Science terms starting with A

1,045 terms

  1. apical dominance The phenomenon where growth of lateral (axillary) bud s in a plant is inhibited by the presence of the terminal (apical) bud on the branch.
  2. apical meristem A region of the tip of each shoot and root of a plant in which cell division is continually occurring to produce new stem and root tissue, respectively.
  3. APO Arizona Projects Office.
  4. Apocalypse A Greek word translated approximately to mean “disclosure of things previously hidden,” it is a term most often applied to the end of the world, the…
  5. apoenzyme Inactive enzyme that has to be associated with a co-enzyme in order to function. The apoenzyme/co-enzyme complex is called a holoenzyme.
  6. Apogee The farthest distance between the moon and earth or the earth and sun.
  7. apomixis The production of an embryo in the absence of meiosis. Apomictic higher plants produce asexual seeds, derived only from maternal tissue.
  8. apoptosis (A-pop-TOH-sis) A type of cell death in which a series of molecular steps in a cell leads to its death.
  9. Apparent Day A solar day; an interval between successive transits of the sun's center across an observer's meridian; the time thus measured is not equal to clock time.
  10. Apparent luminosities The brightness of an object as it appears from the earth. The apparent luminosity does not take into account the distance from the earth to the object…
  11. Apparent Power (kVA) This is the voltage-ampere requirement of a device designed to convert electric energy to a non-electrical form.
  12. Apparent Temperature A measure of human discomfort due to combined heat and humidity (e.g., heat index).
  13. Apparent Wind The speed and true direction from which the wind appears to blow with reference to a moving point. Sometimes called RELATIVE WIND.
  14. Appendix A small, fingerlike pouch that sticks out from the cecum (the first part of the large intestine near the end of the small intestine).
  15. Appliance A device for converting one form of energy or fuel into useful energy or work.
  16. Appliance Energy Efficiency Ratings The ratings under which specified appliances convert energy sources into useful energy, as determined by procedures established by the U.S.
  17. Appliance Standards Standards established by the U.S. Congress for energy consuming appliances in the National Appliance Energy Conservation Act (NAECA) of 1987, and as…
  18. Application efficiency The ratio of the average depth of irrigation water infiltrated and stored in the root zone to the average depth of irrigation water applied, expressed as…
  19. Application for Certification (AFC) Document required for submission to the California Energy Commission by proponents of power-generating facilities in California that have nameplate…
  20. Applied water (delivered water) Water delivered to a user. Applied water may be used for either inside uses or outside watering. It does not include precipitation or distribution losses.
  21. Appraisal estimate An estimate used in an appraisal study as an aid in selecting the most economical plan by comparing alternative features or for determinimg whether more…
  22. Appraisal level of detail The level of detail necessary to facilitate making decisions on whether or not to proceed with a detailed study and evaluation of any alternative.
  23. Appraisal study (appraisal report) A study incorporating an appraisal level of detail.
  24. Approach channel The channel upstream from that portion of the spillway having a concrete lining or concrete structure.
  25. Appropriate Management Level (AML) The maximum number of animals (wild horses or burros) sustainable on a yearlong basis.
  26. Appropriation The provision of funds, through an annual appropriations act or a permanent law, for federal agencies to make payments out of the Treasury for specified…
  27. Appropriation Doctrine The system of water law primarily used in the western United States under which: 1.
  28. Appropriations Refers to the process of divvying out water right allotments and beneficial uses within a water management district.
  29. Appropriative Water rights to or ownership of a water supply which is acquired for the beneficial use of water by following a specific legal procedure.
  30. Appurtenant Structures Auxiliary features of a dam such as outlet, spillway, powerhouse, tunnel, etc.
  31. Appurtentant structures Outlet works, spillways, bridges, drain systems, tunnels, towers, etc.
  32. APRCH Approach
  33. APRCHG approaching
  34. APRNT apparent
  35. Apron (fore apron) A section of concrete or riprap constructed upstream or downstream from a control structure to prevent undercutting of the structure.
  36. APST Aviation Products and Services Team
  37. aptamer A polynucleotide molecule that binds to a specific molecule, often a protein.
  38. AQIA air quality impact analysis.
  39. AQMD Air Quality Management District.
  40. AQMP Air Quality Management Plan.
  41. Aquaculture Farming of aquatic organisms, including fish, molluscs, crustaceans and aquatic plants.
  42. Aquatic Having to do with water.
  43. Aquatic algae Microscopic plants that grow in sunlit water containing phosphates, nitrates, and other nutrients.
  44. Aquatic biota Collective term describing the organisms living in or depending on the aquatic environment.
  45. Aquatic ecosystem The distinctive ecosystem dominated by water, aquatic plants, or aquatic animals.
  46. Aquatic habitats Areas associated with water that provide food and cover and other elements critical to the completion of an organism's life cycle (e.g.
  47. Aquatic opportunists Species that occupy both temporary and permanent waters.
  48. aquatic plants The aquatic biomass resources, such as algae, giant kelp, other seaweed, and water hyacinth.
  49. Aquatic Protected Area A marine protected area consisting of freshwater resources.
  50. Aqueduct Man-made canal or pipeline used to transport water.
  51. Aqueous Having to do with water.
  52. Aquiclude A layer of clay which limits the movement of ground water.
  53. Aquifer A water-bearing geologic formation, sometimes confined between clay layers and sometimes on the surface.
  54. Aquifer-basin-fill An aquifer located in a basin surrounded by mountains and composed of sediments and debris shed from those mountains.
