  Given self-adjoint operators $A, B\in\mathbb{B}(\mathscr{H})$ it is said
$A\leq_uB$ whenever $A\leq U^*BU$ for some unitary operator $U$. We show that
$A\leq_u B$ if and only if $f(g(A)^r)\leq_uf(g(B)^r)$ for any increasing
operator convex function $f$, any operator monotone function $g$ and any
positive number $r$. We present some sufficient conditions under which if
$B\leq A\leq U^*BU$, then $B=A=U^*BU$. Finally we prove that if $A^n\leq U^\ast
A^nU$ for all $n\in\mathbb{N}$, then $A=U^\ast AU$.
