LC12531
Low temperature melting of water nanoparticles
Water nanoparticles play a crucial role in environmental and atmospheric
chemistry as well as in astrophysics. Nevertheless, no experimental data
even of their most fundamental thermodynamic property, the melting
point, was available until now. We present measured caloric curves of
unsupported, size selected 1.4 and 1.9 nm diameter water clusters, which
show a clear onset of melting at about 100 K. This unusually low melting
point demonstrates the peculiarity of the hydrogen bond network
dynamics, and will help to calibrate theoretical models. Our results
represent a first step towards an urgently needed size dependent phase
diagram of water.
***
EDR1044
Percolation and epidemics in clustered networks
The social networks that infectious diseases spread along are
typically clustered. Because of the close relation between percolation
and epidemic spread, the behavior of percolation in such networks
gives insight into infectious disease dynamics. A number of authors
have studied percolation or epidemics in clustered networks, but the
networks often contain preferential contacts in high degree nodes. We
introduce a class of random clustered networks and a class of random
unclustered networks with the same preferential mixing. Percolation in
the clustered networks reduces the component sizes and increases the
epidemic threshold compared to the unclustered networks.
***
EA10490
Heat transfer in low pressure gas is abysmally low
The amount of heat that can be transferred from a hot surface to cooler fluid flowing
over it, or vice-versa, is of great practical significance. Although results for a large
number of cases are available, the problem of rarefied (low pressure) gas flow over a
surface is not very amenable to measurements and is poorly studied. The available
theoretical results show some contradiction amongst themselves, while experimental
data is totally missing. We have made detailed measurements of heat transfer
coefficient for nitrogen flowing in a heated tube. Our results suggest that the
experimental values are substantially (by up to four orders of magnitude) smaller than
expected from any calculations. Such wide disagreement between experiments and
theory is worth noting. These results suggest that a relook at the governing equations
and/or boundary conditions in in order. The results are therefore expected to trigger
development of new theories and further measurements. Our work would have
significant implications for micro and nanoscale science as well.
Thursday, July 2, 2009
Friday, June 26, 2009
June 26, 2009
ED10601
Transition to superdiffusive behavior in intracellular actin-based
transport mediated by molecular motors
Abstract: Intracellular transport of large cargoes, such as organelles,
vesicles or large proteins, is a complex dynamical process that involves
the interplay of ATP-consuming molecular motors, cytoskeleton filaments
and the viscoelastic cytoplasm. In this work we investigate the motion
of pigment organelles (melanosomes) driven by myosin-V motors in
Xenopus laevis melanocytes using a high spatiotemporal resolution
tracking technique. By analyzing the obtained trajectories, we show
that the melanosomes mean-square displacement undergoes a transition
from a subdiffusive to a superdiffusive behavior. A stochastic
theoretical model, which explicitly considers the collective action of
the molecular motors, is introduced to generalize the interpretation of
our data. Starting from a generalized Langevin equation, we derive an
analytical expression for the mean square displacement, which also takes
into account the experimental noise. By fitting theoretical expressions
to experimental data we were able to discriminate the exponents that
characterize the passive and active contributions to the dynamics and to
estimate the "global" motor forces correctly. Then, our model gives
a quantitative description of active transport in living cells with a
reduced number of parameters.
***
LE12418
Dynamical engineering of a quantum hybrid
Water can exist in three different states: solid, liquid, or gaseous.
However, it can never be in
two phases at the same time.
In contrast, such hybrid phases can occur in the quantum world. For
instance, a "supersolid"
phase has been postulated as the crossover between a frictionless
quantum liquid (a
"superfluid") and a regular solid.
In our theoretical work we propose a way of creating such a supersolid
state, using a mixture
of heavy and light atoms trapped by laser light. These atoms are
initially prepared in a
crystalline arrangement, which they "remember" even after they have
entered a superfluid
state. We end up with crystalline matter flowing without friction, a
state which has no
analogue in our everyday experience.
***
LA11941
SEISMIC HAZARD EVALUATION AFTER THE 2009 L'AQUILA EARTHQUAKE
On April 6, 2009, a 5.8 magnitude earthquake struck central Italy, causing
295 casualties, the collapse of more than 4000 buildings and thousands of people to loose their homes. The earthquake has been followed by an intense seismic activity including two big shocks of magnitude 5.3 and 5.1,occurred respectively two days and three days after and producing damages comparable with those caused by the main event. The two aftershocks were unexpected on the basis of standard models for hazard evaluation that usually assumes that the largest expected aftershock magnitude is about 1.2 smaller than the main shock magnitude. Furthermore, the hazard evaluated by the standard approach is very small at distances as large as 15 kms from the mainshock where the M=5.3 aftershock occurred.
Our analysis of seismic sequences in California, has showed that the aftershock spatial organization evolves in time consistently with a static stress diffusion mechanism. These findings define a new model for seismic hazard evaluation. In the attached Figure we apply our model to the L'aquila sequence, focusing in particular to one hour before the two big aftershocks. Hazard is compared with the one obtained by the standard ETAS model currently in use at the INGV department. The comparison shows that the probability of the two shocks is remarkably high, about 100 times larger than the one obtained by the standard method. Furthermore epicenters, indicated as green stars, are very close to the maximum hazard evaluated according to our model. The above results confirm that static stress diffusion is the main mechanism responsible for aftershock triggering and represents a crucial ingredient for the construction of more accurate post-seismic hazard maps.
***
LC12416
Reaching for magnetic monopoles – an analogy for a point source of
magnetic field is found
Two researchers at Helsinki University of Technology (Finland) and the
University of New South Wales (Australia) have found a way to create
so-called Dirac monopoles in Bose-Einstein condensates using methods
routinely employed in experiments. The condensate is only tens of
micrometers in diameter and composes of dilute alkali atom gas cooled
below one millionth of a degree above the absolute zero. Monopoles are
created into an optically-trapped condensate simply by changing currents
in nearby conductors. These Dirac monopoles provide an ideal analogy for
magnetic monopoles, point charges of magnetic field, which have been
theoretically predicted to have formed in the cool-down of the early
universe. They have been intensively sought for decades without success.
The method reported here provides a very promising technique for the
first experimental observation of an analogous monopole thus opening
pathways for studying monopole interactions, decay, and dynamics. Future
experimental studies will, perhaps, bring us a deeper understanding of
our universe.
***
BBR1150
Spin currents without magnetism
The spin of the electron - the electrons magnetic momentum - is the
smallest building block for magnetic phenomena. In particular, the
discovery of the giant magneto resistance has led to the introduction of
magnetoresistive random access memory into logic electronic circuits and
has truly revolutionized information processing technology. However, up
to date both magnetic fields and magnetic materials are needed, and the
switching is both slow and power consuming. In this work, we present
studies on systems, in which the magnetic moments of the electrons can
be controlled in a collective fashion without the need of any external
magnetic field. This is achieved by the so-called Rashba effect, which
allows a controlled rotation of the electron spin along its path through
a material. We show that this effect can be tuned by changing the mixing
ratio of a bismuth/lead alloy formed on a silver surface. Further we
find that such Rashba systems can be used to inject magnetic currents
into non-magnetic materials without the need of magnetic materials or
external magnetic fields. Such concepts are essential in the field of
spintronics, which could lead to more effective information processing
or even quantum computing.
Transition to superdiffusive behavior in intracellular actin-based
transport mediated by molecular motors
Abstract: Intracellular transport of large cargoes, such as organelles,
vesicles or large proteins, is a complex dynamical process that involves
the interplay of ATP-consuming molecular motors, cytoskeleton filaments
and the viscoelastic cytoplasm. In this work we investigate the motion
of pigment organelles (melanosomes) driven by myosin-V motors in
Xenopus laevis melanocytes using a high spatiotemporal resolution
tracking technique. By analyzing the obtained trajectories, we show
that the melanosomes mean-square displacement undergoes a transition
from a subdiffusive to a superdiffusive behavior. A stochastic
theoretical model, which explicitly considers the collective action of
the molecular motors, is introduced to generalize the interpretation of
our data. Starting from a generalized Langevin equation, we derive an
analytical expression for the mean square displacement, which also takes
into account the experimental noise. By fitting theoretical expressions
to experimental data we were able to discriminate the exponents that
characterize the passive and active contributions to the dynamics and to
estimate the "global" motor forces correctly. Then, our model gives
a quantitative description of active transport in living cells with a
reduced number of parameters.
***
LE12418
Dynamical engineering of a quantum hybrid
Water can exist in three different states: solid, liquid, or gaseous.
However, it can never be in
two phases at the same time.
In contrast, such hybrid phases can occur in the quantum world. For
instance, a "supersolid"
phase has been postulated as the crossover between a frictionless
quantum liquid (a
"superfluid") and a regular solid.
In our theoretical work we propose a way of creating such a supersolid
state, using a mixture
of heavy and light atoms trapped by laser light. These atoms are
initially prepared in a
crystalline arrangement, which they "remember" even after they have
entered a superfluid
state. We end up with crystalline matter flowing without friction, a
state which has no
analogue in our everyday experience.
***
LA11941
SEISMIC HAZARD EVALUATION AFTER THE 2009 L'AQUILA EARTHQUAKE
On April 6, 2009, a 5.8 magnitude earthquake struck central Italy, causing
295 casualties, the collapse of more than 4000 buildings and thousands of people to loose their homes. The earthquake has been followed by an intense seismic activity including two big shocks of magnitude 5.3 and 5.1,occurred respectively two days and three days after and producing damages comparable with those caused by the main event. The two aftershocks were unexpected on the basis of standard models for hazard evaluation that usually assumes that the largest expected aftershock magnitude is about 1.2 smaller than the main shock magnitude. Furthermore, the hazard evaluated by the standard approach is very small at distances as large as 15 kms from the mainshock where the M=5.3 aftershock occurred.
Our analysis of seismic sequences in California, has showed that the aftershock spatial organization evolves in time consistently with a static stress diffusion mechanism. These findings define a new model for seismic hazard evaluation. In the attached Figure we apply our model to the L'aquila sequence, focusing in particular to one hour before the two big aftershocks. Hazard is compared with the one obtained by the standard ETAS model currently in use at the INGV department. The comparison shows that the probability of the two shocks is remarkably high, about 100 times larger than the one obtained by the standard method. Furthermore epicenters, indicated as green stars, are very close to the maximum hazard evaluated according to our model. The above results confirm that static stress diffusion is the main mechanism responsible for aftershock triggering and represents a crucial ingredient for the construction of more accurate post-seismic hazard maps.
***
LC12416
Reaching for magnetic monopoles – an analogy for a point source of
magnetic field is found
Two researchers at Helsinki University of Technology (Finland) and the
University of New South Wales (Australia) have found a way to create
so-called Dirac monopoles in Bose-Einstein condensates using methods
routinely employed in experiments. The condensate is only tens of
micrometers in diameter and composes of dilute alkali atom gas cooled
below one millionth of a degree above the absolute zero. Monopoles are
created into an optically-trapped condensate simply by changing currents
in nearby conductors. These Dirac monopoles provide an ideal analogy for
magnetic monopoles, point charges of magnetic field, which have been
theoretically predicted to have formed in the cool-down of the early
universe. They have been intensively sought for decades without success.
The method reported here provides a very promising technique for the
first experimental observation of an analogous monopole thus opening
pathways for studying monopole interactions, decay, and dynamics. Future
experimental studies will, perhaps, bring us a deeper understanding of
our universe.
***
BBR1150
Spin currents without magnetism
The spin of the electron - the electrons magnetic momentum - is the
smallest building block for magnetic phenomena. In particular, the
discovery of the giant magneto resistance has led to the introduction of
magnetoresistive random access memory into logic electronic circuits and
has truly revolutionized information processing technology. However, up
to date both magnetic fields and magnetic materials are needed, and the
switching is both slow and power consuming. In this work, we present
studies on systems, in which the magnetic moments of the electrons can
be controlled in a collective fashion without the need of any external
magnetic field. This is achieved by the so-called Rashba effect, which
allows a controlled rotation of the electron spin along its path through
a material. We show that this effect can be tuned by changing the mixing
ratio of a bismuth/lead alloy formed on a silver surface. Further we
find that such Rashba systems can be used to inject magnetic currents
into non-magnetic materials without the need of magnetic materials or
external magnetic fields. Such concepts are essential in the field of
spintronics, which could lead to more effective information processing
or even quantum computing.
Tuesday, June 23, 2009
June 24, 2009
LE12322
Extreme deformation: First results from the new Radioactive Ion Beam Factory in Japan
The observation of extreme deformation of the exotic nucleus 32Ne
marks the first major scientific discovery at the newly constructed
Radioactive Ion Beam Factory in Japan, a new-generation facility whose
construction started over 10 years ago. Atomic nuclei can assume a
non-spherical shape, which is one of their most fascinating properties
and directly intertwined with the notion of "magic" neutron and proton
numbers. A nucleus composed of a magic number of protons or neutrons
is particularly stable, spherical and difficult to excite. In this
paper, we report on the first strong evidence of very large
deformation of the isotope 32Ne, which is extremely difficult to
produce and investigate in the laboratory, owing to its very
unbalanced ratio of 22 neutrons to only 10 protons, almost at the
limit of nuclear stability. Shooting a beam of 32Ne nuclei with a
velocity of 60% of the speed of light onto a Carbon target, we were
able to observe a single gamma-ray transition with an unexpectedly low
energy, indicative of a very large ground state deformation, despite
its vicinity the magic neutron number N=20. This is further evidence
of a softening of nuclei and an erosion of the usual magic numbers
toward the drip-lines.
***
LB12491B
Sorting electrons by spin: Some surface alloys do the work
At metal surfaces, some electrons behave like a two-dimensional gas:
They move freely along the surface but are trapped in perpendicular
direction. Since electrons possess a spin which can be either `up' (red
spheres in the figure) or `down' (green spheres), the confinement
produces a specific arrangement of the electrons' velocities: The faster
electrons moving, say, to the right are spin-up whereas their slower
colleagues are spin-down (left panel). If they travel in opposite
direction, their spins become reversed. The velocity difference, named
Rashba effect, is particularly large in surface alloys made of heavy
elements (e.g. Bi) on a noble metal surface, for example Ag.
For the surface alloy Bi/Cu(111), we have shown by photoemission
experiments and first-principles calculations that some of the slow and
the fast electrons which move in the same direction can have identical
spins (right panel). Consequently, more spin-up electrons travel to the
right as to the left and vice versa. Spin-up and -down electrons would
gather at opposite sides of a nano-device, turning its edges magnetic.
This `sorting by spin' makes metallic surface alloys promising materials
for future spin-electronics applications.
