History.

On 4 February 1899, FV Werder Bremen was founded by a group of 16-year-old students who had won a football, after they were victorious in a tug of war tournament. The students took the name "Werder" from the German word for "river peninsula", which described the riverside field on which they played their first football games. The club's first match was played on 10 September 1899 against ASC 1898 Bremen, winning 1–0. In 1900, the team was represented at the founding of the German Football Association (DFB) at Leipzig. They then enjoyed some early success, winning a number of local championships. In 1903, all three Werder teams won their local league competitions. In these years, FV participated in qualification rounds for the national championships held by the Norddeutscher Fussball Verband (NFV), one of the seven major regional leagues after the turn of the century, but were unable to advance. Due to the club's early popularity, Werder became the first club in Bremen to charge spectators a fee to attend their games and to fence in their playing field.  Steady growth after the First World War led the club to adopt other sports (athletics, baseball, chess, cricket, and tennis). On 19 January 1920, the team adopted their current name; Sportverein Werder Bremen. Football remained the club's main sport, and in 1922, they became the first club in Bremen to hire a professional coach; Ferenc Kónya. The team made regular appearances in year-end NFV play-offs through the 1920s and on into the early 1930s, but did not enjoy any success. In the mid-1930s, striker Matthias Heidemann became the club's first international.  In 1933, German football was re-organized by the Nazi's into 16 first tier divisions known as Gauligen, as Werder became part of Gauliga Niedersachsen. The team scored their first real successes, capturing division titles in 1934, 1936, and 1937, and participated for the first time in the national play-offs. The shape of the Gauligen changed through the course of the Second World War, and in 1939, the Gauliga Niedersachsen was split into two divisions. SV played in the Gauliga Niedersachsen/Nord where they captured a fourth title in 1942. In 1944–45, German football was suspended after only two matches. Like other organizations throughout Germany, the club was disbanded on the order of the occupying Allied authorities after the war. They re-constituted themselves on 10 November 1945 as Turn- und Sportverein Werder 1945 Bremen, which was changed to Sport-Club Grün-Weiß 99 Bremen on 4 February 1946. The team played in the Stadtliga Bremen, and after winning the competition, participated in the northern German championship, advancing to the quarter-finals. They were able to reclaim the name SV Werder on 25 March 1946 before taking part in the play-offs.  In these years, professionals were not permitted to play in Germany, so it was normal for football players to take on other jobs, often with the club's local patron. In the case of Werder, a number of the players worked at the nearby Brinkmann tobacco factory, and so the side took on the nickname "Texas 11" after one of the company's popular cigarette brands.  Between the end of the Second World War and the formation of the Bundesliga in 1963, the club continued to perform, being recognized as one of the top two teams in northern Germany, along with Hamburger SV. In 1960–61, Werder managed to win their first DFB-Pokal, defeating 1. FC Kaiserslautern. The team consisted of future international Sepp Piontek, former international Willi Schröder, and Arnold Schütz, among others. A second place in the 1962–63 Oberliga Nord, behind Hamburger SV, was enough to qualify as a founder member for the 1963–64 Bundesliga. The first goal of the newly created Bundesliga was scored by Borussia Dortmund's Friedhelm Konietzka against Werder. In the league's second season, Werder won their first national championship, finishing three points clear of 1. FC Köln. One of the team's stars was German international Horst-Dieter Höttges. Werder finished runners-up in 1967–68, but then languished in the bottom half of the table for a dozen years.  In April 1971, in an away match at Borussia Mönchengladbach, Bundesliga history was created. In the 88th minute, Gladbach striker Herbert Laumen fell in Werder's goal, after a collision with Bremen goalkeeper Günter Bernard. The right goalpost subsequently broke, bringing the whole goal down, and could not be repared nor replaced. The referee stopped the game at the score of 1–1, and the DFB later awarded the match to Werder with a score of 2–0. As a consequence, the wooden goals were replaced by aluminium ones. An attempt to improve by signing high-priced players earned the team the derisive nickname of "Millionenelf" (English: "Million squad") and turned out to be an expensive failure. In 1979–80, the club was relegated from the Bundesliga for the first time, after a 17th-place finish.  The team won the 1980–81 2. Bundesliga Nord title and were promoted back to the Bundesliga. Manager Otto Rehhagel was appointed in April 1981, and under his guidance, Werder recovered themselves, as Rehhagel subsequently led the side to a string of successes. Bremen were Bundesliga runners-up in 1982–83, 1984–85 and 1985–86. In 1983 and 1986, the team lost the title both times on goal difference. In 1986, Werder hosted Bayern Munich in the penultimate match of the season; Bremen needed a win to secure their second Bundesliga title. In the 88th minute, with the score of 0–0, they were awarded a penalty kick, which Michael Kutzop took. He missed, as he hit the right goalpost; the game ended 0–0. Bayern won their last match, but Werder lost 1–2 to VfB Stuttgart, and Bayern took the title. Werder won their second league title two years later, in 1987–88, only conceding a then-record 22 goals. They also reached the semi-final of the 1987–88 UEFA Cup, in which they were eliminated by Bayer Leverkusen. In the third round of the 1989–90 UEFA Cup, Bremen defeated defending champions Napoli and their star player Diego Maradona 8–3 on aggregate, after winning 5–1 at home.  Werder reached the DFB-Pokal final in 1989 and 1990, and were victorious in 1991. This was followed by winning the European Cup Winners' Cup in 1991–92, beating AS Monaco 2–0 in the final. In 1992–93, the team won their third Bundesliga title and won their third DFB-Pokal the following year. Werder became the first German club to reach the group stage in the newly re-branded UEFA Champions League in 1993–94. That season saw a memorable comeback against Belgian club Anderlecht, later hailed as one of the examples of the "Wunder von der Weser" (English: "Wonder of the Weser"). Werder were trailing 3–0 after 66 minutes, as they managed to turn the game around and win 5–3. In this period, Werder had numerous internationals, including Mario Basler, Marco Bode, Andreas Herzog, Karl-Heinz Riedle, Wynton Rufer, and Rudi Völler among others.  Bremen finished runners-up in the 1994–95 Bundesliga. At the end of the season, Rehhagel left the club for Bayern Munich, after a then-national record 14-year stint at the club. As Werder's most successful manager, Rehhagel employed a "controlled offensive" style of play on a tight budget during his reign. Rehhagel's successors (Aad de Mos, Dixie Dörner, Wolfgang Sidka, and Felix Magath) could not bring silverware to the club. In May 1999, former Werder defender and youth coach Thomas Schaaf took over. He kept the team in the Bundesliga, and won the DFB-Pokal only weeks later, defeating Bayern on penalties. Werder's league performance stabilized in the following seasons, as they regularly finished in the upper half of the table. In 2003–04, they won the double for the first time, winning both the Bundesliga and the DFB-Pokal, as Bremen became the third club in Bundesliga history to achieve this feat. The team would also regularly qualify for the Champions League during the 2000s. In the last match of the 2005–06 Bundesliga season, Werder won 2–1 at arch-rivals Hamburger SV to qualify for the Champions League as runners-up, instead of Hamburg. Bremen reached the semi-finals of the 2006–07 UEFA Cup, in which they were eliminated by Spanish club RCD Espanyol. In 2008–09, Bremen struggled in their Bundesliga campaign, eventually finishing tenth, their worst league performance in more than a decade. Nevertheless, the club reached the UEFA Cup final, as well as the DFB-Pokal final. Werder lost the UEFA Cup final against Ukrainian team Shakhtar Donetsk; 1–2 after extra time. In the DFB-Pokal final, Bremen fared better, as they defeated Bayer Leverkusen by a scoreline of 1–0. In April and May 2009, Werder had played Hamburg four times in 19 days; once in the Bundesliga, in the semi-final of the DFB-Pokal, and twice in the semi-final of the UEFA Cup. Bremen defeated Hamburg 2–0 in the Bundesliga, and eliminated them from the DFB-Pokal and the UEFA Cup.  During the 2000s and early 2010s, Werder had numerous players who were sold for large transfer fees, including Diego, Torsten Frings, Miroslav Klose, Mesut Özil, and Claudio Pizarro among others. In October 2010, Bremen's Pizarro became the then-record holder of highest foreign goal-scorer in Bundesliga history. Uninspiring league finishes characterised the 2010s and in 2013, Schaaf left the club by mutual consent after a disappointing 14th place in the Bundesliga. The 2015–16 Bundesliga season saw Werder avoiding the Bundesliga promotion-relegation play-offs, beating direct rivals Eintracht Frankfurt by a scoreline of 1–0 in the last match of the season, after a goal in the 88th minute.

Players.

Retired numbers.

12 – Club Supporters (the 12th Man)

Managers.

Werder have had 24 different managers since the beginning of the Bundesliga era in 1963. Otto Rehhagel served the longest term, being in office for fourteen years. Hans Tilkowski, Willi Multhaup, Rudi Assauer, and Otto Rehhagel served two terms each, while Fritz Langner served three.

Crest.

Werder Bremen have used several different crests during their history. Their first crest was created in 1900; a monogram, which spelled "FVW", as the club was then known as "FV Werder Bremen". The logo was replaced in 1902 by a green-coloured crest, which spelled the founding year 1899 in the top left corner, "F.V.W." diagonally in the middle, and "Bremen" in the bottom right corner. It was modified in 1911, as the inscriptions were placed diagonally, and the badge's colours became black with a green stripe that crossed it, along with a change in the crest's outline. In 1924, a green-coloured (with a white outline), oval-shaped crest with a large white-coloured "W" was created. The oval shape was changed into a diamond shape in 1929, to create the club's current crest, save for a spell in the early 1970s when the coat of arms of Bremen was used. In addition, a star is displayed above the crest on the team's shirts to represent their four Bundesliga titles.

Stadium.

