ARE JACKSON POLLOCK'S DRIP PAINTINGS FRACTAL?
Can fractal analysis be used to determine whether a drip painting is
an authentic Jackson Pollock? A highly publicized claim, originally
published in Nature, asserts that Pollock's drip paintings contain
fractal patterns so distinct they can be used to identify and date
his work. The issue is of more than just academic interest since fractal
analysis has recently been invoked to help settle a major debate in the
art world regarding the authenticity of a cache of drip paintings
discovered by Alex Matter.
In this paper we demonstrate conclusively that fractal analysis
provides no useful information about artistic authenticity. To
this end we have analyzed paintings known to be authentic works
by Pollock and drip paintings by local artists. According to fractal
analysis, known Pollocks fail to be authentic, while paintings done
by local artists in 2007 are authentic Pollocks done between 1948
and 1950. We also report the fractal analysis of two Matter
paintings.
In an earlier paper published in Nature we had demonstrated a number
of logical inconsistencies in the application of fractal analysis to
drip paintings. Foremost among these: a childish drawing made by one
of us, depicting about twenty hastily scrawled, five-pointed stars,
was shown to be an authentic Pollock according to fractal analysis.
Together with the painting analysis in the current paper, this
demonstrates the complete ineffectiveness of fractal analysis at
recognizing Pollock's hand.
The painting analysis also motivated us to uncover some new
fractal mathematics. We studied the intrinsic noise in box
counting staircases that are commonly used to determine the
fractal dimension. We found that the noise provides a novel
distinction between fractals and ideal Euclidean objects.
***
LV11223
Mechanical manipulation of single polymers proves classic theory of non-linear spring behavior
Polymers in solution adopt a characteristic ‘self-avoiding’ random walk structure; both Flory and de Gennes received Nobel Prizes, in part, for theoretical description of that structure. Thirty years ago, Pincus extended their work to predict that a self-avoiding polymer can behave as a new type of spring. Pincus showed that, when stretched with an applied force, a self-avoiding polymer will extend in a non-linear fashion (in contrast to standard ‘Hookean’ spring behavior, where length grows linearly with extension). In this paper, Saleh and collaborators report on experiments involving stretching and measuring the length of individual single-stranded DNA molecules that provide the first direct confirmation of the existence of the non-linear elastic regime. By analyzing this new elasticity regime, the authors determined that electrical interactions between charged DNA segments were critical to the non-linear behavior, and showed that it was possible to recover linear elasticity by using salt to turn off the electrical interactions. This work will be important to the theory of charged polymers, the design of polymeric materials, and the study of biological polymers such as DNA and proteins. In addition, the single-molecule stretching technique utilized provides an important new experimental tool in the study of self-avoiding polymers.
***
BXR1063
High-capacity hydrogen storage on the flakes of graphite layers
Hydrogen being lightest element in the universe does not allow an
efficient storage in pressured tanks. Recently, efforts have been devoted
to develop safe and efficent storage of H2 molecules on carbon based
nanostructures. Researchers from UNAM, Bilkent University predicted that
graphene flakes can be used for high-capacity hydrogen storage medium.
Ca atoms can be chemisorbed uniformly above the center of hexagons at both
faces of graphene flakes. Interestingly, each adsorbed Ca atom can hold up
to four H2 molecules attaining a gravimetric storage capacity of 8.4 wt %.
This value is above the value 6 wt % set by DOE for feasible hydrogen
storage. Charge transfer from partially occupied Ca-3d orbitals,
polarization of H2 molecule and van der Waals interaction with other H2
molecules are combined to form a mixed bond between Ca+graphene complex
and H2 molecule. The strength of this weak bond is only 0.4 eV and allows
H2 molecules to be discharged easily upon heating. Recycling of
Ca+graphene complex can be sustainable, since the repulsive Coulomb
interaction between positively charged Ca atoms hinders the formation of
Ca clusters on both faces of graphene.
The storage mechanism predicted through high performance computations
based on quantum mechanics appears to be feasible by using graphene
flakes. This work also reveals another interesting aspect of graphene, a
wonder material offering exceptional properties.
***
LU11425
A new test for quantumness in multi-level systems
We have discovered a surprising new behavior in a simple quantum random
walk that can be used as a definitive test to determine whether certain
multi-level systems behave according to quantum mechanical or classical
laws. Although isolated microscopic systems such as individual atoms
or molecules obey the simple and well-known laws of quantum mechanics, and
macroscopic bodies such as baseballs and rocket ships obey the laws of
classical mechanics, nanoscale systems in the "mesoscopic" regime between
these two extremes can display a wide variety of behaviors characterized
by quantum, classical, or a complicated mixture of the two sets of laws.
