Del

Del, or nabla, is an operator used in mathematics, in particular, in vector calculus, as a vector differential operator, usually represented by the nabla symbol ∇. When applied to a function defined on a one-dimensional domain, it denotes its standard derivative as defined in calculus. When applied to a field (a function defined on a multi-dimensional domain), del may denote the gradient (locally steepest slope) of a scalar field (or sometimes of a vector field, as in the Navier–Stokes equations), the divergence of a vector field, or the curl (rotation) of a vector field, depending on the way it is applied.

Strictly speaking, del is not a specific operator, but rather a convenient mathematical notation for those three operators, that makes many equations easier to write and remember. The del symbol can be interpreted as a vector of partial derivative operators, and its three possible meanings—gradient, divergence, and curl—can be formally viewed as the product with a scalar, dot product, and cross product, respectively, of the del "operator" with the field. These formal products do not necessarily commute with other operators or products.

Rock

Rock commonly refers to:

Rock or Rocks may also refer to:

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Kraken

The Kraken (/ˈkreɪkən/ or /ˈkrɑːkən/) is a legendary sea monster of giant size that is said to dwell off the coasts of Norway and Greenland. A number of authors over the years have postulated that the legend originated from sightings of giant squids that may grow to 12-15 meters (40-50 feet) in length, despite the fact that the creature in the original tales was not described as having tentacles and more closely resembled a whale or crab. The sheer size and fearsome appearance attributed to the kraken have made it a common ocean-dwelling monster in various fictional works.

Etymology

The English word kraken is taken from Norwegian. In Norwegian and Swedish, Kraken is the definite form of krake, a word designating an unhealthy animal or something twisted (cognate with the English crook and crank). In modern German, Krake (plural and declined singular: Kraken) means octopus, but can also refer to the legendary kraken.

History

In the late-13th-century version of the Old Icelandic saga Örvar-Oddr is an inserted episode of a journey bound for Helluland (Baffin Island) which takes the protagonists through the Greenland Sea, and here they spot two massive sea-monsters called Hafgufa ("sea mist") and Lyngbakr ("heather-back"). The hafgufa is believed to be a reference to the kraken: