Background.

In the years between the Second and Third Punic War, Rome was engaged in the conquest of the Hellenistic empires and also of the Illyrian tribes to the east, and suppressing the Hispanian peoples in the west, although they had been essential to the Roman success in the Second Punic War. Carthage, stripped of allies and territory (Sicily, Sardinia, Hispania), was suffering under a large indemnity of 200 silver talents to be paid every year for 50 years.  According to Appian, the senator Cato the Elder usually finished his speeches on any subject in the Senate with the phrase "ceterum censeo Carthaginem esse delendam", which means "Moreover, I am of the opinion that Carthage ought to be destroyed". Cicero attributed a similar statement to Cato in his dialogue "De Senectute". He was opposed by the senator Publius Cornelius Scipio Nasica Corculum, who favoured a different course that would not destroy Carthage, and who usually prevailed in the debates.  The peace treaty at the end of the Second Punic War required that all border disputes involving Carthage be arbitrated by the Roman Senate and required Carthage to get explicit Roman approval before going to war. As a result, in the 50 intervening years between the Second and Third Punic War, Carthage had to take all border disputes with Rome's ally Numidia to the Roman Senate, where they were decided almost exclusively in the latter's favour.  In 151 BC, the Carthaginian debt to Rome was fully repaid, meaning that, in Punic eyes, the treaty was now expired, though not so according to the Romans, who instead viewed the treaty as a permanent declaration of Carthaginian subordination to Rome, akin to the Roman treaties with its Italian allies. Moreover, the retirement of the indemnity removed one of the main incentives the Romans had to keep the peace with Carthage – there were no further payments that might be interrupted.  The Romans had other reasons to conquer Carthage and her remaining territories. By the middle of the 2nd century BC, the population of the city of Rome was about 400,000 and rising. Feeding the growing populace was becoming a major challenge. The farmlands surrounding Carthage represented the most productive, most accessible and perhaps the most easily obtainable agricultural lands not yet under Roman control.

Course of the war.

In 151 BC Numidia launched another border raid on Carthaginian soil, besieging the Punic town of Oroscopa, and Carthage launched a large military expedition (25,000 soldiers) to repel the Numidian invaders. However, Carthage suffered a military defeat and was charged with another fifty year debt to Numidia. Immediately after, however, Rome showed displeasure with Carthage's decision to wage war against its neighbour without Roman consent.  In 149 BC, Rome declared war against Carthage. The Carthaginians made a series of attempts to appease Rome, and received a promise that if three hundred children of well-born Carthaginians were sent as hostages to Rome the Carthaginians would keep the rights to their land and self-government. Even after this was done the allied Punic city of Utica defected to Rome, and a Roman army of 80,000 men gathered there. The consuls then demanded that Carthage hand over all weapons and armor. After those had been handed over, Rome additionally demanded that the Carthaginians move at least 16 kilometres inland, while the city was to be burned. When the Carthaginians learned of this, they abandoned negotiations and the city was immediately besieged, beginning the Third Punic War.  After the main Roman expedition landed at Utica, consuls Manius Manilius and Lucius Marcius Censorius launched a two-pronged attack on Carthage, but were eventually repulsed by the army of the Carthaginian Generals Hasdrubal the Boeotarch and Himilco Phameas. Censorius lost more than 500 men when they were surprised by the Carthaginian cavalry while collecting timber around the Lake of Tunis. A worse disaster fell upon the Romans when their fleet was set ablaze by fire ships which the Carthaginians released upwind. Manilius was replaced by consul Calpurnius Piso Caesonius in 149 after a severe defeat of the Roman army at Nepheris, a Carthaginian stronghold south of the city. Scipio Aemilianus's intervention saved four cohorts trapped in a ravine. Nepheris eventually fell to Scipio in the winter of 147–146. In the autumn of 148, Piso was beaten back while attempting to storm the city of Aspis, near Cape Bon. Undeterred, he laid siege to the town of Hippagreta in the north, but his army was unable to defeat the Punics there before winter and had to retreat. When news of these setbacks reached Rome, he was replaced as consul by Scipio Aemilianus.  The Carthaginians endured the siege, starting 149 BC to the spring of 146 BC, when Scipio Aemilianus successfully assaulted the city. Though the Punic citizens offered strong resistance, they were gradually pushed back by the overwhelming Roman military force and destroyed.

Aftermath.

Many Carthaginians died from starvation during the later part of the siege, while many others died in the final six days of fighting. When the war ended, the remaining 50,000 Carthaginians, a small part of the original pre-war population, were sold into slavery by the victors. Carthage was systematically burned for 17 days; the city's walls and buildings were utterly destroyed. The remaining Carthaginian territories were annexed by Rome and reconstituted to become the Roman province of Africa.  The notion that Roman forces then sowed the city with salt to ensure that nothing would grow there again is almost certainly a 19th-century invention. Contemporary accounts show that the land surrounding Carthage was declared "ager publicus" and that it was shared between local farmers, and Roman and Italian ones. North Africa soon became a vital source of grain for the Romans. Roman Carthage was the main hub transporting these supplies to the capital.  Numerous significant Punic cities, such as those in Mauretania, were taken over and rebuilt by the Romans. Examples of these rebuilt cities are Volubilis, Chellah and Arambys. Volubilis, for example, was an important Roman town situated near the westernmost border of Roman conquests. It was built on the site of the previous Punic settlement, but that settlement overlies an earlier neolithic habitation. Utica, the Punic city which changed loyalties at the beginning of the siege, became the capital of the Roman province of Africa.  A century later, the site of Carthage was rebuilt as a Roman city by Julius Caesar, and would later become one of the main cities of Roman Africa by the time of the Empire.

The Third Punic War (Latin: "Tertium Bellum Punicum") (149–146 BC) was the third and last of the Punic Wars fought between the former Phoenician colony of Carthage and the Roman Republic. The Punic Wars were named because of the Roman name for Carthaginians: "Punici", or "Poenici".


Name.

The generic name was first used by Pliny the Elder (23–79) for a plant also known as "strychnos", most likely "S. nigrum". Its derivation is uncertain, possibly stemming from the Latin word "sol", meaning "sun", referring to its status as a plant of the sun.

Nightshades.

The species most commonly called nightshade in North America and Britain is "Solanum dulcamara", also called bittersweet or woody nightshade. Its foliage and egg-shaped red berries are poisonous, the active principle being solanine, which can cause convulsions and death if taken in large doses. The black nightshade ("S. nigrum") is also generally considered poisonous, but its fully ripened fruit and foliage are cooked and eaten in some areas. The deadly nightshade ("Atropa belladonna") is not in the genus "Solanum", but is a member of the family Solanaceae.

Food crops.

Most parts of the plants, especially the green parts and unripe fruit, are poisonous to humans (although not necessarily to other animals), but many species in the genus bear some edible parts, such as fruits, leaves, or tubers. Three crops in particular have been bred and harvested for consumption by humans for centuries, and are now cultivated on a global scale:  Other species are significant food crops regionally, such as Ethiopian eggplant or gilo ("S. aethiopicum"), naranjilla or lulo ("S. quitoense"), Turkey berry ("S. torvum"), Pepino or Pepino Melon ("S. muricatum"), Tamarillo ("S. betaceum"), Wolf apple (S. lycocarpum), and "bush tomatoes" (several Australian species).

Ornamentals.

The species most widely seen in cultivation as ornamental plants are:

Medicine.

Poisonings associated with certain species of "Solanum" are not uncommon and may be fatal. However, several species are locally used in folk medicine, particularly by native peoples who have long employed them.

Ecology.

"Solanum" species are used as food plants by the larvae of some Lepidoptera species (butterflies and moths) – see list of Lepidoptera that feed on Solanum.

Systematics.

The genus was established by Carl Linnaeus in 1753. Its subdivision has always been problematic, but slowly some sort of consensus is being achieved.  The following list is a provisional lineup of the genus' traditional subdivisions, together with some notable species. Many of the subgenera and sections might not be valid; they are used here provisionally as the phylogeny of this genus is not fully resolved yet and many species have not been reevaluated.  Cladistic analyses of DNA sequence data suggest that the present subdivisions and rankings are largely invalid. Far more subgenera would seem to warrant recognition, with "Leptostemonum" being the only one that can at present be clearly subdivided into sections. Notably, it includes as a major lineage several members of the traditional sections "Cyphomandropsis" and the old genus "Cyphomandra".

Subgenus "Bassovia".

Section "Allophylla" Section "Cyphomandropsis" Section "Pachyphylla"

Subgenus "Leptostemonum".

Section "Acanthophora" Section "Androceras": 12 spp. Section "Anisantherum" Section "Campanulata" Section "Crinitum" Section "Croatianum" Section "Erythrotrichum" Section "Graciliflorum" Section "Herposolanum" Section "Irenosolanum" Section "Ischyracanthum" Section "Lasiocarpa" Section "Melongena" Section "Micracantha" Section "Monodolichopus" Section "Nycterium" Section "Oliganthes" Section "Persicariae" Section "Polytrichum" Section "Pugiunculifera" Section "Somalanum" Section "Torva"

Subgenus "Solanum sensu stricto".

Section "Afrosolanum" Section "Anarrhichomenum" Section "Archaesolanum" Section "Basarthrum" Section "Benderianum" Section "Brevantherum" Section "Dulcamara" Section "Herpystichum" Section "Holophylla" Section "Juglandifolia" Section "Lemurisolanum" Section "Lycopersicoides" Section "Lycopersicon"  Section "Macronesiotes" Section "Normania" Section "Petota" Section "Pteroidea" Section "Quadrangulare" Section "Regmandra" Section "Solanum"

Formerly placed here.

