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Arrangement of lines
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Triangles in arrangements
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It is also of interest to study the extremal numbers of triangular cells in arrangements that may not necessarily be simplicial. Any arrangement in the projective plane must have at least n triangles. Every arrangement that has only n triangles must be simple. For Euclidean rather than projective arrangements, the minimum number of triangles is n−2 , by Roberts's triangle theorem. The maximum possible number of triangular faces in a simple arrangement is known to be upper bounded by n(n−1)/3 and lower bounded by n(n−3)/3 ; the lower bound is achieved by certain subsets of the diagonals of a regular 2n -gon. For non-simple arrangements the maximum number of triangles is similar but more tightly bounded. The closely related Kobon triangle problem asks for the maximum number of non-overlapping finite triangles in an arrangement in the Euclidean plane, not counting the unbounded faces that might form triangles in the projective plane. For some but not all values of n , n(n−2)/3 triangles are possible.
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Arrangement of lines
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Multigrids and rhombus tilings
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The dual graph of a simple line arrangement may be represented geometrically as a collection of rhombi, one per vertex of the arrangement, with sides perpendicular to the lines that meet at that vertex. These rhombi may be joined together to form a tiling of a convex polygon in the case of an arrangement of finitely many lines, or of the entire plane in the case of a locally finite arrangement with infinitely many lines. This construction is sometimes known as a Klee diagram, after a publication of Rudolf Klee in 1938 that used this technique. Not every rhombus tiling comes from lines in this way, however.de Bruijn (1981) investigated special cases of this construction in which the line arrangement consists of k sets of equally spaced parallel lines. For two perpendicular families of parallel lines this construction just gives the familiar square tiling of the plane, and for three families of lines at 120-degree angles from each other (themselves forming a trihexagonal tiling) this produces the rhombille tiling. However, for more families of lines this construction produces aperiodic tilings. In particular, for five families of lines at equal angles to each other (or, as de Bruijn calls this arrangement, a pentagrid) it produces a family of tilings that include the rhombic version of the Penrose tilings.
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Arrangement of lines
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Multigrids and rhombus tilings
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There also exist three infinite simplicial arrangements formed from sets of parallel lines. The tetrakis square tiling is an infinite arrangement of lines forming a periodic tiling that resembles a multigrid with four parallel families, but in which two of the families are more widely spaced than the other two, and in which the arrangement is simplicial rather than simple. Its dual is the truncated square tiling. Similarly, the triangular tiling is an infinite simplicial line arrangement with three parallel families, which has as its dual the hexagonal tiling, and the bisected hexagonal tiling is an infinite simplicial line arrangement with six parallel families and two line spacings, dual to the great rhombitrihexagonal tiling. These three examples come from three affine reflection groups in the Euclidean plane, systems of symmetries based on reflection across each line in these arrangements.
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Arrangement of lines
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Algorithms
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Constructing an arrangement means, given as input a list of the lines in the arrangement, computing a representation of the vertices, edges, and cells of the arrangement together with the adjacencies between these objects, for instance as a doubly connected edge list. Due to the zone theorem, arrangements can be constructed efficiently by an incremental algorithm that adds one line at a time to the arrangement of the previously added lines: each new line can be added in time proportional to its zone, resulting in a total construction time of O(n2) . However, the memory requirements of this algorithm are high, so it may be more convenient to report all features of an arrangement by an algorithm that does not keep the entire arrangement in memory at once. This may again be done efficiently, in time O(n2) and space O(n) , by an algorithmic technique known as topological sweeping. Computing a line arrangement exactly requires a numerical precision several times greater than that of the input coordinates: if a line is specified by two points on it, the coordinates of the arrangement vertices may need four times as much precision as these input points. Therefore, computational geometers have also studied algorithms for constructing arrangements efficiently with limited numerical precision.As well, researchers have studied efficient algorithms for constructing smaller portions of an arrangement, such as zones, k -levels, or the set of cells containing a given set of points. The problem of finding the arrangement vertex with the median x -coordinate arises (in a dual form) in robust statistics as the problem of computing the Theil–Sen estimator of a set of points.Marc van Kreveld suggested the algorithmic problem of computing shortest paths between vertices in a line arrangement, where the paths are restricted to follow the edges of the arrangement, more quickly than the quadratic time that it would take to apply a shortest path algorithm to the whole arrangement graph. An approximation algorithm is known, and the problem may be solved efficiently for lines that fall into a small number of parallel families (as is typical for urban street grids), but the general problem remains open.
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Arrangement of lines
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Non-Euclidean line arrangements
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A pseudoline arrangement is a family of curves that share similar topological properties with a line arrangement. These can be defined most simply in the projective plane as simple closed curves any two of which meet in a single crossing point. A pseudoline arrangement is said to be stretchable if it is combinatorially equivalent to a line arrangement. Determining stretchability is a difficult computational task: it is complete for the existential theory of the reals to distinguish stretchable arrangements from non-stretchable ones. Every arrangement of finitely many pseudolines can be extended so that they become lines in a "spread", a type of non-Euclidean incidence geometry in which every two points of a topological plane are connected by a unique line (as in the Euclidean plane) but in which other axioms of Euclidean geometry may not apply.Another type of non-Euclidean geometry is the hyperbolic plane, and arrangements of hyperbolic lines in this geometry have also been studied. Any finite set of lines in the Euclidean plane has a combinatorially equivalent arrangement in the hyperbolic plane (e.g. by enclosing the vertices of the arrangement by a large circle and interpreting the interior of the circle as a Klein model of the hyperbolic plane). However, parallel (non-crossing) pairs of lines are less restricted in hyperbolic line arrangements than in the Euclidean plane: in particular, the relation of being parallel is an equivalence relation for Euclidean lines but not for hyperbolic lines. The intersection graph of the lines in a hyperbolic arrangement can be an arbitrary circle graph. The corresponding concept to hyperbolic line arrangements for pseudolines is a weak pseudoline arrangement, a family of curves having the same topological properties as lines such that any two curves in the family either meet in a single crossing point or have no intersection.