Extreme deformation: First results from the new Radioactive Ion Beam Factory in Japan
The observation of extreme deformation of the exotic nucleus 32Ne
marks the first major scientific discovery at the newly constructed
Radioactive Ion Beam Factory in Japan, a new-generation facility whose
construction started over 10 years ago. Atomic nuclei can assume a
non-spherical shape, which is one of their most fascinating properties
and directly intertwined with the notion of "magic" neutron and proton
numbers. A nucleus composed of a magic number of protons or neutrons
is particularly stable, spherical and difficult to excite. In this
paper, we report on the first strong evidence of very large
deformation of the isotope 32Ne, which is extremely difficult to
produce and investigate in the laboratory, owing to its very
unbalanced ratio of 22 neutrons to only 10 protons, almost at the
limit of nuclear stability. Shooting a beam of 32Ne nuclei with a
velocity of 60% of the speed of light onto a Carbon target, we were
able to observe a single gamma-ray transition with an unexpectedly low
energy, indicative of a very large ground state deformation, despite
its vicinity the magic neutron number N=20. This is further evidence
of a softening of nuclei and an erosion of the usual magic numbers
toward the drip-lines.
***
LB12491B
Sorting electrons by spin: Some surface alloys do the work
At metal surfaces, some electrons behave like a two-dimensional gas:
They move freely along the surface but are trapped in perpendicular
direction. Since electrons possess a spin which can be either `up' (red
spheres in the figure) or `down' (green spheres), the confinement
produces a specific arrangement of the electrons' velocities: The faster
electrons moving, say, to the right are spin-up whereas their slower
colleagues are spin-down (left panel). If they travel in opposite
direction, their spins become reversed. The velocity difference, named
Rashba effect, is particularly large in surface alloys made of heavy
elements (e.g. Bi) on a noble metal surface, for example Ag.
For the surface alloy Bi/Cu(111), we have shown by photoemission
experiments and first-principles calculations that some of the slow and
the fast electrons which move in the same direction can have identical
spins (right panel). Consequently, more spin-up electrons travel to the
right as to the left and vice versa. Spin-up and -down electrons would
gather at opposite sides of a nano-device, turning its edges magnetic.
This `sorting by spin' makes metallic surface alloys promising materials
for future spin-electronics applications.
Monday, June 22, 2009
June 22, 2009
LE12079
Earthquake cloak
We propose a simple design of a structured thin-plate (Figure, left panel) within which elastic bending waves are smoothly bent around an obstacle fixed to the ground (Figure, right panel).
This new type of invisibility cloak works over a very large range of frequencies and only requires a handful of elastic materials (six isotropic layers in the simplest design).
It opens new vistas in a better control of elastic waves in metamaterials, with applications ranging from anti-vibrating systems in car industry to protection of man-made infrastructures (such as hospitals or schools) in seismic regions.
Nota-Bene: This work is a follow-up of our research on the tsunami cloak.
***
LD12218BR
Sr4V2O6Fe2As2, a new superconductor in the iron-pnictide family found
As ignited by the discovery of superconductivity in the iron-arsenic family
last year, any desire of getting a new superconductor in this family is highly
appreciated. Recently this exploration gives rise to a successful discovery by
Hai-Hu W??’s group in Institute of Physics in Beijing of a new superconductor
Sr4V2O6Fe2As2 which superconducts at a temperature of 40 K. The unique point
for this new compound is that it is superconductive when it is in the
stoichiometric (without doping) state. In addition, it is constructed by the
sandwich structure with FeAs and Sr2VO3 layers as the building blocks
alternatively along c-axis. Its large interlayer spacing distance, 15.67
Angstrom between the FeAs layers makes it the most anisotropic superconductor
so far in this family. The consequence of this is that it may provide a new
system for investigating the pancake vortices and the Josephson vortices in the
iron pnictide superconducting families, which will lead to an possible
application of TeraHertz photon emission. Meanwhile the theoretical calculation
already indicates that the Sr2VO3 layer has a half-metal feature (electrons are
all spin polarized). If this is finally proved by the experiment, we then have
an interesting structure that naturally contains the ferromagnetism and
superconductivity in a single system, a model that many physicists dreamed of.
***
LD12597
Turbulence meets ultracold atoms and gets cooler than ever!
Scientists have observed, by the first time, turbulence occurring in a
sample at billionths of degree above absolute zero. It is the coldest
situation in which turbulence ever happened. Turbulence has threaded science
for a long time, since Leonardo da Vinci, the first to describe that regime,
going through Heisenberg, Landau, Feynman and many other renowned
scientists. Turbulence is also important for its technological consequences
such as airplanes stability, weather prediction, racing cars and so on.
During the last 50 years turbulence has been also studied in superfluid
Helium, a quantum fluid, or in other words, a fluid that flows without
viscosity, thanks to its quantum nature. In that case, turbulence is known
as Quantum Turbulence (QT). In this work, QT has been observed in a
Bose-Einstein condensate (BEC) sample, also a quantum fluid but millions of
times colder. The advantages of studying QT in a BEC are that they are very
controlled samples where one can tune almost every characteristic of the
fluid. Also, a BEC is modeled by quite simple theories, in contrast to the
models for liquid Helium. Finally, in a BEC the turbulent regime can be
directly imaged. Those very first observations certainly open up a new
important ground where turbulence can be studied.
***
LC12066
Physicists Throw Dice Fast and Fair
Albert Einstein claimed that "God does not play dice" but bankers, spies and physicists do, and to do so they need to generate truly random numbers on demand. Encryption, cryptography and Monte Carlo simulations are only a few of the many applications that require random number generation and with ever higher data rates the speed with which random numbers can be generated has become important. Now a group of physicists from Bar Ilan University has demonstrated a method, described in Physical Review Letters, of producing random bits at a rate exceeding 10 Gbits/s using the chaotic fluctuations of a semiconductor diode laser. The method far exceeds the rate of all previous means of generating truly random bits based on physical stochastic processes and can also be implemented using other high bandwidth random noise sources.
Earthquake cloak
We propose a simple design of a structured thin-plate (Figure, left panel) within which elastic bending waves are smoothly bent around an obstacle fixed to the ground (Figure, right panel).
This new type of invisibility cloak works over a very large range of frequencies and only requires a handful of elastic materials (six isotropic layers in the simplest design).
It opens new vistas in a better control of elastic waves in metamaterials, with applications ranging from anti-vibrating systems in car industry to protection of man-made infrastructures (such as hospitals or schools) in seismic regions.
Nota-Bene: This work is a follow-up of our research on the tsunami cloak.
***
LD12218BR
Sr4V2O6Fe2As2, a new superconductor in the iron-pnictide family found
As ignited by the discovery of superconductivity in the iron-arsenic family
last year, any desire of getting a new superconductor in this family is highly
appreciated. Recently this exploration gives rise to a successful discovery by
Hai-Hu W??’s group in Institute of Physics in Beijing of a new superconductor
Sr4V2O6Fe2As2 which superconducts at a temperature of 40 K. The unique point
for this new compound is that it is superconductive when it is in the
stoichiometric (without doping) state. In addition, it is constructed by the
sandwich structure with FeAs and Sr2VO3 layers as the building blocks
alternatively along c-axis. Its large interlayer spacing distance, 15.67
Angstrom between the FeAs layers makes it the most anisotropic superconductor
so far in this family. The consequence of this is that it may provide a new
system for investigating the pancake vortices and the Josephson vortices in the
iron pnictide superconducting families, which will lead to an possible
application of TeraHertz photon emission. Meanwhile the theoretical calculation
already indicates that the Sr2VO3 layer has a half-metal feature (electrons are
all spin polarized). If this is finally proved by the experiment, we then have
an interesting structure that naturally contains the ferromagnetism and
superconductivity in a single system, a model that many physicists dreamed of.
***
LD12597
Turbulence meets ultracold atoms and gets cooler than ever!
Scientists have observed, by the first time, turbulence occurring in a
sample at billionths of degree above absolute zero. It is the coldest
situation in which turbulence ever happened. Turbulence has threaded science
for a long time, since Leonardo da Vinci, the first to describe that regime,
going through Heisenberg, Landau, Feynman and many other renowned
scientists. Turbulence is also important for its technological consequences
such as airplanes stability, weather prediction, racing cars and so on.
During the last 50 years turbulence has been also studied in superfluid
Helium, a quantum fluid, or in other words, a fluid that flows without
viscosity, thanks to its quantum nature. In that case, turbulence is known
as Quantum Turbulence (QT). In this work, QT has been observed in a
Bose-Einstein condensate (BEC) sample, also a quantum fluid but millions of
times colder. The advantages of studying QT in a BEC are that they are very
controlled samples where one can tune almost every characteristic of the
fluid. Also, a BEC is modeled by quite simple theories, in contrast to the
models for liquid Helium. Finally, in a BEC the turbulent regime can be
directly imaged. Those very first observations certainly open up a new
important ground where turbulence can be studied.
***
LC12066
Physicists Throw Dice Fast and Fair
Albert Einstein claimed that "God does not play dice" but bankers, spies and physicists do, and to do so they need to generate truly random numbers on demand. Encryption, cryptography and Monte Carlo simulations are only a few of the many applications that require random number generation and with ever higher data rates the speed with which random numbers can be generated has become important. Now a group of physicists from Bar Ilan University has demonstrated a method, described in Physical Review Letters, of producing random bits at a rate exceeding 10 Gbits/s using the chaotic fluctuations of a semiconductor diode laser. The method far exceeds the rate of all previous means of generating truly random bits based on physical stochastic processes and can also be implemented using other high bandwidth random noise sources.
Wednesday, June 17, 2009
June 17, 2009
LA11702
Paradox of the Cyrano among bats solved after 58 years
The extremely long nose of a bat from the remote rainforests of South
East Asia has perplexed scientists ever since the species was first
described under the scientific name "paradoxolophus" ("paradoxical
crest") 58 years ago.
Now, scientists from Shandong University in
China, Virginia Tech in the United States, and the Vietnamese Academy
of Sciences have presented results demonstrating that this long nose
can be predicted exactly from its impact on the ultrasonic beams the
bats emit. Using computer methods similar to the ones that transform
the characters in animated movies, the scientist conducted a
"Pinocchio experiment" creating a whole set of modified nose lengths
around the value encountered in nature. Some of these modifications
"cosmetically shortened" the bat's nose whereas others made it even
longer. By predicting the width of the ultrasonic beam for each of
these nose jobs with a computational method, the scientist found that
the natural nose length has a special value: Nose shortening caused
significant loss in ultrasonic focus, whereas artificially elongated
noses provided only negligible additional benefits. Hence, this
unusual biological shape can be predicted accurately from its physical
function alone which makes it a clear-cut example for how physical
forces can determine the outcome of evolution.
***
LD12022
Galactic Positron Annihilation Not a Dark Matter Signal
The intense flux of gamma rays created by the annihilation of
electrons with positrons - their anti-matter counterparts -
from the inner part of our Galaxy has been called a great mystery
because of its spatial distribution, and has been evoked by
cosmologists as evidence of a signal of dark matter. In a new
paper in the Physical Review Letters, however, scientists at
the University of California, San Diego and the Claremont Colleges
show that the observed distribution of gamma rays is entirely
consistent with a less exotic explanation - positrons emitted
by the radioactive decay of nickel, titanium and aluminum,
created in the end-of-life supernova explosions of stars more
massive than our Sun. Contrary to the key assumption made in
the dark matter hypotheses that positrons annihilate close to
where they were born, within about a light-year, Drs. Lingenfelter,
Higdon, and Rothschild show that the positrons, like the well-
measured cosmic-ray electrons of the same energy, travel large
distances of over a thousand light-years before they annihilate.
This large distance is dictated by the interaction of the positrons
with magnetic fluctuations, which the authors show are very weak
throughout most of the Galaxy. With such propagation the authors
predict a spatial distribution of annihilation gamma rays that
matches the distribution peaked towards the inner Galaxy, as
recently observed by the INTEGRAL gamma-ray satellite. They
further show that this propagation explains other basic spectral
properties of the annihilation radiation seen by INTEGRAL. Thus,
the authors show no new and unexplained signal for dark matter
is necessary to explain the observed gamma rays.
***
ECR1044E
Microfluidic Mixers
There are many cases where improved methods of fluid mixing are needed, especially in
the small, confining geometries present in microfluidic reactors. In such small cavities it
is notoriously difficult to induce the turbulence that creates efficient mixing. One
approach is to fabricate electromechanical mixing cells or micron-size stir bars, but we
have developed a simpler, more robust approach that uses commonly available magnetic
particles. These particles can be any size Ð from nanoparticles to traditional
micropowders Ð and the concentration required in the fluid is quite low. When a special
type of magnetic field (which we call a "vortex" field) is applied to the particle
suspension the particles chain into countless stir bars that whirl around as rapidly as 1000
times each second, mixing every corner of the fluid volume. These self-assembled stir
bars are strange actors: if the vortex field is altered to make them whirl around faster the
mixing doesn't get stronger! Instead, stronger mixing is achieved by increasing the
strength of the vortex field. This is just backwards from what one would expect, and we
have traced this strange behavior to the volatile, adaptive nature of the particle chains.
Finally, as a practical matter, the vortex field can be created by small magnetic coils
placed around the mixing cell, and when the mixing is over, the particles can be retrieved
with a magnet for reuse.
Paradox of the Cyrano among bats solved after 58 years
The extremely long nose of a bat from the remote rainforests of South
East Asia has perplexed scientists ever since the species was first
described under the scientific name "paradoxolophus" ("paradoxical
crest") 58 years ago.
Now, scientists from Shandong University in China, Virginia Tech in the United States, and the Vietnamese Academy
of Sciences have presented results demonstrating that this long nose
can be predicted exactly from its impact on the ultrasonic beams the
bats emit. Using computer methods similar to the ones that transform
the characters in animated movies, the scientist conducted a
"Pinocchio experiment" creating a whole set of modified nose lengths
around the value encountered in nature. Some of these modifications
"cosmetically shortened" the bat's nose whereas others made it even
longer. By predicting the width of the ultrasonic beam for each of
these nose jobs with a computational method, the scientist found that
the natural nose length has a special value: Nose shortening caused
significant loss in ultrasonic focus, whereas artificially elongated
noses provided only negligible additional benefits. Hence, this
unusual biological shape can be predicted accurately from its physical
function alone which makes it a clear-cut example for how physical
forces can determine the outcome of evolution.
***
LD12022
Galactic Positron Annihilation Not a Dark Matter Signal
The intense flux of gamma rays created by the annihilation of
electrons with positrons - their anti-matter counterparts -
from the inner part of our Galaxy has been called a great mystery
because of its spatial distribution, and has been evoked by
cosmologists as evidence of a signal of dark matter. In a new
paper in the Physical Review Letters, however, scientists at
the University of California, San Diego and the Claremont Colleges
show that the observed distribution of gamma rays is entirely
consistent with a less exotic explanation - positrons emitted
by the radioactive decay of nickel, titanium and aluminum,
created in the end-of-life supernova explosions of stars more
massive than our Sun. Contrary to the key assumption made in
the dark matter hypotheses that positrons annihilate close to
where they were born, within about a light-year, Drs. Lingenfelter,
Higdon, and Rothschild show that the positrons, like the well-
measured cosmic-ray electrons of the same energy, travel large
distances of over a thousand light-years before they annihilate.
