DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

the fraction η of the rest mass falling onto the
black hole per unit time, ( ˙M), that is converted
into radiating energy, a limiting accretion rate
is associated to the Eddington luminosity. See
quasar.
Eddington luminosity See Eddington limit.
Eddington ratio The ratio between the bolometric
luminosity of a source, and the Eddington
luminosity. The Eddington ratio can be equivalently
defined from the accretion rate. The Eddington
ratio is a parameter expected to influence
the structure and the radiating properties
of an accretion disk in a fundamental way: If
the Eddington ratio is < ∼ 1 a geometrically thin
disk is expected to form, while if > ∼ 1 the accretion
disk may inflate to form a torus whose
thicknessissupportedbyradiationpressure. See
Eddington limit.
eddy A current that runs in a direction other
than that of the main current; generally “spins
off” from a larger flow and defines a circular
path.
eddy correlation method Method to directly
compute turbulent fluxes of scalars. Turbulent
velocity fluctuations cause a net transport of
scalar properties of the fluid. The turbulent flux
is then given by the time or space averaged product
v ′ θ ′ of the velocityv and the scalarθ, where
the primes denote the fluctuations (see Reynolds
decomposition) and the over-bar denotes the average.
For example, the fluctuations of vertical
velocityw and temperatureT may be combined
to give the vertical flux of heat, Cw ′ T ′ , where
C is the specific heat.
eddy diffusivity An analog to molecular diffusivity,
used to model diffusion in a turbulent
flow.
eddy flux The flux of chemical properties,
momentum, energy, heat, etc. via the eddies in
turbulent motion.
eddy-resolving Eddy-resolving models are
able to describe the turbulent flow down to a resolution
including all scales on which viscosity
is not dominant.
© 2001 by CRC Press LLC
effective couplings
eddy viscosity An analog to molecular viscosity,
used to describe shear stresses in a turbulent
flow. A coefficient of proportionality to
relate shear stress to rate of strain (velocity gradient)
in turbulent flow.
edge wave Waves that are trapped at a coast
by refraction. Waves strike the shore and some
energy is reflected, and then turned by refraction.
Depending on the incident angle and
bathymetry, some of this energy will be trapped
at the coast. The trapped wave moves in the
longshore direction as a progressive wave.
effective charge A somewhat obsolete expression
in field theory for the renormalized
quantities which have logarithmic dependence
of the scale parameter µ. “Effective charge” is
sometimes used instead of the more common
“effective coupling constant,” “effective mass,”
“effective parameter,” etc. See effective couplings.
effective couplings The values of the coupling
constants in quantum field theory depend
on the dimensional parameter µ, which measures
the typical scale of the energy of the interaction.
This dependence is governed by the
renormalization group and it has, in general, logarithmic
form. Thus, instead of constant coupling,
one finds some function of µ. For example,
in quantum electrodynamics (QED) the
charge of the electron is running (in the one-loop
approximation) as
e(µ)
e =
1 − 2
3
e 2
µ
ln
(4π) 2
µ0
−1
where e = e(µ0) and µ0 corresponds to some
fixed scale. The minus sign in the bracket indicates
the lack of asymptotic freedom in QED.
This leads to the well-known formal problem
(problem of charge zero, or Landau zero) because
for some µ corresponding to a very high
energy the bracket becomes zero and the effective
coupling infinite. This in turn makes the
perturbation theory inapplicable and addresses
serious questions about the fundamental validity
of the theory. Indeed, the resolution of this problem
is beyond the scope of QED. It is supposed
that at these very high energies QED is not an
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