You can take a special depreciation allowance to recover part of the cost of qualified property (defined next), placed in service during the tax year. The allowance applies only for the first year you place the property in service. For qualified property placed in service in 2013, you can take an additional 50% special allowance. The allowance is an additional deduction you can take after any section 179 deduction and before you figure regular depreciation under MACRS for the year you place the property in service.
http://www.irs.gov/publications/p946/ch03.html