History.

IRC was created by Jarkko Oikarinen in August 1988 to replace a program called MUT (MultiUser Talk) on a BBS called OuluBox at the University of Oulu in Finland, where he was working at the Department of Information Processing Science. Jarkko intended to extend the BBS software he administered, to allow news in the Usenet style, real time discussions and similar BBS features. The first part he implemented was the chat part, which he did with borrowed parts written by his friends Jyrki Kuoppala and Jukka Pihl. The first IRC network was running on a single server named tolsun.oulu.fi. Oikarinen found inspiration in a chat system known as Bitnet Relay, which operated on the BITNET.  Jyrki Kuoppala pushed Oikarinen to ask Oulu University to free the IRC code so that it also could be run outside of Oulu, and after they finally got it released, Jyrki Kuoppala immediately installed another server. This was the first "irc network". Oikarinen got some friends at the Helsinki University and Tampere University to start running IRC servers when his number of users increased and other universities soon followed. At this time Oikarinen realized that the rest of the BBS features probably wouldn't fit in his program.  Oikarinen got in touch with people at the University of Denver and Oregon State University. They had their own IRC network running and wanted to connect to the Finnish network. They had obtained the program from one of Oikarinen's friends, Vijay Subramaniam—the first non-Finnish person to use IRC. IRC then grew larger and got used on the entire Finnish national network—Funet—and then connected to Nordunet, the Scandinavian branch of the Internet. In November 1988, IRC had spread across the Internet and in the middle of 1989, there were some 40 servers worldwide.

EFnet.

In August 1990, the first major disagreement took place in the IRC world. The "A-net" (Anarchy net) included a server named eris.berkeley.edu. It was all open, required no passwords and had no limit on the number of connects. As Greg "wumpus" Lindahl explains: "it had a wildcard server line, so people were hooking up servers and nick-colliding everyone". The "Eris Free Network", EFnet, made the eris machine the first to be Q-lined (Q for quarantine) from IRC. In wumpus' words again:

Undernet fork.

Another fork effort, the first that really made a big and lasting difference, was initiated by 'Wildthang' in the U.S. October 1992 (it forked off the EFnet ircd version 2.8.10). It was meant to be just a test network to develop bots on but it quickly grew to a network "for friends and their friends". In Europe and Canada a separate new network was being worked on and in December the French servers connected to the Canadian ones, and by the end of the month, the French and Canadian network was connected to the US one, forming the network that later came to be called "The Undernet".  The "undernetters" wanted to take ircd

DALnet fork.

During the summer of 1994, the Undernet was itself forked. The new network was called DALnet (named after its founder: dalvenjah), formed for better user service and more user and channel protections. One of the more significant changes in DALnet was use of longer nicknames (the original ircd limit being 9 letters). DALnet ircd modifications were made by Alexei "Lefler" Kosut. DALnet was thus based on the Undernet ircd server, although the DALnet pioneers

IRCnet fork.

In July 1996, after months of flame wars and discussions on the mailing list, there was yet another split due to disagreement in how the development of the ircd should evolve. Most notably, the "european" (most of those servers were in Europe) side that later named itself IRCnet argued for nick and channel delays where the EFnet side argued for timestamps. There were also disagreements

Modern IRC.

IRC has changed much over its life on the Internet. New server software has added a multitude of new features. , a new standardization effort is under way under a working group called IRCv3, which focuses on more advanced client features like instant notifications, better history support and improved security., no major IRC networks have fully adopted the proposed standard.  After its golden era during the 1990s and early 2000s (240,000 users on QuakeNet in 2004), IRC has seen a significant decline, losing around 60% of users between 2003 and 2012, with users moving to newer

Technical information.

IRC is an open protocol that uses TCP and, optionally, TLS. An IRC server can connect to other IRC servers to expand the IRC network. Users access IRC networks by connecting a client to a server. There are many client implementations, such as mIRC, HexChat and irssi, and server implementations, e.g. the original IRCd. Most IRC servers do not require users to register an account but a nick is required before being connected.  IRC was originally a plain text protocol (although later extended), which on request was assigned port 194/TCP by IANA. However, the "de facto" standard has always been to run IRC on 6667/TCP and nearby port numbers (for example TCP ports 6660–6669, 7000) to avoid having to run the IRCd software with root privileges.  The protocol specified that characters were 8-bit but did not specify the character encoding the text was supposed to use. This can cause problems when users using different clients and/or different platforms want to converse.  All client-to-server IRC protocols in use today are descended from the protocol implemented in the irc2.4.0 version of the IRC2 server, and documented in RFC 1459. Since RFC 1459 was published, the new features in the irc2.10 implementation led to the publication of several revised protocol documents (RFC 2810, RFC 2811, RFC 2812 and RFC 2813); however, these protocol changes have not been widely adopted among other implementations.  Although many specifications on the IRC protocol have been published, there is no official specification, as the protocol remains dynamic. Virtually no clients and very few servers rely strictly on the above RFCs as a reference.  Microsoft made an extension for IRC in 1998 via the proprietary IRCX. They later stopped distributing software supporting IRCX, instead developing the proprietary MSNP.  The standard structure of a network of IRC servers is a tree. Messages are routed along only necessary branches of the tree but network state is sent to every server and there is generally a high degree of implicit trust between servers. However, this architecture has a number of problems. A misbehaving or malicious server can cause major damage to the network and any changes in structure, whether intentional or a result of conditions on the underlying network, require a net-split and net-join. This results in a lot of network traffic and spurious quit/join messages to users and temporary loss of communication to users on the splitting servers. Adding a server to a large network means a large background bandwidth load on the network and a large memory load on the server. Once established, however, each message to multiple recipients is delivered in a fashion similar to multicast, meaning each message travels a network link exactly once. This is a strength in comparison to non-multicasting protocols such as Simple Mail Transfer Protocol (SMTP) or Extensible Messaging and Presence Protocol (XMPP).  An IRC daemon can also be used on a local area network (LAN). IRC can thus be used to facilitate communication between people within the local area network (internal communication).

Challenges.

Issues in the original design of IRC were the amount of shared state data being a limitation on its scalability, the absence of unique user identifications leading to the nickname collision problem, lack of protection from netsplits by means of cyclic routing, the trade-off in scalability for the sake of real-time user presence information, protocol weaknesses providing a platform for abuse, no transparent and optimizable message passing, and no encryption. Some of these issues have been addressed in "Modern IRC".

Attacks.

Because IRC connections may be unencrypted and typically span long time periods, they are an attractive target for DoS/DDoS attackers and hackers. Because of this, careful security policy is necessary to ensure that an IRC network is not susceptible to an attack such as a takeover war. IRC networks may also K-line or G-line users or servers that have a harming effect.  Some IRC servers support SSL/TLS connections for security purposes. This helps stop the use of packet sniffer programs

Abuse prevention.

One of the most contentious technical issues surrounding IRC implementations, which survives to this day, is the merit of "Nick/Channel Delay" vs. "Timestamp" protocols. Both methods exist to solve the problem of denial-of-service attacks, but take very different approaches. The problem with the original IRC protocol as implemented was that when two servers split and rejoined, the two sides of the network would simply merge their channels. If a user could join on a "split" server, where a channel that existed on the other side of the network was empty, and gain operator status, they would become a channel operator of the "combined" channel after the netsplit ended; if a user took a nickname that existed

Clients.

Client software.

Client software exists for various operating systems or software packages, as well as web-based or inside games. Many different clients are available for the various operating systems, including Windows, Unix and Linux, Mac OS X and mobile operating systems (such as iOS and Android). On Windows, mIRC is one of the most popular clients.  Some programs which are extensible through plug-ins also serve as platforms for IRC clients. For instance, a client called

Bots.

A typical use of bots in IRC is to provide IRC services or specific functionality within a channel such as

Bouncer.

A program that runs as a daemon on a server and functions as a persistent proxy is known as a BNC or bouncer. The purpose is to maintain a connection to an IRC server, acting as a relay between the server and client, or simply to act as a proxy. Should the client lose network connectivity, the BNC may stay connected and archive all traffic for later delivery, allowing the user to resume their IRC session without disrupting their connection to the server.  Furthermore, as a

Search engines.

