Bubble formation in stout beers

EC10816

We show theoretically and experimentally that the same cellulose fibre
nucleation sites responsible for bubble formation in champagne can
also create bubbles in stouts beers, although at a substantially
slower rate. A rough calculation suggests that it may be possible to
replace the widgets of canned stout beers with a coating of cellulose
fibres on the inside of the can. We have extended a model of bubble
formation in champagne, a supersaturated solution of carbon dioxide,
to the case of stout beers, which are supersaturated solutions of
nitrogen and carbon dioxide. This model reveals that the low
solubility of nitrogen retards the rate of bubble formation within a
cellulose fibre, explaining why widgets are necessary to trigger
foaming in canned stout beers. However, the results suggest that a
coating of millions of cellulose fibres, covering an area the size of
a postage stamp might be able to generate the hundred million bubbles
needed to form the head of a pint of stout in the recommended pouring
time of thirty seconds.

Fluid mixing from viscous fingering

LZ11988

In this paper, we explain how the mixing of two fluids can be enhanced
by hydrodynamic instabilities when the mixing fluids have different
viscosities.

For flows at high velocities, turbulence creates chaotic flow
conditions that get a volume of fluid mixed very quickly (which is why
we stir our coffee to get the sugar dissolved quickly). At low
velocities and in small geometries, however, the flow is laminar and,
typically, mixing occurs very slowly. This is important in nature, for
instance, in flows through porous media, because biological activity
and chemical reactions are limited by how fast the fluids come into
contact. It is also important in engineering applications, especially
in the context of microfluidics, where it is difficult to get the
reactants to mix quickly. Many methods have been proposed to achieve
fast mixing in small devices, but all the strategies explored so far
assume that the fluids to be mixed have the same viscosity. In this
paper, we explain how mixing efficiency can be enhanced when the
fluids are of different viscosities. In that case, the flow is
unstable (through a phenomenon called 'viscous fingering'), which
creates disorder in the flow and leads to faster mixing.

LW12496

How Venom Flows

In some snakes the fang delivers deadly venom in much the same way that a hypodermic needle delivers medicine -- by rapid injection of a pressurized mass of fluid. But there is a second means of envenomation that is more common, and, perhaps, also biophysically more elegant. In the majority of venomous snakes and in all other venomous reptiles, the venom is not released under pressure, but rather seeps from the venom gland along an open groove. Nevertheless, to be effective against other organisms, the venom has to penetrate through the superficial layer of skin and infiltrate the deeper tissue. How does venom infiltrate in the absence of pressure? By using a combination of analytical techniques, experiments, and biophysical modeling, a team of researchers has solved the above paradox. Two key findings have emerged. First, the surface tension acting on the venom is the dominant physical force underlying envenomation; it literally shapes the flow of the venom, and ensures that it sticks when necessary while waiting for prey whereas any break in the prey's skin will act as a venom attractant and suck the venom into the deeper tissues. Second, the influence of surface tension is enhanced by the presence of open grooves on the surface of the tooth or fang. A grooved fang is common among living and extinct reptiles. The contours of the groove enable the venom to conform and flow in such a way that, as a consequence of surface tension, it minimizes the surface energy. In this way it can also be understood how during evolution the groove contour might well adapt to the nature of the prey's skin cover, such as feathers.

LY11974

-Small-scale lab experiments reveal new physics possibly responsible
for nebula structure formation-

Interstellar clouds consist mostly of hydrogen, helium, and cosmic
dust. When a massive star explodes as a nova (or supernova), a shock
wave from the explosion produces a complicated structure of giant
swirls in the expanding envelope of gases from the star and in the
surrounding interstellar medium. It has been known for a while that some of
that structure emerges due to Richtmyer-Meshkov instability that
occurs when a shock wave crosses a boundary between two gases of
different densities. However, our recent study shows that swirling
motion will also emerge if the shock travels through a cloud
composed of one gas non-uniformly seeded with dust (like the ubiquitous
dusty hydrogen plasma). We see such swirls form in laboratory experiments
where shock accelerates an air jet seeded with droplets of vapor
made by a theatrical fog machine or with smoke particles. This
observation is important not just for astrophysics, but for many
practical problems, where it changes our understanding of what will
happen – scramjets, where droplets of fuel are injected into a high-speed
gas flow, strong explosions carrying dust, and even inertial
confinement fusion.

