CiteULike: dchens Zhou

Novel Phase Transformation in ZnO Nanowires under Tensile Loading

Ambarish Kulkarni — 2008-07-24T18:34:11-00:00

Physical Review Letters, Vol. 97, No. 10. (2006)

We predict a previously unknown phase transformation from wurtzite to a graphitelike (P63/mmc) hexagonal structure in [010]-oriented ZnO nanowires under uniaxial tensile loading. Molecular dynamics simulations and first principles calculations show that this structure corresponds to a distinct minimum on the enthalpy surfaces of ZnO for such loading conditions. This transformation is reversible with a low level of hysteretic dissipation of 0.16 J/m3 and, along with elastic stretching, endows the nanowires with the ability to recover pseudoelastic strains up to 15%.

The formation of multiple adiabatic shear bands

F Zhou — 2007-08-26T22:54:30-00:00

Journal of the Mechanics and Physics of Solids, Vol. 54, No. 7. (July 2006), pp. 1376-1400.

In a previous paper, Zhou et al. [2006. A numerical methodology for investigating adiabatic shear band formation. J. Mech. Phys. Solids, 54, 904-926] developed a numerical method for analyzing one-dimensional deformation of thermoviscoplastic materials. The method uses a second order algorithm for integration along characteristic lines, and computes the plastic flow after complete localization with high resolution and efficiency. We apply this numerical scheme to analyze localization in a thermoviscoplastic material where multiple shear bands are allowed to form at random locations in a large specimen. As a shear band develops, it unloads neighboring regions and interacts with other bands. Beginning with a random distribution of imperfections, which might be imagined as arising qualitatively from the microstructure, we obtain the average spacing of shear bands through calculations and compare our results with previously existing theoretical estimates. It is found that the spacing between nucleating shear bands follows the perturbation theory due to Wright and Ockendon [1996. A scaling law for the effect of inertia on the formation of adiabatic shear bands. Int. J. Plasticity 12, 927-934], whereas the spacing between mature shear bands is closer to that predicted by the momentum diffusion theory of Grady and Kipp [1987. The growth of unstable thermoplastic shear with application to steady-wave shock compression in solids. J. Mech. Phys. Solids 35, 95-119]. Scaling laws for the dependence of band spacing on material parameters differ in many respects from either theory.

Stimuli-responsive polymer gels

Suk-Kyun Ahn — 2008-06-20T14:55:03-00:00

Soft Matter, 2008, 4, 1151 - 1157, DOI: 10.1039/b714376a

Stimuli-responsive polymer gels have received considerable attention due to their singular mechanical properties, which make them materials of choice for niche applications. Polymer gels comprising either physical or chemical cross-links can undergo controlled and reversible shape changes in response to an applied field. The stimulus or external field applied may include thermal, electrical, magnetic, pH, UV/visible light, ionic or metallic interactions or combinations thereof. The shape change can manifest itself in two-dimensional actuation, bending motion, or three-dimensional actuation, volume change. This reversible contraction and expansion of polymer gels as well as their mechanical properties are similar to that of biological muscles. This review will describe and critique some of the recent advances in the field of stimuli-responsive polymer gels including the design of new classes of polymeric gels, controlled actuation in response to external stimuli, and ability to tailor material properties for different applications.

Solvent-Induced DNA Conformational Transition

B Gu — 2008-05-07T23:28:21-00:00

Physical Review Letters, Vol. 100, No. 8. (2008)

Modified water models with scaled charges are used to investigate solvent polarity effects on DNA structure. Several intensive molecular dynamics simulations of the DNA EcoRI dodecamer d(CGCGAATTCGCG) in different model solvents are performed. When the polarity of the solvent molecule decreases, from overpolarized to less polarized, DNA experiences the conformational transitions of constrainedB form(A-B)mixA form. We demonstrate that one important cause of these structure changes is the competition between hydration and direct cation coupling to the free oxygen atoms in the phosphate groups on DNA backbones.

Pressure-driven flow of suspensions of liquid drops

Hua Zhou — 2008-04-27T00:15:54-00:00

Physics of Fluids, Vol. 6, No. 1. (1994), pp. 80-94.

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Measurement of Forces Inside a Three-Dimensional Pile of Frictionless Droplets

J Zhou — 2008-01-01T22:04:40-00:00

Science, Vol. 312, No. 5780. (16 June 2006), pp. 1631-1633.

We present systematic and detailed measurements of interparticle contact forces inside three-dimensional piles of frictionless liquid droplets. We measured long-range chainlike correlations of the directions and magnitudes of large forces, thereby establishing the presence of force chains in three dimensions. Our correlation definition provides a chain persistence length of 10 mean droplet diameters, decreasing as load is applied to the pile. We also measured the angles between contacts and showed that the chainlike arrangement arises from the balance of forces. Moreover, we found that piles whose height was comparable to the chain persistence length exhibited substantially greater strain hardening than did tall piles, which we attributed to the force chains. Together, the results establish a connection between the microscopic force network and the elastic response of meso- or macroscopic granular piles. The conclusions drawn here should be relevant in jammed systems generally, including concentrated emulsions and piles of sand or other heavy particles. 10.1126/science.1125151