“Book/Definitions”
`Electrical Engineering Dictionary.
`Ed. Phillip A. Laplante
`Boca Raton: CRC Press LLC, 2000
`
`

`

`Special
`Symbols
`
`(cid:11)-level set
`a crisp set of elements belong-
`ing to a fuzzy set A at least to a degree (cid:11)
`A(cid:11) D fx 2 X j (cid:22)A.x/ (cid:21) (cid:11)g
`
`See also crisp set, fuzzy set.
`
`common symbol for bandwidth, in
`
`1f
`hertz.
`
`common symbol for gallium ar-
`(cid:15)rGaAs
`senide relative dielectric constant. (cid:15)rGaAs D
`12:8.
`
`common symbol for silicon relative
`(cid:15)rSi
`dielectric constant. (cid:15)rSi D 11:8.
`
`symbol for permitivity of free space.
`(cid:15)0
`(cid:15)0 D 8:849 (cid:2) 10
`−12 farad/meter.
`
`common symbol for relative dielectric
`(cid:15)r
`constant.
`
`common symbol for DC to RF con-
`(cid:17)DC
`version efficiency. Expressed as a percent-
`age.
`
`common symbol for power added ef-
`(cid:17)a
`ficiency. Expressed as a percentage.
`
`common symbol for permeability of
`(cid:22)0
`free space constant. (cid:22)0 D 1:257 (cid:2) 10
`−16
`henrys/meter.
`
`common symbol for relative perme-
`
`(cid:22)r
`ability.
`
`!
`
`common symbol for radian frequency
`in radians/second. ! D 2 (cid:1) (cid:25) (cid:1) frequency.
`(cid:18)C
`common symbol for positive transition
`angle in degrees.
`
`(cid:18)−
`common symbol for negative transi-
`tion angle in degrees.
`
`common symbol for conduction an-
`(cid:18)cond
`gle in degrees.
`
`common symbol for saturation angle
`(cid:18)sat
`in degrees.
`
`common symbol for FET channel-
`(cid:18)CC
`(cid:14)
`C/watt.
`to-case thermal resistance in
`
`common symbol for bipolar junction-
`(cid:18)J C
`(cid:14)
`C/watt.
`to-case thermal resistance in
`A(cid:3)
`common symbol for Richardson’s
`constant. A(cid:3) D 8:7 amperes (cid:1) cm=(cid:14)
`K
`
`BVGD
`voltage.
`
`BVGS
`voltage.
`
`See gate-to-drain breakdown
`
`See gate-to-source breakdown
`
`rate of change of voltage with-
`dv=dt
`stand capability without spurious turn-on of
`the device.
`
`Hci
`
`See intrinsic coercive force.
`
`common symbol for total or true effi-
`(cid:17)t
`ciency. Expressed as a percentage.
`
`common symbol for source reflec-
`0opt
`tion coefficient for optimum noise perfor-
`mance.
`
`ne
`watts.
`
`ns h
`watts.
`
`common symbol for excess noise in
`
`common symbol for shot noise in
`
`c(cid:13)2000 by CRC Press LLC
`
`

