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


Black Hole
A massive star that has collapsed to such a small size that its gravitationalforce is so strong that not even light can escape from its 'surface'.First law of black hole dynamicsFor interactions between black holes and normal matter, the conservation laws of mass-energy, electric charge, linear momentum, and angular momentum, hold. This is analogou…

Black Light
Electromagnetic radiation not visible to the human eye. The portion of the spectrum generally used influorescent inspection falls in the ultraviolet region between 3300 and 4000 A, with the peak at 3650 A.

Black, Joseph (1728-1799)
Scottish chemist who laid the foundations for thermodynamics, worked with gases and showed that a gas could combine with a solid. Also, he recognized the importance of accurate weighing in chemical research.

Blackbody
An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A black body also absorbs all the radiant energy in the near visible spectrum incident upon it.No actual substance behaves as a true black body, although platinum black and other soots rather closely approximate this ideal…

Blackbody Radiation
The electromagnetic radiation emitted by an ideal black body; it is the theoretical maximum amount of radiant energy of all wavelengths which can be emitted by a body at a given temperature.The spectral distribution of black-body radiation is described by Planck law and the related radiation laws. If a very tiny opening is made into an otherwise co…

Blackett, Patrick Maynard Stuart
English chemist who developed the cloud chamber. See also: Meson, Positron.

Blackman Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis. This is described as the Blackman window where the coefficients are limited to two decimal places.whereThe exact form of the Blackman window is:

Blackman-Harris Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.The Blackman-Harris windows are a family of three and four term windows. The variations on the coefficients allow a trade between main-lobe width and side-lobe level.3 term -67dB side-lobewherew(t) = weighting as a function of timet = timeN = total …

Blacksmithing
The ancient art of forging and working metal, especially iron. See also: Anvil, Forging, Fullering, Hammer, Heat Treatment, Iron.

Blade
An arm of a propeller or a rotating wing.Specifically, restrictive, that part of a propeller arm or of a rotating wing from the shank outward, i.e., that part having an efficient airfoil shape and that cleaves the air. See blade shank.A vane (in sense 2), such as a rotating vane or stationary vane in a rotary air compressor, or a vane of a turbine …

Blade Passing Frequency
A potential vibration frequency on any bladed machine (turbine, axial compressor, fan, etc.). It is represented by the number of blades times shaft-rotating frequency. See also: Blade, Frequency.

Blank Carburizing
Simulating the carburizing operation without introducing carbon. This is usually accomplishedby using an inert material in place of the carburizing agent, or by applying a suitable protective coating to theferrous alloy.

Blanking Distance
Minimum sensing range in an ultrasonic proximity sensor. Blanking distance is a function of the ring down time of the transducer as the transducer must ring down before it can receive the sound reflected from the target.

Bleach
A dilute solution of sodium hypochlorite or calcium hypochlorite which kills bacteria and destroys coloured organic materials by oxidizing them. See also: Calcium Hypochlorite.

Bleeder Current
A current drawn continously from a souce. Bleeder current is used to stabilize the output voltage of a source.

Bleeder Resistor
A resistor that allows a small current drain on a power source to discharge filter capacitors or to stabilize an output. See also: Resistor.

Blind Experiment
In a blind experiment, the subjects do not know whether they are in the treatment group or the control group. In order to have a blind experiment with human subjects, it is usually necessary to administer a placebo to the control group.

Blind Hole
A hole made in a workpiece that does not pass through it. See also: Drill Bits.

Block Companding
Normalising of the digital representation of an audio signal within a certain time period.

Block Copolymer
A linear copolymer in which identical mer units are clustered in blocks along the molecular chain. See also: Copolymer.

Blood
A liquid that circulates inside the bodies of animals. Blood carries oxygen and food substances to cells in the body. It removes carbon dioxide and other waste materials from the cells. See also: Oxygen, Unit of Blood, Vein.

