The effective particles inhabiting the two-dimensional fractional quantum Hall
world are said to have "quantum statistics" fundamentally different from those
of the fermions and bosons which constitute our three-dimensional world. In
this paper, we pinpoint the signatures of these particles which have
'fractional statistics' and compare them to their bosonic and fermionic
counterparts. While fermions tend to have an extreme exclusion behavior, not
allowing two identical fermions to be at the same point in space and time,
and bosons tend to bunch, we show that these fractional particles exhibit an
intermediate exclusion that depends on the fraction "nu" characterizing the
quantum Hall state. Another instance where statistics comes into play is in
the angular dependence of scattered particles - it is known that two fermions
approaching one another have zero chance of scattering at ninety
degrees. We show that fractional particles in the quantum Hall system
also reveal dramatic angular dependent correlation effects due to their
statistics. The prospect of detecting these and related effects in
experiments promises to be truly exciting as it would establish the existence of
fundamentally different quantum behavior. LE11009
***
Chaos control in the heart lead to less shocking defibrillators.
Physics for EP room : cardiac chaos can be terminated with hundreds times less shock energy
During the past few years, the energy needed to terminate arrhythmias
with
an external defibrillator (4,000- 5,000 Volts, 15-20 A) was decreased
by defibrillators manufacturers by no more than 40%. We found that a
better understanding of
the physics of the heart could permit to decrease it several orders of
magnitude (hundreds and thousands times).
Earlier results in this direction showed how to terminate one
rotating wave
anchored to an anatomical obstacle, by a small amplitude electric shock
(PRL2004 and AFS focus "Physics for EP room") and Nature news
("Cardiac Defibrillators becoming less shocking") were devoted.
Experiments
on rabbit heart preparations confirmed that termination of a single
vortex
could be achieved with an energy 20 times smaller than defibrillation
shocks.
A far more difficult and important task is to suppress fully chaotic
regimes
by using reduced electric field. Defibrillators suppress all existing
waves
by exciting the tissue, using the heterogeneities of the cardiac
tissue as
'virtual electrodes'. Indeed, the heart is filled with many
heterogeneities,
spanning a wide range of spatial scales. With a given geometry,
diminishing the
amplitude of the electric field simply reduces the number of 'virtual
electrodes' that act as a wave source. The strategy proposed in the new
article (PRL 2007) consists in using fewer electrodes, but pacing the
tissue
periodically. The results of a numerical study, as well as of
experimental
study using cell cultures, suggest that very significant gains in
energy could
be achieved. Theoretical arguments suggest gains in energy of several
orders
of magnitude.
This study, based on simple physical principles, shoud be
complemented by
experiments with real hearts. It may open the way to a completely new
strategy
with heart defibrillators. LC11418
***
Physical modeling explains statistical fluctuations in genetically
homogeneous biological populations
We present and study a model describing the nonequilibrium statistical
mechanics of protein distributions in a proliferating cell population.
Our model describes how total protein variation in the population is
composed of a stochastic source internal to the cells and variation in
division and inheritance at the population level. It enables us to
assess the contribution and character of each of these components of
variation separately. We find that, even if production is deterministic,
cell division can generate a large variation in protein distribution. We
draw an analogy between the dynamics of protein distributions along cell
generations and that of stress in layers of granular material. In both
cases, a model with deterministic production and uniform division can be
solved exactly. However, in contrast with the model for stress
distribution in granular packings, where a universal tail had been
found, here we find sensitivity to the division function due to the
inheritance structure of the biological population. At the other limit
of extremely noisy protein production internal to the cells, the details
of division do not affect the tail of the distribution. LD11645
***
A 2-PHOTON IS NOT "2 PHOTONS + SPOOKY ACTION"
What is the essence of quantum physics? The best way of sorting the many candidate features (indeterminism, contextuality, non-locality...) consists in proposing and testing alternative models, which look "reasonable" but deviate from the quantum predictions. Local models were falsified by Aspect in 1982 and by many subsequent experiments. In 2002, some non-local models were tested in Geneva: a bound was put on the speed of quantum information in a "quantum ether", and temporal order in quantum correlations was falsified. In this work, we study another non-local model, proposed in 2003 by Nobel Laureate Anthony Leggett. We provide its conclusive experimental falsification, after deriving a new criterion, which (contrary to the one used by Zeilinger's group for an experiment earlier this year) can be tested without invoking additional assumptions. Leggett's model formalizes the idea that each photon of a pair is in a well-defined local quantum state, the non-locality being due to some additional "spooky action-at-a-distance". Quantum entanglement, on the contrary, postulates no such action but denies individual properties to each photon. The falsification of the Leggett model strongly vindicates the counter-intuitive quantum description. This is a step further in the still on-going quest for the essence of quantum physics. LH11270
***
May quantum mechanics drive black holes into naked singularities?
