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Binary (disambiguation)

Binary (disambiguation)

Binary may mean:
- Binary (novel), a 1972 novel by Michael Crichton (writing as John Lange).
- Binary (music), a musical form that consists of two parts.
- Binary (comics), a superheroine in the Marvel Universe.
- Binary (chemical weapon), one that contains two capsules, each of which contains a chemical, that when combined with the contents of the other, will react to make a toxic agent.
- Binary explosive, composed of two non-explosive substances which only become explosive when mixed.
- Binomial nomenclature, in the taxonomy of living organisms, is sometimes called binary nomenclature.
- Binary star, a stellar system consisting of two nearby stars that revolve around a common center of mass.
- Binary thinking, a term to describe dichotomous perspectives on an issue.
- Binary numeral system, a representation for numbers that uses only zeroes and ones as digits.
- Binary and text files, a computer file that comprises a sequence of encoded numerical values rather than human-readable text
- Executable, a computer file containing machine code that can be executed by the operating system.
- In higher education, an education system that includes both polytechnic, or college, and university style institutions. These institutions are often intended to complement each other and form an important basis in the overall education policy and infrastructure of a country or region. ja:バイナリ

Binary (novel)

Binary is a techno-thriller novel written by Michael Crichton in 1972. The villain is a political extremist, who arranges for the theft of an army shipment of the two precursor chemicals that form a deadly nerve agent. The novel was originally published under the pen-name John Lange.

Musical form

The term musical form is used in two related ways:
- a generic type of composition such as the symphony or concerto
- the structure of a particular piece, how its parts are put together to make the whole; this too can be generic, such as binary form or sonata form Musical form (the whole or structure) is contrasted with content (the parts) or with surface (the detail), but there is no clear line between the two. In most cases, the form of a piece should produce a balance between statement and restatement, unity and variety, contrast and connection. There is some overlap between musical form and musical genre. The latter term is more likely to be used when referring to particular styles of music (such as classical music or rock music) as determined by things such as harmonic language, typical rhythms, types of musical instrument used and geographical origin. The phrase musical form is typically used when talking about a particular type or structure within those genres. For example, the twelve bar blues is a specific form often found in the genres of blues and rock and roll music.

Descriptions of musical form

Forms and formal detail may be described as sectional or developmental, developmental or variational, syntactical or processual (Keil 1966), embodied or engendered, extensional or intensional (Chester 1970), and associational or hierarchical (Lerdahl 1983). Form may also be described according to symmetries or lack thereof and repetition. A common idea is formal "depth", necessary for complexity, in which foregrounded "detail" events occur against a more structural background. For example: Schenkerian analysis. Fred Lerdahl (1992), among others, claims that popular music lacks the structural complexity for multiple structural layers, and thus much depth. However, Lerdahl's theories explicitly exclude "associational" details which are used to help articulate form in popular music. Allen Forte's book The American Popular Ballad of the Golden Era 1924-1950 analyses popular music with traditional Schenkerian techniques, but this is only possible because pre-rock popular ballads are the genre most accessible similar to the Romantic music that those theories were designed to analyse. (Middleton 1999, p.144) Extensional music is, "produced by starting with small components - rhythmic or melodic motifs, perhaps - and then 'developing' these through techniques of modification and combination." Intensional music "starts with a framework - a chord sequence, a melodic outline, a rhythmic pattern - and then extends itself by repeating the framework with perpetually varied inflections to the details filling it in." (Middleton, p.142) :Western classical music is the apodigm of the extensional form of musical construction. Theme and variations, counterpoint, tonality (as used in classical composition) are all devices that build diachronically and synchronically outwards from basic musical atoms. The complex is created by combination of the simple, which remains discrete and unchanged in the complex unity...If those critics who maintain the greater complexity of classical music specified that they had in mind this extensional development, they would be quite correct...Rock however follows, like many non-European musics, the path of intensional development. In this mode of construction the basic musical units (played/sung notes) are not combined through space and time as simple elements into complex structures. The simple entity is that constituted by the parameters of melody, harmony, and beat, while the complex is built up by modulation of the basic notes, and by inflexion of the basic beat. All existing genres and sub-types of the Afro-American tradition show various forms of combined intensional and extensional development (Chester 1970, p.78-9). Syntactic music is "centred" on notation and "the hierarchic organization of quasilinguistic elements and their putting together (com-position) in line with systems of norms, expectations, surprises, tensions and resolutions. The resulting aesthetic is one of 'embodied meaning.'" Non-notated music and performance "foreground process. They are much more concerned with gesture, physical feel, the immediate moment, improvisation; the resulting aesthetic is one of 'engendered feeling' and is unsuited to the application of 'syntactice' criteria" (Middleton 1990, p.115). Middleton (p.145) also describes form, presumably after Gilles Deleuze’s Difference and Repetition (1968, translated 1994), through repetition and difference. Difference is the distance moved from a repeat and a repeat being the smallest difference. Difference is qualitative and quantitative, how far different and what type of difference.

Formal structures

In classical and popular music, there are many labels applied to forms, abstract formal designs, as contrasted with the principals and procedures of combining materials: form.

Single-movement forms

In a sectional form, the larger unit (form) is built from various smaller clear-cut units (sections) in combination, sort of like stacking legos (DeLone, 1975):
- Strophic form (AA...)
- Binary form (AB)
- Ternary form, less often tertiary (ABA)
- Arch form, (ABCBA) Sections include:
- Introduction or Intro
- Exposition
- Verse
- Chorus or refrain
- Bridge or interlude
- Conclusion
- Coda or outro, and Fadeout Developmental forms, larger unit (form) is built from small bits of material given different presentations and combinations, usually progressive (DeLone, 1975):
- Sonata form, also called sonata-allegro Variational forms, larger unit (form) is built from sections treated to one type of presentation at a time, but varying successively (DeLone, 1975):
- Rondo (ABACADA...)
- Variation form, sometimes theme and variation (AA'A"A"'...)
- Passacaglia and Chaconne These structures are defined by the distribution of different thematic material, melodies, key centres, and other materials used. While many of the above forms are partly defined by their tonal schemes these forms may be applied to music which has a differing or no tonal scheme (DeLone et. al. (Eds.), 1975, chap. 1). More than one formal method may be used, including in-between types, and music which is not composed with the above or any other model is called through composed. Especially recently, more segmented approaches have been taken through the use of stratification, superimposition, juxtaposition, interpolation, and other interruptions and simultaneities. Examples include the postmodern "block" technique used by composers such as John Zorn, where rather than organic development one follows separate units in various combinations. These techniques may be used to create contrast to the point of disjointed chaotic textures, or, through repetition and return and transitional procedures such as dissolution, amalgamation, and gradation, may create connectedness and unity. Composers have also made more use of open forms such as produced by aleatoric devices and other chance procedures, improvisation, and some processes. (ibid)

Multi-movement forms

Types of piece which may or may not incorporate one or more of the above structures as part of their overall makeup include:
- Ballet, larger musical composition intended for Ballet dance form
- Cantata
- Chorale
- Concerto
- Dance, smaller musical composition intended for presentation of a dance, either as accompaniment for dancing or as music as such
- Duet
- Etude or study
- Fantasia
- Fugue
- Mass
- Opera
- Oratorio
- Prelude
- Requiem
- Rhapsody
- Sonata
- Suite
- Symphonic poem
- Symphony Forms of chamber music are defined by instrumentation (string quartet, piano quintet and so on). The structure of a chamber work is typically similar to a sonata.

External links

- [http://www-student.furman.edu/users/r/rkelley/form.htm Study Guide for Musical Form A Complete Outline of Standardized Formal Categories and Concepts by Robert T. Kelley]

References

- DeLone et. al. (Eds.) (1975). Aspects of Twentieth-Century Music. Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0130493465.
- Lerdahl, Fred (1992). "Cognitive Constraints on Compositional Systems", Contemporary Music Review 6 (2), pp. 97-121.
- Richard Middleton. "Form", in Horner, Bruce and Swiss, Thomas, eds. (1999) Key Terms in Popular Music and Culture. Malden, Massachusetts. ISBN 0631212639. ja:楽式

Binary (comics)

Carol Danvers, also known as Ms. Marvel, Binary and Warbird, is a fictional character in the Marvel Comics universe. She first appeared in Marvel Super Heroes #13 (March 1968).

Fictional Biography

Early years

Carol Danvers was a United States Air Force pilot who later joined the Central Intelligence Agency. She served alongside her lover Michael Rossi and is known to have encountered Wolverine and Nick Fury during this time. She eventually became a close ally and possible love interest of Captain Marvel (Mar-Vell), an alien of the Kree military who gave up his mission of conquering the Earth and instead chose to protect it.

Ms. Marvel and the Avengers

Kree Carol Danvers became Ms. Marvel after she was subjected to the "psyche-magnitron", a device of Kree origins. Her DNA was altered to resemble that of the Kree and in the process she also gained superhuman strength and durability, the ability to fly and a "seventh sense" (apparently a sense beyond that of the "normal" sixth sense), which provided her with premonitions. Her first costume was based directly on Mar-Vell's second costume, a red outfit with blue mask, gloves and boots; her second, more prominently featured costume was a blue ensemble with a stylized lightning bolt across the chest, along with a red sash around her waist. As Ms. Marvel, she fought a number of villains who would go on to become prominent supervilains, including Mystique and Deathbird. Many of these villains were co-created by writer Chris Claremont, who would amplify Ms. Marvel's already prominent feminist characteristics. Ms. Marvel joined the Avengers, but several months later was sidelined due to a surprise pregnancy. The pregnancy progressed at freakish speed and within weeks she gave birth to a son. The son quickly grew to adulthood. Her son, Marcus, revealed that he had come from Limbo, a dimension outside of time and had fallen in love with Carol. He had kidnapped Carol during a previous mission and had used mind control devices to force her to fall in love with him. He had seduced and impregnated her, then transferred his essence into her womb, essentially becoming his own son. After he made this revelation to Carol and her fellow Avengers, she somewhat inexplicably agreed to be his partner and left the team with him for this other dimension. It was later revealed that she was still under Marcus's influence at that point. After she left with him, his accelerated aging continued until he withered away to a husk, at which point she used his technology to return to Earth.

