March 30, 2009

LX11472


Strained layers curl up into hyperlenses

Rolled-up three-dimensional metamaterials with tunable plasma frequency
might pave the way to the realisation of hyperlenses working in the visible
regime.

We propose and demonstrate that three-dimensional radial metamaterials can
be created in a strain relaxation process by rolling-up planar
metal-semiconductor double layers with multiple rotations. The walls of the
resulting rolled-up-carpet like structures represent high quality
three-dimensional radial superlattices with accurately tunable unit cells
and lattice constants. Transmission experiments through these superlattices
reveal that they can be described as radial metamaterials with an effective
plasma frequency which is, in contrast to natural metals, not restricted to
the ultra violet but tunable over a broad range in the visible regime by
adjusting the ratio between metal and semiconductor layer thickness.
Effective-medium-picture-based considerations to use these radial
metamaterials as easy to process freestanding hollow hyperlenses for the
visible are confirmed by finite difference time domain simulations.

***

LW10937

Studying Spectacular Exploding Stars

Using the Daresbury Recoil Separator and Holifield Radioactive Ion Beam Facility at Oak Ridge National Lab, we have directly measured a nuclear reaction with radioactive nuclei crucial to our understanding of exploding stars. In stars that are denser, hotter and smaller than the sun, like the "Pup Star" Sirius B, thermonuclear runaways can occur once the temperature and pressure on the surface are high enough. These nuclear explosions, known as novae, release huge amounts of energy, and create lots of radioactive isotopes which are expelled into space. In order to understand just how powerful these explosions are and how much of any given isotope they produce, we have to know the rates of the nuclear reactions taking place. Usually, we have to measure these rates indirectly because of the almost insurmountable difficulties involved; but for the first time we have measured directly the rate of proton capture on radioactive fluorine-17, an important step in the chain of nuclear reactions during these explosions.

***

LW11137

Quantum Ghosts Are Useful

The idea that far distant particles can somehow 'talk' to each other so
perturbed Einstein that he called such weirdness 'spooky action'.
Scientists today are learning how to use the quantum entanglement that
gives rise to spooky correlations as a resource and now a team of
physicists at the University of Bristol have harnessed this phenomenon to
shed light on another unusual and previously intractable aspect of quantum
physics - that of distinguishing between two similar quantum operations.
In the everyday world any process can be visualised as some black box with
an input and an output; if you would like to identify a box you simply
apply some input, measure the output and deduce what happened in between.
But quantum black boxes are different. Distinguishing between two quantum
black boxes that are similar can be impossible with only single particle
inputs since it is not generally possible to then distinguish the different
outputs. The Bristol team demonstrate how distinguishing between two
similar quantum boxes becomes possible when quantum entanglement is used.
Apart from providing insight into the fundamentals of quantum physics, this
work is also crucial for future quantum technologies - how else could a
future quantum engineer build a quantum computer if she can't tell which
circuits she has!

***

LB11950


A new quasiparticle state found in oxide nanostructures

Oxide heterointerfaces frequently produce unexpected and unusual
electronic and magnetic states: magnetic, orbitally ordered, charge
ordered, and conducting behavior that is borderline between insulating
and magnetic, with the metal-insulator transition be triggered by
subtle effects. Nanolayers of VO2 provide a distinctly different class
of novel phenomenon in oxide nanostructures: (1) the ions are not
pushed away from their formal valence state, so there is no impending
"polar catastrophe," (2) a topologically distinct electronic structure
results for a specific thickness of VO2 slab encased in insulating
TiO2: a single point in (momentum) k space separates filled and
unfilled states. This point Fermi surface is analogous to the Dirac
point in graphene, but is even more unusual. First, the VO2 slab is
half metallic -- only majority spin states appear near or at the Fermi
level. Second, the (two dimensional) dispersion of the two bands away
from the point is Dirac-like (linear) along one principal axis, while
it is effective-mass-like (quadratic) along the other. This
"semi-Dirac point" carries with it different transport properties than
a Dirac
point, different behavior with doping, different behavior in a
magnetic field. This unique new state displaying a novel type of
quasiparticle behavior is a theoretical discovery, but there is strong
reason to expect it to be realizable with current technology.
Especially because it is a magnetic, conducting, nanoscale system, it
could well have applications in the spintronics arena.


***

LZ11496

Bouncing atoms off of light

In this paper, we demonstrate the ability to “bounce” atoms off of
light. Whenever atoms scatter light, they get a momentum kick that
can be used to manipulate their motion. With careful control, the
kicks can be made very precise and repeatable. We applied this
technique to atoms that were falling in gravity. We dropped the atoms
and, when they were moving at the correct speed, applied a laser pulse
that reversed their motion just as if they had bounced off a surface.
Eventually gravity pulled the atoms back down, and the pulse was
applied again. This could be repeated up to a hundred times before
the atoms were lost due to imperfections in the laser... many more
bounces than you can get with a rubber ball. The bouncing technique
has a number of potential uses. We explored the measurement of
gravity, which has applications in geophysics, energy exploration, and
inertial navigation. We could obtain the strength of gravity simply
by measuring the time interval between the bounces. Other possible
applications include simulating zero-gravity (without the expense of
spaceflight), cooling the atoms to the lowest possible temperatures,
and improving the accuracy of atomic clocks.

***

LV11622B

Information content in x-ray emission spectra of liquid water.

Ab initio molecular dynamics simulations are used to evaluate the claims
from x-ray spectroscopy of liquid water.
Recent high-resolution oxygen x-ray emission spectra show two distinct
lone-pair peaks for liquid water.
Does the fine-structure in oxygen K-edge x-ray emission imply that
liquid water is a two-component mixture
or is it the signature of a transient OH species arising in the
core-excitation process?

Just as the interpretation of x-ray absorption of liquid water, this
question is intensely discussed in the x-ray
spectroscopy community, because x-ray emission is an independent probe
of the electronic structure containing
complementary information. In this paper, ab initio molecular dynamics
simulations are used to show that the water
lone-pair features are of fundamentally different origin. One is
primarily due to the lone-pair of the intact water
molecules, the other is assigned to a transient OH species formed by
ultra-fast photo-dissociation.
Hence, x-ray emission cannot be taken as evidence of a two-component
mixture model of liquid water with classes
of molecules in distinctly different H-bond environment. Instead x-ray
emission is a unique technique to study
the ultra-fast response to high-energy radiation.


***

EX10270

But, just where is the interface?

For several years now, molecular computer simulations have been providing a
wealth of information about phase coexistence: the conditions at which two
phases are simultaneously stable, and the details concerning the molecular
region that separates them: the interface. For instance, "explicit
simulations of interfaces" are able to directly model interfaces, such as the
liquid-vapor interface. However, it turns out that the exact location of the
interface is delicate to define, at least in mathematical terms. In this
paper, a new proposal employs concepts taken from the field of
computational geometry, where the definition of the "shape" of a set of
points is a well-known problem. In particular, the alpha-shape construction,
which was originally introduced in order to identify the boundary of a set of
points, is used in order to define our interfacial molecules.

Image Caption: A snapshot from a simulation of liquid-vapor coexistence of a model
for noble gases. Solid spheres are the atoms that are identified to be "at"
the surface by our method. Also shown, the interface is modeled by the
triangulated surface (red triangles and blue ridges).


***

LY11398B

Photoionization can be a useful tool for studying single-electron
transistors and other nanodevices

In this paper, we demonstrate for the first time, based on theoretical
results, that photoionization can be a useful tool to investigate
single-electron transistors, and encourage experimentalists to use it for
these and other devices of interest for nanoelectronics. The reason is
that photoionization permits to obtain information on how many electrons
occupy a quantum dot and the charging energy in a direct manner. This is
very important, because experiments carried out up to now, which measure
the electric conductance, only allow to determine these quantities
indirectly. It is worth emphasizing that in the photoionization processes
considered by us, an electron absorbs a photon with energy of the order of
the work functions (typically, 1 eV) and is ejected into the vacuum. This
phenomenon is completely different from the widely studied photo-assisted
tunneling considered by previous investigators, involving much lower
photon energies (typically, a few meV). We give concrete suggestions on
how to conduct experiments using photoionization alone or in combination
with transport measurements. Monitoring zero kinetic energy (ZEKE)
photoelectrons is especially recommended, because ZEKE--spectroscopy
offers a better resolution than standard photoemission.