Bloom
Generally a rolled product from an ingot generally greater than 36 square inches in area, this is the first operation in the production of bars or structurals. See also: Ingot.

Blow By
Passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil. See also: Piston.

Blowhole
A defect in a casting caused by trapped steam or gas. See also: Casting.

Blue Brittleness
Brittleness exhibited by some steels after being heated to some temperature within the range of150 to 350°C, and more especially if the steel is worked at the elevated temperature. Killed steels are virtually freeof this kind of brittleness.

Blue Shift
The apparant (Doppler) shift of the wavelength towards the higher frequency region of radiation emitted by an approaching object. The opposite to the famous red shift which indicated the universe is expanding away from us. See also: Doppler Effect, Redshift.

Blue Supergiant
A supergiant star with spectral type O or B. See also: Star, Supergiant.

Blueprint
A pen or ink line drawing reproduced (printed) on sensitised paper by direct exposure.

Blueprinted Engine
Ensuring the dimensions of the parts in the engine are more accurate and, therefore, closer to the original engine blueprint values. See also: Engine.

BNC Connector
A twist lock bayonet coaxial connector commonly used in applications involving small coaxial cables.

Boat
A small craft that floats on water. See also: Rudder.

Bobbiere Metal
A brass made with 66% copper and 34% zinc.

Bode Plot
A plot of the frequency response function that includes log magnitude versus frequency plus phase versus frequency. For a single-degree of freedom, the magnitude is a maximum at the natural frequency and the phase shift is 90°.In most vibration analysis work the phase spectrum is not important and is either ignored or not recorded. In two-channel v…

Body Centred Cubic
About 15% of elements crystallize with a body centred cubic structure.e.g. Lithium, Sodium, Potassium, Iron, Tungsten ...Volume of conventional cella3Lattice points per cell2Volume of primitive cell1/2a3Lattice points per unit volume2/a3Number of nearest neighbours8Nearest neighbour distance3
Body Force
An external force acting throughout the mass of a body. Gravity is a body force. An inertial force is a body force. See also: Concentrated Force, External Force, Force, Surface Force.

Bohman Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.whereIn the time domain this function is shown below:The frequency response of this window is shown along with that of a rectangular window for comparison:

Bohr Magneton
Unit of magnetic moment. For an electron it is defined as:wheree = electron charge = 1.602x10-19 Ch = Planck's constant = 6.626x10-34 Jsme = electron rest mass = 9.109x10-31 kgc = velocity of light = 2.997924580x108 ms-1µB = 9.27400899x10-24 Am2ttle='…

Bohr Radius
The distance corresponding the mean distance of an electron from the nucleus in the ground state of the hydrogen atom.a0 = 5.291772x10-11 mttle='Bohr Radius';consttxt='a0';constval=5.291772e-11;constunt='m';The Bohr model of atoms states:An electron moves around the nucleus in a circular orbit under the influence of…

Boiling Point
The temperature at which the vapour pressure of a liquid is equal to the external pressure on the liquid. The standard boiling point is the temperature at which the vapour pressure of a liquid equals standard pressure.Click on an item to paste into clipboard or use clipboard symbol at end to clipboard all values Acetaldehyde 293.55 KClip Acetamide …

Boiling Point Elevation
The boiling point of a solution is higher than the boiling point of the pure solvent. Boiling point elevation is a colligative property. See also: Boiling Point.

Bolide
A brilliant meteor, especially one which explodes, a detonating fireball.

Bolometer
A device for measuring minute amounts of radiant energy by determining the changes of resistance in an electric conductor caused by changes in its temperature.

Bolt
A cylindrical threaded fastener. See also: Nut, Screw, Thread.

Bolt Cutters
Photograph courtesy of Draper.co.ukCutters with strong jaws and long handles designed for manually cutting through thick steel bolts. See also: Side Cutters.

