London's Air Ambulance its second MD 902, registration G-LNDN. Built in 2008, the aircraft was previously registered in Qatar as A7-NHA. In addition to the standard livery, it bears the masonic Square and Compasses symbol on each side, with the words "London Freemasons" lettered under the doors, to reflect the significant funding from the organisation. At night or when the helicopters are offline the medical crew, including a paramedic and senior trauma doctor, still respond to emergencies, but travel in a specially equipped rapid response car. The six cars, Škoda Octavias and also Škoda Superbs, occasionally operate during the day, carrying backup medical
Square root of a matrix a "positive-semidefinite matrix" has precisely one positive-semidefinite square root, which can be called its "principal square root". While the square root of a nonnegative integer is either again an integer or an irrational number, in contrast an "integer matrix" can have a square root whose entries are rational, yet not integer. For example, the matrix formula_8 has the non-integer square root formula_9 as well as the integer square root matrix formula_10. The 2×2 identity matrix is another example. A 2×2 matrix with two distinct nonzero eigenvalues has four square roots. More generally, an matrix with "distinct nonzero eigenvalues" has 2