Rogue

Carol was not seen again until Avengers Annual #10, in which Ms. Marvel lost her powers permanently when the mutant supervillain Rogue ambushed her outside her San Francisco apartment building. This was because Carol had once stumbled upon an arms deal that Mystique, Rogue's foster mother and by then, the leader of the Brotherhood of Evil Mutants, was coordinating behind the scenes and had foiled her carefully laid plans. Mystique's partner and lover, the precognitive mutant Destiny, glimpsed Carol's future and warned Mystique that Ms. Marvel was intimately tied to a great tragedy which would harm Rogue. Determined to shield her daughter from this danger, Mystique developed an obsessive hatred for Carol. When she learned that Carol had resurfaced in San Francisco following her departure from the ranks of the Avengers, she plotted to end this threat to Rogue once and for all. Rogue overheard her mother's angry words and concerns and determined to deal with Ms. Marvel herself. The fight continued far longer than Rogue expected and she permanently absorbed Carol Danvers' abilities and memories. She threw Danvers off the Golden Gate Bridge. Rogue thought she'd rid herself of Carol Danvers not knowing the intervention of Spider-Woman saving Danvers' life. Professor X helped Danvers recover her memories, but she was unable to feel the emotions she once felt for friends and family. What once was love would now be only mild affection. When the Avengers attempted to express their sorrow, she berated them for letting her go so easily, especially considering that she had been under Marcus' mind control.

Binary and the X-Men

Professor X Danvers stayed away from the Avengers for quite some time and had a series of adventures with the X-Men which culminated in the entire team being kidnapped and sent to outer space by the war-mongering alien race known as the Brood. Painful medical experiments on Danvers caused her to gain tremendous superpowers, including the ability to survive in space, to manipulate cosmic energy and superhuman strength; the source of these powers were attributed to a "white hole"--a virtually limitless source of cosmic power. Danvers became known as Binary; in her "Binary" form, her hair became a corona of flame and she donned a red-and-white costume with a stylized black starburst on the breast. When the X-Men chose to let the severely disturbed Rogue join their school, Danvers cut all ties to the group and spent the next several years in space, often battling alongside the Starjammers.

Warbird

Eventually Danvers' link to the white hole was broken, and as a result, she lost her cosmic-level powers as Binary, but retained a level of superhuman strength, flight, resistance to injury and enhanced senses comparable to those she had once possessed before her battle with Rogue, as well as the power to manipulate and absorb energy. She rejoined the Avengers and changed her code name to Warbird, again donning her classic blue Ms. Marvel costume. She was no longer as powerful as she was as Binary, but she was considerably more powerful as she was in her early days as Ms. Marvel. Insecurity about her powers no longer being what they once were caused her to become an alcoholic. When she was unable to function in any coherent capacity, a humiliated Danvers quit the team rather than be expelled. With the help of fellow alcoholic Tony Stark (Iron Man), Danvers curbed her drinking and stabilized her powers. She rejoined the Avengers for a few missions but left again in 2003 to work for S.H.I.E.L.D. and is currently working with the newest incarnation of the Thunderbolts, although she is not a member of that group. As of recently, she seems to have retaken the Ms. Marvel name.

External links

- [http://www.geocities.com/Area51/Portal/2001/mainpage.htm THIS WOMAN, THIS WARRIOR: The Carol Danvers Homepage] Danvers, Carol Danvers, Carol Danvers, Carol Danvers, Carol

Binary chemical weapon

Binary Chemical Weapons are chemical weapons wherein the toxic agent is not contained within the weapon in its active state, but in the form of two chemical precursors, physically separated within the weapon. The precursors are designed to be significantly less toxic than the agent they make when mixed, and this allows the weapon to be transported and stored more safely than otherwise. The safety provided by binary chemical weapons is especially important for people who live near ammunition dumps. The chemical reaction takes place while the weapon is in flight. Firing the munition ruptures the capsules. The munition spins rapidly in flight, which thoroughly mixes the two precursors, so they can react with one another. Finally a bursting charge aerosolizes and distributes the nerve agent. One example of a binary chemical weapon is the United States Army M687. In the M687, methylphosphonyl difluoride and a mixture of isopropyl alcohol and isopropyl amine are held in chambers within the weapon, separated by a partition. When the weapon is fired, acceleration causes the partition to break, and the precursors are mixed by the rotation of the weapon in flight, producing sarin nerve gas. Category:Chemical weapons

Explosive

:This article is concerned solely with chemical explosives. There are many other varieties of more exotic explosive material, and theoretical methods of causing explosions such as nuclear explosives and antimatter, and other methods of producing explosions, such as abrupt heating with a high-intensity laser or electric arc. Any explosive material has the following characteristics:
- It is chemically or otherwise energetically unstable.
- The initiation produces a sudden expansion of the material accompanied by the production of heat and large changes in pressure (and typically also a flash or loud noise) which is called the explosion.

Chemical explosives

Explosives are classified as low or high explosives according to their rates of decomposition. Low explosives burn rapidly (or deflagrate). High explosives undergo detonation. There is no sharp line of demarcation between low and high explosives, due to the difficulties inherent in precisely observing and measuring rapid decomposition. The chemical decomposition of an explosive may take years, days, hours, or a fraction of a second. The slower forms of decomposition take place in storage and are of interest only from a stability standpoint. Of more interest are the two rapid forms of decomposition, burning and detonation. The term "detonation" is used to describe an explosive phenomenon whereby the decomposition is propagated by the explosive shockwave penetrating the explosive material. The shockwave front is capable of passing through the high explosive material at massive speeds. Explosive force is released at 90 degree angles from the surface of an explosive. If the surface is cut or shaped the explosive forces can be focused directionally, and will produce a greater effect. This is known as a shaped charge. In a low explosive, the decomposition is propagated by a flame front which travels much slower through the explosive material. The properties of the explosive indicate the class into which it falls. In some cases explosives may be made to fall into either class by the conditions under which they are initiated. Almost all low explosives can undergo true detonation like high explosives in sufficiently massive quantities. For convenience, low and high explosives may be differentiated by the shipping and storage classes.

Explosive compatibility groupings

differentiated Shipping tags will include a UN or US DOT hazardous material class with compatibility letter as follows.
- 1.1 Mass Explosion Hazard
- 1.2 Nonmass explosion, fragment-producing
- 1.3 Mass fire, minor blast or fragment hazard
- 1.4 Moderate fire, no blast or fragment: consumer fireworks are 1.4G or 1.4S
- 1.5 Explosive substance, very insensitive (with a mass explosion hazard)
- 1.6 Explosive article, extremely insensitive A Primary explosive substance (1.1A, 1.2A) B An article containing a primary explosive substance and not containing two or more effective protective features. Some articles, such as detonator assemblies for blasting and primers, cap-type, are included. (1.1B, 1.2B, 1.4B) C Propellant explosive substance or other deflagrating explosive substance or article containing such explosive substance (1.1C, 1.2C, 1.3C, 1.4C) D Secondary detonating explosive substance or black powder or article containing a secondary detonating explosive substance, in each case without means of initiation and without a propelling charge, or article containing a primary explosive substance and containing two or more effective protective features. (1.1D, 1.2D, 1.4D, 1.5D) E Article containing a secondary detonating explosive substance without means of initiation, with a propelling charge (other than one containing flammable liquid, gel or hypergolic liquid) (1.1E, 1.2E, 1.4E) F Article containing a secondary detonating explosive substance with its means of initiation, with a propelling charge (other than one containing flammable liquid, gel or hypergolic liquid) or without a propelling charge (1.1F, 1.2F, 1.3F, 1.4F) G Pyrotechnic substance or article containing a pyrotechnic substance, or article containing both an explosive substance and an illuminating, incendiary, tear-producing or smoke-producing substance (other than a water-activated article or one containing white phosphorus, phosphide or flammable liquid or gel or hypergolic liquid) (1.1G, 1.2G, 1.3G, 1.4G) H Article containing both an explosive substance and white phosphorus (1.2H, 1.3H) J Article containing both an explosive substance and flammable liquid or gel (1.1J, 1.2J, 1.3J) K Article containing both an explosive substance and a toxic chemical agent (1.2K, 1.3K) L Explosive substance or article containing an explosive substance and presenting a special risk (e.g., due to water-activation or presence of hypergolic liquids, phosphides or pyrophoric substances) needing isolation of each type (1.1L, 1.2L, 1.3L) N Articles containing only extremely insensitive detonating substances (1.6N) S Substance or article so packed or designed that any hazardous effects arising from accidental functioning are limited to the extent that they do not significantly hinder or prohibit fire fighting or other emergency response efforts in the immediate vicinity of the package (1.4S)

Low Explosives

Low explosives are normally employed as propellants. Most low explosives are mixtures; most high explosives are compounds, but to both there are notable exceptions. They undergo deflagration at rates that vary from a few centimeters per second to approximately 400 meters per second. Included in this group are smokeless powders, and pyrotechnics such as flares and illumination devices.

