  We consider Euler-Bernoulli operators with real coefficients on the unit
interval. We prove the following results:
  i) Ambarzumyan type theorem about the inverse problems for the
Euler-Bernoulli operator.
  ii) The sharp asymptotics of eigenvalues for the Euler-Bernoulli operator
when its coefficients converge to the constant function.
  iii) The sharp eigenvalue asymptotics both for the Euler-Bernoulli operator
and fourth order operators (with complex coefficients) on the unit interval at
high energy.
