An All-optical, Pain-free Method for Blood Glucose Testing

EC11052

- Pain-free blood glucose testing is highly desirable for diabetes management which requires frequent blood glucose monitoring. For many decades a search for a non-invasive blood glucose concentration detection method has been a major, yet elusive goal. Optical methods have been confined in the near-infrared where glucose has absorption peaks but is hard to identify due to multiple overlapping absorptions by other blood constituents. The development of clinically viable non-invasive glucose biosensors has been hampered by lack of specificity and sensitivity. In this paper we introduce theoretically and experimentally a new non-invasive method, Wavelength-Modulated Differential Photothermal Radiometry (WM-DPTR), for non-invasive, non-contact blood glucose monitoring. WM-DPTR features glucose specificity and sensitivity by combining laser excitation by two out-of-phase modulated beams at wavelengths near the peak and the baseline of a prominent and isolated mid-IR glucose absorption band. A theoretical photothermal model of WM-DPTR signal generation and detection has been developed. Simulation results on water-glucose phantoms within the human blood-range glucose concentration (0-300 mg/dl) demonstrated high sensitivity and resolution to meet wide clinical detection requirements. The model has also been validated by experimental data of the glucose-water system obtained using WM-DPTR.

The Fastest Way to Pour Syrup

LC13080ER

- A thick liquid flows quickest if you pour it from the corner, rather than the side, of a carton.

Pouring a fluid out of a container is an everyday process that is also relevant in a wide range of industrial situations. Despite this fundamental interest, this fundamental problem has apparently never been addressed before. The authors derive the time required for the fluid to begin discharging after tipping the container and the volume of the fluid yet to be discharged at subsequent times. The authors consider two different geometric configurations and find noticably different pouring characteristics. The theoretical predictions are compared successfully with experiments.

The results of the present study are applicable to situations where it is desirable to retrieve viscous fluids in minimal time from containers, such as buckets of detergent, cans of paint, and tanks of oil. They provide a point of reference to gauge the influence of a rich variety of effects that could be incorporated to extend the simplified model.

Deciphering the very first contact between virus particles and host cells

LD13184

- A virus replication cycle is initiated by virus binding to receptors presented on the surface of a host cell. An in-depth understanding of the very first steps of virus binding to cell membranes is therefore crucial for the development of antiviral therapies, vaccines and high-performance diagnostics. Studies of the initial interaction between a virus and the host cell membrane were so far mainly focused on identifying the binding sites on the virus and / or the cell membrane, while significantly less is known about the kinetics of the interaction. With single virus sensitivity, we quantify in this work the energy barrier for the virus-membrane association. We were able to discriminate between two structurally very similar receptors, which interaction kinetics could not be distinguished using conventional methods. We also observed that the virus release kinetics appears logarithmic over a long time span. Such interaction behavior is rarely observed in natural sciences and was earlier not reported in the context of virus binding. In our study, this feature has been explained by multiple receptor-virus contact points and membrane deformation. Such situations may occur at receptor-enriched cell-membrane regions with positive curvature, allowing us to suggest that the logarithmic kinetics may take place in vivo.



Description of the illustration:

Illustration of how surface-bound virus-like particles were used to probe their interaction with cell-membrane receptors incorporated into fluorescent-labeled lipid vesicles. By probing the rate of binding and the time individual vesicles remain bound (the residence time), we could simultaneously investigate weak (few receptor contacts) and strong (multiple receptor contacts) interactions. The virus-like particle was from the norovirus genogroup II.4 Dijon strain, being the major causative agent of acute viral gastroenteritis worldwide causing yearly up to 200, 000 children deaths, and the receptors were glycosylated sphingolipids.

X-rays vaporize water

LF13057EJ

- When ionizing radiation i s illuminated to water, it removes electrons from water molecules and ! ionizes them. This ionization can modify water surface tension (PRL 100, 217403, 2008), potentially affecting thermodynamic behavior of water: an important example is vaporization, since vaporization enthalpy depends on surface tension. The interaction between ionizing photons (x-rays or gamma-rays) and soft matter becomes important to scientists, with growing applications of x-ray techniques to soft matter systems.

In a paper in Physical Review E, researchers address for the first time (on a quantitative basis) that liquid water is vaporized by x-rays. They precisely measure the vaporization rate of water confined in a capillary tube during x-ray irradiation using high-resolution, high-speed x-ray microscopy. Intere! stingly, a reversible switching between vaporization and condensation repeatedly occurs with x-ray on-off switching.

