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

Bridge Rectifier
A full-wave rectifier in which there are four arms - each containing a diode. Converts an AC voltage to a pulsating DC voltage.The 4 diodes form a bridge rectifier. This rectifies both halves of the AC signal. Note that a capacitor across the DC out terminals is required to smooth the ripple.

Bright
In acoustic terms this refers to too much high frequency energy. See also: Sound.

Brilliance
In concert hall acoustics, a bright, clear, ringing sound, rich in harmonics, is called brilliant. In a brilliant sound the treble frequencies are prominent and decay slowly. This means that the high frequencies are diminished only by the natural absorption of the sound in the air itself.

Brinell Hardness Test
A test for determining the hardness of a material by forcing a hard steel or carbide ball ofspecified diameter into it under a specified load. The result is expressed as the Brinell hardness number, which isthe value obtained by dividing the applied load in kilograms by the surface area of the resulting impression insquare millimeters.Diameter of i…

Brinelling
A form of mechanical damage in which metal is displaced or upset without attrition. Permanent deformation of the bearing surfaces where the rollers (or balls) contact the races. Brinelling results from excessive load or impact on stationary bearings.

Bristol Metal
A brass made with 75.5% copper and 24.5% zinc.

British Standard Brass
A specialist thread form based upon the Whitworth thread and consisting of 26 threads per inch whatever the thread diameter. See also: British Standard Whitworth.

British Standard Fine
A thread form based upon the British Standard Whitworth form but with a finer thread.This thread form was first introduced in 1908, the thread form is specified in BS 84: 1956. See also: British Standard Whitworth.

British Standard Whitworth (BSW)
A symmetrical V thread with an angle between the threads measured in the axial plane of 55°. ¹/₆ of the V, i.e. the point is truncated with arcs blended tangentially into the flanks. The following table lists tapping and clearance drill sizes in imperial and metric.This thread form was developed by Sir Joseph Whitworth in 1841…

British Thermal Unit
The amount of heat required to raise the temperature of 1 lb of water by 1 degree Fahrenheit. Normally taken as 60° to 61°F.

Brittle Crack Propagation
A very sudden propagation of a crack with the absorption of no energy except that stored elastically in the body. See also: Brittle Fracture, Brittleness.

Brittle Fracture
Separation of a solid with little or no macroscopic plastic deformation; fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture; brittle tensile fractures have a bright, granular appearance and exhibit little or no necking; typical fracture mode of a glass or ceramic. See also: Brittle Crack Propagation…

Brittleness
The tendency of a material to fracture without first undergoing significant plastic deformation.Typically, brittle materials have lower impact and higher stiffness properties. See also: Brittle Crack Propagation, Brittle Fracture.

Broach
A long, tapered cutting tool with serration's which, when forced through a hole or across a surface, cuts a desired shape or size.

Broad Band Signal
A random signal containing a wide range of frequency components. Some types of electrical noise in a cable and acoustic noise from turbulent flow tend to be broad band. See also: Broadband Noise.

Broadband Noise
Noise with components over a wide range of frequencies. See also: Broad Band Signal, Noise.

Bromine
Dark red fuming liquid with a choking smell. Compunds are used in photography and medicine. Occurs naturally as magnesium bromide. Symbol Br

Bromoethane
A colourless volatile liquid that has an ether-like odour. Symbol C₂H₅Br Also known as Ethyl Bromide

Bromomethane
A colorless, nonflammable gas with no distinctive smell. Symbol CH₃Br Also known as Methyl Bromide, Monobromomethane

Bronze
A yellow to yellow-brown alloy that contains mostly copper and tin. However, the name is now applied to other alloys that do not contain tin.Discovered2500BC bronze is developed in Mesopotania.

Brookfield Viscosity
Apparent viscosity determined by Brookfield viscometer. This measures the torque required to rotate a spindle at constant speed in oil of a given temperature. Used for measuring low temperature viscosity of lubricants.