`

`common symbol for thermal noise in
`
`nt
`watts.
`
`deux indices,” IRIA Rapport Laboria, No.
`31, Sept. 1973.
`
`10base2
`a type of coaxial cable used to
`connect nodes on an Ethernet network. The
`10 refers to the transfer rate used on standard
`Ethernet, 10 megabits per second. The base
`means that the network uses baseband com-
`munication rather than broadband communi-
`cations, and the 2 stands for the maximum
`length of cable segment, 185 meters (almost
`200). This type of cable is also called “thin”
`Ethernet, because it is a smaller diameter ca-
`ble than the 10base5 cables.
`
`10base5
`a type of coaxial cable used to
`connect nodes on an Ethernet network. The
`10 refers to the transfer rate used on stan-
`dard Ethernet, 10 megabits per second. The
`base means that the network uses baseband
`communication rather than broadband com-
`munications, and the 5 stands for the max-
`imum length of cable segment of approxi-
`mately 500 meters. This type of cable is also
`called “thick” Ethernet, because it is a larger
`diameter cable than the 10base2 cables.
`
`10baseT
`a type of coaxial cable used to
`connect nodes on an Ethernet network. The
`10 refers to the transfer rate used on standard
`Ethernet, 10 megabits per second. The base
`means that the network uses baseband com-
`munication rather than broadband communi-
`cations, and the T stands for twisted (wire)
`cable.
`
`a 2-D model described
`
`2-D Attasi model
`by the equations
`xiC1;jC1 D −A1A2xi;j C A1xiC1;j
`C A2xi;jC1 C Buij
`yij D Cxij C Duij
`i; j 2 ZC (the set of nonnegative integers).
`Here xij 2 Rn is the local state vector,
`uij 2 Rm is the input vector, yij 2 Rp is
`the output vector, and A1, A2, B; C; D are
`real matrices. The model was introduced by
`Attasi in “Systemes lineaires homogenes a
`
`c(cid:13)2000 by CRC Press LLC
`
`a 2-D
`
`2-D Fornasini–Marchesini model
`model described by the equations
`xiC1;jC1 D A0xi;j C A1xiC1;j
`C A2xi;jC1 C Buij
`(1a)
`yij D Cxij C Duij
`(1b)
`i; j 2 ZC (the set of nonnegative integers)
`here xij 2 Rn is the local state vector,
`uij 2 Rm is the input vector, yij 2 Rp is
`the output vector Ak .k D 0; 1; 2/, B; C; D
`are real matrices. A 2-D model described by
`the equations
`xiC1;jC1 D A1xiC1;j C A2xi;jC1
`C B1uiC1;j C B2ui;jC1
`.2/
`i; j 2 ZC and (1b) is called the second 2-D
`Fornasini–Marchesini model, where xij , uij ,
`and yij are defined in the same way as for (1),
`Ak, Bk .k D 0; 1; 2/ are real matrices. The
`model (1) is a particular case of (2).
`
`a 2-D model de-
`
`2-D general model
`scribed by the equations
`xiC1;jC1 D A0xi;j C A1xiC1;j
`C A2xi;jC1 C B0uij
`C B1uiC1;j C B2ui;jC1
`yij D Cxij C Duij
`i; j 2 ZC (the set of nonnegative integers)
`here xij 2 Rn is the local state vector, uij 2
`Rm is the input vector, yij 2 Rp is the output
`vector and Ak, Bk .k D 0; 1; 2/, C; D are real
`matrices. In particular case for B1 D B2 D 0
`we obtain the first 2-D Fornasini–Marchesini
`model and for A0 D 0 and B0 D 0 we obtain
`the second 2-D Fornasini–Marchesini model.
`
`a 2-D
`
`2-D polynomial matrix equation
`equation of the form
`AX C BY D C
`.1/
`where A 2 Rk(cid:2)p [s], B 2 Rk(cid:2)q [s], C 2
`Rk(cid:2)m [s] are given, by a solution to (1) we
`
`

