LP11892

Morphology scaling of drop impact onto a granular layer

The collision between water and sand is very familiar phenomenon. Nevertheless, we had not known its true physics at all. Only dry granular impacts by solid projectiles have been studied well so far to understand the crater formation dynamics and the fundamental granular physics. In this paper, we investigated the impact between a water droplet and a granular layer. The crater morphology includes some counterintuitive results. We often observe craters with an inner ring (ring type crater). In a certain situation, lower speed impact is better to make a deeper crater (sink type crater). In other cases, higher speed impact can produce a bump whose peak height is higher than an initial level (convex bump type crater). On the other hand, we found that the crater radius can be scaled by a simple dimensionless number. Moreover, this phenomenon might be also relevant to the long (over 150 year) debated problem of "fossil rain drops" which are small circular pit‑like depressions in fine grain sediment and whose origin is still a subject of controversy.




***

EL10617

"Hairy" capsid proteins can lead to inefficient packaging of synthetic cargo

In the macroworld of efficient packing the crate always has to be just slightly bigger
then the cargo it is supposed to secure. It is exclusively the size of the cargo that determines
the size of the crate. In the nanoworld of simple plant viruses such as CCMV,
this ceases to be the case, when CCMV capsid proteins assemble around a charged nanoparticle core.
We show that for encapsidation of charged nanospheres by virus proteins it is
the size of the nanosphere as well as its charge that determines the size of the spontaneously
assembled capsid around the core. Depending on the surface charge of the nanosphere one can
detect capsids with a radius larger then would be dictated by pure geometry. The reason for this
"inefficient" packing of the synthetic cargo is a competition between electrostatic interactions,
inextensibility of the N-tail "hair" of capsid proteins facing the oppositely charged core, as well as
their steric confinement in the space between the core and the inner surface of the assembled capsid.
An important consequence of this discovery is that in an experiment one can expect to observe
a polydisperse distribution of capsid sizes even if the encapsulated cores all have the same size.


***

LP11773A

Programmed superconductors can trap cold atoms

Magnetic traps are one of todays major technique to obtain samples of ultra-cold atoms and are a key ingredient for realizing quantum degenerate gases. This paper presents our recent experiments, which use superconducting micro-strips to set up the high-gradient field for trapping ultracold atoms. Our micro-trap differs radically from others because no electric current is sent through the narrow superconductor to create the magnetic field. (Other micro-traps use thin wires—either superconducting or conventional—as electromagnets, generating magnetic field when transport current flows through them.) We instead prepare the micro-wire as a trap by “programming” it with a strong pulsed field that magnetizes it in a controlled manner. When the programming pulse sequence ends, the microstrip retains a stable magnetization pattern that provides the high-gradient field. This enables a number of different field geometries, including one that requires no connection to external power supplies to operate the atom trap. This electrical isolation from the outside world, combined with the electrical properties of the superconductor, may foster an exceptionally quiet and stable environment for precise measurements on ultracold atoms.

LK11976

Fluid flows hibernate to save energy

At low speed, flow in a pipe or over an aircraft is smooth and steady. At higher speeds, flow becomes turbulent ‑‑ the smooth motion gives way to fluctuating eddies that sap the fluid's energy and make it more difficult to pump the fluid through the tube or to propel the aircraft through the air. For flowing liquids, adding a small amount of very large polymer molecules can dramatically affect the turbulent eddies, reducing their deleterious effects on energy efficiency. This phenomenon is used, for example, in the Alaska pipeline, but it is not well‑understood, and no comparable technology exists to reduce turbulent energy consumption in flows of gases, in which polymers cannot be dissolved. In our paper, we demonstrate that many of the features of turbulent flow in polymer solutions can also arise in turbulent flow of simple fluids, including gases, potentially leading to new approaches to improved energy efficiency in a wide range of flow processes. The discovery hinges on the identification of two kinds of turbulence, "active" turbulence, which dominates flows without additives and leads to substantial energy consumption, and "hibernating" turbulence, which drains much less energy from the fluid. Hibernating turbulence is prevalent at high levels of additives, but still occurs occasionally in their absence, and future research will focus on strategies other than polymer addition to coax turbulent flows into the hibernation state.

LQ12348

Enhancement of the thermal conductivity of nanotube‑based materials


In this paper, we report the results of analytical and computational
investigation of the heat transfer in carbon nanotube (CNT) ‑ based
materials, such as CNT mats, films, and "buckypaper". The use of a novel
mesoscopic dynamic model allows us to reproduce, for the first time, a
self‑organization of individual CNTs into an interconnected network of
bundles, typical for CNT materials. We find that the values of the thermal
conductivity in the networks of bundles significantly, by almost an order
of magnitude, exceed the values predicted for the random arrangements of
individual nanotubes. This increase is explained by an efficient heat
transfer along the bundles, with each bundle serving as a "highway" for the
thermal transport in the continuous network of bundles. The strong
structural dependence of the thermal transport properties of the CNT
networks explains the large variability of the experimental data reported
for CNT films and mats and points to the feasibility of targeted design of
CNT‑based materials for controlling and directing the heat flow at nano‑
and micro‑scale.



***

BPJ1107

Amplifying quantum signal using classical physics

We report a demonstration of significant sensitivity enhancement for a superfluid interferometer by allowing the matter waves to interact with classical resonant features of the experimental apparatus.
When constant pressure and/or temperature differentials are applied across nanoscale apertures separating two reservoirs of superfluid, the fluid within the apertures counterintuitively exhibits oscillation. If we place two such arrays in a torus filled with superfluid, the signal becomes the sum of two oscillations (from two arrays) with an overall amplitude dictated by the phase difference between the two "matter waves." This forms the core of a superfluid-based matter wave interferometer.
In an experiment reported here, we show that we can amplify the interference signal (governed by pure quantum mechanics) by classical means. We adjust the frequency of quantum oscillations to match the classical resonance of the apparatus and harness significant amplification. The capability to employ this type of technique that bridges quantum and classical physics is remarkable and it is rooted in the fact that with ~10^(23) atoms involved in superfluidity, quantum mechanics results in fluid flow that is macroscopic.

With a thirty-fold sensitivity enhancement achieved here, the reported technique makes superfluid-based interferometers great candidates for applications such as geodesy, seismology, inertial navigation etc. as well as a unique tool for fundamental physics.

LQ12029

WHY KICKED BLACK HOLES SOMETIMES KICK‑BACK

The merger of two black holes leads in general to a third black hole with
a recoil velocity, ie a "kick". The generation of a large kick has a
direct impact in astrophysics: Depending on its size, in fact, it
determines the number of galaxies containing supermassive black holes at
their centres. The generation of this kick can be understood in terms of
an unbalanced emission of gravitational radiation. Sometimes, however,
the merged black hole shows a deceleration, ie the "anti‑kick", before
reaching a final constant velocity. No straightforward conceptual
explanation was found for this deceleration. This paper provides such an
explanation and a simple interpretation of the physics of this process.
In essence, the anti‑kick is due to the radiation from a deformed black
hole where the anisotropic curvature distribution on the horizon
determines the direction and intensity of the kick. This work is
important because it gives a simple and intuitive explanation to a
process whose mathematical details are horribly complex. Also, it
suggests a methodology to probe the physics around a black hole by
monitoring the geometry near its horizon. This approach may help
understanding some fundamental aspects of black‑hole physics.