Bolt of Cloth
A standard unit of length used in the fabric industry.Conversions1 bolt of cloth=36.576 m1 bolt of cloth=120 feet1 bolt of cloth=40 yards1 bolt of cloth=1440 inchesttle='bolt of cloth';xiunt='m';yiunt='bolt of cloth';mconv=36.576;cconv=0.0; See also: Denier.

Boltzmann's Constant
A constant which describes the relationship between temperature and kinetic energy for molecules in an ideal gas. Equal to the ideal gas law constant divided by Avogadro's number.k = 1.38062x10-23 JK-1ttle='Stefan-Boltzmann Constant';consttxt='s';constval=1.38062e-23;constunt='Wm-2K-4';

Bond Energy
Energy change per mole when a mole is broken in the gas phase for a particular substance. See also: Primary Bond, van der Waals Bond.

Bond Enthalpy
enthalpy change per mole when a bond is broken in the gas phase for a particular substance.

Bond Length
The average distance between the nuclei of two bonded atoms in a stable molecule.

Bond Order
In Lewis structures, the number of electron pairs shared by two atoms.In molecular orbital theory, the net number of electron pairs in bonding orbitals (calculated as half the difference between the number of electrons in bonding orbitals and the number of electrons in antibonding orbitals.

Bond Strength
Some measure of how difficult it is to break a chemical bond, for example, a bond energy or a bond bond enthalpy.

Bonding Energy
The energy required to separate two atoms that are chemically bonded to each other.

Bone
A material which makes up the skeleton of an animal. Primarily based on phosphate and carbonate. Bones are strong because they contain calcium. Bones are hollow and contain a soft substance called bone marrow.

Bone Black
An impure animal charcoal prepared from bones and blood. See also: Charcoal.

Books
AerodynamicsMechanics of Flight By D.R. Philpott, A.C. Kermode, R.H. Barnard, Published By: Prentice-Hall.Competition Car Aerodynamics: A Practical Handbook By Simon McBeath, Published By: Haynes Group.

Boomy
Listening term, refers to an excessive bass response that has a peak(s) in it. Often used to describe noise in the frequency range 50 to 125Hz. See also: Drumming Noise.

Bore
The interior diameter of a cylinder.To enlarge and finish the surface of a cylindrical hole by the action of a rotating boring bar (cutting tool) or by the action of a stationary tool pressed (fed) against the surface as the part is rotated. See also: Cylinder, Stroke.

Born, Max (1882-1970)
German physicist. While at Edinburgh University in 1954 he won the Nobel Prize in Physics 'for his fundamental research in quantum mechanics, especially for his statistical interpretation of the wavefunction'. See also: Quantum Mechanics.

Boron
Boron is a non-metallic element which occurs in several allotropes. It is rarely found in nature, normally occurring as borates or orthoboric acid. Hard yellow crystals or brown amorphous powder. Amorphous boron is the more common allotrope and exists as a dark powder which is unreactive towards water, oxygen, acids and alkalis. Boron finds importa…

Bose-Einstein Statistics
Quantum statistics for particles not obeying the exclusion principle, based on the assumption that in a given physical system consisting of indistinguishable particles and regions all distinguishable arrangements of the particles have equal probability. See also: Exclusion Principle, Quantum Mechanics.

Bosons
Particles which do not obey the Pauli exclusion principle, for example, photons. Thus there is no limit to the number that can occupy the same region at the same time yet have the same quantum numbers; so, for example, there is no limit to the brightness of light or the loudness of sound. A boson is a particle that has integer intrinsic angular mom…

Boss
A projection or an enlarged section of a casting through which a hole may be machined.

Bottle
A unit of volume. In Britain, a common bottle size was 2/3 Imperial quart (757.68 milliliters), a unit known as the reputed quart. Today wine is customarily sold in bottles containing 750 millilitres.

Bottom
The flavor of the fifth quark. See also: Charm, Down Quark, Quark, Top.

Bottom Dead Centre
The position of the crank when the piston is in its closest position to the crankshaft, in its farthest position from the cylinder head. Abbreviated bdc. See also: Top Dead Centre.

