Which preposition to use with unperturbed

by Occurrences 1%

Unperturbed by this terrible proof of the danger of his position, the commanding officer stuck to his post, and for further shelter placed the body of his junior over his body.

by Occurrences 1%

It all moved me greatly, but I could see that the soldiers thought nothing of it, and were quite unperturbed by the fearful demonstration that was going on above.

Which preposition to use with  unperturbed