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neptunium

(Encyclopedia)neptunium nĕpto͞oˈnēəm [key], radioactive chemical element; symbol Np; at. no. 93; mass number of most stable isotope 237; m.p. about 640℃; b.p. 3,902℃ (estimated); sp. gr. 20.25 at 20℃; va...

neutron star

(Encyclopedia)neutron star, extremely small, extremely dense star, with as much as double the sun's mass but only a few miles in radius, in the final stage of stellar evolution. Astronomers Baade and Zwicky predict...

niobium

(Encyclopedia)niobium nīōˈbēəm [key], metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.90638; m.p. about 2,468℃; b.p. 4,742℃; sp. gr. 8.57 at 20℃; valence +2, +3, +4, or +5. Niobium is a rare...

nonmetal

(Encyclopedia)nonmetal, chemical element possessing certain properties by which it is distinguished from a metal. In general, this distinction is drawn on the basis that a nonmetal tends to accept electrons and for...

parthenogenesis

(Encyclopedia)parthenogenesis pärˌthənōjĕnˈəsĭs [key] [Gr.,=virgin birth], in biology, a form of reproduction in which the ovum develops into a new individual without fertilization. Natural parthenogenesis ...

La Paz, city, Bolivia

(Encyclopedia)La Paz lä päs [key], city (1992 pop. 713,378), W Bolivia, administrative capital (since 1898) and largest city of Bolivia. The constitutional capital is Sucre. La Paz, the highest capital in the wor...

pit viper

(Encyclopedia)pit viper, poisonous snake of the family Crotalidae, primarily a New World family. Like the Old World true vipers (family Viperidae), pit vipers have long, hollow, erectile fangs that are folded back ...

ceramics

(Encyclopedia)ceramics sərămˈĭks [key], materials made of nonmetallic minerals that have been permanently hardened by firing at a high temperature, or objects made of such materials. Most ceramics resist heat a...

samarium

(Encyclopedia)samarium səmârˈēəm [key], metallic chemical element; symbol Sm; at. no. 62; at. wt. 150.36; m.p. 1,072℃; b.p. 1,791℃; sp. gr. 7.54 at 20℃; valence +2 or +3. Samarium is a lustrous silver-wh...

red giant

(Encyclopedia)red giant, star that is relatively cool but very luminous because of its great size. All normal stars are expected to pass eventually through a red-giant phase as a consequence of stellar evolution. A...