Turbulent black holes grow fractal skins as they feed - physics-math - 28 April 2014 - New Scientist

Turbulent black holes grow fractal skins as they feed - physics-math - 28 April 2014 - New Scientist: "We showed that when you throw stuff into a black hole, the surface of the black hole responds like a fluid – and in particular, it can become turbulent...  More precisely, the horizon itself becomes a fractal..."

To investigate what the horizon of a black hole looks like at mealtime, Adams took advantage of a mathematical duality between Einstein's equations of general relativity – which describe gravity near black holes – and fluid dynamics...

Led by Paul Chesler, who is a post-doc researcher at Harvard, the team first modelled a turbulent fluid system. They then translated it into the black hole regime and let it develop with time. When they looked again, the horizon of the black hole appeared to have developed an infinite surface area.

'Black holes' of the ocean could curb climate change - environment - 26 September 2013 - New Scientist

'Black holes' of the ocean could curb climate change - environment - 26 September 2013 - New Scientist: Swirling masses of water in the ocean are mathematically the same as the warped regions of space-time around cosmic singularities...

In this so-called photon sphere, light is trapped in loops that spin around the black hole forever.


"The boundaries of water-carrying eddies satisfy the same type of differential equations that the area surrounding black holes do in general relativity..."

When fluid dynamics mimic quantum mechanics | KurzweilAI

When fluid dynamics mimic quantum mechanics | KurzweilAI: In the experiments reported in PRE, the researchers mounted a shallow tray with a circular depression in it on a vibrating stand. They filled the tray with a silicone oil and began vibrating it at a rate just below that required to produce surface waves.

They then dropped a single droplet of the same oil into the bath. The droplet bounced up and down, producing waves that pushed it along the surface.

The waves generated by the bouncing droplet reflected off the corral walls, confining the droplet within the circle and interfering with each other to create complicated patterns. As the droplet bounced off the waves, its motion appeared to be entirely random, but over time, it proved to favor certain regions of the bath over others...

The statistical description of the droplet’s location is analogous to that of an electron confined to a circular quantum corral and has a similar, wavelike form.

Particles defy gravity, float upstream | Physics | Science News

Particles defy gravity, float upstream | Physics | Science News: Shinbrot set up two tanks side-by-side and elevated one of them, with water flowing down through a channel to bridge the 1-centimeter height gap. Sure enough, within seconds of adding chalk and mate tea to the bottom tank, particles began climbing up the channel to contaminate the upper tank.

Shinbrot’s experiments led him to the conclusion that Altshuler’s team had also reached: The particles overcome gravity and the current thanks to a property of water called surface tension.

First fluid knots created in the lab

First fluid knots created in the lab: To investigate, Dustin Kleckner and William Irvine of the University of Chicago, Illinois 3D-printed strips of plastic shaped into a trefoil knot and a Hopf link. Crucially, the strips had a cross section shaped like a wing, or hydrofoil (see picture).

Next, the researchers dragged the knots through water filled with microscopic bubbles. Just as a wing passing through air creates a trailing vortex, the acceleration of the hydrofoils created a knot-shaped vortex that sucked in the bubbles. The result was a knot-shaped flow of moving bubbles – the first fluid knot created in a lab – which the team imaged with lasers.

How to model a white hole in your kitchen sink

How to model a white hole in your kitchen sink: When a stream of tap water hits the flat surface of the sink, it spreads out into a thin disc bounded by a raised lip, called the hydraulic jump… More recently, physicists have suggested that, if the water waves inside the disc move faster than the waves outside, the jump could serve as an analogue event horizon. Water can approach the ring from outside, but it can't get in.

"The jump would therefore constitute a one-directional membrane or white hole," wrote physicist Gil Jannes and Germain Rousseaux of the University of Nice Sophia Antipolis in France and colleagues in a study on ArXiv Oct. 8. "Surface waves outside the jump cannot penetrate in the inner region; they are trapped outside in precisely the same sense as light is trapped inside a black hole."

'Crowd Quakes' Were A Key Factor In LoveParade Disaster

'Crowd Quakes' Were A Key Factor In LoveParade Disaster: Helbing and Mukerjee say most deaths occurred elsewhere in the crowd because of a phenomenon known as crowd quakes. These occur when the density of a crowd becomes so great that individuals are forced into bodily contact with each other.
When this happens, the forces are transmitted through the crowd in chains  from one body to the next. Crucially, when this happens, the transmitted forces add up...
And this is what kills: not the overall density of the crowd but the transmission of lethal force through the crowd in ways that are almost random. This causes people to fall, creating a domino effect that crushes people to death.

Blog - Demonstration of Actuation-at-a-Distance Effect for Labs on a Chip

Blog - Demonstration of Actuation-at-a-Distance Effect for Labs on a Chip: Today, he and his pal Matthieu Gaude put the photoelectrowetting effect into action. These guys have made a cantilever sitting above an insulated conductor and placed a droplet of water between them so that it fills the gap by capillary action (see above).

Zapping this system with light changes the wetting angle the droplet makes with the cantilever and the electrode below. This makes the droplet thinner, pulling the cantilever down.

The ability to actuate at a distance using light alone could have many applications because it eliminates the need for the complex circuitry and pumps now used to transport droplets. It could also allow optical addressing of autonomous, wireless sensors.

