Q
QCD
See
quantum chromodynamics
.
QED
See
quantum electrodynamics
.
QFD
Quantum
Û
avourdynamics.
See
electroweak theory
.
QSG
See
quasars
.
QSO
See
quasars
.
QSS
See
quasars
.
quadrat
An ecological sampling unit
consisting of a small square area of
ground within which all species of inter-
est are noted or measurements taken.
Quadrats may be spaced over a larger
area to form an overall view when a total
survey would be impracticable, or they
may be used to sample along a
*
transect.
quadrate
A paired bone in the upper
jaw of bony
Ü
shes, amphibians, reptiles,
and birds that articulates with the lower
jawbone. It is absent in mammals, being
reduced to a small bone (the incus) in the
middle ear (
see
ear ossicles
).
quadratic equation
An equation of
the second degree having the form
ax
2
+
bx
+
c
= 0. Its roots are:
x
= [–
b
±√
(
b
2
– 4
ac
)]/2
a
.
quadrature
The position of the moon
or an outer planet when the line joining
it to the earth makes a right angle with a
line joining the earth to the sun.
quadrivalent
Having a valency of four.
qualitative analysis
See
analysis
.
qualitative variation
See
discontinu-
ous variation
.
quality of sound
(timbre)
The quality
a musical note has as a result of the pres-
ence of
*
harmonics. A pure note consists
only of the fundamental; however, a note
from a musical instrument will have sev-
eral harmonics present, depending on the
type of instrument and the way in which
it is played. For example, a plucked string
(as in a guitar) produces a series of har-
monics of diminishing intensity, whereas
a struck string (as in a piano) produces a
series of harmonics of more nearly equal
intensity.
quantitative analysis
See
analysis
.
quantitative inheritance
See
poly-
genic inheritance
.
quantitative variation
See
continu-
ous variation
.
quantization
The process of construct-
ing a quantum theory for a system, using
the original classical theory as a basis.
The starting point for such a process is to
write the
*
Lagrangian or
*
Hamiltonian of
the classical system. The formulation of
the quantum theory for the system can
be performed using a formalism such as
*
matrix mechanics, or
*
wave mechanics.
The application of these methods leads to
the conclusion that energy levels in sys-
tems, such as atoms, are discrete (
quan-
tized
) rather than continuous. Before the
discovery of quantum mechanics in the
mid 1920s, quantization involved a series
of ad hoc postulates for atomic systems,
such as the
*
Bohr theory and its exten-
sions.
quantum
(
pl.
quanta
) The minimum
amount by which certain properties, such
as energy or angular momentum, of a sys-
tem can change. Such properties do not,
therefore, vary continuously, but in inte-
gral multiples of the relevant quantum,
and are described as
quantized
. This con-
cept forms the basis of the
*
quantum
theory. In waves and
Ü
elds the quantum
can be regarded as an excitation, giving a
particle-like interpretation to the wave or
Ü
eld. Thus, the quantum of the electro-