Wood

Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants.

It has been used for thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or it is defined more broadly to include the same type of tissue elsewhere such as in the roots of trees or shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients between the leaves, other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber.

The Earth contains about 434 billion cubic meters of growing stock forest, 47% of which is commercial. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 1991, approximately 3.5 cubic kilometers of wood were harvested. Dominant uses were for furniture and building construction.

Knot

A knot is a method of fastening or securing linear material such as rope by tying or interweaving. It may consist of a length of one or several segments of rope, string, webbing, twine, strap, or even chain interwoven such that the line can bind to itself or to some other object (the "load"). Knots have been the subject of interest for their ancient origins, their common uses, and the area of mathematics known as knot theory.

Use

There is a large variety of knots, each with properties that make it suitable for a range of tasks. Some knots are used to attach the rope (or other knotting material) to other objects such as another rope, cleat, ring, or stake. Some knots are used to bind or constrict objects. Decorative knots usually bind to themselves to produce attractive patterns.

Teaching

While some people can look at diagrams or photos and tie the illustrated knots, others learn best by watching how a knot is tied. Knot tying skills are often transmitted by sailors, scouts, climbers, cavers, arborists, rescue professionals, stagehands, fishermen, linemen and surgeons. The International Guild of Knot Tyers is an organisation dedicated to the Promotion of Knot tying.

Glossary of graph theory

This is a glossary of graph theory. Graph theory is the study of graphs, systems of nodes or vertices connected in pairs by edges.

!$@

A

B

C

D

E

F

G

H

I

K

κ(G) is the size of the maximum clique in G; see clique.

L

M

N

O

P

Q

R

S

T

U

V

W

References

Knot (papermaking)

Knots are unwanted, large, dark aggregates of wood fibres when making chemical pulp.

Knots are incompletely cooked wood chips coming out of the digester. Their origin is often dense parts of branches, such as compression wood or timber knots – hence the name. Knots can also stem from large/oversized wood chips due to insufficient impregnation with cooking liquors. The content of lignin is very high. In kraft pulping knots are typically 0.5–3.0 % of the digester throughput. The knots are screened from the pulp, because if left in the pulp they may damage washing equipment and consume large amounts of bleaching chemicals. They are normally sent back to the digester and re-cooked so that their fibres are not wasted.

See also

References