This large distance is dictated by the interaction of the positrons
with magnetic fluctuations, which the authors show are very weak
throughout most of the Galaxy. With such propagation the authors
predict a spatial distribution of annihilation gamma rays that
matches the distribution peaked towards the inner Galaxy, as
recently observed by the INTEGRAL gamma-ray satellite. They
further show that this propagation explains other basic spectral
properties of the annihilation radiation seen by INTEGRAL. Thus,
the authors show no new and unexplained signal for dark matter
is necessary to explain the observed gamma rays.
***
ECR1044E
Microfluidic Mixers
There are many cases where improved methods of fluid mixing are needed, especially in
the small, confining geometries present in microfluidic reactors. In such small cavities it
is notoriously difficult to induce the turbulence that creates efficient mixing. One
approach is to fabricate electromechanical mixing cells or micron-size stir bars, but we
have developed a simpler, more robust approach that uses commonly available magnetic
particles. These particles can be any size Ð from nanoparticles to traditional
micropowders Ð and the concentration required in the fluid is quite low. When a special
type of magnetic field (which we call a "vortex" field) is applied to the particle
suspension the particles chain into countless stir bars that whirl around as rapidly as 1000
times each second, mixing every corner of the fluid volume. These self-assembled stir
bars are strange actors: if the vortex field is altered to make them whirl around faster the
mixing doesn't get stronger! Instead, stronger mixing is achieved by increasing the
strength of the vortex field. This is just backwards from what one would expect, and we
have traced this strange behavior to the volatile, adaptive nature of the particle chains.
Finally, as a practical matter, the vortex field can be created by small magnetic coils
placed around the mixing cell, and when the mixing is over, the particles can be retrieved
with a magnet for reuse.
Tuesday, June 16, 2009
June 16, 2009
EC10747
Skipping stones down a washboard road?
Drivers of backcountry dirt roads know it well: that teeth-rattling
feeling of rolling over washboard ripples. How does washboard form?
Why doesn't the passage of all those wheels pound the road flat? Now
researchers from France, the UK and Canada have some answers. The
washboard bounces the car on its suspension, but the existence of
washboard does not depend on having a suspension, or even a wheel! By
dragging a flat, inclined "plow" blade over a flat surface of sand,
the researchers showed that ripples formed spontaneously above a
certain speed, even though the plow had no springy suspension at all.
Instead, the bouncing process was more similar to skipping a stone
over the surface of water. Too slow, and the stone sinks or no
ripples form; move fast enough and the forces developed throw the
stone right off the surface. On a sandy road, the ripples are
amplified by successive passing wheels. The research showed that the
washboard road phenomnenon could be understood using similar
mathematical arguments to those used previously for skipping stones.
Unfortunately, the bad news is that a flat sandy road is intrinsically
unstable: ripples will always form above a threshold speed, just as a
stone must always skip if thrown fast enough.
***
AD10607
Joining quantum worlds: manipulating ultracold atoms without touching them
We develop a novel direction in quantum physics, quantum optics with quantum
gases, which will close the gap in the understanding of the interaction between
light and matter. On the one hand, optics, which considers the quantum
particles of light (photons), but classical atomic motion, is one of the most
successful fields of modern physics. On the other hand, a new field, quantum
atom optics, treats the motion of ultracold atoms trapped in light-created
potentials quantum mechanically. However, even in very involved problems, the
light potentials are still considered classically. Here we consider the
ultimate quantum limit of light-matter interaction, where the quantum natures
of both ultracold matter, e.g., a Bose-Einstein condensate (BEC), and light are
equally important. We use one of the most intriguing predictions of quantum
mechanics, which claims that the state of one quantum system (in our case,
ultracold gas) can be changed by the distant measurement of another system
(light), even if they do not interact. The key point is the concept of the
“entanglement”, which is possible only in the quantum world. We show, how to
prepare various quantum states of matter (e.g. Schroedinger cat states) by
simply measuring the photons scattered.
Skipping stones down a washboard road?
Drivers of backcountry dirt roads know it well: that teeth-rattling
feeling of rolling over washboard ripples. How does washboard form?
Why doesn't the passage of all those wheels pound the road flat? Now
researchers from France, the UK and Canada have some answers. The
washboard bounces the car on its suspension, but the existence of
washboard does not depend on having a suspension, or even a wheel! By
dragging a flat, inclined "plow" blade over a flat surface of sand,
the researchers showed that ripples formed spontaneously above a
certain speed, even though the plow had no springy suspension at all.
Instead, the bouncing process was more similar to skipping a stone
over the surface of water. Too slow, and the stone sinks or no
ripples form; move fast enough and the forces developed throw the
stone right off the surface. On a sandy road, the ripples are
amplified by successive passing wheels. The research showed that the
washboard road phenomnenon could be understood using similar
mathematical arguments to those used previously for skipping stones.
Unfortunately, the bad news is that a flat sandy road is intrinsically
unstable: ripples will always form above a threshold speed, just as a
stone must always skip if thrown fast enough.
***
AD10607
Joining quantum worlds: manipulating ultracold atoms without touching them
We develop a novel direction in quantum physics, quantum optics with quantum
gases, which will close the gap in the understanding of the interaction between
light and matter. On the one hand, optics, which considers the quantum
particles of light (photons), but classical atomic motion, is one of the most
successful fields of modern physics. On the other hand, a new field, quantum
atom optics, treats the motion of ultracold atoms trapped in light-created
potentials quantum mechanically. However, even in very involved problems, the
light potentials are still considered classically. Here we consider the
ultimate quantum limit of light-matter interaction, where the quantum natures
of both ultracold matter, e.g., a Bose-Einstein condensate (BEC), and light are
equally important. We use one of the most intriguing predictions of quantum
mechanics, which claims that the state of one quantum system (in our case,
ultracold gas) can be changed by the distant measurement of another system
(light), even if they do not interact. The key point is the concept of the
“entanglement”, which is possible only in the quantum world. We show, how to
prepare various quantum states of matter (e.g. Schroedinger cat states) by
simply measuring the photons scattered.
Monday, June 15, 2009
June 15, 2009
LB12052
Better Solar Cells
Organic solar cells based on conjugated polymers are promising
candidates for efficient low-cost photovoltaics, and have recently
reached power conversion efficiencies exceeding 6%. This is a
formidable achievement, considering that the light-generated positive
and negative charges are expected to be hardly separable, as they
attract each other much more strongly than in inorganic materials. In
our paper, we show why the separation of the charge pairs is so
efficient. Our considerations are based on a computer programme, a so-
called Monte Carlo simulation, by which the complex movement of charge
pairs in polymer-fullerene solar cells can be approximated very well.
We show that if the one constituent of a charge pair sits on an
polymer chain segment, it is attracted by the other charge the less
the longer the polymer chain is. This leads to the very efficient
separation of the charge pairs. Indeed, our simulations show a ten-
fold improvement of the resulting photocurrent when increasing the
length of the polymer chain segment from 1 to 10 nanometers, the
latter being a typical value for a conjugated polymer. Thus, our
findings explain why state-of-the-art polymer based organic solar
cells show such a good conversion of light to current.
***
LW11716
Liquid Jets from Nanorumbles Could Form Next Generation Inhalation Therapy
or Ink-Jet Printing Devices
Nanometer amplitude sound waves that travel on the surface in a manner
similar to earthquakes could very soon be exploited to effectively deliver
drug-laden aerosols and powders to our lungs or for ink-jet printing.
These nanometer 'surface acoustic waves', as they are known, are focussed
underneath a millimeter sized liquid drop. The very efficient transfer of
sound energy into the liquid then results in the generation of a
cylinder-like liquid jet that protrudes from the drop and persists over
centimeters in length. The jet then breaks up into micrometer sized
aerosol droplets as it stretches. As the liquid can act as a carrier for
drugs or even consist of ink or fuels, these surface acoustic waves could
well be on the way to comprise the next-generation inhalation therapy,
ink-jet printing or fuel injection devices.
***
LX11325E
Water-walking machine
We report the generation of directed self-propelled motion of a droplet
of aniline oil with a velocity on the order of centimeters per second on
an aqueous phase. The self-propelled motion persists for hours. The
droplet is preferred to control. It is promise that the self-propelled
motion will inspire the design of water-walking machine and transporter.
It is found that, depending on the initial conditions, the droplet shows
either circular or beeline motion in a circular Petri dish. The motion
of a droplet depends on volume of the droplet and concentration of
solution. The velocity decreases when volume of the droplet and
concentration of solution increase. Such unique motion is discussed in
terms of Marangoni-driven spreading under chemical nonequilibrium.
***
LA12348
A gravitational wave detector probes fluctuation theories of
nonequilibrium systems
Dissipative systems, like motors or living cells, need a power input to
sustain their functions. When the system is small, this power heavily
fluctuates around its mean value, due to the noisy imprint of the
underlying atomistic nature. However a system must not be necessarily as
small as a pollen particle to be dominated by microscopic fluctuations:
in this paper we use a ton-size resonant gravitational wave detector as
a test bench for statistical mechanics theories. First, we analyze the
active cooling scheme used to keep the Auriga detector at an effective
temperature of 20 milli-Kelvin (20 thousandths of a degree above
absolute zero), showing that it sustains an energy flow through the
system. Then, we study the fluctuations of the power exchanged with the
surroundings, reporting data obtained from the output of the detector
since the beginning of its operation in 2005. The availability of such a
large amount of experimental data make possible the analysis of rare
fluctuations, and gives a clear evidence for a model recently proposed
to describe power injection phenomena.
Better Solar Cells
Organic solar cells based on conjugated polymers are promising
candidates for efficient low-cost photovoltaics, and have recently
reached power conversion efficiencies exceeding 6%. This is a
formidable achievement, considering that the light-generated positive
and negative charges are expected to be hardly separable, as they
attract each other much more strongly than in inorganic materials. In
our paper, we show why the separation of the charge pairs is so
efficient. Our considerations are based on a computer programme, a so-
called Monte Carlo simulation, by which the complex movement of charge
pairs in polymer-fullerene solar cells can be approximated very well.
We show that if the one constituent of a charge pair sits on an
polymer chain segment, it is attracted by the other charge the less
the longer the polymer chain is. This leads to the very efficient
separation of the charge pairs. Indeed, our simulations show a ten-
fold improvement of the resulting photocurrent when increasing the
length of the polymer chain segment from 1 to 10 nanometers, the
latter being a typical value for a conjugated polymer. Thus, our
findings explain why state-of-the-art polymer based organic solar
cells show such a good conversion of light to current.
***
LW11716
Liquid Jets from Nanorumbles Could Form Next Generation Inhalation Therapy
or Ink-Jet Printing Devices
Nanometer amplitude sound waves that travel on the surface in a manner
similar to earthquakes could very soon be exploited to effectively deliver
drug-laden aerosols and powders to our lungs or for ink-jet printing.
These nanometer 'surface acoustic waves', as they are known, are focussed
underneath a millimeter sized liquid drop. The very efficient transfer of
sound energy into the liquid then results in the generation of a
cylinder-like liquid jet that protrudes from the drop and persists over
centimeters in length. The jet then breaks up into micrometer sized
aerosol droplets as it stretches. As the liquid can act as a carrier for
drugs or even consist of ink or fuels, these surface acoustic waves could
well be on the way to comprise the next-generation inhalation therapy,
ink-jet printing or fuel injection devices.
***
LX11325E
Water-walking machine
We report the generation of directed self-propelled motion of a droplet
of aniline oil with a velocity on the order of centimeters per second on
an aqueous phase. The self-propelled motion persists for hours. The
droplet is preferred to control. It is promise that the self-propelled
motion will inspire the design of water-walking machine and transporter.
It is found that, depending on the initial conditions, the droplet shows
either circular or beeline motion in a circular Petri dish. The motion
of a droplet depends on volume of the droplet and concentration of
solution. The velocity decreases when volume of the droplet and
concentration of solution increase. Such unique motion is discussed in
terms of Marangoni-driven spreading under chemical nonequilibrium.
***
LA12348
A gravitational wave detector probes fluctuation theories of
nonequilibrium systems
Dissipative systems, like motors or living cells, need a power input to
sustain their functions. When the system is small, this power heavily
fluctuates around its mean value, due to the noisy imprint of the
underlying atomistic nature. However a system must not be necessarily as
small as a pollen particle to be dominated by microscopic fluctuations:
in this paper we use a ton-size resonant gravitational wave detector as
a test bench for statistical mechanics theories. First, we analyze the
active cooling scheme used to keep the Auriga detector at an effective
temperature of 20 milli-Kelvin (20 thousandths of a degree above
absolute zero), showing that it sustains an energy flow through the
system. Then, we study the fluctuations of the power exchanged with the
surroundings, reporting data obtained from the output of the detector
since the beginning of its operation in 2005. The availability of such a
large amount of experimental data make possible the analysis of rare
fluctuations, and gives a clear evidence for a model recently proposed
to describe power injection phenomena.
Friday, June 12, 2009
June 12, 2009
LT11557AR
Recovering entanglement from environmental noise
Quantum entanglement, a fundamental property
ensuring security of key distribution and
efficiency of quantum computing, is extremely
sensitive to noise. The presence of noise alters
or even invalidates the transmission of quantum
information through communication channel, by
spoiling entanglement. In this paper we report
the proposal and the first realization of a
method which allows to restore entanglement after
its propagation over a strongly noisy channel.
In fact, up today different procedures have been
developed in order to recover entanglement but,
besides a certain amount of noise, entanglement
is anyhow completely lost, since all the present
techniques require a certain amount of
entanglement left after the transmission over the
noisy channel that is, the channel has not to be
an “entanglement-breaking” one. Here we report
the experimental realization of a new protocol,
the entanglement localization, which restores
entanglement from an entanglement breaking
channel. This method is based on the measurement
of environmental light (noise) which interacts
with the entangled signal leading to the loss of
entanglement and a quantum feed-forward
correction, revealing entanglement even if this
one completely disappeared. A direct application
of this entanglement localization can be
envisaged to improve in-line quantum communication, and in quantum computation.
***
EA10480
Human group formation in online guilds and offline gangs driven by a
common team dynamic
Quantifying human group dynamics represents a unique challenge. Unlike
animals and other biological systems, humans form groups in both real
(offline) and virtual (online) spaces - from potentially dangerous
street gangs populated mostly by disaffected male youths, through to
the massive global guilds in online role-playing games for which
membership currently exceeds tens of millions of people from all
possible backgrounds, age-groups and genders. We have compiled and
analyzed data for these two seemingly unrelated offline and online
human activities, and have uncovered an unexpected quantitative link
between them. Although their overall dynamics differ visibly, we find
that a common team-based model can accurately reproduce the
quantitative features of each simply by adjusting the average
tolerance level and attribute range for each population. By contrast,
we find no evidence to support a version of the model based on
like-seeking-like (i.e. kinship or `homophily').
***
LC12134
Graphene pseudospintronics: A new twist on spin-based electronics
In an article appearing in Physical Review Letters, we propose a new electronic device based upon a unique property of graphene.
