The reversible reactions A + A ⇀ ↽ C and A + B ⇀ ↽ C are investigated. From the exact Langevin equations describing our model, we set up a systematic approximation scheme to compute the approach of the density of C particles to its equilibrium value. We show that for sufficiently long time t, this approach takes the form of a power law At −d/2 , for any dimension d. The amplitude A is also computed exactly, but is expected to be model dependent. For uncorrelated initial conditions, the C density turns out to be a monotonic time function. The cases of correlated initial conditions and unequal diffusion constants are investigated as well. In the former, correlations may break the monotonicity of the density or in some special cases they may change the long time behavior. For the latter, the power law remains valid, only the amplitude changes, even in the extreme case of immobile C particles. We also consider the case of segregated initial condition for which a reaction front is observed, and confirm that its width is governed by mean-field exponent in any dimension.

A prevailing common-sense hypothesis (the "hue-heat " hypothesis) is that an environment which has dominant light frequencies toward the red end of the visible spectrum feels warm and one with dominant blue frequencies feels cool. Twenty-one students made thermal comfort ratings while wearing red, blue, and clear goggles during three 20-min. runs in which air conditions were "comfortable" and wall temperatures were varied from about 60' to 100°F and back. Four analyses were conducted of the temperatures at which subjects changed their thermal comfort judgment from one category t o another. While subject and direction-of-temperaturechange effects were significant, no hue main effects or interactions were found. I t was concluded that hue produces a strictly intellectual effect, a belief that one is warmer or cooler but does not affect one's thermal comfort.

Ballistic annihilation kinetics for a multi-velocity one-dimensional ideal gas is studied in the framework of an exact analytic approach. For an initial symmetric three-velocity distribution, the problem can be solved exactly and it is shown that different regimes exist depending on the initial fraction of particles at rest. Extension to the case of a n-velocity distribution is discussed.

We study the kinetics of ballistic annihilation for a one-dimensional ideal gas with continuous velocity distribution. A dynamical scaling theory for the long time behavior of the system is derived. Its validity is supported by extensive numerical simulations for several velocity distributions. This leads us to the conjecture that all the continuous velocity distributions φ(v) which are symmetric, regular and such that φ(0) = 0 are attracted in the long time regime towards the same Gaussian distribution and thus belong to the same universality class. Moreover, it is found that the particle density decays as n(t) ∼ t −α , with α ≃ 0.785 ± 0.005.

A class of d-dimensional reaction-diffusion models interpolating continuously between the diffusion-coagulation and the diffusion-annihilation models is introduced. Exact relations among the observables of different models are established. For the one-dimensional case, it is shown how correlations in the initial state can lead to non-universal amplitudes for time-dependent particles density.