Structure-property relationships from universal signatures of plasticity in disordered solids.

When deformed beyond their elastic limits, crystalline solids flow plastically via particle rearrangements localized around structural defects. Disordered solids also flow, but without obvious structural defects. We link structure to plasticity in disordered solids via a microscopic structural quantity, "softness," designed by machine learning to be maximally predictive of rearrangements. Experimental results and computations enabled us to measure the spatial correlations and strain response of softness, as well as two measures of plasticity: the size of rearrangements and the yield strain. All four quantities maintained remarkable commonality in their values for disordered packings of objects ranging from atoms to grains, spanning seven orders of magnitude in diameter and 13 orders of magnitude in elastic modulus. These commonalities link the spatial correlations and strain response of softness to rearrangement size and yield strain, respectively.

The distribution of homogeneously grafted nanoparticles in polymer thin films and blends.

Polymer nanocomposites are an important and growing class of materials where nanoparticles are mixed in a polymer matrix. Much of the interest in polymer nanocomposites is derived from the nanoparticles' ability to impart properties to the polymer not commonly found in polymer materials, such as tunable optical, electrical, and mechanical properties. Grafting polymer chains to the surface of a nanoparticle is one of the most common routes towards promoting dispersion of nanoparticles in a polymer matrix. However, we only understand the thermodynamics of grafted nanoparticles in a polymer matrix in the simplest of cases, and this problem is exacerbated by the lack of theoretical and computational tools capable of efficiently predicting the structure of phase separated grafted nanoparticle/polymer blends. In this work, we extend a recently developed field theoretic framework to study the distribution of homogeneously grafted nanoparticles in homopolymer thin films and blends. We demonstrate that our method reproduces trends observed experimentally in homopolymer thin films, and then we examine how the nanoparticle size, grafting density, and the length of the grafted chains relative to the matrix chains affects the distribution of the grafted nanoparticles in phase separated polymer blends. We find that position of the nanoparticles relative to the interface in the blends is sensitive to the brush conformation, even when the nanoparticles are miscible in one of the two homopolymer phases.

Autonomous requirements for the segment polarity gene armadillo during Drosophila embryogenesis.

Embryos hemizygous for armadillo produce a "segment polarity" phenotype in which the naked posterior two-thirds of each segment is replaced by denticles with reversed polarity. Small patches of homozygous arm cells induced by mitotic recombination also form such denticles, indicating that the changes in cellular fate observed in homozygous arm embryos are autonomous at the level of single cells. Clonally derived arm patches do not, however, show the characteristic arm polarity reversals, arguing that this feature of the phenotype depends on cell interactions in fully mutant embryos. Few, if any, clones were found in the posterior-most regions of the naked cuticle, and none were found in the posterior compartments of the thorax.

The disease resistance response in pea is associated with increased levels of specific mRNAs.

A cDNA library was constructed using poly(A)(+)RNA fromPisum sativum which had been treated for 8 h with the fungusFusarium solani f. sp.phaseoli. Two thousand four hundred recombinant colonies were screened by differential colony hybridization using(32)P-labelled cDNAs prepared from RNA extracted from either noninoculated or inoculated pea tissue. cDNA clones were then selected, which showed greater hybridization with cDNA prepared from pea RNA 8 h post-inoculation than with a cDNA probe from 0 h. Seven distinct hybridization classes were chosen for further study. Northern blot analyses of total cellular RNAs inoculated for 16 h with eitherF. solani phaseoli or water demonstrated that each cDNA clone selected represents an mRNA species which increases substantially in abundance during infection.Results of(3)H-uridine pulse-labelling experiments suggested that enhanced synthesis is at least partially responsible for the accumulation of the fungus-inducible mRNAs which hybridized with the clones.