# Qu

**Quad**- Unit of energy equivalent to 1e15 BTU.
**Quadrangle**- A four-sided polygon.
**Quadrangular Prism**- A prism whose base is a quadrilateral.
**Quadrangular Pyramid**- A pyramid whose base is a quadrilateral.
**Quadrant**- In Cartesian Coordinate geometry, the coordinate plane is divided into four quadrants.
**Quadrat**- A square frame with sides of 1 metre which is used to enable the sampling of organisms.
**Quadratfrei**- Square free.
**Quadratic Equation**- An equation of the second order.
**Quadrature**- The quadrature of a geometric figure is the determination of its area.
**Quadrature Amplitude Modulation**- A combined phase- and amplitude-modulation scheme that is used to modulate the carrier signal in phase quadrature.
**Quadrature Circuit**- A circuit designed to provide a 90° signal phase displacement.
**Quadrature Phase-Shift Keying**- A digital phase-modulation scheme that is used to modulate the carrier signal in phase quadrature.
**Quadric Curve**- The graph of a second degree equation in two variables.
**Quadric Surface**- The graph of a second degree equation in three variables.
**Quadridecagon**- A 14 sided polygon.
**Quadrilateral**- A four sided polygon.
**Quadrillion**- A number equal to 10
^{15}. **Quadrinomial**- An algebraic expression consisting of 4 terms.
**Qualitative Analysis**- A chemical analysis that detects the presence of a substance in a sample.
**Quality Factor**- The quality factor defines the sharpness of resonance.
**Quanta**- The plural of quantum, the smallest unit of a discrete property.
**Quantative Analysis**- A chemical analysis that determines the concentration of a substance in a sample.
**Quantative Structure Activity Relationship**- A mathematical connection between chemical structure and biological activity, established by statistical analysis or pattern recognition techniques.
**Quantization Error**- When a continuous time signal is digitized, because there isn′t an infinite number of discrete digital levels, the difference between the actual analog value and the digital representation of that value is defined as the quantization error.
**Quantum**- The smallest unit of a discrete property.
**Quantum Charge Ratio**- h/e = 4.135708x10
^{-15}JsC^{-1} **Quantum Chromodynamics**- The quantum theory of the strong interaction.
**Quantum Electrodynamics**- The quantum theory of the electromagnetic interaction.
**Quantum Mechanics**- The rules for the behavior of particles at the atomic and subatomic levels.
**Quantum Mechanics Books**- Lists all Quantum Mechanics Books in the Encyclopaedia
**Quantum Mechanics Calculations**- Lists all Quantum Mechanics Calculations in the Encyclopaedia
**Quantum Mechanics Conversions**- Lists all Quantum Mechanics Conversions in the Encyclopaedia
**Quantum Mechanics Weblinks**- Lists all Quantum Mechanics Weblinks in the Encyclopaedia
**Quantum Number**- A number giving the value of a quantized quantity.
**Quark**- A constituent of hadrons. Quarks come in six flavors and three colors each.
**Quark Theory of the Structure of Matter**- The theory that all hadrons, such as the protons and neutrons in the nucleus, are made of quarks.
**Quarry Tile**- A large clay floor tile, usually unglazed.
**Quart**- A unit of volume.
**Quarter**- One of four equal parts. An outdated British unit of weight 1 quarter = 28 pounds (lb).
**Quarter Wave Antenna**- A quarter-wave antenna that is operated with one end grounded and is positioned perpendicular to the earth.
**Quarter Wave Tube**- A resonator used most commonly on automotive air intake systems to reduce resonance.
**Quartet**- A group of four items.
**Quartic**- A polynomial equation of degree 4.
**Quartiles**- Statistics which divide the observations in a numeric sample into 4 intervals, each containing 25% of the data.
**Quartz****SiO**_{2}Found naturally as faceted crystals. Its birefringent properties are used in the production of optical quarter-wave plates and polarizers.

**Quasi Periodic**- A deterministic signal whose spectrum is not a harmonic series, but nevertheless exists at discrete frequencies.
**Quasi Static**- Refers to forces or displacements which vary slowly with time.
**Quasineutral Plasma**- A plasma in which positive and negative charges are present in approximately equal numbers, so that there are no strong net electric fields.
**Quaternary**- The geological period covering about 2 million years ago to the present.
**Quench Hardening**- Hardening a ferrous alloy by austenitizing and then cooling rapidly enough so that some or all of the austenite transforms to martensite.
**Quenching**- Rapid cooling.
**Quenching Oil**- A high-quality, oxidation-resistant petroleum oil used to cool metal parts during their manufacture, and is often preferred to water because the oil′s slower heat transfer lessens the possibility of cracking or warping of the metal.
**Quick Disconnect Coupling**- A coupling which can quickly join or separate a fluid line without the use of tools or special devices.
**Quick to Break**- A device that has a high contact opening speed which is independent of the operator.
**Quick to Make**- A device that has a high contact closing speed which is independent of the operator.
**Quicklime**- Another name for Calcium Oxide.
**Quicksilver**- Ancient name for Mercury.
**Quiescence**- The operating conditions that exist in a circuit when no input signal is applied to the circuit.
**Quiescent Current**- The standing current that flows in a circuit when the signal is not applied. The quiescent current is usually very low or lower than when processing a signal.
**Quiescent Operating Point**- The zero-signal voltage and current values in a circuit or amplifier.
**Quiescent State**- The period during which a transistor, tube, or other circuit element is not performing an active function in the circuit.
**Quiet Sun**- The sun when it is free from unusual radio wave or thermal radiation such as that associated with sunspots.
**Quill Shaft**- A shaft with splines. A male spline on one shaft fits with a female spline on a second shaft and allows the transmission of torque.
**Quintal**- A hundredweight in the metric system, 100kg.
**Quintic**- A polynomial equation of degree 5.
**Quintile**- Statistics which divide the observations in a numeric sample into 5 intervals.
**Quintillion**- A number equal to 10
^{18}. **Quire**- 25 sheets of paper.
**Q unit**- A unit of heat energy equal to one quintillion (10
^{18}) Btu. **Quod Erat Demonstrandum**- Normally abbreviated as QED and used to denote the end of a proof.
**Quotes**- Famous quotes from science and engineering.
**Quotient**- The result when one number or quantity is divided by another.