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A,

first letter of the alphabetalphabet
[Gr. alpha-beta, like Eng. ABC], system of writing, theoretically having a one-for-one relation between character (or letter) and phoneme (see phonetics). Few alphabets have achieved the ideal exactness.
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. A is a usual symbol for a low central vowel, as in father; the English long a (ā) is pronounced as a diphthong of ĕ and y. The corresponding letter of the Greek alphabet is named alpha. Alpha and omega, the last letter of the Greek alphabet, symbolize the beginning and the end and, in the New Testament, Christ. In musical notationmusical notation,
symbols used to make a written record of musical sounds.

Two different systems of letters were used to write down the instrumental and the vocal music of ancient Greece. In his five textbooks on music theory Boethius (c.A.D. 470–A.D.
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 the letter is the symbol of a note in the scale.

a

(electricity)
(physics)

A

(electricity)
(mechanics)

Å

(mechanics)

A

1. Abbr. for ampere, a unit of electric current.
2. Abbr. for area.

dB(A)

A unit of sound-level; a reading taken on the A-scale of a sound-level meter.

a

, A
the first in a series, esp the highest grade or mark, as in an examination
References in periodicals archive ?
The 7-OH of A-ring and 3-OH of C- ring of flavonoids are important for the antiplatelet activity.
Feasibility studies for the project have been completed, following which the company finalized the location on A-Ring Road, three minutes from Musherireb, and implemented the initial design phase.
The a-ring lactone of brevetoxin PbTx-3 is required for sodium channel orphan receptor binding and activity.
Temporarily designated 1981 S13, the tiny moon apparently creates the 320-kilometer-wide "Encke's gap" in the planet's A-ring, the outermost of its clearly visible rings.
This molecule, denoted PbTx-1, is very similar to the PbTx-2 structure in that both possess lactone functionality in the A-ring and a series of relatively rigid rings that form a ladder structure, and both terminate in an identical, very reactive [alpha],[beta]-unsaturated aldehyde side chain.
The band labeled "E' on the cover is found where field lines link the planet with the E-ring and Saturn's moon Enceladus, while the dart points to a band linked with the inner part of the A-ring.