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Small nucleolar RNA SNORA63
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Small nucleolar RNA SNORA63
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In molecular biology, Small nucleolar RNA SNORA63 (E3) belongs to the H/ACA class of snoRNAs, is involved in the processing of eukaryotic pre-rRNA and has regions of complementarity to 18S rRNA. E3 is encoded in introns in the gene for protein synthesis initiation factor 4AII.
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MIS416
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MIS416
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MIS416 is an experimental drug developed by Innate Immunotherapeutics which underwent clinical trials to treat secondary progressive multiple sclerosis. It is derived from the bacteria that causes acne and targets myeloid cells through TLR9 and NOD2. In one of its first rounds of clinical trials, the drug was shown to be "safe and well tolerated", with 80% of secondary-progressive multiple sclerosis patients exhibiting more than 30% improvement in at least one area of their MS status. However, Phase II clinical trials were unable to prove that the drug provided a benefit to patients. It is also being researched as a potential treatment for cancer.
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MIS416
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Development
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MIS416 is a microparticle derived from the cytoskeleton of P. acnes, a species of bacteria present on the skin of most adults that causes acne.MIS416 was originally developed as a vaccine adjuvant, a component of vaccines that helps to activate an immune response against the vaccine target. Bacteria-derived microparticles have several advantages over traditional adjuvants related both to their size and biological properties.Because MIS416 is engulfed by immune cells, it is being investigated as an immunotherapy-based treatment for solid tumors.The drug was used to treat multiple sclerosis under a compassionate use law in New Zealand before clinical trials began. It is administered as an intravenous infusion. In 2017, clinical trials in people with secondary progressive multiple sclerosis failed to meet the primary endpoint of slowed progression of the disease.
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MIS416
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Phase II trial and aftermath
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On June 22, 2017, Innate Immunotherapeutics announced that clinical trials undertaken to evaluate the efficacy of MIS416 in managing secondary progressive multiple sclerosis (SPMS) had "failed to show any clinically meaningful benefit or statistical significance". As a result, the company's stock dropped by 92 percent and crashed on the Australian Securities Exchange.US Congressman Chris Collins, a member of the company's board of directors and 17-percent stock holder, was subsequently indicted on charges of insider trading in connection with the poor clinical trial results. Collins had allegedly obtained word from the company about the results and informed his son, Cameron Collins, who immediately sold his US stock. Cameron allegedly tipped off shareholder Stephen Zarsky, who informed three others, thus preventing a total loss of $768,000 in stocks. Zarsky was indicted together with Collins and his son.
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18-Methylaminocoronaridine
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18-Methylaminocoronaridine
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(–)-18-Methylaminocoronaridine (18-MAC) is a second generation synthetic derivative of ibogaine developed by the research team led by the pharmacologist Stanley D. Glick from the Albany Medical College and the chemist Martin E. Kuehne from the University of Vermont.
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Tyre label
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Tyre label
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The Tyre Label is a mark for motor vehicle tyres. Manufacturers of tyres for cars, light and heavy trucks must specify fuel consumption, wet grip and noise classification of every tyre sold in EU market starting in November 2012.For passenger car, light truck and truck tyres the information must be available in technical promotional literature (leaflets, brochures, etc.), including the manufacturer website. For passenger and light truck tyres, the manufacturers or importers have the choice of either putting a sticker on the tyre tread or a label accompanying each delivery of batch of tyres to the dealer and to the end consumer. The tyre label will use a classification from the best (green category "A") to the worst performance (red category "G").
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Tyre label
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Tyre label
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This initiative results from a regulation by the EU Commission released in 2009. It is part of the Energy Efficiency Action Plan, designed to improve the energy performance of products, buildings and services to reduce energy consumption by 20% until 2020. The EU has already created a system for marking of electrical household appliances such as refrigerators, washing machines and televisions with the intent to better inform the European population about the level of their consumption.
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Tyre label
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Rolling resistance
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Rolling resistance is the main key factor in measuring the energy efficiency of a tyre and has direct influence on the fuel consumption of a vehicle. A set of tyres of the green class "A" compared to a "G" class can reduce fuel consumption by 9% of a passenger car; even more for trucks.
'D' Grading is not used in rolling resistance grading for Passenger Cars and Light Trucks while it is used for Heavy Trucks
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Tyre label
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Wet grip
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As at January 2019, the wet grip tests for passenger car tyres (EU category C1) are specified in a 2011 amendment, Regulation No 228/2011 to the original 2009 Regulation No 1222/2009 "on the labelling of tyres with respect to fuel efficiency and other essential parameters". The wet grip index (WGI) is calculated from the results of two tests specified in the regulations. The first test measures the maximum achievable average deceleration of a vehicle as it slows from 85 ± 2 km/h (52.8 mph) to 20 ± 2 km/h (12.4 mph). The second test (the "skid trailer" test) is usually performed using a tow vehicle and trailer. The trailer is fitted with the tyres being tested and the average maximum braking force that can be applied through the tyres, under a high proportion (60 - 90%) of the tyres' maximum load, is measured as the combination travels at a constant speed of 65 ± 2 km/h.
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Tyre label
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Wet grip
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Results of at least three runs of each test are combined to produce the wet grip index, yielding ratings of A - G (although D and G are not used for passenger cars), where A is the best.
When buying tyres, it is worth noting that the braking distance (in the wet) from the reference speed of 85 km/h, to a standstill, varies by something of the order of 3m from one class to the next.
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Tyre label
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Noise emission
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The driving by noise is quoted as an absolute value in decibel and as a 3 classes sound wave symbol. A continuous sound level above 80 decibel can cause health problems.
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Tyre label
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Tyres that must be labeled
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The Tyre Label will generally apply to Car and SUV tyres Van tyres Truck tyres Exceptions from labelling Tyres for cars made before 1 October 1990.
