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Potts model and enables us to extend it to tricritical exponents as well.The two-dimensional q-state Potts model is defined by the Hamiltonian' where the summation is over all nearest-neighbor pairs on a lattice. Each spin variable s; can assume q values. The transition temperatures of the Potts model, J, '(q), are known by duality relations for the square' and triangular lattices. ' As noted above, Baxter' inferred for the square lattice that the phase transition is first order for q & q, and continuous for q~q "where q, = 4. It

Persistent currents in small nonsuperconducting rings threaded by a magnetic flux are a manifestation of novel quantum effects in submicron systems. We present theoretical results for one-channel and multichannel systems concerning the dependence of the current amplitude on the number of channels and geometry, temperature, and degree of disorder. Inelastic scattering is considered for one-channel loops only. We also discuss the observability of the effect.

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