Re

Re
A rare element that is a silvery coloured metal which resists corrosion and oxidation but slowly tarnishes in moist air.
Reactance
The opposition to the flow of electricity posed by capacitors and inductors.
Reactance Amplifier
A low-noise amplifier that uses a nonlinear variable reactance as the active element instead of a variable resistance.
Reactance Tube
A tube connected in parallel with the tank circuit of an oscillator.
Reactance Tube Modulator
An FM modulator that uses a reactance tube in parallel with the oscillator tank circuit.
Reactants
Substances initially present in a chemical reaction.
Reaction
A reaction is a force exerted by a support on an object: sometimes called support reaction.
Reaction Mechanism
A list of all elementary reactions that occur in the course of an overall chemical reaction.
Reaction Order
The sum of concentration exponents in the rate law for the reaction.
Reaction Quotient
The product of the concentrations of the products, divided by the product of the concentrations of the reactants, for a chemical reaction which is not necessarily at equilibrium.
Reaction Rate
A reaction rate is the speed at which reactants are converted into products in a chemical reaction.
Reaction Time
The time taken to react to an event.
Reactive Absorber
A sound absorber, such as the Helmholtz resonator which involves the effects of mass and compliance as well as resistance.
Reactive Intermediate
A highly reactive substance that forms and then reacts further during the conversion of reactants to products in a chemical reaction.
Reactive Power
Power that flows back and forth between the inductive windings of the generator and the inductive windings of motors, transformers, which are part of the electrical load.
Reactive Silencer
A silencer that uses reflection effects for its action.
Reactive Sound Field
A sound field in which the particle velocity is 90 out of phase with the pressure.
Reactivity Index
The reactivity index in a given direction at a point is defined as the difference between the sound intensity level and the sound pressure level measured in the given direction at that point.
Reactor
Vessel which contains nuclear or chemical reactions.
Reagent
A substance or mixture that is useful in chemical analysis or synthesis.
Real Axis
The x-axis of an Argand diagram.
Real Image
An image formed by the convergence of light.
Real Modes
In a real mode, all points on the structure reach a maximum or a minimum value at the same time and all pass through equilibrium at the same time.
Real Number
Any of the conventional numbers, including fractions and irrationals.
Real Part
The real number x is called the real part of the complex number x+iy where x and y are real and i=sqrt(-1).
Real Time Monitoring
Observing measured results as they are happening.
Real Variable
A variable whose value ranges over the real numbers.
Really Simple Syndication
Automated system for gathering information, usually news, from multiple sources and bringing it together in one place, usually a website - more commonly known by abbreviation RSS.
Ream
500 sheets of paper.
Rear Wheel Drive
A vehicle designed to have power applied to the rear wheels.
Rearrangement Reaction
A reaction in which a reactant and product are isomers of each other.
Reaumur Temperature Scale
On the Reaumur temperature scale, abbreviated to R, the ice point is 0R and the steam point is 80R.
Rebar Size
Numerical size designations for steel reinforcing bars used to strengthen concrete.
Rebound
The motion of the suspension as the strut is extending.
Receiver
Equipment that converts electromagnetic energy into an electrical signal that can be further processed.
Receiver Antenna
The device used to pick up the RF signal from space.
Receiver Noise Figure
A measure of signal-to-noise ratio degradation as the signal passes through the receiver.
Receiver Sensitivity
The degree to which a receiver can usefully detect a weak signal.
Receiving Room
In architectural acoustical measurements, the room in which the sound transmitted from the source room is measured.
Recency Effect
An increase in correct recall rate for the most recently presented items of a list compared with those presented earlier in the list.
Receptance
Displacement per unit force.
Receptor Site
A molecule or surface in a cell that recognizes and binds to a specific messenger molecule, leading to a biological response.
Rechargeable Battery
A battery in which the chemical reaction system providing the electrical current is easily chemically reversible.
Reciprocal
A number that is made into a fraction.The reciprocal of 2 is 1/2.
Reciprocal Megakelvin
A unit used in colorimetry and photography to measure the wavelength of light, especially for selecting filters to adjust the colour temperature.
Reciprocating
Having a back-and-forth or up-and-down linear motion, such as an engine piston.
Reciprocating Air Compressor
Air compressor in which the compressing element is a piston having a reciprocating motion in a cylinder.
Reciprocity
If in a space filled with air which is partly bounded by finitely extended fixed bodies and is partly unbounded, sound waves being excited at any point A, the resulting velocity-potential at a second point B is the same both in magnitude and phase, as it would have been at A, had B been the source of the sound.