LZ11975

New light on microscopic motors

Laser light can be used as delicate and precise fingers to control and
move tiny beads. Many scientific areas have found in optical
micromanipulation a great tool for exploring new horizons. Such is the
case of the study of transport phenomena in the microscopic realm. In
particular, the field of ratchets tries to understand the emergence of
directional motion even though the acting forces add to zero; this was
motivated in part by the study of molecular motors inside cells. Here
we present an experimental realization of an optical ratchet by
creating a periodic and asymmetric pattern of light and an unbiased
external oscillating force. We put our tiny beads on this landscape of
light and we manage to observe a systematic motion. The interplay
between the optical force and the oscillating force gives rise to a
surprising dynamics, even in the simplest case when thermal noise is
negligible. Namely, by properly tuning experimental parameters it is
possible to control the average velocity of the beads and even the
direction of motion in real time. The simplicity and versatility of
our system shine new light, literally, in the fields of ratchets and
transport of microscopic motors.

LA12735

-Negative Effective Gravity in Water Waves by Periodic Resonator Arrays-

Water waves, such as ocean waves including tsunami, are mechanical waves with a restoring force of gravity. Usually, the gravity has a positive value, namely pointing to the center of the earth. As a result, water waves can propagate along water surfaces.

In this paper, we show that near a low resonant frequency, water waves cannot propagate through a periodic array of resonators (bottom-mounted split tubes, see the attached image) as if water waves experience a negative effective gravity. This gives rise to a low frequency range in which water waves can be strongly reflected by the resonator array. The results provide a mechanism for blocking water waves and could find applications in ocean wave energy extraction.

LB13334

-Carbon in the universe and the Hoyle state-

In 1953 the English astronomer Fred Hoyle predicted the existence of a new excited state of the carbon nucleus to explain the abundance of carbon in the universe and its production in stars. Although the predicted Hoyle state was seen experimentally over half a century ago, theorists were unsuccessful in describing the nature of this state from first principles. Researchers have now produced the first ab initio calculation of the low-lying states of the carbon nucleus using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, the authors find a resonance with all of the properties of the Hoyle state and in agreement with theexperimentally observed energy. These lattice simulations provide insight into the structure of this unique state and new clues as to the amount of fine-tuning needed in nature for the production of carbon in stars.

LR12680

-First Images of a Spin-Torque Driven Magnetic Nano-Oscillator-

While conventional electronics are based on manipulating the charges of electrons, the rapidly emerging field of spintronics explores the manipulation of the electronic spin for information technologies. Current spintronics areas of intense technological development include the transfer of angular momentum from a spin-polarized current to a nanoscale ferromagnetic structure for the fast, energy efficient writing of non-volatile information, and for the excitation of microwave oscillations in ferromagnetic nanostructures. Our focus here is on dc-driven precession of a nanomagnet, similar to a dc motor. This process may lead to highly-tunable microwave nano-oscillators for high-frequency, on-chip devices that can operate without the need for applied magnetic fields. Until now, details of this phenomenon have been elusive due to its fast time scale (nanosecond) and small size (nanometer). Using a novel X-ray technique we obtained the first images of the steady-state oscillation of a magnetic vortex that is driven by a dc spin-current. These time-resolved, real-space images reveal the details of the complex magnetization dynamics, while alsopointing to possible limitations of current theoretical models.

-Nuclear security, deep water drilling, black hole signal flares and more at 2011 APS annual meeting-

The physics of deep water drilling, new energy technologies, science at the LHC, tests of gravity at both very large and small scales, and much more cutting edge science will be featured in talks at this year's April meeting of the American Physical Society (APS). The meeting runs from April 30 to May 3 at the Hyatt Hotel Orange County in Anaheim, CA.

Journalists are invited to attend the meeting free of charge. Registration information can be found at the end of this release.

MEETING HIGHLIGHTS
The items below highlight some of the interesting talks and sessions at the meeting.

WATCHING NUCLEAR REACTORS WITH NEUTRINOS
Under the Nuclear Non-Proliferation Treaty, the International Atomic Energy Agency (IAEA) has installed nuclear safeguard systems to monitor nuclear reactors. These systems, while effective, lack certain attractive features: they cannot provide real-time monitoring of reactor activities and some of them interfere with reactor operations. Antineutrino detectors can provide a continuous, real-time, and less intrusive method for monitoring reactors, according to Fangfei Shen of the Massachusetts Institute of Technology. This proposed safeguards system, tested at reactors in Russia and the United States, is a spin off from antineutrino experiments, many of which use reactors to produce antineutrinos. Monitoring antineutrino flux can detect illicit activities in reactors, such as the diversion of plutonium. Sensitivity to changes in fissile content in a few months using only antineutrino data has been demonstrated with greater than 99 percent confidence. In the last few years, the IAEA has begun to consider the potential of this technology for its reactor safeguards regime, said Gregory Keefer of Lawrence Livermore National Laboratory (LLNL). An upcoming experiment, to be described by Timothy Classen of LLNL will monitor antineutrinos at a nuclear reactor in Canada through its construction to operation.
Q13.00001
Q13.00002
Q13.00003

