Electrical engineering dictionary A-K

380 Pages·2000·1.978 MB·English

by  Laplante P.A. (ed.)

“Book/Definitions”
Electrical Engineering Dictionary.
Ed. Phillip A. Laplante
Boca Raton: CRC Press LLC, 2000
(cid:22) commonsymbolforpermeabilityof
0
free space constant. (cid:22) D 1:257(cid:2)10−16
0
Special henrys/meter.
(cid:22)r common symbol for relative perme-
ability.
Symbols
! commonsymbolforradianfrequency
inradians/second. !D2(cid:1)(cid:25) (cid:1) frequency.
(cid:18)C commonsymbolforpositivetransition
(cid:11)-levelset acrispsetofelementsbelong- angleindegrees.
ingtoafuzzysetAatleasttoadegree(cid:11)
(cid:18)− common symbol for negative transi-
A Dfx 2X j(cid:22) .x/(cid:21)(cid:11)g tionangleindegrees.
(cid:11) A
Seealsocrispset,fuzzyset. (cid:18)cond commonsymbolforconductionan-
gleindegrees.
1f common symbol for bandwidth, in
(cid:18) commonsymbolforsaturationangle
hertz. sat
indegrees.
(cid:15) common symbol for gallium ar-
serGniadAesrelativedielectricconstant. (cid:15) D (cid:18)CC common symbol for FET channel-
rGaAs (cid:14)
12:8. to-casethermalresistancein C/watt.
(cid:15)rSi commonsymbolforsiliconrelative (cid:18)toJ-Ccasecthoemrmmaolnrseysimstbaonlcfeoirnbi(cid:14)pCo/lwarajtut.nction-
dielectricconstant. (cid:15) D11:8.
rSi
A(cid:3) common symbol for Richardson’s
(cid:15)0 symbol for permitivity of free space. constant. A(cid:3) D8:7amperes(cid:1)cm=(cid:14)K
(cid:15) D8:849(cid:2)10−12 farad/meter.
0
BVGD See gate-to-drain breakdown
(cid:15)r commonsymbolforrelativedielectric voltage.
constant.
BVGS See gate-to-source breakdown
(cid:17)DC commonsymbolforDCtoRFcon- voltage.
version efficiency. Expressed as a percent-
age. dv=dt rate of change of voltage with-
standcapabilitywithoutspuriousturn-onof
(cid:17)a commonsymbolforpoweraddedef- thedevice.
ficiency. Expressedasapercentage.
Hci Seeintrinsiccoerciveforce.
(cid:17)t commonsymbolfortotalortrueeffi-
ciency. Expressedasapercentage. ne common symbol for excess noise in
watts.
0 common symbol for source reflec-
opt
tion coefficient for optimum noise perfor- nsh common symbol for shot noise in
mance. watts.
(cid:13)c2000byCRCPressLLC
nt commonsymbolforthermalnoisein deux indices,” IRIA Rapport Laboria, No.
watts. 31,Sept. 1973.
10base2 atypeofcoaxialcableusedto 2-DFornasini–Marchesinimodel a2-D
connectnodesonanEthernetnetwork. The modeldescribedbytheequations
10referstothetransferrateusedonstandard
x DA x CA x
Ethernet,10megabitspersecond. Thebase iC1;jC1 0 i;j 1 iC1;j
meansthatthenetworkusesbasebandcom- CA2xi;jC1CBuij (1a)
municationratherthanbroadbandcommuni- yij DCxij CDuij (1b)
cations, and the 2 stands for the maximum
lengthofcablesegment,185meters(almost i;j 2 ZC (the set of nonnegative integers)
200). Thistypeofcableisalsocalled“thin” here xij 2 Rn is the local state vector,
Ethernet,becauseitisasmallerdiameterca- uij 2 Rm is the input vector, yij 2 Rp is
blethanthe10base5cables. theoutputvectorAk .k D 0;1;2/, B;C;D
arerealmatrices. A2-Dmodeldescribedby
10base5 atypeofcoaxialcableusedto theequations
connectnodesonanEthernetnetwork. The
x DA x CA x
10 refers to the transfer rate used on stan- iC1;jC1 1 iC1;j 2 i;jC1
dardEthernet,10megabitspersecond. The CB1uiC1;j CB2ui;jC1 .2/
base means that the network uses baseband
i;j 2 ZC and(1b)iscalledthesecond2-D
communicationratherthanbroadbandcom-
Fornasini–Marchesinimodel,wherexij,uij,
munications, and the 5 stands for the max-
andyij aredefinedinthesamewayasfor(1),
imum length of cable segment of approxi-
Ak, Bk .k D 0;1;2/arerealmatrices. The
mately500meters. Thistypeofcableisalso
model(1)isaparticularcaseof(2).