Werder have played their home games at the same location since 1909. That year saw the construction of a shared sports venue with a wooden grandstand, built by the Allgemeinen Bremer Turn- und Sportverein. In 1926, the stadium was renovated; a new grandstand with dressing rooms and a restaurant were constructed, costing 1,250,000 RM. At the time, the venue was known as the "ATSB-Kampfbahn", and was also used for political mass gatherings. In 1930, it was called the "Weserstadion" for the first time. Five years later, the stadium was known as the "Bremer Kampfbahn", and in the following years it was mostly used by the Nazi Party, as sporting activities were rarely practiced. In the first years after the Second World War, only American sports like baseball and American football were practiced at the venue (now known as the "IKE-Stadium"). In 1947, the stadium was reopened as a shared sports venue and took its former name "Weserstadion".  Following Werder's first Bundesliga title in 1965, the corner stands were expanded with a second tier, enlarging the capacity in the process. In 1992, Bremen became the first German club to install skyboxes in their stadium. Six years later, in 1998, under-soil heating was implemented. In 2002, the cinder track was removed, thereby expanding the capacity. From 2008 to 2011, the venue was completely rebuilt. The façade was coated with photovoltaic panels and a new roof was built on top of the old roof supporting structure (the old roof itself was torn down). Both ends (east and west) were torn down and rebuilt parallel to the endline of the pitch, removing what was left of the old athletics track. The current capacity is 42,100.

Supporters and rivals.

Werder Bremen have a long-standing rivalry with fellow northern German club Hamburger SV, known as the Nordderby (English: North derby). It goes beyond football, as there is also a historic rivalry between the cities of Hamburg and Bremen, dating back to the middle ages. The cities are only separated by a hundred kilometers and they are also the two biggest metropolises in northern Germany. Bayern Munich are another rival, dating back to the 1980s, when both clubs were competing for domestic honours. Bremen have developed a recent dislike of Schalke 04, after they have poached some of Werder's top players over the years (including Aílton, Fabian Ernst, Mladen Krstajić, Oliver Reck, Frank Rost, and Franco Di Santo).  Werder have seven ultra groups: "Wanderers-Bremen", "The Infamous Youth", "Caillera", "L'Intesa Verde", "HB Crew", "Ultra Boys", and "UltrA-Team Bremen". Werder fans maintain friendly relationships with Rot-Weiss Essen, Austrian club SK Sturm Graz, and Israeli club Hapoel Katamon Jerusalem.  The official anthem of Werder Bremen is "Lebenslang Grün-Weiß" by Bremen-based band Original Deutschmacher, which is also sung before every home game. After each Bremen goal, the song I'm Gonna Be (500 Miles) by The Proclaimers is played, preceded by the sound of a ship's horn.

Honours.

Werder's honours include the following:

Domestic.

Bundesliga  2. Bundesliga Nord  DFB-Pokal  DFL-Ligapokal  DFL-Supercup  DFB-Hallenpokal

Regional.

Gauliga Niedersachsen

International.

UEFA Cup Winners' Cup  UEFA Europa League  UEFA Super Cup  UEFA Intertoto Cup  Kirin Cup

Youth.

German amateur football championship  Under 19 Bundesliga  Under 19 Bundesliga North/Northeast

Regional.

Bremen Cu

Sportverein Werder Bremen von 1899 e. V. (), commonly known as Werder Bremen or simply Werder, is a German professional sports club based in Bremen, Free Hanseatic City of Bremen. Founded on 4 February 1899, they are best known for their professional football team, who are competing in the Bundesliga, the top tier of the German football league system. Werder hold the record for most seasons played in the Bundesliga and are second in the all-time Bundesliga table, behind Bayern Munich.

SV Werder Bremen (celým názvem: Sport-Verein Werder Bremen) je německý sportovní klub, který sídlí ve městě Brémy. Založen byl 4. února 1899 pod názvem Fußballverein Werder von 1899. Svůj současný název nese od roku 1946. Od sezóny 1981/82 působí v Bundeslize, německé nejvyšší fotbalové soutěži. Své domácí zápasy odehrává na stadionu Weserstadion s kapacitou 42 500 diváků. Klub měl v roce 2020 přes 40 000 členů. Úhlavním rivalem Werderu je Hamburger SV.


History.

Demographic thoughts traced back to antiquity, and were present in many civilisations and cultures, like Ancient Greece, Ancient Rome, China and India. Demography is made up of two word Demos and Graphy. The term Demography refers to the overall study of population.  In ancient Greece, this can be found in the writings of Herodotus, Thucidides, Hippocrates, Epicurus, Protagoras, Polus, Plato and Aristotle. In Rome, writers and philosophers like Cicero, Seneca, Pliny the elder, Marcus Aurelius, Epictetus, Cato, and Columella also expressed important ideas on this ground.  In the Middle ages, Christian thinkers devoted much time in refuting the Classical ideas on demography. Important contributors to the field were William of Conches, Bartholomew of Lucca, William of Auvergne, William of Pagula, and Muslim sociologists like Ibn Khaldun.  One of the earliest demographic studies in the modern period was "Natural and Political Observations Made upon the Bills of Mortality" (1662) by John Graunt, which contains a primitive form of life table. Among the study's findings were that one third of the children in London died before their sixteenth birthday. Mathematicians, such as Edmond Halley, developed the life table as the basis for life insurance mathematics. Richard Price was credited with the first textbook on life contingencies published in 1771, followed later by Augustus de Morgan, ‘On the Application of Probabilities to Life Contingencies’ (1838).  In 1755, Benjamin Franklin published his essay "Observations Concerning the Increase of Mankind, Peopling of Countries, etc.", projecting exponential growth in British colonies. His work influenced Thomas Robert Malthus, who, writing at the end of the 18th century, feared that, if unchecked, population growth would tend to outstrip growth in food production, leading to ever-increasing famine and poverty (see Malthusian catastrophe). Malthus is seen as the intellectual father of ideas of overpopulation and the limits to growth. Later, more sophisticated and realistic models were presented by Benjamin Gompertz and Verhulst.  In 1855, a Belgian scholar Achille Guillard defined demography as the natural and social history of human species or the mathematical knowledge of populations, of their general changes, and of their physical, civil, intellectual and moral condition.  The period 1860-1910 can be characterised as a period of transition wherein demography emerged from statistics as a separate field of interest. This period included a panoply of international ‘great demographers’ like Adolphe Quételet (1796–1874), William Farr (1807–1883), Louis-Adolphe Bertillon (1821–1883) and his son Jacques (1851–1922), Joseph Körösi (1844–1906), Anders Nicolas Kaier (1838–1919), Richard Böckh (1824–1907), Émile Durkheim (1858-1917), Wilhelm Lexis (1837–1914), and Luigi Bodio (1840–1920) contributed to the development of demography and to the toolkit of methods and techniques of demographic analysis.

Methods.

There are two types of data collection—direct and indirect—with several different methods of each type.

Direct methods.

Direct data comes from vital statistics registries that track all births and deaths as well as certain changes in legal status such as marriage, divorce, and migration (registration of place of residence). In developed countries with good registration systems (such as the United States and much of Europe), registry statistics are the best method for estimating the number of births and deaths.  A census is the other common direct method of collecting demographic data. A census is usually conducted by a national government and attempts to enumerate every person in a country. In contrast to vital statistics data, which are typically collected continuously and summarized on an annual basis, censuses typically occur only every 10 years or so, and thus are not usually the best source of data on births and deaths. Analyses are conducted after a census to estimate how much over or undercounting took place. These compare the sex ratios from the census data to those estimated from natural values and mortality data.  Censuses do more than just count people. They typically collect information about families or households in addition to individual characteristics such as age, sex, marital status, literacy/education, employment status, and occupation, and geographical location. They may also collect data on migration (or place of birth or of previous residence), language, religion, nationality (or ethnicity or race), and citizenship. In countries in which the vital registration system may be incomplete, the censuses are also used as a direct source of information about fertility and mortality; for example the censuses of the People's Republic of China gather information on births and deaths that occurred in the 18 months immediately preceding the census.

Indirect methods.

Indirect methods of collecting data are required in countries and periods where full data are not available, such as is the case in much of the developing world, and most of historical demography. One of these techniques in contemporary demography is the sister method, where survey researchers ask women how many of their sisters have died or had children and at what age. With these surveys, researchers can then indirectly estimate birth or death rates for the entire population. Other indirect methods in contemporary demography include asking people about siblings, parents, and children. Other indirect methods are necessary in historical demography.  There are a variety of demographic methods for modelling population processes. They include models of mortality (including the life table, Gompertz models, hazards models, Cox proportional hazards models, multiple decrement life tables, Brass relational logits), fertility (Hernes model, Coale-Trussell models, parity progression ratios), marriage (Singulate Mean at Marriage, Page model), disability (Sullivan's method, multistate life tables), population projections (Lee-Carter model, the Leslie Matrix), and population momentum (Keyfitz).  The United Kingdom has a series of four national birth cohort studies, the first three spaced apart by 12 years: the 1946 National Survey of Health and Development, the 1958 National Child Development Study, the 1970 British Cohort Study, and the Millennium Cohort Study, begun much more recently in 2000. These have followed the lives of samples of people (typically beginning with around 17,000 in each study) for many years, and are still continuing. As the samples have been drawn in a nationally representative way, inferences can be drawn from these studies about the differences between four distinct generations of British people in terms of their health, education, attitudes, childbearing and employment patterns.

Common rates and ratios.

A stable population does not necessarily remain fixed in size. It can be expanding or shrinking.  Note that the crude death rate as defined above and applied to a whole population can give a misleading impression. For example, the number of deaths per 1,000 people can be higher for developed nations than in less-developed countries, despite standards of health being better in developed countries. This is because developed countries have proportionally more older people, who are more likely to die in a given year, so that the overall mortality rate can be higher even if the mortality rate at any given age is lower. A more complete picture of mortality is given by a life table, which summarizes mortality separately at each age. A life table is necessary to give a good estimate of life expectancy.

Basic equation.

