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A variety of phonon-gas phenomena in nonmetals are discussed in a unified manner using a set of macroscopic equations developed from the solution of the linearized phonon Boltzmann equation. This set of macroscopic equations, appropriate for the description of a low-temperature phonon gas, is solved for a cylindrical sample in the limit ) z(&R; ) &)~*))R'. Here X& is the normal-process mean free path, Xz' is the mean free path for momentum-loss scattering calculated in the Ziman limit, and R is the radius of the sample. The solution in this limit exhibits Poiseuille flow of the phonon gas as first discussed by Sussmann and Thellung. An equation for the thermal conductivity which correctly includes this phenomenon is found. Using this equation, the possible outcomes of steady-state thermal-conductivity measurements are discussed in terms of the microscopic scattering rates. Heat-pulse propagation is discussed from a similar point of view. The existence of Poiseuille Row in steady-state thermal-conductivity measurements bears directly on the possibility of observing second sound in solids. A quantitative analysis of available data on LiF suggests that the chemical purity of these samples sets very stringent limits on the observation of either of these effects. The observation of Poiseuille How in solid He' samples by Mezov-Deglin strongly suggests that this material is a prime subject for investigations of second-sound propagation.

A squash ball almost doesn't bounce; a Superball bounces first left then right, seeming to have a mind of its own. Remarkable and complex elastic behavior isn't confined to sports equipment and toys. Indeed, it can be found in some surprising places. When the elastic behavior of a rock is probed, for instance, it shows extreme nonlinearity hysteresis and discrete memory (the Flint-stones could have had a computer that used a sandstone for random-access memory). Rocks are an example of a class of unusual elastic materials that includes sand. soil, cement, concrete, ceramics and, it turns out, damaged materials, Many members of this class are the blue-collar materials of daily life: They are in the bridges we cross on the way to work, the roofs over our heads and the ground beneath our cities—such as the Los Angeles basin (home to many earthquakes). The elastic behavior of these materials is of more than academic interest.

Experimental properties of a new form of creep dynamics are reported, as manifest in a variety of sandstones, limestone, and concrete. The creep is a recovery behavior, following the sharp drop in elastic modulus induced either by nonlinear acoustic straining or rapid temperature change. The extent of modulus recovery is universally proportional to the logarithm of the time after source discontinuation in all samples studied, over a scaling regime covering at least 10(3) s. Comparison of acoustically and thermally induced creep suggests a single origin based on internal strain, which breaks the symmetry of the inducing source.

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