Copy of `DiracDelta - Science & Engineering encyclopedia`

The wordlist doesn't exist anymore, or, the website doesn't exist anymore. On this page you can find a copy of the original information. The information may have been taken offline because it is outdated.

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

Sodium Hypochlorite
Sold as a solution under a variety of trade names for use as liquid bleach. Symbol NaOCl

Sodium I Bromide
White crystalline solid. Symbol NaBr

Sodium I Fluoride
White crystalline solid. Symbol NaF

Sodium I Iodide
White crystalline solid. Symbol NaI

Sodium I Oxide
Yellow crystalline solid. Symbol NaO₂

Sodium Oxide
White solid. Symbol Na₂O

Sodium Peroxide
Pale yellow solid. Symbol Na₂O₂

Soft Room
Room with highly sound absorptive surfaces.

Soft Solder
50% Sn and 50% Pb

Solar Cell
A cell that produces current under sunlight.In a square kilometre of sunlight there are 1,000 megawatts of solar power, the equivalent of a large nuclear power plant. Even if only 10 or 20 percent of the sunlight`s energy is extracted as electricity, the area of the solar cells will not be much larger than what we currently devote to nuclear, gas, …

Solar Cycle
The approximately 11 year quasi-periodic variation in frequency or number of solar active events. See also: Sun.

Solar Flare
Sudden violent explosion on the Sun which occurs above complex active regions in the photosphere. They usually last only a few minutes, but their temperatures may reach hundreds of millions of degrees. Most of their radiation is emitted as X-rays, but they can also be observed in visible light and radio waves. Charged particles ejected by flares ca…

Solar Storm
Violent outburst of explosive activity on the Sun. See also: Solar Flare, Sun.

Solar System
Meaning our sun and all of the bodies that orbit the sun.

Solar Wind
The wind from the Sun. More specifically, particles, usually electrons and protons, continually streaming away from the corona of the Sun at up to 900 km s^-1. The solar wind is extremely sparse, containing only a few fast moving particles per cubic centimetre at the Earth. The exact geometry and extent of the solar wind is not well known…

Solder
A low melting point alloy, usually of lead (Pb) and tin (Sn), that can wet copper, conduct current, and mechanically join conductors. See also: Lead, Soldering, Tin.

Soldering
A group of welding processes for joining metallic surfaces by heating them to suitable temperature and using a filler metal having a liquidus state not exceeding 450 °C and below the solidus of the base materials. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action. See also: Brazing, Flux, Solder.

Solid
MathematicsThe union of the surface and the region of space enclosed by a 3-D figure.PhysicsMatter with a definite size and shape.

Solid of Revolution
A solid formed by rotation a plane figure about an axis in three-space.

Solid Solution
A single solid homogeneous crystalline phase containing two or more chemical species.

Solidification Range
The temperature between the liquidus and solidus. See also: Solidus.

Solidus
MathematicsThe slanted line in a fraction such as a/b dividing the numerator from the denominator. PhysicsIn a constitution or equilibrium diagram, the locus of points representing the temperatures at which variouscompositions finish freezing on cooling or begin to melt on heating.

Solute
What is dissolved in a solution eg, the salt in saltwater. See also: Heat of Solution, Precipitate.

Solution
Mixture of a solid and a liquid where the solid never settles out, eg saltwater. See also: Colligative Properties.

Solution Heat Treatment
Heating an alloy to a suitable temperature, holding at that temperature long enough toallow one or more constituents to enter into solid solution, and then cooling rapidly enough to hold the constituentsin solution. The alloy is left in a supersaturated, unstable state and may subsequently exhibit quench aging.

Solvent
Liquid in which something is dissolved, eg the water in saltwater.