Suppose that a country (or other entity) contains "Population" persons at time "t". What is the size of the population at time "t" + 1?  Natural increase from time "t" to "t" + 1:  Net migration from time "t" to "t" + 1:  This basic equation can also be applied to subpopulations. For example, the population size of ethnic groups or nationalities within a given society or country is subject to the same sources of change. When dealing with ethnic groups, however, "net migration" might have to be subdivided into physical migration and ethnic reidentification (assimilation). Individuals who change their ethnic self-labels or whose ethnic classification in government statistics changes over time may be thought of as migrating or moving from one population subcategory to another.  More generally, while the basic demographic equation holds true by definition, in practice the recording and counting of events (births, deaths, immigration, emigration) and the enumeration of the total population size are subject to error. So allowance needs to be made for error in the underlying statistics when any accounting of population size or change is made.  The figure in this section shows the latest (2004) UN projections of world population out to the year 2150 (red = high, orange = medium, green = low). The UN "medium" projection shows world population reaching an approximate equilibrium at 9 billion by 2075. Working independently, demographers at the International Institute for Applied Systems Analysis in Austria expect world population to peak at 9 billion by 2070. Throughout the 21st century, the average age of the population is likely to continue to rise.

Science of population.

Populations can change through three processes: fertility, mortality, and migration. Fertility involves the number of children that women have and is to be contrasted with fecundity (a woman's childbearing potential). Mortality is the study of the causes, consequences, and measurement of processes affecting death to members of the population. Demographers most commonly study mortality using the Life Table, a statistical device that provides information about the mortality conditions (most notably the life expectancy) in the population.  Migration refers to the movement of persons from a locality of origin to a destination place across some predefined, political boundary. Migration researchers do not designate movements'migrations' unless they are somewhat permanent. Thus demographers do not consider tourists and travellers to be migrating. While demographers who study migration typically do so through census data on place of residence, indirect sources of data including tax forms and labour force surveys are also important.  Demography is today w Great Depressionn many universities across the world, attracting students with initial training in social sciences, statistics or health studies. Being at the crossroads of several disciplines such as sociology, economics, epidemiology, geography, anthropology and history, demography offers tools to approach a large range of population issues by combining a more technical quantitative approach that represents the core of the discipline with many other methods borrowed from social or other sciences. Demographic research is conducted in universities, in research institutes as well as in statistical departments and in several international agencies. Population institutions are part of the Cicred (International Committee for Coordination of Demographic Research) network while most individual scientists engaged in demographic research are members of the International Union for the Scientific Study of Population, or a national association such as the Population Association of America in the United States, or affiliates of the Federation of Canadian Demographers in Canada.  Social surveys:

See also.

Organizations:  Scientific journals:

Demography (from prefix "demo-" from Ancient Greek δῆμος "dēmos" meaning "the people", and "-graphy" from γράφω "graphō", ies "writing, description or measurement") is the statistical study of populations, especially human beings.

Demografie ("démos" - lid "graféin" - psát, popisovat) je věda, která studuje proces reprodukce lidských populací. Objektem studia demografie tedy jsou lidské populace, předmětem jejího studia je proces demografické reprodukce, tedy přirozený proces obnovy obyvatelstva důsledkem rození a vymírání. Procesy demografické reprodukce jsou úmrtnost (též mortalita), nemocnost, porodnost (též natalita), potratovost, sňatečnost a rozvodovost. Tyto procesy jsou také v centru demografického zájmu.


History.

Pentaerythritol tetranitrate was first prepared and patented in 1894 by the explosives manufacturer Rheinisch-Westfälische Sprengstoff A.G. of Cologne, Germany. The production of PETN started in 1912, when the improved method of production was patented by the German government. PETN was used by the German Military in. It was also used in the MG FF/M autocannons and many other weapon systems of the Luftwaffe in World War II, specifically in the high explosive Mine shell.

Properties.

PETN is practically insoluble in water (0.01 g/100 ml at 50 °C), weakly soluble in common nonpolar solvents such as aliphatic hydrocarbons (like gasoline) or tetrachloromethane, but soluble in some other organic solvents, particularly in acetone (about 15 g/100 g of the solution at 20 °C, 55 g/100 g at 60 °C) and dimethylformamide (40 g/100 g of the solution at 40 °C, 70 g/100 g at 70 °C). PETN forms eutectic mixtures with some liquid or molten aromatic nitro compounds, "e.g." trinitrotoluene (TNT) or tetryl. Due to steric hindrance of the adjacent neopentyl-like moiety, PETN is resistant to attack by many chemical reagents; it does not hydrolyze in water at room temperature or in weaker alkaline aqueous solutions. Water at 100 °C or above causes hydrolysis to dinitrate; presence of 0.1% nitric acid accelerates the reaction.  The chemical stability of PETN is of interest, because of the presence of PETN in aging weapons. A review has been published. Neutron radiation degrades PETN, producing carbon dioxide and some pentaerythritol dinitrate and trinitrate. Gamma radiation increases the thermal decomposition sensitivity of PETN, lowers melting point by few degrees Celsius, and causes swelling of the samples. Like other nitrate esters, the primary degradation mechanism is the loss of nitrogen dioxide; this reaction is autocatalytic. Studies were performed on thermal decomposition of PETN.  In the environment, PETN undergoes biodegradation. Some bacteria denitrate PETN to trinitrate and then dinitrate, which is then further degraded. PETN has low volatility and low solubility in water, and therefore has low bioavailability for most organisms. Its toxicity is relatively low, and its transdermal absorption also seems to be low. It poses a threat for aquatic organisms. It can be degraded to pentaerythritol by iron.

Production.

Production is by the reaction of pentaerythritol with concentrated nitric acid to form a precipitate which can be recrystallized from acetone to give processable crystals.  Variations of a method first published in US Patent 2,370,437 by Acken and Vyverberg (1945 to Du Pont) form the basis of all current commercial production.  PETN is manufactured by numerous manufacturers as a powder, or together with nitrocellulose and plasticizer as thin plasticized sheets (e.g. Primasheet 1000 or Detasheet). PETN residues are easily detectable in hair of people handling it. The highest residue retention is on black hair; some residues remain even after washing.

Explosive use.

The most common use of PETN is as an explosive with high brisance. It is more difficult to detonate than primary explosives, so dropping or igniting it will typically not cause an explosion (at atmospheric pressure it is difficult to ignite and burns relatively slowly), but is more sensitive to shock and friction than other secondary explosives such as TNT or tetryl. Under certain conditions a deflagration to detonation transition can occur.  It is rarely used alone, but primarily used in booster and bursting charges of small caliber ammunition, in upper charges of detonators in some land mines and shells, and as the explosive core of detonation cord. PETN is the least stable of the common military explosives, but can be stored without significant deterioration for longer than nitroglycerin or nitrocellulose.  During World War II, PETN was most importantly used in exploding-bridgewire detonators for the atomic bombs. These exploding-bridgewire detonators gave more precise detonation, compared with primacord. PETN was used for these detonators because it was safer than primary explosives like lead azide: while it was sensitive, it would not detonate below a threshold amount of energy. Exploding bridgewires containing PETN remain used in current nuclear weapons. In spark detonators, PETN is used to avoid the need for primary explosives; the energy needed for a successful direct initiation of PETN by an electric spark ranges between 10–60 mJ.  Its basic explosion characteristics are:

In mixtures.

PETN is used in a number of compositions. It is a major ingredient of the Semtex plastic explosive. It is also used as a component of pentolite, a 50/50 blend with TNT. The XTX8003 extrudable explosive, used in the W68 and W76 nuclear warheads, is a mixture of 80% PETN and 20% of Sylgard 182, a silicone rubber. It is often phlegmatized by addition of 5–40% of wax, or by polymers (producing polymer-bonded explosives); in this form it is used in some cannon shells up to 30 mm caliber, though it is unsuitable for higher calibers. It is also used as a component of some gun propellants and solid rocket propellants. Nonphlegmatized PETN is stored and handled with approximately 10% water content. PETN alone cannot be cast as it explosively decomposes slightly above its melting point, but it can be mixed with other explosives to form castable mixtures.  PETN can be initiated by a laser. A pulse with duration of 25 nanoseconds and 0.5–4.2 joules of energy from a Q-switched ruby laser can initiate detonation of a PETN surface coated with a 100 nm thick aluminium layer in less than half of a microsecond.  PETN has been replaced in many applications by RDX, which is thermally more stable and has a longer shelf life. PETN can be used in some ram accelerator types. Replacement of the central carbon atom with silicon produces Si-PETN, which is extremely sensitive.

Terrorist use.

Ten kilograms of PETN was used in the 1980 Paris synagogue bombing.  In 1983, 307 people were killed after a truck bomb filled with PETN was detonated at the Beirut barracks.  In 1983, the "Maison de France" house in Berlin was brought to a near-total collapse by the detonation of of PETN by terrorist Johannes Weinrich.  In 1999, Alfred Heinz Reumayr used PETN as the main charge for his fourteen improvised explosive devices that he constructed in a thwarted attempt to damage the Trans-Alaska Pipeline System.  In 2001, al-Qaeda member Richard Reid, the "Shoe Bomber", used PETN in the sole of his shoe in his unsuccessful attempt to blow up American Airlines Flight 63 from Paris to Miami. He had intended to use the solid triacetone triperoxide (TATP) as a detonator.  In 2009, PETN was used in an attempt by al-Qaeda in the Arabian Peninsula to murder the Saudi Arabian Deputy Minister of Interior Prince Muhammad bin Nayef, by Saudi suicide bomber Abdullah Hassan al Asiri. The target survived and the bomber died in the blast. The PETN was hidden in the bomber's rectum, which security experts described as a novel technique.  On 25 December 2009, PETN was found in the underwear of Umar Farouk Abdulmutallab, the "Underwear bomber", a Nigerian with links to al-Qaeda in the Arabian Peninsula. According to US law enforcement officials, he had attempted to blow up Northwest Airlines Flight 253 while approaching Detroit from Amsterdam. Abdulmutallab had tried, unsuccessfully, to detonate approximately of PETN sewn into his underwear by adding liquid from a syringe; however, only a small fire resulted.  In the al-Qaeda in the Arabian Peninsula October 2010 cargo plane bomb plot, two PETN-filled printer cartridges were found at East Midlands Airport and in Dubai on flights bound for the US on an intelligence tip. Both packages contained sophisticated bombs concealed in computer printer cartridges filled with PETN. The bomb found in England contained of PETN, and the one found in Dubai contained of PETN. Hans Michels, professor of safety engineering at University College London, told a newspaper that of PETN—"around 50 times less than was used—would be enough to blast a hole in a metal plate twice the thickness of an aircraft's skin". In contrast, according to an experiment conducted by a BBC documentary team designed to simulate Abdulmutallab's Christmas Day bombing, using a Boeing 747 plane, even 80 grams of PETN was not sufficient to materially damage the fuselage.  On 12 July 2017, 150 grams of PETN was found in the Assembly of Uttar Pradesh, India's most populous state.