Recombination
The process by which a positive and a negative ion join to form a neutral molecule or other neutral particle, also process by which radicals or dissociations species join to form molecules.
Recombination Era
The time when matter and radiation first separated.
Recruitment
Lists all Recruitment topics in the Encyclopaedia
Recruitment Weblinks
Lists all Recruitment Weblinks in the Encyclopaedia
Recrystallization
The formation of a new set of strain-free grains within a previously cold-worked material; normally an annealing heat treatment is necessary.
Recrystallization Annealing
Annealing cold worked metal to produce a new grain structure without phase change.
Recrystallization Temperature
The approximate minimum temperature at which complete recrystallization of a cold worked metal occurs within a specified time.
Rectangle
A quadrilateral with 4 right angles.
Rectangular Coordinates
Coordinates where the position of a point is described by the distance it is from 2 lines in 2 dimensional space or from 3 planes in 3 dimensional space.
Rectangular Window
An amplitude weighting used to truncate continuous time signals to fit within the length of the DFT window.
Rectifier
A device that passes current in only the forward direction.
Recursion
Given some starting information and a rule for how to use it to get new information, the rule is then repeated using the new information.
Recursive Filter
A filter in which there is no need to store past measurements for the purpose of calculating current estimates.
Recycling
The re-use of material.
Red Giant
An old star that has used up all the hydrogen in its nucleus and uses other elements as fuel to keep shining.
Red Iron Oxide
Old name for Iron III Oxide.
Red Supergiant
A supergiant with spectral type M. These are the largest stars in the universe.
Redox Indicator
An organic molecule that has reduced and oxidized forms with different colours, interconversion of the reduced and oxidized forms of the indicator must be reversible.
Redox Potential
The potential of a redox electrode.
Redox Reaction
A reaction in which one or more electrons are transferred.
Redox Titration
A titration based on a redox reaction.
Redshift
When the light an object emits is displaced toward the red end of the spectrum it is said to be redshifted.
Reduced Instruction Set Computer
A computer architecture that has reduced chip complexity by using simpler processing instructions.
Reducing Agent
A substance that reduce another substance by supplying electrons to it.
Reductant
A substance that reduce another substance by supplying electrons to it.
Reduction
A gain of one or more electrons by an atom, molecule, or ion.
Reduction Half Reaction
That part of a redox reaction that involves gain of electrons.
Reduction of Area
Measure of the ductility of metals obtained in a tensile test.
Reduction Reaction
A reaction in which a substance gains at least one electron.
Reference Electrode
An electrode that has a well known and stable equilibrium electrode potential.
Reference Line
A line to which other parts of the system are measured.
Reference Oil
An oil of known performance characteristics, used as a basis for comparison.
Reference Point
A point to which are other parts of the system are measured.
Reference Sound Source
A calibrated source of sound power with well defined operating characteristics and a predictable performance.
Reference System
A collection of objects not moving relative to each other that can be used to describe the motion of other objects.
Reflect
In a tessellation, reflect means to repeat an image by flipping it across a line so it appears as it would in a mirror.
Reflected Sound
That portion of a sound wave which bounces off a surface and reverses direction.
Reflected Wave
The portion of the wave that has been reflected.
Reflecting Telescope
A type of telescope using a mirror as the objective.
Reflection
Reflection occurs when a wave is incident upon an opaque surface.
Reflection Nebula
A type of nebula that shines by reflected light.
Reflection Phase Grating
A diffuser of sound energy using the principle of the diffraction grating.
Reflex Angle
An angle between 180° and 360°.
Reflex Klystron
A klystron with a reflector electrode in the place of a second resonant cavity used to redirect the velocity-modulated electrons back through the cavity that produced the modulation.
Reflow Soldering
Process of joining metallic surfaces through the mass heating of solder or solder paste to form solder fillets at metallized areas.
Reformate
The output of a fuel reformer.
Reformer
A device that extracts pure hydrogen from hydrocarbons.
Reforming
A chemical process in which hydrogen-containing fuels react with steam, oxygen, or both to produce a hydrogen-rich gas stream.
Reformulated Petrol
Petrol that is blended so that, on average, it reduces volatile organic compounds and air toxic emissions significantly relative to conventional petrols.
Refracting Telescope
A type of telescope using a lens as the objective.
Refraction
The bending of light that occurs at the interface between two transparent media.
Refractive Index
This is the ratio of the velocity of light in free space to that in the material.
Refractory
A metal or ceramic that may be exposed to extremely high temperatures without deteriorating rapidly or without melting.
Refrigerant
The working fluid used in refrigerators.
Refrigerator
A heat engine running backward.
