| Hadron: A particle made of strongly-interacting constituents (quarks and/or gluons). These include the mesons and baryons. Such particles participate in residual strong interactions. |
| Half Bridge: Two active elements or strain gages.
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| Half-Duplex: One way at a time data communication; both devices can transmit and receive data, but only one at a time. |
| Half-Life: The time in which half the atoms of a radioactive substance will have disintegrated, leaving half the original amount. Half of the residue will disintegrate in another equal period of time.
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| Hall Effect: The measurement of the transverse voltage across a conductor when placed in a magnetic field. By this measurement, it is possible to determine the type, concentration, and mobility of carriers in silicon. |
| Handshake: An interface procedure that is based on status/data signals that assure orderly data transfer as opposed to asynchronous exchange. |
| Handshaking: Method by which data is exchanged between devices only when each device has signalled that it is ready. |
| Hardcopy: Output in a permanent form (usually a printout) rather than in temporary form, as on disk or display terminal.
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| Hardness: The measure of a materials resistance to deformation by surface indentation or by abrasion. |
| Hardware: The electrical, mechanical and electromechanical equipment and parts associated with a computing system, as opposed to its firmware or software.
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| Harmonic Distortion: A type of communications line interface that is caused by erroneous frequencies that are generated by non-linearities in the system.
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| Harmonic: A frequency that is a multiple of the fundamental. See also Distortion and Non-Linearity.
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| HART: Highway Addressable Remote Transducer.
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| Haversine: An inverted cosine offset by half its amplitude. A continuous haversine would look like a sine wave whose negative peak is at zero volts.
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| HDTV: High Definition Television.
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| Head Loss: The loss of pressure in a flow system measured using a length parameter (i.e., inches of water, inches of mercury).
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| Head Pressure: Expression of a pressure in terms of the height of fluid, r = yrg, where r is fluid density and y = the fluid column height. g = the acceleration of gravity.
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| Header: The portion of a packet, preceding the actual data, containing source and destination addresses and error-checking fields.
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| Heat Sink: 1. Thermodynamic. A body which can absorb thermal energy. 2. Practical. A finned piece of metal used to dissipate the heat of solid state components mounted on it.
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| Heat Transfer: The process of thermal energy flowing from a body of high energy to a body of low energy. Means of transfer are: conduction; the two bodies contact. Convection; a form of conduction where the two bodies in contact are of different phases, i.e. solid and gas. Radiation: all bodies emit infrared radiation.
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| Heat Treating: A process for treating metals where heating to a specific temperature and cooling at a specific rate changes the properties of the metal.
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| Heat: Heat, like work, is a measure of the amount of energy transferred from one body to another because of the temperature difference between those bodies. Heat is not energy possessed by a body. We should not speak of the "heat in a body." The energy a body possesses due to its temperature is a different thing, called internal thermal energy. The misuse of this word probably dates back to the 18th century when it was still thought that bodies undergoing thermal processes exchanged a substance, called caloric or phlogiston, a substance later called heat |
| Henry: The unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second. |
| Henry`s Law: The relationship between the partial pressure of a compound and the equilibrium concentration in the liquid through a proportionality constant known as the Henrys law constant. |
| Hermetic : The airtight sealing of an object.
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| Hertz (Hz): Units in which frequency is expressed. Synonymous with cycles per second.
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| Heterotrophic: Designating or typical of organisms that derive carbon for the manufacture of cell mass from organic matter.
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| HEU: Highly Enriched Uranium.
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| Hexadecimal: Refers to a base sixteen number system using the characters 0 through 9 and A through F to represent the values. Machine language programs are often written in hexadecimal notation.
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| HGDB: Hydraulicaly Driven Gas Booster. Uses a Electric Motor as the Prime Mover , which drives a hydraulic pump. the Hydraulic fluid is then directed to a circuit which controls the linear actuators, that move the gas section pistons to compress the gas. |
| Holy Point Ground: The one point in a system that connects multiple grounds and returns. Also known as star ground, or single point ground.