Sonar
Acronym for 'sound navigation and ranging'. A system using reflected sound waves to determine the position of some target.Passive SonarThe noise produced by the target is observed using a reciever or number of receivers from which the location can be calculated by triangulation.Active SonarA pulse is emitted at the transmitter that travels to the t…

Sone
The unit of measurement for loudness. One sone is the loudness of a sound whose loudness level is 40 phons. Loudness is proportional to the sound's loudness rating, e.g., two sones are twice as loud as one sone. See also: Phon.

Sonic Boom
A body moving through the air pushes the air aside. Small disturbances move away at the speed of sound. Disturbances from a slowly moving body go out in circles, like ripples from a pebble in a pond. If the body moves faster, the circles are closer in the direction of travel. If the body is supersonic, then the circles overlap. The envelope of circ…

Sonoluminescence
In the early 1930s Frenzel and Schultes discovered that photographic plates became 'fogged' when submerged in water exposed to high frequency sound. More recent experiments have succeeded in suspending a single luminous pulsating bubble in a standing wave acoustic field, visible in an undarkened room. Generally sonoluminescence is light emission fr…

Sound
Energy that is transmitted by pressure waves in air or other materials and is the objective cause of the sensation of hearing. Commonly called noise if it is unwanted. Sound, physical phenomenon that stimulates the sense of hearing. In human beings, hearing takes place whenever vibrations of frequencies between about 15 and 20,000 hertz reach the i…

Sound Absorption
Reduction of sound pressure level through sound absorption.Examples of porous absorbers are carpets, curtains, mineral wool and foam.The absorption of low frequency sound increases with the thickness of the absorber. The absorption will be more effective where the particle velocity is high. Close to the boundary of the room the particle velocity wi…

Sound Attenuation
The reduction of the intensity of sound as it travels from the source to a receiving location. Sound absorption is often involved as, for instance, in a lined duct. Spherical spreading and scattering are other attenuation mechanisms. See also: Sound Propagation.

Sound Barrier
The first aircraft in the world to break the sound barrier was the Bell X1. On the 14 October 1947 it reached 670mph at 42000feet (Mach 1.015). The X1 was launched by a Boeing B29 at 30000 feet, once released the rocket motor on the X1 was fired and it would begin it's ascent.Concept that the speed of sound, or sonic speed (about 1,220 kph/760 mph …

Sound Definition
The definition of a sound may be described by: this compares ‘useful` sound with total sound. ‘Useful` sound reflections are those which arrive at the listener`s position within 50ms of the direct sound.

Sound Energy
Energy added to an elastic medium by the presence of sound, consisting of potential energy in the form of deviations from static pressure and of kinetic energy in the form of particle velocity.

Sound Energy Density
The quotient obtained when the sound energy in a region is divided by the volume of the region. The sound energy density at a point is the limit of that quotient as the volume that contains the point approaches zero.

Sound Exposure Level
Sound exposure level abbreviated as SEL and L_AE, is the total noise energy produced from a single noise event. The Sound Exposure Level is a metric used to describe the amount of noise from an event such as an individual aircraft flyover. It is computed from measured dBA sound levels. The Sound Exposure Level is the integration of all th…

Sound Focusing
Focusing of sound can be caused by reflection from large concave surfaces. Certain sounds will be heard too loudly near the focus of a curved surface.

Sound Growth
The growth of sound in the room is described by:where? = rate at which sound is being produced [W]A = sound absorption of the room [sabin]c = speed of sound [ms^-1]?₀ = density of air [kgm^-3]V = volume of room [m³]After an infinite length of time the pressure in the room will be:Note that using the above e…

Sound Insulation
The capacity of a structure to prevent sound from reaching a receiving location. Sound energy is not necessarily absorbed; impedance mismatch, or reflection back toward the source, is often the principal mechanism.

Sound Intensity
The quotient obtained when the average rate of energy flow in a specified direction and sense is divided by the area, perpendicular to that direction, through or toward which it flows. The intensity at a point is the limit of that quotient as the area that includes the point approaches zero.Sound intensity is a vector quantity. It describes as a fu…

Sound Isolation
The degree of acoustical separation between two locations, especially adjacent rooms. See also: Sound Transmission Class, Sound Transmission Coefficient, Sound Transmission Loss.

