Chemicals group AZ Electronic is the best performer after being upgraded from 'neutral' to a 'buy' by UBS after the stock's recent underperformance. "When initiating in December 2010, we said two things would make us a buyer of AZ: a cheaper valuation and establishing a track record during more difficult times in semis. Both falling in place now," the broker said. Not far behind is events and publishing group United Business Media, which is on track to hit its full year targets after a first quarter that saw underlying year on year revenue growth of 7.5%.Meanwhile, retailers Dixons Retail, Carpetright and Home Retail are among the worst performers of the day.Oil and gas firm Heritage Oil is off the mark after losses widened in 2010 as the group wrote off $10.5m relating to expenditure on licence areas in Africa. Also providing some downward pressure is UBS who downgraded its rating for Heritage as a result of increased uncertainty following the recent case set forth by rival Tullow Oil, who is seeking $313m for an alleged 'breach of contract'.Emerging markets lender International Personal Finance is higher after it posted a fourfold increase in pre-tax profit during the first quarter after a bumper performance in Poland and as it reduced impairment charges. ---bcFTSE 250 - RisersAZ Electronic Materials SA (WI) (AZEM) 266.30p +7.16%United Business Media Ltd. (UBM) 596.50p +4.19%Afren (AFR) 156.90p +3.77%Howden Joinery Group (HWDN) 112.90p +3.39%Ocado Group (OCDO) 236.90p +3.18%Micro Focus International Plc (MCRO) 316.50p +3.16%Persimmon (PSN) 454.90p +3.11%Inchcape (INCH) 355.60p +3.10%Bodycote (BOY) 320.00p +2.99%Petropavlovsk (POG) 878.00p +2.87%FTSE 250 - FallersDixons Retail (DXNS) 13.23p -3.43%Carpetright (CPR) 658.00p -1.86%Rotork (ROR) 1,665.00p -1.54%RPC Group (RPC) 319.30p -1.45%Exillon Energy (EXI) 422.00p -1.40%Home Retail Group (HOME) 213.20p -1.39%Shanks Group (SKS) 114.20p -1.30%TalkTalk Telecom Group (TALK) 138.30p -1.21%Cable & Wireless Worldwide (CW.) 50.00p -1.19%Heritage Oil (HOIL) 249.30p -0.91%