Table Of Contentratio of the power per unit solid angle scat-
teredinaspecificdirectionofthepowerunit
R
areainaplanewaveincidentonthescatterer
fromaspecifieddirection.
RADHAZ radiationhazardstopersonnel
asdefinedinANSI/C95.1-1991IEEEStan-
RS commonly used symbol for source
dard Safety Levels with Respect to Human
impedance.
Exposure to Radio Frequency Electromag-
neticFields,3kHzto300GHz.
RT commonlyusedsymbolfortransfor-
mationratio.
radial basis function network a fully
R-ALOHA SeereservationALOHA. connected feedforward network with a sin-
gle hidden layer of neurons each of which
RL Typicalsymbolforloadresistance. computesanonlineardecreasingfunctionof
the distance between its received input and
Rabi frequency the characteristic cou- a “center point.” This function is generally
plingstrengthbetweenanear-resonantelec- bell-shaped and has a different center point
tromagnetic field and two states of a quan- for each neuron. The center points and the
tum mechanical system. For example, the widths of the bell shapes are learned from
Rabifrequencyofanelectricdipoleallowed trainingdata. Theinputweightsusuallyhave
transitionisequalto(cid:22)E/hbar,where(cid:22)isthe fixed values and may be prescribed on the
electric dipole moment and E is the maxi- basisofpriorknowledge. Theoutputshave
mum electric field amplitude. In a strongly linear characteristics, and their weights are
driven2-levelsystem,theRabifrequencyis computedduringtraining.
equal to the rate at which population oscil-
latesbetweenthegroundandexcitedstates.
radial intensity histogram a histogram
of average intensities for a round object in
racecondition asituationwheremultiple
circular bands centered at the center of the
processesaccessandmanipulateshareddata
object,withradialdistanceastherunningin-
with the outcome dependent on the relative
dex. Suchhistogramsareeasilyconstructed,
timingoftheseprocesses.
and, suitablynormalised, formthebasisfor
scrutinizing round objects for defects, and
raceway a channel within a building
formeasuringradiusandradialdistancesof
whichholdsbareorinsulatedconductors.
cylindricallysymmetricalfeatures.
radar an instrument that transmits elec-
tromagneticwavesandreceivespropertiesof radialsystem anetworkofstraightwires
thereflectedelectromagneticwavefromthe or other conductors radiating from the base
target, which can be used to determine the ofaverticalmonopoleantennathatsimulates
natureanddistancetothetarget. Radarisan the presence of a highly conducting ground
acronym that stands for radio detection and plane beneath the antenna. Typically, ra-
ranging. dialwiresareapproximatelyaquarterwave-
lengthlongandarearrangedtohaveequian-
radarcrosssection(RCS) ameasureof gularspacingbetweenthem. Theradialwire
thereflectivestrengthofaradartarget;usu- endsatthebaseofthemonopoleareelectri-
ally represented by the symbol s, measured cally bonded together and to one conductor
insquaremeters,anddefinedas4(cid:25)timesthe ofthefeedline.
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radiated emission an electromagnetic radiationefficiency inantennatheory,the
fieldpropagatedthroughspace. ratioofradiatedpowertotheamountofinput
powertotheantenna. Hasavaluebetween0
radiatingaperture abasicelementofan and1,inclusive.
antennathatinitselfiscapableofeffectively
radiating or receiving radio waves. Typical radiation intensity in antenna theory, a
example of a radiating apertures are a slot, far-field quantity that is a function of angle
and horn antennas or a truncated metallic thatgivesthelevelofradiationinaspecific
waveguide. direction. Radiation intensity is the radial
componentofthetimeaveragePoyntingvec-
torwithallthetermsassociatedwiththedis-
radiation the phenomenon by which
tancefromtheantennanormalizedout. The
sources generate energy, which propagates
unitsarewattspersquareradian.
awayfromthemintheformofwaves.
radiationpattern aplotofthefar-fieldra-
radiationboundarycondition(RBC) a
diationasafunctionoftheanglephiortheta
boundary condition that is imposed to trun-
whiletheotherangleisheldconstant. Ara-
catethecomputationaldomainofadifferen-
diationpatterncanbeeitherpolarorrectan-
tial equation method so that it satisfies the
gular,andcanbeeitherlogarithmicorlinear.
