Ha

ha
An abbreviation of hectare, a derived SI unit of area that is mainly used in agriculture to describe the area of fields.
Haas Effect
Delayed sounds are integrated by the auditory system if they arrive at the ear within 20 to 40 msec of the direct sound.
Haber Process
An industrial process in which ammonia is manufactured by direct combination of its elements.
Habituation
The process by which an organism ceases to respond to some recurring or familiar stimulus.
Hacksaw
A metal blade of hardened steel having small, close teeth on one edge, held under tension in a U-shaped frame.
Hadean
The geological eon covering about 4.6 billion years ago to 3.9 billion years ago.
Hadrons
The family of particles that participate in the strong interaction.
Haematite
A common mineral; a form of iron oxide with the formula Fe2O3.
Haeme
The iron-porphyrin prosthetic group of heme proteins.
Haemeprotein
A protein containing a haeme as a prosthetic group.
Haemoglobin
A haeme protein of erythrocytes which functions in oxygen transport.
Hafnium
A silvery coloured, ductile metal which is found in all minerals containing zirconium.
Hair Cell
Sensory cells in the cochlea which transform the mechanical energy of sound into nerve impulses.
Hair Hygrometer
Measures atmospheric relative humidity by means of the variation in length of a bundle of human hairs as they adsorb atmospheric water vapour.
Half
One of two equal parts.
Half a Dozen
Six pieces of something.
Half Century
Fifty of something.
Half Duplex
Describes a circuit capable of transmitting in either direction, but only one direction at a time.
Half Life
The amount of time it takes for half an initial amount to disintegrate.
Half Line
A ray.
Half Male Centre
A dead center that has a portion of the 60 degree cone cut away.
Half Nut
A lever-operated mechanism that resembles a split nut that can be closed on the lead screw of a lathe when threads are being cut.
Half Plane
The part of a plane that lies on one side of a given line.
Half Reactions
The two parts of an oxidation-reduction reaction, one representing oxidation, the other reduction.
Half Wave Dipole Antenna
An antenna, consisting of two rods in a single line, that radiates electromagnetic energy.
Half Wave Rectifier
A tube or solid-state diode which passes current in only one direction and thus converts ac to pulsating dc by rectification of one alternation of each cycle.
Halide
A compound composed of two elements, one of which is a halogen (flourine, chlorine, bromine, iodine and astatine).
Hall Effect
The phenomenon whereby a force is brought to bear on a moving electron or hole by a magnetic field that is applied perpendicular to the direction of motion.
Hall Mobility
A measure of the flow of charged particles perpendicular to both a magnetic and an electric field.
Halley, Edmund
Mathematician and astronomer.
Halo
A ring of light that appears around the Sun or Moon.
Halogen
Group of elements with similar bonding properties, consisting of flourine, chlorine, bromine, iodine and astatine.
Halon
Organic chemical compounds containing one or two carbon atoms, together with bromine and other halogens.
Hammer
A hand tool with a metal head and a handle. It is used to force one item against or through another.
Hammer Welding
A forge welding process.
Hamming Window
An amplitude weighting of the time signal used with gated continuous signals to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum.
Hand
Unit of measure. Used for measuring the height of a horse.
Hand Brace
A hand tool used for drilling holes.
Hand Layup
A fabrication method in which reinforcement layers, preimpregnated or coated afterwards, are placed in a mould by hand.
Hand Plane
A tool to smooth and true wood surfaces, consisting of a blade fastened in frame at an angle with hand grips to slide it along the board.
Hand Saw
The most common saw. This has a wide tapering blade with teeth cut along one edge and a handle riveted to the wide end.
Hand Tool
A equipment held in hand and used to do many tasks.
Handbrake
Vehicle brake that is applied by hand to hold the vehicle when stationary.
Handshaking
The initial exchange between two communications systems prior to and during transmission to ensure proper data transfer.
Handwheel
Any adjusting or feeding mechanism shaped like a wheel and operated by hand.
Hankel Matrix
A matrix in which all the elements are the same along any diagonal that slopes from northeast to southwest.
Hann Otto
Discovered protactinium with Lise Meitner, first to recognize nuclear fission and shared Nobel Prize for chemistry with Fritz Strassmann for this development.
Hanning Window
An amplitude weighting of the time signal used with gated continuous signals to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum.
Hanning-Poisson Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.
Haploid
Having only one copy of each chromosome.
Haptic
Pertaining to the sense of touch, from the Greek word haptein, to grasp.
Haptotropism
Response of a plant to touch such as tendrils on a climbing plant wrapping themselves around other plants or supports.
Hard Disc Drive
The main storage for programs and data on a computer.
Hard Facing
A particular form of surfacing in which a coating or cladding is applied to a surface for the main purpose of reducing wear.
Hard Room
A room in which the surfaces have very low values of sound absorption and are therefore highly reflective.
Hard Surfacing
The application of a hard, wear-resistant alloy to the surface of a softer metal.
Hard X-Rays
Higher-energy part of the X-ray spectrum ranging from approximately 5 keV to 100 keV.
Hardenability
In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.
Hardener
A substance used to promote or control curing action by taking part in it; as opposed to catalyst.
Hardening
Increasing the hardness by suitable treatment, usually involving heating and cooling.
Hardness
Resistance of metal to plastic deformation usually by indentation.
Hardware
Physical equipment.
Harmonic
If a signal is composed of a number of components of frequencies which are all integer multiples of one frequency, these components are said to form a harmonic train.
Harmonic Analysis
Statistical method for determining the amplitude and period of certain harmonic or wave components in a set of data with the aid of Fourier series.
Harmonic Distortion
Distortion of a signal by adding content that is harmonically related to the original signal. Clipping overload of an amplifier adds odd-order harmonics to the signal.
Harmonic Division
A line segment is divided harmonically by two points when it is divided externally and internally into the same ratio.
Harmonic Mean
The harmonic mean of two numbers a and b is 2ab/(a + b).
Harshness
A typical transient interdisciplinary phenomenon of noise and vibration.
Hartley
A unit of information content equal to one of ten possible and equally likely values or states of anything used to store or convey information.
Hartree
The atomic unit of energy, named after the British physicist Douglas Hartree.
Hartshorn
Another name for Ammonium Bicarbonate.
Hatchet
A tool doing both the jobs as a hammer and as an axe.
Havilland, Sir Geoffrey de
One of the most successful of all British aviation pioneers.
Hawking Radiation
A theory first proposed by British physicist Stephen Hawking, that due to a combination of properties of quantum mechanics and gravity, under certain conditions black holes can seem to emit radiation.
Hawking, Stephen
Known for his contributions to the fields of cosmology and quantum gravity, especially in the context of black holes.
Hawking Temperature
The temperature inferred for a black hole based on the Hawking radiation detected from it.
HAWT
Abbreviation of Horizontal Axis Wind Turbine.
Hay Bridge
A bridge circuit in which two opposite arms are resistors, the third arm C and B in series, and the fourth arm L and R in series.
Hazard
The potential that the use of a product will result in an adverse effect on a person or the environment.
Hazard and Operability Studies
HAZOP studies examine each part of an entire system to determine how deviations from the intended function or performance can lead to undesirable outcomes.
Hazard Indices
These can be used to analyze different system options in order to identify that option having the lowest risk.
Hazard Quotient
The ratio of the potential exposure to the substance and the level at which no adverse effects are expected.
Hazardous Air Pollutants
Pollutants that are known to cause or suspected of causing cancer or other serious health effects, such as developmental effects or birth defects.
HAZOP
Abbreviation of Hazard and Operability Studies.