There are numerous search engines available to aid the user in finding what they are looking for on IRC. Generally the search engine consists of two parts, a "back-end" (or "spider/crawler") and a front-end "search engine".  The back-end (spider/webcrawler) is the work horse of the search engine. It is responsible for crawling IRC servers to index the information being sent across them. The information that is indexed usually consists solely of channel text (text that is publicly displayed in public channels). The storage method is usually some sort of relational database, like MySQL or Oracle.

Character encoding.

IRC still lacks a single globally accepted standard convention for how to transmit characters outside the 7-bit ASCII repertoire. IRC servers normally transfer messages from a client to another client just as byte sequences, without any interpretation or recoding of characters. The IRC protocol (unlike e.g. MIME or HTTP) lacks mechanisms for announcing and negotiating character encoding options. This has

File sharing.

Much like conventional P2P file sharing, users can create file servers that allow them to share files with each other by using customised IRC bots or scripts for their IRC client. Often users will group together to distribute warez via a network of IRC bots.  Technically, IRC provides no file transfer mechanisms itself; file sharing is implemented by IRC "clients", typically using the Direct Client-to-Client (DCC) protocol, in which file transfers are negotiated through the exchange of private messages between clients. The vast majority of IRC clients feature support for DCC file transfers, hence the view that file sharing is an integral feature of IRC. The commonplace usage of this protocol, however, sometimes also causes DCC spam. DCC commands have also been used to exploit vulnerable clients into performing an action such as disconnecting from the server or exiting the client.

Internet Relay Chat (IRC) is an application layer protocol that facilitates communication in the form of text. The chat process works on a client/server networking model. IRC clients are computer programs that users can install on their system or web based applications running either locally in the browser or on a 3rd party server. These clients communicate with chat servers to transfer messages to other clients. IRC is mainly designed for group communication in discussion forums, called channels, but also allows one-on-one communication via private messages as well as chat and data transfer, including file sharing.

Internet Relay Chat, kurz IRC, bezeichnet ein textbasiertes Chat-System. Es ermöglicht Gesprächsrunden mit einer beliebigen Anzahl von Teilnehmern in so genannten Gesprächskanälen („Channels“), aber auch Gespräche mit nur zwei Partnern (Query). Neue Channels können von jedem Teilnehmer eröffnet werden, ebenso kann man gleichzeitig an mehreren Channel-Gesprächen teilnehmen.


Life and career.

Jean-Pierre Jeunet was born in Roanne, France. He bought his first camera at the age of 17 and made short films while studying animation at Cinémation Studios. He befriended Marc Caro, a designer and comic book artist who became his longtime collaborator and co-director. They met at an animation festival in Annecy in the 1970s.  Together, Jeunet and Caro directed award-winning animations. Their first live action film was "The Bunker of the Last Gunshots" (1981), a short film about soldiers in a bleak futuristic world. Jeunet also directed numerous advertisements and music videos, such as Jean Michel Jarre's "Zoolook" (together with Caro).  Jeunet's films often resonate with the late twentieth century French film movement, "cinéma du look", and allude to themes and aesthetics involving German expressionism, French poetic realism, and the French New Wave.  Jeunet and Caro's first feature film was "Delicatessen" (1991), a melancholy comedy set in a famine-plagued post-apocalyptic world, in which an apartment building above a delicatessen is ruled by a butcher who kills people in order to feed his tenants.  They next made "The City of Lost Children" (1995), a dark, multi-layered fantasy film about a mad scientist who steals children's dreams so that he can live indefinitely. The success of "The City of Lost Children" led to an invitation to direct the fourth film in the "Alien" series, "Alien Resurrection" (1997). This is where Jeunet and Caro ended up going their separate ways as Jeunet believed this to be an amazing opportunity and Caro was not interested in a film that lacked creative control working on a big-budget Hollywood movie. Caro ended up assisting for a few weeks, with costumes and set design but afterwards, decided to work on a solo career in illustration and computer graphics.  Jeunet directed "Amélie" (2001), the story of a woman who takes pleasure in doing good deeds but has trouble finding love herself, which starred Audrey Tautou. "Amélie" was a huge critical and commercial success worldwide and was nominated for several Academy Awards. For his work on the film, Jeunet won a European Film Award for Best Director.  In 2004, Jeunet released "A Very Long Engagement", an adaptation of the novel by Sébastien Japrisot. The film, starring Audrey Tautou and Jodie Foster, chronicled a woman's search for her missing lover after World War I.  In 2009, he released "Micmacs" which is about a man and his friends who come up with an intricate and original plan to destroy two big weapons manufacturers.  Jeunet has also directed numerous commercials including a 2'25" film for Chanel N° 5 featuring his frequent collaborator Audrey Tautou.  In 2013, Jeunet released "The Young and Prodigious T.S. Spivet" an adaptation of Reif Larsen's book "The Selected Works of T.S. Spivet" that starred Kyle Catlett.  In 2016, Jeunet and Romain Segaud co-directed the 3-minute stop-motion animation film "Deux escargots s'en vont", based on a poem by Jacques Prévert.  Since his last release, Jeunet has tried to get other projects funded but has found it impossible to find investors willing to take a risk on his quirky films. He stated in 2019 that he may go to Netflix "as a last resort."

Filmography.

Technical Advisor

Jean-Pierre Jeunet (; born 3 September 1953) is a French film director, producer, and screenwriter. His films mix elements of fantasy, realism and science fiction either to create idealized realities or to give relevance to mundane situations. A former animator, his movies are marked by quirky, slapstick humor, alongside surrealist visuals.

Jean-Pierre Jeunet (* 3. September 1953 in Roanne, Département Loire, Frankreich) ist ein französischer Regisseur. Zu seiner künstlerischen Handschrift gehören skurrile Charaktere und eine außergewöhnlich ausgeprägte inszenatorische Gestaltungskraft.


Geography.

According to the definition established in a 1932 convention signed by Denmark, Norway and Sweden (registered in the League of Nations Treaty Series 1933–1934), the northern boundary between the Kattegat and Skagerrak is found at the northernmost point of Skagen on Jutland, while the southern boundary towards Øresund is found at the tip of Kullen Peninsula in Scania.  Major waterways that drain into the Kattegat are the rivers of Göta älv at Gothenburg, together with the Lagan, Nissan, Ätran and Viskan in the province of Halland on the Swedish side, and the river of Gudenå in Jutland, in Denmark.  The main islands of the Kattegat are Samsø, Læsø and Anholt; the latter two are, due to their relatively dry climate, situated in what is called "the Danish desert belt".  A number of noteworthy coastal areas abut the Kattegat, including the Kullaberg Nature Reserve in Scania, Sweden, which contains a number of rare species and a scenic rocky shore, the town of Mölle, which has a picturesque harbour and views into the Kullaberg, and Skagen at the northern tip of Denmark.  Since the 1950s, a bridge project usually referred to as "Kattegatbroen" (The Kattegat Bridge) connecting Jutland and Zealand across the Kattegat has been considered. Since the late 2000s, the project has seen a renewed interest from several influential politicians in Denmark. The bridge is usually envisioned as connecting Hov (a village south of Odder in the Aarhus area) with Samsø and Kalundborg.

Extent.

The International Hydrographic Organization defines the limits of the "Kattegat, Sound and Belts" (that is, the Kattegat, Øresund, Great Belt, and Little Belt) as follows:

Etymology.

According to "Den Store Danske Encyklopædi" and "Nudansk Ordbog", the name derives from the Dutch words'("cat's") and'("hole, gate"). It derives from late medieval navigation jargon, in which captains of the Hanseatic trading fleets would compare the Danish Straits to a hole so narrow that even a cat would have difficulty squeezing its way through, on account of the many reefs and shallow waters. At one point, the passable waters were a mere wide. The name of the Copenhagen street "Kattesundet" has a comparable etymological meaning, namely "narrow passage".  An archaic name for both the Skagerrak and Kattegat was the "Norwegian Sea" or "Jutland Sea" (Knýtlinga saga mentions the name "Jótlandshaf"). Its ancient Latin name was "".

History.

Control of the Kattegat, and access to it, have been important throughout the history of international seafaring. Until the completion of the Eider Canal in 1784, the Kattegat was the only sea route into and out of the Baltic region.  Beginning in 1429 in the Middle Ages, the Danish royal family – and later the state of Denmark – prospered greatly from the Sound dues, a toll charged for passage through the Øresund, while Copenhagen provided shelter, trade and repair opportunities and protection from piracy. The dues were eventually lifted in 1857.

Biology.

In the Kattegat, the salinity has a pronounced two-layer structure. The upper layer has a salinity between 18‰ and 26‰ and the lower layer – separated by a strong halocline at around – has a salinity between 32‰ and 34‰. The lower layer consists of inflowing seawater from the Skagerrak, with a salinity on level with most other coastal seawaters, while the upper layer consists of inflowing seawater from the Baltic Sea and has a much lower salinity, comparable to brackish water, but still a great deal higher than the rest of the Baltic sea. These two opposing flows transport a net surplus of seawater from the Baltic to the Skagerrak every year. During stronger winds, the layers in the Kattegat are completely mixed in some places, such as the Great Belt, so the overall salinity is highly variable in this small sea. This sets some unique conditions for the sealife here.  Cold seeps, locally known as "bubbling reefs" (), are found in the northern Kattegat. Unlike cold seeps in most other places (including the North Sea and Skagerrak), the Kattegat bubbling reefs are at relatively shallow depths, generally between below the surface. The seeps rely on methane deposited during the Eemian period and during calm weather the bubbles can sometimes be seen on the water surface. Carbonate cementation and lithification form slaps or pillars up to tall, and support a rich biodiversity. Because of their unique status, the Kattegat bubbling reefs receive a level of protection and are recognized as a Natura 2000 habitat (type 1180) by the European Union (EU).

Ecological collapse.

The Kattegat was one of the first marine dead zones to be noted in the 1970s, when scientists began studying how intensive industrial activities affected the natural world. Since then, studies and research has provided much insight into processes like eutrophication, and how to deal with it. Denmark and the EU have initiated costly and far-reaching domestic projects in order to stop, repair and prevent these environmentally destructive and economically damaging processes, since the first Action Plan for the Aquatic Environment in 1985, and are now busy implementing the fourth Action Plan. The action plans sums up a broad range of initiatives and includes the so-called Nitrate Directives. The action plans have generally been viewed as a success, although the work is not finished and all goals are not completely met yet.

Protections and regulation.

Due to the very heavy sea traffic and many large coastal settlements, the Kattegat has been designated as a Sulphur Emission Control Area as part of the Baltic Sea since 2006. The benchmark for sulphur in fuels was recently lowered to 0.1%, to be effectuated from 1 January 2015.  Several larger areas of the Kattegat are designated as Natura 2000 and under various bird protections such as the Ramsar Convention. The remaining larger shallow reefs are among the protections, as they are important spawning and feeding grounds for fish and marine mammals and they support a thriving but threatened biodiversity. Protected areas includes:  Denmark  Sweden

The Kattegat (; ; ) is a sea area bounded by the Jutlandic peninsula in the west, the Danish Straits islands of Denmark to the south and the provinces of Västergötland, Scania, Halland and Bohuslän in Sweden in the east. The Baltic Sea drains into the Kattegat through the Danish Straits. The sea area is a continuation of the Skagerrak and may be seen as a bay of the Baltic Sea or the North Sea or, as in traditional Scandinavian usage, neither of these.

Das Kattegat (Dänisch "Kattegat" [], Schwedisch "Kattegatt") ist ein 20.000 km2 bis 35.000 km2 großes und durchschnittlich rund 80 Meter tiefes, äußerst schwierig zu befahrendes Meeresgebiet zwischen Jütland (Dänemark) und der schwedischen Westküste. Bei Skagen grenzt es an das Skagerrak.


Characteristics.

The allotropes of carbon include graphite, one of the softest known substances, and diamond, the hardest naturally occurring substance. It bonds readily with other small atoms, including other carbon atoms, and is capable of forming multiple stable covalent bonds with suitable multivalent atoms. Carbon is known to form almost ten million compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements. At atmospheric pressure it has no melting point, as its triple point is at and, so it sublimes at about. Graphite is much more reactive than diamond at standard conditions, despite being more thermodynamically stable, as its delocalised pi system is much more vulnerable to attack. For example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C(COH), which preserves the hexagonal units of graphite while breaking up the larger structure.  Carbon sublimes in a carbon arc, which has a temperature of about 5800 K (5,530 °C or 9,980 °F). Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest-melting-point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper, which are weaker reducing agents at room temperature.  Carbon is the sixth element, with a ground-state electron configuration of 1s2s2p, of which the four outer electrons are valence electrons. Its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7 kJ/mol, are much higher than those of the heavier group-14 elements. The electronegativity of carbon is 2.5, significantly higher than the heavier group-14 elements (1.8–1.9), but close to most of the nearby nonmetals, as well as some of the second- and third-row transition metals. Carbon's covalent radii are normally taken as 77.2 pm (C−C), 66.7 pm (C=C) and 60.3 pm (C≡C), although these may vary depending on coordination number and what the carbon is bonded to. In general, covalent radius decreases with lower coordination number and higher bond order.  Carbon compounds form the basis of all known life on Earth, and the carbon–nitrogen cycle provides some of the energy produced by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers. It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures, carbon reacts with oxygen to form carbon oxides and will rob oxygen from metal oxides to leave the elemental metal. This exothermic reaction is used in the iron and steel industry to smelt iron and to control the carbon content of steel:  Carbon monoxide can be recycled to smelt even more iron:  with sulfur to form carbon disulfide and with steam in the coal-gas reaction: Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools.  The system of carbon allotropes spans a range of extremes:

Compounds.

Organic compounds.

Carbon can form very long chains of interconnecting carbon–carbon bonds, a property that is called catenation. Carbon-carbon bonds are strong and stable. Through catenation, carbon forms a countless number of compounds. A tally of unique compounds shows that more contain carbon than do not. A similar claim can be made for hydrogen because most organic compounds contain hydrogen chemically bonded to carbon or another common element like oxygen or nitrogen.  The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other atoms, known as heteroatoms. Common heteroatoms that appear in organic compounds include oxygen, nitrogen, sulfur, phosphorus, and the nonradioactive halogens, as well as the metals lithium and magnesium. Organic compounds containing bonds to metal are known as organometallic compounds ("see below"). Certain groupings of atoms, often including heteroatoms, recur in large numbers of organic

Inorganic compounds.

Commonly carbon-containing compounds which are associated with minerals or which do not contain bonds to the other carbon atoms, halogens, or hydrogen, are treated separately from classical organic compounds; the definition is not rigid, and the classification of some compounds can vary from author to author (see reference articles above). Among these are the simple oxides of carbon. The most prominent oxide is carbon dioxide (). This was once the principal constituent of the paleoatmosphere, but is a minor component of the Earth's atmosphere today. Dissolved in water, it forms carbonic acid (), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite. Carbon disulfide () is similar. Nevertheless, due to its physical properties and its association with organic synthesis, carbon disulfide is sometimes classified as

Organometallic compounds.

Organometallic compounds by definition contain at least one carbon-metal covalent bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (for example, tetraethyllead), η-alkene compounds (for example, Zeise's salt), and η-allyl compounds (for example, allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands (for example, ferrocene); and transition metal carbene complexes. Many metal carbonyls and metal cyanides exist (for example, tetracarbonylnickel and potassium ferricyanide); some workers consider metal carbonyl and cyanide complexes without other carbon ligands to be purely inorganic, and not organometallic. However, most organometallic chemists consider metal complexes with any carbon ligand, even 'inorganic carbon' (e.g., carbonyls, cyanides, and certain types of carbides and acetylides) to be organometallic in nature. Metal complexes containing organic ligands without a carbon-metal covalent bond (e.g., metal carboxylates) are termed "metalorganic" compounds.  While carbon is understood to strongly prefer formation of four covalent bonds, other exotic bonding schemes are also known. Carboranes are highly stable dodecahedral derivatives of

History and etymology.

The English name "carbon" comes from the Latin "carbo" for coal and charcoal, whence also comes the French "charbon", meaning charcoal. In German, Dutch and Danish, the names for carbon are "Kohlenstoff", "koolstof" and "kulstof" respectively, all literally meaning coal-substance.  Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizations. Diamonds were known probably as early as 2500 BCE in China, while carbon in the form of charcoal was made around Roman times by the same chemistry as it is today, by heating wood in a pyramid covered with clay to exclude air.  In 1722, René Antoine Ferchault de Réaumur demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon. In 1772, Antoine Lavoisier showed that diamonds are a form of carbon; when he burned samples of charcoal

Production.