The group finds a hidden fundamental linkage among ionization, surface tension, and vaporization: how effectively photons vaporize water depends on charging density. This finding could provide insights into topics concerning radiological or electrohydrodynamic phenomena such as radiation-induced bubble formation or cosmic-ray-induced cloud formation.

Sand physics: taking the rough with the smooth.

EE11020


- Why do the slopes of some piles of soil or sand slip very easily, while
other piles remain extremely stable? Answering this question holds the
key to the understanding of many fundamental physical questions, for
example the onset of landslides. For a long time scientists have assumed
that the surface roughness of the individual grains plays a keys role in
this process. However, this common-sense assumption has never been
verified experimentally. Here, for the first time, we provide the
necessary methodological concepts and succeed in proving this
hypothesis. We do so as follows.

We have invented a chemical recipe to increase the roughness of glass
and we use it to systematically tune the roughness of sub-mm glass spheres.

We measure the roughness of individual grains using light interference,
and the roughness of the whole granular sample using Coca-Cola.

We then measure the friction between the grains by looking at the slope
of the pile they form at the bottom of an hour glass.

We look at the correlation between roughness and friction. Our results
show that changing the roughness of grains allows us to tune the
friction between them, making friction a control parameter. And this
hands us the key to understanding real-life granular systems.

Packing of balls into a jar: first ask if the balls are all the same size

EGR1074

- How spheres pack into containers is a problem that’s been studied for decades. Recent computer simulations show that such packings appear to have large-scale density fluctuations if the spheres aren’t all exactly the same size. More significantly, the simulations show that careful consideration of each particle’s size reveals that the density fluctuations are smoother than they first appear. However, it is very hard to detect subtle particle size differences in experiments. Previously experiments had to assume all particles are the same, which is an approximation; the simulations showed that this approximation is an unfortunate one to have to make. We imaged half a million microscopic spheres in a container and developed a novel method for determination of each particle’s size. Using our data, we confirmed the prior computer simulation results. We expect our method will be quite useful for a variety of experimental studies of sand and particle suspensions.

Attosecond intramolecular electron dynamics observed

LF13695

- The current article provides an exceptional view into the microscopic,
ultrafast world of one single electron inside nature's most simple
molecule.

Our experimental and theoretical work shows how an ultrashort and strong
laser drives the only electron in the chemical bond of a hydrogen
molecular ion on an attosecond time scale (1 attosecond = 10^{-18}
seconds), makes it slosh around and finally splashes it out of the
molecule. This wild splashing electron waves come as a surprise to
scientists who previously assumed that a laser field frees electrons
gently through a narrow tunnel "drilled" into the molecule by the light.
Our work further shows the exciting prospect that the invisible dynamics
of the electron inside a molecule can be mapped onto the momenta of the
electron once it left the molecule and where they become observable.

Look Ma, No Hands!

BE11548

- During early 1960s, NASA scientists developed the first magnetic liquids (ferrofluids) as an alternative means to move liquid fuels in a gravity-free environment. Since that time, ferrofluids have found many other uses within industrial, commercial and biomedical settings, but the original goal of practical liquid manipulation in a compact system with magnetic fields alone remained elusive... Until now. In this paper, we experimentally demonstrate for the first time a general approach that allows direct pumping of ferrofluids at controllable speeds in closed-loop geometries without any mechanically moving parts. Since the pumping action involves nanoparticle rotation within the entire liquid body, the physics of this ferrohydrodynamic pumping mechanism is easily scalable to all sizes – from microfluidic devices to industrial-scale pumping systems. Here, we illustrate the simplicity of this “no-hands” pumping scheme utilizing a stereo amplifier, ordinary plumbing materials from the local hardware store and a commercially available mineral oil/magnetite ferrofluid that is easy to make and safe to handle. We believe our approach could lead to highly compact, integrated, completely quiet and very efficient liquid cooling schemes for portable, high-performance consumer electronics. With biocompatible ferrofluids, direct ferrohydrodynamic pumping could enable highly compact chambers for continuous-flow cellular perfusion and incubation, as well.

