Electrical engineering dictionary L-Q

180 Pages·2000·0.931 MB·English

by  Laplante P.A. (ed.)

termeffect,andshouldnotbeconfusedwith
imageretention,imageburn,orsticking.
L
lagcircuit asimplepassiveelectroniccir-
cuitdesignedtoaddadominantpoletocom-
pensatetheperformanceofagivensystem. A
lagcircuitisgenerallyusedtomakeasystem
L-band frequencybandofapproximately more stable by reducing its high-frequency
1–2GHz. gain and/or to improve its position, veloc-
ity, or acceleration error by increasing the
L-L Seelinetolinefault. lowfrequencygain. Anondominantzerois
included in the lag circuit to prevent undue
label a tag in a programming language destabilizationofthecompensatedsystemby
(usuallyassemblylanguage,alsolegalinC) theadditionalpole.
that marks an instruction or statement as a
possibletargetforajumporbranch. lag network a network where the phase
angleassociatedwiththeinput–outputtrans-
ferfunctionisalwaysnegative,orlagging.
labeling (1) the computational problem
ofassigninglabelsconsistentlytoobjectsor
lag-lead network the phase shift versus
object components (segments) appearing in
frequencycurveinaphaselag-leadnetwork
animage.
is negative, or lagging, for low frequencies
(2)atechniquebywhicheachpixelwithin
andpositive,orleading,forhighfrequencies.
adistinctsegmentismarkedasbelongingto
The phase angle associated with the input–
that segment. One way to label an image
outputtransferfunctionisalwayspositiveor
involves appending to each pixel of an im-
leading.
agethelabelnumberorindexofitssegment.
Anotherwayistospecifytheclosedcontour
Lagrange formulation a formulation
ofeachsegmentandtouseacontourfilling
wheretheequationsofmotionarederivedina
techniquetolabeleachpixelwithinacontour.
systematicwaybychoosingasetofgeneral-
izedcoordinates,formingtheLagrangianof
ladderdiagram (1)theconnectionofthe
themechanicalsystem(asadifferenceofto-
coils and contacts used in a control circuit
talkineticenergyandpotentialenergyofthe
shownonelineaftertheotherthatlookslike
system) and by solving the Lagrange equa-
aladder.
tions
(2) a visual language for specifying the
Boolean expressions, which are the core of d @L @L
thecontrollawofPLC. dt @qP − @q D(cid:28)i i D1;:::;n
i i
laddertron amicrowavevacuumtubeos- whereLstandsforLagrangian,qiisthegen-
cillator with a slow-wave structure coupled eralized coordinate, qPi is its derivative, and
toasingle-cavityresonator. (cid:28)i isageneralizedforce,andndenotesnum-
ber of degrees of freedom of the mechani-
lag theinabilityofanimagingtubetore- calsystem. Lastequationsestablishtherela-
spondtoinstantaneouschangesinlight. For tionsexistingbetweenthegeneralizedforces
measurementpurposes,laghastwocompo- appliedtothemanipulatorandthejointpo-
nents: riselagistheresponsetimefromdark sitions, velocities, and accelerations in so
to light, whereas decay lag is the response calledclosedform. SeealsoNewton–Euler
timefromlighttodark. Lagisaveryshort- recursivealgorithm.
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Lagrangestablestate Seeboundedstate. Lambertiansurface asurfacewithper-
fect diffusion properties, i.e., for which the
Lagrangianinterpolation aclassicinter- reflectancefunctiondependsonlyonthean-
polationprocedureusedinnumericalanaly- gleofincidenceofillumination.
sis. Thesamplingtheoremisaspecialcase.
laminatemulti-chipmodule(MCM-L)
Laguerre polynomial a solution to the a multi-chip module built using advanced
differential equation xy00 C .1 − x/y0 C PCBmanufacturingtechniques.
ny D 0. Laguerre polynomials L .x/ D
0
1;L1.x/ D 1−x;L2.x/ D 1−2xCx2=2, lamination athinsheetofmetalusedto
andL3 D1−3xC3x2=2−x3=6. Additional build up the core of an electromagnetic de-
Laguerrepolynomialsmaybeobtainedfrom vice. Laminations are insulated from each
therecursionformula.nC1/LnC1.x/−.2nC other to reduce the losses associated with
1−x/Ln.x/CLn−1.x/D0. eddycurrents.