`

`mean any pair X 2 Rp(cid:2)m [s], Y 2 Rq(cid:2)m [s]
`satisfying the equation. The equation (1)
`has a solution if and only if the matrices
`[A; B; C] and [A; B; 0] are column equiva-
`lent or the greatest common left divisor of A
`and B is a left divisor of C. The 2-D equation
`AX C Y B D C
`.2/
`A 2 Rk(cid:2)p [s], B 2 Rq(cid:2)m [s], C 2 Rk(cid:2)m [s]
`are given, is called the bilateral 2-D polyno-
`mial matrix equation. By a solution to (2) we
`mean any pair X 2 Rp(cid:2)m [s], Y 2 Rk(cid:2)q [s]
`(cid:20)
`(cid:21)
`(cid:20)
`(cid:21)
`satisfying the equation. The equation has a
`solution if and only if the matrices
`
`A 0
`0 B
`
`are equivalent.
`
`and
`
`A C
`0 B
`
`"
`
`a 2-D model de-
`
`#
`
`(cid:20)
`
`(cid:21)
`
`2-D Roesser model
`scribed by the equations
`
`#
`
`(cid:20)
`
`(cid:21)"
`C
`D
`iC1;j
`xh
`xh
`A1 A2
`B1
`ij
`uij
`i;jC1
`xv
`xv
`A3 A4
`B2
`"
`#
`ij
`i; j 2 ZC (the set of nonnegative integers),
`yij D C
`C Duij
`
`ij 2 Rn1 and xvij 2 Rn2 are the hori-
`Here xh
`zontal and vertical local state vectors, respec-
`tively, uij 2 Rm is the input vector, yij 2 Rp
`is the output vector and A1, A2, A3, A4, B1,
`B2, C, D are real matrices. The model was
`introduced by R.P. Roesser in “A discrete
`state-space model for linear image process-
`ing,” IEEE Trans. Autom. Contr., AC-20,
`No. 1, 1975, pp. 1-10.
`
`xh
`ij
`xv
`ij
`
`2-D shuffle algorithm an extension of the
`Luenberger shuffle algorithm for 1-D case.
`The 2-D shuffle algorithm can be used for
`checking the regularity condition
`det [Ez1z2 − A0 − A1z1 − A2z2] 6D 0
`for some .z1; z2/ 2 C(cid:2)C of the singular gen-
`eral model ( See singular 2-D general model).
`
`c(cid:13)2000 by CRC Press LLC
`
`The algorithm is based on the row compres-
`sion of suitable matrices.
`
`2-D Z-transform
`F .z1; z2/ of a dis-
`crete 2-D function fij satisfying the condi-
`tion fij D 0 for i < 0 or/and j < 0 is
`1X
`1X
`defined by
`F .z1; z2/ D
`
`fij z−i
`
`1
`
`−j
`z
`2
`
`jD0
`iD0
`An 2-D discrete fij has the 2-D Z-transform
`if the sum
`
`1X
`
`1X
`
`iD0
`
`jD0
`
`exists.
`
`fij z−i
`
`1
`
`−j
`z
`2
`
`2DEGFET
`See high electron mobility
`transistor(HEMT).
`
`2LG See double phase ground fault.
`
`3-dB bandwidth
`for a causal low-pass
`or bandpass filter with a frequency function
`H .j !/ the frequency at which j H .j !/ jdB
`is less than 3 dB down from the peak value
`j H .!P / j.
`
`3-level laser
`a laser in which the most
`important transitions involve only three en-
`ergy states; usually refers to a laser in which
`the lower level of the laser transition is sepa-
`rated from the ground state by much less than
`the thermal energy kT. Contrast with 4-level
`laser.
`
`3-level system
`a quantum mechanical
`system whose interaction with one or more
`electromagnetic fields can be described by
`considering primarily three energy levels.
`For example, the cascade, vee, and lambda
`systems are 3-level systems.
`
`4-level laser
`a laser in which the most
`important transitions involve only four en-
`ergy states; usually refers to a laser in which
`the lower level of the laser transition is sep-
`arated from the ground state by much more
`
`

`

`ty of the image. For example a leak factor of
`31
`32 the prediction decay is maintained at the
`center of the dynamic range.
`
`(cid:0)
`
`L D 128 C 31
`X−
`32
`
`(cid:1)
`
`X− − 128
`
`:
`
`Finally, a clipper at the coder and decoder
`is employed to prevent quantization errors.
`
`90% withstand voltage
`a measure of
`the practical lightning or switching-surge im-
`pulse withstand capability of a piece of power
`equipment. This voltage withstand level is
`two standard deviations above the BIL of the
`equipment.
`
`than the thermal energy kT . Contrast with
`3-level laser.
`
`45 Mbs DPCM for NTSC color video
`a codec wherein a subjectively pleasing pic-
`ture is required at the receiver. This does
`not require transparent coding quality typical
`of TV signals. The output bit-rate for video
`matches the DS3 44:736 Megabits per second
`rate. The coding is done by PCM coding the
`NTSC composite video signal at three times
`the color subcarrier frequency using 8 bit per
`pixel. Prediction of current pixel is obtained
`by averaging the pixel three after current and
`681 pixels before next to maintain the sub-
`carrier phase. A leak factor is chosen before
`computing prediction error to main the quali-
`
`c(cid:13)2000 by CRC Press LLC
`
`