High Explosives

High explosives are normally employed in mining, demolitions and military warheads. They undergo detonation at rates of 1,000 to 8,500 meters per second. High explosives are conventionally subdivided into two classes and differentiated by sensitivity:
- Primary explosives are extremely sensitive to shock, friction, and heat. They will burn rapidly or detonate if ignited.
- Secondary or Base explosives are relatively insensitive to shock, friction, and heat. They may burn when ignited in small, unconfined quantities, but detonation can occur. These are sometimes added in small amount to blasting caps to boost their power. Dynamite, RDX, PETN, HMX, and others are secondary explosives. Some definitions add a third category:
- Tertiary, also called blasting agents. These are so insensitive to shock that they cannot be detonated by practical quantities of primary explosive, and instead require an intermediate explosive booster of secondary explosive. Some examples would be an Ammonium Nitrate/Fuel Oil mixture commonly known as ANFO and slurry or 'Wet Bag' explosives. These are primarily used in large scale mining and construction operations. Note that many if not most explosive chemical compounds may usefully deflagrate as well as detonate, and are used in high as well as low explosive compositions. This also means that under extreme conditions, propellant can detonate. For example, nitrocellulose deflagrates if ignited, but detonates if initiated by a detonator.

Detonation of an Explosive Charge

Also called an initiation sequence or a firing train, this is the sequence of events which cascade from relatively low levels of energy to cause a chain reaction to initiate the final explosive material or main charge. They can be either low or high explosive trains. Low explosive trains are something like a bullet - Primer and a propellant charge. High explosives trains can be more complex, either Two-Step (e.g. Detonator and Dynamite) or Three-Step (e.g. Detonator, Booster and ANFO). Detonators are often made from tetryl and Fulminates.

Composition of the material

Mixtures of an oxidizer and a fuel
- Black powder: potassium nitrate, charcoal and sulfur
- Flash powder: fine metal powder (usually aluminium or magnesium) and a strong oxidizer (e.g. potassium chlorate or perchlorate).
- Ammonal: ammonium nitrate and aluminium powder.
- Armstrong's mixture: potassium chlorate and red phosphorus. This is a very sensitive mixture. It is a primary high explosive in which sulfur is substitute for some or all phosphorus to slightly decrease sensitivity.
- Sprengel explosives: a very general class incorporating any strong oxidizer and highly reactive fuel, although in practice the name most commonly was applied to mixtures of chlorates and nitroaromatics
- ANFO: ammonium nitrate and fuel oil.
- Cheddites: chlorates or perchlorates and oil
- oxyliquits: mixtures of organic materials and liquid oxygen Chemically pure compounds
- Nitroglycerin: an unstable liquid known as dynamite when mixed into sawdust, powdered silica or most commonly diatomaceous earth, which act as stabilizers.
- Acetone peroxide: A very unstable white organic peroxide
- TNT: Yellow insensitive crystals that can be melted and molded without detonation.
- Nitrocellulose: A variantly nitrated polymer which can be a high or low explosive depending on nitration level and conditions.
- RDX, PETN: Very strong explosives which can be used pure or in plastic explosives.
- C4: An RDX plastic explosive plasticized to be adhesive and malleable.

Chemical explosive reaction

A chemical explosive is a compound or mixture which, upon the application of heat or shock, decomposes or rearranges with extreme rapidity, yielding much gas and heat. Many substances not ordinarily classed as explosives may do one, or even two, of these things. For example, a mixture of nitrogen and oxygen can be made to react with great rapidity and yield the gaseous product nitric oxide; yet the mixture is not an explosive since it does not evolve heat, but rather absorbs heat. :N₂ + O₂ → 2NO - 43,200 calories (or 180 kJ) per mole of N₂ For a chemical to be an explosive, it must exhibit all of the following:
- Exhibit Rapid Expansion (eg. rapid production of gasses or rapid heating of surroundings)
- Evolution of heat
- Rapidity of reaction
- Initiation of reaction

Formation of gases

Gases may be evolved from substances in a variety of ways. When wood or coal is burned in the atmosphere, the carbon and hydrogen in the fuel combine with the oxygen in the atmosphere to form carbon dioxide and steam, together with flame and smoke. When the wood or coal is pulverized, so that the total surface in contact with the oxygen is increased, and burned in a furnace or forge where more air can be supplied, the burning can be made more rapid and the combustion more complete. When the wood or coal is immersed in liquid oxygen or suspended in air in the form of dust, the burning takes place with explosive violence. In each case, the same action occurs: a burning combustible forms a gas.

Evolution of heat

The generation of heat in large quantities accompanies every explosive chemical reaction. It is this rapid liberation of heat that causes the gaseous products of reaction to expand and generate high pressures. This rapid generation of high pressures of the released gas constitutes the explosion. It should be noted that the liberation of heat with insufficient rapidity will not cause an explosion. For example, although a pound of coal yields five times as much heat as a pound of nitroglycerin, the coal cannot be used as an explosive because the rate at which it yields this heat is quite slow.

Rapidity of reaction

Rapidity of reaction distinguishes the explosive reaction from an ordinary combustion reaction by the great speed with which it takes place. Unless the reaction occurs rapidly, the thermally expanded gases will be dissipated in the medium, and there will be no explosion. Again, consider a wood or coal fire. As the fire burns, there is the evolution of heat and the formation of gases, but neither is liberated rapidly enough to cause an explosion. For those who know something about electronics, this can be likened to the energy discharge of a battery, which is slow; to a flash capacitor, like that in a camera flash and releases its energy all at once.

Initiation of reaction

A reaction must be capable of being initiated by the application of shock or heat to a small portion of the mass of the explosive material. A material in which the first three factors exist cannot be accepted as an explosive unless the reaction can be made to occur when desired.

Military explosives

To determine the suitability of an explosive substance for military use, its physical properties must first be investigated. The usefulness of a military explosive can only be appreciated when these properties and the factors affecting them are fully understood. Many explosives have been studied in past years to determine their suitability for military use and most have been found wanting. Several of those found acceptable have displayed certain characteristics that are considered undesirable and, therefore, limit their usefulness in military applications. The requirements of a military explosive are stringent, and very few explosives display all of the characteristics necessary to make them acceptable for military standardization. Some of the more important characteristics are discussed below:

Availability and cost

In view of the enormous quantity demands of modern warfare, explosives must be produced from cheap raw materials that are nonstrategic and available in great quantity. In addition, manufacturing operations must be reasonably simple, cheap, and safe.

Sensitivity

Regarding an explosive, this refers to the ease with which it can be ignited or detonated—i.e., the amount and intensity of shock, friction, or heat that is required. When the term sensitivity is used, care must be taken to clarify what kind of sensitivity is under discussion. The relative sensitivity of a given explosive to impact may vary greatly from its sensitivity to friction or heat. Some of the test methods used to determine sensitivity are as follows:
- Impact Sensitivity is expressed in terms of the distance through which a standard weight must be dropped to cause the material to explode.
- Friction Sensitivity is expressed in terms of what occurs when a weighted pendulum scrapes across the material (snaps, crackles, ignites, and/or explodes).
- Heat Sensitivity is expressed in terms of the temperature at which flashing or explosion of the material occurs. Sensitivity is an important consideration in selecting an explosive for a particular purpose. The explosive in an armor-piercing projectile must be relatively insensitive, or the shock of impact would cause it to detonate before it penetrated to the point desired.

Stability

Stability is the ability of an explosive to be stored without deterioration. The following factors affect the stability of an explosive:
- Chemical constitution. The very fact that some common chemical compounds can undergo explosion when heated indicates that there is something unstable in their structures. While no precise explanation has been developed for this, it is generally recognized that certain groups, nitro dioxide (NO₂), nitrate (NO₃), and azide (N₃), are intrinsically in a condition of internal strain. Increased strain through heating can cause a sudden disruption of the molecule and consequent explosion. In some cases, this condition of molecular instability is so great that decomposition takes place at ordinary temperatures.
- Temperature of storage. The rate of decomposition of explosives increases at higher temperatures. All of the standard military explosives may be considered to be of a high order of stability at temperatures of -10 to +35 °C, but each has a high temperature at which the rate of decomposition becomes rapidly accelerated and stability is reduced. As a rule of thumb, most explosives become dangerously unstable at temperatures exceeding 70 °C.
- Exposure to sun. If exposed to the ultraviolet rays of the sun, many explosive compounds that contain nitrogen groups will rapidly decompose, affecting their stability.
- Electrical discharge. Electrostatic or spark sensitivity to initiation is common to a number of explosives. Static or other electrical discharge may be sufficient to inspire detonation under some circumstances. As a result, the safe handling of explosives and pyrotechnics almost always requires electrical grounding of the operator.

