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Electrical Engineering Dictionary - part 104

load-pull measurement

See

active load-

pull measurement

harmonic load-pull mea-

surement

load/store architecture

a system design

in which the only processor operations that
access memory are simple register loads and
stores.

load/store unit

a computer based on the

load/store architecture.

loaded Q

dimensionless ratio of the

average over any period of time (

T =

1/frequency) of the ratio of the maximum en-
ergy stored (

max

) to the power absorbed or

dissipated (

absorbed

= p

− p

out

) in a pas-

sive component or circuit, including external
loading effects, expressed as a dimensionless
ratio. For most applications, the higher the
Q, the better the part.

local area network

a network of comput-

ers and connection devices (such as switches
and routers) that are located on a single site.
The connections are direct cables (such as
UTP or optical fiber) rather than telecommu-
nication lines. The computer network in a
university campus is typically a local area
network.

local bus

the set of wires that connects a

processor to its local memory module.

local controllability of generalized 2-D
model

the generalized 2-D model

i+1,j+1

= A

+ A

i+1,j

+ A

i,j+1

+ B

i+1,j

+ B

i,j+1

i, j ∈ Z

(the set of nonnegative integers)

is called locally controllable in the rectangle
[0

, N

]

× [0, N

] if for admissible bound-

ary conditions

for

i ∈ Z

and

for

j ∈ Z

, there exists a sequence of inputs

for 0

≤ i ≤ N

+ n

and 0

≤ j ≤ N

+ n

such that

= 0 where x

∈ R

the local semistate vector,

∈ R

is the

input vector,

E, A

(k = 0, 1, 2) are

real matrices with

E possibly singular, and

, n

) is the index of model. See also

local

reachability of generalized 2-D model

local decision unit

control agent or a part

of the controller associated with a given sub-
system of a partitioned system; local decision
unit is usually in charge of the local decision
variables and is a component of a decentral-
ized or a hierarchical control system.

local decision variable

control inputs as-

sociated with a given subprocess (subsystem)
of the considered partitioned process (sys-
tem); local decision variables can be either
set locally by local decision unit, or globally
by a centralized controller.

local field effect

effect associated with

the distinction that occurs in condensed mat-
ter between the spatially averaged electric
field and the field that acts on a represen-
tative molecule of the material system. A
consideration of local field effects leads to
the Lorentz–Lorenz and Clausius–Mossotti
relations.

local memory

memory that can be ac-

cessed by only one processor in a multipro-
cessor or distributed system. In many multi-
processors, each processor has its own local
memory. See also

global memory

local minimum

a minimum of a function

that is not the global minimum.

local mode oscillation

this mode of os-

cillation is associated with the swinging of
units at a generating station with respect to
the rest of the power system. The oscilla-
tions are thus localized to within a small part
of the system.

local observability of 2-D Fornasini–
Marchesini model

the 2-D Fornasini–

Marchesini model

i+1,j+1

= A

i+1,j

+ A

i,j+1

+ B

i+1,j

+ B

i,j+1

= Cx

2000 by CRC Press LLC

i, j ∈ Z

(the set of nonnegative integers)

is called locally observable in the rectangle
[0

, N

]

× [0, N

] if there is no local states

6= 0 and x

6= 0 such that for zero inputs

for 0

≤ i ≤ N

and 0

≤ j ≤ N

and zero

boundary conditions

= 0 for i ≥ 2 and

for

j ≥ 2 the output is also zero y

= 0

for 0

≤ i ≤ N

and 0

≤ j ≤ N

. The model

is locally observable in [0

, N

]

× [0, N

] if

and only if

rank








...

−1,0

...

−1

...