Laguerre–Gaussian beam electromag-
land pattern a combination of lands in-
netic beam solution of the paraxial wave
tended for the mounting, interconnection,
equation in which the field is a product of
andtestingofaparticularcomponent.
aLaguerrepolynomialandaGaussianfunc-
tionofdistancefromthebeamaxis.
Landauer formula describes the con-
ductanceasafundamentalpropertyofwave
Lambdip decreaseinoutputpowerofa
(electron)transmissionthroughastructure.
Doppler-broadened standing-wave laser os-
cillator as a function of length tuning when
Lange coupler four coupled lines used
the resonant frequency is within approxi-
with interconnections to provide tight cou-
mately one homogeneous linewidth of gain
pling. Apracticalimplementationtoincrease
center; results from the interaction of both
thecouplingbetweenedge-coupledlinesby
the right and left travelling waves with the
usingseverallinesparalleltoeachother, so
sameatomsforline-centertuning.
that the fringing fields at edges of the line
contributetocoupling.
lambdasystem a3-levelsysteminwhich
thelowesttwoenergystatesarecoupledby
Langevin, Paul (1872–1946) Born:
electromagneticfieldstoacommoninterme-
Paris,France
diate state of higher energy. This system is
sonamedbecauseschematicrepresentations Langevinisbestknownasthedeveloperof
of it often look like the capital Greek letter echolocation,whichistheprecursortomod-
lambda,3. ernsonar. Langevinwasthefirsttodescribe
paramagnetismanddiamagnetism.
Lambert’scosinelaw alawstatingthat,
for a ideal matte (Lambertian) surface, the LAOS Seelight-amplifyingopticalswitch.
apparentbrightnessofthesurfaceispropor-
tionaltothecosineoftheangleofincidence
andindependentofboththeangleofreflec- lapwinding anarmaturewindingonaDC
tionandthephaseanglebetweentheincident machineinwhichthetwoendsofeachcoil
andreflectedbeams. are connected to adjacent bars on the com-
mutatorring. Thelapwindingprovides“P”
Lambertian source a source whose di- parallelpathsthroughthearmaturewinding,
rectionalemissionpatternfollowsLambert’s where P is the number of poles in the ma-
law;acosinevariation. chine.
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Laplace’s equation a partial differen- Laplacianpyramid asetofLaplacianim-
tial equation mathematically described by agesatmultiplescalesusedinpyramidcod-
r2(cid:30) D 0, where r2 is the Laplacian and ing. AninputimageG isGaussianlowpass
1
(cid:30)istheequation’ssolution. filteredanddownsampledtoformG . Typi-
2
callyG isonequarterthesizeofG ,i.e.,it
2 1
Laplace, Pierre-Simon, Marquis de isdownsampledbyafactorof2ineachdirec-
(1749–1827) Born: Beaumont-en-Auge, tion. G isupsampledandGaussianlowpass
2
Normandy,France filteredtoformR whichisthensubtracted
1
Laplace is best known for his develop- fromG togiveL . Theprocessthenrepeats
1 1
ment of basic tools of mathematical anal- using G as input. The sets of multiresolu-
2
ysis including the Laplace transform, the tion images so generated are called “pyra-
Laplace theorem, and the Laplace coeffi- mids”: G1 ...Gn formaGaussianpyramid;
cients. LaplacestudiedinPariswiththegreat L1...LnformaLaplacianpyramid.
mathematician Jean d’Alembert. Laplace
was heavily involved in politics throughout lapped orthogonal transform (LOT) a
hiscareerandheldmanygovernmentposts. criticallysampledblocktransform,wherethe
Laplace’stheoreticalworkwasheavilyinthe blocks overlap, typically by half a block.
fieldofcelestialmechanics. Hehelpedtoes- EquivalentlytheLOTisacriticallysampled
tablish the mathematical basis for the field filterbank,wheretypicallythefilterlengths
and in doing so confirmed significant parts areequaltotwicethenumberofchannelsor
ofNewton’swork. filters. TheLOTwasmotivatedbyreducing
theblockingeffectintransformcodingbyus-
Laplace transform the transform of a ingoverlappingblocks. Acosinemodulated
functionf.t/givenby filterbankisatypeofLOT.
