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Holmium is a member of the lanthanide group with properties closely resembling those of erbium and dysprosium.
Hob
A cylindrical cutting tool shaped like a worm thread and used in industry to cut gears.
Hobbing
The operation of cutting gears with a hob.
Hoe
A tool with a flat blade fixed at a right angle to a long handle and used for gardening.
Hogging
The upwards bending in a beam, usually over its piers, that is the counterbalance to sagging in other sections of the beam.
Hohlraum
A cavity whose walls are in radiative equilibrium with the radiant energy within the cavity.
Hole
Particle associated with an empty electron level in an almost filled band.
Hole Flow
Current carriers (in transistors) which have a flow in a direction opposite to electron movement.
Hole Saw
A tube with teeth on one end and a drill in the centre used in a hand or powered drill for cutting holes.
Holes
Torus has a hole, sphere does not. If every curve on a surface can be continuously shrunk into a point the surface has no holes.
Holes in Acoustic Barriers
A hole in an acoustic barrier drammatically reduces the acoustic performance.
Hollow Box
A structural element made up of a combination of vertical and horizontal walls that together carry the loads.
Holmium
A member of the lanthanide group with properties closely resembling those of erbium and dysprosium.
Holocene
The current geological time period that started about 10,000 years ago.
Hologram
A three-dimensional record of visual information.
Holography
The photographic process for producing three-dimensional images.
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Homeomorphism
A one-to-one continuous transformation that preserves open and closed sets.
Homogeneous
Having uniform properties or composition.
Homogeneous Catalysis
A form of catalysis in which the catalyst is in the same physical state as the reactants.
Homogeneous Equations
A differential equation may be described as homogeneous.
Homogeneous Linear System
A system of linear equations Ax = b is homogeneous if b = 0.
Homogeneous Mixture
A sample of matter consisting of more than one pure substance with properties that do not vary within the sample.
Homologous Chromosome
One of two copies of a chromosome.
Homologous Series
A series of organic compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass.
Homomorphism
A function that preserve the operators associated with the specified structure.
Homopolymer
A polymer having a chain structure in which all mer units are of the same type.
Homozygous
Having two identical alleles of the same gene.
Hone
To sharpen a tool by hand on a stone.
Honing
The process of finishing ground surfaces to a high degree of accuracy and smoothness.
Hookes Joint
A universal joint arrangement designed to cancel out the vibrations caused when the joint angle between the two driveshafts is varied while power is applied.
Hookes Law
A Law stating that, in a linear system, the restoring force is proportional to the displacement of the body, acting in a direction as to restore equilibrium.
Hoop Stress
Circumferential stress in a cylindrically shaped part as a result of internal or external pressure.
Hopper, Grace Murray
Developed the first computer compiler in 1952 and the computer program language COBOL. Upon discovering that a moth had jammed the works of an early computer, Hopper popularized the term "bug."
Horizontal Axis Wind Turbine
A wind turbine where the axis of rotation is horizontal and a conventional propeller that absorbs the wind power.
Horizontal Deflection Plates
A pair of parallel electrodes that moves the electron beam from side to side in a CRT.
Horizontal Line
A line whose slope is zero.
Horizontal Plane
A plane parallel to the surface of the earth.
Horizontal Range
The maximum distance in the horizontal direction that one can see.
Horizontally Opposed Engine
An engine with an even number of cylinders that are arranged either side of the crankshaft.
Horizontally Polarized
Waves radiated with their E field component parallel to the surface of the earth.
Hormone
A molecule produced by endocrine glands that controls specific biological processes like growth and metabolism.
Horn
A funnel-shaped section.
Horn Radiator
A tapered, tubular or rectangular microwave antenna that is widest at the open end.
Horsepower
Mechanical engineering unit of power.
Horseshoe Magnet
A permanent magnet or electromagnet bent into the shape of a horseshoe or having a U-shape to bring the two poles near each other.
Host
Term used in the Internet community to describe any device attached to the network that provides application-level service.
Hot Air Engine
The Stirling Engine is an external combustion engine.
Hot Bolting
This term is used for the completion of maintenance work on a bolted joint when the joint is under load.
Hot Carrier
A carrier, which may be either a hole or an electron, that has relatively high energy with respect to the carriers normally found in majority-carrier devices.
Hot Carrier Diode
A semiconductor diode in which hot carriers are emitted from a semiconductor layer into the metal base.
Hot Crack
A crack that forms due to internal stresses developed from shrinkage during solidification of a metal casting.
Hot Dip
To coat metal parts by immersion in molten metal, such as tin or zinc.
Hot Dipped Galvanized
Process to coat steel to offer environmental resistance to corrosion.
Hot Glue Gun
A tool with a heating element that is used to apply a thermoplastic glue.
Hot Isostatic Pressing
A process that subjects a component to both elevated temperature and isostatic gas pressure.
Hot Pressing
A method used to increase the density of a material.
Hot Rolled
Hot rolled products are those products that are rolled to finish at temperatures above the re-crystallisation temperature.
Hot Rolled Steel
Steel which is rolled to finished size while hot.
Hot Short
A condition which occurs when a metal is heated to that point, prior to melting, where all strength is lost but the shape is still maintained.
Hot Spot
A region of high heat flow.
Hot Wire Ignition Test
Required of a material when it is in contact with or in close proximity (typically within 0.8 mm) to uninsulated live parts.
Hot Wire Meter Movement
A meter movement that uses the expansion of a heated wire to move the pointer of a meter; measures DC or AC.
Hot Working
Any metal forming operation that is performed above a metal recrystallization temperature.
Hotchkiss Suspension
A live-axle rear suspension in which leaf springs handle both the axle′s springing and its location.
Hot-Spot Volcanoes
Volcanoes related to a persistent heat source in the mantle.
Hot-Stuck Piston Ring
A piston ring that is stuck when the piston and ring are at room temperature, and inspection shows that it was stuck during engine operation.
Hot-Wire Airflow Meter
A constant-temperature hot-wire sensing device, used in electronic fuel injection systems, which measures the rate of a mass airflow into the engine by measuring the current needed to keep the hot wire at the same temperature.
Hot-Wire Anemometer
Uses the wind induced changes in the temperature of a metal wire that is heated by an electric current and cooled by convective heat loss.
Hour
A unit of time equal to 60 minutes or 3600 seconds in length.
Housing
An enclosure for electrical or mechanical parts.