| Mach effect | The appearance of a light or dark line on a radiograph where there is a concave or convex interface in the subject, a physiological optical form of edge enhancement. See: Mach's band. (05 Mar 2000) |
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| Mach line | The apparent line of contrasting density bordering a soft tissue shadow on a radiograph; it is an optical illusion constructed by the observer's retina. (05 Mar 2000) |
| Mach number | A number representing the ratio between the speed of an object moving through a fluid medium, such as air, and the speed of sound in the same medium. (05 Mar 2000) |
| Mach Zehnder system | Interferometric system in which the original light beam is divided by a semi transparent mirror: object and reference beams pass through separate optical systems and are recombined by a second semi transparent mirror. Interference fringes are displaced if the optical path difference for the reference beam is greater and this can be compensated with a wedge shaped auxiliary object. The position of the wedge allows the phase retardation of the object to be measured. The Mach Zehnder system was used in a microscope designed by Leitz. (18 Nov 1997) |
| Mach's band | A relatively bright or dark band perceived in a zone where the luminance increases or decreases rapidly. (05 Mar 2000) |
| Mach, Ernst | <person> Austrian scientist, 1838-1916. See: Mach's band, Mach number. (05 Mar 2000) |
| mach-zender interferometer | <radiobiology> This is a variation of the Michelson interferometer which is used mainly in measuring the spatial variation in the refractive index of a gas (or plasma). A Mach-Zender interferometer uses two semi-transparent mirrors and two fully reflective mirrors located at the corners of a rectangle. The incoming beam is split in two at the first semi-transparent mirror, and the two halves of the beam travel along separate paths around the edge of the rectangle, meeting at the opposite corner. Typically one beam is a control, and the other travels through the system under study. The two beams meet at the second semi-transparent mirror, after which they are mixed together and interfere. (09 Oct 1997) |
| Machado-Guerreiro test | A complement-fixation test for infection with Trypanosoma cruzi. (05 Mar 2000) |
| Machado-Joseph | A rare form of hereditary ataxia, characterised by onset in early adult life of progressive, spinocerebellar and extrapyramidal disease with external ophthalmoplegia, rigidity dystonia symptoms, and, often, peripheral amyotrophy; found predominantly in people of Azorean ancestry; autosomal dominant inheritance. Synonym: Azorean disease, Portuguese-Azorean disease. Origin: Surnames of two families studied in major descriptions of the disease. (05 Mar 2000) |
| machado-joseph disease | A progressive degenerative disease of the central nervous system occurring in portuguese-azorean families, having a variety of forms and inherited as an autosomal dominant trait. There are four major types: type I: with pyramidal and extrapyramidal deficits; type II: with cerebellar, pyramidal and extrapyramidal deficits; type III: with cerebellar deficits and distal sensorimotor neuropathy; type IV: with parkinsonism and distal sensory neuropathy. It was originally reported in two portuguese-azorean families in massachusettes (machado), then in another portuguese family (thomas), and later in a third family in california (joseph, who settled there in 1845). It has been reported also in japanese families. (12 Dec 1998) |
| machairodus | <paleontology> A genus of extinct mammals allied to the cats, and having in the upper jaw canine teeth of remarkable size and strength; hence called saber-toothed tigers. Origin: NL, fr. Gr. Dagger + tooth. Source: Websters Dictionary (01 Mar 1998) |
| machiavelian | Of or pertaining to Machiavel, or to his supposed principles; politically cunning; characterised by duplicity or bad faith; crafty. Origin: From Machiavel, an Italian writer, secretary and historiographer to the republic of Florence. Source: Websters Dictionary (01 Mar 1998) |
| machiavellianism | A personality dimension characterised by the manipulation of others. (12 Dec 1998) |
| machine | 1. In general, any combination of bodies so connected that their relative motions are constrained, and by means of which force and motion may be transmitted and modified, as a screw and its nut, or a lever arranged to turn about a fulcrum or a pulley about its pivot, etc.; especially, a construction, more or less complex, consisting of a combination of moving parts, or simple mechanical elements, as wheels, levers, cams, etc, with their supports and connecting framework, calculated to constitute a prime mover, or to receive force and motion from a prime mover or from another machine, and transmit, modify, and apply them to the production of some desired mechanical effect or work, as weaving by a loom, or the excitation of electricity by an electrical machine. The term machine is most commonly applied to such pieces of mechanism as are used in the industrial arts, for mechanically shaping, dressing, and combining materials for various purposes, as in the manufacture of cloth, etc. Where the effect is chemical, or other than mechanical, the contrivance is usually denominated an apparatus, not a machine; as, a bleaching apparatus. Many large, powerful, or specially important pieces of mechanism are called engines; as, a steam engine, fire engine, graduating engine, etc. Although there is no well-settled distinction between the terms engine and machine among practical men, there is a tendency to restrict the application of the former to contrivances in which the operating part is not distinct from the motor. 2. Any mechanical contrivance, as the wooden horse with which the Greeks entered Troy; a coach; a bicycle. 3. A person who acts mechanically or at will of another. 4. A combination of persons acting together for a common purpose, with the agencies which they use; as, the social machine. "The whole machine of government ought not to bear upon the people with a weight so heavy and oppressive." (Landor) 5. A political organization arranged and controlled by one or more leaders for selfish, private or partisan ends. 6. Supernatural agency in a poem, or a superhuman being introduced to perform some exploit. Elementary machine, a name sometimes given to one of the simple mechanical powers. See Mechanical. Infernal machine. See Infernal. Machine gun.See Gun. Machine screw, a screw or bolt adapted for screwing into metal, in distinction from one which is designed especially to be screwed into wood. Machine shop, a workshop where machines are made, or where metal is shaped by cutting, filing, turning, etc. Machine tool, a machine for cutting or shaping wood, metal, etc, by means of a tool; especially, a machine, as a lathe, planer, drilling machine, etc, designed for a more or less general use in a machine shop, in distinction from a machine for producing a special article as in manufacturing. Machine twist, silken thread especially adapted for use in a sewing machine. Machine work, work done by a machine, in contradistinction to that done by hand labour. Origin: F, fr. L. Machina machine, engine, device, trick, Gr, from means, expedient. Cf. Mechanic. Source: Websters Dictionary (01 Mar 1998) |
| machine learning | This is the study of how to create computers that will learn from experience and modify their activity based on that learning (as opposed to traditional computers whose activity will not change unless the programmer explicitly changes it). This discipline is a sub-set of Artificial Intelligence. (09 Oct 1997) |
| magnetic mach number | <physics> A dimensionless number equal to the ratio of the velocity of a fluid to the velocity of Alfven waves in that fluid. (13 Nov 1997) |
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