Article history: Received 1 October 2008 Received in revised form 11 February 2009 Accepted 18 February 2009 Available online 28 February 2009

Article history: Received 21 February 2013 Received in revised form 13 February 2014 Accepted 18 February 2014 Available online 19 March 2014

Article history: Received 31 July 2014 Received in revised form 9 February 2015 Accepted 10 February 2015 Available online 18 February 2015 Communicated by V.Y. Pan

Article history: Received 3 June 2010 Received in revised form 18 February 2011 Accepted 19 February 2011 Available online 24 February 2011 Editor: B. Sherwood Lollar

Article history: Received 3 January 2011 Received in revised form 18 February 2012 Accepted 20 February 2012 Available online 21 February 2012

Article history: Received 6 August 2008 Accepted 18 February 2009 Available online 27 February 2009

Article history: Received 18 December 2016 Accepted 16 February 2017 Available online 25 February 2017