Sommerfieldradiationcondition.
radiative broadening a spectral line
radiation condition the condition that broadening mechanism that arises due to
specifiesthefieldbehavioratinfinity;infact, spontaneousdecayoftheexcitedstate.
for an unbounded domain it is necessary to
specify the field behavior on the surface at radiative heat transfer the process by
infinity. By assuming that all sources are which long-wave electromagnetic radiation
contained in a finite region, only outgoing transportsheatfromasurfacetoitssurround-
wavesmustbepresentatlargedistancesfrom ings.
thesources;hencethefieldbehavioratlarge
distances from the sources must meet the radioastronomy thestudyofcelestialob-
physicalrequirementthatenergytravelaway jectsbasedontheinvestigationoftheirradio
fromthesourceregion. Thisrequirementis frequencyelectromagneticwavesspectrum.
the Sommerfield “radiation condition” and
constitutesaboundaryconditiononthesur- radiofrequency(RF) ageneraltermused
face at infinity. Let us denote with A any to refer to radio signals in the general fre-
fieldcomponenttransversetotheradialdis- quency range from thousands of cycles per
tancer andwithk thefree-spacewavenum- second(kHz)tomillionsofcyclespersecond
ber. The transverse field of a spherically (MHz). Itisalsooftenusedgenericallyand
diverging wave in a homogeneous isotropic interchangeablywiththetermmicrowaveto
medium decays as 1=r at large distances r distinguishthehighfrequencyACportionof
from the source region; locally, the spher- a circuit or signal from the DC bias signal
ical wave behaves like a plane wave travel- orthedownconvertedintermediatefrequency
lingintheoutwardrdirection. Assuch,each (IF)signal.
fieldcomponenttransversetor mustbehave
likeexp.−jkr/=r; thisrequirementmaybe radiofrequencychoke aninductance(a
phrasedmathematicallyas coilofwire)intendedtopresentaveryhigh
impedance at radio frequencies. Such fre-
(cid:18) (cid:19)
@A quenciesspantherangeofkilohertztohun-
lim r CjkA D0
r!1 @r dredsofmegahertz.
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radiofrequencyintegratedcircuit(RFIC) radius of curvature one of the parame-
integratedcircuitdesignedtooperateatra- terscharacterizingthereflectingsurfaceofa
dio frequencies as amplifiers, mixers, oscil- sphericalmirror.
lators, detectors or combinations of above.
Typically,RFICsareconfiguredforspecific radix the base number in a number sys-
applicationtooperateasacompleteRFsys- tem. Decimal(radix10)andbinary(radix2)
tem. aretwoexamplenumbersystems.
radio frequency interference (RFI) radixcomplement inasystemthatuses
electromagnetic phenomenon that either di- binary(base2)datanegativenumbers,canbe
rectly or indirectly contributes to degrada- represented as the two’s complement of the
tionintheperformanceofareceiverorother positive number. This is also called a true
RF system, synonymous with electromag- complement.
neticinterference. Seealsoelectromagnetic
interference. Radontransform theRadontransformof
afunctionf.x;y/;r.d;(cid:30)/isitslineintegral
along a line inclined at angle (cid:30) from the y
radiohorizon themaximumrange,from
axisandatadistanced fromtheorigin.
transmittertoreceiveronEarth’ssurface,of
direct (line-of-sight) radio waves. This is
radwaste a contraction for "radioactive
greaterthantheopticalhorizon,becausethe
waste," usually referring to mildly radioac-
radiowavesfollowacurvedpathasaresult
tive sludge removed from the coolant in a
of the continuous refraction it undergoes in
nuclearreactor.
theatmosphere.