***

BZ10479

Graphene Stays Cool No Matter What

It was recently discovered experimentally that graphene, which is just a
single layer of carbon atoms arranged in a honeycomb pattern, exhibits far
better thermal conductivity than any known material including diamond and
carbon nanotubes. This discovery opened a new window to graphene
applications in electronics and thermal management. At the same time, the
physical mechanisms behind this superior thermal property of graphene
remained a mystery. In this paper, we have shown theoretically that the
dynamic properties of graphene crystal lattice and its strictly
two-dimensional nature are responsible for extremely high thermal
conductivity of graphene. Phonons, quanta of crystal lattice vibrations,
which carry heat in graphene, propagate with high velocities and do not
scatter as strongly as they do in conventional three-dimensional bulk
crystals. We also explain why the thermal conductivity of graphene depends
on the width of graphene flakes. The results of the paper help to pave the
way for graphene applications in heat removal from electronic chips. The
chip overheating is now one of the most serious problems faced by the
electronic industry.

***

LT11155BR

The parent compounds of high-Tc cuprates become superconducting!

The parent compounds of high-Tc cuprates have long been
considered to be antiferromagnetic Mott insulators. For example,
La2CuO4 with the K2NiF4 structure is an insulator with no doubt.
R2CuO4 (R: rare-earth element) with the Nd2CuO4 (abbreviated usually
as T’) structure has also been believed as a Mott insulator since
the discovery of “electron-doped” superconductors, T’-(R,Ce)2CuO4
in 1989. Our recent work, however, has demonstrated T’-R2CuO4 to be
superconducting. The origin of the sharp contradiction between the
past and our results can be traced to impurity oxygen at the apical
site. Impurity oxygen atoms in T’ cuprates play the role of a very
strong scatterer as well as a Cooper-pair breaker. Therefore the
generic behavior of T’-cuprates can be reached only after complete
removal of impurity oxygen atoms. We employed a new thin-film
process, low-PO2 firing followed by low-temperature reduction, to
clean up impurity oxygen atoms, then achieved superconductivity in
the parent compounds, T’-R2CuO4. Our results, although further
works are required, throw strong skepticism on the currently accepted
“doped Mott-insulator” scenario for high-Tc superconductivity:
high-Tc superconductivity develops upon doping of either holes or
electrons in Mott-Hubbard insulators

***

LA11699

The Knizhnik-Polyakov-Zamolodchikov Formula Finally Proven

The famous KPZ formula appeared in 1988 as a striking application of
string theory to two-dimensional statistical mechanics: it predicted the
existence of a precise relation between the fractal dimension of a
random subset of the plane and its dimension in the presence of
two-dimensional quantum gravity. More than twenty years after its
discovery, this formula is finally rigorously proven in this paper,
within the realm of probability theory and Liouville quantum gravity.

In Liouville quantum gravity, the usual Euclidean area element dxdy of
the standard xy plane is replaced by a quantum area element,
dA=exp[h(x,y)] dxdy, where h(x,y) is the so-called Gaussian free field,
a stochastic two-dimensional generalization of Brownian motion.
Measuring geometrical sets with this quantum metric is tantamount to
randomly exploring very high mountains and very deep valleys at all
(infinitesimal) scales. In this paper, the proof rests on a fine
mathematical analysis of the local averages of the 2D Gaussian free
field. By focusing on the average values of the field restricted to
concentric circles, we reduce the problem to a calculation involving a
standard one-dimensional Brownian motion.

Perhaps most surprisingly, our method shows that the KPZ formula holds
for all planar fractals, and not only for restricted classes of
conformally invariant sets, as originally assumed. Several of the most
fundamental open problems in 2D quantum gravity (such as proving that
"discrete quantum gravity" based on random triangulations has Liouville
quantum gravity as a continuum limit, and identifying the geometrical
nature of quantum geodesic paths) can now be precisely formulated and,
we hope, settled using the framework we introduce here.

***

LC12080

From three to four: a quantum leap in few-body physics

Already in the 1970's, the Russian theorist Vitaly Efimov found a
stunning solution to the quantum three-body problem, predicting a series
of ultra-weakly bound trimer states. It took more than 35 years until
first evidence of the mysterious "Efimov" three-body states was found in
ultracold samples of optically trapped Cs atoms (Kraemer et al.,
Innsbruck, 2006). After this long time the field is now taking off at an
amazing speed, and an increasing number of ultracold atomic and
molecular systems reveal traces of Efimov states.

The addition of a further particle, the step from three to four bodies,
leads to an enormous increase in complexity with great challenges for
its theoretical description. Recently, two theory groups (Hammer and
Platter, Bonn & Ohio, 2007; von Stecher, D'Incao, and Greene, Boulder,
2008) predicted the existence of pairs of four-body states being closely
tied to Efimov trimers. The experiment of the Innsbruck group now
confirms the central theoretical predictions. The results on
recombination in an ultracold gas of cesium atoms show a pair of
resonances caused by four-body processes as fingerprints of the
predicted pair of four-body states.

***

LV11317A

Linking algebra of qubit pairs to projective geometry

A coupled pair of quantum spins ("qubits") describes many
interesting phenomena in quantum cryptography, quantum teleportation,
and quantum computing. These topics are also increasingly of applied
interest. The mathematics that physicists use in these descriptions
is called Lie and Clifford algebras. However, other branches of
mathematics such as projective geometry and design theory have not
been associated with qubits. But this paper points out such links,
and also to a set of "hypercomplex" numbers called octonions (which
are generalizations beyond reals, complex numbers and quaternions,
all of which have applications throughout physics). A striking
feature of projective geometry is a duality between points and lines
so that any valid theorem remains so upon interchanging points and
lines (not true of ordinary geometry). Thus, a diagram of seven
points and seven lines, with each point lying on three lines and each
line containing three points, occurs both as the smallest projective
plane and for describing the multiplication table of the seven
octonions. This diagram is now linked in this paper to one of the
algebras involved in quantum logic gates built out of two qubits.
These connections may be mutually exploited in both Lie algebras and
projective geometry.

***

LZ11585A

SUDDEN DEATH AND SUDDEN BIRTH OF ENTANGLEMENT WITH MEMORY

Entanglement is "the characteristic trait of quantum mechanics", as
Schrödinger stated almost a century ago. It constitutes a key resource
for a number of applications of modern physics, offering a new way of
transmitting information and performing controlled interactions on
quantum bits. Entanglement will certainly be an essential ingredient in
the realization of quantum computers.
However, quantum properties are very fragile, decoherence is
omnipresent, and sometimes entanglement can be completely destroyed in a
finite time. So in order to control decoherence and preserve
entanglement, a deep understanding of the disentanglement process in
realistic situations must be achieved.
In our paper we study the exact entanglement dynamics of two quantum
bits (qubits) in a common environment characterized by memory, for
example two atoms in a leaky cavity. Such a system exhibits interesting
features as the resurrection of the qubit-entanglement after a period of
death, or the revivals of disentanglement after the sudden birth of
entanglement. Our results shed new light on the role that the
environmental memory plays in the entanglement dynamics, and might help
to understand how to exploit such a crucial resource in the future.

***

EX10283

Capsule in micro channel flow

In this paper, we investigated the initial motion of capsule in micro channel flow just after release by a novel numerical simulation method, which combines two methods, one for solving the mechanical problem of fluids inside and outside the capsule membrane, and the other for tracking the capsule membrane. Studying the motion of capsule in micro channel flow is quite important in physics, physiology, and pharmaceutics. For example, it may deepen our understanding of red blood cell behavior in blood vessels. Our results show that the capsule behavior depends on initial capsule shape, initial capsule position, and membrane mechanical properties. Off-center capsules, whose initial center positions are not on the center-line of tube, tend to migrate towards the tube center-line because of the influence of fluid flow. This leads to the development of a cell-free layer around the tube wall. At the same time, off-center capsules experience tank-treading motion, i.e. the membrane rotates around the interior fluid.

***

BZ10683

Magnetism at the interface between non-magnetic oxides.