Power

The term power (or more properly, performance) as it is applied to an explosive refers to its ability to do work. In practice it is defined as its ability to accomplish what is intended in the way of energy delivery (i.e., fragments, air blast, high-velocity jets, underwater bubble energy, etc.). Explosive power or performance is evaluated by a tailored series of tests to assess the material for its intended use. Of the tests listed below, cylinder expansion and air-blast tests are common to most testing programs, and the others support specific uses.
- Cylinder expansion test. A standard amount of explosive is loaded in a cylinder usually manufactured of copper. Data is collected concerning the rate of radial expansion of the cylinder and maximum cylinder wall velocity. This also establishes the Gurney constant or 2E.
- Cylinder fragmentation test. A standard steel cylinder is charged with explosive and fired in a sawdust pit. The fragments are collected and the size distribution analyzed.
- Detonation pressure (Chapman-Jouget). Detonation pressure data derived from measurements of shock waves transmitted into water by the detonation of cylindrical explosive charges of a standard size.
- Determination of critical diameter. This test establishes the minimum physical size a charge of a specific explosive must be to sustain its own detonation wave. The procedure involves the detonation of a series of charges of different diameters until difficulty in detonation wave propagation is observed.
- Infinity diameter detonation velocity. Detonation velocity is dependent on landing density (c), charge diameter, and grain size. The hydrodynamic theory of detonation used in predicting explosive phenomena does not include diameter of the charge, and therefore a detonation velocity, for an imaginary charge of infinite diameter. This procedure requires a series of charges of the same density and physical structure, but different diameters, to be fired and the resulting detonation velocities extrapolated to predict the detonation velocity of a charge of infinite diameter.
- Pressure versus scaled distance. A charge of specific size is detonated and its pressure effects measured at a standard distance. The values obtained are compared with that for TNT.
- Impulse versus scaled distance. A charge of specific size is detonated and its impulse (the area under the pressure-time curve) measured versus distance. The results are tabulated and expressed in TNT equivalent.
- Relative bubble energy (RBE). A 5 to 50 kg charge is detonated in water and piezoelectric gauges are used to measure peak pressure, time constant, impulse, and energy. ::The RBE may be defined as K_x 3 ::RBE = K_s ::where K = bubble expansion period for experimental (x) or standard (s) charge.

Brisance

In addition to strength, explosives display a second characteristic, which is their shattering effect or brisance (from the French meaning to "break"), which is distinguished from their total work capacity. This characteristic is of practical importance in determining the effectiveness of an explosion in fragmenting shells, bomb casings, grenades, and the like. The rapidity with which an explosive reaches its peak pressure is a measure of its brisance. Brisance values are primarily employed in France and Russia. The sand crush test is commonly employed to determine the relative brisance in comparison to TNT. No single test is capable of directly comparing the explosive properties of two or more compounds; it is important to examine the data from several such tests (sand crush, trauzl, and so forth) in order to gauge relative brisance. True values for comparison will require field experiments.

Density

Density of loading refers to the unit weight of an explosive per unit volume. Several methods of loading are available, and the one used is determined by the characteristics of the explosive. The methods available include pellet loading, cast loading, or press loading. Dependent upon the method employed, an average density of the loaded charge can be obtained that is within 80-95% of the theoretical maximum density of the explosive. High load density can reduce sensitivity by making the mass more resistant to internal friction. If density is increased to the extent that individual crystals are crushed, the explosive will become more sensitive. Increased load density also permits the use of more explosive, thereby increasing the strength of the warhead.

Volatility

Volatility, or the readiness with which a substance vaporizes, is an undesirable characteristic in military explosives. Explosives must be no more than slightly volatile at the temperature at which they are loaded or at their highest storage temperature. Excessive volatility often results in the development of pressure within rounds of ammunition and separation of mixtures into their constituents. Stability, as mentioned before, is the ability of an explosive to stand up under storage conditions without deteriorating. Volatility affects the chemical composition of the explosive such that a marked reduction in stability may occur, which results in an increase in the danger of handling. Maximum allowable volatility is 2 ml of gas evolved in 48 hours.

Hygroscopicity

The introduction of moisture into an explosive is highly undesirable since it reduces the sensitivity, strength, and velocity of detonation of the explosive. Hygroscopicity is used as a measure of a material's moisture-absorbing tendencies. Moisture affects explosives adversely by acting as an inert material that absorbs heat when vaporized, and by acting as a solvent medium that can cause undesired chemical reactions. Sensitivity, strength, and velocity of detonation are reduced by inert materials that reduce the continuity of the explosive mass. When the moisture content evaporates during detonation, cooling occurs, which reduces the temperature of reaction. Stability is also affected by the presence of moisture since moisture promotes decomposition of the explosive and, in addition, causes corrosion of the explosive's metal container. For all of these reasons, hygroscopicity must be negligible in military explosives.

Toxicity

Due to their chemical structure, most explosives are toxic to some extent. Since the effect of toxicity may vary from a mild headache to serious damage of internal organs, care must be taken to limit toxicity in military explosives to a minimum. Any explosive of high toxicity is unacceptable for military use.

Measurement of chemical explosive reaction

The development of new and improved types of ammunition requires a continuous program of research and development. Adoption of an explosive for a particular use is based upon both proving ground and service tests. Before these tests, however, preliminary estimates of the characteristics of the explosive are made. The principles of thermochemistry are applied for this process. Thermochemistry is concerned with the changes in internal energy, principally as heat, in chemical reactions. An explosion consists of a series of reactions, highly exothermic, involving decomposition of the ingredients and recombination to form the products of explosion. Energy changes in explosive reactions are calculated either from known chemical laws or by analysis of the products. For most common reactions, tables based on previous investigations permit rapid calculation of energy changes. Products of an explosive remaining in a closed calorimetric bomb (a constant-volume explosion) after cooling the bomb back to room temperature and pressure are rarely those present at the instant of maximum temperature and pressure. Since only the final products may be analyzed conveniently, indirect or theoretical methods are often used to determine the maximum temperature and pressure values. Some of the important characteristics of an explosive that can be determined by such theoretical computations are:
- Oxygen balance
- Heat of explosion or reaction
- Volume of products of explosion
- Potential of the explosive

Oxygen balance (OB%)

Oxygen balance is an expression that is used to indicate the degree to which an explosive can be oxidized. If an explosive molecule contains just enough oxygen to convert all of its carbon to carbon dioxide, all of its hydrogen to water, and all of its metal to metal oxide with no excess, the molecule is said to have a zero oxygen balance. The molecule is said to have a positive oxygen balance if it contains more oxygen than is needed and a negative oxygen balance if it contains less oxygen than is needed. The sensitivity, strength, and brisance of an explosive are all somewhat dependent upon oxygen balance and tend to approach their maximums as oxygen balance approaches zero. The oxygen balance (OB) is calculated from the empirical formula of a compound in percentage of oxygen required for complete conversion of carbon to carbon dioxide, hydrogen to water, and metal to metal oxide. The procedure for calculating oxygen balance in terms of 100 grams of the explosive material is to determine the number of moles of oxygen that are excess or deficient for 100 grams of a compound. :

OB% = \frac \times (2X + (Y/2) + M - Z)

where X = number of atoms of carbon, Y = number of atoms of hydrogen, Z = number of atoms of oxygen, and M = number of atoms of metal (metallic oxide produced). In the case of TNT (C₆H₂(NO₂)₃CH₃), Molecular weight = 227.1 X = 7 (number of carbon atoms) Y = 5 (number of hydrogen atoms) Z = 6 (number of oxygen atoms) Therefore :

OB% = \frac \times (14 + 2.5 - 6)

:OB% = -74% for TNT Because sensitivity, brisance, and strength are properties resulting from a complex explosive chemical reaction, a simple relationship such as oxygen balance cannot be depended upon to yield universally consistent results. When using oxygen balance to predict properties of one explosive relative to another, it is to be expected that one with an oxygen balance closer to zero will be the more brisant, powerful, and sensitive; however, many exceptions to this rule do exist. More complicated predictive calculations, such as those discussed in the next section, result in more accurate predictions. One area in which oxygen balance can be applied is in the processing of mixtures of explosives. The family of explosives called amatols are mixtures of ammonium nitrate and TNT. Ammonium nitrate has an oxygen balance of +20% and TNT has an oxygen balance of −74%, so it would appear that the mixture yielding an oxygen balance of zero would also result in the best explosive properties. In actual practice a mixture of 80% ammonium nitrate and 20% TNT by weight yields an oxygen balance of +1%, the best properties of all mixtures, and an increase in strength of 30% over TNT.

Heat of explosion

When a chemical compound is formed from its constituents, the reaction may either absorb or give off heat. The quantity of heat absorbed or given off during transformation is called the heat of formation. The heats of formations for solids and gases found in explosive reactions have been determined for a temperature of 15 °C and atmospheric pressure, and are normally tabulated in units of kilocalories per gram molecule. (See table 12-1). Where a negative value is given, it indicates that heat is absorbed during the formation of the compound from its elements. Such a reaction is called an endothermic reaction. The convention usually employed in simple thermochemical calculations is arbitrarily to take heat contents of all elements as zero in their standard states at all temperatures (standard state being defined as the state at which the elements are found under natural or ambient conditions). Since the heat of formation of a compound is the net difference between the heat content of the compound and that of its elements, and since the latter are taken as zero by convention, it follows that the heat content of a compound is equal to its heat of formation in such nonrigorous calculations. This leads us to the principle of initial and final state, which may be expressed as follows: "The net quantity of heat liberated or absorbed in any chemical modification of a system depends solely upon the initial and final states of the system, provided the transformation takes place at constant volume or at constant pressure. It is completely independent of the intermediate transformations and of the time required for the reactions." From this it follows that the heat liberated in any transformation accomplished through successive reactions is the algebraic sum of the heats liberated or absorbed in the different reactions. Consider the formation of the original explosive from its elements as an intermediate reaction in the formation of the products of explosion. The net amount of heat liberated during an explosion is the sum of the heats of formation of the products of explosion, minus the heat of formation of the original explosive. The net heat difference between heats of formations of the reactants and products in a chemical reaction is termed the heat of reaction. For oxidation this heat of reaction may be termed heat of combustion. In explosive technology only materials that are exothermic — that is, have a heat of reaction that causes net liberation of heat — are of interest. Hence, in this text, heats of reaction are virtually all positive. Reaction heat is measured under conditions either of constant pressure or constant volume. It is this heat of reaction that may be properly expressed as "heat of the explosion."