Graphene is a conducting material made up of a single layer of carbon atoms
which supports a new quantum number called pseudospin. Pseudospin is
manifested in many exotic properties of graphene, including the unusual
sequencing of plateaus in the quantum Hall effect, suppression of
backscattering, and Klein tunneling at interfaces.
The presence of pseudospin in graphene draws parallels with the physical
spin of electrons, including the possibility of exploiting the pseudospin
degree of freedom in a similar way as physical spin in spintronics and
quantum computing applications. So far, this has proved elusive because of
chirality in graphene: the orientation of an electron's pseudospin is
inextricably linked to the direction of its momentum, preventing its use as
an independently-tuneable degree of freedom.
We propose that "pseudospintronics" can be realized in
two coupled layers of graphene by applying external gate potentials. Their
numerical calculations demonstrate the performance of two devices: a
pseudospin-based version of a spin valve and a pseudospin-based spin-valve
transistor with a large on-off ratio.
***
BDR1159
Hybrid light-matter 'particles' created in films of silver nanostructures
New modes of light called polaritons can be created when there is a
very strong interaction between light and matter. Control and
manipulation of these new 'particles' is of considerable interest for
the development of novel devices including lasers, sensors and fast
optical switches which could one day replace electronic transistors.
In this paper we have created films of silver nanostructures which
capture and strongly confine light. This trapped light then interacts
with electrons in a surrounding layer of dye molecules, resulting in
the formation of new coupled electromagnetic modes. By controlling the
energy and strength of these hybrid particles, we have observed a
massive enhancement in Raman scattering from the dye molecules. Raman
scattering is a normally weak optical emission which provides a
spectroscopic fingerprint from molecules, and is therefore an important
analytical tool for molecular sensors.
***
LB12391
IS SUPERCONDUCTIVITY IN THE IRON AGE DRIVEN BY
SCHIZOPHRENIA OF FRUSTRATED ELECTRONS?
Superconductivity recently entered the "iron age" with discovery
of ferropnictides, where magnetism gives way to a superconductor
upon carrier doping. This unexpected finding is reinforced by an
equally unusual causal connection: the non-superconductive metal
lies outside the scope of the "standard model" of metals, where
long-lived electronic states carry the current. Thus, ferropnictides
resemble the famous cuprates in this respect.
Here, we propose a new mechanism for superconductivity in ferropnictides.
Previously, we showed how a combination of "frustrated" and "dualistic"
electrons unable to choose between localization and free motion gave
birth to an unusual metal. We explore how such a state contains the
seeds of the electronic glue that pairs electrons into cooper pairs in
these fascinating materials. This superconductive state is very unusual:
the pair amplitude switches sign between electron and hole-like fermi
sheets. In addition, we propose that the pair amplitude vanishes on
parts of the full Fermi surface. We also show how our work quantitatively
describes a wide range of experimental benchmarks in a natural way, and
reconciles apparently conflicting interpretations from different probes.
Seemingly, as opposed to normal human experience, dualistic
"schizophrenia"
and frustration in combination can lead to fascinating outcomes in
condensed
matter.
***
LA12438
Medium Modifications Resolve Anomalous NuTeV Result
A new calculation of nuclear medium effects may resolve
the NuTeV anomaly, a puzzling experimental result that
had indicated strong disagreement with the Standard Model
of particle physics.
The NuTeV anomaly came about when experimenters at
Fermilab's NuTeV (Neutrinos at the Tevatron) experiment
measured the ratio of two types of particles, neutrinos
and muons, emerging from high energy collisions of neutrinos
with an iron target. They found that about one percent
fewer collisions produced neutrinos than predicted by the
Standard Model.
One common assumption that was used in the analysis of the
NuTeV data involved a correction for an imbalance in the
number of protons and neutrons in the nucleus of iron. In
the NuTeV analysis, this correction was made by simply
subtracting the contribution of the excess neutrons.
In this Letter, a collaboration involving researchers
from Tokai University, the University of Washington and
the Department of Energy's Jefferson Lab has revealed a
novel EMC effect in which the isovector nuclear force
generated by those extra neutrons results in a subtle
change in the quark structure of every nucleon in the
nucleus.
The discovery of this isovector EMC effect implies that it
is not enough to simply subtract the scattering from the extra
neutrons, because the structure of the remaining nucleons is
still modified by their presence. This leads to a residual
correction, of a sign and magnitude which is essentially model
independent and which removes at least half of the NuTeV anomaly.
When this effect is combined with the well known correction for
charge symmetry violation in the nucleon itself, the NuTeV data
is in fact in excellent agreement with the Standard Model.
In this sense, the NuTeV anomaly may be seen as providing crucial
evidence for a conceptual change in our understanding of nuclear
structure in which the quark structure of the bound nucleon is
fundamentally modified by the medium -- a result arguably as
important as the original interpretation in terms of physics
beyond the Standard Model.
***
EC10577
Magnetic Drugs
Drugs attached to magnetic particles can be manipulated inside the
bloodstream by means of applied magnetic fields, making it possible to
greatly decrease the side-effects of e.g. chemotherapy. In this paper
we derive a scaling relation between the magnetic force and the amount
of particles that can be localized at a desired target location,
revealing that
a four times higher force is initially needed to double the efficiency
of a specific treatment. This result helps explaining a wide variety of
experimental results and follows naturally from the observation that the
blood
flow velocity close to the vessel wall increases approximately linearly
with
distance. For more accurate predictions, formulas are derived for the
particle
motion in idealized arterial flows. The obtained results can also be
useful for
the magnetic separation of materials in the laboratory, the testing of
numerical
codes, and a possible future application to the treatment of
atherosclerosis.
***
AE10616
Isotope effect in dissociative electron attachment to acetylene
"Towards the understanding of electron-driven
chemistry in polyatomic molecules"
Breaking molecules by hitting them with free
electrons is very important for a number of
technologies, such as plasma processing in the
manufacture of integrated circuits or for
radiotherapy in medicine. It is relatively easy
to determine that a molecule breaks when hit by
an electron, but much harder to measure exactly
how much they break, how many molecules are
broken by a given number of electrons. This
information is available for only few molecules,
particularly for only few molecules larger than
two atoms. In this paper, we present some
significant improvements of the instrumentation
required to obtain this information, and results
for the prototype molecule acetylene. We further
measured that acetylene where hydrogen is
replaced by heavy hydrogen (deuterium) is
15-times more resistant to breaking by electron
impact than normal acetylene. The importance of
the results lies also in the fact that theory has
advanced to the point where such reactions can be
studied. This allows an interplay between theory
and experiment, with experiment validating
the theory and theory helping to explain the mechanisms in the experiment.
Recovering entanglement from environmental noise
Quantum entanglement, a fundamental property
ensuring security of key distribution and
efficiency of quantum computing, is extremely
sensitive to noise. The presence of noise alters
or even invalidates the transmission of quantum
information through communication channel, by
spoiling entanglement. In this paper we report
the proposal and the first realization of a
method which allows to restore entanglement after
its propagation over a strongly noisy channel.
In fact, up today different procedures have been
developed in order to recover entanglement but,
besides a certain amount of noise, entanglement
is anyhow completely lost, since all the present
techniques require a certain amount of
entanglement left after the transmission over the
noisy channel that is, the channel has not to be
an “entanglement-breaking” one. Here we report
the experimental realization of a new protocol,
the entanglement localization, which restores
entanglement from an entanglement breaking
channel. This method is based on the measurement
of environmental light (noise) which interacts
with the entangled signal leading to the loss of
entanglement and a quantum feed-forward
correction, revealing entanglement even if this
one completely disappeared. A direct application
of this entanglement localization can be
envisaged to improve in-line quantum communication, and in quantum computation.
***
EA10480
Human group formation in online guilds and offline gangs driven by a
common team dynamic
Quantifying human group dynamics represents a unique challenge. Unlike
animals and other biological systems, humans form groups in both real
(offline) and virtual (online) spaces - from potentially dangerous
street gangs populated mostly by disaffected male youths, through to
the massive global guilds in online role-playing games for which
membership currently exceeds tens of millions of people from all
possible backgrounds, age-groups and genders. We have compiled and
analyzed data for these two seemingly unrelated offline and online
human activities, and have uncovered an unexpected quantitative link
between them. Although their overall dynamics differ visibly, we find
that a common team-based model can accurately reproduce the
quantitative features of each simply by adjusting the average
tolerance level and attribute range for each population. By contrast,
we find no evidence to support a version of the model based on
like-seeking-like (i.e. kinship or `homophily').
***
LC12134
Graphene pseudospintronics: A new twist on spin-based electronics
In an article appearing in Physical Review Letters, we propose a new electronic device based upon a unique property of graphene.
Graphene is a conducting material made up of a single layer of carbon atoms
which supports a new quantum number called pseudospin. Pseudospin is
manifested in many exotic properties of graphene, including the unusual
sequencing of plateaus in the quantum Hall effect, suppression of
backscattering, and Klein tunneling at interfaces.
The presence of pseudospin in graphene draws parallels with the physical
spin of electrons, including the possibility of exploiting the pseudospin
degree of freedom in a similar way as physical spin in spintronics and
quantum computing applications. So far, this has proved elusive because of
chirality in graphene: the orientation of an electron's pseudospin is
inextricably linked to the direction of its momentum, preventing its use as
an independently-tuneable degree of freedom.
We propose that "pseudospintronics" can be realized in
two coupled layers of graphene by applying external gate potentials. Their
numerical calculations demonstrate the performance of two devices: a
pseudospin-based version of a spin valve and a pseudospin-based spin-valve
transistor with a large on-off ratio.
***
BDR1159
Hybrid light-matter 'particles' created in films of silver nanostructures
New modes of light called polaritons can be created when there is a
very strong interaction between light and matter. Control and
manipulation of these new 'particles' is of considerable interest for
the development of novel devices including lasers, sensors and fast
optical switches which could one day replace electronic transistors.
In this paper we have created films of silver nanostructures which
capture and strongly confine light. This trapped light then interacts
with electrons in a surrounding layer of dye molecules, resulting in
the formation of new coupled electromagnetic modes. By controlling the
energy and strength of these hybrid particles, we have observed a
massive enhancement in Raman scattering from the dye molecules. Raman
scattering is a normally weak optical emission which provides a
spectroscopic fingerprint from molecules, and is therefore an important
analytical tool for molecular sensors.
***
LB12391
IS SUPERCONDUCTIVITY IN THE IRON AGE DRIVEN BY
SCHIZOPHRENIA OF FRUSTRATED ELECTRONS?
Superconductivity recently entered the "iron age" with discovery
of ferropnictides, where magnetism gives way to a superconductor
upon carrier doping. This unexpected finding is reinforced by an
equally unusual causal connection: the non-superconductive metal
lies outside the scope of the "standard model" of metals, where
long-lived electronic states carry the current. Thus, ferropnictides
resemble the famous cuprates in this respect.
Here, we propose a new mechanism for superconductivity in ferropnictides.
Previously, we showed how a combination of "frustrated" and "dualistic"
electrons unable to choose between localization and free motion gave
birth to an unusual metal. We explore how such a state contains the
seeds of the electronic glue that pairs electrons into cooper pairs in
these fascinating materials. This superconductive state is very unusual:
the pair amplitude switches sign between electron and hole-like fermi
sheets. In addition, we propose that the pair amplitude vanishes on
parts of the full Fermi surface. We also show how our work quantitatively
describes a wide range of experimental benchmarks in a natural way, and
reconciles apparently conflicting interpretations from different probes.
Seemingly, as opposed to normal human experience, dualistic
"schizophrenia"
and frustration in combination can lead to fascinating outcomes in
condensed
matter.
***
LA12438
Medium Modifications Resolve Anomalous NuTeV Result
A new calculation of nuclear medium effects may resolve
the NuTeV anomaly, a puzzling experimental result that
had indicated strong disagreement with the Standard Model
of particle physics.
The NuTeV anomaly came about when experimenters at
Fermilab's NuTeV (Neutrinos at the Tevatron) experiment
measured the ratio of two types of particles, neutrinos
and muons, emerging from high energy collisions of neutrinos
with an iron target. They found that about one percent
fewer collisions produced neutrinos than predicted by the
Standard Model.
One common assumption that was used in the analysis of the
NuTeV data involved a correction for an imbalance in the
number of protons and neutrons in the nucleus of iron. In
the NuTeV analysis, this correction was made by simply
subtracting the contribution of the excess neutrons.
In this Letter, a collaboration involving researchers
from Tokai University, the University of Washington and
the Department of Energy's Jefferson Lab has revealed a
novel EMC effect in which the isovector nuclear force
generated by those extra neutrons results in a subtle
change in the quark structure of every nucleon in the
nucleus.
The discovery of this isovector EMC effect implies that it
is not enough to simply subtract the scattering from the extra
neutrons, because the structure of the remaining nucleons is
still modified by their presence. This leads to a residual
correction, of a sign and magnitude which is essentially model
independent and which removes at least half of the NuTeV anomaly.
When this effect is combined with the well known correction for
charge symmetry violation in the nucleon itself, the NuTeV data
is in fact in excellent agreement with the Standard Model.
In this sense, the NuTeV anomaly may be seen as providing crucial
evidence for a conceptual change in our understanding of nuclear
structure in which the quark structure of the bound nucleon is
fundamentally modified by the medium -- a result arguably as
important as the original interpretation in terms of physics
beyond the Standard Model.
***
EC10577
Magnetic Drugs
Drugs attached to magnetic particles can be manipulated inside the
bloodstream by means of applied magnetic fields, making it possible to
greatly decrease the side-effects of e.g. chemotherapy. In this paper
we derive a scaling relation between the magnetic force and the amount
of particles that can be localized at a desired target location,
revealing that
a four times higher force is initially needed to double the efficiency
of a specific treatment. This result helps explaining a wide variety of
experimental results and follows naturally from the observation that the
blood
flow velocity close to the vessel wall increases approximately linearly
with
distance. For more accurate predictions, formulas are derived for the
particle
motion in idealized arterial flows. The obtained results can also be
useful for
the magnetic separation of materials in the laboratory, the testing of
numerical
codes, and a possible future application to the treatment of
atherosclerosis.
***
AE10616
Isotope effect in dissociative electron attachment to acetylene
"Towards the understanding of electron-driven
chemistry in polyatomic molecules"
Breaking molecules by hitting them with free
electrons is very important for a number of
technologies, such as plasma processing in the
manufacture of integrated circuits or for
radiotherapy in medicine. It is relatively easy
to determine that a molecule breaks when hit by
an electron, but much harder to measure exactly
how much they break, how many molecules are
broken by a given number of electrons. This
information is available for only few molecules,
particularly for only few molecules larger than
two atoms. In this paper, we present some
significant improvements of the instrumentation
required to obtain this information, and results
for the prototype molecule acetylene. We further
measured that acetylene where hydrogen is
replaced by heavy hydrogen (deuterium) is
15-times more resistant to breaking by electron
impact than normal acetylene. The importance of
the results lies also in the fact that theory has
advanced to the point where such reactions can be
studied. This allows an interplay between theory
and experiment, with experiment validating
the theory and theory helping to explain the mechanisms in the experiment.
