Pa

Pa
Protactinium is a radioactive element.
Pa
The SI derived unit of pressure is the pascal.
Pace
The distance between two successive falls of the same foot.
Packing
A material used to seal a joint against leakage or to displace one part relative to another.
Packing Density
The fractionof a volume filled by a given collection of solids.
Packing Rings
Rubber rings used to form a watertight joint at the bottom of the cylinder liner.
Page
Unit of information in computer science, usually equal to 256 bytes.
Pagoda
A temple or sacred building, typically in an Asian nation, usually pyramidal, forming a tower with upward curving roofs over the individual stories.
PAH
Abbreviation of Polynuclear Aromatic Hydrocarbons.
Paint
A generally opaque coating including resin, a solvent and additives.
Paintbrush
Brush used to apply paint.
Pair Annihilation
When a particle encounters its antiparticle, they annihilate each other, disappearing in a burst of photons.
Pair Production
The conversion of energy into matter in which a particle and its antiparticle are produced.
Palaeocene
The geological period covering about 65 million years ago to 56.5 million years ago.
Paleozoic
The geological era covering about 570 million years ago to 245 million years ago.
Palermo Scale
Used by astronomers to assess the risk of an impact on the earth by a comet or asteroid.
Palindrome
A positive integer whose digits read the same forward and backwards.
Palindromic
A positive integer is said to be palindromic with respect to a base b if its representation in base b reads the same from left to right as from right to left.
Palladium
A member of the platinum group of metals. It is silvery white in colour, is malleable and ductile, and is one of the most reactive in the group
PAM
Abbreviation of Pulse Amplitude Modulation
Pandiagonal Magic Square
A magic square in which all the broken diagonals as well as the main diagonals add up to the magic constant.
Pandigital
A decimal integer is called pandigital if it contains each of the digits from 0 to 9.
Panel Hammer
A special hammer for metalworking.
Panel Saw
Also known as a hand saw.
Paper
Made by pressing a pulp of rags, straw and wood into thin sheets.
Paper Glue
Many different forms of paper glue, the most common being the solid stick form.
Paper Sizes
There are a number of different systems and standards for paper sizes. The most common is the ISO Paper Size system, but there are others in use.
Parabolic Reflector
An antenna reflector in the shape of a parabola.
Paraboloid
A paraboloid of revolution is a surface of revolution produced by rotating a parabola about its axis.
Parabrake
Deceleration parachute.
Paracetamol
Another name for Acetaminophen.
Parachute
Used to decelerate an object.
Paradox
A statement that appears to contradict itself, for example, suggesting a solution which is actually impossible.
Paraffin Oil
A term describing a whole series of saturated aliphatic hydrocarbons, also known as alkane hydrocarbons.
Paraffin Wax
Obtained as a residue from the distillation of petroleum.
Paraheliotropism
Movement of a plant in response to light.
Parallax
Change in the apparent position of objects when viewed from two widely separated positions.
Parallel
Two or more lines are said to be parallel if they are in the same plane, but never intersect. Two or more planes are parallel if the planes never intersect.
Parallel Circuit
Two or more electrical devices connected to the same pair of terminals so separate currents flow through each.
Parallel Hybrid Vehicle
The power may be provided by the internal combustion engine or the electric motor or a combination of the two.
Parallel Limiter
A resistor and diode, connected in series with the input signal, in which the output is taken across the diode.
Parallel Negative Limiter
A resistor and diode, connected in series with the input signal, in which the output is taken across the diode and the negative alternation is eliminated.
Parallel Planes
Planes that have no points in common.
Parallel Port
A special socket for plugging a printer into a computer.
Parallel Positive Limiter
A resistor and diode connected in series with the input signal, in which the output is taken across the diode and the positive alternation is eliminated.
Parallel Resonant Circuit
A resonant circuit in which the source voltage is connected across a parallel circuit to furnish a high impedance to the frequency at which the circuit is resonant.
Parallel Transfer
A transfer of multiple bits from one register to another simultaneously.
Parallelepiped
A prism whose bases are parallelograms.
Parallelogram
A quadrilateral in which opposite sides are parallel.
Parallelogram of Forces
A method of resolving two forces acting on an object. This is also a great way of visualising the forces and hence resultant.
Paramagnetic Material
A material having a permeability slightly greater than 1.
Paramagnetism
A relatively weak form of magnetism that results from the independent alignment of atomic dipoles (magnetic) with an applied magnetic field.
Parametric Amplifier
A low-noise amplifier that uses a nonlinear variable reactance as the active element instead of a variable resistance.
Parametric Device
A device whose operation depends essentially upon the time variation of a characteristic parameter, usually reactance.
Parana Pine
A yellowish with red streaks softwood that has good working qualities and can be obtained without knots.

Parasitic Array
An antenna array containing one or more elements not connected to the transmission line.
Parasitic Element
The passive element of an antenna array that is connected to neither the transmission line nor the driven element.
Parasol Monoplane
A fixed-wing aircraft which has its single wing strut-mounted above the fuselage.
Paraxial Optics
Optical characteristics limited to infinitesimally small pencils of light.
Parent Isotope
An element that undergoes nuclear decay.
Parenthesis
The symbols ( and ) used for grouping expressions.
Pareto Distribution
A distribution used for random variables which are constrained to be greater or equal to 0.
Paris Bronze
A term given to brass containing 88% copper, 10% zinc and 2% lead used to produce trinkets and souvenirs.
