Science terms starting with H

545 terms

H Prefix used to designate the human form of an enzyme. For example, hGH is human growth hormone.
H-Alpha In solar-terrestrial terms, this absorption line of neutral hydrogen falls in the red part of the visible spectrum and is convenient for solar…
H-component of the Geomagnetic Field (Geomagnetic Elements) In solar-terrestrial terms, the components of the geomagnetic field at the surface of the earth.
H0 On a buoy report, Significant Wave Height is the average height (meters) of the highest one-third of the waves during a 20 minute sampling period.
H5 500 millibar level height (in a standard atmosphere this is near 5,500 meters (18,000 ft)
H7 height of the 700 millibar level. In a standard atmosphere this is near 3,000 meters (10,000 ft)
H8 height of the 850 millibar level.
H<sub>0</sub>, Hubble Constant A measure of the expansion rate and age of the universe. It appears to be between 60 and 80 kilometers per second per megaparsec.
Habitat The natural environment where people, animals and plants live. In an aquatic environment, it includes the water, topography, structure and cover present…
Habitat alteration A change in the particular environment or place where an organism or species lives.
Habitat Areas of Particular Concern (HAPC) A habitat area designated by a Fishery Management Council under the Magnuson-Stevens Fishery Conservation and Management Act of 1976 to help focus…
Habitat degradation Decline in habitat quality that accompanies non-natural forms of disturbance.
Habitat Fragmentation Division of large tracts of natural habitat into smaller, disjunct parcels.
Habitat generalist (species) See Generalist
Habitat type An aggregation of all land areas potentially capable of producing similar plant communities at climax.
habituation The phenomenon whereby, after a number of sub-cultures, cells can grow without the addition to the tissue culture medium of previously obligatory factors.
HAC Abbreviation for human artificial chromosome.
haemoglobin Protein containing iron, located in erythrocytes of vertebrates; important for the transportation of oxygen to the cells of the body.
haemolymph The mixture of blood and other fluids in the body cavity of an invertebrate.
haemophilia A sex-linked hereditary bleeding disorder in which it takes a long time for the blood to clot and abnormal bleeding occurs.
Hague Line The North Atlantic boundary between the U.S. and Canada fishing waters as determined by the World Court in The Hague, Netherlands.
Hail Showery precipitation in the form of irregular pellets or balls of ice more than 5 mm in diameter, falling from a cumulonimbus cloud.
Hail Contamination A limitation in NEXRAD rainfall estimates whereby abnormally high reflectivities associated with hail are converted to rainfall rates and rainfall…
Hail Index An indication of whether the thunderstorm structure of each storm identified is conducive to the production of hail.
Hail Size Typically refers to the diameter of the hailstones. Warnings and reports may report hail size through comparisons with real-world objects that correspond…
Hail Spike An area of reflectivity extending away from the radar immediately behind a thunderstorm with extremely large hail.
hailstones Transparent or partially opaque particles of ice that range in size from that of a pea to that of golf balls.
Haines Index This is also called the Lower Atmosphere Stability Index. It is computed from the morning (12Z) soundings from RAOB stations across North America.
hairpin loop A region in one strand of a polynucleotide which, due to an inverted repeat in the sequence, may under appropriate conditions fold back on itself and form…
hairy root culture A culture consisting of highly branched roots of a plant. A plant tissue is treated with the bacterium Agrobacterium rhizogenes containing the Ri plasmid…
hairy root disease A disease of broad-leaved plants, where a proliferation of root-like tissue is formed from the stem.
Half-graben A geological term that describes a sedimentary basin where one side is bounded by a normal (extensional) fault.
Half-life The time in which half the atoms of a particular radioactive nuclide disintegrate. The half-life is a characteristic property of each radioactive isotope.
haline related to salt.
Halo Any of a variety of bright circles or arcs centered on the sun or moon, caused by the refraction or reflection of light by ice crystals suspended in the…
Halocarbons Compounds containing either chlorine, bromine or fluorine and carbon. Such compounds can act as powerful greenhouse gases in the atmosphere.
Halons Compounds, also known as bromofluorocarbons, that contain bromine, fluorine, and carbon.
halophyte A plant species adapted to soils containing a concentration of salt that is toxic to most plant species. See: salt tolerance.
Halophytic Salt-loving. Plants that thrive in soils that contain salt and/or sodium. A plant that grows in salty or alkaline soil.
Hammermill A device consisting of a rotating head with free-swinging hammers which reduce chips or hogged fuel to a predetermined particle size through a perforated…
Hand pile A pile of slash constructed by a crew, not by machine. Hand piles are typically less than 10´ high and less than 12´ in diameter.
Hanger A support for pipe.
Hanging (ice) dam A mass of ice composed mainly of frazil or broken ice deposited underneath an ice cover in a region of low flow velocity.
Hanging drop method A technique used to culture embryonic stem cells so that they develop into embryoid bodies.
hanging droplet technique See: microdroplet array.
Haploid A cell or organism containing one of each of the pairs of homologous chromosomes found in the normal diploid cell.
Haploid cell A cell containing only one set, or half the usual (diploid) number, of chromosomes.