Some plants of other genera were formerly placed in "Solanum":

Solanum is a large and diverse genus of flowering plants, which include three food crops of high economic importance, the potato, the tomato and the eggplant. It also contains the nightshades and horse nettles, as well as numerous plants cultivated for their ornamental flowers and fruit.


History.

Early use of the term.

The ancient Greeks (among others) had much to say on discourse; however, some scholars consider Austria-born Leo Spitzer's "Stilstudien" ("Style Studies") of 1928 the earliest example of "discourse analysis" (DA). Michel Foucault translated it into French. However, the term first came into general use following the publication of a series of papers by Zellig Harris from 1952 reporting on work from which he developed transformational grammar in the late 1930s. Formal equivalence relations among the sentences of a coherent discourse are made explicit by using sentence transformations to put the text in a canonical form. Words and sentences with equivalent information then appear in the same column of an array.  This work progressed over the next four decades (see references) into a science of sublanguage analysis (Kittredge & Lehrberger 1982), culminating in a demonstration of the informational structures in texts of a sublanguage of science, that of Immunology, (Harris et al. 1989) and a fully articulated theory of linguistic informational content (Harris 1991). During this time, however, most linguists ignored such developments in favor of a succession of elaborate theories of sentence-level syntax and semantics.  In January 1953, a linguist working for the American Bible Society, James A. Lauriault/Loriot, needed to find answers to some fundamental errors in translating Quechua, in the Cuzco area of Peru. Following Harris's 1952 publications, he worked over the meaning and placement of each word in a collection of Quechua legends with a native speaker of Quechua and was able to formulate discourse rules that transcended the simple sentence structure. He then applied the process to Shipibo, another language of Eastern Peru. He taught the theory at the Summer Institute of Linguistics in Norman, Oklahoma, in the summers of 1956 and 1957 and entered the University of Pennsylvania to study with Harris in the interim year. He tried to publish a paper "Shipibo Paragraph Structure", but it was delayed until 1970 (Loriot & Hollenbach 1970). In the meantime, Kenneth Lee Pike, a professor at University of Michigan, Ann Arbor, taught the theory, and one of his students, Robert E. Longacre developed it in his writings. Harris's methodology disclosing the correlation of form with meaning was developed into a system for the computer-aided analysis of natural language by a team led by Naomi Sager at NYU, which has been applied to a number of sublanguage domains, most notably to medical informatics. The software for the Medical Language Processor is publicly available on SourceForge.

In the humanities.

In the late 1960s and 1970s, and without reference to this prior work, a variety of other approaches to a new cross-discipline of DA began to develop in most of the humanities and social sciences concurrently with, and related to, other disciplines, such as semiotics, psycholinguistics, sociolinguistics, and pragmatics. Many of these approaches, especially those influenced by the social sciences, favor a more dynamic study of oral talk-in-interaction. An example is "conversational analysis", which was influenced by the Sociologist Harold Garfinkel, the founder of Ethnomethodology.

Foucault.

In Europe, Michel Foucault became one of the key theorists of the subject, especially of discourse, and wrote The Archaeology of Knowledge. In this context, the term 'discourse' no longer refers to formal linguistic aspects, but to institutionalized patterns of knowledge that become manifest in disciplinary structures and operate by the connection of knowledge and power. Since the 1970s, Foucault's works have had an increasing impact especially on discourse analysis in the social sciences. Thus, in modern European social sciences, one can find a wide range of different approaches working with Foucault's definition of discourse and his theoretical concepts. Apart from the original context in France, there is, at least since 2005, a broad discussion on socio-scientific discourse analysis in Germany. Here, for example, the sociologist Reiner Keller developed his widely recognized 'Sociology of Knowledge Approach to Discourse (SKAD)'. Following the sociology of knowledge by Peter L. Berger and Thomas Luckmann, Keller argues, that our sense of reality in everyday life and thus the meaning of every object, actions and events are the product of a permanent, routinized interaction. In this context, SKAD has been developed as a scientific perspective that is able to understand the processes of 'The Social Construction of Reality' on all levels of social life by combining Michel Foucault's theories of discourse and power with the theory of knowledge by Berger/Luckmann. Whereas the latter primarily focus on the constitution and stabilisation of knowledge on the level of interaction, Foucault's perspective concentrates on institutional contexts of the production and integration of knowledge, where the subject mainly appears to be determined by knowledge and power. Therefore, the 'Sociology of Knowledge Approach to Discourse' can also be seen as an approach to deal with the vividly discussed micro–macro problem in sociology.

Perspectives.

The following are some of the specific theoretical perspectives and analytical approaches used in linguistic discourse analysis:  Although these approaches emphasize different aspects of language use, they all view language as social interaction and are concerned with the social contexts in which discourse is embedded.  Often a distinction is made between 'local' structures of discourse (such as relations among sentences, propositions, and turns) and 'global' structures, such as overall topics and the schematic organization of discourses and conversations. For instance, many types of discourse begin with some kind of global'summary', in titles, headlines, leads, abstracts, and so on.  A problem for the discourse analyst is to decide when a particular feature is relevant to the specification required. A question many linguists ask is: "Are there general principles which will determine the relevance or nature of the specification?"

Topics of interest.

Topics of discourse analysis include:

Prominent academics.

Political discourse.

Political discourse analysis is a field of discourse analysis which focuses on discourse in political forums (such as debates, speeches, and hearings) as the phenomenon of interest. Policy analysis requires discourse analysis to be effective from the post-positivist perspective.  Political discourse is the formal exchange of reasoned views as to which of several alternative courses of action should be taken to solve a societal problem.

Corporate discourse.

Corporate discourse can be broadly defined as the language used by corporations. It encompasses a set of messages that a corporation sends out to the world (the general public, the customers and other corporations) and the messages it uses to communicate within its own structures (the employees and other stakeholders).

Discourse analysis (DA), or discourse studies, is an approach to the analysis of written, vocal, or sign language use, or any significant semiotic event.


Early life.

His father was Rudolf Keller (1791-1824), a lathe-worker from Glattfelden; his mother was a woman named Elisabeth Scheuchzer (1787–1864). The couple had six children, four of whom died, meaning Keller only had his sister Regula (*1822) left. After his father died of tuberculosis, Keller's family lived in constant poverty, and, because of Keller's difficulties with his teachers, in continual disagreement with school authorities. Keller later gave a good rendering of his experiences in this period in his long novel, "Der grüne Heinrich" (1850–55; 2nd version, 1879). His mother seems to have brought him up in as carefree a condition as possible, sparing for him from her scanty meals, and allowing him the greatest possible liberty in the disposition of his time, the choice of a calling, etc. With some changes, a treatment of her relations to him may be found in his short story, “Frau Regel Amrain und ihr jüngster” (in the collection "Die Leute von Seldwyla").

Career.

Keller's first true passion was painting. Expelled in a political mix-up from the "Industrieschule" in Zürich, he became an apprentice in 1834 to the landscape painter Steiger and in 1837 to the watercolourist Rudolf Meyer (1803–1857). In 1840, he went to Munich (Bavaria) to study art for a time at the Royal Academy of Fine Arts.  Keller returned to Zürich in 1842 and, although possessing artistic talent, took up writing. He published his first poems, "Gedichte", in 1846. Jacob Wittmer Hartmann characterizes these six years at Zürich (1842–48) as a time of almost total inactivity, when Keller inclined strongly toward radicalism in politics, and was also subject to much temptation and indulged himself. From 1848 to 1850 he studied at the University of Heidelberg. There he came under the influence of the philosopher Feuerbach, and extended his radicalism also to matters of religion.  From 1850 to 1856, he worked in Berlin. Hartmann claims it was chiefly this stay in Berlin which molded Keller's character into its final shape, toned down his rather bitter pessimism to a more moderate form, and prepared him (not without the privations of hunger), in the whirl of a large city, for an enjoyment of the more restricted pleasures of his native Zürich. It was in Berlin that he turned definitely away from other pursuits and took up literature as a career.  In this period, Keller published the semi-autobiographical novel "Der grüne Heinrich" ("Green Henry"). It is the most personal of all his works. Under the influence of Jean-Jacques Rousseau's doctrine of a return to nature, this book was at first intended to be a short narrative of the collapse of the life of a young artist. It expanded as its composition progressed into a huge work drawing on Keller's youth and career (or more precisely "non-career") as a painter up to 1842. Its reception by the literary world was cool, but the second version of 1879 is a rounded and satisfying artistic product. He also published his first collection of short stories, "Die Leute von Seldwyla" ("The People of Seldwyla"). It contains five stories averaging 60 pages each: “Pankraz der Schmoller,” “Frau Regel Amrain und ihr jüngster,” “Die drei gerechten Kammacher,” “Romeo und Julia auf dem Dorfe,” and “Spiegel das Kätzchen.” Hartmann characterizes two of the stories in "Die Leute von Seldwyla" as immortal: “Die drei gerechten Kammacher” he views as the most satyric and scorching attack on the sordid petit bourgeois morality ever penned by any writer, and “Romeo und Julia auf dem Dorfe” as one of the most pathetic tales in literature (Shakespeare's "Romeo and Juliet" plot in a Swiss village setting).  Keller returned again to Zürich and became the "First Official Secretary" of the Canton of Zürich ("Erster Zürcher Staatsschreiber") in 1861. The routine duties of this position were a sort of fixed point about which his artistic activities could revolve, but Hartmann opines that he produced little of permanent value in these years. In 1872, Keller published "Seven Legends" ("Sieben Legenden"), which dealt with the early Christian era. After 15 years at this post, he was retired in 1876, and began a period of literary activity that was to last to his death, living the life of an old bachelor with his sister Regula as his housekeeper. In spite of his often unsympathetic manner, his extreme reserve and idiosyncrasy in dealing with others, he had gained the affection of his fellow townspeople and an almost universal reputation before his death.