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
some "cosmic censorship" 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
discuss the formation of naked singularities from a quantum rather than
classical perspective. We show that the quantum tunneling of a particle
with large angular momentum into a charged hole could overspin
it leading the event horizon to possibly disappear. A final veredictum
whether any stable naked singularity eventually appears may depend
on spacetime backreaction effects to be computed with some full quantum
gravity theory. LE11746
***
Universality and the critical Casimir effect
The critical Casimir force found experimentally in Helium 4 at the
superfluid transition [1] has been calculated theoretically for the
first time. The excellent agreement of theory and experiment are an
impressive example of the concept of universality at phase transitions,
because the considered systems are very different at the first sight:
While Helium 4 is liquid at low temperatures and becomes superfluid at
the transition temperature 2.1768 Kelvin, the theoretical calculations
were performed using computer simulations of a classical magnetic spin
system on a lattice. Nevertheless, the results coincide within the error
bars without any free parameters. These results may lead to a better
understanding of the Casimir effect, which presently is an active
research area from cosmology to nanotechnology. LF11623
***
Metal oxides exhibiting high dielectric constants recently attracted tremendous interest due to their application in microelectronics as novel materials for the gate dielectrics (the so-called high-k dielectrics) in the latest generation devices. One of the major obstacles for practical introduction of these materials is their ability to capture electrons and holes that may result in the instability of the device performance. It has long been believed that these charge trapping properties originate from the structural imperfections in the high-k dielectrics. Based on this understanding, significant efforts were devoted to improving material stoichiometry. However, as is theoretically demonstrated in this publication, both electrons and holes may experience self-trapping by forming polarons in the structurally perfect highly polarizable high-k dielectric, such as HfO2. In this case the interaction of an electron or hole with the perfect lattice creates a potential energy well that traps the electron (hole), as a deformation of a thin rubber film traps a billiard ball. The prediction that at low temperatures electrons and holes in these materials can move by hopping between trapping sites rather than propagate as a wave can have important practical implications for their electrical properties. This new understanding of the polaron-formation properties of the transition metal oxides opens interesting possibilities for suppressing undesirable material characteristics and will stimulate further research on the polaronic features in high-k dielectrics. The obtained results also suggest that materials where both hole and electron polarons co-exist may be more common than is currently assumed. For the first time, theoretical modelling provided a direct look inside polaron structure in a transition metal oxide material, indicating that electron and hole localization as polarons can be a defining characteristic of these materials. LG11473
***
Cardiac Defibrillators becoming less shocking - for saving lives.
Physics for EP room : cardiac chaos can be terminated with hundreds
times less shock energy
During last 5 years, a huge electric shock delivered by an automatic
cardiac defibrillator ( 4,000- 5,000 Volts, 15-20 A) was decreased only
by 40% of its energy. We found physics permitting to decrease it
several orders of magnitude (hundreds and thousands times) for
terminating cardiac chaos.
To our first result in this direction: physics of termination of only
one rotating vortex in the heart by an electric field shock (PRL 2004),
AFS focus ("Physics for EP room") and Nature news ("Cardiac Defibrillators
becoming less shocking" ) were devoted. Later, experiments on rabbit heart
preparations confirmed energy decrease 20 times for termination a single
vortex. Now, we created a method to terminate developed cardiac chaos
(consisting of a large number of rotating vortices). An important
difficulty to decrease the energy was: it is well established that an
electric field shock with an energy smaller than that used by
conventional defibrillation, not only remove vortices but also creates
new vortices and fibrillation. We found that this happens only if a shock
amplitude is above the Maxwell level (in conceptional physical models),
corresponding to the Lower Level of Vulnerability (LLV) in cardiac
experiments. We applied these concepts to create a method for cardiac
chaos termination that requires shocks energy below LLV thus does not
create new vortices and fibrillation. It can significantly advance
implanted and clinical devices used to terminate cardiac chaos (250,000
implanted cardiac defibrillators and many clinical devices used for
several million patients with atrial fibrillation and ventricular
disturbances). LC11418
***
How to follow a jumping surface atom
Pulsed synchrotron x-radiation can probe diffusion jumps of single atoms
directly in time domain in the range of nanoseconds and on the space
scale of Angstroms. Diffusion in and on surfaces is an important process
for producing nanostructures and has recently been followed
experimentally by scanning tunneling microscopy. The interaction of the
microscope tip with the surface atoms can be exploited for manipulating
the surface, but at the same time strongly influences the diffusion
process, and even with the fastest microscopes only the result of
diffusion events can be seen, the elementary diffusion jump happening on
a time scales a thousand times shorter. To probe this time scale becomes
possible with synchrotron radiation. We develop the theory for jump
diffusion in two-dimensional systems and refer to a first experiment
which has proven the feasibility of such investigations. This is to our
knowledge the first time that jumps of single atoms on and at surfaces
can be followed and opens the way for detailed studies of the atomistics
of surface diffusion. LE10964
***
Tunneling between a tremble and a swing
New research from Canada and Germany is challenging the notion that
quantum mechanics is the science of the small and the static. Research
published in the Physical Review Letters suggests that quantum
tunneling, one of several phenomena associated exclusively with the
quantum level, may also occur with larger and dynamic systems.
