Tuesday, May 3, 2011

Quantum walking over rough terrain: How obstacles influence the propagation of quantum particles

LA12856

- Quantum physics allows particles to spread quadratically faster than their classical counterparts in a discrete, uniform environment. We have implemented an experimental setup that demonstrates how the dynamics drastically change, if temporal and spatial inhomogeneities are introduced. Fast fluctuations in time lead to a full suppression of the quantum behavior, forcing the particle to act entirely classically. On the other hand, spatial disorders result in a stagnation of the propagation, thus trapping the quantum particle around its initial position, which is in high contrast to
any classical description. Quantum walks serve as underlying theoretical model to explain processes in a variety of different physical systems, as for example, the energy transfer in photosynthesis. The dynamics in such biological systems are hard to measure and highly influenced by disorder and thermal fluctuations. Using controllable photonic quantum networks, we were now able to simulate similar environmental influences and carry out detailed studies of their impact on quantum systems. The experiment not only confirms the theoretical predictions, but opens up new routes for quantum simulations and information processing in mesoscopic structures based on coherent state transfer.

Medley swimming of sleeping sickness parasites.

LW12592


- Though cell locomotion has been examined almost since the discovery of the cell itself, advances in microscopy and biochemical studies have paved the way to a more fundamental understanding of cell motility. More recently, a physical, quantitative approach to understanding the world at the micron scale has gained momentum. This work is a detailed, quantitative characterization of trypanosome motility. Trypanosomes, parasites responsible for deadly disease in humans and cattle, swim with the aid of an appendage called a flagellum. The flagellum, produces rapid undulatory movements that result in cell locomotion. We followed single trypanosomes in a homogeneous environment and found that cells that swim faster also exhibit stronger fluctuations in velocity. Statistical analysis allowed us to develop a mathematical model that could reproduce the diverse trajectories followed by the trypanosomes. Finally, we were able to show that the rapid movements of the body (with time scales on the order of 0.1s) are a result of an active process (requiring energy) and thus cannot be described as simple thermal fluctuations. On the whole, such studies provide insight into basic mechanisms of motility, allow for modeling of cell movement, and may eventually even provide design ideas for artificial microswimmers.

Researchers Study the Interplay between Electric and Magnetic Modes Inside a Material … by Looking Outside

LA12855B

- By examining how garnet crystals reflect and transmit light, we observed the rare occurrence of a hybrid mode where the material displays electric and magnetic characteristics simultaneously. Amazingly, evidence of the hybrid mode vanishes from the reflectivity spectra but remains strong for the transmitted light. We developed an explanation called the Adjusted Oscillator Strength Matching (AOSM) condition to describe this unique electric and magnetic behavior. A possible application of this effect is in antireflection coatings. Using a variety of complementary optical techniques, such as reflectivity, transmittance and ellipsometry, we measured the material’s dielectric permittivity and magnetic permeability in the far infrared frequency range. This work is important in furthering the understanding of when coupling between magnetic excitations such as magnons and electric excitations such as phonons occurs inside a material.

Thursday, April 28, 2011

How can you compact a thin sheet of paper?

LB13270

- You can crumple this sheet as a paper ball but the growth of a network of high energy ridges and vertices (d-cones) will hinder the formation of a dense object. It is indeed very difficult to attain 50% of compaction even by applying very large forces !

On the contrary, you can try to make with great care regular folds following a complex origami scheme to get the most compact morphology, i.e., the smallest volume for a given sheet but this is rather time consuming !

Why not using self-organization of folds ?

Here, we show that you can produce very easily optimal self-similar patterns of fold by constraining a sheet at one edge, i.e., a hanging curtain. By exploring these self-organized curtains, we uncover an universal law governing the shape of the sheet whatever the used materials, from graphene to fabrics. In addition, we show that these spontaneous patterns can be manipulated by adding a simple tensile force, regularizing the complex hierarchy of folds.

BOOMERANG BEHAVIOUR OF MASSIVE PARTICLES IN BLACK-HOLE RADIATION

DB10717

- The traditional view on Hawking radiation is that black holes emit (massless)
photons as well as massive particles, provided that the latter have an energy
at least equal to their rest mass. We have demonstrated that this image is
actually not correct for the massive particles: these are radiated from the
black hole horizon independently of their energy. However, the particles with
an energy smaller than their rest mass only arrive at a finite distance from
the black hole before bouncing back in a boomerang-like fashion and being
re-absorbed by the black hole. We have also suggested several examples of
analogue gravity systems (systems where sound waves or other perturbations
behave as if they were moving in a black-hole spacetime) where such an effect
could realistically be detectable in a laboratory setting.