called“thick”Ethernet,becauseitisalarger
diametercablethanthe10base2cables.
2-D general model a 2-D model de-
scribedbytheequations
10baseT atypeofcoaxialcableusedto
connectnodesonanEthernetnetwork. The x DA x CA x
iC1;jC1 0 i;j 1 iC1;j
10referstothetransferrateusedonstandard CA x CB u
2 i;jC1 0 ij
Ethernet,10megabitspersecond. Thebase
CB u CB u
meansthatthenetworkusesbasebandcom- 1 iC1;j 2 i;jC1
y DCx CDu
municationratherthanbroadbandcommuni- ij ij ij
cations, and the T stands for twisted (wire)
i;j 2 ZC (the set of nonnegative integers)
cable.
herexij 2 Rn isthelocalstatevector,uij 2
2-DAttasimodel a2-Dmodeldescribed Rmistheinputvector,yij 2Rpistheoutput
bytheequations vectorandAk,Bk.k D0;1;2/,C;Darereal
matrices. InparticularcaseforB DB D0
1 2
x D−A A x CA x weobtainthefirst2-DFornasini–Marchesini
iC1;jC1 1 2 i;j 1 iC1;j
modelandforA D0andB D0weobtain
CA x CBu 0 0
2 i;jC1 ij thesecond2-DFornasini–Marchesinimodel.
y DCx CDu
ij ij ij
2-Dpolynomialmatrixequation a2-D
i;j 2 ZC (the set of nonnegative integers). equationoftheform
Here xij 2 Rn is the local state vector,
uij 2 Rm is the input vector, yij 2 Rp is AXCBY DC .1/
the output vector, and A , A , B;C;D are
1 2
realmatrices. Themodelwasintroducedby where A 2 Rk(cid:2)p[s], B 2 Rk(cid:2)q[s], C 2
Attasi in “Systemes lineaires homogenes a Rk(cid:2)m[s] are given, by a solution to (1) we
(cid:13)c2000byCRCPressLLC
meananypairX 2Rp(cid:2)m[s],Y 2Rq(cid:2)m[s] Thealgorithmisbasedontherowcompres-
satisfying the equation. The equation (1) sionofsuitablematrices.
has a solution if and only if the matrices
[A;B;C] and [A;B;0] are column equiva- 2-D Z-transform F.z1;z2/ of a dis-
lentorthegreatestcommonleftdivisorofA crete 2-D function fij satisfying the condi-
andBisaleftdivisorofC. The2-Dequation tion fij D 0 for i < 0 or/and j < 0 is
definedby
AXCYB DC .2/
X1 X1
A2Rk(cid:2)p[s],B 2Rq(cid:2)m[s],C 2Rk(cid:2)m[s] F .z1;z2/D fijz1−iz2−j
aregiven,iscalledthebilateral2-Dpolyno- iD0jD0
mialmatrixequation. Byasolutionto(2)we An2-Ddiscretefij hasthe2-DZ-transform
meananypairX 2 Rp(cid:2)m[s],Y 2 Rk(cid:2)q[s] ifthesum
satisfying the equation. The equation has a
X1 X1
solutionifandonlyifthematrices f z−iz−j
ij
(cid:20) (cid:21) (cid:20) (cid:21) 1 2
A 0 AC iD0jD0
and
0 B 0 B exists.
areequivalent.