Record-Low Error Rate for Quantum Information Processing with One Qubit Achieved

LE13372AR

- Thanks to advances in experimental design, physicists have achieved a
record-low probability of error in quantum information processing with
a single quantum bit (qubit) - the first published error rate below
the theoretical threshold for building viable quantum computers. A
quantum computer could potentially solve certain problems that are
intractable using today’s technology, even supercomputers. The NIST
experiment, with a single beryllium ion qubit, is a milestone for
simple quantum logic operations, demonstrating a probability of error
of only 1 per 50,000 logic operations. For comparison, one error per
10,000 logic operations is a commonly agreed upon target for a low
enough error rate to use error correction protocols in a quantum
computer. However, a working quantum computer will also require
two-qubit logic operations with comparably low error rates. The record
low error rate was made possible by two changes in the group’s
experimental set-up. First, the scientists manipulated the ion using
microwaves instead of the usual laser beams. Second, the ion trap was
placed inside a copper vacuum chamber and cooled to 4.2 K with a
helium bath to reduce errors caused by magnetic field fluctuations in
the lab.

Primordial black holes could ring the Sun like a bell

LE13715

- Approximately 25% of the energy density of the universe consists of dark matter. One possible candidate for this dark matter is primordial black holes produced in the first second after the Big Bang. A primordial black hole in the Galaxy's dark-matter halo could pass through our Sun without accreting appreciably, but its
gravitational tidal field would cause the Sun to oscillate like a ringing bell. In this paper, we calculate for the first time the amplitude and frequencies of these solar oscillations. NASA's Solar Dynamics Observatory could detect these oscillations if the mass of the primordial black hole exceeds 10^21 g, the mass of a large
asteroid. Given the inferred local density of dark matter, the event rate for such primordial black holes passing through the Sun is about 10^-7 per year. These oscillations may also be detectable in other stars by reanalyzing the same observations used to search for extrasolar planets.

IS THE UNIVERSE A FRACTAL?

LF12878DR

- A spacetime with fractal geometry may help in unifying the gravitational
force with quantum mechanics, and bridge a gap between the observed
reality and theories postulating that Nature is discrete.

One of the greatest worries of physicists are infinities: If we hope
that Nature be described by the language of mathematics, then we expect
that everything be described by a finite set of observable quantities.
However, things go wrong when trying to merge general relativity with
quantum mechanics, and infinities arise. The author of this research
argues that a cure to this problem is to replace ordinary geometry with
fractal geometry. While in the former case concepts such as volume and
dimension have an intuitive meaning, in the latter they experience
radical transformations. At very small distances a discrete spacetime
texture emerges, thus opening up the possibility that the continuum
geometry we observe at large scales is only an effect of a coarse
resolution. Also, the dimension of spacetime is predicted to change with
the probed scale (as in multifractals), to be noninteger and smaller
than four. This phenomenon of dimensional reduction can render field
theories finite.

ATOM-LASER MAKES MEASUREMENT OF GRAVITY

LY12724A

- Compared to a thermal light source, such as a light bulb, the optical laser revolutionised the precision of optical measurements, which utilise the interference of light waves in devices known as interferometers. In the same way, atom-interferometers, which use matter waves, should benefit from the use of an atom-laser; the direct analogy of an optical laser. This paper presents the first direct comparison of a thermal and laser-like atom sources used in an atom-interferometer that measures gravity. Everyday, many people take advantage of the optical laser’s measurement precision, for example, by using a DVD player. Perhaps less obvious is the permeation of atom-interferometers into society. Atomic clocks are examples of atom-interferometers, again affecting many people daily via their use of GPS, which requires exquisite precision in the measurement of time. More recently, atom-interferometers have been used for precision inertial measurements, such as measuring gravitational acceleration. Indeed, the most precise gravity sensors include atom-interferometers, and the measurement of gravity has applications ranging from fundamental tests of physical theories, through to Earth sciences, mineral exploration, and navigation. This work represents an important step forward in the development of the next generation precision inertial sensors.

Watching Flames Spread in Microgravity

LU12255EJ

- Waves of chemical reaction spreading through a heterogeneous media are found throughout biology, chemistry, and physics. Most theories to understand how these waves spread assume that individual particles can be neglected and their effect is smoothed over the media. Our paper shows that for some systems, this assumption fails and an unusual regime of wave propagation can occur which we call the “discrete regime.” Examples of familiar systems that might exhibit this behavior include clouds of combustible dust in air, forest fires, or flames propagating through a rocket propellant. In the discrete regime, even if the particles burn infinitely fast, the reactive wave (or flame) is still limited by the time it takes the heat released by one particle to spread to the neighboring particles. Therefore, the overall process becomes statistical, being influenced by the randomized position of the particles in three-dimensional space. In addition to theoretical and computer-based solutions, we experimentally observed this discrete regime by igniting flames in suspensions of iron particles in air, where the nitrogen had been replaced by xenon in order to decrease the heat conductivity of the gas. The slow propagation speed of the flames (3 to 5 cm/s) made them sensitive to being disrupted by gravity and necessitated conducting the experiments in a reduced-gravity (freefall) environment onboard an airplane flying along a parabolic trajectory.

