Tractor Beam Created Using Water Waves� — The Physics arXiv Blog — Medium

Tractor Beam Created Using Water Waves� — The Physics arXiv Blog — Medium: This fluid jet carries any floating particles along with the waves...

But as the waves get bigger, they become unstable and their behaviour changes dramatically...

Punzmann and co say the interaction between the waves in this non-linear regime changes the direction of the jet at the centre of the wave maker. “It now pushes floaters inward, towards the wave maker and against the wave propagation,” they say. Any floaters caught in this jet, are therefore pulled.

To test this idea, Punzmann and co have recreated exactly this situation in a wave tank with an elongated wave maker. They place a ping-pong ball on the water and then measure its movement as well as the shape of the water surface and the fluid flow on the surface.

Sure enough, when the amplitude of the waves is small, the ping-pong ball moves in the same direction as the waves. But as the waves become larger, the ping-pong ball reverses direction and moves back towards the wave maker...

Team finds new way to use X-rays to probe properties of solid materials

Team finds new way to use X-rays to probe properties of solid materials: The energy and power density of incoming laser light can get so high that photons actually work together and nonlinear effects result from their interaction with matter. This results in materials greatly enhancing certain colors of light. In other words, if you irradiate a crystal with green light, the light that gets irradiated is actually red. This color can be precisely correlated with the structural properties of the material that is being analyzed.
Now, Alexander F�hlisch from the HZB and his team were able to observe through a series of experiments at Hamburg's short-pulse X-ray laser FLASH that these types of effects can also be achieved using soft X-rays and that this method works on solids as well. "Normally, inelastic scattering processes using soft X-rays are ineffective," explains Martin Beye, the study's primary author: "Our experiment allowed us to document how inelastic X-ray scattering can be intelligently intensified. Just like a laser, the different photons are actually working together and amplifying each other and we end up with a very high measurement signal."

Weird waves help model tsunamis' destructive potential

Weird waves help model tsunamis' destructive potential: Once thought to be extremely rare, X- and Y-shaped waves with unusually high peaks regularly appear in ankle-deep water under certain conditions...


Linear interaction between ocean waves creates a peak that cannot be greater than the sum of the individual wave heights. But X- and Y-shaped waves are created when two waves hit each other at an angle, causing a non-linear interaction. That means their combined height can be more than the sum of the original peaks...

"People thought you might see them once every few years. The surprise is that they occur every day..."

Two stopped light pulses interact with each other

Two stopped light pulses interact with each other: (Phys.org) -- For the first time, physicists have experimentally demonstrated the interaction of two motionless light pulses. Because the stopped light pulses have a long interaction time, it increases the efficiency with which one photon can switch the path of a second photon.

Rubidium Detector Converts Infrared Images Directly to Visible Light

Rubidium Detector Converts Infrared Images Directly to Visible Light: These guys use a process known as four waving mixing, in which the interaction of three different wavelengths in certain media produces a fourth wavelength. This is usually done in non-linear crystals using high power lasers.

The trick these guys have pulled off is is to achieve this in a small container of rubidium gas using two ordinary diode lasers. The idea is that the lasers excite certain electronic states in the rubidium atoms. These states are chosen so that the atoms emit visible light when they relax.

But the system is set up so that the addition of a little extra infrared light triggers the emission of visible red light.

Ship in Bottle, Meet Rogue Wave in Tub - ScienceNOW

Ship in Bottle, Meet Rogue Wave in Tub - ScienceNOW: That equation has several weird solutions, including one with the basic properties of a rogue wave. Discovered in 1983, the so-called Peregrine solution consists of a single peak that suddenly emerges out of a smoothly varying wave train (a so-called sine wave) by sucking energy out of it, zipping along for a while, and then disappearing back into the sine wave. In October 2010, experimenters produced an optical version of that wave with light.

Now, mathematician Amin Chabchoub and physicist Norbert Hoffmann at the Hamburg University of Technology in Germany and physicist Nail Akhmediev of Australian National University in Canberra have produced a Peregrine rogue wave in a water tank 15 meters long, 1.6 meters wide, and filled to a depth of 1 meter.

Observations: Physics tricks could make for one-way soundproofing

Observations: Physics tricks could make for one-way soundproofing: "By stacking layers of nonlinear materials along with ordinary linear layers in an asymmetric fashion, the researchers have calculated, a wave would be able to pass through in one direction but would almost completely bounce off when it arrives from the other direction. The one-way bias isn't universal, however—the researchers note that each particular implementation would have a sweet spot of wave amplitudes and frequencies for which it would work best."

Scientists See The One-way Light - Science News

Scientists See The One-way Light - Science News: Casati mathematically modeled the behavior of light passing through two layers of nonlinear material. The light changes the properties of the materials as it passes through, which in turn changes the behavior of light in complex ways.

Thanks to this back-and-forth dance, the frequency of light that can pass through these materials depends on the direction of the light...