2DEGFET See high electron mobility
transistor(HEMT).
2-D Roesser model a 2-D model de-
scribedbytheequations
2LG Seedoublephasegroundfault.
" # (cid:20) (cid:21)" # (cid:20) (cid:21)
xh A A xh B
iC1;j D 1 2 ij C 1 u 3-dB bandwidth for a causal low-pass
xv A A xv B ij
i;jC1 3 4 ij 2 orbandpassfilterwithafrequencyfunction
i;j 2ZC(thesetofnonnegativeintegers), H.j!/thefrequencyatwhichj H.j!/ jdB
is less than 3 dB down from the peak value
" #
xh jH.!P/j.
y DC ij CDu
ij xv ij
ij 3-level laser a laser in which the most
Herexihj 2 Rn1 andxivj 2 Rn2 arethehori- important transitions involve only three en-
zontalandverticallocalstatevectors,respec- ergystates;usuallyreferstoalaserinwhich
tively,uij 2Rmistheinputvector,yij 2Rp thelowerlevelofthelasertransitionissepa-
istheoutputvectorandA ,A ,A ,A ,B , ratedfromthegroundstatebymuchlessthan
1 2 3 4 1
B ,C,D arerealmatrices. Themodelwas thethermalenergykT. Contrastwith4-level
2
introduced by R.P. Roesser in “A discrete laser.
state-space model for linear image process-
ing,” IEEE Trans. Autom. Contr., AC-20, 3-level system a quantum mechanical
No. 1,1975,pp. 1-10. system whose interaction with one or more
electromagnetic fields can be described by
2-Dshufflealgorithm anextensionofthe considering primarily three energy levels.
Luenberger shuffle algorithm for 1-D case. For example, the cascade, vee, and lambda
The 2-D shuffle algorithm can be used for systemsare3-levelsystems.
checkingtheregularitycondition
4-level laser a laser in which the most
det[Ez z −A −A z −A z ]6D0 important transitions involve only four en-
1 2 0 1 1 2 2
ergystates;usuallyreferstoalaserinwhich
forsome.z ;z /2C(cid:2)Cofthesingulargen- thelowerlevelofthelasertransitionissep-
1 2
eralmodel(Seesingular2-Dgeneralmodel). arated from the ground state by much more
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than the thermal energy kT. Contrast with tyoftheimage. Forexamplealeakfactorof
3-levellaser. 31 thepredictiondecayismaintainedatthe
32
centerofthedynamicrange.
45 Mbs DPCM for NTSC color video
acodecwhereinasubjectivelypleasingpic-
(cid:0) (cid:1)
ture is required at the receiver. This does X− D128C 31 X−−128 :
L
32
notrequiretransparentcodingqualitytypical
ofTVsignals. Theoutputbit-rateforvideo Finally,aclipperatthecoderanddecoder
matchestheDS344:736Megabitspersecond isemployedtopreventquantizationerrors.
rate. ThecodingisdonebyPCMcodingthe
NTSCcompositevideosignalatthreetimes 90% withstand voltage a measure of
thecolorsubcarrierfrequencyusing8bitper thepracticallightningorswitching-surgeim-
pixel. Predictionofcurrentpixelisobtained pulsewithstandcapabilityofapieceofpower
byaveragingthepixelthreeaftercurrentand equipment. This voltage withstand level is
681 pixels before next to maintain the sub- twostandarddeviationsabovetheBILofthe
carrierphase. Aleakfactorischosenbefore equipment.
computingpredictionerrortomainthequali-
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two-port networks. Sometimes referred to
aschainparameters. ABCDparametersare
A
widelyusedtomodelcascadedconnections
of two-port microwave networks, in which
case the ABCD matrix is defined for each
two-port network. ABCD parameters can
alsobeusedinanalyticformalismsforprop-
a posteriori probability See posterior agatingGaussianbeamsandlightrays. Ray
statistics. matrices and beam matrices are similar but
areoftenregardedasdistinct.