Metamaterial-based model of warp drive

LY11889BJ

- Electromagnetic metamaterials are capable of emulating many exotic space-time geometries, such as black holes, rotating cosmic strings, and the big bang singularity. Here we present a metamaterial-based model of the Alcubierre warp drive, and study its limitations due to available range of metamaterial parameters. It appears that the material parameter range introduces strong limitations on the achievable “warp speed”, so that ordinary magnetoelectric materials cannot be used. On the other hand, newly developed “perfect” bi-anisotropic non-reciprocal magnetoelectric metamaterials should be capable of emulating the physics of warp drive gradually accelerating up to 1/4 the speed of light.

The figure here shows an example of a metamaterial geometry, which
explicitly violates spatial and time reversal symmetries in ways that make warp drive simulation possible.

Has the black hole at our Galaxy's center been feeding lately?

LD13673

- The recent discovery of huge `bubbles' emitting gamma-rays high above
and on either side of the galactic plane has puzzled the astrophysical
community and challenged long held beliefs: Has the supermassive black
hole at the centre of the Milky Way been shooting out jets of plasma?
Just how are high-energy particles being produced so far away from all
the stars in the Galaxy? We present a model that can explain these
mysterious structures and will allow us to answer such questions in the
near future.

The Milky Way is generally perceived as a flat thin disk of stars
visible by its faint glow in the night sky. Recently, this view has been
challenged by data from the Fermi-LAT satellite experiment. High-energy
particles must be radiating in huge bubble-like structures extending far
above and below the stellar disk which are shining in gamma-rays. This
is all the more surprising as the massive black hole at the centre of
our Galaxy is believed to be quiescent, in contrast to active galaxies
where we can see jets of plasma being shot out as the central black hole
swallows up stars and gas. We show that such activity may have occurred
in our own Galaxy just a few million years ago and that high energy
electrons can be accelerated by the resulting plasma turbulence and
produce high-energy gamma-rays. Our model explains the appearance of the
bubbles and the spectrum of their emission and makes detailed
predictions for future observations which can test the model further. It
appears that our Galaxy may not be such a quiet place as we had imagined
all this time.

Spin Transistors at Practical Temperatures

LE13564

- A European team of researchers has discovered that new electronic states in the so-called topological insulator Bismuth Selenide could prove the key to room temperature operation of a radically new type of computing technology. The ubiquitous transistor, on which almost all electronics is based, relies on the ability to tune the electrical conductivity of a semiconductor by applying a small external voltage to move charge around. For decades, researchers have been aspiring to create a faster and more energy efficient transistor by utilizing a different fundamental property of the electron - its tiny magnetic moment known as
its spin. This goal has proved remarkably elusive as the so-called Rashba effect, on which this spin-transistor is based, is miniscule. Consequently, to feel a large enough effect, electrons must travel long distances without being kicked off their path. This is only possible if the whole device is kept at a temperature below −270°C - hardly a practical requirement for everyday use. Now, in a paper to be published in Physical Review Letters, it has been shown that Bismuth Selenide can support an electrostatically tuneable Rashba effect which is over one hundred times larger than in any other known semiconductor and persists well above room temperature. This sets the stage for building a spin-transistor to work at realistic temperatures, and may well provide the first practical applications of the newly-famed topological insulators.

Violation (and Restoration) of Einstein’s Equivalence Principle by the Hawking/Unruh effect

LC13069

- Einstein’s Equivalence Principle, the principle which forms the conceptual basis of General Relativity, says that an observer can't (locally) distinguish between acceleration or being in a gravitational field. Einstein imagined comparing an observer in an accelerating elevator with an observer in the same elevator at rest on the surface of the Earth; in each case the observer feels an identical downward force. In our work we’ve found that an observer confined to such an elevator can distinguish between the two cases by using two related quantum phenomena: the Hawking effect and the Unruh effect.

Due to quantum fluctuations of fields an observer in the gravitational field of a black hole will measure a temperature – the Hawking temperature. Similarly an accelerating observer will measure a temperature – the Unruh temperature. We have shown that if the two different observers measure the same local acceleration they will measure different temperatures – the observer in the gravitational field will measure a higher temperature.