Re-treaded tyres Motorcycle tyres Racing/sports car tyres Studded tyres Spare tyres Vintage car tyres Professional off-road tyres
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Tyre label
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Tax on noisy tyres
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Tyres that make too much roadway noise as determined by the EU, will have an extra tax/penalty imposed on them from November 2012.
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Tyre label
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Reporting requirements
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Tyre manufacturer For passenger car, light truck and truck tyres the information must be available in the technical promotional literature (leaflets, brochures, etc.), including the manufacturer website For passenger and light truck tyres, the manufacturers or importers have the choice of either putting a sticker on the tyre tread or a label accompanying each delivery of batch of tyres to the dealer and to the end consumer Tyre dealer Must ensure tyres which are visible to consumers at the point of sale carry a sticker or have a label in their close proximity which is shown to the end user before the sale Must give the information during the purchase process when the tyres offered for sale are not visible to the end-user Must give the information on or with the bill Car manufacturer Must declare the tyre wet grip and fuel efficiency class and external rolling noise measured value of the tyre type(s) that are offered in option, when different from those fitted normally on the basic vehicle.
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Tyre label
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Reporting requirements
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As soon as the customer is given a choice either in the size / type of tyres fitted on the basic rim or a choice of rim and tyre size, the labelling information must be provided before sale.
There might be no obligation to provide information only in those cases where there is a choice of rim with tyres types and sizes that are strictly identical to those which are sold automatically with the new vehicle.
EU-Commission Detailed information about contents and design of the label.
Each EU member state is to organise monitoring and impose penalties in cases of non-compliance.
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Tyre label
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Critical View
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The new label is designed to show information regarding 3 criteria, however there are many other important performance factors to consider including: Resistance to aquaplaning Driving stability Handling and steering precision on wet and dry roads Durability Braking performance on dry roads Capabilities in winter conditionsPublished tyre tests take these performance factors into account and are a source of information regarding the total performance of a tyre.
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Tyre label
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Critical View
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Tyres that make too much noise as determined by the EU, will have an extra tax/penalty imposed on them from November 2012.
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Tyre label
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Driving Proviso
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Actual fuel savings and road safety also depend heavily on the behaviour of drivers when using their cars, and in particular the following: Eco-driving can significantly reduce fuel consumption Tyre pressure should be regularly checked to optimise wet grip and fuel efficiency performance Stopping distances should always be strictly respected
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Trompo
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Trompo
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A trompo is a top which is spun by winding a length of string around the body, and launching it so that lands spinning on its point. If the string is attached to a stick the rotation can be maintained by whipping the side of the body. The string may also be wound around the point while the trompo is spinning in order to control its position or even lift the spinning top to another surface.
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Trompo
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Etymology
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These toys are popular in Latin America where the name trompo emerged, but there are many different local names. In Spain, these toys may be called trompo or peonza, perinola, and pirinola. In the Philippines, they are called trumpo or turumpo, while in Portugal they are called pião.
In India it is called Bugari (Kannada); children make these tops by nailing wood and spin them with twisted jute rope. In Japan, similar tops are known as koma, with most cities having a particular design.
In Germany a Peitschenkreisel may also be called Doppisch, Dildop, Pindopp, Dilledopp, Triesel or Tanzknopf (roughly dancing top) In Morocco it is called Trombia, and it is often made out of wood and painted in a reddish brown color.
In Dutch it is called "priktol" (see https://nl.wikipedia.org/wiki/Priktol). A "tol" is a top. An other type of top is the "zweeptol". A "zweep" is a whip. (see https://nl.wikipedia.org/wiki/Kinderspelen and find "zweep" on that page)
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Trompo
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History
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There is historical evidence suggesting the existence of trompos as early as 4000 BCE, and trompos have been found on the bank of the Euphrates river, likely belonging to an ancient civilization. There is also evidence that members of the ancient Greek and Roman civilizations used trompos as well.
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Trompo
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Description of motion
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The gyroscopic effect allows the trompo to spin over its point until the force of gravity ends up at an angle with respect to the top's axis of rotation, causing a variation in the location of the center of gravity as the trompo undergoes precession (where the axis of rotation of the trompo moves in a circular path). The fall of the top is directly proportional to the angle between the direction of gravity on the trompo and the top's axis of rotation. The fall is also directly proportional to the magnitude of the force of gravity and is inversely proportional to the trompo's angular velocity.
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Trompo
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Description of motion
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As air resistance and friction with the ground begin to slow the trompo's spin, its center of gravity begins to destabilize and the top's bottom point begins to trace a circular path with the ground. Soon the trompo becomes fully unbalanced and it falls to the ground, rolling until it comes to rest.
This general motion is largely shared among many trompo variants, but differences in several design parameters (such as the mass distribution, friction between the bottom point and the ground, and the spinning method) can still lead to significant variation in the aforementioned variables.
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Trompo
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Form
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The trompo's form has varied enormously throughout history. Though trompos have traditionally been cone-shaped, there are also diverse variations in trompo form across regions. However, despite these regional differences in design, all trompos are constructed to be capable of employing the gyroscopic effect.
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Trompo
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Form
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Trompos generally have an approximately pear-shaped body and are usually made of a hard wood such as hawthorn, oak or beech, although new resins and strong plastic materials have also been used. Clay trompos have also been found from ancient civilizations near the Euphrates river. Whipping tops often have a more cylindrical shape to provide a bigger surface to be struck by the whip.
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Trompo
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Form
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A trompo has a button-shaped on top, usually bigger than the tip on which it spins, and it is generally made of the same material as the rest of the body.
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Trompo
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Form
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The base of a trompo is a stud or spike which may have a groove or roller-bearing to facilitate lifting the spinning trompo with a whip or string without imposing much friction on the body.The trompo surface may be painted or decorated, and some versions incorporate synthetic sound devices. The small size diameter and low mass of most trompos means that mechanical whistles would cause excessive drag (physics) and reduce their spinning time.
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Trompo
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Form
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The Philippine trumpo differs in the tip, which is straight and pointed. It usually looks like a nail embedded in a wooden spheroid.