DEEP WATER DRILLING
Kenneth Gray, of the University of Texas at Austin, will talk about his recently-patented Dynamic Density Control (DDC) system that might soon make drilling deepwater wells safer, faster and more economical. He will also introduce some of the technical terms surrounding deepwater drilling and describe the challenges posed by extreme depths and high pressures. Jonathan Katz, of Washington University in St. Louis, will talk about the failure of mineral slurries – or mud – to kill out-of-control wells from above, as in the case of the Macondo/Deepwater Horizon oil well. Adding a new polymer to the slurry mix could enable the mix to successfully kill a well. Brian Clark, of Schlumberger, an oilfield services provider, will give an overview of the role of physics in drilling, for example in locating hydrocarbons. Hydrocarbons are found largely in crude oil, where decomposing organic material produces large amounts of carbon and hydrogen that bond to form hydrocarbons.
Q5

SIGNAL FLARES FROM THE CENTER OF THE GALAXY
The recently-identified black hole at the center of our galaxy, likely part of the Sagittarius A* (“Sagittarius A-Star”) radio source, appears to be producing flares similar to those given off by our Sun. The black hole’s flares, which are emitted at radio, millimeter, infrared and X-ray wavelengths, are much more energetic than flares coming from the Sun. Farhad Yusef-Zadeh, of Northwestern University, will talk about the discovery of these flares and his attempts to learn how they are physically related to one another. “We don’t know exactly where [the flares are] being produced, but we think it is very close to the event horizon of a black hole,” Yusef-Zadeh said. The event horizon is the turning point at the edge of a black hole where material wandering by is sucked in with no hope of return and where space and time are distorted. The team has also noticed that there is a time delay between the observation of infrared flares and X-ray flares. They hypothesize that the X-ray flares are echoes of the infrared flares. If they are correct, it would confirm a theoretical model about black hole flaring called inverse Compton scattering.
L3.00002

A NEW WAY TO CREATE ELECTRICITY FROM CHEMISTRY
When atoms and molecules interact at a surface, a lot of chemistry goes on, some of it still surprising. One idea that had been understood as possible for decades is now being shown to actually work at a practical level: the chemovoltaic (CV) effect. The CV effect happens when a chemical reaction taking place at the surface of a material also creates high-energy electrons in the material that can be used as a source of electrical current. This is in contrast to a fuel cell or battery that requires separate anodes and cathodes with materials to separate positive and negative charges between them, making them bulky. New studies by Eduard Karpov, of the University of Illinois at Chicago, have shown that through the CV effect hydrogen-to-water oxidation can occur next to platinum-based surfaces just nanometers thick. In this way, the CV effect can exceed other electronic effects that have been well known for some time, leading to the possibility of novel energy transport devices to compete with fuel cells and batteries.
E13.00007

TESTING GRAVITY WITH LEVITATED MICROSPHERES
Gravity is the least understood among the forces of nature. According to some theories, the gravitational interaction between objects will show an anomalous increase at distances under a millimeter. Andrew Geraci of the University of Nevada and colleagues at the National Institute of Standards and Technology are developing a supersensitive gravitational test that relies on levitating tiny glass spheres. The spheres are suspended and cooled in a virtual container made from lasers. Slight displacements of the beads that occur when heavy objects are placed nearby should reveal any exotic forces beyond those produced by gravity at larger scales. The researchers propose that the new method could be over 100,000 times more sensitive than previous gravitational experiments at micrometer distances.
T13.00002

SCREENING NUCLEAR MATERIALS WITH GAMMA RAYS
Researchers at Duke University’s High Intensity Gamma-Ray Source (HIGS) are investigating a new method for distinguishing enriched uranium, which could be developed into nuclear weapons, from the more benign, depleted form of the heavy metal. To accomplish the feat, the researchers irradiated uranium samples with a high-energy polarized gamma-ray and measured the pattern of neutrons the samples emitted. Eventually, the technique may lead to a novel method of detecting enriched uranium in cargo containers. Jonathan Mueller, of Triangle Universities Nuclear Laboratory, will describe the progress in developing the screening method as well as their efforts in developing a model to explain the unexpected differences in neutron patterns the two types of uranium emit under gamma-ray exposure.
Q10.00007

FASTER THAN LIGHT PARTICLES ILLUMINATE BIOLOGY
Cerenkov radiation is emitted by particles that move faster than the speed of light in a given material. Although the radiation has been helpful for gathering data in particle detectors for years, biologists working with radioactive isotopes have just begun to make use of it in living organisms. Cerenkov Light Imaging (CLI) can be done with charge-coupled devices (CCDs) typically used for fluorescence or bioluminescence imaging. Nicole Ackerman, of Stanford University, will present simulation results in comparison to data collected from living creatures and tissue samples at the Stanford Small Animal Imaging Core Facility in an attempt to get a handle on the limitations of the imaging technique.
L7.00003

