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Notes: A general theory of the relaxation of a system in contact with a second system (called the heat bath) which need not be in equilibrium is presented. The theory, which avoids the use of projection operators, is developed in such a fashion that the effects of the interaction between the system and the heat bath can be consistently approximated by an ordering in terms of the degree of the fluctuation in the heat bath variables. This gives a natural classification in terms of differing regimes, the lowest nontrivial of which is the quadratic, or Gaussian, regime. The cubic and higher order fluctuations represent increasingly complex regimes. The exact equations of motion for the average of the single time system variables and for the two-time correlation functions involving the system variables are found in the Gaussian regime. (The general theory is not limited to the two-time correlation functions.) In the classical limit these lead to equations of motion for the three quantities: the average of the single time variables; the two-time, or pair, fluctuations; and the average of the Poisson bracket of a pair of system variables (thedissipative function) for systems in and not in equilibrium. Some exact consequences of the equations when the heat bath and the system are in thermal equilibrium are found. In particular the exact equilibrium distribution function of the system variables is determined and it is demonstrated that the system variables obey the fluctuation–dissipation theorem. Various approximation schemes are devised. When the bath and the system are in thermal equilibrium the approximate equations of motion obey the fluctuation–dissipation theorem and have as a possible steady state solution the exact equilibrium distribution. The theory is applied to the relaxation of a rigid rotor constrained to rotate in two dimensions. The first corrections to the diffusion constant D due to the nonzero correlation times of the bath variables and a finite moment of inertia of the rotor are found. Connection is made with dielectric friction when the rotor is endowed with a permanent dipole moment which interacts with the bath variables via an electric field. A symmetrized version of the Nee–Zwanzig friction constant gives one contribution to the diffusion constant. In addition, when the moment of inertia is finite and the correlation time of the bath variables is nonzero, there is a contribution which tends to increase the diffusion constant.

Notes: General formulas are found for all the multitime correlation functions and susceptibilities of a simple two-dimensional rotor, the motion of which is governed by a Langevin equation containing Gaussian white noise as the torque. A sufficient condition that the equal time Poisson bracket of the angle with its conjugate momentum be satisfied at all times is inferred from the fluctuation–dissipation theorem applied to the fluctuating torque. The formulas include inertial effects, a necessity if high frequency behavior is to be correctly reproduced. The Fourier transforms of the two- and four-time dipole susceptibilities are extracted from the general results in the large friction constant limit. For the particular case of the rotor subjected to a strong constant background field and a weak time dependent probe field, we find that at low frequencies, the rotor exhibits saturation as measured by the real component of the four-time susceptibility. The imaginary part of the parallel component of the four-time susceptibility is found to be negative over the entire range of frequencies, this merely indicating that the overall dissipation in the system is decreased in the presence of a strong field. The Appendix determines the most general form of the correlation functions of the torque when it is specified that the two-time Poisson bracket of the torque is independent of the torque and of the system variables and that the fluctuation–dissipation theorem holds. They are a bit more general than Gaussian.

Notes: Objective: To report an unusual manifestation of acetaminophen intoxication in a dog. Case Summary: A Miniature Pinscher was presented for evaluation of lethargy and facial swelling after ingestion of 500–750 mg/kg of acetaminophen. Laboratory testing revealed eccentrocytes, Heinz bodies, hemoglobinemia, and a declining packed red cell volume consistent with oxidative damage to the erythrocytes. Hepatocellular damage, as monitored by serum alanine aminotransferase, was not documented. The dog responded well to therapeutic intervention, and was discharged from the hospital. The dog returned to the hospital 2 days later with clinical signs and diagnostic tests consistent with acute keratoconjunctivitis sicca, which was assumed to be due to a toxic etiology. The dog responded well to therapy, regaining normal levels of tear production within six weeks. New or Unique Information Provided: Acetaminophen intoxication may be associated with severe erythrocytic oxidative damage in the absence of detectable hepatic injury in dogs. Acetaminophen intoxication may have the potential to cause acute keratoconjunctivitis sicca in dogs. (J Vet Emerg Crit Care 2001; 11(2): 123–126)