Electrical resistivity and conductivity ions. In biological membranes, currents are carried by ionic salts. Small holes in cell membranes, called ion channels, are selective to specific ions and determine the membrane resistance. The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire
Thermal conductivity containing "I" terms have to be zero. Now if we assume that where "δ" is the Dirac delta function, "I" terms get the following expressions By substituting these expressions to the equation for "λ", we see that it goes to zero. Therefore, "P"("x") has to be delta function. In an isotropic medium the thermal conductivity is the parameter "k" in the Fourier expression for the heat flux where formula_2 is the heat flux (amount of heat flowing per second and per unit area) and formula_66 the temperature gradient. The sign in the expression is chosen so that always "k" >