Wednesday, June 10, 2009
June 10, 2009
LA12407
A Direct Insight on How Strain at Grain Boundaries Suppresses High-Temperature Superconductivity
A new study shows how a reduction in mechanical strain at grain boundaries in high-temperature superconductors (HTS) can significantly improve their performance. One of the main challenges in developing long-length, high-quality HTS wires is to mitigate the effect of granularity on their current-carrying capability. Grains with near perfect crystalline structure can sustain current densities on the order of 10 million amperes per square centimeter at very low temperatures. These currents have a hard time crossing boundaries between grains, since crystalline imperfections at grain boundaries introduce large strain fields that are prone to block current flow. Researchers showed that the current blocking in thin-film yttrium-barium-copper-oxide (YBCO) superconductors can be largely reduced by compressing the grain boundaries. The applied compression tends to reduce the grain boundary strain fields and significantly raise the maximum sustainable current density. These results could lead to lower cost and significantly improved performance of superconductors in a wide variety of applications, such as electric power transmission, electric power grid reliability, and advanced physics research.
***
LU11972
Squeezing more information in a single photon
In the emerging field of quantum information, a
single photon of light is commonly used for
carrying one elementary piece of information,
that is a so-called “qubit”. This qubit is
typically encoded in the polarization of the
photon, a property associated with the
orientation of its electromagnetic field. There
is however a possibility to squeeze additional
information in a single photon, by exploiting
other degrees of freedom of light. One such
additional degree of freedom that is promising to
this purpose is the orbital angular momentum,
associated with the helical wavefront structure
of the photon (or to quantum light vortices). To
this purpose, however, it is essential to be able
to freely transfer information back and forth
between the two degrees of freedom of the photon.
In this paper, we have developed and demonstrated
for the first time optical devices enabling just
this transfer. This accomplishment will open the
way for future more convenient schemes for
quantum cryptography and other applications of the quantum properties of light.
***
LW11544
Maxwell's Demon's Peaceful Coexistence with the Second Law of Thermodynamics
After a long controversy by numerous scientists and philosophers since 1867,
we have made a critical step toward the resolution of the paradox of
“Maxwell’s demon,” which is often claimed to have the capability of
extracting useful energy from an environment like a perpetual motion, by
performing information processing at a microscopic level. The demon was
proposed by J. C. Maxwell, a giant in modern physics, and has ever
threatened the foundation of the second law of thermodynamics. In this
Letter, we have explicitly shown that famous proposals of the resolution of
the paradox proposed in 1950’s and 80’s break down in general, and jointed
them by establishing a novel framework of theoretical physics, which we call
“information thermodynamics.” Our result can generally be applied to
nanoscale information processing; we have found the general lower bound of
the energy cost needed for typical information processing (including quantum
regime), such as measurement, erasure of information, and feedback control.
It has turned out that the Maxwell’s demon is no longer an archaic paradox,
but can be realized as an actual device which would play an important role
in the modern and future nanotechnologies such as artificial nanomachines.
***
LY11606
A New Way of Understanding Interference
In this work, a novel approach toward understanding interference in
quantum dynamics is proposed. Within this hydrodynamical formulation,
the formation of new time-dependent topological structures, called
quantum caves (in analogy to stalactites and stalagmites observed in
a geological cave) develop around vortices and stagnation points in
the probability flow field, showing a new way to describe the
quantization of the circulation of trajectories. Analysis of the
head-on collision of two wave packets is carried out in the complex
plane and the corresponding interference is associated with a
resonant process, the lifetime of which can be analyzed and calculated.
Quantum interference is involved in a very wide range of experiments
going from superconducting devices, coherent control of chemical
reactions, interferometry to quantum information and computing.
A Direct Insight on How Strain at Grain Boundaries Suppresses High-Temperature Superconductivity
A new study shows how a reduction in mechanical strain at grain boundaries in high-temperature superconductors (HTS) can significantly improve their performance. One of the main challenges in developing long-length, high-quality HTS wires is to mitigate the effect of granularity on their current-carrying capability. Grains with near perfect crystalline structure can sustain current densities on the order of 10 million amperes per square centimeter at very low temperatures. These currents have a hard time crossing boundaries between grains, since crystalline imperfections at grain boundaries introduce large strain fields that are prone to block current flow. Researchers showed that the current blocking in thin-film yttrium-barium-copper-oxide (YBCO) superconductors can be largely reduced by compressing the grain boundaries. The applied compression tends to reduce the grain boundary strain fields and significantly raise the maximum sustainable current density. These results could lead to lower cost and significantly improved performance of superconductors in a wide variety of applications, such as electric power transmission, electric power grid reliability, and advanced physics research.
***
LU11972
Squeezing more information in a single photon
In the emerging field of quantum information, a
single photon of light is commonly used for
carrying one elementary piece of information,
that is a so-called “qubit”. This qubit is
typically encoded in the polarization of the
photon, a property associated with the
orientation of its electromagnetic field. There
is however a possibility to squeeze additional
information in a single photon, by exploiting
other degrees of freedom of light. One such
additional degree of freedom that is promising to
this purpose is the orbital angular momentum,
associated with the helical wavefront structure
of the photon (or to quantum light vortices). To
this purpose, however, it is essential to be able
to freely transfer information back and forth
between the two degrees of freedom of the photon.
In this paper, we have developed and demonstrated
for the first time optical devices enabling just
this transfer. This accomplishment will open the
way for future more convenient schemes for
quantum cryptography and other applications of the quantum properties of light.
***
LW11544
Maxwell's Demon's Peaceful Coexistence with the Second Law of Thermodynamics
After a long controversy by numerous scientists and philosophers since 1867,
we have made a critical step toward the resolution of the paradox of
“Maxwell’s demon,” which is often claimed to have the capability of
extracting useful energy from an environment like a perpetual motion, by
performing information processing at a microscopic level. The demon was
proposed by J. C. Maxwell, a giant in modern physics, and has ever
threatened the foundation of the second law of thermodynamics. In this
Letter, we have explicitly shown that famous proposals of the resolution of
the paradox proposed in 1950’s and 80’s break down in general, and jointed
them by establishing a novel framework of theoretical physics, which we call
“information thermodynamics.” Our result can generally be applied to
nanoscale information processing; we have found the general lower bound of
the energy cost needed for typical information processing (including quantum
regime), such as measurement, erasure of information, and feedback control.
It has turned out that the Maxwell’s demon is no longer an archaic paradox,
but can be realized as an actual device which would play an important role
in the modern and future nanotechnologies such as artificial nanomachines.
***
LY11606
A New Way of Understanding Interference
In this work, a novel approach toward understanding interference in
quantum dynamics is proposed. Within this hydrodynamical formulation,
the formation of new time-dependent topological structures, called
quantum caves (in analogy to stalactites and stalagmites observed in
a geological cave) develop around vortices and stagnation points in
the probability flow field, showing a new way to describe the
quantization of the circulation of trajectories. Analysis of the
head-on collision of two wave packets is carried out in the complex
plane and the corresponding interference is associated with a
resonant process, the lifetime of which can be analyzed and calculated.
Quantum interference is involved in a very wide range of experiments
going from superconducting devices, coherent control of chemical
reactions, interferometry to quantum information and computing.
Friday, June 5, 2009
June5, 2009
BB10965
Birth of the Saser
In this paper we describe a new type of acoustic laser device, or saser
(for sound amplification by stimulated emission of radiation), based on
a semiconductor nanostructure pumped by a light beam. Such a device has
the potential to transform the field of acoustics just like the laser
has transformed optics in the half-century since its invention. We
present experimental evidence for the device working as a saser, which
is a pumping power threshold above which the sound emission increases in
intensity rapidly and becomes more directional. These properties are
analogous to those of the light emission from semiconductor lasers
common in optical disc readers etc. The experimental evidence is backed
up by theoretical calculations which predict that saser oscillation is
indeed possible in the device. This is not the first saser device to be
demonstrated, we previously demonstrated an electrically pumped device.
However, we believe this is the first to emit transverse-polarized, or
shear, sound waves in the terahertz frequency range. Such sound waves
have applications in imaging and testing of nanostructures and for the
control of the electrical, optical and magnetic properties of
nanodevices.
Birth of the Saser
In this paper we describe a new type of acoustic laser device, or saser
(for sound amplification by stimulated emission of radiation), based on
a semiconductor nanostructure pumped by a light beam. Such a device has
the potential to transform the field of acoustics just like the laser
has transformed optics in the half-century since its invention. We
present experimental evidence for the device working as a saser, which
is a pumping power threshold above which the sound emission increases in
intensity rapidly and becomes more directional. These properties are
analogous to those of the light emission from semiconductor lasers
common in optical disc readers etc. The experimental evidence is backed
up by theoretical calculations which predict that saser oscillation is
indeed possible in the device. This is not the first saser device to be
demonstrated, we previously demonstrated an electrically pumped device.
However, we believe this is the first to emit transverse-polarized, or
shear, sound waves in the terahertz frequency range. Such sound waves
have applications in imaging and testing of nanostructures and for the
control of the electrical, optical and magnetic properties of
nanodevices.
Tuesday, June 2, 2009
June 2, 2009
LZ11522
Plasma Reduces Drag, Enhances Lift
Airplanes may some day travel the skies enveloped in glowing layers of plasma, thanks to research that shows that plasma can dramatically improve air flow. The result comes from experiments on cylinders equipped with radio frequency plasma generators. The plasma decreased the production of drag-inducing, energy-wasting vortexes behind the cylinder. Although plasma generators require energy to operate, the energy savings that come with reduced drag would far outweigh the cost of running the generators. In a recent experiment, plasma discharges decreased drag on a cylinder by 8%. This is a significant drag reduction, which could lead to major fuel savings if the technology can be successfully applied to aircraft. In addition, the technique could be useful in other industrial applications where gas flow is important.
***
EA10480
Team spirit links millions of online gamers to urban street gangs
What do the 11 million players of the world's most popular Internet
game World of Warcraft, have in common with street-gang members in
downtown Long Beach, California? They are both driven by the same team
spirit, according to a recent study by an interdisciplinary team of
physicists, gaming experts, and gang sociologists. In 1828 Bulwer-
Lytton Pelham said "It is literally true in the systematised roguery
of London, that 'birds of a feather flock together", an idea which
stems back to ancient Greek times in the apocryphal book of
Ecclesiasticus and which underpins much of our current theories about
how animals group or flock. However, while members of a given species
(e.g. birds) undoubtedly group together, the researchers found that
such groups actually prefer a diversity of *characters*. It is like a
successful Superbowl team -- they are all football players, yet they
would be doomed to failure if they were all quarterbacks, no matter
how great they were individually. Sounds reasonable, but proving it
was hard since it required state-of-the-art databases and also
exhaustive comparisons between team-based and kin-based models. The
results are not only new for sociology, they represent new physics in
that a full mathematical description requires generalizing coalescence-
fragmentation theory to include the distinct 'character' of individual
objects. Practical applications could eventually include the
predictive evolution of human groups in other online and offline
scenarios, including terrorist activity.
***
LA12436
A model of navigation in social networks deciphered
Two groups, one in Switzerland (EPFL) and the other a collaboration
between Israel (Bar-Ilan) and US (Clarkson) universities,
simultaneously and independently unfolded a paradigmatic model of
searching in social networks, partly unsolved for almost a decade.
It is well known that individuals in a social network are separated by
just "six degrees", that is, six steps on the network. Yet the
question of how these short paths are actually found is still open. In
a seminal paper published in 2000, Jon Kleinberg proposed a social
network model in which long-range links render a social network
``small-world’’, and at the same time provide the means for efficient
delivery of messages (Nature 406, 845). However, only approximate
estimates, in the form of upper and lower bounds, were known for the
actual delivery time. After almost a decade, the two groups have
finally succeeded in deriving an exact expression for the dependence
of the delivery time on the number of individuals, partly confirming
Kleinberg’s conjectures on the nature of the long-range links that
makes the search process effective. Remarkably, the two groups have
used different mathematical approaches, nevertheless reaching the very
same conclusions. The proposed solution has also enriched our
understanding of the conditions that make networks navigable: it
addresses the issues of network construction and maintenance costs and
the possibility of losing messages, which are further criteria that
must be taken into account for network models and search algorithms to
be relevant for real networks.
***
LE11894
Splitting spacetime back into space and time as a road to Quantum
Gravity
Despite the tremendous individual successes of General Relativity and
Quantum Field Theory, conventional approaches at merging them in order
to construct a theory of Quantum Gravity generally fail. Petr Horava
has recently proposed that such difficulties might be overcome by
refraining from treating space and time on equal footing at small
scales, with the hope of arranging for an approximate recovery of the
notion of spacetime and the related symmetries (Lorentz invariance)
only at relatively low energies.
In our article we begin to connect these abstract ideas with
observational reality: based on Horava's initial proposal we develop
step by step a theory that in principle has enough richness to be
compatible with experiments. It contains an adjustable Newton's
constant and an independently adjustable cosmological constant. The
departure of the theory from the standard spacetime picture is
characterized by a relatively small set of coupling constants, and
kept under tight control. There are still many detailed precision
tests that this model would have to pass before physicists would
consider it a serious candidate for a quantum theory of gravity. At
present, it is promising and seems to have all the right ingredients.
Plasma Reduces Drag, Enhances Lift
Airplanes may some day travel the skies enveloped in glowing layers of plasma, thanks to research that shows that plasma can dramatically improve air flow. The result comes from experiments on cylinders equipped with radio frequency plasma generators. The plasma decreased the production of drag-inducing, energy-wasting vortexes behind the cylinder. Although plasma generators require energy to operate, the energy savings that come with reduced drag would far outweigh the cost of running the generators. In a recent experiment, plasma discharges decreased drag on a cylinder by 8%. This is a significant drag reduction, which could lead to major fuel savings if the technology can be successfully applied to aircraft. In addition, the technique could be useful in other industrial applications where gas flow is important.
***
EA10480
Team spirit links millions of online gamers to urban street gangs
What do the 11 million players of the world's most popular Internet
game World of Warcraft, have in common with street-gang members in
downtown Long Beach, California? They are both driven by the same team
spirit, according to a recent study by an interdisciplinary team of
physicists, gaming experts, and gang sociologists. In 1828 Bulwer-
Lytton Pelham said "It is literally true in the systematised roguery
of London, that 'birds of a feather flock together", an idea which
stems back to ancient Greek times in the apocryphal book of
Ecclesiasticus and which underpins much of our current theories about
how animals group or flock. However, while members of a given species
(e.g. birds) undoubtedly group together, the researchers found that
such groups actually prefer a diversity of *characters*. It is like a
successful Superbowl team -- they are all football players, yet they
would be doomed to failure if they were all quarterbacks, no matter
how great they were individually. Sounds reasonable, but proving it
was hard since it required state-of-the-art databases and also
exhaustive comparisons between team-based and kin-based models. The
results are not only new for sociology, they represent new physics in
that a full mathematical description requires generalizing coalescence-
fragmentation theory to include the distinct 'character' of individual
objects. Practical applications could eventually include the
predictive evolution of human groups in other online and offline
scenarios, including terrorist activity.