Understanding this regime is important both for practical applications,
such as nanoscale electronic devices used in a range of information
processing devices, and for improving our fundamental knowledge about
physics at the boundary between the quantum and classical worlds. In our
work, we find that the average displacement of a particle executing a
quantum random walk through a ladder-like network of decaying states is
quantized exactly as an integer. For systems described by this model,
quantization shows up as a discontinuous behavior of measurable
properties as parameters are varied; for a classical system, a smooth
dependence will be observed. This technique can be used as a test for
quantumness in a variety of technologically relevant systems such as
superconducting circuits and trapped atoms/ions.
***
LU11847
Unveiling a new elementary structural building block on silicon surfaces
For the construction of complex ordered structures at the atomic or molecular level, nature often employs a method called self-assembly. Self-assembly makes use of tiny structural building blocks to form organized structures of higher complexity without external direction. Examples in nature range from the formation of crystals to the folding of DNA. Due to its potential for nanotechnology to form small functional devices, physicists at the Université de Neuchâtel in Switzerland in collaboration with theoreticians from the Università di Milano in Italy explored the mechanism of self-assembly on silicon surfaces, which remains the standard substrate of the semiconductor industry. They were able to reveal the so-called silicon pentamer (see image), composed only of five silicon atoms, as a new elementary structural building block used by nature. Further investigations aim to understand the electronic properties of these atomic-scale building blocks in more detail.
***
BV10924
Exciting plasmons in double fishnet metamaterials
In 1998, surface plasmon polaritons (SPPs) were suggested to be responsible of the light transmission enhancement through metallic sheets drilled with subwavelenght holes. The particular wavelengths at which the phenomenon of extraordinary transmission occurs are related to SPPs running on the metal surface resonantly excited by the impinging light. In our paper, we study the connection between the extraordinary transmission phenomenon and SPPs in two drilled metallic layers separated a distance enough as to allow coupling of the SPPs bound to the inner metallic interfaces. In this situation, transmission peaks appear from the excitation of, not only, external SPPs, but also, internal ones at wavelengths predicted by our developed model. In addition, internal SPPs show certain unique properties different from the external ones: they can give rise to a magnetic response strong enough as to lead to a negative effective permeability, allowing the possibility to achieve negative index metamaterials with extraordinary transmission.
***
LW11442
The Makings of an Electron Crystal
In the 1930's, Wigner predicted that, at densities and temperatures
sufficiently low for Coulomb repulsion to dominate, an electron system
would crystallise into a periodic array, i.e., a lattice, to minimise
energy. This phenomenon aroused enormous interest in the physics community,
prompting many experimental investigations in the régime where strong
interactions might produce such a lattice. In this work, we study the
behaviour of a quantum wire (or line of electrons) formed from a
two-dimensional electron gas when the potential creating the
one-dimensional confinement is weakened. The electron topology is inferred
from the conductance plateaux, quantised in units of 2e^2/h for a ballistic
one-dimensional electron gas, which is well understood on the basis of
one-electron physics and a simple model of wave-function confinement.
Surprisingly, as the confinement is weakened, the electron system relaxes
to form two rows, whereupon the conductance jumps directly to 4e^2/h,
indicative of two parallel rows, both spin degenerate. Applying a parallel
magnetic field introduces mixing of spin-aligned levels when the two rows
are sufficiently close together. The breakdown of the simple "particle in a
box" model characterising one-dimensional wires, replaced instead by a
ground state of two degenerate rows, is an important step in the
exploration of the formation and properties of a two-dimensional Wigner
lattice.
***
LX11576
Coffee Inspired Nanostructures
Differential evaporation and convection rates in the drops of spilled coffee drive the granules to the rim to leave stain rings on the table. Substitute the coffee with a suspension of 20 nm gold particles and left to dry on a glass plate topped with a 2D layer of closely packed (50 – 100 µm) latex microspheres which act as geometric template and regulator of the evaporation rate, the end result can be remarkable networks of fully interconnected and conducting gold wires made up of the gold nanoparticles (see photo). Such networks, up to a few square centimetres dimension, are remnants of the meniscus network on the substrate that comprise of pendular rings around the base of the microspheres and interconnecting bridges. “A range of topologies of the wire network can be tuned by just the right combination of evaporation rate, microsphere disposition and surfactant concentration in gold suspension,” said Ivan Vakarelski, lead author of the paper in Physical Review Letters, “and we can even make networks on 3D substrates and hopefully 3D wire network with photonic applications, for instance.” With a little caffeine powered ingenuity this low cost, low environmental impact approach can replace expensive and complex fabrication facilities.
