Showing papers by "Jeffrey W. Kysar published in 2014"

Computational strain gradient crystal plasticity

Abstract: A numerical method for viscous strain gradient crystal plasticity theory is presented, which incorporates both energetic and dissipative gradient effects. The underlying minimum principles are discussed as well as convergence properties of the proposed finite element procedure. Three problems of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically oriented face centered cubic crystals are developed in terms of the crystallographic slip parameters. The effect on geometrically necessary dislocation structures introduced by plastic deformation is investigated as a function of the ratio of void radius to plasticity length scale.

Microanatomic analysis of the round window membrane by white light interferometry and microcomputed tomography for mechanical amplification.

Abstract: OBJECTIVE The round window membrane (RWM) is increasingly becoming a target for amplification using active middle ear implants. However, the current strategy of using available transducer tips may have negative consequences for the RWM. We investigated the microanatomy of the RWM to establish a basis for the design of the transducer tip for the RWM driver. STUDY DESIGN Using the guinea pig as an animal model, microcomputed tomography (μCT) and white light interferometry were used to study the topography of the RWM and RW niche (RWN). The curvatures of the RWM surface were calculated using the topography data. MAIN OUTCOME MEASURES The 3-dimensional structure of the scala tympani terminal, saddle-shaped surface topography, and surface curvature were determined. RESULTS The size of the scala terminal was approximated as an ellipse for which the major and minor axes were 1.29 and 0.95 mm. The average minimum and maximum radii of curvature around the center of RWM were -0.44 and +0.70 mm along the minor and major axis. CONCLUSION The microanatomies of the RWM and RWN have important implications for the design of the transducer tip to maximize energy transfer while minimizing its distortion and permanent disruption. Our results suggest that the size of the transducer tip should be smaller than the minor axis of the scala terminal to avoid collision with the RWN. The driver should be designed to conform to the topography and radius of curvature of the center portion of the RWM, which for a guinea pig is 0.44 mm.

Comment on "Ideal strength and phonon instability in single-layer MoS 2 "

Abstract: Li's paper [Phys. Rev. B 85, 235407 (2012)] presents density functional theory (DFT) results of stress as a function of different strain states. The work of Cooper et al. [Phys. Rev. B 87, 035423 (2013)] performs the same DFT calculations as part of an investigation into the nonlinear elastic properties of ${\mathrm{MoS}}_{2}$. Some of the DFT results of Li are substantially different from our recently published paper, Cooper et al. [Phys. Rev. B 87, 035423 (2013)]. Although both papers agree on states of equibiaxial stress, there is substantial disagreement on states of uniaxial tensile stress. In this Comment we show that our DFT computations are properly executed and consistent across three different DFT codes, including the one used by Li.

Cellular response to surface with nanoscale heterogeneous rigidity

Abstract: An elastomeric substrate comprises a surface with regions of heterogeneous rigidity, wherein the regions are formed by exposing the elastomeric substrate to an energy source to form the regions such that the regions include a rigidity pattern comprising spots.