A Tsirelson bound is an upper limit to quantum mechanical correlations between distant events. Given that quantum mechanics is non-local, i.e., that quantum mechanical correlations violate Bell inequalities, a natural question to ask is "how non-local can quantum mechanics be?", or, more precisely, by how much can the Bell inequality be violated. The answer is precisely the Tsirelson bound for the particular Bell inequality in question. In general this bound is lower than what would be algebraically possible, and much research has been dedicated to the question of why this is the case. The Tsirelson...

The red-billed teal or red-billed duck (Anas erythrorhyncha) is a dabbling duck which is an abundant resident breeder in southern and eastern Africa typically south of 10° S. This duck is not migratory, but will fly great distances to find suitable waters. It is highly gregarious outside the breeding season and forms large flocks. The red-billed teal is 43–48 centimetres (17–19 in) long and has a blackish cap and nape, contrasting pale face, and bright red bill. The body plumage is a dull dark brown scalloped with white. Flight reveals that the secondary flight feathers are buff with a black stripe...