***
LA12436
A model of navigation in social networks deciphered
Two groups, one in Switzerland (EPFL) and the other a collaboration
between Israel (Bar-Ilan) and US (Clarkson) universities,
simultaneously and independently unfolded a paradigmatic model of
searching in social networks, partly unsolved for almost a decade.
It is well known that individuals in a social network are separated by
just "six degrees", that is, six steps on the network. Yet the
question of how these short paths are actually found is still open. In
a seminal paper published in 2000, Jon Kleinberg proposed a social
network model in which long-range links render a social network
``small-world’’, and at the same time provide the means for efficient
delivery of messages (Nature 406, 845). However, only approximate
estimates, in the form of upper and lower bounds, were known for the
actual delivery time. After almost a decade, the two groups have
finally succeeded in deriving an exact expression for the dependence
of the delivery time on the number of individuals, partly confirming
Kleinberg’s conjectures on the nature of the long-range links that
makes the search process effective. Remarkably, the two groups have
used different mathematical approaches, nevertheless reaching the very
same conclusions. The proposed solution has also enriched our
understanding of the conditions that make networks navigable: it
addresses the issues of network construction and maintenance costs and
the possibility of losing messages, which are further criteria that
must be taken into account for network models and search algorithms to
be relevant for real networks.
***
LE11894
Splitting spacetime back into space and time as a road to Quantum
Gravity
Despite the tremendous individual successes of General Relativity and
Quantum Field Theory, conventional approaches at merging them in order
to construct a theory of Quantum Gravity generally fail. Petr Horava
has recently proposed that such difficulties might be overcome by
refraining from treating space and time on equal footing at small
scales, with the hope of arranging for an approximate recovery of the
notion of spacetime and the related symmetries (Lorentz invariance)
only at relatively low energies.
In our article we begin to connect these abstract ideas with
observational reality: based on Horava's initial proposal we develop
step by step a theory that in principle has enough richness to be
compatible with experiments. It contains an adjustable Newton's
constant and an independently adjustable cosmological constant. The
departure of the theory from the standard spacetime picture is
characterized by a relatively small set of coupling constants, and
kept under tight control. There are still many detailed precision
tests that this model would have to pass before physicists would
consider it a serious candidate for a quantum theory of gravity. At
present, it is promising and seems to have all the right ingredients.
Tuesday, May 26, 2009
May 26, 2009
LB11715
Starting up a quantum engine
How to put a purely quantum engine into action?
This challenge can now be achieved via suitably manipulating cold atoms.
Our group at the University of Augsburg unravelled this task by presenting
a first realization of this objective. Astonishingly, although our devised
quantum engine utilizes solely those ideal, non-classical principles
of quantum dynamics its response nevertheless acquires many features
of a conventional, classical electric motor. The stylized quantum motor
consists of two interacting cold quantum particles, one the ``rotor''
and another one acting as the ``starter'', that are trapped in a ring-shaped
optical potential (see figure). The ``rotor''-atom is set into directed
controllable rotational motion by exerting a time-periodic magnetic field.
The quest for harvesting unidirectional rotor motion rests upon the key element
of using a non-biased drive that dynamically breaks the forward-backward symmetry.
Exploring the intriguing operational range of the motor near resonances
paves the way for such a quantum engine to perform reliable work against
an external load.
***
EC10646
Collision and adhesion of solid particles
A particle colliding with a wall may either bounce off or adhere to the surface. If it bounces off, it will do so with a reduced velocity, having lost mechanical energy as we can observe when throwing a rubber ball against a wall. Mathematical models can predict the velocity and rate of rotation of a spherical particle after a collision. The physical principles behind these models are well-known, such as Newton's second law: mass times acceleration equals the forces acting on the sphere. However, quantifying these forces is difficult. During collision the particle deforms elastically and plastically, slides and may roll. Additionally, the wall attracts the particle due to molecular interactions. The elastic deformation generates a force acting away from the wall, tending to make the particle rebound; however, with a sufficiently strong attractive force the particle will not escape but adhere (a "potential-well" effect). We do not often see a rubber ball adhere, but for very small particles (micro- or nanometers) this adhesive force is relatively much stronger. Kosinski and Hoffmann at the University of Bergen have extended the well-known "hard-sphere" collision model of Crowe et al. to account also for attractive forces and thus possible deposition. This is relevant for a variety of physical systems, such as sand, wax or hydrate particles flowing in oil pipelines, fine particles in pneumatic conveying or even ash in the crater of a volcano.
***
LC12765
Identifying a Black Hole's 'Fingerprint'
Worldwide, a race is underway to detect gravitational radiation generated by
pairs of black holes as they spiral together and coalesce. However,
inspiralling binaries represent only a small fraction of a much larger
population of mostly 'quiescent' black holes, which are far harder to
detect. It has been suggested that the presence of quiescent black
holes may be inferred from the 'fingerprint' they impose upon
radiation which impinges upon them. In this paper, we investigate one
possible fingerprint: the scattering and polarization pattern created
when a planar electromagnetic wave interacts with a (non-rotating)
black hole. The interference of rays passing in opposite senses around
the black hole creates a distinctive oscillatory diffraction
pattern. A segment of the incident wavefront undergoes a complete
orbit to create a 'glory' in the backward direction. This is manifest
as a bright ring around the pole at 180 degrees, whose angular
diameter is proportional to the wavelength. We present a unified
picture of the scattering of all waves (scalar, spinor,
electromagnetic and gravitational) for the first time, and demonstrate
that the 'glory' depends strongly on the intrinsic 'spin' of the wave,
in agreement with a prediction made over two decades ago.
Starting up a quantum engine
How to put a purely quantum engine into action?
This challenge can now be achieved via suitably manipulating cold atoms.
Our group at the University of Augsburg unravelled this task by presenting
a first realization of this objective. Astonishingly, although our devised
quantum engine utilizes solely those ideal, non-classical principles
of quantum dynamics its response nevertheless acquires many features
of a conventional, classical electric motor. The stylized quantum motor
consists of two interacting cold quantum particles, one the ``rotor''
and another one acting as the ``starter'', that are trapped in a ring-shaped
optical potential (see figure). The ``rotor''-atom is set into directed
controllable rotational motion by exerting a time-periodic magnetic field.
The quest for harvesting unidirectional rotor motion rests upon the key element
of using a non-biased drive that dynamically breaks the forward-backward symmetry.
Exploring the intriguing operational range of the motor near resonances
paves the way for such a quantum engine to perform reliable work against
an external load.
***
EC10646
Collision and adhesion of solid particles
A particle colliding with a wall may either bounce off or adhere to the surface. If it bounces off, it will do so with a reduced velocity, having lost mechanical energy as we can observe when throwing a rubber ball against a wall. Mathematical models can predict the velocity and rate of rotation of a spherical particle after a collision. The physical principles behind these models are well-known, such as Newton's second law: mass times acceleration equals the forces acting on the sphere. However, quantifying these forces is difficult. During collision the particle deforms elastically and plastically, slides and may roll. Additionally, the wall attracts the particle due to molecular interactions. The elastic deformation generates a force acting away from the wall, tending to make the particle rebound; however, with a sufficiently strong attractive force the particle will not escape but adhere (a "potential-well" effect). We do not often see a rubber ball adhere, but for very small particles (micro- or nanometers) this adhesive force is relatively much stronger. Kosinski and Hoffmann at the University of Bergen have extended the well-known "hard-sphere" collision model of Crowe et al. to account also for attractive forces and thus possible deposition. This is relevant for a variety of physical systems, such as sand, wax or hydrate particles flowing in oil pipelines, fine particles in pneumatic conveying or even ash in the crater of a volcano.
***
LC12765
Identifying a Black Hole's 'Fingerprint'
Worldwide, a race is underway to detect gravitational radiation generated by
pairs of black holes as they spiral together and coalesce. However,
inspiralling binaries represent only a small fraction of a much larger
population of mostly 'quiescent' black holes, which are far harder to
detect. It has been suggested that the presence of quiescent black
holes may be inferred from the 'fingerprint' they impose upon
radiation which impinges upon them. In this paper, we investigate one
possible fingerprint: the scattering and polarization pattern created
when a planar electromagnetic wave interacts with a (non-rotating)
black hole. The interference of rays passing in opposite senses around
the black hole creates a distinctive oscillatory diffraction
pattern. A segment of the incident wavefront undergoes a complete
orbit to create a 'glory' in the backward direction. This is manifest
as a bright ring around the pole at 180 degrees, whose angular
diameter is proportional to the wavelength. We present a unified
picture of the scattering of all waves (scalar, spinor,
electromagnetic and gravitational) for the first time, and demonstrate
that the 'glory' depends strongly on the intrinsic 'spin' of the wave,
in agreement with a prediction made over two decades ago.
Thursday, May 21, 2009
May 21, 2009
EA10445
How cargo can be transported in the cell, forward or backward?
It is very important for the cell to transport products and rubbish out of it and take raw materials and nutrition into it. It is well known that almost all these works are done by the cooperation of different molecular motors. But why these cargos can be transported in certain direction?. In my recent research, this enigmatic story is partly unclosed. The initial numbers of different molecular motors which bind to the moving track determines the direction of the cargo movement. I believe this theoretical result will be demonstrated experimentally in the future.
***
LH11208E
Genomes at the Edge of Chaos
Even to experts, genomes, or genomic sequences, look far more like scrambled
texts than the Books of Life they are. In this paper we use a new quantity,
the order index, to measure the randomness -- or order -- of sequences to
show genomes are characteristically at the "edge of chaos" and thereby gain
insight on how genomes grew. The order index, denoted by the Greek letter
phi, maps sequences of descending order (or increasing randomness) to a phi
ranging from 1 to 0. The phi of a random sequence of length L (in bases) is
proportional to the reciprocal of the root of L; phi becomes zero only when
the length approaches infinity. Phi decreases exponentially with the number
of random mutations per site a sequence suffers, and an ordered sequence
about 1 million to 1 billion bases long -- range of typical genome length --
becomes random after it suffers about four mutations per site. We find that
the phi’s of complete genomes congregate in a small range within a factor of
two of 0.03. This means that genomes, regardless of their true lengths, are
as random as an ordered sequence becomes after it has suffered 1.5 to 2.1
mutations per site; hence the edge-of-chaos metaphor. Our simulations of
genome growth based on random segmental duplications suggest that the
universal value 0.03 represents a "fixed-point" that is a property of the
dynamics of a robust and stochastic process of genome growth and evolution.
***
ACR1026
Flux-Equipped Quantum Cloak makes Ideal Matter-Wave Interferometer
Harry Potter’s invisibility cloak that can hide an object from being detected by
electromagnetic waves and is externally invisible has been proved feasible in recent
studies. An interesting generalization of such a Sci-fi tool in the quantum territory
that hides an object from matter waves has also been proposed.
In this paper, we explore the quantum interference effect of matter waves caused by a
magnetic flux hidden in the cloaked region. We show that although the quantum cloak
perfectly guides the charged matter waves detouring the cloaking shell, the global
quantum interference effect (the Aharonov-Bohm effect) is inevitable just like in the
non-cloaked case.
According to our results, the flux-equipped quantum cloak not only provides an ideal
setup to cloak an object from the detection of matter waves but also is an ideal matter-
wave interferometer that helps to reveal the global interferences of charged matter
waves. Similar ideas may be developed in the future to help manifesting other
mysterious global quantum interference effects such as the AB-EPR effect, Aharonov-
Casher effect, and so forth.
***
LA12210
Traffic jams in the cell: lost in translation
The process by which proteins are made in the cell is called translation. In this process, huge molecular machines, called ribosomes, translate a sequence of nucleotides -a messenger RNA molecule- into a sequence of amino acids -a protein. This process can be modelled by particles in a lattice that hop from one site to the next with a certain probability. Each site of the lattice has associated a different hopping probability, since at eachsi of the mRNA molecule, the ribosome has to wait on average a different time interval to get the appropriate amino acid. Therefore, if one ribosome has to wait a long time at a certain site, a queue of ribosomes can form behind, leading to a traffic j.
In this paper, we have studied how the configuration of slow sites influences the current of particles on the lattice, or equivalently, the current of ribosomes on the mRNA molecule. We have shown that depending where the slow sites of the lattice are positioned, the current of particles can be subject to a first order phase transition. We have analysed 500 mRNA sequences from yeast and found that we can classify them into two main groups, depending whether they experience a phase transition or not. Most importantly, these two groups of mRNA molecules translate into proteins with two very distinct biological functions. Therefore, our theory predicts a clascation of mRNA sequences purely based on the dynamics of the ribosome trac, and we have shown that this classcation matches perfectly the biological function, providing thus the link between the phase transition and biological function.
***
ET10332
Water harvesting using a conducting polymer
Currently, the most important environmental issue is the global climate
change. The significance of climate change extends, however, beyond being
the reason for some of the phenomena that are occuring in Nature, as it
also provides a new framework for recognizing the severity of a whole host
of other problems. One such problem is water scarcity. A recent report by
a United Nations panel on climate change stated that there is water
shortage for 1.1 - 3.2 billion people around the world. Such dire warnings
have given rise to the research field of water harvesting, which is
focused on developing new methods of harvesting water from various
sources. One such source is the atmosphere that has many advantages over
other sources, such as the purity of its water. It is estimated that there
are as much as 50,000 km^3 of water in the atmosphere at any given time.
We have been studying, both experimentally and by molecular dynamics
simulations, the possibility of using doped polyaniline (PANI), a conducting
polymer, as a water adsorbent by measuring the amount of water vapor that is
adsorbed on the PANI, when it is exposed to water-vapor containing air.
Due to ionic solvation, PANI absorbs large amounts of water. While there are
many polymers that absorb a significant amount of water, they do not
desorb it readily. But, by passing a very weak current through PANI, the water
is recovered. Our study indicates promise for the method, particularly for
arid and isolated areas.
***
LC12857ER
Chemo-motion
We reveal a new structure caused by interaction between the reaction-
diffusion process and a surface-tension-driven effect with motor-like
surface motion via chemo-mechanical transduction. Recently, increasing
attention has been focused on the self-organized pattern formation in
nonlinear complex systems far from equilibrium. The ideal reaction-
diffusion systems have been extensively investigated to understand the
mechanism of pattern formation. For example, the excitable Belousov–
Zhabotinsky (BZ) reaction coupled with diffusion can exhibit a large
variety of spatial patterns. On other hand, chemically driven
convection can lead to a complex hydrodynamic phenomena spontaneously
induced by spiral waves. In this paper, we report on superimposed
spiral structures that are chemical spiral waves and a rotating global
structure with motor-like surface motion, providing evidence of a
hierarchical self-organized order that connects two complex phenomena
involving the coupling of a reaction–diffusion pattern with
convection. Thus, chemo-mechanical transduction in a reaction-
diffusion-convection system offers wide flexibility for designing a
hierarchical structure in nonlinear systems far from equilibrium.
