Abstract
The individual spins of the Ising model are assumed to interact with an external agency (e.g., a heat
reservoir) which causes them to change their states randomly with time. Coupling between the spins
is introduced through the assumption that the transition probabilities for anyone spin depend on
the ".a~ues of the neighboring ~I?in:" This dependence is determined, in part, by the detailed balancing
condItion obeyed by the equihbnum state of the model. The Markoff process which describes the
spin functions is analyzed in detail for the case of a closed N-member chain. The expectation values
of the individual spins and of the products of pairs of spins, each of the pair evaluated at a different
are found explicitly. The influence of a uniform, time-varying magnetic field upon the model
IS dIscussed, and the frequency-dependent magnetic susceptibility is found in the weak-field limit.
Some fluctuation-dissipation theorems are derived which relate the susceptibility to the Fourier
transform of the time-dependent correlation function of the magnetization at equilibrium.
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