***

LM12274ER


Fluctuation-induced Casimir-like forces between membrane inclusions fluctuate

Two uncharged metallic plates placed in vacuum attract each other.
This attractive force, named after its discoverer Casimir, originates
from the boundary conditions imposed by the plates on the fluctuations
of the electromagnetic field. Similar fluctuation-induced forces exist
in many other contexts.
Inclusions in a cell membrane, for instance proteins, impose
constraints on the thermal fluctuations of the membrane. This gives
rise to a long-range force between these inclusions, which is
analogous to the Casimir force. Although this fluctuation-induced
force is by essence inseparable from its fluctuations, only its
average value is well-known.
In this paper, we study the fluctuations of the Casimir-like force
acting between two membrane inclusions. We show that this force
fluctuates strongly: in fact, it is dominated by its fluctuations.
Furthermore, we find that these fluctuations depend on the distance
between the two inclusions. This distance dependence shares a common
physical origin with the Casimir force itself.



***

LN11801

Enhancing proton migration with laser light.

In this paper we show that resonant infrared laser light increases the proton hop rate in oxides by nine orders of magnitude. This giant enhancement is significant because proton conduction is the underlying process behind important technologies such as fuel cells and hydrogen production by electrolysis. The mechanism behind this photo-enhanced effect is vibrational excitation of proton-oxygen (O-H) bonds in the oxide material. When a photon's wavelength is resonant with the stretching motion of the O-H bond, the photon is absorbed and adds energy to the proton. This excitation effectively helps the proton become mobile and contribute to bulk diffusion or conduction. Ultimately this work provides new fundamental insight into the microscopic dynamics of hydrogen in solids.

***

LK12367

Amplification of photon pairs in semiconductors

Two-photon gain is a unique process predicted by quantum mechanics, in which photons are duplicated in pairs, causing light to be amplified with nonlinear intensity dependence. We directly observed the phenomenon of two-photon gain in a semiconductor miniature device, designed to enable direct conversion of electrical current into photon-pair amplificaiton. The nonlinear intensity-dependence enables giant pulse generation in a chain-reaction like process. Since gain is the fundamental ingredient for lasing, it may now be possible to realize two-photon lasers with exceptional classical and quantum charcteristics. Previously, two-photon gain was realized in dilute atomic systems in a maser-like configuration with low powers and optical pumping. Achieving two-photon gain in solids, in particular semiconductors, has several benefits, similar to those which stimulated the evolution of the maser to a diode laser: orders of magnitude higher emitter densities, micro-fabrication technology, and electrical pumping. The observation of semiconductor two-photon gain paves the way for the realization of efficient and miniature devices significant for bio-imaging, spectroscopy, quantum-information and fundamental light-matter interaction studies.


***

LN12122


Wireless goes to the nanoscale!

Wireless gadgets such as cell phones and Bluetooth are all around us,
and ensure flexible and long‑range connectivity. More difficult has been
to fully translate these concepts to the visible: can we have a wireless
link with light at the nanoscale? In their upcoming paper in Phys. Rev.
Lett, researchers from the University of Pennsylvania and the University
of Texas at Austin have theoretically proposed and modeled a wireless
link between optical nanoantennas. By suitably loading and matching
silver‑nanowire antenna pairs with optical nanocircuits, they have
numerically demonstrated an optical wireless connection between
nanoscale emitters and receivers, which may have several advantages,
such as reduced absorption loss, over regular plasmonic waveguide links.
This approach may one day compete with current optical interconnects in
chip‑scale data processors and computational systems.


***

LM12327


Testing quantumness

Statistical uncertainties occur in any physical measurement
and the question whether or not a discovery is significant is
of central importance in fields like astrophysics or particle
physics. In quantum physics, many experiments nowadays aim at
the generation of multiparticle entanglement, which is considered
to be a central resource for quantum information processing.

In this paper, we investigate theoretically and experimentally
the significance of entanglement detection. Theoretically, we
point out which kind of measurements one has to perform in
order to detect the quantum correlations in a physical system
unambiguously with a small statistical uncertainty. Experimentally,
we observe the predicted phenomenon in a four‑photon experiment.

Our results provide novel theoretical ways to detect entanglement
with high statistical significance, allowing for unambiguous
statements on quantum correlations. This is important for future
experiments, since the event numbers decrease with increasing
the numbers of particles, so the statistical uncertainties
become more relevant.

LM12564

Water molecules queue into nanotubes

Researchers have, for the first time, demonstrated that
water can enter ultrathin carbon nanotubes ‑ tubes with a wall consisting of a
single layer of carbon atoms and a diameter down to half of a billionth of a
meter (0.548 nanometer) ‑ thin enough to prevent water molecules from passing
each other inside the tube. This first experimental proof of such single‑file
transport of water occurring in nanotubes holds promise for the design of
ultraselective filter membranes and, eventually, nanofluidic devices where
water or other fluids would be transported and manipulated at the molecular
scale in a "first‑in‑first‑out" manner.

While intuitively unexpected because of the highly water‑repellent carbon
surface of the tubes, transport of water through carbon nanotubes has been the
subject of many theoretical studies. In the present work, the researchers
caused nanotubes of specific diameters and structures to vibrate, using a wide
range of lasers of different wavelengths (colors). They could distinguish
water‑filled and empty nanotubes, as these vibrate at different frequencies ‑
in much the same way as a water‑filled glass resonates at a higher pitch than
an empty glass.

The team found water‑filling in extremely thin tubes ‑ thinner than generally
predicted by theory ‑ and the results even indicate that the water molecules
are forced to adopt specific orientations and arrangements depending on the
exact nanotube structure.


***

EL10710

Solving the mystery of raindrop formation

We have experimentally discovered a new physical mechanism for the formation of local small-scale concentrations of inertial particles (e.g. droplets) suspended in turbulent nonisorthermal flow. The mechanism of rain formation is not yet sufficiently understood and remains an outstanding problem in atmospheric physics. Calculations based on the assumption of uniform spatial distribution of droplets yield unrealistically long times for rain formation. One of the most important mechanisms of rain formation is associated with appearance of small-scale clusters of droplets ("inch" clouds) due to cloud turbulence. All previous studies of inertial particle clustering were performed for isothermal turbulence, while temperature distribution in clouds is inhomogeneous. The new effect of small-scale clustering in the presence of non-uniform mean temperature distribution is much stronger than inertial clustering in isothermal turbulence and leads to formation of small-scale concentrations even of very fine droplets. This effect elucidates the mechanism of rain formation in turbulent clouds and can be also significant in various industrial multi-phase turbulent flows (e.g. internal combustion engines).

BG11574

Arranging atoms in a nanowire to halt heat flow

The lowering of the thermal conductivity, which describes the ease of heat flow in a substance, is of interest for many practical applications such as thermoelectric energy conversion. It has been known since the 90's, from the works of Dresselhaus and Hicks, that lower‑dimensional structures such as nanowires have drastically lower thermal conductivities compared to bulk materials. Before that, the mixing of different types of atoms in a material had been used to lower the thermal conductivity. But what about a combination of nanostructuring and atomic arrangements? Through computational techniques of molecular dynamics, cluster expansion and genetic algorithm optimization, researchers have tackled the problem of finding optimal arrangements for atoms in a nanowire to obtain the lowest possible thermal conductivity. They investigated silicon‑germanium nanowires which are promising for thermoelectric applications. They used molecular dynamics simulations which model the dissipation of random heat currents in equilibrium, in turn giving the resistance of the nanowires to heat flow. Using insights from previous experimental and computational work, they reduced the thermal conductivities of the nanowires by roughening the nanowire surfaces in the simulation. Then the astronomical combinatorial problem of arranging two types of atoms in the nanowires is reduced to a tractable problem by the cluster expansion technique. The best arrangements of silicon and germanium atoms in the nanowire are obtained using the cluster expansion from a "survival of the fittest" genetic algorithm optimization. The resulting nanowire structure, showing complete planes of Ge, is predicted to have a thermal conductivity more than 100 times lower than bulk silicon.


***

AN10495

Counting Photon Holes

This paper introduces a new device that is capable of detecting whether a photon has been removed from a certain place in a weak laser beam,while affecting neither the laser beam, nor the photon hole. It has been found that such photon holes can show nonclassical characteristics, such as entanglement, making them an alternative to photons in future quantum computers.

Thus far, photon hole signals have been detected by photon detectors, which absorb the background photons, demolishing the signal. The proposed method is based on a phenomenon which renders a dense medium, in this case a cell filled with rubidium atoms, completely transparent to a probe pulse, only if the signal contains no photon hole. As soon as a photon hole enters the cell, the probe pulse stops propagating, a phenomenon known as light stopping. This results in a delay of the probe pulse which can be detected. Still, the signal beam exits the cell without any significant distortion. The measured photon hole signal can then be reused for other purposes. Such "nondemolition measurements" play a key role in the implementation of future quantum computing circuits.

LL12274

A beam with an unusual stability

We report on the observation of a wave beam that does not follow the
usual laws of optics. In contrast to nearly all other wave beams, this
beam does not spread its width while propagating through a solid.
Neither reflectors nor lenses are needed to create this beam, as it
forms spontaneously when the wave is emitted by a small antenna. This
effect is not determined by the beam intensity and happens because the
wave properties depend on the propagation direction in a specific way.
In our experiments these conditions have been fashioned for spin waves,
elementary excitations of a magnetic material. We have experimentally
shown that a spin-wave beam of a width of about 0.7 mm does not broaden
itself, and remains stable over propagation distances of more than 10
mm, which is the size of the studied sample. An accompanying theoretical
prediction suggests this will hold for propagation distances more than
100-fold larger (1 m)! Due to the directivity of wave properties, these
beams do not bounce off a mirror the way light does. Instead, reflection
is governed by the application of an external magnetic field, which is
also used to steer the beam within the material.

***

LK12585

Lucky Accident Could Slash Costs of Future Fusion Power Plants

Prospects for low-cost, clean energy through nuclear fusion just got brighter, thanks to a lucky accident at Sandia National Laboratories in Albuquerque, New Mexico. For almost 40 years, research teams around the world have been pursuing energy production by tiny nuclear explosions lasting only billionths of a second within a reactor. This approach, called inertial confinement fusion or ICF, requires that tremendous power be concentrated almost instantaneously onto tiny hydrogen pellets.

Researchers had been attempting to boost the power that could be delivered to such fusion targets by fastening small cartridges to Sandia’s Saturn pulsed power generator. The cartridges worked better than hoped, doubling the generator’s current. But the researchers nearly overlooked the results, because the dramatic boost in electrical power occurred unexpectedly, only long after the Saturn generator pulse had ended. In a paper appearing in Physical Review Letters, the team theorizes that material heated off the cartridge walls blocked the current pulse, allowing electrical energy to accumulate inside the cartridge before releasing the energy suddenly into the target volume. Such a means of producing high-power pulses from low-power generators could result in savings of hundreds of millions of dollars per facility in future ICF power plants.

LK12445

Physics of Folding Two-Dimensional Lattices

Research, reported in a recently accepted Physical Review Letter,
shows a new pathway to form nanotub- like carbon nanostructures at the
edge of folded graphene. Unlike carbon nanotbes, which can be formed
with any chirality, the folded graphene predominantly are either
armchair or zigzag. To explain, the authors of the paper carried a
combined experimental and theoretical study of the physics of graphene
folding. Materials with two-dimensional (2-D) lattices, such as
graphene or single sheet of Boron nitride, can be folded under
mechanical forces in any directions. Once a 2-D lattice folds, it
creates a nanotube-like edge from the balance of the elastic stiffness
and adhesion of the lattice. However, the structure of the edge and
its stability strongly depend on the strength of adhesion between the
overlapping region, which leads to the interesting physics of folding
2-D lattices. In the work reported, the free folding of graphene was
achieved by random forces generated by ultrasound. Electron
diffraction of ~100 folded graphene offers conclusive evidence that
graphene prefers to fold either parallel or at 30 ° to the
carbon-carbon bond direction, forming the so-called armchair and
zigzag edges. Atomistic simulations show that these two folding
directions correspond to two energy minima induced by a partial or
full AB stacking of the graphene lattice. The results show that a much
better control over the atomistic structure can be obtained using the
symmetry dependence of 2-D lattice adhesion.

Caption of the figure attached: Among the 100 folded graphene we
investigated, statistically ~1/3 have armchair and ~1/3 have zigzag
folded edges. This preference was explained by the stacking of
graphene lattice from atomistic simulations.


***

LN11661

Wave-vector dependence of magnetic-turbulence spectra in the solar wind

Three-dimensional spatial structure of turbulence was determined
for the first time in space. Astrophysicists believe that turbulence
is a widespread phenomenon in the extraterrestrial world such as
stellar winds and the interstellar medium. Turbulence furthermore plays
an essential role in accretion disks and cosmic ray transport, too.
In astrophysics, gases are mostly in an ionized state, called the plasma, and
its turbulence properties are different from that of ordinary gas dynamics.
In particular, plasmas are electrically conducting and make the
ambient magnetic field fluctuate once plasmas are set into turbulent motion.
Scientists have been studying turbulence properties in situ in the
interplanetary space since 1960s, but with single spacecraft it
was not possible to distinguish between temporal oscillations and
spatial structures in the measurements.
In this paper, we use four-spacecraft measurements of the Cluster mission
and determine the three-dimensional spatial structure of turbulent
fluctuations of the interplanetary magnetic field.
We discover that turbulence develops in the plane
perpendicular to the ambient magnetic field, exhibiting
the geometry of displaced field lines without being bent.
This field line structure may be one of the fundamental properties
of astrophysical turbulence and the key of cosmic ray transport.