−1,N

−1








[

, A

]

= 2n

where the transition matrix

of the model

is defined by












for

i = j = 0

= A

i−1,j

+ A

i,j−1

for

i, j ≥ 0 (i + j 6= 0)

= 0 for i < 0 or/and j < 0

local observability of 2-D Roesser model

the 2-D Roesser model

i+1,j

i,j+1

= C

i, j ∈ Z

(the set of nonnegative integers)

is called locally observable in the rectangle
[0

, N

]

× [0, N

] if there is no local ini-

tial state

6= 0 such that for zero inputs

= 0 for 0 ≤ i ≤ N

and 0

≤ j ≤ N

and

zero boundary conditions

= 0 for j ≥ 1

and

= 0 for i ≥ 1, the output is also zero

= 0 for 0 ≤ i ≤ N

and 0

≤ j ≤ N

where

∈ R

and

∈ R

are the hori-

zontal and vertical local state vectors, respec-
tively,

∈ R

is the input vector,

∈ R

is the output vector, and

C are real matrices. The model is locally

observable in [0

, N

]

× [0, N

] and only if

rank








...








= n

where the transition matrix is defined by












I for i = j = 0

for

i = 1, j = 0 ;

for

i = 0, j = 1 and

i−1,j

+ T

i,j−1

for

i, j ∈ Z

(i + j 6= 0)

= 0 for i < 0 or/and j < 0

local oscillator

(1) an oscillator or circuit

that produces a periodic signal whose func-
tion is to be utilized in the demodulation of
a received radio signal. This periodic sig-
nal is typically a sinusoid and the oscillator
is typically located in a radio receiver. The
tuning of the radio to a given channel, or sta-
tion, typically involves the tuning of the local
oscillator. The local oscillator is part of the
radio frequency (RF) front end of a radio re-
ceiver and is an important component in a
heterodyne receiver.

(2) the signal applied to a mixer circuit

that is of a sufficient level to bias the diodes
within the mixer into a nonlinear region so
that the mixing process may occur.

local oxidation of silicon (LOCOS)
masked oxidation of silicon to provide elec-
tronic isolation between devices. Made pos-
sible by relatively slow oxidation of silicon
nitride, which is used as a mask.

2000 by CRC Press LLC

local reachability of generalized 2-D model

the generalized 2-D model

i+1,j+1

= A

+ A

i+1,j

+ A

i,j+1

+ B

i+1,j

+ B

i,j+1

i, j ∈ Z

(the set of nonnegative integers)

is called locally reachable in the rectangle
[0

, N

]

× [0, N

] if for admissible bound-

ary conditions

, i ∈ Z

and

, j ∈ Z

and every vector

∈ R

there exists a se-

quence of inputs

for 0

≤ i ≤ N

+ n

and 0

≤ j ≤ N

+ n

such that

= x

where

∈ R

is the local semistate vec-

tor,

∈ R

is the input vector,

E, A

(k = 0, 1, 2) are real matrices with E possi-
bly singular. The model is locally reachable
in [0

, N

]

× [0, N

] if and only if

rank

, M1

, . . . , M

, M

, . . . , M

1 ¯

, M

, . . . , M

, ¯

= n

= T

−1,N

−1

:= T

−p,N

−1

+ T

−p−1,N

−1

for

p = 1, . . . , ¯

= N

+ n

:= T

−1,N

−q

+ T

−1,N

−q−1

for

q = 1, . . . , ¯

= N

+ n

:= T

−p−1,N

−q−1

+ T

−p,N

−q−1

+ T

−p−1,N

−q

for

p = 1, . . . , ¯

q = 1, . . . , ¯

and the transition matrix

is defined by












−1,−1

+ A

,−1

−1,0

+ I for p = q = 0

p−1,q−1

+ A

p,q,−1

p−1,q

for

p 6= 0 and/or q 6= 0

and

[

− A

]

−1

∞

p=−n

∞

q=−n

−(p+1)
1

−(q+1)
2

pair

, n

) of positive integers n

such

that

= 0 for p < −n

and/or

q < −n

is called the index of the model.

local stability

See

stable state

local wavelength

distance between the

phase fronts of a non-planewave signal in-
ferred from measurements that are local in
space; 2 pi over the magnitude of the lo-
cal propagation constant, which is the gradi-
ent of the total phase. See also

wavelength

instantaneous frequency

locality

one of two forms of program

memory relationships.

1. Temporal locality: if an object is being

used, then there is a good chance that the
object will be reused soon.

