The structure of controlled high-strain-rate shear bands generated in Ti-Si reactive powders has been investigated by means of the radd symmetric collapse of a thick-walled cylinder. Shear localization developed at global strains of 0.2-0.4 and a strain rate of lo4 s-I. Within the shear bands, local shear strains were up to 100 9d local shear strain rates were lo7 s-'. Chemical reactions were i...

We report a novel form of xylem dysfunction in angiosperms: reversible collapse of the xylem conduits of the smallest vein orders that demarcate and intrusively irrigate the areoles of red oak (Quercus rubra) leaves. Cryo-scanning electron microscopy revealed gradual increases in collapse from approximately -2 MPa down to -3 MPa, saturating thereafter (to -4 MPa). Over this range, cavitation re...

We report a novel form of xylem dysfunction in angiosperms: reversible collapse of the xylem conduits of the smallest vein orders that demarcate and intrusively irrigate the areoles of red oak (Quercus rubra) leaves. Cryo-scanning electron microscopy revealed gradual increases in collapse from approximately 22 MPa down to 23 MPa, saturating thereafter (to 24 MPa). Over this range, cavitation re...

We studied the natural history of Perthes' disease in 62 children in whom the onset of symptoms was in adolescence. Three patterns of disease were noted, namely, late-onset pattern, segmental collapse, or destructive with failure of revascularisation. In the late-onset pattern, the disease followed the sequence of healing seen in younger children, but adequate epiphyseal remodelling did not occ...

Dynamic pore collapse in porous materials is studied by analyzing the finite deformation of an elastic/viscoplastic spherical shell under impulsive pressure loading. Effects of dynamic loading rate, pore size, initial porosity, strain-rate sensitivity, strain hardening, thermal softening, and mass density of the matrix material on the pore collapse process are examined and results are compared ...

A transition from surface-roughening collapse to a random network collapse has been investigated in fatty acid Langmuir monolayers. In contrast to the random network crack pattern, the surface-roughening crack pattern grows on a much longer time scale and on a much shorter length scale. A change in the isotherm from a surface pressure "spike" to a "plateau" occurs at the transition. In the surf...

A photogeologic and physical modeling study indicates that Hebes Chasma, Mars, formed by collapse of the megaregolith. Local heating facilitated drainage of ~105 km3 of brines and entrained particulates through fractures in the chasma fl oor and into a regional aquifer. A megaregolith rich in salts and water is implied by massive, low-gradient allochthonous fl ows that terminate in deep pits an...

An abrupt onset of the new tongue-shaped deformation of magnetic surface in magnetized plasmas, which was conjectured in since the 1960s but has not been observed, is experimentally identified just before an abrupt onset of a large-scale collapse event. Two novel properties of the event are identified. First, the transition of symmetry of perturbation (rather than a growth of linearly unstable ...

tunnelling through cities underlain by soft soil, commonly associated with soil movement around the tunnels and subsequent surface settlement. the predication of ground movement during the tunnelling and optimum support pressure could be based on analytical, empirical or the numerical methods. the commonly used earth pressure balance (epb) tunneling machines, uses the excavated soil in a pressu...