What is "coma"

Envelope \En"vel*ope\ (?; 277), Envelop \En*vel"op\ (?; 277), n.

1. That which envelops, wraps up, encases, or surrounds; a wrapper; an inclosing cover; esp., the cover or wrapper of a document, as of a letter.

2. (Astron.) The nebulous covering of the head or nucleus of a comet; -- called also coma.

3. (Fort.) A work of earth, in the form of a single parapet or of a small rampart. It is sometimes raised in the ditch and sometimes beyond it.
   --Wilhelm.

4. (Geom.) A curve or surface which is tangent to each member of a system of curves or surfaces, the form and position of the members of the system being allowed to vary according to some continuous law. Thus, any curve is the envelope of its tangents.

   4. A set of limits for the performance capabilities of some type of machine, originally used to refer to aircraft; -- it is often described graphically as a two-dimensional graph of a function showing the maximum of one performance variable as a function of another. Now it is also used metaphorically to refer to capabilities of any system in general, including human organizations, esp. in the phrase push the envelope. It is used to refer to the maximum performance available at the current state of the technology, and therefore refers to a class of machines in general, not a specific machine.

   push the envelope to increase the capability of some type of machine or system; -- usually by technological development.

state of prolonged unconsciousness, 1640s, from Latinized form of Greek koma (genitive komatos) "deep sleep," which is of uncertain origin. A term for "coma" in Middle English was false sleep (late 14c.).

"head of a comet," 1765, from Latin coma, from Greek kome "hair of the head," which is of unknown origin. Earlier in English as a botanical term for a tuft of hairs (1660s).

Etymology 1 n. A state of sleep from which one may not wake up, usually induced by some form of trauma. Etymology 2

n. 1 (context astronomy English) A cloud of dust surrounding the nucleus of a comet. 2 (context optics English) A defect characterized by diffuse, pear-shaped images that should be points. 3 (context botany English) A tuft or bunch, such as the assemblage of branches forming the head of a tree, a cluster of bracts when empty and terminating the inflorescence of a plant, or a tuft of long hairs on certain seeds.

1. n. a state of deep and often prolonged unconsciousness; usually the result of disease or injury [syn: comatoseness]

2. a usually terminal tuft of hairs especially on a seed

3. (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed

4. [also: comae (pl)]

Coma is a profound state of unconsciousness.

Coma may also refer to:

Coma is Robin Cook's first major published novel, published by Signet Book in 1977. Coma was preceded in 1973 by Cook's lesser known novel, The Year of the Intern (also published by Signet Book).

Coma is a Polish rock band which was founded in June 1998 in Łódź. It is one of the most successful rock bands on the Polish music scene of the last decade. As of 2013, the band has released four Polish-language studio albums (three of which have topped the Polish sales chart OLiS), two English-language studio albums, and two live albums.

The name "Coma" was chosen at random: the band members tossed a coin to decide on it, as they had an appointment for an interview with Radio Łódź.

Coma is a state of unconsciousness in which a person cannot be awakened; fails to respond normally to painful stimuli, light, or sound; lacks a normal wake-sleep cycle; and does not initiate voluntary actions. A person in a state of coma is described as being comatose. A distinction is made in the medical community between a coma and a medically induced coma, the former is a result of circumstances beyond the control of the medical community, while the latter is a means by which medical professionals may allow a patient's injuries to heal in a controlled environment.

A comatose person exhibits a complete absence of wakefulness and is unable to consciously feel, speak, hear, or move. For a patient to maintain consciousness, two important neurological components must function. The first is the cerebral cortex—the gray matter that forms the outer layer of the brain. The other is a structure located in the brainstem, called reticular activating system (RAS). Injury to either or both of these components is sufficient to cause a patient to experience a coma. The cerebral cortex is a group of tight, dense, "gray matter" composed of the nuclei of the neurons whose axons then form the "white matter," and is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.

RAS, on the other hand, is a more primitive structure in the brainstem which includes the reticular formation (RF). The RAS area of the brain has two tracts, the ascending and descending tract. Made up of a system of acetylcholine-producing neurons, the ascending track, or ascending reticular activating system (ARAS), works to arouse and wake up the brain, from the RF, through the thalamus, and then finally to the cerebral cortex. A failure in ARAS functioning may then lead to a coma. The word is from the Greek koma, meaning "deep sleep")

The coma is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimes. This gives a comet a "fuzzy" appearance when viewed in telescopes and distinguishes it from stars. The word coma comes from the Greek "kome" (κόμη), which means "hair" and is the origin of the word comet itself.

The coma is generally made of ice and comet dust. Water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The HO parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization. The solar wind plays a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path while smaller particles are pushed away from the Sun into the comet's tail by light pressure.

