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The Green–Kubo relations (Melville S. Green 1954, Ryogo Kubo 1957) give the exact mathematical expression for transport coefficients in terms of integrals of time correlation functions: :. ==Thermal and mechanical transport processes== Thermodynamic systems may be prevented from relaxing to equilibrium because of the application of a mechanical field (e.g. electric or magnetic field), or because the boundaries of the system are in relative motion (shear) or maintained at different temperatures, etc. This generates two classes of nonequilibrium system: mechanical nonequilibrium systems and thermal nonequilibrium systems. The standard example of a mechanical transport process is Ohm's law, which states that, at least for sufficiently small applied voltages, the current ''I'' is linearly proportional to the applied voltage ''V'', : As the applied voltage increases we expect to see deviations from linear behavior. The coefficient of proportionality is the electrical conductance which is the reciprocal of the electrical resistance. The standard example of a mechanical transport process would be Newton's Law of viscosity which states that the shear stress is linearly proportional to the strain rate. The strain rate is the rate of change streaming velocity in the x-direction, with respect to the y-coordinate, . Newton's Law of viscosity states : As the strain rate increases we expect to see deviations from linear behavior : Another well known thermal transport process is Fourier's Law of Heat conduction, stating that the heat flux between two bodies maintained at different temperatures is proportional to the temperature gradient (the temperature difference divided by the spatial separation). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Green–Kubo relations」の詳細全文を読む スポンサード リンク
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