Magnetic retarders are similar to the electric retarder discussed below. The most common admixtures are retarders and accelerators. These include accelerants, activators, retarders and inhibitors. The same is true for small etalons, retarders and polarizers. Vapor retarders slow the rate of vapor diffusion into the thermal envelope of a structure. Retarders are generally glycol or glycerin-based additives. Thus, the science of accelerators and retarders was born. Electric retarders use electromagnetic induction to provide a retardation force. The gun's recoil mechanism is composed of two hydraulic retarders and a hydropneumatic assembly. It had a hump for shunting, which used Westinghouse retarders and 31 sidings. These had Voith hydraulic retarders installed to the transmissions. These are composed of time-variable optical retarders. Major applications include capacitive touch panels, 3D televisions (3D TV), and glass retarders. Tughlakabad marshalling yard is a mechanized hump yard with retarders. The marshalling of wagons is done by a hump yard fitted with mechanical retarders.