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 The information may have been taken offline because it is outdated.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


Perpendicular
At right angles to. A line at right angles to another line or to a plane. See also: Orthogonal.

Pesticide
A chemical or biological agent that kills pests. A pest can be an animal, fungi, insect, plant or any unwanted species.

Petrol
A volatile, flammable liquid mixture of hydrocarbons, obtained from petroleum and used as a fuel for internal-combustion engines.

Petrol Engine
An internal-combustion engine in which the fuel is petrol that is drawn or injected into the cylinder along with air and ignited with an electric spark. See also: Engine, Four-Stroke Engine, Internal Combustion Engine, Petrol, Two-Stroke Engine.

Petroleum
An oily, thick, flammable, usually dark coloured liquid that is a form of bitumen or a mixture of various hydrocarbons, occurring naturally in various parts of the world and often separated by distillation into petrol, naphtha, benzene, kerosene and paraffin.

Pewter
Tin-base white metal containing antimony and copper; 1 to 8% Sb and 0.25 to 3% Cu. Originally pewter would have contained 15% lead, now most pewters are lead-free.

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

pH
Measures the acidity of a solution. It is the negative logarithm of the concentrationof the hydrogen ions in a substance. If the hydrogen ion concentration of asolution is 1x10-n mol litre-1, then the pH of the solution is n.The lower the pH, the more acid the solution. A pH of 7 corresponds to a neutral solution.pH0 hydrochlo…

Phase
Phase is the measure of progression of a periodic wave. Phase identifies the position at any instant which a periodic wave occupies in its cycle. It can also be discribed as the time relationship between two signals.andA portion of a material system whose properties and composition are homogeneous and which is physically distinct from other parts o…

Phase Change
The change from gas to liquid to solid.solid ? liquid = meltingliquid ? solid = freezingsolid ? gas = subliminggas ? solid = condensingliquid ? gas = evaporatinggas ? liquid = condensing

Phase Diagram
Graphical representation of the temperature and composition limits of phase fields in an alloy or ceramic system; it can be an equilibrium diagram, approximation to an equilibrium diagram, or a representation of metastable conditions or phases. See also: Alloy, Phase, Phase Change, Phase Transformation.

Phase Shift
The time or angular difference between two signals.

Phase Transformation
Changes that can occur within a given material system, how one or more phases in an alloy change into a new phase or mixture of phases. Transformation occurs because the initial state of the alloy is unstable relative to the final state. At constant temperature and pressure the relative stability of a system is determined by its Gibbs free energy. …

Phase Velocity
The velocity with which planes of equal phase, crests or troughs, progress through themedium.wherevp = phase velocity [ms-1]? = angular frequency [rads-1]k = wavenumber [m-1]f = frequency [Hz]? = wavelength [m]

Phenol
Used as a strong disinfectant. Symbol C6H5OH Also known as Carbolic acid

Phenolic Resin
A condensation reaction polymer. A key characteristic of phenolic resin is the ability to withstand high temperature, along with mechanical load with minimal deformation or creep. In other words, cured phenolic resin provides the product rigidity necessary to maintain structural integrity and dimensional stability even under severe conditions.

Phlogiston
A hypothetical elastic fluid which was seen as a metalizing and combustible principle. Metals were seen as the result of combining calces with phlogiston, smelting expelled the phlogiston. See also: Caloric, Ether.

Phon
The unit of measurement for loudnes level. See also: Equal Loudness Contour, Loudness, Sone, Zwicker Loudness.

Phoneme
The basic classes of sounds used to form the words of a language. Examples in English are 'k', 'oo', and 'th'. They are often represented by single written letters.

Phonon
A single quantum of vibrational or elastic energy.

Phosphorescence
The property of a material whereby it continues to emit visible light after it has been illuminated by ultraviolet light.

Phosphorus
A non-metallic element. Applied to the inner face of a cathode ray tube that when bombarded with electrons will emit light of various colours. Symbol PDiscoveredIn 1667 Hennig Brand accidentally discovers the element phosphorus during an experiment with urine, but he keeps it secret and Robert Boyle later discovers and describes the element.

Photochemistry
The study of the effects of light on chemical reactions.

Photoelectric Effect
The ejection of electrons from metallic surfaces by illuminating light. The effect was explained by Albert Einstein and demonstrates that light seems to be made up of particles, or photons. Light can excite electrons (photoelectrons in this context) to be ejected from a metal. Light with a frequency below a certain threshold, at any intensity, will…

Photoluminescence
Luminescence caused by absorption of optical radiation.

Photometer
An instrument which measures luminous intensity.

Photons
Massless packet of energy, which behaves like both a wave and a particle. In the duality of mass/energy this is considered a “particle� of radiation.Einstein`s generalization of the concept of the quantum introduced by Max Planck. See also: Eddington Limit, Stimulated Emission, Wave Particle Duality.

Photosphere
The layer of the Sun from which all visible light reaches us. The Sun is too hot to have a solid surface and the photosphere consists of a plasma at about 5500 degrees centigrade. See also: Sun.

Photosynthesis
Process by which green plants convert light to energy by transforming carbon dioxide and water into carbohydrates.

Photovoltaic Cell
A unit which generates a voltage related to the light intensity impinging on it. See also: Electromotive Force, Solar Cell.

Physical Constants
Avogadro's numberN6.022045x1023 mol-1Bohr Magnetonß9.27x10-24 Am2Boltzmann's constantk1.38062x10-23JK-1Stefan-Boltzmann Constants5.67x10-8 Wm-2K-4Impedance of Free SpaceZ0 376.730313461 OhmElectron volteV1.6021892x10-19 JElectron…

Physics Books
Vibrations and Waves By A.P. French, Published By: Nelson Thornes.University Physics with Modern Physics By Hugh D. Young, Roger A. Freedman, T.R. Sandin, A. Lewis Ford, Published By: Addison Wesley.Transistors: from Crystals to Integrated Circuits By M. Levinshtein, G. Simin, Published By: World Scientific Publishing.The Works of Archimedes By edi…

Physics Calculations
AccelerationThe change in velocity divided by the time it takes to make the change.Angular FrequencyThe frequency of a steady recurring phenomenum in radians per second.Angular MomentumA vector quantity giving the rotational momentum.Angular VelocityThe rate of change of angle turned in radians.AveragingIn any process it is often necessary to avera…

Physics Conversions
AbampereThe CGS electromagnetic unit of current equal to 10 Amperes.AbcoulombThe CGS unit of electric charge equal to 10 Coulomb.AbhenryThe CGS unit of inductance equal to 1.0x10-9Henry.AbmhoThe CGS unit that is the reciprocal of the ohm equal to 1.0x109Siemens.AbohmThe CGS unit of electrical resistance equal to 1.0x10-9<…

Pi
Pi is the number of times the diameter of a circle can be divided into the circumference.p = 3.141592653589793238462643 .......ttle='Pi';consttxt='pi';constval=3.141592653589793238462643;constunt='';given by:

Pi Bonds
A type of covalent bond in which the electron density is concentrated around the line bonding the atoms formed from the overlap of two parallel p-orbitals. See also: Covalent Bond, Sigma Bonds.

Piano Wire
High quality steel wire used for making springs.

Pica
An old print size that is approximately the same as 12 point. See also: Point Type Face.

Pickling
The chemical removal of surface oxides and other contaminants from a material by immersion in an aqueous acid solution. Sulphuric and hydrochloric acids are common pickling solutions.

picometre
A distance equal to 10-12 metres. See also: Bicron, Metre.

picosecond
A period of time equal to 10-12 seconds. See also: Second.

Picture
Visual representation of something. See also: Pixel.

Pie Chart
A strong representation of data with the size of the slice representing the fraction of the total.

Piezoelectric
Any material which provides a conversion between mechanical and electrical energy.Piezo is a Greek term which means “to squeeze�.For a piezoelectric crystal, if mechanical stresses are applied on two opposite faces, electrical charges appear on some other pair of faces. Conversely, when an electrical voltage is applied across a piezoelectric materi…

Pilot Hole
A starting hole for large drills to serve as a guide, reduce the resistance, and aid in maintaining the accuracy of the larger hole. Also known as a Lead Hole.

Pin Connection
In two dimensions, a pin connection restrains two translation degrees of freedom but does not restrain rotation. Since the rotation degree of freedom is unrestrained at a pin connection, it transfers no moment. See also: Roller Support.

Pine
Easily worked and used where moderate strength and durability are required. Turpentine is obtained from the pine.

Pinhole
A small, sharp-edge hole without a lens which can function as an aperture or eye lens.

Pink Noise
A random-like signal in which power is proportional to the inverse of frequency. At twice the frequency, we would expect half the power, which is a 3dB decrease. This is a frequency-response slope of -3dB / octave, or -10dB/decade. As opposed to white noise, which has the same level at all frequencies, pink noise has more low-frequency or 'red' com…

Pint
The pint is a derived unit in the British system of units.Conversions1 pint=20 fluid ounces1 gallon (UK)=8 pints1 quart=2 pints4 quarts=1 gallonttle='Volume';xiunt='pint';yiunt='litre';mconv=1.75975;cconv=0.0; See also: Volume.

Pion
The least massive meson. The pion has three charge states: + 1, 0, and - 1. The particle that mediates the strong force. See also: Meson.

Piston
A cylindrical part which reciprocates in the cylinder bore of an engine and transmits the force of the gas pressure through the connecting rod to the crankshaft.Oil-Control RingsThe piston ring, usually located at the lower part of the piston, that prevents an excessive amount of lubricating oil from being drawn up into the combustion space during …

Pitch
AcousticsThe auditory attribute on the basis of which tones may be ordered on a musical scale. Two aspects of the notion of pitch can be distinguished in music: one related to the frequency (or fundamental frequency) of a sound (measured in Hz) which is called pitch height, and the other related to its place in a musical scale which is called pitch…

Pixel
Single picture element of a detection device. See also: Picture.

Planck's Constant
A fundamental physical constant, the elementary quantum of action, It is the ratioof the energy of a photon to its frequency.h = 6.62606877x10-34Jsttle='Plancks Constant';consttxt='h';constval=6.62606877e-34;constunt='Js';alternatively in electron volt secondsh = 4.13566727×10-15 eV s

Plane
A two-dimensional group of points that goes on infinitely in all directions; made up of infinite lines.

Plane Angle
The plane angle between two radii of a circle which cut off on the circumferencean arc equal in length to the radius.Secondary SI UnitThe secondary SI unit for the plane angle is the radian.

Plane Section
The intersection of a figure with a plane. See also: Plane.

Plane Wave
Wave in which the wavefronts are everywhere parallel planes normal to the direction of propagation.The general solution for the acoustic pressure of a plane wave is:the wave propagating in the +x direction is given by the termthe wave propagating in the -x direction is given by the termwherep = acoustic pressure [Pa]A = magnitude of the positive tr…

Plane Wood
A North American wood that resembles beech, durable in water but not in air.

Planet
A spherical ball of rock and/or gas that orbits a star. The Earth is a planet. Our solar system has nine planets. These planets are, in order of increasing average distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. See also: Atmosphere, Pole, Prebiotic, Protoplanetary Disc.

Planetary Nebula
A bright cloud of dust and gas surrounding an old star, namely a red giant. Towards the end of its life the star ejects the dust and gas violently, losing most of its mass and becoming a white dwarf. The nebula disappears after approximately 100 000 years. They are called 'planetary' because originally astronomers thought they looked like planetary…

Plasma
The fourth state of matter (along with the other states of matter: solids, liquids and gases) in which one or more electrons have been stripped from the atoms forming an ion gas. Therefore, capable of conducting electric currents. It is estimated that more than 99% of matter in the universe exists as plasma; examples include stars, nebulae, and int…

Plaster of Paris
Partly dehydrated gypsum. Calcium sulphate monohydrate. Symbol (CaSO4)2 . H2O

Plastic
A solid material in the primary ingredient of which is an organic polymer of high molecular weight. See also: Acetic Anhydride, Bakelite, Polymethyl Methacrylate Resin, Polystyrene, Polytetrafluoroethylene, Polyvinyl Acetate, Thermoplastic.

Plastic Deformation
Deformation that is permanent or nonrecoverable after release of the applied load. See also: Plasticity.

Plasticine
Modelling clay.

Plasticity
The inverse of elasticity. A material that tends to stay in the shape or size to which it is deformed has high plasticity. See also: Elasticity, Plastic Deformation.

Plasticizer
A low molecular weight polymer additive that enhances flexibility and workability and reduces stiffness and brittleness. See also: Polymer.

Plate Techtonics
Motion of the plates that make up the surface of the Earth. See also: Earth, Richter Scale.

Platinum
Platinum is a member of the platinum group metals and is lustrous, malleable and ductile. Of the group of six metals (Pt, Pd, Os, Ir, Rh and Ru), it is the most important. It is unaffected by oxygen and water and is only soluble in aqua regia or fused alkalis. Applications for platinum are many and varied; for example, it is used to make weights an…

Plato (427-347 BC)
A Greek philosopher, pupil of Socrates and Aristotle`s teacher. Dealt with the nature of the universe; developed atomic theory of chemical change; ascribed geometric forms composed of bounding planes to the elements of earth, fire, air and water based upon their physical properties; held that elements could convert into one another through rearrang…

Pliers
A gripping tool with two hinged arms and serrated jaws. The pliers shown on the left are general purpose pliers with serrated jaws for gripping, side cutters closer to the hinge point and on either side of the hinge cutters for heavier gauge wire cutting. Pliers are also available in many other shapes and sizes to suit different jobs.Bent-Nose Plie…

Plus
The symbol: +

Pluto
The outermost planet in our solar system and it's double Charon. Pluto is much smaller than the Moon. Its highly eccentric orbit, with an average radius of 39.4 AU sometimes takes it within the orbit of Neptune. Pluto has a very thin atmosphere consisting mainly of methane and nitrogen. The average surface temperature is 50 K.Click on an item to pa…

Plutonium
A product of the radioactive decay of neptunium. Symbol Pu

Plywood
Thin sheets of wood glued together with the grains running in different directions to improve the strength of the resultant board. In it's simplest form it consists of three layers of wood with the centre layer grain at right angles to the two outer layers. This construction reduces the tendancy to shrink or swell and means that the strength is uni…

PNP Transistor
Type of bipolar transistor using p-type, n-type, n-type semiconductor material. See also: Field Effect Transistor, NPN Transistor, Transistor.

Pockels Cell
A Pockels Cell is a device which contains a photo refractive electro-optic crystal. When a voltage is applied to this crystal it can change the polarisation or phase of the light beam.Depending on the orientation of the crystal either the polarisation can be altered or a phase change can be introduced.Polarisation & Intensity ModulationA Pockel Cel…

pOH
Measures the basicity of a solution. It is the negative logarithm of the concentration of the hydroxide ions. See also: Acid, Base, pH.

Point
A zero-dimensional figure. Usually left undefined, has four main representions - the dot, the node, the location, and the ordered pair of numbers. See also: Dot, Line, Plane.

Point (Type Face)
Unit of measurement for type faces.Conversions1 point=0.351 mm1 point=0.0138 inches1 cicero=12.839 points1 agate=5.5 pointsttle='Type';xiunt='m';yiunt='point';mconv=0.351e-3;cconv=0.0; See also: Pica.

Point Defect
A crystalline defect associated with one or, at most, several atomic sites.

Pointer
A register that holds an address of data rather than the data. See also: Register.

Poise
Named after the physicist Poiseuille this is the CGS derived unit of dynamic viscosity of a fluid.When a force of 1 dyne maintains unit rate of shear of a film of unit thickness betweensurfaces of unit area dyne sec cm-2Conversions1 poise=0.10 kg m-1s-11 poise=0.1 N s m-21 poise=0.0020885 lbf s ft-2<…

Poiseuille`s Equation
The volume flow rate of an incompressible fluid in a round pipe is given by:whereQ = volume flow rate [m3s-1]r = radius of pipe [m]p1-p2 = pressure difference between points 1 and 2 [Nm-2]µ = dynamic viscosity of fluid [Nsm-2]L = distance between points 1 and 2 [m]

Poisson Equation
A fundamental equation of mathematical physics, describing the spatial variation of a potential function for given source terms. It is applicable in a wide range of studies, from electrostatics to ocean modelling.

Poisson's Ratio
Ratio of strain in the lateral direction to strain in the axial direction, when a tensile stress is applied to a material. Its value for many solids, is close to 1/3. For elastomers it is just under 0.5. Click on an item to paste into clipboard or use clipboard symbol at end to clipboard all values Aluminium 0.33 Clip Brass 0.35 Clip Bronze 0.34 Cl…

Polar Coordinates
The position of a point is defined as the distance from the origin, r and an angle relative to the X axis, ?.The transformation from polar to rectangular coordinates is:The transformation from rectangular to polar coordinates is:

Polar Molecules
A molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions. See also: Molecule.

Polarity
The positive or negative direction of an electrical, acoustical or magnetic force. Two identical signals in opposite polarity are 180 degrees apart at all frequencies. Polarity is not frequency dependent.

Polarization
ElectronicFor an atom, the displacement of the center of the negatively charged electron cloud relative to the positive nucleus, which is induced by an electric field.IonicPolarization as a result of the displacement of anions and cations in opposite directions.OrientationPolarization resulting from the alignment (by rotation) of permanent electric…

Polarized
A property of a transverse wave when its vibrations are all in a single plane.

Pole
PhysicsUsually the coldest regions on a planet, being the areas around an axis through the planet perpendicular to the plane of rotation about the Sun.UnitsAn old English unit of length. Also known as a Rod.

Pole Strength
The concept of an isolated magnetic pole (magnetic monopole) has been abandoned. However, it is used as a concept in magnetometry. Pole strength is defined as that which when placed in a unit induction experiences a force of 1 newton. See also: Force.

Polonium
Polonium is a radioactive element. Symbol Po

Polyatomic Ion
An ion formed by the loss or gain of electrons from a molecule or chemical group composed of two or more atoms. See also: Ion.

Polycrystalline
Referring to crystalline materials that are composed of more than one crystal or grain.

Polyethylene
Plastic used heavily in the packaging industry.

Polygon
Regular polygon of n sides, each of length b