126 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
Minimum-consumption discrimination of quantum states via globally optimal adaptive measurements
Reducing the average resource consumption is the central quest in
discriminating non-orthogonal quantum states for a fixed admissible error rate
. The globally optimal fixed local projective measurement (GOFL)
for this task is found to be different from that for previous minimum-error
discrimination tasks [PRL 118, 030502 (2017)]. To achieve the ultimate minimum
average consumption, here we develop a general globally optimal adaptive
strategy (GOA) by subtly using the updated posterior probability, which works
under any error rate requirement and any one-way measurement restrictions, and
can be solved by a convergent iterative relation. First, under the local
measurement restrictions, our GOA is solved to serve as the local bound, which
saves 16.6 copies (24%) compared with the previously best GOFL. When the more
powerful two-copy collective measurements are allowed, our GOA is
experimentally demonstrated to beat the local bound by 3.9 copies (6.0%). By
exploiting both adaptivity and collective measurements, our work marks an
important step towards minimum-consumption quantum state discrimination
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
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