Surprisingly in regions of stronger gravitational field the two temperatures approach the same value. Thus as the gravitational field becomes stronger the Equivalence Principle is restored, hinting that gravity and quantum mechanics are more compatible (not less) for strong gravitational fields.

Imaging atomic interactions

LE12909

- We have developed an atom-imaging technique that allows us to detect the
positions of individual Rydberg atoms, which are atoms with a highly
excited outer electron. Using this technique, we provide the first
spatially resolved images that demonstrate the “Rydberg blockade.” This
effect is at the core of proposals for a quantum computer architecture
based on neutral atoms

A Rydberg atom has such a tenuous grasp on its excited electron that the
atom is extremely sensitive to external electric and magnetic fields,
and interacts very strongly with other Rydberg atoms. The interaction
between Rydberg atoms is so strong that a Rydberg atom can “block” the
laser-excitation of another Rydberg atom by shifting the energy levels
of the second atom out of resonance with the laser. This is termed the
Rydberg blockade effect. This process leads to quantum entanglement,
which can be used in quantum computation algorithms.

A second Rydberg atom can only be excited if it is farther than a
“blockade radius” from the first atom. We directly measured this
blockade by laser-exciting Rydberg atoms in a cold atomic vapor and
measuring the Rydberg atom positions. We observe a blockade radius of
about 10 microns, which is about 100,000 times larger than the radius of
a ground state atom.

Information could escape from black holes after all

LB12889

- New research suggests that information could escape from black holes after all. The research, which appears in the latest issue of Physical Review Letters, uses the basic tenets of quantum mechanics to give a new description of information leaking from a black hole.

Our results didn’t need the details of a black hole’s curved space-time geometry. That lends support to recent proposals that space, time and even gravity itself may be emergent properties within a deeper theory. Our work subtly changes those proposals, by identifying quantum information theory as the likely candidate for the source of an emergent theory of gravity. The results actually extend the predictions made by standard techniques that rely on a detailed knowledge of space time and black hole geometry.

We cannot claim to have proven that escape from a black hole is truly possible, but that is the most straight-forward interpretation of our results. Our results suggest that quantum
information theory will play a key role in a future theory combining quantum mechanics and gravity.

ELECTROMAGNETIC WAVE PROPAGATION EXCEEDING THE SPEED OF LIGHT

LX12496B

- This work demonstrates theoretically and experimentally that the peak of a pulse can emerge from a metallic plate perforated with tiny holes and sandwiched between dielectrics before the pulse enters the sandwiched subwavelength-hole array. The effect known as superluminality arises because of the coupling interference between two states: one coming up from a mode supported by the grounded dielectric slab, and the other emerging from the periodic pattern. While being counterintuitive, this phenomenon is physical and does not violate the causality principle, which is defined with respect the pulse turn-on time occurring before the peak time. In contrast previous works, the presented superluminal mechanism is scalable to any wavelength regime from radio frequencies to visible light, it uses a simple structure without any special (e.g. gain or absorptive) materials, and it occurs for substantial values of the transmittance. This
work expands our fundamental understanding of periodic gratings and may find applications in pulse re-shaping, tunable delay element with canceled group velocity dispersion, and beam spectral analysis.

Single-photon router

LB13197

- In recent years, quantum information science has advanced rapidly, both at the level of fundamental research and technological development. For instance, quantum cryptography systems have become commercially available. These systems are examples of quantum channels, serving mainly to distribute quantum information. There is a significant effort to combine these quantum channels with quantum nodes that would offer basic processing and routing capability. The combination of these channels and nodes would create a quantum network enabling applications simply impossible today. Quantum networks connecting simple quantum processing nodes are also a promising architecture for a scalable
quantum computer.

In this letter, we demonstrate an example of a rudimentary quantum node, a single-photon router. The active element of the router is a single ”artificial atom”, a superconducting qubit, strongly coupled to a superconducting transmission line. Exploiting the phenomenon of electromagnetically induced transparency (EIT), we show that we can route a single-photon signal from an input port to either of two output ports with an on-off ratio of 99%. The switching time of the device is shown to be a few nanoseconds, consistent with theoretical expectations and the device parameters. The device is a nanofabricated circuit offering a clear path to scalability. For instance, it is straight forward to extend this router
to select between multiple output channels.

