NEW YORK ( TheStreet) -- CHANGE IN RATINGS Abiomed ( ABMD) upgraded to buy at TheStreet Ratings. Akorn ( AKRX) rated new Buy at BofA/Merrill. $18 price target. Company operates in attractive niche areas. Bristow Group ( BRS) downgraded at Goldman to Sell from Neutral, Goldman Sachs said. $52 price target. Valuation call. Camtek ( CAMT) downgraded to hold at TheStreet Ratings. Carnival ( CCL) downgraded at Jefferies to Hold from Buy, Jefferies said. $37 price target. Valuation call. Chesapeake Energy ( CHK) downgraded at Stifel from Buy to Hold, Stifel Nicolaus said. Valuation call. Cepheid ( CPHD) rated new Overweight at JP Morgan. $47 price target. Company can generate 20% annual sales growth through 2015. Carpenter Technology ( CRS) rated new Buy at Topeka. $70 price target. Company's growth strategy continues to gain traction. Electronic Arts ( EA) downgraded at BofA/Merrill from Buy to Neutral, Bank of America/Merrill Lynch said. $15 price target. Stock is up 15% from its lows and the company lacks near-term catalysts. MarketAxess ( MKTX) downgraded at Credit Suisse from Neutral to Underperform, Credit Suisse said. Valuation call, based on a $28 price target. Marvell Technology ( MRVL) downgraded at Canaccord to Hold, Canaccord Genuity said. $9 price target. Company is losing market share. Paccar ( PCAR) downgraded at Baird to Neutral, Robert Baird said. $39 price target. Sector has performed well, despite declining fundamentals. Sigma Aldrich ( SIAL) downgraded at UBS to Neutral from Buy, UBS said. $76 price target. Valuation reflects SIAL's safe haven status. SanDisk ( SNDK) downgraded at JMP from Outperform to Market Perform, JMP Securities said. Estimates also cut, given lower demand trends. Synnex ( SNX) downgraded at Needham from Strong Buy to Buy, Needham said. $40 price target. Company is leveraged to weak consumer spending and pricing pressure. Texas Instruments ( TXN) downgraded at Oppenheimer to Perform from Outperform, Oppenheimer said. Wireless strategy shift. Waste Connections ( WCN) rated new Buy at Keybanc. $37 price target. Company is market leader and deserves a premium valuation. Waste Management ( WM) rated new Hold at Keybanc. Do not expect a material waste volume recovery in the near term.