Paper  bibtex   

@article{duran_arching_1993,
	title = {Arching effect model for particle size segregation},
	volume = {70},
	url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.70.2431},
	number = {16},
	urldate = {2015-05-11TZ},
	journal = {Physical Review Letters},
	author = {Duran, J. and Rajchenbach, J. and Clément, E.},
	year = {1993},
	pages = {2431}
}