upward gradient
21fluid mechanics — an applied science dealing with the basic principles of gaseous and liquid matter. Cf. fluid dynamics. [1940 45] * * * Study of the effects of forces and energy on liquids and gases. One branch of the field, hydrostatics, deals with fluids at… …
22angiosperm — /an jee euh sperrm /, n. Bot. a plant having its seeds enclosed in an ovary; a flowering plant. Cf. gymnosperm. [ANGIO + SPERM] * * * ▪ plant Introduction any member of the more than 300,000 species of flowering plants (division Anthophyta) …
23photoreception — photoreceptive, adj. /foh toh ri sep sheuhn/, n. the physiological perception of light. [1905 10; PHOTO + RECEPTION] * * * Biological responses to stimulation by light, most often referring to the mechanism of vision. In one celled organisms such …
24Extratropical cyclone — Part of the Nature series on Weather   Calendar seasons Spring · Summer Autumn  …
25permafrost — /perr meuh frawst , frost /, n. (in arctic or subarctic regions) perennially frozen subsoil. Also called pergelisol. [1943; PERMA(NENT) + FROST] * * * Perennially frozen earth, with a temperature below 32 °F (0 °C) continuously for two years or… …
26physical science, principles of — Introduction the procedures and concepts employed by those who study the inorganic world. physical science, like all the natural sciences, is concerned with describing and relating to one another those experiences of the surrounding… …
27SOFAR channel — The SOFAR channel (short for Sound Frequency and Ranging channel), or deep sound channel (DSC),[1] is a horizontal layer of water in the ocean at which depth the speed of sound is minimal. The SOFAR channel acts as a waveguide for sound, and low… …
28metamorphic rock — Any of a class of rocks that result from the alteration of preexisting rocks in response to changing geological conditions, including variations in temperature, pressure, and mechanical stress. The preexisting rocks may be igneous, sedimentary,… …
29tropical cyclone — a cyclone that originates over a tropical ocean area and can develop into the destructive storm known in the U.S. as a hurricane, in the western Pacific region as a typhoon, and elsewhere by other names. Cf. extratropical cyclone, hurricane (def …
30digestive system, human — Introduction the system used in the human body for the process of digestion. The human digestive system consists primarily of the digestive tract (alimentary canal), or the series of structures and organs through which food and liquids pass… …
