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Awarded videos of fluid motion presented at the APS DVD meeting. Very cool stuff. #0084 is done with the setup I used for my master thesis.

More than a century after the idea was first floated, physicists have finally figured out how to tie water in knots in the laboratory. The gnarly feat, described today in Nature Physics1, paves the way for scientists to experimentally study twists and turns in a range of phenomena - ionized gases like that of the Sun's outer atmosphere, superconductive materials, liquid crystals and quantum fields that describe elementary particles.

Lord Kelvin proposed that atoms were knotted "vortex rings" - which are essentially like tornado bent into closed loops and knotted around themselves, as Daniel Lathrop and Barbara Brawn-Cinani write in an accompanying commentary. In Kelvin's vision, the fluid was the theoretical 'aether' then thought to pervade all of space. Each type of atom would be represented by a different knot.

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Kelvin's interpretation of the periodic table never went anywhere, but his ideas led to the blossoming of the mathematical theory of knots, part of the field of topology. Meanwhile, scientists also have come to realize that knots have a key role in a host of physical processes.

Ionic fluids in thrusters for microsatellites. Here also a link to a paper on the topic: .pdf

Seems looking into turbulence is a source of innovative concepts. After the black hole modelling here was found a mathematical expression which describes "how turbulence can alter the shape and course of a flock of birds, a swarm of insects or even an algal bloom (phytoplankton!) and could help us to better predict them". More relevant for motions in air and sea, rather than space, where the fluids are dense enough to exhibit turbulence ; but what about a swarm moving in and exploring an exoplanet's atmosphere?

Technion researchers have demonstrated, for the first time, that laser emissions can be created through the interaction of light and water waves, in practice mechanical oscillations in fluids at the nanoscale. Interesting concept on the verge of two so far different fields!

A team of researchers in TU berlin and Caltech used Schrödinger's equation to visualise superfluidic flow (fluids with zero viscosity). Smoke and dry ice are close to this state in nature. Strangely enough for an equation that describes subatomic particles, it works, and reproduces experimental results better that Euler and Langrange schemes.

Nanometre-sized rods of carbon can expel water in puffs of vapour when the air is already humid. Materials such as carbon and silica gels typically pick up moisture as humidity increases. But Satish Nune and his colleagues at the Pacific Northwest National Laboratory in Richland, Washington, found that their carbon-based nanorods take up water at low humidity and then give off about half of it when the relative humidity exceeds 50-80%. The team thinks that water condenses between adjacent rods and then capillary forces draw the rods together until the water bursts from the ends of the rods and evaporates.

any idea how this works - who wants to have a closer look at it?

Wouldn't it be worth having a closer look?

it's still not clear to me how to get electricity in and out of this thing?

nice article - with related podcast interviewing the former prof of Johannes ... my usual question: can we use it for space :-)

Eventually for damping purposes. Place a payload in it, surrounded by the fluid, and high frequency shocks might be damped. Of course, damping properties might turn out to be not good.

some biomimicry used in energy systems... maybe it sparks some ideas

not much new that has not been shared here before ... BUT: we have done relativley little on any of them. for good reasons?? don't know - maybe time to look into some of these again more closely Energy Efficiency( Termite mounds inspired regulated airflow for temperature control of large structures, preventing wasteful air conditioning and saving 10% energy.[1] Whale fins shapes informed the design of new-age wind turbine blades, with bumps/tubercles reducing drag by 30% and boosting power by 20%.[2][3][4] Stingray motion has motivated studies on this type of low-effort flapping glide, which takes advantage of the leading edge vortex, for new-age underwater robots and submarines.[5][6] Studies of microstructures found on shark skin that decrease drag and prevent accumulation of algae, barnacles, and mussels attached to their body have led to "anti-biofouling" technologies meant to address the 15% of marine vessel fuel use due to drag.[7][8][9][10] Energy Generation( Passive heliotropism exhibited by sunflowers has inspired research on a liquid crystalline elastomer and carbon nanotube system that improves the efficiency of solar panels by 10%, without using GPS and active repositioning panels to track the sun.[11][12][13] Mimicking the fluid dynamics principles utilized by schools of fish could help to optimize the arrangement of individual wind turbines in wind farms.[14] The nanoscale anti-reflection structures found on certain butterfly wings has led to a model to effectively harness solar energy.[15][16][17] Energy Storage( Inspired by the sunlight-to-energy conversion in plants, researchers are utilizing a protein in spinach to create a sort of photovoltaic cell that generates hydrogen from water (i.e. hydrogen fuel cell).[18][19] Utilizing a property of genetically-engineered viruses, specifically their ability to recognize and bind to certain materials (carbon nanotubes in this case), researchers have developed virus-based "scaffolds" that

