What crumpled aluminum in common with liquid crystals?
Take a sheet of aluminum foil from your kitchen and crumple it
as hard as you can. Give it a few whams with a hammer before
throwing the ball into the water. You will be surprised to find
this metal ball floating, which suggests that it still contains more
than 70% of air. An architect will be dying to know the secret to
this amazingly strong structure out of such magically little material.
In this paper, we employed a special version of microtomography,
similar to the CT scan in medical hospitals, to study the interior of
a crumpled aluminum ball. Patches of ordered domain were found to
appear near the crust, which is reminiscent of the lamellae phase in
lyotropic liquid crystals. We believe the strong resistance offered by
a crumpled ball is intimately related to these brick-like domains whose
lateral size shortens while thickness grows with further compression.
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LH12192
Whispering Gallery Tube Resonator for Spin Waves
We present a novel type of spin wave resonator which resembles the universal concept of whispering-gallery modes as discovered by Lord Rayleigh in 1910, and well known from acoustics and optics, for spin waves.
We employ strain driven ‘rolled-up nanotech’ to curl up permalloy/semiconductor nanolayers with multiple rotations into a rolled-up-carpet shaped micro tube (cf. teaser image). The homogeneous magnetization in our rolled-up structures resembles the refractive index in optical resonators or the stiffness in acoustic materials and can be tuned simply by changing the external magnetic field.
In contrast to spin-wave resonators presented so far in literature, which are often dominated by complicated inhomogeneous magnetization patterns arising from the edges of the structures, our rolled up structures exhibit well separated sharp spin-wave resonances. The frequencies of the resonances can be understood considering the mode interference in a closed geometry very similar to acoustic or optical whispering gallery modes. The modes exist over a broad magnetic field range and can be tuned over several GHz. These findings are not only appealing from a general standpoint of physical aesthetics but also of high importance for future logic spin-wave devices which require high quality tuneable spin-wave filters.
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EK10568
Not so spherical bubbles
Small bubbles in liquids are round because surface tension forces them into a shape with minimum surface. Yet bubbles in nature happen in all shapes, in particular when external forces act on them, such as gravity or an external flow. Researchers from the Nanyang Technological University now devised a new technique to create bubbles on demand with arbitrary shapes. They are using a laser and a digital hologram to create, ellipsoidal, toroidal, and square shaped bubbles. All these bubbles are short lived and therefore have to be recorded with a high-speed camera. Some of the bubbles change shape during their lifetime. Their dynamics is compared to simulations and excellent agreement is found. Initially their research was curiosity driven, yet interesting applications open up from these not so round bubbles. These bubbles create unique flow patterns which have not been available so far, e.g. a compression only flow is occurring at the center of a donut shaped bubble. This and other flow patterns are promising to assess mechanical properties of elastic objects in liquids, such as the rigidity of biological cells or the stability of emulsions.
