Science terms starting with V

227 terms

V Notch A radar reflectivity signature seen as a V-shaped notch in the downwind part of a thunderstorm echo.
V region Variable region in antibodies. See: CDR.
V&V Abbreviation for volume per volume. The relative proportion of each liquid in a mixture.
V-notch weir A weir that is V-shaped, with its apex downward, used to accurately measure small rates of flow.
VAAC Volcanic Ash Advisory Centers
vaccination Treatment with a vaccine.
vaccine A substance or group of substances meant to cause the immune system to respond to a tumor or to microorganisms, such as bacteria or viruses.
Vaccinia The cowpox virus used to vaccinate against smallpox and, experimentally, as a carrier of genes for antigenic determinants cloned from other disease…
vacuole A fluid-filled membrane-bound cavity inside many plant cells, in which various plant products and by-products are stored.
vacuum distillation The separation of two or more liquids under reduced vapor pressure; reduces the boiling points of the liquids being separated.
Vacuum Energy A theorized energy everywhere in space, arising from quantum mechanics.
Vacuum Evaporation The deposition of thin films of semiconductor material by the evaporation of elemental sources in a vacuum.
VAD Velocity Azimuth Display
VAD Wind Profile A radar plot of horizontal winds, derived from VAD data, as a function of height above a Doppler Radar.
Vadose Zone The locus of points just above the water table where soil pores may either contain air or water. This is also called the zone of aeration.
VALDRIFT An air pollution transport and diffusion model developed to determine pesticide drift from aerial spraying operations in valleys.
Valence Band The highest energy band in a semiconductor that can be filled with electrons.
Valid Time The period of time during which a forecast or warning, until it is updated or superseded by a new forecast issuance, is in effect.
Valid Time Event Code (VTEC) - The Valid Time Event Code (VTEC) always is used in conjunction with, and provides supplementary information to, the Universal Geographic Code…
Valley Exit Jet A strong elevated down-valley air current issuing from a valley above its intersection with the adjacent plain.
Valley floor The gently sloping to nearly level bottom surface of a valley.
Valley segment That portion of a stream network with similar morphologies and governing geomorphic processes identified by valley bottom and sideslope geomorphic…
Valley Volume Effect The reduction in volume of a valley (or basin) as compared to an equal depth volume with a horizontal floor.
value-added product (VAP) Physical models using ARM instrument data as inputs used to fulfill some of the unmet measurement needs of the ARM Program and to improve the quality of…
Valve A device used to control the flow in a conduit, pipe, or tunnel that permanently obstructs a portion of the waterway.
Vane shear test An in-place shear test in which a rod with thin radial vanes at the end is forced into the soil and the resistance to rotation of the rod is determined.
Vapor Pressure The partial pressure of water vapor in an air-water system.
Vapor Retarder A material that retards the movement of water vapor through a building element (walls, ceilings) and prevents insulation and structural wood from becoming…
Variable costs Input costs that change as the nature of the production activity of its circumstances change; for example, as production levels vary.
variable domain Regions of antibody molecules that have different amino acid sequences in different antibody molecules.
variable expressivity Variation in the phenotype caused by different alleles of the same gene and/or by the action of other genes and/or by the action of non-genetic factors.
variable number tandem repeat (Abbreviation: VNTR). A DNA sequence, present as tandem repeats, for which the number of copies varies greatly between unrelated genotypes.
Variable Stars Stars which brighten and dim, some with precise regularity. For Cepheid variables, their period allows determination of their brightness, and so their…
variable surface glycoprotein (Abbreviation: VSG). One of a battery of antigenic determinants expressed by a micro-organism to elude immune detection.
Variable surface glycoprotein (VSG) One of a battery of antigenic determinants expressed by a microorganism to elude immune detection.
Variable Wind Same as Variable Wind Direction; a condition when (1) the wind direction fluctuates by 60° or more during the 2-minute evaluation period and the wind…
Variable Wind Direction A condition when (1) the wind direction fluctuates by 60° or more during the 2-minute evaluation period and the wind speed is greater than 6 knots; or…
Variable-Speed Wind Turbines Turbines in which the rotor speed increases and decreases with changing wind speed, producing electricity with a variable frequency.
Variance A special exemption of a zoning law to allow the property to be used in a manner different from an existing law.
variant An individual that is genetically distinct from others in the population.
Variation Differences in the frequency of genes and traits among individual organisms within a population.
variegation The occurrence, within a single tissue, organ or organism, of mosaicism. Usually referring to plants showing either both green and albino colouration in a…
Variety 1. A naturally occurring subdivision of a species, with distinct morphological characters. 2.
varve annual layer of sediment deposited in an ocean or lake.
Varved A sedimentary bed or lamination that is deposited within one year's time.
Vascular Plant tissue specialized for the conduction of water or nutrients
vascular bundle A strand of tissue containing and primary phloem (and procambium if present) and frequently enclosed by a bundle sheath of parenchyma or fibres.
vascular cambium In biennials and perennials, cambium giving rise to secondary phloem and secondary xylem.
vascular plant Plant species possessing organized vascular tissues.
vascular system 1. A specialized network of vessels for the circulation of fluids throughout the body tissue of an animal. 2. The system of in plants.