Bounce
A term which is used to describe the oscillations of a rigid body, for example, the sprung and unsprung masses of a vehicle, that consists primarily of vertical displacement. See also: Frequency.

Bound State
This is a state in which a particle is confined within a composite system, for example an atom or a nucleus, because it does not have enough energy to escape. An electron in a atom is bound because of its electrical attraction to the nucleus, which makes the mass of the atom slightly less than the sum of the masses of the electron plus the rest of …

Boundary Element Method
A mathematical formulation used to predict acoustic parameters such as pressure and power. This technique may be applied to interior and exterior acoustic problems. See also: Finite Element Method, Statistical Energy Analysis.

Boundary Layer
The portion of a fluid flowing past a body that is in the immediate vicinity of the body and that has a reduced flow due to the forces of adhesion and viscosity.ExampleThe layer of air next to the Earth's surface, typically a few hundred metres thick. Ordinarily, only the boundary layer is appreciably affected by the properties of the surface. The …

Bow Shock
The shock wave caused by the edge our Solar System travelling through deep space. See also: Heliopause, Heliosheath, Solar System, Solar Wind, Termination Shock.

Box
A surface made up of rectangles; a rectangular parallelpided.

Box Annealing
Annealing a metal or alloy in a sealed container under conditions that minimize oxidation. In boxannealing a ferrous alloy, the charge is usually heated slowly to a temperature below the transformation range, butsometimes above or within it, and is then cooled slowly; this process is also called 'close annealing' or 'potannealing.'

Box-Wood
Very compact hard wood suitable for machining small parts from e.g. sheaves of pulley blocks and bearings in machinery. It is of a bright yellow colour.

Boyle, Robert (1627-91)
He will be forever known for that scientific law named after him, Boyle's Law, a principle which he published in 1662.Boyle`s law states:The volume of a given mass of gas, the temperature being constant, varies inversely as the pressure; or, that the pressure and volume of a gas are inversely proportional.

Boyle's Gas Law
For a fixed mass of gas at constant temperature the product of pressure and volume is constant. Therefore, if the pressure increases, the volume decreases and visa versa. For example, if the volume if halved, then the pressure is doubled. If the temperature is held constant, it becomes an isothermal process. Discovered by Robert Boyle (1627-1691), …

Bracket
A horizontally projecting support. See also: Cantilever Beam.

Brackett Series
The series which describes the emission spectrum of hydrogen when the electron is jumping to the fourth orbital. All of the lines are in the infrared portion of the spectrum. See also: Balmer Series, Hydrogen.

Bradawl
Photograph courtesy of Draper.co.ukA sharp tool for making small holes either through thin materials or into soft block materials. See also: Drill Bits, Wood Screws.

Bragg's Law
When a beam of x-rays strikes a crystal surface in which the layers of atoms or ions are regularly separated, the maximum intensity of the reflected ray occurs when the complement of the angle of incidence, ?, the wavelength of the x-rays, ?, and the distance between layers of atoms or ions, d, are related by the equationwheren = an integer? = wave…

Brahe, Tycho (1546-1601)
Danish astronomer who made precise observations of the sky and made a significant contribution to astronomy.He passed on records of his observations to Jahannes Kepler. It was based on these observations that Kepler produced his three laws of planetary motion.

Brake Graunch
The name given to the noise made by the brakes when they are just slipping when starting (or stopping) from rest. The brake graunch is mainly exhibited on the vehicles fitted with automatic transmission, but can also occur on manual vehicles e.g., on a steep hill. It is caused by brake pad stick-slip when static and dynamic friction is very similar…

Brake Horse Power
This is the useful power available at the flywheel of an engine. Nowadays engine power is often quoted in PS. 1PS=0.9863bhp.It was first used by the engineer James Watt, who employed it to compare the power of steam engines with that of horses. In the UK, one horsepower is equal to 550 foot-pounds per second or 745.7 watts. In the USA this figure h…

