  Let g be a complex, semisimple Lie algebra. Drinfeld showed that the quantum
loop algebra U_h(Lg) of g degenerates to the Yangian Y_h(g). We strengthen this
result by constructing an explicit algebra homomorphism Phi defined over Q[[h]]
from U_h(Lg) to the completion of Y_h(g) with respect to its grading. We show
moreover that Phi becomes an isomorphism when the quantum loop algebra is
completed with respect to its its evaluation ideal. We construct a similar
homomorphism for g=gl_n and show that it intertwines the geometric actions of
U_h(L gl_n) and Y(gl_n) on the equivariant K-theory and cohomology of the
variety of n-step flags in C^d constructed by Ginzburg and Vasserot.
