Galaxies and galaxy clusters are observed to have a rather non-trivial radial behaviour. The observations show that the radial profiles change from one power-law profile near the centre to another power-law profile in the outer region. We present a simple explanation for this complex behaviour by finding the analytical solutions to the governing hydrodynamic equations. We see that the origin of...

Cilia hoist dust out of the lungs, propel sperm toward the egg, and enable us to catch the scent of fresh coffee. The structures also help some cells attach to their surroundings, Schouteden et al. reveal (1). A cilium is built around the axoneme, an internal shaft of microtubules that sprouts from a structure known as the basal body. Between the axoneme and the basal body lies the transition z...

We follow the dynamic evolution of a cluster of Ising spins pointing up surrounded by other spins pointing down, on a lattice. The cluster represents a liquid drop. Under a microscopic point of view, the short range ferromagnetic coupling between these spins plays the role of the van der Waals attraction. Alternatively , under a macroscopic point of view, the same ferromagnetic coupling gives r...

B urkart et al. describe how a secreted protease helps egg cells avoid being fertilized by more than one sperm. Because polyspermy disrupts em-bryonic development, oocytes take several steps to ensure they only fuse with a single sperm. One key step is to prevent additional sperm from binding to the surface of an already-fertilized egg, a blockade that involves the release of secretory granules...