On the eigenvalues of a second order elliptic operator in an unbounded domain
Denton Hewgill · Pacific Journal of Mathematics · 1974
Let E be an open set in R n which satisfies the "narrowness at infinity" condition:for all a > 0 and some β > 0. It is known that a uniformly strongly elliptic self-adjoint partial differential operator, on such a set E, has a discrete spectrum of eigenvalues {λj}.This paper is concerned with the growth rate of the functionThe main result of the paper is to give an upper bound for N(λ).This upper bound will be a function of the β from the "narrowness" condition.