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

Sequential Access Memory
A memory in which access of the registers must be in sequential order. e.g. Magnetic tape.

Serial Communications
Transmission of binary data from one device to another one bit at a time. See also: Interface, Parallel Transfer.

Series
The sum of a finite or infinite sequence. See also: Binomial Theorem, Series Expansions.

Series Expansions
for all x-1 < x = 1-1 < A < 1for all Afor all A-p/2 < A < p/2-p/2 < A < p/2-p < A < p-p < A < p-1 < A < 1-1 = A = 1A > 1A < -1for all Afor all A-p/2 < A < p/2

Set Point
Value of a controlled variable, departure from which causes a controller to operate to reduce the error and restore the intended steady state.

Set Screw
A plain screw used principally for locking adjustable parts in position.

Settling Time
When a change in a signal occurs, this is the time taken for it to settle to its new value. See also: Signals.

Sexagesimal
In the sexagesimal system calculations are done in the base 60 as used by the Ancient Babylonians. The remnants of sexagesimal notation remain in our method of telling time and measuring angles. See also: Plane Angle, Time.

Sextet
A unit of quantity equal to 6.

Sextillion
A number equal to 10²¹. See also: Quintillion, Septillion.

Sextuple
A group of six items. See also: Triple.

Seyfert Galaxy
Type of galaxy with a point-like nucleus and very faint spiral arms, first described in 1943 by American astrophysicist Carl Seyfert. Such galaxies have since been shown to belong to a wider class of objects known as active galactic nuclei.

Sferics
The study of atmospherics, especially from a meteorological point of view. This involves techniques of locating and tracking atmospherics sources and evaluating received signals (waveform, frequency, etc.) in terms of source. See also: Sferics Fix.

Sferics Fix
The estimated location of a source of atmospherics, presumably a lightning discharge. See also: Sferics.

Shadow
Darkness in a region, caused by an obstruction between the source of light and the region.By extension, the term is applied to a similar condition when any form of radiant energy is cut off by an obstruction, as a radar shadow. The darkest part of a shadow in which light is completely cut off is called the umbra; a lighter part surrounding the umbr…

Shadowgraph
A picture or image in which steep density gradients in the flow about a body are made visible, the body itself being presented in silhouette.The optical method or technique by which this is done. A shadowgraph differs from a schlieren photograph in that the schlieren method depends on the first derivative of the refractive index while the shadow me…

Shake
Shake can be described as unpleasant vibration perceived in the vehicle. A variety of mechanisms can cause shake depending on the degree and type of interaction between the major vehicle systems e.g., engine, suspension and body etc. Common examples of shake are: Idle shake which manifests itself when the vehicle is stationary with the engine is id…

Shake Table Test
A laboratory test for vibration tolerance, in which the device to be tested is placed on a vibrator. See also: Shaker.

Shaker
An electromagnetic device capable of imparting known vibratory acceleration to a given object. See also: Shake Table Test.

Shank
That part of a tool or similar object which connects the principal operating part to the handle, socket, or chuck by which it is held or moved.That portion of a bolt between the head and the threaded portion.

Shapiro-Wilks Test
A test to determine whether or not a sample comes from a normal distribution, conducted by regressing the quantiles of the observed data against that of the best-fitting normal distribution. See also: Sample.

Shear Mode
Mode of vibration in which the cross sections of a structure undergo translation with very little rotation. Usually found in buildings where the mass is concentrated at various horizontal levels or tapered tower structures where the taper restricts rotation.

Shear Modulus
The shear modulus is the initial, linear elastic slope of the stress-strain curve in shear. The shear modulus is related to the Young's modulus and Poisson's ratio for isotropic materials:whereG = shear modulus [Nm^-2]E = Young's modulus [Nm^-2]? = Poissons ratioThe shear modulus is related to the bulk modulus and Poisson's rati…

Shear Strain
Strain measuring the intensity of racking in the material. Shear strain is measured as the change in angle of the corners of a small square of material.

Shear Stress
Stress in the cross-sectional plane of a material that is in the same plane as the shearing force acting on it. See also: Bending Stress, Compressive Stress, Stress, Tensile Stress.

Shear Wave
The axis of vibration is perpendicular to the direction of propagation of the wave. With this, the bonding between the particles within the solid experiences shearing forces.

Shed
A unit of nuclear cross-section.ttle='Area';xiunt='m²';yiunt='shed';mconv=1e-52;cconv=0.0; See also: Barn.