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Trompo
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Play
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Playing with a trompo consists of throwing the top and having it spin on the floor. Due to its shape, a trompo spins on its axis and swirls around its conic tip which is usually made of iron or steel. A trompo uses a string wrapped around it to get the necessary spin needed. The player must roll the cord around the trompo from the metallic tip up. The user must then tie the string in a knot on the button-shaped tip before releasing it. When rolling the cord around the trompo, the cord must be tightly attached to it. The technique for throwing a trompo varies. One end of the cord must be rolled around the player's fingers and with the same hand the trompo must be held with the metallic tip facing upwards.
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Trompo
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Play
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Championships are held in different Latin American countries, especially in Mexico, Colombia, Peru, Cuba, Nicaragua, and Puerto Rico where it is very popular among children of the middle and lower classes.
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Trompo
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Play
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In Mexico most trompos sold are made of plastic, with a metal tip, and sometimes they are made of wood. There is a popular game called picotazos, where the main goal is to destroy the opponents' trompo. Another game is where a circle is drawn on the ground and a coin is placed in the middle, and the goal here is to strike the coin.
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Trompo
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Play
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In Puerto Rico, trompos are sometimes played similarly to certain marble games, with trompos being placed in a circle drawn on the ground. The goal of this variant is to knock the trompos out of the circle. Failure to spin or spinning in the circle causes your trompo to be placed in the circle, and another person has a turn to spin. Trompos in Puerto Rico and Chile are frequently modified to have a sharper point.
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Trompo
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Play
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José Miguel Agrelot, a Puerto Rican comedian, hosted a long-standing television program, Encabulla y Vuelve y Tira, whose name described the action of throwing and spinning a trompo. One of his comedic characterizations, mischievous boy Torito Fuertes, was a one-time sponsor of a line of trompos.
The Filipino trumpo is basically played in the same manner, except that a knot is not tied into the tip before throwing it for the spin.
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Split tunneling
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Split tunneling
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Split tunneling is a computer networking concept which allows a user to access dissimilar security domains like a public network (e.g., the Internet) and a local area network or wide area network at the same time, using the same or different network connections. This connection state is usually facilitated through the simultaneous use of a LAN network interface controller (NIC), radio NIC, Wireless LAN (WLAN) NIC, and VPN client software application without the benefit of an access control.
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Split tunneling
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Split tunneling
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For example, suppose a user utilizes a remote access VPN software client connecting to a campus network using a hotel wireless network. The user with split tunneling enabled is able to connect to file servers, database servers, mail servers and other servers on the corporate network through the VPN connection. When the user connects to Internet resources (websites, FTP sites, etc.), the connection request goes directly out the gateway provided by the hotel network. However, not every VPN allows split tunneling. Some VPNs with split tunneling include Private Internet Access (PIA), ExpressVPN, and Surfshark.Split tunneling is sometimes categorized based on how it is configured. A split tunnel configured to only tunnel traffic destined to a specific set of destinations is called a split-include tunnel. When configured to accept all traffic except traffic destined to a specific set of destinations, it is called a split-exclude tunnel.
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Split tunneling
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Advantages
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One advantage of using split tunneling is that it alleviates bottlenecks and conserves bandwidth as Internet traffic does not have to pass through the VPN server.
Another advantage is in the case where a user works at a supplier or partner site and needs access to network resources on both networks. Split tunneling prevents the user from having to continually connect and disconnect.
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Split tunneling
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Disadvantages
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A disadvantage is that when split tunneling is enabled, users bypass gateway level security that might be in place within the company infrastructure. For example, if web or content filtering is in place, this is something usually controlled at a gateway level, not the client PC.
ISPs that implement DNS hijacking break name resolution of private addresses with a split tunnel.
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Split tunneling
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Variants and related technology
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Inverse split tunneling A variant of this split tunneling is called "inverse" split tunneling. By default all datagrams enter the tunnel except those destination IPs explicitly allowed by VPN gateway. The criteria for allowing datagrams to exit the local network interface (outside the tunnel) may vary from vendor to vendor (i.e.: port, service, etc.) This keeps control of network gateways to a centralized policy device such as the VPN terminator. This can be augmented by endpoint policy enforcement technologies such as an interface firewall on the endpoint device's network interface driver, group policy object or anti-malware agent. This is related in many ways to network access control (NAC).
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Split tunneling
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Variants and related technology
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Dynamic split tunneling A form of split-tunneling that derives the IP addresses to include/exclude at runtime-based on a list of hostname rules/policies. [Dynamic Split Tunneling] (DST) IPv6 dual-stack networking Internal IPv6 content can be hosted and presented to sites via a unique local address range at the VPN level, while external IPv4 & IPv6 content can be accessed via site routers.
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Sleeve coupling
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Sleeve coupling
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A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. In a more general context, a coupling can also be a mechanical device that serves to connect the ends of adjacent parts or objects. Couplings do not normally allow disconnection of shafts during operation, however there are torque-limiting couplings which can slip or disconnect when some torque limit is exceeded. Selection, installation and maintenance of couplings can lead to reduced maintenance time and maintenance cost.
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Sleeve coupling
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Uses
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Shaft couplings are used in machinery for several purposes. A primary function is to transfer power from one end to another end (ex: motor transfer power to pump through coupling).
Other common uses: To alter the vibration characteristics of rotating units To connect the driving and the driven part To introduce protection To reduce the transmission of shock loads from one shaft to another To slip when overload occurs
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Sleeve coupling
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Types
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Beam A beam coupling, also known as helical coupling, is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset and even axial motion, of one shaft relative to the other. This design utilizes a single piece of material and becomes flexible by removal of material along a spiral path resulting in a curved flexible beam of helical shape. Since it is made from a single piece of material, the beam style coupling does not exhibit the backlash found in some multi-piece couplings. Another advantage of being an all machined coupling is the possibility to incorporate features into the final product while still keep the single piece integrity.
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Sleeve coupling
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Types
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Changes to the lead of the helical beam provide changes to misalignment capabilities as well as other performance characteristics such as torque capacity and torsional stiffness. It is even possible to have multiple starts within the same helix.