Z
1
F.s/D f.t/e−stdt largecell cellwiththeradiusof5–35km
−1 (suchasthosefoundinGroupeSpecialMo-
bilesystems). Seealsocell.
wheres DaCj!isacomplexvariable. The
one sided or unilateral Laplace transform is
large disturbance a disturbance for
given by the same equation except that the
which the equation for dynamic operation
lower limit is 0 and not −1. The region
cannotbelinearizedforanalysis.
of convergence of the Laplace integral is a
vertical strip R in the s-plane. The inverse
large-scale integration (LSI) (1) term
Laplacetransformisgivenby
usuallyusedtodescribethelevelofintegra-
Z
tionatwhichentireintegratedcircuitscanbe
f.t/D1=.2(cid:25)j/ F.s/estds placedonasinglechip.
L
(2)anintegratedcircuitmadeofhundreds
where L is a vertical line in R. The Fourier tothousandsoftransistors.
Transformoff.t/isgivenbyF.j!/.
large-scaleprocess(system) partitioned
Laplacianoperator thesecond-orderop- complexprocess(system)composedofsev-
erator, defined in Rn as r2 D @2=@x2 C eral sub-processes (subsystems) that are ei-
1
(cid:1)(cid:1)(cid:1)C@2=@n2. The zero crossings of an im- ther physically interconnected or must be
agetowhichtheLaplacianoperatorhasbeen considered jointly due to the nature of the
applied usually correspond to edges, as in controlobjectives.
suchpointsapeak(trough)ofthefirstderiva-
tivecomponentscanbefound. Alsosimply LASCR See light-activated silicon
calledtheLaplacian. controlledrectifier
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laser acronymthatstandsforlightampli- laser transition transition in a medium
ficationbystimulatedemissionofradiation. that has the capability of exhibiting more
Usuallyreferstoanoscillatorratherthanan stimulatedemissionthanabsorptionorspon-
amplifier; commonly also refers to similar taneousemission.
systemsthatoperateatnon-opticalfrequen-
ciesorwithnonelectromagneticwavefields. last-in-first-out(LIFO) Seefirst-in-last-
out.
laseramplifier usuallyreferstoamedium
thatamplifieslightbytheprocessofstimu- latch asmalltemporaryholdingcellfora
latedemission;sometimesreferstoamplifi- value,thevalueontheinputwiresisbuffered
cation of some other field (nonoptical elec- upon occurrence of some event, such as a
tromagnetic,phonon,exciton,neutrino,etc.) clockpulseorrisingedgeofaseparatelatch
orsomeotherprocess(nonlinearoptics,Bril- signal.
louinscattering,Ramanscattering,etc.).
latency (1) total time taken for a bit to
laser array systematic distribution of passthroughthenetworkfromorigintodes-
lasersintendedtoprovidemorepowerthana tination.
singlelaser. (2)thetimebetweenpositioningaread/write
head over a track of data and when the be-
laser beam localized electromagnetic ginningofthetrackofdatapassesunderthe
fielddistributionproducedbyalaser. head.
lateral (1)alateralonaprimarydistribu-
laserefficiency outputpowerfromalaser
tion line is a short tap from the main distri-
divided by the input power (sometimes the
butionlinewhichservesalocalsetofloads.
pumppowerintothelasermediumandsome-
Singlephaselateralsarecommoninresiden-
timesthewall-plugpower).
tialdistricts.
(2) a three-phase or single-phase power
lasermedium thematerialinalaserthat
line which supplies the distribution trans-
emitslight;itmaybeagas,solid,orliquid.
formersalongastreet. Seefeeder.
laseroscillator oscillatorusuallyproduc-
lateral inhibition in the human visual
ing an optical frequency output and usually
system,theinhibitoryeffectbetweennearby
based on amplification by stimulated emis-
cellswhichactstoenhancechanges(tempo-
sioninaresonantcavity.
ralorspatial)inthestimulus.
laserpumping mechanismforobtaining
lateralsuperlattice referstoalithograph-
apopulationinversioninalasermedium;the
ically defined structure in which a periodic
useofalaserbeamtopumpanotherlaser.
