21Vianet Group Inc (NASDAQ:VNET), Ulta Salon, Cosmetics & Fragrance, Inc. (NASDAQ:ULTA) and Flexion Therapeutics Inc (NASDAQ:FLXN) are today’s top-gaining billionaire stock picks midday. The biggest losers are North Atlantic Drilling Ltd. (NYSE:NADL), Stemline Therapeutics Inc (NASDAQ:STML) and Ruckus Wireless Inc (NYSE:RKUS).

Flexion Therapeutics

Flexion Therapeutics Surges Yet Again

The share price of 21Vianet Group Inc (NASDAQ:VNET) soared +24.68% this morning, rebounding from a major sell-off this week spurred by Ponzi scheme accusations made by Trinity Research Group. George Soros initiated a position in the Chinese internet company during the first quarter of this year, and Farallon Capital picked up a stake in Q2. Today’s bounce comes as a relief to both parties, though this story is far from over.

Ulta Salon, Cosmetics & Fragrance, Inc. (NASDAQ:ULTA) climbed +19.82% after raising its guidance for the full fiscal year 2014 and getting a price target increase from Morgan Stanley to $121.00. Billionaire hedge fund manager Steve Mandel initiated a position in the beauty company in Q1 2012 and as of Q2 2014 holds 5.2 million ULTA shares.

[drizzle]Taking the third and final spot on today’s list of midday gainers is Flexion Therapeutics Inc (NASDAQ:FLXN), up +7.54%. The Soros pick has had a stellar run this week, with its price climbing more than +45% over the past five days.

Russia Sanctions Take a Toll on North Atlantic Drilling

North Atlantic Drilling Ltd. (NYSE:NADL) dipped -7.33% early in the day this Friday following the admission of company CEO John Fredriksen this week that international sanctions against Russia may affect a deal with OCO Rosneft.

The share price of Stemline Therapeutics Inc (NASDAQ:STML) dropped -6.29% today. Despite today’s dip, this week has been a strong one for the biopharmaceutical company thanks to increased earnings estimates and higher trading volumes. STML has climbed nearly +33% over the past five days.

Down -5.55% is Ruckus Wireless Inc (NYSE:RKUS), the third and final company on today’s list of midday losers. Investment analysts at Buckingham Research have downgraded the stock from a buy to a neutral rating, and Morgan Stanley assumed coverage of the company, issuing an underweight rating and a $13.00 price objective. This George Soros pick is up a slight +1.41% YTD.