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X-AXIS

The longitudinal, or roll, axis of an aircraft. Cf axis.

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X-BAND

Microwave band lying roughly between eight and 12 GHz; slight discrepancy between US and UK band limits. Widely used for 3 cm radar which is now correcdy designated Cx-band.

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X-GUIDE

A transmission line with an X-shaped cross- section dielectric, used for guiding surface waves,

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X-HEIGHT

The height of the lower case letters from the baseline excluding extenders; specifically the height of the lower case x. See fig. at typeface.

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X-INACTIVATION

Permanent condensation in early development of one or other X-chromosome in female mammalian cells, with accompanying repression of most of the genes on that chromosome,

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X-ORGAN

A neurosecretory organ in the eye-stalks of certain Crustaceans.

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X-PLATES

Pair of electrodes in a cathode-ray tube to which horizontal deflecting voltage is applied in accordance with cartesian co-ordinate system.

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X-RAY

An electromagnetic wave of short wavelength ca 10

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X-RAY ASTRONOMY

The study of the emission of astronomical objects at X-ray wavelengths. Observations are made at high altitude above approx 150 km as the Earth

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X-RAY CRYSTALLOGRAPHY

Study of crystalline structures using diffraction of X-rays. The Debye and Scherrer method uses diffraction of monochromatic rays from a powdered crystalline sample giving a range of angles of incidence with respect to crystallographic axes. The arrangement of atoms in space can be inferred from the distribution of intensity in the diffraction pattern. The unit cell determines the geometry of diffraction maxima while the distribution of atoms within the unit cell controls the intensity of each reflection. The Line method examines polychromatic diffraction from a single crystal. See Bragg equation

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