Evaluation.

Hartmann bases Keller's fame chiefly on 15 short stories, the five mentioned above; the five contained in the second volume of "Die Leute von Seldwyla" (1874): “Die missbrauchten Liebesbriefe,” “Der Schmied seines Glücks,” “Dietegen,” “Kleider machen Leute,” and “Das verlorene Lachen”; and five in "Züricher Novellen" (1878): “Hadlaub,” “Der Narr auf Manegg,” “Der Landvogt von Greifensee,” “Das Fähnlein der sieben Aufrechten,” and “Ursula.” The milieu is always that of an orderly bourgeois existence, within which the most manifold human destinies, the most humorous relations develop, the most peculiar and hardy types of endurance and reticence are manifested. Some of the stories contained a note that was new in German literature and that endeared them particularly to Germans as embodying an ideal as yet unrealized in their own country: they narrate the development of character under the relatively free conditions of little Switzerland, portraying an unbureaucratic civic life and an independence of business initiative.  Also noteworthy are his "Collected Poetry" ("Gesammelte Gedichte") (1883), and the novel "Martin Salander" (1886).

Gottfried Keller Foundation.

In 1890, shortly before the end of her tragic life, Lydia Escher (1858–1891) invested the Escher fortune in a foundation which she named after Gottfried Keller, to whom her father gave consistent support. With her remaining substantial asset – Villa Belvoir including swing and marketable securities totaling nominally 4 million Swiss Francs – Lydia Escher established the foundation's base. According to the will of Lydia Escher, the foundation was established on 6 June 1890, and was managed by the Swiss Federal Council, thus, Lydia Escher wished to accomplish a "patriotic work". The foundation should also promote the "independent work of women, at least in the field of the applied Arts," according to the original intention of the founder. This purpose was adopted but at the urging of Emil Welti not in the deed of the foundation. The Gottfried Keller Foundation became though an important collection institution for art, but the feminist concerns of Lydia Escher were not met.

Gottfried Keller (19 July 1819 – 15 July 1890) was a Swiss poet and writer of German literature. Best known for his novel "Green Henry" (German: "Der grüne Heinrich"), he became one of the most popular narrators of literary realism in the late 19th century.


Production of a single boson.

If the initial two particles are elementary (not composite), then they may combine to produce only a single elementary boson, such as a photon (), gluon (),, or a Higgs boson (). If the total energy in the center-of-momentum frame is equal to the rest mass of a real boson (which is impossible for a massless boson such as the ), then that created particle will continue to exist until it decays according to its lifetime. Otherwise, the process is understood as the initial creation of a boson that is virtual, which immediately converts into a real particle+antiparticle pair. This is called an s-channel process. An example is the annihilation of an electron with a positron to produce a virtual photon, which converts into a muon and anti-muon. If the energy is large enough, a could replace the photon.

Examples.

Electron–positron annihilation.

When a low-energy electron annihilates a low-energy positron (antielectron), they can only produce two photons, since the electron and positron do not carry enough mass-energy to produce heavier particles, and the creation of only one photon is forbidden by momentum conservation—a single photon would carry nonzero momentum in any frame, including the center-of-momentum frame where the total momentum vanishes. Both the annihilating electron and positron particles have a rest energy of about 0.511 million electron volts (MeV). If their kinetic energies are relatively negligible, this total rest energy appears as the photon energy of the photons produced. Each of the photons then has an energy of about 0.511 MeV. Momentum and energy are both conserved, with 1.022 MeV of photon energy (accounting for the rest energy of the particles) moving in opposite directions (accounting for the total zero momentum of the system).  If one or both charged particles carry a larger amount of kinetic energy, various other particles can be produced. Furthermore, the annihilation (or decay) of an electron-positron pair into a "single" photon can occur in the presence of a third charged particle to which the excess momentum can be transferred by a virtual photon from the electron or positron. The inverse process, pair production by a single real photon, is also possible in the electromagnetic field of a third particle.

Proton-antiproton annihilation.

When a proton encounters its antiparticle (and more generally, if any species of baryon encounters the corresponding antibaryon), the reaction is not as simple as electron-positron annihilation. Unlike an electron, a proton is a composite particle consisting of three "valence quarks" and an indeterminate number of "sea quarks" bound by gluons. Thus, when a proton encounters an antiproton, one of its quarks, usually a constituent valence quark, may annihilate with an antiquark (which more rarely could be a sea quark) to produce a gluon, after which the gluon together with the remaining quarks, antiquarks, and gluons will undergo a complex process of rearrangement (called hadronization or fragmentation) into a number of mesons, (mostly pions and kaons), which will share the total energy and momentum. The newly created mesons are unstable, and unless they encounter and interact with some other material, they will decay in a series of reactions that ultimately produce only photons, electrons, positrons, and neutrinos. This type of reaction will occur between any baryon (particle consisting of three quarks) and any antibaryon consisting of three antiquarks, one of which corresponds to a quark in the baryon. (This reaction is unlikely if at least one among the baryon and anti-baryon is exotic enough that they share no constituent quark flavors.) Antiprotons can and do annihilate with neutrons, and likewise antineutrons can annihilate with protons, as discussed below.  Reactions in which proton-antiproton annihilation produces as many as nine mesons have been observed, while production of thirteen mesons is theoretically possible. The generated mesons leave the site of the annihilation at moderate fractions of the speed of light, and decay with whatever lifetime is appropriate for their type of meson.  Similar reactions will occur when an antinucleon annihilates within a more complex atomic nucleus, save that the resulting mesons, being strongly interacting, have a significant probability of being absorbed by one of the remaining "spectator" nucleons rather than escaping. Since the absorbed energy can be as much as ~2 GeV, it can in principle exceed the binding energy of even the heaviest nuclei. Thus, when an antiproton annihilates inside a heavy nucleus such as uranium or plutonium, partial or complete disruption of the nucleus can occur, releasing large numbers of fast neutrons. Such reactions open the possibility for triggering a significant number of secondary fission reactions in a subcritical mass, and may potentially be useful for spacecraft propulsion.

Higgs production.

In collisions of two nucleons at very high energies, sea quarks and gluons tend to dominate the interaction rate, so neither nucleon need be an anti-particle for annihilation of a quark pair or "fusion" of two gluons to occur. Examples of such processes contribute to the production of the long-sought Higgs boson. The Higgs is directly produced very weakly by annihilation of light (valence) quarks, but heavy or sea or produced quarks are available. In 2012, the CERN laboratory in Geneva announced the discovery of the Higgs in the debris from proton-proton collisions at the Large Hadron Collider (LHC). The strongest Higgs yield is from fusion of two gluons (via annihilation of a heavy quark pair), while two quarks or antiquarks produce more easily identified events through radiation of a Higgs by a produced virtual vector boson or annihilation of two such vector bosons.

In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.


Mechanism.

Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases above the surface, and is a function of the mass of the planet, the radius of the surface, and the amount and composition of the gases and their vertical distribution in the atmosphere. It is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition.

Mean sea-level pressure.

The "mean sea-level pressure" (MSLP) is the atmospheric pressure at mean sea level (PMSL). This is the atmospheric pressure normally given in weather reports on radio, television, and newspapers or on the Internet. When barometers in the home are set to match the local weather reports, they measure pressure adjusted to sea level, not the actual local atmospheric pressure.  The "altimeter setting" in aviation is an atmospheric pressure adjustment.  Average "sea-level pressure" is. In aviation, weather reports (METAR), QNH is transmitted around the world in millibars or hectopascals (1 hectopascal = 1 millibar), except in the United States, Canada, and Colombia where it is reported in inches of mercury (to two decimal places). The United States and Canada also report "sea-level pressure" SLP, which is adjusted to sea level by a different method, in the remarks section, not in the internationally transmitted part of the code, in hectopascals or millibars. However, in Canada's public weather reports, sea level pressure is instead reported in kilopascals.  In the US weather code remarks, three digits are all that are transmitted; decimal points and the one or two most significant digits are omitted: is transmitted as 132; is transmitted as 000; 998.7mbar is transmitted as 987; etc. The highest "sea-level pressure" on Earth occurs in Siberia, where the Siberian High often attains a "sea-level pressure" above, with record highs close to. The lowest measurable "sea-level pressure" is found at the centers of tropical cyclones and tornadoes, with a record low of.

Surface pressure.

"Surface pressure" is the atmospheric pressure at a location on Earth's surface (terrain and oceans). It is directly proportional to the mass of air over that location.  For numerical reasons, atmospheric models such as general circulation models (GCMs) usually predict the nondimensional "logarithm of surface pressure".  The average value of surface pressure on Earth is 985 hPa. This is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea-level for locations above or below sea-level. The average pressure at mean sea-level (MSL) in the International Standard Atmosphere (ISA) is 1013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury.  Pressure (p), mass (m), and the acceleration due to gravity (g), are related by P = F/A = (m*g)/A, where A is surface area. Atmospheric pressure is thus proportional to the weight per unit area of the atmospheric mass above that location.

Altitude variation.

Pressure on Earth varies with the altitude of the surface; so air pressure on mountains is usually lower than air pressure at sea level. Pressure varies smoothly from the Earth's surface to the top of the mesosphere. Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases. One can calculate the atmospheric pressure at a given altitude. Temperature and humidity also affect the atmospheric pressure, and it is necessary to know these to compute an accurate figure. The graph was developed for a temperature of 15 °C and a relative humidity of 0%.  At low altitudes above sea level, the pressure decreases by about for every 100 metres. For higher altitudes within the troposphere, the following equation (the barometric formula) relates atmospheric pressure "p" to altitude "h": formula_1  where the constant parameters are as described below:

Local variation.

