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 DiracDelta - Science & Engineering encyclopedia
Category: Sciences > Science & Engineering
Date & country: 01/12/2007, UK
Words: 4470


Isothermal Transformation
A change in phase at any constant temperature. See also: Isothermal, Isothermal Expansion.

Isotopes
Two atoms having the same number of protons but different numbers of neutrons are said to be isotopes of each other. See also: Abundance Ratio, Calutron, Daughter Isotope, Parent Isotope.

Isotropic
Having identical values of a property in all crystallographic directions.

Izod Test
A pendulum type of single-blow impact test in which the specimen, usually notched, is fixed at one endand broken by a falling pendulum. The energy absorbed, as measured by the subsequent rise of the pendulum, isa measure of impact strength or notch toughness.The 10mm square, 75mm long test piece has a notch 2mm deep, 0.25mm root radius and 45° incl…

Jack
Mechanical or hydraulic device for lifting heavy equipment off the floor. Can also be used where a force needs to be applied between two points.Bottle JackPhotograph courtesy of Draper.co.ukA small hydraulic jack.Inflatable JackPhotograph courtesy of Draper.co.ukA strong sealed bag that is placed under the object to be lifted and inflated with air.…

Jackscrew
A bolt or screw attached to the baseplate or foundation that is used to move or position the machine that is being moved.

Jarno
A standard taper having 0.600 inch taper per foot used on some machine tools. See also: Morse Taper.

Jerk
A vector quantity that specifies time rate of change of acceleration. See also: Acceleration.

Jet Engine
An engine that discharges a fast moving jet of fluid. See also: Brayton Thermodynamic Cycle, Engine, Gas Turbine.

Joint
Interface between two parts. See also: Clamping Force, Lap Joint, Tee Joint.

Joist
Horizontal wood framing member set from wall to wall to support the boards of a floor or ceiling. See also: Ceiling Attenuation Class.

Jominy Test
The Jominy test is used for determining end-quench hardenability. It consists in water quenching,under closely-controlled conditions, one end of a 1-in. diameter specimen of the steel under test and measuring thedegree of hardness at regular distances from the quenched end along the side. See also: Direct Quenching, Hardenability, Hardening, Interr…

Jordan Matrix
A matrix whose diagonal elements are all equal (and nonzero) and whose elements above the principal diagonal are equal to 1, but all other elements are 0. See also: Matrix.

Josephson Effects
Electrical effects observed when two superconducting materials are separated by a thin layer of insulating material. See also: Superconductivity.

Joule
The SI unit of energy is the joule. Defined as:1 joule is the work done by a force of 1 newton moving a distance of 1 metre in the direction of the force.It may also be defined in electrical terms as:the amount of energy needed to sustain 1 amp for 1 sec in a 1-ohm resistance.

Jubilee Clip
A worm-gear hose clip

Julian Calendar
Introduced in 46 BC by the Roman ruler Julius Ceasar, this calendar assumes a year of 365.25 days, and uses a cycle in which 3 'ordinary' years of 365 days are followed by a 'leap year' with 366 days. Leap years are the years whose number is divisible by 4. See also: Gregorian Calendar, Julian Day.

Julian Day
Instituted by J. Julius Scaliger in 1582. The Julian date is independent ofvarious calendars and chronological events and is valid for dates from the onsetof the Gregorian calendar 15 October 1582 and represents the number of days sinceGreenwich mean noon 1 January 4713 BCfunction init(){}Note: 1 January 2000 = 2451545 Julian Days See also: Gregori…

Jump Discontinuity
A discontinuity in a function where the left and right-hand limits exist but are not equal to each other.

Jupiter
The largest planet in our solar system.Click on an item to paste into clipboard or use clipboard symbol at end to clipboard all values Equatorial diameter 142984000 mClip Average Density 1330 kgm-3Clip Axial tilt 3.1 degreesClip Rotational period 9.92 hoursClip Average surface temperature -120 °CClip Maximum apparent magnitude -2.8 Clip …

Jury Evaluation
A name given to a field where the customer is given the opportunity to compare products and rank one versus the other. This may be done through blind testing or by exposing the customer to certain features of the products. See also: Sound Quality.

Kaiser Bessel 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.The Kaiser-Bessel window is superior to other windows with respect to selectivity. This is mainly due to the low level of the highest sidelobe, which is found …

Kalman Filter
A technique for estimating an unknown state of a linear dynamic system given observations of the system which have additive (Gaussian) noise. Can be used for non-linear systems by an approximate linear model. It creates an optimum solution to such a system by minimising the state error correlation matrix. It makes use of a recursive algorithm in wh…

Kaon
A meson containing a strange quark and an anti-up (or anti-down) quark, or an anti-strange quark and an up (or down) quark. See also: Meson, Quark.