EXPLORING THE DIGITAL DIVIDE
In the first decade of the 21st century, huge progress was made in bridging the digital divide between developed and developing nations. This was largely due to the explosive growth of mobile technologies, which saw mobile cellular subscriptions rise from under 500 million to over five billion in just ten years. With household mobile phone penetration rates of over 50 percent even in rural areas of developing countries, the dream of bringing all the world's people within reach of communications technology has been achieved, Hamadoun Tourè, Secretary-General of the International Telecommunications Union, said. In his talk, Tourè will argue that we must now replicate the mobile miracle for the Internet, and especially broadband. Meanwhile there has been progress in South America, where a network of optical cables has been laid. The network is enhancing advanced computing applications and collaboration there, Michael Stanton, of the Brazilian National Research and Education Network, said. The African continent, however, is falling further behind the developed world, Roger Cottrell of the SLAC National Accelerator Laboratory said, but potential can be seen through the huge boost in optical fiber connectivity improvements ahead of soccer’s 2010 World Cup held in South Africa.
J6.00001
J6.00002
J6.00003

LHC MEDIA AVAILABILITY
A large suite of talks will discuss the latest results from the Large Hadron Collider (LHC) at CERN, the European Organization for Nuclear Research. Earth-shattering results are not expected at this meeting but there will be many scientists available to discuss what has been achieved so far, including the replication of the discovery of the standard model of particle physics and what is expected to come in the next year’s running. LHC representatives will be available to speak with the media about the latest results.
Various sessions including overviews in Session R2

PHYSICS FUN FOR EVERYONE
Session C13, devoted to educating and exciting the public about physics, will answer questions like: Is it possible for a TV program to be both funny and scientifically accurate? Bill Prady, the executive producer and co-creator of The Big Bang Theory, will talk about the first TV comedy to employ a physicist consultant and how the show brings together science and entertainment. Or, why do humans place artificial barriers between fields of study, like art and science, when people from different disciplines could benefit from one another, like a neuroscientist learning new problem-solving methods from a filmmaker? K.C. Cole, of the University of Southern California’s Annenberg School for Communication & Journalism, will talk about overcoming the tendency to force subjects into confining categories. Linda Shore, from the Exploratorium science museum in San Francisco, will talk about the museum’s goal of encouraging children and adults to do science both at the museum and at home.
C13

SUPERCONDUCTIVITY CENTENNIAL
Session J2 celebrates the centennial of the discovery of superconductivity. Peter Pesic, of St. John’s College, will talk about Heike Kamerlingh Onnes and his colleagues who discovered superconductivity in 1911. David Larbalestier, of Florida State University’s National High Magnetic Field Laboratory and Department of Physics, will talk about the superconducting materials developed over the last century as well as about strategies for creating new superconducting materials over the next century. Anthony Zee, of the University of California, Santa Barbara, will talk about “superconductivity beyond superconductors,” discussing superconductivity’s role in particle physics and quantum field theory.
J2

ATOMIC NUCLEUS DISCOVERY CENTENNIAL
This year marks the centennial of the discovery of the nuclear structure of the atom. Session C1 will celebrate Ernest Rutherford’s nuclear model for the atom. Before Rutherford’s discovery, scientists thought that electrons were scattered in atoms like raisins in a plum pudding (Thomson model). Rutherford discovered that electrons were in orbit around an atomic nucleus, a discovery he called the “most incredible event” in his life. “It was almost as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back to hit you,” Rutherford said of his experimental results. John Heibron, of the University of California, Berkeley, will talk about Rutherford and his colleagues, including Niels Bohr and Charles Darwin (grandson of the famous naturalist). Suman Seth, of Cornell University, will discuss several early atomic models that followed the Rutherford discovery. Nobel laureate Jerome I. Friedman, of the Massachusetts Institute of Technology, will talk about the Rutherford model’s continuing influence on modern work in sub-atomic physics.
C1

###

MORE INFORMATION FOR JOURNALISTS
- Main meeting site
- April Meeting abstracts

REGISTERING AS A JOURNALIST
Science writers intending to go to the meeting should contact James Riordon (riordon@aps.org, 301-919-2173) about complementary registration. Onsite registration is possible in the pressroom throughout the meeting, but to speed the process journalists are encouraged to register in advance. Press badges can be picked up in the pressroom and will allow you to attend any session at the meeting.