Look ma, no hands: Engineers invent a magnetic fluid pump with no moving parts

Look ma, no hands: Engineers invent a magnetic fluid pump with no moving parts: The ferrohydrodynamic pump method works when electrodes wound around a pipe force magnetic nanoparticles within the ferrofluids to rotate at varying speeds.  Those particles closest to the electrodes spin faster, and it is this spatial variation in rotation speed that propels the ferrofluid forward. "We don't rely on any other material; no magnets, nothing moving but the ferrofluid that we're pumping," Koser says.

New Scientist TV: Born to be Viral: How a ball could sink forever

New Scientist TV: Born to be Viral: How a ball could sink forever: ...it's possible for a sufficiently heavy object to reach a constant speed when flung into a grainy substance - and continue to plummet indefinitely if there's no bottom. In this video, you can see a computer simulation they created of this scenario. Until now, it was assumed that an object quickly loses energy and stops when it plunges into a grainy material.

Water can flow below -130 C

Water can flow below -130 C: Water is extremely difficult to chill in a way that makes it sluggishly flowing. Ove Andersson has accomplished this feat by exposing crystalline ice, in which the atoms are arranged in an orderly manner, to increased pressure at temperatures below -130o C. The order of the molecules and the ice collapsed into amorphous ice, with random order among the water molecules.
“When I then raised the temperature, the ice transformed into sluggishly flowing water. This water is like regular water but its density is 35 percent higher, and the water molecules move relatively slowly, that is, the viscosity is high.”

Short Sharp Science: 'Liquid fire' created by fluids in a tight spot

Short Sharp Science: 'Liquid fire' created by fluids in a tight spot: Normally, fluids do not mix well in tight spaces because there is not enough room for disorder. But if the fluids exhibit highly contrasting viscosities, such as those of molasses and water, the researchers discovered that finger-like appendages known as viscous fingers project out of the thinner liquid (the lighter fluid pictured). As these fingers probe the thicker fluid, new appendages branch off. Collectively these tiny appendages help the two liquids mix together quickly without the aid of microfluidic devices.

Quantum Whirls - Science News

Quantum Whirls - Science News: ...His experiments involved spinning a cylinder the size of a skateboard and watching how the liquid helium sloshed inside.
Frustrated that none of the tracer particles he could buy would float, he created a new technique to freeze hydrogen, the only element lighter than helium, into a fog of ice particles. He sprinkled the hydrogen particles like snow onto the helium. They floated...
...Bewley shined a laser onto the supercold liquid with the hydrogen snow. He was shocked to see Feynman’s vortices pop into existence and bump into each other. A few days later, he and his adviser caught the whole dance on tape...
...The way that vortices snapped away from each other is similar to how Drake imagined magnetic field lines twisting in the sun...

Boiling bubbles are cool in space

Boiling bubbles are cool in space: NPBX uses a polished aluminum wafer, powered by heaters bonded to its backside, and five fabricated cavities that can be controlled individually. The experiment will study single and/or multiple bubbles generated at these cavities. It will measure the power supplied to each heater group, and cameras will record the bubble dynamics. Analysis of the heater power data and recorded images will allow investigators to determine how bubble dynamics and heat transfer differ in microgravity.

Make: Online : Jaw-dropping "unmixing" demo appears to reverse entropy

Make: Online : Jaw-dropping "unmixing" demo appears to reverse entropy: Obviously, there is no real "violation" of the second law of thermodynamics, here, but because almost all of our intuitions about how liquids are going to behave are formed under conditions of turbulent flow, it sure does seem like it.

Can fluid dynamics offer insights into quantum mechanics?

Can fluid dynamics offer insights into quantum mechanics?: In Couder’s system — which Bush plans to explore further at MIT — a fluid-filled tray is placed on a vibrating surface. The intensity of the vibrations is held just below the threshold at which it would cause waves — so-called Faraday waves — on the surface of the fluid. When a droplet of the same fluid is placed on the surface, it’s initially suspended on a cushion of air. Although the surface of the fluid appears perfectly placid, the vibration of the tray flings the droplet upward before the cushion of air dissolves, and the droplet begins bouncing. The bouncing causes waves, and those waves, in turn, propel the droplet along the surface. Bush and Couder call these moving droplets “walkers.”
“One of their first experiments involved sending walkers towards a slit,” Bush says. “As they pass through the slit, they appear to be randomly deflected, but if you do it many times, diffraction patterns emerge.” That is, the droplets strike the far wall of the tray in patterns that reproduce the interference patterns of waves. “Their system is a macroscopic version of the classic single-photon diffraction experiments,” Bush says.
Wave-borne fluid droplets mimic other quantum phenomena as well, Bush says. One of these is quantum tunneling, subatomic particles’ apparent ability to pass through barriers. A walking droplet approaching a barrier across the tray will usually bounce off it, like a hockey puck off the wall. But occasionally, the droplet will take enough energy from the wave that it hops right over the barrier.

Computational model of swimming fish could inspire design of robots, medical prosthetics

Computational model of swimming fish could inspire design of robots, medical prosthetics: "When a fish moves in a fluid, muscles contract, but the fluid also moves against the body. So, the amount the body moves depends on the internal muscle force and the external reaction of fluids," explained Eric D. Tytell, who conducted this research as a postdoctoral researcher in the laboratory of Professor Avis Cohen, Department of Biology. "Previous studies examined body mechanics separately from fluid mechanics because it is a very hard problem to solve. This is the first time that anyone has put together a computational framework to simulate this for large, fast animals like fishes."