(superlattice) potential is induced onto the
surfaceofanormalsemiconductor(ormetal-
laserthreshold theconditionunderwhich lic)system. Sincetheperiodicpotentialisin-
the round-trip gain in a laser is equal to the ducedinthelateralvariationsofthesurface,
round-triploss. itiscalledalateralsuperlattice.
lasertransient atime-dependentlaserbe- lateralwave wavegeneratedbyabeamof
havior such as mode-locking, loss switch- boundedextentincidentatananglecloseto
ing, spontaneous pulsations, relaxation os- thecriticalangle. Itmanifestsbyproducing
cillations. alateralshiftoftheboundedreflectedwave.
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latticeconstant thelengthofthesidesof and drain-source impedance ro is shown as
thethreedimensionalunitcellinacrystal. anexample;itcanbesubstitutedbyabipolar
transistor; this essentially does not change
latticestructure afilterusedinlinearpre- the results), a load resistor, and three reac-
dictionthathastwooutputs,theforwardpre- tances (if X and X are coils, the mutual
1 2
dictionerrorfmTnUandthebackwardpredic- reactanceXmshouldbeconsideredaswell).
tionerrorgmTnU. Thesetwoerrorsignalsare The frequency of oscillation is given by
definedrecursively:
thecondition
fmTnUDfm−1TnUCKmgm−1Tn−1U
gmTnUDKm(cid:3)fm−1TnUCgm−1Tn−1U X1CX2CX3C2Xm D0
wheretheKm arethecalledthelatticecoef- and the threshold condition for self-starting
ficientsofthepredictor. is
r R X CX
lattice vector quantization (1) a struc- g o L (cid:21) 2 m
m
tured vector quantizer where the reproduc- roCRL X1CXm
tionvectorsarechosenfromahighlyregular IfX isatunedcoilinthegate,X isthedrain
1 2
geometrical structure known as a “lattice.” coil,2Xm isthemutualinductancebetween
Themethodisemployedmainlybecauseof
thetwocoils,thecircuitiscalledtuned-gate
the reduction in storage capacity obtained
oscillator,ifthesingletunedcircuitismoved
(comparedtooptimalvectorquantization).
intothedrain,thecircuitiscalledtuned-drain
(2)vectorquantization,wherecodewords
oscillator. Other frequently used configura-
representprototypevectorsarrangedinareg-
tions are Colpitts oscillator and Hartley os-
ularlatticeinn-dimensionalspace.
cillator.
latticeVQ Seelatticevectorquantization.
LCD Seeliquidcrystaldisplay.
lawofexcludedmiddle alogicallawstat- LCI Seeload-commutatedinverter.
ing that for Boolean variable X, X must be
eitherZornotZ. LCLV Seeliquidcrystallightvalve.
law of the first wavefront See Haas
LDD Seelightlydopeddrain.
effect.
lead a conductive path, usually self-
layout specifies the position and dimen-
supporting;theportionofanelectricalcom-
sion of the different layers of materials as
ponentthatconnectsittooutsidecircuitry.
theywouldbelaidonthesiliconwafer.
LC-oscillator a type of oscillator that is lead circuit a simple passive electronic
practicalatthefrequenciesabove50kHzand circuit designed to add a dominant zero to
up to 500 MHz, where it is rational to use compensatetheperformanceofagivensys-
high-Q tuned circuits for frequency selec- tem. Itisgenerallyusedtomakeanoscilla-
tion (as a result, sometimes they are called tory system more damped. A nondominant
tuned-circuitoscillators). Itisimpossibleto pole must be included to make the circuit
classify all circuits of LC-oscillators, yet a causal. This pole also limits the high fre-
widegroupofLC-oscillatorsarereducedto quencygainoftheleadcircuit,therebyavoid-
thecircuitthatincludesoneactivedevice(a ingexcessiveamplificationandtransmission
FET characterized by transconductance gm ofundesirablenoise.