Parity
Applies to situations where two items or their properties may be juxtaposed as being opposites (in a certain context) of each other.
Parity Bit
A bit added to a binary code group which is used to indicate whether the number of recorded 1 or 0 is even or odd.
Parquet Floor
A floor covering laid out in a geometric design composed of small pieces of wood.
Parsec
1 Parsec = 3.2615 Light Years
Parsons, Charles Algernon
English engineer, best known for his invention of the steam turbine.
Partial Correlation
A measure of the strength of the relationship between two or more numeric variables having accounted for their joint relationship with one or more additional variables.
Partial Miscibility
Two liquids are considered partially miscible if shaking equal volumes of the liquids together results in a meniscus visible between two layers of liquid, but the volumes of the layers are not identical to the volumes of the liquids originally added.
Partial Oxidation
Occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas which can then be put to further use.
Partial Pressures
The pressure exerted by a certain gas in a mixture.
Partial Vacuum
A volume that contains traces of gas at very low pressure.
Partial Zero Emission Vehicle
A vehicle that meets SULEV tailpipe emissions and has zero fuel evaporative emissions.
Particle Accelerator
A device for accelerating charged particles to high velocities.
Particle Beam
A stream of particles guided into a defined direction by a particle accelerator.
Particle Board
A building panel composed of small particles of wood and resins bonded together under pressure.
Particle Velocity
A fluctuating velocity superimposed by the presence of sound on the other velocities with the particles of the medium may have.
Particulate
Composed of distinct particles.
Parting
When used in lathe or screw-machine operations, this process separates a completed part from chuck-held or collet-fed stock by means of a very narrow, flat-end cutting, or parting, tool.
Parting-off Tool
A tool used in a lathe to cut the workpiece from the main stock held in the chuck.
Partition
A division between two volumes.
Partition Function
A central construct in statistics and statistical mechanics, and it is a bridge between thermodynamics and quantum mechanics because it is formulated as a sum over the energies of states of a macroscopic system at a given temperature.
Parts per Billion
A unit of proportion equal to 10-9. Abbreviated as ppb.
Parts Per Million
Used to describe the amount of a trace element or substance present in the main substance.
Parts Per Million by Volume
Used to describe the amount of a trace element or substance present in the main substance as measured by volume.
Parts Per Million by Weight
Used to describe the amount of a trace element or substance present in the main substance as measured by weight.
Parts per Quadrillion
A unit of proportion equal to 10-15.
Parts per Thousand
A unit of proportion equal to 0.001 abbreviated ppth and also called per mill.
Pascal
The SI derived unit of pressure.
Pascal, Blaise
French philosopher and mathematician whose many achievements include the invention of an adding machine and the development of the modern theory of probability.
Pascal Distribution
A discrete probability distribution useful for characterizing the time between Bernoulli trials.
Pascal Second
The SI unit of dynamic viscosity, equal to 10 poise.
Pascal′s Law
When an external pressure is applied to any confined fluid at rest, the pressure is increased at every point in the fluid by the amount of external pressure applied.
Pascal′s Triangle
Each number is the sum of the two numbers above. The sum of each row is equal to a power of 2.
Paschen Law
Theoretical relationship for the direct-current breakdown voltage of parallel-plane electrodes immersed in a gas as a function of the gas pressure and electrode separation.
Paschen Series
The series which describes the emission spectrum of hydrogen when the electron is jumping to the third orbital.
Pass-by Noise
Another name for Vehicle Exterior Noise.
Passenger Compartment Acoustic Absorption
The noise within a passenger compartment are controlled by a number of parameters, one of those is the acoustic absorption within the compartment.
Passivation
The process of rendering a metal surface chemically inactive, either by electrochemical polarization or by contact with a passivating agent.
Passivator
A type of corrosion inhibitor that appreciably changes the potential of a metal to a more positive value.
Passive Absorber
A sound absorber that dissipates sound energy as heat.
Passive Cell Balancing
This operates by discharging cells with high SoC through a resistor and thus equalling out the SoC on the cells as a whole.
Passive Crossover
A loudspeaker crossover not requiring power for operation.
Passive Diffusion
Diffusion of a molecule across a biological membrane via a protein transporter down a concentration gradient.
Passive Satellite
A satellite that reflects radio signals back to earth.
Passive Transport
Transport of a molecule across a membrane down a concentration gradient which does not require the input of energy.
Password Authentification Protocol
A protocol used for identifying and authenticating a user and his or her password.
Pasteur, Louis
Remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax.
Patch Panel
A panel used to tie electronics components together.
Patent
A document granting an inventor sole rights to an invention.
Path Function
A property that is dependent on the path taken.
Path Length
In absorption spectroscopy, the length of a path taken by radiation through a sample.
Path Loss
The power attenuation of a signal over the path between a transmitting antenna and a receiving antenna, due to all causes.
Pathogen
Any microorganism or substance that causes disease.
Patina
A thin layer of corrosion products with a distinctive colouration that forms on a metal surface exposed to air and water.
Pattern
Recognizable regularities in situations such as in nature, shapes, events, sets of numbers.
Pattern Recognition
A computational technique used to find patterns and develop classification schemes for data in very large data sets.
Pauli Exclusion Principle
No two electrons can have the same set of quantum numbers.
Pauling, Linus
American chemist, biochemist, peace activist, author and educator. Among the first scientists to work in the fields of quantum chemistry and molecular biology.
Payback Time
The number of years an improved system must be operated to offset the increased cost of the technology.