|
Jakob Nielsen (mathematician)
Jakob Nielsen (15 October 1890 in Mjels, Als – 3 August 1959 in Helsingør) was a Danish mathematician known for his work on automorphisms of surfaces. He was born in the village Mjels on the island of Als in North Schleswig, in modern-day Denmark. His mother died when he was 3, and in 1900 he went to live with his aunt and was enrolled in the Realgymnasium. In 1907 he was expelled for membership to an illicit student club. Nevertheless, he matriculated at the University of Kiel in 1908. Nielsen completed his doctoral dissertation in 1913. Soon thereafter, he was drafted into the German Imperial Navy. He was assigned to coastal defense. In 1915 he was sent to Constantinople as a military adviser to the Turkish Government. After the war, in the spring of 1919, Nielsen married Carola von Pieverling, a German medical doctor. In 1920 Nielsen took a position at the Technical University of Breslau. The next year he published a paper in Mathematisk Tidsskrift in which he pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jakob Nielsen
Jacob or Jakob Nielsen may refer to: * Jacob Nielsen, Count of Halland (died c. 1309), great grandson of Valdemar II of Denmark * , Norway (1768-1822) * Jakob Nielsen (mathematician) (1890–1959), Danish mathematician known for work on automorphisms of surfaces * Jakob Nielsen (usability consultant) (born 1957), Danish web usability consultant * Jakob Axel Nielsen (born 1967), Danish lawyer and politician * Jakob Nielsen (actor) Jakob Nielsen (8 June 1900 – 4 April 1979) was a Danish actor. He appeared in more than 45 films between 1937 and 1976. Selected filmography * ''Life on the Hegn Farm'' (1938) * '' Those Blasted Kids'' (1947) * '' Det Sande Ansigt'' (1951 ... (1900-1978) * Jacob Nielsen (cyclist) (born 1978), Danish cyclist * Jakob Ahlmann Nielsen (born 1991), Danish footballer {{hndis, Nielsen, Jacob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Technical University Of Denmark
The Technical University of Denmark ( da, Danmarks Tekniske Universitet), often simply referred to as DTU, is a polytechnic university and school of engineering. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmark's first polytechnic, and it is today ranked among Europe's leading engineering institutions. It is located in the town Kongens Lyngby, north of central Copenhagen, Denmark. Along with École Polytechnique in Paris, École Polytechnique Fédérale de Lausanne, Eindhoven University of Technology, Technical University of Munich and Technion – Israel Institute of Technology, DTU is a member of EuroTech Universities Alliance. History DTU was founded in 1829 as the "College of Advanced Technology" (Danish: Den Polytekniske Læreanstalt). The Physicist Hans Christian Ørsted, at that time a professor at the University of Copenhagen, was one of the driving forces behind this initiative. He was inspired by the École Polytechnique in Paris, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1890 Births
Year 189 ( CLXXXIX) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Silanus and Silanus (or, less frequently, year 942 ''Ab urbe condita''). The denomination 189 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years. Events By place Roman Empire * Plague (possibly smallpox) kills as many as 2,000 people per day in Rome. Farmers are unable to harvest their crops, and food shortages bring riots in the city. China * Liu Bian succeeds Emperor Ling, as Chinese emperor of the Han Dynasty. * Dong Zhuo has Liu Bian deposed, and installs Emperor Xian as emperor. * Two thousand eunuchs in the palace are slaughtered in a violent purge in Luoyang, the capital of Han. By topic Arts and sciences * Galen publishes his ''"Treatise on the various temperaments"'' (aka ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nielsen Realization Problem
The Nielsen realization problem is a question asked by about whether finite subgroups of mapping class groups can act on surfaces, that was answered positively by . Statement Given an oriented surface, we can divide the group Diff(''S''), the group of diffeomorphisms of the surface to itself, into isotopy classes to get the mapping class group π0(Diff(''S'')). The conjecture asks whether a finite subgroup of the mapping class group of a surface can be realized as the isometry group of a hyperbolic metric on the surface. The mapping class group acts on Teichmüller space. An equivalent way of stating the question asks whether every finite subgroup of the mapping class group fixes some point of Teichmüller space. History asked whether finite subgroups of mapping class groups can act on surfaces. claimed to solve the Nielsen realization problem but his proof depended on trying to show that Teichmüller space In mathematics, the Teichmüller space T(S) of a (real) topological ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nielsen–Thurston Classification
In mathematics, Thurston's classification theorem characterizes homeomorphisms of a compact orientable surface. William Thurston's theorem completes the work initiated by . Given a homeomorphism ''f'' : ''S'' → ''S'', there is a map ''g'' isotopic to ''f'' such that at least one of the following holds: * ''g'' is periodic, i.e. some power of ''g'' is the identity; * ''g'' preserves some finite union of disjoint simple closed curves on ''S'' (in this case, ''g'' is called ''reducible''); or * ''g'' is pseudo-Anosov. The case where ''S'' is a torus (i.e., a surface whose genus is one) is handled separately (see torus bundle) and was known before Thurston's work. If the genus of ''S'' is two or greater, then ''S'' is naturally hyperbolic, and the tools of Teichmüller theory become useful. In what follows, we assume ''S'' has genus at least two, as this is the case Thurston considered. (Note, however, that the cases where ''S'' has boundary or is not orie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nielsen Theory