***
BX10924
Copper oxide reshaped
Just like carbon changes its properties under extreme pressures to form
diamond, copper oxide can be morphed into a different crystal structure
by using thin film epitaxial stabilization. When copper oxide is
deposited onto single crystal SrTiO3, under the right conditions a more
symmetric crystal structure is formed, which resembles its form found in
High Tc cuprate superconductors. Natural CuO (tenorite) is the
exceptional member of the rock salt series as one traverses the periodic
table from MnO to CuO. It deviates substantially from the trends
exhibited by the members with lower atomic number. All the others have
the cubic rock salt structure and all are correlated antiferromagnetic
insulators. The properties of CuO in higher symmetry structures would be
of great fundamental interest in understanding correlated materials. The
results demonstrate that higher symmetry phases of this important
correlated oxide are possible and now available for physical studies. If
such a high-J CuO could be doped, its properties would be of great
interest in the context of the earlier mentioned high-Tc
superconductors.
***
LY11510
Discovery of Unusually Shaped Combustion Particles May Lead to
Nano-Engineering of Particle Properties
Nanoparticles emitted by high-temperature combustion are formed through aggregation of small spheres into complex shapes. These shapes previously have been found to be uniformly open structured (—a characteristic that affects Earth’s radiation balance, climate, visibility, and human health. A multi-institutional team led by Rajan Chakrabarty and Hans Moosmüller from the Desert Research Institute (DRI) reports for the first time that some aggregates from a premixed flame have different, much more linear shapes. Electric fields in flames orient some aggregates and make some individual spheres move preferentially along electric field lines, resulting in aggregates with a more linear shape. This effect may be enhanced further by application of an external electric field, opening the door to nano-engineering of aggregate shape. Applications of this novel nano-engineering technique include industrial production of nanomaterials including carbon black, titania, and silica nanoparticles, allowing for control of shape-dependent material properties such as the blackness of carbon black particles.
***
LX11459
Exotic relativistic effects of particles moving at ultra-slow speeds
Relativistic effects are well known to occur at the speeds of particles close to that of light. Can you image that relativistic effects may also be present for particles moving at ultra-slow speeds? In this paper, a relativistic Dirac-like equation is established for ultra-cold atoms moving at speeds around a centimeter per second, a magnitude of 10 orders less than the speed of light in vacuum. It is shown that particles described by the Dirac-like equation can be massless, just like photons. Remarkably, these massless particles are entirely delocalized in disordered one-dimensional systems due to a so-called chiral symmetry, in sharp contrast to a famous conventional wisdom on Anderson localization: any disorder leads to the localization of all non-relativistic electrons in one-dimensional systems. It is also elaborated how to detect experimentally the predicted relativistic effects with the current technology available for ultra-cold atoms.
***
LD12562
How to Make the Smallest Atoms
Researchers have shown how to create and observe atoms a hundred times
smaller than those that make up ordinary matter. Instead of being
composed of electrons, protons, and neutrons, these atoms are made from
muons, short-lived particles that are frequently created in nature when
cosmic rays strike the earth's upper atmosphere. Nevertheless, the same
electric and magnetic fields that hold together ordinary atoms also make
these "true muonium" atoms possible. The tiny atoms decay after only
some trillionths of a second, but the researchers have uncovered
unambiguous methods by which the signature of their formation and decay
can be readily detected in particle accelerators. In one method, the
electron and positron beams intersect at a sharp angle, creating true
muonium atoms that are not only thrown clear of the clutter of beam
particles, but at relativistic speeds that greatly enhance their
lifetimes, making them easier to detect. In the other method, the
electron and positron beams collide in the traditional head-on manner,
but the true muonium atom is created alongside an extra photon against
which it recoils, again kicking it out of the beam clutter; such
processes can occur even at today's existing accelerators. In either
case, state-of-the-art laser techniques can be used to study the true
muonium atoms in detail.
***
LT11375AR
Probing quantum chaos with an atom interferometer
Coherence and interference are fundamental properties of quantum mechanical
systems that cause quantum dynamics to be different from classical dynamics.
With the advent of the atomic quantum kicked rotor, the quantum equivalent of a
classically chaotic delta kicked rotor system, it has been possible to probe
striking quantum features and to study a boundary between classical and quantum
dynamics in a single system. One of the most intriguing features of such system
are sharp peaks in the energy spectra, known as quantum resonances and quantum
accelerator modes, which occur when the period of perturbation equals the
characteristic times of a quantum system. Previous studies of quantum kicked
rotor that measure only the energy had low resolution that limits experimental
exploration of all the predicted phenomena. In our work, we demonstrate a
matter-wave interferometry scheme with cold atoms in which landmark features of
the quantum kicked rotor are produced and directly probed by momentum coherences
with high contrast. Our observations indicate that quantum resonances preserve
the matter-wave coherence rather than destroy it. High resolution of the atom
interferometer allows us to explore fundamental fractional effects of the
quantum kicked rotor and develop new atom-optics-based sensors.
How cargo can be transported in the cell, forward or backward?
It is very important for the cell to transport products and rubbish out of it and take raw materials and nutrition into it. It is well known that almost all these works are done by the cooperation of different molecular motors. But why these cargos can be transported in certain direction?. In my recent research, this enigmatic story is partly unclosed. The initial numbers of different molecular motors which bind to the moving track determines the direction of the cargo movement. I believe this theoretical result will be demonstrated experimentally in the future.
***
LH11208E
Genomes at the Edge of Chaos
Even to experts, genomes, or genomic sequences, look far more like scrambled
texts than the Books of Life they are. In this paper we use a new quantity,
the order index, to measure the randomness -- or order -- of sequences to
show genomes are characteristically at the "edge of chaos" and thereby gain
insight on how genomes grew. The order index, denoted by the Greek letter
phi, maps sequences of descending order (or increasing randomness) to a phi
ranging from 1 to 0. The phi of a random sequence of length L (in bases) is
proportional to the reciprocal of the root of L; phi becomes zero only when
the length approaches infinity. Phi decreases exponentially with the number
of random mutations per site a sequence suffers, and an ordered sequence
about 1 million to 1 billion bases long -- range of typical genome length --
becomes random after it suffers about four mutations per site. We find that
the phi’s of complete genomes congregate in a small range within a factor of
two of 0.03. This means that genomes, regardless of their true lengths, are
as random as an ordered sequence becomes after it has suffered 1.5 to 2.1
mutations per site; hence the edge-of-chaos metaphor. Our simulations of
genome growth based on random segmental duplications suggest that the
universal value 0.03 represents a "fixed-point" that is a property of the
dynamics of a robust and stochastic process of genome growth and evolution.
***
ACR1026
Flux-Equipped Quantum Cloak makes Ideal Matter-Wave Interferometer
Harry Potter’s invisibility cloak that can hide an object from being detected by
electromagnetic waves and is externally invisible has been proved feasible in recent
studies. An interesting generalization of such a Sci-fi tool in the quantum territory
that hides an object from matter waves has also been proposed.
In this paper, we explore the quantum interference effect of matter waves caused by a
magnetic flux hidden in the cloaked region. We show that although the quantum cloak
perfectly guides the charged matter waves detouring the cloaking shell, the global
quantum interference effect (the Aharonov-Bohm effect) is inevitable just like in the
non-cloaked case.
According to our results, the flux-equipped quantum cloak not only provides an ideal
setup to cloak an object from the detection of matter waves but also is an ideal matter-
wave interferometer that helps to reveal the global interferences of charged matter
waves. Similar ideas may be developed in the future to help manifesting other
mysterious global quantum interference effects such as the AB-EPR effect, Aharonov-
Casher effect, and so forth.
***
LA12210
Traffic jams in the cell: lost in translation
The process by which proteins are made in the cell is called translation. In this process, huge molecular machines, called ribosomes, translate a sequence of nucleotides -a messenger RNA molecule- into a sequence of amino acids -a protein. This process can be modelled by particles in a lattice that hop from one site to the next with a certain probability. Each site of the lattice has associated a different hopping probability, since at eachsi of the mRNA molecule, the ribosome has to wait on average a different time interval to get the appropriate amino acid. Therefore, if one ribosome has to wait a long time at a certain site, a queue of ribosomes can form behind, leading to a traffic j.
In this paper, we have studied how the configuration of slow sites influences the current of particles on the lattice, or equivalently, the current of ribosomes on the mRNA molecule. We have shown that depending where the slow sites of the lattice are positioned, the current of particles can be subject to a first order phase transition. We have analysed 500 mRNA sequences from yeast and found that we can classify them into two main groups, depending whether they experience a phase transition or not. Most importantly, these two groups of mRNA molecules translate into proteins with two very distinct biological functions. Therefore, our theory predicts a clascation of mRNA sequences purely based on the dynamics of the ribosome trac, and we have shown that this classcation matches perfectly the biological function, providing thus the link between the phase transition and biological function.
***
ET10332
Water harvesting using a conducting polymer
Currently, the most important environmental issue is the global climate
change. The significance of climate change extends, however, beyond being
the reason for some of the phenomena that are occuring in Nature, as it
also provides a new framework for recognizing the severity of a whole host
of other problems. One such problem is water scarcity. A recent report by
a United Nations panel on climate change stated that there is water
shortage for 1.1 - 3.2 billion people around the world. Such dire warnings
have given rise to the research field of water harvesting, which is
focused on developing new methods of harvesting water from various
sources. One such source is the atmosphere that has many advantages over
other sources, such as the purity of its water. It is estimated that there
are as much as 50,000 km^3 of water in the atmosphere at any given time.
We have been studying, both experimentally and by molecular dynamics
simulations, the possibility of using doped polyaniline (PANI), a conducting
polymer, as a water adsorbent by measuring the amount of water vapor that is
adsorbed on the PANI, when it is exposed to water-vapor containing air.
Due to ionic solvation, PANI absorbs large amounts of water. While there are
many polymers that absorb a significant amount of water, they do not
desorb it readily. But, by passing a very weak current through PANI, the water
is recovered. Our study indicates promise for the method, particularly for
arid and isolated areas.
***
LC12857ER
Chemo-motion
We reveal a new structure caused by interaction between the reaction-
diffusion process and a surface-tension-driven effect with motor-like
surface motion via chemo-mechanical transduction. Recently, increasing
attention has been focused on the self-organized pattern formation in
nonlinear complex systems far from equilibrium. The ideal reaction-
diffusion systems have been extensively investigated to understand the
mechanism of pattern formation. For example, the excitable Belousov–
Zhabotinsky (BZ) reaction coupled with diffusion can exhibit a large
variety of spatial patterns. On other hand, chemically driven
convection can lead to a complex hydrodynamic phenomena spontaneously
induced by spiral waves. In this paper, we report on superimposed
spiral structures that are chemical spiral waves and a rotating global
structure with motor-like surface motion, providing evidence of a
hierarchical self-organized order that connects two complex phenomena
involving the coupling of a reaction–diffusion pattern with
convection. Thus, chemo-mechanical transduction in a reaction-
diffusion-convection system offers wide flexibility for designing a
hierarchical structure in nonlinear systems far from equilibrium.
***
BX10924
Copper oxide reshaped
Just like carbon changes its properties under extreme pressures to form
diamond, copper oxide can be morphed into a different crystal structure
by using thin film epitaxial stabilization. When copper oxide is
deposited onto single crystal SrTiO3, under the right conditions a more
symmetric crystal structure is formed, which resembles its form found in
High Tc cuprate superconductors. Natural CuO (tenorite) is the
exceptional member of the rock salt series as one traverses the periodic
table from MnO to CuO. It deviates substantially from the trends
exhibited by the members with lower atomic number. All the others have
the cubic rock salt structure and all are correlated antiferromagnetic
insulators. The properties of CuO in higher symmetry structures would be
of great fundamental interest in understanding correlated materials. The
results demonstrate that higher symmetry phases of this important
correlated oxide are possible and now available for physical studies. If
such a high-J CuO could be doped, its properties would be of great
interest in the context of the earlier mentioned high-Tc
superconductors.
***
LY11510
Discovery of Unusually Shaped Combustion Particles May Lead to
Nano-Engineering of Particle Properties
Nanoparticles emitted by high-temperature combustion are formed through aggregation of small spheres into complex shapes. These shapes previously have been found to be uniformly open structured (—a characteristic that affects Earth’s radiation balance, climate, visibility, and human health. A multi-institutional team led by Rajan Chakrabarty and Hans Moosmüller from the Desert Research Institute (DRI) reports for the first time that some aggregates from a premixed flame have different, much more linear shapes. Electric fields in flames orient some aggregates and make some individual spheres move preferentially along electric field lines, resulting in aggregates with a more linear shape. This effect may be enhanced further by application of an external electric field, opening the door to nano-engineering of aggregate shape. Applications of this novel nano-engineering technique include industrial production of nanomaterials including carbon black, titania, and silica nanoparticles, allowing for control of shape-dependent material properties such as the blackness of carbon black particles.
***
LX11459
Exotic relativistic effects of particles moving at ultra-slow speeds
Relativistic effects are well known to occur at the speeds of particles close to that of light. Can you image that relativistic effects may also be present for particles moving at ultra-slow speeds? In this paper, a relativistic Dirac-like equation is established for ultra-cold atoms moving at speeds around a centimeter per second, a magnitude of 10 orders less than the speed of light in vacuum. It is shown that particles described by the Dirac-like equation can be massless, just like photons. Remarkably, these massless particles are entirely delocalized in disordered one-dimensional systems due to a so-called chiral symmetry, in sharp contrast to a famous conventional wisdom on Anderson localization: any disorder leads to the localization of all non-relativistic electrons in one-dimensional systems. It is also elaborated how to detect experimentally the predicted relativistic effects with the current technology available for ultra-cold atoms.
***
LD12562
How to Make the Smallest Atoms
Researchers have shown how to create and observe atoms a hundred times
smaller than those that make up ordinary matter. Instead of being
composed of electrons, protons, and neutrons, these atoms are made from
muons, short-lived particles that are frequently created in nature when
cosmic rays strike the earth's upper atmosphere. Nevertheless, the same
electric and magnetic fields that hold together ordinary atoms also make
these "true muonium" atoms possible. The tiny atoms decay after only
some trillionths of a second, but the researchers have uncovered
unambiguous methods by which the signature of their formation and decay
can be readily detected in particle accelerators. In one method, the
electron and positron beams intersect at a sharp angle, creating true
muonium atoms that are not only thrown clear of the clutter of beam
particles, but at relativistic speeds that greatly enhance their
lifetimes, making them easier to detect. In the other method, the
electron and positron beams collide in the traditional head-on manner,
but the true muonium atom is created alongside an extra photon against
which it recoils, again kicking it out of the beam clutter; such
processes can occur even at today's existing accelerators. In either
case, state-of-the-art laser techniques can be used to study the true
muonium atoms in detail.