In quantum physics, quantum tunneling draws on micro and nanoscopic
phenomenon in order to allow a particle to pass through a barrier that
is too high to overcome by classical physical events. It has been widely
assumed that the larger a macroscopic system becomes, the less likely it
is for the quantum physics effects, such as tunneling, to occur.
New results from Ioana Serban, of the University of Munich, and Frank
Wilhelm, of the University of Waterloo, suggest that quantum tunneling
may be more common than expected and can occur in macroscopic quantum
mechanical systems. They suggest that tunneling can occur not only
between two places, but between two patterns of motion. In particular,
it may be possible for a nanomechanical clapper to generate both a
pendulum swing and a tiny tremor at the same time. The discovery will
advance the development of detectors to be used in quantum computing. LF11625
***
Quantum information can’t travel down a rocky road
Suppose a quantum particle like an electron is flying towards a material with a random distribution of matter, like a rocky road. Then, even though the particle is moving so fast that it should be able to zoom through the material, it bounces back. It’s like saying a bullet shot at a soft mattress will bounce back! This is the celebrated Anderson localisation phenomenon first explained in 1958, and is one of the many intriguing peculiarities of quantum mechanics. Another oddity of quantum mechanics, understood only recently, is that by exploiting the ability of quantum objects to be in two places at once, two parties should be able to communicate information very quickly via processes like “quantum teleportation”. Thus the question arises: could one take advantage of tricky quantum effects like teleportation to overcome the Anderson localisation phenomenon? In our paper we study this possibility and we show that this is impossible: Anderson localisation is such a powerful effect that not only single particles bounce back, but all possible quantum ways of secreting information amongst collections of such particles will bounce back as well. Anderson localisation trumps quantum communication: quantum information cannot travel down a rocky road. LE10961
***
Exotic nuclear excitation mechanism is most efficient in isomer triggering
Atomic nuclei can exist in so-called isomeric states -
long-lived excited states which are much more energetic
than the lowest ground state. We show that interactions
with electrons in a process called nuclear excitation by
electron capture can be a surprisingly efficient way of
releasing this energy on demand. The search for practical
methods to trigger isomeric states has been the subject
of a number of sometimes controversial investigation in the
last decades. Major motivations for this are fundamental such
as the challenge of understanding the formation and the role
of nuclear isomers in the creation of the elements in the
universe, but also a number of fascinating potential applications
have been suggested. These applications usually rely on the
controlled release of energy, e.g., in isomeric nuclear
batteries which operate without fusion or fission. An
experimental verification of our findings at the borderline
of atomic and nuclear physics may be provided by upcoming
ion storage ring facilities and ion beam traps which will
commence operation in the near future. LG11685
***
Atomic correlations of tellurium nanoparticles
This article presents nature of atomic correlations in nanoparticles of
tellurium (Te) which has a highly anisotropic structure. It is known that
trigonal Te has hierarchical structure, that is, primary structure is covalently
bound chains, and secondary structure is formed by binding together of the
chains. Our results reveal that in spite of microparticulation the primary
structure is preserved in contrast with reduction of the secondary structure.