Signature of hydrogen-bonded supramolecular assemblies at dye-sensitized solar cell interfaces

LC13086B


- Due to the growing global demand for energy, the development of efficient ways of harnessing solar power has become a key scientific challenge. Among promising low-cost alternatives to silicon photovoltaics, dye-sensitized solar cells based on mesoporous TiO2 films sensitized with the dye Ru(dcbpyH2)2(NCS)2 (N3 dye) have gained prominence due to their relatively high energy conversion efficiencies. In dye-sensitized cells the photocurrent is generated via ultrafast electron transfer from the photoexcited dye sensitizer to the semiconductor. As a result the atomistic nature of the semiconductor/dye interface plays a critical role in the performance of these solar cells. Substantial efforts have been devoted to elucidating the structure of this interface, and yet its atomistic nature remains highly controversial. Here we perform a systematic comparison between measured core-level photoemission spectra at the TiO2/N3 interface and the spectra calculated by us from first principles for a variety of atomistic interface models. This analysis suggests that systematic
hydrogen-bonding between dyes occurs on the TiO2 surface, leading to a supramolecular assembly. The present finding hails a paradigm shift in our understanding of dye-sensitized solar cells and bears on the design of more efficient nanoscale photovoltaics.

Physicists Change the Color and Shape of Single Photons

LE13282

- Physicists have simultaneously changed the color and shape of a single photon, the smallest unit of light. The work represents an important step towards implementing communication over long distances with privacy secured by the laws of quantum physics. The photon was extracted from a quantum dot, a semiconductor version of an atom that emits photons one at a time, using a specially-designed optical fiber. Then, the single photon was combined with a much stronger, pulsed laser beam inside a crystal that enables the two light beams to interact efficiently. After exiting the crystal, the color or wavelength of the single photon had been shifted by almost 600 nm, an amount greater than the size of the entire visible spectrum. Because the researchers were using a pulsed laser, its pulse shape became imprinted on the single photon during the color-conversion process. Researchers utilizing different quantum technologies, which often require single photons of a specific wavelength and shape, can now use this approach to link their systems together in a large-scale network for quantum information processing applications.

Why can't we avoid queues in MANHATTAN-like road networks?

LE13030

- As a Mayor of a growing city with traffic issues: would you choose
Manhattan-like road patterns or more “disordered” old European styles?
As a cellular biologist: do you understand how active transport on
biofilament networks organizes inside a cell?

The question of how the structure of a network affects its transport
properties dates back to 19th century Kirchhoff's work on the
conductance of resistor networks. Kirchhoff's well-known linear laws are
nowadays the basis of any electric circuit “current-voltage” analysis.

Network transport characteristics, however, are trickier if the conveyed
species reciprocally interact in narrow channels or on filamentous
structures: non-linear collective phenomena such as queues or jams can
appear.

A paradigmatic model to study traffic phenomena is the Totally
Asymmetric Simple Exclusion Process: particles move stochastically along
one-way lanes and cannot occupy the same position in space.

Via this model, we show that connectivity is very important for traffic
issues on networks. "Regular" connectivities, with junctions having an
equal number of incoming and outgoing segments, produce fluctuating jams
at each junction. Differently and surprisingly, in “irregular”
connectivities traffic jams as such disappear altogether, leaving high
or low dense traffic lanes with small transport fluctuations.

In urban traffic, these results would suggest that rationally designed
Manhattan-like road layouts could lead to traffic jams everywhere,
whereas the anarchy of historically grown cities could help avoiding
this problem. Speculations on the complex layout of cytoskeletal
transport in living cells are tempting…

Beautiful physics in a cup of water

LE13271

- Everyone who has ever observed the surface ripples that form in a simple vibrating cup of water served in an airplane or a train has unconsciously performed the experiment carried out for the first time in 1831 by Faraday. It consists in the rhythmical vertical shaking of a recipient filled with water and ever since Faradays first observations the developing surface waves are known as Faraday Waves. Only a few researchers have paid attention to another phenomenon which seems to be linked to these surface waves: the induced movements of tiny particles added to the fluid. In this paper, we determine for the first time the whole surface velocity field and its statistics using a technique called Particle Image Velocimetry (PIV). Surprisingly the energy spectra of this fluid flow show characteristics typical for 2-dimensional turbulence which is an important approximation for natural systems such as currents in the ocean or circulations in the atmosphere. In contrast to three-dimensional turbulence it includes the possibility of passing energy from small to large spatial scales, a process which explains a seemingly contradiction: the creation of large structures such as eddies when stirring only happens on much smaller scales.