Hot research fronts in 2008

	Research topic	Core papers	Citations	Citations per paper	Mean year
1	Multiple M2 branes and Bagger-Lambert theory	17	189	11.12	2008.0
2	Iron-based superconductors	14	298	21.29	2007.7
3	Unparticle physics	40	817	20.43	2007.7
4	Graphene	16	234	14.62	2007.5
5	Human-induced pluripotent stem cells		1,842	68.22	2007.3
6	Inflammatory bowel disease gene and Crohn’s disease susceptibility	34	1,629	47.91	2007.2
7	Three-year Wilkinson Microwave Anisotropy Probe (WMAP) observations	4	1,1	317.75	2007.0
8	Treatment-resistant depression and deep-brain stimulation	4	1	67.75	2007.0
9	Dark energy	23	5,551	241.35	2005.7
10	Autophagy	32	5,505	172.03	2005.1

Thomson Reuters has developed co-citation methodologies over the years and employs them in its Essential Science Indicators database to construct so-called research fronts. A research front consists of a group of highly cited papers that are co-cited, meaning that the core papers are cited in pairs. By collecting the core papers cited pairwise (A and B, B and C, C and D, D and A, C and B, B and D, A and C, and so on depending on the size of the core literature), a cluster of highly related papers can be identified. These typically represent subspecialties. By examining the average age (mean year) of the co-cited core papers, hot research fronts emerge. A hot research front, in which the core, or foundation, papers are of recent vintage, suggests new, rapidly developing areas. The table above lists a selection of hot research fronts, ranked by the mean year of the core papers. These were chosen for their age, size and apparent weight within their representative subject areas. Science magazine recently named the area ranked fifth, which it termed “reprogramming cells”, its Breakthrough Area of the Year for 2008 in its 19 December 2008 issue. It also listed the field ranked second as a runner-up.