DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

Curie (Ci)
Curie (Ci) The special unit of radioactivity
equal to 2.2 × 10 12 disintegrations per minute.
Curie point The temperature above which
magnetization is eliminated in a material that is
ferromagnetic at low temperatures.
Curie point survey A method to estimate
depth distribution of temperature at which spontaneous
magnetism of ferromagnet is lost (Curie
point, about840K)frommeasurementofthegeomagnetic
field by magnetic exploration in the
air. Assuming that the average geothermal gradient
is 30 K/km, the depth of Curie point in the
crust is about 20 km. Curie point surveys are
used for geothermal prospecting.
curl An antisymmetric derivative of a vector,
defined as a (pseudo)vector: (curlV)x =Vy,z−
Vz,y, where V is a vector, and the notation ,y
means partial derivative with respect to y. This
expression gives the x−component of the curl,
and the other components are given by cyclic
permutation of the component indices.
current carrier (cosmic string) A particle
physics model for a topological defect in
general, and that of a cosmic string in particular,
may contain various couplings between the
Higgs field and other particle fields. Whenever
these particles are charged and have the possibility
to move along the defect, they will induce
a current, and are, therefore, called current
carriers. See cosmic topological defect, Witten
conducting string.
current, curvature In a guiding center
plasma, the part of the electric current due to
the curvature drift.
current generation (cosmic string) A cosmic
string is a topological defect of the vacuum
where a Higgs field is responsible for the existence
of a large energy density confined in a
linelike configuration. In grand unified models,
this Higgs field is often coupled to many other
fields whose dynamics will be different depending
on whether the background space is the core
of the string or the outside space. In particular,
they might condense, i.e., acquire a net nonzero
value inside the core.
© 2001 by CRC Press LLC
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For complex fields, the core condensate will
have a well-defined phase. At the time of condensation,
this phase will take random values
along the string; any mismatch between those
values will generate a gradient: it is precisely the
gradient in the phase of one of these (charged)
fields that powers the currents. See conducting
string, current carrier (cosmic string), Witten
conducting string.
current, gradient In a guiding center
plasma, the part of the electric current due to
the gradient drift.
current instability (cosmic string) In many
grand unified models, cosmic strings have the
ability to carry persistent currents. These currents
could have drastic effects on the evolution
of a network of strings as they could, for instance,
imply the existence of vortons. However,
not all such currents are completely stable
for at least two reasons: other phase transitions
subsequent to that leading to the formation
of strings and currents, and classical and quantum
perturbations could in fact destabilize the
currents, leaving just an ordinary, nonconducting
string. See conducting string, cosmic string,
current carrier (cosmic string), vorton.
current, magnetization In a guiding center
plasma, the part of the electric current due to
∇×M, with M being the magnetization term.
Intuitively, this is the current associated with
variations in density across the plasma, e.g., the
current at the edge of a finite body of plasma.
current, polarization In a guiding center
plasma, the current associated with the change
of the electric field, dE/dt. If the electric field
E changes, the energy associated with the electric
drift E ×B/B 2 changes, and the polarization
current transmits that energy.
current quenching See current saturation
(cosmic string).
current saturation (cosmic string) The
mechanism of current saturation (or quenching)
in cosmic strings takes place when the magnitude
of the current flowing along the core becomes
comparable (in appropriate units) with