HoistThe mechanism by which a bucket or blade is lifted, or the process of lifting it.
HoleThe vacancy where an electron would normally exist in a solid; behaves like a positively charged particle.
hollow fibreA tube of porous material, with an internal diameter of a fraction of a millimetre, making its ratio of surface area to internal volume very large.
Hollow-jet valveA valve having a closing member that moves upstream to shut off the flow. The hollow-jet valve discharges a hollow or annular jet dispersed over a wide…
holocelluloseThe total carbohydrate fraction of wood; cellulose plus hemicellulose.
HoloceneThe past 10,000 years of geologic time. The most recent epoch of the Quaternary period.
Holocene epochan epoch of the Quaternary period dating from the end of the Pleistocene approximately 11,500 years ago until the present.
holometabolousAn insect that undergoes complete metamorphosis to the adult from a morphologically distinct larval stage.
holoprosencephalyA birth defect where the forebrain does not separate properly into two halves during early fetal life.
Home Energy Rating Systems (HERS)A nationally recognized energy rating program that gives builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise…
HomeoboxA highly conserved 180 bp DNA sequence that controls body part-, organ- or tissue-specific gene expression, most particularly involved in segmentation in…
homeotic genesGenes that act in concert to determine fundamental patterns of development.
homeotic mutationA mutation that causes a body part to develop in an inappropriate position in an organism, such as the mutation in Drosophila melanogaster that causes…
homoalleleOne of a number of otherwise identical alleles which differ at the same site in their sequence.
homodimerA protein comprising two identical polypeptide chains, or a dimer of identical residues.
homoduplex DNAA double-stranded fully complementary DNA molecule.
homoeologousReferring to chromosome s which are descended from a common progenitor, but which have evolved to be no longer fully homologous.
homogameticProducing similar gametes with regard to the sex chromosomes . In mammals, the female is homogametic (XX), and the male is heterogametic (XY).
HomogeneousLooking the same at every location. Homogeneous milk has no lumps or impurities; it remains the same no matter where you look.
Homogeneous earthfill damAn embankment dam construction throughout of more or less uniform earth materials, except for possible inclusion of internal drains or blanket drains.
Homogeneous Rolled Earth DamAn embankment dam constructed of similar earth material throughout, except for possible inclusion of internal drains or drainage blankets; distinguished…
homogenotizationAn allele replacement technique, in which a bacterial cell is transformed with a plasmid containing an altered copy of the target sequence, and a double…
HomojunctionThe region between an n-layer and a p-layer in a single material, photovoltaic cell.
homokaryonA cell with two or more identical nuclei as a result of fusion. Opposite: heterokaryon.
HomologIn diploid organisms, one member of a pair of matching chromosomes.
Homologous1. General definition: from the same source, or having the same evolutionary function or structure. 2.
Homologous chromosomeChromosome containing the same linear gene sequences as another, each derived from one parent.
Homologous chromosomesChromosomes that have the same linear arrangement of genes--a pair of matching chromosomes in a diploid organism. See Chromosomes.
Homologous FlaresIn solar-terrestrial terms, solar flares that occur repetitively in the same active region, with essentially the same position and with a common pattern…
Homologous recombinationThe exchange of DNA fragments between two DNA molecules or chromatids of paired chromosomes (during crossing over) at the site of identical nucleotide…
Homology1. The degree of identity between individuals, or characters. 2. The degree of identity of sequence (nucleotide or amino acid) between a number of DNA or…
homomultimerA protein consisting of a number of identical subunits.
homoplasmyThe condition in which all copies of an organelle in a cell are genetically identical. Opposite: heteroplasmy.
homopolymerA polymer (nucleic acid, polypeptide, etc.) which contains only one kind of residue (e.g. the polynucleotide GGGGGGGGG...).
Hook EchoA radar reflectivity pattern characterized by a hook-shaped extension of a thunderstorm echo, usually in the right-rear part of the storm (relative to its…
HopperA storage bin or a funnel that is loaded from the top, and discharges through a door or chute in the bottom.
HorizonThe distant line along with the earth and sky appear to meet. Obstructions are not considered as part of the horizon.
Horizon lineThe apparent line in the landscape formed by the meeting of the visible land surface and the sky.