Graphite.

Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin, found in association with quartz, mica and feldspars in schists, gneisses and metamorphosed sandstones and limestone as lenses or veins, sometimes of a metre or more in thickness. Deposits of graphite in Borrowdale, Cumberland, England were at first of sufficient size and purity that, until the 19th century, pencils were made simply by sawing blocks of natural graphite into strips before encasing the strips in wood. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.  There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphous graphite is the lowest

Diamond.

The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world (see figure).  Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed in this process and subsequently the particles are sorted by density. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.  Historically diamonds were known to be found only in alluvial deposits in southern India. India led the world in diamond production from the time of their discovery in approximately the 9th century BC to the mid-18th century AD,

Applications.

Carbon is essential to all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon other than food and wood is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is distilled in refineries by the petrochemical industry to produce gasoline, kerosene, and other products. Cellulose is a natural, carbon-containing polymer produced by plants in the form of wood, cotton, linen, and hemp. Cellulose is used primarily for maintaining structure in plants. Commercially valuable carbon polymers of animal origin include wool, cashmere and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chain. The raw materials for many of these synthetic substances come from crude oil.  The uses of carbon and its compounds are extremely varied. It can form alloys with iron, of which the most common is carbon steel. Graphite is combined with clays to form the 'lead' used in pencils used for writing and drawing. It is also used as a lubricant and a pigment, as a molding material in glass manufacture, in electrodes for dry batteries and in electroplating and electroforming, in brushes for electric motors and as a neutron moderator in nuclear reactors.  Charcoal is used as a drawing material in artwork, barbecue grilling, iron smelting, and in many other applications. Wood, coal and oil are used as fuel for production of energy and heating. Gem quality diamond is used in jewelry, and industrial diamonds are used in drilling, cutting and polishing tools for machining metals and stone. Plastics are made from fossil hydrocarbons, and carbon fiber, made by pyrolysis of synthetic polyester fibers is used to reinforce plastics to form advanced, lightweight composite materials.  Carbon fiber is made by pyrolysis of extruded and stretched filaments of polyacrylonitrile (PAN) and other organic substances. The crystallographic structure and mechanical properties of the fiber depend on the type of starting material, and on the subsequent processing. Carbon fibers made from PAN have structure resembling narrow filaments of graphite, but thermal processing may re-order the structure into a continuous rolled sheet. The result is fibers with higher specific tensile strength than steel.  Carbon black is used as the black pigment in printing ink, artist's oil paint and water colours, carbon paper, automotive finishes, India ink and laser printer toner. Carbon black is also used as a filler in rubber products such as tyres and in plastic compounds. Activated charcoal is used as an absorbent and adsorbent in filter material in applications as diverse as gas masks, water purification, and kitchen extractor hoods, and in medicine to absorb toxins, poisons, or gases from the digestive system. Carbon is used in chemical reduction at high temperatures. Coke is used to reduce iron ore into iron (smelting). Case hardening of steel is achieved by heating finished steel components in carbon powder. Carbides of silicon, tungsten, boron and titanium, are among the hardest known materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interior surfaces in the built environment other than glass, stone and metal.

Precautions.

Pure carbon has extremely low toxicity to humans and can be handled safely in the form of graphite or charcoal. It is resistant to dissolution or chemical attack, even in the acidic contents of the digestive tract. Consequently, once it enters into the body's tissues it is likely to remain there indefinitely. Carbon black was probably one of the first pigments to be used for tattooing, and Ötzi the Iceman was found to have carbon tattoos that survived during his life and for 5200 years after his death. Inhalation of coal dust or soot (carbon black) in large quantities can be dangerous, irritating lung tissues and causing the congestive lung disease, coalworker's pneumoconiosis. Diamond dust used as an abrasive can be harmful if ingested or inhaled. Microparticles of carbon are produced in diesel engine exhaust fumes, and may accumulate in the lungs. In these examples, the harm may result from contaminants (e.g., organic chemicals, heavy metals) rather than from the carbon itself.  Carbon generally has low toxicity to life on Earth; but carbon nanoparticles are deadly to "Drosophila".  Carbon may burn vigorously and brightly in the presence of air at high temperatures. Large accumulations of coal, which have remained inert for hundreds of millions of years in the absence of oxygen, may spontaneously combust when exposed to air in coal mine waste tips, ship cargo holds and coal bunkers, and storage dumps.  In nuclear applications where graphite is used as a neutron moderator, accumulation of Wigner energy followed by a sudden, spontaneous release may occur. Annealing to at least 250 °C can release the energy safely, although in the Windscale fire the procedure went wrong, causing other reactor materials to combust.  The great variety of carbon compounds include such lethal poisons as tetrodotoxin, the lectin ricin from seeds of the castor oil plant "Ricinus communis", cyanide (CN), and carbon monoxide; and such essentials to life as glucose and protein.

Carbon (from "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, C and C being stable, while C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.

Kohlenstoff (von urgerm. "kul-a-, kul-ō(n)-",Kohle‘) oder Carbon (von lat. "carbō",Holzkohle‘, latinisiert "Carboneum" oder "Carbonium") ist ein chemisches Element mit dem Elementsymbol C und der Ordnungszahl 6. Im Periodensystem steht es in der vierten Hauptgruppe bzw. der 14. IUPAC-Gruppe oder Kohlenstoffgruppe sowie der zweiten Periode.


History.

In July AD 754, the track which carried the dead Saint Boniface rested in the village over night. To the honour of the saint, the Bonifatiuskapelle (chapel of Boniface) was built.  Kriftel was first mentioned documentary in 790.  The Thirty Years' War damaged Kriftel including the chapel, which was not rebuilt until 1755. It took so long because a big fire destroyed almost the entire village (34 houses out of 38) in 1661.  From 1945 up until the oil crisis in 1973, Kriftel experienced a population explosion due to massive immigration from urban sprawl and workers of the Hoechst-AG, who were offered cheap land to build their housing units.  In 1959, the chapel had to be relocated due to community growth.  During the mid-1970s, Kriftel fought for independence because Hofheim, the capital of the Main-Taunus district, wanted it to belong to it.  Airaines has been Kriftel's French sister city since 1981. The "Platz von Airaines" (Place of Airaines) at the train station was named after this partnership.

Today.

Kriftel has two churches, the catholic "St. Vitus" and the protestant "Auferstehungskirche". There are three schools, an elementary school (Lindenschule [Linden School]), a comprehensive school (Weingartenschule [Vineyard School]) and a vocational training school (Konrad-Adenauer-Schule). Kriftel lies at the federal motorway A 66 and the regional train line S 2 (From Niedernhausen over Frankfurt to Dietzenbach).  Kriftel is known for its good leisure facilities. In addition to multiple playgrounds, Kriftel has a large play park (Freizeitpark). This sports an outdoor swimming pool, sports fields including for football and volleyball, a miniature/crazy golf course, a quarter pipe for skating and extensive playgrounds. The village is also hosts various club activities. The most important clubs are the SV 07 Kriftel (soccer) and the Turn- und Sportverein Kriftel (sports in general especially volleyball and trick cycling). There are also large community festivals. The most prominent are the Lindenblütenfest (Feast of the blossom of the linden) in summer and the Krifteler Kerb (Kriftel's Kermesse) in autumn.

Town partnerships.

Kriftel is twinned to the following town:

Kriftel is a municipality in the Main-Taunus district, in Hesse, Germany. It is situated 16 km west of Frankfurt (centre).

Kriftel ist eine Gemeinde im südhessischen Main-Taunus-Kreis und liegt zentral im Rhein-Main-Gebiet zwischen Frankfurt am Main und der Landeshauptstadt Wiesbaden.


Description.

During classical antiquity, according to various accounts, priestesses and priests in the sacred grove interpreted the rustling of the oak (or beech) leaves to determine the correct actions to be taken. According to a new interpretation, the oracular sound originated from bronze objects hanging from oak branches and sounded with the wind blowing, similar to a wind chime.  According to Nicholas Hammond, Dodona was an oracle devoted to a Mother Goddess (identified at other sites with Rhea or Gaia, but here called Dione) who was joined and partly supplanted in historical times by the Greek deity Zeus.

