Browse the Annual Review of Materials Research Volume 47 table of contents.

I am thrilled to introduce you to “Physical Dynamics of Ice Crystal Growth” by Libbrecht. This article provided me with a welcome break from the heat and inspired a great deal of respect for this field (as well as a snow dance in my office chair). It’s a really great article and I hope you go take a look—even if just to gaze in wonder at the figures.

“The winter clouds produce a great diversity of snow-crystal forms, from slender columns to thin plates, at times branched, sectored, hollowed, and faceted, as shown in Figure 1. Yet extensive laboratory and theoretical investigations have still not determined why these varied structures appear under different growth conditions. For example, we do not yet possess even a qualitative understanding of why snow crystal growth alternates between plate-like and columnar forms as a function of temperature, as seen in Figure 1, although this behavior was first observed more than 75 years ago.”

I would be willing to bet that most of us have bent a spoon while attempting to scoop hard ice cream. A few of us have gone on to write scientific papers about it, as I discovered in the article by Sethna et al. “Deformation of Crystals: Connections with Statistical Physics.”

“A metal spoon will spring back into its original shape under ordinary use, but when scooping hard ice cream, one may bend the spoon too far for it to recover (Figure 1). The spoon is made up of many crystalline grains, each of which has a regular grid of atoms. To permanently deform the spoon, atomic planes must slide past one another. Such glide happens through the motion of dislocation lines. The dynamics, interactions, and entanglement of these dislocation lines form the microscopic underpinnings of crystal plasticity, inspiring this review.”

It’s a noisy world out there and I’ve often wished for better soundproofing.  I was not aware of the complexity of those sound barriers until discovering Yang & Sheng’s article, “Sound Absorption Structures: From Porous Media to Acoustic Metamaterials.” I particularly enjoyed the early section on “traditional porous materials such as plastic foam, fiber glass, and mineral wool.”

“Because sound is associated with very small air displacement velocities, its dissipation as a function of frequency must obey the linear response theory, in which the generalized flux (e.g., electrical current density, flow rate, heat flux) is linearly proportional to the generalized force (e.g., gradients of electrical potential, pressure, temperature). Because dissipative force varies linearly as function of the rate (e.g., dynamic friction varies linearly as a function of relative velocity) and dissipated power is given by the product of force and flux, it follows that sound dissipation is a quadratic function of frequency, as shown below. Hence, for low frequency sound, dissipation is inherently much weaker than for high-frequency sound.”

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