Horizontal angle of viewThe angle of landscape viewed in sharp focus, measured along the horizon, without turning the head. See also Vertical angle of view; Angle of view
Horizontal gene transferTransmission of DNA between species, involving close contact between the donor's DNA and the recipient, uptake of DNA by the recipient, and stable…
Horizontal Ground LoopIn this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are laid out in a plane parallel to the…
horizontal windThe horizontal wind in terms of either speed and direction, or the zonal (u) and meridional (v) components.
Horizontal-Axis Wind TurbinesTurbines in which the axis of the rotor's rotation is parallel to the wind stream and the ground.
hormone(HOR-mone) One of many chemicals made by glands in the body. Hormones circulate in the bloodstream and control the actions of certain cells or organs.
HornblendeBlack blade-like mineral common in igneous and metamorphic rocks.
HornfelsFine-grained, gray-green metamorphic rock produced by "baking" of sedimentary rocks by an igneous intrusion in which sedimentary features may still be…
Horsehead (false set)A temporary support for forepoles used in tunneling soft ground.
Horsepower (hp)A unit of rate of operation. Electrical hp: a measure of time rate of mechanical energy output; usually applied to electric motors as the maximum output…
Horsepower Hour (hph)One horsepower provided over one hour; equal to 0.745 kilowatt-hour or 2,545 Btu.
HorstAn elongated crustal block that is relatively raised between two parallel normal faults or grabens. See also Half-graben
hostIn a network, the central computer which controls the remote computers and holds the central databases.
host-specific toxinA metabolite, produced by a pathogen, and which is responsible for the adverse effects of the pathogen.
Hot Air FurnaceA heating unit where heat is distributed by means of convection or fans.
Hot Dry RockA geothermal energy resource that consists of high temperature rocks above 300 F (150 C) that may be fractured and have little or no water.
Hourly Precipitation Data (HPD)It contains data on nearly 3,000 hourly precipitation stations (National Weather Service, Federal Aviation Administration, and cooperative observer…
Housing ElementA comprehensive assessment of current and projected housing needs for all economic segments of the community.
Hox genesConsists of at least 38 encoded nucleotides that contain genes found in four clusters on four different chromosomes.
HP Stormor HP Supercell - High-Precipitation storm (or High-Precipitation supercell). A supercell thunderstorm in which heavy precipitation (often including hail)…
HPAHectopascal- A unit of pressure equal to a millibar (1 hPa = 1 mb).
HSA (Hydrologic Service Area)A geographical area assigned to Weather Service Forecast Office's/Weather Forecast Office's that embraces one or more rivers.
HSC markersCell-surface molecules that are used to identify hematopoietic stem cells.
HSPOne of a group of proteins that help protect cells from stresses such as heat, cold, and low amounts of oxygen or glucose (sugar).
HubA network device that connects multiple computers/peripherals together and allows them to share data.
Hub HeightThe height above the ground that a horizontal axis wind turbine's hub is located.
Hubble's LawThe redshift in light coming from distant galaxies is proportional to their distance from earth.
human artificial chromosome(Abbreviation: HAC). Analogous to yeast artificial chromosome, a construct comprising a human centromere and telomeres, which would allow for the cloning…
Human artificial chromosome (HAC)A vector used to transfer or express large fragments of human DNA. HACs behave and are constructed like human chromosomes. See also chromosome, vector
Human embryonic stem cellA stem cell that is derived from the inner cell mass of a blastocyst and can differentiate into several tissue types in a dish.
Human environmentNatural and physical environment and the relationship of people with that environment, including all combinations of physical, biological, cultural…
Human Genome InitiativeCollective name for several projects begun in 1986 by DOE to create an ordered set of DNA segments from known chromosomal locations, develop new…
Human Genome ProjectAn international research project to map each human gene and to completely sequence human DNA. See also gene, mapping
Human growth hormone (HGH, somatotrophin)A protein produced in the pituitary gland that stimulates the liver to produce somatomedins, which stimulate growth of bone and muscle.
Human Leukocyte Antigen (HLA)A distinguishing series of proteins that exist on the surface of every white blood cell to help the cells discriminate between "friendly" cells and…