# diameter

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Related to anteroposterior diameter: external conjugate diameter

## diameter

a. a straight line connecting the centre of a geometric figure, esp a circle or sphere, with two points on the perimeter or surface
b. the length of such a line
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Diameter

The diameter of a circle is the chord that passes through the center of the circle. Moreover, the diameter of a circle is the length of this chord, equal to two radii.

In analytic geometry the diameter of a conic section (or of a curve of the second order) is understood to mean the straight line that passes through the midpoints of a set of parallel chords. For central curves of the second order (circles, ellipses, hyperbolas) this is the straight line passing through the center of the curve. In the case of the parabola, all diameters are parallel to its axis.

The concept of the diameter of a circle as the length of a segment is applied to other geometric figures and to sets of a more general nature. The diameter of a figure (or a set in metric space) is precisely the upper bound of the distances between all possible pairs of points of this figure. In this sense, the diameter of an ellipse is equal to the length of the semimajor axis, and the diameter of a square is equal to the length of its diagonal.

## diameter

[dī′am·əd·ər]
(mathematics)
A line segment which passes through the center of a circle, and whose end points lie on the circle.
The length of such a line.
For a conic, any straight line that passes through the midpoints of all the chords of the conic that are parallel to a given chord.
For a set, the smallest number that is greater than or equal to the distance between every pair of points of the set.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## diameter

The diameter of a graph is the maximum value of the minimum distance between any two nodes.

## Diameter

An authentication, authorization and accounting (AAA) protocol that replaces RADIUS (Diameter is a play on the word RADIUS). Like RADIUS, Diameter uses a challenge/response method; however, unlike RADIUS, Diameter uses the reliable TCP and SCTP protocols rather than the unreliable UDP for transport. Diameter also supports error reporting and is better at scaling than RADIUS. See RADIUS, network access server and challenge/response.
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References in periodicals archive ?
Patient demographics Unilateral isolated high-Grade HN n=44 % Gender Male 34 77 Female 10 23 Laterality Right 14 32 Left 30 68 SFU Grade3 24 54.5 Grade 4 20 45.5 APD >15 mm 19 43 [less than or equal to] 15 mm 25 57 DRF [greater than or equal to] 40% 35 79.5 < 40% 9 20.5 APD: anteroposterior diameter; DRF: differential renal function; HN: hydronephrosis; SFU: Society for Fetal Urology.
Eisenstein's two large anatomic studies of skeletons found the lower anteroposterior diameter of the spinal canal in adults to be 12 mm and 13 mm.
The left ventricular diameters, left ventricular ejection fraction and left atrial anteroposterior diameter were also determined from M-mode traces that had been recorded from the parasternal long axis view, according to established standards (25).
The skin-traction method increases the cross-sectional area of the internal jugular vein by increasing its anteroposterior diameter. J Anesth 2007; 21:467-471.
Gross evaluation indicated that the right eye had an anteroposterior diameter of 19 mm.
The fact that the transverse diameter of a Morgagni hernia is substantially more than its anteroposterior diameter makes this hernia amenable to this technique.
The anteroposterior diameter from the frontal pole to the occipital pole of a human brain measures 17 cm in a male and 16 cm in a female person.
UTRI being the ratio of anteroposterior diameter to length would always remain relatively constant in the four categories of subjects.
The 28 percent increase in the pelvic outlet--1cm in the transverse diameter and 2cm in the anteroposterior diameter (Russell, 1982) of active birthing is greater than that which is normally achieved by symphysiotomy, which, primarily, increases the transverse diameters by 1cm (Menticoglou, 1990).
The mass was approximately 5 cm wide, and its anteroposterior diameter was 2.5 cm.
Further assessment of the MRI scans showed a reduction in the mediolateral diameter of the spinal cord compared with the anteroposterior diameter in patients with either subclinical or established DSP.

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