VCNTY Vicinity
VCP Volume Coverage Pattern - A volumetric sampling procedure designed for the surveillance of one or more particular meteorological phenomena.
Vebe time The time for concrete to fully consolidate in a Vebe cylinder.
vector any living creature that transmits an infectious agent to humans.
Veering A clockwise shift in wind direction (for example, south winds shifting to the west).
Veering Winds Winds which shift in a clockwise direction with time at a given location (e.g., from southerly to westerly), or which change direction in a clockwise…
Vegetative controls Nonpoint source pollution control practices that involve plants (vegetative cover) to reduce erosion and minimize the loss of pollutants.
vegetative propagation See: asexual propagation.
Vehicle Categories A system of classifying vehicles (e.g., passenger cars, commercial vehicles, trailers, off-road vehicles, and special-purpose vehicles).
Vehicle miles traveled (VMT) One vehicle traveling the distance of one mile. Thus, total vehicle miles is the total mileage traveled by all vehicles.
Vehicle Weight Class The size of vehicles. Includes light-duty, medium-duty, and heavy-duty vehicles based on their gross vehicle weight rating (the weight of a vehicle on its…
Vein (vayn) a vessel through which blood passes from various organs or parts back to the heart.
Velocity The rate and direction of change of an object's position. The speed and direction at which something is moving.
Velocity Azimuth Display A WSR 88-D product which shows the radar derived wind speeds at various heights.
Velocity Cross Section This WSR-88D radar product displays a vertical cross section of velocity on a grid with heights up to 70,000 feet on the vertical axis and distance up to…
velocity density gradient centrifugation A procedure used to separate macromolecules based on their rate of movement through a density gradient.
Velocity Zones Areas within the floodplain subject to potential high damage from waves. These sometimes appear on flood insurance rate maps.
velogenetics The combined use of marker-assisted selection and embryo technologies such as OPU, IVM and IVF, in order to increase the rate of genetic improvement in…
Vent A component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.
Vent Damper A device mounted in the vent connector that closes the vent when the heating unit is not firing.
Vent Pipe A tube in which combustion gases from a combustion appliance are vented out of the appliance to the outdoors.
Vented Heater A type of combustion heating appliance in which the combustion gases are vented to the outside, either with a fan (forced) or by natural convection.
Ventilation The process of moving air (changing) into and out of an interior space either by natural or mechanically induced (forced) means.
Ventilation Air That portion of supply air that is drawn from outside, plus any recirculated air that has been treated to maintain a desired air quality.
Ventilation Index Product of the mixing depth and transport wind speed, a measure of the potential of the atmosphere to disperse airborne pollutants from a stationary…
Venturi A pressure jet that draws in and mixes air.
Venturi Effect The speedup of air through a constriction due to the pressure rise on the upwind side of the constriction and the pressure drop on the downwind side as…
Ver High Frequency (VHF) That portion of the radio frequency spectrum from 30 to 300 MHz
vermiculite Material made from expanded mica used as a rooting medium and as a soil additive.
Vernal pool Seasonally-flooded depressions found on soils with an impermeable layer such as a hardpan, claypan, or volcanic basalt.
vernalization Chilling juvenile plants for a minimum period in order to induce flowering. Some plants require veRNA lization to flower, but others have no such…
Vernier A device permitting finer measurement or control than standard markings or adjustments.
Vertebrate Any species having a backbone or spinal column including fish, amphibians, reptiles, birds, and mammals.
Vertical angle of view Elevation of viewer relative to the elevation of the proposed action, and the resulting angle of difference.
Vertical curve The meeting of different gradients in a road or pipe.
Vertical Ground Loop In this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are laid out in a plane perpendicular to the…
Vertical lift gate All rectangular gates set in vertical guides within which the gate moves vertically in its own plane. The hoist is usually on a runway overhead.
Vertical transmission Inheritance of a gene from parent to offspring.
Vertical Velocity The component of velocity (motion) in the vertical. The evaluation of areas of upward vertical velocity is key to forecasting areas of active weather.
Vertical Wind Shear the change in the wind's direction and speed with height. This is a critical factor in determining whether severe thunderstorms will develop.
Vertical-Axis Wind Turbine (VAWT) A type of wind turbine in which the axis of rotation is perpendicular to the wind stream and the ground.
Vertically Stacked System A low-pressure system, usually a closed low or cutoff low, which is not tilted with height, i.e., located similarly at all levels of the atmosphere.
Very Low Frequency (VLF) That portion of the radio frequency spectrum from 3 to 30 kHz
Very Windy 30 to 40 mph winds.
Vesicular (vesicles) Containing many small cavities formed by the expansion of a gas bubble or steam when the rock solidifies.
Vessel A series of xylem elements whose function is to conduct water and nutrients in plants.
vessel element A type of cell occurring within the xylem of flowering plants. Many are water-conducting vessels.
VFR Visual Flight Rules
viability The capability to live and develop normally.
viability test Assay of the number or percent of living cells or plants in a population following a specific treatment.