Brown Dwarf
These straddle the domain between stars and giant planets. Brown Dwarfs are thought to form in much the same way as stars, by the gravitational collapse of clumps of cold gas and dust in dense molecular clouds. For reasons not yet entirely clear, some clumps end up with masses less than about 7.5% of that of our Sun, or 75 times the mass of planet …

Brown, Robert (1773-1858)
Scotsman who discovered the brownian movement of minute particles (1828), a phenomenon that provides a basis for demonstrating molecular motion.1825 He classified gymnosperms and separated them from true, flower-bearing angiosperms. He discovered the minute areola (spaces) in pollen grains, which he regarded as points for the production of pollen t…

Brownian Motion
Small particles suspended in liquid move spontaneously in a random fashion. The motion is caused by unbalanced impacts of molecules on the particle. Brownian motion provided strong circumstantial evidence for the existence of molecules.Historical Notes1827 Brown discovered Brownian motion.1905 Einstein published papers on Brownian motion, the photo…

Brun's Constant
The sum of the reciprocals of all twin primes.B = 1.9021605824ttle='Brun's Constant';consttxt='B';constval=1.9021605824;constunt='';given by:

Brush DC Motors
The Brush DC motors use commutators and carbon brushes to apply current through the windings as the motor rotates. The Brush DC motor utilizes wound elements in the rotor and permanent magnets attached to a stationary stator ring. In a Brush DC motor, electrically separated motor windings are connected to the commutator ring. Current is carried by …

Brushless DC Motors
The BLDC motor uses electronic commutation to control the current through the windings. The BLDC motors use permanent magnets on the rotor. The BLDC motor contains rotor position sensor electronics so that the power input wave form to the windings is in sequence with the proper rotor position. Motor efficiency is enhanced because there is no power …

Brösted Acid
A material that gives up hydrogen ions in a chemical reaction. See also: Acid, Brösted Base.

Brösted Base
A material that accepts hydrogen ions in a chemical reaction. See also: Base, Brösted Acid.

Bubble Chamber
A chamber filled with liquid at low pressure chosen so that small bubbles form along the path of any charged particle. After each beam pulse a photographic record is made of the chamber and then it is depressurized to clear the bubbles.

Buckling
Distortion cuased by too much or uneven load. Such as that caused by the heat of a welding process. See also: Buckling Load.

Buckling Load
Pinned-Pinned BeamwhereF = force [N]L = length [m]I = second moment of area [m⁴]E = Young's Modulus [m^-2]

Buckminsterfullerene
Photograph of a buckyball-buckminsterfullerence, courtesy of Indigo® Instruments.A form of carbon consisting of 60 carbon atoms bound together to make a roughly spherical 'buckyball'. Symbol C₆₀

Buff
To polish to a smooth finish of high luster with a cloth or fabric wheel to which a compound has been added.

Buffer
ComputingA memory location in a computer or digital instrument which is set aside for temporarily storing digital information while it is waiting to be processed.ElectronicsAn isolating circuit used to prevent a driven circuit from influencing a driving circuit. See also: Memory.

Buffer Solutions
Solutions that resist changes in their pH, even when small amounts of acid or base are added. See also: Acid, Base.

Bug
A mistake or problem in software or hardware. An incident with an early vacuum tube computer that failed when insects got into the computer cabinet resulted in this term.

Building Acoustics
Acoustics associated with the operation and use of a building. See also: Acoustic Barriers, Reverberation Time, Room Acoustics.

Bulk Modulus
The bulk modulus of a gas is a measure of its compressibility (elastic property).whereK = bulk modulus [Nm^-2]P = pressure [Nm^-2]V = volume [m³]The difference in pressure for a fractional change in volume, a volume increase with a fall in pressure giving the negative sign. The value of B depends on whether the change…

Bump Steer
A generally undesirable condition in which a wheel steers slightly as its suspension compresses or extends.

Bunsen Burner
A gas burner with adjustable air intake, commonly used in laboratories. See also: Bunsen, Robert Wilhelm.

Bunsen, Robert Wilhelm (1811-1899)
German chemist; helped to develop the spectroscope.1855 Introduced the Bunsen burner that was developed by his laboratory assistant, Peter Desaga.1860 discovered the element caesium.1861 Discovered the element rubidium.

Buoyant Force
The upward force exerted by a fluid on a submerged or floating object.The buoyancy of hot air, the force that also lifts hot-air balloons, is the main cause of weather related flows in the Earth's atmosphere.The buoyant force is given by:

Buret
Buret photograph courtesy of Indigo® Instruments.A Buret or Burette. A cylindrical glass tube closed by a stopcock on one end and open on the other, with volume gradations marked on the barrel of the tube, used to precisely dispense a measured amount of a liquid.

Burgers Vector
A vector that denotes the magnitude and direction of lattice distortion associated with a dislocation. See also: Edge Dislocation.

Burn In
The operation of a newly fabricated device or system prior to application with the intent to stabilize the device, detect defects, and expose infant mortality.

Burnishing
The process of finishing a metal surface by contact with another harder metal to improve it. To make smooth or glossy by or as if by rubbing; polish.

Burr
The sharp edge left on metal after cutting or punching.

Bus
Transmission medium for electrical or optical signals that perform a particular function, such as computer control.

Busbar
Copper bar or section used for carrying heavy currents, generally rigid when compared to cables. See also: Copper.

Bushel
A dry or liquid measure equal to eight gallons. Note that there are a number of variations on the conversion in the US.Conversions1 bushel=0.03524 m³1 bushel=0.3048 barrels1 bushel=8 gallons (dry)1 bushel=4 pecks1 bushel=2150 in³1 bushel=1192 oz (liquid)ttle='bushel';xiunt='m³';yiunt='bushel';mconv=0.03524;cconv=0.0…

Bushing
A sleeve or a lining for a bearing or a drill jig to guard against wear.

Butane
An alkane hydrocarbon. Commonly used in compressed form for portable heaters and cookers. Symbol C₄H₁₀

Butanol
An alcohol containing four carbon atoms. Derived from butane that is used in organic synthesis and as a solvent.

Buttress
An exterior masonry structure that opposes the lateral thrust of an arch or a vault and adds extra support.

By-Pass Capacitor
A capacitor that provides a path of low impedance - low resistance to AC signals. See also: Capacitor.

Byte
A group of binary digits that combine to make a word. Generally 8 bits. Half byte is called a nibble. Large computers use 32 bits and 64 bits.In order to remove the confusion between the SI abbreviations (such as kilo) and the definition used in computing a new system was devloped and published in 1999.NameAbbreviationFactorkibiKi2¹⁰ = 1…

Cable Length
Originally the length of a ship's anchor cable, 120 fathoms.Conversions1 cable=120 fathoms1 cable=219.456 m1 cable=720 feet1 cable=0.1185 nautical milesttle='cable length';xiunt='m';yiunt='cable';mconv=219.456;cconv=0.0; See also: Fathom, Length, Nautical Mile.

Cadmium
Cadmium is a white metallic element. It is readily accessible as it occurs in concentrated ores and is easily extracted by heating the oxide with carbon and distilling the metal. Cadmium has been used in applications as diverse as plating, the manufacture of batteries and as a yellow pigment for paint. However, its high toxicity means that its use …

Cadmium Oxide
Commonly used in glasses, plastics, ceramics and porcelain enamels as a coloring agent for reds, oranges, and yellows.

Cadmium Sulphate
Colourless, odourless crystals that are freely soluble. Symbol CdSO₄

Cadmium Sulphide
Found as the mineral greenockite, it is used together with selenium to produce strong reds and yellows. Symbol CdS

Caesium
Caesium is a soft metal which is often liquid at room temperature due to its relatively low melting point (28.5°C). It is an extremely reactive metal, reacting violently in contact with water and being rapidly attacked in air. As with other alkaline group metals, caesium can be prepared by electrolysis of the fused halides but, in addition, it can …

Caesium Bromide
White crystalline solid. Symbol CsBr

Caesium Chloride
White crystalline solid. Symbol CsCl

Caesium Fluoride
White crystalline solid. Symbol CsF

Caesium Hydride
White crystalline solid. Symbol CsH

Caesium Iodide
White crystalline solid. Symbol CsI

Caesium Oxide
Yellow to orange crystalline solid. Symbol Cs₂O

Caesium Peroxide
Yellow crystalline solid. Symbol Cs₂O₂

Caesium Sulphide
White to pale yellow crystalline solid. Symbol Cs₂S

Caesium Superoxide
Yellow to orange crystalline solid. Symbol CsO₂

Caffeine
Photograph of a caffeine molecular model, courtesy of Indigo® Instruments.A substance found in tea, coffee, and cola that acts as a stimulant. It is extremely soluble in supercritical fluid carbon dioxide and somewhat soluble in water; aqueous solutions of caffeine quickly break down. Symbol C₈H₁₀N₄O₂

Calcination
A high-temperature reaction whereby one solid material dissociates to form a gas and another solid.