History.

Early history.

Although the earliest inscriptions at the site date to c. 550–500 BCE, archaeological excavations conducted for more than a century have recovered artifacts as early as the Mycenaean era, many now at the National Archaeological Museum of Athens, and some in the archaeological museum at nearby Ioannina. There was an ancient tradition that Dodona was founded as a colony from the city, also named Dodona, in Thessaly.  Cult activity at Dodona was already established in some form during the Late Bronze Age (or Mycenaean period). During the post-Mycenaean period (or "Greek Dark Ages"), evidence of activity at Dodona is scant, but there is a resumption of contact between Dodona and southern Greece during the Archaic period (8th century BCE) with the presence of bronze votive offerings (i.e. tripods) from southern Greek cities. Archaeologists also have found Illyrian dedications and objects that were received by the oracle during the 7th century BCE. Until 650 BCE, Dodona was a religious and oracular centre mainly for northern tribes: only after 650 BCE did it become important for the southern tribes.  Zeus was worshipped at Dodona as "Zeus Naios" or "Naos" (god of the spring below the oak in the "temenos" or sanctuary, cf. Naiads) and as "Zeus Bouleus" (Counsellor). According to Plutarch, the worship of Jupiter (Zeus) at Dodona was set up by Deucalion and Pyrrha.  The earliest mention of Dodona is in Homer, and only Zeus is mentioned in this account. In the "Iliad" (circa 750 BCE), Achilles prays to "High Zeus, Lord of Dodona, Pelasgian, living afar off, brooding over wintry Dodona" (thus demonstrating that Zeus also could be invoked from a distance). No buildings are mentioned, and the priests (called "Selloi") slept on the ground with unwashed feet. No priestesses are mentioned in Homer.  The oracle also features in another passage involving Odysseus, giving a story of his visit to Dodona. Odysseus's words "bespeak a familiarity with Dodona, a realization of its importance, and an understanding that it was normal to consult Zeus there on a problem of personal conduct."  The details of this story are as follows. Odysseus says to the swineherd Eumaeus (possibly giving him a fictive account) that he (Odysseus) was seen among the Thesprotians, having gone to inquire of the oracle at Dodona whether he should return to Ithaca openly or in secret (as the disguised Odysseus is doing). Odysseus later repeats the same tale to Penelope, who may not yet have seen through his disguise.  According to some scholars, Dodona was originally an oracle of the Mother Goddess attended by priestesses. She was identified at other sites as Rhea or Gaia. The oracle also was shared by Dione (whose name simply means "deity"). By classical times, Dione was relegated to a minor role elsewhere in classical Greece, being made into an aspect of Zeus's more usual consort, Hera — but never at Dodona.  Many dedicatory inscriptions recovered from the site mention both "Dione" and "Zeus Naios".  According to some archaeologists, not until the 4th century BCE, was a small stone temple to Dione added to the site. By the time Euripides mentioned Dodona (fragmentary play "Melanippe") and Herodotus wrote about the oracle, the priestesses appeared at the site.

Classical Greece.

Though it never eclipsed the Oracle of Apollo at Delphi, Dodona gained a reputation far beyond Greece. In the "Argonautica" of Apollonius of Rhodes, a retelling of an older story of Jason and the Argonauts, Jason's ship, the "Argo", had the gift of prophecy, because it contained an oak timber spirited from Dodona.  In c. 290 BCE, King Pyrrhus made Dodona the religious capital of his domain and beautified it by implementing a series of construction projects (i.e. grandly rebuilt the Temple of Zeus, developed many other buildings, added a festival featuring athletic games, musical contests, and drama enacted in a theatre). A wall was built around the oracle itself and the holy tree, as well as temples to Dione and Heracles.  In 219 BCE, the Aetolians, under the leadership of General Dorimachus, invaded and burned the temple to the ground. During the late 3rd century BCE, King Philip V of Macedon (along with the Epirotes) reconstructed all the buildings at Dodona. In 167 BCE, Dodona was destroyed by the Romans (led by Aemilius Paulus), but was later rebuilt by Emperor Augustus in 31 BCE. By the time the traveller Pausanias visited Dodona in the 2nd century CE, the sacred grove had been reduced to a single oak. In 241 CE, a priest named Poplius Memmius Leon organized the Naia festival of Dodona. In 362 CE, Emperor Julian consulted the oracle prior to his military campaigns against the Persians.  Pilgrims still consulted the oracle until 391-392 CE when Emperor Theodosius closed all pagan temples, banned all pagan religious activities, and cut down the ancient oak tree at the sanctuary of Zeus. Although the surviving town was insignificant, the long-hallowed pagan site must have retained significance for Christians given that a Bishop Theodorus of Dodona attended the First Council of Ephesus in 431 CE.

Herodotus.

Herodotus ("Histories" 2:54–57) was told by priests at Egyptian Thebes in the 5th century BCE "that two priestesses had been carried away from Thebes by Phoenicians; one, they said they had heard was taken away and sold in Libya, the other in Hellas; these women, they said, were the first founders of places of divination in the aforesaid countries." The simplest analysis of the quote is: Egypt, for Greeks as well as for Egyptians, was a spring of human culture of all but immeasurable antiquity. This mythic element says that the oracles at the oasis of Siwa in Libya and of Dodona in Epirus were equally old, but similarly transmitted by Phoenician culture, and that the seeresses – Herodotus does not say "sibyls" – were women.  Herodotus follows with what he was told by the prophetesses, called "peleiades" ("doves") at Dodona: In the simplest analysis, this was a confirmation of the oracle tradition in Egypt. The element of the dove may be an attempt to account for a folk etymology applied to the archaic name of the sacred women that no longer made sense and the eventual connection with Zeus, justified by a tale told by a priestess. Was the "pel-" element in their name connected with "black" or "muddy" root elements in names like "Peleus" or "Pelops"? Is that why the doves were black?  Herodotus adds:  Thesprotia, on the coast west of Dodona, would have been available to the seagoing Phoenicians, whom readers of Herodotus would not have expected to have penetrated as far inland as Dodona.

Strabo.

According to Strabo, the oracle was founded by the Pelasgi: This oracle, according to Ephorus, was founded by the Pelasgi. And the Pelasgi are called the earliest of all peoples who have held dominion in Greece. The site of the oracle was dominated by Mount Tomaros, the area being controlled by the Thesprotians and then the Molossians: In ancient times, then, Dodona was under the rule of the Thesprotians; and so was Mount Tomaros, or Tmaros (for it is called both ways), at the base of which the temple is situated. And both the tragic poets and Pindaros have called Dodona 'Thesprotian Dodona.' But later on it came under the rule of the Molossoi. According to Pindar, the prophecies were originally uttered by men: At the outset, it is true, those who uttered the prophecies were men (this too perhaps the poet indicates, for he calls them “hypophetae” [interpreters] and the prophets might be ranked among these), but later on three old women were designated as prophets, after Dione also had been designated as temple-associate of Zeus. Pindar also reports as uncertain the story that the predecessor of Dodona oracle was located in Thessaly:...the temple [oracle] was transferred from Thessaly, from the part of Pelasgia which is about Scotussa (and Scotussa does belong to the territory called Thessalia Pelasgiotis), and also that most of the women whose descendants are the prophetesses of today went along at the same time; and it is from this fact that Zeus was also called “Pelasgian.” In a fragment of Pindar we find the following: Among the Thesprotians and the Molossians old women are called "peliai" and old men "pelioi," as is also the case among the Macedonians; at any rate, those people call their dignitaries "peligones" (compare the "gerontes" among the Laconians and the Massaliotes). And this, it is said, is the origin of the myth about the pigeons [peleiades] in the Dodonaean oak-tree.

Other commentaries.