In this paper we report the appearance of magnetism at the interface between two non-magnetic oxides due to a surface reaction. Mixing Co3O4 with TiO2 we found room temperature ferromagnetism despite the antiferromagnetic and diamagnetic character of both oxides respectively. The nice point of our work is that we do not need to claim a new kind of magnetic interactions to account for it but we can explain it with the well known theories of magnetism in oxides developed in the 60’s but applied to surfaces and interfaces instead of bulk materials. The key idea is that Co3O4 is very similar to Fe3O4 (which is magnetic at room temperature). The slight differences among them that make Co3O4 non-magnetic disappear when the Co3O4 is mixed with TiO2 due to a surface reaction with transfer of some electrons from one oxide to the other. Thus, a thin layer at the surface of Co3O4 grain becomes ferromagnetic. This surface magnetism “was always there” but now we are able create materials with a large fraction of surface atoms (for which the effect is significant) and we are now able to measure with a extreme precision that was not possible 40 years ago. Similar effects have been recently reported in epitaxial films (explained in terms of new magnetic ordering mechanisms) with a deep control of growing conditions but the possibility to arise them by simple mechanical milling we show here, will increase the possibilities to use and explode it for applications.

***

CB10204

The “middle-of-the-road” nucleus 106Zr

The article predicts the spectroscopic properties of 106Zr, an atomic
nucleus with 106 nucleons of which 40 are protons. As such, it is rich in
neutrons and short lived, and lying just at the limit of current detection
capabilities. Its interest resides in the fact that it sits right in the
middle between the ‘magic’ neutron numbers 50 and 82—numbers that define
the usual shells of a nucleus. According to novel theories, this
traditional shell structure may well be modified in very neutron-rich
nuclei that are increasingly being probed with radioactive-ion beams. So,
whether 106Zr behaves as a nucleus at mid-shell will ultimately depend on
the character—magic or not—of its far-away sibling 122Zr with 82 neutrons.
The comparison of our prediction with future experimental studies of 106Zr
might help to indicate whether the magic number 82 persists in the heavy
zirconium isotopes, long before the nucleus 122Zr itself will become
experimentally accessible.

***

LL11329

Does the zero-bias anomaly always signify Kondo physics?

Summary: Once a conductance peak at zero bias, the so-called zero-bias
anomaly (ZBA), is observed in various mesoscopic systems, it is immediately
associated with the intriguing Kondo effect. Here, in contrast, we show
this is not always correct and the ZBA observed in quantum wires is in fact
very different. This paper presents experimental evidence showing that the
temperature and magnetic field characteristics of the ZBA peaks in quantum
wires are inconsistent with Kondo physics. In addition, it is found that
the single ZBA peak still occurs in a fully spin-polarised regime in which
the Kondo spin-flip is prohibited. We demonstrate that a shift in
one-dimensional (1D) energy levels with source-drain bias can reproduce the
ZBA and, unlike the other systems, the 1D system does not need to have the
Kondo mechanism to give rise to a zero-bias conductance peak. This
manuscript is thus expected to have a significant impact on the general
understanding in this active field and to generate substantial interest in
the community.


***

BAR1150

Electrostatic Noise on the Nanoscale

As it becomes more common to fabricate and study electronic devices
on the nanoscale, techniques that can characterize and predict performance
become essential in understanding new phenomena and can lead to improvements
in fabrication and design. We show
that by using electrostatic force detection techniques one can pinpoint
areas over semiconducting surfaces where certain types of electric
charge noise are prominent.
Fluctuating charge is detected via the resulting electrostatic force by
measuring the resonance frequency of a small conducting cantilever placed
only a few nanometers away from the surface. This method of detection has
been shown capable of detecting the electrostatic force from single
electrons, and in this study has shown lateral resolution of at least 20 nm.
Cockins et al. also show that the noise characteristics can be influenced
by light. As charge noise is almost always detrimental to device operation,
and as the mechanism responsible for this particular type of charge noise is
instrumental in photovoltaic operation, the combination of electrostatic
force detection with surface mapping and optical excitation provides a means
to link nanostructure to device performance.

March 23, 2009

LZ11793

The drunkard returns, coherently.

A group of physicists from the Weizmann Institute of Science and the
Technion - Israel Institute of Technology have shown that one can "see"
the effective dimension of a random walk by looking at its spectrum. In
an experiment exploiting electromagnetically induced transparency, the
random walkers are Rb atoms diffusing in a buffer gas that kicks them
randomly. The atoms are prepared in a coherent superposition of their
two ground states and starts to oscillates like tiny clocks. The atoms
are probed whenever they return to their starting point. Interestingly,
it was proven by G. Polya back in 1932 that a random walker always
returns to the origin in dimensions d=1,2. As the authors explain, by
measuring the average time of return to the origin, one can learn about
the dimensionality of the diffusion. Surprisingly enough, this average
diverges in dimension one and two – a consequence of Polya's theorem.
The authors have measured a related quantity called the "critical
exponent" of the spectrum, which determines this divergency. Using this
spectroscopic probing technique it is possible to learn about the
underlying dynamics of other systems such as quantum billiards or
spintronic devices.

***

LX11147AR

Quantum information processing in optical fibers

Quantum information science aims to harness uniquely quantum effects
to gain advantages in information technologies; photons with their
high-speed transmission and low noise properties appear destined for a
central role. A group of physicists and engineers from the University
of Bristol report a two-photon quantum logic gate implemented entirely
in optical fiber. This all-fiber implementation is of crucial
importance to future applications since it allows the logic gate to be
miniaturized and admits high performance operation. Crucially, such a
fiber approach is compatible with optical fiber communication, which
is expected to form the backbone of future quantum networks that offer
security based on the laws of physics. The controlled-NOT logic gate
reported is also the fundamental building block for many quantum
technologies, including quantum information processing. It was
constructed from specially fabricated fiber couplers (in which two
optical fibers are joined in a short section, enabling photons to hop
from one fiber to the other) that affect the different polarizations
of light in different ways.

***

LA11792

Entanglement, at the heart of quantum computers, can also be a
curse

Entanglement is the key property which enables quantum
mechanical particles to perform some tasks - for example
unconditionally secure cryptography or certain otherwise
intractable computations - which are impossible in the everyday
classical world. Our recent work points to a new aspect of
entanglement: it must come in the right dose to be of use.

In quantum mechanics, two particles are said to be "entangled"
if their behavior is correlated more strongly than classical
physics would allow. While entanglement is a prerequisite for
powerful quantum computers, it also gives rise to the intrinsic
randomness of quantum experiments ("God playing dice").

Any computational scheme must find ways for compensating for
this probabilistic nature. While it is known how to efficiently
cope with the quantum mechanical uncertainty in some specific
cases, no scheme has so far been discovered which could utilize
any quantum system with sufficient entanglement for
computational purposes. Such a universal scheme would have been
very desirable: physicists would like to take advantage of the
states they naturally find in their laboratories, instead of
having to carefully engineer one of the few states known to be
computationally powerful.

Our recent work shows that such a general scheme cannot exist.
We establish that, if the amount of entanglement in a system
grows too large, the intrinsic quantum randomness becomes so
pronounced that no useful information can be extracted.

So while it remains an important and fruitful task to identify
new quantum systems with computational power, researchers must
bear in mind that this property is more elusive than previously
thought.

***

LY11340

NSCL researchers constrain symmetry energy at low density

By analyzing data from several combinations of collisions of tin nuclei,
researchers at Michigan State University National Superconducting Cyclotron
Laboratory (NSCL) have refined understanding of symmetry energy. Their work
marks the first successful theoretical explanation of the common symmetry
energy-related observables – including isospin diffusion and differences in
neutron and proton emitted spectra – in heavy-ion experiments. The result
should help in discerning the properties of neutron stars, particularly in
the crust region

***

BB11168

Thermodynamics goes nano!

A recent study has shown that nineteenth
century thermodynamics can still provide useful insights into
twenty-first century nanosciences; and all this is done with pencil and
paper rather than an expensive super-computer! When the size of
materials becomes smaller than one thousandth the width of a human hair,
matter begins to behave highly exotically. By shrinking the size of
materials, the “surface-to-volume ratio” increases; considering this, we
can study size effects on material properties from macroscopic laws, the
so-called “top-down approach”. In thermodynamics, the Gibb’s energy
concept is particularly adapted to describe the liquid-solid phase
transition, what we mortals call the melting temperature. Interestingly,
Dr Guisbiers, working at IEMN in Northern France, has expressed the
size-dependent relation determining the melting temperature of
nanoparticles. Combining the nano-scale melting temperature with the
bulk phase diagram equations, it has been possible to predict the phase
diagrams of perfectly miscible nano-alloys. Moreover, as the
surface-to-volume ratio governs the size-dependent materials properties;
size effects on the energy bandgap and the melting temperature are
linked. In terms of applications, Dr Guisbiers says that his model can
be used to predict the energy bandgap of nano-semiconductors and to tune
the thermo-optical properties of semiconductor nano-alloys especially
those used in nano-optoelectronics applications.

***

BA11323

RELIEVING THE STRESS OF BEING SMALL

The surface of any material is different from its interior. The atoms in
the surface are half-exposed, so they tend to get closer to and bond
more strongly with their nearest neighbours. This makes surfaces harder,
a phenomenon known as surface tension and familiar to anyone who has
seen an insect walk over water. Small objects have a large surface to
volume ratio, so they can experience considerable stress due to surface
tension.

New research shows that certain materials known as
ferroelastics (a group that includes many ferroelectrics and also
martensitic steels and shape memory alloys) can help relieve the stress
of surface tension by dividing into small regions with different
crystallographic orientations (“domains”). While domain formation (also
known as “twinning”) is common in ferroelastics subject to external
stress (e.g., thin films clamped to rigid substrates), it was not known
that it could be self-imposed in the absence of external forces. Surface
tension twinning is expected to affect not just individual nanodevices,
but also macroscopic samples made of fine-grained powders, including
ceramics.

***

CX10076

“Perfect fluid” observed in RHIC collisions may be more hadronic than
partonic.

Many researchers who study relativistic heavy-ion collisions at the BNL
Relativistic Heavy Ion Collider (RHIC) have concluded that the particles
which take part in these collisions behave as though they make up a
“perfect fluid” since fluid-flow-like effects are seen in measured
observable quantities. The key question about this fluid relates to the
type of particles which mainly composes it: are they partons (i.e.
quarks and gluons) which are fundamental particles, or hadrons (e.g.
pions and nucleons) which are themselves composed of quarks and gluons?
In recent work which is scheduled to be published in Physical Review C,
the author shows results from a simple model which strongly suggests
that the “perfect fluid” may be composed primarily of hadrons rather
than partons. By assuming that the early stage of relativistic gold on
gold collisions is a system of hadrons in a simple geometry and allowing
the hadrons to scattering with each other, the author is able to
qualitatively describe many of the experimental features of RHIC
observables thought to be of fluid flow origin. The author also
extrapolates the model to higher energies to make similar predictions
for lead on lead collisions at the CERN Large Hadron Collider (LHC),
which is scheduled to begin running this Autumn.

March 19, 2009

LX11410

Helium nanodroplets ignited from inside

Clusters can be tailored to contain from a few atoms to some
million atoms. When exposed to strong short laser pulses,
electrons are released from these atoms and trapped by the
cluster forming tiny nano-scale plasmas. Thereby, they absorb
extremely efficiently energy from the laser, outperforming
single atoms and bulk material under similar conditions. We have
discovered a dramatic ignition effect. It turns a naturally
transparent helium cluster, so-called nanodroplet, into a fast
and strong absorber of laser light when doped by only a handful
of xenon atoms. These few seed atoms in the center of the
droplet spark the plasma which grows to an unusual cigar shape.
Such a shape allows for a tremendously strong resonant
absorption within a few femtoseconds only. The energy absorption
is so strong, that a "hole" forms in the middle of the laser
pulse. This leads to a startling possibility, which awaits
exploration as a promising technological application of our
work: The creation of short and intense dark laser pulses

***
LY10902BR

Perfect lens and compensated media unified by transformation optics

Transformation optics has provided us a convenient guideline for designing
exotic electromagnetic devices, such as invisibility cloaks. In this rapid
communication, it is shown that transformation optics also opens new horizon
for interpreting in a unified manner several optical meta-phenomena, namely
Pendry's perfect lens, indefinite media lens, and compensated bilayer media.
The proposal of these devices has created a lot of excitement in recent
years and motivates current metamaterial technology. Here we reveal that
these devices share the same physical root: they are all bilayer media
obtained with the coordinate transformation technique. As an extension of
our finding, we predict and numerically confirmed that, by incorporating the
obstacle in the electromagnetic space, perfect imaging beyond passive
objects or active sources is possible. Such transformed bilayer system can
be naturally extended to arbitrary geometries, such as cylindrical and
spherical ones.

***

LZ10950

RESEARCHERS FIND A NEW VIBRATION

Researchers discovered a new atomic oscillation that could affect a
range of phenomena in solids.

When hydrogen atoms diffuse into the crystal aluminum antimonide, they
form bonds with the aluminum atoms. The bond stretching and bending
vibrations of the hydrogen showed a bizarre isotope effect. While
aluminum-deuterium pairs have one stretch-mode frequency, the
aluminum-hydrogen pairs have two frequencies.

To solve this puzzle, the scientists performed calculations on massively
parallel supercomputers. The computations revealed that there is a
transverse mode where the aluminum and hydrogen atoms oscillate
together, as a single unit. The transverse mode plus two bending modes
just happens to equal the hydrogen stretch-mode frequency. This
accidental resonance causes the stretch mode to split in two.

Normally, a stretch mode is localized. Only the hydrogen atom
oscillates. The neighboring atoms barely move. The accidental resonance,
however, causes its spatial extent to increase dramatically. Instead of
only one atom moving, hundreds do.

The researchers discovered a new quasi-particle that exists somewhere
between a sound wave and a localized vibration. In the future, it is
possible that these strange quasi-particles will be found in many
condensed-matter systems.

***

EZ10345

Mathematical modeling of fluid-particle behavior in ureteral peristalsis

Transport of body fluids in humans, animals and plants generally occur by
peristalsis. This refers to successive waves of contraction along the walls
of a hollow muscular structure that push their contents forward. In the
urinary system, urine flows from the kidney to the bladder by peristaltic
action of the ureteral wall. Sometimes this is accompanied by bacteria or
calcium oxalates. Bacterial attachment to the ureteral wall can produce
inflammation, and calcium oxalates can precipitate and form ureteral stones.
A mathematical model of peristaltic flow with particles is developed in this
work. An analytical solution of the fluid
velocity field is first obtained. This is then used in conjunction with an
equation of motion for a small rigid sphere in nonuniform flow under the
action of several forces to calculate particle motion. Retrograde motion of
particles, such as bacteria or stones, can occur in
the upper urinary tract when there is a partial occlusion of the peristaltic
wave. Some of the particles participate in the formation of a recirculating
bolus, and some are delayed in transit and eventually reach the walls.

***

LT11994

Absence of fundamental length scale explains dynamical dark energy.

Fundamental theories without an explicit length scale are invariant
under a change of scale. In a world with more than three space
dimensions scale invariance can have profound consequences for the fate
of the dark energy in the universe. We discuss the presence of two
phases for possible stable cosmological solutions, somewhat analogous to
the phases in many body physics as vapor and water. Within a given
phase, certain physical properties do not depend on the details of the
unknown fundamental theory. For one of the phases we find that
Einstein's cosmological constant vanishes by a mechanism of
self-adjustment. Due to quantum fluctuations, this phase is approached
only as the cosmological time goes to infinity. Therefore the dark
energy vanishes only in this limit. In the present very old universe a
tiny dynamical dark energy density remains, which is typically of the
magnitude required to explain the cosmological observations.

***


LA12142

When superconductivity meets ferromagnetism in ferropnictides

Summary Text: Superconductivity and ferromagnetism are antagonistic. On one hand, a superconducting state tends to expel magnetic fields. On the other hand, ferromagnetism, which produces strong internal magnetic field, generally kills superconductivity. It is fundamentally interesting to find when and how the two phenomena live together. In this paper we report the coexistence of superconductivity and ferromagnetism induced by isovalent phosphorus doping in a ferropnictide system of EuFe2(As1-xPx)2. On cooling, superconductivity associated with the d-electrons in iron atoms appears first at 26 K, and ferromagnetism due to the f-electrons in europium atoms then comes below 20 K. Strikingly, the zero-resistance superconducting state is robust against the ferromagnetism at low temperatures, making the material as a true ferromagnetic superconductor. Besides, the isovalent phosphorus doping, which generates chemical pressure, provides an alternative route to realize superconductivity in ferropnictides.

***

LX10931

How does the Earth's magnetic field reverse?

The magnetic field of the Earth is roughly a dipole aligned with its
axis of rotation. Paleomagnetic measurements have shown that the direction
of the field is not constant: from time to time the magnetic field reverses and
the poles shift in an apparently random way. In this paper we present a model
that explains how these reversals occur.

We propose that the reversals result from the competition between the dipolar
mode and a second unstable dynamo mode. This explains many features of the
Earth's magnetic field. Not only the existence of reversals that thus can
be triggered by a small amount of fluctuations but also their shape: the
dipolar field first slowly decays to zero and then grows with the
opposite sign on a much faster time scale. Aborted reversals, also called
excursions, are predicted. The statistical properties of the duration
between reversals are calculated and this allows to understand the
existence of long durations without reversals, also named superchrons.

If the second mode is a quadrupole, which is likely from numerical
simulations, we show how reversals of the magnetic field are correlated
with the flow in the Earth's inner core: they require breaking of its
equatorial symmetry. Thus, paleomagnetic records can provide informations
about the history of the internal structure of the flow in the inner core
of the Earth.

***

LX11825

Rise and fall of black hole entropy

We have shown analytically that the rise of the entropy of
a black hole with the area is strongly modulated.
Black holes, which show intriguing thermodynamic features,
have the area in Planck units behaving like an entropy.
The theory of loop quantum gravity has a
way of counting states corresponding to discrete eigenvalues of
the area operator, involving square roots of the
familiar eigenvalues of the squared spin operator.
By counting states with the area approximately fixed,
it had been seen earlier that the spins are distributed
in a Boltzmann fashion, involving an analogue temperature and
the area instead of the energy, while the entropy increases
linearly with the area. In the present work, by recognizing the
irrational nature of the exact area eigenvalues, we have found that the
spins have several segregated classes, each with a Boltzmann distribution
governed by its own analogue temperature,
while the linear rise of the entropy is modulated so that it
rises to peaks lying on the linear curve and falls
drastically between the peaks.
This structure is prominent for small black holes and
recent numerical calculations were puzzled by it.

***

BA11272

Relating superconductivity to structure.

This work indicates that strontium nickel phosphide (SrNi2P2) is a
conventional superconductor with a transition temperature of 1.4 K
(similar to more than 10,000 other compounds which have been
discovered). However, the surprising aspect of this work is that we
establish a trend among this and other related nickel based
superconductors, which mimics that of the structurally similar
iron-arsenide-based cousins. The transition temperatures of the
iron-based systems, which are widely believed to be unconventional
superconductors, reach a remarkable 55 K, second only to the
copper-oxide based superconductors. It is completely unexpected that
structural trends would be identical between a class of
unconventional and conventional superconductors. Whether our work
indicates that the nickel-based systems have a similar pairing
mechanism to the iron-arsenide systems and are simply not as well
optimized, or a deeper relationship between crystal structure and the
general phenomenon of superconductivity is an open question.

***

LA11995

Dancing Algae

Scientists at the University of Cambridge have discovered that freshwater
algae can swim about each other in intricate dances, held together only by
the fluid flows they create. The researchers studied the organism Volvox,
which has thousands of cells arranged on the surface of a spherical matrix
about half a millimeter in diameter. Each of those cells has two hair-like
appendages known as flagella, whose beating propels the organism through the
fluid and simultaneously makes it spin about an axis. When two nearby Volvox
swim close to a surface, the deflection of the flow by the boundary leads to
an attractive interaction that pulls them together. Once the individuals are
close, they can orbit around each other like waltzing dancers, or oscillate
back and forth like a minuet. This behaviour has been explained by
mathematical models, which also suggest that the fluid flows set up by the
individuals could assist with fertilization during the sexual phase of their
life cycle.

***

LY11325

A Chemical Quorum

A quorum, in legal terms, refers to the minimum number of members required at a meeting before
business can be done. In biology, quorum sensing (QS) refers to the ability of cells to "switch on"
behavior in response to an increase in group size or density. QS can be thought of as an example of
emergent or collective behavior, the macroscopic properties of a system that arise as a result of
the interactions of its components. We investigated the collective behavior of catalytic
micro-particles that individually display nonoscillatory steady state behavior when immersed in a
catalyst-free Belousov-Zhabotinsky solution. When the particles are gathered into groups larger
than a critical group size, however, spatiotemporal oscillations are exhibited. The activity of the
particles is regulated by the exchange of species with the surrounding solution. The transition from
steady state behavior in small groups of particles to spatiotemporal oscillations in groups larger
than a critical size has the features of a dynamical quorum sensing transition.

***

LZ11313

Magic-Sized Diamond Nanocrystals

Diamond is known to be the hardest of materials and the strongest of
electrical insulators. Making diamond metallic is possible by doping
this material: the process of inserting into diamond lattice large
amounts of atomic impurities. When the number of such dopants exceeds
the critical limit diamond becomes a metal. Such insulator-to-metal
transitions are well known in physics. The researchers from Air Force
Research Laboratory and North Carolina State University found that
metallic diamond possesses very unique structural properties. Using
scanning tunneling microscopy they found magic-sized nanocrystals of
metallic diamond. These tiny nanocrystals are parallelogram shaped and
are closely-packed into a continuous solid film. The AFRL/NCSU
researchers have noticed that the height-ratio of magic nanocrystals is
extremely close to 2/3, the observation which brought them to the
conclusion that quantized electrons play crucial role in the growth
process of these nanocrystals. Indeed, since the discovery of quantum
physics it was known that quantum effects manifest through quantized
sizes: quantized electron states inside atoms and quantized electron
orbits in magnetic field. Thus, the recent discovery reveals the new
phenomenon: the quantized sizes of "artificial" diamond atoms. Each of
these "artificial atoms" contains 7 electrons.

***

LA12237

Understanding the ashes of supernovae and nuclear reactors

Whether one considers supernovae events or the operation of nuclear fission
reactors, extremely exotic neutron-rich nuclei that beta decay back to the
stable isotopes around us will be created. As these nuclei decay, some can
proceed by the process of beta-delayed neutron emission which changes their
mass thus altering the path to stability and the elemental composition of
the ashes of the supernovae event or nuclear fission reactor. Precise
measurements carried out at the Oak Ridge National Laboratory's Holifield
Radioactive Ion Beam Facility, a DOE national user facility, have revealed
yields for beta-delayed neutron emission in the copper and gallium isotopes
which are two to four times higher than those previously reported. Our
measurements, which have increased accuracy and precision in comparison to
the previous measurements, were made possible by new and improved techniques
in beam purification. Revised theoretical calculations are able to
reproduce our results. Additional measurements are needed to determine if
the lack of accuracy in the previous experiments is systematic or isolated
only to the copper and gallium isotopes.

***

LZ11375

Neutron spins visualize magnetic fields

With the presented novel neutron imaging technique it is possible to visualize quantitatively magnetic fields in- and outside of magnetic samples with a sub-millimeter resolution.
In conventional neutron radiography a neutron beam passing through a sample gets attenuated according to the material properties and one obtains an image similar to an x-ray picture. However, due to the spin with its associated magnetic moment, the neutron also senses the strength of magnetic fields. This interaction results in a subtle change in its Larmor precession frequency, which can be detected with a spin echo method similar to the ones used in neutron scattering or NMR. From this measurement a two dimensional magnetic field map can be reconstructed.
The technique offers a wealth of new possibilities in real space condensed matter research, which could help to shed more light on various macroscopic magnetic phenomena.

The attached image shows the two dimensional projection of the characteristic shape of a dipolar magnetic field in the vicinity of a ferromagnetic steel rod of 9 mm length, obtained with this new technique.

***

Two-way traffic: Coexistence of Melting and Crystallization in Polymers.

Everyday experiences show that substances either melt or crystallize
with an increase or decrease in temperature. In contrast, polymers can
undergo both transitions simultaneously at the same time during a
heating process. Using Molecular Dynamics simulations of long chain
molecules, we have shown that melting and crystallization processes
coexist. Furthermore, we were able to reveal some of the molecular
details which lead to this unusual behavior. In particular, we have
shown that at intermediate stages of heating some micro-crystalline
domains disappear while others continue growing (see picture). Because
polymer crystals are far from thermodynamic equilibrium, heating can
increase their thermal stability. Thus, during a heating process,
micro-crystalline domains "decide" whether they are going to melt or
to become more stable. Based on this effect, treatments with
particular temperature-time characteristics might be developed to grow
polymer crystals with designed structural properties.

***

LZ10969

Spin-wave goes further

Anyone who ever threw a stone into a lake could observe generation of wave whose amplitude rapidly attenuates as it propagates, because of energy dissipation. Spin-wave is the magnetic analogy of wave and thus also rapidly attenuates in general. In this paper, we theoretically show that spin-wave attenuation can be suppressed by injecting an electric current and thus spin-wave can go further. It is caused by nonadiabatic interaction between conduction electron spins and spin-wave. We also find that spin-wave can be amplified at a sufficiently high current (see figure). Our finding is important from the viewpoint of fundamental understanding of spin transport mechanism since it provides a new way to experimentally estimate the magnitude of nonadiabatic interaction, which is highly controversial at this moment. Furthermore, our finding will be potentially useful for spin-wave-active devices such as spin-wave logic devices and spin-wave interconnect buses which require as high signal output as possible.

***

LU11904

Ants hate traffic jams

Have you seen ants marching on a trail in a platoon? The ants are
almost as disciplined as soldiers marching in a line. Sometimes,
analogies have been drawn between the traffic of vehicles on busy
highways and ants on a crowded trail. But, which one is a better
analogy? In their forthcoming letter in PRL, John et al. report
empirical results which demonstrate striking differences between
ant-traffic and vehicular traffic. John et al. have analyzed their
empirical data by computing quantities which are known to characterize
vehicular traffic on highways. Surprisingly, unlike vehicular traffic,
free flow of ants on trails can take place even at high number
densities at which vehicles would be stuck in a jam! In other words,
phenomenon of jamming is practically non-existent in the world of ants!

March APS Meeting Press Conferences

For more information about the 2009 March APS Meeting in Pittsburgh, visit the meeting Virtual Pressroom

Journalists who wish to cover the press conferences by conference call should contact James Riordon at (301) 919-2173 or by email at riordon@aps.org.


Monday, March 16

10,000 Physics Majors and What to do With Them 10:00 a.m.
Theodore Hodapp of the American Physical Society (APS) will explain why the APS and the American Association of Physics Teachers recently endorsed a call to double the number of physics majors in the United States to an all-time high of 10,000 students per year (paper B3.1). Roman Czujko of the American Institute of Physics will join in the press conference to offer an overview of what sorts of careers young physicists are choosing in these troubling economic times. He will also provide suggestions for ways U.S. physics departments can prepare the current crop of 5,000 physics students (or perhaps 10,000 students, if the doubling initiative is successful) for the realities of supply and demand in the scientific workplace (paper J8.1).


The Physics of Facebook, Sports Careers, and a Bump in a Rug 11:00 a.m.
Sessions sponsored by the Group on Statistical and Nonlinear Physics (GSNP) at the APS March Meeting always include a few talks that apply physical methods to intriguing and unexpected questions. Amanda Traud of the University of North Carolina has investigated the structure of online social networks such as Facebook and MySpace. Traud and colleagues at UNC, Harvard, and the University of Oxford have found that they can gain startling insights into secret interests and characteristics of people who are active on social networking sites by analyzing their collections of friends and connections (paper H9.13). Alexander Petersen of Boston University has turned his attention to professional athletes, and put together a definitive plot of the likely length of a player’s career. The trends he discovered are consistent for all sorts of sports in locations around the globe, indicating that one specific type of career distribution holds throughout the sporting world (paper Q15.11). Dominic Vella of the Laboratoire de Physique Statistique in Paris has set his sights a little lower in his studies of the evolution of a bump in a rug. The analysis reveals the fundamental mechanics of how flat objects glide across each other, which applies to various phenomena including the motion of tectonic plates over the Earth’s mantle and interactions between sheets of material at atomic scales (paper J9.12).


Batteries of the Future 1:00 p.m.
Although batteries have improved only incrementally in the last generation, the cell phones, laptops, hybrid cars, and other devices they power have made much more fundamental technological advances. So how might batteries of the future catch up? One emerging technology uses polymers instead of relying on traditional metal/metal oxide electrodes. These new batteries promise to be lighter, safer, and much more long lasting. In paper A4.4, Hiroyuki Nishide of Waseda University in Tokyo will be discussing charge transport and storage within electroactive polymer-based energy devices. In paper B20.1, Mohit Singh of SEEO, Inc., will be discussing polymers for new battery technologies. Also at the press conference will be Nitash Balsara of the University of California, Berkeley, who is chair of session A4.


Tuesday, March 17

New in Nano: Tiny Tools and Hybrid Memory 10:00 a.m.
Abha Misra of Caltech will describe minuscule soldering irons built of iron-filled nanotubes . The nano-soldering irons should be ideal for linking together molecular-scale mechanical and electronic devices (J24.2). Izhar Medalsy and colleagues of the The Hebrew University in Israel have developed a novel memory unit that combines a ring-shaped protein molecule 11 nanometers in diameter with a 5 nanometer particle of silicon. The structure can be electrically charged to store a single bit of information. The achievement is an example of a promising bottom-up approach to building nanoscopic electronics, rather than the top-down technique of carving devices out of silicon, which is getting increasingly challenging as technology moves to ever smaller scales. (A28.11).


The Greening of Pittsburgh 11:00 a.m.
Many 21st century cities are going green in terms of air quality, environmental efficiency, recycling, and building construction. Few cities have had to come as far as Pittsburgh, whose iron works, steel mills, and other industries relied heavily on burning coal for much of the city's history. In session H8, moderated by Brian Schwartz of The Graduate Center of the City University of New York, a panel of local speakers will be discussing Pittsburgh’s history and the city's greener present and future. Joel A. Tarr of Carnegie Mellon University will discuss water, air and land in Pittsburgh environmental history. Alan Traugott of CJL Engineering will talk about green materials and construction. Cliff Davidson of Carnegie Mellon University will describe the city's air quality from its early days to the present. Finally, Mark Leahy, the General Manager of the David L. Lawrence Pittsburgh Convention Center will discuss the greening of the convention center itself, the first of its kind.


Biology at the Smallest Scale 1:30 p.m.
Recent technological advances in optical microscopy have shattered diffraction limits, allowing scientists to directly image a variety of biological processes with unprecedented resolution. In the 2009 Irving Langmuir Prize Lecture, W.E. Moerner of Stanford University will discuss the technique of single-molecule spectroscopy and imaging, which he pioneered. Many aspects of the early low temperature studies have critical roles in today's room temperature bioimaging. He has managed to reveal the shapes of filaments in living bacteria and to resolve single molecules in three dimensions far beyond the diffraction limit. Stefan Hell of MPI for Biophysical Chemistry, Gottingen, Germany, conceived and developed the first far-field optical microscope that breaks the diffraction-limited resolution barrier. He will discuss the importance of this technology for fluorescence imaging with resolution on the nanometer scale and give an overview of the wide range of applications of this rapidly emerging field, from nanoscale imaging of cellular organelles to studies of polymers and crystals. Also at the press conference will be Session H7 chair K.C. Huang of Stanford University.