RAID Seeredundantarrayofinexpensive
radiolocalloop Seewirelesslocalloop.
disks.
radio waves electromagnetic radiation RAKEreceiver areceivertypeinwhich
suitable for radio transmission in the range thereceivedsignalfromeach(orafewdomi-
of frequencies from about 10 kHz to about nating)resolvablepropagationrayisindivid-
300Mhz. ually demodulated and subsequently com-
bined into one decision variable according
tosomecriterion. RAKEreceiversarecom-
radiography an imaging modality that
monly used in wideband transmission sys-
usesanX-raysourceandcollimatortocreate
temssuchasspread-spectrumsystemswhere
a projection image. The image intensity is
thelargebandwidthallowsseveralraystobe
proportional to the transmitted X-ray inten-
resolved, thuscreatingadiversitygain(fre-
sity.
quencydiversity).
radiology the monitoring and control of
RAM Seerandomaccessmemory.
radioactivity, especially in regard to human
exposure,inanuclearpowerplant.
RAM neuron a random access memory
with n inputs and a single output. The in-
radiometer apassivereceiverthatdetects putsdefine2naddressesandpresentationof
energy from a transmitting source or rera- aparticularinputvectorallowsthecontents
diated energy from a target. Typically, ra- ofthe1-bitregisteratthataddresstoberead,
diometers are used in remote sensing appli- or to be written into. Training consists of
cations. writing 1s or 0s into the 1-bit registers, as
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required for the various input vectors in the Raman–Nath diffraction in acousto-
trainingset. optics,theregimewheremanydiffractionor-
dersexistduetothethinnessoftheacoustic
gratingrelativetotheacousticwavelengthin
RAMA See resource auction multiple
thedirectionoflight.
access.
Raman–Nathdiffractionregime regime
ram’shead thetopofatransmissionline
wheretheacousticbeamwidthissufficiently
tower
narrow to produce many diffracted beams
withsignificantpower.
Raman echo a type of photon echo in
whichthestimulatedemissionisassistedby
Raman–Nath mode acousto-optic spec-
aRamantransition.
trum analyzer similar to the acousto-
optic (AO) Bragg-mode spectrum analyzer,
Ramanlaser laserinwhichtheamplifi- butusesilluminationatnormalincidenceto
cationmechanismisconsideredtobeRaman thefaceoftheAOcellthatresultsinmulti-
scattering. plediffractedorders,withthetwofirstorder
beamsbeingusedattheFourierplanetoob-
Raman scatter frequency-shifted light taintheinputRFsignalspectrum.
scatter,utilizedaspowerfulanalyticalchem-
istrytechnique. Raman–Nath scattering the scattering
of light from a periodically varying refrac-
tiveindexvariationinathinmedium,ascon-
Raman scattering scattering of light by
trastedwithBraggscattering,forinstancein
meansofitsinteractionswiththevibrational
theoperationofanacousto-opticmodulator.
response of a molecular system. The scat-
tered light is typically shifted to lower fre-
ramp a linear function of grey level,
quencies ( See Stokes Law); the frequency
usually connecting two contrasting regions.
shift is equal to the vibrational frequency
of the molecule, typically 1013 to 1014 Namedafteritsappearanceinonedimension,
itisoftenusedasonemodelofanedge.
Hz. In spontaneous Raman scattering ( See
spontaneous light scattering), the scattered
light is emitted in nearly all directions. In Ramseyfringe thespectralfeaturegener-
stimulatedRamanscattering(Seestimulated ated when a quantum mechanical transition
lightscattering),thescatteredlightisemitted is excited by two identical-frequency, time-
in theformofanintensebeam. Theemitted separated electromagnetic pulses. Ramsey
beam tends to be intense because it experi- fringes are used in cesium atomic beam
enceslargeamplificationbyanamountgiven clocks.
byegIL,wheregisthegainfactorofstimu-
latedRamanscattering, I istheintensityof randomaccess (1)termdescribingatype
theincidentlaserbeaminunitsofpowerper of memory in which the access time to any
unitarea,andListhelengthoftheinteraction cellisuniform.
region. (2) a method for allowing multiple users
to access a shared channel in which trans-
Raman, Sir Chandrasekhara Venkata missionsarenotcoordinated(orperhapsare
(1888–1970) author of 500 articles and in- partiallycoordinated)intimeorfrequency.
dependent investigator of light scatter and
acoustics. Winner of a Nobel Prize for the random access device See random
discoveryofRamanscattering. access.