aprioriprobability Seepriorstatistics. ABCparametershaveaparticularlyuse-
ful property in circuit analysis where the
A-mode display returned ultrasound
composite ABCD parameters of two cas-
echoes displayed as amplitude versus depth
caded networks are the matrix products of
intothebody.
theABCDparametersofthetwoindividual
circuits. ABCDparametersaredefinedas
A-site inaferroelectricmaterialwiththe (cid:20) (cid:21) (cid:20) (cid:21)(cid:20) (cid:21)
chemical formula ABO , the crystalline lo- v A B v
3 1 D 2
cationoftheAatom. i C D i
1 2
wherev andv arethevoltagesonportsone
A/D Seeanalog-to-digitalconverter. 1 2
andtwo,andi andi arethebranchcurrents
1 2
AAL SeeATMadaptationlayer. intoportsoneandtwo.
ABC Seeabsorbingboundarycondition. aberration animperfectionofanoptical
system that leads to a blurred or a distorted
ABCD propagation of an optical ray image.
throughasystemcanbedescribedbyasim-
ple2(cid:2)2matrix. Inrayoptics,thecharacter- abnormalevent anyexternalorprogram-
isticofasystemisgivenbythecorrespond- generated event that makes further normal
ingraymatrixrelatingtheray’spositionfrom program execution impossible or undesir-
theaxisandslopeattheinputtothoseatthe able,resultinginasysteminterrupt. Exam-
output. ples of abnormal events include system de-
tectionofpowerfailure;attempttodivideby
ABCDformalism analyticmethodusing 0; attempt to execute privileged instruction
two-by-twoABCDmatricesforpropagating withoutprivilegedstatus;memoryparityer-
Gaussianbeamsandlightraysinawideva- ror.
rietyofopticalsystems.
abort (1)incomputersystems,totermi-
ABCD law analytic formula for trans- natetheattempttocompletethetransaction,
forming a Gaussian beam parameter from usually because there is a deadlock or be-
onereferenceplanetoanotherinparaxialop- cause completing the transaction would re-
tics,sometimescalledtheKogelniktransfor- sult in a system state that is not compati-
mation. ABCDreferstotheABCDmatrix. ble with “correct” behavior, as defined by a
consistency model, such as sequential con-
ABCD matrix the matrix containing sistency.
ABCDparameters. SeeABCDparameters. (2) in an accelerator, terminating the ac-
celerationprocessprematurely,eitherbyin-
ABCDparameters aconvenientmathe- hibiting the injection mechanism or by re-
maticalformthatcanbeusedtocharacterize moving circulating beam to some sort of
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dump. Thisisgenerallydonetopreventin- absolutesensitivity denotedS.y;x/,is
jurytosomepersonnelordamagetoacceler- simplythepartialderivativeofywithrespect
atorcomponents. to x, i.e., S.y;x/ D @y=@x, and is used to
establishtherelationshipsbetweenabsolute
ABR Seeavailablebitrate. changes. Seesensitivity,sensitivitymeasure,
relativesensitivity,semi-relativesensitivity.
absolute address an address within an
instructionthatdirectlyindicatesalocationin absolute stability occurs when the net-
theprogram’saddressspace. Comparewith workfunctionH.s/hasonlylefthalf-plane
relativeaddressing. poles.
absoluteaddressing anaddressingmode absorber generic term used to describe
wheretheaddressoftheinstructionoperand materialusedtoabsorbelectromagneticen-
inmemoryisapartoftheinstructionsothat ergy. Generally made of polyurethane
nocalculationofaneffectiveaddressbythe foamandimpregnatedwithcarbon(andfire-
CPUisnecessary. retardantsalts),itismostfrequentlyusedto
Forexample,intheMotorolaM68000ar- linethewalls,floorsandceilingsofanechoic
chitectureinstructionADD5000,D1,a16-bit chambers to reduce or eliminate reflections
wordoperand,storedinmemoryattheword fromthesesurfaces.