"Cuckoos have a bad reputation as home-wreckers, taking over the nests of other birds and killing their chicks. But one species benefits its hosts by producing a smelly fluid that repels predators. "Cuckoos are not always the villains we think they are," says Ros Gloag of the University of Sydney, who was not involved in the study."

So they not only take over part of the nest, but also crap all over the place? Then again, if that is the prize to pay for safety, it might well be worth the inconvenience.. :)

Inserting a droplet of polymer enriched water into oil and manipulating its shape by applying an electric field. The shape remains intact after cease of the forcing. <br /> "Russell (...) points out that the advance holds promise for a wide range of different applications including in drug delivery, biosensing, fluidics, photovoltaics, encapsulation and bicontinuous media for energy applications and separations media."

Researchers in Bangalore, India together with the Indian Space Research organization come up with an intelligent self-healing algorithm that can locate open-circuits faults and repair them in real-time. They used an insulating silicon oil containing conductive particles. Whenever a fault happens, an electric field develops there, causing the fluid to move in a 'thermodynamic automaton' way repairing the fault. The researchers make clear it could be one advantage for electronics in harsh environments, such as in space satellites.

could it be useful in e.g. propellant tanks?

did you see the quote of Andrew Martin at the bottom of the text? he was in the cockroach project.

ah. interesting

#4 is pretty interesting 

There are (even in Science): http://science-mag.aaas.org/cgi/reprint/314/5803/1253.pdf There is also a group at UCAR (lead by S. Solomon, one of the Gods in atmospheric research) who are analyzing this effect: http://www.ucar.edu/news/releases/2006/thermosphere.shtml

for the drag effect, this is well known in fluid mechanics, we use the Knudsen number, which explains this phenomenon ... for a perfect gaz though!

...This slippery surface was bio-inspired by the carnivorous plant I showed you sometimes ago! I was sure it was a good idea! next time I will be quicker!!

And a good lesson that it is important to proceed quickly when you have an idea and don't wait ...

Yes, I will see what we could do, but they really did a good job, from the biomimetic of the surface, up to the realization of the material, and the tests...

An exhaustive overview of all possible advanced rocket concepts, eg.. "As an example, consider a photon rocket with its launching mass, say, 1000 ton moving with a constant acceleration a =0.1 g=0.98 m/s2. The flux of photons with E γ=0.5 MeV needed to produce this acceleration is ~1027/s, which corresponds to the efflux power of 1014 W and the rate of annihilation events N'a~5×1026 s−1 [47]. This annihilation rate in ambiplasma l -l ann corresponds to the value of current ~108 A and linear density N ~2×1018 m−1 thus any hope for non-relativistic relative velocity of electrons and positrons in ambiplasma is groundless." And also, even if it would work, then one of the major issues is going to be heat dispersal: "For example, if the temperature of radiator is chosen T=1500 K, the emitting area should be not less than 1000 m2 for Pb=1 GW, not less than 1 km2 for Pb=1 TW, and ~100 km2 for Pb=100 TW, assuming ε=0.5 and δ=0.2. Lower temperature would require even larger radiator area to maintain the outer temperature of the engine section stable for a given thermal power of the reactor."

The problem is not achieving a high energy density, that we can already do with nuclear fission, the question however is how to confine or harness this power with relatively high efficiency, low waste heat and at not too crazy specific mass. I see magnetic confinement as a possibility, yet still decades away and also an all-or-nothing method as we cannot easily scale this up from a test experiment to a full-scale system. It might be possible to extract power from such a plasma, but definitely well below breakeven so an additional power supply is needed. The fission fragments circumvent these issues by a more brute force approach, thereby wasting a lot of energy for sure but at the end probably providing more ISP and thrust.

Sure. However, the annihilation based photon rocket concept unifies almost all relevant drawbacks if we speak about solar system scales, making itself obsolete...it is just an academic testcase.