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leadframe themetallicportionofthede- antennainplacessuchastunnelsandmines
vice package that makes electrical connec- wheretherangeofradiopropagationislim-
tionsfromthedietoothercircuitry. ited. Comparewithdistributedantenna.
leadlanthanumzirconiumtitanate(PLZT) leakymodes Seetunnelingmodes.
aquadraticelectro-opticmaterialwherethe
refractive index changes quadratically with
leaky wave a wave that radiates sig-
applied electric field. Commonly available
nal power out of an imperfectly closed and
asahot-pressedpolycrystallineceramic,al-
shielded system. Open waveguides are
thoughsingle-crystalfilmisbeingdeveloped.
able, under certain circumstances, to pro-
duceleakywaves,whichcanbeusedforra-
leader anelongatedregionofionizedgas
diation purposes. In this case, a leaky an-
that extends from one electrode to another
tennacouplespowerinsmallincrementsper
justbeforeahigh-voltagebreakdown.
unitlength,eithercontinuouslyordiscretely,
fromaboundmodeoftheopenwaveguide.
leader-follower game See Stackelberg
equilibrium.
learning in neural networks, the collec-
tionoflearningrulesorlawsassociatedwith
leading-edge triggered pertaining to a
eachprocessingelement. Eachlearninglaw
device that is activated by the leading edge
is responsible for adapting the input–output
ofasignal.
behavior of the processing element transfer
functionoveraperiodoftimeinresponseto
leakage thefluxinamagneticcircuitthat
the input signals that influence the process-
doesnotdoanyusefulwork.
ing element. This adaptation is usually ob-
tainedbymodificationofthevaluesofvari-
leakageflux thefluxthatdoesnotlinkall
ables(weights)storedintheprocessingele-
theturnsofawindingorincoupledcircuits,
ment’slocalmemory.
flux that links one winding but not another.
Sometimesneuralnetworkadaptationand
Forexample,themagneticfluxproducedby
learning can take place by creating or de-
theprimarywindingofatransformerthatis
stroyingtheconnectionsbetweenprocessing
notcoupledtothesecondarywinding.
elements. Learningmaybealsoachievedby
replacingthetransferfunctionofaprocess-
leakagereactance theamountofinduc-
ingelementbyanewone.
tive reactance associated with leakage flux.
Theleakagefluxisthefluxwhichtraversesin
learninglaw Seelearningrule.
pathsfartherfromthedesignatedpathssuch
asthemagneticcoreintransformersandthe
air gap in electric machines and constitutes learning rate a parameter in a learning
thenon-usefulflux. Theelectriccircuitsym- rulewhichdeterminestheamountofchange
bolofleakagereactanceisXl. Itisafunction for a parameter during the current iteration.
oftheleakageinductanceandthefrequency Whilealargevaluemayincreasetherateof
ofoperation. Highervaluesofleakagereac- learning,itmayalsopreventalearningalgo-
tance affect the regulation and efficiency of rithmfromconverging.
thesystem. Xl isexpressedinohms.
learningrule inneuralnetworks,anequa-
leakyfeeder anantennaconsistingofaca- tionthatmodifiestheconnectionweightsin
ble that continuously radiates a signal from response to input, current state of the pro-
allpointsalongtheentirelengthofthecable. cessingelement,andpossibledesiredoutput
Suchacableistypicallyusedastheradiating oftheprocessingelement.
(cid:13)c2000byCRCPressLLC
learning vector quantization (LVQ) a least squares an approach to determin-
supervisedlearningalgorithmfirstproposed ing the optimal set of free parameters wE
by Kohonen that uses class information to of an input-output mapping yE D FE.xE;wE/,
move the Voronoi vectors slightly, so as to wherebythesquareofthedifferencebetween
improvethequalityoftheclassifierdecision the output of the functionyE and the desired
regions. outputdEisminimized.