Sheet Steel
Either hot or cold rolled sheets produced on continuous sheet mill where the minimum width produced is 24 inches. Sheet coils when slit to narrower widths is called slit sheet. See also: Mild Steel, Steel.

Shell
A surface made of thin material.

Shellac
A coating made from purified lac dissolved in alcohol, often bleached white.

Shells
Where the electrons generally stay. There are 4 types of electron shells: s, p, d and f shells. See also: Atom, Electron.

Shim
A thin sheet of metal or other material which is inserted between two machine parts to obtain their correct relative location.

Shock Wave
The characteristic cone-shaped wave front that is produced wheneveran object travels faster than the speed of the waves in the surrounding medium.Mach wedgeThe wave front semi-angle for a wake generated by supersonic motion of a body in anon-dispersive medium.Kelvin wedgeFor waves in the wake of a boat (gravity waves). In this case the wedge semi-a…

Short Hundredweight
An imperial unit of weight, equal to 100lbs. Note different to hundredweight.Abbreviated sh cwtConversions1 short hundredweight=100 pounds (lb)1 short hundredweight=45.3592 kg1 hundredweight (cwt)=50.8 kg1 hundredweight (cwt)=112 pounds (lb)ttle='Mass';xiunt='kg';yiunt='short hundredweight';mconv=45.3592;cconv=0.0; See also: Hundredweight, Mass, Po…

Short-Circuit
An un-intended path that conducts electricity. Also called a 'bridge' or 'short' such as when solder from two tracks touch on a PC board.

Shot Blasting
Cleaning surface of metal by air blast, using metal shot as an abrasive. See also: Sandblasting.

Shudder
A term which is used to describe the vibration felt on initial movement in any or combination of the driving modes such as drive-away (flat), hill start both in forward and reverse directions. Mechanism of shudder is known to be strong dynamic interaction between the engine modes and the body structure. See also: Shunt.

Shunt
This generally means parallel connection.

Shutter
A device for controlling the amount of time a light-sensitive medium is exposed to light.

SI Units
The international system of units known as the SI units is based on the seven basic units: Mass, Length, Time, Electric current, Temperature, Amount of substance and Luminous intensity.Basic UnitsThe basic seven quantities from which other units are derived are tabulated below:

Sibilance
A hissing sound produced when pronouncing S and Z.

Side Branch Orifice
The side branch orifice is an acoustic filter element and behaves as a high pass filter.The transmission loss of a side branch orifice is:wherea = radius of main duct [m]a_b = radius of side branch [m]L = length of side branch [m]L' = effective length of side branch, taking into account the end correction [m]if the hole is just a hole in …

Side Cutters
A tool like a pair of pliers except the end opposite the handles have sharp edges used to cut wire, etc.

siemens
The SI unit of electrical conductance. Conductance is the reciprocal of resistance.A conductor has a conductance of one siemens if it carries one ampere of current per volt of potential. See also: Admittance, Conductance, Resistance.

Sieve Of Eratosthenes
The algorithm that determines whether a number is prime. To determine whether n is prime, n is divided by all the primes less than , if none are factors then n is prime. There are more sophisticated sieves for prime numbers.This method was developed by Eratosthenes around 230BC.

Sievert
This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of millionths of a sievert, or micro-sievert. To determine equivalent dose, you multiply absorbed dose (Gray) by …

Sign
The sympol that states whether a number is positive (+) or negative (-). If a sign is not placed immediately before a number, it is taken as positive.

Signal Ground
The common return or reference point for analog signals.

Signal Processing
AutocorrelationThe autocorrelation function gives a measure of the extent to which a signal correlates with a displaced version of itself, as a function of the displacement.Bandpass FilterBandstop FilterBandwidth-Time ProductThe bandwidth-time product is used in calculating the confidence limit of a measurement. Confidence limits describe the uncer…

Signal Processing Books
Psychoacoustics By Eberhard Zwicker, H. Fastl, Published By: Springer-Verlag Berlin and Heidelberg GmbH & Co. KG.Handbook of Modern Sensors By Jacob Fraden, Published By: Springer-Verlag Berlin and Heidelberg GmbH & Co. KG.Fourier Transform and Its Applications By Ronald Bracewell, Published By: McGraw-Hill Book Company Ltd.Fast Fourier Transform a…

Signal Processing Calculations
Bandwidth Time ProductUsed in calculating the confidence limit of a measurement.Circular FrequencyThe frequency of a steady recurring phenomenum in radians per second.

Signal to Noise Ratio
The ratio between a recorded signal and spurious background noise. Background noise is most commonly present due to wires and instrumentation reacting to electro-magnetic emissions from surrounding electrical equipment e.g., are welders, vehicle ignition circuits, machine tools. The signal-to-noise ratio is the ratio between the coherent and the no…

Signed Binary Coding
A coding scheme in which the MSB (Most Significant Bit) represents the sign (positive or negative) of a binary number. In this scheme, -2 is represented by 10000010 and 2 is represented by 00000010. See also: Binary Coded Decimal.

Signs and Symbol s
+addition, plus, positive-subtraction, minus, negativea * ba x baba·b

Silencer
An acoustic filter element used to reduce sound pressure levels inside a duct. See also: Acoustic Filter Elements, Exhaust Tailpipe.

Silica Gel
Precipitated silica acid in the form of lustrous granules, especially prepared for absorption of various vapours. Mildly toxic.

Silicon
Generally present as a silicate, these being found in many rocks, clays and soils. Silicon is obtained by reducing silica (sand, SiO2 ), with carbon. Further purification of the element for applications requiring high purity material (e.g. semi conductor devices) is achieved by zone refining, the resulting purity being better than 1:10⁹.…

Silicon Carbide
Used extensively as a grinding compound and in abrasive wheels. Symbol SiC

Silicon Iron
Adding silicon to low-carbon iron increases both hardness and electrical resistivity.

Silk
Protein based material obtained from cocoons of the silkworm.

Silver
Photograph courtesy of MineraliteA pure white metallic element. The best electrical conductor and used in photographic emulsions. Argentum is Latin for silver, hence the symbol Ag. Symbol Ag Also known as ArgentumDiscoveredSilver was known to ancient civilisations.

Silver Bromide
Pale yellow insoluble salt used in photography. Symbol AgBr

Silver Iodide
Yellow crystalline solid. Symbol AgI

Silver Nitrate
A white soluble crystalline salt used in marking inks, medicine and chemical analysis. Symbol AgNO₃ Also known as Crystals of Silver, Lunar Crystals

Silver Sand
A sand with a very low iron content, and is much favoured in the manufacture of high-quality optical glass. The silver colour is a result of it being almost pure silica and there being virtually no contamination with other minerals.

Silver Sulphide
Black or grey-black crystalline solid. The most important ore of silver, known as Argentite. Symbol Ag₂S

Simple Cubic
Of all the elements only polonium crystallizes to a simple cubic structure over a limited temperature range.Volume of conventional cella³Lattice points per cell1Volume of primitive cella³Lattice points per unit volume1/a³Number of nearest neighbours6Nearest neighbour distanceaNumber of second neighbours12Second neig…

Simple Harmonic Motion
A term describing the motion which occurs when a vibrating structure is displaced and experiences a restoring force proportional to its displacement e.g. a pendulum. In the absence external forces and damping, the variation of displacement with time is sinusoidal.The equations of motion are:

Simply Supported
A term used to describe the constraints imposed on a beam, plate or more complex structure by its foundations. A simply supported beam cannot have any translational displacements at its support points, but no restriction is placed on rotations at these points.

Sinc Function
The function sin of x divided by x.

Sine
function init(){}Note: In this series A is in radians. 7 terms in the series are required to get ananswer accurate to 8 decimal places for . Ten terms in the seriesare required to get an answer accurate to 15 decimal places for the same range of A.There are a number of ways denoting the inverse sine function e.g. sin^-1(A) orarcsin(A) or …

Single Event Noise Exposure Level
The noise exposure level of a single event measured over the time between the initial and final points when the noise level exceeds a predetermined threshold. See also: A Weighting, Community Noise Criteria, Decibel.

Single-Ended Input
An analogue input measured with respect to a common ground.

Sintering
Heating a mass of fine particles for a prolonged time below the melting point, usually to causeagglomeration.

Skew
An expression of the so-called 'third moment'. A tendency for a distribution to lean to the right (or left, when negative), showing a fast dip from the central mean but having an extended tail. The skewness of data is usually measured through a coefficient of skewness which is zero for symmetric distributions such as the normal or uniform distribut…

Skew Lines
Two lines are skew if they are not contained in the same plane.

Skewness
Skewness defines the degree of asymmetry of the distribution around its central value.Skewness is defined aswheres = standard deviation of xN = total number of values of xSkewness is a unitless parameter known as the third order moment of a distribution. Even if the skewness is other than zero it does not necessarily mean that the data is in fact s…

Skin Effect
In the case of high frequency signals, electrons are only conducted on the outer surface, or skin, of a conductor. This phenomenon is known as the skin effect. See also: Conductor.

Skylight
An opening in a roof to admit light. See also: Window.

Slap Back
A discrete acoustic reflection from a nearby surface. See also: Reflection.

Slate
Fine grained metamorphic rock with strong cleavage planes.

Sleeve Valve Engine
The sleeve valve engine was developed by Ricardo prior to World War II and were used during the war for high output spark ignition aero engines.In the sleeve valve engine the conventional valve train was replaced by a ported cylinder liner that was then rotated to align with ports in the block so as to achieve the timing for the intake and exhaust …

Slew Rate
The term used to define the maximum rate of change of an amplifier's output voltage with respect to its input voltage. In essence, slew rate is a measure of an amplifier's ability to follow its input signal.

Slide Rule
A calculating device consisting of two sliding logarithmic scales.

Sliding Friction
Or Dynamic Friction. The frictional force between two surfaces in relative motion. ExamplesMaterialStatic frictionSliding frictionBrakes~0.30.3 - 0.7Clutches0.3 - 0.40.3 - 0.7Earth - Earth0.25 - 1.0 Lignum vitae - Steel 0.1Metal - Metal (dry)0.15 - 0.60.1 - 0.5Nylon - Steel 0.3 - 0.5Perspex - Steel~0.5 PTFE - Steel 0.05 - 0.2Rubber - Steel0.6 - 0.9…

Slope
The measure of the tilt of a line, the rise over run or how much the line moves up for every movement to the right.For a straight line in the plane, the slope is the tangent of the angle it forms with the positive X axis. For a curve the slope is the slope of the tangent line. If the slope is constant a line is straight.

Slug
An old unit of mass. 1 slug = 14.5939 kgConversions1 slug=14.5939 kg12 slug=1 slinch1 slinch=175.1268 kgttle='Mass';xiunt='kg';yiunt='slug';mconv=14.5939;cconv=0.0; See also: Mass.

Slush Hydrogen
A mixture of liquid and frozen hydrogen that is denser than liquid hydrogen. See also: Hydrogen.

Slush Oxygen
A mixture of liquid and frozen oxygen that is denser than liquid oxygen. See also: Oxygen.

Small Circle
The circle formed by the intersection of a sphere and a plane that doesn't contain the centre of the sphere. See also: Circle, Great Circle, Sphere.

Smell
Human can detect around 10000 different smells.Range for smell:Human ~ 1mDog ~ 100 mElephant ~ 3 kmMoth ~ 5 km

Smooth Plane
A general purpose wood plane, often used after the jack plane for final polishing.

Smoothing
Smoothing techniques are used to reduce irregularities in time series data. They provide a clearer view of the true underlying behaviour of the series.

Snells Law
Named after Willebrord Snell (1591 - 1626).Snells law defines the angle of refraction of a light beam when it passes from one medium to another. If the second refractive index (n_b) is higher than the first (n_a) then the beam bends towards the normal, otherwise it bends away from it.function init(){}In the curved atmosphere, Sn…

Sociocusis
Loss of hearing caused by noise exposures that are part of the social environment, exclusive of occupational-noise exposure, physiological changes with age, and disease.

Socrates (470-399 B.C.)
Greek philosopher; emphasized the study of human nature in relationship to society; influence the growth of science through standards for clear definitions and classifications, for logic and order, and for prudent skepticism. See also: Plato.

Sodium
Sodium is a soft, silvery coloured metal which, like other members of the alkali group of metals, is extremely reactive. As for the other members of the group, it can be prepared by electrolysis of the fused halide or hydroxide. Along with potassium, it is one of the more common alkali metals, there being 28300 ppm in the earth`s crust, primarily a…

Sodium Chloride
Commonly known as table salt. Symbol NaCl

Sodium Hydride
White to silver coloured solid. Symbol NaH

Sodium Hydroxide
A caustic metallic base used in the manufacture of pulp, textiles, drinking water, soaps and detergents. Symbol NaOH Also known as Caustic Soda, Lye