Article history: Received 23 October 2011 Received in revised form 20 February 2012 Accepted 20 February 2012 Available online 9 March 2012

Article history: Received 1 December 2012 Received in revised form 5 October 2013 Accepted 9 February 2014 Available online 20 February 2014

Article history: Received 9 October 2013 Accepted 5 February 2014 Available online 26 February 2014 Submitted by M. Tsatsomeros MSC: 05C50

Article history: Received 15 October 2013 Received in revised form 19 February 2014 Accepted 20 February 2014 Available online 19 March 2014

Article history: Received 25 October 2016 Received in revised form 28 December 2016 Accepted 15 February 2017 Available online 22 February 2017 Editor: M. Doser

Article history: Received 27 October 2010 Received in revised form 21 February 2011 Accepted 23 February 2011 Available online 22 April 2011

Article history: As urban areas across the U Received 21 February 2007 Received in revised form 2 October 2008 Accepted 18 December 2008 Available online 20 February 2009

Article history: Received 20 October 2008 Received in revised form 13 February 2009 Accepted 24 February 2009 Available online 4 March 2009