The material used to manufacture the beam coupling also affects its performance and suitability for specific applications such as food, medical and aerospace. Materials are typically aluminum alloy and stainless steel, but they can also be made in acetal, maraging steel and titanium. The most common applications are attaching rotary encoders to shafts and motion control for robotics.
Beam couplings can be known by various names depending upon industry. These names include flexible coupling, flexible beam coupling, flexible shaft coupling, flexure, helical coupling, and shaft coupling.
The primary benefit to using a flexible beam coupling to join two rotating shafts is to reducing vibration and reaction loads which in turn will reduce overall wear and tear on machinery and prolong equipment life.
Bush pin flange Bush pin flange coupling is used for slightly imperfect alignment of the two shafts.
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Sleeve coupling
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Types
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This is modified form of the protected type flange coupling. This type of coupling has pins and it works with coupling bolts. The rubber or leather bushes are used over the pins. The coupling has two halves dissimilar in construction. The pins are rigidly fastened by nuts to one of the flange and kept loose on the other flange. This coupling is used to connect shafts which have a small parallel misalignment, angular misalignment or axial misalignment. In this coupling the rubber bushing absorbs shocks and vibration during its operations. This type of coupling is mostly used to couple electric motors and machines.
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Sleeve coupling
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Types
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Constant velocity There are various types of constant-velocity (CV) couplings: Rzeppa joint, Double cardan joint, and Thompson coupling.
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Sleeve coupling
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Types
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Clamp or split-muff In this coupling, the muff or sleeve is made into two halves parts of the cast iron and they are joined by means of mild steel studs or bolts. The advantages of this coupling is that assembling or disassembling of the coupling is possible without changing the position of the shaft. This coupling is used for heavy power transmission at moderate speed.
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Sleeve coupling
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Types
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Diaphragm Diaphragm couplings transmit torque from the outside diameter of a flexible plate to the inside diameter, across the spool or spacer piece, and then from inside to outside diameter. The deforming of a plate or series of plates from I.D. to O.D accomplishes the misalignment.
Disc Disc couplings transmit torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack. Misalignment is accomplished by deforming of the material between the bolts.
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Sleeve coupling
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Types
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Elastic An elastic coupling transmits torque or other load by means of an elastic component. One example is the coupling used to join a windsurfing rig (sail, mast, and components) to the sailboard. In windsurfing terminology it is usually called a "universal joint", but modern designs are usually based on a strong flexible material, and better technically described as an elastic coupling. They can be tendon or hourglass-shaped, and are constructed of a strong and durable elastic material. In this application, the coupling does not transmit torque, but instead transmits sail-power to the board, creating thrust (some portion of sail-power is also transmitted through the rider's body).
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Sleeve coupling
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Types
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Flexible Flexible couplings are usually used to transmit torque from one shaft to another when the two shafts are slightly misaligned. They can accommodate varying degrees of misalignment up to 1.5° and some parallel misalignment. They can also be used for vibration damping or noise reduction. In rotating shaft applications a flexible coupling can protect the driving and driven shaft components (such as bearings) from the harmful effects of conditions such as misaligned shafts, vibration, shock loads, and thermal expansion of the shafts or other components.
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Sleeve coupling
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Types
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At first, flexible couplings separate into two essential groups, metallic and elastomeric.
Metallic types utilize freely fitted parts that roll or slide against one another or, on the other hand, non-moving parts that bend to take up misalignment.
Elastomeric types, then again, gain flexibility from resilient, non-moving, elastic or plastic elements transmitting torque between metallic hubs.
Fluid Gear A gear coupling is a mechanical device for transmitting torque between two shafts that are not collinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle.
Each joint consists of a 1:1 gear ratio internal/external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth.
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Sleeve coupling
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Types
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Gear couplings and universal joints are used in similar applications. Gear couplings have higher torque densities than universal joints designed to fit a given space while universal joints induce lower vibrations. The limit on torque density in universal joints is due to the limited cross sections of the cross and yoke. The gear teeth in a gear coupling have high backlash to allow for angular misalignment. The excess backlash can contribute to vibration.Gear couplings are generally limited to angular misalignments, i.e., the angle of the spindle relative to the axes of the connected shafts, of 4–5°. Universal joints are capable of higher misalignments.
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Sleeve coupling
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Types
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Single joint gear couplings are also used to connect two nominally coaxial shafts. In this application the device is called a gear-type flexible, or flexible coupling. The single joint allows for minor misalignments such as installation errors and changes in shaft alignment due to operating conditions. These types of gear couplings are generally limited to angular misalignments of 1/4–1/2°.
Geislinger Giubo Grid A grid coupling is composed of two shaft hubs, a metallic grid spring, and a split cover kit. Torque is transmitted between the two coupling shaft hubs through the metallic grid spring element.
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Sleeve coupling
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Types
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Like metallic gear and disc couplings, grid couplings have a high torque density. A benefit of grid couplings, over either gear or disc couplings, is the ability their grid coupling spring elements have to absorb and spread peak load impact energy over time. This reduces the magnitude of peak loads and offers some vibration dampening capability. A negative of the grid coupling design is that it generally is very limited in its ability to accommodate the misalignment.
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Sleeve coupling
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Types
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Highly flexible Highly flexible couplings are installed when resonance or torsional vibration might be an issue, since they are designed to eliminate torsional vibration problems and to balance out shock impacts.
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Sleeve coupling
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Types
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They are used in installations where the systems require a high level of torsional flexibility and misalignment capacity. This type of coupling provides an effective damping of torsional vibrations, and high displacement capacity, which protects the drive. The design of the highly flexible elastic couplings makes assembly easier. These couplings also compensate shaft displacements (radial, axial and angular) and the torque is transmitted in shear. Depending on the size and stiffness of the coupling, the flexible part may be single- or multi-row.
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Sleeve coupling
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Types
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Hirth joints Hirth joints use tapered teeth on two shaft ends meshed together to transmit torque.