Brake Judder
Brake judder is the phenomenon where with medium to heavy braking from high speed, severe vibration is felt throughout the whole vehicle. It is often attributed to a mode of vibration in which the front suspension executes a predominantly fore and aft vibration with the two road wheels in-phase with each other. Excitation is often provided by the o…

Brake Mean Effective Pressure
This is the average effective cylinder pressure that does useful work calculated from the brake horse power.The work accomplished during one engine cycle divided by the engine swept volume. It is essentially the engine torque normalized by the engine displacement. The word “brake� denotes the actual torque/power available at the engine flywheel as …

Brake Pipes
Pipes used to carry hydraulic brake fluid under pressure.

Brake Squeal
High frequency continuous tone when brakes are applied, this may be a single or multiple tones. The sound is generated by vibration on the surface of the disc itself. See also: Brake Graunch, Brake Judder.

Brakes
A device used to reduce the speed of a vehicle or object.Air brakeUsed to reduce the speed of an aeroplane.Foot brakeVehicle brake applied with the foot.HandbrakeVehicle brake that is applied by hand to hold the vehicle when stationary.

Brale
A diamond penetrator of specified sphero-conical shape used with a Rockwell hardness tester for hardmetals. This penetrator is used for the A, C, D and N scales.

Branched Polymer
A polymer having a molecular structure of secondary chains that extend from the primary chains. See also: Polymer.

Brass
A shiny yellow to yellow-orange alloy of 70% copper and 30% zinc, but often other elements such as aluminium, iron, manganese, tin and lead are added.

Bratice
A timber tower, or projecting wooden gallery.

Brayton Thermodynamic Cycle
The thermodynamic cycle of the gas turbine engine. Sometimes known as the Joule Cycle. See also: Gas Turbine, Jet Engine.

Brazing
Joining metals by flowing a thin layer, capillary thickness, of nonferrous filler metal into the space betweenthem. Brazing temperatures are in excess of 427°C.Bonding results from the intimate contact produced by the dissolution of a small amount of base metal in the molten filler metal, without fusion of the base metal. Sometimes, the filler meta…

Breadboard
An assembly of preliminary circuits or parts used to prove the feasibility of a device, circuit, system, or principle without regard to the final configuration or packaging of the parts. See also: Circuit.

Breakdown Voltage
Voltage at which the breakdown of a dialectric or insulator occurs. If the potential gradient becomes too steep, normal conduction is replaced by electrical breakdown: a catastrophic electron-cascade, usually causing permanent damage. The breakdown potential-gradient is the material property that characterises this effect. See also: Avalanche.

Breaking Stress
Also known as the ultimate tensile strength. This is the maximum stress that can be applied to a material. See also: Strain, Stress.

Bremsstrahlung Effect
The emission of electromagnetic radiation as a consequence of the acceleration of charged elementary particles, such as electrons, under the influence of the attractive or repulsive force fields of atomic nuclei near which the charged particle moves.In cosmic-ray shower production, bremsstrahlung effects give rise to emission of gamma rays as elect…

Bremsstrahlung
X-rays emitted when a charged particle (such as an electron) is deceleratedby passing through matter. The word bremsstrahlung is German for 'braking radiation'.whereW = Energy radiated? = Angular frequency = Lorentz factorZe = ionic chargee0 = permittivity of free spacec = speed of lightm = electronic massb = distance of closest approach…

Brewsters Law
Unpolarised light can be polarised by reflection. When unpolarised light is reflected from the surface of an optical material (glass, say) then preferential reflection occurs for the electric-field vector that is perpendicular to plane of incidence. At one particular angle, the polarising angle ?p, no light at all is reflected apart from…

Brick
In it's simplest form a shaped and burnt block of clay.The Brick Taxes from 1784 to 1850 were at first applied based on the number of bricks used. As you could imagine this lead to bricks being made larger.