Regelation
The phenomenon of melting under pressure and freezing again when the pressure is reduced.
Regenerative Braking
The absorption and re-use of energy dissipated whilst braking a vehicle.
Regenerative Detector
A detector circuit that produces its own oscillations, heterodynes them with an incoming signal, and deflects them.
Regenerative Feedback
Feedback in which the feedback signal is in phase with the input signal.
Regenerative Fuel Cells
Several fuel cell types in which fuel and, in some types, the oxidant are regenerated from the oxidation product.
Regenerative Receiver
An amplitude modulated (AM) radio receiver in which positive feedback is used in order to increase the sensitivity and selectivity of the receiver.
Register
An electronic device that holds a binary number.
Regular Polygon
A polygon in which all of the angles and all of the sides are equal.
Regulator
The section in a basic power supply that maintains the output of the power supply at a constant level in spite of large changes in load current or input line voltage.
Regulatory Enzyme
An enzyme which can be regulated by allosteric mechanisms or by covalent modification.
Regulatory Sequence
A DNA sequence involved in regulating the expression of a gene: a promoter or operator.
Rehoboam
The name of a wine bottle equivalent to the volume of 6 standard bottles or 4.5 litres.
Reid Vapour Pressure
A standard measurement of a liquid′s vapour pressure in psi at 100°F. It is an indication of the propensity of the liquid to evaporate.
Reinforced Concrete
Steel bars embedded in concrete and designed to take the tension that occurs on account of loads.
Reinforcing
Where a structure such as a girder or a concrete slab has been strengthened or stiffened by extra material or by the addition of trusses.
Relative Bearing
Bearing of a target measured in a clockwise direction from "dead ahead".
Relative Density
The ratio of the density of the substance to that of water at 4C
Relative Error
The uncertainty in a measurement compared to the size of the measurement.
Relative Frequency
A count of the number of occurrences of a data value in a sample, or the number of values falling within a fixed range, expressed as a proportion of the total number of observations.
Relative Humidity
The ratio of the absolute humidity to the humidity at saturation.
Relative Magnetic Permeability
The ratio of the magnetic permeability of some medium to that of a vacuum.
Relative Standard Deviation
A measure of precision, calculated by dividing the standard deviation for a series of measurements by the average measurement.
Relative Temperature
The difference between the measured temperature value and an arbitrarily selected value, such as the freezing point of water.
Relatively Prime
If the greatest common divisor of a and b is 1 then a and b are known as relatively prime.
Relativistic Kinetic Energy
The energy that a body possesses solely because it is moving.
Relay
Electromechanical device containing a coil and set of contacts. The contacts close when the coil is activated.
Reliability Block Diagram
A graphical frequency analysis technique that uses system models to investigate overall reliability.
Relief
Moldings and ornamentation projecting from the surface of a wall.
Relief Valve
A valve held closed by a spring and forced open when the pressure in the system rises above the desired limit.
Reluctance
The opposition offered by a material to magnetic flux.
rem
This relates to the absorbed dose in human tissue to the effective biological damage of the radiation.
Remainder
The amount left over when one quantity cannot be exactly divided by another.
Remanence
The magnetic induction that remains in a magnetic circuit after the removal of an applied magnetizing force. If there is an air gap in the circuit, the remanence will be less than the residual induction.
Remote Cutoff Tube
An electron tube in which the control grid wires are farther apart at the centres than at the ends.
Remotely Piloted Vehicle
Directed usually by radio by a pilot in another aircraft or based on the ground.
REN
Abbreviation of Ringer Equivalence Number.
Renaissance
Styles existing in Italy in the fifteenth and sixteenth centuries.
Renewable Energy
Energy obtained from sources that are essentially inexhaustible, unlike fossil fuels.
Renewable Parts
Those parts that must be replaced during maintenance as a result of wear.
Repdigit
An integer all of whose digits are the same.
Repeatability
The consistency (or variation) of readings and results between consecutive sets of measurements.
Repeater
A device used in data communication to strengthen a signal as it is passed along the network cable.
Repeating Decimal
A decimal whose digits eventually repeat.
Repeller
An electrode in a reflex klystron with the primary purpose of reversing the direction of the electron beam.
Report
To document technical, economic and other issues surrounding a particular subject.
Repulsive Force
The mechanical force tending to separate bodies having like electrical charges or like magnetic polarity.
Repunit
An integer consisting only of 1′s.
Research Octane Number
The octane as tested in a single-cylinder octane test engine operated under less severe operating conditions.
Reservoir
A container for storage of liquid in a fluid power system.
Residual
The observed value minus the predicted value.
