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K VALUE

Practical measure of molecular mass of polyvinyl chloride, obtained from intrinsic viscosity experi

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K-BAND

US designation of microwave band between 12 and 40 GHz, widely adopted in the absence of internationally agreed standards. Subdivided into Ku-band K-under, 12-19 GHz, K-band, 18-26 GHz and Ka K- above, 26-40 GHz; replacing approximately the UK designations of J-, K- and Q-bands.

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K-CAPTURE

Absorption of an electron from the innermost K shell of an atom into its nucleus. An alternative to ejection of a positron from the nucleus of a radioisotope. Also K-electron capture. See X-ray.

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K-CELL

A cell generally resembling a lymphocyte which bears Fc receptors by which it can bind to other cells to which are attached antibodies against antigens on the cell surface thus exposing the Fc portions. K-cells induce lesions in the membrane of the target cell which kill it. This is an example of antibody-dependent cell-mediated cytotoxicity.

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K-DISPLAY

A form of A-display produced with a lobe- switching antenna. Each lobe produces its own peak and the antenna is direcdy on target when both parts of the resulting double peak have the same height. See R-display.

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K-LINES

Characteristic X-ray frequencies from atoms due to excitation of electrons in the K-shell. Denoted by Ka, K/?, Ky; the lines are all doublets,

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K-SHELL

The innermost electron shell in an atom corresponding to a principal quantum number of unity. The shell can contain two electrons. See panel on Atomic structure.

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K-SPACE

Symbol for momentum space or wavevector space. This is an important concept in semiconductor energy band theory. See Brillouin zone.

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K-STRATEGIST

Organism which assigns relatively little of its resources to reproduction; characteristic of stable, satur

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KAERSUTITE

A hydrated silicate of calcium, sodium, magnesium, iron, titanium and aluminium; a member of the amphibole group crystallizing in the monoclinic sys

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