ring (redirected from vascular ring)

ring, in astronomy

ring, in astronomy, relatively thin band of rocks and dust and ice particles that orbit around a planet in the planet's equatorial plane. All four of the giant planets in the solar system—Jupiter, Saturn, Uranus, and Neptune— have rings, although only those of Saturn are easily visible. The origin of the rings is unknown. One theory is that they may have been formed from moons that were shattered by the impact of comets and meteoroids. Another holds that they might be the remnants of moons or comets that came within the planet's Roche limit and were broken up by gravitational forces.

Saturn has seven rings designated alphabetically as A through G in the order of their discovery; two additional rings, designated as R/2004 S1 and R/2004 S2 were discovered in images returned to earth from the Cassini space probe in 2004. From the planet outward, the rings are D, C, B, A, R/2004 S1, R/2004 S2, F, G, and E. With named gaps occupying the space between several of the rings, Saturn's rings are a highly complex structure stretching almost 167,770 mi (270,000 km) from the planet's center to the farthest edge of ring E. The rings are not perfectly circular, and the gaps are not completely empty. The Columbo and Maxwell Gaps separate the C and B rings, the Cassini Division and Huygens Gap separate the B and A rings, and the Encke Division and Keeler Gap separate the A and R/2004 S1 rings. Except for the A and B rings, which are separated primarily by the 2,920-mi-wide (4,700-km) Cassini Division, the rings are relatively close to one another. The rings appear to be composed of small pieces of water ice mixed with a small amount of rocky material in a wide range of particle sizes, from 1 in. (2.5 cm) to 33 ft (10 m)—although there may be an occasional object as large as a mile (1.6 km) in diameter. Data returned by Cassini indicates that the rings are not uniform; for example, the B ring is very different from the A and C rings (which are similar to one another) found on either side of it. Several of Saturn's small moons appear to be shepherd satellites, maintaining the shape of the rings through gravitational interactions.

Jupiter's rings are similar to those of Saturn but much smaller and fainter. The main ring is about 4,300 mi (7,000 km) wide and has an abrupt outer boundary 80,000 mi (128,940 km) from the center of the planet. The inner main ring is formed from dust and ice particles kicked up when meteoroids collide with the small Jovian satellites Metus and Adrastea. The particles then spiral slowly in toward Jupiter. At its inner edge the main ring merges into the halo. A broad, faint band of dust and particles, the halo is about 6,200 mi (10,000 km) thick and stretches halfway from the main ring down to the top of Jupiter's atmosphere. A pair of broad, faint gossamer rings are located just outside the main ring, one bounded by the orbit of the Jovian shepherd satellite Amalthea and the other by the orbit Thebe.

Uranus has a thin elliptical band of eleven faint, narrow rings composed of ice, rock, and dust. Stretching outward from the planet, the rings are named 1986 U2R, Six, Five, Four, Alpha, Beta, Eta, Gamma, Delta, 1986 U1R, and Epsilon; the distance from the planetary center to the Epsilon ring is 31,750 mi (51,140 km). The rings are distinctly different from those of Jupiter and Saturn. A tenuous distribution of fine dust is scattered throughout the ring system, and the rings all are the same flat, dark color (perhaps from methane or black-carbon ice coating the rock), unlike Saturn's bright rings. The nine main rings consist of a single layer of particles, the monolayer, which had not previously been seen in planetary rings; the particles are kept from drifting away by several shepherd satellites. Because there are ringlets and incomplete rings and a varying opacity in several rings, it is believed that the Uranian ring system may be the remnants of a small moon.

Neptune has four almost circular faint rings composed of small rocks and dust. The rings are not uniform in density and thickness; the thicker parts of the rings are called ring arcs. Stretching outward from the planet, the rings are named Galle, Leverrier (whose outer extension is called Lassel), Arago, and Adams (which includes the ring arcs Liberty, Equality, and Fraternity); the distance from the planetary center to the Adams ring is 39,000 mi (62,930 km). The forces responsible for the development of ring arcs and ring extensions are not well understood, but shepherd satellites and gravitational forces attributable to Neptune's moons are thought to play a significant role. Earth-based observations indicate that the rings are less stable than was originally believed.

