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| Absolute |
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A measure having as its zero point or base the complete absence of the entity being measured.
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| Absolute pressure |
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The pressure above zero absolute, i.e., the sum of atmospheric and gauge pressure. In vacuum related work it is usually expressed in millimeters, or inches, of mercury.
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| Acceptance sampling |
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A statistical quality control method that seeks to determine the quality of a product by sampling a small portion of it. It does not assure that 100 percent of the product is acceptable, but reduces the likelihood of acceptance of a defective product.
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| Accumulator |
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A container in which fluid (generally nitrogen) is stored under pressure as a source of fluid power.
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| Acre (a) |
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A unit of area used in English-speaking countries, equal to 4,840 square yards (0.405 hectares).
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| Actuator |
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A device for converting pneumatic or hydraulic energy into mechanical energy. A motor or cylinder.
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| Adhesive |
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A substance capable of holding materials together by surface attachment. It is a general term and includes cements, mucilage, and paste, as well as glue.
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| Agricultural Residue |
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Plant parts, primarily stalks and leaves, not removed from the fields with the primary food or fiber product. Examples include corn stover (stalks, leaves, husks, and cobs); wheat straw; and rice straw.
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| Amplifier |
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A device for amplifying the error signal sufficiently to cause actuation of the stroke control. Several types of servo amplifiers are used at the present time: electronic (DC, AC, phase sensitive, and magnetic) and mechanical.
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| Amplitude of sound |
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The loudness of a sound.
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| Anaerobic digestion |
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Decomposition of biological wastes by micro-organisms, usually under wet conditions, in the absence of air (oxygen), to produce a gas comprising mostly methane and carbon dioxide.
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| Analog |
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A continuous range of numbers or values.
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| Anisotropic |
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Exhibiting different properties when measured along different axes. In general, fibrous materials such as wood are anisotropic.
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| Annular area |
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A ring shaped area - often refers to the net effective area of the rod side of a cylinder piston, i.e., the piston area minus the cross-sectional area of the rod.
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| Aquatic Plants |
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The wide variety of aquatic biomass resources, such as algae, giant kelp, other seaweed, and water hyacinth. Certain microalgae can produce hydrogen and oxygen while others manufacture hydrocarbons and a host of other products. Microalgae examples include Chlorella, Dunaliella, and Euglena.
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| Atmospheric pressure |
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Pressure exerted by the atmosphere at any specific location. (Sea level pressure is approximately 14.7 pounds per square inch absolute.)
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| Axial force |
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A push (compression) or pull (tension) acting along the length of a member, expressed in kilonewtons (pounds).
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| Axial stress |
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The axial force acting at a point along the length of a member divided by the cross-sectional area of a member, expressed in kilopascals (pounds per square inch).
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