Valve

in biology a piece of tissue attached to the wall of a tube that ensures the flow of blood is in one direction. The most important valves are the ones found in the HEART and VEINS, which prevent a backflow of blood. In engineering, valves are used in a similar way, to control the flow of fluids through pipes.

Taken from Dictionary of Science

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A valve is a device that regulates the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.

Valves are also found in the human body. For example, there are several heart valves which control the flow of blood in the chambers of the heart and maintain the correct pumping action.

Valves are used in a variety of contexts, including industrial, military, commercial, residential, and transportation.

The industries in which the majority of valves are used are oil and gas, power generation, mining, water reticulation, sewerage and chemical manufacturing.

Plumbing valves, such as taps for hot and cold tap water are the most noticeable types of valves. Other valves encountered on a daily basis include gas control valves on cookers, small valves fitted to washing machines and dishwashers, and safety devices fitted to hot water systems.

Valves may be operated manually, either by a hand wheel, lever or pedal. Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.

More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.

Valves are also found in the Otto cycle (internal combustion) engines driven by a camshaft, tappets or push rods where they play a major role in engine cycle control.

Taken from Wikipedia

Magnetic Bubble

a portion of computer memory which consists of a small region in a material such as garnet (a silicate mineral), which is magnetized in one direction. Slices of this material placed on a SUBSTRATE (base material) produce a magnetic chip that under a magnetic field produces magnetic bubbles. Information can be stored on the chip, which may contain up to one million bubbles in 20 square millimetres, in BINARY form, through the presence or absence of a bubble in a specific location.

Taken from Dictionary of Science

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The magnetic bubble apparatus consists of a thin (8-12μm) single crystal film of Ferromagnetic Garnet (FMG) sandwiched between a pair of crossed Polaroids. The FMG crystals are magnetically anisotropic, that is, they have a strong tendency to orient themselves in fixed directions under the influence of an external magnetic field. The preferred or "easy" axis of orientation is perpendicular to (in or out of) the crystal surface. With no external magnetic field, the domains in the crystal orient up or down in roughly equal amounts. Polarized light passing through the crystal will have its plane of polarization rotated by due to interaction with the magnetic field of the domains (an effect called Faraday rotation). For the 'up' domains, the light will be crossed with respect to the exiting Polaroid therefore appearing dark, and for 'down' domains uncrossed (or vice versa) so appearing bright. The domains appear as serpentine patterns of alternating bright and dark (figure 1a.). Application of an external magnetic field (provided by a built-in electromagnet) flips the domains to one preferred orientation. As the field is increased, the serpentine patterns gradually disappear until you are left with one or two strings and isolated "bubbles".

Taken from fas.harvard.edu

Galactic Plane

the plane which passes through the centre of the MILKY WAY, as far as that can be determined.

Taken from Dictionary of Science

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The plane in which the disk of the Milky Way Galaxy lies. By definition, one direction perpendicular to this plane is called above or north, and the opposite direction, also perpendicular to the galactic plane, is called below or south. From Earth, due galactic north is marked by the north galactic pole, which lies in Coma Berenices, near the bright star Arcturus, and due galactic south is marked by the south galactic pole, which lies in Sculptor.

Taken from The Internet ENCYCLOPEDIA OF SCIENCE

Nadir

the lowest point -- the pole which is vertically below the observer in the CELESTIAL SPHERE. It is opposite to the ZENITH.

Taken from Dictionary of Science

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The nadir (from Arabic نظير nathir, "opposite") is the direction pointing directly below a particular location; that is, it is one of two vertical directions at the location, orthogonal to a horizontal flat surface there. Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location. The direction opposite of the nadir is the zenith.

Nadir also refers to the downward-facing viewing geometry of an orbiting satellite, such as is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing an EVA.

The word is also used figuratively to mean the lowest point of a person's spirits.

The term nadir can also be used to represent the lowest point reached by a celestial body during its apparent orbit around a given point of observation. This can be used to describe the location of the Sun, but it is only technically accurate for one latitude at a time and only possible at the low latitudes. The sun is said to be at the nadir at a location when it is at the zenith at the location's antipode.

Taken from Wikipedia