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randomaccessmemory(RAM) direct- random replacement algorithm in a
access read/write storage in which each ad- cacheorapagingsystem, analgorithmthat
dressable unit has a unique hardwired ad- chooses the line or page in a random man-
dressing mechanism. The time to access a ner. A pseudo-random number generators
randomly selected location is constant and maybeusedtomaketheselection, orother
notdependentonitspositionoronanyprevi- approximate method. The algorithm is not
ousaccesses. TheRAMhasasetofkaddress verycommonlyused, thoughitwasusedin
lines(mD2k),nbidirectionaldatalines,and thetranslationbuffersoftheVAX11/780and
asetofadditionallinestocontrolthedirec- theInteli860RISCprocessor.
tion of the access (read or write), operation
andtimingofthedevice. randomsignal asignalX.t/thatiseither
noise N.t/, an interfering signal s.t/, or a
RAM is commonly used for the main
sumofthese:
memoryofacomputerandissaidtobestatic
if power has to be constantly maintained in X.t/Ds .t/C(cid:1)(cid:1)(cid:1)Cs .t/CN .t/C(cid:1)(cid:1)(cid:1)CN .t/
1 m 1 n
order to store data and dynamic if periodic
absences of power do not cause a loss of
data. RAMisusuallyvolatile. Seealsostatic randomtesting theprocessoftestingus-
random access memory, dynamic random ingasetofpseudo-randomlygeneratedpat-
access memory, nonvolatile random-access terns.
memory.
randomvariable acontinuousordiscrete
random behavior response without a valued variable that maps the set of all out-
spectraloramplitudepatternorrelationship comesofanexperimentintotherealline(or
totheexcitation. Theexcitationmaybein- complex plane). Because the outcomes of
ternal,andmaybethermalinnature. anexperimentareinherentlyrandom,thefi-
nalvalueofthevariablecannotbepredeter-
mined.
random coding coding technique in
which codewords are chosen at random ac-
randomvector avector(typicallyacol-
cordingtosomedistributiononthecodeword
umn vector) of random variables. See also
symbols. Commonlyatoolusedinthedevel-
randomvariable,randomprocess.
opmentofinformationtheoreticexpressions.
randomized decision rule a hypothesis
random logic a digital system con-
decision/classification rule that is not deter-
structed with logic gates and flip-flops
ministic (that is, the measurement or obser-
and other basic logic components intercon-
vation does not uniquely determine the de-
nected in an non-specific manner. See also
cision). Althoughtypicallynotusefulgiven
microprogramming.
continuous observations, a randomized rule
canbenecessarygivendiscreteobservations.
random process a mathematical pro- See also receiver operating characteristics
cedure for generating random numbers to curve.
a specific rule called a process, x which
is defined on continuous x.t/;t 2 Rn, range filter an edge detection filter that
or discrete x.k/;k 2 Zn space / time. findsedgesbytakingthedifferencebetween
The value of the process at each point in the maximum and minimum values in a lo-
space or time is a random vector. See also calregionoftheimage. Therangefilteralso
random variable, random vector. See accepts a weight mask the size of the local
alsocorrelation,covariance,autocorrelation, image region that controls pixel values be-
autocovariance. foretheyentertheminimumandmaximum
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calculations. Theweightmaskallowsedges rare gas oxides an excimer molecule
incertaindirectionstobesearchedfor. formed by the reaction of a rare gas atom
andanoxygenatom.
range image an image in which the in-
tensityofpointxisafunctionofthedistance rare-earthmagnet amagnetthathasany
betweenxandthecorrespondingpointinthe oftherare-earthelementsinitscomposition.
