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  2. 10–20 system (EEG) - Wikipedia

    en.wikipedia.org/wiki/10–20_system_(EEG)

    The "10" and "20" refer to the fact that the actual distances between adjacent electrodes are either 10% or 20% of the total front–back or right–left distance of the skull. For example, a measurement is taken across the top of the head, from the nasion to inion. Most other common measurements ('landmarking methods') start at one ear and end ...

  3. List of Mersenne primes and perfect numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_Mersenne_primes...

    [7] [8] [9] It is widely believed, [10] but not proven, that no odd perfect numbers exist; numerous restrictive conditions have been proven, [10] including a lower bound of 10 1500. [11] The following is a list of all 52 currently known (as of January 2025) Mersenne primes and corresponding perfect numbers, along with their exponents p.

  4. 10-20 system - Wikipedia

    en.wikipedia.org/wiki/10-20_system

    10-20 system may refer to: 10-20 system (swimming safety), a technique used by lifeguards; 10-20 system (EEG), an electrode placement method used in ...

  5. Cartesian tensor - Wikipedia

    en.wikipedia.org/wiki/Cartesian_tensor

    A dyadic tensor T is an order-2 tensor formed by the tensor product ⊗ of two Cartesian vectors a and b, written T = a ⊗ b.Analogous to vectors, it can be written as a linear combination of the tensor basis e x ⊗ e x ≡ e xx, e x ⊗ e y ≡ e xy, ..., e z ⊗ e z ≡ e zz (the right-hand side of each identity is only an abbreviation, nothing more):

  6. Vigesimal - Wikipedia

    en.wikipedia.org/wiki/Vigesimal

    D0 20 is equivalent to two hundred and sixty in decimal = (13 × 20 1) + (0 × 20 0) 100 20 is equivalent to four hundred in decimal = (1 × 20 2) + (0 × 20 1) + (0 × 20 0). In the rest of this article below, numbers are expressed in decimal notation, unless specified otherwise. For example, 10 means ten, 20 means twenty. Numbers in vigesimal ...

  7. Vector calculus identities - Wikipedia

    en.wikipedia.org/wiki/Vector_calculus_identities

    Another method of deriving vector and tensor derivative identities is to replace all occurrences of a vector in an algebraic identity by the del operator, provided that no variable occurs both inside and outside the scope of an operator or both inside the scope of one operator in a term and outside the scope of another operator in the same term ...

  8. Decade (card game) - Wikipedia

    en.wikipedia.org/wiki/Decade_(card_game)

    If the total of at least two consecutive cards in the line equals 10, 20 or 30, they are discarded. The cards are treated as if in a straight line, so cards coming from both the front and back of the line that value to ten, twenty, or thirty are not considered consecutive unless they occupy a physically adjacent position to the card. After this ...

  9. Quadrant (plane geometry) - Wikipedia

    en.wikipedia.org/wiki/Quadrant_(plane_geometry)

    The four quadrants of a Cartesian coordinate system. The axes of a two-dimensional Cartesian system divide the plane into four infinite regions, called quadrants, each bounded by two half-axes.