2. Spatial locality: when an object is being

used, there is a good chance that objects in
its neighborhood (with respect to the memory
where these objects are stored) will be used.

These two forms of locality facilitate the

effective use of hierarchical memory. Reg-
isters exploit temporal locality. Caches ex-
ploit both temporal and spatial locality. In-
terleaved memories exploit spatial locality.
See also

sequential locality

localization

refers to the “trapping” of an

electron into a potential well minimum, so
that the wave function ceases to be describ-
able by a propagating wave. This localization
can be “strong” localization such as when an
electron is trapped by an ionized donor or
other ionized potential, or “weak” localiza-
tion in which it is induced by a “self” inter-
ference effect. See also

weak localization

lock

a synchronization variable, used in

shared-memory multiprocessors, that allows
only one processor to hold it at any one time,
thus enabling processors to guarantee that
only one has access to key data structures or
critical sections of code at any one time.

lock range

the range of frequencies in the

vicinity of the voltage controlled oscillator

2000 by CRC Press LLC

(VCO) free-running frequency over which
the VCO will, once locked, remain synchro-
nized with the signal frequency. Lock range
is sometimes called tracking bandwidth.

lock-in amplifier

a system for detect-

ing weak, noisy periodic signals based on
Synchronous detection, and incorporating all
the other components necessary for record-
ing the amplitude profile of the weak in-
coming signal, including input AC amplifier,
diode or other detectors, low-pass filter, DC
amplifier, and any special filters. Such in-
struments are nowadays constructed with in-
creasing amounts of digital and computerized
circuitry, depending on the frequency of op-
eration.

lock-out

phenomenon exhibited during

channel switching that results from a fast au-
tomatic gain control (AGC) system interact-
ing with the horizontal automatic frequency
control (AFC), thereby reducing the pull-in
range of the AFC system.

lock-up-free cache

See

nonblocking

cache

locked-rotor current

the current drawn

by an induction motor when the shaft is not
moving and rated voltage is applied. The
starting current is essentially equal to the
locked rotor current and may be as much as
eight times the rated current of the machine.

locked-rotor torque

the torque produced

in an induction motor when the rotor is locked
and rated AC voltage is applied to the stator.

locking

See

bus locking

lockout

the condition following fault

clearing when the circuit will not attempt a
reclose. Transformers, generators, and buses
typically trip once and lockout immediately.
Transmission lines and distribution lines will
generally attempt one or more recloses, and
will lockout if the fault remains following the
last reclose in the sequence.

lockout relay

an auxiliary relay which

is operated by protective relay(s) that in
turn opens the appropriate circuit breakers or
other fault clearing devices. The lockout re-
lay will remain in the trip position until man-
ually reset, and is used in protective zones
where temporary faults are unusual and the
potential for equipment damage is high.

LOCOS

See

local oxidation of silicon

log periodic antenna

broadband antenna

designed using physical dimensions (lengths,
spacings, diameters, etc.) that vary logarith-
mically. The result of such designs is an an-
tenna whose performance parameters (e.g.,
input impedance) is periodic with respect to
the logarithm of the frequency.

log-likelihood function

the likelihood

function of

y given x is the conditional

PDF,

p(y|x). The log-likelihood function

is the logarithm of the likelihood function,
log(

p(y|x)).

log-normal distribution

probability dis-

tribution with density

f (x) = 1/(

(2π)σx)e

−((log x−µ)

/(2σ

))

where

µ and σ are the mean and standard

deviation of the logarithm.

logarithmic quantization

a method for

non-linear scalar quantization where the in-
put signal is transformed logarithmically and
then coded using uniform quantization. The
transformation is utilized to enhance perfor-
mance for sources having nonuniform prob-
ability distribution, and to give robustness to-
wards varying input signal dynamics.

logic analyser

a machine that can be used

to send signals to, and read output signals
from, individual chips or circuit boards.

logic circuit

a circuit that implements a

logical function, such as AND, OR, NAND,
NOR, NOT, or XOR. (DB)

2000 by CRC Press LLC

Content .. 102 103 104 105 ..