`

`A
`
`a posteriori probability
`statistics.
`
`See posterior
`
`a priori probability
`
`See prior statistics.
`
`A-mode display
`returned ultrasound
`echoes displayed as amplitude versus depth
`into the body.
`
`A-site
`in a ferroelectric material with the
`chemical formula ABO3, the crystalline lo-
`cation of the A atom.
`
`A/D
`
`See analog-to-digital converter.
`
`AAL
`
`See ATM adaptation layer.
`
`ABC
`
`See absorbing boundary condition.
`
`ABCD
`propagation of an optical ray
`through a system can be described by a sim-
`ple 2(cid:2)2 matrix. In ray optics, the character-
`istic of a system is given by the correspond-
`ing ray matrix relating the ray’s position from
`the axis and slope at the input to those at the
`output.
`
`ABCD formalism analytic method using
`two-by-two ABCD matrices for propagating
`Gaussian beams and light rays in a wide va-
`riety of optical systems.
`
`ABCD law
`analytic formula for trans-
`forming a Gaussian beam parameter from
`one reference plane to another in paraxial op-
`tics, sometimes called the Kogelnik transfor-
`mation. ABCD refers to the ABCD matrix.
`
`ABCD matrix
`the matrix containing
`ABCD parameters. See ABCD parameters.
`
`ABCD parameters
`a convenient mathe-
`matical form that can be used to characterize
`
`c(cid:13)2000 by CRC Press LLC
`
`two-port networks. Sometimes referred to
`as chain parameters. ABCD parameters are
`widely used to model cascaded connections
`of two-port microwave networks, in which
`case the ABCD matrix is defined for each
`two-port network. ABCD parameters can
`also be used in analytic formalisms for prop-
`agating Gaussian beams and light rays. Ray
`matrices and beam matrices are similar but
`are often regarded as distinct.
`ABC parameters have a particularly use-
`ful property in circuit analysis where the
`composite ABCD parameters of two cas-
`caded networks are the matrix products of
`the ABCD parameters of the two individual
`circuits. ABCD parameters are defined as
`D
`
`(cid:21)(cid:20)
`
`(cid:21)
`
`v2
`i2
`
`(cid:21)
`
`(cid:20)
`
`(cid:20)
`
`v1
`i1
`
`A B
`C D
`
`where v1 and v2 are the voltages on ports one
`and two, and i1 and i2 are the branch currents
`into ports one and two.
`
`aberration
`an imperfection of an optical
`system that leads to a blurred or a distorted
`image.
`
`abnormal event
`any external or program-
`generated event that makes further normal
`program execution impossible or undesir-
`able, resulting in a system interrupt. Exam-
`ples of abnormal events include system de-
`tection of power failure; attempt to divide by
`0; attempt to execute privileged instruction
`without privileged status; memory parity er-
`ror.
`
`abort
`(1) in computer systems, to termi-
`nate the attempt to complete the transaction,
`usually because there is a deadlock or be-
`cause completing the transaction would re-
`sult in a system state that is not compati-
`ble with “correct” behavior, as defined by a
`consistency model, such as sequential con-
`sistency.
`(2) in an accelerator, terminating the ac-
`celeration process prematurely, either by in-
`hibiting the injection mechanism or by re-
`moving circulating beam to some sort of
`
`

`

`dump. This is generally done to prevent in-
`jury to some personnel or damage to acceler-
`ator components.
`
`ABR
`
`See available bit rate.
`
`absolute address
`an address within an
`instruction that directly indicates a location in
`the program’s address space. Compare with
`relative addressing.
`
`absolute addressing
`an addressing mode
`where the address of the instruction operand
`in memory is a part of the instruction so that
`no calculation of an effective address by the
`CPU is necessary.
`For example, in the Motorola M68000 ar-
`chitecture instruction ADD 5000,D1, a 16-bit
`word operand, stored in memory at the word
`address 5000, is added to the lower word in
`register D1. The address “5000” is an exam-
`ple of using the absolute addressing mode.
`See also addressing mode.
`
`absolute encoder
`an optical device
`mounted to the shaft of a motor consisting
`of a disc with a pattern and light sources and
`detectors. The combination of light detectors
`receiving light depends on the position of the
`rotor and the pattern employed (typically the
`Gray code). Thus, absolute position infor-
`mation is obtained. The higher the resolution
`required, the larger the number of detectors
`needed. See also encoder.
`
`absolute moment
`The pth order absolute
`moment (cid:22)p of a random variable X is the
`expectation of the absolute value of X raised
`to the pth power:
`(cid:22)p D ETjXjUp:
`
`See also central moment, central absolute
`moment. See also expectation.
`
`absolute pressure
`units to measure gas
`pressure in a vacuum chamber with zero be-
`ing a perfect vacuum. Normally referred to
`as psia (pounds per square inch absolute).
`
`c(cid:13)2000 by CRC Press LLC
`
`denoted S.y; x/, is
`absolute sensitivity
`simply the partial derivative of y with respect
`to x, i.e., S.y; x/ D @y=@x, and is used to
`establish the relationships between absolute
`changes. See sensitivity, sensitivity measure,
`relative sensitivity, semi-relative sensitivity.
`
`absolute stability
`occurs when the net-
`work function H .s/ has only left half-plane
`poles.
`
`absorber
`generic term used to describe
`material used to absorb electromagnetic en-
`ergy.
`Generally made of polyurethane
`foam and impregnated with carbon (and fire-
`retardant salts), it is most frequently used to
`line the walls, floors and ceilings of anechoic
`chambers to reduce or eliminate reflections
`from these surfaces.
`
`absorbing boundary condition (ABC)
`a
`fictitious boundary introduced in differential
`equation methods to truncate the computa-
`tional space at a finite distance without, in
`principle, creating any reflections.
`
`absorption
`(1) process that dissipates en-
`ergy and causes a decrease in the amplitude
`and intensity of a propagating wave between
`an input and output reference plane.
`(2) reduction in the number of photons of a
`specific wavelength or energy incident upon
`a material. Energy transferred to the material
`may result in a change in the electronic struc-
`ture, or in the relative movement of atoms in
`the material (vibration or rotation).
`(3) process by which atoms or molecules
`stick to a surface. If a bond is formed, it is
`termed chemisorption, while the normal case
`is physisorption. The absorption process pro-
`ceeds due to, and is supported by, the fact that
`this is a lower energy state.
`
`absorption coefficient
`(1) in a passive de-
`vice, the negative ratio of the power absorbed
`(pabsorbed D pin−pout) ratioed to the power in
`(pin D pincident − preflected) per unit length (l),
`usually expressed in units of 1/wavelength or
`1/meter.
`
`

