David J. Harper Gheorghe Muresan Bicheng Liu Ivan Koychev Dietrich Wettschereck Nirmalie Wiratunga The Robert Gordon University's HARD Track Experiments at TREC 2004. 2004 TREC http://trec.nist.gov/pubs/trec13/papers/robertgordonu.hard.pdf conf/trec/2004 db/conf/trec/trec2004.html#HarperMLKWW04