Science terms starting with A

1,045 terms

  1. Atmospheric Radiation Infrared radiation (energy in the wavelength interval of 3- 80 micrometer) emitted by or being propagated through the atmosphere.
  2. Atmospheric Radiation Measurement (ARM) Program A multi-program, interagency program funded by the U.S. Department of Energy (DOE) since 1989.
  3. atmospheric temperature The temperature indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation.
  4. atmospheric turbulence High frequency velocity fluctuations that lead to turbulent transport of momentum, heat, mositure, and passive scalars, and often expressed in terms of…
  5. atmospheric window A region of the electromagnetic spectrum, from 8 to 12 micrometers, where the atmosphere is transparent to radiation.
  6. ATMP On a buoy report, the air temperature (Celsius).
  7. Atom A particle of matter indivisible by chemical means. It is the fundamental building block of elements.
  8. Atomic number The number assigned to each element on the basis of the number of protons found in the element's nucleus.
  9. Atomic weight The average weight (or mass) of all the isotopes of an element, as determined from the proportions in which they are present in a given element, compared…
  10. Atomic weight (atomic mass) Approximately the sum of the number of protons and neutrons found in the nucleus of an atom.
  11. Atoms The smallest unit of matter that possesses chemical properties. All atoms have the same basic structure: a nucleus containing positively charged protons…
  12. ATP A substance present in all living cells that provides energy for many metabolic processes and is involved in making RNA.
  13. ATP-ase An enzyme that brings about the hydrolysis of adenosine triphosphate, by the cleavage of either one phosphate groups with the formation of ADP and…
  14. Atrium An interior court to which rooms open.
  15. Attainment An area considered to have air quality as good as or better than the National Ambient Air Quality Standards for a given pollutant.
  16. Attainment area A geographic region where the concentration of a specific air pollutant does not exceed federal standards.
  17. attenuated vaccine A virulent organism that has been modified to produce a less virulent form, but nevertheless retains the ability to elicit antibodies against the virulent…
  18. Attenuation A mechanism for controlling gene expression in prokaryotes that involves premature termination of transcription.
  19. attenuator A nucleotide sequence in the 5' region of a prokaryotic gene (or in its RNA ) that causes premature termination of transcription, possibly by forming a…
  20. Atterberg limits (consistency limits) The boundaries (determined by laboratory tests) of moisture content in a soil between the liquid state and plastic state (known as liquid limit), between…
  21. Attic The usually unfinished space above a ceiling and below a roof.
  22. Attic Fan A fan mounted on an attic wall used to exhaust warm attic air to the outside.
  23. Attic Vent A passive or mechanical device used to ventilate an attic space, primarily to reduce heat buildup and moisture condensation.
  24. ATTM At this time
  25. Attribute survey Survey to determine the important components of the recreational experience.
  26. ATV all-terrain vehicle.
  27. Atypical (a-tip'ih-kul) irregular; not conformable to the type; an unusual type.
  28. Audit (Energy) The process of determining energy consumption, by various techniques, of a building or facility.
  29. Auger A rotating, screw-type device that moves material through a cylinder. In alcohol production, it is used to transfer grains from storage to the grinding…
  30. Augmentation Plan A court-approved plan that allows a junior water user to divert water out of priority so long as adequate replacement is made to the affected stream…
  31. Augmentation water Water used for the replacement of out of priority depletions.
  32. Augmented report A meteorological report prepared by an automated surface weather observing system for transmission with certified observers signed on to the system to add…
  33. AUM animal unit months.
  34. AUO administratively uncontrollable overtime.
  35. aureofacin An antifungal antibiotic produced by a strain of Streptomyces aureofaciens. A possible candidate for the transgenic control of plant fungal disease.