***
LA11447 and CU10073
The interference demolished with a Trojan Horse
Despite the Coulomb force is extremely weaker than the nuclear
one, its influence cannot be always disregarded. For example, it
takes considerable energy to force nuclei to fuse, even those of
the lightest element, hydrogen. This is because all nuclei have a
positive charge (due to their protons), and as like charges repel,
nuclei strongly resist being put too close together. This is a
critical point in nuclear astrophysics, that deals with explaining
the nucleosynthesis in the universe via nuclear reactions. At the
relevant temperatures all reactions are strongly inhibited because
of the Coulomb repulsion. An original technique, the Trojan Horse
Method, has been developed to overcome the Coulomb barrier. Its
name was inspired by the Homer Odyssey. There, since the Greeks
knew they could not win against Trojans by "force", they decided
to do this by "trickery": a few of the men hid themselves in the
Trojan Horse. Likewise here, the particle inducing the nuclear
reaction of interest is hidden inside another nucleus. This
technique was applied to a number of reactions providing for the
first time their measured rate. Recently the suppression of the
Coulomb force was checked also in scattering processes by looking
at the Coulomb plus nuclear interference. In the $p-p$ scattering,
such an interference causes a sudden and huge decrease of the
interaction probability. When one of the two interacting protons
is hidden inside a deuteron, the interference effect is missing
and the two protons behave like they would suffer only their
mutual nuclear fields. Astonishingly, we have found a universal
way to suppress the Coulomb interaction, valid for both binary
elastic and rearrangement processes.
***
LX10902
Interacting electrons in carbon-based electronics.
We have demonstrated the importance of the interactions between
electrons in bilayer graphene, and revealed the origin of a previously
unexplained experimental result.
Monolayer graphene is a one atom thick sheet of carbon, where electrons
behave like massless neutrinos in that they exhibit a gapless, linear
relationship between their momentum and energy. Bilayer graphene
consists of two stacked monolayer sheets and the electrons behave in a
hybrid way between traditional systems and monolayer graphene. Bilayer
graphene is a new and very exciting material, and may in time be used to
fabricate high speed (ballistic) transistors, and potentially a host of
other devices.
We have investigated how the interactions between electrons in bilayer
graphene manifest in its electronic properties when it is placed in a
strong magnetic field. We show that these interactions affect the low
energy electrons more strongly than those with higher energy, and that
this leaves a signature in the way that the material absorbs light, as
seen in a recent experiment. In this experiment, the frequency of
absorption was different for bilayer graphene with an excess or deficit
of electrons, in contrast to simple theoretical predictions. Our (more
complete) theory predicts this difference and therefore reveals
fundamentally important information about the electronic properties of
bilayer graphene which must be taken into account in the design of any
device which utilizes this material and so our work will contribute
significantly to the advancement of carbon-based electronics.
***
LP11321E
Biologically Inspired Flexibility
Biological systems work flexibly using mechanisms that are totally
different from those of artificial machines. Although artificial
neural networks have been studied with a view to mimicking brain
functions, they lack certain key features of biological systems
including adaptability and robustness against environmental change. In
this paper, we incorporated stochastic processes into artificial
networks in order to overcome these shortcomings. Using ring circuits
based on the principle of stochastic resonance and an excitable
threshold system, we created attractors that represent quasi-
equilibrium states into which a system settles until disrupted by
environmental change. Furthermore, noise-driven attractor
stabilization and switching were embodied by electronic circuits that
introduced a brain-mimicking inhibitory connection. Noise works as a
power source to stabilize and switch attractors, and endows the system
with hysteresis behavior that resembles that of stereopsis and
binocular rivalry in the human visual cortex.