scene(object)projectedontheimageplane. Typicallystrongerthanothermagnetmateri-
als,theseincludeneodymiumironboronand
rangeofJacobian denotedJ,itisdefined samariumcobalt.
asasubspaceR.J/inRroftheend-effector-
velocitiesthatcanbegeneratedbythejoint rare-earth permanent magnet magnet
velocities,inthegivenmanipulatorposture. made of compounds of iron, nickel, and
SeefullrankJacobian. cobaltwithoneormoreoftherare-earthel-
ements such as samarium. These materials
rank filter an image transform used in combinethehighresidualfluxdensityofthe
mathematical morphology. Assume that to alnico-typematerialswithgreatercoercivity
everypixelponeassociatesawindowW.p/ thanferrites.
containingit. Letkbeaninteger>1which
islessthanorequaltothesizeofeachwin- raster a predetermined pattern of scan-
dow W.p/. The rank filter with rank k and ninglinesusedtoprovideuniformcoverage
windows W.p/ transforms an image I into of the area used for displaying a television
a filtered image I0 whose gray-level I0.p/ picture.
at pixel p is defined as the k-th least value
amongallinitialgray-levelsI.q/forqinthe
raster coordinates coordinates in a dis-
window W.p/. In a dual version, the k-th
playsystemthatspecificallyidentifyaphys-
greatestvalueisselected. WheneachW.p/
icallocationonthedisplaysurface.
isthetranslatebypofastructuringelement
W ofsizen,threeparticularcasesarenote-
rastergraphics acomputergraphicssys-
worthy:
tem that scans and displays an image peri-
1.k D1: therankfilteristheerosionbyW. odically in a raster, or left-to-right, top-to-
2.k Dn: therankfilteristhedilationbyWe, bottomfashion.
thesymmetricofW.
3. n is odd and k D .n C 1/=2: the rank rasterimage Seebitmappedimage.
filterisamedianfilter. Seedilation,erosion,
medianfilter,structuringelement. raster width (1) physical distance be-
tween raster lines on a display surface and
raregas oneoftheraregasesspecifiedin between distinguishable points in the same
theperiodictable,He,Ne,Ar,Kr,Xe. raster line; the two distances are frequently
different.
rare gas halides excimer molecule (2) the physical distance between raster
formedbyareactionofararegasatomand lines on a display surface and between dis-
ahalogenatom: e.g.,XeF,ArF,KrF. tinguishable points in the same raster line.
Thetwodistancesarefrequentlydifferent.
rare gas molecule excimer molecule
formedbyareactionofanexcitedandaneu- rate distortion function the minimum
tralraregasatom,usuallywithathirdatom rateatwhichasourceisrepresentedbyone
present. Forexample,Ar ,Kr . ofasetofdiscretepoints.
2 2
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rate distortion theory a theory aimed tainpointsinthecapacityregionofmultiple
at quantifying the optimum performance of accesschannels.
source coding systems. Using information
theory,forseveralsourcemodelsanddistor- rate-adaptive digital subscriber line
tionmeasures,ratedistortiontheoryprovides (RDSL) a digital subscriber line (DSL)
theoptimumdistortionfunctionandtheop- in which the rates in each direction are ad-
timumratefunction. Thedistortionfunction justedaccordingtothequalityofthechannel.
isoptimuminthatthedistortionforagiven In general, longer loops are associated with
rateisthetheoreticalminimumvalueofdis- lowerrates.
tortionforencodingthesourceatthegivenor
lowerrate. Theratefunctionisoptimumin rate-compatible punctured convolutional
thattherateatagivendistortionisthemin- (RCPC) code one of a family of punc-
imum possible rate for coding the source at tured convolutional codes derived from one
thegivenorlowerdistortion. low-rate convolutional parent code by suc-
cessivelyincreasingthenumberofpunctured
rate equation approximation assump- symbols, given that the previously punc-
tion, in a semiclassical model for the inter- turedsymbolsshouldstillbepunctured(rate-
actionoflightwithatoms,thatallfieldsand compatibility). These codes have applica-
populationschangenegligiblywithintheco- tions in, for example, variable error protec-
herencetimeofthewavefunctions,losesall tionsystemsandinhybridautomaticrepeat
informationaboutthephaseofthefieldsand requestschemesusingadditionaltransmitted
wavefunctions. redundancytobeabletocorrectlydecodea
packet. AlsocalledRCPCcode.