address5000,isaddedtothelowerwordin
registerD1. Theaddress“5000”isanexam- absorbingboundarycondition(ABC) a
ple of using the absolute addressing mode. fictitiousboundaryintroducedindifferential
Seealsoaddressingmode. equation methods to truncate the computa-
tional space at a finite distance without, in
absolute encoder an optical device principle,creatinganyreflections.
mounted to the shaft of a motor consisting
ofadiscwithapatternandlightsourcesand absorption (1)processthatdissipatesen-
detectors. Thecombinationoflightdetectors ergyandcausesadecreaseintheamplitude
receivinglightdependsonthepositionofthe andintensityofapropagatingwavebetween
rotorandthepatternemployed(typicallythe aninputandoutputreferenceplane.
Gray code). Thus, absolute position infor- (2)reductioninthenumberofphotonsofa
mationisobtained. Thehighertheresolution specificwavelengthorenergyincidentupon
required, the larger the number of detectors amaterial. Energytransferredtothematerial
needed. Seealsoencoder. mayresultinachangeintheelectronicstruc-
ture,orintherelativemovementofatomsin
absolutemoment Thepthorderabsolute thematerial(vibrationorrotation).
moment (cid:22)p of a random variable X is the (3)processbywhichatomsormolecules
expectationoftheabsolutevalueofXraised stick to a surface. If a bond is formed, it is
tothepthpower: termedchemisorption,whilethenormalcase
isphysisorption. Theabsorptionprocesspro-
(cid:22)p DETjXjUp: ceedsdueto,andissupportedby,thefactthat
thisisalowerenergystate.
See also central moment, central absolute
moment. Seealsoexpectation. absorptioncoefficient (1)inapassivede-
vice,thenegativeratioofthepowerabsorbed
absolute pressure units to measure gas (p Dp −p )ratioedtothepowerin
absorbed in out
pressureinavacuumchamberwithzerobe- (p Dp −p )perunitlength(l),
in incident reflected
ing a perfect vacuum. Normally referred to usuallyexpressedinunitsof1/wavelengthor
aspsia(poundspersquareinchabsolute). 1/meter.
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(2) factor describing the fractional atten- rameter are closest to the parameters of an
uation of light with distance traversed in a ideal capacitor. Hence, not only a capaci-
medium,generallyexpressedasanexponen- tanceismeasuredintermsofcapacitance(in
tial factor, such as k in the function e−kx, resistive ratio arms bridges), but the induc-
withunitsof(length)-1. Alsocalledattenu- tanceaswellismeasuredintermsofcapac-
ationcoefficient. itance(HayandOwenbridges).
The AC bridges with ratio arms that are
absorption cross section energy ab- tightly coupled inductances allow measure-
sorbed by the scattering medium, normal- mentofaverysmalldifferencebetweencur-
ized to the wavenumber. It has dimensions rents in these inductances, and this fact is
ofarea. usedinverysensitivecapacitancetransduc-
ers.
absorptionedge theopticalwavelength
or photon energy corresponding to the sep-
ACcircuit electricalnetworkinwhichthe
aration of valence and conduction bands in
voltagepolarityanddirectionsofcurrentflow
solids;atshorterwavelengths,orhigherpho-
changecontinuously,andoftenperiodically.
tonenergiesthantheabsorptionedge,theab-
Thus,suchnetworkscontainalternatingcur-
sorptionincreasesstrongly.
rents as opposed to direct currents, thereby
givingrisetotheterm.
absorption grating (1) a diffraction
grating where alternate grating periods are
ACcoupling amethodofconnectingtwo
opaque.
circuits that allows displacement current to
(2) an optical grating characterized by
flow while preventing conductive currents.
spatiallyperiodicvariationintheabsorption
Reactiveimpedancedevices(e.g.,capacitors
of light. Absorption gratings are generally
andinductivetransformers)areusedtopro-
lessefficientthanphasegratings.
vide continuity of alternating current flow
between two circuits while simultaneously
absorption optical fiber the amount of
blockingtheflowofdirectcurrent.
optical power in an optical fiber captured
bydefectandimpuritycentersintheenergy
AC motor an electromechanical sys-
bandgapofthefibermaterialandlostinthe
temthatconvertsalternatingcurrentelectri-
formoflongwaveinfraredradiation.
calpowerintomechanicalpower.
