London's Footsie opened slightly higher on Wednesday morning with the mood boosted by last night's strong showing from US tech giant Apple. In UK news, a raft of economic data is due out this morning, including the minutes from the January meeting of the Bank of England's Monetary Policy Committee and preliminary gross domestic product estimates for the fourth quarter.In other news, only one day after negotiations over the debt swap once again failed between Athens and its private bondholders, the Financial Times (FT) reports in a front page piece that the International Monetary Fund (IMF) is putting the pressure on the European Central Bank (ECB) to also take a haircut on its own €40bn worth of Greek bond holdings.ARM UP ON APPLE RESULTSARM Holdings, the chip designer for many Apple products, was up nearly 4% after Apple's quarterly figures showed robust demand for its trendy iPhones, iPads and Macs. Net income rose to $13.1bn in the first quarter of the company's fiscal year, more than double the $6bn achieved in the first quarter of the previous year. Putting the cherry on the top, Apple also raised earnings guidance for its second quarter.Ashmore was the best performer early on, bouncing back after a poor performance yesterday on the back of a downgrade from Royal Bank of Scotland.Industrial engineer Weir was a high riser after agreeing to acquire US oil and gas pump valve maker Novatech for $176m (£113m) in cash. Weir is looking to further strengthen its presence in the US unconventional oil and gas markets following the recent $675m acquisition of wellhead solutions provider Seaboard Holdings which was completed in December. Sector peer IMI was also in demand.Media giant WPP fell after making its third acquisition in three days after purchasing a majority stake in a newly incorporated Jordanian company which will acquire the assets of marketing communications firm IDEA. This is already WPP's seventh purchase in 2012.FTSE 250 MOVERS: RENISHAW ROCKETS AFTER INTERIM RESULTSRenishaw, the measurement and medical device manufacturer, surged in early trading after revenues rose 11% in the first half. Geographically, revenue in Europe increased by 25% over the comparable period and the Americas were ahead by 23%.Bookshop and newsagent chain WH Smith was in demand as the decline in like-for-like sales eased in the final month of 2011. An improvement had been expected over the longer period, however, given that the company was facing soft comparatives from December 2010, when the UK was hit by severe weather conditions which made travel difficult. Irish mining company Kenmare Resources has reported 'robust' demand for its products in 2011, with revenues up 83% year-on-year.Soft drinks maker and bottler Britvic said carbonated drinks put some fizz into its Christmas trading, with revenues rising 2.5% in the final three months of 2011. Shares edged higher.3i Infrastructure, the company that invests in infrastructure projects worldwide, said its portfolio continues to perform well and is delivering a good yield.In other news, AIM-listed upmarket furnishing, fabrics and wallpapers designer Colefax sank after it warned this year's pre-tax profit will be significantly below current market expectations after a weak performance from its decorating division and a slower than expected recovery in its core US market.BCFTSE 100 - RisersAshmore Group (ASHM) 373.70p +5.27%ARM Holdings (ARM) 601.00p +3.62%IMI (IMI) 861.50p +2.74%Weir Group (WEIR) 1,970.00p +2.23%Essar Energy (ESSR) 139.60p +1.82%Burberry Group (BRBY) 1,348.00p +1.58%InterContinental Hotels Group (IHG) 1,322.00p +1.38%Capita (CPI) 654.00p +1.24%Eurasian Natural Resources Corp. (ENRC) 719.50p +1.20%Fresnillo (FRES) 1,773.00p +1.20%FTSE 100 - FallersSSE (SSE) 1,228.00p -2.00%Royal Bank of Scotland Group (RBS) 26.55p -1.85%Schroders (Non-Voting) (SDRC) 1,203.00p -0.82%Schroders (SDR) 1,472.00p -0.74%Compass Group (CPG) 603.00p -0.74%Imperial Tobacco Group (IMT) 2,229.00p -0.67%Randgold Resources Ltd. (RRS) 6,930.00p -0.50%BP (BP.) 475.30p -0.44%WPP (WPP) 749.00p -0.33%Royal Dutch Shell 'A' (RDSA) 2,309.50p -0.26%FTSE 250 - RisersRenishaw (RSW) 1,298.00p +12.38%Halfords Group (HFD) 321.70p +4.45%Aegis Group (AGS) 159.80p +4.38%Imagination Technologies Group (IMG) 571.50p +3.53%Dixons Retail (DXNS) 15.08p +3.15%Misys (MSY) 320.00p +2.89%Unite Group (UTG) 178.30p +2.83%WH Smith (SMWH) 545.50p +2.54%Tullett Prebon (TLPR) 307.30p +2.50%New World Resources A Shares (NWR) 456.00p +2.49%FTSE 250 - FallersAllied Gold Mining (ALD) 151.60p -2.19%Phoenix Group Holdings (DI) (PHNX) 571.00p -1.55%Berendsen (BRSN) 454.10p -1.45%Go-Ahead Group (GOG) 1,259.00p -1.33%Edinburgh Dragon Trust (EFM) 235.00p -1.30%Jupiter Fund Management (JUP) 222.10p -1.29%PZ Cussons (PZC) 292.40p -1.22%Impax Environmental Markets (IEM) 99.00p -1.10%Galliford Try (GFRD) 485.90p -0.84%Aberdeen Asset Management (ADN) 236.20p -0.76%