Corn ethanol production, food exports, and indirect land use change

The approximately 100 million tonne per year increase in the use of corn to produce ethanol in the U.S. over the past 10 years, and projections of greater future use, have raised concerns that reduced exports of corn (and other agricultural products) and higher commodity prices would lead to land-use changes and, consequently, negative environmental impacts in other countries. The concerns have been driven by agricultural and trade models, which project that large-scale corn ethanol production leads to substantial decreases in food exports, increases in food prices, and greater deforestation globally. Over the past decade, the increased use of corn for ethanol has been largely matched by the increased corn harvest attributable mainly to increased yields. U.S. exports of corn, wheat, soybeans, pork, chicken, and beef either increased or remained unchanged. Exports of distillers' dry grains (DDG, a coproduct of ethanol production and a valuable animal feed) increased by more than an order of magnitude to 9 million tonnes in 2010. Increased biofuel production may lead to intensification (higher yields) and extensification (more land) of agricultural activities. Intensification and extensification have opposite impacts on land use change. We highlight the lack of information concerning the magnitude of intensification effects and the associated large uncertainties in assessments of the indirect land use change associated with corn ethanol.

Evanescent-wave scattering by electrophoretic microparticles: a mechanism for optical switching

The total internal reflection of light occurring at the interface between glass and a low-index liquid containing suspended microparticles can be electrically controlled. The particles are charged and the glass is coated with a thin, transparent conductor. When the conductor is biased to attract the particles, they scatter and absorb light from the evanescent optical field near the interface, thus reducing the reflectivity. When the conductor is biased to repel the particles, total internal reflection is achieved. Experimental results are given for the time, voltage, and angle-of-incidence dependence of the reflectivity at the interface between an In-Sn-oxide-coated glass surface and a suspension of 0.47-µm-diameter silica particles in acetonitrile. The switching is found to be fast (~ 100 ms) and reproducible. In certain conditions the on/off ratio for a single reflection can be as large as 2:1. A simple theoretical model is developed to interpret these experiments. The model gives a reasonable fit to the data and allows one to extract information such as the particle mobility and the particle density in the evanescent-wave region.