A self-propelled particle model is introduced to study cell sorting occurring in some living organisms. This allows us to evaluate the influence of intrinsic cell motility separately from differential adhesion with fluctuations, a mechanism previously shown to be sufficient to explain a variety of cell rearrangement processes. We find that the tendency of cells to actively follow their neighbors greatly reduces segregation time scales. A finite-size analysis of the sorting process reveals clear algebraic growth laws as in physical phase-ordering processes, albeit with unusual scaling exponents.

The authors study the arrangement of cells in undifferentiated vegetable tissues of five different species. The distribution of the number of sides, the average area (a_n), perimeter (p_n) and side length (l_n) of n-sided cells are determined as well as the correlation between the number of sides of a cell and of its neighbours. The results show that vegetable cellular nets obey Aboav-Weaire's law. They also discuss Lewis' law and a possible relation between (p_n) and n. The analysis of these structures provides a different example of random cellular structures and helps to show general aspects of the ideal one.

Ultrathin films of ${\mathrm{Al}}_2{\mathrm{O}}_3$ deposited on Si were submitted to rapid thermal annealing in vacuum or in oxygen atmosphere, in the temperature range from $600$ to $800°\mathrm{C}$. Nuclear reaction profiling with subnanometric depth resolution evidenced mobility of O, Al, and Si species, and angle-resolved x-ray photoelectron spectroscopy revealed the formation of Si-Al-O compounds in near-surface regions, under oxidizing atmosphere at and above $700°\mathrm{C}$. Under vacuum annealing all species remained essentially immobile. A model is presented based on diffusion-reaction equations capable of explaining the mobilities and reproducing the obtained profiles.

We present a simulation of the growth of a two-dimensional biological cellular system in which the cells experience mitosis whenever the area-to-perimeter ratio reaches a critical value. The model also includes the effect of interfacial energy and temperature. A stationary state with a constant average area is attained. We calculate the distribution of cells as a function of area, perimeter, and number of sides and also the two-cell correlation function. The results depend on temperature and are in agreement with experimental data, simulations, and theoretical models.

We perform extensive Potts model simulations of three-dimensional dry foam coarsening. Starting with 2.25 million bubbles, we have enough statistics to fulfill the three constraints required for the study of statistical scale invariance: first, enough time for the transient to end and reach the scaling state; then, enough time in the scaling state itself to characterize its properties; and finally, enough bubbles at the end to avoid spurious finite size effects. In the scaling state, we find that the average surface area of the bubbles increases linearly with time. The geometry (bubble shape and size) and topology (number of faces and edges), as well as their correlations, become constant in time. Their distributions agree with the data of the literature. We present an analytical model (universal, up to parameters extracted from the simulations) for a disordered foam minimizing its free energy, which agrees with the simulations. We discuss the limitations of the simulations and of the model.