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dentistry

(Encyclopedia)dentistry, treatment and care of the teeth and associated oral structures. Dentistry is mainly concerned with tooth decay, disease of the supporting structures, such as the gums, and faulty positionin...

designer drug

(Encyclopedia)designer drug, chemical substance synthesized in a laboratory that is intended to have effects similar to those of a drug that is a controlled substance, such as methamphetamine, marijuana, LSD, or an...

molecular weight

(Encyclopedia)molecular weight, weight of a molecule of a substance expressed in atomic mass units (amu). The molecular weight may be calculated from the molecular formula of the substance; it is the sum of the ato...

Union Pacific Railroad

(Encyclopedia)Union Pacific Railroad, transportation company chartered (1862) by Congress to build part of the nation's first transcontinental railroad line. Under terms of the Pacific Railroads Act, the Union Paci...

radar

(Encyclopedia)radar, system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, ...

seafloor spreading

(Encyclopedia)CE5 Schematic model of the oceanic crust, showing seafloor spreading seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwate...

pesticide

(Encyclopedia)pesticide, biological, physical, or chemical agent used to kill plants or animals that are harmful to people; in practice, the term pesticide is often applied only to chemical agents. Various pesticid...

compound

(Encyclopedia)compound, in chemistry, a substance composed of atoms of two or more elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound...

gas laws

(Encyclopedia)gas laws, physical laws describing the behavior of a gas under various conditions of pressure, volume, and temperature. Experimental results indicate that all real gases behave in approximately the sa...

lubrication

(Encyclopedia)lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid...