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.

***

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.

***

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.


***

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.

***

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.

February 26, 2010

BL11361

Lateral Casimir force opens new horizons for micromachines

The Casimir force is an attraction between two bodies in vacuum. It arises because the vacuum is not an absolute emptiness, but is filled with an infinite number of virtual quanta. The usual Casimir force acts perpendicular to the surfaces. In this paper some new features of the lateral Casimir force acting along the boundary surfaces are observed for the first time. It is shown that the lateral Casimir force can be asymmetric, i.e., its profile can deviate from a perfect sine function. The symmetric lateral Casimir force acting between sinusoidally corrugated sphere and a plate was first experimentally demonstrated in 2002 by U. Mohideen and his collaborators, following the 1997 theoretical prediction by R. Golestanian and M. Kardar.

Later it was suggested to use this phenomenon in new generations of micromachines for noncontact transduction of motion without friction. Note that for half a century theorists were incapable of calculating the Casimir force precisely except in a few simplest cases. Only recently, have calculational methods been developed which are applicable to arbitrary bodies. In this work such methods are first applied to experiments and the measurements are found to be in an excellent agreement with the theory. This makes practical applications of the asymmetric lateral Casimir force straightforward.

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LM11808

Superatoms for Cheap Hydrogen Production

In the manuscript, “hydrogen production from water using aluminum-cluster catalysts,” to appear in Physical Review Letters, a multidisciplinary team of physicists, computer scientists and materials scientists introduces a unique nanotechnology-based approach to accelerate hydrogen production from water, which is of great significance for the global energy problem.

Hydrogen production by metal particles in water could provide a renewable energy cycle [A. Seinfeld, Solar Energy 78, 603 (2005); T. Yabe et al., Appl. Phys. Lett. 89, 261107 (2006)] to address the global energy problem [N. S. Lewis, Science 315, 798 (2007)]. Unfortunately, a recent study has concluded that the conventional metal-water reaction kinetics is not fast enough to make it commercially viable [J. Petrovic and G. Thomas, U.S. Department of Energy Report (2008)]. Thus the central question is how to accelerate metal-water reactions?

Here, first-principles molecular dynamics simulation at USC suggests a possible nanotechnology-based solution to this problem, in which chemical reactivity at the nanoscale is enhanced by many orders-of-magnitude compared to its macroscopic counterpart. The simulation results reveal a rapid hydrogen production mechanism by a cluster (or “superatom” pioneered by Professor Castleman’s group at Penn State and Professor Khanna’s group at Virginia Commonwealth University) consisting of a magic number of aluminum atoms, Aln (for instance, n = 12 or 17) [P. J. Roach et al., Science 323, 492 (2009)], in water. The USC-Kumamoto team has discovered a low activation-barrier mechanism, in which a pair of Lewis acid and base sites on the Aln surface preferentially catalyzes hydrogen production at room temperature. This reaction is immensely assisted by rapid proton transport in water [C. J. Wu et al., Nature Chem. 1, 57 (2009); E. Vöhringer-Martinez et al., Science 315, 497 (2007)] via a chain of hydrogen-bond switching events similar to the Grotthuss mechanism [D. Marx et al., Nature 397, 601 (1999)], which converts hydroxide ions to water molecules at the Lewis-acid sites and supplies hydrogen atoms at the Lewis-base sites. Under acidic conditions, these superatoms can continuously produce hydrogen molecules at room temperature. The reaction specificity and efficiency achieved by superatoms and the autocatalytic behavior of water presented here may be applicable to much broader applications, e.g., direct splitting of water using photocatalysts [Z. G. Zhou et al., Nature 414, 625 (2001); K. Maeda et al., Nature 440, 295 (2006)].

February 23, 2010

LM11860

Bacterial spreading with randomly oriented motors

How can randomly oriented molecular motors generate cellular movement? We have addressed this question in the human pathogen Neisseria gonorrhoeae which employs grappling hooks called type IV pili for pulling itself over surfaces. We found that up to twenty randomly oriented pili generate persistent cellular movement and we suggest a tug-of-war mechanism for movement.
Many bacterial pathogens live at surfaces. On the one hand they must attach firmly to avoid clearance but on the other hand they must be motile to spread. The type IV pilus is a polymeric cell appendage that has solved this problem; it elongates through polymerization, attaches to the surface and generates force on the cell body by retraction.
In this paper we showed that pilus-mediated movement is persistent even though the orientation of pilus motors is random. Persistence increased with the number of pili per cell. To resolve this discrepancy, we demonstrated that the force at which a single pilus detached from the surface was 10 times smaller than the motor force. We suggest a tug-of-war mechanism, in which the winning motors pull the opposing motors off the surface thereby generating directed movement.

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LM12636

First Experimental Demonstration of Selective and Efficient Quantum
Evolution Characterization


The characterization of the temporal evolution of quantum systems is
not only one of the most important tasks in physics, it is also one of
the most difficult ones. In fact, the implementation of 'Quantum
Process Tomography' (the technical name under which the above task is
known) requires resources that scale exponentially with the size of
the system, making it practically impossible for large systems.
Moreover even extracting partial useful information about the
evolution also turns out to be exponentially hard. Quantum Process
Tomography is essential to achieve quantum information processing and
quantum computation (as it is required to device appropriate quantum
error correcting strategies to protect quantum information from
natural degradation inducing decoherence). Only recently methods have
been developed which can extract useful partial information about
quantum processes efficiently for systems of any size. In this paper
the authors present the first experimental implementation of a quantum
algorithm of this kind. The experiment, performed at a quantum optics
laboratory recently set up in Buenos Aires (Argentina) involves the
manipulation and detection of single photons where quantum information
is encoded both in the polarization and momentum degree of freedom.

***


LL11804

Bacteria stampede

Who gets trapped in the burning building: the stampeding crowd or the calm individual? The answer might be obvious if you're dealing with human beings, but we show that in the microscopic world of bacteria, it pays to stampede.

We create a microchannel no wider than a few human hairs, but more than one centimeter long, and fill it with about one hundred fish-trap like barriers that are difficult for incoming E. coli bacteria to cross. Although E. coli bacteria can migrate great distances, it is virtually impossible for a single cell to cross all 100 fish traps in sequence. If we add food on the other side of each barrier, however, something interesting happens: several hundred cells team up and collectively swim against all the barriers.

We show that the bacteria achieve collective escape because they are attracted by the food: if we allow the cells to deplete the nutrients, they no longer defeat the fish traps. This behavior also depends on the number of cells present: too few bacteria in the initial injection means they lack the critical density they need to escape the burning building and reach the banquet next door.

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February 22, 2010

LM11942

Quantum Hindsight

Researchers have shown that by changing the way they process data, quantum-limited measurement devices can be twice as sensitive as they were previously thought to be. This means that scientists will be able to produce more precise measurements of the tiny objects that make up the quantum world.

Until recently, it was thought that the best strategy was to use a data processing technique known as quantum filtering which is based only on past observations. This paper presents the findings of recent experiments that demonstrate an idea introduced by M. Tsang only 6 months ago called quantum smoothing, which uses past and future observations.

Remarkably, the new technique can produce more precise results than filtering, without requiring any changes to the actual measurement device. Such a result is very significant for quantum sensing applications like gravitational wave detectors where it is more important to have precise rather than real-time measurement.

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BK11152

HOW CARBON NANOTUBES CAN HELP IMPROVE MATERIALS?

Aircraft fatigue is a term generally used for failure of aircraft components under stress. Researchers now have found a possible solution for aircraft fatigue by designing improved materials. They used large scale computer simulations to fabricate composite materials by embedding carbon nanotubes (CNTs), one of the strongest materials known, into the nickel matrix, primary ingredients for air-craft engine. This work will be helpful for experimentalists to fabricate materials with stronger properties, which may eventually be applied to commercial airlines. The results predict that single-walled nanotubes do not help to improve the mechanical properties that determine strength of the materials. However, multi-walled carbon nanotubes with higher concentration are the material of choice for fabrication of composite materials and this improves materials properties. The research also predicts that there is strong interaction between nickel-matrix and carbon nanotubes.

February 19, 2010

BMR1106

Strong optomechanical interaction is achieved in novel bi-layer photonic crystals

Bi-layer systems have been studied in various fields in physics, such as quantum Hall
systems, quantum wells, graphenes, superconductors, and strongly-correlated electron
systems. Here, the authors realized a novel bi-layer photonic crystal * system (schematically
shown in the figure), for the first time, which can retain most of high performance in conventional
single-layer photonic crystal slabs but of which new degree of freedom in the
vertical direction leads to enormously large optomechanical interaction. Usually, optical
force (that is , radiation force) is very weak because a photon has very small momentum,
but it can be greatly enhanced by this structure. The authors experimentally demonstrated
large displacement of the slab by optical pumping via optically-generatged force. The energy
conversion efficiency is as large as 0.4microN/pJ, which is much larger than conventional
optical tweezers. This bi-layer configuration of photonic crystals may have strong impact
on emerging optomechanics engineering, and has potential to be applied to ultra-energy-
efficient optical force generators.

***

LJ12295




How the motion of micro-organisms can change the viscosity of liquids?

Take a droplet of liquid and estimate its viscosity by shearing it
between your fingers. This is the common perception of viscosity. If
some particles (like pollens for example) are present in the droplet, we
call it a suspension. The viscosity of a suspension increases in a
non-linear way with the number of particles. Now, instead of pollen
seeds, imagine that the particles are micro-organisms such as
spermatozoa, micro-algae or bacteria which can swim in fluids and are
classified as micro-swimmers or motile cells. In this letter, we show
that a given number of motile micro algae (Chlamydomonas Reinhardtii)
suspended in a droplet of water drastically changes the viscosity of the
resulting suspension (when compared to the same suspension made out of
dead cells). It is therefore possible to quantify the averaged motility
of a large population of a billion of cells. We believe that this study
will pave the way towards reliable quantitative study on other
suspension of swimming cells such as spermatozoa for example, for which
motility has a direct impact on fertility.

February 17, 2010

LL11905

Weighing "Invisible" Particles at the LHC through Singularities

We proposed a novel and powerful method for determining the masses of the
so-called "invisible" particles at the Large Hadron Collider (LHC).
These "invisible" particles, which escape direct detection because they
are electrically neutral and interact weakly, are expected in many ideas
for new physics at the Tera-electron volt (TeV) scale, and are in fact of
particular importance because they may make up the dark matter of the
universe. To test this hypothesis, it is crucial to measure their masses.

Mass measurement techniques based on studying specific kinematic
variables have been proposed, but previous approaches are not systematic
and are highly dependent on the process in question. In this paper, we made the key
observation that invisible particle mass measurements rely on mathematical
singularities in the distribution of the momenta of the observable
particles; these singularities arise because this distribution is a
projected image of the full (nonsingular) distribution of the particle
momenta. Based on this observation, we proposed the "algebraic singularity
method," a systematic method for finding all singularities and
constructing optimized kinematic variables for determining the invisible
particle masses. The algebraic singularity method generalizes and improves
upon the previously known techniques by providing a more mathematically
rigorous approach that can be applied in general situations. The method will be an
invaluable tool in the search for new physics and the tests of the TeV
scale dark matter hypothesis at the LHC.

February 14, 2010

LM12448

How do plastic balls break?

Fragmentation phenomena are ubiquitous in nature and play a crucial
role in numerous industrial processes related to mining and ore
processing. The most interesting feature of
fragmenting systems is that the size/mass distribution of pieces
exhibits a surprising universality, i.e. power law distributions are
obtained independent of materials' details and of the way of energy
input. Detailed laboratory experiments on the breakup of disordered
solids have revealed that mainly the effective dimensionality of the
system determines the value of the exponent, according to which
universality classes of fragmentation phenomena can be distinguished.