Atmospheric pressure varies widely on Earth, and these changes are important in studying weather and climate. See pressure system for the effects of air pressure variations on weather.  Atmospheric pressure shows a diurnal or semidiurnal (twice-daily) cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with an amplitude of a few millibars, and almost zero in polar areas. These variations have two superimposed cycles, a circadian (24 h) cycle and semi-circadian (12 h) cycle.

Records.

The highest adjusted-to-sea level barometric pressure ever recorded on Earth (above 750 meters) was measured in Tosontsengel, Mongolia on 19 December 2001. The highest adjusted-to-sea level barometric pressure ever recorded (below 750 meters) was at Agata in Evenk Autonomous Okrug, Russia (66°53'N, 93°28'E, elevation: ) on 31 December 1968 of. The discrimination is due to the problematic assumptions (assuming a standard lapse rate) associated with reduction of sea level from high elevations.  The Dead Sea, the lowest place on Earth at below sea level, has a correspondingly high typical atmospheric pressure of 1065hPa. A below-sea-level surface pressure record of was set on 21 February 1961.  The lowest non-tornadic atmospheric pressure ever measured was 870 hPa (0.858 atm; 25.69 inHg), set on 12 October 1979, during Typhoon Tip in the western Pacific Ocean. The measurement was based on an instrumental observation made from a reconnaissance aircraft.

Measurement based on depth of water.

One atmosphere (101.325 kPa or 14.7 psi) is also the pressure caused by the weight of a column of fresh water of approximately 10.3 m (33.8 ft). Thus, a diver 10.3 m underwater experiences a pressure of about 2 atmospheres (1 atm of air plus 1 atm of water). Conversely, 10.3 m is the maximum height to which water can be raised using suction under standard atmospheric conditions.  Low pressures such as natural gas lines are sometimes specified in inches of water, typically written as "w.c." (water column) gauge or "w.g." (inches water gauge). A typical gas-using residential appliance in the US is rated for a maximum of 1/2 psi, which is approximately 14 w.g. (3487 Pa or 34.9 millibars). Similar metric units with a wide variety of names and notation based on millimetres, centimetres or metres are now less commonly used.

Boiling point of water.

Pure water boils at at earth's standard atmospheric pressure. The boiling point is the temperature at which the vapor pressure is equal to the atmospheric pressure around the water. Because of this, the boiling point of water is lower at lower pressure and higher at higher pressure. Cooking at high elevations, therefore, requires adjustments to recipes or pressure cooking. A rough approximation of elevation can be obtained by measuring the temperature at which water boils; in the mid-19th century, this method was used by explorers.

Measurement and maps.

An important application of the knowledge that atmospheric pressure varies directly with altitude was in determining the height of hills and mountains thanks to the availability of reliable pressure measurement devices. In 1774, Maskelyne was confirming Newton's theory of gravitation at and on Schiehallion mountain in Scotland, and he needed to accurately measure elevations on the mountain's sides. William Roy, using barometric pressure, was able to confirm Maskelyne's height determinations, the agreement being to within one meter (3.28 feet). This method became and continues to be useful for survey work and map making.

Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as, which is equivalent to 760mm Hg, 29.9212inchesHg, or 14.696psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth, that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.


Development.

Viktor Kaplan, living in Brünn, Austria-Hungary (now Brno, Czechia), obtained his first patent for an adjustable blade propeller turbine in 1912. But the development of a commercially successful machine would take another decade. Kaplan struggled with cavitation problems, and in 1922 abandoned his research for health reasons.  In 1919 Kaplan installed a demonstration unit at Poděbrady (now in Czechia). In 1922 Voith introduced an 1100 HP (about 800 kW) Kaplan turbine for use mainly on rivers. In 1924 an 8 MW unit went on line at Lilla Edet, Sweden. This launched the commercial success and widespread acceptance of Kaplan turbines.

Theory of operation.

The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. Power is recovered from both the hydrostatic head and from the kinetic energy of the flowing water. The design combines features of radial and axial turbines.  The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is directed tangentially through the wicket gate and spirals on to a propeller shaped runner, causing it to spin.  The outlet is a specially shaped draft tube that helps decelerate the water and recover kinetic energy.  The turbine does not need to be at the lowest point of water flow as long as the draft tube remains full of water. A higher turbine location, however, increases the suction that is imparted on the turbine blades by the draft tube. The resulting pressure drop may lead to cavitation.  Variable geometry of the wicket gate and turbine blades allow efficient operation for a range of flow conditions. Kaplan turbine efficiencies are typically over 90%, but may be lower in very low head applications.  Current areas of research include computational fluid dynamics (CFD) driven efficiency improvements and new designs that raise survival rates of fish passing through.  Because the propeller blades are rotated on high-pressure hydraulic oil bearings, a critical element of Kaplan design is to maintain a positive seal to prevent emission of oil into the waterway. Discharge of oil into rivers is not desirable because of the waste of resources and resulting ecological damage.

Applications.

Kaplan turbines are widely used throughout the world for electrical power production. They cover the lowest head hydro sites and are especially suited for high flow conditions.  Inexpensive micro turbines on the Kaplan turbine model are manufactured for individual power production designed for 3 m of head which can work with as little as 0.3 m of head at a highly reduced performance provided sufficient water flow.  Large Kaplan turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%. They are very expensive to design, manufacture and install, but operate for decades.  They have recently found a new home in offshore wave energy generation, see Wave Dragon.

Variations.

The Kaplan turbine is the most widely used of the propeller-type turbines, but several other variations exist:

References.

The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level.


Description.

Balsam fir is a small to medium-size evergreen tree typically tall, occasionally reaching a height of. The narrow conic crown consists of dense, dark-green leaves. The bark on young trees is smooth, grey, and with resin blisters (which tend to spray when ruptured), becoming rough and fissured or scaly on old trees. The leaves are flat and needle-like, long, dark green above often with a small patch of stomata near the tip, and two white stomatal bands below, and a slightly notched tip. They are arranged spirally on the shoot, but with the leaf bases twisted so that the leaves appear to be in two more-or-less horizontal rows on either side of the shoot. The needles become shorter and thicker the higher they are on the tree. The seed cones are erect, long, dark purple, ripening brown and disintegrating to release the winged seeds in September.

Reproduction.

The male reproductive organs generally develop more rapidly and appear sooner than the female organs. The male organs contain microsporangia which divide to form sporogenous tissue, composed of cells which become archesporial cells. These develop into microspores, or pollen-mother cells, once they are rounded and filled with starch grains. When the microspores undergo meiosis in the spring, four haploid microspores are produced which eventually become pollen grains. Once the male strobilus has matured the microsporangia are exposed at which point the pollen is released.  The female megasporangiate is larger than the male. It contains bracts and megasporophylls, each of which contains two ovules, arranged in a spiral. These then develop a nucellus in which a mother cell is formed. Meiosis occurs and a megaspore is produced as the first cell of the megagametophyte. As cell division takes place the nucleus of the megaspore thickens, and cell differentiation occurs to produce prothallial tissue containing an ovum. The remaining undifferentiated cells then form the endosperm.  When the male structure releases its pollen grains, some fall onto the female strobilus and reach the ovule. At this point the pollen tube begins to generate, and eventually the sperm and egg meet at which point fertilization occurs.

Varieties.

There are two varieties:

Ecology.

Balsam firs tend to grow in cool climates, ideally with a mean annual temperature of, with consistent moisture at their roots. They typically grow in the following four forest types:  The foliage is browsed by moose and deer. The seeds are eaten by American red squirrels, grouse, and pine mice; the tree also provides food for crossbills and chickadees, as well as shelter for moose, snowshoe hares, white-tailed deer, ruffed grouse, and other small mammals and songbirds. The needles are eaten by some lepidopteran caterpillars, for example the Io moth ("Automeris io").  "Abies balsamea" is one of the most cold-hardy trees known, surviving at temperatures as low as (USDA Hardiness Zone 2). Specimens even showed no ill effects when immersed in liquid nitrogen at.

Pests.

The balsam fir is the preferred main host of the eastern spruce budworm, which is a major destructive pest throughout the eastern United States and Canada. During cyclical population outbreaks, major defoliation of the balsam fir can occur, which may significantly reduce radial growth. This can kill the tree. An outbreak in Quebec in 1957 killed over 75% of balsam fir in some stands.

Cultivation.

Christmas trees.

Both varieties of the species are very popular as Christmas trees, particularly in the northeastern United States. Balsam firs cut for Christmas are not taken from the forest, but are grown on large plantations. The balsam fir is one of the greatest exports of Quebec and New England. It is celebrated for its rich green needles, natural conical shape, and needle retention after being cut, and it is notably the most fragrant of all Christmas tree varieties.  Many of these plantations are family farms handed down from generation to generation. The techniques of shearing, growing, and other cultivation secretly passed down from grandparents to grandchildren. Families like the Rousseau's of Quebec, Rose of New Brunswick, and Kessler's (North Pole Xmas Trees) of New Hampshire have kept family traditions for almost a century.  The balsam fir was used six times for the US Capitol Christmas Tree between 1964 and 2019.  In northern areas of Minnesota, Michigan, and Wisconsin balsam fir branches (boughs) are used to make Christmas wreaths.

Horticulture.