Balancing chemical explosion equations

In order to assist in balancing chemical equations, an order of priorities is presented in table 12-2. Explosives containing C, H, O, and N and/or a metal will form the products of reaction in the priority sequence shown. Some observation you might want to make as you balance an equation:
- The progression is from top to bottom; you may skip steps that are not applicable, but you never back up.
- At each separate step there are never more than two compositions and two products.
- At the conclusion of the balancing, elemental forms, nitrogen, oxygen, and hydrogen, are always found in diatomic form. Example, TNT: :C₆H₂(NO₂)₃CH₃; constituents: 7C + 5H + 3N + 6O Using the order of priorities in table 12-1, priority 4 gives the first reaction products: :7C + 6O → 6CO with one mol of carbon remaining Next, since all the oxygen has been combined with the carbon to form CO, priority 7 results in: :3N → 1.5N₂ Finally, priority 9 results in: 5H → 2.5H₂ The balanced equation, showing the products of reaction resulting from the detonation of TNT is: :C₆H₂(NO₂)₃CH₃ → 6CO + 2.5H₂ + 1.5N₂ + C Notice that partial moles are permitted in these calculations. The number of moles of gas formed is 10. The product, carbon, is a solid.

Volume of products of explosion

The law of Avogadro states that equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. From this law, it follows that the molar volume of one gas is equal to the molar volume of any other gas. The molar volume of any gas at 0 °C and under normal atmospheric pressure is very nearly 22.4 liters or 22.4 cubic decimeters. Thus, considering the nitroglycerin reaction. :C₃H₅(NO₃)₃ → 3CO₂ + 2.5H₂O + 1.5N₂ + 0.25O₂ the explosion of one mole of nitroglycerin produces in the gaseous state: 3 moles of CO₂; 2.5 moles of O₂. Since a molar volume is the volume of one mole of gas, one mole of nitroglycerin produces 3 + 2.5 + 1.5 + 0.25 = 7.25 molar volumes of gas; and these molar volumes at 0 °C and atmospheric pressure form an actual volume of 7.25 × 22.4 = 162.4 liters of gas. (Note that the products H₂O and CO₂ are in their gaseous form.) Based upon this simple beginning, it can be seen that the volume of the products of explosion can be predicted for any quantity of the explosive. Further, by employing Charles' Law for perfect gases, the volume of the products of explosion may also be calculated for any given temperature. This law states that at a constant pressure a perfect gas expands 1/273.15 of its volume at 0 °C, for each degree Celsius of rise in temperature. Therefore, at 15 °C the molar volume of an ideal gas is, :V₁₅ = 22.414 (288.15/273.15) = 23.64 liters per mole Thus, at 15 °C the volume of gas produced by the explosive decomposition of one mole of nitroglycerin becomes :V = (23.64 l/mol)(7.25 mol) = 171.4 l

Explosive strength

The potential of an explosive is the total work that can be performed by the gas resulting from its explosion, when expanded adiabatically from its original volume, until its pressure is reduced to atmospheric pressure and its temperature to 15 °C. The potential is therefore the total quantity of heat given off at constant volume when expressed in equivalent work units and is a measure of the strength of the explosive. An explosion may occur under two general conditions: the first, unconfined, as in the open air where the pressure (atmospheric) is constant; the second, confined, as in a closed chamber where the volume is constant. The same amount of heat energy is liberated in each case, but in the unconfined explosion, a certain amount is used as work energy in pushing back the surrounding air, and therefore is lost as heat. In a confined explosion, where the explosive volume is small (such as occurs in the powder chamber of a firearm), practically all the heat of explosion is conserved as useful energy. If the quantity of heat liberated at constant volume under adiabatic conditions is calculated and converted from heat units to equivalent work units, the potential or capacity for work results. Therefore, if Q_mp represents the total quantity of heat given off by a mole of explosive of 15 °C and constant pressure (atmospheric); Q_mv represents the total heat given off by a mole of explosive at 15 °C and constant volume; and W represents the work energy expended in pushing back the surrounding air in an unconfined explosion and thus is not available as net theoretical heat; Then, because of the conversion of energy to work in the constant pressure case, :Q_mv = Q_mp + W from which the value of Q_mv may be determined. Subsequently, the potential of a mole of an explosive may be calculated. Using this value, the potential for any other weight of explosive may be determined by simple proportion. Using the principle of the initial and final state, and heat of formation table (resulting from experimental data), the heat released at constant pressure may be readily calculated. m n Q_mp = v_iQ_fi - v_kQ_fk 1 1 where: Q_fi = heat of formation of product i at constant pressure Q_fk = heat of formation of reactant k at constant pressure v = number of moles of each product/reactants (m is the number of products and n the number of reactants) The work energy expended by the gaseous products of detonation is expressed by: :W = P dv With pressure constant and negligible initial volume, this expression reduces to: :W = P·V₂ Since heats of formation are calculated for standard atmospheric pressure (101 325 Pa, where 1 Pa = 1 N/m²) and 15 °C, V₂ is the volume occupied by the product gases under these conditions. At this point W/mol = (101 325 N/m²)(23.63 L/mol)(1 m³/1000 L) = 2394 N·m/mol = 2394 J/mol and by applying the appropriate conversion factors, work can be converted to units of kilocalories. W/mol = 0.572 kcal/mol Once the chemical reaction has been balanced, one can calculate the volume of gas produced and the work of expansion. With this completed, the calculations necessary to determine potential may be accomplished. For TNT: :C₆H₂(NO₂)₃CH₃ → 6CO + 2.5H₂ + 1.5N₂ + C for 10 mol Then: :Q_mp = 6(26.43) - 16.5 = 142.08 kcal/mol Note: Elements in their natural state (H₂, O₂, N₂, C, etc.) are used as the basis for heat of formation tables and are assigned a value of zero. See table 12-2. :Q_mv = 142.08 + 0.572(10) = 147.8 kcal/mol As previously stated, Q_mv converted to equivalent work units is the potential of the explosive. (MW = Molecular Weight of Explosive) Potential = Q_mv kcal/mol × 4185 J/kcal × 10³ g/kg × 1 mol/(mol·g) Potential = Q_mv (4.185 × 10⁶) J/(mol·kg) For TNT, Potential = 147.8 (4.185 × 10⁶)/227.1 = 2.72 × 10⁶ J/kg Rather than tabulate such large numbers, in the field of explosives, TNT is taken as the standard explosive, and others are assigned strengths relative to that of TNT. The potential of TNT has been calculated above to be 2.72 × 10⁶ J/kg. Relative strength (RS) may be expressed as :R.S. = Potential of Explosive/(2.72 × 10⁶)

Example of thermochemical calculations

The PETN reaction will be examined as an example of thermo-chemical calculations. :PETN: C(CH₂ONO₂)₄ :Molecular weight = 316.15 g/mol :Heat of formation = 119.4 kcal/mol (1) Balance the chemical reaction equation. Using table 12-1, priority 4 gives the first reaction products: :5C + 12O → 5CO + 7O Next, the hydrogen combines with remaining oxygen: :8H + 7O → 4H₂O + 3O Then the remaining oxygen will combine with the CO to form CO and CO₂. :5CO + 3O → 2CO + 3CO₂ Finally the remaining nitrogen forms in its natural state (N₂). :4N → 2N₂ The balanced reaction equation is: :C(CH₂ONO₂)₄ → 2CO + 4H₂O + 3CO₂ + 2N₂ (2) Determine the number of molar volumes of gas per mole. Since the molar volume of one gas is equal to the molar volume of any other gas, and since all the products of the PETN reaction are gaseous, the resulting number of molar volumes of gas (N_m) is: :N_m = 2 + 4 + 3 + 2 = 11 V_molar/mol (3) Determine the potential (capacity for doing work). If the total heat liberated by an explosive under constant volume conditions (Q_m) is converted to the equivalent work units, the result is the potential of that explosive. The heat liberated at constant volume (Q_mv) is equivalent to the liberated at constant pressure (Q_mp) plus that heat converted to work in expanding the surrounding medium. Hence, Q_mv = Q_mp + work (converted). :a. Q_mp = Q_fi (products) - Q_fk (reactants) ::where: Q_f = heat of formation (see table 12-2) ::For the PETN reaction: :::Q_mp = 2(26.343) + 4(57.81) + 3(94.39) - (119.4) = 447.87 kcal/mol ::(If the compound produced a metallic oxide, that heat of formation would be included in Q_mp. :b. Work = 0.572N_m = 0.572(11) = 6.292 kcal/mol :As previously stated, Q_mv converted to equivalent work units is taken as the potential of the explosive. :c. Potential J = Q_mv (4.185 × 10⁶ kg)(MW) = 454.16 (4.185 × 10⁶) 316.15 = 6.01 × 10⁶ J kg :This product may then be used to find the relative strength (RS) of PETN, which is :d. RS = Pot (PETN) = 6.01 × 10⁶ = 2.21 Pot (TNT) 2.72 × 10⁶

External links

- [http://www.blasterexchange.com Blaster Exchange - Explosives Industry Portal]
- [http://www.fas.org/man/dod-101/navy/docs/fun/part12.htm Military Explosives]
- [http://globalsecurity.org/military/systems/munitions/explosives-class.htm UN hazard classification code]
- [http://environmentalchemistry.com/yogi/hazmat/placards/class1.html Class 1 Hazmat Placards]

References

- Army Research Office. Elements of Armament Engineering (Part One). Washington, D.C.: U.S. Army Material Command, 1964.
- Commander, Naval Ordnance Systems Command. Safety and Performance Tests for Qualification of Explosives. NAVORD OD 44811. Washington, D.C.: GPO, 1972.
- Commander, Naval Ordnance Systems Command. Weapons Systems Fundamentals. NAVORD OP 3000, vol. 2, 1st rev. Washington, D.C.: GPO, 1971.
- Departments of the Army and Air Force. Military Explosives. Washington, D.C.: 1967.
- USDOT Hazardous Materials Transportation Placards Category:Explosives ja:火薬