`

`(2) factor describing the fractional atten-
`uation of light with distance traversed in a
`medium, generally expressed as an exponen-
`tial factor, such as k in the function e−kx,
`with units of (length)-1. Also called attenu-
`ation coefficient.
`
`absorption cross section
`energy ab-
`sorbed by the scattering medium, normal-
`ized to the wavenumber. It has dimensions
`of area.
`
`absorption edge
`the optical wavelength
`or photon energy corresponding to the sep-
`aration of valence and conduction bands in
`solids; at shorter wavelengths, or higher pho-
`ton energies than the absorption edge, the ab-
`sorption increases strongly.
`
`absorption grating
`(1) a diffraction
`grating where alternate grating periods are
`opaque.
`(2) an optical grating characterized by
`spatially periodic variation in the absorption
`of light. Absorption gratings are generally
`less efficient than phase gratings.
`
`absorption optical fiber
`the amount of
`optical power in an optical fiber captured
`by defect and impurity centers in the energy
`bandgap of the fiber material and lost in the
`form of longwave infrared radiation.
`
`AC
`
`See alternating current.
`
`AC bridge
`one of a wide group of
`bridge circuits used for measurements of re-
`sistances, inductances, and capacitances, and
`to provide AC signal in the bridge transducers
`including resistors, inductors, and capacitors.
`The Wheatstone bridge can be used with
`a sinusoidal power supply, and with an AC
`detector (headphones, oscilloscope), one can
`use essentially the same procedure for mea-
`surement of resistors as in DC applications.
`Only a small number of other AC bridges are
`used in modern electric and electronic equip-
`ment. A strong selection factor was the fact
`that in a standard capacitor the electrical pa-
`
`c(cid:13)2000 by CRC Press LLC
`
`rameter are closest to the parameters of an
`ideal capacitor. Hence, not only a capaci-
`tance is measured in terms of capacitance (in
`resistive ratio arms bridges), but the induc-
`tance as well is measured in terms of capac-
`itance (Hay and Owen bridges).
`The AC bridges with ratio arms that are
`tightly coupled inductances allow measure-
`ment of a very small difference between cur-
`rents in these inductances, and this fact is
`used in very sensitive capacitance transduc-
`ers.
`
`AC circuit
`electrical network in which the
`voltage polarity and directions of current flow
`change continuously, and often periodically.
`Thus, such networks contain alternating cur-
`rents as opposed to direct currents, thereby
`giving rise to the term.
`
`AC coupling
`a method of connecting two
`circuits that allows displacement current to
`flow while preventing conductive currents.
`Reactive impedance devices (e.g., capacitors
`and inductive transformers) are used to pro-
`vide continuity of alternating current flow
`between two circuits while simultaneously
`blocking the flow of direct current.
`
`AC motor
`an electromechanical sys-
`tem that converts alternating current electri-
`cal power into mechanical power.
`
`AC plasma display
`a display that em-
`ploys an internal capacitive dielectric layer
`to limit the gas discharge current.
`
`AC steady-state power
`the average
`power delivered by a sinusoidal source to a
`network, expressed as
`P Dj V j (cid:1) j I j cos.(cid:18) /
`p
`p
`2(cid:1) jV j and
`2(cid:1) jI j are the peak
`where
`values, respectively, of the AC steady-state
`voltage and current at the terminals. (cid:18) rep-
`resents the phase angle by which the voltage
`leads the current.
`
`

