# arc

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## arc,

in electricity, highly luminous and intensely hot discharge of electricity between two electrodes. The arc was discovered early in the 19th cent. by the English scientist Sir Humphry Davy, who so named it because of its shape. An arc is characterized by a high current, low voltage, and indefinite duration. It is usually started when two electrodes carrying an electric current are drawn apart. At the instant the electrodes are parted, strong electric forces draw electrons from one electrode to the other, initiating the arc. The discharge consists of a current composed of these electrons and charged gas particles, called ions, that form between the electrodes. The first practical electric light, the arc lamp, made use of the arc formed between two carbon rods (see lightinglighting,
light produced by artificial means to allow visibility in enclosures and at night. For stage lighting, see scene design and stage lighting. Early Sources of Artificial Lighting
). Today the use of the arc lamp is limited to special purposes, e.g., in searchlights and in research applications. The principle of the electric arc is employed in weldingwelding,
process for joining separate pieces of metal in a continuous metallic bond. Cold-pressure welding is accomplished by the application of high pressure at room temperature; forge welding (forging) is done by means of hammering, with the addition of heat.
(as in the hydrogen arc, where hydrogen is introduced between tungsten electrodes) and also in generating heat in the electric furnace. A spark, like an arc, is a discharge of electricity between two points, but it has a high voltage and a short duration. Lightning is an example of a spark.

## arc,

in geometry, a curved line or any part of it; in particular, a portion of the circumference of a circle. The length s of an arc of a circle of radius r and subtending a central angle of θ radians is s=rθ; if θ is measured in degrees, then the arc is given by s=2πrθ/360.

## ARC

Abbrev. for Astrophysical Research Consortium. See Apache Point Observatory.

## Arc

(also called simple arc or Jordan arc), a part of a curve that is contained between two of its points and does not have multiple points. The arc is more accurately defined on a plane, with the coordinates of its points being given as the continuous functions x = φ(t) and y = ψt of some parameter t, atb. It is assumed that the different points correspond to the different values of t.

## arc

[ärk]
(electricity)
(engineering)
The graduated scale of an instrument for measuring angles, as a marine sextant; readings obtained on that part of the arc beginning at zero and extending in the direction usually considered positive are popularly said to be on the arc, and those beginning at zero and extending in the opposite direction are said to be off the arc.
(geology)
A geologic or topographic feature that is repeated along a curved line on the surface of the earth.
(mathematics)
A continuous piece of the circumference of a circle.

## Arc

[ärk]
(astronomy)
A radio source consisting of two bundles of parallel filaments adjoining the source Sagittarius A near the center of the Milky Way Galaxy.

## ARC

AIDS-related complex

## arc

1. The luminous column of gas in an arc discharge; caused by the flow of electric current between separated electrodes in a gas.
3. Any part of the circumference of a circle.
4. An angular measure.

## arc

The track over ground of an aircraft flying at a constant distance from a navigational aid by reference to distance-measuring equipment.

## arc

1. a luminous discharge that occurs when an electric current flows between two electrodes or any other two surfaces separated by a small gap and a high potential difference
2. Astronomy a circular section of the apparent path of a celestial body
3. Maths a section of a curve, graph, or geometric figure

## ARC

AIDS-related complex: an early condition in which a person infected with the AIDS virus may suffer from such mild symptoms as loss of weight, fever, etc.

(1)

## arc

(file format, tool)
An old archive format for IBM PC. The format is now so obscure that it is only likely to be supported by jack-of-all-trades decompression programs such as WINZIP.

## arc

(mathematics, data)
An edge in a tree. "branch" is a generally more common synonym.

## ARC

(1) (Audio Return Channel) See HDMI ARC.

(2) PC compression programs from System Enhancement Associates, Inc., Clifton, NJ. ARC was one of the first compression utilities to become popular in the early 1980s. ARC+Plus provides enhanced features and speed.

(3) The ARC extension was previously used by PKWARE Inc. in its PKARC program.

(4) (Advanced RISC Computing) An earlier open system specification based on the MIPS R3000 and R4000 CPUs. It included EISA and TURBOchannel buses.
References in periodicals archive ?
The combination of the painful arc sign, drop-arm sign, and weakness in external rotation (positive infraspinatus muscle strength test) produced the best likelihood ratios (LRs) for detecting frill-thickness rotator cuff tears (TABLE).
TABLE Comparison of tests to detect full-thickness rotator cuff tear Test Sensitivity Specificity Painful arc (2) 75.
In this case study, a definitive cause of the painful arc cannot be established and is therefore open to speculation.

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