# Ap

**Aperiodic**- Vibrations or oscillations with no apparent period.
**Aperture**- An opening through which radiation can pass.
**Aperture Delay**- In an analog-to-digital converter, the delay in time from when the user requests the analog input to be sampled and the actual time when this occurs.
**Aperture Illumination**- The field distribution, in amplitude and phase, over the antenna physical aperture.
**Aperture Jitter**- The amount of variance in the aperture delay.
**Apgar Scale**- Standardized scale that is used to determine the physical status of an infant at birth.
**Apgar, Virginia**- Professor of anesthesiology at the New York Columbia-Presbyterian Medical Center, devised the Apgar Scale in 1953.
**Aphelion**- The point in a planet's orbit furthest from the Sun.
**API Gravity**- An arbitrary scale adopted by the American Petroleum Institute to designate the specific gravity of mineral oils.
**Apical Turn**- The final turn in the spiral of the cochlea furthest from the oval and round windows.
**A-Pillar**- The first, or most forward, roof support pillar located on either side of the windshield.
**Apoapsis**- That point in an orbit farthest from the centre of attraction.
**Apocentre**- The point on a spacecraft′s orbit at which it is furthest away from the body it is orbiting.
**Apocynthion**- That point in the orbit of a moon satellite which is farthest from the moon.
**Apodize**- To apodize is to remove or smooth a sharp discontinuity in a mathematical function, an electrical signal or a mechanical structure.
**Apofocus**- The point on an elliptic orbit at the greatest distance from the principal focus.
**Apogee**- Maximum altitude of a rocket above a reference plane, typically mean sea level.
**Apollo Asteroids**- Have orbits that cross the Earth′s orbit.
**Apostilb**- A unit of surface luminance used when defining diffusing surfaces equal to 1 lumenm
^{-2} **Apothecaries Ounce**- Once used as a measurement of weight for drugs and other medical substances.
**Apparent Elastic Limit**- Arbitrary approximation of the elastic limit of materials that do not have a significant straight line portion on a stress strain diagram.
**Apparent Horizon**- Where the shy appears to meet the Earth.
**Apparent Mass**- Force per unit acceleration.
**Apparent Particle Density**- The mass of a particle divided by its apparent particle volume.
**Apparent Particle Volume**- The total volume of the particle, excluding open pores, but including closed pores.
**Apparent Position**- The position on the celestial sphere at which a heavenly body would be seen from the centre of the earth at a particular time.
**Apparent Powder Density**- The mass of a powder divided by its apparent volume.
**Apparent Powder Volume**- The total volume of solid matter, open pores and closed pores and interstices.
**Apparent Power**- That power apparently available for use in an ac circuit containing a reactive element. It is the product of effective voltage times effective current expressed in volt-amperes. It must be multiplied by the power factor to obtain true power available.
**Apparent Source Width**- Discovered and developed by A. H. Marshall, ASW is a subjective parameter of spaciousness in concert halls, and is related to the level, at the listener's ears, of lateral reflections in the first 50 to 80 milliseconds after the arrival of the direct sound.
**Apple**- A hard and dense wood that when stained is a good substitute for ebony.
**Apple Talk**- Communication Protocol used on the Local Talk networks as well as on the Ethernet and Token Ring.
**Applet**- A small application, often downloaded from a remote server and run in a controlled environment.
**Application**- Software that lets users do relatively complex tasks.
**Application Specific Integrated Circuit**- An integrated circuit designed for a custom requirement, frequently implemented in a gate array or field programmable array.
**Appold Dynamometer**- This is a friction based dynamometer with a water cooled drum and automatically corrects any variations of load due to changes in the coefficient of friction.
**Approximate**- Lists all Approximate topics in the Encyclopaedia
**Approximate Area**- Approximate area of something with examples as comparison.
**Approximate Books**- Lists all Approximate Books in the Encyclopaedia
**Approximate Calculations**- Lists all Approximate Calculations in the Encyclopaedia
**Approximate Conversions**- Lists all Approximate Conversions in the Encyclopaedia
**Approximate Density**- Approximate density of something with examples as comparison.
**Approximate Energy**- Approximate energy of something with examples as comparison.
**Approximate Length**- Approximate length of something with examples as comparison.
**Approximate Mass**- Approximate mass of something with examples as comparison.
**Approximate Speed**- Approximate speed of something with examples as comparison.
**Approximate Volume**- Approximate volume of something with examples as comparison.
**Approximate Weblinks**- Lists all Approximate Weblinks in the Encyclopaedia
**Apron**- A slab of concrete extending beyond the entrance to a building, particularly at an entrance for vehicle traffic.
**Aprotic Solvent**- A solvent that does not act as an acid or as a base.
**Apse**- A semicircular area; in most churches it contains the altar.
**APU**- Abbreviation of Auxiliary Power Unit.