Supersolid Crystal Gas 2:30 p.m.
Even though scientists know a lot about atoms and about chemical bonds, the nature of matter still holds surprises, especially as manifested in a variety of quantum phenomena. One of the weirdest of these is the possible existence of superfluid solids. The idea of supersolids arose a few years ago when it appeared that at least part of a solid helium sample was able to pass through the rest of the sample without friction. Interpretation of these helium results remains controversial, but physicists continue to explore the phenomenon in other systems. Charles Clark of NIST, a coauthor of numerous papers at the meeting dealing with supercold atoms (eg, W16.7, T16.6), will describe his modeling of a one-dimensional supersolid consisting of atoms held in place by an optical lattice. Dan Stamper-Kurn of the University of California, Berkeley will report experimental evidence for a two-dimensional gas of rubidium atoms which, in the form of magnetic domains, exhibits supersolid behavior (paper P6.3). (For a brief animated video depicting a supersolid in motion, see http://physics.aps.org/articles/v1/16)

Wednesday, March 18

Super-Computations: Space Clouds, Hurricanes, and Other Fluids 1:00 p.m.
From the collapse of planet-forming dust clouds to the coursing of blood through the human body to the aerodynamics of hurricanes, many of nature's most fascinating phenomena are all forms of fluid flow. As supercomputers have grown larger and larger in the last decade, scientists have found unprecedented opportunities to model the dynamics of these widely varied phenomena -- the subject of an invited session on fluid dynamics and computational science. Paolo Padoan of the University of California, San Diego will discuss how the dynamics of dust grains in turbulent flows plays an important role in many astrophysical processes, including the formation of precursor planets. George Karniadakis of Brown University will present a model of the human circulatory system that describes blood flow in vessels ranging in size from large arteries to tiny capillaries. Jacqueline Chen of Sandia National Laboratories will present high-fidelity simulations of a turbulent reacting flow -- an ethylene-air jet flame. Fuqing Zhang of Penn State University will discuss the use of high-performance computing facilities to model hurricanes. Said Elghobashi of the University of California, Irvine will focus on particle-laden turbulent flows, which are ubiquitous in nature (e.g. dust storms on Earth and Mars) and in industrial applications (e.g. liquid fuel and pulverized coal sprays in combustion chambers). Also at the press conference will be Pui-Kuen Yeung of Georgia Institute of Technology, who is chair of Session P5.


The Physics of the Great Painters 2:30 p.m.
Science and art are two different ways of portraying the world. Science cannot interpret art but it can comment on some of the physical attributes of art, which can have a bearing on such things as the authentication of paintings. Here four scientists will report on their computer analysis of patterns in the works of notable artists. Charles Falco, University of Arizona will speak about extending his study of optical effects (carried out in collaboration with the painter David Hockney) to the works of Monet and Renoir. Katherine Jones-Smith of Case Western University will provide a much-improved study of the supposed fractal nature of the drip paintings of Jackson Pollock. James Wang of Penn State who had previously tendered qualitative assessments of the paintings of Vincent van Gogh, will describe his ability now to provide a fuller accounting of brush strokes -- size, curvature, and relation to neighboring strokes. Peter Lu of Harvard will describe the origins of the complex tiling patterns evident in many medieval Islamic buildings. The tiles are arranged with a deceptively crystal-like orderliness that changes slightly from one place to the next, much like natural quasicrystals that straddle the line between true crystals and randomly ordered glass.

March 12, 2009

LV11472

A TAPESTRY OF VORTICES INTERTWINED IN SIMPLE SHEAR FLOW

Systematic explorations of the Navier-Stokes equations that govern
the dynamics of fluids have been pursued since the advent of
powerful hardware a couple of decades ago.
Equilibrium states of these equations are very important as they may
provide powerful insights into the world of turbulence understanding
and control.
The minute investigation by the authors recently leads to the
identification of an unexplored equilibrium state in turbulent
shear flow with the most simple configuration.
The vortical pattern of the new equilibrium state has the shape of
a hairpin, which lifts up the low-speed momentum fluid near
the boundary in a staggered way, as if a tapestry of knots is
intertwined with vortex lines.
Such a shape of hairpin vortex has been believed to play a crucial role
in turbulent boundary layer because of ubiquitous observations in
numerical and experimental studies, but has never been before
isolated theoretically.

***


EA10519


Viscosity extends the lifetime of interstellar clouds

Our numerical investigation has proved that the lifetime of
interstellar clouds is remarkably extended by viscosity.
In interstellar media, dense-gas regions where stars are born
are called interstellar clouds:
such clouds are consistently produced and evaporated.
Recently, interstellar clouds with long evaporation times,
that is long lifetimes, have been observed.
In most of numerical studies so far, interstellar clouds are
transient substances and the origin of the long lifetimes observed
has not been sufficiently explained.
In this paper, we performed precise numerical simulations
that deal with both of the viscosity and the pressure, which have been
ignored or at most implemented implicitly by most of previous researchers.
We have found that the frictional force due to viscosity
balances with the force due to pressure around the interstellar clouds.
This balance, though higher order effect, suppresses the
evaporation of clouds and also extraordinarily extends lifetime of the clouds
depending on their initial conditions.
Our study suggests that the precise treatment of the viscosity is
necessary to discuss the formation and saturation processes of the clouds.

***

LZ11705

SHINING A NEW LIGHT ON CORRELATED QUANTUM PHASES

Inelastic scattering of waves or particles is used in many fields of
physics to gain information on the structure of matter. The linear
response of many-body systems to these external spectroscopic probes
gives access to the excitation spectrum (through the dynamical
structure factor) from which crucial properties can be inferred. This
is particularly true for strongly correlated quantum phases for which
a complete theoretical description is lacking. Such correlated phases
are now realized in a highly controlled way manipulating ultra-cold
atomic gases in arrays of light potentials. The measurement of their
dynamical structure factor should shine new light on the behaviour of
these complex systems. In this work, inelastic light scattering is
used to measure the linear response of correlated one-dimensional Bose
gases, in superfluid as well as in insulating phases. This
spectroscopic technic allows to clearly distinguish the superfluid
state from the Mott-insulating state and to identify the position of
the transition. Novel experimental signatures related to the
particular properties of correlated phases are observed both in the
superfluid and the insulating states. This work paves the way for a
more complete characterisation of atomic Mott-insulating states which
are promising candidates for developping quantum simulation and
quantum information processing schemes.

March 11, 2009

LA11904

Fullerene polymers for batteries and fuel cells

Fuel cells and Li-ion batteries, the energy storage devices for engines
running on non-fossil fuel, rely on the quality of ionic conductors.
Presently, only amorphous or disordered materials possess high enough ion
mobility to be used in these systems. This paper provides unambiguous
experimental evidence for an extraordinarily large ionic conductivity in
Li4C60, a lithium intercalated fullerene polymer. Unlike most other ionic
conductors, this material is crystalline, and the Li ions easily move within
the rigid network of polymeric sheets of C60 molecules. It is demonstrated
that there is a regular arrangement of empty spaces in the polymeric network
that allows a fast diffusion of Li ions at ambient temperatures (see
attached image). The outstanding ionic conductivity of Li4C60 is a first
step towards applying fullerenes in energy storage devices.

***


LZ11553

Metamaterials reveal "new light"

Researchers have experimentally demonstrated the excitation of a new, or
additional optical wave in metamaterials. Light is usually composed of
two beams that differ by their polarization. One of these is called the
"s-" or "TE" wave and the other one the "p-" or "TM" wave. However, it
appears that this simple picture of the world needs to be substantially
changed for at least one class of metamaterials - the nanostructured
composites made from arrays of aligned metallic nanorods (left panel in
figure) that have recently been suggested for negative refraction and
cloaking applications. As shown in the upcoming Letter, in addition to
the "usual" TE wave, the nanorod structure supports not one, but two TM
waves. The implications of this discovery are enormous. First, the
additional wave represents a new information channel that can be used
for communications or for security. Second, the additional wave
drastically changes the refraction in nanorods, as evident from
interference pattern in the right panel in the figure, and may affect
the image formation in the metamaterial lens and cloaking process.
Lastly, the additional wave should be the generic property of the
so-called "epsilon-near-zero" metamaterials, reflecting important
parallels between physics of metamaterials, and physics of
low-temperature crystals.

***

Power and pressure fluctuations in elastic turbulence over a wide range of polymer concentrations

Probability distribution functions of power and pressure fluctuations in a spatially smooth (just a few spatial modes) and random in time flow such as elastic turbulence in polymer solutions in a wide range of polymer concentrations are found to be non-Gaussian, intermittent, and strongly resemble the statistical behavior of these variables in other hydrodynamic systems, such as hydrodynamic turbulence, wave turbulence and turbulent convection, which are in contrast to elastic turbulence exhibit an energy cascade in a wide range of both spatial and temporal modes involved in dynamics. In spite of the similarity in statistical behavior, different physical mechanisms in these turbulent systems are responsible for the intermittency. So based on this finding, it is suggested that there exists a common universal mechanism, which determines the similar intermittent statistics in all hydrodynamic non-equilibrium systems.

