Page 65 - Electrical Engineering Dictionary

atom a particle of matter indivisible by ATRC SeeAdvancedTelevisionResearch
chemicalmeans, whichischemicallyneutral. Consortium.
It is the fundamental building block of the
chemical elements. attachment one of the events which pre-
cede a lightning stroke to the earth. Attach-
ment occurs when the stepped leader from
atomic beam a source of atoms trav-
the thundercloud makes contact with one of
eling primarily in one direction. In prac-
several streamers which emanate from the
tice, atomic beams are usually realized by
ground or structures on the earth. The return
the expansion of an atomic vapor into a vac-
stroke follows immediately. See streamer,
uum through a small aperture. The resulting
stepped leader, return stroke.
expanding cloud of atoms is usually made
nearly unidirectional by a collimator that
attachment process a process that occurs
blocks or otherwise removes all atoms not
in lightning when one or more stepped leader
propagating within a narrow range of angles.
branches approach within a hundred meters
or so of the ground and the electric field at
atomic force microscope (AFM) a
the ground increases above the critical break-
microscope in which a sharp probe tip is
downfieldofthesurroundingair. Atthattime
scanned across a surface, with piezoelectric
one or more upward-going discharges is ini-
ceramics being used to control position in
tiated. After traveling a few tens of meters,
three dimensions. The lateral (in-plane, or x-
one of the upward discharges, which is essen-
y) positions are raster scanned, while the ver-
tially at ground potential, contracts the tip of
tical dimension is controlled by a feedback
one branch of the stepped leader, which is at
circuit that maintains constant force. The im-
a high potential, completing the leader path
age produced is a topograph showing surface
to ground.
height as a function of position in the plane.
attainable set for discrete system the set
atomic instruction an instruction that of all the possible ends of system trajectories
consistsofdiscreteoperationsthatareallexe- at time t 1 starting from zero initial conditions
cuted as a single and indivisible unit, without at time t 0 . Denteod K(t 0 ,t 1 ).
interruption by other system events. See also K(t 0 ,t 1 ) is defined for zero initial state as
test-and-set instruction, atomic transaction. follows
n
atomictransaction thesameasanatomic K (k 0 ,k 1 ) = x ∈ R :
instruction, except that the notion of being j=k 1 −1
X
atomic applies to a transaction, which may x = F (k 1 ,j + 1) B(j)u(j) :
be a sequence of operations, no intermedi- j=k 0
ate states of which may be seen or operated u(j) ∈ R m
upon by another transaction. See also atomic
instruction.
Therefore, controllability in [k 0 ,k 1 ] for
discretedynamicalsystemisequivalenttothe
atomic transition coupling of energy condition
levels in an atom by means of absorption or
emission processes. K (t 0 ,t 1 ) = R n

atomic vapor a material composed of Using the concept of the attainable set it
atoms that preferentially exist as monomers is possible to express the remaining types of
in the vapor phase. controllability for discrete system.

c
2000 by CRC Press LLC