rate equation model model for the in-
rate-distortiontheory ClaudeShannon’s
teraction of light with atoms in which the
theory for source coding with respect to a
atoms are represented only by their popula-
fidelity criterion, developed during the late
tionsorpopulationdensitiesandtheelectro-
1940s and the 1950s. Can be viewed as
magnetic field is represented only by its in-
ageneralizationofShannon’searliertheory
tensity,power,energy,orphotondensity.
(late 1940s) for channel coding and infor-
mation transmission. The theory applies to
rateequations coupledordinarynonlin- the important methods for vector quantiza-
ear differential equations governing the in- tionandpredictsthetheoreticallyachievable
teraction of an electromagnetic field (repre- optimumperformance.
sentedbyanintensity,energydensity,orpho-
tondensity)withanatomicormolecularlaser ratedvoltage thevoltageatwhichapower
medium (represented by populations of the lineorelectricalequipmentisdesignedtoop-
energystates);phaseinformationrelatingto erate.
the fields and wavefunctions is absent from
theseequations. ratio detector a circuit for recovering
(demodulating) baseband information (usu-
rate split multiple access coding tech- allyaudio)fromafrequencymodulated(FM)
nique for the multiple-access channel in wave.
which each user splits their information
stream into two or more streams, which rational function a function that is the
are independently encoded. These encoded ratio of two polynomials. Rational func-
streams are multiplexed according to some tionsoftenariseinthesolutionofdifferential
rulepriortotransmission. Usedtoshowthat equations by Laplace transforms. See also
time-sharing is not required to achieve cer- Laplacetransform.
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ray oneofafamilyoflines(rays)usedto pathfadingstatisticsinnon-line-of-sightmo-
representthepropagationofanelectromag- bileradiosystems.
netic wave; most useful in real media when
thewaveamplitudevariesslowlycompared Rayleighlength distanceoverwhichthe
tothewavelength(seegeometricaloptics). spotsizeofaGaussianbeamincreasesfrom
its value at the beam waist to a value 2.5
ray equation set of second-order differ- larger;ameasureofthewaistsizeofaGaus-
entialequationsgoverningthetrajectoryofa sian beam, (cid:25) times waist spot size squared
lightraypropagatingalonganarbitrarypath. dividedbywavelength; halfoftheconfocal
parameter.
rayoptics approximaterepresentationof
electromagnetic wave propagation in terms Rayleigh noise the envelope of a zero
oflightrays,mostusefulinrealmediawhen mean, wide-sense stationary, narrowband
thewaveamplitudevariesslowlycompared Gaussiannoiseprocess. Theprobabilityden-
tothewavelength. sity function of a sinusoid in narrowband
noiseisageneralizedRayleighdistribution,
ray tracing (1) a high-frequency elec- p.z/ D (cid:27)ze−2z(cid:27)22, z (cid:21) 0. Also known as a
tromagneticanalysistechniqueinwhichthe
Riciandistribution.
propagationpathismodeledbyfluxlinesor
“rays.” The ray density is proportional to
Rayleighscattering (1)theoryforthein-
thepowerdensity,andfrequently,bundlesof
teraction between light and a medium com-
theseraysarecalledraytubes.
posedofparticleswhosesizeismuchsmaller
(2) a rendering technique in which the than the wavelength. According to it, the
pathsoflightraysreachingtheviewpointare scatteringcrosssectionisproportionaltothe
computed to obtain realistic images. Given fourth power of the wavelength of the scat-
a 3-D description of a scene as a collection tered light. This explains both the red and
ofsurfacescharacterizedbydifferentoptical bluecolorsofthesky.