***


EA10566

FACING CLUSTERING PROCESSES IN COMPLEX SYSTEMS

Exploring space-time chaos dynamics in a 1D array of thermoconvective oscillators or hotspots allows to understand how a global synchronization transition is reached from an initial state of irregular clusters. Research on complex systems has given rise to an extraordinary variety of space-time cluster phenomena. In nature, for example, we find clusters of synchronized oscillators in biology (from bacteria colonies to the beats of pacemakers cells in the heart), in chemistry (spirals in reaction-diffusion systems), in neurobiology (epileptic activity of neurons) and in physics (coupled arrays of superconductors and semiconductor lasers). Our experiment consists on a 1D array of 80 nonlinearly coupled convective oscillators that are destabilized from a basic multicellular pattern by increasing their temperature. We characterize the way in which the phase synchronization spreads over the array using Fourier demodulation techniques. A weak nonlinear coupling between oscillators enables a synchronization towards a space-time chaos regime of inhomogeneously spread irregular clusters with an average size of 30 mm. For higher values of temperature, these irregular clusters gain space-time coherence undergoing a second order transition towards a space-time beating phenomenon. These beats develops robust coherent domains of 80 mm width with time periodicity of 62 s, as it is shown in the figure. We show that the splitting of the critical space-time frequencies in a narrow band is responsible for this beating regime.

***

LZ11332

Squeezing solids with a flash of light

In this paper, we have used short pulses of x rays to watch how the
atoms of a crystal move away from their average positions after the
bonds that hold the atoms together are suddenly weakened by a short,
intense pulse of laser light. The bond weakening from the light leads
to a "squeezing" of the atomic vibrations in the crystal, since the
atoms are initially closer to their average positions than is normally
allowed. We then watch the atomic vibrations in time as they quickly
oscillate and reach their new values. This is the first demonstration
of squeezing in a solid that has looked directly at the motion of the
atoms. It shows how bright pulses of laser light can drive a solid to
behave very differently from what we would normally expect.

***


BZ10927


Towards fully parameter free simulation of materials properties

In this article, we present a novel theoretical approach to simulate the temperature dependence of materials properties with hitherto not achievable accuracy. This approach represents a major step towards materials design solely on the computer and without any experimental input. Moreover, it can be used to resolve long standing uncertainties about physical mechanisms, which dominate the high-temperature behavior of metals and eventually the transition from the solid to the liquid phase. One of the decisive problems, which remained unresolved for over 90 years, is the detailed balance of contributions to the heat capacity (the amount of heat needed to change a material’s temperature) of a metal (such as, e.g., aluminum) before melting. Our new approach allowed for the first time an accurate quantification of the relevant excitation mechanisms and surprisingly revealed that none of the previously suggested concepts was right.

***


LZ11075


New Kinetic Plasma Equilibria Found

The kinetic version of a family of plasma equilibria has been found,
which so far was only known in the fluid regime. The newly found
equilibria open up new avenues in the investigation of plasma
stability and dynamics, in particular for space and astrophysical
plasmas. In collisionless plasmas magnetic activity processes, e.g.
solar flares, often taken place in current sheets, which are
approximately one-dimensional layers of strongly enhanced electric
current density. The new family of equilibria includes the
well-known Harris sheet, the standard model for a collisionless
current sheet, but also presents for the first time kinetic solutions
for the force-free Harris sheet and all intermediate cases between
the two extremes. Whereas for the Harris sheet the current density is
perpendicular to the magnetic field and force balance is maintained
by the plasma pressure gradient, in the case of the force-free Harris
sheet the current density is parallel to the magnetic field and force
balance is maintained by an additional magnetic field component,
while plasma pressure and density are constant.


***

LZ11494

Two long standing mysteries might be nearing a resolution...


There are a number of long standing mysteries in the fields of physical
chemistry and biophysics. The Hofmeister
effect, which has now been known for over $120$ years is,
perhaps, one of the oldest and most puzzling ones.
Hofmeister observed that
different ions have very different effect on
stability of protein solutions.
A related mystery, which is also very old, has to do with the surface
tensions.
Some hundred years ago
Heydweiller noted that adding a strong electrolyte to water leads to
increase in the
surface tension of the water-air interface.
While the dependence on the type of cation is weak,
there is a strong variation of the excess surface
tension with the type of anion --- the lighter halides lead to
larger excess surface tension than the heavier ones.
Both effects are completely unaccounted for by the current theories
of electrolytes. In this paper a new class of electrolyte models is
introduced.
Unlike the previous approaches, the polarizability of ions are
explicitly taken into account.
Contrary to the classical expectations, the theory predicts that larger
halogen anions are adsorbed at the water-vapor and the water-oil
interfaces, while the alkali metal cations are repelled from it. The
degree of adsorption predicted by the theory is
in accordance with the Hofmeister and Heydweiller effects.

***

LX10962EJ

Revealing the physics hidden behind universalities occurring in
ultra-viscous liquids

The ultra-viscous liquid phase above the glass transition temperature of
super-cooled liquids has several peculiarities, such as the enormous
values of viscosity (about 10^15 of that of ambient water). Experiments
and computer simulations converge to the point that some properties of
this state of matter (often called “solid that flows”)
exhibits universal behavior, independently of the type of the viscous
liquid (for example, different values of dynamic quantities collapse on a
master curve when plotted against some quantities, such as density and
temperature. A physical reasoning why universalities occur was missing
until. A.N. Papathanassiou, in his paper appearing Phys. Rev. E, proved
that when long-standing standard elastic solid-state point defect models
are used to describe the viscous liquid and are combined with fundamental
thermodynamics, density scaling law of diffusivity at various pressures
are obtained, in agreement with recently published results of computer
simulations. Elastic models (according to which the dynamic process are
controlled by the elastic properties of the material) were suspected to
hide behind the peculiar properties of viscous liquids, but it was the
above-mentioned publication that revealed the physics underlying
universalities in a definite way.


***

BA11139

FEAST for eigenvalue problems

The eigenvalue problem arises from a wide range of applications in
sciences and engineering, and it is known as one of the most challenging
numerical processes- also called diagonalization procedure or spectral
decomposition.
Solving eigenvalue problems has been a central topic in numerical linear
algebra for the past decades where powerful tools and numerous numerical
library packages have been developed from Jacobi method and power
iterations to iterative Krylov subspace techniques including Arnoldi and
Lanczos methods or other Davidson-Jacobi techniques. These traditional
numerical algorithms are yet facing new challenges for addressing the
current large-scale simulation needs for ever higher level of
efficiency, accuracy, and scalability in modern parallel architectures.
This paper presents a fast, robust, and scalable algorithm design for
solving the symmetric eigenvalue problem—named FEAST— which deviates
fundamentally from the techniques above and takes its inspiration from
the density-matrix representation and contour integration in quantum
mechanics. FEAST combines simplicity and efficiency, as the main
computational tasks consists of solving few independent linear systems
and one reduced eigenvalue problem order of magnitudes size smaller than
the original one. As presented in particular in the paper, this general
purpose solver is expected to significantly augment numerical
performances and capabilities in modern large-scale electronic structure
calculations



***

EX10328

Combinatorial signals shape cellular patterns

Cells continually have to make logic decisions, many of which are taken through cis-regulatory modules (CRMs).
From viewpoints of evolutionism, these CRMs are changeable, e.g., cis-regulatory mutations, thus leading to
different cellular patterns at different developmental stages. Both deciphering the codes and elucidating
the functions of CRMs involved in various developmental processes are a major challenge in biology and biological
physics. In this paper, we demonstrated that, using computational and mathematical models of synthetic bacterial
genetic oscillators coupled by quorum sensing, different CRMs for integration of both intracellular and
extracellular signals drive fundamentally different cellular patterns, independent of network topology of the
core oscillator. This qualitative result implies that the diversity of CRMs arising possibly from cis-regulatory
mutations can provide a flexible platform for revolutionarily tuning response behaviors for optimal fitness.
As an interesting corollary of our study, the genetic network architecture found in synchronous circadian clocks
is constrained since complete synchronization the circadian clocks display takes place only with a particular CRM.