According to Sir Richard Claverhouse Jebb, the epithet "Neuos" of Zeus at Dodona primarily designated "the god of streams, and, generally, of water". Jebb also points out that Achelous, as a water deity, received special honours at Dodona. The area of the oracle was quite swampy, with lakes in the area and reference to the "holy spring" of Dodona may be a later addition.  Jebb mostly follows Strabo in his analysis. Accordingly, he notes that the Selloi, the prophets of Zeus, were also called "tomouroi", which name derived from Mount Tomares. "Tomouroi" was also a variant reading found in the "Odyssey".  According to Jebb, the Peleiades at Dodona were very early, and preceded the appointment of Phemonoe, the prophetess at Delphi. The introduction of female attendants probably took place in the fifth century. The timing of change is clearly prior to Herodotus (5th century BC), with his narrative about the doves and Egypt.  Aristotle ("Meteorologica", 1.14) places 'Hellas' in the parts about Dodona and the Achelous and says it was inhabited by "the Selloi, who were formerly called Graikoi, but now Hellenes."  The alternative reading of "Selloi" is "Helloi". Aristotle clearly uses "Dodona" as the designation of the whole district in which the oracle was situated. Thus, according to some scholars, the origin of the words "Hellenes" and "Hellas" was from Dodona. Also, the word "Greece" may have been derived from this area.

Sodium chloride, commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/mol respectively, 100 g of NaCl contains 39.34 g Na and 60.66 g Cl. Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. In its edible form of table salt, it is commonly used as a condiment and food preservative. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses. A second major application of sodium chloride is de-icing of roadways in sub-freezing weather.

Natriumchlorid (auch Kochsalz genannt) ist das Natriumsalz der Salzsäure mit der chemischen Formel NaCl – nicht zu verwechseln mit Natriumchlorit (NaClO), dem Natriumsalz der Chlorigen Säure.


History.

John McCarthy developed Lisp in 1958 while he was at the Massachusetts Institute of Technology (MIT). McCarthy published its design in a paper in "Communications of the ACM" in 1960, entitled "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I". He showed that with a few simple operators and a notation for anonymous functions borrowed from Church, one can build a Turing-complete language for algorithms.  Information Processing Language was the first AI language, from 1955 or 1956, and already included many of the concepts, such as list-processing and recursion, which came to be used in Lisp.  McCarthy's original notation used bracketed "M-expressions" that would be translated into S-expressions. As an example, the M-expression is equivalent to the S-expression. Once Lisp was implemented, programmers rapidly chose to use S-expressions, and M-expressions were abandoned. M-expressions surfaced again with short-lived attempts of MLisp by Horace Enea and CGOL by Vaughan Pratt.  Lisp was first implemented by Steve Russell on an IBM 704 computer using punched cards. Russell had read McCarthy's paper and realized (to McCarthy's surprise) that the Lisp "eval" function could be implemented in machine code. The result was a working Lisp interpreter which could be used to run Lisp programs, or more properly, "evaluate Lisp expressions".  Two assembly language macros for the IBM 704 became the primitive operations for decomposing lists: ("Contents of the Address part of Register" number) and ("Contents of the Decrement part of Register" number), where "register" is used to refer to registers of the computer's central processing unit (CPU). Lisp dialects still use and ( and ) for the operations that return the first item in a list and the rest of the list, respectively.  The first complete Lisp compiler, written in Lisp, was implemented in 1962 by Tim Hart and Mike Levin at MIT. This compiler introduced the Lisp model of incremental compilation, in which compiled and interpreted functions can intermix freely. The language used in Hart and Levin's memo is much closer to modern Lisp style than McCarthy's earlier code.  The first garbage collection routines were developed by MIT graduate student Daniel Edwards.  During the 1980s and 1990s, a great effort was made to unify the work on new Lisp dialects (mostly successors to Maclisp such as ZetaLisp and NIL (New Implementation of Lisp) into a single language. The new language, Common Lisp, was somewhat compatible with the dialects it replaced (the book "Common Lisp the Language" notes the compatibility of various constructs). In 1994, ANSI published the Common Lisp standard, "ANSI X3.226-1994 Information Technology Programming Language Common Lisp".

Major dialects.

Common Lisp and Scheme represent two major streams of Lisp development. These languages embody significantly different design choices.  Common Lisp is a successor to Maclisp. The primary influences were Lisp Machine Lisp, Maclisp, NIL, S-1 Lisp, Spice Lisp, and Scheme. It has many of the features of Lisp Machine Lisp (a large Lisp dialect used to program Lisp Machines), but was designed to be efficiently implementable on any personal computer or workstation. Common Lisp is a general-purpose programming language and thus has a large language standard including many built-in data types, functions, macros and other language elements, and an object system (Common Lisp Object System). Common Lisp also borrowed certain features from Scheme such as lexical scoping and lexical closures. Common Lisp implementations are available for targeting different platforms such as the LLVM, the Java virtual machine, x86-64, PowerPC, Alpha, ARM, Motorola 68000, and MIPS, and operating systems such as Windows, macOS, Linux, Solaris, FreeBSD, NetBSD, OpenBSD, Dragonfly BSD, and Heroku.  Scheme is a statically scoped and properly tail-recursive dialect of the Lisp programming language invented by Guy L. Steele, Jr. and Gerald Jay Sussman. It was designed to have exceptionally clear and simple semantics and few different ways to form expressions. Designed about a decade earlier than Common Lisp, Scheme is a more minimalist design. It has a much smaller set of standard features but with certain implementation features (such as tail-call optimization and full continuations) not specified in Common Lisp. A wide variety of programming paradigms, including imperative, functional, and message passing styles, find convenient expression in Scheme. Scheme continues to evolve with a series of standards (Revised Report on the Algorithmic Language Scheme) and a series of Scheme Requests for Implementation.  Clojure is a recent dialect of Lisp that targets mainly the Java virtual machine, and the Common Language Runtime (CLR), the Python VM, the Ruby VM YARV, and compiling to JavaScript. It is designed to be a pragmatic general-purpose language. Clojure draws considerable influences from Haskell and places a very strong emphasis on immutability. Clojure provides access to Java frameworks and libraries, with optional type hints and type inference, so that calls to Java can avoid reflection and enable fast primitive operations. Clojure is not designed to be backwards compatible with other Lisp dialects.  Further, Lisp dialects are used as scripting languages in many applications, with the best-known being Emacs Lisp in the Emacs editor, AutoLISP and later Visual Lisp in AutoCAD, Nyquist in Audacity, Scheme in LilyPond. The potential small size of a useful Scheme interpreter makes it particularly popular for embedded scripting. Examples include SIOD and TinyScheme, both of which have been successfully embedded in the GIMP image processor under the generic name "Script-fu". LIBREP, a Lisp interpreter by John Harper originally based on the Emacs Lisp language, has been embedded in the Sawfish window manager.

Language innovations.

Lisp was the first language where the structure of program code is represented faithfully and directly in a standard data structure—a quality much later dubbed "homoiconicity". Thus, Lisp functions can be manipulated, altered or even created within a Lisp program without lower-level manipulations. This is generally considered one of the main advantages of the language with regard to its expressive power, and makes the language suitable for syntactic macros and metacircular evaluation.  A conditional using an "if–then–else" syntax was invented by McCarthy in a Fortran context. He proposed its inclusion in ALGOL, but it was not made part of the Algol 58 specification. For Lisp, McCarthy used the more general "cond"-structure. Algol 60 took up "if–then–else" and popularized it.  Lisp deeply influenced Alan Kay, the leader of the research team that developed Smalltalk at Xerox PARC; and in turn Lisp was influenced by Smalltalk, with later dialects adopting object-oriented programming features (inheritance classes, encapsulating instances, message

Syntax and semantics.

Symbolic expressions (S-expressions).

Lisp is an expression oriented language. Unlike most other languages, no distinction is made between "expressions" and "statements"; all code and data are written as expressions. When an expression is "evaluated", it produces a value (in Common Lisp, possibly multiple values), which can then be embedded into other expressions. Each value can be any data type.  McCarthy's 1958 paper introduced two types of syntax: "Symbolic expressions" (S-expressions, sexps), which mirror the internal representation of code and data; and "Meta expressions" (M-expressions), which express functions of S-expressions. M-expressions never found favor, and almost all Lisps today use S-expressions to manipulate both code and

Lists.

A Lisp list is written with its elements separated by whitespace, and surrounded by parentheses. For example, is a list whose elements are the three "atoms",, and. These values are implicitly typed: they are respectively two integers and a Lisp-specific data type called a "symbol", and do not have to be declared as such.  The empty list is also represented as the special atom. This is the only entity in Lisp which is both an

Operators.

