Coal mining generates significant adverse environmental impacts. Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. Underground mining hazards include suffocation, gas poisoning, roof collapse and gas explosions.
The term 'OVD' (Optically Variable Device) is used to describe both laser generated hologram images and electron beam generated images. These optically variable devices are created in highly-secure facilities and are at the forefront of overt asset and brand protection programmes.
A night vision device (NVD) is an optoelectronic device that allows images to be produced in levels of light approaching total darkness.cientists at the University of Michigan have developed a contact lens that can act as night vision device. The lens has a thin strip of graphene between layers of glass that reacts to photons to make dark images look brighter.