  55. Aquifer-carbonate rock An aquifer found in limestone and dolomite rocks. Carbonate aquifers typically produced hard water, that is, water containing relatively high levels of…
  56. Aquifer-confined Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under…
  57. Aquifer-unconfined An aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.
  58. Aquifer-volcanic rock An aquifer in which the rock matrix is composed of volcanic rocks, (e.g., tuffs or basalt flows).
  59. Aquifuge A geologic formation which has no interconnected openings and cannot hold or transmit water.
  60. Arabidopsis A genus of flowering plants in the Cruciferae. A. thaliana is used in research as a model plant because it has a small fully sequenced genome, can be…
  61. arabinan The polymer of arabinose with a repeating unit of C5H804. Can be hydrolyzed to arabinose. (Source: Voet, D.; Voet, J. G. Biochemistry.
  62. arabinose A five-carbon sugar - C5H1005. A product of hydrolysis of arabinan found in the hemicellulose fraction of biomass.
  63. Arable Suitable for farming. Having soil or topographic features suitable for cultivation.
  64. Arable land Land which when farmed in adequate size units for the prevailing climatic and economic setting, and provided with the essential on-farm improvements of…
  65. Arable lands Refers to all lands generally under rotation whether it is under temporary crops, temporarily fallowed, or used as temporary meadows.
  66. ARAM Aviation, Range, and Aerospace Meteorology
  67. ARAR applicable or relevant and appropriate requirement.
  68. Arbitrage Arbitrage is the technique of simultaneously buying at a lower price in one market and selling at a higher price in another market to make a profit on the…
  69. arbitrarily primed polymerase chain reaction (Abbreviation: AP-PCR) An application of the polymerase chain reaction to generate DNA fingerprints .
  70. arbitrary primer An oligonucleotide primer whose sequence is chosen at random, rather than one whose sequence matches that of a known locus.
  71. Arch Dam A concrete or masonry dam which is curved upstream in plan so as to transmit the major part of the water load to the abutments and to keep the dam in…
  72. Arch Filament System (AFS) In solar-terrestrial terms, a bright, compact plage crossed by a system of small, arched filaments, which is often a sign of rapid or continued growth in…
  73. Arch-buttress dam (or curved buttress dam) A buttress dam which is curved in plan.
  74. Arch-gravity dam An arch dam which is only slightly thinner than a gravity dam.
  75. Archaea Single-celled life forms adapted to existence in high pressure, anaerobic, environments such as at extreme ocean depths.
  76. Archaeological site Any location where humans have altered the terrain or discarded artifacts during prehistoric or historic times.
  77. Archaic In American archeology, a cultural stage following the earliest known human occupation in the New World (about 5,500 B.C. to A.D. 100).
  78. Archeology Study of human cultures through the recovery and analysis of their material relics.
  79. Archimedean screw An ancient water-raising device attributed to Archimedes, made up of a spiral tube coiled about a shaft or of a large screw in a cylinder, revolved by…
  80. Arching The transfer of stress from a yielding part of a soil or rock mass to adjoining less-yielding or restrained parts of the mass.
  81. Arctic The region within the Arctic Circle, or, loosely, northern regions in general, characterized by very low temperatures.
  82. arctic air A very cold and dry air mass that forms primarily in winter and the northern interior of North America.
  83. Arctic air mass Arctic air mass Mass of very cold air in the Arctic regions which invades lower latitudes at irregular intervals.
  84. Arctic Circle Arctic Circle The line of latitude 66° 32' N (often taken as 66.5° N). Along this line the Sun does not set on the day of the summer solstice, and does…
  85. Arctic front The boundary or front separating deep, cold arctic air from shallower, relatively less cold polar air.
  86. Arctic haze Arctic haze Haze in Arctic regions which reduces horizontal and slant visibility and which may extend to a height of about 10 km.
  87. Arctic high Arctic high A weak high which appears over the Arctic Basin during late spring, summer and early autumn, one of the centers of action in the atmosphere.
  88. Arctic mist Arctic mist A mist of ice crystals; a very light ice fog.
  89. Arctic Oscillation (abbrev. AO)- The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive…
  90. Arctic Sea Smoke Steam fog, but often specifically applied to steam fog rising from small open water within sea ice.
  91. Arctic tundra A treeless area between the icecap and the tree line of Arctic regions that has permanently frozen subsoil and supports low-growing vegetation such as…
  92. Arcus A low, horizontal cloud formation associated with the leading edge of thunderstorm outflow (i.e., the gust front).
  93. Area Must have legally defined geographical boundaries, and may be of any size, except that the site must be a subset of the U.S.
  94. Area Forecast Discussion This National Weather Service product is intended to provide a well-reasoned discussion of the meteorological thinking which went into the preparation of…
  95. Area of Influence The area covered by the drawdown curves of a given pumping well or combination of wells at a particular time.
  96. Area of influence of a well Area surrounding a well within which the piezometric surface has been lowered when pumping has produced a maximum steady rate of flow.
  97. Area of Potential Effect (APE) The geographic area or areas within which an undertaking (project, activity, program, or practice) may cause changes in the character or use of any…
  98. Area Source An array of pollutant sources, so widely dispersed and uniform in strength that they can be treated in a dispersion model as an aggregate pollutant…
  99. Area sources (emissions) Any source of air pollution that is released over a relatively small area but which cannot be classified as a point source.
  100. Area Wide Hydrologic Prediction System (Abbrev. AWHPS) - A computer system which automatically ingests areal flash flood guidance values and WSR-88D products and displays this data and other…