field. His 40 times were solid, averaging 4.50 seconds and his position work was outstanding. Allen quickly moved in reverse displaying NFL caliber footwork and smooth hips. He looked athletic in all the routines and proved himself worthy of a middle round selection.

Marcus Gilchrist/DB/Clemson: One of the better safety prospects to take the field on Tuesday, Gilchrist ran well, getting under 4.45 seconds on his second 40, then showed a variety of polished defensive back skills. Considering many teams feel Gilchrist can line up at cornerback and safety, Tuesday's workout will only further enhance his draft stock.

Ahmad Black/S/Florida: Black failed to impress anyone on Tuesday as he was slow in the 40 and poor in position drills. He struggled to get under the 4.75-second mark on his runs and Black's ability to move in reverse was equally poor. His backpedal was slow, he was constantly off balance and Black showed little in the way of a burst to the ball.

Robert Sands/S/West Virginia: Sands ran adequate 40 times which averaged in the high 4.5-second range. His position drills were another story. The Mountaineer junior looked slow, mechanical and poorly balanced in most all the drills. He did nothing to dispel the belief he's a safety that can only make plays moving forwards and struggles in reverse.

Kendric Burney/CB/North Carolina: Burney, who showed well at the Senior Bowl and also displayed solid defensive back skills at the combine, will have his draft grade significantly downgraded as he could not break 4.7-seconds in the 40.

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