The training algorithm for LVQ is simi-
lar to its unsupervised counterpart with su- least squares algorithm an adaptive al-
pervised error correction. After the winner gorithmthatadjuststheweightsofadigital
is found, the weights of the winner and its filter to minimize a least squares (LS) cost
neighbors will be updated according to the criterion. Forequalization,thiscostcriterion
followingrules: is
Xi
Iftheclassiscorrect,
wi−kjb −y j2
k k
wi.t C1/Dwi.t/C(cid:11)(cid:1).xi.t/−wi.t//; kD1
wherebk isthetransmittedsymbol,yk isthe
otherwise filter output, both at time i, and where w is
an exponential weighting factor which dis-
wi.t C1/Dwi.t/−(cid:11)(cid:1).xi.t/−wi.t//; countspastdata.
Seealsoself-organizingsystem,self-organiz-
least squares filter the optimal filter,
ingalgorithm.
in the least squares sense, for restoring a
corrupted signal. Specifically, given obser-
least mean square (LMS) algorithm vations of a signal xTnU, the least squares
in some cases of parameter estimation for filtPer produces the xOTnU, which minimizes
stochastic dynamic systems, it is not feasi- ET jxTnU−xOTnUj2U. SeealsoWienerfilter.
bletousetheleastsquaresbasedalgorithms
due to the computational effort involved in
leastsquaressolution thesetoffreepa-
updating and storing the P.t/ (probability)
rametersthatsatisfiestheleastsquarescrite-
matrix. Thisisespeciallysowhenthenum-
rion.
ber of parameters is large. In this case, it
is possible to use a variant of the stochastic least-significant bit (LSB) in a binary
gradientalgorithm—theleastmeansquare word,abitwiththelowestwightassociated
(LMS)algorithm,whichhastheform withit.
(cid:18)O.t C1/D(cid:18)O.t/C(cid:30).t/.y.t C1/
least-square-errorfit analgorithmorset
−(cid:30)T.t C1/(cid:18)O.t// ofequationsresultingfromfittingapolyno-
mialorothertypecurve,suchaslogarithmic,
where(cid:18)O isaparameter’sestimatesvector,(cid:30) todatapairssuchthatthesumofthesquared
isaregressorvector. errors between data points and the curve is
minimized.
least recently used (LRU) algorithm a
replacementalgorithmbasedonprogramlo- LED Seelightemittingdiode.
calitybywhichthechoiceofanobject(usu-
ally a page) to be removed is based on the LEF Seelightingeffectivenessfactor.
longest time since last use. The policy re-
quiresbookkeepingofessentialinformation left-handcircularpolarization thestate
regarding the sequence of accesses, which ofanelectromagneticwaveinwhichtheelec-
maybekeptasLRUbitsorasanLRUstack. tric field vector rotates anticlockwise when
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viewedinthedirectionofpropagationofthe Lempel-Ziv-Welch (LZW) coding a
wave. variantofthedictionary-basedcodingscheme
inventedbyZivandLempelin1978(LZ78),
left–rightmodels typicalhiddenMarkov wherestringsofsymbolsarecodedasindices
models adopted in automatic speech recog- into a table. The table is built up progres-
nition. Thestatediagramforthesemodelsis sively from the input data, such that strings
adirectedacyclicgraph,thatis,thereareno alreadyinthetableareextendedbyonesym-
cyclesapartfromself-loops. boleachtimetheyappearinthedata.
legacy system applications that are in a
lengthenedcode acodeconstructedfrom
maintenance phase but are not ready for re-
anothercodebyaddingmessagesymbolsto
tirement. thecodewords. Thusan.n;k/originalcode
becomes, after the adding of one message
Legendrefunctions acollectionoffunc- symbol,an.nC1;kC1/code.
tions,typicallydenotedasP(cid:23).x/andQ(cid:23).x/,
thatsatisfyLegendre’sequation:
lens opticalelementforfocusingordefo-
d2f df cusingelectromagneticwaves.
.1−x2/ −2x C(cid:23).(cid:23)C1/f D0;
dx2 dx
where f is equal to either P(cid:23) or Q(cid:23); (cid:23) is lensaberrations anydeviationofthereal
the order of the function and x is its argu- performanceofanopticalsystem(lens)from
ment. Typically,Legendrefunctionsarisein itsidealperformance. Examplesoflensaber-
boundaryvalueproblemsthatarebasedupon rations include coma, spherical aberration,
asphericalcoordinatesystem. field curvature, astigmatism, distortion, and
chromaticaberration.