The paper is a first step to demonstrate our model “Yarn model” (see attached
figure) that long chains compared to size of the nanoparticles are folded and
tangled like yarn. In other words, surface effects may be non-existent or
negligible in the Te nanoparticles. This kind of uniformity of the nanoparticles
can be expected for the exotic structure of tellurium but not isotropic elements. LE11298
***
Explaining vortex nucleation in a rotating Bose-Einstein condensate is
a recurrent and difficult problem. In this Letter, we propose a resonant
mechanism, based on a formal analogy with the Zeeman effect. This
mechanism, suggested by the Larmor theorem, yields the only existing
theory in the literature that explains all experimental results which
have been obtained by the three leading groups in the field, namely JILA
(Boulder, CO), MIT and ENS (Paris, France). A Bose-Einstein condensate
is the coldest, purely quantum-mechanical, state of the matter
(temperature about a few nanokelvins) and displays strong analogies with
superfluidity. Immediately following its experimental discovery in 1995
on atomic vapors, the creation (or "nucleation") of a few vortices
resembling those previously obtained in superfluids was achieved by
rotating (actually by laser-stirring) the condensate. But the
experimental value of the condensate rotation that yields the first
vortex has long remained a theoretical puzzle. LA11484
***
Hot heavy nuclei behave like drops of syrup
In heavy-ion induced fission an atomic nucleus is hit by an energetic projectile nucleus. The two nuclei fuse into one united nucleus, which after a short delay time splits into two fission fragments. We have determined the delay time for 32S, 48Ti, and 58Ni ions bombarding a tungsten crystal, using the spacing of atoms in the crystal as a yardstick to measure the small recoil of the united nucleus before fission. The measured delay times are of order 10-18 s, a billionth of a billionth of a second. Although this is a very short time it is very long on the nuclear time scale, and it is orders of magnitude longer than derived from previous, more indirect experiments. Our observations indicate a complete break-down of the standard model for nuclear fission, developed by Bohr and Wheeler shortly after the discovery of fission. The delay is here determined mainly by an energy barrier towards fission, and this barrier is very small for the united nuclei in our experiments. The fission delay may instead be due to very viscous flow of hot nuclear matter: the united nucleus behaves like a drop of syrup rather than like a drop of water. LC11842
***
Taming heat for information processing
Heat has always been considered as useless and harmful for information processing. However, the latest work by Wang and Li [1] from National University of Singapore, may overturn this long perception. According to their work, heat can be used to carry and process information.
Wang and Li present thermal logic gates, which are made of properly combined thermal transistors [2], can do all the logic operations: REPEATE, NOT, AND and OR. Therefore, the basic components of a computer -logic gates- are realized for phonons. The thermal (phonon) computer might not challenge the existing electronic computer, however provides a smart and efficient way to control and manipulate heat in molecular level, and to process thermal signals locally without convert them into electronic signals and processed by electronic devices, unless necessarily.
Given the fact that the solid state thermal rectifier has been realized experimentally in 2006 [3], only a few years after the theoretical models, the authors believe that the thermal logic gates can be also realized experimentally in a foreseeable future. LG11007
***
LIMIT OF THE LHC GLIMPSED AT RHIC
The Relativistic Heavy Ion Collider (RHIC) at
Brookhaven Laboratory, near New York, has provided a glimpse of a
long-anticipated physical process that may eventually limit the
performance of the Large Hadron Collider, soon to be turned on at CERN,
near Geneva. RHIC typically collides gold nuclei ("heavy ions") of
energy 19.7 TeV (a TeV is a trillion electron volts) and the LHC will
collide lead nuclei of energy 574 TeV (both machines also collide proton
beams).
Nuclei are collided at these energies primarily in
order to "melt" their constituent protons and neutrons into a plasma of
quarks and gluons interacting via the strong nuclear force, a state of
matter that existed in the first microseconds of cosmic history. But
heavy-ion collisions also provide access to electric forces of
phenomenal intensity. Relativistic length contraction dramatically
squashes the electric field lines emerging from each highly-charged
nucleus into a flat pancake. Sparks fly, so to speak, when these
pancakes interact and large numbers of electron-positron (anti-electron)
pairs are ripped out of the vacuum. In some cases, the electron of the
pair is attached to one or other nucleus, converting a small fraction of
the beam to one-electron ions. These soon stray from the path of the
main beam and are lost in a patch of the surface of the beam pipe.