Sound Level
Of airborne sound, a sound pressure level obtained using a signal to which a standard frequency-weighting has been applied.

Sound Level Meter
Device used to measure sound pressure level with a standardized frequency weighting and indicated exponential time weighting for measurements of sound pressure level, or without time weighting for measurement of time-average sound pressure level or sound exposure level. See also: A Weighting, B Weighting, Decibel, Sound, Sound Pressure Level.

Sound Masking
The process of using electronic masking sound to cover unwanted or intrusive sound such as speech or equipment noise, typically used to enhance speech privacy and productivity. See also: Speech Privacy.

Sound Power
In a specified frequency band, the rate at which acoustic energy is radiated from a source. In general, the rate of flow of sound energy, whether from a source, through an area, or into an absorber.Sound power is not measured directly, but may be estimated in a number of ways from measurements of sound pressure or sound intensity. There a number of…

Sound Power Level
Of airborne sound, ten times the common logarithm of the ratio of the sound power under consideration of the standard reference power of 1 pW. The quantity so obtained is expressed in decibels.function init(){}multicalc_form(4)For a simple monopole in free space the sound power is expressed as:where? = sound power [W]?₀ = density of air …

Sound Pressure Level
Ten times the logarithm of the ratio of the time-mean-square pressure of a sound, in a stated frequency band or with a stated frequency weighting, to the square of the reference sound pressure of 20x10^-6Pa.

Sound Pressure
A fluctuating pressure superimposed on the static pressure by the presence of sound. In analogy with alternating voltage its magnitude can be expressed in several ways, such as instantaneous sound pressure or peak sound pressure, but the unqualified term means root-mean-square sound pressure. In air, the static pressure is barometric pressure.

Sound Propagation
At distances large compared to the size of the source, sound intensity diminishes according to the inverse square law.This is relatively simple to reliably calculate, provided the source is small and outdoors where no echoes occur. In a reverberant sound field the calculation is more complex.If the noise source is outdoors and its dimensions are sm…

Sound Quality
Pertaining to the quality or other aspects of the machine that might be inferred from the sound it makes.Sound Quality MetricsThere are a number of pro's and con's with the whole subject of metrics. The psychoacoustics of hearing is a very complicated subject based on the fact that the ear and the processing of sounds is a very complicated subject.…

Sound Receiver
One or more observation points at which sound is evaluated or measured. The effect of sound on an individual receiver is usually evaluated by measurements near the ear or close by.

Sound Transmission Class
In acoustics, a single number rating for describing sound transmission loss of a wall or partition.The STC is calculated from the 1/3 octave transmission loss (TL) measurement of the partition over the 1/3 octave centre frequencies from 125Hz to 4000Hz. These 1/3 octave values are compared with a set of reference curves. The curve is chosen as that…

Sound Transmission Coefficient
Of a partition, in a specified frequency band, the fraction of the airborne sound power incident on the partition that is transmitted by the partition and radiated on the other side.

Sound Transmission Loss
Of a partition, in a specified frequency band, ten times the common logarithm of the ratio of the airborne sound power incident on the partition to the sound power transmitted by the partition and radiated on the other side. The quantity so obtained is expressed in decibels, it is 10 times the logarithm to the base 10 of the reciprocal of the sound…

Sound Waves
Sound waves can be thought of like the waves in water. Frequency determines the length of the waves; amplitude or volume determines the height of the waves. At 20Hz and where the speed of sound is 340ms^-1 the wavelength is 17 metres. It should be noted that sound waves are longitudinal waves ie the vibrations of the medium are parallel t…

Soundstage
A listening term that refers to the placement of a stereo image in a fashion that replicates the original performance. A realistic soundstage has proportional width, depth and height.

Source Room
In architectural acoustical measurements, the room that contains the noise source or sources. See also: Sound Transmission Loss.

Space Weather
The changing conditions in interplanetary space caused by fluctuations in the solar wind. See also: Solar Wind.

Spacetime
A combination of time and three-dimensional space that forms a four-dimensional geometry expressing the connections between space and time. See also: Time.

Spall
Small chips or fragments which are sometimes given off by electrodes during the welding operation.

Spanner
A tool used to turn a nut and bolt. Wrench is another name for spanner.Adjustable spannerPhotograph courtesy of Draper.co.ukA crescent spanner or pipe wrench. A tool which has a fixed jaw and a movable jaw which is controlled by a spiral gear. This is useful as the one spanner fits many different size nuts and bolts. The adjustable comes in a varie…

Spark Advance
The number of degrees of crankshaft rotation before TDC (Top Dead Centre) where the spark plug is fired.

Special Constants
1°0.017453292519943 radianslog₁₀(2)0.301029995663981log₁₀(e)0.434294481903252log₁₀(3)0.477121254719662log₁₀(pi)0.497149872694134?0.577215664901532ln(2)0.693147180559945ln(3)1.0986122886681101.2599210498948701.4142135623731001.4422495703074101.6487212707001301.7320508075688801.7724538509055205.885277250018…

Special Products and Factors
(x + y)² = x² + 2xy + y²(x - y)² = x² - 2xy + y²(x + y)³ = x³ + 3x²y + 3xy² + y³(x - y)³ = x³ -3x²y + 3xy² - y³(x + y)⁴ = x⁴ + 4x³y + 6x<sup>…

Special Theory of Relativity
A comprehensive theory of space and time that replaces Newtonian mechanics when velocities get very large. First Postulate of Special RelativityThe laws of physics are the same for all inertial reference systems.Second Postulate of Special RelativityThe speed of light in a vacuum is a constant regardless of the speed of the source or the speed of t…

Specific Airflow Resistance
The product of the airflow resistance of a specimen and its area. This is equivalent to the quotient of the air pressure difference across the specimen divided by the linear velocity, measured outside the specimen, of airflow through the specimen. See also: Airflow Resistance.

Specific Fuel Consumption
The amount of fuel needed to provide a given power for a given period.ExamplesRamjet0.61 kg/kWhTurbo-prop0.49 kg/kWhOtto Cycle0.3 kg/kWhDiesel Cycle0.24 kg/kWhOtto-Compound engine0.23 kg/kWhTurbocharged Diesel0.23 kg/kWhTurbocharged & Intercooled Diesel0.22 kg/kWhDiesel-Compound engine0.21 kg/kWh See also: Fuel Consumption.

Specific Gas Constant
This is the molar gas constant divided by the molecular weight of the gas in question.wherer = specific gas constant [JK-1kg-1]M = molecular weight of gas [kg mol-1</sup>]R = molar gas constant = 8.31441 JK^-1mol^-1

Specific Gravity
The density (mass per unit volume) of any material divided by that of water at a standard temperature, specific gravity of water = 1:00. See also: Density, Hydrometer.

Specific Heat Capacity
The amount of heat required to raise the temperature of 1kg of a substance through 1K.Units of specific heat capacity are Jkg^-1K^-1It is measured by the standard technique of calorimetry.

Spectral Balance
Balance across the entire frequency spectrum of the audio range. See also: Audio Frequency.

Spectrogram
A three-dimensional intensity plot displaying the amplitude of spectral components as a function of both time and frequency. Usually the horizontal and vertical axes correspond to time and frequency, whereas the intensity corresponds to the amplitude.

Spectrometer
An instrument which measure the position of spectral lines. See also: Mass Spectrometer, Mossbauer Spectrometer, Spectroscopy.

Spectrophotometer
An instrument which determines the energy distribution in a spectrum.

Spectroscopy
Study of a radiation spectrum, emitted, absorbed or diffused. See also: Spectrometer.

Spectrum
A spectrum is a definition of the magnitude of the frequency components that constitute a quantity. The spectrum may be either a line spectrum or a continuous spectrum.There are three kinds of spectra that interest astronomers.Continuous SpectraThe surface of a star is heated to such an extent that it glows with a particular colour. Red for cool st…

Spectrum Analyser
An instrument for measuring, and usually recording, the spectrum of a signal. See also: Fast Fourier Transform, Octave, Spectrum.

Specular Reflections
Mirrorlike reflections of sound (angle of incidence equals angle of reflection) from a flat surface. Reflections that do not spread out. See also: Diffuse Reflection, Reflection.

Speculum
A copper-tin alloy with 33 to 45% of tin that has very high optical reflectivity when polished. Used in Gaul and Britain during the period around the time of Caesar's invasion.

Speech Coding
Excellent speech quality implies that coded speech is indistinguishable from the original and withoutperceptible noise. On the other hand, bad (unacceptable) quality implies the presence of extremelyannoying noise and artefacts in the coded speech.Signal-to-Noise RatioThe speech quality may be gauged from the signal-to-noise ratio, SNRwheres(n) = o…

Speech Interference Level
A calculated quantity providing a guide to the interference of a noise with the reception of speech. The speech-interference level is the arithmetic average of the octave band levels of the interfering noise in the most important part of the speech frequency range. The levels in octave bands centred at 500, 1000, and 2000 Hz are commonly averaged t…

Speech Privacy
There are a number of ways of classifying speech privacy.Confidential privacy - meaning of spoken message is unintelligibleto nearby coworkers who can only hear muffled words, and thisdoesn't cause noise distraction from work.Normal privacy - speech volume level isn't distracting to work, andmost sentences are unintelligible.Transitional privacy - …

Speech Transmission Index
A single number that indicates the effect of a transmission system on speech intelligibility. See also: Speech Interference Level.

Speed of Sound
Depends on the elastic and inertial properties of the particular medium. It also depends on the temperature of the medium. In air, the speed of sound at 20°C is 343ms^-1.GasesIn a perfect gaswhere? = ratio of specific heatsP₀ = pressure [Pa]?₀ = density [kgm^-3]T = temperature [K]r = specific gas constant […

Sphere
The surface area and volume of a sphere of radius, rSurface area, AVolume, V

Spherical Aberration
A defect caused by grinding the surface of a lens or mirror to a spherical rather than a parabolic shape. See also: Aberration.

Spherical Triangles
A triangle on the surface of a unit sphere.Sine formulaCosine formulasAnalogue formulaFour-parts formulaArea or Spherical Excess

Spherical Trigonometry
The branch of mathematics dealing with measurements on the sphere. See also: Sphere.

Spherical Wave
Wave in which the wavefronts are concentric spheres. See also: Longitudinal Wave, Sphere, Transverse Wave, Wavefront.

Spheroid
An aggregate of iron or alloy carbides of essentially spherical shape dispersed through-out a matrix offerrite.

Spheroidizing
Heating and cooling to produce a spherodial or globular form of carbide in steel.

Spindle Speed
The rotational speed at which a machine is set. See also: Spindle.

Spirit
An essence or extract that can be prepared from another substance as by distillation. Can mean alcohol. See also: Alcohol.

Spirit Level
A tool for testing if a surface is level (or vertical) using a glass tube containing an air bubble. Invented by Jean Thevenot in 1666.

Split Pin
Photograph courtesy of Draper.co.ukA metal pin with two arms which is passed through a hole and held in place by the springing apart of the arms.

Spontaneous Reaction
A reaction that will proceed without any outside energy. See also: Endothermic, Exothermic.

Spring Constant
The amount of force required to stretch a spring by 1 unit of length. Measured in newtons per meter. See also: Air Spring, Hookes Law, Metre, Newton, Springs.

Spring Dividers
Dividers whose legs are held together at the hinged end by the pressure of a C-shaped spring.