Movement of electrons about a central nucleus is a concept by whom?

Bohr.

Explanation:

In 1913, N.Bohr proposed an atomic model for atom. He proposed that in an atom there is a central nucleus and electrons move around this center in a fixed path known as shell.

The shells or path have a fixed size and energy. The electrons do not lose energy during this movement.

There is possibility of energy change (emit or absorb) in an electron if they move from one shell to another.

the link still does not work even when adding it to the url bar

explanation:

smooth muscle is composed of involuntary muscles found within the walls of organs and structures such as the esophagus, stomach, intestines, and blood vessels. those muscles push materials like food or blood through organs. unlike skeletal muscle, smooth muscle can never be under your control.