Science terms starting with P

1,062 terms

Power Transmission Line An electrical conductor/cable that carries electricity from a generator to other locations for distribution.
Power, electrical A unit of electrical energy, usually expressed in watts (W), kilowatts (kW), or megawatts (MW). One watt equals 3.14 Btu per hour.
Powerplant Structure that houses turbines, generators, and associated control equipment.
Powerplant capacity The capacity for powerplants is the nameplate rating in kW (kilowatts) and generally includes only the main generating units, except for very large plants…
PPA See U.S. Department of Agriculture.
PPF Abbreviation for photosynthetic photon flux.
PPI Plan Position Indicator
PPINE P lan P osition I ndicates N o E choes, referring to the fact that a radar detects no precipitation within its range.
PPM Abbreviation for parts per million.
PQPF Probabilistic QPF; a form of QPF (see below) that includes an assigned probability of occurrence for each numerical value in the forecast product.
PR protein Abbreviation for pathogenesis related protein.
PRBLTY Probability
PRBLY probably
PRCP Precipitation
pre-filter A coarse filter used to screen out large particles from a fluid or gas, before it is passed through a much finer filter.
Pre-Frontal Squall Line A line of thunderstorms that precedes an advancing cold front.
Pre-Frontal Trough An elongated area of relatively low pressure preceding a cold front that is usually associated with a shift in wind direction.
Pre-Hurricane Squall Line It is often the first serious indication that a hurricane is approaching. It is a generally a straight line and resembles a squall-line that occurs with a…
Pre-implantation embryo The very early, free-floating Embryo, from the time the egg is fertilized until implantation in the mother's womb is complete.
Pre-implantation embryos Fertilized eggs (zygotes) and all of the developmental stages up to, but not beyond, the blastocyst stage.
pre-mRNA See: primary transcript.
pre-transplant A stage in micropropagation - the rooting and hardening process prior to transfer to soil.
Precambrian The oldest and largest division of geologic time, between the consolidation of the Earth's crust and the beginning of the Cambrian period.
Precast dam A dam constructed mainly of large precast concrete blocks or sections.
precautionary principle The approach whereby any possible risk associated with the introduction of a new technology is avoided, until a full understanding of its impact on…
PRECD Precede
Precession The comparatively slow torquing of the orbital planes of all satellites with respect to the Earth's axis, due to the bulge of the Earth at the equator…
precession (of the equinoxes) the slow clockwise motion of the equinoxes along the path of the earth's orbit due to the wobble of the earth's axis.
Precipitable Water Measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given…
Precipitation The total measurable amount of water received in the form of snow, rain, drizzle, hail, and sleet.
Precipitation Attenuation The loss of energy that radar beam experiences as it passes through an area of precipitation.
Precipitation Mode The standard, or default, operational mode of the WSR-88D. The radar automatically switches into precipitation mode from clear-air mode if the measured…
Precipitation Processing System The WSR-88D system that generates 1-hour running, 3-hourly, and running storm total precipitation accumulations.
Precision The accuracy with which a number can be represented, i.e., the number of digits used to represent a number.
precocious germination Early germination of a seed or embryo, prior to the full maturation of the embryo.
Precommercial thinning Thinning for timber stand improvement purposes, generally in young, densely stocked stands.
Precursor Cells In fetal or adult tissues, these are partly differentiated cells that divide and give rise to differentiated cells. Also known as progenitor cells.
Predominant period The period(s) at which maximum spectral energy is concentrated.
Predominant Wind The wind that prevails and generates the local component of the significant sea conditions across the forecast area.
Preference Priority access to Federal power by public bodies and cooperatives.
Preference customers Publicly owned systems and non-profit cooperatives which, by law, have preference over investor-owned systems for purchase of power from Federal projects.
Preheater (Solar) A solar heating system that preheats water or air that is then heated more by another heating appliance.
Prehistoric The time period before the appearance of written records. In the New World this generally refers to indigenous, precontact societies.
Prehistoric resources Refers to any material remains, structures, and items used or modified by people before Euro-Americans established a presence in the region.
Preimplantation With regard to an embryo, preimplantation means that the embryo has not yet implanted in the wall of the uterus.
preliminary data Data that have not necessarily been subjected to review, quality control and/or documentation by a responsible investigator.
Preliminary Report Now known as the "Tropical Cyclone Report". A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone.
Premature chromosome condensation (PCC) A method of studying chromosomes in the interphase stage of the cell cycle.
Preparative Regimen The chemotherapy or radiation given before transplant.
Prepper An apocalyptically-minded individual preparing themselves for survival during an imminent societal or global change and, likely, disaster.
PRES Pressure
Prescribed burning Deliberate setting and careful control of surface fires in forests to help prevent more destructive fires and to kill off unwanted plants that compete…
Prescribed elevation The elevation as called out or dictated in notes, drawings or specifications paragraphs.