PRESSROOM INFORMATION
A dedicated and staffed pressroom will operate throughout the meeting in the Hyatt Hotel Orange County. Phones, computers, printers, and free wireless Internet access will be available to reporters using the pressroom.
- Pressroom Location: Granada Room, Hyatt Hotel Orange County
- Hours: Sat., April 30 – Mon., May 2, 7:30 a.m. to 5:30 p.m. and Tue., May 3, 7:30 a.m. to noon
- Food service: breakfast and lunch will be provided each day except for Tue., May 3 (breakfast only)
- Press conferences: a schedule of press conferences will be released at the end of April. Reporters wishing to dial in will be able to call the press conference line at 800-944-8766, access code 79886#, to participate in the events remotely.

ABOUT APS
The American Physical Society is a non-profit membership organization working to advance and diffuse the knowledge of physics through its outstanding research journals, scientific meetings, and education, outreach, advocacy and international activities. APS represents 48,000 members, including physicists in academia, national laboratories and industry in the United States and throughout the world. Society offices are located in College Park, MD (Headquarters), Ridge, NY, and Washington, DC.

LV12464

- Bio-mimetic carbon nanotube competes with platinum in fuel cell technology -

Cathodic oxygen reduction reaction (ORR) is the rate-limiting step for low-temperature fuel cells such as proton-exchange membrane and direct methanol fuel cells. To expedite the rate-limiting ORR for practical power applications, one has to use a large amount of platinum (Pt) as a catalyst. At the moment, Pt is the only meaningful ORR catalyst in industry. However, Pt is very costly and rare. Also it is not stable for extensive use. Here, from collaborative efforts of theory and experiment, we report a new, biomimetic carbon nanotube-based material as an excellent and extremely stable ORR catalyst that could compete Pt in fuel cell technologies. The novel material is a kind of composite between catalytic Fe-porphyrins and electron conducting carbon nanotubes. The facile plasma-enhanced CVD synthesis of the material is justified with photoemission spectroscopies and electrochemical ORR half-cell experiments, as well as density-functional theory calculations. This nano-bio hybrid catalyst would not impact only on fuel-cell technologies, but also, taking advantage of functional diversities of metal-porphyrin complexes and carbon nanotubes/graphenes, metal-porphyrin incorporated carbon nanotubes or graphenes could have significant implications in various emerging nano-technologies, including sensors, energy storage, solar cells, artificial photosynthesis, and nano-biomedical applications.

LB12826

-Recasting Einstein's General Relativity-

It is now well known that Einstein's general relativity cannot be the
final say in gravity. Any attempt to extend Einstein's general relativity
by incorporating higher order corrections is usually plagued with
problems, either conceptual or technical. At the conceptual level, one
asks if there is a fundamental explanation for any such extension. At the
technical level, one asks if there are a finite or infinite set of such
corrections. In this work, we show that an infinite order extension of
Einstein's theory in the form of a square-root action of the type
postulated by Dirac, Born and Infeld in the early 20th century for
electrodynamics, arises naturally in 2+1 dimensions. Gauge/gravity duality
in the form of the AdS/CFT correspondence plays a crucial role in the
derivation of this action. The resulting action can be rewritten in terms
of the gauge field used to recast Einstein's theory in 2+1 dimensions in
terms of a Chern-Simons theory and may have implications in the
mathematics of knots.

DA11000E

-The brain as a topological quantum computer-

What is common among solar flares, brain activity, large-scale Universe,
biological evolution, earthquakes, and spin glasses? The answer is
Self-Organized Criticality (SOC) - a concept put forward by Bak, Tang,
and Wiesenfeld over twenty years ago. Since then, this ultimately
ubiquitous phenomenon has been proving itself stubborn and elusive
for theoretical investigations. No satisfactory mathematical model
was found to capture the SOC's peculiar properties. Such a model
would certainly provide a deeper understanding of various aspects
of physical and biological worlds, or even establish a mathematical
link between them.

In this paper, we show that such mathematical model was actually
hiding all these years under the name of Witten-type Topological
Field Theory (W-TFT). Interestingly, "SOC" and "TFT" were coined the
same year (1989). Further investigations of the proposed connection
between SOCs and W-TFTs may lead to intriguing results. For example,
it may turn out that brain performs a sort of (room-temperature!)
fault-tolerant topological quantum computations.

LC13768

-Scattering lens resolves nanoscale objects-

A new type of lens that exploits strong scattering of laser light is
shown to resolve structures at sub-100 nm resolution. Light scattering
was once thought of as a nuisance in microscopy. However, scattering can
enhance imaging when combined with computer-controlled spatial light
modulators. An opaque layer of scattering material can couple light to
modes that cannot propagate in air, thereby increasing the potential
resolution in a similar way to metamaterial superlenses. Such scattering
layers are very easy to produce but they inconveniently scramble all
optical information into a disordered interference pattern called
speckle. In a scattering lens digital spatial light modulators are used
to unscramble the information and transform the speckle into a clear and
tight focus. In the present work researchers have combined such a lens
with a high-refractive-index material to create a focus that is tighter
than any other lens has made before. They scanned this focus in two
dimensions to image a test object - a collection of gold nanoparticles -
and found a resolution of 97 nm. Because the lens produces a real
scanning focus, in future it can be combined with many other methods
ranging from new metamaterial structures to ultrafast fluorescence
methods, to further enhance resolution.

Figure: left - Reference image of a collection of gold nanoparticles.
Right - same image with the scattering lens. The white scale bar is 300
nm.

EB10854



-From burning to exploding: modeling the deflagration-to-detonation transition (DDT)-

In this paper we used probably the most detailed high resolution simulations yet performed to reveal and to explain mechanism of DDT. In contrast to previous studies which used a simplified single-step chemical reaction model we used a real chemical mechanism and were able to explain how flame accelerates and how the transition to detonation occurs. This phenomenon is known as the transition from a slow combustion (deflagration) to detonation or deflagration-to-detonation transition (DDT). Over the years DDT was one of the least understood phenomena in combustion science. Significant efforts have been devoted to understand the nature of the flame acceleration and mechanism of DDT because of its importance for industrial and the nuclear industry safety. If DDT were to occur the integrity of the containment could be jeopardized. Unfortunately, the recent accident at the Fukushima Daiichi Nuclear Power Plant has shown how important it is a correct understanding of the DDT nature and origin.

LZ12159

Tuned transition from quantum to classical for macroscopic quantum states

The boundary between the classical and quantum worlds has been intensely studied. It remains fascinating to explore how far the quantum concept can reach with use of specially fabricated elements. We performed an experiment on a superconducting flux qubit, which is the 'classical' example of a macroscopic object that can be made to behave as a quantum particle. It is characterized by two states with opposite macroscopic currents in a loop. We were able to control the tunnel barrier between these states over a very wide range. We tuned qubit energy levels below the barrier and the same time e effectively cool the sample to near zero temperature. This allowed us to study the qubit behavior when we go from the range of low barriers and strong quantum tunneling to the regime where quantum tunneling gradually disappears as the barrier is increased. In particular, we manage to observe the natural quantum oscillations manifested in the tunneling of the long-living macroscopic magnetic moments. At very high barriers we see the how these oscillations fade away as the barrier is increased.

LY12135

ONE-WAY PROPAGATION OF WAVES: NONLINEARITY CAN!

Deterministic chaos, fractal structures and other beautiful phenomena are
manifestations of the nonlinear character of forces which govern our world.
Besides a revolutionary change in our approach to predictability, these
discoveries had great impact on technological applications. In this letter a
new unexpected effect of nonlinearity is discovered which may lead to new
technologically important devices: the possibility to control wave transmission
by breaking the simmetry between opposite propagation directions.

The simplicity of the model and the great generality of the results which-
by exploiting distinctive nonlinear properties of materials like
multistability and resonance shifts, lead to asymmetric wave transmission-
will likely allow actual implementation e.g. in layered media with suitably
tailored nonlinear properties.

The attached figure is a dramatic illustration of the effect: a wavepacket
coming from the left passes trough the wall (the nonlinear medium). If the
packet comes from the right it is reflected back!

LX12109BR

-Dragging Electrons in Graphene-

Researchers have realized a device where two graphene layers are brought to within a few nanometers, while remaining electrically isolated from each other. The device allows a direct measurement of the mutual scattering of electrons residing in opposite layers.

Electrons and holes, the particles that carry current in semiconductors are electrically charged, and as such they repel or attract each other by virtue of Coulomb force, leading to scattering. Probing this phenomenon provides unique insight into the electron physics in a semiconductor, but is challenging since electrons scatter primarily off of charged impurities and lattice vibrations (phonons), while electron-electron scattering is a small perturbation. In this paper, two graphene layers were brought to within a few nanometers of each other, while separated by an Al2O3 dielectric. Owing to Coulomb repulsion, electrons flowing in one layer meet an opposing force drag) from electrons in the opposite layer. Consequently, current flowing in one layer leads to a voltage drop in the opposite layer, a direct measurement of electron-electron scattering.

LX12173E

-A WHITE HOLE IN YOUR KITCHEN SINK-

Open your kitchen tap and the impacting jet of water creates a circular jump: a ring-like ridge where the water level suddenly changes. Physicists believe the jump to be a hydrodynamic analogue of white holes, the time-reverse of a black hole: waves on the fluid's surface can approach the jump from the outside, but they cannot get in. In this paper, we show experimentally how to prove this assertion by measuring the Mach cone associated to the fluid flow. We show that the flow is supersonic inside the jump, smoothly evolves towards a critical value on the boundary, and finally disappears just outside the jump. This finally confirms a hypothesis that was first formulated by Lord Rayleigh in 1914. It also proves that, indeed, water waves cannot enter the jump. This provides a simple example of a hydrodynamic horizon analogous to the astrophysical horizon of black holes.

LZ12745

Electrons and protons working together for a big molecular bang

When a strong laser pulse hits a molecule, one or more electrons might be stripped off - the molecule becomes ionized. In our letter we describe the discovery of a novel highly efficient ionization mechanism in hydrocarbon molecules of various sizes that drives the molecules into unexpectedly high charge states at very moderate laser intensities. Subsequently it leads to the complete molecular decomposition via a two-stage Coulomb explosion that involves the concerted emission of all protons with remarkably high kinetic energies. We explain our observations by a dynamic ionization mechanism in which the motion of electrons and nuclei is strongly coupled that is well known for diatomic molecules. In our experiment we observe for the first time that this dynamic ionization can proceed in parallel at many carbon-hydrogen chemical bonds within a hydrocarbon molecule. We show this unique fragmentation process for hydrocarbon molecules, but such a molecular decomposition should also occur in general classes of polyatomic molecules, as long as the time-scale of the intra-molecular nuclear motion matches the laser pulse duration. Our finding shows experimentalists an efficient route for controlling laser-induced fragmentation of molecules using the pulse duration as a control knob.

LZ12650

Control of Molecular Rotors by Selection of Anchoring Sites

We demonstrate a new method to switch on and off the rotational motion of a long-chain molecule by controlling the bonding geometry between the molecule and a substrate. An azobenzene derivative molecule adsorbed on a Au(111) surface is immobile only when its three rotation centers, comprised of two phenyl rings and a nitrogen-nitrogen bond, are located at hollow sites of the Au(111) surface, as observed by scanning tunneling microscopy. Rotational motion can be activated by exciting the vibrational modes and inducing hopping motion away from the immobile site with a voltage pulse. Our results suggest that this is the simplest way to control a single molecular rotor on a surface.

LA13023AR

Curiosity Doesn't Kill the Cat

In Schroedinger's famous thought experiment, a cat might exist in a nebulous quantum state, in which it is neither alive nor dead. But upon an observer looking to *see* if the cat is alive or not, it reverts immediately to one of the two possibilities, destroying the quantum weirdness. Physicists at the University of Massachusetts at Boston have shown how such a nebulous quantum state could be viewed, and even controlled in real-time, without forcing the "cat" into being alive or dead. The experimenter's curiosity need not kill the cat. In this case, the "cat" is actually a nano-scopic mechanical "guitar string", fabricated on a micro-chip. The string is placed in a nebulous state in which the string is at two different positions at the same time. By using a superconducting circuit to monitor the resonator, an experimenter could control the motion of the string, while it continues to exist at both locations.

LU12546

How does water play around biomolecules?

How important is water for biological tissues? For the bottom-up understanding of the importance from molecular level, it is essential to clarify the hydration states of biomolecules precisely, i.e., we need to know how many water molecules are perturbed by the biomolecules. Such the hydration effect has been usually estimated from the extent of slowing down of water dynamics at the surface of the biomolecule. Although water dynamics should be observed in sub-picosecond time scale to detect the slight effect of hydration in detail, past studies could not reach such the observation in the ultrafast time scale. In this paper, we clarify the precise hydration state of a model biomembrane (phospholipid bilayer) from observation of ultrafast dynamics of water molecules by using terahertz spectroscopy. In combination with the structural information of the stacking model biomembranes by X-ray scattering, this advanced technique reveals that the volume of perturbed hydration water is five times as much as previously thought, and it reaches up to 1 nm far from the membrane surface. This indicates most of water between the membranes does not behave as normal water.

***

EYJ1044

Travelling salesmen should follow their noses

Research published in Physical Review E shows how cells of the immune system can solve the 'travelling salesman problem' and so minimise the time taken to eradicate multiple sites of infection. This becomes crucial when airborne bacteria get distributed throughout the lungs. The 'Travelling Salesman Problem' is easily stated but notoriously different to solve. The problem is to find the shortest possible route between many cities (infection sites), visiting each city just once. Even the best computers struggle with the problem. There are, after all, more than 2 million, million, million, million ways to travel between just 20 cities. The new research shows that good solutions will be found if the salesmen, like immune cells, were guided by their sense of smell, moving up gradients in the combined smell produced by the cities. This provides new insights into the workings of the immune system, and into the movement patterns of the diverse range of organisms that sniff out their prey.


***

LV12113

Quantum Fuzziness Reduced

The weird laws of quantum mechanics predict a fundamental fuzziness in where a quantum arrow points in space, akin to having a compass whose needle is hard to read no matter how hard you squint. The fuzziness of these arrows, called spins, can be reduced by using lots of identical arrows and averaging where they each point. This approach is called the standard quantum limit (SQL). To go beyond the standard quantum limit, one can combine the compasses into a single super-compass in which the fuzziness of each compass partially cancels. The glue that holds the compasses together is called quantum entanglement. Researchers now have used quantum measurements to create entanglement that glued together the equivalent of a million pairs of rubidium atoms. To do this, the researchers placed the atoms between two mirrors and watched how light was modified as it bounced between the mirrors. The measurement process caused the atoms to undergo a quantum "collapse" into an entangled state with reduced fuzziness when the researchers analyzed their measurements. In the future, this approach may help improve the global positioning system or monitor changes in the physical laws of the universe.

***
LZ12781

Superconducting Vacuum

The main result of this paper is that the vacuum, in the presence of a very strong magnetic field, becomes a superconductor. Moreover, the properties of the superconducting state of the vacuum are drastically different from those of a "textbook" superconductor. All textbooks state that one of the key properties of a superconductor is that it expels a weak external magnetic field. The textbooks also stress that a sufficiently strong external magnetic field will destroy the superconductivity property. Finally, it is taken for granted that a superconductor is a material object; i.e. it is composed of ordinary matter. In our paper we demonstrate that the vacuum becomes a superconductor if it is exposed to an enormous magnetic field. We show that the vacuum, which is by definition the absence of matter, becomes a superconductor due to magnetic field-induced condensation of certain quantum fluctuations. The superconducting state is a high temperature superconductor which is able to survive high temperatures of the order of billions degrees Kelvin (a typical scale of strong interactions). Magnetic fields of the required magnitude may be generated for short times during the evolution of the early Universe, and in heavy-ion collisions at the Large Hadron Collider facility at CERN.

2011 March Meeting Video Gallery

See some of the most exciting videos to be featured in talks at the upcoming APS March meeting in the Virtual Press Room Video Gallery.

Here are a few sample videos from the gallery.

Swimming Diode

A diode is an object that conducts electric current in only one direction. Powering a diode with an alternating current (AC) electric field causes the diode in this video to pump water over its surface, propelling it back and forth on the water surface. Modifying the AC field causes the diode to change direction.


Carbon Nanotube Material vs. Silicone Rubber

The shaking tables in this, part one of three videos, show that a new carbon nanotube-based material stays flexible over a wide range of temperatures, from -190C to room temperature (RT) to 900C. The paper sumo wrestlers easily keep their feet when riding on a cushion of carbon nanotube material, regardless of the material’s temperature, while the silicone rubber only helps the wrestlers at room temperature.


Syrup Falling on Waffles

This computer simulation shows how a thick fluid behaves when falling on a moving conveyor belt. It also simulates the extremely complicated movement of hair and shows how a gooey fluid would behave when draped over objects, like syrup being poured on waffles.



Visit the video gallery to see more videos from the 2011 March Meeting.

2011 March Meeting Image Gallery

See some of the prettiest pictures to be featured in talks at the upcoming APS March meeting in the Virtual Press Room Image Gallery.

Here are a few sample images from the gallery.

Atomic Transistors

This microscopic image of the surface of gallium arsenide (GaAs) shows how the arrangement of atoms on the GaAs surface affects its electric field. The image illustrates the manipulation of individual atoms to allow for very precise tuning of the characteristics of GaAs-based transistors.

Four Qubits on One Chip

This computer chip includes four superconducting qubits that comprise a quantum mechanical version of a computer microprocessor. Quantum computers are expected to be able to solve various problems that are far too difficult to be handled by conventional computers.


First Superconducting Magnet

The world’s first superconducting magnet, consisting of a wire coil made of lead, was manufactured in the Leiden (The Netherlands) Physics Laboratory in 1912. Superconductivity had been discovered the year before, in 1911, by Heike Kamerlingh Onnes in mercury cooled to -269 degrees Celsius.

Visit the Image Gallery to see more images from the 2011 March Meeting

LZ12650

On-off Control of a Nanometer-size Molecular Motor

A 2.7 nanometer long molecular motor is demonstrated. The rotor is made of a long chain molecule called an azobenzen derivative and it can maintain thermally excited rotational motion above 77K. In addition to the motion, they were able to control the on-off state by selecting the anchoring site of the rotor. That was possible by inducing a hopping between immobile and mobile sites. All operation and control were imaged with low temperature scanning tunneling microscopy. This concept can be adopted in future design of nano-electro-mechanical systems.