Kapok
Used as an insulating or flotation material it comes from the seed hairs of the kapok tree (Ceiba Pentranda).

KDP
K.D.P. (Potassium D Phosphate) is a crystal often used in non-linear optics within Pockels Cells and Kerr Cells to vary the polarisation and phase of light.With the correct orientation KDP can also be used as a frequency doubling crystal in lasers.Crystal Structure Code : ????? See also: Polariser.

Keir Metal
Brass containing 55% copper, 40% zinc and 5% iron. Patented in 1779 by James Keir (Chemist, Geologist, Industrialist and Inventor) and used for the manufacture of window frames.

Kelvin
The SI unit of TemperatureThe kelvin is the unit of thermodynamic temperature. It is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

Kepler's Laws
Three laws of planetary motion, published by Johannes Kepler using accurate observations by Tycho Brahe and shown by Isaac Newton to be a direct result of his theory of gravitation and his laws of motion:The orbit of each planet is an ellipse which has the sun at one of its foci.This corrected the simpler model of Copernicus, which assumedcircles. …

Kerf
The space from which metal has been removed by a cutting process.e.g. The width of cut made by a Saw.

Kerr Black Hole
A rotating black hole. See also: Black Hole, Schwarzschild Black Hole.

Kerr Cell
A Kerr Cell is most commonly used as a Q-Switch device in pulsed lasers. See also: Kerr Effect.

Kerr Effect
The ability of certain substances to differently refract light waves whose vibrations are in different directions when the substance is placed in an electric field. See also: Kerr Cell.

Ketone
Compunds containing a carbonyl group (-CO-) attached to two hydrocarbon radicals. The simplest ketone is acetone (CH3COCH3).

Kidney
An organ in the body which is used for excretion. The kidney filters the blood and removes waste, urea water and salts.

Killed Steel
Steel treated with a strong deoxidizing agent, such as aluminum or silicon, in order to reduce the oxygen content to a level so no reaction occurs between carbon and oxygen during solidification.

Kiln
A furnace in which ceramics are fired.

kilo electron volts
Abbreviated as keV, one thousand electron volts.The temperature associated with 1 keV is 1.16x107K

kilo pounds per square inch
A unit of pressure used in the imperial system of units.

Kilogram Force
Equivalent to the force exerted by 1 kilogram due to the local acceleration due to gravity.Conversions1 kilogram-force (kgf)=9.80665 N1 kilopond=1 kgf1 pound-force (lbf)=4.44822 N1 ton-force9964.02 Nttle='Force';xiunt='N';yiunt='kgf';mconv=9.80665;cconv=0.0; See also: Force.

Kilometres Per Hour
Unit of velocity used by most land based vehicles.Conversions1 mile per hour (mph)=1.609 kilometres per hour (kph)1 ms-1=3.280839 fts-1ttle='Velocity';xiunt='kph';yiunt='mph';mconv=1.609;cconv=0.0; See also: Miles Per Hour, Velocity.

Kinematic Viscosity
The dynamic viscosity of a fluid divided by the fluid density.where? = kinematic viscosity [m2s-1]µ = dynamic viscosity [Nsm-2]? = density [kgm-3]

Kinematics
A branch of mechanics dealing with the motion of rigid bodies without reference to their masses or the forces acting on the bodies.

Kinetic Energy
The energy that a body possesses solely because it is moving.wherem = mass of the body, [kg]v = velocity of the body, [ms-1]

Kinetic Heating
Heating as a result of air friction.

Kinetics
The study of how fast reactions occur.In many chemical reactions where there are a number of possible products, the first one formed may be the one that is formed most quickly, not necessarily the one that is most stable. Leave the reaction going and eventually the product that involves the greatest change in bond energy will be formed.

Kirchhoff's Law
Kirchhoff's Current LawThe basic law which states that the sum of currents flowing into any junction of an electric circuit is equal to the sum of currents flowing out of the junction.whereIi = currents impinging on nodeKirchhoff's Voltage LawThe basic law which states that the sum of voltage sources around any closed circuit is equal to…

Kirkwood Gaps
Gaps in the asteroid belt, caused by resonance effects from Jupiter. Similar gaps exist in Saturn's rings, due to the resonance effects of shepherd moons.

Kite
A quadrilateral which has two pairs of adjacent sides equal. See also: Quadrilateral.

Klystron
An evacuated electron tube used as an oscillator or amplifier at microwave frequencies. In the klystron, an electron beam is velocity modulated (periodically bunched) to produce large amounts of power. See also: Electron.

Knight's Tour
A knight's tour of a chessboard is a sequence of moves by a knight such that each square of the board is visited exactly once. See also: Magic Square, Magic Tour.