The breakup of heterogeneous brittle materials (rocks, concrete,
ceramics, glass,...) is very well understood by today, however, hardly anything
is known about the fragmentation of materials with more complicated
rheological behaviors such as plastic. In order to
understand how plastic materials fragment, we accelerated
polypropylene balls of a few millimeter diameter and impacted them
against a hard wall. In the experiments we found
again a power law distribution of fragment masses; however, the value
of the exponent 1.2 is astonishingly small compared to any known
exponents 1.9-2.4 of bulk materials. To understand the physical origin
of this novel behavior we worked out a discrete model
of plastic and performed computer simulations of the impact process of
balls. The simulations reproduce both the large permanent deformation
of plastic during impact, and the novel value of the mass distribution
exponent. We demonstrated that the dominance of shear in the crack
formation and the plastic material response are the key
features which give rise to the emergence of the novel universality
class of fragmentation phenomena.

Attached figure:
Final states of impact at low impact velocities in the experiment
(a) and in the simulation (b). In the contact area with the hard
wall large permanent deformations occur due to compression, while
above it vertical cracks are formed due to tensile stresses.
The simulations are in very good agreement with the measurements.



***

EL10508
Order and Chaos in the Slashdot Body Problem

Click image for animation

A novel analysis highlights the fascinating mix of simplicity and complexity in the orbits of a slash and a dot. A massive line segment or slash (/) and a massive point or dot (.) interact gravitationally to form a slashdot (/.) system. The resulting dynamics is especially beautiful, balancing order with chaos. Online movies and three dimensional strobed animations communicate the graceful pirouettes of this pas de deux. [http://www3.wooster.edu/Physics/Lindner/Research/SlashdotTrailsLarge.mov] The extension of the slash provides an extra degree of freedom that enables the interplay between rotation and revolution, which characterize actual planets, natural and artificial satellites, but not the interaction of idealized points. The International Space Station and a docking space shuttle form an extended million-pound system that is definitely not well-approximated by two points. The asteroid Ida and its moonlet Dactyl form a natural slashdot body system. The slashdot body problem is an instructive semi-solvable model problem in the vicinity of the famous two and three body problems that anchor celestial mechanics.


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LC12642B

Thermal rectifiers; from nano-electronic devices to energy-saving buildings

Generally, rectification is a transport process that is faster in one direction than in the opposite. This phenomenon is well-known for the current of charges; diodes are electric rectifiers. Thermal rectification, i.e., the non-equivalence of the heat transport in two opposite directions, however, has been detected only recently. Thermal rectification phenomena can be used to create thermal diodes and hence lead to a revolution in the nano/micro devices. Moreover, based on this phenomenon, in macroscopic world, special walls and windows for the energy efficiency of buildings can be designed. Using molecular dynamics simulations, we have demonstrated that thermal rectification can be forced in mass-graded systems (i.e., via isotope substitution), via a gradient in the force-constant (i.e., via impurity doping), or in special designed topologies.


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AH10518


Classical structures smaller than Planck constant do influence Quantum Mechanics.

It is a commonly held belief that dynamical classical structures smaller than Planck constant can not be "see" by quantum wave-functions and therefore have no effect on their evolution in time. This paper shows that this is not true in general: a correspondence is found between classical resonances (the ratio of two frequencies of the system being equal to the ratio of two integer numbers) and a number of quantum resonances (interactions between energy levels). In the system studied, the resonant quantum states reproduce the underlying resonant classical structures in phase space, even when these structures are smaller than Planck constant. Classical related quantum resonances are present only when the distance between two levels allows them to interact through the classical resonance itself. Varying one of the system parameters, several quantum levels can get close enough to enter resonances related to small classical structures, leading to significant population transfer. In the case studied in this paper, this results in to a remarkable agreement between classical, quantum, and experimental results. Studies of small classical structures could be used to improve methods for the transfer of population among quantum states.