In this paper, we successfully tested our ability to
predict the details of this phenomenon for the LHC by measuring it for
the first time with 6.3 TeV copper nuclei at RHIC. The heat generated by
the lost ion impacts inside the magnets of RHIC was quite harmless,
similar to the peak output of a firefly (the losses were only just
detectable with instruments outside the massive magnets). At the LHC the
heating will be comparable to that of a reading lamp, taking the
ultra-cold magnets close to the brink of "quenching" out of their
superconducting state. This experiment gives us some confidence that our
calculations are correct and will help avoid unscheduled and costly
halts of the huge machine. LF11298
***
Molecular unbinding in cytoskeletal networks
Cells make use of various proteins to interconnect cytoskeletal polymers into complex networks. In contrast to a covalent chemical bond these interconnections are transient. This allows for continuous remodelling of the cytoskeleton, a hallmark of adaptability in cells. In this paper we show that under mechanical load the bond between distinct actin bundles can be forced to unbind in vitro – even in a complex network of bundles: the higher is the bundle interconnectivity, the larger stresses the bundle network can endure before single bonds are forced to unbind. We observe a logarithmic dependence of this yield stress on the force loading rate as also reported for single molecular bonds.
We introduce a novel principle of ‘polymer interconnectivity/time superposition’ which combines these molecular unbinding events with the self-similar network structure. This principle of superposition can be employed to rationalize both the mechanical behavior of interconnected biopolymer networks under high forces and the shape of the frequency response. Our results have broad implications for the understanding of adaptable biomaterials. The observed forced unbinding may even turn out to be an important mechanism cells employ for mechanosensing tasks. LE11747
***
Fat freezes water on a molecular scale
Fat people are not very mobile. We now show that fat also has an
immobilizing effect on a molecular scale. Fats and oil are so-called
hydrophobic, i.e. water-fearing compounds. We have used ultrafast laser
techniques to study the motion of water molecules around hydrophobic
molecules. We have discovered that these molecules lead to a very strong
immobilization of their immediately surrounding water molecules. These
water molecules show a reorientation that is >4 times slower than that of
"normal" water molecules. With this finding we solved a long-lasting
controversy: thermodynamic studies indicated that water surrounding
hydrophobes behaves ice-like, but spectroscopic studies did not find any
evidence for the presence of ice-like structures. We now find that the
dynamics of water surrounding hydrophobes are ice-like, while the structure
remains similar to that of liquid water. The interaction between water and
hydrophobic solutes plays an important role in biological processes, such
as the self-assembly of cell membranes, the folding of proteins, and the
binding of drugs to proteins. Our results shed light on the role of water
in these processes and can aid in their understanding. LE10862
***
New optical gain mechanism in quantum wires discovered
Scientists from Japan (University of Tokyo) and from two US organizations (Arizona State University and Bell Laboratories) have discovered a new gain mechanism in a one dimensional semiconductor. This new mechanism involves splitting of a 4-particle complex (bi-exciton) into a two-particle complex (exciton) and a photon, instead of involving high-density plasma.
The scientists measured both light emission and absorption simultaneously over a wide range of electron density in super-clean T-shaped GaAs quantum wires formed by advanced molecular-beam epitaxy called cleaved-edge overgrowth. They observed that optical gain in this system appeared at a much lower electron density than people normally expect. Furthermore, the appearance of the gain does not require ionization of bound complexes (excitons, bi-excitons etc).
This discovery allows scientists to reduce the threshold (the minimum energy input required to make a laser) of a semiconductor lasers dramatically. It also sheds light on a long-standing controversial issue in condensed matter physics: the Mott transition, which was predicted more than five decades ago. This discovery shows that optical gain is not necessarily indicative of the Mott transition and that there is likely an intermediate stage where multi-particle complexes co-exist before excitons fully ionize into plasmas. LX10043
***
String theory describes the spontaneous collapse of spatial dimensions
In their recent Letter, ``Charting the landscape of supercritical
string theory,'' S. Hellerman and I. Swanson describe a new set
of solutions to string theory, in which spatial dimensions
can spontaneously vanish from the universe. This process
of ``dimension quenching'' connects theories dynamically
in any number of spacetime dimensions. The so-called second
string theory revolution was sparked in 1995 by the discovery
that five known versions of ten-dimensional superstring theory
actually emerge as different versions of the same underlying
theory (known as M theory). These five theories, however,
constitute just a small slice of a much larger space of
consistent string theories. This larger space includes, for
example, an infinite number of theories living in any number of
spacetime dimensions. The results described in this Letter
bring this infinite tower of string models into contact
with the so-called ``duality web'' of theories that launched
the second string revolution. Within the same class of solutions
the authors have also found a transition that connects the
superstring to an entirely distinct class of theory, known as
bosonic string theory (which is the first string theory ever
discovered). These transitions have radically extended the
science of quantum gravity. LE11624
***
The Core Matters
During writing a bit in a so-called vortex-memory cell a vortex/antivortex pair is created and again annihilated
in less than 50 ps (see Hertel PRL 98, 117201 (2007)), because particles and anti-particles cannot coexist.