`

`AC/AC converter
`a power electronics
`device in which an AC input voltage of some
`magnitude, frequency, and number of phases
`is changed to an AC output with changes to
`any of the previously mentioned parameters.
`AC/AC converters usually rectify the input
`source to a DC voltage and then invert the
`DC voltage to the desired AC voltage.
`
`are ea D 1Ka and Ka D lims!inf ty s2q.s/,
`
`ation error to a constraint on the gain of the
`open loop system. The relevant equations
`
`where q.s/ is the transfer function model
`of the open loop system, including the con-
`troller and the process in cascade, and s is
`the Laplace variable. See also position error
`constant, velocity error constant.
`
`AC/DC converter
`
`See rectifier.
`
`AC-DC integrated system a power sys-
`tem containing both AC and DC transmission
`lines.
`
`ACARS
`aircraft communications ad-
`dressing and reporting. A digital commu-
`nications link using the VHF spectrum for
`two-way transmission of data between an air-
`craft and ground. It is used primarily in civil
`aviation applications.
`
`ACC
`
`See automatic chroma control.
`
`accelerated testing
`tests conducted at
`higher stress levels than normal operation but
`in a shorter period of time for the specific
`purpose to induce failure faster.
`
`accelerating power
`the excess electric
`power at a synchronous machine unit which
`cannot be transmitted to the load because of
`a short circuit near its terminals. This energy
`gives rise to increasing rotor angle.
`
`acceleration error
`the final steady dif-
`ference between a parabolic setpoint and the
`process output in a unity feedback control
`system. Thus it is the asymptotic error in po-
`sition that arises in a closed loop system that
`is commanded to move with constant acceler-
`ation. See also position error, velocity error.
`
`accelerator
`(1) a positive electrode in a
`vacuum tube to accelerate emitted electrons
`from its cathode by coulomb force in a de-
`sired direction.
`(2) a machine used to impart large kinetic
`energies to charged particles such as elec-
`trons, protons, and atomic nuclei. The ac-
`celerated particles are used to probe nuclear
`or subnuclear phenomena in industrial and
`medical applications.
`
`acceptable delay
`the voice signal de-
`lay that results in inconvenience in the voice
`communication. A typically quoted value is
`300 ms.
`
`acceptance
`in an accelerator, it defines
`how "large" a beam will fit without scrap-
`ing into the limiting aperture of a transport
`line. The acceptance is the phase-space vol-
`ume within which the beam must lie to be
`transmitted through an optical system with-
`out losses. From an experimenters point
`of view acceptance is the phase-space vol-
`ume intercepted by an experimenter’s detec-
`tor system.
`
`acceptor
`(1) an impurity in a semicon-
`ductor that donates a free hole to the valence
`band.
`(2) a dopant species that traps electrons,
`especially with regard to semiconductors.
`
`acceleration error constant
`a gain Ka
`from which acceleration error ea is read-
`ily determined. The acceleration error con-
`stant is a concept that is useful in the design
`of unity feedback control systems, since it
`transforms a constraint on the final acceler-
`
`access channel
`a channel in a communi-
`cations network that is typically allocated for
`the purpose of setting up calls or communi-
`cation sessions. Typically the users share the
`access channel using some multiple access
`algorithm such as ALOHA or CSMA.
`
`c(cid:13)2000 by CRC Press LLC
`
`