Leibniz’sformula aformulathatissatis-
fiedbythethreetypesofLiederivatives, lensarray atwo-dimensionalarrayof(of-
LTf;gUhDhrh;Tf;gUiDLgLfh−LfLgh: tensmall)lensesfabricatedonasinglesub-
strate.
Leibniz, Gottfried Wilhelm (1646–
lensdesign themathematicaldetermina-
1716)Born: Leipzig,Germany
tionoftheparametersoftheopticalelements
Leibniz is best known for his work in
in an optical instrument or system required
mathematics. Leibniz’s work was an im-
to satisfy its performance goals. Rays are
portant contribution to the development of
tracedthroughthesystemtopredictitsper-
differentialcalculusandlogic. Leibnizalso
formance and then changes of one or more
improvedPascal’searlycalculatingmachine,
parameters are made to improve its perfor-
extendingitscapacitytoincludemultiplica-
mance. Nowperformedusingcomputersoft-
tion and division. Leibniz’ later years were
warepackages.
embitteredbythechargethathehadplagia-
rized some of Isaac Newton’s work on the
lensletarrayinterconnect free-spacein-
developmentofthecalculus. Subsequentin-
terconnectthatuseslensletarraystocontrol
vestigations have proved this charge to be
opticalpathsfromsourcestodetectors. Each
baseless.
lensletimagesthesourcearrayontothede-
Lempel–Ziv coding See Ziv–Lempel tector array. It has no property of dynamic
coding. reconfiguration.
Lempel–Ziv compression See Ziv– lenslikemedium beampropagationmed-
Lempelcoding. iuminwhichthegainandindexofrefraction
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mayhavelinearorquadraticvariationswith 1. The derivative of a vector field with
distanceawayfromtheopticalaxis. respect to a vector field that is also known
as the Lie bracket. If f;g V Rn ! Rn are
levelcrossingrate Seefadingrate. twodifferentiablevectorfields,thentheirLie
bracketis
level-1cache insystemswithtwoseparate @f @g
setsofcachememorybetweentheCPUand Tf;gUD g− f ;
@x @x
standard memory, the set nearest the CPU.
Level-1 cache is often provided within the where @f and @g aretheJacobianmatricesof
@x @x
sameintegratedcircuitthatcontainstheCPU.
thevectorfieldsf andg,respectively. Often
Inoperation,theCPUaccesseslevel-1cache
thenegativeoftheaboveisused.
memory; if level-1 cache memory does not 2.Thederivativeofafunctionhwithre-
contain the required reference, it accesses
specttoavectorfieldf definedas
level-2cachememory,whichinturnaccesses
standardmemory,ifnecessary. L hDhrh;fiD.rh/T f ;
f
level-2 cache in systems with two sepa- whererhVRn !Rnisthegradientofh.
ratesetsofcachememorybetweentheCPU 3. The derivative of dh D .rh/T with
andstandardmemory,thesetbetweenlevel-1 respecttothevectorfield,
cacheandstandardmemory. (cid:18) (cid:19)
@rh T @f
L .dh/D f C.rh/T :
level-sensitive pertainingtoabistablede- f @x @x
vicethatusesthelevelofapositiveornega-
SeealsoLeibniz’sformula.
tivepulsetobeappliedtothecontrolinput,
tolatch,capture,orstorethevalueindicated
lifetimebroadening aspectrallinebroad-
bythedatainputs.
ening mechanism that is a consequence of
the finite lifetime of the excited state. Nu-
level-triggered Seelevel-sensitive.
merically, the lifetime broadened linewidth
isequaltotheinverselifetimeoftheexcited
Levenshteindistance Seeeditdistance.
state.
LFSR Seelinear-feedbackshiftregister. LIFO Seefirst-in-last-out.