Prescribed Fire A management ignited or natural wildland fire that burns under specified conditions where the fire is confined to a predetermined area and produces the…
Prescribed fires Application of fire (by planned or unplanned ignitions) to fuels in either their natural or modified states, under specified conditions, to allow the fire…
Prescription A direction written by the physician to the pharmacist for the preparation and use of a medicine or remedy.
Present Movement The best estimate of the movement of the center of a tropical cyclone at a given time and given position.
Present value The current value of a future cash flow or series of cash flows discounted at an appropriate interest rate or rates.
Present Weather The type of weather observed at the reporting time. These conditions may include types and intensity of precipitation such as light rain or heavy snow, as…
Pressure The load divided by the area over which it acts.
Pressure Altimeter An aneroid barometer calibrated to indicate altitude in feet instead of units of pressure.
Pressure Altitude The altitude in standard atmosphere at which a given pressure will be observed.
Pressure Change The net difference between the barometric pressure at the beginning and ending of a specified interval of time, usually the three hour period preceding an…
Pressure Characteristic The pattern of the pressure change during the specified period of time, usually the three hour period preceding an observation.
Pressure Couplet It is an area where you have a high pressure area located adjacent to a low pressure area.
Pressure Drop The loss in static pressure of a fluid (liquid or gas) in a system due to friction from obstructions in pipes, from valves, fittings, regulators, burners…
Pressure Falling Rapidly A decrease in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inch or more.
Pressure Gage A device for registering the pressure of solids, liquids, or gases. It may be graduated to register pressure in any units desired.
Pressure Gradient The amount of pressure change occurring over a given distance.
Pressure Gradient Force A three-dimensional force vector operating in the atmosphere that accelerates air parcels away from regions of high pressure and toward regions of low…
Pressure Head The amount of force or pressure created by a depth of one foot of water.
Pressure Ice Floating sea, river, or lake ice that has been deformed, altered, or forced upward in pressure ridges by the lateral stresses of any combination of wind…
Pressure Induced Wave A rare type of wave that does not develop from wind or seismic activity. Instead, these waves develop as a pressure perturbation moves over the water…
Pressure Jump A sudden, sharp increase in atmospheric pressure, typically occurring along an active front and preceding a storm.
pressure potential The pressure generated within a cell, being the net difference between the cell's osmotic potential and the water potential of the external environment.
Pressure Relief Pipes Pipes used to relieve uplift or pore-water pressure in a dam foundation or in the dam structure.
Pressure Rising Rapidly An increase in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inch or more.
Pressure Tendency The character and amount of atmospheric pressure change during a specified period of time, usually 3-hour period preceding an observation.
Pressure Unsteady A pressure that fluctuates by 0.03 inch of mercury or more from the mean pressure during the period of measurement.
Pressure-driven Channeling Channeling of wind in a valley by synoptic-scale pressure gradients superimposed along the valley's axis. Compare forced channeling.
Pressurization Testing A technique used by energy auditors, using a blower door, to locate areas of air infiltration by exaggerating the defects in the building shell.
Prestressed dam A dam, the stability of which depends in part on the tension in steel wires, cables, or rods that pass through the dam and are anchored into the…
Preternatural Instead of being connected to the spiritual realm, like supernatural matters, the preternatural applies to things that are of the natural world but…
Prevailing Visibility The visibility that is considered representative of conditions at the station; the greatest distance that can be seen throughout at least half the horizon…
Prevailing Westerlies The westerly winds that dominant in middle latitudes.
prevailing wind The wind direction most frequently observed during a given period.
Prevailing Winds A wind that consistently blows from one direction more than from any other.
Prevention of Significant Deterioration A program, specified in the Clean Air Act, whose goal is to prevent air quality from deteriorating significantly in areas of the country that are…
Prevention of significant deterioration (PSD) Under the Clean Air Act, a planning and management process for air quality when a new source of air pollution is proposed in an area where ambient air…
Prevention of Significant Deterioration (PSD) Program A Federal air pollution permitting program intended to ensure that air quality does not diminish in attainment areas which meet national ambient air…
preventive immunization Infection with an antigen to elicit an antibody response that will protect the organism against future infections. Synonym: vaccination.
Prey base The assemblage of prey (food) animals available in a given area or habitat to support a predator such as a hawk or cougar.
Pribnow box Consensus sequence near the mRNA start-point of prokaryotic genes. See: TATA box.
Price Current Meter A current meter with a series of conical cups fastened to a flat framework through which a pin extends.
Price discovery The process of making prices visible and readily available to interested parties and, in some cases, the public.
Price/Earnings Ratio (P/E Ratio) A company’s stock price divided by its annual earnings, a widely used equity valuation measure.
PRIM Primary
Primacy The responsibility for ensuring that a law is implemented, and the authority to enforce a law and related regulations.
primary First in order of time or development.
Primary (or Principal) Spillway The spillway which would be used first during normal inflow and flood flows.