Knoop Hardness Test
An indentation hardness test using calibrated machines to force a rhombic-based pyramidal diamond indenter having specified edge angles, under specified conditions, into the surface of the test material and to measure the long diagonal after load removal. See also: Brinell Hardness Test, File Hardness, Hardening, Superficial Rockwell Hardness Test,…

Knot
A speed of 1 nautical mile per hour.ttle='Velocity';xiunt='ms-1';yiunt='knot';mconv=0.5144444;cconv=0.0; See also: Nautical Mile, SI Units, Velocity.

Knurl
A decorative gripping surface of straight-line or diagonal design made by uniformly serrated rolls called knurls. See also: Knurling.

Knurling
The process of finishing a part by scoring or pressing patterns on the surface of the work. See also: Knurl.

Krypton
One of the noble gases. Symbol Kr

Kurtosis
An expression of the so-called 'fourth moment'. A tendency for a distribution to form a sharp narrow peak in the center (or, when negative, a broad flat plateau). It is a unitless parameter. If the value is positive it indicates that the distribution of the signal has longer tails than the Gaussian distribution (a spikier signal). If the value is n…

Lacquer
A fast-drying usually clear coating that is highly flammable and dries by solvent evaporation only. Can be reconstituted after drying by adding solvent. The word lacquer is derived from the word lac, which describes the secretions of the lac beetle. This insect, found mainly in Asia, deposits its secretions on branches of trees and this crop is lat…

Lagrangian Points
In a system of two large bodies (Sun-Earth or Earth-Moon), these are the points where a small third body will keep a fixed position relative to the other two.Named for French astronomer Louis Lagrange (1736-1813) who first studied them and who showed there existed 5 such points. In the Sun-Earth system only two are important, both on the Earth-Sun …

Lambert's Laws
Lambert's First LawThe illuminance on a surface illuminated by light falling on it perpendicularly from a point source is proportional to the inverse square of the distance between the surface and the source.Lambert's Second LawIf the rays meet the surface at an angle, then the illuminance is proportional to the cosine of the angle with the normal.…

Lance-Wood
An elastic wood suitable where some degree of bending is required.

Land
That surface on the periphery of a rotary cutting tool, such as a milling cutter, drill, tap, or reamer, which joins the face of the flute or tooth to make up the basic cutting edge.

Landauer's Principle
A principle which states that it doesn't explicitly take energy to compute data, but rather it takes energy to erase any data, since erasure is an important step in computation. See also: Computer.

Lanthanum
Lanthanum is a soft, ductile, white metal which oxidises rapidly in air. It is one of the most reactive of the lanthanide group of elements, reacting with water to produce hydrogen gas. At very low temperatures, lanthanum is super conducting (at 6K). It is used to manufacture special grades of optical glass which have specific refractive properties…

Lap
A tool made of soft metal and charged with fine abrasives for precision finishing of metal surfaces.

Lap Joint
A joint between two overlapping members. See also: Joint.

Laplace Transform
The Laplace transform is used to convert certain types of inital value problems into algebra problems. The algebra problems are solved and then the inverse Laplace transform is used to give the solution of the initial value problem.The Laplace Transform, of f isfor all s such that this improper integral converges.

Laplacian
The divergence of a gradient.Laplacian of a scalar in rectangular coordinates:Laplacian of a vector in rectangular coordinates:In spherical and cylindrical coordinates:

Lapping
A surface finishing operation used to achieve a fine polish and close tolerances.

Lapse Rate
The rate at which temperature decreases with height in the atmosphere. This has the opposite sign from the temperature gradient a physicist would use, so be careful. See also: Temperature.

Larch
An extremely durable wood used for rough work. It warps a lot when dried, but can be polished to a fine finish when dry.

Lard Oil
An oil made from animal fats usually mixed with mineral oils to reduce its cost and improve its qualities. Used in engineering as a cutting oil.

Laser
An acronym for Light Amplification by Stimulated Emission of Radiation. A device that uses stimulated emissions to produce a coherent beam of electromagnetic radiation.Common types of lasers include solid state (glass or cystalline bulk material), semiconductor (based on p-n junctions), and gas lasers. Fibre lasers are doped glass lasers designed t…

Laser Diode
A laser which uses a forward biased semiconductor junction as the active medium. See also: Diode, Laser.

Laser Vibrometer
A sensing system which uses laser beams to measure the motion of a vibrating surface. See also: Accelerometer.

Latent Heat
The amount of heat required to melt (or vapourize) 1 kilogram of a substance. The same amount of heat is released when 1 kilogram of the same substance freezes (or condenses). The heat is absorbed at constant temperature, the melting temperature. Amorphous solids, including many polymers, do not have a sharp melting point. When these pass from a so…

Lathe
A machine tool which spins a block of material to perform various operations to create an object which has symmetry about an axis of rotation. See also: Drill Press, Faceplate, Facing, Roughing.

