Ability of a substance to rotate the plane of polarization of a beam of light passed through it, either as crystals or in solution. Clockwise rotation as one faces the light source is “positive,” or dextrorotary; counterclockwise rotation “negative,” or levorotary. Louis Pasteur was the first to recognize that molecules with optical activity are stereoisomers (see isomerism). Optical isomers occur in pairs that are nonsuperimposable mirror images of one another. They have the same physical properties except for their effect on polarized light; in chemical properties they differ only in their interactions with other stereoisomers (see asymmetric synthesis).
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Successive cultivation of different crops in a specified order on the same fields. Some rotations are designed for high immediate returns, with little regard for basic resources. Others are planned for high continuing returns while protecting resources. A typical scheme selects rotation crops from three classifications: cultivated row crops (e.g., corn, potatoes), close-growing grains (e.g., oats, wheat), and sod-forming, or rest, crops (e.g., clover, clover-timothy). In general, cropping systems should include deep-rooting legumes. In addition to the many beneficial effects on soils and crops, well-planned crop rotations make the farm a more effective year-round enterprise by providing more efficient handling of labour, power, and equipment, reduction in weather and market risks, and improved ability to meet livestock requirements.
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Rotation-powered pulsar is one of the major classes of pulsars. A Rotation-powered pulsar is a rapidly rotating neutron star, whose electromagnetic radiation is observed in regularly spaced intervals, or pulses. It differs from other types of pulsars in that the source of power for the production of radiation is the loss of rotational energy.
Millisecond pulsars are thought to have been spun up to high rotational speed by infalling matter pulled off a companion star.
Of interest to the study of the state of the matter in a neutron stars are the glitches observed in the rotation velocity of the neutron star. This velocity is decreasing slowly but steadily, except by sudden variations. One model put forward to explain these glitches is that they are the result of "starquakes" that adjust the crust of the neutron star. Models where the glitch is due to a decoupling of the possibly superconducting interior of the star have also been advanced. In both cases, the star's moment of inertia changes, but its angular momentum doesn't, resulting in a change in rotation rate.
In 2003 observations of the Crab nebula pulsar's signal revealed "sub-pulses" within the main signal with durations of only nanoseconds. It is thought that these nanosecond pulses are emitted by regions on the pulsar's surface 60cm in diameter or smaller, making them the smallest structures outside the solar system to be measured.