Page 82 - Electrical Engineering Dictionary

class c i , P(x k ) is the probability of pattern beam hardening a phenomenon that
x k , P(x k |c i ) is the class conditional proba- occurs when a polychromatic X-ray beam
bility that the pattern is x k provided that it passes through a material. Lower energy
belongs to class c i , P(c i |x k ) is the a pos- photons are absorbed more readily than
teriori conditional probability that the given higher energy photons, increasing the ef-
pattern class membership is c i , given pattern fective energy of the beam as it propagates
x k , then through the material.

P (x k |c i ) P (c i ) beam intensity the average number of
P (c i |x k ) = .
P (x k ) particles in a beam passing a given point dur-
ing a certain time interval. For example the
The membership of the given pattern is de-
number of protons (electrons) per pulse or
termined by
protons per second.
beam loading the beam being accelerated
max P (c i |x k ) = max P (x k |c i ) P (c i ) . by an RF cavity and it changes the gradient
c i c i
and phase of the RF in the cavity.
Hence, the a posteriori probability can be
determined as a function of the a priori prob- beam mode confined electromagnetic
ability. field distributions of a propagating wave that
match the boundary conditions imposed by
BCD See binary-coded decimal. a laser or aperture. For example, Hermite–
Gaussian or Laguerre–Gaussian.
BCH code cyclic block forward error
control codes developed by Bose and Chaud- beam parameter one of several complex
huri, and independently by Hocquenghem. numbers employed to characterize the prop-
These codes are a superset of the Hamming agation of a beam; most common parameter
codes, and allow for correction of multiple combines in its real and imaginary parts the
errors. phase front curvature and spot size of a Gaus-
sian beam.
BCLA See block carry lookahead adder.
beam pulsing a method used to control
beam (1) transverse spatial localization the power output of a klystron in order to im-
of the power in a wave field. prove the operating efficiency of the device.
(2) a slender unidirectional stream of par-
ticles or radiation. beam roll a periodic change in horizontal
and/or vertical positions during spill. This
beam cooling the process by which a par- does not include changes caused by humans.
ticle beam’s phase space volume is reduced,
while conserving Liouville’s theorem (empty beam solid angle a parameter that quali-
spaces between particles exist). Beam cool- tatively describes the angular distribution of
ing is manifest by a reduction in the trans- radiated power from an antenna. The val-
verse beam size (betatron cooling) or by a ues range from very small numbers for very
smaller momentum spread (momentum cool- focused antennas to 4π steradians for an
ing). isotropic radiator.

beam divergence the geometric spread- beam stop a thick metal shield that moves
ing of a radiated electromagnetic beam as it into the beam line to prevent beam from en-
travels through space. tering a specific area.

c
2000 by CRC Press LLC