Science terms starting with A

1,045 terms

A Abbreviation for adenine.
A AMS Arctic Air Mass
A Index A daily index of geomagnetic activity derived as the average of the eight 3-hourly a indices.
A&E (A/E) architectural and engineering.
A-site Abbreviation for aminoacyl site.
AAAS American Association for the Advancement of Science
AAC All American Canal.
AADT See Average Annual Daily Traffic
AAHU average annual habitat units.
AAM annual arithmetic mean.
AAR alkali-aggregate reaction.
AAWU Alaskan Aviation Weather Unit
AB Abbreviation for antibody.
ABC activity based cost accounting - an accrual-based accounting method for determining unit-based costs of delivering services by allocating the costs to…
ABC model Widely accepted model of flower organ identity that appears generally applicable to distantly related dicotyledon ous, although less well to monocotyledon…
Aberrant Atypical, departing from the normal type or structure.
Aberration With regards to physics, a discontinuity or distortion in an image produced by a lens.
Abiotic Absence of living organisms.
Abiotic stress Outside (nonliving) factors which can cause harmful effects to plants, such as soil conditions, drought, extreme temperatures.
Ablation (a-BLAY-shun) In medicine, the removal or destruction of a body part or tissue or its function.
ABNDT Abundant
Abrasion Wearing away of surfaces by friction.
abrupt climate change a change in the climate (for example, temperature or precipitation) that takes place over a few decades or less, persists for at least a few decades, and…
abscisic acid A phytohormone implicated in the control of many plant responses to abiotic stress, such as extent of stomatal opening under water deficit (i.e.
absolute dating the process of determining a specific, numerical age for an old material. This may be accomplished using one of a variety of methods, including…
Absolute Humidity The ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air.
Absolute pressure Atmospheric pressure plus gauge pressure.
Absolutely Stable Air An atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic lapse rate.
Absolutely Unstable Air An atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic lapse rate.
Absorbed dose Energy imparted to a body by radiation, measured per unit mass (kg) of tissue.
Absorbed water Water held mechanically in a soil or rock mass and having physical properties not substantially different from ordinary water at the same temperature and…
Absorbent A material that extracts one or more substances from a fluid (gas or liquid) medium on contact, and which changes physically and/or chemically in the…
Absorber The component of a solar thermal collector that absorbs solar radiation and converts it to heat, or, as in a solar photovoltaic device, the material that…
Absorption (ub-SORP-shun) The process of taking nutrients from the digestive system into the blood so they can be used in the body.
Absorption Chiller A type of air cooling device that uses absorption cooling to cool interior spaces.
Absorption Coefficient In reference to a solar energy conversion devices, the degree to which a substance will absorb solar energy.
Absorption Cooling A process in which cooling of an interior space is accomplished by the evaporation of a volatile fluid, which is then absorbed in a strong solution, then…
Absorption factor The fraction of a chemical making contact with an organism that is absorbed by the organism.
Absorption of radiation The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted. See radiation.
Absorption Refrigeration A system in which a secondary fluid absorbs the refrigerant, releasing heat, then releases the refrigerant and reabsorbs the heat.
Absorption Spectra The spectra of electromagnetic radiation transmitted through a substance, with dark lines indicating the absorption of specific wavelengths.
absorptivity In a solar thermal system, the ratio of solar energy striking the absorber that is absorbed by the absorber to that of solar energy striking a black body…
ABT About
Abutment That part of the valley wall against which the dam is constructed. The part of a dam that contacts the riverbank.
Abutment Seepage Reservoir water that moves through seams or pores in the natural abutment material and exits as seepage.
Abutment Seeping Reservoir water that moves through seams or pores in the natural abutment material and exits as seepage.
ABV Above
Abzyme See Catalytic antibody.
AC Armor Class or Defense.
ac-ft acre-foot, acre-feet.
acaricide A pesticide used to kill or control mites or ticks.
ACC synthase Abbreviation for 1-aminocyclopropane-1-carboxylase. The enzyme catalyses the rate limiting step in the ethylene biosynthetic pathway, and is particularly…
ACCAS (usually pronounced ACK-kis) - A lto C umulus CAS tellanus; mid-level clouds (bases generally 8 to 15 thousand feet), of which at least a fraction of…
Accelerating Universe One where distance increase faster with time, in contradiction to those where the gravitational attraction of ordinary matter slows down the expansion.
