Article history: Received 15 September 2008 Received in revised form 24 June 2011 Accepted 5 July 2011 Available online 23 July 2011

Article history: Received 11 September 2010 Received in revised form 29 May 2011 Accepted 1 July 2011 Available online 14 July 2011

Article history: Received 24 May 2011 Revised 28 July 2011 Accepted 5 September 2011 Available online 22 September 2011 Communicated by Stephen D. Cohen

Article history: Received 16 September 2007 Received in revised form 1 July 2008 Accepted 16 September 2008 Available online 5 November 2008

Article history: Received 25 June 2014 Received in revised form 8 July 2014 Accepted 14 September 2014 Available online 27 September 2014

Article history: Received 4 July 2012 Received in revised form 31 August 2012 Accepted 26 September 2012 Available online 28 September 2012 Communicated by J.L. Fiadeiro

Article history: Received 25 July 2014 Received in revised form 8 July 2014 Accepted 15 September 2014 Available online 17 October 2014

Article history: Received 25 June 2014 Received in revised form 8 July 2014 Accepted 25 August July 2014 Available online 29 September 2014

Article history: Received 10 September 2014 Received in revised form 19 May 2015 Accepted 4 July 2015 Available online 10 July 2015

Article history: Received 11 September 2013 Received in revised form 3 May 2014 Accepted 3 July 2014 Available online 16 July 2014