Binary star

:This article is about a star system. For the rap group, see Binary Star (rap). A binary star system consists of two stars both orbiting around their barycenter. For each star, the other is its "companion star". The term "binary star" was apparently first coined by Sir William Herschel in 1802 to designate "a real double star — the union of two stars that are formed together in one system by the laws of attraction". Any two stars seen close to one another form a double star, the most famous being Mizar and Alcor in the Big Dipper. Odds are, though, that a double star is probably a foreground and background star pair that only looks like a binary system —the two stars are, in reality, widely separated in space but just happen to lie in roughly the same direction as seen from our vantage point. Such "false binaries" are termed optical binaries. With the invention of the telescope, many such pairs were found. Herschel, in 1780, measured the separation and orientations of over 700 pairs that appeared to be binary systems and found that about 50 pairs changed orientation over two decades of observation. A binary star is thus a pair of stars that are held together by the force of gravity. Systems in which the individual stars that compose a binary star can be resolved (distinguished) with a powerful enough telescope (including by interferometric methods) are known as visual binaries. In other cases, the only indication of binarity is obtained from the Doppler shift of the spectral lines. These systems, known as spectroscopic binaries, consist of relatively close pairs of stars whose orbital plane is substantially inclined with respect to the plane of the celestial sphere, such that the spectral lines of both stars are seen to shift regularly to the blue and then to the red, as they orbit towards and away from us. If the orbital plane is very nearly perpendicular to the plane of the celestial sphere, such that the two stars actually occult each other regularly, one has an eclipsing binary. Binary stars that are simultaneously visual and spectroscopic binaries are rare, and they are a precious source of valuable information when found. Visual binary stars, unless they are relatively close to Earth, have a large true separation, and consequently their orbital speeds are usually too small to be measured spectroscopically. Conversely, spectroscopic binary stars move fast in their orbits, and this is because they are close together — usually too close to be detected as visual binaries. Binaries that are both visual and spectroscopic are thus usually relatively close to us. Scientists have discovered some stars that seem to orbit around an empty space. Astrometric binaries, for example, are relatively nearby stars which can be seen to wobble around a middle point, with no visible companion. With some spectroscopic binaries, there is only one set of lines shifting back and forth. The same arguments for ordinary binaries can be used to infer the mass of the missing companion. The companion could be very dim, such that it is currently undetectable or lost in the glare of its primary, or it could be an object that doesn't shine in visible light, like a neutron star. In some instances, one can make a very strong case that the missing companion is in fact a black hole —a star with such strong gravitational force that no light is able to get out. Perhaps the best example of such a system is Cygnus X-1, where the mass of the unseen companion is about nine times the mass of our sun —far exceeding the maximum mass of a neutron star, the other likely candidate for the companion. Binaries are particularly crucial as one of the primary methods by which astronomers can directly measure the mass of a distant star. The gravitational pull between the individual stars of a binary causes each to orbit around the other. From the orbital pattern of a visual binary, or the time variation of the spectrum of a spectroscopic binary, the mass of its stars can therefore be determined. Because a majority of stars exist in binary systems, binaries are particularly important to our understanding of the processes by which stars form. In particular, the period and masses of the binary tell us about the amount of angular momentum in the system. Because angular momentum is a conserved quantity in physics, binaries give us important clues about the conditions in which the stars were themselves formed.

Binary star classifications

At present, binary stars are classified into four types according to their observable properties:
- visual binaries
- spectroscopic binaries
- eclipsing binaries
- astrometric binaries Any star can belong to several of these classes, e.g., several spectroscopic binaries are also eclipsing binaries. Another three-category classification is based on the distance of the stars, relative to their sizes :
- detached binaries
- semi-detached binaries
- contact binaries

Research findings

During the past 200 years a large amount of research has been carried out on binary stars leading to some general conclusions. It is believed that at least a quarter of all stars are at least binary systems, with as many as 10% of these systems containing more than two stars (ternary etc.). There is a direct correlation between the period of revolution of a binary star and the eccentricity of its orbit, with systems of short period having smaller eccentricity. Binary stars may be found with any conceivable separation, from pairs orbiting so closely that they are practically in contact with each other, to pairs so distantly separated that their connection is indicated only by their common proper motion through space. Remarkably, among gravitationally-bound binary star sytems, there exists a log normal distribution of periods, with the majority of these systems orbiting with a period of about 100 years. In pairs where the two stars are of equal brightness, they are also of the same spectral type. In systems where the brightnesses are different, the fainter star is bluer if the brighter star is a giant star and redder if the brighter star belongs to the main sequence. Since mass can be determined only from gravitational attraction, and the only stars (with the exception of the Sun, and gravitationally-lensed stars) for which the gravitational attraction can be determined are binary stars, binaries constitute a uniquely important class of stars. In the case of a visual binary star, after the orbit has been determined and the stellar parallax of the system obtained, the combined mass of the two stars may be obtained by a direct application of the Keplerian harmonic law. Unfortunately, it is impossible to obtain the complete orbit of a spectroscopic binary unless it is also a visual or an eclipsing binary, so from these objects only a determination of the joint product of mass and the sine of the angle of inclination relative to the line of sight is possible. Therefore, without additional information regarding the angle of inclination, the mass can only be inferred in a statistical sense. In the case of eclipsing binaries which are also spectroscopic binaries it is possible to make a complete solution for the specifications (mass, density, size, luminosity, and approximate shape) of both members of the system. Science Fiction has often featured planets of binary or ternary stars as a setting. In reality, some orbital ranges are impossible for dynamical reasons (the planet would be expelled from its orbit relatively quickly, being either ejected from the system altogether or transferred to a more inner or outer orbital range), whilst other orbits present serious challenges for eventual biospheres because of possible extreme variations in surface temperature over time. Detecting planets around multiple star systems introduces all sorts of additional technical difficulties, which may be why so far (July 2005) only one such planet has been found: HD 188753 Ab.

Binary star examples

- Albireo
- Algol (triple, eclipsing binary)
- Alpha Centauri (triple)
- Castor (sextuple)
- Procyon
- Sirius

External links

- [http://en.wikibooks.org/wiki/GAT:_binary_star Wikibooks: Glossary of Astronomical Terms (GAT): Binary star] Category:Star types Category:Star systems ko:쌍성 ja:連星

Binary thinking

In critical theory, a binary opposition is a pair of theoretical opposites, often organized in a hierarchy. In structuralism, the binary opposition is thought to be a powerful tool to elucidate the fundamental structure of human thought, culture, and language. The structuralist view has been criticized, however, by post-structuralists, who view the binary opposition not as a fundamental organizer of human thought worldwide, but as an artifact of Western thought. A classic example of a binary opposition is the rational-emotional dichotomy, of which the West imbues rational with a higher status than emotional. Another example is the dichotomy between presence and absence, with presence occupying a higher status in Western thought than absence. The similarities between each of the "higher" Western concepts such as rational and presence, as well as others such as male (vs. female) and speech (vs. writing) are thought to betray a historic bias in Western thought called logocentrism or phallogocentrism. The critique of binary oppositions is an important part of post-feminism, post-colonialism, post-anarchism, and critical race theory, which argue that the perceived binary dichotomy between man/woman, civilized/savage, and caucasian/non-caucasian have perpetuated and legitimized Western power structures favoring "civilized" white men. Post-structural criticism of binary oppositions is not simply the reversal of the opposition, but its deconstruction, which is described as apolitical—that is, not intrinsically favoring one arm of a binary opposition over the other. Deconstruction is the "event" or "moment" at which a binary opposition is thought to contradict itself, and undermine its own authority.

Binary numeral system

The binary numeral system represents numeric values using two symbols, typically 0 and 1. More specifically, binary is a positional notation with a radix of two. Owing to its relatively straightforward implementation in electronic circuitry, the binary system is used internally by virtually all modern computers.

History

Ancient Indian mathematician Pingala presented the first known description of a binary numeral system in the 3rd century BC, which coincided with his discovery of the concept of zero. The modern binary number system was fully documented by Gottfried Leibniz in the 17th century in his article Explication de l'Arithmétique Binaire. Leibniz's uses 0 and 1, like the modern binary numeral system. In 1854, British mathematician George Boole published a landmark paper detailing a system of logic that would become known as Boolean algebra. His logical system proved instrumental in the development of the binary system, particularly in its implementation in electronic circuitry. In 1937, Claude Shannon produced his master's thesis at MIT that implemented Boolean algebra and binary arithmetic using electronic relays and switches for the first time in history. Entitled A Symbolic Analysis of Relay and Switching Circuits, Shannon's thesis essentially founded practical digital circuit design. In November of 1937, George Stibitz, then working at Bell Labs, completed a relay-based computer he dubbed the "Model K" (for "kitchen", where he had assembled it), which calculated using binary addition. Bell Labs thus authorized a full research program in late 1938 with Stibitz at the helm. Their Complex Number Computer, completed January 8, 1940, was able to calculate complex numbers. In a demonstration to the American Mathematical Society conference at Dartmouth College on September 11, 1940, Stibitz was able to send the Complex Number Calculator remote commands over telephone lines by a teletype. It was the first computing machine ever used remotely over a phone line. Some participants of the conference who witnessed the demonstration were John Von Neumann, John Mauchly, and Norbert Wiener, who wrote about it in his memoirs.