Detection.

In the wake of terrorist PETN bomb plots, an article in "Scientific American" noted PETN is difficult to detect because it does not readily vaporize into the surrounding air. The "Los Angeles Times" noted in November 2010 that PETN's low vapor pressure makes it difficult for bomb-sniffing dogs to detect.  Many technologies can be used to detect PETN, including chemical sensors, X-rays, infrared, microwaves and terahertz, some of which have been implemented in public screening applications, primarily for air travel. PETN is one of the explosive chemicals typically of interest in that area, and it belongs to a family of common nitrate-based explosive chemicals which can often be detected by the same tests.  One detection system in use at airports involves analysis of swab samples obtained from passengers and their baggage. Whole-body imaging scanners that use radio-frequency electromagnetic waves, low-intensity X-rays, or T-rays of terahertz frequency that can detect objects hidden under clothing are not widely used because of cost, concerns about the resulting traveler delays, and privacy concerns.  Both parcels in the 2010 cargo plane bomb plot were x-rayed without the bombs being spotted. Qatar Airways said the PETN bomb "could not be detected by x-ray screening or trained sniffer dogs". The Bundeskriminalamt received copies of the Dubai x-rays, and an investigator said German staff would not have identified the bomb either. New airport security procedures followed in the U.S., largely to protect against PETN.

Medical use.

Like nitroglycerin (glyceryl trinitrate) and other nitrates, PETN is also used medically as a vasodilator in the treatment of heart conditions. These drugs work by releasing the signaling gas nitric oxide in the body. The heart medicine "Lentonitrat" is nearly pure PETN.  Monitoring of oral usage of the drug by patients has been performed by determination of plasma levels of several of its hydrolysis products, pentaerythritol dinitrate, pentaerythritol mononitrate and pentaerythritol, in plasma using gas chromatography-mass spectrometry.

Pentaerythritol tetranitrate (PETN), also known as PENT, PENTA, TEN, corpent, or penthrite (or, rarely and primarily in German, as nitropenta), is an explosive material. It is the nitrate ester of pentaerythritol, and is structurally very similar to nitroglycerin. Penta refers to the five carbon atoms of the neopentane skeleton. PETN is a powerful explosive material with a relative effectiveness factor of 1.66. When mixed with a plasticizer, PETN forms a plastic explosive. Along with RDX it is the main ingredient of Semtex.

Pentrit (pentaerythritol tetranitrát) je silná výbušnina, běžně označovaná zkratkou PENT, PETN, PENTA nebo TEN. Využívá se také ve farmakologii jako vasodilatans.


Detention before charge or trial.

The pre-charge detention period is the period of time during which an individual can be held and questioned by police, prior to being charged with an offence. Not all countries have such a concept, and in those that do, the period for which a person may be detained without charge varies by jurisdiction.  The prohibition of prolonged detention without charge, "habeas corpus", was first introduced in England about a century after the 1215 Magna Carta; the use of "habeas corpus ad subjiciendum" in 1305 was cited by William Blackstone.

Czech Republic.

Under Article 8 of the Charter of Fundamental Rights and Basic Freedoms of the Czech Republic, which has the same legal standing as the Czech Constitution, a suspect must be immediately familiarized with the grounds of detention, must be interviewed and within 48 hours either released or charged and handed over to a court. The court then has a further 24 hours either to order a custody, or to release the person detained.  Detailed rules of detention are included in the Criminal Procedural Code. The police may arrest and detain a suspect after obtaining prosecutor's consent. In an urgent case the police may detain a suspect without the consent. In both cases, however, the police detention may take place only when grounds for pre-trial detention exist (see below). The statutory limits of 48 + 24 hours must be complied with and reaching the time limit should aways trigger immediate release, unless a court has ordered pre-trial custody.  Anybody may detain a person, who was caught while perpetrating a crime (not a misdemeanor) or immediately after it, when capturing of the perpetrator is necessary to either ascertain the perpetrator's identity or to prevent the perpetrator from escaping or to secure evidence. The perpetrator must immediately be handed over to the police, or when that is not possible, detention of the perpetrator must be immediately reported to the police.

United States.

In the United States, a person is protected by the federal Constitution from being held in prison unlawfully. The right to have one's detention reviewed by a judge is called "habeas corpus". The U.S. Constitution states that "The Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it". A declaration of a state of emergency can suspend the right to "habeas corpus".  The Sixth Amendment requires criminal defendants to be "informed of the nature and cause of the accusation". The U.S. Bill of Rights thus grants some protection against being held without criminal charge, subject to the courts' interpretation of what due process means. Federal authorities have also exercised the power to arrest people on the basis of being a material witness. Involuntary commitment of the mentally ill is another category of detention without criminal prosecution, but the right of "habeas corpus" still applies. The scope of such detentions is also limited by the Bill of Rights.  The executive's military powers have been used to justify holding enemy combatants as prisoners of war, unlawful combatants, and civilian internees; the latter two practices have been controversial, especially with regard to the indefinite detention implied by uncertainty as to when the "War on Terror" might be declared to have ended. Administrative detention, a term applied to many of these categories, is also used to imprison illegal immigrants.

Sweden.

In Swedish law, "Häktning" is a pre-trial supervision measure, where a suspect can be jailed for crimes that have a prison term of at least one year. There are two degrees of suspicion: reasonable suspicion is the lower level, and probable cause is the higher level.  Remanding occurs if the committed crime has a statutory minimum penalty of at least one year, and includes:  Alternatively, remanding occurs for probable cause suspicion (and lesser crimes) when:  A person may be held in custody normally for no more than 14 days (or seven days if the degree of suspicion is reasonable suspicion). Afterwards, a new remand hearing is normally held. For suspects under age 18, "serious reasons" for detention decisions are needed and should be notified to court.  When a person is facing less serious crimes, they are given a summary penalty order by prosecutors.  A person who was remanded but was not sentenced or freed after trial is entitled to financial compensation, which is determined by the Chancellor of Justice. The compensation can vary, but it is usually 30,000 SEK for the first month; 20,000 SEK for every subsequent month, up to and including the sixth month; and 15,000 SEK for every month after that. Any loss of income is also compensated. In 2007, 1200 people were compensated.  If a prisoner is sentenced, the remand time counts as part of the prison time, such that less time remains after the trial.  The Committee for the Prevention of Torture of the Council of Europe has repeatedly criticized pre-trial detention in Sweden for the high percentage of cases where restrictions on communication are applied. In Sweden, communication restrictions include no visits, no telephone calls, no newspapers, and no TV.

Detention during trial.

The term "remand" may be used to describe the process of keeping a person in detention rather than granting bail. A prisoner who is denied, refused or unable to meet the conditions of bail, or who is unable to post bail, may be held in a prison on remand. Although remanded prisoners are usually detained separately from sentenced prisoners, due to prison overcrowding they are sometimes held in a shared accommodation with sentenced prisoners. Reasons for being held in custody on remand vary depending on the local legal system, but may include:  In most countries, remand prisoners are considered innocent until proven guilty by a court and may be granted greater privileges than sentenced prisoners. For example, most jurisdictions that prohibit convicted criminals from voting in elections will still allow remand prisoners to vote, unless they have been disqualified from voting for some other reason. Other privileges commonly granted include:  Not all remand prisons grant these privileges, in particular, remand prisoners are often forced to wear prison uniforms and denied additional visitation rights, supposedly for safety reasons, although some facilities allow remand prisoners to wear a uniform that is a different color or otherwise clearly distinguishable from the uniforms of convicted criminals. Often they are denied all visits and all newspaper and media access, for risk of interfering with the investigation, such as communicating a story with fellow remand prisoners.

Czech Republic.

Under Article 8 (5) of the Charter of Fundamental Rights and Basic Freedoms, which has the same legal standing as the Constitution, nobody shall be taken into custody except on the basis of a court decision, and for reasons and a detention period stipulated by the law.  Detailed rules of remand custody are contained in the Criminal Procedural Code. A person may be remanded in custody by the decision of a court only when a number of preconditions is met cumulatively:  At the same time, there must be reasonable concern, that the charged person may either  The charged person may be remanded in custody subject to maximum terms as follows: one third of the maximum detention periods time may be exhausted in pre-trial proceedings and two thirds may be exhausted during the trial. Reaching the maximum time is always reason for immediate release.  An exception to the time limits above arises in cases of remand due to concern of "(b)" interfering with witnesses or similar frustration of proceedings, in which case the maximum pre-trial detention period may be only three months, except where the charged person has already been influencing witnesses or otherwise frustrating the proceedings.  The court must review the reasons for the pre-trial custody every three months and decide either to continue it, or to release the charged person. Both the prosecutor and the person in custody may file a complaint against any decision on custody, which leads to review by an appellate court.  Special rules of remand pertain to persons who are processed for extradition, e.g. illegal foreigners, those detained due to international (foreign) warrant or the European Arrest Warrant.

Conditions in Czech remand prisons.

In the Czech Republic, remand takes place in remand prisons or in separated sections of standard prisons. Remand prisons are often in city centres and appertain to court houses. Most remand prisons are over 80 years old, with some, like Pankrác Prison, being more than 125 years old. Men, women and juveniles are held separately. Also persons charged with committing different types of crimes (e.g. unintentional, intentional, violent, etc.) are held separately.  Cells have capacity varying between 1—8 beds, with most having between 2—4 beds. Some remand prisons have rooms intended for watching TV, gyms or chapels, but these are exceptional mainly due to overcrowding and lack of space. All have special areas for interviews between the inmates and their attorneys, visiting rooms and courtyards for out-walks.  Each cell has a WC divided from the rest of the cell-space and running cold water. Each cell-mate has own bed, storage locker and chair.  Inmates which are held due to concern of influencing witnesses are held in isolation with very limited possibility of contact with other inmates as well as the outer world (apart from interviews with own attorneys).  At any given time in 2011, there were around 2.500 inmates in the Czech remand prisons (including ~170 women and ~45 juveniles), compared to some 20.500 convicted inmates (for 10,6 million population). The average length of remand custody is around 100 days, with few inmates spending in remand more than 2 years.  More than half of foreign inmates of the Czech remand prisons are from Slovakia, Ukraine and Vietnam. Other numerous foreigners are from Bulgaria, Moldova, North Macedonia, Poland, Romania, Russia and Serbia. When it comes to non-European states, there are numerous detainees from Nigeria, Algeria, Morocco, Uzbekistan, Kazakhstan and Mongolia. There are mostly only few individuals of other nationalities.

