London is set to continue the firmer trend seen late in the afternoon session yesterday with sentiment boosted by Wall Street's strength yesterday and strong gains overnight in Japan and Hong Kong.City sources predict the FTSE 100 will open 45 points up from the previous close of 4,690.Mining giant Rio Tinto saw profits fall by more than half in the six months to June 30 as it felt the impact of sharply lower commodity prices amid tough economic conditions globally.Pre-tax profits for the period totalled $4.39bn, compared with $9.82bn over the same period the previous year, as sales fell to $19.52bn from $30bn.Sterlite Industries, a subsidiary of Indian miner Vedanta Resources, is to increase its offer terms for the purchase of most of the assets of Asarco LLC. The purchase price is being upped by $500m to around $2.1bn.Tesco Personal Finance (TPF), the banking arm of supermarket top dog Tesco, is to create more than 800 jobs in Glasgow with the opening of a new customer service centre.Support services group Carillion said its joint venture with technology services firm Telent has signed a letter of intent with BT's Openreach for a support services contract worth in the region of £1bn.Building products group SIG posted a sharp fall in profits as weakness in the construction market persisted into the first half of 2009. Pre-tax profits in the six months to June 30 fell to £15.4m from £48.5m over the same period the previous year as revenue fell to £1.34bn from £1.44bn. Spirax-Sarco saw interim profits tumble 28% as higher impairment charges and challenging trading conditions weighed. Pre-tax profit fell to £30.2m from £41.9m on sales in the half year that rose 5% to £251.6. At constant exchange rates, sales declined 8% against a comparatively strong first half of 2008. The interim divi has been raised 5% to 10.5p.