"Abies balsamea" is also grown as an ornamental tree for parks and gardens. Very hardy down to or below, it requires a sheltered spot in full sun. The dwarf cultivar "A. balsamea" 'Hudson’ (Hudson fir), grows to only tall by broad, and has distinctive blue-green foliage with pale undersides. It does not bear cones. It has gained the Royal Horticultural Society's Award of Garden Merit.  Other cultivars include:-

Other uses.

The resin is used to produce Canada balsam, and was traditionally used as a cold remedy and as a glue for glasses, optical instrument components, and for preparing permanent mounts of microscope specimens. Given its use as a traditional remedy and the relatively high ascorbic acid content of its needles, historian Jacques Mathieu has argued that the balsam fir was the "aneda" that cured scurvy during the second expedition into Canada of Jacques Cartier. The wood is milled for framing lumber (part of SPF lumber), siding and pulped for paper manufacture. Balsam fir oil is an EPA approved nontoxic rodent repellent. The balsam fir is also used as an air freshener and as incense.  Prior to the availability of foam rubber and air mattresses, balsam fir boughs were a preferred mattress in places where trees greatly outnumbered campers. Many fir limbs are vertically bowed from alternating periods of downward deformation from snow loading and new growth reaching upward for sunlight. Layers of inverted freshly cut limbs from small trees created a pleasantly fragrant mattress lifting bedding off the wet ground; and the bowed green limbs were springs beneath the soft needles. Upper layers of limbs were placed with the cut ends of the limbs touching the earth to avoid uncomfortably sharp spots and sap.  The Native Americans used it for a variety of medicinal purposes.

Tree emblem.

Balsam fir is the provincial tree of New Brunswick.

Abies balsamea or balsam fir is a North American fir, native to most of eastern and central Canada (Newfoundland west to central Alberta) and the northeastern United States (Minnesota east to Maine, and south in the Appalachian Mountains to West Virginia).


Development.

Water wheels of different types have been used for more than 1,000 years to power mills of all types, but they were relatively inefficient. Nineteenth-century efficiency improvements of water turbines allowed them to replace nearly all water wheel applications and compete with steam engines wherever water power was available. After electric generators were developed in the late 1800s; turbines were a natural source of generator power where potential hydropower sources existed.  In 1826 Benoit Fourneyron developed a high-efficiency (80%) outward-flow water turbine. Water was directed tangentially through the turbine runner, causing it to spin. Jean-Victor Poncelet designed an inward-flow turbine in about 1820 that used the same principles. S. B. Howd obtained a US patent in 1838 for a similar design.  In 1848 James B. Francis, while working as head engineer of the Locks and Canals company in the water wheel-powered textile factory city of Lowell, Massachusetts, improved on these designs to create more efficient turbines. He applied scientific principles and testing methods to produce a very efficient turbine design. More importantly, his mathematical and graphical calculation methods improved turbine design and engineering. His analytical methods allowed design of high-efficiency turbines to precisely match a site's water flow and pressure (water head).

Components.

A Francis turbine consists of the following main parts:  Spiral casing: The spiral casing around the runner of the turbine is known as the volute casing or scroll case. Throughout its length, it has numerous openings at regular intervals to allow the working fluid to impinge on the blades of the runner. These openings convert the pressure energy of the fluid into kinetic energy just before the fluid impinges on the blades. This maintains a constant velocity despite the fact that numerous openings have been provided for the fluid to enter the blades, as the cross-sectional area of this casing decreases uniformly along the circumference.  Guide and stay vanes: The primary function of the guide and stay vanes is to convert the pressure energy of the fluid into kinetic energy. It also serves to direct the flow at design angles to the runner blades.  Runner blades: Runner blades are the heart of any turbine. These are the centers where the fluid strikes and the tangential force of the impact causes the shaft of the turbine to rotate, producing torque. Close attention to design of blade angles at inlet and outlet is necessary, as these are major parameters affecting power production.  Draft tube: The draft tube is a conduit that connects the runner exit to the tail race where the water is discharged from the turbine. Its primary function is to reduce the velocity of discharged water to minimize the loss of kinetic energy at the outlet. This permits the turbine to be set above the tail water without appreciable drop of available head.

Theory of operation.

The Francis turbine is a type of reaction turbine, a category of turbine in which the working fluid comes to the turbine under immense pressure and the energy is extracted by the turbine blades from the working fluid. A part of the energy is given up by the fluid because of pressure changes occurring in the blades of the turbine, quantified by the expression of degree of reaction, while the remaining part of the energy is extracted by the volute casing of the turbine. At the exit, water acts on the spinning cup-shaped runner features, leaving at low velocity and low swirl with very little kinetic or potential energy left. The turbine's exit tube is shaped to help decelerate the water flow and recover the pressure.

Blade efficiency.

Usually the flow velocity (velocity perpendicular to the tangential direction) remains constant throughout, i.e. and is equal to that at the inlet to the draft tube. Using the Euler turbine equation,, where "e" is the energy transfer to the rotor per unit mass of the fluid. From the inlet velocity triangle,  and Therefore  The loss of kinetic energy per unit mass becomes.  Therefore, neglecting friction, the blade efficiency becomes  i.e.

Degree of reaction.

Degree of reaction can be defined as the ratio of pressure energy change in the blades to total energy change of the fluid. This means that it is a ratio indicating the fraction of total change in fluid pressure energy occurring in the blades of the turbine. The rest of the changes occur in the stator blades of the turbines and the volute casing as it has a varying cross-sectional area. For example, if the degree of reaction is given as 50%, that means that half of the total energy change of the fluid is taking place in the rotor blades and the other half is occurring in the stator blades. If the degree of reaction is zero it means that the energy changes due to the rotor blades is zero, leading to a different turbine design called the Pelton Turbine.  The second equality above holds, since discharge is radial in a Francis turbine. Now, putting in the value of 'e' from above and using formula_7 (as formula_8)

Application.

Francis turbines may be designed for a wide range of heads and flows. This versatility, along with their high efficiency, has made them the most widely used turbine in the world. Francis type units cover a head range from, and their connected generator output power varies from just a few kilowatts up to 800 MW. Large Francis turbines are individually designed for each site to operate with the given water supply and water head at the highest possible efficiency, typically over 90%.  In contrast to the Pelton turbine, the Francis turbine operates at its best completely filled with water at all times. The turbine and the outlet channel may be placed lower than the lake or sea level outside, reducing the tendency for cavitation.  In addition to electrical production, they may also be used for pumped storage, where a reservoir is filled by the turbine (acting as a pump) driven by the generator acting as a large electrical motor during periods of low power demand, and then reversed and used to generate power during peak demand. These pump storage reservoirs act as large energy storage sources to store "excess" electrical energy in the form of water in elevated reservoirs. This is one of a few methods that allow temporary excess electrical capacity to be stored for later utilization.

The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts.


Biography.

Weierstrass was born in Ostenfelde, part of Ennigerloh, Province of Westphalia.  Weierstrass was the son of Wilhelm Weierstrass, a government official, and Theodora Vonderforst. His interest in mathematics began while he was a gymnasium student at the in Paderborn. He was sent to the University of Bonn upon graduation to prepare for a government position. Because his studies were to be in the fields of law, economics, and finance, he was immediately in conflict with his hopes to study mathematics. He resolved the conflict by paying little heed to his planned course of study, but continued private study in mathematics. The outcome was to leave the university without a degree. After that he studied mathematics at the Münster Academy (which was even at this time very famous for mathematics) and his father was able to obtain a place for him in a teacher training school in Münster. Later he was certified as a teacher in that city. During this period of study, Weierstrass attended the lectures of Christoph Gudermann and became interested in elliptic functions.  In 1843 he taught in Deutsch Krone in West Prussia and since 1848 he taught at the Lyceum Hosianum in Braunsberg. Besides mathematics he also taught physics, botany, and gymnastics.  Weierstrass may have had an illegitimate child named Franz with the widow of his friend Carl Wilhelm Borchardt.  After 1850 Weierstrass suffered from a long period of illness, but was able to publish mathematical articles that brought him fame and distinction. The University of Königsberg conferred an honorary doctor's degree on him on 31 March 1854. In 1856 he took a chair at the Gewerbeinstitut, which later became the Technical University of Berlin. In 1864 he became professor at the Friedrich-Wilhelms-Universität Berlin, which later became the Humboldt Universität zu Berlin.  At the age of fifty-five, Weierstrass met Sofia Kovalevsky whom he tutored privately after failing to secure her admission to the University. They had a fruitful intellectual, but troubled personal relationship that "far transcended the usual teacher-student relationship". The misinterpretation of this relationship and Kovalevsky's early death in 1891 was said to have contributed to Weierstrass' later ill-health. He was immobile for the last three years of his life, and died in Berlin from pneumonia.

Mathematical contributions.

Soundness of calculus.

