1 You have signs of infection, such as: 2  Increased pain, swelling, warmth, or redness around the bite. 3  Red streaks leading from the bite. 4  Pus draining from the bite.  A fever.
A negative index of refraction due to three-dimensional chirality is demonstrated for abilayered metamaterial based on pairs of mutually twisted planar metal patterns in parallel planes, which alsoshows negative electric and magnetic responses and exceptionally strong optical activity and circular dichro-ism.
The ratio of the velocity of light in a vacuum to the velocity of light in the medium under study. That's what I was taught, anyway. The rest are all mathematical definitions as far as I know. The refractive index is the ratio between the speed of light in vacuum and the speed of light in that particular medium. The refractive can be complex (which it is for e.g. metals), and if we're talking about group velocity of light then it's always a number larger than one, meaning it's always slower than the speed of light in a vacuum.