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"Phosphorus pentafluoride, PF5, is a phosphorus halide. It is a colourless, toxic gas that fumes in air. Preparation Phosphorus pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride, which remains a favored method: :3 PCl5 \+ 5 AsF3 → 3 PF5 \+ 5 AsCl3 Structure Single-crystal X-ray studies indicate that the PF5 has trigonal bipyramidal geometry. Thus it has two distinct types of P−F bonds (axial and equatorial): the length of an axial P−F bond is distinct from the equatorial P−F bond in the solid phase, but not the liquid or gas phases due to Pseudo Berry Rotation. Fluorine-19 NMR spectroscopy, even at temperatures as low as −100 °C, fails to distinguish the axial from the equatorial fluorine environments. The apparent equivalency arises from the low barrier for pseudorotation via the Berry mechanism, by which the axial and equatorial fluorine atoms rapidly exchange positions. The apparent equivalency of the F centers in PF5 was first noted by Gutowsky. The explanation was first described by R. Stephen Berry, after whom the Berry mechanism is named. Berry pseudorotation influences the 19F NMR spectrum of PF5 since NMR spectroscopy operates on a millisecond timescale. Electron diffraction and X-ray crystallography do not detect this effect as the solid state structures are, relative to a molecule in solution, static and can not undergo the necessary changes in atomic position. Lewis acidity Phosphorus pentafluoride is a Lewis acid. This property is relevant to its ready hydrolysis. A well studied adduct is PF5 with pyridine. With primary and secondary amines, the adducts convert readily to dimeric amido-bridged derivatives with the formula [PF4(NR2)]2. A variety of complexes are known with bidentate ligands. Hexafluorophosphoric acid (HPF6) is derived from phosphorus pentafluoride and hydrogen fluoride. Its conjugate base, hexafluorophosphate (PF6–), is a useful non-coordinating anion. References Category:Inorganic phosphorus compounds Category:Fluorides Category:Phosphorus(+5) compounds "
"The Szilassi polyhedron is a nonconvex polyhedron, topologically a torus, with seven hexagonal faces. Coloring and symmetry Each face of this polyhedron shares an edge with each other face. As a result, it requires seven colours to colour all adjacent faces, providing the lower bound for the seven colour theorem. It has an axis of 180-degree symmetry; three pairs of faces are congruent leaving one unpaired hexagon that has the same rotational symmetry as the polyhedron. The 14 vertices and 21 edges of the Szilassi polyhedron form an embedding of the Heawood graph onto the surface of a torus. Complete face adjacency GIF animation The tetrahedron and the Szilassi polyhedron are the only two known polyhedra in which each face shares an edge with each other face. If a polyhedron with f faces is embedded onto a surface with h holes, in such a way that each face shares an edge with each other face, it follows by some manipulation of the Euler characteristic that :h = \frac{(f - 4)(f - 3)}{12}. This equation is satisfied for the tetrahedron with h = 0 and f = 4, and for the Szilassi polyhedron with h = 1 and f = 7. The next possible solution, h = 6 and f = 12, would correspond to a polyhedron with 44 vertices and 66 edges. However, it is not known whether such a polyhedron can be realized geometrically (rather than as an abstract polytope). More generally this equation can be satisfied precisely when f is congruent to 0, 3, 4, or 7 modulo 12. History The Szilassi polyhedron is named after Hungarian mathematician Lajos Szilassi, who discovered it in 1977. The dual to the Szilassi polyhedron, the Császár polyhedron, was discovered earlier by ; it has seven vertices, 21 edges connecting every pair of vertices, and 14 triangular faces. Like the Szilassi polyhedron, the Császár polyhedron has the topology of a torus. References *. *. *. *. * External links *. Szilassi Polyhedron – Papercraft model at CutOutFoldUp.com Category:Nonconvex polyhedra Category:Toroidal polyhedra "
"Teleradio-Moldova is the state-owned national radio and television broadcaster. It owns the TV channels Moldova 1 and TVMI and the radio channels Radio Moldova and Radio Moldova Internaţional. TRM was admitted as a full active member of the European Broadcasting Union on 1 January 1993, under its former name Radioteleviziunea Nationala din Moldova (RTNM). History The radio in Chișinău in 1937 The first radio transmission in Moldova was broadcast on November 1, 1928 by the Radiotelephonic Broadcasting Company in Bucharest. On 30 October 1930, in Tiraspol started broadcasting a Soviet radio station of 4 kW whose main purpose was the anti-Romanian propaganda to Moldova between Prut and DniesterRadio Moldova se revendica de la Radio Tiraspol A new radio