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A cord connecting a muscle to another structure, often a bone. A tendon is a passive material, lengthening when the tension increases and shortening when it decreases. This characteristic contrasts with the active behavior of muscle.
Industry:Science
A coupling device which permits the engagement and disengagement of coupled shafts during rotation. There are four major types: positive, friction, hydraulic, and electromagnetic.
Industry:Science
A crustacean order within the class Malacostraca, superorder Peracarida. Few spelaeogriphacean species are known, four extant species and two supposed fossil species. <i>Spelaeogriphus lepidops</i> is from a stream in a cave in Table Mountain, South Africa. <i>Potiicoara brasiliensis</i> inhabits a pool in a cave in the Mato Grosso, Brazil. <i>Mangkurtu mityula</i> (see <b>illustration</b>) and <i>M. kutjarra</i> have been reported from aquifers in the Pilbara region of Western Australia. <i>Acadiocaris novascotica</i> is a fossil from Carboniferous marine sediments in Canada, and <i>Liaoningogriphus quadripartitus</i> is a fossil from lacustrine (lake-associated) deposits of Jurassic age in China. It is probable that <i>Acadiocaris</i> is truly a spelaeogriphacean, but it is less certain that <i>Liaoningogriphus</i> is; on the basis of characters visible in fossils, its classification in this order or any other is impossible to justify.
Industry:Science
A crustacean within the Malacostraca: Peracarida. All have a well-developed carapace which is fused dorsally with at least the first three thoracic somites and which overhangs the sides to enclose a branchial cavity. The telson may be free or may appear lacking because it is fused with the last abdominal somite. Eyes are sessile and, except for a few genera, are coalesced in a single median organ or wholly wanting. There are eight pairs of thoracic appendages, the first three modified as maxillipeds and the last five as peraeopods. The first maxillipeds bear an epipodite forming a respiratory organ with a forward-directed siphon and a posterior part carrying branchial lobes. Natatory exopodites may be present on the third maxillipeds and the first four pairs of peraeopods or some of them. The uropods are styliform. There is no free larval stage. In the few species whose life history has been investigated there are five to seven molts after release from the brood pouch.
Industry:Science
A crystalline igneous rock that consists largely of alkali feldspar (typically perthitic microcline or orthoclase), quartz, and plagioclase (commonly calcic albite or oligoclase). Its average grain size is 0.04–1.0 in. (1–25 mm); finer-grained rocks of this composition include rhyolite and aplite, and coarser-grained ones are granite pegmatite.
Industry:Science
A cubic mineral and member of the spinel structure type, space group Fd3m, with composition (Fe<sup>3+</sup>)<sup>IV</sup>(Fe<sup>2+</sup>Fe<sup>3+</sup>)<sup>VI</sup>O<sub>4</sub>. It possesses the inverse spinel structure, in which half the ferric iron is tetrahedrally coordinated and the remaining half as well as all ferrous iron are octahedrally coordinated by the cubic close-packed oxygen atoms. The color is opaque iron-black and streak black, the hardness is 6 (Mohs scale), and the specific gravity is 5.20. The habit is octahedral (see <b>illus.</b>), but the mineral usually occurs in granular to massive form, sometimes of enormous dimensions. Though possessing no cleavage, some specimens show an octahedral parting. Limited Al<sup>3+</sup> may substitute for Fe<sup>3+</sup>; and Ca<sup>2+</sup>, Mn<sup>2+</sup>, and Mg<sup>2+</sup> for Fe<sup>2+</sup>.
Industry:Science
A current source is an electronic circuit that generates a constant direct current which flows into or out of a high-impedance output node. A current mirror is an electronic circuit that generates a current which flows into or out of a high-impedance output node, which is a scaled replica of an input current, flowing into or out of a different node.
Industry:Science
A current-controlled switching device based on superconductivity for use primarily in computer circuits. The early version has been superseded by the tunneling cryotron, which consists basically of a Josephson junction. In its simplest form (see <b>illus.</b>) the device has two electrodes of a superconducting material (for example, lead) which are separated by an insulating film only about 10 atomic layers thick. For the electrodes to become superconducting, the device has to be cooled to a few degrees above absolute zero. The tunneling cryotron has two states, characterized by the presence or absence of an electrical resistance. They can be considered as the “on” and “off” states of the switch, respectively. Switching from on to off is accomplished by a magnetic field generated by sending a current through the control line on top of the junction. The device can switch in a few picoseconds and has a power consumption of only some microwatts. These properties make it an attractive switching device for computers, promising performance levels probably unattainable with other devices.
Industry:Science
A curve shaped like the figure eight (see <b>illus.</b>), referred to by Jacques Bernoulli in 1694. Let <i>F</i><sub>1</sub>, <i>F</i><sub>2</sub> be points of a plane π, with <i>F</i><sub>1</sub><i>F</i><sub>2</sub> = 2<i>a</i>, <i>a</i> > 0. The locus of a point <i>P</i> of π which moves so that <i>PF</i><sub>1</sub> · <i>PF</i><sub>2</sub> = <i>b</i><sup>2</sup>, where <i>b</i> is a positive constant, is called an oval of Cassini. The lemniscate is obtained when <i>b</i> = <i>a</i>. Its equation in rectangular coordinates is (<i>x</i><sup>2</sup> + <i>y</i><sup>2</sup>)<sup>2</sup> = <i>a</i><sup>2</sup>(<i>x</i><sup>2</sup> − <i>y</i><sup>2</sup>) and in polar coordinates ρ<sup>2</sup> = <i>a</i><sup>2</sup> cos 2θ. It is the locus of the point of intersection of a variable tangent to a rectangular hyperbola with the line through the center perpendicular to the tangent. The area enclosed by the lemniscate ρ<sup>2</sup> = <i>a</i><sup>2</sup> cos 2θ is <i>a</i><sup>2</sup>.
Industry:Science
A curve traced in the plane by a point on a circle that rolls, without slipping, on a line. If the line is the <i>x</i> axis of a rectangular coordinate system, at whose origin <i>O</i> the moving point <i>P</i> touches the axis, parametric equations of the cycloid are <i>x</i> = <i>a</i>(θ − sin θ), <i>y</i> = <i>a</i>(1 − cos θ), when <i>a</i> is the radius of the rolling circle, and the parameter θ is the variable angle through which the circle rolls (see <b>illus.</b>). One arch is obtained where θ assumes all values from 0 to 2π. The length of an arch is 8<i>a</i>, and the area bounded by an arch and the <i>x</i> axis is 3π<i>a</i><sup>2</sup> (three times the area of the rolling circle).
Industry:Science