Nielsen theory is a branch of mathematical research with its origins in topological fixed-point theory. Its central ideas were developed by Danish mathematician Jakob Nielsen, and bear his name. The theory developed in the study of the so-called ''minimal number'' of a map ''f'' from a compact space to itself, denoted ''MF'' 'f'' This is defined as: :\mathit = \min \, where ''~'' indicates homotopy of mappings, and #Fix(''g'') indicates the number of fixed points of ''g''. The minimal number was very difficult to compute in Nielsen's time, and remains so today. Nielsen's approach is to group the fixed-point set into classes, which are judged "essential" or "nonessential" according to whether or not they can be "removed" by a homotopy. Nielsen's original formulation is equivalent to the following: We define an equivalence relation on the set of fixed points of a self-map ''f'' on a space ''X''. We say that ''x'' is equivalent to ''y'' if and only if there exists a path ''c'' from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nielsen Transformation
In mathematics, especially in the area of abstract algebra known as combinatorial group theory, Nielsen transformations, named after Jakob Nielsen, are certain automorphisms of a free group which are a non-commutative analogue of row reduction and one of the main tools used in studying free groups, . They were introduced in to prove that every subgroup of a free group is free (the Nielsen–Schreier theorem), but are now used in a variety of mathematics, including computational group theory, k-theory, and knot theory. The textbook devotes all of chapter 3 to Nielsen transformations. Definitions One of the simplest definitions of a Nielsen transformation is an automorphism of a free group, but this was not their original definition. The following gives a more constructive definition. A Nielsen transformation on a finitely generated free group with ordered basis ''x''1, ..., ''x''''n'' can be factored into elementary Nielsen transformations of the following sorts: * Switch ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fenchel–Nielsen Coordinates
In mathematics, Fenchel–Nielsen coordinates are coordinates for Teichmüller space introduced by Werner Fenchel and Jakob Nielsen. Definition Suppose that ''S'' is a compact Riemann surface of genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ... ''g'' > 1. The Fenchel–Nielsen coordinates depend on a choice of 6''g'' − 6 curves on ''S'', as follows. The Riemann surface ''S'' can be divided up into 2''g'' − 2 pairs of pants by cutting along 3''g'' − 3 disjoint simple closed curves. For each of these 3''g'' − 3 curves γ, choose an arc crossing it that ends in other boundary components of the pairs of pants with boundary containing γ. The Fenchel–Nielsen coordinates for a point of the Teichmü ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UNESCO
The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations (UN) aimed at promoting world peace and security through international cooperation in education, arts, sciences and culture. It has 193 member states and 12 associate members, as well as partners in the non-governmental, intergovernmental and private sector. Headquartered at the World Heritage Centre in Paris, France, UNESCO has 53 regional field offices and 199 national commissions that facilitate its global mandate. UNESCO was founded in 1945 as the successor to the League of Nations's International Committee on Intellectual Cooperation.English summary). Its constitution establishes the agency's goals, governing structure, and operating framework. UNESCO's founding mission, which was shaped by the Second World War, is to advance peace, sustainable development and human rights by facilitating collaboration and dialogue among nations. It pursues this objectiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Harald Bohr
Harald August Bohr (22 April 1887 – 22 January 1951) was a Danish mathematician and footballer. After receiving his doctorate in 1910, Bohr became an eminent mathematician, founding the field of almost periodic functions. His brother was the Nobel Prize-winning physicist Niels Bohr. He was a member of the Danish national football team for the 1908 Summer Olympics, where he won a silver medal. Biography Bohr was born in 1887 to Christian Bohr, a professor of physiology, from a Lutheran background, and Ellen Adler Bohr, a woman from a wealthy Jewish family of local renown. Harald had a close relationship with his elder brother, which ''The Times'' likened to that between Captain Cuttle and Captain Bunsby in Charles Dickens' '' Dombey and Son''. Mathematical career Like his father and brother before him, in 1904 Bohr enrolled at the University of Copenhagen, where he studied mathematics, obtaining his master's degree in 1909 and his doctorate a year later. Among his tutors were ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University Of Copenhagen
The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public research university in Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in Scandinavia after Uppsala University, and ranks as one of the top universities in the Nordic countries, Europe and the world. Its establishment sanctioned by Pope Sixtus IV, the University of Copenhagen was founded by Christian I of Denmark as a Catholic teaching institution with a predominantly theological focus. In 1537, it was re-established by King Christian III as part of the Lutheran Reformation. Up until the 18th century, the university was primarily concerned with educating clergymen. Through various reforms in the 18th and 19th century, the University of Copenhagen was transformed into a modern, secular university, with science and the humanities replacing theology as the main subjects studied and taught. The University of Copenhagen consists of six different ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nazis
Nazism ( ; german: Nazismus), the common name in English for National Socialism (german: Nationalsozialismus, ), is the far-right totalitarian political ideology and practices associated with Adolf Hitler and the Nazi Party (NSDAP) in Nazi Germany. During Hitler's rise to power in 1930s Europe, it was frequently referred to as Hitlerism (german: Hitlerfaschismus). The later related term " neo-Nazism" is applied to other far-right groups with similar ideas which formed after the Second World War. Nazism is a form of fascism, with disdain for liberal democracy and the parliamentary system. It incorporates a dictatorship, fervent antisemitism, anti-communism, scientific racism, and the use of eugenics into its creed. Its extreme nationalism originated in pan-Germanism and the ethno-nationalist '' Völkisch'' movement which had been a prominent aspect of German nationalism since the late 19th century, and it was strongly influenced by the paramilitary groups that emerge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.svg "Click for more on -> Nazis")