Weierstrass was interested in the soundness of calculus, and at the time, there were somewhat ambiguous definitions regarding the foundations of calculus, and hence important theorems could not be proven with sufficient rigour. While Bolzano had developed a reasonably rigorous definition of a limit as early as 1817 (and possibly even earlier) his work remained unknown to most of the mathematical community until years later, and many mathematicians had only vague definitions of limits and continuity of functions.  Delta-epsilon proofs are first found in the works of Cauchy in the 1820s. Cauchy did not clearly distinguish between continuity and uniform continuity on an interval. Notably, in his 1821 "Cours d'analyse," Cauchy argued that the (pointwise) limit of (pointwise) continuous functions was itself (pointwise) continuous, a statement interpreted as being incorrect by many scholars. The correct statement is rather that the "uniform" limit of continuous functions is continuous (also, the uniform limit of uniformly continuous functions is uniformly continuous). This required the concept of uniform convergence, which was first observed by Weierstrass's advisor, Christoph Gudermann, in an 1838 paper, where Gudermann noted the phenomenon but did not define it or elaborate on it. Weierstrass saw the importance of the concept, and both formalized it and applied it widely throughout the foundations of calculus.  The formal definition of continuity of a function, as formulated by Weierstrass, is as follows:  formula_1 is continuous at formula_2 if formula_3 such that for every formula_4 in the domain of formula_5, formula_6 In simple English, formula_1 is continuous at a point formula_2 if for each formula_4 close enough to formula_10, the function value formula_11 is very close to formula_12, where the "close enough" restriction typically depends on the desired closeness of formula_12 to formula_14 Using this definition, he proved the Intermediate Value Theorem. He also proved the Bolzano–Weierstrass theorem and used it to study the properties of continuous functions on closed and bounded intervals.

Calculus of variations.

Weierstrass also made significant advancements in the field of calculus of variations. Using the apparatus of analysis that he helped to develop, Weierstrass was able to give a complete reformulation of the theory which paved the way for the modern study of the calculus of variations. Among the several significant axioms, Weierstrass established a necessary condition for the existence of strong extrema of variational problems. He also helped devise the Weierstrass–Erdmann condition, which gives sufficient conditions for an extremal to have a corner along a given extrema, and allows one to find a minimizing curve for a given integral.

Honours and awards.

The lunar crater Weierstrass and the asteroid 14100 Weierstrass are named after him. Also, there is the Weierstrass Institute for Applied Analysis and Stochastics in Berlin.

Karl Theodor Wilhelm Weierstrass ( ; 31 October 1815 – 19 February 1897) was a German mathematician often cited as the "father of modern analysis". Despite leaving university without a degree, he studied mathematics and trained as a school teacher, eventually teaching mathematics, physics, botany and gymnastics. He later received an honorary doctorate and became professor of mathematics in Berlin.


Etymology.

The Ossetians and Ossetia received their name from the Russians, who adopted the Georgian designations "Osi" (ოსი) (sing., pl.: "Osebi" (ოსები)) and "Oseti" ("the land of Osi" (ოსეთი)), used since the Middle Ages for the single Iranian-speaking population of the Central Caucasus and probably based on the old Alan self-designation "As". As the Ossetians lacked any single inclusive name for themselves in their native language, these terms were accepted by the Ossetians themselves already before their integration into the Russian Empire.  This practice was put into question by the new Ossetian nationalism in the early 1990s, when the dispute between the Ossetian subgroups of Digoron and Iron over the status of the Digoron dialect made the Ossetian intellectuals search for a new inclusive ethnic name. This, combined with the effects of the Georgian-Ossetian conflict, led to the popularization of "Alania", the name of the medieval Sarmatian confederation, to which the Ossetians traced their origin, and inclusion of this name into the official republican title of North Ossetia in 1994.

Culture.

Mythology.

The folk beliefs of the Ossetian people are rooted in their Sarmatian origin and Christian religion, with the pagan gods having been converted into Christian saints. The Nart saga serves as the basic pagan mythology of the region.

History.

Pre-history (Early "Alans").

The Ossetians descend from the Alans, a Sarmatian tribe (Scythian subgroup of the Iranian ethnolinguistic group). The Alans were the only branch of the Sarmatians to keep their culture in the face of a Gothic invasion (c. 200 CE), and those who remained built a great kingdom between the Don and Volga Rivers, according to Coon, "The Races of Europe". Between 350 and 374 CE, the Huns destroyed the Alan kingdom, and the Alan people were split in half. One half fled to the west, where they participated in the Barbarian Invasions of Rome, established short-lived kingdoms in Spain and North Africa, and settled in many other places such as Orléans, France. The other half fled to the south and settled on the plains of the North Caucasus, where they established their medieval kingdom of Alania.

Middle Ages.

In the 8th century a consolidated Alan kingdom, referred to in sources of the period as Alania, emerged in the northern Caucasus Mountains, roughly in the location of the latter-day Circassia and the modern North Ossetia–Alania. At its height, Alania was a centralized monarchy with a strong military force and had a strong economy that benefited from the Silk Road.  After the Mongol invasions of the 1200s, the Alans were forced out of their medieval homeland south of the River Don in present-day Russia. Due to this, the Alans migrated toward the Caucasus Mountains, where they would form three ethnographical groups; the Iron, the Digoron, and the Kudar. The Jassic people were a fourth group that migrated in the 13th century to Hungary.

Modern history.

In more-recent history, the Ossetians participated in the Ossetian–Ingush conflict (1991–1992) and Georgian–Ossetian conflicts (1918–1920, early 1990s) and in the 2008 South Ossetia war between Georgia and Russia.  Key events:

Language.

The Ossetian language belongs to the Eastern Iranian (Alanic) branch of the Indo-European language family.  Ossetian is divided into two main dialect groups: Ironian (os. – Ирон) in North and South Ossetia; and Digorian (os. – Дыгурон) in western North Ossetia. In these two groups are some subdialects, such as Tualian, Alagirian, and Ksanian. The Ironian dialect is the most widely spoken.  Ossetian is among the remnants of the Scytho-Sarmatian dialect group, which was once spoken across the Pontic–Caspian Steppe. The Ossetian language is not mutually intelligible with any other Iranian language.

Religion.

Prior to the 10th century, Ossetians were strictly pagan. They were partially Christianized by Byzantine missionaries in the beginning of the 10th century. By the 13th, most Ossetians were Eastern Orthodox Christians as a result of Georgian influence and missionary work.  Islam was introduced during the 16th and 17th century by the converted members of the Circassian Kabarday tribe (who had been introduced to that religion by Tatars during the 15th century), who had taken over territory in Western Ossetia occupied by the Digor. However, Islam did not successfully spread to rest of the Ossetian people.  In 1774 Ossetia became part of the Russian Empire, which strengthened Orthodox Christianity considerably by sending Russian Orthodox missionaries there. However, most of the missionaries chosen were churchmen from Eastern Orthodox communities living in Georgia, including Armenians and Greeks, as well as ethnic Georgians. Russian missionaries were not sent, as this would have been regarded by the Ossetians as too intrusive.  Today, the majority of Ossetians from both North and South Ossetia follow Eastern Orthodoxy. Assianism ("Uatsdin" or "Assdin" in Ossetian), the Ossetian ethnic religion, is also widespread among Ossetians, with ritual traditions like animal sacrifices, holy shrines, non-Christian saints, etc. There are temples, known as "kuvandon," in most villages. According to the research service "Sreda", North Ossetia is the primary center of Ossetian Paganism, and 29% of the population reported practicing pagan faiths in the 2012 Russian census. Assianism has been rising in popularity since the 1980s.  According to a 2013 estimate, up to 15% of North Ossetia’s population practice Islam.

Economy.

The northern Ossetians export lumber and cultivate various crops, mainly corn. The southern Ossetians are chiefly pastoral, herding sheep, goats, and cattle. Traditional manufactured products include leather goods, fur caps, daggers, and metalware.

Demographics.

Outside of South Ossetia, there are also a significant number of Ossetians living in Trialeti, in north-central Georgia. A large Ossetian diaspora lives in Turkey, and Ossetians have also settled in Belgium, France, Sweden, Syria, the United States (primarily New York City, Florida and California), Canada (Toronto), Australia (Sydney), and other countries all around the world.

Russian Census of 2002.

The vast majority of Ossetians live in Russia (according to the Russian Census (2002)):

Genetics.

The Ossetians are a unique ethnic group of the Caucasus, speaking an Indo-European language surrounded mostly by Caucasian ethnolinguistic groups, the other non-Caucasian tribes include the Karachays and Balkars. The Y-haplogroup data indicate that North Ossetians are more similar to other North Caucasian groups, and South Ossetians to other South Caucasian groups, than the two are to each other. With respect to mtDNA, Ossetians are significantly more similar to some Iranian groups than to Caucasian groups. It is thus suggested that there is a common origin of Ossetians from the Proto-Iranian Urheimat, followed by subsequent male-mediated migrations from their Caucasian neighbours.

The Ossetians or Ossetes (;, '; дигорӕ, дигорӕнттӕ, ') are an Iranian ethnic group of the Caucasus Mountains, indigenous to the ethnolinguistic region known as Ossetia. They speak Ossetic, an Eastern Iranian (Alanic) language of the Indo-European language family, with most also fluent in Russian as a second language. Although Ossetian is related to the Indo-European languages owing to its origin, it is not mutually intelligible with any other language of the family today. Ossetic, a remnant of the Scytho-Sarmatian dialect group which was once spoken across the Pontic–Caspian Steppe, is one of the few Iranian languages inside Europe.


Biography.

Provenance and early years.

Pieck was born as the son of the coachman Friedrich Pieck and his wife Auguste in the eastern part of Guben, Germany, which is now Gubin, Poland. Two years later, his mother died. The father soon married the washerwoman Wilhelmine Bahro. After attending elementary school, the young Wilhelm completed a four-year carpentry apprenticeship. As a journeyman, he joined the German Timber Workers Association in 1894.  As a carpenter, in 1894 Pieck joined the wood-workers' federation, which steered him towards joining the Social Democratic Party of Germany (SPD) the following year. Pieck became the chairman of the party urban district in 1899, and in 1906 became full-time secretary of the SPD. In 1914, he moved to a three-room apartment in Berlin-Steglitz. By now he had his own study with many shelves full of books. In May 1915, he was arrested at the big women's demonstration in front of the Reichstag and kept in "protective custody" until October. As Bremen Party secretary in 1916, Pieck had asked Anton Pannekoek to continue teaching socialist theory in the party school. Although the majority of the SPD supported the German government in World War I, Pieck was a member of the party's left wing, which opposed the war. Pieck's openness in doing so led to his arrest and detention in a military prison. After being released, Pieck briefly lived in exile in Amsterdam. Upon his return to Berlin in 1918, Pieck joined the newly founded Communist Party of Germany (KPD). On 16 January 1919 Pieck, along with Rosa Luxemburg and Karl Liebknecht was arrested while meeting at Berlin Eden Hotel. Liebknecht and Luxemburg were then killed while "being taken to prison" by a unit of Freikorps. While the two were being murdered, Pieck managed to escape. In 1922, he became a founding member of the International Red Aid, serving first on the executive committee. In May 1925, he became the chairman of the Rote Hilfe.

