Spinning Doughnuts in your Coffee, with Video
Everyone knows that after about 10 minutes a hot cup of coffee will cool but if you could spin it about its axis, not only would it cool much less rapidly, but you would not need a doughnut to go with it—they would form right in the cup! Not doughnuts of the usual variety of course (one cannot make dough from water alone) but patterns that underlie the basic physical processes at work in all fluids when their free surfaces are cooled; coffee cups, planetary atmospheres, oceans and any other rotating fluid body. A coffee or tea drinker who takes milk knows that a splash of the cold white stuff sinks to the bottom. If one does not stir with a spoon after a while “clouds” of milk appear at the surface. How? That last bit of water on your back after a shower feels cool because the latent heat of evaporation is taken away from your body. Here, we find that if the cup of coffee is rotated, the cold dense sinking fluid does not go straight down. Rather, for a period of time while the fluid sinks it also rotates with the rest of the liquid, its motion resisted solely by the intrinsic fluid shear viscosity. During this state, using a highly quantitative optical methodology in which we track the motion of all of the fluid parcels in the cup, we observe a concentric pattern of rings forming—doughnuts—from the inside to the outside of the fluid (see b below). Thus, the cup of coffee cools more rapidly in the center than in the outside. Eventually, the relative motion of the rings creates a sufficient shear that they break down into a grid of vortices which characterize not only what is typically assumed to be the usual state of affairs in planetary fluids, but also magnetic vortices in solid materials and other vortex states. All in a cup of coffee…breakfast anyone? See the saga unfold in the movie below and the sequence below taken from it: http://pantheon.yale.edu/~jw378/Convec_rings_vortices.avi
***
AQ10637
The shortest pulse in the world with commercial lasers
The world in the extremely small and fast scale is always mysterious
to human being. One possible "bridge" to this amazing world are
isolated ultrashort pulses. With the shortest pulse as our "eyes" and
"hands", we could watch, touch and even control the inner world.
Researches here may change our view of the nature. However, the
"ticket" to this world is quite expensive: only a few laboratories
have short and strong enough lasers to generate ultrashort pulses. To
debase the high requirement on lasers, some groups have done some
researches about ultrashort pulses generation with commercial lasers,
mainly depend on combining two general lasers instead of one short and
strong laser. Besides their complexity, the final result is not
perfect. The choice of the two lasers and the way to combining them
should be more exact. In this paper, we propose an appropriate combine
of two commercial lasers to generate the shortest pulse in the world
and it's readily available in most laboratories.
***
BR11054
Imaging with Evanescent Waves
Evanescent waves of light can convey information of sub‑wavelength
structures, for example, nanoparticles, polymers, or proteins, but
usually decay exponentially. So, how can we transport the evanescent
waves of light for long distance? This is one of the important questions
for the metamaterial superlens that enables us to realize sub‑wavelength
imaging beyond the diffraction limit. In order to answer the question,
this paper describes experimental and numerical studies of resonant
photon transport through multilayers consisting of silver and insulator.
The authors have clearly demonstrated that the complex, at times,
interplay between various electromagnetic modes including surface
plasmon polaritons in the metal‑insulator‑metal (MIM) system is
important to obtain large tunneling probabilities over relatively large
distances approaching the wavelength. Moreover, this study suggests that
a possible application of plasmonic MIM structures will be a novel type
of hyperlens, which converts evanescent waves to propagating waves of
light.