Arithmetic operators are treated similarly. The expression  evaluates to 10. The equivalent under infix notation would be "".  Lisp has no notion of operators as implemented in Algol-derived languages. Arithmetic operators in Lisp are variadic functions (or "n-ary"), able to take any number of arguments. A C-style '++' increment operator is sometimes implemented under the name incf giving syntax  equivalent to (setq x (+ x 1)),

Lambda expressions and function definition.

Another special operator,, is used to bind variables to values which are then evaluated within an expression. This operator is also used to create functions: the arguments to are a list of arguments, and the expression or expressions to which the function evaluates (the returned value is the value of the last expression that is

Atoms.

In the original LISP there were two fundamental data types: atoms and lists. A list was a finite ordered sequence of elements, where each element is either an atom or a list, and an atom was a number or a symbol. A symbol was essentially a unique named item, written as an alphanumeric string in source code, and used either as a variable name or as a data item in symbolic processing. For example, the list contains three

Conses and lists.

A Lisp list is implemented as a singly linked list. Each cell of this list is called a "cons" (in Scheme, a "pair"), and is composed of two pointers, called the "car" and "cdr". These are respectively equivalent to the and fields discussed in the article "linked list".  Of the many data structures that can be built out of cons cells, one of the most basic is called a "proper list". A proper list is either the special (empty list) symbol, or a cons in which the points to a datum (which may be another cons structure, such as a list), and the points to another proper list.  If a given cons is taken to be the head of a linked

S-expressions represent lists.

Parenthesized S-expressions represent linked list structures. There are several ways to represent the same list as an S-expression. A cons can be written in "dotted-pair notation" as, where is the car and the

List-processing procedures.

Lisp provides many built-in procedures for accessing and controlling lists. Lists can be created directly with the procedure, which takes any number of arguments, and returns the list of these arguments.  Because of the way that lists are constructed

Shared structure.

Lisp lists, being simple linked lists, can share structure with one another. That is to say, two lists can have the same "tail", or final sequence of conses. For instance, after the execution of the following Common Lisp code:  the lists and are and respectively. However, the tail is the same structure in both lists. It is not a copy; the cons cells pointing to and are in the same memory locations for both lists.  Sharing structure rather than copying can give a dramatic performance improvement. However, this technique can interact in undesired ways with functions that alter lists passed to them as arguments. Altering one list,

Self-evaluating forms and quoting.

Lisp evaluates expressions which are entered by the user. Symbols and lists evaluate to some other (usually, simpler) expression – for instance, a symbol evaluates to the value of the variable it names; evaluates to. However, most other forms evaluate to themselves: if entering into Lisp, it returns.  Any expression can also be marked to prevent it from being evaluated (as is necessary for symbols and lists). This is the role of the special operator, or its abbreviation (one quotation mark). For instance, usually if entering the symbol, it returns the value of the corresponding variable (or an error, if there is no such variable). To refer to the literal symbol, enter or, usually,.  Both Common Lisp and Scheme also support

Scope and closure.

The Lisp family splits over the use of dynamic or static (a.k.a. lexical) scope. Clojure, Common Lisp and Scheme make

List structure of program code; exploitation by macros and compilers.

A fundamental distinction between Lisp and other languages is that in Lisp, the textual representation of a program is simply a human-readable description of the same internal data structures (linked lists, symbols, number, characters, etc.) as would be used by the underlying Lisp system.  Lisp uses this to implement a very powerful macro system. Like other macro languages such as C, a macro returns code that can then be compiled. However, unlike C macros, the macros are Lisp functions and so can exploit the full power of Lisp.  Further, because Lisp code has the same structure as lists, macros can be built with any of the list-processing functions in the language. In short, anything that Lisp can do to a data structure, Lisp macros can do to code. In contrast, in most other languages, the parser's output is purely internal to the language implementation and cannot be manipulated

Evaluation and the read–eval–print loop.

Lisp languages are often used with an interactive command line, which may be combined with an integrated development environment (IDE). The user types in expressions at the command line, or directs the IDE to transmit them to the Lisp system. Lisp "reads" the entered expressions, "evaluates" them, and "prints" the result. For this reason, the Lisp command line is called a "read–eval–print loop" (REPL).  The basic operation of the REPL is as follows. This is a simplistic description which omits many elements of a real Lisp, such as quoting and macros.  The function accepts textual S-expressions as input, and parses them into an internal data structure. For instance, if you type the text at the prompt, translates this into a linked list with three elements: the symbol, the number 1, and the number 2. It so happens that this list is also a valid piece of Lisp code; that is, it can be evaluated. This is because the car of the list names a function—the addition operation.  Note that a will be read as a single symbol. will be read as the number

Control structures.

Lisp originally had very few control structures, but many more were added during the language's evolution. (Lisp's original conditional operator,, is the precursor to later structures.)  Programmers in the Scheme dialect often express loops using tail recursion. Scheme's commonality in academic computer science has led some students to believe that tail recursion is the only, or the most common, way to write iterations in Lisp, but this is incorrect. All oft-seen Lisp dialects have imperative-style iteration constructs, from Scheme's loop to Common Lisp's complex expressions. Moreover, the key issue that

Examples.

Here are examples of Common Lisp code.  The basic "Hello world" program:  Lisp syntax lends itself naturally to recursion. Mathematical problems such as the enumeration of recursively defined sets are simple to express in

Object systems.

Various object systems and models have been built on top of, alongside, or into Lisp, including:

Lisp (historically LISP) is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation. Originally specified in 1958, Lisp is the second-oldest high-level programming language in widespread use today. Only Fortran is older, by one year. Lisp has changed since its early days, and many dialects have existed over its history. Today, the best-known general-purpose Lisp dialects are Racket, Common Lisp, Scheme and Clojure.

Lisp ist eine Familie von Programmiersprachen, die 1958 erstmals spezifiziert wurde und am Massachusetts Institute of Technology (MIT) in Anlehnung an den ungetypten Lambda-Kalkül entstand. Es ist nach Fortran die zweitälteste Programmiersprache, die noch verbreitet ist.


Etymology.

Together with the two elements at the top of group 3, scandium and yttrium, the trivial name "rare earths" is sometimes used to describe all the lanthanides; a definition of rare earths including the group 3, lanthanide, and actinide elements is also occasionally seen, and rarely Sc + Y + lanthanides + thorium. The "earth" in the name "rare earths" arises from the minerals from which they were isolated, which were uncommon oxide-type minerals. However, the use of the name is deprecated by IUPAC, as the elements are neither rare in abundance nor "earths" (an obsolete term for water-insoluble strongly basic oxides of electropositive metals incapable of being smelted into metal using late 18th century technology). Group 2 is known as the alkaline earth elements for much the same reason.  The "rare" in the "rare earths" name has much more to do with the difficulty of separating out each of the individual lanthanide elements than scarcity of any of them. By way of the Greek "dysprositos" for "hard to get at," element 66, dysprosium was similarly named; lanthanum itself is named after a word for "hidden." The elements 57 (La) to 71 (Lu) are very similar chemically to one another and frequently occur together in nature, often anywhere from three to all 15 of the lanthanides (along with yttrium as a 16th) occur in minerals such as samarskite, monazite and many others which can also contain the other two group 3 elements as well as thorium and occasionally other actinides as well. A majority of the rare earths were discovered at the same mine in Ytterby, Sweden and four of them are named (yttrium, ytterbium, erbium, terbium) after the city and a fifth *(holmium) after Stockholm; scandium is named after Scandinavia, thulium after the old name Thule, and the immediately-following group 4 element (number 72) hafnium is named for the Latin name of the city of Copenhagen.  Samarskite (a mineral which is the source of the name of the element samarium) and other similar minerals in particular also have these elements in association with the nearby metals tantalum, niobium, hafnium, zirconium, vanadium, and titanium, from group 4 and group 5 often in similar oxidation states. Monazite is a

Physical properties of the elements.

<nowiki>*</nowiki> Between initial Xe and final 6s electronic shells  <nowiki>**</nowiki> Sm has a close packed structure like the other lanthanides but has an unusual 9 layer repeat  Gschneider and Daane (1988) attribute the trend in melting point which increases across the series, (lanthanum (920 °C) – lutetium (1622 °C)) to the extent of hybridization of the 6s, 5d, and 4f orbitals. The hybridization is believed to be at its greatest for cerium, which has the lowest melting point of all, 795 °C. The lanthanide metals are soft; their hardness increases across the series. Europium stands out, as it has the lowest density

Chemistry and compounds.

