Dark Ages Cultural period
in Greece between 1100 and 750 BC, subsequent to the
Mycenaean age and
followed by the Archaic
period. During this period
Greece was occupied by the Dorians.
Dating Determination of
a date, in absolute chronology, in the
Christian reference system [before Christ (BC), after Christ (AC);
before
or after our era).
Declination (D) Angle between
geographic north (true north) and magnetic north of the
geomagnetic field.
Also angle between geographic north and the
horizontal component of the magnetic
remanence of a sample.
Demagnetisation
by applying a
sufficiently strong alternating magnetic field which decreases smoothly
towards zero.
thermal
demagnetisation
Demagnetisation
by heating above the
Curie-or Néel-temperature
followed by cooling in zero magnetic
field to room temperature.
Depositional remanent magnetisation Remanent magnetisation acquired by a
sediment at the
air/water sediment interface, by alignment of the magnetic particles.
This
remanent magnetisation may not be preserved at geological timescales
due to bioturbation, cryoturbation, incomplete mechanical blocking of
magnetic grains and diagenetic processes (see also
post-depositional remanent
magnetisation).
Diamagnetism In materials
with paired electrons (even number of electrons). All
materials brought in a magnetic field show the effect of diamagnetism
often masked by other more important effects of paramagnetism or
ferromagnetism. The
diamagnetic susceptibility is weak and negative.
Examples: the most important constituents of rocks (quartz, feldspar,
calcite).
Dipole field The Earth
magnetic field resembles to the field of a magnet placed at the
centre
of the Earth and inclined with respect to the Earths rotation
axis and characterised by a magnetic north and south pole (dipole).
Other
forms of fields, designated multipolar fields, are called
non-dipole
fields.