Science — page 90 of 132

13,110 terms including subtopics (0 terms filed directly here)

Science terms

pharmacokinetics (FAR-muh-koh-kih-NEH-tix) The activity of drugs in the body over a period of time, including the processes by which drugs are absorbed, distributed in the…
Phase Alternating current is carried by conductors and a ground to residential, commercial, or industrial consumers.
Phase Change A method of storing information on rewritable optical discs.
phase state The coupling or repulsion of two linked genes.
Phase Transition Change from one state of energy to another.
Phase-Change Material A material that can be used to store thermal energy as latent heat. Various types of materials have been and are being investigated such as inorganic…
PHB Abbreviation for polyhydroxybutyrate.
Phenocopy An environmentally induced, non hereditary variation in an organism, resembling a genetically determined trait.
phenolic oxidation Common aspect of the wound response in plants. Phenolic oxidation is often indicated by blackening of tissue and it may be a precursor to growth…
phenolics Compounds with hydroxyl group(s) attached to the benzene ring, forming esters, ethers and salts.
Phenomenological Model A computer model used to calculate air pollution concentrations. A phenomenological model focuses on an individual phenomenon, such as plume impingement…
Phenotype The observable characteristics of an organism, the expression of gene alleles (genotype) as an observable physical or biochemical trait. See Genotype.
Phenotypic characteristics The genetically and environmentally determined physical characteristics of an organism.
Pheromone A hormone-like substance that is secreted into the environment.
Phiezometer In hydrologic terms, an instrument used to measure pressure head in a conduit, tank, soil, etc. They are used in dams to measure the level of saturation.
Philadelphia rod A leveling rod in which the hundredths of feet, or eights of inches, are marked by alternate bars of color the width of the measurement.
phloem Specialized vascular plant tissue for the transport of assimilates (generally sugars) from the point of synthesis (in the leaf) to other parts of the…
Phosphatase An enzyme that hydrolyzes esters of phosphoric acid, removing a phosphate group.
phosphodiester (phospho-diester) bond A bond in which a phosphate group joins adjacent carbons through ester linkages.
Phosphodiester bond A bond in which a phosphate group joins adjacent carbons through ester linkages.
phospholipase A2 An enzyme which degrades type A2 phospholipids.
phospholipid A lipid (fat) that contains phosphorus. Phospholipids are a major part of cell membranes.
phosphorolysis The cleavage of a bond by orthophosphate; analogous to hydrolysis referring to cleavage by water.
Phosphorous A chemical element used as a dopant in making n-type semiconductor layers. An essential chemical food element that can contribute to the eutrophication of…
Phosphorylation The addition of a phosphate group to a compound.
photo-bioreactor Bioreactor dependent on sunlight, which is taken up by its content of plant material, usually algae.
photoautotroph See:.
Photobiological Hydrogen Production A hydrogen production process that process uses algae. Under certain conditions, the pigments in certain types of algae absorb solar energy.
Photochemical Smog Air pollution containing ozone and other reactive chemical compounds formed by the reaction of nitrogen oxides and hydrocarbons in the presence of…
photoconversion Conversion of light into other forms of energy by chemical, biological, or physical processes.
Photocurrent An electric current induced by radiant energy.
Photoelectric Cell A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in…
Photoelectrochemical Cell A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen…
Photoelectrolysis Hydrogen Production The production of hydrogen using a photoelectrochemical cell.
Photogalvanic Processes The production of electrical current from light.
Photogrammetry Techniques of obtaining precise measurements from images. This process can derive elevation from specially created stereo pairs of aerial photos.
photoheterotroph See: heterotroph.
Photon A photon is both a wave and a particle. A beam of light is composed of these particles.
photoperiod The length of daylight or period of daily illumination provided for growth.
photoperiodism The photoperiod required by a plant to switch from the vegetative to the reproductive stage.
photophosphorylation The formation of ATP from ADP and inorganic phosphate using light energy harvested by photosynthesis.
photoreactivation A light dependent DNA repair process.
Photosphere The Sun’s surface, from which the light we actually see (with the human eye) is emitted. Temperatures average 5,800 K (9,900°F).
photosynthate The carbohydrates and other compounds produced in photosynthesis.
Photosynthesis A chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight.
photosynthetic Able to use sunlight energy to convert atmospheric carbon dioxide into organic compounds.
photosynthetic efficiency Efficiency of converting light energy into organic compounds.
photosynthetic photon flux (Abbreviation: PPF). A measure of the intensity of light utilized by plants for photosynthetic activity.
photosynthetically active radiation (Abbreviation: PAR). The part of the radiant energy that is capturable by natural photosynthetic systems (approximately equivalent to the natural light…
phototropism The tendency of plants to direct shoot growth towards the source of light.