On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, HCO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON). On 2 June 2015, NASA reported that the ALICE spectrograph on the Rosetta space probe studying comet 67P/Churyumov–Gerasimenko determined that electrons (within above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma.

Coma is a 1978 suspense film based on the 1977 novel of the same name by Robin Cook. The film rights were acquired by director Michael Crichton, and the movie was produced by Martin Erlichmann for Metro-Goldwyn-Mayer. The cast includes Geneviève Bujold, Michael Douglas, Elizabeth Ashley, Richard Widmark, and Rip Torn. Among the actors in smaller roles are Tom Selleck, Lois Chiles, and Ed Harris.

The story was adapted again into a two-part television miniseries broadcast September 2012 on A&E television network.

"Coma" is a song by American rock band Guns N' Roses. It appears on the 1991 album Use Your Illusion I. At 10 minutes, 14 seconds it is the longest track released by the band, even though it lacks choruses.

Coma is a five-part series co-produced by two South Korean firms, SIO Film and OCN. It is a horror-mystery film set in a hospital that is being shut down due to its dubious practices.

It was shown at the 7th Jeonju International Film Festival in 2006.

Coma is a 2009 Austrian film written and directed by Ludwig Wüst.

The film premiered at the Moscow International Film Festival in 2009. It received critical acclaim particularly in the French Canadian press.

Due to his gloomy style director Ludwig Wüst is often compared with fellow Austrian directors Michael Haneke and Ulrich Seidl.

Coma is the first Austrian film and one of the first films in Europe that had a world-wide release on the internet as video on demand on the renowned cinema website mubi.com simultaneously with its theatrical release.

In optics (especially telescopes), the coma, or comatic aberration, in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components that results in off-axis point sources such as stars appearing distorted, appearing to have a tail ( coma) like a comet. Specifically, coma is defined as a variation in magnification over the entrance pupil. In refractive or diffractive optical systems, especially those imaging a wide spectral range, coma can be a function of wavelength, in which case it is a form of chromatic aberration.

Coma is an inherent property of telescopes using parabolic mirrors. Unlike a spherical mirror, a bundle of parallel rays parallel to the optical axis will be perfectly focused to a point (the mirror is free of spherical aberration), no matter where they strike the mirror. However, this is only true if the rays are parallel to the axis of the parabola. When the incoming rays strike the mirror at an angle, individual rays are not reflected to the same point. When looking at a point that is not perfectly aligned with the optical axis, some of the incoming light from that point will strike the mirror at an angle. This results in an image that is not in the center of the field looking wedge-shaped. The further off-axis (or the greater the angle subtended by the point with the optical axis), the worse this effect is. This causes stars to appear to have a cometary coma, hence the name.1

Schemes to reduce spherical aberration without introducing coma include Schmidt, Maksutov, ACF and Ritchey-Chrétien optical systems. Correction lenses, " coma correctors" for Newtonian reflectors have been designed which reduce coma in telescopes below f/6. These work by means of a dual lens system of a plano-convex and a plano-concave lens fitted into an eyepiece adaptor which superficially resembles a Barlow lens.

Coma of a single lens or a system of lenses can be minimized (and in some cases eliminated) by choosing the curvature of the lens surfaces to match the application. Lenses in which both spherical aberration and coma are minimized at a single wavelength are called bestform or aplanatic lenses.

Vertical coma is the most common higher-order aberration in the eyes of patients with keratoconus. Coma is also a common temporary symptom of corneal injuries or abrasions, in which case the visual defect gradually resolves as the cornea heals.

"Coma" is the third single by Australian ambient house band Pendulum. The single was released in July 1997 and peaked at #46 on the ARIA Singles Chart spending just 2 weeks on the Chart. It was later included on the album 3 Knocks and Triple J Hottest 100, 1997, where it ranked #32. It was the final single release from the band as they split in early 1998.

• The song contains the lyrics "Hug me till you drug me honey; Kiss me till I'm in a coma", a rhyme taken from the novel Brave New World.
• The song also contains the sound of a doorbell; presumably a soundbyte from the movie A Clockwork Orange (film), specifically the doorbell at Mr. Frank Alexander's house.
• The start of the song contains the sample "Ever since I was born I've been trained to serve you", a line from the 1988 movie Coming to America
• The track also contains sounds cuts from the movie Natural Born Killers.

Coma is an American television miniseries based on the 1977 novel Coma by Robin Cook and the subsequent 1978 film Coma. The four-hour medical thriller was originally broadcast on A&E on September 3–4, 2012.

The series was directed by Mikael Salomon and produced by Ridley Scott and his brother Tony Scott, the same team that adapted The Andromeda Strain into the 2008 miniseries on A&E. The film is dedicated to Tony Scott, who died in August 2012, only weeks before its broadcast premiere.