One Direction was signed to Simon Cowells record label becuase when they were on the X-Facetor, he was their mentor. When they were eliminated, Simon thought they were too talented to let go of so he signed them and started their career.
Sammy Kershaw
Sony music I think or it might be syco music
SyCo records, signed by Simon Cowell
February 1st 1994. at 5:35am
The heart is the organ that keeps the blood flowing. Valves in the heart ensure the flow is only in one direction.
One directional valves keep blood in the heart flowing in the right direction. There are three valves: biscupid valve, semilunar valve and tricuspid valve. These open to let the blood flow through then close to prevent the blood flowing back in the wrong direction making the heart less efficient.
They ensure that the blood flows only in one direction (back toward the heart).
The valve that prevents blood from flowing in the wrong direction is called a heart valve. These one-way valves ensure that blood flows in a forward direction and prevents backflow.
. . . then that would be alternating current, or simply, 'AC'.
Alternating current would fit this description.
There are valves in the heart which open and close that allow the blood to be pumped in one direction only. See the related link for more information.
Polarity
Current flowing in only one direction.
Valves
The easy answer is it allows electricity to flow in one direction but prevents it from flowing the other direction.
The heart has valves for to allow blood flow in one direction only. They close as the blood passes each. Hooweestik.