United Kingdom.

In England and Wales, a suspect may be remanded after charge if: Remanding a suspect following arrest and until their first hearing at a magistrates' court is a decision made by the police using the criteria set above. Any such person ‘remanded in police custody’ will be transported from the police cells to the next available sitting magistrate's court. This may be the same day, or may require the remanded individual to stay in police custody overnight or over the weekend. At the first hearing, the court will decide whether it necessary to remand the suspect until the end of the trial. If the suspect is not remanded the court may issue bail conditions for suspect to abide to until the trial. Adults will be held on court remand at a regular prison, while those below the age of 18 will be held at a secure centre for young people. If a remanded suspect is convicted and given a prison sentence, the time they spent on remand is deducted from the length of the sentence. In some cases, a convicted suspect has been released immediately after being sentenced, if the time they spent on remand was longer than or equal to the sentence they received.

United States.

The Eighth Amendment to the United States Constitution prohibits excessive bail. Under the US Code, pretrial detention of federal suspects is allowed only under certain circumstances, such as when the defendant is a danger to witnesses or jurors.

Impact.

Two 2018 studies in the "American Economic Review" and "the Journal of Law, Economics, and Organization" found that pretrial detention significantly increases the probability of conviction, largely because individuals who would otherwise be acquitted in trial enter guilty pleas. The AER study found that pretrial detention also lowers the defendants' prospects in the labor market. The JLEO study found that pretrial detention caused 42% longer incarceration sentence and 41% higher nonbail court fees owed. The JLEO study notes that "the use of money bail contributes to a “poverty-trap”: those who are unable to pay bail wind up accruing more court debt."

Criticisms.

Pre-trial detention has been described as a "necessary evil". A 2013 report by the Centre for Crime and Justice Studies concluded that pre-trial detention was being overused worldwide, and that most were being held for minor crimes. A 2014 report by the Open Society Foundations called it a "massive and widely ignored pattern of human rights abuse". A person must be found guilty "beyond reasonable doubt" in order to be convicted at a trial. However, pre-trial detention requires a lower threshold such as "reasonable suspicion". In most countries, the prosecution only need to prove that the charges are well-founded and that there is a sufficient threat that the defendant will commit another crime or undermine the judicial process. In the United States, the system of money bail means that a defendant can be detained even if neither of these threats can be identified, solely because nobody was willing or able to deposit the bail money for them.  In the "Harvard Law Review", Stephanie Bibas also noted its impact on plea bargaining. Pretrial detention alters a defendant's incentives by making his or her best-case scenario not zero days in jail, but the length of time served pretrial. Therefore, a defendant may be more likely to plead guilty if the chance of acquittal is low, or if the expected sentence on a guilty plea is less than the amount of jail time that would be served pretrial. Pretrial detainees may also find it harder to mount an effective defense.  The Open Society Foundation report also concluded that some detainees face worse conditions than convicted prisoners; for example the suicide rate is three times higher worldwide.

Remand (also known as pre-trial detention or provisional detention) is the process of detaining a person who has been arrested and charged with an offense until their trial. A person who is on remand is held in a prison or detention center, or held under house arrest. Varying terminology is used, but "remand" is generally used in common law jurisdictions and in Europe "preventive detention". Detention before charge is referred to as custody and continued detention after conviction is referred to as imprisonment.

Vazba je mimořádné opatření na základě důkazů v trestním řízení, které slouží k zajištění obviněné osoby po dobu nezbytně nutnou pro účely týkající se trestního řízení a následného výkonu trestu. Účelem vazby je zabránit obviněnému, aby se vyhýbal trestnímu řízení nebo trestu, aby mařil či ztěžoval provádění důkazů, aby dokonal trestný čin či páchal další trestnou činnost. Podstatou vazby je dočasné (nicméně zpravidla delší, řádově trvající týdny, měsíce, výjimečně i roky) omezení osobní svobody obviněného rozhodnutím soudu ve specializované vazební věznici či ve vazebním oddělení věznice běžné. Vazba má pouze zajišťovací funkci, nelze ji pokládat za trestní sankci či prostředek nápravy, zároveň také nijak dopředu neurčuje výsledek trestního stíhání (budoucí odsouzení obviněného). Vazbu je třeba odlišovat od zadržení, které je jiným trestněprocesním institutem k zajištění osob a od zajištění, které je upraveno zákonem o Policii České republiky.


Biography.

Wirth was born in Winterthur, Switzerland, in 1934. In 1959, he earned a Bachelor of Science (B.S.) degree in electronic engineering from the Swiss Federal Institute of Technology Zürich (ETH Zürich). In 1960, he earned a Master of Science (MSc) from Université Laval, Canada. Then in 1963, he was awarded a PhD in Electrical Engineering and Computer Science (EECS) from the University of California, Berkeley, supervised by the computer design pioneer Harry Huskey.  From 1963 to 1967, he served as assistant professor of computer science at Stanford University and again at the University of Zurich. Then in 1968, he became Professor of Informatics at ETH Zürich, taking two one-year sabbaticals at Xerox PARC in California (1976–1977 and 1984–1985). He retired in 1999.  In 2004, he was made a Fellow of the Computer History Museum "for seminal work in programming languages and algorithms, including Euler, Algol-W, Pascal, Modula, and Oberon."

Programming languages.

Wirth was the chief designer of the programming languages Euler, Algol W, Pascal, Modula, Modula-2, Oberon, Oberon-2, and Oberon-07. He was also a major part of the design and implementation team for the Lilith and Oberon operating systems, and for the Lola digital hardware design and simulation system. He received the Association for Computing Machinery (ACM) Turing Award for the development of these languages in 1984, and in 1994 he was inducted as a Fellow of the ACM.

Publications.

His book, written jointly with Kathleen Jensen, "The Pascal User Manual and Report", served as the basis of many language implementation efforts in the 1970s and 1980s in the United States and across Europe.  His article "Program Development by Stepwise Refinement", about the teaching of programming, is considered to be a classic text in software engineering. In 1975 he wrote the book "Algorithms + Data Structures = Programs", which gained wide recognition. Major revisions of this book with the new title "Algorithms + Data Structures" were published in 1985 and 2004. The examples in the first edition were written in Pascal. These were replaced in the later editions with examples written in Modula-2 and Oberon respectively.  His textbook, "Systematic Programming: An Introduction", was considered a good source for students who wanted to do more than just coding. Regarded as a challenging text to work through, it was sought as imperative reading for those interested in numerical mathematics.  In 1992, he published (with Jürg Gutknecht) the full documentation of the Oberon OS. A second book (with Martin Reiser) was intended as a programmer's guide.

Wirth's law.

In 1995, he popularized the adage now named Wirth's law, which states that software is getting slower more rapidly than hardware becomes faster. In his 1995 paper "A Plea for Lean Software" he attributes it to Martin Reiser.

Niklaus Emil Wirth (born 15 February 1934) is a Swiss computer scientist. He has designed several programming languages, including Pascal, and pioneered several classic topics in software engineering. In 1984 he won the Turing Award, generally recognized as the highest distinction in computer science, for developing a sequence of innovative computer languages.

Niklaus E. Wirth (* 15. února 1934 Winterthur, Švýcarsko) je švýcarský informatik. V roce 1959 vystudoval elektrotechniku na Eidgenössische Technische Hochschule (ETH) v Curychu, v roce 1960 obdržel magisterský titul na Lavalské univerzitě v Kanadě, v roce 1963 pak získal titul Ph.D. na kalifornské univerzitě v Berkeley.


History.

Following the Hungarian conquest of the Carpathian Basin at the turn of the 9th and 10th centuries, Prince Árpád gave Komárom and the Komárom county vicinity to tribal chieftain Ketel. Ketel was the first known ancestor of the famous Koppán (genus) clan. At the beginning of the 12th century, this tribe founded the town's Benedictine Monastery in honor of the Blessed Virgin, mentioned in 1222 by the name of Monostorium de Koppán. The Turks destroyed much of the monastery and its surroundings in 1529, and the area was thus depopulated. Later references refer to it as the Pioneer Monastery (Pusztamonostor). Presently, it is called Koppánymonostor (Koppán's Monastery) in honor of its founding family. Roman ruins (including a stone mile marker and watchtowers) still stand today.  The town was heavily damaged in the 1763 Komárom earthquake.  Between 1850 and 1871 the Fort Monostor (Monostori Erőd) was built nearby.  In 1920 Komárom was split by the newly created border of Czechoslovakia. In 1920 Hungary was forced to sign the Treaty of Trianon recognizing the new imposed borders including the border with Czechoslovakia. The loss of its territory created a sizable Hungarian minority in Slovakia. The Slovak part is today Komárno, Slovakia. In 1938 the entire city was returned to Hungary, its Regent, Admiral Horthy receiving a tumultuous welcome from the citizens as he crossed the old bridge and entered the formerly dismembered part. At the end of World War II the city was again divided between Hungary and Czechoslovakia.  After World War II the occupying Soviets built the country's biggest ammunition storage in the Fortress of Monostor. Thousands of wagons of ammunition were forwarded from this strictly guarded area. One of a series of forts, the Monostor is today open to the public as a museum.  Komárom and Komárno are connected by two bridges: The older iron bridge, and a newer lifting bridge. Currently a third bridge is under construction with estimated completion by late 2019. The vast majority of its funding coming from the European Union's Connecting Europe Facility.  The two towns used to be a border crossing between Czechoslovakia (today Slovakia) and Hungary, until both countries became part of the Schengen Area, resulting in all immigration and customs checks being lifted on December 12, 2007.

Twin towns — sister cities.

