Ongoing concerns over the Federal Reserve's impending withdrawal of quantitative easing are expected to weigh on markets again on Tuesday morning.With the economic data schedule looking pretty empty for the second day in a row, all eyes are expected to focus on the Fed ahead of the minutes of its latest policy meeting due out tomorrow.Both US and Asian markets slid overnight as investors speculated the future of monetary policy, with rising bond yields in the States doing little to help sentiment. The yield on the US 10-year Treasury note was up seven basis points (bp) at a fresh two-year high of 2.89% yesterday with many analyst now expecting the US central bank to begin scaling back stimulus as early as September. City sources predict the FTSE 100 in London will open down around 30 points from yesterday's close of 6,465.73. Stocks to watchFirst-half results from the merged Glencore Xstrata showed encouraging progress in integrating the two businesses with synergies and cost savings materially higher than previous guidance/ A statutory goodwill impairment of $7.6bn was made after the merger due to negative mining industry sentiment and the heightened risks associated with greenfield and large scale expansion projects, with a further $776m writedown from other operations.CRH has swung to a loss for the half year period after sales revenue dropped 3.0% and the profit on disposals declined significantly. The building materials group reported a loss of €71m, compared to a profit of €102m for the same half the previous year. The group blamed ongoing weakness in construction activity, and warned it expects challenging trading conditions in Europe for the remainder of 2013. Oil and gas services company Wood Group said it enjoyed good growth in first half of the year and anticipates a full-year performance in line with expectations. The FTSE 100 energy giant said profit from continuing operations before tax and exceptional items rose 16.6% to $186.6m. Revenue from continuing operations firmed 3.0% to $3.4bn. Adjusted diluted EPS rose 19.0% to 44.5 cents.FTSE 250 oil exploration and production company Premier Oil is to offload its stake in two blocks in the Norwegian North Sea to sector peer Cairn Energy. Chief Executive Simon Lockett said that this was part of Premier's ongoing programme of non-core asset disposals. Premier Oil has sold its 20% interest in PL378 and PL378B to Cairn's subsidiary, Capricorn Norge, for a cash consideration of $16m.