AC Seealternatingcurrent.
AC plasma display a display that em-
ploys an internal capacitive dielectric layer
AC bridge one of a wide group of
tolimitthegasdischargecurrent.
bridgecircuitsusedformeasurementsofre-
sistances,inductances,andcapacitances,and
AC steady-state power the average
toprovideACsignalinthebridgetransducers
power delivered by a sinusoidal source to a
includingresistors,inductors,andcapacitors.
network,expressedas
TheWheatstonebridgecanbeusedwith
a sinusoidal power supply, and with an AC
detector(headphones,oscilloscope),onecan P DjV j(cid:1)jI jcos.(cid:18)/
useessentiallythesameprocedureformea- p p
surementofresistorsasinDCapplications. where 2(cid:1) j V jand 2(cid:1) j I jarethepeak
OnlyasmallnumberofotherACbridgesare values, respectively, of the AC steady-state
usedinmodernelectricandelectronicequip- voltage and current at the terminals. (cid:18) rep-
ment. Astrongselectionfactorwasthefact resentsthephaseanglebywhichthevoltage
thatinastandardcapacitortheelectricalpa- leadsthecurrent.
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AC/AC converter a power electronics ationerrortoaconstraintonthegainofthe
deviceinwhichanACinputvoltageofsome open loop system. The relevant equations
magnitude,frequency,andnumberofphases are ea D K1a and Ka D lims!inftys2q.s/,
ischangedtoanACoutputwithchangesto where q.s/ is the transfer function model
anyofthepreviouslymentionedparameters. oftheopenloopsystem, includingthecon-
AC/AC converters usually rectify the input troller and the process in cascade, and s is
source to a DC voltage and then invert the theLaplacevariable. Seealsopositionerror
DCvoltagetothedesiredACvoltage. constant,velocityerrorconstant.
AC/DCconverter Seerectifier. accelerator (1)apositiveelectrodeina
vacuumtubetoaccelerateemittedelectrons
AC-DCintegratedsystem apowersys- from its cathode by coulomb force in a de-
temcontainingbothACandDCtransmission sireddirection.
lines.
(2)amachineusedtoimpartlargekinetic
energies to charged particles such as elec-
ACARS aircraft communications ad-
trons, protons, and atomic nuclei. The ac-
dressing and reporting. A digital commu-
celeratedparticlesareusedtoprobenuclear
nications link using the VHF spectrum for
or subnuclear phenomena in industrial and
two-waytransmissionofdatabetweenanair-
medicalapplications.
craftandground. Itisusedprimarilyincivil
aviationapplications.
acceptable delay the voice signal de-
laythatresultsininconvenienceinthevoice
ACC Seeautomaticchromacontrol.
communication. Atypicallyquotedvalueis
300ms.
accelerated testing tests conducted at
higherstresslevelsthannormaloperationbut
acceptance in an accelerator, it defines
in a shorter period of time for the specific
how "large" a beam will fit without scrap-
purposetoinducefailurefaster.
ing into the limiting aperture of a transport
line. Theacceptanceisthephase-spacevol-
accelerating power the excess electric
ume within which the beam must lie to be
poweratasynchronousmachineunitwhich
transmitted through an optical system with-
cannotbetransmittedtotheloadbecauseof
out losses. From an experimenters point
ashortcircuitnearitsterminals. Thisenergy
of view acceptance is the phase-space vol-
givesrisetoincreasingrotorangle.
umeinterceptedbyanexperimenter’sdetec-
torsystem.
