base (redirected from al-Qaeda)

base: see acids and bases.

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base

In chemistry, any substance that in water solution is slippery to the touch, tastes bitter, changes the colour of acid-base indicators (e.g., litmus paper), reacts with acids to form salts, and promotes certain chemical reactions (e.g., base catalysis). Examples of bases are the hydroxides of the alkali metals and alkaline earth metals (sodium, calcium, etc.; see caustic soda) and the water solutions of ammonia or its derivatives (amines). Such substances produce hydroxide ions (OH⁻) in water solutions. Broader definitions of bases cover situations in which water is not present. See also acid-base theory; alkali; nucleophile.

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base

(1) A starting or reference point.

(2) In a bipolar transistor, the elements that act as a switch. In NMOS and PMOS transistors, which make up CMOS circuits, the base is called the "gate." See transistor.

(3) A multiplier in a numbering system. In a decimal system, each digit position is worth 10x the position to its right. In binary, each digit position is worth 2x the position to its right.

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base¹

1. a chemical compound that combines with an acid to form a salt and water. A solution of a base in water turns litmus paper blue, produces hydroxyl ions, and has a pH greater than 7. Bases are metal oxides or hydroxides or amines

2. Biochem. any of the nitrogen-containing constituents of nucleic acids: adenine, thymine (in DNA), uracil (in RNA), guanine, or cytosine

3. the inorganic material on which the dye is absorbed in lake pigments; carrier

4. Biology

a. the part of an organ nearest to its point of attachment

b. the point of attachment of an organ or part

5. Architect

a. the lowest division of a building or structure

b. the lower part of a column or pier

6. the lower side or face of a geometric construction

7. Maths

a. the number of distinct single-digit numbers in a counting system, and so the number represented as 10 in a place-value system

b. (of a logarithm or exponential) the number whose powers are expressed

c. (of a mathematical structure) a substructure from which the given system can be generated

d. the initial instance from which a generalization is proven by mathematical induction

8. Logic Maths the initial element of a recursive definition, that defines the first element of the infinite sequence generated thereby

9. Electronics the region in a transistor between the emitter and collector

10. Photog the glass, paper, or cellulose-ester film that supports the sensitized emulsion with which it is coated

11. a starting or finishing point in any of various games

12. Baseball any of the four corners of the diamond, which runners have to reach in order to score

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base²

1. English history

a. (of land tenure) held by villein or other ignoble service

b. holding land by villein or other ignoble service

2. Music an obsolete spelling of bass

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(mathematics)

base - radix.