[Figure]
Magnetic energy distribution in the three-dimensional
wave vector domain. The energy distribution extends primarily in the direction
perpendicular to the mean magnetic field direction (denoted as B0).

***

LK12458A

Straight to the point – ultra-secure communications for specified locations

Researchers have developed a quantum communication process able to deliver unprecedented levels of security for high-sensitivity communications.

The development shows that quantum communications, which already allow unbreakable encryption, can provide an additional level of security through “unconditional location verification”.

This would ensure that, even if a secret code has fallen into the wrong hands, a secure message could only be seen by a recipient at an agreed geographic point.

With this process you can send data to a person who is at a particular location. If they are not at that location the process would detect that, and you can stop the communication.

The concept, which has potential applications in e-commerce, digital rights distribution and defence, is reported in the May edition of the American Physical Society journal Physical Review A.

It means any message or data can be received only at a particular receiver – a laptop, handset or desktop computer – at an agreed location.

The system works by sending paired qubits – particles, such as photons, which have been manipulated to contain specific quantum information – over a fibre optic or wireless network to a recipient. The recipient must send a return message, using information from the decoded qubits, to a number of reference points to open up a secure communications channel. Because quantum networks operate at the speed of light, and quantum information cannot be copied, the time to return the message can be accurately constrained, ensuring that the message has come from only one possible place.

Due to the nature of quantum mechanics, any effort to intercept the communication at a different location would be immediately detectable and, because the system is based on the laws of physics rather than computational resources, it is impossible to attack.

This is basically a new application that can be deployed on current and emerging quantum networks.

It opens up a range of new information security applications for both fibre and wireless communication networks. There are many industries and organisations – banks for example – that would be interested in delivering information content in the sure knowledge a recipient is at an agreed-upon location.

***

LK12472


Tunable Table Top Soft-X Rays for Biology and Medicine

Coherent bright soft x-ray sources are sought for the visualization
and manipulation of nanostructures and biomolecules with many
potential applications in biology and medicine. Current synchrotrons
and free-electron laser sources are large scale facilities with
limited access and therefore small table top sources available in
regular laboratories and hospitals are in high demand. High harmonic
sources are a table top alternative but currently lack in photon
yield. We report on a feasibility study to produce bright coherent
soft x-ray radiation by using DC electric fields in a tabletop high
harmonic generation device. The mechanism presented allows full
tunability in the short wavelength range of the electromagnetic
spectrum, from extreme-ultraviolet to soft-x-ray radiation thus
represents an important advance in overcoming a critical challenge in
high order harmonic generation and coherent x-ray science.

LN11818

Exploiting time for super-lensing

Imaging and focusing are subject to the diffraction barrier which limits
the resolution of images or equivalently the size of focal spots to at
best half a wavelength. In the past few years, the quest for a perfect
lens, which would break this barrier has attracted an enormous interest.
Various monochromatic approaches have been proposed, mainly based on
negative index materials. In this work we introduce a broadband lens, the
“resonant metalens”, whose resolution is no more limited by diffraction.
Its broadband mechanism permits it to capture the spatial profile of an
object, even very small compared to the wavelength, and code it into a
temporal signature. Then, owing to the resonant nature of the lens, this
signature is efficiently sent in the far-field of the object for imaging
beyond the diffraction limit. Our work demonstrates a forty fold
improvement over the smallest details that can be imaged using radio-waves
and antennas. This concept has many potential applications in medical
imaging or therapy, wireless communications or sensing. Furthermore, the
generality of the approach suggests that resonant metalenses can be
designed throughout the electromagnetic spectrum up to the visible,
opening up new avenues for diffraction free imaging and focusing systems.

***

BNR1108


Structure giving the highest Tc in the elements

Successive structural transitions consisting of face-centered cubic (Ca-I) - body-centered cubic (Ca-II) - simple cubic (Ca-III) - P41212 (Ca-IV) - Cmca (Ca-V) have been reported in compressed calcium. The superconducting transition temperature Tc of calcium is only 2 K at 44 GPa, however, the Tc increases by pressure and reaches 25 K at 161 GPa, which is the highest record among all the elements. The relation between the high-Tc and the crystal structure has been of high interest. We performed x-ray diffraction measurements of calcium at pressure up to 172 GPa at room temperature and discovered another higher pressure phase "Ca-VI" above 158 GPa. The structure was determined to be an orthorhombic Pnma by a Rietveld analysis and confirmed the structure with a density-functional theory calculation. We claim that Ca-VI gives the highest Tc of 25 K.

***

LK12505

Bands in Particle Tumblers Finally Explained

Over 70 years ago, an obscure Japanese researcher discovered that the harder one tries to mix granular particles of two different sizes in a long rotating tumbler, the more they unmix by forming bands of small and large particles. The explanation for this counter-intuitive phenomenon has eluded researchers for all this time. In this paper, we obtained detailed information on what all particles do at all times by applying Newton’s Second Law simultaneously to many thousands of particles in a computer simulation of the flow. Miniscule flows related to friction at the tumbler walls occur parallel to the axis of the tumbler. These flows cause larger particles near the surface to be carried to a different axial position than smaller particles that end up deeper in the flowing layer because they fall into spaces between large particles. This results in a band of large particles near each end of the tumbler, and these bands lead to more bands. Many practical situations for processing pharmaceuticals, minerals, grains, and polymers run into this effect. One may want to eliminate this effect or exploit it. Unmixing is problematic when mixing is desired but could be useful for separating particles in other applications.

BJ11313

SPINTRONICS WITH ANTIFERROMAGNETS

Nanoscale magnetic devices whose state is controlled by a
spin-polarized current now being extensively explored both for probing
the fundamental physics of magnetic dynamics, and for applications in
storage technology. Key elements of the spintronic devices, that
enable information coding, control and manipulation by an electric
current, are two ferromagnetic layers. However, recent experiments
clearly demonstrate that the spin-polarized current may also
influence the state of another, generally accessory, element of a
nanodevice – an antiferromagnet, that shows no bare macroscopic
magnetization but still has a magnetic structure. In the present paper
we report on a nontrivial magnetic dynamics of thin antiferromagnetic
layer subjected to a spin torque from the electric current.
Comparatively high sensitivity of antiferromagnetic layer to a
spin-polarized current allows improvement of the switching process in
the whole device and opens the way to increase the speed of
reading/writing. In the presence of steady current an
antiferromagnetic layer successfully "works" as a high-frequency
oscillator and thus can be considered as a promising candidate for the
magnetic bit with no magnetic moment.

Chilling Complexity: Laser Cooling of Dysprosium

In an upcoming publication in Physical Review A, researchers report on an experiment in which a single laser is used to cool atoms of dysprosium, a rare-earth element with a notoriously complex spectrum. The goal is to produce a well collimated atomic beam to be used in an a search for time variation of fundamental constants. Earlier, the group demonstrated the first successful laser 'pushing' of a dysprosium beam, but in this publication they show actual laser cooling of all stable isotopes of the element. Laser cooling allows one to bring atoms to temperatures well below those achieved with conventional cooling methods. Dysprosium has long been thought prohibitively difficult to cool with lasers due to its complex structure, a problem shared by molecules, but progress is being made. Researchers have now reported on the laser 'pushing' of a beam of molecules, and others have demonstrated that dysprosium can also be captured in a magneto-optical trap.