Komárom is twinned with:

Komárom (, German: "Komorn") is a city in Hungary on the south bank of the Danube in Komárom-Esztergom county. Komárno, Slovakia, is on the northern bank. Komárom was formerly a separate village called. In 1892 Komárom and Újszőny were connected with an iron bridge and in 1896 the two towns were united under the name city of Komárom. The fortress played an important role in the Hungarian Revolution of 1848 and many contemporary English sources refer to it as the Fortress of Comorn.

Komárom (, ) je město v okrese Komárom v župě Komárom-Esztergom v severozápadním Maďarsku, u hranic se Slovenskem na pravém břehu Dunaje, který je odděluje od slovenského Komárna. V Komáromu žije 19 577 obyvatel (2008), je zde významný říční přístav. Se svým slovenským jmenovcem je město spojeno železničním a silničním mostem.


History.

Lynx was a product of the Distributed Computing Group within Academic Computing Services of the University of Kansas, and was initially developed in 1992 by a team of students and staff at the university (Lou Montulli, Michael Grobe and Charles Rezac) as a hypertext browser used solely to distribute campus information as part of a "Campus-Wide Information Server" and for browsing the Gopher space. Beta availability was announced to Usenet on 22 July 1992. In 1993, Montulli added an Internet interface and released a new version (2.0) of the browser.  Garrett Blythe created DosLynx in April 1994 and later joined the Lynx effort as well. Foteos Macrides ported much of Lynx to VMS and maintained it for a time. In 1995, Lynx was released under the GNU General Public License, and is now maintained by a group of volunteers led by.

Features.

Browsing in Lynx consists of highlighting the chosen link using cursor keys, or having all links on a page numbered and entering the chosen link's number. Current versions support SSL and many HTML features. Tables are formatted using spaces, while frames are identified by name and can be explored as if they were separate pages. Lynx cannot inherently display various types of non-text content on the web, such as images and video, but it can launch external programs to handle it, such as an image viewer or a video player.  Unlike most web browsers, Lynx does not support JavaScript or Adobe Flash, which some websites require to work correctly.  The speed benefits of text-only browsing are most apparent when using low bandwidth internet connections, or older computer hardware that may be slow to render image-heavy content.

Privacy.

Because Lynx does not support graphics, web bugs that track user information are not fetched; therefore, web pages can be read without the privacy concerns of graphic web browsers. However, Lynx does support HTTP cookies, which can also be used to track user information. Lynx therefore supports cookie whitelisting and blacklisting, or alternatively cookie support can be disabled permanently.  As with conventional browsers, Lynx also supports browsing histories and page caching, both of which can raise privacy concerns.

Configurability.

Lynx accepts configuration options from either command-line options or configuration files. There are 142 command line options according to its help message. The template configuration file codice_1 lists 233 configurable features. There is some overlap between the two, although there are command-line options such as codice_2 which are not matched in codice_1. In addition to pre-set options by command-line and configuration file, Lynx's behavior can be adjusted at runtime using its options menu. Again, there is some overlap between the settings. Lynx implements many of these runtime optional features, optionally (controlled through a setting in the configuration file) allowing the choices to be saved to a separate writable configuration file. The reason for restricting the options which can be saved originated in a usage of Lynx which was more common in the mid-1990s, i.e., using Lynx itself as a front-end application to the Internet accessed by dial-in connections.

Accessibility.

Because of its refreshable braille display and text-to-speech–friendly interface, Lynx can be used for internet access by visually impaired users. As Lynx substitutes images, frames and other non-textual content with the text from codice_4, codice_5 and codice_6 HTML attributes and allows hiding the user interface elements, the browser becomes specifically suitable for use with cost-effective general purpose screen reading software. A version of Lynx specifically enhanced for use with screen readers on Windows was developed at Indian Institute of Technology Madras.

Remote access.

Lynx is also useful for accessing websites from a remotely connected system in which no graphical display is available. Despite its text-only nature and age, it can still be used to effectively browse much of the modern web, including performing interactive tasks such as editing Wikipedia.

Web design and robots.

Since Lynx will take keystrokes from a text file, it is still very useful for automated data entry, web page navigation, and web scraping. Consequently, Lynx is used in some web crawlers. Web designers may use Lynx to determine the way in which search engines and web crawlers see the sites that they develop. Online services that provide Lynx's view of a given web page are available.  Lynx is also used to test websites' performance. As one can run the browser from different locations over remote access technologies like telnet and ssh, one can use Lynx to test the web site's connection performance from different geographical locations simultaneously. Another possible web design application of the browser is quick checking of the site's links.

Supported platforms.

Lynx was originally designed for Unix-like operating systems, though it was ported to VMS soon after its public release and to other systems, including DOS, Microsoft Windows, Classic Mac OS and OS/2. It was included in the default OpenBSD installation from OpenBSD 2.3 (May 1998) to 5.5 (May 2014), being in the main tree prior to July 2014, subsequently being made available through the ports tree, and can also be found in the repositories of most Linux distributions, as well as in the Homebrew and Fink repositories for macOS. Ports to BeOS, MINIX, QNX, AmigaOS and OS/2 are also available.  The sources can be built on many platforms, e.g., mention is made of Google's Android operating system.

Lynx is a customizable text-based web browser for use on cursor-addressable character cell terminals., it is the oldest web browser still in general use and active development, having started in 1992.

Lynx je textový webový prohlížeč www stránek používaný na znakových terminálech. Při prohlížení stránek v Lynxu jsou odkazy zvýrazňovány a přeskakuje se mezi nimi pomocí kurzorových kláves se šipkami. Je-li zapnut mód číslovaných odkazů, lze odkaz vybrat prostým napsáním jeho čísla. Současná verze podporuje mnoho vlastností HTML a SSL. Tabulky jsou linearizovány (buňky sesazeny jedna vedle druhé bez zachování struktury tabulky), zatímco rámce mají jména a uživatel je může prohlížet, jako by šlo o separátní stránky.


Background.

A DNA transcription unit encoding for a protein may contain both a "coding sequence", which will be translated into the protein, and "regulatory sequences", which direct and regulate the synthesis of that protein. The regulatory sequence before ("upstream" from) the coding sequence is called the five prime untranslated region (5'UTR); the sequence after ("downstream" from) the coding sequence is called the three prime untranslated region (3'UTR).  As opposed to DNA replication, transcription results in an RNA complement that includes the nucleotide uracil (U) in all instances where thymine (T) would have occurred in a DNA complement.  Only one of the two DNA strands serve as a template for transcription. The antisense strand of DNA is read by RNA polymerase from the 3' end to the 5' end during transcription (3' → 5'). The complementary RNA is created in the opposite direction, in the 5' → 3' direction, matching the sequence of the sense strand with the exception of switching uracil for thymine. This directionality is because RNA polymerase can only add nucleotides to the 3' end of the growing mRNA chain. This use of only the 3' → 5' DNA strand eliminates the need for the Okazaki fragments that are seen in DNA replication. This also removes the need for an RNA primer to initiate RNA synthesis, as is the case in DNA replication.  The "non"-template (sense) strand of DNA is called the coding strand, because its sequence is the same as the newly created RNA transcript (except for the substitution of uracil for thymine). This is the strand that is used by convention when presenting a DNA sequence.  Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for copying DNA. As a result, transcription has a lower copying fidelity than DNA replication.

Major steps.

Transcription is divided into "initiation", "promoter escape", "elongation," and "termination".

Initiation.

Transcription begins with the binding of RNA polymerase, together with one or more general transcription factors, to a specific DNA sequence referred to as a "promoter" to form an RNA polymerase-promoter "closed complex". In the "closed complex" the promoter DNA is still fully double-stranded.  RNA polymerase, assisted by one or more general transcription factors, then unwinds approximately 14 base pairs of DNA to form an RNA polymerase-promoter "open complex". In the "open complex" the promoter DNA is partly unwound and single-stranded. The exposed, single-stranded DNA is referred to as the "transcription bubble."  RNA polymerase, assisted by one or more general transcription factors, then selects a transcription start site in the transcription bubble, binds to an initiating NTP and an extending NTP (or a short RNA primer and an extending NTP) complementary to the transcription start site sequence, and catalyzes bond formation to yield an initial RNA product.  In bacteria, RNA polymerase holoenzyme consists of five subunits: 2 α subunits, 1 β subunit, 1 β' subunit, and 1 ω subunit. In bacteria, there is one general RNA transcription factor known as a sigma factor. RNA polymerase core enzyme binds to the bacterial general transcription (sigma) factor to form RNA polymerase holoenzyme and then binds to a promoter. (RNA polymerase is called a holoenzyme when sigma subunit is attached to the core enzyme which is consist of 2 α subunits, 1 β subunit, 1 β' subunit only).  In archaea and eukaryotes, RNA polymerase contains subunits homologous to each of the five RNA polymerase subunits in bacteria and also contains additional subunits. In archaea and eukaryotes, the functions of the bacterial general transcription factor sigma are performed by multiple general transcription factors that work together. In archaea, there are three general transcription factors: TBP, TFB, and TFE. In eukaryotes, in RNA polymerase II-dependent transcription, there are six general transcription factors: TFIIA, TFIIB (an ortholog of archaeal TFB), TFIID (a multisubunit factor in which the key subunit, TBP, is an ortholog of archaeal TBP), TFIIE (an ortholog of archaeal TFE), TFIIF, and TFIIH. The TFIID is the first component to bind to DNA due to binding of TBP, while TFIIH is the last component to be recruited. In archaea and eukaryotes, the RNA polymerase-promoter closed complex is usually referred to as the "preinitiation complex."  Transcription initiation is regulated by additional proteins, known as activators and repressors, and, in some cases, associated coactivators or corepressors, which modulate formation and function of the transcription initiation complex.

Promoter escape.