Hydrodynamic Jaw Jaw coupling is also known as spider or Lovejoy coupling.
Magnetic A magnetic coupling uses magnetic forces to transmit the power from one shaft to another without any contact. This allows for full medium separation. It can provide the ability to hermetically separate two areas whilst continuing to transmit mechanical power from one to the other making these couplings ideal for applications where prevention of cross-contamination is essential.
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Sleeve coupling
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Types
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Oldham An Oldham coupling has three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove. The tongue and groove on one side is perpendicular to the tongue and groove on the other. The middle disc rotates around its center at the same speed as the input and output shafts. Its center traces a circular orbit, twice per rotation, around the midpoint between input and output shafts. Often springs are used to reduce backlash of the mechanism. An advantage to this type of coupling, as compared to two universal joints, is its compact size. The coupler is named for John Oldham who invented it in Ireland, in 1821, to solve a problem in a paddle steamer design.
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Sleeve coupling
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Types
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Rag joint Rag joints are commonly used on automotive steering linkages and drive trains. When used on a drive train they are sometimes known as giubos.
Rigid Rigid couplings are used when precise shaft alignment is required; any shaft misalignment will affect the coupling's performance as well as its life span, because rigid couplings do not have the ability to compensate for misalignment. Due to this, their application is limited, and they're typically used in applications involving vertical drivers.
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Sleeve coupling
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Types
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Clamped or compression rigid couplings come in two parts and fit together around the shafts to form a sleeve. They offer more flexibility than sleeved models, and can be used on shafts that are fixed in place. They generally are large enough so that screws can pass all the way through the coupling and into the second half to ensure a secure hold. Flanged rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts can then be installed in the flanges to hold them together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined.
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Sleeve coupling
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Types
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Schmidt Sleeve, box, or muff A sleeve coupling consists of a pipe whose bore is finished to the required tolerance based on the shaft size. Based on the usage of the coupling a keyway is made in the bore in order to transmit the torque by means of the key. Two threaded holes are provided in order to lock the coupling in position.
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Sleeve coupling
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Types
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Sleeve couplings are also known as box couplings. In this case shaft ends are coupled together and abutted against each other which are enveloped by muff or sleeve.
A gib head sunk keys hold the two shafts and sleeve together (this is the simplest type of the coupling) It is made from the cast iron and very simple to design and manufacture. It consists of a hollow pipe whose inner diameter is same as diameter of the shafts.
The hollow pipe is fitted over a two or more ends of the shafts with the help of the taper sunk key. A key and sleeve are useful to transmit power from one shaft to another shaft.
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Sleeve coupling
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Types
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Tapered shaft lock A tapered lock is a form of keyless shaft locking device that does not require any material to be removed from the shaft. The basic idea is similar to a clamp coupling but the moment of rotation is closer to the center of the shaft. An alternative coupling device to the traditional parallel key, the tapered lock removes the possibility of play due to worn keyways. It is more robust than using a key because maintenance only requires one tool and the self-centering balanced rotation means it lasts longer than a keyed joint would, but the downside is that it costs more.
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Sleeve coupling
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Types
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Twin spring A flexible coupling made from two counter-wound springs with a ball bearing in the center, which allows torque transfer from input to output shaft. Requires no lubrication to consistently run as it has no internal components.
Universal joint
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Sleeve coupling
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Maintenance and failure
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Coupling maintenance requires a regularly scheduled inspection of each coupling. It consists of: Performing visual inspections Checking for signs of wear or fatigue Cleaning couplings regularly Checking and changing lubricant regularly if the coupling is lubricated. This maintenance is required annually for most couplings and more frequently for couplings in adverse environments or in demanding operating conditions.
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Sleeve coupling
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Maintenance and failure
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Documenting the maintenance performed on each coupling, along with the date.Even with proper maintenance, however, couplings can fail. Underlying reasons for failure, other than maintenance, include: Improper installation Poor coupling selection Operation beyond design capabilities.External signs that indicate potential coupling failure include: Abnormal noise, such as screeching, squealing or chattering Excessive vibration or wobble Failed seals indicated by lubricant leakage or contamination.
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Sleeve coupling
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Balance
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Couplings are normally balanced at the factory prior to being shipped, but they occasionally go out of balance in operation. Balancing can be difficult and expensive, and is normally done only when operating tolerances are such that the effort and the expense are justified. The amount of coupling unbalance that can be tolerated by any system is dictated by the characteristics of the specific connected machines and can be determined by detailed analysis or experience.
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Fowkes Formation
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Fowkes Formation
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The Fowkes Formation is a geologic formation in Wyoming. It preserves fossils dating back to the Paleogene period.
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Arf invariant of a knot
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Arf invariant of a knot
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In the mathematical field of knot theory, the Arf invariant of a knot, named after Cahit Arf, is a knot invariant obtained from a quadratic form associated to a Seifert surface. If F is a Seifert surface of a knot, then the homology group H1(F, Z/2Z) has a quadratic form whose value is the number of full twists mod 2 in a neighborhood of an embedded circle representing an element of the homology group. The Arf invariant of this quadratic form is the Arf invariant of the knot.
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Arf invariant of a knot
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Definition by Seifert matrix
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Let V=vi,j be a Seifert matrix of the knot, constructed from a set of curves on a Seifert surface of genus g which represent a basis for the first homology of the surface. This means that V is a 2g × 2g matrix with the property that V − VT is a symplectic matrix. The Arf invariant of the knot is the residue of mod 2).
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Arf invariant of a knot
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Definition by Seifert matrix
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Specifically, if {ai,bi},i=1…g , is a symplectic basis for the intersection form on the Seifert surface, then Arf lk lk mod 2).
where lk is the link number and a+ denotes the positive pushoff of a.