properties,raysaretracedbackwardfromthe
(2) an intrinsic effect of glass that con-
viewpointthroughtheimageplaneuntilthey
tributes to attenuation of the guided optical
hitoneofthesurfacesorgoofftoinfinity.
wave. Theeffectisduetorandomlocalized
variations in the molecular structure of the
raytransfermatrix realtwo-by-twoma-
glasswhichactsasscatteringcenters.
trix governing the transformation of the ray
displacementandslopewithrespecttoafixed Rayleigh–Ritz procedure a procedure
axis. for solving functional equations. See also
momentmethod.
Rayleigh criterion a method of distin-
guishingbetweenroughandsmoothsurfaces Rayleigh-wing scattering of light the
in order to determine whether specular re- scatteringoflightwithnochangeincentral
flection will occur. A surface is consid- frequency, and with moderate (of the order
eredsmoothifthephasedifferencebetween of 1011 Hz) broadening of spectrum of the
wavesreflectedfromthesurfaceislessthan light. Rayleigh-wingscatteringoccurswhen
ninetydegrees. lightscattersfromanisotropicmolecules.
Rayleighdistribution theprobabilitydis- RBC Seeradiationboundarycondition.
tributionofthemagnitudeofacomplexquan-
titywhoserealandimaginarypartsareinde- RC time constant the time needed for
pendentGaussianrandomvariableswithzero signaltravelingfromanendtotheotherend
mean. Frequentlyusedtoapproximatemulti- of a wire is constant when the wire and the
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whole chip is scaled down. As the length withdelays,thesetwonotionsareessentially
of a wire shrinks by a factor of k and the different. For infinite-dimensional systems,
cross-sectionalareaofthewireisreducedby the relations between reachability and con-
afactorofk2,thecapacitanceofthewirede- trollability depend on the properties of the
creasesbyafactorofk whiletheresistance semigroupS.t/generatedbytheoperatorA.
increasesbyafactorofk. TheRCtimere-
mains constant, and thus the input charging reactancegrounded anelectricalsystem
timeremainsthesame,independentofscal- inwhichtheneutralisintentionallygrounded
ing. Consequently, the scaling down of the through a reactance. Frequently used in
chipcannotincreasethespeedofthechipif theneutralofgeneratorsandtransformersto
wireisused. Opticalinterconnectscanspeed limit the magnitude of line to ground fault
upthechip. currents.
RCPCcode Seerate-compatiblepunctured reactance modulator modulator nor-
convolutionalcode. mally using phase or frequency modulation
where the reactance of the circuit is depen-
RCS Seeradarcrosssection. dentonchangesintheinputmodulatingvolt-
age.
RCT Seereverseconductingthyristor.
reaction afunctionalinelectromagnetics
RDSL Seerate-adaptivedigitalsubscriber
thatrelatesasetoffieldsandsourcestoone
line.
another. Reactionconceptsareoftenusedin
thediscussionoffieldreciprocity.
re-entrancy termdescribingthenumber
of times that a multiplex armature winding
reactionrange sumofend-to-endround-
ofacommutatedmachineclosesuponitself
tripdelayandprocessingtime.
via the commutator ring. For example, du-
plex windings can be either singly or dou-
reactivecompensation processofcoun-
bly re-entrant. In a doubly re-entrant du-
teractingthereactivecomponentofadevice
plex winding, the ends of the two winding
bymeansofcapacitorsandinductors. Both
circuits close only on themselves and not
seriesandshuntcompensationareprevalent.
on each other, creating two distinct circuits
throughthecommutatorandtwodistinctcir-
reactivecongestioncontrol inpacketnet-
cuit closures. Conversely, in a singly re-
works, a congestion control system whose
entrantduplexwinding,thetwowindingsare
actions are based on actual congestion oc-
connectedinseriesthroughthecommutator
currence.
ringcreatingonlyasinglecircuitclosure.