  36. Aurora A display of colored light in the atmosphere, caused by collisions between charged particles from a planet’s magnetosphere and atmospheric gases near…
  37. Aurora Australis Same as Aurora Borealis, but in the Southern Hemisphere. Also known as the southern lights; the luminous, radiant emission from the upper atmosphere over…
  38. Aurora Borealis Also known as the northern lights; the luminous, radiant emission from the upper atmosphere over middle and high latitudes, and centred around the earth's…
  39. Auroral Oval The ring-shaped belts of auroral activity around the north and south magnetic poles.
  40. Auroral Substorms They are caused by streams of charged particles in the magnetotail that are accelerated to high energies and collide with atoms in the upper atmosphere…
  41. authentic protein A recombinant protein that has all the properties - including any post-translational modifications - of its naturally occurring counterpart.
  42. Author's signature This is the signature of the person or persons with primary responsibility for writing the document.
  43. Authorization The issuance of approval, by a credit card issuer, merchant, or other affiliate, to complete a credit card transaction.
  44. Authorized Reclamation project A congressionally approved Bureau of Reclamation project that has been authorized for specific purposes.
  45. auto-immune disease Disorder in which the immune systems of affected individuals produce antibodies against molecules that are normally produced by those individuals (called…
  46. auto-immunity A disorder in the body's defence mechanism in which an immune response is elicited against its own (self) tissues.
  47. Autoantibody An antibody that reacts with antigens found on the cells and tissues of an individual's ownbody. Autoantibodies can cause autoimmune diseases.
  48. autocatalysis Catalysis in which one of the products of the reaction is a catalyst for the reaction.
  49. autocatalytic reaction See: autocatalysis.
  50. autoclave (AW-toh-KLAYV) A device that uses steam under high pressure to sterilize medical and laboratory supplies and equipment.
  51. autogenous control The action of a gene product to inhibit (negative autogenous control) or enhance (positive autogenous control) the expression of the gene that codes for…
  52. Autoignition Temperature The lowest temperature at which a flammable gas vapor will ignite spontaneously, without a source of ignition, after several minutes of exposure to…
  53. Autoimmune disease (AW-toh-ih-MYOON...) A condition in which the body recognizes its own tissues as foreign and directs an immune response against them.
  54. Autoimmune Lymphoproliferative syndrome (ALPS) A human disease caused by failure of lymphocytes to die once they have finished doing their job.
  55. Autologous (aw-TAH-luh-gus) Taken from an individual's own tissues, cells, or DNA.
  56. autologous cells Cells taken from an individual, cultured (or stored), and, possibly, genetically manipulated before being transferred back into the original donor.
  57. Autologous Stem Cell Transplant A transplant involving the infusion of a patient's own bone marrow or stem cells to produce new, healthy marrow.
  58. Autologous transplant Cell, tissue or organ transplants from one individual back to the same individual. Such transplants do not induce an immune response and are not rejected.
  59. autolysis The process of self destruction of a cell, cell organelle, or tissue, through the action of lysosomic enzymes.
  60. Automated Event Reporting Gage (see Tipping Bucket Rain Gage); for river stage gages, IFLOWS pressure transducer type gages can be programmed to report if water surface rises or falls…
  61. Automated Local Evaluation in Real Time (ALERT) A local flood warning system where river and rainfall data are collected via radio signals in real-time at an ALERT base station.
  62. Automated mitigation procedure A procedure under which the bids of individual suppliers are capped under certain predetermined conditions.
  63. Automated Report A meteorological report prepared by an automated surface weather observing system for transmission, and with no certified weather observers signed on to…
  64. Automated Surface Observing System The ASOS program is a joint effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the Department of Defense (DOD).
  65. Automated Tone Dial Telephone Data Collection System (ATDTDCS) Data collection system where cooperative observers collect precipitation, stage, and temperature data then transmit the data to the NWS ATDTDCS computer…
  66. Automatic (or Remote) Meter Reading System A system that records the consumption of electricity, gas, water, etc, and sends the data to a central data accumulation device.
