The topological structure of 2D disordered cellular systems

We analyze the structure of two dimensional disordered cellular systems generated by extensive computer simulations. These cellular structures are studied as topological trees rooted on a central cell or as closed shells arranged concentrically around a germ cell. We single out the most significant parameters that characterize statistically the organization of these patterns. Universality and specificity in disordered cellular structures are discussed.Comment: 18 Pages LaTeX, 16 Postscript figure

Interaction of the 89K murine cytomegalovirus immediate-early protein with core histones

The conditions that permit the interaction of immediate-early proteins of murine cytornegalovirus (MCMV) with DNA were studied. Chromatography of extracts from infected cells on MCMV DNA cellulose and calf thymus DNA cellulose showed that pp89, the regulatory major immediate-early protein, interacts with DNA and dissociates at salt concentrations between 0.3 and 0.6 M NaCl. pp76, a cleavage product of pp89, and additional minor ie1 proteins eluted already at low ionic strength. Cellular DNA-binding factors were required for association of pp89 with DNA. These factors were identified as core histones. Chromatography of IE proteins on histone-Sepharose in the absence of DNA revealed a high-binding affinity that was resistant to 2 M NaCl. These results suggest that pp89 has no direct DNA-binding activity. A role for an amino acid sequence homology in the N-terminal region of pp89 with histone H2B in the pp89-histone-DNA Interaction is discussed

Avalanches of popping bubbles in collapsing foams

We report acoustic experiments on foam systems. We have recorded the sound emitted by crackling cells during the collapsing of foams. The sound pattern is then analyzed using classical methods of statistical physics. Fundamental processes at the surface of the collapsing foam are found. In particular, size is not a relevant parameter for exploding bubbles.Comment: 8 pages, 4 figures, submitted for publicatio