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Arf invariant of a knot
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Definition by pass equivalence
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This approach to the Arf invariant is due to Louis Kauffman. We define two knots to be pass equivalent if they are related by a finite sequence of pass-moves.Every knot is pass-equivalent to either the unknot or the trefoil; these two knots are not pass-equivalent and additionally, the right- and left-handed trefoils are pass-equivalent.Now we can define the Arf invariant of a knot to be 0 if it is pass-equivalent to the unknot, or 1 if it is pass-equivalent to the trefoil. This definition is equivalent to the one above.
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Arf invariant of a knot
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Definition by partition function
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Vaughan Jones showed that the Arf invariant can be obtained by taking the partition function of a signed planar graph associated to a knot diagram.
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Arf invariant of a knot
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Definition by Alexander polynomial
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This approach to the Arf invariant is by Raymond Robertello. Let Δ(t)=c0+c1t+⋯+cntn+⋯+c0t2n be the Alexander polynomial of the knot. Then the Arf invariant is the residue of cn−1+cn−3+⋯+cr modulo 2, where r = 0 for n odd, and r = 1 for n even.
Kunio Murasugi proved that the Arf invariant is zero if and only if Δ(−1) ≡ ±1 modulo 8.
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Arf invariant of a knot
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Arf as knot concordance invariant
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From the Fox-Milnor criterion, which tells us that the Alexander polynomial of a slice knot K⊂S3 factors as Δ(t)=p(t)p(t−1) for some polynomial p(t) with integer coefficients, we know that the determinant |Δ(−1)| of a slice knot is a square integer. As |Δ(−1)| is an odd integer, it has to be congruent to 1 modulo 8. Combined with Murasugi's result this shows that the Arf invariant of a slice knot vanishes.
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Summer term
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Summer term
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Summer term is the summer academic term at many British schools and universities and elsewhere in the world.
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Summer term
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Summer term
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In the UK, 'Summer term' runs from the Easter holiday until the end of the academic year in June or July, and so corresponds to the Easter term at Cambridge University, and Trinity term at Oxford, and some other places. 'Summer term' is defined in some UK statutory instruments, such as the Education (Assessment Regulations) (Foundation to Key Stage 3) Order (Northern Ireland) 2007, which says: "summer term" means the period commencing immediately after the Easter holiday and ending with the school year.
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Summer term
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Summer term
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The Education (National Curriculum) (Key Stage 1 Assessment Arrangements) (England) Order 2004 says more simply: "summer term" means the final term of the school year.
Covering the possibility of six-term academic years, the School Finance (England) Regulations 2008 say "summer term" means the third term of the school year where a school has three terms, or the fifth and sixth terms where a school has six terms
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Materion
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Materion
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Materion Corp. is a multinational company specializing in high-performance engineered materials. Among their products are precious and non-precious metals, inorganic chemicals, specialty coatings, beryllium, specialty engineered beryllium, beryllium copper alloys, ceramics, and engineered clad and plated metal systems.
The company's engineered materials are used in the telecommunications, consumer electronics, automotive medical, industrial components, aerospace, defense, and optical coating industries.
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Materion
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History
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Beginning in the 1940s, Brush Wellman Inc. produced large amounts of beryllium for the United States government.Brush Engineered Materials Inc. changed its name to Materion Corporation on March 8, 2011, and now trades under the symbol MTRN.In March, 2017 Jugal K. Vijayvargiya was appointed president and chief executive officer of Materion Corporation, replacing Richard J. Hipple, who had served in that position for 11 years. Vijayvargiya was also named a director of the corporation. A graduate of the Ohio State University, Vijayvargiya spent 26 years at Delphi Corporation in a variety of management positions. Hipple will become executive chairman.
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HP-15C
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HP-15C
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The HP-15C is a high-end scientific programmable calculator of Hewlett-Packard's Voyager series produced between 1982 and 1989.
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HP-15C
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Models
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HP-15C The HP-15C is a high-end scientific pocket calculator with a root-solver and numerical integration. A member of Hewlett-Packard Voyager series of programmable calculators, it was produced between 1982 and 1989. The calculator is able to handle complex numbers and matrix operations. Although out of production, its popularity has led to high prices on the used market. The HP-15C was a replacement for the HP-34C. The 15C used CMOS technology for its processor, resulting in very low power consumption.
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HP-15C
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Models
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HP 15C Limited Edition After showing a prototype labelled "HP 15c+" at the HHC 2010, HP announced the HP 15C Limited Edition (NW250AA) on 1 September 2011. It is based on a flashable controller utilizing the same ARM7TDMI core already used in the 2008 revision of the 12C but in a different package, an Atmel AT91SAM7L128-AU running an emulator written by Cyrille de Brébisson to execute the old HP Nut code much faster than on the original hardware. The calculator was released alongside the HP 12c 30th Anniversary Edition. This model is powered by two CR2032 batteries, and can easily be differentiated from the original model by the "Limited Edition" script below the company logo as well as the black text on brushed metal back label, as opposed to the white text on black of the original. The power consumption of the processor is greater than that of the original HP-15C, as HP did not use the same technology in any of the future models.
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HP-15C
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Models
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HP 15C Collector’s Edition In May 2023, a Collector's Edition was announced and was released in July 2023 by the HP Development Company, L.P.'s licensees Moravia Consulting spol. s r.o. and Royal Consumer Information Products, Inc. It supports up to 672 steps for programs and up to 99 registers. The initial firmware has received fixes for the known bugs shown below and others; it is emulated on the same CPU as the 2015 and 2022 variants of the HP-12C, the Microchip ATSAM4LC2CA (ARM Cortex-M4). The calculator is also powered by two CR2032 batteries.
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HP-15C
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Models
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The test menu (Off, g+↵ Enter+ON) officially offers three choices. A fourth choice (4) is undocumented and permits to enter two hidden modes: "15.2" (more memory, but with some limitations like 8×8 inversion matrices, the three-digit step number display) and "16" (emulating a HP-16C).