***
LY11078A
Cloaking with optimized homogeneous anisotropic layers
We present a method to reduce the scattering from arbitrary objects by
surrounding them with shells composed of several layers of homogeneous
anisotropic materials. An optimization procedure is used to find the
material parameters for each layer, the starting point of which is a
discretized approximation of a coordinate transformation cloaking
shell. We show that an optimized, three layer shell can reduce the
maximum scattering of an object by as much as 15 dB more than a one
hundred layer realization of a coordinate transformation cloaking
shell. Moreover, using an optimization procedure can yield high
performance cloaking shell solutions that also meet external
constraints, such as the maximum value of permittivity or
permeability. This design approach can substantially simplify the
fabrication of moderate size cloaking shells.
***
LT11564
Real-time Observation of a Qubit
In recent experiments, the time evolution of solid-state qubits has
been observed with destructive measurements, where a time trace must be
reconstructed from many experimental runs. In our work we propose a less
invasive measurement scheme, which allows the time-resolved observation
of coherent qubit oscillations already in a single run.
The situation in quantum mechanics is quite different from the
classical world: Taking photographs of a moving classical particle,
for example, does not alter its motion. A quantum measurement,
however, acts back on the measured object. This leads to the collapse
of the wavefunction, and eventually the system is found in a
particular state with a given outcome probability. One has the average
over many runs in order to reconstruct the full information on the
system. A compromise are weak measurements, where one tries to extract
incomplete information on the system state while keeping the
backaction low.
The main idea of our work is to drive the qubit with a high-frequency
signal. The time-dependent phase of the outgoing macroscopic signal
contains information about the low frequency dynamics of the
qubit. This phase can be revealed readily in an experiment by lock-in
techniques. This enables time-resolved monitoring of coherent qubit
oscillations.
***
EW10456
A Model of Creativity and Innovation in Cities
In this paper, we develop a network model based on the
interactions between residents of a city to show how creative output can
occur in large urban settings. While it has been observed that cities obey a
fast-growing mathematical relationship between their populations and their
rates of productivity and innovation (the larger a city is, the greater the
increase in productivity per person), a mathematical model had not been
previously developed to explain this phenomenon.
Our model demonstrates that the larger the city is, the greater
the chance of there being socially distant ties between individuals, which
are the foundation for fruitful and productive interactions. In this way, we
demonstrate how large urban areas can have the advantage when it comes to
creative output, be it producing patents, generating economic growth, or
even employing more people in research and development fields.
***
LV11385
Changing the frequency of light in a similar way we do with a guitar allows us to manipulate photons just like electrons
If you have a guitar, you can easily demonstrate adiabatic frequency shifting in acoustic regime. You can change the tone of a guitar by modulating the tension of the string even after it has been plucked. This is what we call an adiabatic frequency shifting. Our careful investigation on a dynamic photonic crystal nanocavity directly showed that a same phenomenon is taking place in light frequency. The frequency of light changes when we modify the resonance of a nanocavity. This new type of controlling light allows us to manipulate photons just like electrons. Indeed, we showed that light can be trapped and released from a high-Q photonic crystal nanocavity when we use adiabatic frequency shifting. And the operation of this device is described by an analogy with a field-effect transistor. Such analogical view may open possibility for developing various novel photonic functional devices.
***
EU10429
Light Leads to Crystals
Researchers have now discovered studied how intense light can trigger the crystallization of small organic
molecules dissolved in water. They have built a strong case that the
electric field of light is aligning molecules, helping them to get
organized into a crystal. The phenomenon can be used to crystallize
pharmaceuticals and other industrially important substances.
In an effort to test the alignment hypothesis over a wider range of
materials, they set out to see if an analogous phenomenon
exists in liquid crystals, which are materials that flow like liquids
but are orientationally ordered, like crystals. When cooled, many
liquid crystals undergo a transition from a disordered "isotropic"
state to an ordered "nematic" state. The researchers found that, when
the liquid crystal was exposed to intense laser pulses as it was
cooled, the molecules in the resulting nematic state tended to be
oriented in the direction of the electric field of the light. This
observation provides evidence that the electric-field-induced
alignment of molecules plays a key role in the ordering process in
liquid crystals. The phenomenon thus encompasses a broader range of
materials and disorder-to-order transitions than was previously
realized.