Photovoltaic A system that converts direct sunlight to electricity using semi-conductor materials.
Photovoltaic (Conversion) Efficiency The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.
Photovoltaic (PV) (PV) Literally, "light" (photo) and "electricity" (voltaic). The class of equipment used to generate electricity directly from sunlight.
Photovoltaic (PV) array (PV) An interconnected system of PV modules that function as a single electricity-producing unit.
Photovoltaic (PV) cell (PV) The smallest semiconductor element within a PV module that converts incident sunlight into electrical energy (direct current voltage and current).
Photovoltaic (PV) facility (PV) A solar energy facility that uses photovoltaic cells to produce electricity and that includes all components, such as the PV system, power conditioning…
Photovoltaic (PV) module (PV) An assembly of solar cells (flat-plate type) or receiver(s) and optics (concentrator type) and ancillary parts, such as interconnects and terminals…
Photovoltaic (PV) panel (PV) A collection of modules, either flat-plate or concentrator type, mechanically fastened, electrically interconnected, and designed to provide a…
Photovoltaic (PV) power plant (PV) See Photovoltaic (PV) facility
Photovoltaic (PV) receiver (PV) An assembly of one or more PV cells that accepts concentrated sunlight and incorporates means for thermal and electric energy removal.
Photovoltaic (PV) system (PV) See Photovoltaic (PV) facility
Photovoltaic (PV; Solar) Array A group of solar photovoltaic modules connected together.
Photovoltaic (Solar) Cell Treated semiconductor material that converts solar irradiance to electricity.
Photovoltaic (Solar) Module or Panel A solar photovoltaic product that generally consists of groups of PV cells electrically connected together to produce a specified power output under…
Photovoltaic (Solar) System A complete PV power system composed of the module (or array), and balance-of-system (BOS) components including the array supports, electrical…
Photovoltaic and solar thermal energy Energy radiated by the sun as electromagnetic waves (electromagnetic radiation) that is converted into electricity by means of solar (i.e.
Photovoltaic Device A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the…
Photovoltaic Peak Watt see Peak Watt.
Photovoltaic-Thermal (PV/T) Systems A solar energy system that produces electricity with a PV module, and collects thermal energy from the module for heating.
Photovoltaics (PV) (PV) Technologies that utilize semiconducting materials that convert sunlight directly into electricity.
Phreatic surface The free surface of water seeping at atmospheric pressure through soil or rock.
Phreatic vegetation Vegetation supported by groundwater below the land surface.
Phreatic water Water within the earth that supplies wells and springs; water in the zone of saturation where all openings in rocks and soil are filled, the upper surface…
Phreatic Zone The locus of points below the water table where soil pores are filled with water. This is also called the zone of saturation.
Phreatophyte Water-loving plant. Vegetation that consumes much water.
Phreatophytes Any plant, typically living in the desert, that obtains its water from long taproots that reach the water table.
phylogeny The deduced evolutionary history of related organisms.
Physical basis Describes a physical natural gas purchase for the following month where the price is tied to the closing price of the expiring Nymex futures contract.
Physical map A map showing physical locations on a DNA molecule, such as restriction sites, and sequence-tagged sites. (See Mapping.)
Physical Vapor Deposition A method of depositing thin semiconductor photovoltaic) films. With this method, physical processes, such as thermal evaporation or bombardment of ions…
Physiography The physical geography of an area or the description of its physical features.
phyto- (Prefix) To do with plants.
phytochemical (FY-toh-KEH-mih-kuhl) A substance found in plants. Some phytochemicals may reduce the risk of cancer.
phytochrome A pigment, found in the cytoplasm of green plants, which can exist in two forms Pr (biologically inactive) and Pfr (biologically active).
phytohormone A substance that stimulates growth or other processes in plants. Major species are auxin s, abscisic acid, cytokinin s, gibberellin s and ethylene.
phytokinin See: cytokinin.
phytoparasite Parasite on plants.
phytoparasitic (adj.) See: phytoparasite.
phytopathogen A plant pathogen.
Phytophagous Plant eating.
Phytoplankton Small, often single-celled plants that live suspended in bodies of water.
phytoremediation The use of plants actively to remove contaminants or pollutants from either soils (e.g. polluted fields) or water resources (e.g. polluted lakes).
phytosanitary Plant health, including quarantine.
phytostat Apparatus designed for the semi-continuous chemostatic culture of plant cells.
phytosterol A plant-based compound that can compete with dietary cholesterol to be absorbed by the intestines, resulting in lower blood cholesterol levels.
PIBAL Pilot balloon. A small helium-filled meteorological balloon that is tracked as it rises through the atmosphere to determine how wind speed and direction…
Pico A prefix meaning "one trillionth".
Pictograph A design drawn in pigment upon an unprepared or ground rock surface.
Piezometer A nonpumping well, generally of small diameter, for measuring the elevation of a water table.
Piezometric Level (or Surface) Confined groundwater is usually under pressure because of the weight of the overburden and the hydrostatic head.