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halogen

(Encyclopedia)halogen hălˈəjĕn [key] [Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromin...

electron tube

(Encyclopedia)CE5 Triode electron tube electron tube, device consisting of a sealed enclosure in which electrons flow between electrodes separated either by a vacuum (in a vacuum tube) or by an ionized gas at l...

bacteriophage

(Encyclopedia)bacteriophage băktērˈēəfājˌ [key], virus that infects bacteria and sometimes destroys them by lysis, or dissolution of the cell. Bacteriophages, or phages, have a head composed of protein, an i...

Ordovician period

(Encyclopedia)Ordovician period ôrdəvĭshˈən [key] [from the Ordovices, ancient tribe of N Wales], second period of the Paleozoic era of geologic time (see Geologic Timescale, tablegeologic timescale, table) fr...

slime mold

(Encyclopedia)slime mold or slime fungus, a heterotrophic organism once regarded as a fungus but later classified with the Protista. In a recent system of classification based on analysis of nucleic acid (genetic m...

rabbit

(Encyclopedia)rabbit, name for herbivorous mammals of the family Leporidae, which also includes the hare and the pika. Rabbits and hares have large front teeth, short tails, and large hind legs and feet adapted for...

friction

(Encyclopedia)friction, resistance offered to the movement of one body past another body with which it is in contact. In certain situations friction is desired. Without friction the wheels of a locomotive could not...

interstellar matter

(Encyclopedia)interstellar matter, matter in a galaxy between the stars, known also as the interstellar medium. The interstellar gas, which constitutes about 99% of the interstellar matter, consists mostly of hyd...

concrete

(Encyclopedia)concrete, structural masonry material made by mixing broken stone or gravel with sand, cement, and water and allowing the mixture to harden into a solid mass. The cement is the chemically active eleme...

conduction

(Encyclopedia)conduction, transfer of heat or electricity through a substance, resulting from a difference in temperature between different parts of the substance, in the case of heat, or from a difference in elect...