6,407 research outputs found
Orientation-dependent handedness and chiral design
Chirality occupies a central role in fields ranging from biological
self-assembly to the design of optical metamaterials. The definition of
chirality, as given by Lord Kelvin, associates chirality with the lack of
mirror symmetry: the inability to superpose an object on its mirror image.
While this definition has guided the classification of chiral objects for over
a century, the quantification of handed phenomena based on this definition has
proven elusive, if not impossible, as manifest in the paradox of chiral
connectedness. In this work, we put forward a quantification scheme in which
the handedness of an object depends on the direction in which it is viewed.
While consistent with familiar chiral notions, such as the right-hand rule,
this framework allows objects to be simultaneously right and left handed. We
demonstrate this orientation dependence in three different systems - a
biomimetic elastic bilayer, a chiral propeller, and optical metamaterial - and
find quantitative agreement with chirality pseudotensors whose form we
explicitly compute. The use of this approach resolves the existing paradoxes
and naturally enables the design of handed metamaterials from symmetry
principles
Rectification of energy and motion in non-equilibrium parity violating metamaterials
Uncovering new mechanisms for rectification of stochastic fluctuations has
been a longstanding problem in non-equilibrium statistical mechanics. Here,
using a model parity violating metamaterial that is allowed to interact with a
bath of active energy consuming particles, we uncover new mechanisms for
rectification of energy and motion. Our model active metamaterial can generate
energy flows through an object in the absence of any temperature gradient. The
nonreciprocal microscopic fluctuations responsible for generating the energy
flows can further be used to power locomotion in, or exert forces on, a viscous
fluid. Taken together, our analytical and numerical results elucidate how the
geometry and inter-particle interactions of the parity violating material can
couple with the non-equilibrium fluctuations of an active bath and enable
rectification of energy and motion.Comment: 9 Pages + S
Fracture surface characteristics of notched angleplied graphite/epoxy composites
Composite fracture surface characteristics and related fracture modes have been investigated through extensive microscopic inspections of the fracture surfaces of notched angleplied graphite/epoxy laminates. The investigation involved 4 ply laminates of the configuration + or - theta (s) where theta = 0 deg, 3 deg, 5 deg, 10 deg, 15 deg, 30 deg, 45 deg, 60 deg, 75 deg, and 90 deg. Two-inch wide tensile specimens with 0.25 in. by 0.05 in. through-slits centered across the width were tested to fracture. The fractured surfaces were then removed and examined using a scanning electron microscope. Evaluation of the photomicrographs combined with analytical results obtained using the CODSTRAN computer code culminated in a unified set of fracture criteria for determining the mode of fracture in notched angleplied graphite/epoxy laminates
The Life of a Vortex Knot
The idea that the knottedness (hydrodynamic Helicity) of a fluid flow is
conserved has a long history in fluid mechanics. The quintessential example of
a knotted flow is a knotted vortex filament, however, owing to experimental
difficulties, it has not been possible until recently to directly generate
knotted vortices in real fluids. Using 3D printed hydrofoils and high-speed
laser scanning tomography, we generate vortex knots and links and measure their
subsequent evolution. In both cases, we find that the vortices deform and
stretch until a series of vortex reconnections occurs, eventually resulting
several disjoint vortex rings.
This article accompanies a fluid dynamics video entered into the Gallery of
Fluid Motion at the 66th Annual Meeting of the APS Division of Fluid Dynamics.Comment: Videos are included; this submission is part of the DFD Gallery of
Fluid Motio
Factors Controlling Initial Establishment of Western White Pine and Associated Species
The principal object of the study was to determine the roles played by important physical factors of site, chiefly as these vary with overhead shade and hence are within the control of the silviculturist at the time of logging. No special effort was made to study the effect of biotic agents under natural conditions. Indeed, in order to insure as large a sample of seedlings as possible on which to follow losses caused by physical factors, biotic agents were discouraged wherever feasible. But as records of all mortality losses were kept by cause, some information was collected on the activity of biotic factors. Seedlings were classified as to cause of death only after a careful diagnosis and with knowledge of the important agents operating at the time death occurred. Certain check quadrats were used effectively in segregating causes; but the most satisfactory control came in instrumental measurement of important site . factors, including surface soil temperature and soil moisture. As a necessary adjunct in following the occurrence of critical soil moisture conditions, current measurements were made of root penetration
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