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


Bass Ratio
In concert hall acoustics, the ratio of the average reverberation times at 125 and 250 Hz to the average of the RT's at 500 and 1000 Hz. It is determined only for a hall when fully occupied. See also: Reverberation Time.

Bastard
Threads, parts, tools, and sizes that are not standard, such as 'bastard nuts,' 'bastard plus,' 'bastard fittings,' and so forth. The term also refers to a standard coarse cut file.

Bath Metal
A cheap bronze made with 21 parts copper and 5 parts zinc. The same as pinchbeck.

Batten
The narrow strips of wood nailed vertically over the joints of boards to form board-and-batten siding.

Batter
An inclined face of wall; hence battered.

Batter Boards
Horizontal boards at exact elevations nailed to posts just outside the corners of a proposed building. Strings are stretched across the boards to locate the outline of the foundation of the foundation for workmen.

Battery
A group of voltaic cells connected in series.Bichromate2 voltsDry cell1.5 voltsBunsen1.9 voltsNickel Cadmium1.3 voltsDaniell1.08 voltsNickel Iron1.4 voltsGrove1.8 voltsZinc-silver oxide1.8 voltsLeclanche1.46 voltsClark cell1.4333 volts (absolute)Weston cell1.0186 volts (absolute)Note: Weston and Clark cells are standard cells used as references, al…

Baud Rate
The speed of information being transmitted across a serial interface, expressed in units of bits per second (bps). For example, a baud rate of 9600 refers to bits being transmitted (or received) from one piece of equipment to another at a rate of 9600 bps. Thus, a seven bit ASCII character plus parity bit plus one stop bit (total nine bits) would b…

Bauxite
An ore of aluminum consisting of moderately pure hydrated alumina. Symbol Al2O32H2O

Bay
A subdivision of the interior space of a building. In Romanesque and Gothic churches, the transverse arches and piers of the arcade divide the building into bays.

Bay Window
A window placed in a projection of an exterior wall of a building is called a bay window when the wall projection extends all the way down to a corresponding projection of the foundation. In plan view, the wall projection may be rectangular, polygonal or segmental (curved). See also: Window.

Bayes Rule
A rule for finding conditional probability. See also: Probability.

Beam
OpticsA collection of rays that may be parallel, convergent, or divergent.

Beam Steering
The method of steering the main lobe of a transducer to a certain direction. Three typical means of beam steering include:Placement of a reflector (e.g., a cone or parabola) behind an acoustic source.Phasing of narrowband signals emitted or received by an array of transducers or transducer elements.Shifting replicas of signals emitted or received b…

Beam Width
The width of the main beam lobe, in degrees, of the transducer. It is usually defined as the width between the 'half power point' or '-3dB' point.

Bearing
Primarily two types, rolling element and sleeve or plain bearing. Rolling element bearings consist of four parts: an inner race, an outer race, balls or rollers, and a cage to maintain the proper separarion of the rolling elements. A sleeve bearing is a cylinder of alloy metal surrounding the rotating shaft. Contact between the shaft and sleeve is …

Bearing Partition
A partition that supports any vertical load in addition to its own weight. See also: Bearing Wall.

Bearing Plate
A metal plate that provides support for a structural member.

Bearing Wall
A wall that supports a weight above in additional to its own weight. See also: Bearing Partition, Brick.

Beats
Periodic fluctuations that are heard when sounds of slightly different frequencies are superimposed.There is confusion in some areas between beating and amplitude modulation, which also can produce an undulating vibration level. Amplitude modulation is different from beating, and is caused by a high-frequency component being multiplied by a lower-f…

Beaufort Scale
In 1805 Admiral Beaufort drew up a scale of wind strengths related to commonly observable phenomena.

Becquerel
The Becquerel is a unit used to measure a radioactivity. One Becquerel isthat quantity of a radioactive material that will have 1 transformations inone second. As a result of having one Becquerel being equal to one transformationper second, there are 3.7x1010 Bq in one curie.ttle='Radioactivity';xiunt='Bq';yiunt='curie';mconv=3.7e10;ccon…

Bed Moulding
A moulding in an angle, as between the overhanging cornice, or eaves, of a building and the sidewalls.

Bedrock
A general term for solid rock that lies beneath soil, sediments, or other unconsolidated material.

Beech
A very hard wood with a compact grain and smooth surface, it is almost unaffected when exposed to water. Therefore, it is used for keels of ships and flood gates. On account of its hardness it was used for wheels and railway sleepers.

Beeswax
Produced by bees to make their honeycombs.

Behavioural Envelope
Envelope of response versus frequency.

Bell Metal
Copper tin alloy with much higher tin content than conventional bronze in order to make it hard and sonorous. It is too brittle to be used for many other applications.

Bell Mouth
The flaring or tapering of a machined hole, usually made at the entrance end because of misalignment or spring of the cutting tool.

Bell, Alexander Graham (1847-1922)
Invented the telephone (with Thomas Watson) in 1876. Bell also improved Thomas Edison's phonograph. Bell invented the multiple telegraph (1875), the hydroairplane, the photo-sensitive selenium cell (the photophone, a wireless phone, developed with Sumner Tainter), and new techniques for teaching the deaf to speak. In 1882, Bell and his father-in-la…

Bell's Inequality
A quantum mechanical theorem which demonstrates that quantum mechanics must have nonlocal properties. See also: Quantum Mechanics.

Belt Course
A horizontal board carried at the same level across or around a building. It is usually made of a flat member and a moulding.

Belt Drive
A belt used to transmit power between two shafts.Toothed Belt Drive

Belt Noise
There are many different mechanisms by which drive belts generate noise.ImpactProduced from the impact between timing belt and pulley. The resultant displacement of the belt will propagate away from the impact point. The impact will result in the pulley vibrating and hence radiating noise. The design of the pulley should be such that the first mode…

Belville Washer
Often used on smaller angular contact arrangements to provide a preload.

Bench Grinder
Photograph courtesy of Draper.co.ukA small grinding machine for shaping and sharpening the cutting edges of tools.

Bench Lathe
A small lathe mounted on a bench ortable.

Bench Vice
Photograph courtesy of Draper.co.ukA device attached to a bench with two jaws that can be moved parallel to each other and used to hold a workpiece. See also: Bench Work.

Bench Work
Work done primarily at a bench with hand tools. See also: Bench Vice.

Bending Mode
Mode of vibration in which cross sections of a beam, shaft or structure undergo translation and rotation. Type of translational mode usually found in slender structures with evenly distributed mass and stiffness.

Bending Stress
Stress on the cross-sectional area of a beam due to the bending moment of the beam under load. See also: Compressive Stress, Shear Stress, Stress, Tensile Stress.

Benzaldehyde
A colourless to yellow liquid with an almon like odour. Symbol C6H5CHO Also known as Benzoic Aldehyde, Almond Artificial Essential Oil, Benzenecarbonal, Benzene Carboxaldehyde, Oil of Bitter Almond.

Benzene
An aromatic hydrocarbon used in the manufacture of many organic compounds.There are many different ways of representing te benzene ring, three of which are shown below:The most common representation of a benzene ring is now as shown in the diagram below: Symbol C6H6

Benzoic Acid
Used as a fruit preservative. At room temperature it is a colourless solid forming glistening needles and plates, sublimes easily and is volatile in steam. Symbol C6H5.COOH

Berkelium
A transuranic element and member of the actinide series. Symbol BkDiscoveredFirst synthesized in 1949 by the American scientific team under the American chemist Glenn T. Seaborg

Bernoulli's Principle
In an irrotational fluid, the sum of the static pressure, the weight of the fluid per unit mass times the height, and half the density times the velocity squared is constant throughout the fluid. Bernoulli`s equation expresses the energy conservation in the fluid.The pressure in a fluid decreases as its velocity increases.where:P = pressure [Nm
Beryllium
Beryllium is a light and lustrous metal which is obtained by the electrolysis of a fused halide (e.g. BeCl2 ). It is resistant to attack by air or water, even at elevated temperatures. Beryllium is non-magnetic, a good thermal conductor and is used as an alloying addition to copper or nickel, the alloys having excellent thermal, mechanic…

Beryllium Copper
Heat treatable copper-beryllium alloy of high strength and hardness. Used for making springs and non-sparking tools.

Bessemer, Henry (1813-1898)
English engineer and inventor; developed an inexpensive steel-making process that burnt off the impurities in molten pig iron through the use of a hot-air blast. See also: Steel.

Beta Particle
An electron emitted by a radioactive nucleus, when a neutron decays into a proton and an electron. In some cases, beta radiation consists of positrons, 'antielectrons' which are identical to electrons but carry a +1 charge. Note that beta particles are created in nuclear decay; they do not exist as independent particles within the nucleus. See also…

Bevel
Any surface that is not at right angles to another surface. Also, the name given a tool used for measuring, laying out, or checking the accuracy of work machined at an angle or bevel.

Bhabda Scattering
Scattering of positrons by electrons. See also: Electron, Positron.

Bias
AudioUsed in recording signals on a magnetic media (tape). As the tape passes the recording head, the head generates a varying magnetic field corresponding to the analogue signal to be recorded. The problem is that if the magnetising force is in the form of a sine wave, (with excursions either side from zero), the resulting flux is non linear due t…

Bicron
Obsolete unit of distance referencing the double prefix micron-micron and equal to 10-12m. See also: Decimal Prefixes, Metre, picometre.

Bifilar Winding
Two conductors wound in parallel. See also: Transformer.

Bifunctional Monomer
A monomer unit that has two active bonding positions. See also: Monomer.

Big Bang Theory
A theory that suggests that the universe started with a giant explosion. The Big Bang theory is the most accepted theory so far to describe the origin and evolution of the Universe. According to it, all the matter and energy in the Universe was originally contained in a very small 'point' - technically called a 'singularity' - at an almost infinite…

Big End
The connection between the conrod and crankshaft in an internal combustion engine. See also: Connecting Rod, Crankshaft.

Big Endian
A byte ordering system where the most-significant byte of a multiple bytenumber is placed in memory at the lowest address. See also: Byte, Little Endian.

Billet
Rectangular or square bar of raw material.

Billion
A number equal to 109. See also: Million, Trillion.

Billon
An alloy of copper and silver with more than 50% copper.

Bimester
A unit of time equal to 2 months. See also: Time.

Bimetallic Strip
Two metals with different thermal expansion coefficients are bonded together and wound into a spiral. The spiral will unwind or tighten depending on the temperature versus it's original value.A bimetallic strip using brass and iron, the brass expands more than iron.

Bimillennium
Unit of time equal to 2000 years. See also: Millennium, Time.

Bimodal
AudioIn the home entertainment context, pertaining to presentations involving the visual and auditory sensory modalities.MathematicsHaving two modes.

Bimolecular Step
Two species are reacting and form the transition state.

Binary Coded Decimal
A number system where each decimal digit is separately represented by a 4-bit binary code;for examplethe decimal number 23 is represented as 0010 0011 (2 = 0010 and 3 = 0011, grouped together as shown), while in straight binary notation, 23 is represented as 10111.

Binary Coded Digit
A digit of any number system that is represented as a fixed number of binary digits; example:the decimal digit 23 is represented as 10111.

Binary Compund
A compound that contains two different elements. NaCl is a binary compound; NaClO is not.

Binary Notation
ExampleIn order to understand how anumber in binary notation is constructed, we will first discuss decimalnotation. Let's use the decimal-notation number '231' as an example.

Binary Number
A number written to base 2. See also: Binary Notation.

Binary Star
Pair of stars bound together by mutual gravitation and orbiting their common centre of mass. See also: Star.

Binaural
A situation involving listening with two ears. Binaural sound also refers to a specific sound playback technology, used mainly in headphones-based research and virtual reality applications, in which an individual's Head Related Transfer Functions (HRTF's) are determined and synthesized to enable 3-D auditory experiences that are indistinguishable f…

Binding Energy
The amount of energy required to take a nucleus apart. The analogous amount ofenergy for other bound systems.The potential energy associated with holding a systemtogether, such as the coulomb force between a hydrogenproton and its electron.The difference between the rest energies of the individualparticles of a system and the rest energy of a the b…

Binomial Formula
for positive nif n = 1,2,3,4,5,6.. thenthis may be rewritten in terms of binomial coefficientsthe coefficients are known as binomial coefficients and are given by

Biochemistry
The chemistry of living things, including the structure and function of biological molecules and the mechanism and products of their reactions.