Representation

A binary number can be represented by any sequence of bits (binary digits), which in turn may be represented by any mechanism capable of being in two mutually exclusive states. The following sequences of symbols could all be interpreted as different binary numeric values: 1 0 1 0 0 1 1 - | | - - x x x o x o o n y y n bit to express binary values. In this clock, each column of LEDs shows a binary-coded decimal numeral of the traditional sexagesimal time. ]] The numeric value represented in each case is dependent upon the value assigned to each symbol. In a computer, the numeric values may be represented by two different voltages; on a magnetic disk, magnetic polarities may be used. A "positive", "yes", or "on" state is not necessarily equivalent to the numerical value of one; it depends on the architecture in use. In keeping with customary representation of numerals using arabic numerals, binary numbers are commonly written using the symbols 0 and 1. When written, binary numerals are often subscripted or suffixed in order to indicate their base, or radix. The following notations are equivalent: :100101 binary (explicit statement of format) :100101b (a suffix indicating binary format) :bin 100101 (a prefix indicating binary format) :100101₂ (a subscript indicating base-2 notation) When spoken, binary numerals are usually pronounced by pronouncing each individual digit, in order to distinguish them from decimal numbers. For example, the binary numeral "100" is pronounced "one zero zero", rather than "one hundred", to make its binary nature explicit, and for purposes of correctness. Since the binary numeral "100" is equal to the decimal value four, it would be confusing, and numerically incorrect, to refer to the numeral as "one hundred."

Counting in binary

Counting in binary is similar to counting in any other number system. Beginning with a single digit, counting proceeds through each symbol, in increasing order. Decimal counting uses the symbols 0 through 9, while binary only uses the symbols 0 and 1. When the symbols for the first digit are exhausted, the next-higher digit (to the left) is incremented, and counting starts over at 0. In decimal, counting proceeds like so: :00, 01, 02, ... 07, 08, 09 (rightmost digit starts over, and the 0 is incremented) :10, 11, 12, ... 17, 18, 19 (rightmost digit starts over, and the 1 is incremented) :20, 21, 22, ... When the rightmost digit reaches 9, counting returns to 0, and the second digit is incremented. In binary, counting is similar, with the exception that only the two symbols 0 and 1 are used. When 1 is reached, counting begins at 0 again, with the digit to the left being incremented: :000, 001 (rightmost digit starts over, and the second 0 is incremented) :010, 011 (middle and rightmost digits start over, and the first 0 is incremented) :100, 101 (rightmost digit starts over again, middle 0 is incremented) :110, 111...

Binary Simplified!

Okay, for those of us, like me, who have trouble understanding binary, think of it like this... We use a base ten system. What this means, exactly, is that the value of each position in a numerical value can be represented by one of ten possible symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9 We are all familiar with these and how the decimal system works using these ten symbols. When we begin counting values, we should start with the symbol 0, and proceed to 9 when counting. We call this the "ones" place. The "ones" place, with those digits, might be thought of as a multiplication problem. 5 can be thought of as 5 X 10^0 (10 to the zeroeth power, which equals 5 X 1, since any number to the zero power is one). [10^0 = 1] As we move to the left of the ones place, we increase the power of 10 by one. Thus, to represent 50 in this same manner, it can be thought of as 5 X 10^1, or 5 X 10.

500 = (5  -  10^2) + (0  -  10^1) + (0  -  10^0) =  5  -  100

$5000 = (5 - 10^3) + (0 - 10^2) + (0 - 10^1) + (0 - 10^0) = 5 - 1000$

When we run out of symbols in the decimal numeral system, we "move to the left" one place and use a '1' to represent the "tens" place. Then we reset the symbol in the "ones" place back to the first symbol, zero. Binary is a base two system which works just like our decimal system, however with only two symbols which can be used to represent numerical values: 0 and 1. We begin in the "ones" place with 0, then go up to 1. Now we are out of symbols, so to represent a higher value, we must place a '1' in the "twos" place, since we don't have a symbol we can use in the binary system for 2, like we do in the decimal system. In the binary numeral system, the value represented as 10 is 0 times (1
- 2^1) + (0
- 2^0). Thus, it equals '2' in our decimal system.

Binary - to - Decimal equivalence:

$1 = 1 - 2^0 = 1 - 1 = 1$

$10 = (1 - 2^1) + (0 - 2^0) = 2 + 0 = 2$

$100 = (1 - 2^2) + (0 - 2^1) + (0 - 2^0) = 4 + 0 + 0 = 4$

While this is in the conversion guide, it is 'hidden', and the conversion guide makes it a little more complicated.

Binary arithmetic

Arithmetic in binary is much like arithmetic in other numeral systems. Addition, subtraction, multiplication, and division can be performed on binary numerals.

Addition

decimal, which adds two bits together, producing sum and carry bits.]] The simplest arithmetic operation in binary is addition. Adding two single-digit binary numbers is relatively simple: :0 + 0 = 0 :0 + 1 = 1 :1 + 0 = 1 :1 + 1 = 10 (the 1 is carried) Adding two "1" values produces the value "10", equivalent to the decimal value 2. This is similar to what happens in decimal when certain single-digit numbers are added together; if the result exceeds the value of the radix (10), the digit to the left is incremented: :5 + 5 = 10 :7 + 9 = 16 This is known as carrying in most numeral systems. When the result of an addition exceeds the value of the radix, the procedure is to "carry the one" to the left, adding it to the next positional value. Carrying works the same way in binary: 1 1 1 1 1 (carry) 0 1 1 0 1 + 1 0 1 1 1 ------------- = 1 0 0 1 0 0 In this example, two numerals are being added together: 01101 (13 decimal) and 10111 (23 decimal). The top row shows the carry bits used. Starting in the rightmost column, 1 + 1 = 10. The 1 is carried to the left, and the 0 is written at the bottom of the rightmost column. The second column from the right is added: 1 + 0 + 1 = 10 again; the 1 is carried, and 0 is written at the bottom. The third column: 1 + 1 + 1 = 11. This time, a 1 is carried, and a 1 is written in the bottom row. Proceeding like this gives the final answer 100100.

Subtraction

Subtraction works in much the same way: :0 - 0 = 0 :0 - 1 = 1 (with borrow) :1 - 0 = 1 :1 - 1 = 0 One binary numeral can be subtracted from another as follows:
-
-
-
- (starred columns are borrowed from) 1 1 0 1 1 1 0 - 1 0 1 1 1 ---------------- = 1 0 1 0 1 1 1 Subtracting a positive number is equivalent to adding a negative number of equal absolute value; computers typically use the two's complement notation to represent negative values. This notation eliminates the need for a separate "subtract" operation. For further details, see two's complement.

Multiplication

Multiplication in binary is similar to its decimal counterpart. Two numbers A and B can be multiplied by partial products: for each digit in B, the product of that digit in A is calculated and written on a new line, shifted leftward so that its rightmost digit lines up with the digit in B that was used. The sum of all these partial products gives the final result. Since there are only two digits in binary, there are only two possible outcomes of each partial multiplication:
- If the digit in B is 0, the partial product is also 0
- If the digit in B is 1, the partial product is equal to A For example, the binary numbers 1011 and 1010 are multiplied as follows: 1 0 1 1 (A) × 1 0 1 0 (B) --------- 0 0 0 0 ← Corresponds to a zero in B 1 0 1 1 ← Corresponds to a one in B 0 0 0 0 + 1 0 1 1 --------------- = 1 1 0 1 1 1 0 See also Booth's multiplication algorithm.

Division

Binary division is again similar to its decimal counterpart: __________ 1 0 1 | 1 1 0 1 1 Here, the divisor is 101, or 5 decimal, while the dividend is 11011, or 27 decimal. The procedure is the same as that of decimal long division; here, the divisor 101 goes into the first three digits 110 of the dividend one time, so a "1" is written on the top line. This result is multiplied by the divisor, and subtracted from the first three digits of the dividend; the next digit (a "1") is included to obtain a new three-digit sequence: 1 __________ 1 0 1 | 1 1 0 1 1 - 1 0 1 ----- 0 1 1 The procedure is then repeated with the new sequence, continuing until the digits in the dividend have been exhausted: 1 0 1 __________ 1 0 1 | 1 1 0 1 1 - 1 0 1 ----- 0 1 1 - 0 0 0 ----- 1 1 1 - 1 0 1 ----- 1 0 Thus, the quotient of 11011 divided by 101 is 101₂, as shown on the top line, while the remainder, shown on the bottom line, is 10₂. In decimal, 27 divided by 5 is 5, with a remainder of 2.

Bitwise logical operations

Though not directly related to the numerical interpretation of binary symbols, sequences of bits may be manipulated using Boolean logical operators. When a string of binary symbols is manipulated in this way, it is called a bitwise operation; the logical operators AND, OR, and XOR may be performed on corresponding bits in two binary numerals provided as input. The logical NOT operation may be performed on individual bits in a single binary numeral provided as input. Sometimes, such operations may be used as arithmetic short-cuts, and may have other computational benefits as well. For example, discarding the last bit of a binary number (also known as binary shifting), is the decimal equivalent of division by two. See Bitwise operation.

