19 research outputs found
Mechanics of Tunable Helices and Geometric Frustration in Biomimetic Seashells
Helical structures are ubiquitous in nature and engineering, ranging from DNA
molecules to plant tendrils, from sea snail shells to nanoribbons. While the
helical shapes in natural and engineered systems often exhibit nearly uniform
radius and pitch, helical shell structures with changing radius and pitch, such
as seashells and some plant tendrils, adds to the variety of this family of
aesthetic beauty. Here we develop a comprehensive theoretical framework for
tunable helical morphologies, and report the first biomimetic seashell-like
structure resulting from mechanics of geometric frustration. In previous
studies, the total potential energy is everywhere minimized when the system
achieves equilibrium. In this work, however, the local energy minimization
cannot be realized because of the geometric incompatibility, and hence the
whole system deforms into a shape with a global energy minimum whereby the
energy in each segment may not necessarily be locally optimized. This novel
approach can be applied to develop materials and devices of tunable geometries
with a range of applications in nano/biotechnology
Nonlinear geometric effects in mechanical bistable morphing structures
Bistable structures associated with non-linear deformation behavior,
exemplified by the Venus flytrap and slap bracelet, can switch between
different functional shapes upon actuation. Despite numerous efforts in
modeling such large deformation behavior of shells, the roles of mechanical and
nonlinear geometric effects on bistability remain elusive. We demonstrate,
through both theoretical analysis and table-top experiments, that two
dimensionless parameters control bistability. Our work classifies the
conditions for bistability, and extends the large deformation theory of plates
and shells.Comment: 3 figure
Evolution of interfacial structure of the joints between a tungsten-copper composite and austenitic stainless steel
Joining of CuW70 composite and 0Cr18Ni9 stainless steel was successfully achieved at temperatures 1150 °C with durations from 15 to 90 min after adding a pure copper intermediate layer. Microstructure, phase composition and elemental distribution at the interfacial region were studied. The optimum joining interface with a dense microstructure was obtained at a joining temperature of 1150 °C with a duration of 60 min. Interdiffusion of atoms occurred at the interface between the tungsten-copper composite and stainless steel, resulting in formation of various compounds such as W _0.6 Cu _0.4 , Cu _3.8 Ni and Fe _0.946 Ni _0.054 . An iron chromium-rich layer was formed at the interface near the tungsten-copper composite side, and an island structure containing Cr, Cu, and Ni was formed near the stainless steel side
Face Normals “in-the-wild” using Fully Convolutional Networks
Leftward twisting of the embryonic chick brain subjected to surface tension in an abnormal chick embryo with a leftward looped hear
Supplementary Figure S1 from How the embryonic chick brain twists
Measurement of the torsional angle from the OCT image
Erratum: Mechanics of tunable helices and geometric frustration in biomimetic seashells
Original article: EPL, 105 (2014) 6400