Page 28 - Electrical Engineering Dictionary

two-port networks. Sometimes referred to
as chain parameters. ABCD parameters are
A widely used to model cascaded connections
of two-port microwave networks, in which
case the ABCD matrix is defined for each
two-port network. ABCD parameters can
also be used in analytic formalisms for prop-
a posteriori probability See posterior agating Gaussian beams and light rays. Ray
statistics. matrices and beam matrices are similar but
are often regarded as distinct.
a priori probability See prior statistics. ABC parameters have a particularly use-
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
into the body.
the ABCD parameters of the two individual
circuits. ABCD parameters are defined as
A-site in a ferroelectric material with the

chemical formula ABO 3 , the crystalline lo- v 1 AB v 2
=
cation of the A atom. i 1 CD i 2
where v 1 and v 2 are the voltages on ports one
A/D See analog-to-digital converter.
and two, and i 1 and i 2 are the branch currents
AAL See ATM adaptation layer. into ports one and two.
ABC See absorbing boundary condition. aberration an imperfection of an optical
system that leads to a blurred or a distorted
ABCD propagation of an optical ray image.
through a system can be described by a sim-
ple 2×2 matrix. In ray optics, the character- abnormal event any external or program-
istic of a system is given by the correspond- generated event that makes further normal
ing ray matrix relating the ray’s position from program execution impossible or undesir-
the axis and slope at the input to those at the able, resulting in a system interrupt. Exam-
output. ples of abnormal events include system de-
tection of power failure; attempt to divide by
ABCD formalism analytic method using 0; attempt to execute privileged instruction
two-by-two ABCD matrices for propagating without privileged status; memory parity er-
Gaussian beams and light rays in a wide va- ror.
riety of optical systems.
abort (1) in computer systems, to termi-
ABCD law analytic formula for trans- nate the attempt to complete the transaction,
forming a Gaussian beam parameter from usually because there is a deadlock or be-
one reference plane to another in paraxial op- cause completing the transaction would re-
tics, sometimes called the Kogelnik transfor- sult in a system state that is not compati-
mation. ABCD refers to the ABCD matrix. ble with “correct” behavior, as defined by a
consistency model, such as sequential con-
ABCD matrix the matrix containing sistency.
ABCD parameters. See ABCD parameters. (2) in an accelerator, terminating the ac-
celeration process prematurely, either by in-
ABCD parameters a convenient mathe- hibiting the injection mechanism or by re-
matical form that can be used to characterize moving circulating beam to some sort of

c
2000 by CRC Press LLC