<nowiki>*</nowiki> Not including initial [Xe] core  The colors of lanthanide complexes originate almost entirely from charge transfer interactions between the metal and the ligand. f → f transitions are symmetry forbidden (or Laporte-forbidden), which is also true of transition metals. However, transition metals are able to use vibronic coupling to break this rule. The valence orbitals in lanthanides are almost entirely non-bonding and as such little effective vibronic coupling takes, hence the spectra from f → f transitions are much weaker and narrower than those from d → d transitions. In general this makes the colors of lanthanide complexes far fainter than those of transition metal complexes. f → f transitions are not possible for the f and f configurations of Ce and Yb and thus these ions are colorless in aqueous solution.

Effect of 4f orbitals.

Going across the lanthanides in the periodic table, the 4f orbitals are usually being filled. The effect of the 4f orbitals on the chemistry of the lanthanides is profound and is the factor that distinguishes them from the transition metals. There are seven 4f orbitals, and there are two different ways in which they are depicted: as a "cubic set" or as a general set. The cubic set is "f", "f", "f", "f", "f", "f" and "f". The 4f orbitals penetrate the [Xe] core and are isolated, and thus they do not participate in bonding. This explains why crystal field effects are small and why they do not form π bonds. As there are seven 4f orbitals, the number of unpaired electrons can be as high as 7, which gives rise to the large magnetic moments observed for lanthanide compounds. Measuring the magnetic moment can be used to investigate the 4f electron configuration,

Lanthanide oxidation states.

The ionization energies for the lanthanides can be compared with aluminium. In aluminium the sum of the first three ionization energies is 5139 kJ·mol, whereas the lanthanides fall in the range 3455 – 4186 kJ·mol. This correlates with the highly reactive nature of the lanthanides.  The sum of the first two ionization energies for europium, 1632 kJ·mol can be compared with that of barium 1468.1 kJ·mol and europium's third ionization energy is the highest of the lanthanides. The sum of the first two ionization energies for

Separation of lanthanides.

The similarity in ionic radius between adjacent lanthanide elements makes it difficult to separate them from each other in naturally occurring ores and other mixtures. Historically, the very laborious processes of cascading and fractional crystallization were used. Because the lanthanide ions have slightly different radii, the lattice energy of their salts and hydration energies of the ions will be slightly different, leading to a small difference in

Coordination chemistry and catalysis.

When in the form of coordination complexes, lanthanides exist overwhelmingly in their +3 oxidation state, although particularly stable 4f configurations can also give +4 (Ce, Tb) or +2 (Eu, Yb) ions. All of these forms are strongly electropositive and thus lanthanide ions are hard Lewis acids. The oxidation states are also very stable; with the exceptions of SmI and cerium(IV) salts, lanthanides are not used for redox chemistry. 4f electrons have a high probability of being found close to the nucleus and are thus strongly affected as the nuclear charge increases across the series; this results in a corresponding decrease in ionic radii referred to as the lanthanide contraction.  The low probability of the 4f electrons existing at the outer region of the atom or ion permits little effective overlap between the orbitals of a lanthanide ion and any binding ligand. Thus lanthanide complexes typically have little or no covalent character and are not influenced by orbital geometries. The lack of orbital interaction also means that varying the metal typically has little effect on the complex (other than size), especially when compared to transition metals. Complexes are held together by weaker electrostatic

Physical properties.

Magnetic and spectroscopic.

All the trivalent lanthanide ions, except lanthanum and lutetium, have unpaired f electrons. However, the magnetic moments deviate considerably from the spin-only values because of strong spin-orbit coupling. The maximum number of unpaired electrons is 7, in Gd, with a magnetic moment of 7.94 B.M., but the largest magnetic moments, at 10.4–10.7 B.M., are exhibited by Dy and Ho. However, in Gd all the electrons have parallel spin and this property is important for the use of gadolinium complexes as contrast reagent in MRI scans. Crystal field splitting is rather small for the lanthanide ions and is less important than spin-orbit coupling in regard to energy levels. Transitions of electrons between f orbitals are forbidden by the

Occurrence.

The lanthanide contraction is responsible for the great geochemical divide that splits the lanthanides into light and heavy-lanthanide enriched minerals, the latter being almost inevitably associated with and dominated by yttrium. This divide is reflected in the first two "rare earths" that were discovered: yttria (1794) and ceria (1803). The geochemical divide has put more of the light lanthanides in the Earth's crust, but more of the heavy

Applications.

Industrial.

Lanthanide elements and their compounds have many uses but the quantities consumed are relatively small in comparison to other elements. About 15000 ton/year of the lanthanides are consumed as catalysts and in the production of glasses. This 15000 tons corresponds to about 85% of the lanthanide production. From the perspective of value, however, applications in phosphors and magnets are more important.  The devices lanthanide elements are used in include superconductors, samarium-cobalt and neodymium-iron-boron high-flux rare-earth magnets, magnesium alloys, electronic polishers, refining catalysts and hybrid car components (primarily batteries and magnets). Lanthanide ions are used as the active ions in luminescent materials used in optoelectronics applications, most notably the laser. Erbium-doped fiber amplifiers are significant devices in optical-fiber communication systems. Phosphors with lanthanide dopants are also widely used in cathode ray

Life science.

As mentioned in the industrial applications section above, lanthanide metals are particularly useful in technologies that take advantage of their reactivity to specific wavelengths of light. Certain life science applications take advantage of the unique luminescence properties of lanthanide ion complexes (Ln(III) chelates or cryptates). These are well-suited for this application due to their large Stokes shifts and extremely long emission lifetimes (from microseconds to milliseconds) compared to more traditional fluorophores (e.g., fluorescein, allophycocyanin, phycoerythrin, and rhodamine). The biological fluids or serum commonly used in these research applications contain many compounds and proteins which are naturally fluorescent. Therefore, the use of conventional, steady-state fluorescence measurement presents serious limitations in assay sensitivity. Long-lived fluorophores, such as lanthanides, combined with time-resolved

Possible medical uses.

Currently there is research showing that lanthanide elements can be used as anticancer agents. The main role of the lanthanides in these studies is to inhibit proliferation of the cancer cells. Specifically cerium and lanthanum have been studied for their role as anti-cancer agents.  One of the specific elements from the lanthanide group that has been tested and used is cerium (Ce). There have been studies that use a protein-cerium complex to observe the effect of cerium on the cancer cells. The hope was to inhibit cell proliferation and promote cytotoxicity. Transferrin receptors in cancer cells, such as those in breast cancer cells and epithelial cervical cells, promote the cell proliferation and malignancy of the cancer. Transferrin is a protein used to transport iron into the cells and is needed to aid the cancer cells in DNA replication. Transferrin acts as a growth factor for the cancerous cells and is dependent on iron. Cancer cells have much higher levels of transferrin receptors than normal cells and are very dependent on iron for their proliferation. Cerium has shown

Biological effects.

Due to their sparse distribution in the earth's crust and low aqueous solubility, the lanthanides have a low availability in the biosphere, and for a long time were not known to naturally form part of any biological molecules. In 2007 a novel methanol dehydrogenase that strictly uses lanthanides as enzymatic cofactors was discovered in a bacterium from the phylum Verrucomicrobia, "Methylacidiphilum fumariolicum". This bacterium was found to survive only if there are lanthanides present in the environment. Compared to most other nondietary elements, non-radioactive lanthanides are classified as having low toxicity.

The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.

Lanthanoide [] („Lanthanähnliche“; griech.: Endung "-ειδἠς" ("-eides") „ähnlich“) ist eine Gruppenbezeichnung ähnlicher Elemente. Zugerechnet werden ihr das Lanthan und die 14 im Periodensystem folgenden Elemente Cer, Praseodym, Neodym, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium und Lutetium. Im Sinne des Begriffs gehört Lanthan nicht zu den Lanthanähnlichen. Hier folgt die Nomenklatur der IUPAC aber dem praktischen Gebrauch. Die Verwendung der alten Bezeichnung Lanthanide ist weiterhin erlaubt. Alle Lanthanoide sind Metalle und werden auch als "Elemente der Lanthanreihe" bezeichnet. Sie sind ein Teil der Gruppe der Metalle der Seltenen Erden.