Nazi years and Moscow exile.

On 4 March 1933, one day before the Reichstag election, Pieck's family left their Steglitz apartment and moved into a cook's room. His son and daughter had been in the Soviet Union since 1932 while Elly Winter was still in Germany. At the beginning of May 1933, he left first to Paris and then to Moscow. In Moscow, Pieck served the Communist Party in a variety of capacities. From 1935 until 1943, he held the position of Secretary of the Communist International. In 1943 Pieck was among the founders of the National Committee for a Free Germany, which planned for the future of Germany after World War II.  On 22 June 1941 Pieck and his family were in their country house on the outskirts of Moscow. Pieck came downstairs at six o'clock to his children's bedroom and said: "Children, get up, it was announced on the radio that war is over. Hitler invaded the Soviet Union, but that will be the end". In March 1942 the family was able to return there after the Soviet Armed Forces won the Battle of Moscow.

Home to the Soviet occupation zone.

At the conclusion of the war in 1945 Pieck returned to Germany with the victorious Red Army. A year later, he helped engineer the merger of the eastern branches of the KPD and SPD into the Socialist Unity Party of Germany. He was elected as the merged party's co-chairman, alongside former SPD leader Otto Grotewohl.

President of East Germany.

In October 1949, the Soviet occupation zone was relaunched as the Soviet sponsored German Democratic Republic (East Germany). Pieck was elected president of the new country. He served as East Germany's first (and last) president until his death in 1960. He lost the chairmanship of the ruling SED (party) in 1950, when Walter Ulbricht became the party's first secretary. Nonetheless, due to Joseph Stalin's trust in him, he retained his other posts.

Last years.

Pieck was already 73 years old at the time of his initial election as president. Although he nominally held the second highest state post in the GDR (behind Prime Minister Grotewohl) and served as SED co-chairman for the first four years of the party's existence, he never played a major role in the party.  On 13 July 1953, he suffered a second stroke. He also had progressive liver cirrhosis and existing ascites. A detailed medical report composed before the second stroke mentioned mild paralysis on the right, a slight drooping of the corner of the mouth, breathing wheezing or snoring, slowed down pulse, tone of the limb musculature lowered...".  In August 1960 he moved to new summer residence, the former, converted mansion of the Hermann Göring Leibförsters near "Karinhall".  Pieck lived at Majakowskiring 29, Pankow, East Berlin.

Family.

He was married to Christine Häfker, a garments worker whom he met in a large dance hall in Bremen. At first, her parents did not want her to go out with a "red", but once she was pregnant, she was allowed to marry Wilhelm on 28 May 1898, on the condition that a traditional wedding in a church would still take place. On the wedding day Christine waited impatiently for Pieck to arrive at the church. At the last minute, he finally did, still carrying communist leaflets. In November 1936, his wife contracted pneumonia for the third time, dying on 1 December of the same year.  The Piecks' daughter, Elly Winter (1898–1987), held various posts in the SED and East German government. Their son Arthur Pieck (1899–1970) served as head of the East-German national airline Interflug from 1955–1965, after having held various administrative posts in East Germany, for instance at the German Economic Commission. The youngest child, Eleonore Staimer, (1906–1998), worked as a party official and, for a time, low level diplomat.

Friedrich Wilhelm Reinhold Pieck (; 3 January 1876 – 7 September 1960) was a German communist politician. In 1949, he became the first President of the German Democratic Republic, an office abolished upon his death. His successor as head of state was Walter Ulbricht, who served as chairman of the Council of State.


Name.

Roller Hockey (Quad) was referred to as Hardball Hockey in the United States until November 2008 when the USOC adopted the sport's more common name, Rink Hockey. Other names for the sport include Hardball Roller Hockey, Ball Hockey, International Style Ball hockey, International hockey, Quad Hockey, Hockey, English Roller Hockey, Hockey Sobre Patines, Hockey pista, Hóquei em patins, Hockey Skids, Traditional Hockey, Cane Hockey, Rollhockey, Rolhockey, Hokej na koturaljkama, Rulleskøjtehockey and Rulluisuhoki.

The rink.

The rink has usually a polished wooden surface, but any flat, non-abrasive and non-slippery material such as treated cement is acceptable. Likewise, it is allowed for rink owners to put advertisements in the playing area, as long as they don't interfere with ball or skate motion, which includes both physically (must be at exactly the same level as the remaining area) and visually (dark colours or any other pattern which can mask the ball).  It can have one out of three standard sizes (a minimum of 34x17 meters, an average of 40x20 and a maximum of 44x22) or any size between the minimum and maximum values that has a 2:1 size ratio with a 10% margin of error.  The rink has rounded corners (1 m radius) and is surrounded by a 1 m wall. The wall also has a wooden base 2 cm wide and at least 20 cm high. Behind the goals there is a 4 m high net, even if there are no stands (to avoid the ball bouncing back from a wall and hitting a player). If the ball hits the net, it's considered to be out of bounds.  The markings are simple. The halfway line divides the rink into halves, and 22 m from the end wall an "anti-play" line is painted. The area is a 9 X 5.40 m rectangle, placed from 2.7 to 3.3 m ahead of the end table. It has a protection area for goalkeepers, a half-circle with 1.5 m radius. All markings are 8 cm in width. The goal (painted in fluorescent orange) is 105 cm high by 170 cm wide. Inside the goal there is a thick net and a bar close to ground to trap the ball inside (before, two extra referees stayed behind the goal to judge goal decisions), and 92 cm deep. While not attached to the ground, it is extremely heavy to prevent movement.

Rules.

World Skate provides the current rulebook at its website. According to the rule book, the playing time can be reduced depending on the age of the players (competitions played by younger players will have a lower playing time) and the sequence of the competition's matches (a competition disputed in consecutive days can have the playing time reduced with the aim to preserve the health and recovery of the players). The playing time must be defined before the start of each competition.

History.

The first recorded Hardball Roller Hockey game was played in 1878 at the Denmark Rink in London, England. It was first known as “roller polo” due to the introduction of Polo in 1876, skaters took polo to the rinks. The sport was introduced into the United States in 1882 with the formation of the National Roller Polo League in Dayton, Ohio, with teams in seven cities. Roller Polo League In 1884 the Massachusetts Roller Polo league was operating with 14 teams Organized roller skating sports developed as the popularity of roller skates increased in the late 19th and early 20th centuries. Roller hockey teams were playing throughout Europe as early as 1901. Roller Hockey was played by the famous silent film stars, Stan Laurel and Charlie Chaplin, in the early 1900s. The first World Championships in roller hockey were held in 1936 in Stuttgart, Germany. Since 2017, the World Championships have been part of the World Roller Games organised by World Skate.  Rink Hockey as it was called in Europe was not organized by the RSROA in the United States until 1959 and name roller hockey The sport debuted at the US National Championships in 1961. The Pan American Games introduced roller skating as a sport in 1979 and debuted roller hockey the same year. It was one of the Pan American Games sports in 1979, 1987, 1991 and 1995. It has since been discontinued. Roller hockey was present as an exhibition sport at the 1992 Summer Olympics in Barcelona, Spain.

International competitions.

There are several international competitions with national teams. There are three world championships, one for men, the Roller Hockey World Cup, one for women, the Women's Roller Hockey World Cup and the Roller Hockey World Cup U-20. Since 2017 World Skate has organised the World Roller Games, comprising all three of the world championships as regulated by the World Skate international federation.

Roller hockey (in British English), rink hockey (in American English) or quad hockey is a team sport that enjoys significant popularity in a number of Latin countries, and in Europe is an sport practised specially in Portugal, Spain (mainly Catalonia and Galicia) and Italy (being very popular in the region of the Veneto).


Canyoning around the world.

In most parts of the world canyoning is done in mountain canyons with flowing water. The number of countries with established canyoning outfitters is growing yearly.

Asia.

In Vietnam you can try in Dalat, its call "Dalat Canyoning Challenge", organized by Viet Challenge Tours. In Japan ("sawanobori") and Taiwan canyoning is called "river tracing" and typically involves traveling upstream.

Europe.

Canyoning in the United Kingdom has gained in popularity over recent years. In the UK, Wales, Scotland, Cumbria and Yorkshire and some areas of Cornwall are recognized as the prime locations for this activity. In the Welsh language, canyoning is called "cerdded ceunant". It is also referred to as "gorge walking", which the UK Scout Association defines as "the activity of following a river bed through a gorge. This often includes climbing, swimming, abseiling and scrambling depending upon the environment".  Ticino, Switzerland, is a popular canyoning destination because of its granite rock, crystal green pools and its pleasant Mediterranean climate.  Spain has also emerged as a popular canyoning spot, owing to its warm climate and abundance of rock formations conducive to canyoning.  Portugal also has canyoning in the Azores and Madeira.

North America.

