DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

K
Kaiser–Stebbins effect (1984) Anisotropies
in the cosmic microwave background generated
by cosmic strings present after the time of the
decoupling of the cosmic radiation. For a string
moving transversely to the line of sight, light
rays passing on opposite sides of the string will
suffer different Doppler shifts. The result is
then the existence of step-like blackbody effective
temperatureT discontinuities, with relative
magnitude change on different sides of the string
given by
δT/T = 8πGUγsˆn· vs ׈s
where γs is the relativistic Lorentz factor, vs is
the string velocity with respect to the observer, ˆs
is the string segment orientation and ˆn points in
the direction of the line of sight. G is Newton’s
constant, units are chosen so that ¯h=c= 1
and U is the (effective) mass per unit length of
the (wiggly) cosmic string. See cosmic string,
cosmic topological defect, deficit angle (cosmic
string).
katabatic wind A wind that is created by
air flowing downhill; wind flowing down slope
at night as the valley floor cools. Examples of
drainage winds are the Mistral in France and
the Santa Ana in California. Another example
is winds from the Greenland plateau where a
pool of cold dense air forms and if forced off
the plateau seaward accelerates downslope.
K corona The K (or kontinuerlich) corona is
generated by the scattering of photospheric radiation
from coronal electrons. The high speeds
of the scattering electrons smear out the Fraunhofer
lines except the H- and K-lines. The K
corona dominates below ∼ 2R⊙ where its intensity
ranges from 10 −6 to 10 −8 of the diskcenter
intensity. The K corona is polarized by
the electron scattering with the electric vector
parallel to the limb.
Kelvin temperature scale
k-correction A necessary correction in observing
redshifted objects. Since the visual or
blue magnitudes in such sources correspond to
absolute luminosities at higher frequencies than
is the case for nearer sources, the k-correction
for this effect depends on modeling the spectrum
of the source.
Kelvin–Helmholtz instability Also called
“shear instability”. An instability of an unbounded
parallel shear flow to the growth of
waves with phase speed in the flow direction approximately
equal to the speed of the inflection
point of the shear. The instability occurs due to
a resonant coupling between wave-like disturbances
on either flank of the shear flow where
the gradient of the shear is non-zero.
Kelvin material Also called a Kelvin solid.
A viscoelastic material that, in response to a
suddenly imposed constant loading, deforms as
an incompressible, linearly viscous fluid over a
short time but as a linearly elastic solid over a
long time. The stress for the Kelvin material is
the combination of the elastic stress according
to Hooke’s law and the viscous stress according
to the Newtonian flow law. The relation
between the volumetric strain θ = εii and pressure
p = σii/3 is elastic: p = Kθ, where K
is the bulk modulus. The constitutive relation
for the deviatoric strain ε ′ ij = εij − θδij /3 and
deviatoric stress σ ′ ij = σij − pδij is
σ ′
ij = 2Gε′ ij + 2µ∂ε′ ij
∂t
where G is shear modulus, and µ is viscosity.
Quantity τK = µ/G is called the Kelvin relaxation
time, a time roughly defining the transition
from predominantly viscous to predominantly
elastic behavior after a suddenly imposed constant
loading.
Kelvin temperature scale Absolute temperature
scale. At 0 K all thermal motion of
matter would be at a standstill; thus, in the
Kelvin scale no negative temperatures can exist.
0 K correpsonds to −273.15 ◦ C; therefore,
absolute temperatures T in the Kelvin scale
are related to temperatures θ in centigrades by
T = θ + 273.15 K.
© 2001 by CRC Press LLC
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