`

`access control
`a means of allowing ac-
`cess to an object based on the type of ac-
`cess sought, the accessor’s privileges, and the
`owner’s policy.
`
`access control list
`a list of items associ-
`ated with a file or other object; the list con-
`tains the identities of users that are permitted
`access to the associated file. There is infor-
`mation (usually in the form of a set of bits)
`about the types of access (such as read, write,
`or delete) permitted to the user.
`
`access control matrix
`a tabular repre-
`sentation of the modes of access permitted
`from active entities (programs or processes)
`to passive entities (objects, files, or devices).
`A typical format associates a row with an ac-
`tive entity or subject and a column with an
`object; the modes of access permitted from
`that active entity to the associated passive en-
`tity are listed in the table entry.
`
`access line
`a communication line that
`connects a user’s terminal equipment to a
`switching node.
`
`access mechanism
`a circuit board or an
`integrated chip that allows a given part of a
`computer system to access another part. This
`is typically performed by using a specific ac-
`cess protocol.
`
`access protocol
`a set of rules that estab-
`lishes communication among different parts.
`These can involve both hardware and soft-
`ware specifications.
`
`access right
`permission to perform an
`operation on an object, usually specified as
`the type of operation that is permitted, such
`as read, write, or delete. Access rights can
`be included in access control lists, capability
`lists, or in an overall access control matrix.
`
`access time
`the total time needed to re-
`trieve data from memory. For a disk drive
`this is the sum of the time to position the
`read/write head over the desired track and the
`
`c(cid:13)2000 by CRC Press LLC
`
`time until the desired data rotates under the
`head. (LW)
`
`accidental rate
`the rate of false coinci-
`dences in the electronic counter experiment
`produced by products of the reactions of more
`than one beam particle within the time reso-
`lution of the apparatus.
`
`accumulation
`(1) an increase in the ma-
`jority carrier concentration of a region of
`semiconductor due to an externally applied
`electric field.
`
`accumulator
`(1) a register in the CPU
`(processor) that stores one of the operands
`prior to the execution of an operation, and
`into which the result of the operation is
`stored. An accumulator serves as an implicit
`source and destination of many of the pro-
`cessor instructions. For example, register A
`of the Intel 8085 is an accumulator. See also
`CPU.
`(2) the storage ring in which successive
`pulses of particles are collected to create a
`particle beam of reasonable intensity for col-
`liding beams.
`
`achievable rate region
`for a multiple
`terminal communications system, a set of
`rate-vectors for which there exist codes such
`that the probability of making a decoding er-
`ror can be made arbitrarily small. See also
`capacity region, multiple access channel.
`
`achromatic
`the quality of a transport line
`or optical system where particle momentum
`has no effect on its trajectory through the sys-
`tem. In an achromatic device or system, the
`output beam displacement or divergence (or
`both) is independent of the input beam’s mo-
`mentum. If a system of lenses is achromatic,
`all particles of the same momentum will have
`equal path lengths through the system.
`
`ACI
`
`See adjacent channel interference.
`
`

`

`acknowledge
`(1) a signal which indicates
`that some operation, such as a data transfer,
`has successfully been completed.
`(2) to detect the successful completion of
`an operation and produce a signal indicating
`the success.
`
`acoustic attenuation
`the degree of am-
`plitude suppression suffered by the acous-
`tic wave traveling along the acousto-optic
`medium.
`
`acoustic laser
`a laser (or maser) in which
`the amplified field consists of soundwaves or
`phonons rather than electromagnetic waves;
`phonon laser or phaser.
`
`acoustic memory
`a form of circulating
`memory in which information is encoded in
`acoustic waves, typically propagated through
`a trough of mercury. Now obsolete.
`
`acoustic velocity
`the velocity of the
`acoustic signal traveling along the acousto-
`optic medium.
`
`acoustic wave
`a propagating periodic
`pressure wave with amplitude representing
`either longitudinal or shear particle displace-
`ment within the wave medium; shear waves
`are prohibited in gaseous and liquid media.
`
`acousto-optic cell
`a device consisting of
`a photo-elastic medium in which a propa-
`gating acoustic wave causes refractive-index
`changes, proportional to acoustic wave am-
`plitude, that act as a phase grating for diffrac-
`tion of light. See also Bragg cell.
`
`acousto-optic channelized radiometer
`See acousto-optic instantaneous spectrum
`analyzer in Bragg mode.
`
`acousto-optic correlator
`an optical sys-
`tem that consists of at least one acousto-
`optic cell, imaging optics between cells and
`fixed masks, and photodetectors whose out-
`puts correspond to the correlation function of
`the acoustic wave signal within one cell with
`
`c(cid:13)2000 by CRC Press LLC
`
`another signal in a second cell, or with fixed
`signals on a mask.
`
`acousto-optic deflector device
`device
`where acousto-optic interaction deflects the
`incident beam linearly as a function of the
`input frequency of the RF signal driving the
`device.
`
`acousto-optic device
`descriptor of
`acousto-optic cells of any design; generally
`describes a cell plus its transducer struc-
`ture(s), and may encompass either bulk,
`guided-wave, or fiber-optic devices.
`
`acousto-optic effect
`the interaction of
`light with sound waves and in particular the
`modification of the properties of a light wave
`by its interactions with an electrically con-
`trollable sound wave.
`See also Brillouin
`scattering.
`
`acousto-optic frequency excisor
`similar
`to an acousto-optic spectrum analyzer where
`the RF temporal spectrum is spatially and se-
`lectively blocked to filter the RF signal feed-
`ing the Bragg cell.
`
`acousto-optic instantaneous spectrum an-
`alyzer in Bragg mode
`device in which the
`temporal spectrum of a radio frequency sig-
`nal is instantaneously and spatially resolved
`in the optical domain using a Fourier trans-
`form lens and a RF signal-fed Bragg cell.
`
`acousto-optic modulator
`a device that
`modifies the amplitude or phase of a light
`wave by means of the acousto-optic effect.
`
`acousto-optic processor
`an optical sys-
`tem that incorporates acousto-optic cells con-
`figured to perform any of a number of math-
`ematical functions such as Fourier trans-
`form, ambiguity transforms, and other time-
`frequency transforms.
`
`acousto-optic scanner
`a device that uses
`an acoustic wave in a photoelastic medium
`
`