Calcium
Calcium is a silvery white metal which is obtained by the electrolysis of molten calcium chloride. Calcium compounds have many applications; for example, calcium chloride is used extensively to dry gases as it is capable of absorbing moisture from the atmosphere. Calcium oxide (lime), produced by heating limestone, has many applications including t…

Calcium Carbide
Usually formed by fusing lime and hard coal in a furnace. Symbol CaC₂

Calcium Carbonate
Photograph of Calcite courtesy of MineraliteA white insoluble solid, occuring naturally as chalk, limestone, marble and calcite. Symbol CaCO₃

Calcium Chloride
Absorbs moisture from the atmosphere and is used for drying gases. Symbol CaCl₂

Calcium Hypochlorite
More commonly known as bleaching powder. Symbol CaCl(OCl)

Calcium Oxide
Also know as Quicklime. Symbol CaO

Calcium Sulphate
Used to make plaster of paris and plaster. Symbol CaSO₄

Calculations
AerodynamicsDrag CoefficientA dimensionless value that allows the comparison of drag incurred by different sized and different shaped bodies.Kinematic ViscosityThe dynamic viscosity of a fluid divided by the fluid density.ViscosityA measure of the internal friction within a fluid.

Caliban Puzzle
A logic puzzle in which one is asked to infer one or more facts from a set of given facts.

Calibration
When recording or analysing any signal it is necessary to calibrate the system with a known signal.Acoustic CalibratorA device which produces a known sound pressure on the microphone of a sound level measurement system, and is used to adjust the system to Standard specifications. The standard acoustic calibrator produces a pure tone of 94dB at 1kHz…

Californium
A man-made element with an atomic number of 98. Symbol Cf

Caliper
A measuring instrument used to measure the distance between two points or the inside or outside dimensions of an object.CaliperInside CaliperOutside CaliperHistorical Notes220AD Han scientists used curved calipers and the cubit rule to accurately measure objects.

Caloric
A postulated elastic fluid associated with heat. See also: Ether, Phlogiston.

Calorie
A unit of energy in the British system of units. Still used to define the amount of energyamount of energy contained in foods. Defined as the amount of energy required toraise the temperature of 1 gram of water from 14.5°C to 15.5°C.Conversions1 calorie=4.184 J1 calorie=3.087 ft lbwt1 calorie=3.968x10^-3Btu1 kCal=4.184 kJttle='Energy';xiu…

Calorimeter
An insulated vessel for measuring the amount of heat absorbed or released by a chemical or physical change, originally a device that measured heat energy deposited, thus a calorie-meter.In particle physics, any device that can measure the energy deposited in it by particles.

Calorimetry
The science of measuring heat flow. See also: Heat Flow Rate.

Calutron
A device that separates isotopes by ionizing the sample, accellerating the ions in a strong electric field, and then passing them through a strong magnetic field. The magnetic field bends the trajectories of the ions with high charge-to-mass ratio more, allowing ions to be separated by mass and collected. See also: Isotopes.

Cam
A device for converting regular rotary motion to irregular rotary or reciprocating motion. Sometimes the effect of off-centre lathe operations or the cam in an engine used to operate valves. See also: Cam Follower, Camshaft, Eccentric.

Cam Follower
That part of the push rod that is in contact with the cam. See also: Cam, Internal Combustion Engine, Valves.

Camera
An instrument for taking photographs consisting of a lightproof box, shutter, adjustable aperture and a lens through which an image is focussed on a light sensitive film or sensor.Kodak No. 2 Brownie box camera introduced around 1910.Kodak Brownie 127 introduced in 1952. The body was made from Bakelite.Olympus Trip 35 First introduced in 1968 this …

Camera Obscura
A room with a small hole in one wall used by artists to produce images. First described by Leonardo da Vinci in 1515. See also: Camera.

Campbell Diagram
A mathematically constructed diagram used to check for coincidence of vibration sources with natural resonances. The form of the diagram is like a spectral map, but the amplitude is represented by a circular or rectangular plot, the larger the amplitude the larger the circle or rectangle.In this particular example the even engine orders are plotted…

Camshaft
The shaft which carries the various cams required for the operation of inlet, exhaust, fuel, and starting-air valves. See also: Cam, Internal Combustion Engine, Poppet Valve, Rocker Arm, Valves, Valvetrain.

Canal
An artificial channel of water used by boats and originally designed for the transportation of goods.

Canard
A horizontal pitch control surface on an aircraft that is forward of the main wing. See also: Aircraft, Elevator.

Candela
The SI unit of Luminous IntensityThe candela is the luminous intensity, in a given direction, of a source that emitsmonochromatic radiation of frequency 540x10¹² hertz and that has a radiantintensity in that direction of 1/683 watt per steradian. The candela is abbreviated cd.