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HP-15C
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Bugs and problems
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HP-15C: CHS stack lift bug (and fix) The non-responsive reset procedure documented in the 15C manual had the side effect of rotating the X register by 22 bits which could then be used to perform synthetic programming.HP-15C Limited Edition: One of the more significant bugs in the released firmware version (dated 2011-04-15 in the self-test) is that PSE only works once in a program and subsequently blanks the display until the program stops or is stopped. Downgrading the firmware resolves the PSE bug, however, other bugs will also be reintroduced.
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HP-15C
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Bugs and problems
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The original HP-15C self-test keystrokes do not work with the HP-15C LE and can corrupt memory contents. Although a new functional self-test procedure was added, the original manual did not document it.hp 15C Collector's Edition: No known bugs in the officially supported "15" mode yet; the bugs above and others have been fixed in the firmware, or in the case of the nonfunctional self-test procedure, instructions to switch to the new self-test in the accompanying documentation. There are a number of bugs and shortcomings in the undocumented "15.2" and "16" modes.
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HP-15C
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Legacy
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Emulators An official PC emulator for the 15C is available as freeware from Hewlett-Packard. Another version is commercially available for Android and iOS devices.
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HP-15C
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Legacy
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Clones On 6 February 2012, SwissMicros (previously known as RPN-Calc) introduced a miniature clone named DM-15CC approximating the size of an ID-1 credit card (88 mm × 59 mm × 7 mm). It closely emulates the functionality of the original HP-15C by running the original ROM image in an emulator on an ARM Cortex-M0-based NXP LPC1114 processor. Newer DM15 models feature a better keyboard and more RAM (LPC1115). With a modified firmware (M80 and M1B), the additional memory allows for up to 129 or even 230 registers and up to 1603 or 896 programs steps. A DM15 Silver Edition in a titanium case is available as well in three color variants (metal, brown, blue). Deviating from the original, these calculators feature a dot-matrix display, switchable fonts and clock speeds, and, based on a Silicon Labs CP2102 converter chip, they come with a USB (Mini-B) serial interface to exchange data with a PC etc. for backup purposes and possibly to communicate with applications (like PC-based HP-15C emulators) or to update the firmware. In September 2015, SwissMicros introduced the DM15L, a version of the calculator about the same size as the original HP-15C. It still comes with a USB Mini-B connector. Powering via USB is not supported.
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1,2,4-Trioxane
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1,2,4-Trioxane
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1,2,4-Trioxane is one of the isomers of trioxane. It has the molecular formula C3H6O3 and consists of a six membered ring with three carbon atoms and three oxygen atoms. The two adjacent oxygen atoms form a peroxide functional group and the other forms an ether functional group. It is like a cyclic acetal but with one of the oxygen atoms in the acetal group being replaced by a peroxide group.
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1,2,4-Trioxane
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1,2,4-Trioxane
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1,2,4-Trioxane itself has not been isolated or characterized, but rather only studied computationally. However, it constitutes an important structural element of some more complex organic compounds. The natural compound artemisinin, isolated from the sweet wormwood plant (Artemisia annua), and some semi-synthetic derivatives are important antimalarial drugs containing the 1,2,4-trioxane ring. Completely synthetic analogs containing the 1,2,4-trioxane ring are important potential improvements over the naturally derived artemisinins. The peroxide group in the 1,2,4-trioxane core of artemisinin is cleaved in the presence of the malaria parasite leading to reactive oxygen radicals that are damaging to the parasite.
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Radiopaedia
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Radiopaedia
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Radiopaedia is a wiki-based international collaborative educational web resource containing a radiology encyclopedia and imaging case repository. It is currently the largest freely available radiology related resource in the world with more than 50,000 patient cases and over 16,000 reference articles on radiology-related topics. The open edit nature of articles allows radiologists, radiology trainees, radiographers, sonographers, and other healthcare professionals interested in medical imaging to refine most content through time. An editorial board peer reviews all contributions.
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Radiopaedia
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Background
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Radiopaedia was started as a past-time project to store radiology notes and cases online by the Australian neuroradiologist Associate Professor Frank Gaillard in December 2005, while he was a radiology resident. He later became passionate in building the website and decided to release it on the web, advocating free dissemination of knowledge.The domain name for radiopaedia.org was registered on 11 January 2007.The Radiopaedia.org platform and text content are owned by Radiopaedia Australia Pty Ltd, a privately held company for which Gaillard is the chief executive officer. One of its investors is Investling and its revenue derives from ads, courses, and paid supporters. For image content, contributors reserve some rights and license the content to Radiopaedia and its users under a Creative Commons license.The site was initially programmed using MediaWiki, the same program platform as Wikipedia, but now runs on a bespoke code written by TrikeApps.In 2010, almost all of the article and image collection from radswiki (a similar wiki-based radiology educational site) was donated to Radiopaedia.Its article content is currently limited to English.
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Radiopaedia
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Purpose
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Radiopaedia’s mission is "to create the best radiology reference the world has ever seen and to make it available for free, for ever, for all." Its intention is to benefit the radiology community and wider society and it relies on benevolent collaborations from radiologists and others with an interest in medical imaging.
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Radiopaedia
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Purpose
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Similarly to Wikipedia, registered users of the site are allowed to freely add and edit the majority of the content. This allows content to be progressively upgraded over years and for radiologists and society, in general, to continuously refine article content through time. The site also allows registered users to maintain their own personal case library of teaching cases. Rather than individually publishing articles, users are encouraged to integrate content with links to cases and journal articles and collaboratively refine content. In an attempt to reduce vandalism and to peer-review content, an editorial board moderates changes to ensure that the presented material is as accurate and relevant as possible. As with similar open edit sites, unreliability of content has been a concern; however, despite its open edit nature, it is ranked relatively high among user reviews.A survey done in 2020 shows that 90% of on-call radiology trainees in the United States are using Radiopedia and StatDx as the first and second line options to help them during their work. Educational benefit was also demonstrated when integrating Radiopedia-based training in medical curriculum.
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Radiopaedia
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Sub sites
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Radiopaedia also maintains several other educational subsites which include Radiology Signs - a tumblr feed with selected signs Radiology Channel - a YouTube channel containing educational videos
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