Residual Elongation
Measure of ductility of plastics.
Residual Induction
This is the point at which the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material.
Residual Intensity
This is the sound intensity level measured when the same signal is fed to both channels of a sound intensity measuring system, or it is exposed to a purely reactive sound field.
Residual Magnetism
Magnetism remaining in a substance after removal of the magnetizing force.
Residual Plot
A plot of the residuals from the regression against the explanatory variable.
Residual Stress
Internal stress in a material often resulting from thermal or mechanical straining.
Residual Terms
Terms added to a curve fit algorithm to take into account the effects of modes outside the range being fitted.
Residue
The substances left after an evaporation or distillation.
Resilient Mounting
A suspension system or cushioned mounting designed to reduce the transmission of vibration between a device and the mounting surface.
Resin
A material, generally a polymer, that has an indefinite and often high molecular weight and a softening or melting range and exhibits a tendency to flow when it is subjected to stress.
Resin Transfer Moulding
A moulding process in which catalyzed resin is transferred into an enclosed mould into which the fibre reinforcement has been placed, cure normally is accomplished without external heat.
Resistance
The electrical resistance of a conductor.
Resistance Brazing
Bonding is produced by the heat obtained from resistance to the flow of electric current in a circuit of which the workpiece is a part.
Resistance Thermometer
An electrical-type thermometer that utilzes a thermal element consisting of a material whose electrical resistance varies with temperature.
Resistive Load
An electrical load where the time phase sequence of the current and the voltage is such that the current and the voltage are in phase with each other.
Resistivity
The resistance measured in ohms of a unit volume of a substance to the flow of electric current.
Resistor
Passive component with a known resistance. The value of resistance is usually shown by a set of coloured bands on the body of the component.
Resolution
The smallest change or amount a measurement system can detect.
Resolver
A rotary, electromechanical device used to perform trigonometric computations by varying the magnetic couplings between its primary and secondary windings.
Resonance
The resonant frequency of a system is defined as the frequency for which the response of the system is a maximum.
Resonance Effect
Difference in electron density at particular points in a molecule.
Resonant Circuit
A circuit that contains both inductance and capacitance and is resonant at one frequency.
Resonant Frequency
Any system has a resonance at some particular frequency.
Resonant Line
A transmission line that has standing waves of current and voltage.
Resonator
An acoustic element which is used to attenuate the sound at narrow band frequencies in ducts and tubes.
Respiration
The process of generating energy from the oxidation of organic compounds, with the electrons transferred to oxygen as the final electron acceptor.
Response
The response of a device or system is the motion (or other output) resulting from an excitation under specified conditions.
Rest Energy
Rest energy is the energy an object has due to its mass.
Rest Frequency
The carrier frequency during the constant-amplitude portions of a phase modulation signal.
Rest Mass
The rest mass of a particle is the mass defined by the energy of the isolated (free) particle at rest, divided by the speed of light squared.
Retrograde
The motion of a planet or other Solar System body in a clockwise direction.
Retroreflectors
Three flat mirrors at right angles to each other that reflect light back to its source.
Reulatory Gene
A gene that gives rise to a product involved in the regulation of the expression of another gene.
Reverberant Sound Field
A sound field made of reflected sounds in which the time average of the mean square sound pressure is everywhere the same and the flow of energy in all directions is equally probable.
Reverberation
The persistence of sound in an enclosed space, as a result of multiple reflections, after the sound source has stopped.
Reverberation Room
Room having a long reverberation time, specially designed to make the sound field therein as diffuse as possible.
Reverberation Time
The time in seconds required for sound pressure at a specific frequency to decay 60 dB after a sound source is stopped.
Reverse Address Resolution Protocol
A protocol used by a host to obtain an IP address based on the address of the host′s adapter card.
Reverse Bias
An external voltage applied to a diode or semiconductor junction to reduce the flow of electrons across the junction.
Reverse Osmosis
Pressure is applied to the more concentrated solution to force the flow of solvent to go from more concentrated to more dilute solution.
Reversible Fuel Cell
A reversible, or regenerative, fuel cell can operate as a fuel cell, or in reverse like an electrolyser.
Revolution
A rotation through a full circle, or 360 degrees.
Revolutions per Kilometre
A unit for the number of times a tyre rotates in one kilometre of travel.
Revolutions per Minute
Unit to describe the rate of rotation of a body.
Revolutions per Second
Unit to describe the rate of rotation of a body.
Reyn
British unit of dynamic viscosity.
Reynolds Number
This is a non-dimensional number (consistent units) which describes whether fluid flow is laminar, turbulent, or transitional between the two.