Patterns found in laboratory spark insight into nature and society

Patterns found in laboratory spark insight into nature and society: Epstein says non-linear dynamics and exotic reactions like oscillating chemical reactions are quite rare in chemistry but very important in biology, because every living system is full of reactions in which concentrations increase and decrease, typically on a daily cycle. Unraveling this phenomenon in chemistry is offering insights into pattern formation in other systems, such as human and animal populations.
 To better understand diffusion, cross-diffusion and oscillatory chemical reactions, Epstein revisits a science demo popular with the elementary school set: The glass of water and drop of food coloring...
“Chemists and physicists have largely ignored cross-diffusion,” says Epstein. “When you study diffusion in an introductory chemistry or physics course, the standard treatment completely ignores the possibility that if there are two different chemicals present one might influence the diffusion of the other..."

“Instead of having blue molecules and red molecules, maybe you have populations of two different ethnic groups that either like to be near each other or prefer to avoid each other,” says Epstein. “This might affect population patterns in a city or region.”

The Memristor � American Scientist

The Memristor � American Scientist
The favored layout for memristor memory is a crossbar structure, where perpendicular rows and columns of fine metal conductors are separated by a thin, partially doped layer of TiO2. In this way a memristor is formed at every point where a column crosses a row. Each bit in the memory is individually addressable by selecting the correct combination of column and row conductors. A signal pulse applied to these conductors can write information by setting the resistive state of the TiO2 junction. A later pulse on the same pair of conductors reads the recorded information by measuring the resistance...

One intriguing way to exploit analog memristors would be to build a machine modeled on the nervous system. In biological neural networks, each nerve cell communicates with other cells through thousands of synapses; adjustments to the strength of the synaptic connections is thought to be one mechanism of learning. In an artificial neural network, synapses must be small, simple structures if they are to be provided in realistic numbers. The memristor meets those requirements. Moreover, its native mode of operation—changing its resistance in response to the currents that flow through it—suggests a direct way of modeling the adjustment of synaptic strength.

Extreme lasers at work

Extreme lasers at work: "Under extremely intense illumination materials may exhibit so-called nonlinear optical properties such as ceasing to absorb light beyond a certain brightness, or becoming highly ionized. Yasumasa Hikosaka, Mitsuru Nagasono and colleagues at RIKEN and several other Japanese research institutes have now described the details of this ionization process by using very short bursts of bright laser light. Their finding is relevant to a broad range of pure and applied research, including x-ray imaging of biological molecules, ultrafast optical switches, fusion and astrophysics."

Physicists Build Diode for Electromagnetic Waves - Technology Review

Physicists Build Diode for Electromagnetic Waves - Technology Review: The mathematics of electromagnetic wave propagation suggests that certain types of material should allow polarized waves to pass in one direction but not the other when bathed in a magnetic field. Engineers can readily build such a device but its effect is what physicists call linear, meaning that the amount of light you get out is proportional to the mount you put in...

A microwave passing through wires generates currents in each that tend to interact. At certain frequencies these currents re-reinforce or cancel out. Adding a nonlinear diode to one of the wires makes the effect of the metamolecule nonlinear too.

For rapid non-linear information processing in the brain, small synaptic impulses are key

For rapid non-linear information processing in the brain, small synaptic impulses are key: "At issue was the conventional theory of spiking neuronal networks, which approximates impulses in the limit where they become vanishingly tiny and infinitely numerous, limiting the capabilities of individual neurons to simple addition of inputs.
Using a newly-developed high-precision method for simulating nonlinear neuron models (see references), the team had previously uncovered contradictions in this theory. To unravel this mystery, the researchers developed a new analytic framework which explicitly incorporates the finite effect of each input at the critical boundary near the firing threshold. With this change, they show that not only can neurons process information far faster than previously believed, they can also perform nonlinear operations such as multiplication that are key to complex information processing.
While more accurately capturing the network aspect of neural dynamics, the new framework also reveals how cooperation between seemingly uncoordinated input signals enables neurons to perform many non-linear operations at the same time."

Peregrine's 'Soliton' observed at last

Peregrine's 'Soliton' observed at last: "The Peregrine 'Soliton', discovered over 25 years ago by the late Howell Peregrine (1938-2007), an internationally renowned Professor of Applied Mathematics formerly based at the University of Bristol, is a localised solution to a complex partial differential equation known as the nonlinear Schrodinger equation (NLSE).
The Peregrine solution is of great physical significance because its intense localisation has led it to be proposed as a prototype of ocean rogue waves and also represents a special mathematical limit of a wide class of periodic solutions to the NLSE.�"

How Terahertz Waves Tear Apart DNA - Technology Review

How Terahertz Waves Tear Apart DNA - Technology Review: Alexandrov and co have created a model to investigate how THz fields interact with double-stranded DNA and what they've found is remarkable. They say that although the forces generated are tiny, resonant effects allow THz waves to unzip double-stranded DNA, creating bubbles in the double strand that could significantly interfere with processes such as gene expression and DNA replication. That's a jaw dropping conclusion.

And it also explains why the evidence has been so hard to garner. Ordinary resonant effects are not powerful enough to do do this kind of damage but nonlinear resonances can. These nonlinear instabilities are much less likely to form which explains why the character of THz genotoxic
effects are probabilistic rather than deterministic, say the team.