LOCAL VOLUME FRACTION FLUCTUATIONS IN RANDOM-MEDIA

Although the volume fraction is a constant for a statistically homogen eous random medium, on a spatially local level it fluctuates. We study the full distribution of volume fraction within an observation window of finite size for models of random media. A formula due to Lu and To rquato for the standard deviation or ''coarseness'' associated with th e local volume fraction xi is extended for the nth moment of xi for an y n. The distribution function F-L Of the local volume fraction of fiv e different model microstructures is evaluated using analytical and co mputer-simulation methods for a wide range of window sizes and overall volume fractions. On the line, we examine a system of fully penetrabl e rods and a system of totally impenetrable rods formed by random sequ ential addition (RSA). In the plane, we study RSA totally impenetrable disks and fully penetrable aligned squares. In three dimensions, we s tudy fully penetrable aligned cubes. In the case of fully penetrable r ods, we will also simplify and numerically invert a prior analytical r esult for the Laplace transform of F-L In all of these models, we show that, for sufficiently large window sizes, F-L can be reasonably appr oximated by the normal distribution. (C) 1997 American Institute of Ph ysics.