06413_13 - M machine A device capable of making the...

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M machine A device capable of making the performance of mechanical work eas- ier, usually by overcoming a force of re- sistance (the load) at one point by the application of a more convenient force (the effort) at some other point. In phys- ics, the six so-called simple machines are the lever, wedge, inclined plane, screw, pulley, and wheel and axle. Mach number The ratio of the relative speeds of a Û uid and a rigid body to the speed of sound in that Û uid under the same conditions of temperature and pres- sure. If the Mach number exceeds 1 the Û uid or body is moving at a supersonic speed . If the Mach number exceeds 5 it is said to be hypersonic . The number is named after Ernst Mach (1838–1916). Mach’s principle The * inertia of any particular piece of matter is attributable to the interaction between that piece of matter and the rest of the universe. A body in isolation would have zero inertia. This principle was stated by Ernst Mach in the 1870s and was made use of by Ein- stein in his general theory of * relativity. The signi Ü cance of Mach’s principle in general relativity theory is still a con- tentious issue. Maclaurin’s series See taylor series . macrofauna The larger animals, collec- tively, which can be observed without the aid of a microscope ( compare micro- fauna ). The macrofauna sometimes in- cludes small soil-dwelling invertebrates, such as annelids and nematodes, but these may be separated into an interme- diate category, the mesofauna . macromolecular crystal A crystalline solid in which the atoms are all linked to- gether by covalent bonds. Carbon (in dia- mond), boron nitride, and silicon carbide are examples of substances that have macromolecular crystals. In effect, the crystal is a large molecule (hence the al- ternative description giant-molecular ), which accounts for the hardness and high melting point of such materials. macromolecule A very large molecule. Natural and synthetic polymers have macromolecules, as do many proteins and nucleic acids. See also colloids . macronutrient A chemical element required by plants in relatively large amounts. Macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulphur, magnesium, calcium, and iron. See also essential element . Com- pare micronutrient . macrophage A large phagocytic cell ( see phagocyte ) that can ingest pathogenic microorganisms (e.g. bacteria, protozoa) or cell debris and forms part of the body’s immune system. Macrophages develop from precursor cells (promono- cytes) in bone marrow, become wander- ing * monocytes in the bloodstream, and then settle as mature macrophages in var- ious tissues, including lymph nodes, con- nective tissues (as histiocytes ), lungs, the linings of liver sinusoids and the spleen, skin, and nervous tissues ( microglia ). Tis- sue macrophages can also contribute to in Û ammation by secreting various cyto- kines. Collectively the macrophages make up the mononuclear phagocyte sys- tem .
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06413_13 - M machine A device capable of making the...

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