acceleration error the final steady dif-
ferencebetweenaparabolicsetpointandthe
acceptor (1) an impurity in a semicon-
process output in a unity feedback control
ductorthatdonatesafreeholetothevalence
system. Thusitistheasymptoticerrorinpo-
band.
sitionthatarisesinaclosedloopsystemthat
iscommandedtomovewithconstantacceler- (2) a dopant species that traps electrons,
ation. Seealsopositionerror,velocityerror. especiallywithregardtosemiconductors.
acceleration error constant a gain Ka accesschannel achannelinacommuni-
from which acceleration error ea is read- cationsnetworkthatistypicallyallocatedfor
ily determined. The acceleration error con- thepurposeofsettingupcallsorcommuni-
stantisaconceptthatisusefulinthedesign cationsessions. Typicallytheuserssharethe
of unity feedback control systems, since it access channel using some multiple access
transforms a constraint on the final acceler- algorithmsuchasALOHAorCSMA.
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access control a means of allowing ac- time until the desired data rotates under the
cess to an object based on the type of ac- head. (LW)
cesssought,theaccessor’sprivileges,andthe
owner’spolicy.
accidental rate the rate of false coinci-
dences in the electronic counter experiment
accesscontrollist alistofitemsassoci-
producedbyproductsofthereactionsofmore
atedwithafileorotherobject; thelistcon-
thanonebeamparticlewithinthetimereso-
tainstheidentitiesofusersthatarepermitted
lutionoftheapparatus.
accesstotheassociatedfile. Thereisinfor-
mation (usually in the form of a set of bits)
aboutthetypesofaccess(suchasread,write, accumulation (1)anincreaseinthema-
ordelete)permittedtotheuser. jority carrier concentration of a region of
semiconductor due to an externally applied
access control matrix a tabular repre- electricfield.
sentation of the modes of access permitted
fromactiveentities(programsorprocesses) accumulator (1) a register in the CPU
topassiveentities(objects,files,ordevices). (processor) that stores one of the operands
Atypicalformatassociatesarowwithanac- prior to the execution of an operation, and
tive entity or subject and a column with an into which the result of the operation is
object; the modes of access permitted from stored. Anaccumulatorservesasanimplicit
thatactiveentitytotheassociatedpassiveen- source and destination of many of the pro-
tityarelistedinthetableentry. cessorinstructions. Forexample,registerA
oftheIntel8085isanaccumulator. Seealso
access line a communication line that CPU.
connects a user’s terminal equipment to a
switchingnode. (2) the storage ring in which successive
pulses of particles are collected to create a
accessmechanism acircuitboardoran particlebeamofreasonableintensityforcol-
integrated chip that allows a given part of a lidingbeams.
computersystemtoaccessanotherpart. This
istypicallyperformedbyusingaspecificac- achievable rate region for a multiple
cessprotocol. terminal communications system, a set of
rate-vectorsforwhichthereexistcodessuch
accessprotocol asetofrulesthatestab- thattheprobabilityofmakingadecodinger-
lishescommunicationamongdifferentparts. ror can be made arbitrarily small. See also
These can involve both hardware and soft- capacityregion,multipleaccesschannel.
warespecifications.
achromatic thequalityofatransportline
access right permission to perform an
oropticalsystemwhereparticlemomentum
operation on an object, usually specified as
hasnoeffectonitstrajectorythroughthesys-
thetypeofoperationthatispermitted, such
tem. Inanachromaticdeviceorsystem,the
as read, write, or delete. Access rights can
outputbeamdisplacementordivergence(or
beincludedinaccesscontrollists,capability
both)isindependentoftheinputbeam’smo-
lists,orinanoverallaccesscontrolmatrix.
mentum. Ifasystemoflensesisachromatic,
allparticlesofthesamemomentumwillhave
accesstime thetotaltimeneededtore-
equalpathlengthsthroughthesystem.
trieve data from memory. For a disk drive
this is the sum of the time to position the
read/writeheadoverthedesiredtrackandthe ACI Seeadjacentchannelinterference.
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