Both mentioned quasiparticles can exist in two different states, which are characterized by the core polarization.
One fascinating fact of micromagnetism stems from the fact that vortices and antivortices can be found in a stable
configuration, so called cross-tie walls.
In this paper we have studied the dynamic vortex-antivortex interactions. We employed an advanced microscopy technique
for observing the vortex-antivortex dynamics involving a stroboscopic imaging allowing a very high time resolution.
Furthermore we performed accompanying simulations. Depending on the respective core polarizations the dynamic
interactions between the cores are completely different, what can lead to some unexpected effects like the “quenching”
of the antivortex movement. We demonstrate that the core polarization configuration can be determined from the dynamic
interactions even though the vortex core size is below the lateral resolution limit of our microscope. LC10878
Caption Fig. 1: Micromagnetic simulation showing the magnetization pattern of a single cross-tie in the ground
state (top) and after a field pulse excitation (bottom).
***
Physics of Laser Microsurgery in vivo
Sweeping away extraneous details is generally a strength of physicists;
however, those working at the interface with biology are often criticized
by our biological colleagues for broadly extrapolating from measurements
in systems that are just too simple. A perfect example is the physics of
pulsed laser microsurgery. This technique is widely used to probe
biological systems through the targeted disruption of cellular and
sub-cellular structures. The underlying physics ¿ including laser-induced
plasma formation and cavitation bubble dynamics ¿ has been previously
studied in distilled water; however, biological systems obviously differ
from water in important ways. In this paper, we describe the plasma and
cavitation dynamics observed during pulsed laser microsurgery in a model
biological system (fruit fly embryos). We find important differences in
the plasma and cavitation dynamics observed in water and those observed in
the fly embryos (i.e. in vivo). One of these - physical constraint of
cavitation bubbles by the biological matrix - was anticipated in the
earlier studies and mentioned as a potential complication in vivo. The
other - a reduction in the plasma threshold due to biological molecules
that could serve as sources of seed electrons at low intensities - was
not. The fully complex in vivo system has revealed new and relevant
physics ¿ an important lesson for any physicist who works across
disciplinary borders. LE11486
***
Distinguishing noise from chaos
Chaotic systems share with stochastic processes (noise) several properties that make them almost undistinguishable: a wide-band power spectrum, a delta-like autocorrelation function, an irregular behavior of the measured signals, etc. This similitude makes it possible to replace stochastic series by chaotic ones in many practical applications. In this paper a method is devised that easily identifies the underlying nature of the process and allows one to discriminate between them by recourse to an appropriate graphic representation, whose starring role is played by a statistical quantifier called "complexity measure". Several well known, model-generated time series (the Logistic Map, the Henon's Map, the Lorenz Map of Rossler's oscillator, Schuster Maps, Noises with f ¡ k power spectrum, fractional Brownian motion and fractional Gaussian noise), usually regarded as being of either stochastic or chaotic nature, are used as examples that illustrate on the approach. The main achievement is thus to open the possibility of clearly distinguishing between stochacity and chaoticity in our representation space, something that is rather difficult otherwise. LF11384
***
A Perfect Spin Sieve
We predict that an interface between graphite or graphene and a
suitably oriented ferromagnetic metal will filter electron spins
in the same way as a polaroid film polarizes light - except that
in our case the polarization is complete.
Electrons have an intrinsic spin which comes in two flavours, up and
down. Most materials, including graphite and graphene, contain equal
numbers of each spin flavour and are not magnetic. Ferromagnets are
magnetic because they have a partial spin imbalance. Our calculation
shows that a graphene or graphite layer on top of nickel or cobalt
acts as a perfect sieve because it allows only electrons with one
spin flavour to pass.
The origin of the effect lies in the very special electronic structure
of graphite and graphene: it only matches that of nickel or cobalt for
one spin direction. This can happen because there is a near perfect
matching of the lattice constant of graphite with those of nickel or
cobalt when these are oriented in the (111) direction.
By introducing a sandwich structure with two interfaces, it should be
possible to construct an improved magnetic field sensor of the type
used in hard disk drives and numerous automotive applications. LF11085