Conversion to and from other numeral systems

Decimal

This method works for conversion from any base, but there are better methods for bases which are powers of two, such as octal and hexadecimal given below. In place-value numeral systems, digits in successively lower, or less significant, positions represent successively smaller powers of the radix. The starting exponent is one less than the number of digits in the number. A five-digit number would start with an exponent of four. In the decimal system, the radix is 10 (ten), so the left-most digit of a five-digit number represents the 10⁴ (ten thousands) position. Consider: :97352₁₀ is equal to: ::9 times 10⁴ (9 × 10000 = 90000) plus ::7 times 10³ (7 × 1000 = 7000) plus ::3 times 10² (3 × 100 = 300) plus ::5 times 10¹ (5 × 10 = 50) plus ::2 times 10⁰ (2 × 1 = 2) Multiplication by the radix is simple. The digits are shifted left, and a 0 is appended to the right end of the number. For example, 9735 times 10 is equal to 97350. So one way to interpret a string of digits is as the last digit added to the radix times all but the last digit. 97352 equals 9735 times 10 plus 2. An example in binary is 1101100111₂ equals 110110011₂ times 2 plus 1. This is the essence of the conversion method. At each step, write the number to be converted as 2
- k + 0 or 2
- k + 1 for an integer k, which becomes the new number to be converted. :118₁₀ equals ::59 x 2 + 0 ::(29 x 2 + 1) x 2 + 0 ::((14 x 2 + 1) x 2 + 1) x 2 + 0 ::(((7 x 2 + 0) x 2 + 1) x 2 + 1) x 2 + 0 ::((((3 x 2 + 1) x 2 + 0) x 2 + 1) x 2 + 1) x 2 + 0 ::(((((1 x 2 + 1) x 2 + 1) x 2 + 0) x 2 + 1) x 2 + 1) x 2 + 0 ::1 x 2⁶ + 1 x 2⁵ + 1 x 2⁴ + 0 x 2³ + 1 x 2² + 1 x 2¹ + 0 x 2⁰ ::1110110₂ So in the algorithm to convert from an integer decimal numeral to its binary equivalent, the number is divided by two, and the remainder written in the ones-place. The result is again divided by two, its remainder written in the next place to the left. This process repeats until the number becomes zero. For example, 118₁₀, in binary, is: Reading the sequence of remainders from the bottom up gives the binary numeral 1110110₂. To convert from binary to decimal is the reverse algorithm. Starting from the left, double the result and add the next digit until there are no more. For example to convert 110010101101₂ to decimal: and the result is 3245₁₀. The fractional parts of a numbers are converted with similar methods. They are again based on the equivalence of shifting with doubling or halving. In a fractional binary number such as .11010110101₂, the first digit is 1/2, the second 1/2², etc. So if there is a 1 in the first place after the decimal, then the number is at least 1/2, and vice versa. Double that number is at least 1. This suggests the algorithm: Repeatedly double the number to be converted, record if the result is at least 1, and then throw away the integer part. For example, (1/3)₁₀, in binary, is: which is the repeating fraction 0.0101...₂ Or for example, 0.1₁₀, in binary, is: which is also a repeating fraction 0.000110011...₂ It may come as a surprise that terminating decimal fractions can have repeating expansions in binary. It is for this reason that many are surprised to discover that 0.1 + ... + 0.1, (10 additions) differs from 1 in floating point arithmetic. In fact, the only binary fractions with terminating expansions are of the form of an integer divided by a power of 2, which 1/10 is not. The final conversion is from binary to decimal fractions. The only difficulty arises with repeating fractions, but otherwise the method is to shift the fraction to an integer, convert it as above, and then divide by the appropriate power of two in the decimal base. For example, Another way, perhaps quicker and more efficient than the previous, of converting from binary to decimal, is to do so indirectly- first converting (x binary) or (x decimal) to (x hexidecimal) and then converting (x hexidecimal) to the opposite of the former, respectively.

Hexadecimal

Binary may be converted to and from hexadecimal somewhat more easily. This is due to the fact that the radix of the hexadecimal system (16) is a power of the radix of the binary system (2). More specifically, 16 = 2⁴, so it takes exactly four digits of binary to represent one digit of hexadecimal. The following table shows each hexadecimal digit along with the equivalent four-digit binary sequence: To convert a hexadecimal number into its binary equivalent, simply substitute the corresponding binary digits: :3A₁₆ = 0011 1010₂ :E7₁₆ = 1110 0111₂ To convert a binary number into its hexadecimal equivalent, divide it into groups of four bits. If the number of bits isn't a multiple of four, simply insert extra 0 bits at the left (called padding). For example: :1010010₂ = 0101 0010 grouped with padding = 52₁₆ :11011101₂ = 1101 1101 grouped = DD₁₆

Octal

Binary is also easily converted to the octal numeral system, since octal uses a radix of 8, which is a power of two (namely, 2³, so it takes exactly three binary digits to represent an octal digit). The correspondence between octal and binary numerals is the same as for the first eight digits of hexadecimal in the table above. Binary 000 is equivalent to the octal digit 0, binary 111 is equivalent to octal 7, and so on. Converting from octal to binary proceeds in the same fashion as it does for hexadecimal: :65₈ = 110 101₂ :17₈ = 001 111₂ And from binary to octal: :101100₂ = 101 100₂ grouped = 54₈ :10011₂ = 010 011₂ grouped with padding = 23₈

Representing real numbers

Non-integers can be represented by using negative powers, which are set off from the other digits by means of a radix point (called a decimal point in the decimal system). For example, the binary number 11.01₂ thus means: :1 times 2¹ (1 × 2 = 2) plus :1 times 2⁰ (1 × 1 = 1) plus :0 times 2^-1 (0 × (1/2) = 0) plus :1 times 2^-2 (1 × (1/4) = 0.25) For a total of 3.25 decimal. All dyadic rational numbers p/2^a have a terminating binary numeral -- the binary representation has only finitely many terms after the radix point. Other rational numbers have binary representation, but instead of terminating, they recur, with a finite sequence of digits repeating indefinitely. For instance :1/3₁₀ = 1/11₂ = 0.0101010101...₂ :12₁₀/17₁₀ = 1100₂ / 10001₂ = 0.10110100 10110100 10110100...₂ The phenomenon that the binary representation of any rational is either terminating or recurring also occurs in other radix-based numeral systems. See, for instance, the explanation in Decimal. Another similarity is the existence of alternative representations for any terminating representation, relying on the fact that 0.111111... is the sum of the geometric series 2^-1 + 2^-2 + 2^-3 + ... which is 1. Binary numerals which neither terminate nor recur represent irrational numbers. For instance,
- 0.10100100010000100000100.... does have a pattern, but it is not a fixed-length recurring pattern, so the number is irrational
- 1.0110101000001001111001100110011111110... is the binary representation of √2, the square root of 2, another irrational. It has no discernible pattern, although a proof that √2 is irrational requires more than this. See irrational number.

Binary humor

- "Binary is as easy as 1, 10, 11."
- "There are 10 kinds of people in the world - those who understand binary numbers, and those who don't."

External links

- [http://www.insidereality.net/site/content/math/base_conversion.php Simple Conversion Methods]
- [http://www-history.mcs.st-andrews.ac.uk/history/Projects/Pearce/index.html Indian mathematics]
- [http://www.cut-the-knot.org/binary.shtml Base Converter] at cut-the-knot
- [http://www.cut-the-knot.org/do_you_know/BinaryHistory.shtml Binary System] at cut-the-knot
- [http://www.cut-the-knot.org/blue/frac_conv.shtml Conversion of Fractions] at cut-the-knot
- [http://leetkey.mozdev.org This FireFox extension supports ASCII/Binary conversions and typing]
- [http://www.permadi.com/tutorial/numHexToDec/ Converting Hexadecimal to Decimal]
- [http://www.permadi.com/tutorial/numDecToHex/ Converting Decimal to Hexadecimal]
- [http://www.paulschou.com/tools/xlate/ Online tool] to translate ASCII to/from Binary, Hex, Decimal and Base64 Category:Computer arithmetic Category:Elementary arithmetic Category:Numeration 2 ja:2進数 th:เลขฐานสอง

Binary and text files

Computer files can be divided into two broad categories: binary and text. Text files are files which contain ordinary textual characters with essentially no formatting; binary files are all other files. Or, rather, text files are a special case of binary files, since any file is fundamentally a sequence of bits, and many computer components (for example, all hard disk circuitry and most system software) make no distinction between file types. However, a large percentage of application programs can understand and use text files in some way, but few programs can typically understand and use the contents of a particular binary file. Hence the distinction can be useful to computer users.

Text files

Text files (or plain text files) are files where most bytes (or short sequences of bytes) represent ordinary readable characters such as letters, digits, and punctuation (including space), and include some control characters such as tabs, line feeds and carriage returns. This simplicity allows a wide variety of programs to display their contents. The similar term plaintext is most commonly used in a cryptographic context. The similarity sometimes causes confusion, especially among those new to computers, cryptography, or data communications. Generally, a text file contains characters in an ASCII-based encoding, or much less commonly an EBCDIC-based encoding, without any embedded information such as font information, hyperlinks or inline images. Text files are often encoded in an extension of ASCII; these include ISO 8859, EUC, a special encoding for Windows, a special encoding for Mac OS, and Unicode encoding schemes (common on many platforms) such as UTF-8 or UTF-16. Although many text files are generally meant for humans to read, some are (also) used for data storage by computer programs. Text files are sometimes advantageous even for data storage because they avoid certain problems with binary files, such as endianness, padding bytes, or differences in the number of bytes in a machine word. Plain text is often used as a readable representation of other data that is not itself purely textual: for example, a formatted webpage is not plain text, but its HTML source is. Similarly, source code for computer programs is usually stored in text files, but is compiled into a binary form for execution. Text files usually have the MIME type "text/plain", usually with additional information indicating an encoding. Prior to the advent of Mac OS X, the Mac OS system regarded the content of a file (the data fork) to be a text file when its resource fork indicated that the type of the file was "TEXT". The Windows system regards a file to be a text file if the suffix of the name of the file is "txt". However, source code for computer programs are also text, but usually have file name suffixes indicating which programming language the source is written in. Unix, Macintosh,