***
LT11375AR
Probing quantum chaos with an atom interferometer
Coherence and interference are fundamental properties of quantum mechanical
systems that cause quantum dynamics to be different from classical dynamics.
With the advent of the atomic quantum kicked rotor, the quantum equivalent of a
classically chaotic delta kicked rotor system, it has been possible to probe
striking quantum features and to study a boundary between classical and quantum
dynamics in a single system. One of the most intriguing features of such system
are sharp peaks in the energy spectra, known as quantum resonances and quantum
accelerator modes, which occur when the period of perturbation equals the
characteristic times of a quantum system. Previous studies of quantum kicked
rotor that measure only the energy had low resolution that limits experimental
exploration of all the predicted phenomena. In our work, we demonstrate a
matter-wave interferometry scheme with cold atoms in which landmark features of
the quantum kicked rotor are produced and directly probed by momentum coherences
with high contrast. Our observations indicate that quantum resonances preserve
the matter-wave coherence rather than destroy it. High resolution of the atom
interferometer allows us to explore fundamental fractional effects of the
quantum kicked rotor and develop new atom-optics-based sensors.
Monday, May 11, 2009
LB12072
Invisibility cloak made using curved waveguides
Most researchers believe that sophisticated artificially engineered
materials are required to build an invisibility cloak. Such
“metamaterials” exhibit high losses and work for only one color. The
resulting invisibility cloaks are tiny, and cannot hide anything if
another color of light is used. Now the team of researchers from BAE
Systems, Towson University and Purdue University demonstrated a
different approach to cloaking. Instead of sophisticated metamaterials,
they use a waveguide, which is curved to mimic the metamaterial
properties. This approach leads to all-color invisibility cloak with
much lower losses. As a result, the researchers built a large optical
cloak, which is about hundred times larger than the cloaks built
previously. This “see-through” cloak bends light around itself and thus
differs from the “invisibility carpet,” which camouflages bumps on a
metal surface. The team believes that further size increase is possible,
and that the same technique may be applied to other tasks, which require
the use of metamaterials, such as building new “hyperlenses” which
considerably surpass the resolution limit of conventional lenses.
Figure: Schematic of a tapered waveguide acting as an optical cloak.
***
LB12032DR
CAN QUANTUM MECHANICS FOOL THE COSMIC CENSOR?
Summary: According to general relativity space and time loose their
meaning and the present laws of physics become useless at the
singularities hidden inside black holes. Despite it, they are harmless
because the event horizons of the holes, which "dress" them, keep
the rest of the universe protected. On the other hand, "undressed"
(i.e., naked) singularities can influence a whole region of the
universe in an unpredictable way. This "immoral behavior" led
R. Penrose to conjectured the existence of "cosmic censors" to
preclude the formation of naked singularities. Today we ignore
whether (I) "physical initial conditions evolved through Einstein
equations could generate naked singularities". This led S. Hawking,
J. Preskill and K. Thorne to run a celebrated bet, where Preskill
and Thorne favor (I) in contrast to Hawking.
In our paper, we revisit the mechanism for violating the weak
cosmic-censorship conjecture (WCCC) by overspinning a
nearly-extreme charged black hole suggested sometime ago by
some of us. The mechanism consists of an incoming massless
neutral scalar particle, with low energy and large angular
momentum, tunneling into the hole. We investigate the effect
of the large angular momentum of the incoming particle on the
background geometry and address recent claims that such a
back-reaction would invalidate the mechanism. We show that
the large angular momentum of the incident particle does not
constitute an obvious impediment to the success of the
overspinning quantum mechanism, although the induced
back-reaction turns out to be essential to restoring the validity
of the WCCC in the classical regime. These results and the fact
that quantum gravity should unveil the physics of naked
singularities and recover the predictability of the Universe
seem to endorse the view that "the cosmic censor" would be
oblivious to processes involving quantum effects. Finally, also
based on our results, we eventually raise a thought provoking
conjecture connecting naked singularities to elementary particles,
namely, that "naked singularities and elementary particles
would be low-energy manifestations of a same quantum gravity
structure" and argue that, if this is the case, the Higgs (scalar)
boson expected to be found in the LHC would be a composite
rather than an elementary particle.
***
LC12174
A "nuclear clock" could find out whether the fundamental constants of
nature are changing in time.
Laboratory searches for variation of fundamental constants, such as
the speed of light, work by comparing two or more atomic clocks over
the course of a few years. Each clock is essentially a different
physical system, with different dependence on fundamental constants.
Therefore if the speed of light (for example) changes, the two clocks
will react differently and one will seem to "speed up" relative to the
other. The discovery of changes in the constants would revolutionize
our understanding of physics, forcing us to reconsider the Standard
Model of particle physics and Einstein's General Relativity.
The setup could be massively improved by taking advantage of a
"nuclear clock" made from thorium-229. While such a clock has yet to
be built, it is expected to be the most precise clock ever made. In
this paper we have proposed experiments that can measure the
sensitivity of the clock to variation of fundamental constants. The
nuclear clock is expected to be several-orders-of-magnitude more
sensitive than atomic clocks, and hence be an excellent probe of
whether the fundamental constants of nature are changing in time.
***
LB12130
A little dirt can go a long way
It is well known that the transport of particles in a narrow channel is
slowed down considerably by the presence of other particles. this
phenomena, predicted theoretically over 30 years ago, has been
demonstrated in recent experiments on colloidal particles and in
experiments on transport in narrow biological channels. Now, scientists
at Los Alamos National Laboratory and Boston University predict that
the transport of such particles can be dramatically enhanced by addition
of very small amount disorder, which in practice can take the form of
impurities, dust, or variations in the channel width.
***
LX11566
Jet Imaging of Quark-Gluon Plasma Hints at its ¡°Yin-Yang¡± Duality
A novel energy loss pattern near the QCD confinement transition
at temperature Tc has been proposed for a jet penetrating the
quark-gluon plasma (QGP), which solves a long-standing puzzle about
the observed jet geometry. An energetic jet --- a quark or gluon with
large momentum --- loses its energy and thus makes imaging when
passing through the QGP --- the matter once occupying the early
universe and nowadays only created at laboratory by smashing heavy
nuclei head-on with a speed close to the light. In most such collisions,
the ¡°thickness¡± of the created matter is spatially anisotropic and
leads to nontrivial angular dependence of the jet energy loss --- a
geometric imaging on the ¡°opacity¡± of the QGP. In this paper, we first
pointed out the opacity of the matter has --- instead of linear growth ---
actually nonlinear dependence on the matter density and develops a peak
near Tc. Based on this, we were able to explain the measured jet
anisotropy which denied past model descriptions. The microscopic
mechanism of such novel pattern lies in the ¡°Yin-Yang¡±, or Electric-Magnetic
duality for QGP proposed in our previous paper (PRL101:162302,2008),
according to which magnetic monopoles dominate the QGP near Tc. A jet
as a moving electric charge loses substantial energy to heat up such a
magnetic plasma just like how a conduction cooker works by vertue of the
Faraday's law. These innovative ideas may eventually elucidate the
decades-old mystery of how QCD confinement transition exactly occurs
in nature.
***
EBR1046
evolution of cooperation
Our work reveals that diversity of individual rationality has great
influence on the evolution of cooperation, and the
moderate-ranked individuals are found to play a critical role. Since the
organization of society largely depends on the emergence of cooperation, our
findings might help us to understand some social phenomena, especially
concerning the middle class. In the study of evolutionary game dynamics,
most works focus on the influence of network topology and strategy
complexity, but not the diversity of individual properties. These works show
that cooperation can often be promoted while cooperators form compact
clusters. In our work, we take into concern the diversity of an
intrinsic social property, individual rationality, and discover that the
cluster forming mechanism of cooperators can either be highly enhanced or
severely deteriorated by different distributions of rationality. Slight
change in the rationality distribution may transfer the whole system from
all-cooperator state to all-defector state. Moreover, analysis of the
stability of cooperative clusters reveals the critical role played
by individuals with moderate connectivity in the evolution of the whole
system, which has not been fully discussed in former works. The inspiration
from our work might yield new insights towards the social function of the
middle class.
Invisibility cloak made using curved waveguides
Most researchers believe that sophisticated artificially engineered
materials are required to build an invisibility cloak. Such
“metamaterials” exhibit high losses and work for only one color. The
resulting invisibility cloaks are tiny, and cannot hide anything if
another color of light is used. Now the team of researchers from BAE
Systems, Towson University and Purdue University demonstrated a
different approach to cloaking. Instead of sophisticated metamaterials,
they use a waveguide, which is curved to mimic the metamaterial
properties. This approach leads to all-color invisibility cloak with
much lower losses. As a result, the researchers built a large optical
cloak, which is about hundred times larger than the cloaks built
previously. This “see-through” cloak bends light around itself and thus
differs from the “invisibility carpet,” which camouflages bumps on a
metal surface. The team believes that further size increase is possible,
and that the same technique may be applied to other tasks, which require
the use of metamaterials, such as building new “hyperlenses” which
considerably surpass the resolution limit of conventional lenses.
Figure: Schematic of a tapered waveguide acting as an optical cloak.
***
LB12032DR
CAN QUANTUM MECHANICS FOOL THE COSMIC CENSOR?
Summary: According to general relativity space and time loose their
meaning and the present laws of physics become useless at the
singularities hidden inside black holes. Despite it, they are harmless
because the event horizons of the holes, which "dress" them, keep
the rest of the universe protected. On the other hand, "undressed"
(i.e., naked) singularities can influence a whole region of the
universe in an unpredictable way. This "immoral behavior" led
R. Penrose to conjectured the existence of "cosmic censors" to
preclude the formation of naked singularities. Today we ignore
whether (I) "physical initial conditions evolved through Einstein
equations could generate naked singularities". This led S. Hawking,
J. Preskill and K. Thorne to run a celebrated bet, where Preskill
and Thorne favor (I) in contrast to Hawking.
In our paper, we revisit the mechanism for violating the weak
cosmic-censorship conjecture (WCCC) by overspinning a
nearly-extreme charged black hole suggested sometime ago by
some of us. The mechanism consists of an incoming massless
neutral scalar particle, with low energy and large angular
momentum, tunneling into the hole. We investigate the effect
of the large angular momentum of the incoming particle on the
background geometry and address recent claims that such a
back-reaction would invalidate the mechanism. We show that
the large angular momentum of the incident particle does not
constitute an obvious impediment to the success of the
overspinning quantum mechanism, although the induced
back-reaction turns out to be essential to restoring the validity
of the WCCC in the classical regime. These results and the fact
that quantum gravity should unveil the physics of naked
singularities and recover the predictability of the Universe
seem to endorse the view that "the cosmic censor" would be
oblivious to processes involving quantum effects. Finally, also
based on our results, we eventually raise a thought provoking
conjecture connecting naked singularities to elementary particles,
namely, that "naked singularities and elementary particles
would be low-energy manifestations of a same quantum gravity
structure" and argue that, if this is the case, the Higgs (scalar)
boson expected to be found in the LHC would be a composite
rather than an elementary particle.
***
LC12174
A "nuclear clock" could find out whether the fundamental constants of
nature are changing in time.
Laboratory searches for variation of fundamental constants, such as
the speed of light, work by comparing two or more atomic clocks over
the course of a few years. Each clock is essentially a different
physical system, with different dependence on fundamental constants.
Therefore if the speed of light (for example) changes, the two clocks
will react differently and one will seem to "speed up" relative to the
other. The discovery of changes in the constants would revolutionize
our understanding of physics, forcing us to reconsider the Standard
Model of particle physics and Einstein's General Relativity.
The setup could be massively improved by taking advantage of a
"nuclear clock" made from thorium-229. While such a clock has yet to
be built, it is expected to be the most precise clock ever made. In
this paper we have proposed experiments that can measure the
sensitivity of the clock to variation of fundamental constants. The
nuclear clock is expected to be several-orders-of-magnitude more
sensitive than atomic clocks, and hence be an excellent probe of
whether the fundamental constants of nature are changing in time.
***
LB12130
A little dirt can go a long way
It is well known that the transport of particles in a narrow channel is
slowed down considerably by the presence of other particles. this
phenomena, predicted theoretically over 30 years ago, has been
demonstrated in recent experiments on colloidal particles and in
experiments on transport in narrow biological channels. Now, scientists
at Los Alamos National Laboratory and Boston University predict that
the transport of such particles can be dramatically enhanced by addition
of very small amount disorder, which in practice can take the form of
impurities, dust, or variations in the channel width.
***
LX11566
Jet Imaging of Quark-Gluon Plasma Hints at its ¡°Yin-Yang¡± Duality
A novel energy loss pattern near the QCD confinement transition
at temperature Tc has been proposed for a jet penetrating the
quark-gluon plasma (QGP), which solves a long-standing puzzle about
the observed jet geometry. An energetic jet --- a quark or gluon with
large momentum --- loses its energy and thus makes imaging when
passing through the QGP --- the matter once occupying the early
universe and nowadays only created at laboratory by smashing heavy
nuclei head-on with a speed close to the light. In most such collisions,
the ¡°thickness¡± of the created matter is spatially anisotropic and
leads to nontrivial angular dependence of the jet energy loss --- a
geometric imaging on the ¡°opacity¡± of the QGP. In this paper, we first
pointed out the opacity of the matter has --- instead of linear growth ---
actually nonlinear dependence on the matter density and develops a peak
near Tc. Based on this, we were able to explain the measured jet
anisotropy which denied past model descriptions. The microscopic
mechanism of such novel pattern lies in the ¡°Yin-Yang¡±, or Electric-Magnetic
duality for QGP proposed in our previous paper (PRL101:162302,2008),
according to which magnetic monopoles dominate the QGP near Tc. A jet
as a moving electric charge loses substantial energy to heat up such a
magnetic plasma just like how a conduction cooker works by vertue of the
Faraday's law. These innovative ideas may eventually elucidate the
decades-old mystery of how QCD confinement transition exactly occurs
in nature.
***
EBR1046
evolution of cooperation
Our work reveals that diversity of individual rationality has great
influence on the evolution of cooperation, and the
moderate-ranked individuals are found to play a critical role. Since the
organization of society largely depends on the emergence of cooperation, our
findings might help us to understand some social phenomena, especially
concerning the middle class. In the study of evolutionary game dynamics,
most works focus on the influence of network topology and strategy
complexity, but not the diversity of individual properties. These works show
that cooperation can often be promoted while cooperators form compact
clusters. In our work, we take into concern the diversity of an
intrinsic social property, individual rationality, and discover that the
cluster forming mechanism of cooperators can either be highly enhanced or
severely deteriorated by different distributions of rationality. Slight
change in the rationality distribution may transfer the whole system from
all-cooperator state to all-defector state. Moreover, analysis of the
stability of cooperative clusters reveals the critical role played
by individuals with moderate connectivity in the evolution of the whole
system, which has not been fully discussed in former works. The inspiration
from our work might yield new insights towards the social function of the
middle class.
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