Biodiesel
Diesel fuel derived from renewable lipid feedstocks, such as vegetable oils and animal fats. See also: Biodiesel B100, Biodiesel B20.

Biodiesel B100
100% (neat) biodiesel. The mono alkyl esters of long chain fatty acids derived from renewable lipid feedstocks, such as vegetable oils and animal fats, diesel engines

Biodiesel B20
A blend of biodiesel fuel with petroleum-based diesel where 20% of the volume is biodiesel.

Biology Conversions
Unit of BloodUnit of volume for human blood and its components.

Biomass
Burning wood, crop residues and dung is the most widespread source of energy for heating and cooking in the rural developing world.But burning biomass is a growing threat to surviving forests and a big source of smoke pollution.May be revived in high-tech form as liquid biofuels, such as ethanol and biodiesel.

Biometrics
The recognition of people from characteristics such as fingerprints, facial-geometry, iris patterns or voice.

Biosensor
Either a sensor to detect a biological substance or a sensor which incorporates the use of biological molecules such as antibodies or enzymes.

Biot-Savart Law
The magnetic flux density at a point P which is a distance r from a very short length of a conductor carrying a current I is given by:where = magnetic flux density [tesla] = short length of conductor [m]? = angle between the short length and the line joining it to P [radians]r = distance from the short length to P [m]I = current [A]

Biplane
An airplane with two sets of wings, one on top of the other. Historically the biplane configuration was used as it improves the bending stiffness of the wing that was otherwise difficult to achieve in early monoplane designs. Struts were used to maintain the angle between the upper and lower surfaces and wire braces used to tie the whole structure …

Bipolar
A signal that swings both above and below analog ground, thus having positive and negative values.

Birch
Strong flexible wood that has many uses. Amongst the uses are furniture making, building as well as being used for agricultural implements in the past.

Bisect
Bisect means to cut something in half. For example, to bisect an angle, you would draw a line through the vertex of the angle such that the two angles created are equivalent in measure. See also: Trisect.

Bismuth
Bismuth is a brittle metal which is silvery in colour with a pink tinge. It is stable in air and water. It has poor thermal and electrical properties and finds applications in the manufacture of fusible alloys, a range of materials with low melting points which are suitable for various applications including solders and thermal fuses. Pure bismuth …

Bistable
Circuit that has two stable states. See also: Astable, Flip Flop, Monostable.

Bit
An abbreviation of binary digit, the smallest unit of binary data. A single character of a language employing only two distinct kinds of characters. A quantity of intelligence which is carried by an identifiable entity and which can exist in either of two states.A unit of storage capacity; the capacity in bits of a storage device is the logarithm t…

Bit Depth
The number of bits used to represent each pixel in an image, determining its colour or tonal range. See also: Colour.

Bitrate
The rate at which the compressed bitstream is delivered from the storage medium to the input of a decoder. See also: Bit, Bitstream.

bits per second
A measurement of data transmission speed in a communications system, the number of bits transmitted or received each second. See also: Baud Rate, Bit, Byte.

Bitstream
An ordered series of bits that forms the coded representation of the data. See also: Bit, Bitrate.

Bittern
Waste solution of magnesium salts and bromides from the preparation of salt from sea-water by evaporation.

Bitumen
A name used to describe many different mixtures of hydrocarbons, also called asphalt or tar, bitumen is the brown or black viscous residue from the vacuum distillation of crude petroleum. Often produced by the processing of coal or oil, used in asphalt or tar for road surfacing or waterproofing. It also occurs in nature as asphalt 'lakes' and 'tar …

Black Annealing
Box annealing or pot annealing ferrous alloy sheet, strip or wire.

Black Box
A unit whose output is a specified function of the input, but for which the method of converting input to output is not necessarily specified.Colloquially, any unit, usually an electronic device such as an amplifier, which can be mounted in, or removed from, a rocket, spacecraft, or the like as a single package.