Hns is equal to (4/(n*(d+2*r+2)))^(2/(d+2*r+4))*var(x), n = sample size, d = dimension of data, r = derivative order. hns is the analogue of Hns for 1-d data.
References
Chacon J.E., Duong, T. & Wand, M.P. (2011). Asymptotics for
general multivariate kernel density derivative
estimators. Statistica Sinica. 21, 807-840.