Latin Square
An n by n array of numbers in which only n numbers appear. No number appears more than once in any row or column.

Latitude
The angular distance of a point on the Earth from the equator, measured along the meridian through that point. See also: Earth, Longitude.

Lattice
An orderly arrangement of atoms in a material, usually thought of as an infinite series of 'cells' forming a 'latticework' of atoms in 3-dimensions See also: Body Centred Cubic, Crystal, Face Centred Cubic, Lattice Parameter, Miller Indices, Miller-Bravis Indices.

Lattice Parameter
The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry. See also: Crystal, Lattice.

Lattice Point
A point with integer coordinates. See also: Integer.

Laue Pattern
The pattern produced on a photographic film when high-frequency electromagnetic waves (such as x-rays) are fired at a crystalline solid. See also: Crystal, X ray.

Lawrencium
The only known isotope has a half life of 8 seconds. Symbol LrDiscoveredFirst artificially created in 1961 by a team led by American chemist Albert Ghiorso.

Lawson Criterion
A criterion specifying the product of density and confinement time required to satisfy some power balance condition in a fusion reactor. There are in fact several Lawson criteria, depending on the kind of power balance being used. For fairly realistic assumptions, the acceptable power balance for a reactor requires the product of density (particles…

Leaching
the process by which soluble materials in the soil, such as salts and nutrients, are washed into a lower layer of soil or are dissolved and carried away by water. See also: Water.

Lead
Photograph of the ore galena courtesy of MineraliteLead is a soft, malleable and ductile metal. Lead oxidises readily in moist air, is stable to oxygen and water, but dissolves in nitric acid. It is a poor electrical and thermal conductor but has reasonable corrosion resistance. Applications for this metal are wide and varied; for example, its rela…

Lead Acid Battery
A battery with electrodes of lead oxide and metallic lead that are separated by an electrolyte of sulphuric acid.Some batteries manufactured for use in very hot or very cold climates may have stronger or weaker acid. If so, it is usually marked on the battery.Most Lead-Acid batteries will have a specific gravity in the range of 1.1 to 1.3, with mos…

Lead II Carbonate
Decomposes readily into Lead II Oxide and carbon dioxide at 200°C and can be reduced to lead using carbon monoxide. Its use as pigment in paint was discontinued in the early 1950s by industry consensus standard, and banned by the Consumer Products Safety Commission in 1978 because of its toxicity. Symbol PbCO3 Also known as White Lead

Lead II Chromate IV
Used as a pigment due to the strong yellow colour. Symbol PbCrO4

Lead II Oxide
Lead monoxide varies in colour from pale yellow to brown, used in the manufacture of glass, paints, varnishes and glazes. Symbol PbO Also known as Litharge

Lead II Sulphide
Grey crystalline solid. Symbol PbS

Lead IV Oxide
Lead dioxide a dark brown powder, strong oxidizing agent. Symbol PbO2

Leaf Springs
Either a simple beam used as a spring or laminations of steel.

League
Old imperial unit of distance.Conversions1 league (UK nautical)=3.4545455 miles1 league (US)=3 miles1 league (International nautical)=3.4523383 miles1 league (UK nautical)=5559.552 mttle='League';xiunt='m';yiunt='league (UK nautical)';mconv=5559.552;cconv=0.0; See also: Length.

Leakage
In a Fourier Transform the signal is assumed to be periodic.Therefore, a continuous sine wavepure sine wave in the time domainwill transform to a single spectral line in the frequency domainsingle spectral line in the frequency domainHowever, in the case of the Discrete Fourier Transform a finite section of the time history is transformed. If a pur…

Least Common Multiple
The least common multiple of a set of integers is the smallest integer that is an exact multiple of every number in the set.

Least Significant Bit (LSB)
The bit within a digital word that represents the smallest possible coded value; hence, the LSB is a measure of precision. See also: Binary Notation, Bit, Most Significant Bit (MSB).

Leclanché Cell
A electrolytic cell Also known as a dry cell that uses a moist paste rather than a liquid as an electrolyte. Flashlight batteries are dry cells with a zinc cup for an anode, a carbon rod for a cathode, and a paste made of powdered carbon, NH4Cl, ZnCl2, and MnO2 for an electrolyte.Zn + 2 MnO2 + 2 NH4
Left Hand Rule
The procedure for finding electron-flow direction in a wire by grasping it so the fingers point in the direction of the magnetic lines of force. The thumb now points to electron-flow direction. For a single-layer inductor, the thumb indicates the north-pole end of the coil when the fingers point in the direction of electron flow. For conventional c…