Optically induced crystals of submicron particles

EY10506

- Laser beams sent through microscope lenses are widely used in
physics and biology to trap and manipulate small particles in a solution.
In these so-called optical tweezers, micron-sized particles floating in the
microscope's field of view become trapped at the focal spots of the laser
beams, allowing mechanical control of tiny objects under the microscope.
Using several laser beams, multi-site optical tweezers have been realized
that enable the assembly and control of ensembles of such particles. In the
present work, we use optical tweezers formed by four interfering laser beams
to grow and control large, optically induced crystals of submicron particles
in aqueous solution. In contrast to crystals in the usual sense, these are
non-frozen, periodic particle assemblies held together by the optical forces
generated by the lasers. Several thousands of particles can be arranged into
nearly defect-free, three-dimensional crystals with high packing density.
The crystal structure is controlled by laser beam polarizations and angles,
while the crystal size can be controlled by laser beam diameters and powers.
Future applications of the work may include studies of artificially
crystallized biological matter (bacteria, viruses, proteins) using soft
x-ray Bragg scattering. The research may also lead to the creation of novel
tools for photonics applications, such as materials with a tunable photonic
bandgap.

Break-Up in Granular Jets

LW12658
- Attractive forces between the intimate particles of matter (atoms
or molecules) are at the heart of the conception of cohesion of matter.
This is why matter stick together : gases condense to liquids,and
liquids freeze to solids. Granular jets falling out of a funnel shaped
container, subjected to small vertical vibrations, under the action of
gravity display a strikingly liquid-like appearance. Such jets start out
spatially uniform and break up into clusters farther downstream as may
happen for ordinary liquids under the action of surface tension forces.
This is surprising since attractive forces between grains (at the heart
of surface tension or capillary forces in liquids) are much weaker than
other mechanical forces at play (gravity, friction, inelasticity).
From an analysis of the long wavelength variations of the jet
radius (induced by the vertical vibration), it turns out that these
modes are unstable and produce a long wavelength break up of the jet
which is reminiscent of a "Rayleigh-Plateau" capillary instability
(that leads to drop formation for liquids). This instability and the
break up of the jet can be inhibited when the effect of the surrounding
medium (air) is reduced by enclosing the jet in an evacuated chamber,
showing that the effective surface tension measured is the result of a
strong interaction with the surrounding air.

Two telescope views on drifting constants in the early universe

LC12995

- Since the days of Dirac scientists have been wondering about the possibility that fundamental constants may have varied over the history of the universe. In the past decade this question has been made operational through the comparison of spectral lines observed in objects, known to be old, in comparison with spectral lines observed in the laboratory, i.e. in the present epoch. The mass ratio between a proton and an electron is such an important fundamental constant, which may be tested by looking at hydrogen molecules. Now very detailed observations of the largest set of hydrogen lines so far (over 90) of the brightest know quasar system (J2123-005 at redshift =2.05) with a lookback time of over 10 billion years from the two largest optical telescopes in the world (the Very Large Telescope in Paranal, Chile and the Keck Telescope in Hawaii) show that such observations on "old hydrogen" can be made, and are not overwhelmed by systematic effects. The results from both telescopes perfectly agree with each other and give a slight indication of a change of a fundamental constant. However, the evidence is too small to call proof. More observations will be needed (of other quasar systems), but we know now better about the trustworthyness of such observations.

Monday, April 25, 2011

Quantum “Tricks” in the Biochemical Reactions of the Avian Compass Mechanism

LW12015E

-“Quantum” and “Bio” are two phrases rarely seen together in a scientific context. The idea that quantum physics is underlying biological systems has been entertained for a long time, with evidence, however, being scarce. We here show that a sort of biochemical reactions, namely radical-ion-pair reactions, at the heart of the avian magnetic compass mechanism and central in photosynthesis, are full of the counter-intuitive quantum-mechanical traits usually encountered in experiments dealing with the simplest of quantum objects, atoms or photons. One of the central themes of quantum physics is the infamous Young's double slit experiment, which beautifully manifests the particle-versus-wave duality and the principle of quantum interference, both cornerstones of quantum physics. In this paper we show that radical-ion-pair reactions are governed by the same principles, only now it is the spin of the electrons that is the main actor. Electrons are spinning little magnets, and their magnetic orientation determines the fate of these reactions, as the electrons hop between neighboring molecules. We have unraveled the rich quantum dynamical behavior of these reactions that has been overlooked for more than 40 years, providing further evidence that Nature has invented quantum physics well ahead of quantum physicists and has genuinely applied it in large dangling biomolecules living in the “wet and warm” biological environment.

Friday, April 22, 2011

Undulating Underperformance: Swimming in Elastic Fluids

LB13132

-The main findings from this work is that fluid elasticity, the property that gives materials like silly putty, yogurt, gels, and human mucus their unusual and useful texture, hinders both the swimming speed and efficiency of live micro-organisms. This is a surprising result because many organisms live, move, feed, and reproduce in fluids possessing elasticity, and many biological process of vital importance take place in such media. Examples include the motion of spermatozoa in the female reproductive track (human reproduction), the beating of cilia in the respiratory track (removal of foreign agents), and the motion of worms in wet soil (soil aeration). We find that fluid elasticity decreases swimming speed of the nematode C. elegans up to 35% compared to ordinary fluids. The undulatory motion of C. elegans is typical of many limbless organisms of different sizes including eels, snakes, worms, cilia and flagellated eukaryotes. This is the first study that systematically investigates in experiments the role of fluid elasticity on swimming, which will help in developing and guiding theoretical models in the future.

Hot and Fast

LC13073

-When a drop of water falls onto a hot plate, the vapor layer between the drop and the plate provides levitation and lubrication that allows the drop to skate rapidly over the surface – an effect familiar to every chef. A novel application of this phenomenon, known as the Leidenfrost effect, has shown that a hot solid sphere under free fall in liquid can travel over twice as fast as a cold sphere by maintaining a continuous, robust, thin lubricating vapor layer around the sphere (see Figure). High-speed video imaging showed that the vapor layer reduced the adhesion between the liquid and the sphere surface resulting in a smoother liquid flow pattern and dramatic reduction in hydrodynamic drag (Videos available on EPAPS). These findings complement related lubricating vapor layer technologies such as using superhydrophobic surfaces, microbubbles injection, and supercavitation in the quest for efficient energy usage and reduced carbon emission in high speed under water propulsion applications.

Thursday, April 21, 2011

Why chaos is warmer than order?

LB13044

Glasses are remarkably different from crystals at low temperature.
They accumulate more heat and conduct less. This anomaly is related
to a particular ensemble of atomic motions called the "boson peak",
which is universally observed for all glasses. Its nature, however,
remained unknown for more than 50 years. Because of this lengthy
research period, the boson peak has been called the last puzzle of
solid state physics. Most models explain the boson peak by additional
vibrational modes created by the chaos of the atomic positions,
while others attribute it to sound waves. We compared atomic motions
in a glass and a crystal using the nuclear inelastic scattering
technique which determines an exact number of vibrational states.
The results show that around the boson peak, the number of states
in a glass is exactly the same as the number of sound wave states
in the crystal. Furthermore, application of pressure causes a
gradual transformation of the boson peak towards a particular
(van Hove) singularity of the crystal created by sound waves with
a period equal to the crystal periodicity. These observations
unambiguously identify the boson peak with sound waves. Thus,
more heat can be stored in a glass not because chaos allows for
more vibrations, but because it changes sound waves.

Tuesday, April 19, 2011

Cosmic Dynamos—Coherent Motions, Not Turbulence, Generate Large-Scale Magnetic Fields

LY12726

From whence come the highly-organized, large-scale magnetic fields observed
around planets, stars, galaxies, AGN, and the giant radio lobes emanating from AGN.
According to many theories, dynamo action—the stretching, twisting, and folding of
magnetic flux needed to grow magnetic fields—should arise naturally from turbulent
motions in the molten metal cores of planets or the hot plasmas in the Sun, stars, and AGN. However, in the last few years, laboratory tests of that idea using liquid sodium have yielded negative results. Rather than enhancing the growth of magnetic fields, strong turbulence appears to diffuse magnetic flux and dissipate it away as fast as it’s generated.

Reported here for the first time, a dynamo experiment with liquid sodium has succeeded in shearing a radial magnetic field and wrapping it up in the toroidal direction to create a toroidal field 8 times larger that the original radial field. The secret was to keep the turbulence very low by creating a very rapidly rotating shear flow (Couette flow) stabilized against turbulence by the differential rotation (decrease in angular momentum) between a rapidly rotating inner cylinder and a less rapidly rotating outer cylinder. This type of stabilization occurs in the Keplerian flow of accretion disks around stars and super-massive black holes. Stabilization is achieved in the interior of stars by an entropy gradient at the base of the convective zone, and by viscosity in planets.

The new experiment has demonstrated the omega effect (amplification through stretching) of a classic alpha-omega dynamo. To demonstrate that this field could grow exponentially large from a small seed value, the experiment will add the coherent twisting motion of plumes (the alpha effect) to rotate a small fraction of the toroidal field back into the original radial field. In astrophysics such plumes occur naturally when a small number of early stars plunge back and forth through accretion discs, or convective plumes rise in the convective zone of stars or planets. Thus, the experimental results so far suggest that coherent flows, not turbulence, are the likely origin of the magnetic fields that produce the most dramatic effects of astrophysics—the Earth’s aurora, solar and stellar flares, massive magnetized jets from AGN, and ultra high energy cosmic rays.

Monday, April 18, 2011

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.

Wednesday, April 13, 2011

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.

Saturday, April 9, 2011

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.

Friday, April 8, 2011

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.

Thursday, April 7, 2011

-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.
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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

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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.

Wednesday, April 6, 2011

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.