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In knot theory, the writhe is a property of an oriented link diagram. The writhe is the total number of positive crossings minus the total number of negative crossings. A direction is assigned to the link at a point in each component and this direction is followed all the way around each component. For each crossing one comes across while traveling in this direction, if the strand un
In general, the number of secondary twists in the native, supertwisted chromosome is expected to be the "normal" Watson–Crick winding number, meaning a single 10-base-pair helical twist for every 34 Å of DNA length. Wr, called "writhe," is the number of superhelical twists.
The Advent wreath was first used by Lutherans in Germany in the 16th century, [13] and in 1839, Lutheran priest Johann Hinrich Wichern used a wreath made from a cart wheel to educate children about the meaning and purpose of Christmas, as well as to help them count its approach, thus giving rise to the modern version of the Advent wreath. For ...
While the others writhe around shaking them off, the ever-resourceful Data pulls out a car battery he’s been lugging around and electrocutes the bloodsuckers.
However, this added condition does not change the definition of linking number (it does not matter if the curves are required to always be immersions or not), which is an example of an h-principle (homotopy-principle), meaning that geometry reduces to topology.
[14] [15] Closed-circular double-stranded DNA can be described by 3 parameters: Linking number (Lk), Twist (Tw) and Writhe (Wr) (Fig. 1). Where Lk refers to the number of times the two strands are linked, Tw refers to the number of helical turns in the DNA, measured relative to the helical axis, and Wr quantifies the coiling of the path of the ...
It has long been known that most of the simple knots, such as the trefoil knot and the figure-eight knot are invertible. In 1962 Ralph Fox conjectured that some knots were non-invertible, but it was not proved that non-invertible knots exist until Hale Trotter discovered an infinite family of pretzel knots that were non-invertible in 1963. [2]
The figure-eight knot has played an important role historically (and continues to do so) in the theory of 3-manifolds.Sometime in the mid-to-late 1970s, William Thurston showed that the figure-eight was hyperbolic, by decomposing its complement into two ideal hyperbolic tetrahedra.