***
BW10785
Engineering Magnetic Tornadoes at the Nanoscale
Magnetoresistive random access memories (MRAM) promise revolutionary changes in computer architecture. New research shows that memories using magnetic vortices, or nanoscale-size ‘tornadoes,’ can show improved efficiency and stability. MRAM can preserve stored information without consuming power, and is an attractive candidate for both storage media and magnetic logic. Unlike current MRAM technology, which can store only a single bit of information in a cell, vortex-based MRAM can store two bits of information while maintaining superior thermal stability. This paper points to ways of controlling vortex switching by designing the magnetic multilayered structure of the memories, so that they can be robustly used in a variety of applications. Just like a real tornado, the ‘magnetic tornado’ can have a clockwise or anticlockwise chirality, but its core (polarity) can point either up or down. While scientists can control the polarity of a magnetic tornado relatively easily with magnetic fields or pulses of current, manipulating the chirality in a controllable fashion has proved more difficult. Previous research used large field gradients or exploited asymmetries in the shape of the memory element. In our approach, we tailored magnetic interactions within the multilayer that enabled us to control the tornado’s chirality with an uniform field, which is easier to produce than large field gradients. The memory elements are disk-shaped with no asymmetries, which reduces memory losses caused by the bit-bit interaction. While being thermally stable, the written states are also resettable, a property which may prove useful in re-configuring magnetic logical circuits to adapt to different tasks.
***
LV11556BR
Gilded Metallicity
Though it is now well known that disorder can drive a thin
superconducting into a highly correlated insulating phase, the
precise nature of this superconductor-insulator transition remains
unknown. Recent speculation that the insulating phase is, in fact,
mediated by localized, incoherent, Cooper pairs has been supported by
the observation that metallicity can be reestablished in highly
disordered films by the application of a magnetic field. The high
field phase, termed the quantum metal state, has now been observed in
low atomic mass films such as Be and TiN. We show that by "dusting"
Be films with a sub-monolayer coating of gold, we can strengthen the
localized Cooper pairs against the applied field. This, in effect,
pushes the quantum metal phase to field scales well above that
attainable with typical laboratory solenoids, thus explaining why the
phase has not been generally observable in films comprised of heavier
elements.
***
LS11700E
CRUSHING VIRUSES WITH OSMOTIC PRESSURE
The protein coatings (or capsids) of bacteriophages, viruses that attack
bacteria,
withstand huge pressures from the DNA that they protect. The pressure is
of the order
of 50 atmospheres and seems to be an important prerequisite for the
injection of
the viral DNA in bacteria. In order to preserve functionality and
stability of
a virus, the protein-protein interactions in the viral coating must be strong
enough so that the capsid can resist the pressure. Little is known about the
resistance of capsids to pressure that acts not from the interior, but from
the exterior of a virus and that may induce collapse of capsids. The
experiments
that probe such response of viruses can be performed by dissolving empty
viruses
(without their DNA or RNA molecule) in a solution that contains molecules
that
cannot diffuse through the viral capsid (such as poly-ethylene-glycol),
creating
thus the osmotic pressure. We have performed the calculations for such
experiments.
We find that there are criticaly large pressures that induce the buckling
of the
capsids. We numerically demonstrate that there is a universality in the
buckling
so that the appropriately scaled critical pressures depend only on the
dimensionless
parameter related to the elastic properties of the capsids. This number is
known in the theory
of elastic deformation of plates as the Foppl-von Karman number and is
known to
also determine the details of the shape of non-pressurized viral capsids.
The scaling
properties of critical pressures can be nicely explained utilizing a large
body of
mathematical and physical studies on collapse of spherical and cylindrical
shells
under hydrostatic pressure. We also obtain the buckled shapes and propose
a ''buckling scenario''
visualizing deformations that transform the critically pressurized
icosahedral
shape into a buckled one that lacks the icosahedral symmetry. Our studies
predict
that the critical pressures that would have to be reached in order to
observe buckling
of viral shells should be of the order of 5 atmospheres which is easily
achievable
by present day osmotic pressure techniques.
***
LY11264
Roundabout for Vortices
When caught in the current, vortices usually flow happily down stream.
However, in this work we have discovered that quantum vortices can
behave very differently. When the number of particles and holes in a
lattice are roughly equal, as more and more particles are added, the
vortices exhibit an abrupt change in their behavior and flow vigorously
upstream. This jump in their behavior will happen as soon as there are
more particles then holes in the lattice. When the number of particles
and holes are exactly equal, the vortices don’t have a preference to
flow up or down the current, and another peculiarity happens. The
vortices acquire a spin half quantum number, whose state determines the
particle distribution at the heart of the vortex. Moreover, we have been
able to estimate their mass using an exact numerical study, and have
found it to be very light. The small mass opens the possibility for
observing a novel state of matter, a quantum liquid of spin half vortices.
***
