Near-atomic resolution structures of interdigitated nucleosome fibres

Chromosome structure at the multi-nucleosomal level has remained ambiguous in spite of its central role in epigenetic regulation and genome dynamics. Recent investigations of chromatin architecture portray diverse modes of interaction within and between nucleosome chains, but how this is realized at the atomic level is unclear. Here we present near-atomic resolution crystal structures of nucleosome fibres that assemble from cohesive-ended dinucleosomes with and without linker histone. As opposed to adopting folded helical ‘30 nm’ structures, the fibres instead assume open zigzag conformations that are interdigitated with one another. Zigzag conformations obviate extreme bending of the linker DNA, while linker DNA size (nucleosome repeat length) dictates fibre configuration and thus fibre–fibre packing, which is supported by variable linker histone binding. This suggests that nucleosome chains have a predisposition to interdigitate with specific characteristics under condensing conditions, which rationalizes observations of local chromosome architecture and the general heterogeneity of chromatin structure.

Compressive behaviour of fibre reinforced plastic with random fibre packing and a region of fibre waviness

A critical limitation of fibre reinforced plastic is its large variability on mechanical performance, especially the longitudinal compressive strength. The influence of fibre random packing and waviness on the compressive strength of UD fibre reinforced plastic is studied in this paper. Three-dimensional geometrically non-linear finite element model is constructed to investigate the compressive behaviour, and an improved approach named Latin hypercube sampling based on random sequential expansion is proposed to generate random fibre distribution across the cross-section. Latin hypercube sampling based on random sequential expansion provides high computation efficiency and good distribution characteristics in comparison to previously proposed methods. Fibre waviness defect with different misalignment angles is also incorporated in the finite element model. It is shown that random fibre packing tends to result in a stochastic detriment of fibre reinforced plastic compressive strength in comparison with uniform fibre packing condition, and the stochastic variation of compressive strength tends to follow normal or lognormal distribution.

The effects of different fibre packing geometries on the transverse matrix strain magnification and fibre strain reduction in uniaxially aligned continuous fibre-reinforced composites

Expressions for transverse matrix strain magnification and fibre strain reduction are derived for square and hexagonal fibre array reinforced composites. Respective transverse matrix and fibre strain magnification and reduction, for the square arrays are shown to be higher for all reinforcing fibre volume fractions than those for the hexagonal arrays. The respective magnification and reduction of the transverse matrix and fibre strains are shown to decrease with increasing values of the ratio of elastic modulus ( Em/ Ef) for both reinforcing fibre arrays. The magnified transverse matrix strains in axially loaded longitudinally aligned continuous fibre-reinforced composites are shown to be higher than the applied longitudinal strains for all square array reinforcing fibre volume fractions and for all hexagonal array reinforcing fibre volumes fractions above 31%. This raises possibilities of longitudinal matrix splitting before interfacial bond failure and transverse matrix failure, in a strain based rather than stress-based failure mode.