In the United States, descending mountain canyons with flowing water is sometimes referred to as "canyoning", although the term "canyoneering" is more common. Most canyoneering in the United States occurs in the many slot canyons carved in the sandstone found throughout the Colorado Plateau. Outside of the Colorado Plateau, numerous canyoneering opportunities are found in the San Gabriel, Sierra Nevada, Cascade, and Rocky Mountain ranges.

Oceania.

Canyoning is common in Australia in the sandstone canyons of the Blue Mountains National Park, known for their technical abseil starts and lack of fast flowing water.

Hazards.

Canyoning can be dangerous. Escape via the sides of a canyon is often impossible, and completion of the descent is the only possibility. Due to the remoteness and inaccessibility of many canyons, rescue can be impossible for several hours or several days.

High water flow / hydraulics.

Canyons with significant water flow may be treacherous and require special ropework techniques for safe travel. Hydraulics, undercurrents, and sieves (or "strainers") occur in flowing canyons and can trap or pin and drown a canyoneer. A 1993 accident in Zion National Park, Utah, USA, in which two leaders of a youth group drowned in powerful canyon hydraulics (and the lawsuit which followed) brought notoriety to the sport.

Flash floods.

A potential danger of many canyoning trips is a flash flood. A canyon "flashes" when a large amount of precipitation falls in the drainage, and water levels in the canyon rise quickly as the runoff rushes down the canyon. In canyons that drain large areas, the rainfall could be many kilometers away from the canyoners, completely unbeknown to them. A calm or even dry canyon can quickly become a violent torrent due to a severe thunderstorm in the vicinity. Fatalities have occurred as a result of flash floods; in one widely publicized 1999 incident, 21 tourists on a commercial canyoning adventure trip drowned in Saxetenbach Gorge, Switzerland. Authorities in Switzerland have set in the last few years high standards on safety, "Safety in adventures" label is becoming the standard for all companies to prove they are following the standard safety procedures.

Hypothermia and hyperthermia.

Temperature-related illnesses are also canyoning hazards. In arid desert canyons, heat exhaustion can occur if proper hydration levels are not maintained and adequate steps are not taken to avoid the intense rays of the sun. Hypothermia can be a serious danger in "any" canyon that contains water, during "any time" of the year. Wetsuits and drysuits can mitigate this danger to a large degree, but when people miscalculate the amount of water protection they will need, dangerous and sometimes fatal situations can occur. Hypothermia due to inadequate cold water protection is cited as a cause of a 2005 incident in which two college students drowned in a remote Utah canyon.

Keeper potholes.

Some canyoneering, especially in sandstone slots, involves escaping from large potholes. Also called "keeper potholes," these features, carved out by falling water at the bottom of a drop in the watercourse, are circular pits that often contain water that is too deep to stand up in and whose walls are too smooth to easily climb out of. Canyoneers use several unique and creative devices to escape potholes, including hooks used for aid climbing attached to long poles and specialized weighted bags that are attached to ropes and tossed over the lip of a pothole.

Very narrow slots.

Narrow slot canyons, especially those narrower than humans, present difficult obstacles for canyoners. At times a canyoner is forced to climb up (using chimneying or off-width climbing techniques) to a height where one can comfortably maneuver laterally with pressure on both walls of the canyon. This tends to be strenuous and can require climbing high above the canyon floor, unprotected, for long periods of time. Failure to complete the required moves could result in being trapped in a canyon where rescue is extremely difficult. Past rescues have required extensive rigging systems and dishsoap to extract stuck canyoners.  Narrow sandstone slot canyons tend to have abrasive walls which rip clothing and gear, and can cause painful skin abrasion as a canyoner moves or slides along them.

Exposure to water-borne diseases.

Immersion in water may lead to exposure to diseases such as Weil's Disease (Leptospirosis), dermatitis and gastroenteritis. Ingestion of water should be avoided and taking a shower immediately after canyoning or gorge walking is recommended.

Rockfall.

Canyons are changing environments and falling rocks, including chockstones, are not uncommon. A moving chockstone caused Aron Ralston's 2003 accident where he was forced to amputate his forearm.

Becoming lost.

Many canyons are located in remote areas with limited or sparse trails, and due to their harsh environments, straying from established areas can be dangerous.

Education and training.

As the sport of canyoneering begins to grow, there are more and more people looking to learn the skills needed to safely descend canyons. There are several reputable organizations that are now offering classes of various forms to the public; some organizations are training organizations that offer certifications, while other commercial operations offer classes in addition to purely recreational guided tours. The latter is particularly popular in tourist destinations around the world, such as Costa Rica, Hawaii, the Philippines, and Utah. Most programs have multiple levels of skill-set classes. The lowest levels usually cover the basics such as rappelling, rope work, navigation, identification of gear and clothing, and rappel setups. The higher levels cover more complex situations such as anchor building and strategies on how to descend various types of canyons. Other higher level and specialty classes typically cover rescue situations, wilderness first aid, and swift water canyons. <br> For professional canyoning guide training there are a number of organisations spread throughout the world. In Europe the CIC (Commission Internationale de Canyon) was one of the first organisations, (formerly CEC) for professionals to teach over multiple countries. Recently ICO Pro (International Canyoning Organisation for Professionals), ICA (International Academy of Canyoning Association) and the ACA (American Canyoneering Association), CGI (Canyon Guides International) all teach in multiple countries. There are also many certification systems governed by single countries, many which are based on the original CEC methodology.

Canyoning (canyoneering in the United States, kloofing in South Africa) is travelling in canyons using a variety of techniques that may include other outdoor activities such as walking, scrambling, climbing, jumping, abseiling (rappelling), and swimming.


Code format.

The format of the ISSN is an eight-digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits. The last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code (also named "ISSN structure" or "ISSN syntax") can be expressed as follows: or by a Perl Compatible Regular Expressions (PCRE) regular expression:  The ISSN of the journal "Hearing Research", for example, is 0378-5955, where the final 5 is the check digit, that is codice_2=5. To calculate the check digit, the following algorithm may be used:  To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right (if the check digit is X, then add 10 to the sum). The modulus 11 of the sum must be 0. There is an online ISSN checker that can validate an ISSN, based on the above algorithm.

Code assignment, maintenance and look-up.

ISSN codes are assigned by a network of ISSN National Centres, usually located at national libraries and coordinated by the ISSN International Centre based in Paris. The International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government.

Linking ISSN.

"ISSN-L" is a unique identifier for all versions of the serial containing the same content across different media. As defined by "ISO 3297:2007", the "linking ISSN (ISSN-L)" provides a mechanism for collocation or linking among the different media versions of the same continuing resource. The "ISSN-L" is one of a serial’s existing ISSNs, so does not change the use or assignment of "ordinary" ISSNs; it is based on the ISSN of the first published medium version of the publication. If the print and online versions of the publication are published at the same time, the ISSN of the print version is chosen as the basis of the "ISSN-L".  With "ISSN-L" is possible to designate one single ISSN for all those media versions of the title. The use of "ISSN-L" facilitates search, retrieval and delivery across all media versions for services like OpenURL, library catalogues, search engines or knowledge bases.

Register.

The International Centre maintains a database of all ISSNs assigned worldwide, the "ISDS Register" (International Serials Data System), otherwise known as the "ISSN Register". the ISSN Register contained records for 1,943,572 items. The Register is not freely available for interrogation on the web, but is available by subscription.

Comparison with other identifiers.

ISSN and ISBN codes are similar in concept, where ISBNs are assigned to individual books. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change.

Extensions.

Since the ISSN applies to an entire serial a new identifier, other identifiers have been built on top of it to allow references to specific volumes, articles, or other identifiable components (like the table of contents): the Publisher Item Identifier (PII) and the Serial Item and Contribution Identifier (SICI).

Media versus content.

Separate ISSNs are needed for serials in different media (except reproduction microforms). Thus, the print and electronic media versions of a serial need separate ISSNs, and CD-ROM versions and web versions require different ISSNs. However, the same ISSN can be used for different file formats (e.g. PDF and HTML) of the same online serial.  This "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, and the Web, it makes sense to consider only "content", independent of media. This "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier (DOI), an ISSN-independent initiative, consolidated in the 2000s.  Only later, in 2007, ISSN-L was defined in the new ISSN standard (ISO 3297:2007) as an "ISSN designated by the ISSN Network to enable collocation or versions of a continuing resource linking among the different media".

Use in URNs.

An ISSN can be encoded as a uniform resource name (URN) by prefixing it with "". For example, "Rail" could be referred to as "". URN namespaces are case-sensitive, and the ISSN namespace is all caps. If the checksum digit is "X" then it is always encoded in uppercase in a URN.

Problems.

The URNs are content-oriented, but ISSN is media-oriented:  A unique URN for serials simplifies the search, recovery and delivery of data for various services including, in particular, search systems and knowledge databases. ISSN-L (see Linking ISSN above) was created to fill this gap.

Media category labels.

The two standard categories of media in which serials are most available are "print" and "electronic". In metadata contexts (e.g., JATS), these may have standard labels.

Print ISSN.

"p-ISSN" is a standard label for "Print ISSN", the ISSN for the print media (paper) version of a serial. Usually it is the "default media" and so the "default ISSN".

Electronic ISSN.

"e-ISSN" (or "eISSN") is a standard label for "Electronic ISSN", the ISSN for the electronic media (online) version of a serial.

Statistics.

In March 2020, 0.93% of all references on the English Wikipedia had an ISSN.

An International Standard Serial Number (ISSN) is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is especially helpful in distinguishing between serials with the same title. ISSNs are used in ordering, cataloging, interlibrary loans, and other practices in connection with serial literature.