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Possible definitions for valvae

valve
In mechanical engineering, a device for controlling the flow of fluids (liquids, gases, slurries) in a pipe or other enclosure. It exerts control by means of a movable element that opens, shuts, or partially blocks an opening in a passageway. Valves are of seven main types: globe, gate, needle, plug (cock), butterfly, poppet, and spool. Some valves operate automatically; check (or nonreturn) valves, for example, are self-acting valves that permit flow in only one direction. Safety valves open at a predetermined pressure; the movable element usually has a weighted lever or a spring strong enough to hold the valve closed until a particular pressure is reached.


algae
Any of a group of mostly aquatic, photosynthetic organisms (see photosynthesis) that defy precise definition. They range in size from the microscopic flagellate Micromonas to giant kelp that reach 200 ft (60 m) in length. Algae provide much of the earth's oxygen, serve as the food base for almost all aquatic life, and provide foods and industrial products, incl. petroleum products. Their photosynthetic pigments are more varied than those of plants, and their cells have features not found among plants and animals. The classification of algae is changing rapidly as new taxonomical information is discovered. Algae were formerly classified into three major groups--the red, brown, and green seaweeds--based on the pigment molecules in their chloroplasts. Many more than three groups are now recognized, each sharing a common set of pigment types. Algae are not closely related to each other in an evolutionary sense. Specific groups can be distinguished from protozoans and fungi (see fungus) only by the presence of chloroplasts and their ability to carry out photosynthesis, and thus have a closer evolutionary relationship with the protozoa or fungi than with other algae. Use of algae is perhaps as old as mankind; seaweeds are eaten by coastal societies, and algae are served in many restaurants. They are common on "slimy" rocks in streams (see diatoms) and as green sheens on pools and ponds.


Alvarez
U.S. experimental physicist. Born in San Francisco, he joined the faculty of UC-Berkeley in 1936, where he would remain until 1978. In 1938 he discovered that some radioactive elements decay when an orbital electron merges with the atom's nucleus, producing an element with an atomic number smaller by 1, a form of beta decay. In 1939 he and Felix Bloch (1905-1983) made the first measurement of the magnetic moment of the neutron. During World War II he developed a radar guidance system for landing aircraft and participated in the Manhattan Project to develop the atomic bomb. He later helped construct the first proton linear accelerator and constructed the liquid hydrogen bubble chamber. With his son, the geologist Walter Alvarez (b.1940), he helped develop the theory that links the dinosaurs' extinction with a giant asteroid or comet impact. ...

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