Haploid human cell A cell such as an egg or sperm that contains only twenty-three chromosomes.
haploinsufficiency A situation in which the protein produced by a single copy of an otherwise normal gene is not sufficient to assure normal function. See also gene, protein
Haplotype A specific allelic constitution at a number of loci within a defined linkage block.
haplozygous See: hemizygous.
hapten A small molecule, which by itself is not an antigen, but which as a part of a larger structure when linked to a carrier protein, can serve as an antigenic…
haptoglobin A serum protein that interacts with haemoglobin during recycling of the iron molecule of haemoglobin. Synonym: alpha globulin.
Harassment The intentional or unintentional disturbance of individual animals causing them to flee a site or avoid use of an area.
Hard water Water may be considered hard if it has a hardness greater than the typical hardness of water from the region.
hardening off Adapting glasshouse or controlled environment grown plants to outdoor conditions by reducing availability of water, lowering the temperature, increasing…
Hardness A characteristic of water determined by the levels of calcium and magnesium. Water hardness is largely the result of geological formations of the water…
Hardpan A dense, often impermeable soil horizon cemented with silica, iron oxides, calcium carbonate, or organic matter.
hardwood One of the botanical groups of dicotyledonous trees that have broad leaves in contrast to the conifers or softwoods.
Hardwoods Usually broad-leaved and deciduous trees.
Hardy-Weinberg equilibrium The frequencies of genotypes at a locus resulting from random mating at that locus; for two alleles, A1 and A2, with respective frequencies in a…
Harmonic(s) A sinusoidal quantity having a frequency that is an integral multiple of the frequency of a periodic quantity to which it is related.
Harrow An agricultural tool that loosens and works the ground surface.
Harvest In a recreational fishery, refers to numbers of fish that are caught and kept. See catch.
Harvesting The process of retrieving or collecting electronic data from storage media or devices; an EDiscovery vendor harvests electronic data from computer hard…
Hatchery A facility where fish and raised for stocking.
Haul distance The distance measured along the center line or most direct practical route between the center of the mass of excavation and the center of mass of the fill…
Haunches (haunch) The outside areas between the springline and the bottom of a pipe. In pipe, the sides of the lower third of the circumference.
Hazard Something (e.g., a dam) that creates the potential for adverse consequences such as loss of life (LOL), property damage, and adverse social and…
Hazard classification The rating for a dam based on the potential consequences of failure. The rating is based on potential for loss of life and damage to property that failure…
Hazardous air pollutant (HAP) Substances that have adverse impacts on human health when present in ambient air.
Hazardous material Any material that poses a threat to human health and/or the environment. Hazardous materials are typically toxic, corrosive, ignitable, explosive, or…
Hazardous materials Materials that pose the potential for grave, immediate, future, and genetic injury and illness when handled without proper equipment and precautions.
Hazardous substances Element or compound other than oil which when discharged into the environment, in any quantity, presents an imminent or substantial threat to public…
Hazardous waste By-products of society that can pose a substantial or potential hazard to human health or the environment when improperly managed.
Hazardous Waste Indicators Indicators that may signal the presence of hazardous materials include stressed vegetation or unusual lack of vegetation; dead or sick domestic stock…
Hazardous waste sites Any spill, authorized or unauthorized dumping, abandoned, or inactive waste disposal sites containing or suspected of containing hazardous materials.
Hazardous Weather Outlook A narrative statement produced by the National Weather Service, frequently issued on a routine basis, to provide information regarding the potential of…
Hazards Assessment CPC's Hazards Assessment provides emergency managers, planners, forecasters and the public advance notice of potential hazards related to climate, weather…
Haze (abbrev. HZ)- An aggregation in the atmosphere of very fine, widely dispersed, solid or liquid particles, or both, giving the air an opalescent appearance…
hCNS Human central nervous system stem cell.
HDD Heating Degree Days- A form of degree day used to estimate energy requirements for heating.
HDRAIN An Hourly Digital Rainfall Product of the WSR-88D.
Head The upper horizontal part of a window frame or window opening.
Head Loss The energy lost from a flowing fluid due to friction, transitions, bends, etc.
Head Race A channel which directs water to a water wheel; a forebay.
Header A masonry wall unit of brick which is laid so that its short end is exposed.
Heading In a tunnel, a digging face and its work area.
Headrace. See forebay.
Headwall An upstream wall.
Headward Erosion Erosion which occurs in the upstream end of the valley of a stream, causing it to lengthen its course in such a direction.
Headwater (1) The source and upper reaches of a stream; also the upper reaches of a reservoir; (2) the water upstream from a structure or point on a stream; (3) the…
Headwater Advisory Program (ADVIS) A Program which uses the Antecedent Precipitation Index (API) method of estimating runoff, unit hydrograph theory and stage-discharge ratings to produce…
Headwater Advisory Table A table developed by a River Forecast Center for a Headwater Guidance Point; a pre-computed matrix of values allows a forecaster to ascertain an…
Headwater Basin A basin at the headwaters of a river. All discharge of the river at this point is developed within the basin.
Headwaters Streams at the source of a river.
Health physics That science devoted to recognition, evaluation, and control of all health hazards from ionizing radiation.
Heap The soil carried above the sides of a body or bucket.
Heat Pressure and intimidation used by a casino to discourage card counters.
Heat Absorbing Window Glass A type of window glass that contains special tints that cause the window to absorb as much as 45% of incoming solar energy, to reduce heat gain in an…