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Thermal conductivity is measured by transient heating of an isotropic material with a known heating power generated from a source of known geometry and measuring the temperature change with time. The needle probe contains a heater wire and calibrated thermistor. It is assumed to be a perfect conductor because it is much more conductive than unconsolidated sediments. With this assumption, the temperature of the probe has a linear relationship with the natural logarithm of the time after initiation of heating:
T(t) = (q/4pk4πk) ln(t) + C,
where:
T = temperature,
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