***

LL12024B

Shaking quantum vortices

We have introduced a local imaging technique with high resolution which
allows us to directly visualize the oscillatory motion of individual
flux quantum units subjected to an ac magnetic field modulation.
Usually, the efficiency of pinning sites in superconductors is
determined using the well established ac-susceptibility technique.
However, one of the drawbacks of this method is that the recorded signal
is averaged over millions of pinning sites. In this report, we combine
scanning Hall probe microscopy and local ac-susceptibility measurements
to directly visualize the pinning-depinning transition when increasing
the ac-modulation amplitude and to accurately determine the temperature
at which each individual vortex freezes in a field-cooling experiment. This technique is very promising and powerful to
investigate on the microscopic scale, e.g., the penetration length of ac
fields or the motion on magnetic domain walls in ferromagnets.

Figure caption:
(a) Scanning Hall probe microscopy image of a 9 µm wide stripe with two
vortices obtained at 4.2 K and H = 1.3 G. (b), (c), and (d) scanning
ac-susceptibility microscopy images showing the subsequent freezing of
the vortex motion when lowering the temperature.


***

LM11939

Discovery of physical mechanism governing motion of DNA in living
bacteria

Many elegant physical models have been developed for non-living
systems that share some of the essential features of living matter.
Classical polymer physics was developed to describe the behavior of
the polymer molecules that comprise materials such as milk bottles and
plastic wrap. We have extended classical polymer theory to describe
the motion of DNA inside living cells. Despite the complexity of the
live cellular environment, we find that simple modifications of the
classical theory are sufficient to describe the motion of living
bacterial chromosomes surprisingly well. Specifically, we have found
that individual genetic loci on bacterial chromosomes move as a random
walk with memory of previous steps, even when DNA replication is not
proceeding. The motion of the DNA segments can be fully explained
with the concept that the densely crowded macromolecular soup within a
living cell has viscoelastic properties. Viscoelastic materials have
characteristics of both fluids, like water, and elastic materials,
like rubber bands. This finding has profound consequences on
molecular transport in vivo, affecting processes such as gene
expression and cellular organization.

***

EM10571

Less waste, more speed for your laptop

A quantum leap in recycling the waste heat from your laptop is now within sight! A recent finding to be published in Phys Rev E suggests that energy-saving nano-scale thermal computers can simply be constructed from single carbon nanotubes. This would pave the way for recycling the waste heat from your laptop as well as speeding it up at the same time! Researchers found that under certain conditions the thermal conduction behaviour of a one-dimensional homogeneous solid mimics the electrical conduction behaviour of the tunnel diode, an important invention by Leo Easki that won him the 1973 Nobel Prize in Physics. How far are we from being able to incorporate such energy-saving ¨thermotronics〃 into the electronics of your laptop? This new research will provide a hint.

LM12275

Geometry and light: A strong team works together

A particle, confined to a surface, retains some knowledge of the surrounding higher-dimensional space in which the surface is embedded. As predicted by quantum mechanics, due to the wave nature of the particle it slightly penetrates into the higher dimension and “feels” its presence via an effective geometric potential.

This phenomenon was now experimentally demonstrated for the first time in an optical setting. The particle is simulated by an optical wave packet, squeezed on an undulated wave guiding layer. Although the inner curvature (i.e. the curvature which can measured directly on the surface) of this layer vanishes, the wave packet experiences a geometric potential caused by the layer’s external curvature (i.e. the curvature, which can be measured only from the surrounding medium). As a result, the constrained wave behaves like if the medium were periodic (similar to a crystal), although the guiding layer is only curved and in all other respects fully homogeneous. Hence, the results constitute the first demonstration of a purely topological crystal, which relies solely on the geometry of space.

LL11967

Controlling light in a network

Networks are now a part of everyone’s daily life: social networks, transportation networks, the electricity grid and high speed data networks. Now networks also are a key element embedded inside a new type of artificial photonic material called a resonant guided wave network. The first ever resonant guided wave network, which is being reported in the April 2010 issue of Physical Review Letters, consists of dense interconnected arrays of subwavelength plasmonic waveguides. The network generates optical dispersion via phase-coherent splitting and recombination at waveguide junctions. By manipulating the phase relationships between guided waves in the network, it is possible to generate dispersive slow waves and photonic bandgaps, giving photonic materials researchers a new platform on which to manipulate light.

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LG12676

Reversing the Brazil Nut Effect

By vibrating bi-mixtures, the large particles usually rise to the top of bed, a phenomenon of "Brazil Nut" separation, while the reverse separation occurs in gas-fluidized bed. Researchers who introduced a gas flow into a vibrating bed from its perforated bottom and studied the separation during the transition process from "BN" separation to its reverse have found new, interesting phenomena which cannot be explained by present known mechanisms. They tried using a new model to clarify the mechanisms of size separation, especially the effects of gas flow.

LH12355

Of Ghostly Holograms

Traditionally, an image is formed when photons carry information from an object to a detection plane. However, the strong position correlations found in entangled photons allow one to construct an image by querying an object with one photon, while measuring the position of its entangled partner. As more and more photons pairs are used, a "ghost image" is formed. In a recent experiment researchers carried out a ghost imaging experiment in which only a few photons were needed in order to identify an object. The experiment employed a new method in which a hologram is used to sort single photons based on what image they are carrying. In this case, the hologram was used to sort single photons carrying "ghost image" information, i.e., photons that had not directly interacted with the object being queried. Such a technique overcomes the limitations of using slow optical detectors such as CCDs and could be very useful when querying a small set of objects using only a very small number of photons.

***

LP11872

Guiding current pathway through Ag–SnPc–Ag junctions

Single atoms and molecules on surfaces are being explored for their
potential of leading to small electronic devices. One challenge in this
field is to understand how an electrical current flows through a single
atom or molecule. Over the last 2 decades, tremendous effort has been made
to investigate this issue. In the present Letter, we use single molecule
chemistry to demonstrate that the current in a molecular junction, which
is comprised of atomically controlled Ag electrodes and a single
Sn-Phthalocyanine molecule, can be directionally guided along particular
pathways by selectively modifying the bonds between the molecule and an
electrode.

SnPc molecules adsorbed on Ag(111) were contacted with the tip of a
cryogenic scanning tunneling microscope. By systematically manipulating
the chemical bonding between SnPc and Ag(111) through selective cutting
hydrogen atoms from SnPc together with an single atom manipulation
technique, the conductance of single molecule junctions was controllably
varied from 1 to 25 micro-Siemens. Ab initio calculations using density
functional methods and non-equilibrium Green’s function techniques enable
a quantitative analysis of electron transport through Ag-SnPc-Ag junctions
and a visualization of the guided current flow.

