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A possible approach to the statistical description of granular assemblies starts from Edwards' assumption that all blocked states occupying the same volume are equally probable (S.F. Edwards, R. Oakeshott, Physica A 157, 1080 (1989)). We performed computer simulations using two-dimensional polygonal particles excited periodically according to two different protocols: excitation by pulses of "negative gravity" and excitation by "rotating gravity". The first protocol exhibits a non-monotonous dependency of the mean volume fraction on the pulse strength. The overlapping histogram method is used in order to test whether or not the volume distribution is described by a Boltzmann-like distribution, and to calculate the inverse compactivity as well as the logarithm of the partition sum. We find that the mean volume is a unique function of the measured granular temperature, independently of the protocol and of the branch in $\phi(g)$ and all determined quantities are in agreement with Edwards' theory., Comment: 12 pages, 12 Figures, accepted in Physical Review E

Recently, Pantina and Furst (Phys. Rev. Lett., 94(13), 138301, 2005) experimentally demon- strated that there are tangential forces between bonded colloidal particles and that bonds between colloidal particles are capable of supporting bending moments. We introduce a model to be used in computer simulations that describes these tangential interactions. We show how the model parame- ters can be determined from experimental data. Simulations using the model are able to reproduce the measurement of Pantina and Furst. Application of the model to an aggregate with fractal structure leads to more realistic behavior than using classical approaches only., Comment: 7 pages, 8 figures

The linear dashpot model for the inelastic normal force between colliding spheres leads to a constant coefficient of normal restitution, $\epsilon_n=$const., which makes this model very popular for the investigation of dilute and moderately dense granular systems. For two frequently used models for the tangential interaction force we determine the coefficient of tangential restitution $\epsilon_t$, both analytically and by numerical integration of Newton's equation. Although $\epsilon_n=$const. for the linear-dashpot model, we obtain pronounced and characteristic dependencies of the tangential coefficient on the impact velocity $\epsilon_t=\epsilon_t(\vec{g})$. The results may be used for event-driven simulations of granular systems of frictional particles., Comment: 12 pages, 12 figures

In contrast to a still common belief, a steadily flowing hourglass changes its weight in the course of time. We will show that, nevertheless, it is possible to construct hourglasses that do not change their weight., Comment: 2 pages, 1 figure

The noiseless limit of a thermal ratchet device using ferrofluids is studied in detail. Contrary to previous claims it is proved that no directed transport can occur in this model in the absence of fluctuations., Comment: 10 pages, 2 figures