`

`to deflect light to different angular positions
`based on the frequency of the acoustic wave.
`
`acousto-optic space integrating convolver
`device that is the same as an acousto-optic
`space integrating convolver except that it im-
`plements the convolution operation.
`
`acousto-optic space integrating correlator
`an acousto-optic implementation of the cor-
`relation function where two RF signals are
`spatially impressed on two diffracted beams
`from Bragg cells, and a Fourier transform
`lens spatially integrates these beams onto a
`point sensor that generates a photo current
`representing the correlation function.
`
`acousto-optic spectrum analyzer
`an
`acousto-optic processor that produces at a
`photodetector output array the Fourier de-
`composition of the electrical drive signal of
`an acousto-optic device.
`
`acousto-optic time integrating convolver
`same as the acousto-optic time integrating
`correlator, except implements the signal con-
`volution operation. See acousto-optic time
`integrating correlator.
`
`acousto-optic time integrating correlator
`an acousto-optic implementation of the cor-
`relation function where two RF signals are
`spatially impressed on two diffracted beams
`from Bragg cells, and a time integrating sen-
`sor generates the spatially distributed corre-
`lation results.
`
`acousto-optic triple product processor
`signal processor that implements a triple inte-
`gration operation using generally both space
`and time dimensions.
`
`acousto-optic tunable filter (AOTF)
`an
`acousto-optic device that selects specific op-
`tical frequencies from a broadband optical
`beam, depending on the number and frequen-
`cies of acoustic waves generated in the de-
`vice.
`
`c(cid:13)2000 by CRC Press LLC
`
`acousto-optics
`the area of study of in-
`teraction of light and sound in media, and
`its utilization in applications such as signal
`processing and filtering.
`
`ACP
`
`See adjacent channel power.
`
`acquisition
`(1) in digital communica-
`tions systems, the process of acquiring syn-
`chronism with the received signal. There
`are several levels of acquisitions, and for a
`given communication system several of them
`have to be performed in the process of setting
`up a communication link: frequency, phase,
`spreading code, symbol, frame, etc.
`(2) in analog communications systems,
`the process of initially estimating signal pa-
`rameters (for example carrier frequency off-
`set, phase offset) required in order to begin
`demodulation of the received signal.
`(3) in vision processing, the process by
`which a scene (physical phenomenon) is
`converted into a suitable format
`that al-
`lows for its storage or retrieval. See also
`synchronization.
`
`across the line starter
`a motor starter that
`applies full line voltage to the motor to start.
`This is also referred to as “hard starting” be-
`cause it causes high starting currents. Larger
`motors require reduced voltage or “soft start-
`ing.”
`
`ACRR
`
`See adjacent channel reuse ratio.
`
`ACSR
`aluminum cable, steel-reinforced.
`A kind of overhead electric power conduc-
`tor made up of a central stranded steel cable
`overlaid with strands of aluminum.
`
`ACT
`
`See anticomet tail.
`
`action potential
`a propagating change in
`the conductivity and potential across a nerve
`cell’s membrane; a nerve impulse in common
`parlance.
`
`activation function
`in an artificial neural
`networ