After the first bond is synthesized, the RNA polymerase must escape the promoter. During this time there is a tendency to release the RNA transcript and produce truncated transcripts. This is called abortive initiation, and is common for both eukaryotes and prokaryotes. Abortive initiation continues to occur until an RNA product of a threshold length of approximately 10 nucleotides is synthesized, at which point promoter escape occurs and a transcription elongation complex is formed.  Mechanistically, promoter escape occurs through DNA scrunching, providing the energy needed to break interactions between RNA polymerase holoenzyme and the promoter.  In bacteria, it was historically thought that the sigma factor is definitely released after promoter clearance occurs. This theory had been known as the "obligate release model" however later data showed that upon and following promoter clearance, the sigma factor is released according to a stochastic model known as the "stochastic release model".  In eukaryotes, at an RNA polymerase II-dependent promoter, upon promoter clearance, TFIIH phosphorylates serine 5 on the carboxy terminal domain of RNA polymerase II, leading to the recruitment of capping enzyme (CE). The exact mechanism of how CE induces promoter clearance in eukaryotes is not yet known.

Elongation.

One strand of the DNA, the "template strand" (or noncoding strand), is used as a template for RNA synthesis. As transcription proceeds, RNA polymerase traverses the template strand and uses base pairing complementarity with the DNA template to create an RNA copy (which elongates during the traversal). Although RNA polymerase traverses the template strand from 3' → 5', the coding (non-template) strand and newly formed RNA can also be used as reference points, so transcription can be described as occurring 5' → 3'. This produces an RNA molecule from 5' → 3', an exact copy of the coding strand (except that thymines are replaced with uracils, and the nucleotides are composed of a ribose (5-carbon) sugar where DNA has deoxyribose (one fewer oxygen atom) in its sugar-phosphate backbone).  mRNA transcription can involve multiple RNA polymerases on a single DNA template and multiple rounds of transcription (amplification of particular mRNA), so many mRNA molecules can be rapidly produced from a single copy of a gene. The characteristic elongation rates in prokaryotes and eukaryotes are about 10-100 nts/sec. In eukaryotes, however, nucleosomes act as major barriers to transcribing polymerases during transcription elongation. In these organisms, the pausing induced by nucleosomes can be regulated by transcription elongation factors such as TFIIS.  Elongation also involves a proofreading mechanism that can replace incorrectly incorporated bases. In eukaryotes, this may correspond with short pauses during transcription that allow appropriate RNA editing factors to bind. These pauses may be intrinsic to the RNA polymerase or due to chromatin structure.

Termination.

Bacteria use two different strategies for transcription termination – Rho-independent termination and Rho-dependent termination. In Rho-independent transcription termination, RNA transcription stops when the newly synthesized RNA molecule forms a G-C-rich hairpin loop followed by a run of Us. When the hairpin forms, the mechanical stress breaks the weak rU-dA bonds, now filling the DNA–RNA hybrid. This pulls the poly-U transcript out of the active site of the RNA polymerase, terminating transcription. In the "Rho-dependent" type of termination, a protein factor called "Rho" destabilizes the interaction between the template and the mRNA, thus releasing the newly synthesized mRNA from the elongation complex.  Transcription termination in eukaryotes is less well understood than in bacteria, but involves cleavage of the new transcript followed by template-independent addition of adenines at its new 3' end, in a process called polyadenylation.

Inhibitors.

Transcription inhibitors can be used as antibiotics against, for example, pathogenic bacteria (antibacterials) and fungi (antifungals). An example of such an antibacterial is rifampicin, which inhibits bacterial transcription of DNA into mRNA by inhibiting DNA-dependent RNA polymerase by binding its beta-subunit, while 8-hydroxyquinoline is an antifungal transcription inhibitor. The effects of histone methylation may also work to inhibit the action of transcription.

Endogenous inhibitors.

In vertebrates, the majority of gene promoters contain a CpG island with numerous CpG sites. When many of a gene's promoter CpG sites are methylated the gene becomes inhibited (silenced). Colorectal cancers typically have 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations. However, transcriptional inhibition (silencing) may be of more importance than mutation in causing progression to cancer. For example, in colorectal cancers about 600 to 800 genes are transcriptionally inhibited by CpG island methylation (see regulation of transcription in cancer). Transcriptional repression in cancer can also occur by other epigenetic mechanisms, such as altered expression of microRNAs. In breast cancer, transcriptional repression of BRCA1 may occur more frequently by over-expressed microRNA-182 than by hypermethylation of the BRCA1 promoter (see Low expression of BRCA1 in breast and ovarian cancers).

Transcription factories.

Active transcription units are clustered in the nucleus, in discrete sites called transcription factories or euchromatin. Such sites can be visualized by allowing engaged polymerases to extend their transcripts in tagged precursors (Br-UTP or Br-U) and immuno-labeling the tagged nascent RNA. Transcription factories can also be localized using fluorescence in situ hybridization or marked by antibodies directed against polymerases. There are ~10,000 factories in the nucleoplasm of a HeLa cell, among which are ~8,000 polymerase II factories and ~2,000 polymerase III factories. Each polymerase II factory contains ~8 polymerases. As most active transcription units are associated with only one polymerase, each factory usually contains ~8 different transcription units. These units might be associated through promoters and/or enhancers, with loops forming a "cloud" around the factor.

History.

A molecule that allows the genetic material to be realized as a protein was first hypothesized by François Jacob and Jacques Monod. Severo Ochoa won a Nobel Prize in Physiology or Medicine in 1959 for developing a process for synthesizing RNA "in vitro" with polynucleotide phosphorylase, which was useful for cracking the genetic code. RNA synthesis by RNA polymerase was established "in vitro" by several laboratories by 1965; however, the RNA synthesized by these enzymes had properties that suggested the existence of an additional factor needed to terminate transcription correctly.  In 1972, Walter Fiers became the first person to actually prove the existence of the terminating enzyme.  Roger D. Kornberg won the 2006 Nobel Prize in Chemistry "for his studies of the molecular basis of eukaryotic transcription".

Measuring and detecting.

Transcription can be measured and detected in a variety of ways:

Reverse transcription.

Some viruses (such as HIV, the cause of AIDS), have the ability to transcribe RNA into DNA. HIV has an RNA genome that is "reverse transcribed" into DNA. The resulting DNA can be merged with the DNA genome of the host cell. The main enzyme responsible for synthesis of DNA from an RNA template is called reverse transcriptase.  In the case of HIV, reverse transcriptase is responsible for synthesizing a complementary DNA strand (cDNA) to the viral RNA genome. The enzyme ribonuclease H then digests the RNA strand, and reverse transcriptase synthesises a complementary strand of DNA to form a double helix DNA structure ("cDNA"). The cDNA is integrated into the host cell's genome by the enzyme integrase, which causes the host cell to generate viral proteins that reassemble into new viral particles. In HIV, subsequent to this, the host cell undergoes programmed cell death, or apoptosis of T cells. However, in other retroviruses, the host cell remains intact as the virus buds out of the cell.  Some eukaryotic cells contain an enzyme with reverse transcription activity called telomerase. Telomerase is a reverse transcriptase that lengthens the ends of linear chromosomes. Telomerase carries an RNA template from which it synthesizes a repeating sequence of DNA, or "junk" DNA. This repeated sequence of DNA is called a telomere and can be thought of as a "cap" for a chromosome. It is important because every time a linear chromosome is duplicated, it is shortened. With this "junk" DNA or "cap" at the ends of chromosomes, the shortening eliminates some of the non-essential, repeated sequence rather than the protein-encoding DNA sequence, that is farther away from the chromosome end.  Telomerase is often activated in cancer cells to enable cancer cells to duplicate their genomes indefinitely without losing important protein-coding DNA sequence. Activation of telomerase could be part of the process that allows cancer cells to become "immortal". The immortalizing factor of cancer via telomere lengthening due to telomerase has been proven to occur in 90% of all carcinogenic tumors "in vivo" with the remaining 10% using an alternative telomere maintenance route called ALT or Alternative Lengthening of Telomeres.

Transcription is the first of several steps of DNA based gene expression in which a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase.

Transkripce („přepis“) je proces, při němž je, podle genetické informace zapsané v řetězci DNA, vyráběn řetězec RNA. RNA obvykle představuje prostředníka mezi genetickým materiálem a bílkovinami, jež se podle něho vyrábí. Existují však i některé nekódující RNA, které vznikají z DNA, ale nikdy z nich protein nevzniká. Transkripce je důležitá součást tzv. centrálního dogmatu molekulární biologie. Probíhá u všech známých organizmů včetně virů. U bakterií se odehrává volně v cytoplazmě, u některých vyšších organizmů (tzv. eukaryota) probíhá v buněčném jádře.


Introduction.

The word "fractal" often has different connotations for the lay public as opposed to mathematicians, where the public are more likely to be familiar with fractal art than the mathematical concept. The mathematical concept is difficult to define formally, even for mathematicians, but key features can be understood with little mathematical background.  The feature of "self-similarity", for instance, is easily understood by analogy to zooming in with a lens or other device that zooms in on digital images to uncover finer, previously invisible, new structure. If this is done on fractals, however, no new detail appears; nothing changes and the same pattern repeats over and over, or for some fractals, nearly the same pattern reappears over and over. Self-similarity itself is not necessarily counter-intuitive (e.g., people have pondered self-similarity informally such as in the infinite regress in parallel mirrors or the homunculus, the little man inside the head of the little man inside the head...). The difference for fractals is that the pattern reproduced must be detailed.  This idea of being detailed relates to another feature that can be understood without much mathematical background: Having a fractal dimension greater than its topological dimension, for instance, refers to how a fractal scales compared to how geometric shapes are usually perceived. A straight line, for instance, is conventionally understood to be one-dimensional; if such a figure is rep-tiled into pieces each 1/3 the length of the original, then there are always three equal pieces. A solid square is understood to be two-dimensional; if such a figure is rep-tiled pieces each scaled down by a factor of 1/3 in both dimensions, there are a total of 3 = 9 pieces. We see that for ordinary self-similar objects, being n-dimensional means that when it is rep-tiled into pieces each scaled down by a scale-factor of 1/"r", there are a total of "r" pieces. Now, consider the Koch curve. It can be rep-tiled into four sub-copies, each scaled down by a scale-factor of 1/3. So, strictly by analogy, we can consider the "dimension" of the Koch curve as being the unique real number "D" that satisfies 3 = 4. This number is what mathematicians call the "fractal dimension" of the Koch curve; it is certainly "not" what is conventionally perceived as the dimension of a curve (this number is not even an integer!). The fact that the Koch curve has a fractal dimension differing from its "conventionally understood" dimension (that is, its topological dimension) is what makes it a fractal.  This also leads to understanding a third feature, that fractals as mathematical equations are "nowhere differentiable". In a concrete sense, this means fractals cannot be measured in traditional ways. To elaborate, in trying to find the length of a wavy non-fractal curve, one could find straight segments of some measuring tool small enough to lay end to end over the waves, where the pieces could get small enough to be considered to conform to the curve in the normal manner of measuring with a tape measure. But in measuring an infinitely "wiggly" fractal curve such as the Koch snowflake, one would never find a small enough straight segment to conform to the curve, because the jagged pattern would always re-appear, at arbitrarily small scales, essentially pulling a little more of the tape measure into the total length measured each time one attempted to fit it tighter and tighter to the curve. The result is that one must need infinite tape to perfectly cover the entire curve, i.e. the snowflake has infinite perimeter.