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ring, piece of jewelry

ring, small ornamental hoop usually worn on finger or thumb, but it may be attached to the ear or the nose. Finger rings made of bronze, gold, and silver from the period c.2500–1500 B.C. have been found in the Indus valley in India; in Egypt rings from c.1600 B.C. served as a symbol of status and were exchanged as a pledge or seal of faith. They were often also used as money. The signet ring grew from the custom of wearing a cylindrical seal suspended from the arm or neck, developed in Egypt, and was widely adopted as a seal of authority. Numerous rings were worn by Egyptian women, sometimes as many as three on a finger. In Greece gold bands were worn; later they were engraved with cameos or intaglios. Talismanic rings, endowed with many charms and powers, were also worn. In the middle and latter part of the Roman civilization the type of ring worn was governed by law. Iron rings were worn by the mass of the people; gold rings were reserved for those of civil or military rank. Later the gold ring was permitted to freeborn citizens, silver to freedmen, and iron to slaves. The Romans also used poison rings for assassination or suicide in the case of capture by an enemy. In addition there were key rings, which, worn by a matron, symbolized her authority to carry the keys of the house. The betrothal ring, used by Egyptians, Greeks, and Romans, was adopted by early Christians in the 2d cent. and later evolved into the wedding ring. The engagement ring set with a precious gem came into use in the Middle Ages; the diamond attained popularity in the 15th cent. and became customary c.1800. From the Middle Ages rings have figured in the coronation of kings and the consecration of bishops as emblems of authority or mystical significance. Since that time a gold seal ring (Fisherman's ring) with an intaglio of St. Peter in a fishing boat has been given each pope and is destroyed when he dies. By the 16th cent. the extravagant use of rings had reached its height. Highly decorated with enamel and jewels, they were sometimes worn on every finger and on several joints. At that time, too, the gold wedding band became popular, and signet rings were engraved with the family crest. Later, memorial rings and mourning rings became fashionable.

Bibliography

See W. Jones, Finger-Ring Lore (1898, repr. 1968); S. Bury, Rings (1985).

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ring, mathematical system

ring, in mathematics, system consisting of a set R of elements and two binary operations, such that addition makes R a commutative group and multiplication is associative and distributes over addition (see commutative law; associative law; distributive law). A commutative ring is one in which the commutative law also holds for multiplication. Examples of commutative rings are the sets of integers (see number) and real numbers. Square matrices (see matrix) furnish examples of non-communtative rings.

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ring

Circular band of gold, silver, or other precious or decorative material usually worn on the finger, but sometimes on the toes, the ears, or the nose. The earliest examples were found in the tombs of ancient Egypt. In addition to being worn as adornment, rings have functioned as symbols of authority, fidelity, or social status. In the early Roman republic, most were made of iron, gold being reserved for persons of high status; but by the 3rd century BC anyone except a slave could wear a gold ring. The Romans are thought to have originated engagement rings, symbolizing a promise of marriage. In the Middle Ages, signet rings were important in religious, legal, and commercial transactions; memorial, posy, and keepsake rings served sentimental purposes; occult rings supposedly had magical powers; and poison rings had hollow bezels that could be filled with poison for the purpose of suicide or homicide.

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ring

In modern algebra, a set of elements with two operations, referred to as “addition” and “multiplication,” that conform to certain conditions. These specify that the set is closed under both operations, the associative law holds for both operations, the commutative law holds for addition, the distributive law holds, there is an additive identity (known as zero), and every element has an additive inverse (see inverse function). The set of integers is a ring. See also field theory.

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ring

A privilege level in the computer. When software is assigned to a ring, it may be limited to executing certain instructions in the computer. Ring 0 has the highest privilege and can access all instructions. The operating system or the virtual memory monitor (VMM) resides in ring 0.

Applications typically reside in ring 3, which has a lower priority, and are prohibited from executing instructions that address the hardware. If an application attempts to execute a prohibited instruction, an error indication (fault) is generated. Rings 1 and 2 are available in some computers, but may or may not be used. See virtual machine monitor.

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ring¹

1. a square apron or raised platform, marked off by ropes, in which contestants box or wrestle

2. the ring the sport of boxing

3. an area reserved for betting at a racecourse

4. a circular strip of bark cut from a tree or branch, esp in order to kill it

5. Geometry the area of space lying between two concentric circles

6. Maths a set that is subject to two binary operations, addition and multiplication, such that the set is an Abelian group under addition and is closed under multiplication, this latter operation being associative

7. Botany short for annual ring

8. Chem a closed loop of atoms in a molecule

9. Astronomy any of the thin circular bands of small bodies orbiting a giant planet, esp Saturn

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ring²

Electronics the damped oscillatory wave produced by a circuit that rings

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Ring

A tie member or chain link. Tension or compression applied through the center of a ring produces bending moment, shear, and normal force on radial sections. Because shear stress is zero at the boundaries of the section where bending stress is maximum, it is usually neglected.

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ring

worn on fourth finger, left hand, symbolizes love. [Western Folklore: Brewer Dictionary, 919]

See : Love

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ring

represents the cyclical nature of time. [Pop. Culture: Cirlot, 273–274]

See : Time