LL11813

Watching DNA nanotechnology in action

A ground-breaking model developed by researchers at the University of Oxford allows scientists to observe, for the first time, how DNA nanostructures self-assemble. DNA, the molecule that contains our genetic code, is increasingly used by physicists and chemists to build an amazing array of precise structures and devices on the nanometre length scale. However, how DNA nanostructures so reliably self-assemble has remained a mystery until now, and the design of complex nanodevices, such as DNA walkers, proceeds by educated guesswork about the details of the structural changes involved in their operation. Through the use of a simplified representation of each DNA base that captures the essential physics of their interaction, the Oxford group's model allows DNA nanostructures to be simulated reliably on a computer. This breakthrough has opened up the field of DNA nanotechnology to rational computational design strategies based on the direct visualization of DNA nanodevices in action.

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LK11816BR

Two kinds of electrons in novel iron based superconductors

Admittedly, life as a free spirited electron in a complex
quantum system is not an easy matter. There are so many
different paths you can follow, so many bewildering
choices. Iron atoms, with their five accessible orbitals,
do not make your decisions any easier. Then you have
others of your own kind that you need to cope with.
Because of your very negative (charge) nature, you try to
avoid one another in a very antisocial way (Coulomb
repulsion). However, by thinking collectively and
benefiting from your environment (lattice, orbitals,
spins), interesting options can arise. For example, under
the right conditions, you can create a superconducting
state that enables you to propagate with others
effortlessly.


On the other hand, you have to admit that the life of a
physicist, who is trying to describe and understand your
quirky decisions, is not so simple either. Surprisingly,
from time to time we manage. In the case of the novel
iron-based superconductors, when we shone the light we
identified two groups of charge carriers by measuring the
optical conductivity. We can see that one group is
incoherent and basically independent of temperature. The
other group, which is responsible for the interesting
physical properties of these materials, is the one that
attracts our attention. We observe that by collective
efforts you can form either a spin-density wave or a
superconducting state. Interestingly, before you become
cooperatively superconducting, we detect a type of selfish
behavior that we haven’t seen too much before. There we
see that you do not care too much about one another and we
can be describe you (by a Drude term) as noninteracitng
quasi-particles (Fermi liquids) exhibiting a T2
temperature dependence of the scattering rate.

BN11234

That's amoir

Moir patterns are often unwanted artifacts in digital imaging. The commensurate/incommensurate beating of two spatially-periodic patterns (e.g., pixels in the image and pixels on a display) creates an extra superlattice that detracts from the image quality. In multilayer graphene, moir patterns signal the presence of rotational stacking faults between graphene layers; a desired product produced when multilayer graphene is grown on the carbon face of silicon carbide. Researchers at the Georgia Institute of Technology and the National Institute of Standards and Technology, show that the analysis of the resulting atomic moir patterns in epitaxial graphene can be used to determine not only the rotation angles between layers, but the strain in the layers.


When grown on the carbon-terminated (000 -1) surface of hexagonal silicon carbide, graphene layers grow in a non-graphitic form where each layer is rotated with respect to the previous one. Remarkably, as shown in a number of experiments [2-4], this configuration typically results in an electronic structure indistinguishable from single-layer graphenewith apparently little influence of the substrate. In this paper, we analyze in detail scanning tunneling micrographs of this unique material, and show that moir patterns due to as many as 4 layers are visible in the imaging. Using Fourier methods to investigate the relative periods and phases of these patterns, the authors extracted the small relative strain between layers. The methods are analogous to those employed for strain measurement via optical moir interferometry, but the periodic pattern is the atomic lattice of graphene itself. Strains less than 0.37% were detected, and strain variations could be resolved over a size scale comparable to the moir superlattice cell. The method should prove to be useful for studies of the influence of strain on the electronic and transport properties of graphene.


***

LK12221E

Sucking Genes

Flexible polymers, such as long DNA, RNA molecules and proteins, can pass through a narrow pore whose size is
comparable to their molecular thickness. We highlight the richness and complexity involved in the dynamics of this
unique mode of molecular transport, called "translocation", actively driven by external forces. We show that a key
to understanding this important process lies in the response property of a chain-like flexible object to a pulling
(sucking) force, i.e., it cannot respond all at once, a fact familiar to anyone who has pulled a flexible rope in
daily life. The underlying physical picture is now starting to be unveiled, and we believe its essential character
will prove interesting to a general audience. The proposed molecular picture provides a first ever generic theory
consistent with various experimental reports, hence should be indispensible for the design of new experiments
towards an ultimate goal: a rapid, innovative method of biopolymer sequencing as well as the deeper insight into
the cellular transport of biopolymers.

LL12337

Diversity of a peptide phase diagram

Proteins are chain molecules that have an intrinsic ability to form
structural motifs such as alpha-helices (right-handed coiled or spiral
conformations) and beta-sheets (fully extended stretches of amino
acids). This leads to a complex phase behavior in which proteins can
assemble into various types of aggregates including highly ordered
crystalline phases, dense liquid-like phases, and highly ordered
amyloid fibrils associated with devastating diseases such as
Alzheimer's disease. Although a phase diagram is a prerequisite to
understand fundamental aspects of formation of ordered structures of
proteins, the experimental and theoretical determination of such a
diagram is extremely challenging. Here we use a coarse-grained protein
model that enables us to perform kinetic Monte Carlo simulations for
determining the phase diagram of alpha-helical and beta-sheet forming
peptides. The simulations reveal the existence of various metastable
peptide phases. The dense liquid-like phases are metastable with
respect to the fibrillar phases, and there is a hierarchy of metastability.
The phase diagram provides a fundamental insight into the peptide
self-assembly, insight that may be used to design novel biomaterials or
to prevent the peptides from forming disease-related amyloid fibrils.

***

LJ11846E

Oscillating Drops



The oscillation of free drops has attracts much attention in various fields, such as fluid physics, aerography, astronomy, material science and chemical engineering, with focus on the underlying mechanism, practical applications as well as models to astral and nuclear physics. There have been extensive investigations about the axisymmetric oscillation of free drops; however, few attempts are made about the more difficult case of non-axisymmetric oscillation. Here we report the non-axisymmetric sectorial oscillations of acoustically levitated drops up to the 7th mode. These oscillations are found to be parametrically excited and could be controlled by modulating the sound field. The oscillation frequency increases with increasing mode number but decreases with equatorial radius for each mode. The data can be well described by a modified Rayleigh equation, without use of additional parameters. These results may bring in a new approach to the noncontact measurement of surface tension for liquids, as well as a method of imposing forced convection within acoustically levitated drops during containerless processing. Supplementary movies for the 2nd~7th mode sectorial oscillations are presented in EPAPS Document.


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LH12640

Structure determination of an epitaxial graphene layer on a metal surface

Graphene/metal systems are playing an increasingly important role in graphene research, mainly because the epitaxial growth of graphene on metal surfaces offers one promising route to a controlled synthesis of graphene monolayers. The contact with the metal affects the electronic structure of the graphene layer and its geometry, e.g., by causing a corrugation. The magnitude of the geometrical effects has not been experimentally determined before. The main reason is that the large unit cells of the typical moir‚ structures, resulting from the mismatch between the graphene and the metal lattice, make a structure determination very difficult. By an extensive Low Energy Electron Diffraction (LEED)-I(V) analysis the structure of the moir‚ superstructure of graphene on Ru(0001) has been determined. It is found that, in quantitative agreement with the DFT result, the graphene layer is strongly corrugated (1.5 angstroms), and that the distance to the metal is quite short at the corrugation minima (2.1 angstroms). The findings provide an explanation for the electronic structure changes in the graphene layer that have been observed before.

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AQ10464

Filaments of white light take curved paths

Propagation of powerful femtosecond light pulses in transparent solids
reveals surprising features on the nature of light and matter
interactions. One of its ultimate manifestations is self-focusing and
spontaneous break-up of intense elliptical laser beams into
self-organized periodic arrays of narrow white-light beams, termed light
filaments. In this paper, we demonstrate that although white-light
filaments emerge in apparently regular patterns, the individual
filaments propagate in curved trajectories (see Figure). The full
three-dimensional picture of a filament bundle, captured with high
spatial and temporal resolution, resembles optically turbulent
propagation in fused silica slab. Our observation unveils an exciting
physics of the nonlinear light and matter interactions, which facilitate
the beam break-up process and force the light to propagate along the
curved paths. These paths emerge as a result of the generation of new
optical fields, whose coherence is neither spatial nor temporal, but is
rather skewed in the unified space-time domain.

***

LM11965

Weak and empty... and yet, dominant

Gravity: the weakest of all the fundamental interactions, has always
been considered to play only a sub-dominant role when it comes to
quantum phenomena. (Even black holes, which are the arena where gravity
reigns almighty, are only able to induce particle creation, the Hawking
radiation, at a rate which, in spite of its conceptual importance, is
virtually unobservable in realistic astrophysical situations.) Vacuum:
the state whose rich structure unveiled by quantum physics is usually as
evasive as the ``emptiness'' of classical physics. Separately, each
is believed to play only very subtle roles when it comes to observable
consequences involving quantum processes. Together, however, they may
engender an explosive combination! We report on the discovery of a novel
effect according to which well-behaved gravitational fields play a
crucial role by exponentially amplifying the energy density of the
vacuum. This leads to a scenario where the vacuum eventually dominates,
through its own gravitational field, the evolution of the system. The
formation of compact objects (e.g., neutron stars) and large-scale
structures are promising contexts where this gravity-induced vacuum
dominance may be triggered, which would lead to unexpected implications
for astrophysics and cosmology.

***

LN11877

New data from recent thought experiment: Speed of light still constant

Albert Einstein is probably best known for his thought experiments leading
to the theory of Special Relativity, which then gave rise to
General Relativity, explaining gravity as the curvature of space-time.
Einstein's theory of gravity has so far withstood
all attempts to marry it with quantum theory. Recently it has
been claimed that photons from distant gamma ray bursts, measured
with the Fermi Space Telescope, could reveal modifications
of Special Relativity that are believed to arise from quantum effects of
gravity in a certain class of models. These modifications would show up
as an energy-dependence of the speed of light while still preserving the
relativity of restframes. It would mean that high energetic photons
were slower than low energetic ones.

A thought experiment however reveals that such modification of
Special Relativity would have more severe consequences than previously
realized. It would be incompatible with data confirming Special Relativity
on the one hand and extensively studied elementary particle interactions
on the other hand - data that has been available since more than three
decades. Using this data, it can be shown that to excellent accuracy the
speed of light must be constant.

This is the probably least expensive high precision test of fundamental
physics you'll ever get: a thought experiment combined with decades
old data. Sometimes a pen, a notebook, and a theoretical physicist is
enough.


***

LN11873

The retina is inverted – for a reason

Using optical analysis, it is possible for the first time to understand how the structure of the retina helps sharpen our view of the world. Our eyes are built like a digital camera, with a lens in front and a detector – the retina - at the back. At the far side of the retina lie the detecting photocells, strangely covered with transparent layers of neurons. The neurons serve as wiring that process and pass the detected image to the brain, but also distort the same image. It is not clear why this wiring is not behind the detector cells, and why this feature is common to so many animals. Then three years ago it was found that glial (Muller) cells, which intersect the retina across the neural layers, are able to transmit light. Now researchers at the Technion have constructed an optical model of the retina, and passed light through this volume. They found out that only light which came through the center of the pupil was captured in the glial cells and guided directly to the photocells. Light leaking from the neighboring cells or coming from the periphery, which would clutter our sight, was rejected and scattered away. This feat could not be achieved if the photocells came before the neural layers.

LM12455


NANOTUBE BLACK HOLE

Cold-atom and nanoscale science have each provided exciting new systems for study and applications. Here we report the first experimental realization of a combined cold atom-nanostructure system that represents a new paradigm at the interface of these two disciplines. Atoms are laser cooled to microkelvin temperatures and then launched towards a single, freely suspended carbon nanotube charged to hundreds of volts. The nanotube acts as a 'black hole': Atoms are attracted to the nanotube from distances more than a hundred times the tube diameter, and spiral towards the tube under dramatic acceleration with orbit times reaching just a few picoseconds. Close to the nanotube, an atom's valence electron tunnels into the tube converting the atom into an ion that is ejected at high energy and easily detected. The system demonstrates sensitive probing of atom, electron, and ion dynamics at the nanoscale, and opens the door to a new generation of cold atom experiments and nanoscale devices.

Figure caption:
Launched laser-cooled atoms are captured by a single, suspended, single-wall carbon nanotube charged to hundreds of volts. A captured atom spirals towards the nanotube (white path) and reaches the environs of the tube surface, where its valence electron (yellow) tunnels into the tube. The resulting ion (purple) is ejected and detected, and the dynamics at the nanoscale are sensitively probed.

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LJ12217

Temperature mapping at the nanoscale

As nano-sources of heat remotely controllable with laser light, plasmonic structures appear as a unique tool to design a temperature landscape at the nanoscale. However experimental research in this area remained poorly developed mainly because of a lack of an efficient thermal microscopy technique.

Reporting in Physical Review Letters, researchers managed to map both the temperature profile and the heat origin inside plasmonic structures. This thermal imaging technique consists in mapping the fluorescence polarization anisotropy of molecules surrounding the plasmonic nanostructures. The authors compare the optical and thermal near-fields of a gap nano-antenna and show that the spatial origin of heat and the spatial origin of light are complementary unravelling what seems to be a universal rule in plasmonics. As a consequence, the design of efficient plasmonic nano-source of heat and efficient nano-sources of light follow different rules, as illustrated by the measurement of heat generation in a holy plasmonic structure.

LH12013

The shape of fair weather clouds

Simple descriptions of complex systems are rare. The key is to ask the
right question. For the cloud, it is the shape. Clouds have bumps.
Thermal plumes have humps. Clouds are formed by convection currents,
which also give rise to plumes. Can we understand the shape of clouds in
terms of thermal plumes ?

This simple model achieves that, starting from a simple description of
the plumes in terms of mathematical singularities (sources and sinks).
The cloud is a collection of droplets, advected by the (random) flow
field created by randomly generated plumes. Each time a plume goes
through the cloud, it leaves behind a hump in the spatial distribution
of droplets. This process dynamically generates the characteristic
“cauliflower” shape of cumulus (“fair weather”) clouds.

What’s important about this work is that it describes (quantitatively)
one specific aspect (the shape) of a complex system (the cloud) in terms
of the coherent structures in the system (the thermal plumes). Usually
one cannot do this with complex non-linear systems. In this case, this
procedure gives a simple description of a complex everyday phenomenon.


***


LF12638

Designing supermarket checkouts? Ask purple bacteria

Getting customers through the door, processed, and out again as
efficiently as possible, is a primary goal for large supermarkets and
fast-food chains. But managers constantly face the major dilemma of
how many checkout lanes to have. Too many, and you leave employees
unoccupied while also sacrificing valuable floor space. Too few, and
you run the risk of large lane queues and hence losing customers. But
instead of adopting the latest market consulting fad, a new paper in
suggests taking the advice of some of the oldest
and most primitive life forms on the planet: Purple bacteria. For the
past billion years, purple bacteria -- which are all around us, from
the side of rivers to the colorful corals under the sea -- have been
solving this problem by adapting the number and arrangements of their
'checkouts' according to the flux of 'customers'. Photons from the sun
create excitations which enter the bacterial membrane like customers
through a door, wander through the nanoscale aisles (represented by
the LH2 quasi-ordered lattice) and then arrive at the nanoscale
checkouts (LH1 complex) before leaving the store (membrane) as a food
supply. Analytic theory, backed up by numerical
simulations, includes a key biological feature whose analog is well-
known to any shopper who has been stuck in a checkout lane: Each
customer (i.e. photon excitation) passing through a particular
checkout (i.e. LH1) leaves this checkout blocked for a finite time as
the bagging takes place (i.e. chemical reaction in the LH1 reaction
center). The theory shows that the interplay between
having many active checkouts (i.e. LH1s) but few lost customers (i.e.
dissipated excitations) explains why very different arrangements of
checkouts emerge under conditions of high light intensity (i.e. a high
flux of photon 'customers' arriving at the LH1 'checkouts' all the
time) and low light intensity (i.e. relatively few photon
'customers'). They are currently using their theory to fine-tune
Nature's own architectures in the hope of uncovering some super-
efficient designs for harvesting the free, renewable energy from
sunlight. So the next time your local store introduces some novel
checkout layout which manages to reduce overall checkout times, just
remember that a bacteria may have found it first -- nearly one billion
years ago.

***

LG12498

A crack in a long standing ceramic problem

Ceramics are renowned for their excellent resistances to the extreme environments including high temperature and chemical corrosion, but their poor resistance to thermal shock that often occurs in the engines with ceramic components and in routine daily activities such as cooling a boiling egg in iced water has been a long standing problem in the thermal engineering. In this paper, we propose a novel method to make ceramics insensitive to thermal shock up to their melting temperature. In this method the surface of ceramics was biomimetically roughened into nano-finned surface that creates a thin air layer enveloping the surface of the ceramics during quenching. This air layer drastically increases the heat transfer resistance by about 10,000 times so that the strong thermal gradient and stresses produced by the steep temperature difference in thermal shock did not occur both on the actual surface and in the interior of the ceramics. This method effectively extends the applica
tions of existing ceramics in the extreme thermal environments.

LL12368

Optical chirality and its interaction with matter: Super-Twisty Light

Scientists have discovered a new property of light called “optical
chirality” that measures how different a light wave is from its mirror
image. They used this measure to design super-chiral electromagnetic
fields: fields that have left-right asymmetry in some regions of space
hundreds of times larger than that found in circularly polarized
light.

Ever since Louis Pasteur’s experiments on tartaric acid in 1848,
scientists have known that some molecules—called chiral
molecules—exist in distinct mirror-image forms. Electromagnetic
fields, e.g. light, can also be chiral. Circularly polarized light is
the best known chiral electromagnetic field, and is often used to
study chiral molecules. But until now, nobody asked whether some
fields could be more chiral than others, or how one would quantify the
chirality of an electromagnetic field.

The theoretical discovery of optical chirality sheds new light on the
fundamental symmetries of the electromagnetic field, and paves the way
to ultrasensitive detection and control of chiral molecules with
light.

***

LN11781

Computing with a molecule

A simple diatomic molecule on the angstrom scale has executed
ultrafast Fourier transform (UFFT) within femtoseconds.
Wave functions of atoms and molecules can be used as information
carriers to replace real charges in the present Si-based circuit,
whose further integration will result in a possible disaster where
current-leakage is unavoidable with insulators thinned to atomic
levels. Furthermore, a shaped femtosecond laser pulse can access many
vibrational wave functions in a single molecule simultaneously,
encoding more than one million different kinds of information to a
simple diatomic molecule on the angstrom scale. This information
density is higher than the best possible DRAM to be developed by 2020
by two orders of magnitudes. We have experimentally demonstrated a
new logic gate based on the temporal evolution of molecular wave
functions. Optically tailored wave functions in a simple diatomic
molecule on the angstrom scale implements 4- and 8-element discrete
Fourier-transform with arbitrary real and imaginary inputs. The
evolution time is 145 femtoseconds, which is shorter than the typical
clock period of the current fastest Si-based computers by three
orders of magnitudes (the maximum clock rate of IBM Power 6 is 5.0
GHz, giving its clock period to be 200 picoseconds).

***

LL11852

NEW QUANTUM SENSOR BEATS OLD QUANTUM LIMIT

Researchers have invented an optical sensor that beats an unbeatable quantum limit to sensitivity. The breakthrough has a broad array of applications — from gravity wave observatories seeking to observe distant and bizarre astrophysical phenomena, to optical gyroscopes used in commercial navigation. Optical interferometers are some of the most sensitive devices on Earth, and they have a 100 year long history at the forefront of breakthroughs in science — from turn-of-the-century experiments measuring the speed of light (and paving the way for Einstein’s theory of relativity) — to current-day laser interferometer antennas that scan the skies for evidence of gravity waves emitted from colliding black holes. Practical applications are navigational gyroscopes found in jet planes and magnetic field sensors used in oil drills. It was thought that there was an ultimate limit on the sensitivity of such devices imposed by the laws of quantum physics. Research has now demonstrated conclusively that this limit can be broken. This work exploits quantum properties of light to design the most sensitive optical interferometer ever devised.

BN11475

Controlling Electrons with Light

When a laser pulse is focused tightly onto the apex of a metallic tip with nanometer sharpness, the maximal intensity of light appears on the shadow side with respect to the laser exposure. The intense light induces electron emission, and thereby the emission pattern becomes strongly asymmetric between the shadow and directly exposed sides to the light, as shown in the figure where the emission currents are imaged on a two-dimensional detector. This phenomenon can be used to control electron-emission sites on the scale of a few tens of nanometers. An electron source with optical control of spatiotemporal emission properties is thus established which opens new opportunities for addressing fundamental properties of electron waves, or for new directions in electron holography.