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X-ray
Electromagnetic radiation of extremely short wavelength (100 nanometres to 0.001 nanometre) produced by the deceleration of charged particles or the transitions of electrons in atoms.
X-ray astronomy
Study of astronomical objects and phenomena that emit radiation at X-ray wavelengths.
X-ray diffraction
Phenomenon in which the atoms of a crystal, by virtue of their uniform spacing, cause an interference pattern of the waves in an incident beam of X-rays.
Xanthus
Ancient city of Lycia, Anatolia.
Xavier, Saint Francis
Spanish-born French missionary to the Far East.
Xenakis, Iannis
Romanian-born Greek-French composer.
Xenocrates
Greek philosopher.
xenon
Chemical element, chemical symbol Xe, atomic number 54.
Xenophanes of Colophon
Greek poet, religious thinker, and reputed precursor of philosophy of the Eleatics.
Xenophon
Greek historian.
xerography
Image-forming process that relies on a photoconductive substance whose electrical resistance decreases when light falls on it.
Xerox Corp.
Major U.S. corporation.
Xerxes I
Persian king (486–465 BC) of the Achaemenian dynasty.
Xhosa
People living primarily in East Cape province, South Africa.
Xi River
River system, southern China.
Xi Xia
Kingdom of Tangut tribes that was established in the 11th century and flourished through the early 13th.
Xia dynasty
(c. 2070–c. 1600 BC) Quasi-legendary first dynasty of China, preceding the Shang.
Xia Gui
Chinese master of landscape painting.
Xi'an
City (pop., 2003 est.: 2,657,900), capital of Shaanxi province, central China.
Xi'an Incident
(1936) Seizure of Nationalist leader Chiang Kai-shek by one of his generals, Chang Hsüeh-liang (Zhang Xueliang; 1898–2001), in order to persuade Chiang to postpone his war on the Chinese communists until the invading Japanese had been defeated.
Xiang River
River, Hunan province, southeastern China.
Xiang Yu
Chinese aristocratic general and cultural hero.
xiao
In Confucianism, the attitude of obedience, devotion, and care toward one's parents and other elders considered fundamental to moral conduct.
Xingu River
River, central and northern Brazil.
Xining
City (pop., 1999 est.: 604,812), capital of Qinghai province, western China.
Xinjiang
Autonomous region (pop., 2002 est.: 19,050,000), northwestern China.
Xiongnu
Nomadic pastoral people of Central Asia.
Xipe Totec
Pre-Columbian god of spring and new vegetation who was venerated by the Toltecs and Aztecs.
Xiuhtecuhtli
Aztec god of fire and creator of all life.
Xiwangmu
In ancient Chinese Daoist mythology, the queen of the female immortals.
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