Acceleration The right of the lender to demand payment on the outstanding balance of a loan.
Acceleration (peak horizontal) A measure of earthquake acceleration (i.e., shaking) on the ground surface expressed in g, the acceleration due to the Earth's gravity.
Accelerogram The record from an accelerometer showing acceleration as a function of time.
Accent lighting Draws attention to special features or enhances the aesthetic qualities of an indoor or outdoor environment.
Acceptable daily intake (ADI) Estimate of the largest amount of a chemical to which a person can be exposed on a daily basis that is not anticipated to result in adverse effects…
acceptor control The regulation of the rate of respiration by the availability of ADP as a phosphate acceptor.
acceptor junction site The junction between the 3' end of an intron and the 5' end of an exon. See: donor junction site.
access charge A charge levied on a power supplied, or its customer, for access to a utility's transmission or distribution system.
Access control point A location staffed to restrict entry of unauthorized personnel into a risk area during emergency and/or disaster events.
Access roads Gravel or dirt roads (rarely paved) that provide overland access to transmission line and pipeline rights-of-way (ROWs) and facilities for construction…
Access shaft Concrete portion of an outlet works between the shaft house and the gate chamber. The access shaft provides vertical access to the gates.
accessory bud A lateral bud occurring at the base of a terminal bud or at the side of an axillary bud.
Accessory Cloud A cloud which is dependent on a larger cloud system for development and continuance.
Accessory Dwelling Unit (ADU) A self-contained housing unit incorporated within a single-family dwelling (not within accessory structures, except with a Special Permit) that is clearly…
Accident assessment The evaluation of the nature, severity, and impact of an accident. Dam operating personnel are primarily responsible for accident assessment for incidents…
Acclimation Adjustment of an organism to a new habitat or environment.
acclimatization The adaptation of a living organism (plant, animal or micro-organism) to a changed environment that subjects it to physiological stress.
Accretion Process of growth whereby material is added to the outside of nonliving matter.
ACCUMS accumulation
Accumulating shear A feller-buncher shearhead that is capable of accumulating and holding 2 or more cut stems.
accumulation used in paleoclimatology to describe the deposition of sediment or other material over time.
Accumulator A component of a heat pump that stores liquid and keeps it from flooding the compressor.
Accuracy Department of Defense parlance for the notion that information has been maintained and transferred in such a way as to be inviolate (the information has…
ACEC area of critical environmental concern.
acellular Tissues or organisms that are not made up of separate cells but often have more than one nucleus.
acentric chromosome Chromosome fragment lacking a centromere.
ACER Assistant Commissioner - Engineering and Research.
ACES Automated Coastal Engineering System.
acetic acid An acid with the structure of C2H4O2. Acetyl groups are bound through an ester linkage to hemicellulose chains, especially xylans, in wood and other…
acetyl co-enzyme A (Abbreviation: acetyl CoA) A compound formed in the mitochondria when an acetyl group (CH3CO-) - derived from breakdown of fats, protein s, or…
acetyl CoA Abbreviation for acetyl co-enzyme A.
ACGIH American Conference of Government Industrial Hygienists.
ACHP Advisory Council on Historic Preservation.
ACID A solution that has an excess of hydrogen ions (H+).
Acid deposition A comprehensive term for the various ways acidic compounds precipitate from the atmosphere and deposit onto surfaces.
acid detergent fiber (ADF) Organic matter that is not solubilized after one hour of refluxing in an acid detergent of cetyltrimethylammonium bromide in 1N sulfuric acid.
Acid hydrolysis A chemical process in which acid is used to convert cellulose or starch to sugar.
acid insoluble lignin Lignin is mostly insoluble in mineral acids, and therefore can be analyzed gravimetrically after hydrolyzing the cellulose and hemicellulose fractions of…
Acid Precipitation Precipitation, such as rain, snow or sleet, containing relatively high concentrations of acid-forming chemicals that have been released into the…
Acid Rain A term used to describe precipitation that has become acidic (low pH) due to the emission of sulfur oxides from fossil fuel burning power plants.
acid soluble lignin A small fraction of the lignin in a biomass sample is solubilized during the hydrolysis process of the acid insoluble lignin method.
Acid Solution Any water solution that has more hydrogen ions (H+) than hydroxide ions (OH-); any water solution with a pH less than 7. See basic solution.
Acidic The condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.
Acidified The addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0.
ACLD Above Cloud Level
ACP Abbreviation for acyl carrier protein.