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| Hooke?s Law: Defines the basis for the measurement of mechanical stresses via the strain measurement. The gradient of Hooke?s line is defined by the ratio of which is equivalent to the Modulus of Elasticity E (Young?s Modulus).
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| Hooke`s Law: Stress is proportional to strain in the elastic range. The value of the stress at which a material ceases to obey Hooke`s law is known as the elastic limit.
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| Host: The primary or controlling computer in a multiple part system.
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| Hot Gas Reflow : A solder reflow process that engages a heated gas, including air, as the mode of heat transfer.
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| HPLC: High Performace Liquid Chromotagraphy. |
| HTML -- (HyperText Markup Language): The coding language used to create Hypertext documents for use on the World Wide Web. HTML looks a lot like old-fashioned typesetting code, where you surround a block of text with codes that indicate how it should appear. The "hyper" in Hypertext comes from the fact that in HTML you can specify that a block of text, or an image, is linked to another file on the Internet. HTML files are meant to be viewed using a "Web Browser". HTML is loosely based on a more comprehensive system for markup called SGML. |
| HTTP -- (HyperText Transfer Protocol) The protocol for moving hypertext files across the Internet. Requires a HTTP client program on one end, and an HTTP server program on the other end. HTTP is the most important protocol used in the World Wide Web (WWW). |
| Hub: A central node in a star network to which all other nodes are connected by means of point-to-point communications links.
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| Humidity: The presence of water vapor in air or other gases Some people use "humidity" to mean relative humidity only. Strictly speaking, "humidity" also refers to all kinds of absolute indications of humidity. For very low humidities, other more specific terms tend to be used .
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| Hydraulic Conductivity: A coefficient of proportionality describing the rate at which water can move through a permeable medium. Hydraulic conductivity is a function of both the intrinsic permeability of the porous medium and the kinematic viscosity of the water which flows through it. Also referred to as the coefficient of permeability.
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| Hydrogen Ion Activity (aH+): Activity of the hydrogen ion in solution. Related to hydrogen ion concentration (CH+) by the activity coefficient for hydrogen (f H+).
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| Hydrogeologist: A person who studies and works with groundwater |
| Hydrogeology: The geology of ground water, with particular emphasis on the chemistry and movement of water. |
| hydrophilic Having a strong affinity (liking) for water. The opposite of hydrophobic |
| Hydrophilic: Having an affinity for water, or capable of dissolving in water; soluble or miscible in water.
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| hydrophobic Having a strong aversion (dislike) for water. The opposite of hydrophilic |
| Hydrophobic: Tending not to combine with water, or incapable of dissolving in water; insoluble or immiscible in water. A property exhibited by non-polar organic compounds, including the petroleum hydrocarbons.
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| Hydrophone: A hydrophone converts acoustic energy into electrical energy and is used in underwater passive systems for listening only. Hydrophones are usually used below their resonance frequency over a much wider frequency band where they provide uniform output levels.
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| Hygrometer: Any instrument for measuring humidity. |
| Hygrometry: The subject of humidity measurement. |
| Hygroscopic: Tending to absorb water vapor.
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| Hypercavitation: The creation of a pocket of low-pressure gas around an underwater shape. This reduces water resistance and allows the shape to move more quickly than would otherwise be possible. |
| Hypertext: Generally, any text that contains links to other documents - words or phrases in the document that can be chosen by a reader and which cause another document to be retrieved and displayed. |
| Hysteresis (Electrode Memory): When an electrode system is returned to a solution, equilibrium is usually not immediate. This phenomenon is often observed in electrodes that have been exposed to the other influences such as temperature, light, or polarization.
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| Hysteresis: The maximum difference between output readings for the same measured point, one point obtained while increasing from zero and the other while decreasing from full scale. The points are taken on the same continuous cycle. The deviation is expressed as a percent of full scale.
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