reachability a term that indicates that a reactiveionetching theprocessofetch-
dynamical system can be steered from zero ingmaterialsbytheuseofchemicallyreac-
initialstatetoanyfinalstateinagiventimein- tive ions or atoms. Typically, the reactive
terval. Formanydynamicalsystems,reach- ions or atoms are generated in a RF plasma
ability is equivalent to controllability. This environmentorinamicrowavedischarge.
is always true for linear finite-dimensional
continuous-time dynamical systems. How- reactiveload aloadthatispurelycapac-
ever,indiscretecase,controllabilitymaybe itiveorinductive.
thestrongernotionthanreachability. Inthis
case, the two concepts are equivalent if and reactive matching impedance transfor-
onlyifrankA D n. Fordynamicalsystems mation achieved by employing a matching
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network constructed of only reactive ele- read instruction an assembly language
ments. instruction that reads data from memory or
theinput/outputsystem.
reactivenearfield theregionclosetoan
antennawherethereactivecomponentsofthe read phase the first portion of a trans-
electromagnetic fields from charges on the action during which the executing process
antennastructureareverylargecomparedto obtains information that will determine the
theradiatingfields. Considerednegligibleat outcomeofthetransaction. Anytransaction
distancesgreaterthanawavelengthfromthe can be structured so that all of the input in-
source (decay as the square or cube of dis- formation is obtained at the outset, all the
tance). Reactivefieldisimportantatantenna computation is then performed, and finally
edgesandforelectricallysmallantennas. all results are stored (pending functionality
checksbasedonthelockingprotocolsinuse).
reactive power (1) electrical energy per
unit time that is alternately stored, then re- read-after-writehazard Seetruedata
leased. For example, reactive power is as- dependency.
sociated with a capacitor charging and dis-
charging as it operates on an AC system. read-modify-writecycle atypeofmem-
SymbolizedbyQ,withunitsofvolt-amperes orydeviceaccessthatallowsthecontentsata
reactive(VAR),itistheimaginarypartofthe singleaddresstoberead,modified,andwrit-
complexpower. tenbackwithoutotheraccessestakingplace
betweenthereadandthewrite.
(2) the power consumed by the reactive
part of the load impedance, calculated by
read-mostlymemory memoryprimarily
multiplying the line current by the voltage
designedforreadoperations,butwhosecon-
across the reactive portion of the load. The
tentsalsocanbechangedthroughprocedures
unitsarevars(volt-amperereactive)orkilo-
morecomplexandtypicallyslowerthanthe
vars.
read operations. EPROM, EEPROM, and
flashmemoryareexamples.
reactor acontainerwherethenuclearre-
actiontakesplace. Thereactorconvertsthe
read-only(ROM)memory semiconduc-
nuclearenergytoheat.
tormemoryunitthatperformsonlytheread
operation;itdoesnothavethewritecapabil-
reactor containment See containment
ity. Thecontentsofeachmemorylocationis
building.
fixedduringthehardwareproductionofthe
device and cannot be altered. A ROM has
reactorcore anarrayofnuclearfuelrods asetofkinputaddresslines(thatdetermine
thatarearrangedsoastoencourageachain thenumberofaddressablepositions2k)and
reactionandthusheatwatertosupplyapower a set of n output data lines (that determine
forthesteamturbineinanuclearpowerplant. thewidthinbitsoftheinformationstoredin
each position). An integrated circuit ROM
reactorrefueling theprocessofshutting may also have one or more enable lines for
downanuclearreactorformaintenanceand interconnecting several circuits and make a
fuel replacement, typically every 12 to 24 ROMwithlargercapacity. PlainROMdoes
months. not allow erasure, but programmable ROM
(PROM)does. StaticROMdoesnotrequirea
read ahead on a magnetic disk, reading clockforproperoperation,whereasdynamic
moredatathanisnominallyrequired,inthe ROMdoes. Seealsorandomaccessmemory,
hopethattheextradatawillalsobeuseful. programmableread-onlymemory.
(cid:13)c2000byCRCPressLLC