  67. Automatic Damper A device that cuts off the flow of hot or cold air to or from a room as controlled by a thermostat.
  68. AUTOMATIC GAIN CONTROL Any method of automatically controlling the gain of a receiver, particularly one that holds the output level constant regardless of the input level.
  69. Automatic generation control The automatic regulation of the power output of electric generators within a prescribed range in response to a change in system frequency, or tie-line…
  70. Automatic generation control (AGC) Computerized power system regulation to maintain scheduled generation within a prescribed area in response to changes in transmission system operational…
  71. autonomous A term applied to any biological unit that can function on its own, i.e. without the help of another unit, such as a transposable element that encodes an…
  72. autonomous(ly) replicating segment (or sequence) (Abbreviation: ARS). Any eukaryotic DNA sequence that initiates and supports chromosomal replication; they have been isolated in yeast cells.
  73. autopolyploid A polyploid whose constituent genomes are derived from the same or nearly the same progenitor.
  74. autoradiograph A technique for visualizing the presence, location and intensity of radioactivity in histological preparations, paper chromatograms or electrophoretic gel…
  75. Autoradiography A technique that uses X-ray film to visualize radioactively labeled molecules or fragments of molecules; used in analyzing length and number of DNA…
  76. Autosomal dominant A pattern of Mendelian inheritance whereby an affected individual possesses one copy of a mutant allele and one normal allele.
  77. Autosome A chromosome that is not involved in sex determination.
  78. autotroph Organism capable of self-nourishment utilizing carbon dioxide or carbonates as the sole source of carbon and obtaining energy from radiant energy or from…
  79. autotrophic (adj.) See: autotroph.
  80. Autumn The season of the year that is the transition period from summer to winter, occurring as the sun approaches the winter solstice.
  81. Autumnal Equinox The equinox at which the sun approaches the Southern Hemisphere, marking the start of astronomical autumn in the Northern Hemisphere.
  82. Auxiliary Energy or System Energy required to operate mechanical components of an energy system, or a source of energy or energy supply system to back-up another.
  83. Auxiliary equipment Accessory equipment necessary for the operation of a generating station.
  84. Auxiliary Spillway A spillway, usually located in a saddle or depression in the reservoir rim which leads to a natural or excavated waterway, located away from the dam which…
  85. auxin A group of plant growth regulators (natural or synthetic) which stimulate cell division, enlargement, apical dominance, root initiation, and flowering.
  86. auxin-cytokinin ratio The relative proportion of auxin to cytokinin present in plant tissue culture media.
  87. auxotroph A mutant cell or micro-organism lacking one metabolic pathway present in the parental strain, and that consequently will not multiply on a minimal medium…
  88. AVADS Automated Vacancy Announcement Distribution System.
  89. Availability A reflection of the form and location of nutritional elements and their suitability for absorption.
  90. Available capacity The amount of water held in the soil that is available to the plants. See water holding capacity.
  91. Available Heat The amount of heat energy that may be converted into useful energy from a fuel.
  92. Avalanche A mass of snow, rock, and/or ice falling down a mountain or incline. In practice, it usually refers to the snow avalanche.
  93. Avalanche Advisory A preliminary notification that conditions may be favorable for the development of avalanches in mountain regions.
  94. AVBL Available
  95. Average A stock market average is a mathematical way of reporting the composite change in prices of the stocks that the average includes.
  96. Average Annual Daily Traffic (AADT) A measurement representing the total number of vehicles passing a given location, based upon 24-hour counts taken over an entire year.
  97. Average annual runoff For a specified area, the average value of annual runoff amounts calculated for a selected period of record that represents average hydrologic conditions.
  98. Average Cost The total cost of production divided by the total quantity produced.
  99. Average degree of consolidation The ratio of the total volume change in a soil mass at a given time to the total volume change anticipated in the soil mass due to primary consolidation.
  100. Average Demand The demand on, or the power output of, an electrical system or any of its parts over an interval of time, as determined by the total number of…