Liapunoff SeeLyapunov,AlexandrM. lift-offprocess alithographicprocessby
whichthepatterntransfertakesplacebycoat-
Liapunov SeeLyapunov,AlexandrM. ing a material over a patterned resist layer,
thendissolvingtheresistto“liftoff”thema-
Lichtenburgfigure apatternproducedon terialthatisontopoftheresist.
apowder-coatedflatelectrodeoruponphoto-
graphicfilmheldbetweenapairofflatelec- light emitting diode (LED) a forward-
trodes subjected to a high voltage impulse biased p-n junction that emits light through
asfromalightningstroke. Impulsepolarity, spontaneous emission by a phenomenon
magnitude and waveform can be estimated termedelectroluminescence.
byexaminationofitscharacteristicpattern.
light guide system of lenses, mirrors,
lid thefuse-holderportionofacut-out. gradedindex,orgradedgainmediathathas
thecapabilityofovercomingdiffractionand
Liederivative oneofthreetypesofspe- guiding an electromagnetic wave at optical
cialderivatives. frequencies.
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lightlossfactor(LLF) theratiooftheil- oflightingisusuallyrequired. Otherapplica-
luminationwhenitreachesitslowestlevelat tionshaveotherrequirementsforuniformity,
thetaskjustbeforecorrectiveactionistaken, frequency,andintensity.
totheinitiallevelifnoneofthecontributing Structured lighting schemes are used to
lossfactorswereconsidered. collectmultipleimagesofasceneeachhav-
ing different illumination .
lightpen aninputdevicethatallowsthe Strobe lights can be used to effectively
user to point directly to a position on the freezemotion,andare usefulformany visual
screen. This is an alternative to a mouse. inspection tasks. See also structured light.
Unlikeamouse,alightpendoesnotrequire
anyhand/eyecoordinationskills,becausethe
userspointtowheretheylookwiththepen.
lightly doped drain (LDD) in an MOS
transistor, an extension to the source/drain
lightscattering (1)spreadingofthelight
diffusion that is separated slightly from the
asitpassesorisreflectedbyanopticallyin-
gate region which contains lower doping
homogeneousmedium.
thanthatusedforthesource/draindiffusions.
(2) the process in which a beam of
Since the source and drain diffusions are
light interacts with a material system and
heavily doped, the lightly doped extension
becomes modified in its frequency, polar-
tendstoincreasethewidthofthedepletionre-
ization, direction of propagation, or other
gionaroundthedrainwhichlowerstheelec-
physical property. See also spontaneous
tricfieldintensity,toincreasethebreakdown
light scattering, stimulated light scattering,
voltageofthedrainregionofdeepsubmicron
Brillouinscattering,Ramanscattering.
devices.
lightvalve Seespatiallightmodulator.
lightning arrestor a voltage-dependent
resistor which is connected in parallel with
light-activated silicon controlled rectifier
lightning-susceptible electrical equipment.
a silicon controlled rectifier in which the
Itprovidesalow-resistanceelectricalpathto
gate terminal is activated by an optical sig-
ground during overvoltage conditions, thus
nalratherthananelectricalsignal.
divertingdestructivelightningenergyaround
theprotectedequipment.
light-amplifyingopticalswitch(LAOS)
vertically integrated heterojunction photo-
lightning choke one of several arrange-
transistor and light emitting diode that has
ments of conductors, usually a single or
latching thyristor-type current-voltage char-
multi-turncoil,usedtoreducelightningcur-
acteristics.
rentsbyincreasingapowerline’simpedance
atlightningfrequencies.
lighting effectiveness factor (LEF) the
ratioofequivalentsphereilluminationtoor-
lightwavecommunications opticalcom-
dinarymeasuredorcalculatedillumination.
munications techniques that used guided
waveopticaldevicesandfiberoptics.
lightingsystem anyschemeusedforillu-
minatingascene,usuallyforacquisitionbya
digitalsystem. Illuminationiscrucialtodig- lightwave technology technology based
italimages,sinceevenilluminationgradients ontheuseofopticalsignalsandopticalfiber
thatcannotbeperceivedbytheeyecanhave forthetransmissionofinformation.
aninfluenceontheresultsofdigitalprocess-
ing. Forinspectiontasksanddocumentdig- likelihood ratio the optimum processor
itization,auniform,reproducable,highlevel for reducing a set of signal-detection mea-
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