History.

The history of fractals traces a path from chiefly theoretical studies to modern applications in computer graphics, with several notable people contributing canonical fractal forms along the way. According to Pickover, the mathematics behind fractals began to take shape in the 17th century when the mathematician and philosopher Gottfried Leibniz pondered recursive self-similarity (although he made the mistake of thinking that only the straight line was self-similar in this sense). In his writings, Leibniz used the term "fractional exponents", but lamented that "Geometry" did not yet know of them. Indeed, according to various historical accounts, after that point few mathematicians tackled the issues and the work of those who did remained obscured largely because of resistance to such unfamiliar emerging concepts, which were sometimes referred to as mathematical "monsters". Thus, it was not until two centuries had passed that on July 18, 1872 Karl Weierstrass presented the first definition of a function with a graph that would today be considered a fractal, having the non-intuitive property of being everywhere continuous but nowhere differentiable at the Royal Prussian Academy of Sciences. In addition, the quotient difference becomes arbitrarily large as the summation index increases. Not long after that, in 1883, Georg Cantor, who attended lectures by Weierstrass, published examples of subsets of the real line known as Cantor sets, which had unusual properties and are now recognized as fractals. Also in the last part of that century, Felix Klein and Henri Poincaré introduced a category of fractal that has come to be called "self-inverse" fractals.  One of the next milestones came in 1904, when Helge von Koch, extending ideas of Poincaré and dissatisfied with Weierstrass's abstract and analytic definition, gave a more geometric definition including hand-drawn images of a similar function, which is now called the Koch snowflake. Another milestone came a decade later in 1915, when Wacław Sierpiński constructed his famous triangle then, one year later, his carpet. By 1918, two French mathematicians, Pierre Fatou and Gaston Julia, though working independently, arrived essentially simultaneously at results describing what are now seen as fractal behaviour associated with mapping complex numbers and iterative functions and leading to further ideas about attractors and repellors (i.e., points that attract or repel other points), which have become very important in the study of fractals. Very shortly after that work was submitted, by March 1918, Felix Hausdorff expanded the definition of "dimension", significantly for the evolution of the definition of fractals, to allow for sets to have non-integer dimensions. The idea of self-similar curves was taken further by Paul Lévy, who, in his 1938 paper "Plane or Space Curves and Surfaces Consisting of Parts Similar to the Whole", described a new fractal curve, the Lévy C curve.  Different researchers have postulated that without the aid of modern computer graphics, early investigators were limited to what they could depict in manual drawings, so lacked the means to visualize the beauty and appreciate some of the implications of many of the patterns they had discovered (the Julia set, for instance, could only be visualized through a few iterations as very simple drawings). That changed, however, in the 1960s, when Benoit Mandelbrot started writing about self-similarity in papers such as "How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension", which built on earlier work by Lewis Fry Richardson. In 1975 Mandelbrot solidified hundreds of years of thought and mathematical development in coining the word "fractal" and illustrated his mathematical definition with striking computer-constructed visualizations. These images, such as of his canonical Mandelbrot set, captured the popular imagination; many of them were based on recursion, leading to the popular meaning of the term "fractal".  In 1980, Loren Carpenter gave a presentation at the SIGGRAPH where he introduced his software for generating and rendering fractally generated landscapes.

Definition and characteristics.

One often cited description that Mandelbrot published to describe geometric fractals is "a rough or fragmented geometric shape that can be split into parts, each of which is (at least approximately) a reduced-size copy of the whole"; this is generally helpful but limited. Authors disagree on the exact definition of "fractal", but most usually elaborate on the basic ideas of self-similarity and the unusual relationship fractals have with the space they are embedded in.  One point agreed on is that fractal patterns are characterized by fractal dimensions, but whereas these numbers quantify complexity (i.e., changing detail with changing scale), they neither uniquely describe nor specify details of how to construct particular fractal patterns. In 1975 when Mandelbrot coined the word "fractal", he did so to denote an object whose Hausdorff–Besicovitch dimension is greater than its topological dimension. However, this requirement is not met by space-filling curves such as the Hilbert curve.  Because of the trouble involved in finding one definition for fractals, some argue that fractals should not be strictly defined at all. According to Falconer, fractals should, in addition to being nowhere differentiable and able to have a fractal dimension, be only generally characterized by a gestalt of the following features;  As a group, these criteria form guidelines for excluding certain cases, such as those that may be self-similar without having other typically fractal features. A straight line, for instance, is self-similar but not fractal because it lacks detail, is easily described in Euclidean language, has the same Hausdorff dimension as topological dimension, and is fully defined without a need for recursion.

Common techniques for generating fractals.

Images of fractals can be created by fractal generating programs. Because of the butterfly effect, a small change in a single variable can have an unpredictable outcome.

Simulated fractals.

Fractal patterns have been modeled extensively, albeit within a range of scales rather than infinitely, owing to the practical limits of physical time and space. Models may simulate theoretical fractals or natural phenomena with fractal features. The outputs of the modelling process may be highly artistic renderings, outputs for investigation, or benchmarks for fractal analysis. Some specific applications of fractals to technology are listed elsewhere. Images and other outputs of modelling are normally referred to as being "fractals" even if they do not have strictly fractal characteristics, such as when it is possible to zoom into a region of the fractal image that does not exhibit any fractal properties. Also, these may include calculation or display artifacts which are not characteristics of true fractals.  Modeled fractals may be sounds, digital images, electrochemical patterns, circadian rhythms, etc. Fractal patterns have been reconstructed in physical 3-dimensional space and virtually, often called "in silico" modeling. Models of fractals are generally created using fractal-generating software that implements techniques such as those outlined above. As one illustration, trees, ferns, cells of the nervous system, blood and lung vasculature, and other branching patterns in nature can be modeled on a computer by using recursive algorithms and L-systems techniques. The recursive nature of some patterns is obvious in certain examples—a branch from a tree or a frond from a fern is a miniature replica of the whole: not identical, but similar in nature. Similarly, random fractals have been used to describe/create many highly irregular real-world objects. A limitation of modeling fractals is that resemblance of a fractal model to a natural phenomenon does not prove that the phenomenon being modeled is formed by a process similar to the modeling algorithms.

Natural phenomena with fractal features.

Approximate fractals found in nature display self-similarity over extended, but finite, scale ranges. The connection between fractals and leaves, for instance, is currently being used to determine how much carbon is contained in trees. Phenomena known to have fractal features include:

In creative works.

Since 1999, more than 10 scientific groups have performed fractal analysis on over 50 of Jackson Pollock's (1912–1956) paintings which were created by pouring paint directly onto his horizontal canvases Recently, fractal analysis has been used to achieve a 93% success rate in distinguishing real from imitation Pollocks. Cognitive neuroscientists have shown that Pollock's fractals induce the same stress-reduction in observers as computer-generated fractals and Nature's fractals.  Decalcomania, a technique used by artists such as Max Ernst, can produce fractal-like patterns. It involves pressing paint between two surfaces and pulling them apart.  Cyberneticist Ron Eglash has suggested that fractal geometry and mathematics are prevalent in African art, games, divination, trade, and architecture. Circular houses appear in circles of circles, rectangular houses in rectangles of rectangles, and so on. Such scaling patterns can also be found in African textiles, sculpture, and even cornrow hairstyles. Hokky Situngkir also suggested the similar properties in Indonesian traditional art, batik, and ornaments found in traditional houses.  Ethnomathematician Ron Eglash has discussed the planned layout of Benin city using fractals as the basis, not only in the city itself and the villages but even in the rooms of houses. He commented that "When Europeans first came to Africa, they considered the architecture very disorganised and thus primitive. It never occurred to them that the Africans might have been using a form of mathematics that they hadn’t even discovered yet."  In a 1996 interview with Michael Silverblatt, David Foster Wallace admitted that the structure of the first draft of "Infinite Jest" he gave to his editor Michael Pietsch was inspired by fractals, specifically the Sierpinski triangle (a.k.a. Sierpinski gasket), but that the edited novel is "more like a lopsided Sierpinsky Gasket".

Physiological responses.

Humans appear to be especially well-adapted to processing fractal patterns with D values between 1.3 and 1.5. When humans view fractal patterns with D values between 1.3 and 1.5, this tends to reduce physiological stress.

Applications in technology.

Ion propulsion.

When two-dimensional fractals are iterated many times, the perimeter of the fractal increases up to infinity, but the area may never exceed a certain value. A fractal in three-dimensional space is similar; such a fractal may have an infinite surface area, but never exceed a certain volume. This can be utilized to maximize the efficiency of ion propulsion when choosing electron emitter construction and material. If done correctly, the efficiency of the emission process can be maximized.

In mathematics, a fractal is a self-similar subset of Euclidean space whose fractal dimension strictly exceeds its topological dimension. Fractals appear the same at different levels, as illustrated in successive magnifications of the Mandelbrot set. Fractals exhibit similar patterns at increasingly small scales called self similarity, also known as expanding symmetry or unfolding symmetry; if this replication is exactly the same at every scale, as in the Menger sponge, it is called affine self-similar. Fractal geometry lies within the mathematical branch of measure theory.

Fraktál je podle původní Mandelbrotovy definice množina, jejíž Hausdorffova dimenze je větší než dimenze topologická. Lze jej také definovat poněkud jednodušeji (méně obecně) jako geometrický objekt, který má následující vlastnosti: