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


Normalized Noise Reduction
Between two rooms, in a specified frequency band, the value that the noise reduction in a given field test would have if the reverberation time in the receiving room were 0.5s. See also: Noise Reduction, Reverberation Time.

Normalizing
Heating a ferrous alloy to a suitable temperature (approximately 38°C) above the transformation range and then cooling in air to a temperature substantially below the transformation range.This heat treat operation is used to erase previous heat treating results in carbon steels to 0.4% carbon, low alloy steels, and to produce a uniform grain struct…

North Pole
That end of the axis of rotation of a celestial body at which, when viewed from above, the body appears to rotate in a counter-clockwise direction.

not equal to
A definite statement that the quantity on the left hand side is not equal to the quantity on the right hand side. See also: Equality, Mathematical Symbol s.

Not Gate
Logic element that acts as an inverter. See also: AND Gate, Nand Gate, Nor Gate, Or Gate, Truth Table.

Nova
A star which suddenly becomes many times brighter than previously, and then gradually fades. See also: Star.

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

Nuclear Equations
These show the changes that take place in the nuclei. They are similar to chemical equations in that reactants are shown to the left of the arrow and products are shown to theright of the arrow.

Nuclear Fusion
The combining of light nuclei to form a heavier nucleus. See also: Fusion.

Nuclear Reaction
A reaction involving the nucleus of an atom that alters the energy, composition or structure of the atom. Two energy releasing nuclear reactions are fission, the splitting of heavy elements and fusion, the combining of light elements to form a heavier element. In nuclear reactions of interest for power production large quantities of energy are rele…

Nucleation
The initial stage in a phase transformation. It is evidenced by the formation of small particles (nuclei) of the new phase, which are capable of growing.

Nucleic Acid
A polymer made of repeating nucleotides. Examples are DNA and RNA. See also: Deoxyribonucleic Acid.

Nucleon
Either a proton or a neutron.

Nucleus
The central part of an atom that contains the protons and neutrons. Plural nuclei. The nuclei of atoms are positively charged and contain by far most of their mass, all but about 0.05% or less. See also: Atom, Neutron, Proton.

Null
A low or minimum point on a graph. A minimum pressure region in a room. See also: Node.

Null Set
The null set is a set that contains no objects. Also known as the empty set.

Number Line
A line on which each point represents a real number.

Numeral
A numeral is just an object or symbol that stands for a number. For example, 5 is the Arabic numeral for five, and V the Roman numeral for five.

Numerator
The quantity or value on the top of a fraction. See also: Denominator, Division, Divisor, Fraction, Proper Fractions.

Nut
A type of hardware fastener with a threaded hole. See also: Bolt, Thread.

Nylon
A synthetic polymer used in the manufacture of fibres. DiscoveredPatented by Wallace Carothers, which he invented in 1934. Marketed by Du Pont in 1939.

Nyquist Frequency
Half the sampling frequency. Any analog frequency component above the Nyquist frequency will, after sampling, be converted (aliased) to a frequency below the Nyquist frequency. See also: Aliasing, Anti-Aliasing Filter.

Nyquist Plot
A plot of real versus imaginary spectral components that is often used in servo analysis. Should not be confused with a polar plot of amplitude and phase.For a single degree of freedom system, the Nyquist plot is a circle.In the Nyquist plot, a resonance shows up as a circle, but there is no indication what its frequency is -- the Nyquist plot is l…

Oak
The strongest and most durable wood that lasts for long periods in either wet or dry conditions.

Objective
The optical element which receives light from the object and forms the first or primary image in telescopes, microscopes and other optical systems.

Oblate Spheroid
An ellipsoid produced by rotating an ellipse through 360° about its minor axis. See also: Ellipse.

Oblique Angle
An angle that is not a right angle.

Oblique Coordinates
A coordinate system in which the axes are not perpendicular. See also: Coordinates.

Oblique Triangle
A triangle that is not a right triangle.

Observation
Observations refer to repeated values of a data variable. The rows of a column represent the observations. See also: Statistic.

Obtuse Angle
An angle larger than 90° but smaller than 180°. See also: Acute Angle, Angles, Obtuse Triangle.

Obtuse Triangle
A triangle that contains an obtuse angle. See also: Angles, Obtuse Angle.

Occulation
Interruption of the light from an object to an observer when a body in interposed.

Octadecagon
An 18 sided polygon. See also: Polygon.

Octagon
A polygon with 8 sides. Each internal angle is 135° and the sum of the internal angles is 1080°. See also: Heptagon, Hexagon, Polygon.

Octahedral Position
The void space among closed-packed, hard sphere atoms or ions for which there are six nearest neighbours. An octahedron (double pyramid) is circumscribed by lines constructed from centres of adjacent spheres.

Octahedron
A polyhedron with 8 faces. See also: Polyhedral.

Octal
A number system using the base-8, i.e., each digit can be any of 8 values, represented by the digits 0-7. Each octal digit can also be represented by a three-bit binary number. See also: Binary Notation.

Octane
Flammable liquid compounds found in petroleum and natural gas. There are 18 different octanes- they have different structural formulas but share the molecular formula C8H18. Octane is used as a fuel and as a raw material for building more complex organic molecules. It is the eighth member of the alkane series. Symbol C8
Octane Number
A rating of the 'knock' characteristics of motor fuels. The octane number is equal to the numerical value of the percentage by volume of iso-octane, C8H18, in a mixture of iso-octane and heptane, C7H16, having the same knock characteristics as the fuel being tested.

Octant
Any one of the 8 portions of space determined by the 3 coordinate planes. See also: Coordinates.

Octave
Two frequencies are an octave apart if the ratio of the higher frequency to the lower frequency is two.Band NumberNominal Centre Frequency HzExact Centre Frequency HzPassband Hz322.001.41 - 2.82643.982.82 - 5.62987.945.62 - 11.2121615.8511.2 - 22.41531.531.6222.4 - 44.7186363.1044.7 - 89.121125125.8989.1 - 17824250251.19178 - 35527500501.19355 - 70…

Octet
A set of eight valence electrons. See also: Valence Electrons.

Octet Rule
A guideline for building Lewis structures that states that atoms tend to gain, lose, or share valence electrons with other atoms in a molecule until they hold or share eight valence electrons. The octet rule almost always holds for carbon, nitrogen, oxygen, and fluorine; it is regularly violated for other elements.

Octillion
A number equal to 1027. See also: Nonillion, Septillion.

Ocular
Pertaining to or in relation with the eye. See also: Eye, Oculogyric.

Oculogyric
Referring to movements of the eyes. See also: Eye, Ocular.

Odd Function
A function f(x) is called an odd function if f(x)=-f(-x) for all x.

Odd Number
An integer that is not divisible by 2. See also: Even Number.

Oersted
The unit of magnetizing force representing the magnetic field intensity at a distance of 1 centimeter in air or vacuum from the unit magnetic pole.

of the order of
Used when estimating a quantity and means that it is roughly equal to. See also: Equality, Mathematical Symbol s.

Off Centre
Not centred; offset, eccentric, or inaccurate. See also: Eccentricity.

Offset Binary Coding
For bipolar signals, offset binary is a digital coding scheme in which the most negative value is represented by all zeros (00000000) and the most positive value is represented by all ones (11111111). See also: Binary Coded Decimal.

Offset Error
If you get a reading other than zero for a zero condition then you have an offset error, every reading will be inaccurate by this amount.

Ohm
Defined as the resistance of a conductor through which a current of one ampereis flowing when the potential difference across it is one volt.Ohm's law:whereV = potential difference across RI = current through R [A]R = resistance [ohm]

Ohmmeter
Device used to measure electrical resistance. See also: Ohm, Resistance.

Oil
An oil is any substance that is in a viscous liquid state at ambient temperatures or slightly warmer, and is both hydrophobic and lipophilic. See also: Barrel, Paraffin Oil, Paraffin Wax, Wax.

Oil Hardening
A process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and quenching in oil. See also: Hardening.

Oil Mist
A means of lubricating by injecting oil into an air stream, producing a finely atomized spray which suites high speed bearing use. Often found on high speed spindle assemblies.

Oil Whirl-Whip
An unstable free vibration whereby a fluid-film bearing has insufficient unit loading. Under this condition, the shaft centerline dynamic motion is usually circular in the direction of rotation. Oil whirl occurs at the oil flow velocity within the bearing, usually 40 to 49% of shaft speed. Oil whip occurs when the whirl frequency coincide with (and…

Oilstones
Moulded abrasives in various shapes used to hand-sharpen cutting tools.

Oleoresin
A natural plant product that contains oil and resins, an example is turpentine. See also: Turpentine.

Olive Oil
Obtained from the fruit of Olea Europaea.

Omni
Prefix meaning all.

On This Day
Events in science and engineering that happened on a particular day.January11894 The Manchester Ship Canal was opened to traffic.

Opacity
The condition of being non-transparent.

Open Circuit Voltage
The voltage between the terminals of a battery or power source when no current is flowing. See also: Battery, Voltage.

Open Interval
An interval that does not include its two endpoints.

Open Loop
A system operating without feedback. See also: Closed Loop, Open Loop Gain.

Open Loop Gain
Gain of an amplifier when no feedback is present. See also: Amplification, Open Loop.

OpenGL
A graphics standard providing advanced rendering capabilities. See also: Programming Languages.

Operational Amplifier
One of the basic building blocks of analogue circuits - a high gain stable amplifier with a voltage gain of 100 to 100,000 or more. Operational amplifiers are widely used for signal processing and computational work.Non-Inverting AmplifierInverting AmplifierDifferentiating AmplifierIntegrating Amplifier

Opposition
The point at which a planet that is further away from the Sun than the Earth, lines up with the Sun and Earth. Opposition is a good time for observation because the planet is near its closest point to Earth.

Optic Axis
A line passing through the center of a curved mirror and the center of the sphere from which the mirror is made. See also: Focal Plane.

Optical Axis
A line passing through the centres of curvature of a lens or series of lenses in an optical system.

Optical Cavity
Space between the laser mirrors where lasing action occurs.A periodic structure of thin films comprised of two quarter-wave stack reflectors separated by a dielectric spacer. Cavities are the building blocks of bandpass filters. See also: Laser.

Optical Flat
A piece of glass with one or both surfaces polished flat. Also known as a test plate, test glass or reference flat.

Optical Interference
The interaction of two light waves on the total intensity of light. See also: Interference.

Optical Pumping
The excitation of the lasing medium by the application of light rather than electrical discharge. See also: Laser.

Optical Pyrometer
An instrument for measuring the temperature of heated material by comparing the intensity oflight emitted with a known intensity of an incandescent lamp filament.

Optics Calculations
Pockels CellA Pockels Cell is a device which contains a photo refractive crystal. When a voltage is applied to this crystal it can change the polarisation or phase of the light beam.Snells LawSnells law defines the angle of refraction of a light beam when it passes from one medium to another.

Optics Conversions
CandelaThe SI unit of luminous intensity.cdAn abbreviation of candela, the SI unit of luminous intensity.

Or Gate
Logic gate whose output willbe a 1 if any of it imputs is at 1.The truth table for the OR Gate is:An OR Gate made from NAND gates is shown in the following diagram:

Orbit
The path of a body in space, generally under the influence of gravity. See also: Decaying Orbit, Elliptical Orbit, Keplers Laws, Periapsis.

Orbit Acquisition
Reception of the telemetry containing the information about the orbital parameters of the spacecraft.

Orbital
A wavefunction that describes what an electron with a given energy is doing inside an atom or molecule. See also: Atom, Degenerate Orbital, Molecule.

Order
Harmonic of the rotational speed of rotating machinery. As an example, in the case of the shaft rotating at 6,000 rpm, the first order component occurs at a frequency of 100 Hz (6,000/60), whereas the third order component would occur at a frequency of 300 Hz.wheref = frequency [Hz]n = orderN = rotational speed [rpm]

Order Tracking
Tracking the evolution of a specific order as rpm changes. See also: Order.

Ordered System
A system with an arrangement belonging to a group with the smallest number (possibly one) of equivalent arrangements.

Ordinate
The y-coordinate of a point in the plane. See also: Abscissa.

Ore
A natural mineral mined and treated for extraction of its components. See also: Assay.

Organic Chemistry
The branch of chemistry that deals with the properties and reactions of carbon-based compounds. See also: Carbon, Organic Compound.

Organic Compound
Compounds that contain carbon chemically bound to hydrogen. They often contain other elements (particularly O, N, halogens, or S). Organic compounds were once thought to be produced only by living things. We now know that any organic compound can be synthesized in the laboratory. See also: Carbon, Hydrogen, Organic Chemistry.

Orichalchum
A Roman brass that consisted of 80% copper and 20% zinc.

Origin
In Cartesian coordinates, it is the point (0, 0) and located at the intersection of the x- and y-axes.

Original Equipment Manufacturer
Products supplied by the company which first created the product.

Ormolu
An alloy of copper, zinc and tin in various proportions with at least 50% copper.

Ornithopter
A flying machine that is supposed to support itself in the air through the use of flapping wings.

Orthogonal
Mutually perpendicular. See also: Perpendicular.

Oscillation
Oscillation is the variation, usually with time, of the magnitude of a quantity with respect to a specified reference when the magnitude is alternately greater and smaller than the reference.