mast, M. Gorky, built in 1936 in Tiraspol, allowed a greater coverage of the territory of Bessarabia. In that context, in 1937, Chişinău City Hall gave the Romanian Radio Broadcasting Company a building to open the first radio station in Chişinău, to counter Soviet propaganda. Experimental programs began in the early days of June 1939. The transmitter installed by Marconi Company in Chişinău was the best in Romania.Revista Radio Universul 1939. The first radio station in Chişinău was "twice stronger than that of Bucharest or that one in Tiraspol" wrote Gazeta Basarabiei in July 1939. Radio Basarabia in 1940 The company was launched on 8 October 1939, as Radio Basarabia, the second radio station of the Romanian Radio Broadcasting Company. On October 8, 1939, Radio Basarabia (with own shows in Romanian and Russian) was launched in Chişinău by the Romanian Radio Broadcasting Company.IPNA Compania Teleradio Moldova A religious service was broadcast from the Nativity Cathedral at the launching of the first radio station in Chişinău. Emission power could be increased from 20 kW to 200 kW and the reception was possible in Moscow or Leningrad due to direct wave propagation. There were three studios, the biggest for symphony orchestras, choirs and opera band, the middle for chamber music and soloists, and the third allocated to lecturers and announcer, equipped with the most modern equipment. Radio Bessarabia had six services: the Secretariat, Technical Service, Service Programs, Administrative Service, Litigation department, and Commercial department.Radiofonie românească: Radio Basarabia With the Soviet occupation in June 1940 most of the backup material, personnel and the archive were withdrawn at Huși, but not the transmitter. The Red Army blew up the building and the bodies of those who remained to work for the radio were found in a water well. In 1958, Nicolae Lupan became the first chief redactor of Teleradio-Moldova. Services =Radio= *Radio Moldova: founded on 8 October 1939 as "Radio Bessarabia", Radio Moldova is the public radio station. Its programming is informative. *Radio Moldova Tineret: station aimed at young audiences, with music and magazine programmes. *Radio Moldova Muzical: radio specialized in classical and academic music. From 1992 to 2013 there was an international version (Radio Moldova Internaţional) that offered programs in Russian, English, French and Spanish. =Television= *Moldova 1: Founded on April 30, 1958, Its programming is general. *Moldova 2: Opened in 2016, it is an alternative to the first channel. TRM also had its own international channel, TV Moldova Internaţional, that launched in January 2007 but was closed in January 2013 for financial reasons. Leadership On December 31, 2009, the Supervisory Board of Teleradio-Moldova dismissed the director of Radio Moldova, Veaceslav Gheorghişenco, after on December 30 they dismissed the company's chairman, Valentin Todercan, and the director of Moldova 1, Adela Răileanu. The board's members grounded their decision on the fact that over the past years the company turned into a political instrument, violated the right to expression and the principle of impartiality and pluralism of opinions. Also, the Supervisory Board announced a contest for these vacancies.Managers of Moldovan public broadcasting companies dismissed Constantin Marin is the new head of "Teleradio-Moldova". Since 2004, he was principal of the Journalism and Communication Sciences faculty at State University of Moldova. Before, he was editor-in-chief at Radio Moldova Internaţional and superior lector at History of Journalism department. He is the author of "The Civil Society between Political Myth and Social Plea", "Institutional Communication" and "Community Development and Participation".`Teleradio-Moldova` new director`s CV summary = Directors = * Feodosie Vidraşcu (1957–1961) * Vladimir Croitoru (1961–1965) * Leonid Culiuc (1965–1967) * Ştefan Lozan (1967–1989) * Adrian Usatîi (1989–1997) * Tudor Olaru (1997–2000) * Iulian Magaleas (2000–2003) * Ion Gonţa (2002–2003) * Artur Efremov (June 2003–March 2004) * Ilie Teleşcu (March 2004–April 2007) * Valentin Todercan (10 April 2007 – 30 December 2009) * Constantin Marin (5 February 2010–November 2014) * Olga Bordeianu (4 June 2015–present) = Editors in chief = * Nicolae Lupan * Valeriu Saharneanu (1991–1994) See also * Union of Journalists of Moldova * Străşeni TV Mast References External links * Teleradio Moldova Official Site * Bordeianu Olga a fost aleasă de către CO în funcţia de preşedinte al TRM Category:Television in Moldova Category:European Broadcasting Union members Category:Multilingual broadcasters Category:Radio stations established in 1928 Category:Television channels and stations established in 1958 Category:Mass media in Chișinău Category:1928 establishments in Romania "